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ABSTRACT: Lower Tertiary Wilcox and Midway Sequences in the Subsurface, Down Dip Rio Grande Embayment South Texas


Over 85 wells were used for a detailed analysis of the stratigraphy, from the base Reklaw to top Cretaceous, in the southern, downdip, subsurface, portion of the Rio Grande embayment. Well selection was based on the availability of samples, as each well was examined for lithology and mineralogy, missing sections (faults and unconformities), faunal content and time lines, paleobathymetry, and e-log correlation.

The Wilcox Formation is divisible into upper (Eocene P-6), middle (Paleocene P-5) and lower (Paleocene P4) sequences. The Midway is dealt with as one unit (Paleocene P 1-3).

The results identify eight regional unconformities, which separate seven stratigraphic sequences. They are from youngest to oldest: Top Wilcox; Lower, Upper Wilcox; Middle Wilcox: Lower Middle Wilcox and Lower Middle Wilcox, expanded; Lower Wilcox; Lower Wilcox expanded; and Midway.

Depending upon the dip position and structural complexity at any given well location, the presence, absence, andor thickness of the sequences can vary.

Additional wells outside the area of the study, show the above sequences are correlative through central Texas and northward into the Southeast Texas Salt Dome Basin.


AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas