Geophysical exploration in the Lautertal at the Combat Maneuver Training Center, Hohenfels, Germany

Abstract

Geophysical exploration was conducted in the Lautertal at the Combat Maneuver Training Center, Hohenfels, Germany, to determine the shallow geological framework of a typical dry valley in this karstic environment. The complementary methods of electromagnetic surveying, vertical electrical soundings, and seismic refraction profiling were successful in determining the depth and configuration of the bedrock surface, the character of the unconsolidated deposits resting on the bedrock surface, and the nature of the bedrock surface. Channels and other depressions in the bedrock surface are aligned with structurally induced fractures in the bedrock. The unconsolidated deposits consist of coarse alluvium and colluvium, which are confined to these channels and other depressions, and fine-grained loam and loess, which cover most of the Lautertal. Wide ranges in the electrical and elastic parameters of the bedrock surface are indicative of carbonate rock that is highly fractured and dissolved at some locations and competent at others. Most local groundwater recharge occurs in the uplands where the Middle Kimmeridge (Delta) Member of the Maim Formation (Jurassic) is widely exposed. These carbonate rocks are known to be susceptible to dissolution along the fractures and joints; thus, they offer meteoric waters ready access to the main shallow aquifers lower in the Malm Formation. These same rocks also form the bedrock surface below many of the dry valleys, but in the Lautertal, the infiltration of meteoric waters into the subsurface is generally impeded by the surficial layer of fine-grained loam and loess, which have low hydraulic conductivity. Further, the rocks of the Middle Kimmeridge Member appear to be closely associated with the localized occurrence of turbidity in such perennial streams as the Lauterach.