Shallow gas in the Holocene mud wedge along the inner East China Sea shelf

High-resolution seismic surveys were carried out in the inner shelf of the East China Sea to investigate the distribution of shallow gas in Holocene sediments. Shallow gas is distributed extensively in the Holocene strata of the shelf which is dominated by the Yangtze River. Organic-rich, fine-grain sediments deposited throughout the Holocene are essential for gas generation and accumulation. The thickness of the Holocene sediment is the main controlling factor determining the distribution of shallow gas. Gas seepages were found mostly at a water depth up to 20 m, where sediment erosion mainly occurs. Coincidence between shallow gas seepage and high methane concentration in the water column suggests that gas emission from these sediments is a potentially significant source of greenhouse gas. The interaction between shallow gas migration and coastal erosion would therefore potentially lead to increased greenhouse gas emission and accelerated sediment erosion. Such results can be applied to other costal locations around the world. •The distribution of shallow gas is controlled by the Holocene sediment thickness.•Active gas seepage occurs mainly in the coastal erosion dominated area.•The shallow gas is potentially a significant source of methane in water column.