Discovery of gas-discharged pits (gas pit) in the plains of the Yellow River delta
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A kind of special sedimentary structures are developed in the overwater plains of the Yellow River delta. They look like funnels: round or nearly round, concave of pit-like, with a diameter ranging from several centimeters to 20 or 30 cm, and depth from several millimeters to over 20 cm. There is a vertical pipe (called gas discharging conduit) in the center, with a diameter of several millimeters to 1 cm, depth of several centimeters to more than 10 cm. There may be a lip-like relief (called “lip-like relief”) on the periphery or some parts of the periphery, with ring structures showing horizontal stratification on the inner margin. Plant debris carbonized, plant fragments or dark-colored minerals may sometimes be found in the center of the pits. Such structures are usually developed in silt (with minor clay laminations), often underlain by one or more thin layers of mud matter. Our studies find that they are genetically related with gas discharging of organic matter during biological degradation. Therefore, they are called “gas-discharged pits”.
Keywordsgas-discharged pits overwater plains delta the Yellow River
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