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Abstract
Interpreting how far organisms within fossil assemblages may have been transported and if they all originated from the same location is fundamental to understanding whether they represent true palaeocommunities. In a three-factorial experimental design, we used an annular flume to generate actualistic sandy sediment-density flows that were fast (2 ms−1) and fully turbulent in order to test the effects of flow duration, sediment concentration, and grain angularity on the states of bodily damage experienced by the freshly euthanized polychaete Alitta virens. Results identified statistically significant effects of flow duration and grain angularity. Increasing sediment concentration had a statistically significant effect with angular sediment but not with rounded sediment. Our experiments demonstrate that if soft-bodied organisms such as polychaetes were alive and then killed by a flow then they would have been capable of enduring prolonged transport in fast and turbulent flows with little damage. Dependent upon sediment concentration and grain angularity, specimens were capable of remaining intact over flow durations of between 5 and 180 min, equating to transport distances up to 21.6 km. This result has significant palaeoecological implications for fossil lagerstätten preserved in deposits of sediment-density flows because the organisms present may have been transported over substantial distances and therefore may not represent true palaeocommunities.
Highlights
IntroductionSites of exceptional fossil preservation (lagerstätten) provide insight into major events in the evolution of life on Earth [1]
Sites of exceptional fossil preservation provide insight into major events in the evolution of life on Earth [1]
More importantly, our results demonstrate that even in fully turbulent sandy flows travelling at a mean velocity of 2 ms−1, A. virens is capable of remaining intact over the considerable distances of 21.6 km
Summary
Sites of exceptional fossil preservation (lagerstätten) provide insight into major events in the evolution of life on Earth [1]. Interpreting these fossil assemblages requires understanding of the processes that allow this type of preservation to occur [2,3]. Experiments allow us to investigate the important processes that must take place during this critical time period in order for preservation of soft-bodied organisms to occur. Most previous research has focused on the importance of post-depositional decay and the mechanisms of soft-tissue mineralization [3,4,5,6,7,8,9,10], rather than understanding the implications of transport and flow dynamics. Annular flume experiments by Duncan et al [22] investigated the effect of transport duration on cockroach preservation, but in a non-counter-rotating annular flume and did not investigate the effects of sediment concentration or angularity
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