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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 299

Last Page: 299

Title: Structural Control on Molasse Sedimentation: Example of Siwalik Group of Northern Pakistan: ABSTRACT

Author(s): Robert G. H. Raynolds, Gary D. Johnson

Article Type: Meeting abstract


Molasse sediments accumulate in elongate foredeeps during orogenic episodes induced by plate collision. These sediments are typically fluvial, but may grade distally into marine sediments. Molasse lithofacies exhibit a variety of syndepositional structural controls. Structural controls can be subdivided conveniently into 3 scale-dependent categories: (a) regional (basin-wide) control in which the fundamental asymmetric basin architecture is established by the collision process, (b) subregional in which structural control on the location of river systems influences facies distribution and preservation, and (c) local control in which developing folds and faults influence the character of the rock record. New data derived from paleomagnetic stratigraphy and fission-track dat ng has permitted refinement of lithofacies correlation in the Siwalik molasse sediments of northern Pakistan. A suite of 8 dated sections illustrates the structural controls on molasse facies distribution in the Himalayan foredeep between 3.4 and 1.6 m.y. Subregional and local structural controls are critical factors defining the facies of the proximal molasse sequence. Variable rates of sediment accumulation, differing efficiency of sediment preservation, structurally controlled unconformities, and abrupt time-transgressive lithofacies transitions are documented. Facies patterns preserved in the rock record are compared to analogous modern environments in India. The observed patterns indicate profound structural control on the distribution and interconnectedness of reservoir facies in f uvial-dominated foredeep settings.

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