Sergio N. Santillana

Provenance, environmental and paleogeographic controls on sandstone composition in an incised-valley system: the Eocene La Meseta Formation, Seymour Island, Antarctica

Abstract The Eocene La Meseta Formation is the youngest exposed unit of the back-arc James Ross Basin, Antarctic Peninsula, cropping out in Seymour (Marambio) Island. The formation comprises 720 m of clastic sedimentary rocks of deltaic, estuarine and shallow marine origin. It was subdivided into six unconformity-based units (Valle de Las Focas, Acantilados, Campamento, Cucullaea I, Cucullaea II and Submeseta Allomembers) grouped into three main facies associations. Facies association I represents valley-confined deposition in a progradational/aggradational tide-dominated and wave-influenced delta front/delta plain environment. Facies association II includes tidal channels, mixed tidal flats, tidal inlets and deltas, washover and beach environments. Facies association III represents nonconfined tide- and storm-influenced nearshore environments. La Meseta Formation sandstones are quartzofeldspathic with some hybrid arenites (glauconite and carbonate bioclasts-rich). Sandstone detrital modes are subdivided into two distinctive petrofacies: the low quartz petrofacies (petrofacies I, Q 12%), interpreted to retain the original provenance signal, and the high quartz petrofacies (petrofacies II, Q>55% and L 1.4) is clearly dominated by volcanic-derived clasts; it developed at times of high sea level and/or during later stages of the valley fill, when an “energy fence” at the shoreline prevented delivery of sediment from the Antarctic Peninsula, thus enhancing the relative participation of local volcanic sources.

Record of Late Miocene glacial deposits on Isla Marambio (Seymour Island), Antarctic Peninsula

Abstract We report and describe two new small diamictite outcrops on Isla Marambio (Seymour Island), Antarctic Peninsula. These rocks rest on an erosional unconformity on top of the Eocene La Meseta Formation and are unconformably covered by glaciomarine rocks of the ?Pliocene–Pleistocene Weddell Sea Formation. The lithology, fossil content and isotopic ages obtained strongly suggest that the rocks belong to the Hobbs Glacier Formation and support a Late Miocene age for this unit. Additionally, the dated basalt clast provides the oldest age (12.4 Ma) for the James Ross Island Volcanic Group recorded up to now. The here described diamictite cannot be confidently correlated with a glaciomarine unit previously assigned to the Late Eocene–Lower Oligocene taken as proof that initial expansion of ice on Antarctica encompassed the entire continent synchronously in the earliest Oligocene. However, it is now evident that there are likely to be more, short but important, stratigraphic sequences of key regional and Antarctic wide interest preserved on the plateau of Isla Marambio.

A new Eocene crab (Crustacea, Decapoda) from Seymour Island, Antarctica

A new xanthid crab, Tumidocarcinus foersteri n. sp. is described from the La Meseta Formation on Seymour Island, Antarctica. The fossils were obtained from the Allomember Submeseta of Late Eocene age. As other representatives of the genus Tumidocarcinus were only known from New Zedand and Australia, this finding provides new insights on the palaeobiogeography of high latitude faunas during the Early Tertiary.

Eocene ungulate mammals from West Antarctica: implications from their fossil record and a new species

Abstract Here we describe a new terrestrial mammal from the Eocene of Seymour Island (Isla Marambio) represented by a lower left third molar and assigned to a new species of Sparnotheriodontidae, an ungulate family with a broad palaeobiogeographical distribution in South America. The specimen was found in the Cucullaea I allomember of the La Meseta Formation, in a new mammalian locality (IAA 2/16). Notiolofos regueroi sp. nov. shares a brachyodont, lophoselenodont and bicrescentic molar pattern with N. arquinotiensis, recorded for a stratigraphic sequence of 17.5 Ma in Antarctica. The criteria for the species differentiation are the absence of mesial and labial cingulids, the larger paraconid, the wider talonid basin, the accentuated distal projection of the hypoconulid, the centroconid development and the smaller size. Together with the astrapotherian Antarctodon sobrali, they represent the medium to large terrestrial mammals of the early Eocene Antarctic landscape that was mostly dominated by closed forests of Nothofagus. Dental wear facets and differences in their body mass are inferred and discussed as possible evidence of niche differentiation. Additionally, the presence of land mammals with Patagonian affinities in the Eocene of Antarctica reinforces the Cretaceous–Palaeocene presence of the Weddellian Isthmus, a functional land corridor between Antarctica and South America.

A new elasmosaurid from the upper Maastrichtian López de Bertodano Formation: new data on weddellonectian diversity

O’Gorman, J.P., Panzeri, K.M., Fernández, M.S., Santillana, S., Moly, J.J. & Reguero, M. July.2017. A new elasmosaurid from the upper Maastrichtian López de Bertodano Formation: new data on weddellonectian diversity. Alcheringa 42, 575-586. ISSN 0311-5518. Elasmosaurids are one of the most frequently recorded marine reptiles from the Weddellian Province (Patagonia, Western Antarctica and New Zealand). Improvements in our knowledge of elasmosaurid diversity have been problematic because of their conservative postcranial morphology. However, recent studies have helped to improved our understanding of the diversity of this group. Here, a new elasmosaurid specimen from the upper Maatrichtian horizons of the López de Bertodano Formation, Antarctica, MLP 14-I-20-16, is described. MLP 14-I-20-16 is one of the youngest non-aristonectine weddellonectian elasmosaurids from Antarctica. We confirm the coexistence of aristonectine and non-aristonectine elasmosaurids in Antarctica until the end of the Cretaceous. MLP 14-I-20-16 shows distinctive short and broad posterior cervical vertebrae, a feature only shared among the weddellonectian elasmosaurids by the Maastrichtian Morenosaurus stocki, although the same vertebral proportions are also recorded for the giant Cenomanian elasmosaurids Thalassomedon haningtoni. Comparison between MLP 14-I-20-16 and other elasmosaurids from the Maastrichtian of Antarctica indicates that at least two different non-aristonectine elasmosaurids were present in Antarctica during the late Maastrichtian. José P. O’Gorman, [joseogorman@fcnym.unlp.edu.ar], División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA, La Plata, Argentina, CONICET, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina; Karen M. Panzeri[panzerikaren@gmail.com], División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA, La Plata, Argentina; Marta S. Fernández [martafer@fcnym.unlp.edu.ar], División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA, La Plata, Argentina; CONICET, Sergio Santillana [ssantillana@dna.gov.ar], Instituto Antártico Argentino, 25 De Mayo 1143, San Martín Provincia De Buenos Aires, Argentina; Juan J. Moly [juanjomoly@fcnym.unlp.edu.ar], División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA, La Plata, Argentina; Marcelo Reguero[mreguero@dna.gov.ar], División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA, La Plata, Argentina; Instituto Antártico Argentino, 25 De Mayo 1143, San Martín Provincia De Buenos Aires Argentina.