- National Oceanography Centre
European Way
Southampton
SO14 3ZH
- I am a marine sedimentologist at the NOC. Before embarking on PhD studies, I completed a BSc in Geology and MSc in P... moreI am a marine sedimentologist at the NOC. Before embarking on PhD studies, I completed a BSc in Geology and MSc in Petroleum Geoscience, specialising in terrestrial and shallow marine reservoir sedimentology. In 2008, I completed the journey from hinterland to abyssal plain by starting a PhD in turbidite sedimentology and geochemistry at the NOC. On completion of my PhD I have continued at the NOC as a PDRA and project manager of the £2.2Million LANDSLIDE-TSUNAMI project funded by the NERC Arctic Research Programme.edit
Volcanic island inception applies large stresses as the ocean crust domes in response to magma ascension and is loaded by eruption of lavas. There is currently limited information on when volcanic islands are initiated on the seafloor,... more
Volcanic island inception applies large stresses as the ocean crust domes in response to magma ascension and is loaded by eruption of lavas. There is currently limited information on when volcanic islands are initiated on the seafloor, and no information regarding the seafloor instabilities island inception may cause. The deep sea Madeira Abyssal Plain contains a 43 million year history of turbidites among which many originate from mass movements in the Canary Islands. Here, we investigate the composition and timing of a distinctive group of turbidites that we suggest represent a new unique record of large-volume submarine landslides triggered during the inception, submarine shield growth, and final subaerial emergence of the Canary Islands. These slides are predominantly multi-stage and yet represent among the largest mass movements on the Earth's surface up to three or more-times larger than subaerial Canary Islands flank collapses. Thus whilst these deposits provide invaluable information on ocean island geodynamics they also represent a significant, and as yet unaccounted, marine geohazard.
The Agadir Basin is a mixed siliciclasticvolcaniclastic deepwater turbidite system derived from several sedimentary sources. Estimating the influence of these sources requires detailed geochemical profiles of sediment cores. This is... more
The Agadir Basin is a mixed siliciclasticvolcaniclastic deepwater turbidite system derived from several sedimentary sources. Estimating the influence of these sources requires detailed geochemical profiles of sediment cores. This is achieved using an ITRAX µXRF core scanner that normally produces elemental profiles in units of counts or count rate. Improved insights are achieved if the ITRAX data are calibrated to produce concentration data. Turbidite geochemistry can then be used to more reliably infer the sources of flows and identify primary sediment sources, which are the Moroccan slope for siliciclastic beds and the western Canary Islands for volcaniclastic turbidites. Crossplots of the geochemical data discrimi nate variations between different siliciclastic and volcaniclastic beds. For example, differences between two distinctive volcaniclastic marker beds, named A2 and A14, reflect differences in their respective Canary Island sources and indicate a primi tive basaltic source for bed A2 and an evolved source for bed A14. Compositional variations between siliciclastic deposits reflect potential variations in the sediment source that failed or the location of the failure on the Moroccan continental slope. Keywords Turbidite · Sediment provenance · Agadir Basin · ITRAX · Submarine Landslides
Generation of tsunamis from submarine landslides is sensitive to several parameters such as their volume, failure mechanism and location of failure relative to sea level. These conditions are often difficult to resolve for past events.... more
Generation of tsunamis from submarine landslides is sensitive to several parameters such as their volume, failure mechanism and location of failure relative to sea level. These conditions are often difficult to resolve for past events. However, previous studies of turbidites generated from landslides offer insight into the tim ing, total event volume and failure mechanism. This study confirms the ~ 165 ka Icod landslide originating from the northern flank of Tenerife as a retrogressive multistage landslide. It also shows that the latest volcanic flank collapse from the Canary Islands, the ~ 15 ka El Golfo landslide, is a retrogressive multistage failure. These inferences are developed using high resolution Itrax μXRF bulk geochemis try to better identify and correlate these subunits in a number of core examples of the Icod (seven subunits) and El Golfo (five subunits) event beds. Subunit varia tions identified through Itrax studies also allow examination of bulk intrasubunit geochemical heterogeneities. These heterogeneities reflect discrete landslides from a single source. A systematic decrease in calcium composition (proxy for carbon ate) suggests initial submarine collapses that retrogressively fail the flank leading to an increasing component from subaerial collapses. However, both grain size and density sorting influence bulk geochemical compositions. The geochemistry of vol canic glasses (determined from Eagle III μXRF analyses) from the subunits of the Icod and El Golfo event beds from Agadir Basin demonstrate that these subunits represent discrete separate failures.
Deciphering the signal within Xray fluorescence (XRF) core scanner data can be complex in comparison to conventional laboratory XRF analysis where samples are milled and pelleted or beaded. One complicating factor is that the downcore... more
Deciphering the signal within Xray fluorescence (XRF) core scanner data can be complex in comparison to conventional laboratory XRF analysis where samples are milled and pelleted or beaded. One complicating factor is that the downcore variability in water content and grainsize can affect element count rates thereby potentially leading to inaccurate interpretations. Experiences using an Itrax XRF core scanner data highlight some of the pitfalls that can occur when the sedi ment is inhomogeneous. We show that over a threshold of 25 wt.% coarse grained material (> 63 µm) within the sediment there is a potential for causing significant variability in certain elements. It is also shown that water content variability has a major effect above 40 %.
Older sequence stratigraphic models suggested that submarine and slide and turbidite activities are greatest during sea-level lowstands. However, growing evidence indicates that many turbidite systems are also active during sea-level... more
Older sequence stratigraphic models suggested that submarine and slide and turbidite activities are greatest during sea-level lowstands. However, growing evidence indicates that many turbidite systems are also active during sea-level transgressions and highstands. The Moroccan Turbidite Systemcomprises three depocentres, of which Agadir Basin is closest to the Moroccan slope and Canary archipelago. The very large volumes of sediment transported by individual sediment flows in this system suggest that they are triggered by landslides. Extensive core coverage and dating control for the Agadir Basin deposits have provided an excellent opportunity to derive accurate records of turbidite (and associated landslide) frequency for the last 600 ka. Previous studies in the more distal Madeira Abyssal Plain depocentre have indicated that large volume (N50 km3) turbidites occurred
at oxygen isotope stage (OIS) boundaries. This study of Agadir Basin confirms that two major turbidites (beds A5 and A12) occurred during glacial–interglacial transitions associated with OIS4 and OIS6. However, this association is based on just two examples, and two other large-volume turbidites (beds A7 and A11), did not occur at a stage boundary. The main conclusion of this study is that 90% of turbidites and landslides occurred during rising
and high sea level, which represents 40% of the total time during the last 600 ka. Only 10% of the turbidites and
landslides occurred during glacials (40% of the time), with a paucity of turbidites and landslides at peak glacial
lowstands. A comparison to sediment accumulation rates in the source area of the turbidite suggests that landslides
did not occur preferentially during periods of more rapid sedimentation rate, although sedimentation
rates in this area only varied from 4 to 6 g cm−2 ka−1.
at oxygen isotope stage (OIS) boundaries. This study of Agadir Basin confirms that two major turbidites (beds A5 and A12) occurred during glacial–interglacial transitions associated with OIS4 and OIS6. However, this association is based on just two examples, and two other large-volume turbidites (beds A7 and A11), did not occur at a stage boundary. The main conclusion of this study is that 90% of turbidites and landslides occurred during rising
and high sea level, which represents 40% of the total time during the last 600 ka. Only 10% of the turbidites and
landslides occurred during glacials (40% of the time), with a paucity of turbidites and landslides at peak glacial
lowstands. A comparison to sediment accumulation rates in the source area of the turbidite suggests that landslides
did not occur preferentially during periods of more rapid sedimentation rate, although sedimentation
rates in this area only varied from 4 to 6 g cm−2 ka−1.
Research Interests:
Volcaniclastic turbidites in the Madeira Abyssal Plain provide a record of major landslides from the Western Canary Islands in the last 1.5 Ma. These volcaniclastic turbidites are composed of multiple fining-upwards turbidite sands, known... more
Volcaniclastic turbidites in the Madeira Abyssal Plain provide a record of major landslides from the Western Canary Islands in the last 1.5 Ma. These volcaniclastic turbidites are composed of multiple fining-upwards turbidite sands, known as subunits. The subunits indicate that the landslides responsible for the sediment gravity flows occurred in multiple stages. The subunits cannot result from flow reflection or splitting because the compositions of volcanic glasses from each individual subunit in an event bed are subtly different. This indicates that each subunit represents a discrete failure as part of a multistage landslide. This has significant implications for geohazard assessments, as multistage failures reduce the magnitude of the associated tsunami. The multistage failure mechanism reduces individual landslide volumes from up to 350 km3 to less than 100 km3. Thus although multistage failure ultimately reduce the potential landslide and tsunami threat, the landslide events may still generate significant tsunamis close to source.
Research Interests:
During the last two decades numerous studies have focused on resolving the landslide histories of the Canary Islands. Issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate... more
During the last two decades numerous studies have focused on resolving the landslide histories of the Canary Islands. Issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages. However, submarine landslides often disaggregate and generate sediment gravity flows. Volcaniclastic turbidites sampled from Madeira Abyssal Plain piston cores represent a record of eight large-volume failures from the Western Canary Islands in the last 1.5 Ma. During this time there is a mean recurrence rate of 200 ka, while the islands of El Hierro and Tenerife have individual landslide recurrences of 500 ka and 330 ka, respectively. Deposits from the 15 ka El Golfo landslide from El Hierro and 165 ka Icod landslide from Tenerife are examined. This study also identifies potential deposits associated with the Orotava (535 ka), Güímar (850 ka) and Rogues de García landslides (1.2 Ma) from Tenerife, El Julan (540 ka) and El Tiñor (1.05 Ma) landslides from El Hierro, and the Cumbre Nueva landslide (485 ka) from La Palma. Seven of eight landslides occurred during major deglaciations or subsequent interglacial periods, which represent 55% of the time. However, all of the studied landslides occur during or at the end of periods of protracted island volcanism, which generally represent 60% of the island histories. Although climate may precondition failures, it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for Canary Island landslides.
Research Interests:
Turbidity currents are an important process for transporting sediment from the continental shelf to the deep ocean. Submarine channels are often conduits for these flows, exerting a first order control on turbidity current flow processes... more
Turbidity currents are an important process for transporting sediment from the continental shelf to the deep ocean. Submarine channels are often conduits for these flows, exerting a first order control on turbidity current flow processes and resulting deposit geometries. Here we present a detailed examination of the Madeira Channel System, offshore northwest Africa, using shallow seismic profiles, swath bathymetric data and a suite of sediment cores. This shallow (<20 m deep) channel system is unusual because it was fed infrequently, on average once every 10, 000 years, by very large volume (>100 km3) turbidity currents. It therefore differs markedly from most submarine channels which have well developed levees, formed by much more frequent flows. A northern and a southern channel comprise the Madeira Channel System, and channel initiation is associated with subtle but distinct increases in sea-floor gradient from 0.02° to 0.06°. Most of the turbidity currents passing through the northern channel deposited laterally extensive (>5 km), thin (5–10 cm) ripple cross-laminated sands along the channel margins, but deposited no sand or mud in the channel axis. Moreover, these flows failed to erode sediment in the channel axis, despite being powerful enough to efficiently bypass sediment in very large volumes. The flows were able to reach an equilibrium state (autosuspension) whereby they efficiently bypassed their sediment loads down slope, leaving no trace of their passing.
Research Interests:
Sediments in deep water basins often include turbidites that record sediment input from adjacent continental margins. In seismically active areas, where turbidity currents are triggered by earthquakes, the basinal turbidite sequence may... more
Sediments in deep water basins often include turbidites that record sediment input from adjacent continental margins. In seismically active areas, where turbidity currents are triggered by earthquakes, the basinal turbidite sequence may thus contain a record of palaeoseismicity, which can be used to infer the frequency of earthquakes affecting the margins of the basin. This is particularly useful where large earthquakes have a recurrence interval than is greater than the historical record. However, turbidity currents can be triggered by several processes, and it is often difficult to trace individual turbidites to their precise source areas and to assign a definite trigger to a particular turbidite. Here, we demonstrate that turbidites emplaced at ∼6600 and ∼8300 Cal yr BP in the Tagus Abyssal Plain, off Portugal, correlate with erosional hiatuses in two submarine canyons on the continental margin. The turbidites are sourced from simultaneous landsliding in both canyons, requiring regional triggers interpreted as earthquakes. An earthquake recurrence interval for the continental margin of ∼4000 years is estimated by extrapolation to deeper turbidites in the basin sequence. However, the example of the 1755 earthquake, which caused widespread devastation in southwest Iberia, shows that palaeoseismic interpretations must be made with caution. The 1755 earthquake had a magnitude >8.5 and yet the associated turbidite in the abyssal plain is typically ∼5 cm thick, while older turbidites can be >1 m thick. Given the large 1755 earthquake magnitude, the difference in turbidite thickness is unlikely to be related to the relative size of triggering earthquakes. Instead, we suggest that the offshore location of the 1755 earthquake, coupled with low sedimentation rates during the Holocene, may have limited the size of the associated turbidite.
Research Interests:
Volcanic island landslides can pose a significant geohazard through landslide-generated tsunamis. However, a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained. The... more
Volcanic island landslides can pose a significant geohazard through landslide-generated tsunamis. However, a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained. The study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process, such as total event volume and whether landslides occurred as single or multiple events. The northern flank of Tenerife has undergone multiple landslide events, the most recent being the Icod landslide dated at ∼165 ka. The Icod landslide generated a turbidite with a deposit volume of ∼210 km3, covering 355,000 km2 of seafloor off northwest Africa. The Icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals (named subunits SBU1–7). Evidence from subunit bulk geochemistry, volume, basal grain size, volcanic glass composition and sand mineralogy, combined with petrophysical and geophysical data, suggests that the subunit facies represents multistage retrogressive failure of the Icod landslide. The basal subunits (SBU1–3) indicate that the first three stages of the landslide had a submarine component, whereas the upper subunits (SBU4–7) originated above sea level. The presence of thin, non-bioturbated, mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure. These results have important implications for tsunamigenesis from such landslides, as multistage retrogressive failures, separated by several days and with both a submarine and subaerial component, will have markedly lower tsunamigenic potential than a single-block failure.
Research Interests:
Direct observation of deepwater turbidity currents is difficult owing to their infrequent occurrence, destructive power and deepwater setting. As a result, modern piston core datasets supplemented by geophysical and geochemical studies... more
Direct observation of deepwater turbidity currents is difficult owing to their infrequent occurrence, destructive power and deepwater setting. As a result, modern piston core datasets supplemented by geophysical and geochemical studies provide invaluable datasets. These studies show the importance of understanding the role of mud (0-32 μm) in these systems and the insights into the basin depositional history that can be gleaned from its study. Due to hydrodynamic sorting during the flow pathway, the sand fraction of turbidity currents is often unsuitable for use in provenance studies. Turbidite mud geochemistry provides major insights into the source of the turbidity currents, and due to the similar grain-size distribution intra- and inter-basin comparisons of compositions are more robust. ITRAX μXRF of turbidites from the mixed siliciclastic-volcaniclastic Moroccan Turbidite System has shown an ability to resolve differences in provenance for the event beds. Comparing the geochemical composition of correlated siliciclastic turbidites before and after exit of the Agadir Canyon has shown that large volume events are erosive (changing geochemical composition) while smaller flows are non-erosive (unchanging geochemical composition). While turbidite muds do not vary in composition between sites solely within Agadir Basin, showing that these flows are principally non-erosion once unconfined, regardless of volume.
The depositional mechanisms exerted on turbidite muds is complex owing to the inherent cohesive properties. Metre-thick mudcaps have been recorded in the Madeira Abyssal Plain. These turbidite muds have been found to pond into the centre of basin and between rift ridges. Previous studies have indicated potential for non-turbulent processes to be in operation. Geochemical studies of these muds has resolved the turbulent primary transport mechanism, laminar flow transformation on deposition, and final post-depositional remobilisation. These turbidite muds comprise TOC >2% in some cases with volumes of >100 km3. Diagenesis can dramatically reduce the TOC through the propagation of oxidation fronts. High resolution geochemical studies have allowed a better understanding of case examples. Indeed, although affected by the action of oxidation fronts the metre-thick nature of the deposits preserves and buries large quantities of carbon.
The depositional mechanisms exerted on turbidite muds is complex owing to the inherent cohesive properties. Metre-thick mudcaps have been recorded in the Madeira Abyssal Plain. These turbidite muds have been found to pond into the centre of basin and between rift ridges. Previous studies have indicated potential for non-turbulent processes to be in operation. Geochemical studies of these muds has resolved the turbulent primary transport mechanism, laminar flow transformation on deposition, and final post-depositional remobilisation. These turbidite muds comprise TOC >2% in some cases with volumes of >100 km3. Diagenesis can dramatically reduce the TOC through the propagation of oxidation fronts. High resolution geochemical studies have allowed a better understanding of case examples. Indeed, although affected by the action of oxidation fronts the metre-thick nature of the deposits preserves and buries large quantities of carbon.
Modern deepwater turbidite systems have shown deposition of large volume unconfined turbidity currents on the Western European passive margin. The modern core dataset held at BOSCORF at the NOC has allowed the detailed study of deposits... more
Modern deepwater turbidite systems have shown deposition of large volume unconfined turbidity currents on the Western European passive margin. The modern core dataset held at BOSCORF at the NOC has allowed the detailed study of deposits from nine deepwater abyssal plains in order to critique the depositional processes affecting the turbidites. Turbidite muds pose significant heterogeneities within potential reservoir intervals and comprise potential sealing facies. Moreover, turbidite muds from the modern northeast passive margin also contain >2% TOC. Thus, these deposits could present analogues for potential hydrocarbon sources from turbidite muds. Understanding the processes of deposition and controls on distribution from these modern systems is important; since this detail can be applied to analogous ancient systems representing regions under exploration or development.
Metre-thick mudcaps have been observed to thicken in subtle basin lows. Previous studies have eluded to deposition from highly concentrated non-turbulent (laminar) flows. Grain-size and geochemical vertical and spatial profiles indicate that fluid turbulence is instead the primary transport mechanism for sediment dispersal. However, during sedimentation yield-strength fluids are generated as the fine-grained material consolidates. This is then able to flow under laminar flow conditions and redistribute the mudcap preferentially into the basin lows as fluid muds.
On basin margins there is additional evidence to suggest that the rapid deposition of metre-thick mudcaps has led to destabilisation of the accumulation. This has led to remobilisation of the mudcap deposit as a yield-strength mudflow. Understanding the architectures of these turbidite muds and the controls on their distribution is captured here in an unparalleled core and geophysical dataset. The hope is that the heterogeneities resolved in the present study can be used to aid petroleum system evaluations both from reservoir and source rock perspectives.
Metre-thick mudcaps have been observed to thicken in subtle basin lows. Previous studies have eluded to deposition from highly concentrated non-turbulent (laminar) flows. Grain-size and geochemical vertical and spatial profiles indicate that fluid turbulence is instead the primary transport mechanism for sediment dispersal. However, during sedimentation yield-strength fluids are generated as the fine-grained material consolidates. This is then able to flow under laminar flow conditions and redistribute the mudcap preferentially into the basin lows as fluid muds.
On basin margins there is additional evidence to suggest that the rapid deposition of metre-thick mudcaps has led to destabilisation of the accumulation. This has led to remobilisation of the mudcap deposit as a yield-strength mudflow. Understanding the architectures of these turbidite muds and the controls on their distribution is captured here in an unparalleled core and geophysical dataset. The hope is that the heterogeneities resolved in the present study can be used to aid petroleum system evaluations both from reservoir and source rock perspectives.
Volcanic islands naturally facilitate the occurrence of large-scale landslides due to eruptions, seismic activity and the generation of over-steepened edifices. Landslide-induced tsunami generation is sensitive to a number of parameters... more
Volcanic islands naturally facilitate the occurrence of large-scale landslides due to eruptions, seismic activity and the generation of over-steepened edifices. Landslide-induced tsunami generation is sensitive to a number of parameters including: landslide volume, initial acceleration, maximum velocity and retrogressive behaviour. These parameters are difficult to calculate from events in the geologic record, since the volcanic island debris aprons are complex areas and involve overprinting of events. Furthermore, predicted conditions for future events are based on information from the proximal landslide area, and are often over-estimated.
Turbidites are generated from volcanic island flank collapses and records of landslide occurrence can be constructed from these more distal gravity flow archives. With appropriate mapping of a respective turbidite with sediment cores, accurate volume estimates can be made and added to those from the proximal debris avalanche. In addition, recent studies have shown that the landslide mechanism (single block or multi-stage) can be deduced from the turbidite architecture by the presence/lack of subunits (repeating sequences of turbidite sand and mud). Subunits represent multistage events, and furthermore, the study of the interbedded mud intervals can provide details on the time required between events to allow the mud to settle and consolidate.
The Icod turbidite in the Moroccan Turbidite System originating from the northern flank of Tenerife (165 ka) is composed of a series of seven subunit events. These have developed from a multistage retrogressive failure during the Icod landslide. Of the 360 km3 volume of the landslide, 210 km3 comprises the turbidite. This is then divided between the subunits, where the initial three are the most volumetrically significant (70-75 km3) compared to the upper four (15-25 km3). Geochemical, grain-size, petrological and geotechnical data have shown the subunit events are the product of the landslide mechanism, rather than flow reflection, multiple sources or multiple pathways. Analysis of the distal deposit highlights the presence of seven upwards-fining sands with intervening muds. These muds present suspension fallout deposition between each failure and demonstrate conservative time intervals of 3 to 22 days. From studying the turbidite associated with the landslide numerous properties of the landslide event can be gleaned. Firstly, the Icod flank collapse has been shown to be multistage and retrogressive. Therefore, the overall considerable volume has been shown to be distributed amongst the subunit events. The result here is that the mass entering the ocean at once is decreased, and thus the potential tsunami wave amplitude is reduced. Study of the debris avalanche shows considerable slide material disaggregation and flow transformation from avalanche to debris flow. This shows the slide material has low coherency, which will affect the tsunami wave properties. Importantly, this case study is not ubiquitous and can be applied to others in the study area. The implication is that catastrophic volcanic landslides in the Canary Islands are commonly multistage and not single block failures, so the tsunamigenic potential is much reduced.
Turbidites are generated from volcanic island flank collapses and records of landslide occurrence can be constructed from these more distal gravity flow archives. With appropriate mapping of a respective turbidite with sediment cores, accurate volume estimates can be made and added to those from the proximal debris avalanche. In addition, recent studies have shown that the landslide mechanism (single block or multi-stage) can be deduced from the turbidite architecture by the presence/lack of subunits (repeating sequences of turbidite sand and mud). Subunits represent multistage events, and furthermore, the study of the interbedded mud intervals can provide details on the time required between events to allow the mud to settle and consolidate.
The Icod turbidite in the Moroccan Turbidite System originating from the northern flank of Tenerife (165 ka) is composed of a series of seven subunit events. These have developed from a multistage retrogressive failure during the Icod landslide. Of the 360 km3 volume of the landslide, 210 km3 comprises the turbidite. This is then divided between the subunits, where the initial three are the most volumetrically significant (70-75 km3) compared to the upper four (15-25 km3). Geochemical, grain-size, petrological and geotechnical data have shown the subunit events are the product of the landslide mechanism, rather than flow reflection, multiple sources or multiple pathways. Analysis of the distal deposit highlights the presence of seven upwards-fining sands with intervening muds. These muds present suspension fallout deposition between each failure and demonstrate conservative time intervals of 3 to 22 days. From studying the turbidite associated with the landslide numerous properties of the landslide event can be gleaned. Firstly, the Icod flank collapse has been shown to be multistage and retrogressive. Therefore, the overall considerable volume has been shown to be distributed amongst the subunit events. The result here is that the mass entering the ocean at once is decreased, and thus the potential tsunami wave amplitude is reduced. Study of the debris avalanche shows considerable slide material disaggregation and flow transformation from avalanche to debris flow. This shows the slide material has low coherency, which will affect the tsunami wave properties. Importantly, this case study is not ubiquitous and can be applied to others in the study area. The implication is that catastrophic volcanic landslides in the Canary Islands are commonly multistage and not single block failures, so the tsunamigenic potential is much reduced.
Volcanic islands naturally facilitate the occurrence of large-scale landslides due to eruptions, seismic activity and the generation of over-steepened edifices. Landslide-induced tsunami generation is sensitive to a number of parameters... more
Volcanic islands naturally facilitate the occurrence of large-scale landslides due to eruptions, seismic activity and the generation of over-steepened edifices. Landslide-induced tsunami generation is sensitive to a number of parameters including: landslide volume, initial acceleration, maximum velocity and retrogressive behaviour. These parameters are difficult to calculate from events in the geologic record, since the volcanic island debris aprons are complex areas and involve overprinting of events. Furthermore, predicted conditions for future events are based on information from the proximal landslide area, and are often over-estimated.
Turbidites are generated from volcanic island flank collapses and records of landslide occurrence can be constructed from these more distal gravity flow archives. With appropriate mapping of a respective turbidite with sediment cores, accurate volume estimates can be made and added to those from the proximal debris avalanche. In addition, recent studies have shown that the landslide mechanism (single block or multi-stage) can be deduced from the turbidite architecture by the presence/lack of subunits (repeating sequences of turbidite sand and mud). Subunits represent multistage events, and furthermore, the study of the interbedded mud intervals can provide details on the time required between events to allow the mud to settle and consolidate.
The Icod turbidite in the Moroccan Turbidite System originating from the northern flank of Tenerife (165 ka) is composed of a series of seven subunit events. These have developed from a multistage retrogressive failure during the Icod landslide. Of the 360 km3 volume of the landslide, 210 km3 comprises the turbidite. This is then divided between the subunits, where the initial three are the most volumetrically significant (70-75 km3) compared to the upper four (15-25 km3). Geochemical, grain-size, petrological and geotechnical data have shown the subunit events are the product of the landslide mechanism, rather than flow reflection, multiple sources or multiple pathways. Analysis of the distal deposit highlights the presence of seven upwards-fining sands with intervening muds. These muds present suspension fallout deposition between each failure and demonstrate conservative time intervals of 3 to 22 days. From studying the turbidite associated with the landslide numerous properties of the landslide event can be gleaned. Firstly, the Icod flank collapse has been shown to be multistage and retrogressive. Therefore, the overall considerable volume has been shown to be distributed amongst the subunit events. The result here is that the mass entering the ocean at once is decreased, and thus the potential tsunami wave amplitude is reduced. Study of the debris avalanche shows considerable slide material disaggregation and flow transformation from avalanche to debris flow. This shows the slide material has low coherency, which will affect the tsunami wave properties. Importantly, this case study is not ubiquitous and can be applied to others in the study area. The implication is that catastrophic volcanic landslides in the Canary Islands are commonly multistage and not single block failures, so the tsunamigenic potential is much reduced.
Turbidites are generated from volcanic island flank collapses and records of landslide occurrence can be constructed from these more distal gravity flow archives. With appropriate mapping of a respective turbidite with sediment cores, accurate volume estimates can be made and added to those from the proximal debris avalanche. In addition, recent studies have shown that the landslide mechanism (single block or multi-stage) can be deduced from the turbidite architecture by the presence/lack of subunits (repeating sequences of turbidite sand and mud). Subunits represent multistage events, and furthermore, the study of the interbedded mud intervals can provide details on the time required between events to allow the mud to settle and consolidate.
The Icod turbidite in the Moroccan Turbidite System originating from the northern flank of Tenerife (165 ka) is composed of a series of seven subunit events. These have developed from a multistage retrogressive failure during the Icod landslide. Of the 360 km3 volume of the landslide, 210 km3 comprises the turbidite. This is then divided between the subunits, where the initial three are the most volumetrically significant (70-75 km3) compared to the upper four (15-25 km3). Geochemical, grain-size, petrological and geotechnical data have shown the subunit events are the product of the landslide mechanism, rather than flow reflection, multiple sources or multiple pathways. Analysis of the distal deposit highlights the presence of seven upwards-fining sands with intervening muds. These muds present suspension fallout deposition between each failure and demonstrate conservative time intervals of 3 to 22 days. From studying the turbidite associated with the landslide numerous properties of the landslide event can be gleaned. Firstly, the Icod flank collapse has been shown to be multistage and retrogressive. Therefore, the overall considerable volume has been shown to be distributed amongst the subunit events. The result here is that the mass entering the ocean at once is decreased, and thus the potential tsunami wave amplitude is reduced. Study of the debris avalanche shows considerable slide material disaggregation and flow transformation from avalanche to debris flow. This shows the slide material has low coherency, which will affect the tsunami wave properties. Importantly, this case study is not ubiquitous and can be applied to others in the study area. The implication is that catastrophic volcanic landslides in the Canary Islands are commonly multistage and not single block failures, so the tsunamigenic potential is much reduced.
Due to the excellent core coverage and ability to correlate single event beds over 1000km the deepwater Northeast Atlantic basins pose a natural laboratory to test theories of flow processes. From the Canary archipelago to northern Spain... more
Due to the excellent core coverage and ability to correlate single event beds over 1000km the deepwater Northeast Atlantic basins pose a natural laboratory to test theories of flow processes. From the Canary archipelago to northern Spain these deepwater depositional systems include: South Canary Pathway, Moroccan Turbidite System, Horseshore Abyssal Plain, Tagus Abyssal Plain, Iberian Abyssal Plain and Biscay Abyssal Plain. These depocentres are located in >3800m water depths between 15-50km from the continental mainland. Though sheet-like in overall geometry these gravity flows present complexities in internal facies relationships and grain-size distributions. The first aim of this study is to build stratigraphic frameworks for the respective systems. Once these are in place, provenance and facies analyses can be undertaken to deduce source direction and methods of emplacement of the respective gravity flows.
The Moroccan turbidite system (MTS) is located on the northwest African margin north of the Canary archipelago. It is composed of three interconnected basins: Agadir Basin, Seine Abyssal Plain and the Madeira Abyssal Plain (Wynn et al., 2002). The system here is the site of infrequent but large volume (>75km3) volcaniclastic (Tenerife and El Hierro) and siliciclastic (Moroccan margin) turbidity current events in the last 200ka. The turbidites display an array of architectures from single to stacked events. Furthermore, there is a prevalence of grain-size breaks, contorted mudcaps and well developed linked debrites.
The Horseshoe Abyssal Plain (HAP) is fed by the Sao Vincente and Portimão canyons from southwest Iberia. While the Tagus Abyssal Plain (TAP), immediately to the north, is fed by the Cascais, Lisbon and Sebúbal canyons. Here the Tagus and Sado rivers release sediment laden outflows directly into the canyons feeding the TAP; while along-shore drift in primarily responsible for sediment reaching the Sao Vincente canyon to the HAP. High turbidite sedimentation rates are facilitated by high sediment flux to the basins and intermittent high magnitude earthquake activity. The deposits are atypical to textbook turbidite models with a dominance of ripple-laminations, prevalence of grain-size breaks and thick contorted mudcaps.
The Iberian Abyssal Plain (IAP) represents the site of a number of large volume organic-rich siliciclastic turbidites and debrites. The IAP is fed by the Nazare, Aveiro and Porto canyons with a number of intervening sub-basins. Like the turbidites of the TAP and HAP biotite, muscovite and quartz are the dominant grain types. However, many turbidites contain an abundance of silt to granule-sized organic carbon particles. There is an increasing influence of laminar flow processes here with highly contorted muds and sands, principally owing to the higher mud content.
This study presents a culmination in decades of core recovery in the Northeast Atlantic. This has allowed detailed event histories and sediment budgets to be calculated for the respective depocentres. However, in providing bed-scale correlations invaluable information can be gleaned in regards to the depositional processes. The present study highlights the prevalence of linked debrites and the strong influence of mud content on the depositional mechanism along the entire margin.
The Moroccan turbidite system (MTS) is located on the northwest African margin north of the Canary archipelago. It is composed of three interconnected basins: Agadir Basin, Seine Abyssal Plain and the Madeira Abyssal Plain (Wynn et al., 2002). The system here is the site of infrequent but large volume (>75km3) volcaniclastic (Tenerife and El Hierro) and siliciclastic (Moroccan margin) turbidity current events in the last 200ka. The turbidites display an array of architectures from single to stacked events. Furthermore, there is a prevalence of grain-size breaks, contorted mudcaps and well developed linked debrites.
The Horseshoe Abyssal Plain (HAP) is fed by the Sao Vincente and Portimão canyons from southwest Iberia. While the Tagus Abyssal Plain (TAP), immediately to the north, is fed by the Cascais, Lisbon and Sebúbal canyons. Here the Tagus and Sado rivers release sediment laden outflows directly into the canyons feeding the TAP; while along-shore drift in primarily responsible for sediment reaching the Sao Vincente canyon to the HAP. High turbidite sedimentation rates are facilitated by high sediment flux to the basins and intermittent high magnitude earthquake activity. The deposits are atypical to textbook turbidite models with a dominance of ripple-laminations, prevalence of grain-size breaks and thick contorted mudcaps.
The Iberian Abyssal Plain (IAP) represents the site of a number of large volume organic-rich siliciclastic turbidites and debrites. The IAP is fed by the Nazare, Aveiro and Porto canyons with a number of intervening sub-basins. Like the turbidites of the TAP and HAP biotite, muscovite and quartz are the dominant grain types. However, many turbidites contain an abundance of silt to granule-sized organic carbon particles. There is an increasing influence of laminar flow processes here with highly contorted muds and sands, principally owing to the higher mud content.
This study presents a culmination in decades of core recovery in the Northeast Atlantic. This has allowed detailed event histories and sediment budgets to be calculated for the respective depocentres. However, in providing bed-scale correlations invaluable information can be gleaned in regards to the depositional processes. The present study highlights the prevalence of linked debrites and the strong influence of mud content on the depositional mechanism along the entire margin.
Repeat talk of ISC 2010 presentation of the same name.
Numerous dedicated coring expeditions to the Canary archipelago and surrounding deepwater depocentres have resulted in excellent core coverage. Volcanic islands naturally provide over-steepened edifices and flanks that can become... more
Numerous dedicated coring expeditions to the Canary archipelago and surrounding deepwater depocentres have resulted in excellent core coverage. Volcanic islands naturally provide over-steepened edifices and flanks that can become destabilised and fail, producing large volume landslides and associated turbidity currents. In addition climatic barranco outwash events produce sediment accumulations that can also destabilised and fail, producing localised deposits. Another style of volcaniclastic deposition involves failures of volcaniclastic material draping seamounts, which produce turbidite currents with the potential to be basin-wide in magnitude.
There are three primary examples of major flank collapses recorded as turbidites, including: El Golfo, Icod and Las Playas II events. A common feature of the facies architecture of the turbidite deposits of these events is the vertically stacked interbedded sands and muds. Grain-size and geochemical evidence suggests that this facies can signify multistage collapses mechanisms at source. These large-volume multistage collapse events are in stark contrast to large volume siliciclastic events, which occur as single-stage events.
The stacked multistage signature in the turbidite record is not ubiquitous to major flank collapses. Indeed, events of smaller magnitude which are not tied to such collapses also show this facies. These smaller events can be linked to collapses of terminal barranco accumulations, which destabilise and failure. However, the mechanism of these smaller scale failures can be deemed to be multistage.
There are also a number of deposits represented by coarse-grained massive sands capped by a grain-size break and a limited mudcap. This facies architecture can be attributed to either proximal bypass or a record of a surging behaviour in the flow (Mulder & Alexander, 2001). These have attributed to barranco outwash events and/or small scale single failures.
The development of turbidity current associated bedforms (parallel laminations, cross laminations, and convolute laminations) appears to only be present in large volume surge-like flows that have develop a long enough flow bodies (Mulder & Alexander, 2001). In contrast shorter duration, lower volume events may not possess the length of flow body required to develop bedforms.
Sylvester and Lowe (2004) quantified the grain-size ranges and mud content over which turbidity current associated bedforms were found to develop in Oligocene turbidites in the East Carpathians. The analytical technique is applied to these modern volcaniclastic sediment systems where grain-size analysis can be quantified by use of a laser-diffraction particle analyser. This study aims to assess some of the controls on sedimentation, bedform development and facies association with particular flow behaviours.
There are three primary examples of major flank collapses recorded as turbidites, including: El Golfo, Icod and Las Playas II events. A common feature of the facies architecture of the turbidite deposits of these events is the vertically stacked interbedded sands and muds. Grain-size and geochemical evidence suggests that this facies can signify multistage collapses mechanisms at source. These large-volume multistage collapse events are in stark contrast to large volume siliciclastic events, which occur as single-stage events.
The stacked multistage signature in the turbidite record is not ubiquitous to major flank collapses. Indeed, events of smaller magnitude which are not tied to such collapses also show this facies. These smaller events can be linked to collapses of terminal barranco accumulations, which destabilise and failure. However, the mechanism of these smaller scale failures can be deemed to be multistage.
There are also a number of deposits represented by coarse-grained massive sands capped by a grain-size break and a limited mudcap. This facies architecture can be attributed to either proximal bypass or a record of a surging behaviour in the flow (Mulder & Alexander, 2001). These have attributed to barranco outwash events and/or small scale single failures.
The development of turbidity current associated bedforms (parallel laminations, cross laminations, and convolute laminations) appears to only be present in large volume surge-like flows that have develop a long enough flow bodies (Mulder & Alexander, 2001). In contrast shorter duration, lower volume events may not possess the length of flow body required to develop bedforms.
Sylvester and Lowe (2004) quantified the grain-size ranges and mud content over which turbidity current associated bedforms were found to develop in Oligocene turbidites in the East Carpathians. The analytical technique is applied to these modern volcaniclastic sediment systems where grain-size analysis can be quantified by use of a laser-diffraction particle analyser. This study aims to assess some of the controls on sedimentation, bedform development and facies association with particular flow behaviours.
The northern flank of Tenerife has been prone to multiple mass wasting events, including the Icod landslide dated to ~160,000ka (Watts & Masson, 1995). The Icod landslide has generated a turbidite of 208km3 volume. The turbidite is... more
The northern flank of Tenerife has been prone to multiple mass wasting events, including the Icod landslide dated to ~160,000ka (Watts & Masson, 1995). The Icod landslide has generated a turbidite of 208km3 volume. The turbidite is recorded over an area of >350,000km2 through the Moroccan Turbidite System, deepwater northwest African margin. Not only has the turbidite flowed up-gradient through the Agadir Basin, but shows an atypical depositional architecture consisting of a stacked sequence of graded sand and mud intervals. This ‘subunit’ architecture can be construed as representing a retrogressive failure mechanism at source (Wynn & Masson, 2003). Evidence from mineralogy, subunit bulk and volcanic glass geochemical, grain size data and event volumes support a multistage retrogressive failure. This evidence can rule out earthquake induced multi-provenance processes and flow reflections. The implication is that this major flank collapse has propagated as a series of failures , rather than failing as a single block slide.
Indeed there are seven spatially correlated events within the Icod turbidite. The bulk chemistries for these intervals has been ascertained using standard ICP-AES and ICP-MS methodologies and supplemented with more novel techniques such as ITRAX μXRF. These bulk signatures show an evolutionary trend, becoming increasingly evolved, with a progressively higher content of phonolitic glasses. Major element chemistries of the glasses show that material from the Diego Hernendez Formation have been failed. The glasses were analysed using standard SEM EDS, but also supplemented by using a tabletop SEM EDS (TM1000) and μXRF using the Eagle III. The uppermost failures do not include any highly altered glasses or minerals, which indicate that the Cañadas III edifice was not failed in the Icod landslide. Given that the edifice was not involved in the flank collapse and the high volume of volcanic glass it could be speculatively stated that the wall of the Las Cañadas caldera does not represent the landslide scar. The reduced volumes of the deposits, reduction in grain-size and calculated time lags for the events, indicate that the tsunamigenic potential for these failure events in greatly reduced.
Thus distal turbidites prove a vital constituent when studying landslide processes. In regards to completing hazard assessments of marine regions such as oceanic volcanic islands or continental margins, the study of turbidites provide vital insights. This investigation also highlights the importance of a multidiscipline approach to the study of turbidites.
Indeed there are seven spatially correlated events within the Icod turbidite. The bulk chemistries for these intervals has been ascertained using standard ICP-AES and ICP-MS methodologies and supplemented with more novel techniques such as ITRAX μXRF. These bulk signatures show an evolutionary trend, becoming increasingly evolved, with a progressively higher content of phonolitic glasses. Major element chemistries of the glasses show that material from the Diego Hernendez Formation have been failed. The glasses were analysed using standard SEM EDS, but also supplemented by using a tabletop SEM EDS (TM1000) and μXRF using the Eagle III. The uppermost failures do not include any highly altered glasses or minerals, which indicate that the Cañadas III edifice was not failed in the Icod landslide. Given that the edifice was not involved in the flank collapse and the high volume of volcanic glass it could be speculatively stated that the wall of the Las Cañadas caldera does not represent the landslide scar. The reduced volumes of the deposits, reduction in grain-size and calculated time lags for the events, indicate that the tsunamigenic potential for these failure events in greatly reduced.
Thus distal turbidites prove a vital constituent when studying landslide processes. In regards to completing hazard assessments of marine regions such as oceanic volcanic islands or continental margins, the study of turbidites provide vital insights. This investigation also highlights the importance of a multidiscipline approach to the study of turbidites.
The quiescent environment of the abyssal plain is thought to be the site of deposition of distal turbidites with sheet geometries (Rothwell et al. 1992). However, flume experiments have shown that decelerating turbulent flows are not... more
The quiescent environment of the abyssal plain is thought to be the site of deposition of distal turbidites with sheet geometries (Rothwell et al. 1992). However, flume experiments have shown that decelerating turbulent flows are not mechanically simple and can produce an array of depositional facies owing to mud content, grain size, flow velocity and sedimentation rate (Sumner et al., 2008). This study aims to demonstrate an array of these complexities that govern the distribution of sediment in the deepwater realm. Indeed, a newly discovered process has been found to profoundly influence the distribution of mudcap thicknesses of distal turbidites.
The volcaniclastic turbidites associated with the geologically recent El Golfo and Icod landslides show unusual dispersal patterns, in that they appear to record multistage failures at source. The vertically stacked sequences of interbedded turbidite sands and muds in the Icod turbidite, Agadir Basin, demonstrate individual failures in a multistage event. This is based on basal grain-size data and geochemical heterogeneities. The inter-event suspension deposits from these succinct failures demonstrate processes of topographic interaction and proximal erosive removal.
Another major control on the distribution of the Icod volcaniclastic turbidite is post-depositional remobilisation of the thick mudcap that was initially deposited. Mudcap isopachs of the Icod turbidite show excess thickening on the southern margin of the Agadir Basin. The mudcaps also show contorted laminations of silt within an ungraded clay matrix. Grain-size analysis shows that this contorted facies represents the grain-sizes and distributions associated with laminated muddy silts (Bouma Td) and graded muds (Bouma Te).
A model for a process of remobilised mudflow is proposed here:
1) Deposition from a decelerating turbidity current commences, depositing massive sands (T¬a), parallel laminated sands (Tb), and ripple laminated sands (Tc).
2) Convolute laminated clay-rich sands develop, where flocculated clays trap water and instigate overpressure during burial. The application of shear stress to the developing ripples results in plastic deformation and convolution of the original bedforms.
3) Deposition of planar silty clay-dominated laminations (Td) proceeds, again with the development of overpressure due to accumulation rate and nature of impermeable clays involved.
4) Commencement of graded clays (Te) further develops overpressure to a critical point. Upon Te deposition, overpressure diffuses vertically through the coarser Tc interval and builds up in the Td interval.
5) Failure commences in the Td interval due to the action of bed shear stress and gravitational potential on the basin margins, facilitated by the development of overpressure.
6) The mudcap comprising the Td and Te intervals are remobilised as a laminar mudflow. There is little energy in the flow to overcome cohesive forces, enabling preservation of silt laminations as plastically deformed contortions and larger silty clasts. The remobilised mudflow deposits at the base of slope on the basin margin.
This study shows that distal turbidite deposition involves a complex interplay of many mechanisms that can profoundly influence the final architecture of the deposits. This study also highlights a previously undocumented flow process of remobilised mudflow. This process can be potentially categorised amongst other processes that develop the hybrid bed or cogenetic linked debrite facies.
The volcaniclastic turbidites associated with the geologically recent El Golfo and Icod landslides show unusual dispersal patterns, in that they appear to record multistage failures at source. The vertically stacked sequences of interbedded turbidite sands and muds in the Icod turbidite, Agadir Basin, demonstrate individual failures in a multistage event. This is based on basal grain-size data and geochemical heterogeneities. The inter-event suspension deposits from these succinct failures demonstrate processes of topographic interaction and proximal erosive removal.
Another major control on the distribution of the Icod volcaniclastic turbidite is post-depositional remobilisation of the thick mudcap that was initially deposited. Mudcap isopachs of the Icod turbidite show excess thickening on the southern margin of the Agadir Basin. The mudcaps also show contorted laminations of silt within an ungraded clay matrix. Grain-size analysis shows that this contorted facies represents the grain-sizes and distributions associated with laminated muddy silts (Bouma Td) and graded muds (Bouma Te).
A model for a process of remobilised mudflow is proposed here:
1) Deposition from a decelerating turbidity current commences, depositing massive sands (T¬a), parallel laminated sands (Tb), and ripple laminated sands (Tc).
2) Convolute laminated clay-rich sands develop, where flocculated clays trap water and instigate overpressure during burial. The application of shear stress to the developing ripples results in plastic deformation and convolution of the original bedforms.
3) Deposition of planar silty clay-dominated laminations (Td) proceeds, again with the development of overpressure due to accumulation rate and nature of impermeable clays involved.
4) Commencement of graded clays (Te) further develops overpressure to a critical point. Upon Te deposition, overpressure diffuses vertically through the coarser Tc interval and builds up in the Td interval.
5) Failure commences in the Td interval due to the action of bed shear stress and gravitational potential on the basin margins, facilitated by the development of overpressure.
6) The mudcap comprising the Td and Te intervals are remobilised as a laminar mudflow. There is little energy in the flow to overcome cohesive forces, enabling preservation of silt laminations as plastically deformed contortions and larger silty clasts. The remobilised mudflow deposits at the base of slope on the basin margin.
This study shows that distal turbidite deposition involves a complex interplay of many mechanisms that can profoundly influence the final architecture of the deposits. This study also highlights a previously undocumented flow process of remobilised mudflow. This process can be potentially categorised amongst other processes that develop the hybrid bed or cogenetic linked debrite facies.
The Moroccan Turbidite System encompasses three interconnected depocentres: Agadir Basin, Seine Abyssal Plain and Madeira Abyssal Plain (Wynn et al. 2002). Both siliciclastic and volcaniclastic turbidites are discovered within these... more
The Moroccan Turbidite System encompasses three interconnected depocentres: Agadir Basin, Seine Abyssal Plain and Madeira Abyssal Plain (Wynn et al. 2002). Both siliciclastic and volcaniclastic turbidites are discovered within these basins using piston coring, but have been found to behave differently according to their source and site of entry. The Agadir Basin is fed directly by the Agadir Canyon, which is the primary source for siliciclastic shelf-edged derived turbidity currents. The Agadir Basin also represents a proximal site of deposition for volcaniclastic turbidites derived directly from Madeira, Tenerife, Las Palma and El Hierro. Though these mixed deposits are also found in the Seine and Madeira Abyssal Plains, the focus of this presentation will be the Agadir Basin. Focusing this study is primarily because it removes the added complexity of these flows passing through the regions interconnecting the basins, but also because of the higher quality of coring completed in the Agadir Basin.
Siliciclastic turbidty currents here are affected by both grain-size bypass and flow transformations owing to sensitive interactions with topography (Talling et al. 2006). These deposits form tabular sheets through the centre of the basin, with bypass within the Madeira Channel System and recommencing deposition in the distal Madeira Abyssal Plain. Volcaniclastic deposits vary in their behaviour since they travel up-gradient through the Agadir Basin, with the deposit architectures not only affected by topographic interactions but with the characteristics of the landslide failures that generated them. Large scale volcaniclastic turbidites, such as those from Tenerife and El Hierro, exhibit a vertically stacked sand facies relating to the failure mechanism at source. This facies architecture is maintained >400km away from source in the Agadir Basin. In comparison smaller flank failures generate localised turbidite lobes feeding off small aprons, which have been found to be restricted by basin topography. There are also a number of small volcaniclastic turbidites relating to barranco canyon outwash events, which though not regionally extensive, could still yield important information regarding climate controls on weathering rates. Adding to these siliciclastic and volcaniclastic deposits are a number of carbonate-rich turbidites originating from volcaniclastic draped seamounts such as the Selvage Islands.
Understanding the provenance area of each turbidite, its composition and pathway are pivotal in understanding the mechanics of the gravity flows that deposited them. Understanding how turbidity currents, debris flows and debris avalanches react to the basin settings is in turn important, since this records how the basin is evolving through time both distally here in the deep sea and within the hinterland.
Siliciclastic turbidty currents here are affected by both grain-size bypass and flow transformations owing to sensitive interactions with topography (Talling et al. 2006). These deposits form tabular sheets through the centre of the basin, with bypass within the Madeira Channel System and recommencing deposition in the distal Madeira Abyssal Plain. Volcaniclastic deposits vary in their behaviour since they travel up-gradient through the Agadir Basin, with the deposit architectures not only affected by topographic interactions but with the characteristics of the landslide failures that generated them. Large scale volcaniclastic turbidites, such as those from Tenerife and El Hierro, exhibit a vertically stacked sand facies relating to the failure mechanism at source. This facies architecture is maintained >400km away from source in the Agadir Basin. In comparison smaller flank failures generate localised turbidite lobes feeding off small aprons, which have been found to be restricted by basin topography. There are also a number of small volcaniclastic turbidites relating to barranco canyon outwash events, which though not regionally extensive, could still yield important information regarding climate controls on weathering rates. Adding to these siliciclastic and volcaniclastic deposits are a number of carbonate-rich turbidites originating from volcaniclastic draped seamounts such as the Selvage Islands.
Understanding the provenance area of each turbidite, its composition and pathway are pivotal in understanding the mechanics of the gravity flows that deposited them. Understanding how turbidity currents, debris flows and debris avalanches react to the basin settings is in turn important, since this records how the basin is evolving through time both distally here in the deep sea and within the hinterland.
The study of modern deep-sea systems through targeted piston coring has enabled detailed investigations into the process mechanics of turbidity currents. In complex systems such as the Moroccan Turbidite System the derivation of... more
The study of modern deep-sea systems through targeted piston coring has enabled detailed investigations into the process mechanics of turbidity currents. In complex systems such as the Moroccan Turbidite System the derivation of provenance is of vital importance, since flows from different sources in this system have been found to behave differently. Early provenance studies in the Madeira Abyssal Plain found that bulk sand-fraction geochemical analysis through ICP-AES could enable successful attribution of provenance to specific turbidites alongside electron microprobe analysis (de Lange, Jarvis & Kuijpers, 1987; Pearce & Jarvis, 1992). These sources including the Moroccan siliclastic shelf, Tenerife, Las Palma, El Hierro and Madeira. ICP-AES, MC-ICP-MS and XRF have been utilised here, however these present destructive methodologies, using 0.1-5g of material >63µm. Deep-sea piston cores are also expensive to collect, and often there is not enough material to remove for analysis without compromising the core. Furthermore, routine sampling, preparation and analysis using the destructive methods stated above are undertaken at considerable cost and analytical time. The successful use of non-destructive instruments to yield quantitative geochemical has become paramount at the NOC.
This presentation serves to show the successful application of the TM-1000 tabletop SEM EDS analyser, ITRAX micro-XRF analyser and the GEOTEK XYZ logger, in coincidence with traditional destructive methods. These instruments can only supply semi-quantitative data, unless correct calibration can be achieved, and will be shown here.
The 160,000ka Icod landslide from Tenerife generated a 150km3 debris avalanche with a runout of 105km and a >180km3 turbidity, which will form the case study for application of these instruments. The vertically stacked subunit facies of the Icod turbidite has been attributed to generation from a multistage retrogressive failure (Wynn & Masson, 2003). Here there have been five regular subunit packages identified and correlated. This failure mechanism would have significant consequences of decreasing ensuing tsunamigenic potential. Variations in subunit mineralogy, bulk geochemistry, and volcanic glass geochemistry could yield results to support this hypothesis, and rule out other generation mechanisms such as flow reflection.
ITRAX micro-XRFmeasurements taken every 100µm show variations in bulk geochemistry. Major element (K, Ca, Ti, Fe) and trace element (Zr, Y an Sr) demonstrate this when plotted in Harker variation diagrams against silica. However these variations, along with those from ICP-AES, ICP-MS and XRF, could be accounted for by density fractionation of basaltic mafic clasts and volcanic glass constituents within the turbidity current. In regards to the mineral composition, the basal subunit contains altered volcanic glass with authigenic Ti-Fe oxide growths, seen using the TM-1000 SEM, compared to unaltered glasses found in the later four intervals. Furthermore, focussed studies of the volcanic glasses using the TM-1000 SEM EDS showed that the basal subunit had volcanic glasses of different major element compositions compared to the later four subunit intervals. This study, demonstrates the application of non-destructive geochemical analytical tools in not only discriminating provenance, but being able to aid deciphering of flow mechanical problems. Also, using non-destructive geochemical instruments will help discern provenance of further deposits around the Canary Islands.
This presentation serves to show the successful application of the TM-1000 tabletop SEM EDS analyser, ITRAX micro-XRF analyser and the GEOTEK XYZ logger, in coincidence with traditional destructive methods. These instruments can only supply semi-quantitative data, unless correct calibration can be achieved, and will be shown here.
The 160,000ka Icod landslide from Tenerife generated a 150km3 debris avalanche with a runout of 105km and a >180km3 turbidity, which will form the case study for application of these instruments. The vertically stacked subunit facies of the Icod turbidite has been attributed to generation from a multistage retrogressive failure (Wynn & Masson, 2003). Here there have been five regular subunit packages identified and correlated. This failure mechanism would have significant consequences of decreasing ensuing tsunamigenic potential. Variations in subunit mineralogy, bulk geochemistry, and volcanic glass geochemistry could yield results to support this hypothesis, and rule out other generation mechanisms such as flow reflection.
ITRAX micro-XRFmeasurements taken every 100µm show variations in bulk geochemistry. Major element (K, Ca, Ti, Fe) and trace element (Zr, Y an Sr) demonstrate this when plotted in Harker variation diagrams against silica. However these variations, along with those from ICP-AES, ICP-MS and XRF, could be accounted for by density fractionation of basaltic mafic clasts and volcanic glass constituents within the turbidity current. In regards to the mineral composition, the basal subunit contains altered volcanic glass with authigenic Ti-Fe oxide growths, seen using the TM-1000 SEM, compared to unaltered glasses found in the later four intervals. Furthermore, focussed studies of the volcanic glasses using the TM-1000 SEM EDS showed that the basal subunit had volcanic glasses of different major element compositions compared to the later four subunit intervals. This study, demonstrates the application of non-destructive geochemical analytical tools in not only discriminating provenance, but being able to aid deciphering of flow mechanical problems. Also, using non-destructive geochemical instruments will help discern provenance of further deposits around the Canary Islands.
The Icod landslide from the northern flank of Tenerife not only generated a debris avalanche phase (Watts & Masson, 1995; Masson et al. 2002), but produced a volcaniclastic turbidite that spans three interconnected basins. The Icod... more
The Icod landslide from the northern flank of Tenerife not only generated a debris avalanche phase (Watts & Masson, 1995; Masson et al. 2002), but produced a volcaniclastic turbidite that spans three interconnected basins. The Icod turbidite (160,000ka) was reported and correlated during work in the Madeira Abyssal Plain (Pearce & Jarvis, 1992; Rothwell, Pearce & Weaver, 1992). Here it forms a series of vertically stacked sand bodies accumulating into a single event bed. However, the Madeira Abyssal Plain is fed from the Agadir Basin by a series of channels, thus invoking a level of complexity to the deposit with the flow exiting channels at different times. The Icod turbidite can be found deposited more proximally to source in the Agadir Basin as a 0.3-0.6m stacked sand with accompanying 0.2-1.5m mudcap. With this stacked sand facies present here a number of other mechanisms can still be viable: (1) multistage retrogressive landslide failure, (2) flow reflection and (3) internal waves.
Geochemical methodologies including ICP-AES, ICP-MS, XRF, ITRAX micro-XRF, SEM EDS and laser-diffraction grain-size analysis have been employed here to investigate the potential of a retrogressive failure at source being the driver of this facies. Evidence suggests that this stacked sand facies in this case is derived from the failure mechanism at source.
Five vertical sand packages have been identified and correlated through the Agadir Basin, with the initial basal package representing the thickest. However, this amalgamated sand displays degrees of complexity with correlated internal erosional surfaces marked by sand-sand grain-size breaks. There are also sand-sand grain-size breaks found at the transition between facies associated with flow properties i.e. Bouma Tb parallel laminations and Bouma Tc ripple laminations. Each of the stacked sand intervals also has a sand-mud grain-size break present at the top of the package. This sand-mud break could possibly indicate (1) bypass of coarse silt or (2) removal of previously deposited silt by erosion of a post-depositional mudflow associated with mudcap remobilisation.
Further to the stacked subunit facies and grain-size breaks, there are additional complexities to the deposit. An omission of a typical Bouma Ta facies is observed, replaced with a thick well-developed banded Bouma Tb, representing density sorting and flow fractionation of dense basaltic clasts and >100μm foraminifera. Above developing ripple laminations associated with Bouma Tc development is a 0.2-0.5m thick convolute laminated sand. This convoluted sand represents increasing shear stress across developing ripples.
Geochemical methodologies including ICP-AES, ICP-MS, XRF, ITRAX micro-XRF, SEM EDS and laser-diffraction grain-size analysis have been employed here to investigate the potential of a retrogressive failure at source being the driver of this facies. Evidence suggests that this stacked sand facies in this case is derived from the failure mechanism at source.
Five vertical sand packages have been identified and correlated through the Agadir Basin, with the initial basal package representing the thickest. However, this amalgamated sand displays degrees of complexity with correlated internal erosional surfaces marked by sand-sand grain-size breaks. There are also sand-sand grain-size breaks found at the transition between facies associated with flow properties i.e. Bouma Tb parallel laminations and Bouma Tc ripple laminations. Each of the stacked sand intervals also has a sand-mud grain-size break present at the top of the package. This sand-mud break could possibly indicate (1) bypass of coarse silt or (2) removal of previously deposited silt by erosion of a post-depositional mudflow associated with mudcap remobilisation.
Further to the stacked subunit facies and grain-size breaks, there are additional complexities to the deposit. An omission of a typical Bouma Ta facies is observed, replaced with a thick well-developed banded Bouma Tb, representing density sorting and flow fractionation of dense basaltic clasts and >100μm foraminifera. Above developing ripple laminations associated with Bouma Tc development is a 0.2-0.5m thick convolute laminated sand. This convoluted sand represents increasing shear stress across developing ripples.
The Icod Turbidite represents the deposit from a turbidity current generated by the ~160,000ka Icod Landslide from the northern flank of Tenerife. The Agadir Basin represents a proximal depocentre for this turbidity current and has been... more
The Icod Turbidite represents the deposit from a turbidity current generated by the ~160,000ka Icod Landslide from the northern flank of Tenerife. The Agadir Basin represents a proximal depocentre for this turbidity current and has been cored extensively. This turbidite is composed of a stacked vertical sequence of interbedded sands and muds (subunit facies), which have been theorised as being generated by a multistage landslide failure at source (Rothwell, Pearce and Weaver, 1992; Wynn & Masson, 2003). Though extensive grain-size dating has removed flow reflexion as a causal mechanism, only geochemical analyses can attribute a multistage landslide failure proximally to the generation of this facies.
The non-destructive and high resolution (500μm) methodology of the ITRAX µXRF core logger highlights this instrument’s importance as an analytical tool. Results from each subunit sand are compared in core CD166/27, and show variations in the bulk geochemical signatures. There are five separate subunit sands (SBU1-5), of which the basal sand interval is composed of three further compositional divisions (SBU1a-c). Within chemical variation plots there is a distinct field for SBU1a, while SBU1b-c and SBU2-3 fall within a similar field, and SBU4-5 fall within another distinct field. To quantify the results further, bulk XRF measurements were taken from the subunits sands, lower pelagic interval and mudcap to attempt a calibration of the incoherence normalised raw counts to give oxide wt% of major elements and ppm concentrations of trace elements.
However, it may be argued that density sorting may contribute to the generation of these chemical variations. Data from volcanic grains of similar hydrodynamic properties may yield unequivocal results in determining subtle variations in provenance on the northern Tenerife flank. Volcanic glasses 100-150μm were targeted using the Eagle III µXRF analyser chemical to supplement the ITRAX results. Here volcanic glasses from SBU1a-c develop disparate geochemical fields to those of volcanic glasses from SBU2-5.
The implications of the ITRAX and Eagle III results are that catastrophic volcanic flank collapses, such as the Icod landslide, may occur as multistage events rather than as a single event. In addition to the inferences to landslide and turbidite process mechanisms, there is a major implication to tsunami generation from volcanic island flank collapses. Since the Ward and Day (2001) mega-tsunami model of a La Palma landslide relies on a single slab block failure, the results discovered in this study could imply that flank collapses occur in multiple stages, thus generating smaller tsunami hazards.
The non-destructive and high resolution (500μm) methodology of the ITRAX µXRF core logger highlights this instrument’s importance as an analytical tool. Results from each subunit sand are compared in core CD166/27, and show variations in the bulk geochemical signatures. There are five separate subunit sands (SBU1-5), of which the basal sand interval is composed of three further compositional divisions (SBU1a-c). Within chemical variation plots there is a distinct field for SBU1a, while SBU1b-c and SBU2-3 fall within a similar field, and SBU4-5 fall within another distinct field. To quantify the results further, bulk XRF measurements were taken from the subunits sands, lower pelagic interval and mudcap to attempt a calibration of the incoherence normalised raw counts to give oxide wt% of major elements and ppm concentrations of trace elements.
However, it may be argued that density sorting may contribute to the generation of these chemical variations. Data from volcanic grains of similar hydrodynamic properties may yield unequivocal results in determining subtle variations in provenance on the northern Tenerife flank. Volcanic glasses 100-150μm were targeted using the Eagle III µXRF analyser chemical to supplement the ITRAX results. Here volcanic glasses from SBU1a-c develop disparate geochemical fields to those of volcanic glasses from SBU2-5.
The implications of the ITRAX and Eagle III results are that catastrophic volcanic flank collapses, such as the Icod landslide, may occur as multistage events rather than as a single event. In addition to the inferences to landslide and turbidite process mechanisms, there is a major implication to tsunami generation from volcanic island flank collapses. Since the Ward and Day (2001) mega-tsunami model of a La Palma landslide relies on a single slab block failure, the results discovered in this study could imply that flank collapses occur in multiple stages, thus generating smaller tsunami hazards.
Giant landslides are prevalent during the erosional phase of volcanic island evolution, and have been found to affect the islands of Tenerife, La Palma and El Hierro in recent geologic time (Masson et al. 2002, and references therein).... more
Giant landslides are prevalent during the erosional phase of volcanic island evolution, and have been found to affect the islands of Tenerife, La Palma and El Hierro in recent geologic time (Masson et al. 2002, and references therein). These landslides are potentially tsunamigenic, and thus warrant detailed study to understand their failure/emplacement processes and access their recurrence interval. Many landslides and debris avalanches generate long runout turbidity currents. This study will provide an overview of these volcaniclastic flow deposits recovered in cores from around the western Canary archipelago. The aim will be to constrain event frequency, pathways and processes, in addition to resolving the source failure mechanisms.
The studied cores have been visually logged and mineralogical analysis of turbidite samples carried out. Provenance of turbidites has been ascertained using a variety of bulk and grain-specific geochemical techniques. In addition, petrophysical examinations have been completed to enable correlations between cores, which have been aided by the use of biostratigraphic coccolithophore dating. Foraminiferal studies have yielded δ18O curves using stable isotope analytical techniques, resulting in correlation of events to key climatic episodes.
Volcaniclastic turbidites demonstrate a variety of compositions, supporting deposition from 1) erosional outflows from barrancos, 2) large scale flank collapses, and 3) remobilisation of volcanic and biogenic material previously deposited on seamounts. Provenance analysis of individual events has highlighted the high flux of turbidites derived from El Hierro compared to Tenerife or La Palma. Furthermore, the presence of thick (>1.0m) granular turbidite deposits in the El Julan Fan (southwest El Hierro) has contributed to the generation of the Canary Debris Flow “concrete facies”.
The studied cores have been visually logged and mineralogical analysis of turbidite samples carried out. Provenance of turbidites has been ascertained using a variety of bulk and grain-specific geochemical techniques. In addition, petrophysical examinations have been completed to enable correlations between cores, which have been aided by the use of biostratigraphic coccolithophore dating. Foraminiferal studies have yielded δ18O curves using stable isotope analytical techniques, resulting in correlation of events to key climatic episodes.
Volcaniclastic turbidites demonstrate a variety of compositions, supporting deposition from 1) erosional outflows from barrancos, 2) large scale flank collapses, and 3) remobilisation of volcanic and biogenic material previously deposited on seamounts. Provenance analysis of individual events has highlighted the high flux of turbidites derived from El Hierro compared to Tenerife or La Palma. Furthermore, the presence of thick (>1.0m) granular turbidite deposits in the El Julan Fan (southwest El Hierro) has contributed to the generation of the Canary Debris Flow “concrete facies”.
Two widespread volcaniclastic turbidites in the Moroccan Turbidite System can be linked to the volcanic flank collapses of northern El Hierro (El Golfo landslide; dated at ~15ka) and Tenerife (Icod landslide; dated at ~160,000ka). The... more
Two widespread volcaniclastic turbidites in the Moroccan Turbidite System can be linked to the volcanic flank collapses of northern El Hierro (El Golfo landslide; dated at ~15ka) and Tenerife (Icod landslide; dated at ~160,000ka). The distribution of these volcaniclastic turbidites is significant, as it indicates that both flows have travelled along- or up-slope through the Agadir Basin for distances up to ~1,000km from source. Furthermore, the sedimentary facies of these two deposits includes a distinctive series of vertically stacked sequences of turbidite sands interbedded with turbidite muds. The presence of this ‘subunit’ architecture within these two turbidites in the Agadir Basin can be linked to either (1) multistage retrogressive failure of the source landslide, or (2) basin margin reflections of the turbidity current.
A multidisciplinary approach has been adopted to study both of these widespread deposits, in an attempt to decipher whether multistage retrogressive failure is the primary cause of the stacked subunit architecture. Analysed datasets include: visual logs, grain size analysis, petrographic composition, bulk and grain-specific geochemistry and petrophysics.
Initial results for the Icod turbidite are encouraging, with five regular subunit packages being identified and correlated. Variations in subunit mineralogy and bulk geochemistry, in addition to grain size analysis, invoke a multistage event generated at source rather than an effect of flow reflection. Furthermore, investigations of the Icod turbidite demonstrate added complexities to the process of its emplacement, with grain size breaks and internal erosion surfaces indicating flow bypass, convolute rippled laminations indicating periodic dewatering, and a widespread contorted mudcap facies indicating post-depositional remobilisation.
A multidisciplinary approach has been adopted to study both of these widespread deposits, in an attempt to decipher whether multistage retrogressive failure is the primary cause of the stacked subunit architecture. Analysed datasets include: visual logs, grain size analysis, petrographic composition, bulk and grain-specific geochemistry and petrophysics.
Initial results for the Icod turbidite are encouraging, with five regular subunit packages being identified and correlated. Variations in subunit mineralogy and bulk geochemistry, in addition to grain size analysis, invoke a multistage event generated at source rather than an effect of flow reflection. Furthermore, investigations of the Icod turbidite demonstrate added complexities to the process of its emplacement, with grain size breaks and internal erosion surfaces indicating flow bypass, convolute rippled laminations indicating periodic dewatering, and a widespread contorted mudcap facies indicating post-depositional remobilisation.
The Moroccan continental margin and Canary Islands have been subjected to repeat submarine mass wasting. This thesis aims to investigate the sediment gravity flow deposits associated with these submarine landslides. The Agadir Basin... more
The Moroccan continental margin and Canary Islands have been subjected to repeat submarine mass wasting. This thesis aims to investigate the sediment gravity flow deposits associated with these submarine landslides. The Agadir Basin represents a deepwater depocentre and conduit for turbidity currents sourced from the Agadir Canyon and Western Canary Islands. A previous basin stratigraphy is re-analysed and extended to cover the last 600 ka. This stratigraphy is validated by using down-core geophysics and chemostratigraphy. ITRAX mudcap geochemistry has been used to assess turbidite provenance. Siliciclastic turbidites in this record have been shown to
occur predominantly at transitions from glacial to interglacial periods. The latest landslides identified from the Western Canary Islands, the El Golfo and Icod landslides, have been proposed to be multistage. This is based on the resence of multiple fining-upwards sequences, known as subunits, within the associated sediment gravity flow deposits. Grain-size data, core petrophysics, bulk geochemistry and volcanic glass geochemistry has shown that the subunits within the Icod deposit originate from a multistage collapse. The Late Quaternary volcaniclastic turbidites in the Madeira Abyssal Plain in the last 1.5 Ma are also investigated, and found to potentially represent the El Golfo, Icod, Cumbre Nueva, Orotava, El Julán, Güímar, Tinor and Rogues de García landslides from the Western Canary Islands. These deposits also represent multistage landslides, which show that this failure mechanism is more common and has major implications for tsunamigenesis. Furthermore, analysis of ODP volcaniclastic turbidites (0-17 Ma) shows that deposits are coincidental in age and provenance with periods of voluminous and explosive volcanism on specific islands.
occur predominantly at transitions from glacial to interglacial periods. The latest landslides identified from the Western Canary Islands, the El Golfo and Icod landslides, have been proposed to be multistage. This is based on the resence of multiple fining-upwards sequences, known as subunits, within the associated sediment gravity flow deposits. Grain-size data, core petrophysics, bulk geochemistry and volcanic glass geochemistry has shown that the subunits within the Icod deposit originate from a multistage collapse. The Late Quaternary volcaniclastic turbidites in the Madeira Abyssal Plain in the last 1.5 Ma are also investigated, and found to potentially represent the El Golfo, Icod, Cumbre Nueva, Orotava, El Julán, Güímar, Tinor and Rogues de García landslides from the Western Canary Islands. These deposits also represent multistage landslides, which show that this failure mechanism is more common and has major implications for tsunamigenesis. Furthermore, analysis of ODP volcaniclastic turbidites (0-17 Ma) shows that deposits are coincidental in age and provenance with periods of voluminous and explosive volcanism on specific islands.
Research Interests:
Research Interests: Landslides and Turbidites
Research Interests:
Sequence stratigraphic models suggest that submarine landslide and turbidite activity is greatest during sea-level lowstands. However, growing evidence indicates that many turbidite systems are also active during sea-level highstands. The... more
Sequence stratigraphic models suggest that submarine landslide and turbidite activity is greatest during sea-level lowstands. However, growing evidence indicates that many turbidite systems are also active during sea-level highstands. The Moroccan Turbidite System is a mixed siliciclastic-volcaniclastic deepwater province offshore Northwest Africa. It comprises three depocentres, of which Agadir Basin is closest to the Moroccan shelf and Canary archipelago. The excellent core coverage and dating control
afforded to Agadir Basin deposits has provided an unparalleled opportunity to derive accurate records of turbidite (and associated landslide) frequency and volume for the last 600 ka. Previous studies in the more distal Madeira Abyssal Plain depocentre of the Moroccan Turbidite System have indicated that large volume (>50 km3) turbidites occurred at oxygen isotope stage (OIS) boundaries. This study of Agadir Basin confirms that major turbidites (>50 km3) occurred at high sea-levels either immediately prior to or after each OIS boundary. Patterns in siliciclastic turbidite frequency indicate increases in the number and magnitude of events during the transgression from glacial lowstand to interglacial highstand. However, numerous large-volume and smallervolume events also occur during mid-OIS interglacial highstands. In addition to climate change and associated rising sea-level, the present study indicates that sediment flux, including ocean productivity, continental erosion (siliciclastic) and effusive volcanism (volcaniclastic) are potentially significant preconditioning factors for submarine landsliding and turbidite generation.
afforded to Agadir Basin deposits has provided an unparalleled opportunity to derive accurate records of turbidite (and associated landslide) frequency and volume for the last 600 ka. Previous studies in the more distal Madeira Abyssal Plain depocentre of the Moroccan Turbidite System have indicated that large volume (>50 km3) turbidites occurred at oxygen isotope stage (OIS) boundaries. This study of Agadir Basin confirms that major turbidites (>50 km3) occurred at high sea-levels either immediately prior to or after each OIS boundary. Patterns in siliciclastic turbidite frequency indicate increases in the number and magnitude of events during the transgression from glacial lowstand to interglacial highstand. However, numerous large-volume and smallervolume events also occur during mid-OIS interglacial highstands. In addition to climate change and associated rising sea-level, the present study indicates that sediment flux, including ocean productivity, continental erosion (siliciclastic) and effusive volcanism (volcaniclastic) are potentially significant preconditioning factors for submarine landsliding and turbidite generation.
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The use of ITRAX μXRF in the study of sediment cores in Agadir Basin has enabled a detailed appraisal of the turbidite stratigraphy and provenance. Evaluation of the mudcap geochemistry of basin turbidites has supported the original... more
The use of ITRAX μXRF in the study of sediment cores in Agadir Basin has enabled a detailed appraisal of the turbidite stratigraphy and provenance. Evaluation of the mudcap geochemistry of basin turbidites has supported the original distinction of siliciclastic, volcaniclastic and calcareous turbidite types. Indeed, this detailed ITRAX μXRF study has also highlighted three separate provenances for the three volcaniclastic turbidites as theorised in previous studies. These include determination of the phonolitic Tenerife source for A14, and individual basaltic sources for A2 (El Hierro) and A8 (Madeira). Further study of siliciclastic mudcap geochemisties has shown that, although a similar regional source (Moroccan shelf/slope) is theorised, there are subtle variations in composition indicating different local sources or thickness of sediment column failed. Previous and ongoing research has indicated that siliciclastic turbidity currents exiting the Agadir Canyon are erosive. Thus basinal turbidite compositions could be the result of differential erosion at the canyon mouth. Indeed, on comparison of the composition of the same large-volume turbidites from the Agadir Canyon and Agadir Basin sites, the canyon composition is offset from that of the basin. Small-volume turbidites are found to have similar compositions in the canyon and in the basin, thus unlike the largervolume flows, these small-volume events are principally non-erosive. Analysis of the complete series of turbidites in the Agadir Canyon displays subtly different geochemical compositions, supporting early notions of different local sources within the same geographic area.
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Volcanic island landslides can pose a significant geohazard through landslide-generated tsunamis. However, a lack of direct observations means that factors influencing the tsunamigenic potential of landslides remain poorly constrained.... more
Volcanic island landslides can pose a significant geohazard through landslide-generated tsunamis. However, a lack of direct observations means that factors influencing the tsunamigenic potential of landslides remain poorly constrained. The study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process, such as total event volume and whether landslides occurred as single or multiple events. The northern flank of Tenerife has undergone multiple landslide events, the most recent being the Icod landslide dated at ~165 ka. The Icod landslide generated a turbidite with a deposit volume of ~210 km3, covering 355,000 km2 of seafloor off northwest Africa. The Icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals (named subunits SBU1-7). Evidence from subunit bulk geochemistry, volume, basal grain size, volcanic glass composition and sand mineralogy, combined with petrophysical and geophysical data, suggests that the subunit facies represents multistage retrogressive failure of the Icod landslide. The basal subunits (SBU1-3) indicate that the first three stages of the landslide had a submarine component, whereas the upper subunits (SBU4-7) originated above sea level. The presence of thin, non-bioturbated, mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure. These results have important implications for tsunamigenesis from such landslides, as multistage retrogressive failures, separated by hours to several days and with both a submarine and subaerial component, will have markedly lower tsunamigenic potential than a single-block failure.
Research Interests:
Volcaniclastic turbidites in the Madeira Abyssal Plain provide a long-term record of potentially very hazardous volcanic island landslides from the Canary Islands. These volcaniclastic turbidites are recovered in piston cores that span... more
Volcaniclastic turbidites in the Madeira Abyssal Plain provide a long-term record of potentially very hazardous volcanic island landslides from the Canary Islands. These volcaniclastic turbidites are recovered in piston cores that span the last 1.5 Ma and ODP cores that extent back to 17 Ma. The timing, provenance and volumes of these turbidites potentially provide key information about the age, frequency and emplacement dynamics of submarine landslides from the Canary Islands, especially the western islands of Tenerife, La Palma and El Hierro. These records indicate that landslides coincided with protracted periods of volcanic edifice growth. This indicates that loading of the volcanic edifices is a key preconditioning factor for landslide occurrence. Evidence from the last large-volume failures from Tenerife suggests possible correlations with explosive eruptions at the end of eruptive cycles. In addition, the majority of large-volume landslides occur during warmer and wetter climates associated with sea level rise and subsequent highstand.
Research Interests:
The record of volcaniclastic turbidites in the Madeira Abyssal Plain represents a history of the largest Late Quaternary volcanic island landslides from the Western Canary Islands. These 0-1.5 Ma volcaniclastic turbidites are composed of... more
The record of volcaniclastic turbidites in the Madeira Abyssal Plain represents a history of the largest Late Quaternary volcanic island landslides from the Western Canary Islands. These 0-1.5 Ma volcaniclastic turbidites are composed of multiple finingupwards turbidite sands, known as subunits. The subunits indicate that the landslides responsible for the sediment gravity flows were multistage. The compositions of volcanic glass assemblages from each individual subunit in an event bed are subtly different. This indicates that each subunit is discrete, implying that the subunit represents a separate failure as part of a multistage landslide. This has significant implications for geohazard assessment. Multistage failures distribute the total landslide volume amongst numerous smaller failures, therefore reducing the volume of rock entering the ocean at any one time. The multistage failure mechanism reduces individual landslide volumes from 200-300 km3 to less than 100 km3. Thus although multistage failures ultimately reduce the potential landslide and tsunami threat, the events will still have significant consequences.
Research Interests:
Work included in this chapter include: + Quaternary landslide-induced volcaniclastic turbidites in the Canary Basin: a systematic investigation of distribution, provenance and event history. + Relationship between caldera-forming... more
Work included in this chapter include:
+ Quaternary landslide-induced volcaniclastic turbidites in the Canary Basin: a systematic investigation of distribution, provenance and event history.
+ Relationship between caldera-forming eruptions and major flank collapses.
+ Growth of the Canary Islands recorded in the distal turbidite record.
+ Turbidite record of Northwest African Continental Slope Landslides.
+ Quaternary landslide-induced volcaniclastic turbidites in the Canary Basin: a systematic investigation of distribution, provenance and event history.
+ Relationship between caldera-forming eruptions and major flank collapses.
+ Growth of the Canary Islands recorded in the distal turbidite record.
+ Turbidite record of Northwest African Continental Slope Landslides.
Future work includes:
+ Canary Island Submarine Landslides
+ Turbidite Records of the deepwater basins of the NE Altantic
+ Deepwater Depostional Processes
+ Burial of Organic Carbon in Turbidites
+ Canary Island Submarine Landslides
+ Turbidite Records of the deepwater basins of the NE Altantic
+ Deepwater Depostional Processes
+ Burial of Organic Carbon in Turbidites