Soil Developmental Stages of Layered Cambisols and Calcisols on Socotra Island, Yemen

Abstract

Abstract Semiarid tropical regions are very suitable to study the polygenesis of layered substrates and soils. To determine relic and recent soil features of tropical soils, pedons in the northern part of Socotra Island, Yemen, were investigated. The aim of the study was to create developmental stages of widely distributed soils, which in particular are layered Cambisols and Calcisols. In most layers of those investigated soils, denudative components occur, which clearly indicate the relocation of coverloams and coverclays with an incorporation of extraneous materials, such as small pieces of relic clayey loams with different shapes. These fragments indicate strong chemical weathering, preceding erosion, and redistribution and/or embedding into younger sediments. Calcium carbonate found at a depth of up to 30 cm in 52% of the layered soils is very typical of an increasing aridity in parts of the semiarid tropics, particularly in areas with high groundwater levels and interflow. In addition, oxidation features and clay illuviation in noncalcareous substrates were detected. At the end, two major soil developmental stages of layered Cambisols and Calcisols were defined and demonstrated at two selected profiles. We assume that patterns of soil polygenesis depend not only on the composition of the respective substrates but also on changing climate conditions. Geochemical and soil physical methods as well as micromorphological analysis were used to describe and classify the soils.