The chemical alteration indexes and their significance for the Nanhuan Liangjiehe Formation in northeastern Guizhou

There has been much debated recently concerning the issue whether or not the Nanhuan Liangjiehe Formation may be classified into the interglacial deposits. The values of chemical alteration index (CIA) for the Liangjiehe Formation in the Miaoshaoxi section, northeastern Guizhou may directly provide geochemical evidence for the approaches to the palaeoclimatological features in this region. The values of chemical alteration index presented in this study generally vary from 55.48 to 89.33, with an average of 72.49. Except the values 55.48 and 89.33, all the other ones range between 65 and 75, indicating the warm and humid palaeoclimatic conditions during the deposition of the Liangjiehe Formation. The integration of rock assemblages, sedimentary structures and palaeoclimatological features show that the Liangjiehe Formation should be assigned to the interglacial deposits, and may be correlated to the middle and upper parts of the Fulu Formation.