Mutiple proxy approach to Terrestrial Paleoclimate - The Late Triassic Ischigualasto Basin, NW Argentina

在过去的二十年里，基于古土壤的陆地古气候代用指标激增。这项研究的结果通过交叉核对单个盆地内矿物提供的结果，在某些情况下，单个古土壤剖面提供的结果，为众多古气候代用物提供了急需的测试。此外，这项研究的结果应该提供有助于确定哪些地球化学指标最不可能存在于地质记录中的信息。为此，本研究记录了古土壤中所含矿物的成土史和成土后历史，确定了哪些古气候的地球化学指标最有可能在被埋藏的情况下被保留下来，其中哪些指标为盘古大陆南部Ischigualasto盆地晚三叠世古气候提供了可靠的定量记录。本研究有两个主要目标：(1)记录古土壤中矿物的矿物组成、稳定同位素组成和40Ar-39Ar年龄，以描绘矿物结晶的时间框架，并利用特定矿物作为古环境的代用物。感兴趣的矿物包括层状硅酸盐、氢氧化物和碳酸盐，因为这些是常见的成土矿物，在地质记录中含量丰富。(2)利用多种矿物学指标重建晚三叠世大气PCO2的演化，并阐明大气温室气体浓度变化与古温度、古降水等其他古气候参数之间的关系。对“深时间”地质记录的古气候研究为全球变暖或变冷的重复、突然间隔以及极端气候状态之间的过渡提供了令人信服的证据。许多这样的气候事件引发了重大的生物更替，并导致生物地球化学循环的大规模变化。此外，最近的发展也引发了对过去5亿年间二氧化碳浓度-气候模式有效性的争论。这些问题与目前人们关注的气候变化辩论平行，从而突出了充分了解地球气候系统及其变率的必要性。开发同等时空分辨率的海洋和陆地古气候档案对于记录此类大尺度环境扰动的全球性质以及描述地球气候系统动力学的全范围特征至关重要。总的来说，这项研究的重要性超越了任何一个地点或时间（例如，阿根廷晚三叠纪），因为这项研究提供了一个更好的理解，即古土壤对古气候重建的有用程度。

Terrestrial paleoclimate proxies based on paleosols have proliferated over the past two decades. The results of this study provide a much-needed test of the numerous paleoclimate proxies by crosschecking of the results provided by minerals within a single basin and, in some instances, a single paleosol profile. In addition, the results of this study should provide information that help to determine which geochemical proxies are least likely to survive into the geological record. To that end, this research documents the pedogenic and post-pedogenic history of the minerals contained within paleosols, determines which geochemical proxies of paleoclimate are most likely to be retained in spite of burial, and which of these provide a robust and quantitative record of Late Triassic paleoclimate in the Ischigualasto basin of southern Pangea.This research is directed by two main objectives: (1)Documentation of the mineralogical composition, stable isotopic composition, and 40Ar-39Ar ages of minerals contained within paleosols in order to delineate the temporal framework of mineral crystallization and the utility of a particular mineral as a proxy of paleoenvironment. The minerals of interest include phyllosilicates, oxyhydroxides and carbonates, as these are common pedogenic minerals and are abundant within the geological record. (2) To reconstruct the evolution of Late Triassic atmospheric PCO2 from multiple mineralogical proxies and elucidate any robust trends between changing atmospheric green house gas concentrations and other paleoclimate parameters such as paleotemperature and paleoprecipitation.Paleoclimate studies of 'deep-time' geologic records provide compelling evidence for repeated, abrupt intervals of global warming or cooling, and transitions between extreme climate states. Many of these climate events triggered significant biotic turnover and led to wholesale changes in biogeochemical cycling. Moreover, recent developments have fueled a debate over the validity of the pCO2-climate paradigm over the past half billion years. These issues parallel the climate change debate of concern at present, thus highlighting the need to fully understand Earth's climate system and its variability. The development of marine and terrestrial paleoclimate archives at equal spatial and temporal resolution is critical to documenting the global nature of such large-scale environmental perturbations, and to characterizing the full range of Earth climate-system dynamics. In total, the importance of this research transcends any one place or time (i.e., Late Triassic of Argentina), because this study provides a better understanding of just how useful paleosols may be for paleoclimate reconstructions in general.