Structures of the Appalachian Foreland Fold-Thrust Belt: New York City, to Knoxville, Tennessee, June 27-July 8, 1989

92 Pages·7.111 MB·English

Structures of the Appalachian
Foreland Fold-ThnISt Belt
New York City, to Knoxville, Tennessee
June 27-July 8, t 989
Field Trip Guidebook Tt66
Leaders:
Terry Engelder, Editor; Bill Dunne,
Peter Geiser, Steve Marshak,
R. P. Nickelsen and David Wiltschko
American Geophysical Union, Washington, D.C.
Copyright 1989 American Geophysical Union
2000 Florida Ave., N.W., Washington, D.C. 20009
ISBN: 0-81590-586-2
Printed in the United States of America
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COVER Profiles for section lines through the valley and ridge of
West Virginia.
Leaders:
Terry Engelder
Department of Geosciences
Pennsylvania State University
University Park, PA 16802
Bill Dunne
Department of Geological Sciences
University of Tennessee
Knoxville, TN 37996
Peter Geiser
Geology Department
University of Connecticut
Storrs, CT 06268
Steve Marshak
Department of Geology
University of Illinois
Urbana, IL 61801
R. P. Nickelsen
Department of Geology
Bucknell University
Lewisburg, PA 17837
David Wiltschko
Center for Tectonophysics
Texas A&M University
College Station, TX 77843
TRIP 166: STR-UCTURES OF THE
APPALACHIAN FORELAND FOLD-THRUST BELT
Editedby
TerryEngelder
DepartmentofGeosciences,ThePennsylvaniaStateUniversity, UniversityPark, Pennsylvania
FOREWORD During nine days, field trip T166 stops at outcrops
within three distinct subprovinces ofthe Appalachian
TheAppalachianOrogenicBelt,whichextendsalong Valley and Ridge, and two subprovinces of the
theeasterncoastofNorthAmericafrom Newfoundland Appalachian Plateau (Figure 1). The field trip
to Alabama is a structural geologist's delight. assembles at Kennedy Airport in New York Cityfor a
Geologists divide the mountain belt into several drive to Rosendale, NewYork andthe startofthe trip.
geological provinceseach having theirown unique set This drive crosses all the major provinces of the
ofstructures and structural problems. Majorprovinces Appalachianforelandfold-thrustbeltexceptthePlateau.
includetheAppalachianPlateau,theValleyandRidge, Starting at Rosendale the first day, the field trip
the Blue Ridge, and the Piedmont. The focus ofthis traverses the Hudson Valley subprovince, a 2 - 6 Ian
field tripis thePlateauandtheValley andRidgewhere widefold-thrustbeltofdefonnedSilurianandDevonian
sedimentary rocks show the least indication of carbonate and clastic rocks. Although much narrower
metamorphism. During mapping of Paleozoic than other portions of the Appalachian Valley and
deformation in these two provinces, the 19th century Ridge, structural features of this belt have many the
geologists, H.D. and W.B. Rogers, first realized that characteristics found in other larger fold-thrust belts.
there was structural regularity along strike to both Ofspecialinterestis thecorrelationofthedevelopment
asymmetric folds and thrust faults. Although the anddistributionofspacedcleavage andclaycontentin
Rogers brothers' initial observations are still valid, thecarbonatesoftheUpperPaleozoic.
detailedmapping during the subsequent 145 years has Attention during the second day focuses on
shown that several subprovinces of the Appalachian mesoscopic structures Uoints, solution cleavage,
foreland have theirown characteristic structures. The pencils, anddeformedfossils) thatdevelop priorto the
purpose of field trip T166 is to examine variation in growth of first-order folds in the Valley and Ridge.
style of foreland deformation along a strike-parallel These structures are well exposed on the Appalachian
traverseof 1200Ianfrom easternNew York toeastern Plateau of New York where they developed under
Tennessee. The Appalachians are particularly conditionsoflayer-parallel shorteningabove aSilurian
convenientfor such a study ofstructural style because saltdecollement. OntheAppalachian Plateau, the trip
thismountain beltisexhumed,exposingdeep structures route will pass through the Devonian Catskill Delta to
which are only detected seismically or in well data in examine the effect of stratigraphic position on the
youngerbelts. development ofjoints prior to and during Alleghanian
Fieldtrip T166 visits classic localitieswhere thrust layer-parallel shortening. The role of high fluid
geometry was first understood. Some localities are pressureonthedevelopmentofjointswillbestudiedin
reinterpreted in light of current knowledge about the detail.
developmentofstructuresinfold-thrustbelts. Subjects On days three throu~h six the trip moves south into
which will be stressed during the trip include: A) the Central Appalachian Valley and Ridge, a
Deformation mechanisms associated with the subprovince found in the states of Pennsylvania,
development anddistribution ofmesoscopic structures Maryland, and West Virginia, where the early layer
such as joints, cleavage, pencils, and sliding surfaces; parallel shortening fabric as seen on the Appalachian
B) Distribution of strain in both strike and transverse Platau is overprinted by first-order folding. In the
sections of the Appalachians; C) A comparison of anthracitecoaldistrictrocksarehighergradethaninthe
overthrust terranes involving blind thrusts versus Juniata culmination. The stratigraphic section of the
e~mergentthrusts; and D) The analysis ofthree general ValleyandRidge subprovinceisdividedintotwomajor
architectural stylesofthe Appalachian fold-thrust belt. mechanicalunits: LowerPaleozoiccarbonates (thestiff
These three architectures include: 1) a style where layer) andMiddletoUpperPaleozoicclastics(thecover
layer-parallel shortening byvolume-loss strain permits layer). During the development of first-order
decollement slip without major folding; 2) a style structures,the lowerpackagefracturedandstackedina
where shortening is accomplished by the development duplex under the clastic rocks. The upper package
offIrst-order folds; and 3) a style where shortening is shortened by folding and pervasively straining, and
absorbed by the stacking ofthrust sheets. Modes for draped over the carbonate duplex. Horses of Lower
thrust propagation differ among these architectural Paleozoic carbonates have a floor thrust in Cambrian
styles. These thrust propagation modes are labeled shalesandapassiveroofthrustintheReedsvilleShale.
layer shortening, decollement, and imbricate, RocksintheMarylandandWestVirginiaportionofthe
respectively (Geiser, 1988). Valley and Ridge differfrom the Pennsylvania section
T166: 1
byonly slightchangesinthelithologyandstratigraphic
thickness. This area marks the northern end of the
/ transition from central Appalachian to southern
I/ Appalachainstructures.
I On the seventh day, the field trip visits a third
t , ,/ subprovince of the Valley and Ridge, the southern
, ,/
J / Appalachian Valley and Ridge. In this subprovince,
\ '\\
( / emergent thrusts cut LowerPaleozoic rocks; the map
.\ pattern of this subprovince contrasts with the central
If, "......... / /
HU~::e~~ley Appalachians where major thrusts did not cut cover
'") NewYork .... ' rocks. Stratigraphic studies have shown that the
{
southern Appalachians did not have the same thick
,./ cover which was responsible for blind thrusting in the
( central Appalachians. The southern portion of the
~.-J Ithaca Valley and Ridge locally consistsof3 tomore than 10
// ....•. / majorthrustsheets,whicharetraceablealongstrikefor
I - : /
I ..... AppalachianPlateau --, hundredsofkilometers.
\'\...". \..······..0../ / :......./.......\ The final days, eight and nine, will be spent in a
Wellsville / ,. I second subprovince of the Appalachian Plateau, the
\.
,,' Pine Mountain thrust block of the Southern
I f
/\
J / " Appalachians. Here the boundary between the Valley
,.I. ,/ ,/\." "--- andRidgeandtheAppalachianPlateauismarkedbythe
J '.... / ", frrst thrust sheetto the southeastofthe Pine Mountain'
I,I, ...,.... ", Block, the Wallen Valley sheet. This block, where
, MaryIInd , Rich (1934) first proposed the concept of ramp-flat
, geometry, formed over a major bedding parallel
, '"\./'~Washington
, /" , decollement before breaking through to the surface.
Unlike the AppalachianPlateauofNew York, thePine
I' (' (,-I' --
" Mountain Block shows very little evidence for the
,\, developmentoflayer-parallelshorteningfabrics.
\'',/,/
\
\,
l
(.I
VirJinia
(
~ WestVirpnia
""'S'
~
t.
> ....
) ....
"'-'-J ""
"
'-""'" r- ;I'
'"'""-....1.'\ --) ,/ ;I'
~
,/
I ( .... /
Ten_
\ ;I'
,/
FIGURE 1 Route of IGC field trip T166 which
focuses on the structures ofthe Appalachian foreland
fold-thrust belt. Thetriprouteisindicatedbythedotted
line. Nightly stopsareinicatedbycirclesatRosendale,
NY, Ithaca, NY, Wellsville, NY, State College, PA,
Cumberland, MD, Harrisonburg, VA, Kingsport, VA,
CumberlandCap TN,Knoxville, TN, andWashington,
DC.
T166: 2
INTRODUCTION TO APPALACHIAN GEOLOGY:
A GEOLOGICL SKETCH OF SOUTHEASTERN NEW YORK STATE
StephenMarshak
DepartmentofGeology, UniversityofIllinois,Urbana, lliinois
INTRODUCTION
TheAppalachianMountainscontaintherecordofat
least three complex Paleozoic contractional orogenic
events (Rodgers, 1970): the Taconic orogeny (Mid- to
Late Ordovician), the Acadian orogeny (Mid- to Late
Devonian), and the Alleghanian orogeny
(Pennsylvanian to Permian time). Subsequent to the
Alleghanian orogeny, the range was beveled by
erosion, and then in middle Mesozoic time it was
subjectedto arifting eventwhich ultimately led to the
openingoftheAtlantic Ocean. Topographic details of
the range reflect structural features created during the
Paleozoic orogenies, but the uplift that resulted in the
overallelevationthatwenowseeisamorerecentevent,
probablyrelatedtorifting.
The sinuous map-view trace of the Appalachian
Mountains(Figure 1)reflectsrealbendsinthe structural
grain ofthe range. Southeastern New York lies in the
apex of the New York recess, a bend that is concave
toward the craton and lies between the Pennsylvania
salientand the New England Appalachians (Figure 1).
TheAppalachianMountainsareverynarrowintheNew
York recess, so on the drive from Kennedy Airport to
Rosendale, we pass through eight
geologic/physiographic belts. In order to make the
drive geologically more meaningful, we now describe
thesebelts andadjacentgeologicprovinces(Figure2).
Atlantic Coastal Plain
Kennedy Airportis builtonLongIsland, arelictof
Pleistocene glaciation. Most ofthe ground surface of
Long Island is composed of glacial till and outwash
plain sedimentwhich was deposited at the front ofthe
Wisconsin ice sheet on exposed continental shelf.
Beneath the glacial veneer are Cretaceous deposits
(clay, silt, sand, and gravel) which represent onlap of
the Atlantic coast passive-margin wedge onto the
(a)
continent when there was a eustatic rise in sea level
(Owens, Minard, and Sohl, 1968). Long Islandmarks
the northeast edge ofthe Atlantic coastal plain; to the FIGURE 1 Trendline map of the Appalachians,
north,crystallinerocksoftheAppalachiansextendright showing the outcrop of Grenville Precambrian
tothe shore, andtothesouth, thecoastalplainbroadens crystalline terrane and the traces of structrures in the
andinplacesis almost200Ianwide. Appalachian fold-thrust belt. Principal salients and
recessesarelabeled.
Manhattan Prong
Upon crossing the East River at the western
tenninusofLongIsland,weentertheManhattanProng include from base to top: Fordham Gneiss
composed of metamorphic rocks of Precambrian (Precambrian, representing NorthAmericanGrenville
through Middle Ordovician age. These rocks, which age basement), Lowerre Quartzite (Cambrian,
form the bedrock ofNew York City (Schaffel, 1975), representing the base of the Early Paleozoic passive-
T166: 3
I
/
New I
/
I
(
\
~ \
.............. ~ TACONIC
I
MOUNTAINS!Z
!Z
Zr:,IO
·'0
,I
I
L. PaleozoIc
I
I
GEOLOGIC-PHYSIOGRAPHIC
LOCATION MAP OF
SOUTHEASTERN
NEW YORK STATE
o, miles 10
o km 10
FIGURE 2 Map of the principal
geologic/physiographicprovincesofthe Appalachians.
Major fault boundaries are shown by heavy lines with
theteethonthehanging-wallsheet
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margin wedge thatdeveloped subsequentto the rifting the Cortland Complex, a 435 myoid intrusion
ofLaurentiain Late Precambrianandthe development consisitingofperidotite,pyroxenite,anddiorite.
of the Proto-Atlantic Ocean), Inwood Marble
(Cambrian, representing the Lower Paleozoic Hudson Highlands/Gap of Wingdale
miogeoclineofeastern NorthAmerica), andManhattan
Schist (Middle Ordovician, composed of The Hudson Highlands (average elevation 200
metamorphosed shales and sandstones). Recent work 450m) formpartofachainofGrenville-age (~ 1.1 by)
suggests that three "Manhattan Schists" exist. crystallinerockstherunthelengthofthe Appalachians.
Manhattan Schist "A" was deposited unconformably In southeastern New York, the Highlands include both
over the Inwood Marble and is a para-autochthonous paragneiss(biotite-hornblende-quartzplagioclasegneiss
"flysch sequence" signalling the inception of the interlayeredwithcalc-silicaterockandamphibolite) and
Taconic Orogeny. Manhattan Schists "B" and "C" orthogneiss (horneblende granite and granite gneiss)
represent allochthonous deeper-water portions of the (Hall and others, 1975). The paragneiss occurs
LowerPaleozoic passive-margin wedge andwere later dominantly in the Eastern Highlands and the
thrust westwards over Schist A (Hall, 1968). The orthogneiss occurs dominantly in the Western
rocks of the Manhattan prong are poly-deformed and Highlands. Itis likely that the crystalline rocks ofthe
metamorphosed. ProminantfIrst-orderfoldscontrolthe Hudson Highlands are allochthonous, and have been
topographyofNew YorkCity. Gneiss and schistform thrust to the northwest. The northwest edge of the
the ridges, and marble lies beneath the valleys. The' Highlands is complex, and includes a large infolded
eastern limitofthe ManhattanProngcrystallineterrane syncline of Paleozoic rocks (Jaffe and-Jaffe, 1967).
is ductile shear zone called "Cameron's Line" To the northwest ofthis syncline, lie a string ofsmall
(Merguerian, 1983). Along this shear zone, Lower klippen placing Precambrian rocks over Ordovician
Paleozoic eugeosynclinal strata (now metamorphosed) strata.
of the Hutchinson River Group were transported To the northeast, the crystalline rocks of the
westward and juxtaposed against rocks of the Hudson Highlands plunge beneath metamorphosed
ManhattanProng. LowerPaleozoic'sedimentary rocks, in aregion called
the "Gap of Wingdale". The metamorphic grade of
Newark Basin and Ramapo Fault theserocksincreasesprogressivelyfrom westtoeastin
aclassic Barrovian succession (Bence and McLelland,
Upon crossing the Hudson River, we enter the 1976).
Newark Basin. By Late Triassic time, the New York
City region had been beveled down to a peneplain Hudson Valley Ordovician Clastic Belt
surface. At this time, the region was broken by
extensionalfaulting, and the Newark Basin developed. Continuingnorthwestoffofthe Hudson Highlands,
The basin is basically a half-graben filled with up to we enter a region of low'relief underlain by various
5000 m ofcontinental sedimentary deposits called the Ordovicianclasticunits thathavebeenmetamorphosed
NewarkGroup (Savage, 1968),whichconsistsofthree toonlylowgrade(argilliteunitswithinthesequenceare
interfingering formations, namedfrom base to top: the nowslate). Atleastthreeunitshavebeendistinguished
LockatongFormation (argilliteandshale), the Stockton intheregion thatwe traverse, butthecontactsbetween
Formation (arkose and shaly mudstone), and the the units are not well exposed. The Austin Glen and
Brunswick Formation (red mudstone, sandstone, and MartinsburgFormationsconsistofturbiditesdeposited
shale). The unconformityatthe baseofthetheNewark unconformably over Lower Paleozoic carbonate
Group dips gently westward, andits map tracefollows platform deposits. The Austin Glen sequence were
theHudsonRiver. probably thrustoverthe Martinsburg sequence (Fisher
Development of· the Newark Basin was and Rickard, 1973). The Martinsburg contains
accompanied by mafic igneous activity. The most substantial intervals of slate. The Quassaic Group
prominentigneousfeature isthePalisades sill, a300m includes conglomeratic units and sandstones.
thick diabase intrusion which forms the cliff Ordovician strataofthe Hudson Valley were possibly
overlooking the Hudson River across from New York deposited atthe baseofan accretionary prismadjacent
City. Towards its top, the Newark Group is to an offshore volcanic arc that converged on an east
interlayered with three thick flows which stand out in dipping subduction zone and collided with North
ridgescalledtheWatchungMountains. America during the Taconic Orogeny (Bosworth and
• The western boundary ofthe Newark basin is the Vollmer, 1981).
Ramapo fault (Ratcliffe, 1971), which separates the
sedimentary strata of the basin from the resistant Hudson Valley Fold-Thrust Belt
Precambrian gneiss that underlies the Hudson
Highlands. Seismic activityis quitefrequent alongthe A sequence of Silurian through lower Middle
fault. The Newark Basin.does not extend east of the Devonian shallow marine carbonate and clastic rocks
Hudson River, so east ofthe river, the Ramapo Fault were deposited unconformably over the Ordovician
cuts into the Hudson Highlands, dividing it into the clastic sequence. In most places, the unconformity is
EasternHighlands andWestern Highlands. Justtothe angular,fortheOrdovicianrocksweredeformedduring
southoftheRamapofaultontheeastsideofthe·riveris the Taconic orogeny. Silurian units pinch out
T166: 5
progressivelytothe north, sothatbythe latitudeofthe Mountains arenearlyflat-lying withadipofonlyafew
town ofCatskill, only about 1mofrock liesbelow the degrees to the west. Coarse strata of the Catskill
basalDevonianunit. ThebeltofSilurianthroughlower Mountains grade westwards with the Devonian
Middle Devonian strata is a west-verging, miniature siltstones and shales that we will study onthe second
fold-thrustbeltcalledtheHudsonValleyfold-thrust belt dayofthisfieldtrip.
(Marshak:, 1986). This will be the subject ofthe fIrst
dayofourfieldtrip.
Taconic Mountains
Catskill Mountains
Alongtheeasternborder·ofNewYorkState,eastof
The Catskill Mountains are a relatively high and the Hudson River, lie the Taconic Mountains. These
fugged portion of the Appalachian Plateau. The mountainsareunderlain by asequenceofdeeper-water
bedrock ofthe mountains is composed of the Middle Lower Paleozoic strata which were thrust westwards
andUpperDevonian "Catskill sequence" composedof overtheLowerPaleozoiccarbonateplatfonnofeastern
shales, red sandstones, and conglomerates (Fletcher, North America during the Taconic orogeny (Zen,
1962). These rocks were deposited in a huge delta 1972). At least five distinct thrust sheets have been
complex, the Catskill clastic wedge, whose preserved identified in the Taconic Mountains; together, they
thickness is at least 3.5 Ian. The wedge was derived comprise the Taconic allochthon. Eastofthe Taconic
from erosion ofthe Acadian highlands to the east, and Mountains is the Berkshire Massif, consisting of an
wasdepositedin aforeland basin. StrataoftheCatskill allochthonoussheetofGrenville-agecrystallinerock.
T166: 6