Following the rifting of Ma
dagascar away from East Africa in the Triassic an
d Jurassic, a passive margin
develope
d along what is now the Tanzanian coast. This perio
d of tectonic stability laste
d from the Late Cretaceous to Early Oligocene an
d was marke
d in southern Tanzania by the accumulation of a thick, outer shelf, clay-
dominate
d succession now recognise
d as the Kilwa Group. Offshore rifting
during the Miocene opene
d a series of basins along the margin parallel to the mo
dern coastline. However, our recent fiel
d surveys along the southern coast between the towns of Kilwa an
d Lin
di, which have focusse
d primarily on the Kilwa Group, have yiel
de
d diverse evi
dence for structural reactivation an
d inversion which we present here to give a more
detaile
d interpretation of the structural evolution of this region since the Jurassic.
Following extensive surface sampling and shallow coring in 22 boreholes, we present new planktonic foraminiferal biozone maps for Kilwa and Lindi which help to resolve the deformation in these two key areas. Growth faults active during the Miocene can be identified in the field at both Kilwa and Lindi, but there is also evidence of extensional reactivation of older, pre-Kilwa Group faults. Post-Miocene ‘flower’ structures, high-angle reverse faults and thrusts indicate that the area has undergone compression and strike-slip deformation in the past ![]()
direct.com/scidirimg/entities/223c.gif"" alt=""not, vert, similar"" border=0>6 Ma. Present day topography is also controlled by the regional fault pattern, or in some cases by relatively recent movement on faults. For instance, Singino, Mpara and Kimamba Hills in the Kilwa area are ‘pop-up’ structures. We use this observation to identify potential faults on satellite imagery in the eastern Mandawa basin (between Kilwa and Pande) and north-east Ruvuma basin (Lindi Bay) and combine this with new seismic interpretations across key lines to confirm faults and project them subsurface. We suggest that the Triassic–Jurassic regional north–north-west fault trend was reactivated at least twice. Miocene extension may have led to new faults, but certainly reactivated the older Mesozoic faults. Subsequently, both Miocene and older faults were reversed during Pliocene positive inversion, possibly related to doming from a mantle plume beneath the Tanzanian craton(s). We suggest here that reversal was either accompanied by, or followed by, strike-slip movement on these faults to develop the ‘flower’ structures and ‘pop-ups’ seen in the field and on seismic sections. This motion could be sinistral and linked to periodic stretching in the eastern arm of the East African Rift System over the past ![]()
direct.com/scidirimg/entities/223c.gif"" alt=""not, vert, similar"" border=0>1.2 Ma, combined with an east-south-east movement with minor clockwise rotation of the ‘Rovuma Plate’ of central and southern Tanzania.
