Jack C. Pashin1
(1) Geological Survey of Alabama, Tuscaloosa, AL
Abstract: Using flooding surfaces in coal-bearing strata to model accommodation space: example from the Black Warrior foreland basin, Alabama
Flooding-surface bounded depositional cycles were used to make 3-D models of accommodation space and total effective subsidence in the Lower Pennsylvanian Pottsville Formation of the eastern Black Warrior basin. A key goal of this research was to demonstrate the utility of regionally extensive flooding surfaces in coal-bearing strata for quantifying spatial and secular variation of the distribution of accommodation space in sedimentary basins. The principal methods used in this study were analysis of cores and geophysical well logs, backstripping, and computer gridding.
The Black Warrior foreland basin underwent tectonic loading during Pottsville deposition, and the regional subsidence pattern reflects superposition of an Appalachian depocenter on an older Ouachita flexural moat. Modeling cycle duration within the constraints of biostratigraphy and foreland-basin geodynamics indicates a transition from moderate-frequency (1 my) cyclicity to high-frequency cyclicity that may be equivalent to the 0.4- and 0.1-my Milankovitch orbital eccentricity periods. Computer mapping demonstrates that regional strike and the distribution of accommodation space changed from cycle to cycle. These changes are most pronounced in the distal part of the basin and reflect interaction of shifting tectonic and sediment loads with far-field tectonic processes. Geographic and temporal excursions of subsidence rate indicate that high-frequency tectonic activity that has not been considered in stratigraphic and geophysical models of foreland basins can be detected by backstripping and mapping flooding-surface bounded depositional cycles in coal-bearing strata.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana