TY - JOUR A1 - Foster, William J. A1 - Lehrmann, Daniel J. A1 - Yu, Meiyi A1 - Martindale, Rowan C. T1 - Facies selectivity of benthic invertebrates in a Permian/Triassic boundary microbialite succession: Implications for the "microbialite refuge" hypothesis JF - Geobiology N2 - Thrombolite and stromatolite habitats are becoming increasingly recognized as important refuges for invertebrates during Phanerozoic Oceanic Anoxic Events (OAEs); it is posited that oxygenic photosynthesis by cyanobacteria in these microbialites provided a refuge from anoxic conditions (i.e., the "microbialite refuge" hypothesis). Here, we test this hypothesis by investigating the distribution of ~34, 500 benthic invertebrate fossils found in ~100 samples from a microbialite succession that developed following the latest Permian mass extinction event on the Great Bank of Guizhou (South China), representing microbial (stromatolites and thrombolites) and non-microbial facies. The stromatolites were the least taxonomically diverse facies, and the thrombolites also recorded significantly lower diversities when compared to the non-microbial facies. Based on the distribution and ornamentation of the bioclasts within the thrombolites and stromatolites, the bioclasts are inferred to have been transported and concentrated in the non-microbial fabrics, that is, cavities around the microbial framework. Therefore, many of the identified metazoans from the post-extinction microbialites are not observed to have been living within a microbial mat. Furthermore, the lifestyle of many of the taxa identified from the microbialites was not suited for, or even amenable to, life within a benthic microbial mat. The high diversity of oxygen-dependent metazoans in the non-microbial facies on the Great Bank of Guizhou, and inferences from geochemical records, suggests that the microbialites and benthic communities developed in oxygenated environments, which disproves that the microbes were the source of the oxygenation. Instead, we posit that microbialite successions represent a taphonomic window for exceptional preservation of the biota, similar to a Konzentrat-Lagerstatte, which has allowed for diverse fossil assemblages to be preserved during intervals of poor preservation. KW - anoxia KW - extinction KW - microbialite KW - Permian KW - Triassic KW - refuge Y1 - 2019 U6 - https://doi.org/10.1111/gbi.12343 SN - 1472-4677 SN - 1472-4669 VL - 17 IS - 5 SP - 523 EP - 535 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Foster, William J. A1 - Heindel, Katrin A1 - Richoz, Sylvain A1 - Gliwa, Jana A1 - Lehrmann, Daniel J. A1 - Baud, Aymon A1 - Kolar-Jurkovsek, Tea A1 - Aljinovic, Dunja A1 - Jurkovsek, Bogdan A1 - Korn, Dieter A1 - Martindale, Rowan C. A1 - Peckmann, Jörn T1 - Suppressed competitive exclusion enabled the proliferation of Permian/Triassic boundary microbialites JF - The Depositional Record : the open access journal of the International Association of Sedimentologists N2 - During the earliest Triassic microbial mats flourished in the photic zones of marginal seas, generating widespread microbialites. It has been suggested that anoxic conditions in shallow marine environments, linked to the end-Permian mass extinction, limited mat-inhibiting metazoans allowing for this microbialite expansion. The presence of a diverse suite of proxies indicating oxygenated shallow sea-water conditions (metazoan fossils, biomarkers and redox proxies) from microbialite successions have, however, challenged the inference of anoxic conditions. Here, the distribution and faunal composition of Griesbachian microbialites from China, Iran, Turkey, Armenia, Slovenia and Hungary are investigated to determine the factors that allowed microbialite-forming microbial mats to flourish following the end-Permian crisis. The results presented here show that Neotethyan microbial buildups record a unique faunal association due to the presence of keratose sponges, while the Palaeotethyan buildups have a higher proportion of molluscs and the foraminifera Earlandia. The distribution of the faunal components within the microbial fabrics suggests that, except for the keratose sponges and some microconchids, most of the metazoans were transported into the microbial framework via wave currents. The presence of both microbialites and metazoan associations were limited to oxygenated settings, suggesting that a factor other than anoxia resulted in a relaxation of ecological constraints following the mass extinction event. It is inferred that the end-Permian mass extinction event decreased the diversity and abundance of metazoans to the point of significantly reducing competition, allowing photosynthesis-based microbial mats to flourish in shallow water settings and resulting in the formation of widespread microbialites. KW - Competitive exclusion KW - Permian KW - Triassic KW - mass extinction KW - microbialites KW - palaeoecology Y1 - 2019 U6 - https://doi.org/10.1002/dep2.97 SN - 2055-4877 VL - 6 IS - 1 SP - 62 EP - 74 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Christ, Nicolas A1 - Immenhauser, Adrian A1 - Amour, Frederic A1 - Mutti, Maria A1 - Preston, Rosalind A1 - Whitaker, Fiona F. A1 - Peterhänsel, Arndt A1 - Egenhoff, Sven O. A1 - Dunn, Paul A. A1 - Agar, Susan M. T1 - Triassic Latemar cycle tops - Subaerial exposure of platform carbonates under tropical arid climate JF - Sedimentary geology : international journal of applied and regional sedimentology N2 - The Triassic Latemar platform in the Dolomites, Italy, is the site of several ongoing controversies. Perhaps the most interesting debate focuses on apparent cyclic deposition within the Latemar platform, whose nature and duration are still open to debate. Further disagreement concerns the lack of meteoric diagenesis-related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence. Here, an evaluation of the nature of Latemar cycle tops is presented combining evidence from previous work and new field, petrographic and geochemical data. Cycle tops are ranked according to increasing exposure duration and spatial extent: type I surfaces lacking unequivocal evidence of prolonged supratidal conditions; type II dolomite caps formed in warm, evaporitic, intertidal lagoonal waters followed by exposure of perhaps intermediate duration; type III clastic-rich, red calcareous horizons with some showing platform-wide extent, representing prolonged supratidal conditions, and type IV discontinuities in tepee belts, genetically related to type II and III surfaces, but likely representing shorter-lived exposure stages. Petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking. This is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that, where present, are here interpreted as marine-vadose in origin. The scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid-Triassic climate. The low latitude, tropical but arid setting of the Latemar, situated in the western extension of the Tethys ocean, its isolation from nearby continental areas and overall short-term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops. High amounts of aeolian clastic material beneath some cycle tops, along with high Fe and Mn elemental abundances argue for intermittent subaerial conditions. This study proposes an enhancement of the classical Allan and Matthews (1982) isotope model for subaerial exposure under strongly arid climates. As the subaerial exposure nature of Latemar cycle tops, and therefore eustasy as the cause for cyclicity, have been previously challenged due to the lack of meteoric-induced isotopic signatures, the outcome of this study is of significance for the ongoing Latemar stratigraphic controversy. KW - Triassic KW - Latemar KW - Subaerial exposure KW - Carbonate platforms KW - Carbon and oxygen stable isotopes KW - Diagenesis Y1 - 2012 U6 - https://doi.org/10.1016/j.sedgeo.2012.02.008 SN - 0037-0738 VL - 265 IS - 28 SP - 1 EP - 29 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Akal, Cuneyt A1 - Koralay, O. Ersin A1 - Candan, Osman A1 - Oberhänsli, Roland A1 - Chen, Fukun T1 - Geodynamic significance of the early triassic karaburun granitoid (Western Turkey) for the opening history of Neo-Tethys JF - Turkish journal of earth sciences = Türk yerbilimleri dergisi N2 - The Karaburun Peninsula, which is considered part of the Anatolide-Tauride Block of Turkey, contains clastic and carbonate sequences deposited on the northern margin of Gondwana. The Palaeozoic clastic sequence, which is intruded by the Early Triassic granitoid and tectonically overlies a Mesozoic melange sequence, can be divided into three subunits: a lower clastic subunit consisting of a sandstone-shale alternation, an upper clastic subunit consisting of black chert-bearing shales, sandstone and conglomerate, and a Permo-Carboniferous carbonate subunit. The lower Triassic Karaburun I-type granitoid has a high initial Sr-87/Sr-86 ratio (0.709021-0.709168), and low Nd-143/Nd-144 ratio (0.512004-0.512023) and epsilon Nd (-5.34 to -5.70) isotopic values. Geochronological data indicate a crystallization (intrusion) age of 247.1 +/- 2.0 Ma (Scythian). Geochemically, the acidic magmatism reflects a subduction-related continental-arc basin tectonic setting, which can be linked to the opening of the northern branch of Neo-Tethys as a continental back-arc rifting basin on the northern margin of Gondwana. This can be related to the closure through southward subduction of the Palaeotethys Ocean beneath Gondwana. KW - Karaburun KW - Neo-Tethys KW - Palaeo-Tethys KW - diorite KW - Triassic KW - magmatism Y1 - 2011 U6 - https://doi.org/10.3906/yer-1008-1 SN - 1300-0985 VL - 20 IS - 3 SP - 255 EP - 271 PB - Tübitak CY - Ankara ER -