Implications of an integrated late Ediacaran to early Cambrian stratigraphy of the Siberian Platform, Russia

Abstract

The transition from the terminal Ediacaran to early Cambrian (ca. 550−530 Ma) witnessed both the decline of Ediacaran-type soft-bodied and skeletal biota and the rapid diversification of Cambrian-type skeletal biota, which dominate the Terreneuvian (ca. 538.8−521 Ma) fossil record. This interval hosts globally widespread positive and negative δ13Ccarb excursions, including a negative δ13Ccarb excursion near the Ediacaran-Cambrian boundary termed the 1n/BACE. Efforts to produce a global composite chemostratigraphic and biostratigraphic correlation through this interval are complicated by stratigraphic incompleteness and a dearth of radiometric ages with which to constrain δ13Ccarb chemostratigraphy. Extensive and richly fossiliferous open-marine carbonates of the Siberian Platform were deposited from the terminal Ediacaran to beyond Cambrian Series 2, and they offer a unique archive to refine this chemostratigraphic and biostratigraphic framework. Here, we present new δ13Ccarb data from two sections of the southeastern Siberian Platform, and we synthesize these with published δ13Ccarb data from multiple sections throughout the Siberian Platform that record near-continuous carbonate deposition from the latest Ediacaran to Cambrian Series 2. This compilation allowed the construction of two possible chemostratigraphic age models that conform to a coherent framework of lithostratigraphic correlation and platformwide stratal stacking patterns. These age models were then used to test alternative calibrations of fossil first appearances and the spatiotemporal evolution of carbonate deposition on the Siberian Platform. Both models support a pre-1n/BACE appearance of anabaritids in the most distal open-marine sections, and they confirm a transitional Ediacaran-Cambrian biotic assemblage that consisted of co-occurring cloudinids and anabaritids. Sedimentologic and sequence stratigraphic analysis on the Siberian Platform also provides strong evidence to indicate that the 1n/BACE marks the onset of a gradual, pulsed rise in relative sea level that was sustained throughout the Terreneuvian and Series 2 of the Cambrian.

Cambrian radiation speciation events driven by sea level and redoxcline changes on the Siberian Craton

“…These can be correlated with similar records in the Laolin and Xiaotan sections of South China and the Oued Sdas section of Morocco (19,37) and calibrated relative to the δ 13 C carb record and archaeocyath biostratigraphy on the Siberian Craton only. These show a consistent pattern with δ 13 C carb (26,32)]. (C) Cambrian paleogeography at 520 Ma ago after (29,30) with position of the Siberian Craton and possible ocean currents.…”

“…( A ) Tommotian to Atdabanian. ( B ) Botoman to Toyonian, and Amgan [modified from ( 26 , 32 )]. ( C ) Cambrian paleogeography at 520 Ma ago after ( 29 , 30 ) with position of the Siberian Craton and possible ocean currents.…”

“…( A ) International (ICC) and Siberian time scale ( 26 ). Regional stages: Fortun., Fortunian; ND, Nemakit-Daldynian; To., Toyonian.…”

“…Formations: U’-Y, Ust’-Yudoma; Ket., Keteme; T., Titary; Elan., Elanka. ( B ) Chemostratigraphic age model calibrating carbonate carbon isotopes [updated after ( 26 )] (see Supplementary Data) and carbonate associated sulfate sulfur isotopes ( 20 ). ( C ) Uranium isotopes from Siberia (gray; Sukharikha and Bol’shaya Kuonamka rivers), South China (blue), and Morocco (orange) (all data points are larger than 2 SE) ( 19 ).…”

“…We incorporate both outcrop and newly compiled subsurface borehole occurrence data within a revised age model (see Material and Methods, table S1, figs. S1 and S2, and Supplementary Data) ( 26 ). Reef communities are also loci of high biodiversity and, therefore, exert a major control on total marine diversity.…”