PROVENANCE OF THE NEOPROTEROZOIC WINDERMERE TURBIDITE SYSTEM (SOUTHERN CANADIAN CORDILLERA): ASSESSING SCALES OF CONTINENTAL DRAINAGE

Turbiditic sandstone and conglomerate is one of the most prevalent facies in the Neoproterozoic Windermere Supergroup of the southern Canadian Cordillera. Recent stratigraphic correlations and mapping suggest that the turbidites formed part of an extensive depositional system (Windermere turbidite system, WTS) which, when corrected for the effects of Mesozoic shortening, may have been at least 100,000km2 in area, comparable to modern deep sea fans such as the Mississippi and Amazon. In order to examine the scale of the subaerial drainage basin and nature of the feeder channels that supplied this system we examined detrital zircons from a range of stratigraphic levels. Individual submarine channel complexes tend to be characterized by a distinctive provenance. The most locally derived examples are those that are filled with detritus derived from the crystalline basement of northern Alberta (prominent peaks at 2.0-2.3 Ga) and delivered to the WTS by structural capture of fluvial drainage. The most distally sourced examples contain a modest population of ages consistent with derivation from the Grenville province (1.0-1.2 Ga) admixed with grains derived potentially from the mid-Continent granite-rhyolite terrane (ca. 1450 Ma) and more proximal Shield sources such as TransHudson orogen (1.8-1.9 Ga). Compositional contrasts within channel complexes (quartzose vs. arkosic) share a common provenance suggesting that the differences in framework mineralogy largely reflect residence time and winnowing effects on the shelf. Although the scale of the WTS is comparable to modern fans the drainage basin appears to be significantly smaller perhaps reflecting the effects of a lack of terrestrial vegetation in preSilurian drainage systems on river length.