Abstract Drilling for coalbed gas in the Upper Cretaceous Ferron Sandstone of central Utah during the 1990s has resulted in one of the most successful plays of this kind. Development through the year 2003 has resulted in three fields, as well as a potential fairway 6-10 mi (10-16 km) wide and 20-60 mi (32-96 km) long, corresponding to shallow coal occurrence at depths from 1100-3500 ft (330–1060 m) in the Ferron, a sequence of interbedded fluvial-deltaic sandstone, shale, and coal in the lower part of the Cretaceous Mancos Shale. The major reservoirs in this interval consist of thin to moderately thick (3-30 ft [1-10 m]) coalbeds of relatively low rank (high-volatile B bituminous) and variable gas content, ranging from 100 scf/ton (3.0 cm 3 /g) or less in the south to as high as 500 scf/ton (15.6 cm 3 /g) in the north. Other lithologies also contain gas and contribute a minor portion of the produced gas. Productive wells have averaged over 500 mcf/day and, after several years of production, continue to typically show increases in gas production. In the major productive area, Drunkards Wash unit, the first 33 producers averaged 974 mcf and 85 bbl of water per day after five years of continuous production. Estimated ultimate recoverable reserves for individual wells in this unit average about 1.9 bcf, with one standard deviation about that mean of ±1.5 bcf. Based on several criteria, including gas content, thermal maturity, and chronostratigraphy, the play is divided into northern and southern parts. The northern part is characterized by coals that have the following characteristics: (1) high gas contents; (2) moderate thermal maturity (e.g. vitrinite reflectance [R o ] values of 0.6-0.8%); (3) good permeabilities (4-20 md); (4) lack of exposure; and (5) overpressuring, due to artesian conditions. Southern coals have much lower gas contents (<100 scf/ton [3.0 cm 3 /g]), lower thermal maturity (R o = 0.4-0.6%), and they are partially exposed along an extensive, 35-mi (56-km) outcrop belt that may have allowed a degree of gas flushing. These coals, however, are slightly thicker and more extensive than those to the north and thus may retain some potential. Northern coals appear to contain a mixture of gas from three sources: in-situ thermogenic methane, migrated thermogenic methane from more mature sources, and late-stage biogenic gas. Current development is focused on the northern portion of the stated fairway, where well control and an existing infrastructure are present. Indications are that coalbed methane development in the Ferron will increase by at least one hundred in the near future from the 754 wells producing as of the end of 2003.

Abstract A transect of three holes drilled across the Blake Nose, western North Atlantic Ocean, retrieved cores of black shale facies related to the Albian Oceanic Anoxic Events (OAE) 1b and 1d. Sedimentary organic matter (SOM) recovered from Ocean Drilling Program Hole 1049A from the eastern end of the transect showed that before black shale facies deposition organic matter preservation was a Type III–IV SOM. Petrography reveals that this SOM is composed mostly of degraded algal debris, amorphous SOM and a minor component of Type III–IV terrestrial SOM, mostly detroinertinite. When black shale facies deposition commenced, the geochemical character of the SOM changed from a relatively oxygen-rich Type III–IV to relatively hydrogen-rich Type II. Petrography, biomarker and organic carbon isotopic data indicate marine and terrestrial SOM sources that do not appear to change during the transition from light-grey calcareous ooze to the black shale facies. Black shale subfacies layers alternate from laminated to homogeneous. Some of the laminated and the poorly laminated to homogeneous layers are organic carbon and hydrogen rich as well, suggesting that at least two SOM depositional processes are influencing the black shale facies. The laminated beds reflect deposition in a low sedimentation rate (6m Ma −1 ) environment with SOM derived mostly from gravity settling from the overlying water into sometimes dysoxic bottom water. The source of this high hydrogen content SOM is problematic because before black shale deposition, the marine SOM supplied to the site is geochemically a Type III–IV. A clue to the source of the H-rich SOM may be the interlayering of relatively homogeneous ooze layers that have a widely variable SOM content and quality. These relatively thick, sometimes subtly graded, sediment layers are thought to be deposited from a Type II SOM-enriched sediment suspension generated by turbidites or direct turbidite deposition.

Abstract This two-day excursion will travel to the Yampa coal field located in parts of Moffat, Rio Blanco, and Routt Counties, northwestern Colorado. The excursion will visit classic regression/transgression successions in the Upper Cretaceous coal-bearing Mesaverde Group, which was deposited along the western edge of the Cretaceous seaway. It includes visits to inactive and active mine sites where past and current mining practices will be discussed. This guide summarizes the stratigraphy, sedimentology, and coal geology of the Yampa coal field. The trip will emphasize the depositional setting, sedimentology, and quality of the Upper Cretaceous coals and coal-bearing strata of the Mesaverde Group.

Abstract The papers presented in this volume make it clear that luminescence microscopy and spectroscopy are being employed in an ever wider array of geological studies. The editors suggest several ways that luminescence studies can be employed or improved: (1) to assist in the integration of trace element, isotope, fluid inclusion and mineral studies using CL results to assure that the same zones and (or) mineral compositions are utilized; (2) more reliable tracing of zones whether microscopic or of regional extent; (3) better interpretation of diagenetic, mineralization and alteration events because of the control and discrimination of crosscutting relationships and subtle changes in chemistry that often become obvious using luminescence; (4) as a tool for direct detection of rare earth element deposits, Mississippi Valley type Pb-Zn ores and in some cases oil reservoirs; (5) introduction of standard materials and methods for calibrating spectrometers and possibly increasing the uniformity of subjective observations; (6) improvements in instrumentation to diminish thermal quenching effects at the same time gains are necessary in the level of activation of luminescence and in the quality of the microscopic image transmitted to the observer; (7) more efforts at experimental determination of the causes of luminescence and their interpretation relative to conditions that exist in natural systems.

Abstract Fluorescence and phosphorescence, for prompt and kinetically delayed emission of light, respectively, are photoluminescence processes. Photoluminescence is the subset of luminescence processes due to excitation by photons rather than electrons (cathodoluminescence) or thermal energy (thermoluminescence, see Walker and Burley, this volume). In geologic applications, fluorescence carries strong historical connotations of ultraviolet excitation at either the long wavelength line at 366 nm (longwave UV) or the short wavelength line at 254 nm (shortwave UV) of amercury arc lamp. Mercury arc lamps are important sources for fluorescence excitation, especially in fluorescence microscopy, but photoluminescence excitation can occur at wavelengths throughout the optical spectrum from deep in the UV (< 200 nm) to the infrared (> 3000nm) depending only on the energy of the electronic transitions within the material under study. The goal of this chapter is to review practical aspects of the application of fluorescence microscopy to the study of petroleum fluid inclusions and minerals. The discussion will emphasize those aspects of fluorescence microscopy that can cause artifacts in the color and intensity of fluorescence emission and, more importantly, cause non-fluorescent inclusions to appear to be fluorescent. Thorough understanding of the technical limitations of fluorescence microscopes is critical to the proper interpretation of fluorescence observations. We know that differences in fluorescence color of petroleum fluid inclusions must indicate differences in composition (Burruss, 1981), but the geochemical significance of these color differences is difficult to ascertain. Several authors have related differences in visual color to relative differences in density or API gravity (Burruss, et al. 1983, 1985; Barker and Halley, 1986; McLimans, 1987) and Tsui (1990) used spectrophotometric measurements of color to make semi-quantitative estimates of API gravity. Gas chromatographic analysis of petroleum fluid inclusions of relatively uniform fluorescence color, within a single petroleum basin shows that chemical composition can vary widely without significantly affecting the fluorescence color (Jensenius and Burruss, 1990). Interpretation of mineral fluorescence must be based on understanding the limitations of the fluorescence microscope, especially when comparing fluorescence observations to cathodoluminescence observations.

Abstract: Luminescence in calcite and dolomite is governed by physical phenomena that are common to all oxygen-dominated crystalline substances, including other carbonates and silicates. Absorption of excitation energy, energy transfer, and emission involve predictable transitions between electronic energy levels. Strong emission in various colors is always caused by impurities which function as activators of luminescence. Visible luminescence is not expected from pure, undistorted insulators, including carbonates. However, a faint blue ‘intrinsic’ luminescence, with a broad emission peak (band) around 400 nm, presumably caused by lattice defects, occurs in pure calcite and dolomite, and even in some samples containing impurities. The most important activators in carbonates are transition elements and rare earth elements. Luminescence spectra can be used for activator identification. These spectra are largely independent of the type of excitation, e.g., electron beam (cathodoluminescence = CL), photon (photoluminescence = PL), X-Ray (radioluminescence = RL) excitation, and others. Emission intensities depend on activator, sensitizer, and quencher concentrations, and on the method of excitation. At a given activator concentration, the luminescence intensity generally increases with an increase in excitation energy from PL (relatively weak) to CL (strong). Changes in visual luminescence color between different excitation methods are caused by relative changes in emission peak heights. Mn 2+ appears to be the most abundant and important activator in natural calcite and dolomite. Substituting for calcium in both minerals, its emission is orange-red to orange-yellow, with a fairly broad band between 570-640 nm (maximum between 590-620 nm). The emission band maximum of Mn 2+ substituting for Mg 2+ (in dolomite) is located around 640-680 nm. As little as 10-20 ppm Mn 2+ in solid solution are sufficient to produce visually detectable luminescence, if total Fe contents are below about 150 ppm. Sm 3+ activated luminescence can be visually indistinguishable from that activated by Mn 2+ . The spectrum of Sm 3+ emission, however, is quite distinct from that of Mn 2+ and consists of three narrow bands at 562 nm, 604 nm, and 652 nm. Tb 3+ and Dy 3+ activate green and cream-white luminescence, respectively. The main emission of Tb 3+ is at 546 nm. The emission of Dy 3+ consists of three bands, located at 484 nm, 578 nm, and 670 nm. Emission from Eu-containing calcite is red or blue. Narrow spectral bands of 590 nm, 614 nm, and 656 nm are caused by Eu 3+ and correspond to the red emission. A broad emission spanning a large range of shorter wavelengths is caused by Eu 2+ and corresponds to the blue emission. As in the case of Sm 3+ -activated luminescence, the red Eu 3+ luminescence can be mistaken visually for Mn 2+ -activated luminescence. Visual luminescence detection limits for rare earths are on the order of 10 ppm. Pb 2+ is an activator, with an emission band around 480 nm, but it also is a sensitizer of Mn 2+ -activated luminescence in carbonates. Another recognized sensitizer for Mn 2+ in carbonates is Ce 3+ . Sensitizers appear to be effective at concentrations as low as 10 ppm in calcite. Quenchers of Mn 2+ -activated luminescence in carbonates are Fe 2+ , Co 2+ , Ni 2+ , and Fe 3+ . The concentrations at which quenchers appear to be effective may vary from element to element and with host mineralogy. Effective minimum concentrations as low as 30-35 ppm have been reported for calcite. The interplay of Mn 2+ and Fe 2+ , commonly regarded to be the most important activator and quencher, respectively, in determining the luminescence characteristics of natural carbonates is not well understood because the available data are partially inconsistent. The Mn/Fe ratio may exert a control on luminescence intensity. Mn and Fe concentrations at which ‘bright’ CL changes to ‘dull’ can be determined only semi-quantitatively. The available data on the concentration of Mn 2+ at which quenching starts are partially inconsistent. Consequently, the Mn 2+ concentration at which concentration extinction occurs has not been determined unequivocally. The data presented and summarized in this paper can be used as a basis for the interpretation of luminescence of geological materials. In particular, knowledge of the possibilities and complexities of activation, sensitization, and quenching has great potential for the interpretation of diagenetic carbonate cements.

Abstract: The use of characteristic X-ray emission for analysis of mineral specimens began with the development of the electron probe in the early 1960's. Cathodoluminescence (CL) observations were a by-product of this work and soon became a very important independent area of study, leading to the development of simpler, microscope-mounted, electron beam sources using a cold cathode as the source of the electrons. The type of electron gun used in these cathodoluminescence microscope attachments (CMA), based on a cold cathode discharge, is simple and rugged. It also provides a neutralizing environment so conductively coated samples are not necessary, facilitating sample preparation. X-rays are produced during the electron bombardment that produces cathodoluminescence. The attachment of an X-ray detector to the CMA provides a versatile facility for combining CL and transmitted light observations with the capability for performing a rapid elemental analysis. The cathodoluminescence microscope attachments have a large beam current and large spot diameter, compared to these same quantities in the electron microprobe or the scanning electron microscope. This difference can be used to advantage in obtaining rapid analyses (because of high count rates) and in making average analyses of fine-grained samples. Examples are presented to illustrate the distinction between K-feldspar and Ca, Na-containing feldspars. In fine-grained limestones one can find evidence of contaminants such as Si, K, Al, and Cl, possibly from fine-grained silica and clay minerals. Peat samples can be easily prepared for examination because a conductive coating is not required with the cold cathode electron source. Another novel method of sampling is the analysis of streaks of samples.

Abstract: At least twenty six factors govern the cathodoluminescence (CL) color, intensity, and zonation of diagenetic carbonates, i.e., (1) potential activators, sensitizers, and quenchers; (2) distribution coefficients and activity (concentration) ratios, determined by (2a) activity coefficients, (2b) activity of calcium, (2c) growth rates, (2d) temperature, (2e) crystal surface structure, (2f) various chemical species in solution, (2g) bulk solution disequilibrium partitioning; (3) types of zonation, i.e., (3a) concentric zoning, (3b) sector(al) zoning; (4) concentrations of activators, sensitizers, and quenchers in diagenetic fluids, i.e., (4a) changes in redox-potential [(i) phases controlling Mn 2+ and Fe 2+ concentrations, (ii) chemical equilibrium, kinetics, and microbes, (iii) interdependent redox-reactions, (iv) electrochemical equilibrium, (v) interdependent partitioning], (4b) closed system diagenesis, (4c) organic matter and clay mineral diagenesis, (4d) exotic fluid sources; (5) temporal and spatial variations in solution chemistry, i.e., (5a) saturation states, (5b) Eh, Mn 2+ and Fe 2+ concentration variations, (5c) rates of change of fluid parameters; (6) integration of the above factors. Some of the above factors are considered in conventional CL work. However, many previously unconsidered factors also can have significant effects on CL. For example, at invariant pH/Eh, CL zonation in diagenetic carbonates can be generated solely from changes in Ca 2+ activity, precipitation rate, or temperature. CL zonation may also result from changes in salinity or pH/Eh. On the other hand, determining pH and Eh at the time of precipitation from observed CL and corresponding Mn 2+ and Fe 2+ concentrations, which has been common practice, is impossible with the present state of knowledge. Furthermore, data from modern groundwater aquifers indicate that it is unlikely that diagenetically coeval calcite cements form over more than a few km to a few tens of km of flow distance, let alone several tens to hundreds of km, except under very uncommon circumstances. Interpretations using CL, particularly those applying pH/Eh diagrams and cement stratigraphy, are likely to be incorrect unless they consider as many of the above factors as possible. Studies published over the last 20 years applying CL to carbonate diagenesis should be reinterpreted. This requires consideration of the above factors and a synergistic approach integrating CL with isotope studies, fluid inclusion data, and other analytical methods.

Abstract: Cathodoluminescence (CL) petrography provides a unique capability for documenting physical and chemical diagenetic processes in sandstones, particularly those cemented by quartz. Mostdetrital quartz grains display relatively intense CL owing to lattice defects and trace cation inclusions inherited from crystalline source rocks. In contrast, most authigenic quartz contains fewer lattice defects and trace cations, and therefore displays less intense CL. Detrital grains, cement, and porosity can be objectively identified and measured using CL petrography. These measurements allow quantitative evaluation of total compaction, which is inferred by calculating intergranular volume (intergranular cement plus intergranular porosity), and cementation. An estimate of chemical compaction can also be made by subjectively reconstructing original grain boundaries at intergranular pressure solution contacts and measuring overlap quartz. These quantitative estimates can be used to interpret silica budgets, to evaluate porosity, and to assess the relative importance of various diagenetic events to porosity reduction. CL petrography also permits valuable qualitative observations that can rarely be made using only transmitted light techniques. Brittle grain fracture and plastic deformation of ductile lithic fragments, both indicative of mechanical compaction, can commonly be documented in CL. Cement zonation, particularly in quartz overgrowths, can provide the key to unraveling complex paragenetic relationships.

Abstract: CL color in silicates is apparently related to several causes, including crystallographic dislocations, defects, and trace element concentration. To the extent that these factors are dictated by source rock lithology and environment of crystallization, CL of silicates is a function of provenance. Several investigators have used quartz CL, either in varietal or population-based studies, to infer provenance of sandstones. Although feldspar CL is very sensitive to trace elemental composition, little use has been made of it in provenance study. Three critical assumptions must be made before CL can provide legitimate provenance information: (1) CL coloris characteristic of the grain and does not change with time or exposure to the sedimentary environment; (2) CL color is invisible to sedimentary processes such that grains are not segregated appreciably based on their CL color, (3) stratigraphic units under consideration are sufficiently well mixed so that CL color distributions are sensibly uniform over a broad area. Each assumption, while reasonable, is subject to verification by empirical observation and must be more thoroughly tested before CL will be a reliable indicator of provenance.

Abstract: Compositional zoning patterns in carbonate minerals consist of two major types that are distinguished by the relative spatial arrangements of growth surfaces and composition interfaces. Concentric zoning exists where the composition interface coincides with an existing or prior crystal growth surface, and it provides a temporal record of crystal morphology. Concentric zoning generally results from changing fluid properties, although determination of the exact causes is commonly problematic. Some examples of concentric zoning, such as oscillatory zoning, do not necessarily result from changes in bulk fluid properties, but rather are inherent to the growth mechanism. Sector-related zoning exists where the composition interface does not coincide with the growth surface. This results from spatial differences in element partitioning on the growing surface associated with differences in detailed surface structure. Sectoral zoning and intrasectoral zoning are two types distinguished according to whether the composition interface coincides with a growth sector boundary or exists within a growth sector. Sector-related zoning patterns are evidence for non-equilibrium partitioning of trace elements. The interplay of concentric and sector-related zoning produces complex zoning patterns in cathodoluminescence, and their study can provide new insight to understanding crystal growth and trace element partitioning behavior in carbonates.

Abstract: Cathodoluminescence (CL) petrography is now a routine technique that can provide essential information on provenance, growth fabrics, diagenetic textures and mineral zonation, in addition to enabling more precise quantification of constituents and fabrics. Without the support of CL spectroscopy, however, CL petrography can only remain a fabric analysis technique. Although subtle variations in CL colour recorded on film give important information, describing luminescence intensity and colour from a photographic record is a dubious and subjective affair. The actual CL colour is determined by the number and type of emission and quenching centres present. Superposition of several luminescence bands of different intensities can combine to produce an apparent ‘colour’, shade or hue. The combination of emission spectroscopy, excitation spectroscopy and pulsed beam technique provide quantitative data on the wavelength and intensity of luminescence and the nature of the luminescing centres. CL spectroscopy should become a standard technique used by the luminescence petrographer because it is the only means of recording CL colours and emission intensity objectively and quantitatively, in addition to providing unique information on the nature of luminescence centres.

Abstract: Luminescence microscopy is used to identify stages of cementation in petroleum reservoirs and classify the physical and chemical properties of oils and oil inclusions. The lifetime of fluorescence induced by a pulsed laser is related to the API gravity of oil and can be used to determine API gravity on microliter samples of oil or oil in inclusions. Luminescence microscopy data are combined with geological (burial history, stratigraphy, tectonics, environment of deposition) and geochemical (fluid inclusion P-T-X values, stable isotopes, trace elements, petroleum geochemistry) data to determine the timing of geological events and constrain models of diagenesis, oil migration, and reservoir prediction. This method is applied to studies of reservoir diagenesis and petroleum maturation, migration, and correlation for the Mishrif Formation, Dubai, the Kais Formation, Indonesia, the Ellenburger Dolomite, Texas, and the Great Oolite Limestone, England. In the Great Oolite Limestone, cathodoluminescence of cements shows that occurrence of zoned cements correlates with high reservoir porosity consistent with a model of porosity perservation resulting from diagenesis in a mixing zone between freshwater and marine phreatic environments. Photoluminescence of oil inclusions in cements of the Great Oolite shows that inclusions are more mature near the basin depocenter. In the Ellenburger Dolomite, Texas, several episodes of fracture development and sealing are shown by cathodoluminescence enabling a relative timing to be determined. Temperature and composition data from fluid inclusions are collected with respect to the cathodoluminescence and used to quantify the environment of cementation.

Abstract: Organic petrography is the study of the optical properties of the solid organic constituents (termed macerals) in sedimentary rocks whether the rocks be organic-rich coals, oil shales, petroleum source-rocks or shales, sandstones and limestones with trace dispersed organic matter (DOM). In traditional methods for studying macerals, transmuted light microscopy is used to study thin sections and strew mounts and incident white light is used to examine polished blocks. A more successful technique is to combine reflected white light microscopy and fluorescence mode microscopy. Strongly fluorescing macerals are derived from hydrogen-rich organic matter deposited with or without clastic material or from the alteration of othermacerals during diagenesis and/or metamorphism. Macerals can be described in terms of morphological and optical properties. The abundance and type of organic matter, that is, type and abundance of macerals, can be the basis for an organic classification of rocks. One such classification gives a primary grouping of humic coal, oil shale, and bitumen-impregnated rock. Oil shale can be further subdivided into six types - cannel coal, torbanite, lamosite, marinite, tasmanite and kuckersite.

Abstract: Luminescence microscopy makes it possible to recognize unique microstratigraphic patterns in gangue minerals deposited with ore. Such patterns can be traced over hundreds of kilometers within and between mineralized districts. The ability to recognize, sample, and analyze equivalent zones is essential if trace element, isotope, and other analytical studies are to yield useful information. Examples from several mineralized districts in Tennessee (including the Mascot-Jefferson City, Copper Ridge, and Central Tennessee districts) are employed to illustrate the use of luminescence microscopy to trace zoned carbonate gangue and to distinguish diagenetic and epigenetic events. Care must be taken to distinguish those features developed during early diagenesis from those which are clearly epigenetic in origin. Two end-member models that might explain the luminescent patterns that can be traced over thousands of square kilometers are proposed; however, neither model is totally realistic. Many questions concerning how these patterns can be developed remain unanswered.

Abstract: Correlation of compositional zones of cement is one of the basic building blocks of cement stratigraphy. Compositional zones are correlated by describing the most complete and representative sequence of cement zones, and by matching unique aspects of that zonal sequence to pores in the same sample and nearby samples in the stratigraphic sequence. "Lumping" packages of zonal sequences may aid correlation if a one-to-one correlation is lacking, but for some sequences, no correlation can be established because of the spatial and temporal variation in diagenetic history. Zonal correlations may be diachronous or nearly time synchronous. Establishing the time significance of correlations is an important part of cement stratigraphy. It is best established by developing cross-cutting relationships and determining the oxygen isotopic variability of cement zones. Cement stratigraphy in vertical stratigraphic sections should be integrated with a sequence-stratigraphic framework that subdivides a stratigraphic sequence with diagenetically important surfaces such as surfaces of subaerial exposure. Lateral correlation of early events of cementation is established through correlation of the diagenetically important surfaces, rather than through the lateral correlation of cement zones over the long distances that are more applicable to later cements. Cement stratigraphy of zoned calcite cement from the Pennsylvanian Holder Formation of New Mexico shows that cement precipitated during events of intraformational subaerial exposure. These meteoric calcite cements are most abundant on shelf-crest and shelf-edge settings. Similar zoned calcite cements occur in the Pennsylvanian Lansing-Kansas City groups of northwestern Kansas and southwestern Nebraska. In relative paleotopographic low areas, fluid inclusion data show that early cements precipitated at a low temperature, but from concentrated brines that likely originated from reflux during deposition of Permian evaporites. In a relative paleotopographic high area, reconnaissance fluid inclusion data on petrographically similar zoned cement suggests precipitation from low-temperature brackish waters. Overall distribution of meteoric-derived calcite cement suggests it is best developed in the paleotopographically high areas. Despite a similar setting and age for the three localities, samples with similar cathodoluminescence have three totally different modes of origin, hence, demonstrating the need for careful studies of cement stratigraphy.

Abstract: Carbonate cement stratigraphy has been extremely successful in establishing paragenetic sequences, timing of diagenetic events and quantification of cementation episodes in much greater detail and accuracy than otherwise possible. Correlation of major concentric compositional cement zones over regions of 10 2 to 10 5 square kilometers has allowed regional mapping of cement stratigraphy. Mapping of stratigraphics, especially distributions of non-luminescent zones, has resulted in a variety of paleo-hydrologic models that invoke meteoric groundwater systems and interpret their recharge areas, flow directions, size of flow systems, and relationships to unconformities. Most calcite cements contain usable concentric zoning as revealed by cathodoluminescence and staining. One of the most common stratigraphics comprises an older non-ferroan cement sequence containing non-luminescent zones separated by luminescent zones (OBC cements), which in tum is overgrown by a ferroan cement sequence that is luminescent and broadly zoned or unzoned (YFC). A second common stratigraphy comprises an olderfully luminescent, non-ferroan sequence overgrown by YFC cements, and often interpreted to be equivalent to part or all of the OBC cements. The OBC cements and in some cases their subzones have been correlated over large regions and through tens to hundreds of meters of section. Interpretations of the time significance of OBC cements and their subzones vary from their being synchronous to their being completely diachronous, and have resulted in three major models: 1) Each package of subzones within the OBC cements were precipitated synchronously throughout the studied region, and through most or all of the stratigraphic thickness of the host formation. Their distributions reflect the oxic portions of meteoric paleo-groundwater systems that were mainly established beneath post-formational subaerial unconformities; 2) Packages of subzones within the OBC cements were precipitated synchronously, but were formed later than packages that occur stratigraphically lower in the host formation, resulting in the entire OBC sequence becoming younger up-section. Distribution of these packages reflects relatively small oxic meteoric-water lenses established beneath intra-formational subaerial exposure surfaces; 3) OBC cements precipitated in marine pore waters, each subsequent OBC zone within a sample representing a different redox horizon below the sea floor. Each subzone is entirely diachronous, becoming younger up-section, and has no meaning in terms of the regional groundwater flow system. Regional distributions of OBC cements has revealed three end-member patterns: 1) Major lateral change from OBC cements to fully luminescent non-ferroan cements is interpreted to represent strong lateral components of groundwater flow commonly recharged in a tectonically active highland, the OBC cements representing oxic waters nearer recharge and the fully luminescent equivalents representing reduced groundwaters downflow; 2) Major vertical change from OBC cements to fully luminescent non-ferroan cements is interpreted to represent a significant vertical component of recharge through a subaerial unconformity either directly into an unconfined paleo-aquifer or through a leaky paleo-aquitard; 3) Nearly uniform distribution of OBC cements, interpreted to reflect cementation in marine pore waters, or in oxic meteoric lenses established during post-formational or intra-formational subaerial unconformities. Important problems in cement stratigraphy to be addressed include an improved assessment of the time significance of cement zones where traced over large areas and through thick stratigraphic sections, an improved understanding of causes of concentric zoning in natural cements, and an improved understanding of the precipitation environments of the OBC cements, in particular whether they are marine or non-marine.

Abstract: Cathodoluminescence is commonly observed in ancient carbonate rocks, yet relatively few examples of geologically young cathodoluminescent carbonates have been reported. Review of young cathodoluminescent carbonates provides constraints on formation of cathodoluminescence by pre-burial processes and aids in interpreting ancient carbonates. Modem skeletal grains are rarely cathodoluminescent. Cathodoluminescence observed in ancient skeletal grains, although not necessarily indicative of diagenetic alteration, certainly should encourage the petrographer to consider the possibility of replacement or recrystallization. Modem inorganic marine precipitates are generally not cathodoluminescent either, although cathodoluminescent magnesian calcite cements have been reported from both deep-water and shallow-water marine environments. Cathodoluminescence in these examples is apparently the result of formation in low-Eh porewaters in which divalent manganese is available. However, these conditions are not necessarily reflected in the trace cation and stable carbon isotope composition of the cements. Pleistocene cathodoluminescent carbonates have been reported from bank-margin settings where these sediments underwent subaerial exposure during glacio-eustatic sea-level lowstands. Meteoric diagenesis during subaerial exposure does not always result in a cathodoluminescent product, however. For example, the post-Miocene coral cap of Enewetak Atoll lacks cathodoluminescence despite ample textural and geochemical evidence of subaerial exposure and recrystallization in meteoric water.

Abstract: Mappable variations in the metallic ion concentration of late diagenetic carbonate cements at the surface above Velma oil field can be correlated to a qualitative measure of cathodoluminescence (CL). This proposed measure, the carbonate CL index or CCI, compares trace element quencher and activators of CL in carbonates to visual estimates of CL intensity. The late diagenetic aureole at Velma is well developed. In surface sandstone, the aureole contains abundant Fe sulfides and associated ferroan carbonate cement which imparts a dark-reddish-brown color to the rock. The aureole is surrounded by Fe-poor sandstone. Prior studies of the Permian siliciclastic rocks in the near-surface show that changes in Fe and Mn concentrations in carbonate cement result from Eh-pH zonation in the diagenetic aureole across the production area. Fe 2+ and Mn 2+ ions are, respectively, the common quencher and activator of cathodoluminescence (CL) in carbonate minerals. Atomic absorption (AA) analysis shows these trace elements are present over a wide range of concentrations in our samples. Cements with Mn concentration (concentration annotated as [Mn] in units of ppm) greater than [Fe] commonly have bright CL, and those with [Mn] less than [Fe] will have dull orno CL. Comparison of CL quenchers and activator indices ([Fe] alone, [Mn] alone, [Fe]/[Mn]) to visual CL characteristics at Velma shows only fair agreement. Therefore, we apply a new carbonate CL index, CCI = ([Mn]-[Fe])/([Mn]+[Fe]), in an attempt to qualitatively describe the significant CL active trace element composition relative to the subjectively determined visual luminescence character. We find CCI is better than [Fe]/[Mn], [Fe], or [Mn] as a descriptor of CL because it shows a more systematic variation and clearer relationship to CL intensity than the other chemical CL indices. CCI can vary over the range -1 to 0 to +1, dovetailing with major categories of visual descriptors of intensity (non (or no), dull, or bright CL). At CCI of about -1 no luminescence will be observed from the carbonate cement; at CCI of near but less than 0, dull luminescence; and at CCI >0 the cements are brightly luminescent. The general cathodoluminescence pattern observed in the carbonate cements at Velma is related to CCI with dull- or non-luminescent cement (greater [Fe] than [Mn]) over the production area and dull to bright luminescence (less [Fe] than [Mn]) on its flanks. CCI is mostly negative over the production area and zero or positive on its flanks.