Aurell, Marcos¹, Beatriz Bádenas¹, Ernest A. Mancini², William C. Parcell³, Juan Carlos Llinas⁴
(1) Universidad de Zaragoza, 50009 Zaragoza, Spain
(2) University of Alabama, Tuscaloosa, AL
(3) Wichita State University, Wichita, KS
(4) Center for Sedimentary Basin Studies and Department of Geological Sciences, University of Alabama, Tuscaloosa, AL

ABSTRACT: Use of Upper Jurassic Coral-Microbial and Thrombolite Reef Buildups of Northeast Spain as Outcrop Analogs for Upper Jurassic Microbial Reef Petroleum Reservoirs

Upper Jurassic (Kimmeridgian) coral-microbial and coral-bearing thrombolitic reefal buildups are excellently preserved in outcrops around Jabaloyas, Tormón, and Arroyo Cerezo, northeast Spain. Characterization of these patch reefs greatly facilitates the design of hydrocarbon exploration and development strategies for Upper Jurassic microbial reefs in the subsurface. These Spanish reefs occur as irregularly spaced, cylindrical to conical shaped buildups with steep slopes (pinnacles up to 16 m in height) on a continuous ramp gradient over a distance of 15 km chiefly in proximal to distal middle carbonate ramp settings in the Iberian Basin. Associated reef facies include pre-reef and inter-reef (oncoidal, ooid, peloidal and bioclastic grainstone and packstone to skeletal wackestone, from proximal to distal areas) and post-reef (ooid and bioclastic grainstone and packstone in middle ramp areas). The facies are mappable and predictable. Reef growth is initiated on a cemented and encrusted (microbial crust), sediment starvation surface developed during flooding of the ramp. Reef growth occurred chiefly during the time of sea level rise. Corals (Thamnasteria, Microsolena), chaetitids and stromatoporoids with microbial (micritic and peloidal) crusts dominate the reef assemblage of the proximal buildups. The assemblage of the distal buildups are characterized by coral-bearing thrombolites of up to 12 m in height. During sea level highstand conditions, the relative proportion of microbial crusts to corals decreased, and the growth of the reef is reduced. Characterization of the stratigraphic and geographic distributions, lateral and vertical facies changes, geometries, and dimensions of these Spanish patch reefs provide an exploration strategy and development scenario for Upper Jurassic coral-microbial and microbial reef petroleum reservoirs.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004