Source Rocks

Several source horizons were identified in the Amoco wells within the Upper Triassic to mid Jurassic section.

To better understand the significance of these sources it is important to first consider the tar balls that occur on several islands in the Seychelles. These tar balls have been collected and analysed and have been shown to be from a local source. 

In fact two Seychelles oil families are evident from analysis of the tar balls. The first family is Early Jurassic to Upper Triassic in age and the second is found to be Upper Cretaceous in age and shares some affinity to the Bombay High oils. 

Recent work undertaken to attempt to correlate migrant hydrocarbons from side wall cores from the wells and the tar balls have shown that there is very good correlation in the biomarker assemblages supporting the fact that the tar balls are from a local source that can be correlated with the known source rock occurences in the wells. 

A paleogeographic picture of the Lower Mesozoic shows that once east and west gondwana had rifted, a vast restricted marine environment existed within which an extensive and potent source rock would have developed. This source rock is believed to have sourced the Tsimororo heavy oils in Madagascar, the Songo Songo gas field, the Tudaua seep on Pemba island and other oil and gas occurences in the region. This same source rock is believed to extend to the Seychelles basins.