THE STRUCTURE OF THE NATURALISTE PLATEAU AND TROUGH

1977 ◽  
Vol 17 (1) ◽  
pp. 3 ◽  
Author(s):  
Derk Jongsma ◽  
Peter Petkovic
Keyword(s):  
Sea Level ◽  
Early Cretaceous ◽  
Continental Margin ◽  
Deep Sea ◽  
Magnetic Anomalies ◽  
Seismic Profiles ◽  
Northern Margin ◽  
Reflection Seismic ◽  
Southwest Australia ◽  
Water Depths

The Naturaliste Plateau is a broad, relatively flat feature lying at a depth below sea level of around 2500 m off the continental margin of southwest Australia. A northerly trending trough with water depths of 3000 to 4000 m separates the Plateau from the continental shelf. Reflection seismic profiles over the Plateau reveal 500 to 1000 m thicknesses of post-Neocomian sediments on the Plateau and up to 2000 m thicknesses in the Trough. An erosional unconformity which is thought to be of Neocomian age separates folded, faulted sediments and intruded metamorphic and igneous basement from the overlying sediments. Deep sea drilling has shown the upper section as being composed of deep-sea clays and oozes. Several hiatuses occur in this upper section.Magnetic anomalies over the Plateau are intense and have magnitudes of up to 850 nT. The anomalies are much more subdued over the Trough. Depths to the bodies causing the magnetic anomalies are estimated to be between zero and three km below the Neocomian unconformity. The gravity field over the Plateau indicates that the crust is of intermediate thickness. A phase of rifting in the Early Cretaceous gave rise to a gently sloping northern margin, whereas rifting in the Eocene produced a steep, faulted, southern margin. The Plateau appears to have been at its present depths since the Early Cretaceous. Prospectivity for petroleum over the Plateau and Trough is poor.

Seismic stratigraphy and structure of the east Canadian continental margin between 41 and 52°N

1985 ◽  
Vol 22 (5) ◽  
pp. 686-703 ◽  
Author(s):  
L. M. Parson ◽  
D. G. Masson ◽  
C. D. Pelton ◽  
A. C. Grant
Keyword(s):  
Early Cretaceous ◽  
Continental Margin ◽  
Magnetic Anomalies ◽  
Seismic Stratigraphy ◽  
Sedimentary Sequence ◽  
The West ◽  
Grand Banks ◽  
Late Precambrian ◽  
Oceanic Basement ◽  
Iberian Margin

The seismic stratigraphy of the eastern Grand Banks continental margin is examined, and a five-fold division of the sedimentary sequence overlying basement is proposed. Oceanic basement of Cretaceous age underlies the eastern part of the study area; to the west, continental basement ranging in age from Late Precambrian to ?Jurassic underlies the Grand Banks. The sediment units, ranging in age from Early Cretaceous to Recent, have been dated by extrapolation of both commercial and DSDP drilling results from the Grand Banks and from the formerly conjugate Iberian margin. Identification of oceanic magnetic anomalies in the Newfoundland Basin agrees with the proposed age of the two oldest, Early Cretaceous units.

2. Seafloor spreading and magnetic anomalies

2015 ◽  
pp. 17-35
Author(s):  
Peter Molnar
Keyword(s):  
Sea Level ◽  
Deep Sea ◽  
Magnetic Anomalies ◽  
Seafloor Spreading ◽  
Ocean Floor ◽  
Sea Level Changes ◽  
Ocean Ridges ◽  
The Pacific ◽  
History Of ◽  
The Difference

‘Seafloor spreading and magnetic anomalies’ begins with the Vine–Matthews Hypothesis, which proposed that strips of seafloor parallel to the mid-ocean ridges, where two plates diverge from one another, were magnetized in opposite directions because the Earth’s field had reversed itself many times. A test of the Vine–Matthews Hypothesis, which required determining the age of the seafloor, became a test of seafloor spreading. Dating the ocean floor using magnetic anomalies detected by magnetometers towed behind ships and core samples extracted during the Deep-Sea Drilling Project confirmed the hypothesis. With magnetic anomalies to date the seafloor and a curve relating seafloor depth and age, the difference between the Atlantic, with its ‘ridge’, and the Pacific and its ‘rise’ became comprehensible. With a theory for predicting the depths of oceans, it was also possible to understand the history of sea-level changes.

Upper Wisconsinan Submarine End Moraines off Cape Ann, Massachusetts

1985 ◽  
Vol 24 (2) ◽  
pp. 187-196 ◽  
Author(s):  
R.N. Oldale
Keyword(s):  
New England ◽  
Sea Level ◽  
Gulf Of Maine ◽  
Silty Clay ◽  
Seismic Profiles ◽  
Late Wisconsinan ◽  
Water Depths

Seismic profiles across the southwest end of Jeffreys Ledge, a bathymetric high north of Cape Ann, Massachusetts, reveal two end moraines. The moraines overlie upper Wisconsinan glacialmarine silty clay and are composed mostly of subaqueous ice-contact deposits and outwash. They were formed below sea level in water depths of as much as 120 m during fluctuations of a calving ice front. The moraines are late Wisconsinan in age and were formed after the Cambridge readvance, about 14,000 yr B.P., and before the Kennebunk readvance, about 13,000 yr B.P. They represent fluctuations of the ice front during overall retreat of Laurentide ice from the Gulf of Maine and New England.

Lift-off moraines: markers of last ice-flow directions on the Scotian Shelf

2000 ◽  
Vol 37 (12) ◽  
pp. 1723-1734 ◽  
Author(s):  
Michael R Gipp
Keyword(s):  
High Resolution ◽  
Continental Margin ◽  
Flow Direction ◽  
Seismic Profiles ◽  
Scotian Shelf ◽  
Ice Flow ◽  
Reflection Seismic ◽  
Flow Directions ◽  
Lift Off ◽  
Seismic Lines

Lift-off moraines are acoustically incoherent, subparallel ridges observed on sidescan sonograms and high-resolution reflection seismic profiles on the southeastern continental margin of Canada. They are up to 3 m high, 20–80 m wide, and are commonly overlain by stratified proglacial sediments. Although little is known about them, detailed study of high-resolution seismic profiles from the Emerald Basin and the LaHave Basin, on the Scotian Shelf, show that their height:width ratio varies with the sounder–seabed separation, suggesting that the ridges may be narrower than they appear. Their morphology is similar to DeGeer moraines or cross-valley moraines, which form perpendicular to ice-flow direction. As their orientations can be estimated at the intersection of seismic lines, they can be used to estimate ice-flow directions. Since proglacial sediments are draped directly over top of them, they are assumed to record the direction of last ice flow. This directional data suggests that ice retreated not only northward (to Nova Scotia), but also toward local topographic highs on the continental shelf, which acted as anchoring points for ice rises around both the Emerald and LaHave Basins. This pattern of ice-flow directions suggests that ice flowed from the high ground of banks, converging into basin deeps, suggesting that small moraines within the basins are probably of interlobate origin.

scholarly journals A 180-Million-Year Record of Sea Level and Ice Volume Variations from Continental Margin and Deep-Sea Isotopic Records

Oceanography ◽  
2011 ◽  
Vol 24 (2) ◽  
pp. 40-53 ◽  
Author(s):  
Kenneth Miller ◽  
Gregory Mountain ◽  
James Wright ◽  
James Browning
Keyword(s):  
Sea Level ◽  
Continental Margin ◽  
Deep Sea ◽  
Ice Volume ◽  
Isotopic Records

scholarly journals New Findings on Submerged Patch-reefs and Reefal Carbonate Rocks at Water Depths of 70-100 meters on the Insular Shelf off Miyako-jima, South Ryukyus, Japan

2020 ◽  
Author(s):  
Takahiko Inoue ◽  
Kohsaku Arai
Keyword(s):  
Sea Level ◽  
Tectonic Setting ◽  
Ryukyu Island ◽  
Seismic Profiles ◽  
Offshore Area ◽  
New Findings ◽  
Bathymetric Mapping ◽  
Convex Upward ◽  
Sediment Layers ◽  
Water Depths

Abstract Sub-bottom profiling (SBP) surveys and bathymetric mapping conducted off the shore of Miyako-jima, which belongs to the southern Ryukyus in the Ryukyu Island Arc, have revealed the presence of mound-shaped structures 3-8 m high and 50-120 m wide at depths ranging from 70-100 m. The SBP surveys showed that the mounds possess strong distinct, convex upward reflector shapes at the top, which we interpret as submerged reefs and reefal sediments. Additionally, modern stratified sediment layers that cover these mound-shaped structures indicate that those reefs began forming and advancing shoreward in a back-stepping fashion as a result of sea level rise. An analysis of the mound distribution shown by SBP and multibeam echo sounding (MBES) surveys suggest that they might have been formed during the lowstand stage of sea level change, which includes the last glacial period, because the distribution of these mounds is limited to water depths of 70 m to 100 m, which are deeper than where present-day reefs grow. The SBP images hint that such high-resolution seismic profiles, accompanied by detailed bathymetric mapping off the reefal area, have the potential to provide effective indicators of not only coral reef paleoenvironment development, but also the tectonic setting of this offshore area.

scholarly journals New Findings on Submerged Patch Reefs and Reefal Carbonate Rocks at Water Depths of 70-100 meters on the Insular Shelf off Miyako-jima, Southern Ryukyus, Japan

2020 ◽  
Author(s):  
Takahiko Inoue ◽  
Kohsaku Arai
Keyword(s):  
Sea Level ◽  
Tectonic Setting ◽  
Ryukyu Island ◽  
Seismic Profiles ◽  
Offshore Area ◽  
New Findings ◽  
Bathymetric Mapping ◽  
Convex Upward ◽  
Sediment Layers ◽  
Water Depths

Abstract Sub-bottom profiling (SBP) surveys and bathymetric mapping conducted off the shore of Miyako-jima, which belongs to the southern Ryukyus in the Ryukyu Island Arc, have revealed the presence of mound-shaped structures 3-8 m high and 50-120 m wide at depths of 70-100 m. The SBP surveys showed that the mounds possess strong distinct, convex upward reflector shapes at the top, which we interpret as submerged reefs and reefal sediments. Additionally, modern stratified sediment layers that cover these mound-shaped structures indicate that those reefs began forming and advancing shoreward in a back-stepping fashion as a result of sea-level rise. An analysis of the mound distribution shown by SBP and multibeam echo sounding (MBES) surveys suggest that they might have been formed during the lowstand stage of sea-level change, which includes the Last Glacial Period, because the distribution of these mounds is limited to water depths of 70 m to 100 m, deeper than where present-day reefs grow. The SBP images hint that such high-resolution seismic profiles, accompanied by detailed bathymetric mapping off the reefal area, have the potential to provide effective indicators of not only coral reef paleoenvironment development, but also the tectonic setting of this offshore area.

Neogene history of the northeastern New Caledonia continental margin from multichannel reflection seismic profiles

2008 ◽  
Vol 340 (1) ◽  
pp. 68-73 ◽  
Author(s):  
Dominique Chardon ◽  
James A. Austin ◽  
Guy Cabioch ◽  
Bernard Pelletier ◽  
Steffen Saustrup ◽  
...  
Keyword(s):  
Continental Margin ◽  
New Caledonia ◽  
Seismic Profiles ◽  
Reflection Seismic ◽  
History Of

scholarly journals New findings on submerged patch reefs and reefal carbonate rocks at water depths of 70–100 m on the insular shelf off Miyako-jima, southern Ryukyus, Japan

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Takahiko Inoue ◽  
Kohsaku Arai
Keyword(s):  
Sea Level ◽  
Tectonic Setting ◽  
Ryukyu Island ◽  
Seismic Profiles ◽  
Offshore Area ◽  
New Findings ◽  
Bathymetric Mapping ◽  
Convex Upward ◽  
Sediment Layers ◽  
Water Depths

Abstract Sub-bottom profiling (SBP) surveys and bathymetric mapping conducted off the shore of Miyako-jima, which belongs to the southern Ryukyus in the Ryukyu Island Arc, have revealed the presence of mound-shaped structures 3–8 m high and 50–120 m wide at depths of 70–100 m. The SBP surveys showed that the mounds possess strong distinct, convex upward reflector shapes at the top, which we interpret as submerged reefs and reefal sediments. Additionally, modern stratified sediment layers that cover these mound-shaped structures indicate that those reefs began forming and advancing shoreward in a back-stepping fashion as a result of sea-level rise. An analysis of the mound distribution shown by SBP and multibeam echo sounding (MBES) surveys suggest that they might have been formed during the lowstand stage of sea-level change, which includes the Last Glacial Period, because the distribution of these mounds is limited to water depths of 70 to 100 m, deeper than where present-day reefs grow. The SBP images hint that such high-resolution seismic profiles, accompanied by detailed bathymetric mapping off the reefal area, have the potential to provide effective indicators of not only coral reef paleoenvironment development, but also the tectonic setting of this offshore area.

The challenge of producing oil and gas in deep water

1978 ◽  
Vol 290 (1366) ◽  
pp. 113-124 ◽  
Keyword(s):  
Present State ◽  
Continental Margin ◽  
Deep Water ◽  
Deep Sea ◽  
Oil And Gas ◽  
State Of The Art ◽  
Oil Industry ◽  
Water Depths ◽  
Successful Production ◽  
Drilling Project

The paper outlines the present state of the art of deep sea drilling and discusses some of the problems with the ‘controlled’ as well as the ‘uncontrolled' techniques. The first method is being developed by the contract drilling companies under the auspices of the oil industry, while the second method was introduced by the Deep Sea Drilling Project under the guidance of a group of oceanic institutions (Joides). The oil industry has drilled controlled in water depths of up to 1000 m and slightly over, and is now capable of extending the technique to 2000 m. Joides contemplates controlled drilling in water depths to 3650 m, say by the end of 1981. It is suggested that not only the slope but also the rise of the continental margin should soon be investigated in a number of suitable localities in order to assess adequately the potential of the last remaining major unexplored frontier for oil and gas. The paper emphasizes that it is already possible today to carry out controlled exploration even to water depths of over 4000 m. If such exploration were successful, production could also be achieved by making use of the presently developing underwater technology in 200-300 m of water.

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