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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 49 (1965)

Issue: 3. (March)

First Page: 352

Last Page: 352

Title: A Depositional Model for the Jackfork (Mississippian) Group of Arkansas: ABSTRACT

Author(s): Robert C. Morris

Article Type: Meeting abstract


Two linear, isolated belts of Jackfork clastics in the Arkansas Ouachita Mountains exhibit differences in sand-shale percentages, sedimentary structures, composition, and thickness, permitting one to make assumptions concerning the depositional model. Along the Frontals, the 5,400-foot-thick section is 70 per cent shale, generally lacking fissility and siliceous marker beds and is often contorted, containing irregular sandstone blocks. Medium bedded, fine grained arenites contain laminations, cross-stratification, ripple marks, and scattered tool marks oriented 255°, whereas massive, ridge-forming arenites are almost structureless. The 6,000-foot-thick southern section is approximately 70 per cent fine grained, poorly sorted arenites, containing schist fragments and eldspar. The remaining wackes, siltstones, and mudstones show little evidence of strong currents or steep slopes.

Petrographic and paleocurrent studies suggest the derivation of the clastics from a large, well-drained provenance to the east, consisting predominantly of quartzites and mature sandstones. Some clastics may have bypassed the Illinois Basin, the resulting laminated and cross-stratified arenites having formed from southwest flowing traction currents. Rubble bedding, possibly initiated by faulting, resulted when subaqueous mudflows disrupted the non-lithified arenites to form rounded exotic blocks. Structureless, generally massive arenites may have entered the basin by mass sediment flow from a more eastern or southeastern direction, possibly being swept off the Appalachian land mass by westward flowing currents.

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Copyright 1997 American Association of Petroleum Geologists