A Sequence Stratigraphic Interpretation of the Middle Mississippian Strata in the Black Warrior Foreland Basin, Alabama and Mississippi

Carrie A. Kidd and William A. Thomas
Geology, University of Kentucky, Lexington, KY

The middle Mississippian (lower Chesterian) Hartselle/Pride Mountain synorogenic clastic wedge contains four sandstones (Hartselle, Evans, “middle”, and Lewis, in descending order) and is overlain by the Bangor Limestone carbonate ramp in the Black Warrior foreland basin in northern Mississippi and Alabama. The Lowndes-Pickens block, a synsedimentary fault block with orthogonal boundaries in the southern part of the basin, controlled sediment dispersal in the Hartselle/Pride Mountain interval. Approximately 200 geophysical well logs, 10 well cuttings descriptions, and outcrop data support construction of cross sections, isopach maps, and sequence stratigraphic depositional models.

The deposition of the Pride Mountain Formation marked the beginning of basin subsidence and sea level rise at the start of the Ouachita orogeny. The Pride Mountain Formation is a lowstand systems tract with four parasequences defined by marine-flooding surfaces above coarsening and/or fining upward cycles of shale and sandstone. The Pearce siltstone, previously unidentified and found only in the subsurface, is an equivalent facies of the Hartselle Sandstone. The Lewis sandstone and Bangor Limestone extend across the boundary of the block with no significant change in thickness; whereas, the middle and Evans sandstone and the Pearce siltstone onlap against the block indicating short-term movement. The Bangor Limestone is laterally continuous and highly cyclic in the upper part of the ramp and grades from oolitic shoals in the northeast southwestward into a condensed section, the Neal black shale, at the toe of the ramp. Floyd/Neal shale is a potential unconventional gas play averaging 100 feet thick at depths around 4500 feet in east-central Mississippi.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas