| Abstrakt: |
Abstract: Distribution of the clay minerals in the Jurassic - Tertiary consolidated sediments of the Kopet Dagh Basin (KD) was investigated to study the origins of the clay minerals and to reconstruct the paleoclimate of the area. The entire sedimentary rock sequences of the KD were sampled for XRD, XRF, high resolution microscopy, and optical microscopy examinations. Illite, illite - smectite (IS) mixed - layer minerals, kaolinite, smectite, chlorite and palygorskite were found in the studied deposits. The presence of the clay minerals in the studied rocks was related partly to deep burial diagenesis and partly to the pedogenetic detrital origins. The thick sediments (total of 6000m) of the Lower Cretaceous and Jurassic suggest the possibility of the burial digenetic origin to explain the high occurrence of illite and low smectite mainly due to the illitization of smectite. Gradual increase in IS and smectite toward the Upper Cretaceous may indicate the gradual disappearance of deep burial diagenesis and the presence of the favorable conditions for the detrital input. The low thickness of the sediments of Upper Cretaceous and younger deposits also confirms the possibility of the detrital pedogenetic origin rather than the burial diagenesis. Smectite was proved to be of the montmorillonite type (dioctahedral). The higher occurrences of IS and smectite and its coexistence with some palygorskite in most parts of the Upper Cretaceous and younger deposits could indicate the prevailing of a semi - arid climate and hot seasonal droughts. Dominance of seasonal and semi - arid conditions extends to all Paleogene and Neogene sediments. Clay mineralogical data is suggested to be used along with other proxies to have a more reliable paleoclimate interpretations. |
