Speaker: Dr. Mark Leckie (UMass-Amherst)
Global tectonics had a profound influence on climate, weathering, sea level, and seawater chemistry during Mesozoic time. The linkages between tectonic activity, planktic foraminiferal evolution and environmental perturbations, including the so-called Mesozoic ‘Oceanic Anoxic Events’ (OAEs) are compelling. Diversification and extinction are closely tied with the major OAEs beginning in the Early Jurassic and extending through the mid-Cretaceous. Foraminifera invaded the plankton multiple times during the past 160 myr. The early Toarcian OAE may have been the first of these invasions. Innovation, such as clavate chambers developed during the widespread OAE1a in the early Aptian (~121 Ma). Great diversification during the Aptian was squelched by the multiple events of OAE1b across the Aptian/Albian boundary (~112 Ma), a period that includes the second largest turnover in planktic forams (K/Pg boundary being the largest). Submarine volcanism and hydrothermal activity influenced carbonate chemistry during the mid-Cretaceous that favored calcite-producing organisms after the Aptian, including calcareous nannoplankton. The planktic forams recover, diversify, increase in size, and stratify in the upper water column during the Albian. OAE2 across the Cenomanian/Turonian boundary (~94 Ma) again resulted in extinction and subsequent radiation of planktic forams. Global warming, rising sea level and spread of epeiric seas, partitioning of nutrients and fluctuating levels of marine productivity, expanded oxygen minima, and changes in ocean circulation associated with the opening of the north-south Atlantic Ocean basin provided a backdrop for the evolution of planktic and benthic forams and other plankton groups during the Late Cretaceous.