Late Quaternary Environmental History of the Noatak Basin, Northwestern Alaska

该奖项支持一项研究阿拉斯加西北部诺亚塔克盆地第四纪晚期古环境条件的项目。诺亚塔克盆地是阿拉斯加布鲁克斯山脉西部的一片广阔的低地，由向西流淌的诺亚塔克河排干。在晚更新世，大型冰川沿着诺亚塔克河谷向下延伸，并在盆地内终止。发源于德隆山脉更西边的其他冰川向东流入盆地，堵塞了诺阿塔克河，形成了一连串的湖泊，面积达4400平方公里。该项目将结合多种方法，包括古生态分析(花粉、植物大型化石和昆虫)、地层学和地貌学，以了解诺阿塔克河和卡特勒河沿线众多大型悬崖沉积物中保存的古环境记录。这项研究的重点是暴露在悬崖上的富含有机物质的沉积物。这些悬崖的基本地层和地貌填图已经完成，1993年和1994年进行古生态研究的测试样本产生了丰富的、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，这些数据将被置于严格限制的年代学和地层学背景下。诺阿塔克盆地包含了上一次冰川/间冰期循环的极好记录，保存在一系列暴露在河流悬崖上的有机沉积物中。排水不良的湖床覆盖了诺阿塔克盆地的底部，相关的冰川末端冰川反映了冰川从山脉向北、向东和向西的推进。在间冰期和间歇期，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。它们形成了充满砾石的水道，上面覆盖着富含有机物质的沼泽、沼泽和泛滥平原沉积。62个测量的河流悬崖暴露剖面提供了横跨湖底的沉积相记录。悬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，它们被具有间歇性和间冰性的河流沉积分隔开来。来自泛滥平原沉积的泥炭层和富含有机物质的粉砂层产生了可识别的木材、植物大型化石、花粉和昆虫遗骸，以及其他作为生物地层标志和提供古生态信息的化石。在过去的135,000年中，泥炭和富含有机物质的粉砂和沙子在几个关键时期沉积。该项目的九个研究地点包括最有可能追溯到最后一次间冰期、布特利耶(威斯康星州中部)间期、威斯康星州晚期(27,000-17,000年前)、晚期冰期(13,500-10,000年前)和全新世的有机沉积物。研究区域位于诺阿塔克国家保护区内，诺阿塔克国家保护区是美俄贝林贾国际公园的拟议组成部分之一。它的位置靠近白令大陆桥的东缘，使其处于一个即使在最后一次冰川盛期也是有机丰富的河岸栖息地占优势的地区。诺阿塔克盆地的古生态研究对于破译更新世冰川、现代景观形成和生物对气候变化的响应的异常漫长和复杂的记录至关重要。这些研究还将为诺阿塔克地区目前正在重建的丰富考古记录提供环境基础。

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.