HYBRID FACIES AND MECHANISM FOR THE FORMATION OF THE MIXED DEVONIAN CARBONATE-SILICICLASTIC SEDIMENTS IN THE LONGMEN MOUNTAIN AREA,SICHUAN

Four hybrid facies and fourteen hybrid subfacies are recognized in the Emsian to early Givetian (Devonian) mixed siliciclastic-carbonate sediments from the frontal zone of the Longmen Mountain area,Sichuan on the westren Yangtze platform.They may be assigned, on the basis of hybrid processes and background sediments,to two types;the hybrid type Ⅰ sediments dominative of shelf shales controlled by punctuated mixing,in-situ mixing and source mixing,and the hybrid type Ⅱ sediments dominated by sandy and limy littoral and shallow shelf deposits. The authors contend that the punctuated mixing of the hybrid type I sediments is re-lated to the processes of storm wave and reflux,while the in-situ mixing has a connection with birth growth and death of biological communities after the storms ceased.The mixing of the main hybrid facies in the hybrid type Ⅰ sediments is in general governed by relative sea level fluctuations and the supply cycles of different orders are also discussed in the pre-sent paper.