Yorkshire Geology Month
The White Limestone and chalk of Jamaica
*Now on Zoom, not in person*
Event by Hull Geological Society
Lecture by Prof Simon Mitchell of the University of the West Indies.
If you were to go and look in quarries or road cuts on the north coast of Jamaica you would see chalks with bands of flint and thin marlstone beds. Although the climate is notably warmer, you could conceive that you are looking at the chalk of Yorkshire. Yet a quick look at the fossils tells a different story – no echinoids, inoceramids or belemnites, but Larger Benthic Foraminifers (LBF) preserved in graded beds (turbidites). You can travel south and go onto the carbonate platform that supplied these fossils (the Clarendon Block), and here you have a history of the middle part of the Cenozoic – the deposition of the White Limestone. Once considered a time of quiescence without tectonic activity, we now know that White Limestone time saw episodes of gradual subsidence interspersed with tectonic events (folding and faulting). I find analogies to this in the Bajocian limestones of the Cotswolds. Our understanding of the stratigraphy and platform/basin evolution can only be understood by looking at the fossils (LBF). LBF lived in the photic zone (depths down to 60–70 m) and are fascinating fossils. To fully appreciate them, you have to cut orientated sections so that you can fit them into their evolutionary pathways. They provide a high-resolution biostratigraphy that allows us to understand the evolution of Jamaica during the Cenozoic, but are equally valuable around equatorial latitudes worldwide. So why do we have chalks with flints in Jamaica? Well the environment was deep water and the marl bands (volcanic ash falls from Central America) provide a source for the silica – so why not? It has been a strange journey from the chalks of Yorkshire to the White Limestone of Jamaica; but for me, the comparisons are obvious and clear!
For details please visit Hull Geological Society’s website below.