Controls on Differential Carbonate Platform Evolution: Triassic, Nanpanjiang Basin, South China

Lehrmann, Daniel J.
Department of Geology, University of Wisconsin Oshkosh, Oshkosh, WI

The Nanpanjiang Basin occurs in the southern margin of the Yangtze micro-plate. Marine sedimentation continued from Early Paleozoic to Late Triassic when synorogenic turbidites filled the basin. Triassic platforms include diverse architectures and evolutionary histories that reflect differences in tectonics, subsidence rates, carbonate-production rates, and timing of siliciclastic influx.

The Yangtze platform (YP) margin that rims the basin extends 530 km from Guizhou to Yunnan. Four isolated platforms (IP) occur in southern Guizhou and Guangxi. The basin expanded in the Late Permian during a regional transgression. The YP and IP evolved from low-angle ramps with oolite margins in the Early Triassic to steepening Tubiphytes reef margins in the Middle Triassic (Anisian). Basin-wide shift from ramp to steepening-margins was stimulated by the evolution of reef-building organisms. The western YP and the northernmost IP developed high-relief, retreating escarpments during the Ladinian while the northeastern YP changes along-strike from aggradation to progradation. The western YP was drowned and buried by turbidites in the Late Triassic (Carnian) whereas shallow-water sedimentation continued until burial by siliciclastics in the northeast. Along-strike differences in evolution of the YP resulted from faster subsidence and syndepositional wrench faulting in the western sector and slower subsidence and earlier arrival of basin-filling siliciclastics in the northeastern sector.

The IP show a southward pattern of platform stepback, development of pinnacle platforms, and earlier termination and siliciclastic burial. These differences resulted from faster subsidence rates probably caused by the collision of an arc along the southern margin of the Yangtze plate.

Dramatic differences in platform architecture, especially apparent at platform margins, were driven by differential tectonic subsidence, syndepositional faulting and timing of siliciclastic flux. Despite these differences, eustacy drove in a basin-wide sequence stratigraphic signal that is best expressed in platform interior facies stacking patterns.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004