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A Laterally Accreting Grainstone Margin from the Albian of Northern Mexico: Outcrop Model for Cretaceous Carbonate Reservoirs

By
David A. Osleger
David A. Osleger
Department of Geology, University of California, Davis, California, U.S.A.
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Roger Barnaby
Roger Barnaby
ExxonMobil Upstream Research Co., Houston, Texas, U.S.A.
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Charles Kerans
Charles Kerans
Bureau of Economic Geology, University of Texas, Austin, Texas, U.S.A.
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Published:
January 01, 2004

ABSTRACT

Exceptional exposures of progradational platform margin slopes of Albian age were mapped along a 5-km, near-continuous, dip-oriented transect in northern Mexico with the goal of producing an outcrop model for analogous Cretaceous reservoirs. The study area at the El Cedral is located along the western margin of the Devils River grainstone belt flanking the muddy, intrashelf Maverick Basin. Four relatively complete clinothems and portions of two adjacent clinothems are recognized in the Las Pilas Formation in the study area. The Las Pilas clinothems exhibit complex sigmoid-oblique geometries and have dimensions of 40–60 m of vertical relief, depositional dip angles of foreset beds ranging from 8 to 15°, and dip-oriented lengths of 1–2 km. Internally, in foresets of clinothems, thick- to massively bedded, sigmoid- to oblique-shaped lenses exhibit overlapping, seaward-stepping patterns toward the southeast.

The primary sediment fabrics of topset, foreset, and bottomset beds of the Las Pilas clinothems are grainstones and grain-rich packstones. Coated grains are the predominant grain type, with subordinate amounts of micritized mollusk fragments and intraclasts. Porosity is predominantly moldic, but primary interparticle porosity is common. These lime sands were winnowed, coated, and micritized along the high-energy topsets of clinoforms before being exported seaward toward the breakpoint, where they cascaded onto the steep frontal slopes as sporadic grain flows or mass flows. The master bounding surfaces that define the clinothems likely represent episodes of nondeposition and abandonment of the surface, perhaps occurring during shifts in the locus of deposition laterally along the shoal margin.

The architecture and composition of the Las Pilas clinoforms provide observable data for comparison with analogous subsurface reservoirs in the Aptian Shuaiba Formation (Bu Hasa field) and Cenomanian Mishrif Formation (e.g., Umm Adalkh field) of the Arabian Gulf.

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Contents

AAPG Memoir

Integration of Outcrop and Modern Analogs in Reservoir Modeling

G. Michael Grammer
G. Michael Grammer
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Paul M. “Mitch” Harris
Paul M. “Mitch” Harris
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Gregor P. Eberli
Gregor P. Eberli
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American Association of Petroleum Geologists
ISBN electronic:
9781629810478
Publication date:
January 01, 2004

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