[ History of soil surveys in Sabah ] [ On acid igneous rocks ] [ On alluvium ] [ On basic igneous rocks ] [ On intermediate igneous rocks ] [ On limestone ] [ On mudstone/sandstone ] [ On ultrabasic igneous rocks ]

On alluvium

Note: All information on soils were from the Land Resource Study 20 series of books (Volumes 1 to 5), published by the Land Resources Division, Ministry of Overseas Development , UK.

There are 20 soil associations on alluvium, corresponding to the first 20 numbers in the legend of the soil maps (hard copy, not provided for in this website).

1. Tidal swamps and beaches

Three associations are mapped on tidal swamps and beaches and of these, the Weston Association is by far the most extensive. It covers large areas of mangrove and nipah swamps composed largely of sulphidic alluvium. The Usukan and Tanjong Aru Associations are restricted to beaches of calcareous and siliceous sand respectively.

2. Floodplains

The soils of the river floodplains have been grouped into 4 associations, which together form a sequence extending from the meander belts across the true floodplains to backswamps. The Tuaran Association is mapped on the meander belts and with distance from the river this passes into the Kinabatangan Association on the true floodplains. The Sapi Association occurs in swamps and the Klias Association in peat swamps.

3. Valley floors and associated terraces

Four soil associations have been mapped in the narrow valleys and upper reaches of many rivers. They all include a wide range of soils and are separated largely on the basis of the origin of the alluvial parent materials. The soils of the Binalik Association are formed on alluvium derived largely from ultrabasic rocks. The soils of the Karamuak Association are formed on alluvium derived largely from basic rocks. The Labau and Binkor Associations are both formed on alluvium derived from sandstone and mudstone and contain a similar range of soils; they could probably be merged.

4. Terraces

Seven associations are mapped on terraces. Of these, the Brantian, Sook, Sinarun, Kepayan and Sipitang Associations are closely related and there is considerable overlap of soil units. The Brantian Association is the most extensive and occurs on coastal terraces, valley terraces and on terraces in the inland plains. It consists mainly of well-drained Orthic Acrisols on medium- and fine-textured old alluvium. In contrast, the Sook Association consists largely of poorly-drained Gleyic Acrisols on medium- to coarse-textured alluvium. Dissected terraces with well-drained Orthic Acrisols on old alluvium and on sandstone and mudstone, exposed by dissection, are included in the Sinarun Association. Inextensive areas of Podzols and Histosols are included the Kepayan and Sipitang Associations respectively.

The Tungku Association of Luvisols occurs on a coastal terrace of calcareous alluvium. The Tapang Association, in which Ferralsols are dominant, occurs mainly on alluvium derived from basic and ultrabasic igneous rocks.

5. Plateaus