Print this pageA 4-Phase
Evolution of a Channellized Fairway in a 
System
,
Mellere, Donatella1, Pau
Arbués2 (1) Norske Shell,
The Eocene Ainsa foredeep is an elongate
basin oriented east-west on the footwall of an active thrust system. It hosts a
number of turbidite channel-fills and associated overbank, splay and
slump-sheet elements. The O-Grao channel complex is one of the sandiest of the
mud-prone slope. It is up to 80m thick and has been investigated along a 6.5x3
km wide outcrop section.
The complex shows four distinctive phases
of development: 1. a proto fairway excavated by gravitational collapse of the
muddy slope induced by tectonic oversteepening; 2. building up phase associated
to an abrupt input of high density turbidite flows that partially excavate and
filled the underlying slumped topography with two channel lobe systems (O-Grao1
and 2, 15m thick, 1000m wide); 3. Channel incision and sediment by-pass
associated to an active sinuous fairway associated to the progradation of the
coeval shelf-edge margin (O-Grao 3); 4. a phase of
abandonment, dominated by thin bedded turbidites and by backstepping channel
levee complexes.
The O-Grao system developed in an active
tectonic setting dominated by the growth of the Mediano anticline in the
southern margin of the foredeep. The mass wasting complex is interpreted to be
directed linked to thrust rejuvenation and growth of the Mediano Anticline. The
sandy O-Grao 1 and 2 formed as distributary system
in a confined minibasin
bounded by the positive structure. O-Grao 3 represents a phase of active
by-pass where sediment cut and spill beyond the anticline.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California