James M. Parks

Use of thermoluminescence of limestones in subsurface stratigraphy

The thermoluminescence of the limestones of the Meramecian and Chesteran series (middle and upper Mississippian) of the Illinois basin was studied in an attempt to develop the thermoluminescence of limestones into a useful research tool in subsurface geology. A powder method of sample preparation is described which makes accurate quantitative measurement of thermoluminescence possible. The apparatus used in measuring and recording thermoluminescence is described briefly. The analysis of patterns of variation in intensity of thermoluminescence and in glow-curve shapes vertically through a formation appears to have some usefulness in subsurface stratigraphy in (a) identifying and characterizing a formation, (b) assisting in recognizing tops and bottoms of limestone formations where lithologic breaks are not present, (c) splitting thick carbonate rock sequences into small units useful in correlation, and (d) recognizing erosion or non-deposition of zones by the absence of parts of the typical pattern of variation. Within certain limitations, the variations in radioactivity of the limestones appear to be the dominant factor in the cause of variations in thermoluminescence.

Fluvial Sand Shapes: Effects of Tributary Mixing: ABSTRACT

Similarities and differences in gross shapes of fluvial quartz sand grains contain information useful for interpretation of sediment transport history. The shapes of sand grains in a given river depend on the source, or sources, of sand within the drainage basin and on the abrasion and shape sorting that has occurred during transport. It is highly unlikely that 2 major streams will carry precisely similar-shaped grain suites. Therefore, when 2 streams join, the resulting sand can be recognized, on the basis of shape, as being mixtures of the 2 input streams. The multiple rotations method of quantitative shape analysis characterizes sets of grain shapes with 5 or 6 numerical factor loadings, and individual grains are described by 5 or 6 factor scores. Trends of shape changes, such as those that occur along the length of a river, show up well on bivariate-factor score plots. These trends are interrupted and offset by mixing of sands contributed by tributary streams. Shapes of sands obtained from the Missouri River above the junction with the Platte River in Nebraska are different from those from below the Platte; but when Platte River sand shapes are subtracted, the remaining differences are insignificant. Farther downstream, sands from the Kansas River show the same relationships. The relative contributions of sand from a river and its tri utaries, and the rates of mixing of the sands, can be estimated from quantitative shape analysis of several samples. End_of_Article - Last_Page 295------------

Relationship Between Morphological Variation and Environment in Holocene North Atlantic Benthic Foraminifera: ABSTRACT

Previous workers have found that morphological variability recognized in foraminifera is due in part to the effects of environment. The various environmental factors (water depth, temperature, salinity, etc) generally act interdependently, although one factor may be more influential than another in causing observed changes. C. E. Pflum and W. E. Frerichs suggested in 1976, that water depth may be most important in creating shape variation within a genus. Taxonomic problems are inherent, as species may be inaccurately named on the basis of form when, in reality, they actually represent a morphological continuum rather than several biological species. The multiple rotation method of quantitative shape analysis is a new approach to measuring shapes of foraminifera. The outlines of many foraminifera are digitized, rotated to a standard orientation, and radial measurements are reduced to a few numerical descriptors by factor analysis. The relationship between quantitative morphological variation and environmental factors, such as water depth, are then determined by correlation analysis. North Atlantic specimens of Cibicides and Uvigerina from 36 stations in 4 transects off Cape Cod were used in this study. Water depths ranged from 100 to nearly 4,200 m. The observed quantitative morphologic changes with depth tend to confirm previous hypotheses of the strong influence of environment. Results of this study may form the basis for a tool useful to paleontologists in making environmental interpretations from microfossil assemblages. Testing of the actual species boundaries is feasible, perhaps aiding in the solution of many taxononic problems. End_of_Article - Last_Page 235------------

Quantitative Shape Analysis of Carbonate Sands by Use of Contour Registration and Template Matching: ABSTRACT

Carbonate sands are composed of relatively few particle types (e.g., Halimeda, coralline algae, corals, mollusks, and foraminifera). The shape of a particular sand grain is highly dependent on the particle type of which it is composed. Previous, studies of modern carbonate environments show that the composition of sand substrates from different subenvironments are dependent on the organisms that inhabit them. These depositional environments can thus be distinguished from each other according to their constituent particle compositions and, therefore, also by analysis of particle shapes. Template (shape) matching can be accomplished only after the digitized shapes have been normalized to a unit-sized circle and registered. Registration involves the simple computation of shape-specific points within, on, or near the 2-dimensional contour of the sand grain. Shapes are subsequently rotated so that all of the shapes are in a similar position relative to their shape-specific points, allowing more meaningful comparisons between particles. After registration, 36 equi-angular radial lengths are calculated for grain from the center of mass to the boundary outline. A template-matching algorithm was devised in order to determine the relative percentages of several reference shape types, representing the constituents contained within 35 samples from 4 carbonate beaches and associ ted subtidal environments from the Florida Keys. Reference shapes may be chosen arbitrarily or obtained by computing average shapes of the various constituents. The precision of the shape classifications may be enhanced by adding supplemental reference shapes to the algorithm. End_of_Article - Last_Page 287------------

Recognition of Sand Body Depositional Environments: Limitations of Fourier Analysis and New Approach to Grain-Shape Analysis: ABSTRACT

In searching for subtle depositional traps, it would be useful to have a reliable method for determining the depositional environment of sand bodies from internal evidence. Attempts using various grain-size parameters have met with limited success. Recent advances in grain-shape analysis have not lived up to initial hopes. The potential of Fourier analysis is reduced when harmonic amplitudes are used without considering phase angles. Two types of errors can occur: (1) dissimilar shapes can produce similar sets of amplitudes, and (2) similar (but not identical) shapes can produce dissimilar sets of amplitudes. Phase angles can be compared between grains only when the grains are rotated to comparable positions; this can be accomplished by cross-correlation with an empirical asymmetric reference shape. Data reduction is desirable, but paired variables cannot be easily handled by standard multivariate techniques. After rotation to standard position, raw shape data (sets of radial lengths) are adequate shape descriptors. These can be reduced by factor analysis that can be compared between grains and between large sets of grains more meaningfully than can Fourier descriptors (which provide a poor basis for comparisons between grains). Results from the two approaches are compared in a preliminary re-study of the river-beach-dune discrimination problem. Gross grain shapes are classified into natural categories by multivariate analysis of rotated radials. End_Page 968------------------------------ Distinguishable associations of shape categories are quantitatively related to specific environments. Shape sorting, in combination with size sorting (different responses to transport processes), may extend the discriminating power. End_of_Article - Last_Page 969------------

Multivariate Facies Maps: ABSTRACT

Facies maps are constructed from paleontologic and lithologic data to depict major and subtle depositional environment differences across a region during a specified time span. Ratio maps and three-component maps exhibit a lack of discrimination because they cannot incorporate all available data. Factor analysis and cluster analysis techniques can be used to construct truly multivariate facies maps. Earlier attempts at factor or cluster analysis multivariate facies maps had one or more deficiencies: (1) inability to handle a sufficient number of variables and locations; (2) inability to handle mixed-mode data (presence-absence, coded states, integer counts, and continuously variable measurements); (3) inability to take into account redundant or highly correlated variables and (4) inability to accommodate to missing data. A new cluster analysis classification computer program has been written to overcome these deficiencies. The FORTRAN IV program can utilize up to 200 variables on as many as 1,000 stations. It performs a distance function principal components analysis to compute orthogonal (uncorrelated) factor measurements for a distance function cluster analysis of locations. This combination will handle mixed-mode data and will adjust to missing data. From the resulting multivariate classification of paleontologic and lithological data, a facies map showing the distribution of the various classes was constructed and compared with previously published facies maps. An example using multivariate lithologic data from coded AmStrat sample-description logs from central Montana demonstrates the potentialities of this method. End_of_Article - Last_Page 735------------

Cluster Analysis Applied to Multivariate Geologic Problems: ABSTRACT

When 20 or more measurements and (or) counts are made on 100 or more samples (thin sections, bottom samples, pollen or foram concentrates, heavy minerals, etc.), the resulting table of data is so large that interpretation by eye becomes difficult. In some geologic studies it is desirable to group together similar samples and to measure the degree of similarity between different groups of samples. Several measures of similarity are available: the product-moment correlation coefficient, cosine-theta (Imbrie, 1962), the matching coefficient, and the distance function (Sokal, 1961). The resulting matrix of intercorrelations is still too large for direct interpretation. Cluster analysis, a technique developed by psychologists, is a method of searching for structure, or relationships, in a matrix of correlation coefficients. Although not so sophisticated as factor analysis, cluster analysis is a useful tool. The results of a cluster analysis can be presented in an hierarchical diagram in two dimensions that will show where the natural breaks occur between groups. A computer program has been written for the IBM 704 that will handle up to 150 measurements on as many as 200 samples. Non-overlapping clusters are used; that is, a sample can appear in only one cluster. A 12 variable 40-sample problem based on constituent particle composition of Bahamian sediment samples (Imbrie and Purdy, 1962) is used to demonstrate the options of the program. The clear-cut groups in the cluster analysis solution are similar to the facies described by Imbrie and Purdy (1962) based on factor analysis. The cluster can be used as a basis for facies maps. End_of_Article - Last_Page 540------------