ABSTRACT: Evolution of Platform and Basin Architecture in Mixed Carbonate-Siliciclastic Sequences: Latest Leonardian through Guadalupian, Delaware Basin

FITCHEN, W. M., M. H. GARDNER, and C. KERANS, Bureau of Economic Geology, University of Texas at Austin, Austin, TX, L. LITTLE, Conoco, Inc., Houston, TX, M. D. SONNENFELD, Colorado School of Mines, Golden, CO, S. W. TINKER, Marathon Research, Littleton, CO, and B. R. WARDLAW, U.S. Geological Survey, Reston, VA

Synthesis of more than 18 km of new measured sections with recently acquired biostratigraphic dates and existing stratigraphic data provides a high-resolution sequence stratigraphic framework for this classic mixed carbonate-siliciclastic terrane. A 900 m by 50+ km dip-oriented cross-section illustrates detailed facies and correlation relationships that encompass the 12 Ma evolution of a carbonate platform and its adjacent siliciclastic-dominated deep-water basin.

Four major phases of deposition are recognized: (1) a latest Leonardian to earliest Guadalupian landward-stepping to aggradational platform and starved basin (platform units: uppermost Victorio Peak Formation, lower-middle San Andres Formation, and upper San Andres Formation "1" and "2," uppermost Victorio Peak Formation; basin units: Cutoff Formation, Pipeline shaIe); (2) a mid-Guadalupian progradational platform with siliciclastic bypass across single surface (platform units: upper San Andres Formation "3"; basin units: Brushy Canyon Formation); (3) a mid-late Guadalupian strongly progradational platform with siliciclastic bypass across multiple surfaces (platform units: upper San Andres Formation "4," Grayburg Formation; basin: Cherry Canyon Formation); and (4) a late Guadalupian c mpound strongly progradational/aggradational platform, with siliciclastic bypass across multiple surfaces (platform units: Queen, Seven Rivers, Yates, and Tansill formations; basin: Cherry Canyon and Bell Canyon formations).

Evolutionary trends in the platform stratigraphy include a change from ramp to deep-rimmed shelf, increasing proportion of shelf-margin boundstone facies, greater volumetric ratio of highstand to transgressive systems tracts, contraction of all carbonate platform-top and slope facies tracts, a long-term increase in preservation of platform-top siliciclastics, and an increase in number of slope siliciclastic bypass surfaces. Long-term trends in the basin are reflected by a period of sediment starvation (phase 1) followed by three large-scale (300 m), asymmetric mixed carbonate-siliciclastic cycles (phases 2-4) that each show an upward increase in sandstone. Successive asymmetric cycles show a decrease in grain size and an increase in the proportion of basinal carbonate beds. Internally these cycles are composed of eolian-derived turbidites forming higher frequency symmetric cycles bounded by time-significant, organic-rich siltstones.

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