U-Pb systematics of fossilized biogenic tissues as a tracer of long-term diagenetic processes

矿化（骨骼、牙齿）和非矿化有机组织（木材）的石化是一个复杂的死后改变或成岩过程，涉及许多平行或随后的运输和反应步骤。这些过程与某些地质过程有关，例如流体相的动员和/或温度变化，可能会在几天甚至几百万年的短时间内发生，并且尚未完全了解。尽管通过详细的岩石学、矿物化学和结构调查，可以在化石木材和骨骼中确定相对的过矿化和替代序列，但这些过程的绝对时间尺度和持续时间尚不清楚，特别是对于前更新世化石。如果一个生物成因模板在早期成岩过程中包含了微量元素的放射性同位素，在死亡后相对迅速，并且在整个地质时期保持一个封闭的系统，那么地质年代学方法应该返回与近沉积或地层年龄一致的辐射年龄。然而，现有的数据表明，化石组织所记录的年代不一定与预期的地层年龄一致。相反，它们可能提供一种工具来揭示一系列不同的成岩蚀变过程，这些过程无法被识别，并最终与最早的成岩状态相一致。U-Pb体系非常适合研究低温过程。现代质谱分析技术，如激光烧蚀电感耦合等离子体质谱、离子微探针、纳米二级离子质谱和原子探针层析成像，为研究有机组织化石中涉及的复杂结构非晶或微至纳米晶相的U-Pb同位素系统开辟了新的途径。该项目的主要目标是揭示不同成岩过程的时间，如元素运输、矿化或在不同长度尺度上的再结晶，以增加我们对长期石化过程的理解。此外，我们希望找到地球化学、质地或矿物学标准，以筛选最有希望的石化木材和化石骨骼样品或样品域，用于“直接”U-Pb测年。骨骼化石中给出接近沉积时代的区域也将与稳定的同位素系统保持接近，这对于古饮食、古环境和古生态重建的代用物的应用至关重要。

Fossilisation of mineralised (bone, tooth) and non-mineralised organic tissue (wood) is a complex, post-mortem alteration or diagenetic process that involves a number of parallel or subsequent transport and reaction steps. These processes are related to certain geological processes, such as the mobilisation of a fluid phase and/or temperature changes, may run over short time scales of days to even several millions of years and are not yet fully understood. Although relative permineralisation and replacement sequences can be identified in fossil wood and bones by detailed petrographic and mineral-chemical and -structural investigations, the absolute time scales and durations of such processes are not yet known, particular for pre-Pleistocene fossils. If a biogenic template has incorporated radioactive isotopes of trace elements during early diagenetic processes, relatively rapidly after death, and remained a closed system throughout geologic time, then geochronological methods should return a radiometric age consistent with the near-depositional or stratigraphic age. The available data, however, suggests that fossil tissues do not necessarily record dates that are concordant with the expected stratigraphic age. Instead, they might provide a tool to unravel a sequence of different diagenetic alteration processes, not otherwise identifiable, and eventually consistent with the earliest diagenetic state accessible. The U-Pb system is well suited to study low temperature processes. Modern mass spectrometric analytical techniques such as laser ablation inductively-coupled plasma mass spectrometry, ion microprobe, nano-sized secondary ion mass spectrometry, and atom probe tomography opens up new avenues to investigate the U-Pb isotope system of complexly-structured amorphous or micro- to nano-crystalline phases that are involved in the fossilisation of organic tissue. The prime objective of this project is to unravel the timing of different diagenetic processes such as element transport, mineralisation, or recrystallisation at different length scales in order to increase our understanding of the long-term fossilisation process. In addition, we want to find geochemical, textural, or mineralogical criteria for screening the most promising petrified wood and fossil bone samples or sample domains for "direct" U-Pb dating. Domains in fossilised bone that give near depositional ages are expected to also remain close with respect to stable isotope systems, which is critical for the application of proxies for palaeodietary, palaeoenvironmental, and palaeoecological reconstructions.