The North West Shelf of Australia is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the Northwest Shelf. Porosity data is used to assess the effect of facies related porosity changes onto the creation of seismic reflections. Generally, porosity values are high (~60%) where sediments are composed of fine-grained aragonite needle mud whereas bioclastic or non-skeletal grain rich sediments display lower porosities (40-50%). In effect, strong acoustic impedance contrasts are observed wherever facies changes into fine-grained aragonite mud. This agrees with observations in seismic, which reveal the occurrence of strong seismic reflections wherever larger facies changes occur.

Porosity was determined on discrete samples on shipboard during Expedition 356. Selected samples where saturated with seawater and subsequently tried to determine wet and dry weight and volume. Based on these parameters porosity was calculated.