Landscape around Carnarvon Gorge was eroded in sheets by retreating floodwaters

Carnarvon Gorge sits at the junction of two major sedimentary basins, the Surat and Bowen basins. This is illustrated in the geological section to the left¹ which looks to the north west and cuts through the south wall of Carnarvon Gorge just east of its entrance.

The sedimentary strata to the west (left) of the figure belong to the Surat Basin. They are almost horizontal in the field (the slopes are exaggerated in this image) and labelled with a J indicating Jurassic sediments.² These sediments comprise the inner and outer walls of Carnarvon Gorge, with the lower white cliffs of the inner gorge exposing the Precipice Sandstone (Jlp).

It’s clear that these strata once continued to the east (right) but they have been eroded away exposing the underlying sediments of the Bowen Basin. The cross-section passes through a small remnant of the basalt cap that sits on top of the plateau (coloured red and labelled Tb; Tertiary basalt). From the section we can see that, before the basalt erupted and flowed over the area, considerable landscape erosion had already taken place. After the basalt lava erupted further erosion took place dissecting the basalt cap.

The strata comprising the Bowen Basin just to the east of Carnarvon Gorge sit beneath the Surat Basin and have been folded to form an anticline (inverted U-shaped fold). These sediments have been labelled as R (for Triassic³) and P (for Permian). It’s clear from the way the anticline has been shaved off that these sediments have also been greatly eroded. Note that the member labelled Re (Clematis Sandstone) sticks up higher than the rest of the eroded sediments. We’ll talk about this in a future post about water gaps.

This massive erosion of the landscape is to be expected as the waters of the Flood were receding into the oceans. Biblical geologist, Roy Holt called this phase the ‘Erodozoic’, a term Mike Oard has also used (e.g. see figure 14 of The remarkable African Planation Surface).

Initially the retreating floodwaters would have flowed across the landscape in sheets. We can see from the cross section that this phase of erosion produced generally flat surfaces on the landscape, something that standard geological thinking does not have a satisfactory explanation for (See, It’s plain to see). Biblical geology predicts such flat surfaces.

Biblical geology is an approach that opens up many exciting research opportunities as we seek to understand the processes that took place at this time.

The section covers a width of about 16 kilometres.
From the top of the basalt to the base of the sediments shown is about 1,600 metres.
Vertical exaggeration is 4 times.

Notes

1. Geological section is from the 1:250,000 scale geological map SG 55-7 Eddystone, Bureau of Mineral Resources, Canberra, 1967. Available from Geoscience Australia.

2. The names of the Jurassic sediments are as follows (top to bottom):
   Jlh = Hutton Sandstone (Lower Jurassic)
   Jlw = Westgrove Ironstone Member (of the Evergreen Formation)
   Jlb = Boxvale Sandstone Member (of the Evergreen Formation)
   Jle = Evergreen Formation (Lower Jurassic; includes Boxvale and Westgrove members)
   Jlp = Precipice Sandstone (Lower Jurassic)

3. The symbol is actually a T and R joined together.

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