A 136 m section of Pleistocene-Holocene carbonate sediments in the Ashdod Yam 15/0 water well, which penetrates the coastal plain aquifer of Israel, was chosen for a study of carbonate diagenesis. The following diagenetic parameters were used to diagnose vadose, phreatic and marine diagenetic environments: original textures of aragonitic molluscan shells, kind and distribution of carbonate cements, trace-element (Sr and Mg) concentration and carbonate mineralogy. Comparison of the diagenetic parameters with the present hydrologic regime in the borehole indicates the following: 1) the preservation of vadose features well within the present fresh-water phreatic zone; 2) abundant intergranular and moldic porosity in a leached interval coinciding with a brackish-water mixing zone; 3) clear signs of fresh-water alteration, including leaching and recementation of molluscs and complete occlusion of pore space by drusy cement, in a permeable layer in a highly saline zone of sea-water intrusion; 4) the preservation of original metastable carbonate mineralogy, molluscan microstructure, and marine cements in the thin permeable layers shielded by impermeable shales; 5) extensive fresh-water alteration (coalescive neomorphic recrystallization, leaching, and occlusion of pore space by drusy cement) in thick permeable intervals.

First Page Preview

First page PDF preview
You do not currently have access to this article.