Micropaleontological assemblages from Ekelöf Point (Upper Cretaceous) of southeast james ross island, Antarctic Peninsula

Abstract

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. Thestudy is based on the analysis of foraminifera and palynomorphs from six fossiliferous samples of astratigraphic section (ca. 200 meters of thickness). This consists of dark grey siltstones and claystonesalternating with very thin indurated tuff levels and yellow claystones. At the top of the section acondensed horizon with concretions containing trace fossils interpreted as a maximum transgressiveevent is recognised. The foraminifera assemblage is characterised by benthic species. Except onesample, with only five specimens of the calcareous Gavelinella sandidgei (Brotzen) and one indeterminatefragment, the other ones are mainly composed of agglutinated species (70-80%). Bathysiphon, themost common genus in the section is dominant in different samples. Reticulophragmoides aff. jarvisi(Thalmann), Rzehakina minima (Cusman and Renz) and the calcareous species Gavelinella sandidgeiare also common. Furthermore, taxa from the following genera were recognised: Haplophragmoides,Reophax, Ammodiscus, Karreriella, Recurvoides, Dentalina, Lingulonodosaria and Lagena. Althougha few samples are suitable for suggesting only tentative conclusions, epibenthic foraminifera aredominant and the agglutinated ones dominated by species with tubular morphology suggest atranquil bathyal palaeoenvironment. It is noteworthy the taxonomical change in a sample justbelow the concretional level with a dominance of Spiroplectammina chicoana together with deeperinfauna (Reophax). Considering that Spiroplectammina is a genus characteristic of shelf and marginalmarine environments, a decrease in water-depth or a down-slope transport of shelf foraminiferacould be possible explanations of such change. Palynomorphs are abundant in all levels and consistof dinocysts, pollen and spores in variable amounts. The continental palynomorphs represents 21to 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 Isabelidinium/Manumiella complex, which are commonin proximal marine environments. Palaeoenvironmental interpretations based on foraminiferaare consistent with sedimentological studies which indicate an outer-shelf palaeoenvironment,evidenced by a monotonous sedimentary succession produced by sediment fallout with occasionalash fall from a volcanic arc. The dominance of peridinacean cysts and the continuous terrigenousinput can be explained by the existence of a short shelf where the material quickly runs down theslope and would be deposited in the deep marine environment.