Abstract The Bolshoi Karatau carbonates of southern Kazakhstan record the development of a 4,500–m–thick platform that evolved close to the North Caspian Basin of western Kazakhstan during the Late Devonian and Carboniferous. Carbonate facies in the Bolshoi Karatau Mountains provide outcrop analogs for coeval reservoirs in supergiant oil and gas fields in the North Caspian Basin. The carbonate platforms in the Bolshoi Karatau and the North Caspian basin are similar in several important ways. First, both the Bolshoi Karatau and the Tengiz oil field carbonate platforms were initiated in the Late Devonian and ended in the Bashkirian, a span of about 50–55 Myr. Second, the stratigraphic thickness and facies of the Bolshoi Karatau and the Tengiz oil field are similar. Third, the proven oil reserves in Tengiz occur in the Visean through Bashkirian, and these strata are very well exposed in the Bolshoi Karatau. The seaward margin of the Bolshoi Karatau carbonate platform was probably structurally controlled by the rifted edges of a passive continental margin. The overall geometry of the carbonate platform was controlled by thermal subsidence and local tectonics. Over a 50-55 Myr period of time this passive margin underwent thermal subsidence, normal faulting, and numerous sea-level fluctuations of varying amplitudes. Sedimentation rates suggest that subsidence decreased exponentially. Sediment accumulation rates were 185-285 m/Myr during the Late Devonian, 60-100 m/Myr during the Tournaisian, 35-50 m/Myr during the Visean, 15-30 m/Myr during the Serpukhovian, and 20-50 m/Myr during the Early Bashkirian. The net result was a carbonate platform that evolved from reef and sand-shoal-rimmed platforms in the Devonian to deep-water ramps and skeletal mounds in the Tournaisian and Early Visean and to skeletal mounds and sand-shoal-rimmed margins in the Middle-Late Visean, Serpukhovian, and Bashkirian. Depositional sequences, sequence boundaries, and facies were controlled by relative sea-level oscillations, sedimentation rate, climate, subsidence, and biotic changes through time. Relative sea-level changes were responsible for shelf-margin flooding and backstepping, multiple stacked sequence sets in shelf interiors, paleosols, extensive meteoric diagenesis, and karst and collapse breccia. Five depositional supersequences (second-order cycles), of seismic stratigraphic scale, are recognized in the Bolshoi Karatau: (1) Supersequence #1 includes Frasnian and Famennian Girvanella-Renalcis algae-bryozoan-sponge boundstone and cementstone reef-rimmed facies. Shelf interiors contain skeletal mud mounds, carbonate sands, cryptalgal laminites, evaporitic laminites, and a 90-m-thick regionally extensive karst and evaporite collapse breccia. Basin margins contain carbonate turbidites and megabreccia debris-flow aprons. (2) Supersequence #2 comprises Tournaisian-Lower Visean ramps of brachiopod-crinoid biostromes and abundant tidal-flat facies. Seaward ramp settings contain Waulsortian skeletal mud mounds and bioclastic turbidite aprons. (3) Supersequence #3 comprises Lower Visean-Upper Visean carbonates that have both Waulsortian skeletal mud mound shelf margins and shoal-rimmed shelf margins. Waulsortian skeletal mud mound margins and upper and lower slopes are sponge-Tubiphytes-algal-bryozoan boundstone and cementstone. Deeper-water parts of these slopes contain carbonate turbidite aprons. Shelf-interior facies consist of interbedded ooid and bioclastic sands. Shoal-rimmed platform margins are dominated by cross-bedded ooid-bioclastic sands and turbidite aprons. (4) Supersequence #4 comprises Upper Visean-Lower Bashkirian basinal carbonate turbidites and upper-slope Waulsortian skeletal mud mounds made up of Donezella algae-Tubiphytes-sponge-bryozoan boundstone and algal rudstone. These upper-slope mounds developed in a setting that was receiving abundant carbonate turbidites and debris flows. Shelf margins and shelf-interior facies consist of interbedded ooid and bioclastic sands and phylloid algae-rich sands. (5) Supersequence #5 encompasses Lower Bashkirian Waulsortian skeletal mud mounds that formed on upper-slope and drowned-shelf-lagoon settings. Waulsortian mound facies are dominated by phylloid algae-Donezellid algae-Archaeolithoporella algae-gastropod-brachiopod boundstone and cementstone facies. The boundstone facies are typically interbedded with algal rudstone and possible pisoid facies. Drowned shelf-lagoon facies comprise lime mudstones and carbonate turbidites derived from an ooid-bearing shelf margin. In the Bolshoi Karatau, thick stacks of upward-shallowing cycles of dolomitized and karsted shelf-margin and shelf-interior ooid-bioclastic sands form potential reservoirs, whereas lower-slope and upper-slope Waulsortian skeletal mud mounds contain abundant marine cement and are relatively tight. Reservoir enhancement is related to early dolomitization and meteoric diagenesis. These geometric and diagenetic patterns are analogous to some reservoirs in the North Caspian Basin such as in the Karachaganak and Tengiz fields and the newest supergiant, the Kashagan oil field. Bolshoi Karatau studies provide important data on the heterogeneity of the reservoirs in terms of their facies types, their cyclicity and stacking patterns, the origins of these stacking patterns, porosity-enhancing conditions associated with this cyclicity, and the spatial distribution of these reservoirs in the platform. These outcrop studies should be valuable for better understanding and predicting the characteristics and development of the North Caspian Basin oil and gas reservoirs as well as the oil and gas reservoirs in the Timan-Pechora and Volga Ural basins of Russia.

Abstract Pennsylvanian and Lower Permian organic carbonate buildups mostly lack large massive reef-building organisms, but rather were constructed by relatively small organisms, such as calcareous algae, calcisponges, and bryozoans, Microbial encrustation and submarine cementation often played significant roles in the construction of the buildups. These buildups consist of a spectrum of mound and reef types whose organic and inorganic compositions are controlled mainly by seawater temperature and light availability, which in turn are related directly to paleolatitude and/or water depth, and growth position. Lower Upper Carboniferous (Bashkirian-lower Moscovian, Morrowan-lower Desmoinesian), shallow shelf to shelf-margin, organic carbonate buildups are mostiy broad low banks and mounds constructed by calcareous algae (e.g., Dvinella/Donezella, Komia, Cuneiphycus , phylloid algae), Chaeleles sponges, and microbialites, In Japanese seamount reefs, which were located in high-energy open sea settings, rugose corals, tabulate corals, and chaetetids were the important constructors. Steep platform slopes during this time were apparently supported mainly by microbialite and synsedimentary cementation. Upper Upper Carboniferous (Desmoinesian-Virgilian/“Bursumian”, Moscovian-Gzhelian/Orenburgian) tropical shallow-water shelf and shelf-margin carbonate buildups are predominantly bafflestones composed mostly of erect udoteacean phylloid algae. In contemporaneous, slightly deeper-water, mound-flank to intermound areas, communities of calcareous sponges, laminar encrusting red algae, and bryozoans built smaller boundstone reefs. In Lower Permian (Wolfcampian, Asselian-Sakmarian) tropical paleolatitudes, those two buildup communities merged and constructed bafflestone-boundstono reefs in shelf-margin settings that were composed of a framework (baffler guild) of erect phylloid algae, calcareous sponges, and fenestellid and ramose bryozoans, which were encrusted by (binder guild) laminar red algae ( Archaeolithophyllum), Archaeolithoporella, Tuibiphytes , and fistuliporid bryozoans (Chiorosponge association). Many tropical shelf-margin buildups are rich in originally aragonitic botryoidal radial fibrous cements, and in some, heliosponges and specialized Permian reef brachiopods are locally abundant. Such Lower Permian aigal-calcisponge-cement reefs are known throughout the Permian circum-equatorial belt, from present-day southwestern and midcontinent North America, to the circum-Mediterranean region, to southeast and East Asia. That integrated reef-building community radiated and persisted through the rest of Permian time, reaching its acme of development in Middle and Upper Permian tropical reefs, such as the Capitan Reef of the Permian Basin. At more subtropical to warm temperate paleolatitudes, upper Upper Carboniferous to Lower Permian shallow-water shelf to shelf-margin buildups were constructed mainly by Palaeoaplysma , with varying proportions of intermixed phylloid algae, and sometimes botryoidal radial fibrous cements (Chloroforam association). Paleoaplysina buildups are known from around the northern margin of the paleocontinent Laurasia, which includes the present-day northwestern United States, Arctic Canada, the Barents Sea region, and the Russian Ural Mountains region. As seen in Arctic Canada and Russia, contemporaneous, somewhat deeper-water, upper slope buildups were constructed by fenestrate bryozoans and Tubiphytes , and those buildups commonly have pervasive originaily calcitic radiaxial cements tones (Brynoderm to Brynoderm-extended association). The Palaeoaplysina -phylldalgal algal and fenestra tebryozoan-Tubiphytes reef communities intermixed in buildups at intermediate water depths, and the latter buildup type sometimes shallowed upward into the former buildup type. In adjacent deeper-water, lower slope to basinal settings, siliceous sponges constructed organic carbonate buildups (Hyalosponge association) that commonly included intermixed bryozoans and brachiopods at intermediate depths. Most shallow-water, tropical and subtropical buildups were composed predominantly of originally aragonitic organic and inorganic elements (e.g., phylloid algae, Palacoaplysina , calcareous sponges, botryoidal radial fibrous cements), whereas buildups in deeper and/or cooler water were dominated by Mg-calcite constituents (e.g., bryozoans, Tubiphytes , radiaxial cements). Many of the cooler- water biotic elements were also contributors to warm-water reefs, but there they were usually greatly diluted by the more prolific tropical biota.