GEOL 340 Sedimentology and Stratigraphy
Lecture 31
1. Chemostratigraphy
strontium isotopes
Strontium Isotopes
Radiogenic Fractionation Mechanisms
87Rb = 87Sr + b- + v + Q
b- = beta particle (-) expeled from decay of nuetron
nuetron = proton + electron
v = antinuetrino kinetic energy balancing b-
Q = decay energy
87Sr = 87Sri + 87Rb(elt-1)
Sr easily replaces Ca in CaCO3, so important to carbonate work
Seawater 87Sr/86Sr
a. 86Sr a constant background abundance
b. 87Sr various from different sources according to
amount of Rb
age of the source
c. balanced sources include
young spreading centers and volcanics (low 87Sr/86Sr)
old cratonic sialics (high 87Sr/86Sr)
marine carbonates (moderate to variable 87Sr/86Sr, old seawater)