Section III. DISCUSSION 



Miocene strata of the Chesapeake Group underlie the entire study 

 region and can be correlated at the group level throughout. In wells 

 on southern Delmarva Peninsula, and on the southeastern Virginia 

 coastal plain the top of the Miocene has been assigned a Yorktown age 

 (Sinnott and Tibbetts 1957, Oaks and Coch 1965, Oaks 1964, Harrison 

 et al 1965) . Miocene sediments penetrated by Bridge Tunnel borings 

 near Chesapeake Channel are considered to be no younger than St. Marys 

 age by McLean (1966) indicating that Yorktown sediments were either 

 eroded from this area or never deposited. 



Several CERC cores in the vicinity of Thimble Shoals Channel are 

 judged to have penetrated to the Miocene surface on the basis of 

 lithologic correlation with nearby Bridge-Tunnel borings; no fossil 

 evidence was obtained in these cores. Core 36 near Chesapeake Channel 

 (Figure 2) penetrated material containing well-preserved, unworn macro- 

 fossils of definite Miocene Age but uncertain formational affiliation. 



Post-Miocene deposits of the southeastern Virginia Coastal Plain 

 have been described in detail by Oaks and Coch (1963) and Oaks (1964) . 

 Post-Miocene stratigraphy under the southern Delmarva Peninsula has not 

 been detailed, and known deposits are assigned to the Pleistocene 

 Columbia Group undifferentiated. 



No direct relationship between post-Miocene sedimentary units in 

 the study area and those described from the adjacent land areas of 

 southern Delmarva Peninsula and southeastern Virginia can be shown. If 

 such a relationship exists, it seems most likely to be between the 

 coarse gravelly sand ( Unit E) outcropping in the study area at Thimble 

 Shoals Channel, the lithologically similar gravelly sands occurring in 

 Columbia Group deposits on southern Delmarva Peninsula, and gravelly 

 sand occurring in the lower member of the Great Bridge Formation 

 (Pleistocene) under the southeastern Virginia Coastal Plain (Oaks 1964) . 

 Other gravel bearing units in the southeastern Virginia coastal plain: 

 the Kilby facies, Bacons Castle Formation; members of the Norfolk 

 Formation; the Kempsville Formation and Londonbridge Formations are 

 possible correlatives of Unit E. However the Kempsville and London- 

 bridge Formations are not known to occur lower than -17 feet MSL nor to 

 directly overlie the Miocene surface while Unit E occurs as deep as -90 

 MSL and characteristically overlies an eroded surface in Miocene strata. 

 The Bacons Castle Formation has not been identified east of Suffolk 

 Scarp which lies several miles west of the study area. The Norfolk 

 Formation containing gravelly members and found as deep as -35 feet MSL 

 is a possible but less likely correlative to unit A than the Great 

 Bridge . 



Because of the coarse character of Unit E sediment and its apparent 

 relationship to buried stream channels, it is believed to be a relic of 

 lower sea level; thus late Wisconsin glacial or earlier in age. Unit D 

 peat which occupies with Unit E the same stratigraphic horizon on the 



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