Processes and
Modeling of Deep Water Flows: the Evolution of Hybrid and Transitional Flow
Types
Haughton, Peter1, William
McCaffrey2, Christopher Davies1, Simon Barker3
(1) University College Dublin, Dublin, Ireland (2) University of Leeds, Leeds,
United Kingdom (3) BG, Berkshire, United Kingdom
Gravity transport in deep-water basins is
often ascribed to either debris flows or turbidity currents. However, cogenetic
flows involving linked turbulent and laminar components, or clay-prone
transitional flows characterised by mixed or oscillating behaviour, are common.
The former can give rise to turbidite-debrite couplets, the latter to banded
and other ‘slurry' fabrics, although the term slurry has been loosely used and
is probably best avoided. Linked and transitional flows are increasingly
recognised in both outcrop and cores, and curiously seem to be best developed
in distal and lateral fan settings. Care must be taken to distinguish genuine
hybrid flow components from partial remobilisation and secondary mixing bodies
(sand autoinjection and substrate deformation) with which they may be confused.
In some systems, single events preserve evidence of flows evolving from
turbulent through transitional to laminar flow regimes, suggesting longitudinal
suppression of turbulence and flow transformation. Many of these hybrid event
beds seem to be related to periods of up-dip incision, either on inbound slopes
or on the basin floor. Local erosion may choke and collapse part of a sandy
turbidity current to partition the flow into a relatively low velocity debris
flow and/or transitional flow that propagates over, and interacts with, the
just-deposited turbidite sand. The presence of these hybrid beds may identify
disequilibrium slopes up-dip that were steep enough to
promote significant flow incision. Where hybrid beds dominate the distal fan
stratigraphy, this implies parts of the flow routeways were continually out-of
grade to force repeated flow partitioning.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California