AAPG Bulletin Research Articles

04/02275 Origin of minerals in joint and cleat systems ofthe Pottsville formation, Black Warrior basin, Alabama: implications for coalbed methane generation and production: Pitman, J. K. et al. AAPG Bulletin, 2003, 87, (5), 713–731

04/02275 Origin of minerals in joint and cleat systems ofthe Pottsville formation, Black Warrior basin, Alabama: implications for coalbed methane generation and production: Pitman, J. K. et al. AAPG Bulletin, 2003, 87, (5), 713–731

04/02235 Geochemical characteristics and correlation of oiland nonmarine source rocks from Mongolia: Johnson, C. L. et al. AAPG Bulletin, 2003, 87, (5), 817–846

04/02235 Geochemical characteristics and correlation of oiland nonmarine source rocks from Mongolia: Johnson, C. L. et al. AAPG Bulletin, 2003, 87, (5), 817–846

04/01183 Paleoenvironments and paleogeography of the Lower and lower Middle Jurassic coal measures in the Turpan-Hami oil-prone coal basin, northwestern China: Shao, L. et al. AAPG Bulletin, 2003, 87 (2), 335–355

04/01183 Paleoenvironments and paleogeography of the Lower and lower Middle Jurassic coal measures in the Turpan-Hami oil-prone coal basin, northwestern China: Shao, L. et al. AAPG Bulletin, 2003, 87 (2), 335–355

04/00682 Coalbed methane, cook inlet, south-central Alaska: A potential giant gas resource: Montgomery, S. L. et al. AAPG Bulletin, 2003, 87, (1), 1–13

Heteroatom containing molecules in South Banko coal liquid (SBCL) distillate were identified with a gas chromatograph equipped with an atomic emission detector (GC-AED). Thiophenes and benzothiophenes were found to be the major sulfur compounds. Pyridines, anilines, and phenols were the major nitrogen and oxygen compounds, respectively. Reactivities of heteroatom containing species in hydrotreatment over conventional NiMoS/Al2O3, NiMoS/Al2O3–SiO2 catalysts were very different according to their cyclic structure as well as the kind of heteroatom in the species. The sulfur species were completely desulfurized over the catalysts examined in the present study by 60 min at 360 °C under initial hydrogen pressure of 5 MPa. However, hydrodenitrogenation was more difficult than hydrodesulfurization even at 450 °C. Anilines were found the most refractory ones among the nitrogen species. Hydrodeoxygenation of SBCL was also difficult in the hydrotreatment conditions examined in the present study. Dibenzofuran was the most refractory molecule among the oxygen species. A two-stage reaction configuration at 340 and 360 °C improved HDN and HDO reactivities, although the conversions were still insufficient. Increasing the acidity of the support as well as the loading of the metals on the NiMoS/Al2O3 catalysts improved very much the heteroatom reduction to achieve complete removal of nitrogen by two-stage reaction configuration at 340–360 °C and oxygen at 360 °C, respectively. The addition of H2S in the reaction atmosphere inhibited the HDN reaction but increased markedly the HDO conversion. The acidic support increased the activity in hydrotreatment through enhancing the hydrogenation activity, while H2S maintained the catalyst in a sufficiently sulfided state.

Interpreter's Corner—Seismic amplitudes from low gas saturation sands

In Tertiary age sediments, P-wave seismic amplitudes are generally regarded as the most robust direct hydrocarbon indicators. Exploration prospects based on a sound geologic model and supported by seismic amplitude anomalies are highly prospective and are usually assigned a high probability of success. However, a fraction of such prospects, perhaps 10–30%, result in dry holes. Postdrill appraisal can usually assign these results to one or more of the following factors: When a dry hole cannot be explained by any of these causes, the seismic amplitude anomaly is often ascribed to low gas saturation in the reservoir. Seismic amplitudes are strong indicators of the presence of gas in a reservoir, but poor indicators of gas saturation. As a result, a reservoir with low gas saturation will have a seismic amplitude response comparable to that of a reservoir with high, commercial level saturation. The problem with this explanation lies in the difficulty in measuring low gas saturation in-situ; any independent measurements to confirm the presence of low gas saturation in the reservoir (implied by seismic amplitude analysis) are rare. This raises the question of whether such low gas saturation sands occur in nature with the appropriate rock properties to yield an anomalous seismic amplitude response. In a study of amplitude-supported prospects in deepwater Gulf of Mexico, Gross and Oliver (AAPG Bulletin , 1998) reported that 67% of these prospects were successful, encountering a net hydrocarbon sand interval of 15 ft or greater. However, 18% failed due to low gas saturation, which they were able to identify based on wireline logs. This paper presents …

Writer's Block—Writing abstracts—A basic approach

I am writing this article in a state of irritation. I am irritated because I just read a GEOPHYSICS manuscript that left me (and fellow reviewers) with the unhappy feeling that the abstract was insufficient and needed to be redone. We gave specific suggestions and guidelines, which included Landes’ useful and often-reprinted article (1951, 1966, 1990 AAPG Bulletin) and my more pedestrian TLE article (1993). I have reread those articles and, frankly, I cannot understand how after reading them, authors continue to miss the point about abstracts. What’s the problem? Abstract writing is not a mystery! Why should you care about abstracts? After all, if an

Stratigraphic architecture and gamma ray logs of deeper ramp carbonates (Upper Jurassic, SW Germany)

The objective of this paper is to contribute to the development of sequence stratigraphic models for extensive epicontinental carbonate systems deposited over cratonic areas. Epicontinental carbonates of the SW German Upper Jurassic were analysed in terms of microfacies, sedimentology and sequence stratigraphy based on 2.5 km of core, 70 borehole gamma ray logs and 24 quarries. Facies analysis revealed six major facies belts across the deeper parts of the carbonate ramp, situated generally below fair-weather wave base, and mostly below average storm wave base but in the reach of occasional storm events. Observed stratigraphic patterns differ in some aspects from widely published sequence stratigraphic models: 1. Elementary sedimentary cycles are mostly more or less symmetrical and are, thus, referred to as “genetic sequences” or “genetic units” [AAAPG Bull. 55 (1971) 1137; Frazier, D.E., 1974. Depositional episodes: their relationship to the Quaternary stratigraphic framework in the northwestern portion of the Gulf Basin. University of Texas, Austin, Bureau of Economic Geology Geologicalo Circular 71-1; AAPG Bull. 73 (1989) 125; Galloway, W.E., Hobday, D.K., 1996. Terrigenous Clastic Depositional Systems. 489 pp., Springer; Cross, T.A., Baker, M.R., Chapin, M.S., Clark, M.S., Gardner, M.H., Hanson, M.S., Lessenger, M.A., Little, L.D., McDonough, K.J., Sonnenfeld, M.D., Valasek, D.W., Williams, M.R., Witter, D.N., 1993. Applications of high-resolution sequence stratigraphy to reservoir analysis. Edition Technip 1993, 11–33; Bull. Cent. Rech. Explor. Prod. Elf-Aquitaine 16 (1992) 357; Homewood, P., Mauriaud, P., Lafont, F., 2000. Best practices in sequence stratigraphy. Elf EP Mem. 25, 81 pp.; Homewood, P., Eberli, G.P., 2000. Genetic stratigraphy on the exploration and production scales. Elf EP Mem. 24, 290 pp.], in contrast to the asymmetrical, shallowing-upward “parasequences” of the EXXON approach. 2. Neither sequence boundaries nor maximum flooding surfaces could be clearly delineated. Cycle boundaries are generally not represented by sharp stratal surfaces but are always transitional and, thus, referred to as “turnarounds” [Nor. Pet. Soc. Spec. Publ. 8 (1998) 171]. Several types of genetic sequences were delineated. Both major types of facies and sequences show characteristic gamma ray log signatures. Based on the cycle stacking and the gamma ray patterns, a hierarchy of sequences was recognized, probably driven in part by 100,000- and 400,000-year Milankovitch signals. The cyclicity allowed regional correlations across various depositional environments such as sponge–microbial bioherms and coeval basins. The basin-wide correlation revealed evidence for a subtle clinoform-type stratigraphic architecture along very gentle slopes, rather than a so far assumed simple “layer cake” pattern.

Introduction to AAPG Bulletin thematic issue on fault seals

Russell Davies is the United States operations manager and consulting structural geologist for Rock Deformation Research, Dallas, Texas. He received a Ph.D. in structural geology from Texas A&M University. He has worked in the oil and gas industry for more than 10 years in exploration and production with Shell and in research on topics including fault interpretation methods, structural styles, and seal analysis with ARCO.Jim Handschy received a Ph.D. in geology and geophysics from Rice University. He has worked in the oil and gas industry for 17 years on exploration, development, research, and technology services projects for Phillips Petroleum, Shell Oil, and El Paso Natural Gas. He has experience in prospect development and evaluation, complex structural interpretation, and trap analysis from around the world. He has served as team leader and project manager for various groups, as chief geologist, and is currently manager of Global Geology for Upstream at ConocoPhillips. This volume of the AAPG Bulletin presents a review of the processes, calibration, and prediction of fault-seal mechanisms and their capacity to support hydrocarbon columns. Geological seals are commonly low-permeability rocks that retard the flow of hydrocarbons. Top seals, for example, are low-permeability strata, such as shales, that overlie hydrocarbon reservoirs and stall the upward migration of hydrocarbons. Fault seals also trap hydrocarbons but by mechanisms that reduce the permeability along a fault. Mechanisms controlling fault seals in unlithified sediments have been identified primarily as (1) shale gouge or smear in the fault zone or (2) juxtaposition of reservoir against nonreservoir lithologies. The low-permeability lithology along the fault surface is the fault rock. Early studies of fault-sealing mechanisms proposed that the smearing of clay-rich layers, such as shale, along a fault plane created a lower permeability fault rock, or seal, between two reservoirs (Smith, 1966, 1980; Weber et …

Effect of evaporation on C7 light hydrocarbon parameters

Light hydrocarbons are commonly used to evaluate crude oils to determine oil families, in-reservoir alteration processes such as evaporative fractionation, water washing, incipient biodegradation, maturity, and temperatures at which oil is expelled from source rocks. Light hydrocarbons in the C7 range will evaporate under ambient conditions, and losses can occur during sample collection, handling, or storage. However, the impact of partial evaporation on interpretation of light hydrocarbon data has not been reported previously. Laboratory evaporation experiments show that the rate of evaporation of each C7 hydrocarbon is different, and these differential rates will affect the measured concentrations of these compounds, certain ratios, and other calculations or plots using these data. The paraffinicity/aromaticity ratio of Thompson [Marine Pet. Geol. 5 (1988) 237], parameters utilized in the transformation and correlation star diagrams of Halpern [AAPG Bull. 79 (1995) 801], and the oil typing ternary plot of Jarvie [The Mountain Geologist 38 (2001) 19] are affected by evaporation. Other interpretive schemes such as P2 versus N2/P3 and the invariant ratio [Science 273 (1987) 514; Geochim. Cosmoschim. Acta 54 (1990) 1315] are not grossly affected by partial evaporation because these parameters are primarily controlled by the concentration of methylhexanes or by offsetting rates of evaporation in certain compounds. By careful evaluation of these parameters and various interpretive plots, the extent of evaporation can be qualitatively assessed and discrimination of oil types, alteration effects, and evaporative artifacts can still be reasonably ascertained. This study demonstrates that preservation of crude oils from evaporation is essential for accurate application of all light hydrocarbon parameters, although some parameters may still be utilized when partial evaporation has occurred.

Introduction to unconventional petroleum systems

Ben Law is a consultant and sole proprietor of Pangea Hydrocarbon Exploration LLC. His research interests include basin-centered gas and coalbed methane systems. Prior to his consulting position, he was a member and chief of the U.S. Geological Survey Western Tight Gas Sand Project and regional coordinator of South Asia for the U.S. Geological Survey World Energy Project. He received B.S. and M.S. degrees from San Diego State University, California.John B. Curtis is associate professor and director, Petroleum Exploration and Production Center/Potential Gas Agency at the Colorado School of Mines. He is an associate editor for the AAPG Bulletin and The Mountain Geologist. As director of the Potential Gas Agency, he works with a team of 145 geologists, geophysicists, and petroleum engineers in their biennial assessment of remaining United States natural gas resources. The collection of articles included in this theme issue of the AAPG Bulletin originated in the AAPG …

James Limestone, northeastern Gulf of Mexico: Refound opportunity in a Lower Cretaceous trend

Recent offshore exploratory success has focused industry interest on porous Lower Cretaceous carbonates of the James Limestone in the eastern Gulf of Mexico. The current offshore play targets the interior James platform trend in the Viosca Knoll and Mobile areas, south of Mississippi and Alabama, where water depths are 30-60 m (98-197 ft). James reservoirs in this area consist mainly of patch reef debris halos and interior platform grainstone facies at drilling depths of 4358-4632 m (14,300-15,200 ft). These facies comprise a belt parallel to, but up to 25 km (15.5 mi) behind (updip from), the James shelf margin. Diagenetic alteration, including dolomitization and dissolution of original calcite grains and cement, cause porosities of 8-19% and permeabilities in the range of 20-30 md. To date, seven fields have been discovered. Individual wells in these fields have been completed at rates ranging from 10-39 MMCFGD and have produced as much as 15.9 bcf in less than 3 yr. The new play represents an extension into the offshore of scattered, older production in the James that occurs from east Texas to southern Mississippi. When combined with the onshore part of the play, the new success in the James suggests that significant regional potential still exists in many areas of the northern and northeastern Gulf. Scott L. Montgomery is a petroleum consultant and author. He received his B.A. degree in English from Knox College in 1973 and his M.S. degree in geological sciences from Cornell University in 1978. He is widely published in the geosciences and since 1996 has been principal author of the E & P Notes series in the AAPG Bulletin. His other publications include seven books on topics in petroleum geology, science education, and the history of science, plus articles and monographs related to frontier plays, new technologies, field studies, and reservoir characterization.Andrew J. Petty is currently a geologist with the Minerals Management Service (MMS) in New Orleans, Louisiana. He joined the MMS in 1979, where he worked in the Rate Control Section, served as the Corpus Christi District Geologist, and is now with the Regional Analysis Unit. Andy received his B.S. degree in geology from Stephen F. Austin State University in 1973 and his M.S. degree in geology from the University of Texas at El Paso in 1975. Paul J. Post is a geologist with the Minerals Management Service (MMS) in New Orleans, Louisiana. He has more than 30 years of diverse exploration experience in an array of United States and international basins with major and independent companies, as a consultant, and with MMS. His primary technical expertise is in regional synthesis, new venture/play development and prospect evaluation, basin analysis, basin modeling, economic analysis, and risk assessment. Paul has a B.S. degree in geology from Virginia Polytechnic Institute.

The influence of organic matter on the boron isotope geochemistry of the gulf coast sedimentary basin, USA

Large variations in the boron isotopic composition of sedimentary environments make boron an attractive monitor of fluid/rock interactions during diagenesis. Studies of B in marine sediments have shown that preferential adsorption of 10B on clay minerals leaves pore waters enriched in 11B. During diagenesis, clay minerals recrystallize and incorporate 10B into the mineral structure (Spivack, A.J., Palmer, M.R., Edmond, J.M., 1987. The sedimentary cycle of the boron isotopes. Geochim. Cosmochim. Acta 51, 1939–1949). This process should cause a depletion of B in the pore water with an increase in the δ 11B. In the Gulf Coast sedimentary basin (USA), however, there is a general increase in B-content of formation waters (Land, L.S., Macpherson, G.L., 1992. Origin of saline formation waters. Cenozoic Section, Gulf of Mexico Sedimentary Basin. Geochim. Cosmochim. Acta 76, 1344–1362; Moldovanyi, E.P., Walter, L.M., 1992. Regional trends in water chemistry, Smackover Formation, Southwest Arkansas: Geochemical and physical controls. AAPG Bull. 76, 864–894.) and a decrease in δ 11B with depth. This suggests that another source of 10B exists in deep basinal environments. We know that oil reservoir brines are commonly enriched in boron (Collins, A.G., 1975. Geochemistry of Oilfield Waters. Elsevier, New York, p. 496.), therefore this study examines organic matter as a possible source of boron during thermal maturation. Samples of water, oil, and cored sediments were collected from three stacked hydrocarbon reservoirs in the Gulf of Mexico sedimentary basin at a depth of 3500–4350 m. Extraction of boron from organic matter (oil and kerogen) was done by Parr Bomb volatilization, with mannitol used as a B-complexing agent. The isotope ratios were measured using negative thermal ionization and compared to in situ analyses using secondary ion mass spectrometry. The δ 11B values of pore filling clays in sandstone reservoirs is −2±2‰. The B-content of the clay averages 144 ppm. Oil field waters show a range in B-content from 8–85 ppm and δ 11B values from +28 to +37‰, increasing from the lowest to the uppermost reservoir. There is an apparent 11B-enrichment of fluids with progressive migration through clay-rich sediments. Very little B (ppb) was found in the oil, but kerogen extracted from the oil source rock (Sassen, R., 1990. Lower Tertiary and Upper Cretaceous source rocks in Lousiana and Mississippi: implications to Gulf of Mexico crude oil. AAPG Bull. 74, 857–878.) contains significant B (140 ppm) with a δ 11B of −2±2‰, similar to the pore filling clay minerals in the sandstones. While kerogen comprises only ∼2% of the sedimentary basin, its influence can be significant if B with distinctly low δ 11B is released over a specific temperature interval during thermal maturation. The release of B from organic compounds could cause the observed regional 10B enrichment in waters deep in the Gulf Coast basin.

The Oil and Gas Habitats of the South Atlantic. N. R. Cameron, R. Bate, V. Clure & D. Smith (eds) . Geological Society, London, Special Publication 153. ISBN 1-86239-030-4 (HB), 1999, 474 pp. US$148/£89. Geological Society members US$65/£39.

A quick review of my stockpile of journals revealed how poorly documented the petroleum geology of this region of the world is: I found, for instance, five African papers in ten years’ copies of the AAPG Bulletin . The editors of this book are, therefore, to be complimented on the efforts they have made to fill this yawning gap in the documentation of the world’s petroleum reserves. The editors set themselves two objectives, first to overview the petroleum geology of the region and second to demonstrate the contribution that universities and service companies can make to background work supporting South Atlantic exploration. In the case of the first objective, they have struggled – chiefly because of the well known reciprocal relationship that exists between prospectivity and willingness to publish. The contents page of the volume will prove disappointing to some as a result: there are no papers on Nigeria or Gabon, one on Angola and two on Brazil, whereas Namibia and the Falklands attract eight papers between them. And, unfortunately, we do not see a cross-section or seismic line across an oil field anywhere in the volume. These failings arise …

An Introduction to this Special Section: Immersive Visualization

As humans we have several orders of magnitude more input bandwidth through our eyes than through any of our other senses. When linked to modern computer technology, this innate visual bandwidth proves an underutilized resource. Visualization is especially worthwhile when we wish to increase the quantity, and, because of the pattern-recognition capabilities of our brain, the quality of information entering our mind. In a much-referenced article in the 1952 AAPG Bulletin (“Towards a philosophy of oil finding”), Wallace Pratt recognized and was the first to state that it is in our minds where hydrocarbons are first found. This special section continues the process of showing how we can extend our minds with technology.

Isotopic fingerprints of shallow gases in the Western Canadian sedimentary basin: tools for remediation of leaking heavy oil wells

Thousands of wells have been drilled in northeastern Alberta and adjacent Saskatchewan in order to develop the heavy oil reservoirs of the Lower Cretaceous Mannville Group. In a large number of these wells, vertical migration of gas from unknown sources to the surface via well casings and surrounding soils represents a serious environmental problem. Mud samples from new wells drilled in the area were collected at approximately 50 m intervals from the surface to the completion depth, and the gases contained within the muds (‘mud-gases’) were analyzed for 13C/ 12C composition. Gases from the various Mannville Group sands do not show unique isotopic signatures; they comprise bacterial methane ( δ 13C C1=−70‰ to −60‰ (PDB)), with trace C 2+ components that are residues from biodegradation processes. Gases from each of the overlying Upper Cretaceous Colorado Group shale units are, however, isotopically distinct. The δ 13C of methanes in the shales have values equivalent to those within the Mannville sands, but the δ 13C of the C 2+ components are unambiguously different. C 2+ gases from the shallower Colorado shales are incipient thermal gases and fit the isotopic maturity diagram of James, A.T., 1983. AAPG Bull. 67, 1176–1191, and also of Chung, H.M., Gormly, J.R., Squires, R.M. 1988. Chem Geol. 71, 97–103. We believe these gases may include the most immature suite of thermogenic gases reported ( δ 13C C2=−63‰ to −32‰, δ 13C C3=−42‰ to −22‰, δ 13C nC4=−37‰ to −23‰). Carbon isotope fingerprints from mud-gases are used to identify specific source depths of migrated gases. Comparisons between the isotopic characteristics of the shallow gases and the migrated gases collected near surface infer that most of the migrated gases are actually generated in the Colorado Group shales, and not the Mannville sands in which the wells were completed. The ability to estimate the source depth of the migrated gases greatly aids remediation of ‘leaking’ wells within the Western Canadian Sedimentary Basin (WCSB).

Sequence Stratigraphy and Composition of Late Quaternary Shelf-Margin Deltas, Northern Gulf of Mexico

High-resolution seismic profiles and foundation borings from the northwestern Gulf of Mexico record the physical attributes and depositional histories of several late Quaternary sequences that were deposited by wave-modified, river-dominated shelf margin deltas during successive periods of lowered sea level. Each progressively younger deltaic sequence is thinner and exhibits a systematic decrease in the abundance and concentration of sand, which is attributed to a shift in the axis of trunk streams and greater structural influence through time. Our study shows that (1) contemporaneous structural deformation controlled the thickness of each sequence, the oblique directions of delta progradation, the axes of major fluvial channels, and the geometries of delta lobes at the shelf margin, (2) sedimentation was rapid in response to rapid eustatic fluctuations and structural influence, (3) boundaries of these high-frequency sequences are the correlative conformities of updip fluvial incision, and coincide with downlap surfaces at the shelf margin, (4) the downlap surfaces are not true surfaces, but zones of parallel reflections that become progressively higher and younger in the direction of progradation, (5) the downlap zones are composed of marine muds that do not contain high concentrations of shell debris that would be expected in condensed sections, (6) possible paleosols capping the two oldest sequences are regressive surfaces of subaerial exposure that were preserved during transgressions, and (7) no incised valleys or submarine canyons breach the paleoshelf margin, even though incised drainages were present updip and sea-level curves indicate several periods of rapid fall. (Published in American Association of Petroleum Geologists Bulletin 80: 505 530.) R. A. Morton and J. R. Suter AAPG Bulletin, Vol. 80, No. 4, AAPG 1996, reprinted by permission of the American Association of Petroleum Geologists whose permission is required for future use.

Isotopic biogeochemistry of the Neocomian lacustrine and Upper Aptian marine-evaporitic sediments of the Potiguar Basin, Northeastern Brazil

Systematic variations in the abundances of 13C in kerogens and in saturated hydrocarbons were used to assess the paleoenvironments of the Neocomian lacustrine and Aptian lagoonal to restricted marine-evaporitic sediments of the Pendência and Alagamar Formations, respectively, from the Potiguar Basin, Brazil. In the Pendência Formation, the isotopic compositions of compounds formed in the photic zone, i.e., pristane, β-carotane, and some of the n-alkanes, vary only slightly with depth, suggesting invariable conditions in the surface environment. However, dramatic changes occur in the carbon-isotopic compositions of hopanoid biomarkers produced by organisms inhabiting the lower part of the water column of the Pendência paleolake. Parts of the section having finely laminated sediments with no burrowing coincide with the most significant 13C depletion of the hopanoids relative to algal products, indicating effective stratification of the water column and active recycling of methane. In the Alagamar Formation, isotopic compositions of the n-alkanes vary systematically with depth but not with carbon number, indicating dominance of a single source for all n-alkanes, independent of carbon number, and secular variations in the isotopic composition of that source. The latter variations can be correlated with global changes in the isotopic composition of marine dissolved inorganic carbon associated with the oceanic anoxic event that occurred in the Upper Aptian (OAE-1, [Arthur, M. A. and Schlanger, S. O. (1979) AAPG Bull. 63, 870–885]). The 17 α(H),21 β(H)-C 30 hopane is the most depleted in 13C among the compounds and reflects contributions from chemoautotrophs, and in extreme cases from methanotrophs. The covariations between the δ 13C values of pristane and phytane, and these acyclic isoprenoids and β-carotane suggest a common origin from phytoplankton. Gammacerane has δ 13C values compatible with a derivation from bacterivorous ciliates feeding on algae and cyanobacteria growing under variable paleoenvironmental conditions.

About this title

The role and importance of structural geology in exploration and production of hydrocarbons is increasing with the tendency towards the development of smaller, more complex structural prospects and satellite fields. The availability of high-powered computer hardware and sophisticated software has facilitated a quantum leap in the accessibility of structural restoration, modelling and visualization techniques and made the rapid and accurate manipulation of large data sets possible. Many papers in this volume fully reflect use of this latest technology and demonstrate a broad range of capabilities. The book provides anyone wishing to undertake structural interpretation in complex areas with a comprehensive review of the latest techniques available. ... I certainly learned a great deal reading through it. Structural geologists working in or with industry will want a copy for their bookshelves. Basin Research, 9, 88-89. The volume is an excellent mixture of review and research papers that underscore the importance of multidisciplinary approaches to improve interpretations of complex structures. There is a good trade off between academic research and industrial applications, and I recommend this book as a library reference. AAPG Bulletin November 1997. ... I am certain that this Special Publication will be regarded as a valuable source of techniques for structural interpretation and validation of fault geometries. I can certainly recommend this volume as an essential, and indeed, a worthwhile purchase, for academic and industry structural geologists alike. Geological Magazine.

Pickens Field--A New Look at an Old Field: ERRATUM

A abstract entitled Field--A New Look at an Old Field, by William M. Frew, appearing in the September 1992 AAPG Bulletin (v. 76, no. 9, p. 1457-1458) was printed missing some words. The first sentence of the last paragraph of the abstract should have read as follows. A migrated CDP seismic line shot across Pickens field and the Pickens graben fault system in 1982 displays a structural complexity not evident from subsurface mapping. End_of_Article - Last_Page 135------------

Lithodemes, suites, supersuites, and complexes: intrusive, metamorphic, and genetically mixed assemblages of rocks now embraced by North American Code of Stratigraphic Nomenclature

Geologists engaged in the study and mapping of intrusive, highly deformed, and/or highly metamorphosed and genetically mixed assemblages of rock will find that a useful and logical classification for such rocks is now a part of the North American Stratigraphic Code (North American Commission of Stratigraphic Nomenclature (NACSN), 1983 ). The present note is intended to achieve broader professional readership for this part of the Code than was achieved by the original publication (AAPG Bulletin), and is an official statement from NACSN. In its most recent form, the Code is greatly modified from the preceding version (American Commission of Stratigraphic Nomenclature, 1970), and now embraces the above-mentioned kinds of rocks, which have not been regarded traditionally as stratigraphic units. Collectively, these rock bodies are called lithodemic, rather than lithostratigraphic, units. Such rock units generally lack primary stratification and usually do not conform to the Law of Superposition, but each is defined on objective lithologic characteristics, and is a mappable entity.