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First-cycle sandstone composition and color of associated fine-grained rocks as an aid to resolve Gondwana stratigraphy in peninsular India

By
Prodip K. Dutta
Prodip K. Dutta
Department of Geography and Geology, Indiana State University, Terre Haute, Indiana 47809, USA
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Published:
January 01, 2007

A stratigraphic problem in most Gondwana basins in peninsular India has persisted for more than a century. Originally, in the type area of Damodar valley, the stratigraphy was established based on the order of superposition without the aid of fossils. However, fossils were used to classify the Gondwana succession into Lower Gondwana (Early Permian to Late Triassic), characterized by Glossopteris flora (considered to have become extinct by the end of Triassic), and Upper Gondwana, which has Ptilophyllum flora (Jurassic). The problem started as the work extended further outside the type area, where Glossopteris flora was discovered in Upper Gondwana rocks of Early Jurassic age. At this point, fossils took precedence in determining the relative age of strata under the assumption that Glossopteris flora could not extend beyond the Triassic. Therefore, Glossopteris-bearing Upper Gondwana–looking rocks were assumed to be of pre-Jurassic age. Thus, Upper Gondwana rocks were relegated to Lower Gondwana status. The confidence on fossils to determine the relative age of strata was so strong that the necessity to confirm their relative age based on the law of superposition was thought unnecessary. This happened in spite of the fact that ages based on a fossil are conceptual entities, whereas establishing the order of superposition is the ultimate proof of relative age of strata.

Gondwana sedimentation coincided with the global climatic change from an ice-house state in the late Paleozoic to a greenhouse state in the Mesozoic. Climate played the most important role in controlling sandstone composition and other lithological attributes. A strong correlation between sand/sandstone composition and climate is well established. Any perceptible change in climate brings a perceptible change in sand/sandstone composition. Such compositional transition would be expected in the stratigraphic column as the climate changed between the two extremes. Sandstone composition of the Gondwana succession in the Raniganj basin, India, supports such a hypothesis. In addition, color of fine-grained rocks in the Gondwana succession, which to some extent is also influenced by climate, uniquely identifies each lithostratigraphic unit.

Stratigraphy must be based on the law of superposition. But sandstone composition along with the color of fine-grained rocks could serve as additional criteria to stratigraphic interpretation. Such an approach may be useful in structurally overturned sequences and in reconstructing the subsurface stratigraphy from borehole cores.

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Contents

GSA Special Papers

Sedimentary Provenance and Petrogenesis: Perspectives from Petrography and Geochemistry

José Arribas
José Arribas
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Mark J. Johnsson
Mark J. Johnsson
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Salvatore Critelli
Salvatore Critelli
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Geological Society of America
Volume
420
ISBN print:
9780813724201
Publication date:
January 01, 2007

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