Abstract

The Cô Tô Formation is composed of polymineralic coarse-grained sandstone, polymictic gritstone, tuffaceous sandstone, tuffaceous siltstone, tuffaceous clayey siltstone, silty claystone, chlorite claystone, cherty claystone, dark grey to black grey clay shale containing graptolites. Grain content of sediments is usually composed of quartz, feldspar, fragments of acidic effusives, granophyre, chert-quartzite, chert, clay-sericite schist, sericite and chlorite schist, etc… Rock fragments are usually angular, irregular, weakly to very weakly rounded and sorted.

Lithological characteristics, flyschoid, turbulent, confused and irregular structures, and inhomogeous material composition typical for turbidite formation are the evidences showing that sediments of the Cô Tô Formation were formed during processes of tectonic activities in the continental slopes.