There are five Quaternary sedimentary sequences in the Red River Delta, Vietnam. The forming of each sequence is related to transgression and regression phases. The sequences, which was formed in transgression period, composed mainly of fine grained size leading to the water bearing capacity is very low and plays a role as aquicludes. Besides, in these fine grain size layers, the contents of arsenic and iron are high, especially in dark clay, silty clay rich in organic material .
