Beef and cone-in-cone calcite fibrous cements associated with the end-Permian and end-Triassic mass extinctions： Reassessment of processes of formation

This paper reassesses published interpretation that beef and cone-in-cone （B-CIC） fibrous calcite cements were precipitated contemporaneously just below the sea floor in uncon- solidated sediment, in limestones associated with the end-Permian （P/T） and end-Triassic （T/J） mass extinctions. That interpretation introduced the concept of a sub-seafloor car- bonate factory associated with ocean acidification by raised carbon dioxide driven by volcanic eruption, coinciding with mass extinction. However, our new fieldwork and petrographic analysis, with literature comparison, reveals several problems with this concept. Two key points based on evidence in the T/J transition of the UK are： （I） that B-CIC calcite deposits form thin scattered layers and lenses at several horizons, not a distinct deposit associated with volcanic activity; and （2） B-CIC calcite is more common in Early Jurassic sediments after the extinction and after the end of the Central Atlantic Magmatic Province volcanism proposed to have supplied the carbon dioxide required. Our samples from Late Triassic, Early Jurassic and Early Cretaceous limestones in southern UK show that B-CIC calcite occurs in both marine and non-marine sediments, therefore ocean processes are not mandatory for its formation. There is no proof that fibrous calcite was formed before lithification, but our Early Jurassic samples do prove fibrous calcite formed after compaction, thus interpretation of crystal growth in uncon- solidated sediment is problematic. Furthermore, B-CIC crystals mostly grew both upwards and downwards equally, contradicting the interpretation of the novel carbonate factory that they grew preferentially upwards in soft sediment. Finally, Early Jurassic and Early Cretaceous examples are not associated with mass extinction. Three further key points derived from the literature include： （I） B-CIC calcite is wide- spread geographically and stratigraphically, not clustered around mass extinctions or the Paleocene-Eocene Thermal Maximum （PETM） event; （2） isotope signatures suggest B-CIC calcite formed under high pressure in burial at 70-120℃, incompatible with interpretation of formation of B-CIC calcite at the redox boundary below the ocean floor; and （3） B-CIC calcite reported in P/T boundary microbialites in one site in Iran is the only occurrence known despite extensive published studies of similar shallow marine settings, demon- strating its formation is localized to the Iran site. Based on the above evidence, our opinion is that B-CIC calcite is best explained as a later diagenetic feature unrelated to rapid Earth-surface environmental change associated with mass extinctions; thus a novel carbonate factory is highly unlikely.

Glossopterids survived end-Permian mass extinction in North Hemisphere

Recently,more attention has been paid to Glossopteris,the most significant representative fossil of the Gondwanan Supercontinent in the Paleozoic.It has been regarded as an important clade of Angiophytes on the basis of its reproductive organ related to Angiosperms.Since Brongniart erected Glossopteris in 1928,reliable Glossopterids attached by fertile organs were only collected from the Permian Gondwanaland.Here,the authors found a new element of Glossoptetids,Sinoglossa sunii gen et sp.nov.,with attached female organs from the Middle Triassic Linjia Formation in Benxi,Northeast China.This demonstrates that Glossoptetids not only distributed in South Hemisphere,but also in North Hemisphere,and successfully survived the end-Permian mass extinction in North Hemisphere.The distinguished environment in Northeast China influenced by both warm and cold currents,probably resulted in the Paleozoic relic elements,such as Glossopterids associated with Lobatannularia successfully survived the end-Permian mass extinction.

Age and General Characteristics of the Calimicrobialite near the Permian-Triassic Boundary in Chongyang, Hubei Province

The calimicrobialites of Chongyang （崇阳）, Hubei （湖北） Province, occur above the mass extinction line in the Late Permian reef facies. Below the boundary are the sponge reef limestone, crinoid limestone and algae-foraminifer bioclastic limestone of the Changxing （长兴） Formation. The calimicrobialites are generally composed of mid-coarse grains and microlite calcite with a structure of ＂graniphylc fabric＂ and stromatolite. The fossils discovered in the calimicrobialites include globular cyanobacteria, ostracods, micro-gastropods, bivalves, fish teeth and some micro-problematical fossils. Conodont fossils of Hindeodus parvus, H. typicalis and H. latidentatus were also found in the calimicrobialites. According to the conodonts, the calimicrobialites spanned the latest Permian and earliest Triassic in the Chongyang Section. The upper part above the first occurrence of Hindeodus parvus should be attributed to the earliest Triassic, and the lower part to the Changhsingian. The sedimentary structure, fossil composition and conodont zonation of the Chongyang calimicrobialites can be well correlated with the calimicrobialites found in other areas of South China.

End-Permian conodont fauna from Dongpan section:Correlation between the deep-and shallow-water facies

This paper systematically investigated the conodonts from the uppermost Permian to the Lower Triassic at the Dongpan Section, Southern Guangxi, South China, and obtained abundant Late Permian conodonts from the syndepositional limestone lenses of beds 3 and 5-2 at this section. One genus and eight species of conodont P1 element including one new species, Neogondolella dongpanensis sp. nov., have been identified. The feature of conodont fauna indicates that conodonts collected from beds 3 and 5 at the Dongpan Section belong to the Neogondolella yini conodont zone, and correspond to bed 24 at the Meishan Section. Based on these conodont data, we suggest that the Neoalbaillella optima radiolarian zone at the Dongpan Section at least extended to the upper part of the N. yini conodont zone.

Microbialite of anoxic condition from Permian-Triassic transition in Guizhou,China

Spherical microfossils are present in the Hindeodus parvus zone of the Lower Triassic in Ziyun,Guizhou Province. They generally range from 0.15 to 0.30 mm across,with micritic wall and filled by micro-sparry calcites,and are evenly scattered in micritic matrix. Their abundance makes the rock as-signed to microbialites. The accompanied organisms include ostracods and algal mat,but no gastro-pods or bivalves. Presence of small (<7 μm) pyrite framboids indicates that this bed formed in anoxic conditions. In some sections,this bed is overlain and underlain by tidal-flat micritic limestone with microgastropods and small burrows. Occurrence only in deposits on reef top indicates that the micro-bial organism was benthic,and needed sunlight in life. The size of the microbial fossil exceeds that of any bacteria or cyanobacteria. Thus,it does not belong to these two phyla. It may belong to lower green algae,and is assigned to a new species in a new genus,Ziyunosphaeridium sinensis gen. et sp. nov. Up to now,the rocks described as microbialites from the Permian-Triassic transition include six types: (1) porous micritic limestone such as that descried from Japan by Sano and Nakashima (1997),(2) limestone with rich globular microfossils such as that described from the Nanpanjiang Basin in China by Lehrmann (1999),(3) dendroidal limestone such as that described from the vicinity of Chongqing by Kershaw et al. (1999),(4) spherical microbial limestone adapted to anoxic environments described from Ziyun,Guizhou reported in this paper,(5) limestone with cyanobacterial fossils such as that described by Wang et al. (2005),and (6) stromatolites. All these microbialites are not reefs in the proper sense,and the argument that Permian reef ecosystems extended into the Mesozoic is incorrect.

Coevality of the sea-level fall and main mass extinction in the Permian-Triassic transition in Xiushui, Jiangxi Province, southern China

A continuous Permian-Triassic boundary （PTB） section has been found and studied for the first time in Xiushui, Jiangxi Province, South China. Evidence for a large sealevel fall has been found in the horizon of 0.8 m below the PTB, from the beginning of Hindeodus changxingensis zone （correlatable to Hindeodus typicalis Zone of the Meishan section）. Sedimentary record indicates that the sea level kept at Iowstand, or occasionally rose slowly during the whole Hindeodus parvus zone, except another substantial sea-level fall in early H. parvus zone. It began a quick rise from the beginning of Isarcicella staeschei zone, kept rising for the whole/, staeschei zone, and probably caused the stagnation of sea water. The first severe change in the biota, marked by the sudden disappearance of all steno- tropic organisms such as fusulinids and dasycladacians, happened at the same time as the first sea-level fall, and is regarded as the first and main episode of the end-Permian mass extinction in this area. A microbe-dominated biota followed the first extinction, and spanned the late H. changxingensis zone and the whole H. parvus zone. All the microbes and some other eurytropic organisms including gastropods and ostracods disappeared at the end of the H. parvus zone, and the following biota in the/. staeschei zone is very simple. The coevality of the main sea-level fall and the main extinction episode might be causal： both of them might be caused by a drastic climatic cooling.

Different accretion and diagenetic patterns within the fabrics of the Permian–Triassic boundary microbialites on the Leye isolated carbonate platform, South China Block

A comprehensive study on the accretion and diagenesis of the Permian–Triassic boundary microbialites is conducive to a better understanding of the ecological community after the end-Permian mass extinction. Here we studied the special microbialite sequences at the Tianba section of Leye isolated carbonate platform, South China Block. The microbialites are shown as small columnar stromatolites, stromatolitic thrombolites, spotted thrombolites,and domical digitate thrombolites in an ascending order. Thin section analyses, coupled with cathodoluminescence photos and oxygen isotopic data, reveal that all types of microbially-mediated laminae/clots are partly recrystallized.Layers of the Polybessurus-like fossils commonly occur in the recrystallized fabrics of stromatolitic laminae. However,the Polybessurus-like fossils are rare in quantity and generally fragmentary and structureless in stromatolitic clots and spotted clots. Such taphonomic features are likely interpreted as the early decomposition by heterotrophic bacteria in an oxygen-depleted microenvironment caused by rapid accumulations of organic matter in the calm water.More enrichments of ~(13)C in the laminae of stromatolite and in the clots of stromatolitic thrombolite and spotted thrombolite than in adjacent interstitial matrixes signify the photosynthesis-dominated isotopic fractionation during the growth of microbial communities. Rare calcimicrobial structures but many calcite crystal fans were found in the ~(13)C-depleted digitate clots. These phenomena indicate that seawater on the carbonate platform was ~(12)C-enriched and supersaturated, accelerating carbonate precipitations and decompositions of organic matter within the microbial community. Different preservations of the Polybessurus-like fossil revealed the complicated microbiallydominated sedimentation and post-depositional diagenesis in the abnormal seawater after the catastrophe.