Basalt flows around Carnarvon Gorge, Central Queensland, erupted under water

posted in: Landscapes | 1
Geological map showing Tertiary basalt from area just north of Carnarvon Gorge
Geological map showing Tertiary basalt from area just north of Carnarvon Gorge. Width of map ~38 km.
The Consuelo Tableland to the north of Carnarvon Gorge would have been one of the first areas of land to emerge in Queensland as the waters of Noah’s Flood were receding from Australia. A rough calculation shows it would have been at least 224 days after the Flood began before the tableland emerged. The receding floodwaters carved the remarkable landscape around the tableland, including Carnarvon Gorge, when they drained from the land as the tableland emerged.

One prominent feature of the Consuelo Tableland is that it is capped by flows of basalt lava, which accumulated to as much as 300 metres thick in places. This basalt initially covered a much larger geographical area, but has been extensively eroded until, in many places, only remnants remain.

The above geological map illustrates these features. It shows portion of the geology of the Consuelo Tableland and surrounds, just north of Carnarvon Gorge.1 The basalt cap is coloured pink (and labelled Tb for Tertiary basalt). The figure illustrates the degree to which erosion has removed the basalt cap and cut into the underlying sandstone strata, which are coloured blue.

The Flood scenario outlined above suggests that the basalt flows were erupted while the landscape was under water, after considerable erosion (mainly in wide sheets) had already occurred. Is there any indication in the geological literature that the basalt erupted underwater?

When we check the geological reports for the area we see that the basalt has been interpreted as being deposited in a terrestrial environment.2,3,4,5 One report describes the basalt as being “extruded subaerially”6 while another describes it as being “submarine”.5 Many of the basalt flows have been described as “deeply weathered”,8 which means they have been chemically altered to produce a soil-like friable layer on their surface.

Geological reports for the area describe the basalts as being interbedded with Tertiary sediments,9 sediments that are described as pebbly sandstone, shale, and conglomerate. The interfingering of these sediments with the basalt is certainly consistent with deposition while there was much water flowing around. The environment of deposition of the Tertiary sediments has been interpreted as fluvial (flowing water) and lacustrine (still water, like a lake).10

In one report11 the interbeds are described as of friable sandstone from 60 to 120 cm thick. The sand is medium to fine-grained and composed of feldspar grains, rather than quartz. (Feldspar would tend to weather to clay if exposed to the elements for a long period of time.) The sandstone interbeds are commonly weathered and strongly stained by brown iron minerals. In places the interbeds have been metamorphosed by the overlying basalt. In the notes for Taroom sheet12 the sandstone interbeds are described as commonly from 2 to 4 feet (60 to 120 cm) thick. No fossils have been found in the beds.

Interestingly, the notes for the Taroom sheet12 describe the basalt a occupying a large valley in the underlying Hutton Sandstone. This is consistent with the basalt flows occurring after a significant amount of erosion has already occurred, erosion that involved wide flowing sheets of water, producing the “large valley” the notes describe.

The presence of these interbeds in the basalt caps, the nature of the sediments, and the ‘weathering’ of the basalt are clues that fit with the idea that the basalt was extruded under water. Biblical geologists Woodmorappe and Oard concluded a similar depositional environment for the Columbia River Basalt province in north-west USA (see Field studies in Field studies in the Columbia River basalt, Northwest USA). There is a need to carry out field investigations into the basalt flows in central Queensland looking for similar tell-tale evidence for underwater deposition.

References and Notes

  1. From: Springsure SG/55–3 Geological Sheet, Australia 1:250,000 Geological Series, Bureau of Mineral Resources, Canberra, 1967. Available free from Geoscience Australia. (

  2. Mollen, R.G., 1:250,000 Geological Series—Explanatory Notes Springsure, Queensland, Sheet SG/55–3, Bureau of Mineral Resources, Canberra, 1972.

  3. Mollen, R.G., et al., Geology of the Eddystone, Taroom, and Western Part of the Mundubbera Sheet Areas, Queensland, Report 142, Bureau of Mineral Resources, Canberra, 1972.

  4. Exon, N.F., 1:250,000 Geological Series—Explanatory Notes Eddystone, Queensland, Sheet SG/55–7, Bureau of Mineral Resources, Canberra, 1968.

  5. Forbes, V.R., 1:250,000 Geological Series—Explanatory Notes Taroom, Queensland, Sheet SG/55–8, Bureau of Mineral Resources, Canberra, 1968.

  6. Mollen, ref. 2, p. 10. I suspect that the “subaerial” interpretation is incorrect and that further field work should reveal evidence for submarine emplacement.

  7. Exon, ref. 4, p. 10.

  8. Mollen, et al., ref. 3, p. 72.

  9. E.g., Exon, ref. 4, Table 3 opposite p. 10.

  10. Mollen, ref. 2, Table 4.

  11. Mollen et al., ref. 3, p. 73.

  12. Forbes, ref. 5, p. 10.

  1. Jon O'Brien

    Great article Tas! Very interesting. I will have a look at the other recent articles also.