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A study of pedogenesis in the Rocky Mountain Trench region of South-Eastern British Columbia Darcel, Francis Clift

Abstract

A study was undertaken of the pedogenesis of a Brown Wooded, a Grey Wooded and a Podzolized Grey Wooded soil developed over the highly calcareous Wycliffe till in the southern portion of the Rocky Mountain Trench, British Columbia. The investigation was divided into three phases. These were a study of the till at the three sites, its genetic relationship to the solum and the relative degree of soil formation and weathering in the three profiles. Analyses included mechanical analyses using the hydrometer and pipette procedures, plasticity measurements and soil reaction. Carbonates were measured by the gravimetric loss of carbon dioxide, exchangeable cations by ammonium acetate extraction and free iron by Mackenzie's dithionite technique. Samples of the clay fraction were separated by sedimentation, cleaned of sesquioxide coatings by Mackenzie's method, and analyzed for total chemical composition. Piper's sodium carbonate fusion and Corey and Jackson's hydrofluoric acid procedure were used to bring the clay into solution. Ferron and Tiron reagents were used for the spectrophotometric analysis of iron and aluminum and iron and titanium, respectively. Silica was determined gravimetrically by Piper's method. Calcium and magnesium were found by the versenate technique of Cheng and Bray after the removal of interfering heavy metals with sodium diethyl thiocarbamate. Potassium was analyzed with a Perkin-Elmer flame photometer. Other tests on the clay included determinations of the cation exchange capacity by Mackenzie's micro-Kjeldahl technique, X-ray diffraction patterns and dehydration curves. A mineralogical study was made of the very fine sand fraction. A method was devised for counting the magnetite grains in samples of from 1,000 to 2,000 heavy minerals using a magnetized needle. It was found that although there was considerable variation in the till at the three sites, particularly in mechanical composition, there were similarities in the mineralogical composition of the fine sand and clay fractions. Indeed, no satisfactory basis could be found for subdividing the till into two types. Variations down the profile of the relative abundance and composition of the coarse fraction, the shape of the summation percentage curves and the proportion of magnetite in the heavy minerals of the very fine sand indicated that the Wycliffe profile was composite while the Kinbasket was an A-B-C profile. The possibility was also noted that the Yoho profile could also be composite. The main soil formation processes were studied, including de-calcification and the movement of iron, organic matter, bases and clay. Results show that most soil development has taken place in Podzolized Grey Wooded profile, with somewhat less in the Grey Wooded soil and least in the Brown Wooded. Mineralogical studies of the very fine sand and clay fractions, however, indicate that there has not been appreciable weathering of the mineral constituents even in the intensely leached A₂[subscript p] horizon of the Podzolized Grey Wooded Soil.

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