THE WINDERMERE TURBIDITE SYSTEM: A WINDOW INTO THE NEOPROTEROZOIC DEEP-WATER WORLD

The Windermere Supergroup (circa 9 km th) in the southern Canadian Cordillera is unique globally for its widespread preservation of deep-water facies which includes basin floor and slope turbidite systems that shoal into shelf facies. The geochemical characteristics of this sedimentary system provide insight into the reduced geochemical sink and offer an essential complement to the existing databases from oxidized shallow water and upper slope facies prevalent throughout the world. The Windermere turbidite system developed along the ancestral continental margin of the Pacific Ocean and overlies rift facies at the base of the Windermere Supergroup that host an older (Sturtian?) glacial deposit. The turbidite system has been correlated throughout the southern Canadian Cordillera on the basis of several through-going marker units, including a deep-water cap carbonate dated at circa 609 Ma and several deep-water carbonate units. The reconstructed size of the turbidite system is at least 160,000 km2, comparable in scale to modern passive margin turbidite systems such as the Amazon and Mississippi fans. Systematic geochemical studies have examined total organic carbon contents of shales, and the isotopic composition of associated organic matter and interbedded carbonates. Total organic carbon (TOC) ranges from fractional values up to nearly 4% locally in slope facies. Despite low-grade regional greenschist metamorphism diversity in isotopic signatures that vary systematically with stratigraphic position suggests preservation of primary signatures of most carbonate carbon and organic matter isotope signatures. The regional pattern established thus far shows a significant excursion to negative carbon values (-10 permil) in the deep water cap carbonate and a return to values near to +2 and eventually rising to +6 in overlying post-glacial strata. The patterns of organic matter and mineral carbonate compare favorably with reconstructed curves in the literature based solely in carbonate carbon from shelf facies further suggesting preservation of a primary signature.