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The Stuart City Trend—South Texas

P.L. Inderwiesen
P.L. Inderwiesen
Texaco, Incorporated
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January 01, 1983


The seismic line depicting the Stuart City Reef is located in LaSalle County, Texas (Figure 1). The line is oriented in a north-to-south direction and is approximately 9.8 mi (15.8 km) long.

Summarizing the introduction in Bebout and Loucks (1974), the Stuart City Trend represents a narrow, linear zone of biogenic carbonate buildup which occurred on the margin of a broad shelf in South Texas during the Lower Cretaceous time (Figure 1). The shelf-margin sediments making up the Stuart City Trend average less than 2 mi (3.2 km) in width and separate the open-marine environment of the ancestral Gulf of Mexico to the east from a 400-mi-wide (644-km-wide) carbonate shelf to the west. The carbonate shelf is divided into several paleogeographic regions discussed in detail by Fisher and Rodda (1969). The abundance of marine organisms over the shelf area is attributed to the warm-water environment resulting from shallow-water depths of a few to 200 ft (61 m). On a larger scale this broad shelf and carbonate accumulation are found to encircle most of the Gulf of Mexico.

Bebout and Loucks (1974) have classified five major depositional environments across the Stuart City Trend based on facies relationships found from core samples. These environments, from east to west, are:

(1) an open-marine environment consisting of planktonic foraminifer wackestone accumulated in water greater than 60 ft (18.3 m) deep;

(2) a lower shelf-slope environment consisting of intraclast grainstone, echinoid packstone, and echinoid-mollusk wackestone accumulated in water 30 to 60 ft (9.1 to 18.3 m) deep;

(3) an upper shelf-slope environment consisting of localized patch reefs composed of coralstromatoporoid boundstone which are isolated from the shelf-margin environment by caprinidcoral wackestone. Water is 10 to 30 ft (3.0 to 9.1 m) deep;

(4) a shelf-margin environment consisting of (a) reed and banks composed of requienid and coralcaprinid boundstones formed in water 5 to 15 ft (1.5 to 4.6 m) deep, (b)various sand bodies including beaches, tidal bars, spits, and channel fill composed of rudist grainstone formed in water depths less than 10 ft (3.0 m) in depth, and (c) stable grain flat composed of algae-encrusted miliolid-coral caprinid packstone formed in water 1 to 5 ft (0.3 to 1.5 m) deep; and

(5) a shallow-water shelf-lagoon environment consisting of miliolid wackestone, mollusk wackestone, toucasid wackestone, and mollusk-miliolid grainstone formed in water less than 20 ft (6.1 m) deep.

The Cretaceous stratigraphic section of the Stuart City Trend is given in Figure 2. The overall regional dip is toward the Gulf of Mexico in response to basinal subsidence. The Stuart City formation corresponds to the shelf-margin environment discussed previously and has a total sediment accumulation of 2,000 to 2,500 ft (609.6 to 762.0 m) (Bebout and Loucks, 1974). Also, the Stuart City carbonate facies is progradational and is terminated by deep-water shelf carbonates deposited in response to a major transgression due to subsidence which lasted through Late Cretaceous (Bebout and Loucks, 1974).

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AAPG Studies in Geology

Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces

A. W. Bally
A. W. Bally
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American Association of Petroleum Geologists
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Publication date:
January 01, 1983




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