چینه شناسی، رسوب شناسی و پالئونتولوژی ذخایر کرتاسه بالای روزنوتاک، جزیره برف هیل، قطب جنوب

Day Nunatak exposes an actively emergent stratigraphic section located on Snow Hill Island to the east of the Antarctic Peninsula. Strata exposed on Snow Hill Island were deposited in the James Ross Basin, which includes marine units of Cretaceous–Paleogene (K–Pg) age. Here we provide the first report of the sedimentology and paleontology of Day Nunatak, and place it into the broader stratigraphic context of the basin. Day Nunatak was previously unexplored due to difficulties accessing the site, and the historically poor exposure which has recently improved due to warming of the Antarctic Peninsula. Deposits exposed at Day Nunatak are assigned to the Karlsen Cliffs Member (KCM) of the Snow Hill Island Formation, and are better preserved than deposits at the type section of the KCM at Karlsen Cliffs, which has been altered by cross-cutting basaltic dikes. Correlation of lithostratigraphic and biostratigraphic data from Day Nunatak with other outcrops in the basin allows the section to be placed within a previously developed stratigraphic framework, and assigned an early Maastrichtian age. Our observations, and previous descriptions of the KCM, are consistent with a middle- to inner-shelf depositional environment below storm-wave base. Ammonites of the genus Gunnarites are very common, with other ammonite genera and benthic mollusks an order of magnitude less common. Stable carbon and oxygen isotope values obtained from bivalve shells are similar to values previously reported from Seymour Island, and suggest seawater temperatures of ∼7 °C. Measured bedding orientations suggest the presence of a structural offset between Day Nunatak and other sections exposed further north on Snow Hill Island. Day Nunatak preserves a similar depositional environment to deposits reported from the uppermost Maastrichtian on Seymour Island, and is the deeper-water equivalent of contemporaneous proximal sections reported from Vega Island.