Kowanyama Deep Refraction Seismic Survey

The Carpentaria Basin in the west/central portion of Cape York Peninsula is largely unexplored for petroleum, and there is an apparent ambiguity in the basement depths interpreted from gravity and aeromagnetic data. It was decided that deep seismic refraction surveys at a variety of sites should prove cost-effective in defining the geologic model for the basin. Of particular interest is the possible existence of a north-south trending elongate infrabasin inferred qualitatively from a strong gravity low shown Figure 1.

Results of the refraction work indicate that the magnetic and gravity data suggestive of the presence of an infrabasin are probably related to lithological variations within basement. Furthermore, it is improbable that the thickness of the sedimentary pile anywhere within the area of investigation exceeds 1100 metres.

Basement velocities are high, from 5500m/sec to 6200m/sec, typical of fresh igneous and/or metamorphic lithologies. Carbonates could not be totally excluded on the basis of these velocities alone, but are improbable in view of the gravity and magnetic data.

At some locations there is evidence for the presence of an intermediate section of higher velocity within the sedimentary sequence. This is thought to be quite thin, and possibly representative of the Toolebuc Formation.