Climate cycles of the Cretaceous era are riddled

Researchers are studying lime / marl layers in Spain

Lime and marl layers University of W rzburg
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The alternating layers of limestone and marl in northern Spain are 94 million years old and thus formed in the extreme greenhouse climate of the Cretaceous. Researchers at the University of Würzburg have now unraveled the genesis of these formations and reconstructed the climatic events of that time.

In the Middle Cretaceous, 120 to 90 million years ago, the earth was in a major phase of upheaval. Intensive volcanism at that time greatly increased the carbon dioxide content of the atmosphere and caused an extreme greenhouse climate. Added to this was one of the most important ocean advances in the history of the earth: vast areas of the continents were flooded and covered by marine sediments.

For geoscientists, these deposits are like an archive of the earth's history, from which the global change of the time and climate cycles can be read off. Markus Wilmsen of the Institute for Paleontology of the University of Würzburg is doing research in this field.

In northern Spain, near Santander, together with his colleague Birgit Niebuhr and geologist Helga de Wall, the scientist studied lime / marl alternating layers that were formed some 94 million years ago, in the so-called Cenomanian period. For their analysis, among other things, the natural gamma radiation was measured in the field. The Würzburg researchers took samples for geochemical analyzes.

Climate cycles lasted 20, 000 years

"These layers were deposited in a former shelf sea at the border of the former subtropics to the warm-temperate climate zone, " explains Wilmsen. The aim of the investigations was to analyze the climate change from the sediment package. As a result, knowledge about the complex interactions between the atmosphere and the ocean, as well as the biosphere and lithosphere, is growing in times of a global greenhouse climate. display

The studied profile is 18 meters thick and contains 14 limestone-marl cycles. It documents a period of almost 300, 000 years, during which sediments were deposited at an average rate of 6.25 centimeters per thousand years. All this happened at a depth of 100 to 200 meters. Furthermore, the Würzburg researchers found that the marl layers formed in times when precipitation increased. In contrast, the limestones formed in drier periods. The climate cycles lasted about 20, 000 years each.

The scientists presented the first results of the study in September 2005 at the 7th International Cretaceous Symposium in Neuchâtel.

(idw - University of Würzburg, 02.11.2005 - DLO)