Variations in the magnetic properties of quaternary sediments from various physiographic regions along the bank of Matla River, Sundarban, West Bengal, India

Magnetic susceptibility measurements at low and high frequencies (χ _lf , χ _hf ) and rock magnetic experiments (i.e., Curie curve analysis, Isothermal Remanent Magnetization, Hysteresis) are carried out on quaternary mangrove sediments from the bank of Matla River, Sundarban, West Bengal, India. Magnetic investigations being simple, fast, cost-effective, and non-destructive, are utilized to gather extensive data as a proxy for the spatial distribution of pollution. The study emphasizes magnetic parameters, such as concentration-dependent factors (magnetic susceptibility, isothermal remanent magnetization) and feature-dependent factors (coercivity of remanence, magnetic susceptibility ratio), as indicators of pollution. This study aims to investigate the application of magnetic parameters to determine magnetic property enhancement within the mangrove sediments along Matla River and thereby evaluate anthropogenic activities. The analysis of variations of χ _lf and frequency-dependent susceptibilities (χ _fd and χ _fd% ) indicate that the superparamagnetic (SP) grains dominate in the soil samples which mainly supports the magnetic susceptibility enhancement with few exceptions. The thermomagnetic curve identifies Curie temperature of the magnetic minerals and tracks magnetic carrier transformations during heating and cooling, showing both reversible and irreversible magnetization-temperature (J-T) behaviours. The Isothermal Remanent Magnetization (IRM) curve saturates at ~ 300 mT, characteristic of ferrimagnetic minerals like magnetite or maghemite, while some samples remain unsaturated at ~ 800 mT, suggesting high coercivity minerals like hematite or iron sulfides. Moving downstream, increasing coercivity indicates higher concentrations of these minerals. Hysteresis parameters (M _rs /M _s vs. B _cr /B _c ) on a Day plot show samples within the Pseudo Single Domain (PSD) range, likely a mix of Single Domain (SD) and Multi Domain (MD) grains.