| 论晚期共和古湖时代、演化过程及其与地壳运动和黄河发育的关系 |
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| 引用本文：赵希涛,杨艳,贾丽云,胡道功,李维东,张耀玲,林旭.2021.论晚期共和古湖时代、演化过程及其与地壳运动和黄河发育的关系[J].地球学报,42(4):451-471. |
| DOI：10.3975/cagsb.2020.120702 |
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| 中文摘要:青海共和盆地, 是青藏高原东北部晚新生代期间形成的北西西—南东东走向构造盆地, 由西北部的茶卡小内流盆地, 中部非典型的达连海内流盆地和东南部被黄河及其支流深深切割的外流盆地三部分组成。该盆地中充填了上、下两套厚度普遍均在200～300 m间, 而最厚部分可达500～600 m的相互叠置的共和组与曲沟组河湖相地层。由这两套湖相地层所重建的古湖被分别称为早期和晚期共和古湖。本文重点讨论的是基于共和组湖相地层而重建的晚期共和古湖。石英热活化法ESR测年结果表明, 湖相共和组地层开始形成于(4.31±0.40) Ma之前, 持续到(2.58±0.20) Ma/(2.54±0.20) Ma之后的上新世时期。以尕玛羊曲村附近为顶点的黄河扇三角洲相两套均厚逾200 m砾石层中之上砾石层, 形成于(3.15±0.30)—(3.07±0.30) Ma之间, 其前缘水下三角洲相砾石层为(2.91±0.25) Ma, 而来自北部山前的同期洪积砾石层则为(2.97±0.27) Ma, 表明晚期共和古湖在(3.07±0.30) Ma与(2.91±0.15) Ma之间的上新世晚期达到其最盛期。此时, 湖面高度达到其最大值海拔(3 160±10) m左右, 古湖是一个面积近7 000 km2、深逾300 m的大型外流的淡水深湖。黄河在尕玛羊曲附近注入古湖, 并由盆地东北角的尕海以东流出, 经唯一通道古多隆河流入贵德古湖。当古湖面上升到超过共和与贵德两盆地的基岩分水岭时, 黄河在现今的龙羊峡位置切割出新的河道——龙羊峡, 从而导致了早更新世初古多隆河因“截弯取直”而非“溯源侵蚀”被废弃, 开始了黄河逐步下切、T21到T16形成与共和古湖逐渐消亡的过程。共和古湖经历了茶卡盆地开始与古湖主体分离, 中部湖区与东南部湖区分离、排干和东南部湖区被完全泄空等3个阶段。这一过程是随着中国区域地壳运动性质发生的根本性变化而发生的。此时, 共和盆地及邻近盆地, 甚至中国第一、二大地势阶梯上的大多数盆地, 除银川—河套盆地与汾渭盆地等个别盆地外, 都由差异性升降的盆-山运动转为整体性的隆升运动。发生于共和盆地的这一运动, 曾被徐叔鹰等命名为“恰卜恰(共和)运动”, 只是其所指的时代为中更新世晚期。但这一名称被李吉均等改称为“共和运动”, 作为青藏运动的延续, 意指黄河于10或15万年前因该运动而切穿龙羊峡, 溯源至共和盆地。作者建议保留原“恰卜恰(共和)运动”的名称与基本含义, 而该运动发生时间的争议仍待今后进一步深入研究解决。 |
| 中文关键词:共和盆地 共和古湖 ESR测年 上新世 古湖演化 黄河发育 恰不恰(共和)运动 |
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| A Discussion on the Age and Evolution Process of the Late Gonghe Paleolake and Its Relations with the Crustal Movement and the Development of the Yellow River |
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| Abstract:Gonghe Basin, as one of the numerous basins in northeastern Tibetan Plateau, is a kind of medium-scale tectonic basin, consisting of three parts: endorheic basin—the Chaka Salt Lake in the northwest, nontypical endorheic basin represented by small salt water lake such as the Dalian Lake in the middle, and external basin incised by the Yellow River and its tributaries in the southeast. There are two series of contraposed stratigraphic units: Gonghe Formation in the upper part and Qugou Formation in the lower part, which are filled in the Gonghe Basin. The thicknesses of these two sets of strata are mainly between 200 and 300 m, with the thickest reaching 500~600 m. The facies types are mainly coarse clastic deposits from the foothills around the basin and lacustrine fine-grained deposits in the center. The latter strata have redder color, stronger diagenesis, and wider distribution ranges, and experienced more tectonic activities. The paleolake, reconstructed by these two strata, is named Gonghe Paleolake. The early Gonghe Paleolake was reconstructed by the Qugou Formation, and the late one, the Gonghe Formation. The late Gonghe Paleolake, which is the focus of this paper, experienced the vegetation change process of stappe, forest-steppe, stappe, forest-steppe, stappe, forest-steppe and present steppe, indicating that the change from warm temperate zone to temperate zone, experiencing several times of climatic changes of cold-warm and dry-humid, and the general trend being aridification. During the maximum stage, the paleolake reached its maximum height, being (3 160±10) m a.s.l.. The Gonghe Paleolake was a deep freshwater lake, with the area of nearly 7 000 km2 and the depth of more than 300 m, where the Yellow River flowed in from the Gamayangqu Village, Xinghai Countay, and flowed out from east of the Gahai, through the ancient Duolong River, and hence the Yellow River was a river flowing through Duolonggou and Qunaihai Village to Guide Paleolake. During the period of the strongest development of paleolake, the Yellow River flowed into the Gonghe Basin and Gonghe Paleolake nearby the Gamayangqu, around which a large, northward extending, and irregularly shaped-fan delta system was formed The alluvial fan-delta system consists of two sets of gravel beds: the upper and the lower, with each bed having thickness of more than 200 m. When the lake level rose and exceeded the bedrock watershed of Gonghe and Guide basins in the south part of Waligang Mountain, a new channel was formed in the Longyang Gorge. With the basins changing from sinking-depositing to rising-eroding, the ancient Duolong River flowing around Waliguan Mount was abandoned. Meanwhile, the Gonghe Paleolake began to die gradually. The dying process consisted of three stages. During the first stage, the 21th and 20th terraces of the Yellow River were formed and the surface of the paleolake was less than 3 108 m a.s.l., the Chaka Salt Lake in the northwest began to separate from the main Gonghe Paleolake. During the second stage, the 16th terrace was formed, the surface of the Gonghe Paleolake was between 2 850 m and 2 865 m a.s.l., and most of the paleolake in the middle area was drained because of leakage. When the height of the riverbed of the Yellow River was 2 650~2 700 m a.s.l. or earlier because of the eroding action by the Yellow River, the paleolake area in the southeast had been probably already emptied. There were only some small salt water lakes such as Dalianhai (dried up), Genggahai and Yingdehai, and the Chaka Salt Lake developed to the stage of NaCl extraction. According to the quartz thermal-active ESR data, the ages of the above-mentioned strata and geological events are as fallows: the Gonghe Formation of lacustrine facies began to form before (4.31±0.40) Ma and continued to about (2.58±0.20) Ma/(2.54±0.20) Ma; The upper gravels of the fan-delta of the Yellow River near the Gamayangqu were formed between (3.15±0.30) Ma and (3.07±0.30) Ma, and the gravels in the delta front were formed at about (2.91±0.25) Ma, while the age of the synchronous proluvial gravels from the mountain front in the north is (2.97±0.27) Ma, which indicates that the late Gonghe Paleolake developed to the highest level in the late Pliocene between (3.07±0.30) Ma and (2.91±0.15) Ma. The ages of the 21th, 19th, 18th, 17th, 16th terraces of the Yellow River are (2.47±0.30) Ma, (2.36±0.20) Ma/(2.32±0.30) Ma, (2.31±0.20) Ma, (2.23±0.20) Ma, (2.12±0.15) Ma, respectively. When the late Gonghe Paleolake reached its maximum extension between (3.07±0.30) Ma and (2.91±0.15) Ma, the nature of regional crustal movement changed. The move state of the basins changed from the differential uplift and subsidence to the whole uplift, and this included Gonghe Basin, adjacent basins, and even most of the basins in the first and second ladder of topography of China, except Yinchuan–Hetao Basins and Fenwei Basin. This movement is named “Qiabuqia (Gonghe) Movement” by XU Shu-ying and some others. However, this name has been changed into “Gonghe Movement” and used as the continuation of Qingzang (Qinghai–Tibet) movement by LI Ji-jun and some others, indicating that the Yellow River eroded to the Gonghe Basin and the source area through incision of the Longyang Gorge around 100 or 150 thousand years ago. Due to the fact that the ancient Duolong River connected Gonghe and Guide Paleolakes and the formation of the Longyang Gorge was caused by “the bends of the cut-off” instead of headward erosion, the authors suggest retaining the name and basic meaning of the “Qiabuqia (Gonghe) movement”. As to the debate about the time of the movement, it can be solved by further research. |
| keywords:Gonghe Basin late Gonghe Paleolake ESR dating Pliocene evolution of the paleolake the Yellow River development Qiabuqia (Gonghe) Movement |
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