Global Change: Quaternary Paleoclimate Record from Salt Cores (Death Valley, Saline Valley and Bristol Dry Lake, California)

在美国西部三个干旱的封闭盆地中，含有盐岩的蒸发岩出现在相当深的地方，保存了200多万年的古气候记录。该项目将利用2个钻孔的现有样品和材料，研究过去3个冰期-间冰期(约30万年)这些盆地盐类沉积的古气候记录。重点是对原生盐岩和其他蒸发岩矿物晶体中的流体包裹体进行化学分析，以获得：H2O的活度和主要元素化学(显微测温和渗滤液分析)，流体包裹体水的氢和氧同位素组成(质谱仪)，以及含有滞留空气的晶体的大气气体组成(四极质谱仪)。流体包裹体和辅助资料(沉积学、矿物学、岩石学)可能被用来解释古气候：(1)盆地干旱，(2)相对温度，(3)大气化学，(4)湖水化学和卤水演化，(5)闭合盆地沉积环境。通过将数据与第四个闭合盆地(西尔勒斯湖)、大盆地脉方解石、极地冰芯和海洋氧同位素记录进行比较，将区分局部和全球对古气候的影响。将在布里斯托尔干湖考察热液流体对水文记录可能产生的局部影响，在那里，全新世火山活动得到了很好的记录。岩盐的测年将使用U系列方法和36Cl进行，并将得到年代学的补充。需要对水圈和大气进行长期记录，以记录大陆的古气候以及这种气候如何受到全球和地方过程的影响。陆相蒸发岩和与之相关的闭合盆地沉积物，由于其形成所需的特殊气候和水文条件，为理解古代大陆气候提供了巨大的希望。

Halite-bearing evaporites occur to substantial depths in 3 arid closed-basins in the western U.S. and preserve a record of paleoclimate for more than 2 million years. This project will examine the paleoclimate record in salt deposits from these basins over the last 3 glacial-interglacial cycles (approximately 300,000 years) using existing samples and materials from 2 boreholes to be drilled to depths of 100 m. Emphasis will be on chemical analyses of fluid inclusions in crystals of primary halite and other evaporite minerals to obtain: activity of H2O and the major element chemistry (microthermometry and leachate analysis), hydrogen and oxygen isotopic composition of fluid inclusion waters (Mass spectrometry), and atmospheric gas composition, for those crystals which contain trapped air (quadrupole mass spectrometry). Fluid inclusions and supplementary data (sedimentology, mineralogy, petrography) may potentially be used to interpret paleoclimates, in terms of: (1) basin aridity, (2) relative temperatures, (3) atmospheric chemistry, (4) lacustrine water chemistry and brine evolution, and (5) closed-basin depositional settings. Local and global influences on paleoclimate will be distinguished by comparing data with the record from a fourth closed-basin (Searles Lake), Great Basin vein calcites, polar ice cores, and the marine oxygen isotope record. Possible local influences of hydrothermal fluids on the hydrologic record will be examined at Bristol Dry Lake, where Holocene volcanic activity is well documented. Dating of halite will done using U-series methods and 36Cl, and will be supplemented by tephrachronology. Long term records of the hydrosphere and atmosphere are needed to document continental paleoclimates and how such climates have been influenced by global and local processes. Nonmarine evaporites and associated closed-basin sediments, because of the special climatic and hydrologic conditions necessary for their formation, hold great promise for understanding ancient continental climates.