Research On Sedimentary Facies Of Qum Formation, Kashan Exploration Area, Central Iran Basin

Kashan Area is located in the sub-basin of the southeastern part of Central Iran Basin, a back-arc basin extending from northwest to southeast, where Qum Formation as a carbonate succession was deposited. Therefore, Qum Formation of the study area has the great significance for both theoretic study and oil exploration. Generally, previous studies, outcrops, wells and seismic profiles obtained recently allowed me to carry out a further study of Qum Formation, in terms of the sedimentlogy.To be more specifically speaking, this thesis had carefully studied the depositional facies, facies model and depositional evolution of Qum Formation, with the approaches of sedimentlogy, petro-geology and sequence stratigraphy, geology, lithofacies paleogeography and petrology. The findings that had been reached were as following:1. To begin with, the facies marks, such as lithology, sedimentary structure and biological trail etc., had been carefully studied, by observing outcrops, wells and micro-pictures of rocks, which help recognizing the lithofacies of Qum Formation.2. Based on the study of lithofacies above, two major facies provinces of Qum formation were recognized, thus mix-deposited shelf facies province and platform facies province. Accordingly, mix-deposited shelf facies province was sub-divided into neritic shelf, shoal, littoral and coastal facies, deposited from A member to C₁ sub-member; restricted platform, open platform and basin margin belonged to platform facies province, developed from C₄ sub-member to F member. As a result, dispositional pattern was constructed then.3. One first-order sequence(â… S), three second-order sequences(â…¡S) and four third-order sequences(â…¡S) had been recognized, by interactive sequence identification, lithostrigraphic and trace fossil study. And then, sequence stratigraphic framework was established, by studying the correlations between the outcrops and wells of the study area, on the same platform.4. In conclusion, after processing the data from percentage of strata, carbonatite, gypsum and terrigenous rocks as well as their variations, the integrated methodology provided lithologic expression for the succession of Qum Formation to be inserted into the gross geometric framework, through sequence stratigraphic mapping. Consequently, the stratigraphic lithofacies maps based on sedimentary tracts (S1, S₂TST, S₂HST, S₃TST, S₃HST, S₄TST, S₄HST), clearly indicated the depositional evolution of Qum Formation within the study area.