1,720,974 research outputs found
Tunisian Desert: a perfect place to simulate the landing on Mars
No full textGuide book of a field trip in the southern Tunisian chott
Geomorphosites of Tozeur Region (South-West Tunisia)
No full textTozeur is the most important tourist town of south-western Tunisia, situated in between the two salt lakes Chott El Djerid to the south and Chott El Gharsa to the north. This area is known for its luxuriant oasis in the middle of the desert (Tozeur, Gafsa, Nefta etc.), the mountain chains to the north close to the border with Algeria with its villages and waterfalls (Tameghza, Chebìka, Midès), the mountain chain east of Tozeur (Jbel Morra etc.) with its arid canyons, and the wide salt plains (Chotts). Tourists usually visit the region rapidly without staying overnight, overlooking and ignoring the great geomorphologic and geological interesting places and landscapes. Therefore, in the framework of a Research Project performed by the Department of Geology of the University of Cagliari in collabora- tion with the Institut des Régions Arides at Medenine and with the "Faculté de Sciences Humaines et sociales" of Tunis and financed by the Sardinian Regional Government (R.L. 11 Aprile 1996, n° 19), our multidisciplinary Research Team has studied twenty-one geo- sites and geological landscapes in the region of Tozeur, with the purpose of constituting a network of geosites in these arid and semi- arid areas.
Field work combined with remote sensing techniques have enabled to start preparing thematic maps of these geosites which, together with their description (genesis, evolution, state of conservation, proposals of valorisation, etc.) will be useful for obtaining financial aid for their protection and valorisation. The definition of morphostructural units landform analysis at a large/medium scale was performed by TeleGIS Laboratory, involved in these studies on southern Tunisia from 1997 in collaboration with the Institute des Régions Arides, applying remote sensing techniques on multi-spectral satellite images. During this project the interpretation keys for the image classification were created in the different steps of field observations and digital image processing. The radiometric and geometric responses were used for the discrimination of spectral units (lithological sequences) and textural units defined by photo- interpretation techniques (structural and landscape units like anticlines, fault-controlled valleys or forms like chevron, etc.).
Many of the studied geomorphosites are represented by canyons (Gorges de Ben Nebhana, Sidi Bou Helal, Thelja, En Negueb, Chaabet Es Sfa, Ben Hamed, Midès, etc.) and waterfalls (Grande Cascade and Cascade de l'Oasis at Tameghza, Cascade de Chebìka and its geological-structural features). Others are related to aeolian and meteoric processes (Barchan dunes of El Ghadayer, morpho-sculpture of Ong El Jmel, Yardangs of El Ghadayer, Nebkha fields of Chamsa). The remaining geosites are an ancient lacu- strine coastline testified by a lumachelle with Cardium in the Jehim oasis near Tozeur, the anticline of Brikis close to Tameghza, and an ancient phosphate mine at Chouabin (Jbel Chouabin close to Redeyef), a representative part of Chott el Djerid, the Delta of Oued Mellah and the alluvial cone of Oued Foum el Khanga and the ancient oasis (Corbeille) of Nefta.
These sites and landscapes of geological and geomorphological interest represent the entire geological history of the Tozeur and the Chotts region fairly well. This history starts from Early Cretaceous, and the various sites narrate the sedimentary and tectonic events, the palaeo-environmental and palaeo-climate episodes, the birth, development and extinction of animal and plant species, the geo- morphological processes and depositional events, explaining the present morphology, climate and landscape in a most interesting scientific and educational way.
The linking of all these places of geological and geomorphologic interest in networks of Geosites along a thematic issue (the "Living Desert" network with Nebkha and Barchan dunes, Yardangs and Aeolian sculptures, the "Rocks and Water" network with waterfalls, mountains and canyons, the "Earth’s Memory" network across the canyons of Jbel Morra-Sidi Bou Helal passing through more than 100 million years of Earth's geological history, the “Phosphate Route” network with active and abandoned phosphate mines and their environmental impact and the “Changing Environment and Climate” network with salt pans, fossil shorelines and abandoned oasis) give an interesting opportunity of telling the history of the Earth, promoting geology and geomorphology to the local people and to the visitors. In fact, geological heritage can and should become a cultural and economical resource for the local people, and therefore these inhabitants should be taught understanding their natural and cultural environment, enabling them to use these elements in the framework of a touristic and sustainable development of their region
Geomorphosites of Tozeur region (south-west Tunisia).
No full textTozeur is the most important tourist town of south-western Tunisia, situated in between the two salt lakes Chott El Djerid to the south and Chott El Gharsa to the north. This area is known for its luxuriant oasis in the middle of the desert (Tozeur, Gafsa, Nefta etc.), the mountain chains to the north close to the border with Algeria with its villages and waterfalls (Tameghza, Chebìka, Midès), the mountain chain east of Tozeur (Jbel Morra etc.) with its arid canyons, and the wide salt plains (Chotts). Tourists usually visit the region rapidly without staying overnight, overlooking and ignoring the great geomorphologic and geological interesting places and landscapes.
Therefore, in the framework of a Research Project performed by the Department of Geology of the University of Cagliari in collaboration with the Institut des Régions Arides at Medenine and with the "Faculté de Sciences Humaines et sociales" of Tunis and financed by the Sardinian Regional Government (R.L. 11 Aprile 1996, n° 19), our multidisciplinary Research Team has studied twenty-one geosites and geological landscapes in the region of Tozeur, with the purpose of constituting a network of geosites in these arid and semi-arid areas.
Field work combined with remote sensing techniques have enabled to start preparing thematic maps of these geosites which, together with their description (genesis, evolution, state of conservation, proposals of valorisation, etc.) will be useful for obtaining financial aid for their protection and valorisation. The definition of morphostructural units landform analysis at a large/medium scale was performed by TeleGIS Laboratory, involved in these studies on southern Tunisia from 1997 in collaboration with the Institute des Régions Arides, applying remote sensing techniques on multi-spectral satellite images. During this project the interpretation keys for the image classification were created in the different steps of field observations and digital image processing. The radiometric and geometric responses were used for the discrimination of spectral units (lithological sequences) and textural units defined by photo-interpretation techniques (structural and landscape units like anticlines, fault-controlled valleys or forms like chevron, etc.).
Many of the studied geomorphosites are represented by canyons (Gorges de Ben Nebhana, Sidi Bou Helal, Thelja, En Negueb, Chaabet Es Sfa, Ben Hamed, Midès, etc.) and waterfalls (Grande Cascade and Cascade de l'Oasis at Tameghza, Cascade de Chebìka and its geological-structural features). Others are related to aeolian and meteoric processes (Barchan dunes of El Ghadayer, morpho-sculpture of Ong El Jmel, Yardangs of El Ghadayer, Nebkha fields of Chamsa). The remaining geosites are an ancient lacustrine coastline testified by a lumachelle with Cardium in the Jehim oasis near Tozeur, the anticline of Brikis close to Tameghza, and an ancient phosphate mine at Chouabin (Jbel Chouabin close to Redeyef), a representative part of Chott el Djerid, the Delta of Oued Mellah and the alluvial cone of Oued Foum el Khanga and the ancient oasis (Corbeille) of Nefta.
These sites and landscapes of geological and geomorphological interest represent the entire geological history of the Tozeur and the Chotts region fairly well. This history starts from Early Cretaceous, and the various sites narrate the sedimentary and tectonic events, the palaeo-environmental and palaeo-climate episodes, the birth, development and extinction of animal and plant species, the geomorphological processes and depositional events, explaining the present morphology, climate and landscape in a most interesting scientific and educational way.
The linking of all these places of geological and geomorphologic interest in networks of Geosites along a thematic issue (the "Living Desert" network with Nebkha and Barchan dunes, Yardangs and Aeolian sculptures, the "Rocks and Water" network with waterfalls, mountains and canyons, the "Earth’s ..
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
La carta della unità geomorfologiche della regione di Medenine (Tunisia meridionale)
No full textQuesta carta rappresenta una proposta di
metodologiaQuesta carta rappresenta una proposta di
metodologia di analisi di dati telerilevati per la definizione
di un sistema di interpretazione delle forme del
paesaggio. In questo lavoro viene studiato un settore
della Tunisia meridionale nella regione di Medenine,
dove un progetto di ricerca ha coinvolto il Laboratorio
TeleGIS dell’Università di Cagliari, l’Università di Tunisi
ed il Centro di studi sulla desertificazione dell’IRA
(Insitut des Regions Arides) di Medenine. La creazione
delle chiavi di interpretazione delle immagini telerilevate
si è svolta attraverso una serie di campagne sul terreno
per la creazione di un sistema di classificazione mirato
all’analisi delle dinamiche morfologiche.
L’area in studio copre una settore della piattaforma
sahariana, divisa in unità geomorfologiche differenziate
in base all’evoluzione morfo-tettonica e climatica. La definizione
di queste unità in un sistema di classificazione
multispettrale è stata svolta anche mediante l’integrazione
di un modello digitale dell’elevazione sul quale sono
state cartografate le principali discontinuità strutturali.
Questa interpretazione ha permesso di confermare l’interazione
tra la tettonica recente legata alle ultime fasi
dell’orogenesi dell’Atlas ed il cambio climatico del settore.
Il carattere morfologico dominante è rappresentato
dalle strutture monoclinali che costituiscono una serie di
rilievi a cuesta controllati dal sistema tettonico distensivo
della faglia di Gafsa-Medenine. Questa unità morfologica
costituisce un limite non solo morfo-strutturale ma anche
morfo-climatico tra la Piana di Medenine ed i rilievi
marnoso-calcarei mesozoici, con differenze di quota di
circa 500 metri. La Piana di Medenine è costituita da una
superficie debolmente inclinata limitata verso ovest dai
versanti evolutisi per arretramento parallelo. Sono evidenti
intensi fenomeni di erosione lineare e localmente
crolli per erosione differenziale; la fascia pedemontana e
la base dei versanti è ondulata per la presenza di conoidi
coalescenti inattive. Il glacis è coperto quasi totalmente
da crostoni carbonatici e gessosi ben differenziabili dall’analisi
spettrale e la dinamica eolica, con importanti
aspersioni sabbiose, condiziona fortemente l’uso agricolo
del suolo.This map is a methodological purpose of remote
sensing application for a new definition of a system
of landform interpretation. In this paper a satellite study
is proposed on an area that covers the south western
side of Medenine (southern Tunisia), where a research
project involves the Italian TeleGIS Lab of University
of Cagliari, Tunisian IRA Centre on desertification and
degradation problem and the University of Tunis.
The Saharan platform in southern Tunisia is divided
into different geomorphologic units connected to recent
structural neotectonic evidence and climate evolution.
The remote sensing over a DTM model approach has
been applied to study geomorphologic analysis and morpho-
dynamic evolution by photo interpretation, field
work and digital processes on Landsat TM data. This interpretation
confirms the interaction between the most
recent tectonics of the Atlas orogeny and the rapid drying
of the climate.
The main morphological feature is represented by
monoclinal structures which constitute a cuesta system
controlled by the Gafsa-Medenine distensive fault trend.
This monocline system is a morpho-structural and morpho-
climatic limit between the plain of Medenine and
the Mesozoic carbonate landform with differences of altitude of 500 metres. The plain of Medenine constitutes
the evolution of the parallel retreat of slopes with intense
phenomena of sheet and gully erosion and locally
a slope replacement; the piedmont zone and the knick
along the scarp is undulated because of coalescing of adjacent
alluvial fans. The glacis area mainly is covered by
gypsum and calcareous crust; the aeolian dynamics and
the lack of soil limit the agricultural use and the vegetation
growth. These processes are causing prohibitive
conditions for agricultural use and grazing is the principal
economical resource. The Morpho-unit of Mesozoic
carbonate is constituted by a series of structural surfaces
of the monoclinal system that disappears beneath the
dunes of the Grand Erg Oriental. The aeolian dynamics
is actually active and visible on satellite image like
crescent shaped sand-dunes (barchans) with direction of
prevailing wind from south-west. The tectonic control
is well exposed along the rivers as meandering valleys
and terraces with different degree of deepness developed
in different climatic regime and correlated to other base
level. Interesting information was been carried out from
the integration with DTM model in terms of landform
classification
- …
