Digital Mapping Techniques '01 -- Workshop Proceedings
U.S. Geological Survey Open-File Report 01-223
Geology of the Cretaceous West Gulf Coastal Plain in Southwestern Arkansas
By William D. Hanson and Daniel K. Smith
Arkansas Geological Commission
3815 West Roosevelt Road
Little Rock, AR 72204
Telephone: (501) 296-1877
Fax: (501) 663-7360
e-mail: doug.hanson@mail.state.ar.us
Cretaceous units in southwestern Arkansas are currently being mapped under the National Cooperative Geologic Mapping Program-STATEMAP Project number 1434-94-A-1223. Twenty-two 7.5-minute quadrangles have been mapped to date. By July 1, 2001 seven more maps will be completed. Next fiscal year (2001-2002), the Onia and Fifty-Six quadrangles in north-central Arkansas will be mapped. ArcView 3.2 and Canvas 6.0 are used to create the digital maps. Paper copies of these maps are available from the Arkansas Geological Commission as Open-File Reports. Geologic worksheets, geologic maps reduced to 1:48,000, are being produced from digitized geologic maps. Each will have a brief lithologic description of the units on the back of each sheet.
Cretaceous rocks of the West Gulf Coastal Plain in southwestern Arkansas consist of the Lower Cretaceous Trinity Group, which includes the Dierks Limestone Lentil and DeQueen Limestone Member, and the Upper Cretaceous Woodbine Formation, Tokio Formation, Brownstown Marl, Ozan Formation, Annona Chalk, Marlbrook Marl, Saratoga Chalk, Nacatoch Sand, and Arkadelphia Marl. The Trinity Group consists of sand, clay, limestone, gravel, and gypsum, while the Upper Cretaceous units consist of sand, clay, marl, chalk, and water-laid volcanic tuff. These units are primarily sedimentary in origin and were deposited in a near-shore marine environment. Most of these formations are bounded by unconformities. Lower Cretaceous units strike east-west and dip to the south approximately 80-100 feet per mile. Upper Cretaceous units strike northeast-southwest and dip to the south approximately 80 feet per mile.
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