Abstract

Two methods of exploratory data analysis--a numerical classification system applied in conjunction with an ordination technique--were used to facilitate environmental interpretation of 61 Tonoloway Limestone samples from Pinto, Maryland. We suggest that the scheme of multivariate analysis presented here, because it involves nonparametric methods, is more applicable to typical geologic data than other strategies. In the Tonoloway Limestone 7 facies (clusters) were identified by Q-mode cluster analysis: (1) micrite, (2) micrite-dolomite, and (3) dolomite microfacies from the supratidal zone; (4) a micrite-peloid microfacies of the intertidal mud flat; (5) intraclast and (6) ooid-calcite cement microfacies representing a shallow-subtidal environment; and (7) a peloid-calcite cement microfacies from the deeper-subtidal environment. Multidimensional scaling illustrated interrelationships among the clusters and the gradational nature of samples; neither factor was observed by cluster analysis alone. Recognition of the gradational nature of samples then led to interpretations of three environmental gradients that were normal to the paleoshoreline. Hydrodynamic energy was low on both the tidal flat and offshore near wave base and systematically increased from both directions toward the shallow-subtidal environment. Petrographic fossil diversity was highest near wave base with a second, lesser peak on the intertidal mud flat; this variable decreased into the shallow-subtidal high-energy belt and also onto the supratidal mud flat. Dolomitization, apparently of two modes, was most pronounced in rocks of the schizohaline supratidal zone.

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