Project 580 - Application of Magnetic susceptibility on Paleozoic Sedimentary Rocks
Quantitative magnetic susceptibility (MS) measurements have become widely used in the sedimentology of rocks from the Recent to the Paleozoic. The basic principle of the technique is the following: MS measurements on sedimentary rocks are considered as a proxy for impurities delivered to the sedimentary environments. Although the common sandstones or limestones have very low magnetic response, many weathering products coming from the erosion of the main land commonly have high MS values. So the measurement of MS in sediment is considered as a proxy for such detrital input. This relationship is interesting because it is hypothetized that climatic and eustatic sea level variations will affect the detrital input. A sea-level fall increases the proportion of exposed continent and siliciclastic supply and therefore increases magnetic mineral deposition. Furthermore, an increase of rainfall or a glaciation will also increase erosion. Bulk MS measurements have been used in sedimentology for correlations and for reconstruction of sea level or climatic changes. MS of Holocene, Pleistocene, and Tertiary sediments and sedimentary rocks is widely used as a paleoclimatic proxy. The use of MS in Paleozoic sediments is becoming more common but still suffers from some controversy. One of the problems is the origin of the magnetic minerals. The dominant hypothesis for sedimentologists is that magnetic minerals are mainly related to lithogenic inputs. But are these related to fluvial or eolian sources? Are these lithogenic input variations related to climatic, sea level or tectonic changes? These different influences are probably acting at different time-scales and to differentiate the different impacts, a strong interdisciplinary characterization of facies, cyclostratigraphy and the MS signal and its carriers is needed. Furthermore, considering the study of Paleozoic rocks, the influence of diagenesis in creating or destroying magnetic minerals has to be assessed. In order to solve these issues, an efficient and truly international collaboration between geoscientists from various disciplines like sedimentology, paleontology, stratigraphy, paleoclimatology, geochemistry, paleomagnetism and geophysics should be initiated and encouraged.
This project concerns three main issues. The first one consists of compiling the available MS data from the different researchers (with a main focus on the Devonian) and to continue to collect new data in the field, to test the correlative power of the technique and the influence of facies and sedimentological parameters on MS signal. The second issue is the main interdisciplinary part of the project and will focus on the identification of the origin of the MS signal. It will need a strong collaboration between sedimentologists, geophysists, magnetic properties specialists and geochemists. And the last issue will be in the light of the obtained results, to better compel the application of MS in applying MS for correlations and to reconstruct climatic variations. MS is a technique that can be performed very quickly and economically. Connected to biostratigraphy, it can be an effective and high-resolution tool for correlations. In addition, the extreme conditions and secular trends in the climate parameters of the past have also potential to contribute the research in actual climate changes. The global and interactive goal of this research could be carried on only by a worldwide network of researchers from different geoscience disciplines. Furthermore, this project can strongly benefit from the IGCP 499, which compiled abundant data and documented correlations of Devonian sections that can be used for MS measurements. The project website will be provided from Liege University network on the current MS projects as a communication platform for participants. This website will also intent to propose a list of people working in environmental MS other data which make the collaborations easier.