Abstract It has been recognized for the past century that copper deposits, in common with those of many other metals, are heterogeneously concentrated in Earth's upper crust, resulting in areally restricted copper provinces that were generated during several discrete metallogenic epochs over time intervals of up to several hundred million years. Various segments of circum-Pacific magmatic arcs, for example, have total contained copper contents that differ by two orders of magnitude. Each metallogenic epoch introduced its own deposit type(s), of which porphyry copper (and related skarn), followed by sediment-hosted stratiform copper and then iron oxide copper-gold (IOCG), are globally preeminent. Nonetheless, genesis of the copper provinces remains somewhat enigmatic and a topic of ongoing debate. A variety of deposit-scale geometric and geologic features and factors strongly influence the size and/or grade of porphyry copper, sediment-hosted stratiform copper, and/or IOCG deposits. For example, development of major porphyry copper deposits/districts is favored by the presence of clustered alteration-mineralization centers, mafic or massive carbonate host rocks, voluminous magmatic-hydrothermal breccias, low sulfidation-state core zones conducive to copper deposition as bornite ± digenite, hypogene and supergene sulfide enrichment, and mineralized skarn formation, coupled with lack of serious dilution by late, low-grade porphyry intrusions and breccias. Furthermore, the copper endowment of all deposit types undoubtedly benefits from optimization of the ore-forming processes involved. Tectonic setting also plays a fundamental role in copper metallogeny. Contractional tectonomagmatic belts, created by flat-slab subduction or, less commonly, arc-continent collision and characterized by crustal thickening and high rates of uplift and exhumation, appear to host most large, high-grade hypogene porphyry copper deposits. Such mature arc crust also undergoes mafic magma input during porphyry copper formation. The premier sediment-hosted stratiform copper provinces were formed in cratonic or hinterland extensional sedimentary basins that subsequently underwent tectonic inversion. The IOCG deposits were generated in association with extension/transtension and felsic intrusions, the latter apparently triggered by deep-seated mafic magmas in either intracratonic or subduction settings. The radically different exhumation rates characteristic of these various tectonic settings account well for the secular distribution of copper deposit types, in particular the youthfulness of most porphyry relative to sediment-hosted stratiform and IOCG deposits. Notwithstanding the importance of these deposit-scale geologic, regional tectonic, and erosion-rate criteria for effective copper deposit formation and preservation, they seem inadequate to explain the localization of premier copper provinces, such as the central Andes, southwestern North America, and Central African Copperbelt, in which different deposit types were generated during several discrete epochs. By the same token, the paucity of copper mineralization in some apparently similar geologic settings elsewhere also remains unexplained. It is proposed here that major copper provinces occur where restricted segments of the lithosphere were predisposed to upper-crustal copper concentration throughout long intervals of Earth history. This predisposition was most likely gained during oxidation and copper introduction by subduction-derived fluids, containing metals and volatiles extracted from hydrated basalts and sediments in downgoing slabs. As a result, superjacent lithospheric mantle and lowermost crust were metasomatized as well as gaining cupriferous sulfide-bearing cumulates during magmatic differentiation—processes that rendered them fertile for tapping during subsequent subduction-or, uncommonly, intraplate extension-related magmatic events to generate porphyry copper and IOCG districts or belts. The fertile lithosphere beneath some accretionary orogens became incorporated during earlier collisional events, commonly during Precambrian times. Relatively oxidized crustal profiles—as opposed to those dominated by reduced, sedimentary material—are also required for effective formation of all major copper deposits. Large sedimentary basins underlain by or adjoining oxidized and potentially copper-anomalous crust and filled initially by immature redbed strata containing magmatic arc-derived detritus provide optimal sites for large-scale, sediment-hosted stratiform copper mineralization. Translithospheric fault zones, acting as giant plumbing systems, commonly played a key role in localizing all types of major copper deposits, districts, and belts. These proposals address the long-debated concept of metal inheritance in terms of the fundamental role played by subduction-metasomatized mantle lithosphere and lowermost crust in global copper metallogeny.

Abstract This chapter reviews how paleontology can help solve exploration, exploitation, and production problems. It is not, however, a manual; paleontology is a diverse and highly specialized discipline, and no earth scientist will learn how to apply these paleontological approaches merely by reading this chapter. The authors, listed within the sections they helped write, have summarized several complex and specialized subdisciplines, with emphasis on conveying a sense of the potential paleontological applications rather than an exhaustive or detailed treatment. Ideally, earth scientists involved in hydrocarbon recovery will recognize from these discussions the variety of contributions which paleontological approaches can make to geologic problem-solving and will seek assistance from a practitioner.

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Abstract While working as a civil engineer in England, William Smith played a key role in establishing the science of biostratigraphy when he noted that different species of invertebrate fossils characterized the successive Secondary formations in England (Rudwick, 1976). From this, Smith formulated what geologists now recognize as the principle of faunal succession about sixty years before Darwin (1859) published the Origin of Species . Darwin’s theory of evolution, through variation and natural selection, explained why the geologic succession of organisms occurs. Augmenting the principle of superposition with the principle of faunal succession not only allowed geologists to develop a better relative geologic time scale, but it also enabled them to extend their correlations geographically. Although biostratigraphy, paleobiogeography, and paleoecology address temporal and spatial distributions of fossils in rocks, biostratigraphers place primary emphasis on the vertical sequence of fossils and use this sequence to place strata in temporal order and to correlate rocks separated in space. Since conceptualization of the fossil zone in the 19 lh Century, biostratigraphers have traditionaliy used zonal schemes to establish the relative time scale. Idealiy, biostratigraphic zones are temporaliy confined, spatialiy widespread, and possess approximately synchronous boundaries. Biostratigraphic zones carry time significance and are recognized in rocks where the fossils are present (Johnson, 1992). Despite a number of factors that limit the distribution and preservation of organisms in rocks (e.g., facies control, ecologic barriers, migration, dispersai barriers, local extermination, taphonomic effects, misidentification, erosion, and metamorphism), geologists have been able to define zones and erect a

Abstract As organizer of the Burlington symposium on graphic correlation of March, 1993, Dr. Mann invited me to open this volume with a review of the birth and early history of graphic correlation. From the Summer of 1949 through the Summer of 1955, I taught invertebrate paleontology at the University of Wyoming. While there, I used the conventional zonal approach to biostratigraphy that I had learned in school. However, when I went to work in the Denver Area office of Shell Oil Company in the Fall of 1955, I was immediately faced with a problem that conventional zonation could not solve. At that time the big play in the Rocky Mountain region was for Mississippian oil in the Williston basin of North Dakota and adjacent Montana. Production from the basin had sparked interest in Mississippian rocks elsewhere, and Shell had recently supported Union Oil in the coring of the Union Otter Woman Morning Gun No. 1, drilled in the foreland just east of the Folded Belt in western Montana. My first assignment at Shell was to study the Morning Gun core to verify the correlations that had been made between it and the Williston basin. The Williston basin Mississippian is naturally divisible into three parts: the upper, oil producing dolomites and evaporites of the Charles Formation, the massive limestones of the Mission Canyon Formation in the middle, and the thin bedded limestones of the Lodgepole Formation (Fig. 1).

Abstract Graphic correlation, based on a Cartesian coordinate system, is a tool which is used to derive precise, consistent, and highly resolved biostratigraphic correlations among wells and/or measured outcrop sections thereby reducing technical risk in hydrocarbon exploration. Non-paleontological data may also be correlated using this method. A database of fossil ranges, the composite standard, is created by graphic correlation. Graphic correlation and composite standard construction are readily handled by computer software. Large quantities of biostratigraphic data can be compiled, organized, retrieved, and applied to future correlation studies. The enhanced resolution of this method facilitâtes recognition of unconformities and Condensed sections, resulting in interpretations well suited for sequence stratigraphic basin studies. Used in conjunction with log and seismic data, this technique improves the explorationist’s ability to identify and exploit subtle stratigraphic traps. It can also facilitate recognition of ancestral structural features masked by unconformities and overlying flat lying beds. The technique is a mainstay in Amoco’s approach to biostratigraphy. It is a powerful tool for evaluating and interpreting paleontological data generated in-house as well as that acquired from vendors, through data trades, in acreage bid round data packages purchased from foreign governments, and from the literature. This method does not replace traditional paleontological techniques; it is a tool for data handling and display designed to enhance traditional methods.

Abstract Graphic correlation is a geometric construction in which the locations of correlatable horizons in two sections plot as points on an xygraph, and the line of correlation (LOC) is formed from the infinite number of points representing these horizons. In theory, the LOC belween any two correlatable sections must exist; the geologist must weigh all the evidence at hand to deduce or to approximate where the LOC must be, and there is no way to “look up the answers in the back of the book.” The LOC can have as many doglegs as are needed, but it cannot have a negative slope. In practice, not all the lowest and highest stratigraphic occurrences of taxa have timesignificance. Furthermore, one must always check the axis labels and the scaling of any graph used in graphic correlation because there are few standard conventions in graphic correlation, and many computer programs are designed around the size of the screen or printer paper, not around the user’s convenience. In reality, the hardest part of graphic correlation is generating reliable data. Graphic correlation is a means to an end; a tool to solve problems in stratigraphy, basin analysis, paleobiogeography, or evolutionary history. One should also use graphic correlation to find out where further investigation is needed, and then one should investigate further.

Abstract Accurate estimation of the line of correlation (LOC) is an important goal of graphic correlation. Since wide variety of both qualitative and quantitative methods are currently available to guide LOC estimation, it is crucial that the procedure used to infer a working LOC be completely specified and, thus, reproducible. The most popular LOC estimation technique, termed “splitting tops and bases,” takes advantage of inherent differences in the chronostratigraphic implications of biostratigraphic first and last appearance datums (FADs and LADs, respectively). This method takes, as its starting point, a Standard Reference Section (SRS) that contains occurrences of a large number of species distributed over a long stratigraphic interval with no obvious gaps, hiatuses, or structural complications. If the SRS is well-chosen, a large number of its constituent taxa may occur at horizons corresponding to their global FADs and LADs. In such instances, graphic comparison of the SRS with datum positions from other sections or cores will result in the grouping of FADs and LADs on opposite sides of the true LOC. Using this relationship, the geometry of the LOC can be inferred by finding that line which divides FADs from LADs in the most efficient manner. Adjunct criteria that may be useful in establishing a qualitatively-defined LOC or distinguishing between alternative LOC geometries include consideration of key beds, datum weighting, and parsimony. Regression analysis can also be used to quantitatively estimate LOC positions. Unlike qualitative LOC estimation, regression-based techniques make no assumptions with respect to differences between biostratigraphic datum types. Least squares linear regression has a long history of use in graphic correlation as a LOC estimation technique. However, least-squares methods make a necessary distinction between independent and dependent variables ( = sections or cores). This distinction, along with its implicit corollary of a cause and effect relationship between variables, seems out of place in the context of a graphic correlation problem. Reduced major axis and major axis regression models provide a much closer match between the assumptions of the regression model and the nature of stratigraphic data, in addition to providing a better estimate of the bivariate linear trend. Reduced major axis regressions have the added advantage of being much easier to calculate than either least squares or major axis regressions. These alternative regression algorithms can be modified to take key beds and weighted data into consideration. Significance tests are available for least squares and major axis regressions, but these are, at best, indirect tests of the quality of the fit between the estimated LOC and the underlying data. Analysis of residual deviations from the LOC provides the best indication of this fit. Linear regression methods minimizē standard measures of fit between the LOC and the underlying data. While minimization of these parameters usually involves straightforward computations, these numerical recipes often fail to respect the stratigraphic implications of the minimization procedures, specifically those involving the inferred extension of local stratigraphic ranges. The sum of all local range extensions implied by a LOC has been termed the “economy of fit.” No deterministic formula leads directly from the raw stratigraphic data to the LOC exhibiting the best economy of fit. However, iterative constrained optimization procedures are available to efficiently search for LOCs with very good economy of fit characteristics. In most instances, LOCs with the best economy of fit or smallest net range extension exhibit a piecewise linear geometry. Constrained optimization search strategies can also be combined with a multivariate representation of raw stratigraphic data to locate highly economica! LOCs for all sections simultaneously.

Abstract Stratigraphic correlation involves three distinct tasks: establishing the temporal sequence of marker events (sequencing task), determining the relative sizes of the intervals between those events (spacing task), and locating the horizons that correspond in age with each event in every section (locating task). Stratigraphic sections do not yield enough information to solve this problem exactly. Instead, stratigraphers must search for the approximation that “best” fits all local stratigraphic observations. The concept of economy of fit, as used in graphic correlation, provides a rigorous definition of “best” and implies the existence of a penalty function that can be used to rank possible solutions. Unfortunately, traditional graphic correlation requires severe simplifying assumptions about accumulation rates because it attempts to solve all three tasks at the same time, and yet it incorporates the local sections into the solution one at a time. Using a penalty function based on economy of fit, an alternative solution technique naturally emerges in the form of constrained optimization. This technique is J dimensional, in the sense that it treats the observations in all J sections simultaneously. It can complete the sequencing task before making assumptions necessary to the spacing task. Constrained optimization eliminates impossible solutions (constraint) and then searches for the best of all the possible ones (optimization). For realistic instances of the problem, it is not feasible to calculate the penalty function for all possible solutions. Instead, we use a probabilistic search procedure termed “simulated annealing” to find very good solutions without an exhaustive search. Simulated annealing does not maintain any memory of the search path or search exhaustively at the local scale. We reject an alternative procedure that incorporates these features because it proved difficult to tallor to produce satisfactory solutions. Our J -dimensional procedure quickly finds solutions for Palmer’s (1954) classical data set (/= 7 sections from the Cambrian of Texas) that are comparable to the solution Shaw (1964) achieved by traditional graphic correlation. The expert judgements that the stratigrapher uses to draw the traditional lines of correlation and which give the appearance of excessive subjectivity, in fact, derive primarily from a knowledge of all the sections. By treating all sections at once, constrained optimization eliminates much of the apparent subjectivity associated with traditional graphic correlation. Constrained optimization still allows the user to explore the consequences of different and genuinely subjective judgements about the relative reliability of different taxa and sections.

Abstract Two enhancements to the graphic correlation technique, average composite sections and derived correlations between comparison sections, help refine correlations and increase the robustness of geological interpretations. Average composite sections match the observed ranges of most taxa more closely than maximum composite sections and therefore better constrain the respective lines of correlation. Comparison of the two approaches using a hypothetical taxon first-occurrence surface and a published dataset comprising 10 DSDP sites from the Atlantic and Pacific ocean basins documents the refinements possible using average composite sections. Analysis of the hypothetical taxon first-occurrence surface demonstretes that the expected error of correlating with a maximum composite section increases rapidly as additional comparison sections are included; whereas, the expected error of correlating with an average composite section remains relatively stable. Analysis of Pliocene planktonic foraminifers and calcareous nannofossils from 10 DSDP sites documents that correlations based on average composite sections match the independent paleomagnetic constraints more closely than correlations based on maximum composite sections alone. Average composite sections should be based on potential maximum events which excludes those ranges that are truncated by a substanţial hiatus or by the limits of sampling in a comparison section. Derived correlations use the implied correlation between comparison sections to help evaluate and refine the original interpretations of how each comparison section correlates with the composite section. Analysis of three DSDP sites from the eastern and central equatorial Pacific document that substanţial refinements are possible. Using derived correlations, a hiatus missed on an original interpretation was identified, and several smaller hiatuses were adjusted to better match the additional constraints. Derived correlations take advantage of the multidimensional nature of biostratigraphic datasets that has traditionally been under utilized, and they provide a powerful mechanism for evaluating alternative interpretations.

Abstract The composite standard method of biostratigraphy, described by Shaw (1964), provides a consistent temporal framework for stratigraphic analysis of a basin. The method enables geologists to graphically correlate deposition in individual sections to an ideal composite Standard reference section, quantifying deposition and stratigraphic lacuna. Sequence stratigraphy (Posamentier and Vail, 1988; Van Wagoner and others, 1990) is a stratigraphic interpretation method that genetically relates deposits in a dip profile to relative changes in sea level, based on physical surfaces in the rock record. Weaknesses in graphic correlation (underuse and static application) match well with strengths in sequence stratigraphy (widespread use and dynamic application). Weaknesses in sequence stratigraphy (documentation and consistency) can be equally well matched with the strengths of graphic correlation. Sequence stratigraphic key bounding surfaces cause predictable patterns in the graphic correlation of biostratigraphic data. Integration of graphic correlation and sequence stratigraphy enhances the utility of both stratigraphic tools and provides a powerful basin analysis technique.

Abstract Since the publication of Shaw’s Time in Stratigraphy in 1964, paleontologists of Amoco Corporation have concentrated on developing a Phanerozoic biostratigraphic database for use in graphic correlation applications and composite standard development. This developmental phase brought the company to a position where it can routinely utilize its composite database to solve problems of correlation related to hydrocarbon exploration and production. This experience shows that two kinds of composite standards maximize data value. These are (1) Worldwide and (2) local composite standards. A Worldwide composite standard develops a comprehensive fossil occurrence database that establishes an accurate understanding of the global ranges of fossil species. Fossil datums are placed into a chrono - sequence scaled to a framework of Worldwide reference sections. With database evolution through graphic correlations, traditional zonal resolution is usually exceeded due lo the factoring of all fossil data, not just zonal markers and familiar accessory forms. Paleontologists in industry commonly must use multisource, multivintage data of varying qualities within the same project. Systematic comparisons of such information to a Worldwide standard are particularly beneficial in overcoming the incongruities of multiple zonal schemes and varied taxonomies that make up such datasets and which tend to confound traditional biostratigraphic analysis. They also are helpful in identifying and removing spurious data. A worldwide composite standard may distort the value of local species ranges linked to regional paleoenvironmental and geographic restrictions. These foreshortened ranges may otherwise be very valuable in establishing intrabasinal correlations. For these reasons, the concept of a “local” composite standard developed within Amoco to maximize basin evaluations and regional stratigraphic applications. A local composite standard captures the regional biostratigraphic signincance of all fossil occurrences, including those localities calibrated initially to the Worldwidestandard. These calibrated localities have lines of correlations that place a local fossil sequence within a worldwide context. The resulting database provides optimum refinement for regional correlations, while resolving important basinwide time-stratigraphic breaks undetected by purely local zonations.