The Mid-Atlantic Ridge Near 45 °N. XXII. Sedimentary Deposition and Lithogenesis on Mid-Atlantic Ridge Mountain Tops

1974 ◽  
Vol 11 (8) ◽  
pp. 1157-1167 ◽  
Author(s):  
Charles T. Schafer
Keyword(s):  
Surface Sediments ◽  
Bottom Current ◽  
Current Direction ◽  
Sediment Distribution ◽  
Rock Types ◽  
Rock Cores ◽  
Rapid Changes ◽  
Unconsolidated Sediment ◽  
Mid Atlantic Ridge ◽  
Coralline Limestone

Bottom photographs and drilled rock cores collected on several mountain tops along the crest of the Mid-Atlantic Ridge near 45°N describe the sediment distribution, sediment dynamics and shallow stratigraphy of these sites. Lag pebble deposits and pebble waves indicate rapid changes in bottom current direction and velocities that may approach 100 cm/s (>2 knots) one meter above the bottom so that surface sediments are often not indicative of sediment and rock types sampled using shallow drilling techniques. Absolute dates (14C) of coralline limestone, which underlies coarse unconsolidated sediment at most drilling sites, suggest deposition and initial lithification of these deposits during a middle Wisconsin interstadial period.

The Mid-Atlantic Ridge near 45° N. XII. Coercivity, secondary magnetization, polarity, and thermal stability of dredge samples

1970 ◽  
Vol 7 (6) ◽  
pp. 1499-1514 ◽  
Author(s):  
J. K. Park ◽  
E. Irving
Keyword(s):  
Coercive Force ◽  
Empirical Relationship ◽  
Blocking Temperature ◽  
Lower Intensity ◽  
Volcanic Zone ◽  
Rock Types ◽  
Mid Atlantic Ridge ◽  
The Mean ◽  
Force Range ◽  
Thermal Stability Of

The mean coercivities of natural (n.r.m.), anhysteretic (a.r.m.), and isothermal (i.r.m.) remanent magnetization in 34 samples of submarine basalt from the Mid-Atlantic Ridge are 270, 250, and 370 oersteds respectively, showing their magnetization to be stable. The spectra of coercive force of n.r.m. and a.r.m. of these basalts are similar, although, because of small secondary components, there are small differences in the low coercive force range (0 to 100 Oe). The magnitude and sign of these differences are used to derive an empirical relationship between coercivity and the magnitude of secondary components, and to infer the polarity of primary components. The inferred polarities of samples from within the Median Valley of the Ridge are all normal, whereas both normal and reversed polarities are found from the adjacent mountains and plateaus. Experiments show that warming specimens from the Median Valley to 100 °C for 90 h causes the production of a new component with a lower intensity, and higher blocking temperature, but with the same direction as the original natural remanence. Similar effects may occur in the axial volcanic zone, and may have caused the decrease in intensity with distance from the axis. The magnetic properties of various other rock types from the Mid-Atlantic Ridge are also described.

Near-bottom current direction inferred from comatulid crinoid feeding postures on the Terre Adélie and George V shelf, East Antarctica

2011 ◽  
Vol 58 (1-2) ◽  
pp. 163-169 ◽  
Author(s):  
Marc Eléaume ◽  
Robin J. Beaman ◽  
Huw J. Griffiths ◽  
Ben Best ◽  
Martin J. Riddle ◽  
...  
Keyword(s):  
East Antarctica ◽  
Bottom Current ◽  
Current Direction ◽  
Terre Adélie

scholarly journals The characteristics of the surface sediments in Co To island

2020 ◽  
Vol 61 (2) ◽  
pp. 33-40
Author(s):  
Chi Kim Thi Ngo ◽  
Long Van Hoang ◽  
Binh Van Phan ◽  
Tinh Nguyen Trinh ◽  
Trung Tu Do ◽  
...  
Keyword(s):  
Surface Sediments ◽  
Research Area ◽  
Field Investigation ◽  
Silty Sand ◽  
Sediment Provenance ◽  
Muddy Sand ◽  
Material Source ◽  
Sediment Distribution ◽  
Sandy Gravel ◽  
Flow Energy

552 grain size samples and 33 mineral quality defined samples have been collected in the Co To island, Tonkin Bay of Vietnam, to study the distribution and the sediment provenance. The field investigation method, the grain analysis, and the detrital composition examination method have been used to study the characteristics of the surface sediments in Co To island. The obtained results show that the surface sediments in the area consist of ten different fields, namely: sandy gravel, gravelly sand, sand, gravelly muddy sand, sand mixed gravel, muddy sand, gravelly mud mixed sand, silty sand, muddy sandy gravel, and sandy mud. The mineral component method shows that quartz is the main contain of the surface sediment (72,0÷90,6%), less rock detritus, felspat, mica, and very few of the shells. It is to confirm that the continent is the main primary material source of the study area. The distribution of the sediment is complicated. As the East-Southeast side of the research area, the sediment distribution following gravity way, coarse grain near the shore (gravel, sandy gravel,…), finer grain far off the shore (gravelly muddy sand, silty sand,…), choice level is very low. Which This is saying that the movement of sediment in the area is dominant, ; the flow energy is governed by the topography near the island and seafloor. In tMhe meanwhile, the west-northwest side, the topography of seafloor is the complicated, coarse sediment grains (gravel, sand), ); the roundness is bad, which is saying that the hydrodynamic flow there plays an important role in the sediment distribution.

scholarly journals The Geological Work of the Baudin Expedition in Australia (1801-1803): The Mineralogists, the Discoveries and the Legacy

2009 ◽  
Vol 28 (2) ◽  
pp. 293-324 ◽  
Author(s):  
Wolf Mayer
Keyword(s):  
Sea Level ◽  
Sedimentary Rocks ◽  
Left Behind ◽  
Rock Types ◽  
Geological Surveys ◽  
Scientific Staff ◽  
Unconsolidated Sediment ◽  
Geological Work ◽  
Definition Of ◽  
Mistaken Identification

The Baudin expedition to Australia included among its scientific staff Louis Depuch and Joseph Charles Bailly, the first professionally educated geologists to visit this country. Together with the zoologist François Péron, they carried out the earliest geological surveys along large parts of its coast. Their views on the origin of the major rock types were mainly guided by Neptunist thinking. However, in line with the beliefs of a number of French geologists at the time, they recognized basalt as a volcanic rock. Their identification of earth materials was hampered by the still imprecise definition of the physical properties of minerals and rocks. Their work provided the first detailed descriptions of the major rock types and their distribution along the margins of the continent and its islands, and led to some tentative conclusions with regard to the presence of mountains in the country's interior. The three investigators concluded that Australia was built on a foundation of granite, overlain by a variety of sedimentary rocks and fringed by extensive deposits of largely unconsolidated sediment, left behind by a retreating sea. Their mistaken identification of dolerite as basalt led them to believe that they had discovered evidence of volcanic activity in Australia. Issues such as the presence of marine organisms in rocks now above sea level, and the finding of various species of mollusks on Australia's shores, known to be extinct in Europe, led to lively discussions among a number of European naturalists.

IV. Regional studies. Hudson Geotraverse: geology of the Mid-Atlantic Ridge at 45° N/ Petrology of submarine volcanics from the NE Pacific

1971 ◽  
Vol 268 (1192) ◽  
pp. 623-651 ◽  
Keyword(s):  
Complex Structure ◽  
Ocean Floor ◽  
Ice Age ◽  
Coarse Grained ◽  
Rock Types ◽  
Shield Volcanoes ◽  
Ocean Floor Spreading ◽  
Rate Of Increase ◽  
Mid Atlantic Ridge ◽  
Last Ice Age

A strip across the Crest Mountains and High-Fractured Plateau of the Mid-Atlantic Ridge has been surveyed systematically between latitudes 45 and 46° N. Continuous bathymetric, magnetic and gravimetric data have been obtained. Seismic refraction experiments have revealed a complex structure lineated parallel to the axis of the Ridge. Seismic reflexion studies have revealed a picture of the sediment cover, and have shown the possible existence of block faulting of the underlying rocks, with faults alined both parallel and at right angles to the axis of the Ridge. The major rock types found in 46 dredge stations can be grouped as follows: (1) Ubiquitous basalts and tuffs (ranging from theoleiites to alkali basalts, with a few ferro-basalts and high-Al basalts). Basalts rich in resorbed high-calcic plagioclase xenocrysts are common; these occur both on the slopes of shield volcanoes and in the deepest hole of the Median Valley. A nearby fault scarp yielded coarse-grained gabbros. (2) Serpentinized mafic and ultramafic rocks are not restricted to elongated, presumably blockfaulted seamounts, but are also common on the slopes of what had been interpreted on morphological grounds as shield volcanoes; they are absent, however, on the Median alley floor and its immediate scarp slopes. The pre-serpentinization rock types include dunites, harzburgites, gabbros, troctolitic gabbros and amphibolitic peridotites showing crude cumulate textures. (3) The lower parts of the steep inner walls of the Median Valley have yielded metabasalts and metadiabases showing alteration within the greenschist facies of etamorphism, whilst still retaining original igneous characteristics. (4) Restricted to the fault scarps of elongated seamounts further removed from the Median Valley are higher grade metamorphic rocks of the almandine amphibolite facies of metamorphism. These rocks have lost all igneous textures and exhibit a strong gneissic fabric. (5) Three localities yielded dioritic rocks in association with serpentinized ultramafics. The diorites vary in character from hornblende-rich quartz diorites to more siliceous, almost hornblende-free trondhjemites. The latter show considerable albitization. The whole suite of rocks shows great affinities with similar suites found as late stage intrusives in alpine-type ultramafic complexes. About 23% of the specimens collected included gneissic, granitic and sedimentary rock types of erratic origin, ice rafted into the area in the Pleistocene. A study of their distribution indicates that there are no erratics in the Median Valley, that they are scarce on the mountain ranges immediately flanking the Valley, but beyond these areas they are abundant and are randomly distributed over the whole area. Such a distribution may be a result of ocean-floor spreading, indicating that the Median Valley is younger than the last ice age, or that extrusions subsequent to the last ice age have engulfed any erratics present in the Median Valley. The thickness of manganese coating on extrusive rocks and their K/Ar and fission track ages increase systematically with distance on either side of the axis of the M.A.R., strongly supporting the ocean-floor spreading hypothesis. The ages and coatings both show a marked change in their rate of increase beyond a distance of 50 to 60 km on either side of the axis. The position at which this occurs coincides with the thickening in these areas of sediments found in the inter-volcanic valleys, and the morphological changes between the Crest Mountains and the High-Fractured Plateau. The combined data strongly suggest that there was either a quiescent period sometime in the Pliocene during which ocean-floor spreading was inactive, or that the rate of spreading had accelerated during the Pliocene from less than 1 cm a -1 to a computed 2.5 cm a -1 in Pleistocene times.

Thermal expansion, diffusivity, and cracking of rock cores from Darlington, Ontario

1982 ◽  
Vol 19 (2) ◽  
pp. 154-166 ◽  
Author(s):  
K. Y. Lo ◽  
R. S. C. Wai
Keyword(s):  
Thermal Expansion ◽  
Thermal Diffusivity ◽  
Threshold Temperature ◽  
Deep Hole ◽  
Velocity Measurements ◽  
Granitic Gneiss ◽  
Rock Types ◽  
Rock Cores ◽  
Rate Of Heating ◽  
Mineral Constituents

Measurements of the thermal diffusivity and expansion coefficient for rock cores of a limestone and granitic gneiss, recovered from a deep hole at Darlington Generating Station, Ontario were carried out. Results showed that the diffusivity decreases whereas the coefficient of expansion increases with temperature for both rock types. Thermal cracking occurs above a threshold temperature that is independent of the rate of heating as indicated by wave velocity measurements; this appears to be a result of thermal mismatch of the mineral constituents. These results are of direct relevance to the design of underground facilities in energy-related projects.

scholarly journals Potential microbial contamination from drilling lubricants into subseafloor rock cores

2021 ◽  
Vol 29 ◽  
pp. 49-57
Author(s):  
H. Lizethe Pendleton ◽  
Katrina I. Twing ◽  
Shahrzad Motamedi ◽  
William J. Brazelton
Keyword(s):  
Microbial Contamination ◽  
Ambient Air ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Core Samples ◽  
Rock Cores ◽  
Atlantis Massif ◽  
Mid Atlantic Ridge ◽  
New Methodologies ◽  
International Ocean Discovery Program

Abstract. International Ocean Discovery Program (IODP) Expedition 357: “Serpentinization and Life” drilled shallow cores into the Atlantis Massif near the Mid-Atlantic Ridge in October 2015 using seabed drills. Serpentinization and other geochemical processes occurring within the Atlantis Massif release hydrogen, methane, and other chemicals that can potentially fuel microorganisms through chemosynthesis. The subseafloor rock cores collected during IODP Exp. 357 are the first of their kind, meaning the analysis and interpretation of these samples required new methodologies, including a specialized approach for distinguishing endemic subsurface inhabitants from potential contaminants from various sources. Background samples of various potential contamination sources were collected during sampling: 109 samples of seawater collected before, during, and after drilling; 20 samples of greases and oils associated with the drilling equipment; and samples of the laboratory's ambient air. Despite the widespread usage of drilling lubricants and the importance of controlling contamination in drill-core samples for microbiological analyses, no studies to date have looked at DNA in drilling greases and oils. In this study, drilling lubricants were analyzed as possible sources of microbial contamination of subseafloor rock core samples by environmental sequencing of 16S rRNA genes. We find that microbial signatures from drilling lubricants are only found in low abundance in seafloor samples (at most a few percent of total sequence counts), with laboratory contaminants being a greater source of contamination.

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