Climate-Rift Interactions and Stratigraphic Record of Long-Lived Lakes: Model Results and Subsurface Observations from The East Africa Rift

Ancient lakes and active rifts are especially valuable natural systems for evaluating the long-term interactions of tectonic processes such as continental extension and normal faulting, and surface processes driven by hydroclimate variability. Unlike many marine systems, lakes are almost always closed sedimentary systems, and large tectonic lakes contain long-duration stratigraphic records (e.g. >5 million years) that extend over many climate cycles, and which average out transient or stochastic events that may overprint small basins. We couple observations from an extensive suite of geophysical and geological data, including basin-scale multichannel and high-resolution reflection seismic data which are chronologically and lithologically constrained by scientific drill cores, to numerical models, to evaluate the forcing mechanisms that produced the observed sedimentary architecture of the active Lake Malawi (Nyasa) Rift.

The expansive catchment of Lake Malawi extends over five degrees of latitude and erodes terranes ranging in age from Proterozoic to Holocene, containing a wide range of lithologies including Precambrian metamorphic and igneous rocks, Mesozoic continental sedimentary rocks, and Holocene volcanoclastic material. The rift is comprised of several rift segments, each >140 km long, whose structurally-controlled relief constrains catchment evolution, and hence syn-rift stratigraphic architecture. In some parts of the lake basin syn-rift sediment fill exceeds 6 km. Hydroclimate variations in the Pleistocene have been extreme, forcing changes in lake levels over orbital-scale time frames of more than 550 m in what is now a 700 m-deep lake.

Here we show how sediment delivery varied under end-member conditions of profound aridity and moderately wet/humid climate, using landscape evolution models and a source-to-sink approach. Forward models of rift basin stratigraphic architecture provide insights into system behavior and feedbacks between normal fault and surface processes.