A Modern High-Energy Siliciclastic-Carbonate Platform: Continental Shelf Adjacent to Northern Rio Grande do Norte State, Northeastern Brazil
Helenice Vital, Karl Stattegger, Venerando E. Amaro, Klaus Schwarzer, Eugênio P. Frazão, Werner F. Tabosa, Iracema M. Silveira, 2008. "A Modern High-Energy Siliciclastic-Carbonate Platform: Continental Shelf Adjacent to Northern Rio Grande do Norte State, Northeastern Brazil", Recent Advances in Models of Siliciclastic Shallow-Marine Stratigraphy, Gray J. Hampson, Ronald J. Steel, Peter M. Burgess, Robert W. Dalrymple
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The continental shelf adjacent to the northern coast of Rio Grande do Norte State, northeastern Brazil, represents a modern, highly dynamic mixed siliciclastic-carbonate shelf system developed in shallow water (< 60 m). Sediment dynamic processes are driven by waves, winds, tides, and the west- to northwest-directed North Brazil Current. This high-energy setting is associated with the presence of highly variable seabed features. This paper describes the spatial distribution of the mapped bedforms, in order to relate them to sedimentary processes and physical characteristics of the environment, and to the sedimentary history of this shoreline-shelf system. In a novel approach, the integrated data set presented here includes remote sensing, bathymetric, oceanographic, hydroacoustic, and sedimentologic data supported by diving. In addition, the high-energy mixed siliciclastic-carbonate shelf system contains a different sedimentary inventory than most well-studied siliciclastic or carbonate shelf environments. A variety of bedforms, which range from kilometers to tens of centimeters in scale, is present in the study area. Sediment reworking is accountable for the recent formation and migration of mobile bedforms which are superimposed on older relict structures. The integrated approach led to the identification of six main groups of large-scale bedforms: (I) very large longitudinal dunes, (II) very large transverse dunes, (III) small dunes, (IV) isolated shallow-marine sand bodies, (V) submerged beachrock chains, and (VI) incised-valley systems. The continental shelf off Rio Grande do Norte has experienced regressions and transgressions during the last glacial cycles. Outside the incised valley of the Rio Açu a continuous strong reflector, identified in all boomer profiles, represents the most recent sea-level lowstand surface that separates Pleistocene deposits below from early Holocene deposits above. During the Holocene sea-level rise, at least two beachrock lines formed at 20 m and 10 m of modern water depth.
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Siliciclastic shallow-marine deposits record the interface between land and sea, and its response to a variety of forcing mechanisms: physical process regime, the internal dynamics of coastal and shelfal depositional systems, relative sea level, sediment flux, tectonic setting, and climate. These deposits have long been the subject of conceptual stratigraphic models that seek to explain the interplay between these various forcing mechanisms, and their preservation in the stratigraphic record. This volume arose from an SEPM research conference on shoreline–shelf stratigraphy that was held in Grand Junction, Colorado, on August 24–28, 2004. The aim of the resulting volume is to highlight the development over the last 15 years of the stratigraphic concepts and models that are used to interpret siliciclastic marginal-marine, shallow-marine, and shelf deposits.