ABSTRACT: Facies Contrasts across an Ancient Extensional Lake-Basin: The Apache Canyon Formation, Southeastern Arizona

SOREGHAN, MICHAEL J., University of Arizona, Tucson, AZ

The Apache Canyon Formation is a mixed carbonate-clastic sequence that was deposited within the extensional Bisbee basin. The Bisbee basin, of latest Jurassic and Early Cretaceous age, has been genetically related to the Chihuahua Trough of northern Mexico. The Apache Canyon Formation lies between two fluvial units; together these three units comprise the syntectonic fill of the Bisbee basin. Previous work on the Apache Canyon Formation has been primarily descriptive; no detailed study to date has attempted to place the Apache Canyon Formation into a coherent paleogeographic setting.

Previous structural and tectonic studies have delineated a series of east-west- to northeast-southwest-trending normal faults of Early Cretaceous age with significant vertical offsets. The Apache Canyon was studied in detail at two sites: (1) immediately adjacent to one of these faults, and (2) approximately 40 km perpendicular to the trend of this fault. Both study sites consist of a series of shoaling-upward clastic-carbonate cycles that range from 3 to >10 m thick. However, there are significant differences between the sites in total stratal thickness, facies composition, and vertical and lateral facies transitions. The summed differences in stratigraphy between the sites suggest that they represent lake-margins which experienced different environmental conditions induced by str ctural asymmetry of the basin.

The observed first-order facies contrasts supports the inference that the Apache Canyon Formation was deposited within an ancient half-graben lake-basin. The cyclic nature of the sequence suggests lake-level experienced numerous, high-frequency fluctuations that may have been climatically induced. Work on the origin and possible paleoclimatic significance of the cycles is continuing.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)