Late Proterozoic–Early Phanerozoic ‘Taphonomic Windows’: The Environmental and Temporal Distribution of Recurrent Modes of Exceptional Preservation

Abstract

Exceptional biotas—those in which the non-biomineralized tissues of organisms are preserved—are an important record of the evolutionary biology of the late Neoproterozoic—early Phanerozoic interval. Most of these biotas exhibit one of four modes of preservation: preservation of either 1) internal and external detail (Doushantuo-type preservation) or, 2) external cuticles (Orsten-type preservation) in calcium phosphate; 3) coating in pyrite films and infills (Beecher's Bed-type preservation); and 4) preservation of organic remains (Burgess Shale-type preservation). The global environmental and temporal distribution of each mode of preservation is reasonably well constrained, but not why these taphonomic windows existed when they did. The late Neoproterozoic – early Phanerozoic interval is characterized by complex, interlinked, physical, geochemical and biological changes to the Earth's biosphere and geosphere. The changing ecology of marine environments (from matground to mixgrounds: the ‘Agronomic Revolution’) occurred via an intermediate phase of stiffened, but not microbially bound sediments that extended the interval over which exceptional preservation occurred. Prolonged eustatic sea-level rise across flat-lying continental platforms ensured environments conducive to exceptional preservation were developed and, critically, sustained over large contiguous areas. During this, regolith on continental surfaces was recycled, providing an integral source of sediment and ions relevant to mineral authigenesis. Superimposed on these broad-scale changes are specific drivers that controlled the duration of individual taphonomic windows; elucidating these requires a better understanding of the environmental context and diagenetic history of fossiliferous successions at the intra-basinal scale.