Nizar Abu-Jaber

Origin of ultramafic-hosted vein magnesite deposits

Abstract Large deposits of magnesite (MgCO3) occur either as carbonated ultramafic rocks or as sedimentary beds. The origins of both sedimentary and ultramafic-hosted deposits remain controversial, as does the relationship between them. Ultramafic-hosted deposits are reviewed herein, with an emphasis on veins rather than massive bodies. Magnesium apparently has been supplied to magnesite veins by their ultramafic host. Uncertainties concerning ultramafic-hosted deposits include the source, state, and mode of transportation of carbon, the cause of its precipitation, and the mineralogy of the initial precipitate. Genetic questions about ultramafic-hosted vein deposits are summarized with the aid of flow charts. The preferred route through these charts attributes most vein magnesite to an influx of metamorphic-degassing CO2 and CH4 into groundwater which flows through serpentinite or peridotite. The source of CO2CH4 is considered to be deeper than 10 km because metamorphism (>300°C) is required to release carbonaceous volatiles of the type which apparently induced observed magnesite mineralization. However, vein magnesite precipitation generally has occurred within just a few hundred meters of the Earths surface. Vein deposits are considered to be genetically related to massive bodies but the massive bodies typically contain less 12C. The 12C-rich CO2, which has produced vein deposits, is attributed to a fluid phase (variably mixed CH4COCO2) which rose until it reached upper-crustal groundwater. The hypothetical water-poor fluid presumably became slightly oxidized, hence richer in soluble CO2, as it encountered near-surface, sulfate-bearing water. CO2-enriched water is envisioned to have been expelled regionally due to tectonic processes, leaving little mineralogical evidence of its expulsion through non-ultramafic rock. CO2-rich water which happened to encounter either serpentinite or peridotite presumably has produced magnesite vein deposits and a common silicate byproduct, nontronite, according to the following reaction: 12 Mg3Si2O5(OH)4 (serpentine)+36 HCO3−+4 Fe3O4+O2→12 FeSi2O5(OH) (nontronite)+36 MgCO3 (magnesite)+36 OH−+18H2O.

A new look at the chemical and hydrological evolution of the Dead Sea

Abstract Hydrological models of the Dead Sea (DS) indicate that subrecent equilibrium conditions have been maintained by input and evaporation of about 1600 × 106 m3/yr of surface waters. Recent diversions of the headwaters have led to a drop of about 0.95 m/yr, suggesting that waters stored in adjacent aquifers are being drained at a rate of about 200 × 106 m3/yr. Chemical modeling of the DS indicates that the chemical evolution of the waters can be explained by a simple mixture and evaporation model. This model requires the input of 50 × 106 m3/yr of hot spring waters similar to those emanating at Zohar and evaporation factors of about 50. This model suggests that the DS salts have accumulated over the past 5000 years. This indicates that the initiation of the present DS was triggered by the onset of the Mid Holocene pluvial stage as well as by draining of the freshwater lakes present upstream from the lake. Review of the data of the springs responsible for the chemical nature of the DS suggests that these waters are of meteoric-continental origin and that it is likely that these waters have experienced deep circulation in the rift system before discharging at the surface due to convective forces operating in the rift.

Documentation and Protection of the Quarries of Gerasa

Abstract The Roman quarries in the environs of Gerasa provide an interesting insight into how stone was extracted and shaped for the purpose of building the monumental city. Ancient quarries carry aesthetic, educational and scientific values that future generations deserve to enjoy. Despite this, little has been done to document or protect these quarries, and many of them are not even officially listed as archaeological sites. In this paper, we describe an effort to build a database for these quarries, and make a case for protecting some of them as examples of how quarrying was executed in order to emphasize the importance of this industry and the sophistication of its technology. One site (Thughrat ‘Usfūr) was chosen for detailed mapping, and it is herein proposed that this site be developed as a destination for visitors of the monumental city, offering the opportunity to understand stone extraction as well as the landscape in which the city grew.

Geology and Hydrochemistry of the Deep Sandstone Aquifers of Jordan

The deep sandstone aquifer complex of Jordan consists of hundreds of meters of Paleozoic to Lower Cretaceous sandstones that extend from the Saudi Arabian border in the south up to northern Jordan. In the south, this aquifer is known as the Disi Aquifer and is near the surface, well understood and heavily exploited. Toward the north, thick accumulations of later Mesozoic and Cenozoic sedimentary sequences cover the complex. The depth of the aquifer in this area makes it less viable as a water resource. Thus, little is known about its origin, movement and chemical evolution. A number of exploration and production wells have penetrated this aquifer throughout central and northern Jordan. The data from these wells can help to draw a reasonable understanding about this aquifer and its water. Most of the aquifer is under artesian pressure, and the piezometric head data point to a general flow north with drainage of the aquifer into the Dead Sea Rift Basin. Stable isotopes show that the water differs from modern meteoric water in the region and thus is possibly Late Pleistocene in age. The water is slightly brackish, and according to Jordanian Standards, it can be used for drinking under certain conditions. Geochemical modeling shows that here is no evidence that the salinity is primarily the result of prolonged water–rock interactions, but more likely the result of mixing with possibly trapped connate water throughout the complex.

Petrology of Middle Islamic Pottery from Khirbat Faris, Jordan

Abstract Geological investigation of the environment of Khirbat Faris reveals that the most suitable clay materials in the area for pottery production are from the marl-rich carbonate layers of the Upper Cretaceous sequence in the area. Petrographic analysis of the pottery from the Ayyubid-Mamluk site shows two types of pottery according to provenance. Wheel-thrown glazed pottery and wheel-thrown cream-slipped ware appear to have been imported to the site whereas the hand-made geometrically-painted ware and the black cooking wares appear to have been produced locally. Refiring tests of the locally-produced pottery suggest relatively low temperature firing conditions.