(Table 2) Trace element composition of seleceted clast and matrix materials from ODP Site 125-786

Shipboard examination of volcanic and sedimentary strata at Site 786 suggested that at least four types of breccias are present: flow-top breccias, associated with cooling and breakup on the upper surface of lava flows; autobreccias, formed by in-situ alteration at the base of flows; fault-gouge breccias; and true sedimentary breccias derived from weathering and erosion of underlying flows. It is virtually impossible to assess the origin of breccia matrix by textural and mineralogical analyses alone. However, it is fundamental for our understanding of breccia provenance to determine the source component of the matrix material. Whether the matrix is uniquely clastderived can be determined by geochemical fingerprinting. Trace elements that are immobile during weathering and alteration do not change their relative abundances. A contribution to the matrix from any source with an immobile trace element signature different from that of the clasts would appear as a perturbation of the trace element signature of the matrix. Trace element analysis of bulk samples from clasts and matrix material in individual breccia units was undertaken in a fashion similar to that used by Brimhall and Dietrich (1987, doi:10.1016/0016-7037(87)90070-6) in analyzing soil provenance: (1) to help distinguish between sedimentary and volcanic breccias, (2) to determine the degree of mixing and depth of erosion in sedimentary breccias, and (3) to analyze the local provenance of the individual breccia components (matrix and clasts). The following elements were analyzed by X-ray fluorescence (XRF): Rb, Sr, Ba, U, Zr, Cu, Zn, Ti, Cr, and V. Of these elements, Zr and Ti probably exhibit truly immobile behavior (Humphris and Thompson, 1978, doi:10.1016/0016-7037(78)90222-3 ). The remaining elements are useful as a reference for the extent of compositional change during the formation of matrix material (Brimhall and Dietrich, 1987, doi:10.1016/0016-7037(87)90070-6).

Strontium isotope ratios of pore waters and planktonic foraminifera from DSDP holes

A detailed record of the strontium-87 to strontium-86 ratio in seawater during the last 100 million years was determined by measuring this ratio in 137 well-preserved and well-dated fossil foraminifera samples. Sample preservation was evaluated from scanning electron microscopy studies, measured strontium-calcium ratios, and pore water strontium isotope ratios. The evolution of the strontium isotopic ratio in seawater offers a means to evaluate long-term changes in the global strontium isotope mass balance. Results show that the marine strontium isotope composition can be used for correlating and dating well-preserved authigenic marine sediments throughout much of the Cenozoic to a precision of +/- 1 million years. The strontium-87 to strontium-86 ratio in seawater increased sharply across the Cretaceous/Tertiary boundary, but this feature is not readily explained as strontium input from a bolide impact on land.