EARLY CAMBRIAN TRILOBITES CONFIRM SIBERIA-WEST LAURENTIA PALEOCONTINENTAL CONNECTION

Detailed analyses of Early Cambrian trilobite genera indicate that the SE edge of the Siberian craton lay within 1500 km of the SW edge of Laurentia during the early Atdabanian Stage. Trilobite bio-zones of the Cordilleran and Arctic margins of Laurentia calibrate early Cambrian rates of trilobite dispersion that ranged from ~1500 to 2000 km/m.y.; average early trilobite genera within those bio-zones spanned < 0.75 m.y. Evolution thus limited specific early trilobite genera to occupy <1500 km of their coastal habitats. Archaeaspis, the earliest genus of the Fallotaspis trilobite bio-zone, occurs in the Esmeralda basin of Nevada as well as in the Lena River basin of SE Siberia (Hollingsworth, 2007), indicating that those sites lay within 1500 km of each other at ~520 Ma. The distribution of coeval archeocyathan reefs agrees with trilobite dispersal patterns. The genetic bullseye provided by the trilobites, in both time and space, confirms the Siberia-west Laurentia connection of Sears and Price (1978). Furthermore, it requires linkage of Siberia and west Laurentia back to ~2 Ga, as no geologic evidence supports a collision to have joined the cratons after formation of the ~2 Ga Nuna supercontinent. The connection satisfies numerous Proterozoic-aged piercing points across the conjugate margins, and falsifies several ambiguous Precambrian paleocontinental reconstructions. It independently constrains the behavior of the Precambrian geomagnetic field, and may aid in the evaluation of controversial hypotheses concerning episodes of true polar wander.