John's New England Minerals and General Geology Blog: crinoid

Friday, 11 December 2015

THE ASHFORD LIMESTONE CAVES

THE ASHFORD LIMESTONE CAVES

From the Ashford Tourism website

The Ashford limestone caves are located about 20km north-west of the town of Ashford, between Inverell and the Queensland border. What was once a crown reserve (set apart in 1915) is now part of the Kwiambal National Park (pronounced Kiamble), best known for the spectacular MacIntyre Falls, near which is a delightful camping area at Lemon Tree Flat. Picnic and toilet facilities are also provided at the caves.

These caves are not in the same league as the well-known show caves at Jenolan, Wombeyan and Yarrangobilly, in fact there are very few speleothems (decorations) to be found. What you will find is bats, guano (bat droppings) and a sense of adventure as you explore the unknown (to you) cave system. If you would like to read a fascinating account of “An Excursion to the Severn River and the Wallangra Caves” dating from 1892 (here) you will appreciate that some things have not changed, but others have considerably. The most notable change has been the removal of thousands of tonnes of phosphorus-rich guano for use as fertiliser, a process that was underway long before the reserve was established and continued as late as 1967.

There is a lot of information available about the geology, history and biology of Ashford Caves. I have given a list of downloadable resources at the end of the blog.

The caves have been formed in a bed of Lower Carboniferous limestone (probably, though estimates range from Devonian to Permian), which has been considerably deformed and largely converted to marble. It contains marine fossils (mainly crinoid and coral fragments), but remember that this is a National Park (no collecting allowed) and beyond the fences is private property, which limits the collecting possibilities to road reserves outside the Park. As the limestone has been traced for more than 10 km there must be some accessible outcrops, since the road basically follows the strike of the limestone. If you locate specimens of interest, tell us about it by adding a comment below.

There are a few typical karst features, notably the dolines where caves below have collapsed. You

Calcite formations 1999 (my photo)

might also come across solution grooves, widened joints and potholes as you walk around the limestone hill.

Early references note the existence of two main caves. The removal of so much guano has lowered the cave floors considerably and the two caves are now joined, making a through trip possible. There are a few other small caves but none appear to have much potential for new discoveries.

Three species of bat frequent the caves: Miniopteris schreibersii (the eastern bent-wing bat), Rhinophilus megaphyllus (the eastern horseshoe bat) and Eptesicus pumilus. Most of those you will see are bent-wing bats. Do not disturb them by making loud noises or shining lights on them. During the summer breading season, do not enter the main cave at all.

Bats 1999 (my photo)

The guano had accumulated to a depth of several metres in the most favourable places. A typical chemical analysis reveals that it contains 5-10% of phosphorus. Especially during the Second World War, when supplies of phosphate from Nauru and Ocean Island were cut off by the Japanese (both islands were occupied by them) alternative supplies were identified all over Australia. Ashford Caves was one of these.

Some useful references.

The Ashford Tourism site (here); (missing: you will have to search for it)

Guide to NSW Karst and Caves pp 10-11 (here); (missing. Try DIGS website or search Trove)

DIGS website (needed for the listings below) here. (missing - please let us know if you find it)

Annual Reports of the Department of Mines, New South Wales, for the period 1939-1945 (DIGS reference R00001425). This includes cave maps and guano analyses (beginning on page 82).

The Limestone Deposits of New South Wales (DIGS R00050689). An excellent report from 1919 giving information about all the then known limestone deposits.

The Limestone Deposits of NSW (1986) Lishmund, Dawood and Langley (DIGS R00056921). A modern, revised version of the above.

Geological Age of the Ashford Caves Limestone (DIGS R00019198). Report by Raggatt and Booker, 1940.

A Report on a Visit to the Ashford Cave, Northern NSW (DIGS R00023521). 1973 Anonymous.

https://johnsbluemountainsblog.blogspot.com/2013/12/links-to-all-blog-entries-and-relevant.html All Blue Mountains blogs and videos

https://johnsnewenglandminerals.blogspot.com/2013/12/list-of-all-blog-entries-to-date.html

All New England and other Geology blogs and videos

https://www.blogger.com/blog/posts/1325599670344725659?pli=1

Limestone Caves of NSW

https://www.blogger.com/blog/post/edit/1147003616874115974/2430103125095714141

Song Studies. Bible studies based on hymns and songs

https://www.blogger.com/blog/posts/1515863000684737715

Shoalhaven District Geology.

Wednesday, 21 January 2015

SCREW TIN – EMMAVILLE’S UNIQUE CASSITERITE FOSSILS

SCREW TIN – EMMAVILLE’S UNIQUE

CASSITERITE FOSSILS

From the Mindat Entry on Doctor's Gully Emmaville

Marine fossils have been found in many places in NSW, of course – even in some of the ancient sedimentary rocks near Emmaville – but what makes the fossils described here unique is the fact that they are preserved in cassiterite (SnO₂). Generally speaking, most marine fossils are preserved as calcite or quartz or simply as impressions in what was once soft mud or sand. To the best of my knowledge, Emmaville is the only location where the replacing mineral is cassiterite.

This is a piece of information I’ve known about for many years, but I have no specimens of my own; however I have found a photograph in the Mindat entry on Doctor’s Gully at Emmaville (here). There may be specimens in the Emmaville Mining Museum (there ought to be) and there probably are in museum and university collections elsewhere, but I don’t have access to these. From the photograph and the reports listed below you will see that the fossils are of two main types.

The first (the so-called screws) are segments of the stems of marine animals called crinoids. These are plentiful in sedimentary rocks ranging from the Silurian to the Permian period and are usually preserved in calcite . Crinoids resemble sea urchins and starfish; however they are attached to the sea floor by long stems made up of individual plates or ossicles. When seen from the edge, sections of these stems do resemble the thread of a screw or bolt, except that a little observation shows that that are not spirals, merely stacked discs. The miners who gave them their name probably weren’t fooled, but similar fossils in rocks have given rise to silly stories about ancient machines being found embedded in solid rock.

The second type of fossil is of a small gastropod (snail) of a species commonly found in Permian sediments. Similar fossils (preserved in calcite) are common in Shoalhaven Group sediments at Gerroa on the south coast of NSW. Thus we have references to “screw tin” and “snail tin”. Here is a quote from the Wingham Chronicle and Manning Observer (Friday 9^th April 1937, page 1):

“Queerly shaped specimens which Emmaville miners have been finding in their claims, and which they have been calling "screw tin," and "snail tin" from the shape of the crystals, have been identified by Mr. T. Hodge-Smith, mineralogist at the Australian Museum as sea lilies and gastropods (star fish and sea snails) which countless thousands of years have turned into tin oxide. Such specimens have not been found anywhere else in the world, and prove that many thousands of years ago the sea swept over what is now the Tablelands.” Why this particular newspaper chose to report this information I can’t imagine. Did they issue a press release in 1937 after a field trip to investigate reports of cassiterite fossils being found near Emmaville?

The locality I’ve known about is Doctor’s Gully, an alluvial tin area near the Emmaville Golf Course (Gulf Road). However, it turns out that several other places nearby have also produced these fossils and there might have been others. It was just plain tin to the miners and worth money as such, so into the bags went beautiful specimens any of us would be proud to own. From the maps you can see that Doctor’s Gully has at least two tributaries gullies, called “Steele’s Gully” and “Charcoal Gully”. They are listed in the various reports as being 2km north of Emmaville. The Grafton-Maclean Mine Data sheets describe them as “fossil placers (fluvial)”. The Mine Data reference for all three is 1166. There is an additional reference (1266) to “Screw Tin Gully”, 3km north of Emmaville, described as “modern placer (fluvial)”. I can find no further reference to Screw Tin Gully but it is apparently in the same general area as the others.

Don’t imagine that you can just turn up at Emmaville and expect to find examples of these very special fossils. Read Jim Sharpe’s account of his experience in the Newsletter of the Mineralogical Society of NSW for November 2013 (here). Finally, a scholarly report on these fossils appeared in the Journal and Proceedings of The Royal Society of NSW for 1952. The article, by LJ Lawrence, may be downloaded here. It’s nearly at the end of the document and no plates have been reproduced. Note to the Royal Society: it’s time to make your records freely available in modern PDF format!

From Rasmus 1972. Check DIGS for the original

From the Grafton-Maclean Mine Data records