Quantifying the limits of paleontological resolution using a global compilation of individually-dated skeletal remains

Marine fossil assemblages typically include remains of non-contemporaneous organisms that accumulated over time or were subsequently mixed by bioturbation or reworking. The resulting time averaging (temporal mixing) imposes the fundamental limit on the temporal resolution of paleontological samples and thus restricts the range of processes that can be studied in the fossil record. Over the last decades, numerous case studies have estimated time averaging based on post-mortem age distributions of individually-dated skeletal remains preserved in late Quaternary sediments. However, the limited scope of previous studies constrains our understanding of the variation in temporal resolution of paleontological samples across different taxa and depositional settings, and factors controlling it.

Here, we present a global compilation of data from multiple projects focused on age-dating of marine invertebrate remains sampled from present-day seabeds and Quaternary sediment cores. The dataset aggregates radiocarbon and amino-acid racemization ages of skeletal elements and links them to a broad range of standardized variables describing sampling methodology, intrinsic characteristics of skeletal producers, as well as stratigraphic, sedimentary and environmental context. Currently, the dataset includes postmortem age estimates for over 7,500 specimens representing 383 monospecific collections of 10 or more individually dated specimens coming from 291 sampling units (core increments, grabs, dredges, hand collections or suction samples). The sampling locations range from nearshore to continental slope settings in seven warm-temperate, subtropical, and tropical regions.

Preliminary analyses suggest that the majority of the analyzed samples underwent multi-centennial to supra-millennial time averaging, although a significant portion of them (14-23% depending on the age dispersion measure) was time-averaged to less than 100 years. The dataset is strongly dominated by aragonitic bivalves (>80% of samples and dated specimens), with much more limited data available for other mollusk taxa, brachiopods and echinoids. Outer shelf and slope environments are also poorly represented with only 7% of the sampling sites coming from water depths below 100 m. Our compilation highlights the lack or relative paucity of quantitative time-averaging estimates from deep-water and high-latitude settings, as well as for taxa with low durability or multi-elemental skeletons (such as echinoderms and arthropods). Increasing the taxonomic and environmental coverage of the data is thus crucial for improving our current understanding of the temporal resolution of the fossil record.