Scholarly record
MINERALOGIC AND GEOCHEMICAL FEATURES OF NEOGENE AGED SEDIMENTARY UNITS OF POLATLI, SW ANKARA (TURKEY)
Abstract
Upper Paleozoic aged metamorphic rocks, which consist of micaschist, phyllite, metasandstone, marbles, meta dolomitic limestones were located at the basement. Upper Cretaceous ultrabasics have been overturned upon the Paleozoic metamorphic rocks. The Late Upper Cretaceous plutonic rocks are unconformably overlain by the Late Miocene-Early Pliocene volcanics, volcanism composed mainly tuffs and minor amount of volcanic breccia, agglomerate, trachyte and trachyandesitic lava flows and lacustrine volcano-sedimentary rocks. The volcano-sedimentary rocks generally composed of clastic, clayey, calcareous rocks (dolomitic and calcitic), tuffceous, evaporitic and silicified sediments. Mineralogic and geochemical properties of Neogene aged sedimentary units were investigated along from fourteen stratigraphic sections. Dolomite and dolomite+sepiolite are found in the bottom layers while calcite+dolomite and mainly calcite occur in the upper layers. In addition to carbonate minerals, some clay and nonclay minerals are determined, generally in the middle layers of some sections. Non clay minerals are mainly quartz, feldspar and gypsum. Palygorskite, smectite (montmorillonite and) saponite and illite minerals are other clay minerals that are found in less quantity. Brown, pale brown and white sepiolite types were defined by means of colour. XRD, chemical analysis, SEM and EDS were made in all samples, and also $\delta$18O and $\delta$13C isotope analysis of calcite and dolomite were made. Mineralogic composition, REE, TRTE, HFS and LIL element content of different stratigraphic section were determined. Mineralogic composition was generally controlled by major element content. Sepiolite content of the sections are controlled by generally SiO2, detrital mineral and partly MgO content. The composition of most calcites and dolomites are relatively homogeneous and low-Mg or high-Ca to near stoichiometry (3.029 REE, LIL, HFS, TRT elements generally present strongly positive correlation to each other and also LIL and REE element show strongly positive correlation to Al2O3, while SiO2 Al2O3and have strongly negative or moderately negative to CaO and MgO. LREE elements were enriched to HREEs. The depositional conditions were a shallow, quiet, perennial lacustrine and partly fluviative influx basin with fresh to slightly saline and slightly alkaline water chemistry. REE, TRTE, HFS elements indicate that sepiolites and carbonate minerals formed from felsic source rocks.
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References17
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