The tertiary history of the Atlantic coast between Cape Cod and Cape Hatteras

Palaeogeography, Palaeoclimatology, Palaeoecology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands

TH E T E R T I A R Y H I S T O R Y OF T H E A T L A N T I C COAST BETWEEN CAPE COD A N D CAPE H A T T E R A S HORACE G. R1CHARDS Academy of Natural Sciences, Philadelphia, Pa. (U.S.A.) (Received April 8, 1967)

SUMMARY The erratic displacements of the Tertiary shoreline in this area, both from place to place and with passing time, indicate that tectonics, rather than isostasy or glacio-eustasy, has been the dominant factor in determining the present vertical position of Tertiary shoreline indicators. Paleocene-Early Eocene The lowermost Tertiary shorelines of New England were apparently east of those of the present day, although much of the coastal plain in New Jersey was submerged during Paleocene and Early Eocene time. The sea did not cover the entire coastal plain south of New Jersey. Middle-Late Eocene A few fossils of Middle Eocene age on Marthas Vineyard indicate that the shoreline crossed the present day coast in that region. Much of the coastal plain from New Jersey to North Carolina was submerged; it is possible that the Late Eocene seas crossed the Fall Line near Raleigh. Oligocene The only submergence indicated is that of extreme eastern North Carolina. Miocene A possible submergence in eastern North Carolina is suggested for the Early Miocene. Two submergences (Calvert-Choptank and St. Marys) are indicated for New Jersey, Delaware, and Maryland. In late Miocene time, the coast north of Virginia had emerged while subsidence was fairly extensive from Virginia Palaeogeography, Palaeoclimatol., Palaeoecol., 5 (1968) 95-104

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southward (Yorktown Formation). The equivalent Cohansey Formation of New Jersey is probably alluvial and deltaic. Pliocene

During the Early Pliocene the shoreline was east of the present coast in North Carolina. The Late Pliocene was a time of general emergence along the entire coast.

INTRODUCTION

Relative changes in the position of sea and land can be brought about by various factors. The most important are (1) eustatic changes in sea level, (2) isostatic readjustment because of the weight of glacial ice, and (3) tectonic movements of the land not related to ice. The first factor--eustatic changes of sea level--has played an important part in the Pleistocene history of the Atlantic coastal plain as well as in all other parts of the world. How much it was involved in the Tertiary history of the Atlantic coastal region is not well understood. Inasmuch as there is no evidence of glaciation along the Atlantic coast during Tertiary time, the second factor--changes in shoreline because of isostatic readjustment caused by the weight of ice--can be ignored. The third factor-tectonic movements--can be looked for in any part of the world, and is probably the main cause of Tertiary changes in shoreline along the Atlantic coast between Cape Cod and Cape Hatteras. Other less understood factors have undoubtedly played a part in the Tertiary history of the shoreline of the region under discussion. As has been pointed out by various writers including ZEUNER (1959) and FAmBRIDGE (1961), fluctuations in sea level caused by eustatic glacial control may have been superimposed on some major cause that has depressed sea level throughout Pleistocene time and probably as far back as the Early Tertiary or even earlier. Following this hypothesis, sea level of the Early Pleistocene glacial stages may have actually been higher than today. This might explain the cold elements in the fauna of the Calabrian of Italy and the Red Crag of East Anglia (England) even though these deposits are well above present sea level. The cause of this general fall of sea level from the Tertiary to the present is not known. Possibly some deep ocean basins may have formed in Cenozoic times, thus causing a general lowering of sea level. This hypothesis has been used to explain the presence of Tertiary deposits well above present sea level in the United States, Europe, North Africa and elsewhere. An adaptation of the isostatic factor mentioned above should also be considered. It was pointed out by HIGGINS (1967) at the I N Q U A Congress held in Boulder, Colorado, in 1965, that the weight of water brought about by the Palaeogeography, Palaeoclimatol., Palaeoecol., 5 (1968)95-104

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submergence of land would have had the effect of further depressing the land. This depression would have been differential in view of certain variables such as the stability of the bedrock, the depth of the water and other factors. Thus no simple cause can be found to explain the changes in sea level along the Atlantic coast between Cape Cod and Cape Hatteras. However, for the reasons to be outlined below, it is believed that tectonic movements of the land played the most important role. Let us now review the Tertiary history of the region in question. This is partly adapted from a book and from a manuscript now in press, both by the present writer (RIc'tlARDS, 1953, 1967).

PALEOCENE--EARLY EOCENE

Because of the lack of detailed investigations it is difficult to map the extent of the Paleocene (Midway) and Lower Eocene (Wilcox) deposits of the Atlantic Coast north of North Carolina. Whereas on the Gulf Coast there is a definite break between the Midway and Wilcox deposits, it is not clear that such a break or unconformity occurs on the Atlantic Coast, at least north of Cape Hatteras. Or, if there is an unconformity, it may be difficult to identify. The lowermost Tertiary shorelines of New England were probably east of those of the present day, for no marine deposits of these ages are known north of New Jersey, or, if at one time present, they may have been removed by Pleistocene erosion. Much of the coastal plain of New Jersey was submerged during the Paleocene and Early Eocene and the highly fossiliferous Hornerstown and Vincentown formations date from those epochs. The Vincentown Formation is world-famous for its extensive fauna of Bryozoa, Foraminifera and other fossils. It has been correlated with either the Danian or Sparnacian of Europe, which are regarded as Paleocene. There is no record of any major unconformity at either the beginning or end of Wilcox time in New Jersey. In fact it is thought that the Vincentown Formation may be partly of Midway and partly of Wilcox age. It is thought that the shoreline extended across New Jersey from near Salem to Keyport, although it may have extended a little farther westward. If it did extend farther west, the deposits have subsequently been removed by erosion. The considerable amount of glauconite, especially in the Hornerstown, is a feature of these formations. Similar deposits of glauconite occur in Delaware, especially near Drawyers, and it is probable that these can be correlated with the Hornerstown of New Jersey. It has been impossible to separate the Hornerstown from the Vincentown in Delaware. The exact correlation to the south is not clear. The Brightseat Formation of Maryland, exposed on the outskirts of Washington, D.C., is regarded as basal Paleocene, equivalent to the Hornerstown of New Jersey or possibly slightly older. Palaeogeo.~,raphy, Palaeoclimatol., Palaeoecol., 5

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Elsewhere in Maryland and in Virginia the Aquia Formation, also highly glauconitic, is either Midway or Wilcox in age, or both. The presence of such deposits at the type locality, Aquia Creek, near Fredericksburg on the Fall Line, suggests a fairly extensive submergence of the coastal plain of Virginia during Paleocene-Early Eocene time. CEDERSTROM (1945) has postulated the existence of a fault in the basement rock in the James River area of Virginia. Evidence for this is found in the greater thickness of the Paleocene-Eocene north of James River as contrasted with that south of that river. Only a relatively slight submergence of the coastal plain of North Carolina is indicated for the Paleocene-Early Eocene. Fossils of these ages are known from deep wells at Cape Hatteras and elsewhere. Also, the Beaufort Formation of Paleocene age is known from the coastal plain of North Carolina, but only from the subsurface, and it is not known south or west of Pitt County (see BROWN, 1958, 1963).

MIDDLE EOCENE(CLAIBORNE) A few fossils of Middle Eocene age on Marthas Vineyard indicate that the shoreline crossed that of the present day in that region. The Manasquan-Shark River and Nanjemoy Formations represent this epoch between New Jersey and Virginia and indicate a partial submergence of the coastal plain, but at least in New Jersey it was not as extensive as during the earlier episodes of the PaleoceneEocene. On the other hand, it is probable that the Middle Eocene seas extended far inland in North Carolina and actually crossed the Fall Line. Fossils of Middle or Late Eocene age have been found at Clayton, Raleigh, Lillington and elsewhere in the Piedmont Province (RICHARDS,1950). Because of the poor preservation of the fossils, the exact age is uncertain and they may well be Late Eocene.

LATE EOCENE(JACKSON) No record of Late Eocene submergence is known north of New Jersey, and no actual outcrops are known north of North Carolina, the only records being from the subsurface. As indicated by these subsurface fossils, the submergence of New Jersey and Delaware was only slight and did not extend as far inland as the seas of the Paleocene, Early Eocene and Middle Eocene. Fossils of Jackson age have been found in wells along the coast between Atlantic City and Cape May and near the present shoreline of Delaware, Maryland and Virginia. Palaeogeography, PalaeoclimatoL, Palaeoecol., 5 (1968) 95-104

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At least half of the coastal plain of North Carolina was submerged by the Late Eocene sea as indicated by the presence of deposits of the Castle Haye Formation, a highly fossiliferous formation which is generally correlated with the Jackson of the Gulf Coast, although part of it may be older and date from the Middle Eocene. Although farther south than the area covered in this paper, it should be mentioned that there was probably a promontory near present Cape Fear in southern North Carolina. This might have been the beginning of the structural feature known as the Great Carolina Ridge or the Cape Fear Arch. In any case, the Castle Hayne Formation is well developed both north and south of Wilmington, N.C., whereas the bed rock is relatively close to the surface ( 1,109 ft.) near that city. In summary, the irregularity of the various shorelines seems to be apparent with definite inw~sions or depressions and uplifts, h does not seem possible to explain this on the basis of eustasy alone, if at all, but rather by various tectonic movements that may have taken place along the coast. The Fort Monroe High and the Great Carolina Ridge are merely two structural features that may have played a part in determining the Early Tertiary shorelines between Cape Cod and Cape Hatteras (Fig.l).

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( Fig.I. Approximate position of Eocene shorelines between Cape Cod and Cape Hatteras. Palaeogeography, Palaeoclimatol., Palaeoecol., 5 (1968)95 104

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OLIGOCENE

The Oligocene shorelines were apparently east of the present shore north of North Carolina as inferred by the complete lack of Oligocene sediments in the outcrop or subsurface. Oligocene microfossils have been reported from wells at Cape Hatteras and elsewhere in eastern North Carolina, so it is probable that the Oligocene seas crossed the present shoreline somewhere north of Cape Hatteras. (As mentioned below, it is possible that the Trent Formation dates from the Oligocene rather than from the Lower Miocene.) In any case, the complete lack of Oligocene deposits north of North Carolina argues against a eustatic origin of the submergence and in favor of tectonic causes.

EARLY MIOCENE ("TRENT")

This is not the place to review in detail the "Trent problem". Suffice it to say that much of the material formerly called the Trent Formation in North Carolina is either older (Eocene) or younger (Upper Miocene). However, some sediments near Belgrade and Silverdale in Onslow County show relationship to the Tampa Formation of Florida and may be Early Miocene age, although recent studies have suggested that these deposits may be Oligocene (LAWRENCE, 1966; personal communication from A. A. Olsson). In any case the term "Trent Formation" may have to be abandoned because the localities along the Trent River are most probably of Late Miocene age correlated with the Yorktown Formation. However, for convenience, the term "Trent" will be retained for this brief discussion. No submergence of this age is indicated north of North Carolina. Only a slight submergence, extending inland to the region of Silverdale and Belgrade, constitutes the Trent marine invasion which, as stated above, may be of Late Oligocene or Early Miocene age. In any case this marine invasion is mainly south of the area covered in this paper.

MIDDLE MIOCENE (CALVERT)

The next marine invasion of the land north of the "Carolina Ridge" was in Calvert time. Some fossils of unspecified Miocene age occur on Marthas Vineyard whereas similar material has been dredged from Georges Bank and elsewhere off the coast of Cape Cod. The shoreline probably extended across New Jersey from Asbury Park to near Salem and then across Delaware, Maryland and Virginia to the vicinity of Petersburg, Va. The Calvert Formation disappears from the surface near the Virginia-North Carolina line and it is probable that the depression of the land did not extend much farther south and that the shoreline turned abPalaeogeography, Palaeoclimatol., Palaeoecol., 5 (1968) 95-104

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ruptly toward the present coast. As shown by the Calvert fossils the climate was warmer than that of the present time in the same latitudes. In New Jersey the lower part of the Kirkwood Formation is equivalent to the Calvert Formation of M a r y l a n d (R1CHARDS and HARBISON, 1942). During Calvert time the "Carolina Ridge" probably extended far out into the sea. The Choptank Formation of Maryland was probably laid down at the close of Calvert time. Possibly there was a withdrawal of the sea and a readvance to form the Choptank Formation, but it is more likely that the Choptank merely represents a late, sandy phase of the Calvert, possibly formed during a retreating sea. As evidenced by the Choptank fossils, the water temperature was somewhat cooler. There was probably a period of uplift and erosion following the deposition of the Calvert-Choptank Formations.

MIDDLE MIOCENE (ST. MARY'S)

The next advance of the sea was in St. Mary's time. The maximum depression of the land was slightly farther south than during Calvert time and the St. Mary's shoreline probably crossed New Jersey from somewhere near Atlantic City to Millville, and then crossed Delaware, Maryland and Virginia; but it never reached as far inland as the Calvert shoreline. Near Richmond, Va., the St. Mary's shoreline overlapped that of the Calvert and thus the maximum advance of the sea was somewhere near Richmond. The shoreline probably extended south into North Carolina although the deposits are largely buried at the present time and evidence is lacking to determine this point. Just as in the case of the Calvert sea, the St. Mary's shoreline probably turned abruptly toward the coast in central North Carolina and southern North Carolina including the "Carolina Ridge" was probably above water. In New Jersey the upper part of the Kirkwood Formation is equivalent to the St. Mary's of Maryland and Virginia (RICHARDS and HARBISON, 1942). The climate during St. Mary's time was somewhat cooler than it had been during the Calvert (RICHARDS and HARBISON, 1942, p.245).

LATE MIOCENE (YORKTOWN)

The withdrawal of the St. Mary's sea was followed by further erosion. Then the land was depressed again and the Yorktown sea advanced. The sea did not extend as far north as New Jersey but crossed the present strand line somewhere not far north of Yorktown, Va. It overlapped the Calvert and St. Mary's shorelines near Richmond, Va., and extended a few miles over the Piedmont rocks, and Palaeogeography, Palaeoclimatol., Palaeoecol., 5 (1968) 95-104

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LOWER - CALVERT . . . . 51~ HARYS. . . . . . YORK~'l~Wi~i ....... //" /

Fig.2. Approximate position of Miocene shorelines between Cape Cod and Cape Hatteras.

then extended south across the coastal plain of North Carolina. By this time the "Carolina Ridge" was submerged and consequently the shelf sea was probably continuous from Virginia to Florida. New Jersey, Delaware and most of Maryland were above water during Yorktown time for no marine fossils of that age are found in those regions. It is probable that the Cohansey Formation of New Jersey and possibly the North Keys Sand of Maryland (HACK, 1955) are the non-marine equivalents of the Yorktown Formation. The above sketch of the Miocene history of the region between Cape Cod and Cape Hatteras strongly suggests a series of maximum invasions at different places along the coast and thus favors a tectonic origin of changes in shoreline (Fig.2).

EARLY PLIOCENE

It is probable that Yorktown time was followed by another period of erosion and a withdrawal of the sea. Apparently the next advance of the sea was in Early Pliocene time when the Waccamaw Sea covered the eastern portion of the coastal plain of the Carolinas and farther south. North of the vicinity of the VirginiaNorth Carolina line, the land remained above sea level for no marine Pliocene deposits are known in that region. Palaeogeography, Palaeoclimatol., Palaeoecol., 5 (1968) 95-104

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It has been suggested that the Waccamaw Formation might be of Early Pleistocene age rather than Pliocene (DUBAR, 1959). However, the present author favors a Pliocene age because of the close relationship of the Waccamaw molluscan fauna to that of the underlying Miocene and because of the relative high percentage of extinct species.

LATE PLIOCENE

North of the Virginia Capes the land was probably high throughout the Pliocene. The rise of the land from Virginia to New Jersey may have had some connection with a renewed uplift of the Appalachian Mountains. At any rate, this uplift brought a rejuvenation of the streams causing them to carry increased amounts of gravel which spread out over parts of the coastal plain. With continued uplift these gravel deposits were eroded so that the gravel occupies only the tops of the higher hills. Such gravel caps some of the higher hills of New Jersey and makes up the Beacon Hill Formation. This gravel is thought to have been laid down during the Late Pliocene when the shoreline was considerably east of that of the present day. Similar "high level" gravels occur in Delaware, Maryland, Virginia and North Carolina. The presence of large boulders in the Beacon Hill Formation of New Jersey has suggested that these might be of glacial origin, and thus the formation might possibly be of Early Pleistocene age. The lack of fossils makes any actual dating impossible.

REFERENCES BROWN, P. M., 1958. Well logs from the coastal plain of North Carolina. N. Carolina, Dept. Conserv. Develop., Div. Mineral Resources, Bull., 72" 100 pp. BROWN, P. M., 1963. The Geology of Northeastern North Carolina--Guidebook 4th Ann. Fiehl Conference, Atl. Coastal Plain Geol. Assoc., N. Carolina, Dept. Conserv. Deveh~p., Spec. Publ., 44 pp. CEDERSTROM, D. J., 1945. Structural Geology of Southeastern Virginia. Bull. Am. Assoc. Petrol. Geologists, 29: 71-95. DUBAR, J., 1959. The Waccamaw and Croatan Deposits of the Carolinas. S. Carolina, State Develop. Board, Div. Geol., Geol. Notes, 3(6): 1-9. FMRBRIDGE, R. W., 1961. Eustatic changes in sea level. In: L. H. AHRENS, K. RANKAMA, F. PRESS and S. K. RUNCORN (Editors), Physics and Chemistry of the Earth. Pergamon, London, 4: 99-185. HACK, J. T., 1955. Geology of the Brandywine area and origin of the upland of southern Maryland. U.S., Geol. Surv. Profess. Papers, 267A: 21-43. HIGGINS, C. G., 1967. Isostatic effect of sea level changes. Proc. Intern. Assoc. Quart. Res., VII, 16 (in press). LAWRENCE, U., 1966. Paleoecology of an Oligocene Oyster Deposit at Belgrade, North Carolina. Program, Southeastern Sect. Geol. Soc., Am., p.32 (abstract).

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RICHARDS, H. G., 1950. Geology of the coastal plain of North Carolina. Trans. Am. Phil. Soc., 40: 1-83. RICHARDS, H. G., 1953. Record of the Rocks. Ronald Press, New York, N.Y., 413 pp. RICHARDS, a . G., 1967. Stratigraphy of Atlantic coastal plain between Long Island and Georgia: Review. Bull. Am. Assoc. Petrol. Geol., 51 : 2400-2429. RICHARDS, a . G. and HARBISON, A., 1942. Miocene Invertebrate Fauna of New Jersey. Proc. Acad. Nat. Sci. Phila., 94: 167-250. ZEUNER, F., 1959. The Pleistocene Period. Hutchinson Scientific and Technical, London, 447 pp.

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