Search for: All records

Abstract The Antarctic ice sheet blankets >99% of the continent and limits our ability to study how subglacial geology and topography have evolved through time. Ice-rafted dropstones derived from the Antarctic subglacial continental interior at different times during the late Cenozoic provide valuable thermal history proxies to understand this geologic history. We applied multiple thermochronometers covering a range of closure temperatures (60–800 °C) to 10 dropstones collected during Integrated Ocean Drilling Program (IODP) Expedition 318 in order to explore the subglacial geology and thermal and exhumation history of the Wilkes Subglacial Basin. The Wilkes Subglacial Basin is a key target for study because ice-sheet models show it was an area of ice-sheet retreat that significantly contributed to sea-level rise during past warm periods. Depositional ages of dropstones range from early Oligocene to late Pleistocene and have zircon U-Pb or 40Ar/39Ar ages indicating sources from the Mertz shear zone, Adélie craton, Ferrar large igneous province, and Millen schist belt. Dropstones from the Mertz shear zone and Adélie craton experienced three cooling periods (1700–1500 Ma; 500–280 Ma; 34–0 Ma) and two periods of extremely slow cooling rates (1500–500 Ma; 280–34 Ma). Low-temperature thermochronometers from seven of the dropstones record cooling during the Paleozoic, potentially recording the Ross or Pan-African orogenies, and during the Mesozoic, potentially recording late Paleozoic to Mesozoic rifting. These dropstones then resided within ~500 m of the surface since the late Paleozoic and early Mesozoic. In contrast, two dropstones deposited during the mid-Pliocene, one from the Mertz shear zone and one from Adélie craton, show evidence for localized post-Eocene glacial erosion of ≥2 km. 

Tephra is a unique volcanic product that plays an unparalleled role in understanding past eruptions, the long-term behavior of volcanoes, and the effects of volcanism on climate and the environment. Tephra deposits also provide spatially widespread, extremely high-resolution time-stratigraphic markers across a range of sedimentary settings and are used by many disciplines (e.g. volcanology, seismotectonics, climate science, archaeology, ecology, public health and ash impact assessment). In the last two decades, tephra studies have become more interdisciplinary in nature but are challenged by a lack of standardization that often prevents comparison amongst various regions and across disciplines. To address this challenge, the global tephra community has come together through a series of workshops to establish best practice recommendations for tephra studies from sample collection through analysis and data reporting. This new standardized framework will facilitate consistent tephra documentation and parametrization, foster interdisciplinary communication, and improve effectiveness of data sharing among diverse communities of researchers. One specific goal is to use the best practice guidelines to inform digital tool and data repository development. Here we report on 1) a new set of templates for tephra sample documentation, geochemical method documentation and data reporting using recommended best- practice data and metadata fields, 2) a new tephra module added to StraboSpot, an open source geologic mapping and data- recording multi-platform software application, and 3) new implementations and cross-mapping of metadata requirements at SESAR (System for Earth Sample Registration) and EarthChem. Addition of tephra-specific fields to StraboSpot enables users to consistently collect and report essential tephra data in the field which is then automatically saved to an online data repository. A new tephra portal on the EarthChem website will allow users to follow simple workflows to register tephra samples at SESAR and submit microanalytical data to EarthChem.