مرکز منطقه ای اطلاع رساني علوم و فناوري -

چكيده لاتين :

The rudist biostrome was formed in the eastern portion of the Kopet-Dagh Basin, NE Iran during the Late Maastrichtian time. Hippuritidae and Radiolitid ae are the most common rudists in this organic buildup . Petrography, elemental and stable isotopic analysis of multilayer bimineralic shells of these rudists as well as mud filling internal pores were studied for understanding of the diagenetic processes on these shells. Oxygen and carbon isotope values ranging between -2.50 to -6. 17% and +1.01 to +2.04% POB respectively, while mud filling pores are ranging from -2.38 to -5.49% POB and +1.12 to + 1.40% POB. Variation in Sr and Na with Mn concentration revealed two stages of diagenetic stabilization. In the first stage, inversion of aragonite to low Mg calcite involves by high depletion of Sr and Na, while in the second stage, recrystallization of low Mg calcite (dLMC) involves by high enrichment of Mn. These variations along with depletion of oxygen isotope values are similar to those observed in warm shallow marine ancient limestones affected by meteoric diagenesis. Mud with original aragonit e mineralogy shows higher effects of meteoric diagenesis than rudist shells with LMC mineralogy. Rudist biostrome of the study area is deposited in warm, relatively saline water and low energy lagoonal environment. The calculated paleotemperature of the ambient water ranges from 22.5-27 °C.