Red Mediterranean Soils in Jordan: New insights in their origin, genesis, and role as environmental archives

Abstract

It is disputed whether Terrae Rossae form mainly out of the bedrock residue, from allochthonous material like aerosols, or by isovolumetric replacement. Furthermore, whether they are mainly relic soils or are still forming is subject to debate. These questions were addressed by comparing the geochemistry of several limestone and basalt based Red Mediterranean Soils with Lithosols on sandstone and limestone in Jordan. The bedrock residue was included at all test sites. Paleosols and initial soils on the limestone Regolith of historic ruins delivered insights into the possible time frame of soil development. A major reduction of elements in the soils compared to bedrock could be observed for CaO in carbonaceous, SiO 2 in arenaceous, and Fe 2 O 3 and MgO in basaltic rocks. All Terrae Rossae, however, are characterised by a significant increase of SiO 2 , Al 2 O 3 , TiO 2 , Fe 2 O 3 , K 2 O, and a range of mainly metallic minor elements that cannot be derived from the bedrock. A reasonable explanation could be input via aeolian transfer of minerals, with clay minerals as the major carrier plus quartz. This input probably originates in Egypt and Sudan and has remained largely unchanged over long periods. Growing aridity during the Holocene has apparently increased the share of silt while clay deposition and soil development has been reduced. At some sites, metasomatic processes have contributed to soil development and might help to explain the depth of some profiles. However, formation of red soils during the Holocene seems very limited, and the Red Mediterranean Soils may represent remains of a paleolandscape.

Composition of Modern Dust and Holocene Aeolian Sediments in Archaeological Structures of the Southern Levant

“…Exceptional is Fe 2 O 3 , which falls on a correlation trendline common for all samples, including bedrocks. This suggests a consistent and similar chemical behavior of Al and Fe in oxidized weathering environments of sedimentary rocks, sediments and soils in the region as has been recorded in previous studies [62][63][64]. In contrast to the Petra region, enrichment of TiO 2 , Al 2 O 3 , Fe 2 O 3 or of other oxides is not observed in the archaeological soils.…”

“…High concentrations of P 2 O 5 , such as in the hilltop ruin at the central wadi, are interpreted as a marker of organic refuse. Similarly elevated phosphorus concentrations have been reported from hilltop ruins in Northern Jordan [61,64]. Debris from ruined settlements could have been subject to short-range aeolian deposition onto associated hilltops, which was indicated by the single-grain structure and low bulk density of 0.9 g/cm 3 (similar to the hilltop ruin soils of this study [61]).…”

“…Extractable iron, chemical weathering indices, and magnetic susceptibilities are sensible indicators of weathering processes, which are suited to characterize in-situ pedogenesis of soils in semi-arid regions [22,64]. However, Lucke et al [19] found no in-situ weathering in hilltop ruins, but that varying amounts of pre-weathered iron were inherited from diverse sources including the sandstone rocks in the Petra region.…”

“…The importance of local sources for dust deposition in the Levant could in general have been underestimated due to a focus on well-rounded or subangular quartz grains indicating aeolian abrasion [61,64,79]. In this context, a scanning electron microscope (SEM) study of the above mentioned hilltop ruin soil in Northern Jordan found a soil matrix consisting mainly of microfossils from chalk, angular calcite pieces, and bone and pottery fragments [61].…”

Anthropogenic Disturbances and Precipitation Affect Karst Sediment Discharge in the Nandong Underground River System in Yunnan, Southwest China

“…Previous studies showed that it required one-to three-quarters of a million years and a 25-m thickness of carbonate rocks to form just a 1-m soil layer in a typical karst ecosystem [14]. However, it is important to remark that, until recently, many authors believed there was no evidence that soil genesis on limestone could be possible due to the parent material, or at least that the parent material could represent a key factor in soil genesis [15]. While the conservation of water and soil is very important, such efforts are often restricted by the geology, gravitational (underground) erosion, and surface water erosion.…”