Study of the depositional environments of the Halfway Formation, British Columbia, Canada

Abstract

The upper sands of the discontinuous Halfway Formation to the northeast of Fort St. John were formed as barrier islands deposited perpendicular,or nearly perpendicular to the dip of the paleoslope of the Western Canadian Sedimentary Basin. These upper sands of the area of study were deposited during a transgressive phase of the Triassic sea to the northeast,and formed the basal unit of an onlapping sequence comprising the Halfway and the Charlie Lake Formations that disconformably overstepped the erosional surface on the silty dolomite of the Doig Formation. The Weasel sand body was deposited during a pause in the transgression,and then was submerged by a rapid rise in sea level. The Wildmint to Beatton barrier islands trend was deposited during a second pause in the transgression.These barrier islands would appear to have been deposited under arid conditions resulting in restricted lagoonal environments. The lower sands of the discontinuous Halfway Formation which only occur at a few locations in southern Willow and Wildmint ,would appear to have resulted from tidal inlet action that eroded channels into the Doig Formation below the base of the upper sands forming the barrier island complex. These later were filled with sand. Then this barrier island trend was submerged by renewed transgression of the Triassic sea.The source of the sediments comprising the discontinuous Halfway Formation probably was to the north and northeast of the area of study.