Fluxos combinados e a arquitetura faciológica da porção superior da Formação Teresina - Bacia do Paraná, RS

Abstract

Despite the wide use of classic processes to understand high-energy elements’ formation, the comprehension of the full formative process of tempestites and hummocky cross-stratification (HCS) still lacks analysis and information. Recent investigations have shown wide configuration possibilities for HCS, both for classic and simple to more complex and composite models. The major difficulty on tempestites and HCS interpretation is given mainly due to limited field and sample observation. Because it is generally restricted to vertical and lateral visualization of outcrops and boreholes, lacking a regional basin perspective that evidences the relationship of distal and proximal facies of these deposits. Besides that, small-scale flow model experiments do not allow a faithful reproduction of depositional processes and bed configurations. Another issue that impacts the interpretation is the lack of HCS-like structures in the modern record, as they cannot be observed directly in the vast majority of cases. Therefore, analogs for such big bedforms of tempestites and HCS successions are nearly nonexistent. Also, the current bed morphologies are generally small to make a solid conclusion regarding HCS identification. Usually, the description of intra-facies variability of HCS is neglected, which hinders the development of a new depositional model. This fact, coupled with the hypothesis that HCS structures are probably products of more than one depositional mechanism, makes the process even harder to evaluate. Thus, this work proposes the study of the control processes of tempestites and HCS, aiming to comprehend the mechanisms involved in the genesis and faciology of these. With this purpose, high-frequency surveys and orthophotography interpretation of lateral exposures have been made using outcrops from the Teresina Formation (Upper Permian) located in the southern Parana Basin. This unit is included in the Passa Dois Group and frequently related to a continentalization interval due to the restriction to water incursions between the inner Parana Basin and the Panthalassa Ocean. After facies interpretation, the outcrop was categorized into three intervals according to the dominant hydrodynamic condition. The lower interval is dominated by oscillatory flows, the central interval by combined flows of an oscillatory domain, and the upper interval by combined flows with the great influence of unidirectional flows. Thus, it was observed a tendency of more intense unidirectional flows to the top of the sequence.