Quaternary sedimentation, parna, landforms, and soil landscapes of the Wagga Wagga 1 : 100 000 map sheet, south-eastern Australia

Abstract

The Wagga Wagga 1 : 100 000 map sheet is on the Western Slopes of southern New South Wales. The regional topography changes from hills in the east and south-east to gently sloping rises and alluvial plains in the west. Aeolian clays (parna) form a consistent clay regolith regardless of the underlying geology in the gently sloping areas. In some alluvial plains and on some lower hill slopes, the surficial sediments contain a significant portion of reworked parna. In hilly areas, parna is poorly preserved except on some remnant ancient land surfaces, such as dissected plateaux and piedmont plains.

The soil pattern in the area is well controlled by landform processes and history. On relatively steep hill slopes, locally derived materials from weathering of bedrock are usually the dominant components of the soils, and geology is the dominant factor controlling soil distribution. In contrast, the Murrumbidgee high floodplain is covered by uniform silty clay with deep clayey soils (brown/grey Dermosols). Before the mid-Holocene, the alluvium mainly comprised sands and gravels, which were reworked by wind forming sand sheets and sand mounds (source-bordering dunes) on which deep sandy soils (Rudosols) now occur. The sediments and soils on the alluvial plains of local streams vary according to their distance from the source area and the flooding frequency. Areas considered to be mantled by parna, uniform red clayey soils (haplic red Kandosols/Chromosols) occur.

Although the distribution pattern of the soils is controlled by the landform evolution, the relationships between soil morphological properties and topography are not readily quantified. On the alluvial and gently sloping landforms, soil properties usually show little change even though slope gradient and slope length vary. Some soils, e.g. the Rudosols on the sand sheets, rarely show any topographic features which may indicate their presence. In limited areas, e.g. on steeper hills formed on metasedimentary rock, the soil properties vary with changes in topographic parameters (slope gradient and slope length).