ORGANIC-MATTER BEARING CLASTS AND GRANULES IN UPPER PROTEROZOIC OF CONGO

We show the occurence of anthracite and immature organic matter bearing talc clasts or granules within the regressive sequence of the Schisto-calcaire cycle (West Gongolian Supergroup) which is interpreted as a carbonate ramp. The sedimentary succession of the Makanfou river corresponds to a reflective beach. The supratidal withish dolomite (SCIIIc) bears immature organic matter bearing talc clasts and layers. The SCIIIb facies corresponds to the intertidal domain marked out by a dark stratiform dolomitic stromatolite composition. It also corresponds to the infratidal domain. A slice of dark dolomite bears immature organic matter bearing algal lamines, angular, ribbon like shaped or ovoid clasts, and mature organic matter bearing brownish granules matter which are more often radial with micritic cones. The particular preservation of the organic matter is effectued in a poor oxygeny water of lagoon. Clasts bearing anthracite and mature organic matter deposited away dark limestones at deeper water. These black talc clasts likely correspond to slices of the intertidal stromatolites. Moreover, immature organic matter bearing granules with radial brownish cones occur within a pebble of the fluvio-estuarine SCIV facies. The occurrence of immature and mature organic matter in such ancient sediments shall be underlined. The sedimentary evolution of the algal lamines started by a mechanical disruption followed by a dynamic erosion of the clasts. Then, the organic matter undergone a brown coloration by coloration by centrifuge and/or centripete migration which also developped as radial penetrative cone. Eventually, a centripete radial micritisation may affect the brown clasts. The brown coloration modified mature organic matter rather than the micritisation which destroyed the organic matter. The organic matter bearing radial granules do not correspond to oolites or micro-organisms. They are biodetrital matter derived from algal lamines.