Assessment of the eruptive activity and identification of the mud breccia's source in the Olimpi mud volcano field, Eastern Mediterranean

Abstract

Even though the intensity and frequency of the eruptive episodes of deep-sea mud volcanoes (MVs) substantially regulate the methane fluxes into the hydrosphere and the development of the near-seafloor sulfate zone that affects the position of the gas hydrate stability zone, these factors are not yet adequately investigated. Moreover, the evaluation of the eruptive sediment's thermal maturity may provide solid documentation of the petroleum generation potential in high depths below seafloor (bsf). Hence, the present study, through the integration of sedimentary facies analysis with hydrocarbon biomarker analysis (based on the concentrations of long-chain (C25–C35) n-alkanes, hopanes and steranes), supported by swath bathymetry data, examined five sediment cores recovered from the Gelendzhik, Moscow, Milano, Leipzig and Heraklion MVs of the Olimpi mud volcano field (OMVF) on the central Mediterranean Ridge. The main objective of this investigation was to assess the ‘modern’ eruptive activity in the OMVF and identify the mud breccia's origin and mobilization depth (based on its maturity level), and the ages of the source beds. Among the studied MVs, Milano, Leipzig and Heraklion appear ‘recently’ active, while Moscow perhaps remains in dormancy for at least one century. The eruptive activity in the OMVF seems to be, generally, vigorous and persistent, while it is linked with several source beds of variable stratigraphy or environmental condition. The multiple eruptive episodes, occurring as uninterrupted events or via pulses, create conditions that perhaps favour high releases of methane into the water column as well as the growth of the gas hydrate phase near the seafloor. The identified ‘modern’ mudflows appear thermally immature for oil generation, while they most probably originate from terrestrial source beds located not deeper than 2 km bsf. A Messinian age could be suggested for the principal sources of the very soft to soft mud breccias of the OMVF, while stratigraphic horizons of Early-Middle Miocene might be proposed as the likely major sources for the firm to very stiff mud breccias of the area.