Petrography, Geochemistry and Origin of Lower Liassic Dolomites in the Aydıncık Area, Mersin, Southern Turkey

Authors: MUHSİN EREN, MERYEM YEŞİLOT KAPLAN, SELAHATTİN KADİR

Abstract: In the Aydıncık area, the Lower Liassic carbonates consist predominantly of dolomites, including limestone and dolomitic limestone intervals. These carbonates were deposited in peritidal environments, and later underwent early and late stage dolomitization. Petrographically, three dolomite-types are determined: (1) very fine to fine crystalline dolomite (T1) with crystal size of 13-65 µm and a good fabric preservation, (2) coarse crystalline sucrosic dolomite (T2) with size of 65 to 270 µm and fabric destruction, and (3) dolomite cement (T3) that occurs as a clear outer rim to cloudy coarse dolomite crystals (T2) or as a pore-lining and cement-fill of fenestral pores. The T1-type dolomites characterize the early stage of dolomitization formed from seawater by syn-sedimentary replacement of peritidal sediments. T2-type dolomites are derived from T1-type dolomites by recrystallization at increased burial temperature of ~50 °C. T3-type dolomites are precipitated as a cement from the same dolomitizing fluid. The recrystallization caused changes in texture, crystal ordering, isotope compositions and trace element contents. X-ray diffraction data indicates that the recrystallized dolomite (T2) is slightly better ordered and less calcium-rich than early dolomites (T1). More negative \delta^{18}O values and lower Sr contents of the coarse crystalline dolomites (T2) reflect an equilibration with late diagenetic fluid during the recrystallization. The covariant trend between \delta^{18}O and Sr values of T2-type dolomites shows an inverse relationship with their crystal size, suggesting progressive recrystallization. The \delta^{13}C values of both dolomites are almost in the same range indicating the typical marine values that suggest little modification during late dolomitization. The T2-type dolomite geometry pinching out to the southward indicates an invasion of dolomitizing fluid from the north to the seaward into the platform carbonates, as a result of early compaction.

Keywords: dolomitization, burial, replacement, recrystallization, Liassic, Turkey

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