Flow Behavior of Ponded Turbidity Currents

Abstract

7Sea-floor topography can constrict, deflect, or reflect turbidity currents resulting in a range of 8 distinctive deposits. Where flows rebound off slopes and a suspension cloud collects in an enclosed 9 basin, ponded or contained turbidites are deposited. Ponded turbidites have been widely recognized 10 in slope mini-basins and on small, structurally confined basin floors in strike-slip and foreland-basin 11 settings. They can have a variable internal structure the significance of which remains poorly 12 understood in terms of flow behavior. New experiments demonstrate that the ponding process can 13 comprise up to four phases: 1) cloud establishment, 2) inflation, 3) steady-state maintenance, and 4) 14 collapse. The experiments explored the behavior of sustained turbidity currents draining into small 15 basins and show that the ponded suspensions that form are characterized by an important internal 16 interface; this divides a lower outbound-moving layer from an upper return layer. The basal layer 17 evolves to constant concentration and grain size, whereas the upper layer is graded (concentration 18 and grain size decrease upward). During the cloud inflation stage, the concentration and velocity 19 profiles of the ponded suspension evolve, and this phase can dominate the resulting deposit. 20Outbound internal waves can travel along the interface between the outbound and return layers and 21 impinge against the confining slope, and their amplitude is highest when the density contrast 22 between layers is greatest, e.g., when the input flows are thin and dense. The experiments show 23 that flow reversals can arise in several ways (initial rebound, episodic collapse of the wedge of fluid 24 above the counter slope, "grounding" of the internal velocity interface) and that despite steady 25 2 input, velocities decay and the deposit grades upwards. Internal waves emanate from the input 26 point, i.e., do not form as reflections off the counter slope. The internal grain-size interface within 27

Response of unconfined turbidity current to deep‐water fold and thrust belt topography: Orthogonal incidence on solitary and segmented folds

“…). This generalized two dimensional (2D) picture of the flow behaviour concurs with earlier conceptual notions and inferences from laboratory experiments (Shanmugam & Moiola, ; Kneller et al ., ; Hodgson et al ., ; Clayton, ; Alexander & Morris, ; Kneller, ; Simpson, ; Kneller & McCaffrey, ; Sinclair & Tomasso, ; Baas et al ., ; Lamb et al ., ; Clark & Cartwright, ; Patacci et al ., ).…”

“…This phenomenon resembled the ‘basal flow reversal’ described by Patacci et al . (), but involved no true flow ponding. The backward stripping of deposited sediment is attributed to the current's attempt to reduce the counter‐slope by erosion, while being incapable of carrying the re‐suspended sediment over the fold crest.…”

“…; e.g. Shanmugam & Moiola, ; Kneller et al ., ; Hodgson et al ., ; Clayton, ; Haughton, , ; Kneller, ; Kneller & McCaffrey, ; Al‐Ja'Aidi, ; McCaffrey & Kneller, ; Sinclair & Tomasso, ; Lamb et al ., ; Clark & Cartwright, ; Bakke et al ., ; Salles et al ., ; Patacci et al ., ; Kneller et al ., ). Turbidity currents in these settings commonly encounter thrusts with fault‐propagation folds as transverse obstacles when descending sea‐floor slopes folded by contractional tectonics or diapirism, or when overriding the slump topography of mass‐transport complexes.…”

Fill to spill stratigraphic evolution of a confined turbidite mini-basin succession, and its likely well bore expression: The Castagnola Fm, NW Italy

“…ripple drift lamination) in the upper sections in favour of repeated normal grading and wavy to hummocky-like laminations would suggest that pulsating or even oscillatory flow conditions (Tinterri 2011) lasted to the final stage of sedimentation, prior to deposition of the thick ponded mud cap (Pickering and Hiscott, 1985;Haughton 1994Haughton , 2000. The vertical sequence of sedimentary structures along with the average thickness of both the sandstone and the mud cap of type A beds suggest deposition from large volume turbidity currents ponded by the enclosing topography (Lamb et al, 2004;Toniolo et al, 2006a, b;Patacci et al, 2015).…”

“…Flow stripping occurs when the most dilute upper part of a turbidity current suspension cloud is able to escape the basin spilling over the confining topography (Sinclair and Tomasso 2002). Flow stripping can occur either as a transient run-up effect in low relief confined situations (Muck and Underwood 1990), or when large volume, long-lived flows inflate the suspension cloud to the level of a basin sill (Toniolo et al 2006a, b;Patacci et al, 2015).…”