TIGHTENING THE SIBERIAN CONNECTION TO WESTERN LAURENTIA

Abstract

Newly available geological and geophysical data tighten the Proterozoic connection between the rifted margins of the northern Siberian craton and western Laurentia, and permit a Siberia-Laurentia-Australia troika, with northern Australia connected to the southern margin of the Siberian craton. The continental assembly is linked by a prominent 2.0-1.8 Ga collisional belt and the ca. 1.3-1.0 Ga Grenville orogen. The reconstruction also aligns a 1.5-1.45 Ga dike/sill swarm that extends from the Wyoming province, through the Belt-Pureell basin, into the northern Siberian craton. Separation of Australia and Siberia may have occurred by the early Neoproterozoic, but separation of Siberia and Laurentia may not have been completed until the Early Cambrian. Continental extension began along the zigzag Siberia-Laurentia rift zone in the early Mesoproterozoic. Rift-related igneous and sedimentary assemblages dated at ca. 1.5, 1.38, and 1.2 to 1.0 Ga correlate across the reconstructed Siberia-Laurentia rift zone. Renewed rifting in the Neoproterozoic and Vendian culminated with seafloor spreading and thermal subsidence of the conjugate rift shoulders. Correlative archeocyathan reefs, endemic olenellid trilobite fauna, and exchange of detritus between the cratons imply that the rift may have remained relatively narrow until the Atdabanian stage. Black sulfidic shales buried the archeocyathan reefs on the rapidly subsiding rift margins during the Botomian Sinsk event.