Current Research--Brownfield et al.--page 7 of 9

Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 241, part 2
Distribution of the Bandera Shale of the Marmaton Group, Middle Pennsylvanian of Southeastern Kansas--page 7 of 9

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Depositional Environment

From the data, observations, and reconstructions presented above, we postulate that sandstones and mudrocks of the Bandera were transported into the Desmoinesian seaway of the Midcontinent from east to west by a fluvial system that drained the craton during sea-level lowstand. This formed an extensive siliciclastic sediment wedge on the eastern shelf of the seaway at lowstand and during the early phases of the subsequent marine transgression, as indicated by the thickness of the interval between the Lake Neosho and Anna black shales in the study area (fig. 6). Limited outcrop control and extensive, subsurface well-log control indicate that most of the siliciclastic complex consisted of sand and mud that were reworked during a subsequent marine transgression. Sandstone units, thick enough to be resolved by gamma-ray logs, appear to coarsen (lower clay content) upward, indicating that final deposition was as bars rather than channel forms. The dominant northeast-southwest trend of sandstone thicks shown on the Bandera sandstone isolith map (fig. 7) indicates that reworked sand-body complexes may have paralleled a postulated paleoshoreline. These bodies may have been shaped in response to currents generated by marine processes, such as tides and storms, rather than from coast-perpendicular or oblique currents that may be expected from a deltaic distributary channel flow jet.

Coastal-plain marsh environments are represented by the Mulberry coal bed, its thin underclay, and a thin coal below the Amoret Limestone Member. These marshes formed as rising sea levels elevated the water tables of coastal plains up to land-surface positions. The Mulberry coal bed, which is traceable over most of the study area, represents a laterally extensive marsh that existed prior to marine regression and deposition of Bandera siliciclastics. The thin, unnamed coal below the Amoret Limestone Member probably represents marshes formed in ever-wet coastal-plain areas just prior to complete marine flooding that led to Amoret carbonate deposition.

Outcrops along the northern margin of the Bandera siliciclastic wedge consist mostly of fine-grained sandstone beds interbedded with clay shale lamina and of thicker sets of cross-bedded sandstone (fig. 9). These lithologies are calcite cemented; some contain trace fossils attributed to marine organisms (fig. 10). Some units are laminated in a rhythmic fashion (fig. 11A); others are flaser stratified (fig. 11C), suggesting tidal influence, while nearby units are contorted (fig. 11B) or are loaded into underlying units (fig. 9C), indicating rapid deposition. These characteristics, along with the well-sorted, calcite-cemented nature of sandstone units, strongly suggest that deposition was in a shallow marine setting, where the primary sediment-moving agents were tide-generated and storm- or flood-generated currents.

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Kansas Geological Survey
Web version June 24, 1998
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