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Biogeostatistics confirm: Even a low total number of red wood ant nests provide new information on tectonics in the East Carpathian Orogen (Romania)

Berberich, Gabriele M., Klimetzek, Dietrich, Paraschiv, Marius, Stancioiu, Petru T., Grumpe, Arne
Ecological indicators 2019 v.101 pp. 486-500
Formica, Miocene epoch, Pliocene epoch, ant nests, deaeration, environmental indicators, sediments, statistical analysis, tectonics, Carpathian region
Recent statistical analyses revealed that the spatial distribution of nests of red wood ants (RWA; Formica rufa-group) and actively degassing fault zone are strongly correlated. We now applied the modified Hough Transform (mHT) and Iterative Mode Detection (IMD) to RWA nest positions in four study areas of the Eastern Carpathian Orogen. The aim of this analysis was (1) to evaluate relationships between spatial distribution of RWA nests and complex tectonic stress regimes in the Eastern Carpathian Orogen, (2) to test if this procedure is also applicable even when only a low total number of RWA nests is available, and (3) to further verify the validity of this statistic approach. By applying a double-blind study, we minimized bias by researchers’ preconceptions. Since irregular shapes of the study areas were found to strongly influence the findings of distribution patterns, all subsequent analyses were carried out for circular areas. Statistical results substantiated our hypothesis that RWA nest distributions clearly show very pronounced directions even in complex tectonic environments such as the Eastern Carpathian Orogen. Dominant NW-SE directions (scattering between 120° and 150°) are corresponding to the 1st order regional stress field in the East Carpathians. Additionally, our analyses revealed the 2nd order stress field in NE-SW orientation. Furthermore, directions of re-activated shear systems, e.g. from Late Miocene and Pliocene that had been modified by overprinting due to changes of the main stress field, could be identified. For the Moldavian and East European Platform, which are characterized by thick sediment cover, our analyses could significantly contribute to otherwise concealed tectonics. Furthermore, the mode of some faults identified in previous tectonic studies could be complemented and specified and assigned to the corresponding tectonic regime. Our study thus confirms the validity of our statistic approach even when the total number of RWA nests is low.