Abstract:

 Chromatic methods have been well used in paleoclimate research for unconsolidated or semiconsolidated sediments. However, few researches based on these methods have been reported from diagenetic rocks, since their primary compositions and colors may be altered in the process of diagenesis and postdiagenesis. Thus, the deeptime research by means of chromatometry is still open to question. Ninetyeight Cretaceous rock samples collected from the Gongza Section, Tingri, southern Tibet, were studied using chromatic methods, together with microscopic observations and major elements analysis. Main conclusions were drawn as follows. (1) In the CIE1976 L* a* b* color space, the variation trends of L* and a*, with mirror symmetry, indicate two main semiperiods of 92 m and 18 m obtained by Fast  Fourier Transformation; while L* and b* values show similar variation trends. (2) Correlation analysis between chromatic indices and major elements suggests that L* value has a positive correlation with the content of carbonate, b* value is mainly influenced by manganese content, and together they can put some constraints on the chemical change of paleoocean; whereas a* value is largely controlled by the content of clay minerals, which reflects paleoclimatic changes.

Key words: Key words: chromatometry; paleoclimate; southern Tibet; Gongza Section; Cretaceous; Cenomanian/Turonian boundary