Shimon Feinstein

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

Abstract 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 >C20n-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.

Thermal history of Canadian Williston basin from apatite fission-track thermochronology—implications for petroleum systems and geodynamic history

Abstract Apatite fission track (AFT) thermochronology has been applied to a composite depth profile of Precambrian basement rocks underlying the Phanerozoic Canadian Williston Basin. Thermal histories derived from the AFT data record cycles of heating and cooling which follow the pattern of regional burial history, but which also indicate major temporal and geographic variations in the timing and degree of maximum Phanerozoic temperatures. These variations in the thermal history were not previously recognised from organic maturity indicators and subsidence models. Specifically, our study suggests a late Paleozoic heat flow anomaly with a geographic extent closer to that of Middle Devonian–Carboniferous Kaskaskia subsidence patterns than to that of the Williston Basin proper. This thermal anomaly has both economic and geodynamic significance. The recognition that potential Upper Cambrian–Lower Ordovician petroleum source rocks became fully mature during the late Paleozoic distinguishes that petroleum system from others that entered the main hydrocarbon generation stage in latest Cretaceous and Paleogene time. The late Paleozoic heat flow anomaly suggested from the AFT data implies a geodynamic coupling between inelastic Kaskaskia subsidence and previously inferred late Paleozoic lithospheric weakening. While the temporally varying heat flow model is preferred, the lack of independent constraints on the maximum thickness of upper Paleozoic strata precludes the outright rejection of the previous constant heat flow model. The AFT data provide important new constraints on the evolution of the epicratonic Williston Basin and its geodynamic models.

Thermal history of the eastern margin of the Gulf of Suez, I. reconstruction from borehole temperature and organic maturity measurements

Abstract The Gulf of Suez is a Tertiary continental rift associated with prominent flank uplift. Despite numerous studies which focused mainly on the western and central parts of the graben, the thermo-mechanics controlling the tectonic evolution of the Gulf of Suez is still enigmatic. We have integrated borehole temperatures and organic maturity measurements in the eastern margin of the Gulf of Suez, in order to study rift-related paleothermometry and the present-day thermal regime. The data obtained suggest that the present thermal regime represents the maximum heat flow and temperatures for the sedimentary section in the basin. Furthermore, lateral distributions of geothermal gradient and heat flow in the Gulf of Suez do not correlate, mainly because of extensive variability in lithology and thermal conductivity. Rift-related heat flow increases systematically and subparallel to the rift axis, from about 60 mW/m2 in the Darag subbasin in the north to about 80 mW/m2 in the Ras Garra area in the south. Both values are higher than 45 mW/m2, the average heat flow assumed for the pre-rift stage and the characteristic level for the present-day heat flow away from the rift. The north to south increase in heat flow probably reflects the southward increase of extension as well as lateral transfer of heat flow from the Red Sea. This latter conclusion is supported by the fact that heat flow in the southern Gulf of Suez recorded by the paleothermometric reconstructions and borehole temperature data is somewhat higher than that estimated by model calculations for the extension derived from structural and subsidence reconstruction.

A major Late Devonian-Early Carboniferous (Hercynian) Thermotectonic event at the NW Margin of the Arabian-Nubian Shield: Evidence from zircon fission track dating

Zircon fission track (ZFT) ages of 17 Precambrian samples from deep boreholes and outcrops in southern Israel and Sinai fall within the range 328–373 Ma (Late Devonian-Early Carboniferous). Single zircon grain age distributions are unimodal with a high chi-square probability. The age data indicate total resetting of the ZFT clocks but only partial resetting of coexisting sphenes, constraining the temperatures attained to about 225° ± 50°C, followed by relatively rapid regional cooling at the times indicated. In the study area, the lower Paleozoic section presently overlying Precambrian rocks is limited to Cambrian strata, up to 300 m thick. Further, stratigraphic evidence for sub-Carboniferous erosion is preserved only in SW Sinai. To the east, in southern Jordan, a 2–2.5 km thick lower Paleozoic succession is reported. Despite the lack of stratigraphic evidence in the study area, the ZFT data (1) strongly suggest that an equivalent or thicker section also existed, (2) constrain the timing of the erosion to Late Devonian-Early Carboniferous (Hercynian), and (3) indicate that thermal gradients may have reached ≥50°C/km prior to the uplift/erosion event. Regional stratigraphic evidence indicates that the Late Devonian-Early Carboniferous event was confined to a relatively narrow belt extending from the Gulf of Suez area to the vicinity of NE Syria and SE Turkey.

Subsidence and Thermal History of Southern Oklahoma Aulacogen: Implications for Petroleum Exploration

Reconstructed subsidence curves and the thermal history of the Southern Oklahoma aulacogen support the concept of thermally controlled isostatic subsidence for the formation of the basin and indicate the significance of this concept for petroleum exploration. Two mechanisms--initial elastic flexure, followed by detachment and differential subsidence of the aulacogen--are inferred from the subsidence curves. Two methods have been used for reconstruction of the thermal history. A tectonophysics model in combination with a history of basin evolution demonstrates that geothermal gradient and depth-of-burial were dynamic variables during the subsidence stage; maximum paleotemperatures were attained during Sylvan (Late Ordovician) time near the close of subsidence; and most of the Arbuckle Group had been subjected to the temperature conditions of oil formation (the oil liquid window) prior to the possible phase of fluid migration in Sylvan time. The second method, involving reconstruction of the geothermal history on the basis of geothermometry (palynomorph carbonization), suggests: (1) paleotemperatures exerted a significant effect on the level of organic metamorphism in the sedimentary rocks; (2) the geothermal gradient varied during the subsidence stage; (3) paleotemperatures were higher than those predicted by the theoretical model and support the hypothesis of formation of the basin by thermally controlled subsidence, and the application of this concept for petroleum exploration.

Effect of mineral matrix and seam thickness on reflectance of vitrinite in high to low volatile bituminous coals: an enigma

Abstract The variation of vitrinite reflectance with respect to mineral matrix (lithology), the thickness of coal seams and coal lenses and the type of organic matter was studied from two cores in a 550 m sedimentary succession from the Upper Jurassic to Lower Cretaceous Kootenay Group. The data obtained indicate that reflectance in high to low volatile bituminous coals (%RO, max = 0.8–1.35) with depth of burial is affected by the percentage of organic matter in the samples. A positive correlation between the vitrinite reflectance and the percentage of organic matter and a negative correlation with the percentage of mineral matter exist and the thicker the coal interval, the higher the vitrinite reflectance. Thick coal seams (>1 m) with a mineral content 20%. Vitrinite dispersed in sandstone and to a lesser extent siltstone and carbonaceous shale has the lowest reflectance. Variations in vitrinite reflectance may be attributed to chemical differences in the organic matter, possibly induced by degradation and diagenesis syn- or post-depositionally, and to the effect of some clay minerals present in the sediments, which may act as catalysts. Differences in the thermal conductivity of the strata have demonstratably not accounted for the observed variations in reflectance with lithology. The differences in the vitrinite reflectance of organic matter between lithotypes is substantial and is thus an important consideration in resolving the time-temperature history and generation of hydrocarbons from a sedimentary succession.

Effect of maceral subtypes and mineral matrix on measured reflectance of subbituminous coals and dispersed organic matter

Abstract The variability in reflectance of huminite (texto-ulminite, eu-ulminite A and B, different types of corpohuminite) and liptinite groups of macerals in subbituminous coals was examined using reflected light microscopy. All macerals were selected from coal and interbedded carbonaceous shale and carbonate sediment samples from the 515-m-thick coal deposit No. 2 located in the Hat Creek valley of south-central British Columbia. The measurements obtained reveal that, in addition to burial depth, reflectance distribution depends on maceral subtypes and associated mineral matrix. Huminite in the coals and sediments (kerogen) consists mainly of humotelinite, with eu-ulminite B being the dominant maceral sub-type. Reflectance values determined on huminite in coals and Type IIIb kerogen increase from eu-ulminite A and phlobaphinite type 1 through eu-ulminite B and phlobaphinite type 2 to gelinite. The reflectance of all five huminite maceral subtypes studied increases with depth. However, the increase of phlobaphinite type 1 and gelinite reflectance with depth is irregular. A comparison of the reflectance values obtained for the same maceral subtype (eu-ulminite B) from the interbedded coal, shale and carbonate samples records consistent differences, implying some dependence of the reflectance (and perhaps rate of organic maturation) on the mineral matrix. Generally, the highest eu-ulminite B reflectance was recorded from carbonate rocks and the lowest from shale, whereas coal matrix produced intermediate values. At present, it is not known whether differences in reflectance of eu-ulminite found in the above lithologies are due to differential retention, efficiency of reaction products removal, thermal conductivity of the lithologies, or existence of a calcium carbonate catalyst.

Thermal history of the eastern Gulf of Suez, II. Reconstruction from apatite fission track and 40Ar39Ar K-feldspar measurements

Abstract Apatite fission track (AFT) measurements from Miocene graben-fill sediments of the eastern Gulf of Suez in three deep boreholes (Belayim 113 M-2/6, Ras Garra M-1 and Alma-2) yield a wide range of ages (from 125 to 320 Ma) and mean track-lengths (∼10.1–12.7 μm). This range is similar to that recorded from Precambrian crystalline basement flanking the graben which is the major source for the rift fill. Since the AFT ages exceed the age of the host strata, which are presently at their highest post-depositional temperatures, the rift-related thermal regime is one of only moderate heating. Downhole AFT data in the Belayim 113 M-2/6 borehole attest to a higher rift temperature than in the Ras Garra M-1 borehole, some 85 km to the south, where little or no thermal overprinting is evident. These findings are consistent with previously reported bottom hole temperatures and vitrinite reflectance data in the study area. Despite the higher syn-rift thermal regime indicated for Belayim 113 M-2/6, apatite provenance ages in Ras Garra M-1 are considerably younger. Thus, the AFT data in the Ras Garra M-1 area do not record significant rift-related thermal effects, but rather, they mainly retain a pre-rift provenance signature which reflects the order and depth of erosion at the uplifted flanks. The younger AFT ages in Ras Garra M-1, despite the weaker rift-related thermal effect, suggest a deeper level proportional to an additional ∼5–10°C of exhumation of the uplifted crystalline basement southwards along the eastern rift flank by Mid-Miocene time. This result is consistent with earlier findings which indicate both increased extension and heat flow southwards in the Gulf of Suez, and earlier exhumation of the rift flank. Immediately preceding extension and opening of the Gulf of Suez, the most deeply exhumed basement rocks presently exposed on the rift flanks were heated to temperatures ≥110°C (total annealing of apatite), but 40 Ar 39 Ar data and non-resetting of zircon FT clocks in sinai, 40 Ar 39 Ar data from granite penetrated in graben drilling at ∼3.89 km further corroborates pre-rift palaeotemperatures

Constraints on the thermal history of the Dead-Sea Graben as revealed by coal ranks in deep boreholes

Abstract Coal ranks have been studied by vitrinite reflectance measurements in three boreholes; Zuk Tamrur 1 and Zohar 8 on the Judea Desert plateau (adjacent to the graben margin) and Amiaz 1 on a down-faulted block at the southwest Dead-Sea Graben. In the plateau boreholes, time-temperature index (TTI) calculations reveal that the coalification profile probably evolved under a Late Cretaceous thermal event with a thermal gradient of 35°–38°C/km followed by gradual decay to the present level c. 20°C/km by Miocene time. In Amiaz 1, the highest coal rank encountered, 0.5% Ro, is marginal for independent TTI calculations, however, some constraints on thermal history can be inferred. Stratigraphic and structural relationships between the 0.5% Ro isoreflectance in Amiaz 1 and the plateau boreholes reveals that most of the coalification measured in Amiaz 1 pre dates the formation of the graben and that an additional 3.4 km of Miocene-Holocene graben fill barely affected the coalification. Cessation of coalification despite increasing burial indicates that the post-Miocene thermal gradient in the Amiaz block could not have exceeded 20°–23°C/km. This finding is consistent with present day heat flow and other geophysical information. Tectonic models for the evolution of the Dead Sea Graben requiring a high thermal regime are inconsistent with the presented data. This raises questions as to the mechanism involved in the formation of rhomb-shaped grabens in general, on the one hand and for the hypothesis of the “leaky” nature of the Dead Sea transform north of the Gulf of Elat, on the other.

Cretaceous to present paleothermal gradients, central Negev, Israel: Constraints from fission track dating

Abstract Apatite and zircon fission track ages (FTA), vitrinite reflectance (VR) data and burial history curves were integrated for reconstruction of Early Cretaceous to present maximum thermal gradients in four deep boreholes in the central Negev, Israel. The most complete data set is available from the Ramon 1 borehole. Supplementary data were obtained from Hameishar 1, Makhtesh Qatan 2, and Kurnub 1 boreholes. Between ca. 122-90 Ma the constraints on thermal gradient obtained from apatite FTA overlap with those derived from zircon FT and VR data, restricting them to Thermal constraints derived from apatite FTA and VR data in Makhtesh Qatan 2 and Kurnub 1 boreholes are consistent with those obtained post-56 Ma for Ramon 1. For pre-56 Ma, only VR data are available and these indicate considerably lower maximum gradients than those obtained for the same time period from Ramon 1. This dichotomy reflects different Early Cretaceous-Early Tertiary thermal regimes between the northern and southern parts of the study area.