Brent C. Ward

Chapter 44 – Pleistocene Glaciation of British Columbia

Abstract The Cordilleran Ice Sheet developed over British Columbia and surrounding areas repeatedly during the Pleistocene and most recently during Marine Oxygen Isotope Stage 2 (ca. 25-10 ka). Landforms and deposits of the last glaciation are dominant surface materials; older glacial sediments locally occur below the last-glacial sediments. The ice sheet deformed the lithosphere on which in rested; the deformation is captured in raised and deformed marine and lake shorelines.

Impacts of the 2007 Landslide-Generated Tsunami in Chehalis Lake, Canada

On 4 December 2007, a 3 Mm3 debris avalanche entered Chehalis Lake, British Columbia, Canada. The resulting tsunami caused extensive shoreline damage as far away as the outlet (7.5 km) and far down lower Chehalis River (>15 km). We documented impacts of the tsunami through a multifaceted investigation that included field surveys and collection and analysis of SONAR data, LiDAR data and high-resolution orthophotographs. Geomorphic impacts included a wide range of erosional and depositional features, many of which provide information on wave energy, direction, run-up and inundation along much of the lakeshore. Our characterization of the geomorphic impacts of the Chehalis Lake event advances understanding of landslide-generated tsunami in several ways: it aids identification of events elsewhere by providing insight into their geomorphic signature; it provides an opportunity to verify hydrodynamic numerical models; and it improves regional understanding of hazard and risk.

Cordilleran Ice Sheet mass loss preceded climate reversals near the Pleistocene Termination

Disappearance of an ice sheet The Cordilleran Ice Sheet is thought to have covered westernmost Canada until about 13,000 years ago, even though the warming and sea level rise of the last deglaciation had begun more than a thousand years earlier. This out-of-phase behavior has puzzled glaciologists because it is not clear what mechanisms could account for it. Menounos et al. report measurements of the ages of cirque and valley glaciers that show that much of western Canada was ice-free as early as 14,000 years ago—a finding that better agrees with the record of global ice volume (see the Perspective by Marcott and Shakun). Previous reconstructions seem not to have adequately reflected the complexity of ice sheet decay. Science, this issue p. 781; see also p. 721 The last deglaciation of western Canada began earlier than previously thought. The Cordilleran Ice Sheet (CIS) once covered an area comparable to that of Greenland. Previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost Canada as late as 12.5 thousand years ago (ka). New data indicate that substantial areas throughout westernmost Canada were ice free prior to 12.5 ka and some as early as 14.0 ka, with implications for climate dynamics and the timing of meltwater discharge to the Pacific and Arctic oceans. Early Bølling-Allerød warmth halved the mass of the CIS in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise. Dozens of cirque and valley glaciers, along with the southern margin of the CIS, advanced into recently deglaciated regions during the Bølling-Allerød and Younger Dryas.

Geochemical and mineralogical dispersal in till from the Mount Polley Cu-Au porphyry deposit, central British Columbia, Canada

The Quesnel terrane in the Interior Plateau of British Columbia, Canada, is highly prospective for locating new porphyry deposits; however, the bedrock in this region is obscured by a nearly continuous blanket of till, making mineral exploration challenging. Located within the Quesnel terrane is the Mount Polley deposit. It is an alkaline, silica-undersaturated, Cu-Au porphyry deposit mined by Imperial Metals Corporation. Eighty-six basal till samples were collected for geochemical and mineralogical analyses in the region of this deposit. Ore elements (Ag, Au and Cu), as well as pathfinder element (Hg and Zn) contents in till reflect detrital glacial dispersal from the Mount Polley deposit. The distribution of anomalous mineral counts of andradite garnet, apatite, chalcopyrite, epidote, jarosite and native gold also reflect glacial dispersal from the deposit. Outcrop-scale ice-flow indicators indicate a dominant ice-flow event to the NW that was preceded by a southwestward glacial advance. The element and mineral signatures of the Mount Polley Cu-Au porphyry deposit are dispersed in sub-glacial surface tills up to 12 km in the down-ice (NW) direction. We demonstrate that till geochemistry and mineralogy can serve for mineral exploration of Cu-Au porphyry mineralization in drift covered areas. Supplementary material: Complete data set for element and mineral results and ice-flow measurement is available at www.geolsoc.org.uk/SUP18828

Deglacial valley fill sedimentation, Pelly river, Yukon territory, Canada

Abstract A thick sequence of deglacial valley fill was studied along the Pelly River, Yukon Territory. Late Wisconsinan deglaciation was by regional stagnation of the Cordilleran Ice Sheet, resulting in complex sequences of sediments deposited in glacial lakes, many above stagnant ice. More than 30 sections were described and measured and eight facies were recognized and interpreted. The distribution of sediment reflects control by several systems: (1) ice depositing basal tills; (2) debris flows in glacial lakes depositing diamicton; (3) meltwater streams depositing sorted sediment; and (4) melting of underlying ice remobilizing and deforming previously deposited sediment. A model is constructed that helps to explain sedimentation along Pelly River. Material was deposited into lakes from melting ice, valley slopes and adjacent valleys. Basal tills are relatively rare with most diamictons representing deposition by sediment gravity flows. The presence of large thicknesses of highly disturbed sediments indicates that the sediments were deposited onto ice and subsequently failed. Undisturbed glaciolacustrine sediments were deposited either in more distal parts of the basin or after most of the ice had ablated. The adjacent topography and the height of the glacial limits also influenced sedimentation: steeper topography provided coarser sediments for deposition; while low elevation of glacial limits reduced the availability of sediment even if steep slopes were present. This study further contributes to models of supraglacial sedimentation by documenting that sedimentation was in several lake basins, that lateral gradations in grain size are present, and that fairly significant amounts of diamicton can be present.

Till geochemistry and mineralogy: vectoring towards Cu porphyry deposits in British Columbia, Canada

Regional till sampling was completed near four Cu porphyry mineralized zones in south-central British Columbia, Canada: Highland Valley Copper (Cu-Mo), Gibraltar (Cu-Mo), and Mount Polley (Cu-Au-Ag) deposits, and the Woodjam (Cu-Au-Mo) prospect. At all sites, Cu concentrations in the clay-sized fraction and chalcopyrite grains (0.25 – 0.5 mm; >3.2 specific gravity) are found in greater abundance in till near and down-ice from mineralized zones compared to surrounding background regions. At Mount Polley, the abundance of gold grains in till defines a dispersal train extending at least 3 km down-ice (SW and NW) from mineralization. At three sites out of four, epidote in till heavy mineral concentrates occurs in greater percentage near and down-ice from mineralized zones compared to background regions suggesting that this mineral could be an indicator of propylitic alteration associated with porphyry mineralization. The distribution pattern of Cu concentrations and chalcopyrite grains in till is controlled by the distribution of Cu-porphyry mineral occurrences in bedrock and the direction of ice-flow movements which prevailed during the last glaciation. By comparing study sites, there is a positive relationship between the areal extent of bedrock mineralization that was exposed to glacial erosion and the absolute values of Cu concentrations and chalcopyrite grain counts in till. In the Woodjam region where the till is thick (>10 m), eight samples with background Cu concentrations in the clay-sized fraction of till contain >4 grains of chalcopyrite/10 kg which is indicative of mineralization. This study demonstrates that a combination of till geochemistry and mineralogy is an efficient method for mineral exploration for Cu porphyry deposits covered by variable amounts of glacial sediments. Supplementary material: The full data sets on till geochemistry and mineralogy are available at: https://doi.org/10.6084/m9.figshare.c.3291503

Warmings in the far northwestern Pacific promoted pre-Clovis immigration to America during Heinrich event 1: Comment: COMMENT

[Sarnthein et al. (2006)][1] suggest Late Pleistocene climatic forcing of New World peopling via Beringia, but pre-Clovis archaeological site dates remain debatable and American midcontinent dates can only be minima for colonization events. It is premature to assign pre-Clovis migration to a