The Quaternary geological period, beginning roughly two million years ago, is the most recent, and ongoing, period of Earth's history. It comprises a particularly dynamic timespan, characterized by major shifts in climate, expansion and contraction of continent-sized ice sheets, rises and falls in global sea level, migrations and extinctions of fauna and flora, and not least, the evolution and exponential rise in population of modern humans. These sequences of dramatic changes in the Earth's climate and biosphere have frequently imprinted themselves within natural proxy records – as physical, chemical and isotopic variations within sediments or ice. Such proxy records, if they can be retrieved and deciphered, allow us to identify the timing, rate and mechanisms of past changes in climate and environment. This information is increasingly critical. It provides the context and perspective for both our present understanding and future prediction of climate, at a time when human modification of the climate system, via greenhouse gas emissions and pollutant aerosols, appears significantly under way.
This book aims to examine the Quaternary palaeoclimatic and environmental information recorded by magnetic proxies. Magnetic grains, dominantly iron oxides and sulphides, occur virtually ubiquitously in Quaternary sediments, soils, dusts and organisms, albeit often in minor or trace concentrations. As is widely known, such grains may act as palaeomagnetic recorders of the Earth's ancient magnetic field. Additionally, however, they may act as sensitive magnetic recorders of palaeoclimatic and palaeoenvironmental change. Changes in climate produce changes in the environment, including sedimentary and soil-forming environments. The mineralogy, concentration, magnetic grain size and morphology of magnetic grains may all vary according to the origins of the magnetic grains and their subsequent post-depositional sedimentary history.