Gas charged sediments and gas seepages
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Date
2023-10-27
Authors
Γιαννόπουλος, Νίκος
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Abstract
Seabed fluid flow involves the flow of gases and liquids through the seabed and water-column. This process can be found in seas and oceans all over the world, both in shallow and deep environments, and has many effects for the environment and mankind. Pockmarks are crater-like depressions forming in seabed sediments through gas escape and their discovery encouraged significant research to be conducted around fluid dynamics and migration.
The Patras Gulf Pockmark field is located in shallow waters in the southeastern part of the Gulf of Patras, Western Greece. It was formed in soft layered Holocene silts and is currently situated offshore of the new Patras Port. Since 1993, several studies have been carried out regarding the morphology and activity of the field, which has often been linked with seismic events. Chemical analysis has revealed that the escaping fluids are mainly composed of methane of microbial origin.
This study uses a newly acquired dataset from high-resolution marine remote sensing techniques, including sub-bottom profiler, side-scan sonar and multibeam echosounder, to examine the morphometric parameters of the pockmarks, their spatial distribution patterns, as well as sub-seafloor and water column acoustic anomalies related to gas activity. It also provides complete mapping of the Holocene/Pleistocene interface, which is presumed to be a gas accumulative horizon, along with the gas horizon within the sediments. The dataset showed that local tectonism and stratigraphy are closely related to the development of the field and revealed indicators of ongoing pockmark activity.
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Keywords
Marine geophysics, Seabed fluid flow, Gas seepage, Sub-bottom profiler, Side-scan sonar, Seismic profiles, Pockmarks, Methane, Patras Gulf