Large rivers, such as The San Francisco, are dynamic systems whose evolution depends on internal and external forces, particularly tectonics, sea level and climate. The São Francisco River is one of the main rivers in Brazil, with an extension of 2,900 km and corresponding to 7.4% of the Brazilian territory. The San Francisco flows north through different climatic zones, with its upper course in a semihumid setting, but with its basin predominantly under semiarid conditions.
Because the São Francisco River basin is in tectonically stable areas and controlled by local-based levels, its deposits are an excellent river sedimentary record to understand how large tropical river systems have responded to past climate change. To understand the controls on erosion, transport and sediment deposition in the plateau area to the plain, 200 km of the São Francisco River in northeastern Brazil were investigated.
Several geomorphological zones were characterized, mapped and dated by optically stimulated luminescence (OSL). The results allowed the recognition of at least four phases of fluvial deposition (> 90 ky; 66 to 39 ky; 18 to 9.5 ky and 380 years to recent), three phases of fluvial incision (I1 – 85 to 66 ky; I2 – 39 to 18 ky and I3 – 9.5 to 1.0 ky) and two stages of stabilization of the wind dune field (25 to 15 ky and 5 ky until recent).
The fluvial incision events were probably triggered by the increase in river discharge produced by the intensification of the Monsoon of South America, which has a great influence on precipitation over the headwaters of San Francisco. The development of wind dunes occurred under drier conditions in the area, when the winds reworked the sediments deposited in the river plain. Thus, it was interpreted that the cycles of deposition-incision of the São Francisco River during the last 100,000 are products of the millenary variation of precipitation.
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Article: Mescolotti, P.C., Pupim, F.N., Ladeira, F.S.B., Sawakuchi, A.O., Santa Catharina, A., & Assine, M.L. 2021. Fluvial aggradation and incision in the Brazilian tropical semi-arid: Climate-controlled landscape evolution of the São Francisco River. Quaternary Science Reviews, 263, 106977.
