Research ArticleGEOCHEMISTRY

Nitrogen isotope ratios trace high-pH conditions in a terrestrial Mars analog site

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Science Advances  26 Feb 2020:
Vol. 6, no. 9, eaay3440
DOI: 10.1126/sciadv.aay3440

Figures

  • Fig. 1 Map showing the location of the Ries crater and the Nördlingen 1973 drill hole.

    Adapted from Arp et al. (8).

  • Fig. 2 Stratigraphic trends in the Nördlingen 1973 drill core.

    Orange shading indicates inferred hyperalkaline interval with coinciding high modeled pH and high δ15N, δ18Ocarb, δ13Ccarb, and TOC, scarcity of macrofauna, and abundant diagenetic zeolite minerals. Lithostratigraphy is taken from Füchtbauer et al. (10), δ18Ocarb and δ13Ccarb are taken from Rothe and Hoefs (12), and the pH model is taken from Arp et al. (8). Diatom abundances are according to Schauderna (45).

  • Fig. 3 Carbon-nitrogen scatterplots.

    (A) Covariance between TOC and TN. (B) Covariance between TN δ15N. (C) Lack of covariance between molar organic carbon to TN ratios and δ15N indicating absence of metamorphic alteration.

  • Fig. 4 Model calculations and nitrogen behavior.

    (A) Model calculation of glass dissolution in nearly pure water with either fixed atmospheric Pco2 (buffered) or progressively consumed CO2 (not buffered). The latter simulates a water-glass reaction in the subsurface (see Materials and Methods for details on input parameters). (B) Model calculation of evaporation of fluid after reaction with 0.4 g of glass from (A) and in constant equilibrium with atmospheric CO2. Both scenarios of (A) result in the same evaporation effect because the load of dissolved solids is the same. (C) pH relationship of ammonium (NH4+) and ammonia (NH3) at standard pressure and temperature. (D) Isotopic effect of NH3 volatilization on residual dissolved NH4+ for kinetic and equilibrium fractionation models.

Tables

  • Table 1 Geochemical data from core Nördlingen 1973.

    Average reproducibility for δ15N and δ13Corg are 0.4‰ (1 SD) and 0.1‰, respectively. Average relative errors (1 SD/mean) are 6.5% for TN and 4.4% for TOC. Notes highlight enrichment in organic carbon. n.d., not determined.

    Depth (m)Notesδ15N (‰)δ13Corg (‰)TN (wt %)TOC (wt %)
    Claystone member (centimeter-scale laminated mud, dark gray)
    21.557.47−23.230.040.88
    27.555.86−24.410.071.01
    28.555.21−27.230.101.68
    29.555.65−26.490.071.13
    32.957.31−28.250.090.95
    35.955.92−28.030.090.87
    37.95Coal seam6.31−28.610.5923.46
    38.957.23−24.180.174.37
    43.586.62−24.610.080.99
    49.16.64−26.370.121.87
    Marl member (calcareous pale gray mudstone, massive to centimeter-scale bedding)
    52.18.63−25.090.163.36
    55.17.39−25.450.142.56
    58.17.84−25.180.080.77
    59.18.09−25.420.060.82
    63.19.35−27.960.121.21
    65.19.10−27.620.162.51
    788.43−23.880.243.87
    85.79.63−27.140.142.43
    88.78.11−27.100.110.95
    95.57.99−26.410.101.54
    98.59.20−26.100.122.32
    105.510.65−26.170.162.39
    106.510.02−29.330.172.96
    107.59.35−26.380.162.46
    109.59.75−27.180.163.02
    Laminite member (millimeter-scale plane laminated mudstone, carbonaceous to bituminous)
    111.59.24−27.460.172.32
    113.59.96−25.570.132.59
    118.59.29−27.960.143.14
    121.510.68−27.140.143.00
    125.57.91−26.810.225.88
    127.5Bituminous13.33−29.190.4820.44
    134.511.65−23.530.368.32
    140.510.70−29.290.348.50
    146.510.20−27.420.245.42
    152.511.23−20.860.296.00
    154.5Bituminous10.80−11.960.4415.56
    158.510.57−22.120.235.05
    162.510.85−21.140.213.43
    166.510.31−21.700.182.70
    170.511.58−19.640.255.33
    171.511.95−19.100.388.65
    173.5Bituminous11.25nd0.3131.82
    174.5Bituminous11.08nd0.2814.84
    176.511.94nd0.265.96
    177.5Bituminous13.12−16.620.4419.30
    178.511.86−21.230.244.51
    182.511.10−21.620.305.37
    183.512.42−22.070.275.21
    185.5Bituminous12.78−21.260.5514.96
    186.5Bituminous12.72−30.840.377.57
    188.5Bituminous13.52−21.990.439.39
    191.5Bituminous11.42−21.480.5310.50
    192.5Bituminous12.85−22.900.4313.90
    195.5Bituminous12.20−19.650.3813.98
    198.513.53−23.660.415.28
    202.512.34−27.380.656.62
    204.5Bituminous12.46−24.650.7812.58
    206.512.73−23.910.324.21
    209.513.66−24.030.304.14
    211.514.48−24.160.223.05
    212.514.38−24.200.589.36
    214.513.13−22.350.333.84
    215.512.63−22.570.302.95
    218.513.05−22.720.495.39
    226.510.91−25.470.826.64
    228.5Bituminous13.73−25.760.6111.98
    230.5Bituminous15.24−26.840.6113.50
    232.514.19−24.360.334.85
    233.514.46−24.320.344.71
    234.516.09−25.090.356.87
    236.513.67−34.000.303.14
    237.514.56−24.310.254.85
    239.5Bituminous14.39−24.940.4411.00
    241.5Bituminous17.47−23.030.5913.98
    245.5Bituminous13.60−27.990.4312.66
    248.5Bituminous11.60−26.440.4313.99
    252.5Bituminous10.95−26.090.1910.68
    254.54.29−26.730.123.85
    Basal member (sandstone with interlaminated carbonaceous mudstone)
    258.53.82−26.710.113.72
    260.54.73−35.970.134.45
    261.56.64−27.030.105.20

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