Submarine morphology offshore Crotone (Calabrian accretionary prism, Central Mediterranean): Pockmark fields and mud extrusion in a mobile shale domain

Abstract

The narrow Calabrian Arc accretionary prism, in the Mediterranean Sea, is known to be populated by mud volcanoes, although only a few of them have been extensively documented. The Ionian Sea offshore the Crotone Promontory offers examples where the expressions of fluid expulsion and sediment mobilization are visible both in the subsurface and at the seafloor. The analysis of a proprietary 3D seismic data cube allows characterization of pockmark patterns and identification of a mud diapir, which appears at the seafloor as a large mud pool, ca. 1200 m in diameter. The high resolution 3D seismic profiles allow differences to be inferred about the mechanisms of fluid focusing at very shallow sub-seafloor depths. Fluid focusing and pockmark formation are aided by normal faults arising from both outer arc extension and dilation in shallow unconsolidated sediments influenced by sharp increases in slope gradient. In some instances, it can be shown that fluid venting also contributed to destabilizing the uppermost sedimentary strata, triggering small landslides along the slope. The mud diapir has apparently been mobilized along an extensional fault, which tapped into a mobile shale domain. A fossil mud pool has also been recognized in the study area. This fossil mud pool is sealed by undeformed sedimentary strata which constrains a minimum age for fluid and sediment mobilization in the accretionary prism. Seismic reflection amplitudes suggest that the fossil conduit still acts as a preferential fluid seepage pathway, contributing to destabilization of the overlying slope sediments.