Late Quaternary Environmental History of the Noatak Basin, Northwestern Alaska

点击翻译按钮获取中文摘要

This award supports a project to investigate the late Quaternary paleoenvironmental conditions of the Noatak basin in northwestern Alaska. The Noatak basin is a broad lowland in the western Brooks Range of Alaska, drained by the west-flowing Noatak River. During the late Pleistocene, large glaciers extended down the Noatak River valley and terminated within the basin. Other glaciers that originated farther west in the DeLong Mountains flowed eastward into the basin, damming the Noatak River and forming a succession of lakes with surface areas as large as 4400 square kilometers. This project will bring together a combination of approaches, including paleoecological analyses (pollen, plant macrofossils, and insects), stratigraphy, and geomorphology, to understand the paleoenvironmental records preserved in deposits in the numerous large bluffs along the Noatak and Cutler Rivers. The research focuses on organic-rich sediments exposed in the bluffs. Basic stratigraphic and geomorphologic mapping of these bluffs has already been accomplished and test samples taken for paleoecological study in 1993 and 1994 have yielded abundant, well-preserved macrofossils (plants and insects) and pollen assemblages. This project will yield significant paleoenvironmental data that will be placed in well-constrained chronological and stratigraphic contexts. The Noatak basin contains an excellent record of the last glacial/interglacial cycle, preserved in a series of organic deposits exposed in river bluffs. Poorly drained lake beds cover the floor of the Noatak basin, and associated end moraines reflect glacial advances from mountains to the north, east, and west. During interglacial and interstadial intervals, the Noatak River and its tributaries incised these glacial deposits and glaciolacustrine complexes. They formed gravel-filled channels capped by organic-rich bog, marsh, and floodplain deposits. Sixty- two measured sections of river-bluff exposures provide a record o f depositional facies across the lake floor. The sedimentary sequences exposed in the bluffs define multiple glacial advances and corresponding lake stages separated by fluvial sediments of both interstadial and interglacial character. Peat beds and organic-rich silt horizons from floodplain deposits have yielded identifiable wood, plant macrofossils, pollen, and insect remains, and other fossils that serve as biostratigraphic markers and provide paleoecological information. Peats and organic-rich silts and sands were deposited during several key intervals throughout the last 135,000 years. The nine study sites that are part of this project include organic deposits that most likely date to the last interglacial period, the Boutellier (mid- Wisconsin) interstadial, the late Wisconsin maximum, (27,000- 17,000 years ago), the late glacial interval (13,500-10,000 years ago), and the Holocene. The study region lies within the Noatak National Preserve, one of the proposed component parks of the U.S./Russian Beringia International Park. Its position near the eastern margin of the Bering Land Bridge places it within a region where organic-rich riparian habitats prevailed during even the last glacial maximum. Paleoecological studies in the Noatak basin are essential to help decipher an unusually long and complex record of Pleistocene glaciation, modern landscape formation, and biotic response to climate change. These studies will also provide the environmental underpinning of the rich archaeological record that is presently being reconstructed in the Noatak region.