Evaluation of microfacies, sedimentary environment and original mineralogy of the Garau Formation in Aligudarz section, Lorestan

Document Type : Original Article

Authors

1 Department of Sedimentary Basin and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran.

2 Department of Sedimentary Basin and Petroleum, School of Earth Sciences, Shahid Beheshti University, Tehran, Iran

3 Department of Sedimentary Basin and Petroleum, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

Abstract

In order to study the microfacies, sedimentary environment, original mineralogical composition and diagenetic environment of the Garau Formation with the age of Aptian-Albian (Lower Cretaceous), in the high Zagros zone, Aligudarz section in Ghali-Kooh (Lorestan South East) was selected and studied. The Garau Formation with a thickness of 483 meters was identified so that the thin sections were prepared and studied from 235 samples of this surface section. Lithology consists mainly of limestone, shale and shaly limestone. The lower boundary of the Garau Formation with brrecia limestones is equivalent to the Gotnia Formation in the form of unconformity and the upper boundary is not clear due to its location in the syncline core. Based on the sedimentary textures, petrographic studies and present fauna, 7 different microfacies have been identified. These microfacies are formed in a deep-sea facies belt belonging to a ramp-type carbonate platform. Petrographic evidence and changes in major and minor elements and comparisons with the ranges presented by various researchers for calcite and aragonite mineralogy show that the Sr/Na ratio, the changes of Sr, Na and Sr/Mn versus Mn suggest original aragonite mineralogy for the Garau Formation. The plot of Sr/Ca versus Mn showed that the Garau Formation is affected by meteoric diagenesis in a closed to open diagenetic system with high and low water/ rock interaction, respectively. By plotting Fe versus Mn, a relative increasing trend between iron and manganese were calculated. This phenomena could be due to anoxic conditions or the effect of meteoric diagenesis.

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