The dissolution of siliceous microfossils in surface sediments of the eastern tropical Pacific

Abstract

Three assemblages of Quaternary siliceous microfossils were dissolved for varying lengths of time in natural seawater. Changes in the relative abundances of certain radiolarians, diatoms, and sponge spicules were measured, and a dissolution index scheme was developed. This scheme allows an objective assessment of the preservation of tropical siliceous microfossil assemblages of Quaternary age. Its application to a study of near-surface sediments in the eastern tropical Pacific shows that the siliceous microfossil preservation pattern roughly reflects surface water productivity. Two second-order features are superimposed upon this pattern. First, preservation is usually better at deeper depositional sites at most latitudes, and this is attributed primarily to sediment redistribution processes. Second, the best preservation is found not in equatorial sediments, but in those obtained from an area near 10°N, 117°W. This is attributed to the unusually high abundance of fragments of the diatom genus Ethmodiscus found in those sediments.