Geochemical well logging in basalts: the Palisades Sill and the oceanic crust of Hole 504B

Abstract

Geochemical well logging provides a continuous record of the variations in elemental abundances of the major rock-forming oxides of Si, Al, Ca, Fe, Ti and K, as well as S, Gd, U, Th, and the H and Cl in the formation and pore fluid. Through the additional measurement of the photoelectric capture cross section of the rock, the sum of Mg+Na can also be estimated. In this paper, the elemental yields from geochemical logging in basalts are calibrated against extensive XRF analyses of cutting samples from the Lamont 2 test well into the diabases of the Palisades Sill, New York. Accuracy and precision of the log-derived analyses are determined in the lower part of the well, and calibration equations are derived, which are then tested against core-derived "standards' from the upper part of the well. These calibrations are then applied to geochemical logs from the oceanic crustal basalts of Ocean Drilling Program hole 504B, where core recovery was less than 20% of the section. -from Authors