Detailed facies analysis and depositional systems interpretation with outcrop, cores and well data, associated with seismic and palynological data, provided a suitable input for a more consistent paleoenvironment interpretation and stratigraphic regional correlation of the study area. Five megasequences (2nd order cycles) are proposed, based on major erosional unconformities: Upper Devonian (Iquiri-Itacua), Tupambi- Tarija, Escarpment-San Telmo, Elvira/Cangapi and Ichoa-Cajones megasequences. These five megasequences are split into several 3rd order cycles, which are widespread correlated within the area. Except for the Upper Devonian megasequence interpreted as shallow marine and glaciomarine, all other megasequences represent a thick continental section. Each 3rd order cycle within the Tupambi-Tarija and Escarpment-San Telmo megasequences starts with an erosional surface and presents fining upward arrangement. They are formed by polymitic conglomerate, massive or cross-bedded sandstone, covered by mudstone, shale and diamictite. There is a relationship between observed cyclicity, erosional surface and depositional systems explained by sea level change and glaciation. Right after glacial stage while sea level is rising, an isostatic rebound and decompaction locally cause a relative base level fall, triggering erosion, paleovalleys carving and sediment bypassing. During transgression and highstand periods the paleovalleys are infilled by backsteping fluvial deposits, gradually changing to flood plain and/or lacustrine deposits. A new climatic change drives glacial expansion causing local erosion, glaciotectonic deformation, glacial diamictites and periglacial deposits. The sandstone reservoirs are widespread in the study area and continuous above Escarpment- San Telmo megasequence. The thick glacigenic diamictites and lacustrine shales/mudstone facies, with regional extension, provide effective seals for the carboniferous interval.


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