basement, with the possible exception of some local occurrences of 

 Jurassic deposits (Kraft, Biggs, and Halsey, 1973). The deposits, 

 dominantly interbedded lenses of lignitic light-gray and white quartz 

 sand and various colored suites of silt and clay, represent deposition 

 in a deltaic environment of shifting river channels, flood plains, and 

 swamps. Overlying the thick nonmarine Cretaceous sediments are marine 

 Cretaceous deposits of lignitic quartz sand, glauconitic quartz sand, 

 clay, and silt. Sand bodies are generally laterally continuous. The 

 basal transgressive unit of this sequence is the Magothy Formation, 

 which represents the lagoonal or estuarine phase. 



Marine sediments of Paleocene and Eocene age overlie the Cretaceous 

 deposits. Glauconite, which consists of dark-gray and greenish-gray 

 clay, silt, and sand, is a key constituent of all deposits. Glauconite 

 abundance is often used as a distinguishing criteria. Concentrations of 

 presumably phosphatic material have been noted at the base of the Paleo- 

 cene (Minard, et al . , 1969) and of bentonite at the same stratigraphic 

 level (Jordan and Adams, 1962). Disconformably overlying the Eocene 

 sediments are marine Miocene sands, silts, and clays (the Oligocene is 

 not represented). Shells and shell beds are common in these sediments; 

 glauconite decreases markedly in abundance from that of underlying beds. 

 In the study area, the Miocene is composed of the Chesapeake group (Cal- 

 vert, Choptank, St. Marys, and Yorktown Formations, in ascending order) 

 which contains numerous important aquifers (see Table 1). Weigle (1974) 

 cites recent studies as questioning the presence of the Yorktown Formation 

 in the Ocean City area. Regardless of the correct nomenclature, the top 

 of the Miocene (Pliocene?) generally lies at about 27 to 43 meters (90 to 

 140 feet) below the Maryland coast; the top of the St. Marys Formation is 

 given as about -145 meters (-475 feet) mean sea level (MSL) at Ocean City. 

 Owens and Denny (1974) assigned the Beaverdam sand (formerly Pleistocene 

 age) and the Pocomoke aquifer (formerly Miocene age) to a Pliocene age. 



b. Quaternary Sediments . Several investigations of Quaternary 

 deposits of Delmarva have been made (Owens and Denny, 1974; Mixon, et al . , 

 1974; Denny, 1974). In general, the truncated surfaces of unconsolidated 

 Coastal Plain strata of Delmarva are disconformably overlain by two types 

 of Quaternary deposits: fluvial sands and gravels; littoral and shallow 

 marine clay, silt, and sand. The fluvial deposits, which comprise the 

 majority of Pleistocene-age sediments in northern and central Delmarva, 

 are tan and brown, iron-stained, coarse sands. and gravels deposited in 

 braided and coalescing streams. South of Easton, Maryland, fluvial 

 sediments grade into littoral and shallow marine beds. Mixon, et al . 

 (1974) and Denny (1974) discuss the presence of beach ridge and dune 

 deposits composing the "backbone" of the lower peninsula. According to 

 these authors, Weigle (1974), and Owens and Denny (1974), the coastal 

 deposits are pre-Sangamon, Sangamon, and Wisconsin in age. Upper Pleisto- 

 cene sediments are primarily of barrier, back-barrier, and foreshelf 

 origin; the lower Pleistocene comprises the Beaverdam sand (identified 

 as Pliocene by Owens and Denny, 1974). In general, Pleistocene beds of 

 marine or estuarine blue and gray clay and silt and fine gray sand 



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