Pockmark Distribution and Genesis in the Mediterranean and Black Seas: A Regional Synthesis

Abstract

Pockmarks are ubiquitous seafloor depressions formed by the fluid/gas seepage through marine sediments, with implications for geohazards, benthic ecosystems, and climate-related processes. Despite extensive research, the mechanisms controlling the formation and spatial distribution of pockmarks are not completely understood, owing to the diverse and site-specific geo-environmental conditions. In this study, we provide a first review of over 7500 pockmarks mapped across the Mediterranean and Black seas, showing their relationship with depth range, slope gradient, seafloor lithology, proximity to tectonic faults, and sediment thickness. Our analysis reveals that pockmarks are predominantly located at intermediate water depths (100-700 m), with two main clusters around 100-200 and 500-700 m. They are commonly found on gently sloping seafloor (<4 degrees), often clustering around slope breaks. In detail, two slope-related peaks around 1.5 degrees and 3.5 degrees suggest distinct geological settings for pockmark formation: sediment-rich and low-energy environments versus more dynamic slope domains. Fault proximity plays a critical role, with over 40% of pockmarks occurring within 1 km of mapped faults, indicating that structural discontinuities act as preferential fluid pathways. Pockmarks concentrate in areas with moderate Plio-Quaternary sediment thickness (300-600 m), suggesting an optimal window for overpressure generation and fluid expulsion. A strong lithological control is evident: 74% of pockmarks occur on muddy sand or sand-rich substrates. In terms of ongoing to recent seepage/activity, similar to 27% of pockmarks show evidence of ongoing fluid seepage (e.g., acoustic gas flares, seismic wipeouts), particularly in regions such as the Black Sea, Aegean, and Central Tyrrhenian, where faulting, salt tectonics, or hydrothermal systems enhance permeability. Conversely, pockmarks in the Western Mediterranean appear to be generally inactive and buried. These findings underscore the influence of tectono-sedimentary architecture on seafloor fluid escape and provide essential insight into methane seepage, slope stability, and benthic habitats. This pedagogic review enhances our understanding of pockmark systems and establishes a foundation for future geohazard assessment, climate studies, and marine resource exploration.