Stratigraphic Revision of Upper Miocene and Lower Pliocene Beds of the Chesapeake Group, Middle Atlantic Coastal Plain GEOLOGICAL SURVEY BULLETIN 1482-D Stratigraphic Revision of Upper Miocene and Lower Pliocene Beds of the Chesapeake Group, Middle Atlantic Coastal Plain By LAUCK W. WARD and BLAKE W. BLACKWELDER CONTRIBUTIONS TO STRATIGRAPHY GEOLOGICAL SURVEY BULLETIN 1482-D UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 198.0 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard Director Library of Congress Cataloging in Publication Data Ward, Lauck W Stratigraphic revision of upper Miocene and lower Pliocene beds of the Chesapeake group-middle Atlantic Coastal Plain. (Contributions to stratigraphy) (Geological Survey bulletin ; 1482-D) Bibliography: p. Supt. of Docs. no. : I 19.3:1482-D 1. Geology, Stratigraphic-Miocene. 2. Geology, Stratigraphic-Pliocene. 3. Geology- Middle Atlantic States. I. Blackwelder, Blake W., joint author. II. Title. III. Series. IV. Series: United States. Geological Survey. Bulletin ; 1482-D. QE694.W37 551.7'87'0975 80-607052 For sale by Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Abstract __ Dl Introduction 1 Acknowledgments ____________________________ 4 Discussion ____________________________________ 4 Chronology of depositional events ______________________ 7 Miocene Series _________________________________ g Eastover Formation ___________________________ 8 Definition and description ___________________ g Stratigraphic relationships __________________ 12 Claremont Manor Member ___________________ 12 Cobham Bay Member ______________________ 19 Pliocene Series _________________________________________ 28 Yorktown Formation __________________________ 28 Previous work __________________________ 28 Redefinition and description _________________ 29 Stratigraphic relationships __________________ 29 Paleogeography _________________________ 31 Age and correlation ______________________ 31 Paleoenvironment ________________________ 32 Sunken Meadow Member ____________________ 32 Rushmere Member __________________________ 35 Morgarts Beach Member ____________________ 40 Moore House Member _____________________ 43 Summary of depositional and structural history _____________ 4g Locality register __________________________________ 54 References cited ________________________________ ILLUSTRATIONS [Plates follow "References Cited"] Plate 1. Mollusks from the Claremont Manor Member. 2. Mollusks from the Cobham Bay Member. 3. Mollusks from the Cobham Bay Member. 4. Mollusks from the Sunken Meadow Member. 5. Mollusks from the Rushmere, Morgarts Beach and Moore House Members. Ill IV CONTENTS Page Figure 1. Selected outcrops that are listed in the "Locality Register" D2 2. Correlation chart showing stratigraphic relationship of the members of the Eastover and Yorktown Formations __________________________ 3 3. Location of type section of the Eastover Formation ___ 9 4. Type locality of Eastover Formation ____________ JQ 5. Location of the type section of the Claremont Manor Member of the Eastover Formation and the Sunken Meadow Member of the Yorktown Formation _____ 13 6. Type locality of the Claremont Manor Member, Eastover Formation, and of the Sunken Meadow Member, Yorktown Formation ______________ 14 7. Basin configuration of the Claremont Manor Member, Eastover Formation ____________________ 17 8. Location of the type section of the Cobham Bay Member, Eastover Formation _______________ 20 9. Type locality of the Cobham Bay Member, Eastover Formation __________________________ 21 10. Basin configuration of the Cobham Bay Member, Eastover Formation ____________________ 26 11. Yorktown Formation overlying laminated clays of the Eastover Formation 30 12. Piankatank River, Va., near Martiau showing shelly beds of the Sunken Meadow Member ___________ 33 13. Extent of outcrops of the Sunken Meadow Member of the Yorktown Formation _________________ 34 14. Location of Yorktown Formation lectostratotype near Rushmere, Isle of Wight Co., Va. Type locality of the Rushmere Member ____________ 36 15. Lectostratotype of the Yorktown Formation and type locality of the Rushmere Member ____________ 37 16. Extent of outcrops of the Rushmere and Morgarts Beach Members of the Yorktown Formation ______ 39 17. Location of the type section of the Morgarts Beach Member, Yorktown Formation __________________ 41 18. Type locality of the Morgarts Beach Member _______ 42 19. Location of the type section of the Moore House Member, Yorktown Formation ______________ 43 20. Type locality of the Moore House Member ________ 44 21. Extent of outcrops of the Moore House Member of the Yorktown Formation _________________ 46 22. Schematic sections along major Virginia rivers ______ 49 23. View of the cliffs just below Wilmont Wharf on the Rappahannock River ____________________ 50 24. Location of structural features in part of the Virginia Coastal Plain ________________________ 51 25. View of the cliffs at Burhans Wharf on the Rappahannock River ____________________ 53 CONTRIBUTIONS TO STRATIGRAPHY STRATIGRAPHIC REVISION OF UPPER MIOCENE AND LOWER PLIOCENE BEDS OF THE CHESAPEAKE GROUP, MIDDLE ATLANTIC COASTAL PLAIN By LAUCK W. WARD and BLAKE W. BLACKWELDER Abstract The Eastover Formation, a newly recognized upper Miocene marine unit within the Chesapeake Group, is herein named and described. The Eastover Formation is divided into two members: a lower, burrowed, silty, fine-grained sand - the Claremont Manor Member - and an upper, shelly, fine­ grained sand - the Cobham Bay Member. The Eastover Formation extends from southern Maryland to North Carolina and as far inland as Richmond. Although beds of the Eastover Formation have previously been assigned to the Yorktown Formation, the Yorktown is a distinct unit that can be divided into four members: the Sunken Meadow, Rushmere, Morgarts Beach, and Moore House. Sediments assigned to the Eastover Formation have also been assigned erroneously to the Calvert, Choptank, and St. Marys Formations. INTRODUCTION The Eastover Formation is herein named and described for a 5- to 28-m-thick sequence of upper Miocene sediments underlying the Coastal Plain of Virginia and the adjacent areas of North Carolina and Maryland (fig. 1). Some sediments previously included in the Calvert, Choptank, St. Marys, and Yorktown Formation (Clark and Miller, 1906, 1912; Olsson, 1917; Mansfield, 1928, 1931, 1943) are now included in the Eastover and Yorktown Formations. Although superficially resembling parts of the Calvert, Choptank, St. Marys, and Yorktown Formations, the Eastover Formation is a lithologically distinct assemblage of sediments occupying a unique depositional basin and containing a characteristic fossil assemblage. The Eastover Formation unconformably overlies Cretaceous, Paleocene, Eocene, Oligocene, and Miocene marine units as well as pre- Mesozoic Piedmont metamorphic rocks. Contacts are sharp and Dl D2 CONTRIBUTIONS TO STRATIGRAPHY .21 "'44^... 2«4,^-< -..6o;v;,*.T-i\,.* 74jStr'Ljc 3-*&71 4, ¥v« ;- 87, r .-v ^ 30' : . .* *^ sm^w^e?* - ' v , '-. 50 «.«M«a 29;. L """*' 0 10 20 30 40 50 60 KILOMETERS I i I I I I I I 0 10 20 30 40 MILES Figure 1. Selected outcrops that are listed in the "Locality Register." CHESAPEAKE GROUP, MIDDLE ATLANTIC COASTAL PLAIN D3 well-defined. The Eastover Formation is 28 m thick in the Claremont area of Surry County, Va., and is approximately 5 to 10m thick in exposures over much of its outcrop belt across the central Virginia Coastal Plain. The Eastover Formation is composed of a lower unit, the Claremont Manor Member that is a silty burrowed sand, and an upper unit, the Cobham Bay Member that is a shelly fine sand. These members of the Eastover Formation are of Tortonian (late Miocene) Age. Some earlier workers (for example Clark and Miller, 1906, 1912; Gibson, 1970, 1971) included sediments of the Eastover Formation in the Yorktown Formation. Therefore, the Yorktown is redefined and divided into four members: the Sunken Meadow, Rushmere, Morgarts Beach, and Moore House Members. A correlation chart (fig. 2) shows the stratigraphic succession of these units. These formations, the Eastover and the Yorktown, are part of the Chesapeake Group. ACKNOWLEDGMENTS Appreciation is expressed to J. E. Hazel, N. F. Sohl, T. M. Cronin, and R. M. Forester, all of the U.S. Geological Survey, for technical assistance and help in the field. G. B. Lawrence and J. B. Green, Jr., Richmond, Va., C. H. Lee, University of South Carolina, S.C., Thor Hansen, Washington, D.C. and C. E. Mason, the George Washington University, Washington, D.C., assisted in various phases of field and laboratory work. C. E. Ray, Smithsonian Institution, provided valuable advice. DISCUSSION Early stratigraphic studies in Virginia included sediments, herein assigned to the Eastover Formation, within the "Appomattox" or "Lafayette" Formation. McGee (1888) placed the "orange-colored sands and clays" at Petersburg, Va., in his Appomattox Formation. In 1891, McGee rejected the name Appomattox and, with Barton (1891), revived the name Lafayette Formation. Later work showed that these orange sands, included earlier in the Appomattox Formation and later in the Lafayette Formation, were of various ages and represented the weathered residuum of many different marine units. The term Lafayette Formation has since been abandoned (Wilmarth, 1957, p. 1129). Beds herein assigned to the Eastover Formation were placed in the Calvert,