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A proper understanding of the palaeoceanographic evolution of the Drake Passage during the Palaeogene is hampered by the lack of precise tools to date and correlate the sedimentary units of areas adjacent to the region. In this work, considering recently published radiometric U–Pb dates, we revised the age of a previous dinoflagellate zones for the middle to upper Eocene units of the Austral–Magallanes Basin. The quantitative analysis of middle to late Eocene dinoflagellate cyst assemblages from different localities close to the Drake Passage allowed us to reconstruct the palaeoenvironmental conditions and the possible surface ocean currents during this time in the area. Assemblages dated between 41.3 and 38.1 Ma represent relatively warm waters in inner shelf settings, while those ranged between 36 and 35 Ma reflect coastal areas with cool, nutrient‐rich surface waters. The proposed surface ocean circulation pattern, based on dinoflagellate cysts distribution between 41.3 and 38.1 Ma, agrees with the results of a palaeoclimatic numerical model simulation performed with a Drake Passage shallow opening of 100 m depth. At c. 36 Ma, several Antarctic gonyaulacacean taxa tolerant to relatively warmer waters were replaced by some Antarctic peridinacean species better adapted to colder conditions. This change could be linked to a progressive deepening of the Drake Passage that is estimated to have reached 1000 m depth promoting a cooling in the South Atlantic. Such passage depth would have enabled stronger flows from the Pacific to the Atlantic Ocean, which is reflected by the increase of cosmopolitan species. [ABSTRACT FROM AUTHOR]

The fossil record of chondrichthyans in Argentina is still poorly known. The aim of the present contribution is to describe teeth representing a chondrichthyan assemblage from Man Aike Formation (late Eocene) exposed in the Lago Argentino area, at Santa Cruz province, Argentina. This report includes Striatolamia macrota, Macrorhizodus praecursor, Carcharias sp., a possible member of the family Pristiophoridae, for the Argentine territory. Previous Eocene reports of Striatolamia macrota from Argentina are based on incorrect determination of specimens. The shark association, especially the abundance of lamniforms, may be indicative of litoral and shallow (less than 30 m depth) temperate to cold waters, as suggested by micropaleontological content. • For the first time a late Eocene chondrichthyan assemblage is described from Santa Cruz province, Argentina. • Striatolamia macrota , Macrorhizodus praecursor , Carcharias sp., and Pristiophoridae are reported. • Species here described are frequent in fish faunas from the North Atlantic seas. [ABSTRACT FROM AUTHOR]

An understanding of paleonvironmental and paleoceanographic evolution of the Southwestern Atlantic Ocean during the Palaeogene is prevented by the lack of precise tools to date and correlate the sedimentary units. Palynological samples collected in the upper portion of the Man Aike Formation, which crops out southern Lago Argentino area, in the southwest of the Austral Basin (50°21′45″S–72°14′30″W), contain well preserved marine organic dinoflagellate cysts, which are potentially important biostratigraphic and paleoenvironmental indicators. Herein we describe the composition of the Man Aike Formation's dinoflagellate cyst assemblages and compare them to similar assemblages collected in the same basin in the upper member of the Río Turbio Formation using Compositional Statistical Analysis. The dinoflagellate cyst assemblages from the upper part of the Man Aike Formation are highly correlated to the assemblages from the upper member of the Río Turbio Formation from outcropping sections (51°31′13″S–72°15′11″W) and with the lower part of sediment cores drilled by Yacimientos Carboníferos Fiscales in the Río Turbio Formation area. These dinoflagellate cyst assemblages show a very low correlation with the assemblages from the upper part of the Yacimientos Carboníferos Fiscales's cores. The comparison of our results with the high-resolution Southern Pacific Ocean dinoflagellate cyst zonation for the late Palaeocene to late Eocene allow us to date some of the dinoflagellate events recorded in formations of southwestern Patagonia. The assemblages from the Man Aike Formation and the lower part of the upper member of the Río Turbio Formation relate to the zones SPDZ11 and SPDZ12 and are assigned to the mid-middle Eocene (late Lutetian to early Bartonian). The biostratigraphy proposed herein constrains the age of the Man Aike Formation and equivalent units based on calcareous microfossil data, mollusks affinities and 87Sr/86Sr isotopic values to an age ranging between ∼42 and 39 Ma. The assemblages from the upper part of the upper member of the Río Turbio Formation relate to the SPDZ13 Zone, which corresponds to the late Eocene (early Priabonian). The dinoflagellate cyst assemblages indicate that they were under the influence of relatively warm, marine open waters in an inner-shelf environment for the lower part of the sections. In the upper part of the sections, the assemblages suggest shallow marine waters associated with coastal areas and high trophic levels, possibly as a result of freshwater inputs. [ABSTRACT FROM AUTHOR]

The Middle Eocene Man Aike Formation of southern Patagonia, Argentina, offers the opportunity to study the palaeoecological and palaeoenvironmental significance of Macaronichnus ichnofabrics in a tide-dominated, coastal embayment compound-dune complex. Four recurrent Macaronichnus ichnofabrics are recognized: Macaronichnus IF-1 characterized by Macaronichnus segregatis segregatis; Macaronichnus IF-2 with M. segregatis segregatis, Ophiomorpha nodosa, Skolithos linearis and rare Palaeophycus tubularis; Macaronichnus IF-3 typified by M. segregatis segregatis, O. nodosa, Asterosoma radiciforme and rare S. linearis; and Macaronichnus IF-4 consisting of M. segregatis segregatis, Nereites missouriensis, A. radiciforme, O. nodosa, Rosselia socialis, S. linearis, P. tubularis, Planolites isp. and Chondrites isp. Variations in these ichnofabrics are linked to changes in local hydraulic conditions in the upper and lower trough areas of the compound dunes. In high-energy, shallow and marginal marine environments, the Macaronichnus tracemaker is commonly the first to colonize the shifting, sandy substrates. Overprinting by other ichnoguilds occurs only after the physiochemical conditions became favourable and the colonization window length increases. [ABSTRACT FROM AUTHOR]

Abstract: Integration of sedimentologic, ichnologic and sequence-stratigraphic data supports that the upper member of the Río Turbio Formation records sediment accumulation in tide-dominated, outer-estuarine and coastal-plain environments. Outer-estuarine assemblages comprise facies that were deposited in channel-thalweg, subtidal-sandbar complex, oyster-reef and reef-margin environments. Coastal-plain facies assemblages include distributary-channel, floodplain, salt-marsh, swamp, and swamp margin deposits. Twelve ichnogenera assigned to soft-, stiff- and firmground suites were identified. Surfaces demarcated by autogenic and allogenic expressions of the Glossifungites Ichnofacies were recognized. The trace fossils Thalassinoides, Psilonichnus, and Bergaueria were documented within the autogenic stiffground suites, whereas Gastrochaenolites was found in both autogenic and allogenic firmground suites. Allogenically produced surfaces occur on a regional scale, creating major discontinuities, while minor autogenically produced surfaces extended laterally only over a few meters. Integrating the data derived from the substrate-controlled ichnofacies with the vertical and lateral distribution of the paleoecological data provided a more thorough understanding of the importance and scale of the erosional discontinuities. Estuarine and coastal-plain deposits contain low-diversity trace fossil assemblages inferred to have been produced by opportunistic, impoverished marine infauna, indicative of brackish-water settings. The overall distribution of ichnocoenoses within the lower portion of the upper member of the Río Turbio Formation appears to have been controlled largely by the salinity gradient, with other factors such as energy and sedimentation rate playing a more limited role. [Copyright &y& Elsevier]