Lacustrine stromatolites were widespread in the Miocene Wudaoliang Group (stromatolites of the Wudaoliang Group), northern Tibetan Plateau; but only at one location nearby the Wudaoliang Town, they occurred intensively in thick, laterally traceable beds (Wudaoliang stromatolites). Although deposited in lacustrine environment, the lack of fossils in these rocks hampers determining whether the stromatolites formed in freshwater or saline conditions. To address this problem, and in an attempt to identify criteria to distinguish differences of freshwater and saline conditions, we studied the laminae microfabrics, stable carbon and oxygen isotope ratios, rare earth element patterns and biomarkers of the stromatolites. These stromatolites can be divided into fenestral stromatolites and agglutinated stromatolites. The fabric of fenestral stromatolites is formed by microcrystalline carbonate enclosing spar-cemented, angular crystal traces. Essentially, this fabric is interpreted as pseudomorph after former formed evaporite crystals. Faecal pellets identical to that of the present-day brine shrimp Artemia, lack of other eukaryotic fossils, and stable isotopic signals point to a shallow, evaporation-dominated hypersaline lake setting. Covariation of carbon and oxygen isotopes indicates hydrologically closed conditions of the Miocene lake on northern Tibetan Plateau.However, if compared to other lacustrine carbonates of the Wudaoliang Group, the high δ13C values of the investigated Wudaoliang stromatolites reveal an additional photosynthetic effect during the deposition of the stromatolites. Furthermore, although no direct evidence is available from field observations and microfabrics, a positive europium anomaly of Wudaoliang stromatolites indicates that a palaeo-hydrothermal inflow system had existed in the outcrop area. These new results favour a hypersaline lake setting subject to hot spring inflow for the Wudaoliang stromatolites, in contrast to earlier interpretations suggesting a freshwater lake setting (e.g. Yi et al., Journal of Mineralogy and Petrology 28: 106–113, 2008; Zeng et al., Journal of Mineralogy and Petrology 31: 111–119, 2011). This approach may be appropriate for other lacustrine, unfossiliferous microbialites in settings where the environmental conditions are difficult to determine.

中文翻译：

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青藏高原北部中新世五道梁​​群湖相叠层石古环境背景

湖相叠层石广泛分布于青藏高原北部中新世五道梁​​群（五道梁群叠层石）；但仅在五道梁镇附近的一处，它们密集地出现在厚的、横向可追踪的层（五道梁叠层石）中。尽管沉积在湖相环境中，但这些岩石中缺乏化石阻碍了确定叠层石是在淡水还是盐水条件下形成的。为了解决这个问题，并试图确定区分淡水和盐水条件差异的标准，我们研究了叠层石的薄层微结构、稳定的碳和氧同位素比、稀土元素模式和生物标志物。这些叠层石可分为窗孔叠层石和凝集叠层石。窗孔叠层石的结构是由微晶碳酸盐包裹着晶莹剔透的、棱角分明的晶体痕迹形成的。从本质上讲，这种织物被解释为先前形成的蒸发晶体后的假晶。粪便颗粒与当今丰年虾卤虫的粪便颗粒相同，缺乏其他真核生物化石，稳定的同位素信号指向浅层、以蒸发为主的高盐度湖环境。碳氧同位素的共变表明青藏高原北部中新世湖泊的水文封闭条件。然而，如果与五道梁群其他湖相碳酸盐岩相比，所研究的五道梁叠层石的高δ13C值揭示了在沉积过程中额外的光合作用效应。叠层石。此外，虽然没有从野外观察和微织物中获得直接证据，但五道梁叠层石的铕正异常表明露头区存在古热液流入系统。这些新的结果有利于五道梁叠层石的温泉流入的高盐度湖泊环境，与早期的淡水湖环境解释形成对比（例如 Yi 等人，矿物学和岩石学杂志 28：106-113，2008 年；Zeng 等人al., Journal of Mineralogy and Petrology 31: 111–119, 2011)。这种方法可能适用于环境条件难以确定的其他湖相、无化石微生物岩。五道梁叠层石铕正异常表明露头区存在古热液流入系统。这些新的结果有利于五道梁叠层石的温泉流入的高盐度湖泊环境，与早期的淡水湖环境解释形成对比（例如 Yi 等人，矿物学和岩石学杂志 28：106-113，2008 年；Zeng 等人al., Journal of Mineralogy and Petrology 31: 111–119, 2011)。这种方法可能适用于环境条件难以确定的其他湖相、无化石微生物岩。五道梁叠层石铕正异常表明露头区存在古热液流入系统。这些新的结果有利于五道梁叠层石的温泉流入的高盐度湖泊环境，与早期的淡水湖环境解释形成对比（例如 Yi 等人，矿物学和岩石学杂志 28：106-113，2008 年；Zeng 等人al., Journal of Mineralogy and Petrology 31: 111–119, 2011)。这种方法可能适用于环境条件难以确定的其他湖相、无化石微生物岩。矿物学和岩石学杂志 28: 106–113, 2008; Zeng 等人，矿物学与岩石学杂志 31：111–119，2011 年）。这种方法可能适用于环境条件难以确定的其他湖相、无化石微生物岩。矿物学和岩石学杂志 28: 106–113, 2008; Zeng 等人，矿物学与岩石学杂志 31：111–119，2011 年）。这种方法可能适用于环境条件难以确定的其他湖相、无化石微生物岩。