THE DISTINCTION BETWEEN GROUNDWATER GLEY AND SURFACE-WATER GLEY PHENOMENA IN TERTIARY PALEOSOLS OF THE EBRO BASIN, NE SPAIN

In studies of paleosols, the distinction between iron segregation due to either surface water or ground water fluctuations is hardly ever ma de. Recognition of subsequent hydromorphic phases is even more rare. N evertheless, such distinctions can be made and are very useful in dete rmining the paleoenvironment. In this study we demonstrate that subseq uent stages of hydromorphism and their sequence can be recognized in P aleogene paleosols of the Ebro basin. It appears that, in these carbon ate-rich hydromorphic soils, goethite iron segregations are due to gro und water influence, while hematitic segregations are due to surface w ater. The preservation of original mineralogy in this case is due to a bsence of late-diagenetic transformations. The results contradict the thesis that red colours in such paleosols would be the result of late diagenesis. In the studied samples, mottled colour patterns frequently indicate fairly advanced soil formation, although weathering of prima ry minerals is almost absent. Detailed study of colour patterns gives much additional information on the post-depositional environment.