EFFECTS OF SURGING DURING DEPOSITION OF A SUBAQUEOUS TRANSITIONAL FLOW

Preliminary results from flume experiments show that surging within a single sediment gravity flow can produce multiple thin, normally graded layers within an overall fining upward event bed. Each layer has a sand-rich base which grades into a clay-rich top. It is possible that successions of thin beds, laminae and banding in deepwater environments are deposited by flow surging within single events.

Experimental sediment slurry concentrations range from dilute turbidity currents to debris flows. The sediment slurry is episodically released from a head tank to the flume tank to produce surging. Inlet measurements of discharge record the fluctuations in flow. High-resolution photographs and videos document the experimental flow. Acoustic imaging using an ultrasonic transceiver non-invasively tracks mixing and sediment deposition within the flow. Post-depositional photographs and freeze cores are utilized to characterize the structure and fabric of deposits.

This research calls into question simple interpretations of sediment gravity flow deposits. Previously, every thin, fining upward layer may have been classified as repeated T_a and T_e beds after the Bouma Sequence. It appears that sets of thin-bedded turbidites, laminae and banding may all be related to surging within a single continuous turbidity current. By utilizing the information gleaned from experiments, it may be possible to distinguish depositional processes in deepwater settings by employing subtle differences in the deposit character.