Deep confined karst detection, analysis and paleo-hydrology reconstruction at a basin-wide scale using new geophysical interpretation of borehole logs

Abstract

summary Deep karst voids can be identified by a new method of geophysical interpretation of commonly used borehole logs in deeply confined carbonate aquifers. We show that deep, buried karst voids can be characterized by combining this geophysical interpretation together with geological and hydrological data, and with known speleological constraints. We demonstrate how this characterization can reveal past hydrological regimes and allow mapping of karst distribution on a basin-wide scale. A combined analysis of geophysical, geological, hydrological, and speleological data in the confined Yarkon–Taninim aquifer, Israel, led us to reconstruct past groundwater levels at different relief and sea levels, with the karst voids as a marker for long-term flow close to the water table. Paleo-canyons along the Mediterranean Sea shoreline strongly affected the region’s paleo-hydrology, by serving as major outlets of the aquifer during most of the Cenozoic. We conclude that intensive karstification was promoted by flow periods of longer duration and/or higher flux and flow velocities close to the aquifer’s past and present outlets. In addition, we suggest that karst voids found under shallow confinement were developed by renewed aggressivity due to hypogene water rising in cross-formational flow becoming mixed with fresh lateral water flow from the east.