Restriction of a late neoproterozoic biotope: Ediacaran faunas, microbial structures, and trace fossils from the proterozoic-phanerozoic transition, Great Basin, United States of America.

摘要

Key elements of the Proterozoic-Phanerozoic transition in the Great Basin, USA include shifts in the paleoenvironmental and temporal distribution of soft-bodied Ediacaran fossils, suspect-microbial structures, and horizontally-oriented trace fossils. These features are regarded herein as characteristic features of the “late Neoproterozoic” biotope.; Ediacaran faunas are documented from the uppermost Vendian - Lower Cambrian Wood Canyon Formation of western Nevada, and pinpoint the first occurrence of typical late Neoproterozoic paleocommunities in the region. Ediacaran fossil fragments are also documented from the upper Wood Canyon Formation, and from the middle member of the Poleta Formation in the White Mountains in eastern California. Odd sedimentary structures known as wrinkle structures are also common in these settings, and based on comparisons with modernmicrobially dominated settings, they can be formed by microbial mats. Such wrinkle structures are commonly associated with horizontally-directed trace fossils, some of which appear to reflect active ingestion of suspect microbially-bound sediment.; In latest Vendian-earliest Cambrian settings, all three of these elements were common in shallow siliciclastic environments, but during the Cambrian, became increasingly rare in shallow settings. By the Ordovician, this biotope was completely restricted to deeper marine settings. Although the timing of this retreat coincides with increasing diversity and abundance of metazoans, the advent of skeletonization, the escalation and development of systematic and vertically-directed burrowing activity, as well as colonization of the deep-sea realms, it is not known if or how such patterns are linked.