Understanding the mechanisms that control longevity, architecture, and sequence variability of carbonate platforms is of fundamental 8importance in scientific studies of carbonate platforms as recorders of ancient environments and in hydrocarbon exploration and exploitation. However, interpretations of internal facies architecture and sequence-stratigraphic correlation's of carbonate platforms are commonly based on an assumption: fluctuations in sea level are the essential controlling mechanism.
We propose a collaborative project between Universities of Kansas and Wisconsin-Oshkosh to evaluate the roles of both regional and local variables including sea-level changes, subsidence, tectonic activity, siliciclastic influx, excess nutrient flux, and carbonate production rates on platform architecture. Evaluation of these controls will be accomplished through a comparative analysis of coeval Triassic platforms of various scales, architectures and settings distributed over an area of 650 kn2 within the Nanpanjiang Basin of south China. We have chosen the Nanpanjiang Basin because we know of no other area that allows outcrop study of as great a diversity of platform scales and morphologies, including both landward-attached platforms and isolated platforms.
We will determine sequence-stratigraphic architecture from mapping outcrops that expose continuous two-dimensional transects through the platforms. Comparison of synchronous intervals will aid in separating regional and local controls. We will use detailed biostratigraphy and magnetic-reversal stratigraphy to ensure that synchronous events are evaluated in the separation and interpretation of controlling mechanisms. With this stratigraphic and age data we will construct subsidence histories to isolate local variations so we can examine possible causes for synchronous differences in the stratigraphy between platforms or along strike within platforms. For example, for coeval intervals with similar subsidence and eustatic histories we will use facies analysis to evaluate the impact of variables such as influx of siliciclastics or excess nutrients on interruptions or termination of carbonate platform growth and to evaluate the impact of basin-filling siliciclastics on progradation geometries. The end product will be a series of depositional models that illustrate actual architectural variability in carbonate platforms and a quantitative understanding of the mechanisms that control variability.
