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The Late NeoProterozoic metavolcanic Tibbit Hill Formation (THF) covers a large crustal segment exposed along a belt about 250 km long in the Appalachian fold belt (Quebec-Vermont). It is predominantly basaltic in composition but contains a minor component of felsic and intermediate alkaline volcanic lithologies. Geochemically, the Tibbit Hill Formation forms a continuum in composition and exhibits a wide range of SiO 2 (44-76 wt. percent), covering the entire spectrum from alkali basalt to trachyte and comendite. This mildly alkaline suite is relatively enriched in incompatible elements and exhibits a wide range of Zr (138-1493 ppm), Nb (15-139 ppm), and Y (18-185 ppm) concentrations, among other elements. The concentrations of the HFSE and the REE gradually increase toward the more evolved lithologies. The chondrite normalized REE patterns are fractionated (LREE-enriched over HREE), parallel to subparallel, and generally uniform but with negative Eu-anomalies developed in the more felsic varieties. These geochemical features underline the comagmatic nature of the entire suite and are consistent with a fractionated basalt to comendite suites. The incompatible element profiles suggest that most of these elements including Nb, Zr, Ti, Y, and the REE have not been affected by metamorphism, as they remained largely intact within the THF rocks. Chemical features of the mafic rocks are typical of within-plate basalts and suggest that their melts were derived from a fertile or plume-related mantle source. Chemical features of the felsic and intermediate rocks are typical of anorogenic A 1 type suites, related to hotspots, mantle plumes, or continental rift zones. This is consistent with the regional geological context with the volcanism, associated with an Iapetan RRR triple junction, occurring shortly before the onset of seafloor spreading. Geochemical modelling shows that the THF basaltic magma was produced by a very small degree of batch partial melting (F ‫؍‬ 2.5 percent) of a garnetbearing primitive mantle source (garnet lherzolite). A final basaltic melt segregation depth is estimated at 80 to 100 km. Melting probably occurred within the thermal anomaly of a rising mantle plume beneath the Sutton Mountains triple junction (near the Quebec-Maine border). Fractionation of THF basaltic magma produced minor trachytic and comenditic magmas. The volcanic assemblage of the Afar rift (for example, Boina centre) appears to represent a modern analogue to the THF volcanic suite.

The Lebanese crustal segment is part of a much larger carbonate platform deposited along the northwestern margin of the Arabian Plate, in the eastern Mediterranean region. It is made up mainly of Jurassic–Cretaceous carbonate rocks. Most of this stratigraphic sequence is exposed in the Nahr Ibrahim canyon and surrounding areas in central Lebanon. The various formations, from the oldest unit (the Lower Jurassic Kesrouane Formation) to the Upper Cretaceous Chekka Formation, are made up of different types of carbonate rocks including micritic limestone, medium‐ to coarse‐grained dolostone, biomicritic (chalk), biosparrudite limestone, micritic dolostone, pelmicrite, marl and marly limestone.Results of this first chemical investigation on the Lebanese carbonate platform show that the micritic limestone of the Kesrouane Formation is relatively enriched in Ca, Na and Sc, and has low rare‐earth element (REE) contents. The marl units of the Hammana Formation are enriched in Al, Fe, K, Ti, Rb, Ga, Nb, U, Th and REE. The chalk of the Chekka Formation shows the highest phosphorus content. A significant increase in P and Sr contents with time (from the Lower Jurassic to the Upper Cretaceous carbonate units) characterizes the Lebanese sequence; this is interpreted to be related to a possible increase in continental weathering rates during the Mesozoic. Enrichment in Ni, Ti and Nb in some formations is interpreted to be linked to Mesozoic volcanism in central Lebanon. The Cretaceous formations are subdivided according to their REE patterns into two distinct groups: limestones (Mdairej, Sannine and Maameltain formations) which are depleted in REE; and marl/chalk (Hammana and Chekka formations) which are significantly enriched in REE. On several geochemical variation diagrams, such as the K–Ti–P triangular plot, the Lebanese Mesozoic carbonate formations are found to occupy distinct compositional fields. Thus, carbonate geochemistry could prove to be a powerful tool (especially when combined with petrographic data) in characterizing and correlating carbonate formations (chemical stratigraphy), particularly in regions where field evidence may be limited. Results of this study have significant implications for the entire carbonate platform that covers a large part of the eastern Mediterranean region. Copyright © 2002 John Wiley & Sons, Ltd.

Reservoir quality of carbonate rocks is usually controlled by the interplay of both the primary depositional and secondary diagenetic parameters. The assessment of the respective impact of these controls together with the understanding of the field-scale sedimentological organisation and diagenetic trends assist in the reconstruction of reservoir architecture and help production and appraisal programs. This work focuses on three formations recorded in the onshore Abu Dhabi area with the final aim of understanding their field-scale architecture through the study of six wells. Sediments reflect deposition in clay-prone and cleaner inner ramp to distal mid-ramp, where biotic assemblage is either dominated by Lithocodium/Bacinella (i.e. within lower Shuaiba and lowermost Lekhwair), rudists or peloids (i.e. within Kharaib). The sedimentological framework has been established through a detailed sedimentological description of c.2545ft of core and sequence stratigraphy interpretation. The occurrence of diagenetic processes (i.e. dissolution, cementation and fracturing/compaction) and their respective impact on pore system have been assessed through the observations of 804 thin-sections and the structural logging of c. 1936ft of core. The integration of the field-scale sedimentological organisation together with the distribution of the assessed reservoir quality controls and porosity/permeability data results in the establishment of the reservoir architectures of the three formations. In this area, the depositional fabric is characterised to be the primary parameter on the reservoir properties of the cored Thamama deposits with the exception of the lowermost cored Lekhwair and fractured reservoir: the best reservoir quality is found within inner ramp (locally dominated by Lithocodium/Bacinella) to backshoal grainstones and rudist-rich floatstones associated with a grainstone matrix. The reservoir quality decreases with the progressive increase in micrite matrix and clay content. The lowest porosity/permeability values are linked to the clay-rich inner ramp deposits recorded within the Dense Units, forming thick seals between the cleaner carbonate reservoir units. The localised occurrence of late dissolution phases has locally enhanced pore connectivity and preferentially affects the deposits which are initially characterised by good pore connectivity and volume (as observed in the lowermost Lekhwair and upper Kharaib Formations). Finally, cementation only locally decreases the reservoir properties and is broadly preferentially developed within and nearby clay-enriched deposits and at sharp lithological contacts often overprinted by stylolites. The focus of cementation on these surfaces results in one extensive ft-thick baffle within the Kharaib reservoir while a similar baffle is locally breached by rare 20cm-long fractures in Lower Shuaiba reservoir developed at the hinge of the anticline. Finally, the abundant and connected fracture network occurring within the lower Lowermost Lekhwair is likely to play a role on fluid flow in subsurface. The reservoir architecture will be integrated in the rock typing workflow to assist in the prediction of rock type vertical distribution and their lateral extent.