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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Fluvial Sedimentology — Memoir 5, 1977
Pages 487-510
Ancient Fluvial Systems

Coarse-Grained Point Bar Structure in a Molasse-Type Fluvial System, Eocene Castisent Sandstone Formation, South Pyrenean Basin.

W. Nijman, C. Puigdefabregas

Abstract

A large coarse-grained point bar lithosome in the upper part of a multi-storey fluvial sheet sandstone, the Castisent Formation, is described. This sandstone forms a major fluvial system within the Eocene Montanana Deltaic Complex in the Tremp-Graus section of the South Pyrenean Basin. The point bar unit has a crescent-shaped wedge geometry, shows two forms of lateral accretion units, and is characterised by a vertical sequence of scour pool conglomerate, lower point bar trough-fill cross-strata, a well-defined transverse bar facies restricted to the downstream half of the point bar body, upper point bar festoon-beds and an accretionary bank with meander scroll structure, interrupted by a flat-based chute. Perfect outcrop conditions allow the documentation of both the vertical sequence and the point bar relief forms, the cut bank and abandonment fill included.

A comparison is made with some modern examples of coarse-grained point bars.


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