Erosion of fine-grained marine sediments: Sea-floor and laboratory experiments

摘要

Estimates of threshold erosion velocities have been obtained in the field and in the laboratory for marine mud relatively rich in organic matter and having an active infauna. A sea-floor flume was used to erode undisturbed sediments on the sea floor, and a laboratory flume was used to study the effects of sampling, redeposition, bioturbation, organic-matter content, and compaction time on erosion resistance. Critical shear velocity, u*_c, for erosion of muds in situ ranged from 0.32 to 0.84 cm/s, and u*_c was apparently independent of season or bulk physical properties. Erosion was often but not always initiated in biogenically disturbed parts of the bed. Lee drifts around small bed-roughness elements were the most common constructional bedforms observed during the sea-floor experiments, and narrow and shallow longitudinal furrows were the most commonly observed erosional features. Tidal u*_c values measured at the field site were of the same magnitude as the u*_c values measured with the sea-floor flume. Mean u*_c for muds redeposited and bioturbated for 1 to 60 days in the laboratory flume (0.92 cm/s) was greater by a factor of two than mean u*_c for muds eroded in situ (0.45 cm/s). As bioturbation time in the laboratory increased, u*_c decreased. Increases in sediment organic content were found to increase u*_c systematically in flat, nonbioturbated laboratory beds.