干旱区生态环境知识资源中心

This paper presents karstological prospecting of selected areas in Ras Al-Khaimah Emirate, UAE. Several locations in Musandam Mountains have been explored for caves, karst springs and surface karst features. Two karst springs, Khatt and MeBreda, were analyzed for basic physical, chemical and microbiological parameters. Although they are both recharged from karst aquifers, they differ significantly. The first one is a thermal spring in which infiltrated rain water is mixed with more saline and mineralized water from greater depths. The location of the second one at the high altitude of 710 m a. s. l. is conditioned by the existence of a less permeable zone within a carbonate aquifer with a larger share of dolomite. There were increased concentrations of nitrates probably due to grazing goats around the spring but on the other hand there was surprisingly low number of total bacterial counts; however detected Escherichia coli indicated probable fecal contamination. None of the water from any of the tested sites matched the ISO criteria for direct human consumption. Surface rock relief resulted from different karst processes was studied in river beds and side walls of wadis and on the mountain plateaus. The slopes of the wadis are often dissected by large recesses, relatively rare subsoil forms, and karren with microrills and rain flutes. More extensive karren are found on the tops of the mountains. The rocky riverbeds of wadis were shaped by rapid water currents and corrosion at the contact with sediment. In the study area at the northern slopes of mountains no big cave was found. The largest discovered cave was in fact tectonic fracture which was extended due to the gravitational sliding of part of a mountain along a fissure. But several small (10-20 m long) solutional caves have been discovered and surveyed on the wadis slopes. They exhibit relatively simple assemblage of dominantly deadend passages. Caves are vertically distributed at several levels above the wadis. The rocky relief of the caves indicates the paragenetic development of the caves. Some of the studies caves were fully and some partially filled with yellow clastic sediments. Also few layers of flowstone, calcite crystals and gypsum crystals were found. Mineralogical analyses shows very similar composition of sediments: different minerals such as quartz, gypsum, kaolinite, smectite, illite, calcite and palygorskite in various proportions. Calcite and gypsum represent precipitates from the cave (crusts, crystals, cements) and the other minerals were brought to the cave most probably by water or wind from eroded rocks and/or soils from wadis catchment areas.