Zambezi: a new palaeodrainage evolution.
A new, more complete Zambezi paleodrainage evolution is presented, based on timing of Karoo rift reactivations and subsequent stream capture events (see also Bonne & Caracciolo 2017).
Our alternative Zambezi River evolution is based on high-resolution geomorphology constraints and the evolution of regional and local stress fields. The river evolution is controlled by the propagation of rifting and graben formation of the East African Rift System, into southern Africa, forking into the continent as the southwestern branch of the East African Rift System, ending in the Okavango rift.
Well-constrained timings of rift initiation and using the knowledge of drainage development upon incipient rift systems and associated structures, the Late Cenozoic palaeodrainage evolution of the Zambezi River is found to differ from the publically accepted (and undisputed) evolution. This is due to different timings of reactivation and the subsequent changes in erosional base level, needed for a trunk stream to be able to capture hinterland drainage.
Based on the combined analysis of fluvial and tectonic landforms, the linkage of the Upper and Lower Zambezi, forming the Victoria Falls, is believed to have occurred at a different time.
Some study outcomes Zambezi palaeodrainage:
- The modern, large Zambezi is a recent phenomenon, but also the older, shorter Zambezi had at some moments in time a significantly high solid sediment flux, in turn having a considerable impact on sedimentation in the Zambezi Depression.
- Capture mechanisms of the Zambezi River, and changing sandstone compositions.
Changes in the exact location of the outlet of the Zambezi River, dictated by fault activity.
Interactions of the downstream Zambezi River with the Pungoé and Buzi rivers.
Changes in offshore sandstone mineralogy, reflecting hinterland uplifts, river captures, active erosion in sub-basins with varying outcrop lithologies, gradual erosion of Karoo LIP basalts, exposure at rift shoulders of various Precambrian metasedimentary, metamorphic and magmatic basement suites, erosion of Karoo, Cretaceous and EARS rift sediments.