The upper boundary of a tsunami deposit often comprises a mud-dominated layer, called a mud cap, resulting from the different settling times of various grain sizes in the suspended sediment. This mud cap is often visibly indistinguishable from muds that can be deposited under normal circumstances following a tsunami. In fact, dating organic material immediately above the sandy tsunami deposit often produces significantly older ages than the actual age of the event because of the mud cap contains a wide variety of entrained material. Herein, we present several analytical results related to mud caps. Our results indicate that mud caps are difficult to recognize visually, whereas CT and XRF analyses enable us to recognize them in a non-destructive way. For the dating of tsunami deposits, it is crucially important to conduct such non-destructive analyses before sampling to recognize unfavorable stratigraphic components for dating. Such careful sampling is extremely important for accurate dating of tsunami deposit which is essential for reconstruction of paleotsunami size and its frequency. Therefore, our finding will also contribute to tsunami hazard assessment.
- Mud cap
- Radiocarbon dating