Sedimentology and Environment of Carbonate Gravity- Flows on the Wester Margin of Lower Triassic. Sichuan Basin.

Key words: 
• Carbonate gravity flow /
• paleo-slope angle /
• Lower triassic epoch /
• Association sequence /
• Evolution and model of gravity flow. /

Abstract: Deposits of carbonate gravity flows on the western margin of Lower Triassic Sichuan bsain may be divided into two parts : debris current and turbidity current. Debris current deposits mainly consist of four kinds of calcirudites with 1. horizontal structure ( type A ),2. graded structure ( type B ),3. disorder fabric (type C),4. matrix supported (type D). Turbidity current deposits are composed of 1. calcarenite for low density current, 2. containcalcirudite calcarenite for high dentity current. Distribution frequency curves of carbonate gravity flow deposits may be classified into four groups. It's importantly disscured differing from curves of debris and turibidity current and varying with their characteristic parameters. Assocaition sequences of gravity flow sediments may show origin and evolution of gravity flow deposits. The association sequences are as follows:1. association with debris flow deposits and micritic limestone in half-deep water environment. 2. association with cohesive debris current(type D) and turbulent debris current(type A B C). 3. association with debris current and turbidity current deposits. 4. complex association with calcilutite-debris current-turbidity current-calcilutite deposits. 1t' s studied that paleo-slope is along northeast-southwest. It dipsfo the is southeast. direction of gravity flow is from northwest to southeast. Its slope angle is about 2-9. Gravity flow deposits have linear distribution. It' s non-water channel gravity flow deposits controlled by a marginal growth fault on the background of plateform geosyncline.