MAGNETIC ANALYSIS OF FLUVIAL SOILS MAY AID IN RECONSTRUCTION OF ETHIOPIAN PALEOENVIRONMENTS

Recent archaeological and palaeoclimate studies show that climatic shifts occurring during the Holocene may have impacted cultural evolution and played a role in settlement patterns. The history of the Tigray Plateau in the northern highlands of Ethiopia is characterized by a succession of different civilizations and thus makes it an ideal location for assessing these possible impacts.

The magnetic properties of fluvial sediments from five soil profiles in study sites near the towns of Adi Kolen , Mai Maikden, and Adigrat were analyzed in an attempt to aid in the reconstruction of the regional palaeoenvironmental history. Measurements included magnetic susceptibility (c), anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM), S ratios, coercivity distributions of IRM, and hysteresis loops.

A comparison with nonmagnetic data shows that most palaeosol horizons do not show any signs of magnetic enhancement. Modern soils from sites AKIII, MMII, and ATI are characterized by increases in concentration parameters (increases in c, ARM, and IRM values) but grain-size dependent parameters indicate that the added ferrimagnetic minerals are coarse-grained (ARM-ratios decrease). Modern soils in all five sites are heavily disturbed and may be difficult to use for calibration of palaeosols.

For palaeosol horizons at AKIII (200-400 cm), however, magnetic properties (increases in c, ARM, IRM, and ARM ratios) indicate some degree of pedogenesis and some soils could be interpreted as magnetically enhanced. This possible magnetic enhancement occurs during a time period when non-magnetic indicators suggest higher rainfall, more fire, and vegetation change and may therefore be of importance for the cultural history of the region.