Abstract: The distribution of permeability and chemical character of groundwater in carbonate aquifers is significantly influenced by the many diagenetic processes
and reactions that occur in the early development of these rocks. Many of these diagenetic processes occur in the transition zone formed as the carbonate sediments emerge from the marine environment and become fresh-water aquifers. Analyses of trace elements and isotopes
indicate that calcite cements and dolomites are formed in this groundwater mixing zone. Reverse reactions such as mineral dissolution and dedolomitization occur in carbonate aquifer systems. The geochemical reactivity of the fresh-water/salt-water mixing zone results from the nonlinearity of geochemical parameters as a function of ionic strength and causes extensive dissolution in coastal carbonate rocks. Interpretation of geochemical reactions and isotopic composition of groundwater provides a method to determine hydrological parameters
such as porosity, hydraulic conductivity, and groundwater flow rates. This geochemical method is largely independent of the more conventional approach of determining these parameters by an evaluation of physical properties of aquifer systems.

Abstract: The palaeoenvironmental and palaeoclimatic evolution of the Serres basin from the end of mid-Miocene to the end of the Miocene is examined. Lignites were deposited over a thick sequence of conglomerates and sands. Fossils found in the lignites indicate a lacustrine environment with tropical-subtropical climatic conditions. The climate became progressively drier and only small lakes were reserved during the Messinian salinity crisis. Deposition of lake sediments finally ended with the world-wide Pliocene marine transgression. A correlation of the Serres basin with other lacustrine basins in the Aegean area is attempted.