Geomechanical attributes of the Cenozoic sediments of ODP leg 161, western Mediterranean Sea and its implications as geological proxy

This work characterizes the rock-mechanical properties and in-situ stress magnitudes of the Cenozoic sedimentary succession encountered in the ODP Leg 161 holes of the western Mediterranean Sea. This study attempts to infer the link between the variation of the rock-mechanical parameters within the Pliocene–Pleistocene stratigraphy with mineralogy and depositional environment. Wireline logs and bulk mineralogical compositions of five scientific holes drilled in the Central Tyrrhenian Basin (974C), South Balearic margin (975C) and Alboran Basin areas (976B, 977A and 979A) were evaluated. Study infers that a lower sedimentation rate in the greater water depths of the Central Tyrrhenian Basin resulted in increased inter-grain bonding and thus higher rock strengths in the Hole 974C sediments when compared to the other drilling sites. Estimated Young’s modulus and elastic property-based brittleness index gradually increase with depth within the lower part of the Pliocene–Pleistocene formation as carbonate % increases in response to the depositional environment shifting from Pleistocene hemipelagic environment to pelagic condition in Pliocene. Our results indicate that the rock strength and elastic brittleness properties can be utilized as confident geological proxies for depositional environments in the western Mediterranean sea region. Density-derived porosity shows an overall normal sediment compaction trend yielding hydrostatic pore pressure. Interpreted vertical stress (13.68–17.45 MPa/km) and minimum horizontal stress (12.19–14.56 MPa/km) gradients infer a normal to strike-slip tectonic regime. Due to the unavailability of calibration data, we inferred the upper bound of maximum horizontal stress (SH) gradient, ranging between 13.88 and 18.47 MPa/km. E-Quality wellbore breakouts interpreted from the acoustic image logs in Miocene Basement (Hole 976B) suggested NW–SE to N-S SH azimuth western Alboran Basin, parallel to the African and Eurasian plate movement direction.