Testing the isothermal thermoluminescence dating method to constrain mid-Pleistocene speleothem growth phases in the Bleßberg Cave

洞穴沉积物（次生洞穴碳酸盐）的广泛分布及其对高精度和高精度230 Th/U测年的特殊适用性使其成为过去气候和环境变化的非凡陆地档案。230 Th/U年龄上限约为1000年。600 ka的其他方法需要达到更深的地质过去，包括热释光（TL）定年。方解石的热释光信号在非常高的剂量下饱和，从而提供了一种潜在的手段，将洞穴沉积物的年龄范围扩展到数百万年。然而，热释光测年的应用一直受到阻碍1）假热释光信号从方解石在高温下，2）在环境剂量率估计的大不确定性。近年来，为了克服假热释光信号的影响，发展了方解石的等温热释光（ITL）测年方法。然而，这种ITL测年方法尚未在具有独立年龄控制的样品上进行测试。在此，我们建议全面研究洞穴沉积物的ITL信号特征，并制定最合适的ITL测年方案。我们将使用来自Bleßberg洞穴的样品，并评估影响环境剂量率准确性的关键因素，如α有效性，U系列不平衡和放射性元素的非均匀分布。MC-ICPMS 230 Th/U年龄将作为独立的年龄控制点。Bleßberg洞穴非常适合于ITL方法的评估，因为230 Th/U定年的洞穴沉积物可以追溯到大约1000年。360，000年是现成的。样本BB 2 -1尤其将是验证国际交易日志测年方法的理想测试案例。成功地评价和实施这一方法将开辟一条途径，为那些由于碎屑污染或铀浓度低而无法用铀系测年法测年的样品建立年表。

The wide distribution of speleothems (secondary cave carbonates) and their exceptional suitability for high accuracy and precision 230Th/U dating make them extraordinary terrestrial archives of past climatic and environmental changes. With the upper age limit of 230Th/U dating at ca. 600 ka other methods are required to reach deeper into the geological past, including thermoluminescence (TL) dating. The TL signal of calcite saturates at very high dose, thus offering a potential means to extend the age range of speleothems to several millions of years. However, application of TL dating has been hampered by 1) a spurious TL signal from calcite at high temperatures, and 2) the large uncertainty in environmental dose rate estimation. Recently isothermal TL (ITL) dating of calcite has been developed to overcome the influence of the spurious TL signal. However, this ITL dating method has not been tested on samples with independent age control yet. Here, we propose to comprehensively study the characteristics of the ITL signal of speleothems, and develop the most suitable ITL dating protocol. We will use samples from Bleßberg Cave and evaluate critical factors that influence the accuracy of environmental dose rates, such as alpha effectiveness, U-series disequilibrium, and heterogeneous distribution of radioactive elements. MC-ICPMS 230Th/U ages will serve as independent age control points. Bleßberg Cave is ideally suited for the evaluation of the ITL method as 230Th/U-dated speleothems reaching back to ca. 360,000 years are readily available. Sample BB2-1 in particular will be an ideal test case to validate the ITL dating method. Successful evaluation and implementation of this method would open a pathway to establish chronologies for samples that remain inaccessible by U-series dating due to detrital contamination or low uranium concentrations.