Samples of chert, porcellanite, and chalk/limestone from Cretaceous chert-bearing sections recovered during Leg 198 were studied to elucidate the nature and origin of chert color zonations with depth/age. Sedimentary structures, trace fossils, compactional features, sediment composition, texture, geochemistry, and diagenetic history were compared among lithologies. Trends in major and minor element composition were determined. Whereas geochemical analyses demonstrate systematic elemental differences among the different lithologies, there are less distinct patterns in composition for the colored cherts. The color of the chert appears to be related primarily to the amount of silica and secondarily to the proportion of other components. Red cherts are almost pure silica with only minor impurities. This may allow pigmentation from fine Fe oxides to dominate the color. These red cherts are from places where geophysical logs indicate that chert is the dominant rock type of the section. These red chert intervals cannot be unequivocally distinguished from surrounding chert-bearing lithologies in terms of sedimentary structures.
1Fontilea, K., Marsaglia, K.M., and Dean, N., 2006. A petrological and geochemical study of Cretaceous siliceous rocks from Shatsky Rise. In Bralower, T.J., Premoli Silva, I., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 198 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/198_SR/107/107.htm>. [Cited YYYY-MM-DD]
2Department of Geological Sciences, California State University Northridge, 18111 Nordhoff Street, Northridge CA 91330-8266. Correspondence author: kristinfontilea@mac.com
3Department of Chemistry and Biochemistry, California State University Northridge, 18111 Nordhoff Street, Northridge CA 91330-8266.
Initial receipt: 1 March 2004
Acceptance: 14 September 2005
Web publication: 27 March 2006
Ms 198SR-107