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The authors designed and developed this field guidebook and associated posters for field seminars they organised and led in Jabal Nafusa from 2005 to 2009. The aim was to introduce geoscientists working for the petroleum industry to the Mesozoic geology of Jabal Nafusa, of the Jifarah arch, NW Libya.

Le but de cet article est de démontrer l'existence d'horizons atériens chronologiquement,echnologiquement et typologiquement différents, qui représentent divers groupes culturels adaptés àconditions de milieu variées dans la Libye septentrionale et méridionale. Bien que certaines techniques et outillages communs appairassent sur un territoire étendu, ils sont séparés par de dizaines de millénaires. Il est probable que les populations atériennese sont organisées socialement de manière isolée. Un tel système pourrait expliquer la longue durée des traditions technologiques du MSA ancien à I'Atérien nord-african tardif et pourrait justifier leur diffirsion à un rythme très lent sur ce vaste territoire

Carbonate and clastic sediments of Jurassic and Cretaceous age are exposed along the fault-scarp of Djebel Nefusa in north-western Libya. Previous geological investigations have been mainly restricted to the eastern sector of the scarp. Recent studies by the authors in the western sector of Djebel Nefusa and on equivalent sediments in southern Tunisia have allowed the first regional interpretation of these rocks. The area studied lies geographically and geologically at the edge of the Saharan Platform, a large cratonic block, composed of rocks of Precambrian-Palaeozoic age. To the north and east lies a downfaulted sedimentary basin (Gabes-Sabratha Basin) containing a large thickness of Mesozoic sediments. The location of the sections measured along Djebel Nefusa are depicted in Fig.1. The stratigraphic nomenclature of the rock succession of Djebel Nefusa was first established in the east and continued laterally towards the west by later workers. Difficulties in the application of this nomenclature are presented by the recognition of facies changes previously overlooked by earlier investigators. However, as a framework for understanding these changes and the sedimentary processes which caused them, the stratigraphy erected by Magnier (1963) is adopted.

Paleomagnetic and K/Ar whole rock absolute age data are described for material from the Garian area of Libya, centered at 13°E, 32°N. Within-unit cleaned paleomagnetic directions from the essentially unaltered lavas are very well defined and can almost certainly be taken as reliable measurements of the geomagnetic field direction during the initial cooling of each flow. However, the distributions of mean direction, from which the effect of repeated sampling of the field at one time has been removed, does not suggest that a reversing axial dipole field has been recorded in a representative manner. Both N and R groups of directions are azimuthally elongated, and the average poles for the N and R groups differ by 21°, or four times the 95% level uncertainty for each average pole. A number of possible physical explanations for the paleomagnetic results are discussed. The conventional overall average pole at 88°N, 123°E, δp: 3°, δm: 7 °does not differ significantly from the geographic pole, a result which agrees closely with that of Schult and Soffel (1973). However, the value of these overall average poles in estimating absolute plate motion must await an understanding of the sources of the asymmetries in the paleomagnetic data.

The mineralogic-petrographical character of the raw materials of the Late Palaeolithic/Neolithic stone industries, collected at several open air-sites in the area of Jabal Nefusa, have been studied and the origin of the raw materials have been recognized. Two types of Upper Cretaceous (Nalut Formation) cherts (the coloured and the striped ones), used for the manufacture of implements, have been distinguished. They may be considered either local or short-distance imported raw materials.

Abstract The Quaternary deposits of the Gefara Plain are comprised of three major facies – alluvial fan facies of sands and gravels which blankets the base of the Jebel Nafusa escarpment; floodplain facies of fluvial sands and silts with aeolian dunes which underlies most of the Gefara Plain and, aeolian coastal dune facies, predominantly calcarenitic, which is confined to a narrow coastal zone. Well exposed sections in the eastern part of the plain allow sub-division of the floodplain deposits into a number of mappable units defined and bounded by surfaces of stratigraphic discontinuity. The lithologies of these units are described and compared from selected type sections. The relationships between the units, their geometry, and the nature of the surfaces of stratigraphic discontinuity are discussed. It is proposed that, the lithostratigraphic sequence displayed by the Quaternary floodplain deposits of the eastern Gefara region provides a firm basis for correlation, not only with floodplain deposits in other parts of the plain but also with the other major facies developed in the area. In addition, the recognition of significant stratigraphic breaks in the sedimentary sequence combined with facies analysis lays a firm foundation for an interpretation of the geological history of the region.

In recent years basic regional geological mapping of northern Libya by the Industrial Research Centre, Tripoli, together with the UNESCO Libyan Valleys Survey of eastern Tripolitania and the work of the author and Dr S. M. Ghellali in the Jifarah Plain and Jabal Nafusah, have greatly added to our knowledge of Quaternary deposits in the region. This work is described and evaluated against the background of earlier studies. The succession of major depositional, soil forming and erosional events which characterise the fluvio-aeolian deposits of the Jifarah Formation can be recognised in, and thus used to subdivide, laterally equivalent aeolianite, fangravel and wadi gravel deposits in the Jifarah Plain. Comparisons of this succession with others from throughout the region indicate that the events are of regional significance and that the Jifarah sequence provides a sound framework for lithostratigraphic correlation and a basis for facies analysis and chronostratigraphic studies. This review is largely limited to the northern margins of Libya north of the 30th parallel (Fig. 1). It is convenient to subdivide the zone into several regions. These are: (a) The Jifarah Plain and foothills of the Jabal Nafusah. (b) The Hammada Al Hamra Plateau and major valleys of eastern Tripolitania. (c) The coastal region from Misratah to Ajdabiyah. (d) Cyrenaica from Soluq to Al Bardia.

Major and trace element data of Jabal Nafusah phonolites are compared with those of other phonolitic provinces: Rhoen, Hegau and Kaiserstuhl (West Germany); Massif Central and Velay (France); and - with data from the literature - Kenyites and other phonolites of Kenya. In this geochemical comparison the character of the Jabal Nafusah phonolites can be specified exactly. Additional new analytical data are given for the elements Nb, U, Th, F, S and Cl. Between Zr, Nb, U and Th there are positive correlations. Plots of Rb versus Nb, and particularly Nb versus Zr reveal "fans", illustrating the individual differentiation trends of the distinct phonolite provinces. A plot on hyperbolic axes brings the data of the diverging fan to a common curve. Each province occupies its own field on this diagram; the Jabal Nafusah phonolites are situated in an extreme position. On triangular plots it can be shown that the Jabal Nafusah phonolites are enriched (relative to other elements) in Al, Na, Fe, Ca, K, Ti, Zr, F, Cl and Th as compared with other phonolitic provinces; but depleted in Mg, S, Nb and P.