RE-OS GEOCHRONOLOGY AND OS ISOTOPE STRATIGRAPHY OF THE NEOPROTEROZOIC CALLISON LAKE DOLOSTONE: INSIGHTS INTO DEPOSITIONAL ENVIRONMENTS, NEOPROTEROZOIC MICROFOSSILS AND CORRELATION OF CORDILLERAN STRATIGRAPHY

The Neoproterozoic Callison Lake Dolostone (CLD) of Yukon, Canada is unconformably bound below by the Fifteenmile Group and above by the Mount Harper conglomerate, Mt. Harper Volcanics, and Sturtian-age glacial deposits of the Rapitan Group. The CLD consists of >300 m of microbially-bound carbonate interbedded with talc-rich carbonaceous black shale. Exceptionally well-preserved vase shaped microfossils (VSMs) present in the CLD are comparable to those found in the ~742 Ma Chuar Group of Arizona. Existing U-Pb CA-ID TIMS zircon geochronological data from the Ogilvie Mountains constrain deposition of the CLD between 811 and 717 Ma. We report new Re-Os geochronological data that provides a direct date on the shale in the uppermost CLD that contains the VSMs and is consistent with existing U-Pb data. These data help refine correlations of Neoproterozoic strata across Laurentia. Complementing the Re-Os geochronology data, initial Os isotope data from the Callison Lake Deposit provides a unique insight into the environment of deposition. The Os isotope data represents a balance between radiogenic inputs from continental weathering and unradiogenic mantle-sourced inputs from hydrothermal sources. Our preliminary data indicate that the Callison Lake Dolostone was deposited in a restricted and possibly lacustrine setting.