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The Gettysburg Formation is a mapped bedrock unit consisting primarily of sandstones, conglomerates, and shales. The Gettysburg Formation was first described in the Gettysburg area of Adams County, Pennsylvania in 1929,〔 and over the following decade was mapped in adjacent York County, Pennsylvania〔Stose, G.W., and Jonas, A.I., 1939, Geology and mineral resources of York County, Pennsylvania: Pennsylvania Geological Survey County Report, 4th series, no. 67, 199 p.〕 and Frederick County, Maryland.〔Jonas, A.I., and Stose, G.W., 1938, Geologic map of Frederick County and adjacent parts of Washington and Carroll Counties (Maryland): Maryland Geological Survey County Geologic Map, 1 sheet, scale 1:62,500〕 It was then typically called the "Gettysburg shale," and was described as "thick red shales and soft red sandstones." The majority of this early mapping was done by G. W. Stose, A. I. Jonas, and Florence Bascom. Later workers described it as "Red, medium- to fine-grained sandstone and shale."〔 The rock unit was formalized into a Formation in 1963 by J. D. Glaeser.〔Glaeser, J.D., 1963, Lithostratigraphic nomenclature of the Triassic Newark-Gettysburg basin: Pennsylvania Academy of Science Proceedings, v. 37, p. 179-188.〕 Glaeser re-mapped some areas previously mapped as the Gettysburg Formation to the Hammer Creek Formation. A major groundwater resources study of the Gettysburg Formation and other formations of the Newark Supergroup in Pennsylvania was published by Charles R. Wood in 1980.〔Wood, C. R., 1980, Groundwater resources of the Gettysburg and Hammer Creek Formations, southeastern Pennsylvania: Pennsylvania Geological Survey, 4th ser., Water Resource Report 49, 87 p. ((web release )).〕 ==Depositional Environment== The Gettysburg Formation and other formations of the Newark Supergroup were deposited in the Gettysburg Basin, just one of many Triassic rift basins existing on the east coast of North and South America, which formed as plate tectonics pulled apart Pangaea into the continents we see today. The conglomerates within the formation were most likely alluvial fan or mudflow deposits, or possibly talus, eroding directly from the Precambrian and early Paleozoic rocks to the north and south.〔 The sandstones and shales were most likely deposited in the flooded rift valley as deltas. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gettysburg Formation」の詳細全文を読む スポンサード リンク
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