Application to Great Artesian Basin, Australia

© Tas Walker  May 05

Does the model work in practice?

Now that the biblical model has been developed we are in a position to classify rocks in the field. Every rock formation on Earth can be classified somewhere within the biblical model because the model covers the entire geological history of the planet from its initial creation to the present time. Classification will be achieved using a process of elimination based on criteria relevant to the biblical model and the geological structure under consideration. It is important to treat a range of characteristics rather than one characteristic in isolation.

The rocks of the Great Artesian Basin, Australia, have attributes which, you will see, make them easy to classify within the biblical geological framework. You need to be familiar with the biblical geological model, its classification criteria, and the characteristics of different phases to appreciate the following discussion. The topics considered are:

Scale

We first consider the physical size of the Great Artesian Basin which, as can be seen from the figure, is immense. Together with some associated peripheral basins it covers a significant portion of the Australian continent and is, indeed, the largest artesian basin of its kind in the world.

Artesian water is held under pressure in porous sandstone aquifers capped by impervious shale beds. When a drill penetrates the shale hot artesian water flows to the surface in great quantities. The aquifer sandstones can be traced across the basin from the eastern margin where they are exposed. In the deeper parts they are more than 2000 m below the surface. The stratigraphic units comprising the Great Artesian Basin sit conformably upon each other but the whole sequence is bounded below and above by unconformities.

The huge size of the basin limits the possible times when the sediments could have been deposited. The Creation event is one time when large scale structures would be anticipated, particularly during the Formative stage as the Lost-World continents emerged from the sea on Day 3. The Inundatory stage of the Flood is another time when the basin could have been deposited as the waters rose to flood the whole Earth. Continental scale structures could also be anticipated during the early Recessive stage of the Flood event (the Abative phase) but deposition would be anticipated at the edges of the continent as water flowed off the land in sheets.

A structure the size of the Great Artesian Basin would not form during the Dispersive phase of the Flood because the volume of water, although considerable, would deposit sediment in regional and local scale watercourses. Finally, we would not expect a structure the size of the Great Artesian Basin to be deposited during the Lost-World or New-World eras. Geological processes were too feeble for the short time available.

Fossils

The presence of fossils further constrains where the rocks fit the biblical model. Vast coal deposits testify enormous quantities of plant material including leaves, wood, pollen, spores and microspores. Species identified include liverworts, lycopods, horsetails, ferns, cycads and conifers. Many other fossils have been reported including foraminifers, dinoflagellates, acritarchs, bryozoa, brachiopods, marine and freshwater bivalves, gastropods, scaphopods, ammonites, belemnites, crustacea, starfish, fish, shark teeth, turtles, and jaw fragments of the labyrinthodont.

Because fossils are present we can rule out the entire Creation event since life had not been created. (Only tiny marine planktonic organisms would be anticipated for the Biotic phase, not the diverse range of creatures actually present.) What remains is the Inundatory stage and the Abative phase of the Flood event.

Footprints

Fossil footprints are significant and strongly constrain the timing of the Great Artesian Basin. Series of dinosaur footprints, some up to 50 cm long, have been found toward the base of the stratigraphy in a number of coal mines in the Walloon Coal Measures west of Brisbane. The impressions are located underground on the tops of the coal seams, in-filled with shale and revealed after the seam has been mined. The majority are of three-toed bipedal dinosaurs and often contain claw marks. A much smaller broad four-toed single footprint has also been reported.

Well-preserved dinosaur footprints are also reported toward the top of the stratigraphic sequence in the Winton Formation at Lark Quarry, a site 120 km south-west of Winton in central Queensland. Excavations in 1976 by a large labour force of volunteers revealed several thousand footprints representing the trackways of over 100 bipedal dinosaurs, many apparently no bigger than chickens.

The presence of footprints of live animals is important because it rules out the Recessive stage of the Flood event. After the Flood peaked the Bible records that "Everything on dry land that had the breath of life in its nostrils died" (Genesis 7:22). Dead animals do not produce footprints. The Great Artesian Basin must therefore have been deposited during the Inundatory stage of the Flood.

Disturbance

The sediments which comprise the Great Artesian Basin display only minimal disturbance and are characterised by gentle dips. Unusually steep dips are related either to disruption caused by emplacement of later intrusives or to post-depositional normal faults generally along old fault planes. Being undeformed and subhorizontal it is relatively easy to correlate distinctive strata across the majority of the structure. Minimal disturbance favours deposition late in the Flood when crustal movements were in decline after peaking in the early phases of the event after the breaking up of the fountains of the deep. Minimal disturbance makes the Eruptive stage of the Flood implausible. Deposition during the Ascending phase is possible but less likely. With the Recessive stage eliminated by the presence of fossil footprints, the latest possible time when the basin could have been deposited is the Zenithic phase.

Erosion

For sediments deposited during the Zenithic phase of the Flood, post-depositional erosion can provide clues to the relative timing. Conspicuous erosion over very large areas of the Great Artesian Basin following deposition is a characteristic that has drawn comment from numerous quarters. It is evident that after the rocks were deposited the sea retreated and the land surface was extensively beveled and deeply weathered.

The effect of this erosion is illustrated in the adjacent cross-section of the Great Artesian Basin. At the edges of the basin, and to the east of centre where the strata have been pushed up, it can be seen that the stratigraphy is eroded to form the present land surface. (Because of the large vertical exaggeration the angle at which the strata are cut is distorted in the figure. In reality the angle of intersection of the land surface is very small.) Material has been removed in large sheets across the whole landscape. In the western and central parts of the basin the uppermost Winton Formation shows evidence of widespread sheet erosion. The quantity of material removed is unknown. In the Brisbane area to the east, erosion has exposed the lower parts of the structure, with the removal of more than 1000 m of material. Here erosion is confined in area but extends deeper.

Such beveling of the Great Artesian Basin is consistent with erosion of sediments by the receding Flood waters. Initially, during the Abative phase, erosion would occur in broad, flat sheets, as is preserved in the western and central part of cross-section. Later, during the Dispersive phase as the volume of water gradually decreased, erosion was confined to the established channels. One such channel is seen in the eastern part of the cross-section between Toowoomba and Brisbane where the Brisbane River now flows in a wide deep valley. Cut during the Dispersive phase such watercourses form the valleys for the drainage systems that exist today.

Because the structure has been so eroded it could not have been deposited during the Abative or Dispersive phases. Sediments deposited during these phases were not exposed to widespread erosion by receding Flood waters. Erosion also indicates that the top of the Zenithic phase is not preserved, at least not in those sediments which are eroded. Deposition could have occurred early in the Zenithic phase or perhaps during the Ascending phase. The erosion characteristics observed are not consistent with deposition during the Eruptive phase.

Flat Topped Landforms

Another consequence of the erosive patterns associated with the Recessive stage of the Flood is the formation of flat-topped structures such as plateaus, mesas and buttes at the same stratigraphic level where sediment bedding has remained essentially horizontal.

Almost perfectly flat landforms with horizontal to sub-horizontal bedding are reported on the Great Artesian Basin in the Surat Basin area where the thickest part of the sequence is preserved. It is significant that these residuals form the high divide between major river systems. In areas where the flat-topped mantle of deeply-weathered material has been stripped away, a rolling downs topography has developed.

The presence of flat-topped landforms in the Surat Basin area suggests that these surfaces represent the very top of the Zenithic phase. Elsewhere on the Great Artesian Basin the uppermost sediments of the sequence have been eroded by the receding Flood water to reveal earlier deposited strata, forming a gently undulating rolling downs topography.

Summary

The fact that the Great Artesian Basin is of continental scale restricts its timing to the Creation or Flood event. However the Creation event is eliminated by the presence of fossilised plants and animals. The Recessive phase of the Flood event is eliminated because dinosaur footprints are found in a number of locations within the strata forming the basin. This leaves the three Inundatory phases from which to select, the Eruptive, Ascending and Zenithic.

Because the structure has only experienced minimal disturbance, deposition must have occurred when crustal movement was in decline late in the Inundatory stage. This means the Zenithic phase or perhaps the Ascending phase. The presence of significant post-depositional erosion over the surface of the structure similarly indicates deposition late in the Inundatory stage. Those parts of the structure which remain after erosion could not have been deposited at the very top of the Zenithic phase. However, the presence of flat-topped landforms, such as plateaus, mesas and buttes in the thickest part of the sequence, the Surat Basin area, suggests the flat-topped land surface represents the very top of the Zenithic phase.

We conclude therefore that the uppermost strata of the Great Artesian sequence fit at the top of the Zenithic phase. The remainder of the structure would have been deposited earlier during the Zenithic phase.

Comments

I think you will agree that the Great Artesian Basin was relatively easy to classify within the biblical geological model. The goodness of fit reflected in the harmony between the various classification criteria is remarkable and heartening.

Personally, I was surprised that the Great Artesian Basin fits the Inundatory stage. I anticipated a significant portion of the geology of Australia to have been deposited after the Flood peak during the Recessive stage. However, the finding that the Great Artesian Basin fits to the top of the Inundatory stage means that most of the geology of the continent of Australia was deposited before the Flood reached its peak.

It is of interest that on the standard geological column the Great Artesian Basin is classified from early Jurassic to late Cretaceous. This model provides a simple explanation for the extinction of the dinosaurs at the end of the Cretaceous. They were destroyed when the Flood reached its peak and covered the whole earth.

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