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Abstract Studies of paleocommunities and trophic webs assume that multispecies assemblages consist of species that coexisted in the same habitat over the duration of time averaging. However, even species with similar durability can differ in age within a single fossil assemblage. Here, we tested whether skeletal remains of different phyla and trophic guilds, the most abundant infaunal bivalve shells and nektobenthic fish otoliths, differed in radiocarbon age in surficial sediments along a depth gradient from 10 to 40 m on the warm-temperate Israeli shelf, and we modeled their dynamics of taphonomic loss. We found that, in spite of the higher potential of fishes for out-of-habitat transport after death, differences in age structure within depths were smaller by almost an order of magnitude than differences between depths. Shell and otolith assemblages underwent depth-specific burial pathways independent of taxon identity, generating death assemblages with comparable time averaging, and supporting the assumption of temporal and spatial co-occurrence of mollusks and fishes.
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Multiple phyla, one time resolution? Similar time averaging in benthic foraminifera, mollusk, echinoid, crustacean, and otolith fossil assemblages
Abstract Time averaging of fossil assemblages determines temporal precision of paleoecological and geochronological inferences. Taxonomic differences in intrinsic skeletal durability are expected to produce temporal mismatch between co-occurring species, but the importance of this effect is difficult to assess due to lack of direct estimates of time averaging for many higher taxa. Moreover, burial below the taphonomic active zone and early diagenetic processes may alleviate taxonomic differences in disintegration rates in subsurface sediments. We compared time averaging across five phyla of major carbonate producers co-occurring in a sediment core from the northern Adriatic Sea shelf. We dated individual bivalve shells, foraminiferal tests, tests and isolated plates of irregular and regular echinoids, crab claws, and fish otoliths. In spite of different skeletal architecture, mineralogy, and life habit, all taxa showed very similar time averaging varying from ~1800 to ~3600 yr (interquartile age ranges). Thus, remains of echinoids and crustaceans—two groups with multi-elemental skeletons assumed to have low preservation potential—can still undergo extensive age mixing comparable to that of the co-occurring mollusk shells. The median ages of taxa differed by as much as ~3700 yr, reflecting species-specific timing of seafloor colonization during the Holocene transgression. Our results are congruent with sequestration models invoking taphonomic processes that minimize durability differences among taxa. These processes together with temporal variability in skeletal production can overrule the effects of durability in determining temporal resolution of multi-taxic fossil assemblages.
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- Award ID(s):
- 1855381
- PAR ID:
- 10469067
- Publisher / Repository:
- Geological Society of America
- Date Published:
- Journal Name:
- Geology
- Volume:
- 50
- Issue:
- 8
- ISSN:
- 0091-7613
- Page Range / eLocation ID:
- 902 to 906
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Paleobiological and paleoecological interpretations rely on constraining the temporal resolution of the fossil record. The taphonomic clock, that is, a correlation between the alteration of skeletal material and its age, is an approach for quantifying time-averaging scales. We test the taphonomic clock hypothesis for marine demersal and pelagic fish otoliths from a 10–40 m depth transect on the Mediterranean siliciclastic Israeli shelf by radiocarbon dating and taphonomic scoring. Otolith ages span the last ~8000 yr, with considerable variation in median and range along the transect. Severely altered otoliths, contrary to pristine otoliths, are likely to be older than 1000 yr. For pelagic fish otoliths, at 30 m depth, taphonomic degradation correlates positively with postmortem age. In contrast, no correlation occurs for demersal fishes at 10 and 30 m depth, mostly because of the paucity of very young pristine (<150 yr) otoliths, possibly due to a drop in production over the last few centuries. Contrary to molluscan and brachiopod shells, young otoliths at these depths are little affected and do not show a broad spectrum of taphonomic damage, because those that derive from predation are excreted in calcium- and phosphate-rich feces forming an insoluble crystallic matrix that increases their preservation potential. At 40 m depth, all dated otoliths are very young but rather damaged because of locally chemically aggressive sediments, thus showing no correlation between taphonomic grade and postmortem age. Our results show that local conditions and the target species population dynamics must be considered when testing the taphonomic clock hypothesis.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1130/G49970.1
