999 resultados para 72-517


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This paper presents data on trace elements (Sr, Mg, Na, K, Mn, Fe, Ni, Cr) and isotopes (13C, 18O) on the carbonate fraction of bulk sediments from the Coniacian to Paleocene samples of Hole 516F. Relationships of trace elements to mineralogy and stratigraphic position are discussed at length, with special emphasis on 1) the differences between Hole 516F and other oceanic sites, and 2) the transitions observed at the Cretaceous/Tertiary boundary. Isotope data are compared to those obtained in other localities of the same age. The sections show the same major 13C variations at the Cretaceous/Tertiary boundary, indicating that this event is a planetary phenomenon.

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The geochemistry of basalts recovered during Leg 72 is described with emphasis on trace elements. Only Hole 516F penetrated basement; the basalts recovered are plagioclase-phyric and olivine-phyric and pervasively altered. Chemically, the basalts from Hole 516F are rather uniform in composition. However, four distinct geochemical units can be recognized, although the chemistry of two of the units appears to be controlled by chemical mobility associated with alteration. The two less-altered units cannot be related by fractional crystallization processes. Hole 516F basalts have a trace element chemistry characteristic of T-type mid-ocean ridge basalt; rare-earth element patterns (as indicated by Ce/Y ratios) are mildly fractionated flight rare-earth element enriched), and a number of incompatible element ratios are close to chondritic.