Remnants of a submerged pre-Jurassic (Devonian?) landscape on Orphan Knoll, offshore eastern Canada

1984 ◽  
Vol 21 (1) ◽  
pp. 61-66 ◽  
Author(s):  
L. M. Parson ◽  
D. G. Masson ◽  
R. G. Rothwell ◽  
A. C. Grant
Keyword(s):  
Long Range ◽  
Seismic Reflection ◽  
Alternative Explanation ◽  
Random Distribution ◽  
Eastern Canada ◽  
Sea Floor ◽  
Large Group ◽  
Seismic Reflection Profiles ◽  
Conical Form ◽  
Water Depths

A large group of discrete peaks occurs on the northeastern surface of Orphan Knoll at water depths between 1800 and 2800 m. Long-range side-scan sonographs are used in conjunction with seismic reflection profiles to establish their flattened conical form. They commonly rise to 300 m above the sea floor and occupy basal areas up to 2 km in diameter at that level. Inclusion of the buried lower parts of these mounds may double estimates of both the height and diameter. The sonographs indicate that the mounds have a random distribution within an elongate northwesterly trending belt. Previous suggestions of their possible origin, such as remnants of dykes or ridges of resistant sedimentary strata, are rejected and an alternative explanation of a zone of partially buried Devonian reef knolls is proposed.

Seismic reflection profiles across the "Mine Series" in the Noranda camp of the Abitibi belt, eastern Canada

1995 ◽  
Vol 32 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Pierre Verpaelst ◽  
A. Shirley Péloquin ◽  
Erick Adam ◽  
Arthur E. Barnes ◽  
John N. Ludden ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Reflection ◽  
Mineral Exploration ◽  
Drill Hole ◽  
Seismic Survey ◽  
Volcanic Complex ◽  
Eastern Canada ◽  
Crustal Layer ◽  
High Resolution Data ◽  
Seismic Reflection Profiles

The Abitibi–Grenville Lithoprobe project completed a regional (line 21) and a high-resolution (line 21-1) seismic survey in the Noranda Central Volcanic Complex of the Blake River Group, Abitibi, Quebec. Line 21 provides a regional framework in which the Archean crust is divided into three layers, two of which are discussed here: the uppermost layer, which corresponds to the Blake River Group, is the least reflective, and lies above 4 s (12 km), and the mid-crustal layer, which is composed of a complex pattern of generally east-northeast-dipping reflectors and lies between 4 and 8 s. Within the regional data, the Mine Series of the Central Volcanic Complex is imaged as a semitransparent series of reflectors overlying a highly reflective east-facing structure interpreted as the subvolcanic Flavrian pluton. The high-resolution data (line 21-1) were collected in the vicinity of the Ansil mine. The seismic images in this region can be controlled by surface geology and extensive drill-hole data, and the project was designed to test the applicability of seismic reflection profiling in providing structural and stratigraphic information for use in mineral exploration: shallow-dipping reflectors correlate well with lithological variations or contacts in the volcanic sequence; strong subhorizontal reflectors correspond to diorite and gabbro dykes and sills; several abrupt lateral changes in the reflectivity coincide with known intrusive contacts such as the Lac Dufault pluton.

Evidence for Wisconsinan Glaciations in the Verrill Canyon Area, Scotian Slope

1989 ◽  
Vol 31 (1) ◽  
pp. 27-40 ◽  
Author(s):  
David C. Mosher ◽  
David J. W. Piper ◽  
Gustavs V. Vilks ◽  
A. E. Aksu ◽  
Gordon B. Fader
Keyword(s):  
High Resolution ◽  
Continental Slope ◽  
Seismic Reflection ◽  
Outer Shelf ◽  
Scotian Shelf ◽  
Radiocarbon Dates ◽  
Oxygen Isotopic ◽  
Late Wisconsinan ◽  
Seismic Reflection Profiles ◽  
Water Depths

AbstractA composite thickness of about 25 m of sediment has been cored from the Verrill Canyon on the Scotian Slope. It is interpreted that the majority of this sequence was deposited in a glaciomarine environment during oxygen isotopic stage 2 and the top of stage 3. These sediments, as seen in high-resolution seismic reflection profiles, are well stratified, become thicker upslope, are laterally variable in thickness, and pass upslope into possible outer shelf tills. Three wedge-shaped units of incoherent reflections interfinger with the parallel reflections and terminate in water depths greater than 700 m. These wedge-shaped units are interpreted as slumped diamict and outwash deposits. The age of the uppermost wedge-shaped unit is 26,000–21,000 yr based on extrapolation of radiocarbon dates. This unit documents a late Wisconsinan glacier readvance on the outer Scotian Shelf. The underlying wedge-shaped unit, estimated to be 70,000 yrs old, extends further west along the continental slope, and may represent a more extensive early Wisconsinan ice advance. A third wedge-shaped unit, inferred to have formed during isotopic stage 6, is possibly a remnant of the first glaciation in the study area.

SEISMIC REFLECTION AND MAGNETIC STUDY OFF BOMBAY, INDIA

Geophysics ◽  
1970 ◽  
Vol 35 (4) ◽  
pp. 603-612 ◽  
Author(s):  
R. N. Harbison ◽  
B. G. Bassinger
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Seismic Reflection ◽  
Magnetic Field Intensity ◽  
Shelf Area ◽  
Cambay Basin ◽  
Seismic Reflection Profiles ◽  
20 Nm ◽  
The Magnetic Field ◽  
Water Depths

As part of the 1967 Global Expedition of the USC&GS Ship OCEANOGRAPHER, approximately 1700 km (920 nm) of reconnaissance seismic reflection and total magnetic field intensity traverses were made between 17° and 21° N latitude, over the shelf and slope off Bombay, India. This investigation was designed to determine why the shelf area off Bombay is as much as three times wider than the rest of the western Indian shelf. Near the landward edge of the continental shelf, the seismic reflection profiles show strata dipping west from Bombay. To the west, these profiles indicate that the configuration of the continental slope is influenced by anticlinal structures, suggesting that the western Indian shelf in the study area is a sediment‐filled structural basin. The greater shelf width off Bombay is due to the location of the anticlinal trends. Within the basin, a buried north‐south trending anticlinal high is present approximately 75 km (40 nm) west of Bombay in water depths of about 50 m (165 ft). The structural basin and subsurface anticlinal trend off Bombay may continue northward into the Cambay Basin, where similar features are present. This continuation may be locally interrupted by the westward extension of a fault zone from the Narbada Valley into the southern Cambay Basin. The magnetic field is relatively flat, except for a zone of high frequency anomalies, which may be caused by dikes extending from the Bombay coast westward for approximately 40 km (20 nm).

The Origin and Distribution of Subbottom Sediments in Southern Lake Champlain

1980 ◽  
Vol 14 (2) ◽  
pp. 224-239 ◽  
Author(s):  
R. P. Freeman-Lynde ◽  
D. R. Hutchinson ◽  
D. W. Folger ◽  
B. H. Wiley ◽  
M. J. Hewett
Keyword(s):  
High Resolution ◽  
Water Level ◽  
Seismic Reflection ◽  
Late Glacial ◽  
Sedimentation Rates ◽  
Lake Champlain ◽  
Alluvial Deposits ◽  
Proglacial Lake ◽  
Seismic Reflection Profiles ◽  
Water Depths

AbstractThree units, correlatable with recent Lake Champlain, late-glacial marine Champlain Sea, and proglacial Lake Vermont sediments, have been identified from about 200 km of high-resolution seismic reflection profiles and eight piston cores collected in southern Lake Champlain. Lake Vermont deposits are nonfossiliferous and range from thin to absent nearshore and on bedrock highs to more than 126 m thick near Split Rock Point. Champlain Sea sediments contain marine foraminifers and ostracodes and are fairly uniform in thickness (20–30 m). Recent Lake Champlain sediments range in thickness from 0 to 25 m. Average sedimentation rates for Lake Vermont are considerably higher (4–8 cm/yr) than those for the Champlain Sea (0.8–1.2 cm/yr) and Lake Champlain (0.14–0.15 cm/yr). Bedrock, till, and deltaic and alluvial deposits were also identified on the acoustic records but were not sampled. An unconformity separating Champlain Sea deposits from Lake Champlain deposits is associated with numerous benches at water depths of 20–30 m. These benches, the alluvial deposits, and the onset of deltaic deposition are probably associated with a low water level stillstand at the close of the Champlain Sea episode.

The Sedimentary Framework of the Southern Basin of Lake George, New York

1981 ◽  
Vol 15 (1) ◽  
pp. 44-61 ◽  
Author(s):  
D.R. Hutchinson ◽  
W.M. Ferrebee ◽  
H.J. Knebel ◽  
R.J. Wold ◽  
Y.W. Isachsen
Keyword(s):  
New York ◽  
Seismic Reflection ◽  
Lake Level ◽  
Adirondack Mountains ◽  
Tectonic Disturbances ◽  
Sedimentary Framework ◽  
Seismic Reflection Profiles ◽  
Wood Fragment ◽  
Lake George ◽  
Water Depths

AbstractInformation from 240 km of high-resolution seismic reflection profiles has been analyzed to show the bathymetric and subsurface configuration of southern Lake George in the southeastern corner of the Adirondack Mountains, New York. Three units have been identified and sampled in 13 piston cores as long as 7 m and 4 grab samples; they are glacial drift, glaciolacustrine nonorganic clay, and Holocene lake mud rich in organic material. Three deep bedrock basins controlled glacial, glaciolacustrine, and postglacial deposition within the lake. Glaciolacustrine clay is more than 30 m thick in these basins but is generally absent in water depths less than 20 m. An unconformity separates glaciolacustrine clay from overlying Holocene mud in water depths less than 30 m, but the contact is conformable and transitional in deeper water. The unconformity may have originated from subaqueous or subaerial erosion during a low stage of lake level which probably occurred between 10,000 and 700 yr B.P. Holocene lake mud is thin to absent in the shallower waters separating the three basins, but reaches 15-m thickness near the entrance to The Narrows. A new radiocarbon date of 6950 ± 60 yr B.P. was obtained from a wood fragment which was found in the Holocene lake mud. We found no clear evidence of postglacial tectonic disturbances of the lake sediments although recent releveling profiles suggest that the Adirondack Mountains are undergoing contemporary uplift.

Probable Late Wisconsinan ice margin on the upper continental slope off St. Pierre Bank, eastern Canada

1988 ◽  
Vol 25 (6) ◽  
pp. 853-865 ◽  
Author(s):  
Denis Bonifay ◽  
David J. W. Piper
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Seismic Reflection ◽  
Radiocarbon Dating ◽  
Shear Stresses ◽  
Eastern Canada ◽  
Late Wisconsinan ◽  
Acoustic Facies ◽  
Seismic Reflection Profiles ◽  
Basal Shear

Seismic reflection profiles from the continental slope off St. Pierre Bank show a distinctive acoustic facies characterized by incoherent reflections (unit E) overlain by 5–20 m of stratified sediments (units D–A). Cores from unit E include poorly sorted silty diamict, locally overconsolidated and including in places some foraminifera. Stratified sediments also occur in places in this facies.The overlying sediments of units D–A, except for the topmost metre of unit A, have a foraminiferal fauna dominated by Elphidium excavatum forma clavata and Cassidulina reniforme, which has been interpreted elsewhere as indicating ice-margin sedimentation. The sediments contain turbidites and rare ice-rafted detritus, and are bioturbated. Accelerometer mass spectrometer radiocarbon dating of shells from the stratified sediments yielded dates between 3.3 and 11.8 ka. Facies E, the top of which has an extrapolated age of 11.5–12.0 ka, is interpreted as slumped morainal diamict and proglacial sediment resulting from a late Wisconsinan ice surge through Halibut Channel. Low basal shear stresses in this thin ice surge left little record in the mud-accumulating basins of the continental shelf.

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