Paleocene-Pliocene deltaic to inner shelf palynostratigraphic zonation, depositional environments and paleoclimates in the Imperial Adgo F-28 well, Beaufort-Mackenzie Basin

Abstract

The Imperial Adgo F-28 well (lat. 69°30N, long. 135°45W) penetrates more than 10 000 ft (3200 m) of Cenozoic deltaic and delta-front clastic sediments representing transgressive-regressive cycles. Stratigraphic ranges of more than 200 species of palynomorphs in the Pliocene through upper Paleocene interval are documented based on cuttings samples composited over 100-foot intervals. An interval zonation for the well is established based on last appearance datums (stratigraphic range tops) of selected terrestrial species supplemented by other palynomorph assemblage information. The zonation is correlated with other sections in the Beaufort-Mackenzie Basin and Arctic Archipelago and ages are determined by comparison with biostratigraphic data from Cenozoic sections within and outside the basin. The Iperk Sequence (Late Pliocene) is characterized by the Laevigatosporites Zone and the upper part of the Chenopodipollis Zone. The subjacent Mackenzie Bay Sequence (Early-Middle Miocene) is characterized by the Tsugaepollenites Zone. At approximately 2800 ft, Miocene sediments rest on the late Eocene Integricorpus Zone (Richards Sequence). Below this are more than 7000 ft (2130 m) of Taglu Sequence (latest Paleocene-Middle Eocene) and Aklak Sequence (Late Paleocene). These two sequences are divided into six interval zones (from top to bottom, the Pesavis tagluensis, Punctodiporites, Paraalnipollenites, Fusiformisporites, Ctenosporites, and Multicellaesporites-Pluricellaesporites zones). The Paleocene-Eocene boundary occurs within the Ctenosporites Zone near the bottom of the Taglu Sequence. Scattered intervals within the Taglu Sequence and lower part of the Richards Sequence (spanning collectively Lower through Upper Eocene) are characterized by dinoflagellate cyst assemblages of low diversity indicating sporadic marine to hyposaline incursions consistent with a fluctuating inner shelf/prodelta/delta-front depositional environment. Some of the Eocene dinoflagellate flora appear to be endemic to the basin, but other species indicate connections with lower latitude assemblages. Upper Paleocene spore-pollen floras are of low diversity and contrast with the rich Eocene palynofloras. The highly diverse Lower through Upper Eocene terrestrial palynofloras in general indicate warm temperate climates. Warm temperate climates may have recurred in the early Miocene. Cool temperate climates are indicated for the late Miocene and Pliocene, possibly becoming boreal at the end of Pliocene times. Fungal palynomorphs and embryophyte spores and pollen new to the area are illustrated and listed taxonomically. These include 8 new species, 16 species described in open nomenclature, 6 new combinations, and an additional 45 species new to the area but previously described from outside the Beaufort-Mackenzie Basin.