The influence of biogenic silica on seismic lithostratigraphy at ODP Sites 642 and 643, eastern Norwegian Sea

Abstract

Drilling at ODP Sites 642 and 643 revealed a 250 m-thick section of diatomaceous Pliocene to Miocene sediments on the outer Voring Plateau, eastern Norwegian Sea. These biogenic silica-rich sediments have a significantly lower saturated bulk density than the surrounding sediments, causing a decrease in acoustic impedance, which is seismically expressed as a negative polarity reflection. Variations in sonic velocity, the other key parameter in seismic analysis, is only of secondary importance in creating impedance contrasts in our study. Synthetic seismograms were produced from shipboard physical property measurements corrected for in situ conditions. These synthetic seismograms are in good agreement (≤6 m) with high-resolution air-gun seismic profiles shot during extensive seismic surveys on the Voring Plateau and provide the basis for correlations between the seismic record and the borehole. The ability to unambiguously identify seismic horizons associated with biogenic silica deposits on the Voring Plateau will permit the mapping of Miocene productivity patterns. -Authors