2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 13
Presentation Time: 11:45 AM


KELLER, Gerta, Geosciences, Princeton Univ, Guyot Hall, Princeton, NJ 08544, gkeller@princeton.edu

The K/T mass extinction is commonly believed to be a geologically instantaneous event caused by the Chicxulub impact. What if this impact predated the K/T mass extinction by 300 ky and caused no species extinctions as shown in Texas and Mexico? What if increasing environmental and biotic stresses from Deccan volcanism, greenhouse warming and the Chixculub impact during the last 400 ky of the Maastrichtian predisposed marine organisms to extinction by K/T time? There is now ample evidence of increasing biotic stress during the late Maastrichtian with benthic and planktic foraminifera responding with species dwarfing (lilliput effect) and decreasing diversity regardless of the specific cause. This survival strategy fails large specialized species with small population sizes, which disappear early. Only small species with large population sizes tend to survive high stress environments. The diversity decline follows an ordered sequence of elimination: complex, large tropical-subtropical species (K-strategists) living in deeper waters disappear first, accompanied by increasing abundance of small low O2 tolerant heterohelicids, which indicate increased nutrients and expansion of the O2 minimum zone. Higher environmental stress leads to elimination of most small species (R-strategists) and blooms of the tiny disaster opportunist Guembelitria, which thrived in eutrophic waters. The ecosystem collapse appears to be primarily the result of high nutrient and trace element influx (from volcanism, climate change (i.e., erosion) and impacts) leading to eutrophication and phytoplankton blooms (i.e., primary producers), which results in toxic conditions for foraminifera. In the Brazos environment, the mass extinctions at the K-T boundary is absent. Instead there is a gradual decrease in diversity associated with increasing environmental stress and dwarfing of all species (benthic and planktic) during the last 400 ky of the Maastrichtian, leaving only small dwarfed survivor species.