Corrigendum to “Geochemistry of central Tethyan Upper Permian and Lower Triassic strata, Abadeh region, Iran” [Sedimentary Geology 137 (2000) 85–99] (original) (raw)
International Journal of Earth Sciences, 2004
Pelagic deposits at Abadeh represent a complete biostratigraphic record across the Permian/Triassic boundary (PTB). The presumed water depth during deposition of these sediments was between 60 and 90 m. Similar to other Permian/Triassic boundary sections, the succession at Abadeh is characterised by a negative carbon isotope shift of approximately 4‰. The values start to decrease in the lower C. changxingensis - C. deflecta s.l. Zone, reach −0.12‰ (V-PDB) in the uppermost Permian just below the PTB, remain low to the early I. isarcica Zone (−0.32‰) and increase subsequently in the upper I. isarcica Zone. For the time interval of the PTB negative carbon isotope excursion, between the C. iranica and the I. isarcica Zones, no correlation exists between the δ13Ccarb and the δ18Ocarb. The above observations argue against the conclusion of Heydari et al. (2001) that the carbon isotope event at the P/T transition is an alteration artefact and not a global signal. The decrease in δ13Ccarb is accompanied by a ~5‰ (and potentially up to 10‰) increase in δ34SSSS. Together, these features are thought to reflect a complex global event, notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves. For the carbon isotope drop, other factors, such as the collapse of ocean primary productivity may also have played a role. The 87Sr/86Sr ratios of Dzhulfian seawater show only a minor increase from 0.70705 to 0.70710, reaching 0.70720 in the Dorashamian. The increase becomes steeper in the Early Triassic reaching 0.70754 in the N. dieneri Zone. The rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost Permian (C. meishanensis - H. praeparvus Zone) and the lack of a dense land vegetation in the Early Triassic, prior to the Spathian (Upper Olenekian).
Geochemistry and sedimentary environments of Permian deposits in Eastern-Central Iran
2004
Permian of Eastern-Central Iran is represents of Jamal and Khan Formations. These formations are studied in three areas named Kalmard, Shotori and Shirgesht. Khan Formation composed of predominantly delataic to eolian coarse to very coarse silisiclastics that interbedded with thin shallow limestone. Jamal Formation includes predominantly shallow, but sometimes deeper water carbonate sediments. The purpose of this study was to
Permian–Triassic boundary sections in the Julfa (NW Iran) and Abadeh (Central Iran) regions display a succession of three characteristic rock units, (1) the Paratirolites Limestone with the mass extinction horizon at its top, (2) the ‘Boundary Clay’, and (3) the earliest Triassic Elikah Formation with the conodont P–Tr boundary at its base. The carbonate microfacies reveals a facies change, in the sections near Julfa, within the Paratirolites Limestone with an increasing number of intraclasts, Fe–Mn crusts, and biogenic encrustation. A decline in carbonate accumulation occurs towards the top of the unit with a sponge packstone in the sections, and finally resulting in a complete demise of the carbonate factory. The succession of the ‘Boundary Clay’ differs in the two regions; thin horizons of sponge packstone are present in the Julfa region and ‘calcite fans’ of probably inorganic origin in the Abadeh Region. The skeletal carbonate factory of the Late Permian was restored with the deposition of microbial carbonates at the base of the Elikah Formation, where densely laminated bindstone, floatstone with sparry calcite spheres, and oncoid wackestone/floatstone predominate.
Palaeobiodiversity and Palaeoenvironments
Sections at Baghuk Mountain, 45 km NNW of Abadeh (Central Iran), have excellent exposures of fossiliferous marine Late Permian to Early Triassic sedimentary successions. Detailed bed-by-bed sampling enables the analysis of microfacies changes of three successive rock units across the Permian–Triassic boundary. The Late Permian Hambast Formation is mainly the result of biogenic carbonate production. Its carbonate microfacies is dominated by biogen-rich and bioturbated nodular limestones, indicating a well-oxygenated aphotic to dysphotic environment. The biogen-dominated carbonate factory in the Permian ceased simultaneously with the main mass extinction pulse, which is marked by a sharp contact between the Hambast-Formation and the overlaying Baghuk Member (= ‘Boundary Clay’). The clay and silt deposits of the Baghuk Member with some carbonate beds show only a few signs of bioturbation or relics of benthic communities. The Early Triassic Claraia Beds are characterised by a partly mic...
Austrian Journal of Earth Sciences
The Upper Triassic (Norian–Rhaetian) Nayband Formation is situated at the southwestern margin of Central East Iranian Microcontinent and records Eo-Cimmerian events. The formation is composed of mixed carbonate-siliciclastic deposits. This study presents information on the tectonic reconstruction and palaeoclimate of the southwestern margin of Central East Iranian Microcontinent during the Late Triassic. Petrography and modal analyses of sandstones show a variety of quartz-rich petrofacies including subarkose, lithic arkose, sublitharenite, feldspathic litharenite and litharenite. The combined modal analysis and geochemical results of major and trace elements of the sandstone samples represents mixed sedimentary, intermediate, felsic igneous rocks and moderate- to high-grade metamorphic provenance areas. The major elements and modal analyses of the Nayband Formation sandstone samples suggest an active continental margin tec-tonic settings. The palaeoclimatic conditions were sub-humi...
Gondwana Research, 2020
Late Neoproterozoic-Early Cambrian calc-alkaline granitoids are ubiquitous in the continental basement of Iran and indicate formation within a Cadomian arc system at the northern margin of Gondwana. A basement complex comprising mainly mica schist, paragneisses, and metagranite along with metabasite and rare pegmatite is exposed in the Zayanderud region north of Shahrekord located in the hinterland of the Zagros mountain range. This complex is unique in the Neotethyan realm because it includes eclogites with Jurassic metamorphic ages implying involvement of continental crust at the onset of subduction. Ion microprobe U Pb zircon dating along with trace element and oxygen isotope analyses for metagranites define two zircon age clusters of ca. 552 and 565 Ma confirming connection with the other Ediacaran age basement arc plutons in the belt. Zircon geochronology for pegmatite, by contrast, yielded a concordant age population averaging 176.5 ± 3.3 (2σ) Ma. Zircon crystals from the pegmatite also have unusually low rare earth element (REE) abundances with sharp increases towards the heavy REE. Along with an absence of a negative Eu anomaly, this indicates a high-grade metamorphic origin of zircon crystallizing from a pegmatite which was formed by melting of mica schist and possibly amphibole eclogite during decompression where incipient garnet breakdown released Zr and HREE to form zircon, and LREE were retained in stable apatite and titanite. Corresponding 40 Ar/ 39 Ar phengite dates from the pegmatite and the mica schist country-rock are overlapping with or only slightly postdate the U Pb zircon ages, indicating rapid cooling after reaching maximum metamorphic pressure in the Early Jurassic. The Zayanderud basement complex is thus potentially a rare example of deep burial of continental crust and rapid exhumation due to buoyant escape during the incipient stages of subduction, well before the ultimate closing of the Neotethys ocean basin between Arabia and Eurasia in the mid-Tertiary.