Multiple climate proxies indicate episodic changes in moisture levels within an ∼1 Ma duration (early–mid Pliocene) interval. Limestones within the Opache Formation, Calama Basin, Atacama Desert region, Chile, contain evidence for wetter and drier periods on short time scales. Proxies include carbonate lithological changes, paleontology (stromatolites, oncolites, gastropods, ostracods and diatoms), O and C stable isotopes, geochemistry, and mineralogical changes (aragonite, calcite, Mg-calcite, dolomite and gypsum) throughout a 30 m stratigraphic section. Stromatolite fossil cyanobacteria dark and light laminations and mesohaline to hypersaline diatom species suggest Pliocene annual seasonality. Short-term changes between wetter and drier conditions indicate that at least this part of the Atacama region was experiencing relatively rapid early–mid Pliocene climate instability. The predominance of limestone in the Opache Formation, in contrast to the 1500 m of Oligocene-Miocene siliciclastic conglomerates and sandstones, interpreted as arid climate alluvium, that underlie it, indicates a shift from arid or hyperarid climate to a semi-arid climate. Semi-arid conditions promoted limestone deposition in a shallow lacustrine-palustrine environment. In this setting, events such as storms with associated surface water flow, erosion, siliciclastic sand, gravel, and intraclast deposition, coupled with significant biological activity, represent sedimentation during more humid periods in a shallow lacustrine depositional environment. In contrast, limestone characterized by mudcracks, Navicula diatoms, and vadose syndepositional cementation, reflect periods of enhanced evaporation, water shallowing, and episodic desiccation, characteristic of a palustrine depositional system. These facies shifts, in conjunction with geochemical and isotopic proxy evidence, yield a sedimentary record of wetter and drier climate shifts.

中文翻译：

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陆相浅湖相-碳酸盐相碳酸盐中保存的上新世短期气候变化：智利阿塔卡马沙漠的西部奥帕奇组

多种气候指标表明，在大约1 Ma的持续时间内（上新世早期至中期），水分含量发生了周期性变化。智利阿塔卡马沙漠地区卡拉马盆地奥帕切组内的石灰石包含短时间尺度上较干和较干时期的证据。代理包括整个30 m地层剖面中的碳酸盐岩岩性变化，古生物学（叠层石，硬岩，腹足纲动物，原虫和硅藻），O和C稳定同位素，地球化学以及矿物学变化（文石，方解石，Mg方解石，白云石和石膏）。基质间质化石蓝细菌的暗层和浅层以及中盐到高盐硅藻物种表明上新世每年都有季节性。较干燥和较干燥的条件之间的短期变化表明，至少阿塔卡马地区的这一部分正经历着上新世早期—中新世气候不稳定。与1500 m的渐新世-中新世硅质碎屑砾岩和砂岩相反，Opache组中的石灰岩占主导地位，这表明它是干旱的气候冲积层，表明它已从干旱或超干旱气候转变为半干旱气候。半干旱条件促进了浅湖湖相环境中的石灰石沉积。在这种情况下，诸如风暴以及相关的地表水流，侵蚀，硅质碎屑，砾石和碎屑内沉积，以及显着的生物活性等事件，代表了在浅湖相沉积环境中更湿润时期的沉积。相反，石灰岩的特征是泥裂，纳维库拉硅藻和渗流沉积作用，反映出蒸发增加，水浅化和偶发干燥的时期，这是palustrine沉积系统的特征。这些相变，再加上地球化学和同位素替代证据，产生了干湿气候变化的沉积记录。