Time Averaging in the Formation of Fossil Assemblages

PI将调查死亡集结形成所需的时间跨度，以及形成过程中的时间事件和社区的时间历史被离散保存的程度。要做到这一点，需要一种廉价的方法来测定贝壳的死亡时间。正在开发的方法是基于观察到双壳类贝壳中的蛋白质基质逐渐分解，释放蛋白质结合的氨基酸然后积累，以及这些游离氨基酸逐渐扩散出贝壳。因此，蛋白质基质的剩余程度和存在的游离氨基酸的数量(由生产和扩散损失的平衡决定)都是壳的时间相关属性。要使这项技术有用，它必须能在货架组件上使用。大陆架的特点是小物种占多数，跨大陆架的温度梯度很大，每一种都会对这项技术的能力造成负担。因此，这一建议的目的是证明氨基酸测年方法能够回答以下关于死亡组合形成的重要问题：(1)碎屑沉积体系中死亡组合形成所需的时间跨度是多少？(2)群落中哪些时间事件是离散的在死亡集合体形成过程中保存下来(不考虑它们在地层上的挤压程度，但它们是否被谨慎地保存在地层序列中)？(3)能确定攻丝改造的速率吗？或者至少能测量攻丝改造与贝龄(死亡时间)相关的程度吗？

PI will investigate the time span required for death assemblage formation and the extent to which the temporal events in its formation, and hence the temporal history of the community, are discretely preserved. To do so requires an inexpensive method for dating time-since-death of shells. The method under development is based on the observation that the proteinaceous matrix in the shells of bivalves gradually decomposes, freeing protein-bound amino acids which then accumulate, and the observation that these free amino acids gradually diffuse out of the shell. Accordingly, the degree of proteinaceous matrix remaining and the amount of free amino acid present (determined by the balance of production and diffusional loss) are both time dependent properties of the shell. For the technique to be useful, it is essential that it be usable on shelf assemblages. The shelf is typified by a preponderance of small species and a significant cross-shelf thermal gradient, each of which would tax the capabilities of the technique. Accordingly, the purpose of this proposal is to demonstrate the ability of the amino acid dating method to answer the following important questions about death assemblage formation: (1) What time span is required for death assemblage formation in clastic depositional regimes? (2) Which temporal events in the community are discretely preserved during death assemblage formation (not how stratigraphically compressed they are, but are they discreetly preserved in stratigraphic sequence)? (3) Can the rates of taphonomic alteration be determined or at least can the extent to which taphonomic alteration is correlation with shell age (time-since-death) be measured?