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We report on the distribution and character of fossil charcoal found in the Lower Cretaceous Guantou Formation in the Xinchang Petrified Wood National Geopark, eastern South China. All charcoal fragments studied so far exhibit well-preserved anatomical features of Araucarioxylon, consistent with the taxonomic classification assigned to this geopark's widely known silicified tree trunks. Homogenized cell walls and high vitrinite reflectance values of charcoal particles, and the synchronous presence of tuffaceous deposits within the associated sequence, suggest that charcoal in the Xinchang Geopark may have mainly formed under conditions of complete exclusion of air by entombment in hot pyroclastic flows. Scattered charcoal fragments in several sandstone beds overlying the lahar sediments and locally high concentrations of fragments on channel-scoured surfaces are consistent with postformation reworking and transport of charcoal material. Zircon U–Pb SHRIMP dating of the volcanic interbeds of the Guantou Formation and underlying units define an age of Early Cretaceous (Aptian) for the charcoal. Both the fossil charcoal and associated petrified wood within the Guantou Formation may have an intimate genetic relationship with synchronous volcanism in the Xinchang Basin, eastern South China.
In order to assess taphonomic pathways leading to preservation of land snail assemblages, the agreement between the death (DAs) and living assemblages (LAs) of land mollusk communities was evaluated in six forest habitats along an altitudinal and soil acidity gradient in Northern Italy, using data obtained by visual search and sorting of leaf litter and soil. Death assemblages were considered both as overall DAs and as DAs consisting solely of pristine (i.e., fresh) shells. Both calcareous and acidic soils showed high fidelity in richness and evenness, in particular leaf litter and soil samples, as can be expected in depositional environments with reduced time averaging. Lack of rank-order agreement in species relative abundance was observed in visual search (r = −0.37–0.45), while significantly high rank-order agreement (r = 0.61–0.89) in leaf litter and soil. Time averaging and interspecific variation in life span and in shell durability appear to determine the observed live-dead mismatch, which, in contrast, was probably not affected by between-habitat transport and temporal changes in community composition. Between-habitat differences are generally preserved in the DAs. DAs based on pristine shells do not show higher rank abundance correlations and smaller differences in ordinations than DAs based on all shells. But in terms of species richness and evenness, DAs composed only of pristine shells were more similar to the LA, in particular in leaf litter and soil, supporting terrestrial ecologists' approach in considering pristine shells in inventories of species richness. Distinguishing between pristine and worn empty shells is especially useful for actualistic studies in highly calcareous sites, where DAs are expected to encompass a longer temporal duration.
Shells of the cephalopod Nautilus macromphalus were collected in 2011 from three bays on the island of Lifou in the South Pacific six months after a tropical cyclone passed over the island. All three bays were on the east side of the island; Bays 1 and 2 were 200 m apart whereas Bay 3 was 25 km to the north. Nautilus shells in Bays 1 and 2 were studied in 2008 after six years without tropical cyclones. Greatest damage occurred in shells from Bay 1 and the least from Bay 3. Shell encrustation was lowest in Bay 1. In comparison to the 2008 assemblage, Bay 1 had significantly higher levels of damage and lower levels of encrustation whereas Bay 2 had a higher abundance of severe damage. The Bay 3 assemblage, however, was statistically similar to the 2008 assemblage. An exposed beach cut at Bay 3 revealed a recently buried Nautilus deposit. Nautilus specimens from this deposit displayed damage and encrustation levels similar to shells from Bay 1. Previously buried shells are likely being exposed, damaged, and redeposited in the bays. Spatial variability indicates that, on a short time scale, this is a localized phenomenon. Use of cephalopod fossils as tools in paleoenvironmental reconstruction requires an understanding of the processes that affect their shells. Using the Lifou deposits as analogs, fossil cephalopod shells deposited in shallow water near beaches and where intense storms are periodically present will have extensive breakage. Cephalopod shells would, therefore, be unlikely to survive similar beach conditions unless they were completely buried and not periodically reexhumed by storm events.
The taphonomic pathways of “Ephemeropsis trisetalis” nymphs (mayfly larvae) were systematically investigated based on fossils of different preservational types, collected during three high–stratigraphic-resolution (mm to cm) excavations in the Lower Cretaceous Yixian Formation in the Sihetun area of western Liaoning, China. All fossils studied are fully articulated either in three or two dimensions, which indicates that decay was terminated at a stage before the exoskeleton became disarticulated. We conclude that the Jehol organic skeletons represent at least two general types of preservation produced by pyritization and collapse/compression, respectively. The two-dimensional compressions show no evidence for authigenic minerals, but the three-dimensionally preserved fossils are wholly or partially pyritized. Our study also indicates that aluminosilicate clay and pyrite mineralization are closely associated with fossil “Ephemeropsis trisetalis” nymphs, suggesting that both clay and pyrite played important roles in lacustrine fossil preservations, as in some marine fossil Lagerstätten. We propose a general model for organic tissue fossilization in the Jehol Lagerstätte based on study of taphonomy of “Ephemeropsis trisetalis” nymphs.
The Indo-Pacific marine biodiversity hotspot originated between the late Eocene and the early Miocene. Its origin coincides with an increase in availability of shallow-marine habitats driven by the opening of the South China Sea and the collision of Australia with the Pacific arcs and the southeast Asian margin. However, little is known about the distribution and diversity of past Indo-Pacific marine habitats. Understanding habitat diversity is key for understanding the significance of biodiversity origins and a necessary prerequisite for interpreting biodiversity patterns through time. Here we describe and interpret past carbonate platform environments in Sarawak, Malaysia during a time of active tectonism. We examine upper Eocene to lower Miocene marine shallow-water carbonate deposits from six localities in two limestone formations: the large ramplike Melinau carbonate platform (middle Eocene to early Miocene) and the unattached Subis carbonate platform (early Miocene). Deposits examined in this study represent paleoenvironments. Our analysis reveals an increase in habitat diversity from the Eocene to the Miocene. Mesophotic to oligophotic low-energy environments are typical for the Eocene sites. The corals first appear in the Oligocene deposits, but genuine reef depositional settings are not observed until the Miocene. This study provides both insight into the evolution of the carbonate platform environments along the Sarawak margin, and context for the origin of the Indo-Pacific marine biodiversity hotspot.