Alluvial fan sedimentation in the Cretaceous Athgarh Gondwana basin, Orissa, India

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  • 白亜紀アトガー・ゴンドワナ堆積盆における扇状地堆積作用
  • Alluvial fan sedimentation in the Creta

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Abstract

The Athgarh Formation forms an important stratigraphic unit of Upper Gondwana sediments of Peninsular India. The regional palaeocurrent indicates a consistent southeasterly dispersal of clastics from the Archaean source terrain located to the northwest of the basin. The Athgarh Formation represents deposition in an alluvial fan environment with the development of proximal, mid-, and distal fan subenvironments and the distal part of the fan merging into a lake. The buildup of the Athgarh alluvial fan system occurred in a humid climate. Stream-flow processes dominated and a fan was drained by braided channels. Debris flow processes also operated, but were prominent only in the proximal fan zone. Several fans coalesced along the basin margin, forming a southeasterly sloping, broad and extensive alluvial plain terminating to a lake in the center of the basin. Aggradation of fans along the subsiding margin of the basin resulted in the Athgarh succession showing a remarkable lateral facies change in the down-slope direction. The proximal fan conglomerates pass into the sandstone-dominated mid-fan deposits, which, in turn, grades into the cyclic sequences of sandstones and mudstones of a distal fan origin. Further down slope, thick sequence of lacustrine shales occurs.

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