Matthew R. Buoniconti1,
Christopher A. Scholz2
(1) University of Miami - RSMAS, Miami, FL
(2) Syracuse University, Syracuse, NY
Abstract: Climatic and volcanic modulation of tectonic and sedimentary processes in the Livingstone Basin, Lake Malawi, East Africa
The Songwe Delta lies along the axial margin of Lake Malawi, the southernmost large lake of the East African Rift System. The drainage enters the basin medial to the shoaling margin and the basin-bounding Livingstone Border Fault (LBF). Tectonics and sediment supply play complimentary roles in basin development in this setting. About 500 km of intermediate resolution (50-500 Hz) seismic reflection data reveal that tectonics and sediment supply are not equally important during all depositional intervals as tectonic and sediment-input rates were temporally modulated by rift-related volcanism and by insolation changes.
Two groups of seismic stratigraphic sequences are identified from these data. In the lower group of sequences, a deeply subsided lake persisted when tectonically-driven subsidence outpaced sediment supply, and the lake level was modulated by changes in evaporation/precipitation due to insolation variations. During deposition of the upper group of sequences, sediment supply dominated and outpaced subsidence, allowing for development of coherent coarse-grained facies. The effects of climate change during the upper sequences are pronounced, as subaerial lowstand delta deposits accumulated 50 km basinward from the modern delta front in what is now 500 m water depth. Hydrologic modeling of this interval shows that Lake Malawi lost up to 98% of its water volume during this lowstand, that we speculate occurred about 0.13 Ma.
The change between these two groups of sequences may be attributed to the onset of rift-related volcanism in the Rungwe volcanic field 50 km to the north between 1.75 and 0.12 Ma. Construction of volcanic edifices significantly enhanced the availability of coarse-grained sediments for transport by the Songwe river system.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana