M Fatehi Marji - Faculty of Mining Engineering, Yazd University, Yazd, Iran
A Hossein Morshedy - Faculty of Mining Engineering, Yazd University, Yazd, Iran
M Shadan - M.sc. student, sediment logy, univ. Of Shahid beheshti

Studying some of isotope elements was the strongest tools in the Geochemistry field. changing the isotope Relativity rate deal may include several reaction. One of the important isotopes is Strontium That studying ratio 87Sr/86Sr in the various periods and called: strontium-isotope stratigraphy (SIS). This method using bivalves shells, rudist, benthic foraminifers and micrites and estimate the Strontium with the fossil in Ancient periods. Determination 87Sr/86Sr about the formations and regions have oil &gas .For example the Asmari calcic depend on define periods and contains of oil. when you were observing the result of experiment about the ratio 87Sr/86Sr and compare the results about two regions , realized the 2th region depend on the other time(for example Cretaceous) and not good oil source .This method confine the place of drilling and economizing in the times and expenses.

Strontium-isotope, Stratigraphy , ratio 87Sr/86Sr, Oil Exploration