HR: 0830h
AN: T61A-01
TI: Intricate BSR and Bright Spot distribution of the Yaquina Forearc Basin, Peru
AU: * Huebscher, C P
EM: huebscher@dkrz.de
AF: University of Hamburg, Bundesstrasse 55, Hamburg, 20146 Germany
AU: Greinert, J
EM: jgreinert@geomar.de
AF: GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: Kukowski, N
EM: nina@gfz-potsdam.de
AF: GeoForschungsZentrum GFZ, Telegrafenberg, Potsdam, 14473 Germany
AU: Pecher, I A
EM: ingo@ig.utexas.edu
AF: University of Texas, 412 Spicewood Springs Rd., Bldg. 600, Austin, tx 78759-8500 United States
AU: Wagner, M
AF: University of Hamburg, Bundesstrasse 55, Hamburg, 20146 Germany
AU: Bialas, J
EM: jbialas@geomar.de
AF: GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany

AB: In order to study the interaction between BSR occurrence, gas abundance, tectonic uplift, and sedimentation in the Yaquina Basin we carried out a high-resolution reflection seismic survey in the frame of the GEOPECO project (SONNE Leg 146). The Yaquina Basin is located between 8 deg. S and 10 deg. S on the midslope of the Andean Continental Margin. This part of the Peruvian Margin has undergone tectonic uplift and, subsequently subsidence by the oblique subduction of the Nazca Ridge. The seismic lines were tied to the ODP sites of Leg 112, which allows correlation between seismic data and core stratigraphy. We used GI-Gun sources to avoid misinterpretations due to bubble generation. The most striking observations have been made at the widest part of the basin at 8 deg. 30 min. S in water depth of about 900 m. Perpendicular to the slope a bright spot changes abruptly into a weak BSR. Several disrupted bright spots are resolved some 10 ms beneath the BSR, indicating strong vertical variations in the gas content. A downslope oriented seismic line reveals a strong undulating BSR, which runs neither horizontal nor parallel to the seafloor. Upslope of this basin the BSR runs along the sea floor between water depth of app. 450 m and 600 m. Upwards and downwards the BSR is located beneath the seafloor. Further downslope the reflection characteristics change: there are strong indications of a double BSR with about 200 ms interval between them. A bubble can be excluded for interpretation. There are several indications of a relationship between tectonic and BSR occurrence. Faults act as boundaries for particular BSR related reflection pattern and as vertical migration paths. Where particular reflections crop out at the seafloor authigenic carbonate complexes (Chemoherms) of some 100 m could be discovered with a towed TV-sled and living clams (Calyptogena), tube worms (Vestimentifera) and bacterial mats could be observed. Both, carbonates and the chemoautotrophic organisms prove a recent active venting of H2S- and methane-rich fluids. The abundance of BSRs increases from south to north. It can be assumed that this is related to the increasing age of tectonic uplift, caused by the subduction of the Nazca Ridge. If the resulting uplift caused the destabilization of gas hydrates, we expect reformation of gas hydrates in the older region of this tectonic regime.

DE: 3022 Marine sediments--processes and transport
DE: 0935 Seismic methods (3025)
DE: 0999 General or miscellaneous
SC: T
MN: Fall Meeting 2000