Origin of red color of the Lower Siwalik palaeosols: A micromorphological approach |
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Authors: | Seema Singh B Parkash Arun K Awasthi |
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Institution: | (1) Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee, 247667, India |
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Abstract: | Palaeosols of the Siwalik Group are associated with fluvial and lacustrine deposits that occur as thick multiple pedocomplexes.
The bright red color of the palaeosol beds has been earlier interpreted as a result of hot and arid palaeoclimate. However,
as against this view, our investigations of the bright red palaeosol beds of the Lower Siwaliks suggest that the climate was
cool and subhumid, instead of hot and arid during the deposition of these beds. Since cold climate is not very conducive to
impart red coloration, further research is needed to explain the cause of these red beds. For this, the micromorphological
study of soil thin sections was done which showed the presence of features such as dissolution and recrystallisation of quartz,
feldspar and mica, compaction, slickensides, presence of calcite spars, subrounded and cracked nature of quartz grains, microfabric,
complex patterns of birefringence fabrics, pigmentary ferric oxides, thick cutans and cementation by calcite. These features
indicate that diagenesis took place on a large scale in these sediments. The positive Eh and neutral-alkaline pH of soils
also suggest that the conditions were favorable for the formation of diagenetic red beds. During burial diagenesis of sediments,
the hydroxides of ferromagnesian minerals got converted into ferric oxide minerals (hematite). During deep burial diagenesis
smectite was converted into illite and the preponderance of illite over smectite with increasing depth of burial also indicates
the diagenesis of sediments. Thus, the red color of the Lower Siwalik palaeosols seems to be due mainly to the burial diagenesis
of sediments and does not appear to be due to the then prevailing climatic condition. |
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Keywords: | Palaeosols C3 type vegetation diagenetic red beds calcite spars |
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