Dolomitized calcrete in the Middle Devonian Winnipegosis carbonate mounds, subsurface of south–central Saskatchewan, Canada

Abstract

Dolomitized calcrete is a widespread diagenetic feature in the uppermost portions of the Middle Devonian Winnipegosis mud mounds in the subsurface of south–central Saskatchewan. Individual calcrete profiles are composed of 2 to 5 horizons, including (in descending order) laminar crust, massive, pisolitic, breccia, chalky and transitional horizons. The calcrete profiles are interpreted to be pedogenic in origin, formed by diagenetic alteration of the host carbonate deposits during subaerial exposure of the mud mounds. This interpretation is based on the occurrence of an orderly set of well-differentiated horizons, disconformities, vadose pisoids, micritic stringers, circumgranular cracks, linkage coatings, and gradational contacts between the calcrete and underlying host carbonate rocks. Lack of root-related structures, such as rhizoconcretion and alveolar–septal fabric in the Winnipegosis calcrete, suggests a limited influence of macrophytes on the formation of calcrete. The occurrence of up to three discrete pedogenic calcrete profiles in a single Winnipegosis calcrete succession indicates the mounds underwent three periods of subaerial exposure that resulted from drops of water level in the Elk Point Basin of Saskatchewan during Middle Devonian time.