Flinders Ranges; Fossils

Friday, Apr 27, 2012 at 09:00

MEMBER - Darian, SA

ExplorOz members interested in fossils may find the following of use when visiting the Flinders Ranges National Park in South Australia. Fossils abound in these ranges, but it seems that the location of most are known by relatively few people. My wife and I recently located a few and thought I’d simply share that experience here. Most of the objects I have noted in this blog were learned of via information on websites, books and leaflets, interpretive signage and then found by trekking the ground (with a camera, notebook and GPS in hand). Note that the objects I have seen were all discovered years ago, probably by scientific professionals in the main: I’m simply mentioning the exact locations of specific instances, as I know them. Most locations noted here are identified with GPS coordinates, as: degrees, minutes, seconds (to one decimal): and the datum is WGS 84.
Disclaimer (you knew there had to be one :-o): Information provided here is in ‘good faith’ and as I have understood, or interpreted it from a variety of sources. I cannot personally vouch for any of the scientifically orientated details regarding the geology, the timeframes or the identity of the fossils (but they really are there :-o). Please let me know of any errors or significant omissions you may notice in this text.
Thanks to David and Michelle at Exploroz, for the use of this great blog facility. Click on any of the photographs, for a larger view.
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Part A
Cambrian Period – Marine Fossils (Archaeocyatha)
BRACHINA GORGE (and Wilkawillina Gorge)
At the western entrance to Brachina Gorge, there is an excellent interpretive facility at the lookout – a number of graphic displays explain the geology of the ranges. This lookout is at: S 31, 20, 16.3 // E 138, 31, 48.7
Of particular interest to me are the approximately 550M year old Archaeocyatha fossils found in the Wilkawillina limestone outcrops that occur in several places in the Brachina creekbed. These lifeforms were first identified by the famous South Australian born geologist, Reg Sprigg and are among the very earliest fossils of any kind found anywhere on earth (the earliest lifeforms to have a ‘skeleton’).
Note: Reg actually found even earlier fossils (Ediacarans; possibly THE earliest anywhere) on nearby Nilpena station back in the 1940’s, but access for the public is prohibited due to their world importance (and black market value). Examples can be seen in the SA Museum; there is also a good permanent display of actual fossils just outside the Parachilna Pub (3 pics. just below).


Driving east into the gorge from the lookout, the first outcrop I located was at: GPS S 31, 20, 10.4 // E 138, 32, 18.3 The fossils are generally in evidence in these 3 large sections of rock (see the left photograph, below), but they do need to be searched for.



Around on the north eastern side of the largest rock section is a small darker grey segment, jam packed with the fossils (see the centre photograph, above).

Further east along the gorge, there is a smaller outcrop (see the right photograph, above) at GPS: S 31, 20, 16.3 // 38, 32, 47.9 Here, there are a number of smooth ‘sand polished’ rock sections all jam packed with fossils, so prominent that they can easily be seen while driving past ! The darker (unwashed - unpolished) rocks in the background are the same limestone. There is an interpretive sign a few metres behind.



Wilkawillina Gorge
The Wilkawillina limestone found at west Brachina Gorge and Wilkawillina Gorge was once a common flat sedimentary layer under the sea. It was uplifted with the adjacent sedimentary layers into the huge mountain range (higher than Everest, it seems) that once existed in this region, then got weathered away over time. The two exposed extremities of that layer are seen here at Wilkawillina Gorge and at west Brachina Gorge.
Note: Wilkawillina Gorge could be seen as somewhat remote for those not experienced in bush travel – it is an approximate 80km return drive from Brachina East (using the short cut to the Wirrealpa road, near Oraparinna - but a vehicle with good ground clearance may be necessary in places on this short cut, due to seasonal track washouts – if in doubt, take the longer drive starting further south on the Wilpena - Blinman road). Take provisions too and if you don’t have effective distance communications equipment, make sure someone responsible knows of your plans.
The excellent reference we had for this activity, is the Wilkawillina Gorge walk leaflet produced by the Royal Geographic Society of Australasia (SA). We found ours at the Mount Billy Creek trailhead information point, at the gorge itself. The walk is promoted as an 11.4 km one-way walk; if walking the whole distance one way, transport to and from the respective ends needs to be arranged. Note that seeing the fossils in the boulders only requires a relatively short approximate 2.5km walk in, from the Mount Billy trailhead.
The fossil bearing limestone rocks in the riverbed here are much smaller than those at Brachina Gorge west, but still hold plenty of Archaeocyatha. They occur variously in the general locality: GPS S 31, 16, 33.31 // E 138, 52, 44.56
Please note: When last there in 2011, I did not personally note the GPS coordinates – those supplied above are an estimate (via a Google Earth™ view). It is common for great floods to rage through these gorges, so the rocks that I saw may be buried by silt, or even moved – if so, I’m confident that others will still be found (and its a great gorge to visit anyway, mainly due to the colourful geology).
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Part B
PreCambrian Period - Stromatolites (petrified layered mounds, built by marine cyanobacteria around 600+M years ago).
While they occur in many places throughout the Flinders, the Trezona geological formation, east of Brachina Gorge holds plenty of accessible examples. They are underfoot at one stage of a gazetted walk mentioned here; we also found them in the middle of a roadway that enters the park. Those mentioned in this text are on, or near, the Trezona Walk (one of the gazetted ‘Hayward Huts” walks) and in adjacent creek beds.
I must admit that some people might see these stromatolites as ‘dull’ in themselves, but their significance gets my attention ! The bacteria that formed these objects were probably the only life forms to be found anywhere on Earth, at the time). 600+M years later though, these bacteria are still making stromatolites around the globe, includingHamelin Pool, Western Australia.
Well designed leaflets for this walk (by The Walking Trails Support Group) are available in the weatherproof bin at the trailhead at the eastern end of the Trezona campground.
Please note the section ‘For Your Safety’ in those leaflets. Also note that described here is the first section of a clockwise walk on the marked trail. The pathway is common in places with the long distance Mawson (cycling) and Heysen (hiking) trails – the various identification posts can be seen here and there. The old Hawker to Blinman roadway forms part of this walk too. Watch out for rabbit warrens on this Trezona walk – there are lots of them, some very close to the path and often obscured by shrubs – don’t fall in and break a leg !
On our last stromatolite hunt in this area in mid April 2012, we followed the Trezona walk up toward Youngoona then left the trail and continued up the Enorama Creek for another 500m or so. We then returned to the Trezona campground by following the Enorama creekbed back downstream.

The following covers our approximate movements.
1.
Commence at the Trailhead, eastern end of the Trezona Campground.
GPS: S 31, 19, 51.8 // E 138, 37, 39.7. See the photograph below (Wilpena Pound in the distance).



2.
Following the trail generally east alongside the Enamora creek, we come to the world famous ‘Golden Spike’ geological point – a brass plaque inserted into one of the creekbank’s sedimentary layers, at GPS: S 31, 19, 53.6 // E 138, 38, 00.2
In the photograph below, you can see a number of core sampling holes drilled into that Ediacaran layer – some of that material was used on an scientific project some years back, concerning a large impact crater on Eyre Peninsula. Try the links Aus GeoNews andWalking Trails Support Group for further information (there are other web references too).
Also, adjacent the Golden Spike is a large creek-crossing swathe of the red glacial tillite found in this area.

3.
The trail continues upstream then crosses the Enorama creekbed and exits up the bank on the northern side at GPS: S 31, 19, 51.6 // E 138, 38, 09.9

4.
The trail then wanders across a gently rising plain, but the erosion in places is getting right out of hand – is this just nature, or caused by rabbits ? (see the photograph below, left). As for the rabbit warrens; we saw dozens of them, in this region of the park (see the photograph, above right).

5.
T junction (Point T2) – our Trezona walking trail turns right here, while the Heysen trail carries on generally northward.
This general locality carries petrified stromatolites in abundance. They are identified by a general mound, or group of mounds, obviously built in layers – you can see the layering within them. When being built by the cyanobacteria, silt was trapped in layers. The bacteria eventually die off and the mounds can remain and become petrified.

The two photographs below (centre and right) were taken a few metres away from the T2 junction post.



The circular pattern is what I assume to be the remnants of a single circular mound (very common among stromatolites) at GPS: S 31, 19, 34.3 // E 138, 38, 33.7 (see the centre photograph above). One example of the interwoven layered mounds (very common) is at GPS: S 31, 19, 34.3 // E 138, 38, 32.9 (see the photograph above, right) - this is a small example though and seemingly on one extremity of the larger overall grouping.

6.
Valley of the Stromatolites !
The walking trail now runs roughly southeast down a short valley back to the Enorama creek. Along this short descending walk, starting from the top of the rise, watch for the mainly interwoven stromatolites on both sides of the walk. The more prominent examples are to your right (higher ground) side (photograph below left), but importantly they are also underfoot on the path (see the photograph below, centre).



7.
Once down in the Enorama creek, the marked trail crosses ( at GPS: S 31, 19, 43.1 // E 138, 38, 38.2) and continues eastward along the southside bank, in the direction of Youngoona trailhead (in places, the trail is in the actual creekbed).

As seen in the photograph above right, at GPS: S 31, 19, 44.7 // E 138, 39, 03.2 there is an impressive embankment of petrified stromatolites . Where else can you sit and rest on such ancient fossils ? These are probably much older than the stromatolites seen earlier, because they are in a lower (earlier) sedimentary layer.
There is also a less prominent bank of the same stromatolites a few metres away on the downstream side.

Note that further up this riverbed, the walking trail exits at S 31, 19, 47.0 // E 138, 38, 48.6 – the marker pole may, or may not be there – the annual, often violent floods play havoc with creekbed signage in this region !

8.
Further east along the creek at GPS: S 31, 19, 49.5 // E 138, 39, 03.2 there is a set of two stromatolite embankments and a ledge of ripple stone. Ripple stone is very common and occurs all over Australia in high and low terrain – it is formed in ancient times by water lapping on sands and sediments (such as seen at a beach or river bank etc.) and then gets trapped and petrified over millions of years. Ancient geological upheavals often leave it at a variety of angles to the original horizontal. See the photograph below, left.



9.
We abandoned the Trezona walk here and proceeded up to the wonderful Youngoona waterhole area. On the top side of that wet area, we took the left branch of two joining watercourses and found an impressive tree at GPS: S 31, 19, 45.7 // E 138, 39, 18.3. Across this region in general, there are some monstrous gum trees in and along the creeklines. While this one is not particularly huge overall, the butt certainly is significant. See the photograph above, centre.

10.
From this point, we made our way back to the Trezona campground by staying in the Enorama creekbed all the way. On that journey, we found what we consider to be many more examples of stromatolite formations in a number of places, ranging from the obvious to somewhat obscure. They were seen in cliff faces, rock ledges and outcrops.
For example, the cliff seen in the photograph above right is at a point where the creek takes a pronounced right angled turn (approximate location GPS: S 31, 19, 57.86 // E 138, 38, 30.37). It has suggestions of stromatolites in various of it’s layers.

In the other photograph below left, the pale horizontal layer in that rock face also seems to have stromatolite mounds as part of the makeup. I don't have a GPS point for that location.

11.
In the last two photographs below (centre and right), the sedimentary rock embankment that emerges from the creekbed and slopes away up the hill appears to have plenty of stromatolite mounded formations in it - GPS: S 31, 19, 52.7 // E 138, 38, 19.8 I presume the two trees commenced their lives in soil that once covered the rocks – raging torrents have since swept it all away as the creek became much deeper.



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Whatever folks – we found it of great interest – others might too. This area of South Australia has huge attraction for those interested in the natural environment – fauna, flora, geological features galore, wonderful scenery, gazetted walking trails and no phone or TV coverage !

Darian, SA - member 446.



"The world needs lots of stupid people.....so that we select few appear really smart :-)".
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