Abstract

In the Dong Van area in northeast Vietnam, lower part of Upper Cambrian carbonate succession, more specifically the lower part of Chang Pung Formation in the Lung Cu outcrop consists of a succession of oolitic pack- to grainstones, oncolite pack- to grainstones, intraclast to lithoclast grainstones, wackestone and mudstones. The integration of microfacies and diagenesis of these carbonate successions in the Lung Cu outcrop are interpreted based on conventional microscopy and cathodoluminescence (CL) microscopy analysis. On the basis of lithology, texture, grain composition, and sedimentary structures, eight microfacies have been recognized including:1- Marl (Facies 1); 2- Parallel bedded limestone (Facies 2); 3- Wavy bedded limestone (Facies 3); 4- Oncoid- intraclast (Facies 4); 5- Floatstone-intraclast-extraclast (Facies 5); 6- Bioclast-lithoclast-ooid (Facies 6); 7- Ooid-bioclast-oncoid (Facies 7); 8- Ooid-lithoclast (Facies 8). These microfacies reflect deposition in peritidal to mid-ramp in shallow-marine depositional environments with differences in wavy energy conditions in the near tropical conditions of the South China plate. Diagenetic processes identified consist of micritization, cementation, dissolution, dolomitization and dedolomitization and compaction. These processes reflect syndepositional marine, subaerial meteoric, near-surface marine, vadose-marine and meteoric-phreatic diagenetic realms. Of importance is the presence of paleokarsts originated where shallow marine limestones have become subaerially exposed by a fall in relative sea level.