Original paper

Klimaperioden lateritischer Verwitterung und ihr Abbild in den synchronen Sedimentationsräumen

[Climatic Periods of Lateritic Weathering and their Reflection in Synchroneous Sedimentary Basins]

Valeton, Ida

Kurzfassung

Im Verlaufe der Erdgeschichte zeichnen sich mehrmals extrem warm-humide Klimaoptimum-Zeiten im terrestrischen wie im marinen Bereich ab. Diese waren gleichzeitig Phasen intensiver chemischer Verwitterung mit oft mehreren hundert Meter mächtigen Latosolen - mit Erosionsminima auf den Kratonen und Erosionsmaxima in den Orogenbereichen. Am Beispiel der Klimaoptimum-Phase Oberkreide-Alttertiär wird versucht, die räumlich-zeitliche Auswirkung der chemischen Verwitterung aufzuzeigen. Auf den Gondwana-Kontinenten ergibt sich eine Zuordnung von lagerstätten-führenden Latosolen zu morphogenetischen Flächen der Oberkreide und des Alttertiärs. Die prä-alttertiären Latosole mit Erzanreicherung zeichnen sich neben sehr großer Mächtigkeit durch relativ geringe vertikale und laterale Differenzierung aus, während es in den alttertiären erzführenden Latosolen zu einer extremen vertikalen und horizontalen Elementtrennung, die oft zu Duricrustbildung mit Gelgefügen führt, gekommen ist.

Abstract

Several times during earth's history, warm-humid climate periods are represented as well in the terrestrial as in the marine environment. These periods were, at the same time, phases of intense chemical weathering, often with several hundreds of meters of latosol formations during times of minimal erosions on the stable shields, and optimal erosions in the orogenetic belts. The results of deep chemical weathering during Upper Cretaceous to Lower Tertiary time are presented as an example for the effects of mineral decomposition and soil formation within phases of climatic optima. Ore-bearing latosols on the Gondwana continent are related to the planation phases of Upper Cretaceous and Lower Tertiary. The pre-Tertiary latosols with ore concentration are, besides a large thickness, characterized by a relatively little vertical and lateral differentiation, whereas the Paleogene ore-bearing latosols show an extreme vertical and horizontal separation of the chemical elements by dissolution and precipitation which led to the formation of duricrusts with gel-like textures. The regional distribution of the supergene ore deposits during this period of climatic optimum represents a more extended warm humid climate belt on both sides of the equator in comparison with the recent time. The synchronous association of terrestrial sediments is characterized by: red beds with high chemical and low textural maturity - in situ kaolinitic claystone (flint clay) or Mg-claystone (sepiolite, attapulgite) - ferricretes or silcretes - in situ soil formations with root horizons - swamp or lignite formations with sulphides or sulphates (jarosite, alunite). Contemporaneously with the intense chemical decomposition on the continents - sometimes with a certain delay - a maximal chemical or biochemical sedimentation in marine environment took place. Corresponding to the local marine conditions, the following fades associations can be formed: chalk - chert - phosphate - montmorillonite - sepiolite - attapulgite - glauconite - siderite. The regression to a colder climate since the Oligocene led to an extreme climatic zonation and to a destruction of the vegetation cover and an increasing erosion, due to the relief activation by the marine regression. The contribution of detritus to the marine environment replaces or covers the chemical sediments.

Keywords

GondwanaUpper CretaceousPaleogenecontinental environmentpaleoclimate (climatic optimum)chemical weatheringlateric weatheringlatosolspaleosolsduricrustore depositmorphogenesiscorrelationsynchroneoussedimentation basinsmarine e