Abstract: Preservation and Dissolution of Radiolaria in Low-Productivity Areas--Pathways into Sediment
Kenneth J. McMillen
Living radiolarians and their empty tests are abundant in waters from the Gulf of Mexico and Caribbean Sea, but they are absent from most Neogene sediments, apparently the victims of dissolution. Siliceous tests, unlike calcareous tests, do not dissolve during decomposition of the protoplasm after death of the organism, as laboratory observations show. In the water column, empty tests are abundant in shallow water but much less so in deep water. Comparison of the percentage abundances of radiolarian species using chi-square analyses shows that the assemblage of radiolarian tests in the near-surface sediment is dissimilar to the assemblage of living radiolarians but similar to the assemblage of empty tests in the water column. Therefore, fluctuations in populations of livi g radiolarians are time averaged in both the water column and sediments, suggesting that the tests sink slowly, possibly taking years to reach the seafloor. During this time, dissolution or, more likely, incorporation into fecal pellets that settle rapidly could account for the decrease in numbers in deep water.
Dissolution of radiolarian tests in sediment is rapid, with no selective preservation of radiolarian species. Radiolarian abundance is uniform in the upper 6 cm of sediment, and decreases rapidly below 6 cm. The average depth of burrowing in the sediment by macroinfauna is 6 cm, suggesting that the distribution of radiolarian tests in the sediment is a result of sediment reworking by infauna rather than of rates of dissolution.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC