The bog in upper stream formed early, and had begun in early Middle Holocene;
上游形成时间较早，始于中全新世前期；
Heituhu formation is gray and gray-black silty clay with limnological facies in early and middle period of Holocene, and bearing lots of spiral case;
黑土湖组为全新世早—中期湖沼相沉积的灰—灰黑色粘土类粉砂质粘土，含大量淡水螺蚌介壳；
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