Turbidite-Debrite Couplets in
Deep Sea Fan Systems – Evidence for Flow Partitioning and Transformation from
Subsurface and Outcrop Examples
Davis, Christopher E.1, Peter
Haughton1, William McCaffrey2 (1) University College
Dublin, Dublin, Ireland (2) University of Leeds, Leeds, United Kingdom
The deposits of turbidity currents and
debris flows dominate the record of deep water fan systems and are commonly
ascribed to separate remobilisation events However,
beds suggesting repeated coupling between a forerunner
turbidity current and an ensuing debris flow are now recognised
across a range of systems. Such composite event beds dominate the record of the
lateral and distal Forties fan system in the northern North
Sea, and the early fill of Carboniferous deep water toughs in NW Europe. In the
case of the Forties system, outer fan event beds comprises a
m-scale transitional association between massive and dewatered sandstone
(=turbidity current), commonly overlain by banded sandstone (=transitional
flow) and then a clast-rich and variably carbonaceous
argillaceous sand (=debris flow). Most events are capped by a thin (cm-scale)
laminated and graded sand to silt cap (= trailing dilute turbidity current).
The composite beds are found both close to and remote from salt highs and
therefore do not reflect local remobilisation on
distal slopes. They are instead interpreted as products of inner fan incision.
Analogous m-scale turbidite-debrite couplets in the
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California