7 research outputs found
Data report: d34S and d18O measurements of dissolved sulfate from interstitial water samples, IODP Expedition 311
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Hydrogen sulfide–hydrates and saline fluids in the continental margin of South Australia
Large-scale stable isotope characterization of a Late Cretaceous dinosaur-dominated ecosystem
In the Cretaceous of North America, environmental sensitivity and habitat specialization
have been hypothesized to explain the surprisingly restricted geographic ranges of many
large-bodied dinosaurs. Understanding the drivers behind this are key to determining broader
trends of dinosaur species and community response to climate change under greenhouse
conditions. However, previous studies of this question have commonly examined only small
components of the paleo-ecosystem or operated without comparison to similar modern systems
from which to constrain interpretations. Here we perform a high-resolution multi-taxic \u3b413C
and \u3b418O study of a Cretaceous coastal floodplain ecosystem, focusing on species interactions
and paleotemperature estimation, and compare with similar data from extant systems. Bioapatite
\u3b413C preserves predator-prey offsets between tyrannosaurs and ornithischians (large
herbivorous dinosaurs), and between aquatic reptiles and fish. Large ornithischians had
broadly overlapping stable isotope ranges, contrary to hypothesized niche partitioning driven
by specialization on coastal or inland subhabitat use. Comparisons to a modern analogue
coastal floodplain show similar patterns of ecological guild structure and aquatic-terrestrial
resource interchange. Multi-taxic oxygen isotope temperature estimations yield results for
the Campanian of Alberta (Canada) consistent with the few other paleotemperature proxies
available, and are validated when applied for extant species from a modern coastal floodplain,
suggesting that this approach is a simple and effective avenue for paleoenvironmental
reconstruction. Together, these new data suggest that dinosaur niche partitioning was more
complex than previously hypothesized, and provide a framework for future research on
dinosaur-dominated Mesozoic floodplain communities
Methane hydrate formation in turbidite sediments of northern Cascadia, IODP Expedition 311
Expedition 311 of the Integrated Ocean Drilling Program (IODP) to northern Cascadia recovered gas-hydrate bearing sediments along a SW–NE transect from the first ridge of the accretionary margin to the eastward limit of gas-hydrate stability. In this study we contrast the gas gas-hydrate distribution from two sites drilled ~ 8 km apart in different tectonic settings. At Site U1325, drilled on a depositional basin with nearly horizontal sedimentary sequences, the gas-hydrate distribution shows a trend of increasing saturation toward the base of gas-hydrate stability, consistent with several model simulations in the literature. Site U1326 was drilled on an uplifted ridge characterized by faulting, which has likely experienced some mass wasting events. Here the gas hydrate does not show a clear depth-distribution trend, the highest gas-hydrate saturation occurs well within the gas-hydrate stability zone at the shallow depth of ~ 49 mbsf. Sediments at both sites are characterized by abundant coarse-grained (sand) layers up to 23 cm in thickness, and are interspaced within fine-grained (clay and silty clay) detrital sediments. The gas-hydrate distribution is punctuated by localized depth intervals of high gas-hydrate saturation, which preferentially occur in the coarse-grained horizons and occupy up to 60% of the pore space at Site U1325 and > 80% at Site U1326. Detailed analyses of contiguous samples of different lithologies show that when enough methane is present, about 90% of the variance in gas-hydrate saturation can be explained by the sand (> 63 μm) content of the sediments. The variability in gas-hydrate occupancy of sandy horizons at Site U1326 reflects an insufficient methane supply to the sediment section between 190 and 245 mbsf