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   

Albian oceanic anoxic events in northern Tunisia: Biostratigraphic and geochemical insights   总被引：1，自引：0，他引：1  

Moez Ben Fadhel  Mohsen Layeb  Afif Hedfi  Mohamed Ben Youssef 《Cretaceous Research》2011,32(6):685-699

Albian pelagic successions of the Nebeur area in northwestern Tunisia consist of radiolarian-bearing and organic-rich black shale beds, which represent the lower part of the Fahdene Formation. The carbonate content of the organic-rich beds ranges between 40 and 48%. Total organic carbon (TOC) analyses via Rock Eval pyrolysis yielded values ranging between 0.7 and 2.8% and a mixed marine/terrestrial origin. T_max values vary between 424 and 450 °C, indicative of submature to mature organic matter. High resolution planktic foraminiferal and radiolarian biostratigraphy suggest that the black shales beds span the mid- to late Albian, confined to the middle part of the Ticinella primula zone, upper Biticinella breggiensis zone and lower appeninica + buxtorfi zone. Episodes of organic-rich deposition in the “Tunisian Trough” are interpreted as being the sedimentary record of the global oceanic anoxic events OAE1b, c, and d respectively. Age-diagnostic radiolarian assemblages recovered from late Albian organic-rich black shales lie within the UA13–UA14 boundary biochronozones. The abundance of radiolarian and calcispheres (i.e. pithonella) within the black shales suggests high productivity periods and eutrophic conditions probably triggered by upwelling currents.  相似文献   

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (δC, δN and δD) as environmental tracers     

Francisco Ramírez  Aida Abdennadher  Carola Sanpera  Lluís Jover  Leonard I. Wassenaar  Keith A. Hobson 《Estuarine, Coastal and Shelf Science》2011

Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ¹³C, δ¹⁵N and δD measurements of a euryhaline fish, the Mediterranean toothcarp (Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern (Sternula albifrons) and Little Egret (Egretta garzetta), was inferred trough a triple-isotope (δ¹³C, δ¹⁵N and δD) Bayesian mixing model. Isotopic trends for fish δ¹⁵N and δD across the salinity gradient followed the equations: δ¹⁵N = e^{(1.1 + 47.68/Salinity)} and δD = −175.74 + Salinity + Salinity²; whereas fish δ¹³C increased as salinity rose (δ¹³C = −10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ¹³C for salinities <60 = −5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.  相似文献   

Temporal and spatial changes of the submarine Cretaceous paleoslope in Northern Tunisia,inferred from slump folds analysis     

Chahreddine Naji  Mohamed Gharbi  Amara Masrouhi  Olivier Bellier 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(1):40-56

This paper presents the first comprehensive, non-exhaustive, study of the genetic relationship between slump folds and the synsedimentary paleoslope during Cretaceous time in northern Tunisia. Slump folds occur mainly in the Cretaceous marl-dominated lithofacies, which exposes numerous slump folds structures. In addition, fault kinematic analysis is conducted to define the paleostress fields and the stress states characterizing the Cretaceous extension that triggers soft-sediment deformation and slumping. The MAM and the APM methods are used to deduce the paleoslope in several localities. The calculated values of paleoslope trend derived from MAM and APM methods precise the variation of the paleoslope trend during Cretaceous times in northern Tunisia. This paleoslope is ～NW-dipping during Berriasian, ～SSW-dipping during Valanginian, ～NW-dipping during the Barremian and ～N- to ～NNE or ～S- to ～SSW-dipping during Aptian–Albian period. The results of the back-tilted fault diagram show a ～North to ～Northeast-trending tectonics extension. The back-tilting of Cenomanian slump axis and poles of axial planes (MAM and APM methods) give close results with ～Southward or ～Northward-dipping paleoslope. The restored fault diagrams show ～North to ～Northeast-trending extension during Cenomanian times. Coniacian-Santonian marls deposits seal all the gravity-driven deformation structures. North Tunisian area exposes evidences for abundant soft-sediment deformation and slumping atop a northward facing submarine slope, which was probably dominant from the Early Cretaceous to Santonian with ～North-South tectonic extension related to the Southern Tethyan rifted continental margin evolution.  相似文献   

Spatial scale variability in shoot density and epiphytic leaves of Posidonia oceanica on Kerkennah Island (Tunisia) in relation to current tide effects          下载免费PDF全文

Mounir Ben Brahim  Lotfi Mabrouk  Asma Hamza  Mabrouka Mahfoudhi  Abderahmen Bouain  Lotfi Aleya 《Marine Ecology》2015,36(4):1311-1331

A study was undertaken of the patterns of spatial variability, epiphytic biomass and distribution of epiphytic fauna and flora of Posidonia oceanica. Samples were taken at four stations located approximately 4 km apart, exposed to different current conditions. Stations A and B, situated near the Oued Mimoun tidal channel with its relatively strong bi‐directional flows, were affected by high current tide. The other two stations, North Oued Mimoun (L1) and South Oued Mimoun (L2), were located further from the channel, in low current tide conditions. Sampling was conducted in the Attaya area of Kerkennah Island (Tunisia) in August 2009 at depths between 2 and 3 m, with the results indicating differences among the stations. Shoot density decreased when exposed to high levels of hydrodynamic activity generated by current tides whereas the epiphytic biomass of P. oceanica leaves decreased at sheltered stations located far from the channel. Epiphytic algae such as Heterokontophyta, Rhodophyta and Chlorophyta, and epiphytic fauna represented by Bryozoa, Hydrozoa, Annelida, Porifera and Tunicata, dominated the epiphytic assemblages and were abundant at the station most exposed to high current tide hydrodynamics. Cyanobacteria, however, were dominant in stations exposed to low current tide.  相似文献   

Saltwater intrusion modelling in Jorf coastal aquifer,South‐eastern Tunisia: geochemical,geoelectrical and geostatistical application     

Belgacem Agoubi  Adel Kharroubi  Habib Abida 《水文研究》2013,27(8):1191-1199

Marine intrusion is the most serious problem facing the coastal Jorf shallow aquifer, located in south‐eastern Tunisia on the Mediterranean Sea. Jorf Aquifer is intensively exploited to supply the growing needs of agriculture and domestic sectors. This work proposes a multidisciplinary investigation, involving hydro‐geochemical, geoelectrical survey and geostatistical techniques for modelling the saltwater intrusion. For this purpose, 36 water samples were conducted and analysed. Electric conductivity, pH, total dissolved solids and major ions were measured and analysed. Pie and Durov Diagrams, Q‐mode hierarchical cluster and geostatistical analysis were considered to identify the main groundwater mineralization processes. Results revealed that the Na‐Cl‐Ca‐SO₄ is the dominant water type suggesting that dissolution of halite and gypsum was the main mineralization source of groundwater in the central and southern part of study area. However, saltwater intrusion was shown to control groundwater quality essentially in coastal areas. Variographic analyses were used to select the variographic model that best fits the spatial development of apparent resistivity. Kriged apparent resistivity profiles showed an abnormal decrease of resistivity values in the coastal zone, implying highly saline water because of seawater intrusion. Apparent resistivity values also decrease considerably in the faulted areas, suggesting a contribution of faults to seawater intrusion. Finally, saltwater mixing ratio was computed for each sample, and a refined seawater intrusion map was developed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Investigation of the rainfall variability in central Tunisia / Investigations sur la variabilité pluviométrique en Tunisie centrale     

《水文科学杂志》2013,58(3)

Abstract

The decrease in runoff of the Merguellil basin, Tunisia recorded during the decade 1989–1998 led to the study of several time series derived from daily rainfall. It was found that variability characteristics related to daily rainfall greater than 30 mm are significantly different among successive time periods. In addition, the probability distributions of these rains, recorded at different raingauge sites, are significantly different between the period 1976–1989 and the prior and posterior observation periods. Furthermore, the surface covered by daily rains greater than 30 mm decreased between 1976 and 1989. It was also noted that the probability distributions of the surfaces covered changed significantly after 1976. The combination of human action and pluviometric variability (rainfall increase in the period 1989–1998, notably the increase in the number of days of rainfall greater than 30 mm) may explain the decrease in runoff of Merguellil Wadi.  相似文献   

The sandy beach macrofauna of Gulf of Gabès (Tunisia)     

Silvia Pérez-Domingo  Carolina Castellanos  & Juan Junoy 《Marine Ecology》2008,29(S1):51-59

This study describes the macrofauna of the three beaches situated in central Gulf of Gabès (Tunisia): Ouderef, Gabès and Zarrat. The Gulf of Gabès has the largest tides in the Mediterranean and the beaches showed a wide intertidal zone. The beaches were sampled once during the spring low tides of June 2005. A transect was extended at each beach, from above the drift line to below the swash line at five sampled levels; at each level six 0.05 m² replicates were taken to a depth of 30 cm and sieved through a 1-mm mesh, and the organisms collected and preserved. The three beaches showed a different physical environment. Sediment type was medium sand at the steeper Ouderef beach, fine sands at Gàbes beach, and very fine sands at the flatter Zarrat beach. The total number of species collected was 31: 12 crustaceans, 10 polychaetes, four molluscs and five insects. The supralittoral and mediolittoral zones were very different. The supralittoral zone was dominated by Talitrus saltator and insects. The most abundant mediolittoral species were the amphipod crustacean Bathyporeia guilliamsoniana at Ouderef beach (23069 ind.m⁻¹), the surf clam Donax trunculus at Gabès beach (60711 ind.m⁻¹) and the spionid polychaete Scolelepis mesnili at Zarrat beach (18345.6 ind.m⁻¹).  相似文献   

Study of a Neogene basin dynamics: The “Bizerte basin”, northeastern Tunisia: relevance to the global Messinian Salinity Crisis     

Salah Harrab  Beya Mannai-Tayech  Mohsen Rabhi  Fouad Zargouni 《Comptes Rendus Geoscience》2013,345(5-6):251-261

The Messinian sediments of northeastern Tunisia were deposited under an active tectonic setting. They are organized in sequences indicating a transitional deposit from margin – littoral to lacustrine – continental facies. These series unconformably overlie the Serravallian–Tortonian silty clays packages, and are overlain by the transgressive Early Pliocene marl (Zanclean). The presence of evaporitic strata points out to the Messinian Salinity Crisis described in the peripheral basins of the western Mediterranean. The Messinian sedimentation was found to have been closely controlled by transtensive tectonics and differential subsidence at a large spatio-temporal scale. It is organized in sequences typical of a depositional environment controlled by eustatism, tectonic and maybe by climate changes. Despite the existence of some local specific sedimentological characteristics, our results corroborate previous findings that pointed out to the Messinian times as a singular period all around the Mediterranean Basin. Field and subsurface seismic profile data helped reconstructing either the sedimentary or tectonic unconformities existing between the studied Messinian series and older Neogene successions.  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