GEOBIOSCIENCE: RED WOOD ANT MOUNDS AS BIOLOGICAL INDICATORS FOR NEOTECTONIC EARTHQUAKE-BEARING FAULT SYSTEMS

The volcanic West Eifel (Germany) is part of the Variscan folded Rhenoherzynikum that was tectonically sheared in Mesozoic and Cenozoic times according to multiple changes of principal stress directions. The current stress field with a NW-SE-trending main stress direction opens pathways for geogenic gases. At the same time, Variscan faults that are part of a conjugated shear system, are reactivated. In the 1990s, equidistant neotectonic W-E-trending strike-slip fault systems were identified in coalmines of the Ruhr Carboniferous. The question was if it is possible to identify these fault systems also in areas without any mines or outcrops by bioindicators as red wood ants (RWA, genus Formica).

RWA have a strong affinity for gas-permeable earthquake-bearing neotectonic fault systems. There are first indications, that geogenic gases ascending from faults play a decisive role. Whether the higher CO₂ concentrations provided by these faults create an optimal mound climate and supports the respiration system are discussed.

In the West Eifel, a comprehensive investigation of an area of 1,140 km² and about 490 km² forest area was successfully conducted and the correlation between RWA mound sites and neotectonic fault systems established (Berberich 2010). The results show linear arrays and clusters of more than 2,900 RWA mounds. The linear distribution correlates with strike-slip fault systems documented by quartz, ore veins and slickensides. The clusters represent intersections of two dominant fault systems and can be correlated with voids caused by crustal block rotation.

Due to the sub-recent volcanism, numerous mineral springs arise on the fault systems. Gas analysis of CO₂, Helium and Radon of soil air and mineral springs reveal limiting concentrations for the distribution of mounds and colonisation. The almost complete absence of mounds in the core area (159 km²) of the Quaternary volcanic field is striking. Occasionally occurring H₂S in the fault systems that is toxic at miniscule concentrations to the ants might be the reason. Viewed overall, the results are showing a strong dependence of the distribution of RWA mounds on the neotectonic faults in the Eifel.

Berberich, G. (2010): Identifikation junger gasführender Störungszonen in der West- und Hocheifel mit Hilfe von Bioindikatoren. Dissertation. Essen, 2010.