Old basalts, young soils - Age constraints for the Golan Heights plateau volcanic soils

Abstract

The Golan Heights plateau in northern Israel is underlaid by volcanic rocks ranging in age from ~5.5 to 0.1 Ma. Throughout the Golan Heights, these rocks are covered by shallow soils that rarely exceed 0.5 m in depth. The soils are generally assumed to form a chronosequence, in which their ages correspond to those of the basalts they cover. Such age correspondence would imply that the soils have been slowly accumulating over hundreds of thousands to a few million years, suggesting a generally stable system. The ages of these soils and their temporal correlation to the basalts, however, have never been determined or tested.

Here, we present age constraints for the soils of the Golan Heights. Soils were surveyed and sampled with their corresponding basalt bedrock. Mass balance calculations based on conservative immobile elements, coupled with ³⁶Cl-based basalt denudation rates, suggest that the soil ages are decoupled from the ages of the underlying basalts, and represent up to a few thousand years of soil production, at most. This time frame is orders of magnitude shorter than the basalt age, challenging the prevalent assumption that the soils form a chronosequence.

Our findings strongly suggest that erosion is a significant factor controlling soil formation and accumulation on the plateau, despite the generally flat morphology of the Golan Heights. The erosion is associated with tectonic activity along the Dead Sea transform, with the development of the Kinarot and Hula valleys, and with the consequential development of drainage systems of various sizes on the plateau. Throughout the Golan Heights, the timing of volcanic activity in relation to the development of the valleys and drainage systems also appears to strongly affect soil development and accumulation.