Mixed clastic-carbonate deposits are widely distributed in the fine-grained sedimentary rocks from the 2

nd

Member of the Kongdian Formation in Cangdong Sag.The mixing styles of the fine-grained sedimentary rocks can be divided into componential mixtures(CM) and structural mixtures(SM).The componential mixtures are characterized by mixing of different minerals within one lamina.The structural mixtures feature in vertical overlying of different single-mineral laminae and componential mixture laminae.Through detailed core description

thin section observation and X-ray diffraction analysis

it was considered that there develop two types of componential mixtures in the 2

nd

Member of Kongdian Formation in Cangdong Sag

namely clay-carbonate(CM1) and felsic-carbonate-clay(CM2) componential mixtures.And there also develop four types of structural mixtures

namely felsic/clay-carbonate(SM1)

felsic/clay/carbonate(SM2)

clay/carbonate(SM3) and clay-carbonate/clay-organism(SM4) structural mixtures.There are two kinds of vertical combinations both with a bottom-up order change from massive structure to bedded structure and lamina structure.The vertical combination dominated by dolomitic(limy) fine-grained mixed sedimentary rocks is formed due to climate changes.And the vertical combination dominated by felsic fine-grained mixed sedimentary rocks is due to the changes in supply intensity of terrigenous materials.