Turkish Journal of Earth Sciences




Quaternary calcretes in the Adana area (southern Turkey) are widespread and occur in a variety of forms such as nodular, columnar/tubular, fracture-infill, laminated hardpan, and conglomeratic crusts. Palygorskite associated with calcrete nodules, tubes, and fracture-infills in the columnar horizon and adjacent host-rock mudstones suggests a cogenetic formation. The Beta-fabric (biogenic) constituents and stable isotope values of calcretes support a pedogenic origin for calcretes and also palygorskite. Extensions of palygorskite fibre and fibre bundles from euhedral to subhedral calcite crystals in calcretes and from smectite flakes in adjacent host-rock mudstone suggest an authigenic origin related to calcretisation in which precipitation and dissolution/precipitation are the main processes for palygorskite formation, respectively. The presence of palygorskite in subspherical aggregates containing calcite crystals, and with smectitic clay coatings around the palygorskite aggregate, similarly suggests a relationship of pedogenic evolution between the 2 clays. Palygorskite precipitated in a vadose zone from strongly evaporated alkaline water, rich in Si and Mg and low in Al and Fe, at elevated temperatures and at an advanced stage of calcrete formation. Development of palygorskite mainly on relict calcite crystals indicates its formation during or shortly following calcite formation in calcretes. Palygorskite precipitation on relative large crystal surfaces has resulted in encrusted and platy fan-like crystal morphologies, whereas its nucleation on the crystal edge relief triggers fibre-like morphologies from crystal edges.


Authigenesis, calcrete, geochemistry, mineralogy, palygorskite, pedogenesis, Quaternary, smectite

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