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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 2. (February)

First Page: 342

Last Page: 343

Title: Transport and Deposition of Coarse Clastics in Turbidite Basin in French Alps: ABSTRACT

Author(s): Hugh E. Hendry

Article Type: Meeting abstract

Abstract:

Marine breccias of Jurassic to Early Cretaceous ages are present in the Breccia Nappe of the French Prealps. Breccia types Ia and Ib are restricted to the lower part of the sequence in the Lower Shale, Lower Breccia, and Upper Shale formations. Type Ia breccias occur in beds from a few centimeters to tens of meters thick. They contain clasts up to more than 1 m in diameter, and are sometimes graded. Sole markings occur but are not common. Tops of some beds have large scale cross-stratification or parallel bedding, usually in granule-pebble grade material. Individual beds are of limited lateral extent--of the order of 1-2 km along the depositional strike and in places up to 7-8 km across it. The breccias have a clast framework and interstitial material is usually pebble or granule size. There is a continuous spectrum, with change in relative proportions of gravel and sand, from the breccias to pebbly turbidite sandstones.

Type Ib is much less common than Ia. It has clasts of the same composition and size but it is characterized

End_Page 342------------------------------

by more than 50% sand-grade matrix. Beds are less than 200 cm thick, parallel-sided, and have an uppermost sand-silt layer with convolute lamination.

Type Ia is interpreted as a deposit from mass flow of coarse granular debris where internal shear was extensive enough to allow development of grading. For the transport of Type Ib beds, a slide mechanism is favored.

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