泥河湾古湖初期的形成时代及其环境变化

The Nihewan Basin is located in the transition zone between the North China Plain and the Inner Mongolian Plateau. This basin is filled with Late Pliocene to Holocene lacustrine, fluvial, and wind-blown deposits. The Nihewan Beds provide an important source of mammalian faunas and Paleolithic settlements, and therefore Quaternary land mammal evolution and early human occupation in the high-latitude temperate East Asia. Recently, a plenty of investigations concerning magnetostratigraphic dating of the fluvio-lacustrine sequence in the Nihewan Basin, northern China, has been conducted, which has improved significantly to our understanding of the chronological framework of the complex stratigraphy and depositional systems in the Nihewan Basin, and further permitted the precise timing of a series of terrestrial Nihewan Formation, important Paleolithic sites and Nihewan faunas. .The Youth Science Foundation of China goes fluently according to the application plan. High-resolution magnetic polarity stratigraphy indicates that Xiashagou Fauna (that is, the Nihewan Fauna sensu stricto) resides in the Matuyama chron, resulting in an estimated age of ca. 1.7-2.2Ma. The combined evidence of our study and previously published magnetostratigraphic data documents a magnetochronological sequence of the mammalian faunas in the Nihewan Basin, which have been revised to a time range of ca. 2.6-0.8 Ma. Under the foundation of the project the Huojiadi Paleolithic site has been conducted that the Huojiadi stone artifact layer resides in the Jaramillo chron, resulting in an estimated age of ca. 1.0 Ma for the Huojiadi Paleolithic site. The combined our new and previously published magnetostratigraphic data documents a robust magnetochronological sequence of early human colonization during the early Pleistocene in the Nihewan Basin, constrained between the termination of the Olduvai subchron and the Matuyama–Brunhes geomagnetic reversal, that is between 1.77 Ma and 0.78 Ma..In this program we intend to work closely around the research progress of the Youth Science Foundation of China and focus on timing framework of the red clay which is located in the bottom of Nihewan formation using a combination of lithostratigraphy, sedimentology, magnetostratigraphy and environmental geochemical analyses, to get the age of initiation of the Nihewan paleolake and its environmental change and the precise location of the Pliocene/Pleistocene boundary. We will select representative cross-sections to obtain stringent age control on the Nihewan fluvio-lacustrine sequence and get the information of environment and climate changes at the Pliocene/Pleistocene boundary in the Nihewan Basin. We believe our research will make a significant comtribution to the chronostratigraphic framework of the Nihewan Basin and detailed study of the environment and climate changes of the Nihewan paleolake.

青年科学基金按照原定研究计划顺利进行，建立了下沙沟剖面的磁极性倒转序列，从磁性地层学的角度厘定了典型的下沙沟动物群的确切年代，结合前人研究结果，获得了泥河湾动物群的年代序列；同时完成了对霍家地遗址进行磁性地层学定年，结合已发表的泥河湾盆地其他旧石器遗址地点，建立了泥河湾盆地旧石器遗址的年代序列。本项目拟开展的工作是青年科学基金项目的延续和深化，拟在详细的地层学和沉积学研究的基础上，选择有代表性的剖面进行精细的磁性地层年代学测定，建立泥河湾盆地新生代地层层序的年代框架，确定泥河湾古湖的形成时代及泥河湾盆地底部红粘土的年代，进一步确定泥河湾盆地湖相沉积物底部上新世/更新世界线的可靠位置，揭示上新世/更新世界线前后的环境变化。

泥河湾盆地是中国北方第四纪地层、环境、动物群和古人类遗址最完整的湖泊记录之一。上世纪20年代自英国地质学家巴尔博首次调查泥河湾盆地第四纪地层以来，国内外学者对该盆地的研究从未中断过，泥河湾盆地已成为国内外有关学者经久不衰的研究热点。上世纪50年代我国学者确定‘泥河湾层’为华北早更新世标准地层，此后众多学者又陆续对泥河湾盆地哺乳动物化石、古人类化石、旧石器遗址、地层学及年代学等各领域开展了大量的研究工作。泥河湾盆地从上新世至更新世末发育泥河湾古湖。.本项目主要调查湖相沉积物及下伏红粘土，选择了大南沟-红崖一带壶流河两岸上新统至更新统代表性连续湖相沉积泥河湾层，确定底界达到上新统的代表性连续湖相沉积剖面。对选定的上新统至更新统代表性连续湖相沉积剖面和其他重要剖面进行系统的岩石磁学研究，确定了沉积物中磁性矿物的类型、粒度和含量及其变化特征，并在此基础上进行高分辨率的磁性地层学结合适当的同位素定年，建立了泥河湾盆地新生代沉积序列的精细年代框架。在泥河湾盆地地层学及沉积学研究的基础上，研究泥河湾湖相沉积及下伏红粘土的形成时代，确定泥河湾古湖的发育演化历史，获得了泥河湾盆地湖相沉积物底部可靠的上新世/更新世界线(2.6Ma)位置，提取选定典型剖面的上新世/更新世环境剧烈环境变化信息，建立了泥河湾盆地新生代地层层序的年代框架，确定了泥河湾层下部湖相沉积物开始发育的时代及其下伏风成红粘土的形成时代，为研究泥河湾古湖的发育演化历史提供了年代制约。