Processes of post-burial change in soils under archaeological monuments: a micromorphological study with particular reference to the processes of clay and iron redistribution

Abstract

The micromorphological examination of soils buried beneath archaeological sites has been an important source of information concerning past pedogenesis, environmental conditions and anthropogenic activity. An assumption inherent in these studies has been that burial preserves the character of the original soil fabric. However, over the past two decades, wealth of evidence to the contrary has been emerging. This study aims to investigate he nature of changes in the soil micro-fabric that may result from burial; and in particular to examine the causes and implications of post-burial iron redistribution and clay translocation.

Soils were examined that had been buried beneath archaeological sites of different ages, in a number of study regions each with different parent materials. Within these sites profiles with contrasting depths of burial were studied. The micromorphological, and bulk physical and chemical characteristics of the buried soils and their overburdens were determined. Statistical analysis of the results confirms that after burial a wide range of physical, chemical, and biological processes operate resulting in the formation of secondary soil features and the alteration of the micro-fabric of all the buried soils studied.

The nature of the processes operating after burial is influenced by factors of parent material, site age and the depth to which the soil was buried. Two distinctive sets of processes were identified, firstly those related to near surface processes of pedogenesis that result in the biological, chemical and physical welding of relatively shallowly buried soils within the developing surface profile, and secondly those processes distinctive to the burial environment. The second suite of processes includes the redoximorphic redistribution of iron to form pans and nodules, and processes of clay translocation related to the internal slaking of overburden materials. These processes tend to operate in more deeply buried profiles. Soil texture appears to be important in determining the depth of burial required for isolation from surface processes. Time since burial controls the period of time over which processes operate and that pedofeatures have to adjust to the burial environment. Site age also appears to influence the constructional, climatic and parent material burial factors that initiate iron redistribution and clay translocation within buried soils and their overburdens.