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This study describes the compositional changes of Mesozoic-Cenozoic palynologic assemblages in Patagonia, the succession of phytogeographic scenarios and some evolutionary key events. The Triassic 'Ipswich Microflora', characterized by bisaccate pollen and high frequencies of trilete spores, represents the warm-temperate province of south-western Gondwana (Dicroidium Flora), followed in time, in Patagonia, near the Triassic/Jurassic boundary, by the 'Classopollis Microflora', indicating warm and (seasonal) arid conditions. Araucariaceans and podocarpaceans grew on Jurassic uplands. The exclusively Early Cretaceous taxa Cyclusphaera and Balmeiopsis (Coniferae) appeared in the Valanginian. The oldest angiospermous pollen types of Argentina appear in the Barremian-Aptian of southern Patagonia. During the Maastrichtian, the Nothofagaceae and Myrtaceae are incoming. In the Palaeocene, a vegetation dominated by tropical elements would have developed in Patagonia. Increasing Nothofagidites frequency in northern Patagonia during the Middle to Late Eocene indicates climatic change from warm to temperate. Of three Early to Middle Miocene phytogeographic provinces (NeotropicalTransitional and Austral), the Transitional one was replaced during the Late Miocene-Pliocene by the xerophytic Proto Espinal/Steppe with a shrubby-herbaceous vegetation. The Pleistocene and Holocene times were characterized by frequent latitudinal and altitudinal changes in the vegetation distribution, as a response to recurrent climatic oscillations, fluctuations of sea level and ice extent, and changing patterns of atmospheric circulation.

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Paleolimnological data are presented relating trophic development to sea level variation in Lake Blanca, a small (0.6 km 2 ), coastal fresh waterbody in southern Uruguay. Using a sediment core that extended to 7300 years BP, analyses of grain size, thin sections, organic matter, carbonate, total carbon, nutrients, diatoms and palynomorphs, allowed us to infer changes in trophic state and paleosalinities, which were closely related to Holocene sea level variation. Higher trophic states were observed during regressive events, most probably due to increases in runoff and erosion as regression progressed. Four diatom association zones (DAZ) were identified in the sediment core. The basal core section pre-dated the first Holocene marine transgression, contained no diatoms, chrysophyte cysts or non-siliceous microalgae, and showed C/N ratios values higher than 20. Thus, it is likely that the system exhibited terrestrial characteristics. In the second section ($6500-2200 years BP, following the first Holocene transgression), there was dominance of marine/ brackish diatom species. The lowest trophic states of the core were observed in this section. The third section (2200-1100 years BP), represented the system as it became separate from the Atlantic Ocean, and showed a dominance of brackish/freshwater species and increases in trophic state were observed. In the last section (after 1100 years BP), the system became fully freshwater as no marine or brackish diatom species were found, but a trend to oligotrophication was observed, probably due to nutrient depletion. However, after $1967 AD, eutrophication intensified because of forestry and soil fertilization in the catchment. Pollen association zones (PAZ) allowed us to identify four sections. Below 250 cm (2200 years BP), the core contained no pollen grains as redox potential and pH values were not conducive for pollen preservation. After 2200 years BP (when the system started to separate from the ocean), xerophilic taxa typical of coastal dunes colonized the catchment. Only after $1100 years BP (after fully freshwater conditions established) pollen grains of trees were observed.

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The Cañadón Asfalto basin, central Chubut, Argentina, comprises a volcano-sedimentary sequence related to the opening of the Atlantic Ocean during Mesozoic times. The Lonco Trapial, Cañadón Asfalto and Cañadón Calcáreo formations are the main units related to the evolution of this basin. The Las Chacritas and Puesto Almada members are distinguished in the Cañadón Asfalto Formation. LA-HR-ICP-MS U-Pb and Lu-Hf data on zircon were obtained on these units. The Lonco Trapial Formation gave a weighted average age of 172.3±1.8 Ma. A pyroclastic level from the Las Chacritas Member gave a weighted average age of 168.2±2.2 Ma. Two U-Pb concordant ages of 160.3±1.7 Ma on a laminated tuffite and 158.3±1.3 Ma on a pyroclastic level were obtained for the Puesto Almada Member. Two maximum depositional ages constrain the sedimentary provenance areas for the basin: 1) A sample from the Sierra de la Manea range, where a