Some Soils and Surficial Deposits in the Kokoda Valley, Papua and New Guinea

ABSTRACT: The upper two of a series of four fan surfaces in the Kokoda Valley, Papua and New Guinea, are covered with volcanic ash. Soils on these two surfaces have fine-grained textures and well-developed structural characteristics. The plasma of these soils is isotropic in thin section. Differences in color and in the kinds of clay minerals present in these two soils are attributed to the drainage conditions of the underlying material. The lower two of the four fan surfaces have soils developed mainly from alluvium. Some soil profiles on the older of these two surfaces are partially derived from reworked volcanic ash. The alluvial soils are coarser grained and shallower than the volcanic ash soils. The plasma of the alluvial soils exhibits increasing birefringence with decreasing amounts of volcanic ash. The soil pattern proved useful in interpreting aspects of the geomorphic history of the study area