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The dynamics of changes in the distribution of europium and [DELTA] [sup.13]c during the catagenesis of sapropelites in the Bazhenov Suite of Western Siberia.


The catagenetic transformation of the organic matter (OM) of sedimentary rocks is followed by the formation of different oil components [7,15], some of which are able to interact with rare earth elements (REE) [9,5] by extracting them from the mineral part of sediments, probably in the form of organic complexes of REE as a result of sorption processes. [14] As it was stated in [1], among all REE, europium, able to be reduced to [Eu.sup.2+], optimally concentrates in mineral oil; (Evans, 1976) its content is 1-2 orders of magnitude higher in relation to other REE. [10] This can also be illustrated by the analysis of REE concentration in organic part of rocks, acid extract (AE) and insoluble residue (IR) of the rock deposits of the Khvoinoe and Gerasimovskoe oil and gas fields. (Table 1). [1] Hence, similar processes can also be assumed for the sapropelites in the Bazhenov Suite of West Siberian Plate. [10


The content of europium (Eu) in sapropelites was defined by instrumental neutron activation analysis technique (INAA). Rare earth elements in high-molecular compounds were defined by ICP MS method.


Table 1. Concentration of REE in oil collectors (rocks and their fractions, ppm). The extent of Eu * accumulation in relation to the nearest Sm and Gd in the rock or fraction counted in compliance with the content of these elements in a standard sample of the Russian Platform (RP) (Gd concentration was estimated for the normalized values of Sm and Tb). (Eu|Sm) N are given for the normalized values of these lanthanides for coaly chondritis - C1 [7].

Corresponding Author: Klimenty S. Tsoy, Federal State Autonomous Educational Institution of Higher Education National Research Tomsk State University", 634050, Tomsk, Russia.
Fractions       La        Ce         Pr          Nd

"Khvoinoe" field, top (No 27, interval 2696,7 m.)

Sandstone     22,500    56,200     39,000      21,800
OB             0,065     n.def      n.def      n.def
KB            41,000    261,00     173,750     86,500
HO            19,200    39,500     28,300      17,100

Middle part (No 30, interval 2698,2 m.)

Sandstone     29,600    61,000     37,650      14,300
OB             0,018     n.def      n.def      n.def
KB            589,00    1670,0     977,000    284,000
HO            20,500    39,100     25,150      11,200

Bottom (No 34, interval 2699,3 m.)

Sandstone     36,300    72,000     48,050      24,100
OB             0,870     n.def      n.def      n.def
KB            1560,0    3100,0    2030,000    960,000
HO             9,900    28,600     19,750      10,900

"Gerasimovskoe" field, top (No 679, interval 2757,4 m.)

Argillite     46,400    71,400     54,750      38,100
OB             0,400     n.def      n.def      n.def
KB             6,300    20,900     18,450      16,000

Middle part (No 682, interval 2764,9 m.)

Sandstone     19,400    39,900     27,350      14,800
OB             0,240     n.def      n.def      n.def
KB             9,000     7,500     11,750      16,000

Bottom (No 746, interval 2777,2 m.)

Argillite     35,200    59,500     42,750      26,000
OB             3,000     n.def      n.def      n.def
KB            44,900    100,00     82,500      65,000

Fractions       Sm        Eu        Gd        Tb

"Khvoinoe" field, top (No 27, interval 2696,7 m.)

Sandstone      5,200     1,600     1,015    0,430
OB             0,080     4,900     2,462    0,024
KB            12,900     7,400     4,250    1,100
HO             n.def     0,900     0,660    0,420

Middle part (No 30, interval 2698,2 m.)

Sandstone      5,100     0,900     0,590    0,280
OB             0,030     0,100     0,063    0,025
KB            51,900     6,400     4,575    2,750
HO             4,100     0,740     0,490    0,240

Bottom (No 34, interval 2699,3 m.)

Sandstone      3,800     1,500     0,950    0,400
OB             0,052     2,500     1,263    0,026
KB            110,00    52,000    27,800    3,600
HO             2,350     0,540     0,450    0,360

"Gerasimovskoe" field, top (No 679, interval 2757,4 m.)

Argillite      7,700     2,920     1,785    0,650
OB             0,180     1,180     0,609    0,037
KB             5,100     3,090     1,790    0,490

Middle part (No 682, interval 2764,9 m.)

Sandstone      3,000     1,000     0,660    0,320
OB             0,810     0,830     0,675    0,520
KB             4,500     3,400     2,235    1,070

Bottom (No 746, interval 2777,2 m.)

Argillite      5,200     1,600     1,065    0,530
OB             0,440     5,000     2,630    0,260
KB            19,500     4,500     3,125    1,750

Fractions       Yb      Eu/Sm     Eu *     [(Eu/Sm).sub.N]

"Khvoinoe" field, top (No 27, interval 2696,7 m.)

Sandstone      0,400    0,300     1,640         0,790
OB             0,590    61,25     128,0        161,200
KB             1,800    0,570     3,100         1,500
HO             0,300    0,210     1,100         0,550

Middle part (No 30, interval 2698,2 m.)

Sandstone      0,900    0,170     1,020         0,440
OB             0,130    3,300     6,500         8,700
KB            18,700    0,120     0,760         0,310
HO             0,610    0,180     1,080         0,470

Bottom (No 34, interval 2699,3 m.)

Sandstone      3,200    0,390     2,010         1,020
OB             n.def    48,07    127,00        126,500
KB            51,300    0,470     3,200         1,230
HO             1,550    0,230     1,020         0,600

"Gerasimovskoe" field, top (No 679, interval 2757,4 m.)

Argillite      3,400    0,380     2,080         1,000
OB             1,120    6,500    26,300        17,100
KB             0,540    0,400     3,600         1,570

Middle part (No 682, interval 2764,9 m.)

Sandstone      0,800    0,330     1,750         0,870
OB             0,510    1,030     1,400         2,710
KB             0,720    0,750     3,100         1,970

Bottom (No 746, interval 2777,2 m.)

Argillite      3,700    0,300     1,600         0,790
OB             1,140    11,40    30,500        30,000
KB             3,000    0,230     1,300         0,600

Table 2. Isotopic and microelement composition of OM concentrates within the West Siberian Plate. OM Concentrates (sapropelites) are extracted from argillites of Bazhenov Suite in Siberian Scientific-Research Institute of Geology, Geophysics and Natural Resources" (Novosibirsk). Catagenesis stages of organic matter are also defined there. [TEXT NOT REPRODUCIBLE IN ASCII]. Catagenesis stages: B - brown coal, C - cannel coal, G - gas, F - fat. Eu and Fe concentrations are estimated by the instrumental neutron activation analysis technique (INAA).
Area, well                    Interval, m      Layer       Stage

1                             2                3           4

Aizaskaya IP                  2720,0-2736,0    volzhsky    B
Pudinskaya IP                 2516,0-2533,0    berrias     B
Omskaya IP                    2301,5-2303,5    volzhsky    B
Novo-Vasyuganskaya IP         2538,0-2543,0    volzhsky    BC
Kiev-Eganskaya 350IP          2610,5-2616,5    volzhsky    BC
Maloichenskaya IP             2467,0-2496,0    volzhsky    C
Sergievskaya IP               2540,9-2547,0    volzhsky    C
Vorobyovskaya IP              2486,9-2492,0    volzhsky    C
Poludennaya 222P              2278,0-2295,0    volzhsky    C
Chupalskaya 57P               2946,1-2951,1    volzhsky    CG
Yuzhno-Cheremshanskaya 336P   2690,7-2895,4    volzhsky    G
Verhne-Salymskaya 14P         2831,5-2838,5    volzhsky    GF

Area, well                    Content             [[delta].sup.13]C,
                                                  [per thousand]
                              Eu, ppm    Fe %

1                             5          6        7

Aizaskaya IP                  0,40       11,00    -30,80
Pudinskaya IP                 0,26       9,10     -29,40
Omskaya IP                    0,60       6,80     -29,20
Novo-Vasyuganskaya IP         1,00       5,70     -31,20
Kiev-Eganskaya 350IP          1,00       18,40    -31,80
Maloichenskaya IP             0,30       6,80     -30,40
Sergievskaya IP               0,70       9,00     -30,20
Vorobyovskaya IP              0,57       11,80    -31,00
Poludennaya 222P              0,94       17,60    -31,10
Chupalskaya 57P               0,40       6,70     -30,70
Yuzhno-Cheremshanskaya 336P   0,46       11,50    -31,00
Verhne-Salymskaya 14P         0,10       10,10    -30,00


The comparison of the data on europium concentration and isotopic composition of carbon ([[delta].sup.13]) in sapropelites extracted from the Volzhsky layer rocks of this suite in a number of areas in Western Siberia showed that between the changes of Eu content and [[delta].sup.13] values there exists parallelism, which is not connected with the depth of original organic matter burial but correlated with the catagenesis stages B-GF (pic.1, table 1).

At the same time, within the range of catagenesis stages cyclicity is observed in the changes of both geochemical parameters, one of which ([[delta].sup.13]C) in fact fixes the catagenesis stages of the Bazhenov Suite organic matter, the other (Eu) reflects, apparently, the intensity of catagenesis products interaction with the mineral component of sediments with the changing of the oxidation-reduction environment in the sedimentary rock masses in the process of catagenesis [11]. Consider such cyclisity within the stages of OM transformation.

Stage B, In the beginning of the brown coal stage the depletion of original OM in [sup.13]C isotope takes place due to the predominant carbon dioxide emission, wherein methane amounts to a fraction of a percent of the OM transformation products and does not play any significant role in the balance of carbon isotopic composition [10]. At this stage Eu concentration in the OM is not high and probably are inherited from the diagenetically transformed OM of the Bazhenov Suite sediments.

Stage BC, The transition from stage B to stage BC (brown-cannel coal) indicates to the end of diagenesis and beginning of catagenetic transformation of organic matter. [10] The abrupt changes of [[delta].sup.13]C and Eu concentration let us assume the presence of factors which lead to the qualitative transformations of the original organic matter. The abrupt depletion of original OM in [sup.13]C isotope, connected with the removal of a mass of C[O.sup.2] enriched in [sup.13]C, leads to the change of oxidation-reduction environment due to the depletion of oxidizing components in the rock and the end of C[O.sup.2] emission [11] towards the appearing of highly reducing environment, which is indicated by the high mobility of Eu [1]. In fact, it is this stage where the maximal extraction of Eu into the sapropellite organic matter is recorded (pic. 1). As soon as the stage BC is characterized by the formation of bitumoids [6], they must be the main europium extractants. The validity of such explanation is verified during the study of the distribution of europium, [], tars fractions and pyrobitumens in the oil complex within the cut of the Gerasimovskoe oil and gas-condensate field in Western Siberia, where the distinct correlation of maximums of relative concentration of Eu ([delta]Eu) with the accumulation of tars and pyrobitumens or both of these factions is observed (pic.2). There is a sharp difference in europium concentrations in the top a), in the bottom b) and in the middle part (R2) c).

Stage C-CD, The further transformation of organic matter during the transition from the stage BC to the stage C-CD is followed by its deep destruction [3], maximal quantity of liquid and gas hydrocarbons (up to 1835% of the mass of organic matter) is extracted.


Consequently, stages BC-C-CD apparently correspond to the interval of the main oil and gas formation phase (MOGP), when the main components of oil are formed, such as hydrocarbon comounds of paraffin series, aromatic compounds, heterocompounds, tars and pyrobitumens. According to [6], the migration of light hydrocarbons starts at the stage BC and intensifies at the stages C-CD. As soon as these compounds are enriched in [sup.12]C isotope, their migration and emigration leads to the inversion change of the isotopic composition of the residual organic matter--to the relative accumulation of [sup.13]C in it (pic. 1). This process is followed by the drop of Eu concentration in the residual product. If europium is only connected with tars and pyrobitumens, as it was previously considered [3], which follows from pic.2, the sharp change of Eu concentration in organic matter at the stage C-CD is hard to explain because migration and emigration of heavy fractions (pyrobitumens) are hardly probable [3]. It can ony be assumed that light fractions of bitumoids are also capable of concentrating REE. This is proved by the analysis of the content of REE in oils, tars and pyrobitumens in the residual oil of Samotlorskoe field in Western Siberia, where the following quantitative yield of oil fractions was discovered: oils - 69,4%, tars--25,8%, pyrobitumens--4,8% (according to the data of IPCh SB RAS). The concentration of REE is correspondingly: [SIGMA]P[contains as member][(TR).sub.oils]--23,77ppm, [SIGMA]P3[contains as member][(TR).sub.tars]--6,28ppm [??] [SIGMA]P3[contains as member][(TR).sub.pyrobltumens] 36,22ppm. Thus, we can see that the percentage of mobile fractions of oil hydrocarbons is high, and the sum of REE there is close to the sum of REE in pyrobitumens and is much bigger then the sum of REE in tars. It is the migration of mobile fractions of oil hydrocarbons that could explain the observed effect. If it is so, then the joint loss of europium and these bitumoids must be followed by the appearance of additional Eu concentrations throughout the periphery of oil collectors, where it is possible to talk about the emigration of lighter oil hydrocarbons. Indeed, the excess of europium is found beyond the screens of oil pools, which can be easily seen from the redistribution of REE fractions of acid extract (1.8% HCL) in relation to the rocks swell. It is obvious that such redistribution can only be realized at the expense of the migration of hydrocarbons of oil and gas into deposits (pic.2,3,4).


a) the sum of samples No 1 - No 3 (R1) is the REE beyond the upper area of the top; the sum of samples No 8 No 15 (R2) is the REE composition in the zone of Corg maximum inside the bed; the sum of samples 698 - 706 (R3) is the REE composition in the middle part of the bed, no pyrobitumens found; b) the sum of samples 679 - 680 is the REE composition in the top of the bed; the sum of samples 743 - 746 is the REE composition in the bottom of the bed.

Oils and pyrobitumens fractions were extracted in IPCh SB RAS, Tomsk.



The interval between the points 5-15 is the most oil-saturated zone in the field's cut. Europium and Samarium anomalies point to more reducing environment, migration and accumulation of these lanthanides in bivalent state in the areas of bottom and middle part. The Tb maximum is typical for more oxidizing environment as a result of increased porosity and penetrability in the upper part of the field, and its accumulation in tetravalent state is possible [14].

Stage G-GF, In general, during the transition from the stage CG to G-GF, judging by the increased [[delta].sup.13] and decreased concentration of Eu, the tendency to the changing of both geochemical parameters is similar to the one observed at the C-CG. However, during the transition from the stage CG to G capability of organic matter to generate liquid hydrocarbons decreases, polymerization and polycondensation processes come to an end, the synthesis of liquid hydrocarbons of oil stops. Instead, the processes of residual condensate destruction are developed due to deasphalting by bitumens gases [11]. Deep bonds breakage leads to the formation of net methane gas and its homologs. As gas formation occurs in a substance differentially enriched by [sup.13]C isotope, the total changing of isotopic composition in pyrobitumens after the removal of gases and a part of bitumens is insignificant. At the same time, the loss of light gases at the stage G should increase the concentration of impurity elements including Eu in residual pyrobitumens. This probably conditions the [delta] [sup.13]C correlation and Eu content at the stage G. We can see that the "intermediate" effect of [delta] [sup.13]C and Eu variations at this stage does not change in fact the main tendency towards directed change of [delta] [sup.13]C and Eu connected with the most important factor of the buried organic matter transformation in the sedimentary cycle--increasing of catagenesis temperature from the stage BC to the stage GF in the sapropelites of the Bazhenov Suite (pic. 1).


Using the results of the geochemical research of REE together with the change of isotopic composition of carbon in the sedimentary cycle emphasizes the dynamics of the change of two different geochemical parameters during the catagenetic processes of OM and allow us to talk about the migration capabilities of microelements (REE) and their accumulation together with hydrocarbons of oil and gas depending on the stage of organic matter transformation. Hence, it is obvious that applied and practical direction of geochemical works connected with identification of source deposits in the sedimentary cover is worthwhile. And it is important to conduct the identification with the data on the degree of transformation of buried organic matter. With the establishing of europium concentration in the organic part of rocks (Eu--1ppm) and value of light-weight carbon composition (-32[per thousand]), we can state with high degree of assurance that the main phase of oil and gas generation takes place in sedimentary rocks and buried organic matter and therefore these sedimentary rocks do generate oil and gas.


The synchronism of two different geochemical parameters changes allows to determine the degree of buried organic matter transformation more accurately.


Article history:

Received 15 April 2014

Received in revised form 22 May 2014

Accepted 25 May 2014

Available online 15 June 2014


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Klimenty S. Tsoy

Federal State Autonomous Educational Institution of Higher Education "National Research Tomsk State University", 634050, Tomsk, Russia

Corresponding Author: Klimenty S. Tsoy, Federal State Autonomous Educational Institution of Higher Education National Research Tomsk State University", 634050, Tomsk, Russia.
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Author:Tsoy, Klimenty S.
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:4EXRU
Date:Jun 1, 2014
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