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Oladimeji akinsile seminar presentation


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The principles application of carbon and oxygen isotope in geological studies . (Paleoceanography, paleoclimatology, Dating, Mineral exploration, etc

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Oladimeji akinsile seminar presentation

  2. 2. PRESENTATION OUTLINE  Introduction  Objectives of the review  Principles and instrumentation  Fractionation processes  Application of carbon and oxygen in geological studies  Selected case studies  Conclusions
  3. 3.  What is isotope ?  Basics of isotope  Stable and unstable isotopes
  4. 4. TABLE 1: ATOMIC WEIGHT OF CARBON(C)) and OXYGEN(O) ISOTOPE ( Walker et al 1989) ELEMENT ISOTOPE ATOMIC WEIGHT(amu) ABUNDANCE (%) CARBON ( 6) 12C 12.00000 98.90 13C 13.00335 1.1 OXYGEN (8) 16O 15.9994 99.76 17O 15.994915 0.04 18O 17.999160 0.20
  5. 5. OBJECTIVES OF THE REVIEW  To discuss the principles and instrumentation involved in the carbon and oxygen isotope.  To discuss the application of carbon and oxygen isotopes in geological studies.
  6. 6. PRINCIPLES Element occur in the earth system in multiple isotopes , both stable and unstable Proportions of stable isotopes in the earth are constant The lighter isotopes (16O , 12C ) are more reactive than heavier isotopes (18O, 13C) In higher temperature,lighter isotopes are preferentially lost.
  7. 7. MEASURING ISOTOPES Prepare sample Introduce sample Convert to gas Flow through GC to seperate CO2 Inject reference gas to IRMS Inject sample to IRMS Figure 1:Schematic diagram of Isotope-ratio mass spectrometer used to measure stable isotope ratios, with gas bench in foreground After Williams, 1998.
  8. 8. ISOTOPE STANDARD  VSMOW – Vienna standard mean ocean water (bunch of ocean water kept in austria) . The standard for the oxygen isotope is 0.002004  PDB- Pee Dee Belemnite – Fossil of a belemnite from the Pee Dee formation in canada . The standard carbon oxygen isotope is 0.011056  CDT- Canyon Diablo Troilite Source: After J. Hoefs (1980) (Stable isotope Geochemistry)
  9. 9. FRACTIONATION PROCESSES This is a reaction or process which selects for one of the stable isotope of a particular elements. If the process selects for the heavier isotope. The reaction product is heavy and vice versa  Types Equilibrum isotope fractionation kinetic isotope fractionation
  10. 10. Calculations It is given as per mil (‰) difference (δ) compared to a standard. For Oxygen isotope this is calculated as For carbon isotope it is calculated as The result is multiplied by 1000 simply to make the resulting ratio more meaningful
  11. 11. APPLICATIONS  Geochronology it is assumed that the atmosphere is in equilibrum with respect to 14C poduced by the cosmic ray flux which is equal to the rate of decay of 14C , so that the abundance in the atmosphere remains constant N = N = Noe-lt Where No is the number of atoms present at t = 0. This is the basic form of the radioactive decay equation. N = number of atoms left t = time when organism from which the sample was taken died Fig 2 : diagram showing the 14C dating curve After Libby and Arnold (1949)
  12. 12.  Paleoenvironment :To distinguish between the sedimentary rocks of marine origin and those deposited in terrestial environment. Fig 3 :Distribution of δ18O and δ13C values in various types of marine carbonates . After milliam, . J. D., 1974)
  13. 13.  Geothermometry – the utility of oxygen isotopes has to do with fractionation that occurs during evaporation and condensation of water and CaCO3 T(°C) = 16.9 – 4.38 (dc –dw) + 0.10(dc-dw)2 where dc = the equilibrum oxygen isotope of calcite dw= oxygen isotopic composition of the water from which the calcite was precipitated  Paleoceanography • Paleoclimate reconstruction Fig 4: Diagram showing δ18O trends in the glacial-interglacial swings in the longterm record cooling of the deep ocean. K.G. Miller et al., Paleoceanography 2, 1, 1987.
  14. 14. Fig 5: Schematic illustration of the relationship between continental glaciations and the 18O content of ocean water during the last 150,00 years . *Note that 18O values become less negative (more heavy oxygen) during stages of continental glaciation and lowered sea level .After Williams et al., 1988
  15. 15.  Hydrothermal ore deposit. This is the large interaction of cooling magma and large volume of meteoric water helps in understanding its origin and related alteration in the country rocks which has a deep seated origin.Low δ13C value of -4 to -12 suggesting deep seated origin. While most carbonates minerals formed early in hydrothermal veins have value of -6 to -9 but those formed in paragnetic sequence are rich in 13C and may have positive value.
  16. 16.  Fossil fuel it can be used to detect fossil fuel contribution to the atmosphere because the burning of fossil fuel has increased the CO2 content of the atmosphere and has caused immeasurably decrease in 13C value because of the enrichment in 12C.
  17. 17. To achieve maximum stratigraphic precision and age control Fig 6: showing carbon isotope stratigraphy of bulk carbonates sediments from deep sea drilling project (After shackleton, N.J and M.A Hall, 1984)
  18. 18. Figure 7: Geological map of dahomey embayment Nigeria part Carbon and oxygen isotopic compositions and diagenesis of the Ewekoro Formation in the eastern Dahomey Basin, southwestern Nigeria O.A Adekeye, S.O Akande. R.B. Bale and , B.D. Erdtmann 2005
  19. 19. Table.2 : Regional Stratigraphic Setting of Dahomey Basin (Modified from Idowu et al., 1993)
  20. 20. Table 3 . Carbon and Oxygen isotopic compositions of the selected Ewekoro Carbonates in Sagamu Quarry Sample No Locations Age Sample description %o PDB δ13C %o PDB δ18O Unaltered oyster shells S-1ai S1aii S3a S13ai S13aii Sagamu quarry Paleocene Unaltered oyster shell 0.86 0.91 0.87 0.59 0.62 -4.46 -4.31 -4.49 -4.51 -4.41 Unaltered sea urchins S1b S3b S13b Sagamu Quarry Paleocene Unaltered sea urchins 1.01 0.14 -0.14 -3.41 -4.12 -4.83 Whole sample S5a S10a S11a S12a S18a S18aii S25a S28a Sagamu Quarry Paleocene Bulk sample -1.39 0.07 -0.23 0.34 - 0.83 - 0.58 - 0.24 - 0.23 -4.77 -4.39 -4.65 -5.37 -5.37 -5.13 -5.06 -5.02 Recrystallized calcite sample S1c S3c S5b S10b S11b S12b S13c S20s Sagamu Quarry Paleocene Recrystallized calcite 0.07 -1.22 -0.80 -1.18 -1.02 0.12 -2.44 -2.26 -4.46 -6.32 -7.34 -7.68 -6.54 -6.24 -7.12 -7.53
  21. 21. Fig 8: Plot showing carbon and oxygen composition in the Ewekoro Formation
  22. 22. RESULT AND INTERPRETATION From the table, it is concluded that the carbon and oxygen isotopic compositions of the carbonate rocks vary from -3.41 ‰ to -7.68 ‰ δ18O PDB and ±1.01 ‰ to -2.44 ‰ δ13C PDB for tertiary sea water suggest that the heavier oxygen and carbon are recorded in the unaltered carbonates and the lighter fractions in the late stage recrystallized carbonates, due to the indicative of isotopic fractionation. Estimated formational paleotemperature for the carbonates vary from 26.650c to 32.520c based on the calculations from and the unaltered carbonates δ18O values indicating only very limited burial and lack of severe hydrothermal alterations .
  23. 23. CASE STUDY TWO • Depositional environment and carbon/oxygen isotopic composition of the Paleocene carbonates exposed around Kalambaina, Sokoto basin, Nigeria O.A Adekeye, S.O Akande, B.D and Erdtmann, B.D (2013) Figure 9: Geological sketch map of northwestern Nigeria showing Kalambaina Formation type locality (modified from Obiosio et al., 1998).
  24. 24. Figure 10: Generalised stratigraphic setting of the Sokoto Basin (modified from Obiosio et al., 1998)
  25. 25. Table 4: showing carbon and oxygen isotopic composition of the selected kalabaina carbonates in kalambaina quarry Carbon and oxygen isotopic composition vary from -5.29%o to -6.55%o δ18O PDB and -1.24%o to -3.40%o PDB δ13C in the whole rock
  26. 26. RESULT AND INTERPRETATION The lighter oxygen and carbon fractions in the samples is a reflection of the depletion of heavier isotope of oxygen and carbon as a result of late stage recrystallization, which suggests that carbonates of the Kalambaina Formation were deposited in shallow marine environment during the Paleocene marine transgression into the Sokoto basin. No evidence of hydrothermal alteration was observed in the carbonates, brings organic rich water with low 13C/12C ratio (δ13C) into the shallow marine water environments of the primary carbonate build up (Marshall, 1992).
  27. 27. Fig 11: Synthetic sedimentological log of Jibou Formation in Rona area and location of samples under study (R1-R46 ) Rona Limestone is a lens shaped body located in the NW of transylvania having a local development. The classic outcrop is located westwards from the neighbourhood of jibou and rona , the deposit has maximum thickness of about 300m,towards the NE, it gradually becomes thinner until it disappears in the area of caselor and Gardbrookes (Popescu, 1984) The age of Rona Limestone is Late Paleocene - Early Eocene (Gheerbrant et al., 1999). GEOLOGICAL BACKGROUND CARBON AND OXYGEN ISOTOPE RATIOS IN RONA LIMESTONE, ROMANIA STELA CUNA1, DANA POP2, ALEXANDRU HOSU2
  28. 28. METHODOLOGY AND RESULT Carbon and oxygen isotope measurements were done on 10 samples and the carbon 13 range from δ13C (-3.12 to -6.78) and δ18O (-9.41 to -14.13) Table 5 : Showing the carbon and oxygen isotopic data
  29. 29. • Table 5: carbon and oxygen isotope ratios in carbonate rocks according to previous references
  30. 30. Fig. 12:Distribution of δ18O vs. δ13C (‰ PDB) values in various types of carbonate rocks, including this study (After Veizer, 1983)
  31. 31. RESULT AND INTERPRETATION The oxygen and carbon isotope data indicate a freshwater depositional environment with the δ13C mean value (-4.96‰ PDB) is, generally, representative for fresh-water carbonates of the Tertiary period.
  32. 32. Conclusion  Isotopic variations in stable and non stable isotopes are often produced by exchange reactions, kinetic reactions in biological system such as evaporation or diffusion. The fractionation of stable isotope decreases with increase in temperature hence stable isotopes show greater fractionation in sedimentary systems than in magamatic rocks.  Carbon and oxygen isotope has a very wide application in geological studies including, the study of igneous, sedimentary and metamorphic rocks, application to temperature (paleothermometry), study of hydrothermal ore deposits, determination of fossil fuel to know the various carbon contents, and to distinguish marine from non marine carbonates.