Holocene age. The small grain size and poor sorting, as well as diagnos- 

 tic benthonic forams, pelecypods, and plant debris, suggest a protected 

 brackish environment. 



The lowermost sediment unit sampled is unit A, a sequence of Pleisto- 

 cene sediments. Included in this unit are rarely occurring leached sands 

 and iron-stained gravels (sediment type V) . The unit represents a number 

 of different environments of deposition ranging from fluvial to estuarine, 

 lagoonal, and subaerial. Muds are not abundant but they do exist locally 

 and are identifiable by their compact, dewatered nature which indicates a 

 probable history of subaerial exposures. 



It is generally accepted that streams of the U.S. east coast no 

 longer contribute significant quantities of sand to the shelf (Meade, 

 1969; Nieheisel, 1973). Sands transported from the upper reaches of 

 major streams are trapped in the estuaries, which are apparently also 

 filled by transport of material from the shelf. In the mid-Atlantic 

 Bight, sediment sources that are significant to other shelves, such as 

 authigenesis, biogenesis, aeolian and glacial transport, are either com- 

 pletely lacking or of little importance. This suggests that shelf sands 

 in the study area are all locally derived, presumably by reworking of 

 older shelf deposits. The presence of gravelly sands of fluvial origin 

 in the shallow subsurface of the northern Delmarva shelf is supported 

 directly by at least one core and indirectly by geophysical data showing 

 channels. Few cores were collected off Delaware; however, there are 

 many areas on the inner shelf where iron-stained, gravelly sands lie 

 within 0.3 meter of the sea floor. The fine-grained, lagoonal and estu- 

 arine deposits lying beneath the surficial sand body contain appreciable 

 quantities of sand-size material, perhaps up to 10 percent by volume. 

 Geophysical and sediment data presented elsewhere in this study show that 

 this unit is periodically exposed on the shelf and subject to erosion. 

 Certain identifiable constituents (peat clasts and brackish water mollusks) 

 are found in the base of the overlying shoal sands and it seems reasonable 

 that sand grains eroded from unit A are included in the shoal sand. The 

 coastline itself is predominantly sand. In plan view, the back-barrier 

 lagoons are a major part of the coastal facies; however, three-dimensional 

 data show that the mud deposits are not exceedingly thick or laterally 

 extensive. Deposition of sand in tidal deltas and inlet throats tends to 

 maintain a coarse texture for the retreating barrier complex. As the 

 barrier retreats, older subsurface sediments are exhumed on the shoreface 

 and although they are often poorly sorted, they comprise adequate quanti- 

 ties of sand-size material for sorting and deposition of the surface sand 

 unit. 



The foregoing discussion can be simplified to summarize the Quaternary 

 evolution of the shallow sedimentary record of the inner shelf subsurface. 

 Sediments on the shelf were derived originally from the adjacent landmass 

 and were transported and deposited under fluvial conditions. Delaware 

 River was a major avenue of transport but other numerous streams crossed 

 the Maryland Eastern Shore. At times of high sea level (interglacials) 

 ancestral coastal deposits were repeatedly laid down and partially eroded 



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