Over time, subterranean fluids progressively change the rocks. When using rocks as climate archives, these processes need to be taken into account. Together with international colleagues, Dr. Mathias Müller of the Sediment and Isotope Geology research group at Ruhr University Bochum, Germany, has described the types of climate information that have been retained in 380 million-year-old limestones from Hagen-Hohenlimburg.
Furthermore, he can make judgements regarding the rock's suitability for deep geothermal use today based on his investigations. On July 1, 2024, the journal Geochimica et Cosmochimica Acta published the findings of his investigation.
The rock's climate archiveExamining historical records can be beneficial in gaining insight into the current state of affairs. For this, scientists employ what are known as proxies, which are indirect markers of climate found in natural archives like dripstones, tree rings, and ice cores.
According to Mathias Müller, "we examine sedimentary rocks that may even have stored the seawater temperature from hundreds of millions of years ago if we want to learn anything about the climate several million or even billions of years ago."
The subsequent alteration in the climate fingerprints contained in these rocks is one factor that could make this kind of extensive climate research much more challenging. Diagenesis is the term for this process. It can last till today and starts soon after sediment deposition in saltwater. According to Mathias Müller, "very old rocks are usually buried to depths of several kilometres.
From the mountains to the shallow sea
In collaboration with a global research team, Mathias Müller meticulously restored which climate data from the Devonian shallow sea is still preserved in the rock in the Hagen-Hohenlimburg region, as well as the processes and circumstances that have altered it throughout time. Using petrographic and geochemical techniques, the researchers examined a large number of methodically obtained rock samples from the Steltenberg quarry.
In collaboration with a global research team, Mathias Müller meticulously restored which climate data from the Devonian shallow sea is still preserved in the rock in the Hagen-Hohenlimburg region, as well as the processes and circumstances that have altered it throughout time. Using petrographic and geochemical techniques, the researchers examined a large number of methodically obtained rock samples from the Steltenberg quarry.
