Spurenanalytische Untersuchungen an Tiefseetonen aus dem Atlantik: Ein Beitrag zur Deutung der geochemischen Sonderstellung von pelagischen Tonen

Abstract

The data from these minor element investigations of Atlantic bottom samples shall contribute to a geochemical comparison of pelitic sediments from different oceans. General considerations about the source of abnormally high abundances of some elements in pelagic clays in comparison with near-shore argillaceous sediments should depend on representative data of best quality. Therefore only methods of X-ray fluorescence, d.c.-arc spectroscopy and colorimetry with less or about 10 per cent standard deviation have been applied for this investigation. Eighteen samples and two composites (with no or moderate carbonate content) have been analysed for the following minor elements: Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Mo, Ba, La, Pb. Data of the same elements in near-shore clays and shales have been revised and supplemented. Some analyses of Pacific samples could be checked. The main result of this investigation is the grouping of elements into three classes with different geochemical behaviour: 1. (a) The average abundances of Ti, V, Cr, Ga, Rb and Zr are the same in near-shore and pelagic clays within the limits of analytical error. 2. (b) On the average the elements La, Sc, Y and Ba are as abundant in near-shore clays as in pelagic clays from the Atlantic but are more abundant in those from the Pacific. 3. (c) The average abundances of Zn, Ni, Pb, Cu, Co, Mn and Mo increase from near-shore argillites to Atlantic clays and from there to Pacific clays regardless of similar composition in their major elements. The fact that elements like Ti, V, Cr are not enriched in these clays shows that there is no enhanced contribution from submarine weathering of volcanics and pyroclastics. For the discussion of higher abundances of Group B elements in Pacific clays one should consider the evidence of organic contributions to the sediment and mobilization during diagenesis. The abundances of the Group C elements in clays from the two oceans exceeding that of near-shore argillites are presented in a diagram. It shows a striking proportionality between the sediments from the Atlantic and the Pacific in relation to the abundances of these elements. This should be interpreted as the result of one uniform process. Most of these elements exceed the values required for balance computations of weathered average crust material, if the portion of pelagic clays in all the sediments is estimated as 10 per cent. This figure of 10 per cent is supported as a minimum by geological and geophysical experience. Extraterrestrial sources cannot supply the above-mentioned element association in the abundances established. However, this association seems to be typical for volcanic exhalations. An influence of the secular air-contaminating action of these emanations on sediments with a rate of sedimentation in the range of mm per thousand years must be taken in account according to thermodynamical and geological evidence. The proportion 1: 3·4 in the diagram probably reflects the different average rates of sedimentation in the two oceans.