The calcium isotope (44Ca/40Ca), radiogenic strontium isotope (87Sr/86Sr), and stable strontium isotope (88Sr/86Sr) systems have been utilized to evaluate changes in mass fluxes during environmental perturbations. These systems can react in unique ways, and a quantitative model showing these changes has yet to be produced. To better understand these interactions, we have created a box model using modern and Cretaceous values for input and output fluxes for 44Ca/40Ca (δ44Ca), 87Sr/86Sr, and 88Sr/86Sr (δ88Sr).