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.

Appalachian Orogen in Canada

1979 ◽  
Vol 16 (3) ◽  
pp. 792-807 ◽  
Author(s):  
Harold Williams
Keyword(s):  
Continental Margin ◽  
Eastern North America ◽  
Early Paleozoic ◽  
The West ◽  
Late Precambrian ◽  
Northwest Africa ◽  
Iapetus Ocean ◽  
History Of ◽  
Appalachian Orogen ◽  
Andean Type

The Appalachian Orogen is divided into five broad zones based on stratigraphic and structural contrasts between Cambrian–Ordovician and older rocks. From west to east, these are the Humber, Dunnage, Gander, Avalon, and Meguma Zones.The westerly three zones fit present models for the development of the orogen through the generation and destruction of a late Precambrian – Early Paleozoic Iapetus Ocean. Thus, the Humber Zone records the development and destruction on an Atlantic-type continental margin, i.e., the ancient continental margin of Eastern North America that lay to the west of Iapetus; the Dunnage Zone represents vestiges of Iapetus with island arc sequences and mélanges built upon oceanic crust; and the Gander Zone records the development and destruction of a continental margin, at least in places of Andean type, that lay to the east of Iapetus.The Precambrian development of the Avalon Zone relates either to rifting and the initiation of Iapetus or to subduction and a cycle that preceded the opening of Iapetus. During the Cambrian Period, the Avalon Zone was a stable platform or marine shelf.Cambrian–Ordovician rocks of the Meguma Zone represent either a remnant of the continental embankment of ancient Northwest Africa or the marine fill of a graben developed within the Avalon Zone.Silurian and younger rocks of the Appalachian Orogen are mixed marine and terrestrial deposits that are unrelated to the earlier Paleozoic zonation of the system. Silurian and later development of the orogen is viewed as the history of deposition and deformation in successor basins that formed across the already destroyed margins and oceanic tract of Iapetus.

Paleomagnetism of some late Precambrian and lower Paleozoic sediments from L'Adrar de Mauritanie, West Africa

1978 ◽  
Vol 15 (2) ◽  
pp. 253-262 ◽  
Author(s):  
W. A. Morris ◽  
C. M. Carmichael
Keyword(s):  
West Africa ◽  
Early Phase ◽  
Late Phase ◽  
West African ◽  
Sedimentary Sequence ◽  
Chemical Cleaning ◽  
The West ◽  
Lower Paleozoic ◽  
West African Craton ◽  
Late Precambrian

Palaeomagnetic results are reported from three formations from the late Precambrian to lower Paleozoic sedimentary sequence of L'Adrar de Mauritanie, on the West African Craton. Each of the formations recorded complex magnetizations, the sequence of which could only be resolved after detailed thermal and chemical cleaning. Most of these complexities have arisen from post depositional hematite coating on both magnetic and non-magnetic grains. Formation I2 with a probable age of 1020 Ma records an early, presumably original remanence directed along D = 034°, I = +60° (α95 = 6°) and a later remanence D = 336°, I = +37° (α95 = 11°). Specimens from formations CO8 and CO10 (Cambro–Ordovician boundary) record a common late phase remanence at D = 128°, I = +24° (α95 = 8°). The CO10 early phase remanence is D = 033°, I = +61° (α95 = 7°), whereas the poorly isolated early phase remanence of CO8 approximates D = 060°, I = +51° (α95 = 20°).

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.

Pre-Katangan geochronology of Zambia and adjacent parts of Central Africa

1968 ◽  
Vol 5 (3) ◽  
pp. 621-628 ◽  
Author(s):  
J. R. Vail ◽  
N. J. Snelling ◽  
D. C. Rex
Keyword(s):  
Lake Tanganyika ◽  
Central Africa ◽  
New Age ◽  
Orogenic Belt ◽  
Eastern Africa ◽  
Sedimentary Sequence ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Orogenic Belts ◽  
Age Determinations

The significance of new age determinations on pre-Katangan (Late Precambrian) rocks and minerals from Zambia and adjacent parts of Tanzania and Rhodesia is discussed. In northwestern Rhodesia, the Lomagundi-Piriwiri sediments were deposited between 2500 and 2000 m.y. ago and were folded along meridional trends at circa 1940 m.y. A later episode of folding and metamorphism along similar trends occurred about 1700 m.y. ago, but only affected the western part of the sedimentary sequence (the Piriwiri Series). This latter date is comparable to that which appears to characterize the Tumbide trend, a N- to NE-trending fold system, in Zambia.In Zambia the Tumbide trend is the oldest tectonic episode preserved in the basement and is found only in isolated blocks and cores into which later tectonisms have not penetrated. The dominant pre-Katangan tectonism is represented by the NE to ENE Irumide trend. Such tectonic trends are particularly well developed in the Irumide Orogenic Belt of northern Zambia and adjacent Tanzania. Age determinations set a younger limit of circa 900 m.y. to this trend and the existence of an Irumide Cycle between about 1600 and 900 m.y. is suggested. The possibility that the relatively unmetamorphosed sediments of the Upper Plateau Series and Abercorn Sandstones at the southern end of Lake Tanganyika, the Mafingi Series of northern Malawi, and the Konse Series of Tanzania, represent near-contemporaneous platform deposition associated with the Irumide belt is considered.From this and other recent studies the distribution of orogenic belts in central and eastern Africa can be revised and a number of features of their pattern and inter-relationships noted.

Anorogenic magmatism and the Grenvillian Orogeny

1989 ◽  
Vol 26 (3) ◽  
pp. 479-489 ◽  
Author(s):  
Brian F. Windley
Keyword(s):  
United States ◽  
South America ◽  
Continental Margin ◽  
South Atlantic ◽  
Island Arc ◽  
The South ◽  
The West ◽  
Continental Block ◽  
Grenvillian Orogeny ◽  
Alkaline Complexes

The Grenvillian Orogeny was preceded by extensive anorogenic volcanism and plutonism in the period 1500–1300 Ma in the form of rhyolites, epizonal granites, anorthosites, gabbros, alkaline complexes, and basic dykes. An analogue for the mid-Proterozoic anorogenic complexes is provided by the 2000 km by 200 km belt of anorogenic complexes in the Hoggar, Niger, and Nigeria, which contain anorthosites, gabbros, and peralkaline granites and were generated in a Cambrian to Jurassic rift that farther south led to the formation of the South Atlantic. An analogue for the 1 × 106 km2 area of 1500–1350 Ma rhyolites (and associated epizonal granites) that underlie the mid-continental United States is provided by the 1.7 × 106 km2 area of Jurassic Tobifera rhyolites in Argentina, which were extruded on the stretched continental margin of South America immediately preceding the opening of the South Atlantic. The mid-Proterozoic complexes were intruded close to the continental margin of the Grenvillian ocean and were commonly superimposed by the craton-directed thrusts that characterized the final stages of the Grenvillian Orogeny. The bulk of the Keweenawan rift and associated anorogenic magmatism formed about 1100 Ma at the same time as the Ottawan Orogeny in Ontario, which probably resulted from the collision of the island arc of the Central Metasedimentary Belt attached to the continental block in the east with the continental block to the west. The most appropriate modern equivalent would be the Rhine Graben, which formed at the same time as the main Alpine compression.

Sign in / Sign up

Export Citation Format

Share Document