Monsoon-Induced Hyperpycnal Flows
Recorded in the Gulf of Oman
(NW Indian Ocean)*
J. Bourget1, S. Zaragosi1, T. Mulder1,
T. Garlan2, N.
A. VanToer4, and J-L. Schneider1
Search and Discovery Article #50068 (2008)
*Adapted from extended abstract prepared
for AAPG Hedberg Conference, “Sediment Transfer from Shelf to Deepwater
– Revisiting the Delivery Mechanisms,” March 3-7, 2008 –
1Université Bordeaux I, Département de Géologie et Océanographie, UMR 5805 EPOC, 33405 Talence cedex, France
2SHOM, Centre Hydrographie, BP 426, 29275 Brest cedex, France
3IFP, 4 rue Bois Préau, Rueil-Malmaison 92141 cedex, France
4LSCE/IPSL, Laboratoire CEA-CNRS-UVSQ, Avenue de la Terrasse 91198 Gif sur Yvette cedex France
The MARABIE (2000, 2001) and CHAMAK (2004) surveys allowed us to investigate Quaternary deep sea gravity sedimentation along both the Oman and Makran margins. In this study we examined several piston cores recovered in a widespread range of environments (e.g., slope ridges, levees, channel floors, abyssal plain). Several facies were recognized (i.e., slumps, lobe sands, fine-grained turbidites, thick-ponded muds, hemipelagites, and pelagites). Very high resolution grain- size analysis, X-ray images, geochemical data, petrographical analysis of thin-sections of indurated sediment allowed us to describe the turbidite-bed morphology and nature (Figure 2).
northern margin is characterized by the Makran accretionnary wedge,
correspond to a very fine-grained slope-apron (Stow et al., 2002),
multi-sourced system. It is also sediment-fed by the wadis that form a
relatively dense network along the Iranian and Pakistani coasts. The
part of the submerged prism is marked by thrust faulting, responsible
formation of accreted ridges with steep flanks (Ellouz et al., 2007),
dissected by several canyons that reach the abyssal plain at
Sedimentation in the deep, central abyssal plain is characterized by uncommon very fine-grained thick-ponded turbidites, which probably originated from the Makran margin. Here the flows are not channelized but form sheet-like deposits. Most of the turbidites show a complex structure with silt-bed recurrence and wispy laminae in the Te subdivision (in Bouma sequence), suggesting that the flows at the origin of such deposits did not occur as discrete flow, but probably as successive surges occurring in a single, thick muddy turbidity current (Tripsanas et al., 2004). Such deposits are believed to be generated by successive retrogressive mass-failures in the prism.
layer in some of the turbidites (Figure 2) suggest that, at least some
are flood-generated (Mulder et al., 2003). This implies that sustained
turbidity currents generated at the shelf edge by very intense
cross the Makran slope and create very fine-grained hyperpycnites as
with inversely graded basal unit (hyperpycnites) have been recognized
different depositional environments (
The evolution of the gravity sediment supply since the Last Glacial Maximum has been studied in order to evaluate the impact of eustacy, tectonics, and climate on the turbidite activity in the Gulf of Oman, along two different margin morphologies (i.e., Makran and Oman margins), both of which are subjected to the same Asian-monsoon forcing.
Investigating the gravity sedimentation in such a complex area, where strong tectonics and climatic forcing interplay, should provide significant insights into the impact of external forcings on deep-sea clastic sedimentation.
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