temperatures of dolomitizing fluids in the feixianguan formation from the northeastern sichuan basin

SCIENCE CHINA Earth Sciences

© Science China Press and Springer-Verlag Berlin Heidelberg 2012 earth.scichina.com www.springerlink.com

*Corresponding author (email: [email protected])

• RESEARCH PAPER • October 2012 Vol.55 No.10: 1627–1640

doi: 10.1007/s11430-012-4438-8

Temperatures of dolomitizing fluids in the Feixianguan Formation from the Northeastern Sichuan Basin

HU ZuoWei1*, HUANG SiJing1, LI ZhiMing2, QING HaiRuo3, FAN Ming2 & LAN YeFang1

1 State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China;

2 Wuxi Research Institute of Petroleum Geology, SINOPEC Exploration & Production Institute, Wuxi 214151, China; 3Department of Geology, University of Regina, Regina SK, S4S 0A2, Canada

Received May 19, 2011; accepted January 17, 2012; published online May 19, 2012

The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an im-portant breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years. Because of the dolomite-hosted reservoirs in the Feixianguan Formation, these dolomites and their formation mechanisms have been a re-search focus for sedimentary geologists and petroleum geologists. Based on the homogenization temperatures of fluid inclu-sions, oxygen isotopic composition and their calculated temperatures, and the burial and thermal history of the typical well, it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation, Northeastern Sichuan Basin. Only a minority of dolomites are formed by high-temperature dolomitizing fluids. The ending depth interval of low-temperature dolomitizing fluids was about 1000–2500 m, of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic. The main depth interval of high-temperature dolomitizing fluids was about 3200–4500 m, of which the correspondingly main timing interval was ap-proximately early-middle Middle Jurassic. The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation, Northeast-ern Sichuan Basin.

Triassic, Feixianguan Formation, dolomite, fluid inclusion, oxygen isotope, Northeastern Sichuan Basin

Citation: Hu Z W, Huang S J, Li Z M, et al. Temperatures of dolomitizing fluids in the Feixianguan Formation from the Northeastern Sichuan Basin. Sci China Earth Sci, 2012, 55: 1627–1640, doi: 10.1007/s11430-012-4438-8

Such huge natural gas reserves and good-quality deep-burial reservoirs in the Triassic Feixianguan Formation from the Northeastern Sichuan Basin are very rare in marine car-bonate strata around the world. Grainy dolomites with orig-inal textures and crystalline dolomites (i.e., residual oolitic dolostones and sparry dolostones) are the primary reservoir rocks of the Triassic Feixianguan Formation in the North-eastern Sichuan Basin [1–3], and more than 95% of natural gas reserves are from bedded-massive dolomite reservoirs

with a high degree of dolomitization [4]. Furthermore, the origin of dolomites is still an ongoing controversial problem in geology. Therefore, the study on the origin of dolomites in the Triassic Feixianguan Formation, Northeastern Si-chuan Basin, is of great practical and theoretical signifi-cance. Many previously detailed studies have been done on the dolomites in the Triassic Feixianguan Formation, Northeastern Sichuan Basin, and different dolomitization processes were, moreover, proposed to the grainy dolomites with original textures and crystalline dolomites with much more significant pore volumes, such as mixed-water model [4, 5], seepage-reflux model [6, 7], burial model [8, 9],

1628 Hu Z W, et al. Sci China Earth Sci October (2012) Vol.55 No.10

seepage-reflux and burial model [10, 11], mixed-water and burial model [1, 2, 12–16]. However, many problems have not yet been satisfactorily resolved in these studies, such as the nature of the dolomitizing fluids, the source of the dol-omitizing fluids, and the timing of dolomitization.

The temperatures of dolomitizing fluids, or the formation temperatures of dolomites, are important environmental constraints on the sources of dolomitizing fluids. If the temperatures of dolomitizing fluids are taken as a given, the physical and chemical conditions of the formation environ-ment of dolomites can be largely delineated, and they could provide real clues to further understand and reveal the for-mation and evolution of dolomites. Although many geolo-gists always look for more accurate or even direct access to gain temperatures of dolomitizing fluids, it is impossible to directly measure the temperatures of dolomitizing fluids, as the real-time dolomitizing fluids in the dolomitization pro-cesses cannot be attained, and the composition and physical and chemical properties of dolomitizing fluids more or less changed in the later diagenetic processes. Nevertheless, many geologists still attempt to retrieve the temperatures of the dolomitizing fluids using some indirect methods. Cur-rently, the common methods include homogenization tem-peratures of fluid inclusions, oxygen isotope thermometer and so on [17, 18]. In this paper, the temperatures of dolo-mitizing fluids were discussed through the homogenization temperatures of fluid inclusions and calculated temperatures of oxygen isotopes of dolomites from the Triassic Feixian-guan Formation, Northeastern Sichuan Basin, and then the depth and timing of the dolomitizing fluids were inferred on

the basis of the regional burial and thermal history.

1 Geological setting

The Northeastern Sichuan Basin is located in northeastern Sichuan Province and northern Chongqing (Figure 1), and it is an overlap region between the arcuate tectonic belts of the Daba Mountains and the high-steep tectonic belts of eastern Sichuan in the Northwestern Yangtze Plate [22], including the South Central arcuate tectonic belts of the Daba Moun-tains and the northeastern high-steep tectonic belts of east-ern Sichuan. The surface and subsurface tectonic structures in the Northeastern Sichuan Basin are very complex, and are associated with the multi-phase and multi-type strong extension, extrusion, and thrust tectonics since late Paleo-zoic [23]. Despite the stratigraphic breaks of the Devonian in the region and the Carboniferous in the northern part, the Sinian, Paleozoic, and Mesozoic sedimentary strata with great stratigraphic thickness and diverse sediment types are mainly complete in the Northeastern Sichuan Basin (Figure 1) [24]. The Northeastern Sichuan Basin could be divided into three basic depositional units in the Induan (early Early Triassic, corresponding to the depositional time of the Feixianguan Formation), including Kaijiang-Liangping Trough (basin), shelf (slope) and carbonate platform. And there are mainly six types of depositional facies (evapora-tive platform, restricted platform, open platform, platform marginal shoal, slope, and basin facies) and three types of rocks (carbonate rocks, calcareous mudstones, gypsum

Figure 1 Structural location and integrated gas system column of the Northeastern Sichuan Basin (synthetically drawn from refs. [16, 19–21]).

Hu Z W, et al. Sci China Earth Sci October (2012) Vol.55 No.10 1629

evaporates etc.) [5, 25]. Currently, the dolomite reservoirs in the Triassic Feixianguan Formation, Northeastern Si-chuan Basin, are distributed mainly in the platform marginal oolitic bank subfacies and platform interior oolitic shoal subfacies from the carbonate platform facies in both the east and west sides of the Kaijiang-Liangping Trough [3, 19].

The hydrocarbon exploration in the Northeastern Sichuan Basin began during the petroleum investigation in the late 1950s, but the oil and gas exploration guided by the notion that “structural traps act as the main exploration targets” has not achieved a major breakthrough for more than 30 years. Since the discovery of gas reservoirs in dolomites of the Triassic Feixianguan Formation from the Dukouhe structural trap in 1995, the ideas of hydrocarbon exploration of CNPC and SINOPEC companies were changed into that the “structural-lithological trap complexes with porous dolo-mite reservoirs in the reef and oolitic facies of the Chang-xing Formation and Feixianguan Formation act as the main exploration targets” [19], and then the two companies achieved a major breakthrough in oil and gas exploration. Many giant gas fields are discovered in the Feixianguan Formation dolomites (partially in the Changxing Formation dolomites), such as the Tieshanpo, Luojiazhai, Puguang, Gunziping and Longgang gas fields, and some gas-bearing traps are also discovered, such as the Jinzhuping, Mao-bachang, Zhengbanan and Qilibei gas-bearing traps [1, 20]. Especially, the Puguang gas field, SINOPEC, is the largest assembled marine gas field in China and its current proven natural gas reserves are more than 4000×108 m3. The gas reservoirs in the Feixianguan Formation dolomites from the Northeastern Sichuan Basin belong to the typical high- efficiency gas reservoirs, characterized by the huge reserves, high abundance, high yield, deep burial, high H2S content and common pressure [1].

2 Materials and methods

The core samples were collected from Du5 well in Dukouhe gas field, Luojia2 well and Luojia6 well in Luojiazhai gas field, Puguang5 well and Puguang8 well in Puguang gas field, and Maoba3 well in Maoba gas-bearing trap. The de-tailed locations of sampling wells were shown in Figure 1. The samples are mainly from the member 1 and member 2 of the Feixianguan Formation, and several samples are from the member 4 of the Feixianguan Formation. The rock types of samples include mainly dolomite, slightly calcitic dolo-mite and calcitic dolomite. Based on the observation of the core samples, the composition and fabric of rocks, homoge-nization temperature of fluid inclusions and oxygen isotopic composition were measured using standard thin sections, blue resin vacuum impregnated thin sections, scanning elec-tron microscopy (SEM), fluid-inclusion microthermometry, and stable isotope mass spectrometer.

The petrographic analysis of standard thin sections and

blue resin vacuum impregnated thin sections stained with Alizarin Red-S and potassium ferricyanide were performed at the State Key Laboratory of Oil & Gas Reservoir Geo- logy and Exploitation, Chengdu University of Technology. SEM, fluid-inclusion, and oxygen isotope analyses were carried out at the Wuxi Research Institute of Petroleum Geo- logy, SINOPEC Exploration & Production Institute. The SEM analyses were performed using a Philips XL-30 TMP scanning electron microscope (with an Oxford INCA EDS) from Netherlands. The homogenization temperature (Th) and final melting temperature (Tm) of fluid inclusions were measured using a Linkam MDS 600 heating and freezing stage (with a Carl-Zeiss Axioplan2 microscope) from Great Britain, and the errors are ±0.1°C when the testing tempera-tures are less than 0°C, ±0.5°C when the testing tempera-tures are 0–30°C, and ±1°C when the testing temperatures are more than 30°C. The beginning heating rate is con-trolled within 10°C/min, and the later heating rate is con-trolled within 1°C/min when the testing temperatures are close to the temperatures of critical phase transition. Oxy-gen isotopic compositions were analyzed using a Finigan MAT 253 gas isotope mass spectrometer from Germany. Samples were ground to 200-mesh in an agate mortar, and baked 2 hours under 110°C. About 10 mg samples and 5ml dewatering 100% pure phosphoric acid were degassed un-der vacuum, and then were reacted in the reaction bottles for 1 hour at 75°C. The obtained CO2 gas was purified and collected, and then analyzed using a stable isotope mass spectrometry. The relative error was less than ±0.2‰.

3 Results

3.1 Types of rock

There are many textural and genetic types of dolomites in the Feixianguan Formation, Northeastern Sichuan Basin [4, 6–10]. Based on the types of original textures and their pre-served conditions and crystal sizes of dolomites, Huang et al. [2, 14] divided those dolomites into three main end-member types: micritic dolomites (including dolomicrites), grainy dolomites with original textures, and crystalline dolomites. The former two end-member types of dolomites are charac-terized by well original textures, and the latter one is char-acterized by well sparry textures. In this paper, the main division scheme of different types of dolomites is still con-sistent with the classification scheme from Huang et al. [2, 14], and some samples of mixed dolomites and calcites are divided into transitional rock types with different mineral compositions (Table 1). There are numerous euhedral coarse-crystalline dolomite crystals filling dissolved vugs and caves in several grainy dolomites and crystalline dolo-mites. Therefore, we separated the euhedral coarse-crystalline dolomites as an independent fabric type: void-filling dolomite.


Table 1 Fluid-inclusion microthermometric data of the Feixianguan Formation dolomites from the Northeastern Sichuan Basin

Well Depth

(m) Member

Rock typea)

Host mineral

Heating data

Freezing data

Measured points

Size (m)

V/Lb) ratio (%)

Th (°C) Average Th (°C)

Measured points

Tm (°C) Average salinity

(%, NaCl) Du5 4804.18 1 CD calcite 9 3.6–12.9 5–10 128.6–158.3 140.09 3 2.2 – 1.6 3

Du5 4807.61 1 SCD calcite 8 3.9–9.8 5–10 137.6–153.2 144.67

Luojia2 3223.18 2 GD calcite 11 3.8–12 10 121.3–134.4 128.36 7 8.6 – 5.7 10.8

Luojia2 3225.03 2 SCD calcite 8 3.4–6.1 10 95.7–107.6 102.23

Luojia2 3234.67 2 CD dolomite 1 3.6 10 98.7

Luojia2 3244.7 2 CD dolomite 2 3.2–4.7 10 114.3–117.5 115.9

Luojia2 3250.59 1 CD dolomite 5 4.1–8.4 5–10 110.3–125.3 117.54

Luojia2 3254.46 1 CD calcite 8 4.1–8.8 10–15 165.3–184.3 173.2

Luojia2 3256.6 1 CD calcite 5 3.6–6.6 5–10 154.7–163.2 159.52

Luojia2 3258.51 1 CD dolomite 2 6.2–7.6 10 117.3–126.7 122

Luojia2 3285.89 1 CalD calcite 15 4.2–9.8 10–15 114.2–133.7 125.31 4 30.3 – 9.3 21.1

Maoba3 3876 4 DL calcite 7 5.1–10.5 10–15 116.5–130.7 122.01 1 3.4 5.5

Maoba3 4014.8 3 SDL calcite 2 6.5–8.3 10 134.6–138.5 136.55

Pugauang5 4889.4 3 DL calcite 12 3.2–9.8 10–15 103.2–155.4 121.38

Pugauang8 5351.35 2 DL calcite 18 4–15.2 10–15 94.3–142.3 124.38 2 3 – 2.8 4.7

a) CD, crystalline dolomite; SCD, slightly calcitic dolomite; GD, grainy dolomite; CalD, calcitic dolomite; DL, dolomitic limestone; SDL, slightly dolo-mitic limestone. b) V/L, vapor/liquid.

3.2 Homogenization temperature and salinity data of fluid inclusions

There are varying amounts of fluid inclusions from dolo-mite and calcite crystals in the Feixianguan Formation do-lomites, Northeastern Sichuan Basin (Figure 2). The types of fluid inclusions include vapor-liquid two-phase aqueous fluid inclusions, single-phase aqueous fluid inclusions, va-por-liquid hydrocarbon fluid inclusions, liquid hydrocarbon fluid inclusions, and vapor hydrocarbon fluid inclusions etc. It is noteworthy that the homogenization temperature data of fluid inclusions were obtained in only fifteen thin sec-tions, and a small amount of freezing data of fluid inclu-sions were also obtained in five thin sections from thirty- five samples. The fluid inclusions were observed mainly in the vug- or fracture-filling large euhedral dolomite and sparry calcite crystals, with the sizes between 3.2 μm and 15.2 m, and the vapor/liquid ratios between 5% and 15% (Table 1). In fact, the major measured heating data of fluid inclusions were from the sparry calcite crystals, only ten homogenization temperature data were from dolomite crys-tals, and their corresponding freezing data were not ob-tained (Table 1), due to the small size and irregular shapes of fluid inclusions, the blur boundaries between the fluid inclusions and host minerals, etc.

3.2.1 Homogenization temperature data of fluid inclusions from dolomite crystals

Because there were a few aqueous fluid inclusions to heat in dolomite crystals, only ten temperature data were obtained, with the minimum value of 98.7°C and the maximum value of 126.7°C (Table 1). And 90% of the fluid inclusions were in the range of 110–130°C (Table 2, Figure 3), and this temperature range could basically represent the homogeni-

zation temperature data of fluid inclusions in dolomite crystals, so these dolomites might form in the relative high-temperature conditions and their precipitation timing was relatively late. It is noteworthy that these heating measured fluid inclusions were observed mainly in the large dolomite crystals (about fine- to medium-crystalline) (Fig-ure 2(a)). However, the suitable aqueous fluid inclusions were not always obtained to the homogenization tempera-ture data in all large dolomite crystals, because they were too few in amounts (Figure 2(b)) or too small in sizes (Fig-ure 2(c)) to obtain these data in many large dolomite crys-tals, such as very fine-, fine-, medium-, and mixing hetero- granular-crystalline dolomites.

The two-phase aqueous fluid inclusions were not ob-tained in very fine- to fine-crystalline dolomite crystals of oolitic bank subfacies and micritic dolomites (dolomicrites) from lagoon and patch shoal subfacies, and only a small amount of single-phase aqueous fluid inclusions were ob-served in a few dolomite crystals. However, a large number of vapor-liquid hydrocarbon fluid inclusions, vapor hydro-carbon fluid inclusions, and bitumen fluid inclusions were observed in the medium- to coarse-crystalline dolomite crystals within the fractures and stylolites, and in the me-dium-crystalline dolomites (as the products of the burial dolomitization) that selectively replaced the calcareous oo-lites. Over 80% of previous homogenization temperature data of aqueous fluid inclusions from the Feixianguan For-mation dolomites were mainly in the range of 90–130°C (Table 2, Figure 3) [4, 9, 10, 12, 13, 26, 27]. Moreover, the range of homogenization temperature data of aqueous fluid inclusions in this study showed a good agreement with the previous data of aqueous fluid inclusions of medium- to coarse-crystalline dolomite crystals (Table 2, Figure 3), and thus these data in this study had high reliability.


Figure 2 Microphotographs of fluid inclusions of the Feixianguan Formation dolomites, Northeastern Sichuan Basin. (a) Many fluid inclusions were ob-served in fine- to medium-crystalline dolomite crystals, with a mainly star-like scatter and various sizes. Luojia2 well, 3250.59 m, the member 2 of the Feixianguan Formation. (b) Few two-phase fluid inclusions were observed in fine- to medium-crystalline dolomite crystals; however, several isolated sin-gle-phase fluid inclusions were observed, with various sizes. Du5 well, 4761.63 m, the member 1 of the Feixianguan Formation. (c) Many fluid inclusions were observed in very fine- to fine-crystalline dolomite crystals, with a mainly star-like scatter, but the sizes of fluid inclusions were too small to measure. Luojia2 well, 3240.25 m, the member 2 of the Feixianguan Formation. (d) Many fluid inclusions were observed in coarse-crystalline calcite crystals, with a mainly star-like scatter and various sizes. Luo2 well, 3223.18 m, the member 2 of the Feixianguan Formation. Scale = 50 m.

Table 2 The homogenization temperature data of aqueous fluid inclusions from the Feixianguan Formation dolomites, Northeastern Sichuan Basin

Host mineral

Th (°C) ≥70 <80

≥80 <90

≥90 <100

≥100 <110

≥110 <120

≥120 <130

≥130 <140

≥140 <150

≥150 <160

≥160 <170

≥170 <180

≥180 <190

Dolomite Measured points 1 7 2

Frequency (%) 10 70 20

Dolomitea) Measured points 2 8 15 25 16 20 7 2

Frequency (%) 2.11 8.42 15.79 26.32 16.84 21.05 7.37 2.11

Calcite Measured points 4 12 10 27 23 9 8 5 4 1

Frequency (%) 3.88 11.65 9.71 26.21 22.33 8.74 7.77 4.85 3.88 0.97

a) Burial dolomites, the measured data were from ref. [26].

3.2.2 Homogenization temperature and salinity data of fluid inclusions from calcite crystals

Only a small amount of vapor-liquid two-phase aqueous fluid inclusions were measured in a few large dolomite crystals (mainly fine- to medium-crystalline dolomites) (Figure 2(a)), however, a large number of vapor-liquid two-phase aqueous fluid inclusions were observed from sparry calcite crystals (Figure 2(d)), and they were also ad-vantageous to be measured. Therefore, the homogenization

temperature data of these fluid inclusions were measured to make up for the lack of heating data of fluid inclusions from dolomite crystals. Furthermore, these data could help to test the reconstruction of evolutionary histories of the tempera-tures of dolomitizing fluids.

One hundred and three homogenization temperature data of aqueous fluid inclusions from sparry calcite crystals were obtained in this study, and overall they showed a normal distribution (Table 2, Figure 4), with the minimum value of


Figure 3 The histogram of the homogenization temperature data of aqueous fluid inclusions from the Feixianguan Formation dolomite crystals, Northeastern Sichuan Basin. Previous data were from ref. [26], which are the heating data of aqueous fluid inclusions in burial dolomites.

Figure 4 The histogram of the homogenization temperature data of aqueous fluid inclusions from the Feixianguan Formation calcite crystals, Northeastern Sichuan Basin.

94.3°C and the maximum value of 184.3°C (Table 1). These data adequately indicated that sparry calcites could precipi-tate in the large temperature range of diagenetic fluids, and almost continuously recorded the temperatures of diagenetic fluids. Because over 85% of homogenization temperature data were in the range of 100–150°C, this temperature range could basically represent the homogenization temperature data of fluid inclusions in calcite crystals (Table 2, Figure 4). Moreover, the final melting temperatures of some above- mentioned aqueous fluid inclusions were almost below 2.07°C, i.e., the salinity data of most aqueous fluid inclu-sions were above 3.5% NaCl equivalent of normal seawater salinity, whereas only two salinity data of one sample from Du5 well were in the range of 2.5%–3% NaCl equivalent (Table 1). These salinity data indicated that most sparry calcites might precipitate from the relatively high tempera-ture and salinity diagenetic fluids. Furthermore, over 50% of homogenization temperature data of aqueous fluid inclu-sions from sparry calcite crystals were in the range of

90–130°C (Table 2, Figure 4), and this temperature range was similar to the range of homogenization temperatures of above-mentioned aqueous fluid inclusions from medium- to coarse-crystalline dolomites (Table 2, Figure 3, Figure 4). Therefore, these data also showed that the precipitation of most sparry calcites followed the precipitation of medium- to coarse-crystalline dolomites.

Therefore, it could be considered that the dolomitizing fluids (including the fluids of the calcite precipitation) were more active in the range of 90–130°C and other neighboring temperature range according to the homogenization temper-ature data of aqueous fluid inclusions, and then a small amount of medium- to coarse-crystalline dolomites precipi-tated. Because of the burial, uplift, deformation or later thermal events, the fluid inclusions from carbonate minerals often had unusually high homogenization temperature [28]. Especially, the Feixianguan Formation dolomites from the Northeastern Sichuan Basin had undergone deep burial, significantly tectonic uplift, and strong tectonic deformation. Moreover, it is still difficult to determine the temperatures of dolomitizing fluids for the large dolomite crystals (in-cluding very fine-, fine-, medium-, and mixing heterogran-ular-crystalline dolomites), due to few aqueous fluid inclu-sions to measure (but some very small single-phase fluid inclusions could be observed (Figure 2(b), (c))). Dix et al.

[29] proposed that the temperature of dolomites with small liquid phase fluid inclusions did not exceed 60–80°C. In other words, if the temperature of dolomites could be specu-lated by the amount, size or single-phase of fluid inclusions, the precipitation of most dolomites (dolomitizing fluids) in the Feixianguan Formation, Northeastern Sichuan Basin, might occur at less than 80°C.

3.3 Oxygen isotope thermometry

Urey et al. [30] first proposed that the contents of 18O from carbonate rocks could be used to determine the formation temperatures of carbonate rocks, and then they applied this to determine the temperatures of Late Cretaceous palaeo- ocean in England, Denmark, and the southeastern United States. Based on the different research objects, the oxygen isotope thermometry could be divided into the external ther-mometry, internal thermometry, and monomineralic ther-mometry [31]. The external oxygen isotope thermometry is a more common method, based mainly on the principles of oxygen isotope exchange equilibrium reactions between minerals and water [17, 18, 32, 33], and is used to calculate the formation temperatures of minerals using the oxygen isotope fractionation equations and corresponding calibra-tion curves, which had been obtained by the experiments and theoretical calculations [31, 32]. Although many oxy-gen isotope fractionation equations between dolomites and water were reported, all these equations between ordered dolomite and water were established above 200°C, such as 300–510°C [34] and 252–295°C [35]. In this study, we ap-


plied the oxygen isotope fractionation equation of Vascon-celos et al. [36] to calculate the temperatures of the Feixian-guan Formation dolomites, Northeastern Sichuan Basin.

1000 lndolomite-water = 2.73 × 106 × T2 + 0.26,

where dolomite-water is the oxygen isotope fractionation factor between dolomite and water, and T is Kelvin temperature (K). This equation is a recently proposed oxygen isotope fractionation equation between ordered dolomite and water, which is based on the microbial culture experiments under the low-temperature conditions (within the range of 25–45°C), and is also a successful case under the lowest experimental temperatures as yet.

Because a relatively reasonable value of the oxygen iso-topic composition of dolomitizing fluids should be assumed when the dolomite-water oxygen isotope thermometry was applied [17, 37], whereas the original dolomitizing fluids of the Feixianguan Formation dolomites, Northeastern Sichuan Basin, have been more or less changed, even exhausted in the later geological processes, it is almost unrealistic to ob-tain the oxygen isotopic composition of these dolomitizing fluids. Furthermore, there were no published oxygen isotopic composition data of the formation water, and therefore it is very difficult to determine the oxygen isotopic composition of dolomitizing fluids from the Feixianguan Formation, Northeastern Sichuan Basin. However, the dolomitizing fluids from the Feixianguan Formation, Northeastern Si-chuan Basin, were considered to relate more with the evapo-rated seawater or marine fluids from the isolated evapora-tive carbonate platform [2, 4–6, 14]. A large amount of widespread evaporite minerals and gypsum (anhydrite)-salt beds in the Feixianguan Formation, Northeastern Sichuan Basin, were the typical evidence for this speculation. There-fore, the oxygen isotope values of the dolomitizing fluids were distinctly higher than that of Triassic seawater (0‰ (SMOW) [38]). Spötl et al. [39] proposed 1‰ (SMOW) as the oxygen isotope value of weakly evaporitive Triassic seawater. However, the strongly evaporitive seawater oc-curred in the Feixianguan Formation, Northeastern Sichuan Basin, could have higher oxygen isotope values. Therefore, 2‰ (SMOW), twice as much as the proposed value of Spötl et al. [39], was used as the oxygen isotopic composition of the dolomitizing fluids in the Feixianguan Formation, Northeastern Sichuan Basin. This value was consistent with the initial value in the major range of the oxygen isotopic composition (2‰–5‰ (SMOW) [40]) of the gas field brine from the adjacently overlying Triassic Jialingjiang and Lei-koupo formations and underlying Permian, Sichuan Basin (including the Northeastern Sichuan Basin) (Figure 5).

The oxygen isotopic compositions of dolomites in the Feixianguan Formation, Northeastern Sichuan Basin, showed a relatively positive excursion, and ranged between 2.5‰ and 6.5‰ (PDB). The calculating results of the dolomite-water oxygen isotope thermometry were shown in Table 3. Overall, the calculated temperatures of the dolo-

Figure 5 The D and 18O crossplot of different formation brines in the gas fields of Sichuan Basin (including the Northeastern Sichuan Basin) (after ref. [40]). The dashed box: the major range of the oxygen isotopic composition (2‰–5‰, SMOW) of the gas field brine from the adjacently overlying Triassic Jialingjiang and Leikoupo formations and underlying Permian. 1-Xujiahe Fm.; 2-Member 3 of Leikoupo Fm.; 3-Member 5 of Jialingjiang Fm. and Member 1 of Leikoupo Fm.; 4-Members 1–3 of Jialingjiang Fm.

mite-water oxygen isotope thermometry were relatively in the range of 50–90°C, with the minimum value of 54.7°C and the maximum value of 81.2°C (Table 3, Figure 6(a)). Over 80% of the calculated temperatures were in the range of 60–80°C, 17% of the calculated temperatures were in the range of 50–60°C, and only less than 3% of the calculated temperatures were in the range of 80–90°C (Figure 6(b)). It is noteworthy that these calculated temperatures of dolo-mite-water oxygen isotope thermometry were more likely to indicate the final formation temperatures of the Feixianguan Formation dolomites, Northeastern Sichuan Basin. The do-lomites might merely undergo the precipitation of the later dolomites, or overlap the recrystallization after the later dolomite precipitation. Certainly, the dissolution-precipitation in the recrystallization processes of dolomites still re-quired the dolomitizing fluids. In other words, the recrystal-lizing fluids of dolomites were still the dolomitizing fluids.

The calculated temperatures of different types of dolo-mites using the dolomite-water oxygen isotope thermometry were within the different temperature intervals. The calcu-lated temperatures of crystalline dolomites and void-filling dolomites with the highest calculated temperatures were mainly in the range of 60–80°C, and several calculated temperatures were above 80°C (Figure 6(a), Figure 7). The calculated temperatures of grainy dolomites with original textures (mainly oolitic dolomites) were in the range of 50–60°C (Figure 6(a), Figure 7), which were the minimum calculated temperatures of all types of dolomites. The cal-culated temperature of micritic dolomite was in the range of 60–70°C (Figure 6(a), Figure 7), which was similar to the calculated temperatures of crystalline dolomites. This cal-culated temperature was distinctly contrary to the tempera-


Table 3 The calculated temperatures of the Feixianguan Formation dolomites, Northeastern Sichuan Basin, using the dolomite-water oxygen isotope ther-mometry

Well Member Depth (m) Rock type a) 18O (‰, PDB)

Assumed 18O value of fluids (‰, SMOW)

Calculated temperature (°C)

Source

Du5 1 4761.63 GD 3.34 2 58.7 [2]

Du5 1 4779.77 GD 3.38 2 58.9 [2]

Du5 1 4789.5 SCD 3.16 2 57.5 [2]

Du5 1 4796.39 CD 4.63 2 67.7 [2]

Du5 1 4804.18 CD 6.38 2 81.2 [2]

Du5 1 4807.61 SCD 4.96 2 70.1 [2]

Du5 1 4810.47 SCD 4.56 2 67.2 [2]

Luojia2 2 3196.22 MD 4.32 2 65.5 [2]

Luojia2 2 3205.81 SCD 4.67 2 68 [2]

Luojia2 2 3211.16 GD 2.73 2 54.7 [2]

Luojia2 2 3213.52 GD 2.99 2 56.4 [2]

Luojia2 2 3216.63 CD 6.06 2 78.6 [2]

Luojia2 2 3220.08 CD 5.02 2 70.6 [2]

Luojia2 2 3223.18 GD 2.91 2 55.8 [2]

Luojia2 2 3225.03 SCD 3.28 2 58.3 [2]

Luojia2 2 3227.89 CD 5.11 2 71.3 [2]

Luojia2 2 3230.25 CD 4.69 2 68.1 [2]

Luojia2 2 3232.84 CD 4.87 2 69.5 [2]

Luojia2 2 3234.67 CD 5 2 70.4 [2]

Luojia2 2 3236.04 CD 4.57 2 67.3 [2]

Luojia2 2 3237 CD 4.48 2 66.6 [2]

Luojia2 2 3240.25 CD 4.44 2 66.3 [2]

Luojia2 2 3241.4 CD 4.19 2 64.5 [2]

Luojia2 2 3243.6 CD 5.42 2 73.6 [2]

Luojia2 2 3244.7 CD 5.62 2 75.2 [2]

Luojia2 2 3246.9 CD 4.41 2 66.1 [2]

Luojia2 2 3248.71 CD 4.8 2 68.9 [2]

Luojia2 2 3249.66 CD 5.35 2 73.1 [2]

Luojia2 2 3250.59 CD 6.1 2 79 [2]

Luojia2 2 3252 CD 5.53 2 74.5 [2]

Luojia2 2 3254.46 CD 5.8 2 76.6 [2]

Luojia2 2 3256.6 CD 5.03 2 70.7 [2]

Luojia2 2 3258.51 CD 5.98 2 78 [2]

Luojia2 2 3260.6 CD 4.55 2 67.1 [2]

Luojia2 2 3266.13 CD 4.48 2 66.6 [2]

Luojia2 2 3277.19 CD 4.79 2 68.9 [2]

Luojia2 1 3299.11 SCD 4.7 2 68.2 [2]

Luojia6 2 3935.32 SCD 6.13 2 79.2 This study

Maoba3 4 3880.89 SCD 5.33 2 72.9 This study

Puguang5 2 4893.3 CD 5.72 2 75.9 This study

Puguang5 2 4893.3 VFD 5.19 2 71.9 This study

Puguang5 1 5061 CD 5.5 2 74.2 This study

a) GD, grainy dolomite. SCD, slightly calcitic dolomite. CD, crystalline dolomite. MD, Micritic dolomite. VFD, void-filling dolomite.

tures of their formation environment. The temperatures of the dolomitizing fluids of micritic dolomites should be equal, or close, to the surface temperature, for the micritic dolo-mites were generally believed to form by primary precipita-tion or penecontemporaneous replacement [2, 9, 12–14, 41]. Such high calculated temperatures might be related to the oxygen isotope reequilibrium of micritic dolomites in the later recrystallization processes. Therefore, the temperatures of dolomitizing fluids of micritic dolomites would not be

discussed further in this study. The calculated temperatures of the slightly calcitic dolomites were in the range of 50–80°C (Figure 6(a), Figure 7). The calculated tempera-tures of slightly calcitic grainy dolomites were similar to grainy dolomites (within the range of 50–60°C) and the calculated temperatures of slightly calcitic crystalline dolo-mites were similar to crystalline dolomites (within the range of 60–80°C). Thus it is clear that the oxygen isotopic com-positions of slightly calcitic dolomites had not been signifi-


Figure 6 The calculated temperatures of the Feixianguan Formation dolomites, Northeastern Sichuan Basin (assuming the 18O value of dolomitizing fluids = 2‰ (SMOW)).

Figure 7 The histogram of the calculated temperatures of different types of the Feixianguan Formation dolomites, Northeastern Sichuan Basin (as-suming the 18O value of dolomitizing fluids = 2‰ (SMOW)).

cantly affected by the sparry calcites.

4 Discussion

In contrast to the homogenization temperatures of aqueous fluid inclusions from dolomites, the calculated temperatures of the Feixianguan Formation dolomites, Northeastern Si-chuan Basin, were significantly low. The former homoge-nization temperatures were mainly in the range of 90–130°C, and the latter calculated temperatures were mainly in the range of 50–80°C. Therefore, the maximum temperature difference between former and latter temperatures was more than 70°C. What results in such a large temperature differ-ence? Was this related to the limitations of dolomite-water

oxygen isotope thermometry or the deviation of the as-sumed 18O value of dolomitizing fluids? Based on the low-temperature experimental results, Vasconcelos et al. [36] proposed an oxygen isotope fractionation equation with higher reliability than the other oxygen isotope fractionation equations obtained using extrapolations of high-temperature experimental results or theoretical calculations. Although 2‰ (SMOW) as the oxygen isotope value of the dolomitiz-ing fluids remained a certain degree of subjectivity, ±1‰ (SMOW) change of oxygen isotopic composition of the dolomitizing fluids could merely result in about 5－8˚C changes of the calculated temperatures [17]. The calculated temperatures using the dolomite-water oxygen isotope thermometry would merely result in a deviation of about 10–16°C even if there was ±2‰ (SMOW) of the error for the assumed 18O value of dolomitizing fluids (2‰, SMOW). Therefore, the deviation of over 10°C was still acceptable, as the Feixianguan Formation in the Northeast-ern Sichuan Basin had undergone about 8000 m of the maximum burial depth and over 200°C of the maximum burial temperature (Figure 8). In other words, there were no significantly substantial affects on the calculated tempera-tures, which arose from the partial deviation of the assumed 18O value of dolomitizing fluids, and thus the chief cause of temperature difference was not the above-mentioned factors. We considered that different stages of dolomitizing fluids with different temperatures were the chief causes of temperature difference. In other words, there were two dolomitizing fluids with different temperatures in the Feixianguan Formation, Northeastern Sichuan Basin, and they were not in the same stage.

Currently, the boundary between the low-temperature and high-temperature dolomitizing environment in geologi-cal processes were still controversial. Lovering [42] sug-gested that 100°C could be acted as the boundary between


Figure 8 The depth intervals and timing of different dolomitizing fluids in the Feixianguan Formation, Northeastern Sichuan Basin. The burial and thermal history curves were from ref. [16].

the low-temperature and high-temperature dolomitizing environment. Machel [43] considered that the range of 50–80°C could be acted as the approximate boundary be-tween the low-temperature and high-temperature dolo-mitizing environment. If the boundary of low-temperature and high-temperature dolomitizing environment was 80°C, and then the boundary of low-temperature and high-temperature dolomitizing fluids was also 80°C, most dolo-mitizing fluids could be low-temperature, and only a few dolomitizing fluids could be high-temperature in the Feixianguan Formation, Northeastern Sichuan Basin (Figure 6).

4.1 Low-temperature dolomitizing fluids

Based on the above-mentioned boundary between low- temperature and high-temperature dolomitizing fluids, the grainy dolomites with original textures (including slightly calcitic grainy dolomites) within the range of 50–60°C, crys-talline dolomites (including slightly calcitic crystalline do-lomites) within the main range of 60–80°C and void-filling dolomites were obviously the products of the low-temperature dolomitizing fluids (Figure 6(a), Figure 7). However, the range of 50–80°C could merely represent the tempera-tures of the final stage of dolomitizing fluids of the grainy dolomites with original textures, crystalline dolomites and void-filling dolomites, and it was not to be sure of the initial formation temperature of those dolomites because the cal-culated temperatures of dolomite-water oxygen isotope

thermometry were more likely to indicate the final for-mation temperatures of dolomites. Therefore, the range of 50–60°C corresponded to the ending temperatures of pre-cipitation or recrystallization of grainy dolomites with orig-inal textures, and the range of 60–80°C corresponded to the ending temperatures of precipitation or recrystallization of crystalline dolomites and void-filling dolomites. By contrast, the ending temperatures of the grainy dolomites with origi-nal textures were distinctly lower than those of crystalline dolomites and void-filling dolomites (Figures 6(a), 7). The-se differences might be related to the individual processes or overlap processes from different stages of low-temperature dolomitizing fluids with different temperatures. In other words, there were two different temperature intervals repre-senting two stages of different low-temperature dolomitizing fluids. The former stage of low-temperature dolomitizing fluids were relatively cold, and the latter stage of low-temperature dolomitizing fluids were relatively hot. Currently, the interpretation for the origin of these low-temperature dolomitizing fluids aroused much contro-versy. The origin of these low-temperature dolomitizing fluids might be from the near-surface supratidal, Sabkha, seepage reflux, seawater or mixed-water environments and their thermal fluids in the burial environment [2, 4, 6, 7, 12–16], or other sources in the burial environment [2, 9, 12–16]. Thus it was still difficult to determine the initial temperatures of dolomitizing fluids. However, the calculat-ed temperatures using the dolomite-water oxygen isotope thermometry could indicate the ending temperatures of dif-


ferent stages of low-temperature dolomitizing fluids. Based on the reconstruction of the burial and thermal

history of the typical well (Puguang2 well) in the North-eastern Sichuan Basin, we considered that the different stages of low-temperature dolomitizing fluids correspond to different ending depth and ending timing of burial in the Feixianguan Formation, Northeastern Sichuan Basin. The ending depth interval of the former relatively cold low-temperature dolomitizing fluids was about 1000–1500 m, and the ending timing interval was approximately early- middle Middle Triassic. The ending depth interval of the latter relatively hot low-temperature dolomitizing fluids was about 1500–2500 m, and the ending timing interval was approximately from late Middle Triassic to early-middle Late Triassic (Figure 8). Therefore, the ending depth and timing of these low-temperature dolomitizing fluids were consistent with the corresponding depth and timing of burial before the large-scale emplacement of liquid hydrocarbons, and that was a congruous and matched process with the thermal evolution of source rocks from beginning to end. When the burial depth of the Feixianguan Formation, Northeastern Sichuan Basin, was greater than 2500 m and its temperature was higher than 80°C, the organic matters in the main source rocks (Upper Permian source rocks) as the origin of the liquid hydrocarbons of the Feixianguan For-mation, Northeastern Sichuan Basin, had entered the mature phase and the oil generation threshold in the middle-late Late Triassic [1, 8, 16, 20, 21, 44, 45]. The strong em-placement of the numerous liquid hydrocarbons would lead to the rapid decline of water/rock ratio because the liquid hydrocarbons had begun to form, migrate, and accumulate into the pore volumes of the Feixianguan Formation reser-voirs, and then the occurrence of the massive dolomitization was almost inhibited, and the precipitation and growth of dolomites also gradually tended to a standstill. The dolo-mitization of dolomite reservoir bodies and the formation of most dolomites within currently dolomite reservoirs re-quired that the low-temperature dolomitizing fluids should be finished before the large-scale emplacement of liquid hydrocarbons. The surfaces of euhedral dolomite crystals or the pore volumes between euhedral dolomite crystals would be attached or filled by the film-like and droplet-like bitu-men (Figure 9). Therefore, the formation of euhedral dolo-mites (the dolomitization of dolomitizing fluids) was dis-tinctly earlier than the emplacement of liquid hydrocarbons in the paleo-oil pools. The previous studies also have shown that the formation and recrystallization of reservoir dolo-mites in the Feixianguan Formation, Northeastern Sichuan Basin, occurred before the formation of the paleo-oil pools [1, 3, 8, 15, 16].

4.2 High-temperature dolomitizing fluids

In addition to the low-temperature dolomitizing fluids, there were also some high-temperature dolomitizing fluids in the

Figure 9 The occurrence of dolomite crystals and bitumen in the Feixianguan Formation dolomites, Northeastern Sichuan Basin. The sur-faces of euhedral dolomite crystals or the pore volumes between euhedral dolomite crystals would be attached or filled by the film-like bitumen (white arrows) and droplet-like bitumen (black arrows), and the intergran-ular porosity was developed. Puguang5 well, the member 1 of the Feixian-guan Formation, 5061 m. SEM photomicrograph.

Feixianguan Formation, Northeastern Sichuan Basin. The above-mentioned homogenization temperatures of aqueous fluid inclusions could represent the real-time temperatures of high-temperature dolomitizing fluids. The temperatures of high-temperature dolomitizing fluids were in the range of >80°C, especially in the range of 100–130°C (Figure 3, Figure 6(b)). Therefore, these temperatures were distinctly higher than the temperatures of low-temperature dolomitiz-ing fluids. A few crystalline dolomites composed of large dolomite crystals (mainly fine- to medium-crystalline dolo-mites) and medium- to coarse-crystalline dolomites along the pore lining, fractures and stylolites were formed by the dolomitization of high-temperature dolomitizing fluids. These high-temperature dolomitizing fluids might be formed as a result of the further thermal evolution of the former low-temperature dolomitizing fluids. However, they might be also from other sources of burial diagenetic fluids [2, 9, 12–16], and they might even be the products of the mixtures of both fluids.

Based on the reconstruction of the burial and thermal history of the typical well (Puguang2 well) in the North-eastern Sichuan Basin, we considered that the depth interval of the high-temperature dolomitizing fluids was about 2500–5500 m, and the timing interval was approximately from middle-late Late Triassic to late Middle Jurassic, es-pecially the main depth interval of the high-temperature dolomitizing fluids was about 3200–4500 m, and the main timing interval was approximately early-middle Middle Jurassic (Figure 8). Although the dolomitization of low-temperature dolomitizing fluids could be incomparable with the continued dolomitization of high-temperature dolomitizing fluids with such great depth and timing inter-val, the large-scale emplacement of liquid hydrocarbons had almost replaced the majority of dolomitizing fluids in the


original pore volumes because the organic matters in the main source rocks (Upper Permian source rocks) as the origin of the liquid hydrocarbons of the Feixianguan For-mation, Northeastern Sichuan Basin, had entered the nu-merous oil generation phase in the late Late Triassic-Early Jurassic [1, 8, 16, 20, 21, 44, 45]. These residual or new dolomitizing fluids occupying limited pore volumes could be more likely to play a role during a gap or weak phase of the emplacement of liquid hydrocarbons, and thus the activi-ties of these high-temperature dolomitizing fluids were greatly weaker than those of low-temperature dolomitizing fluids, directly resulting in the greatly less amount of dolo-mites formed by high-temperature dolomitizing fluids with higher temperatures than that of dolomites formed by low-temperature dolomitizing fluids.

4.3 Significance of different dolomitizing fluids

There were many types of pore volumes in the Feixianguan Formation dolomite reservoirs, Northeastern Sichuan Basin, including intergranular primary porosity, intergranular sec-ondary porosity, intragranular secondary porosity, intercrys-talline porosity, moldic porosity, and dissolution-enlarged porosity, and a few fractures and pressure-solution stylolites could be observed [1, 2, 7–10, 14, 16]. Obviously, the de-velopment and preservation of the pore volumes were closely related to the dolomites (Figure 9). Many other pre-vious studies had also considered that the dolomitization was an important enhancement of diagenetic processes in the formation and evolution of pore volumes [1, 2, 7–10, 14, 16]. But in fact, we considered that the dolomites of the Feixianguan Formation, Northeastern Sichuan Basin, were more likely to play a role of retention diagenesis, which preserved (or conversed) the majority of original pore vol-umes in predecessors (oolitic limestones) by the dolomitiza-tion, and then the dolomite reservoirs of the Feixianguan Formation, Northeastern Sichuan Basin, were still shown excellent reservoir qualities in the deep or ultra-deep burial.

The low-temperature dolomitizing fluids acted as the main dolomitizing fluids in the Feixianguan Formation oc-curred in the early timing and shallow burial, and the sig-nificant water-rock interaction between these fluids and the oolitic limestones happened before the predecessors (oolitic limestones) had undergone destructive cementation and compaction. Moreover, the dolomitization of the oolitic limestone bodies would be finished before the strong em-placement of numerous liquid hydrocarbons, and the major-ity of original pore volumes in the oolitic limestones were chiefly preserved by the strong and rapid dolomitization of low-temperature dolomitizing fluids, and then a large amount of available pore volumes were provided to the subsequently strong emplacement of numerous liquid hy-drocarbons (Figure 9). Therefore, the low-temperature dolomitizing fluids were of great significance to the for-mation and evolution of pore volumes in the dolomite res-

ervoirs of the Feixianguan Formation, Northeastern Sichuan Basin. By contrast, the high-temperature dolomitizing fluids occurred in the later stage and deeper burial after the pri-mary dolomitization of the oolitic limestones had been fin-ished and numerous liquid hydrocarbons had emplaced the pore volumes, and thus the dolomitization of high-temperature dolomitizing fluids could be more likely to play a role in the limitedly unoccupied pore volumes without former liquid hydrocarbons. However, the precipitation and growth of dolomites should distinctly occupy the original pore volumes, and then the decrease of pore volumes would pre-vent the later emplacement and accumulation of liquid hy-drocarbons. On the other hand, the early emplacement of numerous liquid hydrocarbons could prevent the damage of high-temperature dolomitizing fluids to the dolomite reser-voirs, and therefore the high-temperature dolomitizing flu-ids were not necessarily beneficial to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation and even were more likely to dam-age them in many cases.

5 Conclusions

(1) The homogenization temperatures of aqueous fluid inclusions in a small number of large dolomite crystals (mainly fine- to medium-crystalline dolomites) and a large number of sparry calcite crystals were mainly in the range of 90–130°C and other neighboring temperature range. It is considered that only a minority of dolomites were formed in high-temperature conditions, whereas the majority of the dolomite precipitation (dolomitizing fluids) might occur in the range of less than 80°C from the Feixianguan Formation, Northeastern Sichuan Basin.

(2) The oxygen isotopic compositions of different types of dolomites ranged between 2.5‰ and 6.5‰ (PDB), and most of the calculated temperatures using the dolo-mite-water oxygen isotope thermometry were in the range of 50–80°C. It is considered that most dolomites were formed by the dolomitization of low-temperature dolo-mitizing fluids, and only a few dolomites were formed by the dolomitization of high-temperature dolomitizing fluids in the Feixianguan Formation, Northeastern Sichuan Basin.

(3) The different stages of dolomitizing fluids with dif-ferent temperatures corresponded to the different depths and timing of dolomitization in the Feixianguan Formation, Northeastern Sichuan Basin. The ending depth interval of low-temperature dolomitizing fluids was about 1000–2500 m, and the ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic. The main ending depth interval of high-temperature dolo-mitizing fluids was about 3200–4500 m, and the main end-ing timing interval was approximately early-middle Middle Jurassic.

(4) The low-temperature dolomitizing fluids were of


great significance to the formation and evolution of pore volumes in the dolomite reservoirs of the Feixianguan For-mation, Northeastern Sichuan Basin, but the high-temperature dolomitizing fluids were not necessarily beneficial to the formation and evolution of the pore volumes of dolo-mite reservoirs in the Feixianguan Formation and even were more likely to damage them in many cases.

We would like to thank Xu Ershe, Zhang Wentao and Zhang Xuehua for their assistance in the fieldwork, and the anonymous reviewers and editors for their critical comments that greatly improved the manuscript. This study was supported by National Natural Science Foundation of China (Grant Nos. 40839908 and 40672072) and the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050616005).

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temperatures of dolomitizing fluids in the feixianguan formation from the northeastern sichuan basin

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