科研之友
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摘要
The Pranhita-Godavari Graben (PGG) represents a major lineament in south Indian Peninsular cratonic province, which preserves a thick column of sediments. In geological time scale, these sedimentary units correspond to Mesoproterozoic to Mesozoic period. The Mesoproterozoic sedimentation has been confined mainly to southern part of the PGG, while Neoproterozoic sediments are exposed at northern tip of the graben. In the area of investigation siliciclastic sedimentation units are exposed, wherein five major lithofacies have been marked out. These lithofacies are i) breccia (Br), ii) large scale trough cross-bedded sandstone (Ls), iii) small-scale trough cross-bedded sandstone (Sss), iv) horizontal bedded sandstone (Hs) and v) ripple laminated sandstone (Rs). The amalgamation of these lithofacies strongly divulges that the lower part of the succession was deposited in braided-streams, whereas the upper part was deposited in erg environment. The unimodal paleocurrent is evident in lower part of the succession while bimodal paleocurrent is noticed from sandstones at upper part of the succession. In general, the sandstones exhibit northwesterly paleocurrent direction. The petrographic studies point out that the sandstones are arenites and were deposited in interior type of continental block provenance under semi-arid to hot humid palaeoclimate. The high percentage of floating grains and the low percentage of interpenetrative contacts as well as the low value of contact index for these sandstones divulge that the grains did not suffer much compaction thereby pointing to shallow burial. The sub-angular zircon and tourmaline suggest that these minerals have travelled short distance from the source rocks. The high percentage of garnet and presence of epidote, staurolite, sillimanite, zoisite, amphibole and kyanite indicate that the sediments were derived from the nearby metamorphic source rocks.
- 出版日期2014-4
