Basin Architecture and Sedimentary Pathways in the East African Malawi Rift

Tectonics and climate exert control on landscape dynamics, erosion, sediment routing, and timing of regional scale drainage-capture. Unfortunately, appropriate field laboratories—where coupled watershed/tectonic evolution can be directly linked to a basin that captures and records the history of landscape evolution—are rarely available. In the Malawi rift, an early-stage segmented rift valley, we seek to explore how rift architecture modifies and interacts with subaerial and sublacustrine sediment-dispersal pathways in a closed basin through time.

Sedimentation in the north and central half-grabens of Lake Malawi is controlled by sediment flux and base level fluctuation driven by changing climate. This hypothesis is testable using a comparison of sedimentation patterns and rates with a lake level record to ~1.2Ma, obtained in previous drilling projects. To characterize sedimentation, we map onshore sedimentary units (e.g. alluvial fans) and correlate these with offshore units  (e.g. fan deltas, submerged axial channels) utilizing seismic data. We use a “source-to-sink” sampling strategy in accordance with our goals, taking advantage of existing piston cores, deep cores, and seismic data sets, to examine erosion rate, vegetation proxies, and provenance (through detrital zircons).

Preliminary detrital zircon U-Pb data confirms we can trace sediment in the cores to one of several sources: (1) proximal exhumed footwall rocks and associated fans, (2) distally-sourced hangingwall sediments, and (3) axial channels from the north. Ongoing work concentrates on constraining sediment fluxes from these sources, and on building our understanding of how spatio-temporal changes in these sedimentary pathways are driven by base level fluctuation.