Abstract

This study investigates the Quaternary stratigraphy of the north Okanagan Valley to inform hydrogeological studies. The north Okanagan Valley extends from the north end of Okanagan Lake to Enderby in the southern interior of British Columbia, Canada. Prior surficial geology mapping, provincial and private borehole data, historical seismic profiling, and a new 5 km high-resolution seismic reflection profile were examined to characterize up to 580 m thickness of unconsolidated sediments. A mixture of glacial and interglacial sediments of uncertain Pleistocene age infills bedrock lows that extend below sea level. These are unconformably overlain by a sand and gravel unit of at least Early Wisconsin age (>65 000 years BP). It is in turn unconformably onlapped by nonglacial, organic-rich, lacustrine and alluvial deposits of Middle Wisconsin age (65 000 – 23 000 years BP). This unit was eroded and overlain by a fine sand to silty sand unit deposited immediately prior to, or during, the Fraser Glaciation advance (>23 000 years BP). Diamict and glacial deposits including valley-side kame overlie these sands at some of the valley margins. Glaciolacustrine sediments of the end of the Fraser Glaciation have no appreciable organic matter and overlie the fine sands in the main Okanagan Valley; these form the majority of the surface outcrop. Recessional glaciodeltaic sediments overlie, and in some places may interfinger with, these glaciolacustrine sediments, which indicates an open proglacial lake environment during late glacial stages. These materials and fan-shaped periglacial debris flow deposits are incised by late Holocene fluvial downcutting. The north Okanagan Valley stratigraphy preserves the record of several glacial and interglacial periods, which suggests that overdeepening of the bedrock surface of the Okanagan Valley may be older than previously suggested.

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