Evaluation of δ13C chemostratigraphy for intrabasinal correlation: Vendian strata of northeast Siberia

Abstract

Integrated sedimentologic, stratigraphic, and geochemical (δ 13 C, δ 18 O, 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 δ 13 C chemostratigraphy for high-resolution intrabasinal correlation. The Vendian δ 13 C 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 δ13C from +2‰ at the base to near 0‰ at the top, and a negative excursion 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.