The Silurian type Ⅲ kerogen from the northern and southern margins of the Sichuan Basin and its geological significance

The analysis of the kerogen from the marine environments on the northern and southern margins of the Sichuan Basin shows that the type Ⅲ kerogen,which comprises the vascular plant compositions such as tracheid,lignin and cellulose,occurs in large quantities in the Lower Silurian strata near the old land,whereas type Ⅰ kerogen has been found in the areas far away from the old land. The findings suggest that the vascular plants began to land in the study area even early in the Ordovician when the old land came into being,and abounded during the early Early Silurian,and that the environmental conditions may have exerted an important influence on the evolution of the plants.