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1.
The quantitative inversion of present-day downhole thermal indicator information enables (a) assessment of the effective paleoheat flux recorded by thermal indicators, and (b) determination of geological parameters related to the dynamical burial history of sedimentary strata. The logic of the general inversion scheme underlying seven thermal indicators, viz. vitrinite reflectance, sterane, and/or hopane isomers, sterane aromatization, optical rotation,39Ar/40Ar, pollen translucency, and fission scar tracks in apatite is presented, and their capability for resolving paleoheat flux is noted. In a second paper, determination of chemical and physical parameters, as well as several other quantities of geological interest (such as the sizes and erosion times of multiple unconformities, stratigraphic ages, paleo-overpressure, igneous intrusion timing, overthrust timing and frictional heat generation, fault and slump timing, thermal effects due to radioactive layer emplacement, and salt emplacement and dissolution timing) are discussed. Such events impact on both burial and thermal histories of sedimentary layers.Resolution problems are discussed also in the second paper, as is an attractive scheme called thermal indicator tomography for sorting out degrees of resolution, precision, and uniqueness of the relevant geological parameters for each process in combination with determination of the effective paleoheat flux. Detailed statements on the mechanics of implementing the tomographic approach are provided.  相似文献   

2.
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   

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.
Stratigraphic modeling based on physical and geologic principles has been improved by more sophisticated process models and increased computer power. However, such efforts may reach a limit in their predictive power because of the stochastic, multiscaled nature of the physical processes involved. Building on techniques from the geostatistical literature, a conditional simulation method, dubbed SimStrat, has been developed to improve predictions of stratigraphic architecture from limited data. No physical processes are invoked. Rather, the prediction is based solely on geometric and statistical principals. The method takes as input sonar bathymetry, seismically defined stratigraphic horizons, and core-defined horizons. Each stratigraphic horizon is characterized using spectral modeling and coherence modeling for adjacent horizons. Predictions of subsurface horizons are improved where seafloor bathymetry conforms with the underlying strata. Conditional simulations can then be generated that conform to available data constraints and statistical characterization. Tests with synthetic data in one and two dimensions for differing spectral models confirm the reliability of the method.  相似文献   

5.
In previous investigations, nearshore pyritic shale horizons in the Mid-Proterozoic Newland Formation were interpreted to be due to non-clastic colloidal iron supply by streams. New data on the chemical composition of shales in the Newland Formation support this interpretation. In these shales, Fe and Al show a positively correlated trend that intercepts the Fe axis above the origin. These relationships suggest control of Fe by clays (via iron oxide coatings on clay minerals), and the presence of an additional, non-clastic iron component. Shales from stratigraphic intervals during which pyritic shale horizons were deposited plot above the Fe/Al trend typical for the remainder of the Newland Formation.Pyritic shale horizons in sediments are favourable hosts for base-metal deposits of the pyrite-replacement type. Fe/Al relationships as found in the Newland Formation may help to identify stratigraphic horizons in other sedimentary basins that contain pyritic shale horizons and potentially base-metal mineralization.  相似文献   

6.
Presence of young groundwater (post-1950) in the Goose River basin is demonstrated with 3H and 85Kr analyses. A total of 96 wells and four springs were sampled quarterly from 1999 to 2001 to determine the extent of any recent recharge and to what depth hydraulic continuity existed in the groundwatershed (33.3 km2). Recharge groundwater is less than 50 years in about 31% (3H) to 37% (85Kr) of sampled wells and 75% of sampled springs. Young groundwater ages are recorded in wells up to 320 m in depth within fractured- and arsenic-bearing crystalline bedrock. Total arsenic 10 g L–1 occurs significantly in drinking water with young groundwater flowing through the pumping well intervals. Astotal occurs in 89% (85Kr) to 93% (3H) of all wells with post-1950 groundwater ages. Young groundwater recharge and elevated geogenic arsenic were discovered only in the anatectic granitoids and migmatized country rock of the southwestern part of the Goose River basin.  相似文献   

7.
White mica bearing fractions ranging in grain size from 0.4 m to 6.3–20 m were separated from metapelites and intercalated metatuffs of the eastern Rheinisches Schiefergebirge (FRG). The stratigraphic age of these rocks is Middle Devonian (Eifelian), and they contain detrital material of northwestern provenance (Old Red Continent, probably mainly derived from the Caledonian Orogen). Folding in the Carboniferous was associated with cleavage formation and an apparently synkinematic anchizonal metamorphism. Apparent K-Ar ages of metapelite fractions display a marked positive correlation with grain size illustrating the detrital influence which is diminished with decreasing grain size and increasing metamorphism (determined by illite crystallinity). Contrasting grain morphologies observed by SEM enable the interpretation of apparent age/ grain size relationship for coarse fractions. The anticipated lack of detrital mica in metatuffs is confirmed by the fairly consistent apparent K-Ar ages determined for the coarser than 0.63 m size fractions which date the anchizonal metamorphism at ca. 330 Ma. Comparison of metatuff and metapelite apparent ages suggests that the extent of rejuvenation in the latter was largely dependent on grain size. Rejuvenation was also somewhat controlled by the degree of anchizonal metamorphism as suggested by differences in K-Ar results of metapelites which were metamorphosed at variable anchizonal conditions. Fractions <0.63 m from upper anchizonal metapelites record ca. 330 Ma ages similar to those of the 0.63–20 m sizes in metatuffs. Together those results confirm the limited applicability of conventional K-Ar dating on bulk clay fractions (<2 m) of very-low grade (anchizonal) metamorphic rocks in dating metamorphic events and concomitant cleavage formation.  相似文献   

8.
The Erquy series (Côtes du Nord, France) consists, in its upper part, of spilitic pillow lavas with some interbedded volcano-sedimentary horizons.The Rb-Sr system of the pillows allowed the construction of a whole-rock isochron at 482±10 M.a. with an initial87Sr/86Sr ratio of 0.7055±0.0002. These rocks and the associated keratophyres give, on the other hand, K-Ar ages of 285±16 M.a. interpreted as the consequence of late-hercynian tectonism.A volcano-sedimentary horizon interbedded with such pillow flows has been studied from petrographic, mineralogical, geochemical and isotopic (Rb-Sr and K-Ar) points of view. The sequence keeps a sedimentary memory. Its clay fractions <2 m and corresponding whole-rocks fit an isochron which is identical to that of the volcanic rocks: 494±11 M.a. with an initial87Sr/86Sr ratio of 0.7052±0.0005. The clay fractions give K-Ar data at about 450 M.a., but those which contain important amounts of volcanic glass, at the top of the horizon, have K-Ar values as low as 400 M.a., and those which contain almost no glass have a K-Ar age close to the Rb-Sr age at 480 M.a.This study emphasizes the possibility of a complete reset of the K-Ar system of spilitic rocks by a tectonic event without notice-able temperature increase. This result may have important implications on combined paleomagnetic and K-Ar studies: it seems that a least for spilites and keratophyres, the Curie point and Ar blocking temperature can be very different.  相似文献   

9.
An end-member analysis was performed using algorithms ofExtended cabfac qmodel on 21 sample distributions of vitrinite reflectance (VR) by depth from the Inigok well in the National Petroleum Reserve of Alaska (NPRA). Eight end members, which account for 99% of the variance, adequately recreate the VR distributions. These eight end members contain stratigraphic information based on systematically increasing or decreasing mixing proportions with depth. Paleoheat flux determined from end members, or from orthogonally filtered sets of end members, is not significantly different from paleoheat flux determined from arithmetic mean values of VR, indicating that the arithmetic mean provides an adequate representation of each VR distribution analyzed in this well. Additionally, use of filtering devices to assess the degree of trustworthiness of signal in VR distributions enables an assessment to be made of the degree of stability of paleoheat flux variation estimates.  相似文献   

10.
何生  陶一川 《地球科学》1995,20(3):328-334
根据实测地温资料和岩石骨架热导率测试结果对本区今地温场的特征进行限分析，利用镜质体反射率反演古热流、成岩期原生矿物流体包裹体均一法测温和磷灰石裂变烃迹的热中分析研究了本区的地热演化，所获得的认识对松辽分地东南隆起区的油气地质研究和勘探评价很有意义。  相似文献   

11.
Thirty-five illite and muscovite concentrates were extracted from Triassic and Permian claystones, shales, slates and phyllites along a cross-section from the diagenetic Alpine foreland (Tabular Jura and borehole samples beneath the Molasse Basin) to the anchi- and epimetamorphic Helvetic Zone of the Central Alps. Concentrates and thin sections were investigated by microscopic, X-ray, infrared, Mössbauer, thermal (DTA and TG), wet chemical, electron microprobe, K-Ar, Rb-Sr, 40Ar/39Ar and stable isotope methods.With increasing metamorphic grade based on illite crystallinity data (XRD and IR) the following continuous changes are observed: (i) the 1Md2M1 polymorph transformation is completed in the higher grade anchizone; (ii) K2O increases from 6–8 wt. % (diagenetic zone) to 8.5–10% (anchizone) to 10–11.5% (epizone), reflecting an increase in the total negative layer charge from 1.2 to 2.0; (iii) a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone/ epizone boundary; iv) a shift of an endothermic peak in differential thermal curves from 500 to 750° C; (v) K-Ar and Rb-Sr apparent ages of the fraction <2 m decrease from the diagenetic zone to the epizone, K-Ar ages being generally lower than Rb-Sr ages. The critical temperature for total Ar resetting is estimated to be 260±30° C. K-Ar and Rb-Sr ages become concordant when the anchizone/ epizone boundary is approached. The stable isotope data, on the other hand, show no change with metamorphic grade but are dependent on stratigraphic age.These results suggest that the prograde evolution from 1 Md illite to 2M1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals, however this is not a recrystallization process. This restructuration is completed approximately at the anchizone/epizone boundary. The isotopic data indicate significant diffusive loss of 40Ar and 87Sr prior to any observable lattice reorganization. The restructuration progressively introduces a consistent repartition of Ar and K in the mineral lattices and is outlined by the 40Ar/39Ar age spectra.Concordant K-Ar and Rb-Sr ages of around 35-30 Ma. with concomitant concordant 40Ar/39Ar release spectra are representative for the main phase of Alpine metamorphism (Calanda phase) in the Glarus Alps. A second age group between 25 and 20 Ma. can probably be attributed to movements along the Glarus thrust (Ruchi phase), while values down to 9 Ma., in regions with higher metamorphic conditions, suggest thermal conditions persisting at least until the middle Tortonian.  相似文献   

12.
    
Patterns of inter-well correlations in map view can yield insight into the architecture of an area such as a petroleum reservoir. Preferred directions of fluid communications, discontinuities, and structural or depositional grain of an area often can be identified. In coherence mapping, large numbers of wells are compared in pairs, using a similarity coefficient. Sliding cross-correlation techniques of sections can be used to adjust for some normal stratigraphic inconsistencies. The calculated parameters are mapped as vector spider plots for each well, or as link-lines between well pairs with line thickness proportional to the strength of correlation. The resulting maps display areas of coherence and lines of discontinuities which can be interpreted according to the geologic style of the region. The method works best for areas with relatively great density of wells and uniform distribution. The database should contain logs digitized over the interval of interest and at least one stratigraphic marker. A pilot study of a carbonate reservoir with some 150 wells provided useful suggestions for reinterpretation of the field in terms of steeply dipping clinoforms of basin margin deposits.Paper presented at 15th Geochautauqua, Calgary, 4 October 1986.  相似文献   

13.
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   

14.
In dividing supracrustal strata, formation and horizon have been and are basic stratigraphic units. Stratigraphic boundaries of a formation, a natural geologic body, are drawn mostly on the basis of its composition. Paleontological remains constrain the formation in time and spatially locate it in the Earth's crust. Boundaries between formations can be of three types: strictly stratigraphic, parastratigraphic, and allostratographic. The stratigraphic interval can range from a fraction of a horizon or chronozone to several stages. At the boundary between two systems the adjacent parts of the formation can relate to both systems. The main stratigraphic characteristics for recognizing horizons are paleontologic (biostratigraphic) features, revealed by zonal, paleoecosystemic (ecostratigraphic), bioeventual, and other methods to make a basis for their immanent signature. Horizon can be characterized by boundaries of only two types: strictly stratigraphic and allostratigraphic. The stratigraphic interval of a horizon can vary from a single chronozone to a stage. Boundaries of neighboring horizons at the contact between two stages or systems should coincide with the latter. The stratigraphic units of the International Stratigraphic Chart, in contrary to formation and horizon, are characterized by borders of only one type — strictly stratigraphic.  相似文献   

15.
Zusammenfassung Mischungen von Forsterit und Enstatit werden bei Zugabe von wenigen Prozent K2O in Anwesenheit eines Wasserüberschusses unter Drucken von 1 bis 5 Kilobar bereits bei sehr niedrigen Temperaturen (etwa 550–700° C) teilweise aufgeschmolzen. Da auch in den Gesteinen des Erdmantels die Gegenwart von Alkalien und Wasser zu erwarten ist, können diese Komponenten zur Bildung von Ultrabasit-Schmelzbreien im Oberen Erdmantel führen, welche in höhere Stockwerke, d. h. in die Erdkruste, intrudieren können. Die Anwesenheit von Alkalien in Ultrabasitschmelzen vor und während deren Platznahme kann sich durch Alkalimetasomatosen im Nebengestein äußern, da die Alkalien bei noch niedrigeren Temperaturen vorwiegend in eine leichtflüchtige Gasphase eingehen, welche die Intrusion verläßt.
Mixtures of forsterite and enstatite show partial melting in the pressure range 1–5 kb at very low temperatures (approximately 550–700° C), if small amounts of K2O are added in the presence of excess H2O. Since alkalies and water are also expected to be minor constituents of the material forming the earth's mantle, they may cause, in this region, the formation of ultrabasic crystal mushes that may intrude into higher levels, i. e. the earth's crust. The presence of alkalies in ultrabasic melts before or during their emplacement may result in alkali metasomatism of the adjoining country rocks, because most of these alkalies are being incorporated at still lower temperatures in a gas phase leaving the intrusion.
Résumé On a trouvé qu'en présence de K2O et d'un excès d'eau des mélanges de forsterite et d'enstatite peuvent être fondues en partie à des températures très basses (550–700° C), sous une pression d'un à 5 kilobars. La présence des alkalis et de l'eau dans l'enveloppe pierreuse externe est probable. Conséquemment on pourrait supposer la formation de magmas d'ultrabasite par ces components dans l'enveloppe pierreuse externe. Ces magmas pourraient pénétrer dans des étages élevés. La présence des alkalis dans les magmas d'ultrabasite, avant et aussi bien au cours de la formation de ces dernières, pourrait se manifester par des métasomatoses d'alkali dans la roche encaissante, puisque à des températures encore plus basses les alkalis sont présents en phase volatile; cette phase peut quitter l'intrusion.
. — .

Wir danken der Deutschen Forschungsgemeinschaft für die Bereitstellung der Apparaturen zur Durchführung der Experimente.

Anschrift der Verfasser: Dr. F.Seifert, Prof. W.Schreyer, Institut für Mineralogie der Ruhr-Universität Bochum, Lehrstuhl für Petrologie, z. Z, 23 Kiel. Olshausenstr. 40–60.  相似文献   

16.
In the geothermal Euganean area (Veneto region, NE Italy) water temperatures range from 60 to 86°C. The aquifer considered is rocky and the production wells in this study have a depth ranging from 300 to 500 m. For exploitation purposes, it is important to identify zones with a high probability that the temperature is more than 80°C and zones with a high probability that the temperature is less than 70°C. First, variographic analysis was conducted from 186 temperature data of thermal ground waters. This analysis gave results that are consistent with the main regional tectonic structure, the NW-SE trending Schio-Vicenza fault system. Then indicator variograms of the second, fifth, and eighth decile were compared to identify the spatial continuity at different thresholds. The unacceptability of a multigaussian hypothesis of the random function and the necessity to know the cumulative distribution function in any location, suggested the use of a nonparametric geostatistical procedure such as indicator kriging. Thus, indicator variograms at the cutoffs of 65, 70, 73, 75, 78, 80, 82, and 84°C were analyzed, fitted, and used during the indicator kriging procedure. Finally, probability maps were derived from postprocessing indicator kriging results. These maps identified scarcely exploited areas with a high probability of the temperature being higher than 80°C, between 70 and 80°C and areas with high probability of the temperature being below 70°C.  相似文献   

17.
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   

18.
Specimens from strata-bound/stratiform Kieslager, lineament-bound, and unconformity-related Pb occurrences from the NE Bavarian Saxothuringian and Moldanubian belts and samples from stibnite and polymetallic Sb-Au quartz veins were analyzed for their lead isotope composition.The strata-bound Pb at Bodenmais yielded an Upper Proterozoic 207Pb/206Pb model age which correlates with the assumed stratigraphic age of the host rock. Late Precambrian rift activity may have triggered the formation of this ore mineralization. This type of Pb was also found in the Kieslager at Waldsassen hosted by Early Paleozoic country rocks and in the fluorite veins at Kittenrain.The vein-type lineament-bound, and unconformity-related Pb occurrences show a similar isotopic pattern which suggests that this type of Pb originated from the same source. The 207Pb/206Pb model ages which are too old compared to the assumed age of formation and the accelerated 208Pb evolution indicate that the detritus of the source rock underwent a high-grade metamorphism in the Precambrian.The formation of the unconformity-related Pb concentrated in galena of fluorite-barite veins is correlated with late Variscan magmatic intrusions. The older model ages of about 100–150 Ma from the lineament-bound lead, located along deep-seated lineamentary fault zones, suggest an earlier separation of this type of Pb possibly triggered by the Caledonian A-subduction-related metamorphism.  相似文献   

19.
This paper deals with barite from stratiform, karst, and vein deposits hosted within Lower Paleozoic rocks of the Iglesiente-Sulcis mining district in southwestern Sardinia. For comparison sulfates from mine waters are studied. Stratiform barite displays 34S=28.8–32.1, 18O=12.7–15.6, and 87Sr/86Sr=0.7087, in keeping with an essentially Cambrian marine origin of both sulfate and strontium. Epigenetic barite from post-Hercynian karst and vein deposits is indistinguishable for both sulfur and oxygen isotopes with 34S=15.3–26.4 and 18O=6.6–12.5; 87Sr/86Sr ratios vary 0.7094–0.7140. These results and the microthermometric and salinity data from fluid inclusions concur in suggesting that barite formed at the site of mineralization by oxidation of reduced sulfur from Cambrian-Ordovician sulfide ores in warm, sometimes hot solutions consisting of dilute water and saline brine with different 18O values. The relative proportion of the two types of water may have largely varied within a given deposit during the mineralization. In the karst barite Sr was essentially provided by carbonate host rocks, whereas both carbonate and Lower Paleozoic shale host rocks should have been important sources for Sr of the vein barite. Finally, 34S data of dissolved sulfate provide further support for the mixed seawater-meteoric water composition of mine waters from the Iglesiente area.  相似文献   

20.
在对两个褐煤样品进行同时考虑生烃和排烃模拟实验的基础上，本文对其甾、萜标记物的组成、分布和演化进行了研究，探讨了其生源意义、成熟演化及与自然演化的异同和甾、萜参数作为运移指标的意义。  相似文献   

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