Evidences of Fluid Escape Structures and Mud Volcanoes on the Nile Deep Sea Fan

By

 Jean Mascle¹, Lies Loncke², Olivier Sardou³, Paul J. Boucher⁴, Vince Felt⁵

(1) Geosciences Azur, 06235 Villefranche-sur-Mer, France (2) Géosciences Azur, 06235 Villefranche-sur-mer, France (3) Géosciences Azur, 06235 Villefranche/Mer, France (4) BP Egypt, Egypt (5) BP Amoco, Houston, TX

 At continental margins, fluids are emitted into the ocean via the sea floor. The forms of emissions vary from diffusive fluid flow to focused flow through seeps and vents, often associated with over-pressured mud constructions. Marine geophysical data show that these features are variably expressed on the sea floor, as pock-marks, mud volcanoes and/or sub-circular, flat, mud ÇcakesÈ.

Extensive swath mapping (bathymetry and backscatter images) and seismic profiling (including a few 3D seismic data) from deep-water Egypt, have revealed the presence on the sea floor of many features interpreted to be evidences of fluid releases and associated mud flows. A field, characterized by many small mud cones (few hundred meters in diameter), lies on the lower slope in the north-west of the Nile deep sea fan, by water depth around 3000 m. In the same area, caldera-like, subdued depressions (up to 8 km in diameter) are detected on the sea floor. These features are associated with numerous growth faults that cut across this area of the continental slope. Isolated, sub-circular, gas chimneys (characterized by transparent or chaotic seismic signature), or clusters of important mud volcanoes, are seen in several regions of the upper slope, around 800-1000 m of water depth. These structures are either associated to recent sedimentary destabilizations, to growth faults, or to sets of cross-cutting active faults. Finally, many pock-marks, well revealed by backscatter signatures, are identified in several domains of the deep sea fan, particularly within its central province, where exist evidences of important slumps and debris flows.