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1.
Using the logic for quantitative inversion of present-day downhole thermal indicators, the inversion procedure can be used to determine unknown, or poorly known, chemical and physical parameters as well as other geological quantities of interest which impact on burial history and thermal history of an evolving sedimentary basin. Some such quantities are: amount of erosion and timing of unconformities, paleo-overpressuring, stratigraphic age, timing of igneous intrusion and insertion temperature, overthrust timing and frictional heating, fault and slump timing, effects due to emplacement of a radiocative layer, and salt emplacement and dissolution timing. Combining a priori unknown values of these chemical/physical and geological parameters with unknown (a priori) paleoheat flux variations, a theoretical scheme, called thermal indicator tomography, is developed for the systematic determination of all parameters at the same time and on the same footing. Case histories will be discussed in subsequent papers in this series.  相似文献   

2.
Thermal indicator data are used in an inverse mode to determine ages of stratigraphic horizons simultaneously with paleoheat flux. Results from blind tests on wells with horizon ages ranging from Ordovician through Carboniferous and Jurassic to Miocene indicate that thermal indicator inversions are capable of resolving such ages to within about 10% uncertainty. Results using the inversion procedure with one thermal indicator (vitrinite reflectance) were comparable to the results using another independent thermal indicator (sterane isomerization) in the same well. The activation energy for sterane isomerization was determined to be 30±15 kJ mol–1. In addition: (a) the age of a stratigraphic horizon, the thickness of eroded sediments at an unconformity, and the variation of paleoheat flux with time were determined simultaneously by thermal indicator inversion in a single well; (b) two neighboring wells, less than 10 km apart, provided essentially identical ages for the same formation when tested using the inversion procedure. The ability to determine stratigraphic horizon ages from inversion of thermal indicator data implies that sedimentation rates can be determined; thus, basinal evolution can be inferred to a degree of resolution not previously obtainable from assumed interpolation methods applied to determine the age of horizons between a limited set of stratigraphic horizons of known ages.  相似文献   

3.
Multiple thermal indicator tomography is a non-linear inversion procedure which permits simultaneous determination of geological, chemical kinetic, and thermal parameters in the burial and thermal histories of sediments. The procedure is based on inverting measurements with depth in a well of multiple thermal indicators, each of which must have experienced the same thermal history. For two wells from diverse geological settings, tomography is used to assess the paleoheat-flux variations with time most consistent with all the thermal indicator data. Resolution and sensitivity of the results are also addressed. For the case history of well X in the North Sea, with both vitrinite reflectance and sterane isomer thermal indicators, a generally decreasing heat flux from past to present is obtained roughly halving every 50 Ma. The activation energy for the sterane isomer is also determined simultaneously to be 42±20 kJ/mole. For the second case history of the Irma Mclean well in the onshore Gulf of Mexico, data from four thermal indicators are available: vitrinite reflectance, sterane and hopane isomers, and sterane aromaticity. A general decrease in paleoheat-flux from amount 2.8 heat flux units (HFU) at 100 MaBP to 1.25 HFU at the present day is obtained, the activation energy for the sterane isomer is simultaneously determined to be around 50±20 kJ/mole, while the corresponding values are around 80±20 kJ/mole for the hopane isomer, and around 65±20 kJ/mole for sterane aromatization.  相似文献   

4.
A quantitative tomographic method to determine simultaneously several geological, geochemical, and geothermal parameters associated with reconstruction of the geohistory and thermal history of sediments in a well is presented. Using vitrinite reflectance data from the well Inigok-1, National Petroleum Reserve of Alaska, the numerical algorithm was tested and found to be effective in delineating the variation of heat flux with time. In addition, the size and timing of a major unconformity also were bracketed. Application of tomography using apatite fission track distributions with depth as a thermal indicator enabled not only the thermal history of two wells in the NW Canning Basin of Australia to be determined, but also the chemical parameters associated with fission track annealing to be constrained. Results of both the Alaska study and the Australian study were consistent with the qualitative behavior inferred from current geological models.  相似文献   

5.
We present a multi‐chronometric approach for reconstructing deep‐time thermal histories using southern Baffin Island as a case study. This continuous thermal history begins with the Palaeoproterozoic Trans‐Hudson Orogeny and is derived from inverse and forward models that integrate thermochronometers spanning some 500°C: new apatite U–Pb ages and K‐feldspar 40Ar/39Ar multi‐diffusion domain data, published (U–Th)/He zircon ages and new multi‐kinetic fission‐track results. Integration of data from a wider temperature range reduces ambiguities in thermal‐history modelling and permits us to constrain the timing of geological processes including, extended post‐orogenic cooling, enhanced later Proterozoic cooling, and then episodic burial and exhumation in the Palaeozoic–Mesozoic.  相似文献   

6.
INTRODUCTIONVitrinitereflectance(R.)canprovideagreatdealinfor-mationonthermalhistoryofabasin.Itisafunctionofmaximumpaleotemperatureandeffectiveheatingtime,inotherwords,afunctionofdepositionalrateandgeothermalgradientwithirreversiblecharacteristics.Butitalsohasacumulativeeffectthroughoutgeothermalevents.Paleotemperaturesaremainlycontro1ledbythebasalheatflowandheatgenerationfromradioactivesourceswithinthecrust.Themodelforde-terminingpaleoheatflowoflinearchangewithtimefr0mvitri-nitereflecta…  相似文献   

7.
Present-day observed downhole quantities, which a dynamical model of basin evolution should account for, include: total depth drilled, formation thicknesses, variations of porosity, permeability and total fluid pressure with depth, and depths of unconformities. Following a line of logic previously employed with multiple thermal indicators, it is shown how the observed quantities can be used in a nonlinear inverse sense to determine, or at least constrain, parameters and functions entering quantitative models of dyanmical sedimentary evolution. A procedure is given so that the inverse methods can be used: (a) with single well data; (b) with multiple well data; and (c) simultaneously with thermal indicator data, which have already been previously successfully inverted using a tomographic procedure. Parameters that can be evaluated using the dynamical indicator inversion (dynamical tomography) include, but are not limited to, values dealing with geological events (such as unconformity timing and amount of material eroded, the openness or shutness of faults; critical fracture pressure, etc.), as well as values dealing with intrinsic, or assumed, lithologic equations of state (such as power law values in connections between permeability and void ratio, or between frame pressure and void ratio). The dynamical tomography procedure can be used with or without weighting the data and/or the dynamical indicators; is guaranteed to produce a closer correspondence between predicted and observed behaviors at each nonlinear iteration; and is guaranteed to keep all parameters within any chosen domain. When used in a multiple well setting, the dynamical tomography method enables an assessment to be made of the assumed invariance to spatial location of parameters in equations of state, as well as allowing geologic process parameters to vary with well location. The procedure also automatically incorporates the ability to determine precision, resolution, sensitivity, and uniqueness of any or all parameters, both associated with equations of state and associated with geological processes. Thus, a sharper understanding is achieved of the trustworthiness and uncertainty of quantitative basin analysis models in respect of: (i) intrinsic assumptions of a model; (ii) implicit or explicit parameter dependences for both geological events and imposed functional dependences of variables; (iii) resolution with respect to finite sampling and measurement error or uncertainty in the quality and quantity of observed data.  相似文献   

8.
根据伊利石Ｋ－Ａｒ测年法研究，确定鄂尔多斯盆地存在两期与构造运动有关的成岩作用事件：即与早期燕山运动有关的侏罗纪（１７０—１６０Ｍａ）和与晚期加里东运动有关的志留－泥盆纪（４２０－３７０Ｍａ）成岩作用时代。为了揭示碎屑物质对Ｋ－Ａｒ年龄的影响和伊利石成岩作用的机制，本文提出了一个通过观察Ｋ－Ａｒ年龄随深度变化的趋势来进行判断的模式。在Ｋ－Ａｒ年龄小于地层时代的条件下，Ｋ－Ａｒ年龄与深度呈正相关，或者很相近的Ｋ－Ａｒ年龄与深度变化无关均标志着没有或很少有碎屑物质的影响；同时，前者指示逐渐埋藏条件下的成岩作用，而后者则反映短暂的热事件引起的成岩作用事件。  相似文献   

9.
One‐dimensional thermal (1DT) modelling of an Acadian (Devonian) tectonothermal regime in southern Vermont, USA, used measured metamorphic pressures and temperatures and estimated metamorphic cooling ages based on published thermobarometric and geochronological studies to constrain thermal and tectonic input parameters. The area modelled lies within the Vermont Sequence of the Acadian orogen and includes: (i) a western domain containing garnet‐grade pre‐Silurian metasedimentary and metavolcanic rocks from the eastern flank of an Acadian composite dome structure (Rayponda–Sadawga Dome); and (ii) an eastern domain containing similar, but staurolite‐ or kyanite‐grade, rocks from the western flank of a second dome structure (Athens Dome), approximately 10 km farther east. Using reasonable input parameters based on regional geological, petrological and geochronological constraints, the thermal modelling produced plausible P–T paths, and temperature–time (T –t) and pressure–time (P–t) curves. Information extracted from P–T –t modelling includes values of maximum temperature and pressure on the P–T paths, pressure at maximum temperature, predicted Ar closure ages for hornblende, muscovite and K‐feldspar, and integrated exhumation and cooling rates for segments of the cooling history. The results from thermal modelling are consistent with independently obtained pressure, temperature and Ar cooling age data on regional metamorphism in southern Vermont. Modelling results provide some important bounding limits on the physical conditions during regional metamorphism, and indicate that the pressure contemporaneous with the attainment of peak temperature was probably as much as 2.5 kbar lower than the actual maximum pressure experienced by rocks along various particle paths. In addition, differences in peak metamorphic grade (garnet‐grade versus staurolite‐grade or kyanite‐grade) and peak temperature for rocks initially loaded to similar crustal depths, differences in calculated exhumation rates, and differences in 40Ar/39Ar closure ages are likely to have been consequences of variations in the duration of isobaric heating (or ‘crustal residence periods’) and tectonic unroofing rates. Modelling results are consistent with a regional structural model that suggests west to east younging of specific Acadian deformational events, and therefore diachroneity of attainment of peak metamorphic conditions and subsequent 40Ar/39Ar closure during cooling. Modelling is consistent with the proposition that regional variations in timing and peak conditions of metamorphism are the result of the variable depths to which rocks were loaded by an eastward‐thickening thrust‐nappe pile rooted to the east (New Hampshire Sequence), as well as by diachronous structural processes within the lower plate rocks of the Vermont Sequence.  相似文献   

10.
The thermal regime of the Northeastern-German Basin from 2-D inversion   总被引：2，自引：0，他引：2  
The thermal regime and the distribution of heat flow at the base of sedimentary basins is fundamental to the understanding of the process of basin evolution and the associated mobilization and migration of hydrocarbon and other fluids. For the Northeastern-German sedimentary basin, available information on structure, temperature, and thermal properties along a seismic DEKORP reflection profile allow high resolution 2-D forward and inverse simulations. This approach is attractive in situations where much information is available, if only with considerable uncertainty. In particular, this allows to introduce “soft” information into the analysis. In our case, forward simulations yield initial a priori estimates of the parameters while inversion calculations yield a posteriori estimates of the parameters and their uncertainty. The a priori parameters as well as their assumed uncertainty are input for a Bayesian parameter estimation scheme. In respect to the Northeastern-German sedimentary basin, the inverse analysis postulates a significant and characteristic a posteriori variation of thermal conductivity of the Zechstein unit along the entire profile as well as a generally large a posteriori thermal conductivity of the (pre-Permian) basement in the northern part of the basin. For inverse calculations, we used two alternative scenarios: One assumes the thermal conductivity of the Zechstein unit to be homogeneous along the profile while the other allows a lateral variation. A posteriori heat flow across the base of the model varies from 40 to 60 and 50 to 65 mW m−2 for models in which values for thermal conductivity and radiogenic heat generation rate were either based on literature values or direct measurements, respectively.  相似文献   

11.
Three different types of methods are used to assess the ability to determine erosion amounts and to provide estimates of uncertainty. In the situation of dynamical indicator methods, such as seismic velocity, sonic logs, density logs, or drilling exponent methods, intrinsic assumptions and parameter values used provide only a broad statement on the resolution of uplift/erosion events. None of the methods is more accurate, at best, to better than ± 1 km and likely much worse. For geological model procedures, exemplified by considerations of Airy isostasy and by bed upturning near a salt dome in the Nordkapp Basin of the Barents Sea, the uncertainties are again of the order of ± 500–1000 m. With thermal indicator procedures, the bulk of the constraint information from available data is needed to determine paleoheat flux with little left over to constrain the erosion, implying a minimum uncertainty of ± 500 m on erosion determinations. No method seems capable of resolving erosional events to better than a minimum uncertainty of ± 500 m, and likely no better than ± 1 km.  相似文献   

12.
The Multiple Diffusion Domain (MDD) theory of Ar loss, based on the 40Ar/39Ar method, has been used to obtain thermal histories, over tens of millions of years, in the range 500 °C to near-surface temperatures, of alkali feldspars from slowly cooled geological environments and recovered in situ from sedimentary basins and geothermal systems. It assumes that Ar diffuses in Nature, over geological time, from the same domains, and by the same processes, that control its diffusion during laboratory step-heating experiments. Mathematically the model has many stringent requirements: the domains must form at T above those being modelled and must remain unchanged during geological time and during step heating, must not interact, must occur in discrete size ranges sharing one simple geometrical shape, contain no compositional gradients in 40K, and release Ar into an infinite reservoir. We describe the nature of possible diffusion domains, and the fast pathways for diffusion between them, known to exist in alkali feldspars from direct electron microscopic observations, and explore their time–temperature evolution, based on established phase behaviour, both over geological time and during step heating. Strain-controlled microtextures, whose morphology is controlled by the minimization of coherency strain energy, do not provide fast pathways for Ar loss, and behave as crystallographically complex but single domains for Ar. Subregular dislocations may form over a range of T in some strain-controlled intergrowths, but in Nature the majority form closed loops and do not provide pathways to the crystal surface. Deuteric microtextures cut across strain-controlled microtextures, and are composed of microporous subgrain and grain mosaics with many pathways and a wide spectrum of possible domain sizes and shapes. The deuterically altered zones provide pathways for Ar diffusion out of the crystal, although some Ar is retained in fluid inclusions. All microtextures likely to define diffusion domains form below 500 °C, over a range of T and (in slowly cooled rocks) of times. The most important involve fluid–feldspar reactions, which can reset Ar, and continue to surface T. Feldspars in geothermal systems and young sedimentary basins are subject to ongoing chemical and microtextural changes. Because the microtextures are metastable during step-heating experiments in the T range over which most Ar is released, domains and pathways for rapid diffusion of Ar between domains will be significantly modified during step heating, particularly above 750 °C, when departures from a simple Arrhenius diffusion law are most marked. Pre-melting is likely to be an important cause of complexity in Ar loss behaviour. Few, if any, of the requirements of the MDD model are met, and we conclude that thermal histories cannot be obtained from alkali feldspars using this method. Received: 21 September 1998 / Accepted: 1 March 1999  相似文献   

13.
《Applied Geochemistry》1991,6(6):653-664
An examination has been made of strategies to estimate kinetic parameters (activation energy and pre-exponential factor) for organic reactions from geological data. Least squares regression and a direct-search algorithm were applied to a set of sterane isomerization data from Volador 1, an oil exploration well in the Gippsland Basin, Australia. The best fit kinetic parameters depend on the number and quality of data points used, as well as the thermal history. Because both the data and thermal history have intrinsic uncertainties, a range of kinetic parameters can explain the data to a specified level of misfit. For reasonable variations in the thermal history, the effective kinetic parameters for the data from Volador 1 are E = 75–100kJ/mol and A = 10−1−10−5/s. It is observed that the range of acceptable parameter pairs has a linear relation of the form ln (A) = a + bE, and the slope b is dependent on the thermal history. Small departures of either parameter from this relation lead to significant variations in the predicted values for the reaction progress.  相似文献   

14.
Distinctive compositional features of cyclic saturated hydrocarbon biomarkers have been established in oils from the main petroliferous lithostratigraphic complexes of various structural zones in the Timan-Pechora petroliferous province (TPPP). Four geochemical families (types) of oils in TPPP are recognized based on the variations in the geochemical parameters of steranes and terpanes including sterane ratios C27/C29 and C28/C29, K1 mat and K2 mat, diasterane/regular sterane, pregnane (C21–22)/sterane (C21–22 + C27–29), as well as terpane Ts/Tm parameters, adiantane C29/hopane C30, neoadiantane/adiantane, tryciclic terpane/pentacyclic terpane, hopane/sum of C29 steranes, etc. The distribution of various types of oil in the sedimentary sequence of TPPP makes it possible to infer source rocks for each of the four selected types.  相似文献   

15.
This paper describes an approach for verifying thermal maturity data in a large historical dataset from the Canadian Arctic Islands. A compilation of more than 6000 maturity measurements (vitrinite reflectance and Rock-Eval Tmax) collected over the span of three decades involved a rigorous assessment of data quality. Some common anomalies in interpreting thermal maturity dataset include: (i) elevated thermal maturity due to Cretaceous igneous intrusion in the region, (ii) reworking of refractory material from older rocks into younger strata during the Triassic period, (iii) suppression of vitrinite reflectance and Tmax in hydrogen-rich samples, (iv) low maturity values due to cross-contamination by the younger sediments during drilling process (caving), and (v) offset maturity values obtained from different maturity measurements. The study discusses various independent checks to verify the obtained maturity parameters. The comparison between thermal maturity data with the sonic velocity of shale resulted in a satisfactory correlation. While such a correlation may vary in different sedimentary basins, it produces a useful independent assessment of thermal maturity. The results indicate that increased heat flow during the Jurassic–Early Cretaceous rifting of the Canada Basin may have caused the elevated maturity beyond the expected burial level as suggested by the discrepancy between thermal maturity and sonic velocity data. Given the fact that vitrinite reflectance records only the maximum temperature to which the enclosing rocks were exposed, deviation of the collected reflectance values from the current depth of burial serves as an indicator for the amount of geological uplift.  相似文献   

16.
Quantitative techniques that link sediments to their sources are needed to understand a range of tectonic, climate, and anthropogenic driven Earth surface processes. Many provenance techniques exist for sand-sized material but fewer are available for fine-grained sediment archives. In this respect, bulk 40Ar/39Ar ages from silt-sized sediment show potential, but many questions remain about the significance of a bulk sediment 40Ar/39Ar age. We interrogate bulk sediment 40Ar/39Ar ages by step heating mixtures of well-constrained 40Ar/39Ar mineral standards crushed to silt-sized. Silt-sized end member components Alder Creek Sanidine, Taylor Creek Sanidine and Heidelberg Biotite all yield plateau ages within uncertainty of their coarse-grained counterparts. High-resolution step heating (as many as 43 steps) of the mineral mixtures shows that biotite degasses first at lower temperatures compared to the two sanidines that degas generally in concert. Concordant age steps develop at both low and high temperatures and the transition from the isotope signal being dominated by one mineral phase to another is clearly observed. We show that age spectra for the mineral standard mixtures can be modeled and predicted for all mixtures by assuming a (simplistic) Gaussian distributed release of Ar, and by using the degassing maxima, variance, K concentration, and 40Ar/39Ar age of each monitor mineral. Thus, bulk sediment 40Ar/39Ar ages can be robust indicators of the average cooling/crystallization age of all contributing K-bearing minerals to a depositional center. Furthermore, we discuss the potential to deconvolve individual mineral age populations by model inversion. The application of this bulk sediment provenance technique should not be considered a replacement for single grain analyses. It should be applied to environments that do not provide sand-sized sediment archives (e.g., distal terrigenous sedimentary archives) when information about source changes through time are more important than precise sediment source identification.  相似文献   

17.
KAr isochron techniques can provide, in principle, an experimental reconstruction of the time evolution of the atmospheric 40Ar/36Ar ratio if minerals can be found which contain samples of argon from the ancient atmosphere and which have had a simple geologic history. Authigenic sedimentary minerals with low potassium content appear to be the best candidates. An experimental reconstruction of the evolution of the atmospheric 40Ar/36Ar ratio will serve as a test of various models for the chemical and thermal evolution of the Earth.40Ar39Ar studies of five chert samples from the Swaziland sequence and the Bulawayan and Gunflint Formations indicate that lower Precambrian cherts do not contain appreciable samples of the ancient atmospheric argon and have experienced complicated geologic histories. The chert sample from the Kromberg Formation contains excess 40Ar. The other four samples yield age spectra which are complicated but which are interpretable in terms of geologically reasonable ages.The lack of evidence for argon loss in the chert data suggests that some cherts may prove to be datable sedimentary minerals.  相似文献   

18.
The post‐Variscan thermal history of the Erzgebirge (Germany) is the result of periods of sedimentary burial, exhumation and superimposed hydrothermal activity. The timing and degree of thermal overprint have been analysed by zircon and apatite (U–Th)/He and apatite fission track thermochronology. The present‐day surface of the Erzgebirge was exhumed to a near‐surface position after the Variscan orogeny. Thermal modelling reveals Permo‐Mesozoic burial to temperatures of up to 80–100 °C, although the sedimentary cover thins out towards the north resulting in maximum burial temperatures of less than 40 °C. This thermal pattern was locally modified by Cretaceous hydrothermal activity that reset the zircon (U–Th)/He thermochronometer along ore veins. The thermal models show no significant regional exhumation during Cenozoic times, indicating that the peneplain‐like morphology of the basement is a Late Cretaceous feature.  相似文献   

19.
The Permian Cape Fold Belt (CFB) of South Africa forms part of a major orogenic belt that originally extended from Argentina, across southern Africa and into Antarctica. The CFB is dominated by complexly folded and faulted rocks of the siliciclastic Cape Supergroup that were deposited in the Cape Basin. The provenance of the Cape Supergroup, timing of deformation and tectonic setting are poorly constrained. U-Pb detrital zircon provenance studies suggest that the Cape Basin received sedimentary detritus from the African Mesoproterozoic Namaqua-Natal Metamorphic Belt, Neoproterozoic-Cambrian Pan-African Belts and the Brasiliano orogenic belts of South America, Africa and Antarctica. However, as zircon is able to survive multiple orogenic and sedimentary transport cycles, complementary provenance tools are required to confirm Cape Supergroup provenance. Previous studies have suggested both uni-modal and multi-modal models for the timing of CFB orogenesis. In the current study, structurally controlled, muscovite-bearing samples were collected along several north-south traverses across the CFB. Detailed textural and mineral chemistry analyses identified multiple muscovite populations, commonly with complex intergrowth features. High precision 40Ar/39Ar analyses reveal a dominant 490–465 Ma detrital muscovite population, lending support to a largely South American provenance for the Cape Supergroup. Lesser detrital muscovite populations in the range 650–500 Ma and >730 Ma, corroborate previous zircon provenance studies suggesting Pan-African/Brasiliano terranes and the Namaqua-Natal Metamorphic Belt as significant sediment sources, respectively. Detailed 40Ar/39Ar analyses of multiple neo-crystallised muscovite samples are consistent with a single major phase of CFB deformation occurring between 253.4 and 249.6 Ma. This age is interpreted to represent either the peak or final dominant phase of CFB deformation.  相似文献   

20.
Based on gas chromatography and gas chromatography mass spectrometry techniques, the authors examined biomarker characteristics of the Ganquan Formation source rocks in the area of Dahulishan, Ejina, and analyzed the information and petroleum geological significance that were indicated by the source of organic matter, sedimentary environment and maturity and so on. Gas chromatography peak of saturated hydrocarbons from the Ganquan Formation source rocks showed "the former peak" of the single peak distribution, the main peak of carbon being C18 , indicating the main sources of organic matter with marine organic matter. Pr/Ph ranges from 0.3 to 0.6, indicating a strongly reducing sedimentary environment. Biomarker assemblages of the Ganquan Formation source rocks are abundant in tricyclic terpane with long side chains, with a high level of gammacerane, showing dominant distribution of C27 sterane. High contents of gammacerane in organic matter show organic facies of source rocks in the saltwater sedimentary environment. That average hopane/sterane ratio is 0.59, showing that algae have made more contributions to organic matter than bacteria. And the high level of C27 steranes shows that algae are the main source of hydrocarbon precursors. The Ganquan Formation’s methylphenanthrene index, which is an effective molecular parameter index to measure thermal evolution of organic matter, ranges from 0.35 to 0.50, and the conversion of vitrinite reflectance Rc from it is within the range of 2.00-2.09, indicating that the Ganquan Formation source rocks are in the over-mature stage of thermal evolution.  相似文献   

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