LI Xiang1, CAI Yuan-feng2,3
(1. Wuhan Center of Geological Survey, Wuhan 430223, China;
2. State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China;
3. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China)
Abstract：To identify the colouration minerals and their forms of occurrence in Cretaceous Oceanic Red Beds (CORBs) and to better understand the constraining factors and genetic models of CORBs, the red and non-red specimens collected from the CORBs, including both of the Chuangde section in Tibet, the Vispi Quarry section in Italy and the ODP Hole 1049C Core from the North Atlantic, were measured using X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS). The calibration specimens composed of hematite (“kidney ore” or “specularite”) and calcite were also measured using the diffuse reflectance spectroscopy. The results showed that hematite is the principal mineral responsible for colouration of these red beds, although the lithologies of the three sections (or core samples) were different. The red colour of shales in the Chuangde section is caused by two forms of hematite : a detrital one and a fine poorly crystallized one. Hematite with similar crystallinity is responsible for the red colour of limestone from the Vispi Quarry in Italy. As for the loosely cemented sediments from ODP Hole 1049C Core in the North Atlantic, poorly crystallized hematite and goethite are responsible for the colour change of sediments from non-red to red. The occurrence of hematite is affected by the supply of iron ions, the redox state and the diagenesis, which also are the decisive factors for the occurrence of CORBs. Based on analyses made in this study and on summaries of previously produced studies, a further genetic model of CORBs is proposed from a mineralogical perspective.
Key words: Cretaceous Oceanic Red Beds; mineralogical investigation; mineral colouration; control factors; genetic model
E-mail: lixiang_503@163.com
ACTA MINERALOGICA SINICA Vol. 34, No. 4, 2014, Page 451-460
