Sedimentological and microprobe studies of the lime tufas at Åstrup, Zealand

The formation of lime tufa, containing bands of iron and manganese, has been studied. The weathering of glacial sediments in the study-area occurs at a relatively high pH level and low Eh values, lead ing to a removal of calcium, manganese and iron , which are transported in solution until a decrease of C0₂ pressure and increase of Eh occur. This happens typically around springs on the flanks and in the bottom of the investigated valley. The texture and mineralogy of the lime tufa seems to be determined by the physical and chemical environment of formation. Electron microprobe studies of a well-oxidized lim etufa containing thin zones of iron and manganese have shown that the zones are well-defined. The zones presumably represent different geochemical situations in the local weathering environment. The formation of the thin iron zones seems to have involved a replace ment of the manganese and calcium zones, while the manganese zones were apparently formed without replacement. The lime tufa formation in the investigated area has occurred throughout the postglacial epoch at least, and formation still continues. The maximal thickness of lime tufa in the area is approximately 8 metres.