Upper Devonian and Lower Mississippian Sedimentary Record, Western Canada Shelf: ABSTRACT

Abstract

Western Canadian Upper Devonian and Lower Mississippian shelf rocks, several thousand feet thick, are characterized by three sedimentary domains: a carbonate-evaporite area on the southeast (Saskatchewan), a central area dominated by carbonates (Alberta), and a terrigenous clastic and argillaceous carbonate area on the north (northeastern British Columbia). The carbonate-evaporite and carbonate domains include sabkha-type microdolomite-evaporite cycles, as well as barriers and blankets of skeletal and nonskeletal limestones. Although many of these rocks compare closely with sediments of certain Holocene carbonate settings, the makeup of these fossil sediments tends to be distinctive at various stratigraphic levels. To illustrate: within the carbonate domain (Alberta), the Frasnian Stage contains wave-resistant organic reefs in which stromatoporoids and colonial corals are abundant. In contrast, reefs, stromatoporoids, and colonial corals are almost unknown in Fammenian strata, most of which form an extensive blanket of nonskeletal limestone with evaporites and redbeds on the east. A widespread black shale unit caps the Fammenian. Kinderhookian rocks are argillaceous carbonates in which echinoderm detritus increases upward. Although colonial corals reappear in the Kinderhookian, the Mississippian lacks organic reefs. The Osagian is distinguished by an explosive and geologically unique development of echinoderms--the main source of the enormous volumes of skeletal sands of this age which cover muc of the area--and also contains well-developed cyclic lagoon-sabkha sediments. Two dominant factors that influenced Late Devonian-Early Mississippian sedimentary patterns on this continuous shelf are oscillatory variations in water depth (probably tectonically controlled) and change in composition of the dominant fauna and flora from frame-builders to sediment-contributors. End_of_Article - Last_Page 730------------