The Sedimentary Characteristic and Evolution of the Early Middle Triassic Deep Water Carbonate Slope in Guiyang and Zhengfeng Area,Guizhou Province and Its Tectonic Controls

Key words: 
• Guiyang and Zhengfeng area /
• Early-Middle Triassic /
• carbonate slope /
• tectonic control

Abstract: The excellent outcrops developped in Guiyang and Zhengfeng area,Guizhou Province in early and middle Triassic.In the context of the tectonic setting,Guiyang and Zhengfen area,Guizhou province,is situated at the northwestern basinal margin of the Nanpanjiang basin in early and middle Triassic.The sedimentary characteristic of the deep water carbonate developed in this area was made up of in situ and allochthonous carbonates.Furthermore,the allochthonous carbonates were divided into four types,i.e.,debris flow,density modified grain flow,turbidity and sedimentary slumping. The in situ carbonate was characteristic of gray dark gray thin bedded micritic limestone with the sparse faecal pellets and bioturbated structures,indicating the background deposits of the deep water carbonates. The debris flow deposit was a primary type among the allochthonous carbonates,and composed of the floating brecciola and brecciola. The turbidity flow deposit primarily possessed the Bouma sequence T bc and T ab,and sparsely the whole sequence of T abced which occurred in the middle Triassic. The sedimentary slumping formed the slumpong rock.It possessed not only the partial features of the brecciola,but also retained the primitive character with little matrix.It primarily occurred in upper part of the Qinai Formation (middle Triassic) as the thin bedded micritic limestone. And the deep water carbonate slopes developped into the three kinds of models including homocline ramp,sedimentary slope and by pass slope.In the context of the eustatic sea level rise in early middle Triassic epoch,the evolution of the carbonate slope was mainly controlled by the tectonic activity.With the passive margin,development of Nanpanjiang basin in early Triassic,the carbonate slope evolved from the ramp into the prograding sedimentary slope.And in the middle Triassic,accompanying with the development of the peripheral foreland basin,the evolution of the carbonate slope was affected with the flexural extension in the basin.As a result,the carbonate slope developed into the by pass slope with the evolution from the stepping to successive retreat.