The Mid-Atlantic shore to the Appalachian highlands: field trip guidebook for the 2010 joint meeting of the Northeastern and Southeastern GSA Sections (GSA Field Guide 16)

134 Pages·2010·14.47 MB·English

by  Gary Mark Fleeger

The Mid-Atlantic Shore to the Appalachian Highlands:
Field Trip Guidebook for the 2010 Joint Meeting
of the Northeastern and Southeastern GSA Sections
edited by
Gary M. Fleeger
Pennsylvania Geological Survey
3240 Schoolhouse Road
Middletown, Pennsylvania 17057-3534
USA
and
Steven J. Whitmeyer
Department of Geology and Environmental Science
James Madison University
800 S. Main Street, MSC 6903
Harrisonburg, Virginia 22807
USA
Field Guide 16
3300 Penrose Place, P.O. Box 9140 Boulder, Colorado 80301-9140 USA
2010
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Library of Congress Cataloging-in-Publication Data
The Mid-Atlantic shore to the Appalachian highlands : field trip guidebook for the 2010 joint meeting of
the Northeastern and Southeastern GSA Sections / edited by Gary M. Fleeger and Steven J. Whitmeyer.
p. cm. -- (Field guide ; 16)
Includes bibliographical references.
ISBN 978-0-8137-0016-8 (pbk.)
1. Geology--Piedmont (U.S. : Region)--Fieldwork. 2. Geology--Blue Ridge Mountains Region--
Fieldwork. 3. Geology--Middle Atlantic States--Fieldwork. 4. Geology--Appalachian Mountains--
Fieldwork. I. Fleeger, Gary M. (Gary Mark) II. Whitmeyer, Steven J.
QE78.3.M53 2010
557.5--dc22
2010000940
Cover, front: View to the northeast of Germany Valley, West Virginia, from an overlook on Route 33. The
exposed ledges on the left and right margins and the distant center of the picture are outcrops of Silurian
Tuscarora sandstone; the floor of the valley is composed of Ordovician carbonate rocks. Thus, Germany
Valley is a several kilometer-scale breached anticline that plunges shallowly to the northeast. Photo by
Steve Whitmeyer. Back: View from Bearfence Mountain in Shenandoah National Park, looking north
toward the ridges of Massanutten Mountain, with outcrop of Catoctin greenstone in the foreground. Photo
by Chuck Bailey.
10 9 8 7 6 5 4 3 2 1
ii
Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .v

1. The Peach Bottom area in the Pennsylvania-Maryland Piedmont . . . . . . . . . . . . . . . . . . . . . . . . .1
R.T. Faill and R.C. Smith II
2. Soils, geomorphology, landscape evolution, and land use in the Virginia Piedmont and
Blue Ridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
W.C. Sherwood, A.S. Hartshorn, and L.S. Eaton
3. Magmatic layering and intrusive plumbing in the Jurassic Morgantown Sheet,
Central Atlantic Magmatic Province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
L. Srogi, T. Lutz, L.D. Dickson, M. Pollock, K. Gimson, and N. Lynde
4. The early through late Pleistocene record in the Susquehanna River Basin . . . . . . . . . . . . . . . .69
D.D. Braun
5. Stratigraphy, structure, and tectonics: An east-to-west transect of the Blue Ridge and Valley
and Ridge provinces of northern Virginia and West Virginia . . . . . . . . . . . . . . . . . . . . . . . . . . . .103
L.S. Fichter, S.J. Whitmeyer, C.M. Bailey, and W. Burton
6. Teachers guide to geologic trails in Delaware Water Gap National Recreation Area,
Pennsylvania–New Jersey
J.B. Epstein
This guide is available at http://fieldguides.gsapubs.org/ (open access) or as GSA Data Repository
item 2010097 posted at www.geosociety.org/pubs/ft2010.htm or on request from editing@
geosociety.org, Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
iii

Preface
This guidebook features fi eld trips offered during the joint meeting of the Northeastern and Southeast-
ern Sections of the Geological Society of America (GSA) held in Baltimore, Maryland, in March 2010.
Chapters in this guide refl ect the meeting’s theme (“Linking North and South: Exploring the Connections
between Continent and Sea,”) in that they span the lowlands of eastern Pennsylvania to the highlands of
northeastern West Virginia (Fig. 1). Four physiographic provinces are covered: Piedmont (Piedmont Upland
and Gettysburg-Newark Lowland Sections), Blue Ridge, Valley and Ridge, and Appalachian Plateau. The
geologic foci are likewise variable, ranging from Precambrian basement rocks to Pleistocene sediments.
The chapters are organized alphabetically, with premeeting trips listed fi rst (Faill and Smith, Sherwood
et al., Srogi et al.), followed by postmeeting trips (Braun, Fichter et al.) Topics range from surfi cial materi-
als and landscape evolution (Sherwood et al., Braun) to magmatism and igneous processes (Srogi et al.)
to stratigraphy, structure and tectonics (Faill and Smith, Fichter et al.) In addition, at least two of the fi eld
guides are specifi cally targeted at teachers and instructional pedagogy of fi eld-oriented education (Fichter et
al., Epstein).
Field Trip 6, by Epstein, is based on a fi eld guide originally published in conjunction with the 2006
GSA Annual Meeting in Philadelphia. As a result, the fi eld guide for this trip is not being published in this
volume. However, an updated guide, which includes additional material not included in the 2006 version,
is available (open access) at http://fi eldguides.gsapubs.org/, or as GSA Data Repository item 2010097 at
www.geosociety.org/pubs/ft2010.htm.
The editors would like to thank all of the authors, fi eld trip organizers, and leaders for the countless
hours that went into producing this volume. Special thanks to the reviewers who helped improve this volume:
Alan Benimoff, Duane Braun, Lee Daniels, Rick Diecchio, David Eggler, John Haynes, Louis Heidel, Dan
Richter, Bill Sevon, Steve Shank, Scott Southworth, Aaron Thompson, and Gil Wiswall. Many thanks to the
GSA Publications Department staff for help in preparing, formatting, and generally shepherding this guide
through the production process. We hope that geoscientists and educators alike will fi nd the contents of this
fi eld guide thought provoking in discussions of regional geology and pedagogy, as well as useful for planning
future fi eld excursions.
Gary M. Fleeger and Steven J. Whitmeyer
v
Figure 1. Google Maps relief map of the Mid-Atlantic region showing the approximate locations for the fi eld trips covered by the chapters in this volume. Field Trip 1—Faill and Smith; Field Trip 2— Sherwood et al.; Field Trip 3—Srogi et al., Field Trip 4—Braun; Field Trip 5— Fichter et al.; Field Trip 6—Epstein.
6
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vi
The Geological Society of America
Field Guide 16
2010
The Peach Bottom area in the Pennsylvania-Maryland Piedmont
Rodger T. Faill*
3407 Rutherford Street, Harrisburg, Pennsylvania 17111-1850, USA
Robert C. Smith II*
22 Longview Drive, Mechanicsburg, Pennsylvania 17050, USA
ABSTRACT
The Appalachian Piedmont in south-central Pennsylvania and north-central
Maryland contains metasedimentary siliciclastic rocks (phyllites to quartzites) that
were deposited largely offshore of Laurentia, prior to and during the early history
of the Iapetan Ocean. The Peach Bottom area is centered on the belt of Peach Bot-
tom Slate and overlying Cardiff Quartzite, which is surrounded by the late Neopro-
terozoic and early Paleozoic rocks of the Peters Creek and Scott Creek (new name)
Formations. Their provenance was the Brandywine and Baltimore microcontinents
that lay farther offshore of the Laurentian coast. This area also includes an ophiolitic
mélange that formed in front of an advancing island arc in Iapetus. All these rocks
lay largely undisturbed throughout much of the Paleozoic, experiencing only chlorite-
grade greenschist facies metamorphism through deep burial. Alleghanian thrusting
associated with the growth of the Tucquan anticline imparted their present wide-
spread, monocline, steep southeast dip of the bed-parallel foliation.
INTRODUCTION The rocks within the Peach Bottom area have long been
considered part of a regional syncline (Knopf and Jonas, 1923,
The Peach Bottom study covers an ~40 km × 13 km 1929), with the Peach Bottom Slate as the youngest stratigraphic
quadrilateral-shaped area located in Lancaster and York Coun- unit. Traditionally, this core was presumed to be underlain by the
ties, Pennsylvania and Harford and Cecil Counties, Maryland Cardiff Quartzite and Peters Creek Formation, which lay adjacent
(Fig. 1). The south-southeast fl owing Susquehanna River crosses on both the northwest and the southeast limbs. None of the rocks
midway along its length. The boroughs of Delta, Pennsylvania, in the Peach Bottom area support this traditional interpretation.
and Cardiff, Maryland, lay some 10 km southwest of the river.
The distinctive Peach Bottom Slate underlies a narrow out- GEOLOGIC SETTING
crop belt (0.25–2 km wide) for 30 km along the middle of the
Peach Bottom area. The Cardiff Quartzite, which conformably The dominant structure in the south-central Pennsylvania
overlies the slate, surrounds the slate along much of its perimeter. Piedmont siliciclastics is the Tucquan anticline (Frazer, 1880),
Together, they constitute the Peach Bottom Slate Belt. a very large, west-southwest–trending, gently plunging, upright
*[email protected]; [email protected]
Faill, R.T., and Smith, R.C., II, 2010, The Peach Bottom area in the Pennsylvania-Maryland Piedmont, in Fleeger, G.M., and Whitmeyer, S.J., eds., The Mid-
Atlantic Shore to the Appalachian Highlands: Field Trip Guidebook for the 2010 Joint Meeting of the Northeastern and Southeastern GSA Sections: Geological
Society of America Field Guide 16, p. 1–30, doi: 10.1130/2010.0016(01). For permission to copy, contact [email protected]. ©2010 The Geological Society
of America. All rights reserved.
1
2 Faill and Smith
fold (Fig. 2). Its east end lies at or near the southwest terminus middle Ordovician (barring some intervening structure(s)). If a
of Mine Ridge; its west end in the vicinity of the Maryland- thrust, the Peach Bottom area rocks could be much older.
Pennsylvania border is not well defi ned; it either dies out or is The Laurentian carbonate shelf consists of a thick sequence
truncated. The dominant foliation that pervades the metasedi- of largely carbonate rocks ranging in age from lower Cambrian
mentary schists parallels bedding and best displays Tucquan to middle Ordovician. This sequence overlies a thinner sequence
anticline form: subhorizontal along the hinge, northwest dip- of siliciclastic rocks (quartzites to mudstones) that in turn over-
ping north of the hinge, and southeast dipping to the south lies the metabasalts and metarhyolites of the Catoctin Formation.
(Freedman et al., 1964). The Catoctin Formation itself overlies an even thinner sequence
The schists of the Tucquan anticline are bounded on the of the Neoproterozoic Chilhowee siliciclastics to the west. The
northwest by the Martic Line, a fairly sharp transition between Catoctin Formation is Neoproterozoic to lower Cambrian in age
the Tucquan schists and the slope carbonates to the southeast, (564 ± 9 Ma in the north-central Appalachians, Aleinikoff et al.,
and schists to the northwest that accumulated on the Laurentian 1995; Tollo et al., 2004).
continental margin. The nature of the Martic Line lies at the cen- The Baltimore Mafi c Complex and equivalent rocks to the
ter of a long-standing, contentious issue (Miller, 1935; Cloos and southwest in Maryland bound the southeast side of the Tucquan
Hietanen, 1941; Rodgers, 1970; Higgins, 1972; Wyckoff, 1990; schists (Fig. 2). The Baltimore Mafi c Complex consists in large
and Wise and Ganis, 2009), as to whether it is a conformal strati- part of peridotites and pyroxenites that intruded the lower reaches
graphic contact or a thrust fault. The nature of the Martic Line of an island arc (herein called Cecil Island Arc, following Faill,
bears on the Peach Bottom area. If the Line is a conformal con- 1997) in Iapetus at 489 ± 7 Ma (Sinha et al., 1997). The peridotites
tact, the age of the Peach Bottom area rocks may be younger than and pyroxenites have since been altered largely to serpentinites,
Figure 13
Figure 9
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McGuigan Quarries
Bald Friar Hill
Figure 10
Figure 1. Geologic map of the Peach Bottom area in south-central Pennsylvania and north-central Maryland, within portions of the
Conowingo Dam, Delta, Holtwood, and Wakefi eld 7½-minute quadrangles. The Delta Duplex is the fault-bounded zone that contains the
Peach Bottom Slate, Cardiff Quartzite, and Sykesville (north) Formation.
Peach Bottom area, Pennsylvania-Maryland Piedmont 3
talcs, and carbonates (mostly magnesite). During the advance of locally, with subvertical axial surfaces and steeply southeast-
the Baltimore Mafi c Complex, sediments, basalts, and ultramafi c plunging axes. Local faults of various orientations are also pres-
fragments accumulated as a precursory mélange, the Sykesville ent, with displacements of a few meters at most. Crenulations are
Formation (Muller et al., 1989) in front of Baltimore Mafi c Com- common, many of them plunging moderately to the northeast,
plex. The sharp contact of the Sykesville schists, metabasalts, and but gently southwest-plunging crenulations are present as well.
steatized ultramafi tes with the Tucquan schists, the striking lithic
contrast, and the very different provenances support the probabil- THE OCTORARO BASIN
ity of a thrust fault contact between the two at the Martic Line.
The Tucquan schists have been metamorphosed to green- The Rodinian continent was amalgamated by the Gren-
schist facies. Almandine garnets are common in the hinge of villian orogeny (from ca. 1200 to 1000 Ma) at the end of the
the fold. The rocks on either side are at biotite grade, and authi- Mesoproterozoic. What was to become the Peach Bottom area
genic albite is common. Farther away from the hinge, chlorite lay well within Rodinia during the subsequent Neoproterozoic,
is the dominant mineral in the pelitic fractions. This pattern of underlain by rocks of the Grenville orogen. It appears that signifi -
higher-grade metamorphism in the presumably older rocks in cant rifting activity occurred within Rodinia during the middle of
the hinge implies a greater depth of burial for those rocks, and the Neoproterozoic, from 760 to 700 Ma (Tollo and Aleinikoff,
suggests that the metamorphism occurred prior to the develop- 1996; Tollo et al., 2004), as evidenced by the development of the
ment of the anticline. Robertson River Igneous Suite in Virginia (Tollo and Aleinikoff,
Structurally, the Tucquan anticline appears to be simple (Fig. 1996) and possibly the Ocoee basin. Whether true oceanic crust
2). Throughout much of the anticline, the dominant foliation was formed in the rifts, or continental crust was simply attenu-
tends to parallel the compositional layering. This suggests that ated, one or more basins seemed to have developed, which accu-
the foliation (defi ned by the phyllosilicate minerals) developed mulated siliciclastic sediment derived largely from the surround-
concurrently with the burial metamorphism, while the beds were ing Rodinian highlands. The pre-Catoctin Octoraro Formation,
horizontal. The growth of the Tucquan anticline thus postdated if it is indeed Neoproterozoic in age, may have accumulated in
the burial metamorphism. one of the rift basins developed at that time. Additionally, it was
A steeply dipping to subvertical, east-northeast–trending at ca. 735 Ma that the igneous magmas that would become the
foliation transects much of the Tucquan anticline (Freedman et Baltimore Mafi c Complex (Smith and Barnes, 2008) and the 433
al., 1964). This foliation postdates the dominant foliation but is ± 2 Ma Sword Mountain Olivine Melilitite (Smith et al., 2004)
not as penetrative. Its age, character, and attitude suggest it may were separated from the mantle.
be axial-planar, and thus coeval, to the upright Tucquan anticline. Late in the Neoproterozoic, additional crustal attenuation by
Smaller folds (from decimeter to meters in size) are present mantle forces led to a second rifting that split Rodinia largely
EXPLANATION
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Figure 2. Regional geologic map of the Piedmont surrounding the Peach Bottom area, illustrating the locations of the
Tucquan anticline, the microcontinental fragments (Brandywine and Baltimore), and the Cecil Island Arc that contains
the Baltimore Mafi c Complex, the Sykesville Formation, and the James Run Formation.