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

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.

在全新世时期内，旋风和海啸泛滥的波浪块和巨石的田地，它们的使用沿海危险评估是由沿海危险评估的，这些危险评估是在海啸的扩散中的差异。为了生成粗碎屑记录的稳健时间在此提出的是，通过测试E最近开发了沿海界限的创新方法的必要性，该方法最近开发了光学刺激的发光（OSL）表面曝光日期。已知年龄样本的信号深度，OSL表面曝光日期能够模拟巨石传输的直接沉积年龄。以（i）在预期的10-100 ka约会时暴露于（ii）的（ii）巨大的岩性岩性的（iii）适合OSL约会的巨石（III）； （iv）相同的岩性岩石表面校准了特定模型的街机（即岩石表面的局部光通量）因此，假定许多较小的碎屑，我们的跨度较小的平台。作为模型校准的参考样品，应评估拟议的研究，不仅应测试与沿海ULDERS的地理位置，而且还应定量对Trafalgar的极端波动事件的频率数量。海啸，是最大的碎屑。