Sedimentary macro-structures and forming mechanism of debris flow

Abstract

The discussion on sedimentary macro-structures and their forming mechanism of debris flow is based on the data of present processes and ancient deposits of Dongchuan in Yunnan Province, Wudu in Gansu Province and Fuxin in Liaoning Province. Non-cohesive debris flow, which is 1.3–1.7 t/m3 in density, follows hydraulic fluid and granular flow model. In the hydraulic fluid of flood, electrolytic water combines clay into pulp to transport solid debris. The sedimentary structures show fluid processes as stone-line structure, imbricated structure and stone supporting-superimposed structure. A part of non-cohesive debris flow with a density of 1.7–1.9 t/m3 follows granular model. Debris is in the action of friction, collision and dispersion which forces coarse debris moving upward to form reverse graded load. The sedimentary structures of granular flow show reverse graded bedding, reverse-normal graded bedding, imbricated vertical structure and circling linear structure. Cohesive debris flow, which is 1.9–2.3 t/m3 in density, follows structural two-phase flow (viscoplastic) model. The sedimentary structures of cohesive debris flow show reverse graded-chaotic structure, bottom mud-chaotic structure and outwedging structure.