Hematite and goethite concentrations, and reflectance in various color bands for ODP Hole 171-1049C samples (Table 1)

Aptian–Albian sediments in Core 12X of Hole 1049C (ODP Leg 171B) are characterized by high-frequency cycles that consist of alternating layers of red and green/white clayey chalk, and claystone. The first derivative curves of diffuse reflectance spectra (DRS) for samples of different colors reveal that red (brown and orange) samples show clear peaks corresponding to hematite and goethite. Following treatment using the CBD (citrate-bicarbonate-dithionite) procedure, the red samples lost their red color and corresponding peaks in the first derivative curve, and became greenish or whitish. Therefore, hematite and goethite are the minerals responsible for the reddish change in sample color. However, these minerals behave differently from each other in terms of determining the color of sediment: hematite imparts a red color, whereas goethite imparts a yellow color. Therefore, a change in the proportions of hematite and goethite can cause a change in sediment color from orange to brown. To obtain the absolute contents of iron oxides in these sediments, we performed a quantitative analysis using DRS with multiple linear regression. The results reveal that the Albian brown beds contain 0.13–0.82% hematite (average value, 0.51%) and 0.22–0.81% goethite (average value, 0.58%). The Aptian orange beds contain 0.19–0.46% hematite (average value, 0.35%) and 0.29–0.67% goethite (average value, 0.50%). X-ray diffraction analysis of the Aptian and Albian cycles reveals no clear variations in mineral content with sediment color. It is suggested that hematite and goethite were derived from oxic environments during the period of deposition and early diagenesis. The oxic conditions were probably determined by the low accumulation rate of organic matter and the high content of dissolved oxygen in bottom water.