Evaluating color parameters calculated from digital photographs of sediment cores as a tool in paleoenvironmental reconstruction—A case study using IODP Site U1502 from the South China Sea

Qualitative color data of sediments contain rich information on sediment compositions and have been widely used in paleoenvironmental reconstructions. Digital photographs can produce ultra-high resolution color data of sediment sequences. The characteristics of such data, however, are not yet explored adequately, hindering their use in practice. To fill this gap, in this study we calculated color data from digital photographs of sediment cores from Hole U1502A drilled during International Ocean Discovery Program Expedition 368 in the South China Sea, and compared them with their counterparts measured using a Diffuse Reflectance Spectrophotometer (DRS). We found that the luminance parameter L could be influenced by multiple factors, leading to its behavior being transient, while the chromaticity parameters a* and b* are relatively stable. The down-core patterns of photograph-derived L, a* and b* are comparable with their counterparts derived from DRS measurement, although their absolute values can diverge significantly from those DRS-measured ones. The color of the studied core sediments alternates between grayish-brown and greenish-gray, being pelagic deposits and earthquake-induced turbidite deposits, respectively. Such color cycles had been present since ~13 Ma, revealing a dramatic increase in submarine earthquakes due to subduction of the SCS Plate toward the Philippine Plate. Overall, our study demonstrates that color parameters calculated from sediment photographs could be developed as promising tools for studies relating to paleoenvironmental reconstructions.