Early Cretaceous spinicaudatans (“conchostracans”) from lacustrine strata of the Sidi Aïch Formation in the northern Chotts range,southern Tunisia: Taxonomy,biostratigraphy and stratigraphic implication     

《Cretaceous Research》2015

The fossil clam shrimp genus Cratostracus was first described from the Turonian–Coniacian (Upper Cretaceous) Qingshankou Formation in the Jilin and Heilongjiang provinces of China, and it has been found to range down into the Aptian Guantou Formation in Zhejiang Province of southeastern China. Recently, species tentatively attributable to it (Cratostracus? cheni) has been recorded in the well-known Jehol Biota bearing Barremian–lower Aptian (Lower Cretaceous) Yixian Formation in western Liaoning Province of northeastern China. The species described in this paper as Cratostracus? tunisiaensis sp. nov. was recovered from the Sidi Aïch Formation in the Chotts area of southern Tunisia. Although only tentatively attributed to Cratostracus, its occurrence is consistent with a Barremian (Early Cretaceous) age for the formation. This first direct dating of the Sidi Aïch Formation gives a valuable insight for the stratigraphy of the region and will make it possible to more precisely correlate the different outcrops of the Sidi Aïch Formation. Moreover, the new fossil discovery allows a reconstruction of the paralic ecosystem that characterized the study area during the Barremian.  相似文献   

Geochemistry of Triassic Carbonates: Exploration Guide to Pb–Zn Mineralization in North Tunisia          下载免费PDF全文

Nejib Jemmali  Fouad Souissi  Emmanuel John M. Carranza  Mohsen Henchiri 《Resource Geology》2016,66(4):335-350

The Triassic carbonate rocks in Northern Tunisia (Nappes, Domes, Jurassic Mountains zones), consist of massive carbonates, clays and gypsum with authigenic minerals. These are associated with several Pb–Zn deposits and occurrences. At Jebel Ichkeul, Bechateur and Oum Edeboua, these Triassic carbonates exhibit enrichment in Pb (0.32 to 228 ppm), Zn (17 to 261 ppm), Cd (5 to 6 ppm) and Co (0.3 to 89.5 ppm), with respect to their average contents in crustal carbonates. The enrichment is more pronounced at Oum Edeboua (near the ore zone). Permeability is one of the most effective factors of dispersion of metallic trace elements, causing the development of geochemical halos. The genetic relationship of the Triassic carbonate rocks with the ore deposits was controlled by diapirism and tectonic movements, which favored mineralization along the Triassic‐cover contact as well as the remobilization of metals from the mineralized rocks. Analysis of metallic trace elements in Triassic rocks provides clues to the presence of possible mineral deposits. These could be effectively used for both geochemical interpretation and mineral exploration. Carbon and O‐isotope data (– 9.3‰ < δ¹³C < +3‰; +21.9 < δ¹⁸O < +31‰) suggest that the Triassic carbonates of all study areas have marine carbonates as their origin; some of them show significantly lower δ¹⁸O values indicating some exchange with hydrothermal fluids. Calcites associated with mineralization at Oum Edeboua have δ¹³C of –6.2‰ to –8.22‰ and δ¹⁸O of +24.88‰ to +25‰. The C‐isotope compositions of these calcites are ¹³C depleted, indicating an organic origin.  相似文献   

Techniques for measuring rock weathering: application to a dated fan segment sequence in southern Tunisia     

Kevin White  Rob Bryant  Nick Drake 《地球表面变化过程与地形》1998,23(11):1031-1043

There are a number of techniques for estimating the amount of weathering a clast has undergone. These usually have the objective of establishing an ordinal chronology of geomorphological surfaces, or investigation of site-specific conditions affecting weathering rates. Three such techniques are applied to a dated sequence of alluvial fan segments in southern Tunisia. Two of these techniques depend on measuring surface roughness (the micro-roughness meter and a displacement approach) and one uses the structural weakening of the rock fabric (Schmidt hammer). The micro-roughness meter enables calculation of standard deviation of surface height variation, root mean square roughness and surface autocorrelation function. Of these techniques, Schmidt hammer rebound values, standard deviation, root mean square roughness and the displacement technique show systematic changes on the three fan segments which are statistically significant at the 0·05 level. However, the amount of variance in all datasets is very large, indicating the need for caution in application of these techniques for relative dating. © 1998 John Wiley & Sons, Ltd.  相似文献   

Sea-level rise impact on the evolution of a microtidal Mediterranean coastline without human-made structures——a case of the Port aux Princes-Sidi Daoued coastline,Gulf of Tunis,NE-Tunisia     

SA&#;DI Hanen  ZARGOUNI Fouad 《海洋学报(英文版)》2019,38(3):72-77

The evolution of the natural and pristine Mediterranean coastline Port aux Princes-Sidi Daoued(Gulf of Tunis,NE-Tunisia) is studied during the period of 1887–2010 on the basis of an ancient minute of bathymetry(1887) and aerial photographs treated by numerical photogrammetric methods. Morphological changes of the coastline shows a general retreat despite the absence of the various anthropogenic actions. Adding to the drift currents and the currents of high energy that are generated by the N-W dominant waves along steeply sub-marine funds, the erosion is mainly due to the sea level rise which increased since the beginning of the 2000 s. The Port aux PrincesSidi Daoued coastline works as a single littoral cell limited by Jbel Korbous to the SW and the fishing harbor of Sidi Daoued to the N-E.  相似文献   

Geodynamic processes on sandy slope gullies in central Spain field observations,methods and measurements in a singular system     

《Geodinamica Acta》2013,26(2):61-79

Abstract

Gullies developed on sandy lithologies are scarce and few studies have been reported on these landscapes. This paper presents an approach to study such singular landforms. The studied gullies appear on the slopes of a group of mesas and cuestas of Upper Cretaceous sediments located in the Northern piedmont of the Guadarrama Mountains, Spain.

Landforms of these gullied areas were catalogued, characterized and quantified with reconnaissance methods, providing information about the most active geomorphic processes. These are being monitored in a 1.32 ha representative gullied catchment, the Barranca de los Pinos. In its high gradient slopes, where mass movements occur, high resolution topographical surveys are being carried out by Terrestrial Laser Scanning (TLS). On low gradient slopes, runoff and rain splash are being monitored in micro plots; and in the main channel, sediment transport and water discharge are being measured.

This ensemble of methods, some of them novel, is providing patterns of sediment movement within the gully system, and a hypothesis of high activity rates has been confirmed. High gradient sand slopes without carbonate caprock erode fourfold compared to the capped slopes. In the low gradient slopes, those ungullied produce more runoff while exposed sands yield more sediment; sands covered by litter produce the least runoff and sediment. Notably, this catchment yields mainly bedload.

© 2011 Lavoisier SAS. All rights reserved  相似文献   

Water and sediment balances of a contour bench terracing system in a semi-arid cultivated zone (El Gouazine,central Tunisia)     

《水文科学杂志》2013,58(4):883-892

Abstract

Contour benches are earthen structures constructed across cultivated slopes, at intervals down the slope, largely used in semi-arid zones. The results of an experiment to monitor water and sediment balance inside a contour bench terrace system are presented. The study site, located in the El-Gouazine watershed (central Tunisia), includes two terraced plots of approximately 3000 m², one of which was left fallow for several years, while the other was tilled. The characteristics of rainfall—runoff processes and erosion inside both terraced plots during a two-year period (2004–2006) are described. Ploughing reduced runoff by 75%. Erosion was monitored following runoff episodes that produced observable deposits in the bench channel. After ploughing, erosion was reduced by 44% between July 2004 and July 2005 and by 50% between October 2005 and July 2006. However, erosion per millimetre of runoff was about twice as great on the tilled soil as on the fallow. Even though ploughing weakens the soil, it seems to reduce erosion by increasing infiltration. For the studied rain events, ploughing used in combination with contour bench terraces seems to have limited erosion and enhanced the effectiveness of contour bench terrace management.  相似文献   

Sediment yield variability in central Tunisia: a quantitative analysis of its controlling factors     

Imen Ayadi  Habib Abida  Yassin Djebbar  M. Raouf Mahjoub 《水文科学杂志》2013,58(3):446-458

Abstract

This paper refers to the quantification and prediction of the sedimentation rate of 26 hillside-dam reservoirs in Central Tunisia. The objectives of the study are to develop a simple and practical methodology to identify controlling factors of sedimentation, and to propose a regionalization from the study sites. Principal component analysis (PCA) and complementary multi-dimensional statistical methods are used to relate highly variable area-specific sediment yield to hydro-morphometric, lithological, geomorphological and anthropogenic characteristics of catchments. It appears that catchment area is not the main controlling factor of sedimentation in the studied area. The overall slope index, drainage network characteristics and runoff parameters are also important in characterizing sediment yield. Applied to the annual sedimentation rate series, PCA resulted in retaining the first three principal axes, explaining 65% of the total variance. Statistical methods showed that the overall slope index, the total drainage length, the compacity index and the runoff parameters are as important for the sedimentation quantification. This allowed a graphical clustering of the study zone into three distinct groups having similar behaviours: (i) watersheds characterized by high sediment transport rates and high runoff coefficients, (ii) basins distinguished by relatively low values of both flow discharge and sediment transport rates, and (iii) watersheds with an intermediate sediment yield, especially characterized by relatively high relief. In a second step, a multiple regression model including the four characteristic catchment properties was developed, presenting a valuable tool to predict area-specific sediment yield from catchments in central Tunisia. This model shows reasonable efficiency with an absolute prediction error of 81%.

Citation Ayadi, I., Abida, H., Djebbar, Y. & Mahjoub, M. R. (2010) Sediment yield variability in central Tunisia: a quantitative analysis of its controlling factors. Hydrol. Sci. J. 55(3), 446–458.  相似文献   

Spatial soil loss risk and reservoir siltation in semi-arid Tunisia     

Sihem Jebari  Ronny Berndtsson  Akissa Bahri  Mohamed Boufaroua 《水文科学杂志》2013,58(1):121-137

Abstract

Soil erosion vulnerability and extreme rainfall characteristics over the Mediterranean semi-arid region of Tunisia are crucial input for estimation of siltation rate in artificial reservoirs. A comprehensive high-resolution database on erosive rainfall, together with siltation records for 28 small reservoirs, were analysed for this region, the Tunisian Dorsal (the easternmost part of the Atlas Mountains). The general life-span of these reservoirs is only about 14 years. Depending on the soil degradation in the different catchments, the corresponding reservoirs display a wide range of soil erosion rates. The average soil loss was 14.5 t ha^?1 year^?1 but some catchments display values of up to 36.4 t ha^?1 year^?1. The maximum 15-min duration rainfall intensity was used to determine the spatial distribution of rainfall erosivity. The northwestern parts of the Tunisian Dorsal display the most extreme rainfall erosivity. Spatial erosion patterns are to some extent similar; however, they vary greatly according to their location in the “soil degradation cycle”. This cycle determines the soil particle delivery potential of the catchment. In general, the northwestern parts of the Dorsal display modest soil erosion patterns due to the already severely degraded soil structure. Here, the soil surface is often the original bedrock. However, the greatest soil erosion occurs in the mid-eastern parts of the Dorsal, which represents the “degradation front”. The latter corresponds to the area with highest erosion, which is continuously progressing westward in the Dorsal. The large variation between the erosive rainfall events and the annual soil loss rates was explained by two important factors. The first relates to the soil degradation cycle. The second factor corresponds to the degradation front with the highest soil loss rates. At present this front is located at 300 m altitude and appears to be moving along an 80-km westward path starting from the east coast. A better understanding of the above can be used to better manage soils and soil covers in the Tunisian Dorsal area and, eventually, to decrease the soil erosion and reservoir siltation risk.

Citation Jebari, S., Berndtsson, R., Bahri, A. & Boufaroua, M. (2010) Spatial soil loss risk and reservoir siltation in semi-arid Tunisia. Hydrol. Sci. J. 55(1), 121–137.  相似文献   

Apports de la sismique réflexion à l'étude de l'aquifère du Continental Intercalaire du Jérid (Tunisie)     

R. Guellala  H. Ben Marzoug  M. H. Inoubli  L. Moumni 《水文科学杂志》2013,58(6):1040-1052

Résumé

De nombreux travaux de recherche pétrolière par sismique réflexion et sondages profonds ont été réalisés en Tunisie méridionale. La présente étude concerne la réinterprétation de ces données dans le secteur du Jérid en vue d'appréhender la géométrie et le fonctionnement de l'aquifère du Continental Intercalaire (CI), cible potentielle pour l'alimentation en eau. Pour ce faire, nous avons identifié sur les différentes sections sismiques le réflecteur correspondant à la dolomie aptienne qui marque le toit de l'aquifère. Elaborée en conséquence, la carte des isochrones de cet horizon montre l'influence de la tectonique sur la géométrie du CI dans le Jérid. Le plissement des séries du Crétacé inférieur, la réactivation des accidents NE–SO et E–O en failles inverses et le jeu normal des accidents NO–SE sont à l'origine d'un aquifère compartimenté en blocs soulevés et affaissés. Les coupes géosismiques révèlent que cette structuration a des implications sur la profondeur des réservoirs et la circulation des eaux souterraines. Les résultats obtenus permettent de rationaliser les travaux de recherche hydrogéologique qui seront ultérieurement menés dans le secteur du Jérid.

Citation Guellala, R., Ben Marzoug, H., Inoubli, M. H. & Moumni, L. (2011) Apports de la sismique réflexion à l'étude de l'aquifère du Continental Intercalaire du Jérid (Tunisie). Hydrol. Sci. J. 56(6), 1040–1052.  相似文献   

Aptian palaeoclimates and identification of an OAE1a equivalent in shallow marine environments of the southern Tethyan margin: Evidence from Southern Tunisia (Bir Oum Ali section,Northern Chott Chain)     

《Cretaceous Research》2014

Alternations between siliciclastic, carbonate and evaporitic sedimentary systems, as recorded in the Aptian mixed succession of southern Tunisia, reflect profound palaeoceanographic and palaeoclimatic changes in this area of the southern Tethyan margin. The evolution from Urgonian-type carbonates (Berrani Formation, lower Aptian) at the base of the series, to intervals dominated by gypsum or detrital deposits in the remainder of the Aptian is thought to result from the interplay between climate change and tectonic activity that affected North Africa.Based on the evolution of clay mineral assemblages, the early Aptian is interpreted as having been dominated by slightly humid conditions, since smectitic minerals are observed. Near the early to late Aptian boundary, the onset of a gypsiferous sedimentation is associated with the appearance of palygorskite and sepiolite, which supports the installation of arid conditions in this area of the southern Tethyan margin. The evaporitic sedimentation may have also been promoted by the peculiar tectonic setting of the Bir Oum Ali area during the Aptian, where local subsidence may have been tectonically enhanced linked to the opening of northern and central Atlantic. Stress associated with the west and central African rift systems may have triggered the development of NW–SE, hemi-graben structures. Uplifted areas may have constituted potential new sources for clastic material that has been subsequently deposited during the late Aptian.Chemostratigraphic (δ¹³C) correlation of the Bir Oum Ali succession with other peri-Tethyan regions complements biostratigraphic findings, and indicates that a potential expression of the Oceanic Anoxic Event (OAE) 1a may be preserved in this area of Tunisia. Although the characteristic negative spike at the base of this event is not recognized in the present study, a subsequent, large positive excursion with δ¹³C values is of similar amplitude and absolute values to that reported from other peri-Tethyan regions, thus supporting the identification of isotopic segments C4–C7 of the OAE1a. The absence of the negative spike may be linked to either non preservation or non deposition: the OAE1a occurred in a global transgressive context, and since the Bir Oum Ali region was located in the innermost part of the southern Tethyan margin during most of the Aptian, stratigraphic hiatuses may have been longer than in other regions of the Tethys. This emphasizes the importance of integrating several stratigraphic disciplines (bio-, chemo- and sequence stratigraphy) when performing long-distance correlation.  相似文献