UE Marine geophysical workshop

Degrees incorporating this pedagocial element :

Description

This field trip provides first practical experiences of the geophysical and geological methods used in marine geophysics. Especially, during this field trip, the students will board the “Thétys II” scientific vessel, a coastal vessel used for academic research and training. She is part of the French Oceanographic Fleet (CNRS-INSU/Ifremer)

The geographical region targeted during this field work is the North Ligurian continental margin, offshore Nice, French Riviera, a nice case study  of passive margin. The field work will have the students implementing the principal technics of data acquisition in Earth Sciences (with the help of the academic professors and a field technician):

-      The main principles of ship navigation and GPS positioning (GPS, navigation tracking log); 

-      Bathymetry (canyons, sedimentary levees, continental slopes, shelves,...); 

-      Implementation of multi-sensor reflection seismics, along long profiles documenting the whole Ligurian margin.  

The profiles acquired by the students will be supplemented by cross-cutting profiles document the top of the bottom of the slope, to train the students to the 3D interpretation of sedimentary bodies. Back to the classroom, the students will process and interpret the data acquired offshore, within the framework of the regional geology and of the global tectonics. 

The field trip is slightly different depending whether the students are following the “Geophysics” or the “GeoRessources/GeoDynamics” specialties. There will be different weights for the 3 parts tackled during this field trip:

 (1) Offshore data acquisition

(2) Data processing of the seismic profiles with Seismic Unix 

(3) Geological interpretation of seismic profiles 

Students majoring in geophysics will focus on data acquisition and processing. For instance, a they sail longer to perform short experiments to assess the effects of various parameters on the resolution and penetration of the recorded seismic profiles.

 Other students will focus more on the geological interpretation of the seismic profiles. They will be provided with more information on the tectono-sedimentary history of the margin. Students will find within the profiles the legacy of this history, such as the Messinian erosion surface, the discordance of the acoustic basement and of the post-rift sediments, the transgression of the upper evaporites, the deposition mode of the of the turbiditic sequence of the Quaternary (canyons and deep  cone of the Var stream), the tectonic deformation of the foot of the margin (like some salt diapirs, active faults of the foot of the margin and of the basin), the subsiding zone of the foot of the margin, and sometimes the syn-rift sequences and the tilted blocks of the Oligocene (ante-rift sequences).

The number of attendees is limited to 16 students, who be dispatched in 2 groups depend of their major specialty within the STPE master.

The students will be evaluated based on:

  1. A synthetic note to be given just after the field trip. This note will be corrected rapidly by the professors to provide sanitized reference documents.
  2. An oral exam discussing each of the 3 themes of the field trip
    1. Acquisition
    2. Data Processing
    3. Geological Interpretation

Prerequisites

Students should know already the physics of seismic waves and have basic notions of sedimentology.

The processing of the seismic data is done with « Seismic Unix » software, taught in the PAX8GPABTeaching Unit « Exploration Geophysics ». 

 All students participating to this field trip will have to classes sessions of the PAX8GRAC Teaching Unit « Basin analysis ».

Targeted skills

At the end of the field trip, students will have worked on the whole workflow of Marine Geophysics, starting from the offshore data acquisition and ending on the geological interpretation of processed profiles. They should be able to:

-      Identify the key parameters for the acquisition of a high-quality seismic profiles by choosing the right acquisition system and setting the right parameters to the seismic profiles with the expected resolution and penetration 

-      Process the data to get a high-quality seismic profiles, denoised and migrated. 

-      Identify artefacts and avoid wrong interpretation of the seismic profiles.

-      Interpret the sedimentary structures within a series of seismic profiles acquired on a 3D volume and replace these within the tectono-sedimentary history of the studies region.