Abstract

Following the breakup of Rodinia and the initiation of the Pacific Ocean (~725 Ma), Windermere Supergroup (WSG) sedimentation took place along the newly formed passive margin of western Canada (Laurentia). Unconfined, sand-rich, basin-floor, submarine-fan deposits characterize the Upper Kaza Group of the WSG and are well exposed at Castle Creek, British Columbia. Regional correlations of the Upper Kaza Group indicate an unconfined, distal basin-floor setting for the Castle Creek study area, becoming more confined and proximal to the continental slope to the southeast. Detailed sedimentologic and stratigraphic studies identified three depositional intervals in the Castle Creek study area with net-to-gross ratio decreasing upward from 67 to 59%. The lowermost interval (~100 m [328 ft]) is composed of sets of stacked and amalgamated Ta sandstones up to 10 m (33 ft) thick, separated by thin-bedded (~1 cm [~0.4 in.]-scale) Tde turbidites. These thick, amalgamated sandstone packages are interpreted to record deposition in low-relief lobes with shallow channels in the interiors. The middle interval is characterized by the presence of regional (at the scale of the outcrop) erosive surfaces with mudstone breccias and common medium-scale, cross-stratified sandstone. This interval is interpreted to record bypass as lobes accumulated to local base level. The upper interval consists of interbedded, nonchannelized, sheetlike sandstones and thin turbidites interpreted as off-axis or interchannel deposits. Sheetlike debris flows with minimal lateral variation in thickness attest to a subdued basin-floor topography. The vertical succession, which culminates in slope facies of the overlying Isaac Formation, is interpreted to record a prograding, basin-floor, fan-lobe depositional setting, with evidence of a lateral shift from axis (lower and middle interval) to off-axis (upper interval) sedimentation.