The structure of the Central-Eastern Rif (Morocco) and the disregarded subduction of the North-West African paleo-margin

2020 ◽  
Author(s):  
Oriol Gimeno ◽  
Dominique Frizon de Lamotte ◽  
Rémi Leprêtre ◽  
Faouziya Haissen ◽  
Achraf Atouabat ◽  
...  
Keyword(s):  
Late Eocene ◽  
West African ◽  
North African ◽  
Tectonic Event ◽  
North West ◽  
The North ◽  
Before And After ◽  
Rif Belt ◽  
Thrust Sheets ◽  
Gravity Driven

<p>The Rif Belt (Northern Morocco) forms the western edge of the Alpine-Himalayan orogenic system developed during the convergence between the Africa and Eurasia plates. Compared to other mountains belts, the External Rif, which preserves remnants of the North African paleo-margin, presents two unusual features: (1) the presence of metamorphic massifs [External Metamorphic Massifs (EMMs)] and (2) the existence of large allochthonous thrust-sheets that travelled far away [the Higher Nappes]. In this contribution, we combined structural, stratigraphic and metamorphic data, complemented by new field observation and thermochronology results, to revisit the structure of the External Rif and to review its Cenozoic evolution. The External Rif was the site of a poly-phased tectonic evolution recorded before and after of a major unconformity: the so-called “Mesorif Unconformity” postdating an important Midde-Late Eocene deformation. This tectonic event is well-preserved in the North-African paleo-margin because of its under-thrusting (“subduction”) below the Maghrebian Tethys, the former oceanic domain separating Iberia from Africa. The MP-LT metamorphism, recorded in the EMMs (Temsamane Units in Morocco), is a direct vestige of this process.  By contrast, traces of this event are absent in the oceanic units of the Intrarif Domain, element of the Maghrebian Tethys. After the “Mesorif Unconformity”, i.e. during the Miocene, the regional geodynamics is dominated by the westward translation of the Alboran Domain and the coeval deformation of the Ketama Unit (Intrarif) in front of it. This process results directly from the subduction of the Maghrebian Tethys, which happened at that time. The docking of the Ketama Unit against the already exhumed EMMs allowed an uplift and the subsequent detachment of the top of its lithostratigraphic pile, individualizing the Higher Nappes. During their gravity-driven travel towards the foredeep basin, they dragged at their floor the already exhumed Senhadja Nappes, inherited from the distal-most part of the NW African margin. All these elements are integrated in a coherent model integrating the External Rif in the geodynamics of the West Mediterranean.</p>

Turbidite depositional architecture across three interconnected deep-water basins on the north-west African margin

Sedimentology ◽  
2002 ◽  
Vol 49 (4) ◽  
pp. 669-695 ◽  
Author(s):  
Russell B. Wynn ◽  
Philip P. E. Weaver ◽  
Douglas G. Masson ◽  
Dorrik A. V. Stow
Keyword(s):  
Deep Water ◽  
West African ◽  
North West ◽  
The North ◽  
Depositional Architecture

Life before and after implementation of an acoustic noise reduction enclosure

2005 ◽  
Vol 109 (1092) ◽  
pp. 65-74
Author(s):  
B. Timmins
Keyword(s):  
Wind Tunnel ◽  
Noise Reduction ◽  
Acoustic Noise ◽  
Financial Health ◽  
Two Phase ◽  
North West ◽  
The North ◽  
Close Proximity ◽  
Before And After ◽  
Increase Productivity

Abstract This paper looks back on the designs and ambitions of ARA in resolving a long term acoustic noise problem which threatened ARA with closure. This paper today briefly looks back to the original issues but deals more fully with the later phases of a two phase project implementation and construction. ARA is now a truly ‘silent site’, where closure was once threatened, ARA has achieved the implementation of a bespoke noise reduction enclosure where 24-hour running has proved to be a reality. This paper looks at the design and construction phases, the ‘before and after’ noise footprints and at some of the financial benefits ARA has achieved. The ARA transonic wind tunnel is sited on an industrial estate on the north west perimeter of Bedford. When it was first built it was on an original farm site with no appreciable residential houses in close proximity. Since the early 1950s there has been considerable residential development around the ARA site resulting in the local householders complaining about the wind tunnel acoustic noise. In early 1999 ARA was obliged to consider several options for noise reduction measures to reduce the noise to within UK government statutory requirements. This paper deals briefly with the original noise nuisance characteristics and footprint, the noise reduction design and method that ARA selected and shows the construction phases, the further noise treatment ARA had to do on other major ancillary equipment to make ARA a truly quiet industrial site. The paper shows how ARA has utilised the resulting benefits of these investments to increase productivity and reduce costs, and the influence it has had on ARA’s financial health.

Pre-Mesozoic origin and paleogeography of blocks in the Caribbean, South Appalachian and West African domains and their impact on the post “variscan” evolution

2013 ◽  
Vol 184 (1-2) ◽  
pp. 5-20 ◽  
Author(s):  
Michel Villeneuve ◽  
Boris Marcaillou
Keyword(s):  
West Africa ◽  
Atlantic Ocean ◽  
West African ◽  
Large Area ◽  
Tectonic Event ◽  
Western Sahara ◽  
The North ◽  
Gondwana Margin ◽  
The Caribbean ◽  
North American Craton

Abstract New geodynamical data from West Africa bring consistent informations on the pre-Mesozoic reconstruction within a large area running from the western Sahara to the Colombian cordillera. These new data support a Neoproterozoic Ocean (WANO) between the Amazonian (AMC) and West African (WAC) cratons previously to the Iapetus and Rheic oceans. We delineate 31 blocs detached from the surrounding three continents: NAC (North American Craton), AMC and WAC. 7 came from the WAC margin, 7 from the NAC, 6 from the AMC and 11 from an intermediate volcano sedimentary domain (COB) built on a 1200–1000 Ma oceanic crust. These imbricated blocks formed a tight mosaic by the Hercynian/Alleghanian tectonic event which gave way to the Pangea super-continent. But, during the Atlantic Ocean opening these blocks began to move. They were separated by new oceanic basins. However, previously to the Pangea, blocks from the COB domain formed two sets of garlands located on the northwestern Gondwana margin. The northern one moved to the North until the Silurian to collide the NAC (Taconic tectonic event) meanwhile the southern one remains on the Gondwana margin. All together were gathered by the Carboniferous/Permian time. Then, the framework for the opening of the Atlantic Ocean was not totally disconnected from the “Variscan” collage and many variscan weakness zones were re-used as initial breaking zones. Beyond this tectonic impact, the pre-mesozoic assemblage allows us to compare this “Caribbean” island arc with another one: the Indonesian “Banda” arc. Thus, West Africa is a geological key area for correlations between the Caribbean, the Appalachian, the Brazilian “Nordeste” and the West European domains and for the understanding of the Atlantic Ocean opening process.

PETROLEUM EXPLORATION PREVIEW FOR 1967

1967 ◽  
Vol 7 (1) ◽  
pp. 16
Author(s):  
M. A. Condon
Keyword(s):  
Financial Incentives ◽  
Petroleum Exploration ◽  
North West ◽  
The North ◽  
Oil Markets ◽  
Before And After ◽  
Timor Sea ◽  
The Government ◽  
Average Size ◽  
The Cost

Exploration for petroleum in Australia paused in 1966 and this pause is likely to continue in 1967.The number of wells drilled and seismic activity will both be slightly less in 1967 than in 1966, but the work will generally be directed to more specific targets. The cost of exploration will be somewhat higher than in 1966.During the year off-shore drilling should increase and it is expected that five mobile rigs will be drilling in the offshore areas by the end of the year. The immediate structural targets available for these rigs are in the Gippsland, Bass and Otway Basins (Victoria-Tasmania), the North-West Shelf and Timor Sea-Bonaparte Gulf, and in the Gulf of Papua.Onshore exploration will be concentrated in the western Australian basins, the Surat Basin, the central Great Artesian Basin, and the Gidgealpa region of the southwestern Great Artesian Basin.The success or otherwise of the off-shore drilling will determine the rate of exploration over the next few years. If important discoveries are made off-shore, these may and probably would result in more intensive exploration of the same stratigraphic intervals onshore.The exploration patterns of Australia and several other countries before and after first commercial discovery are compared. This indicates that Australian discovery came early, as compared with other countries, where production has developed since the war, but that post-discovery effort in Australia has been very much less. The main obvious differences appear to be that in Australia the average size of the exploration concession is very much larger and the number of operators (having regard to the areas concerned) is much smaller, than in the other successful countries.There has been a gradual movement towards reducing the size of operating areas in Australia either by obligatory relinquihment or by farmout, but if discoveries are to be made at a satisfactory rate more operators are needed in every basin.The economic environment of Australia vis-a-vis Middle East oil and oil markets is probably the main basic reason for the peculiar exploratory pattern, which has impelled the Government to provide financial incentives to encourage exploration and development.

The Palaeovegetation of the Murray Basin, Late Eocene to Mid-Miocene

1993 ◽  
Vol 6 (6) ◽  
pp. 491 ◽  
Author(s):  
HA Martin
Keyword(s):  
Forest Dynamics ◽  
Pollen Dispersal ◽  
Flood Plain ◽  
Late Eocene ◽  
Pollen Spectrum ◽  
Swamp Forest ◽  
North West ◽  
North East ◽  
The North ◽  
Murray Basin

The principles of pollen dispersal and deposition show that the pollen spectrum is produced by the plants of the locality, with a little transported in from long distances. The 'locality' has a radius of no more than 500 m, and it could be much less. Adherence to these principles has allowed a detailed reconstruction of the palaeovegetation. Nothofagus grew throughout the Murray Basin, probably on the dry ground in the flood plain complex. Occasionally it was dominant, but most of the forests were mixed. The fusca-type flourished on well drained sites, especially in the north-east. The menziesii-type became prominent in the mid-Miocene, when the climate was becoming drier. The brassii-type was probably the only type in the deeper, swampier parts of the basin. Gymnosperms were intimately connected with the semi-swamp forest. Araucariaceae–Casuarinaceae forests formed a coastal zone around the Miocene marine incursion. Herbaceous fresh water swamps were found in the north-west, where they formed disjuncts from the swampy margin of Lake Frome. Myrtaceae was found throughout, sometimes abundantly, but eucalypts were rare. Geographic variation, changes through time and forest dynamics, including possibly one very rare modification after burning, are detailed.

Age and growth of the squid Todaropsis eblanae (Cephalopoda: Ommastrephidae) on the north-west African shelf

2000 ◽  
Vol 80 (4) ◽  
pp. 747-748 ◽  
Author(s):  
Alexander I. Arkhipkin ◽  
Vladimir V. Laptikhovsky
Keyword(s):  
High Growth ◽  
West African ◽  
Age And Growth ◽  
Length Frequency ◽  
Annual Life Cycle ◽  
Frequency Distributions ◽  
North West ◽  
The North ◽  
West African Coast ◽  
African Coast

Length composition, maturation and growth of the ommastrephid squid Todaropsis eblanae were studied using length–frequency distributions (LFDs) and statoliths of squid caught off the north-west African coast. Length–frequency distributions were quite similar in all seasons studied, indicating all year round spawning. However, both high proportions of mature squid in the winter and the hatching peak of squid from our sample in spring suggested the winter–spring peak of spawning. Immature and maturing squid had rather high growth rates, attaining 140—150 mm of dorsal mantle length (ML) by the age of 160—170 d. Todaropsis eblanae is likely to have an annual life cycle on the north-west African shelf.

Structural styles of the External Rif and Flysch Domain (Rif belt, northern Morocco) through thermal maturity and structural data

2020 ◽  
Author(s):  
Andrea Schito ◽  
Achraf Atouabat ◽  
Sveva Corrado ◽  
Faouziya Haissen ◽  
Geoffroy Mohn ◽  
...  
Keyword(s):  
Vitrinite Reflectance ◽  
Methodological Approach ◽  
Structural Evolution ◽  
Structural Data ◽  
Thermal Modelling ◽  
Thermal Maturity ◽  
North African ◽  
Data Set ◽  
The North ◽  
Rif Belt

<p>Located in northern Morocco, the Rif belt represents the western edge of the Maghrebides system. This domain underwent a significant Cenozoic alpine compressional deformation, due to the collision between the North African margin and the south-western margin of the exotic Alboran Domain. This collision led to the development of a nappe stack during the Miocene.</p><p>This contribution aims to characterize the main tectonic mechanisms driving the evolution of the Rifain wedge, its burial-exhumation paths and to understand the former architecture of the North African paleo-margin. The work focuses mainly on the Flysch domain, originated from the Maghrebian branch of the Tethys and on the External domain (namely Intrarif, Mesorif and Prerif) that belong to the former north African margin. To define the thrust sheet stacking pattern and their burial-exhumation paths, a regional transect from Chefchaouen and Ouezzane towns (Central Rif), crossing the orogenic wedge from the Flysch to the Prerif Units is constructed.</p><p>The methodological approach consists in combining petrography and Raman micro-spectroscopy on organic matter and 1D thermal modelling, together with field structural data.</p><p>A new paleo-thermal data set of vitrinite reflectance (Ro%) and Raman micro-spectroscopy displays levels of thermal maturity between early and deep diagenetic conditions (Ro% ranges from 0.50% to 1.15%).</p><p>Preliminary results show an abrupt change in the thermal maturity and the rate of shortening in the Loukkos sub-unit (Intrarif Domain) that is structurally squeezed between Tangier sub-unit (Intrarif Domain) and the “Izzaren Duplex” (Mesorif).</p><p>Furthermore, previous studies show that the thickest crust below the Rif fold-and-thrust belt is located below the Izzaren area, suggesting a deep crustal imbrication at the transition between the Intrarif and the Mesorif. These observations joined with the thermal maturity data and 1D thermal modelling allow revisiting the structural evolution of the central part of the Rif belt, by defining the rate of shortening and proposing a new geological restoration with respect to the Mesozoic North African margin structural original setting.</p>

Social Administration of the Kru. A Preliminary Survey

Africa ◽  
1937 ◽  
Vol 10 (1) ◽  
pp. 75-96 ◽  
Author(s):  
H. Scudder Mekeel
Keyword(s):  
West Africa ◽  
West African ◽  
Preliminary Survey ◽  
The South ◽  
North West ◽  
North East ◽  
The North ◽  
Archaeological Work ◽  
Opening Paragraph ◽  
Physical Type

Opening ParagraphThe Kru, a West African Negro group, inhabit the central and southern part of Liberia. They are surrounded by the Basa peoples to the north-west, by the Grebo to the south-east and by the Putu to the north-east. The informant, Thomas Tarbour (Sieh Tagbweh), from whom the following material was derived, was a native of Grand Cess (Siglipo), a large coast town near the border of the Grebo country. The Kru, along with other related groups in that part of West Africa, have a tradition of having migrated from far to the north-east. The physical type is that of the short, stocky Bush negro. No archaeological work has been done in the region, and such ethnological material as has been collected is a mere beginning.

scholarly journals SYNOPTIC ATMOSPHERIC PATTERNS CONTROLLING THE NORTH-WEST AFRICAN OCEANOGRAPHIC VARIABILITY

2020 ◽  
Vol 11 (12) ◽  
Author(s):  
AÏSSA BENAZZOUZ ◽  
KHALID EL KHALIDI ◽  
HASSAN MABCHOUR ◽  
KHALID EL HAD ◽  
SOUMIA MORDANE ◽  
...  
Keyword(s):  
West African ◽  
North West ◽  
The North
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