MAGNETIC SPHERULES IN RECENT LAKE-SEDIMENTS

The record of magnetic spherules in sediments from Crummock Water (the English Lake District) is presented and a method for obtaining magnetic extracts described. It is shown that magnetic spherule concentrations in the Crummock Water sediments increases by nearly two orders of magnitude following the Industrial Revolution, and this can be attributed to increases in fossil fuel combustion particularly after about 1900 A.D. Associated with the increase in spherule numbers are changes in their size distributions, which may reflect the changing sources for the spherules. It is demonstrated that magnetic spherules are distributed regionally and hence form widespread cryptic marker horizons in lacustrine sediments. Location of this horizon in a lake sediment profile provides an approximate dating method and this horizon may be located using susceptibility measurements corroborated by microscopic spherule counts.