Sedimentary facies of the manganese-bearing strata in the Falang Formation,southeastern Yunnan

There is still debate concerning the sedimentary environments of the Middle Triassic Falang Formation as important manganese-bearing strata in southeastern Yunnan: a deep-marine turbidite fan or a shallow-water tidal flat.The authors in this study contend,on the basis of representative sections in the Jianshui-Kaiyuan region,that the Falang Formation represents the turbidite fan deposits.The lowermost part of the Falang Formation is made up of the carbonate slump deposits,debris flow deposits and the interbeds of mudstone and siltstone,followed by the outer-fan to mid-fan braided channel and braided interchannel deposits in the middle-upper part,and inner-fan recharge channel and overbank deposits in the uppermost part of the Falang Formation.On the whole,the sea water became progressively deeper during the early Ladinian,and shallower during the middle and late Ladinian.The manganese ores are mostly hosted in the debris flow deposits in the lowermost part of the Falang Formation,implying that the origin of the manganese ores may be associated with relative sea-level rise during the early Ladinian.