Expanding horizons of paleomagnetic and rock magnetic appplications

Abstract

Techniques of palaeomagnetism and rock magnetism have potential applications to problems in sedimentary geology. Latest applications of these techniques to hydrocarbon exploration and environmental studies are reviewed. For hydrocarbon exploration, the palaeomagnetic data have been applied mainly to the following areas : Borehole core orientation, dating of hydrocarbon migration, magnetic anomalies associated with hydrocarbon seeps and plumes, and magnetostratigraphy for precise dating of the sedimentary strata. Rock magnetism, which provides theoretical basis for palaeomagnetic investigations, has been applied to environmental systems in the study of global environmental change and climatic processes. These studies form a separate discipline of study now known as Environmental Magnetism. Materials that have been studied for environmental magnetism include lake and marine sediments, soils, atmospheric particulates, and biological entities. Various mineral magnetic parameters, such as susceptibility, IRM, SIRM and ARM are sensitive indicators of temporal variations in the concentration and grain size ofterrigenous or lithogenous materials deposited on the seafloor or lake bottom. Studies of downcore susceptibility and palaeointensity variations have led to a better understanding of the environmental and palaeoclimatic conditions involved in the geologic processes in sedimentary records. Environmental magnetic techniques can also distinguish between the magnetic grains from different sources in the atmospheric particulates. Valuable insights into the processes of pedogenesis, authigenic/diagenetic formation of ferrimagnetic phases, and dissolution of magnetic minerals in marine and lake environments could be obtained through mineral magnetic techniques.