Environmental Magnetism of Lower Miocene Strata from the CRP-1 Core, McMurdo Sound, Antarctica

Environmental magnetic data from the early Miocene sequence of the CRP-1 core, from McMurdo Sound, Antarctica, reveal an alternation between zones of high and low ferrimagnetic mineral concentrations. Although magnetite is the main magnetic mineral throughout the sequence, coercivity variations mirror the zonation in magnetic concentration, with high coercivities corresponding to zones of low concentration of ferrimagnetic grains and vice versa. High concentrations of ferrimagnetic grains (unoxidised magnetite) were found in fine-grained sediments that were deposited in a distal position with respect to the ice front, and in the lower part of one diamictite (Unit 6.3). Low concentrations of ferrimagnetic minerals occur in sandstones. We suggest that environmental changes that produced the variations in the amount of magnetite being eroded and transported to the CRP-1 site are best explained by a climatically-driven variation in the physical weathering regime on the Antarctic craton. Such fluctuations must have occurred in a relatively cold climate, below the threshold that would induce a change in the overall weathering regime. However, this interpretation is non-unique and rigorous interpretation of the sediment magnetic record requires validation from other data.