Geologic History of Okanagan Valley and Origin of Lake Okanagan, British Columbia

Dr. Murray A. Roed

Introduction

The geomorphic development of the Okanagan Valley, like anything of value, took a long time. It mostly involves geologic events that are almost impossible to imagine, difficult to understand and hard to believe. The geologic history of the Okanagan Valley is discussed in seven stages, concluding with a somewhat detailed analysis of the events in the last 10,000 years.

1.0 The Precambrian Era

Beginning with the presumed Big Bang 20 billion years ago, Earth was eventually sent hurtling around its Mother Sun at a speed of 29000 kilometers per second in an orbit that was perfect in every way for the eventual colonization by living things. Life forms made an appearance 3 to 4 billion years ago in primitive oceans. This early period is known broadly as the Precambrian Era. One of the major problems facing primordial life much of this time was that the atmosphere lacked oxygen. Nitrogen and carbon dioxide were the main components.

The Precambrian continental crust that first formed was largely granitic in composition occupying a land complex known as Pangaea. This continent was subject to periodic mountain building forces, multiple volcanic eruptions, periods of erosion, glaciations, meteoroic impacts, and finally almost complete fragmentation as it was broken up and sent drifting in all directions. One of these fragments was the ancestral North American Canadian Shield Craton (Laurasia) that has drifted northwestward. This early craton in the Okanagan is represented by a vast thickness of metamorphic and meta sedimentary rocks referred to here broadly as “Shuswap Terrain”. The Shuswap Terrain is over two billion years old and represents the broken edge of the western part of the early craton in western Canada. It is part of the Omineca Belt of rocks that stretches along the Rocky Mountain Trench for 2000 kilometers to Alaska . This rigid remnant of an ancient mountain chain has throughout most of its post-Precambrian history formed a major structural element separating the western Canadian sedimentary basin from other environments in the ancient Pacific basin. Locally, Shuswap rocks are composed mainly of granitic gneiss that have been periodically intruded by granite, notably in the Eocene, about 50,000,000 years ago, which served to “reset” the age of these rocks.

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