The Aptian evaporites of the South Atlantic: a climatic paradox?

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

A lost Tethyan evaporitic basin: Evidence from a Cretaceous hemipelagic meta‐selenite – red chert association in the Eastern Mediterranean realm

“…Warm climatic conditions are reported for the Aptian–Albian times including a gradual warming into the Cenomanian (Huber et al ., ; Clarke & Jenkyns, ; Frakes, ; Pucéat et al ., , ). In the upper Aptian, marginal salt deposits of 1 to 2 km stratigraphic thickness precipitated during the earliest opening stages of the Atlantic (Burke, ; Chaboureau et al ., ) and may, time wise, correlate with Anatolian selenite‐pseudomorph units reported here. The Atlantic evaporite units are interpreted with intermittent spillovers into sub‐sea‐level grabens over a period of 1 to 5 Myr (Burke, ; Davison, ).…”

“…Spillovers from different oceans over structural sills produced massive evaporite units including horizontal and vertical cycles at least for the evaporites south of the Equator. For the northern Aptian Atlantic evaporites, a hydrothermal origin is proposed by some authors (Hardie, ; Chaboureau et al ., ). For the southern Atlantic salt, a desiccation model (Torsvic et al ., ; Chaboureau et al ., ) as well as deep water brines are proposed (Burke, ).…”

“…For the northern Aptian Atlantic evaporites, a hydrothermal origin is proposed by some authors (Hardie, ; Chaboureau et al ., ). For the southern Atlantic salt, a desiccation model (Torsvic et al ., ; Chaboureau et al ., ) as well as deep water brines are proposed (Burke, ). Among these, the Atlantic evaporites are perhaps best comparable to the Rosetta Marble meta‐selenite case example and, therefore, contribute to very significant seawater evaporation that has a bearing on global‐ocean element mass balances of carbon and sulphur (Wortman & Chernyavsky, ).…”

Early Mississippian evaporites of coastal tropical wetlands

“…Using fully coupled ocean‐atmosphere models Chaboureau et al . () showed that high salinity and aridity developed despite the equatorial location. Ziegler et al .…”

Constraining South Atlantic growth with seafloor spreading data

“…[] have argued that the event constitutes a precursor to seafloor spreading. The enhanced geothermal gradient associated with this volcanism is thought to have been a key factor in hydrocarbon generation in the southern segment of the South Atlantic, most of which occurred during Cretaceous times [ Chaboureau et al ., ].…”