Lower Permian Conodont Biostratigraphy and Sequence Stratigraphy of the Aktasty Hills Section, Southern Ural Mountains, Kazakhstan

Upper Paleozoic strata of the Pre-Uralian Foredeep in the southern Ural Mountain region of Russia and Kazakhstan comprise the type area of the Cisuralian Series (Lower Permian), consisting of Asselian, Sakmarian, Artinskian, and Kungurian stages. Current studies in the region will establish stratotypes and precise chronostratigraphic stage and substage boundaries of the Cisuralian based on biostratigraphic and sequence stratigraphic data. Both serve as powerful tools for correlating Cisuralian stages worldwide via recognition of widely distributed faunal and eustatic sequence boundaries. The Aktasty Hills stratigraphic section is a succession (1120 m) of marine/marginal marine strata of Lower Permian (upper Asselian through late Artinskian (Baigendzhinian) age in northwestern Kazakhstan. Mixed carbonate and siliciclastic strata exposed at Aktasty were deposited in the Pre-Uralian foredeep; a foreland basin produced during the Late Paleozoic Uralian orogeny. Relative sea-level changes in the Pre-Uralian foredeep were produced by the interaction of eustatic sea-level changes, tectonic activity and fluctuation in sediment supply. Strata at Aktasty were first studied in detail by Ruzhencev (1951, 1952, 1956) and assigned Lower Permian age (Asselian through Artinskian) based primarily on ammonoid, nautiloid and fusulinid faunas from five localities. More recent studies have shown that the Aktasty Hills section also contains a well-preserved conodont fauna. Conodonts have become increasingly important to high-resolution biostratigraphy and correlation for several reasons including: 1) Permian conodont species tend to be less provincial than ammonoids, 2) conodont preservation is less facies-dependent, 3) conodonts are preserved more frequently throughout a stratigraphic section, and 4) conodonts evolve rapidly and are distinctively morphologically complex, aiding in their identification and correlation. Sequence stratigraphic analysis and biostratigraphy of the Aktasty Hills section suggests: 1) it is an outer ramp/shelf succession deposited in the Late Paleozoic, Pre-Uralian Foredeep, 2) several conodont species can be correlated successfully to specimens found in North America 3) some facies discontinuities at Aktasty appear to match those of proposed global sea level charts, whereas others do not, and 4) the sedimentologic and biostratigraphic characteristics of the section make it a candidate for Global Standard Stratotype-section and Point (GSSP) of the Aktastinian/Baigendzhinian substage boundary