HR: 1330h
AN: GC32A-0206    [PDF]
TI: Identification of bottom-simulating reflectors related to gas hydrates, silicate diagenesis, and other P/T dependent sediment processes
AU: * Berndt, C
EM: cbe@soc.soton.ac.uk
AF: Challenger Division for Seafloor Processes, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: B{\"u}nz, S
EM: stefanb@ibg.uit.no
AF: Department of Geology, University of Troms{\o}, Dramsveien 201, Troms{\o}, 9037 Norway
AU: Clayton, T
EM: tc1@soc.soton.ac.uk
AF: Challenger Division for Seafloor Processes, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Mienert, J
EM: juergen@ibg.uit.no
AF: Department of Geology, University of Troms{\o}, Dramsveien 201, Troms{\o}, 9037 Norway
AU: Saunders, M R
EM: mrs@soc.soton.ac.uk
AF: Challenger Division for Seafloor Processes, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AB: Large quantities of the green-house gas methane exist in the form of gas hydrate within continental margin sediments. Bottom-simulating reflectors (BSR) are the most prominent geophysical indication for such gas hydrate reservoirs, but there are other geological processes that create similar seismic phenomena. It is therefore important to analyse the seismic character of different BSR in order to be able to distinguish between them. Three classes of BSR cross-cut the post-breakup sediments of the mid-Norwegian margin. The first class is caused by gas hydrates, which trap free gas at the base of their pressure- and temperature-dependent stability zone. The second class of BSR is caused by the diagenetic transition from opal A to opal CT. The third class is always observed underneath the opal A / opal CT transition but heat flow data and the amplitude characteristics of this event exclude one of the known silicate diagenetic transitions or gas hydrates as the explanation for this arrival. ODP Site 643 drilling results suggest two possible processes as the reason for this BSR: (a) smectite dewatering, or (b) a sudden increase in the abundance of authigenic carbonates. The genesis of both is pressure- and temperature-dependent and could potentially result in a cross-cutting seismic reflector. The data are not conclusive as to which process is causing the observed third class of BSR. Comparison of the seismic characteristics of the different types of BSR shows that apparent polarity without previously applied automatic gain control is the best way to distinguish between them, as gas hydrate related BSR have reverse polarity and the diagenetic transitions cause normal polarity BSR. On the other hand, seismic amplitude variations can be very similar for all classes of BSR.
DE: 1645 Solid Earth
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting