Journal of Geophysical Research: Earth Surface最新文献

{"title":"Surface-State Controls on Dust Emission Variability in Lower Mesopotamia and Kuwait Using Field and Multi-High-Resolution Satellite Data","authors":"Jasem A. Albanai,&nbsp;Giles F. S. Wiggs,&nbsp;Ali Al-Hemoud,&nbsp;David S. G. Thomas","doi":"10.1029/2026JF009484","DOIUrl":"https://doi.org/10.1029/2026JF009484","url":null,"abstract":"<p>Aeolian dust strongly influences climate, air quality, and biogeochemical cycles, yet identifying source areas and determining their surface-state controls remain challenging. We focus on lower Mesopotamia and Kuwait, a globally significant dust source region where surface characteristics of dust sources remain poorly understood through satellite-guided field studies. We integrate systematic field surveys with high-resolution satellite data to (a) quantify how surface controls regulate emissions from adjacent dust sources, (b) identify the surface-state controls that distinguish dust-emitting surfaces from non-emitting areas within similar geomorphic units, and (c) determine how controls attribute during the dust season differ from their non-dust season states. We derived Sentinel-2 NDVI and NDMI and Landsat 8–9 land surface temperature (LST) data sets for 2015–2024, applying a ±3-day temporal matching window between Sentinel-2 and Landsat observations. The resulting data sets were combined with in situ measurements of crust properties, sediment texture, and climatic variables and subsequently evaluated using ridge-penalized logistic regression and Spearman correlation analyses. Results show that inland sabkhas such as Al-Batha persist as the most recurrent dust sources due to fine, poorly sorted sediments and weak, fragmented crusts in the summer dust season, while coastal sabkhas and tidal flats (Subiya, Bubiyan &amp; Al-Faw) act as episodic emitters linked to tidal desiccation cycles. The North Marshes remain largely inactive despite their textural emission potential because of thicker, moisture-retaining crusts. Ridge-penalized logistic regression confirmed vegetation depletion and independent moisture stress as the dominant predictors controlling dust emission, with LST acting as a secondary amplifier. These integrated field-satellite results reveal that dust emission arises from the coupled effects of surface texture, crust integrity, and ecohydrological dynamics rather than geomorphic setting alone. The study delivers a field evidenced and high-resolution database for dust source controls in lower Mesopotamia and Kuwait, improving process understanding and supporting more targeted monitoring and mitigation.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 9","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2026JF009484","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148849230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lateral Momentum Transfer in Ice-Covered Rivers","authors":"Javad Souri,&nbsp;Berkay Koyuncu,&nbsp;Leonardo P. Chamorro,&nbsp;Trung Bao Le","doi":"10.1029/2025JF008909","DOIUrl":"https://doi.org/10.1029/2025JF008909","url":null,"abstract":"<p>Ice cover alters river hydrodynamics by introducing surface roughness. This roughness modifies momentum redistribution and bed shear stress. Using theoretical arguments, we present an approach for the lateral momentum load in ice-covered streams. This approach is derived from the depth-integrated Reynolds-Averaged Navier–Stokes equations. Field measurements were conducted during the winters of 2022–2025 in a meandering reach of the Red River of the North (Fargo, ND, USA). We used an Acoustic Doppler Current Profiler (ADCP) to obtain time- and depth-averaged velocities across three cross-sections. Results show that secondary flows and Reynolds stresses both contribute to the lateral momentum load. Also, the ice cover suppresses the development of coherent secondary cells. A term-by-term analysis of streamwise momentum budget demonstrates that lateral gradients of momentum load are closely tied to variations in bed shear stress, highlighting the coupling between momentum load and near-bed dynamics. The resulting momentum balance yields three depth-averaged velocity and shear stress models for ice-covered rivers. All models require minimal parameterization and provide practical tools for monitoring and predicting flow profiles under ice conditions.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 9","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025JF008909","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148849228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Beyond Idealized Geometry: Settling Dynamics of Natural Irregularly-Shaped Sediment Particles","authors":"Xiaoyong Cheng,&nbsp;Zhixian Cao,&nbsp;Alistair G. L. Borthwick,&nbsp;Lu Jing,&nbsp;Yu Zhang","doi":"10.1029/2026JF009189","DOIUrl":"https://doi.org/10.1029/2026JF009189","url":null,"abstract":"<p>Fundamental to Earth surface dynamics and engineering is the understanding of sediment particle settling. To date, however, the settling of natural irregularly-shaped sediment particles has remained poorly understood. Here, free settling of individual sediment particles of irregular geometry in still water is investigated using particle-resolved direct numerical simulation. Natural sediment particles from the source region of the Yangtze River, China, are selected, generally comprising compact, oblate, and prolate forms with nine characteristic sizes covering the full range of sands and gravels. The particle nominal diameter ranges from 0.07 to 16.6 mm, with the Galileo number <i>Ga</i> between 1.8 and 6665.7. In addition to rectilinear, zigzag, helical, and chaotic motions, a yaw motion is newly identified within the <i>Ga</i> range from 10² to 10³, where a compact/oblate particle experiences a direction-changing lateral drift in line with vertical autorotation. As for intermediate settling between rectilinear and chaotic regimes, oblate particles adopt yaw or zigzag motions, whereas prolate particles favor helical motions. Sediment particles attain lower terminal velocities than their equivalent spheres or equivalent ellipsoids because shape irregularities lead to enhanced fluid drag. At large particle Reynolds numbers, a particle may follow distinct settling motion patterns, depending on the initial orientation. This indicates multi-stable behavior and reveals the complex role of initial orientation in particle settling. The complex settling dynamics of irregularly-shaped sediment particles implies that existing continuum-based mathematical models for morphodynamic processes need to be modified to better inform applications.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 9","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148816629","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thaw Subsidence of Ice-Rich Permafrost Near Umiujaq, Nunavik (Québec), Canada: 20 Years of Monitoring Using Ground-Based Leveling Methods, LiDAR, and UAV Photogrammetry","authors":"M. St-Cyr,&nbsp;R. Fortier,&nbsp;J. W. Molson","doi":"10.1029/2026JF009218","DOIUrl":"https://doi.org/10.1029/2026JF009218","url":null,"abstract":"<p>Differential thaw subsidence is one of the main effects of ice-rich permafrost degradation, especially in the discontinuous permafrost zone. Although thawing of ice-rich permafrost can lead to thermokarst, water ponding, and major damage to critical northern infrastructure, thaw subsidence is not often monitored due to the lack of long-term commitment and funding. This case study documents two decades of thaw-subsidence monitoring in a discontinuous, ice-rich permafrost environment near Umiujaq, Nunavik (Canada). Monitoring methods included ground-based leveling, airborne and terrestrial Light Detection and Ranging (LiDAR), and unmanned aerial vehicle (UAV) photogrammetry. Concurrent air and subsurface temperatures were also monitored to assess permafrost response to climate warming. Following an increase of more than 3°C in mean annual air temperature at Umiujaq between 1992 and the early 2000s, permafrost temperatures have warmed by approximately 1.8, 0.3 and 0.1°C at depths of 5, 14, and 19 m, respectively, between 2001 and 2024. Over the same period, permafrost thickness decreased by more than 2.1 m, a suprapermafrost talik almost 2 m thick formed, and thaw subsidence has occurred at mean rates between 5.1 and 11.3 cm/year. As observed in 2024, permafrost was extremely warm and approached isothermal conditions with lowest subsurface temperatures of about −0.4°C, suggesting that permafrost degradation and thaw subsidence will continue in the coming decades. This case study provides a robust methodology for monitoring thaw subsidence and highlights the benefits of combining these measurements with air and surface temperatures to better assess the causes and effects of permafrost degradation.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 8","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2026JF009218","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148849041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Soil Voids Evolution in Aeolian Deposited Strata: Insights From Chinese Loess Plateau","authors":"Ling Xu,&nbsp;Siyu Zhang,&nbsp;Yue Dong,&nbsp;Matthew R. Coop,&nbsp;Lu Zuo","doi":"10.1029/2026JF009254","DOIUrl":"https://doi.org/10.1029/2026JF009254","url":null,"abstract":"<p>Loess in the Chinese Loess Plateau (CLP) is a representative of aeolian sediments worldwide. It contains high volumes of voids which results in unique soil properties, yet the voids evolution in CLP remains unexplored. Here we identify that loess strata in CLP have higher void ratios (<i>e</i>) compared to other typical aeolian, glacial, alluvial, and residual sediments on a global scale. In a given profile, void ratio decreases with continuous gravity stress (<i>σ</i>_<i>v</i>) accumulation, satisfying a linear sedimentary compression line (SCL) in <i>e</i>-log₁₀<i>σ</i>_<i>v</i> space. For voids evolution in CLP, the variation of SCLs reveals that void ratios first increase and then decrease from northwest to southeast across the plateau. After eliminating the stress effect, we demonstrate strong correlations among void ratio, magnetic susceptibility, particle size distribution and bonding material content of loess, and identify the critical particle size distribution to achieve the highest void ratio. This research enriches aeolian sedimentation theory and brings potential for breakthroughs in accurate prediction of loess mechanical and hydraulic properties with physical indices. It also provides a soil voids basis for interdisciplinary understanding of soil ecological function and geological processes in CLP.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 9","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148816609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Internal Ice Content of Timpanogos Rock Glacier, Utah, USA From 3-D Bayesian Inversion of Gravity Data","authors":"Bronson Cvijanovich,&nbsp;Michael S. Thorne,&nbsp;Surya Pachhai,&nbsp;Leif S. Anderson,&nbsp;Ivan Tochimani-Hernandez,&nbsp;Christian L. Hardwick,&nbsp;Tonie van Dam","doi":"10.1029/2026JF009214","DOIUrl":"https://doi.org/10.1029/2026JF009214","url":null,"abstract":"<p>Despite the prevalence of rock glaciers in mountain environments, their ice volumes are poorly constrained. Rock glaciers persist in settings unable to support glaciers. They act as climate resilient water stores and refugia for cold-adapted species while also posing a hazard to alpine communities. Imaging the entire internal structure of rock glaciers and estimating their ice volumes is crucial for understanding how these impacts evolve in a warming climate. Ice volume is challenging to measure with methods typically used on glaciers, such as aerial gravity and ground penetrating radar, due to the relatively small size of rock glaciers as well as the presence of internal and overlying debris. In this paper, we use an alternative approach: the terrestrial gravity method. We model the internal structure of Timpanogos Rock Glacier, Utah, USA using a 3-D Bayesian inversion from 232 gravity measurements. Our inversions indicate an ice volume of 1.55 × 10⁶ m³ with an average thickness of 18.8 m and an ice fraction of 83% within the ice core. Measured surface velocities are consistent with ice thicknesses produced by our gravity inversions. Using our model results and measurements from geophysical studies of 10 other rock glaciers, we synthesize a new, linear area-volume scaling relationship for rock glaciers. Using this relationship, we estimate a cumulative water volume equivalent of 48.03 Gt for the world's intact rock glaciers, 11.92 Gt for the western US, 0.99 Gt for the State of Utah, and 0.08 Gt for the Wasatch Mountain Range.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 8","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2026JF009214","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148849042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Base-Level-Driven Erosional and Tectonic Controls on Drainage Divide Asymmetry in Fold-Thrust Belts","authors":"Samantak Kundu,&nbsp;Sanjay Kumar Mandal,&nbsp;Dirk Scherler","doi":"10.1029/2026JF009139","DOIUrl":"https://doi.org/10.1029/2026JF009139","url":null,"abstract":"<p>The topography of many mountain ranges is asymmetric in cross-section, with the main drainage divide offset from the range center. Differential rock uplift is commonly invoked to explain this asymmetry; however, divide position also depends on cross-divide contrasts in erosional efficiency and base-level elevation. Whether base-level contrasts can outweigh differential uplift in controlling divide position remains poorly constrained. Here, we derive analytical solutions from the stream-power incision model that predict steady-state divide positions as functions of rock-uplift rate, erosional efficiency, and cross-divide base-level contrast. From these solutions, we define two dimensionless numbers that each express the ratio of erosional forcing (the product of erosional efficiency and base-level contrast) to tectonic forcing (rock-uplift rate). The divide asymmetry number <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <msub>\u0000 <mi>N</mi>\u0000 <mtext>DA</mtext>\u0000 </msub>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left({N}_{text{DA}}right)$</annotation>\u0000 </semantics></math> applies to landscapes with spatially uniform rock uplift and erosional efficiency. The effective divide asymmetry number <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <msubsup>\u0000 <mi>N</mi>\u0000 <mtext>DA</mtext>\u0000 <mo>∗</mo>\u0000 </msubsup>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left({N}_{text{DA}}^{ast }right)$</annotation>\u0000 </semantics></math> extends the framework to landscapes with linearly varying rock uplift. For both numbers, a value below unity indicates tectonic control on divide position; a value above unity indicates erosional control. We test these predictions with numerical landscape-evolution experiments and apply the framework to four fault-bounded Sub-Himalayan anticlines to address a key question: why do ranges with similar structural styles, lithologies, and climatic settings develop markedly different divide positions? The four anticlines yield <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msubsup>\u0000 <mi>N</mi>\u0000 <mtext>DA</mtext>\u0000 <mo>∗</mo>\u0000 </msubsup>\u0000 </mrow>\u0000 <annotation> ${N}_{text{DA}}^{ast }$</annotation>\u0000 </semantics></math> values ranging from 0 to 2.0, spanning the full transition from tectonically to erosionally controlled divide position. Thus, divide asymmetry in mountain belts does not uniquely reflect tectonic forcing; cross-divide base-level contrasts can produce equivalent asymmetry.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 8","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148848815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tectonic Uplift Outpaces Modern Sea-Level Rise: Recovery of the Valdivia Estuary Following >2-m Subsidence During the M9.5 1960 Chile Earthquake","authors":"N. Wolff,&nbsp;D. Melnick","doi":"10.1029/2026JF009264","DOIUrl":"https://doi.org/10.1029/2026JF009264","url":null,"abstract":"<p>The M9.5 1960 Chile earthquake, the largest instrumentally recorded, caused over 2 m of coseismic subsidence in the Valdivia estuary, converting fluvial terraces into open water and, later, tidal marshes. We quantify the decadal-scale post-seismic recovery of these estuarine wetlands using historical aerial photography, Landsat/Sentinel imagery, GNSS-derived vertical land motion, tide-gauge and satellite altimetry sea-level records, and dated sediment cores. Open water area expanded ∼8.8-fold after the earthquake and has since contracted from ∼94 km² in 1985 to 61 km² in 2024, following a strongly linear trend (<i>r</i> = −0.97) implying recovery to the pre-earthquake fluvial extent by ∼2056. Interseismic uplift across the estuary (6.2–9.5 mm/yr) currently exceeds regional absolute sea-level rise (∼2.3 mm/yr), producing a falling relative sea level that correlates strongly with vegetation expansion across tributary basins, indicating tectonic vertical land motion, rather than climate forcing, dominates wetland recovery at this timescale. Sediment accretion rates increase after subsidence and then decrease from subtidal to intertidal facies, reflecting the open water-to-marsh transition during interseismic emergence. A Monte Carlo projection combining vertical land motion, accretion, and IPCC sea-level scenarios estimates the estuary will return to supratidal elevations by a median year of 2063 (5%–95% range 2047–2099), with coseismic subsidence magnitude and sea-level rise dominating the uncertainty. These findings underscore the need to account for seismic-cycle vertical land motion alongside climate-driven sea-level rise when assessing the long-term resilience and carbon-storage capacity of coastal wetlands in tectonically active subduction zones.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 8","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148784475","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Generalizing Sediment Transport Experiments From Narrow Flumes to Wider Channels","authors":"Eric Deal,&nbsp;J. Taylor Perron,&nbsp;Kyle Kusack,&nbsp;Santiago J. Benavides,&nbsp;Ryan Bradley,&nbsp;Qiong Zhang,&nbsp;Ken Kamrin,&nbsp;Jeremy G. Venditti","doi":"10.1029/2025JF008712","DOIUrl":"https://doi.org/10.1029/2025JF008712","url":null,"abstract":"<p>Laboratory flumes are powerful tools for investigating riverine processes in a controlled environment. However, the proximity of flume sidewalls modifies the flow relative to natural river channels, and sidewall corrections are crucial for obtaining accurate estimates of bed stress. Sidewall corrections are well-studied for flumes with aspect ratios (width/depth) greater than one but not for narrower flumes. There has been an increase in grain-scale dynamics research that uses flumes with widths of just a few grain diameters and aspect ratios down to 0.1 (very narrow flumes). We investigate whether sediment transport experiments in very narrow flumes can be generalized and compared to flow and sediment transport in wider channels. Using a compilation of 400 flume experiments, including 100 with width/depth &lt;1, we find that the influence of sidewalls can be explained by the same theories in very narrow flumes as in wider flumes. However, the classic Vanoni-Brooks sidewall correction makes an approximation that does not work as well in very narrow flumes. For very narrow flumes, we recommend a more recent sidewall correction. We also investigated whether the flume aspect ratio influences grain-scale dynamics by applying the sidewall correction method to experiments on grain shape in bed load transport. Our results suggest that there is no effect of the flume aspect ratio on bulk sediment flux relations or on the influence of grain shapes, indicating that sidewalls do not strongly affect grain-scale dynamics in bed load sediment transport.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 8","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025JF008712","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148784885","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Oldest Known Eocene Loess in the Western United States: Evidence From a Fluvial-Eolian Transition Zone","authors":"Shankhadeep Baul,&nbsp;Majie Fan","doi":"10.1029/2026JF009229","DOIUrl":"https://doi.org/10.1029/2026JF009229","url":null,"abstract":"<p>The timing, stratigraphic development, and mechanisms of late Paleogene loess deposition remain poorly understood, yet they are critical to understanding how tectonics, fluvial reworking, and eolian transport interacted during a key interval of western North American landscape evolution. Here we combine lithofacies analysis with high-resolution grain-size analysis, quartz surface morphology, and detrital zircon U–Pb geochronology to refine the onset and depositional context of lower Eocene loess in western Wyoming and northeastern Colorado. In Wyoming, our data documents a transition from a fluvial to eolian dominant deposition. Loess-like bimodal grain-size distributions with characteristic eolian quartz surface features first emerged at 39.7 ± 0.4 Ma, ∼4 Myr earlier than previously recognized. This is the oldest and coarsest reported Paleogene loess in the western U.S.A. In Colorado, the earliest loess appeared by at least 35.1 ± 0.3 Ma and lasted at least into 31.1 ± 0.4 Ma. This study establishes a previously unrecognized fluvial–eolian transition zone in western Wyoming and supports an eastward younging and fining trend for the loess system. Comparison with coeval global loess records shows that loess systems consistently formed adjacent to major mountains during global cooling, suggesting that rivers originating at high topography supplied the necessary sediment, while concurrent global cooling promoted aridification for wind transport. Furthermore, a comparison to Asian loess shows that similar boundary conditions can produce comparable loess records via different atmospheric processes, implicating that synoptic-scale climate variability may have played a major role in western U.S.A. loess formation.</p>","PeriodicalId":15887,"journal":{"name":"Journal of Geophysical Research: Earth Surface","volume":"131 8","pages":""},"PeriodicalIF":4.1,"publicationDate":"2026-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2026JF009229","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148784098","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}