EOCENE BASIN EVOLUTION IN THE NORTH AMERICAN CORDILLERAN HINTERLAND, SOUTHERN BRITISH COLUMBIA

Mantle-crust interactions and plate boundary dynamics drive the evolution of surface topography including uplift, collapse, sediment deposition, and volcanism. Sedimentary basins in southern BC record the transition from Mesozoic compression to Eocene extensional and transtensional forces. The goals of this study are to correlate sedimentary basin strata, provide a detailed reconstruction of volcanism, and quantify paleotopography to test currently debated tectonic models. Ongoing fieldwork and laboratory analyses include: 1) detailed stratigraphy to determine basin evolution; 2) ⁴⁰Ar/³⁹Ar geochronology and volcanic glass tephrochronology to provide new ages and correlations; and 3) volcanic glass stable isotope analyses to quantify absolute elevations.

Here we present detailed fluvial stratigraphy from sections in the White Lake, Princeton, and Merritt basins, and a preliminary δD_glass value from Princeton fluvial strata. White Lake lithofacies include: 1) planar bounded, broad sheet-like, organic-rich, finely laminated siltstone; 2) planar bounded, wedge shaped, trough cross-bedded sandstone, with interbedded volcanic tuffs; and 3) irregularly-bounded, clast and matrix supported, laterally discontinuous, pebble-boulder conglomerate. Corresponding depositional environments include: 1) floodplain; 2) single-channel fills and dunes; and 3) gravity flows in a meandering fluvial setting. Princeton lithofacies include: 1) concave-up bounded, lenticular sandstone with coal lenses; and 2) planar and concave-up bounded, wedge and lens-like, imbricated, pebble-boulder conglomerate. Depositional environments include: 1) multiple, small, channel fills; and 2) gravity bars in a braided fluvial setting. An ignimbrite sample showed a calculated δ¹⁸O_glass value of -18‰ (± 1‰) which is more distilled than the Methner et al. (2016) calculated δ¹⁸O_water value of -8‰ in the Chumstick Basin, WA. Merritt lithofacies include: 1) concave-up bounded, lenticular, trough cross-bedded sandstone with interbedded volcanic tuffs; and 2) planar and concave-up bounded, sheet and lens-like, organic-rich, finely laminated siltstone, with minor coal lenses. Corresponding depositional environments include: 1) multiple channel fills; and 2) floodplain deposits in a braided fluvial setting.