Table of Content

20 June 2012, Volume 18 Issue 2

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Surface Behavior of Calcite upon Uptake of Cd2+ and Pb2+

TENG H. Henry1, ZHAO Liang2

2012, 18(2):  193. 

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 The behavior of calcite surfaces in the presence of Cd2+ and Pb2+ is investigated by in situ fluid cell Atomic Force
Microscopy (AFM) to determine the differences between Cd/calcite and Pb/calcite interactions and the growth mode of surfaceprecipitate. Experiments are conducted on {101 _4} cleavage faces exposed to Cd- and Pb-bearing solutions that are undersaturatedwith respect to calcite, otavite, and cerussite. Two observations are made: (1) The presence of Cd2+ does not affect the relative stepkinetics along <4_41> steps (i.e.v s+>v s-) during calcite dissolution, whereas Pb2+ strongly retards the retreat of the obtuse <441>+steps to reverse the relative step kinetics; (2) The initial dissolution is followed by a development of surface precipitation afterthe flow-through input is turned off to allow the surfaces to equilibrate with the solutions. The surface precipitate grows in a layerspreading mechanism showing clearly defined directions in the presence of Cd but not Pb.
　　The kinetic effects of cadmium and lead on calcite dissolution are suggested to be related to a selective cation adsorptionin accordance with the cation size, the geometry of adsorption complexes, and the crystallographic direction dependent stepgeometry. The Cd2+ ions, having a slightly smaller ionic radius than Ca2+, are thought to have a stronger presence along the acute<4_41>- steps that are geometrically more confined. In contrast, the much larger Pb2+ ions are believed to form distorted octahedralsurface complexes to adsorb predominantly at the more open <4_41>+ steps. The structural incompatibility between cerussite andcalcite is speculated to account for the lack of step directions for the layer growth on calcite surfaces in the presence of Pb2+. Theoccurrence of layer-by-layer growth indicates that epitaxial growth plays an important role in the formation of (Ca, Cd)CO3 and (Ca,Pb)CO3 solid solutions.

The CO2 Geological Sealing Conditions andPotential Evaluation in Coal Seams in Jiangsu Province

YAO Suping, TANG Zhongyi, TAN Lihua, PEI Wenming

2012, 18(2):  203. 

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The geological conditions of CO2 sequestration in coal seams in Jiangsu Province contain the distribution of
Carboniferous-Permian coal measures，coal resources and coal seam reservoir conditions. According to the comprehensiveresearch about the geological conditions of CO2 sequestration in coal seams，the preliminary assessments of the storage potentialare made for the coal fields in southern Jiangsu，Xuzhou and Fengpei，respectively. The results show that the coal seams in thesecoal fields have considerable potential and disposal prospect for CO2 sequestration. The estimate of CO2 storage resources in coalseams in Jiangsu Province is over three hundred million tons of CO2. Among these coal seams，southern Jiangsu coal area couldsequester 81 million tons of CO2，Xuzhou coal area of nearly 150 million tons of CO2 and Fengpei coal area of 87 million tons ofCO2. The prospect of typical coal-seam CO2 sequestration can be divided into three categories : suitable storage area（ Class A)，less suitable storage area（ B)， and poor storage area（ Class C).

Review and Advancements of Studies on Silicate Weathering
and the Global Carbon Cycle

WU Weihua, ZHENG Hongbo, YANG Jiedong, LUO Chao

2012, 18(2):  215. 

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Silicate weathering is a major sink of the atmospheric CO2, which directly affects the global carbon cycle and the
climate. Since the pioneering work of Walker et al. (1981), studies on“ silicate weathering, carbon cycle and climate changes”
have sprung up in recent years. Many advancements have been obtained from computer models to river water geochemistry andfrom large rivers with a drainage area exceeding to 106 km2 to monolithologic small watershed with tens/hundreds km2 drainagearea,. In the global scale, atmospheric CO2 consumption from silicate weathering is about 0.138-0.169 Gt per year. Compared tothe current atmospheric carbon content of 800 Gt, at first glance, this CO2 consumption rate seems so slow that silicate weatheringwould play only a negligible role in the global carbon cycle. However, atmospheric CO2 removed from silicate weathering istransported by rivers and thereafter precipitated in the ocean as carbonate minerals, and the residence time of carbon in carbonaterocks is in excess of millions of years. Therefore, silicate weathering is an important mechanism that modulates the long-termcarbon cycle. Moreover, researches show that the small watersheds draining basalts/ophiolites in the tropical zones have thehighest silicate weathering and CO2 consumption rates. It is estimated that CO2 consumption from volcanic rocks in the tropicalzones represents about 10% of the global export of carbon by silicate weathering, while the tropical volcanic arcs correspond toonly~1% of the exorheic drainage area worldwide.

Preliminary Estimation of Carbon Dioxide Storage Capacity in the Oil Reservoirs in Subei Basin

WANG Chuansheng, TIAN Rong, JI Junfeng, SUN Bei, ZHANG Ting, HU Gaoming

2012, 18(2):  225. 

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       The CO2 storage in oil reservoirs is one of the most effective ways of reducing the greenhouse gas emission, which is
based on the mechanisms of structural and stratigraphic trapping, residual gas trapping, dissolution trapping and mineral trapping.The universal pyramid method is introduced to assess the CO2 storage capacity for the oil reservoirs. Subei basin has many oil reservoirs with low permeability and water content. Dongtai sag is better than Yancheng-Funing sag on the CO2 storage potential.Gaoyou depression and Jinhu depression have the greatest potential of CO2 storage among the secondary geological units. A series of the small tectonic units in this area are more suitable for CO2 storage, and beneficial to the preservation of late stage. Subei basin has obviously vertical dichotomy on the sealing ability of CO2 storage. The lower cap rocks of upper Cretaceous system and Paleocene series have better sealing capabily than the upper cap rocks of the Eocene epoch. Based on analyzing the mechanism of CO2 storage in oil reservoirs and combining with geological and structural conditions of Subei basin, we estimated that the theoretical storage capacities of CO2 is 1.5054×108 t and the effective storage capacities of CO2 is 0.0828×108 t ~ 0.4421×108 t, which shows the great potential of CO2 storage in Subei basin, Jiangsu Province.

Global Sensitivity Analysis of Leakage Risk for CO2 Geological Sequestration
in the Saline Aquifer of Yancheng Formation in Subei Basin

ZHENG Fei, SHI Xiaoqing, WU Jichun, ZHAO Liang, WANG Chuansheng

2012, 18(2):  232. 

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      TOUGH2/ECO2N code was used to simulate transportation of CO2 plume in the deep saline aquifer of lower part of the
Yancheng Formation in Subei basin. A fault was added to the conceptual model to evaluate the leakage risk after CO2 injection. Simulation results indicate that the effect of multilayer capping for CO2 sequestration is not good because of the clay strata with small thickness and relatively high permeability, although the lower part of the Yancheng Formation has three sequences’ structure (multiple sand-clay layers) and the sand stratum has high permeability and high porosity. Especially when there is a fault conducting all layers the leakage risk for CO2 geological sequestration is significant. Morris method was used to analyze the global sensitivity of the parameters for two scenarios. When only the fault parameters are changed, the parameters related with the capillary pressure have great effect on CO2 leakage along the fault. When all the parameters of fault, sand and clay strata arevaried, the permeability of sand and clay has the highest sensitivity for the leakage risk, while the parameters related with the capillary pressure are secondary. For both scenarios, the sensitivity of porosity and salinity is very small.

Potential Capacity and Feasibility of CO2 Sequestration in Petroleum Reservoirs
of Basaltic Rocks: Example from Basaltic Hydrocarbon Reservoir in the
Xujiaweizi Fault Depression the Songliao Basin, East China

UERNA Amy, WU Changzhi, JI Junfeng, WANG Zhenyu, GU Lianxing, SHU Ping, DING Rix

2012, 18(2):  239. 

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     The Daqing Oilfield, situated in Songliao Basin of Eastern China, is a famous oilfield for its largest production of crude
oil in China. The Xujiaweizi fault depression, located in the north of the basin, covering an area of 4300 km2, developes large
amount of basaltic hydrocarbon reservoirs. In this paper, we analyze the geological features and reservoir characteristics of basaltic hydrocarbon reservoir in the depression. Combined with mineral and chemical compositions of basalts from ten deep drilling wells of the Xujiaweizi fault depression, we evaluate the feasibility of CO2 sequestration in hydrocarbon reservoir of basaltic rocks, and then estimate the CO2 storage capacity from mineral trappimg and gas reservoir trapping in basaltic rocks in the depression. Our results show that reservoir spaces are favorable sites for CO2 sequestration and minerals of the reservoir rocks are easily suffered tocarbonation. Meanwhile, the cap rocks of the hydrocarbon reservoirs can prevent the emission of CO2, and the stability of hydrocarbon reservoir can guarantee the safety of injected CO2. Therefore, hydrocarbon reservoir of basaltic rocks should be an idea target for CO2 sequestration. Estimates of theoretical capacity for CO2 storage assume that all the pore space freed up by the production of recoverable hydrocarbon reserves would be replaced by CO2. In this study, the capacity of CO2 mineral sequestration has been calculated for the mafic minerals in basaltic rock of the hydrocarbon reservoir based on the principle of water-CO2-rock reaction. Moveover, the theoretical storage capacity of the gas reservoir trapping has been estimated based on gas resources in reserved basals
from the local gasfield. According to our preliminary calculations, the potential capacity of mineral trappins for reaction with CO2 is about 89.33×108 tons, while capacity of gas reservoir trapping to CO2 storage is about 6.2×108 tons. So the total trapping capacity of CO2 sequestration for hydrocarbon reservoir of basaltic rocks from the Xujiaweizi fault depression is about 95.53×108 tons.

Evaluation on Potential Carbon Sequestration Capability of Typical Mafic Tailings in Eastern China

WANG Xiaoyan, ZHANG Lijun, YUAN Xuyin, LIU Lianwen, JI Junfeng　

2012, 18(2):  248. 

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       The carbon sequestration by interaction of mafic tailings with CO2 to form a stable carbonate minerals is a new and
promising method for reducing CO2 emission. The evaluation of CO2 sequestration potential of mafic tailings is the essential premise for the reasonable utilization of these tailings. This paper mainly aims at 10 tailings in two typical ultrabasic rock belts (Donghai-Rizhao rock belt and Chicheng-Chaoyang rock belt) of eastern China, and analyzes mineral components, size distributions and major elements of tailing samples. Then a comprehensive evaluation about the carbon sequestration potential is taken for these mafic tailings in the two rock belts based on analysis results. In the Donghai-Rizhao rock belt, tailings are dominated by the serpentine, with higher MgO content (36.81%-41.39%) and relative coarser sizes. Compared with minerals in Donghai-Rizhao tailings, a variety of hornblende are the common minerals in the Chicheng-Chaoyang tailings, with moderate MgO content (5.84%-15.60%), higher CaO content (5.68%-19.28%) and finer sizes. By field survey and calculation with the chemical equation, the carbon sequestration capacity of Chicheng-Chaoyang tailings is estimated about 4.0×108 t, which is much bigger than Donghai-Rizhao tailings. Considering chemical composition, specific surface area, the tailings resources and other factors comprehensively, mafic tailings in Chicheng-Chaoyang rock belt has the large carbon sequestration potential and can be served as one of the most promising storage sites for carbon sequestration.

Characteristics of Clay Minerals and CO2 Consumption Rates of Weathering
Profiles from Cenozoic Basalts in Eastern China

DU Kai, CHEN Yang, JI Junfeng, LI Hui, LONG Xiaoyong, CHEN Jun

2012, 18(2):  256. 

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       Basalt weathering acts as a major atmospheric CO2 sink. Climate conditions have important effect on basalt weathering
and CO2 consumption rate. In this study, typical weathering profiles of Cenozoic basalts from different climatic zones in eastern China were selected to conduct clay mineral analysis and major elements measurement. Results show that as climate changes from dry-cold in the north to humid-hot in the south in the studied region, the assemblages of clay minerals in the profiles transfer as follows: smectite+ illite+ kaolinite → smectite+ kaolinite → kaolinite+ gibbsite. Chemical composition of the weathered samples exhibits correspondent changes. Ca, K, Na and Si in the soils are relatively enriched due to dust input compared to the concentrations of overlying parent basaltic rocks in Inner Mongolia under dry-cold climate. Ca, K and Na begin to be leached in the soils in Shandong and Si is leached in Jiangsu and Anhui under temperate climate. Si is leached heavily while the alkalineelements are almost lost in soils due to intensive weathering in Hainan under humid-hot climate. According to relative percentagechange of elements and normalization using average composition of dust in northern China, CO2 consumption rate from basalt weathering in eastern China can be estimated about 5.37~181.00 t/km2·yr, which is within the similar range provided by Dessert et al.’s (2003).

Impact of Heat-pretreatment on the Reactivity between
Ammonium Chloride and Chrysotile

GAO Xiong, ZHU Chen, ZHAO Liang　

2012, 18(2):  273. 

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       Using recyclable NH4Cl (ammonium chloride) as medium of CO2 mineral sequestration has become an emerging
technology, while the low ammonium chloride leaching rate of chrysotile turn into a bottleneck restricting the development of this
process. To solve the problem, this study carried on heat-pretreatment to modify the property of chryattile. Results show that heatpretreatment
can efficiently increase the reactivity of Mg2+ leached from chryostile. After heated at 600℃, the leaching effuciency of chryostile reacted with NH4Cl can reach to 55.64%, increasing about 43%, compared to reaction without heating. Heatpretreatment at 600℃ can remove the outer hydroxyl group in the layers of chryostile, and greatly increase the reactive surface area of minerals and reactive mg2+ it concentration, leading to the improvement of reaction rate. But if the roasting temperature was increased above 600℃, the leaching efficiency of chryostile dropped again since the reactive Mg2+ ot content decreases after removing inner hydroxyl group in the layers of chryostile.

New Understanding From Comparison of Paleozoic Kinematics
Between Baltica and Siberia

FU Chenjian, LI Jianghai

2012, 18(2):  280. 

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       Paleomagnetism is one of the most effective quantitative methods for examining ancient plate tectonic evolution and
paleogeographic reconstructions. Based on data from the Global Paleomagnetic Database (GPMDB 4.6) and previously published
paleomagnetic data for the Baltic and Siberian plates, a reanalysis and filtering of Baltica and Siberia Paleozoic paleomagnetic
data has been performed in accordance with internationally accepted basic selection criteria (Van der Voo, 1990) determining
the reliability of paleomagnetic data. From this, a reconstruction of the apparent polar wander paths (APWP) and paleogeographic
positions of the Baltic and Siberian plates has been made by using the GMAP software. In addition, further analysis has been
made by comparing the structural evolution and kinematic characteristics. In conclusion, the following is understood for these two
plates during the Paleozoic. Three convergence events took place during the Late Ordovician (~450 Ma), Early Carboniferous (~360
Ma), and Late Permian (~255 Ma), and the processes of plate convergence follow Newtonian kinematic principles in general.
What needs to be stressed is that under the continental plates is the asthenosphere mantle with an extremely high viscosity, so the
Newtonian kinematic principles cannot be obeyed under non-ideal conditions. Three processes of plate convergence have three
different kinematic phenomena. During the late Ordovician (~450 Ma), both Baltica and Siberia drifted northward and converged
gradually. Baltica with higher latitudinal velocity converted its kinetic energy into Siberia with lower latitudinal velocity. Duringthe Early Carboniferous (~360 Ma), Baltica and Siberia moved towards each other and converged. The latitudinal drift direction
of Siberia changed from the south to the north while the latitudinal velocity of Baltica decreased and became toward the south
gradually. During the Late Permian (~255 Ma), Baltica and Siberia drifted towards each other and converged again. Finally, their
kinetic energy canceled out each other, so both latitudinal velocities became zero.

Early Mesozoic Crust- and Mantle-Derived Magmatic Mixing in the Qinling
Orogeny: Evidence From Geochemistry of Mafic Microgranular Enclaves
in the Dongjiangkou Pluton

LI Lei, ZHANG Chengli, ZHOU Ying, TIAN Huiquan, LI Xiaofei

2012, 18(2):  291. 

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The zircon U-Pb ages of 218 Ma and 224 Ma have been obtained from the Dongjiangkou granitoids and their mafic
enclaves, respectively. The disequilibrium magmatic textures can be found in the mafic enclaves, which have some K-feldspars
similar to those of host granitoids and needle-like apatite formed under a quenching condition, indicating a two-end member
magmatic mixing in the early Mesozoic. The two-end member magmatic mixing resulted in similar geochemical compositions and
strong homogenization of Sr-Nd-Pb isotopes between host granitoids and their mafic enclaves. However, Hf isotopic composition
of the mafic enclaves shows a wide range of εHf(t) that varies from -4.58 to 3.31, registering the source features of two-end member
magma. Thus, the positive εHf(t) values (＞10) of zircons from the contemporary mafic enclaves provide evidence that the mafic
magma was derived from the depleted mantle. While, host granitoids with negativeεHf(t ) values (＜10) of zircons were products of
partial melting of the Mid-Proterozoic mantle-derived basic rocks. Since then, the distinct crust- and mantle-derived magmas were
mixed around 224 Ma, resulting in a large number of granitic intrusions with abundant mafic enclaves during the early Mesozoic
in the Qinling orogeny.

Analyses of the Genesis and Potential of Natural Gas in Kebai Area of
Northwest Margin, Jungar Basin

GAO Gang, WANG Xulong, LIU Guangdi, ZHANG Yueqian, HUANG Zhilong

2012, 18(2):  307. 

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Based on the analysis of the natural gas occurrence features, component features, types and sources, this article shows
the contribution of source rock of the Carboniferous and Jiamuhe Formation of the Lower Permian to the gas reservoir and points
out that future research should be strengthened to the source rock geology, geochemistry characteristics, and gas-generating
potential. To natural gas, there is not only dissolved gas in oil pools but also pure gas in gas pools. The dissolved gases distribute
in both the Permian system and the Mesozoic, and were derived from the Fengcheng Formation source rocks. They migrate and
accumulate with crude oil and are oil-type gases. The natural gases in gas pools distribute chiefly in the Jiamuhe Formation and
the Upper Wuerhe Formation which overlays the Jiamuhe Formation in Wuba Area, were derived from the highly mature Jiamuhe
Formation source rock and migrated, accumulated in gaseous phase, and they are coal type gas. The Jiamuhe Formation source
rocks have an important controling role in gas pools in the Jiamuhe Formation and the strata overlying the Jiamuhe Formation. The
Carboniferous source rocks have contribution to coal-type gas in depth. There is certain natural gas exploration potential in the
structural downdip part of the discovered gas pools and deeper parts which will be the next main exploration target.

The Main Controlling Factors on the Enrichment of Natural Gas in Volcanic
Rocks in Ludong-Wucaiwan Area，Junggar Basin

WU Xiaoqi, LIU Deliang, LI Zhensheng

2012, 18(2):  318. 

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Plentiful natural gas resource has been discovered in Carboniferous volcanic rocks in Ludong-Wucaiwan area in
Junggar Basin in recent years. Kelameili and Wucaiwan gas fields were found in this area， and Carboniferous has been one of
the major targets in oil and gas exploration in northern Xinjiang. As a special type of reservoirs，volcanic reservoirs have attracted
wide attention. The natural gas in Ludong-Wucaiwan area was mainly preserved in the weathering crust of volcanic rocks at the
top of Carboniferous，and was mainly coal-derived gas from Carboniferous humic-type source rocks. Ludong-Wucaiwan area
could be divided into several secondary tectonic units，and the gas reservoirs were mainly located at the middle-west parts of
Di’nan Uprise and Wucaiwan Sag. The accumulation properties of oil and gas in volcanic reservoirs are different from those in
conventional ones. Besides the well reservoir quality，the matching of several favorable factors such as hydrocarbon generation,
migration, and preservation were also necessary. Based on the analysis of typical gas reservoirs in Ludong-Wucaiwan area, thispaper is focused on the major controlling factors on the enrichment of natural gas in Carboniferous volcanic rocks. The results
indicate that it is favorable to form reservoirs if the volcanic rocks were adjacent to source rocks and hydrocarbon-generation
sags；The reformation by and tectonism was a key factor to improve the reservoir quality of Carboniferous volcanic rocks in
Ludong-Wucaiwan area and to develope effective reservoir space ；The faults and the unconformity were the favorable pathways
for vertical and lateral migration for oil and gas；The Carboniferous traps and reservoirs in Ludong-Wucaiwan area have been
affected by different degrees in different stages since the Hercynian，in which the favorable source-reservoir-seal assemblages
for the volcanic reservoirs were finalized in the Hercynian; while the Middle Yanshanian period was the key stage for natural gas
accumulation.

The Reservoir Characteristics of Chang 8 Oil Layer Group From the Yanchang Formation in Zhenjing Area, Ordos Basin

ZHANG Xia, LIN Chunming, CHEN Zhaoyou, PAN Feng, ZHOU Jian, YU Hao　

2012, 18(2):  328. 

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The Chang 8 sandstones of the Yanchang Formation in Zhenjing area of Ordos Basin, occurring as one of the major
reservoirs, mainly consist of feldspathic litharenite and lithic arkose. They belong to extra-low porosity and permeability reservoirs,
with dissolved intergranular pores as the chief accumulation space, and the reduced-neck, lamellar and curved lamellar pore
throat as the main throat type. Based on the pattern of capillary pressure curve, porosity, permeability, displacement pressure
and pore throat radius, the Chang 8 sandstones can be classified as type I, II and III, in which the type II are the main reservoirs.
There are four factors affecting the reservoir characteristics of Chang 8 sandstones: sedimentary processes, diagenesis, fractures,
and hydrocarbon emplacement. The best reservoir quality is developed in the subaqueous distributary channels of braided river
delta fronts, and the one of medium sandstones better than that of fine sandstones. Otherwise, the reservoir qualities of sandstones
rich in quartz, feldspars and metamorphic rock fragments are better than those of sandstones with high contents of sedimentary
and igneous rock fragments, as well as mica. The diagenetic processes have exerted dual impacts on the reservoir quality. The
constructive one is characterized by dissolution and pore-lining chlorite cementation, and the sandstone intervals with them
occurring together are the optimum zones for the oil and gas accumulation. The destructive one involves mechanical compactionand the late stage carbonate cementation. The fractures, with the NE-SW tectonic ones formed in the late stage of Cretaceous-
Paleogene as the main type, contribute more to permeability than storage, making the heterogeneity of reservoirs intensified. The
effects of hydrocarbon emplacement on reservoir quality are characterized by the reconstruction and conservation of porosity
dissolved by organic acid in hydrocarbon.

Analysis of the Influencing Factors of Differential Hydrocarbon Distribution in Majiazui Oilfield, Gaoyou Sag

LI Hao, GAO Xianzhi, MENG Xiaoyan, LIU Jian, ZHANG Jie　

2012, 18(2):  341. 

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Based on the modern hydrocarbon accumulation theories, through analyzing causes for hydrocarbon accumulation and
distribution characteristics, this paper analyzes factors that influence differential hydrocarbon distribution in the Majiazui area of
Gaoyou Sag, Subei Basin. The results indicate that fault-lithologic reservoir is the main reservoir type which contains two kinds
of hydrocarbons originatied from the E1f4 source rock in Shaobo sub-sag and hydrocarbon charging occurred in the middle-late
stage of the Eocene. The zonal distribution of different hydrocarbons was caused by different migration pathways, not by different
sources or different migration periods; Zhen② and Hanliu faults serve as the dominant migration pathways; Zhen② fault shows
relatively stronger ability for hydrocarbon migration, thus hydrocarbon that occurred along Zhen② fault shows lower maturity than
that along Hanliu fault. Under the influence of sedimentary microfacies on reservoir properties, reservoirs of middle-terminal fan
far from faults show higher oil-bearing properties than those of root-fan near faults; the degree to which fault-lithologic traps are
filled is determined by matching fault orientations, sand beds pinching-out directions, and strike of strata.

Source-Rock Characteristics and Oil-source Correlation in the Hongqiba Area, Northwestern Junggar Basin

LU Xiaoyu, HUANG Zhilong, ZHANG Meiyan, LIU Fengyan

2012, 18(2):  350. 

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Analyses of geochemical characteristics of oil fractions, C-isotope and biological markers of well cores and crude oil
from the Hongqiba area in the northwestern margin of Junggar Basin reveal that the source rock has low abundance in organic
matter and poor kerogen. Oils from Hongqiba and its adjacent areas show a certain degree of correlations with the source rocks
of the Fengcheng Formation in the Mahu sag with regard to the distribution of C20, C21, C23 tricyclic diterpanes, Pr/Ph, and carbon
isotope. Therefore, we suggest that oils mainly originated from the Fengcheng Formation of the Mahu sag.

Fault Accommodation Zones and Their Controling Effects on Hydrocarbon Distribution in Yong 8 Fault Block, Dongying Sag

TIAN Fei, JIN Qiang, WANG Duanping, WANG Jixiang, YANG Yong

2012, 18(2):  358. 

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Based on the study of fault geometry, kinematics, and dynamics in Yong 8 fault block using 3-d high-resolution
seismic data with oil field geological data, we discovered an east-west striking synthetic-overlapping fault accommodation zone.
The western side of the major fault (Xin 120 Fault) with adjusting faults shows a step-style structural pattern, and the eastern
side of the major fault (Yong 105 Fault) with adjusting faults shows a horst-style structural pattern. When Xin 120 fault activity
becomes weak, Yong 105 Fault and adjusting faults accommodate the displacement. Stress field of Yong 8 accommodation zone
is left-lateral, transextensional. Through the analysis of distribution and source of Yong 8 fault block, characteristics of fault
activities, and fault sealing properties, we constructed the accumulation model of Yong 8 block fault. The eastern side of the major
fault is oil source fault which connected the source and the reservoir, and migrated hydrocarbon during the main hydrocarbon
accumulation period, and adjusting faults stopped activities in the earlier period, formed fault traps, and became barrier faults.
Western part of Yong 8 fault block is the target region for progressive exploration and development.

Development Characteristics and Quantification of Pingnan-Shicun Transfer Structures in Dongying Sag

ZHANG Lin, WU Zhiping, LI Wei, WANG Guangzeng, ZHANG Qi, JIA Haibo, DAI Lei　

2012, 18(2):  365. 

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Synthetic overlapping transfer structure usually evolves from the synthetic approaching structures when the master
faults overlap relatively large areas and the overlapping areas will suffer from an extensional stress in the same direction as the
whole regional one, producing lateral transfer faults (parallel to the master faults). Based on the principle of regional elongation
conservation and the analysis of development features and the controlling factors of synthetic overlapping transfer structures,
“Transfer Degree” is proposed to quantify the degree to which a transfer structure can accommodate the extensional movement
for the master fault. It is defined as the elongation ratio of transfer structure and master fault. In order to reduce errors, the
horizontal displacement of a master fault and its end were used to calculate the transfer degree. As a case study, the Pingnanshicun
synthetic overlapping transfer structure was researched and its transfer degree was calculated. Finally, the calculation
results were compared with those of the balanced cross sections. Both results matched very well, indicating that this method may
be useful and could provide a way to quantify transfer structures.

Study on the Quaternary Tectonic Evolution and Its Significance for
Exploration in the Sanhu Area, Qaidam Basin

GUO Zeqing, SUN Ping, ZHANG Shaosheng, TIAN Jixian, KONG Hua　

2012, 18(2):  372. 

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Stratum thickness can reflect tectonic subsidence and/or uplift. After compiling stratigraphic data of all wells in the
Sanhu area of Qaidam basin, the present stratum thickness was calculated, and isopach maps of different periods were drawed.
These maps show that the formation history of the anticline was not uniform, and the structure started to form from the northeast to
the southwest. Yikeyawuru, Nan Linqiu, and Tuo Fengshan anticlines were formed first and they have been the syn-depositional
anticline since the Quaternary. Then Taijinaier and Sebei 2 began to uplift, which was followed by Sebei 2. Tainan anticline was
the youngest and Sedong nose structure began to uplift after k1 was deposited. No anticlines were formed in the southern slope
until today. The speeds of their uplift are not even, and the speed gradually increased, especially, the anticlines had a tendency
for rapid uplift after k5 was deposited. The understanding of tectonic evolution history is very helpful to search for favorable zones
where low-amplitude structures were developed.

“Impact Ejecta in Taihu Area” Revisted：Evidence from Ferruginous Concretions in Modern Sediments of Taihu Area

HUANG Zhicheng, LIU Guanbang

2012, 18(2):  379. 

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Regarding to the opinion of the impact origin of Taihu lake based on the discovery of the iron-rich siderite ejecta
and iron-poor ejecta, we restudied similar samples by way of mineralogy, geochemistry and chronology. Our data show that

those samples found in Taihu Lake are in fact siderite and limonite concretions which formed in Quaternary mud layer during
diagenesis. Supporting evidence come from that a large number of aquatic plant debris, opal phytolith of plants, bacteria and
a few animal shell fragments were found in those concretions. After high temperature burning, siderite completely changed
into hematite, indicating that the high temperature phase of siderite mineral does not exist. The siderite 14C dating shows that
the various samples formed at different times. δ13C data of siderite indicates a source of inorganic carbon in fresh water, not a carbonate direct source in the Taihu area. The so-called iron-poor ejecta are actually diagenetic calcium concretions found in loess layers. Those evidences showed that the weird-shaped concretions found in the Taihu Lake are diagenetic concretion, which are not impact ejecta.

Reply to The Paper of“ ‘Impact Ejecta in Taihu Area’ Revisted”

WANG Henian，QIAN Handong

2012, 18(2):  390. 

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In this issue, Huang Zhicheng and Liu Guanbang (2012) published their results of several sediment and concretion
samples from the Taihu area in Jiangsu Province. From a sedimentological point of view, they suggest that the stuided siderite concretions are of sedimentary origin. These non-ejecta samples are different from our studied samples of ejecta origin (Wang et al., 2009), but provide a good reference for a comparative study of the impact ejecta. The results indicate that these two types of samples have different shapes, internal structure characteristics, and C-O isotopic compositions. Therefore, their data and conclusions did not provide any solid evidence to against our previous statement for an impact ejecta origin for some certain Taihu samples, and we suggest that further detailed work are needed to solve this problem.

The Deformation Features of Quartz grains In the Sandstone of Taihu Area: Taihu Impact Origin Controversy

Dong Yujie, Xie Zhidong, Zuo Shuhao

2012, 18(2):  395. 

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       The hypothesis of impact origin is one of many origin hypotheses of Tai Lake basin, which were proposed in twenty
years ago and revived in 2009 with many opposite arguments. The goal of this paper is to review and check the similar previous work having been done in twenty years ago based on current observation of the deformation features in quartz grains, and to discuss the Taihu impact hypothesis. Various deformation features of quartz grains in Devonian sandstone of Taihu area, including uneven extinction, fractures, and deformed lamella, are observed under optical microscopy. The preferred orientations of quartz deformed lamella were measured by using the universal stage. The well developed braided micro-fractures and artificial network fractures in the sandstone samples were observed. We also compare the quartz deformation features from sandstone of Taihu area to that from similar formation sandstone from Jiujiang area 300 km away from Taihu, and similar deformed features in quartz debris in the siderite concretions of Taihu area. The results show that the quartz deformed lamella of sandstone of Taihu area are not typical impact-induced planar deformation features (PDF). Most of the deformation features are caused by relatively lower pressure, the origin of these deformation features can be explained by multiple forces. Therefore, the hypothesis of impact origin of Taihu lake is not mature yet, it is rewarded and valuable to intensively study the origin mechanism of Taihu lake basin by multiple approaches.