[N] 2004 Physical evidence for cooling at the K-Pg boundary
Italian, US and Dutch researchers who studied rocks at El Kef in Tunisia which cover the Cretaceous-Paleogene (K-Pg) boundary have found evidence for a global winter following the Chicxulub impact 65 million years ago that is thought to have killed off the dinosaurs 65 million years ago and created a global winter probably caused by a pollutant cloud of sulphate particles released when the asteroid vapourised rocks at Chicxulub, Mexico that blocked out sunlight.
The scientist who reported the results in the journal of Geology, discovered that microscopic cold-water creatures invaded a warm sea just after the space rock struck Earth. During the end of the Cretaceous period El-Kef was part of the warm western Tethys Sea.When the scientists studied the types of microscopic fossil creatures present in the Tunisian rocks, they found some surprising changes after the K-Pg boundary. In this period two new species of benthic foraminifera (simple animals that live near the sea floor) appeared these animals were cold-water types found in more northerly oceans. The scientist also found a curious difference in the shape of a microscopic snail-like creature called Cibicidoides pseudoacutus. This creature\\\'s shell is said to coil in either a left or a right direction. In cold waters there are proportionally more left-coiling individuals, while in warmer waters this pattern is reversed.
The researchers found a proportional increase in left-coiling Cibicidoides, after the K-Pg boundary. According to Dr Simone Galeotti of the University of Urbino, Italy its the first time that physical evidence for cooling at the K-Pg boundary is found. Matthew Huber of Purdue University in Indiana, US, said that the results the team got are fairly consistent with the impact winter decreasing the amount of sunlight hitting the Earth by 90%. The impact-induced darkness would have lasted between one and ten years on land, but there is evidence for a cooling of up to 2,000 years at El Kef. Positive feedback mechanisms may have prolonged the cooling effect of the impact winter in waters of intermediate depth - such as those at El Kef - and deeper. The latest research does help fill in the picture of what was happening to our planet following the impact at Chicxulub.