Abstract: The Significance of the Bemolanga Tar Sands in Madagascar to the Petroleum Prospects in Tanzanian Coast

Samson Mpanda

The Karoo (C3-J1) terrigenous sediments of continental origin forming the base of sedimentary column of Tanzania, have been a subject of study for a long time so as to establish the hydrocarbon potential. The interest on these sediments is due to the presence of some billions of tons of bituminous tar in the Isalo sands formation, forming the upper part of the karoo supergroup in Madagascar. Bituminous tar being the residue of oil after evaporation of its light fractions. This indicates that large amounts of oil were generated in this area.

The study of paleoposition of Madagascar is of major importance since depending on where and when Madagascar was, one can relate its prospectivity to the area which were adjacent to it. Among other evidences, the identification of sequence of east-west trending magnetic anomalies of Mesozoic age in the Somali basin helps to define the paleoposition of this Island during the Gondwana reconstruction.

Detailed study of paleotectonic, paleothermal reconstruction of the tectonic elements of east Africa which was adjacent to Madagascar (model adopted by the author) and calculating the rate of rise of temperature per geological time as a function to oil generation, we established that, vast amount of oil were formed before and during the movement.

Our analysis of temperature and pressure distribution in the Tanzanian coast, justify the existence of liquid hydrocarbons even beyond economic interest depths, since karoo here is covered by thick shales forming tight and effective caprock for hydrocarbon preservations.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France