lake records of northern plains paleoindian and early archaic …yansa/yansa 2007-plains...

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Catherine H. Yansa The “Park Oasis” Hypothesis

Plains Anthropologist, Vol. 52, No. 201, pp.109-144, 2007

Lake Records of Northern Plains Paleoindian andEarly Archaic Environments: The “Park Oasis”

Hypothesis

Catherine H. YansaFossil pollen and other proxies from lake sediments are used to reconstruct past dynamics in

vegetation, climate and local availability of potable water for the northeastern Plains, therebyproviding a landscape context to re-assess local Paleoindian and Early Archaic subsistence strate-gies and settlement patterns. Presented are pollen and plant macrofossil data from two lakes inNorth Dakota and discussion of these results in the context of published paleoenvironmental andarchaeological data for the region. Aridity has characterized the regional climate since deglaciation.From 12,000 to 10,000 14C yr B.P., this aridity was counter-balanced by glacial meltwater saturat-ing much of the landscape, which supported a vegetation of white spruce parkland. The regionalwater table lowered after 10,000 14C yr B.P. As some lakes went dry or became saline others re-ceived ground-water input, thereby creating scattered “oases” in a deciduous parkland, which wouldhave attracted prehistoric people and game alike. Grassland became widespread by 9000 14C yrB.P. Alternating arid and moist intervals characterized the mid-Holocene Altithermal, but someoases existed in the region. This paper supports the hypothesis proposed by some archaeologistsfor the persistence of human occupation of the northern Plains during the Altithermal except, per-haps, during the severest droughts.

Keywords: pollen, drought, Paleoindian, Archaic, Altithermal

Catherine H. Yansa, Department of Geography, Michigan State University, 227 Geography Building, East Lansing, MI 48824-1117, e-mail: [email protected]

Archaeological records typically reconstructdetailed snapshots of local environmental condi-tions and human-environment interactions for dis-crete time intervals and thus have notable chrono-logical gaps. In contrast, the analysis of proxy in-dicators from lake sediments (e.g., pollen, diatoms)provides continuous records of past vegetation,climatic and hydrologic changes since the forma-tion of these lake basins after deglaciation (so longas water levels are maintained). Lake-sedimentdata offer both local and regional reconstructionsof past environmental changes and thus providethe landscape setting for which site-specific ar-chaeological records may be evaluated.

Unfortunately, paleolacustrine records arelimited to where lakes and wetlands exist, whichprecludes most of the Great Plains. Lakes are

common, however, in areas occupied by glaciersduring the Late Wisconsinan: the eastern part ofthe northern Plains (Laurentide Ice Sheet) andhigher elevation areas within the Inter-montaneWest (Cordilleran Ice Sheet). My case study isthe northeastern Plains, that area of eastern SouthDakota, eastern and northern North Dakota, andeastern Montana in the USA and the Canadian prai-ries (southern parts of Alberta, Saskatchewan andManitoba). Even though this glaciated region con-tains numerous lakes, ponds, and ephemeral wet-lands, perennial lakes are still rare, because of thesemiarid to subhumid climate. Most existing wet-lands are saline playas and “sloughs” (also knownas “prairie potholes” and “prairie marshes”), whichfill with water after snowmelt and spring rains butare often dry by late summer. However, many of

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PLAINS ANTHROPOLOGIST VOL. 52, NO. 201, 2007

these sloughs provide truncated fossil recordsfrom the time the basins formed after deglaciationuntil the mid-Holocene (Yansa 1998, 2006). Inthese contexts, the fossils are preserved in satu-rated sediments below the water table and the fos-sils in the overlying sediments have been de-stroyed by oxidation and decay.

In this paper, I present a detailed comparisonof pollen and plant macrofossil (seeds, fruits,leaves, buds and wood) data from two lake sites inNorth Dakota that represent different physi-ographic areas in order to distinguish between re-gional climate changes and local conditions ofgeology and hydrology. Coldwater Lake is a kettlelake situated on the Missouri Coteau upland,whereas the Wendel site was once a paleolake lo-cated on the lower-elevation Glaciated Till Plain(Figure 1). The Wendel site offers a truncated fos-sil record from ca. 11,500 to 8000 14C yr B.P. and

today is an ephemeral wetland. Coldwater Lake isone of a few lakes in the region with a completeHolocene fossil record, but for the purpose ofdataset correlation with the Wendel site I providehere only the oldest portion of the Coldwater Lakerecord up to 6000 14C yr B.P. Furthermore, thevegetation, climate and hydrologic changes atthese sites are correlated with the paleoenviron-mental signals of published reports from otherlake/wetland sites in the northeastern Great Plainsto make some inference about possible human ad-aptations to these environmental changes. Theknown cultural complexes during this time areClovis (11,500 to 10,900 14C yr B.P.), Folsom(10,900 to 10,000 14C yr B.P.), Late Paleoindiantraditions (ca. 10,000 to 8000 14C yr B.P.), andEarly Archaic (8000/7500 to 4500 14C yr B.P.)(Holliday 1997; Sheehan 1995; Taylor et al. 1996).In the Canadian prairies, these complexes are re-

Figure 1. Physiogeography and modern vegetation communities of the study area. Also shown are locations of all plant fossil sitesin the northeastern Plains: WE=Wendel site (this study); CW=Coldwater Lake (this study); RB=Rosebud site (NAPD 2005; Wattsand Wright 1966); PL=Pickerel Lake (Dean and Schwalb 2000; Watts and Bright 1968); MD=Medicine Lake (Radle et al. 1989);CT=Cottonwood Lake (Barnosky et al. 1987; NAPD 2005); BS=Big Stone Lake (Yansa 2002); TP=Trollwood Park site (Yansa andAshworth 2005); MN=Moon Lake (Laird et al. 1996, 1998); SP=Seibold Pond (Newbrey and Ashworth 2004); RL=Rice Lake (Grimm2001b); KL=Kettle Lake (Clark et al. 2002; Grimm 2001b); FS=Flintstone Hill site (Boyd et al. 2003); AD=Andrews site (Yansa 1998,Yansa and Basinger 1999), NF=Neufeld site (Yansa 2006); KY=Kyle site (Yansa 2006); BC=Beechy site (Yansa 2006); CL=ClearwaterLake (Last et al. 1998); HL=Harris Lake (Sauchyn and Sauchyn 1991); GP=Guardipee Lake (Barnosky 1989); and CP=Chappice Lake(Vance et al. 1993).

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ferred to as the Early and Middle Prehistoric pe-riods (10,000 to 4000 14C yr B.P.), because in thisnorthernmost portion of the Great Plains therewere no discernable changes in subsistence adap-tations during the early and mid-Holocene (Dyck1983; Walker 1992).

This paper is the first to reconstruct the se-quence of changes in vegetation, climate, geomor-phology and hydrology that occurred in southernSaskatchewan and the Dakotas with the direct aimof providing a landscape context for archaeologi-cal interpretations. It builds upon Beaudoin andOetelaar’s (2003) comprehensive analysis of LateQuaternary landscape and vegetation changes thatoccurred in southern Alberta and Boyd et al.’s(2003) interpretation of Folsom environments insouthern Manitoba. This paper provides a com-prehensive reconstruction of changes in the spa-tial and temporal distribution of potable water forthe northeastern Plains, further developing the“park oasis” hypothesis first proposed in Yansa(1998). The emphasis of this paper is on lake andpond sites, offering archaeologists a new perspec-tive of prehistoric environments, which up untilnow focused on river valleys (e.g., Artz 2000;Beaudoin and Oetelaar 2003; Bettis and Mandel2002; Frison 1978; Reeves 1973; Walker 1992;Wilson 1983).

In this paper, I identify the onset of climaticwarming and drying, including episodes of drought,which should have affected prehistoric subsis-tence strategies and settlement patterns in thenortheastern Plains. The paper thus contributes tothe ongoing debate about the extent of prehistorichuman occupation in the Great Plains during themid-Holocene Altithermal (Hypsithermal) (e.g.,Antevs 1955; Artz 2000; Forbis 1992; Frison1978, 1992; Holliday 2000; Meltzer 1999, 2004;Reeves 1973; Walker 1992). There are limits tomy interpretations, since evidence for culturalfactors in determining land-use decisions can notbe discerned from lake-sediment core data,thereby reinforcing the need for the correlationof archaeological and paleolacustrine datasets.Furthermore, I agree with the archaeologistsMonaghan and Lovis (2005:95) that “althoughenvironment does not necessarily dictate humanadaptation, it does provide important limitationsand constraints to the kind and structure of those

settlement and subsistence systems that are pos-sible.” In addition, the landscape reconstructioncomplements previous geoarchaeological studiesthat assess archaeological site burial and destruc-tion by geomorphic forces (e.g., Artz 2000;Holliday 1997; Monaghan and Lovis 2005; Wa-ters and Kuehn 1996), and may aid in future pros-pecting for archaeological sites within the north-ern Plains region.

REGIONAL SETTINGAND STUDY SITES

Physiography and GeologyA detailed description of the regional setting

in terms of its physiography, geologic history,modern climate, hydrology and extant vegetationprovides the context to assess past environmentalchanges at the representative study (fossil) sites.These environmental features are midway betweenthe semi-arid steppe of the western uplands andFront Range and the humid forest of the Midwest.

The present-day physiography of the north-ern Plains reflects the bedrock geology underly-ing Quaternary sediments. The bedrock surfacedips down from the foothills of the Rocky Moun-tains eastward, forming a gentle slope, which isinterrupted by two escarpments of resistant bed-rock that form three “prairie steps.” From west toeast, the three prairie steps (Figure 1) are: 1) theMissouri Plateau (about 700 to 1,000 m asl); 2)the Glaciated Till Plain (about 335 to 600 m asl);and 3) the Red River Valley Lowland (about 240to 329 m asl) (Holliday et al. 2002). In Canada,these steps are called the Alberta, Saskatchewan,and Manitoba Plains, respectively.

The northern Great Plains is characterizedby a variety of glacial landforms. The maximumextent of the Late Wisconsinan glaciation was onthe Missouri Plateau, as indicated by end morainecomplexes situated between the present courseof the Missouri River to the west and the Mis-souri Coteau to the east (Figure 1). The MissouriCoteau (Coteau des Missouri) is a narrow (about30 to 120 km wide) northwest-trending upland thatextends nearly 1300 km from south-central SouthDakota to west-central Saskatchewan along theeastern margin of the Missouri Plateau (Clayton1967; Lemke et al. 1965). The last major ice ad-

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vance of the James Lobe of the Laurentide IceSheet, at about 12,300 14C yr B.P., extended overthe Missouri Coteau and the adjacent GlaciatedTill Plain to as far south as southeastern SouthDakota and Iowa (Clayton and Moran 1982;Patterson et al. 2003). After the retreat of theJames Lobe, ice stagnation over the next few thou-sand years resulted in the formation of “knob-and-kettle” hummocky moraine on the MissouriCoteau (Clayton 1967; Clayton and Moran 1982).Locally, melting of the stagnant ice resulted in theformation of numerous closed-drainage kettlelakes and ponds that eventually supported mesicand wetland vegetation (Clayton 1967; Yansa 1998,2006). Fossil records of several of these kettle-hole lakes and ponds on the Missouri Coteau havebeen investigated (Figure 1), including ColdwaterLake.

The Glaciated Till Plain, situated between theMissouri Coteau to the west and the Red Rivervalley and Prairie Coteau (Coteau des Prairies) tothe east and southeast, respectively, is an erodedbedrock surface covered by a thick sequence ofQuaternary glacial deposits (Clayton and Moran1982). This plain of Cretaceous-age shale wasmore deeply eroded by Quaternary glaciers thanthe Tertiary caprock (underlying till) of the Mis-souri Coteau to the west (Clayton and Moran1982). Today, perennial deep lakes are exceed-ingly rare on the till plain, but there are millionsof sloughs that periodically contain shallow wa-ter. The Glaciated Till Plain is also characterizedby several large lake beds that are dry today butonce contained glacial lakes Dakota, Hind, Sourisand others. These glacial lakes were short-lived,having been sequentially impounded next to theretreating front of the James Lobe, from approxi-mately 12,000 to 10,700 14C yr B.P. (Kehew andTeller 1994). These lakes underwent episodic andcatastrophic drainage, which deeply incised (30to 100 m) interconnecting glacial meltwater chan-nels to a remarkable width of 1 to 3 km (Kehewand Teller 1994). Dunes are associated with manyof these dry lake plains (Muhs et al. 1997). An-other feature of this till plain, though not oftenvisible on the surface, is tunnel valleys. These arebelieved to have formed when basal meltwateraccumulating beneath an active ice sheet attaineda hydraulic pressure that exceeded the strength of

the ice, causing the catastrophic release of melt-water that subglacially incised deep valleys(Patterson 1997). When the hydraulic pressuredissipated, the velocity of the discharged waterwould have dropped and these tunnel valleys be-came filled or partially filled with sediment andice chunks (Harris et al. 1998; Patterson 1997).Underlying the Wendel site (Figure 1) is such atunnel valley.

The Prairie Coteau delineates the southeast-ern border of the James River lowland (Figure 1).This upland is “iron-shaped,” because it formedas a wedge of thick (120–220 m) interlobatediamicton (till) deposited between the James Lobeand Des Moines Lobe (Gilbertson and Lehr 1989).Numerous kettle lakes and ponds exist on the Prai-rie Coteau, giving this upland an appearance simi-lar to that of Missouri Coteau. Only Pickerel andMedicine Lakes have been studied so far on thisCoteau.

To the east, the lower elevations of the RedRiver and the Minnesota River valleys are attrib-uted to this area being a pre-glacial bedrock lowthat was further excavated during repeated Qua-ternary glaciations (Bluemle 1972, 1991; Wright1998). The final recession of the Des MoinesLobe, which extended down what are now the RedRiver and Minnesota River valleys into centralIowa, began after 12,300 14C yr B.P. (Patterson etal. 2003). Melting of this ice lobe created GlacialLake Agassiz after 11,700 14C yr B.P., whichdrained south to the Minnesota-Mississippi Riversystem at least twice and persisted in its variousforms until the lake drained into the Tyrell Sea(Hudson Bay) in northern Canada by 7500 14C yrB.P. (Teller 2004). Fossil sites in the Red RiverLowland are rare, because of sediment erosioncaused by the changing drainage of this lake. Buttwo records (Figure 1) exist: 1) for a time whenthe southern part of the lake basin was temporarilydrained (Trollwood Park site, Yansa and Ashworth2005), and 2) after final closure of the lake’ssouthern drainage (Big Stone Lake, Yansa 2002).

Modern Climate and Hydrology The climate of the northern Plains is a result

of the interplay of three major air masses: warmdry flow from the Pacific; cold dry Arctic air; andwarm moist air from the Gulf of Mexico (Bryson

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1980). In the region, the tropical Gulf air massdominates during the warm summer months,whereas the Arctic and Pacific air masses com-pete during the cold winters (Bryson 1980). Nearly75 percent of the precipitation occurs as rain inthe spring and summer and is associated prima-rily with frontal activity (Gulf of Mexico vs. Arc-tic air masses) and, to a lesser extent, convectivethunderstorms (Holliday et al. 2002).

Droughts occur whenever zonal (westerly)flow of Pacific air prevails, because it redirectsthe Gulf moisture eastward into the Great Lakesregion (Bradbury et al. 1993). On a broader scale,persistent droughts in the Great Plains are asso-ciated with La Niña activity (Forman et al. 2001).During regional droughts, frontal activity de-creases, but localized convective thunderstormsactually increase in their frequency, but are un-predictable in their movement and provide lim-ited moisture to only localized areas (Chang andWallace 1987; Katz and Brown 1992). Beaudoin(2002) clarified the terminology pertaining todroughts. She defined drought as <80 percent ofthe normal precipitation and lasting less than fiveyears. Beaudoin (2002) also noted thatpaleoclimate data from lakes are typically atmulti-decadal to centennial scales and thus thesedata reconstruct “aridity” or “arid intervals” insteadof individual “droughts.” Her terminology will befollowed in this paper.

Meteorological records from the northernPlains indicate a high degree of seasonal andinterannual variability in temperature and precipi-tation, reflecting the varying influences of thesedifferent air masses throughout the year and be-tween years. Climate data in Table 1 are from the

meteorological stations located closest (<15 km)to the two study sites (Owenby and Ezell 1992).While temperatures vary little between these sites,since they are located at about the same latitude,there are noticeable differences in precipitationthey receive. Coldwater Lake generally receives80 mm less precipitation each year than theWendel site (located 80 km to the east) (Table 1).

These data (Table 1) reflect a larger-scaleregional pattern where precipitation decreaseswestward, because of reduced inflow of the moistGulf air mass and a greater effect of the RockyMountain’s rainshadow (Bryson et al. 1970;Bryson 1980; Environment Canada 1993). Spe-cifically, the eastern part of the northern Plainsreceives greater average rainfall intensity and re-liability than do the western part of this region.Therefore, the western Plains (Montana, westernDakotas, southern Alberta and southwesternSaskatchewan) are classified as semi-arid, whereasthe eastern Plains (eastern Dakotas, southeasternSaskatchewan and southwestern Manitoba) areconsidered to be subhumid.

This precipitation gradient is reflected byvariations in the level and salinity of lakes withinthe region. While all areas of the northern Plainshave a negative water balance during the growingseason, evapotranspiration exceeds precipitationby 200 mm in western Minnesota, 300 mm in theeastern Dakotas (the study area), and as much as600 mm in Montana (Winter 1989). Not surpris-ingly, lake salinity increases dramatically west-ward, with saline playas being more numerous inMontana and southeastern Alberta (Dean andSchwalb 2000; Last 1992). Playas and ephemeralfreshwater/brackish wetlands (sloughs or prairie

Table 1. Mean Temperatures and Precipitation Values from Meteorological Stations Closest to StudySites Based on the Climate Normal Years 1961–1990 (Owenby and Ezell 1992).

Meteorological Station(study site) Temperature (°C) Precipitation (mm)mean mean mean mean mean meanJan. July annual Jan. July annual

Ashley, North Dakota -13.9 4.646°02’N, 99°22’W(Coldwater Lake)LaMoure, North Dakota -13.3 21.6 5.3 12.9 76.7 520.246°22’N, 98°17’W(Wendel Site)

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potholes) are also common in the region, but pe-rennial lakes are rare. Lake levels are largely de-termined by the amount of autumn precipitation,snowmelt, and early-spring precipitation, becausemuch of the summer precipitation is lost throughevapotranspiration (Winter and Rosenberry 1995).During the spring, many ponds and lakes containwater that slowly recharges underlying aquifers,whereas other water bodies are discharge sites,receiving ground water ultimately derived fromupgradient (upslope) recharge lakes and wetlands(Winter and Rosenberry 1995).

Extant Vegetation and Soils This gradient for increasing moisture towards

the east is reflected by the vegetation cover of thenorthern Great Plains (prior to its extensive modi-fication by European-style agriculture and live-stock grazing). Short-grass prairie exists in south-eastern Alberta, Montana and the western Dako-tas (unglaciated Missouri Plateau), mixed-grassprairie in the eastern Dakotas and southernSaskatchewan (Missouri Coteau and Glaciated TillPlain), and tallgrass prairie is found along the Da-kota-Minnesota border and southern Manitoba(Red River valley) and eastward. The mixed-grassprairie, the focus of this study, has a vegetationconsidered to be transitional because it includesboth tall (C3 and C4) and short (C4) grasses andforbs species (Risser et al. 1981). The dominantgrasses of this vegetation are Agropyron smithii(western wheatgrass) and species of Stipa(needlegrass) (Vankat 1979). This mixed-grassprairie also includes numerous forb species. Ofnote, species of Artemisia (sage) and Ambrosia(ragweed) are fairly common, but the former in-creases in its abundances westward, whereas indi-viduals of the latter becomes more numerous east-ward in the tallgrass prairie and adjacent forests(Great Plains Flora Association 1986).

Zones of different types of prairie wetland(also known as prairie pothole, slough, prairiemarsh, sedge meadow or mudflat) vegetation sur-round lakes and ponds in the northern Plains andare sorted by water depth (Kantrud et al. 1989).Pondweeds and other aquatics inhabit shallowwater (<1 m depth), Typha latifolia (broad-leavedcattail) and some other emergent-aquatic speciesprefer depths of 0.5 m, and the shoreline is inhab-

ited by numerous species of Carex (sedge),Scirpus (bulrush) and Salix (willow). Membersof the Chenopodiaceae (goosefoot family),Asteraceae (aster family), and Fabaceae (bean fam-ily) and several other forb and grass species oc-cupy the surrounding mudflat. The spatial extentof these vegetation zones expands and contractsin relation to fluctuations in water table elevations,and thus responds quickly to climate changes(Kantrud et al. 1989). Many of these plants godormant during droughts and regenerate from seedbanks whenever water levels rise (H.H. Birks1980; Kantrud et al. 1989).

Trees are found where soils are consistentlymoist (more-or-less), such as along river valleysand surrounding the few existing permanent lakes,and thus are uncommon on the northern Plains.These trees include Populus tremuloides (trem-bling aspen or aspen poplar), Quercus macrocarpa(bur oak), Ulmus americana (American elm),Acer negundo (box elder), and other taxa morecommon in the deciduous forest of Minnesota(Great Plains Flora Association 1986). Prior toEuro-American and Euro-Canadian settlement,fires were frequent and helped suppress the ex-pansion of trees into grassland (Anderson 1982).Early European fur traders and explorers fre-quently reported Native Americans and First Na-tions regularly igniting fires to reduce shrubberyand increase grass fodder for bison and other largegame animals (e.g., Anderson 1990). Tramplingof saplings by bison and other large herbivoresalso helped curb tree growth (Anderson 1990).Stands of Populus (poplar) and Betula (birch) aremore abundant farther north in the aspen parklandof southeastern Manitoba, central Saskatchewanand southeastern Alberta (Figure 1). The aspenparkland forms a transitional ecozone between thegrassland and southern boreal forest. This parklandis associated with a 150 mm moisture deficit(Hogg 1994), and thus is slightly moister (andcooler) than the prairies. The eastern boundary ofthe northeastern Plains is the deciduous and coni-fer-hardwood forests of western Minnesota (Fig-ure 1), starting from the Itasca and AlexandriaMoraines.

The modern soils in the study area are typi-cally Mollisols, with high levels of organic mat-ter and bases. Eolian additions of clays, carbon-

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ates, and salts into soils have been significant onthe Great Plains throughout the Holocene andsome of these materials have since been redepos-ited downslope (Holliday et al. 2002; Mason andJacobs 1998). Most of the soils in the glaciatedportion of the northern Plains are calcareous clayloam, which formed in montmorillonite-richdiamicton largely derived of Cretaceous bento-nite shales (Clayton 1967; Holliday et al. 2002).These soils are classified as Typic Argistolls, TypicHaplustolls, or Udic Haplustolls (Soil Survey Staff1994). Soils formed in the beds of former glaciallakes have either a silty clay or silty clay loamtexture. Water-saturated gley soils in present-daywetlands are classified as one of the Aquic subor-ders (Soil Survey Staff 1994). Sandy loam andloamy sand soils developed in glacial outwash andformer deltas and these have been largely reworkedinto parabolic dunes (Holliday et al. 2002; Wolfeand Lemmen 1999). Buried soils are found in thesedunes and in some other deposits, the most well-known being the Leonard Paleosol that formedduring the early Holocene (Clayton et al. 1979;Running 1995).

DATA SOURCES AND METHODS

Primary Fossil Data and Methods Fossil Data from Study Sites. The primary

pollen and plant macrofossil data presented in thispaper are from localities in southeastern NorthDakota: Coldwater Lake (46°01’N, 99°05’W; 452m asl) in McIntosh County and the Wendel site(46°25’N, 98°20’W; 423 m asl) in LaMoureCounty. Coldwater Lake, a kettle lake located onthe Missouri Coteau upland, is one of the fewlakes in the region that maintains water from yearto year. But even this lake is small (0.5 km2) andits surface area expands and contracts dramaticallyin response to droughts and precipitation events.The Wendel site and some of the other sloughssituated in the Glaciated Till Plain were oncepaleolakes within a meltwater-saturated landscape(Clayton and Moran 1982; Yansa et al. 2007).During the Holocene, the levels of lakes and pondsin the region lowered because of droughts, andmany of the shallower basins became saline pla-yas by the early to mid-Holocene.

Only a few lakes on the northern Great Plains

are deep enough to bear complete Holocene fos-sil sequences (e.g., Barnosky et al. 1987; Grimm2001b; Yansa 2002), and most of these have al-ready been studied and are discussed in this paper.Yansa (1998) established that the shallowersloughs (e.g., the Andrews site, southernSaskatchewan) provide valuable, albeit truncated,fossil records dating from the late Pleistocene tothe mid-Holocene. The fossil record of theWendel site is similarly truncated, spanning from11,500 14C yr B.P. to ca. 8000 14C yr B.P. when apaleosol formed in a drying lake bed (Yansa et al.2007). Up until this time, ground-water inflow intothe Wendel basin was sufficient to keep up waterlevels, but after 8000 14C yr B.P. periodic dryingof soils occurred. However, the presence of fos-sils dating from the late-glacial to early postgla-cial at this site indicates that ground-water inflowwas enough to preserve them below the water table.South of the maximum extent of the last glacia-tion, such as in the central Plains, fossil preserva-tion is exceedingly rare and truncated, because ofthe paucity of natural lake basins (Fredlund 1995;Fredlund and Tieszen 1997).

Methods of Sample Collection and FossilAnalysis. Cores were collected from the frozen-ice surface of Coldwater Lake using standardequipment, a Livingston™ corer with extensionrods. The cores, each 1 m in length, were extrudedin the field into longitudinally-split PVC tubes,wrapped and labeled. Firm ground of the Wendelsite allowed use of a CME™ hollow-stem drillrig to collect the cores using a split-spoon core-barrel attachment. Sediment cores were collectedat two locations, 400 m apart, at the Wendel site.Pollen and plant macrofossil data are primarilyderived from the longer WE-3 core (9.1 m long),considered to be representative of an “offshore”location within a bay of a paleolake. These dataare supplemented by the additional identificationof macroscopic plant and fish fossils from theWE-1 core (6.1 m long), thought to be represen-tative of a “nearshore” location of the same bay.Details about the analysis of the Wendel site fos-sil are provided in Yansa et al. (2007) and are justsummarized in this paper, but data for ColdwaterLake are presented here for the first time.

For pollen analysis, sediment samples (1cm3) were collected from the cores of both

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Coldwater Lake and the Wendel site at 5 or 10-cm intervals. The cores were then sliced up forplant macrofossils samples, each 25 cm3 in vol-ume, and every alternate sample was analyzed.Radiocarbon samples of terrestrial plant macro-fossil were derived from some of these samples.

Preparation of pollen samples followingstandard procedures outlined in Faegri and Iversen(1975) with some modifications to deal with theclay- and sand-rich prairie lake sediments (Bateset al. 1978; Shane 1998). Identification and count-ing of pollen grains were made at 400X magnifi-cation and with the use of keys, drawings, and pho-tographs in McAndrews et al. (1973), and com-parison with modern pollen slides housed in thePollen Laboratory, University of Wisconsin atMadison.

All plant macrofossil samples analyzed weregently washed with tap water through nestedscreens of 425 mm and 212 mm openings, fol-lowing standard procedures (H.H. Birks 1980,2001). The organic debris from the screens wasplaced in plastic containers with water and a smallamount of this was sorted at a time in petri dishesunder a binocular microscope (magnification20X). The plant macrofossils were picked, iden-tified, and stored dry in labeled 1-dram glass vi-als. Fossil seeds and other plant macrofossils wereidentified with the aid of keys and published re-ports (e.g., Montgomery 1977), and by compari-son to modern plant materials from extant spe-cies of prairie, parkland, and boreal forest plants.The taxonomic nomenclature, distribution, andhabitat of modern analogs for both plant macro-fossils and pollen were based on the Flora of theGreat Plains (Great Plains Flora Association1986), unless otherwise noted.

Most pollen grains and spores may only beidentified to the family or genus level, whereasthe majority of plant macrofossils can be identi-fied to species (where they are not [but the genusidentifications are certain] I used “cf.” [confer]).For some pollen grains, closely related speciesshare a similar morphology and hence these grainscan only be identified as “type,” for example,Ambrosia-type (ragweed). Table 2 provides thecommon (English) names for the botanical (Latin)nomenclature used in this paper.

For each level analyzed, all pollen and spores

were tabulated during a series of traverses on sev-eral slides until a sum of more than 300 uplandpollen grains was attained, a standard count forthe species-poor Great Plains (Jones and Bryant1998). Pollen and spore percentages were calcu-lated in the Tilia™ spreadsheet (version 2.0.b.4,provided by Grimm 2001a) by using counts oftrees, shrubs, and upland herbs as the denomina-tor, following a well-established protocol in pol-len analysis (e.g., Faegri and Iversen 1975;Whitlock et al. 1993). Deposition of seeds andother plant macroremains (that with burial becomemacrofossils) is heterogenous. Organics are dif-ferentially deposited closer to shore and in lownumbers, and thus macrofossil data should alwaysbe expressed as counts (per sample volume), notpercentages (H.H. Birks 1980, 2001).

A cluster analysis program (CONISS) wasapplied to the pollen data entered into a Tilia™spreadsheet to identify zone boundaries that indi-cate shifts in the species composition and domi-nance within plant communities of the past. Thiscluster analysis is not shown in Figure 2, but wasused to identify the placement of the zone bound-aries. Data in the Tilia spreadsheet were trans-formed into pollen diagrams (Figure 2A,B) by useof the following software: Tilia*graph™, version2.0.b.4 and TGView™, version 1.1.1.1 (Grimm2001a); and Adobe Illustrator™, version 10.0.

Secondary Paleolacustrine Data Additional data used in this paper are from

published studies of pollen and other proxy indi-cators from other lake and pond sites. Also in-cluded are data for the northern Plains from un-published studies that are posted on the NorthAmerican Pollen Database (NAPD 2005) website(www.ngdc.noaa.gov/paleo/napd.html). In addition,I include not just pollen and plant macrofossilsdata (the focus of this paper), but also paleo-environmental information derived from otherlake-sediment proxies, such as diatoms (algae),geochemistry of ostracode shells and sediment,and stable isotopes, which are provided by otherauthors (sites and citations shown in Figure 1 andits caption).

Radiocarbon ChronologiesA regional synthesis, such as presented in this

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Table 2. All Plants Identified from Pollen and Plant Macrofossils at the Study Sites (except for pollen ofthose taxa transported from outside the region): CWL (Coldwater Lake); WE-3 (Wendel site, core 3),including their Latin names, English (common) equivalents and life forms (trees, etc.). The fossil organsidentified are noted: P (pollen); S (seed or fruit); Sp (spore); L (leaf or needle); Wg (seed wing); O (oo-gonium); and Th (thalli).

Scientific (Latin) Name Common Name Study SitesCWL WE-3

Trees:Acer negundo-type box elder P PBetula birch B PBetula papyrifera paper birch FFraxinus nigra-type black ash P PFraxinus pennsylvanica-type green ash POstrya/Carpinus ironwood P PPicea spruce P P, LPicea glauca white spruce Wg WgPopulus balsamifera-type balsam poplar P PPopulus tremuloides-type quaking aspen; aspen poplar P PQuercus oak P PUlmus elm P PShrubs:Alnus crispa (=A. viridis) green alder PAlnus rugosa (=A. incana) speckled alder P PAmelanchier-type service-berry PCorylus hazelnut P PCupressaceae juniper family P PPrunus-type cherry; plum P PSalix willow P PSarcobatus vermiculatus greasewood P PShepherdia argentea buffaloberry PShepherdia canadensis rabbitberry P PSympiocarpus wolfberry, snowberry P PMudflat & Upland Herbs:Ambrosia-type ragweed P PAmorpha-type lead plant, indigo PApiaceae (Umbelliferae) parsley family P PArtemisia wormwood; sage P PAster sp. aster S SAsteraceae, subfam. Tubuliflorae aster subfamily P PAsteraceae, subfam. Liguliflorae dandelion subfamily P PBrassicaceae (Cruciferae) mustard family P, S PCampanulaceae bellflower family PCaryophyllaceae pink family PChenopodiaceae/Amaranthaceae goosefoot/pigweed family P PChenopodium berlandieri pitseed goosefoot SChenopodium rubrum red goosefoot S SEpilobium-type willow-herb PErigeron daisy fleabane SEuphorbia spurge PFabaceae (Leguminosae) bean family PGaura butterflyweed PGentianaceae gentian family PIva annua-type marsh elder; poverty weed P PIva xanthifolia-type marsh elder; false ragweed PLiliaceae lily family PLycopus americanus American bugleweed S SMentha arvensis field mint S SPoaceae grass P P

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Scientific (Latin) Name Common Name Study SitesCWL WE-3

Polygonum sp. smartweed SPolygonum aviculare-type knotweed PPolygonum lapathifolium-type pale smartweed PPotentilla norvegica Norwegian cinquefoil S SRanunculaceae buttercup family PRanunculus cf. R. gmelinii small yellow buttercup SRorippa yellow cress SRosaceae rose family PRumex dock PRumex maritimus golden dock S SSphaeralcea (Malvaceae) red mallow PSolidago goldenrod SThalictrum meadow rue P PXanthium cocklebur P PEmergents: Alisma water plantain PCarex cf. C. rostrata beaked sedge S SCarex cf. C. sychnocephala long-beaked sedge S SCyperaceae sedge family P PEleocharis spike rush SJuncus rush S SSagittaria arrowhead P PScirpus americanus three-square bulrush SScirpus nevadensis Nevada bulrush SScirpus validus common bulrush S SSparganium bur-reed P PTypha latifolia broad-leaved cattail P, S P, SAquatics: Brasenia schreberi water shield PMyriophyllum water milfoil P SNajas flexilis naiad S SNuphar pond lily; cowlily PNymphaea water lily P PPotamogeton pondweed P PPotamogeton filiformis slender pondweed SPotamogeton vaginatus sheathed pondweed SRuppia maritima ditchgrass; wigeon grass P, S PWolffia sp. watermeal ThZannichellia palustris horned pondweed S SNon-Vascular Plants:Chara stonewort (green algae) O ODrepanocladus sickle-branch moss L LDryopteris-type wood fern Sp SpLycopodiaceae clubmoss family Sp SpPediastrum (colonies) green algae Sp SpPolypodiaceae fern family SpPteridium-type bracken fern SpSelaginella densa-type spikemoss Spcf. Sphagnum sphagnum moss Sp

paper, depends on accurate 14C chronologies ob-tained from the dating of terrestrial plant macro-fossils. Several previous reconstructions ofdeglaciation, vegetation changes and, by inference,archaeology (e.g., Christiansen 1979; Dyck 1983;Dyke et al. 2003; Radle et al. 1989; Ritchie and

MacDonald 1986), are based on the 14C dating oforganic lacustrine sediments (including gyttja andmarl), which we now know provide ages that aretoo old by 1,000 to 8,000 years (MacDonald etal. 1991). Organic sediments provide erroneousages, because they contain radioactively dead car-

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bon (fragments of Cretaceous shale) derived fromthe local tills, referred to as the “hard-water ef-fect” (Barnosky et al. 1987; Grimm and Jacobson2004). Also found in lake and pond sediments arefragments of Tertiary-age lignite, which appearlike charcoal, but provide erroneous ages. Withsome training and use of a binocular microscope(20-40X magnification), one can distinguishedlignite from charcoal (which is a good source ofdating material). Lignite lacks cellular structureand has a glossy black sheen and a very hard andbrittle texture (Grimm 2001b, Clark et al. 2002).

Also contained in these sediments are the fossilremains of aquatic plants (e.g., mosses) and ani-mals (e.g., gastropod shells) that incorporated an-cient carbon into their tissues while alive (i.e., the“reservoir effect”) and thus provide erroneous agesas well (MacDonald et al. 1991).

All 14C ages presented in this paper are thoseobtained from terrestrial plant macrofossils and/or charcoal (Table 3), all of which were derivedusing the Accelerator Mass Spectrometry (AMS)14C dating technique, and have been corrected forä13C fractionation. In this paper, years are ex-

Figure 2. Pollen percentage diagrams for A) Coldwater Lake and B) the Wendel site (WE-3 core). Shading (dotted pattern) represents5 percent exaggeration. Cumulative values for Total AP (arboreal, tree and shrub pollen) and Total NAP (non-arboreal, herb pollen)are also shown. Also provided are interpretations of paleovegetation (from pollen) and lake-levels (from plant macrofossils, data notshown).

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pressed in 14C yr B.P., because most paleoenviron-mental and archaeological datasets use this timescale instead of calibrated (calendar) chronolo-gies.

Reconstruction of Ice-Margin Recessionand Changes in Vegetation and

HydrologyFigure 3 illustrates the sequence of ice mar-

gin recession, glacial lake formation, and vegeta-tion changes that I envision based on the ice-mar-gin chronology of Clayton and Moran (1982) andthe paleobotanical data. The lake-core data includenot just those from the Wendel site and ColdwaterLake, but also my data from previous studies ofthe Trollwood Park site, North Dakota (Yansa andAshworth 2005), Big Stone Lake, Minnesota(Yansa 2002), and four sites in southernSaskatchewan (Andrews, Kyle, Beechy andNeufeld; Yansa 1998, 2006; Yansa and Basinger1999). I also include data from fossil studies byother researchers, some of which I have re-inter-preted (see Yansa 2006). The timing for vegeta-tion changes interpreted from pollen and plantmacrofossil data and the corresponding authorsare listed in Figure 1, which the reader may referto in identifying the sources of these data. Thesame goes for the paleoenvironmental changes atthe key lake/pond sites in the region, which aresummarized in Figure 4.

PALEOENVIRONMENTAL RECON-STRUCTIONS AND IMPLICATIONS

FOR ARCHAEOLOGY

Deglaciation and Spruce Parkland (Pre-Clovis? and Clovis Environments)Available paleoenvironmental data predate the

earliest archaeological records for human occu-pation of the northeastern Plains. This is not sur-prising given the volatile geomorphic forces thatoperated during deglaciation (described below),which would have eroded evidence for a pre-Clovisoccupation, if one occurred. Surface finds ofClovis fluted points have been made as far northas southern Saskatchewan (Dyck 1983), whichsuggest that these Early Paleoindians had a widegeographic range. Only one intact Clovis-age sitehas been excavated on the northern Plains so far,the Lange-Ferguson site, which is located outsidethe glacial limit in western South Dakota and datesto 10,700 14C yr B.P., an age considered late forClovis (Meltzer 2004). Therefore, paleoenviron-mental data obtained from lake cores provide theonly available information for pre-Clovis andClovis environments of the northeastern Plains.

Models for the recession of the LaurentideIce Sheet from its southernmost limit in north-central United States into northern Canada simu-late that first the ice sheet thinned by melting be-fore its margin receded (Clark 1994; Patterson et

Table 3. Results of Radiocarbon Age Determinations with Reference to Stratigraphic Depth, Lab SampleNumber (14C laboratory and #), AMS 14C age (with one standard deviation and corrected for *****13C frac-tionation), and Calendar Age (using the INTCAL98 calibration curve of Stuiver et al. (1998)). The mate-rials dated are terrestrial plant macrofossils.

Site Core Depth (cm) Lab Number AMS Age Calibrated Age (cal yr BP)below surface (14C yr BP) 2σ range/50% mean prob.

Wendel WE-1 388.5-391 1AA34340 11,550 ± 90 13,570Wendel WE-1 366-368.5 1AA34339 11,550 ± 65 13,560Wendel WE-3 576.5-579 1AA34342 11,110 ± 410 12,970Wendel WE-3 515.5-518 1AA46442 11,090 ± 210 13,190Wendel WE-3 470-472.5 1AA34341 9,920 ± 110 11,490Coldwater CWL 2369 2 CAMS13047 10,790 ± 70 12,950Coldwater CWL 2250-2252 2CAMS13622 8,300 ± 60 9,350Coldwater CWL 2184-2188 1AA46437 8,120 ± 150 9,080Coldwater CWL 2011-2015 2CAMS13621 7,150 ± 60 8,000Coldwater CWL 1862-1866 2CAMS17041 5,980 ± 60 6,860

1University of Arizona AMS (AA) 14C Laboratory/NSF Facility2Center for Accelerator Mass Spectrometry (CAMS), Lawrence Livermore

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al. 2003). During deglaciation, the ice margin fluc-tuated with periodic advances that would have de-stroyed any vegetation that colonized the area infront of the ice in the mean time. Paleoindiansand game probably inhabited the area along andnear the ice margin. Such a scenario has been re-constructed for the Schaefer and Hebior mammothbutchery sites in southeastern Wisconsin, whichindicate human occupation of ice-margin environ-ments from 12,500 to 12,200 14C yr B.P. (Joyce2006; Overstreet and Kolb 2003).

Climate models estimate past temperaturesand precipitation values based on mathematicalequations for atmospheric dynamics, ice sheetconfigurations and other variables, and astronomi-cal calculations of solar radiation (insolation) (seeKutzbach et al. 1998:475). These data indicate that

during the late-glacial and early postglacial, sum-mertime insolation was greater than it is today andwinters received corresponding less insolation(Kutzbach et al. 1998). These insolation differ-ences translate into temperature estimates for themid-latitudes of interior North America. For14,000 cal yr B.P. (12,000 14C yr B.P.), summertemperatures were about 2° C lower than modern(pre-industrial level, ca. A.D. 1800), but winterswere considerably colder (-8° C) (Kutzbach et al.1998). Precipitation levels were also lower thanthey are today by >4 percent (Bartlein et al. 1998;Kutzbach et al. 1998). Computer models simu-late that the jet stream hugged the southern mar-gin of the Laurentide Ice Sheet at this time, therebydeflecting moist air to the south (Bartlein et al.1998). These modeling results agree with

Figure 3. Reconstruction of the vegetation types that inhabited the northern Plains (as interpreted from pollen and plant macrofossildata) for discrete intervals during the late-glacial and early postglacial. Each icon representative of a plant community is placed overthe location of a fossil site (see Figure 1 for names of the sites and authors). Superimposed are the modern configurations for theMissouri and Prairie Coteaus for site reference. Ice margin positions and their ages are from Clayton and Moran (1982).

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geoarchaeological data from the southern HighPlains, which indicate high lake-levels and peren-nial streams during Clovis time (ca. 11,200 to10,900 14C yr B.P.) (Holliday 2000). These datathus do not support Haynes’ (1991) hypothesis fora Clovis Drought.

The Early Paleoindian climate of the north-ern Plains, close to the ice sheet, was relativelymild during summers, but the winters were brutal.These winters probably provided hardships for thePre-Clovis (if there were such people) and Clovishunters and may have resulted in a north-southmigratory pattern with the seasons. The southernHigh Plains would have been an attractive desti-nation for Early Paleoindians of the northeastern

Plains during winters, because this area to thesouth provided abundant resources, includingample potable water and fodder for game (Holliday1997, 2000). Alternatively, these Beringian colo-nists were able to withstand cold winters, consid-ering their adaptations to Arctic environments.

The paleovegetation for the Dakotas andSaskatchewan reconstructed from plant fossil dataagrees with this paleoclimate interpretation forslightly cooler summers and significantly colderwinters (compared to today) during the late-gla-cial. Initial colonization of the northeastern GreatPlains by white spruce and herbs was a responseto this climate, influenced by the nearby ice sheet.White spruce can withstand -20° C temperatures

Figure 4. Summary diagram illustrating the timing and duration of the plant communities that occupied areas surrounding lakes andpond sites studied on the northern Plains. The onset of the Ambrosia-type (ragweed) pollen peak, indicative of aridity, is also noted.(No Ambrosia peak was evident in the Wendel site pollen record and the Andrews site record is based solely on plant macrofossils.)Also shown are the corresponding lake stands through time, as interpreted from geochemistry, stable isotopes of ostracode calcite,plant macrofossils and/or diatoms.

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without undergoing cellular damage, whereas onlya few deciduous trees can (e.g., species of Populusand Betula) (Grimm and Jacobson 2004). Mean-while, prairie or steppe was established at 12,20014C yr B.P., immediately after deglaciation, in thearea around Guardipee Lake (Figure 1) in centralMontana (Barnosky 1989). This vegetation indi-cates dry conditions and has a wide temperaturerange, from cold to hot.

One would expect that a tundra or tundra-likevegetation would have preceded the white sprucein colonizing the glaciated northern Plains, sincesuch a pioneering flora is observed today whereglaciers are melting, such as in the Yukon (H.J.B.Birks 1980). However, there is no fossil evidencefor such vegetation having existed on the north-ern Plains, unlike the Midwest and Northeastwhere there are several reports of “tundra-like”fossil localities, which range in age from 18,000to 13,000 14C yr B.P. (e.g., Curry and Yansa 2004;Maher et al. 1998). In contrast, deglaciation ofthe northern Plains began much later, after 12,30014C yr B.P., and ice-margin recession lagged be-hind the warming climate (Patterson et al. 2003).

In addition to the late deglaciation of thenorthern Plains, Yansa (2006) also explains theabsence of fossil data for tundra-type vegetationin this region as due to initial landscape (geomor-phic) instability; where erosion and redepositionof sediments (and associated plant remains) werethe dominant processes. Kettles form by the slowmelting of stagnant ice blocks under an insulatingblanket of till, and studies have shown that thisprocess of basin formation took 1,000 to 2,500years (Clayton and Moran 1982; Curry and Yansa2004). By the time these lake basins had formedand were ready to start preserving plant fossils,Picea glauca (white spruce) and other plants hadalready arrived in the area. The colonizing trees,spruce and later some deciduous hardwoods, allhave seeds with attached wings that would haveaided their migration. Ritchie and MacDonald(1986) propose that the rapid northward spreadof white spruce seeds was because of an anticy-clonic circulation (high pressure system) perma-nently set up over the ice sheet, which caused thespiraling outflow of air off the glacier in all di-rections, including to the northwest. This anticy-clonic circulation moved north as the ice sheet

receded. Other early immigrants were aquaticplants, because they have seeds that traveledreadily along interconnecting waterways (longsince dried up) (H.H. Birks 1980). The rest of thecolonizers were probably transported as seeds inmud that adhered to the feet of birds (Wright1976).

Yansa (2006) provides a detailed reconstruc-tion of the timing of white spruce migration inthe northern Plains based on 26 14C ages fromnumerous sites, which is summarized here and il-lustrated in Figure 3. A timeline for vegetation andhydrological changes at lake and pond sites in thenortheastern Plains from 12,250 to 6000 14C yrB.P. is displayed in Figure 4 (site locations andauthors of the lake-core studies are shown in Fig-ure 1). White spruce occupied the Rosebud sitein South Dakota (Figure 1, not shown in Figure4), just south of the last glacial limit, at ca. 12,63014C yr B.P. (Watts and Wright 1966, NAPD 2005).On the glaciated plains, white spruce colonizednorth-central South Dakota (Cottonwood Lake) by11,690 14C yr B.P. (Barnosky et al. 1987, NAPD2005). This species reached southeastern NorthDakota by 11,800 14C yr B.P. (Moon Lake; Lairdet al. 1996, 1998) and 11,500 14C yr B.P. (theWendel site, Figure 2B). White spruce appearedin northwestern North Dakota by 11,080 14C yrB.P. (Kettle Lake, Clark et al. 2002; Grimm2001b), and southern Saskatchewan by 10,300 14Cyr B.P. (Kyle, Beechy and Neufeld sites, Yansa2006; oldest date for the Andrews site is 10,23014C yr B.P., Yansa 1998). The tail end of the sprucephase is recorded at Coldwater Lake (10,800 to10,600 14C yr B.P., this paper) and Rice Lake (ca.9200 14C yr B.P., Grimm 2001b, NAPD 2005),because of lags in the formation of these kettle-hole lakes. White spruce reached what is now thesouthern limit of the boreal forest in westernManitoba sometime before 9570 14C yr B.P.(Ritchie 1969).

The environment that the Paleoindians occu-pied during the Terminal Pleistocene is best de-scribed as an open white spruce parkland, whichlacks an exact modern analog. The spruce trees,shrubs and, in some places, small amounts of de-ciduous trees (Populus tremuloides, Populusbalsamifera, Betula papyrifera, and/or Fraxinusnigra) occupied the lakeshores along with wet-

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land herbs, whereas the uplands were covered byprairie grasses and herbs (Table 2). A facsimile ofthis vegetation is the present-day aspen parkland,but during the late-glacial the dominant tree wasPicea glauca, instead of Populus tremuloides(which at some fossil sites appear to have been asubdominant tree, but in Saskatchewan arrivedlater, during the spruce decline). Only white spruceand a handful of herb species, identified from fos-sils (Table 2), do not exist today in the northernPlains. Instead, spruce and these herbs presentlyinhabit slightly cooler and moister habitats, suchas the boreal forest, higher elevation slopes of theCypress Hills along the Saskatchewan/Albertaborder and the Black Hills of South Dakota, and afew pockets in the aspen parkland (e.g., SpruceWoods in southwestern Manitoba). Previous pol-len researchers assumed that this spruce vegeta-tion was directly comparable to that of the borealforest today (e.g., Last et al. 1998; Radle et al.1989; Ritchie 1969, 1987; Watts and Bright1968). Others thought a better description was aspruce forest, for it lacked jack pine and a fewother boreal trees that are considered to be slowmigrators (Grimm 2001b; Laird et al. 1996, 1998;Watts and Wright 1966). Yansa (2006) refutedthese forest interpretations based on several linesof evidence and offered a parkland interpretationin keeping with the spruce-sedge parkland recon-struction now in vogue for the eastern UnitedStates during the late-glacial (Webb 1987; Webbet al. 2004; Williams et al. 2001).

Pollen and plant macrofossils data from theWendel site and Coldwater Lake (Figure 2), as wellas other coeval sites, indicate an abundance ofherbs in the flora, species that today occupy grass-land and aspen parkland habitats. These herbs in-dicate that the uplands (such as the knobs in “knob-and-kettle” hummocky moraine) were dry, andthereby reflect the true climate signal; not thespruce trees, which before were used to recon-struct a cool moist climate (e.g., Barnosky et al.1987; Grimm 2001b; Radle et al. 1987; Watts andBright 1968). Another consideration is that car-bon dioxide levels (reconstructed from ice-coredata) were significantly lower during the Termi-nal Pleistocene than they are today, which prob-ably affected plant physiology (Sage 1995). Plantgrowth was probably reduced in this low CO2 en-

vironment (Sage 1995), which would have favoredherbs over trees and probably slowed tree growth,further contributing to the openness of the late-glacial vegetation.

Consequently, archaeological data for thenortheastern Plains and regional models of Pre-Clovis (?) and Clovis environments should be re-evaluated in light of this new spruce parkland in-terpretation. For example, Buchner and Pettipas’(1990) interpretation of Clovis settlement andsubsistence patterns in the Lake Agassiz basin wasbased on Jim Ritchie’s closed-canopy boreal for-est interpretation (e.g., Ritchie 1969, 1987). Simi-larly, Dyck’s (1983) reconstruction of the prehis-tory of southern Saskatchewan started severalmillennia too early, because it was based on thedeglaciation chronology of Christensen (1979)(see discussion above regarding problems withdating organic sediments and shells), and he as-sumed limited resources by adhering to Ritchie’spaleovegetation interpretation. The new parklandscenario, when compared to the earlier boreal for-est one, suggests that Early Paleoindians had ac-cess to a wide range of plant food resources andthat fodder would have been abundant, able to sup-port large populations of herbivores.

Many assume that mammoths were restrictedto tundra or steppe environments. However, bonesof Mammuthus primigenius (woolly mammoth)recovered from the (Herman) shoreline of Gla-cial Lake Agassiz date to 11,500 14C yr B.P.(Harington and Ashworth 1986), while not far awayat the Wendel site a white spruce parkland existedat this time (Figure 2B). A mammoth was butch-ered and possibly killed by Clovis hunters at10,700 14C yr B.P. at the Lange-Feguson site inthe Badlands of South Dakota (Meltzer 2004). Thevegetation there, to the west, was most likely al-ready grassland, based on local paleovegetationreconstructions. Barnosky (1989) interpretedfrom pollen that grassland occupied central Mon-tana since 12,200 14C yr B.P. Mixed-grass prairiewas established in the nearby Black Hills by 11,50014C yr B.P., based on the study of phytolith andcarbon isotopes from paleosols in this upland(Fredlund and Tieszen 1997). Similarly, Bouttonet al. (1998) interpreted from the �13C of paleosolorganic carbon from sites in the badlands of west-ern North Dakota that the proportion of the veg-

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etation comprised of C4 plants (warm-seasongrasses) increased dramatically from about 20percent at 11,000 14C yr B.P. to approximately 47percent by 10,700 14C yr B.P.

All proxy indicators from lake sediments(pollen, plant macrofossils, diatoms, ostracode-geochemistry, stable isotopes, etc.) on the north-eastern Plains indicate that during the spruce phasethe regional water table was several meters higherthan it is today. What are now shallow lakes, sa-line playas and ephemeral wetlands were once deeplakes and ponds filled with fresh water. These wa-ter bodies were interconnected during the sprucephase, as indicated by fossils of minnows andPerca flavescens (yellow perch) found in the late-glacial and early postglacial sediments of what arenow ephemeral closed-basin wetlands—theSeibold Pond (Newbrey and Ashworth 2004) andthe Wendel site (Yansa et al. 2007). One speci-men of Esox lucius (northern pike) was also re-covered from Wendel site sediments, which at thistime was a larger and deeper water body than wasSeibold Pond. These finds indicate that fish re-sources were widely available as a Paleoindianfood source during the spruce and subsequent de-ciduous parkland phases, if cultural dietary habitspermitted the consumption of fish. Fresh potablewater and aquatic resources were essentially ev-erywhere on the northeastern Plains and must haveattracted wildlife, waterfowl and people alike tothis area. This interpretation supports the modelof Kelly and Todd (1988) for high mobility ofEarly Paleoindian hunters in the Americas.

This regional high-lake stand does not neces-sarily mean that precipitation rates were high dur-ing the late-glacial; rather climate models (Bartleinet al. 1998, Kutzbach et al. 1998, Hosteler et al.2000) and my fossil data indicate the opposite,that the precipitation regime was low. Yansa (2006)and Yansa et al. (2007) propose that the water camefrom the melting of ice both at the surface, whichprovided the initial water source, and in the sub-surface by the slower release of water from themelting of blocks of stagnant ice buried under till.This “residual meltwater effect” gradually dimin-ished during the Pleistocene-Holocene transition,but for the time it existed it buffered the vegeta-tion from the low precipitation regime (Yansa2002). For several reasons explained in Yansa

(2006), I interpret that the white spruce trees wereprimarily located along the shores of lakes andponds and river banks where soils were perenni-ally moist and that eventually these trees died offand were replaced by deciduous hardwoods.

Transitional Spruce/DeciduousParkland and Onset of Lake-LevelLowering (Transitions in Clovis/

Goshen/Folsom Environments)Interestingly, the timing for shifts in cultural

complexes coincides with the change from spruceparkland to deciduous parkland; further researchis required to determine if this is a correlation ormerely coincidence. Archaeological data fromoutside the region, the western and southwesternUnited States, indicate that sometime around10,900 to 10,800 14C yr B.P. there was a transi-tion from Clovis to Folsom (Taylor et al. 1996).Adding to the confusion is the temporal overlapof Folsom (or Folsom-Midland) with Goshen (orPlainview) occupations from 10,850 to 10,40014C yr B.P. on the northwestern Plains (Fiedel1992, Frison 1998). Furthermore, we have a poorunderstanding of why 14C dates for EarlyPaleoindian projectile points (Folsom-Midland)are contemporaneous with those of LatePaleoindian (Agate Basin-Hell Gap) on the GreatPlains between 10,500 and 10,000 14C yr B.P.(Holliday 1997). Frison (1992) explained thesecoeval traditions as a result of a cultural-economicsplit from about 10,000 to 8000 14C yr B.P. with aPlains group focusing on bison hunting and pro-ducing late Agate Basin and Hell Gap points, whilea Foothills-Mountain group adopted an Archaic-like lifestyle (of diversified resource extraction)and artifacts. This cultural diversity may be relatedto the great variety of habitats that existed in theGreat Plains at this time, especially from south tonorth, but also with elevation. This mosaic of habi-tats was created by the time-transgressive reces-sion of the ice margin and attendant phases of plantcolonization and succession, which on the north-eastern Plains occurred earliest in southern SouthDakota and latest in the Canadian prairies.

My paleobotanical data indicate that duringthe last few centuries of the Pleistocene the con-tinued existence of white spruce in the northeast-ern Great Plains was probably out of phase with

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the warming summertime temperatures, whichwould have favored deciduous trees. White spruceis more drought tolerant than the other boreal co-nifers, including Picea mariana (black spruce)(Ritchie and MacDonald 1986), and so the pres-ence of Picea glauca on the northern Plains I in-terpret as indicative of aridity during the late-gla-cial and early postglacial. Furthermore, once Piceaglauca trees are mature they can tolerate tempera-tures a few degrees above 18° C (the average sum-mertime temperature that delimits the distribu-tion of this species, according to Ritchie andHarrison [1993]) if they receive adequate mois-ture to offset their water losses through transpi-ration (Webb et al. 1993). Abundant soil moisturewas provided along the shores of lakes and pondsduring this time before the regional water tabledropped significantly, and hence explains the pro-longed existence of white spruce (Yansa 2006),when grassland was already present in Montana(Barnosky 1989) and aspen (poplar) parkland in-habited southern Alberta (Beaudoin and Oetelaar2003; MacDonald and Case 2000). Spruce per-sisted latest at Rice Lake, a kettle lake in northernNorth Dakota, until 9240 14C yr B.P. (Grimm2001b), at a time when deciduous parkland wasalready well established in southern Saskatchewan(Yansa and Basinger 1999). The vegetation in thevicinity of Fargo, North Dakota, was a deciduousparkland with scattered spruce trees from 10,230to 9900 14C yr B.P. (Trollwood Park site, Figures1 and 3C), during an episode when Glacial LakeAgassiz drained through other outlets instead offlooding the Fargo area by flowing south (Yansaand Ashworth 2005).

The low precipitation regime continued dur-ing this transitional vegetation phase. Precipita-tion events undoubtedly occurred, but the highrates of evaporation of water and transpirationfrom plants during hot summers began to drawdown the regional water table. At the same time,the subsurface ground-water source from melt-ing stagnant ice was probably diminishing (Yansaet al. 2007). The Wendel site, which was a rela-tively deep paleolake that supported northern pikeand yellow perch during the spruce phase, beganto show its first signs of lake-level lowering at11,100 14C yr B.P. This signal was interpreted froman abrupt spike of Cyperaceae (sedge family) pol-

len (Figure 2B) found associated with seeds ofsedges, bulrushes and cattails and mudflat weeds(Table 2). Macrofossils from kettle lakes on theMissouri and Prairie Coteaus also report an in-crease in shoreline vegetation (Watts and Bright1968; Yansa 1998, 2002), but here the shift fromspruce parkland to deciduous parkland is moreabrupt than at the Wendel site. At the latter site, amixed spruce-deciduous parkland lasted from11,100 to 10,500 14C yr B.P. (Figure 2B). The pro-longed existence of spruce at the Wendel site isattributed to local ground-water inflow from ad-jacent uplands, not from precipitation, because 1)this basin is located downslope from the Coteausand 2) it provides a somewhat different climatesignal than does the nearby kettle lakes (Yansa etal. 2007).

Deciduous Parkland and Lake-LevelLowering (Folsom Environments)The dates for Folsom, from 10,900 to 10,000

14C yr B.P. (Holliday 1997), overlap with thosefor the local extinction of white spruce in NorthDakota and Saskatchewan (Figure 4). Deciduoustrees replaced the spruce trees along the shoresof lakes, ponds and presumably rivers, while theuplands retained their prairie cover. Many of theprairie plants that currently exist in the region to-day had arrived during the spruce parkland phase,while the rest of the flora, those that are slowermigrators, appeared before or during the onset ofthe Holocene.

The deciduous parkland phase in North Da-kota (Figures 1 and 4) lasted from 10,300 to 950014C yr B.P. at Moon Lake (Laird et al. 1996, 1998),10,500 14C yr B.P. to 9300 14C yr B.P. at theWendel site, and 10,600 to 9100 14C yr B.P. atColdwater Lake. This phase began earlier in SouthDakota, from 10,670 to 9400 14C yr B.P. at Pick-erel Lake (Dean and Schwalb 2000; Watts andBright 1968), and ca. 11,200 to 10,800 14C yr B.P.at Cottonwood Lake (Barnosky et al. 1987; NAPD2005), and later in southern Saskatchewan, fromca. 10,000 to 8900 14C yr B.P., at the Andrews site(Yansa and Basinger 1999). At the Flintstone Hillsite in southwestern Manitoba (Figure 1), sprucepopulations began to decline around 9800 14C yrB.P. and the proportion of poplar (aspen) in thevegetation increased (Boyd et al. 2003). In the

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high-elevation Cypress Hills of southwesternSaskatchewan, the earlier spruce phase is not pre-served in the pollen record of Harris Lake (Fig-ure 1), but poplar was widespread in this area by9120 14C yr B.P. (Sauchyn and Sauchyn 1991).

This shift from spruce to deciduous hard-woods has long been attributed to a warming cli-mate. During this time, summertime solar radia-tion was progressively increasing, but had not yetreached its Holocene maximum (Kutzbach et al.1993, 1998). By 11,500 cal yr B.P. (10,000 14Cyr B.P.), temperatures from July through Septem-ber were comparable to, or possibly slightlywarmer (ca. +1° C) than, modern (pre-industriallevel, ca. A.D. 1800), except for areas covered byresidual ice sheets; winters were still several de-grees cooler (Kutzbach et al. 1998). Anticyclonicair flow over the southern part of the Laurentideice sheet was diminishing as the glacier recedednorthwards (Webb et al. 1987), and was being re-placed by a zonal (west-to-east) wind pattern(Knox 1983; Vance 1987). Climate models simu-lated that precipitation values were lower thanmodern by at least 4 percent, which along with thewarmer summers lead to high evaporation rates(Kutzbach et al. 1998). These climate model in-terpretations agree well with the pollen and otherlake-core data (e.g., Shuman et al. 2002; Webb etal. 1987; Yansa 2006). A Younger Dryas cooling(11,000 to 10,000 14C yr B.P.) has been reportedin the north Atlantic region from paleolacustrinerecords (e.g., Delcourt and Delcourt 1991; Webbet al. 2004; Williams et al. 2001), but this has notbeen identified in the records of the northernPlains (Yansa 2006; Yansa and Ashworth 2005).

The deciduous parkland that occupied thenorthern Plains in the early Holocene includedseveral tree species (Table 2), all of which, ex-cept for Populus balsamifera (balsam poplar),currently inhabit the grassland region whereversoils are consistently moist. All sites in this re-gion were inhabited by Populus balsamifera andPopulus tremuloides (trembling aspen), speciesidentification confirmed by the presence of leavesand buds. In southern Saskatchewan, Betulaoccidentalis (river birch) coexisted with the pop-lars (Yansa 1998). But in North Dakota (ColdwaterLake) the species identified in this habitat wasBetula papyrifera (paper birch). Pollen of Ulmus

(elm), Quercus (oak), Acer negundo-type (boxelder), and Fraxinus nigra-type (black ash) arerecovered in sufficient amounts from Dakota lakesto indicate their local presence or the existenceof these trees nearby during this time, but not soin Saskatchewan. All of these trees, but particu-larly elm, indicate the presence of moist soils,but again I interpret this as moist soils restrictedto the shores of lakes and ponds instead of prima-rily a climate signal (though recognizing that someprecipitation occurred). My data support Claytonet al.’s (1976) interpretation for the LeonardPaleosol, a buried soil in Oahe Formation loess,having formed under deciduous tree and grasscover.

The Missouri and Prairie Coteaus and Glaci-ated Till Plains were inhabited by pockets of de-ciduous trees and shrubs around lakes and ponds,some of which were probably fed in part by groundwater. This area of the northern Plains was essen-tially a “park oasis” at a time when Fredlund andTieszen (1997) reported that the unglaciated north-ern Plains (Black Hills) had extensive grasslandcover with presumably little potable water outsideof river valleys. Similarly, the pollen and plantmacrofossil record of the Rosebud site along theSouth Dakota-Nebraska border (Figure 1) is trun-cated at 11,800 14C yr B.P. by drying of thisinterdunal pond (Watts and Wright 1966, NAPD2005). Holliday (1997) reported a decline inPaleoindian site density after ca. 10,000 14C yrB.P. on the southern High Plains and Holliday(2000) attributed this to the onset of episodicdroughts, as interpreted from geoarchaeologicaland soil geomorphic data. This is to be expected,for of all areas of the Great Plains the southernPlains would have become dry first, because ofits lack of a glacial meltwater source and its moresoutherly location receiving greater insolation.Consequently, during the Folsom Drought (10,900to 10,200 14C yr B.P.) and subsequent arid inter-vals on the southern High Plains (Holliday 2000),prehistoric hunters and gatherers probably shiftedtheir ranges northward. Some groups moved ontothe northern Plains, while others migrated to otherareas where there were more reliable watersources and better range conditions for game.

On the northeastern Plains, the first notice-able draw down of the regional water table, as in-

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terpreted from paleolacustrine proxies, was dur-ing the deciduous parkland phase, and this createdvast tracts of forage for migratory herbivores. Theextensive prairie marsh vegetation, comprised ofshallow-water submerged aquatic, sedge fen andshoreline “mudflat plants” (Table 2), contributedsignificantly to the water loss. These herbs havebeen called “draw down weeds” for their remark-able abilities to lower local water tables greatlythrough transpiration (Kantrud et al. 1989). Plantmacrofossils studied at the Wendel site,Coldwater Lake and other fossil localities in theregion indicate that these lakes and ponds becameeutrophic as they shallowed (Yansa 1998, 2002;Yansa et al. 2007). The expansive and productivegrowth of shallow-water submerged aquatic plants,such as species of Potamogeton (pondweed) andMyriophyllum (milfoil), as well as the formationof beds of Chara sp. (stonewort, a green algae),used up a significant amount of the dissolved car-bon dioxide in the water, causing the precipitationof carbonate-rich marls. Marl layers associatedwith fossils of deciduous parkland vegetation havebeen identified at the Wendel site (5-cm thick)and the Andrews site (40-cm thick). With the low-ering of the regional water table, fish becametrapped as basins became closed, such as at theWendel site and Seibold Pond. Fish became ex-tinct in these and other shallow basins by the on-set of the grassland phase when many water bod-ies in the region became ephemeral and eitherbrackish or saline with the increased concentra-tions of Total Dissolved Solids (TDS) in the wa-ter.

The aquatic-emergent vegetation along theshoreline expanded in area with the shallowing oflakes in the region, providing fodder for largepopulations of game animals. Stands of Typhalatifolia (common cattail, which prefers a waterdepth of around 50 cm), and several species ofScirpus (bulrush) and Carex (sedge) ringed theedges of lakes and ponds (Table 2). Boyd et al.(2003) note that the sedges they identified fromplant macrofossils at Flintstone Hill site in south-western Manitoba, Carex rostrata and C.aquatilis, today provide most of the winter for-age for northern bison herds (Bernard and Brown1977). An extensive sedge fen colonized the gla-cial Lake Hind basin in Manitoba after it drained

and soon after this area was occupied by Folsompeople (Boyd et al. 2003). Similarly, my plantmacrofossil research in Saskatchewan and theDakotas has led me to think that there would havebeen large and numerous tracts of forage for bi-son and other game in the drying glacial lake bedsthat existed on the Glaciated Till Plain and RedRiver Valley Lowland, as well as around the shoresof the numerous lakes and ponds that existed onthe Coteaus during this time.

This interpretation for vast pastures on thenorthern Plains agrees with the current thinkingthat bison hunting was an important part of theFolsom economy and that these hunters followedthe seasonal migrations of herds (Corbeil 1995;Meltzer 2004; Meyer and Liboiron 1990; Vickersand Beaudoin 1989). At the Heron Eden site insouthwestern Saskatchewan, for example, five 14Cages obtained from bison bones range from 10,210to 8,160 yr B.P. and are associated with Eden pro-jectile points (Corbeil 1995). During the LatePaleoindian occupations at this site, thepaleoenvironment was an interdunal marsh, whichattracted bison (Corbeil 1995).

Additionally, several species of marsh plantsmay have been gathered by Paleoindians for mul-tiple uses. Ethnohistoric data indicate that cattailwas utilized as a source of food, fiber and medi-cine by Plains Indians (Moerman 1998), and thisplant would have been widely available on thenorthern Plains since deglaciation, based on theplant macrofossils identified from numerous sites.Seeds of Chenopodium berlandieri (pitseedgoosefoot), commonly found at lake sites in theregion (Table 2), are known to have been consumedby prehistoric people in eastern North America(Smith 2002). But the few Folsom sites excavatedon the northern Plains so far have not containedcharred seeds of this or other species.

My interpretation of abundant plant resourcesduring the deciduous parkland phase on the north-ern Plains disagrees with Pettipas and Buchner’s(1983) statement that the scarcity of fluted pointsin Manitoba was due to low game populations in aclosed forest environment and hence fewPaleoindians. Other factors, I suspect, explain thelow numbers of Folsom sites in the region, in-cluding a low birth rate inherit in highly mobilepeople. Another explanation is the destruction of

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sites of Folsom and other cultural traditions dur-ing the remainder of the Holocene by 1) erosionfrom active eolian and colluvial processes, and 2)the deep burial of sites in low-lying settings (Bettisand Mandel 2002; Walker 1992; Waters and Kuehn1996; Wilson 1983), which primarily occurredafter the vegetation became exclusively grassland.

Onset of Grassland and Low-LakeStands (Late Paleoindian and Early

Archaic Environments) The onset of widespread grassland on the

northern Plains was not a biome shift, as was ear-lier thought (e.g., Wells 1970). Rather it was aseries of localized changes in species composi-tion centered along the edges of lake and pondbasins and presumably river banks. Prairie grassesand forbs colonized the northern Plains along withwhite spruce during the late Pleistocene, but atthis time they were primarily restricted to knollsand other drier soils in upland microhabitats (Yansa2002, 2006). When deciduous trees replacedspruce along the shores of lakes, ponds and otherlow-lying areas, the prairie cover persisted andwould have expanded whenever the soils becametoo dry for trees. Eventually, most of these de-ciduous trees disappeared with the drying of localsoils and we can then say that the grassland phasebegan. Grassland existed in Montana sincedeglaciation (Barnosky 1989), and became estab-lished in the central Plains as early as 12,000 14Cyr B.P. (Fredlund 1995; Watts and Wright 1966).But it took over a millennium for the recentlydeglaciated landscape of the northeastern GreatPlains to dry out and become a grassland—a veg-etation signal in synch with the climate changes.Precipitation undoubtedly occurred during thistime before prairie cover became widespread, butit is difficult to discern given the strong signal forground-water input into these basins (Yansa et al.2007). Dune activity probably began at about thetime that grassland was widespread in the region,but this is supposition rather than fact, becausethese dunes have since been reworked and pro-vide younger Optically Stimulated Luminescence(OSL) dates (Muhs et al. 1997, Running 1995).

Maximum (June-August) and minimum (De-cember-February) insolation for the Holoceneoccurred at 11,000 cal yr B.P. (9000 14C yr B.P.)

(Bartlein et al. 1998, Kutzbach et al. 1993, 1998).At this time, temperatures were 2 to 4° C warmerthan modern (pre-industrial level, ca. A.D. 1800)during July through September (a month lag is at-tributed to delays in land surface heating) exceptfor areas covered by residual ice sheets (Kutzbachet al. 1998). Correspondingly, at 9000 14C yr B.P.,winters were cooler than modern by -2 to -5° C(Kutzbach et al. 1998). A zonal flow of dry Pa-cific air was the dominant circulation from ca.10,000 to 7000 14C yr B.P., which is thought tohave formed a wedge between the Arctic and Gulfair masses and thereby significantly reduced pre-cipitation in the northern Plains and Midwest(Bartlein et al. 1998; Knox 1983). However, Gulfmoisture was brought into the northern Plainswhenever a meridional (north-south) pattern de-veloped, which occurred periodically (Vance1987).

Global climate models simulate that precipi-tation values were still lower than modern for thenorthern Plains at 9000 14C yr B.P. (Kutzbach etal. 1998). Available moisture was probably evenfurther reduced, as indicated by the results ofHostetler et al.’s (2000) higher resolution (re-gional) climate model for the vicinity of GlacialLake Agassiz. Their simulation suggested that dur-ing the Emerson phase (9900 to 9400 14C yr B.P.)an anticyclonic circulation existed over the lake,which suppressed precipitation in the area by de-flecting Gulf air to the south. This interpretationis supported by coeval pollen data from nearbyBig Stone Lake and the Wendel site, which recon-struct the transition from deciduous parkland tograssland (Yansa 2002). By about 9000 14C yr B.P.,carbon dioxide had reached pre-industrial (ca. A.D.1800) levels and was probably no longer a con-straint on plant life (Kutzbach et al. 1998; Sage1995).

The timing for the onset of widespread grass-land vegetation on the northern Plains varies fromsite to site, because of local differences in ground-water hydrology. Yansa et al. (2007) propose thatthe Wendel site received ground-water inflow dur-ing the lowering of the regional water table by thesubsurface capture of water from upslope lakes(which caused higher elevation lakes to go dry), aprocess described by Smith et al. (1997) as“ground-water capture.” This hydrologic contri-

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bution to the Wendel site explains why a decidu-ous parkland persisted there until 9300 14C yr B.P.,which would have made this area a park oasis forany Late Paleoindians inhabiting the Glaciated TillPlains. This groundwater inflow was subsequentlyreduced, but was sufficient to maintain low lakelevels at the Wendel site until ca. 8000 14C yr B.P.when a paleosol formed (Figures 2B, 4). After-wards, ground-water input was low, but did notcease, since it helped preserve (saturate) the fos-sils buried beneath the paleosol during the remain-der of the Holocene.

The kettle lakes on the Missouri and PrairieCoteau, such as Coldwater Lake, provide a betterclimate story (Figure 4) than that of the Wendelsite, because the latter received more ground-wa-ter inflow. The kettle-hole records indicate thatextensive grassland cover existed in the area ofCottonwood Lake (Barnosky et al. 1987; NAPD2005) and Pickerel Lake (Watts and Bright 1968,Dean and Schwalb 2000) in northern South Da-kota starting at ca. 10,800 and 9400 14C yr B.P.,respectively (Figure 4). Prairie cover was wide-spread in southern North Dakota by 9500 14C yrB.P. at Moon Lake (Laird et al. 1996, 1998) and9100 14C yr B.P. at Coldwater Lake (Figure 2A).At the Andrews site in southern Saskatchewan, oneor more fires burned balsam poplar, trembling as-pen and river birch trees sometime between 8800and 7700 14C yr B.P. when, presumably, the veg-etation became exclusively grassland (Yansa 1998;Yansa and Basinger 1999). In southeastern Alberta,grassland had replaced a deciduous parkland by9000 14C yr B.P. (Beaudoin 1999).

Associated with the shift from deciduousparkland to grassland vegetation is a dramatic in-crease in the salinity of many lakes with the low-ering of the regional water table (Figure 4).Geochemical data indicate that the onset of lakesalinity in the region occurred at ca. 9,500 to 900014C yr B.P. when these basins became hydrologi-cally closed. The geochemistries of these kettlesites suggest that concentrations of TDS in thewater fluctuated greatly in response to lake-level(water volume) during the remainder of the Ho-locene, particularly during the Altithermal(Hypsithermal).

Re-assessment of the Altithermal(Hypsithermal)

Temporal and Spatial Patterns of Aridity andWarmth. Without a doubt, droughts were commonduring the early and mid-Holocene on the north-ern Plains and adjacent regions, since they havebeen reconstructed not just from paleolacustrinedata (e.g., Bartlein and Whitlock 1993; Clark etal. 2002; Fritz et al. 2000; Grimm 2001b; Wright1992; Yansa et al. 2007), but also from archaeo-logical contexts (e.g., Antevs 1955; Holliday2000; Meltzer 1999; Sheehan 1995; Walker1992). The Altithermal (or Hypsithermal) wasonce considered to be a prolonged drought from7500 to 5000 14C yr B.P. (Antevs 1955), but wenow know that the climate during this time wasmore variable in time and space than thought 50years ago. Fluctuations between severe aridity andmoist intervals between ca. 9,000 and ca. 500014C yr B.P. would have impacted available re-sources, including potable water, during the LatePaleoindian and Early Archaic periods. Whilesome areas became dry, others became “oases”that provided drinkable water and forage for gameanimals. The regional paleolacustrine datasetbroadly supports Benedict’s (1979) “two-droughtAltithermal,” but it elucidates fluctuations be-tween arid and moist intervals at a finer scale thanwere realized several decades ago.

Not well recognized by Quaternary scientistsis that aridity was already a component of the cli-mate of the northeastern Plains before signs ofthe “Altithermal” appear in the paleolacustrine andarchaeological datasets. As discussed above,droughts probably occurred earlier during the late-glacial and early postglacial on the northeasternPlains, but signals for regional aridity were se-questered then, because the landscape was satu-rated with meltwater; a “residual meltwater effect”that supported trees (Yansa 2002). The only cluesfor aridity during the spruce phase are 1) the pol-len and plant macrofossil data for abundant prai-rie/steppe grasses and herbs, which covered theknolls and other upland locales (Yansa 2002), and2) coeval reports of the megaherbivoreMammuthus primigenius (woolly mammoth)(Harington and Ashworth 1986). The shifts from

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spruce parkland to deciduous parkland to grass-land reflect vegetation response to increasingwarmth and aridity. Kutzbach et al. (1998) modelprecipitation as being lower than modern frombefore 9,000 until well after 6000 14C yr B.P. inthe interior of North America, which is amply sup-ported by the pollen data (e.g., Vance et al. 1994;Webb et al. 1993) and archaeology (e.g., Antevs1955; Artz 2000; Benedict 1979). The transitionbetween Late Paleoindian and Early Archaic maybe related to the onset of the first arid interval atca. 8000 14C yr B.P. to affect the entire Great Plains(Figure 4).

Peak summertime insolation occurred be-tween 12,000 to 9000 cal yr B.P. (ca. 10,300 to8,100 14C yr B.P.) with its maximum (in terms ofwatts/m2) at 11,000 cal yr B.P. (9000 14C yr B.P.),as discussed above, and afterwards insolationamounts began to decline, but remained higher thanmodern until well after 6000 14C yr B.P. (Kutzbachet al. 1993, 1998). Areas that were never coveredby glaciers were able to respond the soonest tothis climate, such as the southern High Plains,which experienced droughts since about 11,00014C yr B.P. (Holliday 2000). Following this wasthe central Plains, where the climate became ex-tremely arid at 8500 14C yr B.P., causing uplandtrees to disappear and riparian trees to becomesparse in southeastern Nebraska (Baker et al.2000). On the glaciated northern Plains, those ar-eas situated along the edge of the ice sheets andhence deglaciated first, including the northwest-ern Plains of Montana (Barnosky 1989), exhib-ited signs of greater warmth and dryness at aboutthis time. Peak aridity and warmth in Montana andthe Foothills of Alberta occurred at ca. 9000 14Cyr B.P. (Barnosky 1989; Beaudoin and Oetelaar2003; MacDonald and Case 2000; Schweger andHickman 1989).

The timing of maximum aridity in the north-eastern Plains and the Midwest was delayed, be-cause of the climatic influence of the LaurentideIce Sheet that gradually diminished (Barnosky etal. 1987). The glacial-climate effect was dissi-pated by ca. 9000 14C yr B.P., and then, for thefirst time, the landscapes of these regions wereexposed to the full brunt of the insolation-drivenclimate (Barnosky et al. 1987; Webb et al. 1983;Wright 1992). On the northeastern Plains, peak

aridity during the Holocene took place between8000 and 5000 14C yr B.P. with an interval of se-verest droughts occurring between 6000 and 500014C yr B.P. (discussed in detail below).

In the Midwest USA, tallgrass prairie ex-panded about 100 km eastward of its present for-est/prairie border between 8000 and 5000 14C yrB.P., forming a “prairie peninsula” that reached itsmaximum extent at about 7200 14C yr B.P.(Bartlein et al. 1984; Grimm 1983; Winkler et al.1986; Wright 1992). This eastward prairie expan-sion was driven by both warmer and drier condi-tions during summers, compared to modern. Ofthe two, reduced precipitation was probably moreimportant, because the distribution of grasses andforbs are controlled primarily by precipitation(<600 mm/year) and fire regimes (Risser et al.1981). Bartlein and Whitlock (1993) recon-structed that precipitation was reduced by 100 mmin the Midwest from 8000 to 5000 14C yr B.P.,compared to today, based on pollen-derived esti-mates.

The landscape expression for maximumwarmth and aridity in the northeastern Plains andMidwest, at about 6000 14C yr B.P. (ca. 6000 calyr B.P.), occurred when summertime insolationhad already started to decrease; it was at this point5 percent greater than modern and correspond-ingly 5 percent less insolation occurred duringwinters (Kutzbach et al. 1998). The climate modelsimulation of Kutzbach et al. (1998) and climatedata inferred from pollen of Bartlein and Whitlock(1993) indicate that by 6000 14C yr B.P. summertemperatures were 1–2° C warmer and -1° Ccooler in winter, compared to the pre-industrialcontrol. Historic warming in the northern Plains,because of a global increase in greenhouse gases,was 1° C in the area of Bismarck, North Dakota(EPA 1998), which means that the summertimetemperature difference between 6000 14C yr B.P.and today is slight. Consequently, the Mid-Ho-locene Altithermal should be considered to be areduced precipitation regime rather than a timeof higher temperatures.

Warming at 6000 cal yr B.P. was much morepronounced at higher latitudes (>60° N) (Kutzbachet al. 1998). This warming along with a reported65 mm decrease in annual precipitation explainwhy the boreal forest/aspen parkland/grassland

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ecotones had shifted 200 km northward by 600014C yr B.P. (Zoltai and Vitt 1990). The shift of theseecotones to 53–55° N may be explained by themodeling results of Harrison and Metcalfe (1985),which suggests that the frontal zone shifted north-wards of 56° N during this time. This displace-ment of the jet stream, according to Bartlein et al.(1984, 1998), allowed dry Pacific air to domi-nate south of the front, thereby creating dry con-ditions on the Great Plains and Midwest for muchof the time between 8,000 and 5000 14C yr B.P.Dune orientation in these regions indicate thatprevailing winds came from the northwest(Arbogast and Muhs 2000; Muhs et al. 1997;Wolfe and Lemmen 1999), supporting this inter-pretation of mid-Holocene atmospheric circula-tion.

Droughts were not persistent during theAltithermal on the northern Plains and adjacentregions, but were more common and severe, andwere interspersed with moist intervals that variedin time and space. Katz and Brown’s (1992) de-scription of the precipitation patterns of historicdroughts may apply here. Precipitation during theearly to mid-Holocene may have been predomi-nantly that of high magnitude, low frequency con-vective precipitation events, which provided abun-dant precipitation to some areas, but bypassedother parts of the region. Also, there are subre-gional variations in the amount of precipitationreceived historically (Bryson 1980), and this prob-ably also occurred in the past. Precipitation issomewhat greater and more reliable in the east-ern part of the northern Plains (southeasternSaskatchewan, Manitoba and eastern Dakotas) thanin the western portion of the region (western Da-kotas, Montana, southern Alberta, and southwest-ern Saskatchewan). For example, during the 2002growing season, south-central Alberta experi-enced severe drought (<40 percent of average pre-cipitation), while southeastern Saskatchewan waswell above average (150–200 percent of averageprecipitation) (Beaudoin 2002). This interregionalvariability in moisture may explain the slight varia-tions in timing for different arid and moist inter-vals, as interpreted from the paleolacustrine data.

Discerning Aridity and the Season of Droughtsfrom Paleolacustrine Data. The unspoken assump-tion of the Altithermal is that it entails summer-

time droughts. However, the levels of lakes andponds and their chemistries (i.e., salinities) in thepast were most likely controlled by the amount ofwinter and early spring precipitation, as they aretoday in the region (Winter and Rosenberry 1995).In addition, the duration and magnitude of sum-mertime warmth controls evapotranspiration rates,which, in turn, lowers water levels (Winter 1989).An additional complexity is ground-water flow,which increases and diminishes at rates muchslower than do variations in precipitation amounts(Winter 1989; Wood et al. 2002). Deep aquifersystems can discharge water into lakes even dur-ing droughts (Wood et al. 2002). Also, as notedabove, lakes situated at lower elevations can cap-ture ground water from upslope, causing higher-elevation lakes to go dry (Smith et al. 1997).

An understanding of key proxy indicators andthe correlation of multiple proxies are necessaryto identify arid intervals and possibly infer thedominant season of drought, which are of interestto archaeologists and other Quaternary scientists.Early and mid-Holocene pollen records of thenorthern Plains indicate significant fluctuations,where peaks of Ambrosia (ragweed; identified totype by pollen) are considered indicative ofdroughts; and spikes of Poaceae (grass) and Arte-misia (sage, wormwood) correlate with moist in-tervals (see Figure 2A). Pollen researchers havelong agreed to this interpretation, but recentlyGrimm (2001b) separated out which pollen typesare indicative of precipitation at different seasonsof the year. In his reconstruction, droughts in thepast (like today) created numerous bare-soilpatches that ragweed colonized, whereas in moistyears Ambrosia had difficulty gaining a footholdin the dense thatch of perennial grasses and herbs.Another control on Ambrosia growth is the slowmaturation of this weed, which results in it beingout-competed by other prairie plants for soilmoisture unless its competitors (e.g., grasses andsage) are set back by drought. Ragweed does re-quire adequate summer rains to grow, but Grimm(2001b) contended that this annual, shallow-rooted weed is more apt to take advantage of thismoisture at short notice than are the perennialgrasses and sage. So the Ambrosia pollen spikesactually indicate aridity, which caused soil ero-sion, followed by summer rains. Peaks of peren-

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nial grasses (Poaceae) correlate with those of theperennial shrub/herb Artemisia (sage) and occurduring Ambrosia minima. Poaceae/Artemisia pol-len spikes indicate adequate winter precipitation,which replenished soil moisture that these plantscould access with their deep roots (Grimm2001b). By inference, lake levels in the regionrose with the infiltration of snowmelt, and thuscorrelate with Poaceae/Artemisia pollen maxima.

Seasons of drought cannot be discerned fromother lacustrine proxies, but oscillations betweenaridity and greater effective moisture can be iden-tified. For example, diatom-inferred salinity lev-els have been interpreted from shifts in the spe-cies assemblages of fossil algae preserved in lakerecords. Intervals of higher diatom-inferred sa-linity have been used to identify droughtperiodicities, which over the last 2,000 years (atleast) are considered by Fritz et al. (2000) to beassociated with solar minima. Geochemistry andstable isotopes of lake sediments and ostracodeshells can also indicate arid/moist cycles. Forexample, Xia et al.’s (1997) study of sedimentsfrom the Coldwater Lake core (the same core Ianalyzed for pollen and plant macrofossils) useddeterminations of d18O, d13C, Mg/Ca and Sr/Ca inostracode calcite aided by Sr/Ca in bulk carbon-ates to reconstruct paleosalinity levels. When lakewater had high Mg/Ca and low Sr/Ca ratios therewas a shift from calcite to aragonite precipitation,which indicates higher salinity levels (Aitken etal. 1999; Xia et al. 1997), and thus correlates withpeaks of Ambrosia-type pollen. Conversely, cal-cite layers and pollen peaks of Artemisia/Poaceaeindicate moister intervals (Xia et al. 1997). Coresfrom Coldwater Lake, Medicine Lake and otherlakes in the region typically have alternating thinlayers (laminae) of calcite and aragoniteinterbedded with silty clay (sometimes sandy clay)(Radle et al. 1989; Valero-Garcés et al. 1997; Xiaet al. 1997). This stratigraphy suggests that dur-ing the early to mid-Holocene there was a regionaltrend towards a more variable precipitation regimewith short-term fluctuations in effective moisture,but, on average, the amount of moisture was lower,in most years, than during today.

Onset of Maximum Aridity at ca. 8000 14C yrB.P. Salinities of lakes on the glaciated northernPlains first began to increase after they became

closed basin, no longer connected by surface wa-ter flow, with the lowering of the water table un-der an arid climatic regime. The shift from car-bonate-rich oligotrophic conditions to sulfate-dominated brine conditions in lakes occurred sev-eral centuries, if not millennia, earlier in thoselakes situated in South Dakota, Montana, andAlberta, compared to those located in North Da-kota, Saskatchewan and Manitoba. Bathymetry (ba-sin shape and depth) is also an important consid-eration in determining the rate of salinity increase.For example, the small pond at the Andrews sitein southern Saskatchewan became saline at 10,00014C yr B.P. (Aitken et al. 1999), when a short dis-tance away the deeper Oro Lake became hypersa-line a millennium later (Vance and Last 1996).

This was a time of rapidly increasing lake sa-linities, but still maximum salinities were reportedlater, during the mid-Holocene. A pronouncedspike in lake salinity (Figure 4), as interpretedfrom geochemistry, stable isotopes and, whereavailable, diatoms occurred at about: 8200 14C yrB.P. at Medicine Lake (Radle et al. 1989); 810014C yr B.P. at Pickerel Lake (Dean and Schwalb2000); around 7100 14C yr B.P. (gradual increaseafter 9500 14C yr B.P.) at Moon Lake (Laird et al.1996, 1998); and by 8900 14C yr B.P. at ColdwaterLake (Xia et al. 1997). The transition in lake chem-istry from mesosaline to hypersaline occurred atClearwater Lake in southwestern Saskatchewanbetween 9800 and 8600 14C yr B.P. (Last et al.1998). At Chappice Lake in southeastern Alberta,water levels fluctuated greatly between 7300 and6000 14C yr B.P. and by 6000 14C yr B.P. the lakelevel began to rise, but was still lower than presentuntil after 4400 14C yr B.P. (Vance et al. 1993). AtCeylon Lake in southern Saskatchewan, near theCanada-USA border, the lake chemistry shiftedfrom carbonate-rich water to a sulfate-dominatedbrine between 7000 to 6000 14C yr B.P. as the lakeshallowed, and for the next millennium it under-went periodic drying episodes that subaeriallyexposed the lake basin (Last 1990). Similarly, lakelevels were low and fluctuating in Montana(Barnosky 1989) and the Foothills of Alberta(MacDonald 1989) between 8000 and 6000 14Cyr B.P.

Closely correlated with the onset of lake sa-linity, as interpreted from geochemistry, stable

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isotopes and diatoms, is the Ambrosia-type pol-len peak (Figure 4). This ragweed spike dates to8000 14C yr B.P. at both Moon Lake (Laird et al.1996, 1998) and Coldwater Lake (Figure 2A), and8100 14C yr B.P. at Pickerel Lake on the PrairieCoteau (Dean and Schwalb 2000). This Ambrosiaspike occurred earlier at other sites in South Da-kota (Figure 4). The late date for Pickerel Lake,coeval with those reports from North Dakota, isprobably because this lake received ground-waterinflow that helped dilute surface water in the area(Dean and Schwalb 2000). Shallower basins in theDakotas, such as the Wendel site, did not receiveenough ground-water input to offset evaporativelosses, and so their fossil records became trun-cated at this time (Figure 4).

Using Grimm’s (2001b) pollen/vegetation andclimate reconstruction, I interpret that the land-scape in the vicinity of Coldwater Lake had driedout enough to provide its first drought signal atabout 8500 14C yr B.P. A prolonged dry spell oc-curred in this area from about 8200 to 7800 14Cyr B.P. when maximum Ambrosia values for theHolocene are reached (Figure 2A). But even thensome precipitation did occur, as indicated by theshort-term spikes of Artemisia and Poaceae.These brief moist intervals would have replenishedthe grassland pastures and freshened the water ofthe less saline lakes on the northeastern Plains,alleviating drought conditions for Early Archaicpeople.

Moister Conditions Between ca. 7700 and ca.6000 14C yr B.P. Available evidence suggests thatduring the mid-Holocene there was an interval ofgreater effective moisture in some areas of thenorthern Plains. Droughts still occurred periodi-cally, but were less common and severe comparedto times of greater aridity before (between ca.10,000 and 8000 14C yr B.P.) and after (ca. 6000to 5000/4500 14C yr B.P.). Pollen, plant macro-fossil and geochemical data indicate moister con-ditions at Coldwater Lake, overall, between about7700 and 6000 14C yr B.P. (Figure 2A), evidencedby a decrease in Ambrosia-type pollen and corre-sponding increase in Poaceae and Artemisia pol-len (Xia et al. 1997; Yansa 2002). At the Andrewssite during this time, pond sediments began to bedeposited again over a charcoal layer (represen-tative of one or more fires sometime between

8800 and 7700 14C yr B.P.) and the fossils indi-cate that water levels were higher than they aretoday, supporting a semi-permanent wetland(Yansa 1998; Yansa and Basinger 1999). Similarly,the water of nearby Clearwater Lake (Figure 1)was less saline from 8600 to 6000 14C yr B.P. thanbefore (9800 – 8600 14C yr B.P.), except for shortand periodic episodes of higher salinity between8200 and 7700 14C yr B.P. (Last et al. 1998).

Early Archaic occupation of the Rustad Quarrysite in southeastern North Dakota between 7550and 7180 14C yr B.P. occurred during a relativemoist interval with periodic aridity, as inferredfrom the study of buried soils and carbon isotopes(Running 1995). Likewise, fluctuations in pollenand seed types (especially those of Typhalatifolia) in the Coldwater Lake and Andrews siterecords indicate episodic dry intervals during thistime of somewhat greater effective moisture.Pollen, plant macrofossil, phytolith and carbonisotope data from alluvial deposits in southeast-ern Nebraska indicate that during the peak aridityfrom 8500 and 5800 14C yr B.P. there was a briefinterval around 7000 14C yr B.P. when precipita-tion increased, allowing for an increase in ripar-ian forest cover (Baker et al. 2000). Holliday(1989) reports a short-term increase in precipi-tation and available surface water during theAlithermal on the southern High Plains, but thetiming of this interval is uncertain.

Further research is required to ascertain thetemporal and spatial patterns of what appears tobeen a relatively moister interval in the mid-Ho-locene in the region. Whether this moist intervalis related to the 8.2 ka cold event is uncertain.This cold event, which spanned 8,400 to 8000 calyr B.P. (= 7700 to 7200 14C yr B.P.), was identi-fied from the Greenland ice cores and its causeattributed to the final and catastrophic drainage ofGlacial Lake Agassiz into the North Atlantic(through the Hudson Strait to the Labrador Sea)(Alley et al. 1997; Teller et al. 2002). Shuman etal. (2002) proposed that a meridional (north-south,more-or-less) circulation was established duringthis time (compared to the zonal circulation thatcauses droughts). This meridional pattern of up-per air flow, I suggest here, could explain the in-creased precipitation received during some sum-mers on the northeastern Plains starting at 7700

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14C yr B.P.Hu et al.’s (1997) analysis of varved sedi-

ments and oxygen-isotope composition of sedi-mentary carbonate from Deep Lake, situated justeast of the forest/prairie border in Minnesota, ledthem to reconstruct a pronounced cooling be-tween 8100 and 7500 14C yr B.P. They attributedthis cooling to increased outbreaks of Arctic airrelated to the 8.2 cal cold event and a higher frac-tion of the annual precipitation falling as snow.Therefore, the rise of water levels at the Andrewssite, Coldwater Lake and elsewhere probably re-sulted from an increase in wintertime precipita-tion more so than summertime rainfall.

The cold winters with increased snowfall mayhave encouraged Early Archaic people to seekmilder climates to the south during this season.Alternatively, there may not have been any shift inmobility patterns, since the winters (though coolerthan today) were warmer than during the TerminalPleistocene. People and game most probablyflocked to the northeastern Plains (or at least east-ern North Dakota and southern Saskatchewan)during the summers, because of the higher lakeand presumably river levels and plentiful pasturesof good nutritional quality. Cannon (1996) pro-posed for the Yellowstone area that grass biomassincreases after fires and thus supports more bi-son and other game, both now and in the past. Atleast one fire occurred at the Andrews site between8800 and 7700 14C yr B.P. followed by the estab-lishment of a semi-permanent wetland (Yansa1998). This suggests that periodic droughts driedout the prairie and thus encouraged the ignition offires followed by greater moisture that supportedluxuriant plant growth, creating ideal rangelandconditions to sustain vast herds of bison and otherherbivores. Essentially, much of the northeasternPlains would have been an oasis at times between7700 and 6000 14C yr B.P. when other parts of theGreat Plains were much drier. Aridity was mostpronounced on the southern High Plains from7500 to 5000 14C yr B.P. (Holliday 1995; Meltzer1999). Unfortunately, much of the archaeologi-cal evidence for this interval and earlier ones wereprobably eroded during the next arid interval whendroughts were both frequent and intense.

Severe Aridity: ca. 6000 to ca. 5000 14C yrB.P. A major region-wide dry spell began at about

6000 14C yr B.P., and this interval of aridity wasthe most severe of the entire Holocene. The fos-sil records at Andrews and other sites in southernSaskatchewan were truncated at ca. 6000 to 580014C yr B.P., and ephemeral wetland conditions wereestablished, which continued to the present day.The pollen and diatom records of Harris Lake,located at high elevation in the Cypress Hills (anoutlier of the Rocky Mountains) in southernSaskatchewan, provide a similar climate signal(Sauchyn and Sauchyn 1991; Wilson et al. 1997).This lake contained relatively fresh water for theentire Holocene except between 6500 and 520014C yr B.P. when brackish conditions developed(Wilson et al. 1997).

In North Dakota, Coldwater Lake becamehighly saline starting at 8900 14C yr B.P., but maxi-mum salinity occurred between 6000 and 500014C yr B.P. (Xia et al. 1997). Peak salinity epi-sodes at nearby Moon Lake were 6600 – 6200,5400 – 5200 and 4800 – 4600 14C yr B.P., withsome other arid intervals during the late Holocene(Valero-Garcés et al. 1997). These data fromMoon and Coldwater Lakes indicate that there werebrief moist intervals, as indicated by calcite lay-ers and pollen peaks of Artemisia/Poaceae, dur-ing this interval of frequent and intense multi-yeardroughts.

Large areas of mudflats were exposed when-ever lakes were draw down, and were colonizedby Chenopodium berlandieri (pitseed goose-foot), Iva spp. and other weeds in great abundances(Table 2). Seeds of these weeds are known to be afood source for the prehistoric inhabitants ofNorth America (Smith 2002), including the north-eastern Plains during the late Holocene (Shay ca.1994). These seeds may have been consumed byEarly Archaic people, particularly when resourcesbecame more limited on the northern Plains dur-ing periodic droughts. This interpretation agreeswith the general consensus that Early Archaicpeople of the northern Plains and adjacent regionsconsumed a greater diversity of food resourcesthan did the Paleoindians (e.g., Frison 1992; Shay1971; Sheehan 1995).

This interval of greater aridity was wide-spread, occurring throughout the Great Plains,Midwest, and Foothills/Intermontane West (e.g.,Barnosky et al. 1997; Holliday 2000; Wright

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1992). For example, an erosional unconformityin the stratigraphy of the badlands of westernNorth Dakota has been bracketed by dates of 6600and 4100 14C yr B.P. (Boutton et al. 1998). Simi-larly, a hiatus in sediment deposition occurred atCottonwood Lake in the glaciated area of easternNorth Dakota, between 8000 and 4000 14C yr B.P.(E. Grimm data in NAPD 2005). An erosionalunconformity existed in the stratigraphic recordof the Black Hills between 8000 and 4500 14C yrB.P. (Fredlund and Tieszen 1997), and maximumaridity is reported for this same period in Texas(Holliday 1989; Meltzer 1999). This interpreta-tion is supported by OSL ages on lunettes adja-cent to saline playas on the southern High Plains,which suggest that the local water table droppedsubstantially around 6500 ± 700 cal yr B.P. (ca.5800 14C yr B.P.) and 4900 ± 500 cal yr B.P. (ca.4400 14C yr B.P.) (Wood et al. 2002). These au-thors also report that the 6500 cal yr B.P. (ca. 580014C yr B.P.) drought interval was, of the two, moresevere and responsible for at least 10.6 m of sedi-ment accumulation within a few millennia (Woodet al. 2002). Today, ponds in North Dakota andSaskatchewan, and presumably in the rest of thisglaciated region, are filled with 5–7 m of sedi-ment and the deeper lakes (e.g., Coldwater Lake)have as much as 20 m of sediment accumulationsince the basins formed (Yansa 1998, 2002). Thesehigh sedimentation rates, much of it occurringduring the middle and late Holocene, indicate howmuch upslope soil has been eroded and hence theextent to which archaeological materials may havebeen destroyed and displaced.

My reconstruction of two intervals of greateraridity at around 8000 14C yr (Ambrosia-type pol-len rise, onset of peak lake salinity and the end offossil preservation at the Wendel site) and at ca.6000 14C yr B.P. (desiccation of more lake ba-sins, including truncation of the fossil records ofponds in southern Saskatchewan, and maximumlake salinity) and an intervening interval of greatermoisture (on average), thus broadly agrees withBenedict’s (1979) “two-drought Altithermal.”However, I have identified greater spatial and tem-poral variability of moisture within this tri-partclimatic pattern. This paper furthermore exempli-fies the complexity of climate and landscapechanges that occurred on the northern Plains,

which have bearing upon our understanding of pre-historic human occupation of this region over timeand space, especially during the most challengingof times, the Altithermal.

Oases for Early Archaic People During theAltithermal. The extent of human habitation of theGreat Plains during the Altithermal has been atopic of controversy for decades. Some archae-ologists have proposed the “Hiatus” and “Ref-ugium” models—that these droughts were so se-vere and persistent during the Altithermal, from7500 to 5000 14C yr B.P., to have caused EarlyArchaic people to completely abandon the north-ern Plains and shift their settlements to the pe-riphery, such as the Intermontane West, where bi-son populations were more numerous (Buchner1980; Forbis 1992; Frison 1978; Hurt 1966;Husted 2002; Mulloy 1958; Sheehan 1995). Otherarchaeologists have proposed that human occupa-tion of the northern Plains persisted during theAltithermal, though these people may have con-gregated more along river valleys, and if they didabandon the region it would have been only forshort durations (e.g., Artz 2000; Reeves 1973;Walker 1992). On the southern Plains, there arereports of Early Archaic people intermittently dig-ging wells in dry river valleys to access subsur-face ground water between 6500 and 4500 14C yrB.P. (Holliday 1989; Meltzer 1999). No prehis-toric wells are reported for the central and north-ern Plains, suggesting that droughts were less se-vere to the north (Meltzer 1999), which is sup-ported by my data.

The paleolacustrine data (described above indetail) indicate that even during the severest arid-ity interval, from around 6000 to 5000 14C yr B.P.,there were brief episodes of greater moisture onthe northeastern Plains, which would have allevi-ated the droughts. There were also scattered oa-ses on the northeastern Plains during the severestmid-Holocene droughts, which probably attractedpeople and game. Several mid-Holocene lake “oa-ses” are identified here for the first time.

The southern Lake Agassiz basin in easternNorth Dakota, western Minnesota and Manitobaand its southern outlet along the South Dakota-Minnesota border would have been an area of ref-uge, given that the plant fossil record of Big StoneLake (Figure 1) is continuous throughout the Ho-

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locene (Yansa 2002). Other oases were thosekettle lakes on the Coteaus with a ground-waterhydrology similar to that of Pickerel Lake; thislake maintained fairly fresh water during theAltithermal because of ground-water inflow (Deanand Schwalb 2000). In contrast, nearby MedicineLake became hypersaline at this time (Radle et al.1989). During the severest mid-Holocenedroughts, Coldwater and Moon Lakes containedwater, but it would have been too saline to drink.The water of these lakes, however, was freshened(i.e., made brackish, possibly drinkable by humans,definitely by herbivores) whenever enough pre-cipitation occurred. Grimm (2001b) proposes thatlakes which today have a water depth of <6 m driedout at least once during the Holocene, a statementwhich is supported by my research.

Prehistoric habitation sites probably existedaround the deeper lakes on the Coteau uplandsduring the mid-Holocene. But I predict that manyof these sites were eroded and those located alongthe lower slopes and lakeshores were buried un-der several meters of sediment. Upland locationsin the northern Plains have been largely over-looked by archaeologists as areas for Early Ar-chaic occupation, other than the works of Buchner(1980), Oetelaar (2004) and Oetelaar andBelanger (2005). Oetelaar’s (2004) analysis ofexcavations at the multi-component Stampede sitenear Calgary, Alberta, indicates no long-term aban-donment of this upland site during the Altithermal.This research demonstrates the potential for ob-taining valuable archaeological information fromthe search for, and investigation of, sites in up-land locations.

In contrast to the Agassiz lowlands and Coteauuplands, the Glaciated Till Plain (SaskatchewanPlain) would have offered little or no potable wa-ter, as indicated by truncation of the fossil recordof the Wendel site at ca. 8000 14C yr B.P. Most ofthe lakes that existed in this area were glacial lakesthat were drained by ca. 10,000 14C yr B.P. (Kehewand Teller 1994). The Wendel site is an unusualcase in that it is located in a meltwater channeloverlying what is probably a tunnel valley that af-ter deglaciation was partly filled with till and stag-nant ice that melted. After 8000 14C yr B.P., peri-odic precipitation probably raised the water tableat the Wendel site (so that this basin contained

shallow, standing water) and sustained forage forherbivores, but this area was probably desiccatedmost of the time. This desolate environment ofthe Glaciated Till Plain during much of the mid-Holocene would have inhibited Early Archaic habi-tation as well as caused the erosion of materialsfrom previous occupations. My paleoenvironmentreconstruction, presented here for the first time,may explain why Anfinson (1985) reported a pau-city of archaeological sites for this till plain.

Based on archaeology, Frison (1992) pro-posed that the Black Hills upland was an oasis dur-ing the Altithermal for large bison populations.Periodic moisture probably did sustain grass coverfor the bison herds that occupied this upland, butthe paleoenvironmental data indicate that the BlackHills was not an oasis. Phytolith and carbon iso-topic analyses indicate that severe droughts oc-curred in this area between 8000 and 4500 14C yrB.P. (Fredlund and Tieszen 1997). And, Eric Grimm(personal communication 2002) has been unableto find a lake in the Black Hills that did not dryout completely during the mid-Holocene.

Other oases previously recognized in the ar-chaeological literature are the river valleys of thenorthern Plains. At the height of the Altithermalaridity, at ca. 6000 14C yr B.P., a terrace of theSouth Saskatchewan River near Saskatoon,Saskatchewan, was occupied as a short-durationbison hunting camp (Walker 1992). Intensive bonebreaking at this site for procurement of bone mar-row suggests maximum use of this resource,which may indicate a scarcity of game. Althoughthis Early Middle Prehistoric (Early Archaic) siteis now located at the grassland/parkland ecotone,Zoltai and Vitt’s (1990) reconstruction of thenorthern grassland limit at this time indicate it was200 km to the north. This paleovegetation sce-nario thus indicates Early Archaic occupation ofriver valleys within the grassland region duringmaximum Holocene aridity.

My reconstruction for a severe dry spell start-ing at ca. 6000 14C yr B.P. to 5800 14C yr B.P. insouthern Saskatchewan correlates well withWalker’s (1992:129, Figure 20) archaeologicaldata. Walker’s (1992) study reported the leastnumber of sites/occupations found so far on thenorthern Plains date from 6500 to 6400 14C yrB.P., and that site/occupation occurrences are also

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low from 5800 to 5500 14C yr B.P. This paper il-lustrates that further paleoenvironmental and ar-chaeological research needs to be conducted toidentify the nature of human responses to the ever-changing climate of the northern Plains.

ACKNOWLEDGMENTSReviews by J. Peter Thurmond and Steven Bozarth have

been very helpful in improving this paper. This paper derivesfrom part of my Ph.D. dissertation and I thank my advisor, VanceT. Holliday, for his guidance and support. I also acknowledgemembers of my committee (Jim Knox, Lee Clayton, Lou Maher,Tom Vale and Marjorie Winkler) for their comments on an earlierversion of this paper. I thank Patricia Sanford and MarjorieWinkler for allowing me to conduct my research at the PollenLab in the Center for Climatic Research at University ofWisconsin-Madison, and Peter Knuepfer and William Stein forallowing me to finish this work at Binghamton University. DennisWendel of LaMoure County, North Dakota, kindly granted mepermission to drill on his property and the North DakotaGeological Survey (Ed Murphy) provided the equipment to corethis site. Eric Grimm and Pietra Mueller provided the ColdwaterLake core for my study, which I much appreciate. I thank AllanAshworth and Mike Newbrey for their identifications of thefossil fish bones. Some of the 14C ages for the Wendel site andColdwater Lake were provided free by the University of ArizonaAMS (AA) 14C Laboratory. C. Thomas Shay shared hisunpublished manuscript with me. I thank Alwynne Beaudoin,Garry Running, Ernie Walker, Urve Linnamae, and the late PatriciaFroese for mentoring me over the years.

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and Climate Change in Southern Saskatchewan. InHolocene Climate and Environmental Change in thePalliser Triangle, Southern Canadian Prairies, editedby Donald S. Lemmen and Robert E. Vance, pp. 139–172.Geological Survey of Canada Bulletin 534.

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Wetland in North Dakota, USA: Relative Interactions ofGround-Water Hydrology and Climate Change. Journalof Paleolimnology 38, in press.

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Peatlands in Western Interior Canada. QuaternaryResearch 33:231–240.

lake records of northern plains paleoindian and early archaic …yansa/yansa 2007-plains...

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