MIDDLE EOCENE SEDIMENTATION AND VOLCANISM IN THE EXTENSIONAL WHITE LAKE BASIN, BRITISH COLUMBIA

The middle Eocene White Lake and Skaha Formations in the White Lake Basin, British Columbia record changes in the character of basin infilling that accompanied uplift of the Okanagan metamorphic core-complex. The limited spatial extent and overall lithologic character of these sedimentary and volcanic strata are similar to those of the Klondike Mountain Formation in northernmost Washington. However, White Lake Basin strata are more complexly interstratified, more severely disrupted by post-depositional(normal)faulting, and have a more complete record of core-complex unroofing than the Klondike Mountain Formation strata. Such differences between supposedly genetically similar and correlative deposits underlines the need for caution when applying sedimentary-tectonic-volcanic models in this region.

The 1.1 km thick White Lake Formation includes: 1) Fine to coarse-grained turbidity current deposits, mudstones with abundant organic debris, minor coal lenses, and black shales deposited in lacustrine and overbank settings; 2)Matrix-supported boulder conglomerate and pebble-cobble breccia deposited by alluvial debris flows; 3) Well sorted and cross-stratified gravelly sandstone and clast-supported pebble-cobble conglomerate deposited in fluvial settings; and 4) Volcanic deposits consisting of interbedded block and ash flows, volcanogenic debris flows, pumice-bearing surge deposits, and andesite/rhyolite lava flows. Detrital clasts in the White Lake Formation were derived primarily from underlying volcanic units.

Unconformably overlying White Lake Strata, the 0.3 km thick Skaha Formation consists primarily of: 1)Breccia beds containing Mesozoic-Paleozoic chert, quartzite, and limestone, Cenozoic-Mesozoic granite, and low- to high-grade metamorphic carapace and core- complex rocks (pervasive crackle- and jigsaw textures suggest their emplacement as landslide blocks); and 2)Conglomerate and breccia beds deposited by debris flows. The coarse-grained and shattered nature of these deposits suggests they were emplaced catastrophically following large-scale slope failure. Such slope failures may have been triggered by earthquake activity, climatic fluctuations, volcanism, or some combination thereof.