Chronologies of sedimentary processes in sediments of the FOAM site, Long Island Sound, Connecticut

Abstract

A detailed study of the sedimentation and diagenetic history of diver-taken sediment cores from the FOAM site in Long Island Sound was made by determining the distribution with depth of the following properties: /sup 234/Th/sub XS/, /sup 7/Be, /sup 210/Pb/sub XS/, /sup 239,240/Pu, selected trace elements, /sup 14/C (in both shells and organic fraction), pore water sulfate, and the diagenetic reaction products, solid phase organic carbon and sulfur. The /sup 234/Th/sub XS/ and /sup 7/Be data indicate that the upper 4 cm are well mixed on the time scale of about a year. The distributions of /sup 210/Pb/sub XS/, /sup 239,240/Pu, and anthropogenic trace metal excesses in the (4-15) cm section are controlled by the mixing of the surface (0-4) cm sediment into this layer. The net sediment accumulation rate in the (0-15) cm layer is about 0.03 cm/yr. The average sediment accumulation rate in the (approx. 18-100) cm layer, as determined from /sup 14/C ages of shell layers, is 0.094 +/- 0.021 cm/yr, perhaps a factor of approx. 2 lower than that estimated from diagenetic modelling of solid phase sulfur and organic carbon depth profiles. The sediment structure indicates that the sediment accumulation in this depth zone has beenmore » episodic with the possibility of erosion as well as deposition having occurred. Their study shows that in high energy and dynamic sedimentary environments, such as the FOAM site, the results of steady state diagenetic modelling should be accepted only over time and depth scales permitted by the physical evidence.« less