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1. Quantifying Normal Fault Evolution from River Profile Analysis in the Northern Basin and Range Province, Southwest Montana, USA

   https://doi.org/10.2113/2021/7866219  

   Armstrong, Ian P. ; Yanites, Brian J. ; Mitchell, Nate ; DeLisle, Clarke ; Douglas, Bruce J. ( April 2021 , Lithosphere)

   Valla, Pierre (Ed.)

   Abstract Over the past few decades, tectonic geomorphology has been widely implemented to constrain spatial and temporal patterns of fault slip, especially where existing geologic or geodetic data are poor. We apply this practice along the eastern margin of Bull Mountain, Southwest Montana, where 15 transient channels are eroding into the flat, upstream relict landscape in response to an ongoing period of increased base level fall along the Western North Boulder fault. We aim to improve constraints on the spatial and temporal slip rates across the Western North Boulder fault zone by applying channel morphometrics, cosmogenic erosion rates, bedrock characteristics, and calibrated reproductions of the modern river profiles using a 1-dimensional stream power incision model that undergoes a change in the rate of base level fall. We perform over 104 base level fall simulations to explore a wide range of fault slip dynamics and stream power parameters. Our best fit simulations suggest that the Western North Boulder fault started as individual fault segments along the middle to southern regions of Bull Mountain that nucleated around 6.2 to 2.5 Ma, respectively. This was followed by the nucleation of fault segments in the northern region around 1.5 to 0.4 Ma. We recreate the evolution of the Western North Boulder fault to show that through time, these individual segments propagate at the fault tips and link together to span over 40 km, with a maximum slip of 462 m in the central portion of the fault. Fault slip rates range from 0.02 to 0.45 mm/yr along strike and are consistent with estimates for other active faults in the region. We find that the timing of fault initiation coincides well with the migration of the Yellowstone hotspot across the nearby Idaho-Montana border and thus attribute the initiation of extension to the crustal bulge from the migrating hotspot. Overall, we provide the first quantitative constraints on fault initiation and evolution of the Western North Boulder fault, perhaps the farthest north basin in the Northern Basin and Range province that such constraints exist. We show that river profiles are powerful tools for documenting the spatial and temporal patterns of normal fault evolution, especially where other geologic/geodetic methods are limited, proving to be a vital tool for accurate tectonic hazard assessments. 

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2. Reconstructing Forearc Migration Geodynamics by Inverting River Long Profiles: the Case Study of the Calabrian Forearc (Central Mediterranean)

   Pavano, F. ; Gallen, S. F. ; Pazzaglia, F. J. ( December 2020 , AGU Fall Meeting)

   Interactions between deep Earth geodynamics and Earth surface processes are well documented at various scales, but many challenges remain in how inversion of a fluvially incised landscape should be interpreted in terms of long-term geodynamics or how deep Earth dynamics impact natural hazards. Here, we present results from geomorphic stream channel metrics and modeling of long profiles of streams draining the Tyrrhenian (northern) flank of Sicily (Italy), to assess the inferred, rapid, west-to-east horizontal translation of the Calabrian forearc. A detachment-limited stream power model-based determination of landscape response time and knickpoint migration provides an independent prediction for transient base level fall associated with the sweeping forearc over the past ~4 Ma. The model shows that two pulses of time-transgressive, west-to-east propagating base level fall occurred in the drainages of northern Sicily, where parallel north-flowing streams are arranged across the migrating path of the forearc. The long profile analysis indicates that the paired uplift pulses last ~1 Ma and are separated in time by ~1.5 Ma, consistent with the west-to-east passage first of the forearc high, followed by dynamic uplift in its wake due to sub-lithospheric mantle flow, as proposed in other plate boundary settings. The ongoing surficial response to these dynamics is represented by river incision, knickpoint migration, and drainage divide migration. Furthermore, these processes steepened the landscape, leading to an increase in active landsliding and contributing to the natural hazards in this region. 

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3. The Importance of Hillslope Scale in Responses of Chemical Erosion Rate to Changes in Tectonics and Climate

   https://doi.org/10.1029/2020JF005562  

   Ferrier, K. L. ; Perron, J. T. ( September 2020 , Journal of Geophysical Research: Earth Surface)

   Chemical erosion is of wide interest due to its influence on topography, nutrient supply to streams and soils, sediment composition, and Earth's climate. While controls on chemical erosion rate have been studied extensively in steady‐state models, few studies have explored the controls on chemical erosion rate during transient responses to external perturbations. Here we develop a numerical model for the coevolution of soil‐mantled topography, soil thickness, and soil mineralogy, and we use it to simulate responses to step changes in rates of rock uplift, soil production, soil transport, and mineral dissolution. These simulations suggest that tectonic and climatic perturbations can generate responses in soil chemical erosion rate that differ in speed, magnitude, and spatial pattern and that climatic and tectonic perturbations may impart distinct signatures on hillslope mass fluxes, soil chemistry, and sediment composition. The response time of chemical erosion rate is dominantly controlled by hillslope length and is secondarily modulated by rates of rock uplift, soil production, transport, and mineral dissolution. This strong dependence on drainage density implies that a landscape's chemical erosion response should depend on the relative efficiencies of river incision and soil transport and thus may be mediated by climatic and biological factors. The simulations further suggest that the timescale of the hillslope response may be long relative to that of river channel profiles, implying that chemical erosion response times may be limited more by the sluggishness of the hillslopes than by the rate of signal propagation through river channel profiles.

    

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4. Late Quaternary Tectonics, Incision, and Landscape Evolution of the Calchaquí River Catchment, Eastern Cordillera, NW Argentina

   https://doi.org/10.1029/2019JF005091  

   McCarthy, James A. ; Schoenbohm, Lindsay M. ; Bierman, Paul R. ; Rood, Dylan ; Hidy, Alan J. ( August 2019 , Journal of Geophysical Research: Earth Surface)

   Unraveling the relative impacts of climate, tectonics, and lithology on landscape evolution is complicated by the temporal and spatial scale over which observations are made. We use soil and desert pavement classification, longitudinal river profiles,¹⁰Be‐derived catchment mean modern and paleo‐erosion rates, and vertical incision rates to test whether, if we restrict our analyses to a spatial scale over which climate is relatively invariant, tectonic and lithologic factors will dominate the late Quaternary landscape evolution of the Calchaquí River Catchment, NW Argentina. We find that the spatial distribution of erosion rates, normalized channel steepness indices, and concavity indices reflect active tectonics and lithologic resistance. Knickpoints are spatially coincident with tectonic and/or lithologic discontinuities, indicating local base‐level control by faulting. Catchment mean erosion rates, ranging from 22.5 ± 2.6 to 121.9 ± 13.7 mm/kyr, and paleo‐erosion rates, ranging from 56⁺⁴³/_‐19to 105⁺⁶⁰/_‐33mm/kyr, are similar, possibly suggesting that Quaternary climate changes have not had a strong enough influence on erosion rates to be detected using cosmogenic¹⁰Be. However, punctuated abandonment of pediment and strath terraces at 43.6^+15.0/_‐11.6, 91.2^+54.2/_‐22.2, and 151^+92.7/_‐34.1ka and disparities between vertical incision rates and catchment mean erosion rates could suggest periods of landscape transience, possibly reflecting climate cyclicity. Our results emphasize the role of tectonic uplift and lithologic contrasts in shaping long‐term erosion rates and channel morphology at the relatively local scale of the Calchaqui River Catchment, in contrast to regional‐scale studies which find precipitation to exert the dominant control.

    

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5. Integrated uplift, subsidence, erosion and deposition in a tightly coupled source‐to‐sink system, Pagliara basin, northeastern Sicily, Italy

   https://doi.org/10.1111/bre.12845  

   Pavano, F. ; Pazzaglia, F. J. ; Rittenour, T. M. ; Catalano, S. ; Corbett, L. B. ; Bierman, P. ( January 2024 , Basin Research)

   How tectonic forcing, expressed as base level change, is encoded in the stratigraphic and geomorphic records of coupled source‐to‐sink systems remains uncertain. Using sedimentological, geochronological and geomorphic approaches, we describe the relationship between transient topographic change and sediment deposition for a low‐storage system forced by rapid rock uplift. We present five new luminescence ages and two terrestrial cosmogenic nuclide paleo‐erosion rates for the late Pleistocene Pagliara fan‐delta complex and we model corresponding base level fall history and erosion of the source catchment located on the Ionian flank of the Peloritani Mountains (NE‐Sicily, Italy). The Pagliara delta complex is part of the broader Messina Gravel‐and‐Sands lithostratigraphic unit that outcrops along the Peloritani coastal belt as extensional basins have been recently inverted by both normal faults and regional uplift at the Messina Straits. The deltas exposed at the mouth of the Pagliara River have constructional tops at ca. 300 m a.s.l. and onlap steeply east‐dipping bedrock at the coast to thickness between ca. 100 and 200 m. Five infrared‐stimulated luminescence (IRSL) ages collected from the delta range in age from ca. 327 to 208 ka and indicate a vertical long‐term sediment accumulation rate as rapid as ca. 2.2 cm/yr during MIS 7. Two cosmogenic¹⁰Be concentrations measured in samples of delta sediment indicate paleo‐erosion rates during MIS 8–7 near or slightly higher than the modern rates of ca. 1 mm/yr. Linear inversion of Pagliara fluvial topography indicates an unsteady base level fall history in phase with eustasy that is superimposed on a longer, tectonically driven trend that doubled in rate from ca. 0.95 to 1.8 mm/yr in the past 150 ky. The combination of footwall uplift rate and eustasy determines the accommodation space history to trap the fan‐deltas at the Peloritani coast in hanging wall basins, which are now inverted, uplifted and exposed hundreds of metres above the sea level.

    

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