Depositional Lobes Research Articles

Constraining the sedimentology and stratigraphy of submarine intraslope lobe deposits using exhumed examples from the Karoo Basin, South Africa

Intraslope lobe deposits provide a process record of the infill of accommodation on submarine slopes and their recognition enables the accurate reconstruction of the stratigraphic evolution of submarine slope systems. Extensive exposures of discrete sand-prone packages in Units D/E and E, Fort Brown Formation, Karoo Basin, South Africa, permit analysis of the sedimentology and stacking patterns of three intraslope lobe complexes and their palaeogeographic reconstruction via bed-scale analysis and physical correlation of key stratal surfaces. The sand-prone packages comprise tabular, aggradationally to slightly compensationally stacked lobe deposits with constituent facies associations that can be attributed to lobe axis, lobe off-axis, lobe-fringe and distal lobe-fringe environments. Locally, intraslope lobe deposits are incised by low aspect ratio channels that mark basinward progradation of the deepwater system. The origin of accommodation on the slope for lobe deposition is interpreted to be due to differential compaction or healing of scars from mass wasting processes. The stacking patterns and sedimentary facies arrangement identified in this study are distinct from those of more commonly recognized basin-floor lobe deposits, thereby enabling the establishment of recognition criteria for intraslope lobe deposits in other less well exposed and studied fine-grained systems. Compared to basin floor lobes, intraslope lobes are smaller in volume, influenced by higher degrees of confinement, and tend to show aggradational stacking patterns.

Spatial–temporal evolution of aeolian blowout dunes at Cape Cod

This paper explores historical evolution of blowouts at Cape Cod National Seashore (CCNS), USA — a site that hosts one of the world's highest densities of active and stabilized blowouts. The Spatial–Temporal Analysis of Moving Polygons (STAMP) method is applied to a multi-decadal dataset of aerial photography and LiDAR to extract patterns of two-dimensional movement and morphometric changes in erosional deflation basins and depositional lobes. Blowout development in CCNS is characterized by several geometric (overlap) and movement (proximity) responses, including: i) generation and disappearance, ii) extension and contraction, iii) union or division, iv) clustering and v) divergence by stabilization. Other possible movement events include migration, amalgamation and proximal stabilization, but they were not observed in this study. Generation events were more frequent than disappearance events; the former were highest between 1985 and 1994, while the latter were highest between 2000 and 2005. High rates of areal change in erosional basins occurred between 1998 and 2000 (+3932m2a−1), the lowest rate (+333m2a−1) between 2005 and 2009, and the maximum rate (+4589m2a−1) between 2009 and 2011. Union events occurred mostly in recent years (2000–2012), while only one division was observed earlier (1985–1994). Net areal changes of lobes showed gradual growth from a period of contraction (−1119m2a−1) between 1998 and 2000 to rapid extension (+2030m2a−1) by 2010, which is roughly concurrent with rapid growth of erosional basins between 2005 and 2009. Blowouts extended radially in this multi-modal wind regime and, despite odd shapes initially, they became simpler in form (more circular) and larger over time. Net extension of erosional basins was toward ESE (109°) while depositional lobes extended SSE (147°). Lobes were aligned with the strongest (winter) sand drift vector although their magnitude of areal extension was only 33% that of the basins. These differences in extension responses likely result from more complex and evolving flow-form interactions inside erosional basins. Historical photographs and CCNS documents suggest that blowout evolution may be influenced by land-use changes, such as revegetation campaigns in 1985 that were followed by high blowout generation. High magnitude regional storm events (e.g., hurricanes) also play a role. The analytical framework presented provides a systematic means for two-dimensional geomorphic change detection and pattern analysis that can be applied to other landscapes.

Seepage in Isfjorden and its tributary fjords, West Spitsbergen

Abstract This study analyses pockmark morphology and their spatial distribution in Isfjorden relative to seabed morphology, bedrock geology, fault systems, glacial landforms and processes using multibeam bathymetric data. It provides insight into the possible mechanisms of pockmark formation, high density pockmark field evolution, and fluid migration pathways. A total of 1304 pockmarks occur in the Isfjorden at water depths of 40 to 320 m, varying from circular to elongate in plan-view. Their diameter ranges from 14 to 265 m and their depths from 1 to 11 m. Elongate pockmarks are dominant in the Isfjordbanken and outer Isfjorden where the seafloor is influenced by the West Spitsbergen Current. The West Spitsbergen fold-and-thrust belt and other fault systems sub-cropping at the Isfjorden seafloor correlate spatially with the high density pockmark zones. The pockmarks are preferentially located on the marine sediments draping the bedrock of Isfjorden fjord system. They are most abundant in the areas underlain by Jurassic–Cretaceous and the Triassic–Lower Jurassic bedrock. Pockmarks found ahead of submarine slope failures may have formed due to dewatering of soft sediments as a result of rapid increase of overpressure caused by deposition of glacigenic debris lobes. Fault conduits, potential source rock and thin postglacial sediment layers are found to be crucial for the formation of pockmarks. Modeling results of the near-shore subsea permafrost and potential gas hydrate stability zone imply thawing permafrost and gas hydrate dissociation as additional possible mechanisms for pockmark formation in Isfjorden.

Sedimentología e Icnología de deltas fluvio-dominados afectados por descargas hiperpícnicas de la Formación Lajas (Jurásico Medio), Cuenca Neuquina, Argentina.

There are few recognized examples of fluvial-dominated deltaic systems affected by hyperpycnal discharges. The development of predictive models in those systems are essential to understand the distribution of sedimentary facies and for determining the location of the main sandy bodies, which constitute the potential hidrocarbon reservoirs. In Portada Covunco and Sierra de la Vaca Muerta areas (Neuquén, Argentina), the Lajas Formation constitutes an excellent example of a deltaic fluvio-dominated succession consisting of prodelta and deltaic front deposits, affected by hyperpycnal discharges and reworked by wave action (storm and normal wave action). Prodelta deposits show a strongly tabular geometry alternating between mudstones and fine sandstones with abundant organic matter and development of an impoverished Cruziana ichnofacies. Deltaic-front deposits are integrated by mudstones, fine to coarse sandstones and fine conglomerates showing tabular geometries and development of the Skolithos and Glossifungites ichnofacies, the later related to deltaic lobe avulsión. Normal progradation of this deltaic system shows stratigraphic intervals consisting of tabular and lenticular bodies of variable thicknesses assigned to hyperpycnal-channel and lobe systems. Internally, these deposits show transitional and recurrent passages between different sedimentary structures with marked textural variations, multiple internal reactivation surfaces and abundant organic matter content. Hyperpycnal channels systems have different dimensions and fill patterns. At the foot of the areas with the greatest gradients, hyperpycnal discharges produced mayor channels with aggradational fill, whereas in areas with lower gradients, high sinuosity channels developed. Hyperpycnal lobes were accumulated in areas where hyperpycnal flows lost confinement. The presence of conglomeratic levels affected by wave action on top of the lobe deposits indicates pauses in sedimentation during which colonization windows could develope, allowing the establishment of the benthic fauna.

Arran Field: a complex heterolithic reservoir on the margins of the Forties Fan System

Abstract The Arran Field contains gas-condensate accumulated within the Paleocene Forties Sandstone Member of the Sele Formation. It is located along the margin of the medial Forties turbidite depositional system, on the eastern flank of the Central Graben's Eastern Trough. The field comprises a low-relief southern extension (Arran South) from a high-relief northern closure (Arran North) around a salt diapir. The eastern margin of the field represents the pinch-out of the Forties Sandstone Member against the Jaeren High. As part of the field development planning, a comprehensive re-evaluation of subsurface data was undertaken. A thorough understanding of the reservoir distribution and turbidite architectures was vital to ensure that the appropriate elements were captured within the reservoir model. This was achieved through a thorough integration and multidisciplinary interpretation of all available data including seismic, core, petrophysical and analogue data. These data indicate that the best quality Forties Sandstone Member reservoir consists of stacked, elongate, amalgamated and non-amalgamated fairway sandstone bodies. These thick-bedded and sand-dominated reservoir units pass laterally into, and are extensively interbedded with, linked debrites, heterolithic low-density turbidite lobe fringe deposits, slumps, and debris flows, along with hemipelagic and turbiditic shales. A seismic shale volume ( V shale ), derived from inverted pre-SDM data, together with reflection seismic data, were used to identify and map intra-reservoir depositional lobe geometries. These show large-scale, lobe-like depositional bodies which migrated laterally over time and onlapped on to the Jaeren High to the east. Within these, smaller-scale elongated lobe bodies, generally derived from the NW, are interpreted from layer-parallel extractions of the seismic V shale volume. Possible slump units were also identified, predominantly derived from the edges of the Arran North salt diapir, suggesting that the basin floor topography was mobile during deposition. The seismic V shale volume was used to condition the static facies model, utilizing probability relationships between the seismic data and core facies at the wells, providing a soft linkage between the data and models developed. Core, analogue data and facies interpretations from the seismic data were utilized to ensure that appropriate reservoir body geometries and spatial relationships were maintained in the static model and allowed key reservoir heterogeneities to be captured. This integrated approach also supported analysis of reservoir uncertainties, with specific focus on the vertical and lateral reservoir connectivity within this lobe-dominated reservoir.

Geomorphological evidence for transient water flow on Vesta

Vesta, the second most massive asteroid, has long been perceived as anhydrous. Recent studies suggesting the presence of hydrated minerals and past subsurface water have challenged this long-standing perception. Yet, direct geologic indications of water activity on Vesta's surface were unexpected. Herein we show evidence that transient water flowed on the surface, in a debris-flow-like process, and left distinctive geomorphologic features. Based on detailed analysis of highest-resolution (∼20 m/pixel) images obtained by the Dawn spacecraft, we identify a class of locally occurring, interconnected and curvilinear gully networks on the walls of young (< hundreds of Ma) impact craters, ending in lobate deposits near the crater floors. As curvilinear systems only occur within impact craters, we propose that they formed by a particulate-dominated flow of transient water that was released from buried ice-bearing deposits by impact-induced heating and melting. This interpretation is in accordance with the occurrence of pitted terrain on lobate deposits and crater floors. Pitted terrain is proposed to result from the degassing of volatiles. The proposed buried ice-bearing deposits are likely localized in extent and may be currently extant in Vesta's subsurface. Together with the discovery of water evaporation on Ceres and water activity on several small asteroids, our results support the new paradigm that water is widespread in the asteroid belt.

LITOFACIÁLNÍ ANALÝZA BÁZE HRADECKO-KYJOVICKÉHO SOUVRSTVÍ (NÍZKÝ JESENÍK, MORAVSKOSLEZSKÁ JEDNOTKA ČESKÉHO MASIVU)

A detailed field facies and ichnofacies analysis undertaken in the eastern part of the Nízký Jesník Mts. revealed that the basal part of Hradec-Kyjovice Formation of Upper Viséan age corresponded to coarse-grained siliciclastic turbidite system. Research was focused on detailed measurement of fifteen outcrops in the area. The formation was deposited in deep water environmental of the foreland basin by sediment gravity flows. Five facies were identified in the Hradec Member of the Hradec-Kyjovice Formation: conglomerate facies, pebble to coarse grained sandstone facies, coarse grained sandstone facies, sandstone-siltstone facies and the muddy siltstone facies. The conglomerate facies, pebble to coarse grained sandstone facies and coarse grained sandstone facies represent proximal, coarse grained channel deposits of high-density turbidite currents. The sandstone-siltstone sediments consist of a variety of turbidites deposites in lobes and interchannel environments. The muddy siltstone facies were deposited in interchannel environments by lowdensity turbidite currents. Some depositional lobes contain trace fossils of the Nereites ichnofacies. Sedimentary record of the basal parts of the Hradec-Kyjovice Formation indicates a Late Viséan a change in the development of Culm basin in Upper Viséan and beginning of new sedimentary cycle of sedimentation governed presumably by a compressional tectonic pulse.

Sedimentology of Coastal Deposits in the Seychelles Islands—Evidence of the Indian Ocean Tsunami 2004

The Seychelles, an archipelago in the Indian Ocean at a distance of 4,500–5,000 km from the west coast of Sumatra, were severely affected by the December 26, 2004 tsunami with wave heights up to 4 m. Since the tsunami history of small islands often remains unclear due to a young historical record, it is important to study the geological traces of high energy events preserved along their coasts. We conducted a survey of the impact of the 2004 Indian Ocean tsunami on the inner Seychelles islands. In detail we studied onshore tsunami deposits in the mangrove forest at Old Turtle Pond in the Curieuse Marine National Park on the east coast of Curieuse Island. It is thus protected from anthropogenic interference. Towards the sea it was shielded until the tsunami in 2004 by a 500 m long and 1.5 m high causeway which was set up in 1909 as a sediment trap and assuring a low energetic hydrodynamic environment for the protection of the mangroves. The causeway was destroyed by the 2004 Indian Ocean Tsunami. The tsunami caused a change of habitat by the sedimentation of sand lobes in the mangrove forest. The dark organic rich mangrove soil (1.9 Φ) was covered by bimodal fine to medium carbonate sand (1.7–2.2 Φ) containing coarser carbonate shell fragments and debris. Intertidal sediments and the mangrove soil acted as sources of the lobe deposits. The sand sheet deposited by the tsunami is organized into different lobes. They extend landwards to different inundation distances as a function of the morphology of the onshore area. The maximum extent of 180 m from the shoreline indicates the minimum inundation distance to the tsunami. The top parts of the sand lobes cover the pneumatophores of the mangroves. There is no landward fining trend along the sand lobes and normal grading of the deposits is rare, occurring only in 1 of 7 sites. The sand lobe deposits also lack sedimentary structures. On the surface of the sand lobes numerous mostly fragmented shells of bivalves and molluscs were distributed up to 150 m from the coastline. Intact bivalve shells were mostly found positioned with the convex side upwards. On small ledges of a granitic body at 130–150 m from the shore mostly fragmented and gravel sized shells were deposited at different elevations up to 4 m above sea level. This implies a run up height of at least 4 m above sea level up to 150 m from the present shoreline.

Influence of topography on wind speed over a coastal dune and blowout system at Jockey's Ridge, NC, USA

AbstractThis study examines the spatial distribution of wind speed across a coastal dune system located at Jockey's Ridge State Park, North Carolina. The study area consists of a trough blowout through a foredune ridge, and the landforms that have developed behind the foredune. Wind speed and direction were measured simultaneously with single sensors placed at a fixed height in 13 locations across the blowout/dune complex. Fractional wind speed‐up is computed for sampling stations using data from a mast located on the beach as the reference. Results show that wind speeds were generally accelerated across the study site. The highest speeds were recorded on the foredune ridges adjacent to the blowout. Wind was accelerated through the center of the blowout throat and along the downwind lateral wall. Further into the blowout, at the base of the ramp to the depositional lobe, higher wind speeds shifted to the upwind lateral wall and continued to accelerate up the ramp as air exited to the rear. Significant variations in the wind speed‐up pattern were associated with different wind approach angles, with greater speed‐up occurring when the winds were aligned normal to the dune system. The speed‐up decreased as the angle of approach became increasingly oblique to the ridge. The patterns of wind speed‐up across the site point to the influence of topography on airflow. To quantify the relationship, measures of several topographic variables were obtained along sample transects running upwind from each sample station along flow lines representing different wind approach angles. Examination of correlation coefficients between wind speed‐up and topographic variables suggests that for groups of stations with similar topographic characteristics, 30–50% of the variations in speed‐up may be explained by the upwind topographic variability. Copyright © 2014 John Wiley &amp; Sons, Ltd.

The base-of-slope carbonate breccia system of Céüse (Tithonian, S-E France): Occurrence of progradational stratification in the head plug of coarse granular flow deposits

Once interpreted as a deep-water canyon infilling and later as some kind of tempestite deposit, the Tithonian breccias of Ceüse are here reinterpreted as a small lobe deposit, emplaced at the mouth of a gully cutting into a slope between two deep-water terraces in the eastern part of the subalpine basin. The breccias belong to two basic categories: mostly grain-supported and occasionally mud-supported. Spectacular large-scale oblique geometries (apparent lateral accretions) are observed in the grain-supported breccias, both within the infilling of the lower feeder channel and in the updip part of the lobe. Detailed analyses of these geometries show that they correspond to progradational features. Both laterally and in a more distal position on the lobe, these progradational bodies evolve into a pile of unsorted massive breccias, sometimes showing a crude, even stratification. We thus propose a depositional model for the grain-supported breccias, linking the two facies as follows: the deposition of a gravity flow begins at the toe-of-slope (mouth of the tributary gully) by a progradational head which evolves downslope and laterally to a splay of massive or crudely stratified breccia. The internal oblique stratification flattens distally over a distance of a few kilometres. Elementary beds pile up in morphological compensation to build the 100m thick breccia body of Céüse. Because the breccias are derived from the gravity-reworking of deep-water nodular carbonates, there is no sand-sized material available in the depositional system, or only a little probably produced through an erosive clast grain diminution process during transport. This explains why the thick breccia beds pass quickly eastward to thin-bedded mud turbidites.

Sedimentological characteristics and new detrital zircon SHRIMP U–Pb ages of the Babulu Formation in the Fohorem area, Timor-Leste

Sedimentological characteristics and zircon provenance dating of the Babulu Formation in the Fohorem area, Timor-Leste, provide new insights into depositional process, detailed sedimentary environment and the distribution of source rocks in the provenance. Detrital zircon sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages range from Neoarchean to Triassic, with the main age pulses being Paleozoic to Triassic. In addition, the maximum deposition ages based on the youngest major age peak (ca 256–238 Ma) of zircon grains indicate that the basal sedimentation of the Babulu Formation occurred after the early Upper Triassic. The formation consists predominantly of mudstone with minor sandstone, limestone and conglomerate that were deposited in a deep marine environment. These deposits are composed of six lithofacies that can be grouped into three facies associations (FAs) based on the constituent lithofacies and bedding features: basin plain deposits (FA I), distal fringe lobe deposits (FA II) and medial to distal lobe deposits (FA III). The predominance of mudstone (FA I) together with intervening thin-bedded sandstones (FA II) suggest that the paleodepositional environment was a low energy setting with slightly basin-ward input of the distal part of the depositional lobes. Discrete and abrupt occurrences of thick-bedded sandstone (FA III) within the FA I mudstone suggests that sandstone originated from a collapse of upslope sediments rather than a progressive progradation of deltaic turbidites. This combined petrological and geochronological study demonstrates that the Babulu Formation in the Fohorem area of the Timor-Leste was initiated as a submarine lobe system in a relatively deep marine environment during the Upper Triassic and represents the extension of the Gondwana Sequence at the Australian margin.

Origin, evolution and anatomy of silt‐prone submarine external levées

AbstractSubmarine external levées are constructional features that develop outside slope channel systems, and are a volumetrically significant component of continental margins. However, detailed observations of their process sedimentology and depositional architecture are rare. Extensive exposures of external levées at multiple stratigraphic intervals and well‐constrained palaeogeographic positions in the Fort Brown Formation, Karoo Basin, South Africa, have been calibrated with research boreholes. This integrated data set permits their origin, evolution and anatomy to be considered, including high‐resolution analysis of sedimentary facies distribution and characterization of depositional sub‐environments. An idealized model of the stratigraphic evolution and depositional architecture of external levées is presented, and variations can be attributed to allogenic (for example, sediment supply) and autogenic (for example, channel migration) factors. Initiation of external levée construction is commonly marked by deposition of a basal sand‐rich facies with sedimentary structures indicating rapid deposition from unconfined flows. These deposits are interpreted as frontal lobes. Propagation of the parent channel, and resultant flow confinement, lead to partial erosion of the frontal lobe and development of constructional relief (levées) by flow overspill and flow stripping. Overall fining‐upwards and thinning‐upwards profiles reflect increased flow confinement and/or waning flow magnitude through time. Identification of a hierarchy of levée elements is not possible due to the absence of internal bounding surfaces or sharp facies changes. The down‐slope taper in levée height and increasing channel sinuosity results in increasing numbers of crevasse lobe deposits, and is reflected by the increased occurrences of channel avulsion events down‐dip. External levées from the Fort Brown Formation are silt‐rich; however their stratigraphic evolution and the distribution of many components (such as sediment waves and crevasse lobe) share commonalities with mud‐rich external levées. This unique integrated data set has permitted the first high‐resolution characterization of external submarine levée systems.

Evolution of a deep-water lobe system in the Neogene trench-slope setting of the East Coast Basin, New Zealand: Lobe stratigraphy and architecture in a weakly confined basin configuration

This study presents a new depositional analysis of the stratigraphic architecture of a deep-water lobe system in a trench-slope basin setting by examining the upper Miocene Hikuwai sandstone and Mapiri Formation of the East Coast Basin (ECB) in the Tolaga Bay area, New Zealand. The Hikuwai sandstone is up to 385 m thick and is enveloped by the mud-rich middle and upper Mapiri Formation. Stratigraphic sections measured at centimeter-scale and high-resolution photo-panoramas were collected from sea-cliff exposures for stratigraphic and architectural analysis and definition of six lithofacies. The Hikuwai sandstone is interpreted to represent a succession of frontal lobe deposits that contain a distributary network of meter-scale erosional channels and scours on their surface. Lobe lithofacies depend on their proximity to the sediment source, and their proximity to a distributary channel and/or scour.The late Miocene basin setting is interpreted to be a weakly to moderately confined trench-slope basin. The basin configuration controlled the development of the depositional system through elongate fault-controlled ridges that directed sediment dispersal pathways through longitudinal troughs. The basin filled from north to south in four phases: 1) lobe aggradation related to healed slope accommodation, 2) retrogradation and lateral migration of the system 3) back-stepping of the system upslope causing reduced confinement and allowing flows to become wider, longer, and thinner, and 4) shut off of sediment supply and mass wasting of the upper Mapiri Formation, representing either renewed fault movement or equilibration of the system to the regional slope profile.This paper provides a detailed description of the internal structure of lobes in a trench-slope setting, and a depositional model that relates lobe lithofacies to the filling of healed slope accommodation. Therefore, this work presents an analog applicable for elongate basins, such as in the trench slope or settings with mud diapirism, where only seismic-scale or limited data is available.

Matrix‐rich and associated matrix‐poor sandstones: Avulsion splays in slope and basin‐floor strata

AbstractA common facies observed in deep‐water slope and especially basin‐floor rocks of the Neoproterozoic Windermere Supergroup (British Columbia, Canada) is structureless, coarse‐tail graded, medium‐grained to coarse‐grained sandstone with from 30% to &gt;50% mud matrix content (i.e. matrix‐rich). Bed contacts are commonly sharp, flat and loaded. Matrix‐rich sandstone beds typically form laterally continuous units that are up to several metres thick and several tens to hundreds of metres wide, and commonly adjacent to units of comparatively matrix‐poor, scour‐based sandstone beds with large tabular mudstone and sandstone clasts. Matrix‐rich units are common in proximal basin‐floor (Upper Kaza Group) deposits, but occur also in more distal basin‐floor (Middle Kaza Group) and slope (Isaac Formation) deposits. Regardless of stratigraphic setting, matrix‐rich units typically are directly and abruptly overlain by architectural elements comprising matrix‐poor coarse sandstone (i.e. channels and splays). Despite a number of similarities with previously described matrix‐rich beds in the literature, for example slurry beds, linked debrites and co‐genetic turbidites, a number of important differences exist, including the stratal make‐up of individual beds (for example, the lack of a clean sandstone turbidite base) and their stratigraphic occurrence (present throughout base of slope and basin‐floor strata, but most common in proximal lobe deposits) and accordingly suggest a different mode of emplacement. The matrix‐rich, poorly sorted nature of the beds and the abundance and size of tabular clasts in laterally equivalent sandstones imply intense upstream scouring, most probably related to significant erosion by an energetic plane‐wall jet or within a submerged hydraulic jump. Rapid energy loss coupled with rapid charging of the flow with fine‐grained sediment probably changed the rheology of the flow and promoted deposition along the margins of the jet. Moreover, these distinctive matrix‐rich strata are interpreted to represent the energetic initiation of the local sedimentary system, most probably caused by a local upflow avulsion.

Geologic mapping of Vesta

We report on a preliminary global geologic map of Vesta, based on data from the Dawn spacecraft’s High-Altitude Mapping Orbit (HAMO) and informed by Low-Altitude Mapping Orbit (LAMO) data. This map is part of an iterative mapping effort; the geologic map has been refined with each improvement in resolution. Vesta has a heavily-cratered surface, with large craters evident in numerous locations. The south pole is dominated by an impact structure identified before Dawn’s arrival. Two large impact structures have been resolved: the younger, larger Rheasilvia structure, and the older, more degraded Veneneia structure. The surface is also characterized by a system of deep, globe-girdling equatorial troughs and ridges, as well as an older system of troughs and ridges to the north. Troughs and ridges are also evident cutting across, and spiraling arcuately from, the Rheasilvia central mound. However, no volcanic features have been unequivocally identified. Vesta can be divided very broadly into three terrains: heavily-cratered terrain; ridge-and-trough terrain (equatorial and northern); and terrain associated with the Rheasilvia crater. Localized features include bright and dark material and ejecta (some defined specifically by color); lobate deposits; and mass-wasting materials. No obvious volcanic features are evident. Stratigraphy of Vesta’s geologic units suggests a history in which formation of a primary crust was followed by the formation of impact craters, including Veneneia and the associated Saturnalia Fossae unit. Formation of Rheasilvia followed, along with associated structural deformation that shaped the Divalia Fossae ridge-and-trough unit at the equator. Subsequent impacts and mass wasting events subdued impact craters, rims and portions of ridge-and-trough sets, and formed slumps and landslides, especially within crater floors and along crater rims and scarps. Subsequent to the formation of Rheasilvia, discontinuous low-albedo deposits formed or were emplaced; these lie stratigraphically above the equatorial ridges that likely were formed by Rheasilvia. The last features to be formed were craters with bright rays and other surface mantling deposits. Executed progressively throughout data acquisition, the iterative mapping process provided the team with geologic proto-units in a timely manner. However, interpretation of the resulting map was hampered by the necessity to provide the team with a standard nomenclature and symbology early in the process. With regard to mapping and interpreting units, the mapping process was hindered by the lack of calibrated mineralogic information. Topography and shadow played an important role in discriminating features and terrains, especially in the early stages of data acquisition.

Debris flows: behaviour and hazard assessment

Debris flows are water‐laden masses of soil and fragmented rock that rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form lobate deposits when they spill onto valley floors. Because they have volumetric sediment concentrations that exceed 40 percent, maximum speeds that surpass 10 m/s, and sizes that can range up to ∼109 m3, debris flows can denude slopes, bury floodplains, and devastate people and property. Computational models can accurately represent the physics of debris‐flow initiation, motion and deposition by simulating evolution of flow mass and momentum while accounting for interactions of debris’ solid and fluid constituents. The use of physically based models for hazard forecasting can be limited by imprecise knowledge of initial and boundary conditions and material properties, however. Therefore, empirical methods continue to play an important role in debris‐flow hazard assessment.

Depositional architecture and evolution of progradationally stacked lobe complexes in the Eocene Central Basin of Spitsbergen

AbstractThe down‐dip portion of submarine fans comprises terminal lobes that consist of various gravity flow deposits, including turbidites and debrites. Within lobe complexes, lobe deposition commonly takes place in topographic lows created between previous lobes, resulting in an architecture characterized by compensational stacking. However, in some deep water turbidite systems, compensational stacking is less prominent and progradation dominates over aggradation and lateral stacking. Combined outcrop and subsurface data from the Eocene Central Basin of Spitsbergen provide a rare example of submarine fans that comprise progradationally stacked lobes and lobe complexes. Evidence for progradation includes basinward offset stacking of successive lobe complexes, a vertical change from distal to proximal lobe environments as recorded by an upward increase in bed amalgamation, and coarsening and thickening upward trends within the lobes. Slope clinoforms occur immediately above the lobe complexes, suggesting that a shelf‐slope system prograded across the basin in concert with deposition of the lobe complexes. Erosive channels are present in proximal axial lobe settings, whereas shallow channels, scours and terminal lobes dominate further basinward. Terminal lobes are classified as amalgamated, non‐amalgamated or thin‐bedded, consistent with turbidite deposition in lobe axis, off‐axis and fringe settings, respectively. Co‐genetic turbidite–debrite beds, interpreted as being deposited from hybrid sediment gravity flows which consisted of both turbulent and laminar flow phases, occur frequently in lobe off‐axis to fringe settings, and are rare and poorly developed in channels and axial lobe environments. This indicates bypass of the laminar flow phase in proximal settings, and deposition in relative distal unconfined settings. Palaeocurrent data indicate sediment dispersal mainly towards the east, and is consistent with slope and lobe complex progradation perpendicular to the NNW–SSE trending basin margin.

Shallow-water longshore drift-fed submarine fan deposition (Moisie River Delta, Eastern Canada)

Submarine canyons and associated submarine fans are in some cases located at the end of a littoral cell where they act as conduits for the transfer of eroded terrigenous sediments to the marine environment. Such fans are generally found in deep-water settings at >500 m water depth. Offshore the Moisie River Delta (NW Gulf of St. Lawrence, Eastern Canada), high-resolution multibeam bathymetry and seismic data led to the discovery of an unusually shallow submarine fan (≤60 m) located at the end of a littoral cell. Sediment is transported westward on the shallow coastal shelf, as demonstrated by the downcurrent displacement of oblique nearshore sandbars where the shelf narrows to less than 1 km. The steep slope near the end of the littoral cell is incised by a channel that feeds a submarine fan composed of smaller channels and depositional lobes. According to existing Holocene evolution models for the region, the fan formed within the last 5,000 years. Its evolution is largely due to the transport of sediment by longshore drift. Multibeam echosounder and seismic data also reveal that the gravity-driven accretion of the submarine fan is characterized mainly by two processes, i.e., frequent small-scale, downslope migration of sandwaves on the slope, and more episodic slumping/turbidity-current activity in the deeper part of the fan. This study documents that, besides their common deep-water location, smaller-scale submarine fans can occur also in very shallow water, implying that they could be more frequent than previously thought both in modern environments and in the rock record.

Superficial siderosis with predominant frontal lobe deposition in a person with Lewy body dementia

Superficial siderosis with predominant frontal lobe deposition in a person with Lewy body dementia

Exploratory analyses of regional human brain distribution of the PET tau tracer F18-labeled T807 (AV-1541) in subjects with normal cognitive function or cognitive impairment thought to be due to Alzheimer's disease

Recently, [F-18]-T807 was reported as having high affinity and selectivity to PHF-tau in brain sections from Alzheimer's disease patients (Xia et al, 2013). Chien et al, (2012) described initial imaging results in 6 subjects. We now have extended these initial observations. Ten subjects (6 F / 4 M; mean age 69) were recruited that were either cognitively normal (n=3) or had cognitive impairment of varying degrees thought to be due to Alzheimers Disease (AD; n=7). Mini-Mental State Exam (MMSE) scores ranged from 29 to 30 (mean = 29.7) and 7 to 29 (mean = 20.3), respectively. PET scanning consisted of dynamic (0–60 min) and static (80–100 min) scans after injection of approximately 10 mCi (370 MBq) iv [F-18]-T807 (AV-1541). Static PET scans were visually reviewed and also processed quantitatively by spatial normalization to MNI space and the AAL atlas. Cerebellum uptake was used as a visual and quantitative reference region for SUVr. Pearson's correlations examined possible relationships between [F-18]-T807 uptake and MMSE. Visually, the 3 cognitively normal subjects showed cortical uptake restricted to mesial temporal lobe regions only. In contrast, 6/7 of the cognitively impaired subjects had multiple focal areas of increased uptake (typically parts of lateral and medial temporal, lateral and medial parietal, and occipital lobes). The entire set of AAL regions for all subjects had SUVr range of 0.69 to 2.24. Intra-subject correlations of MMSE scores to mean and peak SUVr values were -0.75 (p=0.011) and -0.76 (p=0.011), respectively. Uptake in some regions, and combinations of regions, showed variably higher correlations to MMSE, up to r = -0.90. The observed patterns of regional [F-18]-T807 uptake are consistent with previous observations at autopsy in AD patients (levels and extent of tau deposits and neurofibrillary tangles correlating with cognitive decline) and non-affected elderly (mesial temporal lobe deposits in Braak stages I-II), and support [F-18]-T807 as a suitable PET tracer for quantification of PHF-tau in human brain. Further studies are important to replicate these results, to better understand the relationship of specific PET brain regions to cognitive function and to comprehensively study tau deposition across the lifespan.