Tectonic Subsidence Analysis of the Illinois Basin

Abstract

Tectonic subsidence curves calculated from three wells indicate that the Illinois Basin formed through initial fault-controlled mechanical subsidence and subsequent thermal subsidence. Thermal subsidence involved an early stage of thermal linear (520-460 Ma) and subsequent thermal asymptotic subsidence (460-350 Ma). This thermal subsidence was in response to mantle intrusion which formed a three-arm rift system. A second subsidence episode of unknown origin was documented from Middle Mississippian through Early Permian time. Subsidence mechanisms controlled sedimentation and subsidence rate trends and also sedimentation patterns for each of the four distinct tectonic subsidence phases. Tectonic subsidence curves were extended across the Sauk-Tippecanoe, Ordovician-Silurian, and Tippecanoe-Kaskaskia unconformities and fit a post-rift thermal contraction model. The Sauk-Tippecanoe, Ordovician-Silurian, and possibly the Kaskaskia-Absaroka unconformities formed because rates of eustatic sea level fall exceede...