Geological Conditions and Petroleum Exploration Potential of the Albertine Graben of Uganda

The Albertine Graben in western Uganda is a Mesozoic-Cenozoic rift basin with petroleum exploration potential. A fundamental evaluation of petroleum potential of the graben is given based on field research, data processing of gravity and magnetism, analysis of graben structure, geochemistry, reservoir and composition research. The basin has a double-layered framework and a large thickness of sediments. Gravity highs shown in a residual anomaly map might indicate central uplift zones. There exist at least two sets of mature or low-maturity source rocks corresponding to a certain source rock in the Cretaceous or Paleogene and Neogene strata. The graben has basement rock with potential reservoirs and Tertiary sandstone reservoirs and thus has petroleum exploration potential.     

Sedimentary Response of Different Fan Types to the Paleogene–Neogene Basin Transformation in the Kuqa Depression, Tarim Basin, Xinjiang Province

A group of alluvial fans formed in the early Paleogene represent marginal sedimentary facies at the foot of the South Tianshan Mountain, Kuqa Depression, Tarim Basin, Xinjiang province. Two types of fans occurred in the middle–late Paleogene Kumugeliemu and Suweiyi formations: one alluvial, and the other fan delta deposited in a lacustrine setting. Within the early Neogene Jidike Formation, coastal subaqueous fans developed, probably in a deeper water lacustrine setting. The three types of fans are stacked vertically in outcrop with the sequence in ascending order: bottom alluvial, middle fan-delta, and top subaqueous. The subaqueous is a typical coarse-fan deposit occurring in the glutinite member of the Jidike Formation in some wells. Laterally, from the foreland to the lacustrine settings, the distribution pattern of sedimentary facies represents the same three fan types sequentially. The spatial distribution of these fans was controlled by the Paleogene–Neogene Basin transformation, and evolution with different types of fans developed in the Kuqa Depression in response. In the Paleogene, the Kuqa Depression was a rift basin where an alluvial fan was deposited in the foreland setting, which, by early Neogene, became a foreland basin when the lake level changed. With any rise in lake level, fan-deltas migrated from lacustrine to foreland settings, whereas when the lake level fell, fan migration was reversed. In the early Neogene, with increasing slope and rising lake level, fans progressed and covered the previous fan-delta and lacustrine mudstone. Eventually, subaqueous fans developed, forming the present spatial configuration of these three fan types.     

HISTORICAL GEOLOGY & STRATIGRAPHY

20050354 Chen Peiji 1187/P, 28 (2), 2004, p. 97-103, 2 illus., 1 table, 20 refs.) Keywords: Cretaceous, Neogene, palynologi cal assemblage, Heilongjiang Province The Cretaceous - Paleogene ( Tertiary)(K/T) boundary is defined by great extinc tions which occurred 65.5 Ma ago. The studyof this boundary attracts the interest of the ge ologists in searching for the causes of the dra matic extinctions. In China, the Cretaceousand Paleogene deposits are mainly terrestrial inor…     

Sedimentary Response of Different Fan Types to the Paleogene-Neogene Basin Transformation in the Kuqa Depression,Tarim Basin,Xinjiang Province

A group of alluvial fans formed in the early Paleogene represent marginal sedimentary facies at the foot of the South Tianshan Mountain,Kuqa Depression,Tarim Basin,Xinjiang province. Two types of fans occurred in the middle-late Paleogene Kumugeliemu and Suweiyi formations:one alluvial,and the other fan delta deposited in a lacustrine setting.Within the early Neogene Jidike Formation,coastal subaqueous fans developed,probably in a deeper water lacustrine setting.The three types of fans are stacked vertic...     

Late Cretaceous-Early Paleogene Foraminiferal Biostratigraphy in Xishan,Gamba,Southern Tibet,China

正1 Introduction The Cretaceous/Tertiary (Paleogene) extinction event was a mass extinction event occurring at about 65 million years ago between the Mesozoic Cretaceous and Cenozoic Tertiary,which is the one closest to today among the five major extinction events in the the geological history period (Renne et al.,2013).At the end of the Cretaceous,the proportion of species declined gradually,reaching a peak as the species disappeared closer to     

Differential Hydrocarbon Enrichment and its Main Controlling Factors in Depressions of the Bohai Bay Basin

Significant differential hydrocarbon enrichment occurs in depressions in a petroliferous basin. There are multiple depressions in the Bohai Bay Basin, and each depression as a relatively independent unit of hydrocarbon generation, migration and accumulation, contains significantly different hydrocarbon generation conditions and enrichment degree. On the basis of previous documents and a large number of statistical data, this work comparatively analyzed the differential hydrocarbon enrichment and its major controlling factors in depressions of the Bohai Bay Basin. The results show that depressions in the Bohai Bay Basin have various hydrocarbon enrichment degrees, and can be categorized into four types, namely enormously oil-rich, oil-rich, oily and oil-poor depressions. In general, the enormously oil-rich and oil-rich depressions are distributed in the eastern part of the basin along the Tan–Lu and Lan–Liao faults, whereas depressions in the western part of the basin are poor in hydrocarbons. Moreover, the vertical distribution of hydrocarbons is also highly heterogeneous, with Pre-Paleogene strata rich in hydrocarbons in the northern and western depressions, Paleogene strata rich in hydrocarbons in the entire basin, and Neogene strata rich in hydrocarbons in the off-shore areas of the Bohai Bay Basin. From early depressions in onshore areas to the late depressions in offshore areas of the Bohai Bay Basin, the source rocks and source-reservoir-cap rock assemblages gradually become younger and shallower, and the hydrocarbon resource abundance gradually increases. Hydrocarbon supplying condition is the key factor constraining the hydrocarbon enrichment for different depressions, while the main source-reservoir-cap rock assemblage, sufficient hydrocarbons and the transportation capacity of faults control the vertical distribution of hydrocarbons. The main factors controlling hydrocarbon enrichment are different for different layers. The hydrocarbon supplying condition of source rocks is the key controlling factor, whereas the source-reservoir configuration, the main source-reservoir-cap rock assemblages, and the fault transportation are the main factors of hydrocarbon enrichment in the Paleogene, Paleogene and Neogene, respectively.     

Late Miocene Pods and Leaves of Albizzia (Leguminosae: Mimosoideae)from Yunnan, SW China and Their Phytogeographic Implications

Albizzia is a leguminous genus belonging to the subfamily Mimosoideae with approximately150 modern species,widely distributed in the tropical and subtropical regions of Asia,Africa,Australia and America.Among them,17 species are mainly distributed in southern and southwestern China.Abundant fossils of the subfamily Mimosoideae,including leaves,pods,flowers and wood,have been reported from the Cretaceous and Paleogene strata of the Northern Hemisphere.However,Neogene records of Mimosoideae are relatively scarce.In this study,fossil pods and leaves belonging to the genus Albizzia from the Bangmai Formation of Yunnan,China were described.They were assigned to three species,including Albizzia scalpelliformis Guo,Li and Xie Emended,Albizzia cf.kalkora(Roxb.) Prain and Albizzia sp.The occurrence of Albizzia fossils from Lincang not only gives important information on the Neogene plant diversity from Yunnan—a worldwide famous biological hotspot—but also provides additional evidence for its phytogeographic history.     

Tectonic Characteristics and Evolution of the Taiwan Strait

The Taiwan Strait is a part of the continental-margin rift of eastern China, which can tectonically be divided into the Taiwan Strait basin, southwestern Taiwan basin and Penhu-Beigang uplift. The basins are structurally semi-graban down-faulted ones in character. The Cretaceous-Cenozoic sedimentary strata in the basins have a maximum thickness of over 10,000 m. The formation and development of the Taiwan Strait rift were not only affected by both the East China Sea basin and South China Sea basin but also closely related to the Central Range collision orogen of Taiwan. In the Cenozoic, the Taiwan Strait area experienced, under the influence of a multiple of tectonic mechanisms, three stages of evolution: poly-centre downfault-ing, down warping-faulting and foreland basin formation. The depositional centres of the basins migrated from west to east during the Tertiary, resulting in the thinning of the Palaeogene strata from west to east but that of the Neogene in the reverse direction. All this determine     

22-Ma eolian deposits in China and long-term climate changes

The history of eolian dust deposition in northern China has been traced back to 22 million years ago （Ma） and the combination of different eolian formations provides a nearly continuous terrestrial climate record since the early Neogene. The spatial distribution of environmental indicators define a roughly EW zonal climate pattern in Asia throughout the Paleogene, attributable to a circulation pattern dominated by a Planetary Wind System （PWS）. A major rearrangement occurred near the Miocene/Oligocene boundary, characterized by a replacement of the zonal PWS by a monsoon circulation similar to that of the present day. This event is also marked by the onset of loess deposition in northern China. The Asian summer monsoon was likely rather weak during the Paleogene. The loess deposition and formation of numerous well-developed paleosols since the Early Miocene indicate that the following features of the modem-day circulation already existed 22 Ma ago： sizeable deserts in the Asian inlands as dust sources, the winter monsoon as dust carrier, and an energetic summer monsoon as a supply of moisture. Uplift of the Himalayan-Tibetan complex and changes in land-sea distribution were likely responsible for these joint changes in circulation and aridity. From 22 to 6 Ma, loess accumulation rates were much lower, suggesting moderate levels of ar/dity and winter monsoon strength. Evolution of the aridity was not strongly correlative with the cooling trends indicated by marine oxygen isotope records, suggesting a smaller impact of global cooling on drying of the Asian interior during this time interval. However, the general aridification history since about 6 Ma matches the ongoing high-latitude cooling and the consequent expansion of Arctic sea-ice/ice sheets. Some increases in aridification also coincide with proposed uplift of portions of the Tibetan Plateau.     

Petroleum Geology in Deepwater Settings in a Passive Continental Margin of a Marginal Sea: A Case Study from the South China Sea

Deepwater oil and gas exploration has become a global hotspot in recent years and the study of the deep waters of marginal seas is an important frontier research area.The South China Sea(SCS)is a typical marginal sea that includes Paleo SCS and New SCS tectonic cycles.The latter includes continental marginal rifting,intercontinental oceanic expansion and oceanic shrinking,which controlled the evolution of basins,and the generation,migration and accumulation of hydrocarbons in the deepwater basins on the continental margin of the northern SCS.In the Paleogene,the basins rifted along the margin of the continent and were filled mainly with sediments in marine-continental transitional environments.In the Neogene–Quaternary,due to thermal subsidence,neritic-abyssal facies sediments from the passive continental margin of the SCS mainly filled the basins.The source rocks include mainly Oligocene coal-bearing deltaic and marine mudstones,which were heated by multiple events with high geothermal temperature and terrestrial heat flow,resulting in the generation of gas and oil.The faults,diapirs and sandstones controlled the migration of hydrocarbons that accumulated principally in a large canyon channel,a continental deepwater fan,and a shelf-margin delta.     

Meso—Cenozoic lithospheric thermal structure in the Bohai Bay Basin,eastern North China Craton

The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study,the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso-Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900-1100℃ in the late stages of the early Cretaceous;820-900℃ in the middle to late Paleogene; and(in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770-810℃ during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from "cold mantle and hot crust" before the Cretaceous to "hot mantle and cold crust" after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events.Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.     

Petroleum Origins and Accumulation Patterns in the Weixinan Sag in the Beibu Gulf Basin, Using Subsag B as an Example

Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin. To determine the source and accumulation mode of this crude oil, 12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them. Based on the geological conditions and the analytical results, the types, origins and accumulation patterns of crude oil in the study area were elucidated. Except for a shallowly-buried and bio...     

Discovery,Genesis and Significance of Metallic Minerals in Evaporate Series in the Kuqa Basin

A large-scale evaporate series is developed in Paleogene-Neogene strata in the Kuqa basin. The series is composed mainly of evaporate with thin beds of clastic rock (mainly mudstone and siltstone). In grayish white medium- and coarse-grained sandstone in Miocene strata, the formation of copper minerals is in close connection with brine. In joint planes, which are developed in vertical strata, are filled with gypsum. Gypsum and copper-mineralized sandstone contains enormous copper minerals, mainly atacamite. According to the SEM analysis for salt rock, gypsum rock, limestone, grayish green siltstone, grayish white medium-coarse-grained sandstone, some minerals are composed of metallic elements including Au, Ag, Cu, Zn, Pb, Co, Ni and U etc., in which Au occurs in a native form, Cu occurs in a native form or as atacamite in salt rock, gypsum rock and limestone, Ag occurs as silver sulfide in gypsum, and Zn, Pb, Co, Ni, U occur as compounds along with the above metallic ions in evaporate or clastic rock. From SEM images, we can see that metallic elements or their compounds (oxides or sulfides) “take root” as grains in salt or gypsum crystals, which belong to primary chemical sedimentation along with evaporate, while some grains “float” on surface of salt or gypsum. In the former case, mineral grains were formed together with salt (gypsum) crystals; while in the latter case, minerals were enriched from internal metallic ions (Paleogene evaporate samples) or external metallic ions (Neogene gypsum samples) in the late stage of evaporate formation. The metallic ions in Paleogene evaporate samples might originate from weathered or denudated materials in the south Tianshan Mountains. The metallic ions in the Neogene evaporate samples might be from metal-bearing brine, which migrated upward to surface along fractures and leached into evaporate (gypsum). Occurrence of metallic minerals and their compounds (elementary substance) in Paleogene evaporate proves that diversified metallic minerals exist in evaporate. The source of metallic ions in the Neogene evaporate series shows that evaporate could provide materials for late-stage metallic mineralization.     

Paleogene and Early Neogene Lacustrine Reefs in the WesternQaidam Basin, China

Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef and thrombolite reef with distinct reef structures, fore-reef, back-reef and reef-plateau. The fore-reef is characterized by a combination of pinnacle reef, thrombolite and algal reef. The back reef is composed of stromatolite reef and algal reef. The pinnacle reefs (micro-atoll), most of which are several tens of centimeters in diameter (whereas some exceptionally big ones are over 200 cm in diameter), and several tens of centimeter to 2 m in height, are situated on the far front-edge of the reef; the pinnacle reef is also often of recumbent form with a gravel-filled circular hole in the center. The algal reef is in the form of dome and irregular beds, and filled with algal detritus, ostracodes, spirorbis fossils, ooid and terrigenous debris, and worm traces; cavities and scour marks are of     

Evolution of Chinese Neogene Rhinocerotidae and Its Response to Climatic Variations

Chinese Neogene Rhinocerotidae has quite a complete record and its temporal range is the Early Miocene to Late Pliocene. The samples include 25 species in 4 tribes of 2 subfamilies. They are used as a foundation for the study of the evolution of the family and its relation to climatic changes. Taxonomic diversity, new records and extinctions are estimated for each Chinese Neogene mammal faunal unit (NMU). The diversity of Chinese Rhinocerotidae varies noticeably throughout the Neogene and is recognized within five stages: the Middle Miocene and Late Miocene are stages of high diversity and the Early Miocene, early Late Miocene and Pliocene are stages of low diversity. Rhinocerotid diversity and morphology are closely related to environmental factors and particularly sensitive to changes in ambient temperature and humidity. The interpretation of climatic variation reflected in the evolution of Rhinocerotidae corresponds precisely with the conclusions drawn from other workers and provides new evidence fen     

Quaternary： status, rank, definition, survival

The long controversy over the term ‘Quaternary‘ as a chronostratigraphic unit may be reaching an apotheosis, judging from recent papers (Pillans and Naish, 2004; Gibbard et al., 2005; and referencest herein). The debate is no longer centered on whether there should be a place in the geological time scale for a unit termed ‘Quaternary‘-despite its dubious past, it cannot be denied that a large body of earth-historical research is strongly identified with this term. The challenge now concerns an appropriate rank and definition of Quaternary with regard to other chronostratigraphic units. Several options have been proposed (Pillans and Naish, 2004), and Gibbard et al. (2005) encourage a debate on these before decision is reached. In this brief note, we describe an arrangement not previously considered that seems advantageous. It is instructive, however, to first review the Pleistocene Series and Neogene System, the two units that are directly affected by introduction of the Quaternary into the chronostratigraphic hierarchy.     

Quantitative Modelling of Multiphase Lithospheric Stretching and Deep Thermal History of Some Tertiary Rift Basins in Eastern China

The stretching process of some Tertiary rift basins in eastern China is characterized by multiphase rifting. A multiple instantaneous uniform stretching model is proposed in this paper to simulate the formation of the basins as the rifting process cannot be accurately described by a simple (one episode) stretching model. The study shows that the multiphase stretching model, combined with the back-stripping technique, can be used to reconstruct the subsidence history and the stretching process of the lithosphere, and to evaluate the depth to the top of the asthenosphere and the deep thermal evolution of the basins. The calculated results obtained by applying the quantitative model to the episodic rifting process of the Tertiary Qiongdongnan and Yinggehai basins in the South China Sea are in agreement with geophysical data and geological observations. This provides a new method for quantitative evaluation of the geodynamic process of multiphase rifting occurring during the Tertiary in eastern China.     

Mesozoic-Cenozoic Basin Features and Evolution of Southeast China

The Late Triassic to Paleogene(T_3-E) basin occupies an area of 143100 km~2,being the sixth area of the whole of SE China;the total area of synchronous granitoid is about 127300 km~2;it provides a key for understanding the tectonic evolution of South China.From a new 1:1500000 geological map of the Mesozoic-Cenozoic basins of SE China,combined with analysis of geometrical and petrological features,some new insights of basin tectonics are obtained.Advances include petrotectonic assemblages, basin classification of geodynamics,geometric features,relations of basin and range.According to basin-forming geodynamicai mechanisms,the Mesozoic-Cenozoic basin of SE China can be divided into three types,namely:1) para-foreland basin formed from Late Triassic to Early Jurassic(T_3-J_1) under compressional conditions;2) rift basins formed during the Middle Jurassic(J_2) under a strongly extensional setting;and 3) a faulted depression formed during Early Cretaceous to Paleogene (K_1-E) under back-arc extension action.From the rock assemblages of the basin,the faulted depression can be subdivided into a volcanic-sedimentary type formed mainly during the Early Cretaceous(K_1) and a red -bed type formed from Late Cretaceous to Paleogene(K_2-E).Statistical data suggest that the area of all para-foreland basins(T_3-J_1) is 15120 km~2,one of rift basins(J_2) occupies 4640 km~2,and all faulted depressions equal to 124330 km~2 including the K_2-E red-bed basins of 37850 km~2.The Early Mesozoic (T_3-J_1) basin and granite were mostly co-generated under a post-collision compression background, while the basins from Middle Jurassic to Paleogene(J_2-E) were mainly constrained by regional extensional tectonics.Three geological and geographical zones were surveyed,namely:1)the Wuyishan separating zone of paleogeography and climate from Middle Jurassic to Tertiary;2)the Middle Jurassic rift zone;and 3)the Ganjiang separating zone of Late Mesozoic volcanism.Three types of basin-granite relationships have been identified,including compressional(a few),strike-slip(a few), and extensional(common).A three-stage geodynamical evolution of the SE-China basin is mooted:an Early Mesozoic basin-granite framework;a transitional Middle Jurassic tectonic regime; intracontinental extension and red-bed faulted depressions since the Late Cretaceous.     

Genetic classification of natural gases in the Bozhong Depression, Bohai Bay, China

The geochemical characteristics of natural gases discovered in the Bozhong Depression are systematically described in this paper. The natural gases are composed mainly of hydrocarbon gases. Natural gases occurring in the Paleogene and older reservoirs are wet gases, whereas those in the Neogene reservoirs are dry gases. Methane and ethane in the gases are significantly different in carbon isotopic composition. The methane carbon isotopic composition of the gases in structure BZ28-1 and the ethane carbon isotopic composition of the gases in structure QHD30-1 are characterized by the heaviest values, respectively. The natural gases are in the mature to highly mature stages. The hydrocarbon gases are of organic origin and can be classified as oil-type gases, coal-derived gases and mixed gases with the third one accounting for the major portion.     

Late Cretaceous Transpressional Fault System: A Case Study of the Yishu Fault Belt, Shandong Province, Eastern China

On the basis of field observations of the structures of three profiles from the Linshu region, deformation characteristics and the tectonic background of the Yishu fault belt in the Late Cretaceous–Early Cenozoic have been discussed in detail.Three structural profiles, whose deformations consist mainly of earlier transpressional faults and later normal faults, were developed for the Mengtuan Formation of the Lower Cretaceous Dasheng Group.Typical positive flower structures, duplex structures, and break-through faults were found in these profiles.On the basis of analyses of the structural deformation and previous geochronological studies, it was concluded that the earlier transpressional faults of the profiles were triggered by the sinistral transpression of the Yishu fault belt in the Late Cretaceous–Early Paleogene, and that the later normal faults, formed during the Late Paleogene–Neogene extension, truncated the earlier transpressional faults.With consideration of the tectonic evolution of the Tan-Lu fault belt and the different drift directions of the Pacific plate since the Cretaceous, we suggest that the major tectonic events of the Late Cretaceous–Neogene in eastern China were mainly controlled by the subduction of the Pacific plate.