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Proceedings 4

Summary of papers

Bevins, R.E. (1984). The Geology of Northern Greenland, p.23

The area is a late Proterozoic basin, with sedimentation influenced by a fold belt. The sequences, structures and mineralogies are described, together with their tectonic setting.

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Dolamore, L. (1984). Joint Field Excursion with the Black Country Geological Society to Black Country Sites, led by Alan Cutler, p.4-6

The area visited included Round Oak Steel Works, with derelict mine workings from which plant fossils were obtained. The afternoon was concerned with the geology adjoining two branches of the Western Boundary Fault in the general area of Wordesley.

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Coope, R. (1984). A Beetle’s Eye View of the Ice Age, p.7-8

After describing the traditional view of ice ages and evolution, attention was drawn to the situation within ice ages where populations are driven into refuges capable of sustaining only a small population, therefore the selection pressures must be very great. Thus ice ages are likely to produce new, novel species, to speed up the process of evolution. Furthermore, when the ice retreats, vast areas of the country become available for colonisation, isolated small populations spread out and in so doing, atypical populations become established. These compete with one another; many will survive to produce new species, and other will become extinct. A correlation was then shown between beetle species and average July temperatures to describe palaeoclimates. The beetles indicate that climatic change can be very sudden and that the intensity of change is enormous. These changes can be correlated with changes in the position of the Gulf Stream North Atlantic Drift.

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Pitcher, W. (1984). Granite for Everyman, p.9-11

Granite is a deceptively simple rock, made up of quartz, two feldspars, mica, hornblende. But that is a gross oversimplification; there are granites and granites, and each has a different geological niche and tells a different story about the earth. The variation in the granitic rocks that you see in a large body of granites is not generally set up locally. These local variations are set up in individual magma chambers but, for example in Peru, the same granitic rock with the same chemistry comes up over 500 km into different intrusions. This means that the variation was already set up when the magma started to come up into the crust. Thus the genesis of granite lies down in higher energy levels of the crust and cannot be studied simply where they are emplaced.

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Tarney, J. (1984). Crustal Growth, p.12-14

The ocean floor is composed largely of basalt, whereas the continents are formed of lighter material of approximately the composition of granite. So where does the acid rock come from? One of the common models proposes that granites are derived from partial melting of the deeper part of the crust, the ‘liquid’ portion formed migrates upwards, forming diapirs, intruding into the upper crust as granites. The implication is that the dry rock left behind is richer in dark mafic minerals – pyroxenes, hornblendes, etc. However, the isotopic characteristics of the granites don’t always concur with an origin in the crust; they must be derived from the mantle. In zones of crustal generation, particularly in a subduction zone where water is taken down, wet magmas are formed, which get stuck in the lower crust and remain there in a ductile condition for a long time. Being very viscous, they flow over a long time period, but fracture easily. Thus they open up and are cut by basaltic dykes. Then, over time, the viscous tonalite intrudes the basic rock, splitting it up, stretching it and spreading it around, forming the veined appearance of black and white rock.

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Brazier, M. (1984). Microfossils in the Lower Cambrian, p.15-17

There are thousands of metres of the Cambrian in parts of the world such as Siberia, Baltic, North America, but relatively few fossils. By contrast, the Cambrian in Britain is condensed and therefore very rich in fossils. There is an identical succession in Nuneaton and Newfoundland, but a different succession occurs in Shropshire. In Shropshire the basal Cambrian rocks are not red as elsewhere – does this indicate that the arkosic succession has been faulted out? In fact, the Shropshire succession can be compared with that in Southern Sweden. Cobbolds work in Shropshire identified six separate limestones in the lower Cambrian, each with different faunas. One of these, Eodiscus bellimarginatus, is a world marker of ocean swimming trilobites. Dr. Brazier has drawn up the first correlation between Nuneaton and Shropshire using fossils which shows that Shropshire is very good for the higher part, and Nuneaton for the lower part. Possibly a reasonable stratigraphy for the English Lower Cambrian could be established in these two areas, but this requires much more work in the Shropshire and Malvern sequences, particularly in the Lower Comley Sandstone.

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Jones, D.M. (1984). Field Excursion to the Church Stretton Area, led by John Pauley, p.18-21

John Pauley’s trip around the Precambrian of the Church Stretton area visited Caer Caradoc, the Cwms, Ashes Hollow and the Stanbatch Conglomerate on the top of the Longmynd.

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Dolamore, L. & Jones, G. (1984). Joint Field Excursion with the Manchester Geological Association to Werrington Anticline, Stoke on Trent, led by David Thompson, p.22-23

The whole day was spent within the confines of the 400 acre park administered jointly by Staffs County Council and Stoke on Trent District Council and lying between Weston Coyney and Hulme, northeast of Longton. This had recently been reclaimed from derelict gravel quarries on the Werrington anticline, in the Triassic, with good exposures of Bunter Pebble and sandstone beds, 600 to 1000 feet thick, lying approximately horizontally. In the same location there are disused mine shafts along the line of an assumed fault, which bounds the eastern side of the Potteries syncline. The “five towns” run along the line of the Coal Measures outcrop (Black Band Group) with clay, limestone, coal and ironstone all along its length.

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Jones, G. (1984). Evening Field Excursion to Criggion Quarry, led by Mr. German, with Notes by Mr. Lawrence Crump, p.24-26

A guided tour of Criggion Quarry. The intrusive body was originally assumed to be laccolithic in form attaining a maximum thickness of 600 ft below Rodneys Pillar. Recent core drilling and associated mapping suggests the igneous mass is much thicker than previously estimated and might be interpreted as plug-shaped or at least substantially discordant. The rock could be referred to as an olivine gabbro.

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Jones, D.M. (1984). Field Excursion to the Tunnel Cement Works, Mold, led by Malcolm Conway, p.27

A guided tour of the Tunnel Cement Works, Mold. Visited Cefn Mawr Quarry, the source of limestone for the cement works. This quarry is in Carboniferous Limestone and good fossils of Lithostrotion Productus, and Spirifer were found, together with some fine samples of fresh galena.

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Cowie, J.W. (1984). International Interest in the Wrekin Area, p.28-29

Visit to the Ercall quarries to examine the granophyre and the basal Cambrian sedimentary strata by members of the Working Group on the Precambrian-Cambrian Boundary which is a part of international investigations sponsored by the International Union of Geological Sciences (I.U.G.S.) in cooperation with the International Geological Cooperation Programme (I.G.C.P.). Report of excavations with a mechanical digger near Charlton Hill in the Rushton district of Telford, Shropshire, to reveal the Comley Limestones.

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Complete volume, p.1-29

All papers
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To cite an article from this publication:

Brazier, M. (1984). Microfossils in the Lower Cambrian. Proceedings of the Shropshire Geological Society4, 15-17. ISSN 1750-855X (Print), ISSN 1750-8568 (Online)

© 1984 Shropshire Geological Society

Proceedings No 4 1984