Sedimentary and Tectonic History of North Dakota Part of Williston Basin

Abstract

The Williston basin is a structural and sedimentary basin which includes 51,600 square miles in North Dakota. It contains sedimentary rocks of every geologic period from the Cambrian through the Tertiary and its history can be divided conveniently into the Sequence subdivision (Sauk Tippecanoe, Kaskaskia, Absaroka, Zuni, Tejas) based on the major unconformities within the preserved section. The maximum known sedimentary thickness is 15,128 feet in a well in McKenzie County in western North Dakota. The Upper Cambrian to Lower Ordovician Epochs are represented by the Deadwood Formation, which is a stable shelf deposit extending eastward from the Cordilleran geosyncline. The Williston structural basin began to be filled in Middle Ordovician time with a relatively thin clastic sequence (Winnipeg Group) followed by predominantly carbonate deposition (Red River, Stony Mountain, and Stonewall Formations). Carbonate deposition continued through Early and Middle Silurian time (Interlake Formation) followed by a period of erosion marked by a major unconformity. During the Middle and Upper Devonian Epochs the Williston basin was a part of the larger western Canada basin of deposition which was characterized by predominantly carbonate deposition with a thick evaporite in the lower part (Prairie Formation) and cyclical carbonate with some thin clastic and evaporite beds in the upper part (Duperow, Nisku, Three Forks). Deposition was continuous or nearly continuous into the Mississippian, but the center of the Madison depositional basin was nearly coincident with the present Williston basin. Mississippian deposition began with predominantly carbonate deposition, evaporites increasing in the upper part. The evaporites are mostly halite in the central basin area and anhydrite toward the flanks of the basin. Predominantly clastic deposition (Big Sn wy Group) followed the evaporites; another unconformity is at the top of the Big Snowy. The Pennsylvanian and Permian Periods are represented by clastics with minor carbonates (Minnekahta Formation) and some evaporites. This was a time of slight subsidence, with the Williston basin area a part of a larger depositional area extending south and west. Similar conditions continued through the Triassic with deposition of fine-grained clastics and some evaporites, which are overlain by some non-marine redbeds and another unconformity. As the Williston structural basin had little effect on Jurassic or Cretaceous sedimentation, these periods are represented by eastward extensions of the predominantly fine-grained clastics from the Rocky Mountain area seas. The Tertiary Period is represented by a wedge of predominantly non-marine beds which thicken westward toward the Rocky Mountain area.