Species Composition and Some Ecological Notes on Diatom Communities of a Lotic Environment in Tarhunãh,Libya Artenzusammensetzung und einige ökologische Notizen über Diatomeengesellschaften eines lotischen Biotops in Tarhunãh/Libyen

Libya occupies a large part of the Sahara Desert, and is a predominantly arid country with extremely scarce freshwaters. Despite aridity, a distinct higher rainfall zone exists along its mediterranean coastal belt. A lotic environment (perennial stream) in Ain-Scersciara, Tarhunãh in northwest Libya was studied for the species composition of diatom communities and their ecological characteristics. The waters are generally alkaline (pH = 7.5) and of hard-water (conductivity = 2008 μS/cm) type. The epiphytic diatom growth on benthic filamentous algae was high (32 taxa) with Amphora veneta as a very common taxon. Gomphonema parvulum var. micropus was an important taxon found in scrapings from the leaves of macrophytes and stony substratum. Nitzschia and Navicula showed high species richness (9 taxa in each) followed by Gomphonema (6 taxa). The ecological attributes of the majority of taxa show an oligohalobe status and alkaliphilous indicator.     

Multiple phases of North African humidity recorded in lacustrine sediments from the Fazzan Basin, Libyan Sahara

The Fazzan Basin of south-west Libya is at present arid with less than 20 mm of rainfall per annum. However, regionally extensive limestones, lacustrine sands and coquina (fossiliferous carbonate rock) deposits show that the Fazzan Basin previously contained a large palaeolake, indicating that the climate in the past was more humid. Optically stimulated luminescence (OSL) dating techniques have been applied to key lacustrine deposits within the basin in an attempt to provide an internally consistent chronology for this humidity record. Results indicate that palaeolake sediments within the Fazzan Basin record a very long history of palaeohydrological change, ranging from present day arid conditions to humidity capable of sustaining a lake with an approximate area of 76,250 km². The existence of humid periods in mid oxygen isotope stage 5 and the early Holocene is confirmed. An older lacustrine event, tentatively correlated to oxygen isotope stage 11, is also recognized. In addition, evidence is presented for at least two humid phases beyond the age range over which the conventional OSL dating technique is applicable. This study demonstrates that OSL dating of palaeolake sediments within the Fazzan Basin offers the potential to provide a detailed record of North African humidity spanning several glacial–interglacial cycles.     

Integrating data from remote sensing,geology and gravity for geological investigation in the Tarhunah area,Northwest Libya

Abstract

The present work deals with the integration of remote-sensing, surface-geology and gravity-survey data to improve the structural knowledge of the Tarhunah area, northwest Libya. Geological information and remote-sensing data provided information about the surface structure. A gravity survey was conducted to decipher the subsurface structure. The results revealed that a basin having a width of 39 to 48 km trends NE. A two-dimensional (2-D) schematic model shows that the basin gradually deepens toward the southwest. Faults determined from a horizontal gradient, tilt derivative, and Euler deconvolution show a depth range of 2.5 to 7.5 km. The integration and interpretation of the results indicate that volcanic activity was related to the tectonic activity of an anticlinal structure called the Jabal Uplift.     

Ecophysiological Studies on Size-fractionated Phytoplankton Populations by Tracer Technique in Wadi el Majanin Dam,Libya

Wadi el Majanin, one of the largest hydraulic structures in Libya was studied for ecophysiological aspects in relation to ambient environment. The waterbody is alkaline (pH=7.2) and characteristic of hydrogen-carbonate (144.8 mg L^–1 CaCO₃) system. Vertical extinction coefficients (> 4.8) indicate very high (biogenic) turbidity. Conspicuous variations of a quantitative kind in algal development (e.g., Pediastrum bloom) together with abundant diatom populations (chlorococcales-diatom assemblage), apart from very common occurrence of cyanobacteria and euglenoids show eutrophic water condition. Winter-summer alternation induced pronounced seasonal variability in the rates of in situ planktonic algal photosynthetic activities (285.7...1305 mg m^–3 d^–1 C). Dark fixation activity, attributed largely to bacterial production, oscillated by order of 2-fold magnitude, characterized by summer maxima (47.6 mg m^–3 d^–1 C). Size-fractional analysis established that smaller forms (< 60 μm), broadly regarded nanno-phytoplankton, frequently dominated (c. 70%) overall algal productivity.     

Integrated remote sensing data utilization for investigating structural and tectonic history of the Ghadames Basin,Libya

This study was initiated to constrain the geological structure of the Ghadames Basin in northwest Libya. Detailed analysis was based on digital integration of surface data, including SRTM DEM, ETM+ and geologic maps with subsurface data, including well logs and potential field data. Integrated analysis of remotely sensed data of the SRTM and ETM+ were utilized to identify geologic lineaments in the area. Ground-based verification of the remote sensing data was achieved with field work. Interpretation and analysis of the lineaments indicate that the Ghadames Basin is controlled by four main fault systems that trend WNW, NNW, NW and ENE. Well logs and potential field data were used to delineate a detailed picture of the subsurface structure. The potential field data reveal two NE and NNE trending sedimentary basins. The depth of the basement inside the main basin ranges from 2 to 6 km. A two-dimensional (2-D) schematic model shows that the basin gradually deepens towards the southwest. The applied data integration gave new insight into the tectonic and structure patterns of the Ghadames Basin and the adjacent areas of northwest Libya.     

Recent trends of temperature change under hot and cold desert climates: Comparing the Sahara (Libya) and Central Asia (Xinjiang, China)

According to trend computations at three stations each in Sahara desert (Libya), characterized by a “hot” desert type (“BWh”, according to the Koeppen climate classification), and in Central Asia (Xinjiang, China) identified as a “cold” desert type (“BWk”, after Koeppen), increasing annual temperatures were detected over the period 1955-2005 corresponding with global temperature warming. From 1955-1978, negative (decreasing) temperature trends were, however, observed at all three hot desert stations and at two of the three cold desert stations. From 1979-2005, strikingly positive temperature trends were seen at all six stations. In seasonal respects, winter (December to February) and summer (June to August) show different temperature trends over the period 1955-2005: the hot desert experienced an increasing temperature trend at a greater extent in summer than in winter; vice-versa, in the cold desert positive trends were computed for winter and negative for summer. It can also be observed that mostly hot desert warming occurred in summer, opposite to cold desert warming in winter.     

Evaporites, petroleum exploration, and the Cenozoic evolution of the Libyan shelf margin, central North Africa

The Mediterranean margin of Libya can be divided into three physiographic provinces, the Pelagian Shelf, the Sirt Embayment, and Offshore Cyrenaica. The petroleum potential of the Pelagian Shelf has been investigated but the Sirt Embayment and Offshore Cyrenaica are almost unexplored. During 2004–2005, new 2D pre-stack time-migrated seismic data were acquired and used to examine the large-scale structural, depositional, and salt tectonic features of the Libyan shelf and slope. The data cover approximately 38,000 line kilometers in water depths ranging from under 50 to over 3000 m.Cenozoic strata along much of the Libyan margin have a demonstrable progradational character punctuated by surfaces of erosion and margin failure. Within the Sirt Embayment the most visible retrogradational surface becomes seismically coincident with the top of Messinian unconformity. This retrogradational surface extends for over 700 km along strike and cuts both sides of the Sirt Embayment. Over 5000 cubic kilometers of material are missing from above this surface. There are two ideas for how retrogradation occurred. One idea relates the retrogradation to margin erosion during the Messinian salinity crisis. The other idea suggests that a large part of the Libyan margin experienced a cataclysmic failure during the late Miocene.Some existing models for offshore Libya have interpreted a widespread layer of halite lying within the Messinian which thickens basinward. This interpretation was probably based on the fact seismic reflection continuity was lost over much of the Sirt Embayment on older data beneath the top Messinian unconformity. The loss of good reflection character adversely affected exploration efforts by obscuring deep structures. Recent seismic data and a current understanding of salt behavior do not support the interpretation of thick halite within the Messinian section. Regional observations do not indicate any mobile halite present in the Sirt Embayment. There is a relatively thin, high amplitude and high velocity layer of non-halite evaporites (mainly anhydrite) which caps the Messinian section. Where this high amplitude and high velocity layer is absent or eroded, seismic continuity within the Messinian interval is restored. Limited available well data support this interpretation.True mobile halite is interpreted to exist in offshore Libya only in the far west of the Pelagian Shelf near the Tunisian border. Beneath the Pelagian Shelf are a series of tight contractional folds that are interpreted to be salt cored. Basins adjacent to the folds display geometries characteristic of salt withdrawal. The fold crests formed bathymetric highs which served as nucleation sites for nummulitic shoal development. These shoals are the principal reservoirs of the Pelagian Shelf.     

A stratigraphic review of the Eocene to Miocene rock units in the al Jabal al Akhdar,NE Libya

This paper presents a revision of the Eocene to Miocene rock units of al Jabal al Akhdar (northeast Libya), based on the study of several surface sections in the vicinity of Benghazi and on earlier studies. The gradual disappearance of deep water marine fauna during the Early Eocene (Apollonia Formation) combined with gradual appearances of large-sized nummulitids and coarsening upwards of allochems during the Middle Eocene (Darnah Formation) indicate a shallowing-up trend, which continued to the end of the Miocene. Upper Eocene deposits are missing in the Benghazi area. The Al Bayda Formation (Oligocene) rests disconformably on the Middle Eocene Darnah Formation. The lower part of the Shahhat Marl Member (lower member of the Al Bayda Formation) is detrital and contains reworked Eocene Nummulites together with in situ Early Oligocene N. fichteli and N. vascus. The Algal Limestone (upper member of the Al Bayda Formation) represents Wilson's facies SMF 4, 5 and 6. Cyclicity in this member is notable and it appears to be associated with the regressive and transgressive global fourth-order Cycles TA4.3 to TA4.4. The lower part of the Al Abraq Formation is attributed to the transgressive global fourth-order Cycle TA4.5 and the upper part to Cycle TB1.1. The lower and middle parts of the Al Faidiyah Formation are attributed to the Miocene transgressive Cycles TB1.4 and TB1.5, with the upper part a result of sea level lowering related to Cycle TB2.1. Wilson's facies SMF 7 and SMF 8 typify this formation.     

The Kufrah paleodrainage system in Libya: A past connection to the Mediterranean Sea?

Paillou et al. (2009) mapped a 900 km-long paleodrainage system in eastern Libya, the Kufrah River, that could have linked the southern Kufrah Basin to the Mediterranean coast through the Sirt Basin, possibly as long ago as the Middle Miocene. We study here the potential connection between the terminal part of the Kufrah River and the Mediterranean Sea through the Wadi Sahabi paleochannel, which may have constituted the northern extension of the lower Kufrah River paleodrainage system. New analysis of SRTM-derived topography combined with Synthetic Aperture Radar images from the Japanese PALSAR orbital sensor allowed the mapping of seven main paleochannels located west of the Kufrah River, each of which is likely to have formed a tributary that supplied water and sediment to the main paleodrainage system. The northernmost four paleochannels probably originated from the Al Haruj relief, a Pliocene alkaline basaltic intracontinental volcanic field, and potentially connected to the Wadi Sahabi paleochannel. The remaining three paleochannels are in the more southerly location of the Sarir Calanscio, North-East of the Tibesti mountains, and barely present a topographic signature in SRTM data. They end in the dunes of the Calanscio Sand Sea, forming alluvial fans. The most southern paleochannel, known as Wadi Behar Belama, was previously mapped by Pachur (1996) using LANDSAT-TM images, and was interpreted by Osborne et al. (2008) as representing part of an uninterrupted sediment pathway from the Tibesti mountains to the Mediterranean Sea. Processing of SRTM topographic data revealed local depressions which allow to connect the seven paleochannels and possibly the terminal alluvial fan of the Kufrah River to the Wadi Sahabi paleochannel, through a 400 km-long, south-north oriented, paleocorridor. These new findings support our previous hypothesis that proposed a connection between the lower Kufrah River in the region of the Sarir Dalmah and the Wadi Sahabi paleochannel, which connected to the Mediterranean Sea. Including the newly mapped paleochannels, the Kufrah River paleowatershed, at its maximum extent, would have covered more than 400,000 km², representing close to a quarter of the surface area of Libya.     

Biogeography of the Saharan Gretaceous and Paleocene epicontinental transgressions

The first trans-Saharan epicontinental transgression began in the Late Cenomanian and peaked in the Early Turonian. The sea entered through rifts (Nigeria) and subsiding areas (north Africa) and, at maximum extent, spilled out onto stable craton. The central Sahara was land in late Early Turonian time; the sea seems to have remained in the central part of the Benue rift, to sally forth again during the minor Coniacian transgressive pulse. The Coniacian transgression went no further than eastern and central Niger Republic. For a short time during the Cenomanian-Turonian link-up between the Tethys and the South Atlantic, some organisms (mainly ammonites and pelecypods) passed across the Sahara. The Coniacian marine deposits of eastern Niger contain several elements typical of the Mungo River Formation of Cameroun, and coastal Nigeria. These faunistic indications imply that the topographical obstacle formed by the Zambuk ridge of northeastern Nigeria was swamped at maximum transgression. A third, very extensive epicontinental transgression began in latest Campanian time and reached its acme in the Early Maastrichtian. In the central Sahara, at least, there was a retreat of the sea in later Maastrichtian times. A final transgression peaked during the Paleocene, after which the sea withdrew permanently from the northwest African hinterland. The same marine ostracod associations occur in the Paleocene of coastal Nigeria, the Sokoto embayment, Mali and Libya, thus providing strong evidence of a marine connexion, albeit brief, between the South Atlantic and the Tethys, despite the lack of outcrop evidence in the crucial Niger valley region.