Sequence stratigraphy of the neoproterozoic Infra Krol Formation and Krol Group, Lesser Himalaya, India

Publication Type  Journal Article
Year of Publication  2002
Authors  Jiang, G. Q.; Christie-Blick, N.; Kaufman, A. J.; Banerjee, D. M.; Rai, V.
Journal Title  Journal of Sedimentary Research
Volume  72
Issue  4
Pages  524-542
Journal Date  Jul
ISBN Number  1527-1404
Accession Number  ISI:000178505800008
Key Words  naini tal syncline; carbonate platform; earth history; northwest-territories; ediacaran fossils; floridan aquifer; passive-margin; 1st record; west texas; evolution
Abstract  

A sequence stratigraphic study of terrigenous and carbonate rocks of the Infra Krol Formation and Krol Group in the Lesser Himalaya fold and thrust belt of northern India was undertaken as part of a broader investigation of the significance of carbon isotope data in Neoproterozoic successions. Eight regional stratigraphic discontinuities were traced over a distance of nearly 300 km, and interpretations were anchored in a series of local studies involving the mapping of key beds and the measurement of closely spaced sections. Three of the regional surfaces are interpreted as sequence boundaries on the basis of (1) locally developed incised valleys < 60 m deep; (2) paleokarstic depressions with < 50 m of mappable relief, (3) subaerial dissolution and weathering products (breccias and calcrete) filling vertical fissures, dikes, cavities, and shallow depressions in underlying carbonate rocks; and (4) small-scale evidence for subaerial exposure at an erosion surface. The remaining five discontinuities are regional flooding surfaces identified on the basis of either facies changes with an abrupt upward deepening across the surface or transitions in facies stacking patterns, typically from forestepping to backstepping. A glacio-eustatic origin is permitted, although not required, for the three sequence boundaries, but no evidence has been found for marked lowering of sea level at other horizons. A mismatch between the stratigraphic location of sequence boundaries and carbon isotope minima suggests that local diagenetic alteration or oceanographic phenomena unrelated to glaciation may be in part responsible for observed isotopic variation, and that small ice sheets may have existed during apparently nonglacial times without producing either cap carbonates or negative carbon isotope excursions.

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