Eocene paleo-physiography and drainage directions, southern Interior Plateau, British Columbia

Abstract

A map of reconstructed Eocene physiography and drainage directions is presented for the southern Interior Plateau region, British Columbia south of 53°N. Eocene landforms are inferred from the distribution and depositional paleoenvironment of Eocene rocks and from crosscutting relationships between regional-scale geomorphology and bedrock geology of known age. Eocene drainage directions are inferred from physiography, relief, and base level elevations of the sub-Eocene unconformity and the documented distribution, provenance, and paleocurrents of early Cenozoic fluvial sediments. The Eocene landscape of the southern Interior Plateau resembled its modern counterpart, with highlands, plains, and deeply incised drainages, except regional drainage was to the north. An anabranching valley system trending west and northwest from Quesnel and Shuswap Highlands, across the Cariboo Plateau to the Fraser River valley, contained north-flowing streams from Eocene to early Quaternary time. Other valleys dating back at least to Middle Eocene time include the North Thompson valley south of Clearwater, Thompson valley from Kamloops to Spences Bridge, the valley containing Nicola Lake, Bridge River valley, and Okanagan Lake valley. During the early Cenozoic, highlands existed where the Coast Mountains are today. Southward drainage along the modern Fraser, Chilcotin, and Thompson River valleys was established after the Late Miocene.

The Cenozoic climatic and topographic evolution of the western North American Cordillera

“…This decrease is a result of changes in rainout and decreasing temperature with latitude. Since the bulk of the study area has been at nearly the same latitude for the Cenozoic (Smith and others, 1981) (Kent-Corson and others, 2006;Carroll and others, 2008;Smith and others, 2008;Davis, 2009aDavis, , 2009bDoebbert and others, 2010 (Smith and others, 1993;Wang and others, 1993;Mack and others, 1994;Fox and Koch, 2004;Horton and others, 2004;Kent-Corson and others, 2006;Horton and Chamberlain, 2006;Fan and others, 2011; this study), paleolake sediments (Rogers and others, 1992;Poulson and John, 2003;Davis and others, 2008Davis and others, , 2009aDavis and others, , 2009b; this study) and fossil bivalves (Fan and Dettman, 2009); squares represent smectite from weathered ashes (Poage and Chamberlain, 2002;Takeuchi and Larson, 2005;Sjostrom and others, 2006); diamonds represent hydrated glasses from volcanic ashes (Mulch and others, 2008;Cassel and others, 2009b); triangles represent kaolinite from weathered stream deposits (Mulch and others, 2006); and pentagons are muscovite from shear zones others, 2004, 2007 documented for southern British Columbia (Mulch and others, 2004;Greenwood and others, 2005;Tribe, 2005;Mulch and others, 2007 18 O values of surface waters east of the Washington Cascades were higher than they are today. Third, the isotopic rain shadow on the east side of the Sierra Nevada had been established by the mid-Miocene and the isotopic values there were similar to modern values.…”

Quaternary stratigraphy and evidence for multiple glacial episodes in the north Okanagan Valley, British Columbia

“…5) could be Devonian-age sediments and metasediments as mapped on the eastern side of the valley, or Eocene-age sediments as mapped on the western side of the valley (Thompson and Unterschultz 2004;Okulitch 2013). The elevation of these materials in section 5 is below the Eocene base level of 350-400 masl noted in Tribe (2005) for the Okanagan, but consistent with mapping of Eocene-age sediments at elevation of ϳ0 masl and higher in the area of Enderby Cliffs (Breitsprecher et al 2000).…”

“…Eocene-age sediments comprising basal conglomerates, with siltstones and sandstones, are present in the bedrock ridge between Sleepy Hollow and Enderby. The Enderby Cliffs located 3 km north of Enderby, British Columbia, include further Eocene deposits, with basal sedimentary units that contain coal, which are overlain by mixed volcanic and sedimentary rocks (Breitsprecher et al 2000;Breitsprecher 2002;Tribe 2005).…”

Fossil palm beetles refine upland winter temperatures in the Early Eocene Climatic Optimum

“…Peak regional tectonic uplift during Okanagan Highlands times resulted in a mountainous topography comparable to the modern British Columbian Coast and Selkirk ranges (34,35). Floral proxies indicate a considerably warmer climate in coeval nearby coastal lowland formations, with a substantial elevational MAT gradient upslope to the cooler Okanagan Highlands (16,17,19,(36)(37)(38)(39).…”