Geologist VOLUME 16 PART 1 AUGUST 2004 East Midlands Geological Society Contents President Vice-President Geobrowser 2 Ian Thomas Tony Morris Mercian News 3 From the Archives 4 Secretary Treasurer Janet Slatter Christine Moore Keith Ambrose and Frank Williams 5 Editorial Board Bibliography of the geology of Leicestershire and Rutland; Part 2: 1971-2003 Tony Waltham Andy Howard John Carney Tony Morris John Travis 27 Alan Filmer Gerry Slavin East Midlands Geological Society, 40 years on: memories of the early years Council Landmark of Geology Beris Cox Gerry Slavin Castle Rock: Tony Waltham & Andy Howard 37 Lesley Dunn Ian Sutton Richard Hamblin John Travis Reports Robert Littlewood Alf Whittaker Leedsychthys problematicus : Alan Dawn 43 Sue Miles John Wolff Abberley & Malvern Geopark: Cheryl Jones 46 Dead Sea Rift: Gerard & Brenda Slavin 48 Correspondence Blue-collar geologists: Eric Robinson 51 The Secretary, E.M.G.S., 100 Main Street, Parinacota, Chile: Tony Waltham 53 Long Whatton, Loughborough LE12 5DG Fossil elephants of Tilos: Alan Filmer 54 01509 843297 [email protected] Excursion Reports Mercian Geologist is published by the East Midlands Bradley Fen Brick Pit: Neil Turner 55 Geological Society, and printed by John Browns. Lincolnshire Wolds: John Aram 56 No part of this publication may be reproduced in printed or Charnwood: PalAss 57 electronic medium without the prior consent of the Society. © 2004 East Midlands Geological Society Lecture Reports Registered Charity No. 503617 Bottled water: John Mather 59 William Smith: Hugh Torrens 60 Alfred Wegener: Clare Dudman 60 Front cover : Triassic sandstone forming the cliff on the southeastern corner of Castle Rock, Essay Review Nottingham, with Mortimer’s Hole behind the left Ecton copper deposits: Trevor Ford 62 door; see p. 37. Photo: Tony Waltham. Book Reviews 65 Back cover : A geological map of Nottingham from the 19th century; see p. 51. The Record 71 GEOBROWSER GEOBROWSER is now supported by studies of clay minerals recovered from Atlantic drill cores (Quaternary Research, 2003, 243), which demonstrate the operation of this process When did the Earth first chill out? at least twice in the recent geological past. The oldest There seems little doubt that soon after its accretion recorded Atlantic meltwater pulse, at about 130,000 the Earth was a highly energetic body, but are the years ago, probably resulted from ice sheet collapse. theories that it began with a prolonged Hadean or The younger event, 77,000 years ago, was of shorter ‘hell-like’ episode extending from 4400 to 4000 duration and may have been caused by the sudden million years (Ma) ago correct? Unfortunately, no discharge of water from Siberian ice-dammed lakes. rocks go back farther than about 4000 Ma • An added complication to short-term global (Contributions to Mineralogy and Petrology, 1999, temperature change, at least during the Holocene p.69) , but older minerals are known, in the form of epoch, was the periodic release of large quantities of 4404 Ma zircon crystals found in Archaean rocks at methane that is otherwise locked up in seafloor Jack Hills, Western Australia. This find is fortunate, sediments – the ‘clathrate gun hypothesis’ (see also, because zircons provide reliable Oxygen 18 Geobrowser in Mercian 2003). Methane release is a measurements, and the occurrence of this particular consequence of sediment instability caused by isotope in relative abundance is believed to be an continental-slope failures, and studies of methane indicator of magmas formed from the melting of rocks contents in ice cores have shown that over the past that had been in contact with low-temperature hydrous 45,000 years there have been two main episodes – fluids – in other words these precursor rocks had 15,000 to 13,000 years and 11,000 to 8000 years ago experienced significant alteration or weathering. The (Geology, 2003, p.53) . These are both glacial- 18 high O values (c.7.5%) in the Jack Hills zircons could interglacial transition periods, but the underlying be due to a number of other factors, but the only theory causes of the slope failure were rather different. The to survive rigorous examination is the crystallization older event followed a deglaciation and occurred at of these zircons under conditions more appropriate to low latitudes; it resulted either from warming of the the ‘cooler’ Earth system that existed much later in the ocean or from enhanced rainfall causing vast loads of Archaean, 3800-2600 Ma ago ( Geology, 2002, p.351). sediment to be conveyed to the continental slope, If this is the correct interpretation, it follows that water which then became unstable. The younger slope may have existed on an Earth that had stabilized well failures were high latitude ones, and were probably before about 4000 Ma. Furthermore, there could not caused by the destabilizing effect of isostatic rebound have been a prolonged ‘high energy’ period of following retreat of the ice sheets. meteorite bombardment between 4450 and 3900 Ma, as some have suggested; instead there may have been a single, relatively short-lived meteorite ‘spike’ at K-T extinction: more complications about 4000-3800 Ma, followed by reversion to quieter Previous Geobrowsers ( Mercian, 2000, 2001) have conditions. reviewed the development of ideas about what really caused the end-Cretaceous (K-T boundary) event that Ever - changing climates wiped out the dinosaurs, and many other types of animal. Since those issues, further detailed The current debate about human involvement in examinations of bolide ejecta layers, iridium layers triggering climate change is increasingly being and faunal changes have been carried out across the balanced by research into the many natural causes of critical Cretaceous/Tertiary transition strata, and a such fluctuations. The time-scales at which these multicausal scenario now looks very appealing. One of factors could have operated are equally varied, as three the most recent contributions (Earth-Science Reviews, recent articles show. 2003, p.327) favours the following event sequence in • On a geological time-scale, it has been proposed the Central American and Caribbean regions: that since the Precambrian (543 Ma ago) at least 66% 1. At the very end of the Cretaceous (but before the of the variance in palaeotemperatures may be due to actual K-T boundary) the first impact occurred, at the galactic cosmic ray flux (CRF), caused by our solar 65.27 Ma. This was the Chicxulub meteorite. In system passing through the spiral arms of the galaxy association with on-going voluminous Deccan (GSA Today, 2003, p.4) . This hitherto unperceived volcanism, which lasted from 68.1 to 61 Ma, it astronomical factor might mean that we are today contributed to rapid global warming and the overestimating the influence of the long-term global consequent terminal decline of planktonic foram CO 2 greenhouse effect. populations. • On a much shorter time-scale, one of the most 2. The actual K-T boundary impact, at 65 Ma, is important predictions is that Arctic ice sheet melting not well represented in many sections, due to could very rapidly cut off the supply of warm tropical intraformational erosion; it marks a major drop in water to the North Atlantic, triggering the onset of primary productivity and the extinction of all more ‘continental’ climatic conditions in the UK. This tropical and subtropical foram species. 2 MERCIAN GEOLOGIST 2004 16 (1) MERCIAN NEWS 3. A third meteorite impact occurred in the earliest explain the origin of similar circular structures, such as Tertiary, and is tentatively dated at about 64.9 Ma; it the Upheaval Dome of Utah and the Compton Valence contributed to the marked delay in recovery of structure of West Dorset, both featuring highly productivity and evolutionary diversity. deformable evaporitic sequences associated with Some of the more doom-laden prophecies about what strike-slip fault systems. might happen to the human race under such a bombardment may, to some extent, be erroneous. Calculations based on the composition of the Chicxulub ejecta layer ( Geology, 2002, p. 99) do not bear out the original scenarios that featured the MERCIAN NEWS shutdown of photosynthesis during a succession of ‘impact winters’ caused by volcanic dust. In fact, more than two orders of magnitude more fine dust than was Cave art at Creswell Crags kicked up by that meteorite would have been necessary Long known for the archaeological material in its to do this. So if not dust, then what caused plants to sediments, Church Cave, in the Permian limestones of cease growing? One of the two most likely theories is Creswell Crags, has now been found to have artists’ that this resulted from soot caused by global fires (GSA impressions of about 90 animals etched into its roof. Special Paper, 1990, p.391) . Research soon to be Partially covered with stalactite, they are genuinely published, however, will suggest that there is a old, and are thought to date from 13,000 years ago, remarkably low amount of charred plant remains in even though the caves were also occupied long before strata at the K-T boundary. If correct, this would leave then. The eroded bas-relief images have only just been only the second theory as viable – that widespread found, because they are only visible in the strong plant death, and consequent destruction of the whole sidelight reflected into the cave from the morning sun. terrestrial ecosystem, was due to acid rains produced Details are in Antiquity v77, pp227-231, or on their from sulphate aerosols released from gypsum deposits website http://antiquity.ac.uk/ProjGall/bahn/ that happened to be present in the Chicxulub target rock (Journal of Geophysical Research, 1997, p. Mam Tor still on the move 21645) , a unique combination of circumstances that The East Midlands home-grown landslide at Mam Tor was unlucky for the dinosaurs but is perhaps unlikely continues to creep downwards (see Mercian Geologist to be repeated.