Saturday, 15 July 2006

Origin of Gravel-Clay Horizons in Soils Developed from Lower Triassic Red Beds in the Holy Cross Mountains (S Poland).

Zbigniew Zagórski, Div of Soil Science, Dept of Soil Environmental Sciences, Warsaw Agricultural Univ- SGGW, Nowoursynowska 159, Warszawa, Poland and Sylwia Grela, Divi of Soil Science, Dept of Soil Environmental Sciences, Warsaw Agricultural Univ - SGGW, Nowoursynowska 159, Warszawa, Poland.

The study was focused on soils developed from red beds of the Lower Triassic Bundsandstein occurring in the south-western part of the Holy Cross Mountains (S-Poland). The main problem in these soils is the assignment of the gravel-clay horizons located at the depth of 50-90 cm to pedogenic illuvial horizons or lithogenic horizons of the soil substrate. The aim of the analyses was a detailed recognition of the micromorphology and submicromorphology, leading thus to explaining the origin of these horizons. Microscopic analysis of thin sections allowed explaining the intense red colour of the soil substrate. It results from the presence of haematite, which may occur on quartz grains. The presence of haematite has been additionally proved by XRD analysis. The fine fraction f (< 0,01 mm) is represented by clay minerals with the domination of kaolinite (XRD). They fill the voids between the microskeleton grains or form uniform zonal infillings. Microscopic analysis in transmitted and reflected light showed a low degree of the clay domain separation. Based on SEM analyses, undisturbed packets of kaolinite in the voids between grains and in individual concentration have been observed. The presence of such concentrations is characteristic of sedimentary rock diagenesis. The diagnostic features of the substrate have been confirmed by SEM analysis of selected grains of the skeleton. Recrystallisation concentrations of quartz microcrystals have been observed there. They form regeneration coats on grains, typical of the Lower Triassic deposits (Barczuk 1979). The obtained results allow a univocal determination of the lithological origin for the gravel-clay horizon in the analysed soils. Both the micromorphological and particularly the submicromorphological features indicate the absence of pedogenetic processes and lack of such phenomena as migration of the clay fraction (undisturbed clay domains) as well as intra-soil weathering caused by soil solutions (preservation of regeneration coats and presence of haematite concentrations).

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