Revised model of the Mesozoic basin evolution of Tanzania based on literature review and input from a case study from the Ruvu Basin

Abstract

The depositional and tectonic history of the Tanzanian basins are currently a topic of debate. Two different theories were adapted in the previous literature concerning the Tanzanian rift history and the evolution of the Tanzanian Karoo and Coastal Basins; The first theory suggest that the Gondwana breakup started during the Triassic, as a response of the Karoo rift system. Currently, this theory is widely adapted in other related studies in Tanzania. The second theory describes two distinct rift events that led to 1) development of Intracratonic grabens during Permo-Triassic times, and 2) the breakup of Gondwana as a result of pericratonic rift evolution starting in the Lower Jurassic. This two-phase theory has received much less attention. The broader aim of this study is to present a revised model of the basin evolution of Tanzania in the context of a single or two-phase rifting history. The following steps were taken: 1) summarizing the recent insights concerning the rift phases of Gondwana breakup, 2) summarizing the lithostratigraphy of the Tanzanian basins, 3) summarizing the common interpretation for basin evolution of Tanzania wherein the continuous rift history is explained, 4) presenting the evidence why two rift systems formed the Tanzanian basins during the Mesozoic. Based on the findings, a revised model of Tanzanian basin evolution is presented that describes two distinct rift events; The Karoo rift event and the Early Jurassic rift event, as accepted in the current Gondwana breakup framework. This model includes a new interpretation for the deposition of the Pindiro Group. It comes forward that little is known about the post-rift setting in the northern Coastal Basin, the Ruvu Basin. A short fieldwork was carried out in the Msolwa quarry in the Ruvu basin, focusing on a petrophysical and sedimentological analysis. The facies suggest that the Msolwa formation was deposited in a (Lower) shoreface to offshore environment. Additionally, the succession comprises debrite stacks with an immature grain content, which point to proximal syn-depositional tectonic activity. Correlating these findings with the revised model, they may be related to faulting during thermal subsidence in the post-rift setting of the Ruvu Basin.