Quartz grain surfaces – A potential microarchive for sedimentation processes and parent material identification in soils of Jordan

Abstract

Using SEM-supported microsurface and analytical methods we studied quartz and rare feldspar grains of the sand fraction >250 μm from three soil profiles in Jordan. The soils including a Lithosol are of different maturity and diagenetic alteration of their bed rocks, which are sandstone, limestone, and basalt. The profiles had been investigated during projects on the environmental history of the region, whereas the quartz grain surface analysis (QGSA) that has been applied for the first time to Jordan soils is an essential part of a supplementary study that was initiated when findings of unusual mineral components in a red basalt soil raised questions of their source and the history of this soil.The major transport processes and environments that were reconstructed for the sandstone Regosol and the Red Mediterranean Soil (RMS) on Early Tertiary limestone are documented by successions and types of grain-morphological features that apparently reflect varying water dynamics partly alternating with aeolian motion – a result, which matches with the known sedimentary history of their bedrocks and supports the reliability of the quartz grain surface analysis (QGSA). The microtexture pattern for the exotic quartz grain community in the basalt soil on an Early Quaternary basaltic rock showed a high similarity to those of the limestone samples. Part of the quartz grains from the basalt soil turned out to be chert as is present in the RMS profile and was an essential indication for the source of quartz. A sufficient explanation for the presence of quartz is that the outcropping, weathered Eocene Umm Rijam Chert Limestone Formation, among them chert nodules, was reworked and transported to the top of the weathering basalt. While a feldspar grain from the sandstone Regosol shows a conformable pattern to the quartz grains, plagioclase single grains from the red basalt soil, in contrast, are primary mineral components of the source rock. These preserved plagioclases exhibit only minor features of chemical weathering corresponding to the young, non-diagenetic bedrock. The size of the grains and situation of the basalt cap in the landscape, as well as preliminary dating suggest a period of heavy storms in Jordan at some time during the Pleistocene.