The gaudryceratid ammonoids from the Upper Cretaceous of the James Ross Basin, Antarctica

We describe new material of the subfamily Gaudryceratinae in Antarctica, including five new species: Gaudryceras submurdochi Raffi and Olivero sp. nov., Anagaudryceras calabozoi Raffi and Olivero sp. nov., Anagaudryceras subcompressum Raffi and Olivero sp. nov., Anagaudryceras sanctuarium Raffi and Olivero sp. nov., and Zelandites pujatoi Raffi and Olivero sp. nov., recorded in Santonian to Maastrichtian deposits of the James Ross Basin. The early to mid-Campanian A. calabozoi Raffi and Olivero sp. nov. exhibits a clear dimorphism, expressed by marked differences in the ornament of the adult body chamber. Contrary to the scarcity of representative members of the subfamily Gaudryceratinae in the Upper Cretaceous of other localities in the Southern Hemisphere, the Antarctic record reveals high abundance and diversity of 15 species and three genera in total. This highly diversified record of gaudryceratins is only comparable with the Santonian–Maastrichtian Gaudryceratinae of Hokkaido, Japan and Sakhalin, Russia, which yields a large number of species of Anagaudryceras, Gaudryceras, and Zelandites. The reasons for a similar, highly diversified record of the Gaudryceratinae in these distant and geographically nearly antipodal regions are not clear, but we argue that they probably reflect a similar paleoecological control

The stratigraphy of Cretaceous mudstones in the eastern Fuegian Andes: New data from body and trace fossils

The stratigraphy of Cretaceous marine mudstones in the Fuegian Andes, roughly equivalent to Charles Darwin's clay-slate formation, remains a still unsolved problem. Previous records of Albian, Turonian-Coniacian, and Santonian-Campanian bivalves are combined with new findings of the Late Albian inoceramid Inoceramus anglicus Woods, and the Maastrichtian ammonites Diplomoceras sp., Anagaudryceras sp., Maorites densicostatus (Kilian and Reboul), Maorites sp., and Pachydiscus (Neodesmoceras) sp. to further constrain the Cretaceous stratigraphy of the eastern Fuegian Andes. In addition, new records of distinctive trace fossils and ichnofabric are meaningful for stratigraphic division and delineation of paleoenvironmental settings in these Cretaceous mudstones. The Lower Cretaceous ichnoassemblage of Chondrites targioni (Brongniart) and Zoophycos isp. is consistent with the inferred slope-volcaniclastic apron settings of the Yahgan Formation; Nereites missouriensis (Weller) reflects distal basin plain depositional settings for the Beauvoir Formation. In the Upper Cretaceous, the "Estratos de Buen Suceso" record the earliest extensively bioturbated horizons, reflecting prolonged well-oxygenated bottom conditions. In the Bahía Thetis Formation, organic-rich, channel margin or distal basin slaty mudstones record the last occurrence of inoceramid bivalves in the Austral Basin; the generalized absence of trace fossils is consistent with dysoxic bottom conditions. The thoroughly bioturbated Policarpo Formation, records a marked change in paleoceanographic conditions. The strong contrast in the intensity of bioturbation between the Upper Campanian-Maastrichtian Bahía Thetis Formation, almost devoid of trace fossils, and the highly bioturbated Maastrichtian-Danian Policarpo Formation reflects a change from dysoxic-anoxic to well ventilated conditions, probably associated with a cooling trend of bottom waters in the austral deep oceans.Fil:Olivero, E.B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Medina, F.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The Upper Cretaceous-Paleogene from the Río Bueno area, Atlantic coast of the Isla Grande de Tierra del Fuego

A composite section, 1400 m thick, is established for the Upper Cretaceous-Paleogene strata in the fold and thrust belt of the Andes Fueguinos, south of 54° 30′S. The basal Policarpo Formation, > 350 m thick, consists of tuffaceous sandstones and bioturbated sandstones and siltstones. The ammonites Maorites densicostatus and Diplomoceras sp.; foraminifera common to the Gaudryina healyi Zone; and the dynocysts Manumiella seelandica and Operculodium cf. azcaratei indicate a Maastrichtian age. The Paleocene to lower Eocene include four new formations. The Cabo Leticia Formation, c.150 m, Paleocene, consists of gravity flows deposits: brecchias; conglomerates; and massive, tuffaceous sandstones. La Barca Formation, c. 220 m, includes two members: LB1, tuffaceous sandstones and intercalated carbonaceous siltstones; and LB2, black mudstones with Palaeocystodinium golzowense and Spiroplectammina spectabilis. P. golzowense and the Bulimina karpatica Assemblage in LB1 indicate a late Paleocene age. Punta Noguera Formation, 380 m, is dominated by glauconite rich, massive, tuffaceous sandstones with interbedded turbidite packages. The dynocyst group Apectodinium, Deflandrea robusta, Palaeocystodinium sp., and Odontodinium askinae; the foraminifera Alabamina creta, Charltonina acutimarginata, Valvulineria teurensis and the first ocurrence of Elphidium and Cribrorotalia suggest an age near the Paleocene/Eocene boundary. The Cerro Ruperto Formation, 200 m, is dominated by glauconite rich, silty very fine sandstones and siltstones; dominance of Deflandrea dartmooria indicate an early Eocene age. Resting on angular unconformity, the Río Bueno Formation, c. 60-80 m, consists of carbonate rocks; its member RB1, rhythmically bedded grainstones, with the planktic foraminifera Planorotalites australiformis and Subbotina linaperta is of early middle Eocene age; and its member RB2, regular alternation of grainstones and bioturbated marls and micrites, with Elphidium saginatum and Bulimina cf. bortonica, is assigned to the mid middle Eocene. The sedimentary and stratigraphic features of the Maastrichtian/Eocene have a strong tectonic control, suggesting that the foreland phase of evolution of the basin has been active at least since the Maastrichtian.Fil:Olivero, E.B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Malumián, N. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Scasso, R.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Marine Phosphates in the Paleogene oflsla Grande de Tîerra del Fuego

Phosphate prospecting in marine sedimentary rocks of the Marginal and Austral basins of the Isla Grande de Tierra del Fuego resulted in the first discovery of phosphatic beds in the Paleogene Rio Claro Formation. Phosphatic anomalies of up to 20.1% P2U5 in concretions and up to 2% PaOs in bulk rock offer promising opportunities for systematic prospection on the Isla Grande de Tierra del Fuego. The phosphatic beds are conglomerates, coquinas and conglomeratic sandstones interbedded with thick mudstone packets. They belong to the condensed-type phosphatic beds, which are the product of erosion and reworking of concretions developed in fine sediments. Phosphate concretions containing glauconite, together with abundant glauconite in the same and closely associated beds, indicate a common syn-sedimentary to earlydiagenetic origin for both minerals, via recycling of sedimentary iron. This process occurred on a shelf with low sedimentation rates, pointing to high sea-level stands and marked interruptions in the sedimentation of the thick Paleogene sedimentary sequence of the Austral Basin . The deposit point to the existence and extension of this early Cenozoic phosphogenic episode to high latitudes in the Southern Hemisphere. © 1998 Asociacidn Geoldgica Argentina.Fil:Olivero, E.B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Scasso, R.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Miretzky, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The oldest elasmosaurs (Sauropterygia, Plesiosauria) from Antarctica, Santa Marta Formation (upper Coniacian? Santonian–upper Campanian) and Snow Hill Island Formation (upper Campanian–lower Maastrichtian), James Ross Island

Elasmosaurs are recorded for the first time in the Lachman Crags Member (Beta Member) of the Santa Marta Formation (lower Campanian) and in the Herbert Sound Member of the Snow Hill Island Formation (upper Campanian). These are the first elasmosaurids from James Ross Island, Antarctic Peninsula. These records greatly improve our knowledge of the taxonomic diversity of plesiosaurs of the Santa Marta Formation and Herbert Sound Member of the Snow Hill Island Formation, and extend the lower limit of the record of Elasmosauridae in Antarctica to the lower Campanian, making this the oldest record of an Antarctic elasmosaur