Isotopic Compositions and Fractionation of Oxygen: Notation, Calculation, and Applications, Slides of Geology

Download Isotopic Compositions and Fractionation of Oxygen: Notation, Calculation, and Applications and more Slides Geology in PDF only on Docsity! 1 Notation for Expressing Isotopic Compositions (abundances) Delta Value (δ) •  Ratios reported relative to a standard in the delta notation expressed as parts per thousand or permil (‰) 10.0‰, = 1.0% R = absolute isotope ratios (heavy/light) 13C/12C 18O/16O d 0 00] g = Rstd Rsamp- Rstd # 1000 d 0 00] g = Rstd Rsamp - 1c m# 1000 Notation for Expressing Oxygen Isotopic Composition (abundances) For example;! •  Rsamp= 18O/16Osamp= 0.0020931! •  Rstd= 18O/16Osamp= 0.0020052! •  ! d18O 0 00] g = 2005.20# 10-6 2009.31# 10-6 - 2005.20# 10-6 # 1000 d18O 0 00] g =2.05 d18O 0 00] g = 18O 16Ostd 18O 16Osamp- 18O 16Ostd # 1000 Docsity.com 2 Notation for Expressing Isotopic (cont.) If Ra > Rstd, δa positive or heavier If δ18Oa = 15.5‰, 18O/16Oa is 1.55% > 18O/16Ostd If Ra < Rstd, δa negative or lighter If δDa = -60‰, D/Ha is 6.0% < D/H std Isotope Fractionation! Redistribution of isotopes of an element among various species or compounds! •  Fractionation factor ( α ) - defines the fractionation associated w/ equilibrium exchange reaction between two substances. αA-B = RA RB 1/3 CaC16O3 + H218O ⇔ 1/3CaC18O3 + H216O For water-calcite 103 ln αCaCO3-H20 = 2.78x106/T2 - 2.79 at 25°C, αCaCO3-H20 = 1.02878 Docsity.com 5 Temperature dependence! fractionation increases w/ lower T! (Erez and Luz, 1983). 103 ln αCaCO3-H20 = 2.78x106/T2 - 2.79 Pelagic Planktonic Foraminifera! Docsity.com 6 •  Lab culturing experiments ∆Orb-H2O = 3.19-0.208T • Plankton Tows & Box Cores, Indian Ocean (20°N-30°S) ∆Orb-H2O = 3.50-0.214T Calibration of Oxygen Isotope Fractionation: Planktonic Foraminifera! Pelagic Benthic Foraminifera! Scale bar (100-250 µm) Docsity.com 7 Calibration of Oxygen Isotope Fractionation : Benthic Foraminifera! • Box Cores • Rio Grande Rise, Norwegian Greenland Sea, E. PacificRise (Belanger et al.,1981, Palaeo3, v.33, p.205-220) C. wullerstorfi Oridorsalis Pyrgo So how are oxygen isotopes used for stratigraphic correlation?! Seawater δ18O frequently changes!! Docsity.com