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

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.Résumé : La présente étude analyse la stratigraphie du Quaternaire du nord de la vallée de l'Okanagan dans le but d'obtenir des données pour des études hydrogéologiques. Le nord de la vallée de l'Okanagan s'étend de l'extrémité nord du lac Okanagan jusqu'à Enderby dans le sud intérieur de la Colombie-Britannique, Canada. Une cartographie antérieure de la géologie de surface, des données provinciales et privées de de forages, des profils sismiques historiques et un nouveau profil sismique réflexion à haute résolution, d'une longueur de 5 km, ont été examinés dans le but de caractériser des sédiments non consolidés atteignant une épaisseur de 580 m. Un mélange de sédiments glaciaires et interglaciaires, d'âge Pléistocène incertain, remplit des creux du socle qui s'étendent sous le niveau de la mer. Une unité de sable et de gravier, d'âge au moins Wisconsin précoce (>65 000 années avant le présent), repose de façon discordante sur ces sédiments. Des dépôts lacustres et alluviaux, riches en matière organique, datant du Wisconsin moyen (65 000 -23 000 années avant le présent), recouvrent à leur tour et de manière discordante transgressive l'unité de sable. Cette derni...

Causes and Mechanisms of Global Warming/Climate Change

“…and continued like that until 31 ka B.P. [81,82]. It is thought that the climate there during that period was similar to today.…”