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ABSTRACT: Regional Stratigraphy and Subdivision, Lower Part of Upper Wilcox, Duval Delta Area, South Texas

HARGIS, RICHARD N. , Independent and Consulting Geologist, San Antonio, TX

This paper provides an overview of the regional stratigraphy and proposes a subdivision of the lower part of the Upper Wilcox covering the Duval Delta area of the South Texas Wilcox fault trend; Live Oak, McMullen, Duval and Webb Counties. The Upper Wilcox was previously subdivided into Upper and Lower Members. The Upper Member was further subdivided but the Lower Member was not. This paper proposes a subdivision of the Lower Member into three stratigraphic units; Reagan Unit, House Unit and Lower House Unit based on the presence of the Duval Delta in the middle of the Lower Member.

The Lower Member is defined by two major transgressive shales, the Clayton shale above and the Yoakum shale at the base. The Reagan Unit is the interval between the Clayton shale and the Duval Delta. The House Unit is the Duval Delta section and the Lower House Unit is the interval between the Duval Delta and the base of the Yoakum shale. The stratigraphy and depositional environment of each Unit is described and two submarine slumps in the Lower House Unit are identified and discussed.

Two regional classifications have been published covering the area of the proposed subdivision that are applicable to the Lower Member, the Stricklin classification and the Tesoro (Debus) classification. Comparison is made with these two classifications.


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