‘Geo-Log’ 2014 Journal of the Amateur Geological Society of the Hunter Valley ‘Geo-Log’ 2014 Journal of the Amateur Geological Society of the Hunter Valley Inc. Contents: Presidents Introduction 2 Pinny Beach and Swansea Heads 3 Foreshore Geology - Nobbys Head to Newcastle South 6 Sea Caves at Snapper Point, Munmorah State Conservation Area 12 Mulbring Quarry 18 South Maitland Coalfield 25 Dinosaur Triangle - Geological Safari 2014 36 Burragurra and Finchley Trig 71 Beecroft Peninsular 73 The Great Numbat Mystery Reconnaissance Tour 81 Geological Mapping Workshop 84 Social Activities 2014 85 Geo-Log 2014 - Page 1 Presidents Introduction. Hello members and friends, I’m sure everyone feels that the year has gone by so fast our feet have barely touched the ground. But the local enthusiasm for earth sciences and nature in general never seems to diminish and this is reflected in our very strong membership and enquiries received on our website. Our greatest attribute as a society is that no-one needs to know anything about geology. We have plenty of members well-versed in that and other disciplines and all that new members require is an eagerness to observe and learn. The activities of the Society have for many years extended well beyond the Hunter Valley, and indeed outside New South Wales as our search for new areas to explore continues. Only occasionally are old areas re-visited as new information becomes available. In 2015 we will return to Alum Mountain with its magnificent bush scenery now that access is again possible after the completion of the Buladelah Bypass. This is one of the most scenic and geological gems in the state. Our extended excursion this year was to northwest Queensland and the Dinosaur Triangle where 5 weeks were spent exploring the scenery, geology and fossils of the Mount Isa Inlier and the surrounding sedimentary basins. The highlight of that trip was the full day spent with Mike Archer at Riversleigh, made possible through an introduction via Joan Henley who used to work with Mike at the Australian Museum. Despite his American accent Mike is Australian and fiercely proud of it. The length of the trip and variety of sites covered required a very lengthy report, making this issue of the Journal the largest ever. Very special thanks go to the Social Committee for their rarely acknowledged input, particularly at Soup and Slides and the Christmas Social. Thanks to Sue and Ian Rogers who made their home available for both Soup and Slides and the Christmas party, the latter organised almost wholly by Sue since Ian had landed himself in hospital a few days beforehand after a heart attack. At the time of writing he was recovering and doing well. Grateful thanks also to Treasurer Leonie Mills, who has kept our finances legal and in order. Our Secretary Ian Rogers continues to get our newsletters out in plenty of time for members to plan ahead and also oversees the Society website. Thanks to those members who organised and ran our activities and contributed to the Journal. Special thanks to Life Member Ron Evans for his dogged determination and dedication in producing another great edition of the Journal. Accolades from the scientific community and the general public continue to come in. I have no doubt that this is the most professional journal of its type in Australia. With very best wishes, Brian. Geo-Log 2014 - Page 2 Pinny Beach and Swansea Heads Leader: Chris Morton. Attendance: 27 members; 8 visitors. Date: Thursday 30th January, 2014. At the risk of overstating the description of this activity, the single word that comes to mind when I think back about this brief geological adventure is stunning. Stunning for the unbelievable attendance and a beautiful sunny 1. Leader Chris delivering a short geological explanation of the features to be found. afternoon with 27°C and a gentle northeast breeze. Stunning scenery; the blue of the Tasman Sea, the golden replaced by chalcedony due to the abundance of silica in sands of our iconic beaches, and the vibrant green of the enveloping ash. the sea grasses that dominate rock pools revealed by the falling tide. The kaleidoscope of colour that saturated the The Excursion. coastal rock escarpment provided the perfect backdrop for the completion of the walk north from Pinny Beach that Participants listened intently to the short geological we started last year but could not complete then due to the introduction delivered at the top of the stairs leading unexpected abundance of fascinating geological features down to Caves Beach from the car park off Caves Beach exposed. Road opposite Bligh Avenue ( photo 1). The scenery and pleasant coastal surrounds here would have satisfied any Geological Background. tourist but the cliffs, rock platforms and sea caves along this stretch of coastline hold enough features to keep This area of coastline south of Newcastle comprises rocks geology enthusiasts occupied for many hours. Whoever belonging to the Boolaroo Subgroup of the Late Permian said sedimentary rocks were boring has never experienced Newcastle Coal Measures (Herbert and Helby, 1980). In the incredible variety of structures and rock types exposed this section the dominant exposures comprise the Reid’s along this coastline. To the experienced scientist all can Mistake Formation that separates the Lower Pilot coal shed light on past environments and climatic conditions. seam in the rock platform and the Upper Pilot coal seam exposed in the adjacent sea cliff. The escarpment above this Walking south along the beach from the base of the stairs sequence consists of massive conglomerate and intercalated we found a number of interesting structures representing sandstone beds of the Belmont Conglomerate Member, various aspects of fluvial sediment deposition. At the one of several isolated channel-filling conglomerates base of the Belmont Conglomerate were many examples present within the Newcastle Coal Measures. of cross bedding and evidence of point bars in those ancient stream beds (photo 2). But the most fascinating Numerous tree stumps (probably the species Dadoxylon) outcrop was an excellent transverse cross-section of one are preserved in situ in the rock platforms. These are the of the anastomosing stream channels characterizing the remnants of a fossil forest which grew in the sediments braided rivers that were active in this region (photo 3). that later formed the Lower Pilot seam. Within the seam This streamlet had gouged a deep channel across earlier the fossil trees were converted to coal and dark brown deposited river sediments and then laid down its own siderite. The presence of this fossil forest was recorded by sequence of draped sediments within the eroded channel Edgeworth David (1907) who stated in his work on the to form what sedimentologists call a scour and fill geology of the Hunter River Coal Measures “The oldest structure. At the edge of the channel lay a great example forest growth which went to form the lowest seam was of partial stream bed collapse, a large chunk of bedded killed off suddenly by being buried under dense showers sandstone lying at a different angle to the other channel of volcanic ash”. fill sediments. Also present were occasional sections of tree branches deposited along the edges of the channel as This volcanic ash now forms the thin blocky tuffaceous driftwood. beds in the Reid’s Mistake Formation exposed in the sea cliffs and nearby rock platforms. In this tuff only the cores Exploring the first of the sea caves, the group found a of the tree trunks were coalified, the remainder being narrow crevice at the back of the cave, which led into a Geo-Log 2014 - Page 3 2. Fluviatile channel deposits near a sea cave. 4. Lower Pilot Seam underlying Reid’s Mistake Fm. narrow amphitheatre with towering rock walls. which extends out across the rock platform (photo 8, page 5). Most of the group could have lingered here longer to The sharp demarcation between the tuff beds at the base explore the other sea caves and more of the fascinating of the Reid’s Mistake Formation and the underlying top sedimentary features. However, not wishing to make of the Lower Pilot seam lies midway out across the rock the same mistake as last year in not completing the day’s platform (photo 4) with a trend approximately parallel to the program, it was time to move on. There was an equally coastal cliffs. Within this relatively thin coaly shale bed lie stunning area to be explored at Reid’s Mistake (Swansea) the impressive remains of a large fossil forest in growth Head, just a few kilometres to the north at the end of position, the trees felled around 260ma by ash flows from Northcote Avenue, Swansea Heads. volcanoes located to the east around 30 kilometres off the present coastline. The trees are rooted in the coaly shale The geological section exposed here is identical to that and many of the stumps project well into the overlying seen at Caves Beach, but the rock platform here at low tide tuff, by as much as 10 metres as seen by Edgeworth David provides a much better exposure so that each layer can be in the nearby Government quarry back in 1907 (David, examined in close detail in cross section. This is due to 1907). But on the rock platform only the stumps remain, the shallow 8° dip of the beds to the west as they slope in the rest of the trees having been removed by marine towards the centre of the Sydney Basin. erosion. David found that the diameter of the trees ranged up to 0.4 metres with an average spacing of 1.5 to 2 metres.