The AIG10 drilling project (Aigion, Greece): interpretation of the litho-log in the context of regional geology and tectonics

Abstract

In the frame of the EU Project Corinth Rift Laboratory (CRL), the AIG10 borehole was successfully drilled from July until September 2002 through the Aigion normal fault in the harbour of Aigion, northern Peloponnesus, Greece. The scientific objective focuses on the investigation of fault mechanics and the relationship with fluid flow and geochemistry, fluid pressure, stress- and strain fields and earthquakes. Recognition of stratification encountered in the AIG10 borehole is based on an online analysis of well cuttings (0–708.8 m and 787.4–1001 m), core descriptions (708.8–787.4 m), monitoring of drilling parameters, as well as a preliminary geophysical well-log interpretation (0–1001 m). Geologically, the area is part of the Olonos–Pindos tectonic nappe, which is overthrusted on the Tripolitza unit during the Alpine orogeny. The litho-log of the AIG10 borehole comprises at first syn-rift deposits (graben fill). At 496 m, the Olonos–Pindos tectonic unit was encountered, however, not as expected in the platy limestones, but in the Olonos–Pindos radiolarite. The borehole has crossed at least one thrust-fault zone and a major normal fault zone at 760 m. This normal fault zone separates well-fractured platy, micritic limestone in the hangingwall from highly fractured radiolarite in the footwall, both of the Olonos–Pindos tectonic unit. The observed succession of multiple imbrication is an indicator of Alpine tectonic activity, whereas normal faulting is of the Miocene–Quaternary extension of the Gulf of Corinth, confirming our expectations gained from geologic-tectonic fieldwork.