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1.
In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy (foraminifera and radiolarians) and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian–Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relatively short period (0.5 Ma), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo-environmental relevant indicators. High Baxs values and Uauth may indicate anoxic conditions at least at the water–sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions.  相似文献   

2.
Rock–Eval pyrolysis analysis, burial history, and 1D thermal maturity modeling have allowed the evaluation of the source rock potential, thermal maturation state, and impacts of the Pabdeh and Gurpi Formations in Cretaceous–Miocene petroleum system in the Naft Safid (NS) and Zeloi (ZE) oilfields, North Dezful Embayment. The total organic carbon (TOC) content of the Pabdeh and Gurpi Formations ranges from 0.2 to 4.7 wt% and 0.3 to 5.3 wt%, respectively. S2 values of the Pabdeh Formation in the ZE and NS oilfields vary from 0.41 to 13.77 and 0.29 to 14.5 mg HC (Hydrocarbon)/g rock, with an average value of 4.48 and 4.14 mg HC/g rock, respectively. These values for the Gurpi Formation in the ZE and NS oilfields range from 0.31 to 16.96 and 0.26 to 1.44 mg HC/g rock, with an average value of 8.54 and 2.43 mg HC/g rock, respectively. The S2 versus TOC diagram reveals a fair to good hydrocarbon generation potential of the Pabdeh Formation and poor to fair potential of the Gurpi Formation. The high values of S2 (S2 > S1) for samples of the both formations in the ZE and NS oilfields show that the samples are not contaminated with petroleum generated from underlying source rocks. The samples of the Pabdeh Formation in the ZE oilfield are characterized by a relatively narrow range of activation energy values with principal activation energy of 46 kcal/mol and frequency factor of 5.27 × 10+11 s?1. It seems that the high sulfur content of the Pabdeh organic matter probably caused the frequency factor and principal activation energy to be lower than usual. Hydrogen index (HI) values of the Pabdeh and Gurpi Formations in the ZE oilfield vary from 71 to 786 and 97 to 398 mg HC/g TOC, with an average value of 310 and 277 mg HC/g TOC, respectively. These values in the NS oilfield range from 66 to 546 and 51 to 525 mg HC/g TOC, with an average value of 256 and 227 mg HC/g TOC, respectively. Plot of HI vs. T max value indicates that the majority of the Pabdeh and Gurpi samples contain predominantly type II kerogen and their organofacies are directly related to the more homogeneous precursor materials. Based on thermal maturity modeling results, kinetic parameters, and Rock–Eval analysis, both formations in the ZE and NS oilfields are thermally mature and immature or early mature stage, respectively.  相似文献   

3.
Twenty organic rich outcrop samples from the Belait and Setap Shale formations in the Klias Peninsula area, West Sabah, were analysed by means of organic petrology and geochemical techniques. The aims of this study are to assess the type of organic matter, thermal maturity and established source rock characterization based primarily on Rock-Eval pyrolysis data. The shales of the Setap Shale Formation have TOC values varying from 0.6 wt%–1.54 wt% with a mean hydrogen index (HI) of 60.1 mg/g, whereas the shal...  相似文献   

4.
The late Cenomanian–early Turonian deposits in Tunisia recording the OAE2 event are commonly attributed to the Bahloul Formation. These deposits are composed of dark clayey limestone and organic-rich black shales with abundant planktic foraminifera. At the Bargou area, Oued Kharroub section, these organic-rich deposits include siliceous beds with abundant radiolarians recalling the “Livello Bonarelli”. A total of 25 radiolarian species are identified with a maximum of 18 species per sample. Moreover, the species skeleton preservation is usually poor to moderate in the most studied samples [estimated preservation index (PI) values ranging between 4 and 6]. Two successive assemblages are distinguished. The oldest one (RI) is dominated by nassellarians, which includes mainly Stichomitra, Pseudodictyomitra and Rhopalosyringium genera. It is included within the upper part of foraminiferal Rotalipora cushmani Zone and lower part of Whiteinella archaeocretacea zone. In contrast, the youngest assemblage (RII), which belongs to the upper part of the W. archaeocretacea zone and the earliest Turonian Watinoceras ammonite assemblage, is dominated by spumellarians and includes mainly Archaeocenosphaera, Cavaspongia, Pseudoeucyrtis and Pyramispongia genera. In addition, major and trace elements are analysed to test whether the geochemical record was synchronous to the biotic event or not. Thus, selected crossplots, Al2O3 vs. SiO2 and Al2O3 vs. TiO2, are used to evaluate the detrital input, and V/Cr vs. V/(V?+?Ni) and U/Th vs. V/(V?+?Ni) are used to evaluate the bottom redox conditions and the primary productivity within the Bahloul Formation. A strong Si/Al increase is marked in the lower part of the siliceous and organic-rich Bahloul Formation that could be explained by a local increase in upwelling-related biogenic SiO2 (silica-secreting organisms). Relative low abundance of terrigenous-related Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba (organic matter related trace elements) suggests that the Bahloul was of relatively elevated primary productivity and minimal detrital input. Enrichments in redox-sensitive trace metals U and V in the Bahloul Formation deposits and redox indices, such as V/(V?+?Ni), U/Th and V/Cr, indicate that oxygen-restricted conditions prevailed during the late Cenomanian–earliest Turonian times and correlate well with relative abundances of some radiolarian and foraminiferal paleo-environmental indicators. In addition, indicators of detrital flux variations are used. Al2O3 shows a slight positive correlation with TiO2 and a less distinct correlation with SiO2.  相似文献   

5.
Organic geochemical analysis and palynological studies of the organic matters of subsurface Jurassic and Lower Cretaceous Formations for two wells in Ajeel oil field, north Iraq showed evidences for hydrocarbon generation potential especially for the most prolific source rocks Chia Gara and Sargelu Formations. These analyses include age assessment of Upper Jurassic (Tithonian) to Lower Cretaceous (Berriasian) age and Middle Jurassic (Bathonian–Tithonian) age for Chia Gara and Sargelu Formations, respectively, based on assemblages of mainly dinoflagellate cyst constituents. Rock-Eval pyrolysis have indicated high total organic carbon (TOC) content of up to 18.5 wt%, kerogen type II with hydrogen index of up to 415 mg HC/g TOC, petroleum potential of 0.70–55.56 kg hydrocarbon from each ton of rocks and mature organic matter of maximum temperature reached (Tmax) range between 430 and 440 °C for Chia Gara Formation, while Sargelu Formation are of TOC up to 16 wt% TOC, Kerogen type II with hydrogen index of 386 mg HC/g TOC, petroleum potential of 1.0–50.90 kg hydrocarbon from each ton of rocks, and mature organic matter of Tmax range between 430 and 450 °C. Qualitative studies are done in this study by textural microscopy used in assessing amorphous organic matter for palynofacies type belonging to kerogen type A which contain brazinophyte algae, Tasmanites, and foraminifera test linings, as well as the dinoflagellate cysts and spores, deposited in dysoxic–anoxic environment for Chia Gara Formation and similar organic constituents deposited in distal suboxic–anoxic environment for Sargelu Formation. The palynomorphs are of dark orange and light brown, on the spore species Cyathidites australis, that indicate mature organic matters with thermal alteration index of 2.7–3.0 for the Chia Gara Formation and 2.9–3.1 for the Sargelu Formation by Staplin's scale. These characters have rated the succession as a source rock for very high efficiency for generation and expulsion of oil with ordinate gas that charged mainly oil fields of Baghdad, Dyala (B?aquba), and Salahuddin (Tikrit) Governorates. Oil charge the Cretaceous-Tertiary total petroleum system (TPS) are mainly from Chia Gara Formation, because most oil from Sargelu Formation was prevented passing to this TPS by the regional seal Gotnia Formation. This case study of mainly Chia Gara oil source is confirmed by gas chromatography–mass spectrometry analysis for oil from reservoirs lying stratigraphically above the Chia Gara Formation in Ajeel and Hamrine oil fields, while oil toward the north with no Gotnia seal could be of mainly Sargelu Formation source.  相似文献   

6.
A worldwide data set of 1,085 samples containing organic matter of the type II/III kerogen from Carboniferous to Cenozoic was used to analyse the evolution of the hydrogen index (HI), quality index (QI), and bitumen index (BI) with increasing thermal maturity. The HImax, QImax and BImax lines were defined, based on statistical analysis and cross-plots of HI, QI and BI versus the vitrinite reflectance (%Ro) and T max (°C). The constructed HI, QI and BI bands were broad at low maturities and gradually narrowed with increasing thermal maturity. The petroleum generation potential is completely exhausted at a vitrinite reflectance of 2.0–2.2 % and T max of 510–520 °C. An increase in HI and QI suggests extra petroleum potential related to changes in the structure of the organic material. A decline in BI signifies the start of the oil window and occurs within the vitrinite reflectance range 0.75–1.05 % and T max of 440–455 °C. Furthermore, petroleum potential can be divided into four different parts based on the cross-plot of HI versus %Ro. The area with the highest petroleum potential is located in “Samples and methods” with %Ro = 0.6–1.0 %, and HI > 100. Oil generation potential is rapidly exhausted at “Results and discussion” with %Ro > 1.0 %. This result is in accordance with the regression curve of HI and QI with %Ro based on 80 samples with %Ro = 1.02–3.43 %. The exponential equation of regression can thus be achieved: HI = 994.81e?1.69Ro and QI = 1,646.2e?2.003Ro (R 2 = 0.72). The worldwide organic material data set defines two range of oil window represented by the upper and lower limits of the BI band: %Ro 0.75–1.95 %, T max 440–525 °C, and %Ro 1.05–1.25 %, T max 455–465 °C, respectively.  相似文献   

7.
In the Lycian Basin (SW Turkey), the Miocene Karabay?r and Karaku?tepe formations consist of algal limestone, conglomerate, sandstone, shale and limestone. Total organic carbon (TOC) analysis of the Miocene units show that these formations are poor in organic matter. TOC values are generally between 0.02 and 0.51%, but reach 3.47% in the Karabay?r Formation. Hydrogen indices (HI) are mostly below 600 mgHC/gTOC, increasing to 1200 mgHC/gTOC in the Karabay?r Formation. S2 vs. TOC diagrams are used to evaluate the sedimentary environments and hydrocarbon potential of the Lower–Middle Miocene sediments (the Isparta, Bucak and Korkuteli‐Elmal? areas). The organic material contains about 63 (type I), 35 (type II) and 29 (type II/III) pyrolysable hydrocarbons, respectively. The dominant organic matter is type II kerogens, and hydrocarbon generating potential is quite low. A positive x‐intercept has been calculated in analysed samples according to S2 vs. TOC diagrams; this value shows a rock‐matrix effect. Clay is the main agent of adsorption. Biomarker characteristics also verify these results. Isoprenoid rates are Pr/Ph: 2, Pr/n‐C17: 1.9, and Pr/n‐C18: 0.5, and a high Pr/Ph ratio (pristane/phytane) indicates an oxic environment; the terpane C29 NH/C30 H ratio is >1 for the Karabay?r Formation, and this value indicates a carbonate lithology. On the other hand, the C25 NH/C30 H ratio is <1 for the Karaku?tepe Formation; this indicates that the hydrocarbons were derived from terrestrial organic matter. According to m/z 191 mass fragmentograms, the Miocene units contain oleanane, indicating a Tertiary age. The abundance of sterane C29>C28>C27 shows that the kerogens formed from algal organic matter.  相似文献   

8.
Total organic carbon (TOC) determination, Rock‐Eval pyrolysis, extractable organic matter content (EOM) fractionation, gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) analyses, were carried out on 79 samples from eleven outcrop cross sections of the Bahloul Formation in central and northern Tunisia. The TOC content varied between 0.23 to 35.6%, the highest average values (18.73%, 8.46% and 4.02%) being at the east of the study area (at Ain Zakkar, Oued Bahloul and Dyr Ouled Yahia localities, respectively). The Rock‐Eval maximum pyrolysis temperature (Tmax) values in the 424–453°C range delineated a general east‐west trend increase in the organic matter (OM) maturity. The disparity in hydrogen index (HI) values, in the range 114–824 mg hydrocarbons (HC) g?1 TOC, is relevant for the discrepancy in the level of OM preservation and maturity among localities and samples. The n‐alkane distributions, maximizing in the C17 to C20 range, are typical for a marine planktonic origin, whereas pristine/phytane (Pr/Ph) average values in the 1–2 range indicate an oxic to suboxic depositional environment. Pr/n‐C17 and Ph/n‐C18 ratios in the 0.38–6.2 and 0.68–3.25 range, respectively, are consistent with other maturity indicators and the contribution of specific bacteria to phytol as a precursor of isoprenoids. The thermal maturity varies between late diagenesis to main‐stage of petroleum generation based on the optic and the cis‐trans isomerisation of the C29 sterane [20S/(20S+20R) and 14β(H),17β(H)/(14β(H),17β(H)+14α(H),17α(H)), respectively] and the terpane [18α(H)22,29,30‐Trisnorneohopane/(18α(H)22,29,30‐Trisnorneohopane+17α(H)22,29,30‐Trisnorhopane): Ts/(Ts+Tm)] ratios. The Bahloul OM is represented by an open marine to estuarine algal facies with a specific bacterial contribution as revealed by the relative abundance of the ααα‐20R C27 (33–44%), C28 (22–28%) and C29 (34–41%) steranes and by the total terpanes/total steranes ratio (1.2–5.33). These results attested that the Bahloul OM richness was controlled both by an oxygen minimum zone induced by high productivity and restricted circulation in narrow half graben structures and around diapirs of the Triassic salt.  相似文献   

9.
To investigate the mechanism of the organic-matter enrichment in the Lower Longmaxi Formation shale, the geochemistry and total organic carbon(TOC) of the Longmaxi Formation black shales in the Jiaoshiba, Zhaotong, and Weiyuan areas of the Sichuan Basin were analyzed. Paleoproductivity proxy parameters(Babio, Siex, and Ni/Al), clastic influx proxies(TiO_2 and Ti/Al), redox indices(V/Cr, Ni/Co, V/(V+Ni), and U/Th), and hydrothermal indicators(Fe, Mn,and Y concentrations; Fe/Ti ratio and a Ni-Zn-Co diagram) were employed to decipher the paleoenvironment of the Lower Longmaxi Formation shales. TiO_2 and Ti/Al indicated low terrigenous detrital influx in all three areas. However, Babio, Siex,and Ni/Al indicated high productivity in the Jiaoshiba area. V/Cr, Ni/Co, and U/Th indicated higher oxygen content with larger fluctuations in the Zhaotong and Weiyuan areas. Fe, Mn, and Y concentrations and the Fe/Ti ratio implied greater active hydrothermal activity in the Weiyuan area. These heterogeneities were considered to be closely related to the paleoenvironment and paleogeography, and the large basement faults that developed during the Chuanzhong paleo-uplift could have provided vents for deep-hydrothermal-fluid upwelling. The redox indices(V/Cr, Ni/Co, and U/Th) and a paleoproductivity proxy(Ni/Al) displayed a significant correlation with the TOC, suggesting that both excellent preservation conditions and high paleoproductivity were the controlling factors for the enrichment of organic matter in the Longmaxi Formation shale. There was no obvious correlation between the clastic influx proxy(Ti/Al) and the TOC due to the extremely low supply of terrigenous debris. The hydrothermal indicator(Fe/Ti) was negatively correlated with the TOC in the Weiyuan area, indicating that hydrothermal activity may have played a negative role in the accumulation of organic matter. This study suggests that the enrichment of organic matter in the Longmaxi Formation marine shale varied according to the paleogeography and sedimentary environment.  相似文献   

10.
The current work investigates the hydrocarbon potentiality of the upper Jurassic–lower Cretaceous rocks in the Marib-Shabwah Basin, Central Yemen, through the Sabatayn-1 well. Therefore, palynological and organic geochemical analyses were carried out on 37 ditch cutting and 12 core samples from the well. Palynofacies analysis of the Madbi (late Oxfordian–early Tithonian) and Nayfa (Berriasian–Valanginian) Formations sediments indicates deposition of their organic-rich shale, calcareous shale and marl in middle to outer shelf environments under dysoxic–anoxic conditions, containing mainly kerogen of types II to III. However, the shales of the lower Sabatayn (Tithonian) Formation were deposited in an inner shelf environment of prevailing dysoxic–suboxic conditions, and show kerogen types III to II. Regional warm and relatively dry palaeoclimate but with local humid conditions developed near the site of the well is thought to have prevailed during deposition of the studied well sediments. The geochemical analyses of the Madbi Formation show higher total organic carbon content (TOC) than the overlying Sabatayn and Nayfa formations: it is varies between 1.2 and 7, and with average 4 wt% TOC, and the obtained S2 values (～3–10, average 7 mg HC/g rock) indicates that the Madbi Formation is mainly good source rock. It shows a good petroleum potential of 4–11 mg HC/g dry rock, and the Rock-Eval pyrolysis indicates mainly kerogen types II to III (oil to gas prone) of hydrogen index values (132–258, and only one sample from Lam Member is of 360 and average 215 mg HC/g TOC). The thermal maturation parameters as T max (425–440 °C), production index (average 0.13 mg HC/g rock) and thermal alteration index (2 to 2+) reflected that this formation is present at margin of maturation to early mature stage oil window. So, the Lam Member (upper part) of the Madbi Formation is considered the main hydrocarbon (oil and gas) source rock in the Marib-Shabwah Basin. Accordingly, we predict that the Meem Member is an active source for gas and oil accumulations in the overlying sandstone reservoir of the Sabatayn Formation in the Sabatayn-1 well.  相似文献   

11.
A detailed geochemical study and a sequence stratigraphic interpretation have been conducted on a sedimentary sequence of the Upper Cretaceous La Luna Formation, in a section outcropping in the eastern flank of the Middle Magdalena Basin (MMB), Colombia. The goals were to evaluate geochemical variability related to lithofacies and organic facies changes, characterize depositional environment and investigate the possible relationship between geochemical data and sequence stratigraphic cycles. The La Luna Formation is composed of organic-rich sediments of monotonous appearance, with good to excellent potential for oil generation. Most of the bulk, petrographic and biomarker parameters display a relatively narrow range of variation. However, the geochemical variations are sufficient to differentiate organic facies types B, BC and C in the Salada Member, B and D in the Pujamana Member and B in the Galembo Member. Certain biomarker ratios are consistent within the La Luna Formation and are characteristic of its depositional environment, for example, average ratios of diasterane/sterane are lower than 1, Ts/Tm averages are less than 0.33, the C35/C34 hopane ratio is more than 0.92, and oleanane/C30 hopane ratios range from 0.02 to 0.19. Regarding depositional condition indicators, the C35/C34 hopane ratio shows a good positive correlation with HI. This suggests that in carbonate environment changes in this parameter are more strongly related to redox condition than to changes in carbonate content. Regarding the possible relationship between organic matter characteristics and sea level changes, in regressive carbonate shelves during shallow stages, HI tends to increase and TOC tends to decrease, while in regressive siliciclastic shelves, both TOC and HI decrease continuously. Some biomarker ratios (oleanane/C30 hopane, C20/C23 tricyclic, Ts/Tm) increase during base level falls. Regarding δ 13C/12C isotope composition, the aromatic fraction and whole bitumen display an isotopic shift associated to the main deepening event in the section.  相似文献   

12.
Fossil shark teeth and coprolites from three major phosphorite occurrences in the Gafsa Basin (southwestern Tunisia) were investigated for their geochemical compositions to improve local stratigraphy and to better assess paleoenvironmental conditions. 87Sr/86Sr isotope ratios of shark teeth from the Early Maastrichtian El Haria Formation and from the Early Eocene Métlaoui s.s. Formation yielded Sr isotope ages of 68 ± 1 and 47.9 ± 1.3 Ma, respectively, which accord with the expected stratigraphic positions of these sediments. Conversely, shark teeth from the Paleocene–Eocene Chouabine Formation have large variation in Sr isotope ratios even within individual layers. After statistical treatment and then elimination of certain outlier samples, three age-models are proposed and discussed. The most reasonable solution includes three subsequent Sr ages of 61.8 ± 2.2 Ma, 57.2 ± 1.8 and 54.6 ± 1.6 for layer IX, layers VIII–V and layers IV–0, respectively. Three scenarios are discussed for explanation of the presence of the outliers: (1) diagenesis, (2) re-working and (3) locally controlled seawater Sr isotope ratio. The most plausible account for the higher 87Sr/86Sr ratios relative to the global ocean in some fossils is enhanced intrabasinal re-working due to low sea level. Conversely, the sample with lower 87Sr/86Sr than the global seawater may link to diagenesis or to seawater influenced by weathering of Late Cretaceous marine carbonates, which latter is supported by model calculation as well. The εNd values of these fossils are very similar to those reported for Paleogene and Late Cretaceous Tethyan seawater and are compatible with the above interpretations. The relatively low oxygen isotope values in shark teeth from the topmost phosphate bed of the Chouabine Formation, together with the Sr isotope results, point toward recovering better connections with the open sea. These δ18O data reflect elevated ambient temperature, which may link to the Early Eocene Climatic Optimum.  相似文献   

13.
Second‐order transgressive–regressive (T–R) cycles, previously recognized using sedimentological criteria in Lower Jurassic hemipelagic deposits from northern Spain, are distinguishable based upon bulk‐rock organic geochemistry [total organic carbon (TOC) and hydrogen index (HI)] and the stable carbon isotope compositions from belemnite rostra. There is a coincidence between regressions and decreasing δ13Cbel, TOC and HI values, and between transgressions and increasing δ13Cbel, TOC and HI values. The δ18O and Mg/Ca records from the belemnite rostra are not always in phase with the T–R cycles. The δ18Obel record reveals, however, a prominent excursion towards higher values within the spinatum Zone that correlates, according to our results, with a regression and with negative shifts in Mg/Ca, δ13Cbel and TOC. On the other hand, an excursion in the δ18Obel towards lower values in the serpentinus Zone also correlates with a peak transgression and with positive shifts in Mg/Ca, δ13Cbel and TOC. These two excursions have been identified in other European regions as geochemical perturbations of the same characteristics. This suggests a link between second‐order relative sea‐level changes and variations in seawater geochemistry that may reflect local and regional palaeoceanographic perturbations in sea‐water temperature, salinity and water circulation during the Early Jurassic. Terra Nova, 18, 233–240, 2006  相似文献   

14.
The Jurassic–Lower Cretaceous aged carbonate sequence is widely exposed in the southern zone of Eastern Pontides. Aptian black bituminous limestone is found in the upper part of this sequence in the Kale area (Gümüşhane). This limestone contains faunal remains (e.g., gastropod, ostracod, characean stems and miliolid type benthic foraminifera) that indicate a freshwater, lacustrine depositional environment.The total organic carbon (TOC) values of the bituminous limestone samples range from 0.11–1.30% with an average TOC value of 0.54%. The hydrogen index (HI) varies from 119–448 mg HC/g TOC (average HI 298 mg HC/g TOC) indicating that the limestone contains gas prone as well as oil prone organic matter. Pyrolysis data prove that the organic matter content in the bituminous limestone consists of Type II kerogen. The average Tmax value for bituminous limestone samples is 438 °C (434–448 °C). Bitumen/TOC ratios for bituminous limestone are 0.05 and 0.04. The Tmax values and the ratios indicate that the bituminous limestone samples contain early mature to mature organic matter.Analysis of solvent extracts from the two richest bituminous limestones show a predominance of high carbon number (C26–C30) n-alkanes. The Pr/Ph ratio and CPI value are 1.34 and 0.96, respectively. C29 is the dominant sterane, with C29 > C27 > C28. The bituminous limestone samples have low C22/C21 ratios, high C24/C23 tricyclic terpane ratios and very low C31R/C30 hopane ratios (<0.25). These data are consistent with the bituminous limestones being deposited in a lacustrine environment.  相似文献   

15.
Organic geochemical characterization of cutting samples from the Abu Hammad-1 and Matariya-1 wells elucidates the depositional environment and source rock potential of the Jurassic and Lower Cretaceous successions and the Middle Miocene to Pleistocene section in the southern and eastern Nile Delta Basin. The burial and thermal histories of the Mesozoic and Miocene sections were modeled using 1D basin modeling based on input data from the two wells. This study reveals fair to good gas-prone source rocks within the Upper Jurassic and Lower Cretaceous sections with total organic carbon (TOC) averaging 2.7% and hydrogen index (HI) up to 130 mg HC/g TOC. The pristane/n-C17 versus phytane/n-C18 correlation suggests mixed marine and terrestrial organic matter with predominant marine input. Burial and thermal history modeling reveals low thermal maturity due to low heat flow and thin overburden. These source rocks can generate gas in the western and northern parts of the basin where they are situated at deeper settings. In contrast, the thick Middle Miocene shows fair source rock quality (TOC averaging at 1.4%; HI maximizing at 183 mg HC/g TOC). The quality decreases towards the younger section where terrestrial organic matter is abundant. This section is similar to previously studied intervals in the eastern Nile Delta Basin but differs from equivalents in the central parts where the quality is better. Based on 1D modeling, the thick Middle Miocene source rocks just reached the oil generation stage, but microbial gas, however, is possible.  相似文献   

16.
Tertiary coals exposed in the north-central part of onshore Sarawak are evaluated, and their depositional environments are interpreted. Total organic carbon contents (TOC) of the coals range from 58.1 to 80.9 wt. % and yield hydrogen index values ranging from 282 to 510 mg HC/g TOC with low oxygen index values, consistent with Type II and mixed Type II–III kerogens. The coal samples have vitrinite reflectance values in the range of 0.47–0.67 Ro %, indicating immature to early mature (initial oil window). T max values range from 428 to 436 °C, which are good in agreement with vitrinite reflectance data. The Tertiary coals are humic and generally dominated by vitrinite, with significant amounts of liptinite and low amounts of inertinite macerals. Good liquid hydrocarbons generation potential can be expected from the coals with rich liptinitic content (>35 %). This is supported by their high hydrogen index of up to 300 mg HC/g TOC and Py-GC (S 2) pyrograms with n-alkane/alkene doublets extending beyond C30. The Tertiary coals are characterised by dominant odd carbon numbered n-alkanes (n-C23 to n-C33), high Pr/Ph ratio (6–8), high T m /T s ratio (8–16), and predominant regular sterane C29. All biomarkers parameters clearly indicate that the organic matter was derived from terrestrial inputs and the deposited under oxic condition.  相似文献   

17.
Seventy-two core and cutting samples of the Ratawi Formation from selected wells of central and southern Iraq in Mesopotamian Foredeep Basin are analysed for their sedimentary organic matters. Dinoflagellates, spores and pollen are extracted by palynological techniques from these rocks. Accordingly, Hauterivian and late Valanginian ages are suggested for their span of depositional time. These palynomorphs with other organic matter constituents, such as foraminifer’s linings, bacteria and fungi, are used to delineate three palynofacies types that explain organic matter accumulation sites and their ability to generate hydrocarbons. Palaeoenvironments of these sites were mainly suboxic to anoxic with deposition of inshore and neritic marine environments especially for palynofacies type 2. Total organic matters of up to 1.75 total organic carbon (TOC) wt.% and early mature stage of up to 3.7 TAI based on the brown colour of the spore species Cyathidites australis and Gleichenidites senonicus with mottled interconnected amorphous organic matter are used for hydrocarbon generation assessment from this formation. On the other hand, these rock samples are processed with Rock-Eval pyrolysis. Outcomes and data calculations of these analyses are plotted on diagrams of kerogen types and hydrocarbon potential. Theses organic matter have reached the mature stage of up to T max?=?438 °C, hydrogen index of up to 600 mg hydrocarbons for each gram of TOC wt.% and mainly low TOC (0.50–1.55). Accordingly, this formation could generate fair quantities of hydrocarbons in Baghdad oil field and Basrah oil fields. Organic matters of this formation in the fields of Euphrates subzone extends from Hilla to Nasiriyah cities have not reached mature stage and hence not generated hydrocarbons from the Ratawi Formation. Software 1D PetroMod basin modelling of the Ratawi Formation has confirmed this approach of hydrocarbon generation with 100 % transformations of the intended organic matters to generate hydrocarbons to oil are performed in especially oil fields of East Baghdad, West Qurna and Majnoon while oil fields Ratawi and Subba had performed 80–95 % transformation to oil and hence end oil generation had charged partly the Tertiary traps that formed during the Alpine Orogeny. Oil fields of Nasiriyah and Kifle had performed least transformation ratio of about 10–20 % transformation to oil, and hence, most of the present oil in this field is migrated from eastern side of the Mesopotamian Foredeep Basin that hold higher maturation level.  相似文献   

18.
《Organic Geochemistry》1999,30(2-3):161-188
Organic-rich source rocks have generally been attributed to enhanced preservation of organic matter under anoxic bottom waters. Here, geochemical analysis of kerogen and whole rock samples of organic-rich (lithofacies B1) and organic-lean (lithofacies B2) laminated mudrocks of the Devonian–Carboniferous Exshaw Formation, Alberta, highlight the importance of primary production in governing the quantity and quality of organic matter. Lower Si/Al, K/Al, Ti/Al and quartz/clay ratios in lithofacies B2, similar maceral types and the laminated fabric of the two lithofacies indicate that the quality and quantity of organic matter are not related to grain size, redox or organic matter source changes. High Total Organic Carbon (TOC) and Hydrogen Index (HI), low Oxidation Index (Ox.I. ratio of oxygen functional groups to aliphatic groups derived by FTIR), lighter δ15Ntot and heavier δ13Corg isotopes indicate that kerogen of lithofacies B1 accumulated during periods of high organic-carbon production and delivery of relatively fresh, labile, well-preserved organic matter to the sea floor. In contrast, low TOC, HI, high Ox.I., heavier δ15Ntot and lighter δ13Corg isotopes indicate low primary productivity and delivery, high recycling and poor preservation of organic matter during accumulation of lithofacies B2.  相似文献   

19.
Carbon isotope chemostratigraphy has been used worldwide for stratigraphic correlation.In this study,δ13Ccarb values are estimated for the Early Cambrian Sugaitebulake section in the Tarim Basin,Xinjiang Autonomous Region,China.As a result,one positive and two negative carbon isotope excursions in the studied section were iden-tified.The δ13Ccarb values reached the maximum negative excursion(N1:-12.39‰) at the basal of the Yuertusi For-mation,and then increased to P1.After P1,δ13Ccarb values sharply decreased to about-7.06‰(N2) in the studied section.The pattern of δ13Ccarb in the Early Cambrian is comparable to the synchronous records of other sections,such as the Laolin section,the Xiaotan section and the Anjiahe section of the Yangtze Platform.It is concluded that the Early Cambrian Yuertusi Formation from the Tarim Basin is within the Nemakit-Daldynian stage,and the lower strata of the Yuertusi Formation may belong to the Zhujiaqing Formation(Meishucun Formation) of the Yangtze Platform.The Ediacaran/Cambrian boundary of the Tarim Block should be located in cherts and phosphorites suc-cessions at the basal of the Yuertusi Formation.The δ13Ccarb negative excursion N1 is just across the PC/C boundary,and may be related to certain biomass extinction due to anoxic sedimentary environment,transgression and/or the oceanic overturn.The second δ13Ccarb negative excursion N2 may account for the sea-level falling in the Early Cam-brian.  相似文献   

20.
Paired organic and carbonate carbon isotope compositions of Late Permian Wujiaping (吴家坪) and Dalong (大隆) formations at Shangsi (上寺), Northeast Sichuan (四川) were analyzed by MAT 251. An abrupt negative excursion in the two isotope records was observed in the middle part of Dalong Formation, in association with a drop in the carbon isotope difference of the two records and an increase of total organic carbon (TOC) content. The negative drop of the paired carbon isotope records issuggestive of the input of 12C-enriched CO2. The molecular ratios of pristane to phytane and dibenzothiophene to phenanthrene indicate the anoxic condition in this interval. The enhanced TOC content is indicative of the elevated preservation of organic matter due to the anoxic condition. These isotopic and organic geochemical data probably infer the occurrence of the upwelUng in this interval. The additional contribution of volcanism activity observed in South China cannot be excluded to the input of 12C-enriched CO2 and the negative shifts in carbon isotope composition of bulk organic matter and carbonate.  相似文献   

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