SEDSIM is a series of computer program modules that simulate the main processes that create sedimentary basins. The representation is three dimensional, except that representation of flow processes are not fully 3-D, with geographic variations in flow velocity in open bodies of water being represented, but variations with depth are not. Processes include wave action, erosion, transport and deposition of clastic sediment, compaction, pore-fluid expulsion, and isostatic compensation. Experiments that linking processes together document the versatility of SEDSIM's procedures to produce highly realistic stratigraphic sequences under controlled conditions, including responses to changing sealevel and wave climate. Experimental results involving stratigraphic sequences produced by falling sealevel followed by rising sealevel are briefly described and compared with the Yegua Formation.

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A 3D numerical block of a rock composed of spherical particles embedded into a matrix is simulated by a computer program which allows also to deform the block with novolume change in a coaxial strain regime for different values of the strain ellipsoid: plane strain, constriction and flattening. The influence of several parameters such as size of particles, minimum distance allowed between two particles, particle/matrix viscosity ratio, particle distribution (anticlustering, graded bedding, clustering) are discussed in order to use the centroid method (Fry's method) for strain measurement. Inside the deformed block, calculated and automatically drawn sections are cut parallel to the three principal strain planes (XY, YZ, XZ) . Using the centroid method, the finite strain is calculated by combining the principal strain planes, and compared to the true strain ellipsoid fixed by the initial conditions of simulation. Graphic images are also plotted from the numerical sections. They are investigated by image analysis, centroid are extracted and strain ellipses and ellipsoid calculated. The good correlation between the real strain ellipsoid, the numerical strain ellipsoid and the calculated strain ellipsoid is assessed. Lastly, the centroid method is applied to naturally deformed samples in which data acquisition of centroid is made by image analysis.

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The reconstruction of ancient sediment fluxes is based on the assumptions that young sediment is generally unconsolidated, has the greatest areal exposure and thus has the greatest probability of being eroded. Young sediment is therefore recycled more rapidly than old sediment which is more consolidated and has a smaller areal exposure. This assumption is the fundamental principle underlying the theory of sediment recycling.
We assume that on a global scale the sedimentary system is in steady state and has a mass that remains constant because most younger sediments are derived from cannibalization of older sediments through erosion. This implies that gains of sediment mass from weathering, erosion, and deposition of igneous and crystalline metamorphic rocks are exactly offset by losses to subduction and metamorphism.
The general decline of sediment mass with age is approximated by a simple exponential decay y=Ae^-bt where y is the remnant of the original sediment flux at time t, that would be observed today after t m.y. of recycling at a constant rate of erosion b (“average recycling proportionality parameter” of Veizer and Jansen, 1985), and a constant depositional rate, A (the rate at which sediment is being deposited at present) .
The new total sediment mass for the Phanerozoic is 2082.6×10²¹g. Based on a least squares fit of an exponential decay curve to the data, we have determined the average zero-age flux rate of Phanerozoic sediment to be 5.756×10²¹g m.y.^-1 and the average rate of sediment recycling to be -2.062×10^-3 m.y.^-1. New estimates of the mass of Proterozoic and Archaean sediments are also presented; these are 845.5×10²¹g and 15.0×10²¹g for the masses of Proterozoic and Archaean sediments respectively.
Because neither rocks of a particular lithology or age can be selectively protected from erosion, it is possible to reconstruct mass-age distributions for different lithologies. Detrital rocks dominate the sedimentary system in terms of mass, and can be regionally confined as a closed system. The recycling rate of detrital rocks can be used on both global and regional scales to reconstruct past sediment fluxes of both detrital and chemically or biologically precipitated materials.

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Rock mass conditions observed in excavated surfaces are generally believed as the result of changes due to weathering during a period of geologic time span, that has resulted in gradation distribution within the rock mass. The gradation distribution however tends to be dependent on the joint planes that are present in the rock mass.
Computer simulation of weathering process in jointed rock masses has been attempted in order to understand the change in rock mass condition and distribution. If the relation of changes is formulated mathematically, and joint distribution as boundary conditions are obtamed, it may be possible to simulate the change of grade using computer.
The probable and basic relation presented here is that the decreased rate in grade at any point is in proportion to its spatial gradient at the given point. Computer simulations have been carried out on the basis of a simple differential equation expressing the relation under any boundary conditions. Several examples of simulated results were observed to appropriately represent the change in gradation distribution of jointed rock masses.
These simulation studies are consequently useful to estimate or predict the rock mass conditions prior to excavation work. In other words, it could provide a powerful tool for engineering geologists in evaluating geologic conditions particularly for construction purposes.

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Models of highly-viscous incompressible nonhomogeneous multi-layer newtonian fluid can be used for studying the process of the formation and evolution of sedimentary basins. Investigations of the dynamics of the layers of the sedimentary cover and the lithosphere above a rising mantle diapir show, that if this diapir is deep and its velocity is low, a depression is formed on the Earth surface. Stretching in the lithosphere can be small. If the velocity of the rising diapir is high or the diapir is shallow a superficial swell can be formed. In any case it is possible to find critical parameters connecting the form of diapirs and their depth and velocity with the structures of the Earth surface. Thermomechanical modeling gives possibility to describe oil-gas generation zones evolution and to connect surface and deep heat flow with basins evolution history and with properties of deep layers.

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Erosional modelings are commonly carried out on geologically homogeneous terrains or on very elementary geological structures, so that results can hardly be compared with actual landscapes resulting from the erosion of geologically contrasted districts.
We are presently developing a software - CARVES - which achieves erosional landscapes by operating simple erosional laws on multifolded geological terrains which may be freely defined by the user. The available erosion laws make it possible to simulate terrain creep and wash, chemical dissolution by infiltrated waters, as well as alluvial deposition. Rock erosion parameters and intensity of rain falls may be chosen by the user.
Modeling goes through numerous iterations. The geology and morphology of the resulting landscape and the river network can be visualized at each stage.
CARVES already allows users to check the relations between contrasted geological structures and landscape evolution. It is thus a potential tool to study quantitative erosion and also to produce artificial landscapes representing mountain district. CARVES is already a flexible and evolutive software that may be subject to many extra refinements in future.

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Seismic modeling techniques provide the mechanics for simulating the geology of the subsurface by depicting the impact of a propagating seismic wavefront on subsurface structures. In practice, seismic data has been used to map the geometry of events in the subsurface, mainly from reflection continuity and the character of reflection packages.
In the Niger Delta, recent development in stratigraphic exploration has induced the examination of more subtle features of reflection mainly polarity, amplitude and waveform to define the limits of seismic resolution, and hence predict the geometry of subsurface fluid and solid interfaces.
The Case History discussed here involved interpretative study for defining the fluid contents of prospective oil and gas leads as indicated by anomalous seismic events on a Niger Delta field located in a water depth of 25 meters.
An appropriate source signal (5-35 Hertz Minimum Phase) is selected and the wavelet is convolved with a practical geologic model to obtain a synthetic seismogram. By an iterative process involving slight modifications in the geologic model, a synthetic seismogram is ultimately derived which matches a field signal, thus providing a more accurate prediction of the geologic formation under study.
The technique was effective (as confirmed by later drilling) in appraising the fluid contents of the targeted pay zones encountered at gas/water, oil/water and gas/oil/water contacts in the 0 - Field, located in the eastern offshore area of the Niger Delta. The method further demonstrated that structural and stratigraphic modeling are effective tools for testing the mapability of a geologic concept and able to evaluate the significance of reflectivity changes or anomalies on uncalibrated seismic data.

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An interpretation system of geophysical fields (including gravity and magnetic prospecting, thermal prospecting, Self-Potential, Induced Polarization and VLF method), developed for variable geological medium and inclined surface, is consisting of a few successive stages. On various stages of the system application rugged relief corrections are calculated, different noises of geological and physical nature are eliminating, inverse problems of geophysics are solved. Most important and effective stage of the developed system is 3-D interactive physical-geological modeling of gravity and magnetic fields by the use of GSFC program. The program allows to calculate all components of magnetic field, Δg_B, Δg_f._a., Δg_obser and as well as second derivatives of gravity potential under conditions of rugged relief and oblique magnetization. The program has following advantage preferences: possibility of terrain relief description by irregularly disposed characteristic points by using a few tenses of profiles; possibility of calculation of boundary influence “earth-air” directly in the process of interpretation by method of selection; possibility of common computing of petrodensity and petromagnetic models. The program is a part of common system IMIGO, allowed to process and to keep various geophysical data files. Using the interpretation system a deep structure of East Caucasus has been exacted and also new peculiarities of geological structure have been revealed. On its basis, for instance a hypogene underthrust of Lesser Caucasus Mesozoic magmatic formations under Greater Caucasus sedimentary deposits has been revealed. The conclusion by results of Saatly Superdeep hole drilling was confirmed.

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The POLYPLI software makes it possible to visualize the geometry of stratified terrain which have been deformed by numerous fold and fault events in a quick and efficient way.
Strata deformation is carried out by simple geometric transformations which affect the various material points. These transformations simulate the displacements which are registered in similar folding. Faults are simulated in a similar way.Stratigraphy, fold profiles wavelength amplitudes and orientations of the various fold phases and of the various faults are interactively defined by the user.POLYPLI can represent unconformities and deformations which simultaneously affect a previously deformed basement and its sedimentary cover.
POLYPLI provides a new type of help for structural analysis : its provides a good approximation to the topology of intricate deformations such as those which are commonly observed in basement located metasedimentary terrains. Run under UNIX operating system, POLYPLI is very interactive and easy to use because of a multiwindow presentation which can input most data with the mouse.

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Most geological systems are three-dimensional in their spatial aspect, anisotropic, and poorly sampled, and the general reconstruction problem for such systems is to determine from limited data the forms of the particular objects that make them up, and their interrelationships. This must involve first determining the topology of each object, and then its geometry. Real geological data, however, are never good enough to eliminate all but the actual topology and geometry of any object, and so only its most likely topology and geometry may be predicted, on the basis of the available data. Subsurface horizons can be reconstructed from seismic and well data by first subdividing the subsurface into a set of triangular prisms controlled by these data, and then using a random walk technique within each triangle to determine the most likely topology. The geometry of the horizons is then obtained by straightforward surface fitting. This approach has a local, probabilistic basis, and can incorporate anisotropy. It is also computationally very reasonable to implement.

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Modeling a faulted domain is difficult because of the multiplicity of solutions for linking traces. The use of interactive software can be very efficient if it provides the opportunity for real 3-D reasoning. The application of geometric modeling to the Soultz horst shows that GOCAD software is a powerful tool for building a realistic geometric model of fault and layer systems, since it enables the geologist to interactively identify inconsistencies between 2-D interpretations of the profiles, take into account complex morphologies such as the subdivision of a fault, and investigate as many hypotheses as needed.

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The Indian Standard Procedure for detailed coal exploration, to enable mine planning, translates into drilling of boreholes at 400m spacing on a square grid. Isochore maps depicting seam thickness variations are prepared contouring the seam thickness met in boreholes using, till recently, triangular plate or three point technique. With increasing availability of computerized contouring techniques, an exercise was undertaken to examine the relative efficiency of some of these methods. Actual measurements of vertical thickness of a fully exposed coal seam in an underground mine, made at spacing varying from 5m to 40m in an area of 0.96 sq.km. were hand-contoured to represent the ‘actual’ seam thickness variations. A transparent overlay of square grid at 400m spacing was prepared for the nodes to represent borehole locations. The grid-overlay was placed at six different orientations over the‘actual’isochore and the seam thickness in boreholes for each case were simulated at nodes.
These simulated borehole thickness data were, in each case, contoured through computer programs employing Triangular Plate, Polynomial Regression, Double Fourier, Cubic Spline and Krigging techniques. The results were evaluated qualitatively as well as quantitatively at sub-nodes at 80m intervals.
It was indicated that the krigging technique produced the most efficient contours with reference to‘actual’ isochore in all the cases. The change in the orientation of the borehole grid was not seen to substantially affect the accuracy of results.

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At present, a global crisis of mineral resources is accelerated at a growing rate and many countries are facing the challenge of time. Therefore, the policy-makers of various countries have formulated appropriate countermeasures to convert tactic goal into strategic objective or combine both to a general pattern as a game of chess. The tendency from traditional type to opening type reflects the difficulty of metallogenic prediction increasing and it is urgently necessary to deepen the exploration for concealed deposit. Traditional classic theory, modern theory and fuzzy theory are commonly adopted to guide research. These theories have respective superiorities, but their common defect is that they can't make long-term control. In order to conquer the insufficiency mentioned above, the authors have discussed on concealed deposit by using the grey theory and discovered that this research area belongs to grey metallogenic system of intension type. Thinking is widened by the dissection of several typical examples. The concept, definition and classification of so-called “concealed deposit” are considered to be further discussed. Hence the new concept “concealed form type deposit” is suggested. Aimed at the grey characters of metallogenic system, the strategic countermeasure researching program of grey prediction and decision making have been formulated. The promise of this new area is extensive, and the theoretical significance of the research in this area and practical guiding action are profound.

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The Geological Survey of Austria is charged with the task of providing the public with all types of geological information to the fullest possible extent. Starting in 1990 the survey has been actively engaged in the development of a data-storage system of the contents of geological maps and in their computer-assisted printing. The current map production process employs both manual and computer-assisted techniques, including ARC/INFO¹, PostScript², Linotronic 530 and several PC-based software-packages. On the whole, the introduction of computer-assisted technology to the map-printing process, by the ADP and Cartography sections, has been beneficial. The paper describes the conceptual framework involved as a result of the experience gained over the years 1990-1992.
(1 ARC/INFO is a registered trademark of Environmental Systems Research Institute, Inc.)
(2 PostScript is a registered trademark of Adobe Systems, Inc.)

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PETROL is a software system developed to assess the economic potential of petroleum exploration for corporate planning and government policy purposes based on present-day economic and technological conditions. Three interrelated main programs carry out:
•economic evaluation of individual petroleum fields (PETROL 1) ;
•statistical analysis of field variables (PETROL 2) ; and
•assessment of the economic potential of petroleum exploration (PETROL 3) .
This paper focuses on PETROL 3, the program that assesses the potential value of petroleum exploration for a country, region, or basin of interest. The cash flow distributions for economic fields evaluated in PETROL 1 and exploration-phase estimates are the main inputs for this program. The evaluation procedure comprises two steps. The first step involves medium-term assessment of the economics of field development, representing the successful result of petroleum exploration. The second step is the long-term assessment of the economic potential of petroleum exploration. Unit exploration costs, discovery risks, and organizational risk criteria are also appraised.
Application of the PETROL 3 program is illustrated by assessing the economic potential of petroleum exploration in the Cooper-Eromanga basin of Australia. The database for this case study includes $1, 334 million^* of petroleum exploration expenditures, 344 new field wildcat wells, 159 technical successes, and 116 possible economic fields discovered as a result of those expenditures up to 1987.
[* All money values are expressed in constant 1990 Australian dollars]

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A geotechnical database has been developed to act as a system for management tool for site investigation data. The system runs on a microcomputer and is capable of producing several sets of geotechnical maps and cross sections.
The resulted analytical maps, clarify those factors, connected with soil features and their geotechnical nature which are of interest to engineers and planners for preliminary site evaluation.
The engineering geological maps have the advantage that every one can give his/her own personal interpretation using such a map.
The paper describes the database system and provides some of its applications in illustration of horizontal and vertical transition of lithof acies, modeling of groundwater flow, maps of N value and lithology in the horizontal plane for arbitrary depths, vertical changes of N values and lithology data, preparation of subsurface cross sections, dominate frequency analysis of the ground shake and cluster analysis of N values data.

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The main aim of given the project is to study worldwide commercialized datamanagement software systems and to choice the most suitable software for an experimental storing and management of hydrogeological data. As a result of the study, the DBASE III PLUS software package was applied for creation of a hydrogeological database of the Northern Provinces of Vietnam, and the AutoCAD 10.0 was applied for computerization of a standard Hydrogeological Map of Hanoi. During the course of implementation, the scientific staff involved in the project has been gaining good skills and experiences on computer-aided datamanagement. The hydrogeological database created in this project is the unique database of this type in Vietnam and is expected to be supplemented and updated during the following period of an expanded project.

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Data base containing the information about active faults on the area of the former USSR has been created. Now it contains information of about 1700 faults; in the near future it will be added by the information about active faults in the whole East hemisphere. The data base is a good tool for studying active faults.

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When production data are not available, gas/oil differentiation is usually performed based upon the FDC/CAL (Formation Density/Neutron Logs) response and sidewall sample (sws) information. The response of the FDC/CNL tools, however, has been regarded as the more reliable indicator of the two methods.
The formations in the Niger Delta consist of sands and shales with the former ranging from fluvial (channel) to fluvio-marine (Barrier Bar), while the later are generally fluviomarine or lagoonal. These Formations are mostly unconsolidated and it is often not feasible to take core samples or make drill stem tests. Formation evaluation is consequently based mostly on logs, with the help of sidewall samples and wireline formation tests.
This case history involves a study of an onshore field located on the West Niger Delta whereby most of the wells drilled have sws petrophysical data and no FDC/CNL and the objettive was to evaluate the adequacy of the available data, and determine a measure of confidence that can be expected when fluid differentiation (gas/oil/water) is done strictly from SWS measurements.
From the comparison between the FDC/CNL separation and SWS petrophysical data, it is possible for fluid differentiation to be done strictly from SWS measurement with a good measure of reliability, in the absence of production data and FDC/CNL logs. It is also noticed that SWS data better differentiated this marginal gas and oil sands of the order of 5-6 ft pay resulting in a potential for reserves/production addition. The FDC/CNL log response are better defined in thick clean sands as against thin marginal sands in this case study.

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For projects of the International Geosphere-Biosphere Program, satellite data in conjunction with existing geoscientific databases provide effective means. These databases cover scattered areas and comprise topographical and geological map data, remotely sensed data (aerial photographs and satellite images at various scales), geophysical and geochemical data files, geological field reports and geoscientif is publications.
For Nepal, the elaboration of modern thematic maps at useful scales has to be based on data from appropriate satellites, primarily from LANDSAT Thematic Mapper taking into account also SPOT data for the High Himalaya where no air photo coverage exists. The combination and evaluation of multisatellite data together with aerial photographs reveal geomorphological, geological, tectonic, soil and vegetation features as well as erosion and landslide phenomena.
The results of satellite data evaluation and air photo interpretation are integrated with existing unbiased geoscience data and supplemented by ground truth data. In selected areas, digital elevation models will be constructed using SPOT data and existing topographic data. The resulting information will be integrated with data from snow-hydrological stations in the Himalayan mountains permitting, for example, the estimation of snow-melting run-off. Using GIS techniques, the results finally achieved will be displayed in thematic maps at different scales.

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A comparison of conodont collections from the Lower Carboniferous indicates that many conodont elements are excellent index fossils. Some of these have a world-wide distribution and always represent the same stratigraphic interval. These, the type A index conodonts, include species of Eotaphrus, Pseudopolygnathus, Siphonodella, and Taphrognathus and are good inter-and intra-regional markers. Type B index conodonts are restricted to specific regions and are good stratigraphic markers within these. Bactrognathus distortus is present in most samples from the middle of the Burlington Formation from that formation's erosional edge in east-central Iowa to just south of St. Louis Missouri, in a few samples from the Floyds Knob Member of the Borden Formation in eastern Kentucky (Goodman, 1975, Baxter 1993a), and in samples from the Andrecito Member of the Lake Valley Formation of New Mexico (Burton, 1964) . This whole region was just south of the equator during the Carboniferous (Baxter, 1993b) . Another type B index conodont is Mestognathus. This taxon is common in collections from Europe, but has also been recovered from exotic, accretionary terrains in Atlantic Canada and Western North America. Type C index conodonts occur word-wide, and although they are good markers within a region, they have different ranges in different regions. Gnathodus texanus and several species of Cavusgnathus range throughout the Visean of North America. In the Midcontinent Region G. texanus occurs throughout this interval but is restricted to the Chester in Western Canada. Cavusgnathus is present throughout the Visean of Western Canada but does not occur below the upper part of the St. Louis Formation in the Midcontinent Region.
Type A index conodonts are essential for word-wide correlation. The other two types are good for correlation within specific regions, but may also serve other purposes. The type B index conodonts may reflect fixed barriers such as restrictive currents or limiting salinity or temperature gradients. This type may also serve to identify exotic terrains and plate movements. Type C index conodonts may be indicative of fluctuations in environmental conditions or may reflect the lateral migration of a taxon.

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The three-dimensional mapping of time-bounded bodies of rock (chronosomes, after Schultz, 1982) forms the basis of quantitative prediction of both rock properties and biostratigraphy in the subsurface as discussed in the accompanying paper by Griffiths and Nordlund.
Over fifty chronosomes from the Paleocene of the North Sea have been mapped in threedimensions. Quantitative shape functions are coupled with digital terrain analysis of the chronosome lower surfaces to increase predictive potential. The results are related to conventional two-dimensional seismic stratigraphy and the relative sea-level curve at different locations on the basin margin. Inter-well correlations, and lithological controls on biostratigraphy are discussed in three-dimensions.

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The three-dimensional mapping of time-bounded bodies of rock (chronosomes, after Schultz, 1982) forms the basis of quantitative prediction of both rock properties and biostratigraphy in the subsurface.
High resolution seismic data can provide mappable reflection-bounded units (RBU's) with a vertical resolution of 10 to 20 ms two-way-time (approximately 10-20m in Tertiary sediments) . Lateral resolution varies from 10m in a 3D survey, to 500 m plus in the case of a regional 2D survey. We can begin with the working hypothesis that seismic reflectors are isochrons and map RBU's to chromosomes. Each chronosome has a unique combination of geological time interval and paleogeographical location. They are composed, generally, of lesser chronosomes below the current observational resolution, and can be combined to form higher-order chronosomes. The chronosome concept is therefore both time, and scale independent. Seismic stratigraphy forms a genetic framework in which the vertical development of chronosomes at any given location can be related to regional and/or global processes. Current seismic stratigraphic concepts and terminologies are essentially two-dimensional, yet sediment distribution throughout a basin is, of course, three-dimensional. Only by mapping chronosome development in three-dimensions can one find the predictive relationships between shape, location and content that are needed both for practical application of quantitative stratigraphy and in the theoretical analysis of causative processes within the basin.

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The physical property parameters of the rocks from Pre-Sinian to Jurassic in the Sichuan Basin and neighboring regions are discussed. These parameters contain the compressional velocity, shear velocity, density, porosity, magnetic capacity, remanent magnetization and electrical resistivity. In the paper, the authors also make preliminary investigation for the various geological factors on a decisive parametric change of the physical properties of the rocks.

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The mathematical methods and computers for stratigraphic correlation of Quaternary deposits have been applied, because on account of various reasons, this problem can't be completely solved using only methods of biostratigraphy and geochronology. The stratigraphic correlation of tills has been executed by using the results of lithological and geochemical investigations and mathematical-statistical methods. The application of the factor and cluster analysis have been most effective. Absolute data of the results of various laboratory investigations have been used for stratigraphic division of geological sections, while relative data (lithological and geochemical coefficients or pair correlation coefficients) have been used for stratigraphic correlation between the sections. Minimum number of samples necessary for statistic characteristics of each till has been obtained experimentally. Therefore the dependence of variation coefficient on the number of samples has been analyzed. The most reliable results of stratigraphic correlation of tills have been obtained using data of chemical (silicate) analysis.

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Use of factor analysis in the earth sciences has shifted in application and purpose with time since early papers in the 1960s. Early applications mirrored the goals of the originators of the methods to detect and measure actual factors that worked through some process to give observed patterns in correlations among measurable parameters. Unresolved was the issue of rotational indeterminacy, and the question: why should natural systems be modeled by linear combinations? However, many researchers discovered the utility of factor analysis and related eigenvector methods as methods for data summary; certainly the clarity of a loadings or scores plot as opposed to verbal summary of correlation matrices outweighed small losses of information and distortions resulting from projecting many dimensions to a few. Almost ignored was the issue of spatial dependence between samples.
Recent years have brought new methods for handling such problems: log-linear models to resolve nonlinearity in compositional data, multi-mode factor analysis to eliminate rotational indeterminancy, and multivariate geostatistics to capture spatial dependence.

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