OSL surface exposure dating of wave-emplaced boulders - Improving the use of coarse-clast records for coastal hazard assessments

波浪巨石的 OSL 表面暴露测年 - 改进粗碎屑记录在沿海灾害评估中的使用

• 批准号: 299464740
• 负责人: Dr. Dominik Brill
• 金额: --
• 依托单位: Geographisches Institut
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/299464740?language=en
• 关键词: OSL; surface; exposure; dating; wave; OSL; surface; exposure; dating; wave

Fields of wave-emplaced blocks and boulders represent impressive evidence of cyclone and tsunami flooding over Holocene time scales. Unfortunately, their use for coastal hazard assessment is impeded by difficulties in the differentiation of tsunami- and storm-transported clasts, and by the absence of appropriate and accurate dating approaches, which are needed to generate robust chronologies of coarse clast records. The commonly applied AMS-14C, U/Th or ESR dating of coral-reef rocks and marine organisms attached to the clasts depends on a - mostly hypothetical - coincidence between the organisms death and boulder displacement, and inferred event chronologies may be biased by the marine 14C-reservoir effect and reworked organisms. The research proposed here addresses the necessity of innovative approaches to date the transport of coastal boulders by testing the recently developed optically stimulated luminescence (OSL) surface exposure dating technique. By measuring the depth-dependent resetting of the luminescence signal in exposed rock surfaces and comparing it to the signal-depth profiles of known-age samples, OSL surface exposure dating is capable to model direct depositional ages for boulder transport. Thereby, it promises to overcome the limitations of existing dating techniques, and to decipher complex transport histories of clasts that underwent multiple phases of exposure and burial. The successful application of OSL surface exposure to rock surfaces in archaeological contexts suggests that candidate coarse-clast records should be characterized by (i) overturned boulders that are exposed for periods shorter than the expected dating range of ~10-100 ka; (ii) a boulder lithology with significant percentages of quartz or feldspar appropriate for OSL dating; (iii) limited erosion of the exposed boulder surfaces; and (iv) known-age rock surfaces of the same lithology to calibrate site-specific model parameters (i.e. the local light flux at the rock surface). Our study site at Cabo de Trafalgar (Cádiz, Spain) offers all of these preconditions. Storm and/or tsunami waves have deposited up to 7 m-long clasts composed of Pleistocene beach rock on the inter- and supratidal platform, and multiple dislocation is assumed for numerous smaller clasts. We thus aim at dating boulders with single and multiple dislocation. Recently exposed rock surfaces, ancient buildings as well as quarries provide surfaces of known exposure age. The use of artificially exposed rock samples (for periods of 1 and 2 years) as reference samples for model calibration shall be evaluated. In the best case, the proposed investigations shall not only test the general suitability of the approach to coastal boulders but also provide quantitative information about the frequency-magnitude relationship of extreme wave events at Trafalgar. Thereby, it will allow to verify or falsify a correlation with the 1755 Lisbon tsunami, which is assumed for the largest clasts.

波长块和巨石的田地代表了全新世尺度上旋风和海啸洪水的令人印象深刻的证据。不幸的是，它们用于沿海危险评估的使用会阻碍海啸和风暴传播的碎屑的分化，并且由于没有适当，准确的约会方法，这是生成强大的粗clast记录时间表所需的。珊瑚园岩石和附属于分类者的珊瑚园岩石和海洋生物的通常应用的AMS-14C，U/TH或ESR的日期取决于生物体死亡和巨石位移之间的一个 - 主要是假设的 - 一致，并推断事件的年代可能会被海洋14C 14C Risservoir Effect和Reworked Organsisms偏置。这里提出的研究探讨了通过测试最近开发的光学刺激发光（OSL）表面暴露日期的必要方法，以期与沿海巨石的运输相关。通过测量裸露岩石表面中发光信号的深度依赖性重置，并将其与已知年龄样品的信号深度分布进行比较，OSL表面暴露日期能够模拟博尔德传输的直接沉积年龄。因此，它有望克服现有约会技术的局限性，并破译经过多个接触和埋葬阶段的经典史的复杂运输历史。 OSL表面暴露于岩石表面在考古环境中的成功应用表明，应候选的粗粉记录的特征是（i）（i）倒转的巨石，这些巨石的暴露时间比预期的约10-100 ka的预期约会范围短； （ii）一个适合OSL约会的石英或长石的巨石岩性； （iii）有限的暴露巨石表面侵蚀； （iv）相同岩性的已知年龄岩石表面，以校准位点特异性模型参数（即岩石表面的局部光通量）。我们位于西班牙Cádiz的Cabo de Trafalgar的研究站点提供了所有这些先决条件。暴风雨和/或海啸波已经沉积了多达7 m长的经典作品，该经典由跨越和上空平台上的更新世海滩岩组成，并且假定许多较小的经典作品都假定多个脱位。因此，我们旨在与单个和多重错位的巨石约会。最近，裸露的岩石表面，古老的建筑物以及采石场提供已知暴露年龄的表面。应评估人工裸露的岩石样品（1年和2年）作为模型校准的参考样品。在最好的情况下，拟议的调查不仅应测试对沿海巨石方法的一般适用性，而且还应提供有关特拉法加极端波事件的频率降低关系的定量信息。因此，它将允许验证或误解与1755里斯本海啸的相关性，这是对最大阶级的假定。