Chemostratigraphic and Sequence Stratigraphic Constraints on Vendian-Cambrian Basin Dynamics, Northeast Siberian Craton

Abstract

$$\delta^{13}$$ chemostratigraphic and sequence stratigraphic data from terminal Vendian and earliest Cambrian strata of northeast Siberia are used to constrain the history of regional basin development. These boundary strata consist of 300 to 500 m of latest Vendian age carbonate ramp deposits and <100 m of Nemakit Daldyn age siliciclastic shelf deposits; the two successions are separated by a regional paleokarst unconformity. Six $$\delta^{13}C$$ chemostratigraphic profiles of the carbonates exhibit patterns of secular variation similar to those in coeval strata, with allowances for local diagenetic and tectonic effects. Isotopic profiles are used to recognize time lines (chemo chrons) within individual depositional sequences and to illustrate the geometry of stratigraphie units, and variation in subsidence and stratigraphie completeness across the basin. The Vendian Khorbosuonka Group and correlative deposits are divided into 3 depositional sequences that record sedimentation from ca. 555 to 543 Ma in a gently subsiding east-facing passive margin basin. On the basis of chemostratigraphy, outer ramp strata were progressively uplifted and eroded to the north, forming a regionally extensive paleokarst. Unconformity development was associated with felsic volca-nism and is considered to reflect the onset of regional rift-related uplift that continued to early Tommotian time (530 Ma). Differential uplift produced a transient reversal in depositional slope, creating a local south-facing basin during onlap of Nemakit Daldyn age shelf strata (sequence 4). Continued synsedimentary tectonism is marked by bimodal volcanic rocks interbedded with shelf deposits and truncation of the sequence to the north. Overlying Tommotian age limestones provide evidence for restoration of a northerly depositional gradient by southward onlap of the exposed shelf. Tommotian and younger age limestones are interpreted to represent a postrift phase of subsidence (flexural and/or thermal) related to decay of thermal anomalies. Regional stratigraphie evidence suggests that rifting developed across the northern margin of Siberia during the Early Cambrian.