A study recently published in Tectonics and conducted by INGV and Sapienza and Roma Tre Universities has highlighted a new potential indicator based on the geometric characteristics of the particles that make up rocks. The model will allow us to define with greater precision the age and geological transformations of sedimentary basins
A collaboration between researchers from theNational Institute of Geophysics and Volcanology (INGV)and Sapienza University of Rome and Roma Tre University has allowed us to develop an innovative model for reconstruct the evolution of mountain ranges.
This is what emerges from the study “Magnetic fabric as a marker of thermal maturity in sedimentary basins: A new approach for reconstructing the tectono-thermal evolution of fold-and- push-belts”, recently published in the scientific journal 'Tectonics'.
To determine the age and transformation of mountain ranges, geoscientists examine the thermal maturity of the sediments, or the heating which the rocks and in particular some indicators present in them - such as clay minerals and wood fragments - have been subjected over geological time.
"Thermal maturity of sediments reflects the degree of evolution of organic matter and the transformations of clay minerals during burial diagenesis", explains Clare Caricchi, researcher at INGV and first author of the article. “This thermal maturity is influenced by factors such as temperature and time, and is a fundamental concept for understanding the formation of energy resources such as oil and natural gas".
La diagenesi is a geological process involving the chemical, physical and biological changes that sediments undergo after their deposition and before their lithification, or transformation into rock. This process occurs at relatively low temperatures (up to about 200 °C) and moderate pressures (2-3 bar), and can last millions of years.
The reliability of a reconstruction of the evolution of mountain ranges depends on the number of usable thermal indicators, which are not always available.
Researchers from INGV, Sapienza and Roma Tre have identified a new potential indicator based on the geometric characteristics of the particles that make up a rock and their mutual orientation relationships. This information is obtained from a property, the so-called “anisotropy of magnetic susceptibility” (AMS), which refers to the tendency of minerals to arrange themselves predominantly in planes perpendicular to the direction of deposition and subsequent compaction of the sediments. A process that occurs when the sediments are progressively covered by other more recent deposits and then carried deep into the crust, where they are subjected to increasing temperatures and pressures, to then re-emerge on the surface during the formation of mountain ranges.
“Our analyses aim to answer the question 'To what depth were the analysed sediments buried before being brought to the surface by the formation of the Apennines?', or 'To what maximum temperatures were they subjected?', explains Leonardo Sagnotti, researcher at INGV and co-author of the article. “AMS is a property that is measured in paleomagnetism laboratories with dedicated instrumentation and that relates the variability of magnetic susceptibility to the direction in which it is measured, which depends - in turn - on the preferential orientation of the minerals that make up the sediment”.
“Our study focused on the Northern Apennines, in an area between Umbria and Tuscany, where we collected samples of coherent sediments for AMS and X-ray diffraction analyses”, adds Luca Aldega, researcher at Sapienza University of Rome and co-author of the article. “The analysis data indicate that The AMS of these clayey sediments can be directly correlated with the depositional and compaction processes, as suggested by the thermal maturity indicators, thus reflecting the evolution of the sediments during sedimentary and/or tectonic burial.".
“This observation allowed us to calibrate a model based on a linear correlation between the AMS parameter and paleothermal indicators that can be successfully applied to define thermal maturity levels in sedimentary basins, overcoming the limitations of classical methods and constraining the diagenesis conditions of sedimentary successions on a time scale”, highlights Massimo Mattei, researcher at Roma Tre University and co-author of the article.
Further future research in this direction may be useful to improve the definition of the correlation in case of advanced thermal maturity stages and in highly deformed sedimentary successions.
Useful links:
National Institute of Geophysics and Volcanology (INGV)
Fig 1 a) Example of deposits analyzed in the study b) sampling for analysis of clay mineralogy, c) woody fragments, d) sampling for analysis of magnetic susceptibility anisotropy.
Fig.2 Correlation between Foliation (AMS parameter) and paleothermal indicators that can be applied to define thermal maturity levels in sedimentary basins
