Geological Journal of China Universities

Kenneth J Hsu, Chen Min-pen, Huang Chao-kai

2003, 9(1): 1-10.

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Natural radioactive decays have been assumed spontaneous．The decays are said to have a constant half-life，despite of experimental and empirical evidence to the contrary．Hsu raised the question if decays are spontaneous，or if they are particle-particle interactions(Hsu K J，1994)．A test of the postulate that beta-decay is a neutrino-neutron interaction has been carried through experimental monitoring of C-14 decay．Our working hypothesis predicted a correlation of the variation of beta-decay rate to the flux of neutrinos．The decay rate of the C-14 sample with its long half-life should be nearly constant during the short duration of the experiment．Our experiments have found，however，rates deviating up to 1% from the theoretical value．The signals of the variation are about 1 000 times greater than the background noise．The variation is not correlative to solar activities，falsifying an assumption that beta decay is caused by collisions of neutrons with solar neutrinos ．There is，however，a positive correlation of the decay rate，during a one and one-half year interval to the intensity of cosmic rays measured at Beijing．The results are consistent with the postulate that beta-decay is activated by neutrinos from cosmic rays ．

Evidence for Early Holocene Cold Event From Lake Sediments

JIN Zhang-dong1 2, SHEN Ji1,WANG Su-min1, ZHANG En-lou1

2003, 9(1): 11-18.

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Analysis of the sediment form an inland closed lake, Daihai Lack, located in the semiarid and semi-humid zone in north China has revealed the decadal to centennial-scale Holocene climate fluctuations provided by chemical weathering records. High-resolution geochemical, physical and biological proxies form the lake sediments indicate that there is a strong cold climate event in the Early to Middle Holocene transition (EMHT) characterized by weak weathering (sediments with higher Rb/Sr ratios) in single watershed, lake productivity decrease and lower lake level. Although its cold magnitude is weaker than that of Younger Dryas, the coinstantaneous cooling records from lakes (North pole, Africa, North America, West Europe, Tibet, Greenland and north China), oceans (North Atlantic, Mediterranean, Caribbean Sea), mollusk sequences form Europe-American continent, and pole ice cores including Greenland GRIP and GISP2 all indicate a global climate signal which is typically centered between 8.0 and 8.5ka B.P.

Chemical Weathering and Environmental Change Records of the Last 2.8 Ma in the Central Tibetan Plateau

CHEN Shi-yue1 2, WANG Su-min1, JING Zhang-dong1, SHEN Ji1

2003, 9(1): 19-29.

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In this paper，we provide a high-resolution vertical distribution of Sr，Rb，Zr，Rb/Sr and Zr/Rb ratios in sediments from the lake of Co Ngoin．Central Tibetan Plateau．Combined with the lithological properties， grain size and clay mineralogy， we discuss the chemical weathering process recorded in lake sediments and reconstruct the history of the weathering intensity and paleoclimatic change in the last 2.8 Ma．The sedimentary records indicate that this region experienced three environmental evolution stages：in the core depth of 197～ 170 m (about 2.8～2.5 Ma)，the lower Sr content，higher Rb/Sr and Zr/Rb ratios indicate a strong tectonic uplift movement with a weaker intensity of chemical weathering；in the core depth of 170- 38.5m (between 2.5 and 0.8 Ma)，the higher Sr content，lower Rb/Sr and Zr/Rb ratios reflect a tectonically relatively stable epoch，with a warm ／cool and wet plateau climate；in the depth of 38.5～O m (about 0.8～O Ma)，the relatively lower Sr content，higher Rb/Sr and Zr/Rb ratios record relatively lower intensity of chemical weathering，caused by a cold climatic period．The plateau was uplifted to above 4 000 m above sea-leve1．

Lake Sediment Records of the Holocene Environmental Evolution in North Xinjiang

JIAG Jia-ming1 2, WU Jing-lu1

2003, 9(1): 30-37.

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Closed lake in arid region is sensitive to the climatic change．Through the analyses of environmental proxies from the sediments in Aibi Lake—a closed one in the arid region．the characteristics of climatic environment in early Holocene epoch were studied．The pollen assemblage and other geochemical indices show that．the temperature was somewhat low in the period of 8.0 to 11.5 cal ka BP as a whole，but in its earlier stage(11.5 to 10.6 cal ka BP)the temperature was higher，acompanied by more precipitation． In the transitional stage from early Holocene epoch to middle Holocene epoch(8.9 to 8.0 cal ka BP)the climate fluctuated remarkably．Especially，the three layers of peat sediments revealed a strong instability of climate in early Holocene epoch in Aibi region．All informations on the development of peat and the experimental data of pollen and stable isotopes imply that the climatic condition at 8.2 cal ka BP．8.6 cal ka BP and 10.5 cal ka BP was noticeably cold and humid, and could be regarded as three cold and humid events in early Holocene epoch．

Sedimentary Characteristics of Weihe Palaeochannel Since Late Pleistocene and Their Control to Modern Salt-Water Intrusion

LIU En-feng1 3, ZHANG Zu-1u2, SHEN Ji1, YANG Li-yuan1 3

2003, 9(1): 47-53.

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The lower reach of Weihe River in the south plain of Laizhou Bay is one of the most typical areas of salt-water intrusion in China． The occurrence， development and movement pattern of the salt-water intrusion are closely related to the sediments composition in the palaeochannel of the Weihe River．A detailed investigation including data collected from more than 100 geologic drillings， analyses of sediment grains and microfossils, 14C and thermoluminescence age data from two typical bores has been conducted to study the distribution and sedimentary characters of the palaeochannel since the Late Pleistocene． The relationship between sedimentary structures and burial characters of palaeochannel and salt-water intrusion are then discussed．The results of this study have suggested that the sediments in the paleochannel can be divided into 4 sedimentary cycles according to grain size．The calculated depth of sand sediment indicates that the thickness of sand layer is about 30 to 50m in the eastern part but lass than 20 m in western par t of Weihe River，an d the continuity of sand layer is also better in the eastern part than in the western part．The difference of sedimentary characteristics lead to the salt-water intrusion earlier in eastern part and became slow recently， while the salt-water intrusion in western part occurred since late 1970’s mainly due to the human exploitation of groundwater and the intrusion distance of salt-water through the paleochannel can reach to 9 or 10km ．The study of paleochannel sediments and its relation to salt-water intrusion can provide scientific reference to ground water exploration and the control measures of salt-water intrusion．

Features of Sea-Level Change in Bianping Section，Guizhou Province Across Zisong Stage and Luodian Stage

DONG Lin, LIU jia-run, YANG Xiang-ning, ZHU Li-ming

2003, 9(1): 54-62.

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Six continuous sea—level fluctuations across the late Zisong stage to Luodian stage of Early Permian at Bianping area were recognized based on sedimentary records of Bianping Section，Ziyun county，Guizhou province．Among these fluctuations，the third is characterized by highest rate of sea-level rise ，the fourth by maximum water depth，and the fifth by supreme uplifted extent．A preliminary analysis has indicated that the heavy loss of fusulinaceans during Ear1y Permian may be related to the above eustatic features．

Upper Devonian Slump Deposition in Shiwengzi of Zhashui County，South Shanxi Province and Its Geological Significance

CUI Hai-feng

2003, 9(1): 63-71.

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Upper Devonian slum p deposition is well developed in Zhashui county of southern Shanxi province and is particularly well exposed in the Shiwengzi area．The slump deposition is composed of terrigenous fine-grain clastic rocks，carbonate rocks，bog lime，siltite and boulder breccia limestone．The source area of deposits was located in the north of Shiwengzi．Formation of the slump deposition was primarily controlled by regmagenesis palaeogeographic framework as well as the source area of deposits．The widely existed unco nformable co ntact between the Early and the Late Paleozoic groups in the southern Qinling further suggests that the southern Qinling had been uplifted when the northern Qining was suffering from the uplifting in the Daledonian orogeny period．Until the Late Devonian，the southern Qinling had been under the control of regmagenesis，which was probably related to the opening of mianlue finite ocean basin．

Sedimentational Geochemical Characteristics of the Sinian Cap Carbonate from the Upper Yangtze Region

YANG Rui-dong1 2, WANG Shi-jie1, DONG Li-rain1, JIANG Li-jun2, ZHANG Wei-hua2, GAO Hui2

2003, 9(1): 72-80.

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A global glaciation happened at about 600 Ma．The earth became a “snowball earth”，which ended abruptly when subaerial volcanic outgassing raised atmospheric carbon dioxide to about 350 times the modern leve1．The rapid termination would have resulted in warming of the snowball earth to extreme greenhouse conditions．The transfer of atmospheric carbon dioxide to the ocean would result in the rapid precipitation of calcium carbonate in warm surface waters and consequently formation of the cap carbonate rocks observed globally．Regionally persistent，thin intervals of carbonate rocks directly and ubiquitously overlie Proterozoic glacial deposits almost on every continent，and are commonly referred to as cap carbonates．Their unusual facies，stratigraphically abrupt basal and upper contacts， and strongly negative carbon isotopic signature(δ13C values between –7.0‰ and 0‰ )suggest a chemical oceanographic origin，the details of which remain unsolved. Here we propose that these enigmatic deposits are related to the destabilization of gas hydrate in terestrial permafros t following rapid post．glacial warming and flooding of widely exposed continental shelves and interior basins．The authors studied geochemistry ，sedimentology and palaeontology of the Sinian cap carbonates in Guizhou and Hunan Province，including common occurrence within the cap carbonates of unusual fabrics，strongly negative carbon isotopic signature，and large amount of asphalt nodule．According to these results，we suggest that the cap carbonates be produced by solid methane seeps．This is in agreement with Kennedy’s view (2001)．In contrast，we disagree with Hoffman et al’s view (1998)．They suggested that the cap carbonate be produced by the transfer of atmospheric carbon dioxide to ocean which would result in the rapid precipitation of calcium carbonate in WaF1TI surface waters．

Intraplate Tectonic Deformation of the Precambrian in the Mufu and Jiuling Mountains Area，North-West Jiangxi

ZHANG Ze-jun, ZHANG Xiong-hua, YI Shun-hua

2003, 9(1): 81-88.

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The middle Proterozoic Shuangqiaoshan Group in area of Mufu and Jiuling Mountains，Northwest Jiangxi is a set of normal sedimentary strata with obvious sequence and is covered by the Sinan with an unconformity．The nearly N folds formed early were modified by the nearly E W folds and synchronous tectonic heat fluid event which is the intraplate trace of the collision between the Yangtze and Cathaysia plates ． The intraplate tectonics and amalgamation belt occurred in a synchronous tectonic movement．K-Ar dating of single mineral of diorites from the Manjiang and the Shanko units which intruded into the E—W folds give ages of 846±7 Ma and 805±75 M a respectively． The palaeo-faults are the companions of the E-W folds． These evidences suggest that the tectonic deformation occurred in the Precambrian before 800 Ma corresponding approximately to the Grenville movement and the existence of the Jiangnan Ancient Land．

Tectonic Setting for Formation of the Early-Middle Cambrian Volcanic Rocks from Baiyin Mining Field，Gansu Province

WANG Jin-rong1, GUO Yuan-sheng1, ZHAI Xin-wei1, LI Shuang-wen1, MENG Gui-sheng2, YANG Yong-jun2

2003, 9(1): 89-98.

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The early-middle Cambrian volcanic rocks from Baiyin mining field are composed mainly of calc-alkaline basalts，rhyolites and minor andesites． They were considered to be resulted from magmatism of continental rift．The results of the geochemial characteristics show that，compared with oceanic ridge basalt (MORB)，the basalts of study area are characterized by low Ti and Ni(Ni<25 at Mg’=40)，obviously negative anomaly of Nb-Ta，enrichment of LREE。re1ative depletion of HFSE，high ratios of Th／Ta(9～15)，Th／La(0.32-0.56) and La／Nb(>1.4)，highly variable range of Ce／Zr，La／Zr and Nb／Zr，and with low Zr／Nb ratio(<16)．(87Sr／86Sr)i=0.704～0.707， Nd(t)= -6.46 and δEu≈ 1.0．However，the rhyolitic rocks have (87Sr／86 Sr)i=0.7026～0.7048，εNd(t )=+5.60～ +6.14，δEu = 0.5～ 1.1，Th／Ta =6～12 and Ti／Zr 6.1～53．Their REE distribution patterns have a negative anomaly of MREE． indicating the presence of amphibole as a residual phase in the mafic lower crust(pre－existing island arc basalts)． According to the geochemistry of the volcanic rocks，it can be inferred that the basalts and rhyolites were resulted from the ma gmatism in normal continental margin arc， but with different sources． The basalts stemmed from enriched sub-continental lithospheric mantleand the mantle-derived magma was strongly contaminated by continental crust． However, the rhyolitic rocks were resulted from mixing of mafic lower crust generated by partial melting of depleted mantle wedge and subduction-related mantle-derived underplating magmas at the same tectonic episode

High Frequency Lake-Level Change of 3rd Member of Shahejie Formation and Prediction of Lowstand Sand Body in Dongpu Depression

JI You-liang1, FENG Jian-hui2, WANG Sheng-lang2, ZHANG Hong-an2

2003, 9(1): 99-112.

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Recent study of lithology and sedimentary characters of the 3 member of Shahejie Formation of the Lower Tertiary in Dongpu Depression，has revealed many evidences indicating shallow water sedimentation and evaporation sequence，which could be used to interprete．The origin of the halite and gypsum interlayered in black colored mud located in the basin center．We is believe that the black colored mud is formed during high-level stage and that the halite and gypsum are deposited during low-level stage caused by evaporation．The paleowater depth is estimated from the data such as the character of sediments distribution，the species and diversity of Ostracode．According to the calculation and estimation，the maximum depth of lake water is 30m．In addition，some evidences indicating frequently fluctuating of the lake level during the sedimentation of the 3rd member of Shahejie Formation have been found，which are：(1)the frequent alternation of black colored mud and gypsum and halite；(2)‘rubble-made sand’in the sandstone，which indicates that the sand deposited during the highstand time was eroded into sand rubble and was transported，deposited with sand during the lowstand time；(3)In the sandstone interbeded with black mud of deep water environment，sandstong with cross bedding that W88 deposited in shallow water environment and current flow was found．The data of lithology，well log and seismic reflection character and the estimated paleowater depth were used to study the lake level fluctuation during the sedimentation of 3rd member of Shaheje Formation．It is believed that in Dongpu Depression，during the sedimentation of 3rd member of Shaheje Formatoin，the lake level fluctuated frequently with large scale cycle and small scale cycle． According to the data of well log，response of resistivity and core，cycles of 6 scales were recognized，and the frequency of 6m scale cycle is lO00／Ma．The minimum extent of lake level fluctuation is calculated according to the thickness of single halite bed or single gypsum bed． Combined with the palaeotopography character，the prossess of large transference of lakeshore line in landscape orientation has been explained．Basied on this study，a dynamic sedimentary modle was eastablished．As revealed in this modle，delta and bech sandbody were deposited along the shoreline and black mud with thin layer carbonate rock was deposited in the deposition center during the highstand time．During the lowstand time，the sandbody previously deposited along the shoreline was eroded and was prograded toward the sedimentation center of the basin，and during the weathering time，salt and gypsum rock was deposited in the center of deposition of the basion.

A Genetic Model for the Deng-2 Oil Pool in the Jiyuan Depression，Henan Province

ZHAO Wei-weiJIN QiangWANG Wei-fengLI Zhao-yang

2003, 9(1): 113-122.

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The Jiyuan Depression is a frontier area of oil and gas exploration in the Henan Province．Because tectonics and petroleum geology are very complicated in the Depression，only a small oil field，i.e. the well Deng-2 oil pool，has been found in the Lower Tertiary．However，controversy exists over the genetics of this oil poo1.Some geologists believe it is a primary oil pool while the others consider it as a secondary pool reformed from the Mesozoic oil pools． In this paper，well will first present results of a series of geochemical experiments on organic/salt-water inclusions and biomarkers in the oil—bearing/bare sandstones from the well Deng-2， which included measurements of homogenization temperature of hydrocarbon/gas-liquid inclusions and GC-MS analysis of biomarkers within and outside the inclusions, and then propose new genetic model for the Deng-2 reservoir．The Deng-2 oil-pool was formed at about 75℃ corresponding to a depth near 2200m with a present burial depth about 690m．Although the oil in the reservoir is biodegraded heavily now ，the biomarkers inside the inclusions show little biodegraded features，which represent watering and biodegrading process accompanied with the reservoir evolution. Investigation on the structure evolution of the Deng-2 trap suggests that the Tertiary reservoir of Deng-2 is a secondary reservoir and its oil was migrated from the previously existed Mesozoic reservoirs below ． Based on n1easurements of the maximum homogenization temperatures of gas-liquid inclusions in oil-bearing sandstones，we believe that the Eocene oil pool of Deng-2 was charged at about 2200m depth in the Late Oligocene．Studies also revealed that the hydrocarbons in the oils of sandstone pores in the Eocene reservoir of Deng-2 are characterized by heavy biodegradation，but those in the inclusions of the Sandstones are lightly biodegraded，indicating that the Eocene oil pool of Deng-2 is a secondary oil pool formed in a bacterial living environment in the Late 0ligocene and the oil in the pores of sandstone has undergone much longer biodegradation than that in the inclusions because of the tectonic uplift．The Eocene oil in the Deng-2 oil-pool was migrated from a primary Mesozoic oil pool by faults around the Deng-2 trap. The result of this study are important to understand the oil distribution in the Eocene reservoirs in the Jiyuan Depression，and to exploring oil in the faulted traps of the Eocene.

A Geometric Proof for the Shear Displacement Fomular

LIU Rui-xun1, LU Gu-xian2, WANG Shi-feng1, XIA Li2

2003, 9(1): 123-127.

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The shear displacement formular is popularly used for studying the ductile shear zones．The algebraic proof of this formular is more complicated and hard to understand in the field of structural geology study．The present authors proposed a geometric proof of this formular which is more visualized and easier to understand

A Fieldowrk Subsystem for Regional Geological Mapping

WANG Min1, WANG Zhi-min2, JlANG Si-min1, ZHU Guo-rong1, WU Ben-jun1, WU Tao1, MA Rui1, HU Bo1

2003, 9(1): 128-138.

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A digital system for geological survey is described in this paper, which is based on teaching requirements of the Nanjing University field base for geological mapping in Chaohu，Anhui Province．Certain advanced techniques，such as GIS，RS and GPS have be en applied in the system．The powerful image manipulation and spatial analysis functions of GIS are fully used to generate the three-dimension digital map of geo logy for the study area ．The application of this system by students has greatly increased the efficiency of geo logical mapping in the field．

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