Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that thr... more Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene–Holocene transition (~ 12.5–9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at ~ 5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~ 2.2–1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can c...
Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern S... more Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern San Juan Mountains of Colorado, provide a record of climate and environmental change since the end of the last glacial maximum (LGM). Cumbres Bog is unusually deep (basal sediments extend 12 m below the surface) for its altitude (~3050 m a.s.l.) and we extracted 7 m core of continuous sediment below ~5 m of water and peat. The resulting record provides strong evidence of: a period of warming immediately after the LGM (~18–13 cal. kyr BP), a cool interval coinciding with the Younger Dryas (~12.8–11.5 cal. kyr BP), a warm stable period from 10 to 6 cal. kyr BP, and a cooler and highly variable climate interval after 6 cal. kyr BP. More specifically, pollen ratios and fossil diatoms indicate that cold periods generally match with previously identified periods of rapid climate change that occurred at 10.6, 8.7–7.9, 7.0–6.9, 5.4–5.2, 3.3–3.0, 2.3, 2.0 and 1.5 cal. kyr BP. This record also adds...
Sedimentation in Brown's Cove of Lake Wylie, North Carolina, can be reconstructed from historical... more Sedimentation in Brown's Cove of Lake Wylie, North Carolina, can be reconstructed from historical records, cores, heavy mineral analysis, geochemical analysis, and 210 Pb data. The sedimentology and sequence stratigraphy of the cores document changing sedimentary provenance, processes, and rates. Brown's Cove was flooded in 1924, resulting in a transgressive sequence composed dominantly of suspension load deposited between 1924 and 1983. Based on air photos and cores, distributary channels on Beaverdam Creek delta supplied sediment to prograding, coarseningupward delta lobes composed of turbidites grading up to traction load deposits. In 1983, a delta lobe began prograding into Brown's Cove and was abandoned ca. 1993, leading to compaction, subsidence, and a second transgression. Another distributary avulsed to the site ca. 2003, resulting in a second prograding delta lobe. Prior to flooding of Brown's Cove, mafic-rich fluvial sediments from the southern part of the watershed were a large component of the sediment. Between 1983 and 1993, felsic-rich sediments from the recently clear-cut northern part of the watershed dominated. The youngest sediments are mafic-rich and likely due to extensive land clearances in the southern part of the watershed that began in 2004. Three methods of estimating sedimentation rates for the main part of Brown's Cove provide comparable results of ,1 cm/yr averaged over the full period of record. This estimate can be refined to ,0.6 cm/yr for the interval 1924-2003, and ,1.8 cm/yr for the interval 2003-2008. Higher rates of sedimentation (,7 cm/yr) occur where delta lobes actively prograde.
Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern S... more Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern San Juan Mountains of Colorado, provide a record of climate and environmental change since the end of the last glacial maximum (LGM). Cumbres Bog is unusually deep (basal sediments extend 12 m below the surface) for its altitude (~3050 m a.s.l.) and we extracted 7 m core of continuous sediment below ~5 m of water and peat. The resulting record provides strong evidence of: a period of warming immediately after the LGM (~18-13 cal. kyr BP), a cool interval coinciding with the Younger Dryas (~12.8-11.5 cal. kyr BP), a warm stable period from 10 to 6 cal. kyr BP, and a cooler and highly variable climate interval after 6 cal. kyr BP. More specifically, pollen ratios and fossil diatoms indicate that cold periods generally match with previously identified periods of rapid climate change that occurred at 10.6, 8.7-7.9, 7.0-6.9, 5.4-5.2, 3.3-3.0, 2.3, 2.0 and 1.5 cal. kyr BP. This record also adds resolution to previous regional records and indicates that the periodicity of climate variability changed from 2000-3000 years to 700-1100 years around 6 cal. kyr BP and to <500 years after 3.5 cal. kyr BP. Overall, our record provides important, relatively high-resolution paleoclimatic information for this remote region of the southern Rockies.
Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that thr... more Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene-Holocene transition (~12.5-9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at~5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~2.2-1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can conclude that erosion does not occur equally throughout the landscape but is focused upslope of headwater streams, along tributary channels, or on ridge tops. This is in contrast to some models which assume equal erosion in headwater basins.
Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that thr... more Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene–Holocene transition (~ 12.5–9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at ~ 5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~ 2.2–1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can c...
Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern S... more Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern San Juan Mountains of Colorado, provide a record of climate and environmental change since the end of the last glacial maximum (LGM). Cumbres Bog is unusually deep (basal sediments extend 12 m below the surface) for its altitude (~3050 m a.s.l.) and we extracted 7 m core of continuous sediment below ~5 m of water and peat. The resulting record provides strong evidence of: a period of warming immediately after the LGM (~18–13 cal. kyr BP), a cool interval coinciding with the Younger Dryas (~12.8–11.5 cal. kyr BP), a warm stable period from 10 to 6 cal. kyr BP, and a cooler and highly variable climate interval after 6 cal. kyr BP. More specifically, pollen ratios and fossil diatoms indicate that cold periods generally match with previously identified periods of rapid climate change that occurred at 10.6, 8.7–7.9, 7.0–6.9, 5.4–5.2, 3.3–3.0, 2.3, 2.0 and 1.5 cal. kyr BP. This record also adds...
Sedimentation in Brown's Cove of Lake Wylie, North Carolina, can be reconstructed from historical... more Sedimentation in Brown's Cove of Lake Wylie, North Carolina, can be reconstructed from historical records, cores, heavy mineral analysis, geochemical analysis, and 210 Pb data. The sedimentology and sequence stratigraphy of the cores document changing sedimentary provenance, processes, and rates. Brown's Cove was flooded in 1924, resulting in a transgressive sequence composed dominantly of suspension load deposited between 1924 and 1983. Based on air photos and cores, distributary channels on Beaverdam Creek delta supplied sediment to prograding, coarseningupward delta lobes composed of turbidites grading up to traction load deposits. In 1983, a delta lobe began prograding into Brown's Cove and was abandoned ca. 1993, leading to compaction, subsidence, and a second transgression. Another distributary avulsed to the site ca. 2003, resulting in a second prograding delta lobe. Prior to flooding of Brown's Cove, mafic-rich fluvial sediments from the southern part of the watershed were a large component of the sediment. Between 1983 and 1993, felsic-rich sediments from the recently clear-cut northern part of the watershed dominated. The youngest sediments are mafic-rich and likely due to extensive land clearances in the southern part of the watershed that began in 2004. Three methods of estimating sedimentation rates for the main part of Brown's Cove provide comparable results of ,1 cm/yr averaged over the full period of record. This estimate can be refined to ,0.6 cm/yr for the interval 1924-2003, and ,1.8 cm/yr for the interval 2003-2008. Higher rates of sedimentation (,7 cm/yr) occur where delta lobes actively prograde.
Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern S... more Pollen assemblages, diatom assemblages, and sedimentology, from Cumbres Bog in the southeastern San Juan Mountains of Colorado, provide a record of climate and environmental change since the end of the last glacial maximum (LGM). Cumbres Bog is unusually deep (basal sediments extend 12 m below the surface) for its altitude (~3050 m a.s.l.) and we extracted 7 m core of continuous sediment below ~5 m of water and peat. The resulting record provides strong evidence of: a period of warming immediately after the LGM (~18-13 cal. kyr BP), a cool interval coinciding with the Younger Dryas (~12.8-11.5 cal. kyr BP), a warm stable period from 10 to 6 cal. kyr BP, and a cooler and highly variable climate interval after 6 cal. kyr BP. More specifically, pollen ratios and fossil diatoms indicate that cold periods generally match with previously identified periods of rapid climate change that occurred at 10.6, 8.7-7.9, 7.0-6.9, 5.4-5.2, 3.3-3.0, 2.3, 2.0 and 1.5 cal. kyr BP. This record also adds resolution to previous regional records and indicates that the periodicity of climate variability changed from 2000-3000 years to 700-1100 years around 6 cal. kyr BP and to <500 years after 3.5 cal. kyr BP. Overall, our record provides important, relatively high-resolution paleoclimatic information for this remote region of the southern Rockies.
Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that thr... more Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene-Holocene transition (~12.5-9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at~5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~2.2-1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can conclude that erosion does not occur equally throughout the landscape but is focused upslope of headwater streams, along tributary channels, or on ridge tops. This is in contrast to some models which assume equal erosion in headwater basins.
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