--> Multi-Pulsed Turbidity Currents — Flow Dynamics and Geological Implications

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Multi-Pulsed Turbidity Currents — Flow Dynamics and Geological Implications

Abstract

It is common practice to infer the longitudinal structure of overpassing turbidity currents from the vertical structure of their deposits. Such currents may initiate with a complex longitudinal flow structure (e.g., by being sourced from retrogressive sea floor slope failures) or acquire such structure during runout (e.g., following flow combination downstream of confluences). A key question is whether, or for how far, such complex flow structure is preserved within turbidity currents as they run out and thus if flow initiation mechanism and/or proximity to source may be inferred from deposits. To address this question, physical modelling has been conducted to investigate and compare the deposits and dynamics of single-event vs. multi-pulsed particle-laden currents, with focus on the relative timing between, and composition of, different pulses. A lock exchange turbidity flow generation methodology was adopted, using two lock boxes set up in series at one end of a flume enabling the generation of multi-stage flows. The relative timing of each lock gate was controlled via pneumatic lock control box. The spatial evolution of flows was captured by an array of five HD interlinked cameras, and the deposits fixed and analysed. Control parameters included the initial volumes and densities of the flows and the gate release timings. For each different setting, the multi-staged flows merged at different times, and different positions relative to the point of release, resulting in a progressive downstream reduction in deposit complexity. The research highlights the importance of flow process modelling in the interpretation of geological deposits, and seeks to establish constraints on the length scales over which signals may be transmitted downstream by turbidity currents and recorded in their deposits.