SEQUENCE ORGANIZATION AND GROWTH PATTERNS OF LATE MESOPROTEROZOIC STROMATOLITE REEFS: AN EXAMPLE FROM THE BUROVAYA FORMATION, TURUKHANSK UPLIFT, SIBERIA

Abstract

The latest Mesoproterozoic Burovaya Formation is a 600–1000 m thick stromatolite/mud dominated carbonate unit demarcated by an erosional unconformity into two subformations containing stromatolite reefs of variable size and geometry. The lower subformation consists of two distinct stratigraphic sequences. The lower sequence records shelf to ramp evolution and includes small-scale stromatolite reefs developed within an upper subtidal shelf settings at the transgressive systems tract and overlying mud-dominated highstand deposits accumulated in lower subtidal to peritidal environments. The second sequence of muddy and fine-grained sediments makes up a lowstand systems tract and documents a progressive structural and environmental differentiation of the Burovaya platform. The upper subformation records a third stratigraphic sequence, containing transgressive and highstand systems tracts represented by reef-bearing and reef-cap facies complexes. The reef-bearing complex characteristic of the transgressive and the bulk of the highstand systems tracts contains a giant (20–25 km wide, 10+ km long, up to 550 m thick) stromatolite reef and surrounding deep-water carbonate mudstones containing sporadic slump block deposits. The reef was located on the distally steepened part of the ramp and contains distinct internal facies organization defined by particular stromatolite microstructure and morphology and prevailing environments. Late highstand development of the Burovaya platform was marked by the termination of reef accretion, infilling of basinal relief by shallow-water carbonate and shale sediments of the cap complex, and subsequent subaerial exposure. The history of the Burovaya reef is indicative of the interplay between reef growth potential and platform geometry defined by regional tectonic and sea-level dynamics.