Abstract: The internal deformation of the Appalachian Plateau décollement sheet has a distinctive style involving kink bands and thrusts. In areas where the décollement sheet is underlain by thin salt, the dominant structures are thrusts developed at shallow levels, underlain by a series of steep kink bands that terminate downwards at the Silurian salt décollement. Where the salt is thick, large asymmetrical anticlines developed with hinterland-verging kinks on their back-limbs that deformed the entire supra-salt sequence. In order to understand the constraints on deformation, we have used analytical mechanical modelling based on the maximum strength theorem. The simplified model consists of three layers: two are fluids and the third, intervening layer is a stratified competent material. The model is compressed horizontally and the predictions made are based on the kinematic approach of classical limit analysis. Two modes of deformation are investigated: the thrust and the kink band. The modelling shows that kink bands dominate deformation at large burial depth. At shallower depth and small regional bedding dip, the dominant mode is thrusting. In areas of open folding it is predicted that through-going hinterland-verging kink bands will form at a critical limb dip angle of about 10°. Supplementary material: Technical details of the mechanical theory behind this article are available at https://doi.org/10.6084/m9.figshare.c.3799492

ABSTRACT This annual meeting of the North-Central Section of the Geological Society of America provides an opportunity to visit a working underground salt mine on a field trip. The trip leaders will take a group into the Detroit Salt Mine, which is located approximately 1200 ft (364 m) deep beneath a portion of the city of Detroit, Michigan. This mine extracts salt through a room and pillar mining process from the Silurian Salina "F" Salt formation. Currently the mined salt is used primarily as crushed salt for ice control throughout the upper Midwest. The company is mining a 30-ft-thick seam of bedded halite. Thin beds of anhydrite and/or dolomite are occasionally interbedded with the high-purity halite.

Abstract Dolomite Reservoirs: Geochemical Techniques for Evaluating Origin and Distribution was written to address the need for a short, clear text that explains commonly used inorganic geochemical techniques and their application to dolomite petroleum reservoirs. This volume contains two parts. Part I consists of chapters on different geochemical techniques, with guidelines on how best to apply them, interpret the data, and recognize and avoid the pitfalls and misconceptions that are commonly encountered. Part II consists of case studies of dolomite petroleum reservoirs that formed in each of the major dolomitization environments. This publication will help geoscientists better understand the many ways in which geochemistry can be used to address dolomite reservoir problems.

Evaporitic conditions in the Michigan Basin commenced in Late Ordovician time and continued into the Early Devonian. Five major evaporite (anhydrite/halite) cycles in the Silurian Salina Group (termed “A-1,” “A-2,” “B,” “D,” and “F”) can be recognized. They are further subdivided into two or more cycles of evaporite deposition by intercalations of less soluble members. Only the lowermost Salina evaporite produced a sylvinite deposit. The water surface was enlarged in subsequent evaporite cycles, which did not go beyond halite saturation, suggesting an enlargement of the water supply. Additional seawater came from the Kokomo Sea in Indiana; continental waters likely also entered at times from the Moose River Basin. The Chatham sag eventually fed Michigan Basin brines into Ohio and Pennsylvania. A progressive overstepping of one evaporite unit over the one below indicates either subsidence affecting a wider area of rising sea level, the latter suggested by the inundation of northern Ohio beginning with the “B” unit of salt deposition. In no case does brine depth appear to have exceeded some tens of meters. The present morphology of reefs is dictated as much by compaction of surrounding micrites as by renewed growth on older reef mounds where rates of subsidence remained moderate. The amount of clay influx in the upper part of the Salina suggests that humid periods became more frequent at the expense of the duration of dryer periods. Post-Salina rocks initially contain numerous short-lived evaporite cycles, and then grade to open-marine sediments, deposited before the Michigan Basin became emergent land in the late Paleozoic