RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES6001, doi:10.2205/2005ES000189, 2005

Trace and Rare Earth Elements

[72]  Tables 8 and 9 report the distribution of the concentrations of trace elements and REE in the vertical section of the sequence, and Table 10 presents the contents of Ir and some other chalcophile elements in transitional layer J at the K/T boundary. The variations of the most informative elements (lithophile Cr, V, Rb, Cs, Ba, Sr, Nb, and Zr; chalcophile Cu, Zn, and Ga; and siderophile Co, Ni, and Mo) are the most dramatic and mutually correlated in the vicinity of transitional layer J.

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Figure 19
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Figure 20
[73]  In terms of the character of these variations, the lower part of the sequence (below layer J ) notably differs from the upper part, which includes a number of units with anomalously high concentration of siderophile, chalcophile (Zn, Cu, and Ni), and some other elements (layers K, S ) (Figures 19, 20). These variations in the upper part of the sequence were caused by the varying conditions in the source area of the sediments, which is also reflected in the amounts of normative quartz (Table 3).

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Figure 21
[74]  The results of correlation analysis for the upper and lower parts of the sequence and for the transitional layer (Tables 4, 5, and 6) reveal differences between the elemental correlations. The most illustrative example is offered by the behavior of Cu: layer J displays negative correlations of Cu with Ni, Co, Sc, V, and many other elements ( r>-0.7 ), whereas these correlations are absent both below and above this layer. It is important to mention that this layer was found out to bear particles of native copper and gold (Figure 21).

[75]  Since layer J is of particular interest, it was subdivided into a number of units (Figure 4) in order to determine how concentrations of Ir and other elements vary from the bottom to top of this layer. It was revealed that the Ir concentration drastically increases from 5 ppm to 9 ppm upward (from J1 to J4 ) and then drops to 3 ppb at J5-J6 (Table 10). The contents of As, Pb, Ag, Au, and Br also change in the same units (Figure 20).

[76]  In contrast to trace elements, variations in the concentrations of REE in the Gams sequence are insignificant (Table 10). In a few samples, REE were analyzed in their whole-rock material and clay fractions. The REE concentration in sample L6 is systematically higher in the clay fraction than in the whole-rock sample.

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Figure 23
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Figure 24
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Figure 25
[77]  The chondrite-normalized REE patterns of the Gams sequence generally confirm the known characteristic of clayey shales, namely, their uniform REE patterns [Taylor and McLennan, 1985]. The most conspicuous features of the REE patterns of the rocks is their pronounced enrichment in LREE and weak Eu anomalies. Compared with the REE patterns of North American Clayey Shales (NASC) (Figure 22), our rocks are poorer in HREE. Figures 23, 24 and 25 demonstrate the NASC-normalized REE patterns of the upper and lower parts of the rock sequence and its transitional layer J. All of these patterns are similar and show weakly pronounced negative anomalies at Ce, Nd, and Dy.

[78]  This flat configuration of the NASC-normalized REE patterns is typical of the rocks of Mesozoic and Cenozoic continental margins (including those in the modern Atlantic) [Murray, 1994] and testify to a significant contribution of terrigenous material to the character of REE fractionation. In this context, the similarities in the REE patterns of rocks from the examined portion of the Gams sequence suggest that the conditions in the source area (which was not far from the marine basin) did not vary.


RJES

Citation: Grachev, A. F., O. A. Korchagin, H. A. Kollmann, D. M. Pechersky, and V. A. Tsel'movich (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.

Copyright 2005 by the Russian Journal of Earth Sciences

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