The geology of south-west Western Australia is characterized by exposed continental cratons, thick sedimentary deposits, vertical crustal tectonics, and widespread erosion. The timing of these features can be connected to the sequence of hydraulic and tectonic processes that occurred during the biblical Flood. The period during which the waters of Noah’s Flood were rising on the earth was marked by widespread deposition of thick sediments across the continent. The following period, when the waters of the Flood receded into the newly forming oceans, was dominated by erosion that planed kilometres of sediment from the cratons. The transition between these two periods was marked by vertical tectonics, initiating the opening of the Indian Ocean, the uplift of the continent, and the return of the floodwaters into the sea. This Flood interpretation was facilitated by connecting the processes identified in a biblical geological model with published geological cross-sections and other geological data for the region.
In order to interpret the geology of any area of the earth, it is necessary to begin with a geological model that connects the events and processes of the past with the present geology. We will interpret the geology of south-west Western Australia from a biblical perspective using the biblical geological model published in 1994 at the International Conference on Creationism (figure 1).1 This area of Western Australia is particularly interesting geologically because of the geographical association of Precambrian cratons with Paleozoic and Mesozoic sedimentation.
The biblical geological model was developed by examining the events of biblical history and envisaging which were significant for the earth’s geology. Then, the processes operating at each of these geologically significant periods were considered in order to decide what geological characteristics could be expected as a result. Once we have the model, the next step to make an interpretation is to gather the relevant geological information. These days there is a wealth of information available for most areas of interest on the globe.
Figure 2 shows some of the main geologic regions of south-west Western Australia. The geology of the south west is dominated by the Yilgarn Craton, which extends some 800 km to the east, and 1,000 km from north to south. The craton is composed predominantly of crystalline rocks such as granite and gneiss, but with sub-linear (almost-linear) belts of other metamorphosed rocks including rich gold-bearing greenstone belts.
Current ideas hold that the craton assembled from a number of huge, broken ‘blocks’, or terranes, of crust that were sheared, metamorphosed, pushed around the earth, and accreted together.2 Over the last few decades, ideas on the timing of this accretion have changed. In the 1980s it was considered that massive granitic intrusions welded the terranes into a stable ‘fixed’ craton early in earth history (3 Ga ago in evolutionary worldview).3 More recently models have had a more plate-tectonic emphasis with the terranes accreting over a much longer period.4 In this assessment we are looking at the relative timing of the geological units, and the model of the way the craton formed does not affect this.
West of the Yilgarn Craton is the Perth Basin which extends some 700 km north-south along the coast and onshore (figure 3). Offshore it extends even further, a total distance of some 1,300 km along the edge of the continent. The Perth Basin is separated from the Yilgarn Craton by the Darling Fault.
Geological maps, especially the standard 1:250,000 series, with their interpreted geological cross-sections, provide an excellent tool for visualizing the big-picture overview to the geology of an area, allowing it to be interpreted within a biblical framework.5 The Perth 1:250,000 scale geological map6 includes two geological sections along the section lines shown in figure 3. The first, labelled A–B (figure 4), runs across the Perth Basin and the second, labelled C–D (figure 5), runs across the west side of the Yilgarn Craton.
We will begin with section C–D which displays the older rocks in the region. The section is about 92 km long and shows a depth of 17 km (figure 5). The vertical and horizontal scales are the same. The left (west) side of the section begins some 45 km north-north-west of Perth, toward the edge of the Yilgarn Craton, and the section runs from west to east. None of the later-deposited Perth Basin is shown on this section. The figure is looking toward the north. All the rock units shown on the section have been classified as Archaean. The cross-section shows graphically how the rocks of the craton are discontinuous and the degree to which they have been folded, upended, sheared, and fragmented. It also illustrates that the top of the craton has been eroded and the portion above the ground surface has been removed. This has left the sub-horizontal (almost-horizontal) land surface, as if the rocks have been cut horizontally at the ground.
Section A–B across the Perth Basin (figure 4) is about 80 km long. Like the first section, it shows a depth of 17 km, has the same vertical and horizontal scales, and is looking to the north. The left (west) side of the section begins in the ocean some 43 km west of Perth and runs to the east-north-east, ending about 37 km inland. The coastline is about halfway along the section (marked).
In contrast with the Yilgarn Craton, the Perth Basin is dominated by thick layers of sub-horizontal sediments. The arrangement of the layers suggests the sediments once formed a continuous horizontal deposit but were subsequently fractured and moved vertically (up and down) by near-vertical faults. These faults are clearly marked on the section, and extend into the ‘basement’ which is considered to be a downfaulted extension of the Archaean Yilgarn Craton.
Of particular interest is that these horizontal sediments terminate abruptly at the east (right) side of the section against the Darling Fault (labelled Darling Fault Zone on the section). The rocks of the basement to the west (left) of the fault are labelled as Archaean, which are the same ‘age’ as the rocks of the Yilgarn Craton to the east (right) of the fault. The detailed geology of the basement beneath the thick horizontal sediments ocean is not known so it is simply shown as undifferentiated Archaean. From the section it is clear that movement on the fault has lowered the rocks to the west (left) of the Darling Fault by some 15 km.
Beginning at the continental surface
Interpretation involves linking a historical event described in the Bible with a physical location on the ground. An obvious and unambiguous place to start is the time when the whole world was covered with water (Genesis 7:20). This occurred at around Day 150 of the Flood. So we can begin our interpretation of the geological section by envisaging a sea level sufficiently high to cover the entire section.
Computer simulations into the effects of higher sea levels on ocean circulation patterns show that the earth’s rotation would generate circulating currents above the flooded continents.7 Some simulations indicated flow velocities ranging from 40–80 m/s, while others suggested lower velocities in the mid-20 m/s range.8Such high-velocity circulating currents are enough to achieve water cavitation which would rapidly erode the land surface. It is possible that the surface at the top of the geological section has been eroded by such circulating flows, although it is unknown whether such circulating cells would have been established over this part of Western Australia.
After reaching their peak, the floodwaters covering the continents began to recede, and continued to do so for seven months until the earth was dry (Genesis 8:14). Initially the waters would have receded in wide, continuous sheets, and these also would have eroded the surface of the continents, producing wide, flat areas. We would expect the direction of water flow would be perpendicular to the present coastline, although this direction would have been affected by any large-scale topography, including the shape of the coastline, as well as by any circulating cells above the land. This flow of water over the surface of the continent toward the coast would likely have been along the sections flowing from east to west (right to left).
Flat horizons have been produced by water erosion at earlier times during the energetic Eruptive and Ascending phases of the Flood, before the waters covered the earth. These erosional surfaces are usually evident on geological sections, such as the contact between the Archaean basement and the thick horizontal sediments in figure 4.
The most helpful large-scale erosion surface for establishing the interpretive link is the current land surface formed during the Recessive Stage of the Flood, when floodwaters receded into the oceans, eroding the landscape. It is widely recognized that an incredible thickness of rock material has been eroded from the continental surface all over the world.9 Geologists of the nineteenth century called this process a period of denudation.10 A well-known area that exhibits such a flat erosional surface is the area around the Grand Canyon, and it has been called the Great Denudation.11 In trying to explain these flat erosion surfaces without the global Flood, uniformitarians have invoked a concept of a peneplain, the final stage of a hypothetical landscape erosion cycle, developed by W.M. Davies, that is now largely discounted.12 However, such flat erosion surfaces are expected from and explained by the Recessive Stage of the Flood.13
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