High resolution sequence stratigraphic architecture of a Mid-Continent Mississippian outcrop in southwest Missouri.

摘要

The Mid-Continent Mississippian Limestone represents a geologically complex system containing different depositional environments and dynamic diagenetic and tectonic histories. This thick (up to 500 ft) carbonate unit was deposited in an east-west oriented belt with a northern and southern boundary within 5°-30° of the paleo-equator. Its subsurface equivalent is an unconventional oil and gas play in Oklahoma and Kansas with well-exposed outcrops in Missouri and Arkansas. The Mississippian-age strata in this area has been interpreted by some to be deposited in a shelf margin environment based on over-simplified paleo-depositional maps. In this study, detailed outcrop analysis has revealed the depositional environment is more consistent with a distally steepened ramp and that complex and dynamic facies mosaics exist across the distally steepened ramp due to lateral migration of facies, complicating the lithology-based nomenclature used throughout the Mid-Continent.;Understanding how primary depositional facies fit into a sequence stratigraphic framework will increase predictability of reservoir facies. The high resolution sequence stratigraphic architecture study at the Jane outcrop provides a basin specific analog for identification of reservoir facies in the subsurface. This study includes analyses of facies vertically and horizontally to identify geometries and vertical stacking patterns on the third-, fourth-, and fifth-order scales. Using an integrated sequence stratigraphic approach combining Gigapan imaging, thin section analysis, scanning electron microscopy, and spectral gamma ray logs identified a repeated shallowing-upward succession of facies ranging from bryozoan-crinoidal wackestones to bryozoan crinoidal grainstones, likely at the 4th order scale.;Integrating this sequence stratigraphic approach with an understanding of the probable complexity of facies mosaics from modern analogs has led to a modified time-series of paleo-depositional maps that better illustrate the complex facies mosaics associated with Milankovitch-scale sea level change. The high resolution sequence stratigraphic architecture developed at the Jane outcrop provides a datum for a more accurate interpretation of how Mississippian lithofacies fit into the sequence stratigraphic framework. A high resolution sequence stratigraphic architecture study that incorporates primary facies, depositional environments, and gamma ray response within a larger scale 2-D geometry for an outcrop can be used as a basin specific analog to identify reservoir facies in the subsurface.