Middle Canyon Research Articles

Overview of Carbon Dioxide Injection and Water-Alternating-Gas Sensitivity

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 179569, “Overview of CO2 Injection and WAG Sensitivity in SACROC,” by Reza Barati Ghahfarokhi, SPE, The University of Kansas, and Steve Pennell, Michael Matson, SPE, and Mark Linroth, SPE, Kinder Morgan, prepared for the 2016 SPE Improved Oil Recovery Conference, Tulsa, 11–13 April. The paper has not been peer reviewed. This paper presents an overview of the SACROC Unit’s activity focusing on different carbon dioxide (CO2) injection and water-alternating-gas (WAG) projects that have made the SACROC unit one of the most successful CO2 injection projects in the world. The main objectives of this were was to review CO2 injection and injection-rate losses with respect to the CO2/WAG miscible displacement process in the SACROC Unit and recommend an injection strategy for WAG-sensitive patterns. Introduction The Kelly-Snyder field is the largest of a chain of fields along the Pennsylvanian Horseshoe atoll in the Midland Basin. Within this field, the Scurry Area Canyon Reef Operators Committee (SACROC) Unit covers approximately 56,000 acres with 2,800 million STB of original oil in place (OOIP). Limestone is the dominant mineral within the Canyon Reef formation, and less than 3% of the formation exists as thin sections of shale (1–10 ft in thickness) that are important stratigraphic markers. The formation is divided into four major zones: the Cisco, the Green Zone (GZ), the Upper Middle Canyon, and the Lower Middle Canyon (LMC). Of these, the GZ shows the highest matrix permeability, significant nonmatrix-flow features, and high-conductivity channels. Moreover, the transition zone (TZ) below the oil/water contact has recently been developed in parts of the SACROC Unit. Review Primary Production. Completed in November 1948, the Standard No. 1 Jessie Brown 2 was drilled to 6,700 ft and produced 530 B/D from the Canyon Reef Formation. Located 9 miles northwest of Snyder, Texas, this well was the discovery well of the North Snyder field. The Texas Railroad Commission eventually merged this field with the neighboring Kelly field upon recognizing that both fields produce from the same reservoir. The reservoir thickness varies from 10 ft on the flanks to 900 ft on the crest of the reef. A map of the unit’s 3D structure and thickness is shown in Fig. 1. By late 1950, 1,600 production wells had been drilled on the Kelly- Snyder field on irregular 40-acre spacing.

The importance of site selection, sediment supply, and hydrodynamics: A case study of submarine paleoseismology on the northern Cascadia margin, Washington USA

The Washington continental margin presents both a classic test of submarine paleoseismology, and an opportunity to explore advancement of the field through analysis of sediment dispersal in a heterogeneous system. New and archive core, bathymetric, backscatter and seismic reflection data from the Washington Cascadia margin show that during high-stand conditions, the northernmost canyons, Barkley, Nitinat, Juan de Fuca (JDF), and to some extent Quillayute are relict systems, with little Holocene recharge. The remaining canyons, Quinault, Grays, Guide, and Willapa, are recharged to a varying degrees by northward transport of Columbia River derived sediment. All systems are nonetheless active conduits for turbidity currents during the Holocene, which are weaker and more restricted than their Pleistocene counterparts. Sedimentologic and CT analysis, supported by radiocarbon ages, micropaleontology, and the Mazama ash datum show that the Holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems, interbedded with hemipelagic sediment. However, the Pleistocene Astoria and Nitinat fans are largely inactive in the Holocene, with turbidity current activity limited to the proximal parts of the main channels. Within active systems, the turbidite record is modulated by local landsliding and growth of active folds and faults.In the relict systems, the turbidite record begins in the middle canyon reaches, as opposed to the actively recharged systems which have a turbidite record in the more proximal canyon reaches. Deposits in the relict systems increase in thickness and modal grain size downstream, suggesting multiple sources and or entrainment of material along the canyon walls.Hydrodynamic models using Monte Carlo model searches for best fitting flow parameters show the most likely pathways by which Holocene and Pleistocene currents flowed through the complex accretionary wedge to the abyssal plain. Model results, supported by heavy mineral distributions, show that the northern canyon systems (Barkley, Nitinat, JDF, Quillayute) are independent of the southern systems, (Quinault, Guide, Grays, Willapa) during the Holocene, supporting the classic “confluence test”. Balancing of sediment volumes required suggests sediment supplied to the slope canyons and abyssal channels in turbidity current events is 2–5 times greater than that supplied by recharge to the canyon heads by external sources. This implies a process that is independent of recharge that scavenges the plentiful relict and hemipelagic sediment supply on the continental slope.Lithostratigraphic correlation and age models suggest similar sequences were deposited in most systems independently, and likely synchronously. The correlated turbidite sequence suggests deposition of ~23 Holocene and 16 post Mazama turbidites in most parts of the canyon systems, with only modest variation, mostly attributable to evidence of bypassing and erosion. The best candidate for triggering of these sequences remains great earthquakes, and the sequence correlates well to onshore and other offshore paleoseismologic evidence.The new data, including new cores in northern Oregon, suggest revisions to segmented rupture boundaries. Several partial ruptures (Segment B) likely extended further north to Juan de Fuca Canyon; one event was resolved into two, and one Washington only event was added. Most “Segment C” ruptures were found to extend further northward to the latitude of Astoria Canyon. Mean recurrence times are therefore revised to ~434years for the Washington Coast, and ~340years for the central and northern Oregon coast. Conditional probabilities in the next 50years also are revised to 10–17% for the Washington coast, and 16–22% for the central and northern Oregon coast.In Cascadia, Sumatra and other locales globally, core siting, spatial sample density, high-resolution analysis of core and regional geophysics and understanding of flow dynamics are critical to capturing a paleoseismic record. Sedimentary records vary across turbidity current systems of varying sediment supply, physiography and sediment sources. Variations in the record will reflect these factors, yet may still present a consistent paleoseismic history. This analysis highlights the importance of a thorough understanding of flow paths, hydrodynamics and the interplay of sedimentation and local tectonics when testing for evidence of earthquakes in the sedimentary record of active margins.

Origin and accumulation of trace elements in sediments of the northwestern Mediterranean margin

Continental margins receive natural and anthropogenic trace elements (TEs) from direct atmospheric deposition of aerosols onto the sea surface and from advection of riverine suspended particles and/or resuspended sediments from the continental shelf/slope. When the margin is incised by submarine canyons, as for example in the Northwestern Mediterranean Sea, most of these particles are preferentially transferred via these topographic features towards their final repositories in the abyssal plain. The Gulf of Lions (GoL) shelf receives the largest particulate riverine input to the Western Mediterranean, with its associated chemical contaminants originating from the industrialized and urbanized Rhone Valley. Sediment samples (grabs, cores and moored traps) collected in the Cap de Creus (CdC) Canyon and its adjacent areas at the Southwestern exit of the GoL were analyzed to explore the origin, dispersion, transfer and accumulation of a suite of TEs (Ag, Cd, Co, Cr, Cu, Ni, Pb, Zn and V) from the GoL shelf to the adjacent continental rise. Distributions of Cu, Cr, Ni, Pb, Zn and V in the surface sediments of the shelf confirm their terrigenous origin in association with clay minerals, whereas Ag and Cd are more associated with organic matter (OM). All these TEs are anthropogenically enriched in the Rhone prodelta sediments. Anthropogenic influence remains clearly discernible in the GoL shelf surface sediments for Ag, Pb and Zn. Hydrodynamical resuspension and sorting of shelf sediments occur at the head of the CdC Canyon during dense shelf-water cascading events. During these events, the material collected in moored sediment traps contains a higher coarse carbonate fraction slightly impoverished in TEs compared to the clays of the nepheloid layer and the organically-rich particles deposited before and at the end of the cascading period. Upper and middle canyon sediments are characterized by high sedimentation rates (~0.2cmyr−1) of fine clay material. Conversely, sediments from the lower continental slope and rise exhibit low sedimentation rates (~0.06cmyr−1) and receive carbonaceous planktonic detritus from the water column. At the lower continental slope, coarse material includes foraminifers and pteropods, whereas at the continental rise finer planktonic-derived material is more abundant. Both in the CdC Canyon and in its adjacent lower continental slope/rise sediments, Co, Cu, Cr, Ni and V are associated with clay, whereas Ag, Cu and Pb are preferentially associated with OM. Cadmium, Cr, and Zn are also associated with OM in canyon sediments. Carbonaceous plankton appears to be especially efficient for scavenging Ag, whereas, Cr, V, Zn and Pb are diluted by biogenic carbonates. An authigenic Mn fraction is enriched with Co and Ni. Lead and Zn concentration levels and vertical profile patterns, along with Pb stable isotopic ratios, indicate that significant parts of Pb and Zn are of anthropogenic origin. A sediment chronology based on 210Pb dating reveals that Pb anthropization, mainly from gasoline additives, culminated between 1960 and 1980, being the current concentrations >40% lower than 30years ago. A similar distribution is observed for Zn, which originates mainly from combustion processes; but the reduction of Zn contamination amounts to only 20% during the same period. The largest anthropogenic Pb accumulation occurs in the middle part of CdC Canyon, with an inventory of 200μgcm−2. At the most distal part of the continental rise anthropogenic Pb accumulation within the first ~10cm below the surface sediment is estimated around 10μgcm−2, which is similar to the direct atmospheric deposition estimate.

Recent sediment transport and deposition in the Cap-Ferret Canyon, South-East margin of Bay of Biscay

The Cap-Ferret Canyon (CFC), a major morphologic feature of the eastern margin of the Bay of Biscay, occupies a deep structural depression that opens about 60km southwest of the Gironde Estuary. Detailed depth profiles of the particle-reactive radionuclides 234Th and 210Pb in interface sediments were used to characterise the present sedimentation (bioturbation, sediment mass accumulation, and focusing) in the CFC region. Two bathymetric transects were sampled along the CFC axis and the southern adjacent margin. Particle fluxes were recorded from the nearby Landes Plateau by means of sediment traps in 2006 and 2007. This dataset provides a new and comprehensive view of particulate matter transfer in the Cap-Ferret Canyon region, through a direct comparison of the canyon with the adjacent southern margin. Radionuclide profiles (234Th and 210Pb) and mass fluxes demonstrate that significant particle dynamics occur on the SE Aquitanian margin in comparison with nearby margins. The results also suggest show three distinct areas in terms of sedimentary activity. In the upper canyon (<500m), there is little net sediment accumulation, suggesting a by-pass area. Sediment focusing is apparent at the middle canyon (500–1500m), that therefore acts as a depocenter for particles from the shelf and the upper canyon. The lower canyon (>2000m) can be considered inactive at annual or decadal scales. In contrast with the slow and continuous accumulation of relatively fresh material that characterises the middle canyon, the lower canyon receives pulses of sediment via gravity flows on longer time scales. At decadal scale, the CFC can be considered as a relatively quiescent canyon. The disconnection of the CFC from major sources of sediment delivery seems to limit its efficiency in particle transfer from coastal areas to the adjacent ocean basin.

External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea

Abstract. Particle fluxes (including major components and grain size), and oceanographic parameters (near-bottom water temperature, current speed and suspended sediment concentration) were measured along the Cap de Creus submarine canyon in the Gulf of Lions (GoL; NW Mediterranean Sea) during two consecutive winter-spring periods (2009–2010 and 2010–2011). The comparison of data obtained with the measurements of meteorological and hydrological parameters (wind speed, turbulent heat flux, river discharge) have shown the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea. Indeed, atmospheric forcing during 2009–2010 and 2010–2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14.2 × 103 W m−2) in winter 2009–2010 that triggered a pronounced sea surface cooling compared to winter 2010–2011 (1.6 × 103 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009–2010, which cascaded at high speed (up to ∼1 m s−1) down Cap de Creus Canyon as measured by a current-meter in the head of the canyon. The lower heat losses recorded in winter 2010–2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation and downslope transport of dense shelf water. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter-spring 2009–2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to the middle canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010–2011. The dominance of the lithogenic fraction in mass fluxes during the two winter-spring periods points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated with the plankton spring bloom during March and April of both years.

Near-bottom particulate matter dynamics in the Nazaré submarine canyon under calm and stormy conditions

Two mooring lines equipped with near-bottom sediment traps were deployed in the axis of the Nazaré submarine canyon at ∼1600 and ∼3300 m depth, respectively. We studied time-series of particle flux, composition (biogenic silica, carbonates, organic matter and lithogenic fractions), granulometry, mineralogy and 210Pb concentration of particulate matter over five sediment trap deployments between October 2002 and December 2004. Current meters equipped with turbidimeters were also deployed at trap depths to monitor the water flow, temperature, salinity and suspended particle concentration. The composition of the collected particles was fairly constant year-round, dominated by the lithogenic fraction and with OC/N ratios in the range 11–21, suggesting an important terrigenous influence inside the canyon. The results show contrasting dynamic environments in the upper (1600 m depth) and middle (3300 m depth) canyon. High current speeds (spring tides up to 80 cm s −1) and high apparent mass fluxes of particulate matter (mean 65 g m −2 d −1; maximum 265 g m −2 d −1) are permanent at the shallowest station. At the deepest site, fluxes were below 10 g m −2 d −1 most of the time and the annual flux was governed by events of sharp flux increase. Storms affecting the continental shelf during autumn and winter are a major driver of down-canyon dispersal of sediments to the middle canyon and beyond. Important nepheloid activity developed inside the canyon in response to storms with significant wave heights between 4 and 6 m, as testified by turbidimeters deployed in midwater and near the seabed at 1600 m water depth. On three occasions during the study period, significant wave heights of incident storms surpassed 7 m, leading to notable episodes of down-canyon transport that were clearly observed in the middle canyon. During one of these stormy periods (January 2003) a sediment gravity flow transporting unusual quantities of sand and coastal plant debris was observed at 3200 m. However, a storm with significant wave heights as low as 5 m was apparently able to trigger a sediment gravity flow reaching beyond the middle canyon. The role of storms in the offshore dispersal of sediments is clearly relevant but seems to be modulated by synergic factors such as river flooding.

Sedimentary processes in the middle Nazaré Canyon

Nazaré Canyon extends from a water depth of 50 m near the Portuguese coast to 5000 m at the edge of the Iberian Abyssal Plain. The system is not connected to a modern river and instead obtains its present day sediment input by capture of along-shelf sediment transport. Much of this sediment is deposited in the middle canyon between about 2700 and 3800 m. However, the middle canyon is a highly heterogeneous environment, with areas of both high and low sedimentation rates, exposed rock outcrop, erosion and stable and unstable slopes in close juxtaposition. This paper explores how the various sedimentary processes interact to create the observed heterogeneous canyon environment, which will influence benthic biodiversity in the canyon. Seafloor heterogeneity is investigated using a nested approach to data interpretation, using local high-resolution data to calibrate regional lower resolution data. Six different data types, ship and ROV-mounted swath bathymetry, 30 kHz sidescan sonar images, sediment cores, seafloor video/photographs and current metre/acoustic backscatter data, were incorporated into the analysis. The main morphological characteristic of the middle canyon is a narrow, steep-sided, axial channel flanked by gently sloping terraces. Small-scale landsliding, active at the present day, is the main process that exposes a variety of substrates, ranging from semi-consolidated Holocene sediments to rock of probable Mesozoic age, on the steep axial channel walls. The axial channel floor is characterised in part by large-scale sediment bedforms and in part by landslide debris, suggesting some reworking of landslide debris by currents within the channel. The terraces are interpreted as inner levees with high sedimentation rates. Cores show a dominantly muddy sequence interrupted by thin turbidite sands emplaced on decadal to centennial timescales. The fine-grained sedimentation is the product of continuous settling from fine-grained flows that range from gravity currents to lateral advection of nepheloid layers. The close proximity of areas of high sedimentation and erosion creates a highly heterogeneous seafloor, with the highest heterogeneity on the steepest slopes.

Canyon conditions impact carbon flows in food webs of three sections of the Nazaré canyon

Submarine canyons transport large amounts of sediment and organic matter (OM) from the continental shelf to the abyssal plain. Three carbon-based food web models were constructed for the upper (300–750 m water depth), middle (2700–3500 m) and lower section (4000–5000 m) of the Nazaré canyon (eastern Atlantic Ocean) using linear inverse modeling to examine how the food web is influenced by the characteristics of the respective canyon section. The models were based on an empirical dataset consisting of biomass and carbon processing data, and general physiological data constraints from the literature. Environmental conditions, most notably organic matter (OM) input and hydrodynamic activity, differed between the canyon sections and strongly affected the benthic food web structure. Despite the large difference in depth, the OM inputs into the food webs of the upper and middle sections were of similar magnitude (7.98±0.84 and 9.30±0.71 mmol C m −2 d −1, respectively). OM input to the lower section was however almost 6–7 times lower (1.26±0.03 mmol C m −2 d −1). Carbon processing in the upper section was dominated by prokaryotes (70% of total respiration), though there was a significant meiofaunal (21%) and smaller macrofaunal (9%) contribution. The high total faunal contribution to carbon processing resembles that found in shallower continental shelves and upper slopes, although the meiofaunal contribution is surprisingly high and suggest that high current speeds and sediment resuspension in the upper canyon favor the role of the meiofauna. The high OM input and conditions in the accreting sediments of the middle canyon section were more beneficial for megafauna (holothurians), than for the other food web compartments. The high megafaunal biomass (516 mmol C m −2), their large contribution to respiration (56% of total respiration) and secondary production (0.08 mmol C m −2 d −1) shows that these accreting sediments in canyons are megafaunal hotspots in the deep-sea. Conversely, carbon cycling in the lower canyon section was strongly dominated by prokaryotes (86% of respiration) and the food web structure therefore resembled that of lower slope and abyssal plain sediments. This study shows that elevated OM input in canyons may favor the faunal contribution to carbon processing and create hotspots of faunal biomass and carbon processing along the continental shelf.

Biodiversity of macrofaunal assemblages from three Portuguese submarine canyons (NE Atlantic)

The macrofaunal assemblages from three Portuguese submarine canyons, Nazaré, Cascais and Setúbal were studied from samples collected at their upper (900–1000 m), middle (3200–3500 m) and lower sections (4200–4500 m) and at the adjacent open slopes (∼1000 m), during the HERMES cruises D297 (R.R.S. Discovery, 2005) CD179 (R.R.S. Charles Darwin, 2006) and 64PE252 (R.V. Pelagia, 2006). The taxonomic composition and patterns in biodiversity, abundance and community structure of the benthic macrofauna were described. Annelida (42.1% of total abundance; 137 species) and Arthropoda (20.6%; 162 species) were, respectively, the most abundant and the most species-rich Phyla among the 342 taxa identified during this study. Multivariate analyses showed significant differences between and within canyons and between canyons and open slope assemblages. At their upper section, canyons supported higher macrofauna abundance but slightly lower biodiversity than the adjacent slopes at similar depth. In all canyons abundance reached the highest value in the middle section and the lowest in the upper section, with marked fluctuations in Nazaré (474–4599 ind. m −2) and lower variability in Cascais (583–1125 ind. m −2). The high abundance and dominance of the assemblages in the middle section of Nazaré and Setúbal was accompanied by depressed biodiversity, while in Cascais, Hurlbert's expected species richness showed increasing values from the upper to the middle canyon, and maintained the high values at the lower section. Overall, the Nazaré Canyon showed the lowest expected species richness (ES (100): 16–39) and the Cascais Canyon the highest (39–54). There was a significant negative Kendall's correlation between total organic carbon concentrations in the superficial sediments and ES (100) and a significant positive correlation between total nitrogen and macrofauna density. The influences of organic enrichment, sediment heterogeneity and hydrodynamic regime on the abundance, diversity and community structure of the macrofauna are discussed. It is suggested that altered and localised environmental conditions in the Portuguese canyons play an important role in modifying more common abundance and diversity bathymetric patterns evident in many continental slope environments.

Geomorphology and sedimentary features in the Central Portuguese submarine canyons, Western Iberian margin

The Central Portuguese submarine canyons (Nazaré, Cascais and Setúbal–Lisbon canyons) dissect the Western Iberian margin in an east–west direction from the continental shelf, at water depths shallower than 50 m, down to the Tagus and Iberian abyssal plains, at water depths exceeding 5000 m. We present an analysis of the geomorphology of the canyons and of the sedimentary processes that can be inferred from the observed morphology of the three canyons, based on a compilation of swath bathymetry data and TOBI deep-towed side-scan sonar imagery. This first complete detailed mapping of the Central Portuguese canyons reveals substantial differences in their morphologies and downslope evolution. The canyons are divided into three sections: 1) canyon head and upper reach, 2) middle canyon, and 3) canyon mouth and distal part. The canyon heads and upper reaches are severely indented into the continental shelf, and they are characterised, in the Nazaré and Setúbal–Lisbon canyons, by sinuous V-shaped valleys entrenched within high canyon walls occupied by rock outcrops dissected by gullies. The Cascais upper canyon is complex, with multiple branches with high axial gradients and signs of mass wasting. Middle canyon sections, indented in the slope, display axial incisions with perched, stacked terraces, and are affected by debris avalanches originating from the canyon walls. At the base of slope, the distal Cascais and Setúbal–Lisbon canyons show many characteristics of channel-lobe transition zones: erosional features such as isolated to amalgamated chevron scours, and depositional bedforms such as mud to gravel waves. Pervasive scouring occurs up to 95 km beyond the canyon mouths. By contrast, the Nazaré canyon opens into a 27 km wide and 94 km long channel, whose flat-bottomed thalweg is occupied by sediment waves, irregular, comet-shaped and crescentic scours, and a second-order channel. Transverse, kilometre-scale sediment waves occupy the overbank area of the southern channel margin. The present morphology of the Central Portuguese canyons is the result of erosive processes, subsequent sediment transport and deposition, and sediment instability, whereas inherited tectonic fabric controls their location. Morphological differences between the canyons are explained by the main mechanisms driving their activity. Overall, these morphological features suggest that these canyons have acted as an efficient conduit of sediment to the deep basin, transporting large quantities of material to the deep sea during high-energy events.

A walk down the Cap de Creus canyon, Northwestern Mediterranean Sea: Recent processes inferred from morphology and sediment bedforms

The Cap de Creus canyon, northwestern Mediterranean Sea, belongs to a complex network of submarine canyons cutting the western Gulf of Lion continental shelf and opening into the larger Sète canyon. Swath bathymetry data, MAK-1M deep-towed side-scan sonar imagery and 5 kHz high resolution seismic reflection profiles show striking morphologies in the Cap de Creus canyon floor and walls. As a consequence of the canyon head and the upper reach severe incision, the continental shelf dramatically narrows in front of the Creus Cape promontory. The upper canyon has a flat-bottomed thalweg incised in a mega-scale sediment furrow field displaying hyperbolic seismic facies. The tens of kilometres long linear furrows extend also over the middle canyon down to 1400 m of water depth. The furrows on either side of the canyon are not parallel but oblique and display varying degrees of excavation. Mid-channel sediment bars are locally present in the thalweg, which is made of sandy lag deposits, as revealed by its acoustic response and verified by sediment samples. The middle canyon is linear and steep, with an up to 700 m high southern wall, contrasting with the sinuous, smooth lower canyon, which is controlled by flowage of the underlying Messinian evaporites. Large sections of the canyon are affected by sediment instability processes. The lower Cap de Creus canyon hangs up to 260 m over its distalmost reach and the Sète canyon through a narrow, less than 1 km wide, gorge. Numerous scours up to 10 m deep suggesting bed load transport occupy the lower Sète canyon immediately downstream of the Cap de Creus canyon mouth. The data set provides the first complete very-high resolution imaging of a submarine canyon from its upper part down to its distalmost reach. The observations evidence a wide set of erosion, transport and deposition processes along the Cap de Creus canyon, including sediment entrapment at the canyon head, furrow-generating dense water cascading through the southern wall, along-channel currents strong enough to excavate specific sections of the channel floor and bed load sediment transport as demonstrated by the presence of mega-ripples, crescent scours and grooves in the lower canyon.

Benthic foraminifera in the Nazaré Canyon, Portuguese continental margin: Sedimentary environments and disturbance

Living (rose Bengal stained) benthic foraminifera were investigated from thirteen stations ranging from 146–4976 m water depth in the Nazaré Canyon, located on the Western Iberian continental margin. The total standing stocks (TSS), species assemblages and in-sediment distributions are compared between stations located on the highly disturbed axis of the upper (< 2700 m) and middle canyon (2700–4000 m), the adjacent low energy terraces and the lower canyon (> 4000 m). In addition, the community changes were investigated in relation to water depth and bio-available, organic carbon. Overall, low total standing stocks of foraminifera were found in the disturbed canyon axis, which experiences frequent sediment resuspension and gravity flows. At the upper canyon axis station at 1118 m a rather exceptional fauna was recovered, dominated by a species of Technitella that made up 75% of the TSS. The highest TSSs were recorded in the upper canyon terrace stations, where fine grained sediment and organic carbon are able to accumulate. Standing stocks on the terraces decreased with increasing water depths. The quiescent terrace stations recorded high abundances of infaunal species, including Melonis barleeanum, Globobulimina spp. and Chilostomella oolina. The occurrence of these species reflects the low pore water oxygen concentrations and high bio-available carbon supply. Several tubular Bathysiphon species were found in the upper canyon terrace stations. Instead, the deepest stations of the lower canyon were dominated by another large agglutinated protozoan, Saccorhiza ramosa. The change in the arborescent/tubular foraminiferal community may reflect the increase in sediment oxygenation with increasing water depth in the canyon, Bathysiphon spp. occurring in sediments with higher bio-available carbon flux and S. ramosa inhabiting more oligotrophic areas.

Recent sediment transport and deposition in the Nazaré Canyon, Portuguese continental margin

Processes, pathways and fluxes of sediment transport and deposition in the Nazaré submarine canyon, Portuguese continental margin, were investigated by water column profiling of suspended particulate matter, recording of near-bottom currents and suspended particulate matter fluxes with benthic landers, and by analysis of surface sediment cores. The results show that fine-grained suspended sediment from the adjacent shelf is captured in the upper canyon and actively transported through the canyon to the abyssal plain under influence of tidal currents and intermittent sediment gravity flows. Tidal currents are actively resuspending and transporting sediment in the upper to middle canyon, as reflected by high concentration of suspended particles in bottom waters, high horizontal and vertical sediment fluxes in the bottom water layer and high sediment accumulation rate on the seabed. Diminishing strength of tidal currents leads to focussed sediment deposition in the middle canyon. Further transport of sediments toward the lower canyon takes place predominantly by sediment gravity flows occurring on yearly or longer timescale. Turbidity currents strong enough to transport sand-sized material to the lower canyon occur only on centennial or longer timescales.

Distribution of meiobenthos in the Nazaré canyon and adjacent slope (western Iberian Margin) in relation to sedimentary composition

Abundance of metazoan meiofauna and foraminifera, and biomass and community structure of nematodes, were investigated in the benthic zone along the Nazare Canyon and adjacent continental slope in relation to concentration of organic matter and its suitability as a food source for the meiobenthos. The Nazare canyon sediments were richer in organic carbon (Corg), total nitrogen, and phytopigments than the adjacent open slope. In addition, phytodetritus was fresher in the canyon sediment than on the slope (higher chlorophyll a: phaeopigments). Nevertheless, the abundance of polychaetes, copepods, bivalves, nematodes, total metazoans, and nematode biomass were not always higher in the canyon than on the adjacent open slope. Lower densities occurred in the upper and middle canyon, and living benthic foraminifers were significantly more abundant on the adjacent slope. The stations in the upper and middle canyon contained infinitesimal numbers of foraminifers. Reduced diversity and evenness and high K-dominance of the nematode assemblages in the upper part of the canyon indicated environmental stress, perhaps related to high Corg content and sedi- ment disturbance. Non-selective deposit-feeders dominated the nematode assemblages of the upper and middle parts of the canyon, whereas a more diverse trophic structure was found in the deeper parts and the open slope. Conditions in the upper and middle areas of the Nazare canyon are harsh, and only opportunistic organisms can survive there.

Megafauna associated with assemblages of deep-water gorgonian corals in Northeast Channel, off Nova Scotia, Canada

The distribution and abundance of benthic megafauna in areas known to be inhabited by dense gorgonian coral assemblages were examined at Northeast Channel, off Nova Scotia, Canada, in August 2001. Using a remotely operated vehicle, 1–5 video transects during each of 1–2 dives at each of four sites (Rips, Middle Canyon, Hell Hole West and Hell Hole East) were conducted. The relationships in the structure of biological assemblages at three spatial scales: within transects (10s of metres); between dive locations (100s of metres); and among sites (10s to 100s of kilometres) were explored. The most abundant epibenthic taxa included the gorgonians Primnoa resedaeformis and Paragorgia arborea, several suspension feeders (Actinauge verrilli, Bolocera tudiae, an unidentified anemone and encrusting sponge, Ophiacantha abyssicola), the deposit feeder Porania pulvillus insignus and the predatory Solaster endeca. The basket star Gorgonocephalus arcticus was present only on colonies of Paragorgia arborea. Despite large variability in abundance and assemblage composition among transects and dive locations, clear patterns were observed among sites. Mean abundance of most cnidarians and echinoderms was greatest at Hell Hole West. No gorgonians were found at Hell Hole East. The encrusting sponge was most abundant at the Rips and least abundant at Hell Hole East. Cluster analysis and multidimensional scaling (MDS) indicated that, when abundance was averaged across transects for each dive, the megafaunal assemblages fall into groups of dives that separated by site. These differences among sites are most likely related to variability in the physical environment. The epibenthic megafaunal assemblages were as diverse in the presence as in the absence of gorgonian corals, at least at the abundances that we observed. However, the apparent low recruitment and abundance, combined with small population size make these assemblages particularly vulnerable to perturbations.

Dense beds of the ophiuroid Ophiacantha abyssicola on the continental slope off Nova Scotia, Canada

Megafaunal distributional patterns in the bathyal and abyssal environments remain largely unknown. Ophiuroids are a significant component of the deep-sea megafauna occurring throughout the world's oceans, generally at densities of <10 s individuals m−2. In this study, we describe the abundance, biomass and size frequency distribution of a dense assemblage of Ophiacantha abyssicola in Northeast Channel on the continental slope off Nova Scotia, Canada. This area is characterized by highly irregular topography and strong tidal currents. Three sites, ranging in depth between 430 and 498 m, were sampled (Middle Canyon, Hell Hole West and Hell Hole East) and 1–4 dives were done at each site with the remotely operated vehicle ROPOS between 20 and 22 August 2001. At each dive, all ophiuroids from 1 to 2 quadrats (0.025–0.163 m2) were collected by suction sampling, and their diameter and wet mass measured. Dry (DM) and ash free dry mass (AFDM) were recorded in 10 individuals from each sample, and 25–35% of individuals from each sample were dissected to determine their gender. Relationships between the three measures of mass derived from the subsamples were used to calculate DM and AFDM for all individuals. Density and biomass were estimated for each quadrat by calculating the size of the sampled area from video frames with image analysis. Percentage cover was calculated on selected frozen video frames (0.197–0.369 m2) by the point method. Mean disk diameter ranged from 6.77 to 9.17 mm, and was smallest at Hell Hole West and greatest at Hell Hole East. Mean abundance at each site ranged from 390 to 1200 individuals m−2, and was greater at Hell Hole West than the other two sites. Percentage cover ranged from 35 to 62%, and was lower in Hell Hole East than the other two sites. The patterns in biomass were similar to those in abundance. Such dense aggregations of ophiuroids are rare in the bathyal and abyssal environments, but have been documented in shallow habitats where they have been attributed to (1) reduced predation intensity or (2) increased food supply. We found only two individuals (out of 50 per dive examined) with evidence of arm regeneration, but observed sustained feeding activity coupled with strong currents. Thus, we propose that the formation and maintenance of the ophiuroid beds that we observed at Northeast Channel is associated with maximizing particle capture rather than reduced predation intensity.

Dense beds of the ophiuroid Ophiacantha abyssicola on the continental slope off Nova Scotia, Canada

Megafaunal distributional patterns in the bathyal and abyssal environments remain largely unknown. Ophiuroids are a significant component of the deep-sea megafauna occurring throughout the world's oceans, generally at densities of <10s individuals m−2. In this study, we describe the abundance, biomass and size frequency distribution of a dense assemblage of Ophiacantha abyssicola in Northeast Channel on the continental slope off Nova Scotia, Canada. This area is characterized by highly irregular topography and strong tidal currents. Three sites, ranging in depth between 430 and 498m, were sampled (Middle Canyon, Hell Hole West and Hell Hole East) and 1–4 dives were done at each site with the remotely operated vehicle ROPOS between 20 and 22 August 2001. At each dive, all ophiuroids from 1 to 2 quadrats (0.025–0.163 m2) were collected by suction sampling, and their diameter and wet mass measured. Dry (DM) and ash free dry mass (AFDM) were recorded in 10 individuals from each sample, and 25–35% of individuals from each sample were dissected to determine their gender. Relationships between the three measures of mass derived from the subsamples were used to calculate DM and AFDM for all individuals. Density and biomass were estimated for each quadrat by calculating the size of the sampled area from video frames with image analysis. Percentage cover was calculated on selected frozen video frames (0.197–0.369m2) by the point method. Mean disk diameter ranged from 6.77 to 9.17mm, and was smallest at Hell Hole West and greatest at Hell Hole East. Mean abundance at each site ranged from 390 to 1200 individuals m−2, and was greater at Hell Hole West than the other two sites. Percentage cover ranged from 35 to 62%, and was lower in Hell Hole East than the other two sites. The patterns in biomass were similar to those in abundance. Such dense aggregations of ophiuroids are rare in the bathyal and abyssal environments, but have been documented in shallow habitats where they have been attributed to (1) reduced predation intensity or (2) increased food supply. We found only two individuals (out of 50 per dive examined) with evidence of arm regeneration, but observed sustained feeding activity coupled with strong currents. Thus, we propose that the formation and maintenance of the ophiuroid beds that we observed at Northeast Channel is associated with maximizing particle capture rather than reduced predation intensity.

Delaware Mountain Group, West Texas, A Case of Refound Opportunity: Part 2--Cherry Canyon Formation (E &amp;amp; P Notes)

Recent drilling activity in the War-Wink area of west Texas has established a new play in submarine channel and levee/overbank sandstones of the middle and lower Cherry Canyon Formation, Delaware Mountain Group (Guadalupian). Previous exploration and development, spanning the 1960s, 1970s, and early 1980s, had focused on the upper part of the formation. The new play, located a few miles west of the Central Basin platform, suggests the existence of multiple channel trends not yet explored in the Delaware basin. Entrapment in the War-Wink area is related to both structural and stratigraphic factors. Lower Cherry Canyon reservoirs have porosities ranging from 18 to 24% and permeabilities ranging from 10 to 60 md and thus are higher in quality than reservoirs of the underlying Brushy Canyon Formation. Core data indicate that permeabilities increase rapidly above a threshold porosity value of about 18%. Lower Cherry Canyon wells are completed by fracture stimulation in one or two main reservoir zones, with several secondary zones commonly behind pipe. Wells usually flow at rates of 100-200 bbl oil per day for up to 1 yr before being put on pump. Main producing zones are capable of recoveries ranging from 50,000 to 120,000 bbl. Attempts at using horizontal drilling in place of fracture stimulation have proved highly successful in certain cases. Use of this approach for Cherry Canyon development, guided by good geologic control, may provide an excellent technique applicable to many portions of the Delaware basin.

Late Quaternary sedimentation on the outer Indus shelf and slope (Pakistan): evidence from high-resolution seismic data and coring

High-resolution seismic ( Parasound) profiles, multibeam bathymetry ( Hydrosweep), under-water photography and sediment cores are used to map the morphology and echo-facies distribution, and to describe the late Quaternary sedimentation on the outer shelf and slope off the Indus delta (Pakistan). The morphology and origin of the Indus Canyon were studied in detail. The upper and middle canyon (from 20- to 1350-m axial depth) is an erosional (degradational) canyon or delta-front trough with steep erosional walls and a meandering axial channel without levees. The lower Indus Canyon (1350- to 1500-m axial depth) is a transitional type between a degradational canyon and the aggradational channel-levee system of the upper Indus Fan. The late Quaternary sedimentation is influenced by fluctuations of fluvial input, delta progradation, canyon erosion and fan aggradation. It is especially controlled by sea-level changes. Four episodes can be distinguished: 1. (1) During interglacial (?Eemian) times and a relatively high sea-level position, a layered sequence of V-shaped, channel-like erosional features were formed below the shelfbreak (135 m) down to an upper slope scarp by slumping or erosion as delta-front or prodelta gullies. 2. (2) During the Last Glacial Maximum, the sea-level lowstand caused the Indus delta to advance across the present shelfbreak and shed fluvial silty clays directly onto the upper slope. This is indicated by layered, gently seaward dipping subparallel reflectors which are interpreted as being prograded prodelta mud units. At this time the Indus Canyon experienced maximum erosion and funnelled turbidity currents to the aggradational channel-levee system on the Indus Fan. Major slumps and debris flows were triggered at the continental slope. 3. (3) During deglaciation and the beginning of the Holocene transgression, several sea-level stillstands are indicated by the formation of biogenic sediments on the outer shelf and the build-up of shallow-water algal bioherms around 9–12 ka BP (presently at a water depth of ~90–100 m). 4. (4) During the late Holocene sea-level highstand, the shelf was flooded and the delta-front sediments of the Indus River were deposited on the innermost shelf. The outer shelf is characterized by a lack of deposition and erosion. The Indus Canyon experienced ongoing (but much decreased) activity of low-density turbidity currents with overbank spilling. The middle and lower continental slope down to ~ 2000 m is covered by hemipelagic sediments showing a layered sequence of distinct subbottom reflectors explained as hemipelagic drape interbedded with turbid layer sediments and/or thin mud turbidites from spillover along natural levees bordering the Indus Canyon. For the past 50 ka, the continental slope (outside the canyon and channels) experienced no turbidite sedimentation.

Sequence Stratigraphy of the Upper and Middle Canyon"Oil and Gas Fields Along the Eastern Edge of the Midland Basin, Irion County, Texas -- the Potential for Future Exploration"

Sequence Stratigraphy of the Upper and Middle Canyon"Oil and Gas Fields Along the Eastern Edge of the Midland Basin, Irion County, Texas -- the Potential for Future Exploration"