Assessment of organic pollutants in coastal sediments, UAE

Twenty-five stations were selected along the UAE coastal region to delineate the distribution and to determine the source of total petroleum hydrocarbon (TPH), total organic carbon (TOC), total Kjeldhal nitrogen (TKN), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The concentrations of TPH ranged between 46 and 223 mg/kg and the level of TOC was in the range from 0.044 to 17.8 wt%, while TPAHs occupied the range of 5–102.2 μg/kg. On the other hand, TPCBs showed values between 60 and 205 μg/kg and TKN ranged from 104 to 1,073 mg/kg. The present study shows that the distribution of organic compounds in UAE sediments were within safe limits comparing with previous studies. The present study revealed that TOC can be used as an indicator of oil pollution in heavily oiled sediments. The highest values of TOC, TPH, TPAHs and TPCBs related to the stations covered in fine sand due to adsorption properties and the large surface areas of the grains. The evaporation of low-boiling point compounds from surface layers leads to the enrichment of sediments with a thick residual. Al Sharjah-1 exhibited the highest values of TPH and TOC at Ras Al-Khaima-5, Umm Al-Quwen-1 and Dubai-1, while the highest values of TPAHs were at KhorFakkan-9, the highest value of TPCBs was at Ajman-2, and the highest values of TKN were at KhorFakkan-1, KhorFakkan-6 and Dubai-1.     

The synorogenic pegmatitic quartz veins of the Guacha Corral Shear zone (Sierra de Comechingones,Argentina): A textural,chemical, isotopic,cathodoluminescence and fluid inclusion study

The quartz veins and pegmatites of the Sierra de Comechingones (Sierras de Córdoba, NE Argentina) belong to the Comechingones Pegmatite field (CPF). For the quartz veins and the zoned pegmatites related parental granites are missing. The country rock of the quartz veins are mylonitic augengneisses in granulite to upper amphibolite facies. Field relations, microscopy, cathodoluminescence, radiometric age data, fluid inclusion, chemical and isotopic composition and literature define the quartz veins as synorogenic formed during the high-temperature phase of the Famatinian (480–460 Ma) event. During the Famatinian up to the Achalian (382–366 Ma) event the synorogenic quartz veins were subjected to high temperature ductile deformation documented by folding, boudinage and finally brittle shearing. K-Ar ages of illite from the shear zones of about 166 Ma document the final cooling of the Sierras Pampeanas below 100 °C. The long lasting thermal and deformational history of the study area is reflected by very different populations of fluid inclusions in vein quartz with remarkably high contents of thermogenic hydrocarbons in the early-formed fluid inclusions. LA–ICP–MS analysis reveals very low lattice-bound trace element contents, i.e. high purity quartz.     

Lipid biomarkers in surface sediments from the Gulf of Genoa,Ligurian sea (NW Mediterranean sea) and their potential for the reconstruction of palaeo-environments

A series of molecular organic markers were determined in surface sediments from the Gulf of Genoa (Ligurian Sea) in order to evaluate their potential for palaeo-environmental reconstructions. Allochthonous input can be characterized by the distributions of n-C₂₉ and n-C₃₁ alkanes, n-C₂₆ and n-C₂₈ alkanols and branched glycerol dialkyl glycerol tetraethers (GDGTs), whose concentrations are generally highest near the river mouths. In the open basin however, terrestrial n-alkanes and n-alkanols may have an additional, eolian source. Autochthonous input is represented by crenarchaeol and isoprenoid GDGTs. Their concentrations are highest in the open basin showing the preference of Thaumarchaeota for oligotrophic waters. Indications of a significant degradation of sterols and C₃₇ alkenones exclude these lipids as reliable productivity proxies. Using terrestrial and aquatic lipids as end-members allows estimating the percentage of terrestrial organic matter between 20% and 58% in the coastal area decreasing to 1–30% in the deep basin. The spatial distribution of sea surface temperature (SST) estimates using the alkenone-based U^K′₃₇ index is very similar to the autumnal (November) mean satellite-based SST distribution. Conversely, TEX^H₈₆-derived SST estimates are close to winter SSTs in the coastal area and summer SSTs in the open basin. This pattern reflects presumably a shift in the main production of Thaumarchaeota from the coastal area in winter to the open basin in summer. This study represents a major prerequisite for the future application of lipid biomarkers on sediment cores from the Gulf of Genoa.     

Geographies of peak oil: The other carbon problem

This extended editorial introduction to a themed issue of Geoforum on geographies of peak oil has three objectives. First, it provides a concise account of the ’peak oil’ claim, identifying the key protagonists in the debate, and outlining different stances with regard to the timing, shape and composition (conventional vs. non-conventional hydrocarbons) of the peak. Second, after briefly characterising the limited engagement with peak oil by human geographers, it offers a provisional set of claims about what a geographical analysis of peak oil might yield. Finally, it introduces each of the papers and, in doing so, makes the case for a fuller and more sustained engagement by geography with this ’other carbon problem.’     

Weathering of fuel oil spill on the east Mediterranean coast, Ashdod, Israel

Residual fuel oil spilled into the sea from the Eshkol power station on 8 February, 1998 contaminated about 9 km of the foreshore north of the Ashdod harbour. A study of the aliphatic, polycyclic alkane and polyaromatic hydrocarbon (PAH) composition of the spilled oil shows rapid weathering in the early stages followed by gradual slowdown after about three months. Weathering of isoprenoids and PAH compounds and variation in Pr/Ph ratio appear to occur almost contemporaneously with that of n-alkanes, at a relatively moderate level of degradation, when much of the >C₂₀ n-alkane envelope is still well preserved. Depletion of various compounds in accordance with molecular size rather than molecular structure appears to imply that physical weathering processes, i.e. evaporation and perhaps flushing due to wave energy, might have played an important role in the degradation of the spilled residual fuel oil in this study case.     

Regional structure and tectonic history of the obliquely colliding Columbus foreland basin, offshore Trinidad and Venezuela

Cenozoic eastward migration of the Caribbean plate relative to the South American plate is recorded by an 1100-km-long Venezuela-Trinidad foreland basin which is oldest in western Venezuela (65-55 Ma), of intermediate age in eastern Venezuela (34-20 Ma) and youngest beneath the shelf and slope area of eastern offshore Trinidad (submarine Columbus basin, 15.0 Ma-Recent). In this study of the regional structure, fault families, and chronology of faulting and tectonic events affecting the hydrocarbon-rich Columbus foreland basin of eastern offshore Trinidad, we have integrated approximately 775 km of deep-penetration 2D seismic lines acquired by the 2004 Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region (BOLIVAR) survey, 325 km of vintage GULFREX seismic data collected by Gulf Oil Company in 1974, and published industry well data that can be tied to some of the seismic reflection lines. Top Cretaceous depth structure maps in the Columbus basin made from integration of all available seismic and well data define for the first time the elongate subsurface geometry of the 11-15 km thick and highly asymmetrical middle Miocene-Recent depocenter of the Columbus basin. The main depocenter located 150-200 km east of Trinidad and now the object of deepwater hydrocarbon exploration is completely filled by shelf and deepwater sediments derived mainly from the Orinoco delta. The submarine Darien ridge exhibits moderate (20-140 m) seafloor relief, forms the steep (12°-24°), northern structural boundary of the Columbus basin, and is known from industry wells to be composed of 0.5-4.5 km thick, folded and thrust-imbricated, hydrocarbon-bearing section of Cretaceous and early Tertiary limestones and clastic rocks. The eastern and southern boundaries of the basin are formed by the gently (1.7°-4.5°), northward-dipping Cretaceous-Paleogene passive margin of South America that is in turn underlain by Precambrian rocks of the Guyana shield.Interpretation of seismic sections tied to wells reveals the following fault chronology: (1) middle Miocene thrusting along the Darien ridge related to highly oblique convergence between the Caribbean plate and the passive margin of northern South America; continuing thrusting and transpression in an oblique foreland basin setting through the early Pleistocene; (2) early Pliocene-recent low-angle normal faults along the top of the Cretaceous passive margin; these faults were triggered by oversteepening related to formation of the downdip, structurally and bathymetrically deeper, and more seaward Columbus basin; large transfer faults with dominantly strike-slip displacements connect gravity-driven normal faults that cluster near the modern shelf-slope break and trend in the downslope direction; to the south no normal faults are present because the top Cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin; (3) early Pliocene-Recent strike-slip faults parallel the trend of the Darien ridge and accommodate present-day plate motions.     

Upper Permian Main Dolomite microbial carbonates as potential source rocks for hydrocarbons (W Poland)

Various microbialite lithofacies were common in the shallow-water environments which flourished under highly saline and arid climate conditions in the Polish part of the Zechstein (Upper Permian) Main Dolomite (Ca2) carbonates. Data came from detailed analysis of 78 cores from wells located at the southern and northern margins of the Main Dolomite basin in west Poland. Microbialite lithofacies are represented by columnar, planar and domal stromatolites, clotted thrombolites and biolaminites developed in high-to-low energy environments within the upper slope, lower parts of oolitic barrier/shoal, restricted lagoon, and tidal flat and tidal channel zones. In barrier environments ooids were predominant whereas in lagoonal settings microbial oncoids and peloids were common. In basinal settings laminated dolomudstones formed which are regarded as hemipelagic and are partly pelagic microbial in origin. Microbial communities coexisted with algae and developed mainly within shallow marine environments. Microbialites are built of cyanobacterial filaments and organo-mineral coccoidal forms possibly of bacterial origin. Organic geochemistry data confirm that organic matter was transformed by cyanobacteria and bacteria which may have played a main role in hydrocarbon generation. This is confirmed by C₂₉ to C₃₅ hopanes, Pr/Ph ratio below 1.0, and the presence of gammacerane as typical for Ca2 profiles. The role and occurrence of algae, as confirmed by C₂₉-steranes, in hydrocarbon generation was possibly minor. Thus it is concluded that the Main Dolomite microbialites could be the likely source rocks for hydrocarbons, with calculated original TOC values from 0.8 to ca 2.0 wt. %. These units also form the reservoir rocks, with porosities reaching 20%.     

Structure of microbial communities and hydrocarbon-dependent sulfate reduction in the anoxic layer of a polluted microbial mat

The bacterial communities in the anoxic layer of a heavily polluted microbial mat and their growth on hydrocarbons under sulfate-reducing conditions were investigated. Microbial communities were dominated by members of Alphaproteobacteria (27% of the total rRNA), Planctomycetes (21.1%) and sulfate-reducing bacteria (SRB: 17.5%). 16S rRNA cloning revealed sequences beloning to the same bacterial groups with SRB affiliated to the genera Desulfobulbus, Desulfocapsa, Desulfomicrobium, Desulfobacterium and Desulfosarcina/Desulfococcus. The derived enrichment cultures on crude oil, hexadecane and toluene were dominated by SRB. While most SRB sequences of the toluene and hexadecane cultures were related to the sequence of Desulfotignum toluolica, the crude oil enrichment showed a more diverse bacterial community with sequences from the genera Desulfotignum, Desulfobacter, Desulfatibacillus, Desulfosalina, and Desulfococcus. We conclude that the anoxic layer of the studied mats contains a diverse community of anaerobic bacteria, dominated by SRB, some of which are able to grow on hydrocarbons.     

Effect of atmospheric humic-like substances on the enhanced dissolution of volatile organic compounds into dew water

Simultaneous sampling of chlorinated hydrocarbons (CHs) and monocyclic aromatic hydrocarbons (MAHs), potentially harmful to humans and/or responsible for the formation of ozone and secondary particles, in dew water and in the ambient air was carried out from August 2004 to July 2005 in Hino City, situated in the western part of Greater Tokyo, Japan. CHs were less contained in dew water than MAHs. Toluene (volume-weighted mean concentration, VWM: 4.77 nM) and m,p-Xylenes (VWM: 5.07 nM) except dichloromethane, which was abnormally high (VWM: 1.14 μM), were abundant among eleven VOCs determined in dew water. Chloroform, carbon tetrachloride, 1,2-dichloroethane, and benzene were not detected in dew water during the study period. Dew water contained higher amounts of VOCs than would have been expected from the ambient gas-phase concentrations and the temperature-corrected Henry's law constants. Following the determination method of humic substances in river water proposed by Hiraide et al. [Hiraide, M., Shima, T., Kawaguchi, H., 1994. Separation and determination of dissolved and particulate humic substances in river water. Mikrochim. Acta 113, 269–276], the VWM of soluble humic and fulvic acid fractions in dew water was found to be 1.00 mg/L and 0.87 mg/L (n = 20), respectively, while the VWM of particulate humic and fulvic acid fractions was found to be 0.61 mg/L and 0.42 mg/L (n = 20), respectively. Surface tension decreased with an increase in dissolved fulvic acid fraction in dew water, indicating that humic-like substances with relatively lower molecular weight, which is soluble in acid solution, could be an effective surface-active species within dew water. The enrichment factors, which were defined as the ratio of the observed VOCs concentration to the estimated, were over 10² for MAHs except for benzene and increased as the increment of total humic-like substances (HULIS) concentration (the sum of humic and fulvic acid fractions in both dissolved and particulate form) normalized by total inorganic ion concentration in dew water. Our results indicate that total HULIS in dew water could enhance the dissolution of atmospheric VOCs into dew droplets.     

Seismic stratigraphic framework and depositional sequences in the Santos Basin,Brazil

The Santos Basin, situated offshore southern Brazil, is one of nine marginal rift basins in the equatorial South Atlantic. It formed by the collapse of a thermal dome in the late Jurassic and by subsequent rifting and opening of the South Atlantic in the early Cretaceous. Rifting was accompanied by immense volcanic outpouring seen at the surface today throughout the onshore Paraná Basin and thought to underlie the entire Santos Basin, and the adjacent São Paulo Plateau. Vulcanism was followed by subsidence of up to 10 km from Aptian to Recent time, and a coastal hingeline coincides with the Serra do Mar uplift. The basin depocentre, which is 700 km long, is bounded to the north and south by basement and volcanic highs, respectively. A restricted water circulation in the ocean basin, which prevailed up to the Santonian stage, has important repercussions for the hydrocarbon potential of the area. The nine genetically related basins have collective reserves of ≈ 5 billion barrels of oil and associated gas. A stratigraphic framework, based largely on seismic data, has been erected for the Santos Basin. Seven regional unconformities, or ‘R’ reflections, can be traced throughout the basin and form the boundaries for seismic sequences. Isopaching the seismic sequences defines the principal depositional units in the basin and also shows how the basin depocentre shifted with time. Limited well control has enabled the seismic sequences to be correlated with litho-environmental sequences which more fully reflect the geological evolution and provide a working exploration model. Finally, an attempt has been made to recognize and map seismic facies within the seismic sequences and to predict the lithofacies in areas away from well control