Remobilized Sediments

Nuclear discharges to the oceans have given rise to significant accumulations of radionuclides in sediments which can later remobilise back into the water column. A continuing supply of radionuclides to aquatic organisms and the human food chain can therefore exist, despite the absence of ongoing nuclear discharges. Radionuclide remobilisation from sediment is consequently a critical component of the modelled radiation dose to the public. However, radionuclide remobilisation fluxes from contaminated marine sediments have never been quantitatively determined in-situ to provide a valid assessment of the issue. Here, we combine recent advances in the Diffusive Gradients in Thin Films (DGT) sampling technique with ultrasensitive measurement by accelerator mass spectrometry (AMS) to calculate the remobilisation fluxes of plutonium, americium and uranium isotopes from the Esk Estuary sediments (UK), which have accumulated historic discharges from the Sellafield nuclear reprocessing facility. Isotopic evidence indicates the local biota are accumulating remobilised plutonium and demonstrates the DGT technique as a valid bioavailability proxy, which more accurately reflects the elemental fractionation of the actinides in the biota than traditional bulk water sampling. These results provide a fundamental evaluation of the re-incorporation of bioavailable actinides into the biosphere from sediment reservoirs. We therefore anticipate this work will provide a tool and point of reference to improve radiation dose modelling and contribute insight for other environmental projects, such as the near-surface and deep disposal of nuclear waste.

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km 2. Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5±9 km 3. The location of the MV field is limited to the pre-Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo-Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived (22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present-day mud flow activity is seen on the seabed seismic reflection in the study area. Cenozoic mud volcano record offshore Indus Fan, Calvès et al.

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km 2. Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5±9 km 3. The location of the MV field is limited to the pre-Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo-Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived (22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present-day mud flow activity is seen on the seabed seismic reflection in the study area. Cenozoic mud volcano record offshore Indus Fan, Calvès et al.

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km 2 . Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5±9 km 3 . The location of the MV field is limited to the pre-Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo-Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived ( 22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present-day mud flow activity is seen on the seabed seismic reflection in the study area.

The Selandien [58 Ma (PP3c-d)] Tyr sand in the Nini area, Siri Fairway, Danish North Sea, is severely in£uenced by the syn-depositional movement of the Nini Salt Diapir.The sand is faulted and remobilized into a degree where no original depositional signature can be recognized.TheTyr sand is drilled (and cored) by a number of wells, and the sand is never found in the same stratigraphic position. In some wells, theTyr sand is injected down into the chalk of the Danian Eko¢sk Formation, whereas other wells show theTyr sand embedded in the SelandienVile Member claystone, with varying degree of remobilization.TheTyr sand is thin (2^7 m) and is therefore below seismic resolution and close to seismic detection. Standard re£ection seismic data has proven problematic in determining the actual thickness and spatial distribution of the thin Tyr sand located within or immediately above the chalk. A simultaneous AVO (amplitude vs. o¡set) inversion using time-aligned angle stack seismic data, has improved resolution of the thin and complex reservoir, allowing a better understanding of the remobilization processes occurring above the rising salt diapir, and thereby an improved understanding of the reservoir and its performance.Three di¡erent remobilization features are described: injection into the chalk, injection up along fault planes and compactional driven injection.The force for the remobilization spans in orders of magnitude from metre scale phenomena, to injections of 100s of metres, moving millions of tons of material and £uids. GEOLOGICAL SETTING The hydrocarbon bearing reservoirs of the Nini Area in the Siri Fairway (Fig. 1) are the Bor, Tyr, Idun, Rind and Kolga Sands (Fig. 2) and are characterized by glauconiterich (20^30 vol%) ¢ne-grained well-sorted sand, embedded in hemipelagic to pelagic mud and marl stones

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km2. Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized ...

Seismic interpretation of mobile shales is challenging, mostly because of their unclear seismic expression. Imaging of mobile shales is difficult because of their low seismic-impedance contrast with many sedimentary rocks, spatial variation of their seismic properties, complex geometries of mobile-shales structures, and their complex internal structures. Furthermore, their seismic properties depend strongly on both overpressure and fluid content, which are difficult to predict.
To unravel this problem, we reviewed the physical properties of shales, merging data from in situ determinations of density and sonic velocities with experimental data and modeling results. We analyzed how diagenetic transformations during shale burial modify their physical properties and seismic characteristics. We reviewed conditions for smectite-illite transformation and gas generation (mostly methane) by oil cracking to evaluate how thermal gradient, shale composition, and hydrocarbon content modify the densities, sonic velocities, and seismic expressions of mobile shales. We then incorporated the amount and type of fluids released in shales during diagenesis into a study of seismic reflectivity of mobile shales.
Results derived theoretically for various types of mobile-shale contacts are compared with high-quality seismic examples, including mud volcanoes and a variety of complex shale diapirs. Observed reflectivity and seismic fabrics are discussed to infer clay composition, fluid content and type, and temperature.

We present results from the first high-resolution seismic reflection survey of the inner Western Indus Shelf, and Indus Delta, Arabian Sea. The results show major regional differences in sedimentation across the shelf from east to west, as well as north to south, both since the Last Glacial Maximum (*20 ka) and over longer time scales. We identify 10 major regional reflectors, interpreted as representing sea level lowstands. Strong compressive folding is observed underlying a reflector we have called Horizon 6 in the north-western shelf, probably compression associated with the transpressional deformation of the Murray Ridge plate boundary. Downslope profiles show a series of well developed clinoforms, principally at the shelf edge, indicating significant preservation of large packages of sediment during lowstands. These clinoforms have developed close to zones of deformation, suggesting that subsidence is a factor in controlling sedimentation and consequently erosion of the Indus Shelf. These clinoforms fan out from dome features (tectonic anticlines) mostly located close to the modern shoreline.

This paper presents a three-dimensional (3D) seismic analysis of sediment remobilization and £uid migration in a 2000-km 2 area above the Gjallar Ridge located in the VÖring Basin, o¡shore Norway. Three distinct types of mounded structures have been identi¢ed as resulting from focused £uid/gas migration and associated mud remobilization and intrusion.Type A structures are gently mounded, and we infer that these structures formed because of in situ remobilization of Middle Eocene to Lower^Middle Oligocene ¢ne-grained sediments in response to £uid and minor sediment injection via deep-seated normal faults.Type B structures comprise relatively steep-sided mounds and are restricted to the pre-Miocene interval.They are often located above narrow zones of discontinuous low-amplitude re£ections resembling gas chimneys. Some of theType B structures are associated with stacked amplitude anomalies and possible mud volcanoes at the base Pleistocene indicating their long-term signi¢cance as vertical £uid conduits.Type C structures comprise discrete mound features that seem to jack up theTop Palaeocene (Top Brygge) horizon.These are similar to hydrothermal mounds found elsewhere on the Norwegian Margin and associated with igneous sill intrusion during North Atlantic breakup.This study highlights the utility of 3D seismic data for mapping of £uid and sediment mobilization through time over large basinal areas.

The North Sea Basin contains an almost complete record of Cenozoic sedimentation, separated by clear regional unconformities. The changes in sediment characteristics, rate and source, and expression of the unconformities reflect the tectonic, eustatic and climatic changes that the North Sea and its margins have undergone. While the North Sea has been mapped locally, we present the first regional mapping of the Cenozoic sedimentary strata. Our study provides a new regional sub-division of the main seismic units in the North Sea together with maps of depocentres, influx direction and source areas. Our study provides a regional synthesis of sedimentation based on a comprehensive interpretation of a regionally covering reflection seismic data set. We relate observations of sediment characteristics and unconformities to the geological evolution. The timing, regional expression and stratigraphic characteristics of many unconformities indicate that they were generated by eustatic sea-level fall, often in conjunction with other processes. Early Cenozoic unconformities, however, relate to tectonism associated with the opening of the North Atlantic. From observation on a regional scale, we infer that the sediment influx into the North Sea during the Cenozoic is more complex than previously suggested clockwise rotation from early northwestern to late southern sources. The Shetland Platform supplied sediment continuously, although at varying rates, until the latest Cenozoic. Sedimentation around Norway changed from early Cenozoic influx from the southwestern margin, to almost exclusively from the southern margin in the Oligocene and from all of southern Norway in the latest Cenozoic. Thick Eocene deposits in the Central Graben are sourced mainly from a western and a likely southern source, indicating that prominent influx from the south did not only occur from the mid-Miocene onwards. We infer a new age for the increased progradational sediment influx in the Pleistocene of 2.5 Ma, coeval with Fennoscandian glaciation.

A 2-day conference entitled 'Subsurface sediment remobilization and £uid £ow in sedimentary basins' was held on 21^22 October 2008 at the Geological Society, London in order to address the manifestations, causes and e¡ects of sediment remobilization and £uid £ow. The conference brought together scientists from a variety of disciplines (geologists, geophysicists, geochemists, engineers) from academic and industrial communities to present and discuss the state-of-the-art understanding of subsurface sediment remobilization and £uid £ow processes. The conference was well attended and contained a stimulating breadth of papers presented as 40 talks and 12 posters and included a special session and press conference on the LUSI mud volcano in East Java.

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km 2 . Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5±9 km 3 . The location of the MV field is limited to the pre-Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo-Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived ( 22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present-day mud flow activity is seen on the seabed seismic reflection in the study area.

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km 2 . Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5±9 km 3 . The location of the MV field is limited to the pre-Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo-Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived ( 22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present-day mud flow activity is seen on the seabed seismic reflection in the study area.

The Selandien ] Tyr sand in the Nini area, Siri Fairway, Danish North Sea, is severely in£uenced by the syn-depositional movement of the Nini Salt Diapir.The sand is faulted and remobilized into a degree where no original depositional signature can be recognized.TheTyr sand is drilled (and cored) by a number of wells, and the sand is never found in the same stratigraphic position. In some wells, theTyr sand is injected down into the chalk of the Danian Eko¢sk Formation, whereas other wells show theTyr sand embedded in the SelandienVile Member claystone, with varying degree of remobilization.TheTyr sand is thin (2^7 m) and is therefore below seismic resolution and close to seismic detection. Standard re£ection seismic data has proven problematic in determining the actual thickness and spatial distribution of the thin Tyr sand located within or immediately above the chalk. A simultaneous AVO (amplitude vs. o¡set) inversion using time-aligned angle stack seismic data, has improved resolution of the thin and complex reservoir, allowing a better understanding of the remobilization processes occurring above the rising salt diapir, and thereby an improved understanding of the reservoir and its performance.Three di¡erent remobilization features are described: injection into the chalk, injection up along fault planes and compactional driven injection.The force for the remobilization spans in orders of magnitude from metre scale phenomena, to injections of 100s of metres, moving millions of tons of material and £uids.

The origin of Upheaval Dome, in Canyonlands National Park of southeastern Utah, has been a topic of controversy among geologists and planetary scientists. The structure has long been thought t o h a v e been created by salt diapirism from the underlying Paradox F ormation. Recent studies have suggested that impact could have formed the dome. To test the various hypotheses, we acquired, processed, and interpreted seismic re ection data within and adjacent to the structure. Both conventionally stacked and prestack-migrated images show 100 m relief in the Paradox F ormation, contrary to salt diapirism hypotheses. Further, we h a v e identi ed features within the images typical of impact structures, such as listric normal faults having displacements toward the center of the dome. Deformation occurs in two depth ranges, with the faulting that created the central uplift appearing only above the Hermosa Formation, in the upper 800 m of the structure. The images also suggest limited fracturing of the Hermosa and salt ow in the Paradox F ormation, perhaps due to gravitational relaxation of the crater form. Our image of a nearly at top of the Paradox salt strongly favors an impact origin for Upheaval Dome.

This paper presents a three-dimensional (3D) seismic analysis of sediment remobilization and £uid migration in a 2000-km 2 area above the Gjallar Ridge located in the VÖring Basin, o¡shore Norway. Three distinct types of mounded structures have been identi¢ed as resulting from focused £uid/gas migration and associated mud remobilization and intrusion.Type A structures are gently mounded, and we infer that these structures formed because of in situ remobilization of Middle Eocene to Lower^Middle Oligocene ¢ne-grained sediments in response to £uid and minor sediment injection via deep-seated normal faults.Type B structures comprise relatively steep-sided mounds and are restricted to the pre-Miocene interval.They are often located above narrow zones of discontinuous low-amplitude re£ections resembling gas chimneys. Some of theType B structures are associated with stacked amplitude anomalies and possible mud volcanoes at the base Pleistocene indicating their long-term signi¢cance as vertical £uid conduits.Type C structures comprise discrete mound features that seem to jack up theTop Palaeocene (Top Brygge) horizon.These are similar to hydrothermal mounds found elsewhere on the Norwegian Margin and associated with igneous sill intrusion during North Atlantic breakup.This study highlights the utility of 3D seismic data for mapping of £uid and sediment mobilization through time over large basinal areas.

A 2-day conference entitled 'Subsurface sediment remobilization and £uid £ow in sedimentary basins' was held on 21^22 October 2008 at the Geological Society, London in order to address the manifestations, causes and e¡ects of sediment remobilization and £uid £ow. The conference brought together scientists from a variety of disciplines (geologists, geophysicists, geochemists, engineers) from academic and industrial communities to present and discuss the state-of-the-art understanding of subsurface sediment remobilization and £uid £ow processes. The conference was well attended and contained a stimulating breadth of papers presented as 40 talks and 12 posters and included a special session and press conference on the LUSI mud volcano in East Java.

Subsurface sediment remobilization and fluid flow processes and their products are increasingly being recognized as significant dynamic components of sedimentary basins. The geological structures formed by these processes have traditionally been grouped into mud volcano systems, fluid flow pipes and sandstone intrusion complexes. But the boundaries between these groups are not always distinct because there can be similarities in their geometries and the causal geological processes. For instance, the process model for both mud and sand remobilization and injection involves a source of fluid that can be separate from the source of sediment, and diapirism is now largely discarded as a deformation mechanism for both lithologies. Both mud and sand form dykes and sills in the subsurface and extrusive edifices when intersecting the sediment surface, although the relative proportions of intrusive and extrusive components are very different, with mud volcano systems being largely extrusive and sand injectite systems being mainly intrusive. Focused fluid flow pipes may transfer fluids over hundreds of metres of vertical section for millions of years and may develop into mud volcano feeder systems under conditions of sufficiently voluminous and rapid fluid ascent associated with deeper focus points and overpressured aquifers. Both mud and sand remobilization is facilitated by overpressure and generally will be activated by an external trigger such as an earthquake, although some mud volcano systems may be driven by the re-charge dynamics of their fluid source. Future research should aim to provide spatio-temporal ‘injectite’ stratigraphies to help constrain sediment remobilization processes in their basinal context and identify and study outcrop analogues of mud volcano feeders and pipes, which are virtually unknown at present. Further data-driven research would be significantly boosted by numerical and analogue process modelling to constrain the mechanics of deep subsurface sediment remobilization as these processes can not be readily observed, unlike many conventional sediment transport phenomena.

As a result of the complex and variable nature of sea floor sedimentary environments and the problems associated with obtaining representative samples of sea floor materials, it has long been accepted that geophysical methods hold the greatest potential for rapid assessment of sea floor sediment physical property variability. This paper presents results of two experimental geophysical studies aimed at developing in situ sea floor sediment classification methodologies applicable to siliciclastic environments. At one of the two study sites, Irvine Bay in the Clyde Sea, an area of approximately 10 km 2 was intensively surveyed using a boomer seismic profiler and digital data acquisition system. Three core samples recovered in the area were used to calibrate seabed reflection responses at spot locations, and once calibrated, the entire geophysical dataset was inverted to produce maps showing the spatial distribution of sediment physical properties (porosity, density and grain size distribution) at the seabed surface. Very good agreement was found between seismic predictions of sediment properties and physical measurements made on independent core and grab samples. Similar levels of agreement were found for seismo-acoustic predictions made after surveying a transect in the Southern Baltic Sea. On the basis of these experimental studies it appears that, with only limited ground truth information, it is possible to invert high-resolution seismic reflection data to produce quantitative information on the spatial distribution of sea floor sediment physical properties. ß

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km2. Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5±9 km3. The location of the MV field is limited to the pre-Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo–Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived (∼22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present-day mud flow activity is seen on the seabed seismic reflection in the study area.