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The late Maastrichtian to early Paleocene marine successions in northern Patagonia and neighboring southwestern Atlantic Ocean Basins provided a valuable organic-walled dinoflagellate cysts record. Assemblages around the Cretaceous–Paleogene boundary and more pronounced in the Danian compare well with those coevals from lower latitudes sites (e.g. Brazil, Uruguay, Tunisia, Israel). Humid-warm climate prevailing in Patagonia together with counterclockwise oceanic circulation along the southwestern South Atlantic Ocean would have favored the exchange of taxa of the marine biota with lower-latitude basins, and helped to explain the similarities of the marine palynoflora from the southernmost part of South America and those from the widely separated Tethyan domains. Quantitative data of Danian dinoflagellate cyts assemblages from the north of Patagonia were used to infer palaeoecological and paleoenvironmental conditions in terms of nutrient availability, salinity, and coastal proximity, providing refined local paleogeography in an epicontinental context. Consistent with Tethyan sites records, assemblages from northern Patagonia exhibit high abundance or dominance of the presumed heterotrophic dinoflagellate cysts, denoting a globally nutrient - enrichment of the watermasses during the Danian. • Maastrichtian to Danian dinocysts reflect marine to freshwater environments in Patagonia. • High proportions of heterotrophic taxa indicated rich-nutrient watermasses. • Humid-warm climate would have favored the exchange of taxa with lower latitudes sites. [ABSTRACT FROM AUTHOR]

The well-exposed marine Eocene units from southwestern Patagonia, Argentina, contain useful information for reconstructing regional climate and oceanographic patterns in an area adjacent to the Drake Passage. The aim of this paper is to integrate dinoflagellate cyst data from three sections of the southwestern Austral Basin (Río Turbio Formation) to propose a zonation scheme, which can be applied to other southwestern Atlantic Ocean sites. Assemblages of organic walled dinoflagellate cysts have been analysed in different cropping-out sections and cores, showing the high potential of this fossil group as biostratigraphic markers. Comparison of dinoflagellate cyst events of the upper member of the Río Turbio Formation with calibrated biostratigraphic ranges in the Palaeogene South Pacific Ocean allowed us to date and correlate these sedimentary sections. The resulting zonation consists of four dinoflagellate cyst zones labelled RTF 1 to RTF 4, between the middle Lutetian and late Priabonian. As a final point, we applied dinoflagellate cyst species with importance as palaeoenvironmental markers to assess long-term climatic and oceanographic evolution for the area. This study shows that the endemic–Antarctic dinoflagellate cyst assemblage is dominant during the middle to late Eocene (RTF 1 to RTF 3), while a significant replacement of these taxa by cosmopolitan species characterizes the upper part of the upper member of the Río Turbio Formation (RTF 4). This turnover seems to be a consequence of changes in the ocean circulation patterns forced by deepening of the southern Atlantic gateways (the Drake Passage and the Tasman Gateway). [ABSTRACT FROM PUBLISHER]

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]

A major climate shift took place about 40 Myr ago—the Middle Eocene Climatic Optimum or MECO—triggered by a significant rise of atmospheric CO2 concentrations. The biotic response to this MECO is well documented in the marine realm, but poorly explored in adjacent landmasses. Here, we quantify the response of the floras from America's southernmost latitudes based on the analysis of terrestrially derived spores and pollen grains from the mid-late Eocene (~46–34 Myr) of southern Patagonia. Robust nonparametric estimators indicate that floras in southern Patagonia were in average ~40% more diverse during the MECO than pre-MECO and post-MECO intervals. The high atmospheric CO2 and increasing temperatures may have favored the combination of neotropical migrants with Gondwanan species, explaining in part the high diversity that we observed during the MECO. Our reconstructed biota reflects a greenhouse world and offers a climatic and ecological deep time scenario of an ice-free sub-Antarctic realm. Reconstructed floras from southernmost South America during the Middle Eocene Climate Optimum show the impact of this warming event on floral diversity. This reconstructed biota reflects a greenhouse world and offers a climatic and ecological deep time scenario of a sub-Antarctic region in the absence of ice. [ABSTRACT FROM AUTHOR]

The fossil record from Cenozoic sediments provides a great deal of information that has direct bearing on the early assembling of modern Patagonian ecosystems. In this synthesis, we revise selected fossil marine and terrestrial records from the last 66 Ma with the aim of understanding major shifts of Patagonian biotas. From the Paleocene to the mid Eocene this region supported outstandingly diverse terrestrial assemblages that show strong connections to modern-day Australasia (e.g. gum trees, casuarinas, monotremes). Nearshore marine biotas confirm peak warmth conditions, with tropical species with Tethyan affinities. The late Eocene and early Oligocene marks the onset of a period of overall regional cooling, drying, and increasingly variable ecological conditions. The rise of palm-dominated flammable biomes in hinterlands and the prevalence of Gondwanan gallery forest (e.g. southern beeches and podocarps) along river-sides supported the existence of mosaic habitats maintained by edaphic and regional climatic conditions. This shift in landscapes reflects the evolution of a wide range of herbivorous mammals (e.g. Notoungulata, Litopterna, and Astrapotheria). The late Oligocene and early-to-mid Miocene witnessed a dramatic modification of landscapes including the incursion of high sea-level episodes, the emergence of specialized coastal (i.e. salt-marsh) plant taxa and the expansion of large herbivorous mammals with predominantly high-crowned teeth (e.g. Notoungulata: Hegetotheriidae, Interatheriidae, and Mesotheriidae). The cooling trend of this interval was interrupted by a mid-Miocene transient warming event, with the dispersion of terrestrial (e.g. platyrrhine monkeys, palms) and marine (e.g. Tuberculodinium vancampoae) elements with tropical affinity into southernmost South American regions. Seasonally-dry conditions increased towards the end of the Miocene, yet subtropical species persisted either in terrestrial (e.g. malpighs, passion vines, capybaras), and marine (e.g. Subtropical and Caribbean molluscs) environments. The increasing aridity caused by the Andean uplift wiped out most of the forest species and promoted the diversification of open-habitat species; the emergence of the current grass-dominated Patagonian Steppe occurred later on, probably during the Quaternary. • Thermophilic (Caribbean/Tethyan) species were common to abundant in Patagonia during greenhouse conditions. • Biotas with predominantly Neotropical or Gondwanan distribution became strongly reduced or extinct across the Paleogene. • The increasing aridity and cooling trend of the late Neogene promoted the diversification of open-habitat species. [ABSTRACT FROM AUTHOR]