麻豆传媒

During the Mesozoic to Early Cenozoic greenhouse climate phase forests grew well within the polar circle. These unique polar forest ecosystems flourished in a warm, high-latitude environment where trees were subjected to months of unbroken winter darkness followed by continuous daylight in the summer and elevated atmospheric carbon dioxide levels (c. 800 ppm). This thesis describes five anatomically preserved wood specimens from a new, Late Cretaceous-Earliest Tertiary, high-latitude (palaeolatitude of 74-78oN) 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 close to the margins of the palaeo-Arctic Ocean. 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 (Taxodioxylon albertense (Penhallow) Shimakura, 1937) and three pinaceous species (Piceoxylon ellesmerensis sp. nov., Pinuxylon woolardii (Tidwell, Parker and Folkman, 1986), Pinuxylon gemenii sp. nov.) 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 that these trees grew under a temperate climate with a high year-to-year variability characterized by frequent disturbances. Common traumatic rings indicate that one such disturbance process was the occurrence of sharp frosts towards the end of the growing season, while abundant false rings suggest that another may have been occasional flooding or ash falls. Finally, intra-annual phenological studies of growth rings suggest that trees possessed a mixture of habits, some being evergreen and other being deciduous. Although pinaceous conifers are the most common group represented by the permineralized woods, additional studies of charred woods, compressed foliage, and palynomorphs from the same site by Falcon-Lang, MacRae & Csank (unpubl. subm., 2002) demonstrate that taxodiaceous conifers were actually the dominant vegetation with pinaceous conifers occurring in only subordinate numbers, together with gingkos, angiosperms and ferns. Physiognomically, the nearest extant equivalent to these polar forests would be the cool-temperate Sequoia-Pseudotsuga forests of British Columbia. The data presented in this thesis therefore shed considerable new light on the community-scale ecology of North Hemisphere, Late Cretaceous-Early Tertiary polar forests, and may provide a useful long-term context for the response of modern boreal forest ecosystems to future global climate change.

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Pages: 165
Supervisor: H. Falcon-Lang