A LATE CRETACEOUS-EARLIEST TERTIARY POLAR FOREST: WHAT FOSSIL WOOD CAN TELL US ABOUT PAST ENVIRONMENTAL CHANGES

During the Mesozoic to early Cenozoic greenhouse climate phase unique polar forest ecosystems flourished in a warm, high-latitude environment.

This paper describes five anatomically preserved wood specimens from a late Cretaceous-earliest Tertiary, high-latitude (palaeolatitude of 74-78°N) fossil plant assemblage from Emma Fiord and Phillips Inlet, NW Ellesmere Island. The fossil wood occurs in the Campanian/Maastrichtian to Danian Hansen Point Volcanics of the Eureka Sound Group, Sverdrup Basin, a stratigraphic unit interpreted as originating in a volcanically disturbed, alluvial plain/peat mire setting.

Quantitative analysis of anatomical features in petrographic thin sections enabled the wood specimens to be assigned to two conifer families, the Taxodiaceae and Pinaceae. One taxodiaceous species and three pinaceous species were identified.

Biometric analysis of the permineralized trunks suggests that the forest canopy was in the order of 15-20 m. Well preserved growth rings indicate a temperate climate with high year-to-year variability characterized by frequent disturbances. Common traumatic rings indicate the occurrence of sharp frosts towards the end of the growing season, while abundant false rings suggest occasional flooding or ash falls. Intra-annual phenological studies of growth rings show that trees possessed a mixture of deciduous and evergreen habits.

Although pinaceous conifers are the most common group represented by the permineralized wood, additional studies of charred woods, compressed foliage and palynomorphs from the same site by other authors demonstrate that taxodiaceous conifers were actually the dominant vegetation with pinaceous conifers occurring in subordinate numbers.

Physiognomically, the nearest extant equivalent to these polar forests would be the cool-temperate forests of British Columbia. The data presented in this paper therefore shed considerable light on the community-scale ecology of Northern Hemisphere, late Cretaceous-early Tertiary polar forests, and may provide a useful long-term context for the response of modern boreal forest ecosystems to global climate change.