--> Controls on Incised Valley Fills in a Post-Rift Basin Complex: Examples from the Upper Carboniferous, UK, by G. J. Hampson; #90986 (1994).

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Abstract: Controls on Incised Valley Fills in a Post-Rift Basin Complex: Examples from the Upper Carboniferous, UK

Gary J. Hampson

The Upper Carboniferous Millstone Grit and Coal Measures, UK, comprise high-frequency siliciclastic sequences deposited by delta systems infilling a linked system of post-rift intracratonic basins. Hydrocarbon reservoir analogs include incised-valley fills which have been recognized at outcrop and in core using high-resolution sequence stratigraphic analysis.

A comparative study of several incised-valley fills reveals considerable variation in potential reservoir development. For example, valley fills in the lower Kinderscout Grit are confined to paleovalleys up to 10 km wide feeding through canyons which had back-cut from the shelf-slope break during relative sea level fall. At the mouths of these paleovalleys, the fills contain giant foresets and cross-beds of very coarse-grained sandstone interpreted as lowstand braid delta deposits. Valley fills in the younger Rough Rock and Farewell Rock comprise multilateral, multistorey medium- to coarse-grained sandstone sheet bodies with area extents of several thousand square kilometres, interpreted as the deposits of lowstand braided fluvial systems on a stable, shallowly dipping ramp developed fter infilling of the earlier deep basin. In contrast, valley fills in the Crawshaw Sandstone comprise the same facies, but their geometries are strongly channelised along synsedimentary fault zones in a tectonically active ramp setting.

Reservoir distribution, geometry and interconnectivity depend upon the paleogeographic location, regional extent, degree of incision and stacking relationships of incised-valley fills. These key parameters may be predictable given knowledge of basin configuration and palaeobathymetry, synsedimentary tectonism and magnitude and timing of relative sea level changes.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994