Mid frequency shallow water fine-grained sediment attenuation measurements

2013 ◽  
Vol 134 (1) ◽  
pp. 131-143 ◽  
Author(s):  
Charles W. Holland ◽  
Stan E. Dosso
Keyword(s):  
Shallow Water ◽  
Fine Grained ◽  
Sediment Attenuation

TWO MODELING APPROACHES FOR REVERBERATION IN A SHALLOW WATER WAVEGUIDE WHERE THE SCATTERING ARISES FROM A SUB-BOTTOM INTERFACE

2009 ◽  
Vol 17 (01) ◽  
pp. 29-43 ◽  
Author(s):  
CHARLES W. HOLLAND ◽  
DALE D. ELLIS
Keyword(s):  
Shallow Water ◽  
Silty Clay ◽  
Sediment Layer ◽  
Angle Distribution ◽  
Vertical Angle ◽  
Fine Grained ◽  
Bottom Interface ◽  
Grazing Angles ◽  
Scattering Kernel ◽  
Sediment Interface

In shallow water environments where the uppermost sediment layer is a fine-grained fabric (e.g. clay or silty-clay), the observed reverberation may be dominated by scattering from the sub-bottom. Here, reverberation predictions from normal mode and energy flux models are compared for the case where the scattering arises from a sub-bottom half-space under a fine-grained sediment layer. It is shown that in such an environment, the position of the angle of intromission, in addition to the angular dependence of the scattering kernel, is a factor controlling the reverberation and its vertical angle distribution. It is also shown that the reverberation from a sub-bottom horizon is typically governed by higher grazing angles than the case where the scattering occurs at the water–sediment interface. There was generally very close agreement between the models as a function of frequency (200–1600 Hz), layer thickness (0–8 m), and range (1–15 km). The model comparisons, showing some differences, illuminate the result of different approximations in the two approaches.

Surficial Sediments of Lake Erie

1976 ◽  
Vol 33 (3) ◽  
pp. 385-403 ◽  
Author(s):  
R. L. Thomas ◽  
J.-M. Jaquet ◽  
A. L. W. Kemp ◽  
C. F. M. Lewis
Keyword(s):  
Grain Size ◽  
Shallow Water ◽  
Lake Erie ◽  
Central Basin ◽  
Sediment Accretion ◽  
Western Basin ◽  
Grab Sampling ◽  
Fine Grained ◽  
Basin Region ◽  
Skewness And Kurtosis

On the basis of extensive echosounding and grab sampling, three major units have been recognized in Lake Erie: till and bedrock, glaciolacustrine clay, and postglacial muds. These units represent the late glacial and postglacial evolution of the basin and occur in an offshore younging sequence. The main basin of the lake is subdivided by residual glacial moraines into four depositional basins: Western, Sandusky, Central, and Eastern basins. The sediment texture has been defined by moment measures (mean, standard deviation, skewness, and kurtosis), the trends of which are related to the mixing of two primary grain-size populations in the sand- and clay-size ranges. A third grain-size mode in the silt size, composed of fine quartz with some carbonate, has been recognized. This mode has a modifying effect on the symmetry of the two primary populations and may, to some extent, be sufficiently abundant to behave as a discrete population. The trends in the textural characteristics, particularly skewness and kurtosis, have been utilized to define energy regimes at the sediment–water interface which indicates three distinct sedimentary or hydraulic regions: 1) Western basin region — Fine-grained sediment accretion in shallow water related to an imbalance in sediment budget, with high input loadings of fine-grained sediment, and deficit in coarse materials, with an excess of input over sediment export to the Central basin region. This results in net sediment accretion in shallow water with texture in disequilibrium with environmental energy, which produces mixing and suspension, followed by redeposition; 2) Central basin region — West to East coarsening of sediment in textural equilibrium with hydraulic energy, as it relates to increasing fetch under westerly and southwesterly prevailing winds; 3) Eastern basin region — Deepwater basin with sediments showing decreasing size offshore with increasing water depth. The deepwater sediment is modified by the influx of substantial quantities of the silt-size material derived from shoreline erosion in the north shore of the Central basin region.The interrelationships of parameters indicate textural dependence on mineralogic composition, particularly important being the relationship of clay concentration to mean grain size. This has particular value in modelling the physical behavior of clay-associated geochemical elements such as phosphorus.

PETROLEUM PROSPECTS, BLIGH WATER, FIJI

1972 ◽  
Vol 12 (1) ◽  
pp. 62
Author(s):  
A.W. Lindner
Keyword(s):  
Shallow Water ◽  
Sedimentary Rocks ◽  
Petroleum Exploration ◽  
Seismic Profiles ◽  
Fine Grained ◽  
Porosity And Permeability ◽  
Oil Seepage ◽  
The Government ◽  
Basement High ◽  
Offshore Petroleum

The Fiji Archipelago constitutes a segment of the island arc system of the southwest Pacific. The islands in the group comprise a mixture of igneous and sedimentary rocks including carbonates. The hydrocarbon potential of the region has been emphasised since the Tonga oil seepage drew the attention of the oil industry to this part of the globe in 1968.Southern Pacific Petroleum (Fiji) Limited was granted the first offshore petroleum concession in Fiji by the Government in 1969 and the negotiation for the concession resulted in the formulation of Fijian offshore petroleum exploration legislation. Reconnaissance sparker seismic shooting indicated the existence of stratified rocks beneath Bligh Water and subsequent aeromagnetics and multiple coverage seismic has confirmed the presence of a sedimentary basin.The oldest dated sedimentary rocks in Fiji are Eocene. They form part of a very thick sequence, including volcanics, ranging into Lower Miocene which regionally has been mildly metamorphosed. Locally this sequence has been intruded by intermediate to basic plutonic stocks which subsequently have been unroofed by widespread intra-Miocene erosion. This sequence constitutes the economic basement in the region. Middle to Upper Miocene and Pliocene clastic, marine, fossiliferous sediments and shallow water carbonates on the two main islands of Fiji were deposited in localised basins, generally in complex association with volcanic rocks.The sedimentary column contains considerable fine grained, dark coloured, marine elastics. Bioclastic limestone, also present in the sequence, has excellent porosity and permeability. Good reservoir character is similarly indicated for some of the coarser elastics, despite the lack of quartz.The seismic data, when integrated with the geology of the islands, infer that the deepest continuous reflection horizon represents the intra-Miocene unconformity; additionally, the data show that the Bligh Water Basin is divided into northern and southern components, divided by a basement high. The southern region appears more attractive for exploration as 7000 ft. (2100 m.) of section is indicated and the area is covered by shallow water. Faulting and drape features are the obvious structural forms present. Several discontinuous reflection events, commonly occurring at equivalent positions on different seismic profiles, may indicate presence of carbonate banks or cays similar to the type of carbonate deposits exposed in the succession onshore.

Summary of a revision of New York State Ordovician eurypterids: implications for eurypterid palaeoecology, diversity and evolution

2003 ◽  
Vol 94 (3) ◽  
pp. 235-242 ◽  
Author(s):  
Victor P. Tollerton
Keyword(s):  
New York ◽  
Shallow Water ◽  
New York State ◽  
Taxonomic Revision ◽  
York State ◽  
Fine Grained ◽  
Diversity Measures ◽  
Extinction Event ◽  
First Occurrence ◽  
Near Shore

ABSTRACTThe record of Ordovician Eurypterida from New York State, USA, is shown to be largely false. Twenty-nine species in 17 genera are here recognised as pseudofossils, reducing by more than 75% the total number of named Ordovician eurypterid taxa. Consequently, 10 families now have their first occurrence either later in the Ordovician or in the Early Silurian. The implications for eurypterid palaeoecology, diversity and evolution are not as straightforward as would be expected from such a drastic taxonomic revision. All Ordovician eurypterids are now known to occur in shallow-water, near-shore shales or fine-grained carbonates. Diversity measures indicate that the end-Ordovician extinction event appears to have had less effect on eurypterids than previously known, and their turnover is level in the Ordovician.

Marine soft-bottom benthic community offshore from Black Rock sewage outfall, Connewarre, Victoria

1980 ◽  
Vol 31 (2) ◽  
pp. 155 ◽  
Author(s):  
JH Dorsey ◽  
RN Synnot
Keyword(s):  
Shallow Water ◽  
Benthic Community ◽  
Sewage Effluent ◽  
Soft Bottom ◽  
Suspension Feeders ◽  
Sewage Outfall ◽  
Fine Grained ◽  
Sandy Sediments

The shallow-water benthic community offshore from Black Rock sewage outfall consists of a moderately diverse crustacean and polychaete infaunal assemblage living in fine-grained, homogeneous, sandy sediments. Most organisms are detritus- or suspension-feeders, with detritus coming largely from planktonic and suspended sources. Sewage effluent may secondarily enrich inshore sediments which support dense populations of spionid polychaetes and Callianassa ceramica.

Sediments of ice-dammed, self-draining Ape Lake, British Columbia

1987 ◽  
Vol 24 (9) ◽  
pp. 1735-1747 ◽  
Author(s):  
Robert Gilbert ◽  
Joseph R. Desloges
Keyword(s):  
Grain Size ◽  
Shallow Water ◽  
Deep Water ◽  
Lake Water ◽  
Average Rate ◽  
Deep Basin ◽  
Varved Sediments ◽  
Fine Grained ◽  
Organic Debris ◽  
Sediment Loads

The glacier damming Ape Lake has withdrawn from its Neoglacial terminal moraines in the lake since early in this century at an average rate of 15 m/a. As a result, the first known drainings of Ape Lake occurred in October 1984 and August 1986. In each event, about 54% of the volume of the lake was lost through a tunnel in the damming glacier. Most of the remaining water was held in the deep basin of the lake behind partially breached Neoglacial terminal moraines. As the glaciers have withdrawn, the character of the sediments has changed. Sediments in the deep basin of the lake are varved, but the grain size, especially of the summer deposits, has decreased and rates of sedimentation have decreased from about 4 mm/a to less than 2 mm/a. In shallow water, deposition of varved sediments has given way to the deposition of massive sediments at rates of less than 1 mm/a. Ice-rafted debris is rare in deep water, despite the presence of calving bergs.During and following the first draining, significant subaerial erosion occurred as a result of the event itself, the drawdown and steepened gradients, and the action of waves on the exposed sediments as the lake refilled. In proximal areas, distinct deposits within the normal winter deposits are recognised. In deep water, deposition of massive, highly underconsolidated, fine-grained sediments occurred. Organic debris released from shallow deposits by erosion has become concentrated in both shallow- and deep-water sediments. Within a year of the first draining, sediment loads in the lake water were returning to normal.

scholarly journals A new ophiacanthid brittle star (Echinodermata, Ophiuroidea) from sublittoral crinoid and seagrass communities of late Maastrichtian age in the southeast Netherlands

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e9671
Author(s):  
Ben Thuy ◽  
Lea Numberger-Thuy ◽  
John W.M. Jagt
Keyword(s):  
New Species ◽  
Shallow Water ◽  
Brittle Star ◽  
Brittle Stars ◽  
Sea Floor ◽  
Fine Grained ◽  
Exceptional Preservation ◽  
Stalked Crinoids ◽  
A New Species

A new species of brittle star, Ophiomitrella floorae, is recorded from the lower two meters of the Gronsveld Member (Maastricht Formation), of late Maastrichtian age (c. 66.7 Ma). These relatively fine-grained biocalcarenites reflect shallow-water deposition in a sheltered setting with a relatively firm sea floor and clear waters, under middle sublittoral and subtropical conditions. Associated echinoderm taxa comprise more robust, sturdy-plated ophiomusaid and ophiodermatid brittle stars and numerous bourgueticrinine sea lilies. The new brittle star described herein belongs to a family whose present-day members are predominantly restricted to bathyal depths. Its small size and the exceptional preservation of a single articulated specimen partially wrapped around the stalk of a bourgueticrinine suggest that O. floorae n. sp. was probably epizoic and specifically associated with stalked crinoids.

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