Abstract
ABSTRACT: The aim of this work was to analyze the sedimentary record of the coastal plain of Pelotas Basin, placing it in the context of temporal and spatial scales, and proposing a stratigraphic hierarchical framework. The coastal plain, located in southern Brazil and in northern Uruguay, is mainly formed by four Quaternary barrier-lagoon systems. Three of these systems were studied through the integration of surface and subsurface data (geomorphological and topographical mapping, outcrops description, geoprocessing, dating and Ground Penetrating Radar - GPR - records) and interpreted as the preserved, onshore portion of depositional sequences mainly controlled by glacioeustatic cycles of about 100 kyr. The stacking pattern comprising these sequences is progradational with seaward downsteping (highest sea-levels measured: 9.5, 8 and 3 m, respectively), comprehending a degradational sequence set, or the regressive/falling stage systems tract of a higher order depositional sequence identified in seismic sections, with about 0.5 Ma. The youngest sequence has diachronous systems tracts - while some sectors have already transitioned from the transgressive to the highstand/falling stage systems tract, others are still under a transgressive context. It indicates that, in this time and scale, the sea level is not the main control of coastal evolution, and autogenic factors are fundamental in the run of geological record.
Highlights
Sequence stratigraphy is a method used to build stratigraphic frameworks and examine the geological record of sedimentary basins through the definition and mapping of coeval, genetically related packages of rock, emerging from the works of Blackwelder (1909), Grabau (1913), Sloss et al (1949), Vail et al (1977), Van Wagoner et al (1988), among others
Starting from the interpretation of seismic sections of Pelotas Basin, it is possible to define that the geological record of the coastal plain is part of a depositional sequence defined by Abreu (1998) with about 0.5 My
The performed analysis resulted in a Sequence Stratigraphic framework which allowed positioning the Quaternary record of the coastal plain of Pelotas Basin in relation to its evolution through a Sequence Stratigraphic view
Summary
Sequence stratigraphy is a method used to build stratigraphic frameworks and examine the geological record of sedimentary basins through the definition and mapping of coeval, genetically related packages of rock, emerging from the works of Blackwelder (1909), Grabau (1913), Sloss et al (1949), Vail et al (1977), Van Wagoner et al (1988), among others. The Pelotas Basin coastal plain, located in Rio Grande do Sul and Santa Catarina states, in southern Brazil and in northern Uruguay, has the most complete record of Quaternary events along the Brazilian coast (Fig. 1). This plain, with 770 km of extension and 15 to 100 km wide, is formed by alluvial fan systems and by the lateral juxtaposition of four barrier-lagoon depositional systems, firstly defined for Rio Grande do Sul by Villwock et al (1986). The understanding of the geological development of the coastal plain can be improved through the application of sequence stratigraphy
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