Writers : Valiani, Z.; Amini, A.
Publishing Year : 1387

Abstract :

The lower parts of Kashafrud Formation in Qara Gheitan Section is dominated by shale and fine siliciclastic facies, where carbonate concretions and thin bedded of sandstones are found useful indicators for environmental analysis. Sedimentological characteristics of the shale and their abundance as well as Helminthopsis trace fossil content indicate that they may have formed under deep marine conditions, where interpretation of relative sea-level change for deeper parts of the basin is rather complicated. Carbonate concretions in this formation are found eodiagenetic on the basis of their calcite content (radial calcimetry), morphology (spherical), and stratigraphic position (parallel to bedding). Detrital calcite, quartz and feldspar found in the concretions are similar to the hosting shales. The hosting shale is marked by abundant illite, kaolinite, and cholorite. The concretions are thought to be developed soon after deposition of sediment, in high stand period, during which no/minor sediments where derived from the land. Interaction of sea water with newly deposited sediments led to the enrichment of some parts by calcite (concretions). Hence, the concretion rich horizons are good indicators for determination of high-stand period (mfs), therefore the sandy sheets within the shaly horizons, turbidites, indicate the low-stand period in the basin, during which sediment supply from the land was significant.

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