Abdulkader M. Abed

Upper Cretaceous (Campanian) phosphorites in Jordan: implications for the formation of a south Tethyan phosphorite giant

A record of sedimentary, authigenic, and biological processes are preserved within the Upper Cretaceous (Campanian) Alhisa Phosphorite Formation (AP) in central and northern Jordan. The AP formed near the eastern extremity of the south Tethyan Phosphorite Province (STPP), a carbonate-dominated Upper Cretaceous to Eocene ‘‘phosphorite giant’’ that extends from Colombia, North Africa to the Middle East. Multidisciplinary research of the AP and associated cherts, chalks, and oyster buildups indicate that phosphatic strata formed on a highly productive, storm-dominated, east–west trending epeiric platform along the south Tethyan margin. The onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the Ajlun Group. Pristine phosphates are associated with well-developed micrite concretionary horizons and contain abundant non-keeled spiral planktic foraminifera and a low diversity benthic assemblage of Buliminacean foraminifera, suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter. The bulk sediment composition and absence of Fe-bearing authigenic phases such as glauconite, pyrite (including pyrite molds), siderite, and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that ‘‘iron-pumping’’ played a minimal role in phosphogenesis. Authigenic precipitation of phosphate occurred in a broad array of sedimentary environments—herein termed a ‘‘phosphorite nursery’’—that spanned the entire platform. This is a non-uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings, wherever the conditions were suitable for phosphogenesis. Sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing, and storm-generated, shelf-parallel geostrophic currents. Economic phosphorites formed through the amalgamation of storm-induced event beds. Stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite. Syndepositional phosphogenesis, reworking, and amalgamation to form phosphorites contrasts sharply with the principles of ‘‘Baturin Cycling’’. A transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis; storm reworking of pristine

Evolving fluvial—transitional—marine deposition through the Cambrian sequence of Jordan

Abstract The Cambrian sequence in Jordan crops out in a belt-like pattern extending over more than 300 km from the Arabian-Nubian Shield source rock in the south, located on a stable shelf platform, to the invading southern (Baltic) side of the Tethys seaway. The analysis of the lithofacies association, ichnofossil content, together with the architecture of fluvial and paralic sandstone bodies reveals the development of the depositional environments of the Cambrian deposits of Jordan. The depositional environment evolved from proximal alluvial fans into major sand flats of braided rivers or directly into distal braidplains dominated by 3-D megaripples. In the following depositional phase, various marine environments prevailed including platform carbonates, clastic-, carbonate- and mixed-tidal flats and supratidal sabkhas, and less common lagoons. All these marine, or marine-influenced environments changed back into distal braidplains or sand flats of braided streams. The latter persisted through the remaining period of the Cambrian. The study has revealed that shales containing Cruziana interbedded within the fluviatile sandstone sequence are time markers that can be used for correlation, and could be deposited in a braidplain, if the detrital influx was very low. It is the latter that enabled the Cruziana-producing trilobites to migrate from the sea through river mouths to reach distal braidplains and lagoons.

Petrography, geochemistry and origin of the NW Jordan phosphorites

Phosphorites from NW Jordan were examined petrographically and chemically. Their mineralogy is basically simple and includes apatite (francolite), carbonate (mainly micritic calcite), some dolomite, and minor clay minerals and organic matter. These mineral phases control the chemistry. The phosphorite deposits are made up of several depositional cycles that indicate shallowing and show decreasing particle size. They are believed to have formed by authigenic precipitation followed by reworking and redeposition in the inner parts of the basin, where only minor amounts of micrite and clay were being deposited.

On the chemical variability of phosphatic particles from Jordanian phosphorite deposits

Abstract The phosphate particles (pellets, intraclasts and skeletal fragments) from thirteen friable samples representing the economic phosphorite horizons in Jordan were hand-picked and then cleaned. A total of 39 particle fractions were chemically analysed for their major and certain trace elements. The chemistry, supported by petrography, proved that the rounded particles are not faecal pellets; they are either rounded intraclasts or the rounded internal molds of bone cavities. The bone fragments have higher contents of CO2, Na20 and S03 and lower P205 and F compared with the pelletal/intraclast particles. These two groups of particles are readily separated chemically. Since the environment of deposition is the same, these differences are postulated to be due to the initial chemical composition of the bone material as carbonate hydroxyapatite (dahlite) and early diagenetic pathway conversion to carbonate fluorapatite (francolite) versus the direct chemical precipitation, as francolite, of the pelletal/intraclast particles from the sediment pore water.

Depositional environments of the early cretaceous Kurnub (Hathira) sandstones, North Jordan

Abstract The Kurnub (Hathira) sandstones in north Jordan, which are most probably of Early Cretaceous age, are about 300 m thick varicoloured, friable quartz-arenitic sandstones. Based on grain-size analysis, sedimentary structures, palaeocurrent, fossil content and petrography, these sandstones are postulated to be dominantly of fluvial origin with a few interfingering shallow marine horizons. A southward displacement of Jordan by at least 100 km would bring these sandstones opposite to similar rocks west of the Jordan-Araba rift, with Jordan being higher during the EArly Cretaceous.

Evidence for shallow-marine origin of a ‘Monterey-formation type’ chert-phosphorite-dolomite seqence: Amman formation (Late cretaceous), Central Jordan

SummaryThe late Cretaceous Amman Formation in central Jordan consists of cherts, porcelanites, dolomites and phosphorites with various limestones types. It is subdivided into five mapable lithological units: Mixed Mineralogy Unit, Porcelanite Unit, Chalk Unit, Main Chert Unit and Phosphorite Unit. The microfacies indicates a deposition within a shallow-marine inner epicontinental shelf environment ranging from supratidal to deep subtidal. The depositional model of the Amman Formation differs, therefore, from that of the Monterey Formation which is generally regarded as a model for a phosphorite-chertdolomite association formed in deeper outer shelf and slope environments. Cherts and porcelanites are of biogenic origin, they were formed by an early diagenetic replacement of lime mudstones and lime packstones.

Depositional facies and environments in the Umm Ishrin Sandstone Formation, Dead Sea area, Jordan

Abstract The Umm Ishrin Sandstone Formation between Wadi Manshala and Wadi Abu Khusheiba, along the northeastern margin of the Dead Sea, consists of a quartz arenite facies and a subordinate heterolithic facies of siltstone and mudstone with sandy lenses. The former are trough cross-bedded with unidirectional northwesterly mode. The Umm Ishrin sediments were deposited on a braidplain and tidal flat in response to periodic shifting of the active part of the braidplain system. Reworking of the abandoned parts of the braidplain by tidal currents and subsidence led to marine incursions and the development of tidal flats.

Un paléolac du dernier interglaciaire pléistocène dans l'Extrême-Sud hyperaride de la Jordanie

Abstract The fossiliferous deposits of a large palaeolake were recently observed in southern Jordan, overlapping into Saudi Arabia. Preliminary U/Th analyses of Cerastoderma sp. shells date the lake at 116 ± 5.3 kyr and 76.8 ± 8.2 kyr. Archaeological sites with Levailoiso-Mousterian artifacts are superimposed on those deposits, which fit a possible sub-stage 5a date. These new data imply a possible geographical continuity of the Last Pleistocene Interglacial humid phase throughout the Sahara-Arabian arid belt, in the same climatic context, as the palaeolakes in northern Mali and Fezzan.

Depositional facies and environments in the Permian Umm Irna Formation, Dead Sea area, Jordan

Abstract The Permian Umm Irna Formation in central Jordan consists of a 60 m thick sequence of clastic sediments which can be divided into two fluvial sedimentary facies. The lowermost facies (1) is characterized by the presence of five sandstone-dominated fining-upward sequences, each sequence comprising an erosively based coarse- to fine-grained, trough cross-bedded sandstone, overlain and laterally intertonguing with maroon siltstone and silty-shale, containing locally abundant carbonaceous plant material. The overlying facies (2) also consists of up to five fining-upward sequences, each comprising an erosively based coarse-grained pebbly sandstone grading up through fine-grained sandstone and siltstone into silty-shale. The sandstones are tabular, and laterally persistent, internally complex units structured by erosively bounded trough cosets. The thickness and grain size of the sandstones and the proportion of siltstone and silty-shale is much greater than in facies (1); it also contains abundant ferruginous concretions (glaebules). Deposition occurred on an unconfined braidplain sloping northwestwards away from an elevated provenance (Arabo-Nubian Shield) in the south and east. The lowermost facies (1) is regarded as a distal environmental equivalent of the overlying facies (2). Deposition was largely controlled by period c shifts of the active channel tract, influenced by a gradual increase in the elevation of the source area, thereby promoting basinwide progradation and vertical stacking of the two major facies components. The ferruginous concretions (glaebules) in facies (2) are thought to have resulted from diagenetic processes in the vadose zone of a humid, possibly tropical climate, characterized by alternating wet and dry seasons and strong leaching. The fluvial depositional system drained basinwards into a shallow-water marine depository along the southern margin of the Tethys Ocean. The ocean may have exerted a maritime influence on the climate of the alluvial plain.

A general aspect in the genesis of nodular limestones documented by the Upper Cretaceous limestones of Jordan

Abstract Upper Cretaceous nodular limestones in Jordan were originated by burrowing organisms of the types Thalassinoides, Callianassa or Ophiomorpha . Although burrows are difficult to recognize in the pure lutitic limestones of northern Jordan, in the south they are filled by early diagenetic stochiometric dolomite or chert. One may conclude that some nodular limestones hitherto described, are products of burrowing organisms and not of purely chemical processes.