Lateritized tephric paleosols from central Patagonia, Argentina: a southern high-latitude archive of Palaeogene global greenhouse conditions

KRAUSE J. M., E. BELLOSI & M. RAIGEMBORN

SEDIMENTOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2010 p. 1721 - 1749

0037-0746

Palaeosols of the Koluel-Kaike Formation, a red colour-banded, pyroclasticsuccession from southern Argentina, constitute a proxy for Eocene climatechanges. Reticulated and vertically elongated ferric mottles, along with iron andmanganese nodules are the most significant climate indicators, whichoriginated by alternating cycles of waterlogging and drying conditionscausing Fe-Mn mobilization and fixation. Clay minerals vary from akaolinite > smectite suite in the lower and middle sections, to asmectite > kaolinite one in the upper part. High concentrations of ironoxides/hydroxides and kaolinite, lack of exchangeable bases, absence ofcarbonate cement, presence of ironstone and redness of hue in most of thepalaeosols suggest intense chemical weathering related to leaching andlateritization processes. Five pedotypes, ordered in a stratigraphic sense, wereidentified. Strongly developed, red to orange Chornk (Fragiaquult) and Ka´penk(Plinthaquult) pedotypes display argillic horizons, abundant ferric nodules andslickensides; they are dominant in the lower and middle sections, and formed inseasonal humid and megathermic (tropical) conditions with a mean annualprecipitation of 1200 to 1300 mm and a mean annual temperature of 15C.Weakly developed, less structured Ornek (Vitrand) and Po´ lnek (Placaquand)pedotypes occur in the middle and upper sections, and originated in sub-humidand mesic-megathermic conditions with a mean annual precipitation around1000 mm and a mean annual temperature around 12 C. The brownish Soorsh(Argialboll) pedotype exhibits a granular structure and is present at theuppermost part of the unit. It developed in sub-humid/semi-arid and mesicconditions, with a mean annual precipitation of 600 to 700 mm and a meanannual temperature around 10 C. This pedotype succession and clay mineraldistribution indicates a decrease in chemical weathering and degree of soildevelopment with time. Koluel-Kaike palaeosols from Central Patagonia aresome of the first continental non-palaeobiological data linked to the EarlyPalaeogene global warming in South America; they show an especially closerelationship with the Early Eocene Climatic Optimum and the following longtermcooling and drying initiated by Middle to Late Eocene time.