Areas Of Nondeposition Research Articles

Influence of an anticline structure on hydrogeological functioning and aquifer interactions in a multilayered aquifer system: the case of Villagrains-Landiras anticline (Gironde, France)

Geological deformations like anticlines have a prominent role in aquifer system functioning. Structural deformations control erosion patterns, areas of nondeposition, lateral facies variations and thickness variations. The nature and geometry of geological bodies have a major impact on the aquifers and interconnections between them. To characterize these features and to quantify their influence on overall hydrogeological functioning, a multidisciplinary approach is proposed at a local scale. In southwestern France, the Aquitaine Basin contains a regional multilayered aquifer system affected by numerous anticlines. The Villagrains-Landiras anticline is a major anticline of the Aquitaine Basin, and near its axis is the subcropping Cenomanian aquifer; thus, the Cenomanian aquifer has potential for drinking water supply. An extensive research program was developed, including reconnaissance drilling, water level measurements, geochemical analyses, and petrophysical tests, and the results were combined with existing data. This integrated work precisely defined the complex architecture of the aquifer and confining units linked with the uplift and the polyphase erosion of the anticline. It resulted in the characterisation of the deposits’ geometries, lithology, and aquifer properties. The areas of aquifer interconnection have been defined and recharge flows have been estimated. A new groundwater circulation pattern constrained by isotopic water residence times was developed. A new geological model was built, which enables a rethink of the local functioning of the aquifer targeted for drinkable-water supply, but also it allows an understanding of the importance of anticline structure on the recharge conditions of the aquifers of this regional multilayered aquifer system.

Spatiotemporal Reproduction and Larval Habitat Associations of Nonnative Silver Carp and Bighead Carp

AbstractThe establishment of nonnative Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis (collectively referred to as “bigheaded carp”) in the central United States may have negative ecological consequences and economic impacts. Our objectives were to quantify patterns and habitat associations of adult bigheaded carp reproduction, larval production, and habitat use; such information is important for control strategies and identifying recruitment sources. During May–August 2011, we sampled adults and larvae at 10 sites distributed adjacent to and within the main channel of the Mississippi River at Pool 26 (study area = 28 river kilometers). Female reproductive status, adult location, and larval density were compared to environmental conditions, including temperature, site velocity, and turbidity. Large females spawned earlier than their smaller counterparts. No clear spawning aggregations of adults were observed, suggesting plasticity in staging habitat. Larvae were distributed across all sites during flooding. Larval density was positively related to velocity and turbidity, suggesting that nondepositional areas may facilitate recruitment. Bigheaded carp larvae comprised 10% of the ichthyofauna. Although pooled reaches are a source of recruitment for bigheaded carp in the Mississippi River system, the low densities of bigheaded carp larvae relative to native larvae cannot explain the dominance of adults in this system. Our findings provide insights into the plastic nature of bigheaded carp reproduction and habitats associated with larval development. Control efforts that target large adult females should be conducted earlier during the spring spawn. To maintain fishing pressure, such control efforts would likely need to continue through the summer, when smaller individuals spawn, discharge decreases, and CPUE increases. However, we found no specific mass staging area or habitat type where adult females could be targeted.Received July 19, 2016; accepted December 14, 2016 Published online March 21, 2017

Relationship of bifenthrin sediment concentrations to grain size and total organic carbon in California waterbodies: implications for ecological risk.

A summary analysis of data sets from six California waterbodies was conducted to determine the relationship of bifenthrin sediment concentrations to: % sand/gravel; % silt; % clay; % silt/clay and % total organic carbon (TOC). The relationship of TOC to % sand/gravel, % silt, % clay, and % silt/clay was also analyzed. Statistically significant and meaningful direct relationships were reported between bifenthrin and % TOC, % silt, % clay and % silt/clay while a significant and meaningful inverse relationship was reported between bifenthrin and % sand/gravel. A significant and meaningful inverse relationship was reported between % TOC and % sand/gravel, while a significant and meaningful direct relationship was reported between % TOC and % silt, % clay and % silt/clay. Significant bifenthrin sediment concentrations would not be expected in non-depositional (sand/gravel) areas which have been reported to be dominant in various streams in California's Central Valley and are also the preferred habitat for many benthic macroinvertebrate taxa.

Sediment dynamics and post-glacial evolution of the continental shelf around the Blanes submarine canyon head (NW Mediterranean)

The Blanes submarine canyon (BC) deeply incises the Catalan continental shelf in the NW Mediterranean Sea. As a consequence of the closeness (only 4km) of its head to the coastline and the mouth of the Tordera River, the canyon has a direct influence on the shelf dispersal system as it collects large amounts of sediment, mainly during high-energy events. Multibeam bathymetry, backscatter imagery and very-high resolution seismic reflection profiles have allowed characterizing the morphology of the continental shelf around the canyon head, also identifying sediment sources and transport pathways into the canyon. The morphological data have also been used to reconstruct the evolution of the continental shelf during the last sea-level transgression so that the current understanding of shelf-to-canyon sediment exchanges through time could be improved.The continental shelf surrounding the BC consists of both depositional and erosional or non-depositional areas. Depositional areas display prominent sediment bodies, a generally smooth bathymetry and variable backscatter. These include: (i) an area of modern coarse-grained sediment accumulation that comprises the inner shelf; (ii) a modern fine-grained sedimentation area on the middle shelf offshore Tossa de Mar; and (iii) a modern sediment depleted area that covers most of the middle and outer shelf to the west of the canyon head. Erosional and non-depositional areas display a rough topography and high backscatter, and occur primarily to the east of the canyon head, where the arrival of river-fed inputs is very small. In agreement with this pattern, the continental shelf north and west of the canyon head likely is the main source of shelf sediment into the canyon. To the north, a pattern of very high backscatter extends from the coastline to the canyon head, suggesting the remobilization and off-shelf export of fines. Additionally, relict near-shore sand bodies developed over the Barcelona shelf that extend to the canyon head rim constitute a source of coarse sediment. High-energy processes, namely river floods and coastal storms, are the main controls over the river-shelf-canyon sediment exchange. River floods increase the delivery of terrigenous particles to the coastal system. Storms, mainly from the east, remobilize the sediment temporarily accumulated on the shelf towards the canyon head, so that the finer fractions are preferentially removed and a coarse lag is normally left on the shelf floor. Exceptionally, very strong storms also remove the coarse fractions from the shelf drive them into the canyon. Processes like dense shelf water cascading, which is much more intense in canyons to the north of BC, and the Northern Current also contribute to the transport of suspended sediment from far distant northern sources.During the last post-glacial transgression the BC had a strong influence on the evolution of the inner continental margin, as it interrupted the shelf sediment dispersal system by isolating the shelves to its north and south, named La Planassa and Barcelona shelves, respectively.

Mapping of depositional and non-depositional areas in Salinas, California streams with concurrent pyrethroid and benthic macroinvertebrate assessments

This study used sediment mapping to determine the spatial extent of depositional and non-depositional areas in the wetted stream bed of four urban streams in Salinas, California. After the stream mapping was completed, 8 pyrethroids were analytically measured from randomly selected sites in 12 depositional and 12 non-depositional areas in the four Salinas streams. Benthic macroinvertebrate samples were collected and identified from depositional and non-depositional areas where pyrethroids were measured. In addition, physical habitat was also evaluated at each site where benthic communities were collected. Based on a random sampling design, 24 % of the 96 sediment sampling sites in the Salinas streams were classified as predominately depositional areas. Mean total pyrethroid concentrations were approximately 2× to 61× times higher in depositional areas of the Salinas streams when compared to non-depositional areas. Physical habitat scores from the 12 depositional and 12 non-depositional areas in the Salinas stream sites were extremely low compared with other California streams thus demonstrating that impaired physical habitat is a critical stressor in these streams. Approximately 6,300 individual macroinvertebrates were picked and identified from 70 taxa from the 24 Salinas stream sites. The most dominant taxa collected were all considered tolerant of environmental stressors and dominant taxa from both depositional and non-deposition areas were similar. Ten different benthic metrics for the Salinas streams were similar for the depositional areas, where pyrethroid concentrations consistently exceeded laboratory based toxicity thresholds, and non-depositional areas where pyrethroid concentrations were much lower. These results suggest that factors other than pyrethroids are responsible for impacting resident benthic communities in these urban Salinas streams.

Mapping the Spatial Extent of Depositional Areas in Agricultural, Urban, and Residential California Streams: Implications for Pyrethroid Toxicity

ABSTRACT Wetted stream-bed mapping at randomly selected sites in an agricultural stream (Del Puerto Creek), urban stream (Arcade Creek), and residential stream (Pleasant Grove Creek) in California was conducted to determine the spatial extent of depositional and non-depositional areas. This study evaluated the “representativeness” of standard sediment sampling approaches used in California by using hydrophobic pyrethroids as an example. Measured background concentrations of eight pyrethroids in sediment and potential sediment toxicity for each stream were discussed within the context of depositional areas. Four percent, 15%, and 12% of the randomly selected transects in Del Puerto Creek, Arcade Creek, and Pleasant Grove Creek, respectively, were depositional areas. For all three streams, depositional areas were more dominant in downstream segments. Pyrethroid concentrations in sediment were higher in depositional areas versus non-depositional areas in Del Puerto Creek and were also higher downstream. Pyrethroid concentrations in sediment were also higher in downstream areas of Arcade Creek but generally higher in upstream areas of Pleasant Grove Creek. The results from this study demonstrate the importance of determining “representativeness” of depositional areas for an entire stream if hydrophobic chemicals (pyrethroids) measured in sediment from depositional areas are suspected to be toxic.

Depositional conditions and organic matter distribution in the Bornholm Basin, Baltic Sea

Information on grain-size distribution and total organic carbon (TOC) content of surface sediment and cores from the Bornholm Basin, together with dating of cores using the 210Pb method and shallow seismic chirp profiling, has been analysed to elucidate long-term accumulation patterns. The presence of non-depositional areas with lag sediments and low TOC content below the wave base indicates that inflows of dense bottom water originating in the North Sea and associated near-bottom currents have strong influence on the depositional patterns of bulk sediment and organic matter in this deep basin. The general fining in mean grain size towards the northeast corresponds to the direction of inflow currents and prevailing winds. Recent and previously found 210Pb-based mean accumulation rates vary greatly within the basin, between 129 and 1,144 g m−2 year−1. The accumulation rate may vary by a factor of three even between stations located only 3–4 km apart. Rates recorded close to a seismic profile are consistent with the variation in Holocene sediment thickness. This variation reflects a depositional system controlled by near-bottom inflow currents, consisting of a large-scale channel and a wedge-formed sediment package. The spatial variation in TOC content depends partly on water depth, presumably due to generally poorer degradation in the deepest part of the basin because of less frequent oxygen supply by inflow water. Moreover, there is a tendency of higher TOC contents in the southern part of the basin, which may be due to the input of sediments originating from the Oder River. Compared to values for the central, deep Baltic Sea, TOC contents show lower values of 4–6% and insignificant temporal variations. This may be due to the Bornholm Basin being located much closer to the source of the more oxic inflow water, resulting in more favourable degradation conditions.

Three-Dimensional Numerical Modeling of Deltaic Depositional Sequences 1: Influence of the Rate and Magnitude of Sea-Level Change

ABSTRACT A three-dimensional numerical model of deltaic deposition is used to investigate the influence of sea-level changes on delta development and sequence variability. Results illustrate the three-dimensional morphology of key stratal surfaces and architecture of stratal units (systems tracts) and highlight the importance of the rate and magnitude of sea-level change in controlling the evolution of deltaic depositional sequences. High rates of sea-level fall lead to the development of a limited number of major incised channels that focus sediment supply to a few elongate, finger-like forced regressive lobes separated by large areas of nondeposition. In contrast, low rates of sea-level fall cause only minor channel incision, which occurs late during sea-level fall. As a result, sediment is supplied more uniformly to the delta front, leading to an attached, laterally continuous forced regressive apron. During lowstand and subsequent sea-level rise, the delta morphology and internal geometry are strongly controlled by the rate of rise. High rates lead to: i) poorly developed lowstand wedges that are drowned early, ii) high-magnitude transgressions, and iii) the late development of maximum flooding surfaces. The stratigraphy developed during sea-level rise is also strongly influenced by the incised-valley system created during the preceding sea-level fall. If deep, major valleys developed that captured most of the sediment supply, the resultant stratigraphy has well developed lowstand wedges that are flooded relatively late during sea-level rise. Even within a single delta, systems tracts and key stratal surfaces show three-dimensional variability and two-dimensional sections often lack significant elements of the stratigraphy. As a result, analysis of two-dimensional sections can often lead to miscorrelation and erroneous interpretations of the controlling processes.

Modelling of Suspended Matter Transport from the Oder River

In order to quantify the riverine sediment flux to the Arkona Basin, the transport pathways and fate of fine-grained suspended matter discharged from the Oder River from October 1996 to October 1997 were simulated using the MIKE3 modelling system, including a cohesive sediment transport module. Results indicate that about 550,000 regular tons of sediment are transported to the Arkona Basin annually. There is some indication that transport is episodic and mainly governed by wind events. There is a general tendency for the sediment transported from the Oder to be diverged into a pathway either to the north towards the Arkona Basin (2/3) or to the east towards the Bornholm Basin (1/3) over time-scales of several months. Primary sedimentation along a vertical transsect from the mouth of the Oder River to the Arkona Basin generally takes place in the form of easily resuspended fluffy material. Critical shear stress for the resuspension of this fluff is 0.02 N/m 2 . Generally, such thresholds are exceeded 5-6 times per month in shallow water (D 10 m) during wind events normally only lasting a few hours. Vertical sedimentation fluxes measured in shallow water are less than 10 g/m 2 /day during short periods with calm weather. A comparison with average rates of 80-115 g/m 2 /day measured during 3-month observation periods indicates that the resuspension rate in shallow water is about 8-10 times higher than the primary sedimentation rate. The shallow water areas above the 20 m isobath are non-depositional areas acting as temporal deposits for sediment transported from the Oder River through Pomeranian Bay to the Arkona Basin or the Bornholm Basin.

Benthic Organic Matter Supply and Metabolism at Depositional and Non-depositional Areas in the North Sea

In 1994, four stations in the southern North Sea, the German Bight and the Skagerrak were visited with the aim to get insight into spatial and temporal variation in the supply of fresh organic matter to the benthos and its subsequent metabolic reaction. Stations were chosen on the basis of differences in sediment type, depth and depositional regime. Sediments were sampled, sliced and analysed for phytopigments, fatty acids and nucleic acids. On-deck sediment core incubations provided the sediment oxygen demand (SOD). Fatty acids as well as chlorophylla indicated a seasonal variation of phytodetritus sedimentation, with highest values in May, reflecting the spring bloom sedimentation. The two stations in the depositional areas German Bight and Skagerrak had the highest input of algal detritus into the sediment. These stations also contained higher concentrations of bacterial and long-chain fatty acids, probably related to the relatively higher proportion of fine particles in the sediment and to the input of terrestrial organic matter and/or refractory marine organic matter, respectively.The metabolic indices, viz. the SOD and the RNA concentrations reflected the benthic metabolic reaction to the labile organic matter supply. The three stations in the southern and south-eastern North Sea had a SOD congruent with the phytodetrital inventories, with highest SOD measured at the German Bight. Surprisingly, the Skagerrak sediment did not have a high oxygen demand, although it contained the highest inventory of labile organic matter and high RNA concentrations. The fluxes of carbon to the sediment at station SK, calculated from the chlorophylla inventory, were about four times higher than the sediment oxygen demand. We hypothesise two mechanisms for this discrepancy; one is the decreased mineralisation rate of labile organic matter due to sorption to clayey sediment particles, the other is advection of labile organic matter from the shallower coastal waters of northern Denmark to and subsequent removal from the deeper Skagerrak sediments by periodically occurring high near-bottom water currents.

Seafloor environments in the Long Island Sound estuarine system

Four categories of modern seafloor sedimentary environments have been identified and mapped across the large, glaciated, topographically complex Long Island Sound estuary by means of an extensive regional set of sidescan sonographs, bottom samples, and video-camera observations and supplemental marine-geologic and modeled physical-oceanographic data. (1) Environments of erosion or nondeposition contain sediments which range from boulder fields to gravelly coarse-to-medium sands and appear on the sonographs either as patterns with isolated reflections (caused by outcrops of glacial drift and bedrock) or as patterns of strong backscatter (caused by coarse lag deposits). Areas of erosion or nondeposition were found across the rugged seafloor at the eastern entrance of the Sound and atop bathymetric highs and within constricted depressions in other parts of the basin. (2) Environments of bedload transport contain mostly coarse-to-fine sand with only small amounts of mud and are depicted by sonograph patterns of sand ribbons and sand waves. Areas of bedload transport were found primarily in the eastern Sound where bottom currents have sculptured the surface of a Holocene marine delta and are moving these sediments toward the WSW into the estuary. (3) Environments of sediment sorting and reworking comprise variable amounts of fine sand and mud and are characterized either by patterns of moderate backscatter or by patterns with patches of moderate-to-weak backscatter that reflect a combination of erosion and deposition. Areas of sediment sorting and reworking were found around the periphery of the zone of bedload transport in the eastern Sound and along the southern nearshore margin. They also are located atop low knolls, on the flanks of shoal complexes, and within segments of the axial depression in the western Sound. (4) Environments of deposition are blanketed by muds and muddy fine sands that produce patterns of uniformly weak backscatter. Depositional areas occupy broad areas of the basin floor in the western part of the Sound. The regional distribution of seafloor environments reflects fundamental differences in marine-geologic conditions between the eastern and western parts of the Sound. In the funnel-shaped eastern part, a gradient of strong tidal currents coupled with the net nontidal (estuarine) bottom drift produce a westward progression of environments ranging from erosion or nondeposition at the narrow entrance to the Sound, through an extensive area of bedload transport, to a peripheral zone of sediment sorting. In the generally broader western part of the Sound, a weak tidal-current regime combined with the production of particle aggregates by biologic or chemical processes, cause large areas of deposition that are locally interrupted by a patchy distribution of various other environments where the bottom currents are enhanced by and interact with the seafloor topography.

Distribution and composition of marine hydrogenetic and hydrothermal manganese deposits in the northwest Pacific

Abstract The distribution and composition of Mn deposits in the northwest Pacific (15–50°N and 120–160°E) are characterized using a Mn deposits database compiled from our original data, published and unpublished papers, published databases, and other international sources. The results demonstrate a close association with geological settings. Hydrogenetic nodules and crusts formed in areas of erosion or nondeposition on Cretaceous seamounts and plateaus of the Pacific plate, and to a lesser extent on seamounts of remnant arcs of Palaeogene to Neogene ages. The Cretaceous seamount deposits are most enriched in Co, and the plateaus less so, while both show moderate Ni enrichment. Nodules and crusts are rare in enclosed backarc basins, which have not been affected by deep water circulation. A slight early-diagenetic influence is observed in some Pacific basin nodules. By contrast, modern hydrothermal Mn deposits are broadly distributed on active submarine volcanoes and backarc rifts. These hydrothermal Mn deposits consist typically of pure Mn oxide containing negligible levels of metals except for Mg, Ba, K and Li. Similar fossil hydrothermal Mn deposits are observed in places on old basement or within deep cores as geological records of past hydrothermal activity.

Oxygen pore water profiles in continental shelf sediments of the North Sea:turbulent versus molecular diffusion

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 145:63-75 (1996) - doi:10.3354/meps145063 Oxygen pore water profiles in continental shelf sediments of the North Sea: turbulent versus molecular diffusion Lohse L, Epping EHG, Helder W, van Raaphorst W Oxygen pore water profiles in North Sea sediments were measured with microelectrodes during 2 contrasting seasons. The measurements were conducted in a wide variety of sediments, including non-depositional areas on the southern shelf as well as depositional areas in the Skagerrak. All measurements were performed within minutes on board at in situ temperature. The curvature of oxygen profiles in sandy sediments on the southern shelf indicated the presence of a surface layer characterised by enhanced diffusion. The occurrence of enhanced diffusion was related to sedimentological and seasonal differences. Quantitative evaluation of the pore water profiles by a diffusion-reaction model indicated that the effective diffusion coefficients in a 0.2 to 16 mm subsurface layer were 1.5 to >100 times higher than the molecular diffusion coefficient. Highest effective diffusion coefficients were reported for non-depositional sediments characterised by low diffusive oxygen fluxes. Oxygen profiles in sediments of the depositional area of the Skagerrak indicated constant diffusivity throughout the sediment column. Diffusive fluxes calculated from profiles ranged from 5.2 to 8.9 mmol m-2 d-1 in August 1991, and were between 0.8 and 6.2 mmol m-2 d-1 in February 1992. Seasonal differences in sediments located in the Skagerrak area were minor. It is proposed that near-bottom tidal currents induce enhanced diffusion transport processes in the upper millimetres of the sandy sediments of the southern North Sea, while less energetic hydrodynamical conditions in the depositional area of the Skagerrak favour sediment-water exchange based on molecular diffusion only. Biogeochemical implications of the enhanced diffusivity close to the sediment-water interface are discussed. Oxygen · Sediment-water exchange · Microelectrode · Molecular diffusion · Turbulent diffusion · Enhanced transport · Bottom shear stress Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 145. Publication date: December 31, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Sedimentary environments within a glaciated estuarine-inner shelf system: Boston Harbor and Massachusetts Bay

Three modern sedimentary environments have been identified and mapped across the glaciated Boston Harbor estuary and adjacent inner shelf of Massachusetts Bay by means of an extensive set of sidescan sonar records and supplemental bathymetric, sedimentary, subbottom and bottom-current data. 1. (1) Environments of erosion and nondeposition appear on the sonographs either as patterns with isolated reflections (caused by outcrops of bedrock, glacial drift, and coastal plain rocks) or as patterns of strong backscatter (caused by coarse-grained lag deposits). Sediments in these environments range from boulder fields to gravelly sands with megaripples. Inside the harbor, areas of erosion or nondeposition are found primarily near mainland and insular shores and within constricted tidal channels, whereas, on the shelf, they are present over extensive areas of hummocky topography near the coast and atop local bathymetric highs offshore. 2. (2) Environments of sediment reworking are characterized on the sonographs by patterns with patches of strong to weak backscatter caused by a combination of erosional and depositional processes. These environments have diverse grain sizes that range from sandy gravels to muds. Within the harbor, the locations of reworked sediments are uncorrelated with the bottom topography, but, on the shelf, they are found on the lower flanks of bathymetric highs, within broad lows and in relatively deep water (30–50 m). 3. (3) Environments of deposition are depicted on the sonographs as uniform patterns of weak backscatter. These areas contain relatively fine-grained muddy sands and muds. Inside the harbor, depositional environments are found over extensive subtidal flats and within sheltered depressions, whereas, on the shelf, they are restricted to broad lows mainly in deep water. The extreme patchiness of modern sedimentary environments within the Boston Harbor-Massachusetts Bay system reflects the interaction between the irregular bottom topography and both geologic and oceanographic processes. The estuarine part of the system is an effective trap for fine-grained detritus because of its protected nature, low wave climate, and large supply of sediments. The open shelf, however, is largely mantled by winnowed and sorted sediments as a result of erosion during past sea-level fluctuations, sediment resuspension and transport by modern waves and currents, and a spatially variable supply of fine-grained sediments.

Carbon fluxes and burial rates over the continental slope and rise off central California with implications for the global carbon cycle

In situ microelectrode, box‐core pore water gradient, and in situ benthic chamber estimates of organic carbon degradation and CaCO3 dissolution are combined with organic‐C and carbonate‐C accumulation rates to approximate the total carbon flux to the seafloor along two transects of the continental slope and rise off central California. Microelectrode profiles of dissolved O2 demonstrate that sediments at 13 sites, ranging in water depth from 580 to 4080 m, become anoxic below the uppermost 0.4–3 cm of the sediment column. If a current‐swept area of nondeposition on the upper slope is excluded, we find total organic‐C and carbonate‐C fluxes to the seafloor vary from 40 to 100 μmol C cm−2yr−1 and from 32 to 91 μmol C cm−2yr−1, respectively. From the distribution of these fluxes there is no indication that total fluxes or remineralization rates of organic or carbonate carbon are influenced markedly by conditions in the oxygen minimum zone. Instead, the upper continental rise with its system of submarine valleys and fans stands out as the most important locus for carbon deposition and remineralization. When benthic fluxes and burial rates are extrapolated over the whole slope and rise of the region, aerobic respiration is the major mechanism of organic matter oxidation, and organic‐C and carbonate‐C recycling are on average 87% and 98% efficient, respectively. These results suggest that modern sediments on the outer regions of continental margins are important sources of CO2 that is injected directly into ocean deep water. However, if benthic carbon fluxes on the central California margin are typical of margins globally, this injection rate is less than 0.7 Gt C yr−1, which does not indicate a significant anthropogenic enhancement of carbon export to continental slopes and rises.

The rock floor of the English Channel and its significance for the interpretation of marine unconformities

The English Channel is for the most part an area of erosion, not of permanent deposition. In an area extending from beyond the Scillies in the west as far as Ostend in the east there is solid rock at or near the seafloor almost everywhere. The overlying superficial sediment is coarse-grained and contains abundant derived fossils—a typical basement bed. The rock floor is suffering continuing erosion, but the materials so released are not accumulating locally, but are being carried towards the continental slope or into the North Sea. The situation appears to be a stable one, with a life expectancy of perhaps 1 m.y. The implications of this large area of marine non-deposition are discussed, using the examples of other unconformities in the earlier history of the Channel region.

Distribution of biogenic silica in the surficial sediments of Lake Michigan

The spatial distribution of biogenic silica (BSi) in the surficial sediments of Lake Michigan is described from Shipek grab samples collected in 1975 and gravity cores obtained in 1983. Significantly smaller surficial BSi concentrations in the 1975 samples were attributed primarily to the inability of a Shipek grab to collect intact surficial sediment samples. Lower concentrations o.f BSi were found in nondepositional and transitional areas of sediment accumulation than in depositional basins. Therefore, BSi accumulation is restricted primarily to the 40% of the lake bottom where sediments are presently accumulating. High concentrations found in Green Bay surficial sediments are related to high productivity in the bay coupled with inputs of new silica from the Fox River. In the open lake, BSi concentrations of surficial sediments in depositional basins appeared to vary inversely with sedimentation rate in that lower BSi concentrations were found in areas with higher sedimentation rates.

3-D Seismic Interactive Interpretation of Complex Stratigraphic Environments: An Example From Grayson County, Texas: ABSTRACT

Interactive interpretation of 3-D seismic data is now an effective tool for mapping complex stratigraphic targets on land. Slicing a 3-D seismic cube through a single reflector provides an insight into complex stratigraphic environments. A case study from Grayson County, Texas, is used as an example. Production from the lower Davis sands of the Atokan series was established in the Southmaud area in 1978. Further development of the field led to a success ratio of only 50%. Stratigraphic complexity of the fluvial to deltaic environment made reservoir prediction and placement of offset wells difficult. A 6-mi2 3-D survey was shot for the purpose of mapping the sand distribution. Acquisition and processing costs were less than the cost of one dry hole. The producing sands were a difficult seismic target. Resolution of these sand bodies was in question due to their vertical and horizontal extent as well as their small reflection coefficients. The interpretation was completed in eighteen hours using Gulf's Interactive Seismic Interpretation System (ISIS). Only one well was used initially to identify seismic horizons. Structural mapping was completed using dual polarity, random vertical lines, and isotime slices. Stratigraphic interpretation was done with discrete amplitude coloring to take advantage of seismic tuning effects. Stratigraphic slices revealed the distribution and thickness of the reservoir sand. Geological features interpreted include a meandering channel with point-bar buildups, a distributary complex, and erosional or nondepositional areas. End_of_Article - Last_Page 525------------

The Hydraulic Equivalence of Mica

ABSTRACT Settling experiments performed on silt- to fine-sand-sized mica flakes with a holographic micro-velocimeter revealed that mica is the hydraulic equivalent of quartz spheres having diameters a factor of 4 to 12 times smaller. Mica in the very fine to fine-sand sizes has been traditionally used by sedimentologists to delineate areas of deposition or nondeposition and potential winnowing of fines, and is here found to be the hydraulic equivalent of silt-sized particles but not of clay. Experiments also showed that mica flakes tend to settle at orientations which are neither perpendicular nor parallel to the gravitational vector and tend to generally maintain their orientation throughout. Equations for the settling of a disc in Lerman and others (1974) and that developed by Komar and Reimers (1978) are shown to be mathematically similar for the coarse-silt to fine-sand ranges of discs and are adequate predictors of settling rates of mica flakes. A comparison of the hydraulic equivalency of quartz spheres to coarse-silt- through fine-sand-sized mica flakes is presented.

Geology of Coal Resources in Eastern Kentucky: ABSTRACT

Since 1976 the Kentucky Geological Survey has been engaged in a Coal Resources Project. During this period over 22,000 new correlated measurements of the coal beds and enclosing rock were made. Other sources provided an additional 3,000 data points. This large data set was analyzed in detail and used in the preparation of coal bed isopach maps. This work has resulted in a definition of the extent of coal beds, variations and trends in thickness, and reevaluation of coal-bed correlations. Coal-bed isopach maps outline basic geologic areas of peat accumulation. Trends outlined by isopachs show channels or related nondepositional areas such as bays. In addition, use of structural maps in conjunction with isopach maps show correlation between coal deposits and structural cont ols such as synclines, anticlines, faults, and troughs. The detailed analysis of coal resource data is an effective tool for determining the geologic condition of coal formation. End_of_Article - Last_Page 1453------------