Journal de géologie et géophysique
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Chemical Variation during Pabdeh Formation Deposition, Zagros Basin: Gurpi-Pabdeh-Asmari Boundaries determination and Paleoenvironmental Condition

Tabatabaei Hossein, Motamed Ahmad, Soleimani Bahman and Kamali Mohammad Reza

Determination of the formation of the Pabdeh boundary is a main challenge in Zagros sedimentary basin area. The work on hand is an attempt to clarify those based on chemical changes. The location under observation is the outcrop of the Pabdeh Formation (Paleocene-Oligocene) in Bangestan Anticline, the southern part of Zagros orogenic belt. The Pabdeh Formation stratigraphy linked to Asmari and Gurpi has been introduced as a gradual type and somewhat vague in this respect. To overcome these problems, 12 fresh samples from Gurpi, Pabdeh, and Asmari have been selected and chemically analyzed. Variation on both major and trace elements during this stratigraphy sequence generally reveal the high peaks of their frequencies in the lower and upper borders of the Pabdeh Formation. This border is different to the border which was determined during normal studies. These variations illustrate that the stratigraphy age reduction in the boundary of expected deposition time is based on present data documented that the Cretaceous-Tertiary boundary (K-T) had started lower than the stratigraphy limit. Geochemical ratios, including Ni/Co, V/Cr, and V/(V+Ni) were used to diagnose the Paleo-environmental conditions of Pabdeh Formation in comparison to Gurpi and Asmari formations. These chemical indicators present variable paleoredox conditions for the Pabdeh Formation.