Abstract The transition from the Late Paleozoic Ice Age (LPIA) to fully postglacial conditions in SW Gondwana is under increasing discussion due to either the radiometric ages of its boundary or the stratigraphic nature of this transition. The record of this transition in the Paraná Basin is found in the glacial and glacially influenced deposits of the upper Mafra and Rio do Sul Formations (upper Itararé Group) and postglacial strata of the Rio Bonito Formation (Guatá Group). Here we address the depositional architecture and stratigraphic evolution of these deposits in the Rio do Sul depocenter, eastern Paraná Basin, Brazil, the main area of subsidence in the basin during this transition in Pennsylvanian-Cisuralian time, bringing an opportunity to examine the characteristics of glacial to postglacial transition. Analyses of facies, stratigraphic logs, stratigraphic correlations, and paleocurrent dispersal trends allowed us to define three evolutionary stages. The first stage registers glacial advance from the south-southwest represented by an erosive surface and subglacial tillites. Gravitational deposits covered the tillites in response to ice retreat (upper Mafra Formation), and the Lontras Shales (lower Rio do Sul Formation) correspond to the marine maximum flooding. The second stage comprises co-genetic deepwater (Rio do Sul Formation) to shallow (Rio Bonito Formation, Triunfo Member) progradational deposits after the Lontras Shale maximum flooding. Paleocurrent data and glacially related features point to glaciated source areas located to the NE, E, and SE for the Rio do Sul depocenter during this stage. The third stage corresponds to retrogradational stacking pattern upon a fluvial subaerial unconformity (incised valley), starting with fluvio-deltaic beds (Triunfo Member), followed by fine-grained deposits of the Paraguaçu Member of Rio Bonito Formation. No features related to glacial influence characterize this third stage. As previously suggested, tectonic uplift likely drove the additional NE source and created the space that allowed the transitional contact between Rio do Sul and Rio Bonito formations in the Rio do Sul depocenter.

ABSTRACT: In this contribution, we present an analysis of the main faciological features of the São Jerônimo da Serra Site, related to the Morro Pelado Member of Rio do Rasto Formation (Middle/Upper Permian), from Paraná State, Brazil, integrated to its taphonomic context. The outcrop, rich in vertebrates and bivalves remains, presents a succession of red siltstones bedded with fine to medium sandstones in which three architectural elements were observed: SF (sheetflood deposits), FF (fine of flood plain) and CS (crevasse). These data, allied to the taphonomic signatures of fossils assigned to eight levels, allowed the identification of three taphofacies. The taphofacies I is characterized by preserved bones in floodplain facies, with different articulation grades and absence of any sign of transport. The taphofacies II is composed by small isolated or fragmented bones and fish scales deposited in terminal splay facies. The taphofacies III is characterized by sandy layers with bivalve shells and fish scales, preserved in crevasse-splay deposits. The obtained data shows that the studied sedimentary succession was generated on a dry trend environment, with sporadic water supply, which conditioned the fossil preservation.

RESUMO: A análise de fácies sísmicas e a geomorfologia sísmica são ferramentas importantes para o estudo de elementos deposicionais em subsuperfície. Neste trabalho foram avaliadas as características e a gênese de elementos deposicionais e de feições erosivas associadas a uma margem progradante desenvolvida no Eoceno no norte da bacia de Santos. As fácies sísmicas identificadas são interpretadas como deltas de margem de plataforma/depósitos de shoreface, clinoformas tangenciais (oblíquas), clinoformas sigmoides, depósitos de topset, depósitos de transporte em massa e turbiditos. As fácies foram agrupadas em associações que representam períodos com condições ambientais relativamente constantes. A associação 1 é composta de deltas de margem de plataforma/depósitos de shoreface, clinoformas tangenciais e depósitos turbidíticos arenosos, dispostos em canais submarinos e espraiamentos frontais. Um aumento progressivo no ângulo das clinoformas culmina na formação de clinoformas sigmoides com grandes dimensões verticais e turbiditos que compõem a associação 2. A associação 3 é constituída de refletores subparalelos a divergentes, interpretados como depósitos continentais a plataformais formados durante subidas do nível de base. Esses refletores são truncados em direção à bacia por cicatrizes de escorregamento formadas em consequência da sobrecarga sedimentar na plataforma durante agradações. A associação 4 consiste em clinoformas sigmoides, depósitos de transporte em massa e turbiditos. As clinoformas mais antigas são mais íngremes, em função da topografia imposta pelas cicatrizes de escorregamento. Os ângulos diminuem progressivamente, enquanto o sistema se aproxima do perfil de equilíbrio. Depósitos de transporte em massa, formados após o colapso do talude, são compostos de diamictitos argilosos com intensa deformação interna.

ABSTRACT: Seismic facies analysis and seismic geomorphology are important tools for the analysis of depositional elements in subsurface. This paper aimed to investigate the character and genesis of depositional elements and erosive features associated with an Eocene progradational shelf margin in northern Santos Basin. Identified seismic facies are interpreted as shelf-margin deltas/shoreface deposits, tangential (oblique) clinoforms, sigmoidal clinoforms, topset reflectors, mass-transport deposits and turbidites. These facies are grouped into four associations representing periods of relatively constant environmental conditions. Association 1 is composed of shelf-margin deltas/shoreface deposits, tangential clinoforms and extensive sand-rich turbidites disposed as submarine channels and frontal splays. A progressive increase in clinoform angle within this association has been identified, culminating in high-relief sigmoidal clinoforms with less voluminous turbidites of facies association 2. Association 3 is composed by subparallel to divergent topset reflectors, interpreted as continental to shelfal deposits placed during base-level rises. These are always truncated basinward by slump scars, formed as a consequence of sediment overload at the shelf margin during aggradations. Association 4 is composed of sigmoidal clinoforms, mass-transport deposits and turbidites. Early clinoforms are steeper as a consequence of the topography of the slump scars. Subsequently, dip angles become progressively gentler as the system approach to the equilibrium profile. The steep physiography was favorable for canyon incision, which played an important role in turbidite deposition. Mass-transport deposits, formed subsequent to slope collapse, are composed of mud-rich diamictites, and show strong internal deformation.

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 encontradas na Bacia do Paraná. As formas de leito examinadas podem ser enquadradas em quatro categorias cuja origem está relacionada a diferentes processos. Formas subglaciais sobre substrato rígido são estruturas geradas por abrasão e/ou remoção de blocos sobre substratos litificados do embasamento precambriano ou de unidades mais antigas da bacia. Incluem formas alongadas e pavimentos estriados formados sob geleiras em avanço. Formas subglaciais sobre leitos moles são superfícies intraformacionais geradas por erosão e deformação de depósitos inconsolidados quando da passagem de geleiras. Marcas de arrasto de quilhas de gelo, por outro lado, são superfícies intraformacionais comumente estriadas e sulcadas, formadas pelo arrasto de quilhas de blocos de gelo livremente flutuantes sobre sedimento de fundo. Pavimentos de clastos estriados são horizontes contendo clastos alinhados submetidos à abrasão subglacial pelo avanço de geleiras sobre sedimentos. Dentre as diferentes formas de leito, apenas aquelas formadas sob geleiras em avanço podem ser utilizadas como indicadores confiáveis do paleofluxo glacial. Com base nisso, a paleogeografia da Bacia do Paraná durante a Era Glacial Neopaleozoica se insere em um modelo com vários lobos glaciais derivados de centros glaciais situados sobre altos topográficos ao invés de um único manto de gelo de dimensões continentais.

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.