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The Paraná Basin, the largest basin in South America, received glacially derived sediments during the Late Palaeozoic Ice Age (LPIA) of the Gondwana supercontinent.Despite the importance of this basin for understanding the continental development of the Gondwana glaciation, and the fact that ca. 95% of this basin is not exposed at the surface, few attempts have been made to connect the exposed glacial strata to the subsurface record. In this paper, exposures of glacial cycles in the Upper Itararé Group in Santa Catarina State, southern Brazil, are analyzed, locally correlated and then linked to the three major glacial cycles previously described from subsurface studies along the basin. Together study areas (Doutor Pedrinho and Vidal Ramos) record five, partially comparable shorter glacial subcycles (relative to the major glacial cycles). These series comprise coarse-grained subaqueous outwash deposits, turbidite sand sheets, marine shales, and diamictites, the latter mostly derived from delta slope failure and ensuing resedimentation. In addition to sedimentological and genetic stratigraphic description and analysis, preliminary age determination based on the palynological content is also presented. Besides, a regional correlation of the described succession to the subsurface record is proposed based on well logs and core information. All the palynomorph associations identified from the exposed successions, which represent the upper third part of the Itararé Group, are related to the Subzone Protohaploxypinus goraiensis, base of the Vittatina costabilis Zone. This zone and correlated ones along the Gondwana are considered Early Permian in age. However, a first isotopic age recently obtained for the upper Itararé Group and published elsewhere is considered within a regional stratigraphic framework once it leads to new insights in terms of the LPIA time span recorded in the Paraná Basin.

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Four megabeds (I to IV) were recognized throughout the Cerro Bola inlier, a glacially influenced depositional area of the Carboniferous Paganzo Basin, south-western La Rioja Province, Argentina. Such anomalous thick beds are associated with the collapse of an unstable basin margin after periods of large meltwater discharge and sediment accumulation. Failure of these previously deposited sediments triggered mass flows and associated turbidity currents into the basin. Megabed I is up to 188 m thick and was deposited during a transgressive stage by re-sedimentation of ice-rafted debris. Also part of the transgressive stage, Megabeds II, III and IV are up to 9 m thick and are associated with a dropstone-free period of flooding. Megabeds were subdivided into three divisions (1 to 3) that represent a spectrum of flow properties and rheologies, indicative of a wide range of grain support mechanisms. These divisions are proposed as an idealized deposit that may or may not be completely present; the Cerro Bola megabeds thus display bipartite or tripartite organization, each division inferred to reflect a rheologically distinct phase of flow. Division 1 is a basal layer that consists of clast-supported and matrixsupported, pebble conglomerate, rarely followed by weak normally graded to ungraded, very coarse-to coarse-grained sandstone. This lower interval is interpreted to be the deposit of a concentrated density flow and is absent in bipartite megabeds. Division 2 is represented by a mud-rich sandstone matrix with dispersed granule to pebble-size crystalline and mudstone clasts. It also includes fragments of sandstone up to boulder size, as well as rafts of cohesive muddy material and wood fragments. Division 2 is interpreted to be a result of debris-flow deposition. A debrite-related topography, resulting from the freezing of high yield strength material, captures and partially confines the succeeding upper division 3, which fills the topographic lows and pinches out against topographic highs. Division 3 is rich in mudstone chips and consists of very coarse-grained, dirty sandstones grading upward to siltstones and mudstones. It is interpreted to be a deposit of a co-genetic turbidity current. Spectral gamma ray and petrographic analyses indicate that both debrite and co-genetic turbidite have high depositional mud content and are of similar composition. One of the megabeds is correlated with an initial slumpderived debris flow, which suggests that the mass flow becomes partitioned both at the top, generating a co-genetic turbidity current and, at the base, segregating into a concentrated density flow that seems to behave as a gravelly traction carpet. 359

ResumoEste capítulo faz uma revisão de conceitos e hipóteses apresentados anteriormente acerca da Bacia do Camaquã (região central do Rio Grande do Sul) à luz de uma série de evidências, dados e estudos realizados desde então, incluindo aí um grande número de estudos geocronológicos. A Bacia do Camaquã continua sendo vista como o resultado da superimposição entre 630 e 510 Ma de diversas bacias independentes, mas sucessivas em um mesmo locus deposicional. Independentes, mas vinculadas aos estágios finais da orogenia Brasiliana o basal) se caracterizou por um vulcanismo basal que evoluiu desde magmas toleíticos e calcialcalinos alto-K a shoshoníticos (Evento Bom Jardim), evoluindo para um vulcanismo bimodal de afinidade alcalina sódica (Evento Acampamento Velho) e culminando com magmas mantélicos básicos alcalinos extraídos da base da crosta recémformada (Evento Rodeio velho). A sucessão sedimentar que se intercalou e sucedeu cada um destes grandes episódios vulcânicos se caracterizou pelo contexto dominantemente marinho na base (Alogrupo Maricá), passando por lacustre profundo com leques de borda associados (Alogrupo Bom Jardim), evoluindo para lacustre raso com deltas e leques (Alogrupo Santa Bárbara), e culminando com fácies lacustres rasas, aluviais e eólicas (Alogrupo Guaritas). Palavras-chave:Evolução geológica, Tectônica, Estratigrafia, Bacia do Camaquã, Rio Grande do Sul. Abstract This chapter presents a revision of concepts and hypotheses previously presented about the evolution of the Camaquã Basin, central portion of the Rio Grande do Sul State (Southernmost Brazil). This review was based on a large number of new pieces of evidence, data and studies performed since earlier publication, including a large number of radiometric, high-quality geochronological data. The Camaquã Basin is still seen as the result of the superimposition between 630 and 510 Ma of a series of independent, but successive basins in the same locus. These basins represent the final stages of the Brasiliano Orogeny in the Rio Grande do Sul State and encompass an evolution from tardi-(Maricá Retroarc Foreland Basin and Western and EasternBom Jardim Strike-Slip basins) to post-orogenic (Western and Eastern Santa Bárbara rifts and Guaritas Rifte) settings. Any tectono-sedimentary cycle (except the basal one) comprise an early volcanism that has evolved throughout the evolution of the entire Camaquã Basin from tholeiitic and calci-alkaline, high-K to shoshonitic (Bom Jardim Event), through bimodal, alkaline (Acampamento Velho Event) to mantle derived, basic magmas derived from the base of the just formed continental crust (Rodeio Velho Event). The sedimentary successions that intercalate and cover the volcanic rocks has evolved from dominantly marine strata at the base (Maricá Allogroup) through deep-(Bom Jardim Allogroup) to shallow-(Santa Bárbara Allogroup) lacustrine facies associated with fan-deltas and axial braid-plain deltas, to shallow-lacustrine, deltaic and eolian deposits (Guaritas Allogroup).

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