Facies architecture and spatio-temporal depositional variability in the Pliocene Sandhan fluvial system, Kutch Basin, India

The glaciation-induced base-level fall and basin physiography straightforward controls fluvial style in any coastal setting. An alternate climatic influence including warm and cold (glacial) conditions may result in marine onlap with interception by unconformity formation and fluvial incursion in a coastal stratigraphic record. Unconformably overlying the marine sediments, the fluvial sandstone in the upper part of Pliocene Sandhan Formation is studied herein for documentation of architectural element and variability in the fluvial sedimentation motif, if any, in space-time framework. The identified architectural elements include channel (CH), gravel bar and bedforms (GB), sandy bedforms (SB), downstream accretion (DA), sediment gravity flow (SG), compound bar (CB) overbank fines (OF) and paleosol (P). From dominance of coarse-grained, granular pebbly sandstone with SB, GB, SG and DA elements, and incidence of 6–12 m thick fining-upward cycles, it is inferred that the Sandhan fluvial system was of Donjek-type braided in character. Only at the Nagmati River section in the south-east, a change in fluvial character is recorded as Platte-type. A role of basin physiography involving median-high across the depositional profile is identified from (i) decrease in thickness of fluvial deposit from north-west to south-southeast, and (ii) reduction in topographic-gradient in the south-southeast. Considering the Pliocene time frame, the fluvial incursion onto the marine system within Sandhan depositional history is identified as a result of base-level fall under influence of global glaciation.