Soil Development as a Function of Time in the Rouge River Basin, South-Central Ontario

Abstract

Three soils of postglacial age, representing a chronosequence in the Rouge River Basin of south-central Ontario, were studied to determine variations in morphological, physical, chemical, and mineralogical properties. These soils, forming in alluvium of mixed mineralogy represent the Late HoIocene (Entisol), Middle Holocene (lnceptisol),and Early Holocene (lnceptisol) surfaces. Horizon differentiation and soil thickness increase with greater age, while pH drops slightly in the sola of the older profiles. Cation exchange capacity (CEC) and organic matter in the surface horizons increases slightly with age, while, for the most part, CaCO3 and Ca/ Mg ratio decrease. Significant changes occur over time, especially with an increase of dithionite-extractable iron with age (from ~ 0.20 in the Late Holocene soil to ~ 0.70 in the Middle to Early Holocene profiles). Illite and illite-smectite tend to decrease with age, being replaced by small amounts of chlorite and vermiculite. In spite of some variability in parent materials due to stratification and preweathering, and minor changes in species composition, the changes in soil properties are attributed to processes of soil formation acting over time.

Clay mineralogical evidence of a bioclimatically-affected soil, Rouge River basin, South-Central Ontario, Canada

“…'u' material;Hodgson 1976). Therefore, soil description and stratigraphy presented here are similar to what was discussed in Mahaney and Sanmugadas (1986). Soil color assessments are based on Oyama and Takehara (1970) soil chips.…”

“…Randomly interstratified illite-smectite and occasional kaolinite and metahalloysite are not authigenic, the former is considered to be inherited from Ordovician shales, the latter from previous interglacial paleosols eroded by incoming ice during Wisconsinan-age ice advances (Mahaney and Ermuth, 1975;Mahaney et al, 2014). However, despite the high ratio of carbonates:silicates (approximately 80:20%) in fluvial sediment, chloritization of illite and slow genesis of vermiculite in middle to Early Holocene profiles (Mahaney and Sanmugadas, 1986) are documented in the basin. Clay mineral genesis is accompanied by degradation of plagioclase and mica, very minor decrease in quartz, and in horizons with lower pH, near complete removal of calcite.…”

“…Wetting depth in middle to Early Holocene fluvial soils in the region, estimated from root depth and thickness of B horizons (Mahaney and Sanmugadas, 1986), allows the throughput of soil moisture sufficient to remove smectite. Thus, the presence of moderate to large amounts of smectite in a soil stratigraphically similar to other Middle and Early Holocene soils in the basin with pedons lacking expandable clay minerals, invokes a means of explaining its genesis.…”

“…Entire profiles in the Rouge catchment reach~1.0 m depth developing over~11 ka which, given well-dated fluctuations of Glacial Lake Iroquois (Jackson et al, 2000;Mahaney et al, 2014), is the maximum age for any riverine profiles in the area. Aside from occasional 14 C dates on younger floodplain soils, the entire soil evolutionary sequence has been dated by relative dating (RD) methods including pebble/sand weathering characteristics, topographic position and soil stratigraphy (Mahaney and Sanmugadas, 1986;Mahaney and Hancock, 1993a,b;Mahaney et al, 2014). Changing profile morphology over time brings staged removal of calcite from soil epipedons over time, slow increase in concentrations of extractable cations and C/N ratios, increases in Fe d /Fe t (dithionite extractable/total Fe) (Mahaney and Sanmugadas, 1986;Mahaney and Hancock, 1993a) along with slow conversion of illite/mica to both chlorite and vermiculite.…”

“…Aside from occasional 14 C dates on younger floodplain soils, the entire soil evolutionary sequence has been dated by relative dating (RD) methods including pebble/sand weathering characteristics, topographic position and soil stratigraphy (Mahaney and Sanmugadas, 1986;Mahaney and Hancock, 1993a,b;Mahaney et al, 2014). Changing profile morphology over time brings staged removal of calcite from soil epipedons over time, slow increase in concentrations of extractable cations and C/N ratios, increases in Fe d /Fe t (dithionite extractable/total Fe) (Mahaney and Sanmugadas, 1986;Mahaney and Hancock, 1993a) along with slow conversion of illite/mica to both chlorite and vermiculite. Randomly interstratified illite-smectite and occasional kaolinite and metahalloysite are not authigenic, the former is considered to be inherited from Ordovician shales, the latter from previous interglacial paleosols eroded by incoming ice during Wisconsinan-age ice advances (Mahaney and Ermuth, 1975;Mahaney et al, 2014).…”