Sequence stratigraphy in the upper cretaceous of the Basco-Cantabrian Basin (northern Spain)

The sedimentary cycles of the Cenomanian to Maastrichtian were investigated in the Basco-Cantabrian Basin (BCB) in northern Spain (Provinces of Alava, Vizcaya and Burgos). The depositional area was a distally steepened carbonate ramp which extended from Catalonia northwestwards to the Basque country. The investigated sediments range from calciturbidites and pelagic marls to marl-limestone alternations deposited on a distal carbonate ramp. Shallow marine limestones, marls and intertidal clastics and carbonates were deposited on the proximal part of the carbonate ramp. The establishment of a regional sequence analysis is based on the investigation of seismic profiles, well logs and outcrop sections. Examples of outcrop sections are interpreted in terms of sequence stratigraphy (unconformities of third- and second-order cycles, depositional geometries, systems tracts). The sequence stratigraphic interpretation of outcrop sections is based on facies analysis, interpretation of observed depositional geometries and correlation of unconformities and marine flooding surfaces through the basin. A biostratigraphic framework is established based on ammonites, inoceramids, planktonic and benthic foraminifera. As a result, a regional sequence stratigraphic cycle chart is presented and compared with published global cycle charts. The correlation of the regional cycle chart with published cycle charts is good. In the Cenomanian and Turonian, several sequence boundaries in the BCB are shifted by up to one biozone compared with the global chart. Some type 1 boundaries of the standard chart are only type 2 in the BCB. Important type 1 boundaries in the BCB are: top Geslinianum Zone with a 100 m lowstand wedge at the basis of the sequence (sequence boundary 92.2) ; base Petrocoriense Zone with a 250 m shallowing-upwards lowstand wedge at the basis (sequence boundary 89.2); and within the Syrtale Zone (sequence boundary 85.0).The Campanian-Maastrichtian sequence record is strongly disturbed by local compressive tectonics. Several sequences are recognizable and can be correlated with the global cycle chart. Correlation is hampered by the low biostratigraphic resolution in the western basin part. Subsidence analysis of several sections of the Upper Cretaceous of the BCB and its interpretation in the regional tectonic context leads to a discussion of the causes of the observed cyclicity. A regional eustatic curve is presented for the Upper Cretaceous of the BCB. Stage and substage names were used according Code-Committee (1977). Correspondence to: K.-U. Gräfe     

层序地层学研究现状及进展:模式多样化

1977年至1988年,层序地层学从诞生逐渐走向成熟,并且形成了一套完整的概念体系和工作方法,这段特殊时期被称为层序地层学的Exxon时代.之后,将最大海泛面作为层序界面的R-T层序模式则代表了后Exxon时代模式多样化的开始.随后,对Exxon层序地层学概念体系不协调的认识则代表了由模式多样化所表征的后Exxon时代...     

An empirical coverage test for the g -sample problem

A nonparametricg-sample empirical coverage test has recently been developed for univariate continuous data. It is based upon the empirical coverages which are spacings of multiple random samples. The test is capable of detecting any distributional differences which may exist among the parent populations, without additional assumptions beyond randomness and continuity. The test can be effective with the limited and/or unequal sample sizes most often encountered in geologic studies. A computer program for implementing this procedure, G-SECT 1, is available.     

Modelling the behaviour of a retaining wall in residual soils for a cut and cover construction of a deep station in Metro do Porto

This paper presents a re-appreciation of the ground characterisation and the criteria to select the most representative geomechanical parameters to consider in a numerical model to predict the behaviour of a retaining wall of a deep excavation in highly weathered granite rock masses and residual soils. This study was focused in the construction of a deep station of Metro do Porto, which involved a cut and cover solution, with unusual proportions (in plant and in depth), built in the typical Oporto's granite weathered profiles, being the excavation conducted with retaining walls consisting of multi-anchored concrete piles. Specific sections were carefully instrumented, due to the presence of historic buildings in the vicinity. The definition of representative model parameters was based on precise laboratory tests over high quality soil samples, including oedometer and high-precision triaxial tests. Geotechnical and geological characterisation of all the area for the original design, was initially based on in situ tests, such as SPT and rock masses classification, and on the local experience on this type of ground. After this construction, the assumptions of parameterisation, using a constitutive modelling based on new laboratory tests over high quality block samples, allowed a reanalysis of the assumptions on the design phase. A back-analysis of monitored displacements and forces during the construction was made, assuming the designed structural solutions, which were in fact implemented in construction, but considering the new approaches on the definition of the geomechanical parameters for the prevailing weathered rock masses, necessary for the numerical simulation based on the commercial software Plaxis®, using the Mohr-Coulomb and “Hardening-Soil” models. Some specific changes of the constructive sequence during the excavation and activation of supporting system were attained, by looking at the information found during the construction. The results of this parametrical re-approach and analysis of the singularities of highly weathered granite and corresponding residual soils masses for modelling of retaining walls of large excavations are discussed.     

Hydraulic testing using a versatile straddle packer system for improved transmissivity estimation in fractured-rock boreholes

Equipment has been developed for straddle packer testing in fractured-rock boreholes to conduct four types of tests (constant-head step tests, slug tests, constant-rate pumping tests, and recovery tests) without deflating the packers or adjusting equipment in the hole between tests. The goal is to achieve improved accuracy and precision in the determination of transmissivity (T). Water-pressure measurements are recorded using pressure transducers positioned above and below the test interval to identify connections from the test interval to the open borehole. Insights concerning the nature of test conditions are gathered with this equipment to assess errors related to deviations from assumptions inherent in the mathematical models used to determine T, including validation of the Darcian flow assumption, validation of slug test assumptions, cross-connection to the open borehole, inadequate borehole development, and dual permeability, thereby giving greater confidence in the calculated T values. When the errors indicated above are minimized, the constant-head step tests, slug tests and constant-rate pumping/recovery tests give nearly identical values. This multiple-test approach to fractured-rock studies increases confidence in test results, which is important when the goal is characterization of fracture networks for contaminant transport and fate assessment.     

Survey of a coastal karstic aquifer by analysis of the effect of the sea-tide: Example of the Kras of Slovenia,Yugoslavia

A hydrodynamic study of a coastal karstic aquifer is attempted by analyzing the effect of sea-tide on its water table Under certain conditions, this approach, which involves quite easy data processing, may yield the hydrodynamic parameters of the aquifers, diffusivity, in particular. The aquifer involved here is the Kras of Slovenia, Yugoslavia, which is bounded on one side by the Adriatic Sea (Bay of Trst)Kras is the Slovenian word from which the wordkarst originates The Kras aquifer is located in a thick carbonate sequence (Cretaceous) with an anticline structure. This sequence outcrops and is affected by opened vertical fractures. The geological setting could suggest a free groundwater with negligible piezometric variations with respect to the thickness of the carbonate sequence The study was carried out by the identification of observed data (fluctuations of the water table) and computed data under various assumptions (confined, semi-confined, free groundwater). The best fit is obtained when considering a groundwater with semi-confined behavior, which, of course, does not agree with the geological setting of the Kras However, this behavior can be justified by the fact that an important karstification occurred below the existing sea-level during the Quaternary and Tertiary marine recessions, creating diffusive zones in lower parts of the saturated karst it should be noted that similar situations must prevail in all the peri-Mediterranean karsts as they too were affected by the Quaternary and Tertiary recessions     

Inversion of dynamical indicators in quantitative basin analysis models. III. Multiwell information and two-dimensional case histories

A dynamical tomography method, which inverts dynamical indicators to evaluate the parameters controlling geological processes as well as those in intrinsic equations of state, was introduced into a 2D fluid flow/compaction model termed GEOPETII (developed at the University of South Carolina), with the assumption of invariance to spatial location of parameters in equations of state, but allowing geologic process parameters to change with well location. Synthetic tests, including sensitivity analysis, are given to illustrate the operation of the system. The nonlinear inverse two-dimensional tomography method, together with a systematic linear search procedure, provides a useful approach to determine and constrain the parameters entering quantitative models of dynamical sedimentary evolution. Applying the method to an interpreted section from a seismic line in the Navarin Basin. Bering Sea. Alaska, the predictions of present-day formation thicknesses, porosity, and fluid pressure with depth are improved at four controlling well locations (Amoco Mishu No. 1, Exxon Redwood 1, Exxon Redwood 2, and Amoco Danielle), relative to previous results which used only a forward model. In this way the geohistory and structural development of the basin can be defined better, which helps in the reconstruction of thermal history, and so of hydrocarbon generation, migration, and accumulation histories in relation to structural and stratigraphic development.     

用水位恢复数据反演越流承压含水层参数

水文地质勘测中,由于水位恢复阶段没有人力和机械因素干扰,由测量数据可以画出平滑的曲线,更适宜于分析水文地质参数,但经典非稳定流Theis公式和Theis水位恢复法所依据的若干假设条件在实际中难以满足。针对越流承压含水层具有补给条件而很快稳定以及非稳定抽水阶段流量常“抖动”的特点,论证了利用稳定流量和Hantush-Jacob越流模型计算的可行性,并用扩展的卡尔曼滤波器反演水文地质参数,经文献中历史数据和实地抽水试验检验结果表明,由该方法反演的预测值和实测值吻合良好。     

Estimating Abrasivity of Rock by Laboratory and In Situ Tests

The degree to which a rock abrades another rock is called its “abrasivity”. Laboratory tests of abrasivity can be broadly divided into four kinds: drilling, rubbing, turning-operation and tumbling tests. The present study was initiated 30 years ago with the objective of investigating and developing methods for measuring rock abrasivity, and making some contribution towards understanding the relationships between the above test methods. Within the range of tests conducted, the turning-operation test turned out to be superior to the drilling test, albeit slightly, in terms of practicality. We have also conducted in situ tests using rock drills for the last 20 years. The results of those tests have been investigated and compared with the results of laboratory tests. There is a large degree of scatter in the data on gauge loss in button bits, which has obscured any correlations with laboratory data. Some correlations were found between height loss in button bits and laboratory findings.     

High-frequency sequences and their stacking patterns: sequence-stratigraphic evidence of high-frequency eustatic cycles

A hierarchy of interpreted eustatic cyclicity in siliciclastic sedimentary rocks has a pattern of superposed cycles with frequencies in the ranges of 9–10 m.y., 1–2 m.y., 0.1–0.2 m.y., and 0.01–0.02 m.y. (second- through fifth-order cyclicity, respectively). Stratigraphic units displaying this cyclicity include composite sequences, sequences, and parasequences. On the Exxon global cycle chart, fundamental third-order cycles (1–2 m.y. average duration) stack into related groups (second-order cycles: 9–10 m.y. duration). A much larger pattern (about 200 m.y.) is interpreted as tectonically controlled eustasy probably related to sea-floor spreading rates.

One and probably two higher orders of cyclicity (fourth-order: 0.1–0.2 m.y.; and fifth-order: 0.01–0.02 m.y.) are now observed in work with well logs, cores, and outcrops in areas of very rapid deposition. These frequencies are in the range of Milankovitch cycles, and may represent part of the Milankovitch hierarchy which has been widely interpreted for cyclical units in carbonate rocks.

High-frequency (fourth-order) sequences, which form at a 0.1–0.2 m.y. cyclicity, have all the stratal attributes of conventional sequences, including constituent parasequences and systems tracts, and play a dominant role controling reservoir, source, and sealing rock distribution. A consistent hierarchy of stratigraphy is observed. Parasequences (probable fifth-order cyclicity) stack into sets to form systems tracts in fourth-order sequences. Groups (sets) of fourth-order sequences are deposited between major third-order boundaries within third-order composite sequences. Sequences in these sets stack in prograding and backstepping patterns to form third-order lowstand, transgressive, and highstand sequence sets.

Third-order sequence boundaries are marked by greater basinward shifts in facies, by larger more widespread incised valleys, and by more extensive onlap than are fourth-order sequence boundaries. Third-order condensed sections commonly are widespread, faunally rich, and widely correlated biozone and mapping markers. Fourth-order sequence analysis helps to understand reservoir, source, and seal distribution at the play and prospect scale. An example from the Gulf of Mexico is discussed.     

Application of universal kriging for estimation of earthquake ground motion: Statistical significance of results

Universal kriging is compared with ordinary kriging for estimation of earthquake ground motion. Ordinary kriging is based on a stationary random function model; universal kriging is based on a nonstationary random function model representing first-order drift. Accuracy of universal kriging is compared with that for ordinary kriging; cross-validation is used as the basis for comparison. Hypothesis testing on these results shows that accuracy obtained using universal kriging is not significantly different from accuracy obtained using ordinary kriging. Tests based on normal distribution assumptions are applied to errors measured in the cross-validation procedure;t andF tests reveal no evidence to suggest universal and ordinary kriging are different for estimation of earthquake ground motion. Nonparametric hypothesis tests applied to these errors and jackknife statistics yield the same conclusion: universal and ordinary kriging are not significantly different for this application as determined by a cross-validation procedure. These results are based on application to four independent data sets (four different seismic events).     

The Roaches and Ashover Grits: sequence stratigraphic interpretation of a ‘turbidite-fronted delta’ system

A single Upper Carboniferous fluvio-deltaic cycle (Namurian, R₂b5) in the south part of the Pennine Basin of northern England has been reinterpreted using a sequence stratigraphic approach. In upward succession the deposits comprise basinal mudstones, localized thick density current deposits, delta slope deposits and delta-top sandstones, followed abruptly by basinal mudstones. Earlier interpretations linked these elements with a single, mainly regressive, cycle, referred to as a turbidite-fronted delta. Recent evidence for strong glacio-eustatic sea-level fluctuations in the Namurian suggests that it is unlikely that the previous simple model can explain the spatial arrangement of all the lithological units. This paper attempts to identify elements of the Exxon sequence stratigraphic model, in which changes of sea level are an essential part. The basinal mudstones represent deep-water deposition and imply a highstand of sea level. Thick density current deposits are now known to be localized close to the basinward limit of delta progradation, so cannot be seen as a ubiquitous component of the depositional system. They may form a detached fan, or a fan located at the foot of the delta slope. Slope siltstones include turbidite-like sandstones, but these are interbedded with tractional sandstones and Pelecypodichnus trace fossils, giving no clear indication of water depth. The delta-top sandstones, some coarse and pebbly, can in places be shown to consist of two parts separated by a significant erosion surface now regarded as a type 1 sequence boundary. The erosion surface is locally incised about 80 m into the delta deposits, forming a major palaeovalley. Giant cross-beds (foresets 20 m thick) forming part of the palaeovalley fill are restricted to the basinward end of this feature. A curve of relative sea level inferred for the R₂b5 interval suggests a fourth-order cycle in which two sharp rises are separated by a gradual fall. Possible minor (fifth-order) rises and falls may be superimposed. © 1997 John Wiley & Sons, Ltd.     

Tests of Significance for Structural Correlations in the Linear Model of Coregionalization

In the linear model of coregionalization (LMC), when applicable to the experimental direct variograms and the experimental cross variogram computed for two random functions, the variability of and relationships between the random functions are modeled with the same basis functions. In particular, structural correlations can be defined from entries of sill matrices (coregionalization matrices) under second-order stationarity. In this article, modified t-tests are proposed for assessing the statistical significance of estimated structural correlations. Their specific aspects and fundamental differences, compared with an existing modified t-test for global correlation analysis with spatial data, are discussed via estimated effective sample sizes, in relation to the superimposition of random structural components, the range of autocorrelation, the presence of correlation at another structure, and the sampling scheme. Accordingly, simulation results are presented for one structure versus two structures (one without and the other with autocorrelation). The performance of tests is shown to be related to the uncertainty associated with the estimation of variogram model parameters (range, sill matrix entries), because these are involved in the test statistic and the degrees of freedom of the associated t-distribution through the estimated effective sample size. Under the second-order stationarity and LMC assumptions, the proposed tests are generally valid.     

Tests of computerised strain analysis methods by the analysis of simulated deformation of natural unstrained sedimentary fabrics

Axial ratio—fluctuation measurements made on markers (oncolites, oolites, quartz grains, and accretionary lapilli) on bedding-perpendicular sections of unstrained sedimentary rocks have been homogeneously strained mathematically by set amounts, using published transformation equations, to provide a simulation of natural tectonic deformation. The resultant data have been used as test input to the strain analysis computer programs of Dunnet and Siddans (1971) and Matthews et al. (1974), which were devised to assess tectonic strain in assemblages of strained elliptical markers, with the use of limited specific assumptions concerning the nature of the pre-tectonic fabrics of the markers. The tests have shown that even slight deviations in the initial fabrics from the assumptions involved in the use of the strain analysis methods may lead to significant errors in the strain determinations. Errors are particularly large when fabrics which were imbricate in the unstrained state are used with the mistaken assumption that they were bedding-symmetric.     

A natural-gradient field tracer test for evaluation of pollutant-transport parameters in a porous-medium aquifer

This paper describes a natural-gradient field tracer test to characterise solute-transport properties in a sand and gravel aquifer in the Hebei Province, northern China. Some laboratory-scale column tests on aquifer material and a local-scale field borehole-dilution test have been conducted previously, but the field test reported herein represents the only large-scale tracer test in the aquifer, which is the sole water supply to the city of Shi Jiazhuang and which is threatened by urban pollution. The aim of the study was to quantify the transport behaviour of nonreactive pollutants in this aquifer. Little quantitative data are available concerning its solute-transport properties; thus, the results of the tracer test are significant and critical for understanding pollutant transport and fate. The in-situ tracer test was carried out in the aquifer using a slug injection of the geochemically conservative, radioactive iodine tracer ¹³¹I. The longitudinal (α _L ) and transverse (α _T ) hydrodynamic dispersivities for solute transport in the field are 1.72 and 0.0013 m, respectively. The ratio of longitudinal dispersivity α _L and the flow length at the field scale is 1:10. The ratio between α _L and α _T from the in-situ test (~1,300:1) demonstrates a dominant longitudinal dispersion in this fluvial sand and gravel aquifer. The tracer test further indicates a relatively short transit time for the aquifer (linear velocities ~13 m/d) under natural-gradient conditions. Electronic Publication     

层序地层学的起源及其发展

层序地层学脱胎于地震地层学，它已经在石油及其它沉积矿产勘探中得到了广泛的应用。目前，国际上层序地层学的应用和研究大体上可以分成3个学术组，即Vail为代表的Exxon组、Callo-way组及Cross组。他们有共同的术语，但概念模型及思路方法又各不相同。本文探讨了层序地层学的起源和演化及各学术组的特点和优势。     

Comparison of size effect for different types of strength tests

SummaryComparison of Size Effect for Different Types of Strength Tests Different theories have been proposed to explain and predict size effect. Notable is Weibull's Weakest link theory. In addition various theories have been founded on strain energy consumption at failure. The present paper suggests a theoretical approach, based on energy considerations and mode of failure, which holds for diverse types of mechanical testing. Maximum size effect is assumed to be associated with failure through development of a single fracture plane and a lack of size effect is associated with failure affecting a volume of material. The quantitative expression of the theoretical approach is based on the relationship between load at failure (P) and cross sectional area of the specimen (A):P=KA ⁿ wheren expresses size effect andK is a constant.The theoretically lowestn-value equals 0.75 expressing maximal size effect whereas the theoretically highestn-value is 1.00 expressing lack of size effect.n-values evaluated from published data for various mechanical tests indeed lie between these limits and appear to be related to type of test, material properties and specimen shape. Point load tests and Brazilian tests are generally associated with large size effects. This may be attributed to the test conditions which promote development of single fracture planes. On the other hand relatively small size effects are generally found for uniaxial compression tests. Failure in these tests characteristically occurs through multiple fracturing and crushing and therefore affects a volume of material rather than a single plane. Brittleness seems to be associated with large size effects and ductility with small size effects.With 4 Figures     

Microgeometry II: Testing for homogeneity in Berea sandstone

Geological sample characterizations rely on statistical assumptions of homogeneity and isotropy. There is also a tacit assumption of homogeneity at some size scale in theoretical geophysics predicated on power spectra or ensemble averaging, for example, acoustics (Devaney and Levine, 1980)or electromagnetics (Lee, 1979).Discussion is presented of a homogeneity test performed on Berea sandstone to develop methods for assessing homogeneity and for delimiting the scale at which homogeneity can be assumed. The Wilcoxon sum-of-ranks and signed-ranks tests are applied to scanning electron microscope image data. Anisotropy is found at some scales, and not at other scales. The homogeneity assumption for Berea sandstone is supported by agreement between estimates which depend for accuracy on homogeneity and values obtained by other independent methods such as bulk measurements or calculations from run-lengths.     

Normality Tests for Spatially Correlated Data

In studies that involve a finite sample size of spatial data it is often of interest to test (statistically) the assumption that the marginal (or univariate) distribution of the data is Gaussian (normal). This may be important per se because, for example, a data transformation may be desired if the normality hypothesis is rejected, or it may provide a way of testing other hypotheses, such as lognormality, by testing the normality of the logarithms of the observations. The most commonly used tests, such as the Kolmogorov–Smirnov (K–S), chi-square (²), and Shapiro–Wilks (S–W) tests, are designed on the assumption that the observations are independent and identically distributed (iid). In geostatistical applications, however, this is not usually the case unless the spatial covariance (semivariogram) function is a pure nugget variance. If the covariance structure has a (practical) range greater than the minimum distance between observations, the data are correlated and the standard tests cannot be applied to the probability density function (pdf) or cumulative probability function (cdf) estimated directly from the data. The problem with correlated data arises not from the correlation per se but from cases in which correlated data are clustered rather than being located on a regular grid. In these cases inferences requiring iid assumptions may be seriously biased because of the spatial correlation among the observations. If unbiased (i.e., de-clustered) estimates of the pdf or cdf are obtained, then normality tests, such as K-S, ², or S–W, can be applied using the unbiased estimates and an effective number of samples equivalent to the iid case. There are three questions to be addressed in these cases: Is the distribution ergodic?     

Evaluation of transfer functions in spatially structured environments

Transfer function training set sites close to each other tend to have similar species assemblages and environmental conditions in both oceanic and terrestrial data sets. This is unremarkable, but as this lack of independence between sites violates the assumptions of many statistical tests, it has severe consequences for transfer function evaluation, possibly resulting in inappropriate model choice and misleading and over-optimistic estimates of a transfer function's performance. In this paper, we develop a simple graphical method to test if spatial autocorrelation affects a training set, develop a Monte Carlo geostatistical simulation as a null model to test the significance of transfer functions in autocorrelated environments, and introduce a cross-validation scheme that is more robust to autocorrelation. We use these tests to show that some recently-published transfer functions have no predictive power, and strongly recommend the use of these tests to make transfer functions more robust to autocorrelation.