Imperial College London

Dr Alex Whittaker

Faculty of EngineeringDepartment of Earth Science & Engineering

Reader in Landscape Dynamics
 
 
 
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Contact

 

+44 (0)20 7594 7491a.whittaker Website

 
 
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Location

 

3.51Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

98 results found

Boulton SJ, Rodés Á, Fabel D, Alçiçek MC, Whittaker ACet al., 2024, Complex erosional response to uplift and rock strength contrasts in transient river systems crossing an active normal fault revealed by <sup>10</sup>Be and <sup>26</sup>Al cosmogenic nuclide analyses, Earth Surface Processes and Landforms, ISSN: 0197-9337

Understanding the influence of bedrock lithology on the catchment-averaged erosion rates of normal fault-bounded catchments and the effect that different bedrock erodibilties have on the evolution of transient fluvial geomorphology remain major challenges. To investigate this problem, we collected 18 samples for 10Be and 26Al cosmogenic nuclide analysis to determine catchment-averaged erosion rates along the well-constrained Gediz Fault system in western Türkiye, which is experiencing fault-driven river incision owing to a linkage event ~0.8 Ma and has weak rocks overlying strong rocks in the footwall. Combined with existing cosmogenic data, we show that the background rate of erosion of the pre-incision landscape can be constrained as <92 mMyr−1, and erosion rates within the transient reach vary from 16 to 1330 mMyr−1. Erosion rates weakly scale with unit stream power, steepness index and slip rate on the bounding fault, although erosion rates are an order of magnitude lower than slip rates. However, there are no clear relationships between erosion rate and relief or catchment slope. Bedrock strength is assessed using Schmidt hammer rebound and Selby Rock Mass Strength Assessments; despite a 30-fold difference in erodibility, there is no difference in the erosion rate between strong and weak rocks. We argue that, for the Gediz Graben, the strong lithological contrast affects the ability of the river to erode the bed, resulting in a complex erosional response to uplift along the graben boundary fault. Weak covariant trends between erosion rates and various topographic factors potentially result from incomplete sediment mixing or pre-existing topographic inheritance. These findings indicate that the erosional response to uplift along an active normal fault is a complex response to multiple drivers that vary spatially and temporally.

Journal article

Yusoff HHM, Johnson HD, Lonergan L, Whittaker AC, Abu Bakar Aet al., 2024, Seismic stratigraphy of Late Pleistocene incised valleys and adjacent environments, eastern Central Luconia Province, offshore north-west Borneo, Sedimentology, Vol: 71, Pages: 319-354, ISSN: 0037-0746

Incised valleys are commonly investigated based on outcrop, modern setting and seismic data, which are often limited by data availability, especially for broad (ca >100 km wide) shelf settings. Consequently, few have described complete depositional systems of the incised valleys, especially those linked to their corresponding modern rivers in a source-to-sink framework to determine comprehensive controlling factors. This study documents Late Quaternary incised valleys and their characteristics in the Balingian – Central Luconia shelf based on regionally-extensive three-dimensional seismic data, two-dimensional high-resolution seismic data and boreholes. The three-dimensional seismic data show that the main Tatau incised valley and tributary Suai incised valley fed the Tatau–Suai shelf-edge delta. The Tatau incised valley is interpreted as the main incised valley based on its broader width, thicker infill, two-tier stratigraphic architecture and its larger drainage basin area compared to the tributary Suai incised valley. The Tatau incised valley shifted its direction towards an active tectonic lineament (West Baram Line) and bypassed sediments to the deep-water via a series of upper slope channels. The Tatau incised valley system comprises the following elements: (i) an upstream segment characterized by rivers dissecting an uplifted hinterland comprising Neogene sedimentary rocks, humid-tropical vegetation, monsoonal climate, extremely high river discharge and sediment supply; (ii) a midstream segment comprising an emergent, vegetated (tropical rainforest to mangroves) and relatively narrow (ca 150 to 200 km wide) shelf, which was characterized by basinward-increasing, tectonically-driven accommodation space, valley incision and deposition; (iii) a downstream segment with increasing tidal-influence where the Tatau and its tributary valley merged; and (iv) a short (15 to 20 km), narrow (10 to 15 km), tectonically-controlled

Journal article

Okwara IC, Hampson GJ, Whittaker AC, Roberts GG, Ball PWet al., 2023, Source‐to‐sink mass‐balance analysis of an ancient wave‐influenced sediment routing system: Middle Jurassic Brent Delta, Northern North Sea, offshore UK and Norway, Basin Research, Vol: 35, Pages: 1555-1589, ISSN: 0950-091X

Sediment mass-balance analysis provides key constraints on stratigraphic architecture and its controls. We use the data-rich Middle Jurassic Brent Delta sediment routing system in the proto-Viking Graben, Northern North Sea, to estimate sediment budgets and mass-balance between source areas and depositional sinks. Published studies are synthesised to provide an age-constrained sequence stratigraphic framework, consisting of four previously defined genetic sequences (J22, J24, J26, J32). Genetic sequence J32 (3.9 Myr) records transverse progradation of basin-margin deltas, sourced from the Shetland Platform to the west and Norwegian Landmass to the east. Genetic sequences J24 (1.1 Myr) and J26 (0.9 Myr) record the rapid progradation and subsequent aggradation of the Brent Delta along the basin axis, sourced from the uplifted Mid-North Sea High to the south, and the western and eastern source regions. Genetic sequence J32 (2.2 Myr) records the retreat of the Brent Delta. Sediment budgets for the four genetic sequences are estimated using palaeogeographical reconstructions, isopach maps, and sedimentological analysis of core and well-log data. The estimated net-depositional sediment budget for the mapped Brent Delta system is 2.0–2.8 Mt/year. Temporal variations in net-depositional sediment budget were driven by changes in tectonic boundary conditions, such as the onset of uplift before the deposition of genetic sequence J24. Over the same time period, the Shetland Platform, Norwegian Landmass and Mid-North Sea High source regions are estimated to have supplied 2.3–5.6, 5.0–14.1, and 2.8–9.4 Mt/year of sediment, respectively, using the BQART sediment load model and independent geometrical reconstruction of eroded volumes, which are constrained by isostatic uplift estimates based on the geochemistry of syn-depositional volcanic rocks. The net-depositional sediment budget in the sink is an order-of-magnitu

Journal article

Valenza JM, Ganti V, Whittaker AC, Lamb MPet al., 2023, Pre-Vegetation, Single-Thread Rivers Sustained by Cohesive, Fine-Grained Bank Sediments: Mesoproterozoic Stoer Group, NW Scotland, GEOPHYSICAL RESEARCH LETTERS, Vol: 50, ISSN: 0094-8276

Journal article

McLeod J, Wood J, Lyster S, Valenza J, Spencer A, Whittaker Aet al., 2023, Quantitative constraints on flood variability in the rock record, Nature Communications, Vol: 14, Pages: 1-12, ISSN: 2041-1723

Floods determine river behaviour in time and space. Yet quantitative measures of discharge variability from geological stratigraphy are sparse, even though they are critical to understand landscape sensitivity to past and future environmental change. Here we show how storm-driven river floods in the geologic past can be quantified, using Carboniferous stratigraphy as an exemplar. The geometries of dune cross-sets demonstrate that discharge-driven disequilibrium dynamics dominated fluvial deposition in the Pennant Formation of South Wales. Based on bedform preservation theory, we quantify dune turnover timescales and hence the magnitude and duration of flow variability, showing that rivers were perennial but prone to flashy floods lasting 4-16 hours. This disequilibrium bedform preservation is consistent across 4 Ma of stratigraphy, and coincides with facies-based markers of flooding, such as mass-preservation of woody debris. We suggest that it is now possible to quantify climate-driven sedimentation events in the geologic past, and reconstruct discharge variability from the rock record on a uniquely short (daily) timescale, revealing a formation dominated by flashy floods in perennial rivers.

Journal article

Mitchell WH, Whittaker AC, Mayall M, Lonergan Let al., 2023, Reconciling bathymetric and stratigraphic expressions of submarine channel geometry, Marine Geology, Vol: 459, Pages: 1-14, ISSN: 0025-3227

Modern submarine channels form distinctive morphological features on the seafloor and play a critical role in shaping the marine sedimentary record. Recent studies have captured the extremely diverse range of cross-sectional geometries in submarine channels from bathymetric data, which typically display aspect ratios markedly different to the stratigraphic record of ancient submarine channels. Here, we compare and reconcile the relationship between the geomorphic expression of submarine channels as observed on the seafloor and the geometry of their stratigraphic bodies as mapped in seismic-reflection data, using the Niger Delta slope an exemplar. For the same channels, our data allows us to contrast the distribution of widths, depths, and aspect ratios from bathymetric data and at two hierarchical scales in the underlying stratigraphy – the channel element and channel system scale. Channel characteristics are also contextualised with respect to two key variables, the underlying structural template and the relative timescale for which the studied systems have been active. Analysis of the seafloor bankfull geometries highlights substantial variability with widths ranging from ∼300 m to ∼4 km and aspect ratios from ∼10:1–100:1. In contrast, the geometry of stratigraphic channel element bodies remains remarkably consistent across the three channels with widths ∼480–620 m and aspect ratios of ∼9:1. At channel system scale stratigraphic width is comparable to that seen in the bathymetric data, but with aspect ratios of 6–23:1. Our results therefore highlight a marked disparity in the cross-sectional geometries on the present-day seafloor and for their associated channels in the stratigraphic record. We demonstrate that a large part of the disparity between modern and ancient submarine channel geometries may be explained by post-abandonment modification of the seabed channels where there is reduced Holocene activity and we argue

Journal article

Sharma N, Whittaker ACC, Watkins SEE, Valero L, Verite J, Puigdefabregas C, Adatte T, Garces M, Guillocheau F, Castelltort Set al., 2023, Water discharge variations control fluvial stratigraphic architecture in the Middle Eocene Escanilla formation, Spain, SCIENTIFIC REPORTS, Vol: 13, ISSN: 2045-2322

Journal article

Wrona T, Whittaker AC, Bell RE, Gawthorpe RL, Fossen H, Jackson CA-L, Bauck MSet al., 2023, Rift kinematics preserved in deep-time erosional landscape below the northern North Sea, Basin Research, Vol: 35, Pages: 744-761, 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.

Journal article

Pizzi M, Whittaker AC, Mayall M, Lonergan Let 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

Journal article

Mair D, Do Prado AH, Garefalakis P, Lechmann A, Whittaker A, Schlunegger Fet 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

Journal article

Wood J, McLeod JS, Lyster SJ, Whittaker ACet 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

Journal article

Hughes A, Rood D, DeVecchio DE, Whittaker AC, Bell RE, Wilcken KM, Corbett LB, Bierman PR, Swanson BJ, Rockwell TKet 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.

Journal article

Lyster SJ, Whittaker AC, Hajek EA, 2022, The problem of paleo-planforms, GEOLOGY, Vol: 50, Pages: 822-826, ISSN: 0091-7613

Journal article

Mitchell WH, Whittaker AC, Mayall M, Lonergan L, Pizzi Met 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

Journal article

Lyster SJ, Whittaker AC, Hajek EA, Ganti Vet 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

Journal article

Hicks S, Goes S, Whittaker A, Stafford Pet 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.

Journal article

Lyster SJ, Whittaker AC, Hampson GJ, Hajek EA, Allison PA, Lathrop BAet 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

Journal article

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.

Journal article

Pizzi M, Whittaker AC, Lonergan L, Mayall M, Mitchell WHet 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.

Journal article

Mitchell WH, Whittaker AC, Mayall M, Lonergan Let 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

Journal article

Scheingross JS, Limaye AB, McCoy SW, Whittaker ACet al., 2021, The shaping of erosional landscapes by internal dynamics (vol 1, pg 661, 2020), NATURE REVIEWS EARTH & ENVIRONMENT, Vol: 2, Pages: 375-375

Journal article

QuyeSawyer J, Whittaker AC, Roberts GG, Rood DHet 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.

Journal article

Harries RM, Gailleton B, Kirstein LA, Attal M, Whittaker AC, Mudd SMet 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

Journal article

Mitchell WH, Whittaker AC, Mayall M, Lonergan L, Pizzi Met 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

Journal article

Kent E, Whittaker AC, Boulton SJ, Alcicek MCet al., 2020, 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

Journal article

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

Journal article

Lipp AG, Roberts GG, Whittaker AC, Gowing CJB, Fernandes VMet 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.

Journal article

Lyster SJ, Whittaker AC, Allison PA, Lunt DJ, Farnsworth Aet 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.

Journal article

Watkins SE, Whittaker AC, Bell RE, Brooke SAS, Ganti V, Gawthorpe RL, McNeill LC, Nixon CWet 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

Journal article

Scheingross JS, Limaye AB, McCoy SW, Whittaker ACet al., 2020, The shaping of erosional landscapes by internal dynamics, NATURE REVIEWS EARTH & ENVIRONMENT, Vol: 1, Pages: 661-676

Journal article

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