Meso- and macro-scale architecture of a Triassic fluvial succession: Denwaformation, Satpura Gondwana basin, Madhya Pradesh

The Denwa Formation (similar to 300m thick) representing a part of the unco nformity bounded Triassic (Pachmarhi-Denwa) succession of the Satpura Gondw ana basin, is characterized by two different fluvial styles marked by contr asting architectural elements within the alluvial system. These fluvial sty les are distinct from the underlying Pachmarhi Formation representing an al luvial plain with channel belts characterised by multiple-channel, sandy br aided rivers. The lower part of the Denwa Formation is characterized by an alternation of medium to fine grained. thick, sheet-like, sandstone bodies and red mudsto ne intervals having centimetre to decimetre scale fine grained sandstone in terlayers. The thick sandstone bodies are comprised of several groups of st oreys, and individual storeys are made up of macroform strata reflecting fr ontal, oblique and vertical accretion. It is evident from the overall archi tecture that the lower part of the Denwa Formation represents an alluvial p lain characterised by sandy, braided channel belts and associated floodplai n / basin. The upper part of the Denwa Formation is characterised by conspicuous absen ce of thick multistorey sandstone bodies. It is predominantly a mudstone do minated, sand-poor succession characterized by ribbon-shaped bodies encased within pedoturbated mudstones. Ribbon-shaped bodies internally show inclin ed heterolithic (sand-mud) stratification representing lateral accretion of channel bars of high sinuosity rivers. The upper part of the Denwa Formati on is interpreted to represent deposits of a network of meander channels la terally separated by well-developed and stable interfluve and floodplain ar eas. The changes in the fluvial styles represented in the Denwa succession have been attributed to changes in the aggradation rate, avulsion frequency and climatic setting.