Stratigraphy, sedimentology and paleontology of Upper Cretaceous deposits of Day Nunatak, Snow Hill Island, Antarctica
By Thomas S. Tobin, David Flannery, and Francis J. Sousac
Summarized by Michael de Koter.
What type of data were used? Newly exposed outcrop on Day Nunatak, a region of sedimentary rock in Snow Hill Island of Antarctica, which was previously inaccessible to the sediments and fossils in the area. Most of these fossils were collected from off the ground, but where possible, they were extracted from in situ (in place). Aerial photography allowed for three-dimensional reconstruction of the area to track glacial ice movement. Hand samples collected in the field underwent petrological and SEM (scanning electron microscope) analysis to determine composition and characteristics.
Methods: Helicopters were used to access the field site where samples were collected by hand from trenches and outcrops. Structure by motion models were also created using data gathered by helicopters equipped to carry out three dimensional analysis. XRD (X-ray diffraction) analysis, petrological analyses via light and electron microscopy, and stable isotope analyses were carried out to learn more about the samples collected from Day Nunatak.
Results: Overall, the fossils and sediments found and tested in the newly exposed outcrops of Day Nunatak are very similar to samples found in previous studies done on nearby Seymour Island of Antarctica. However, the mode of fossil preservation is variable across these outcrops, with fossils being more prevalent and found in pale concretions in Day Nunatak. For the majority of Snow Hill Island, reddish concretions around fossils are more common, though they occur in a lower frequency. No new species were discovered amongst the fossils in the newly exposed area of Day Nunatak. There was an abundance of Gunnarites collected to represent ammonite fossils from the area. Furthermore, there were no new species of mollusks or other types of fossils identified in the samples collected. Most of the sediments of the Day Nunatak sight are composed of quartz-rich sandy-siltstone that play host to carbonate concretions and well-cemented sandstone.
Why is this study important? The study of newly exposed segments of Antarctician stratigraphy allows for a more comprehensive geological history of the region to be created. Fossils and sediments found in the area- especially those that match other nearby regions of Antarctica- provide a wider range of evidence to link identical beds in different geographical areas together more thoroughly and, in so doing, provide a more comprehensive understanding of the region and its history.
The Big Picture: As more of the glacial ice in Antarctica is melting away as a result of global temperature rise, areas previously inaccessible to geologists for study will become more and more available to study. These changes in the observable regions of the continent will allow for stratigraphically relationships to paint a larger picture of the geologic history of the area. This study is one of the first of such that will be possible as glacial ice continues to recede. Thus far, the data demonstrates regional trends in biostratigraphy that are traceable across much of the larger area surrounding Day Nunatak, which helps to paint a more accurate cross section than was available even ten years ago.
Citation: Tobin, T.S., Flannery, D. and Sousa, F.J., 2018. Stratigraphy, sedimentology and paleontology of Upper Cretaceous deposits of Day Nunatak, Snow Hill Island, Antarctica. Cretaceous Research, 84, pp.407-419.