Browsing by Subject "Economic geology"

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Depositional systems and natural resources of the middle Eocene Yegua Formation, south and central Texas coastal plain
(1981) Van Dalen, Stephen Craig; Not available
A regional investigation of the Yegua Formation, using both surface and subsurface data, permits delineation of two genetic units beneath the south and central Texas coastal plain. The lower pro-gradational Yegua unit is composed of a series of wave-dominated delta systems. The principal deltaic complex, the Falcon delta, is located in Webb County and is believed related to the deposition of an ancestral Rio Grande. Facies within the delta include: channel-fill/channel mouth bar; coastal barrier; lagoonal/marsh/floodbasin; prodelta; and transgressive/destructional. The upper Yegua unit consists of stacked barrier bar and lagoonal systems in south Texas. This unit was deposited following abandonment of the Falcon delta, upon avulsion of the Rio Grande and its shift into northeastern Mexico. As the delta foundered, it was replaced by a barrier system supplied with strike-fed sediments from the Mexican delta located to the south. In central coastal Texas, both the upper and lower Yegua consist of a series of small wave-dominated to lobate deltas. The Yegua Formation contains important oil and gas reservoirs in this area. Most production is from the upper genetic unit. Hydrocarbons are accumulated along a trend between the barrier bar and lagoonal systems, where minor structural features combine with pinchouts of barrier sands to provide stratigraphic traps. Another important area of production is along the Mirando-Provident City fault system, where faulted coastal barrier and deltaic sands serve as reservoirs. Because of highly mineralized ground water, the Yegua Formation is not an important aquifer. Commercial deposits of lignite or sedimentary uranium have not been recognized within the study area and sedimentological analysis indicates that discovery of these deposits is very unlikely