SIBUMASU PROVIDES NEW INSIGHTS INTO THE NORTHERN GONDWANAN MARGIN ACROSS THE CAMBRO-ORDOVICIAN BOUNDARY

Between the Cambrian Explosion and Great Ordovician Biodiversification event, biomeres, cycles of radiations and extinctions, perturbed Cambro-Ordovician diversity levels. These biomeres have mostly been studied from Laurentia, but volcanism along the Gondwanan margin may help elucidate the timing and physical-earth controls of the cycles. Late Cambrian volcanics are best documented in Avalonia along Gondwana’s southern margin, but Sibumasu, part of Gondwana’s northern platform has a much greater volume of rhyolites and rhyolitic tuffs, making it the focus of recent investigations into Cambro-Ordovician geochronology and marginal Gondwanan paleogeography. This northern Gondwanan margin comprised the numerous tectonic terranes that now compose most of Asia, but their paleogeography is poorly constrained prior to rifting of these terranes to form the Paleo- and Neotethyan oceans in the mid and late Paleozoic. Recent investigations into biomere geochronology and controls has involved U/Pb TIMS dating of volcanic horizons, detrital zircon analysis of sandstones, sedimentological and stratigraphic consideration of depositional environments, and paleontological studies including an initial description of Myanmar’s Cambrian fauna and revisions to Thailand’s Tarutao fauna. Results include a revised concept of Sibumasu’s biostratigraphic correlations to the rest of Gondwana, geochronologic constraints from rhyolitic tuffs interbedded with Cambro-Ordovician fossiliferous strata in Myanmar and Thailand, and better understanding of depositional conditions along northern Gondwana’s marginal platform. Despite general similarities in detrital zircon patterns throughout the northern Gondwanan terranes and wide spread genus-level similarities, Sibumasu’s overall species-level endemicity suggests moderate to high regional differentiation along the Gondwana margin, possibly contributing to greater sensitivity to extinction and diversification patterns during the late Cambrian.