Lies Loncke

Marine geologic evidence for a Levantine-Sinai plate, a new piece of the Mediterranean puzzle

Marine geophysical data recorded offshore Egypt illustrate the presence of an active fault belt, trending N145°E, that obliquely transects the eastern Nile deep-sea fan. This belt, more than 150 km long, consists of a series of linear transtensive faults, with an apparent right-lateral horizontal component. These fault zones bound thick-sediment-filled grabens where linear salt ridges and diapirs represent likely Messinian salt reactive response to regional transcurrent geodynamics. We infer that this tectonic belt might correspond to an offshore extension of the Gulf of Suez rift system. If our hypothesis is correct, this fault belt might represent the western boundary of a Levantine-Sinai microplate, locked between the major Arabia and Africa plates and the Anatolian-Aegean microplate.

Recent depositional patterns of the Nile deep-sea fan from echo-character mapping

The Nile deep-sea fan was surveyed in 1998 using swath multibeam bathymetry, backscatter imagery, and 3.5 kHz and seismic profiling. On the basis of this new data set, the fan has been divided into three main provinces: western, central, and eastern. Recent sedimentary patterns, as deduced from echo-character mapping, show that gravity-induced sedimentary deposits are predominant and are expressed through either slides, debris flows, or turbidites. Turbidity processes are particularly active in the westernmost province through a well-developed network of deep-sea channels. This network controls turbiditic flows that, subsequently, overflow levees. Mass-wasting processes are extremely efficient all over the Nile deep-sea fan. In the upper central province, a broad allochthonous tongue of mass-flow deposits, generated by slope destabilizations, may have led to channel avulsions and migrations. In the eastern province, a northwest-southeast deformed belt resulting from combined deep-seated and salt-related tectonics contains large proportions of destabilized sediments (i.e., originating from destabilization processes such as mass movements), probably settled by recent tectonic activity. This article highlights (1) the influence of both thin-skinned and thick-skinned tectonics on sedimentary distribution, and (2) the predominance of gravity-induced sediments (turbidites, slides, and mass flows). In such submarine fans, the distribution of debris flows and sedimentary deposits settled by turbidity currents appears fundamental in predicting reservoir geometry and economic potential.

The Nile deep sea fan: preliminary results from a swath bathymetry survey

We present and discuss a set of data, mainly swath bathymetry, backscatter images and a few seismic data, that have been recently recorded over large areas of the Nile deep-sea fan between water depths of 1200 and 3000 m. These data demonstrate the presence of at least three distinct morphostructural provinces where interacting sedimentary, tectonic, and salt tectonic processes control the present day morphology and the recent evolution of the major Mediterranean deep-sea fan. The role of the ongoing collision presently occurring between the continental Eratosthenes Seamount and the Cyprus Arc may have been, and still is, a determining parameter for the development of the Nile deep-sea fan.

Le cône sous-marin du Nil et son réseau de chenaux profonds : nouveaux résultats (campagne Fanil)

The meandrous leveed channels of the Nile Cone show clear evidence of avulsions. Their sedimentary architecture is founded on numerous stacked lens-shaped acoustic units. In the areas of the distal fan, lobe deposits are apparent from multichannel imagery. Huge debris flow deposits, sometimes associated with pockmarks, are recognized. Mud volcanoes and gas seeping are closely associated with faulting. In the East, a very long north-trending channel, originating from the Egyptian coast, merges with a network of channels, very probably originating from the Levantine coasts. Both networks outlet in the sedimentary basin located south of Cyprus.

Interaction compression–extension à la limite Mongolie–Sibérie : analyse préliminaire des déformations récentes et actuelles dans le bassin de Tunka

Abstract The Tunka basin was initiated during Oligocene, under transtensional regime (normal-sinistral) as shown by large-scale structures and geomorphology. Nevertheless, a preliminary analysis of the most recent deformations allows us to evidence transpression on several sites within the basin. These tectonic features together with focal mechanisms and preliminary GPS data, suggest that the kinematics of the Tunka basin has undergone a very recent change, which could be due to the northward propagation of the India–Eurasia collisional strain field.

Mass Movements in a Transform Margin Setting: The Example of the Eastern Demerara Rise

The eastern Demerara Rise located offshore French Guiana was surveyed in 2003 (GUYAPLAC cruise, part of the French EXTRAPLAC program) using multibeam bathymetry and imagery, 6-channel seismic data and 3–5 kHz echosounding. Analysis of seismic data shows that the flank of the Demerara Rise endures repetitive sliding of its Paleogene to Neogene sedimentary cover towards the ocean. Fluid escapes seem to be closely associated with the activity of those slides and deep faults seems to impact the location of the main headscarp. We suspect fluid overpressures and the specific architecture of transform boundaries (“free border”) to be key parameters in the development of wide MTD’s retrogressively eroding the eastern Demerara Rise.

Slope Instability on the French Guiana Transform Margin from Swath-Bathymetry and 3.5 kHz Echograms

Although transform margins represent ~30% of rifted margins around the world, few studies have investigated mass-movement processes in such areas and their links with this specific structural context. The French Guiana transform margin and adjacent Demerara abyssal plain have been surveyed during the GUYAPLAC cruise, collecting multibeam bathymetric data, backscatter imagery, 3.5 kHz echograms and 6-channel seismic profiles. The study area is divided into three domains: the shallow Demerara plateau, the Guiana slope and rise, and the Demerara abyssal plain. The Demerara plateau displays multi-scale slope instabilities from huge deep-seated collapses of the whole margin to surficial creeping folds and recent slumps. Giant elongated pockmarks have been also observed for the first time in this area. Fluid escape is common everywhere on the plateau and probably enhances slope instability. On the Guiana slope and rise, large stacked lobate masses have been identified testifying to repetitive failure events. Fluid escape is also ubiquitous there, suggesting a dewatering of debris flows due to sediment loading. Two main types of sedimentary structures are observed on the Demerara Abyssal Plain: small meandering channels of the Amazon Fan at its eastern edge and sediment waves at its western edge, along the foot of Demerara continental slope.

ABSTRACT: Contribution of Physical Modeling to Understanding Salt Tectonics in the Eastern Nile Deep-Sea Fan

Recent multibeam-bathymetry, backscattering-imagery and seismic-reflection data indicate that the structural pattern of the east part of the Nile deep-sea fan differs drastically from that of its central and west parts. Such differences may result from combined thickskinned, crustal-scale tectonics and thin-skinned, gravity-driven spreading of the Messinian evaporites and their Plio-Pleistocene overburden. The eastern deep-sea fan comprises a long (200 km) NW-SE deformation corridor that was first interpreted as the possible northern prolongation of the rift of Suez. Along dip, the corridor exhibits a structural progression typical of salt-bearing passive margins undergoing gravity spreading, including small distal buckle folds, midslope minibasins surrounded by salt ridges, and proximal normal growth faults. Less typical is the corridor’s being bounded by narrow, NWSE fault zones underlain by narrow salt ridges. We used physical models to test whether such pattern was caused by the presence of NW-SE dormant or active subsalt relief or of a bathymetric high (the Eratosthenes seamount) acting as a buttress during spreading. Model results clearly indicate that the presence of a passive subsalt relief and/or of a buttress, rather than that of an active subsalt relief, has caused this peculiar structural pattern. Early gravity spreading caused radial thin-skinned extension and the formation of minibasins and NW-SE and ENE-WSW salt ridges, a pattern also enhanced if basement steps are present. Later, buttressing by the seamount opposed further northeastward extension. The salt and overburden spread northwestward, reactivating the NW-SE salt ridges as strike-slip zones bounding the corridor.