Physikalische Strukturen von Tiefseesedimenten des Südatlantiks und ihre Erfassung in Echolotregistrierungen.

Abstract

In this thesis geophysical data from two RV METEOR cruises M 6-6 (1988) and M 9-4 (1989) in the Equatorial South Atlantic was used to investigate the genesis of reflections in analogue and digital echosounder records. Analogue black-white paper records of the PARASOUND echosounder system (Krupp Atlas Elektronik) enable a qualitative description of sedimentation- and erosion processes. Three profiles from the Western African continental rise show a decreasing sharpness of the reflection pattern with increasing biogenie productivity and sedimentation rate. Echosounder records from pelagic regions like Walfish Ridge, Angola and Guinea Basin, Mid-Atlantic Ridge and Brasil Basin show clearly stratified reflection patterns, interrupted by topographie highs.Measurements of sediment physical properties on gravity cores allow to calculate synthetic seismogramms and to compare them with analogue PARASOUND echograms and digital PARASOUND seismograms. Detailled core descriptions enable to evaluate the influence of lithologie variations on the reflection patterns in the echosounder records. Acoustic properties like acoustic impedance and reflectivity are mainly controlled by P-wave velocity and wet bulk density. Therefore the dependance of these two parameters on porosity, carbonate and sand content was investigated. Physical properties allow to distinguish between five types of sediment from different depositional environments (continental rise, oceanic highs, deep-sea basins).Terrigeneous turbidite layers produce strong reflection horizons in synthetic seismograms. Smaller variations of the acoustic impedance are caused by carbonate, silt or sand content. Since the carbonate content is linked to glacial/interglacial cycles, acoustic impedance and reflection patterns can contain paleoclimatic signals.Generally there is a good correlation between the synthetic seismograms and analogue and digital PARASOUND records. Additionally, synthetic seismograms and digital echosounder signals provide some semi-quantitative information relating to the amplitudes of reflections, whereas the PARASOUND paper records alone merely shows the energy distribution with depth above a certain threshold level.