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Book Chapter

Digital Outcrop Model of Stratigraph and Breccias of the Southern Franklin Mountains, El Paso, Texas

By
Jerome A. Bellian
Jerome A. Bellian
University of Texas at Austin, Austin, Texas, U.S.A.
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Charles Kerans
Charles Kerans
University of Texas at Austin, Austin, Texas, U.S.A.
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John Repetski
John Repetski
U.S. Geological Survey, Reston, Virginia, U.S.A.
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Published:
January 01, 2012

Abstract

This chapter reviews and synthesizes the lithostratigraphy, biostratigraphy, chronostratigra-phy, and breccia types of the southwestern part of the great American carbonate bank in the southern Franklin Mountains (SFM), ElPaso, Texas. Primary stratigraphic units of focus are the Lower Ordovician El Paso and Upper Ordovician Montoya Groups. These groups preserve breccias formedbycollapse ofapaleocave system. Precambrianand Silurian units are discussed in the context of breccia clast composition and relative timing of breccia emplacement. Specific attention is paid to the juxtaposition of the top-Sauk second-order supersequence unconformity between the El Paso and Montoya Groups and its relationship to breccias above and below it. The unconformity represents a 10-m.y. exposure event that separates Upper and Lower Ordovician carbonates. The top-Sauk exposure has been previously documented as a significant karst horizon across much of North America.

The breccias of the SFM were previously described as the result of collapsed paleocaves that formed during subaerial exposure related to the Sauk-Tippecanoe unconformity. A new approach in this work uses traditional field mapping combined with high-resolution (<1-m [<3.3-ft] point spacing) airborne light detection and ranging (LIDAR) data over 24 km2 (9 mi2) to map breccia and relevant stratal surfaces. Airborne LIDAR data were used to create a digital outcrop model of the SFM from which a detailed (1:2000 scale) geologic map was created. The geologic map includes formation, fault, and breccia contacts. The digital outcrop model was used to interpret three-dimensional spatial relationships of breccia bodies with respect to the current understanding of the tectonic and stratigraphic evolution of the SFM. The data presented here are used to discuss potential stratigraphic, temporal, and tectonic controls on the formation of caves within the study area that eventually collapsed to form the breccias currently exposed in outcrop.

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Contents

Memoir

Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia

James Derby
James Derby
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Richard Fritz
Richard Fritz
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Susan Longacre
Susan Longacre
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William Morgan
William Morgan
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Charles Sternbach
Charles Sternbach
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American Association of Petroleum Geologists
Volume
98
ISBN electronic:
9781629810201
Publication date:
January 01, 2012

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