Article 69

Knowledge Of An Emerging Britain – The Tertiary Period.

In his Chapter 12, Peter Toghill reports that the Tertiary period over Britain was one of remarkable contrasts. While most of the area experienced uplift and erosion to form a distribution of land forms not too dissimilar to today, the far north-west experienced widespread early Tertian volcanism, and the south-east experienced marine sedimentation. Uplift and doming of the area between Greenland and Rockall initiated volcanic activity and sea-floor spreading to commence the formation of the North Atlantic around 63 Ma. Associated volcanic and igneous activity in Scotland and Northern Ireland lasted from 63 Ma to 52 Ma and had thus finished by the early Eocene. Up to 2000 m of basalt lavas were erupted and gabbros and granite intrusions were formed. The North Sea basin subsided to receive 3000 m of marine sediments, and branches of this sea periodically flooded southern England to form a thin (c 500m) sequence of Tertiary sediments up to the Oligocene. About 2000m of sediments formed in the western approaches of the growing Atlantic and this area occasionally joined with the North Sea basin through narrow sea-ways close to the English Channel. The Tertiary sequences of southern England show a constant mixing of marine and non-marine facies as the sea transgressed and regressed. 

Even though Britain moved to its present latitudes during the Tertiary, the climate was warm and humid even as far north as Scotland, where vegetation grew on laterite soils between lava flows. Folding and faulting affected southern England during the Miocene with the formation of well-known, often tight folds in Dorset, the Isle of Wight, and in the inversion fold of the Weald, as well as other areas. This episode of earth movements, often called Alpine, was probably caused by a mixture of tectonic forces, some due to sea-floor spreading in the newly forming North Atlantic, and others due to the effects of the Alpine orogeny further south. Many of the folds are steep mono-clinal structures, and together with faults may be associated with structures in the Variscan basement. Large-scale tear faulting affected south-west England and a number of offshore faults were active, many of which define the present coast-line of Britain. Fault-bounded basins in south-west England (Bovey Tracey) and Cardigan Bay received great thickness of lacustrine and fluvial Oligocene and Miocene sediments derived from nearby highlands, and scattered remnants of late Miocene sediments occur in south-east England. However, marine Pliocene sediments are only found in East Anglia where they grade up into rocks, showing the increasingly cold climate which heralded the onset of the glacial conditions of the Quaternary.

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