阿尔泰山晚新生代以来的古风化壳及其形成时代

阿尔泰山古风化壳研究结果表明，晚新生以来，至少存在两个风化期，形成了不同类型的风化壳，本文阐述这两个风化期的特征及相应形成的风化壳的类型及特点。

THE PALEO-RESIDUA AND THEIR AGES IN THE ALTAY MOUNTAIN SINCE PLIOCENE

The study shows that since pliocene two kinds of paleo-residua, which are the products of different episodes of weathering, have developed in the Altay Mountain. The earlier episode occurred in Pliocene-early Pleistocene under a subarid-subhumid paleo-climate and resulted in the establishment of moderately weathered profiles containing abundant clay minerals, such as montmorillonite, illite and kaolinite. The products of weathering are divided into two submembers based on the geomorphic difference and genesis. Submemeber one is called primary residual red beds because the red pigment is believed to be produced by mother rock weathering in situ and different horizons can be distinguished by their features in weathering profiles. The submember two, the secondary red beds, is considered to be resulted from erosion, transported in a short distance and deposited on the primary residual red beds. Its colour was derived from the mother materials. In this category, the products are characterized by containing much more fine fraction (< 2mm) often in quantities exceeding 90% of the total.The later weathering episode occurred in middle Pleistocene based on the proofs of TL dating and the thickness of weathering rind. This kind of paleo-residua has developed on Quaternary unconsolidated deposits. It can be seen that the variation of boulder and pebble weathering depended on the rock type at outcrops. All of the granitic stones have been weathered into grains, whereas metamorphic and quartz stones are moderately weathered or unweathered respectively. Compared with the old, the younger episode of weathering is believed to have lasted for a shorter period. The chemical analysis of the weathered sediments suggests that the weathering was getting weak since early Pleistocene as the paleo-climate evolved from subhumid to subarid.