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.

Abstract Graphic Correlation - An increasing number of geologists have begun to use graphic correlation because they find this robust technique provides finer stratigraphic resolution and better accuracy and precision than traditional zonations. This volume presents the graphic correlation method, recent methodological developments, and a number of technical papers exemplifying the technique. This collection of papers presents a summary of the technique as currently practiced and it should provide a starting point for those interested in high resolution stratigraphy through graphic correlation. Graphic correlation continues to develop and spread as more geologists use this important and innovative technique. Its potential is only beginning to become realized.

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.

Abstract Microstratigraphic sampling of four measured sections in the Upper Cambrian Ore Hill Member of the Gatesburg Formation in south-central Pennsylvania produced a data set adequate for construction of ‘a composite standard superior to the composite range chart previously erected by Wilson (1951) for trilobite faunas of that unit. This new data set revealed the presence of two thin, widespread units not previously reponed from the central Appalachians: the Irvingella major Subzone al the top of the Elvina Zone and the Parabolinoides Subzone at the base of the Taenicephalus Zone. A new subzone, the Cliffia lataegenae Subzone, is proposed to include that portion of the Elvinia Zone below the base of the Irvingella major Subzone. Restriction of several species to the lower third of that subzone and others to the upper two-thirds on the composite standard suggests the possibility of further subdivision of the Elvinia Zone in the Ore Hill Member, but additional sampling is needed to confirm the mutually exclusive occurrence of those faunas. Some species of Pseudosaratogia and Conaspis display preference for specific lithofacies at the base and top of the Ore Hill, respectively, warranting caution in the use of these genera for chronocorrelation.

Abstract A composite standard (CS), assembled graphically through consideration of the ranges of more than 300 conodont species in measured sections at 127 localities, will apparently be adequate as the backbone for a conodont-based chronostratigraphic framework for the Ordovician System of North America. The SRS is a 374-m core through Middle and Upper Ordovician rocks drilled at a site in north-central Kentucky. Relations between the SRS and additional Ordovician sections have been determined graphically following a compilation strategy that involves extension of the network of correlated sections into older and younger rocks by use of overlapping control sections. The weakest link is currently between Ibexian and lower Whiterockian rocks and the well-controlled upper Whiterockian-Mohawkian-Cincinnatian part of the CS. An undescribed composite section through Whiterockian and lower Mohawkian rocks in east-central Nevada is cited as a promising bridge between these two parts of the Ordovician System. It is not certain if the CS extends to the top of the system, because it is not yet possible to add described North American sections through the Ordovician-Silurian boundary to the network of correlated sections anchored by the SRS described here.

Abstract Middle Ordovician graplolite-rich shales exposed in the southern Appalachians provide an opportunity to apply graphic correlation to what appear to be inadequate data. The fact that the resulting composite standard (CS) is used successfully to address significant geologic problems demonstrates the effectiveness and versatility of the technique. The shales are so strongly diachronous that no single stratigraphic section spans the entire biostratigraphic interval represenled by the shales. The Standard Reference Section (SRS) included only a part of this interval. Therefore, many partially overlapping sections had to be used in the construction of the CS with each section extending the CS upwards or downwards. The completed CS contains the data from 22 stratigraphic sections, is composed of 89 composite standard units (CSUs), and ranges from the lower G. teretiusculus Zone to the C. bicornis Zone. Once we established the CS, we used it as a basis for correlating the basal shale contact. This contact records the subsidence and migration of the foreland basin in which the shales were deposited, and its diachroneity can be expressed in terms of CSUs. With the biostratigraphic correlation of radiometric dates into the CS, the duration of the CSUs could be calibraled in terms of years, and so, too, could the age differences between sections of the diachronous basal shale contact. Because this contact recorded the migration of the basin axis, we used its age difference and the palinspastically restored distance between sections to calculate migration rates. Calculated rates indicate that the basin migrated 50 km cratonward at an average of 13 mm/yr. We were also able to demonstrate that the rate decreased from 40 mm/yr to 9 mm/yr before the migration completely cease4. The foreland basin migration and its subsequent deceleration and halt were produced by arc-continent convergence and collision. Our calculated rate of 40 mm/yr is comparable to modern rates of convergence. We also calculated sediment accumulation rates for selected sections. To do so, we used the slope of the line of correlation (LOC) to determine the number of CSUs and their duration in years corresponding to the stratigraphic thickness of graptolite shales in the section compared to the CS. The rates of 1.8 to 2.8 cm/1000 yrs calculated for intervals of 1.3 to 2.8 Ma are within the ranges of those reported in other studies of pelagic environments. Our rates of basin migration and sediment accumulation are virtually identical to rates determined from a variety of other methods, demonstrating the validity of a CS constructed from what appear to be inadequate biostratigraphic data.

Abstract Graphic correlation of 12 previously uncompiled stratigraphic sections wiih the Silurian composite standard of KJeffner (1989) results in a revised Silurian composite standard (CS) that has Worldwide applicability as a high-resolution chronostraligraphy. The additional range-data on 52 graptolite species, 39 conodont species, 10 events, and one boundary stratotype make it possible to graphically correlate virtually any stratigraphic section (which meets the data requirements of the graphic correlation method) containing representatives of diagnostic conodont and/or graptolite species with the newly revised Silurian CS. The nonannular absolute chronology based on the Silurian CS divides with confidence into 92 standard time units (STUs), a resolution that is a minimum of twice that of any previously proposed Silurian chronostraligraphy. Most sections graphically correlate with the Silurian CS by fitting a straight line of correlation, indicating that the standard reference section (Cellon, Austria) consists of rock which accumulated at a relatively constant rate. The absolute chronology based on the Silurian CS is thereby consonant (or nearly so) with an annular scale, and the 92 STUs it divides into are of equal annular length. Conodont and graptolite chronozones are defined in the Silurian CS according to international rules of stratigraphy and, if they contain at least one STU, can be recognized with confidence in any section that is a part of the Silurian CS or that can be added to it by the graphic correlation method. The conodont and graptolite chronozones defined in the Silurian CS are based on zones proposed by Walliser (1964), Barrick and Klapper (1976), Jeppsson (1988), Aldridge and Schönlaub (1989), Kleffner (1989), and Cocks and Nowlan (1993, for a proposed standard left-hand column for international Silurian correlation Charts). All post-Aeronian Silurian series and stage boundaries can be recognized with confidence in any section that is already or can become a part of the Silurian CS. Three of the series boundaries, the Llandovery/Wenlock, Ludlow/Pridoli, and Pridoli/Lochkovian (Silurian/Devonian), are recognized in the Silurian CS based on the position of the “golden spike” in their boundary stratotypes. Lower boundaries of the graptolite zones that are at the same or approximate leveis as the other Silurian boundaries are used to recognize the positions of those boundaries in the Silurian CS. The Silurian chronostratic scale, based on the range-data on conodont species, graptolite species, events, and boundary stratotypes represented in the Silurian CS, is calibrated by using the Wenlock/Ludlow and Silurian/Devonian tie-points of Harland and others (1989) and STUs as chrons of equal duration to interpolate between and below those tie-points. The Silurian time scale developed by this method provides the best means at present for estimating the durations of the Wenlock, Ludlow, and Pridoli Epochs, and all of the ages that comprise them (except perhaps for the Sheinwoodian and Homerian). The Pridoli was the longest epoch with a duration of 8.4 Ma, compared to 7.1 Ma for the Ludlow and 2.6 Ma for the Wenlock.

Abstract The line of correlation (LOC) in the graphic correlation of the 27 sections in a Frasnian composite standard conforms empirically to the pattern of biostratigraphic events, the bases and tops of ranges of conodont species. The guiding principle is to position the LOC so as to avoid range overlaps of well understood species that have not been observed to overlap in an actuaJ section. Several of the graphs used in the Frasnian composite standard display linear arrays through which the LOC effectively splits the bases and tops of species ranges. The patterns of arrays in other graphs, however, indicate a doglegged solution to the LOC, implying major changes in the accumulation rate within the section plotled against the composite axis. We do nol assume that a uniform rate of accumulation at the standard reference section (from which the scale of the composite axis derives) is necessary for the empirical effectiveness of graphic correlation. The problem of correlation between the mostly mutually exclusive Palmatolepis and Polygnathus Frasnian conodont biofacies has been insoluble by traditional zonal biostratigraphy. The graphic correlations proposed here advance an initial hypothesis toward resolving the correlation of these biofacies. Subdivision of the Frasnian into 34.5 composite standard units represents a far finer resolution than any available through zonal biostratigraphy.

Abstract Regional studies of the Upper Jurassic Wessex Basin of onshore United Kingdom have demonstrated the advantage of using digitally filtered gamma-ray logs to analyze subsequence-scale depositional packages, or cycles. This low-frequency component of the well-log trace (>20-m wavelength) tends to be the most correlatable at a regional scale. This low-frequency component can be enhanced by (i) altering the displayed aspect ratio of the trace by squeezing the vertical scale and stretching the horizontal scale, and changing the horizontal axis to accommodate only the numerical range of log values (i.e., normalization), and (ii) digital filtering of the log values with an appropriate low-pass filter. In the Wessex Basin, gamma-ray and sonic logs treated in this manner readily reveal the longer wavelengths (>20 m) associated with major decreases and increases in log activity. These cycles can be recognized across changes in lifhofacies between wells and can often be correlated over long distances (c. 100 km). Missing cycles testify to hiatuses, and biostratigraphic and seismic calibration suggests that cycles are chronostratigraphic. The striking cyclicity in digitally filtered gamma-ray and sonic logs, facilitates high resolution log correlation over considerable distances, allowing the systematic calibration of biostratigraphic with lithostratigraphic data through graphic correlation. This involves the systematic cross-plotting of biostratigraphic events to produce a composite standard (CS). The scatter of biostratigraphic events is generally such that a line of correlation cannot be drawn with confidence from the biostratigraphic data alone. Independent lines of correlation are established between wells by first pattem-matching cycle boundaries on digitally filtered wireline traces and using these, in addition to the biostratigraphy, as a framework for adding biostratigraphic events to the CS. This has advantages over the convenţional approach in that the effects of outliers in the data are minimized and hiatuses and subtle changes in rock accumulation rates become apparent. By adding all the biostratigraphic events from all wells to the CS a range chart is produced depicting the scatter or dispersion of all biostratigraphic events relative to the log based cycles. The end result is an integrated stratigraphy in which biostratigraphic events are calibrated against rock events giving a measure of dispersion, and hence confidence, for each biostratigraphic event.

Abstract An abrupt lithofacies change occurs in Cenomanian strata of northeastern Wyoming and southeastern Montana. Across a 46.75-km areal extent, calcareous rocks of the Greenhorn Formation change to non-calcareous rocks of the Belle Fourche Shale. The physical conditions that produced the facies change also restricted the lateral extension of biostratigraphically useful fossils. Historically, correlation of these strata have proven difficult. However, supplemented graphic correlation techniques generate high resolution correlations using local nonunique geologic data, such as bentonite and calcarenite beds and foraminiferal biofacies.

Abstract Since the original MacLeod and Keller (1991a, b) graphic correlation study of Cretaceous/Tertiary (K/T) boundary sections and cores, new biostratigraphic data have become available for lowermost Danian successions in high latitudes (Nye Kj0v, ODP sites 690 and 738) and from sequences proximal to the proposed Chicxulub impact structure (Millers Ferry, Mimbral). Graphic analysis of these data provides an opportunity lo test the prediction that rising eustatic sea level during the tians-K/T interval played a major role in Controlling pattems of sediment accumulation in neritic and bathyal settings. In addition, restricling the empirical basis for development of a lowermost Danian Composite Standard (LD-CS) from all available biostratigraphic data (used in the previous study) to only datums from widely-accepled Danian and K/T survivor laxa enables determination of the extent to which previous results were biased by inclusion of data from controversial “Cretaceous” survivor taxa. Results indicate that sequences from neritic and upper bathyal settings (Nye Kİ0V, Mimbral) are temporally complete within their lowermost Danian intervals while sections/cores from very shallow inner neritic settings (Millers Ferry) and the deep sea (ODP Site 690, ODP Site 738) contain incomplete lower Danian stratigraphic records. These findings are consistent wilh results of traditional zone-based biostratigraphic analyses and with predictions of the sequence stratigraphic model. Moreover, this revised LD-CS is essentially identical to the previous K/T-CS (MacLeod and Keller, 1991b) based on total biotic data. Data from a large number of organismal groups now confirm that biotic, sedimentologic, and geochemical studies based solely on deep-sea and very shallow neritic successions are biased toward catastrophic paneras of change as a result of missing section (= time). Biotic patterns from inner neritic through upper bathyal settings have the best chance of preserving temporally complete sequences of lower Danian events. The faunal record from these sequences reveals the lower Danian succession to be characterized by progressive rather than instantaneous turnover in biotic, sedimentologic, and geochemical variables occurring over at least 500,000 years.