DID THE TRANSGONDWANAN SUPERMOUNTAIN TRIGGER THE EXPLOSIVE RADIATION OF ANIMALS ON EARTH?

Abstract

The explosive radiation of animals on Earth during the late Early Cambrian period (~ 530-510 Ma) coincides with the deposition of enormous volumes of continentally derived sedimentary rocks throughout Gondwana. We show here, that these quartz-rich sedimentary units, collected from five continents, display remarkably similar detrital-zircon U-Pb age-patterns and propose that they were sourced from either side of a > 8000-km-long and generally > 1000-km-wide mountain chain (the Transgondwanan Supermountain), which formed following oblique collision between East and West Gondwana, commencing at ~ 650 Ma. The depositional system supplied by this mountain chain was > 100 km3, which is equivalent to covering all 50 states of the USA with ~ 10 km of sediment, and it lasted for at least 260 Myr. The enormous size of the vegetation-free mountain chain, its position close to the equator and the dramatic changes in global plate-motion in response to the cessation in continent-continent collision, together with the possible appearance of biota in the soils that promoted rapid chemical weathering, resulted in extreme erosion and sedimentation rates that are arguably the highest in the geological record. This led to an unprecedented flux of P, Fe, Sr, Ca and bicarbonate ions into the oceans. The addition of Sr was responsible for seawater 87Sr/86Sr building up to the highest levels in Earth's history, whereas the addition of P and Fe provided the essential nutrients that supported a bloom of primitive life that in turn provided abundant food to support the Cambrian explosion of life. The addition of Ca and bicarbonate ions increased CaCO3 supersaturation in the oceans, which allowed species in numerous phyla to simultaneously develop skeletons. © 2006 Elsevier B.V. All rights reserved.