Abstract: The development of low- and hightemperature alteration products in a 23 m section of ocean-floor basalts is described. Analcime, calcite and dioctahedral smectite are ubiquitous. Trioctahedral smectite, smectite-chlorite mixed layers, chabazite and scolecite occur in the deeper sections with Fe³⁺ oxides/hydroxides progressively becoming more abundant in the upper regions. The upper layers of the sequence show marked chemical reduction. High-temperature chemical changes include Na and Mg enrichment accompanied by Ca and Fe²⁺ losses. Superimposed low temperature changes include gains in Fe³⁺ K, Li, and Rb, and losses in Na, Ca, and Fe²⁺ Many trace elements also show consistent behaviour.