Lowstand Turbidites and Delta Systems of the Itararé Group in the Vidal Ramos region (SC), southern Brazil

Abstract

ABSTRACT:Turbidites have captioned the attention of sedimentologists during the last decades due their importance as hydrocarbon reservoirs. However, their relationship to delta systems still deserves further studies. This paper presents examples from a late deglacial to early post-glacial deltaic and turbidite strata exposed in the surroundings of Vidal Ramos (Santa Catarina State, Brazil), southern portion of the Paraná Basin. There, the uppermost part of the Mafra Formation and the Rio do Sul Formation onlap the Proterozoic basement and comprises an up to 360 m thick package. It includes (base to top) black shales, mass transport deposits (MTD) and sandy turbidites (Mafra Formation) as well as thin bedded turbidites (tbt), including one interval of black shales and sandy turbidites, overlain by proximal delta front sandstones (Rio do Sul Formation). The analysis of the succession shows two more than 150 m thick coarsening-upwards deltaic successions composed of turbidite sand sheets at their base (prodelta), followed by partially collapsed thin bedded turbidites (delta slope wedge) and delta front sandstones. Both turbidite sand-sheets abruptly overlay black shale intervals related to maximum flooding surfaces and therefore record correlative conformities. A detailed stratigraphic section elaborated from the correlation of four logs (1/100) suggests that distal delta front sands includes both thin bedded turbidites and wave reworked sands whereas the proximal delta front was dominated by long-lived underflows (hyperpycnal flows). The succession suggests that the most expressive turbidite beds (base of the delta systems) have resulted from relative sea-level falls (early lowstand) whereas the thin-bedded turbidites were related to the development of the late lowstand wedge. Black shales represent the transgressive systems tract and HST were not deposited or preserved in the area. High sediment supply associated with lowstand tracts could explain the occasional (Vidal Ramos) to common occurrence of slope failures (slumps and diamictites) involving thin bedded turbidites and delta front sandstones. This situation is quite logical in terms of deglacial periods, and resulting high sediment supply, within a long-term icehouse context, with prevalence of lowstand to transgressive settings.

Late Palaeozoic glacial cycles and subcycles in western Gondwana: Correlation of surface and subsurface data of the Paraná Basin, Brazil

“…Palynological analysis comprised the taxonomic identification of guide species of spores and pollen grains according to the zonal schemes for the basin (Souza and Marques Toigo, 2005;Souza, 2006). In the Vidal Ramos area, palynological samples were located in a previous stratigraphic column (Puigdomenech et al, 2014).…”

A review on late Paleozoic ice-related erosional landforms in the Paraná Basin: origin and paleogeographical implications

“…5A), which allow to interpret that the ice slid on the bed towards the northwest. This paleo ice-flow is coincident with paleocurrents to the NW measured by Puigdomenech et al (2014) in deglacial deposits that are above the striated surface.…”

“…Equivalent striated pavements can be found in other localities of eastern Santa Catarina, as, for instance, the occurrence noticed by Puigdomenech et al (2014) in Vidal Ramos, where thin striations occur at the bottom and at the sidewall of an elongated groove about 1 m deep carved onto low-grade metamorphic rocks (their Figure 3B). Although these authors did not provide kinematic indicators for paleo ice-flow, new field observations at the same surface found non-striated steps perpendicular to the main striations (Fig.…”

“…An ice source located east of the Paraná Basin is well supported by the moutonnée of Salto (Almeida 1948), subglacial landforms in the Paraná state (Bigarella et al 1967, Trosdtorf et al 2005, the occurrence at Engenheiro Maia (Caetano-Chang et al 1990) and the striated surfaces found on the Precambrian basement in Santa Catarina state (Barbosa 1940, Carvalho 1940, Rocha-Campos et al 1988, Puigdomenech et al 2014. Nevertheless, localities in the southern Paraná state (southern flank of the Ponta Grossa arch) have a different orientation (N-S) when compared to the other localities, which show a consistent NW trend (Fig.…”

“…Kjaer et al 2008). Ice lobes of Santa Catarina state (Alfredo Wagner and Vidal Ramos), on the other hand, probably advanced in a marine environment once the abraded basement in that area is covered by marine shale and turbidites accumulated in relatively deep water settings (Puigdomenech et al 2014).…”