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ABSTRACT: Styles of Sequence Development within Latest Leonardian through Guadalupian Strata of the Guadalupe Mountains

KERANS, C., W. M. FITCHEN, and M. H. GARDNER, Bureau of Economic Geology, University of Texas at Austin, Austin, 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

The current generation of field-oriented research in the classic Guadalupe Mountains has been stimulated in large part by the significant potential for incremental recovery of remaining hydrocarbons within the Permian basin. Multiple depositional sequences were previously recognized within latest Leonardian-Guadalupian strata; however, refined shelf-to-basin correlations highlight four phases within the 12 Ma evolution of the platform and its associated deep-water basin. Each Previous HitphaseNext Hit contains one or more depositional sequences, yet is distinguished by the nature of its facies associations and shelf-to-basin dynamics.

Latest Leonardian to earliest Guadalupian Previous HitPhaseNext Hit I is characterized by platform sequences of an initially landward-stepping to aggradational nature, followed by 15 km of shelf-margin progradation with a highstand progradation to aggradation ratio equal to 70:1. Inner-shelf to toe-of-slope carbonate facies Previous HittractsNext Hit form broad (18 km), low angle (less than or equal to 2 degrees) sigmoidal clinoforms. Platform top sediments within this Previous HitphaseNext Hit involve skeletal to peloidal sands, whereas slope and basin facies are micrite-rich. Rare slope and basin megabreccias are slope-derived and involve carbonate mud matrix.

On the platform, early Guadalupian Previous HitPhaseNext Hit II is characterized by widespread karstification and siliciclastic bypass across a single surface followed by relatively minor shelf-margin progradation of 2.5 km yielding a progradation-aggradation ratio of 80:1. In the basin, Previous HitPhaseNext Hit II is represented by deposition of 300 m of deep-water sandstone and siltstone that forms a symmetrical Previous HitcycleNext Hit with abundant higher-energy features and a paucity of limestone beds.

Mid-late Guadalupian platform sequences in Previous HitPhaseNext Hit III are strongly progradational (15 km) with a progradation to aggradation ratio of 136:1. Previous HitPhaseNext Hit III is characterized by multiple platform surfaces of moderate karstification and siliciclastic bypass. High-frequency alternation between preservation of shelf siliciclastics and bypass to the deep-water basin records the onset of "coupled" shelf and basin depositional Previous HitsystemsNext Hit. Inner shelf to toe-of-slope profiles form contracted (5 km), moderately steep (less than or equal to 17 degrees) sigmoid to oblique clinoforms. Relative to Previous HitPhaseNext Hit II, the 300 m thick basinal strata of Previous HitPhaseNext Hit III form an asymmetric Previous HitcycleNext Hit with an increase in sandstone relative to limestone, an increased diversity of lithofacies, and more poorly organized sediment dispers l patterns.

Late Guadalupian platform sequences in Previous HitPhaseNext Hit IV are distinguished by a steady increase in slope inclination up to 50 degrees together with a progressive decrease in the progradation/aggradation ratio from 41:1 to 5:1. Inner shelf to toe-of-slope profiles contracted even further (1 km) in connection with the onset of a reef-rimmed platform with associated slope megabreccias with carbonate and siliciclastic matrix. Previous HitPhaseNext Hit IV is also marked by an abundance of basinal hemipelagic limestones. High-frequency, asymmetric, eolian-derived turbidite cycles are increasingly well resolved within line-feed basinal strata.

The long-term trend from sequences dominated by transgressive Previous HitsystemsNext Hit Previous HittractsNext Hit and siliciclastic bypass across a single surface (Previous HitPhaseNext Hit I, II) to sequences dominated by highstand Previous HitsystemsNext Hit Previous HittractsNext Hit with siliciclastic bypass across multiple surfaces (Phases III, IV) reflects a progressive decrease in platform accommodation and an increase in sediment flux to the basin. This platform evolution reflects a latest Leonardian to early Guadalupian relative Previous HitseaNext Hit Previous HitlevelTop rise, followed by stillstand or fall. Extrinsic accommodation controls on platform geometries are modified by compound effects from underlying basin margin configurations.


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