Evaporite mineralogy and major element geochemistry as tools for palaeoclimatic investigations in arid regions: A synthesis

Resumen

This paper presents a
synthesis of the applications of evaporite mineralogy and the
relationship between major elements for the palaeoclimatological
research of arid regions, with examples from Playa Oum el Krialate
in Tunisia, Wadi Natron in Egypt, East African Rift Valley, etc. The
numerous evaporite minerals serving as indicators of palaeo-drylands
(salinity and evaporation) include carbonates, sulfates, and Na, K,
Ca, and Mg chlorides. The occurrence of double salts, such as
glauberite, carnallite, kainite, gaylussite, pirssonite, burkeite,
etc., suggests disequilibrium conditions. Apart from that, the
presence of very rare Fe-sulfates, such as rozenite and
szomolnokite, indicates anoxic conditions with higher salinity. The
formation of Na-silicates, such as magadiite and kenyaite, implies a
decrease in pH of a highly alkaline Na concentrated brine. The
Mg-silicates (palygorskite, Mg-montmorillonite and talc) form
quickly and then re-dissolve when conditions change. Identification
of fulgurites in the Sahara has been related to palaeo-lightning. We
have also discussed a simple geochemical approach of using the
ratios of soluble/insoluble elements to identify palaeo-arid events
with examples from loess-soil sequences from Feiran Oasis in the
Sinai Desert (Egypt) and salty silt lacustrine sequences from Thar
Desert (India).