RAPID ENVIRONMENTAL/CLIMATE CHANGES IN THE LATE CRETACEOUS GREENHOUSE

Several events record rapid changes in environments and climate during the long-term greenhouse of the Cretaceous. Two intervals are prominent for extreme environmental conditions during the Late Cretaceous, the Cenomanian-Turonian boundary interval (CTBI) and the Cretaceous/Paleogene boundary (K/Pg). We investigate alpine sections that cover both OAE 2 and CTBI and compare the events duration and recovery.

The CTBI is marked by the global anoxic event OAE 2. Detailed investigations give evidence for a super greenhouse interval as a consequence of extreme volcanism (Carribean LIP). This led to high oceanic productivity in addition to stagnation and prolonged (600 - 800 kyr) burial of organic matter during OAE 2. One hypothesis is that worldwide extensive carbon dioxide burial during OAE 2 initiated climate cooling, and the oceans (except equatorial Atlantic sites and the Western Interior) ran stepwise into a major oxic state marked by CORBs (Cretaceous oceanic red beds) for the next ca. 700 kyr. This trend may have culminated in the short-term Mid-Turonian cool house.

New data from alpine sections indicate a different scenario of OAE 2 in this region. Benthic foraminifera do not show dramatic changes in nutrient distribution, further, no high-productivity and disaster species are present. An explanation for this might be the paleogeographic position of the Penninic Ocean which was a semi-enclosed basin situation during this time. The high productivity in the world ocean during OAE 2 contrasts with the overall absence of high productivity indicators and high foraminiferal diversities in the alpine section. The Penninic Ocean might have served as a refuge during this environmental crisis.

The Cretaceous/Paleogene boundary event was marked by both a large impact and extreme volcanism and occurred within a short time interval after a long-term cooling trend from the mid-Cretaceous super greenhouse. Impact-related environmental catastrophes characterize this boundary and mark the differences to the volcanism-triggered CTBI. After the K/Pg event it took several 100 kyrs for the world oceans to return to a normal state. During this recovery time several bioevents occurred, i.e. an acme of calcareous dinoflagellate cysts succeeded by an acme of coccolith species in one of the alpine sections.