Date of Award
Master of Arts (MA)
The Ratcliffe interval in North Dakota is a log marker-defined unit in the Williston Basin. It is Mississippian in age and crosscuts the lower Charles and upper Mission Canyon Formations of the Madison Group. Study of cross-sections, well core, and thinsections show that the Ratcliffe is comprised of six major facies: 1) brachiopod-bryozoan-echinoderm wackestone/packstone, 2) peloid packstone/wackestone, 3) oolite-peloid packstone, 4) laminated mudstone, 5) quartz siltstone packstone, and 6) anhydrite-dolomite mudstone. These facies were deposited in a regressive setting.
The initial deposition consisted mainly of marine limestones. The environment gradually became more restricted and deposition of large amounts of anhydrite and dolomite occurred around the basin margin. Sabkha tidal flat areas were present. Highly saline conditions at the end of the Ratcliffe allowed deposition of large amounts of halite.
The facies in the studied cores showed that much diagenesis has occurred in the Ratcliffe interval. The most common forms of diagenesis include dolomitization, replacement, recrystallization, cementation, nd dissolution. Fracturing and brecciation also occurred. The Ratcliffe lithologies can be divided into two major diagenetic provinces, the near-shore/supratidal, which consists of rocks which have been moderately to highly altered by diagenesis, and the open marine, which is comparatively much less altered.
Catt, Diane M., "Depositional environments and diagenesis of the Ratcliffe interval, Madison group (Mississippian), Williston Basin, North Dakota" (1982). Theses and Dissertations. 53.