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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 804

Last Page: 804

Title: Comparison of Slope and Basinal Sediments of Marginal Cratonic Basin and Geosyncline: ABSTRACT

Author(s): Martin A. Schupbach

Article Type: Meeting abstract


The transition from slope to basinal facies generally is not so well exposed or understood as it is in the Pennsylvanian of New Mexico's Pedregosa basin and in the Liassic of Switzerland's Piemontais geosyncline.

The shape of the Pedrego basin is controlled by basement faulting; its trend is oblique to the Ouachita-Marathon geosyncline. During periods of stable sea-level stand, carbonate sedimentation prevailed in shelf areas, and bioherms built up at the shelf edge. Bioclastic foresets and huge slumps of brecciated material from these bioherms extended from the shelf edge into the basin, where deep-water carbonates were deposited. During periods of low sea-level stand, rivers cut through the shelf deposits and shelf-edge bioherms and eroded deep valleys on the slope. As sea level rose, the basin was filled mainly with shales, and valleys on the slope were filled with sand. The geometry of these sand bodies at the base of the slope is probably fan- or cone-shaped.

Normal faults in the Liassic slope sediments of the Piemontais geosyncline reflect the structural tension that persisted during early geosynclinal stages. Thick beds of structureless breccias accumulated on the downthrown side of these faults. In the downslope direction, the breccias grade into turbidite facies; farther downslope, thick wedges of turbidite thin at their distal edges. No evidence was found of channels or canyons that would serve as point sources for sediment dispersion down the slope. The turbidites grade upward into radiolarian chert.

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