Sand Remobilization Research Articles

About this title - Subsurface Sand Remobilization and Injection

Sand injectites form during shallow-crustal deformation. Short periods of elevated pore-fluid pressure, which developed regionally, triggered formation of hydrofracture networks into which sand was sometimes injected. Sand injection complexes preserve a record of this process and sandstone intrusions are significant reservoirs in many petroleum systems. Most known subsurface sand injection complexes are from offshore NW Europe and associated with Paleogene strata. Outcrop occurrence is global. Sand injection into unconventional host rocks, including granitoid and metamorphic basement and coal seams, raises awareness of the breadth of geological environments in which sand injection may occur. Discordance between sandstone intrusions and sedimentary hosts occurs on a scale from millimetres to kilometres and is a fundamental diagnostic of intrusions. Microscale textural characterization provides new opportunities to establish possible additional criteria for differentiating intrusions from depositional sandstone. The significance of sand injection complexes in shallow crustal evolution is exemplified by the wide range of lithological hosts and diverse tectonostratigraphic settings documented in this volume. Potential for original research still remains.

Introduction: subsurface sand remobilization and injection

Abstract Observation of basin-scale networks of sandstone intrusions are described from subsurface studies and outcrop locations. Regional scale studies are prevalent in the volume and two new regionally significant subsurface sand injection complexes are described. Higher resolution studies, both outcrop and subsurface, show the small-scale complexity but high level of connectedness of sandstone intrusions. Discordance with bedding at all scales is diagnostic of sandstone intrusions. The propensity of hydraulic fractures to develop and fill with fluidized sand in a broad range of host rocks is demonstrated by examples from metamorphic and magmatic basement, and lignite. Terminology used to describe sandstone intrusions and other elements of sand injection complexes is diverse.

The Norwegian–Danish Basin: a dynamic setting for subsurface sand remobilization – established concepts on distribution and controlling factors

Abstract The Norwegian–Danish Basin is characterized by a depositional environment governed by incised valleys, localized sand deposition and rapid progradation of thick sediment packages during the Paleogene and Neogene. Subsurface sand injectites occur at five locations, with distinctive geometries and injection styles. Such vary from short-distance injectites where injected dykes and sills are in direct contact with the parent sand, to a long-distance sand extrudite >1 km vertically above the proposed parent sand. These endmembers establish the Norwegian–Danish Basin as a dynamic environment for subsurface sand remobilization. Although formation models exist for the injectites at each of the five locations, general considerations of sand injection mechanisms in the Norwegian–Danish Basin remain untested. This study presents a synthesis of geometrical characteristics, sand injection style and controlling factors for sand injection in the Norwegian–Danish Basin. By reviewing the existing literature and including new data, the study qualitatively addresses the effects of parent-sand distribution on injection style at the five locations, the overpressure generating mechanisms and the importance of faulting as a trigger mechanism. The results show that short-distance injectites typically occur in areas with a confined parent sand and that salt-related faulting is locally important as a trigger mechanism for sand remobilization. The main overpressure generating mechanism is differential loading and lateral transfer of pressure. The case studies also show a trend between larger depocentres required for remobilization of more distal parent sands relative to the depocentre. The results confirm the prevailing consensus that local conditions related to parent sand distribution and burial depth partly control injection geometry and style.

Evolution of sand and silt injection and effusion around the rim and depocenter of Paraná volcanic province

The Novo Hamburgo Complex (NHC) occurs widespread in the 1 million km2, Early Cretaceous Paraná volcanic province. Integrated field work with zircon dating and whole rock geochemistry supported the investigation. We used the sensitive high-resolution ion microprobe (SHRIMP II) to determine the U-Pb age of zircon from eight sandstones from pairs of parent Botucatu Formation (1.2 million km2, largest paleoerg in geological history) (n = 3) and injectites, extrudites (n = 5), total = 718 analyses. Samples were collected from south to northeast to northwest of the complex. Integrated age peaks (in Ma) occur at 151 (one grain), 236 (minor), 280–288 (significant), 528-536-544-626-628 (approximate 520–630; highest peak at 544), 1043–1057 (approximate 900–1300), 1734, 1968, 2046–2098, 2691, and 3300 (one grain). U-Pb age distribution barcode is similar for both parent sandstones and injectites, extrudites. No zircon from the Cretaceous Serra Geral Group of basalt and rhyodacite (134 ± 2 Ma) was dated in the sandstones. Differences between parent sandstones and injectites, extrudites originated by elutriation in 1–1700 m-high injection columns. Textural characteristics are bimodal, medium to fine grained in parent beds, and unimodal, fine grained in injectites, extrudites. Chemical differences are increase in Al, K, Na, Ca, Rb, Sr, Ba, ETR, Cu, U, Th in injectites, extrudites compared to parent beds. We conclude that the injected sandstone and contained zircon originated in the Botucatu Formation paleoerg ascending through the volcanic lavas in a sand (estimated 70 vol%) and water (30 vol%) slurry. This is a prime, unique example of paleoerg sand remobilization after aquifer heating and volcanic rock sealing in a huge injection complex.

Multiple episodes of sand injection leading to accumulation and leakage of hydrocarbons along the San Andreas/San Gregorio fault system, California

The presence of sand injections has been shown to enhance the likelihood of hydrocarbon traps within siliciclastic successions. Through the development of large interconnected networks of sills and dykes, sand injection complexes provide a volume of porous and permeable rocks within the low permeability host units. Overall, the formation of sand injection complexes requires extensive fracturing and hydrofracturing, which can be particularly pronounced when sand injections are coupled with brittle tectonic deformation. In some circumstances, this process may threaten the integrity of the reservoir top seal thereby preventing further hydrocarbon accumulation. Studying exceptional exposures along the coastal area of Santa Cruz in California, we report evidence for top seal failure associated with injection episodes. Two distinct sand injection episodes are proposed. The first event, datable to the Late Miocene, resulted in large volumes of sand being emplaced within the top-seal units, and was followed by accumulation of hydrocarbons within the newly injected sandstones. Later, a series of brittle tectonic events, associated with the San Andreas/San Gregorio Fault System, caused remobilization and accumulation of sand along newly formed fault planes. Our case study documents this combination of pervasive brittle deformation and sandstone injection along fault structures, which can ultimately disrupt the integrity of a host unit leading top seal failure and leakage of hydrocarbons.

Petrofacies of Eocene sand injectites of the Tumey Giant Injection Complex, California (USA)

The forearc succession of Great Valley Group in Central California provides some of the best examples of giant sand injection complexes in the world and is therefore considered valuable analogues for injectite systems in the subsurface. Several sand injection complexes are well described in the outcrop and subsurface, however the petrographic characteristics of injectites are still poorly documented. In this paper, we present the results of an integrated study of field observations, quantitative and qualitative sandstone petrography, provenance, and petrofacies analysis of the Tumey Giant Injection Complex (TGIC) in order to understand its lithostratigraphy and petrological evolution, and its impacts on reservoir petrofacies characteristics and fluid migration. The TGIC intrudes into a 450 m thick deep-water succession of slope mudrocks and sandy channel-fills of the Kreyenhagen Shale (Eocene), forming an interconnected network of sandstone sills, dykes and injection breccias. The complex generated a horizontal and vertical plumbing system for fluid migration, connecting isolated sandy channel-fills among low-permeability mudrocks. The primary detrital composition, diagenetic products, microtextures, and provenance signatures allowed for the definition and discrimination of depositional and intrusive petrofacies and their genetic relations. Petrofacies associations confirm that the gypsum-cemented feldspathic litharenites from the Kreyenhagen Shale channel-fills are the only source for the injection complex. Eodiagenetic compaction and extensive gypsum cementation reduced the primary porosity of the complex, while telodiagenetic dissolution of autigenic constituents formed pervasive secondary porosity. The underlying calcite-cemented arkosic sandstones of the Lodo and Domengine formations acted as barriers for fluid flow, aiding lateral fluid migration and overpressure buildup within the overlying Kreyenhagen channel-fills. Intense grain microfracturing occurred during sand remobilization and injection along with erosion of the host mudrocks. This study has significance for the generation of reliable stratigraphic and petrological models for sand injection complex genesis and evolution that consequently can help the understanding and exploration of injectite complexes elsewhere.

Origin of enigmatic sand injectite outcrops associated with non-tectonic forced-folding structure in Bahrah area, northern Kuwait Bay

Abstract This is a quantitative and qualitative study for the first time linking surface with subsurface geology to understand the occurrence and origin of enigmatic sand injectite outcrops in two sites within the Bahrah coastal plain area, northern Kuwait Bay. Field work observations and aerial photography were used to describe and characterize the surface geology and stratigraphy of the study area. Thirty-one rock samples were obtained for petrographical, fluid inclusions and strontium isotopes analyses. 3D seismic data were also used to assess the subsurface geology of the area. The petrography and microthermometry of fluid inclusions were used to understand the origin of fluids and gases associated with the formation of these sand injectites. We found that these surface geological features represent surface manifestation of subsurface geological and biological activities/processes. Therefore, we proposed a near-surface complex focused fluid injection mechanism/model responsible for the formation of the sand pipes. The model consists of five episodes: Episode-1 represents the development of near-surface geobody (? Paleoshoreline) sealed by a shale layer; Episode-2 represents the entrapment of hydrocarbons that migrated laterally up-dip within geobody, interacting with mixed seawater intrusion and fresh groundwater; Episode-3 represents the effect of biodegradation biological processes of the entrapped hydrocarbons generating CH4, CO2 and H2S gases; Episode-4 represents overpressure build-up due to gas generation exceeding pore volume of geobody and forming non-tectonic forced-folds and polygonal to semi-circular joints/fractures network; and Episode-5 represents overpressure release triggered by external factor(s) (seismic activities?) facilitating gases, water and sand remobilisation through weakened zones of natural fractures.

Triggers of sand remobilization in deep marine deposits

Abstract Sand injections are overrepresented in deep marine deposits and other settings with slope instabilities. We have examined seismic data from the North Sea to reveal their main trigger mechanisms. This was performed by inspection of local seismic observations in the Oligocene to Miocene sediments above the Utsira High and analyses of regional distribution of mounds at the top Hordaland Group surface in the northern North Sea. We make the observations that (1) the uplift of jack-up folds is in most cases larger than the sand thickness within the mounds, (2) onlap to mounds is present in periods with sand deposition, but no such onlap is seen in mudstones that were deposited in periods with little or no sand input, (3) onlapping to several Oligocene surfaces is seen above the Utsira High, (4) rim synclines are not present adjacent to Oligocene and Miocene mounds and (5) mounds that affect the top Hordaland Group surface are present in basin flanks and at basin-flank transitions but not in basin centres. We suggest that triggering by incipient slab sliding can explain these observations.

Reconstruction of subsurface sand remobilization from seismic data

Abstract Sand remobilization often occurs in deltaic depositional environments as a result of sediment load and de-watering during sediment compaction. Three-dimensional seismic data from a shelf and fan delta environment in the Central North Sea are interpreted using a colour processing technique which gives clues for reconstructing the depositional environment and remobilizing the sand. The shape and thickness of the sand remobilization features appear to be influenced by the depositional environment of parent sand. In the shallow part of the fan delta, irregular injectite geobodies are observed. In the proximal fan delta, large round saucer-shaped injectites indicate that the pressure release largely occurred in a crater-like shape. With increasing distance from the shelf break, the thickness of the sediment load and, thus, the pressure increases. Thin and extensive sheet-like injectite structures develop along faults. Some of these appear to reactivate pre-existing flanks of giant pockmarks.

Deposition or remobilization of the enigmatic Hefring Member sand, eastern North Sea – A multidisciplinary approach

Abstract Sand remobilization is a well-known and well-studied phenomenon and seismic observations particularly from the North Sea Giant Sand Injectite Province (NSGSIP) combined with outcrop investigations have permitted a good understanding of the physical processes of sand remobilization, trigger mechanisms and resulting seismic geometries. The degree of remobilization and the distinction between depositional and remobilized/injected sand from seismic data alone are however still relatively unconstrained. In this study, we use a multidisciplinary approach based on seismic stratigraphy, petrography and biostratigraphy, to investigate an enigmatic and apparently isolated Eocene sandstone body, the Hefring Member, which in the seismic data shows characteristics of both depositional and remobilized origin. We use the available well logs, cutting samples and side-wall cores to investigate whether we can address the degree of remobilization from seismic data alone, by linking the mapped seismic facies with ‘remobilization degree’ as observed from the well data. In addition to addressing the degree of remobilization, we propose a model for the formation of the Hefring Member which includes laterally restricted submarine channel sand deposition and secondary remobilization with mainly upward and lateral injection. We infer, that the remobilization of the Hefring Member was controlled by local and rapid differential loading, potentially emphasized by activity in the nearby D-1 fault system and triggered by a significant drop in sea level. Understanding the origin and evolution of the Hefring Member is important for unravelling the geological development of the area and because the sand member represents a new reservoir unit comparable to the nearby prolific Siri Canyon sandstone.

Single-crystal hematite (U–Th)/He dates and fluid inclusions document widespread Cryogenian sand injection in crystalline basement

The Tavakaiv Quartzite (informal) in Colorado, USA, is one of the world's largest basement-hosted clastic injectite systems and provides a glimpse into the tectonic and near-surface environment of ancient North America. The age, origin, and significance of Tavakaiv injectites has been debated for over a century, owing to inherent difficulties with assigning absolute age constraints to unfossiliferous sandstone intrusions. Here, we apply an innovative combination of single-crystal hematite (U–Th)/He thermochronometry and fluid inclusion microthermometry to hematite mineralization associated with the injectites to document the age and ambient fluid conditions of Tavakaiv injectite formation. Our approach confirms individual hematite crystals comprising commonly analyzed polycrystalline aggregates are the He diffusion domains and that hematite (U–Th)/He closure temperature increases with crystal size. We apply apatite and zircon fission-track thermochronometry to the Tavakaiv Quartzite and host rock to account for the consequences of Phanerozoic orogenic episodes on the hematite (U–Th)/He dates and explain the observed trends between hematite He date and crystal size. Our results indicate that hematite formed 676 ± 26 million years ago (arithmetic mean date ±1σ), constraining the timing of the Tavakaiv injection event. Fluid inclusion studies reveal that this mineralizing fluid was at least 200 °C and saline (>20 wt% CaCl2 equiv.). Comparison of new and previously published detrital zircon U–Pb age populations from quartzite samples yield a sediment source common to Tavakaiv bodies across a broader region and illuminate the greater areal extent of the Cryogenian injection event. We interpret that formation of basement-penetrating fracture arrays was associated with crustal extension within Rodinia at this time. This was accompanied by sand remobilization that promoted widespread sand injection within horsts bounding Neoproterozoic rift basins. The resulting sand injectites served as permeable pathways for contemporaneous circulation of saline groundwater, driven by fluid gradients in extensional and/or transtensional basins.

Sedimentary facies analysis and seismic interpretation of deep-water reservoirs, “PAC” field, offshore depobelt, Niger Delta basin

A high-resolution study involving the integration of cores, wireline logs and reflection seismic dataset was used to unravel the facies assemblages, reservoir quality and hydrocarbon potential of E1 and H9 reservoirs in the “PAC” field, Offshore Niger Delta. Facies analysis of the cored PAC-14 well shows six lithofacies: massive mudstone, parallel-laminated mudstones with sideritic bands, fine-grained parallel-laminated sandstone, medium-grained parallel-laminated sandstone, fine-grained ripple laminated sandstone, and coarse massive sandstone. These lithofacies were grouped into five facies associations: channel story axis (CSA), channel story margin (CSM), inter-channel thin beds (ICTB), mud-rich thin beds (MRTB) and injectites (INJ). These facies associations are typical of a confined channel and basin floor fan deposit of a deep-water turbidite depositional environment. Reservoir unit E1 was dominated by the facies association CSA while the H9 reservoir consists mainly of the facies associations MRTB and INJ. The observed sand injectites are suggested to have formed due to overloading of compacted sands leading to upward remobilization of sand into the overlying shale. Seismic horizons and faults were mapped to understand the structures, trend and reflections within the study area. Results from petrophysical volumetrics estimated the net hydrocarbon pore volume for the E1 and H9 reservoirs as 456 MMBBL and 378 MMBBL, respectively. Exploration for deep-water reservoir mainly targets high amplitude and bright seismic reflectors and ignores the low amplitude reflectors (dim loops) which are typically interpreted as non-reservoir units. However, this study shows a low-amplitude reflector containing medium-grained sand injectite unit, which has high porosity (31.7%) and permeability (4472 mD) values, and contains recoverable hydrocarbon.

Reconstruction of a Palaeosurface and Archaeological Site Location in an Anthropogenic Drift Sand Area

AbstractKnowledge of the position of archaeological remains in the surface relief provides important basic information for archaeological survey design and interpretation. Geomorphological processes in (pre)history may have resulted in a modification of the local relief around archaeological sites, especially in areas that are prone to sediment erosion and relocation, such as sheet sand and dune landscapes. In this study, we reconstructed and analysed the palaeorelief of an archaeological excavation site in an inland dune area in southern Brandenburg, Germany. The remains of two Mesolithic sites were documented in the archaeological excavations and found to be associated with a buried soil horizon. To gather information on the relief of the buried soil surface, we used a combination of sedimentological and pedological profile descriptions along archaeological survey trenches and geophysical prospection with ground penetrating radar supplemented with microdrone photography and photogrammetry, global positioning system (GPS) surveys, and analysis of LiDAR‐based elevation models. A digital elevation model of the buried surface was generated and analysed using a geographical information system (GIS). A comparison of the palaeosurface model with the recent surface elevation model shows that sand remobilization resulted in a considerable reshaping of the relief. Further, an analysis of the buried surface model shows that the relief position of the two archaeological sites in the study area was considerably more prominent in relation to the corresponding buried soil surface than in relation to the recent surface morphology. The results affirm the significance of Holocene sediment relocation for the local surface morphology and the importance of considering such relief modifications in archaeological surveys. Copyright © 2017 John Wiley & Sons, Ltd.

Discovery of Lower Cretaceous hydrothermal vent complexes in a late rifting setting, southern North Sea: insights from 3D imaging

We present data for 31 kilometre-scale hydrothermal vent complexes and associated sand remobilization that have formed as a consequence of magmatic intrusions within salt strata (southern North Sea, Dutch Sector). This study uses 3D seismic data tied to three wells and artificial neural networks to describe conical and cylindrical vent structures located in the NE part of the Broad Fourteens Basin. The structures are composites of 58 subvertical pipes that form complexes, and are 951 ± 364 m in height and 487 ± 426 m in diameter. Interactions of magma and fluids at depth triggered successive fluid pressure build-ups in Triassic sandstones, resulting in upward-propagated ruptures, followed by the collapse of overlying deposits and the injection and extrusion of fluidized sand. The relationship between vent tops and their overlying deposits indicates a Mid-Hauterivian age, unusual for volcanic activity in the North Sea area. This event could have a significant impact on hydrocarbon exploration, as the hydrothermal vent complexes bypass a regional source-rock and seal, offering new migration routes and connectivity between potential reservoirs. The intrusions also raise questions about the influence of transform tectonics on the focusing of volcanic activity during the late rifting phase of the North Sea. Supplementary material: Tables of seismic attributes and the geometry of the vent complexes as well as a 3D visualisation of the vents are available at https://doi.org/10.6084/m9.figshare.c.3571593

Introduction

Introduction Hilda Kurtz and Deepak Mishra Dear Readers, We are delighted to introduce the latest issue of Southeastern Geographer, which also marks the beginning of our tenure as editors. This issue contains a very thoughtful special forum on the Charleston massacre of June 2015. Five short essays by seven geographers reflect on the implications of the murder of nine African Americans attending bible study in church by a self-proclaimed white supremacist. Different lenses on the tragedy dovetail in compelling ways. We hope that the forum encourages reflection and perhaps debate about how to understand and respond to ongoing racial violence. The special forum is followed by five articles showcasing the diverse nature of our discipline from human to physical geography. Tyner’s article analyzes the speeches of Malcolm X to draw out new understandings of the Black freedom fighter’s legacy. Specifically, Tyner urges readers to rethink Malcolm as at once “a critical theorist of geography and a radical political philosopher.” He focuses on Malcolm’s attention to geographies of the South in the latter’s geopolitical philosophy. Malcolm’s geographical critiques de-emphasized Southern exceptionalism, Tyner shows, and argued that “racial oppression and exploitation were constitutive of U.S. society as a whole.” Markley and Sharma examine the politics surrounding a residential building demolition in suburban Roswell, Georgia as a case of revanchist (sub)urbanism in which working class, nonwhite residents are displaced in the name of revitalizing suburban space. This intriguing case study considers such changes in the suburban landscape in tension with ideas of (sub)urban entrepreneurialism and New Urbanism. Hardy, Hepinstall-Cymerman, and Fowler partnered with two local land trusts to develop a priority map for conservation easement recruitment in the Upper Oconee watershed in northeastern Georgia. In the U.S., more than half of threatened and endangered species and their habitats are estimated to be located on private land, yet few land trusts have the staff and technical skills necessary to conduct conservation assessments of their jurisdictions. Their study provides a framework for partnerships between academic researchers and land trusts working on increasing the effectiveness of private land conservation. Kennedy investigated the possible impact of breached historic mill ponds in the southern Blue Ridge region in terms of their potential to act as sediment sources, elevating regional sediment yield values. Her study demonstrated that small mill ponds were potentially scattered throughout the southern Blue Ridge, impounding low-order streams (2nd and 3rd), and that the abandonment and breaching of these dams resulted in the remobilization of sand-, silt-, and clay-sized particulates. [End Page 3] Brown, Ellis, and Bleakney assessed tornado frequency characteristics and vulnerability within 100 km of three major cities in Tennessee—Nashville, Memphis, and Knoxville. In the past ten years, Tennessee has recorded the highest number of tornado-related fatalities of all states. They found that three cities experienced an annual peak in tornadoes during the spring months; however, tornadoes in Memphis were spread out across more tornado days than in Nashville and Knoxville. Memphis also recorded the greatest number of fatalities among the three cities. Their study help provide insight on how tornado characteristics and associated vulnerability are changing on a regional scale. In short, the articles in this issue demonstrate the rich breadth of inquiry that makes contemporary academic geography so invigorating. We welcome your feedback. Best regards, Hilda Kurtz and Deepak Mishra MEET THE TEAM Greetings Members of SEDAAG, As in the incoming editors of Southeastern Geographer, we would like to introduce ourselves and our vision for the journal, and invite you to contribute in many ways and sundry to SEDAAG’s flagship regional journal. It is a privilege and an honor to continue in the footsteps of past editors Jim Wheeler, Derek Alderman, Scott Lecce, Graham Tobin, Robert Brinkmann, David Cochran, and Andy Reese. Their hard work and savvy innovations, including the move to quarterly publication, the linkage with UNC Press, the inclusion in Project Muse, and the publication of timely and well-received special issues, have positioned the journal as the most cited regional geography journal out there. We wish to thank the SEDAAG leadership for entrusting us to manage Southeastern Geographer for the...

An integrated subsurface analysis of clastic remobilization and injection; a case study from the Oligocene succession of the eastern North Sea

The North Sea giant sand injectite province (NSGSIP) is the global type area for large-scale sandstone intrusion complexes. Despite decades of research on the NSGSIP, this paper presents the first detailed case study in which all aspects of the intrusion process have been constrained, including fluid and sediment sources, injection timing and driving mechanisms. The study describes and analyses high-amplitude discordant amplitude anomalies within the Oligocene succession in the eastern North Sea, which are interpreted as large-scale brine-saturated sand injectites. Potential feeder conduits extending from the top of the Paleocene Lista Formation to the base of the injectites indicate that the source sand was located within the Lista Formation; possibly deposited in a distinct valley cut into the top of the Chalk Group. The geometry of the observed injectites ranges from a basal sill with wings to V-shaped and conical; their dimensions range from 300 to 3700 m in width and up to 150 m in height. In all cases, a significant deformation of the overburden is observed. The study area is located in the Ringkøbing-Fyn High area above the basement high separating two smaller Paleozoic half-grabens. During the Oligocene, rapid and significant differential loading occurred. We interpret that the injectites formed due to remobilization of the source sand facilitated by overpressure caused by differential loading combined with a possible influx of fluids from the deeper succession. The case study has with its assessment of the full injection system, implications for the understanding of subsurface remobilization processes and furthermore for oil and gas exploration in the eastern North Sea.

The influence of intertidal bar-trough morphology on sediment transport on macrotidal beaches, northern France

Sediment transport measurements, coastal hydrodynamics and beach morphological surveys were undertaken on three sandy barred macrotidal beaches of Northern France. Sand trapping took place at several locations across the intertidal zone during rising and falling tides in order to obtain estimates of both longshore and onshore sediment flux from the lower to the upper beach. Results show that intertidal bars are responsible for significant wave energy dissipation leading to a decrease of sand transport towards the upper beach. Sediment transport appeared to be substantially higher on the bars than within the troughs due to wave breaking processes that are responsible for intense sand remobilization. The comparison of onshore sediment transport with longshore transport showed that onshore-directed transport is generally higher than the longshore sediment flux, suggesting that significant amounts of sand are directed shoreward across the bars, contributing to the onshore migration of intertidal bars. Sediment transport rates within the troughs proved to be significant only during runnel drainage when flow channelization was responsible for a local increase in sediment transport, this seaward-directed transport representing a sand recycling mechanism that contributes to the stability of the intertidal bars. Our measurements also showed a low alongshore variability in longshore sediment transport rates, which is an additional factor that plays a role in maintaining the linear bar and trough morphology on these macrotidal beaches.

Beach morphological changes in response to marine turtles nesting: a preliminary study of Awala-Yalimapo beach, French Guiana (South America)

ABSTRACT Peron, C. , Chevallier, D., Martin G., Chatelet A., Anthony, E.J., Le Maho Y., Gardel, A., 2013. Beach morphological changes in response to marine turtles nesting: a preliminary study of Awala-Yalimapo beach, French Guiana (South America) Each year from February through July, Chelonia mydas (green turtles) and Dermochelys coriacea (leatherback turtles) come to nest on Awala-Yalimapo beach. During the nesting season, the presence of gravid turtles may directly affect the general morphology of the beach by provoking sand remobilization during firstly the conception of their nest and then during the nest disguising. Digital elevation models were realized to qualify and quantify the topographic modification conducted by the macro-bioturbation effect of marine turtles. Green turtles and leatherback turtles do not provoke the same perturbation on the beach. C. mydas affect the upper part of the beach by constructing their nest. Whereas D.coriacea provoke more important impact on the lower upper-beach w...

Outcrop-based reservoir characterization of a kilometer-scale sand-injectite complex

This study documents that Danian-aged sand remobilization of deep-water slope-channel complexes and intrusion of fluidized sand into hydraulically fractured slope mudstones of the Great Valley sequence, California, generated 400-m (1312 ft)–thick reservoir units: unit 1, parent unit channel complexes for shallower sandstone intrusions; unit 2, a moderate net-to-gross interval (0.19 sand) of sills with staggered, stepped, and multilayer geometries with well-developed lateral sandstone-body connectivity; unit 3, a low net-to-gross interval (0.08 sand) of exclusively high-angle dikes with good vertical connectivity; and unit 4, an interval of extrusive sandstone. Unit 2 was formed during a phase of fluidization that emplaced on an average 0.19 km3 (0.046 mi3) of sand per cubic kilometer of host sediment. Probe permeametry data reveal a positive relationship between sill thickness and permeability. Reservoir quality is reduced by the presence of fragments of host strata, such as the incorporation of large rafts of mudstone, which are formed by in-situ hydraulic fracturing during sand injection. Mudstone clasts and clay- and silt-size particles generated by intrusion-induced abrasion of the host strata reduce sandstone permeability in multilayer sills (70 md) when compared to that in staggered and stepped sills (586 and 1225 md, respectively). Post-injection cementation greatly reduces permeability in high-angle dikes (81 md). This architecturally based reservoir zonation and trends in reservoir characteristics in dikes and sills form a basis for quantitative reservoir modeling and can be used to support conceptual interpretations that infer injectite architecture in situations where sands in low net-to-gross intervals are anticipated to have well-developed lateral and vertical connectivity.

Impact of atmospheric circulation patterns on coastal dune dynamics, NW Spain

Dunes in temperate latitudes have experienced a significant stabilization in recent times, essentially as a consequence of the expansion of dense vegetation cover. Yet, the causes for this gradual stabilization as well as the causes promoting antecedent aeolian mobilization remain poorly understood. The Traba coastal dune field, located in NW Spain, was examined to explore the causes inducing aeolian activity and subsequent stabilization since 1940. Morphological changes were identified through the combination of aerial photographs and geophysical techniques. Local wind field regimes were simulated using a regional climate model to obtain the variability of the most relevant modes of atmospheric circulation in the North Atlantic and European regions; North Atlantic Oscillation (NAO), Eastern Atlantic (EA) and Scandinavian (SCAND). This allows us to identify the impact of these circulation modes over dune dynamics. Results document an episode of aeolian activity during the 1950s followed by a gradual stabilization and fixation of the dune coincident with a decrease on storm and wind intensity. Yet, aeolian sand movement remained active in small areas (blowouts), occurring mainly during the summer. NE winds associated with a negative phase of the EA explain the movement of sand within the dune field under favorable conditions of sand supply. On the other hand, sand supply to the dune field from the beach was promoted by NW winds coincident with the summer negative phase of NAO. During winter, the negative NAO favored frequent SW winds associated with the passage of intense storms, which in turn explain sand remobilization from the beach making sediment available for the NW winds to blow inland. With this work, it is proven that to understand past and future aeolian activity requires critical consideration of the variability and impact of the two principal modes of atmospheric circulation in the North Atlantic (NAO and EA). The SCAND mode explaining a lower percentage of the local wind field variability was also included to achieve higher significance levels of explained variance.