Regional stratigraphy and structural setting of the Kamloops Group, south-central British Columbia

Abstract

The Kamloops Group is redefined as an assemblage of Lower to Middle Eocene volcanic and sedimentary rocks widespread in south-central British Columbia. In the type area west of Kamloops, the basal Tranquille Formation consists of 500 m of lacustrine and deltaic sediments, pillowed flows, and hyaloclastites. Elsewhere, basal coal-bearing nonvolcanic fluvial and lacustrine units occur, such as the Coldwater Formation at Merritt, the Chu Chua Formation at Barriere, and the Shorts Creek Formation west of Vernon. Overlying these formations are dominantly volcanic units. At the type area, the Dewdrop Flats Formation includes over 1000 m of interstratified basaltic andesite flows, andesitic flow-breccia sheets and cones, basaltic tuff rings, and an andesitic composite cone. Elsewhere, flat-lying basaltic andesite flows about 600 m thick with local flow breccias are common.The basal sediments accumulated in separate fault-bounded basins initiated immediately before the onset of volcanism. These volcanic rocks filled the basin and formed a widespread volcanic blanket, which was disrupted by continued fault movement. The numerous basins are linked by a throughgoing fault network with up to 12 km of net right-lateral strike-slip displacement.

The McAbee flora of British Columbia and its relation to the Early-Middle Eocene Okanagan Highlands flora of the Pacific Northwest

“…The shale beds are capped by flow breccia and sit atop an ash-flow tuff. Tephra deposits bracketed by fossiliferous layers yielded K-Ar dates of 49 ± 2 and 52 ± 2 Ma from plagioclase and 51 ± 2 Ma from biotite contained within a bentonitic tuff (Ewing 1981). These dates generally support the interpretation of a late Early Eocene age.…”

A review of paleobotanical studies of the Early Eocene Okanagan (Okanogan) Highlands floras of British Columbia, Canada, and Washington, USA

“…Ottawa collections from Chu Chua are catalogued under four main locality numbers corresponding to the separate areas of outcrop from which Berry (1926) described taxa. Ewing (1981) refers coal-bearing sediments in this area to the Early Eocene Chu Chua Formation, noting similarities to the Coldwater beds near Merritt that include the Quilchena flora. Wolfe et al (1998) suggested an age of 48-50 Ma for the Chu Chua flora (Fig.…”

Floristic composition and comparison of middle Eocene to late Eocene and Oligocene floras in North America

“…These deposits formed after the geological processes described below: Extensive strikeslip faulting occurred in northeast Washington during the late early to early middle Eocene. During this time, the southern Cordillera of northernmost central Washington, and up into south-central British Columbia, experienced episodes of right-lateral faulting responsible for producing a set of northwest-trending grabens and half-grabens (Ewing 1981, Matthews 1991, Mustoe 2005. A volcanic arc in south-central British Columbia provided a source of large volumes of volcaniclastic sediments and basalt flows in these basins.…”