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Plio-Pleistocene mass extinction of marine bivalves on the U.S. eastern seaboard has been attributed to declines in temperature and primary production. We investigate the relationship of growth rate in the scallop Carolinapecten eboreus to variation in these parameters to determine which contributed to its extinction. We use ontogenetic profiles of shell δ18O to estimate growth rate and seasonal temperature, microgrowth-increment data to validate δ18O-based figures for growth rate, and shell δ13C to supplement assemblage evidence of production. Postlarval growth started in the spring/summer in individuals from the Middle Atlantic Coastal Plain but in the autumn/ winter in some from the Gulf Coastal Plain. Growth rate typically declined with age and was usually higher in summer than winter. Many individuals died in winter but the largest forms typically died in spring, possibly on spawning for the first time. No individuals lived longer than two years and some grew exceedingly fast overall, up to 60% more rapidly than any other scallop species (< 145.7 mm in a year). Faster growth was generally achieved by secreting more rather than larger microgrowth increments. Some very fast-growing individuals lived in settings of high production and low temperature. No individuals grew slowly under high production whereas most if not all grew slowly under ‘average’ production and low temperature. In that the rapid growth evidently enabled by high production would have afforded protection from predators, Plio-Pleistocene decline in production was probably contributory to the extinction of C. eboreus. However, the negative impact of low temperature on growth under ‘average’ production suggests that temperature decline played some part.
The timing and mode of the marine flooding of the southern margin of the Pannonian basin in SE Europe is still a matter of debate. In central Serbia, integrated bio-magnetostratigraphic data and quantified high-resolution records are completely missing. Here, we provide paleoenvironmental and paleoecological constraints from the Slanci section located near Belgrade that has an excellent preservation of micro-fauna and flora, i.e., planktonic and benthic foraminifera and calcareous nannoplankton. We integrate their quantified records with sedimentological, natural gamma radioactivity and magnetic susceptibility logs and include the non-quantified records of mollusks, corals, and ostracods to reconstruct the regional depositional history. The section shows upper bathyal to outer shelf depositional settings and alternating nutrient bottom conditions. The shallowing upwards trend marked by increasing terrestrial input, attributes it to the early Highstand Systems Tract of the first marine third order sequence in this part of the Pannonian Basin. We infer that the marine flooding in central Serbia took place at an age of ∼ 14 Ma, slightly predating the Langhian/Serravallian boundary (13.82 Ma) and the Badenian Salinity Crisis (∼ 13.8–13.4 Ma) in the Central Paratethys. Our results support an eastwards directed, tectonically forced, flooding of the southern Pannonian Basin. This major paleoenvironmental turnover was forced by syn-rift tectonics in the Pannonian Basin system, which started in the late early Miocene in the Styrian Basin (SE Austria) and ended more than 3 Myr later in the late middle Miocene in the Morava depression (E Serbia).
Globally, Upper Devonian sedimentary successions are characterized by multiple organic-rich strata associated with dysoxic to anoxic conditions and biological turnover of varying magnitude, including the Lower and Upper Kellwasser intervals. The cause or causes of the Kellwasser extinction and their relationship to coeval environmental conditions remains actively debated. Here we show that organic-walled microfossils (OWMs) are preserved within the Kellwasser intervals at two localities in western New York State that are otherwise devoid of macrofossils. While OWMs are significantly more abundant within the Upper Kellwasser interval, the assemblages are slightly more diverse within the Lower Kellwasser interval, including two distinct smooth-walled leiosphere populations based on size and, in the more proximal locality, acanthomorphic (spinose) forms. Mo and U concentrations at these localities range from 1–86 ppm and 2–14 ppm respectively, and support oxygen stress, but not persistent anoxia or euxinia, through these events. Notably the Lower Kellwasser exhibits both greater OWM variability and more evidence of anoxic conditions, while the Upper Kellwasser exhibits relatively consistent OWM assemblages and more dysoxic conditions. We interpret OWM abundance, especially large leiosphere forms, as a possible signal of algal blooms potentially associated with eutrophication. Our results suggest that eutrophication may have played a larger role during the Lower Kellwasser event than during the Upper Kellwasser event and demonstrate how OWMs can provide an important link between primary productivity, eutrophication, and the deposition of organic rich-strata.
A continental assemblage of fossil mammals from the Santa Cruz Formation (early Miocene, Burdigalian) recovered from the coast of the Santa Cruz Province (Anfiteatro locality), Argentina, was evaluated taphonomically. Due to its stratigraphic position and age (∼ 17.5 Ma), the fossiliferous level corresponds to the lower section of the Estancia La Costa Member (lower part of the Santa Cruz Formation). The Anfiteatro assemblage (Santacrucian South American Land Mammal Age) is dominated by mammals, but some birds and carnivore coprolites were also recorded. The recorded taphonomic features and the sedimentological interpretation suggest that the bone remains were preserved in a floodplain related to a fluvial system influenced by volcaniclastic input. The assemblage was interpreted as a result of death of mammals over a short period of time. The residence time of carcasses on the surface was variable. Although most bones were quickly buried, the exposure was sufficiently long for the disarticulation and scattering of different skeletal components and the agency of other processes (e.g., trampling, weathering). The loss of skeletal elements is linked to the action of water flows generated in the plain, during overbank floods or rainfalls, which mobilized those elements more susceptible to transport. After burial, the specimens were affected by diagenetic processes (e.g., soil corrosion, infilling, impregnation, deformation). The taphonomic evaluation of the Anfiteatro locality provides a framework for the analysis of other fossil assemblages with similar features worldwide.