A Vendian–Cambrian boundary succession from the northwestern margin of the Siberian Platform: stratigraphy, palaeontology, chemostratigraphy and correlation

Abstract

Siberia contains several key reference sections for studies of biological and environmental evolution across the Proterozoic-Phanerozoic transition. The Platonovskaya Formation, exposed in the Turukhansk region of western Siberia, is an uppermost Proterozoic to Cambrian succession whose trace and body fossils place broad limits on the age of deposition, but do not permit detailed correlation with boundary successions elsewhere. In contrast, a striking negative carbon isotopic excursion in the lower part of the Platonovskaya Formation permits precise chemostratigraphic correlation with uppermost Yudomian successions in Siberia, and possibly worldwide. In addition to providing a tool for correlation, the isotopic excursion preserved in the Platonovskaya and contemporaneous successions documents a major biogeochemical event, likely involving the world ocean. The excursion coincides with the palaeontological breakpoint between Ediacaran-and Cambrian-style assemblages, suggesting a role for biogeochemical change in evolutionary events near the Proterozoic-Cambrian boundary.

Dynamics of the Neoproterozoic carbon cycle

“…The interactions inherent in this system lead naturally to the coincidence of three independent isotopic signals: the onset of quasistatic evolution of the carbon-isotopic records (Fig. 1b) and the negative excursion accompanying it (3)(4)(5); the disappearance of 13 C-enriched secondary biomarkers (18); and the onset of complementarity between the isotopic records of carbonate carbon and oceanic sulfate (31,32). Further correspondences are likely to be found.…”

“…Past changes within the cycle are recorded in the isotopic content of carbonate and organic carbon buried in ancient sediments (2). Extraordinarily large fluctuations occur in the Neoproterozoic [1,000-543 million years ago (Ma)] carbon-isotopic record both immediately preceding the Cambrian diversification of complex animal life (3)(4)(5) and in the Ϸ200 million years before it (6). There is much interest in determining not only the cause of these isotopic events (3-9) but how, if at all, they are related to early animal evolution (10).…”

δ<SUP>13</SUP>C stratigraphy of the Proterozoic Bylot Supergroup, Baffin Island, Canada: implications for regional lithostratigraphic correlations

“…Short-lived negative carbon isotopic excursions in marine carbonate rocks have been attributed either to the input of isotopically light carbon into the ocean-atmosphere system (Dickens et al 1995;Bralower et al 1997), or to the rapid mixing of isotopically light deep waters with the surface ocean (Kaufman et al 1991). During at least part of the Proterozoic, water-body stratification and diminished export of inorganic carbon into the deep ocean could have resulted in increased surface-to-deep gradients (Grotzinger and Knoll 1995;Bartley et al 1998). Ventilation of deep waters has been hypothesized to occur with enhanced circulation (Bartley et al 1998), possibly related to glacial episodes Kaufman et al 1997).…”

“…During at least part of the Proterozoic, water-body stratification and diminished export of inorganic carbon into the deep ocean could have resulted in increased surface-to-deep gradients (Grotzinger and Knoll 1995;Bartley et al 1998). Ventilation of deep waters has been hypothesized to occur with enhanced circulation (Bartley et al 1998), possibly related to glacial episodes Kaufman et al 1997). No evidence for glaciation, however, has been reported from the Mesoproterozoic.…”

The Precambrian-Cambrian Transition in the Southern Great Basin, USA

“…Approximately 70% of all PC-C boundary successions are siliciclastic (Landing, 1994). However, many carbonate successions around the world have been more intensely studied because they record the advent of widespread biomineralization and easily obtainable δ 13 C chemostratigraphic records (summarized in Kaufman et al, 1997;Shields et al, 1997;Bartley et al, 1998;Shields, 1999;Corsetti and Hagadorn, 2000;Shen and Schidlowski, 2000). Due to endemic biotas and facies control, it is difficult to correlate directly between siliciclastic-and carbonate-dominated successions.…”