Helms Deep for Metazoan Reef Builders Found From Permian Extinction era Slovenia?

Equatorial Palaeotethys as the last sanctuary for late Permian metazoan reef-builders: New evidence from the Bellerophon Formation of Slovenia

Authors:

Sremac et al

Abstract:

The rise and demise of warm-temperate Permian reefs and biostromes reflect the complex geologic history of this dynamic period. Environments suitable for reef-builders were devastated by the Guadalupian/Lopingian crisis, and Lopingian reefs have only been recorded at a small number of localities. The uppermost Permian limestones of the Bellerophon Formation, on the Vojsko Plateau (Slovenia), contain small, lenticular biostromes within a bioclastic wackestone/packstone lithofacies. The major biostrome builders are medium-sized coralline sponges (Demospongea and Calcarea), encrusted by smaller sponges, tube worms, sessile foraminifera, calcareous algae (Archaeolithoporella) and Shamovella (i.e., Tubiphytes), all of which are typically covered by microbial crusts. The biostromes are characteristically composed of bafflestone and bindstone, incorporating sporadic framestone. Narrow belts of floatstone surround the buildups, and sponge debris is also present in lenses within the mud matrix between metazoan bafflestones. The fossils are generally well-preserved, although the fine skeletal microstructure has been partially recrystallized. Sponges are heavily calcified, and ontogenic thickening of the skeleton can be observed in some encrusters. Framboidal pyrite, forming thin films on the inner walls of sponge chambers, suggests the presence of sulphate-reducing bacteria. These microbial symbionts may have enabled the sponges to survive in the anoxic marine environments of the uppermost Permian. The Changshingian sponge biostromes of the Vojsko Plateau represent the westernmost known occurrence of contemporary metazoan boundstones in the Palaeotethys.

Three Evolutionary Radiations of Sharks During the Famennian Devonian

Paleogeographical and paleoecological constraints on paleozoic vertebrates (chondrichthyans and placoderms) in the Ardenne Massif: Shark radiations in the Famennian on both sides of the Palaeotethys

Authors:

Derycke et al

Abstract:

Three chondrichthyan radiations are registered in the Famennian of the Ardenne Massif (Belgium). These radiations are already observed in Morocco and in the Carnic Alps, their acme being related with the early expansa transgression. Comparisons of univariate statistical descriptors like Margalef richness and Shannon–Wiener diversity index show variations between both margins of the Paleotethys, variations interpreted in terms of trophic relationships. The Ardenne area, a northern shallow carbonate platform is characterized during the Famennian by endemic shark taxa with durophagous dentition. The southern open deep-sea area, the Variscan Sea, contains large placoderms probably disclosing a negative feedback on “cladodont” chondrichthyans. This supports the hypothesis that the Armorica platelet behaved like a barrier between the central southern Laurussia and northern Gondwana.

Evolution of the Paleo Tethys From the Devonian Through Permian

Devonian to Permian evolution of the Paleo-Tethys Ocean: New evidence from U-Pb zircon dating and Sr-Nd-Pb isotopes of the Darrehanjir-Mashhad “ophiolites”, NE Iran

Authors:

Moghadam et al

Abstract:

Middle to Late Paleozoic ophiolites, which are remnants of the Paleo-Tethys Ocean, are aligned in two main zones in northern Iran: Darrehanjir-Fariman-Mashhad, and Rasht in the north and Jandagh-Anarak ophiolites to the south. Our new U-Pb zircon dating results shows that the ~ 200km long Darrehanjir – Mashhad mafic-ultramafic body is not a single ophiolite but a composite igneous complex composed of Permian pillow lavas and pelagic sediments in fault contact with a small outcrop of Devonian intrusive and ultramafic rocks. Darrehanjir intrusive rocks have U-Pb zircon ages of 380.6 ± 3.7 Ma and 382.9±3.7 Ma respectively, ~ 100 Ma older than published ages for gabbros and radiolarites intercalated with lavas near Mashhad and Fariman. Mantle peridotites from the Devonian complex contain low Cr# spinel, similar to that in MORB-type peridotites. Devonian Darrehanjir gabbros and Permian Mashhad sequences both have boninitic and calc-alkaline signatures, respectively. The δ18Ozircon values from the Devonian ferrodiorite (δ18Ozircon~ 4.6±0.3‰) are slightly lower than the 5.2 to 5.4‰ expected for MORB-type zircons whereas Devonian plagiogranitic zircons mostly have δ18Ozircon < 5‰, perhaps reflecting involvement of hydrothermally altered crust. Similar, strongly positive values of zircon εHf(t) for plagiogranite (av. + 14.9) and ferrodiorite (av. + 13.8) indicate melt derivation from depleted asthenosphere. Darrehanjir-Mashhad ophiolitic rocks can be divided into groups with high εNd (> 10.3) and low εNd (< 5.4) for both Permian and Devonian suites. Most Darrehanjir-Mashhad rocks are characterized by radiogenic 207Pb/204Pb and 208Pb/204Pb, indicating the involvement of subducted terrigenous sediments in the source. The Mashhad-Darrehanjir mafic-ultramafic complex demonstrates that this part of Paleo-Tethys evolved from oceanic crust formation above a subduction zone in Devonian time to accretionary convergence in Permian time. Iranian Paleozoic ophiolites and oceanic igneous complexes along with those of the Caucausus and Turkey in the west and Afghanistan, Turkmenistan and Tibet to the east, define a series of diachronous subduction-related marginal basins that were active from at least Early Devonian to Late Permian time.

Evidence of the Closing of the Paleo Tethys During the Permian Through Triassic in Thailand

Geochemistry and geochronology of the Chatree epithermal gold-silver deposit: Implications for the tectonic setting of the Loei Fold Belt, central Thailand

Authors:

Abhisit Salam, Khin Zaw, Sebastien Meffre, Jocelyn McPhie and Chun-Kit Lai

Abstract:

The Chatree deposit is the largest epithermal Au deposit in mainland SE Asia. Despite its economic significance, the stratigraphy, age, geochemistry and tectonic setting of the host volcanic sequence is poorly documented in the literature. The Chatree deposit is located between Phichit and Phetchabun provinces, central Thailand, and is hosted by Late Permian to Early Triassic volcaniclastic and volcanogenic sedimentary rocks. Detailed field mapping, U-Pb zircon dating, geochemistry and stratigraphy suggest that the volcanic sequence can be subdivided into four stratigraphic units and two volcanic suites. The Late Permian Suite 1 volcanic units are sourced from a more depleted mantle relative to the overlying Early Triassic Suite 2 volcanic units. The Late Permian units Suite 1 probably formed immediately after the beginning of subduction and at the creation of a new island arc. The less depleted Early Triassic Suite 2 units were erupted during ongoing subduction once the system had achieved a steady state. The Chatree Au mineralization appears to have occurred during the switch between the two mantle sources and this switch of magma source is marked by a mixed volcano-plutonic magmatism at the Permo-Triassic boundary (ca. 250 Ma).