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Upper Triassic carbonate platforms from the Panthalassa Ocean remain less-understood and less-studied than their Tethyan equivalents. This imbalance is largely due to the poorer preservation state of Panthalassan carbonate rock successions in terms of rock quality and depositional geometries, which prevents good appreciation of depositional systems. In this context, carbonate exposures from Lime Peak (Yukon, Canada) represent an outstanding exception. There, the remains of an Upper Norian Panthalassan carbonate platform are well-exposed, show remarkably preserved depositional geometries and overall superior rock preservation. In this work, we analyse the carbonates from the Lime Peak area with particular attention to the vertical and lateral distribution of biotic assemblages and microfacies at the platform scale. Results demonstrate that the Lime Peak platform was surrounded by a basin with an aphotic sea bottom. The carbonate complex developed in warm waters characterized by high carbonate saturation. The area was also defined by moderate to high nutrient levels: this influenced the type of carbonate factory by favouring microbialites and sponges over corals. During its growth, Lime Peak was influenced by tectono-eustatism, which controlled the accommodation space at the platform top, primarily impacting the internal platform environments and the stability of the slope. Gaining better knowledge of the spatial distribution and dynamics of Upper Triassic organisms and sedimentary facies of Panthalassa in relation to tectono-eustatism lays the first foundations for reconstructing more robust platform models and understanding the evolution of other, more dismantled Upper Triassic Panthalassan carbonate systems through time. [ABSTRACT FROM AUTHOR]

Upper Triassic calcareous algae, abundant and well-diversified in Tethyan deposits, have rarely been described in rocks of Panthalassan origin. Over the past ten years, several studies were performed on Upper Triassic carbonate deposits of Panthalassan affinity in North America, Japan and Far East Russia, revealing unexpectedly rich and diversified assemblages. The samples were collected from nine localities situated on both sides of the Pacific Ocean. The identified algal assemblage consists of green and red algae, including fourteen dasycladaleans, rare bryopsidaleans, and several rhodophyceans. This paper describes the main algal taxa, including six new species: Holosporella? rossanae Bucur & Del Piero n. sp., Holosporella magna Bucur & Fucelli n. sp., Griphoporella minuta Bucur & Peybernes n. sp., Patruliuspora pacifica Bucur, Del Piero & Peyrotty n. sp., Patruliuspora oregonica Bucur & Rigaud n. sp. and Collarecodium? nezpercae Bucur & Rigaud n. sp. Rivulariacean-like cyanobacteria and thaumatoporellacean algae are also present. The whole Panthalassan algal assemblage comprises both unknown (?endemic) and common taxa of the Tethyan domain. To explain the cosmopolitan distribution of various Upper Triassic benthic organisms (scleractinian corals, calcified sponges, foraminifera), a close connection with the Tethys Ocean was hypothesized by different authors. During the Late Triassic, the Tethys was open to the east on the Western Panthalassa but not to the west, suggesting that Triassic calcareous algae were able to efficiently colonize environments that are estimated to be more than 10'000 km apart. An adventitious transport of calcareous algae and/or their spores is proposed to explain this long-range algal dispersal. [ABSTRACT FROM AUTHOR]

The new, atypical aragonitic foraminiferTubulastella comansgen. et sp. nov. is described from the Late Triassic of Panthalassa (Wallowa terrane, north-east Oregon, USA). This rectilinear, undivided tubular form is closely related to ‘Coptocampylodon?rhaeticus’, a Rhaetianincertae sediscommonly found in the western Tethys. Morphologically and structurally distinct from other aragonitic foraminifers,Tubulastella comansgen. et sp. nov. andT. rhaeticagen. et comb. nov. are part of an independent aragonitic lineage, here embodied by the family Tubulastellidae fam. nov. To understand the origination and taxonomic affinity of this unique taxon, a comparative study betweenTubulastellaand the calcitic syzraniid foraminiferRectostipulinais carried out. Although these forms differ in wall composition, they present identical constructional patterns, providing evidence of their close phylogenetic relationship. The existence of an aragonitic branch in Nodosariata evolution deeply challenges current foraminiferal classifications and evolutionary hypotheses. We here propose to limit the class Nodosariata to a monophyletic group of bi- to plurilocular foraminifers originating from a Silurian earlandiid ancestor, and the order Nodosariida to a monophyletic lineage of primarily single-layered built foraminifers, which takes root in the Middle Pennsylvanian. This new classification reflects an evolutionary transition from calcitic to aragonitic walls, as documented in other shelled organisms, and definitively excludes calcitic unilocular foraminifers (i.e. Ellipsolagenidae and Lagenidae) from the class Nodosariata. http://zoobank.org/urn:lsid:zoobank.org:pub:D8281D59-38FD-4D88-BEC6-14D5C7B8FD2B [ABSTRACT FROM PUBLISHER]

Flat clams are ubiquitous in marine Triassic and Jurassic deep-water environments, where they are often recovered as mono- or pauci-specific assemblages. Their abundance in deep-water facies deposited under oxygen-depleted conditions suggests a potentially unique, but nevertheless debated, paleoecology. The distribution of Halobia cordillerana in an Upper Triassic hemipelagic succession outcropping at Tsiko Lake, Vancouver Island, Canada, serves as a revealing case study. There, deep-water deposits were investigated using a multi-disciplinary approach including facies description (mineralogical, fossil and organic content), taphonomy, morphometry, microscopy (cathodoluminescence, scanning-electron microscope) and independent paleo-redox proxy constraints (framboidal pyrite distributions, Fe speciation). Overall, halobiids' taphonomy at Tsiko Lake is indicative of in situ accumulations with little or no reworking. Among the hemipelagic deposits, three major litho-biofacies (BFC 1, 2, 3) were identified; paleo-redox proxies indicate that these litho-biofacies were deposited under different oxygen conditions ranging from extreme dysoxic (BFC 1) to dominantly euxinic (BFC 3). The distribution of H. cordillerana is shown to be directly influenced by bottom water oxygenation with this organism peaking both in abundance and dimensions under extreme dysoxic to anoxic conditions (i.e. BFC 1 & 2). Conversely, under prevailing euxinic conditions (i.e. BFC 3), the population of H. cordillerana is dominated by forms at larval or post-larval stage which were presumably killed by water-column euxinia. Thus, although the species is here shown to have lived most likely as an epibenthic recliner, an early (larval) planktonic/nektonic stage is needed to explain its mode of occurrence during dominantly euxinic conditions (i.e. BFC 3), and its wide distribution and rapid expansion. Finally, this study highlights the colonizing capacity of halobiids in case of restored oxygen conditions, stressing the potential significance of flat clams for paleoenvironmental reconstruction. • A multi-proxy approach has been undertaken to study the stratigraphic distribution of flat clams. • The development of Halobia cordillerana is influenced by sea-bottom conditions. • Halobia cordillerana was opportunistic and peaked in abundance under dysoxic conditions. • Flat clams could become an extremely useful tool in paleoenvironmental reconstructions. [ABSTRACT FROM AUTHOR]

A more than 300 m thick succession of thick-bedded pink to grey limestone of the Norian – Rhaetian Khodz Group in the NW Caucasus serves to document the development of a temperate carbonate ramp during the final stages of the Cimmerian orogeny. Limestone samples were collected on the west side of Mt. Kolokolnia. The lower part of the Khodz Group contains bioclastic packstone microfacies composed largely of heterotrophic organisms: bryozoans, brachiopods, echinoderms, bivalves, small benthic foraminifers, juvenile ammonoids, agglutinated worm tubes, gastropods, ostracods and sponges. The upper part is comprised of layers of wackestone with frequent evidences of short episodes of emersion. Sponge spicules locally predominate; very few coral fragments also occur. Foraminiferal assemblages of the Khodz Group contain a high proportion of involutinids, including Licispirella violae (Blau), L. iranica (Senowbari-Daryan, Rashidi & Torabi), Coronaserra deminuta (Blau), Coronipora sp., ? Kristantollmanna bicarinata (Blau), Frentzenella perforata Rigaud, Blau, Martini & Rettori, ? Involutina turgida Kristan, ? Trocholina turris Frentzen, and T. ex gr. intermedia / umbo Frentzen, together with porcelaneous foraminifers such as Galeanella tollmanni (Kristan), and Decapoalina schaeferae (Zaninetti, Altiner, Dager & Ducret), which are typical reef dwellers in tropical platforms. Such faunal and foraminiferal association points to a shallow (photic zone) marine depositional environment. Trocholinids are among the most successful survivors of the end-Triassic crisis. The rich occurrence of diversified trocholinids in temperate Triassic seas at high latitudes within the western Eastern Laurasia palaeobiogeographic province suggests that: 1) temperate areas may have played an important role as refugia for marine life during this major biotic event, and 2) the importance of ocean acidification in the selective extinction of marine organisms is overestimated. • Upper Triassic Khodz Group (Great Caucasus) contains diverse Trocholinidae • Depositional setting is shallow part of temperate carbonate ramp • Foraminiferal assemblage belongs to western Eastern Laurasia bioprovince • Trocholinidae retained their diversity during the end-Triassic biotic crisis • Refugia for survivors might be sought at high palaeolatitudes or in deeper sea [ABSTRACT FROM AUTHOR]