PROMESS 1: Past Global Changes Investigated by Drilling Mediterranean Continental Margins
Abstract
Between June, 24th and July, 22nd, 2004, a team of European scientists embarked from Brindisi (Italy) to Barcelona (Spain) onboard the Russian vessel "Bavenit", operated by the Dutch geotechnical company FUGRO, for a drilling expedition in the Adriatic Sea and the NW Mediterranean Sea. The purpose of this cruise was to collect long sediment sections and in situ measurements from two deltaic margins where the history of global changes during the last ca. 400 kyr is particularly well preserved. In the Adriatic, two boreholes were drilled at site PRAD1 (water depth 184 m), where the objective was to study the record of the last 4 glacial cycles. A pilot hole was first drilled for assessing the risk of shallow gases, a downhole logging was carried out in this borehole. A second site allowed continuous coring to the targeted depth (71m below sea-floor) with excellent recovery (better than 95%). Very preliminary interpretation indicates that seismic sequences previously identified correspond to 100 kyr glacial cycles. Downhole logging and physical properties of cores allow to identify magnetic events, and tephras. Site PRAD2 was devoted to the study of the recent most sediments (last 12,000 yrs) near the coastline, at a water depth of 56m. The targeted depth was 32 m below sea floor, sufficient to obtain a good record for the last ca 12,000 years. All together, six boreholes were drilled at PRAD2, including a pilot hole, one for continuous sediment recovery, and additional holes for in situ geotechnical tests and sampling. One of the objectives of these tests is to determine whether the wavy features shaping the sedimentary sequences are caused by near-bottom currents or result from liquefaction of unstable sediments triggered by earthquakes or storms. Site PRGL1 in the Gulf of Lion is at 298 m water depth, and the targeted depth below sea floor was 300 m, allowing to reach an expected age of about 430 kyr BP. A pilot hole was drilled down to 310 mbsf, and logged. Two geotechnical boreholes were drilled, allowing tests and measurements to a depth of 150 mbsf. Another borehole was drilled for continuous coring to the depth of 300 mbsf. The recovery was excellent (>95%). Preliminary estimations of coccolithophore assemblages provide a general time-frame for this site. Marine isotope stage (MIS) 12 was reached at the bottom of the hole. We have also good estimates of the position of the intervals corresponding to MIS 2-3, MIS 4, MIS 5a-d, and the transition between MIS 8 and 7. This shows that, as in the Adriatic Sea, seismic bounding surfaces are linked to 100 kyr cycles, that modify lithology and sedimentation rates on the upper slope. The presence of coarser sediment at the end of each "forced regression", and the occurrence of some biogenic gas, trapped by the overlying clayey sediments deposited during the ensuing warm period, is likely at the origin of seismic anomalies. Site PRGL2 is at 103 m water depth, an area where glacial shorelines that formed duringthe last ca. 500 kyr are the best preserved. A CPTU borehole was first drilled, followed by a sampling borehole, down to 100 mbsf. As expected, many sandy intervals were encountered, but the overall recovery was however quite good, in the order of 82%. Gamma ray downhole logging was performed in the drill pipe afterward. PROMESS 1 is an European Community funded project of the 5th framework programme (EVR1-2001-41). It belongs to the OMARC cluster of projects. It is a companion project of the joint Euro-US "EUROSTRATAFORM" project. The "PROMESS 1" shipboard party: S. Berne, M. Canals, A. Cattaneo, E. Colmenero, G. Floch, B. Dennielou, J. Frigola, R. Gelfort, J. Gravalosa, D. Ridente, T. Schoolmeester, N. Sultan, G. Tulloch, H.J. Wallrabe-Adams
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFMOS11D..01B
- Keywords:
-
- 3344 Paleoclimatology;
- 4219 Continental shelf processes;
- 1815 Erosion and sedimentation;
- 1600 GLOBAL CHANGE (New category)