Lithological Interpretation Research Articles

Photogeomorphological mapping of southern parts of Jadukata-Umngi river valleys, Meghalaya

Photogeomorphological mapping was carried out in parts of the lower reaches of the Jadukata-Umngi river valleys in the southern fringes of Meghalaya. The area has been divided into five geomorphic units. Topography in the area is controlled both by structure and lithology and the geomorphic features greatly facilitate in structural and lithological interpretation. This becomes quite evident from the photogeological map of the corresponding area.

Interpretation of lithology from the formation resistivity of unconsolidated argillaceous/arenaceous sediments

A simple physical model for ionic conduction in shaly sands is modified and adapted to unconsolidated clayey sands. A brief review of the effects of porosity and cation exchange in clays on formation resistivity is made, assuming a linear relationship between clay content and porosity. The formation factor can be expressed in terms of the modified porosity and used to calculate the formation resistivity. The formation resistivity is adjusted for the effects of clay conductance under different saline conditions. Characteristic curves are constructed for particular environments, showing the effects of variations in clay content and porosity on formation resistivity. The use of characteristic curves and equations derived from the model is recommended as a semiquantitative aid to interpreting lithology from apparent resistivity data.

Application of digitally processed and enhanced LANDSAT imagery for geological mapping and mineral targeting in the Singhbhum Precambrian mineralized belt, Bihar-Orissa

Abstract Standard methods of digital processing and enhancement techniques have been followed to generate linearly stretched band products, band-to-band ratio images and normal and ratio colour composites from LANDSAT multispectral data on computer compatible tapes for nine test areas in the Singhbhum Precambrian mineralized belt. The software has been developed at the Space Applications Centre Laboratory, Ahmedabad, The data products have been subjected to general assessment and geological evaluation by visual interpretation methods. The study has resulted in a number of significant conclusions regarding utility and optimization of data products, stratigraphic lithologic and structural interpretations, identifying guides for mineralization and spectral characterization of major rock types.

Landsat 4 Thematic Mapper Imagery: Improved Tool for Geologic Mapping in Eastern Overthrust: ABSTRACT

The central Appalachians were studied using Landsat 4 thematic mapper (TM) data to evaluate the improved spatial resolution (30 × 30 m, 100 × 100 ft) of TM for mapping capabilities. The TM bands 2, 3, and 4 were contrast stretched and edge enhanced using digital processing techniques. Photogeologic analysis of the 1:125,000-scale TM image examined drainage, landform, lineament, and structural features. The study area comprises the junction of the central and southern Appalachians where fold axes change from N30°E to N60°E. Southeast-dipping thrust faults trend northeastward across the area. Cambrian through Devonian rocks are involved in and exposed by the thrust faults. Recognition of drainage relationships (density and pattern) are important in identifying lithologies. Landforms reflect structure and lithology through characteristic topographic expression. Improved identification and delineation of drainage and landform characteristics on TM imagery support structural and lithologic interpretations. Lineaments were identified by drainage, tonal, and topographic characteristics. Two major lineaments trending N83°E and N56°W, at the junction of the southern and central Appalachians, were identified. Identified structural features include fold axes, thrust faults, strike-slip faults, and thrust-faulted folds. Detailed lineament and structural mapping on TM imagery aids in unraveling complex surface geologic patterns in this critical area of the eastern overthrust. Digitally enhanced Landsat 4 TM data proved advantageous for accurate mapping of drainage, landform, lineament, and structural features. Improved accuracy on a regional scale allows reliable geologic mapping and therefore subsurface interpretations, benefiting hydrocarbon exploration. End_of_Article - Last_Page 508------------

Ghosting and marine signature deconvolution: A prerequisite for detailed seismic interpretation

Detailed lithologic interpretation of seismic sections and/or pseudo‐sonic logs generated from seismic data requires that the seismic trace can be modeled as a reflection series convolved with a zero‐phase broadband wavelet. Ghosting and marine signature deconvolution processing is a prerequisite for assuring that the seismic wavelet on a marine CDP section will be zero phase. A deterministic approach to deconvolution is centered around the concept of abandoning the purely statistical method of wavelet estimation and actually measuring the seismic wavelet. A proper signature recording for marine data is, therefore, a crucial component of deterministic deconvolution. Another important element in the deterministic deconvolution sequence is the application of a deghosting filter to remove near‐surface reflections. Proper application of a deghosting filter significantly improves the correlation between log synthetics and the seismic trace. It has been found that statistical deconvolution schemes, because of the number of statistical hypotheses required to produce a deconvolution filter, produce residual wavelets that are highly variable in character and whose average phases cover the entire phase spectrum, modulo 2π. Examples of a Gulf Coast marine line which was shot with Aquapulse™, air gun, and Maxipulse™ sources by the RV Hollis Hedberg are presented to demonstrate the differences between statistical and deterministic deconvolution processing sequences. It will be shown, using sonic logs from wells adjacent to the seismic line, that the deterministic deconvolution sections for all three sources are close to zero phase while the statistical deconvolution sections have residual average phase errors between 180 and 270 degrees. The deterministic deconvolution sections have a high degree of correlation among themselves and to the wells adjacent to the line, while the statistical deconvolution sections correlate poorly to each other and to the wells. Synthetic seismograms and their impedance logs, and the seismic sections and their corresponding pseudo‐sonic logs, are used to demonstrate how deconvolution influences lithologic interpretation. ™Western Geophysics Co.

A statistical wavelet processing system

The increasing use in recent years of ‘wavelet processing’ for seismic reflection data marks a shift in emphasis from processing for a predominantly structural interpretation to processing for a stratigraphic interpretation, which requires a high resolution wavelet of more stable phase characteristics. A wavelet processing system must begin with a ‘model’ or concept of the formation of the reflection wavelets, and such models have tended to become more complex as the sophistication of wavelet processing has increased. The advanced system described here is based on a model of the recorded wavelet as the convolution of a number of component wavelets, due to the source, the earth, and the recording system. After attenuation of noise by frequency-wave number (F-K) domain processing, a pre-stack desig-nature process makes use of the whole shot record for maximum statistics in estimating the effective source wavelet, and corrects that part of the total wavelet to a broad-band, zero phase characteristic. Interrelated post-stack processes then analyse the time variant wavelet components, mostly due to absorption and transmission effects, for correction also to a zero phase characteristic. The input reflection wavelet is assumed to be minimum phase, though this may require preliminary correction processes for certain sources. Problems with this minimum phase assumption in more conventional deconvolution processes are shown to be due to their method of estimating the phase spectrum, rather than with the validity of the assumption itself. This system of wavelet processing results in a final section on which the reflection wavelets have a stable broad-band zero phase characteristic, which not only gives the interpreter maximum resolution, but is also necessary for the application of subsequent inversion processing for lithologic interpretation.

Canadian journal of political science: Donald E. Blake, ‘The Consistency of Inconsistency: Party Identification in Federal and Provincial Politics’, XV:4, December 1982, pp. 691–710

Using single stratigraphic methods in the geological analysis of incompletely or poorly exposed sedimentary successions can lead to non-unique interpretations and increased potential for error. In this study of the Mesaverde outcrops (Eagle Formation, the Claggett Tongue of the Cody Shale, and the Judith River Formation) in the northern Bighorn Basin of Wyoming, which has limited and variable quality exposures, an integrated method utilizing sedimentological, ichnological, and palynological data was used in order to overcome these limitations. Ten facies are identified within the exposures examined. These facies are arranged so as to depict a broadly distal to proximal gradient recording the progradation of fluvial-dominated deltas into a shallow marine environment. The utilization of a Zobaa Ternary Plot and Calgary and Brown factor analysis (CABFAC) for palynofacies analysis in the study allows for corroboration of the lithological interpretation, which has not been possible in previous studies of correlative outcrops. It also enables the identification of environmental trends not seen in the lithological analysis, thus allowing for a more robust stratigraphic analysis. The methods used in this study not only decrease the inherent error in paleoenvironmental analysis of poorly exposed areas and thereby decrease variability in paleoenvironmental interpretations, but also allow identification of changes that are not evident from a single method approach. The result of utilizing this approach in areas of limited or poor quality exposure is a more comprehensive and well-informed regional stratigraphic framework.

Vp/Vs and lithology

Published laboratory investigations suggest an association exists between the ratio of seismic compressional and shear‐wave velocities [Formula: see text] and sedimentary rock lithology. Comparisons of some theoretical models with these laboratory studies suggest that crack, or pore, geometry has a stronger effect on observed [Formula: see text] values than elastic constants of the minerals comprising the matrix. Further, it can be inferred that the observed association between lithology and [Formula: see text] is a result of an association between lithology and distribution of pore and crack shapes. Direct observation of crack shapes for a variety of lithologies is a next step in strengthening these inferences. The present study reviews the empirical relations between [Formula: see text] and lithology and examines two published theoretical models of cracked elastic media. The models suggest that seismic velocities of sandstones may be controlled by cracks and pores with aspect ratios in the range of [Formula: see text] to 1, dolomite in the range of [Formula: see text] to [Formula: see text], and dense limestones, of generally low porosity, in the range of [Formula: see text] to [Formula: see text]. Direct observations of the aspect ratio of cracks and pores in sedimentary rocks would test these inferences and offer a basis for physical and geologic insight into lithologic interpretations of [Formula: see text] ratios.

Anomalous Seismic Character--Bering Sea: ABSTRACT

Seismic data collected within basins along the outer Bering Sea shelf often exhibit a distinct change in seismic character between 1.0 and 2.0 sec two-way time. This change appears on seismic sections as a reflector or as an increase or decrease in amplitude. The feature is of regional extent. This seismic character change is a manifestation of what has been called in other basins a bottom simulating reflector (BSR). BSRs are reflectors that are (1) subparallel with sea-floor topography, (2) discordant with stratigraphy where the sea floor dictates, and (3) do not demonstrate the characteristics of a multiple. Two causes of BSRs are generally accepted. One involves an ice-like mixture of water and gas, termed hydrate, in which gas molecules are trapped within a framework of water molecules. The other cause involves the diagenetic alteration of biogenic opal-A to opal-CT in diatomaceous sediments. BSRs were penetrated at three locations in the Bering Sea in water depths greater than 6,000 ft (1,829 m) on Leg 19 of the End_Page 576------------------------------ Deep Sea Drilling Program (DSDP). The BSRs at these locations were attributed to the diagenetic alteration of opal-A. This same diagenesis of opal-A to opal-CT is interpreted to be the cause of seismic character changes noted in basins on the Bering Sea shelf. This interpretation implies that limits can be placed on lithologic interpretation of the stratigraphic section in these basins. Pitfalls in seismic interpretation may be encountered where this reflector intersects other reflectors at an observable angle. The BSR may look like a sequence boundary with prograding clinoforms above it. This would place constraints on a seismic stratigraphic analysis in terms of predicted paleoenvironments and lithologies. Where this reflector crosses an anticlinal structure, it may appear to be a fluid contact and thus a direct hydrocarbon indicator. Recognition of the presence of this seismic character change is of two-fold importance to explorationists: (1) understanding the geology of the Bering Sea shelf, and (2) avoiding seismic interpretational pitfalls. End_of_Article - Last_Page 577------------

The importance of rock characterization in North Sea reservoir description

Reservoir sandstones may be described in terms of a range of compositional and textural parameters, providing an expanded data base for poroperm and capillary pressure studies, and wireline-log interpretation. The resultant improvement in reservoir description is likely to lead to better development planning and to increased recovery factors. Utilising fundamental geological skills, the initial core examination is carried out with an eye to significant lithological change within or between rock units. A record of structures, texture and composition is supplemented by photography. Having selected representative material with care, samples are subjected to particle-related and pore-related tests in the laboratory. Thin section and scanning electron microscopy, X-ray diffraction analysis, electron microprobe and cathodoluminescence studies together provide a clear picture of authigenic and allogenic mineral constituents, their composition, distribution and concentration. Pore properties such as porosity, permeability and pore-size distribution are measured by means of conventional core laboratory instruments. Particle properties of a sandstone reflect rock history, from source through deposition and diagenesis, and their distributions may be modelled; reservoir quality is, however, a function of pore space properties. A fundamental objective of rock characterization is the establishment of correlations between particle and pore properties to enable modelling and prediction of the latter. Wireline logs are universally available, whereas core samples are not. Consideration must therefore be given, when both are available, to the effect of observed lithological changes on log response, so that improved lithological interpretation is possible where core is absent.

Integrated Stratigraphic and Seismic Approaches to Reservoir Mapping, Mibale Field, Offshore Zaire: ABSTRACT

Located on a north-northwest-trending growth fault block on the continental shelf of offshore Zaire, the Mibale field produces medium grade oil from the Cretaceous Pinda Formation and is sealed by calcareous shales of the overlying Iabe Formation. An integrated geologic-geophysical study of the field resulted in detailed characterization and mapping of the Pinda reservoir, from which locations for future development and water injection wells have been selected. The Albian-Cenomanian carbonates and terrigenous clastics of offshore Zaire form a transgressive sequence comprised of landward thickening supratidal and intertidal deposits, and seaward thickening subtidal deposits. In the Mibale field major lithofacies are: (1) supratidal--thick-bedded sandstones and dolomites, with minor shales and anhydrites; (2) intertidal--thin-bedded shales, dolomites, and sandstones with minor anhydrites; and (3) subtidal--(a) thick-bedded dolomites and sandstones; (b) dolomites; and (c) lime wackestones to packstones containing various skeletal and non-skeletal grains. Cores show that the sandstones and dolomites have better permeabilities than the limestones. The areal distribution of permeable reservoirs is controlled by facies configuration, growth-fault movements, and secondary dolomitization. Within a single facies, thickness variations greater than 300 ft (91 m) occur. Because of the unpredictable thickness variations, seismic inversions (pseudo-sonic logs) were used to define the subsurface configuration of depositional and diagenetic facies across the field. Inversions were carefully calibrated to sonic logs and used for direct interpretation of lithology in areas lacking well control. Structure and gross pay maps, as well as lithologic and petrophysical characteristics of reservoir facies, enabled engineers to develop a three-dimensional simulation model of the field. End_of_Article - Last_Page 996------------

Detailed Temperature Logging as Useful Tool for Lithologic Interpretation: ABSTRACT

Data from an extensive drilling program conducted on the Atlantic coastal plain by the Department of Energy suggest that detailed temperature logs may be useful for interpretation of subsurface lithology and stratigraphy. Temperature was measured to ±0.01°C and was sampled every 0.5 m. Thermal gradients were computed, and compared to lithologic sequences as derived from drill cuttings collected every 3.0 m. Examination of a vertical thermal-gradient curve reveals that breaks in the curve correspond to major grain-size changes. Many of these breaks correspond to stratigraphic boundaries that are associated with a grain-size change. However, stratigraphic boundaries that are not defined by a grain-size change are more difficult to recognize. Preliminary results from the first hole at Fort Monmouth, New Jersey, suggest that the correspondence between thermal gradient and grain size is due to a direct correlation between local thermal gradient and the amount of sediment at that depth that is finer than 4.0 psi. This relation allows detailed interpretation of lithologic sequences. Trends within a stratigraphic unit, such as fining-upward sequences, can be readily identified. Also, thin lithologic units (1 to 2 m thick) that were recovered within sediment cores are recognizable on a thermal-gradient curve. These results suggest that detailed temperature logs can provide valuable, detailed information about subsurface stratigraphy and lithology. End_of_Article - Last_Page 484------------

Performance evaluation of a high-resolution sub-bottom profiling system

The design and performance of a modern digital high-resolution sub-bottom profiling system are reviewed. The system is designed to identify drilling hazards in about the first 3000 ft of sea floor. Performance comparisons with a conventional active sonar are made using metrics such as figure of merit. The sound source is a sparker; the receiver a towed line array. There are two stages of signal processing: the first stage is applied to each hydrophone channel, and the second stage in the combination of all channels. The first stage includes pulse compression (zero phase least-squares Wiener filtering using a source monitoring hydrophone system), the removal of surface-images (“deghosting”), and the reduction of bottom-surface multiple reflections (“dereverberation”). Two near-field moving-focus beam steering second stages are compared; CDP (common depth point) stacking and Tucker et al.'s within-pulse electronic sector scanning. Typical sub-bottom records will be shown and the effectiveness of various processing steps illustrated. Also discussed are techniques for quantifying reflection coefficients to aid in lithologic interpretation and of “seismic modeling” to help unravel records with overlapping returns.

航空写真および切峰面による地質および地質構造の判読 東京都西多摩郡付近について

This is a report of a photogeological survey, supplemented by the analysis of a summit level map, of the Nishitama area, easternmost part of the Kanto Mountains.For the interpretation of lithology and structures of the area, the author has prepared a drainage map on a scale of 1: 20, 000 by means of radial intersection method. Maps showing drainage density and its frequency have been compiled from this map, for the purpose of quantitative drainage network analysis. In addition to these, a summit level map, which may represent macro-relief produced by tectonic movements as well as rock-controlled land-forms, has been compiled using topographic maps on a scale of 1: 50, 000.The photogeological survey of the area, the geology of which consists of Paleozoic and Mesozoic rocks, has been carried out with an aid of these maps and field investigations. The main results obtained by this survey are summarized as follows:1) From the drainage pattern, the difference in the shape of ridges and vegetation types, the area composed of sandstone, and the area where chert or limestone is intercalated can be distinguished.2) The NW-SE trending geological structure, predominant in this area, is identified from both the drainage map and the drainage frequency map. It seems probable that the areas of high drainge density and frequency would correspond to the areas where many fractures originated from faults are found.3) The direction of photographic lineaments and stream courses reflect well the geological structural trend of this area. While photogeologic lineaments coincide with faults, the direction of photogeologic fractures and stream courses, excluding those parallel to the photogeologic lineaments, is presumed to correspond to the strike of strata or joints.4) The summit level map is useful for the analysis of geological structures.

IS SEISMIC ENERGY OF DIAGNOSTIC VALUE?

Since both the intensity of a seismic wave and its energy density are directly related to the square of the particle velocity, a quantity available as the output of a geophone, it is feasible to record energy density as a function of time and space. The energy recorded is a function of the spatial attenuation factors of the media traversed, the partition at reflection boundaries, and the geometric spreading. If a proper correction can be made for the latter two effects, it is possible to generate a function that is diagnostic of the attenuation properties of the geologic model and may be useful for lithologic interpretation. A quantity that is proportional to the logarithm of the peak absolute value of the square of the particle velocity, or the logarithm of the energy density, was recorded along a series of test profiles. Conventional reflection data were also recorded. The purpose of the field program was to gain preliminary experience in energy recording and to seek an answer to the query posed in the title. The main conclusion is affirmative. This, however, must be qualified. It is apparent that several serious impediments must be overcome. It is necessary to develop satisfactory techniques to remove the geometric and reflectivity effects from the recorded energy data, to eliminate measurement errors which can produce magnitude errors of several orders, and, above all, to develop a detailed and accurate set of in‐situ spatial attenuation factor data.

Advances in Interpretation of Offshore Seismic Data: ABSTRACT

The recent advent of long recording spreads and the development of new programs for digital processing have yielded large quantities of detailed information on seismic velocities along each line of recording. These advances have multiplied the ability of the geophysical interpreter to convert his seismic time data properly to more accurate depth displays for proper integration with geologic data, thus narrowing the gap in interpretation of structure and lithology between the geologist and geophysicist. In steep dip areas of offshore California, it is imperative that the individual segments of events appearing on seismic time sections be migrated to their proper original positions. This geometric reconstruction can be approximated successfully by the proper use of velocity data in seismic wave-front methods of migration. Two-dimensional plots of seismic depth sections can be produced economically at present; such plots incorporate changing vertical and horizontal velocity data. Various methods of two-dimensional representation of structure are available. Much greater effort must be devoted to integrated geophysical-geological interpretation of the great masses of seismic data which are being accumulated if management is to realize full return on exploration investments. End_of_Article - Last_Page 458------------

A PALYNOLOGICAL STUDY RELATING TO THE PLEISTOCENE TORONTO FORMATION

The present palynological study is used as a new approach to determine the stratigraphical and chronological position of the Pleistocene interglacial deposits, the Toronto formation, exposed in sections at Toronto, Ontario, Canada.An interpretation of lithology, combined with evidence supplied by the pollen and spore assemblages, indicates that the Don beds, the lower member of the Toronto formation, belong to the Sangamon Interglacial. The Scarborough beds, the upper member of the formation, were deposited during a nonglacial interval, cooler than the present. Conformity between the two members is questioned on grounds of lithological and palynological evidence.Results of palynological studies, as indicated by this investigation, can be used for interpretation of the mode of deposition of certain laminated sediments and for reconstruction of past types of landscape.