Ordovician and Silurian

Abstract

During the early Paleozoic, the paleogeography of northern Yukon and adjacent District of Mackenzie was characterized by an intricate and changing pattern of platforms and adjacent troughs. Relatively deep water persisted in the Richardson and Blackstone troughs throughout most of the Late Cambrian to Early Devonian. Carbonate rocks accumulated on shallow shelves and banks that bordered the two troughs, and carbonate sediments were shed into the basinal depositional environments of the troughs. Unconformities are widespread within the carbonate successions of the Mackenzie Arch and the Porcupine Platform and can be detected locally on the Ogilvie Arch. In contrast, there is little evidence of breaks in the carbonate banks of the White Uplift and the Illtyd Range, located at the north and south ends of the Richardson Trough respectively. The Richardson Trough subsided throughout the interval and the resulting Road River strata have a virtually complete biostratigraphic record spanning some 120 million years. Thermal maturation studies indicate that most of the Ordovician and Silurian rocks have been heated too severely for the retention of oil and gas generated within the sediments. Little is known of the potential for base metal deposits, but the setting is analogous to those of the Selwyn Basin and the Kechika Trough, where significant discoveries have been made of strata-bound deposits in basinal facies. Volcanics are prominent in the Road River Group in those areas, but some possible ash components of micrites are the only records of volcanic activity in the Road River Group in the Richardson and Blackstone troughs.