Abstract
Basic studies of the elemental composition in marine carbonates are carried out to estimate paleoenvironments, such as, paleotemperature and paleosalinity.
(1) A crystal structure control model is introduced to trace element partition between marine carbonates and seawater. Divalent alkaline earths and transition elements occupy regularly the lattice site, while monovalent alkali elements show no tendency to occupy the lattice site in the crystal structure of calcium carbonates.
(2) Four clusters of marine carbonate skeletons, which are the most basic units for the paleoenvironmental research, are dividable based on the strontium and magnesium contents.
(3) Detailed ontogenetic variations of elemental composition in a single shell are newly clarified. Some elements, such as, magnesium, strontium, sodium, and lithium, show a typical seasonal growth variation. These elements give a possibility as paleothermometer.
(4) The ontogenetic variation can be simulated by the following optimum temperature model : Every species indigenously have an optimum temperature value of calcium carbonate metabolism. The intensity of the metabolism gradulally decreases toward lower or higher temperature from the optimum value.
(5) A optimum condition model, which is expanded from the optimum temperature model, also gives a synoptic explanation for the complex phenomena of empirical relations between elemental content of skeletal carbonates and environmental factors.
