Calcium carbonate stratigraphy of ODP Site 177-1090

This is especially well shown in the 100-k.y. cyclicity and in the interval between 24.5 and 21.5 Ma. In both intervals CaCO3 analyses are abundant. An exception occurs in the interval between 2 and 5 meters composite depth (~193 and 240 k.y.).

There, percent CaCO3 and percent reflectance are out of phase. The lack of agreement is not likely to be due to a very wet core, in which water would dominate the spectral reflectance instead of sediment, or to problems with the composite depth slice. The discrepancy remains unexplained and provides clear evidence that when noninvasive measurements are used as proxies for chemical measurements they must be substantiated by the actual chemical or physical measurements.