Magnetic minerals, because of their iron content, are sensitive indicators of chemical weathering. The magnetic properties of soils and loess (windblown silt deposits, somewhat modified by soil formation) can therefore help us understand the moisture and temperature conditions in which soil and loess landscapes formed.
Sediments eroded from the Himalayas during their 50 million years of uplift have largely been carried out to sea and deposited in great cone-shaped piles to the east and west of the Indian subcontinent. The Bengal Fan, the deposit fed by the modern Ganges and Brahmaputra rivers, is by far the larger of these sediment accumulations. In the winter of 2015, I sailed on International Ocean Drilling Program Expedition 354 to sample these sediments. We collected cores from a transect across the middle of the Bengal Fan to track the flow of detritus from the rising Himalayas to its ultimate resting place in the Bay of Bengal.