From time to time in its history, the Earth has suffered an 'Ice Age', when large parts of its land surface have been covered by glaciers and its ocean surface by sea ice. This has happened at least during the late Precambrian, the Ordovician and the Carboniferous. The earth is again in an Ice Age. It began to develop during a phase of global cooling at the Eocene-Oligocene boundary (35-40 Ma) and has intensified during the late Tertiary and Quaternary.
Antarctica is the continent most susceptible to glaciation, and evidence of the first growth of the Antarctic ice sheet from the Middle Miocene (c. 14 Ma) is the first sign of severe cooling. Some stages in progressive cooling are:
2.4 Ma: the first icebergs dropped detritus in the North Atlantic; 2 Ma: the first Arctic marine microfaunas in the North Sea;
0.75-0.8 Ma: detritus dropped from icebergs and glacial tills in the Forth approaches, showing that Scottish-centred ice sheets extended into shallow waters;
0.55 Ma: the first time that a Scottish-centred ice sheet extended to the edge of the western continental shelf.
The cooling of global climate has not however been smooth and gradual. It has shown complex patterns of variation on all timescales. The best continuous evidence of global climate change through the Late Tertiary and the whole of the Quaternary comes from low sedimentation rate cores from the deep ocean that preserve a record of changing oceanic water temperature in changing microfaunal assemblages (Fig. 15.1a)
Figures & Tables
This 4th edition of The Geology of Scotland is edited by Dr Nigel Trewin of the Department of Geology and Petroleum Geology at the University of Aberdeen. The volume is greatly expanded from the previous edition with 34 authors contributing to 20 chapters.
A new format has been adopted to provide a different perspective on the geology of Scotland. A brief Introduction is followed by a chapter outlining some of the important historical aspects that in the 19th century placed Scottish geologists at the forefront of a new science.
Scotland is constructed from a number of terranes that finally combined in roughly their present positions prior to about 410 million years ago. Thus the geology of each terrane is described up to the time of amalgamation, providing chapters on the Southern Uplands, Midland Valley, Northern Highland, Grampian and Hebridean terranes. At the end of this section, a brief synthesis summarizes the events that resulted in the amalgamation of the various terranes into the present configuration.
Traditional practice is followed in the description of the Old Red Sandstone, Carboniferous, Permo-Trias, Jurassic, Cretaceous, Tertiary and Quaternary strata. A separate chapter covers Tertiary igneous rocks. An attempt is made to tell the story of the geological evolution of Scotland, rather than catalogue all areas and formations. Priority is given to the onshore geology, encouraging the reader to go into the field and visit some of the world-class geology on show in Scotland. The chapters are broadly-based, attempting to integrate the sedimentary and igneous histories, and summarize changes in palaeogeography and palaeoenvironments.
Economic aspects are covered with chapters on Metalliferous Minerals, Bulk Resources, Coal and Hydrocarbons. A new departure is a chapter on aspects of Environmental Geology and sustainability.
Additionally, this publication contains a colour section of 32 plates, illustrating aspects of Scottish Geology, as well as a coloured geological map of Scotland.