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The Salton Sea, California, a hypersaline, closed-system lake, experiences high wind event-associated tilapia fish kills. This study reports on the occurrence of several tons of organic spheres taphonomically associated with disarticulated tilapia skeletal parts occurring along the Salton Sea's shorelines. Chemical analyses demonstrate that sphere composition is consistent with soft tissue degradation of tilapia by anaerobic bacteria producing adipocere. Infrared spectroscopy (IR) and gas chromatography (GC) reveal the presence of both triglycerides and salts of free fatty acids. Specifically, GC-MS FAME (fatty acid methyl ester) analysis identified the presence of relatively high concentrations of palmitic, oleic, stearic, pentadecanoic, and myristic acids in the adipocere spheres which are nearly identical to the fatty acid profile of Salton Sea tilapia. SEM studies document the incorporation of fragmented fish bones and detrital grains within the spheres. Formation of adipocere masses in the Salton Sea affects the buoyancy and hydrodynamic equivalence of fish bone fragments, thereby influencing deposition of disarticulated bone materials, and may affect local redox conditions at the burial site.
Authigenic mineralization of embryos (and potentially other soft-bodied organisms) requires first stabilization of cells against rapid self-autolytic destruction, and secondly a role for bacterial biofilms that preserve rather than destructively consume tissue. We predict that the ecology of the second stage in preservation will depend on environmental effects on the bacterial species present, coupled with mutual interactions between the bacteria themselves. We have created a simple experimental model made up of two antagonistic marine bacterial species, tested on a taphonomic target of autolysis-inhibited killed marine embryos. Pseudoalteromonas tunicata forms a three-dimensional preserving biofilm with killed embryos, whereas P. luteoviolacea destroys embryo tissue. Our model system allows controlled laboratory tests of microbial interactions under taphonomic conditions selected to test inferred paleoenvironments present in Lagerstätten. We varied environmental conditions one at a time, and observed the taphonomic outcome for killed embryos in the presence of each species alone, and with both species present in direct competition. Parameters tested include temperature, pH, oxygen level, salinity, and nutrient state. Pseudoalteromonas tunicata was robust in generating preserving biofilm pseudomorphs over a wide range of conditions. In competition, P. luteoviolacea destruction dominated in most conditions. However, we identified conditions of temperature, pH, and salinity where P. luteoviolacea grows poorly and preservation by P. tunicata dominates. Elevated external nutrients reduced the fidelity of P. tunicata pseudomorphs. In low oxygen, P. tunicata physiology was altered and it switched to become a destroyer, dramatically showing the extent to which environment can determine taphonomic outcomes.
The present work analyzes the taphonomic characteristics of an assemblage of Lama guanicoe recovered from the fluvial deposits of Chacra La Blanqueada Formation, at García del Río locality. This locality is situated in the middle valley of the Napostá Grande Creek (south of the Pampean Region, Buenos Aires Province, Argentina). A radiocarbon date of 2342 ± 47 years BP allows the assignment of this assemblage to the late Holocene. The MNI (Minimum Number of Individuals) and the population structure suggest the presence of a family group or part of a mixed group. The available evidence indicates that, throughout their taphonomic history, the remains were affected by processes related to a floodplain subenvironment. Also, the marks of anthropic activity suggest that the death of the animals was circumstantially used as a low-cost and low-risk resource, highlighting the relevant role of this species in the regional hunter-gatherer communities.
The integration of planktonic foraminiferal assemblage, oxygen stable isotope values, and AMS 14C dating allows a more precise chronology of biostratigraphic events recorded in cores GL-74 and GL-75 collected from Campos Basin (southeastern Brazil). This study documents that the third event of disappearance of Pulleniatina plexus (Pulleniatina obliquiloculata biohorizon 3 = YP.3) occurred simultaneously in Campos and Santos Basins around 43 ka. The results also show that the event of higher abundance of Globorotalia crassaformis, the so-called Globorotalia crassaformis Optimum Event (GcOE), occurred between ca. 84 and ca. 71 ka (ca. 13 ka duration), and was also simultaneous in both basins. This study supports the GcOE as an important biostratigraphic marker event in the southeastern Brazilian margin. We propose a revised subdivision of the last glacial Zone Y into subzones Y1, Y2, and Y3. Nevertheless, it is fundamental to establish the true geographic range, as well as building a more robust chronology for the GcOE, using other cores from other South Atlantic basins.
The Cretaceous coastal plain of Arctic Alaska contains the richest concentration of high-latitude dinosaurs on Earth. Three bonebeds (Liscomb, Byers, Sling Point) are found in paleopolar (82°–85° N) coastal-plain deposits of the Prince Creek Formation on Alaska's North Slope. 40Ar/39Ar analysis of a tuff below the oldest bonebed (Sling Point) returned an age of 69.2 ± 0.5 Ma indicating a maximum early Maastrichtian age for these bonebeds. Bonebeds are overwhelmingly dominated by partially articulated to associated late-stage juvenile Edmontosaurus sp. Bone is rarely found in channels; instead high-density accumulations are preserved on floodplains in laterally extensive, muddy alluvium. Bone size grading is vertically nonuniform and most bones are in hydraulic disequilibrium with the surrounding clay-rich matrix. Bones exhibit little evidence of rounding, weathering, predation, or trampling, suggesting short-distance transport and rapid burial. Because these bonebeds are unlike typical debris-flow or streamflow deposits, the mechanism for bonebed emplacement remained poorly understood. All bonebeds contain a current-rippled siltstone containing the largest bone overlain by a distinctive mudstone encasing smaller bones, bone fragments, and subparallel-aligned plant fragments that appear “frozen in flow” within the muddy matrix. We recognize that these bonebeds exhibit a recurring facies pairing and bipartite division of flow consistent with deposition by fine-grained viscous hyperconcentrated flows. We suggest that exceptional discharge events entrained mud and ash stored on point bars and floodplains, increasing suspended-sediment concentrations in rivers and generating erosive hyperconcentrated flows that transported the remains of scores of juvenile dinosaurs onto floodplains adjacent to distributary channels.