Fish – builders of the chalk?

A joint UK/US study of ocean sediments off the coast of the Bahamas has come up with some surprising facts. See www.physorg.com/print218289668.html .. published by the PNAS it says that fish are responsible for a lot of the fined grained carbonite in sea bottom sediments, particularly in shallow sea situations. Until now it was thought they were derived primarily from sea-water absorbing C02 or the breakdown of the skeletons of tiny marine invertebrae and algae. The study shows that a high proportion comes from the intestines of fish which are excreted and end up as part of the sediment. Although the carbonites come from fish guts it is derived from calcium in the sea-water they drink. This research impacts on the formation of chalk – thought to have been laid down in Cretaceous shallow seas over immense periods of time. Until now chalk is assumed, from the microscope, to have been formed from the broken and mangled skeletons of plankton and the algae that fed on them. Why so much chalk was formed in the Cretaceous has never been explained properly – but what was the role of fish? (news release from Exeter University).