Imperial College London

DrLidiaLonergan

Faculty of EngineeringDepartment of Earth Science & Engineering

Reader in Geotectonics
 
 
 
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Contact

 

+44 (0)20 7594 6465l.lonergan Website

 
 
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Location

 

2.51Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

94 results found

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

<jats:title>Abstract</jats:title> <jats:p>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.</jats:p> <jats:p>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 location

Journal article

Galindo PA, Lonergan L, 2021, Sigmoidal normal faults and evidence for vertical-axis block rotation in an oblique convergent margin: a 3D seismic example from offshore Colombia, The Leading Edge, Vol: 40, Pages: 923-930, ISSN: 1070-485X

Sigmoidal fold and fault geometries are typical kinematic indicators of strike-slip fault zones. We document kilometer-scale, normal faults with sigmoidal plan-view geometries within the dextral pull-apart Bahia Basin, at the rear of the obliquely convergent South Caribbean Deformed Belt, offshore Colombia. Using 3D seismic reflection data calibrated to wells, closely spaced, low-displacement, planar normal faults are mapped within the Miocene strata. A series of seismic horizontal (time) slices and computed seismic attributes are used to interpret the 3D configuration of these faults. The closely spaced faults display an east–west trend with a progressive rotation into a northwest–southeast trend. In map view, the fault traces curve toward their tips, describing a sigmoidal-Z geometry that terminates at discrete northeast–southwest-trending fault zones. The structures observed may correspond to either tension fractures, which form theoretically at 45°, or antithetic shear fractures with normal displacement formed at 50°–70° to the boundaries of a dextral shear zone. These scenarios lead to a clockwise block rotation of between 20° and 40° within the shear zone. This study shows the first example of vertical-axis block rotations observed offshore in the western end of the South Caribbean margin and is an important example of the use of 3D seismic data to identify rotations where paleomagnetic studies are not available.

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

Gu Z, Lonergan L, Zhai X, Zhang B, Lu Wet al., 2021, The formation of the Sichuan Basin, South China, during the Late Ediacaran to Early Cambrian, Basin Research, Vol: 33, Pages: 2328-2357, ISSN: 0950-091X

The Upper Ediacaran to Lower Cambrian of the Sichuan Basin in South China has long been considered to be dominated by shallow‐water deposition. Hydrocarbon exploration, however, has revealed that a NW‐SE trending intraplatform trough formed in the basin during the same period. Although different models have been proposed, the formation and evolution of the trough are still not fully understood. In this study, we investigate both the origin of the intraplatform trough and the formation of the Sichuan Basin by integrating seismic interpretation, well correlation and tectonic subsidence analysis. The seismic and well data clearly show three stages of development of the trough. The first stage, in the early Late Ediacaran, is characterized by considerable thinning of the lower two members of the Upper Ediacaran from the platform margins to the trough. In the second stage, in the late Late Ediacaran, the platform margins backstepped and the extent of the trough expanded significantly to a width of ca. ~400 km. The third stage, in the early Early Cambrian, was dominated by gradual filling of the trough and onlapping of the platform margins. Backstripped tectonic subsidence curves show one, or two closely spaced episodes of linear subsidence starting at ~550 Ma and then decreasing exponentially until ~450 Ma. The shape of the subsidence curves is consistent with formation of the Sichuan Basin by low, and slow amounts of lithospheric stretching of thickened cratonic lithosphere. The tectonic subsidence increases from the centre to the NW of the basin. Interestingly the margins of the trough do not correlate with contoured values of increased tectonic subsidence and we infer that the trough was a palaeogeographic embayment in a large carbonate platform that developed in a broad, ramp‐like area of slow and low subsidence tilting down to the proto‐Tethyan ocean located to the NW of the basin.

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

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

Pizzi M, Lonergan L, Whittaker AC, Mayall Met 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

Journal article

Galindo PA, Lonergan L, 2020, Basin evolution and shale tectonics on an obliquely convergent margin: the Bahia Basin, offshore Colombian Caribbean, Tectonics, Vol: 39, Pages: 1-32, ISSN: 0278-7407

Oblique convergent margins accumulate strike‐slip deformation that controls basin formation and evolution. The Bahia Basin is located offshore, proximal to major strike‐slip fault systems that affect northern Colombia. It lies behind the toe of the modern accretionary prism, where the Caribbean Plate is being subducted obliquely beneath South America. This is the first attempt using 3D seismic reflection data to interpret a complex strike‐slip basin at the western end of the southern margin of the Caribbean Plate. Detailed 2D and 3D seismic mapping of regional unconformities and faults is used to describe the structural geometry, timing and evolution of extensional and strike‐slip faults which controlled the formation of the basin. Analysis of the fault zones is coupled with a description of the seismic‐stratigraphic units observed within the Bahia Basin to reconstruct the spatial and temporal evolution of deformation, and to evaluate the influence of the pervasive shale tectonics observed in the area. The results, presented as a series of structural‐paleogeographic maps, illustrate an initial stage of transtension that controlled the formation of shale‐withdrawal minibasins from late Oligocene to late Miocene times. The continuous deformation and northward expulsion of the Santa Marta Massif resulted in transpression during Pliocene times, leading to basin inversion and ultimate closure of the basin. Basin evolution along the southern Caribbean oblique, convergent margin, shows the occurrence of a complex interaction between subduction and major‐onshore strike‐slip fault systems, and illustrates how strain‐partitioning led to the break‐up and lateral displacement of early accretionary prisms formed along the margin.

Journal article

McDermott C, Collier JS, Lonergan L, Fruehn J, Bellingham Pet al., 2019, Seismic velocity structure of seaward-dipping reflectors on the South American continental margin, Earth and Planetary Science Letters, Vol: 521, Pages: 14-24, ISSN: 0012-821X

Seaward dipping reflectors (SDRs) are a key feature within the continent to ocean transition zone of volcanic passive margins. Here we conduct an automated pre-stack depth-migration imaging analysis of commercial seismic data from the volcanic margins of South America. The method used an isotropic, ray-based approach of iterative velocity model building based on the travel time inversion of residual pre-stack depth migration move-out. We find two distinct seismic velocity patterns within the SDRs. While both types show a general increase in velocity with depth consistent with expected compaction and alteration/metamorphic trends, those SDRs that lie within faulted half grabens also have high velocity zones at their down-dip ends. The velocity anomalies are generally concordant with the reflectivity and so we attribute them to the presence of dolerite sills that were injected into the lava pile. The sills therefore result from late-stage melt delivery along the large landward-dipping faults that bound them. In contrast the more outboard SDRs show no velocity anomalies, are more uniform spatially and have unfaulted basal contacts. Our observations imply that the SDRs document a major change in rift architecture, with magmatism linked with early extension and faulting of the upper brittle crust transitioning into more organised, dike-fed eruptions similar to seafloor spreading.

Journal article

Lonergan L, Collier J, McDermott C, Fruehen J, Bellingham Pet al., 2019, Seismic velocity structure of two types of seaward-dipping reflectors on the South American continental margin

© 81st EAGE Conference and Exhibition 2019. All rights reserved. Seaward dipping reflectors (SDRs) are a key feature within the continent-to-ocean transition zone of volcanic passive margins. They are formed by volcanic activity during continental breakup. Along the volcanic margins of South America, we have mapped and documented two distinct types of SDR: Type I that are relatively straight and lie within faulted half-grabens that are partially overlain by Type II that are more curved and have unfaulted basal contacts. Here we conduct an automated, pre-stack, depth-migration imaging analysis on commercial seismic data to determine more about their physical properties. We find that the two SDR classes have distinct seismic velocity characteristics. While both types show a general increase in velocity with depth consistent with expected compaction and alteration/metamorphic trends, the Type I SDRs also have high velocity zones at their down-dip ends. We attribute these elevated velocities to the presence of less porous and/or more mafic rocks. We interpret them as the remnants of volcanic feeder systems along the large landward-dipping faults that bound these SDRs. Our observations imply that the SDRs document a major change in rift architecture, with magmatism linked with early tectonic stretching of the upper brittle crust transitioning into dike-fed eruptions similar to seafloor spreading.

Conference paper

Graham R, Brooke-Barnett S, Csicsek A, Lonergan L, Cellini N, Callot J, Ringenbach Jet al., 2019, Allochthonous salt in the fold and thrust belt of Haute Provence, S.W.Alps

Detailed work in the Provencal sub-Alpine chains shows that salt extrusion can be deduced from the presence of a number of overturned flaps ('megaflaps')which are not internally deformed but show reducedstratigraphic section and commonly contain pinch-outs and unconformities. This has been described before in one Provencal locality (Barles, Graham et al 2012) but here we document it additionally at Chasteuil near Castellane and Gevaudan near Barreme. The one-time glaciers produced by salt extrusion are now welded out. Mostly it is difficult to investigate the details of this process, but in the vicinity of the major transcurrent fault that bisects the arcuate fold belt of Provence we propose that evacuation involved lateral salt migration analagous to that of the Roho systems of the Gulf of Mexico, leaving an Eocene secondary minibasin in its wake. We believe that this may be the first description of such a structure in the Alps. It emphasizes that salt movement accompanied all the major tectonic episodes which occurred in the region, in both the Mesozoic passive margin and the Alpine foreland basin which succeeded it.

Conference paper

Lonergan L, Pizzi M, Doughty-Jones G, Mayall M, Whittaker ACet al., 2019, Structural growth rate and impact on deep-water depositional systems in deep-water fold belts

Examples of slope channels being diverted/deflected by growth folds, salt walls or thrusts are found at the modern seabed and in the subsurface in deep-water fold and thrust belts. We have quantified the shortening rate of thrust-related folds, salt-cored anticlines and faulted salt-detachment folds in three areas (Gulf of Mexico, Lower Congo Basin and Niger Delta), with the aim of investigating whether there are any predictive relationships between structural parameters such as structural relief, growth rate versus sediment accumulation rate, and depositional patterns. Shortening rates in the Niger Delta and t the Gulf of Mexico are comparable. The maxima recorded for the West African salt strutures are lower. However we note that the Pleistocene to Recent channels in the Niger Delta, and the buried Miocene channels in West Africa, are diverted and deflected. by growth rates as low as 30-50 m/Ma. In general, during periods of higher growth, channels are forced to deflect or divert around growing structures. Channels that have established a route through a fold or salt wall can continue to exploit that route down slope as long as the turbidity flows continue to have enough erosive power to keep pace with the growth of the structure.

Conference paper

Lonergan L, Collier J, McDermott C, Fruehen J, Bellingham Pet al., 2019, Seismic velocity structure of two types of seaward-dipping reflectors on the South American continental margin

Seaward dipping reflectors (SDRs) are a key feature within the continent-to-ocean transition zone of volcanic passive margins. They are formed by volcanic activity during continental breakup. Along the volcanic margins of South America, we have mapped and documented two distinct types of SDR: Type I that are relatively straight and lie within faulted half-grabens that are partially overlain by Type II that are more curved and have unfaulted basal contacts. Here we conduct an automated, pre-stack, depth-migration imaging analysis on commercial seismic data to determine more about their physical properties. We find that the two SDR classes have distinct seismic velocity characteristics. While both types show a general increase in velocity with depth consistent with expected compaction and alteration/metamorphic trends, the Type I SDRs also have high velocity zones at their down-dip ends. We attribute these elevated velocities to the presence of less porous and/or more mafic rocks. We interpret them as the remnants of volcanic feeder systems along the large landward-dipping faults that bound these SDRs. Our observations imply that the SDRs document a major change in rift architecture, with magmatism linked with early tectonic stretching of the upper brittle crust transitioning into dike-fed eruptions similar to seafloor spreading.

Conference paper

Lonergan L, Pizzi M, Doughty-Jones G, Mayall M, Whittaker ACet al., 2019, Structural growth rate and impact on deep-water depositional systems in deep-water fold belts

© 81st EAGE Conference and Exhibition 2019. All rights reserved. Examples of slope channels being diverted/deflected by growth folds, salt walls or thrusts are found at the modern seabed and in the subsurface in deep-water fold and thrust belts. We have quantified the shortening rate of thrust-related folds, salt-cored anticlines and faulted salt-detachment folds in three areas (Gulf of Mexico, Lower Congo Basin and Niger Delta), with the aim of investigating whether there are any predictive relationships between structural parameters such as structural relief, growth rate versus sediment accumulation rate, and depositional patterns. Shortening rates in the Niger Delta and t the Gulf of Mexico are comparable. The maxima recorded for the West African salt strutures are lower. However we note that the Pleistocene to Recent channels in the Niger Delta, and the buried Miocene channels in West Africa, are diverted and deflected. by growth rates as low as 30-50 m/Ma. In general, during periods of higher growth, channels are forced to deflect or divert around growing structures. Channels that have established a route through a fold or salt wall can continue to exploit that route down slope as long as the turbidity flows continue to have enough erosive power to keep pace with the growth of the structure.

Conference paper

Lonergan L, Collier J, McDermott C, Fruehen J, Bellingham Pet al., 2019, Seismic velocity structure of two types of seaward-dipping reflectors on the South American continental margin

© 81st EAGE Conference and Exhibition 2019. All rights reserved. Seaward dipping reflectors (SDRs) are a key feature within the continent-to-ocean transition zone of volcanic passive margins. They are formed by volcanic activity during continental breakup. Along the volcanic margins of South America, we have mapped and documented two distinct types of SDR: Type I that are relatively straight and lie within faulted half-grabens that are partially overlain by Type II that are more curved and have unfaulted basal contacts. Here we conduct an automated, pre-stack, depth-migration imaging analysis on commercial seismic data to determine more about their physical properties. We find that the two SDR classes have distinct seismic velocity characteristics. While both types show a general increase in velocity with depth consistent with expected compaction and alteration/metamorphic trends, the Type I SDRs also have high velocity zones at their down-dip ends. We attribute these elevated velocities to the presence of less porous and/or more mafic rocks. We interpret them as the remnants of volcanic feeder systems along the large landward-dipping faults that bound these SDRs. Our observations imply that the SDRs document a major change in rift architecture, with magmatism linked with early tectonic stretching of the upper brittle crust transitioning into dike-fed eruptions similar to seafloor spreading.

Conference paper

Graham R, Brooke-Barnett S, Csicsek A, Lonergan L, Cellini N, Callot J, Ringenbach Jet al., 2019, Allochthonous salt in the fold and thrust belt of Haute Provence, S.W.Alps

© 81st EAGE Conference and Exhibition 2019. All rights reserved. Detailed work in the Provencal sub-Alpine chains shows that salt extrusion can be deduced from the presence of a number of overturned flaps ('megaflaps')which are not internally deformed but show reducedstratigraphic section and commonly contain pinch-outs and unconformities. This has been described before in one Provencal locality (Barles, Graham et al 2012) but here we document it additionally at Chasteuil near Castellane and Gevaudan near Barreme. The one-time glaciers produced by salt extrusion are now welded out. Mostly it is difficult to investigate the details of this process, but in the vicinity of the major transcurrent fault that bisects the arcuate fold belt of Provence we propose that evacuation involved lateral salt migration analagous to that of the Roho systems of the Gulf of Mexico, leaving an Eocene secondary minibasin in its wake. We believe that this may be the first description of such a structure in the Alps. It emphasizes that salt movement accompanied all the major tectonic episodes which occurred in the region, in both the Mesozoic passive margin and the Alpine foreland basin which succeeded it.

Conference paper

Graham R, Brooke-Barnett S, Csicsek A, Lonergan L, Cellini N, Callot J, Ringenbach Jet al., 2019, Allochthonous salt in the fold and thrust belt of Haute Provence, S.W.Alps

© 81st EAGE Conference and Exhibition 2019. All rights reserved. Detailed work in the Provencal sub-Alpine chains shows that salt extrusion can be deduced from the presence of a number of overturned flaps ('megaflaps')which are not internally deformed but show reducedstratigraphic section and commonly contain pinch-outs and unconformities. This has been described before in one Provencal locality (Barles, Graham et al 2012) but here we document it additionally at Chasteuil near Castellane and Gevaudan near Barreme. The one-time glaciers produced by salt extrusion are now welded out. Mostly it is difficult to investigate the details of this process, but in the vicinity of the major transcurrent fault that bisects the arcuate fold belt of Provence we propose that evacuation involved lateral salt migration analagous to that of the Roho systems of the Gulf of Mexico, leaving an Eocene secondary minibasin in its wake. We believe that this may be the first description of such a structure in the Alps. It emphasizes that salt movement accompanied all the major tectonic episodes which occurred in the region, in both the Mesozoic passive margin and the Alpine foreland basin which succeeded it.

Conference paper

Lonergan L, Pizzi M, Doughty-Jones G, Mayall M, Whittaker ACet al., 2019, Structural growth rate and impact on deep-water depositional systems in deep-water fold belts

© 81st EAGE Conference and Exhibition 2019. All rights reserved. Examples of slope channels being diverted/deflected by growth folds, salt walls or thrusts are found at the modern seabed and in the subsurface in deep-water fold and thrust belts. We have quantified the shortening rate of thrust-related folds, salt-cored anticlines and faulted salt-detachment folds in three areas (Gulf of Mexico, Lower Congo Basin and Niger Delta), with the aim of investigating whether there are any predictive relationships between structural parameters such as structural relief, growth rate versus sediment accumulation rate, and depositional patterns. Shortening rates in the Niger Delta and t the Gulf of Mexico are comparable. The maxima recorded for the West African salt strutures are lower. However we note that the Pleistocene to Recent channels in the Niger Delta, and the buried Miocene channels in West Africa, are diverted and deflected. by growth rates as low as 30-50 m/Ma. In general, during periods of higher growth, channels are forced to deflect or divert around growing structures. Channels that have established a route through a fold or salt wall can continue to exploit that route down slope as long as the turbidity flows continue to have enough erosive power to keep pace with the growth of the structure.

Conference paper

Doughty-Jones G, Lonergan L, Mayall M, Dee Set al., 2019, The role of structural growth in controlling the facies and distribution of mass transport deposits in a deep-water salt minibasin, Marine and Petroleum Geology, Vol: 104, Pages: 106-124, ISSN: 0264-8172

We distinguish two types of mass-transport deposits (MTDs) within a salt-related slope minbasin. The locally-derived MTDs are sourced from growing structures bounding the minbasin, and the more extensive, regional, MTDs are sourced from the shelf of the continental margin, at least 100 km east of the study area. The two types of MTDs have different internal characteristics, distribution within the basin and depositional mechanisms. Using a high-resolution 3D seismic dataset we characterise the internal structures and dimensions of the MTDs, and also quantify the deformation history of the salt structures. Through these analyses we demonstrate that the ‘local’ and ‘regional’ MTDs react in different ways to growth on the structures within, and bounding, the slope minbasin.The regionally derived MTDs are debris flows, with individual deposits up to 300 m thick and covering an area of up to 1300 km2 within the minbasin. Seismic facies analysis suggests they are mostly composed of chaotic material but in some places contain discrete blocks of sediment ranging from 50 m to 250 m in length. In contrast, the more locally derived MTDs are submarine slides consisting of translated material from the flanks of salt structures. Each slide has an up-dip extensional domain with normal faults and a down-dip contractional domain with thrusts and folds. They cover areas between 11 and 28 km2 with frontal and lateral ramps up to 200 m high. Relict topography on the top surface of the MTDs is infilled with younger sediment.Shortening analysis of the intra-slope salt structures within and bounding the minbasin is used as a proxy for the growth rate of the structures. This novel approach of combining shortening with the detailed observations of the local and regional MTDs has allowed us to draw new conclusions on the relationship between structural growth and MTD initiation. Local MTDs either form during periods of high structural growth (10–30 m/ma) or in a

Journal article

McDermott C, Lonergan L, Collier JS, McDermott KG, Bellingham Pet al., 2018, Characterization of seaward-dipping reflectors along the South American Atlantic Margin and implications for continental breakup, Tectonics, Vol: 37, Pages: 3303-3327, ISSN: 0278-7407

Thick packages of lavas forming seaward‐dipping reflectors (SDRs) are diagnostic features of volcanic passive margins. Despite their significance to continental breakup studies, their formation mechanism is still debated. We use ~22,000 km of high‐quality, depth‐migrated, seismic data to document the three‐dimensional geometry of SDRs offshore South America. We find two types: Type I are planar and occur as fault‐bounded wedges. Type II are characterized by reflections that become more convex‐upward in the downdip direction and terminate against a subhorizontal base. We interpret the transition from Type I to Type II SDRs to represent a continuum from continental rifting to full plate separation with formation of new, subaerially generated, magmatic crust. Type I SDRs formed in half grabens during the stretching of continental crust, while Type II lavas infill the space produced by flexing of the crust due to the solidification of the underlying feeder dikes as the magmatic crust moved away from the spreading center. Type II SDRs vary in length and thickness along the margin. In the north, close to the Paraná flood basalts, they are long (tens of kilometers), reach thicknesses of up to 15 km, and have an across margin width of up to 600 km. To the south the Type II SDRs are thinner with lava lengths of <10 km. We propose that Type II lavas in the north erupted from a subaerial, plate spreading center above the Tristan mantle plume and that the shorter lava flows to the south indicates eruption into water, consistent with a cooler, off‐plume mantle.

Journal article

Martinez-Garcia P, Comas M, Lonergan L, Watts ABet al., 2018, From extension to shortening: tectonic inversion distributed in time and space in the Alboran Sea, Western Mediterranean, Tectonics, Vol: 36, Pages: 2777-2805, ISSN: 0278-7407

2D seismic reflection data tied to biostratigraphical and log information from wells in the central and southeastern Alboran Sea have allowed us to constrain the spatial and temporal distribution of rifting and inversion. Normal faults, tilted basement blocks, and growth wedges reveal a thinned continental crust that formed in response to NW‐SE extension. To the east, a secondary SW‐NE trend of extension affects the transitional crust adjacent to the oceanic Algerian Basin. The maximum thickness of syn‐rift sediments is ~3.5 km, and the oldest recorded deposits are Serravallian. The WNW‐ESE Yusuf fault formed a buttress separating and accommodating variable extension between two different tectonic domains: the thinned continental crust of Alboran and the oceanic spreading of the Algerian Basin. Late Tortonian to present‐day NW‐SE Africa/Eurasia plate convergence drove shortening and reactivation of some of the earlier extensional structures as reverse and strike‐slip faults, forming complex, compartmentalised subbasins. Tectonic inversion coexisted with the formation of new faults and folds. Inversion was partial along the Habibas Basin and Al‐Idrisi fault, but complete along the Alboran Ridge, where some SW‐NE trending faults were perpendicular to the recent NW‐SE plate convergence and were reactivated as thrusts. The WNW‐ESE Yusuf fault is oblique to the convergence vector, and therefore, reactivation is mainly expressed as transpressional deformation. Volcanic rocks intruded along the Alboran Ridge and Yusuf faults during the latest stages of extension formed rheological anisotropies that localised the later inversion.

Journal article

Wang X, Lei Q, Lonergan L, Jourde H, Gosselin O, Cosgrove Jet al., 2017, Heterogeneous fluid flow in fractured layered carbonates and its implication for generation of incipient karst, Advances in Water Resources, Vol: 107, Pages: 502-516, ISSN: 1872-9657

We use numerical models to investigate fluid flow in layered fractured carbonate rocks, and specifically to investigate the effects of the structural and hydraulic properties of both joints and bedding planes on flow localization. Synthetic fracture networks made up of two jointed layers separated by a horizontal bedding plane are generated to represent the typical layered fracture systems often formed in carbonate rocks. A uniform aperture field is assumed for each joint set and for the bedding plane, but different joint sets and the bedding plane can have non-identical values. The aperture ratio of the joint sets to the bedding plane is found to dominate the behaviour of flow heterogeneity on the bedding plane. Three distinct flow regimes, i.e. joint-dominated, transitional and bedding plane-dominated, are recognized. The magnitude of the aperture ratio controls which flow regime develops. We further suggest that the different flow regimes may be responsible for the initiation of different types of incipient karst morphologies observed in nature: pipe karst, stripe karst and sheet karst.

Journal article

Jolly BA, Whittaker AC, Lonergan L, 2017, Quantifying the geomorphic response of modern submarine channels to actively growing folds and thrusts, deep-water Niger Delta, Geological Society of America Bulletin, Vol: 129, Pages: 1123-1139, ISSN: 1943-2674

The interaction between submarine channels and active seabed deformation controls sediment delivery to the deep sea. Here, we combined seismic and geomorphic techniques to investigate quantitatively how the gravity-driven growth of thrust-related folds in the deep-water Niger Delta has influenced the morphology of four Pleistocene to Holocene submarine channels with present-day geomorphic expression. We extracted the bathymetric long profile of each of these modern seabed channel systems, and we evaluated the down-system evolution of channel widths, depths, and slopes as they have interacted with growing seabed structures. This information was used to derive estimates of bed shear stresses and velocities, to infer morphodynamic processes that have sculpted the channel systems through time, and to evaluate how these channels have responded to actively growing structures in the toe of the delta.The long profiles of these channels are relatively linear, with concavity from −0.08 to −0.34, and an average gradient of ∼1°. They are characterized by small knickpoints that are apparent near mapped structures and therefore implicitly reflect variations in substrate uplift rate. Channel incised depths increase significantly near the active structures, leading to entrenchment, but there is little change in the down-system distribution of channel width, in contrast to rivers crossing active faults, or buried submarine channel complexes. Reconstructed bed shear stresses near faults are estimated to lie in the range of 100−200 Pa, which would be associated with turbidite flow velocities of 2−4 m/s. A comparison of the magnitude and distribution of structural uplift since 1.7 Ma and the distribution of channel incision over this time shows that three of these channels have been able to keep pace with the time-integrated uplift since 1.7 Ma and have likely reached a local topographic steady state. Entrenchment of the submarine channels upstream of gr

Journal article

Freitag UA, Sanderson DJ, Lonergan L, Bevan TGet al., 2017, Comparison of upwards splaying and upwards merging in segmented normal growth faults, Journal of Structural Geology, Vol: 100, Pages: 1-11, ISSN: 1873-1201

A common model for normal fault growth involves a single fault at depth splaying upwards into a series of en-echelon segments. This model is applied to faults as well as a range of extension fractures, including veins, joints and igneous dykes. Examples of splaying growth fault systems in the Columbus Basin, offshore Trinidad, are presented. They include the commonly described upwards splaying type, but also one fault zone with an upward change from disconnected overlapping synthetic faults to a continuous fault. One fault zone with high-displacement fault segments is separated by a relay ramp at depth, becomes breached higher up, developing into a continuous fault at its upper part, where displacements are least. This example suggests that whilst kinematic linkage typically precedes geometric linkage in the evolution of relay ramps, low-displacement parts of a fault system may be geometrically linked whereas higher displacement areas are only kinematically linked.

Journal article

Doughty-Jones G, Mayall M, Lonergan L, 2017, Stratigraphy, facies and evolution of deep-water lobe complexes within a salt-controlled intra-slope mini-basin, AAPG Bulletin, Vol: 101, Pages: 1879-1904, ISSN: 0149-1423

A succession of four deep-water lobe complexes deposited within a salt-controlled minibasin have been imaged in unprecedented detail on high resolution, high frequency 3D seismic reflection data. The ponded interval was deposited over approximately 2.7 m.y. and consists of four discrete sequences, each of which contains one lobe complex. There is a systematic change in the shape and orientation of the lobe complexes through time: the two older lobe complexes are oriented broadly north-south and are up to 10 km (6.2 mi) long by 5 km (3.1 mi) wide, whereas the youngest lobe complexes are oriented southeast-northwest and have a rounder shape (9 km (5.6 mi) long by 8 km (5 mi) wide). The north to south migration of the feeder channel entry point and the change in lobe complex orientation is attributed to growth of the basin-bounding salt structures. Each lobe complex is composed of a feeder channel, multiple individual lobes formed of a trunk channel and a diverging network of smaller distributary channels, commonly fringed by a high amplitude band. The lobes are on average 1.6 km (1 mi) long by 1.3 km (0.8 mi) wide and are fed by trunk channels that range from 60 m (197 ft) to 200 m (656 ft) wide, with thicknesses up to 15 m (49 ft). Variation in lobe shape and spatial location is driven by the response of the lobes to topographic growth along the edge of the basin and as well as inherited seabed relief generated by previous lobe growth. In areas where lobe development is constrained by structural growth along the edge of the basin the lobes become elongated and divert away from the growing topography. Lobe complexes of similar scales have been described in detail in outcrops and in unconfined settings on the seafloor but this is the first study to describe these systems in such detail in the subsurface, resolving the individual lobes and lobe elem

Journal article

Lonergan L, Jolly BA, Whittaker A, 2016, Growth history of fault-related folds and interaction with seabed channels in the toe-thrust region of the deep-water Niger delta, Marine and Petroleum Geology, Vol: 70, Pages: 58-76, ISSN: 0264-8172

The deep-water fold and thrust belt of the southern Niger Delta has prominent thrusts and folds oriented perpendicular to the regional slope that formed as a result of the thin-skinned gravitational collapse of the delta above overpressured shale. The thrust-related folds have grown in the last 12.8 Ma and many of the thrusts are still actively growing and influencing the pathways of modern seabed channels. We use 3D seismic reflection data to constrain and analyse the spatial and temporal variation in shortening of four thrusts and folds having seabed relief in a study area of 2600 km2 size in 2200–3800 m water depth. Using these shortening measurements, we have quantified the variation in strain rates through time for both fault-propagation and detachment folds in the area, and we relate this to submarine channel response. The total amount of shortening on the individual structures investigated ranges from 1 to 4 km, giving a time-averaged maximum shortening rate of between 90 ± 10 and 350 ± 50 m/Myr (0.1 and 0.4 mm/yr). Fold shortening varies both spatially and temporally: The maximum interval shortening rate occurred between 9.5 Ma and 3.7 Ma, and has reduced significantly in the last 3.7 Ma. We suggest that the reduction in the Pliocene-Recent fold shortening rate is a response to the slow-down in extension observed in the up-dip extensional domain of the Niger Delta gravitational system in the same time interval. In the area dominated by the fault-propagation folds, the channels are able to cross the structures, but the detachment fold is a more significant barrier and has caused a channel to divert for 25 km parallel to the fold axis. The two sets of structures have positive bathymetric expressions, with an associated present day uphill slope of between 1.5° and 2°. However, the shorter uphill slopes of the fault-propagation folds and increased sediment blanketing allow channels to cross these structures. Channels that develop coev

Journal article

Wang X, Jardani A, Jourde H, Lonergan L, Cosgrove J, Gosselin O, Massonnat Get al., 2015, Characterisation of the transmissivity field of a fractured and karstic aquifer, Southern France, Advances in Water Resources, Vol: 87, Pages: 106-121, ISSN: 1872-9657

Geological and hydrological data collected at the Terrieu experimental site north of Montpellier, in a confined carbonate aquifer indicates that both fracture clusters and a major bedding plane form the main flow paths of this highly heterogeneous karst aquifer. However, characterising the geometry and spatial location of the main flow channels and estimating their flow properties remain difficult. These challenges can be addressed by solving an inverse problem using the available hydraulic head data recorded during a set of interference pumping tests.We first constructed a 2D equivalent porous medium model to represent the test site domain and then employed regular zoning parameterisation, on which the inverse modelling was performed. Because we aim to resolve the fine-scale characteristics of the transmissivity field, the problem undertaken is essentially a large-scale inverse model, i.e. the dimension of the unknown parameters is high. In order to deal with the high computational demands in such a large-scale inverse problem, a gradient-based, non-linear algorithm (SNOPT) was used to estimate the transmissivity field on the experimental site scale through the inversion of steady-state, hydraulic head measurements recorded at 22 boreholes during 8 sequential cross-hole pumping tests. We used the data from outcrops, borehole fracture measurements and interpretations of inter-well connectivities from interference test responses as initial models to trigger the inversion. Constraints for hydraulic conductivities, based on analytical interpretations of pumping tests, were also added to the inversion models. In addition, the efficiency of the adopted inverse algorithm enables us to increase dramatically the number of unknown parameters to investigate the influence of elementary discretisation on the reconstruction of the transmissivity fields in both synthetic and field studies.By following the above approach, transmissivity fields that produce similar hydrodynamic beh

Journal article

Borgomeo E, Hebditch KV, Whittaker AC, Lonergan Let al., 2014, Characterising the spatial distribution, frequency and geomorphic controls on landslide occurrence, Molise, Italy, Geomorphology, Vol: 226, Pages: 148-161

Journal article

Santos-Betancor I, Soto JI, Lonergan L, Sanchez-Borrego I, Macellari Cet al., 2014, 3D Geometry of an Active Shale-Cored Anticline in the Western South Caspian Basin, MATHEMATICS OF PLANET EARTH, Pages: 771-774, ISSN: 2193-8571

Journal article

Santos-Betancor I, Ignacio Soto J, Lonergan L, Macellari Cet al., 2014, Gravity-Instabilities Processes and Mass-Transport Complexes During Folding: The Case of a Shale-Cored Anticline in the Western South Caspian Basin, MATHEMATICS OF PLANET EARTH, Pages: 775-778, ISSN: 2193-8571

Journal article

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