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Abstract: Depositional Environment of the Downdip Queen City (Eocene) Sandstone, Mestena Grande Field Area, Jim Hogg and Duval Counties, Texas

Jeffrey McCormack

The downdip Queen City sandstone interval in the Mestena Grande field area of the south Texas Gulf Coast basin comprises two sandstone depositional units, referred to in this paper as A Lobe and B Lobe. A total of 583 ft (179 m) of conventional core from 11 wells containing predominantly B Lobe deposits were examined macroscopically. The A Lobe is a thin (6-34 ft; 1.8-10.4 m) fine- to very fine-grained, mostly bioturbated, well-sorted sandstone. The B Lobe is composed of fine to very fine, well-sorted sandstone interbedded with siltstone and mudstone. The trace fossil assemblage of the B Lobe indicates that sediments were deposited in the cruziana ichnofacies. Trace fossils and authigenic minerals also suggest oxygen stratification during deposition. B Lobe contains five subunits, eac up to 13.5 ft (4 m) net sand thickness. These units were deposited as part of a highstands systems tract during the early Lutetian Stage (lower middle Eocene). B Lobe is a primarily aggradational unit composed of storm-generated sandstone and heterolithic deposits of the lower shoreface to inner shelf environment. A Lobe is a coarsening upward unit and represents progradation of the shoreface during late highstand systems tract development. An interlobal mudstone, which separates the units, marks the transition from early to late highstand systems tract development.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994