Map Of Sediment Distribution Research Articles

Seabed Sediment Classification using Multi-Frequency MBES Bathymetric and Its Features

Principally, for a few decades, hydrographical surveys have been only to determine the depth of seawater. Sonar measurement tehcnology is the most widely used to conduct hydrographical surveys employing a singlebeam echosounder (SBES) and multibeam echosounder (MBES). In addition to depth information, seafloor sediment distribution maps are essential for port planning and management. In general, the distribution of seafloor sediments is predicted using backscatter data from SBES and MBES at single and multiple frequencies. The bathymetric data generated by the echosounder can be derived into several bathymetric features such as slope, ruggedness, roughness, aspect, bathymetric position index (BPI), and curvature. This study examines the possibility of using bathymetric measurement and bathymetric derivation of multi-frequency MBES to predict the distribution of seafloor sediments, especially in the harbor pond area. The study used a deep neural network (DDN) to classify the distribution of seabed sediments with bathymetric and bathymetric features input, validated with 74 in situ sediment samples (clayey sand, silt, sandy silt, and silty sand). Up to 75% of data sample sediments are used for training and 25% for validation. The classification results by DNN showed 42.6% clayey sand, 7.4% sandy silt, 46.7% silt, and 3.35% silty sand. The overall accuracy (AO) and Kappa classification of seabed sediments with DDN were 59.5% and 0.54 (moderate), respectively.

Multibeam echosounder backscatter strength analysis for seafloor sediment identification in Damar Besar Island Waters, Thousand Islands

The condition of the Indonesian territory surrounded by the ocean requires technology to obtain seabed information to support the development of social, economic, and security activities. One of the technologies that can be used is the multibeam echosounder (MBES) hydroacoustic technology. MBES can scan seabed in a wide range, resulting in bathymetric data and backscatter values. The value of backscatter can be used to identify seafloor sediments. This study compared backscatter intensity values obtained from the MBES survey to the previous study. After identifying the sediment, the data obtained are mapped to produce a sediment distribution map. The types of sediment identified in the Damar Besar Island Waters are fine silt, medium silt, coarsed silt, silty sand, muddy sand, clayed sand, very fine sand, and fine sand with a range of backscatter values from -34,92 to -19,04 dB. Fine sand sediments are nearby the northern island while muddy sands and silty sands are scattered away from the island.

Comparison between different spatial interpolation methods for the development of sediment distribution maps in coastal areas

Sediment grain size and its spatial distribution is a very important aspect for many applications and processes that occur in the coastal zone. One of these is coastal erosion which is strongly dependent on sediment distribution and transportation. To highlight this fact, surficial coastal sediments were collected from a densely populated coastal zone in Western Greece, which suffers extensive erosion, and grain size distribution was thoroughly analysed, to predict the spatial distribution of the median grain size diameter (D50) and produce sediment distribution maps. Four different geostatistical interpolation techniques (Ordinary Kriging, Simple Kriging, Empirical Bayesian Kriging and Universal Kriging) and three deterministic (Radial Basis Function, Local Polynomial Interpolation, and Inverse Distance Weighting) were employed for the construction of the respective surficial sediment distribution maps with the use of GIS. Moreover, a comparative study between the deterministic and geostatistical approaches was applied and the performance of each interpolation method was evaluated using cross-validation and estimating the Pearson Corellation and the coefficient of determination (R2). The best interpolation technique for this research proved to be the Ordinary Kriging for the shoreline materials and the Empirical Bayesian Kriging (EBK) for the seabed materials since both had the lowest prediction errors and the highest R2.

Deep-sea sediments of the global ocean

Abstract. Although the deep-sea floor accounts for approximately 60 % of Earth's surface, there has been little progress in relation to deriving maps of seafloor sediment distribution based on transparent, repeatable, and automated methods such as machine learning. A new digital map of the spatial distribution of seafloor lithologies below 500 m water depth is presented to address this shortcoming. The lithology map is accompanied by estimates of the probability of the most probable class, which may be interpreted as a spatially explicit measure of confidence in the predictions, and probabilities for the occurrence of five lithology classes (calcareous sediment, clay, diatom ooze, lithogenous sediment, and radiolarian ooze). These map products were derived by the application of the random-forest machine-learning algorithm to a homogenised dataset of seafloor lithology samples and global environmental predictor variables that were selected based on the current understanding of the controls on the spatial distribution of deep-sea sediments. It is expected that the map products are useful for various purposes including, but not limited to, teaching, management, spatial planning, design of marine protected areas, and as input for global spatial predictions of marine species distributions and seafloor sediment properties. The map products are available at https://doi.org/10.1594/PANGAEA.911692 (Diesing, 2020).

Alien foraminifers of the northern and northeastern coastlines of Cyprus Island

The study area covers the northern coasts of Cyprus from the Güzelyurt Gulf to the Famagusta Gulf. This study was carried out in order to reveal the presence of the alien foraminifera, which are widely distributed in the Eastern Mediterranean particularly Amphistegina lobifera in the study area, and the effects of trace elements on faunal assemblages (foraminifera, ostracod and mollusc). The bottom sediment samples were taken from eighteen different points and depths, the faunal assemblages were examined, and the sediment distribution map of the studied area was made by ICP-MS analysis and geochemical evaluations. 30 genera and 48 species of foraminifera have been identified, of which 9 species belonging to 6 genera are the alien foraminifera. These are: Spiroloculina angulosa, S. antillarum, Hauerina diversa, Coscinospira hemprichii, Peneroplis pertusus, P. planatus, Amphisorus hemprichii, Sorites orbiculus and Amphistegina lobifera. Amphistegina lobifera was observed to be abnormally abundant in most of the samples. This foraminiferal assemblage of Red Sea origin constitutes a poor assemblage compared to the alien assemblages in Turkish Mediterranean coastal areas.It has been determined that the ostracod and mollusc genera and species found in the same samples belong to the typical Mediterranean and Aegean Sea community.

Generation of a Large-Scale Surface Sediment Classification Map Using Unmanned Aerial Vehicle (UAV) Data: A Case Study at the Hwang-do Tidal Flat, Korea

Tidal flats are associated with complicated depositional and ecological environments, and have changed considerably as a result of the erosion and sedimentation caused by tidal energy; consequently, the surface sediment distribution in tidal flats must be constantly monitored and mapped. Although several studies have been conducted with the aim of classifying intertidal surface sediments using various remote sensing methods combined with field survey, most of these studies were unable to consider various sediment types, due to the low spatial resolution of remotely sensed data. Therefore, previous studies were unable to efficiently describe precise surface sediment distribution maps. In the present study, unmanned aerial vehicle (UAV) red, green, blue (RGB) orthoimagery was used in combination with a field survey (232 samples) to produce a large-scale classification map for surface sediment distribution, in accordance with sedimentology standards, using an object-based method. The object-based method is an effective technique that can classify surface sediment distribution by analyzing its correlations with spectral reflectance, grain size, and tidal channels. Therefore, we distinguished six sediment types based on their spectral reflectance and sediment properties, such as grain composition and statistical parameters. The accuracy assessment of the surface sediment classification based on these six types indicated an overall accuracy of 72.8%, with a kappa coefficient of 0.62 and 5-m error range related to the Global Positioning System (GPS) device. We found that 11 samples were misclassified due to the effects of sun glint and cloud caused by the UAV system and shellfish beds, while 14 misclassified samples were influenced by surface water related to the elevation, tidal channels, and sediment properties. These results indicate that large-scale classification of surface sediment with high accuracy is possible using UAV RGB orthoimagery.

Rapid sediment mapping and in situ geotechnical characterization in challenging aquatic areas

AbstractYakutat Bay, Southeast Alaska, is characterized by significant spatial variations in sediment type and dynamics. The northwestern side is supplied by sediments from the nearby glaciers, and is affected by longshore sediment transport processes, while the southeastern side has no direct sediment input, and is affected by human activities. In situ seabed investigations can be difficult, and expensive, due to logistical challenges in such remote locations. A portable free fall penetrometer (PFFP) was deployed 149 times along 16 transects in water depths of 2–48 m. The deceleration and pore pressure records during the probe's penetration into the seabed were used to characterize the surficial sediments. Equivalents of quasi‐static bearing capacity were determined using the deceleration‐depth signatures, and yielded strong variabilities ranging from 5 to 107 kPa at sediment depths of 10.3–41.9 cm. Correlating the PFFP results to visual field observations and literature, a regional classification scheme, and an updated sediment distribution map were derived. The pore pressure response was correlated to the different sediment types, and was used to assess the sediment's consolidation state. At the northwestern side, an increasing pore pressure trend indicated underconsolidated cohesive sediments. At the southeastern side, clayey sediments appeared to be more consolidated except of sediments of high organic content near the populated areas. The use of the pore pressure measurements represents a novel way for rapid sediment characterization using PFFP. The presented approach to create rapidly a regional sediment classification scheme offers a time‐ and cost‐effective method to derive seabed sediment maps in areas of difficult access and logistics.

Variability in suspended sediment concentration in the Minas Basin, Bay of Fundy, and implications for changes due to tidal power extraction

The Bay of Fundy in eastern Canada has the world's largest tidal range of over 16m with tidal currents up to 5ms−1 making it an ideal place for tidal power extraction using tidal in-stream energy conversion devices in the Minas Passage. Field observations collected from ship-based and bottom-moored sensors over an 8-day period in 2013 are used to validate a 3D hydrodynamic and sediment transport model of the Minas Basin with measurements of water levels, current profiles, waves, suspended sediment fluxes and suspended sediment concentration (SSC) profiles. The sediment conditions are initialized using a bi-modal sediment distribution map and the model simulates both cohesive and non-cohesive sediments in the Minas Basin. Model results for fine-grained suspended sediment concentrations are compared horizontally, vertically, and temporally to observations and indicate strong data-model agreement for SSC from 5 to 287mgL−1. The implications of constructing a large-scale turbine farm within the Minas Passage and the impacts on suspended sediment within the Minas Basin are investigated using the model. The farm is simulated by adding semi-permeable structures that use an energy loss term in the fluid momentum equations to parameterize turbine regions in the hydrodynamic model. The results emphasize the sensitivity of the system to changes in flow and suggest that a large-scale tidal energy farm that extracts maximum power could reduce SSC by 37% on average across the basin which would influence physical and biological processes particularly on the fine-grained intertidal areas around the macrotidal basin.

3D Modeling of sediment movement by ships-generated wakes in confined shipping channel

Ship-generated waves and return currents are capable of re-suspending significant quantities of bottom and bank sediments. However, most of the previous studies done on the subject do not show how and where sediment is re-suspended by the wakes and the directions of net transport. In this paper, a 3D numerical model based on hydro-sedimentary coupling is presented to search the relationship between the sediment movement, and the pattern of ship-generated waves around and far away from the vessel and the return currents around the ships. The hydrodynamic model is based on 3D Navier-Stokes equations including the standard k-ε model for turbulence processes, and the sediment transport model is based on a 3D equation for the re-suspended sediment transport. The computation results show that the areas of sediment concentration and transport (whether by resuspension or by the bedload) depend mainly on the position, the speed of the ship in the waterways, the kinematics of ship-generated waves and on the return flows. Thus, a map of sediment distribution and the modes of sediment transport generated by the passage of the ship are presented.

Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales

Research Article| September 01, 2009 Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales Brian W. Romans; Brian W. Romans 1Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California 94305, USA *Current address: Chevron Energy Technology Co., San Ramon, California 94583, USA. E-mail: brian.romans@chevron.com Search for other works by this author on: GSW Google Scholar William R. Normark; William R. Normark 2U.S. Geological Survey, Coastal and Marine Geology Division, 345 Middlefield Road, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Mary M. McGann; Mary M. McGann 2U.S. Geological Survey, Coastal and Marine Geology Division, 345 Middlefield Road, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Jacob A. Covault; Jacob A. Covault 1Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Stephan A. Graham Stephan A. Graham 1Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (9-10): 1394–1408. https://doi.org/10.1130/B26393.1 Article history received: 22 Dec 2007 rev-recd: 09 Dec 2008 accepted: 17 Dec 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Brian W. Romans, William R. Normark, Mary M. McGann, Jacob A. Covault, Stephan A. Graham; Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales. GSA Bulletin 2009;; 121 (9-10): 1394–1408. doi: https://doi.org/10.1130/B26393.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Utilizing accumulations of coarse-grained terrigenous sediment from deep-marine basins to evaluate the relative contributions of and history of controls on sediment flux through a source-to-sink system has been difficult as a result of limited knowledge of event timing. In this study, six new radio-carbon (14C) dates are integrated with five previously published dates that have been recalibrated from a 12.5-m-thick turbidite section from Ocean Drilling Program (ODP) Site 1015 in Santa Monica Basin, offshore California. This borehole is tied to high-resolution seismic-reflection profiles that cover an 1100 km2 area of the middle and lower Hueneme submarine fan and most of the basin plain. The resulting stratigraphic framework provides the highest temporal resolution for a thick-bedded Holocene turbidite succession to date, permitting an evaluation of source-to-sink controls at millennial (1000 yr) scales.The depositional history from 7 ka to present indicates that the recurrence interval for large turbidity-current events is relatively constant (300–360 yr), but the volume of sediment deposited on the fan and in the basin plain has increased by a factor of 2 over this period. Moreover, the amount of sand per event on the basin plain during the same interval has increased by a factor of 7. Maps of sediment distribution derived from correlation of seismic-reflection profiles indicate that this trend cannot be attributed exclusively to autogenic processes (e.g., pro-gradation of depocenters). The observed variability in sediment accumulation rates is thus largely controlled by allogenic factors, including: (1) increased discharge of Santa Clara River as a result of increased magnitude and frequency of El Niño–Southern Oscillation (ENSO) events from ca. 2 ka to present, (2) an apparent change in routing of coarse-grained sediment within the staging area at ca. 3 ka (i.e., from direct river input to indirect, littoral cell input into Hueneme submarine canyon), and (3) decreasing rates of sea-level rise (i.e., rate of rise slowed considerably by ca. 3 ka). The Holocene history of the Santa Clara River–Santa Monica Basin source-to-sink system demonstrates the ways in which varying sediment flux and changes in dispersal pathways affect the basinal stratigraphic record. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Coastline changes of the Darss–Zingst Peninsula — A modelling approach

Coastline development is a function of eustasy and isostasy. On a regional scale, the precision of models based on these two components is sufficient for the investigation of coastline scenarios. However, on a local scale sediment dynamic is responsible for the evolution of coastal structures that alter the coastline in detail considerably. The Darss–Zingst Peninsula at the southern coast of the Baltic Sea serves as a example for a case study of such a structure. Longshore sediment transport driven by waves and responsible for the formation of this barrier during the Holocene is simulated for the next 840 years with the sediment transport modelling software package SEDSIM. The main objectives are to test if SEDSIM is a viable tool for the modelling of such structures and if the available data basis is suitable for this task. Basic data used for the modelling are a recent digital elevation model, measured wave time series, a map of sediment distribution, and a modelled eustatic scenario. In result, SEDSIM proved to be a stable and highly configurable program that can handle the requested simulations. Input data have to be improved and must include event data like storm surges.

Oceanography and submarine sediment distribution in the Marmaris – Ka region of southwest Turkey

We present new oceanographic and modern sediment distribution data for transects along Marmaris-Fethiye- Kalkan-Ka-Finike and Antalya Bays (southwestern Turkey). Water temperature, salinity and dissolved oxygen content were measured and mapped for this region. Furthermore, we made short-term current speed measurements at the surface, 20m depth and the sea floor and use this data to interpret sediment movement. Orange peel and other types of grabs were used for surface sediment sampling. Samples were processed with Standard Methods of grain size analysis. Our regional maps of sediment distribution reflect grain size on a 1:100.000 scale. We used correlations between all our grain size data in our maps. Sediment distribution in this region is affected by current systems, bathymetry and both submarine, and terrestrial topographic features of the region. Finer materials do not accumulate in regions with high wave and current energy. Thus we find mostly thin accumulations of coarse material in our study region. Either sediment does not accumulate at all along continental slopes exceeding 10 degrees or very little sediment accumulates there. Sediments in our study area consist of five types of basic sedimentary material: rock, gravel, sand, silt, clay and mud. Gravelly materials are gravel, sandy gravel and muddy sandy gravel. Sandy materials are sand, gravelly sand, gravelly muddy sand, muddy sand, silty sand and clayey sand. Silty material is composed of silt and sandy silt. Muddy materials consist of mud, gravelly mud and gravelly sandy mud. Deep parts of the area contain as well as mud which is high ratio clay. Generally, grain size distribution in this region is transitional from coarse to fine and trends parallel to the coastline. Generally, gravel and sandy gravel material are found in shallow areas and reach thickness of up to 5 meters. Blocks of limestone occur on the seafloor along coasts with steep seaward slopes. Gravel size materials are uncommon. Sandy materials accumulate at approximately 20-50-100-200 meters water depth. Silty materials are deposited at 200-500-750, 500-1200 meters depth at the sea floor. Muddy materials, however, are not found until 1200-2500 meters water depth and clayey materials spread further out to below 2500 meters depth.

Sediment distribution study in the Gulf of Kachchh, India, from 3D hydrodynamic model simulation and satellite data

A fully 3D finite difference baroclinic hydrodynamic model ‘COSMOS’ is applied to the Gulf of Kachchh (GoK) to study tidal variation, ocean currents, residual tidal current, sea surface temperature distribution, etc. The ‘COSMOS’ is based on the hydrostatic and Boussinesq approximations and uses a vertical double sigma coordinate with a step-like grid. In addition to the momentum and continuity equations, the model solves two-transport equations for salinity and temperature and an equation of state to include baroclinic effects. The other objectives are quantitative assessment of suspended sediments by analyzing SeaWiFS data and understand the relation between residual tidal currents and erosion, movement and deposition of sediments. The model results showed that the dominant current system within GoK is controlled by the simulated tidal and residual tidal currents variation. The residual tidal current velocity reduces from the surface towards the bottom. The residual surface current velocity distribution displays cyclonic eddy continuity regions within the GoK. It is concluded that bottom topography variation plays an important role in determining the distribution of residual current velocity and thereby sediment distribution. The residual current velocity distribution map showed conformity with the gross geomorphic subdivisions and the sediment distribution map of Gulf of Kachchh. The suspended sediment plume pattern followed the current pattern obtained from modeling. The model results of the sea surface temperature of the December month showed good agreement with the temperature structure and the pattern obtained form NOAA/AVHRR data.

Sedimentary processes, bedforms and facies, associated with a coastal headland: Portland Bill, Southern UK

This investigation presents new findings on the sedimentary processes and deposits associated with a coastal headland, in a mixed tide–wave setting, using data compilation (bathymetric and sediment distribution maps), collected field data (side-scan sonar and seabed sampling) and sand transport modelling. Sand transport pathways are described: (a) on the basis of coupled-system seabed morphology/sand distribution; and (b) from bed shear stress and (medium-grained) sand transport rate simulations. The presence of a sequence of sedimentary deposits, associated with a complex suite of bedforms and sedimentary facies within an overall framework of limited sediment supply, represents a gradient in shear stress and sand transport towards the headland. These sequences are observed on both sides of Portland Bill, tending towards a symmetrical distribution. The sedimentary facies distribution is combined with sand transport rates and maximum bed shear stress distribution, to suggest a conceptual model for sand dispersal and deposit formation around headlands. Sand dispersal can be explained in terms of a headland-associated eddy/bedload convergent zone concept. Maximum bed shear stress is observed at the tip of the headland and is associated with bedrock exposed on the seabed. The sequence of sedimentary deposits, away from the headland, is: sandbanks (Shambles and Portland Banks); sand/gravel flats; sand shoals (Adamant and West Shoals); and rippled sand sheets. The banks lie in an area of very high bed shear stress ( u * =0.08 m s −1); this is greater than that for other tidal sandbanks, not associated with headlands. Bank formation is the result of the strong convergent (transport) component, enhanced by the development of transient headland eddies. The sandbanks are to some extent also morphologically controlled, i.e. the Portland Bank is affected by the deep bathymetry to the west side of Portland Bill. The principal characteristic of headland-associated eddy/bedload convergent zones is the development of bed shear stress convergent zones, on both sides of the headland. Two conceptually distinct regions of sedimentary processes, associated with the coastal headlands, are recognised: (a) an inner zone, with increasing gradients in sand transport and bed shear stress towards the headland; and (b) an outer zone, in which sand transport is away from the headland, associated with a decrease in the bed shear stress. These zones merge into a bed shear stress (sand bedload transport) convergent zone, which enhances the formation of sandbanks around headlands. Thus, headland-associated sedimentary deposits are a complex system, compared with the occurrence of isolated sandbanks described elsewhere. The identification of a sequence of deposits related to and extending much farther from the headland than previously supposed, demonstrates that the ‘tidal stirring concept’ of headland-associated sandbanks may explain the formation of headland-associated sandbanks; however, it ignores the presence of a suite of sedimentary deposits around such headlands. The conceptual model proposed here provides a sedimentological perspective on the formation and occurrence of headland-associated deposits, including sandbanks.

Map of sediment distribution in the Western Baltic Sea (1: 100,000), Sheet “Darß”

The sheet “Dars” of the Western Baltic sediment distribution map displays several features of the late- and postglacial sediments in the area between 54°00′ and 54°30′ northern latitude and 12°00′ and 13°00′ eastern longitude on a scale of 1: 100,000. The main map shows the surface deposits in this area. Special attention is given to a detailed presentation of the granulometric characteristics of the sandy sedimens which are prevailing here. For this purpose a new way of visualization of grain size data was developed. Six insets provide information on water depth, positions of the sampling sites, areal distribution of median and sorting of sands, depth of the till surface thickness of the late- and postglacial sediments on top of the uppermost till and the bathymetry.

Sedimentological and geotechnical properties of fine-grained sediments in part of the South Sea, Korea

Sedimentary characteristics and geotechnical properties of the fine-grained sediments in the South Sea were analysed on 45 sediment cores collected in part of the sea. A map of surface sediment distribution in the sea is newly presented, based on the compilation of previous localized data. Grain size of the sediment (7–9ϕ) decreases slightly but systematically with water depth, although some variations in size occur locally along the coastal area. Shear strength is substantial near the sea floor (3–5 kPa) and gradually increases downcore, indicative of slow sedimentation. Water content is largely over 100% and uniform vertically. Organic matter and CaCO 3 increase Atterberg limits of the sediment, which is highlighted in the sediment off Ulsan under the influence of coastal upwelling.

Landsat-MSS radiance as a measure of suspended sediment in the Lower Yellow River (Hwang Ho)

A method of converting the Landsat-MSS radiance to an estimate of suspended sediment concentration is presented in this paper. The CCT data for the Lower Yellow River (Hwang Ho) were used in the study. The data were first corrected for instrumental error due to a drift in the sensor response and then converted to the absolute radiance received by the sensor. In order to understand the detected radiance and its variability, radiative transfer in the earth's atmosphere and natural waters are discussed. The radiative transfer equation has been simplified, so that a highly accurate atmospheric correction algorithm for diffuse sky radiance may be developed. However, the MSS is more sensitive to the direct sky radiance, and so an atmospheric correction based on the normalization of the solar angle is considered. Following a logarithmic relationship between radiance and suspended sediment concentration, the corrected remote-sensing radiance is used to estimate suspended sediment concentrations in the Lower Yellow River. The results suggest that the relationship could represent a universal algorithm for estimating suspended sediment concentration, although further detailed study will be needed to investigate this property. There is also sufficient evidence to indicate that remote sensing radiance may be used to infer the sediment size distribution, which represents a very important parameter in sediment transport studies. Finally, cross sections of suspended sediment concentration at Lijin in the Lower Yellow River are derived from the satellite data, and a map of sediment distribution in the estuary is also presented.

Tectonic Development of the Bismarck Sea Based on Gravity and Magnetic Modelling

The Bismarck Sea is a small marginal sea situated north of the island of New Britain and its associated trench. The land areas which surround it on three sides are island arc structures which have been active episodically since the Middle Cretaceous but which were most active during the Tertiary. Magnetic and sediment distribution maps of the Sea have been compiled and the results of two-dimensional magnetic and gravity modelling along five north-south traverses are presented. The magnetic map shows that the general trend of the anomalies is east-west. Individual anomalies can be traced for more than 150 km, mainly in the eastern half of the Sea, but in the western half persistent anomalies are difficult to discern except along the coast of mainland New Guinea. The water depth in the Bismarck Sea is about 2000 m and Bouguer gravity values are of the order of + 150 mGal. There is a substantial sediment-free area across the centre of the Sea, and sediment thickness increases towards land, reaching 2 km along the north New Guinea coast. Magnetic models and sediment distribution indicate that in the eastern half of the Sea north-south extension is taking place, thus implying northwards movement of the North Bismarck Plate relative to the South Bismarck Plate. The extension is occurring at about 8 cm yr−1 and is single limbed, accretion taking place mainly to the south of the Bismarck Sea Seismic Zone. Earthquake focal-mechanism solutions from the eastern part of the seismic zone, which extends E-W across the Sea, indicate that the N-S movement is being accommodated along two north-west-trending segments of the zone, about a pole to the south-west of the Sea. This interpretation supports the concept of an extensional origin for marginal seas. In addition the mechanics of the process are shown to be (a) different from those at mid-ocean ridges, (b) probably episodic, and (c) possibly reactivated across established trends, thus effectively erasing magnetic lineaments. The western half of the Sea is more complex but some north-south extension has occurred at the seismic zone.

New Type of Sediment-Distribution Map: Preliminary Result for Gulf of Mexico: ABSTRACT

Normal sediment-distribution maps present the lithologic characteristics of only the upper 4-6 in. of the sedimentary column. Cores collected from any area commonly reveal considerable changes in lithologic character through the thickness of the beds which are cored. Such variations can be expressed in vertical sections or in fence diagrams. Information concerning the upper sediment column to a depth of at least 30 ft is important for studies on sediment transport and deposition, basin filling, geotechnical properties, placing of laboratories on the sea bottom, salvaging sunken objects, acoustical measurements, and interpretation of high-frequency, shallow-penetration, and continuous seismic-reflection profiling. Standard have been determined from samples collected in long piston cores which penetrated different lithologic units and successions. The new sediment-distribution map constructed on the basis of the 30-ft cores shows the distribution of these standard patterns and thus reveals the sedimentary characteristics of the upper 30 ft. The patterns can be portrayed by colors, shades, and symbols, or combinations. Other properties, such as geotechnical characteristics, can be added to the standards of the map or can be superimposed on the standard presentation. The main divisions of the sediment-distribution map correspond to the boundaries of the physiographic provinces of the Gulf of Mexico. End_of_Article - Last_Page 707------------

Upper Sediment Column of Gulf of Mexico Presented in New Type of Map: ABSTRACT

Many types of investigations actually require information on the lithologic characteristics of the upper sediment column as well as the surface sediment characteristics. Selected cores from the Gulf of Mexico are presented as lithologic models. A chart symbol is used to indicate gross lithology. A numerical code has been developed which expresses lithologic percentages and indicates by positional notation vertical succession or intercalation of facies. For one area several cores were compared to demonstrate the validity of the developed technique and to show ratio changes. This new type of sediment-distribution map is of value in studies of sediment transport and deposition, basin filling, geotechnical properties, sea-laboratory preparation, salvaging of sunken objects, acoustical measurements, interpretation of shallow continuous reflection seismic profiling, etc. The sediment thickness represented on this new map is limited to the depth of penetration of the coring devices. End_of_Article - Last_Page 2033------------