Structures Revealed by High Resolution Geophysics, Offshore Egypt
Dupré, Stéphanie1, John Woodside1,
Ingo Klaucke2 (1) Vrije Universiteit, Amsterdam, Netherlands (2) IFM Geomar,
The Nile deep sea fan system presents a rich variety of fluid
escape structures, gas chimneys, pockmarks and several types of mud volcanoes.
These seep related structures were explored for the first time using the Nautile submersible during the Nautinil
expedition in 2003 and are characterized by high thermal gradients and highly
gas-saturated sediments. More recently, high resolution side scan sonar data
acquired during the Mimes expedition (2004) brings more detail to the
geophysical imagery. The EdgeTech DTS-1 deep tow
sonar was deployed around 100 m above the seafloor and operated at a frequency
of 75 kHz. In addition to the sidescan sonar sensors,
the DTS-1 contains a 2-16 kHz chirp subbottom penetrator. Several gas plumes were detected in the water
column above Isis and Amon
mud volcanoes and the Centre Nile pockmarks. These observations confirm the
intensity of the present-day activity offshore Egypt in terms of seepage
associated with gas emissions and its continuity through time. High-backscatter
patches related to these seeps have been observed in all of the explored sites.
Structures associated with mud flows, such as concentric ridges and gullies,
and subsurface carbonate crust structures were identified on numerous lines.
High variability in the backscattering observed at most of the sites greatly
assists post-processing interpretation, e.g. seafloor geological mapping. The
high-resolution DTS1 data provide the possibility to identify and map fluid
emission areas associated with different types of lithology,
mud flows, carbonate crust and gas plumes when the
backscatter signal is calibrated with in-situ observations.