RUSSIAN JOURNAL OF EARTH SCIENCES, VOL. 12, ISR1107, doi:10.2205/2011ISR007, 2011

Nature of mass extinctions in the Earth's history - Lessons of the past for human race in the future

A. F. Grachev

Abstract

At the end of the Cretaceous (65 Ma ago) the Earth suffered the great biological crisis when the dinosaurs died out. We propose the new approach to this problem based on the detailed micropalaeontological, lithological, geochemical, nanomineralogical, isotopic and petromagnetic investigations of the unique sedimentary sequence at the Cretaceous-Paleogene boundary in the Gams area, Eastern Alps, Austria. Two stages in the evolution of the transitional layer at the Cretaceous-Paleogene boundary have been established. During the earlier one (which lasted for approximately 1500 years, as follows from conservative estimates of the sedimentation rate), the transitional layer was formed under the effect of volcanic aerosol. The later one caused the presence of native gold, copper, silver, platinum, rhenium, sulfides of Fe, As, Cu, Pb, Zn and Mo as well as high concentrations of Ir, As, Pb, Cr, Zn and other elements in the rocks. The occurrence of an Ir anomaly in the lower part of the transitional layer and the presence of native Cu, Au, Ag, Pt and arsenopyrite, pyrite, galena, sphalerite, acanthite with barite and witherite were related to volcanic activity related with mantle plume. During the later stage, the character of sedimentation was affected by the fall of an meteorites, and traces of its material are discernible as spherules of metallic Ni, awaruite, and diamond crystals. The conclusions drawn from the results of our analysis principally differ from all preexisting data on the transitional layer between the Cretaceous and Paleogene and provide another look at the reasons for the mass extinction of living organisms at 65 Ma ago. These data eliminate the need for opposing volcanism to an impact event: both took place, but the changes in the biota were induced by volcanism, as also was the appearance of the Ir anomaly itself, whereas the fall of a cosmic body occurred approximately 500-800 years later. We suppose that nature of the Big Five extinctions during the last 540 My was similar to processes at the Cretaceous-Paleogene boundary in the Gams area (Eastern Alps).

Presented 28 January 2011; published 17 October 2011.

Time 30m 41s

Citation: Grachev, A. F. (2011), Nature of mass extinctions in the Earth's history - Lessons of the past for human race in the future, Russ. J. Earth Sci., 12, ISR1107, doi:10.2205/2011ISR007.