A total of 776 sediment samples were measured for percent CaCO3 using a coulometer. These data are compared with percent blue reflectance (450-550 nm) measured with the Oregon State University split-core analysis track. In previous studies percent blue reflectance has been an excellent proxy for percent CaCO3 and in this study shows many of the main depositional trends (i.e., a 100-k.y. cycle, with a 55% reflectance range is evident in the upper 900 k.y., underlain by sediments exhibiting a 40-k.y. cycle with only a 30% reflectance range). Between ~21 and 5 Ma the average percent reflectance decreases from ~35% to ~8%. A similar decrease is also recorded between ~24 and 22 Ma.
Percent CaCO3 trends closely match those of the percent blue spectral reflectance. 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.
1O'Connell, S., and Ortiz, J., 2002. Data report: Calcium carbonate stratigraphy from sample measurements and diffuse spectral reflectance at Site 1090, ODP Leg 177. In Gersonde, R., Hodell, D.A., and Blum, P. (Eds.), Proc. ODP, Sci. Results, 177 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/177_SR/chap_06/chap_06.htm>. [Cited YYYY-MM-DD]
2Department of Earth and Environmental Sciences, Wesleyan University, Middletown CT 06459, USA.
3Clement 107, Trinity College, 300 Summit St., Hartford CT 06106, USA. soconnell@wesleyan.edu
4Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA. Present address: Department of Geological Sciences, 221 McGilvery Hall, Kent State University, Kent OH 44242, USA.
Initial receipt: 7 July 2001
Acceptance: 19 February 2002
Web publication:
29 May 2002
Ms 177SR-112