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Evolution of Source-Distal to Source-Proximal Fluvial Regimes in the Himalayan Molasse: Abstract
The record of Himalayan tectonism is preserved in a 7000 m sequence of molasse represented by the Neogene and early Quaternary Siwalik Group. Fining upwards sedimentary cycles from strata of the Upper Siwalik sub-Group generally reflect the transition from streams having high sinuosity, well-developed meander-belt structure typical of much of the Siwalik Group, to low-sinuosity and braided stream regimes during the late Pliocene and early Pleistocene (ca. 2.5 m.y. to 0.5 m.y. B.P.). In significant fashion, this transition in sedimentary style of the Himalayan molasse is not an isochronous event but rather a variable response to the morphogenesis of the adjacent schuppenstruktur of the Outer Himalaya, syndepositional deformation of the Himalayan foredeep margin and proximity to major antecedent stream courses which flow from these regions into the foredeep basin.
Constraints on the chronology of these events is provided by a magnetic polarity reversal stratigraphy which is established for the Upper Siwalik sub-Group. This is coupled with radiometric age determination of several volcanic ashes. The events discussed cover the entire Pliocene and Pleistocene record of the evolution of this fluvial molasse in a region of northern Pakistan.
Acknowledgments and Associated Footnotes
1 Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755
Copyright © 2009 by the Canadian Society of Petroleum Geologists