STUDY ON DIAGENESIS OF CLAY MINERALS IN THE WESTERN DEPRESSION OF THE LIAOHE BASIN

Different clay mineral assemblages and their replacement have been formed in different sedimentary and diagenetic environments in the western depression ( Huan-xiling, Xinglongtai and Maquanzhi ): 1.Montmorillonite-I/M-illite-kaolinite mineral assemblage 2.1/M-authigenic illite-atlthigenic chiorite mineral assemblage The weak acidic and weak alkaline environments were transformed into slight alkaine-weak reductive ones with the increase of depth and geothermal and mont-morillonite and I/M turned into illite and trioctahedron chlorite. In the north region of the western depression ( Gaosheng and the local area of Shuguang)t 1. I/M-illie mineral assemblage 2. Glauconite-trioctahedron smectite mineral assemblage 3. Fe-saponite mineral The Sha-4 stage in the area was a slight alkaline-weak reductive sedimentary environment without kaolinite mineral and Ca, Fe3 + Fe2+and Mg were rich in the environment due to the degeneration of the secondary saponite from basalt into trio-dioctahedron smectite. Together with Fe and Mg, K and Al supplied by solubilized K and Al-bearing terrigenous minerals under the higher geothermal moved into I/M crystal lattices and thus forming glauconite. The evidence of mineralogy has shown that the geochemical properties of the sedimentary and diagenetic environments are the principal factors which control low-temperature geochemial behaviors of clay minerals during the diagenesis, and secondly, the temperature also plays an important part during the diagenesis of clay minerals.