IRON-OXIDE CONCRETIONS IN OLIGOCENE AGED SANDSTONE (NE DENIZLI-TURKEY): MINERALOGIC AND GEOCHEMICAL PROPERTIES

Nodules and/or concretions are characteristic sedimentary structures originated from diagenetic processes. In this study, concretions in the Oligocene sandstones, which cover a wide range of exposure in the Denizli Basin, have... [ view full abstract ]

Nodules and/or concretions are characteristic sedimentary structures originated from diagenetic processes. In this study, concretions in the Oligocene sandstones, which cover a wide range of exposure in the Denizli Basin, have been examined. The sandstones are consisted predominantly of quartz, muscovite, and Fe-Ti oxide and lesser amount of calcite and chlorite. These results are also supported by the XRD studies. Their grain size varies between 0.05 and 0.3 mm. Sandstones are quartz sandstone in composition and typically contain reddish-dark brown, spherical or elliptical concretions that have sizes ranging from 5 cm to 20 cm. Concretions have sharp contact with the host rock and some of them have fossil plant in their core, apparently the material that initiated concretionary growth. Main mineralogical composition of these concretions is highly similar to host rocks. The concretions have enrichment of Fe2O3 (18.5-41.6 %), SiO2 (15.5-40.3 %), Al2O3 (5.8-11.7 %), CaO (3.3-6.1 %) and TiO2 (0.3-0.7 %). Other striking elements in lesser amounts are Cr (33.4-65.9 ppm), Ni (25.7-66.9 ppm), Sr (80.6-146.6 ppm), Zr (90.5-248.1 ppm) and Th (6.7-16.2 ppm). Obtained sedimentologic, minero-petrographic data show that these concretions might be developed after the sandstone deposition.

Key Words: Iron concretion, XRD, Denizli Basin, Quartz Sandstone, Oligocene