In search of the lost climate…

 

Magnetic susceptibility as a high-resolution correlation tool and as a climatic proxy in Paleozoic rocks-merits and pitfalls: examples from the Devonian in Belgium.

2013

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Da Silva AC, De Vleeschouwer D, Boulvain F, Claeys P, Fagel N, Humblet M, Mabille C, Michel J, Sardar Abadi M, Pas D, Dekkers M

Marine and Petroleum Geology, 46, 173-189, 2013

 

With current climate change, there is a growing need to study and understand past climate systems. To understand the climate of the past, obviously we can not go directly to measure temperatures or rainfall, so we need what are called climate proxies. Climate proxies should be as direct as possible and should be stable over time (climate information should not be lost or transformed).

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In this paper, we consider magnetic susceptibility and its quality as a climatic proxy for very old sediments. It appears that, depending on the case, magnetic susceptibility can be a good climatic indicator or that climatic information can be transformed or even lost. We propose a protocol for identifying geological sections where climate information is preserved within the magnetic susceptibility signal (based on extensive magnetic measurements and measurements of rock chemistry). Thanks to these techniques, we propose the analysis of a magnetic susceptibility signal of the Devonian (360 Ma) of Belgium which allows us to identify climatic variations. Indeed, it is considered that if rainfall increases, more erosion-related magnetic particles are redistributed within the sediments. Thus, a higher magnetic susceptibility corresponds to a higher rainfall. This allowed us to identify climatic cycles within Belgian cuts and through these cycles to calculate the precise length of time recorded within these Belgian outcrops (see the Milankovitch cycles).
 

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