JURASSIC-CRETACEOUS d13C COMPILATION: THE SEARCH FOR LINKS AMONG THE CARBON CYCLE, PHYTOPLANKTON EVOLUTION, SEA-LEVEL CHANGE, AND GEOLOGIC PROXIES
Events in published faunal and geologic records often correspond to these d13C changes, such as: 1) nannoconid crises in the Valanginian and earliest Aptian; 2) nannofossil extinctions in the Toarcian, Oxfordian, OAE1a, and OAE2; 3) decreases in diatom and dinoflagellate diversity beginning ~OAE2; 4) Sr-isotopic decreases (=probable increases in hydrothermal activity) began immediately prior to the Toarcian, Oxfordian, and OAE2 events; in contrast, a major Sr-decrease post-dates OAE1.
The isotope, faunal, and proxy records compiled here demonstrate that complex interactions among multiple paleoenvironmental parameters affected the evolutionary trends of Mesozoic phytoplankton, ultimately favoring the three orders of eucaryotes that dominate todays oceans (diatoms, dinoflagellates, coccolithophores). Our compilation highlights a first-order correlation between long-term (107 -108 my) sea-level rise and increased diversity of the eucaryotes at the genus and family level; in contrast, short-term (106 my) sea-level change shows little correlation with evolutionary trends. This indicates that major phytoplankton radiations were related to expanded ecological niches and ocean chemistry changes that accompanied long-term continental shelf flooding and increased sea-floor spreading rates. Superimposed on these long-term trends are times of rapid faunal turnover at the species level that often correspond to rapid changes in isotope and proxy records.