In older sequences however, diagenetic alteration combined with greater uncertainties in estimating absolute ages leads to greater uncertainties in the exact shape of the Sr isotope seawater curve. Because of their abundance, fine-scale biostratigraphic resolution, and high strontium contents, conodonts have the potential to improve the seawater curve if it can be shown that they preserve primary isotopic signatures. This dating technique is a robust tool that can provide improvement in stratigraphic resolution over conventional techniques allowing accurate structural modelling. The isotopic information can be used in several ways. For mapping purposes, the raw isotopic ratios can be used and, given the differences that exist between seawater curves, is probably preferable to calculated ages.
Calculated ages are essential for determining local sedimentation rates and tectonic histories.
It has been argued that Sr isotope stratigraphy can be reliably applied only when the carbonates meet a number of geochemical criteria including, for example, a relatively restricted concentration range for Sr. The unthinking application of such criteria may result in the loss of valid age information. Each sample needs to be considered in the context of its geological setting and the detailed petrography for its suitability for Sr isotope dating. Of critical importance is the timing and duration of diagenesis and associated fluid flow events which is determined by petrographic examination. Biostratigraphy also provides an important control on the precision and accuracy of the isotope stratigraphy.