terrane models

Northern Bowen Basin Project
Data Integration

EXISTING GEOLOGICAL MAPS

The most recent geological map products for the northern Bowen Basin are 1:250,000 and 1:500,000 scale maps dating from the late 1980’s. These maps focussed on surface geology and near surface solid geological interpretation.

Since the map publications much new exploration and mining data have been acquired, including coal exploration drilling, regional seismic lines targeting coal bed methane and coal mine open pit developments. Also, the original maps focused on surface geology rather than structure. No attempts were made to classify fault types, or to check if fault interpretations are reconstructable. Therefore it was time to update these existing maps and to provide a new interpretation based on recently acquired geophysics and exploration data and the original data.

These existing maps form the basis for the new interpretation, and were used as a default during the interpretation where no new data were available.

AIRBORNE MAGNETIC SURVEY

The airborne magnetic data were processed into a variety of images, each with its specific application during the interpretation. Total magnetic intensity images, both raw and reduced-to-pole displayed with various shading algorithms proved to be the best all-round images for subsurface geology interpretation. First Vertical Derivative images of the magnetics enhance near surface features and were extensively used to map basalt flows and dykes.

The approach for the interpretation was to start with the most ‘obvious’ features on the magnetic images. These were the basalt flows, intrusive plugs and dykes, followed by a characterisation of the basement outside and underneath the Bowen Basin. The weakly magnetic Bowen Basin succession and its complex thrust structures were interpreted last with a lot of support form the other datasets.

The images were interpreted at 1:100,000 scale for 1:250,000 scale deliverables.

Details about the new airborne geophysical surveys can be found at the DNRM webpage.

AIRBORNE RADIOMETRIC SURVEY AND LANDSAT TM

The airborne radiometric data were displayed with the potassium, thorium and uranium channels as a red-green-blue composite image, which proved most useful in mapping the Late Permian stratigraphy in areas of little cover and in classifying intrusives. A Landsat TM image over the region was provided by the DNRM as a ‘natural colour’ image mostly used as a reference for terrain and culture, but also helped identifying fault scarps and prominent units such as the scarp-forming Clematis Group.

BOUGUER GRAVITY

In addition to the remotely sensed data, ground gravity data aquired at 2.5 km centres, published by Geoscience Australia were used to infer the large-scale basement geometry.

Details about the national gravity database can be found at the Geoscience Australia webpage.

The main uses for the gravity images included:

• Identification of the regional depth-to-basement structure to the Bowen and underlying Drummond Basins.

• Identification of major basement structures such as basement transfer zones that may control the position of faults and intrusives.

BOREHOLES AND SEISMIC LINES

During the 1990’s a series of 2D seismic lines were acquired across the northern Bowen Basin, targeting the Moranbah Coal Measures for coal bed methane. These data were particularly useful for depth-control on the cross sections, and for characterisation of the larger thrust faults.

In addition new open file exploration and government drilling was integrated to add depth control and visibility beneath Tertiary sediments.