Resumen de Water circulation near the mixed-water and microbiologic activity of the mesozoic dolomite sequence, and example from the Central Taurus, Turkey
Turhan Ayyildiz, Erdogan Tekin, Muharrum Satir
Jurassic to Lower Cretaceous units, locating Central Taurus composed of thick dolomite with massive limestones beds and thinner dolomite beds with intercalated limestone are described. Various dolomite types include: Type I) dolomite formed as dolomicrite as mimetic replacement, Type II) dolosparite as a cloudy centre and clear rim in vugs, Type III) The planar-e texture dolomites are scattered in a micrite matrix, Type IV) Mottled dolomite present as zones of light colored dolomite crystals in a darker groundmass, Type V) Fracture and void filling dolomite (zoned dolomite, overgrowth and saddle dolomite). The investigated dolomites exhibit 0.1 to -2.0%o PDB in d18O values relative to their d13C values (0.38 to 1.59%o PDB) in the Middle Jurassic dolomites. The petrographic and isotopic characteristics support that dolomitization fluids were variable mixtures of fresh and marine waters related to changes in sea level. The late dolomitization phase was followed by diagenesis in the presence of meteoric fluids. During this period, calcite cements were precipitated within fractures. These calcites have characteristically low d18O and d13C values (-3.0 to -4.9 and -0.8 to -5.7%o PDB, respectively).
Within the Jurassic dolostone facies, traces of bacterial activity were observed. The morphology of the Jurassic dolomite indicates that bacteria were involved in the formation of the dolomite. This bacterial activity is indicated by dolomite surfaces with knobby textures and bumpy structure.
