Environmental Factors Affecting Large-Bodied Coral Reef Fish Assemblages in the Mariana Archipelago

Large-bodied reef fishes represent an economically and ecologically important segment of the coral reef fish assemblage. Many of these individuals supply the bulk of the reproductive output for their population and have a disproportionate effect on their environment (e.g. as apex predators or bioeroding herbivores). Large-bodied reef fishes also tend to be at greatest risk of overfishing, and their loss can result in a myriad of either cascading (direct) or indirect trophic and other effects. While many studies have investigated habitat characteristics affecting populations of small-bodied reef fishes, few have explored the relationship between large-bodied species and their environment. Here, we describe the distribution of the large-bodied reef fishes in the Mariana Archipelago with an emphasis on the environmental factors associated with their distribution. Of the factors considered in this study, a negative association with human population density showed the highest relative influence on the distribution of large-bodied reef fishes; however, depth, water temperature, and distance to deep water also were important. These findings provide new information on the ecology of large-bodied reef fishes can inform discussions concerning essential fish habitat and ecosystem-based management for these species and highlight important knowledge gaps worthy of additional research

Nothing Lasts Forever: Environmental Discourses on the Collapse of Past Societies

The study of the collapse of past societies raises many questions for the theory and practice of archaeology. Interest in collapse extends as well into the natural sciences and environmental and sustainability policy. Despite a range of approaches to collapse, the predominant paradigm is environmental collapse, which I argue obscures recognition of the dynamic role of social processes that lie at the heart of human communities. These environmental discourses, together with confusion over terminology and the concepts of collapse, have created widespread aporia about collapse and resulted in the creation of mixed messages about complex historical and social processes

Ar-Ar and U-Pb Geochronology of a Late Paleoproterozoic Rift Basin: Support for a Genetic Link with Hudsonian Orogenesis, Western Churchill Province, Nunavut, Canada

The Baker Lake Group (Baker Sequence) represents the record of the formative stage of Baker Lake Basin, a series of generally elongate, northeast-striking, half-graben, and fault-bounded troughs filled with continental redbeds and coeval voluminous ultrapotassic volcanic rocks. An estimate for the time of basin initiation is given by a U-Pb (zircon) age of 18333 Ma, obtained from a basal volcanic flow at the western end of the basin, which is in agreement with a less precise 40Ar/39Ar (phlogopite) step-heating plateau age of 18378 Ma from a flow located at a similar stratigraphic level in the eastern Baker Lake Basin. 40Ar/39Ar analysis of phlogopite phenocrysts in a syenite that intrudes the lower part of the Baker Sequence yielded a plateau age of 181112 Ma. The syenite also intrudes sandstones containing detrital zircons with xenotime (YPO4) overgrowths, known to form during burial diagenesis. In situ U/Pb SHRIMP analysis of these overgrowths yields an upper intercept age of 183827 Ma, which is within analytical uncertainty of the ages obtained from the volcanic flows. Alluvial conglomerates near the top of the Baker Sequence contain discontinuous layers of laminar carbonate cements interpreted as geothermal travertine. Specific calcite layers within the travertine have very high 238U/204Pb values and yield a Pb-Pb isochron age of 17853 Ma, considered to represent aminimum age for deposition of the Baker Sequence. Our data suggest that the Baker Sequence was deposited over an interval of approximately 55 m.yr. (1840–1785 Ma), within error of the predicted periodicity of a second-order sequence. This interval coincides with collisional and postcollisional deformation and magmatism in the Trans- Hudson orogen and thus supports interpretations that the Baker Lake Basin formed in response to related far-field extension