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Home My WebLink AboutGMC Data Report No. 198 Preliminary results of three apatite fission track analyses of core (4296'-4593') and of cuttings (9500'-12400') from the Union Oil Company of California E de K Leffingwell No.1 well, North Slope, Alaska. r~ GE'~O~Q IA- t ~ ~( ÇI:) 0 Received 22 May 1992 Total of 8 pages in report Alaska Geologic Materials Center Data Report No. 198 1 Preliminary Results of 3 Apatite Fission Track Analyses of Samples From Leffingwell #1, North Slope, Alaska. by Paul B. O'Sullivan and John M. Murphy Department of Geology La Trobe University Bundoora, Victoria 3083 Australia May, 1992 Page 118 2 INTRODUCTION This is a preliminary report of apatite fission track analyses of 3 samples from the Leffingwell #1 well, northern Alaska. The samples were collected by O'Sullivan' and Murphy during the 1991 field season from the Alaska Division of Geological and Geophysical Surveys Geologic Materials Center, Eagle River. Samples were processed and counted by O'Sullivan in the laboratories of the La Trobe University Fission Track Research Group, Melbourne, Australia. Grain mounts used for both age and length data are available from the Alaska Geologic Materials Center. Support for this work was by a grant to the authors from the American Chemical Society - Petroleum Research Fund. A guide to read the information is as follows: 91POS03A IRRADIATION SLIDE NUMBER No Ns Ni Na Ratio U(ppm) RHOs RHOi F.T.AGE (Ma) Chi Squared P(chi squared) Variance of SQR N s/Ni -Sample number and information -In-house number for grouping samples from the same irradiation package -Number of individual mount from irradiation package - Number of each grain counted -Number of spontaneous tracks counted -Number of induced tracks counted -Number of area units counted in grain -Ratio of (NS/NI) for each grain -Uranium concentration of each grain (ppm) -Density of spontaneous tracks (per cm2) -Density of induced tracks (per cm2) - Individual fission track grain ages -Statistical test for determining multiple grain populations -probability of less than 5% indicates multiple grain populations -Statistical comparison of values of NS or NI for all grains -Pooled ratio of (Ns/Ni). Uses total number of spontaneous and induced tracks counted for whole sample. Value used in age calculation if sample is of a single population -Average ratio of (Ns/Ni) for grains -Age calculated using Ns/Ni (single population) -Age calculated using weighted "Mean Ratio" (multiple populations; fail Chi-Squared test) The track length distributions for each sample are shown on histograms showing the relative Mean Ratio POOLED AGE CENTRAL AGE numbers of tracks measured in a particular class-interval. Analytical data including age data, mean confined track lengths, standard deviations and the total number of tracks measured for each sample are in Table 1. GMC Data Report No. 198 Page 2/8 3 TECHNIQUES Apatites (and zircons) were separated from samples by conventional heavy liquid and magnetic techniques. The apatite separates were mounted in epoxy resin on glass slides, ground and polished to expose internal surfaces of the grains, then etched in 5M Nitric acid to reveal the fossil fission tracks. Neutron irradiations were carried out in a well thennalized neutron flux in the Australian Atomic Energy Commissions HIFAR reactor. Thennal neutron fluences were monitored by counting tracks recorded in external muscovite detectors attached to NBS standard glass- SRM612. Fission tracks in each mount were counted in transmitted light using a dry 80x objective at a total magnification of 1250x. Wherever possible 20-25 grains were counted on each mount. For further description of fission track counting methodology see Moore et al. (1986) and Green (1986). Fission track ages were calculated using the zeta calibration method and standard fission track age equation (Hurford and Green, 1982). Errors were calculated using the techniques of Green (1981). In samples with a significant spread in single grain ages, the "conventional analysis", (as defined by Green 1981), based purely on Poissonian variation, is not valid. In such cases, which can be detected by the Chi squared statistical test (Galbraith, 1981), the central age is reported (Galbraith, in press). The Chi squared statistic indicates the probability that all grains counted belong to a single population of ages. A probability of less than 5% is evidence of a asymmetric spread of single grain ages. An asymmetric spread in individual grain ages can result either from inheritance of detrital grains from mixed detrital source areas, or from differential annealing in grains of different compositions (Green et al. 1989). Lengths of confined ttacks (Lal et al. 1969) were measured using the procedure outlined by Green (1986) and Green (1989). Only fully-etched and horizontal "confined tracks" were measured (Laslett et al. 1982) in grains with polished surfaces parallel to prismatic crystal faces. Measurements were made under similar conditions as those employed for age determination (e.g. 1250x, dry objective). The lengths of suitable tracks were measured using a projection tube and a HipadTM digitizing tablet calibrated using a stage micrometer (with µm divisions). Table 2 shows the number of tracks per class-interval used in plotting each track length distribution histogram. GMC Data Report No. 198 Page 3/8 Page 4/8 GMC Data Report No. 198 Table 2. Track length data: Leffingwell #1 Sample Track Length Range (µm) Number <5 5-6 6-7 7-8 8·99-10 10-1111-12 12-13 13-14 14-15 15-16 16-17 >17 POS05A - - - - 3 3 5 13 23 30 19 3 1 POS03A - - 1 - 5 3 7 8 4 2 1 POS04A - - - - 2 7 4 3 3 2 Length measurements by P. O'Sullivan Table 1. Apatite fission track analytical results: Leffingwell #1 Sample Number Standard Fossil Induced Chi Fission Uranium Number of track track track square track (ppm) grains density density density probability age (x106cm-2) (xI05cm-2)(xI06cm-2) (%) (Ma) 1.406 3.859 1.271 5.3 74.8 ± 5.5 (3164) (265) (873) 1.406 2.802 93.54 (3164) (118) (394) 1.406 1.724 62.98 (3164) (72) (263) Brackets show number of tracks counted. Standard and induced track densities measured on mica external detectors (g=0.5), and fossil track densities on internal mineral surfaces. * Central age, used where pooled data fail 02 test at 5%. Errors quoted at ±Is. Ages for samples calculated using z=352.7 for dosimeter glass SRM612. Samples listed by depth from top to bottom. 1.49 1.68 1.54 Standard deviation (µm) 4 Mean track length (µm) 12.89 ± 0.15 (100) 10.68 ± 0.30 (31) 10.60 ± 0.33 (21) 5.9 67.5 ± 9.1 98.4 91POS04A 20 8.7 73.8 ± 7.9 100 91POS03A 25 11.8 9IPOS05A 25 SAMPLE RESULTS 5 REFERENCES Galbraith, R.F. (1981). On statistical models for fission track counts. Mathematical Geology, v. 13: 471-488. Green, P.F. (1981). A new look at statistics in fission track dating. Nuclear Tracks 5: 77-86. Green, P.F. (1986). On the thermo-tectonic evolution of Northern England: evidence from fission track analysis. Geology, v. 5: 493-506. Green, P.P. (1989). Thermal and tectonic histoX)' of the East Midlands shelf (onshore UK) and surrounding regions assessed by apatite fission track analysis. Journal of the London Geological Society, v. 146: 755-773. Green, P.F., Duddy, LR., Laslett, G.M., Hegarty, K.A., Gleadow, A.J.W., and Lovering, J.F. (1989). Thermal annealing of fission tracks in apatite 4. Qualitative modelling techniques and extensions to geological timescales. Chemical Geology (Isotope Geoscience Section), v. 79: 155-182. Hurford, A.J. and Green, P.P. (1982). A users' guide to fission-track dating calibration. Earth and Planetary Science Letters, v. 59: 343-354. Hurford, A.J. and Green, P.F. (1983). The zeta age calibration of fission track dating. Isotope Geoscience 1: 285-317 Lal, D., Rajan, R.S. and Tamhane, A.S. (1969). Chemical composition of nuclei of Z > 22 in cosmic rays using meteoric minerals as detectors. Nature, v. 221: 33-37. Laslett, G.M., Kendall, W.S., Gleadow, A.J.W. and Duddy, I.R. (1982). Bias in measurement of fission track length distributions. Nuclear Tracks 6: 79-85. Moore, M.E., Gleadow, A.J.W. and Lovering, J.F. (1986). Thennal evolution of rifted continental margins: new evidence from fission tracks in basement apatites from southeastern Australia. Earth and Planetary Science Letters, v. 78: 255-270. GMC Data Report No. 198 Page 5/8 Page 6/8 .j,~, ~ 10 U 20 TRACK LENGTH (microns) 5A F. T. AGE (Ma) 64.9 ± 32.7 67.3 ± 31.0 54.9 ± 30.4 110.0 ± 16.2 0.0 ± 0.0 49.4 ± 38.3 61.7 ± 30.9 0.0 ± 0.0 183.3 ± 140.1 114.7 ± 52.6 75.0 ± 32.4 61.7 ± 48.8 96.3 ± 37.9 35.3 ± 16.9 40.4 ± 7.4 122.8 ± 75.2 70.5 ± 25.3 103.3 ± 27.0 140.2 ± 62.2 132.9 ± 45.9 105.4 ± 51.5 62.8 ± 13.4 54.9 ± 42.9 98.4 ± 36.9 77.0 ± 39.5 6 fl. 200 10- 20 - 40 - N 30 - 4 - l 2 ~ ~I;;i; ~¡¡¡¡"'~ o :Yrmmm..... mmh..........1 o 50 100 150 FISSION TRACK AGE (Ma) 6 - SA 8 - GMC Data Report No. 198 . ~c; -60 ·1 . ·2 - . _ 100 . . -"",¡o I .... · +2 - 0'" +1 . _ 125 150 '90 i1E.QSQ.~A--AfA~2.i§::. !~U' POOLED AGE = 74.8 ± 5.5 Ma CENTRAL AGE = 78.0 ± 7.8 Ma Ages calculated using a zeta of 352.7 ± 5 for SRM612 glass Rho D = 1.406E+06cm-2; ND = 3164 RHOi 1.056E+06 6.790E+05 6.667E+05 4.691E+06 3.704E+05 4.444E+05 3.527E+05 4.630E+04 1.481E+05 8.333E+05 4.259E+05 4.444E+05 1.065E+06 1.296E+06 6.605E+06 2.778E+05 2.431E+06 1.984E+06 4.321E+05 1.778E+06 4.321E+05 4.074E+06 1.852E+05 9.259E+05 8.889E+05 1.271E+06 Ns/Ni = 0.304 ± 0.021 Mean Ratio = 0.322 ± 0.035 Chi Squared = 36.135 with 24 degrees of freedom P( chi squared) = 5.3 % Correlation Coefficient = 0.856 Variance of SQR(Ns) = 3.13 Variance of SQR(Ni) = 10.01 Age Dispersion = 25.076 % RATIO U (ppm) RHOs 0.263 9.8 2.778E+05 0.273 6.3 1.852E+05 0.222 6.2 1.481E+05 0.447 43.7 2.099E+06 0.000 3.4 O.OooE+OO 0.200 4.1 8.889E+04 0.250 3.3 8.818E+04 0.000 0.4 O.ooOE+oo 0.750 1.4 1.111E+05 0.467 7.8 3.889E+05 0.304 4.0 1.296E+05 0.250 4.1 1.111E+05 0.391 9.9 4.167E+05 0.143 12.1 1.852E+05 0.164 61.5 1.080E+06 0.500 2.6 1.389E+05 0.286 22.6 6.944E+05 0.420 18.5 8.333E+05 0.571 4.0 2.469E+05 0.542 16.6 9.630E+05 0.429 4.0 1.852E+05 0.255 38.0 1.037E+06 0.222 1.7 4.115E+04 00400 8.6 3.704E+05 0.312 8.3 2.778E+05 11.8 3.859E+05 Area of basic unit = .0??oo09 cm-2 91POS05A - 4296'-4593' IRRADIATION LU194 SLIDE NU1v1BER 6 COUNTED BY: P. O'Sullivan No. Ns Ni Na 1 5 19 20 2 6 22 36 3 4 18 30 4 68 152 36 5 0 4 12 6 2 10 25 7 5 20 63 8 0 1 24 9 3 4 30 10 7 15 20 11 7 23 60 12 2 8 20 13 9 23 24 14 5 35 30 15 35 214 36 16 4 8 32 17 10 35 16 18 21 50 28 19 8 14 36 20 13 24 15 21 6 14 36 22 28 110 30 23 2 9 54 24 10 25 30 25 5 16 20 265 873 AFTA DATA FROM LEFFINGWELL #1 Page 7/8 10. .n 1, \ . 5 10 15 20 TRACK LENGTH (mlcro~) s 3A F.T. AGE (Ma) 82.1 ± 54.8 61.7 ± 69.0 49.4 ± 38.3 65.8 ± 37.0 243.3 ± 344.1 60.6 ± 18.1 243.3 ± 344.1 105.4 ± 72.8 49.4 ± 54.1 243.3 ± 243.4 75.8 ± 43.4 49.4 ± 38.3 49.4 ± 54.1 92.3 ± 62.5 61.7 ± 48.8 76.8 ± 20.2 243.3 ± 344.1 82.1 ± 54.8 49.4 ± 31.3 74.7 ± 27.0 95.7 ± 42.7 53.7 ± 26.5 80.8 ± 20.9 82.1 ± 47.5 82.1 ± 67.1 7 \ 200 20 . 40 . N 30 - "'J - .. .. 4 .. .. .. 2 - ~t!!f:~!m~ 0'-- LI...........m~ I o 50 100 150 R SSla.I TRACK AGE (M1) 6 - 3A 8 - GMC Data Report No. 198 -so ·1 . ·2 - _90 ". . . \. . , to. . +1 . o - _ 125 +2 - 250 ~ ~ 200 _ 165 il~¡A--AfAIIlL-i~,2~:; lU,2,2' Ages calculated using a zeta of 352.7 ± 5 for SRM612 glass Rho D = 1.406E+06cm-2; ND = 3164 POOLED AGE = 73.8 ± 7.9 Ma CENTRAL AGE = 73.8 ± 7.9 Ma RHOi 5.000E+05 4.444E+05 1.235E+06 8.333E+05 7.407E+04 2.639E+06 5.291E+04 5. 185E+05 2.315E+05 2.469E+05 8.025E+05 9.259E+05 1.852E+05 7.407E+05 4.444E+05 2.711E+06 6.944E+04 3.333E+05 2.083E+06 1.222E+06 9.524E+05 1.420E+06 2. 824E+06 4.762E+05 7.407E+05 9.354E+05 NsjNi = 0.299 ± 0.031 Mean Ratio = 0.400 ± 0.055 Chi Squared = 7.307 with 24 degrees of freedom P(chi squared) = 100.0 % Correlation Coefficient = 0.979 Variance of SQR(Ns) = 1.02 Variance of SQR(Ni) = 3.88 Age Dispersion = 0.000 % (did not converge) RATIO U (ppm) RHOs 0.333 4.7 1.667E+05 0.250 4.1 1.111E+05 0.200 11.5 2.469E+05 0.267 7.8 2.222E+05 1.000 0.7 7.407E+04 0.246 24.6 6.481E+05 1.000 0.5 5.291E+04 0.429 4.8 2.222E+05 0.200 2.2 4.630E+04 1.000 2.3 2.469E+05 0.308 7.5 2.469E+05 0.200 8.6 1.852E+05 0.200 1.7 3.704E+04 0.375 6.9 2.778E+05 0.250 4.1 1.111E+05 0.311 25.3 8.444E+05 1.000 0.6 6.944E+04 0.333 3.1 1.111E+05 0.200 19.4 4.167E+05 0.303 11.4 3.704E+05 0.389 8.9 3.704E+05 0.217 13.2 3.086E+05 0.328 26.3 9.259E+05 0.333 4.4 1.587E+05 0.333 6.9 2.469E+05 8.7 2.802E+05 Area of basic unit = .00??oo9 cm-2 91POS03A - 9500'-10200' IRRADIATION LU194 SLIDE NUMBER 4 COUNTED BY: P. O'Sullivan No. Ns Ni Na 1 3 9 20 2 1 4 10 3 2 10 9 4 4 15 20 5 1 1 15 6 14 57 24 7 1 1 21 8 3 7 15 9 1 5 24 10 2 2 9 11 4 13 18 12 2 10 12 13 1 5 30 14 3 8 12 15 2 8 20 16 19 61 25 17 1 1 16 18 3 9 30 19 3 15 8 20 10 33 30 21 7 18 21 22 5 23 18 23 20 61 24 24 4 12 28 25 2 6 9 118 394 Page 8/8 GMC Data Report No. 198 :: : r 1., . . 1. . 5 10 15 20 TRACK LENGTH (micron.) FISSION TRACK AGE (Ma 50 300 ~:::¡ 2 ¡ ¡¡¡¡¡;::m1 I : :~:::...... 150 200 00' 50100 - 40 ·1 . ·2 - 4 - ~80 . . to . .. ... 0- +1 . +2 - 30 - 6 - 250 200 - _ 160 _ 125 4A 40 - N 4" 8 - il~!A---AeA~lZ~~~12!~~~ POOLED AGE = 67.S ± 9.1 Ma CENTRAL AGE = 67.5 ± 9.1 Ma Ages calculated using a zeta of 352.7 ± 5· for SRM612 glass Rho D = 1.406E+06cm-2; ND = 3164 NsjNi = 0.274 ± 0.036 Mean Ratio = 0.352 ± 0.066 Chi Squared = 8.246 with 19 degrees of freedom P(chi squared) = 98.4 % Correlation Coefficient = 0.971 Variance of SQR(Ns) = 1.09 Variance of SQR(Ni) = 3.35 Age Dispersion = 0.000 % (did not converge) Area of basic unit = .0000009 cm-2 IRRADIATION LU194 SLIDE NUMBER 5 COUNTED BY: P. O'Sullivan No. Ns Ni Na RATIO U (ppm) RHOs RHOi F.T. AGE (Ma) 1 4 15 16 0.267 9.7 2.778E+05 1.042E+06 65.8 ± 37.0 2 1 1 16 1.000 0.6 6.944E+04 6. 944E+04 243.3 ± 344.1 3 9 35 9 0.257 40.3 1.111E+06 4.321E+06 63.4 ± 23.8 4 1 1 16 1.000 0.6 6.944E+04 6.944E+04 243.3 ± 344.1 5 3 8 15 0.375 5.5 2.222E+05 5.926E+05 92.3 ± 62.5 6 1 6 12 0.167 5.2 9.259E+04 5.556E+05 41.2 ± 44.5 7 1 1 25 1.000 0.4 4.444E+04 . 4.444E+04 243.3 ± 344.1 8 2 8 15 0.250 5.5 1.481E+05 5.926E+05 61.7 ± 48.8 9 5 22 30 0.227 7.6 1.852E+05 8. 148E+05 56.1 ± 27.8 10 20 65 30 0.308 22.4 7.407E+05 2.407E+06 75.8 ± 19.5 11 3 8 40 0.375 2.1 8.333E+04 2.222E+05 92.3 ± 62.5 12 7 19 70 0.368 2.8 1.111E+05 3.016E+05 90.7 ± 40.2 13 0 1 16 0.000 0.6 O.oooE+OO 6.944E+04 0.0 ± 0.0 14 7 29 48 0.241 6.3 1.620E+05 6.713E+05 59.6 ± 25.1 15 1 6 16 0.167 3.9 6.944E+04 4. 167E+05 41.2 ± 44.5 16 0 11 16 0.000 7.1 O.OooE+oo 7.639E+05 0.0 ± 0.0 17 3 9 20 0.333 4.7 1.667E+05 5.000E+05 82.1 ± 54.8 18 1 4 12 0.250 3.4 9.259E+04 3.704E+05 61.7 ± 69.0 19 2 10 30 0.200 3.4 7.407E+04 3.704E+05 49.4 ± 38.3 20 1 4 12 0.250 3.4 9.259E+04 3.704E+05 61.7 ± 69.0 72 263 5.9 1.724 E+05 6.298E+05 91POS04A - 11700'·12400' g.