Facies Relationships and Depositional Environments of Lower Tuscaloosa Formation Reservoir Sandstones in McComb Field Area, Southwest Mississippi

William S. Hamilton, Jr., Christopher P. Cameron

Excellent conventional core control and isolith maps based on core analysis and electric log (SP) signatures provide the opportunity to interpret and compare the McComb and Little Creek fields. Part of the updip lower Tuscaloosa productive trend, these fields are "structurally modified stratigraphic traps," formed by the combination of gentle structural nosing and updip pinch-out of the reservoir sandstones. Cumulative oil production exceeds 100 million bbl in this area.

Productive sandstones of the Little Creek field (Denkman Sand) were deposited by a well-developed, mature stream that meandered with moderate to high sinuosity on a low-gradient flood plain. The thickness and continuity of full point bars identified in the core indicate that the sandstones were deposited by a stream approximately the size of the modern lower Brazos River in Texas.

The McComb sand was deposited as part of a transgressive barrier island complex at a time when sand supply to the area was diminishing. Coarsening-upward sequences highlighted by large-scale, low-angle, planar cross-bedding were identified in 10 of 14 McComb cores, and probably represent shoreface and barrier facies. The remaining cores exhibit generally thinner fining-upward sequences typical of tidal channel and inlet sequences. The McComb sand is surrounded by lagoonal and marine mudstones and siltstones.

The meander-belt deposits occupy a lower stratigraphic position in the formation than the barrier island sandstones. The barrier facies mark the shore zone of the Upper Cretaceous marine transgression in the McComb field area.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.