Fosforlag

Fosforlag is a Norwegian term used in geology and soil science to describe a stratigraphic layer with elevated phosphorus content within sedimentary sequences or soils. Phosphorus enrichment can arise through concentration of phosphate minerals such as apatite, accumulation of organic matter rich in phosphorus (bones, guano, excrement), or diagenetic redistribution of phosphorus under changing conditions.

In marine and lacustrine settings, phosphatic layers may form during intervals of high biological productivity or intense sedimentation of phosphate-bearing detritus. The exact phosphorus form in fosforlag can vary, including mineralized phosphate phases and organically bound phosphorus. Detection and analysis typically involve laboratory measurements of total phosphorus, selective extractions for different phosphorus pools, mineralogical identification of phosphate minerals, and sometimes isotope analyses to establish provenance or age.

Significance lies in both soil fertility and economic geology. Phosphorus-bearing layers can influence the availability of phosphorus to plants and inform agricultural management. Economically, phosphate-rich deposits are mined for fertilizer production, though a single fosforlag is usually part of a larger phosphate-bearing sequence rather than an independent ore body. In archaeology and paleontology, phosphorus-rich layers can aid in locating bone beds or guano deposits.

In English-language geology, the concept is commonly described as phosphate enrichment or phosphatic layers, rather than as a fixed Norwegian term.