Four new^(10)Be-^(26)Al isochron burial ages ranging from 4.4 to 2 Ma on ancestral Colorado River deposits in the lower Colorado River corridor(LCRC)help constrain the river’s evolution during the Pliocene and early ...Four new^(10)Be-^(26)Al isochron burial ages ranging from 4.4 to 2 Ma on ancestral Colorado River deposits in the lower Colorado River corridor(LCRC)help constrain the river’s evolution during the Pliocene and early Pleisto-cene.They help fill a gap between previous work that focused on older and younger deposits:Older dated deposits include the 5 Ma Bouse Formation,which records the integration of the Colorado River through a series of preexisting basins to the Gulf of California and the ca.4.5-3.5 Ma Bullhead Alluvium,a 200 to 300 m thick aggregational package that immediately followed integration.The much younger,100-70 ka,Chemehuevi Formation is another major aggrada-tion package mapped throughout the LCRC.The new burial ages on the facies of Santa Fe Railway(4.37±0.71 Ma),boulder conglomerate of Bat Cave Wash(2.12±0.26 and 2.05±0.31 Ma),and the Palo Verde alluvium(3.03±0.26 Ma)partially fill in a 3.5 M.y.gap between the deposition of the Bullhead Alluvium and the Chemeheuvi Formation and document the timescales over which the Colorado River was able to remove the Bullhead aggradational package and initiate newer and smaller aggradational pulses.展开更多
Drainage divide migration refers to the shifting boundaries between adjacent drainage basins over time,driven by processes such as tectonic uplift,differential erosion,stream capture,and lithological variations.This p...Drainage divide migration refers to the shifting boundaries between adjacent drainage basins over time,driven by processes such as tectonic uplift,differential erosion,stream capture,and lithological variations.This phenomenon has a significant impact on water flow patterns and basin extents,serving as an indicator of the landscape's response to active tectonic forces.One of the key drivers of divide migration is asymmetric uplift,which causes divides to shift from areas of lower uplift to regions experiencing higher uplift.Drainage divides are inherently dynamic,evolving over time as drainage networks develop and adjust to changing conditions.This study focuses on the migration of the main drainage divide along Karιncalιda?,located between Bozdo?an and Karacasu.It employs geomorphic analyses using metrics such as the normalized steepness index(ksn),Chi(χ),and Gilbert metrics.The main divide is categorized into four segments(D1–D4),with the Karacasu Fault,situated along the mountain's north-eastern boundary,identified as the primary factor influencing divide dynamics.Secondary factors include the relatively low elevation of Karιncalιda?,uniform lithology,and consistent rainfall patterns across the region.The results indicate that the main divide is currently stable,suggesting a balance between uplift and erosion.However,higherχvalues in the D4 segment suggest that future erosion may dominate,potentially causing the divide to migrate toward the Bozdo?an Basin.These findings highlight the dynamic nature of drainage divides and the complex interplay of tectonic,erosional,and lithological processes that shape their evolution.Continued monitoring and advanced geomorphic analysis are essential for understanding the long-term stability of the divide and its response to future tectonic activity and erosional modifications.展开更多
This study investigates the morphological characteristics and evolutionary mechanisms of stream potholes in the granodiorite riverbed of the Quanfengtan reach,located in the lower Zijiang River,Hunan Province,China.Fi...This study investigates the morphological characteristics and evolutionary mechanisms of stream potholes in the granodiorite riverbed of the Quanfengtan reach,located in the lower Zijiang River,Hunan Province,China.Field surveys and statistical analyses reveal that these potholes exhibit diverse geometries(calibers:0.2-2.5 m;depths:0.03-1.98 m;depth-to-caliber ratios:0.08-1.63),predominantly elliptical and shallow,reflecting distinct developmental stages.These potholes show no spatial correlation with bedrock joints,and their long-axis orientations diverge from dominant joint trends.Instead,they exhibit consistent alignment with the river’s prevailing flow direction.Furthermore,pothole dimensions(e.g.,depth and diameter)strongly correlate with gravel size,indicating sediment-driven abrasion as the primary formation mechanism.The uplift of the Xuefeng Mountains relative to the Dongting Basin since the Late Quaternary,which drove the incision of the lower Zijiang River,transforming it from an alluvial channel to a bedrock-dominated channel,is the primary precondition enabling pothole development in this region.Additionally,the influence of climatic factors and human activities cannot be overlooked.The progressive formation,coalescence,and evolution of potholes into grooves constitute the primary mechanism driving riverbed erosion by the Zijiang River at Quanfengtan.展开更多
文摘Four new^(10)Be-^(26)Al isochron burial ages ranging from 4.4 to 2 Ma on ancestral Colorado River deposits in the lower Colorado River corridor(LCRC)help constrain the river’s evolution during the Pliocene and early Pleisto-cene.They help fill a gap between previous work that focused on older and younger deposits:Older dated deposits include the 5 Ma Bouse Formation,which records the integration of the Colorado River through a series of preexisting basins to the Gulf of California and the ca.4.5-3.5 Ma Bullhead Alluvium,a 200 to 300 m thick aggregational package that immediately followed integration.The much younger,100-70 ka,Chemehuevi Formation is another major aggrada-tion package mapped throughout the LCRC.The new burial ages on the facies of Santa Fe Railway(4.37±0.71 Ma),boulder conglomerate of Bat Cave Wash(2.12±0.26 and 2.05±0.31 Ma),and the Palo Verde alluvium(3.03±0.26 Ma)partially fill in a 3.5 M.y.gap between the deposition of the Bullhead Alluvium and the Chemeheuvi Formation and document the timescales over which the Colorado River was able to remove the Bullhead aggradational package and initiate newer and smaller aggradational pulses.
文摘Drainage divide migration refers to the shifting boundaries between adjacent drainage basins over time,driven by processes such as tectonic uplift,differential erosion,stream capture,and lithological variations.This phenomenon has a significant impact on water flow patterns and basin extents,serving as an indicator of the landscape's response to active tectonic forces.One of the key drivers of divide migration is asymmetric uplift,which causes divides to shift from areas of lower uplift to regions experiencing higher uplift.Drainage divides are inherently dynamic,evolving over time as drainage networks develop and adjust to changing conditions.This study focuses on the migration of the main drainage divide along Karιncalιda?,located between Bozdo?an and Karacasu.It employs geomorphic analyses using metrics such as the normalized steepness index(ksn),Chi(χ),and Gilbert metrics.The main divide is categorized into four segments(D1–D4),with the Karacasu Fault,situated along the mountain's north-eastern boundary,identified as the primary factor influencing divide dynamics.Secondary factors include the relatively low elevation of Karιncalιda?,uniform lithology,and consistent rainfall patterns across the region.The results indicate that the main divide is currently stable,suggesting a balance between uplift and erosion.However,higherχvalues in the D4 segment suggest that future erosion may dominate,potentially causing the divide to migrate toward the Bozdo?an Basin.These findings highlight the dynamic nature of drainage divides and the complex interplay of tectonic,erosional,and lithological processes that shape their evolution.Continued monitoring and advanced geomorphic analysis are essential for understanding the long-term stability of the divide and its response to future tectonic activity and erosional modifications.
基金the National Natural Science Foundation of China(Grant No.42101005)the Hunan Provincial Natural Science Foundation of China(Grant No.2025JJ50182)the Scientific Research Fund of Hunan Provincial Education Department(Grant No.24A0582).
文摘This study investigates the morphological characteristics and evolutionary mechanisms of stream potholes in the granodiorite riverbed of the Quanfengtan reach,located in the lower Zijiang River,Hunan Province,China.Field surveys and statistical analyses reveal that these potholes exhibit diverse geometries(calibers:0.2-2.5 m;depths:0.03-1.98 m;depth-to-caliber ratios:0.08-1.63),predominantly elliptical and shallow,reflecting distinct developmental stages.These potholes show no spatial correlation with bedrock joints,and their long-axis orientations diverge from dominant joint trends.Instead,they exhibit consistent alignment with the river’s prevailing flow direction.Furthermore,pothole dimensions(e.g.,depth and diameter)strongly correlate with gravel size,indicating sediment-driven abrasion as the primary formation mechanism.The uplift of the Xuefeng Mountains relative to the Dongting Basin since the Late Quaternary,which drove the incision of the lower Zijiang River,transforming it from an alluvial channel to a bedrock-dominated channel,is the primary precondition enabling pothole development in this region.Additionally,the influence of climatic factors and human activities cannot be overlooked.The progressive formation,coalescence,and evolution of potholes into grooves constitute the primary mechanism driving riverbed erosion by the Zijiang River at Quanfengtan.
