Evaporitic Environments and Their Relationship to Porosity of Associated Carbonates in Williston Basin (Mississippian): ABSTRACT

Abstract

Evaporite morphologies, indicative of specific environments of deposition, have been identified in late Cenozoic sediments, and are now recognized in the Williston basin (Mississippian, Little Knife field). The evaporitic environments which are represented include the supratidal (sabkha), the intertidal, and the shallow subaqueous. The development of the sabkha facies exerts a major control on porosity production in associated marine carbonates. Those evaporites forming subaqueously in related lagoons and other water bodies may occlude porosity within similar carbonate sediments. However, subaerial and subaqueous evaporites are now seen in the form of massive to nodular anhydrite and are usually classified together (in cores and well logs), but in fact they contain relic orphologies that permit more precise definition and separation of original facies. Subsequent porosity occlusion and/or creation may also be affected by later deformation of the regional structure and its effect on fluid migration. The recognition of the various evaporitic morphologies leads to a new understanding of porosity development in sediments of varied origins and may aid in distinguishing early from late phases of diagenesis. End_of_Article - Last_Page 626------------