Fernando Farias Vesely

Glacially striated, soft sediment surfaces on late Paleozoic tillite at São Luiz do Purunã, PR

Striae and furrows found on the upper surfaces of three stratigraphically superposed decimetric beds of late Paleozoic lodgement tillite of the Itarare Subgroup in the northern Parana Basin were engraved by ploughing of clasts and possibly also ice protuberances at the base of the glacier, on unconsolidated to partially consolidated sediment. Associated features indicate that the rheology of the bed varied from stiff during lodgement to soft and deformable during ploughing. Poor drainage of meltwater at the glacier-bed interface may have contributed to lower the strength of sediment to deformation. The deformed interval was probably generated during a single glacial phase or advance of a glacier grounding in a marine or lacustrine water body. Changes in the dynamics of the glacier involving slow and fast flow were correlated respectively with alternation of deposition and erosion. The proposed model is analogous to that of lodgement till complexes from the Pleistocene of the northern hemisphere. Retreat of the glacier was probably fast, followed by settling of muds on top of the upper striated and furrowed surface, and progradation of deltaic sands during post-glacial time.

Late Paleozoic glacially related sandstone reservoirs in the Paraná Basin, Brazil

Upper Paleozoic glacially related sandstones of the Itarar Group constitute thick and complex hydrocarbon reservoirs in the intracratonic Paran Basin of southern Brazil. Because these sandstones were deposited in both glacial and nonglacial environments, they show a high degree of variability in facies. In this article, we analyze outcrop and shallow well data to describe facies heterogeneities and their reservoir-quality implications. A regional subsurface sequence-stratigraphic framework was built, based on both strike- and dip-oriented well-to-well correlations. A well-exposed sandstone succession correlative with the main reservoir interval in the subsurface was selected in the eastern part of the basin. The Vila Velha sandstone comprises an up to 100-m (328-ft)-thick, unconformity-bounded, sand-rich succession composed of four stacked facies assemblages. Vertical facies succession shows a transition from glacial and glaciomarine to periglacial shallow-marine and nearshore settings, which define a retrogradational-progradational succession. Channel-mouth bars and wave-modified shoreline sandstones in the progradational section contain stratigraphically predictable reservoir-quality lithofacies. In subsurface, gas-bearing sandstone intervals with the same well-log response occur below unconformities, which control the overall reservoir geometry.

Revisão de formas erosivas relacionadas à ação do gelo no Paleozoico superior da Bacia do Paraná: origem e implicações paleogeográficas

Manuscript ID: 20160050. Received in: 03/30/2016. Approved in: 05/15/2016 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 microto 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.The Late Paleozoic Ice Age is recorded in the Parana Basin as glacial deposits, deformational features and ice-related erosional landforms of the Itarare 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 Parana 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 Parana 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 Parana 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.

Distinção dos elementos deposicionais fluviais, eólicos e lacustres do Membro Morro Pelado, Permiano Superior da Bacia do Paraná

The Late Permian Morro Pelado Member is the upper part of the Rio do Rasto Formation of Parana Basin and is composed of an association of fluvial, eolian and lacustrine deposits. In order to depict its facies associations and depositional elements as well as to characterize the fluvial style, a facies and architectural element analysis was carried out in the eastern outcrop belt in Santa Catarina and Parana States, southern Brazil. Four facies associations (FA) were recognized: FA-A is interpreted as mixed-load meandering fluvial systems, with conspicuous laterally accreted macroforms, levees and floodplain fines; FA-B was deposited as terminal splays in the distal parts of the fluvial system, where sheet floods prevailed; FA-C defines a fluvial-dominated lacustrine delta formed in response to episodes of extreme flooding and rising water table in the terminal splay zone; FA-D comprises eolian dunes, wet and damp interdunes and eolian sand sheets that occur interbedded with the fluvial and lacustrine deposits marking periods of aridization in the alluvial plain. The vertical stacking pattern shows an upward increase in frequency and thickness of eolian deposits recording progressive expansion of the erg systems towards basin margins in response to progressive drying combined with high rates of accommodation and sediment supply.

Seismic expression of depositional elements associated with a strongly progradational shelf margin: northern Santos Basin, southeastern Brazil

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.

Palinomorfos e associações de fácies da Formação Lagoa Azul (Grupo Itararé, Pennsilvaniano da Bacia do Paraná) no sudeste do Estado do Paraná, Brasil

In southeastern Parana state, the Itarare Group rests through an angular unconformity over the preglacial substrate, composed of Precambrian to Devonian units which are increasingly older to the southeast. Because of this stratigraphic configuration, the outcrops of the Itarare Group in the Porto Amazonas region have been interpreted as representing its lowermost levels while those from the Campo do Tenente region, which are located more to the south, are considered to be younger. This paper presents the results of a palynological and facies analysis performed in seven outcrops from the lower portion of the Itarare Group (Lagoa Azul Formation) in the Porto Amazonas, Lapa and Campo do Tenente regions, aiming at the palynostratigraphic positioning. Nine sedimentary facies were identified, representing mostly mass-transport deposits and turbidites, deposited in a relatively deep marine environment under glacial influence. Palynological associations were recorded from all outcrops which are composed of scarce indigenous elements, comprising of spores and monosaccate pollen grains, with varied preservation degree. The general palynological features of the associations and the presence of certain species of spores and pollen grains suggest correlation to the Ahrensisporites cristatus Zone, which corresponds to the lower portion of the Itarare Group (Lagoa Azul Formation), of Pennsylvanian age (late Bashkirian to Kasimovian). The results corroborate the occurrence of glacial deposits of the lower Itarare Group in the outcrop belt. In addition, they demonstrate the importance of the study on processes of pre-Pennsylvanian palynofossils reworking and resedimentation.

Assinatura gamaespectrométrica de depósitos fluviais: estudo de caso na Formação Rio do Rasto, Permiano Superior da Bacia do Paraná

Fluvial channel-fill deposits form highly heterogeneous hydrocarbon reservoirs. The study of outcrop analogs can help in the characterization of these heterogeneities, which are usually not detected by subsurface geophysical methods. The aim of this research is to compare outcrop log signatures with grain size trends and depositional elements of the fluvial deposits of the Late Permian Rio do Rasto Formation. A series of vertical gamma-ray logs were assembled in two outcrops in order to: 1) characterize log-facies in a succession composed of alternated flood plain, channel fill and eolian strata; 2) define within-channel spectral gamma-ray variability of a mixed-load composite point bar deposit and its relationship with grain size trends and lithofacies; 3) correlate log signatures observed in the outcrop sections with deep exploratory wells drilled several tens of kilometers from the study area. The results of this study show that gamma-ray logs have good correlation with grain size trends and that different depositional elements have distinct signatures. On the other hand, point bar deposits exhibit strong lateral changes in log signature due variations in grain size and mud content within lateral accretion strata. Although frequent, the classic bell-shaped log motif was not always detected, which means that the amount of fluvial channel-fill deposits recognized in subsurface can be underestimated. Similar log signatures were detected in the boreholes, at least in the closest ones, helping in paleoenvironmental interpretation in the subsurface.