Abstract
The Early Cretaceous Marizal Formation, which is a product of fluvial and alluvial fan systems, is about 50m thick in The Reconcavo Basin, BA, Brazil. This formation changes gradually from conglomerates into sandstones and mudstones. The presence of good continuous outcrops, was essential to the architectural element analysis. This method was used to subdivide the fluvial deposits into one or more sets of nine basic three dimensional architectural elements. These elements were identified according to their lithofacies assemblage, internai geometry, and the nature of the upper and lower contacts. The study of outcrops in the proximal provided key information to identify regions the SG (sediment gravity flows) and GB (gravei bars and bedforms) elements. In the distai regions, the predominam elements are SB (sandy bedforms), LS (laminated sand sheets), DA (downstream accreted macroforms), and less frequently, CH (channels) and LA (lateral accretion deposits). The FF (floodplain fines) element has been identified in both proximal and distai regions. The distribution of these elements reveals two distinct domains in depositional model of The Marizal Formation. The first domain represents a proximal low sinuosity gravelly rivers associated with sediment gravity flows. The second domain is a result of shallow wide river channel depositional model, with sand bed load and low to intermediate sinuosity. The LS local accumulation are an evidence of flash floods in arid to semi-arid climates during deposition of the sediments.
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