Late Jurassic Carbonate Reefs in the Black Sea-Caspian Region - From Outcrop Analogue Study of Potential Reservoir Facies
Carbonate reef facies were well developed along the northern margin of Tethys during Late Jurassic time and form important reservoir units, most notably in the Amu Dar’ya Basin of Turkmenistan.
Field analogue studies for subsurface potential reservoir units have been carried out around the margins of the Eastern Black Sea, in Crimea, the Russian Western Caucasus and the Pontides. A Late Jurassic palaeogeographic and palaeotectonic review spanning from Ukraine to Turkmenistan has also been undertaken as a means of providing regional context for these outcrop studies. Reef development was initiated in the Late Callovian following a widespread deformational event referred to as the Mid Cimmerian orogeny. In most areas, reef development terminated during or at the end of the Late Jurassic.
Outcrops of well-preserved Late Jurassic reefs can be grouped into coral-dominated, siliceous sponge-microbial and microbial types, as is the case in other north Tethyan settings. Coral-dominated reefs formed from shallow-water platform margins to slightly restricted deeper-water mid shelf settings. Siliceous sponge-microbial and microbial reefs are generally restricted to deeper-water mid-outer shelf environments. The development of these reefs was controlled mainly by local variations in water depth, light, and the availability of nutrients.
The reefs exhibit a complex pattern of porosity development reflecting independent diagenetic histories involving near-surface and deep-burial dissolution, dolomitization and dedolomitization. This includes meteoric dissolution associated with karstic surfaces that have been observed to punctuate the Late Jurassic succession. Porosity is particularly common in coral-dominated reef facies and consists of both primary and secondary types.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009