Re-assessment of the paleoclimate implications of the Shell Bar in the Qaidam Basin, China
Re-assessment of the paleoclimate implications of the Shell Bar in the Qaidam Basin, China
复制标题
重新评估中国柴达木盆地贝壳坝的古气候影响
DOI：
10.1007/s10933-012-9674-6
复制
发表时间：
2014-02-01
影响因子：
2.1
通讯作者：
Zhang, Chengjun
中科院分区：
文献类型：
--
作者：
Mischke, Steffen;Lai, Zhongping;Zhang, Chengjun
贝壳坝是柴达木盆地的一个重要地质特征，它由数百万个密集堆积的贝壳组成。自20世纪80年代中期以来，它一直被认为是在目前极度干旱的柴达木盆地存在海洋同位素阶段（MIS）3的大型湖泊的证据。早期的研究表明，双壳类贝壳堆积在一个大湖的海岸，而最近的研究得出的结论是，贝壳沙洲是在一个更深的水体中形成的。根据对贝壳坝沉积物和化石的重新评价、对贝壳坝上游出露河湖剖面的调查以及对附近现代河流的研究，我们推断贝壳坝为河流存款沉积。保存ofCorbiculashells的不同大小，以及出现许多关节壳，提供了证据，对死后运输和积累沿着海岸。此外，贝壳坝的东南-西北走向与其附近的现代间歇性河床相似，并对应于现今朝向盆地中心进一步西北的斜坡，此外，主要的桑迪沉积物也表明贝壳坝形成于河流中。贝壳坝沉积物中丰富的介形虫贝壳来自贝壳坝附近现代河流中丰富的河流栖息物种，或者部分来自贝壳坝上游暴露的河湖沉积物，这是侵蚀和再沉积的结果。贝壳坝区域冲积细粒沉积物的收缩和大型厚壁贝壳对河流沉积物的保护逆转了以前的河道地貌，并产生了现代出露，这是一个突出的形态特征。柴达木盆地蚬壳的出现表明，在贝壳坝形成期间，气候明显比现在温暖，因为今天的蚬壳并不生活在相似或更高的海拔地区。由于贝壳沙洲不再被认为是湖泊内形成的存款，它的存在并不表明古气候条件比今天更潮湿。
The Shell Bar in the Qaidam Basin, China, is a prominent geological feature composed of millions of densely packedCorbiculashells. Since the mid 1980s, it has been regarded as evidence for existence of a large lake during Marine Isotope Stage (MIS) 3 in the presently hyper-arid Qaidam Basin. Early studies suggested the bivalve shells accumulated at the shore of a large lake, whereas more recent work led to the conclusion that the Shell Bar was formed within a deeper water body. Based on our re-assessment of sediments and fossils from the Shell Bar, investigation of exposed fluvio-lacustrine sections upstream of the Shell Bar and study of nearby modern streams, we infer that the Shell Bar represents a stream deposit.Corbiculais a typical stream-dweller around the world. Preservation ofCorbiculashells of different sizes, as well as occurrence of many articulated shells, provide evidence against post-mortem transport and accumulation along a lake shore. Additionally, the SE-NW alignment of the Shell Bar is similar to modern intermittent stream beds in its vicinity and corresponds to the present-day slope towards the basin centre further NW, and furthermore, the predominantly sandy sediments also indicate that the Shell Bar was formed in a stream. Abundant ostracod shells in the Shell Bar sediments originated from stream-dwelling species that are abundant in modern streams in the vicinity of the Shell Bar, or in part from fluvio-lacustrine sediments exposed upstream of the Shell Bar, as a result of erosion and re-deposition. Deflation of alluvial fine-grained sediments in the Shell Bar region and protection of the stream deposits by the large and thick-walledCorbiculashells reversed the former channel relief and yielded the modern exposure, which is a prominent morphological feature. Occurrence ofCorbiculashells in the Qaidam Basin indicates climate was apparently warmer than present during the formation of the Shell Bar becauseCorbiculadoes not live at similar or higher altitudes in the region today. Because the Shell Bar is no longer considered a deposit formed within a lake, its presence does not indicate paleoclimate conditions wetter than today.