EES 213 Sedimentology, Stratigraphy, and Surficial Processes

Appalachian Basin Field Trip

LAB OBJECTIVES To describe the stratigraphy and sedimentology of two sections of rock, the first located in the vicinity of Lehigh Gap, the second located between Harrisburg and State College. The overall goal is to compare the Lehigh Gap section which is located at the edge of the Appalachian basin to the Harrisburg-State College section which is located in the interior of the Appalachian basin. This project is integrative and will build over a three week period. The main objectives to be accomplished during the weekend field trip are to become familiar with the section, describe the basic rock-types, and collect samples for petrographic analysis. MATERIALS Sedimentary Rocks in the Field textbook, Notebook, hand lens, 10% HCL, measuring tape, metric ruler, Brunton compass, rock color chart, grain size chart, rock hammer, sample bags, sharpie. INTRODUCTION The Appalachian foreland basin stretches across most of Pennsylvania, except for the extreme southeastern part of the state (Figure 1). During the Paleozoic, the basin lay in the foreland of actively growing mountains. Those mountains, which lay in what is now called the Pennsylvania Piedmont and the New Jersey Coastal Plain grew as the result of shortening across the Iapetus Ocean. As they were uplifted and eroded, the sediment washed off of them was swept to the northwest and dumped in a flexural downwarp or moat ringing the thickened crust of the growing mountain range. In this way, the Paleozoic Appalachian Mountains and its foreland basin stand as one of the world’s finest examples of how orogens evolve. That evolution is preserved in the sediments of the foreland basin. It is the goal of this field trip to learn how to read that record, and in the process, understand the evolution of the Appalachian Mountains. Given the amount of work that has already been completed in the Appalachian foreland, it is unreasonable to expect you, the student, to enter this project with no background information. The general story goes something like this (Figure 2): In the early Paleozoic, eastern North America, including all of Pennsylvania was low standing and part of a slowly subsiding passive margin – a tectonic setting very similar perhaps to the modern setting. Both siliciclastic and carbonates were deposited on the shelf of this passive margin. Beginning in the late Ordovician, active mountain building transformed the passive margin to an active, convergent margin. Mountains were thrust up and sediment was shed to the northwest, collecting in the foreland basin. This orogenic event is called the Taconic orogeny. The pattern of mountain building and northwestward shedding of sediment would be repeated at least two more times, once in the late Devonian and the second in the late Pennsylvanian. These orogenies are known as, respectively, the Acadian and Alleghenian orogenies. The Alleghenian orogeny was particularly severe because it involved a continent-continent collision between Africa and North America. That collision propagated deep into the Appalachian foreland, folding and faulting the formerly deposited sediment. It is these folded and faulted sedimentary layers that make up the Ridge and

Valley of Pennsylvania. Places like the southeastern flank of the Ridge and Valley, including the Lehigh Gap area, are located proximal to the former Appalachian Mountains. In contrast, places in the middle of the Appalachian basin, like State College, were distal to the mountains and the source of sediment. This field trip affords us an opportunity to compare proximal and distal parts of the foreland basin as we reconstruct the Appalachian mountain building history. Describing a stratigraphic section (Figure 3) is the most basic and important task that must be learned prior to understanding sedimentary rocks and the processes responsible for their deposition. A properly described section also lies as the cornerstone of every geologic map. That is, there must be a least one place in the area mapped that will stand as a reference section for the rocks that outcrop in the area. Even though the rocks are covered by vegetation over a wide area in the eastern U.S., geologists have learned a great deal about the origin, depositional environment, and subsequent geologic history of the Appalachian Mountains through intensive study of several key outcrops. One of those places lies about 50 km to the north at Lehigh Gap, the place where the Lehigh River carves a narrow gorge through Kittatinny Ridge escaping the Ridge and Valley province and flowing into the Great Valley. Virtually the entire Paleozoic section from the Ordovician through the Mississippian Systems is well exposed. Our project will focus on a section of siliciclastic Silurian System rocks called the Shawangunk and Bloomsburg formations. Time permitting we will expand our investigations to include underlying Ordovician System rocks and younger Devonian System rocks. Our first goal will be to show you as much of the section from the gap to Jim Thorpe. In this way, we will move up section from the Ordovician through Pennsylvanian rocks. GENERAL CHARACTERISTICS OF THE STRATIGRAPHIC SECTION The rocks exposed at Lehigh Gap and north to Jim Thorpe are part of the thick wedge of siliciclastic and carbonate sediments deposited in the Appalachian foreland basin during the Paleozoic. The foreland basin sediments at Lehigh Gap were uplifted and folded along west-verging thrust faults. Today, this area exposes the sedimentary rocks, dipping both to the northwest and southeast as the flanks of northeast-trending folds. For all of the outcrops we will visit, you and your partner must familiarize yourselves with the rocks, locate the contacts, collect basic structural and sedimentologic data (see below), and decide on the likely depositional environment. It will be important to take notes and make a scale sketch of the outcrop in your notebook. When constructing the stratigraphic column, you must record true rock thicknesses. This is easy when the rocks are either perfectly flat, or perfectly vertical – you just stretch out a measuring tape. But when the rocks are dipping, and you are measuring oblique to that dip, you must constantly make a geometric correction. Today, we want you to use a brunton compass to measure the dip of the rocks, record that dip in your notebook, and use the dip value to make the subsequent thickness correction. SEDIMENTARY DESCRIPTIONS You will need to follow our general menu for the description of sedimentary rocks. We define sedimentary rocks as being uniquely defined by their: composition, texture, structure, form, association, and fossils.

For texture, you need to describe grain size, shape, color, orientation, packing, sorting. For sedimentary structures, describe bedding, ripple marks, mudcracks, and cross beds. Both your textbook and lab handouts contain excellent descriptions of sedimentary structures not reproduced here. What you must do in the field for this lab is identify and describe to the professor or TA the following sedimentary structures: • bedding • graded bedding • cross-stratification

• cross-laminations, ripples • trough cross-sets • epsilon cross-stratification • plane-parallel laminations

• channel scours Please refer to the Tucker manual and have your observations confirmed by the professor and/or the TA. SAMPLE COLLECTION Your description of the rocks in the field will be complimented by microscope-based petrography. You have already collected the data for the sed-pet part of this lab in the preceding weeks; now you have the opportunity to see what outcrops those samples came from. You will approach the outcrop with the data already in hand as to the composition and texture of the sedimentary rock. FIELD TRIP We will attempt to visit eleven outcrops in the field on day 1 from which you will make your sedimentologic descriptions (Figure 4). These outcrops are keyed into the locations in Figure 4, and the list below: (1.1) Susquehanna Ave, Allentown - Hardyston Quartzite. (1.2) Whitehall limestone quarries – Benner Group and Jacksonburg Limestone (1.3) Pen-Bigbed slate quarries – Martinsburg formation (1.4) Appalachian trailhead – Martinsburg and Shawangunk formations (1.5) Palmerton – Shawangunk and Bloomsburg formations (1.6) Bowmanstown – Palmerton and Oriskany formations (1.7) Ashiquacola – Palmerton Formation (1.8) Alliance Sand and Gravel – Buttermilk Falls limestone (1.9) Bowmanstown – Mahantango and Trimmers Rock formations (1.10) Lehigh Gorge State Park – Mauch Chunk and Pocono formations (1.11) Jim Thorpe – Pottsville and Llewellyn formations On Day 2, we will travel to the west and deeper into the Appalachian basin. We plan on visiting 4 main exposures.

(2.1) Rt 61 Pottsville – Mauch Chunk, Pottsville, and Llwellyn Formations. (2.2) Rt 322 Millerstown – Rose Hill, Keefer SS, Rochester, McKenzie, and Bloomsburg Fm. (2.3) Rt. 322 Potters Mills – Beakmantown Group carbonates. (2.4) Rt 322 Reeds Gap – Reedsville, Bald Eagle, and Juniata Formations. DELIVERABLES We use two field trips, and two microscope-based sed-pet labs to build your project, which is due before the Thanksgiving break. I will leave it up to you to budget your time accordingly, but to help with not letting everything close in on you at the last minute. (1)Your field notebook with a page devoted to each outcrop that we visit. For each outcrop, you need: a) A sketch of the exposure b) A description of the bedding c) A description of the sedimentary structures d) A description of the texture e) A description of any fossils f) An interpretation of the water depth g) An interpretation of the depositional environment h) An interpretation of the PROCESS that deposited the sediment. (2) A synthesis of < 5 pages, written in your field note that incorporates and displays the following data / graphs: a) The stratigraphic column of eastern PA – take it directly from the handout below. b) Detailed information (collected above) keyed into the stratigraphic column. c) A discussion of how water depth (transgression and regression) changes from the

bottom of the column to the top of the column based on the data you collected in (1). (d) A discussion of how sediment texture and composition changes from the bottom of

the column to the top based on the data you collected in (1) above and from the sed-pet. (e) An interpretation of the general history of the Appalachian Mountains based on the

sedimentological data you have collected. Figure 1. Generalized geologic map of Pennsylvania showing the location of the Appalachian

foreland basin. Figure 2. Generalized tectonic history of the Appalachian Mountains (From Hatcher, 1989,

DNAG v. F-2, p. 528-529). Figure 3. Paleogeographic maps of the Appalachians. Figure 4. Stratigraphic column for the Lehigh Gap area. Figure 5. Geologic map of eastern Pennsylvania showing field trip stops for Day 1. Figure 6. Stratigraphic column for central Pennsylvania. Figure 7. Maps of central Pennsylvania showing field trip stops for Day 2.

Appala

chia

n fore

land

Appala

chia

n fore

land

Pale

ozo

ic A

ppala

chia

n M

ts

Pale

ozo

ic A

ppala

chia

n M

ts

Pre

Cam

brian

Cam

brian

Ord

ovic

ian

Silu

rian

Pa

leo

zo

ic

De

vo

nia

nM

issis

sip

ian

Pe

nn

sylv

an

ian

basement

rocks* granite gneisses; South Mountain; Yba and Ybh or gn and hg

54

45

05

44

04

10

36

03

25

28

62

51

20

6

Hardyston Qtzite*

Leithsville Fm*

Allentown Fm*

Beekmantown Gp*

Jacksonburg Fm

Martinsburg Gp*

Shawangunk cg

Bloomsburg Fm*

Decker, Rondout,Bossard- ville L.S., Poxono Island fms

Trimmers Rock Fm

other

Mahantango Fm

Marcellus Shale

Catskill Fm

Pocono Fm

Mauch Chunk Fm

Pottsville Fm

Llewellyn Fm

Newark Supergroup*

cg = conglomerate, Fm = formation, Gp = group, Qtzite = quartzite *common building stone

fine- to medium-grained, white to dark grey, commonly massive, lowest part sometimes pebbly and coarse; north flanks of South Mountain; Ch or Cha

Me

so

zo

ic

Tria

ssic

Stratigraphic Column for Bucks-Montgomery/Lehigh Valley/Pocono Region

shale, siltstone, fine to coarse-grained sandstone, conglomerate; greyish-red to reddish-brown; south of South Mountain (Bucks and Montgomery counties); JT bl or T b R R

fine- to coarse-grained, light to dark gray dolomite and shale; some interbeds of sand, oolites, phyllite; north and east of South Mountain; Cl or Clv

fine- to coarse-grained, light to dark gray dolomite and limestone; sand, oolites, stromatolites common; Lehigh Valley; OCa or Cal

massive dolomite with some interbedded fine- grained limestone; light to mediumÐdark gray; Lehigh Valley, north of Allentown fm; Oe (Epler member), Or (Rickenbach member) or Ob

"cement rock", shaley limestone, fine-grained; very dark gray; Lehigh Valley, north; Ojn, Ojk, or Oj

medium to dark gray slates and shales; Lehigh Valley, north; Om

fine- to coarse-grained, light to dark gray, sandstone and conglomerate with shale; Blue Mountain; Ss

red, green, gray shale, siltstone, sandstone; Blue Mountain; Sb

thin limestone and shales; north flanks of Blue Mountain into Valley and Ridge

limestone and shale; Valley and Ridge

silty shale and siltstone, medium dark to dark gray; ridges; fossiliferous; Dmh

gray silty shale, fissile; Dm

siltstone, sandstone, black shale; turbidites; Dtr

interbedded red, green, gray silts and sands, some conglomerates; Pocono plateau; Dck (undivided) or several members, e.g., Dcd, Dcpg,

yellow-brown to light gray sandstone, some coal; plateau and ridges; Mp

grayish red shale, siltstone, sandstone, and some conglomerate; plateau and ridges; Mmc or IPMm

yellow-brown, gray, olive; coal-bearing sandstone, siltstone, shale, conglomerate; ridges; IPp

gray to brown, green, or orange; coal-bearing sandstone, siltstone, shale, conglomerate; anthracite common; IP l

? (very ancient rocks)

shallow marine

carbonate banks, reefs

continental slope

continental rise/trench turbidites

shallow marine sands

river/marsh/ beach

shallow marine

alternating shallow

marine and nearshore

delta

rivers/ swamps

swamps

rivers,lakes,alluvial

fans

rifting,opening

ofAtlanticOcean

river/marsh shallow marine

rifting

expansion of proto- Atlantic

(Iapetus)

development of subduction zone off North

America

contraction of proto- Atlantic

closure of proto-

Atlantic(Iapetus)

formation of

Pangaea

Ta

co

nic

oro

ge

ny

Aca

dia

n o

rog

en

yA

lleg

he

nia

n o

rog

en

y

Depositional

Environment

Tectonic

EventsResource

conglomerates, sandstones, dikes

Buttermilk Falls L.S.

Palmerton S.S.Schoharie and Esopus fms

Oriskany S.S.Shriver Chert

New Scotland L.S.

Coeymans FmHe

lde

r-

berg

Grp

gray limestone w/shale; Dbf

quartz pebble conglomerate and sandstone; Dpdark silty and calcareous shale; Dseu

quartz sandstone w/conglomerate, chert at base; Do

prodelta

Time

Ma

Era

Per

iod

buildingstone

buildingstone/

aggregate

limestone/aggregate

naturalPortlandCement

slate

refractorysand

clay

flagstone

flagstone

anthracite

brownstonesbuildingstone

1.2

1.1

1.3

1.41

1.51.61

1.7

1.811.9

1.10

1.11

10 km Figure 5

Stratigraphic section of Cambrian to Silurian Rocks in central PA

Figure 6

2.1

2.3

2.4

2.2

10 km

Figure 7

Q

F L

Cratonic

Interior

Recycled

Orogen

Dissected

Arc

Transitional

Arc Undissected

Arc

Transitional

Continental

Base

ment U

plif

t

PALEOZOIC STRATIGRAPHIC COLUMN of Central Pennsylvania _____________________________________________________________________*Ridge Makers System & Series Formation and Members General Description Llewellyn Formation Cycles of conglomerate or sandstone; underclay coal, shale Pnn. L & N 2000’+ Pottsville Formation* Cycles of conglomerate or sandstone; underclay coal, shale L & M 1400’ Mauch Chunk Grayish red and gray shale M 5000’ Miss. Pocono* Mount Carbon Gray to buff, medium grained, cross-bedded sandstone 1600’ 940’ Beckville Gray to buff, medium grained, cross-bedded sandstone Lower 225’ Spechty Kopf Gray, fine and medium grained sandstone conglomerate 435’ near middle and base Catskill Duncannon Asymmetric, upward-fining fluvial cycles, basal nonred, locally 7250’ 2000’ conglomeratic sandstone is overlain by grayish red sandstone and siltstones Sherman Creek Interbedded grayish red claystone and fine grained, cross- 2400’ bedded sandstone Upper Irish Valley Interbedded, grayish red and olive gray sandstone, siltstone, 2850’ shale, overlain upward-fining cyclic deposits of gray sandstone and red siltstone Trimmers Rock Medium gray siltstone and shale, with fine grained sandstone in 2000’ upper part; graded bedding common Harrell Olive and medium light gray shale 200’ Mahantango Sherman Ridge* Olive gray, fossiliferous, claystone with interbedded fine 1600’ 600’ sandstones which coarsen upward Montebello Olive gray, medium grained, locally conglomeratic, fossiliferous 600’ sandstone, interbedded with siltstone and claystone in upward- Dev. coarsening cycles Fisher Ridge* Laminated gray silty shale Middle 700’ Dalmatia Light olive gray sandstone 300’ Turkey Ridge Light gray, fine to medium grained sandstone 100’ Marcellus Highly fissile, dark gray to black shale; weathers yellowish 106’ orange Onondaga Selinsgrove Medium to dark gray, fossiliferous argillaceous fine grained 165’ 80’ limestone Needmore Medium gray, fissile shale 85’ Lower Old Port* Dark gray, whitish weathering chert, underlain by shale limestone 100’ beds, and locally overlain medium to coarse grained sandstone Keyser Medium gray, fossiliferous, lumpy, fine to coarse grained 200’ limestone Upper Tonoloway Medium gray, laminated thin-bedded, fine grained limestone 600’ Wills Creek Gray calcareous shale with interbedded light gray, calcareous, fine Sil. 700’ grained sandstone, limestone and red silty claystone Bloomsburg* Red claystone shale with fine grained, argillaceous, hematitic Middle 500’ sandstone at base and near top

Mifflintown Dark gray, silty, calcareous shale; bioclastic, f. grain, thin bedded, 160’ limestone Middle Keefer* Gray, fine to coarse grained, fossiliferous, sandstone which is 40’ locally hematitic Sil. Rose Hill Light olive gray, shale, calcareous in upper part; grayish red, fine 950’ to coarse grained, hematitic sandstone near top Tuscarora* Light gray, fine to medium grained quartz sandstone L 600’ Juniata Grayish red, fine to medium grained, cross-bedded, graywacke 750’ sandstone; grayish red siltstone Upper Bald Eagle* Gray, cross bedded, medium to coarse grained sandstone, quartz 730’ pebble conglomerate Reedsville Olive gray silty shale, with increasing interbeds of graded gray 900’ sandstone in upper part Antes Gap Shale Very dark gray fissile, carbonaceous shale graptolite trilobite 200’ fauna Coburn Limestone Well-bedded, dark gray, fine to medium grained fossiliferous 275’ limestone with very dark shale interbeds Salona Limestone Dark gray fine grained limestone, less fossiliferous than Coburn 175’ and containing five or more metabentonite Middle Nealmont Limestone Medium gray, coarse grained highly fossiliferous (crinoids, 70’ bryozoans) limestone “Quarry Limestone” including: Linden Hall Medium gray, thick bedded, fine grained pure limestone 150’ Ord. Snyder Light gray, mudcracked, fine to coarse grained, thin bedded 70’ commonly fossiliferous and dolomitic limestone Loysburg Medium gray, fine grained, 1 footbedded “striped” limestone 400’ and dolomite Bellefonte Dolomite Yellowish gray, fine grained microcrystalline dolomite 1200’ Axeman Limestone Gray, slightly fossiliferous, fine grained, limestone with layers Lower 400’ of dolomite Nittany Dolomite Dark gray, cherty, coarsely crystallite dolomite 1200’ Stonehenge Limestone Gray, well bedded limestone 600’ Mines Dolomite Thick bedded, cherty, oolitic dolomite 250’ Upper Gatesburg Sandstone & Dolomite* Dolomitic sandstone or sandy dolomite Dolomite 1600’___ Warrior Limestone Thin bedded, gray limestone Cam. 1200’ M Pleasant Hill Limestone BLUE RIDGE-GREAT VALLEY SEQUENCE 250’ Elbrook Limestone Waynesboro Formation Waynesboro Formation L Tomstown Dolomite Antietam Quartzite* Eo- Harpers Formation (Montalto Quartzite Member) Cam. Weverton Quartzite* London Conglomerate U Catocton Volcanics Pre- Swift Run Formation Cam. L Gneissic Basement

Day 2

Morning: Proximal Deposits of the

Alleghanian Orogeny at Pottsville PA

From Slingerland et al., 1989

Day 2

Afternoon: Medial Deposits of the Taconian

Orogeny at Reedsville, PA

The Middle Ordovician to earliest Silurian section at Reedsville Gap, PA along US Route 322 provides a

relatively complete look at medial-distal deposits of the Taconian Orogeny. The section starts in mid-

Ordovician carbonates of the Trenton Group and records the foundering of the great North American

carbonate bank as Laurentia collided with an arc-microcontinent complex.

Excerpted from Thompson, 1986

Excerpted from Engelder et al., 1989

REFERENCES Slingerland, Rudy, & Furlong, Kevin P., 1989, Sedimentation and basin analysis in siliciclastic rock sequences; Volume 2, Sedimentology and thermal-mechanical history of basins in the Cen-tral Appalachian Orogen. Field Trip Guidebook T152, Am. Geophys. Union, Washington, DC, United States (USA) Thompson, Allan M, 1986, Stratigraphy of Upper Ordovician clastic rocks in south-central Penn-sylvania. Guidebook for the Annual Field Conference of Pennsylvania Geologists, vol.51, pp.21-26, 1986 Engelder, T., et al., 1989, Structures of the Appalachian Fold-Thrust Belt. Fierld Trip Guidebook T166, Am. Geophys. Union, Washington, DC, United States (USA)