Contentious Issues!
The origin of Blanchetown Clay & the riddle of the Rainbow Cliffs.
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Modern computer technology combined with earth-orbit satellite scans, have increased exponentially the tools & techniques available to geologists, to analyse & probe the Earth's crust. Resulting in a similar exponential increase in the geological data that is nowadays being collected, collated & analysed. So much so, in fact, that I fear some of the modern conclusions, re geological phenomenon relating to the greater Murray/Darling Basin, reflect a human condition that is best described as, "an inability to see the forest for the trees!" ... And! The currently popular MDBC model that depicts the lower-to-middle Pleistocene 'Lake Bungunnia' as a monstrous 33,000 sq-km permanent lake (two versions shown above), that supposedly endured for upward of a million-odd years. Is, I believe, an example of the data misinterpretation to which I refer.
Point being that the very much localised & unique stratum type, so clearly evident in the 'Rainbow Cliffs' at Devil's Elbow, has been ignored. Yet it remains an enigma that wont go away, and it sheds considerable doubt as to the true extent, and the likely nature, of the ancient 'Lake Bungunnia'; - i.e. Was it truly a 33,000 sq-km Lake, as depicted in the MDBC model, or was it for the most part a wetland irregularly flooded; because one may well ask; -
HOW IS IT POSSIBLE THAT SUCH A SINGULARLY UNIQUE STRATUM, SO CONSPICUOUSLY DIFFERENT FROM ALL THAT SURROUNDS IT AND OCCUPYING ONLY SEVERAL HECTARES, CAN EXIST IN THE VERY CENTRE OF, WHAT WE ARE BEING TOLD, WAS A 33,000 SQ-KM FRESHWATER LAKE THAT SUPPOSEDLY ENDURED FOR A MILLION-ODD YEARS?
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Another piece of 'evidence' cited to prove the existence of such a massive lake, and about which I remain extremely sceptical, is the presence of Lungfish jawbones, which easily outnumber the remains of any land based creatures detected in Sunraysia borehole samples. For anyone unfamiliar with the attributes of lungfish, this is an understandable error; - See hereunder.
Lungfish (Genera Lediposiren, Neoceratodus and Protopterus, subclass Dipnoi.) - are found in lakes & rivers of South America, Australia & central Africa, When watercourses evaporate during the dry season, some of these species are capable of burrowing into the mud where they "estivate"; i.e. they encase themself in a mucus bubble and assume a state akin to suspended animation that allows them to survive, for years if necessary, until the next flood inundates the region. ... The Lungfish that is indigenous to Australia (Neoceratodos forste Mn), otherwise known as the Queensland Lungfish, does not, can not, "estivate" and cannot survive for more than a few days out of water.
See; http://www.nativefish.asn.au/lungfish.html
The 'Australian Lungfish' will first survive in whatever water is available as the dry season commences. As other fish die around it from lack of oxygen in the diminishing water supply, this fish begins to take its air from the atmosphere exclusively. These amazing fish have been found, during a drought, surviving in small puddles of water by surfacing for air when necessary. Studies have shown that during these dormant periods the metabolism of the lungfish is greatly diminished, causing them to need very little to survive, with the exception of oxygen. Even more remarkable are the studies that have shown how some lungfish can survive for around two years under these conditions.
See; http://mama.assortment.com/lungfish_rank.htm
>>Note: Eyre Creek in flood: -
- "The floodwater is travelling at a running pace, and the creek is full of fish" - ..
The notion that Lungfish
were the dominant species in a 33,000 sq-km freshwater or saline (take your pick) lake that
is variously reported to have endured for around 1.5 million to 0.7 million years is, quite
frankly, verging on the ludicrous. ... In an environment that was/is periodically flooded
and at other times is reduced to nothing more than a labyrinth of muddy puddles, any of the
Lungfish species, including Neoceratodos forsteri (the Queensland Lungfish), would
thrive. However, the same cannot be said for gill-fish, as they would find such an environment
to be life threatening. On a "floodplain periodically flooded" it would be perfectly
logical to suppose that Lungfish, if they existed in the region at-all, WOULD BE the
dominant species.
I SUGGEST THAT THE PREDOMINANCE OF LUNGFISH REMAINS IN SUNRAYSIA BOREHOLE SAMPLES AUGMENTS THE NOTION OF A FLOODPLAIN PERIODICALLY FLOODED, RATHER THAN NOTION OF IT BEING A PERMANENT LAKE.
...
TO SEE HOW MIND-BOGGLINGLY VAST THE AREA INUNDATED BY AN AUSTRALIAN OUTBACK FLOOD CAN BE.
WE ONLY HAVE TO LOOK AT THE AREA AFFECTED BY THE 1990 FLOODING OF OUTBACK
NSW/QLD. ~~ IN THIS INSTANCE AN AREA LARGER THAN GERMANY.
... <some examples of typical 'outback' floods - click to enlarge> ...
...
I will try to explain my views:
Viewpoint re the “Rainbow Cliffs” phenomenon and the origin of Blanchetown Clay.
Blanchetown Clay: The most visible deposits of Blanchetown Clay are to be seen in the Heading Cliff/Chowilla Dam Site region where up to 15m of it lies immediately atop a widespread but discontinuous series of Pliocene/Lower Pleistocene silicified clay pans otherwise known as the “Karoonda Surface” dated at around 2-million years before present. The fact that such a breadth of essentially uncontaminated Blanchetown Clay does lie directly on top of the Karoonda Surface hereabouts is enough to convince me that it was the first fluvial deposit to be laid down upon this previously arid Pliocene/Lower Pleistocene Landscape. Also the Blanchetown Clay in this precinct is capped only by some minor calcrete and other miscellaneous conglomerate and I remain unconvinced that any permanent body of water, be it fresh or saline, has ever sat atop the Blanchetown Clay in this precinct: - This view in no way precludes the possibility, indeed the probability, that succeeding floods, over thousands of years, continued to transport the same sediment type, sourced from the same geographic location, into the greater Murray Basin floodplain, the destination of any ‘newly arrived’ Blanchetown Clay being determined by the state of the floodplain as it existed at the time.
note; Recipe for clay. I contend that just as it is when you use the same ingredients and follow the same recipe you end up with bread, no matter what oven you bake it in. -- So it is with clay; if you use a soil type of suitable molecularly structure sourced from the same, erstwhile arid, geographical location and 'hydrate' it (as in soak it in water so the soil and water can unite at a molecular level) you end up with clay, it doesn't matter whether you hydrate it in a river, a lake, a billabong, a flood, a marsh, a swamp or even a bathtub; the geographic location of the watery environment is incidental, you still end up with clay, in this instance Blanchetown Clay. I contend the raw materials required to produce Blanchetown Clay were sourced from that silicate rich swathe of country that straddles the NSW/Qld border, and that this material was carried by floodwater to any number of watery destinations, variously located south of the NSW/Qld border; and whether these watery environments, individually, endured for two months or two-hundred-thousand years, didn't matter a whole lot to the Blanchetown Clay thus formed.
The trigger that caused a dramatic influx of water-bourn sediment into the Murray Basin was a well documented global climate change that occurred at around 1.5-million years ago and which produced increased rainfall across a country that was erstwhile unaccustomed to torrential downpours. In this instance I refer particularly to that swathe of ‘silica rich’ country that stretches from Coober Peady to Lightning Ridge and central to this region is the area known as "Corner Country", wherein there exists clear and convincing evidence of widespread erosion as well as evidence of Early Pleistocene uplift in the basement rock; viz the Innamincka Dome. - At this time there would have been no clearly defined water courses worthy of mention anywhere within this region as there was no need for them. This region had, for half-a-million or more years, been an arid landscape shaped by the wind and a drainage pattern similar to what nowadays exists in south western Queensland’s "Channel Country", would have been more than adequate to cater for the conditions that prevailed at the time.
One of many examples of "clear and convincing evidence of widespread erosion". …
The ‘Jump-up’ country, Sturt National Park, "Corner Country"; far north/west NSW.
The country lying to the south and to the east of the Murray Basin was, and is, more
mountainous and/or more fertile and, by reason of its vegetation cover alone, was likely more
able to withstand erosion than the atypical "Corner Country" landscape to the north.
- Notwithstanding that the whole of the southeast quarter of the Continent was subjected to
increased rainfall at this time. I remain convinced that in the central/west portion of the
Murray Basin, for whatever the reason, the fluvial sediment invasions from the north, composed
mostly of what is nowadays dubbed "Blanchetown Clay", pre-dates the sediment invasions
from the east and from the south by a geological smidgen. –
Another less heralded lake that is nowadays suggested occupied a large area in the eastern
extremity of the Murray Basin may have had something to do with it.
Meantime, in the "Corner Country" latitudes, unprecedented rainfall caused
widespread flooding across square kilometres of silica rich countryside. As these
floodwaters gravitated to the south, they entered a "Simpson Desert" type
landscape, of Parilla Sand, wherein floodwater is customarily channelled along the
gutters that lie between the sand-ridges; i.e. exactly where any clay pans, if they
exist at-all, are to be found in such a region. And! In the manner of the
"Todd River" NT, much, if not all, of the floodwater eventually disappeared
beneath the Parilla Sand Desert without ever reaching the sea. Bearing in mind that we
are, after all, referring to that exact same region which, in the mid 1960’s, returned
a "No Gov" to the Chowilla Dam project on account of the land’s inability to
retain surface water. - The suspended sediment carried in the floodwater, however,
remained on the surface. – It would be reasonable to suppose that the NW/SE alignment
of the Parilla Sand Desert’s dunes, caused the sediment contained in the floodwater to
migrate further east than it might otherwise have done.
In due course, as the 'northern-floods' continued to inundate the Parilla Sand desert,
the sand ‘ridges’ would’ve been progressively eroded and their mass added to the
silt content of the floodwater, until the whole, more or less, resembled a ‘flat’ floodplain.
Thereafter, the ‘patches’ of Karoonda Surface, now capped with ‘pure’ Blanchtown Clay,
would likely have been better able to withstand erosion than would the ‘sandier’ tracts
of Parilla Sand that lay between them. So further erosion would result in a ‘mesa’ style
topography of flat-topped mesas, each topped with its own Karoonda/Blanchetown cap,
standing proud of the surrounding plain. At least, that is, until the several instances
of Karoonda Surfaces became undermined; then the flat-topped mesas, in all but a few
exceptions, would be reduced to the same level as the plain that surrounded them.
A notable "exception" was an expansive Karoonda/Blanchetown capped
"peninsula", or "shoulder", of high ground that jutted northward and
was conjoined to that tract of country that nowadays straddles the SA/Vic border and
includes part of the Upper Murray Mallee S.A., and the Murray-Sunset National Park in
Vic.. - Both of which, if not already, were about to be raised up on the fringe of the
Pleistocene tectonic ‘doming’ that up-lifted western Victoria and, to a lesser extent,
the Bordertown/Naracoorte region of SA. - For the sake of identification hereinafter,
I dub this peninsula/shoulder of high ground Reilly’s Promontory.
As the ‘wetter’ conditions endured, the rainfall and the flooding increased and floods now inundated the Murray Basin from every quarter. Such was the influx of water now flooding into the region that a pattern of definable water courses began to appear. Prominent among them, likely because the greatest volume of water continued to enter the basin via that route, was an early version of the River Darling, which shows-up on ‘landsat’ thermal images of the region. Wherein the ancient 'River Darling' crossed the 141ºE longitude (the SA/NSW border) in the vicinity of latter-day Menindee before arcing slowly away towards the south. To where, in a blundering attempt to find the "path of least resistance" to the sea, it pretty much obliterated all remaining traces of the Parilla Sand Desert and, in its place, created the Chowilla floodplain, through which it carved-out an ever changing, ever meandering channel. Once a channel of any description was established, however, 'Darling' floods, oftentimes of mammoth proportions, periodically carried humongous quantities of banchetown-clay-making sediment southward, depositing said sediment all over the Chowilla floodplain as well as every other floodplain it inundated, in its 'fruitless' quest to find the "path of least resistance" to the sea.
Why 'fruitless'? .. Well! Any westerly route to the sea was comprehensively
blocked by The Mount Lofty Ranges. And! Away to the south, between Swan Reach and
Murray Bridge, a lesser range of hills, running west-to-east, blocked any southerly
escape to the sea. With successive floods continuing to travel this route, it only
took a century or two for the floodwater to back-up, creating a great lake of
something like 12,000 sq-Km that extended all the way back to the Waikerie/Berri
latitudes; the so-called 'Lake Bungunnia', which endured until around
0.5-0.7 million years ago, when conditions became marginally drier and the lake's
overflow succeeded in eroding a, albeit circuitous, route through the lesser ranges
that blocked its southerly progress. Allowing for the lake to drain and the river
to eventually find its way to the sea at Encounter Bay SA..
At around this time, the outlook from atop Reilly's Promontory would have been
somewhat similar to that which can nowadays be seen from atop Heading Cliffs SA. To
be precise, a vast floodplain extending to the north and the west, or to the east,
depending on which side of The Promontory you were viewing from; a floodplain
oftentimes flooded in the manner of the 1956 flood, but at other times only
littered with lagoons, creeks, anabranches, reed beds, swamps and marshes. The
significant difference being that '1956-type' floods likely inundated the floodplain
much more frequently than any Europeans, living or deceased, have ever experienced. –
The aforementioned “floodplain oftentimes flooded” corresponds to the
greater portion of what is portrayed as a 33,000 sq-km lake called "Bungunnia"
in current MDBC models. For I consider the greater portion of this region was never
anything other than, at best, a part-time lake and question the veracity of
the popularly held notion about the 33,000 sq-km extent of "Lake Bungunnia".
What remains of the western façade of Reilly's Promontory, as viewed when looking
eastwards, across the Murray River, from the Chowilla floodplain; north of Renmark SA. -
The Karoonda Surface clearly visible as a horizontal line passing from extreme-left to
extreme-right of picture, mid-way up the cliff-face. The material below the Karoonda
Surface layer is semi-consolidated Parilla/Loxton Sand. The material above it is
Blanchetown Clay.
There is no doubt that a pre-historic "Lake Bungunnia" did exist! -- As I envisage it, however, the ancient “Lake Bungunnia” was no larger than about 12,000 sq-km, or thereabouts, as is indicated by the deposits of Bungunnia Limestone, which for the most part lie south of latitude 34°S, or a latitude that would pass in close proximity to the head of Saint Vincent’s Gulf. - Which also, judging by the typically estuarine deposits so evident in the "Bookpurnong Beds" in the Loxton district of SA., more or less, corresponds to the same portion of SA that was inundated by the most recent Southern Ocean invasion, of Pliocene times.
A pseudo dreamtime scenario re "Life atop Reilly's Promontory":
"Reilly’s Promontory”, at one time or another, would’ve extended from the Chowilla floodplain region in SA, westward to the Darling's Great Anabranch region, and north/south for perhaps 100Km, in either direction, from where the River Murray nowadays crosses the SA/NSW border. However, as its perimeter was constantly being "nibbled away at" by the perennial floods that swirled around its base, for explanation purposes, a total ‘upland’ surface area equal to Metropolitan Adelaide will suffice.
Throughout the Pleistocene, the Murray Basin plus the Basins abutting it were subjected to a somewhat hectic progression of landform and seascape reconstruction. It involved extremes of weather, volcanic activity, sea level changes, tectonic warping and uplifts coupled with earth-tremors and earthquakes, enduring snow and glaciers in the high country, plus never ending floods that churned and re-churned the landscape and, in the process, removed mind-boggling quantities of sediment ostensibly dumping much of it off the edge of the Continental Shelf into the Pleistocene ocean.
Throughout all of the above, however, life atop Reilly’s Promontory progressed at a much more leisurely pace. – If it rained, it rained; if it didn’t, it didn’t. – It didn’t make a lot of difference to life atop The Promontory. When it did rain, it didn’t worry the Blanchetown Clay at-all, the rain simply ran off and collected in a central depression where it created a little rainwater lake. Occasionally clouds of white ‘bulldust’ would blow up from the south and settle atop The Promontory giving the landscape the appearance of a snowfield. It was a bit of a nuisance at first because it got up your nose and into your eyes and ears 1 . But when the next shower of rain came along it washed most of it into the little rainwater lake and whatsoever wasn’t washed into the little rainwater lake, the rain turned into slabs of soft white stone, which were not nearly as much of a nuisance as the dust had been. The landscape atop The Promontory soon looked normal again. If, on occasions, the rainfall was too much for the little rainwater lake to hold, the excess simply trickled off the edge of The Promontory. It is said that when some bloke named Sturt saw that place he said it looked like, "falls of muddy water that had suddenly been petrified"';. In time the central depression got pretty deep, 20-metres or so deep maybe more. Some thought all that rainwater seeping through to wherever may have caused a subsidence. Still, it didn’t make a lot of difference to life atop The Promontory. Floods that swirled around the base of The Promontory continued to come and go. Some appeared to know where they were going and passed quickly whereas others had no idea and took ages to make up their mind. Not that it made any difference to life atop The Promontory.
There were other times when, far way to the south, huge clouds of grey-black smoke could be seen rising high in the sky. Someone down that way must have been lighting some pretty big fires. It was rumoured someone was trying to barbecue some old dinosaur eggs they had found and, perchance the wind was blowing from that quarter, it sure enough smelt like it 2 . But aside from being something different to gaze at it made little difference to life atop The Promontory. ... At other times the Land felt like it kind of ‘shivered’ and pretty rings of ripples would converge towards the center of the little rainwater lake. It never lasted any longer than an instant. So apart from causing some temporary excitement among the local bird life, it too was of little consequence to life atop The Promontory 3 . - Floods continued to come and go. They came in a variety of colours and sizes. Lord Knows! There were plenty of them. But they were a highly disorganized lot. If at times it started to look like there might be some pattern to their coming and going, in the blink of an eye, any semblance of a pattern would vanish. At times it was as if several together were falling over themselves in their haste to get "somewhere!" Yet, at other times, a lifetime could pass without sighting a single one.
There did come a time, however, when some of the dirty brown floodwater coming from the southeast got pretty close to overflowing the lower sections of The Promontory. Rumour had it that ice and snow in some far away mountains was starting to melt 4 . The dirty brown floodwater had been becoming more and more impatient lately. It was getting to the point where it didn’t like anything getting in its way, and it was none too happy about having to travel so far north in order to get around the northern tip of The Promontory. But coming from the southeast, as it did, that was the only way it was going to get to the ocean, so it didn’t have much choice. Nonetheless, on its way north it didn’t half vent its wrath on the eastern façade of The Promontory. Inflicting a lot of damage along that eastern side and, particularly, to The Promontory's northern extremities, as it went. And! After it had passed it left a heap of mud lying around in its wake. Right about where it had to make that sharp turn to the north, however, it did gouge out an almighty hole, like as if it had half a mind to burrow under The Promontory at that spot. - Alas! What many had foreseen as the inevitable then happened. An exceptional flood did overflow a lower section of The Promontory and the dirty brown floodwater filled the central depression, where the little rainwater lake lived, to the brim. However, by and by, the flood peak passed and the turmoil the dirty brown floodwater created atop The Promontory shortly faded. - Life atop The Promontory more or less got back to normal, though the little rainwater lake looked rather lacklustre with its lately acquired dirty brown coloured bottom.
The ‘blizzards’ of white gritty powder continued to blow up from the south much as before, and how ever much of it settled atop of The Promontory was soon washed into the little rainwater lake. If not by a series of showers, sometimes accompanied by their sometimes companion the "Rainbow Reptile". Then by a torrential downpour of the type oftentimes accompanied by great rumblings and flashing lights in the sky. Pretty soon the little rainwater lake was looking her old self again, with a spanking new ‘pristine-white’ bottom. – Then! Away down to the south someone had another go at barbecuing some ‘old & rotten’ dinosaur eggs; again! But surely it had to be a different someone because no-one could be so silly as to make that mistake twice; Could they? - Anyway! Life atop The Promontory continued pretty much as it had always been.
On the floodplain below, however, things were beginning to get seriously congested. Barely had one flood cleared the area than another one rushed in to take its place. It was becoming so that it was rare to see the floodplain in an un-flooded state anymore and, at times, it appeared as if floods were piggybacking one upon another. The principal protagonist, by far, was the dirty brown floodwater arriving from the southeast, which, of late, seemed to be increasing its mass xspeedentially with every millennium that passed. Many a time some flood or another came threateningly close to overflowing The Promontory, but the flood peak would pass and the threat pass with it. At least, for a few more millennia that’s how it was! Then things began to go horribly wrong. The dirty brown floodwater, riding atop an earlier flood, overwhelmed The Promontory and overfilled the little rainwater lake, then proceeded to a place where, for what remained of the flood peak, it cascaded off the western side of The Promontory. After that it happened again and again. In fact, it happened so often after that, that the dirty brown floodwater shortly carved out a path for itself right across the middle of the entire Promontory. Life atop The Promontory had changed. It was no longer the nice quiet place it used to be; where time stood still. Things had started to fall apart. – I don’t want to talk about it anymore!
You’ll have to go and see for yourself what happened to the little rainwater lake when the dirty brown floodwater cut the entire Promontory in half.
- More Rainbow
Cliff views. 
... 
... 
If only those dirty-brown coloured layers and white coloured
layers could speak. - I’ll bet they could tell you a thing or two!!
You get the picture?
© Peter J. REILLY; 2004 ...
pereilly@esc.net.au
- GEOLOGICAL TEXT BOOKS VARIOUSLY RECORD:-
Pleistocene Epoch; 2M to 35,000-bp: --- Holocene (also known as Recent) Epoch; 35,000 to present:
1 ...
Throughout the Pleistocene/Holocene, southern ocean levels fluctuated quite dramatically; - Why?
Well! There were some massive increases in the northern hemisphere ice mass at that time nbsp;
As recently as 18,000-bp, sea level along the SA coast is reckoned to have been as low as 90m (300-ft) below current level. South of Kangaroo Island, the drowned riverbed of The Murray can be traced to the edge of the Continental Shelf; 90m below current sea level. Backstairs Passage and Gulf St Vincent were dry land at that time. Notwithstanding that, in the southeast of SA, several lines of stranded beach dunes indicate that, during these same epochs, the sea has, at other times, stood well above the current sea level, at times attaining a level of at least 3m (10ft), and possibly 7m (25ft), above the current sea level. ... Nevertheless, whenever falling sea levels left coral and shell debris stranded, relentless wave action pounded it into a fine calcium-sand and dust, which, from time to time, southern gales whipped-up into massive dust storms and blew it far-and-wide, up to 400-Km inland, across SA. and, wherever it settled, it blanketed the landscape. In due course, the entire breadth of SA, the Nullarbor, as well as western Victoria was blanketed with the stuff. ... Some noteworthy increases in the volume of surface calcium deposited in this manner, occurred around 24,000-bp and also at around 6,000-bp. ... back2 ...
Volcanoes have shaped much of western Victoria's landscape. Over the last 4 million years an extensive volcanic plain stretched from Port Phillip Bay to Encounter Bay. It contains approximately 400 eruption sites, the 'youngest' of which last erupted about 7,500 years ago. ... More recently, like about 4,500-bp, volcanoes in southeast/SA were erupting, mostly large quantities of smoke & ash. And! Even more recently, at about 1,400-bp (600AD), volcanoes in the far southeast of South Australia were again erupting large quantities of smoke and ash. ... back
See; ... Volcanoes & Earthquakes in Oz ... Volcanoes in Victoria ... Recent Seismic History in SE-Australia3 ...
The land shook during the Pleistocene/Holocene. Apart from the tremors customarily associated with volcanic activity. Regional Tectonic Plates also moved. Incremental shifts associated with The Adelaide Geosyncline saw the Mt Lofty Ranges get taller while Gulf St Vincent got deeper. Boreholes indicate that a, once level, Miocene stratum (~ 20M-bp), is nowadays fractured and vertically out-of-line by up to 300m (1,000ft). Similar Tectonic Plate movement occurred in the Flinders Ranges and also, at around 25,000-to-20,000 bp, the Cadell Tilt Block, located downstream of the Barmah Forest, "tilted" creating what's become known as the Barmah Choke. ... back
See (again); ... Recent Seismic History in SE-Australia4 ...
The most recent southern hemisphere "ice age", if you could call it that, occurred during the Late-Pleistocene to Mid-Holocene [around 53,000-bp to 16,000-bp]. At around 53,000-bp, a period of severe glaciation occurred in the Snowy Mountains and, thereafter, at around 32,000-bp; 19,000-bp; & 16,000-bp, the NSW/Victorian highlands experienced a spate of glacier type activity. Meanwhile, Tasmania, New Zealand and South America were experiencing similar glaciation advances, indicating a general southern hemisphere climate change. ... Though local glaciers did not directly affect the Murray Basin, the associated climate change and the eventual, melt-water run-off, most certainly did. ... back
**
Pleistocene/Holocene data variously cited in Australian Geology textbooks: -
1 … Mt. Lofty Ranges progressively rose, while the Gulf St Vincent section dropped; - Boreholes indicate that a once level Miocene stratum ~ (20M-bp), is now fractured and vertically out-of-line by up to 300m (1,000ft). ... There is a discernable ancient valley that traverses the Mt Lofty Range in the Morgan to Port Broughton latitudes. It is speculated that an ancient Murray used to flow through this valley to a river mouth near Port Broughton, where seabed sediment indicates a major river delta, at one time, existed.
2 ... There is not doubt that, at some time or other, the ancient Murray had its westward meandering blocked by the rising Mt Lofty Ranges and was forced to flow southward, where its path was again blocked by the high ground associated with the Marmon-Jabuk Range located in the Bow Hill/Purnong region. ... This caused the water to 'back-up' to around the Waikerie/Berri latitudes creating a, somewhat large, prehistoric lake, named "Lake Bungunnia", which endured until around 500,000-bp when the lake's overflow eventually eroded a path through the high ground and cut a channel to the sea.
3 ... Stranded beach dunes in South-East SA, indicate that the sea has recently stood at least 3m (10ft), and possibly 7m (25ft) above the present level.
4 ... The most recent southern hemisphere "ice age", if you could
call it that, occurred during the Late-Pleistocene to Mid-Holocene [around
53,000-bp to 16,000-bp]. At around 53,000-bp, a period of severe glaciation
occurred in the Snowy Mountains and, thereafter, at around 32,000-bp;
19,000-bp; & 16,000-bp, the NSW/Victorian highlands experienced a spate of
glacier type activity. Meanwhile, Tasmania, New Zealand and South America were
experiencing similar glaciation advances, indicating a general
southern hemisphere climate change. ... Though local glaciers did not directly
affect the Murray Basin, the associated climate change and the eventual,
melt-water run-off, most certainly did.
Contd…/ ** Holocene Epoch; 35,000-bp to present - (otherwise known as Recent Epoch):
24,000-bp... Local sea levels are dropping. Strong windy conditions prevail and wild seas pound the lately stranded coral & shell debris pulverising it into a fine sand/grit. Calcium sand 'sandstorms' are blown far and wide across the land.
18,000-bp... Start of a local arid spell and a re-increase in northern hemisphere ice mass. Sea levels locally are as low as 90m (300ft) below our present-day level.
12,000-bp... Glacial thaw occurs but conditions still cooler than at present. Meteorological conditions generating severe wet/dry cycles.
10,000-bp... Minor ice age occurs about now, but locally seas are rising.
6,000-bp... Arid thermal maximum: - Large deposits of gypsum are formed at this time. As gypsum molecules contain an atom of sulphur (CaSO4 2H2O), it suggests the presence of sulphur gasses in the local atmosphere. The likeliest source of Sulphur gasses in the atmosphere being from volcanic emission of Sulphur Dioxide & Hydrogen Sulphide, not necessarily lava eruption.
3,000-bp... Seas 3-7m (10-23ft) higher than at present: - A fjord of the Southern Ocean extends up the Murray Valley, as far upstream as Waikerie. The countryside south of the Padthaway Ridge is inundated by the sea. ~ ~ In what is nowadays the North-West Bend region, a freshwater flood rose to 12m (40ft) above what we currently regard as normal river-level; i.e. 9m above the sea level that existed at that time.
END.