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Published December 1, 2000 | public
Journal Article

Geochemistry of central Tethyan Upper Permian and Lower Triassic strata, Abadeh region, Iran

Abstract

Nearly 2 km of Upper Permian to Lower Triassic limestones are exposed in the Hambast Mountain, Abadeh region, Iran. Lime mud matrix and most bioclasts of Permian age are recrystallized into large calcite crystals and contain 600–4000 ppm Sr, suggesting a probable aragonite precursor. Low bulk rock δ^(18)O values (−7 to −10‰ PDB) and recrystallized textures are also indicative of diagenetic alteration. Within the Murghabian and Abadehian, two gradual upward increases in carbonate and organic matter δ^(13)C compositions (each roughly 3‰ PDB in magnitude) are documented. Both are attributed to increased organic productivity and sequestration of organic matter in sediments. Within the Julfian and across the Permian–Triassic (P–T) boundary, two sharp upward decreases in carbonate and organic matter δ^(13)C values (each 4‰ PDB in magnitude) are observed. Both are best explained by mixing of a deep-water mass having low δ^(13)C values and a shallow-water mass having high δ^(13)C compositions. Early Triassic δ^(13)C values, initially low (1‰ PDB), increase to 3‰ PDB within 100 m above the P–T boundary. Variations in δ^(13)C compositions of carbonate and organic matter and changes in Δ^(13)C (=δ^(13)Ccar−δ^(13)Corg) indicate that Early Triassic δ^(13)C values were controlled by productivity cycles.

Additional Information

© 2000 Elsevier Science B.V. Received 1 September 1999; accepted 12 July 2000. This study was supported by the Research Council of the University of Tehran. Logistical support was provided by Dr A. Javaherian of the Institute of Geophysics of the University of Tehran. Critical reviews by Drs M. Gruszczyński, B. W. Sellwood, and M. E. Tucker improved the quality of the manuscript.

Additional details

Created:
August 21, 2023
Modified:
October 24, 2023