THE SAGWON BLUFFS PALEOCENE DEPOSITIONAL ENVIRONMENT, VEGETATION AND ECOLOGY

Six depositional parasequences exposed in the Sagwon Bluffs exposure (69° 21' 08” N, 148° 43' 33” W to 69° 26' 26” N, 148° 32' 10” W) of the Prince Creek Fm and Sagwon Mb have fluvial channel or crevasse-splay sediments at their bases, followed by emergent floodplain facies and subsequent deposition of peat mires. Mires gave way to lake sediments with the continued rise in water table and were in turn replaced by floodplain water bodies, which in the oldest and youngest sequences contain brackish water algae. Among the ninety-seven insitu palynomorph taxa recorded are larger specimens of the fungal spore Pesavis tagluensis, and the juglandaceous pollen Caryapollenites imparalis/inelegans indicating an age no older than Upper Paleocene. Taxa characteristic of the PETM throughout the Arctic are not recorded in the Sagwon Bluffs sediments, suggesting that a Late Paleocene age between 58 ma and 56 ma is likely. Correspondence Analysis identified ecological associations in the floodplain sediments: a ‘Taxodiaceae' group, a ‘Riparian' group‘,a ‘Cyathea' group and a lacustrine group, reflecting different substrates and drainage regimes on the Sagwon floodplain. Coal bed analysis shows some originated as lacustrine accumulations of drifted wood later subjected to gleysol formation. Autocthonous coals showed a succession from polypodiaceous fern dominance through mid seam Betulaceae, Myricaceae and Fagaceae rich assemblages, to Taxodiaceae-Nyssaceae dominance. Abundant charcoal indicates that regular wildfires disrupted these mire communities. Two distinct leaf floras have been recovered. The lowermost has strong taxonomic affinities with the Maastrichtian Koryak Flora of NE Russia, while the upper flora has strong affinities with the Danian Upper Tsagaian Flora of the Amur River Region, southern Russian Far East. The similarity between the late Maastrichtian Koryak Flora and the lower Sagwon Flora implies floristic changes near the K/T boundary in the North Pacific Region were not caused by any catastrophic event but were due to long-term climatic and evolutionary change and plant migration. The Koryak Flora sourced many of the early Sagwon taxa. Progressing warming allowed the plants typical of the Danian Upper Tsagaian Flora to invade the Northern Alaska by the time the upper Sagwon Flora was deposited.