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Turbidite Sedimentation
along Topographically Complex Slopes in Convergent Margin: 
Example
of the
Makran Accretionary Prism (Gulf of Oman, NW Indian Ocean)*
Julien Bourget1, Sébastien Zaragosi1, Nadine Ellouz-Zimmermann2, Thierry Garlan3, N. Mouchot4, Raymi A. Castilla2, Jean-Luc Schneider1, Vanessa Teles2
Search and Discovery Article #50197 (2009)
Posted August 28, 2009
*Adapted from oral presentation at AAPG Convention, Denver, Colorado, June 7-10, 2009
1UMR 5805 EPOC, University of Bordeaux, Talence, France (mailto: [email protected])
2Geology-Geochemistry-Geophysics, IFP, Rueil Malmaison, France
3Centre
Hydrographie, SHOM, Brest, France
4Universite de Cergy-Pontoise, GEC, 5, Gay-Lussac, F-95031 Cergy-Pontoise, France
Quaternary
sediment distribution of the Makran turbidite system (Makran subduction zone,
NW Indian Ocean) is investigated through a nearly complete (~ 162,000 km2)
reflectivity and bathymetry mapping of the Oman basin, a large set of coring
data, and 2D seismic recovered during several cruises leaded by the IFP and
SHOM institutes.
The
Makran continental slope is composed by numerous accreted ridges associated to
intra-slope, piggy-back basins. Our results show that the mechanisms of
sediment dispersal in the Makran turbidite system are mostly influenced by the
pre-existing and evolving sea floor topography, that vary along-strike with the
tectonic regime and the magnitude of sediment flux. Abrupt changes of gradients
(up to 20°) along thrust-induced knickpoints generate hydraulic jumps that
enhance preferential deposition of the coarse-grained load of the flows,
substantial erosion, and by-pass of the finer-grained component. At the
deformation front, these processes can lead to the formation of base-of-slope
plunge pools that potentially form wide sand reservoirs. Rapid deposition of
the coarser material downstream of the hydraulic jump lead to a strong
segregation of the sediments, as only the uppermost, finer-grained component of
the turbidity flows is transferred to the abyssal plain. Wide plunge pools
develop at areas where the sediment flux (i.e. erosion rates) is too low to
compensate the deformation rates, leading to non-equilibrium conditions.
Inversely, equilibrium conditions (resulting from higher sediment flux and a
lesser tectonic control) promote channel formation at the canyon mouths and
transfer of coarse-grained material to the trench. Hence, channel formation and
trench fill characteristics depend of the equilibrium conditions of the feeder
system, related to the balance between erosion rates (i.e. fluvial input,
initial sediment load, and slope gradients) and deformation rates. Preliminary
simulations with the process-based model CATS (Salles et al., 2007) were
performed in order to simulate the turbidity flow paths along the
thrust-induced complex slope.
Our results from the Makran turbidite system provide another evidence of how complex submarine slopes may interplay with the sedimentary processes and control the reservoir architecture. It constitutes an excellent modern analogue to deep water sedimentary systems with structurally complex depocenters, in the context of convergent margins.
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