Investigation of the upper cretaceous-paleogene Southeastern Anatolia autochthonous mineralogical-petrographic and geochemical characteristics of the elderly unit

The investigated area is the Germav Formation, which is represented by Upper Cretaceous-Paleocene sedimentary rocks in the area defined as the Southeast Anatolian Autochthonous (GDAO) representing the northern section of the Arabian plate. The Lower Germav Member of the unit surfacing at the Mardin-Dargeçit region has a dark gray colored and fine-grained shale, gray marl and fine-grained sandstone, and the Upper member has a light gray colored sandstone, laminated gray shale, light colored, and fine-grained sandy limestone lithology. As part of the petrographic studies carried out in the rocks which represent the unit, optical microscopy examinations (OM) indicate that the rocks with different sedimentary and chemical origins demonstrate different grain sizes, mineralogical composition and textural relations as clastic, pelitic and carbonate. The common rock species representing the unit is shales rich with fine-grained clay minerals that are of pelitic texture. Sandstones with carbonate are of clastic texture and show medium to good gradation. The matrix is rich in clay and carbonate minerals in cement and flections in muscovite and plagioclase minerals are common. In ellipsoidal pores, clay, polycrystalline and radial quartz mineral occurrences are widely observed. Carbonate rocks are micritic or sparitic - textured and contain abundant amounts of fossil shells. According to the Scanning Electron Microscopy (SEM) examinations, vermiculite formations that are members of phyllosilicates are thick and in the shape of small worms, observed in 1 m dimensions. In the matrix of the sandstones there are C-S and radial/filamentous granular serpantine minerals in ellipsoidal pores in the shape of honeycombs. The sizes of the filaments vary between 25-30 m. The abundances of the rock-forming minerals determined by X-ray diffraction (XRD) method according to general average values are ranked as follows; calcite and phyllosilicate, quartz, feldspar, pyroxene and dolomite. Analcime, hematite and goethite are minerals with a low average. The phyllosilicate minerals observed in the rocks of the unit are represented by illite, chlorite, serpantine, vermiculite and smectite, mixed layers chlorite-smectite (C-S), chlorite-vermiculite (C-V), illite-chlorite (I-C) and illite-vermiculite (I-V) minerals. The abundance of phyllosilicate minerals according to the general average values are ranked as; chlorite, C-S, C-V, vermiculite, illite, and rarely serpantine, I-C and I-V. The phyllosilicate fraction in the Lower Germav member is represented by illite, chlorite, smectite, vermiculite and mixed layer (C-S); and in the Upper Germav member represented by illite, chlorite, smectite, serpantine, vermiculite and mixed layers (C-S, C-V, I-C, I-V). According to the geochemical data obtained in phyllosilicate/clay minerals of Germav Formation; logarithmically an enrichment of about 1000 times and depletion of 10 times are observed in the total trace element concentrations and the total trace element values of the minerals vary between 2021-2767 ppm (mean 2438 ppm). Total values are observed the least for chlorite and the most for vermiculite mineral. According to the average concentrations outside the extreme values; transition metals (Ni, V, Zn); W of granitoid elements; As and Ge of mixed behavioral elements; Ba, Rb, Ga and Sr from low field strength elements; Nb and Zr from high field strength elements exhibit positive anomalies in all the corensite minerals. In addition, the elements Sc, Pb, Mo, Sb, Cs, Tl, Ta and Hf exhibit negative anomalies. When compared to chondrite values; the patterns of the specimens are distinct from each other and from NASC, while the enrichment-depletion changes with respect to the originated rocks, minerals and elements. Phyllosilicate/clay minerals show a distinctive differentiation from the chondrite composition, and all of the clay mineral samples of the Germav formation have lower concentrations than NASC except for the Nb and Ti ratios. The total concentrations (ppm) of elements in normalized chondrite vary between 227.43 for vermiculite, 358.89 for I-C, 409.34 for C-V, 522.36 for C-S and 578.31 for chlorite. From these values, the least enrichment occurs for vermiculite mineral and the most enrichment occurs for the chlorite mineral. Phyllosilicate/clay minerals have a positive anomaly for Th, Ta, Zr and Ti elements; and a negative anomaly for K, Sr and P. The Eu element exhibits a negative anomaly for all phyllosilicate/clay minerals except NASC. The Rare Earth Element (REE) contents of all phyllosilicate / clay minerals show an increase with respect to chondrite, albeit being lower than NASC, with the exception of chlorite mineral. The total REE concentration is lowest in the vermiculite mineral (71.61 ppm) and highest in the chlorite mineral (224.45 ppm). Moreover, LREE concentrations of clay minerals show a decrease with respect to HREE. The Eu element has partially negative anomalies in NASC and all other clay minerals. In addition, it was determined that the Ir values were smaller than 5 ppb in the sandstones and shale rocks taken from different levels to detect iridium (Ir) anomaly with Neutron Activation (INAA) method in order to interpret the Upper Cretaceous-Paleocene transition in the Germav Formation rocks. According to OM, SEM, XRD and geochemical analyses; the illite/mica minerals observed in the Germav Formation rocks are thought to be represented by mica minerals of detrital and/or volcanic origin. OM and SEM analyses show that the chlorite mineral develops authigenously in the rock pores except for the dark colored minerals. Formation of mixed-layered minerals is thought to occur by neoformation and/or transformation processes, while smectite minerals, which are found in the matrix of shale-type rocks, represent authigenic components. Hematite, goethite and pyrite (SEM examinations) minerals were observed in Germav Formation rocks, and these minerals are thought to be diagenetic minerals formed in mid-acidic and reducing conditions. The differences in all lateral and vertical rocks and phyllosilicate/clay mineralogy observed in the Upper Cretaceous Lower Germav and Paleocene Upper Germav members of the Germav formation were evaluated to have been developed as a result of the basin being fed from different provenances at different times. In particular, this feeding was evaluated to be the detritic origin materials that were transported to the basin, indicating the chain of geotectonic events in the Southeastern Anatolian Ophiolitic Zone of the allochthonous origin, representing the remains of the Upper Cretaceous Neotethyan Ocean to the north of the Arabian Plate, and the clay mineral species formed in particular were interpreted as neoformation/transformation developing in particular as a result of the volcanic glass + sea water interaction, and authigenic products.