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Marine sedimentary rocks of the lower Miocene Monte León Formation of southeastern Patagonia (Austral Basin), Argentina are important geological archives for better understanding regional tectonics, paleoenvironments, oceanography, and climate. In this paper, we describe assemblages of invertebrates, palynomorphs, foraminifera, ostracods and calcareous nannofossils in a stratigraphical and sedimentological framework, which suggest deposition during a transgressive-regressive cycle. From base to top, the lowermost outcropping deposits of the Punta Entrada Member represent an inner shelf environment, formed during a transgressive phase. The zone of maximum flooding is marked by a high diversity of protoperidiniaceans (heterotrophic) and offshore dinoflagellate cysts, an increase in the percentage and size of planktonic foraminifera, and a decrease in shallow water benthic foraminifera. Regressive deposits in the upper part of the Punta Entrada Member exhibit a progradational stratal stacking pattern and are characterized by an upward decrease in bioturbation and in the content of marine invertebrates; the dinoflagellate cyst assemblages point toward shallower and more restricted marine conditions than in underlying deposits. The cycle ends with the Monte Observación Member, which contains an impoverished and mostly reworked fauna of invertebrates. The presence of monospecific reefs of Crassostrea orbignyi , the decrease in dinoflagellate cysts and calcareous microfossils diversity, and the increase of continental palynomorphs suggest progressively shallower conditions and increasing influence of freshwater discharge. Although eustatic controls could have contributed to the sedimentary evolution of the Monte León Formation, the upward regressive trend is interpreted as the result of tectonism linked to the Andean orogeny, which led to the uplift, exhumation, and erosion of the highlands in the west. This is supported by the abundance of pyroclastic material, together with reworked specimens of Upper Cretaceous forams and Upper Cretaceous and middle Eocene dinoflagellate cysts in the upper part of the Punta Entrada Member and in the Monte Observación Member. • Multiproxy data indicate that study rocks represent a transgressive-regressive cycle. • A maximum flooding and/or higher organic flux zone was identified at the coastal cliffs. • The regressive trend was the result of tectonics, sediment supply dynamics, and volcanism. • Cretaceous/Eocene forams and dinocysts evidence exhumation and reworking from the Andes. [ABSTRACT FROM AUTHOR]

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]

Palynology of the Neogene marine stratigraphic sequences in tropical latitudes is poorly studied Most studies focus on lower to middle Miocene deposits in the Caribbean, emphasizing the biostratigraphic value of dinoflagellate cysts. The palynological and calcareous nannofossil analysis of 50 samples from DSDP Hole 502A and their integration with the paleomagnetic and planktonic foraminifera data reveal a detailed and reliable chronostratigraphic framework, and the interpretation of the paleobathymetric and paleoenvironmental evolution of the sequence. Fossil content in a continuous late Tortonian to late Gelasian (~7.56-1.80 Ma) sequence of deep-marine sediments serves to calibrate ages of dinoflagellate cysts, and comparison with high latitude records reveals synchronous (Operculodinium janduchenei, Selenopemphix dionaeacysta, Barssidinium taxandrianum, and Lejeunecysta interrupta) and asynchronous events (Quadrina? condita) with biostratigraphic potential for the southwestern Caribbean Sea. Our results highlight the importance of analyzing continental palynomorphs in deep-marine deposits to increase the temporal resolution of future palynostratigraphic schemes. Micropaleontogical data indicate a lower bathyal–abyssal environment and four paleoceanographic settings defined by changes in surface water productivity. These intervals fluctuate from mesotrophic-oligotrophic (~7.56–6.31 Ma) to eutrophic (~6.18–4.98 Ma), oligotrophic (~4.74–3.41 Ma), and mesotrophic surface water conditions (~3.26–1.80 Ma). Changes in trophic conditions are strongly related to the paleoceanographic reorganization associated with the constriction and complete closure of the Central American Seaway, seasonal upwelling episodes, and the input of terrigenous organic matter probably transported from southern Central America and northern South America by turbidity currents. • First palynological study of Late Neogene SW Caribbean Sea deposits. • A new age model was proposed for DSDP Hole 502A. • Two high latitude dinoflagellate cysts were recorded for the first time in tropical latitudes. • A trophic and paleobathymetric model was proposed for the southwestern Caribbean Sea. [ABSTRACT FROM AUTHOR]