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

Bellian, Jerome A.; Kerans, Charles; Repetski, John

This paper reviews and synthesizes lithostratigraphy, biostratigraphy, chronostratigraphy, and breccia types of the southwestern part of the Great American Carbonate Bank in the southern Franklin Mountains, El Paso, Texas. Primary stratigraphic units of focus are the Lower Ordovician El Paso and Upper Ordovician Montoya Groups. These groups preserve breccias formed by collapse of a paleocave system. Precambrian and 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 breccias of the southern Franklin Mountains 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 point spacing) airborne lidar data over 24 km2 to map breccia and relevant stratal surfaces. Airborne lidar data were used to create a Digital Outcrop Model of the southern Franklin Mountains from which a detailed (1:2000 scale) geological map was created. The geological map includes formation, fault, and breccia contacts. The Digital Outcrop Model was used to interpret 3-D spatial relationships of breccia bodies with respect to the current understanding of the tectonic and stratigraphic evolution of the southern Franklin Mountains. 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.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013