Oil gas submarine pipeline generally needs to pass through different shallow sea shelf areas, therefore, may encounter various unstable geological problems unavoidably, such as tidal bank and tidal creek migration, slope soil body slumping and taphrogeny, submarine differential erosion and sand wave migration etc., which lead to suspended span, damage and even breaking-down of pipeline. Based on pipeline route survey and post-lay detection data of oil gas submarine pipeline in shallow sea shelf area, this paper studies the distribution rules, genetic mechanics and hazard to submarine pipeline of the following unstable geological factors, including the migration of tidal creeks and tidal banks in Liaohe River delta, submarine differential erosion in Huanghe River delta and the relict sediment area of continental shelf of northern South China Sea, sand wave activities in the continental shelf of northern South China Sea and the submarine slope soil body slumping in Huanghe River delta etc. Survey data reveal that the maximum migration rate of tidal creeks and tidal banks in Liaohe River delta may reach one hundred meters and the differential height between them is 2m to 5m. The height of submarine differential erosion in abandoned Huanghe River delta varies between 4m and 6m. Slumping and taphrogeny of submarine soil form large amount of disturbed soil strata, slope and silt flow sediment. Differential erosion in the relict sediment area of continental shelf of northern South China Sea may lead to the formation of furrows and ridges with the differential height of above 30m. The height difference between moving sand wave peak and wave hollow may reach 8m. Moving sand waves, which are 3.5m high, may come into being in the shelf seafloor, where the water depth is more than 100m. The study concludes that tidal current and estuary runoff control the migration of tidal creeks and tidal banks in Liaohe River delta, whose moving rate is in positive correlation with tide range and current velocity. Differential erosion, slumping, taphrogeny, landslide in abandoned Huanghe River delta are closely related to sediment types and characteristics, topography, shallow stratum structure, regional scour-and-fill background and hydrodynamic force. Furrows and ridges with the height difference of more than 30m caused by differential erosion in the relict sediment area of continental shelf of northern South China Sea are controlled by stratum structure, hydrodynamic force etc. Sand wave movement in shelf seafloor is mainly affected by typhoon. The submarine pipeline passing through the unstable geological area faces the risks of exposure, suspended span and even breaking-down, therefore, the site selection of pipeline route should try to avoid the unstable areas and increase the burial depth or take appropriate prevention measures when necessary.

As a key sedimentary body connecting the north and South Yellow Sea, the subaqueous clinoform off Shandong Peninsula plays an important role in the sedimentary system of China seas, and it is also a studied example in the study among the major “source to sink” systems. Based on AMS ¹⁴C dating, sediment grain size, major and trace element contents from core WH-05 located at the edge of the clinoform, we discuss changes in the deposition rate, analyze sediment provenance and controlling factors, and reveal the environmental evolution of the source area since the Holocene. Results from core WH-05 show that marine sedimentation began at about 8.5 ka B.P. The deposition rate decreased from the initial 28.37 m/ka to 0.52 m/ka. Sediment provenance suggests that the Huanghe river sediments have been the main source for the study area since the Holocene. The As/Al, V/Sc indicators show that the environmental oxidation environment was gradually weakened and then increased slightly starting from 7.0 ka B.P. The change in redox is consistent with the change in sea level, the deposition rate, and depositional depth.