ORIGIN OF CLAY-RICH BEDS IN TURONIAN CHALKS FROM LOWER SAXONY, GERMANY - A RARE-EARTH ELEMENT STUDY

The mineralogy and REE geochemistry of thin, clay-rich beds from Turon ian chalks of Lower Saxony (Germany) has been studied. Two types of cl ay-rich beds are present. The first is of volcanic origin and is chara cterised by: (1) a REE signature similar to marine argillized volcanic ash bands; and (2) a silicate mineralogy dominated by smectite with m inor corrensite. The second type is of continental origin and is chara cterised by: (1) a REE signature similar to continental shale; and (2) a silicate mineralogy dominated by smectite with minor heulandite-cli noptilolite. The use and misuse of these widespread clay-rich horizons in the Turonian stratigraphy of Lower Saxony is discussed.