A test of terminal Mesozoic “catastrophe”

Abstract

Terminal Mesozoic “catastrophe”-type extinction models that advocate synchronous marine and terrestrial extinctions spanning short time intervals (a few days up to a few millennia) have a common foundation: the simultaneous terminations of geological ranges of some taxa of marine CaCO 3-producing microplankton (and possibly the dinosaurs) at the end of the Cretaceous. Gartner and McGuirk [1] propose a new catastrophe theory that at the end of the Cretaceous fresh-brackish water from the Arctic Ocean spread over the surface of the world's oceans, causing global cooling, aridity, and the extinctions. Like other catastrophe models, this one also fails to address the possibility of hiatus control of ranges at the end of the Cretaceous; a well documented, seemingly nearly universal hiatus of variable and unknown duration separates Cretaceous and Tertiary strata. Documented terminal Cretaceous marine regression (perhaps 10 times more rapid than a typical regression according to Cooper [8] would have caused terrestrial erosion and stripping away of the latest Cretaceous stratigraphic record, thus truncating geological ranges along a seemingly planar datum. The terminal Cretaceous marine CaCO 3 dissolution event would have had the same effect on ranges of marine planktonic CaCO 3-producing microplankton (the event was a shallow-water phenomenon). The simultaneous terminations of geological ranges is thus possibly the result of hiatus control, and the terminal Cretaceous “catastrophe” an illusion. Attempts to use Cretaceous-Tertiary transition floras to support global cooling at the time of the extinctions are not based on sound stratigraphic foundations; realistic paleobotanical-climatic inferences can only be based on the precise correlation of the Cretaceous-Tertiary contact in marine and terrestrial stratigraphic sections, and these correlations have not been made with sufficient precision to support catastrophe theory. The much used “across the Cretaceous-Tertiary boundary” glosses over ignorance of the true terminal Cretaceous scenario, lost forever in most places by the destruction of the terminal Cretaceous stratigraphic record. For now, stable isotope paleotemperature data from marine strata that can be dated radiometrically provide the most reliable estimates of the Cretaceous-Tertiary transition climate; Boersma et al. [5] indicate global warming of deep and shallow oceans “across” the contact (and not surficial cooling only as is required by the spillover model). Older much-cited climate inferences based on leaf physiognomy are suspect in light of Dolph and Dilcher's [23] work that shows little correlation between leaf physiognomy and climate.