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The Paraná Basin (1 600 000 km2) is the largest intracratonic basin in southern South America and contains a thick (1300 m) Permo‐Carboniferous glacial succession (the Itararé Group). This paper describes over 1700 m of drill core recovered during recent exploration for oil and gas. Itararé Group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones, and massive and laminated mudstones. Facies are interpreted as the product of sediment gravity flows in a glacially influenced marine basin. Three stratigraphic formations can be defined across the basin, each consisting of a lowermost sandstone‐rich member overlain by a diamictite‐rich member. Examination of Itararé Group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes. Primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincided with the eastern basin margin during deposition of the Itararé Group. Ice masses fringing the eastern (southern African) and western (Bolivian) basin margins supplied sediment to the basin in the form of fluvio‐glacial deltas, fans and floating ice tongues. This sediment was then resedimented downslope as debris flows and turbidites. Both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step‐wise expansion by outward faulting within Late Proterozoic mobile belts. The position of successive basin margins can be related to specific lineament structures in the underlying basement. Asymmetric expansion of the Paraná Basin occurred along the northern and southern basin margins during deposition of the Itararé Group; this expansion probably reflects shallow crustal adjustments activated by collisional movements along the Andean margin of South America during the Hercynian Orogeny.

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The study of microbial carbonates has acquired new significance with the recognition that they retain valuable information related to biomineralization processes associated with microbial activity throughout geological time. Additionally, microbialites have a demonstrated economic potential to serve as excellent hydrocarbon reservoirs. The Lower Cretaceous Cod o Formation, located in the Parnaiba Basin of north-east Brazil, comprises a unique stratigraphic sequence of up to 20 m thick, well-preserved carbonate microbialites. Deposited in a continental basin during the initial break up and separation of South America from Africa in the Early Cretaceous, this lacustrine carbonate sequence provides an excellent example to investigate the palaeoenvironmental conditions controlling microbialite facies development. Based on macroscopic and microscopic observations of outcrop and drill core samples, four microbialite facies (stromatolite, lamina, massive and spherulite) were defined and distinguished by textures and microbial fossil content. Changes in facies type are related to alternating palaeo-water depths, as reflected by 87 Sr/ 86 Sr cycles resulting from fluctuations in the sources of meteoric water. Clumped isotope measurements of stromatolitic fabrics yield precipitation palaeo-temperatures with an average value of 35°C. The d 18 O values of bulk carbonate (À6Á8 to À1Á5& Vienna Pee Dee Belemnite) imply precipitation from water with calculated d 18 O values between À1Á6& and 1Á8& Vienna Standard Mean Ocean Water, reflecting precipitation from variably modified meteoric waters. The d 13 C values of bulk carbonate (À15Á5 to À7Á2& Vienna Pee Dee Belemnite) indicate a significant input of carbon derived from aerobic or anaerobic respiration of organic matter. Combined, the data indicate that the evolution of the Cod o Formation occurred in a closed lacustrine palaeoenvironment with alternating episodes of contracting and expanding lake levels, which led to the development of specific microbialite facies associations. The results provide new insights into palaeoenvironmental settings, biogenicity and early diagenetic processes involved in the formation of ancient carbonate microbialites and, by extension, improve the knowledge of the reservoir geology of correlative units in deep waters offshore Brazil. 155

Lapa and Vila Velha sandstones (Itararé Group) crop out in the eastern border of the Paraná basin in an area about 7,500 km 2 in Paraná State, southern Brazil. The morphology of the Lapa Sandstones is linear extending for 65km, its about 800m wide and bounded by diamictites, rhythmites, and shales of the Lagoa Azul Fm. The Lapa sandstones are herein interpreted as subaquous channel-filling. The Vila Velha sandstones occur as subhorizontal plateaus overlying shales of the Lagoa Azul Fm. They are herein interpreted as shallow subaquous lobes. Ten sedimentary facies were identified: four of them are made up of sandstones, three are conglomerates, and three are composed of shales and diamictites. The sandstones and conglomerates, the main subject of this work, were deposited by high-to-very high-sediment gravity flows issued from glaciers. There are, however, evidence of hydrodinamic flows suggesting a shallow depositional environment where both, gravitational and hydrodinamic mechanisms/processes, were present stacking a complex conglomerate-sandstone package, not yet well understood. The channel was developed as an incised valley during lowstand sea level, when shales and diamictites of the Lagoa Azul Fm were exposed and partially eroded. A sequence boundary was then created. The lobe deposition, as well as the channel filling comprise, respectively, the late lowstand and transgressive systems tract. Seismic surveys and oil well data show the presence of such channels as deep as 3,000 m. One of them was drilled and had gas and condensate subcommercial flows in drill stem tests.

ABSTRACT:The Late Paleozoic Ice Age is recorded in the Paraná Basin as glacial deposits, deformational features and ice-related erosional landforms of the Itararé Group. Erosional landforms are often employed to build paleogeographic models that depict the location of ice masses and paleo ice-flow directions. This paper provides a review of the literature and new data on micro-to meso-scale ice-related, erosional landforms of the Paraná Basin. Examined landforms can be placed into four broad categories based on their mode of origin. Subglacial landforms on rigid substrates occur on the Precambrian basement or on older units in the Paraná Basin. They include streamlined landforms and striated pavements formed by abrasion and/or plucking beneath advancing glaciers. Subglacial landforms on soft beds are intraformational surfaces generated by erosion and deformation of unconsolidated deposits when overridden by glaciers. Ice-keel scour marks are soft-sediment striated/grooved landforms developed by the scouring of free-floating ice masses on underlying sediments. Striated clast pavements are horizons containing aligned clasts that are abraded subglacially due to the advance of glaciers on unconsolidated deposits. Only those erosional landforms formed subglacially can be used as reliable paleo ice-flow indicators. Based on these data, the paleogeography of the Paraná Basin during the Late Paleozoic Ice Age fits into a model of several glacial lobes derived from topographically-controlled ice spreading centers located around the basin instead of a single continental ice sheet. KEYWORDS:Late Paleozoic Ice Age; Itararé Group; glacial erosion; paleogeography. RESUMO: A Era Glacial Neopaleozoica está registrada na Bacia do Paraná através da sucessão sedimentar do Grupo Itararé e unidades correlatas, bem como por feições glaciotectônicas e formas de leito erosivas relacionadas à ação do gelo. Formas de leito erosivas são comumente utilizadas em análises paleogeográficas visando evidenciar o sentido de fluxo de geleiras e localizar antigos centros irradiadores de gelo. Neste trabalho é apresentada uma revisão da literatura e novos dados sobre formas de leito erosivas de micro a mesoescala

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