Der Einfluß von biogenem Opal auf die Bildung seismischer Reflektoren und die Verbreitung opalreicher Sedimente auf dem Voering Plateau
The distribution of Miocene biogenic opal-rich sediments on the Voering Plateau was mapped based on six ODP- and DSDP drillsites and high resolution multichannel seismic lines. The exceptional physical properties of biogenic opal, which is a major sediment component in Miocene sediments on the Voeri...
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| Format: | Thesis |
| Language: | German |
| Published: |
1989
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| Online Access: | https://oceanrep.geomar.de/id/eprint/49890/ https://oceanrep.geomar.de/id/eprint/49890/1/Hempel%20Diss.pdf https://oceanrep.geomar.de/id/eprint/49890/3/SFB_313_14.pdf |
| Summary: | The distribution of Miocene biogenic opal-rich sediments on the Voering Plateau was mapped based on six ODP- and DSDP drillsites and high resolution multichannel seismic lines. The exceptional physical properties of biogenic opal, which is a major sediment component in Miocene sediments on the Voering Plateau, has a strong impact on the overall physical properties of these sediments: 1. The low grain density of biogenic silica and high porosity causes a low wet bulk density of the sediments. 2. A downhole lowering of the wet bulk density results in low impedance values. Contrasts of the acoustic impedance is here mainly controlled by changes in wet bulk density and to a lesser degree by sonic velocity. 3. The shift from high impedance values in the terrigenous dominated sediments above the biogenic silica-rich deposits leads to a negative reflection coefficient resulting in a prominent negative polarity reflector. Wet bulk densities and sonic velocities as measured at samples of Site 642 and 643 were used to generate synthetic seismograms, which were subsequently compared with the reflection seismic lines. For Site 644 the sonic velocities had to be calculated from a pseudo-sonic-log before a synthetic seismogram could be generated. In order to make a successful correlation between the synthetic and the reflection seismogram a precise depth- to traveltime conversion has to be established. Doing so, the laboratory measurements have to be corrected for in situ - conditions. The difference of only 8 ms TWT on a depth of 400 ms TWT is an indicator for the accuracy by which the measurements were corrected. The distribution of biogenic silica-rich sediments exhibits great thicknesses in the vicinity of the Jan Mayen Fracture Zone and the Voering Fracture Zone and an area of erosion at the Voering Plateau Escarpment until Late Pliocene. Differences in sediment thickness are more likely caused by current activity and tectonic movements, than by local productivity variations. Biogenie silica-rich sediments have a ... |
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