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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.

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

Submarine lobes have various geometries and stacking patterns, whose differences are likely to be the result of variations in flow efficiency and degree of confinement. This study examines four contrasting units with differing flow efficiency and confinement, to evaluate their effects on bed geometries and stacking patterns. Three of these units occur in the Late Palaeozoic Paganzo Basin, north-west Argentina: the Las Lajas system is developed in a 0Á8 km wide palaeofjord; the Cerro Bola system (of which two different units were studied) was deposited in a larger sub-basin, at least 20 km wide. The Paine C system of the late Cretaceous Magallanes Basin in Chile is confined by an incision surface 3 km wide. Seventy-eight individual beds in the four units have been chosen to calculate flow efficiency and degree of confinement. Individual flow efficiency has been estimated semi-quantitatively using the outcrop cross-sectional area of the bed (as a proxy for flow volume) and percentage of mud in the beds (as a relative estimate for that in the flows). The degree of confinement experienced by the flows was assessed semi-quantitatively by dividing the flow efficiency by the maximum preserved basin dimension. It is found that: (i) degree of confinement (efficiency divided by maximum preserved basin dimension) influences individual bed geometry, highly confined flows having a higher tabularity (smaller thinning rate); (ii) in highly confined settings, individual beds stack vertically, whereas in unconfined systems, they stack compensationally; (iii) highly confined or high efficiency flows have higher tabularity (smaller thinning rate), which implies that truly sheet-like systems are only developed in highly confined and high efficiency systems. The generic model of architecture of submarine lobes and turbidite sheet systems, as a function of flow efficiency and degree of confinement, could be applied widely to sheet-like systems both at outcrop and in the subsurface.

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