Overview of Late Quaternary stratigraphy in Saanich Inlet, British Columbia: results of Ocean Drilling Program Leg 169S

Continuous coring in Saanich Met (Ocean Drilling Program, ODP Leg 169S), Br itish Columbia, Canada, yielded a detailed record of Late Quaternary climat e, oceanography, marine productivity, and terrestrial vegetation. Two sites (1033 and 1034) were drilled to maximum depths of 105 and 118 m, recoverin g sediments ranging in age from 13,300 to less than 300 C-14 yr. Earliest s ediments consist of dense, largely massive, gray glaciomarine muds with dro pstones and sand and silt laminae deposited during the waning stages of gla ciation, Deposition of organic-rich olive gray sediments began in the fjord about 12,000 C-14 yr ago, under well-oxygenated conditions as reflected by the presence of bioturbation and a diverse infaunal bivalve community. At about 10,500 C-14 yr, a massive, gray unit, 40-50 cm thick, was emplaced in a very short span of time. The unit is marked by a sharp lower contact, a gradational upper contact and an abundance of reworked Tertiary microfossil s. It has been interpreted as resulting from massive flood events caused by the collapse of glacial dams in the Eraser Valley of mainland British Colu mbia. Progressively greater anoxia in bottom waters of Saanich Inlet began about 7000 C-14 yr ago. This is reflected in the preservation of varved sed iments consisting of diatomaceous spring-summer laminae and terrigenous win ter laminae. Correlation of the sediments was based on: marked lithologic c hanges, the presence of massive intervals (reflecting localized sediment gr avity flow events), the Mazama Ash, occasional thin gray laminae (indicativ e of abnormal flood events in nearby watersheds), varve counts between mark er horizons, and 71 accelerator mass spectrometry (AMS) radiocarbon dates. (C) 2001 Elsevier Science B.V. All rights reserved.