【摘要】 获取合适的气候变化代用指标,检验其在更长时间尺度内应用的有效性对于利用我国西部内陆湖盆沉积反映新生代以来大陆气候变化具有重要意义。易溶盐含量作为一种反映环境变化的代用指标,在沉积相稳定的内陆湖泊沉积物研究中已获得广泛应用。对于存在沉积相变迁的古湖盆沉积物,其适用性需要进行考虑。本文对西宁盆地谢家剖面的一套年代为始新世到中新世的内陆湖相泥岩/石膏沉积进行研究发现,石膏层和泥岩层分别对应于Ca2+、SO2-4和Sr2+的高值和低值变化。石膏层广泛分布的剖面下部Ca2+、SO2-4和Sr2+含量较高,Na+和Cl-含量较低,而石膏层逐渐消失的剖面上部Ca2+、SO2-4和Sr2+整体含量降低,Na+和Cl-含量略有升高。沉积相分析表明红色泥岩层和石膏层分别对应于冲积扇远端和干盐湖化学沉积,剖面下部石膏层和红色泥岩层交替到上部以红色泥岩层为主的岩相变化反映了区域范围上的干旱化进程。谢家剖面易溶盐含量强烈受控于上述沉积相变迁所决定的岩性变化,并清晰揭示出发生在约33 Ma的巨大干旱化事件。因此对于存在沉积相变迁的古湖盆沉积物,易溶盐含量分析不但要考虑内陆湖泊浓缩演化过程中溶解度控制的碳酸盐—硫酸盐—卤化物相继发生的沉淀序列,还需考虑易溶盐在不同沉积相中的赋存迁移规律以及研究时段内的溶质补给类型是否存在差异。更多还原

【Abstract】 It is significant for using China inland basins deposition to obtain the Cenozoic continental climate change records that we appropriately acquire paleoenvironmental proxies and examining their validity for a long-term scale. Water dissolved salts,as a paleoenvironmental proxy,has widely applied to the field of inland lake sediments with stable sedimentation. However,it is required to examine when this proxy has been used to the lake sediments with significant sedimentary facies alternation. In this study,we focus on a set of strata of inland lake sediments consisting of mudstones / gypsum alternations in Xiejia section,Xining Basin,age ranging from Eocene to Miocene. The investigation of water dissolved salts in Xiejia Section sediments shows the strong control of lithology alternations on variations of water dissolved salts concentrations. Specifically,the gypsum and mudstone layers correspond to the high / low concentrations of Ca2 +,SO2-4 and Sr2 +,respectively. The lower part of this section sediments with widely spread gypsum layers has low concentrations of Na+and Cl-and high concentrations of Ca2 +,SO2-4 and Sr2 +; The upper part of this section sediments lack of gypsum layers has slight high concentrations of Na+and Cl-and low concentrations of Ca2 +,SO2-4 and Sr2 +. Based on the sedimentary facies analysis,the gypsum and red mudstones layers are corresponding to shallow playa lake and distal alluvial fan,respectively. The evolution from distal alluvial fan and shallow playa lake alternations in the lower part of this section to distal alluvial fan in the upper part indicates a regional aridification process. The water dissolved salts in Xiejia section,strongly controlled by sedimentary facies alternations, clearly indicate a dry trend occurred at about 33 Ma. Hence,for the inland lake sediments with significant sedimentary facies alternations,not only the solubility limit control on the carbonate-sulfate-halide sequences in the d inland lake water,but the differences of water dissolved salts occurrence and activity between different sedimentary environment,of solute types provided by the source area,should be taken into account.更多还原