Time Averaging in the Formation of Fossil Assemblages

PI将调查死亡集合形成所需的时间跨度，以及形成过程中的时间事件以及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确定贝壳死亡后的时间。正在开发的方法是基于观察到双壳类动物壳中的蛋白质基质逐渐分解，释放出蛋白质结合的氨基酸，然后积累起来，并观察到这些游离氨基酸逐渐扩散出壳。因此，蛋白质基质的剩余程度和存在的游离氨基酸的数量（由产生和扩散损失的平衡决定）都是壳的时间依赖性质。为了使这项技术有用，它必须能在货架上使用。大陆架的典型特征是小物种的优势和显著的跨大陆架热梯度，每一个都将对技术的能力造成负担。因此，本提案的目的是证明氨基酸测年方法的能力，以回答以下关于死亡组合形成的重要问题：(1)在碎屑沉积制度下，死亡组合形成需要什么时间跨度？(2)群落中哪些时间事件在死亡组合形成过程中被离散地保存下来（不是它们被地层压缩的程度，而是它们在地层层序中被谨慎地保存下来）？(3)是否可以确定表音学变异的速率，或者至少可以测量表音学变异与壳年龄（死亡后时间）相关的程度？

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?