Gradient Changes and the Evolution of Sediment Gravity Flows from Non-Equilibrium Slopes

Peter D. Haughton¹, William McCaffrey², Lucie Baudouy¹, Christopher Davis¹, and Simon Barker^3
1School of Geological Sciences, University College Dublin, Dublin, Ireland
²Institute of Geological Sciences, University of Leeds, Leeds, United Kingdom
³BG Energy Holdings Limited, Reading, United Kingdom

Sediment gravity flows are very sensitive to gradient changes imposed by prior deposition, external slope adjustments or tectonic deformation of the sea floor. Here we examine the recovery of a range of systems from supply-, gravity- and tectonically-forced disequilibrium. Flows may be (1) re-routed (2) modified to become more or less erosive (3) partitioned to form hybrid flows (turbidite-debrite couplets) via erosional overloading and (4) undergo partial or whole-scale containment. The flow response depends on factors such as the scale and orientation of the slopes or obstacles encountered, and the flow thickness, volume and degree of internal stratification. Once perturbed, gravity flow systems may show systematic trends as they attempt to re-establish grade, although some systems remain largely out of grade throughout. Where the flow volumes are large relative to the imposed non-equilibrium bed roughness, single events may be able to heal the sea floor, although facies variations with the healing event bed will record the recovery. Stacked linked debrites and hybrid event beds are thought to be key indicators of up-slope non-equilibrium. Vertical changes from hybrid to conventional turbidites record re-attainment of equilibrium, such as following system switch-on, adjustment to increased flow volumes or knickpoint migration in slope channel systems. Where contained flows progressively fill deeper enclosed bathymetry, an increase in the length scale of confinement due to aggradation can result in systematic changes in the character of the stacked contained flow deposits as local relief is healed. Basin floor tilting can induce major instability in just deposited turbidites, producing complex interaction between on-going deposition and rugose slump masses, even during a single event.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas