--> ABSTRACT: Development of a Multiphase Cave System: Ellenburger Formation, Lower Ordovician, West Texas, by U. Hammes, C. Kerans, and F. J. Lucia; #91021 (2010)

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Development of a Multiphase Cave System: Ellenburger Formation, Lower Ordovician, West Texas

HAMMES, URSULA, CHARLES KERANS, and F. JERRY LUCIA

Karst-related processes were of fundamental importance in the development of Lower Ordovician Ellenburger reservoirs of West Texas. A multiphase cave system, related to subaerial exposure during the post-Sauk unconformity, extended as much as 1,000 ft below the top of the Ellenburger Formation. Typically, two main levels of brecciation, which are related to cave formation, are recognized in >1,000-ft-long cores from the Val Verde and Delaware Basins. The upper level is characterized by a distinct tripartite division of breccias and clastic cave-fill deposits. The lower level typically is composed of stacked fracture and chaotic breccias but contains no clastic cave fill. The different breccia levels are separated by undisturbed shallow subtidal to intertidal facies and occasional thin brecciated intervals.

The Ellenburger caves and breccias formed as a result of a multilevel cave system that developed within the vast Ellenburger carbonate platform. Vadose processes contributed karst features close to the unconformity, whereas phreatic and water-table processes formed an extensive, multilevel karst system as deep as 1,000 ft below the pre-Simpson unconformity. Karst-features near the recharge area in the north of the Lower Ordovician platform appear very close to the unconformity, whereas karst features downdip to the south of the platform occur 200 ft below the unconformity. Dissolution of limestone and dolomite by underground streams and vadose processes created the multiple cave levels in the Ellenburger due to the development of a multiphase cave system that evolved with a shift in base level due to continental erosion. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.