--> Abstract: Sequence Stratigraphy of the Middle Devonian Winnipegosis Vadolite and Ratner Laminite of the Elk Point Basin, Southern Saskatchewan: A Falling Stage System Tract, by J. Jin and K. Bergman; #90928 (1999).
[First Hit]

Datapages, Inc.Print this page

JISUO JIN and KATHERINE BERGMAN
Department of Geology, University of Regina, Regina, Saskatchewan, S4S 0A2 Canada

Abstract: Sequence Stratigraphy of the Middle Devonian Winnipegosis Vadolite and Ratner Laminite of the Elk Point Basin, Southern Saskatchewan: A Falling Stage System Tract

The Middle Devonian Winnipegosis carbonate buildups in the southern Saskatchewan portion of the Elk Point Basin contain extensive vadose diegenetic features (e.g., microbial pisolite, Previous HitanhydriteNext Hit cement, and caverns filled by microbialite, pisolite and Previous HitanhydriteNext Hit). Inter-reef, reef slope and basinal facies are characterized by the Ratner Member, which consists of finely laminated, cyclic and laterally extensive dolomite, dolomitic micrite and Previous HitanhydriteNext Hit. The basal cycle usually starts with a relatively thick unit of light brown, millimeter-scale dololaminite, changing upward into reddish brown interbedded dololaminite and Previous HitanhydriteNext Hit and ending with nodular, enterolithic to mosaic Previous HitanhydriteNext Hit. Subsequent cycles generally lack the light brown dololaminite unit. Deposition of the Rather laminite is interpreted as genetically related to the vadose diagenetic processes. A moderate sea-level drop during the Middle Devonian (Givetian) exposed the top of the Presquile Barrier Reef, initiating an evaporative drawdown inside the Elk Point Basin and vadose diagenesis of the top part of the Upper Winnipegosis carbonate. A relatively thick succession of carbonate laminite was accumulated when seepage of fresh marine water through and over the barrier kept pace with the rate of evaporation, preventing a complete drawdown and desiccation of the basin. Carbonate precipitation was probably stimulated by dissolution of the carbonate buildups and by microbial growth in the deeper part of the basin. Upward increase in both the number and the thickness of Previous HitanhydriteNext Hit interbeds in each of the Ratner cycles indicates progressive drawdown when the rate of basin brine evaporation exceeded seepage of fresh marine water into the basin through the barrier. Marine water seeping through the barrier and in-basin carbonate banks was enriched in calcium cations by Mg++ - Ca++ exchange with the limestone (dolomitization) and by dissolution of the reef rocks, and was responsible for the precipitation of calcium sulphite in areas adjacent to the carbonate buildups. During vadose diagenesis of the Winnipegosis reefs/banks and deposition of the Ratner laminated carbonate and Previous HitanhydriteNext Hit, brine level in the barred Elk Point Basin was controlled by the rate of seepage of marine water through the barrier, which was in turn controlled by sea level in the open ocean. The laminated carbonate-Previous HitanhydriteTop cycles of the Ratner are interpreted as parasequences in a Falling Stage System Tract deposited during a progressive and cyclic evaporative drawdown.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas