Provenance evolution of age‐calibrated strata reveals when and how South China Block collided with Gondwana

The South China Block (SCB) has been regarded by many as an integral part of Gondwana, but proposed timing and processes for its accretion to Gondwana vary and remain contentious, largely owing to the lack of reliable Pan‐African age paleomagnetic data and tectono‐magmatic records from the SCB. Integrated in situ U‐Pb ages and Hf‐O isotope analyses of detrital zircons from geochronologically well‐calibrated Ediacaran‐Cambrian sedimentary rocks of western SCB reveal age populations of 2.51, 1.85, 1.20, 0.80, and 0.52 Ga. Detrital zircon age spectra indicate a major tectonic transition for the SCB during 0.56–0.54 Ga, interpreted to reflect the beginning of the collision between SCB‐Indochina and NW India blocks. The collisional event lasted until early Ordovician, leading to the suturing of the SCB‐Indochina to the northern margin of East Gondwana

Sponge grade body fossil with cellular resolution dating 60 Myr before the Cambrian

An extraordinarily well preserved, 600-million-year (Myr)-old, three-dimensionally phosphatized fossil displaying multiple independent characters of modern adult sponges has been analyzed by SEM and synchrotron X-ray tomography. The fossilized animal (Eocyathispongia qiania gen. et sp. nov.) is slightly more than 1.2 mm wide and 1.1 mm tall, is composed of hundreds of thousands of cells, and has a gross structure consisting of three adjacent hollow tubes sharing a common base. The main tube is crowned with a large open funnel, and the others end in osculum-like openings to the exterior. The external surface is densely covered with flat tile-like cells closely resembling sponge pinacocytes, and this layer is punctuated with smaller pores. A dense patch of external structures that display the form of a lawn of sponge papillae has also survived. Within the main funnel, an area where features of the inner surface are preserved displays a regular pattern of uniform pits. Many of them are surrounded individually by distinct collars, mounted in a supporting reticulum. The possibility cannot be excluded that these pits are the remains of a field of choanocytes. The character set evinced by this specimen, ranging from general anatomy to cell type, uniquely indicates that this specimen is a fossil of probable poriferan affinity. So far, we have only this single specimen, and although its organized and complex cellular structure precludes any reasonable interpretation that its origin is abiogenic, confirmation that it is indeed a fossilized sponge will clearly require discovery of additional specimens

Geochronological constraints on stratigraphic correlation and oceanic oxygenation in Ediacaran-Cambrian transition in South China

The continuous late Ediacaran - early Cambrian deep-water successions of South China archive the complete evolution of seawater chemical conditions in the deep ocean during this critical time interval. However, the geochemical data from these poorly fossiliferous and condensed successions lack high-resolution stratigraphic constraints, hampering their interpretation for the spatio-temporal evolution of the sweater chemistry in this time interval. In this study, we report a new SIMS and CA-ID-TIMS zircon U-Pb age 545.76 ± 0.66 Ma (total uncertainty) for an ash bed at the lower Liuchapo Formation in the deep-water Longbizui section in western Hunan Province. The new age suggests that the lower and the middle-upper parts of the Liuchapo Formation in the deep water facies can be correlated with the lower Dengying Formation and the upper Dengying - lower Zhujiaqing formations in the shallow water facies, respectively. This correlation implies that the correlative horizon of the Ediacaran-Cambrian boundary in the deep water facies in South China is likely located near the base of a widespread negative δ13Corg excursion at the upper Liuchapo Formation. Based on our new geochronological framework, the compilations of Fe-speciation, Mo, and U data indicate that the deep ocean was characterized by widespread anoxic, ferruginous water, with intermittent euxinic water impinged on the middle-lower slope in Ediacaran-Cambrian transition, and significant oxygenation events occurred in 533–520 Ma. The compilations do not support any significant oceanic oxygenation events in 551–535 Ma

SIMS U–Pb zircon geochronological constraints on upper Ediacaran stratigraphic correlations, South China

Fossiliferous Ediacaran successions of South China, the Doushantuo and Dengying formations and their equivalents, are key to understanding bio- and geological evolution at the Neoproterozoic–Cambrian transition. However, their absolute ages, especially the upper Ediacaran successions, are poorly constrained. SIMS zircon U–Pb dating results in this study suggest that ash beds at the basal and middle parts of the Jiucheng Member (middle Dengying Formation) in eastern Yunnan Province were deposited at 553.6 ± 2.7/(3.8) Ma and 546.3 ± 2.7/(3.8) Ma, respectively. These new dates indicate that the age for the base of Dengying Formation in eastern Yunnan Province is similar to the 550.55 ± 0.75 Ma date, which is from an ash bed at the top of the Miaohe Member and has been regarded as the age for the base of Dengying Formation in Yangtze Gorges area. These dates do not permit a clear test of the two correlation models for the chronostratigraphic position of the Miaohe Member (uppermost Doushantuo Formation vs. middle Dengying Formation), implying that further integrated intra-basinal stratigraphic correlations and more high-resolution chronological data from the upper Ediacaran deposits of South China are required. New dates of the Jiucheng Member constrain the age of the fossil biotas in the middle Dengying Formation and extend the stratigraphic range of Rangea, Hiemalora and Charniodiscus to 546.3 ± 2.7/(3.8) Ma. The geochronology of the Dengying Formation implies that Ediacaran-type fossils preserved in this formation are younger than the White Sea Assemblage and temporally overlapping with the Nama Assemblage