Subsurface Stratigraphy and Depositional History of Madison Limestone (Mississippian), Williston Basin: ABSTRACT

Abstract

Cyclic carbonate-evaporite deposits of the Madison Limestone (Mississippian) in the Williston basin are made up of four main facies. From basin to shelf, the normal facies transition is from offshore deeper water (Lodgepole) facies to crinoidal-bioclastic banks at the basin to shelf transition, to oolite-algal banks and back-bank fine carbonate, evaporite, and minor terrigenous clastic beds on the shallow shelf. Five major depositional cycles are correlated and mapped on the basis of shaly marker beds identified on gamma-ray-neutron or gamma-ray-sonic logs. The marker beds are interpreted as reworked and redistributed silt and clay-size sediments originally deposited, possibly by eolian processes, on the emergent shelf during low sea level phases of cycle development. Fro oldest to youngest, the first two cycles are characterized by increasing amounts of crinoidal-bioclastic and oolite-algal carbonates, culminating in the Mission Canyon facies of the middle cycle. The upper two cycles are characterized by increasing amounts of evaporite deposits, culminating in the Charles salt facies of the youngest cycle. Much of the Madison section on the south and east flanks of the basin consists of dolomite. Dolomite content decreased toward the basin center, where a major share of Madison petroleum production is located. Reservoir beds in the oil fields are primarily partially dolomitized oolite-algal or crinoidal-bioclastic bank carbonates. Most of the productive petroleum reservoirs are located in the middle cycles of the Madison. End_of_Article - Last_Page 859------------