Journal of Paleolimnology

, Volume 62, Issue 3, pp 279–300 | Cite as

Late-Holocene sedimentation and sodium carbonate deposition in hypersaline, alkaline Nasikie Engida, southern Kenya Rift Valley

  • Gijs De CortEmail author
  • Florias Mees
  • Robin W. Renaut
  • Matthias Sinnesael
  • Thijs Van der Meeren
  • Steven Goderis
  • Edward Keppens
  • Anthony Mbuthia
  • Dirk Verschuren
Original paper


Continental rift systems are often characterized by geothermal activity and associated discharge of hot groundwater, which can substantially impact the water, solute and sediment budgets of rift-valley lakes. Hot-spring inflow can result in complex lake hydro- and geochemistry, but also buffers against the desiccation of closed-basin lakes in dry climate regimes. Consequently, hydrothermally fed lakes can potentially provide continuous sedimentary records from regions where other types of paleoenvironmental archives are lacking. This is illustrated by Nasikie Engida, a shallow hypersaline and alkaline (soda) lake in the semiarid Rift Valley of southern Kenya. Here, inflow of hot-spring water has maintained a shallow but permanent water body and continuous deposition of sediments through past climate episodes when many other lakes in the eastern (Gregory) branch of the East African Rift System stood dry. We present the first data on late-Holocene sedimentation in this remarkable lacustrine system, typified by authigenic nahcolite [NaH(CO3)] formation during part of its recorded history. Our data include measurements of bulk-sediment and mineralogical composition, clastic-mineral grain size and magnetic susceptibility. Analytical issues related to the large amount of salts within the sediments, both as crystals and in solution in the pore water, are discussed. We also present exploratory time series of the stable-isotope composition of bulk organic matter and authigenic nahcolite. Core lithostratigraphy and preliminary radiocarbon dating indicate that Nasikie Engida has accumulated finely laminated sediments continuously since ca. 2850 cal year BP, which is remarkable given its current maximum depth of only 1.6 m. Synsedimentary nahcolite appears abruptly ~ 2260 cal year BP and since then has been deposited regularly, in the form of distinct pure layers up to several cm thick. Its formation has been enabled by high pCO2, supplied principally from geothermal sources, accumulating in a high-density brine. Although Nasikie Engida has likely been saline over the entire time span covered by the studied sediment sequence, variation in nahcolite deposition and bulk-sediment composition suggests multi-decadal to centennial oscillations in water-column stability and stream inflow driven by variation in climatic moisture balance. Further analyses of this paleoenvironmental archive may thus produce the first continuous climate-proxy record from a vast dry region of equatorial East Africa. Moreover, Nasikie Engida’s extraordinary setting makes it a unique modern analogue for the interpretation of ancient nahcolite-bearing salt-lake deposits.


Saline-alkaline lake Kenya Rift Valley Magadi–Natron Hydrothermal lake Salt-lake sedimentology Nahcolite 



This work was conducted as part of the Belgian Science Policy (Belspo) Brain-be project ‘Patterns and Mechanisms of Climate Extremes in East Africa’, BR/121/A2/PAMEXEA, with additional support for fieldwork provided by the Research Foundation Flanders (FWO, grant no. K215514N). RWR acknowledges support from the Hominin Sites and Paleolakes Drilling Project (funded by NSF, ICDP and other agencies) and NSERC (Canada). The authors thank Yoeri Torsy (Limnology Unit, Ghent University), David Verstraeten (Analytical, Environmental and Geo-chemistry, Vrije Universiteit Brussel) and Veerle Vandenhende (MinPet Laboratory, Ghent University) for assistance in laboratory analyses.

Supplementary material

10933_2019_92_MOESM1_ESM.docx (5.6 mb)
Supplementary material 1 (DOCX 5761 kb)


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Authors and Affiliations

  1. 1.Limnology Unit, Department of BiologyGhent UniversityGhentBelgium
  2. 2.Department of Earth SciencesRoyal Museum for Central AfricaTervurenBelgium
  3. 3.Department of Geological SciencesUniversity of SaskatchewanSaskatoonCanada
  4. 4.Analytical, Environmental and Geo-ChemistryVrije Universiteit BrusselBrusselsBelgium
  5. 5.Tata Chemicals MagadiMagadiKenya

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