Jura-Cretaceous (Oxfordian to Cenomanian) stratigraphy of the north-central Bowser Basin, northern British Columbia

Abstract

Three new formations of Late Jurassic and Early to mid-Cretaceous age are defined for a 2000 m thick section of Jura-Cretaceous rocks exposed in the north-central Bowser Basin. The Currier Formation (Oxfordian to Kimmeridgian or Tithonian) consists of 350–600 m of interbedded shales, siltstones, sandstones, coals, and carbonates. The McEvoy Formation (Barremian to as young as Albian) consists of 400–800 m of siltstones and shales with minor sandstones, thin coals, limestones, and conglomerates. The Devils Claw Formation (in part mid-Albian to Cenomanian) consists of 300–600 m of strata characterized by thick pebble and cobble conglomerates, with associated coarse sandstones and minor siltstones and shales.Two successive coarsening-upward sequences are identified in the study area. The first begins with Middle Jurassic marine shales of the Jackson unit grading upwards to coarser Upper Jurassic facies of the Currier Formation. The Currier Formation is conformably or unconformably overlain by siltstones and shales of the Lower Cretaceous McEvoy Formation, which forms the base of a second coarsening-upward sequence. Conglomerates appear with increasing frequency in the upper McEvoy and are the dominant lithology of the overlying Devils Claw Formation. The contact between the McEvoy and Devils Claw formations is gradational. The Devils Claw Formation forms the top of the second coarsening-upward sequence.The Currier Formation (Late Jurassic) is equivalent to the upper units of the Bowser Lake Group. The McEvoy and the Devils Claw formations (Barremian to Cenomanian) are coeval with the Skeena Group (Hauterivian? to Cenomanian). A probable unconformity separating the Upper Jurassic Currier Formation from the Lower Cretaceous McEvoy Formation correlates with a hiatus in the southern Bowser Basin and probably represents a regional unconformity.