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1.
Solid, liquid and gaseous hydrocarbons occur throughout the Dead Sea Basin (Israel and Jordan) both in surface exposures and in drillings. The unaltered asphalts and heavy oils are characterized by very high sulfur content (ca. 11%) with δ34S = +5% and δ13C = −28% to −29%, low content of n-paraffins, pristane to phytane ratio of 0.5 and by containing almost exclusively VO-porphyrins. The distribution of n-paraffins in samples from deep sources shows a smooth enveloped miximizing at C15–20. Surface and shallow samples show clear evidence of biodegradation. The ozokerite, known only from the east side of the basin, is composed primarily of long chain n-paraffins with a maximum at C39. The gases known from the southern margin of the basin are composed mostly of methane.The source for the bitumens is unknown. Two hypotheses are discussed. The first is that the asphalts and heavy oils represent an alteration products of crude oil which migrated into the basin or which might have been generated in the basin itself. The second hypothesis favors an origin from low temperature alteration of organic matter from a thermally immature source.  相似文献   

2.
The hydrocarbon occurrences of asphalts, heavy oils and oil shales in the Dead Sea area and the possible genetic relation between them have been studied. The similarity in organochemical characteristics, i.e., the elemental composition of asphaltenes, the distribution pattern of the saturated hydrocarbons and the predominance of V (over Ni)-porphyrins in both the oils and the asphalts indicate a close relation between them. On the other hand, dissimilarities in the same organochemical characteristics in both the asphalts and the oil shale exclude the hypotheses that asphalt was generated and expelled from the oil shales or that the shales were contaminated by oils. Water washing and biodegradation are considered to be the processes through which preferential depletion of hydrocarbons occurred, altering the oils to asphalts. The burial of the degraded asphalt to a relatively great depth resulted in a secondary generation of small amounts of light saturated hydrocarbons in these asphalts. The oils, which are thought to be the precursors of the asphalts, have either been flushed into the Dead Sea depression from the surrounding elevated areas or have seeped upwards from deep local accumulations in the graben.  相似文献   

3.
A detailed GC/MS study of biological marker compounds in the saturated and aromatic hydrocarbon fractions of oils and asphalts from the Dead Sea area, Israel, provided decisive information to the solution of a long-lasting controversy by showing that the asphalts are products of early generation in an immature stage from the same type of carbonate source rock which generated more mature oils. The asphalts are not biodegraded residues of the oils.Oils from six different wells, and asphalts from wells, outcrops, and a floating block from the Dead Sea all have very similar sterane and triterpane patterns. They all lack rearranged steranes (diasteranes) indicating a carbonate source matrix and compare reasonably well with a sample of Upper Cretaceous bituminous chalk from Nebi Musa. The main difference between the oils and the asphalts is a significantly higher triaromatic to mono- plus triaromatic steroid hydrocarbon ratio in the former. This is explained as a result of rapid subsidence and heating of their source rock close to the deep parts of the Dead Sea graben. The oils thus were generated in the more deeply buried source rock blocks under the graben fill, whereas the asphalts either originate from an immature source rock section closer to the graben rims or represent an earlier phase of generation and expulsion.This study also provides general information on the evolution of biological markers in carbonate source rocks. Low-activation-energy processes, like isomerisation of steranes, appear to occur much faster at low temperatures than in shales. The high sulfur content and less cross-linking of the biogenic organic matter into a complex kerogen structure are suggested to be responsible for this. Care should be taken when using only sterane isomerisation to assess the maturity of hydrocarbons from carbonate rocks and of carbonate-derived oils.  相似文献   

4.
Calcite veins with fluid and solid bitumen inclusions have been discovered in the south-western shoulder of the Dead Sea rift within the Masada-Zohar block, where hydrocarbons exist in small commercial gas fields and non-commercial fields of heavy and light oils. The gas–liquid inclusions in calcite are dominated either by methane or CO2, and aqueous inclusions sometimes bear minor dissolved hydrocarbons. The enclosed flake-like solid bitumen matter is a residue of degraded oil, which may be interpreted as “dead carbon”. About 2/3 of this matter is soot-like amorphous carbon and 1/3 consists of n-C8C18 carboxylic acids and traces of n-alkanes, light dicarboxylic acids, and higher molecular weight (>C20) branched and/or cyclic carboxylic acids. Both bitumen and the host calcites show genetic relationship with mature Maastrichtian chalky source rocks (MCSRs) evident in isotopic compositions (δ13C, δ34S, and δ18O) and in REE + Y patterns. The bitumen precursor may have been heavy sulfur-rich oil which was generated during the burial compaction of the MCSR strata within the subsided blocks of the Dead Sea graben. The δ18O and δ13C values and REE + Y signatures in calcites indicate mixing of deep buried fluids equilibrated with post-mature sediments and meteoric waters. The temperatures of fluid generation according to Mg–Li-geothermometer data range from 55 °С to 90 °С corresponding to the 2.5–4.0 km depths, and largely overlap with the oil window range (60–90 °С) in the Dead Sea rift (Hunt, 1996; Gvirtzman and Stanislavsky, 2000; Buryakovsky et al., 2005). The bitumen-rich vein calcites originated in the course of Late Cenozoic rifting and related deformation, when tectonic stress triggers damaged small hydrocarbon reservoirs in the area, produced pathways, and caused hydrocarbon-bearing fluids to rise to the subsurface; the fluids filled open fractures and crystallized to calcite with entrapped bitumen. The reported results are in good agreement with the existing views of maturation, migration, and accumulation of hydrocarbons, as well as basin fluid transport processes in the Dead Sea area.  相似文献   

5.
It has been reported that the composition of crude oils in the subsurface may be altered by bacterial action to the extent that oil correlations (Winters and Williams, 1969) and the value of the crude (Evans et al., 1971) are severely affected. Experimental documentation of these effects is provided by this study.A crude oil was degraded in a 21-day laboratory experiment by a culture of four aerobic bacteria isolated from an oil-contaminated soil. The progress of the experiment was measured by the changes induced in the chemical composition of the oil fraction boiling above 270°C. These changes were similar to the variations in composition found in the MC5 oils of Saskatchewan, Canada.Normal paraffins through to at least nC34 were severely depleted although the attack was temporarily blocked at nC25 (Jobson et al., 1972). The position of this blockage is a function of the isolate employed. The isoprenoids, pristane and phytane, were metabolised after the disappearance of the n-paraffins. Lower-ring naphthenes and aromatics were attacked at the same time as the lighter normal paraffins and before the heavier ones.The more condensed cyclic hydrocarbons were apparently unaffected. Additional non-hydrocarbon NSO, and particularly asphaltene (both defined under section “Methods”), compounds were formed by the metabolism of the hydrocarbons.The residual oil after attack was heavier by approximately 30° API than the initial crude oil.  相似文献   

6.
This paper consists of two interrelated parts. In the first part, the influence of the composition of sediment organic matter on crude oil composition is discussed. The second part deals with the origin of normal paraffins in petroleum.Source beds with abundant terrestrial plant matter generate heavy hydrocarbons rich in five-ring naphthenes. Unless such source beds are exposed to a high temperature for a prolonged time, the oils released are also rich in five-ring naphthenes. Such oils are rare; thus far the only examples found are some Eocene Wilcox oils from the Texas Gulf Coast and some Eocene Green River oils from the Uinta Basin, Utah. Normally, oil source beds are not rich in terrestrial plant matter and the five-ring naphthene content of the source bed hydrocarbons, as well as that of the produced oils, is low.The n-paraffins generated by oil source beds rich in terrestrial plant matter are characterized by abnormally low (C21 + C22)/(C28 + C29) ratios of 0.6–1.2. In oils of dominantly marine origin, this ratio is in the range 1.5–5.0. The ratio of marine to terrestrial organic matter in source beds appears to influence both the naphthene composition and the n-paraffin composition of the generated oils.Evidence is presented that petroleum n-parainns originate from slow thermal cracking of fatty acids contained in fats and waxes. Reaction equations are discussed which explain the major geochemical observations, including the difference in carbon-number distribution of the assumed parental fatty acids and of their descendant n-paraffins. In normal oils, which originate mostly from fat rich marine organic matter, the n-paraffin concentration tapers off above C20. The molecular weight range of the fatty acids of plant waxes is considerably higher than that of fats. If plant waxes contribute strongly to the oil source material, the molecular weight distribution of the petroleum n-paraffins formed is abnormal and high carbon numbers in the C24-C32 range dominate.  相似文献   

7.
The Dead Sea brine is supersaturated with respect to gypsum (Ω = 1.42). Laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from Dead Sea brine are both slower in comparison with solutions at a similar degree of supersaturation. The slow kinetics of gypsum precipitation in the Dead Sea brine is mainly attributed to the low solubility of gypsum which is due to the high Ca2+/SO42− molar ratio (115), high salinity (∼280 g/kg) and to Na+ inhibition.Experiments with various clay minerals (montmorillonite, kaolinite) indicate that these minerals do not serve as crystallization seeds. In contrast, calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum. This implies that transportation inflow of clay minerals, calcite and local crystallization of minerals in the Dead Sea does not prompt significant heterogeneous precipitation of gypsum. Based on historical analyses of the Dead Sea, it is shown that over the last decades, as inflows to the lake decreased and its salinity increased, gypsum continuously precipitated from the brine. The increasing salinity and Ca2+/SO42− ratio, which results from the precipitation of gypsum, lead to even slower kinetics of nucleation and crystal growth, which resulted in an increasing degree of supersaturation with respect to gypsum. Therefore, we predict that as the salinity of the Dead Sea brine continues to increase (accompanied by Dead Sea water level decline), although gypsum will continuously precipitate, the degree of supersaturation will increase furthermore due to progressively slower kinetics.  相似文献   

8.
Asphalts found as pure lumps or coatings on potsherds were excavated at the Philistine site of Tel Miqne-Ekron (12th to 7th century BC) in the southern Inner Coastal Plain of Israel. They were studied using the techniques of petroleum geochemistry and were compared to some natural asphalts from the area: Dead Sea floating blocks (Israel), Wadi Weida’a asphalt (Jordan) and Hasbeya (Lebanon).Tel Miqne-Ekron bitumens show evidence of weathering, indicating biodegradation and oxidation. They contain less aromatics and more asphaltenes than Dead Sea asphalt. Evaporation and biodegradation are recorded at a molecular level, especially via the phenanthrenes and dibenzothiophenes. However, several isotopic and molecular parameters allowed us to correlate the Tel Miqne-Ekron asphalt with the Dead Sea asphalt from the floating blocks. The asphalts of Hasbeya and Wadi Weida’a do not match the Tel Miqne-Ekron asphalt. The latter, in particular, is much more biodegraded, based on its steranes. The study shows that the Dead Sea asphalt was imported to Tel Miqne-Ekron over a 500 year period. This trade posed no problem in the 7th century BC when Philistia, Israel and Judah were at peace as part of the Pax Assyriaca of the Assyrian Empire. However, trade during the 12th century BC is puzzling since the asphalt had to be transported across Israelite territory that was hostile to the Philistines, as indicated in the Bible (e.g., Samson and Delilah, David and Goliath). Consequently it seems that profitable commerce surpassed ethnic, religious and political conflict, as can also be observed in the contemporary world.  相似文献   

9.
《Applied Geochemistry》2005,20(10):1875-1889
Based on the systematic analyses of light hydrocarbon, saturate, aromatic fractions and C isotopes of over 40 oil samples along with related Tertiary source rocks collected from the western Qaidam basin, the geochemical characteristics of the Tertiary saline lacustrine oils in this region was investigated. The oils are characterized by bimodal n-alkane distributions with odd-to-even (C11–C17) and even-to-odd (C18–C28) predominance, low Pr/Ph (mostly lower than 0.6), high concentration of gammacerane, C35 hopane and methylated MTTCs, reflecting the high salinity and anoxic setting typical of a saline lacustrine depositional environment. Mango’s K1 values in the saline oils are highly variable (0.99–1.63), and could be associated with the facies-dependent parameters such as Pr/Ph and gammacerane indexes. Compared with other Tertiary oils, the studied Tertiary saline oils are marked by enhanced C28 sterane abundance (30% or more of C27–C29 homologues), possibly derived from halophilic algae. It is noted that the geochemical parameters of the oils in various oilfields exhibit regular spatial changes, which are consistent with the depositional phase variations of the source rocks. The oils have uncommon heavy C isotopic ratios (−24‰ to −26‰) and a flat shape of the individual n-alkane isotope profile, and show isotopic characteristics similar to marine organic matter. The appearance of oleanane and high 24/(24 + 27)-norcholestane ratios (0.57–0.87) in the saline oils and source rocks confirm a Tertiary organic source.  相似文献   

10.
Paraffinic crude oils are designated ‘primary’ because their composition is very close or identical to that of the hydrocarbons extracted from the corresponding oil source rocks. Heavy and medium-gravity naphthenic crude oils, on the other hand, typically are quite different compositionally from hydrocarbon mixtures in either mature or immature shales.The normal paraffin carbon number odd/even ratio 2C29/(C28 + C30) of all the heavy to medium-gravity crude oils which could be analysed are in exactly the same range as is observed for the primary paraffinic crude oils, namely 0.95–1.42. The naphthene indices of the medium to heavy gravity naphthenic crude oils and of the primary paraffinic crude oils from the same area are identical or close. These facts are significant because both the n-paraffin carbon number odd/even ratio and the naphthene index of shale hydrocarbons are strongly depth and subsurface temperature dependent. The facts observed demonstrate beyond question that, in the same area, the paraffinic precursors of the heavy to medium-gravity naphthenic crude oils are generated and expelled in the identical depth range, and from the same mature relatively deep oil source beds as the primary paraffinic crude oils. Later, during and/or after a generally upward migration into oil reservoirs, the primary crude may be transformed compositionally into a naphthenic crude oil.In none of the five widely scattered oil basins studied are medium to heavy naphthenic crude oils found at temperatures greater than a limiting subsurface temperature. The abruptness of the temperature cutoff of the change in oil compositions in all five oil basins, as well as the average value of the cutoff temperature of 66°C (150°F), leaves no doubt that the mechanism of this crude oil transformation process is microbial.Optical activity, which was observed in narrow saturate hydrocarbon fractions of the 80–325°C range of all microbially transformed crude oils, but not in the primary untransformed oils, is strong additional evidence for the microbial nature of the crude oil transformation process. The observed optical activity is explained by the microbial digestion at different rates of optical antipodes present in the primary paraffinic crude oils.To gain perspective the vast scale of the microbial oil transformation process in nature is pointed out. Billions of tons of heavy to medium-gravity naphthenic crude oils, originating from the microbial transformation of primary paraffinic oils, are present in oil fields and tar sands all over the world.  相似文献   

11.
The aliphatic hydrocarbon composition (acyclic isoprenoids, hopanoids and steroids) of oils from the most productive fields in the southern geological Province of Cuba have been studied. This province is defined by its position with respect to the Cretaceous overthrust belt generated during the formation of oceanic crust along the axis of the proto-Caribbean Basin. The relative abundances of 18α(H)-22,29,30-trisnorneohopane, gammacerane and diasteranes suggest that Pina oils are related to the carbonate oils from the Placetas Unit in the northern province (low Ts/(Ts+Tm) and C27,29 rr/(rr+sd) ratios). The Cristales and Jatibonico oils exhibit some differentiating features such as higher Ts/(Ts+Tm) and absence of gammacerane. The oils from this province do not exhibit significant differences in either hopane, C32 22S/(S+R) and C30 αβ/(αβ+βα), or sterane, C29 αα 20S/(S+R), maturity ratios. However, the relative content of 5α(H),14β(H),17β(H)-cholestanes (C29 ββ/(ββ+αα) ratio) indicates that Pina oils are more mature than Cristales and Jatibonico oils. Several of these oils (Cristales, Jatibonico and Pina 26) are heavily biodegraded, lacking n-alkanes, norpristane, pristane and phytane (the two former oils do not contain acyclic isoprenoid hydrocarbons). Other biodegradation products, the 25-norhopanes, are found in all the oils. Their occurrence is probably due to mixing of severely biodegraded oil residues with undegraded crude oils during accumulation in the reservoir.  相似文献   

12.
Geochemical characterisation of 18 crude oils from the Potwar Basin (Upper Indus), Pakistan is carried out in this study. Their relative thermal maturities, environment of deposition, source of organic matter (OM) and the extent of biodegradation based on the hydrocarbon (HC) distributions are investigated. A detailed oil-oil correlation of the area is established. Gas chromatography-mass spectrometry (GC-MS) analyses and bulk stable carbon and hydrogen isotopic compositions of saturated and aromatic HC fractions reveals three compositional groups of oils. Most of the oils from the basin are typically generated from shallow marine source rocks. However, group A contains terrigenous OM deposited under highly oxic/fluvio-deltaic conditions reflected by high pristane/phytane (Pr/Ph), C30 diahopane/C29Ts, diahopane/hopane and diasterane/sterane ratios and low dibenzothiophene (DBT)/phenanthrene (P) ratios. The abundance of C19-tricyclic and C24-tetracyclic terpanes are consistent with a predominant terrigenous OM source for group A. Saturated HC biomarker parameters from the rest of the oils show a predominant marine origin, however groups B and C are clearly separated by bulk δ13C and δD and the distributions of the saturated HC fractions supporting variations in source and environment of deposition of their respective source rocks. Moreover, various saturated HC biomarker ratios such as steranes/hopanes, diasteranes/steranes, C23-tricyclic/C30 hopane, C28-tricyclic/C30 hopane, total tricyclic terpanes/hopanes and C31(R + S)/C30 hopane show that two different groups are present. These biomarker ratios show that group B oils are generated from clastic-rich source rocks deposited under more suboxic depositional environments compared to group C oils. Group C oils show a relatively higher input of algal mixed with terrigenous OM, supported by the abundance of extended tricyclic terpanes (up to C41+) and steranes.Biomarker thermal maturity parameters mostly reached to their equilibrium values indicating that the source rocks for Potwar Basin oils must have reached the early to peak oil generation window, while aromatic HC parameters suggest up to late oil window thermal maturity. The extent of biodegradation of the Potwar Basin oils is determined using various saturated HC parameters and variations in bulk properties such as API gravity. Groups A and C oils are not biodegraded and show mature HC profiles, while some of the oils from group B show minor levels of biodegradation consistent with high Pr/n-C17, Ph/n-C18 and low API gravities.  相似文献   

13.
Thirty-one crude oils and 15 source rocks were selected for molecular geochemical and isotopic analyses in order to establish the genetic relationships between discovered oils and petroleum source rocks in the Weixinan Sub-basin, Beibuwan Basin, South China Sea. Three groups of oils were recognized. Group I oils are only found in the upper section of the Liusagang Formation, with a moderate abundance of C30 4-methylsteranes, low oleanane contents and lighter δ13C values, showing a close relation to the shale occurring in the upper section of the Liusagang Formation. Group II is represented by the majority of the discoveries and is distributed in multi-sets of reservoirs having different ages. The oils are characterized by a high abundance of C30 4-methylsteranes, low to moderate abundance of oleanane and heavy δ13C values, and shows a good correlation with the lacustrine shale and oil shale in the middle section of the Liusagang Formation. Group III oils occurred in the lower section of the Liusagang Formation. The oils have a lower concentration of C30 4-methylsteranes, relatively high abundance of oleananes and their δ13C values are intermediate. Oils of this group correlated well with the shallow lake-delta mudstone of the lower section of Liusagang Formation. These oil-source genetic relationships suggest a strong source facies control on the geographic distribution of oil groups within the Weixinan Sub-basin. The geochemical data indicate shale in the middle section of the Liusagang Formation has an excellent oil generation potential and the lower and upper sections contain dark shale and mudstone with good to fair oil potential. Future exploration or assessment of petroleum potential of the sub-basin could be improved by considering the proposed genetic relationship between the oil types and source rocks, as well as their distribution.  相似文献   

14.
Twenty-seven heavy crude oils of diverse origin were geochemically assessed with respect to both bulk and mlecular composition for the purpose of identifying and quanttfying valid biomarker parameters for low maturity oils. The low thermal maturity level of many of these oils is evident from the bulk and alipathic chromatographic data, and oil sourced from both marine and terrigenous organic matter are represented. Selective metastable ion monitoring (SMIM) was employed to measure separately the distribution of C27, C28, and C29 sterane isomers. The useful maturity indicators include the C29 5α(H) 20S/20R ratio, the relative quantity of the biological sterane configuration in each of the total normal C27, C28, and C29 steranes, and the rearranged to normal sterane ratio. In addition, C27 rearranged steran es appear to form at a faster rate than C28 or C29 rearranged steranes. However, the isomerization of the C27 biological component appears to occur at a slower rate than the C29 counterpart suggesting that the former may be used as a maturity parameter at higher levels of thermal maturation. In the triterpane distributions, the C27 trisnorhopane isomers and the moretane to hopane ratios appear to be both source and maturity related and cannot be used as successful maturity parameters in oils unless they share a common source. The C31+ hopane 22S/22R equilibrium ratio appears to increase with increasing molecular weight (C31–C34).  相似文献   

15.
The stable hydrogen isotopic compositions (δD) of selected aliphatic hydrocarbons (n-alkanes and isoprenoids) in eight crude oils of similar source and thermal maturity from the Upper Indus Basin (Pakistan) were measured. The oils are derived from a source rock deposited in a shallow marine environment. The low level of biodegradation under natural reservoir conditions was established on the basis of biomarker and aromatic hydrocarbon distributions. A plot of pristane/n-C17 alkane (Pr/n-C17) and/or phytane/n-C18 alkane (Ph/n-C18) ratios against American Petroleum Institute (API) gravity shows an inverse correlation. High Pr/n-C17 and Ph/n-C18 values and low API gravity values in some of the oils are consistent with relatively low levels of biodegradation. For the same oils, δD values for the n-alkanes relative to the isoprenoids are enriched in deuterium (D). The data are consistent with the removal of D-depleted low molecular weight (LMW) n-alkanes (C14–C22) from the oils. The δD values of isoprenoids do not change with progressive biodegradation and are similar for all the samples. The average D enrichment for n-alkanes with respect to the isoprenoids is found to be as much as 35‰ for the most biodegraded sample. For example, the moderately biodegraded oils show an unresolved complex mixture (UCM), loss of LMW n-alkanes (<C15) and moderate changes in the alkyl naphthalene distributions. The relative susceptibility of alkyl naphthalenes at low levels of biodegradation is discussed. The alkyl naphthalene biodegradation ratios were determined to assess the effect of biodegradation. The dimethyl, trimethyl and tetramethyl naphthalene biodegradation ratios show significant differences with increasing extent of biodegradation.  相似文献   

16.
Research on the molecular fossil characteristics of heavy oil from Well Tadong-2 is of great importance to constrain the source of marine crude oils in the Tarim Basin, Xinjiang, China. The authors synthetically applied the isotope mass spectrograph, chromatography and chromatography-mass spectrography to the studies of molecular fossil characteristics of heavy oil from Well Tadong-2 in the Tarim Basin, and the results obtained revealed that heavy oil from Well Tadong-2 is characterized by high gammacerane, high C28 sterane, low rearranged sterane and high C27-triaromatic steroid, these characteristics are similar to those of Cambrian-Lower Ordovician source rocks, demonstrating that Cambrian crude oils came from Cambrian-Lower Ordovician source rocks; condensed compounds (fluoranthene, pyrene, benzo[a]anthracene, bow, benzo fluoranthene, benzopyrene) of high abundance were detected in heavy oil from Well Tadong-2, and the carbon isotopic values of whole oil are evidently heavy, all the above characteristics revealed that hydrocarbons in the crude oils became densified in response to thermal alteration.  相似文献   

17.
A 3D interpretation of the newly compiled Bouguer anomaly in the area of the “Dead Sea Rift” is presented. A high-resolution 3D model constrained with the seismic results reveals the crustal thickness and density distribution beneath the Arava/Araba Valley (AV), the region between the Dead Sea and the Gulf of Aqaba/Elat. The Bouguer anomalies along the axial portion of the AV, as deduced from the modelling results, are mainly caused by deep-seated sedimentary basins (D > 10 km). An inferred zone of intrusion coincides with the maximum gravity anomaly on the eastern flank of the AV. The intrusion is displaced at different sectors along the NNW–SSE direction. The zone of maximum crustal thinning (depth 30 km) is attained in the western sector at the Mediterranean. The southeastern plateau, on the other hand, shows by far the largest crustal thickness of the region (38–42 km). Linked to the left lateral movement of approx. 105 km at the boundary between the African and Arabian plate, and constrained with recent seismic data, a small asymmetric topography of the Moho beneath the Dead Sea Transform (DST) was modelled. The thickness and density of the crust suggest that the AV is underlain by continental crust. The deep basins, the relatively large intrusion and the asymmetric topography of the Moho lead to the conclusion that a small-scale asthenospheric upwelling could be responsible for the thinning of the crust and subsequent creation of the Dead Sea basin during the left lateral movement. A clear segmentation along the strike of the DST was obtained by curvature analysis: the northern part in the neighbourhood of the Dead Sea is characterised by high curvature of the residual gravity field. Flexural rigidity calculations result in very low values of effective elastic lithospheric thickness (t e < 5 km). This points to decoupling of crust in the Dead Sea area. In the central, AV the curvature is less pronounced and t e increases to approximately 10 km. Curvature is high again in the southernmost part near the Aqaba region. Solutions of Euler deconvolution were visualised together with modelled density bodies and fit very well into the density model structures. An erratum to this article can be found at  相似文献   

18.
《Tectonophysics》2007,429(3-4):165-181
The Dead Sea fault is among the largest active strike–slip fault of the world. This study is focused on the southern part of this fault, from the Sea of Galilee to the Gulf of Aqaba, as monitored mainly by the Jordanian and Israeli seismic networks. The data of arrival times and polarities allowed relocation of earthquakes with a better azimuthal coverage and computation of focal mechanisms. This last step has been realized by inverting the polarities to determine a unique stress tensor for the region and the compatible focal mechanisms. Inversion with different subsets of the data set, based on tectonic regionalization, has also been performed to evaluate the impact of each cluster of earthquakes on the global solution. The population of focal mechanisms is clearly dominated by strike–slip events, with the notable exception of a cluster of earthquakes, south of the Dead Sea, which displays several normal focal mechanisms. This last cluster forces σ1 to be vertical and σ2 to be horizontal. A large number of fault planes, however, are close to the vertical, inhibiting the action of the vertical component of the stress tensor, and acting like under strike–slip stress regime. We observed a good agreement between the location of the earthquakes and the active faults, based on geological data. In addition, there is a good agreement between the fault plane solutions and the orientation of the active faults.  相似文献   

19.
This study presents data on concentrations of n-alkylbenzenes, n-alkylnaphthalenes, phytanylnaphthalene, and methylphytanylnaphthalene in representative crude oils of Tatarstan. The results of the study reveal the elevated concentrations of C19, C21, and C23 homologues of n-alkylbenzenes and n-alkylnaphthalenes, which can be considered as biomarkers. The proposed procedure for comprehensive quantification of this group of biomarkers can be used as an efficient tool to study oils from the major petroleum basins of Russia. Based on the results of the study, four genetic groups of oils in Tatarstan have been distinguished: (1) oils from the north and northwest (Bir saddle, Lower Kama system of linear faults, and Saraily saddle), (2) oils from Devonian terrigenous reservoirs within the South Tatar arch and Melekes depression, (3) oils from Carboniferous reservoirs, and (4) oils from Devonian carbonate reservoirs. All these oils belong to the same genetic macrotype. Based on the results of this study, the sedimentary sections of the Melekes depression cannot be regarded as potential source rocks. It is assumed that oil has migrated to the northern part of the region from the north or east. Some of the possible migration routes for oils from the remaining part of Tatarstan are from the southeast and/or south.  相似文献   

20.
The free, adsorbed and inclusion oils were recovered by sequential extraction from eleven oil and tar containing reservoir rocks in the Tazhong Uplift of Tarim Basin. The results of gas chromatography (GC) and GC–mass spectrometry analyses of these oil components and seven crude oils collected from this region reveal multiple oil charges derived from different source rocks for these oil reservoirs. The initially charged oils show strong predominance of even over odd n-alkanes in the range n-C12 to n-C20 and have ordinary maturities, while the later charged oils do not exhibit any predominance of n-alkanes and have high maturities. The adsorbed and inclusion oils of the reservoir rocks generally have high relative concentrations of gammacerane and C28 steranes, similar to the Cambrian-Lower Ordovician source rocks. In contrast, the free oils of these reservoir rocks generally have low relative concentrations of gammacerane and C28 steranes, similar to the Middle-Upper Ordovician source rocks. There are two interpretations of this result: (1) the initially charged oils are derived from the Cambrian-Lower Ordovician source rocks while the later charged oils are derived from the Middle-Upper Ordovician source rocks; and (2) both the initially and later charged oils are mainly derived from the Cambrian-Lower Ordovician source rocks but the later charged oils are contaminated by the oil components from the Silurian tar sandstones and the Middle-Upper Ordovician source rocks.  相似文献   

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