Geochemistry of central Tethyan Upper Permian and Lower Triassic strata, Abadeh region, Iran
2000; Elsevier BV; Volume: 137; Issue: 1-2 Linguagem: Inglês
10.1016/s0037-0738(00)00138-x
ISSN1879-0968
AutoresEzat Heydari, J Hassandzadeh, William J. Wade,
Tópico(s)Geological formations and processes
ResumoNearly 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 δ18O 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 δ13C 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 δ13C values (each 4‰ PDB in magnitude) are observed. Both are best explained by mixing of a deep-water mass having low δ13C values and a shallow-water mass having high δ13C compositions. Early Triassic δ13C values, initially low (1‰ PDB), increase to 3‰ PDB within 100 m above the P–T boundary. Variations in δ13C compositions of carbonate and organic matter and changes in Δ13C (=δ13Ccar−δ13Corg) indicate that Early Triassic δ13C values were controlled by productivity cycles.
Referência(s)