Ytfelskikt

Ytfelskikt is a geological term used in Swedish-language geology to describe the outermost, weathered layer of rock that sits at or near the Earth’s surface. It comprises the products of weathering derived from the underlying bedrock, together with any unconsolidated deposits that cover it. In many contexts ytfelskikt is synonymous with regolith, though some definitions reserve regolith for all loose material above bedrock, including soils, saprolite, and surface sediments.

Composition and structure

The ytfelskikt includes both unconsolidated material such as soils and surface sediments and partially or fully weathered bedrock (saprolite). Its thickness varies widely, from a few centimeters in stable cliff faces to tens of meters in regions with intense chemical weathering or thick sediment cover. Mineralogy reflects the parent rock and the degree of weathering, commonly featuring clay minerals, iron oxides, quartz, and secondary minerals produced during alteration.

Formation and dynamics

Formation results from mechanical weathering (freeze-thaw, fragmentation) and chemical weathering (hydration, hydrolysis, dissolution), driven by climate, topography, and biological activity. The ytfelskikt evolves over time as weathering progresses, soils develop, and sediments are deposited or removed. It can respond rapidly to changes in climate or land use and may be preserved in geologic records when erosion is limited.

Importance and study

The ytfelskikt is central to soil formation, hydrology, and landscape evolution, governing infiltration, groundwater recharge, and nutrient cycling. It is investigated through field profiling, boreholes, and geophysical methods to image depth and composition, as well as through soil surveys and dating techniques to infer weathering rates and history. The concept helps link bedrock properties to surface processes and ecosystem functions.