Tertiary Stratigraphy and Paleontology, Chesapeake Bay Region, Virginia and Maryland: Chesapeake Bay Region, Virginia and Maryland, July 15-July 17 PDF
Preview Tertiary Stratigraphy and Paleontology, Chesapeake Bay Region, Virginia and Maryland: Chesapeake Bay Region, Virginia and Maryland, July 15-July 17
Tertiary Stratigraphy and Paleontology, Chesapeake Bay Region, Virginia and Maryland Chesapeake Bay Region, Virginia and Maryland July t S-July t 7 Field Trip Guidebook T2t 6 Leaders: Lauck W ward and David S. Powars American Geophysical Union, Washington, D.C. Copyright 1989 American Geophysical Union 2000 Florida Ave., N.W., Washington, D.C. 20009 ISBN: 0-87590-660-5 Printed in the United States of America COVER CalvertCliffs southofPlumPoint, CalvertCounty, Maryland, where cliffson the western shoreofthe ChesapeakeBay areoftenover 100feet high. Leaders: LauckW. Ward VirginiaMuseum ofNaturalHistory Martinsville, Virginia24112 David S. Powars U.S. Geological Survey Reston, Virginia 22092 IGC FIELD TRIP T216: TERTIARY STRATIGRAPHY AND PALEONTOLOGY, CHESAPEAKE BAY REGION, VIRGINIA AND MARYLAND Lauckw. Ward, VirginiaMuseumofNaturalHistory,Martinsville, Virginia24112 David S. Powars U.S. Geological Survey, Reston, Virginia 22092 GEOLOGIC SETTING the various basins, ordepocenters, and the intervening arches, orhighareas. Thesehighandlow areas moved StratigraphicunitsexposedintheChesapeake Bay independently of·each other creating a stratigraphic areaconsistofasuccessionofMesozoic andCenozoic mosaic that is unique from basin to arch to basin. Coastal Plain beds deposited in a tectonic downwarp Various tectonicmodels including block-faultedterrane known as the Salisbury embayment. As shown in andeffectsoflandwardextensions ofoceanictransfonn figure 1, the Salisbury embayment covers parts of faults have beenofferedaspossible causesfor the arch Virginia, Maryland, Delaware, and southern New basin configuration. However, at the present time, Jersey and is bordered on the north and south by the subsurface data is inadequate to determine the causes. South New Jersey arch and the Norfolk arch, Variations in the distribution and thickness of respectively. Subsurface data shows that these arches Cretaceous and Tertiary deposits also suggests the are characterizedbystratigraphicthinningortruncation gradualmigrationofbasins throughtime. Forexample, of Cretaceous and Tertiary formations. Conclusive during the early Tertiary, the main marine depocenter evidence ofbasementhighs associated with the arches withinthe Salisburyembaymentwas alignednortheast is lacking, however, this is strongly suggested by the southwest with a deeper water direction to the evidence at hand, at least for the Norfolk arch. The northeast. This alignment appears to have continued basementcomplexunderlying the embaymentincludes until the middle Miocene when the marine depocenter Precambrian and Paleozoic crystalline rocks and beganto shift southwardtoward the Norfolk arch. In Mesozoic rift-basin fill. Reactivation of Paleozoic the late Miocene, the main marine depoeenter shifted ramps and thrusts is believed to have influenced or dramatically to the south and the dip of the younger controlled the distribution, geometry, and style of beds rotated increasingly to the southeast. This faulting associatedwithearly Mesozoicrift-basins and southeast dip of Coastal Plain beds is existent today. overlying late Mesozoic and Cenozoic Coastal Plain The marine depocenter shiftedincreasingly southward deposits. The Salisbury embayment was the site of until, in the late Pliocene, the locus ofthe depocenter intermittent marine overlap and deposition duringthe hadmovedintothe Albemarleembaymentinnortheast Early and Late Cretaceous and most of the Tertiary. NorthCarolina. Another orderofstructuralmovement Beds are of fluvial, deltaic, and open-shelforigin and inthe Salisburyembaymentis thatof localized, down were depositedinawedge-like configurationwiththeir dropped graben structures that occur along northeast thin, westward edge overlapping the Appalachian southwest trending lineaments. These grabens are Piedmont. To the east the Coastal Plain deposits relatedtoearlyMesozoicrifting andcausecertainareas thickentoseveralthousandfeet. to become unstable. These areas becamereactivatedat The lithology, thickness, and dip of the various certain periods during the Cretaceous and Tertiary, formations deposited in the Salisbury embayment are, possiblyduetosedimentloading,resultinginstructural to agreatextent,structurallycontrolled. Thistectonism highs behind which finer sediments accumulated. was operative at several local and regional scales. Northeast-southwesttrending high-anglereverse faults Tectonism on a regional scale involved tilting of the affecting Cretaceous and Tertiary deposits along the entire Atlantic continental margin. Ofa lesser inner margin ofthe Coastal Plain are interpreted to be importancewas theindependentstructuralmovementof the typical style of deformation for Coastal Plain T216: 1 -,-- 1..----- , . -- /, r-------'-- ~ \ Raritan Embayment \ '. 1\ , .- \ --- South New Jersey Arch :'L--- .--:-.;:-,,- S r ' \,.......... ) /' "", Salisbury Embayment Norfolk Arch ------- -----,~'-.-)---?---.-...~- '1./- Albemarle Embayment / \ " Cape Fear Arch \ (/'--..... Charleston Embayment \ Yamacraw Arch > Southeast Georgia Embayment r---------\.----- ", \ / 100 200 Southwest Georgia Embayment MilES South Florida Embayment FIGURE 1.Map showingprincipalbasinsandarchesoftheAtlantic CoastalPlain. T216: 2 deposits that overlie reactivated Mesozoic border large tracts with substantial mansions. Many ofthese faults. Thus, each ofthese various structuralelements houses still exist and can be seen along the major contributed to the overall depositional patterns on the rivers, the Chesapeake Bay, and other parts of the CoastalPlainandintheSalisburyembayment. embayment. For example, the homes of several Depositional environments in the Lower prominantAmericanpoliticalfigures includingGeorge Cretaceous were principally fluvial and deltaic, Washington's house at Mount Vernon, George consisting of pebbly, coarse to fine, partially arkosic Mason's house at Gunston Hall, George Washington's sands. The early Cretaceous deposits constitute the birthplaceatWakefield, andRobertE. Lee's birthplace greater volume of sediment filling the Salisbury at Stratford Hall can still be seen along the Potomac embayment. Thesesandscontainrelativelythinlenses River(Figure2). of clays, lignitic in part, which contain leaf During the 1800's many of the farms and impressions. During the Late Createcous and most of plantations were abandoneddue to the deterioration of theTertiarytheembaymentwas thesite ofintermittent the soil. In addition, during the mid-1800's the area marine transgressions. These transgressive sequences was the scene of several major Civil War battles. form a cyclic pattern and are separated by regressive Fertilizers andmodemfarming techniques have helped sequences and/or unconformities. The Upper to restore the importance of agriculture in the Cretaceous consists mainly ofdeltaic to marine sands Chesapeake area which, except for the major urban which are commonly quite fossiliferous. Lower centers,remainsmainlyruralincharacter. Tertiary deposits consist of glauconitic silty sands ~ontaining varying amounts of marine shells. The TERTIARY HISTORY OF THE SALISBURY Tertiary beds are principally marine-shelf deposits; EMBAYMENT fluvial, deltaic, andnearshore-shelffacies aregenerally lacking. The sameis truefortheupperTertiarymarine Biostratigraphicandlithostratigraphicrefinement beds whichconsist ofdiatomaceous silts and silty and has made possible the detailed reconstruction of the shelly sands. However, sands and gravels of fluvial complexhistoryofthe Salisburyembaymentduringthe and deltaic origincap mostofthe higherinterfluves in Tertiary. Stratigraphic investigations in the Salisbury the Salisburyembaymentareaandare thoughtto be of embayment areabeganin the 1830's with the workof variousMiocene,Pliocene,Pleistoceneages. W.B. Rogers (Rogers, 1884). Darton(1891) continued The Salisburyembaymenthad awarm-temperate this work, naming and describing several formations. to subtropical marine setting through much of its Clark (1896), Clark and Martin (1901), Shattuck history. During the late Tertiary a portion of the (1904), and Clark and Miller (1906, 1912) further temperate molluscan fauna became endemic so that refined the stratigraphy. Darton (1911, 1948, 1951) abruptcoolinginthe latePliocenecausedamajorlocal followed Clark and Martin's (1901) formational extinctioninvolvingtaxathathadbeensuccessfulsince subdivisionwhentracing the units inthefield. Careful theOligocene. scrutiny of that work by later authors (Ward and Blackwelder, 1980;Ward, 1985)has acknowledgedits HISTORICAL SETTING accuracy, led to some refinements, and established a stratigraphic terminology for beds thatearlierworkers ThehistoryoftheChesapeakeBayis as variedas did not recognize. Based on subsurface data from the geology. In the late 1500's and early 1600's, the continous cores further stratigaphic refinement and fITstEuropeanexplorersfound the areato beinhabited mapping has been done and is possible (Mixon and bynumerousIndiantribes. ExpansionoftheEuropean Powars, 1984; Powars,1986; Mixon, Powars, Ward, settlers into the Chesapeake area caused a gradual and Andrews, 1989; Mixon and Powars, unpublished withdrawal of the Indians. The earliest settlers, data). Note: thestratigraphicdiscussionthatfollows is primarilyEnglish,occupiedtheembayedsectionsofthe primarily basedonoutcropdatacompliedbythesenior various rivers, the Patuxent, Potomac, Rappahannock, author and does not include the other authors York, Mattaponi, Pamunkey, and James, because of subsurfacedata. theirnavigability. MostmajorcitiesintheChesapeake Bay area, including Philadelphia, Baltimore, Paleocene Washington, Fredericksburg, and Richmond, are Tertiary sedimentation in the Salisbury situatedalongtheFallLine. embayment began in the early Paleocene with the The Colonial period saw the development of depositionoftheBrightseatFormation(Figure3). The agriculture along broad areas of the Coastal Plain. depositionalbasinfollowed the northeasternalignment Farmsweregenerallyplantationstyleconsistingofvery T216: 3 38- OO~,r------......a...~----------/-~_.......1_---- ---.J_......,... !..-~....,...._~ ~ " , / , / / / / ,,,, / , , / , ~/ ,, / , (,,, / , / , , , ,, , I4J (J \ \ \ \ I • LaPlata / I I I / I I I I " ST. MARYS COUNTY FIGURE 2Map showinglocationoffield trip stops. T216: 4 begunintheCretaceous(Figure4). Partsof Maryland arch areas were probably positive features (Figure 7). and Virginia east ofthe Chesapeave bay and much of Sediments associated with this transgression were the Virginia Coastal Plain west ofthe bay may have clayey, silty, micaceous, very glauconitic sands been emergent. The Brightseat overlies Upper containing an abundance of moderately diverse CretaceousmarinedepositsandLowerCretaceousbeds molluscan assemblages; they were placed in the of deltaic origin. Mollusks, dinoflagellates, and PotapacoMemberoftheNanjemoyFonnationbyClark ostracodes suggest a shallow-shelf environment of and Martin (1901). This molluscan assemblage, normal or near-normal salinities. These assemblages however, contains few forms in commonwithits age are decidedly provincial, having few taxa in common equivalent unit in the Gulf Coastal Plain, the with those in the Gulf of Mexico province. The Hatchetigbee Formation. Faunal and floral Brightseatoverlies the UpperCretaceous sediments in assemblages indicate warm-temperate, shallow, open Prince Georges County, Maryland, Lower Cretaceous marineconditionsandnormalsalinities. sediments on AquiaCreek, StaffordCounty, Virginia, Afterabriefhiatus,sedimentationresumedinthelate andtheLowerCretaceous onthe RappahannockRiver early Eocene with a very fine, very glauconitic, in Spotsylvania County, Virginia. The unit is not micaceous sand termed theWoodstockMemberofthe knowntocropoutsouthoftheRappahannockRiver. NanjemoyFormation(Figure8). This depocenterwas The nextonlapsequencebeganinthelatePaleocene. clearly more open to marine influence and molluscan Itconsisted ofthree principalpulses and resulted in a assemblages became more diverse, containing much more extensive transgression, still from the approximately 100 species. This shallow-shelf, open northeast, but covering most of the Virginia Coastal marine environment is further suggested by a diverse Plain and possibly lapping over parts of the Norfolk dinoflagellate assemblage. Still,the barriertothesouth arch into the Albemarle embayment (Figure 5). Beds was a strong influence on molluscan migration, and associatedwiththe transgressionare termedthe Aquia few ofthe Woodstock taxa are in commonwith those Formation and consist ofvery glauconitic, fine sands ofthe upperHatchetigbeeFormationofAlabama. The that supported a molluscan assemblage having period ofnondeposition between the Potapaco offlap numerous affmities withlatePaleocenemollusksinthe and the onlap ofthe Woodstockwas briefbutresulted GulfofMexicoprovince. Fossil assemblages indicate in anunconformity thatmay be seen overmuch ofthe shallow-shelf, warm-temperate to subtropical basinintheform ofsharp,well-defmedcontact. conditions. Mollusks found in the Aquia indicate an Following the early Eocene Woodstock onlap, there equivalence with the Naheola, Nanafalia, and was a lengthy 4.5 million-year period of emergence. TuscahomaFormationsofAlabama. Sedimentation in the Salisbury embayment resumed After an apparent structural realignment, a much with a transgression in the middle middle Eocene smallerandmoreprotectedembaymentremainedinthe (Figure 9). The Norfolkarch stillacted as abarrierto latePaleocene. Thisresultedinthedepositionofavery the warm currents of the paleo-Gulf Stream. As a muddy unit named the Marlboro Clay (Figure 6) by result, the sedimentaryregime was strikinglydifferent ClarkandMartin(1901), ClarkandMiller(1912), and from thatto the south. The Salisbury embaymentwas Darton(1948). Sedimentologically,TheMarlboroClay the site of shelly, glauconitic, quartz sand is similarto deposits found ininnerbayenvironments, accumulations termed the Piney Point Formation by but the diversity and abundance of its dinoflagellate Onon(1955); carbonatesedimentationdominatedfrom flora suggest nearly normal marine salinities. NorthCarolinatoAlabama. ThePineyPointisknown Calcareous fossils are lacking probably due to onlyinthe subsurfaceinMaryland,butis wellexposed diageneticcontrolsratherthanenvironmentalones. The alongthePamunkeyRiverinVirginia. ThePineyPoint Marlbororestsunconformably ontheAquiaFormation canbecorrelatedwiththemiddleandupperportionsof and is unconformably overlain by the Nanjemoy the Lisbon Formation ofAlabama, on the basis ofits Formation (lower Eocene). Pollen and dinoflagellate molluscan assemblages. A regression followed the assemblagesindicateaverylatePaleoceneorveryearly Piney Point transgression and sedimentation did not Eoceneageassignment. resume until the late Eocene (Figure 10). Glauconitic sands associated with this transgression have been termed the Chickahominy Formation (Cushman and Eocene Cederstrom, 1945) and are found only in the In the early Eocene a.new transgression covered subsurface. For this reason, nothing is known about essentially the same area as the Aquia transgressions. itsmolluscancontent,andmicrofossils areknownonly Again, thetransgressionappearstohavebeen from the from afew cores. northeast, while the Delmarva Peninsula and Norfolk T216: 5 y ALABAMA CitronelleFormation Chickasawha Limestone Byram Formation MariannaFormation RedBluffFormation GEORGIA CoosaCl~~tchieL2 MarksHeadFormation[g HawthornFormation TampaFormation Suwannee Limestone GlendonFormation MariannaFormation IIIIIIIII I SOUTHCAROLINA CanepatchFormation.WaccamawFormationBearBluffFormation CoosawhatchieClavMember Hawthorn Formation EdistoFormation g-o~AshleyQ;Formationa.ooo NORTHCAROLINA NorfolkFormationIIJamesCityWaccamawFormationFormationCl1ciwanRiverFormationI CobhamBayMemberII...I::(1)0>;::Claremontoas0EManorasoMemberWLL PungoRiver Formation Belgra~eIPoI~8V~ywoodl~Formation...------Mbr. RiverBend Formation I J I VIRGINIA NorfolkFormation howanRiverFormatJo:n· CobhamBayIMember...1::(1)0>;::OasClaremont0EManoras'"OWMemberLL St.Marys Formation Choptank Formation CalvertFormation OldChurchFormation MARYLAND ColumbiaFormation(Darton,1891) CobhamBay~IIQ;Member>;::oasClaremontoEManoras...W0MemberU. lIJ> IG2ui'!BostonCliffsMbr.:!St.LeonardMbr.Q.~DrumcliffMbr. ~I-I----:.:~~..:......-~....(I)-as>EFairhavena;oMember0LL OldChurchFormation n o DELAWARE ColumbiaFormation(McGee,1888) Choptank Formation Calve..t Formati KirkwoodFormation OldChurch(?)Formation ~ EY ti ?) EWJERS hans:~n Kirkwood Formation OldChurch(Formation N ~ I GE zce:I:;:ceenc(~o:I:o zceC'a:::)men~o> RIESISTA I~R OWER IjI-- za:cewzQ.oQ.::)~a:o~ zc:r:::3c:r::W>...Jc:r::C~C~W~en~IAN zce...Jcea:C'w;:Ca:o::)...Jm I-----. z8i.L <C~ zcea:w~Q.~ceQ.::):I:o III zcea:w...J;:WoQ.~...Ja: SE ww(Jo~G)iii...Jn.Wffioo~ wzw(Jo~ wzw(JoC' ..Jo t--3I'\.) 0\ 0'\
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