Abstract:
The Aptian-Albian sediments in the ODP Leg 171B Hole 1049C are characterized by high frequency of cyclothems between oceanic red and grey/white marls. To better understand the origin of these red beds, research on the mineralogy, sedimentology and geochemistry and is carried out by way of diffuse reflectance spectrometry (DRS), magnetic susceptibility and reactive iron analysis. Our data show that hematite and goethite are the minerals which are responsible for the red coulor of the red beds. Characteristic peaks of hematite and goethite occur in brown and orange samples, and their averaged FeR/FeT values are 0.23 and 0.24 respectively, obviously different from other samples. The good positive correlation between magnetic susceptibility and red beds suggest that the magnetic susceptibility changes due to the variety of the hematite or magnetite composition. X-ray diffraction results reveal that all of the samples, no matter what colors they are, contain illite, kaolinite, chlorite and montmorillonite. Their distributions have no correlation with the colors, which probably reflects stable climate of the resource area at that time when deposited. The samples from Hole 1049C show high frequency cyclothems in orange, brown, white, gray, and the interface of different colors is clear, which indicates that hematite and goethite are the results of oxygenation at low temperature. Brown samples have low carbonate content. Furthermore, our data shows that higher oxygen isotope and slightly lower carbon isotopes values of fine fraction carbonate are correlated with red interval. Neodymium isotopes of whole rocks stay relatively stable through the Aptian-Albian core. We suggested that probably oxidizing environment with high content of dissolved oxygen near water-sediment interfaces to which red beds are corresponding, results most probably from low rate accumulation of organic materials.