A geochemical study of some lithified carbonate sediments from the deep-sea

Abstract

Abstract Unconsolidated oozes, partially lithified oozes, recrystallized limestones, dolostones and crystalline aragonite are some of the varieties of carbonate sediment that have been found in the deep-sea; chemical and isotopic analyses of these varieties are presented here. The consolidated oozes and recrystallized limestones are low-Mg calcites and are often associated with basement rock (generally serpentinized peridotite or basalt) detritus. Lithification is suggested to arise from changes in the carbonate-equilibria system of the interstitial waters resulting from chemical degradation of the igneous rocks. When compared to unconsolidated oozes, lithification is seen to be accompanied by loss of Sr and a slight increase in B, Ba, Co, Cr, Ni and Y in most instances. The tuffaceous limestones are also low-Mg calcites, but are characterized by low Sr and relatively high B, Ba, Co, Cr, Cu, Ni, V, Y and Zn concentrations compared to the oozes. Three dolostones are described of very different isotopic and chemical composition, possibly indicating three different pathways of dolomitization. One with much depleted 13 C and high Ba concentrations is probably derived from waters containing carbon from a fractionated organic source. Another is not greatly different from the consolidated limestones in minor and trace element composition and may be derived from them. The third variety is characterized by low concentrations of Sr, B, Ba, Cu and Y and relatively high concentrations of Pb: Crystalline aragonite is commonly found in many areas associated with serpentinized peridotite. This aragonite is characterized by relatively high concentrations of Sr and Ni; petrographic and isotopic analyses indicate precipitation from cold, carbonate-rich solutions percolating through the peridotite.