91 results found
Pizzi M, Whittaker AC, Mayall M, et al., 2023, Structural controls on the pathways and sedimentary architecture of submarine channels: New constraints from the Niger Delta, Basin Research, Vol: 35, Pages: 141-171, ISSN: 0950-091X
In submarine settings, the growth of structurally influenced topography can play a decisive role in controlling the routing of sediments from shelf-edge to deep water, and can determine depositional architectures and sediment characteristics. Here we use well-constrained examples from the deep water Niger Delta, where gravity-driven deformation has resulted in the development of a large fold and thrust belt, to illustrate how spatial and temporal variations in the rate of deformation have controlled the nature and locus of contrasting depositional styles. Published work in the study area using 3D seismic data has quantified the growth history of the thrust-related folds at multiple locations using line-length-balancing, enabling cumulative strain for individual structures over time and along-strike to be obtained. We integrate this information with seismic interpretation and facies analysis, focusing on the interval of maximum deformation (15 to 3.7 Ma), where maximum strain rates reached 7%/Ma. Within this interval, we observe a vertical change in depositional architecture where: (1) leveed-confined and linear channels pass upward in to (2) ponded lobes with erosionally confined channels and finally (3) channelised sheets. Our analysis demonstrate that this change is tectonically induced and diachronous across the fault array, and we characterise the extent to which structural growth controls both the distribution and the architecture of the turbidite deposits in such settings. In particular, we show that leveed-confined channels exist when they can exploit strain minima between growing faults or at their lateral tips. Conversely, as a result of fault linkage and increased strain rates submarine channels become erosional and may be forced to cross folds at their strain maxima (crests), where their pathways are influenced by across-strike variations in shortening for individual structures. Our results enable us to propose new conceptual models of submarine channel d
Wrona T, Whittaker AC, Bell RE, et al., 2022, Rift kinematics preserved in deep-time erosional landscape below the northern North Sea, Basin Research, Pages: 1-18, ISSN: 0950-091X
Our understanding of continental rifting is, in large parts, derived from the stratigraphic record. This record is, however, incomplete as it does not often capture the geomorphic and erosional signal of rifting. New 3D seismic reflection data reveal a Late Permian-Early Triassic landscape incised into the pre-rift basement of the northern North Sea. This landscape, which covers at least 542 km2, preserves a drainage system bound by two major tectonic faults. A quantitative geomorphic analysis of the drainage system reveals 68 catchments, with channel steepness and knickpoint analysis of catchment-hosted palaeo-rivers showing that the landscape preserved a >2 Myr long period of transient tectonics. We interpret that this landscape records a punctuated uplift of the footwall of a major rift-related normal fault (Vette Fault) at the onset of rifting. The landscape was preserved by a combination of relatively rapid subsidence in the hangingwall of a younger fault (Øygarden Fault) and burial by post-incision sediments. As such, we show how and why erosional landscapes are preserved in the stratigraphic record, and how they can help us understand the tectono-stratigraphic evolution of ancient continental rifts.
Mair D, Do Prado AH, Garefalakis P, et al., 2022, Grain size of fluvial gravel bars from close-range UAV imagery - uncertainty in segmentation-based data, Earth Surface Dynamics, Vol: 10, Pages: 953-973, ISSN: 2196-6311
Data on grain sizes of pebbles in gravel-bed rivers are of key importance for the understanding of river systems. To gather these data efficiently, low-cost UAV (uncrewed aerial vehicle) platforms have been used to collect images along rivers. Several methods to extract pebble size data from such UAV imagery have been proposed. Yet, despite the availability of information on the precision and accuracy of UAV surveys as well as knowledge of errors from image-based grain size measurements, open questions on how uncertainties influence the resulting grain size distributions still persist. Here we present the results of three close-range UAV surveys conducted along Swiss gravel-bed rivers with a consumer-grade UAV. We measure grain sizes on these images by segmenting grains, and we assess the dependency of the results and their uncertainties on the photogrammetric models. We employ a combined bootstrapping and Monte Carlo (MC) modeling approach to model percentile uncertainties while including uncertainty quantities from the photogrammetric model. Our results show that uncertainty in the grain size dataset is controlled by counting statistics, the selected processed image format, and the way the images are segmented. Therefore, our results highlight that grain size data are more precise and accurate, and largely independent of the quality of the photogrammetric model, if the data are extracted from single, undistorted nadir images in opposition to orthophoto mosaics. In addition, they reveal that environmental conditions (e.g., exposure to light), which control the quality of the photogrammetric model, also influence the detection of grains during image segmentation, which can lead to a higher uncertainty in the grain size dataset. Generally, these results indicate that even relatively imprecise and inaccurate UAV imagery can yield acceptable grain size data, under the conditions that the photogrammetric alignment was successful and that suitable image formats were sele
Wood J, McLeod JS, Lyster SJ, et al., 2022, Rivers of the Variscan Foreland: fluvial morphodynamics in the Pennant Formation of South Wales, UK, JOURNAL OF THE GEOLOGICAL SOCIETY, ISSN: 0016-7649
Hughes A, Rood D, DeVecchio DE, et al., 2022, Tectonic controls on Quaternary landscape evolution in the Ventura basin, southern California, quantified using cosmogenic isotopes and topographic analyses, Geological Society of America Bulletin, Vol: 134, Pages: 2245-2266, ISSN: 0016-7606
The quantification of rates for the competing forces of tectonic uplift and erosion has important implications for understanding topographic evolution. Here, we quantify the complex interplay between tectonic uplift, topographic development, and erosion recorded in the hanging walls of several active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic 26Al/10Be isochron burial dating and 10Be surface exposure dating to construct a basin-wide geochronology, which includes burial dating of the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our ages for the top of the exposed Saugus Formation range from 0.36 +0.18/-0.22 Ma to 1.06 +0.23/-0.26 Ma and our burial ages near the base of shallow marine deposits, which underlie the Saugus Formation, increase eastwards from 0.55 +0.08/-0.07 Ma to 3.30 +0.30/-0.42 Ma. Our geochronology is used the calculate a rapid long-term fault throw rate of 4.7–6.3 mm yr-1 since ~1.5 Ma for the San Cayetano fault and a slip rate of 1.3–3.0 mm yr-1 since ~1.5 Ma for the Oak Ridge fault, both of which agree with contemporary reverse slip rates derived from GPS data. We also calculate total cosmogenic nuclide (TCN)-derived catchment-averaged erosion rates that range from 0.18–2.21mm yr-1 and discuss the applicability of TCN-derived catchment-averaged erosion rates in rapidly-uplifting, landslide-prone landscapes. We compare patterns in erosion rates and tectonic rates to fluvial response times and geomorphic landscape parameters to show that in young, rapidly-uplifting mountain belts, catchments may attain a quasi-steady state on timescales <105 years, even if catchment-averaged erosion rates are still 34 adjusting to tectonic forcing.
Lyster SJ, Whittaker AC, Hajek EA, 2022, The problem of paleo-planforms, GEOLOGY, Vol: 50, Pages: 822-826, ISSN: 0091-7613
- Author Web Link
- Citations: 1
Mitchell WH, Whittaker AC, Mayall M, et al., 2022, Quantifying structural controls on submarine channel architecture and kinematics, GSA Bulletin, Vol: 134, Pages: 928-940, ISSN: 0016-7606
Over the past two decades, the increased availability of three-dimensional (3-D) seismic data and their integration with outcrop and numerical modeling studies have enabled the architectural evolution of submarine channels to be studied in detail. While tectonic activity is a recognized control on submarine channel morphology, the temporal and spatial complexity associated with these systems means submarine channel behavior over extended time periods, and the ways in which processes scale and translate into time-integrated sedimentary architecture, remain poorly understood. For example, tectonically driven changes in slope morphology may locally enhance or diminish a channel's ability to incise, aggrade, and migrate laterally, changing channel kinematics and the distribution of composite architectures. Here, we combined seismic techniques with the concept of stratigraphic mobility to quantify how gravity-driven deformation influenced the stratigraphic architecture of two submarine channels, from the fundamental architectural unit, a channel element, to channel complex scale, on the Niger Delta slope.From a 3-D, time-migrated, seismic-reflection volume, we evaluated the evolution of widths, depths, sinuosities, curvatures, and stratigraphic mobilities at fixed intervals downslope as the channel complexes interacted with a range of gravity-driven structures. At channel element scale, sinuosity and bend amplitude were consistently elevated over structured reaches of the slope, displaying a nonlinear increase in length, perpendicular to flow direction. At channel complex scale, the same locations, updip of structure, correlated to an increase in channel complex width and aspect ratio. Normalized complex dimensions and complex-averaged stratigraphic mobilities showed lateral migration to be the dominant form of stratigraphic preservation in these locations. Our results explain the intricate relationship between the planform characteristics of channel elements and the cro
Lyster SJ, Whittaker AC, Hajek EA, et al., 2022, Field evidence for disequilibrium dynamics in preserved fluvial cross-strata: A record of discharge variability or morphodynamic hierarchy?, Earth and Planetary Science Letters, Vol: 579, ISSN: 0012-821X
Bedforms preserved in the rock record can provide detailed information on the morphologies and hydrodynamics of ancient fluvial systems on Earth and other planets. Existing process–product relations for bedform preservation assume that fluvial cross strata reflect conditions under which bedforms were equilibrated with the prevailing flow, i.e., steady-state conditions. However, recent theoretical and experimental observations indicate that enhanced bedform preservation can occur in non-steady state, or disequilibrium, conditions, and it is currently unclear how prevalent disequilibrium dynamics are in preserved fluvial strata at outcrop scale. Here we explore whether steady-state assumptions are appropriate for ancient fluvial systems by evaluating the nature of bedform preservation in well studied fluvial deposits of three Upper Cretaceous (Turonian and Campanian) geologic formations in central Utah, USA: the Blackhawk Formation, Castlegate Sandstone, and Ferron Sandstone. In the field, we made systematic measurements of dune-scale cross-strata to quantify the extent to which preserved cross-sets reflect dune preservation in steady-state conditions. Across the three formations, consistently low coefficients of variation in preserved cross-set thicknesses of 0.25–0.5 are inconsistent with bedform preservation in steady-state conditions, and instead point to fluvial systems in which enhanced bedform preservation occurred in disequilibrium conditions. Enhanced bedform preservation in dune-scale cross-stratification can be explained by two independent hypotheses: the effect of flashy flood hydrographs on bedform preservation (flood hypothesis) or bedform preservation in the presence of larger migrating barforms (hierarchy hypothesis). We estimated bedform turnover timescales to quantitatively assess these competing hypotheses and contextualize their implications. Under the flood hypothesis, field measurements are consistent with enhanced bedform preservatio
Hicks S, Goes S, Whittaker A, et al., 2021, Multivariate statistical appraisal of regional susceptibility to induced seismicity: application to the Permian Basin, SW United States, Journal of Geophysical Research. Solid Earth, Vol: 126, ISSN: 2169-9356
Induced earthquake sequences are typically interpreted through causal triggering mechanisms. However, studies of causality rarely consider large regions and why some regions experiencing similar anthropogenic activities remain largely aseismic. Therefore, it can be difficult to forecast seismic hazard at a regional scale. In contrast, multivariate statistical methods allow us to find the combinations of factors that correlate best with seismicity, which can help form the basis of hypotheses that can be subsequently tested with physical models. Whilst strong correlations do not necessarily equate to causality, such a statistical approach is particularly important for large regions with newly emergent seismicity comprising multiple distinct clusters and multi-faceted industrial operations. Recent induced seismicity in the Permian Basin provides an excellent test-bed for multivariate statistical analyses because the main causal industrial and geological factors driving earthquakes in the region remain highly debated. Here, we use logistic regression to retrospectively predict the spatial variation of seismicity across the western Permian Basin. We reproduce the broad distribution of seismicity using a combination of both industrial and geological factors. Our model shows that the proximity to neotectonic faults west of the Delaware Basin is the most important factor that contributes to induced seismicity. The second-most important factor is salt-water disposal at shallow depths, with hydraulic fracturing playing a less dominant role. The higher tectonic stressing, together with a poor correlation between seismicity and large-volume deep salt-water disposal wells indicates a very different mechanism of induced seismicity compared to that in Oklahoma.
Lyster SJ, Whittaker AC, Hampson GJ, et al., 2021, Reconstructing the morphologies and hydrodynamics of ancient rivers from source to sink: Cretaceous Western Interior Basin, Utah, USA, Sedimentology, Vol: 68, Pages: 2854-2886, ISSN: 0037-0746
Quantitative reconstruction of palaeohydrology from fluvial stratigraphy provides sophisticated insights into the response, and relative impact, of tectonic and climatic drivers on ancient fluvial landscapes. Here, field measurements and a suite of quantitative approaches are used to develop a four-dimensional (space and time) reconstruction of palaeohydrology in Late Cretaceous palaeorivers of central Utah, USA – these rivers drained the Sevier mountains to the Western Interior Seaway. Field data include grain-size and cross-set measurements and span five parallel fluvial systems, two of which include up-dip to down-dip transects, across seven stratigraphic intervals through the Blackhawk Formation, Castlegate Sandstone and Price River Formation. Reconstructed palaeohydrological parameters include fluvial morphologies (flow depths, palaeoslopes, palaeorelief and planform morphologies) and various hydrodynamic properties (flow velocities, water discharges and sediment transport modes). Results suggest that fluvial morphologies were similar in space and time; median flow depths spanned 2 to 4 m with marginally greater flow depths in southerly systems. Meanwhile palaeoslopes spanned 10−3 to 10−4, decreasing downstream by an order of magnitude. The most prominent spatio-temporal change is an up to four-fold increase in palaeoslope at the Blackhawk–Castlegate transition; associated alluvial palaeorelief is tens of metres during Blackhawk deposition and >100 m during Castlegate Sandstone deposition. This study observed no change in unit water discharges at the Blackhawk–Castlegate transition, which argues against a climatically driven increase in palaeoslope and channel steepness. These findings instead point to a tectonically driven palaeoslope increase, although one limitation in this study is uncertainty in palaeochannel widths, which directly influences total water discharges. These reconstructions complement and expand on extensive p
Lipp A, 2021, Source region geochemistry from unmixing downstream sedimentary elemental compositions, G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences, Vol: 22, Pages: 1-25, ISSN: 1525-2027
The geochemistry of river sediments is routinely used to obtain information about geologic and environmental processes occurring upstream. For example, downstream samples are used to constrain chemical weathering and physical erosion rates upstream, as well as the locations of mineral deposits or contaminant sources. Previous work has shown that, by assuming conservative mixing, the geochemistry of downstream samples can be reliably predicted given a known source region geochemistry. In this study, we tackle the inverse problem and “unmix” the composition of downstream river sediments to produce geochemical maps of drainage basins (i.e., source regions). The scheme is tested in a case study of rivers draining the Cairngorms, UK. The elemental geochemistry of the urn:x-wiley:15252027:media:ggge22639:ggge22639-math-0001 μm fraction of 67 samples gathered from the beds of channels in this region is used to invert for concentrations of major and trace elements upstream. A smoothed inverse problem is solved using the Nelder-Mead optimization algorithm. Predictions of source region geochemistry are assessed by comparing the spatial distribution of 22 elements of different affinities (e.g., Be, Li, Mg, Ca, Rb, U, V) using independent geochemical survey data. The inverse approach makes reliable predictions of the major and trace element concentration in first order river sediments. We suggest this scheme could be a novel means to generate geochemical baselines across drainage basins and within river channels.
Pizzi M, Whittaker AC, Lonergan L, et al., 2021, New statistical quantification of the impact of active deformation on the distribution of submarine channels, Geology, Vol: 49, Pages: 926-930, ISSN: 0091-7613
Submarine channel systems play a crucial role in governing the delivery of sediments and pollutants such as plastics from the shelf edge to deep water. Understanding their distribution in space and time is important for constraining the locus, magnitude, and characteristics of deep-water sedimentation and for predicting stratigraphic architectures and depositional facies. Using three-dimensional seismic reflection data covering the outer fold-and-thrust belt of the Niger Delta, we determined the pathways of Miocene to Pliocene channels that crossed, at 173 locations, 11 fold-thrust structures for which the temporal and spatial evolution of strain rates has been constrained over a period of 11 m.y. We use a statistical approach to quantify strain and shortening rate distributions recorded where channels have crossed structures compared to the fault array as a whole. Our results prove unambiguously that these distributions are different. The median strain rate where channels cross faults is <0.6%/m.y. (~40 m/m.y.), 2.5× lower than the median strain rate of active fault segments (1.5%/m.y.) with a marked reduction in the number of channel-fault crossings where fault strain rates are >1%/m.y. Our results quantify the sensitivity of submarine channels to active deformation at a population level for the first time and enable us to predict the temporal and spatial routing of submarine channels affected by structurally driven topography.
Kent E, Whittaker AC, Boulton SJ, et al., 2021, Quantifying the competing influences of lithology and throw rate on bedrock river incision, GEOLOGICAL SOCIETY OF AMERICA BULLETIN, Vol: 133, Pages: 1649-1664, ISSN: 0016-7606
- Author Web Link
- Citations: 5
Mitchell WH, Whittaker AC, Mayall M, et al., 2021, New models for submarine channel deposits on structurally complex slopes: Examples from the Niger delta system, Marine and Petroleum Geology, Vol: 129, Pages: 1-22, ISSN: 0264-8172
Submarine channel complexes are often described as having a two-phase stratigraphic evolution where an initial phase of migration is followed by aggradation, generating a ‘hockey-stick shaped’ channel trajectory. However, the role of tectonic forcing in modifying time-integrated sedimentary architectures remains poorly understood. Here, we evaluate how tectonically driven changes in slope modify the evolution—both in terms of morphology and stratigraphic architecture—of submarine channels across a range of spatial scales from the fundamental architectural unit, a channel element, to the scale of a channel complex set, using examples from the Niger Delta system. From a 3D, time-migrated seismic reflection volume, we use amplitude extractions, frequency decomposition and RGB blending to determine channel stratigraphic architectures. These observations are used systematically to evaluate the development of cross-sectional and planform architectures as the channel systems interact with a range of active and pre-existing structural bathymetry. Our results indicate that while a channel complex's stratigraphic architecture may be captured by a two-phase evolution on unstructured slopes, this model fails on structurally complex slopes. Unstructured slope channel complexes display a repeated arrangement of migration dominating the early stratigraphic record and subsequent aggradation. The late aggradational phase signals a decrease in the rate of growth in channel complex width and the rate of change in sinuosity relative to aggradation throughout the complex's development. However, tectonically driven changes in sinuosity and the relative rates of channel migration and aggradation modify complex development significantly. We identify three end-member styles of channel-structure interaction, determined by the timing of bathymetry development and its associated style: (1) pre-channel structural bathymetry; (2) coeval positive relief, and (3) coeval neg
Scheingross JS, Limaye AB, McCoy SW, et al., 2021, The shaping of erosional landscapes by internal dynamics (vol 1, pg 661, 2020), NATURE REVIEWS EARTH & ENVIRONMENT, Vol: 2, Pages: 375-375
QuyeSawyer J, Whittaker AC, Roberts GG, et al., 2021, Fault throw and regional uplift histories from drainage analysis: evolution of southern Italy, Tectonics, Vol: 40, Pages: 1-26, ISSN: 0278-7407
Landscapes can record elevation changes caused by multiple tectonic processes. Here, we show how coeval histories of spatially coincident normal faulting and regional uplift can be deconvolved from river networks. We focus on Calabria, a tectonically active region incised by rivers containing knickpoints and knickzones. Marine fauna indicate that Calabria has been uplifted by >1 km since ∼0.8–1.2 Ma, which we used to calibrate parameters in a stream power erosional model. To deconvolve the local and regional uplift contributions to topography, we performed a spatiotemporal inversion of 994 fluvial longitudinal profiles. Uplift rates from fluvial inversion replicate the spatial trend of rates derived from dated Mid-Late Pleistocene marine terraces, and the magnitude of predicted uplift rates matches the majority of marine terrace uplift rates. We used the predicted uplift history to analyze long-term fault throw, and combined throw estimates with ratios of footwall uplift to hanging wall subsidence to isolate the nonfault related contribution to uplift. Increases in fault throw rate—which may suggest fault linkage and growth—have been identified on two major faults from fluvial inverse modeling, and total fault throw is consistent with independent estimates. The temporal evolution of nonfault related regional uplift is similar at three locations. Our results may be consistent with toroidal mantle flow generating uplift, perhaps if faulting reduces the strength of the overriding plate. In conclusion, fluvial inverse modeling can be an effective technique to quantify fault array evolution and can deconvolve different sources of uplift that are superimposed in space and time.
Harries RM, Gailleton B, Kirstein LA, et al., 2021, Impact of climate on landscape form, sediment transfer and the sedimentary record, EARTH SURFACE PROCESSES AND LANDFORMS, Vol: 46, Pages: 990-1006, ISSN: 0197-9337
- Author Web Link
- Citations: 12
Mitchell WH, Whittaker AC, Mayall M, et al., 2021, Quantifying the relationship between structural deformation and the morphology of submarine channels on the Niger Delta continental slope, Basin Research, Vol: 33, Pages: 186-209, ISSN: 0950-091X
The processes and deposits of deep‐water submarine channels are known to be influenced by a wide variety of controlling factors, both allocyclic and autocyclic. However, unlike their fluvial counterparts whose dynamics are well‐studied, the factors that control the long‐term behaviour of submarine channels, particularly on slopes undergoing active deformation, remain poorly understood. We combine seismic techniques with concepts from landscape dynamics to investigate quantitatively how the growth of gravitational‐collapse structures at or near the seabed in the Niger Delta have influenced the morphology of submarine channels along their length from the shelf edge to their deep‐water counterpart. From a three dimensional (3D), time‐migrated seismic‐reflection volume, which extends over 120 km from the shelf edge to the base of slope, we mapped the present‐day geomorphic expression of two submarine channels and active structures at the seabed, and created a Digital Elevation Model (DEM). A second geomorphic surface and DEM raster—interpreted to closer approximate the most recent active channel geometries—were created through removing the thickness of hemipelagic drape across the study area. The DEM rasters were used to extract the longitudinal profiles of channel systems with seabed expression, and we evaluate the evolution of channel widths, depths and slopes at fixed intervals downslope as the channels interact with growing structures. Results show that the channel long profiles have a relatively linear form with localized steepening associated with seabed structures. We demonstrate that channel morphologies and their constituent architectural elements are sensitive to active seafloor deformation, and we use the geomorphic data to infer a likely distribution of bed shear stresses and flow velocities from the shelf edge to deep water. Our results give new insights into the erosional dynamics of submarine channels, allow us to quantify the extent to which
Watkins SE, Whittaker AC, Bell RE, et al., 2020, Straight from the source's mouth: Controls on field‐constrained sediment export across the entire active Corinth Rift, central Greece, Basin Research, Vol: 32, Pages: 1600-1625, ISSN: 0950-091X
The volume and grain‐size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain‐size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain‐sizes of channel bars and full‐weighted grain‐size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain‐size increases westward along the southern coast of the Gulf of Corinth, with the coarse‐fraction grain‐sizes (84th percentile of weighted grain‐size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse‐fraction of the sieved grain‐size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain‐size export is primarily controlled by the input grain‐size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse‐fraction of the grain‐size distribution are predominantly transported in bedload; however, typical sand‐grade particles are transported as suspended load at bankfull conditions, suggesting disparate source‐to‐sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain‐size‐specific bedload discharged into the Gulf of Corinth using the grain‐size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain‐size of sediment export at the rift scale is particularly
Scheingross JS, Limaye AB, McCoy SW, et al., 2020, The shaping of erosional landscapes by internal dynamics, NATURE REVIEWS EARTH & ENVIRONMENT, Vol: 1, Pages: 661-676
- Author Web Link
- Citations: 23
Lipp AG, Roberts GG, Whittaker AC, et al., 2020, River sediment geochemistry as a conservative mixture of source regions: observations and predictions from the Cairngorms,, UK, Journal of Geophysical Research: Earth Surface, Vol: 125, ISSN: 2169-9011
The elemental composition of sediments in rivers is the product of physical and chemical erosion of rocks, which is then transported across drainage networks. A corollary is that fluvial sedimentary geochemistry can be used to understand geologic, climatic, and geomorphic processes. Here, we predict elemental compositions of river sediments using drainage networks extracted from digital elevation data and erosional models. The Geochemical Baseline Survey of the Environment was used to quantify substrate (i.e., source region) chemistry. Sedimentary compositions in rivers downstream are predicted by formally integrating eroding substrates with respect to distance downstream. Different erosional models, including the Stream Power model and uniform incision rates, are tested. Predictions are tested using a new suite of compositions obtained from fine grained (<150 μm) sediments at 67 sites along the Spey, Dee, Don, Deveron, and Tay rivers, Cairngorms, UK. Results show that sedimentary geochemistry can be predicted using simple models that include the topography of drainage networks and substrate compositions as input. The concentration of numerous elements including Magnesium, Rubidium, Uranium, Potassium, Calcium, Strontium, and Beryllium can be accurately predicted using this simple approach. Predictions are insensitive to the choice of erosional model, which we suggest is a consequence of broadly homogeneous rates of erosion throughout the study area. Principal component analysis of the river geochemical data suggests that the composition of most Cairngorms river sediments can be explained by mafic/felsic provenance and conservative mixing downstream. These results suggest that the elemental composition of river sediments can be accurately predicted using simple erosional models and digital elevation data.
Quye-Sawyer J, Whittaker AC, Roberts GG, 2020, Calibrating fluvial erosion laws and quantifying river response to faulting in Sardinia, Italy, Geomorphology, Vol: 370, Pages: 1-14, ISSN: 0169-555X
It is now widely accepted that rivers modify their erosion rates in response to variable rock uplift rates, resulting in changes in channel slope that propagate upstream through time. Therefore, present-day river morphology may contain a record of tectonic history. The simple stream power incision model can, in principle, be used to quantify past uplift rates over a variety of spatial and temporal scales. Nonetheless, the erosional model's exponents of area and slope (m and n respectively) and ‘bedrock erodibility’ (k) remain poorly constrained. In this paper, we will use a geologically and geomorphically well constrained Plio-Pleistocene volcanic landscape in central Sardinia, Italy, to calibrate the stream power erosion equation and to investigate the slip rate of faults that have been seismically quiescent in the historic past. By analysing digital elevation models, geological maps and Landsat imagery, we have identified the geomorphic expression of several volcanic features (eruption centres and basaltic lava flows) and three normal faults with 6 to 8 km fault traces within the outcrop. Downstream, river longitudinal profiles show a similar transient response to relative base level fall, probably as a result of relief inversion at the edge of the volcanic outcrop. From measurements of incision, local slope and upstream catchment area across eight different rivers, we calculate n ≈ 1, m = 0.50 ± 0.02 and, using a landscape age from literature of 2.7 Ma, bedrock erodibility k = 0.10 ± 0.04 m(1−2m) Myr−1. There are also knickpoints on rivers upstream of two normal faults, and we used numerical inverse modelling of the longitudinal profiles to predict the slip rate of these faults since 2.7 Ma. The results from the inverse model show that the erosional parameter values derived in this study can produce theoretical longitudinal profiles that closely resemble observed river profiles upstream of the faults. The lowest misfit
Lyster SJ, Whittaker AC, Allison PA, et al., 2020, Predicting sediment discharges and erosion rates in deep time—examples from the late Cretaceous North American continent, Basin Research, Vol: 32, ISSN: 0950-091X
Depositional stratigraphy represents the only physical archive of palaeo‐sediment routing and this limits analysis of ancient source‐to‐sink systems in both space and time. Here, we use palaeo‐digital elevation models (palaeoDEMs; based on high‐resolution palaeogeographic reconstructions), HadCM3L general circulation model climate data and the BQART suspended sediment discharge model to demonstrate a predictive, forward approach to palaeo‐sediment routing system analysis. To exemplify our approach, we use palaeoDEMs and HadCM3L data to predict the configurations, geometries and climates of large continental catchments in the Cenomanian and Turonian North American continent. Then, we use BQART to estimate suspended sediment discharges and catchment‐averaged erosion rates and we map their spatial distributions. We validate our estimates with published geologic constraints from the Cenomanian Dunvegan Formation, Alberta, Canada, and the Turonian Ferron Sandstone, Utah, USA, and find that estimates are consistent or within a factor of two to three. We then evaluate the univariate and multivariate sensitivity of our estimates to a range of uncertainty margins on palaeogeographic and palaeoclimatic boundary conditions; large uncertainty margins (≤50%/±5°C) still recover estimates of suspended sediment discharge within an order of magnitude of published constraints. PalaeoDEMs are therefore suitable as a first‐order investigative tool in palaeo‐sediment routing system analysis and are particularly useful where stratigraphic records are incomplete. We highlight the potential of this approach to predict the global spatio‐temporal response of suspended sediment discharges and catchment‐averaged erosion rates to long‐period tectonic and climatic forcing in the geologic past.
Brewer C, Hampson G, Whittaker A, et al., 2020, Comparison of methods to estimate sediment flux in ancient sediment routing systems, Earth-Science Reviews, Vol: 207, ISSN: 0012-8252
The need to predict accurately the volume, timing and location of sediments that are transported from an erosional source region into a basin-depocentre sink is important for many aspects of pure and applied sedimentological research. In this study, the results of three widely used methods to estimate sediment flux in ancient sediment routing systems are compared, using rich input datasets from two systems (Eocene South Pyrenean Foreland Basin, Spain and late-Pleistocene-to-Holocene Gulf of Corinth Rift Basin, Greece) for which mapped, dated sediment volumes provide an independent reference value of sediment accumulation rates. The three methods are: (1) the empirical BQART model, which uses values of drainage basin area, relief, temperature, lithology and water discharge; (2) empirical scaling relationships between characteristic geomorphological parameters of sediment-routing-system segments; and (3) the “fulcrum” model, which uses the palaeohydrological parameters of trunk river channels to estimate downsystem sediment discharge. The BQART model and empirical geomorphological scaling relationships were originally developed using modern sediment routing systems, and have subsequently been applied to ancient systems. In contrast, the “fulcrum” model uses hydrological scaling relationships from modern systems, but was developed principally for application in ancient systems.Our comparative analysis quantifies the sensitivity of the three methods to their input parameters, and identifies the data required to make plausible estimates of sediment flux for ancient sediment routing systems. All three methods can generate estimates of sediment flux that are comparable with each other, and are accurate to at least one order of magnitude relative to independent reference values. The BQART model uses palaeoclimatic and palaeocatchment input data, which are accurate for sub-modern systems but may be highly uncertain in deep-time systems. Corresponding
Pizzi M, Lonergan L, Whittaker AC, et al., 2020, Growth of a thrust fault array in space and time: An example from the deep-water Niger delta, Journal of Structural Geology, Vol: 137, Pages: 1-20, ISSN: 0191-8141
The temporal and spatial evolution of thrust fault arrays is currently poorly understood, and marine fold and thrust belts at the toe of passive margin gravitational systems, imaged by commercial 3D seismic reflection datasets, afford a unique opportunity to investigate this problem in three dimensions. Using an extensive 3D seismic data set and age data, the total cumulative strain (shortening) and interval strain rates have been calculated for 11 thrust-related folds mapped in the toe-thrust region of the southern lobe of the Niger Delta. For the first time, the sequence of thrust nucleation, propagation and linkage through time at a scale of 10 s km both along and across strike is documented. Short thrust segments had nucleated throughout the entire study area by 15 Ma. They then grew largely by lateral growth and linkage, increasing the fault trace length and generating asymmetric strain-distance plots, for the first 50% of their history. Thereafter, growth continued by shortening, with minimal along strike increase in fault length. Changes in shortening-distance data between adjacent structures across strike suggest that the change in growth mode occurred once the thrusts had linked in 3D through the common underlying detachment. Over the entire thrust array the strain rate varies through time, starting slowly (<200 m/Ma), then increasing between 9.5 and 3.7 Ma (200–400 m/Ma) before slowing down in the last ∼ 4 Ma (<150 m/Ma). The variation in strain rate is attributed to a change in boundary conditions of the gravitational system. An increase in sediment supply to the delta occurred in the late Miocene-Pliocene, driving higher shortening rates in the toe area. A subsequent reduction in sediment supply in the last ∼4 Ma led to a reduction in deformation rate and the cessation of activity on a number of the thrusts. Predictions of the critical taper wedge model are used to explain the near-synchronous growth of the entire thrust array over th
Hughes A, Bell RE, Mildon ZK, et al., 2020, Three‐dimensional structure, ground rupture hazards, and static stress models for complex non‐planar thrust faults in the Ventura basin, southern California, Journal of Geophysical Research: Solid Earth, Vol: 125, ISSN: 2169-9313
To investigate the subsurface geometry of a recently discovered, seismically‐active fault in the Ventura basin, southern California, USA, we present a series of cross sections and a new three‐dimensional fault model across the Southern San Cayetano fault (SSCF) based on integration of surface data with petroleum industry well‐log data. Additionally, the fault model for the SSCF, along with models of other regional faults extracted from the Southern California Earthquake Center three‐dimensional Community Fault Model, are incorporated in static Coulomb stress modeling to investigate static Coulomb stress transfer between thrust faults with complex geometry and to further our understanding of stress transfer in the Ventura basin. The results of the subsurface well investigation provide evidence for a low‐angle SSCF that dips ~15° north and connects with the western section of the San Cayetano fault around 1.5–3.5 km depth. We interpret the results of static Coulomb stress models to partly explain contrasting geomorphic expression between different sections of the San Cayetano fault and a potential mismatch in timings between large‐magnitude uplift events suggested by paleoseismic studies on the Pitas Point, Ventura, and San Cayetano faults. In addition to new insights into the structure and potential rupture hazard of a recently discovered active reverse fault in a highly populated area of southern California, this study provides a simple method to model static Coulomb stress transfer on complex geometry faults in fold and thrust belts.
Geurts AH, Whittaker AC, Gawthorpe RL, et al., 2020, Transient landscape and stratigraphic responses to drainage integration in the actively extending central Italian Apennines, GEOMORPHOLOGY, Vol: 353, ISSN: 0169-555X
- Author Web Link
- Citations: 19
Zondervan JR, Whittaker AC, Bell RE, et al., 2020, New constraints on bedrock erodibility and landscape response times upstream of an active fault, GEOMORPHOLOGY, Vol: 351, ISSN: 0169-555X
- Author Web Link
- Citations: 23
Brooke SAS, DArcy M, Mason PJ, et al., 2020, Rapid multispectral data sampling using Google Earth Engine, Computers & Geosciences, Vol: 135, Pages: 104366-104366, ISSN: 0098-3004
The advent of cloud-based GIS tools has enabled the rapid exploration and processing of geospatial datasets. The Google Earth Engine (GEE) platform provides a library of algorithms and a powerful application programming interface (API) to produce flexible cloud-based applications that leverage Google’s computing infrastructure for geospatial analysis. We introduce ”Spectral Point”, a new GUI tool developed in GEE that allows users to explore, process and extract multispectral data rapidly within a single browser window. The ability to access and measure spectral signals from surface deposits using the entire available Landsat and Sentinel 2 archive is of tremendous benefit to geomorphic research, removing the need to download and process terabytes worth of imagery. Spectral values from composite imagery collected in GEE that relate to changes in surface mineral composition agree with corresponding point values using conventional desktop Landsat processing. The ”Spectral Point” tool makes it fast and simple to extract quantitative, contrast-corrected brightness data from multispectral imagery compared conventional desktop-based approaches. At the same time, the user needs no experience developing code, proprietary third-party software or dedicated high-performance computing and only a modern web browser. The ”Spectral Point” tool has many potential applications in the remote study of Earth’s surface; for example, we explore a case study from the western United States that demonstrates how the tool can be used for mapping, geochronology, and estimating weathering rates for Quaternary landforms. With increasing numbers of satellites, we are now faced with a growing deluge of geospatial data. Cloud-based solutions to mapping, field reconnaissance and image processing will be increasingly necessary to handle this valuable but untapped satellite image resource. ”Spectral Point” is an example of a new generation o
Harries RM, Kirstein LA, Whittaker AC, et al., 2019, Impact of recycling and lateral sediment input on grain size fining trends—Implications for reconstructing tectonic and climate forcings in ancient sedimentary systems, Basin Research, Vol: 31, Pages: 866-891, ISSN: 0950-091X
Grain size trends in basin stratigraphy are thought to preserve a rich record of the climatic and tectonic controls on landscape evolution. Stratigraphic models assume that over geological timescales, the downstream profile of sediment deposition is in dynamic equilibrium with the spatial distribution of tectonic subsidence in the basin, sea level and the flux and calibre of sediment supplied from mountain catchments. Here, we demonstrate that this approach in modelling stratigraphic responses to environmental change is missing a key ingredient: the dynamic geomorphology of the sediment routing system. For three large alluvial fans in the Iglesia basin, Argentine Andes we measured the grain size of modern river sediment from fan apex to toe and characterise the spatial distribution of differential subsidence for each fan by constructing a 3D model of basin stratigraphy from seismic data. We find, using a self-similar grain size fining model, that the profile of grain size fining on all three fans cannot be reproduced given the subsidence profile measured and for any sediment supply scenario. However, by adapting the self-similar model, we demonstrate that the grain size trends on each fan can be effectively reproduced when sediment is not only sourced from a single catchment at the apex of the system, but also laterally, from tributary catchments and through fan surface recycling. Without constraint on the dynamic geomorphology of these large alluvial systems, signals of tectonic and climate forcing in grain size data are masked and would be indecipherable in the geological record. This has significant implications for our ability to make sensitive, quantitative reconstructions of external boundary conditions from the sedimentary record.
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