Diagenesis/Metamorphism History of Lower Triassic Cigli Group Rocks in Uludere-Uzungecit (Sirnak) area (Eastern Part of the Southeast Anatolian Autochthone)

Abstract

This study aims to reveal the mineralogical characteristics of the carbonate and pelitic rocks in the Lower Triassic Cigli Group in the Uludere-Uzungecit (Sirnak) region from Southeast Anatolian Autochthone (SEAA). Cigli Group is represented by Yoncali Formation (dolomite-siltstone-shale with limestone intercalation), Uludere Formation (shale/shale with carbonate-clayey limestone intercalated with dolomite) and Uzungecit Formation (limestone with chert nodule-dolomitic limestone-shale) from bottom to top. In order of abundances of minerals obtained by XRD investigations as follows; Yoncali Formation contains carbonate (calcite, dolomite), feldspar, phyllosilicate (illite, chlorite) and goethite minerals, and Uludere Formation is made up of carbonate (calcite, dolomite), quartz, feldspar, phyllosilicate (illite, chlorite, mixed-layered chlorite-vermiculite/C-V, and very minor amount of kaolinite in only a sample) and hematite minerals. Uzungecit Formation has carbonate (dolomite, calcite), silica (quartz, opal-CT, moganite), phyllosilicate (chlorite, illite), and feldspar and hematite minerals. On the basis of illit Kubler Index values; Yoncali Formation reflects the degrees of anchizone; as for Uludere and Uzungecit formations, they have the degrees of anchizone-high diagenesis, respectively. Similarly, Chlorite Arkai Index (AI, degrees 2 theta) values indicate the grades of anchizone-diagenesis. Illites exhibit 2M(1) ve 2M(1) + 1M + 1M(d) polytypes and the values of b unit-cell distances show a composition close to ideal muscovite and low pressure conditions.

The rocks of the Cigli Group offer differences in terms of rare occurrence of kaolinite, appearance of moganite and C-V and the dominance of dolomite and hematite in most levels, and diagenesis/metamorphism grades are also high, when compared with the equivalent units in the Diyarbakir-Hazro area. Lower Triassic series regionally seem to have a deeper depositional environment, and have relatively higher maturation because of the volcanic feeding and tectonic burial in the Diyarbakir-Sirnak direction from west to east.