FACIES AND RESERVOIR-QUALITY VARIATIONS IN THE LATE VISEAN TO BASHKIRIAN OUTER PLATFORM, RIM, AND FLANK OF THE TENGIZ BUILDUP, PRECASPIAN BASIN, KAZAKHSTAN

Abstract

Tengiz field is an isolated carbonate buildup in the southeastern Precaspian Basin, containing a succession of shallow-water platforms ranging in age from late Famennian to early Bashkirian. Platform backstepping from Tournaisian through late Visean resulted in approximately 800 m (2625 ft) of bathy-metric relief above the Famennian platform. This was followed by as much as 2 km (1.2 mi) of Serpukhovian progradation, which formed a depositional wedge around the older platforms referred to as the Serpukhovian rim and flank. Rim and flank facies include lower slope mudstone, volcanic ash, and platform-derived skeletal packstone to grainstone interbedded with boundstone breccia; middle-slope poorly bedded to massive boundstone breccia with subtypes based on clast composition, size, and packing; upper-slope in-situ microbial boundstone; and outer-platform to shallow-platform skeletal, coated-grain, and ooid packstone to grainstone. The upper-slope microbial boundstone represents the