Late-Quaternary Environmental History of the Noatak Basin, NW Alaska

该奖项支持研究阿拉斯加西北部Noatak盆地晚第四纪古环境条件的项目。诺阿塔克盆地是阿拉斯加西部布鲁克斯山脉的一个广阔的低地，由向西流动的诺阿塔克河排干。在晚更新世期间，大型冰川沿着诺阿塔克河流域延伸，并在盆地内终止。其他源自德龙山脉更西部的冰川向东流入盆地，阻塞了诺阿塔克河，形成了一系列表面积达4400平方公里的湖泊。该项目将结合多种方法，包括古生态分析（花粉、植物大化石和昆虫）、地层学和地貌学，以了解保存在诺阿塔克河和卡特勒河沿岸众多大悬崖沉积物中的古环境记录。这项研究的重点是暴露在悬崖上的富含有机物的沉积物。这些断崖的基本地层和地貌测绘已经完成，1993年和1994年为古生态学研究采集的测试样本已经发现了大量保存完好的大型化石（植物和昆虫）和花粉组合。该项目将产生重要的古环境数据，这些数据将被放置在严格限制的年代和地层背景中。诺阿塔克盆地包含了末次冰期/间冰期旋回的优秀记录，保存在一系列暴露在河流断崖中的有机沉积物中。排水不良的湖床覆盖了诺阿塔克盆地的地面，相关的终碛反映了冰川从山脉向北、东、西的推进。在间冰期和间冰期，诺阿塔克河及其支流切割了这些冰川沉积物和冰湖复合体。它们形成了砾石填充的通道，上面覆盖着富含有机物的沼泽、沼泽和洪泛平原沉积物。62个测量过的河崖暴露剖面提供了湖底沉积相的记录。断崖中暴露的沉积序列定义了多个冰期推进和相应的湖泊阶段，这些阶段由间冰期和间冰期特征的河流沉积物分隔。漫滩沉积物中的泥炭床和富含有机物的粉砂层发现了可识别的木材、植物大化石、花粉和昆虫遗骸，以及其他化石，这些化石可作为生物地层标志并提供古生态信息。泥炭和富含有机物的淤泥和沙子是在过去13.5万年的几个关键时期沉积的。作为该项目的一部分，9个研究地点包括最有可能追溯到最后一个间冰期的有机沉积物，布特利尔间冰期（威斯康星中部），威斯康星晚期最大值，（27000 - 17000年前），末冰期（13500 - 10000年前），以及全新世。研究区域位于诺阿塔克国家保护区内，这是美国/俄罗斯白令陆桥国际公园的拟议组成公园之一。它的位置靠近白令海陆桥的东部边缘，使它处于一个富含有机物的河岸栖息地盛行的地区，甚至在最后一次冰川高峰时期也是如此。诺阿塔克盆地的古生态学研究对于帮助破译异常漫长而复杂的更新世冰川作用、现代景观形成和生物对气候变化的反应至关重要。这些研究还将为目前正在诺阿塔克地区重建的丰富考古记录提供环境基础。

Abstract 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 of 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.