Micropaleontological assemblages from Ekelöf Point (Upper Cretaceous) of southeast James Ross Island, Antarctic Peninsula

CARAMÉS, ANDREA; AMENABAR, CECILIA ,R.; SANTOS, ALESSANDRA; CONCHEYRO, ANDREA

Mendoza

Congreso; 4th International Paleontological Congress; 2014

International Paleontological Association, CONICET

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 dinoflagellates cyst. The study comprises findings 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 concretions containing trace fossils interpreted as a maximum transgressive event is recognised. 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 by agglutinated species (70-80%). Bathysiphon, the most frequent 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. Below the concretional level, Spiroplectammina chicoana (Lalicker) is dominant. Furthermore, taxa from the following genera were recognised: Haplophragmoides, Reophax, Ammodiscus, Karreriella?, Recurvoides Dentalina, Lingulonodosaria and Lagena. Although the few samples are suitable for suggesting only tentative conclusions, epibenthic foraminifera are dominant and the agglutinated ones dominated by species with tubular morphology, indicate a tranquil bathyal palaeoenvironment. Particularly, being Spiroplectammina a genus from shelf and marginal marine environments, would be probably that the dominance of S. chicoana in the section, could be related to an extended highstand sea level that allow to Spiroplectammina change to deeper habitat. Palynomorphs are abundant in all levels and consist of marine (dinoflagellate cysts) and continental (pollen and spores) taxa in variable amounts. Strong fluctuations of the marine vs. continental curve indicate a continuous terrestrial influx to the basin. The analyzed section is dominated by peridiniacean cyst, including Isabelidinium cretaceum (Lentin and Williams), Isabelidinium spp. and Isabelidinium/Manumiella complex. The dominance of peridiniacean cyst indicates a proximal marine environment. Palaeoenvironment interpretation based on foraminifera matches with sedimentological studies which indicate an outer-shelf palaeoenvironment, evidenced by the monotonous sedimentary sequence product of decantation with occasional ash fall from the volcanic arc. The dominance of peridinacean cysts and the continuous terrigenous input evidenced by continental palynomorphs can be explained as the existence of a short shelf where the material quickly runs down the slope and would be deposited in the deep marine environment.