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°).

Paleomagnetism of the ~860 Ma Manso dyke swarm, West Africa: implications for the assembly of Rodinia

2021 ◽  
Author(s):  
Paul Yves Jean Antonio ◽  
Lenka Baratoux ◽  
Ricardo Ivan Ferreira Trindade ◽  
Sonia Rousse ◽  
Anani Ayite ◽  
...  
Keyword(s):  
West Africa ◽  
West African ◽  
Dyke Swarm ◽  
Jigsaw Puzzle ◽  
The West ◽  
West African Craton ◽  
Contact Test ◽  
Fine Grained ◽  
Paleomagnetic Pole ◽  
Coarse To Fine

<p>The West African Craton (WAC) is one of the major cratons in the Rodinia jigsaw puzzle (~1000–750 Ma). In the Rodinian models, the position of West Africa is mainly constrained by the assumption that it had been a partner of Amazonia since the Paleoproterozoic. Unfortunately, no paleomagnetic data are available for these cratons when the Rodina supercontinent is considered tectonically stable (~1000-750 Ma). Thus, every new reliable paleomagnetic pole for the West African Craton during the Neoproterozoic times is of paramount importance to constrain its position and testing the Rodinia models. In this study we present a combined paleomagnetic and geochronological investigation for the Manso dyke swarm in the Leo-Man Shield, southern West Africa (Ghana). The ~860 Ma emplacement age for the NNW-trending Manso dykes is thus well-constrained by two new U-Pb apatite ages of 857.2 ± 8.5 Ma and 855 ± 16 Ma, in agreement with baddeleyite data. Remanence of these coarse-to-fine grained dolerite dykes is carried by stable single to pseudo-single domain (SD-PSD) magnetite. A positive baked-contact test, associated to a positive reversal test (Class-C), support the primary remanence obtained for these dykes (13 sites). Moreover, our new paleomagnetic dataset satisfy all the seven R-criteria (R=7). The ~860 Ma Manso pole can thus be considered as the first key Tonian paleomagnetic pole for West Africa. We propose that the West Africa-Baltica-Amazonia-Congo-São Francisco were associated in a long-lived WABAMGO juxtaposition (~1100–800 Ma).</p><p><strong>Keywords:</strong> West Africa, Neoproterozoic, Tonian, Rodinia, paleomagnetism.</p><p> </p>

Évolution paléogéographique de la marge nord-ouest de l'Afrique du Cambrien à la fin du Carbonifère (du Maroc au Libéria)

1991 ◽  
Vol 28 (7) ◽  
pp. 1121-1130 ◽  
Author(s):  
Michel Villeneuve ◽  
Jean-Jacques Cornée
Keyword(s):  
West African ◽  
The West ◽  
Lower Paleozoic ◽  
West African Craton ◽  
Middle Cambrian ◽  
Early Devonian ◽  
Middle Ordovician ◽  
The North ◽  
Marine Platform ◽  
General Regression

Paleogeographic reconstructions of Paleozoic time are presented for the northwest margin of the West-African Craton. An extensional regime and a marine transgression were dominant during the Early Cambrian. During the Middle Cambrian, the Rokélides orogen was responsible for the sea regression to the south, while the proto-Atlantic opening was active to the north of the Reguibat shield. A large stable marine platform was present during Early and Middle Ordovician. A general regression and the formation of the West-African Inlandsis took place during the Late Ordovician. During Silurian time, this sea transgressed over most of the African platform. Incipient Hercynian deformations during the Early Devonian produced horsts and grabens in Morocco. At the end of the Devonian and the beginning of the Carboniferous, the sea was restricted to isolated basins and tectonic trenches. Collision between West Africa and North America during the Late Carboniferous transformed the Lower Paleozoic margin into an Hercynian orogenic belt, whose structure is controlled by the presence of crustal blocks, generated as early as the Cambrian, and probably reflecting, in turn, older Panafrican zones of weakness. [Translated by the Journal]

scholarly journals Promoting research to improve maternal, neonatal, infant and adolescent health in West Africa: the role of the West African Health Organisation

2017 ◽  
Vol 15 (S1) ◽  
Author(s):  
Issiaka Sombie ◽  
Aissa Bouwayé ◽  
Yves Mongbo ◽  
Namoudou Keita ◽  
Virgil Lokossou ◽  
...  
Keyword(s):  
West Africa ◽  
Adolescent Health ◽  
West African ◽  
The West ◽  
African Health

A curious case of nematode parasitism in a West African Hadada, Gevonticus hagedash

1945 ◽  
Vol 21 (2-3) ◽  
pp. 99-103 ◽  
Author(s):  
Phyllis A. Clapham
Keyword(s):  
Small Intestine ◽  
West Africa ◽  
West Coast ◽  
West African ◽  
The West ◽  
The Family ◽  
Nematode Parasitism

In the following article is described an interesting parasitic condition which is difficult to interpret. The small intestine of an Hadada, Geronticus hagedash, was brought back from the West Coast of Africa by Major T. A. Cockburn, M.D., R.A.M.C, who kindly passed it to me for further examination. The bird is a member of the family Plataleidae, living in wooded districts in West Africa in the neighbourhood of water and feeding on invertebrates, mainly annelids and small crustaceans which it finds at the bottom of ponds and streams in the mud.

scholarly journals On What Scale Can We Predict the Agronomic Onset of the West African Monsoon?

2016 ◽  
Vol 144 (4) ◽  
pp. 1571-1589 ◽  
Author(s):  
Rory G. J. Fitzpatrick ◽  
Caroline L. Bain ◽  
Peter Knippertz ◽  
John H. Marsham ◽  
Douglas J. Parker
Keyword(s):  
West Africa ◽  
Noise Analysis ◽  
West African Monsoon ◽  
West African ◽  
New Method ◽  
The West ◽  
African Monsoon ◽  
Spatial Consistency ◽  
Local Stakeholders ◽  
Local Rainfall

Abstract Accurate prediction of the commencement of local rainfall over West Africa can provide vital information for local stakeholders and regional planners. However, in comparison with analysis of the regional onset of the West African monsoon, the spatial variability of the local monsoon onset has not been extensively explored. One of the main reasons behind the lack of local onset forecast analysis is the spatial noisiness of local rainfall. A new method that evaluates the spatial scale at which local onsets are coherent across West Africa is presented. This new method can be thought of as analogous to a regional signal against local noise analysis of onset. This method highlights regions where local onsets exhibit a quantifiable degree of spatial consistency (denoted local onset regions or LORs). It is found that local onsets exhibit a useful amount of spatial agreement, with LORs apparent across the entire studied domain; this is in contrast to previously found results. Identifying local onset regions and understanding their variability can provide important insight into the spatial limit of monsoon predictability. While local onset regions can be found over West Africa, their size is much smaller than the scale found for seasonal rainfall homogeneity. A potential use of local onset regions is presented that shows the link between the annual intertropical front progression and local agronomic onset.

The magmatic evolution at the Moroccan outboard of the West African craton between the Late Neoproterozoic and the Early Palaeozoic

2008 ◽  
Vol 297 (1) ◽  
pp. 329-343 ◽  
Author(s):  
H. Ezzouhairi ◽  
M. L. Ribeiro ◽  
N. Ait Ayad ◽  
M. E. Moreira ◽  
A. Charif ◽  
...  
Keyword(s):  
West African ◽  
Magmatic Evolution ◽  
The West ◽  
West African Craton ◽  
Late Neoproterozoic ◽  
Early Palaeozoic
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