Talk by Malcolm Hart PhD DSc FGS CGeol CSci.
Visitors to Beer in South East Devon are often amazed to see chalk cliffs which they, quite correctly, associate with South East England and places like the Isle of Wight. Chalk is much more extensive than many imagine having at one time covered almost the whole of England, the North Sea Basin, Western Approaches Basin, Celtic Sea basins and the Irish Sea area. The chalk ranges in age from c.100 Ma to the end of the Cretaceous at 65 Ma. The Latin for chalk – creta – gives its name to the Cretaceous System which was founded in 1822 by the Belgian geologist Jean Baptiste Julien d’Omalius d’Halloy. There was no ‘founding’ paper with the ‘Terrain Crétacé’ just appearing in the legend of his map (see Hart, 2024).
The chalk was formed at a time of global ‘hot-house – warm-house’ conditions and, with virtually no ice on the planet, sea levels were exceptionally high, resulting in most of the continents being covered in sea (Scotese et al., 2024). Unusually the chalk is almost 98+% biological in origin, being largely composed of the tiny plates of coccoliths (calcareous brown algae). It has been estimated that there are approximately 8 billion coccoliths per cm3 of normal chalk. Despite their diminutive size blooms of coccoliths can be seen in the surface waters of the world’s oceans from space at the present time and it may well have been like that in the Cretaceous. There are variations in the chalk e.g. the Beer Stone of South East Devon and the Red Chalk of Hunstanton and these are quite distinctive. The other distinctive feature is that of the flints; black silica nodules that are seen in much of the chalk succession. These are biogenic silica (another organic source) but their formation is often quite complicated. In many places they follow a Milanković cyclicity and help in the construction of an astrochronology for parts of the Cretaceous.
Malcolm Hart DSc FGS CSci CGeol is Emeritus Professor in Micropalaeontology at the University of Plymouth. His research on microfossils appears in over 400 scientific publications and a number of edited books. In a research career extending over 60 years, he has undertaken field work all over the world, especially in Europe, USA, India and Brazil. Climate change has figured in this research and recent work on estuaries in Sothwest England is also looking at how these have changed through glacial/interglacial cycles as well as at the present time.