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Integrated [[Delta].sup.13]C chemostratigraphy and sequence stratigraphy are developed for a succession of Vendian strata (Nokhtuisk section) on the southern margin of the Siberian platform. The carbonates exhibit secular variations in [[Delta].sup.13]C and at least three major depositional sequences that encompass the last c. 20 million years (< 565-545 Ma) of Vendian time. Correlation of these events with key sections in eastern Siberia reveals the development of three cratonic sequences that partition the Vendian System of Siberia into high-resolution time slices (third-order sequences). The third-order events form a larger depositional sequence, which is correlated with greater confidence on a global-scale. With the aid of global chemostratigraphic constraints, the second-order sequence in Siberia is interpreted to represent the youngest of at least two sequences of eustatic origin that span the latest 60 million years of terminal Neoproterozoic time. Evidence for repeated glaciations in many basins at this time provides a plausible mechanism for the third-order cratonic sequences in Siberia. However, effects due to sea-floor spreading related to the break-up of the supercontinent Rodinia are invoked as the primary mechanism for the longer-term, second-order sea-level fluctuations. Keywords: Vendian, Siberian Platform, chemostratigraphy, eustasy.

Integrated sedimentologic, stratigraphic, and geochemical ([Delta]13C, [Delta]18O, Fe, Mn, and Sr) data from Vendian-Cambrian carbonate-ramp deposits of the northeast Siberian platform (Olenek uplift and Kharaulakh Mountains region) are used to constrain primary, time-dependent oscillations in the carbon isotope record and to evaluate [Delta]13C chemostratigraphy for high-resolution intrabasinal correlation. The Vendian [Delta]13C record of northeast Siberia reflects global variations seen elsewhere by displaying (in ascending order) a strong positive isotopic shift to values near +6% (herein named the P-interval), an intermediate interval of relatively little isotopic change (I-interval), which shows, in some sections, a monotonic decrease in [Delta]13C from +2% at the base to near 0% at the top, and a negative excursion to [approximately equal to]-4% (N-interval) just beneath the Vendian-Cambrian boundary. In addition to secular isotopic shifts, these strata exhibit local small-scale signals related to intrabasinal variations in subsidence, erosion, and diagenetic alteration (e.g., degradation of organic matter, dolomitization, and hydrothermal and burial effects). These local, intrabasinal processes, in some cases, have modified both the magnitude and form of the primary isotopic excursions, which are used as the basis for correlation in all studies. Carbon isotope profiles provide an important method to evaluate intrabasinal variations in subsidence, erosion, and stratigraphic completeness. These profiles reflect increasing subsidence along the platform-to-basin transition, whereas progressive truncation of isotopic profiles along this trend illustrate pronounced uplift and erosion of ramp strata along unconformity surfaces.

Vendian to Cambrian age sedimentary rocks of the northern Siberian craton record Early Cambrian rifting from [approximately]543 to 530 Ma and the onset of regional thermal subsidence in early Tommotian time. A similar tectonic history in the Franklinian basin of northern Canada and Greenland supports the possibility that both basins formed conjugate margins. This correlation constrains both the configuration of the Siberia-Laurentia connection, also supported by paleomagnetic and paleoclimatic data from Siberia, and timing of continental breakup, which is further supported by regional trilobite biostratigraphy. Prior to breakup, Siberia and Laurentia formed a coherent continent that rifted from a western landmass (Australia-Antarctica-India-South China) at [approximately]720 Ma, forming a continuous passive margin along western Siberia-Laurentia. Nearly orthogonal to this margin, the 723 Ma Natkusiak volcanic rocks and Franklin dike swarm in northern Canada are suggested to represent a failed rift that extended into Siberia-Laurentia. Subsequent Early Cambrian separation of Siberia-Laurentia was possibly influenced by crustal heterogeneity created by the failed rift.

Uses integrated sedimentologic, stratigraphic and geochemical data from Vendian-Cambrian carbonate-ramp deposits of the northeast Siberian platform to constrain primary, time-dependent oscillations in the carbon isotope record and to evaluate delta13C chemostratigraphy for high-resolution intrabasinal correlation. Variations between many delta13C profiles.