scholarly journals Paleomagnetism of Siluro-Devonian rocks from eastern Maine

1980 ◽  
Vol 17 (12) ◽  
pp. 1653-1665 ◽  
Author(s):  
Dennis V. Kent ◽  
Neil D. Opdyke
Keyword(s):  
Reasonable Agreement ◽  
Lower Devonian ◽  
Northeastern North America ◽  
Rock Types ◽  
Magnetic Carriers ◽  
Paleomagnetic Study ◽  
Intrusive Rocks ◽  
The Mean ◽  
Upper Silurian ◽  
Accurate Record

A diverse suite of rocks was collected for paleomagnetic study from two formations in the Eastport area of northeastern Maine: 18 sites (103 samples) from redbeds and diabase sills of the Hersey Formation (uppermost Silurian to Lower Devonian) and 14 sites (74 samples) from lavas, redbeds, and calcareous nodules of the Eastport Formation (Lower Devonian; Rb/Sr age 412 Ma). Characteristic magnetizations based on AF and thermal demagnetization analyses give mean directions, after simple correction for bedding tilt, of D = 163.6°, I = 41.3°, α95 = 6.3°, for N = 16 sites in the Hersey, and D = 179.3°, I = 38.0°, α95 = 9.4°, for N = 14 sites in the Eastport Formation. Baked contact relations, the presence of opposite polarities, and the similarity in directions over different rock types and magnetic carriers point to an acquisition of magnetization near to the time of rock formation. The mean directions correspond to (south) paleopole positions at 19.8°S lat., 308.8°E long. (δp, δm = 4.7°, 7.7°) for the Hersey and 23.7°S lat., 293.7°E long. (δp, δm = 6.6°, 11.1°) for the Eastport Formation.These paleopoles are removed from the Upper Silurian Bloomsburg Formation pole, but are in reasonable agreement with similar age results from central Newfoundland, suggesting that the Acadia displaced terrain encompassed these areas. Siluro-Devonian paleopoles from intrusive rocks in northeastern North America are generally widely divergent and these may not be providing an accurate record of paleomagnetic field in all cases.

The Somerset Island Formation: an upper Silurian to ?Lower Devonian intertidal/supratidal succession, Boothia Uplift region, Arctic Canada

1978 ◽  
Vol 15 (2) ◽  
pp. 181-189 ◽  
Author(s):  
A. D. Miall ◽  
J. Wm. Kerr ◽  
M. R. Gibling
Keyword(s):  
Lower Devonian ◽  
Alluvial Fan ◽  
Similar Sequence ◽  
Island Formation ◽  
Fine Grained ◽  
Rock Types ◽  
Sandstone Rock ◽  
Upper Silurian ◽  
Somerset Island ◽  
Cornwallis Island

The Somerset Island Formation of Somerset Island is a newly defined unit consisting of interbedded fine-grained, grey, planar-laminated dolomite and limestone, grey mottled limestone and dolomite, red quartzose siltstone and red dolosiltite. It forms a transitional unit between the limestone and dolomite of the underlying Read Bay Formation and the sandstone and conglomerate of the overlying Peel Sound Formation, and ranges in thickness from 150 to more than 400 m. The formation was formed predominantly in intertidal and supratidal environments and forms the lowest part of a regressive sequence that culminates in boulder conglomerates of alluvial fan origin in the Peel Sound Formation. The Somerset Island Formation is predominantly Pridolian in age, but may include some strata of Ludlovian and Gedinnian age.The regressive sequence reflects a major pulse of the Cornwallis Disturbance of Boothia Uplift. A similar sequence occurs in Prince of Wales Island, although the lower part of the succession there contains conglomerate and sandstone, rock types that are absent in Somerset Island. These rocks are formally assigned to the Lower Peel Sound Formation but are of similar age to the Somerset Island Formation of the type area.Rocks of similar facies to the Somerset Island Formation of Somerset Island comprise the upper member of the Drake Bay Formation on Russell Island and Member D of the Read Bay Formation on Cornwallis Island. The latter unit is younger than the Somerset Island Formation, reflecting a later commencement of regression in that area.

scholarly journals Hydrodynamic diffusion of a sphere sedimenting through a dilute suspension of neutrally buoyant spheres

1992 ◽  
Vol 236 ◽  
pp. 513-533 ◽  
Author(s):  
Robert H. Davis ◽  
N. A. Hill
Keyword(s):  
Reasonable Agreement ◽  
Trajectory Analysis ◽  
Heavy Particle ◽  
Small Reynolds Number ◽  
Mean Velocity ◽  
Dilute Suspension ◽  
Explicit Formulae ◽  
The Mean ◽  
Neutrally Buoyant ◽  
Large Peclet Number

The motion of a heavy sphere sedimenting through a dilute background suspension of neutrally buoyant spheres is analysed for small Reynolds number and large Péclet number. For this particular problem, it is possible not only to calculate the mean velocity of the heavy particle, but also the variance of the velocity and the coefficient of hydrodynamic diffusivity. Pairwise, hydrodynamic interactions between the heavy sphere and the background sphere are considered exactly using volume integrals and a trajectory analysis. Explicit formulae are given for the two limiting cases when the radius of the heavy sphere is much greater and much less than that of the background spheres, and numerical results are given for moderate size ratios. The mean velocity is relatively insensitive to the ratio of the radius of the background spheres to that of the heavy sphere, unless this ratio is very large, whereas the hydrodynamic diffusivity increases rapidly as the radius ratio is increased. The predictions are in reasonable agreement with the results of falling-ball rheometry experiments.

scholarly journals Is there a trend in cirrus cloud cover due to aircraft traffic?

2005 ◽  
Vol 5 (8) ◽  
pp. 2155-2162 ◽  
Author(s):  
F. Stordal ◽  
G. Myhre ◽  
E. J. G. Stordal ◽  
W. B. Rossow ◽  
D. S. Lee ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Cloud Cover ◽  
Reasonable Agreement ◽  
Global Scale ◽  
Cirrus Cloud ◽  
Positive Trend ◽  
Spatially Correlated ◽  
Upper Limit ◽  
Main Emphasis ◽  
The Mean

Abstract. Trends in cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in cirrus cloud cover due to aircraft traffic. The correlations are only moderate, as many other factors have also contributed to changes in cirrus. Still we regard the results to be indicative of an impact of aircraft on cirrus amount. The main emphasis of our study is on the area covered by the METEOSAT satellite to avoid trends in the ISCCP data resulting from changing satellite viewing geometry. In Europe, which is within the METEOSAT region, we find indications of a trend of about 1-2% cloud cover per decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic contrasts with a general negative trend in cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a mean estimate of 0.03 Wm-2 (lower limit 0.01, upper limit 0.08 Wm-2) for the radiative forcing due to aircraft induced cirrus. The mean is close to the value given by IPCC (1999) as an upper limit.

Étude paléomagnétique des roches protérozoïques de la formation de Sakami, région de la Grande Rivière, Territoire du Nouveau-Québec, Canada

1981 ◽  
Vol 18 (12) ◽  
pp. 1893-1899
Author(s):  
Maurice K. Seguin ◽  
Kamal N. M. Sharma ◽  
Gérard Woussen
Keyword(s):  
Magnetic Memory ◽  
Thermal Demagnetization ◽  
Paleomagnetic Study ◽  
Geological Formation ◽  
The Mean

We describe a paleomagnetic study of Mid-Proterozoic sandstone of the Sakami Formation. The thermal demagnetization is more effective than by alternating field; this indicates that part of the magnetic memory is located in hematite. The mean direction of magnetization after thermal and alternating field treatments is 031, −25 α95 = 7.1°, K = 73 and the corresponding paleopole position is 103°W, 18°S (dm = 11°, dp = 8°). These results are important because a part of this geological formation will be covered with water after completion of the development works of La Grande Rivière. [Journal Translation]

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.

Evaluation of corallite size as a criterion for species discrimination in favositids

1988 ◽  
Vol 62 (1) ◽  
pp. 32-40 ◽  
Author(s):  
D. J. Lee ◽  
J. P. A. Noble
Keyword(s):  
Cross Section ◽  
Statistical Treatment ◽  
Intraspecific Variability ◽  
West Point ◽  
Species Discrimination ◽  
Cross Sectional ◽  
The Best Approximation ◽  
Computer Based ◽  
The Mean ◽  
Upper Silurian

Of all the morphologic characters used in favositid taxonomy, corallite size has most frequently been given more weight than others because of its relative ease of measurement and because it has been generally believed to be less variable. This study evaluates the reliability of corallite size as a criterion by a statistical treatment of several populations of favositids in the Upper Silurian West Point Reef Complex in Gaspé, Québec. Calculation of corallite cross-sectional area was made feasible by computer-based image analysis which provides a quick and accurate measure of size. The present study shows that the mean of the largest 10 percent corallite areas in mature parts of colonies with a minimum sample size of 100 corallites per cross section is the best approximation available of mean adult corallite size.It is suggested that intraspecific variability of corallite size is often too large for this character to be used in practice, probably due to phenotypic plasticity. The same may be true of most other morphologic characters. In some cases, however, one or two characters remain invariate within a species and can be used diagnostically. The same characters may be extremely variable in other species.

DENSITIES OF METAMORPHIC ROCKS

Geophysics ◽  
1971 ◽  
Vol 36 (4) ◽  
pp. 690-694 ◽  
Author(s):  
Scott B. Smithson
Keyword(s):  
Metamorphic Rock ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Rock Density ◽  
Rock Types ◽  
Crystalline Crust ◽  
The Mean ◽  
Few Data

Although metamorphic rocks comprise a large part of the crystalline crust, relatively few data concerning metamorphic rock densities are available. In this paper, we present rock densities from seven different metamorphic terrains. Mean densities for rock types range from [Formula: see text] for biotite granite gneiss to [Formula: see text] for diopside granofels. Mean rock densities for metamorphic terrains range from 2.70 to [Formula: see text]. Rock density may decrease in the lower part of the upper crust. Most mean rock densities for metamorphic terrains fall between 2.70 and [Formula: see text]; the mean density of [Formula: see text] commonly used for the upper crystalline crust is too low.

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