“… Figure 10 (A) Correlation with box plots of Fe d and projected valley incision ages for terraces in the Rouge basin. The floodplain sites (R13, 13A) were staggered from 0.1 to 0.3 × 10 3 14 C YBP (Mahaney and Terasmae 1988; Mahaney et al 2016). Ages of older sites are based on relative age indices as follows: R46 = 6–7 ka (Mahaney 2015); R61, R62, and R60= <11ka, relative height of 15–17 m above the existing stream level in Little Rouge Creek (Mahaney et al 2014b).…”
Section: Discussionmentioning
confidence: 99%
“…The floodplain sites (R13, 13A) were staggered from 0.1 to 0.3 × 10 3 14 C YBP (Mahaney and Terasmae 1988; Mahaney et al 2016). Ages of older sites are based on relative age indices as follows: R46 = 6–7 ka (Mahaney 2015); R61, R62, and R60= <11ka, relative height of 15–17 m above the existing stream level in Little Rouge Creek (Mahaney et al 2014b). Given the young ages for the pedostratigraphic units in the floodplains, all horizons are included in the analysis.…”
Section: Discussionmentioning
confidence: 99%
“…Thus, the thickness of secondary carbonate in Ck horizons increases with age of the pedon. Exceptions to this occur in profiles in landslide debris, discussed by Mahaney (2015), where wetting depth is reduced to a few centimeters, in response to the presence of a unique hydrophilic fern ( Adiantum pedantum ) that produces a unique soil bioclimate greatly reducing the throughput of soil water. Slow leaching increases the ratio of Si:Al to 2:1, and coupled with plentiful Ca, thereby initiates genesis of Ca-smectite, confirmed by XRD.…”
Section: Regional Geology and Study Areamentioning
confidence: 99%
“…Surface runoff in the Rouge and West Duffins basins (Figures 1 A, B) of central Southern Ontario drains across thick till/lacustrine/deltaic-encrusted sediment draped over Ordovician shales of the Whitby Formation (Liberty 1955(Liberty , 1964. Within both catchments, bedrock outcrops are rare, found only in the R46 section (stratigraphy in Mahaney 2015, andin Mahaney andHancock 1993a; site location on Figure 1B), in a prominent outcrop near Twyn Rivers Drive on Little Rouge Creek, located three km north of Lake Ontario, and 1 km north of the confluence with Rouge River. All surface till/lacustrine sections date from the Laurentide Ice Sheet (LIS) and all soil materials are sourced from these sediments.…”
Section: Regional Geology and Study Areamentioning
Fluvial and colluvial deposits of Late Holocene age in South-Central Ontario catchments have provided few 14C dates, most by conventional methods registering century-old ages. Other young deposits, dated by conventional and accelerator mass spectrometry radiocarbon (AMS 14C), have yielded bomb-affected post-1950 ages over variable time limits. Attempts to date the base of Ah and lower-in-section soil horizons, in Early to Late Holocene stream terrace deposits, have yielded atomic bomb effects. Comparing bomb contamination in Late Holocene fluvial deposits, using both conventional and AMS methods, identifies a mix of bomb-affected beds juxtaposed with dated beds, the latter yielding ages with narrow standard deviations. Colluvial deposits overlying key glacial sections in the Rouge Catchment, while rare, yield bracketed AMS ages for an Ahbk horizon that refines weathering times relative to previously obtained conventional 14C dates. Bomb-affected sediment appears variably distributed within floodplain soils and in the ground soil of a colluvial section. Mass wasted deposits, with AMS 14C ages spread over the last few centuries, appear related to Little Ice Age (LIA) changes in climate, corroborated by pollen records. Further, these AMS-14C dated beds calibrate weathering of secondary Fe-Al oxihydroxides over the first half a millennium of weathering time.
“… Figure 10 (A) Correlation with box plots of Fe d and projected valley incision ages for terraces in the Rouge basin. The floodplain sites (R13, 13A) were staggered from 0.1 to 0.3 × 10 3 14 C YBP (Mahaney and Terasmae 1988; Mahaney et al 2016). Ages of older sites are based on relative age indices as follows: R46 = 6–7 ka (Mahaney 2015); R61, R62, and R60= <11ka, relative height of 15–17 m above the existing stream level in Little Rouge Creek (Mahaney et al 2014b).…”
Section: Discussionmentioning
confidence: 99%
“…The floodplain sites (R13, 13A) were staggered from 0.1 to 0.3 × 10 3 14 C YBP (Mahaney and Terasmae 1988; Mahaney et al 2016). Ages of older sites are based on relative age indices as follows: R46 = 6–7 ka (Mahaney 2015); R61, R62, and R60= <11ka, relative height of 15–17 m above the existing stream level in Little Rouge Creek (Mahaney et al 2014b). Given the young ages for the pedostratigraphic units in the floodplains, all horizons are included in the analysis.…”
Section: Discussionmentioning
confidence: 99%
“…Thus, the thickness of secondary carbonate in Ck horizons increases with age of the pedon. Exceptions to this occur in profiles in landslide debris, discussed by Mahaney (2015), where wetting depth is reduced to a few centimeters, in response to the presence of a unique hydrophilic fern ( Adiantum pedantum ) that produces a unique soil bioclimate greatly reducing the throughput of soil water. Slow leaching increases the ratio of Si:Al to 2:1, and coupled with plentiful Ca, thereby initiates genesis of Ca-smectite, confirmed by XRD.…”
Section: Regional Geology and Study Areamentioning
confidence: 99%
“…Surface runoff in the Rouge and West Duffins basins (Figures 1 A, B) of central Southern Ontario drains across thick till/lacustrine/deltaic-encrusted sediment draped over Ordovician shales of the Whitby Formation (Liberty 1955(Liberty , 1964. Within both catchments, bedrock outcrops are rare, found only in the R46 section (stratigraphy in Mahaney 2015, andin Mahaney andHancock 1993a; site location on Figure 1B), in a prominent outcrop near Twyn Rivers Drive on Little Rouge Creek, located three km north of Lake Ontario, and 1 km north of the confluence with Rouge River. All surface till/lacustrine sections date from the Laurentide Ice Sheet (LIS) and all soil materials are sourced from these sediments.…”
Section: Regional Geology and Study Areamentioning
Fluvial and colluvial deposits of Late Holocene age in South-Central Ontario catchments have provided few 14C dates, most by conventional methods registering century-old ages. Other young deposits, dated by conventional and accelerator mass spectrometry radiocarbon (AMS 14C), have yielded bomb-affected post-1950 ages over variable time limits. Attempts to date the base of Ah and lower-in-section soil horizons, in Early to Late Holocene stream terrace deposits, have yielded atomic bomb effects. Comparing bomb contamination in Late Holocene fluvial deposits, using both conventional and AMS methods, identifies a mix of bomb-affected beds juxtaposed with dated beds, the latter yielding ages with narrow standard deviations. Colluvial deposits overlying key glacial sections in the Rouge Catchment, while rare, yield bracketed AMS ages for an Ahbk horizon that refines weathering times relative to previously obtained conventional 14C dates. Bomb-affected sediment appears variably distributed within floodplain soils and in the ground soil of a colluvial section. Mass wasted deposits, with AMS 14C ages spread over the last few centuries, appear related to Little Ice Age (LIA) changes in climate, corroborated by pollen records. Further, these AMS-14C dated beds calibrate weathering of secondary Fe-Al oxihydroxides over the first half a millennium of weathering time.
“…This may well indicate that pre-weathering occurred in the early stage of temperate glacial growth in Antarctica, or before the subsequent onset of dry, cold conditions starting after the mid-Miocene climatic optimum (Mahaney 2015a), the transition slowing sediment weathering rates to near 1 cm/1 My in paleosols (Mahaney, Stewart et al 2001). The presence of vermiculite may signal either an intermediate weathering intergrade between smectite and chlorite and/or the presence of conifers, as vermiculite is often associated with coniferous forest (Mahaney 2015b;Mahaney unpubl. ms).…”
Detailed scanning electron microscopy (SEM) micro-texture and mineralogical analysis of lacustrine sediment recovered from Profound Lake (also known as Uruguay Lake), Antarctica, was conducted in the foreland area of the Collins Glacier, King George Island. Very coarse and coarse sand grade size fractions (2 mm -600 μm) were examined with SEM/ energy dispersive spectrometry, while the total sand fraction and fines (silt + clay) were examined using x-ray diffraction to determine relationships to source rock, weathering and transport history and long-term clay mineral weathering, all of which are poorly understood in polar areas. The mineralogy of these sediments was compared with petrographical information of the country rock to identify potential detrital sources. The association of recovered detrital minerals, sometimes strongly pre-weathered, supports release from source rock of basaltic and andesitic compositions. The micro-texture analysis of quartz, magnetite and various plagioclase grains show micro-features that reveal a complex weathering-diagenesis history tentatively extending into the Paleogene. The bedrock was eroded mostly by glacial processes and mechanical action presumed to result from glacial crushing. Alteration minerals, likely the product of pre-weathering, are probably sourced from weathered bedrock during contact with the sub-aerial atmosphere prior to entrainment. However, amorphous silica precipitation indicates weathering subsequent to glacial erosion from the source bedrock. Cracks of variable dimensions are mostly characteristic of either frost weathering or glacial transport, and involve mechanical and chemical processes.
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