SEQUENCE STRATIGRAPHY BASED ON MICROFACIES ANALYSIS - MFAMOSING LIMESTONE, CALABAR FLANK, NIGERIA

Field observations and petrographic analysis allow a sequence-stratigr aphic interpretation of the intensely karstified Albian Mfamosing Lime stone Formation in the Calabar Flank of the south-eastern Niger Delta. Main criteria for this interpretation are the presence of siliciclast ic intercalations, of prominent hardgrounds, of characteristic microfa cies including stromatolites and of phreatic and vadose diagenetic pat terns. These criteria enable the recognition, from bottom to top in th e type section of the Mfamosing Limestone, of a late phase in the form ation of a highstand systems tract and of a flooding surface followed by a lowstand systems tract in which erosional features have been deve loped locally. The succession is topped by a transgressive systems tra ct. Some of these units and key sequence-stratigraphic boundaries have been traced into other outcrops in the area. In their identification within the heavily karstified outcrops, petrography overprints and ver tical sequence patterns play a significant role. A sedimentation model explains the areal differences in development. Siliciclastic shedding influenced the carbonate system. Time-equivalent carbonate bodies occ ur on either side of the opening South Atlantic Ocean.