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The Early Aptian (120 million years ago) was an age of intense volcanic activity on Earth, eruptions that emitted large amounts of CO2 into the atmosphere, thus causing a revolution in the carbon cycle. As a consequence, great changes happened in the whole of the terrestrial system. Researcher Mara Isabel Milln has studied how these changes happened in the marine environment of the Aralar mountain range (at that time it was under the sea) in the Basque Country, and found more than one surprise. She presented her conclusions in her PhD thesis at the University of the Basque Country (UPV/EHU).
Ms Milln's thesis is entitled Record of Palaeoceanographic changes during the Early Aptian of the Aralar mountain range. Given its geological characteristics, Ms Milln suspected that the changes that took place in the Early Aptian period must have left traces in the sediments of the Aralar mountain range, which straddles the Basque provinces of Gipuzkoa and Navarre. She began to study the outcrops in detail. The researcher observed that the materials representing this period in Aralar are more significant than those studied to date, and this was the first surprise of this thesis. While in other parts of the world the sedimentary series of the Early Aptian that can be studied are some 20 metres thick, Ms Milln found up to 1,000 metres in Aralar.
An unparalleled event
One of the principal global changes that took place in the oceans of the Early Aptian was that known as OAE1a (Oceanic Anoxic Event 1a); that is, a sudden reduction in maritime oxygen at the ocean beds. In order to show that this phenomenon also occurred in Aralar, Ms Milln employed a number of methodologies. On the one hand, she used ammonite fossils, which give very precise dates and which have been found in abundance
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