Composition of Sediments from the Experimental Mohole Project (Guadalupe Site)

Abstract

ABSTRACT Thirty-four selected samples of sediments from the experimental Mohole were analyzed chemically and spectrographically, and their gross mineralogy determined by microscopic and x-ray diffraction techniques. The great majority of the samples consist of variable proportions of calcite (0 to 60 percent), biogenic opal (0 to 50 percent), and normal lithogenous matter (14 to 97 percent), with an average of 20,32, and 48 percent respectively. Abnormal lithogenous matter, produced by heavy contamination with trachytic ash and rhyolitic ash and by development of saponite and dolomite through alteration of basaltic materials, is present in a few samples. The covariance of magnesium oxide, manganese oxide, and phosphate throughout the section suggests a common derivation of a part of these constituents from basaltic materials. The general ratio of manganese oxide to phosphate is distinctly lower than that previously reported for sediments collected on the seafloor, and this lower ratio is probably due to the reducing condition that prevails in the more deeply buried Guadalupe sediments. The concentration of barium seems to be inversely related to the rate of deposition of the sediments. The overall composition of the non-biogenic fraction (lithogenous and hydrogenous matter) of Guadalupe sediments indicates a depositional environment intermediate between near-shore and pelagic.