State of Delaware DELAWARE GEOLOGICAL SURVEY Robert R. Jordan, State Geologist REPORT OF INVESTIGATIONS NO .. 53 GEOLOGY OF THE SEAFORD AREA, DELAWARE by A. Scott Andres and Kelvin W. Ramsey E -10 o o -10 -10 Alluivial deposits Oaf Nanticoke deposits On .. Swamp deposits Osw Beaverdam Formation Tbd With a contribution on palynology by Johan J. Groot University of Delaware Newark, Delaware 1996 State of Delaware DELAWARE GEOLOGICAL SURVEY Robert R. Jordan, State Geologist REPORT OF INVESTIGATIONS NO. 53 GEOLOGY OF THE SEAFORD AREA, DELAWARE by A. Scott Andres and Kelvin W. Ramsey With a contribution on palynology by Johan J. Groot University of Delaware Newark, Delaware 1996 CONTENTS Page Page ABSTRACf 1 Other Quaternary deposits 8 Marsh deposits 8 INTRODUCTION 1 Swamp and alluvial deposits 9 Purpose and Scope 1 Upland bog deposits ............................. .. 9 Location 1 Previous work ........................................ .. 1 GEOMORPHOLOGY 9 Acknowledgments 4 Floodplains 9 Upland Surfaces 10 METHODS OF STUDY 4 PALYNOLOGY OF THE SEAFORD AREA 14 STRATIGRAPHY 4 General Observations 14 Chesapeake Group 4 Palynomorph assemblages ofthe Choptank Formation 4 Beaverdam Formation 14 St. Marys Formation 5 Palynomorph assemblages ofthe Manokin Formation 5 Quaternary Sediments 14 Beaverdam Formation 6 Relation to previously recognized units 6 SUMMARY - GEOLOGIC HISTORY 15 Composition and textures 6 Tertiary 15 Thickness, distribution, and bounding relations 7 Quaternary 15 Nanticoke deposits 7 Quaternary depositional model 20 Relation to previously recognized units 7 REFERENCES CITED 21 Composition and textures 7 Thickness, distribution, and bounding relations 8 ILLUSTRATIONS Page Figure 1. Map showing area ofthe Seaford East and Seaford West quadrangles 2 2. Geologic map ofthe Seaford area, Delaware 3 3. Comparison of stratigraphic column in the Seaford area (this report) with those of previous workers 3 4. Well log showing lithostratigraphic units and natural gamma radiation log from well Oc14-27 in Bridgeville 4 5. A typical sequence of Nanticoke deposits at outcrop Od43-a2 8 6. Soft sediment deformation in the Nanticoke deposits at outcrop Od43-a1 8 7. Cross section showing geology and geomorphology ofthe floodplain and valley walls 9 8. Map ofMiddleford area showing location ofthe cross section in Fig. 7 10 9. Aerial photograph and topographic map of part ofthe outcrop area ofthe Nanticoke deposits 11 10. Dune deposits in the Nanticoke river valley 12 11. Aerial photograph and topographic map ofan area with upland bog deposits 13 TABLES Page Table 1. Summary ofclay mineral data ............................................................................................... 5 2. Summary of light mineral data :......................................................... 6 3. Palynological data 16 ERRATA DELAWARE GEOLOGICAL SURVEY REPORT OF INVESTIGATIONS NO. 53 Delaware Geological Survey Report of Investigations No. 53, Geology ofthe Seaford Area, Delaware by A. Scott Andres and Kelvin W. Ramsey, with contrtibution on palynology by Johan J. Groot, 1996. Following release of the report, it was found that there were several errors in the text. This errata sheet is intended to correct these errors. Page 7, column 2, paragraph 4 under Composition and Textures, and Page 14, column 2, paragraph 4 under Palynomorph Assemblages ofthe Quaternary Sediments (Chenopool!aceae) should read (Chenopodjaceae.) Page 15, column 2, paragraph 1 (early Pleistocene) should read (early or middle Pleistocene) Pages 16-19, Table 3 Title should read Pollen assemblages expressed in percentages of the pollen sum. Page 17, Table 3 Sample number 84834 - (Remarks) Sanquisorba? should read Sanguisorba? Sample numbers 42270, 42266 - (Age) should read 01 Sample number 84662 - (Age) should read 0 Sample number 83836 - (Remarks) should be Polygonaceae, Gordonia Sample number 83947 - (Remarks) shOUld be T, edmundii, few ~aleozoic spore~ Sample numbers 22793, 22782 - (Age) should be 011, 13 Sample number 22826 - (Remarks) should be T. edmundii, Onagraceal! Page 19, Table 3 Sample number 84473 ­ (Remarks) shOUld be Larix; reworked sample number 84472 - (Remarks) should be ~ Page 19, Under Key to Table 3 Column heading Genus P Other dicotyledon~ Climate Column heading Explanation sub subtropical GEOLOGY OF THE SEAFORD AREA, DELAWARE A. Scott Andres and Kelvin W. Ramsey ABSTRACT This report supplements the map "Geology of the Seaford Area, Delaware" (Andres and Ramsey, 1995). The map por­ trays surficial and shallow subsurface stratigraphy and geology in and around the Seaford East and Delaware portion of the Seaford West quadrangles. The Quaternary Nanticoke deposits and Pliocene Beaverdam Formation are the primary lithos­ tratigraphic units covering upland surfaces in the map area. Recent swamp, alluvial, and marsh deposits cover most of the floodplains of modem streams and creeks. The Miocene Choptank, St. Marys, and Manokin formations occur in the shallow subsurface within 300 ft of land surface. The Choptank, St. Marys, and Manokin formations were deposited in progressively shallower water marine environ­ ments. The Beaverdam Formation records incision of underlying units and progradation of a fluvial-deltaic system into the map area. The geologic history of the Quaternary is marked by weathering and erosion of the surface of the Beaverdam and deposition of the Nanticoke deposits by the ancestral Nanticoke River. Depositional environments in the Nanticoke deposits include fresh water streams and ponds, estuarine streams and lagoons, and subaerial dunes. INTRODUCTION geologic conditions and geologic history. In several cases, new sets of observations led to new and sometimes signifi­ Purpose and Scope cantly different interpretations. Interested readers are This report documents the results of investigations of referred to Jordan (1962; 1964; 1974), Owens and Denny the surficial and shallow subsurface geology in and around (1979), and Hansen (1981) for reference lists and discus­ the Seaford East (SEE) and Delaware portion of the Seaford sions ofearlier geologic research and controversies. West (SEW) quadrangles (Fig. 1). Additional geologic data The relationships between stratigraphic sections estab­ not shown on the Seaford area geologic map (Andres and lished by previous and current workers are shown in Fig 3. Ramsey, 1995) and supporting documentation for strati­ Earlier workers in the area of Seaford assigned surficial graphic interpretations are presented. A reproduction of the deposits to the Pleistocene without formational designation map is shown in Fig. 2. Knowledge of the stratigraphy is (Marine and Rasmussen, 1955). Rasmussen et al. (1960) important for understanding the distribution of sand, silt, recognized near-surface units including the Parsonsburg and clay bodies within the map area. These bodies control sand, the Pamlico formation, the Beaverdam sand, and the the distribution, transmission, and quality of ground water Brandywine formation. Of these units, only the Beaverdam that is used for agricultural, public and private supply, and has been retained for usage in Delaware (Jordan, 1974). industrial purposes. Availability and occurrence of mineral Jordan (1964, 1974) assigned near-surface geologic units in resources such as sand and gravel are also dictated by the the map area to the Columbia Group, which in southern distribution of sand, silt, and clay bodies. Delaware consisted of the Beaverdam and Omar forma­ tions. Jordan (1964, 1974) also recognized sandy deposits Location in the Nanticoke River Valley that were associated with a The study area (Fig. 1) is located within the Atlantic topographic feature called the Nanticoke Ridge as well as Coastal Plain physiographic province. The largest incorpo­ subsurface deposits that were unassigned to a particular rated towns are Seaford and Bridgeville. The major hydro­ stratigraphic unit but were considered to be Pleistocene in graphic features are the Nanticoke River basin and portions age. Owens and Denny (1979, fig. 5) extended stratigraphic of the Marshyhope Creek basin. Land surface elevations units recognized in Maryland and New Jersey into range from sea level along the tidal portion of the Nanticoke Delaware; these include the Beaverdam Sand and the River to just above 50 ft along the drainage divide between Pensauken Formation, the latter in a small band southeast the Nanticoke and Marshyhope basins and along the of Bridgeville. Denny et al. (1979, Fig. 1) mapped the Delmarva Peninsula drainage divide in the northeastern part Parsonsburg Sand in the southern area of the Seaford East of the Seaford East quadrangle. map and the Kent Island Formation in the area of the flood­ plain of the Nanticoke River. Ramsey and Schenck (1990) Previous Work mapped the Columbia Formation in the northwestern por­ Previous geological investigations in and around the tion of the map area, the Beaverdam Formation over most Seaford area were typically conducted for regional geologic of the map area, and an informal unit, the Nanticoke interpretation or water resources evaluations and included deposits along the Nanticoke River valley. Andres (1994a) subsurface units deeper than those covered in this investiga­ and Andres and Ramsey (1995) used the nomenclature of tion. An important characteristic of many of these earlier Ramsey and Schenck (1990) but modified some of the studies is that they drew from a relatively small number of lithologic descriptions to reflect newer, more detailed geographically scattered