LITHOFACIES MAPS AND REGIONAL SEDIMENTARY-STRATIGRAPHIC ANALYSIS

ABSTRACT Lithofacies maps may be prepared in numerous ways, and this paper emphasizes a statistical approach which brings out the magnitude and rates of change in lithologic characteristics for selected stratigraphic intervals. The interval is divided into percentages of clastics (conglomerate, sandstone, shale) and non-clastics (limestone, dolomite, evaporites), which are combined into a “clastic ratio” and a “sand-shale ratio.” The data obtained are numerical and provide a basis for contour-type maps on which the two ratios may be combined to obtain the distribution of statistical lithologic associations. For the more detailed analysis of lithofacies variations a series of ratios based on sandstone, shale, and limestone types is available, which helps differentiate basin, shelf, and geosynclinal deposits. Combinations of lithofacies and isopach maps afford data for interpretations of contemporary tectonics, paleogeography, and to some degree the distribution of environments during the depositional cycle.