THE TEMPORAL-SPATIAL DISTRIBUTION OF SOFT-BODIED LAGERSTÄTTEN AND ITS IMPLICATIONS FOR LATE NEOPROTEROZOIC-EARLY PALEOZOIC TAPHONOMIC WINDOWS

Although exceptional taphonomic pathways preserve labile tissues absent in ordinary assemblages, their unequal spacing in time and space has yielded biases in the study of non-biomineralizing organisms. The present study builds upon the much-cited paper by Allison and Briggs (1993), which described the distribution of Lagerstätten through the Phanerozoic in terms of variations in regional-to-global scale controls. A new preliminary distribution of soft-bodied biotas from the Ediacaran to the present, based on a larger, updated list of Lagerstätten (n=262), is presented along with data pertaining to their preservational modes and depositional environments. Fluctuations in the frequencies of these Lagerstätte characters were assessed against a distribution of outcrop area and a compilation sea level curve.

Results affirm that exceptionally-preserved biotas are over-represented in the Cambrian and possibly in the Ediacaran. Subsequent to closure of the well-known Neoproterozoic-Paleozoic windows (e.g. those characterized by Burgess Shale- and Doushantuo-type preservation), two others opened during the Phanerozoic: a Devonian-Triassic ‘marginal marine window’ (dominated by brackish water deposits) and a Jurassic-Cretaceous marine window (consisting of black shale- and Plattenkalk-hosted assemblages). Whereas the latter window corresponds to repeated Mesozoic oceanic anoxic events, the former developed during an intermediary period between marine windows, characterized by high carbon accumulation and low ichnofaunal diversity in transitional environments bordering wholly oxygenated oceans. Together, these windows support hypotheses concerning the roles of anoxia, bioturbation, and sea level in the preservation of late Neoproterozoic and early Paleozoic Lagerstätten.

References

Allison, P. A. and D. E. G. Briggs. 1993. Exceptional fossil record: Distribution of soft-tissue preservation through the Phanerozoic. Geology, 21:527-530.