ISOTOPE RECORDS FROM THE UPPER PERMIAN / LOWER TRIASSIC ABADEH SECTION (IRAN) AND THE GUADALUPIAN DELAWARE MOUNTAIN GROUP (SOUTHEAST NEW MEXICO)

The ⁸⁷Sr/⁸⁶Sr ratios for the Iranian Permian/Triassic profile of Abadeh were measured on conodonts with a CAI of 2. The value for the upper Capitanian was 0.707171, followed by a decline to 0.707038 at the base of the Dzhulfian and a steep rise to 0.707526 in the Brahmanian. For the comparable Cenozoic rise, the causative factors may have been the enhanced weathering of the high alpine orogens complemented by the extended continental glaciations. Such an explanation, however, cannot be applied to the late Permian/lower Triassic ⁸⁷Sr/⁸⁶Sr rise, because none were typical of the contemporaneous Gondwana. This was overall an arid interval, but interspersed by humid phases that may have resulted in an intensified weathering flux. The d¹³C_carb values at Abadeh were measured on micrites. In the Dzhulfian and lower Dorashamian they oscillate between 4.5 and 3 ‰ (PDB), declining rapidly by 3.5 ‰ in the upper Dorashamian, reaching -0.5 ‰ in the lower Triassic. Afterwards, in the lower Brahmanian they rise slightly, reaching values of 1.5 - 2.3 in the middle Brahmanian. The rapid fall of 3.5 ‰ in the marine DIC is probably a consequence of the Permian/Triassic biotic crisis with decimation of the land plant cover and extinction of the marine fauna. This massive extinction led to a release of ¹²C from the organic reservoir into the ocean/atmosphere system. The d¹³Corg for the uppermost Permian at Abadeh are strongly depleted, at -28.6 ‰ (PDB), but the secular trend cannot be shown to be covariant with the d¹³C_carb due to the large spread of values in the organic data. The source of this organic matter was probably of marine type due to a moderate phenanthrene/dibenzotiophene and very high phenanthrene/anthracene ratio. However, this interpretation is only tentative because of the high thermal maturity (equivalent to a vitrinite reflection of about 1.0 ‰) and low TOC concentration (0.01 to 0.1 ‰) of the studied material. Core material from the Guadalupian Delaware Mountain Group (southeast New Mexico) was geochemically investigated. TOC concentrations of shale in the sandstone dominated sediments of the Brushy Canyon, Cherry Canyon and Bell Canyon vary between 0.2 - 2 %. The d¹³C_org values decline in the course of the Capitanian by about 2 ‰ from -25.3 ‰ to -27.2 ‰ (PDB).