Geo junkets: New Zealand, North Island (Part 1)

Jesse Garnet White (USA) Fig. 1. Legend/Key:1 = Sediments (Cretaceous and Cenozoic).2 = Greywacke (Permian and Triassic).3 = Schist (Carboniferous to Cretaceous).4 = Volcanic rocks (Cretaceous and Cenozoic).5 = Sediments and ophiolites (Northland and East Coast allochthon) (Cretaceous and Oligocene).6 = Pyroclastic rocks (Triassic and Jurassic).7 = Limestone, clastics and volcanic rocks (Central and Eastern sedimentary zone) (Cambrian to Devonian).8 = Granitoids (Paleozoic and Cretaceous).9 = West Fiordland metamorphic zone (Paleozoic and Cretaceous).10 = Ophiolites and pyroclastics (Permian).11 = Volcanic rocks (including pyroclastics) (Permian).12 = Mafic and ultramafic complexes (Paleozoic and Cretaceous).13 = Greywacke (Western sedimentary zone) (Cambrian to Ordovician). Auckland and the AVF In a thick brain fog, crusty eyed and yawning, I sat up in bed at 4:30 am. I was in Auckland, New Zealand. It was still dark outside when I drove to Mount Eden (Maungawhau), where I hiked up a narrow dirt trail lined by tall grass stippled with dew. Coming out of the verdure, my shoes, socks and shorts were soaked through. On top of the hill, a shadow-black grouping of trees blocked the creeping morning light from behind the Hanua Ranges. The burnt orange sunrise, obstructed by cumulous, lit up like a distant mountain wildfire. Auckland city centre was under puffy, lavender-white cirrus clouds, reflecting pastel colours across the harbour. Alone in the cool and crisp pre-dawn air, I viewed the various scoria cones in the Auckland Volcanic Field (AVF) bursting through the city neighbourhoods. Fig. 2. Map of New Zealand showing place names. … Read More

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Rudists: A fossil story

Jack Shimon (USA) This article is adapted from a presentation given at the Denver Gem Show, September 17, 2016 by me, Jack Shimon. When I was six and a half years old, my Grandpa took me fossil hunting in central Texas. We went to a Carboniferous Limestone quarry that he had visited earlier and was given permission to enter and collect from. This was one of my first fossil hunting trips and I really enjoyed it. The ancient reef we went to (now a quarry) had huge boulders of limestone and tube-like things in it we later to be found to be rudist bivalves. This article is all about these finds and the efforts we went to, to find out what they were. Fig 1. The author at the quarry. (Photo credit: Mike Hursey.) Fig. 2. This Google satellite image shows the reef we collected from. Two of the three lobes have been excavated for limestone. You can also see smaller pinnacle reefs marked with the short arrows. All of the reefs rise above the flat Texas landscape. (Permission from Google.com: ‘Special Use Guidelines’.)Fossils We spent a lot of time at the quarry observing the massive specimens onsite and then collected some smaller pieces to bring home and look at closer. A simple way of thinking about fossils is to consider them either as a cast or a mould. A mould is formed when an object is placed into a soft substrate and then decomposes or is washed away leaving … Read More

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Clarkia Flora: 16-million-year-old plants offer a window into the past

Margret Steinthorsdottir and Helen K Coxall (Sweden) Near the small town of Clarkia in Shoshone County, Idaho in the USA, exists a rich and unique fossil deposit. The Clarkia fossils, or Clarkia Flora, as the deposit is mostly called due to the abundance of fossil plants, is so well preserved that the assemblage is referred to as a “lagerstätte”, a scientific term reserved for the world’s very finest fossil deposits. The Clarkia fossils are found in sediments that are now known to be about 16 million years old and belong to a period in Earth history called the Miocene. By this time, the (non-avian) dinosaurs were long extinct (the last of these dinosaurs disappeared about 66 million years ago), the Earth’s continents were more or less in the same position as today, and many of the animals and plants would have started looking familiar to modern humans (who emerged much later, about 200,000 years ago). Fig. 1. The entrance to the “Fossil Bowl” motocross racetrack and fossil locality near Clarkia, Idaho. Among the Clarkia fossils can be found various insects, fish and occasionally the remains of small mammals. However, most striking is the wealth of plant fossils in the form of exceptionally well-preserved leaves, nuts, seeds and wood. Impressively, one can find leaves of oak, laurel, pine and birch that look virtually identical to those we find today. If you look quickly when a new fossil is newly exposed from within the host sediments, you may occasionally even see the … Read More

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Stop the press: The Jurassic Coast starts in the Permian

Mervyn Jones (UK) This Geologists’ Association field meeting followed the publication of Professor John Cope’s Geologists’ Association (GA) Guide No 73, Geology of the South Devon Coast. It is also the companion to GA Guide No 22, Geology of the Dorset Coast. John retired in 2003 after lecturing at Swansea and Cardiff universities. Since then, he has been an Honorary Research Fellow at the National Museum Wales in Cardiff, and has a wide field experience in the UK and Europe, with publications covering many fossil groups over a wide stratigraphical range. Most recently he has been working on redrawing the geological map of South Wales, the subject of an upcoming GA lecture. And, each year, for the past six years, he has provided weekend geological trips to the West Country. Fig. 1. Prof Cope demonstrates bedding and cleavage. We met up at Meadfoot Strand to the east of Torquay Harbour. Our mission for the weekend was to examine the complex Devonian succession in the Torbay area and its unconformable relationship to the Permo-Triassic cover. Of great interest was the marine Devonian, first described by Adam Sedgwick, assisted by Roderick Impey Murchison, who finally realised that these facies were contemporaneous with the familiar Old Red Sandstone found north of the Bristol Channel. Since then, the Devonian Stages have been named after rocks in the Czech Republic, Germany and Belgium. The base of the Devonian was the first ‘Global Boundary Stratotype Section and Point’ (GSSP), defined by graptolite zones at Klonk, in … Read More

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Rocks in Roslin Glen: A record of a swampy past

Mark Wilkinson and Claire Jellema (UK) Midlothian is an area of central Scotland that lies to the west of Edinburgh and is an area with strong geological connections due to a history of mining for both coal and oil shale. As a part of the annual Midlothian Science Festival (http://midlothiansciencefestival.com/), the School of GeoSciences at the University of Edinburgh offered a walk to look at some local geology and a talk about climate change research on the Greenland icecap. In addition, a ‘Dino and Rocks Day’ was attended by 380 people, proof (as if it were needed) that dinosaurs continue to fascinate the general public. The Edinburgh Geological Society also contributed with a session about Midlothian Fossils and a local historian talked about the history of coal mining in the area. The geology walk visited local exposures, in this case Carboniferous sediments including what may be the best exposed fluvial sediments in the area. The walk was advertised as “Rocks in Roslin Glen: a Record of a Swampy Past” and all 25 spaces were quickly booked. The location was Roslin Glen, which may sound familiar if you’ve seen the film, The Da Vinci Code, based on the novel by Dan Brown. We have not misspelled the name of the glen incidentally. For some reason, Rosslyn Chapel lies on the edge of Roslin Glen and the country park of the same spelling. The glen itself is a steep-sided valley of around 20m in depth, which carries the River North Esk roughly … Read More

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Whitby Jet and the Toarcian Oceanic Anoxic Event

Arthur Speed (UK) One hundred and eighty million years ago in the Toarcian Stage of the Lower Jurassic Period, the Earth was very different from the world we know today. The continents were all clumped together in a supercontinent called Pangaea, which was just beginning to split apart. Sea level was approximately 100m higher than at present, such that much of Britain (including Yorkshire) lay beneath shallow seas. At this time, the Earth’s oceans were depleted in dissolved oxygen. The chain of events that caused this are complex, but can be traced back to a major volcanic event (Fig. 1). The eruption of the Karoo-Ferrar Large Igneous Province (LIP) spewed lava over what is now southern Africa and released vast amounts of carbon dioxide into the atmosphere. Just as happens now, the carbon dioxide resulted in global warming, which, in turn, had several effects on the oceans: Fig. 1. Volcanism during the eruption of the Karoo-Ferrar LIP may have triggered the Toarcian Oceanic Anoxic Event (Ulrich, 1983). Seawater became deficient in dissolved oxygen, because oxygen solubility decreases with increased temperature.Plankton thrived as a result of the warmer temperatures and increased nutrient supply, using up even more dissolved oxygen.Oceanic circulation was decreased, reducing the supply of cold oxygenated water to the oceanic basins.Warmer water released the green-house gas methane from the ocean floor, further accelerating global warming.The result was the formation of a layer of water that was deficient in oxygen throughout the Earth’s oceans. Its existence was first postulated in … Read More

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Fossil folklore: Molluscs

Paul D Taylor (UK) The final article of this series on fossil folklore focuses on molluscs, excluding the ammonites, which were covered earlier (see Fossil folklore: ammonites in Deposits, Issue 46, pp. 20–23). Molluscs are second only to arthropods in the number of species living today and the resistant calcareous skeletons possessed by the majority of species accounts for their extremely rich fossil record. Most fossil molluscs belong to one of three major groups – bivalves (oysters, clams and so on), gastropods (snails and slugs) and cephalopods (ammonites, belemnites and so on). Added to these are a few minor groups, such as the monoplacophorans and scaphopods (tusk shells). Fossil molluscs are usually recognisable instantly as belonging to this phylum because of their close similarities with the shells of familiar species of modern molluscs. Some, however, are not quite so straightforward. These are more likely to have been the sources of fanciful stories about their origins and significance. Among the more obscure ancient molluscs are those dubbed ‘difficult fossils’ by Martin Rudwick in the context of the early history of palaeontology and doubts over the origin of fossils. They include the solid internal casts (steinkerns) formed by lithification of sediment enclosed by the shell and subsequent loss of the defining shell itself. In addition, there are some mollusc fossils – notably belemnite guards – that bear little resemblance to any living species, adding to their enigmatic nature. Belemnites: thunderbolts and Devil’s Fingers The first fossils I ever came across were belemnites … Read More

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Australia’s Polar Cretaceous mammals

Dr Thomas H Rich (Australia) The Cenozoic Era is commonly referred to as the ‘Age of Mammals’. That is certainly the time in the history of life when their fossils are most abundant and diverse. However, two-thirds of mammalian history was during the Mesozoic Era – and they appeared about the same time as the dinosaurs. All continents except Antarctica have some record of the early, Mesozoic mammals. Of those that do, Australia has the most meagre record of all. Despite this, with this landmass that today has the most distinctive terrestrial mammals on the planet, their Mesozoic origins are so enigmatic that it has motivated a major effort since 1984 to search for fossils of those mammals that lived alongside the dinosaurs on this now isolated continent. Fig. 1. A map of Australia showing the location of the four sites where Cretaceous mammals have been found on the continent. During the Cretaceous, Australia was much further south than at present. Shown here are the lines of latitude at that time on the continent: 50o south, 60o south and 70o south. The famous Lightning Ridge opal field has provided some of the answers – two different early Late Cretaceous egg-laying mammals (the monotremes), as well as a third mammal that may be a monotreme, have been discovered there. One thousand, three hundred kilometres to the south-southwest along shore platforms pounded by the waves of the Southern Ocean, which expose those rocks on south coast of the continent, are three sites … Read More

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All change at Selsey, West Sussex, UK

David Bone (UK) Issue 26 of Deposits magazine in the Spring of 2011 included my article on fossil collecting at Bracklesham Bay in West Sussex, following in the footsteps of my guide book on Fossil hunting at Bracklesham & Selsey, published in 2009. This area has been well known for the foreshore exposures of Palaeogene and Quaternary geology since the mid-nineteenth century and is still very much an area for popular fossil collecting, as well as research. Many readers will have been to Bracklesham or Selsey to collect sharks’ teeth and may have even been lucky enough to find a piece of mammoth bone or tooth. The scientific value of the area is recognised by much of the coastline being designated as a geological Site of Special Scientific Interest (or SSSI). However, this has been impacted by two major coastal defence schemes at Selsey that were completed in 2013, significantly changing access to the foreshore and any exposures of the geology, as well as rendering my guide book in need of a major update. In medieval times, Selsey was effectively an island, although this is no longer the case due to the construction of sea defences and land reclamation. However, Selsey remains a localised area of higher land surrounded by low-lying land prone to flooding (Fig. 1). It has also been an area of coastal erosion and loss of land to the sea throughout recorded history. The relatively unconsolidated Palaeogene and Quaternary sediments exposed in the low cliffs of the … Read More

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