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松辽盆地白云岩沉积环境及成因机理

付秀丽 蒙启安 文政 白月 高波 苏杨鑫

付秀丽, 蒙启安, 文政, 白月, 高波, 苏杨鑫. 松辽盆地白云岩沉积环境及成因机理[J]. 沉积学报, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018
引用本文: 付秀丽, 蒙启安, 文政, 白月, 高波, 苏杨鑫. 松辽盆地白云岩沉积环境及成因机理[J]. 沉积学报, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018
FU XiuLi, MENG QiAn, WEN Zheng, BAI Yue, GAO Bo, SU YangXin. Sedimentary Environment and Genetic Mechanism of Dolomites in the Qingshankou Formation, Songliao Basin[J]. Acta Sedimentologica Sinica, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018
Citation: FU XiuLi, MENG QiAn, WEN Zheng, BAI Yue, GAO Bo, SU YangXin. Sedimentary Environment and Genetic Mechanism of Dolomites in the Qingshankou Formation, Songliao Basin[J]. Acta Sedimentologica Sinica, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018

松辽盆地白云岩沉积环境及成因机理

doi: 10.14027/j.issn.1000-0550.2022.018
基金项目: 

中国石油重大科技专项 2021ZZ10

详细信息

Sedimentary Environment and Genetic Mechanism of Dolomites in the Qingshankou Formation, Songliao Basin

Funds: 

Major Science and Technology Special Project of CNPC, No. 2021ZZ10 2021ZZ10

  • 摘要: 目的 湖相白云岩是松辽盆地发现的一种特殊油气储层类型,为了探讨其沉积环境及成因机理,开展了白云岩宏微观特征及环境参数研究。 方法 通过野外剖面及岩心观察、微观组构观测和元素、同位素组成等多指标综合研究,分析了松辽盆地白云岩的沉积环境及其成因机理。 结果 松辽盆地湖相区白云岩主要为泥晶白云岩,矿物成分主要为铁白云石、黏土和方解石,厚1~25 cm,呈层状或透镜状分布于厚层湖相泥页岩中,具有δ13C值偏正、氧同位素δ18O值偏负、稀土元素δEu明显负异常、热液营养物质Ca、Si、Fe、Mg、Al、Na丰富等显著特征,推测其先期为产甲烷细菌成因的原生白云岩,后期受到热液作用改造,形成于相对干燥气候条件下的咸水湖泊环境。 结论 湖相区白云岩沉积环境及成因机理分析对于研究松辽盆地沉积演化和储层评估具有重要意义。
  • 图  1  松辽盆地构造位置[13]

    Ⅰ. Qijia⁃Gulong Sag; II. Daqing placanticline; III. Sanzhao Sag

    图  2  松辽盆地(a)及青山口组(b)地层综合柱状图

    K2qn. Qingshankou Formation; K2y. Yaojia Formation; K2qn1. First member of the Qingshankou Formation; K2qn2. Second member of the Qingshankou Formation; K2qn3. Third member of the Qingshankou Formation; K2y1. First member of the Yaojia Formation

    图  3  白云岩分布特征野外地质剖面

    图  4  不同类型白云岩岩心特征

    (a) argillaceous dolomite, well A2, 2 351.2 m, lenticular distribution; (b) argillaceous dolomite, well A2, 2 313.7 m, distributed in layers

    图  5  不同类型白云岩微观特征

    (a⁃d) are orthogonal light, single polarized light, fluorescence, and cathodoluminescence of lenticular dolomite, respectively; (e⁃h) are orthogonal light, single polarized light, fluorescence, and cathodoluminescence of layered dolomite, respectively

    图  6  泥晶白云岩薄片及场发射电镜微观特征(A2井)

    (a) lenticular micritic dolomite, 2 351.2 m, single polarization; (b) lenticular micritic dolomite, 2 351.2 m, field emission scanning electron microscope; (c) layered micritic dolomite, 2 313.7 m, distributed in layers, single polarization; (d) layered micritic dolomite, 2 313.7 m, distributed in layers, field emission scanning electron microscope

    图  7  青山口组湖相区白云岩常量元素分布饼状图

    图  8  白云岩微量元素平均值含量直方图(样品数N=52)

    图  9  青山口组泥晶白云岩稀土元素散点图

    图  10  松辽盆地青山口组白云岩稀土元素配分模式及特征

    The abscissa in the lower figure corresponds to a total of 21 samples from A3⁃155 to A3⁃269 in attached table 5 from left to right

    图  11  松辽盆地青山口组构造活动岩心照片

    (a) well B4, K2qn1,volcanic ash, 1 982.01 m; (b) well B2, K2qn1, 2 386.00 m; volcanic ash; (c) well B3, K2qn2, 1 995.58 m, sliding rock; (d) well B1, K2qn2, 2 189.60⁃2 190.20 m, seismolite

    图  12  松辽盆地青山口组、嫩江组及国内其他盆地白云岩碳氧同位素组成与沉积环境分析

    表  附表1  全岩矿物分析表(%)

    样品编号深度/m地区层位岩性描述石英钾长石斜长石方解石铁白云石黏土矿物黄铁矿菱铁矿
    A3-1602 179.80古龙凹陷青二段泥晶白云岩14.403.0078.83.800
    A3-1612 180.30古龙凹陷青二段泥晶白云岩14.706.21.964.311.11.80
    A3-1712 189.70古龙凹陷青二段泥晶白云岩9.401.8082.46.400
    A3-1782 199.90古龙凹陷青一段泥晶白云岩11.507.1056.721.32.80.7
    A3-1832 206.20古龙凹陷青一段泥晶白云岩18.706.9063.610.700
    A3-1932 216.00古龙凹陷青一段泥晶白云岩17.107.3057.516.81.40
    A3-2432 256.90古龙凹陷青一段泥晶白云岩26.201.6060.310.51.40
    A1-32 471.50古龙凹陷青二段泥晶白云岩4.104.40.487.53.700
    A1-42 484.50古龙凹陷青二段泥晶白云岩1.101.7094.92.300
    A1-52 486.20古龙凹陷青二段泥晶白云岩3.201.7092.03.200
    A1-62 487.20古龙凹陷青二段泥晶白云岩8.804.3076.67.52.70
    A1-72 490.50古龙凹陷青二段泥晶白云岩3.202.5091.23.000
    A1-82 493.60古龙凹陷青二段泥晶白云岩14.608.73.360.69.82.40.7
    A1-92 525.20古龙凹陷青一段泥晶白云岩6.103.11.174.312.62.70
    A1-102 542.80古龙凹陷青一段泥晶白云岩7.202.70.976.910.61.70
    A1-112 545.80古龙凹陷青一段泥晶白云岩0.701.30.296.61.200
    A1-122 550.40古龙凹陷青一段泥晶白云岩14.802.43.568.510.800
    A1-132 554.00古龙凹陷青一段泥晶白云岩10.301.40.481.06.900
    A1-142 562.60古龙凹陷青一段泥晶白云岩2.801.3092.42.51.00
    A1-152 570.30古龙凹陷青一段泥晶白云岩13.503.21.269.011.41.70
    A5-11 593.90三肇凹陷青一段泥晶白云岩23.001.9067.47.600
    A5-21 596.90三肇凹陷青一段泥晶白云岩3.602.8086.65.81.20
    A5-31 601.90三肇凹陷青一段泥晶白云岩15.308.3060.114.22.10
    A5-41 604.70三肇凹陷青一段泥晶白云岩11.303.4075.79.500
    A5-51 636.40三肇凹陷青一段泥晶白云岩24.506.6052.116.700
    A5-61 640.30三肇凹陷青一段泥晶白云岩18.502.7069.39.500
    A4-11 805.40三肇凹陷青一段泥晶白云岩7.103.90806.22.70
    A4-21 826.90三肇凹陷青一段泥晶白云岩15.703.0069.710.11.60
    A4-31 870.10三肇凹陷青一段泥晶白云岩27.801.9061.58.700
    下载: 导出CSV

    表  附表2  常量元素分析数据表(%)

    样品编号深度/m岩性SiO2Al2O3Fe2O3CaOMgOK2ONa2OTiO2P2O5MnO
    A3-1552 174.17泥晶白云岩5.612.237.3929.7213.360.440.290.110.140.38
    A3-1582 177.36泥晶白云岩8.102.899.7827.6312.070.400.340.100.190.28
    A3-1602 179.80泥晶白云岩15.332.267.1825.8212.070.220.440.080.210.21
    A3-1642 181.93泥晶白云岩20.236.438.0421.679.171.201.040.261.400.29
    A3-1712 189.70泥晶白云岩16.822.938.8224.8311.320.310.350.090.220.29
    A3-1752 195.59泥晶白云岩26.116.448.8919.638.891.120.790.230.460.27
    A3-1832 206.17泥晶白云岩19.893.867.4623.6110.360.640.500.130.440.28
    A3-1932 216.01泥晶白云岩15.874.878.1323.7811.120.910.460.180.190.32
    A3-1972 219.64泥晶白云岩37.6012.166.9311.296.842.371.000.430.130.14
    A3-2032 227.04泥晶白云岩19.8717.944.0131.2012.013.671.560.600.080.05
    A3-2062 229.58泥晶白云岩19.7618.734.4130.5311.873.771.630.650.100.03
    A3-2082 230.89泥晶白云岩18.6618.484.4330.8611.853.781.620.640.160.05
    A3-2172 238.29泥晶白云岩15.0017.764.8832.5112.893.691.240.590.140.06
    A3-2192 239.58泥晶白云岩23.444.668.2519.8911.150.330.240.100.050.21
    A3-2232 242.09泥晶白云岩19.0617.684.4530.6911.963.231.870.600.110.03
    A3-2272 245.36泥晶白云岩2.341.265.8428.6217.000.230.180.060.260.16
    A3-2292 247.04泥晶白云岩9.183.126.9225.7314.610.180.180.080.150.14
    A3-2432 256.85泥晶白云岩24.125.307.6420.619.750.930.320.180.120.25
    A3-2562 265.97泥晶白云岩27.995.596.2419.3210.040.910.300.170.160.20
    A3-2692 275.36泥晶白云岩7.311.353.2131.1314.890.160.150.040.140.28
    平均值17.617.806.6425.4511.661.420.720.270.240.20
    下载: 导出CSV

    表  附表3  微量元素及其分析表

    样品编号岩性深度/mSrBaLiBeBScVCrCoNiCuZnGaThUw(Sr)/w(Ba)w(Th)/w(U)
    A3-155泥晶白云岩2 174.17843.90213.4013.761.2215.086.9465.8240.142.7816.747.2822.243.312.191.113.951.98
    A3-158泥晶白云岩2 177.36787.60211.3024.351.0613.995.9089.6823.233.3213.077.6126.394.101.781.463.731.22
    A3-160泥晶白云岩2 179.80885.00198.0024.170.5810.962.4554.3212.971.906.824.2220.252.460.990.924.471.07
    A3-164泥晶白云岩2 181.93988.801 134.0021.041.4329.368.9160.5729.305.8113.4214.3259.698.905.974.750.871.26
    A3-169泥晶白云岩2 187.26305.00297.4043.253.1171.418.65100.9041.1222.0840.0842.38125.7019.049.525.531.031.72
    A3-171泥晶白云岩2 189.70939.90561.4031.650.9010.234.5264.2514.242.398.785.0119.073.541.490.881.671.69
    A3-175泥晶白云岩2 195.59659.60382.9039.801.6623.725.4184.5831.215.1815.4515.0750.829.724.532.921.721.55
    A3-183泥晶白云岩2 206.17836.70248.2022.560.8119.983.1545.4316.262.809.997.6824.134.712.371.113.372.13
    A3-193泥晶白云岩2 216.011 065.00253.7029.761.1722.434.1043.1237.674.7219.1613.5739.537.203.631.794.202.03
    A3-197泥晶白云岩2 219.64711.70324.2068.592.2540.055.8396.9646.5011.2726.9232.2872.9115.527.474.302.201.74
    A3-203泥晶白云岩2 227.04215.50248.9061.083.0181.037.95128.3048.5714.8032.7439.11132.2020.428.702.660.873.26
    A3-206泥晶白云岩2 229.58358.10270.5054.093.0779.0110.18124.8045.1612.4830.1137.10114.9020.6510.104.051.322.49
    A3-208泥晶白云岩2 230.89416.70272.8049.193.2394.5010.31138.2057.1214.2328.0243.22123.4022.048.713.791.532.30
    A3-217泥晶白云岩2 238.29427.40224.9057.023.67147.7012.55147.7061.6814.7032.5644.33129.7022.818.893.561.902.50
    A3-219泥晶白云岩2 239.581 145.00235.4096.790.73104.703.8743.4227.688.0320.647.8751.695.131.431.094.861.31
    A3-223泥晶白云岩2 242.09276.40203.1089.853.6370.4110.58130.3056.6511.5328.0036.06133.0023.386.082.251.362.71
    A3-227泥晶白云岩2 245.361 562.00221.0017.600.8312.662.3251.1738.213.4915.484.5216.961.660.810.757.071.08
    A3-229泥晶白云岩2 247.041 335.00205.7065.550.9299.706.7154.4133.764.1516.986.8423.633.291.011.156.490.88
    A3-243泥晶白云岩2 256.85860.10176.4049.171.2515.795.5266.1728.394.4013.1710.7942.746.142.061.234.881.67
    A3-256泥晶白云岩2 265.97174.40143.6075.523.0556.529.49114.0047.6511.8831.0136.10110.5020.195.772.051.212.82
    A3-269泥晶白云岩2 275.36170.00121.1087.643.4256.268.92105.6039.859.9423.2035.21119.6020.725.692.561.402.22
    注:微量元素单位为×10-6
    下载: 导出CSV

    表  附表4  碳氧同位素分析表

    样品编号样品描述层位深度/mδ13C/‰,PDBδ18O/‰,PDB形成温度/℃Z古盐度S/%
    A1-01泥晶白云岩青一段2 518.8111.90-6.4945.0148.428.27
    A1-02泥晶白云岩青一段2 527.722.18-16.79101.4123.417.96
    A1-07泥晶白云岩青一段2 535.3211.03-8.8857.3145.525.87
    A1-10泥晶白云岩青一段2 540.974.86-12.2275.3131.222.53
    A1-11泥晶白云岩青一段2 551.1610.41-7.5350.3144.927.22
    A1-13泥晶白云岩青一段2 558.669.27-9.9763.1141.324.79
    A1-14泥晶白云岩青一段2 575.009.29-7.6550.9142.527.11
    A1-15泥晶白云岩青一段2 544.568.56-9.0658.3140.325.69
    A5-3泥晶白云岩青一段1 601.936.74-10.7567.3135.824.01
    A5-4泥晶白云岩青一段1 604.734.77-10.7867.4131.723.98
    A5-9泥晶白云岩青一段1 610.932.48-12.8178.5126.021.95
    A5-11泥晶白云岩青一段1 618.339.08-7.9952.7141.926.76
    A5-13泥晶白云岩青一段1 638.439.53-9.0258.1142.325.73
    A5-18泥晶白云岩青一段1 646.385.04-10.3465.1132.524.41
    A5-21泥晶白云岩青一段1 650.187.24-9.2859.4137.525.48
    A5-22泥晶白云岩青一段1 653.7813.60-8.0252.8151.226.74
    A2-1泥晶白云岩青二段1 861.4415.17-8.5955.8154.126.16
    A2-2泥晶白云岩青二段1 874.832.54-13.9084.7125.620.85
    A2-3泥晶白云岩青二段1 877.9813.77-8.3254.4151.426.44
    A2-4泥晶白云岩青二段1 894.055.61-13.1980.7132.221.57
    A2-5泥晶白云岩青二段1 905.048.68-12.1174.7139.122.65
    A2-6泥晶白云岩青二段1 918.885.76-13.1680.5132.521.60
    A2-7泥晶白云岩青二段1 923.187.96-11.5171.4137.923.25
    平均值7.56-10.6567.04137.4824.10
    下载: 导出CSV

    表  附表5  稀土元素分析数据表

    样品编号岩性深度/mLaCePrNdSmEuGdTbDyHoErTmYbYLuLREEHREELREE+HREELREE/HREE(La/Yb)N(La/Sm)N(Gd/Yb)NδCeδEu
    A3-155泥晶白云岩2 174.179.2620.192.5010.412.190.582.060.301.590.310.830.120.779.210.1345.1315.3260.442.9512.094.242.691.220.89
    A3-158泥晶白云岩2 177.369.6719.862.5910.482.180.552.050.291.540.290.750.110.668.730.1145.3214.5259.843.1214.614.443.100.940.85
    A3-160泥晶白云岩2 179.804.608.951.084.070.830.260.770.120.650.140.390.060.364.650.0619.797.2026.992.7512.855.522.160.941.04
    A3-164泥晶白云岩2 181.9324.5655.246.7629.116.392.065.850.814.170.792.130.301.8623.450.30124.1139.66163.773.1313.193.853.141.021.12
    A3-169泥晶白云岩2 187.2625.4967.186.9227.785.550.984.960.724.040.812.310.342.2121.000.34133.9036.73170.633.6511.524.592.241.200.61
    A3-171泥晶白云岩2 189.708.0918.882.128.611.860.521.800.271.530.300.830.120.729.390.1140.0715.0655.142.6611.214.352.501.070.92
    A3-175泥晶白云岩2 195.5917.1237.234.0015.653.060.762.920.442.450.501.420.201.3414.920.2177.8224.40102.223.1912.785.602.181.050.83
    A3-183泥晶白云岩2 206.1710.5423.432.6010.302.030.531.980.271.550.310.840.120.709.840.1049.4315.7265.153.1414.975.182.821.050.89
    A3-193泥晶白云岩2 216.0115.2534.663.5814.122.850.732.690.382.130.431.180.161.0512.970.1671.1921.1692.353.3614.545.362.571.090.87
    A3-197泥晶白云岩2 219.6428.2565.786.6425.284.770.884.310.633.510.701.980.291.8119.260.28131.6032.77164.374.0215.595.922.381.120.63
    A3-203泥晶白云岩2 227.0424.3158.505.9421.683.540.622.900.442.620.571.690.271.7514.900.28114.5925.40139.994.5113.916.871.661.140.62
    A3-206泥晶白云岩2 229.5829.8571.817.4128.255.120.814.120.573.170.651.920.291.9417.130.29143.2530.09173.344.7615.375.832.121.130.58
    A3-208泥晶白云岩2 230.8925.9460.136.5524.664.430.773.840.563.200.681.970.301.9217.380.30122.4730.14152.624.0613.505.852.001.080.60
    A3-217泥晶白云岩2 238.2931.3664.737.7828.915.160.954.500.693.720.782.220.352.1321.970.35138.8936.72175.603.7814.716.082.110.970.63
    A3-219泥晶白云岩2 239.587.2316.161.937.711.850.431.790.311.490.300.770.130.729.340.1335.3114.9850.292.3610.103.902.501.020.74
    A3-223泥晶白云岩2 242.0923.1148.885.7921.633.910.713.260.482.740.581.690.271.7016.370.26104.0327.36131.393.8013.595.901.920.990.63
    A3-227泥晶白云岩2 245.364.919.861.204.971.180.331.130.170.770.150.380.060.335.360.0622.448.3930.832.6714.884.163.410.950.92
    A3-229泥晶白云岩2 247.047.4916.272.048.672.100.482.050.291.470.290.800.120.7810.420.1337.0616.3653.412.279.613.562.630.990.78
    A3-243泥晶白云岩2 256.8512.1924.842.9111.272.300.422.070.291.550.300.820.120.7210.480.1153.9316.4670.393.2816.995.292.880.970.63
    A3-256泥晶白云岩2 265.9719.4737.775.1319.753.830.693.300.502.810.591.710.261.6717.470.2686.6328.58115.213.0311.645.081.970.890.62
    A3-269泥晶白云岩2 275.3618.8841.345.6822.934.880.904.380.643.560.701.990.291.8921.260.2994.6235.00129.622.709.973.872.310.950.64
    平均值17.0338.184.3416.963.330.712.990.442.390.481.360.201.2914.070.2080.5523.43103.983.3013.225.022.320.0311.81
    注:稀土元素单位为×10-6
    下载: 导出CSV
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出版历程
  • 收稿日期:  2021-12-02
  • 修回日期:  2022-01-26
  • 录用日期:  2022-03-23
  • 网络出版日期:  2022-03-23
  • 刊出日期:  2024-02-10

目录

    松辽盆地白云岩沉积环境及成因机理

    doi: 10.14027/j.issn.1000-0550.2022.018
      基金项目:

      中国石油重大科技专项 2021ZZ10

      作者简介:

      付秀丽,女,1982年出生,硕士研究生,高级工程师,储层沉积学,E-mail: fuxiuli@petrochina.com.cn

      通讯作者: 蒙启安,男,教授级高工,E-mail: mengqian@petrochina.com.cn
    • 中图分类号: P618.13

    摘要: 目的 湖相白云岩是松辽盆地发现的一种特殊油气储层类型,为了探讨其沉积环境及成因机理,开展了白云岩宏微观特征及环境参数研究。 方法 通过野外剖面及岩心观察、微观组构观测和元素、同位素组成等多指标综合研究,分析了松辽盆地白云岩的沉积环境及其成因机理。 结果 松辽盆地湖相区白云岩主要为泥晶白云岩,矿物成分主要为铁白云石、黏土和方解石,厚1~25 cm,呈层状或透镜状分布于厚层湖相泥页岩中,具有δ13C值偏正、氧同位素δ18O值偏负、稀土元素δEu明显负异常、热液营养物质Ca、Si、Fe、Mg、Al、Na丰富等显著特征,推测其先期为产甲烷细菌成因的原生白云岩,后期受到热液作用改造,形成于相对干燥气候条件下的咸水湖泊环境。 结论 湖相区白云岩沉积环境及成因机理分析对于研究松辽盆地沉积演化和储层评估具有重要意义。

    English Abstract

    付秀丽, 蒙启安, 文政, 白月, 高波, 苏杨鑫. 松辽盆地白云岩沉积环境及成因机理[J]. 沉积学报, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018
    引用本文: 付秀丽, 蒙启安, 文政, 白月, 高波, 苏杨鑫. 松辽盆地白云岩沉积环境及成因机理[J]. 沉积学报, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018
    FU XiuLi, MENG QiAn, WEN Zheng, BAI Yue, GAO Bo, SU YangXin. Sedimentary Environment and Genetic Mechanism of Dolomites in the Qingshankou Formation, Songliao Basin[J]. Acta Sedimentologica Sinica, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018
    Citation: FU XiuLi, MENG QiAn, WEN Zheng, BAI Yue, GAO Bo, SU YangXin. Sedimentary Environment and Genetic Mechanism of Dolomites in the Qingshankou Formation, Songliao Basin[J]. Acta Sedimentologica Sinica, 2024, 42(1): 113-129. doi: 10.14027/j.issn.1000-0550.2022.018
      • 国内外对于白云岩的沉积环境和成因机理的研究一直是地学界比较热门的话题,为海相白云岩储层研究提供了关键理论基础[12],国内在四川盆地、塔里木盆地及鄂尔多斯盆地等都发现了海相白云岩储层[34],并对其成因机制有了比较深入的认识[5]。与海相白云岩相比,我国湖相区,特别是半深湖—深湖相区沉积的白云岩分布相对局限,且多分布在中生代或者新生代地层[67],在渤海湾盆地沙河街组、四川盆地下侏罗统自流井组、柴达木盆地的古近系下干柴沟组、鄂尔多斯盆地的三叠系延长组、准噶尔盆地的二叠系芦草沟组均有不同程度的发现[8]。由于湖相白云岩岩性复杂,储层致密,规模较小,研究程度远不如海相白云岩,对其沉积环境及成因模式需要更多的案例研究,进行进一步的理论归纳总结。

        湖相白云岩作为致密储层类型,具有晶体细小、泥质含量高等特点,在松辽盆地油气储层勘探过程中,时有发现[910]。前人在松辽盆地上白垩统嫩江组一二段深湖—半深湖相也有白云岩发现,认为松辽盆地嫩江组白云岩是在盐度较高的条件中形成的结核白云岩,为海水一淡水混合成因[11],也有学者认为是准同生期被交代的产物,其形成机制是在晚白垩世松辽盆地海侵背景下Mg在准同生期交代由浊积事件、介形虫灭绝事件所产生的泥灰岩沉积而成[12]。但对于松辽盆地青山口组湖相白云岩研究较少,尚未对其沉积环境及成因模式进行系统的研究。本文以松辽盆地野外地质剖面和盆地内多口钻井取心资料观察描述为基础,通过沉积组构和地球化学综合分析,分析了松辽盆地青山口组湖相区白云岩的沉积环境特征,探讨了湖相区白云岩的成因模式,为进一步分析细粒岩的沉积环境及有机质富集提供重要支撑。

      • 松辽盆地位于中国东北部,是当今世界上最大的典型陆相沉积盆地之一。松辽盆地长750 km,宽330~370 km,总面积26×104 km2。盆地分为六个构造单元:北部倾没区、中央坳陷区、东北隆起区、东南隆起区、西南隆起区和西部斜坡区(图1)。主要产油气区为中央坳陷区,包括大庆背斜、齐家—古龙凹陷、三肇凹陷、长岭凹陷和朝阳沟阶地。

        图  1  松辽盆地构造位置[13]

        松辽盆地的形成和发展经历了同裂陷、裂后热沉降和大规模构造反转3个发展演化阶段,形成了同裂陷层序和坳陷层序两套沉积层序[1314]。同裂陷层经历了火石岭组的火山喷发、沙河子组和营城组时期的断陷沉积作用、沙河子组末期和营城组末期的构造反转和抬升剥蚀和其后的沉陷作用、反转作用的改造。坳陷层序构造的发育过程经历了两大阶段四个主要的发展时期,即登娄库组—嫩江组盆地整体沉降(热沉降为主)阶段,四方台组到第四纪盆地收缩和反转阶段(图2a)。

        图  2  松辽盆地(a)及青山口组(b)地层综合柱状图

        已发现油气主要分布在白垩系泉头组—嫩江组及深层营城—沙河子组地层,姚家组的葡萄花油层、萨尔图油层和青山口组的高台子油层为松辽盆地北部中浅层主力油层,其次为泉头组的扶余油层、嫩江组的黑帝庙油层,深层天然气主要发育在营城组和沙河子组[13]。松辽盆地青山口组属于坳陷层序,是盆地首次湖泛形成的地层,发育了以湖相和三角洲相为主的沉积体系[1517]。青山口组从下到上分为青一段、青二段和青三段(图2b),其中青一段沉积时期盆地湖盆面积达到最大,中央坳陷区以深湖相沉积为主,岩性主要为灰色、灰黑色泥岩和黑色页岩沉积,中间夹有薄层白云岩、灰岩或泥质粉砂岩,泥岩累计沉积厚度60~120 m。相关学者先后在松辽盆地姚家站嫩江组野外露头、李家沱子青山口组野外露头上观察到多期次薄层状碳酸盐岩沉积,鲕粒灰岩、介壳灰岩、叠层石灰岩、泥晶白云岩在空间上成层分布,并认为嫩江组可能受到海侵的影响,呈薄层状夹于大套黑色或灰黑色泥岩中间[1112]。青山口组也有沟鞭藻、叠层石、海绿石、微体古生物等化石发现,一些学者根据以上证据也认为可能存在海侵事件[1819]

      • 通过松辽盆地野外露头和盆地内取心井的观察描述,选取青山口乡邢家店青一段白云岩露头样品、盆地内A1井、A2井、A3井、A4井和A5井等5口典型井的岩心样品,进行薄片鉴定、X衍射全岩矿物成分、微量元素、稀土元素、碳氧同位素、阴极发光及场发射扫描电镜等分析测试。

        薄片观察实验采用Zeiss Axio Image Z1偏光显微镜,利用锥光观察技术进行分析;全岩矿物分析采用D8AA25 X射线衍射仪,焦斑大小0.4 mm×12 mm,利用测角仪进行矿物扫描;场发射电镜采用Quanta450扫描电镜,通过BSE-EDS能谱得到矿物分布图;常量元素采用Axios PW4400/40全自动波长色散X射线荧光光谱仪;微量和稀土元素采用ICP-MS-X-Series-2进行测试。碳氧同位素用磷酸处理后采用isoprime 100 JB629进行测试,精度误差±0.05‰,室温环境下进行。

      • 野外露头观察表明松辽盆地白云岩主要有层状白云岩和透镜状白云岩两种类型(图3~5)。层状白云岩平面上具有准连续分布特征,透镜状呈年糕状分布(图3)。岩心观察和镜下薄片鉴定表明,白云岩矿物组成颗粒普遍偏细,颜色以灰黑色、灰色为主(图4),以泥晶结构或者含介屑泥晶结构为主(图5),发育泥晶白云岩,同时还有极少部分含泥粉晶云岩和含介屑泥晶白云岩。

        图  3  白云岩分布特征野外地质剖面

        图  4  不同类型白云岩岩心特征

        图  5  不同类型白云岩微观特征

        泥晶白云岩:泥晶结构,由泥晶白云石、泥质、生物碎屑组成,泥质具重结晶,定向分布(图5)。矿物组分为白云石,占比一般在80%以上,方解石占比小于10%,黏土矿物占比一般小于10%;结构组分泥晶占比95%~85%,生物碎屑占比不超过10%,泥质占比不超过5%。

        含泥泥晶云岩:含泥泥晶结构,矿物组分为白云石,占比85%~95%,黄铁矿占比不超过3%;黏土占比5%~12%。在松辽盆地东南部青山口乡邢家店青山口组也有层状粉晶云岩发育,岩石主要由白云石、少量泥质、方解石组成。粉晶结构,半自形白云石呈镶嵌状紧密排列,少量泥质分布于白云石晶间。岩石裂缝发育,纵横交错,先后被泥质、中—细晶白云石、方解石充填,仅残留少量空隙。

        含介屑泥晶白云岩:含介屑泥晶结构,由泥晶白云石、介屑、泥质、粉砂颗粒和介屑组成;深红色介屑多顺层分布,部分被黄铁矿交代;泥质具重结晶并定向分布,粉砂颗粒分布不均;岩石具纹层构造。矿物组分为白云石,占比75%,方解石占比25%;结构组分泥晶占比75%,碎屑占比17%,泥质占比8%。

      • X射线衍射全岩矿物分析结果表明,松辽盆地湖相区白云岩矿物成分主要为铁白云石、黏土矿物,其次为石英、斜长石和黄铁矿。松辽盆地整体铁白云石含量为54.5%~96.6%,平均为73.1%,黏土矿物含量为1.1%~21.3%,平均为9.5%,石英含量为0.7%~26.2%,平均为10.6%(附表1)。

        表 附表1  全岩矿物分析表(%)

        样品编号深度/m地区层位岩性描述石英钾长石斜长石方解石铁白云石黏土矿物黄铁矿菱铁矿
        A3-1602 179.80古龙凹陷青二段泥晶白云岩14.403.0078.83.800
        A3-1612 180.30古龙凹陷青二段泥晶白云岩14.706.21.964.311.11.80
        A3-1712 189.70古龙凹陷青二段泥晶白云岩9.401.8082.46.400
        A3-1782 199.90古龙凹陷青一段泥晶白云岩11.507.1056.721.32.80.7
        A3-1832 206.20古龙凹陷青一段泥晶白云岩18.706.9063.610.700
        A3-1932 216.00古龙凹陷青一段泥晶白云岩17.107.3057.516.81.40
        A3-2432 256.90古龙凹陷青一段泥晶白云岩26.201.6060.310.51.40
        A1-32 471.50古龙凹陷青二段泥晶白云岩4.104.40.487.53.700
        A1-42 484.50古龙凹陷青二段泥晶白云岩1.101.7094.92.300
        A1-52 486.20古龙凹陷青二段泥晶白云岩3.201.7092.03.200
        A1-62 487.20古龙凹陷青二段泥晶白云岩8.804.3076.67.52.70
        A1-72 490.50古龙凹陷青二段泥晶白云岩3.202.5091.23.000
        A1-82 493.60古龙凹陷青二段泥晶白云岩14.608.73.360.69.82.40.7
        A1-92 525.20古龙凹陷青一段泥晶白云岩6.103.11.174.312.62.70
        A1-102 542.80古龙凹陷青一段泥晶白云岩7.202.70.976.910.61.70
        A1-112 545.80古龙凹陷青一段泥晶白云岩0.701.30.296.61.200
        A1-122 550.40古龙凹陷青一段泥晶白云岩14.802.43.568.510.800
        A1-132 554.00古龙凹陷青一段泥晶白云岩10.301.40.481.06.900
        A1-142 562.60古龙凹陷青一段泥晶白云岩2.801.3092.42.51.00
        A1-152 570.30古龙凹陷青一段泥晶白云岩13.503.21.269.011.41.70
        A5-11 593.90三肇凹陷青一段泥晶白云岩23.001.9067.47.600
        A5-21 596.90三肇凹陷青一段泥晶白云岩3.602.8086.65.81.20
        A5-31 601.90三肇凹陷青一段泥晶白云岩15.308.3060.114.22.10
        A5-41 604.70三肇凹陷青一段泥晶白云岩11.303.4075.79.500
        A5-51 636.40三肇凹陷青一段泥晶白云岩24.506.6052.116.700
        A5-61 640.30三肇凹陷青一段泥晶白云岩18.502.7069.39.500
        A4-11 805.40三肇凹陷青一段泥晶白云岩7.103.90806.22.70
        A4-21 826.90三肇凹陷青一段泥晶白云岩15.703.0069.710.11.60
        A4-31 870.10三肇凹陷青一段泥晶白云岩27.801.9061.58.700

        齐家—古龙地区白云岩以泥晶白云岩为主,全岩矿物成分铁白云石含量为54.5%~96.6%,平均69.8%,黏土矿物含量为1.2%~21.3%,平均为11.1%,石英含量为0.7%~26.2%,平均为12.4%;青二段铁白云石含量为55.6%~96.3%,平均为77.3%,黏土矿物含量为1.1%~19.3%,平均为7.5%,石英含量为0.7%~14.7%,平均为8.4%。

        大庆长垣及以东地区泥晶白云岩铁白云石含量为52.1%~86.6%,平均为69.2%,黏土矿物含量为5.8%~16.7%,平均为9.8%,石英含量为3.6%~27.8%,平均为16.3%。青二段铁白云石含量为74.5%~76.6%,平均为76%,黏土矿物含量为10.6%~11.3%,平均为10.95%,石英含量为8.8%~9.9%,平均为9.35%。

      • 薄片显微分析表明,层状和透镜状白云岩中白云石呈他形或半自形,白云石呈泥晶结构,半自形镶嵌状分布。泥质具重结晶分布于白云石间。见砂质零星分布。荧光照射下透镜状泥晶白云岩不发荧光,场发射电镜下可见白云石具明显多期成因,见半自形—次圆形菱形雾心白云石及含亮边的白云岩。亮边白云石能谱分析显示含铁,全岩分析为铁白云石(图6附表1)。层状白云岩有明显的荧光显示,阴极发光显示橘红色。层状白云岩中白云石具泥晶结构,自形镶嵌状分布,场发射电镜下亦可见白云石多期成因,自形白云石加大边中能谱打点显示含有O、Mg、C、Ca、Fe、Na等物质,白云石加大亮边含铁,为铁白云石,内部暗色白云石铁含量极低(图6)。场发射电镜显示两种类型的白云岩都由暗色白云石和外部亮边的白云岩组成,暗色白云石铁含量极低,外部亮边白云岩铁含量较高,说明松辽盆地白云岩至少存在两期成因。

        图  6  泥晶白云岩薄片及场发射电镜微观特征(A2井)

      • 该区泥晶白云岩中常量元素以CaO、SiO2、MgO为主,其次为Al2O3和Fe2O3。其中w(CaO)变化范围在11.29%~32.51%,平均为25.45%;w(SiO2)变化范围在2.34%~37.60%,平均为17.61%;w(MgO)变化范围在6.84%~17.00%,平均为11.66%;w(Al2O3)变化范围在1.26%~18.73%,平均为7.80%;w(Fe2O3)变化范围在3.21%~9.78%,平均为6.64%。另外还含有少量的P2O5、Na2O、K2O、MnO等常量矿物。w(MnO)为0.2%(图7附表2)。

        图  7  青山口组湖相区白云岩常量元素分布饼状图

        表 附表2  常量元素分析数据表(%)

        样品编号深度/m岩性SiO2Al2O3Fe2O3CaOMgOK2ONa2OTiO2P2O5MnO
        A3-1552 174.17泥晶白云岩5.612.237.3929.7213.360.440.290.110.140.38
        A3-1582 177.36泥晶白云岩8.102.899.7827.6312.070.400.340.100.190.28
        A3-1602 179.80泥晶白云岩15.332.267.1825.8212.070.220.440.080.210.21
        A3-1642 181.93泥晶白云岩20.236.438.0421.679.171.201.040.261.400.29
        A3-1712 189.70泥晶白云岩16.822.938.8224.8311.320.310.350.090.220.29
        A3-1752 195.59泥晶白云岩26.116.448.8919.638.891.120.790.230.460.27
        A3-1832 206.17泥晶白云岩19.893.867.4623.6110.360.640.500.130.440.28
        A3-1932 216.01泥晶白云岩15.874.878.1323.7811.120.910.460.180.190.32
        A3-1972 219.64泥晶白云岩37.6012.166.9311.296.842.371.000.430.130.14
        A3-2032 227.04泥晶白云岩19.8717.944.0131.2012.013.671.560.600.080.05
        A3-2062 229.58泥晶白云岩19.7618.734.4130.5311.873.771.630.650.100.03
        A3-2082 230.89泥晶白云岩18.6618.484.4330.8611.853.781.620.640.160.05
        A3-2172 238.29泥晶白云岩15.0017.764.8832.5112.893.691.240.590.140.06
        A3-2192 239.58泥晶白云岩23.444.668.2519.8911.150.330.240.100.050.21
        A3-2232 242.09泥晶白云岩19.0617.684.4530.6911.963.231.870.600.110.03
        A3-2272 245.36泥晶白云岩2.341.265.8428.6217.000.230.180.060.260.16
        A3-2292 247.04泥晶白云岩9.183.126.9225.7314.610.180.180.080.150.14
        A3-2432 256.85泥晶白云岩24.125.307.6420.619.750.930.320.180.120.25
        A3-2562 265.97泥晶白云岩27.995.596.2419.3210.040.910.300.170.160.20
        A3-2692 275.36泥晶白云岩7.311.353.2131.1314.890.160.150.040.140.28
        平均值17.617.806.6425.4511.661.420.720.270.240.20
      • 微量元素分析表明,该区泥晶白云岩微量元素以Sr、Ba、V、Zn、B、Li元素为主,其次为少量的Cr、Cu、Ni、Ga、Co等。其中w(Sr)变化范围在(170~843.9)×10-6,平均为475.6×10-6w(Ba)变化范围在(121.1~382.9)×10-6,平均为243.3×10-6,其中w(V)变化范围在(45.4~147.7)×10-6,平均为105.6×10-6,w(Zn)变化范围在(22.2~133.0)×10-6,平均为91.2×10-6,其中w(B)变化范围在(13.9~147.7)×10-6,平均为59.2×10-6,w(Li)变化范围在(13.8~89.9)×10-6,平均为52.8×10-6w(Sr/Cu)变化范围在(4.8~115.9)×10-6,平均为34.9×10-6w(Sr)/w(Ba)变化范围在(0.87~3.95)×10-6,平均为1.97×10-6w(V/(V+Ni))变化范围在(0.72~0.87)×10-6,平均为0.81×10-6图8附表3)。

        图  8  白云岩微量元素平均值含量直方图(样品数N=52)

        表 附表3  微量元素及其分析表

        样品编号岩性深度/mSrBaLiBeBScVCrCoNiCuZnGaThUw(Sr)/w(Ba)w(Th)/w(U)
        A3-155泥晶白云岩2 174.17843.90213.4013.761.2215.086.9465.8240.142.7816.747.2822.243.312.191.113.951.98
        A3-158泥晶白云岩2 177.36787.60211.3024.351.0613.995.9089.6823.233.3213.077.6126.394.101.781.463.731.22
        A3-160泥晶白云岩2 179.80885.00198.0024.170.5810.962.4554.3212.971.906.824.2220.252.460.990.924.471.07
        A3-164泥晶白云岩2 181.93988.801 134.0021.041.4329.368.9160.5729.305.8113.4214.3259.698.905.974.750.871.26
        A3-169泥晶白云岩2 187.26305.00297.4043.253.1171.418.65100.9041.1222.0840.0842.38125.7019.049.525.531.031.72
        A3-171泥晶白云岩2 189.70939.90561.4031.650.9010.234.5264.2514.242.398.785.0119.073.541.490.881.671.69
        A3-175泥晶白云岩2 195.59659.60382.9039.801.6623.725.4184.5831.215.1815.4515.0750.829.724.532.921.721.55
        A3-183泥晶白云岩2 206.17836.70248.2022.560.8119.983.1545.4316.262.809.997.6824.134.712.371.113.372.13
        A3-193泥晶白云岩2 216.011 065.00253.7029.761.1722.434.1043.1237.674.7219.1613.5739.537.203.631.794.202.03
        A3-197泥晶白云岩2 219.64711.70324.2068.592.2540.055.8396.9646.5011.2726.9232.2872.9115.527.474.302.201.74
        A3-203泥晶白云岩2 227.04215.50248.9061.083.0181.037.95128.3048.5714.8032.7439.11132.2020.428.702.660.873.26
        A3-206泥晶白云岩2 229.58358.10270.5054.093.0779.0110.18124.8045.1612.4830.1137.10114.9020.6510.104.051.322.49
        A3-208泥晶白云岩2 230.89416.70272.8049.193.2394.5010.31138.2057.1214.2328.0243.22123.4022.048.713.791.532.30
        A3-217泥晶白云岩2 238.29427.40224.9057.023.67147.7012.55147.7061.6814.7032.5644.33129.7022.818.893.561.902.50
        A3-219泥晶白云岩2 239.581 145.00235.4096.790.73104.703.8743.4227.688.0320.647.8751.695.131.431.094.861.31
        A3-223泥晶白云岩2 242.09276.40203.1089.853.6370.4110.58130.3056.6511.5328.0036.06133.0023.386.082.251.362.71
        A3-227泥晶白云岩2 245.361 562.00221.0017.600.8312.662.3251.1738.213.4915.484.5216.961.660.810.757.071.08
        A3-229泥晶白云岩2 247.041 335.00205.7065.550.9299.706.7154.4133.764.1516.986.8423.633.291.011.156.490.88
        A3-243泥晶白云岩2 256.85860.10176.4049.171.2515.795.5266.1728.394.4013.1710.7942.746.142.061.234.881.67
        A3-256泥晶白云岩2 265.97174.40143.6075.523.0556.529.49114.0047.6511.8831.0136.10110.5020.195.772.051.212.82
        A3-269泥晶白云岩2 275.36170.00121.1087.643.4256.268.92105.6039.859.9423.2035.21119.6020.725.692.561.402.22
        注:微量元素单位为×10-6
      • 前人研究证实,年代越新、受后期改造越弱的岩石,其碳同位素和氧同位素值与原始沉积时碳氧同位素值越接近,尤其是中生代以后的样品应用碳酸盐岩碳氧同位素分析沉积环境较为有效。松辽盆地湖相区白云岩样品的w(Mn)/w(Sr)值平均为1.6,小于3,说明测试样品没有或者仅受到弱成岩作用的影响,可以代表沉积环境的原始地球化学特征值[20]。松辽盆地青山口组湖相白云岩的碳同位素δ13C值介于2.2‰~15.2‰,平均为8.0‰;氧同位素δ18O值介于-16.8‰~-6.5‰,平均为-10.5‰。古龙地区湖相区白云岩相对于三肇地区白云岩具有氧偏正、碳偏负的特征(附表3)。根据Keith et al.[21]提出的经验公式,利用碳氧同位素分析结果计算青山口组湖相区白云岩形成的古温度介于45 ℃~101.5 ℃,平均为67.0 ℃,古盐度介于17.95%~28.27%,平均为24.10%;古盐度指数Z介于123.4~154.1,平均为137.5(附表4)。

        表 附表4  碳氧同位素分析表

        样品编号样品描述层位深度/mδ13C/‰,PDBδ18O/‰,PDB形成温度/℃Z古盐度S/%
        A1-01泥晶白云岩青一段2 518.8111.90-6.4945.0148.428.27
        A1-02泥晶白云岩青一段2 527.722.18-16.79101.4123.417.96
        A1-07泥晶白云岩青一段2 535.3211.03-8.8857.3145.525.87
        A1-10泥晶白云岩青一段2 540.974.86-12.2275.3131.222.53
        A1-11泥晶白云岩青一段2 551.1610.41-7.5350.3144.927.22
        A1-13泥晶白云岩青一段2 558.669.27-9.9763.1141.324.79
        A1-14泥晶白云岩青一段2 575.009.29-7.6550.9142.527.11
        A1-15泥晶白云岩青一段2 544.568.56-9.0658.3140.325.69
        A5-3泥晶白云岩青一段1 601.936.74-10.7567.3135.824.01
        A5-4泥晶白云岩青一段1 604.734.77-10.7867.4131.723.98
        A5-9泥晶白云岩青一段1 610.932.48-12.8178.5126.021.95
        A5-11泥晶白云岩青一段1 618.339.08-7.9952.7141.926.76
        A5-13泥晶白云岩青一段1 638.439.53-9.0258.1142.325.73
        A5-18泥晶白云岩青一段1 646.385.04-10.3465.1132.524.41
        A5-21泥晶白云岩青一段1 650.187.24-9.2859.4137.525.48
        A5-22泥晶白云岩青一段1 653.7813.60-8.0252.8151.226.74
        A2-1泥晶白云岩青二段1 861.4415.17-8.5955.8154.126.16
        A2-2泥晶白云岩青二段1 874.832.54-13.9084.7125.620.85
        A2-3泥晶白云岩青二段1 877.9813.77-8.3254.4151.426.44
        A2-4泥晶白云岩青二段1 894.055.61-13.1980.7132.221.57
        A2-5泥晶白云岩青二段1 905.048.68-12.1174.7139.122.65
        A2-6泥晶白云岩青二段1 918.885.76-13.1680.5132.521.60
        A2-7泥晶白云岩青二段1 923.187.96-11.5171.4137.923.25
        平均值7.56-10.6567.04137.4824.10
      • 稀土元素分析数据显示,ΣREE值介于(26.99~175.60)×10-6,平均为103.98×10-6δEu值介于0.58~1.12,平均为0.76(图9)。δCe值介于0.89~1.22,平均为1.04,ΣREE值介于(26.99~175.60)×10-6,反映了ΣREE具有较大的变化范围且总量较高、具有明显的δEu负异常的稀土元素配分模式。其中轻稀土元素LREE值介于(17.79~143.25)×10-6,平均为80.55×10-6;重稀土元素HREE(HREE:Gd⁃Lu),值介于(7.20~39.66)×10-6,平均为23.43×10-6,LREE/HREE、(La/Yb)N、(La/Sm)N和(Gb/Yb)N、平均值分别为3.30、13.22、5.02和2.44,反映了轻、重稀土元素具有较强的分异现象。轻稀土元素LREE明显富集,重稀土元素HREE相对亏损,整体反映出轻稀土元素相对富集的分配模式特征(图10附表5),反映了缺氧热水环境,与其在深湖相泥岩中呈夹层分布的地质特征吻合。

        图  9  青山口组泥晶白云岩稀土元素散点图

        图  10  松辽盆地青山口组白云岩稀土元素配分模式及特征

        表 附表5  稀土元素分析数据表

        样品编号岩性深度/mLaCePrNdSmEuGdTbDyHoErTmYbYLuLREEHREELREE+HREELREE/HREE(La/Yb)N(La/Sm)N(Gd/Yb)NδCeδEu
        A3-155泥晶白云岩2 174.179.2620.192.5010.412.190.582.060.301.590.310.830.120.779.210.1345.1315.3260.442.9512.094.242.691.220.89
        A3-158泥晶白云岩2 177.369.6719.862.5910.482.180.552.050.291.540.290.750.110.668.730.1145.3214.5259.843.1214.614.443.100.940.85
        A3-160泥晶白云岩2 179.804.608.951.084.070.830.260.770.120.650.140.390.060.364.650.0619.797.2026.992.7512.855.522.160.941.04
        A3-164泥晶白云岩2 181.9324.5655.246.7629.116.392.065.850.814.170.792.130.301.8623.450.30124.1139.66163.773.1313.193.853.141.021.12
        A3-169泥晶白云岩2 187.2625.4967.186.9227.785.550.984.960.724.040.812.310.342.2121.000.34133.9036.73170.633.6511.524.592.241.200.61
        A3-171泥晶白云岩2 189.708.0918.882.128.611.860.521.800.271.530.300.830.120.729.390.1140.0715.0655.142.6611.214.352.501.070.92
        A3-175泥晶白云岩2 195.5917.1237.234.0015.653.060.762.920.442.450.501.420.201.3414.920.2177.8224.40102.223.1912.785.602.181.050.83
        A3-183泥晶白云岩2 206.1710.5423.432.6010.302.030.531.980.271.550.310.840.120.709.840.1049.4315.7265.153.1414.975.182.821.050.89
        A3-193泥晶白云岩2 216.0115.2534.663.5814.122.850.732.690.382.130.431.180.161.0512.970.1671.1921.1692.353.3614.545.362.571.090.87
        A3-197泥晶白云岩2 219.6428.2565.786.6425.284.770.884.310.633.510.701.980.291.8119.260.28131.6032.77164.374.0215.595.922.381.120.63
        A3-203泥晶白云岩2 227.0424.3158.505.9421.683.540.622.900.442.620.571.690.271.7514.900.28114.5925.40139.994.5113.916.871.661.140.62
        A3-206泥晶白云岩2 229.5829.8571.817.4128.255.120.814.120.573.170.651.920.291.9417.130.29143.2530.09173.344.7615.375.832.121.130.58
        A3-208泥晶白云岩2 230.8925.9460.136.5524.664.430.773.840.563.200.681.970.301.9217.380.30122.4730.14152.624.0613.505.852.001.080.60
        A3-217泥晶白云岩2 238.2931.3664.737.7828.915.160.954.500.693.720.782.220.352.1321.970.35138.8936.72175.603.7814.716.082.110.970.63
        A3-219泥晶白云岩2 239.587.2316.161.937.711.850.431.790.311.490.300.770.130.729.340.1335.3114.9850.292.3610.103.902.501.020.74
        A3-223泥晶白云岩2 242.0923.1148.885.7921.633.910.713.260.482.740.581.690.271.7016.370.26104.0327.36131.393.8013.595.901.920.990.63
        A3-227泥晶白云岩2 245.364.919.861.204.971.180.331.130.170.770.150.380.060.335.360.0622.448.3930.832.6714.884.163.410.950.92
        A3-229泥晶白云岩2 247.047.4916.272.048.672.100.482.050.291.470.290.800.120.7810.420.1337.0616.3653.412.279.613.562.630.990.78
        A3-243泥晶白云岩2 256.8512.1924.842.9111.272.300.422.070.291.550.300.820.120.7210.480.1153.9316.4670.393.2816.995.292.880.970.63
        A3-256泥晶白云岩2 265.9719.4737.775.1319.753.830.693.300.502.810.591.710.261.6717.470.2686.6328.58115.213.0311.645.081.970.890.62
        A3-269泥晶白云岩2 275.3618.8841.345.6822.934.880.904.380.643.560.701.990.291.8921.260.2994.6235.00129.622.709.973.872.310.950.64
        平均值17.0338.184.3416.963.330.712.990.442.390.481.360.201.2914.070.2080.5523.43103.983.3013.225.022.320.0311.81
        注:稀土元素单位为×10-6
      • 根据白云岩微量元素及其组合参数特征、碳氧同位素特征、稀土元素分布特征等来综合研究青山口组湖相区白云岩沉积环境。

        在现代和古代湖泊环境中,w(Sr)/w(Ba)值均与盐度呈正相关,是判别古盐度的灵敏标志[2223],并且认为w(Sr)/w(Ba)值大于1,指示咸水环境沉积;其w(Sr)/w(Ba)值小于1,指示淡水环境沉积。w(Sr)/w(Ba)普遍大于1(附表3),说明白云岩整体形成于咸水沉积环境。

        根据前人研究认为Z值大于120是咸水标志,小于120为淡水环境[21]。松辽盆地白云岩Z值平均为138.8,整体都大于120,代表了白云岩沉积时水体为咸水环境。微量元素w(Sr)/w(Ba)比值和碳氧同位素特征同时揭示了松辽盆地湖相区白云岩形成于咸水沉积水体环境。

        轻稀土元素LREE明显富集,重稀土元素HREE相对亏损,反映了缺氧热水环境,与其在深湖相泥岩中呈夹层分布的地质特征吻合。松辽盆地青山口组白云岩沉积时期,整体的环境背景为湖相沉积,但存在短暂咸水的沉积水体,在半深湖—深湖相缺氧及相对封闭环境广泛发育的地质背景下沉积了大面积的层状或透镜状湖相白云岩。

      • 前人研究表明松辽盆地上白垩统沉积初期青山口组处于微弱伸展阶段,地震剖面上以正断层为显著特征;整体快速热沉降,形成统一的大型湖盆,发育巨厚的深湖相暗色泥岩[2425],发生过2~3期构造事件,在岩心上可见震积岩、液化砂脉及凝灰岩(图11),这些认识前人也多有论述,如在松辽盆地青山口组发现不同类型的重力流砂体[2627],松科1井南孔的岩心精细描述里也有夹于暗色泥岩中的震积岩和凝灰岩,并认为其成因与火山活动有关[28],这些成果都揭示了当时的地壳处于相对活跃时期,构造运动和火山活动也间断性爆发。构造运动发生时,为岩浆上涌和热液形成提供了通道和地质背景,而热液活动为白云岩沉积带来了丰富的Ca、Si、Fe、Mg、Al、Na等营养物质,为湖相区泥岩中大面积发育的层状泥晶白云岩和透镜状白云岩沉积提供了物质基础,热液活动和整体快速热沉降为白云岩的快速成岩演化奠定了良好的构造环境背景。

        图  11  松辽盆地青山口组构造活动岩心照片

      • 松辽盆地白云岩岩石学和矿物学分析表明,白云岩发育透镜状和层状两种类型的白云岩。不同类型白云岩空间分布形态不同,镜下鉴定多为泥晶白云岩。微观形貌学分析表明泥晶白云岩中白云石呈半自形、次圆状、菱形或自形镶嵌状分布,为暗色雾心白云石,含铁较低;而白云石加大边呈亮色,全岩鉴定结果为铁白云石,至少代表了两期不同的成因类型,并推测为原生白云岩[29]

        湖相碳酸盐沉积物中碳同位素值的变化与无机碳同位素组成及溶解控制,湖水中溶解无机碳的δ13C值碳来源有关,受温度变化的影响较小,前人研究认为咸水湖碳酸盐沉积物的δ13C值在湖水与大气CO2达到平衡时可达5‰,超盐水湖中沉淀的方解石和文石甚至可达13‰。如果湖水中的溶解碳主要来源于有机质氧化解体产生的碳,那么水体中的溶解碳会大大降低,其极限值可达-25‰,造成沉积的碳酸盐矿物的碳同位素组成偏轻,如果湖泊周缘有河流淡水或地下水注入,也可造成水体中溶解碳的碳同位素组成偏轻,其值约-10‰[30]。Sun et al.[31]在研究准噶尔盆地二叠系湖相白云岩时发现微生物产甲烷作用可以使白云石表现出极为正的δ13C值(高达+20‰),极为负的δ18O值,并且随着产甲烷作用的增加,碳同位素会逐渐变重偏正,而随着硫酸盐还原菌作用成因的增强会使碳同位素逐渐变轻偏负,由于产甲烷菌的代谢活动,大量的生物甲烷通过缺氧湖泊沉积物中的产甲烷作用产生。松辽盆地青山口组湖相区泥晶白云岩碳同位素δ13C值一般为6.21‰~15.28‰,平均为8.2‰,具有明显的δ13C值正偏特征,表明原生白云石的形成很可能与细菌参与的甲烷生成作用有关。松辽盆地白云岩以夹层形式形成于厚层、大面积分布有机质丰度的半深湖—深湖相泥页岩中间,具有δ13C值明显偏正的特征,说明咸化环境、微生物产甲烷作用对δ13C的这一“正偏影响”显然大于富含轻碳的物源方向淡水和有机质对其造成的“负偏影响”。

      • 袁剑英等[32]研究柴西地区湖相白云岩时提出碳同位素偏正,与白云岩沉积时水体处于封闭环境有关,同时来自地壳深部热液影响,会使碳同位素偏正,使氧同位素偏负。张浩等[33]认为柴达木盆地英西地区白云岩碳同位素偏重,氧同位素偏轻是受热液影响造成的。松辽盆地青山口组湖相区氧同位素δ18O值一般介于-16.81‰~-6.49‰,平均为-10.65‰,与热液成因的白云岩具有相似特征(图12)。来自地壳深部富含δ18O的热液影响(丰富的Ca、Si、Fe、Mg、Al、Na等营养物质)使得其氧同位素组成偏负。

        图  12  松辽盆地青山口组、嫩江组及国内其他盆地白云岩碳氧同位素组成与沉积环境分析

        松辽盆地湖相区泥晶白云岩中常量元素中w(CaO)平均为25.45%、w(SiO2)平均为17.61%、w(MgO)平均为11.66%、w(Al2O3)平均为7.80%、w(Fe2O3)平均为6.64%,w(MnO)平均为0.2%,w(CaO)值与柴西盆地准同生交代成因白云岩相当,w(SiO2)、w(MgO)、w(Al2O3)、w(Fe2O3)和w(MnO)的平均值也明显高于柴西盆地泥晶白云岩(柴西盆地准同生交代成因泥晶白云岩种CaO的平均含量为26.73%,MgO的平均含量为13.84%,SiO2的平均含量为4.49%,Al2O3的平均含量为2.07%,FeO的平均含量为0.94%,MnO的平均含量为0.05%)[31]。与酒泉盆地青西凹陷受热液影响的湖相泥晶白云岩中的铁锰含量相当(FeO的平均含量为10.18%,MnO的平均含量为0.36%)[34]。说明松辽盆青山口组湖相区泥晶白云岩与准同生交代成因不同,推测受到热液改造作用。

        松辽盆地青山口组白云岩轻稀土元素LREE明显富集,重稀土元素HREE相对亏损,整体反映重稀土元素相对亏损、轻稀土元素相对富集的配分模式特征。与柴达木盆地英西地区渐新统、酒泉盆地青西凹陷白云岩热液白云岩的稀土元素配分模式类似,同时明显的稀土元素δEu负异常及富含Ca2+、Mg2+、Fe2+、Sr2+、Ba2+等热液流体矿物,均代表了湖泊环境特有的热流体稀土元素组成特征。松辽盆地青山口组白云岩很可能是在相对封闭环境的咸化湖盆中经过微生物产甲烷作用形成的原生白云岩,后期受到地下热液作用而形成的不同成因期次的白云岩。

      • 野外地质剖面观察、薄片分析、阴极发光、场发射电镜、全岩矿物、无机元素、碳氧同位素及稀土元素综合分析表明松辽盆地青山口组湖相区白云岩属于半深湖—深湖相沉积背景下形成的泥晶白云岩,白云石呈次圆形、半自形或菱形,矿物成分以铁白云石为主,沉积环境均形成于干旱气候条件的咸水还原环境。

        松辽盆地青山口组湖相白云岩暗色雾心白云石与亮边加大边白云岩代表了两期不同的成因类型,早期呈层状或透镜状顺层形成于大段厚层湖相泥岩中的白云岩,后期在热液改造作用下形成了碳同位素δ13C值偏正,氧同位素δ18O值偏负、轻稀土元素LREE明显富集、重稀土元素HREE相对亏损,稀土元素δEu明显负异常特征。松辽盆地青山口组湖相白云岩为原生白云岩先期形成及其后期受到热液改造作用两期成因。

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