Timing of the Cenozoic magmatic intrusions in the offshore Tanga Basin, Tanzania: correlation to age equivalent deposits in the Eyasi-Wembere Basin and their implications for petroleum potential

Abstract

The offshore Tanga Basin of north-eastern Tanzania contains Cenozoic sedimentary successions that have been poorly studied. The basin development was due to an interplay of multiple factors including periods of active fault movement linked to the East African Rift system (EARs) which influenced the Cenozoic development of the offshore Tanga Basin. The EARs recorded several discrete tectonic episodes that were associated with magmatic activities and massive volcanism. However, there is no report on the possible presence of magmatic intrusions indicative of magmatic activities and volcanism in the history of the Tanga Basin. Timing of occurrence and distribution of magmatic intrusions are among the key components needed to evaluate the petroleum potential of the basin. A detailed 2D qualitative seismic interpretation, coupled with core logging data and analysis of elemental proxies, has been employed to evaluate the petroleum potential of the Cenozoic successions of the offshore Tanga Basin considering the presence and timing of occurrence of the magmatic intrusions. These used data and the associated interpretation techniques have not been used before to meet similar objectives. Both core logging and elemental proxies are newly collected information used in this study. Results suggest that the Tanga Basin has been variedly intruded by magmatic sills and dikes. Seismic well tie and correlation to age-equivalent deposits across the onshore successions in the EWB revealed that the volcanic events occurred during tectonic episodes that influenced the development of the East African Rift basins. Seismic interpretation also suggests that these tectonic episodes occurred possibly during the Miocene, Pleistocene and Holocene periods when magmatic intrusions are believed to have promoted source rock maturation and facilitated the formation of structural elements for petroleum preservation.