Geology

NB-Geology-smThe geology of Nanoose Bay is complex and contains some of the oldest rocks found on Vancouver Island. These include igneous, metamorphic and sedimentary rocks as well as glacially derived tills and eskers left behind from the last Ice Age. The story of Vancouver Island spans hundreds of millions of years. Much of the rock that makes up Vancouver Island actually originated 3,000 kilometres south near the equator in the Pacific Ocean. It is part of a large piece of crust called Wrangellia, that also includes southeast Alaska, the Queen Charlotte Islands and part of the Coast Mountains. 380 million years ago, some of the oldest rock that makes up present day Vancouver Island was formed by undersea lava deposits and limestone (see the blues and greys on the map). During the period from 280 to 225 million years, further volcanic activity formed lava flows and limestone were developed on the sea floor. Wallace Point is largely made up of these latter rocks (green on the map). 185 million years ago, igneous rocks intruded the older rocks. The pink area on the map occupies the eastern part of the peninsular (Fairwinds) and the Winchelsea Islands. About 100 million years ago, Wrangellia collided with the North American continent. Tremendous forces buckled the rocks into mountain ranges. A basin formed about 85 to 65 million years ago and sediments of the Nanaimo Group were laid down, together with the important coal deposits found along the eastern side of VI. The lime green areas on the map consist of sandstones, shales and conglomerates, often containing abundant fossils. The Earth has been subjected to many glacial (cold) and interglacial (warm) periods, throughout its history. These are governed largely by changes in the Earth’s orbit called Milankovich cycles, but also depend on other complex climate processes.  Between 29,000 and 15,000 years ago, the most recent glacial period or “ice age” developed. The ice sheets cut major features in the landscape, including the steep mountain peaks and U-shaped valleys seen everywhere in BC. Their weight was enough to depress the landmass of Vancouver Island by 150 to 300 metres. This caused the sea level at the time to be much higher than today. Between 15,000 years before present and today, the climate began to warm and the ice sheets slowly melted and retreated. The release of the weight of ice caused the land to rebound. This exposed areas of land that were previously submerged. In place of the ice sheets, large deposits of glacial till were left. This was formed from rock that was ground up under the ice sheets, deposited on the surface of the glaciers, or pushed up in front of advancing glaciers. Lakes, like Enos and Dolphin Lakes formed and streams and rivers formed from melting ice. Tony Ransom (with acknowledgements to Drs. Steve Earl and Tim Stokes of VIU)