Soil geomorphological relationships on Tyrebagger Hill, Grampian region
This study attempts to examine soil variability as influenced by topography in an area 8-11 km northwest of Aberdeen. It occupies about 12 km2, and varies in elevation from about 91 m to 233 m above the sea level. The geology is composed of granitic rocks and Dalradian psammitic meta-sediments which are virtually quartzites containing over 80% quartz. The present detailed physiography is largely determined by glaciations of the Pleistocene period. The parent materials are predominantly glacial and solifluction deposits and range in thickness from less than 20 cm on strongly sloping convex sites to more than 2 metres on gently sloping sites and valley bottoms. The light and heavy minerals composition of the sand fraction show similarities at all topographic situations indicating a high degree of homogeneity in the original deposits from which the soils are developed. The soil variability is arranged in three topographic zones; the higher between 233 m and 152 m, the middle between 152 m and 91 m and lower 591 m above sea level. Other landscape features i.e. convex and concave sites, valley bottoms and the slope angles are also considered. An integrated study on soil variations and genesis has been carried out on six soil transects and 74 pedo-units. The soils of Kirkhill forest change from the lower to the higher topographic positions forming soil development sequences of Gleysols - Altosols (Cambisols) - Podzols - Placosols (Placxc Podzols) with varying degrees of soil intergrades. While cultivated soils are different due to horizon mixing by man. The soil morphology, micromorphology, physical and chemical properties show strong indications of a topographic influence on soil variability. But these relationships between slope angles or the distance from top of the hill along the transacts and soil criteria are irregular due to the undulating landscape. This is clearly demonstrated by the computations in which the sites were treated as random samples and the slope angles converted into slope percentages. After completing the investigations, the definitions and identifications of some of the middle horizons particularly husesquons (Hs, Bhs), hudepons (Hd, Bh) and sesquons (Sq, Bs) are modified based on all the data and, given the appropriate symbols.