HR: 0800h
AN: OS21B-1523    [Abstracts]
TI: Internal waves shape the upper Israeli continental slope
AU: * Huebscher, C P
EM: huebscher@dkrz.de
AF: Institut fuer Geophysik, Universitaet Hamburg, Bundesstrasse 55, Hamburg, HH 20146 Germany
AU: Graumann, S
EM: graumann@dkrz.de
AF: Institut fuer Geophysik, Universitaet Hamburg, Bundesstrasse 55, Hamburg, HH 20146 Germany
AU: Graumann, S
EM: graumann@dkrz.de
AF: Geologisch-Palaeontologisches Institut, Universitaet Hamburg, Bundesstrasse 55, Hamburg, HH 20146 Germany
AU: Hall, J K
EM: jkh1@012.net.il
AF: Geological Survey, 30 Malkhei Yisrael St., Jerusalem, 95501 Israel
AU: Paetzold, J
EM: juergen.paetzold@uni-bremen.de
AF: Fachbereich 5 - Geowissenschaften Universitaet Bremen, Klagenfurter Strasse, Bremen, HB 28359 Germany
AU: Quadfasel, D
EM: quadfasel@ifm.uni-hamburg.de
AF: Institut fuer Meereskunde, Universitaet Hamburg, Bundesstrasse 53, Hamburg, HH 20146 Germany
AU: Betzler, C
EM: betzler@geowiss.uni-hamburg.de
AF: Geologisch-Palaeontologisches Institut, Universitaet Hamburg, Bundesstrasse 55, Hamburg, HH 20146 Germany
AU: Sade, A
EM: portolan@zahav.net.il
AF: Geological Survey, 30 Malkhei Yisrael St., Jerusalem, 95501 Israel
AB: Digital sediment sub-bottom profiler data (PARASOUND system) from the Israeli continental shelf and slope show an upper sediment wave field (SWF) in water depths of 80-140 m and a lower SWF between 190 and 350 m between Gaza and Haifa of more than 100 km length. Both SWFs reveal thicknesses of up to 16 m and a width of more than 5 km. The wave amplitudes are up to 4 m. The apparent wave length of the upper SWF varies between 560 to 570 m and that of the lower SWF between 390 and 420 m. An erosive or winnowed 2.5 km wide zone with reduced sediment thickness and little or no internal stratification occurs between 140 m and 190 m between the SWFs and parallels the bathymetric contours. The PARASOUND data show that the sediment waves grow and migrate slightly upslope. A swath sounder survey confirmed that the ridge crests strike parallel to the trend of the outer shelf. The striking direction proves that the causative current arrives from the west and that the waves are not a consequence of, for instance, a contour parallel current. The depth ranges of both SWFs and the erosive zone correspond very well with the depth of different modes of internal waves, which have been calculated from CTD-data. Therefore we interpret the erosive zone as a surf zone where internal waves break. The SWFs are considered to be caused by the internal waves as well. The bases of the sediment waves and the erosive zone between them is represented by a thin and seismically transparent veneer. We determined the AMS 14C age of this veneer, and consequently the age of the base of the SWF, from a sediment (gravity) core. The calculated age of the veneer is 9500 yr, which was after the melt water pulse mwp-1b. The sea-level rise is documented in the upslope shift of the surf zone and the deposition of the sediment waves, respectively. The transparent veneer at the base of the recent SWFs is considered as a transgressive veneer which consists of remobilized sediment. The Holocene SWFs are underlain by an up to 40 m thick sequence which also reveals a wavy reflection pattern. The top of the Late-Pleistocene sequence is erosionally truncated between 160 and 320 m. Since this sequence was deposited during the Late-Pleistocene eustatic sea-level fall of about 110 m, the erosion reflects the downward shift of the surf zone during the sea-level drop. We conclude that the generation of SWFs and the dividing surf zone occurred not only in the Holocene, but at least also during the Late-Pleistocene. It is a reasonable assumption that all resolved unconformities represent transgression phases and glacial-interglacial transitions. Since the sequence beneath the Late-Pleistocene also reveals wavy sediments, and the unconformity between is also erosional, the data presented here trace the impact of internal waves on the sedimentary growth pattern backwards in time.
DE: 3022 Marine sediments: processes and transport
DE: 3025 Marine seismics (0935, 7294)
DE: 4243 Marginal and semi-enclosed seas
DE: 4544 Internal and inertial waves
DE: 4546 Nearshore processes
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005