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The Bureau of Economic Geology is compiling a new Tectonic Map of Texas--a detailed, up-to-date display at 1:500,000 of surface and subsurface structural history for the entire state and adjoining areas of Mexico and the continental shelf and slope. This is the first comprehensive structural mapping of Texas since E. H. Sellards' "Structural Map of Texas" some 40 years ago. A companion illustrated text is also being compiled to systematically describe and summarize the tectonic evolution of the state from Proterozoic to Holocene.
Deformed Precambrian crust is exposed in the Llano uplift and in western Trans-Pecos Texas. It is subdivided by the tectonic setting of the sedimentary rocks and the timing of intrusion and deformation. The late Paleozoic basins and the intervening fault-bounded basement uplifts of west Texas are shown by 200-m and 100-m contours on the top of Precambrian or the top of Ellenburger, depending on the nature of well control. The principal features of the buried Ouachita Overthrust belt are displayed, along with a more detailed rendition of the exposed Ouachita rocks in the Marathon region. The East Texas, Maverick, and Sabinas basins and the inner Gulf coastal plain are shown by contours on the Edwards Limestone and the Austin Chalk; features due to salt tectonism, growth faulting, and C rdilleran deformation are prominent. Seaward of the Cretaceous shelf margin, the growth-fault trends of the Gulf Coast are shown with contours on the Tertiary formations most affected. Available offshore data have been integrated to provide a picture of the shelf, slope, and a corner of the Sigsbee abyssal plain. In the multiply deformed Trans-Pecos region, the surface expressions of structures related to Laramide folding and thrusting, middle Tertiary volcanism, and Miocene to Holocene basin and range faulting are shown, in addition to the Precambrian and Ouachita-Marathon structures, where exposed.
The final edition will be multicolor, with colors emphasizing subsurface contour horizons and depths, tectonic units in deformed or volcanic areas, salt domes, igneous bodies, faults, and axial traces of folds. Faults will be identified, where possible, by their age. Inset maps will include basement age and lithology, gravity, magnetics, and topography. The map and text will provide a valuable summary of Texas structural geology and suggest new approaches to the search for energy resources.
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