12. SEDIMENTOLOGY OF PALYNOMORPHS AND PALYNODEBRIS IN CRETACEOUSCARBONACEOUS FACIES SOUTH OF VIGO SEAMOUNT

Daniel Habib, Queens College, Flushing, New York

ABSTRACT

Palynological study of 94 samples representing the lateHauterivian-Cenomanian carbonaceous section at Site 398, DSDP-IPOD Leg 47B, revealed major fluctuations in the abundance anddistribution of palynomorphs. Three palynofacies were distin-guished, based on the distribution of palynomorphs and palynodebris.The exinitic palynofacies is characterized by numerous specimensand species of sporomorphs to the almost total exclusion ofdinoflagellate cysts and small acritarchs, and by structuredpalynodebris such as vascular plant cuticle and tracheids. It is con-sidered to have been emplaced during times of high rates of sedimen-tation of land plant materials contributed from actively progradingdeltas. The micrinitic palynofacies is characterized by abundantamorphous palynodebris in the form of small, apparently carbonized,opaque or semi-opaque carbonaceous particles and a palynofloracomposed of fewer specimens dominated by Classopollis, bisaccates,and dinoflagellates. It represents the much diminished sedimentationof terrigenous vegetal materials, and was deposited by marine cur-rents which concentrated those sporomorph types morphologicallyadapted for selective transportation. The xenomorphic palynofaciescontains a palynoflora similar to that of the micrinitic fades, but isdistinquished by an abundance of amorphous palynodebris com-posed of optically translucent particles which show safranin stainwell. Palynomorphs may be rare or abundant in this facies.

The close correspondence between the sporomorph abundanceand organic carbon curves indicates that the organic carbon com-position of the more carbonaceous intervals of the investigated sec-tion is terrigenous and derived from land plants. The smallercarbonaceous content of the micrinitic facies may be the result of themuch smaller contribution of land plant materials. The lack of adirect correspondence between the sporomorph assemblages andorganic carbon composition in the xenomorphic facies suggests thatfactors other than, or additional to, the sedimentation of terrigenousplant materials were responsible for the carbonaceous compositionof these sediments.

INTRODUCTION

Site 398 was drilled on Leg 47B in the Galician regionnear the Iberian Peninsula. Its purpose was to study thehistorical development of this continental margin sincethe time of separation of southern Europe from NorthAmerica (Site Report, this volume).

Five holes were drilled at Site 398, located just southof the base of Vigo Seamount, between Portugal andGalicia Bank (Figure 1). Hole 398D was drilled in awater depth of 3890 meters, and penetrated the sea floorto a sub-bottom depth of 1740 meters. Recovery of 138cores represents an almost continuously cored sectionranging in age from late Hauterivian to Pleistocene. Adetailed description of the lithology and sedimentaryhistory of this section is given in the Site Report (thisvolume).

Hole 398D recovered an interval of highly car-bonaceous sediments of late Hauterivian-Cenomanianage. The palynology of this part of the section was in-vestigated for comparison of its stratigraphy with thepalynostratigraphy published on DSDP samples fromthe western North Atlantic (Habib, 1977). The initialresults published in this report indicate that the paly-nology of Hole 398D is different insofar as there aremajor fluctuations in the number of palynomorphs, andthat the more palyniferous samples are characterized bythe abundance of pteridophyte spores and gymno-spermous pollen grains to the almost total exclusion ofdinoflagellate cysts. Many of the spore species, especial-ly those of striate schizaeaceous spores, are absent orrare in the Lower and Middle Cretaceous of the westernNorth Atlantic. There is some comparison, however,with the palynomorph assemblages reported from the

451

D. HABIB

Depth in meters

Figure 1. Geographic location of Site 398, south of VigoSeamount.

Lower and Middle Cretaceous of the Grand Banks andScotian Shelf off eastern Newfoundland (Williams,1975; Williams and Brideaux, 1975).

The chronostratigraphic value of the palynomorphsin the late Hauterivian-Cenomanian part of the sectionfor precise age dating is limited, due to the presence ofintervals where palynomorphs are limited, and to thegeneral paucity of dinoflagellate fossils. Thus, allreferences to the specific ages of the investigated coresare based on the data provided by foraminifers (Sigal,this volume) and nannoplankton (Blechschmidt, thisvolume). Palynomorphs of potential chronostrati-graphic value are discussed in the Site Report (thisvolume).

The carbonaceous interval is represented by Cores 56to 138. This interval is 795 meters thick, extending from945 meters sub-bottom (Core 56) to the bottom of thehole at 1740 meters (Core 138). Arthur (this volume) hasinterpreted the origin of the carbonaceous interval. Twolithostratigraphic units were distinguished within this in-terval. The upper unit is composed of dark laminatedand bioturbated mudstones and claystones gradingdownward into dark organic shales with thin dolomiticlayers. Thin turbiditic sandstones, siltstones, andcalcareous debris flow layers with mudchip con-glomerates occur in the lower part. The unit is 723meters thick and ranges in age from Cenomanian toBarremian. The lower unit is composed of bluish whitenannoplankton limestones interbedded with varvedbrown mudstones. The lower unit is of late Hauterivianage and is 72 meters thick.

MATERIALS AND METHODS

Ninety-four samples from 69 of the cores represen-ting the carbonaceous interval were studied (Table 1).Samples composed of fine-grained, dark-coloreddetrital material were selected wherever possible,although some limestone samples were also included,especially from the lowest part of the section. Becauseof major changes in the composition and size of theresidues recovered after laboratory maceration, it wasdecided to count all palynomorphs mounted on themicroscope slides, and to determine the character andestimate the abundance of the other carbonaceous par-ticles.

Each sample was macerated by digesting the mineralsediment first in hydrochloric acid and then inhydrofluoric acid. The recovered residue was thentreated with nitric acid to partially oxidize the organicmatter, and with potassium hydroxide solution toremove humic acids. The resulting residues consisted ofvarious proportions of dispersed land plant spores andpollen grains (sporomorphs) including spores largerthan 200 microns in diameter, fungal spores andhyphae, small cellular algal(?) bodies, dinoflagellatecysts and small acritarchs (marine organic-walledphytoplankton), vascular plant cuticle, gymnospermoustracheal elements ("wood"), and particles without con-sistent external form. The relative abundance and oc-currence of these materials fluctuates greatly in the sec-tion. For example, the number of palynomorphs on amicroscope slide ranged form zero or a few to 1413from samples in different parts of the section, and thenumber of palynomorph species from zero or one to 54.

Fifty-two of the 94 samples were macerated so thatthe number of palynomorphs per sample of dried sedi-ment could be calculated (Table 1). Each sample wasdried, then weighed, prior to maceration. The weight ofthe samples varied from 0.88 to 1.55 grams. Then, thesample was macerated, and the residue was mounted inglycerine and weighed. A proportion was mounted on amicroscope slide and its weight was determined. Theratio in weight of residue recovered to that mounted onthe slide ranged from 56 to 80 times. The number ofpalynomorphs per gram of sediment was then calculatedby multiplying the ratio of palynomorphs on a slide tothe weight of the original sediment by the ratio of theweight of the macerated residue in glycerine to that ofthe proportion mounted on the slides, after the methoddescribed by Traverse and Ginsburg (1966).

The abundance of palynomorphs on a slide was com-pared with other parameters, such as the character ofthe other carbonaceous matter (structured palynodebris,amorphous palynodebris), the organic carbon percent-ages determined on board Glomar Challenger fromother samples in the same cores, and the proportion ofphytoplankton to sporomorphs. The calculated abun-dance of palynomorphs in the sediments was found tobe generally consistent with the number of palyno-morphs actually counted, and emphasizes the magnitude

452

PALYNOMORPHS AND PALYNODEBRIS

TABLE 1List of Hole 398D Samples Studied

TABLE 1 - Continued

Sample(Interval in cm)

56-2, 25-2756-2, 132-13856-3, 16-1856-3, 89-9156-4, 19-21

57-1, 117-11957-2, 25-2757-4, 69-7158-2,65-7158-2,72-74

59-1,96-9859-4, 1-360-1,77-7960-1, 148-15061-2, 1-3

62-1, 34-3662-5, 60-6262-5, 90-9263-6, 28-3065-2, 20-22

66-2, 74-7667-1,21-2368-5, 47-4969-3, 108-11071-4, 87-89

73-2, 107-10973-6, 67-7174-3, 120-12276-1,42-4476-1, 142-144

76-3, 92-9477-2, 10-1277, CC79-4, 35-3781-4, 6-8

82-2,49-5193, CC84-5, 55-5784, CC85-1,48-50

85-5,121-12386-5, 146-15087-3,128-13088-6, 91-9388, CC

90-3, 35-3790, CC91-3, 120-12292-7, 4-693-6, 89-91

93, CC94-2, 21-2295-6, 129-13196-2, 106-10797, CC

98-2,52-5499, CC100-6, 15-17101-6, 148-150102-3, 26-28

CalculatedNo» Specimen/g Dried Sediment

1527—__-

0_—

36

654_

1599_

36

_472109181

363545

109024,900

-

1024—

6763145-

_

3231_

7890-

11,374_

3074_

5840__

225411,067

-

_27,929

_46,716

_21,792

964358,99017,702

_17,784

_19,037

(Interval in cm)

102, CC103, CC104, CC105-3,97-99106-6, 19-21

107-3,51-53108-5, 123-125111-2, 140-142l l l . C C112-1, 108-110

112,CC113, CC115-1, 30-32115,CC118-7,40-45

119,CC120, CC121,CC122-7, 10-12123-5,72-74

124-4,24-26125, CC126-1,71-73126-2,59-61127, CC

129-7, 38-41130-5,1-5132-2, 148-150133, CC134-2, 127-129

135-2, 112-114136-2, 136-138137-1,65-67138-2,90-92

CalculatedNo. Specimen/g Dried Sediment

_--—

2510

81913321024

-5009

_-125

-

12,64952,039

—71,01329,808

0—

00

-

88,485—

37,8230

15 3

358611,57934,94328,054

with which the abundance of palynomorphs varies in theinvestigated section.

CRETACEOUS PALYNOFACIES AT SITE 398

The palynofacies of the carbonaceous interval wasexamined from the perspective of the sedimentology ofpalynomorphs and palynodebris recovered in themacerated residues (Combaz, 1964). The concept ofpalynodebris, as formulated by Manum (1976, p. 899),was modified to include amorphous carbonaceous par-ticles. Carbonaceous particles which can be identifiedmorphologically, e.g., the plant cuticle and pittedtracheids of vascular plants, are named structuredpalynodebris (cf. Manum, 1976), and those particleswithout consistent form but with distinctive optical prop-erties are called amorphous palynodebris. The struc-tured and amorphous palynodebris at Site 398, as wellas the palynomorphs, are considered to be the productsof marine sedimentary processes (cf. Manum, 1976).

Three palynofacies are distinguished, based on thetype of palynodebris and the general character of thepalynomorph assemblages. These are exinitic, micri-nitic, and xenomorphic.

453

D. HABIB

The exinitic palynofacies is characterized by largenumbers of sporomorph exines, sporomorph species,and the abundance of structured palynodebris (Plate 1,Figure 1), to the almost total exclusion in the paly-nomorph assemblages of marine organic-walled phyto-plankton. The sporomorph assemblages are diverse,and are characterized by the occurrence of striateschizaeaceous spores (Cicatricosisporites, Appendici-sporites), and other larger and more highly ornamentedspecies of pteridophyte spore genera, such as Trilobo-sporites, Pilosisporites, Foveotriletes, Sestrosporites,Microreticulatisporites, Densoisporites, Concavissimi-sporites, Murospora, Converrucosisporites, Dictyo-phyllidites, and Klukisporites. Classopollis torosus(Reissinger) occurs in high relative percentages through-out the Lower Cretaceous in Hole 398D, whethersporomorphs are abundant or rare in the samples. Thesporomorph assemblages are similar to those describedfrom coeval terrestrial sporomorph assemblages (cf.Brenner, 1963; Wolfe and Pakiser, 1971) and dissimilarto those described from the coeval western North Atlan-tic, e.g. DSDP Sites 99, 101, 105, 387, and 391 (de-scribed by Habib, 1977). The structured palynodebrisis equally diverse and abundant, and is represented bylarger (>IOO µm) specimens as well. Pitted trachealelements and cellular plant cuticle comprise most of thispalynodebris, which also include fungal spores andhyphae, and cellular algal (?) masses (Plate 1, Figures 5and 6). Amorphous palynodebris is rare or absent in theexinitic palynofacies.

Both the palynomorphs and structured palynodebrisusually are preserved very well. They are mostly optical-ly translucent, pale yellow to yellow-brown, and showred safranin stain well. However, tracheal elements mayalso be dark brown and semi-opaque.

The micrinitic palynofacies (Plate 1, Figure 3) ischaracterized by an overwhelming abundance of amor-phous palynodebris in the form of small (>20 µm)even-sized, nearly equidimensional carbonaceous par-ticles which appear to lack visible internal morphology.The particles are optically mostly opaque or semi-opaque, and black to dark brown. They do not showstain in red safranin solution. Structured palynodebrismay occur, but it is rare and appears carbonized.

In contrast to the exinitic palynofacies, the numberof palynomorphs is usually much smaller, and the pro-portion of phytoplankton to sporomorphs is high. Thesmall numbers of sporomorphs are represented by highpercentages of Classopollis torosus and species of bisac-cate pollen genera (Alisporites, Pinuspollenites) as wellas consistently lower percentages of other cosmopolitanspecies in the Lower Cretaceous, such as Exesipollenitestumulus Balme, Eucommiidites minor Groot and Pen-ny, Ginkgocycadophytus nitidus (Balme), Taxodia-caepollenites hiatus (Potonié), Cyathidites minorCouper, C. australia Couper, and Gleicheniiditessenonicus Ross sensu Skarby, among others. These taxaoccur in all three palynofacies. The phytoplankton oc-cur in a larger number of species in a sample. Each

species, however, is represented by a small number ofspecimens.

The xenomorphicpalynofacies is characterized by theabundance of amorphous palynodebris with irregularoutline and shredded appearance (Plate 1, Figure 4).Evidence of visible internal structure is lacking and theparticles range in size from very small (>15 µm) torelatively large (50-100 µm). Xenomorphic palynodebrisdiffers form other amorphous palynodebris by its op-tical translucence, its pale yellow or orange color, and itstains in safranin solution, suggesting a comparativelyhigh volatile organic composition.

The number of palynomorphs in a sample is variablein the xenomorphic palynofacies and usually is small.Like the micrinitic palynofacies, the palynomorphassemblages in the Lower Cretaceous are characterizedby high percentages of phytoplankton and a sporo-morph flora dominated by Classopollis torosus andspecies of bisaccate pollen. In those samples wherethere is a large number of palynomorphs, sporomorphsmay be more frequent than phytoplankton, althoughthe sporomorph flora is still dominated by Classopollisand bisaccate pollen grains.

PALYNOSTRATIGRAPHIC INTERVALSSeven palynostratigraphic units are distinguished,

based primarily on the sequence of palynofacies. Figure2 shows the palynostratigraphic units and correspond-ing palynofacies, as well as the number of palyno-morphs per microslide, number of sporomorphs permicroslide, proportion of phytoplankton to sporo-morphs (percentage phytoplankton), and percentage oforganic carbon. The biostratigraphic ages of the unitsare shown for comparison.

Palynostratigraphic Units I and VII are distinguishedon the basis of their contained xenomorphic palyno-facies. The xenomorphic facies also occurs in samplesfrom two cores in palynostratigraphic Unit II, whichis otherwise characterized by the exinitic palynofacies.The exinitic and micrinitic palynofacies form repetitivesequences throughout the major part of the section,in Barremian-Aptian (Units II and III) and Albiansediments (Units IV and V-VI), which suggests a casualrelationship. Units V and VI are both characterizedby a micrinitic facies, but are distinguished by theabundance of palynomorphs and the kind of palyno-morph assemblage.

Palynostratigraphic Unit I (Cores 138 to 133) ischaracterized by an abundance of xenomorphicpalynodebris and a fluctuation in the number ofpalynomorphs. The lower part of the unit (Cores 138 to135) contains a flora composed mostly of Classopollistorosus, and Pinuspollenites spp., as well as minoramounts of the cosmopolitan gymnosperm pollen andpteridophyte spores. Classopollis and Pinuspollenitesvary between 67 and 74 per cent of the palynomorphassemblages. Dinoflagellate species are common, buteach is represented by only a few specimens. Striateschizaeaceous spores are rare, occurring at less than 2

454

Figure 2. Palynomorph abundance profiles compared with organic carbon percentage profile.

D. HABIB

per cent in the samples. The upper part of Unit I (Cores134 and 133) contains very few palynomorphs, whichare represented entirely by small acritarchs. Palyno-morph specimens/gram range from 3,586 to 34,943in the lower part, and from 0 to 153 in the upper. Anaverage of 13,052 specimens/gram was calculated forthe entire interval. Organic carbon percentages arerelatively high. The unit is approximately 63 metersthick and has been dated late Hauterivian.

Palynostratigraphic Unit II (Cores 132 to 119) ischaracterized by the exinitic palynofacies. With the ex-ception of Samples 398D-126-2, 59-61 cm; 398D-126-1,71-73 cm; and 398D-124-4, 24-26 cm, which containabundant xenomorphic palynodebris and are barren ofpalynomorphs, this interval is represented by thegreatest abundance of structured palynodebris, sporo-morphs, and sporomorph species in the section. Thepalynodebris is the most varied, containing vascularplant tracheal elements and cellular cuticle, algal(?)cellular masses, fungal spores and hyphae, and spores200 µm in diameter. The sporomorph assemblages arealso the most varied in the section. Except for Core 119which contains 39 species of sporomorphs, the species inthis interval range from 44 to 54 per sample. In additionto the high percentages (ca. 40%) of Classopollis-bisaccates, the sporomorph assemblages of palyno-stratigraphic Unit II contain many species and speci-mens of striate spores and other larger and highlyornamented spores. For example, in sample 398D-123-5, 72-74 cm, C/ö55θ/7θ///5-biaccates comprise 32per cent of the assemblage, whereas striate sporescomprise 34 per cent in 12 species. The number of striatespore species ranges from 11 to 15 per sample, andaverages 12.6 per sample. The remainder of the assem-blage consists of larger pteridophyte spores (e.g.,Trilobosporites, Converrucosisporites, Densoisporites),and the ubiquitously distributed smaller spores (e.g.,Cyathidites, Gleicheniidites) and pollen grains (e.g.,Eucommiidites, Vitreisporites). Organic-walled phyto-plankton are virtually absent, with no specimens foundin the assemblages from most samples. Sporomorphsare also the most numerous; the specimens per gram ofdried sediment range from 12,649 in Sample 398D-119,CC to 88,485 in 398D-129-7, 38-41 cm, and average48,636 per gram for the interval.

The abundance of sporomorphs and structuredpalynodebris coincides with relatively high organic car-bon percentages (Figure 2). Palynostratigraphic Unit IIis approximately 124 meters thick and is dated asBarremian-early Aptian.

Palynostratigraphic Unit III (Cores 118 to 104) con-tains the micrinitic palynofacies. Micrinitic palyno-debris is abundant. However, in samples from Cores115 and 111, there is an admixture of micrinitic andsmall xenomorphic palynodebris. Palynomorphs aremuch fewer than in Unit II, ranging from 125 speci-mens/gram in Core 115 to 5009 in Core 112. Theaverage abundance is 1803 per gram. Although fewpalynomorph specimens occur on a microscope slide,between 30 and 100 per cent consist of organic-walled

phytoplankton in most samples. An exception occurs inSample 398D-112-1, 108 to 110 cm, where Classopollisand bisaccate species of Pinuspollenites and Alisporitescomprise more than 57 per cent of the total palyno-morph assemblage and where three species of dinoflag-ellates comprise 10 per cent. The number of palyno-morph species is also few, ranging from one species ofacritarchs in Core 115 to 15 species of palynomorphs (ofwhich 12 are sporomorph) in Core 112. Sporomorphspecies are usually slightly more frequent that phyto-plankton species. Striate spores are very rare in this in-terval, and are represented by smaller specimens.

The organic carbon percentages in sediments ofpalynostratigraphic Unit III are low, which coincideswith the small number of palynomorphs of which a highpercentage is phytoplankton. The unit is approximately142 meters thick, and is dated as late Aptian.

Palynostratigraphic Unit IV (Cores 103 to 90) marksthe recurrence of the exinitic palynofacies, within whichthere is a stratigraphic interval (represented by Cores 94to 92) containing the micrinitic fades. Palynomorphsare abundant throughout Unit IV, ranging from 9643 to58,990 specimens per gram, and averaging 27,449 pergram. Sporomorphs are most abundant in this facies, tothe almost total exclusion of marine phytoplankton.The sporomorph assemblages are characterized bystriate spores, but to a lesser extent than in Unit II(Figure 3). For example, the number of striate speciesaverages 7, while it averages 12.6 in Unit II. The numberof species in samples of the exinitic facies ranges from25 to 34, although only 17 were distinguished in sample398D-95-6, 129-131 cm.

The palynomorph assemblages of the micrinitic inter-val in palynostratigraphic Unit IV are also dominatedby sporomorphs. Phytoplankton comprises only up to 4per cent of the assemblage, in Sample 398D-93-6, 89 to

AGE

CENOMANIAN

ALBIAN

APTIAN

BARREMIAN

HAUTERIVIAN

MID

DL

E

LA

TE

>:

J

:

PA

LY

NO

ST

RA

TI•

GR

AP

HIC

U

NIT

S

VII

VI

V

IV

III

II

1

PA

LY

NO

FA

CIE

S

XENOMORPHIC

MICRINITIC

EXINITICMICRINITIC

MICRINITIC

EXINITIC

XENOMORPHIC

Figure 3. Percentage of striate schizaeaceous spores.

456

PALYNOMORPHS AND PALYNODEBRIS

91 cm. In contrast to the exinitic facies, the sporo-morphs are dominated by Classopollis and bisaccates,which together comprise between 64 and 77 per cent ofall palynomorphs; striate spores are few.

Palynostratigraphic Unit IV is similar to Unit II, inthat both contain an exinitic palynofacies characterizedby abundant sporomorphs, sporomorph species, andstructured palynodebris. Unit IV differs from Unit II inthe degree to which the facies is expressed. For example,there are slightly fewer specimens and species in UnitIV. Also, the palynodebris is equally abundant althoughnot as diverse, in that is is composed predominantly oftracheal elements. Comparison of the organic carboncomposition for the two units shows equally high per-centages (Figure 2). The unit is approximately 124 me-ters thick, and has been dated as early Albian.

Palynostratigraphic Unit V (Cores 88 to 69) containsthe micrinitic palynofacies. Characterized by the abun-dance of micrinitic palynodebris, it contains few paly-nomorphs and higher percentages of phytoplankton. Inmost samples, palynomorphs vary from 145 to 11,374specimens/gram, and palynomorph species vary from 2to 24. However, a notable exception occurs in thesample from Core 69, in which 24,900 specimens/gramwere calculated and 27 palynomorph species were ob-served. The average abundance for all samples is 7050per gram. The assemblages are characterized by highpercentages of sporomorphs of Classopollis and bisac-cates, and by phytoplankton. Phytoplankton percent-ages show a generalized increase stratigraphically up-ward through this interval. Organic carbon percentagesremain relatively low. Unit V is approximately 218meters thick and has been dated as middle Albian. It isotherwise distinguished from the previously describedunits by the occurrence of tricolpate angiosperm pol-len throughout, although they remain subordinate inpercentage to Classopollis torosus and species of Pinu-spollenites and Alisporites. Although the palyno-morph assemblages are meager, the dinoflagellate floraappears to become more diverse toward the top of theunit, where species of Deflandrea become importantelements.

Palynostratigraphic Unit VI (Cores 68 to 58) alsocontains abundant micrinitic palynodebris, but is dis-tinguished by even fewer palynomorphs. In all thesamples from this interval, only 36 to 1599 specimens/gram were calculated, and the number of palynomorphspecies in a sample varies from 1 to 12. The averageabundance was calculated to be 505 specimens pergram. Of the few palynomorphs, between 68 and 100per cent are phytoplankton. Organic carbon percentagesare relatively low, similar to that of palynostratigraphicUnits III and V. Palynostratigraphic Unit VI is approxi-mately 105 meters thick and has been dated as late Al-bian, including Vraconian.

Palynostratigraphic Unit VII (Cores 57 to Section56-2) is distinguished by a rich xenomorphic paly-nofacies and few palynomorphs. In most of the sam-ples, xenomorphic palynodebris is extremely abundantin the residues, and few or no palynomorphs were

recovered. In Sample 398D-56-2, 25-27 cm, 42 speci-mens were counted, which calculates to 1527 specimens/gram. The assemblage consists of dinoflagellate speciesof Deflandrea and Subtilisphaera, small acritarchs, andtwo species of Normapolles pollen genera, including cf.Atlantopollis sp.

The organic carbon percentages are relatively low forUnit VII, although the highest value for the entire sec-tion was recorded in a sample from Core 56. The unitis approximately 16 meters thick and has been dated asCenomanian.

SUMMARY AND CONCLUSIONSThe carbonaceous section of Cores 138 to 56 in Hole

398D is interpreted on the basis of the sedimentation ofsporomorphs and organic-walled phytoplankton, ac-cording to their distribution in the exinitic, micrinitic,and xenomorphic palynofacies. The exinitic facies hashigher percentages of organic carbon, and it is conclud-ed that the influx of abundant terrestrial vegetal debriscomposed mainly of sporomorphs, tracheids, andcuticular matter was responsible for its increased car-bonaceous composition. Evidence for this conclusion isdrawn from the fact that the macerated residues arecomposed almost entirely of the materials of landplants. The assemblages show a closer compositional re-lationship to coeval terrestrial assemblages than tocontemporaneous marine assemblages at DSDP sitesdrilled in the western North Atlantic. Additionalevidence for a terrestrial source is taken from the abun-dance of the sporomorphs in this palynofacies. Thisabundance compares with studies of modern sedimentsshowing the concentration of sporomorphs in marinesediments opposite discharge areas of deltas. For exam-ple, Cross et al. (1966) showed that in the Gulf ofCalifornia, major concentrations of sporomorphs,cuticles, and tracheids occur at delta mouths and insome deep submarine channels, as well as in silty claysslightly offshore. Muller (1959) showed similar resultsfor the Orinoco drainage system, where sporomorphswere concentrated in marine sediments near areas ofdeltaic sedimentation. These authors stress the impor-tance of marine currents in redistributing selected mor-photypes away from the areas of major terrigenous in-flux.

The occurrence of numerous striate schizaeaceousspores in the Lower Cretaceous exinitic facies is con-sidered to be significant, because of its rarity in thewestern North Atlantic and in the other palynofacies atSite 398, and its regular occurrence throughout LowerCretaceous terrestrial assemblages. Brenner (1963) re-ported the predominance of striate spores (and Classo-pollis torosus) among other trilete pteridophyte sporesin terrestrial sediments of the Lower Cretaceous Poto-mac Group of Maryland. Wolfe and Pakiser (1971)stressed the stratigraphic utility of these spores intheir study of the Potomac Group, stating that as manyas 75 species of striate spores were distinguished, whichthey correlated with the diverse megascopic flora of theFamily Schizaeaceae in the sediments. They reported an

457

D. HABIB

average of \% species per assemblage in the upper (Al-bian) part of the Potomac Group, which comparesfavorably with the number of striate species occurring inpalynostratigraphic Units II and IV. "Similar results wereobtained in the Lower Cretaceous of the Scotian Shelfand Grand Banks off eastern Canada. Williams (1975)described Neocomian assemblages from the lower partof the fluvio-deltaic Missisauga Formation which aredominated by schizaeaceous spores. Williams andBrideaux (1975) dated a late Albian palynoflora inwhich trilete spores were abundant, including numerousspecies of Cicatricosisporites and Appendicisporites.They interpreted these data to indicate that the locationof their core holes was very close to the Albian shorelineand possibly in a nonmarine locale. In her study ofmarine Aptian and Albian assemblages from southernEngland, Kemp (1970) compared their palynology withthe underlying, largely nonmarine, upper Wealdenfacies, and noted that the abundance and diversity offern spores, particularly those attributable to the FamilySchizaeaceae decreases upwards with a concomitant in-crease in the abundance of bisaccate pollen grains.

Because of the distribution of striate spores in non-marine assemblages throughout the Lower Cretaceous,it is concluded that their more numerous occurrence inthe exinitic facies of Site 398 is a measure of the higherrate of sedimentation of terrigenous organic matter(Figure 3).

In contrast to the exinitic palynofacies, the micriniticfacies is considered to represent the much diminishedterrigenous sedimentation of plant materials. This isbased on the smaller numbers of sporomorphs, the ap-parently sorted sporomorph flora composed mostly ofClassopollis and bisaccates, the higher proportion ofphytoplankton, and the prominence of small micriniticpalynodebris. These assemblages reflect the influence ofmarine currents, which may have sorted out the largerand more ornamented pteridophyte spores, includingstriate spores, and concentrated those sporomorphswhich were morphologically adapted for transporta-tion in currents. The morphotypes represented by Pinu-spollenites-Alisporites and Classopollis, correspondwell to this interpretation. Traverse and Ginsburg (1966)have demonstrated that bisaccate pollen of modern pineare buoyant in water and remains suspended for rela-tively long periods of time. In their study of the palyno-logy of surface sediments of the Great Bahama Bank,which are essentially devoid of terrigenous sediment,they showed that the distribution of these bisaccate pol-len corresponded to marine sedimentation patterns, andnot source vegetation. Pinuspollenites and Alisporitesmay have responded in the same manner, as they possessthe same basic morphology and are presumed to havebeen dispersed from anemophilous conifers. Classopollistorosus is a small (ca. 30 µm), spheroidal pollen specieswith diminutive ornamentation, which was dispersedfrom an extinct group of conifers (Brenner, 1963). Itssmaller size and shape suggest that this species wasmore easily transported by marine currents. C. torosushas a ubiquitous distribution in the Lower Cretaceous inHole 398D. Figure 4 shows that it is abundant in the ex-

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CENOMANIAN

ALBIAN

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initic facies, and occurs in high percentages there as wellas in the palynofacies characterized by fewer sporo-morphs. This suggests that the species was transportedequally with the other sporomorphs of the exiniticfacies, and not at the expense of their sedimentation.This would not be expected if the exinitic faciesrepresented a change of source vegetation. Rather, itmost likely reflects the transportability of Classopollisin marine currents, as this pollen genus is well repre-sented in the relative frequencies of both richly andpoorly palyniferous assemblages.

The association of bisaccates, Classopollis, andphytoplankton in the micrinitic facies can be comparedwith the study of Cross et al. (1966). They indicated thatfor the Gulf of California, pine and mangrove pollen in-crease in relative frequency away from the direct in-fluence of deltaic sedimentation, and that dinoflagellatecysts increase in absolute frequency. Mangrove pollenare similar in gross morphology to Classopollis, in thatboth are small and essentially spheroidal, and thus maybe similarly sedimented.

The abundant, small, even-sized, and apparently car-bonized micrinitic palynodebris may also represent veg-etal materials which have been selectively transported,transported.

The relatively low organic carbon percentagesassociated with the micrinitic palynofacies in Hole 398Dreflect the much smaller contribution of vascular plantmaterials. The contribution of pelagic organic matter tothe composition of these sediments is not clear, sincemarine phytoplankton do occur in high percentages inthe assemblages. Also, there are samples in the micri-nitic facies, e.g., 398D-69-3, 108-110 cm, which con-tain an abundance of sporomorphs, representing epi-sodes of increased terrigenous debris.

The interpretation of the xenomorphic palynofaciesdiffers from those given for the exinitic and micrinitic

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PALYNOMORPHS AND PALYNODEBRIS

facies, as there apparently is no direct correlation be-tween the abundance of palynomorphs and the amountof organic carbon in the sediments. For example, inpalynostratigraphic Unit I, the abundance ofpalynomorphs varies markedly although the organiccarbon percentages are consistently high. In Unit VII,palynomorphs are very few and the organic carbonpercentages are relatively low. However, according tothe Site Report (this volume), the highest organic car-bon content was recorded from a sample of Cenoma-nian age in Core 56 (Unit VII). This lack of cor-respondence between the palynomorph content and theorganic carbon composition in the xenomorphicpalynofacies suggests that factors other than, or in addi-tion to, the contribution of terrestrial plant materialwere responsible for the carbonaceous composition ofthe sediments. The carbonaceous components in Units Iand VII may reflect a large admixture of pelagic carbon,represented perhaps in the abundance of xenomorphicpalynodebris.

The character of the palynomorph assemblages is inaccordance with this interpretation. In palynostrati-graphic Unit I, the assemblages contain high percentagesof Classopollis and bisaccate pollen, as well as smallacritarchs and 15 species of dinoflagellates. In Unit VII,palynomorphs are very few, but phytoplankton in Sam-ple 398D-56-2, 25 to 27 cm comprise more than 80 per-cent of the assemblage. Thus, the character of the assem-blages is similar to that of the micrinitic facies, and thesporomorphs are considered to have been sedimented inresponse to selective sorting by marine currents ratherthan by high rates of terrigenous influx.

The palynological history for most of the lateHauterivian-Cenomanian can be interpreted in terms ofthe episodic sedimentation of terrestrial plant materialsin response to increased, then diminished deltaic activi-ty. Modern deltas are known to be major contributorsof sporomorphs to the marine environment, and duringthe Early Cretaceous much of the margin of the NorthAtlantic was characterized by major deltaic systems.During the Barremian-early Aptian, and again duringthe early Albian, deltaic progradation provided abun-dant land plant sporomorphs, cuticles, and tracheids tothe area south of Vigo Seamount, probably within pro-deltaic distal turbidites (Site Report, this volume). Theexinitic palynofacies which was emplaced during theseintervals is considered to have been responsible for theincreased carbonaceous composition of the represen-tative sediments. In each succeeding time period (e.g.,during the late Aptian and middle Albian), deltaicsedimentation was sharply diminished and marine cur-rents deposited mostly those sporomorphs which weremorphologically adapted for selective transportation, aswell as abundant fine micrinitic palynodebris. The oc-currence in high percentages of dinoflagellate cysts andsmall acritarchs during these episodes may reflect theremoval of the masking effect of high sporomorphsedimentation combined with the increased productivityof organic-walled phytoplankton. The smaller amounts

of spcromorphs in these sediments may account fortheir lesser carbonaceous composition, although thecontribution of pelagic organic carbon is not known. Inthe late Albian, even fewer terrigenous palynomorphswere deposited in the micrinitic palynofacies, as thepalynomorph assemblages formed at this time weremade up almost entirely of dinoflagellate cysts. Thereduction in number of sporomorphs sedimented be-tween the middle and late Albian, despite the relativelyconstant (albeit low) organic carbon sedimented, sug-gests the increased role of pelagic organic carbon.

During the late Hauterivian and the Cenomanian, thexenomorphic palynofacies was deposited in a pelagic en-vironment away from any influence of deltaic sedimen-tation. The high percentages of organic carbon inselected samples from palynostratigraphic Units I andVII may relfect the pelagic origin of xenomorphicpalynodebris, although there is no direct palynologicalevidence from Hole 398D to indicate this.

In conclusion, the close correspondence between thesporomorph and total palynomorph abundance curves(Figure 2) shows that the Hauterivian-Cenomanianassemblages in Hole 398D are composed almost entirelyof land plant sporomorphs, and that dinoflagellates andsmall acritarchs are frequent only in those samples con-taining few palynomorphs. The close correspondencebetween the sporomorph abundance and percentageorganic carbon curves, at least in the Barremian-middleAlbian interval, indicates that the carbonaceous com-position of these sediments was derived from landplants. The exinitic palynofacies was formed duringperiods of increased sedimentation of terrigenousvegetal debris, such as within distal turbidites associatedwith deltaic progradation. The calculated averagegreater abundance of sporomorphs in palynostrati-graphic Unit II than in Unit IV may indicate thatdeltaic sedimentation was more prominent in the areasouth of Vigo Seamount during the Barremian-earlyAptian than during the early Albian. This conclusionis supported by the smaller number of striate sporespecies and the occurrence of micrinitic palynodebrisin palynostratigraphic Unit IV. The micrinitic palyno-facies was formed during periods of decreased deltaicactivity, when marine currents were directly responsiblefor the deposition of selected sporomorph types.

The xenomorphic palynofacies was formed in apelagic environment. Although there is no directpalynological evidence, the xenomorphic palynodebrisnevertheless may be of marine origin. In the sub-surfaceUpper Cretaceous of New Jersey, the xenomorphicpalynofacies occurs in intervals of marine transgressionand the exinitic palynofacies, represented by numerousspecimens and species of angiosperm pollen, is abun-dant in intervals of terrigenous sedimentation duringmarine regression (R. Aurisano, Rutgers University,personal communication).

Based on the pyrolysis of Aptian-Cenomanianorganic matter of Hole 398D, Deroo et al. (this volume)have concluded that it is predominantly detrital and of

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D. HABIB

continental origin. De Graciansky and Chenet (thisvolume) came to the same conclusion on the basis oftheir sedimentological study of the organic matter.

ACKNOWLEDGMENTS

Rochelle Susan Habib assisted in the collection of data.Barbara Ann Barreiro and Valerie Krass macerated the sam-ples. Sheldon Nelson prepared the samples in which the weightabundances of palynomorphs were calculated.

The organic carbon data were collected by Anne Gilbert onboard D/V Glomar Challenger.

This study was supported by a grant from the NationalScience Foundation NSF OCE 76-14619.

H.L. Cousminer reviewed the manuscript.

REFERENCES

Brenner, G.J., 1963. The spores and pollen of the PotomacGroup of Maryland, Maryland, Dept. Geol. Mines WaterRes., Bull. 27.

Combaz, A., 1964. Les palynofacies, Rev. Micropaleontol.,v. 7, p. 205-218.

Cross, A.T., Thompson, G.G., and Zaitzeff, J.B., 1966.Source and distribution of palynomorphs in bottom sedi-ments, southern part of Gulf of California, Marine Geol.,v. 4, p. 467-524.

Habib, D., 1977. Comparison of Lower and Middle Creta-ceous palynostratigraphic zonations in the western NorthAtlantic. In Swain, F.M. (Ed.), Stratigraphic micropaleon-

tology of Atlantic Basin and borderlands: Amsterdam(Elsevier Scientific Publishing Co.), p. 341-367.

Kemp, E.M., 1970. Aptian and Albian miospores from south-ern England, Paleontographica, v. 131, p. 73-143.

Manum, S.B., 1976. Dinocysts in Tertiary Norwegian-Green-land Sea sediments (Deep Sea Drilling Project Leg 38),with observations on palynomorphs and palynodebris inrelation to environment. In Talwani, M., Udintsev, G., etal., Initial Reports of the Deep Sea Drilling Project,v. 38, Washington (U.S. Government Printing Office),p. 398-419.

Muller, J., 1959. Palynology of Recent Orinoco delta andshelf sediments: Reports of the Orinoco Shelf Expedition,Micropaleontology, v. 5, p. 1-32.

Traverse, A. and Ginsburg, R.N., 1966. Palynology of thesurface sediments of Great Bahama Bank, as related towater movement and sedimentation, Marine Geol., v. 4,p. 417-459.

Williams, G.L., 1975. Dinoflagellate and spore stratigraphy ofthe Mesozoic-Cenozoic, offshore eastern Canada, Geol.Surv. Canada, Paper 74-30, v. 2, p. 107-161.

Williams, G.L. and Brideaux, W.W., 1975. Palynologicalanalysis of late Mesozoic-Cenozoic rocks of the GrandBanks of Newfoundland, Geol. Surv. Canada, Bull. 236.

Wolfe, J.A. and Pakiser, H.M., 1971. Stratigraphic interpre-tations of some Cretaceous microfossil floras of the MiddleAtlantic States, U.S. Geol. Surv. Prof. Paper 750-B,p. B35-B47.

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PLATE 1

Figures 1, 2, Exinitic palynofacies.5-7 1. Specimen of Appendicisporites shown, as well

as structured palynodebris in the form oftracheids with bordered pits, and a fungalspore. Sample 398D-123-5, 72-74 cm.

2. Structured palynodebris. Vascular plant cuti-cle. Sample 398D-122-7, 10-12 cm.

5, 6. Structured palynodebris. Multicellular bod-ies of probable algal origin. 5. Sample 398D-132-2, 148-150 cm. 6. Sample 398D-129-7,38-41 cm.

7. Appendicisporites erdtmanii Pocock.Sample 398D-97, CC.

Figure 3 Micrinitic palynofacies. Amorphous palynodebriscomposed mostly of small opaque or semi-opaque, black particles. Sample 398D-62-5, 90-92cm.

Figure 4 Xenomorphic palynofacies. Amorphous palyno-debris composed mostly of optically translucentyellow, brown and orange particles. Sample398D-56-2, 25-27 cm.

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PLATE 1

PALYNOMORPHS AND PALYNODEBRIS

50µm

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D. HABIB

PLATE 2Spores Typical of Exinitic Palynofacies

Figure 1 Trilobosporites crassus Brenner. Sample 398P-123-5, 72-74 cm.

Figure 2 Trilobosporites marylandensis Brenner. Sample 398D-120, CC.

Figure 3 cf. Trilobosporites sp. Valvae are entire and smooth. Sample

398D-123-5, 72-74 cm.

Figure 4 Densoisporites sp. Sample 398D-123-5, 72-74 cm.

Figure 5 Densoisporites microrugulatus Brenner. Sample 398D-97, CC.

Figure 6 Foveosporites sp. Sample 398D-132-2, 148-150 cm.

Figure 7 Concavissimisporites punctatus (Delcourt and Sprumont).Sample 398D-122-7, 10-12 cm.

Figure 8 Concavissimisporites sp. cf. C. variverrucatus Couper. Smallverrucae of equal size distributed evenly on exine. Sample398D-132-2, 148-150 cm.

Figure 9 Densosporites sp. Sample 398D-132-2, 148-150 cm.

Figure 10 Striate spore species. Sample 398D-132-2, 148-150 cm.

Figure 11 Appendicisporites tricornitatus Weyland and Greifeld. Sample398D-97, CC.

Figure 12 Concavisporites sp. Sample 398D-122-7, 10-12 cm.

Figure 13 Cicatricosisporites sp. Sample 398D-132-2, 148-150 cm.

Figure 14 Cicatricosisporites venustus Deak. Sample 398D-123-5,

72-74 cm.

Figure 15 Cicatricosisporites sp. Sample 398D-119, CC.

Figure 16 Costatoperforosporites sp. Sample 398D-97, CC.Figure 17 Appendicisporites sp. cf. A. concentricus Kemp. Sample 398D-

120, CC.Figure 18 Costatoperforosporites sp. Specimen near lower left corner is

Gleicheniidites lamontensis Habib. Sample 398D-120, CC.

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PALYNOMORPHS AND PALYNODEBRIS

13

465

D. HABIB

Figure:

Figure

Figure

Figure

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Figure

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PLATE 3Spores Typical of Exinitic Palynofacies

Appendicisporites jansonii Pocock.1. Sample 398D-122-7, 10-12 cm.2. Sample398D-119, CC.

Appendicisporites sp.Sample 398D-132-2, 148-150 cm.

Costatoperforosporites sp.Sample 398D-122-7, 10-12 cm.

Microreüculatisporites crassiexinous Brenner.Sample 398D-132-2, 148-150 cm.

Converrucosisporites exquisitus Singh.Sample 398D-119, CC.

Appendicisporites sp.cf. A. bifurcatus Singh.Sample 398D-132-2, 148-150 cm.

Appendicisporites sp. cf. Anemia macrorhyza(Maljavkina). Sample 398D-120, CC.

Cicatricosisporites hughesii Dettmann.Sample 398D-122-7, 10-12 cm.

Cicatricosisporites sp.Sample 398D-119, CC.

Appendicisporites sp.Sample 398D-122-7, 10-12 cm.

Cicatricosisporites ludbrookii Dettmann.Sample 398D-122-7, 10-12 cm.

Appendicisporites cristatus (Markova).Sample 398D-122-7, 10-12 cm.

Appendicisporites sp.Sample 398D-122-7, 10-12 cm.

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PALYNOMORPHS AND PALYNODEBRIS

PLATE 3

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467