CONTROLS ON SEISMIC-SCALE SEQUENCE-STRATIGRAPHIC ARCHITECTURE OF TRIASSIC MIXED CARBONATE-SILICICLASTIC SYSTEMS: NANPANJIANG BASIN, SOUTH CHINA

Comparative analysis of platform evolution recorded along multiple and intact 2D platform-to-basin transects of the Yangtze Carbonate Shelf and several isolated platforms in the Triassic Nanpanjiang basin, south China, indicates that laterally-variable tectonic subsidence, rate of clastic deposition at the toe of slope, antecedent topography, and changes in carbonate factory type controlled the evolution, large-scale sequence stratigraphic architecture, and geometry of the platform margin and slope. Lateral and temporal changes in these parameters during the Middle and early Late Triassic resulted in a remarkable vertical and along-strike variability in the observed sequence-sratigraphic architecture and slope profile.

Timing and rates of subsidence largely controlled along-strike variability of stacking patterns, back-step geometries, timing of drowning, and development of marginal pinnacles. Antecedent topography and timing of basin fill dictated differences in platform-margin stability and geometries such as slope angle, relief above basin floor, development of collapse scars, and progradation at basin margins. Changes in slope profile through the Early and Middle Triassic reflect changes in carbonate-factory type and evolving seawater chemistry following the end-Permian extinction. Eustasy, in contrast, had very little influence on platform morphology and large-scale architecture.

Process-based depositional models derived from the Nanpanjiang basin of south China present an important analog for understanding, quantifying, and accurately interpreting facies distribution and sequence-stratigraphic architecture of carbonate systems in other basins, such as the prolific Cretaceous lacustrine carbonates of the South Atlantic.