Abstract
The Precambrian-Cambrian boundary presents an interesting stratigraphic conundrum: the trace fossil used to mark and correlate the base of the Cambrian, Treptichnus pedum, is restricted to siliciclastic facies, whereas biomineralized fossils and chemostratigraphic signals are most commonly obtained from carbonate-dominated sections. Thus, it is difficult to correlate directly between many of the Precambrian-Cambrian boundary sections, and to assess details of the timing of evolutionary events that transpired during this interval of time. Thick sections in the White-Inyo region of eastern California and western Nevada, USA, contain mixed siliciclastic-carbonate lithofacies, and therefore promote correlation between these classic, well-studied lithologic end-members. An integrated stratigraphic approach was applied to the White-Inyo succession, combining lithologic, paleontologic, and chemostratigraphic data, in order to address the temporal framework within the basin, and to facilitate worldwide correlation of the boundary. Results from the southern Great Basin demonstrate that the negative δ13C excursion that is ubiquitous in carbonate-dominated successions containing small shelly fossils occurs within stratigraphic uncertainty of the first occurrence of T. pedum. This global geochemical marker thus provides a link with the primary biostratigraphic indicator for the Precambrian-Cambrian boundary.
Highlights
Tunity to address a variety of related issues, including whether the proposed boundary position marks a major event in Earth history
The Precambrian-Cambrian (PC-C) transi- Approximately 70% of all PC-C boundary points with which to link fossils from silicition records one of the most important successions are siliciclastic (Landing, 1994). clastic sections to the geochemical and cliintervals in the history of life, because it many carbonate successions mate-change data from carbonate-dominatencompasses the appearance and diversifica- around the world have been more intensely ed sections so that we can improve our tion of metazoans, the invasion of the infau- studied because they record the advent of understanding of this critical interval
We have identified bed-parallel tubular trace fossils, including Helminthoidichnites and Planolites (Fig. 5A), in the Wyman Formation; we cannot falsify the hypothesis that some of these are body fossils
Summary
2000; Shen and Schidlowski, 2000). Due to endemic biotas and facies control, it is diffi-. Southern Great Basin, USA This is true for the PC-C boundary interval because lowermost Cambrian biotas are highly endemic and. Results from the southern Great Basin demonstrate that the negative δ13C excursion that is ubiquitous in carbonate-dominated successions containing small shelly fossils occurs within stratigraphic uncertainty of the first occurrence of T. pedum.This global geochemical marker provides a link with the primary biostratigraphic indicator for the Precambrian-Cambrian boundary. As our understanding of this interval of Earth history grows, we focus more on the “bigger picture” issues (e.g., evolution and diversification of the Metazoa), and focus less on the “boundary
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