THE EFFECT ON PALEO-PRODUCTIVITY OF THE FIRST MAJOR DELIVERY OF MID-LAURENTIAN SAPROLITE-DERIVED MATERIAL TO PHANEROZOIC OCEANS: CONTINENT-WIDE MARINE RAVINEMENT DURING SUBMERGENCE-EMERGENCE OF LATE CAMBRIAN NORTH AMERICA, AND THE GLOBAL CARBON ISOTOPE SPICE EVENT
Pre- Aphelaspis central Laurentia was presumably thickly mantled by saprolite, the product of protracted weathering of Precambrian rock. We propose that this saprolite was stripped and remobilized by Aphelaspis zone marine ravinement that culminated the first major transgression of the Phanerozoic. Nutrients that had hitherto been concentrated in a terrestrial repository, were thus delivered to the marine realm, and dispersed to circum-Laurentian oceans by the immediately ensuing latest Sauk II regression. This implies that broad, sweeping, continent-scale, marine ravinement was more effective at eroding the thick rind of weathered material than were the day-to-day geomorphic processes active on the pre-macrovegetated craton. The Carbon isotope record suggests that circum-Laurentia oceanic productivity was in equilibrium with pre- Aphelaspis terrestrial runoff, but was significantly perturbed by the delivery of weathering-products from marine ravinement of the cratonic interior. This interpretation explains the uniqueness of the relationship between the SPICE and sea level change it could happen only once, because of the historical contingency that saw a lower Phanerozoic marine fauna react to the delivery of a previously-untapped bonanza of continental nutrients (presumably a bonanza for some, a calamity for others).