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Deep-Marine Mudrock Chemostratigraphy in the Windermere Turbidite System, Cariboo Mountains, Canada: Implications on Provenance and Sequence Stratigraphy


The Windermere turbidite system is a several km-thick succession deposited off the western margin of Neoproterozoic Laurentia. In the Castle Creek study area (BC Canada), sandstone-rich proximal basin-floor lobe deposits of the Upper Kaza Group (UKG) and sandstone/conglomerate-filled slope channels and levees of the Isaac Formation (IF) form a 2.5 km-thick continuous exposure. This siliciclastic succession is interrupted by an up to 200 m-thick, regionally-extensive mixed siliciclastic-carbonate unit suggesting temporary production and export of platform carbonate during a major episode of elevated sea level.More than 100 mudrock samples were collected across the basin-floor (UKG) to lower slope (IF) transect and analyzed for major, minor and trace elements. The objective was to develop a chemostratigraphic profile to compare with the previously developed sequence stratigraphic framework based on lithostratigraphy and architectural element distribution.Results show that the provenance of siliciclastic sediment was from a uniform, highly weathered (high Al2O3) granitic hinterland in the adjacent Canadian Shield. Also, the overall geochemical makeup of mudstones in the UKG and IF is strikingly similar with only subtle, but nevertheless systematic upward changes. In particular, elements like Zr and Ti that are proxies for terrigenous input tend to be enriched in strata associated with lowstand (i.e. eustatic fall), whereas Ca, Sr, and Mg, which indicate carbonate input, are more abundant in strata related to rising sea level (transgressive and highstand). Furthermore, redox-sensitive elements and ratios, such as U/Th, V/V+Ni, V/Cr, Ni/Co, Zn, and Mo suggest anoxic-oxic fluctuations on the basin floor but strictly oxic conditions on the slope. TOC values, which are generally low throughout the study interval, show a slight but noticeable increase in strata suggestive of rising sea level and associated carbonate input. The P content in most mudrocks is consistently low but ranges up to 15% in randomly interspersed beds, suggesting they reflect short-lived changes in upslope nutrient input and primary paleoproductivity rather than position in a depositional sequence.The close correlation between a number of common mudrock geochemical components and positions of relative sea level provides a possible approach of developing a deep-water sequence stratigraphic framework where lithological or geophysical data are of insufficient resolution or are unavailable.