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Bourget J.,French National Center for Scientific Research | Zaragosi S.,French National Center for Scientific Research | Ellouz-Zimmermann N.,French Institute of Petroleum | Mouchot N.,Cergy-Pontoise University | And 4 more authors.
Sedimentology | Year: 2011

This study investigates the morphology and Late Quaternary sediment distribution of the Makran turbidite system (Makran subduction zone, north-west Indian Ocean) from a nearly complete subsurface mapping of the Oman basin, two-dimensional seismic and a large set of coring data in order to characterize turbidite system architecture across an active (fold and thrust belt) margin. The Makran turbidite system is composed of a dense network of canyons, which cut into high relief accreted ridges and intra-slope piggyback basins, forming at some locations connected and variably tortuous paths down complex slopes. Turbidite activity and trench filling rates are high even during the Holocene sea-level highstand conditions. In particular, basin-wide, sheet-like thick mud turbidites, probably related to major mass wasting events of low recurrence time, drape the flat and unchannellized Oman abyssal plain. Longitudinal depth profiles show that the Makran canyons are highly disrupted by numerous thrust-related large-scale knickpoints (with gradients up to 20° and walls up to 500m high). At the deformation front, the strong break of slope can lead to the formation of canyon-mouth 'plunge pools' of variable shapes and sizes. The plunge pools observed in the western Makran are considerably larger than those previously described in sub-surface successions; the first insights into their internal architecture and sedimentary processes are presented here. Large plunge pools in the western Makran are associated with large scoured areas at the slope break and enhanced sediment deposition downstream: high-amplitude reflectors are observed inside the plunge pools, while their flanks are composed of thin-bedded, fine-grained turbidites deposited by the uppermost part of the turbidity flows. Thus, these architectural elements are associated with strong sediment segregation leading to specific trench-fill mechanisms, as only the finer-grained component of the flows is transferred to the abyssal plain. However, the Makran accretionary prism is characterized by strong along-strike variability in tectonics and fluvial input distribution that might directly influence the turbidite system architecture (i.e. canyon entrenchment, plunge pool formation or channel development at canyon mouths), the sedimentary dynamics and the resulting sediment distribution. Channel formation in the abyssal plain and trench-fill characteristics depend on the theoretical 'equilibrium' conditions of the feeder system, which is related closely to the balance between erosion rates and tectonic regime. Thus, the Makran turbidite system constitutes an excellent modern analogue for deep-water sedimentary systems with structurally complex depocentres, in convergent margin settings. © 2010 The Authors. Journal compilation © 2010 International Association of Sedimentologists.

Bourget J.,University of Bordeaux 1 | Zaragosi S.,University of Bordeaux 1 | Mulder T.,University of Bordeaux 1 | Schneider J.-L.,University of Bordeaux 1 | And 4 more authors.
Sedimentary Geology | Year: 2010

The main sediment depocenter along the Oman margin is the Al Batha turbidite system that develops in the Gulf of Oman basin. It is directly connected to the wadi Al Batha, and forms a typical sand and mud rich point source system that acts as regional sediment conduit and feeds a ~1000 km2 sandy lobe. The Al Batha lobe depositional architecture has been investigated in detail using very high-resolution seismic, multibeam echosounder data and sediment cores. Several scales of depositional architecture can be observed. The Al Batha lobe is composed of several depositional units, made of stacked elementary sediment bodies (thinner than 5 m) that are each related to a single flow event. The lobe is connected to the feeder system through a channel-lobe transition zone (CLTZ) that extends on more than 25 km. The lobe can be divided into proximal, middle and distal lobe areas. The proximal lobe is an area of erosion and by-pass with small axial feeder channels that rapidly splay into several small distributaries. They disappear in the mid-lobe area where deposits consist of vertically stacked tabular to lens-shaped sediment bodies, with a lateral continuity that can exceed 10 km. The distal lobe fringe shows a classical facies transition towards thin-bedded basin plain deposits. Sub-surface deposits consist of sandy turbidites and hyperpycnites, interbedded with fine-grained deposits (thin turbidites, hyperpycnites, or hemipelagites). Although these distal deposits are mainly related to flow transformations and concentration evolution, they highlight the importance of flooding of the wadi Al Batha on the sediment transfer to the deep basin. The thick sandy hyperpycnites recovered in such a distal area are also possibly related to the initial properties of gravity flows, in relation to the flooding characteristics of mountainous desert streams. Finally, the Al Batha lobe depositional architecture is typical of sand-rich lobes found within "small", sand and mud rich turbidite systems fed by mountainous "dirty" rivers. Turbidite sedimentation in the Al Batha system appears to be primarily controlled by the strong climatic and geomorphic forcing parameters (i.e. semi-arid environment with ephemeral, mountainous rivers subjected to flash-flooding). © 2009 Elsevier B.V.

Bourget J.,French National Center for Scientific Research | Zaragosi S.,French National Center for Scientific Research | Ellouz-Zimmermann S.,French Institute of Petroleum | Ducassou E.,French National Center for Scientific Research | And 6 more authors.
Marine Geology | Year: 2010

Late Quaternary turbidite system growth along the Makran convergent margin is investigated through a set of deep-sea cores from upper slope and piggy-back basins to deep basin plain settings. High-resolution stratigraphy in these various depositional environments permits reconstruction of the evolution of sand-to-mud ratio, sedimentation rates, frequencies, and thickness of turbidite deposits during the last 25. ka BP. This study demonstrates how tectonics, climate and eustasy can interplay at high resolution (<20. ka) and control the input of terrigeneous sediment along the tectonically active Makran convergent margin, in a source-to-sink perspective.The Makran turbidite system growth has been continuous throughout sea-level lowstand, transgressive, and highstand conditions. However, the frequency, rates, and nature of sediment supply varied in response to climate, sea-level, and tectonically induced changes in source-to-sink sediment dispersal modes. These changes include conditions of sediment production and availability in the drainage basin, capacity of transport from fluvial systems, and rates of sediment storage on the shelf and upperslope areas. Climate in the hinterland appears as a first-order control on the properties of turbidity currents that feed the turbidite system, controlling the average sand-to-mud ratio in the deep water deposits. The onset of sea-level highstand after ∼8 ka BP resulted in a notable change in turbidite system growth, characterized by the occurrence of large volume, thick turbidity currents (>300. m thick along the continental slope) originated from successive, multiple slide or slump-induced surges. Their related deposits have low recurrence intervals, close to those calculated from the large magnitude earthquake and tsunami record in the Makran area.Comparison with the Nile and Indus turbidite systems growth during the Late Quaternary provides an evaluation of the relative importance of shared forcing parameters (i.e. monsoon-induced phases of arid/humid conditions and post-glacial sea-level rise), in significantly different basin settings. The Indus fan appears mainly controlled by eustasy during the last 25. ka. Inversely, similarities are found between the Nile and Makran turbidite systems, where sea-level changes are modulated by the climate impact on fluvial dynamics in the hinterland. However, the Makran turbidite system growth is continuous through times, because both the uplift in the coastal area and the fluvial dynamics of short, mountainous river systems allow high sediment transfer rates to the marine basin, even though arid conditions and associated low water fluxes. Earthquake-induced highstand turbidite deposits form a thick sedimentary succession in the Oman abyssal plain, and are significant in the geologic record. This study finally illustrates how the complex interplay between external (allogenic) forcings can complicate the interpretation of high-resolution sedimentary successions in turbidite-filled basins. © 2010 Elsevier B.V.

Bourget J.,University of Western Australia | Zaragosi S.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Rodriguez M.,University Pierre and Marie Curie | Rodriguez M.,CNRS Paris Institute of Earth Sciences | And 5 more authors.
Marine Geology | Year: 2013

The Indus sedimentary basin forms one of the largest "source-to-sink" systems of the Quaternary and extends over 106km2 offshore. It is characterized by a complex tectonic setting marked by the Himalayan active orogenic belt in the source area, and the active strike-slip India-Arabia plate boundary (Owen Fracture Zone; OFZ) in its distal reaches. This paper focuses on a Late Quaternary channel-levee system from the Indus Fan captured by the recent opening of the 20°N pull-apart basin, located at 850km off the present-day Indus Delta, along the OFZ. In this area the channel-mouth deposits consist of a set of up to 23m thick megaturbidites trapped in the basin. These deposits form "ponded" lobe deposits in a tectonically-active confined basin. Age determination from radiocarbon dating and extrapolation of local deformation rates show that the older deposits observed on the seismic profiles are up to 358ka BP old (MIS 10). The origin of these Late Quaternary deposits are investigated in the context of the Indus "source-to-sink" system and their significance is placed in a sequence stratigraphic framework. Integration of the stratigraphic architecture of the 20°N Basin megaturbidites with previous work in the area suggests that the Indus Fan evolved from a delta-fed turbidite system with several active canyons and channel-levee during the forced regressive conditions of the last falling stage of sea-level (122-25ka BP), to a point source turbidite system during the sea-level lowstand (Last Glacial Maximum) and early transgressive stages (25-12ka BP). This work sheds new light on the recent evolution of the Indus sedimentary system and illustrates the importance of the delta/river evolution during the fall of sea-level (e.g., incised valley formation) on the timing of sedimentary transfer and sediment distribution at the basin-scale. © 2012 Elsevier B.V.

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