MICROPALEONTOLOGICAL ASSEMBLAGES FROM EKELÖF POINT (UPPER CRETACEOUS) OF SOUTHEAST JAMES ROSS ISLAND, ANTARCTIC PENINSULA

CARAMÉS, A; AMENABAR, C.; SANTOS, A.; CONCHEYRO, A

Mendoza

Congreso; 4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS; 2014

International Paleontological Association

A micropaleontological analysis of a sedimentary succession from the Rabot Formation (Upper Cretaceous) at Ekelöf Point, southeast of James Ross Island, Antarctic Peninsula, is here presented. This unit was dated as late Campanian-early Maastrichtian, based on ammonites and dinocysts. The study is based on the analysis of foraminifera and palynomorphs from six fossiliferous samples of a stratigraphic section (ca. 200 meters of thickness). This consists of dark grey siltstones and claystones alternating with very thin indurated tuff levels and yellow claystones. At the top of the section a condensed horizon with oncretions containing trace fossils interpreted as a maximum transgressive event is recognised. The foraminifera assemblage is characterised by benthic species. Except one sample, with only five specimens of the calcareous Gavelinella sandidgei (Brotzen) and one indeterminate fragment, the other ones are mainly composed of agglutinated species (70-80%). Bathysiphon, the most common genus in the section is dominant in different samples. Reticulophragmoides aff. jarvisi (Thalmann), Rzehakina minima (Cusman and Renz) and the calcareous species Gavelinella sandidgei are also common. Furthermore, taxa from the following genera were recognised: Haplophragmoides, Reophax, Ammodiscus, Karreriella?, Recurvoides, Dentalina, Lingulonodosaria and Lagena. Although a few samples are suitable for suggesting only tentative conclusions, epibenthic foraminifera are dominant and the agglutinated ones dominated by species with tubular morphology suggest a tranquil bathyal palaeoenvironment. It is noteworthy the taxonomical change in a sample just below the concretional level with a dominance of Spiroplectammina chicoana together with deeper infauna (Reophax). Considering that Spiroplectammina is a genus characteristic of shelf and marginal marine environments, a decrease in water-depth or a down-slope transport of shelf foraminifera could be possible explanations of such change. Palynomorphs are abundant in all levels and consist of dinocysts, pollen and spores in variable amounts. The continental palynomorphs represents 21 to 72% of the whole assemblage and indicate a continuous terrestrial influx to the marine basin. The dinocyst assemblage is dominated by peridiniacean taxa including Isabelidinium cretaceum (Lentin and Williams), Isabelidinium spp. and sabelidinium/Manumiella complex, which are common in proximal marine environments. Palaeoenvironmental interpretations based on foraminifera are consistent with sedimentological studies which indicate an outer-shelf palaeoenvironment, evidenced by a monotonous sedimentary succession produced by sediment fallout with occasional ash fall from a volcanic arc. The dominance of peridinacean cysts and the continuous terrigenous input can be explained by the existence of a short shelf where the material quickly runs down the slope and would be deposited in the deep marine environment.