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Laboratory tests indicate that 15% O2, instead of 12%, is required for the propagation of a widespread forest fire, a 3% increase from what was previously assumed. The presence of widespread wildfire records in the Upper Triassic and Lower Jurassic of Central Europe suggests that the lower limit for O2 during this time was at least 15%. Wildfire records are based on the co-occurrence of charcoal fragments and elevated concentrations of pyrolytic polycyclic aromatic hydrocarbons (PAHs). In all samples charcoal fragments are large to medium-sized and angular, suggesting that they were transported by rivers only short distances after charcoalification. Calculated combustion temperatures vary with stratigraphic position and average 295–377 °C, which is characteristic for ground or near-surface wildfires. The most extensive wildfires occurred in the earliest Jurassic and their intensities successively decreased with time. Average concentrations of the sum of pyrolytic PAHs for the lowermost Jurassic Zagaje Formation reached ∼1253 µg/g total organic carbon (TOC), whereas for the Upper Triassic–Lower Jurassic Skłoby Formation they did not exceed ∼16 µg/g TOC. Charcoal-bearing sequences were also characterized by the presence of phenyl-PAHs (Ph-PAHs) and oxygen-containing aromatic compounds. The dominance of the more stable Ph-PAH isomers in these immature to low-maturity sedimentary rocks supports their pyrolytic origin. The oxygenated PAHs may also be derived from combustion processes.
The aim of this study was to determine the paleoecological and paleoenvironmental significance of the trace fossil Macaronichnus segregatis by examining its extant counterpart, feeding burrows of the opheliid polychaete Euzonus, which was periodically sampled on a wave-dominated sandy beach on the Pacific coast of Japan from June to December 2006. The distributions of Euzonus and its feeding burrows normal to the shoreline ranged from 5 m to 40 m. The vertical thickness distributions ranged from 32 cm to 123 cm (Euzonus) and from 34 cm to 126 cm (burrows). These parameters increase with decreasing beach-face gradient. The midpoints (median levels) of the vertical distributions invariably occurred near the midforeshore (corresponding to high-tide level). Foreshore width and vertical thickness also increase with decreasing beach-face gradient. These findings suggest that changes in the distributions of Euzonus and its burrows in the midforeshore environment vary with beach morphodynamics. The vertical thickness of M. segregatis–bearing beds may be a behavioral response to—and, hence, be indicative of—ancient beach morphodynamics. In addition, the consistent occurrence of the midpoint of trace-bearing beds suggests that beds containing M. segregatis might prove useful as an index of midforeshore level.
The Nebraska Sand Hills are a stabilized dune field in the central United States that reflect past conditions of drought. The most recent drought, known as the Medieval Climatic Anomaly, occurred from A.D. 900 to A.D. 1300 and had an enormous effect on the thriving prairie ecosystem, which included large populations of the plains pocket gopher (Geomys bursarius). Burrows of these organisms across a paleosol-eolian sand boundary in the Sand Hills indicate abrupt climate change during the transition from stabilized to active dune field and from humid to arid conditions. Medieval gophers tunneled at greater depths below the surface than do modern gophers, indicating the behavioral changes these animals underwent to survive during the transition. The gophers were likely surviving on roots remaining in the underlying soil as it was buried by sand; they tunneled >1 m up to the surface to deposit mounds of excavated soil and sand. Most of the burrows occur in areas of low-angle bedding, suggesting loss of vegetation occurred first on the crests of the newly formed dunes while vegetation persisted in the interdunes. Optically stimulated luminescence dates from a dune containing ancient gopher burrows are nearly identical throughout the height of the dune, indicating rapid accumulation of sand. As accumulation of sand was rapid, vegetative loss must also have occurred quickly, though not in a uniform pattern across the region. Pocket gophers were apparently able to survive in areas of remaining vegetation for a short time, but in a relatively short period of time, they were unable to reach their food sources and were forced ultimately to abandon the uplands in the region.
The recent advent of low magnification microwear analysis has allowed the efficient study of entire vertebrate faunas using only an optical stereomicroscope. Photographic visualization of microwear by this means has proven difficult, however, and, as a result, few high-resolution photos of low magnification microwear have been published. The repeatability of the method has also been questioned because low magnification microwear analysis involves the visual inspection of microwear features. We show that the use of high dynamic range imaging improves the visualization of microwear features in photographs and that using these photographs as a counting medium increases the repeatability of the method. We also show that counting from the photographs allows us to accurately classify ungulates as browsers, grazers, or mixed feeders.
Detailed sedimentological and quantitative taphonomical analyses of 11,974 fossil specimens from an early Cambrian (Stage 3) Chengjiang-type deposit near Haikou, Yunnan, reveals significant relationships between the original depositional environments and the composition and preservation of their respective fossil assemblages. In general, the Maotianshan Shale is characterized by superimposed couplets of laminated background and thin event mudstone layers representing two distinct taphofacies, A and B, respectively. Fossils in taphofacies A consist predominantly of indeterminate organic elements and fecal or algal strings with few, poorly preserved, soft-bodied animals. Among those, disarticulated arthropods account for 84.3% of specimens (mostly isolated valves of Kunmingella douvillei) and 51.4% of species. Poriferans represent 7.4% of specimens and 22.9% of species. Fossils in this taphofacies have undergone significant pre- or syn-burial decay and represent limited time-averaged assemblages exhibiting low species richness. By contrast, taphofacies B contains greater numbers of species and specimens and better preserved soft-bodied animals. Taphofacies B represents mostly smothered organisms by distal tempestites. Arthropods are also dominant in taphofacies B, both in terms of species richness (41%) and abundance of specimens (44%). Poriferans, priapulids, lobopods, and brachiopods exhibit similar low species richness (6–8% each), but poriferans and lobopods are numerically rare, at around 1% each, whereas priapulids and brachiopods make up 26% and 24% of specimens, respectively. The arthropod Kunmingella douvillei (19%), the priapulid Cricocosmia jinningensis (19%), and the brachiopod Diandongia pista (18%) are the most abundant species in taphofacies B. Fossil assemblages in taphofacies A and B have similar recurrent and abundant species and similar temporal trends in evenness and richness, but taphofacies A captures only a portion of the species that are preserved in taphofacies B. These results suggest that the fossil assemblages present in both taphofacies represent a single local community subjected to two different taphonomic processes and imply similar recurrent environmental conditions within the section studied.
Fossil fungi and arthropod body parts are present in one of 27 unhatched eggs in a turtle egg clutch from the Lower Cretaceous (Albian) Liangtoutang Formation, Zhejiang Province, China. The fossil fungal structures include branching septate hyphae, conidiophores supporting multiple phialides, and chains of up to five basipetal conidia (asexual spores). The morphology of the fossil fungus is similar to extant taxa within the genus Penicillium (order Eurotiales), making it the first reported intact Early Cretaceous asexual ascomycete and the earliest record of a presumed intact Penicillium. Biomineralization, a physiologic response to calcium-rich microenvironments, occurs in some extant fungi and may have facilitated detailed preservation of the fossil specimen. This rare evidence of fungal-animal association provides clues to clutch-related paleoecological interactions. The fungus-bearing egg occurs on the clutch periphery, whereas adjacent and more distant eggs show no evidence of fungal invasion. We suggest that the fungi were opportunistic contaminants invading after the egg was compromised, and the fungus failed to spread to adjacent eggs prior to burial and fossilization.