Clim. Past Discuss., 8, 121-144, 2012
www.clim-past-discuss.net/8/121/2012/
doi:10.5194/cpd-8-121-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
The Aptian evaporites of the South Atlantic: a climatic paradox?
A.-C. Chaboureau1,2,3, Y. Donnadieu2, P. Sepulchre2, C. Robin1, F. Guillocheau1, and S. Rohais3
1Géosciences Rennes, UMR6118, CNRS – Université de Rennes 1, Campus de Beaulieu, Rennes 35042 Cedex, France
2Laboratoire des Sciences du Climat et de l'Environnement (LSCE), unité mixte CNRS-CEA-UVSQ, 91191 Gif-sur-Yvette, France
3IFP Energies nouvelles, 1 et 4 Avenue de Bois-Préau, 92852 Rueil-Malmaison, France

Abstract. For a long time, evaporitic sequences have been interpreted as indicative of an arid climate. Such systematic interpretations led to the suggestion that the central segment of the South Atlantic (20°–0°) was characterized by an arid climate during the upper Aptian. Indeed, synchronous to this period that corresponds to the rifting and to the opening of this part of the South Atlantic, a large evaporitic sequence spreads out from the equator to 20° S. Using the fully ocean atmosphere coupled model FOAM, we test the potential for the Aptian geography to produce an arid area over the central segment. Sensitivity to the altitude of the rift shoulders separating the Africa and the South America cratons, to the water depth of the central segment and to the drainage pattern have been performed. Using seawater salinity as a diagnostic, our simulations show that the southern part of the central segment is characterized by very high salinity in the case of catchment areas draining the water out of the central segment. Conversely, whatever the boundary conditions used, the northern part of the central segment remains humid and salinities are very low. Hence, we conclude that the evaporites deposited in the southern part of the central segment may have been controlled by the climate favouring aridity and high saline waters. In contrast, the evaporites of the northern part can hardly be reconciled with the climatic conditions occurring there and may be due to hydrothermal sources. Our interpretations are in agreement with the gradient found in the mineralogical compositions of the evaporites from the north to the south, i.e. the northern evaporites are at least 4 times more concentrated than the southern one.

Citation: Chaboureau, A.-C., Donnadieu, Y., Sepulchre, P., Robin, C., Guillocheau, F., and Rohais, S.: The Aptian evaporites of the South Atlantic: a climatic paradox?, Clim. Past Discuss., 8, 121-144, doi:10.5194/cpd-8-121-2012, 2012.
 
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