Albian to Turonian stratigraphy and palaeoenvironmental history of the northern Western Interior Sea in the Peel Plateau Region, Northwest Territories, Canada

Abstract

Cretaceous sediments in the Northern Interior Plains are widespread and their interbasinal lithostratigraphic correlations indicate several regional unconformities that require biostratigraphic confirmation. This study proposes a new zonation based on benthic foraminifera utilising the reference section for the Albian to Turonian Arctic Red and Trevor formations located along the Hume River in the Peel Plateau region (Northwest Territories). A new absolute age date of 107.0 ± 1.9 Ma from a bentonite extends the biostratigraphic range of the Early Albian Quadrimorphina albertensis Zone into the Middle Albian. Integration of the new temporal framework with detailed sedimentological observations provides an interpretation of the dynamic depositional history for this northern region of the Western Interior Seaway (WIS). Cretaceous strata in the Peel Plateau record deposition of the initial transgression of the WIS in two pulses of relative sea-level rise (Martin House Formation) and subsequent offshore marine sedimentation in a deep foreland basin (Arctic Red Formation). The global eustatic sea-level minimum at the Albian–Cenomanian boundary and renewed uplift of the Keele Arch impacted palaeogeography in this region with previously unnoticed subaerial exposure and palaeosol development. This unconformity can be correlated to the east into the Mackenzie Plain. Transgression brings anoxic bottom waters during the Early Cenomanian (Slater River Formation) that result in an interval almost barren of foraminifera. During the Turonian, a time of high eustatic sea-level, the study area marks a relatively shallow site where pulses of prograding shorelines are recorded in upward shallowing parasequences bound by pebble lags overlain by flooding surfaces (Trevor Formation). East of the Peel Plateau in the Mackenzie Plain area, an unconformity separates Albian Arctic Red from ?Upper Cenomanian–Turonian strata, there named the Slater River Formation. In order to recognise the significant unconformity associated with the loss of Albian foraminifera and the angular unconformity observed in seismic profile, we propose the use of the Slater River Formation to describe the strata bound by the pisoidal ironstone and the first metre-plus sandstone bed marking the base of the interbedded mudstones and sandstones of the overlying Trevor Formation. The Hume River section is proposed as the type section for the Slater River Formation.