Abstract
The present study aimed to investigate rare earths as trackers of groundwater movement. For this purpose, different, in terms of their morphological and geological characteristics, hydrological basins were chosen, the basin of Xeropotamos-Almyros (province of Mirabello), the basin of Panteli (valley of Sitia), the basin of Lastros-Sfakas-Mochlos and three of the area of Toplou Monastery, which after being studied in terms of their hydrogeological characteristics, were used as the background of the research. The Xeropotamos-Almyros basin has an area of 124 km2 and for the most part consists of the carbonate rocks of the Tripoli zone. The background of the basin is the impermeable rocks of the phylites quartzites series. In the limestones and dolomitic limestones of the Tripoli zone, a karstic aquifer system has been developed that transports groundwater from the supply zone to the W-SW part of the basin to the discharge sources of Almyros. Averagely, the Xeropotamos-Almyros basin receiv ...
The present study aimed to investigate rare earths as trackers of groundwater movement. For this purpose, different, in terms of their morphological and geological characteristics, hydrological basins were chosen, the basin of Xeropotamos-Almyros (province of Mirabello), the basin of Panteli (valley of Sitia), the basin of Lastros-Sfakas-Mochlos and three of the area of Toplou Monastery, which after being studied in terms of their hydrogeological characteristics, were used as the background of the research. The Xeropotamos-Almyros basin has an area of 124 km2 and for the most part consists of the carbonate rocks of the Tripoli zone. The background of the basin is the impermeable rocks of the phylites quartzites series. In the limestones and dolomitic limestones of the Tripoli zone, a karstic aquifer system has been developed that transports groundwater from the supply zone to the W-SW part of the basin to the discharge sources of Almyros. Averagely, the Xeropotamos-Almyros basin receives 117.4x106 m3 of water annually from rainfall of which 41x106 m3 evaporates, 52.8x106 m3 infiltrates to the geological formations and 26.6x106 m3 feeds the surface runoff. Based on the quality characteristics of groundwater, three areas can be distinguished. The first area is designated by water consisting of Ca-Mg-HCO3 and corresponds to the supply zone of the aquifer. The second area is designated by Ca-Mg-Na-HCO3-Cl water and corresponds to the area where fresh water is mixed with seawater. The third region is designated by Na-Cl chemical water, where seawater ions prevail over freshwater ions. The basin of Lastros-Sfaka-Mochlos has an area of 19.6 km2 and is composed of plattenkalk, phyllites-quartzites and pleistocene formations. The basin is located in the eastern part of the ruptured zone of Ierapetra and is a trench of two opposite faults, the fault of Lastros and the fault of Sfaka. The tectonic movements are responsible for the lateral contact of both the plattenkalk with the phyllite-quartzites and the contact of the plattenkalk with the neogene formations. The basin receives annually an average of 20.2x106 m3 of rainfall water. 7.9x106 m3 of that amount evaporates, 3.4x106 m3 infiltrates to the aquifers of the area and 8.9x106 m3 flow superficially and are removed from the basin. The groundwater movement takes place in a S-N direction with supply areas in the southern mountain range of Oreino and their discharge area being the pleistocene formations of Mochlos and Agios Andreas. The contact of the plattenkalk with the quartz phyllites, that in their upper parts present anhydrides and gypsum, results in the degradation of the water in the aquifer of the plattenkalk. The chemical composition of water in the supply region consists of Ca-HCO3 and Ca-HCO3-SO4 until reaching the discharge region which gradually converts to Na-Ca-Cl-HCO3-SO4. The basin of Panteli occupies a total area of 125.8 km2 and is developed on the crevice of Sitia. Most of the basin is occupied by formations of Neogene in its southern and central part, while the northern part, at the outfall of the Panteli river, pleistocene formations are found. The main aquifer of the basin grows in the carbonate conglomerates of Neogene. Groundwater movement is directed from south to north.According to the hydrochemical formula of water, three areas can be distinguished. The first area is located in the SW part of the basin and is composed of water with the chemical formulas of Ca-HCO3 and Ca-Mg-HCO3, the second area occupies its eastern part and is composed of the chemical formula Ca-Mg-Na-HCO3-Cl while the third one occupies the northern part of the basin with the chemical formula of Na-Ca-Mg-Cl-HCO3. The area of Toplou Monastery is located at Cape Sidero and occupies an area of 31.6 km2. The area each year, on average, receives 12.33x106 m3 of rainwater, from which 6.6x106m3 evaporates, 3.25x106m3 penetrates the aquifers of the area and 2.46x106m3 flows superficially. Three main hydrological basins formed by neogene and pleistocene formations that are distinguished have been deposited on impermeable quartz sheets. The main tectonic feature of the area is the existence of two vertical main fault direction rifts E-S and N-S. The first fault is located south of the area and brings the neogene formations in contact with the carbonate formations of the Tripoli zone. The second fault intersects along the area of Toplou Monastery and ends north of it. The supply area of the aquifer that develops within the granular formations of Neogene is located in the southern part of the area, while its discharge takes place west in the area of Analouka and north in the area of Erimoupolis and Vai.The existence of the underlying impermeable rocks of the sheet quartzites limits the extensive intrusion of seawater into the aquifers of the peninsula of Sidero. The intrusion of seawater is observed mainly in the area of Analouka in the west of the area and in the area of Vai and Erimoupolis at the NE end of the cape. Increased concentrations of Na and Cl are observed, as well as K. The chemical formula of these waters is Na-Ca-Mg-HCO3-Cl or Na-Mg-Ca-Cl-HCO3 and gradually switches to Na-Ca-Cl-HCO3. The rare earths of the rock samples that host the aquifers of the research basins were identified after these samples had first been pulverized and digested. The measurements were performed by the method of analysis in ICP-MS. The method of preconcentration samples proposed by Suzuki et al., (1991) was chosen to determine the rare earths in the water samples. The water samples were normalized based on the international standards of the shales of Europe and Japan, as well as with the respective rare earths of the aquifers. The following conclusions emerged from the study and comparison of the normalized rare earth diagrams, from the calculation of the absolute concentrations of rare earths (ΣREE) as well as from the study of the anomalies of Cerium (Ce) and Europium (Eu): Rare earths (ΣREE) vary from aquifer to aquifer. The reason for this differentiation is that the rare groundwater soils inherit the characteristics of the rocks through which they moved. Rare earths track information about groundwater movement. The high speed of groundwater in the karstic system of Almyros Xeropotamos, the dissolution of gypsum in the basin of Lastros-Sfaka-Mochlos, the dissolution of clay minerals and the creation of colloids and hydroxides of Fe in the basins of Panteli and the Monastery Toplou are the main factors that determine the normalized diagrams of rare earths. The differences of the normalized diagrams of rare earths are not only distinguished between the different types of aquifers but also within the aquifers. The change of total groundwater concentrations is determined by the change in its hydrochemical formula from Ca-Mg-HCO3 to Na-Ca-Mg-Cl-HCO3 and finally to Na-Cl. The change in rare earth concentrations is expressed by the reduction of their total from the freshwater zone to the brackish zone and finally to the saline zone. Rare earths are useful tools for tracking chemical processes such as redox, adsorption and complexation reactions. They record the hydrogeological and hydrochemical conditions that prevail in each position of the aquifer as well as their differences in relation to time.
show more
