Abstract

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 base of the Clayton Shale is the top of the Lower Member. The base of the Yoakum Shale is the base of the Lower Member. The Reagan Unit lies between the Clayton Shale and the strata constituting the Duval Delta. The Duval Delta section is represented by the House Unit. The Lower House Unit is the stratigraphic interval between the Duval Delta sequence and the top of the Middle Wilcox (base of Yoakum Shale). The stratigraphy and depositional environment of each unit is described. 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.