Late Tertiary and Early Pleistocene Deposits and History of Banks Island, Southwestern Canadian Arctic Archipelago

Аннотация

Fossil-rich sediments on Banks Island provide an excellent record of events and conditions that prevailed in arctic Canada during the late Tertiary and Early Pleistocene. In the late Tertiary, fluvial sands and gravels of the Beaufort Formation and related deposits were laid down on the coastal plain facing the Beaufort Sea. Relative sea level was lower than today. Both mixed deciduous/coniferous and coniferous forests existed on Banks Island. Mean July temperatures must have been +10 degrees C warmer than present. The Early Pleistocene Worth Point Formation records a period during which preglacial landscapes were modified by fluvial, eolian, and colluvial processes. Continuous permafrost was likely present, sea level was lower than today, and southern Banks Island was covered by an open larch-dominated forest-tundra. Mean July temperatures were probably some 5-7 degrees C warmer than present. Although some evidence indicates possible earlier glaciations, the best record of an early continental ice advance is provided by widespread glacial and marine sediments of the Duck Hawk Bluffs Formation laid down during the Early Pleistocene Banks Glaciation. This advance was distinctly more extensive than Middle or Late Pleistocene ones and glacio-isostacically controlled sea levels were much higher than those of today. During the Early to Middle Pleistocene Morgan Bluffs Interglaciation, climate on Banks Island was cooler than in preglacial times. Although the tree line may have extended to the southern part of the island, fossil remains in seven localities indicate typical low arctic conditions (mean July temperatures 2-5 degrees C warmer than present). Eustatic sea level was some 30 m higher than the present and permafrost was continuous. The Banks Island record provides critical information on periods when conditions in the Arctic were significantly warmer than today. As such it can serve as a basis to understand and forecast the nature and impact of future man-induced atmospheric warming.