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Strontium Isotope Dating

StrataData has for many years offered a strontium isotope dating service to the petroleum industry in collaboration with Isotopic Ltd.

Strontium isotope stratigraphy is now an established technique which provides a numerical age related to a global scale based on the 87Sr/86Sr ratio of past seawaters. Careful selection and preparation of material by experienced StrataData staff is key to the success of this technique. This is matched by world class analysis at one of a number of laboratories. Converting the results of analyses to numerical ages is achieved using a unique Global Strontium Seawater Curve.

Application

Most suitable for dating marine sediments containing unaltered biogenic material (e.g. molluscs, foraminifera, conodonts, fish teeth and calcareous algae) throughout the Phanerozoic. It is also possible to use whole rock samples (carbonates, dolomitised carbonates and evaporites) for analysis providing any diagenesis was early. The accuracy of the age determination depends on the steepness of the global strontium curve, which varies with age.

Cost and turnaround time

Sample preparation and sample analysis - price on application. Reporting costs are based on your requirements. The cost can be reduced for a large projects (50+ samples). Turnaround time is normally 3-4 weeks from receipt of samples. Please contact us for more information.

Technical information

Method

This method provides a numerical age related to a global scale based on the 87Sr/86Sr ratio of past seawaters. The amount of radiogenic strontium in the world’s oceans is principally controlled by contributions from continental runoff, exhalations at oceanic ridges and meteoric waters. In terms of geological time oceanic mixing is instantaneous. The assumption that the 87Sr/86Sr ratio of the world’s oceans has fluctuated uniformly through time has enabled a Global Standard Strontium Curve (GSSC) to be established (Howarth and McArthur, 1997). Since Sr is taken up by aquatic organisms in equilibrium with the surrounding water it is possible to use their fossilised remains as a proxy for oceanic seawater. Suitable material includes molluscs, foraminifera, conodonts, fish teeth and calcareous algae. whole rock samples (carbonates, dolomitised carbonates and evaporites) for analysis providing any diagenesis was early.

Non-oceanic environments will of course give rise to atypical Sr ratios which will differ from the global seawater strontium standard. Closeness to a major river system is one such environment where one would expect Sr ratios to vary from the coeval oceanic values. Data from individual samples are compared to the Howarth and McArthur database. This database includes all published and many unpublished Sr ratios which have first been subjected to a vetting procedure and weighted for stratigraphical, biostratigraphical and chemical accuracy. The figure below illustrates the Pliocene - Pleistocene global seawater Sr curve. In reality the comparison is made with the Global Strandard Strontium Curve using a “look up” table.

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Global standard strontium curve for the Pleistocene and Pliocene (data from Howarth and McArthur, 1997)