Lithostratigraphic revision and biostratigraphy of Upper Hauterivian–Barremian strata from the Kugmallit Trough, Mackenzie Delta, Northwest Territories

Abstract

The Kipnik Formation, named herein, is defined from the Late Hauterivian to Barremian Kugmallit Trough in the Mackenzie Delta, Arctic Canada. The trough was formed by extensional tectonics associated with the opening of the Canada Basin and was infilled by kilometre-thick accumulations of clastic sediments. Samples from the Kugmallit Trough are known only from two exploration wells – Shell Kipnik O-20 and Gulf Mobil Ogruknang M-31. Examination of palynomorphs, foraminifera, and ostracods from cuttings of these wells, integrated with regional subsurface and outcrop correlations, indicated that the existing subsurface stratigraphic interpretations [Upper Jurassic to Barremian] of the Kugmallit Trough were in need of revision. The revised Upper Hauterivian–Barremian succession thus consists of the Siku, Kipnik (new), and Mount Goodenough formations. The Siku and Kipnik formations are known only from the subsurface, but the Mt. Goodenough Formation is widespread and was deposited over a regional unconformity. The Siku to Kipnik deposition is a large-scale transgressive-regressive succession that represents deposition during a period of initial subsidence (transgression) followed by uplift and erosion (regression). The shale dominant Siku Formation contains a distinctive unnamed foraminiferal assemblage that consists of agglutinated species typical of offshore or deeper water. Ostracods of the Siku Formation are contained in the informal Galliaecytheridea postsinuata zone, which is confined to the Siku Formation. Ostracods of the G. postsinuata zone suggest shelf environments. The Kipnik Formation is sand-dominant with thin beds of shale, siltstone and coal. Agglutinated foraminifera occur sparsely because of coarse, rapid sedimentation. Inner shelf environments are suggested by the foraminifera. The lower half of the Mount Goodenough Formation is shale-dominant and the upper half consists of intercalated shale and sandstone. Foraminifera and ostracods occur abundantly in the Mt. Goodenough subsurface and outcrops of the Richardson Mountains. The foraminiferal Convallina mcneili Zone of Barremian age occurs in the Mt. -Goodenough Formation and its composition of agglutinated and calcareous benthic foraminifera suggests outer shelf or deeper environments. Ostracods of the Mt. Goodenough Formation in subsurface and outcrop are assigned to the informal Clithrocytheridea spp. zone. Ostracods suggest an outer shelf or deeper-water environment. Palynomorphs indicate that the Siku Formation is Late Hauterivian, the Kipnik Formation is probably latest Hauterivian to Early Barremian, and the Mount Goodenough Formation is Barremian.