Search

In the present paper a multi-technique approach was followed in order to study the diagenetic alterations of fifteen fossil bones derived from the Miocene site of Sahabi in NE Libya. Specifically, X-ray Diffraction (XRD) supplemented by the Rietveld method, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDS), Electron Probe Microanalysis (EPMA) and Fourier Transform Infrared Spectroscopy in the Mid-IR (FTIR, Mid-IR), were performed on fossilized bone fragments belonging mainly to artiodactyl mammals. From the qualitative observation of bone histology by means of SEM, a moderate preservation of the internal bone morphology and limited microbial attack were inferred. The high percentage (wt.%) of F concentration that the EPMA analyses yielded, combined: (a) with the absorbance bands of carbonate anions in the FTIR spectra and (b) the structural parameters calculated by the Rietveld method, revealed the partial substitution of F − for OH− and CO32− for PO43− in the apatite structure. As a result, one of the basic diagenetic trends was the preservation of the inorganic part of the studied samples as carbonate fluorapatite . Additionally, according to our infrared spectra , CO 32− substituted for OH− and a carbonate species known to be labile was also present. Apart from F, EPMA also detected S and Fe. Sulfur speciation was studied by micro-XANES, that confirmed the presence of S6+ (sulfates). Iron speciation was investigated with Mossbauer spectroscopy , which indicated the possible presence of goethite-type (FeOOH) submicroscopic inclusions. In nearly all specimens, quartz and gypsum were identified as the main secondary phases.

A revision of the nomenclature of lithostratigraphic units of Neogene strata at As Sahabi, northeast Libya, is presented, based on new fieldwork conducted during 2006–2008. The Sahabi units are correlated across the Ajdabya Sheet (NH 34-6) in northeastern Libya. Major conclusions are: (1) Miocene (Langhian through Messinian) strata are predominantly carbonate and should be referred to as formation “M”; (2) A local unconformity of Miocene (early Messinian) age overlies strata of the formation “M”; (3) This unconformity is overlain by Messinian gypsiferous sand and mud (formerly formation “P” and partially member “T”), which are designated as the “lower member” (gypsiferous) of the Sahabi Formation; (4) The “lower member” is overlain by sand and mud of late Messinian age (formerly partially member “T” and members “U1”, “UD”, and “U2”) in a generally fining-upwards sequence, and are designated as the “upper member” (non-gypsiferous) of the Sahabi Formation; (5) The latest Miocene sand and mud of the “upper member” are capped by an unconformity that is correlated with the regression and desiccation of the Mediterranean Sea during the Messinian Salinity Crisis and with Eosahabi Channel cutting; (6) The unconformity is overlain by Pliocene medium, coarse, and pebbly sands, which are referred to as the Qarat Weddah Formation (formerly Garet Uedda Formation); (7) The Pliocene sands of Qarat Weddah Formation are overlain by carbonate soil (calcrete) of Late Pliocene age, which is referred to as formation “Z” (formerly member “Z”). The major outcome of this study is a revised stratigraphic description and nomenclature of the Sahabi units that helps to provide a formal and unified context for understanding paleontological discoveries in northeastern Libya, which will serve to facilitate a broader correlation of the Sahabi units with their equivalents elsewhere in Africa and in Europe and Asia.

Recent excavations and prospecting in the early to middle Miocene deposits of the Maradah Formation in Jabal Zaltan, Libya, yielded a diverse fish assemblage coming from an early Miocene locality. The material described here includes more than 18 marine and freshwater taxa most of which were previously unreported from the area. Jabal Zaltan is one of the very few early Miocene Afroarabian fossil sites that produced such a diverse fish sample. Therefore, the fossils described here provide a unique insight into the composition of the early Miocene fish faunas from the northern African coast; a critical time period for faunas of the continent, as contact with Eurasia ended 100 million years of African isolation. In addition, the Jabal Zaltan fossils help consolidate the validity of Galeocerdo mayumbensis and extend its geographic range to include the Tethys. The Maradah deposits also host the first occurrences of two genera (Pteromylaeus, Distichodus) in the fossil record. The fish finds support the presumed depositional environment that of tropical shallow estuarine to deltaic conditions, and the freshwater fishes document the presence of a modern-type Nilosudanian fauna containing elements with both African and Asian affinities. The Jabal Zaltan ichthyofauna, with its diversity of taxa, has the potential to become a key reference fauna for future studies of early Miocene African fishes.

A large paleo-river of Miocene age traversing Libya from south to north has been previously demonstrated by seismic, stratigraphic, paleontological, and remote sensing data. The depositional environment of As Sahabi Formation in north central Libya is this large and now extinct Eosahabi River. However, the source of this major African river has remained controversial. Dark-colored sedimentary material with magnetic properties suggested a source from the basaltic Haruj as Aswad massif in south central Libya. To test this hypothesis, mineralogical and geochemical study of clayey sediments from three localities, P25, P28 and P96c, from fossiliferous Member U1 of the As Sahabi Formation, were carried out. Results strongly indicate very mature and re-processed sediments of continental origin, and felsic sources with no basaltic contribution. Thus the origin can be traced to an upland area of outcrop of rocks of Precambrian continental origin in northeastern Chad. An alternative scenario is that the Sahabi sediments originated from Precambrian outcrops in Ethiopia through an east–west river connection with the Nile. We consider this hypothesis unlikely, since it is based only on remote sensing data, and lacks any time control or geological supporting evidence. The abundant vertebrate fauna from the Sahabi Formation shows strong similarities with penecontemporaneous fossil faunas in Chad and is supportive of an origin of the Eosahabi River in Neogene mega-Lake Chad.

Fossils recently found in the Late Miocene of Sahabi, Libya, are attributed to the extinct species Semlikiichthys rhachirhinchus. This study enriches our knowledge of the anatomy of this species. The hyomandibula and, putatively, the operculum are for the first time attributed to Semlikiichthys. The fragile laminar supraoccipital crest in the dorsicranium is preserved complete. The material from Sahabi described here extends the Late Miocene distribution of the species to the north and west to include Libya. The paleobiogeographic distribution of Semlikiichthys in Africa, and the freshwater faunal connections between different hydrographical basins in north central Africa, are discussed.