Cretaceous Bio-Events

Abstract

Bio-events occur at local, regional, and global scales, reflecting short-term, extraordinary, environmental changes. They can be classified as Diversification Bio-Events (punctuated evolution, population blooms, colonization and immigration bio-events), or Diversity Reduction Bio-Events (mass mortality, ecosystem shock, extinction and emigration bio-events). High-resolution (cm-dm scale) stratigraphic, geochemical, and paleobiological analyses demonstrate that many regional and most global bio-events are complex, multicausal phenomena. They may consist of two or more, closely spaced levels (“steps”) of biological response to rapid environmental changes — perturbations and their feedback loops — in ocean-climate systems. This is especially true for regional to global mass extinctions, which also tend to be ecologically graded, affecting more tropical, more stenotopic taxa/ecosystems first and most profoundly, and more poleward and/or eurytopic biotas later, and to a lesser degree. Comparisons of the stratigraphic expression of local, regional, and global bio-events are presented for the Cenomanian-Turonian (Ce-Tu: middle Cretaceous) Greenhorn Cyclothem at the Pueblo, Colorado reference section, where seven regional and one global bio-event (the C-T mass extinction) intervals are well defined. Regional and global bio-events are documented for the Americas, Europe, North Africa, and India. Global bio-event intervals include: the Jurassic-Cretaceous mass extinction interval; the Early Aptian Selli Bio-Event; the Late Aptian mass extinction interval; the Middle-Late Albian substage boundary bio-events; the Albian-Cenomanian stage boundary bio-events; the Cenomanian-Turonian boundary mass extinction interval; the Turonian-Coniacian stage boundary bio-events; the Coniacian/Santonian stage boundary bio-events; the Santonian/ Campanian stage boundary bio-events; the 68 Ma (Middle Maastrichtan) extinction interval; and the Cretaceous-Tertiary boundary mass extinction interval.