The formation of peatlands in various kinds of alluvial lowlands in Japan were studied for this article. Peatlands were mainly formed during the period between the latest Pleistocene and the earliest Holocene, and also in the latter half of Holocene. The thickness and extent of peat formations as well as when they began forming are different for each type of alluvial lowland. Peat layers are well developed in alluvial lowlands such as drowned valley, barrier and delta types. Peat layers in the lowlands of drowned valley type are thick and their formation started earlier. In the barrier type lowlands, especially in northern Japan, peatlands are very extensive, and the peat layers are more than 5 meters thick in some places. Peatlands in the delta type lowlands are relatively large but the formation of peat layers started later than the barrier and drowned valley types. There are few peatlands in the alluvial fan type lowlands. The peat layers in the coastal plain type are thin and relatively small.
