Deep-Water Deposition of Upper Wilcox Sandstones, Katy Field, Texas: ABSTRACT

Abstract

Lower Eocene Wilcox sandstones were studied in a continuous core from a depth of 10,357 to 10,607 ft. The sandstones are 6-30 ft thick, very fine grained (0.11 mm), and generally thinly laminated. They consist of quartz, 52%; feldspar, 16%; rock fragments, 7%; other grains, 7%; and clay matrix, 18%. Interbedded shales are dark gray to black, massive, and rarely silty and bioturbated. Sandstones are composed of thin beds that are 1-3 ft thick and commonly show a vertical bedding sequence of (1) a thin, basal zone that contains small, siltstone clasts 1-5 mm in long diameter, (2) a dominant middle zone of inclined laminae that dip at angles of about 5°, and (3) a thin upper zone of horizontally laminated siltstone. Grain size decreases upward from 0.16 mm to 0.05 mm within the thin beds. These units appear to represent a turbidite sequence corresponding appear to represent a turbidite sequence corresponding to a basal graded unit (B1), a middle laminated unit (B2), and an upper laminated unit (D). A thin pelite unit (E) may be present at the top. The ripple-laminated unit (C) is missing or poorly developed. Contorted bedding is present in everal intervals. A minor amount of sandstone also occurs in ripple lenses that are thinly interlaminated with dark-gray, pelagic shales. A deep-water origin is postulated for this section because of the turbiditelike bedding sequence and graded texture, scarcity of organic reworking, and regional location beyond the limits of mapped Wilcox deltas. End_of_Article - Last_Page 1827------------