Biogenic gas in deltaic sediments, Moreton Bay, Queensland

Abstract

High resolution seismic profiling records of the Brisbane River delta show a seismic character that is opaque in places. This seismic character is thought to be caused by the presence of interstitial gas. The gas presence is classified into two zones according to position of the upper gas interface in the seismic record and the opacity of the section. The distribution of gas has been mapped and appears to align with palaeochannels of the Brisbane River formed during the last Glacial sea level low about 18 000 yr BP. The seismic character of the gas-charged sediments is similar to Postglacial gas-charged sediments investigated elsewhere in Australia and overseas. It is considered that the Brisbane River delta gas results from biogenic decomposition of organic matter accumulated in palaeotopographic lows during the Postglacial marine transgression. More research is necessary to determine the exact nature of the gas.