Mineralogy, Petrology and Chemical Composition of Some Calcareous Tufa from the Schwäbische Alb, Germany

  • Georg Irion
  • German Müller

Abstract

Calcareous tufas from the Schwäbische Alb collected and studied botanically by A. Stirn are investigated mineralogically, petrographically, and chemically.

Plant tufas are formed by incrustation of plant fragments (mostly algae and mosses) by calcite; the calcite is deposited around the plants from spring waters, rich in hydrogene carbonate. They commonly exhibit high porosity. Dense calcareous sinter is formed covering calcareous tufas and rubble in water during periods of stagnating plant growth. Mineralogic investigations revealed that more then 99% of crystallized material consists of calcite, small amounts of quartz, kaolinite, montmorillonite and illite are also present. These minerals are detrital and derived from the Upper Jurassic rocks of the drainage area. Some of the tufas still contain small amounts of organic matter.

Mg, Sr, Mn, and Fe only make up a small portion of the HCl-soluble part of tufas. The average is 0.16%, a maximum of 0.6 was found. A clear relationship between Fe and Mn and the amount of HCl-insoluble residue exists. The Sr-content is about ten times lower in comparison with marin carbonate rocks.

Essentially, the fabric of the plant tufas depends on morphology of the incrusted plants. The size of calcite crystals varies between several microns and several millimetres. The larger calcite crystals are mostly euhedrally shaped.

Diagenetic changes (filling of pore spaces, recrystallization) mostly take place in moss tufas and calcareous sinter.

Keywords

Porosity Quartz Calcite Recrystallization Assimilation 

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Copyright information

© Springer-Verlag Berlin · Heidelberg 1968

Authors and Affiliations

  • Georg Irion
  • German Müller
    • 1
  1. 1.Laboratorium für SedimentforschungUniversität HeidelbergGermany

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