The Big Raven Formation is a stratigraphic unit of Holocene age in northwestern British Columbia, Canada.
Description
The Big Raven Formation is part of the Mount Edziza volcanic complex. This is the second largest eruptive centre in the Northern Cordilleran Volcanic Province, attaining a volume of and an area of . It consists of shield volcanoes, stratovolcanoes, cinder cones and lava domes that have formed in the last 12 million years.
Lithology
The Big Raven Formation consists primarily of alkali basalt and hawaiite. These rocks form lava flows and small volcanic cones throughout the Mount Edziza volcanic complex. A small volume of comenditic trachyte pumice is assigned to the Sheep Track Member, the only formally named sub-unit of the Big Raven Formation.
Distribution
The Big Raven Formation has a volume of , making it the least voluminous geological formation of the Mount Edziza volcanic complex. It includes the Desolation Lava Field on the northern slope of Mount Edziza, the Snowshoe Lava Field on the southwestern slope of Ice Peak, the Mess Lake Lava Field east of Mess Lake, Nahta Cone near the northern edge of the Arctic Lake Plateau, Kana Cone on the extreme northern flank of the Mount Edziza volcanic complex, two unnamed cinder cones and associated lava flows in Walkout Creek valley, and Cinder Cliff, Icefall Cone and Ridge Cone on the eastern slope of Mount Edziza.
Age
The Big Raven Formation is the youngest geological formation of the Mount Edziza volcanic complex. It was deposited during the Holocene after Pleistocene glaciation had retreated from the area. As a result, the Big Raven Formation has not undergone glacial erosion. The young age of the Big Raven Formation is also indicated by its almost unchanged geomorphology. A radiocarbon date of 610 CE ± 150 years has been obtained from charred willow twigs preserved beneath a thick layer of Big Raven basaltic tephra from Williams Cone in the Desolation Lava Field.