Abstract
ABSTRACT Previous studies on dilute, multi-pulsed, subaqueous saline flows have demonstrated that pulses will inevitably advect forwards to merge with the flow front. On the assumption that pulse merging occurs in natural-scale turbidity currents, it was suggested that multi-pulsed turbidites that display vertical cycles of coarsening and fining would transition laterally to single-pulsed, normally graded turbidites beyond the point of pulse merging. In this study, experiments of dilute, single- and multi-pulsed sediment-bearing flows (turbidity currents) are conducted to test the linkages between downstream flow evolution and associated deposit structure. Experimental data confirm that pulse merging occurs in laboratory-scale turbidity currents. However, only a weak correspondence was seen between longitudinal variations in the internal flow dynamics and the vertical structure of deposits; multi-pulsed deposits were documented, but transitioned to single-pulsed deposits before the pulse merging point. This early transition is attributed to rapid sedimentation-related depletion of the coarser-grained suspended fraction in the laboratory setting, whose absence may have prevented the distal development of multi-pulsed deposits; this factor complicates estimation of the transition point in natural-scale turbidite systems.
Highlights
Turbidity currents are dilute, subaqueous particle-laden gravity currents (Middleton 1993; Piper & Savoye 1993; Huppert 1998; Xu et al 2004)
Experiments conducted to study the dynamics of single- and multi-pulsed turbidity currents confirm that after an initial period of abruptly waxing velocity, the mean velocity of singlepulsed currents reduces monotonically in the waning phase, whereas that of multi-pulsed flows transitions from waxing-waning cycles to monotonic reduction in their waning phase
This pattern is similar to that observed in the dynamics of multi-pulsed saline flows
Summary
Subaqueous particle-laden gravity currents (Middleton 1993; Piper & Savoye 1993; Huppert 1998; Xu et al 2004). They commonly initiate on continental shelves and transport significant volumes of sediment from the continents to deep marine environments (Simpson 1982; Talling et al 2015), where they build the most spatially extensive sedimentary landforms on the planet (Canals et al 2004; Xu 2011; Dorrell et al.2015; Lintern et al 2016). Because particle-transport competence (i.e., the maximum particle-size that can be transported) decreases as flow wanes (Dorrell et al 2013), turbidites commonly exhibit classic upward-fining grading structures These “single-pulsed” turbidites are interpreted to reflect a single depositing turbidity current event
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