‘Geo-Log’ 2012 Journal of the Amateur Geological Society of the Hunter Valley ‘Geo-Log’ 2012 Journal of the Amateur Geological Society of the Hunter Valley Inc. Contents: President’s Introduction 2 Australian Alps Safari 3 New Hartley Excursion 20 Redhead Bluff: Stratigraphy and Paleoenvironment 29 Varved Shale in the Seaham and Raymond Terrace Area 33 Coolah Tops NP Weekend 37 Some Regional Geology of the Eyre Peninsula, South Australia: Geological Safari 2012 43 Geo-Log 2012 - Page 1 President’s Introduction. Hello members and friends, Yet again we have enjoyed a very successful year. Although the Society has been running for over 30 years, our membership has remained stable and has even increased slightly in recent years, reflecting a continuing enthusiasm for and appreciation of the earth sciences and related activities. A background in geology is not a prerequisite to membership and every member is strongly encouraged to take part regardless of their level of knowledge. Although the initial aim of the Society was the exploration and understanding of Hunter Valley geolo- gy, for several years now we have continued to widen our coverage well beyond the confines of the Valley. Even so, while the organizing committee tries to include new activities into the program each year, this is becoming more difficult. But new members bring new ideas and new experiences which everyone can benefit from. Occasionally old sites are revisited, either for the benefit of new members or where the availability of new information has allowed a greater understanding of earth history. Our first extended excursion was organized (with some trepidation) into the Flinders Ranges in 1995, but this was so successful that similar trips have since taken place annually. This year’s program in- cluded two such trips, the first to the Australian Alps in February and the second to Eyre Peninsula in South Australia in September/October. The latter gave us an insight into the incredible variety of South Australian geology as well as allowing participants to experience some of the frighteningly wild weather the Peninsula occasionally throws up. Our program also benefits greatly from expertise from outside the Society. This year we were again very fortunate to have geologist Chris Herbert give up another day of his time in May to skillfully guide members through the geological history and stratigraphy of the sedimentary sequence at Red- head Bluff. We all hope Chris will continue to be involved with the Society. Very special thanks go to the Social Committee for their rarely acknowledged input at events through- out the year, especially the ‘soup and slides’ night and the Christmas meeting. Thanks also to Sue and Ian Rogers who made their home available for both the AGM and the Christmas social. Grateful thanks also to our Treasurer Leonie Mills who keeps our finances in order and who also this year bore the brunt of preparations for our Flinders Island trip coming up in April. Our Secretary Ian Rogers contin- ues to get our very informative newsletters out in a timely manner and oversees the Society website which provides a window on our activities and continues to attract enquiries which often result in new memberships. Thanks to those members who took part in organizing and running our activities and who contributed to this journal and especially to Life Member Ron Evans for his determination and dedication (in some- times difficult circumstances this year) for putting together another great addition of the Journal that we can all be proud of and which continues to draw accolades from both the scientific community and general public. With very best regards, Brian. Geo-Log 2012 - Page 2 Australian Alps Safari tangara Reservoir. Following the third phase (Bowning Folding) in the early Devonian, ignimbrites Saturday 19th to Friday 25th January of the Kelly’s Plains Volcanics were erupted over the 2012 land surface in the region from just south of Tan- tangara Dam north to include the present–day Coole- man Mountains. Leader: Chris Morton. Spread over around 30 ma, these folding events Attendance: 20 members; 1 visitor. lifted the rocks above sea level to form dry land and thicken the crust. Great blocks of this new continental There were many facets to our trip to the Snowy crust were moved tens to hundreds of kilometres besides the magnificent scenery of the Kosciuszko along major faults. Some of the rocks were forced region. Not least, the complex and diverse geology deep into the crust where high temperature and pres- represented by four periods of time-based divisions, sures metamorphosed them into slate, schist and ° from the Ordovician through to the Holocene. There gneiss. Some were heated above 650 C, temperatures was also the Aboriginal and European history plus high enough to melt them. Ultrabasic rocks (perhaps some 4X4 adventure driving and the comradeship of Cambrian ocean floor basalts) were squeezed up an enthusiastic and eclectic group of participants. along major sub-parallel faults and altered to form belts of serpentinite, such as the Tumut Ponds Serpen- Geology of the Australian Alps – A Brief Summary tinite Belt. Slate is a common rock type throughout the high country, with schist and gneiss occurring to the The Australian Alps are the highest section of south in the Victorian Alps. Australia’s Eastern Highlands, running from northern Queensland down into Victoria. The region contains a Large bodies of granitic rocks were emplaced in wide variety of rock types relating to its complex geo- the crust around the same time and large explosive logical history going back some 520 million years volcanoes erupted ash (ignimbrite) and lava over the (ma). new land surface. The granitic rocks now form much of the high Kosciuszko Plateau. Southeastern Australia has only existed as land for 350 ma. Prior to that it was a region of volcanic During the Silurian and Devonian the geography islands scattered over a wide ocean similar to the pre- of southeastern Australia was quite complex, compris- sent-day eastern Pacific. The oldest rocks in the Aus- ing continuous land masses, islands and small seas. tralian Alps are basalts erupted onto a deep ocean Some of these islands hosted coral reefs in the adja- floor during the Cambrian period around 520 ma. In cent shallow seawater. These reefs developed into the the following period, the Ordovician, vast areas of this limestones of Yarrangobilly and the Cooleman Karst. ocean floor were covered in a several-kilometre thick blanket of sand and mud over the next 80Ma. The re- Around 360 ma in the Late Devonian to Early Car- sulting sandstones, mudstones and shales now form boniferous, there was a final period of folding and much of the modern Alps. During the same period, a mountain building during which southeastern Aus- long chain of volcanic islands erupted basaltic and tralia became a mountain range, but this was not the andesitic lavas and these rocks are now exposed precursor to the Alps. Sand and mud was being de- around Kiandra. posited in rivers and lakes occupying broad valleys between the new mountain ridges, to later become Between the Silurian and Middle Devonian (440- sandstone and mudstone. 360 ma) the sedimentary and volcanic rocks formed during the Cambrian and Ordovician were folded by After this episode of folding, about 340 ma there mountain-building events brought on by collisions was more or less a hiatus with very little happening between several small tectonic plates. This folding during the Carboniferous, Permian, Triassic, Jurassic took place in at least three separate events. The first and Early Cretaceous. Australia was now part of stage (Benambran Folding Stage 1) occurred at the Gondwana and lay in the interior of that huge land end of the Ordovician, after which sands and muds mass. The mountain ranges were being worn down to were deposited in the newly-formed Tantangara a low-lying plain. Trough resulting in the sandstones and shales of the Tantangara Formation now exposed east of Tan- Between 300 and 250 ma there was a global ice Geo-Log 2012 - Page 3 age and Australia lay very close to the South Pole. Ice Monday 19th February sheets covered much of southeastern Australia but nothing has been preserved in the Alpine areas, hav- The group met up 9:30am at the Post Office in the ing since been removed by erosion. main street of Adelong, Tumut Street, on a beautiful summer’s morning (Photo 1). After pleasantries a Just when the Australian Alps became an entity is briefing was held on the proceedings over the coming still hotly debated. The majority of earth scientists be- week. Then from the Post Office we drove the short lieve the Alps rose between 100 and 60 ma. Around distance to the ruins of the Reefer Gold Battery at 130 ma Australia began to break free from Antarctica Adelong Falls, just out of town. and Zealandia. Magma rose though the lithosphere in a line along what is now the east coast of Australia, Hume and Hovel passed through this “rough and causing a large domed plateau to rise to over 2000 difficult country” on their way back to Sydney after metres in the region of the Australian Alps. By 100 ma their 1824-25 expedition, but gold was not reported in the continent had begun top split along this zone of the district until 1841 by the Rev. W.B. Clarke. The magma upwelling and a rift valley was formed along first major alluvial gold was found in a gully off Ade- the centre of the plateau. A modern analogy of this long Creek in 1852, opposite the site of the Royal Ho- process is the East Africa Rift Valley.