RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES6001, doi:10.2205/2005ES000189, 2005
[145] The results obtained for the Gams sequence allowed us to draw the following conclusions:
[146] 1. For the first time it was demonstrated that the evolution of the transitional layer at the Cretaceous-Paleogene boundary had proceeded in two stages.
[147] During the earlier one (which lasted approximately 1500 years, assuming conservative estimates for the sedimentation rate), the transitional layer was formed by volcanic aerosol, which was responsible for the presence of titanomagnetite, Au, Cu, and for high concentrations of Ir, As, Cr, Br, and some other elements. The occurrence of an Ir anomaly in the lower part of the transitional layer was caused by volcanic activity (which also resulted in the presence of titanomagnetite, copper, and gold). The idea that Ir anomalies could be related to volcanic activity was previously expressed with reference to the Deccan flood basalts [Bajapai and Prasad, 2000; Crocket and Paul, 2004; Tandon, 2002].
[148] During the other stage, the character of sedimentation was affected by the fall of an asteroid (meteorite), whose material was detected in the form of trace amounts of metallic Ni, awaruite, and diamond crystals.
[149] 2. The study of distribution of planktonic foraminiferal assemblages inhabiting different levels of the water column including subsurface, thermocline, and sub-thermocline waters, and of their dominating taxa revealed that in the terminal Maastrichtian the species strongly prevailed in subsurface and thermocline waters. This indicates unstable conditions with frequently changing food resources, which repeatedly increased alternately in thermocline and subsurface waters.
[150] We can also suggest that at the early stage of the layer J (unit J -8/9a) (see Table 1) accumulation the thermocline and subthermocline environmental conditions were sharply deteriorated. During the deposition of unit J -8/9b the conditions became still worse and in addition to thermocline layers the subsurface, subthermocline (deep), and bottom waters became uninhabited. All water environment appeared to be completely unsuitable for existence of planktonic and benthic foraminifers. That deterioration could result from an input of arsenic and other siderophile elements as volcanic activity products in water, which resulted in arsenious pollution of water environment.
[151] Our conclusions principally differ from all preexisting interpretations of the transitional layer at the boundary between the Cretaceous and Paleogene and make it possible to resolve the problem of the reasons for the mass extinction of living organisms at 65 Ma. Our research eliminates the need in opposing volcanism to an impact event, because both of them took place, but the changes in the biota were related to volcanism, as also was the appearance of the Ir anomaly itself. The cosmic body fell only some 500-800 years later!
[152] In conclusion, we would like to quote W. Alvarez who wrote that "...the time for unbridled speculation is past" [Alvarez et al., 1984, p. 1186].
Citation: 2005), A new look at the nature of the transitional layer at the K/T boundary near Gams, Eastern Alps, Austria, and the problem of the mass extinction of the biota, Russ. J. Earth Sci., 7, ES6001, doi:10.2205/2005ES000189.
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