The condensates from the Yacheng Gas Field, Ying-Qiong Basins, have unusual chemical characteristics, with distribution dominated by terpanes and steranes derived from higher-plants. Pr/Ph ratios (6-11) are very high....The condensates from the Yacheng Gas Field, Ying-Qiong Basins, have unusual chemical characteristics, with distribution dominated by terpanes and steranes derived from higher-plants. Pr/Ph ratios (6-11) are very high. Drimane, cadinanes and homocadinanes exist in high concentration. Anomalously abundant 18α(H)-oleanane and remarkably abundant bicadinanes are present in Yacheng condensates, while 17α(H)-hopanes are in extremely low concentration. Taraxastane and significantly abundant 17α(H)-diahopanes occur in the condensates. In addition, a number of C 29 and C 30 unknown pentacyclic triterpanes were monitored in the condensates, some of which are abundant. The unknown compounds may be terrestrial biomarkers or their occurrence may suggest a sub-oxic (dyacrobic) clay-rich depositional environment. C 29 homologues are relatively predominant in regular and rearranged steranes. The concentration of diasteranes is markedly higher than that of regular steranes. The characteristics of Yacheng condensates are indicative of terrestrial source input. Based on condensate-condensate and condensate-rock correlations, combined with results of studies on sedimentary facies. Yacheng condensates may be sourced from Yacheng and Lingshui Formations in the Qiongdongnan Basin. The maturity of Yacheng condensate is relatively high, at late oil window stage (corresponding to 0.9%-1.3% R 0), based on sterane and terpane maturity parameters.展开更多
This paper aims to explore whether paleo-suture zone exists in the pre-Cenozoic basement of South China Sea (SCS). By taking advantage of integrated geophysical surveying data, including multi-channel reflection seism...This paper aims to explore whether paleo-suture zone exists in the pre-Cenozoic basement of South China Sea (SCS). By taking advantage of integrated geophysical surveying data, including multi-channel reflection seismicity, oceanic bottom seismicity, gravity and magnetic data as well as paleomagnetism and drilling information, a comprehensive analysis on sedimentary stratigraphy, seismic stratigraphy, magmatic and metamorphic petrology, geochemistry, gravity study, magnetics, paleogeomagnetics as well as geotectonics was carried out, and the results clearly indicate that a pre-Cenozoic suture zone, i.e. “Qiongnan (south Hainan Island) suture zone”, does exist on the north margin of SCS. This suture zone starts in the west from the Jiusuo-Lingshui fault zone in the south of Hainan Island, extends eastward across the continental slope to the north of SCS, and links with Shoufeng fault in Taiwan. It is inferred that the Qiongnan suture zone was sutured approximately in Indosinian (Triassic) Epoch and is actually the vestige of “Qiongnan ocean basin”, the extension of the main paleo-Tethys ocean basin in SCS. The formation of Qiongnan suture zone marked the collision-accretion of the Qiongnan Block toward the Qiongzhong Block. The Qiongnan suture zone is linked to the west with the southward extension of the principal suture zone of the Paleo-Tethys at Bitu-Changning-Menglian-Bentong-Raub, across the southern segment of the Red River-East Vietnam-Wanna strike-slip fault zone, and connected to the east with the suture zone emplaced into the south margin of the Oki-Hida Pre-Jurassic terranes in southwest Japan, across the northerni2 e segment of the Manila trench fault zone in the northeast side of Taiwan Island. The discovery of this suture zone is believed to be potentially significant toward study of the pre-Cenozoic geotectonic pattern of SCS, the temporal and spatial distribution of the east paleo-Tethys structural domain in SCS and the relationship of recombination and superimposition between the east paleo-Tethys structural domain and the west Pacific structural domain, in addition to the oil/gas geological potentials in the pre-Cenozoic marine vestige-superimposed basin in the study area.展开更多
Based on an integrated analysis of high-resolution 2D/3D seismic data and drilling results, this study analyzes the tectonic- sedimentary evolution of the Qiongdongnan Basin （QDNB） since the late Miocene, and discus...Based on an integrated analysis of high-resolution 2D/3D seismic data and drilling results, this study analyzes the tectonic- sedimentary evolution of the Qiongdongnan Basin （QDNB） since the late Miocene, and discusses the controlling factors on the formation and development of the Central Canyon System （CCS）. The sediment failures caused by the relative sea level falling might have discharged deposits from the slope to the canyon. The two suits of the infillings, i.e., turbidites and mass transport complex （MTC）, were derived from the northwestern source and northern source, respectively. The sediment supplies, which differ significantly among different areas, might have led to the variations observed in the internal architectures. Tectonic transformation around 11.6 Ma had provided the tectonic setting for the CCS and formed an axial sub-basin in the central part of the Changchang Depression, which could be called the rudiment of the CCS. The tectonic activity of the Red River Fault （RRF） at about 5.7 Ma might have strengthened the hydrodynamics of the deposits at the junction of the Yinggehal Basin （YGHB） and the QDNB to trigger a high-energy turbidity current. The MTC from the northern continental slope system might have been constrained by the Southern Uplift, functioning as a barrier for the infillings of the CCS. Thanks to a sufficient sediment supply during the Holocene period and the paleo-seafloor morphology, the relief of modern central canyon with the starving landform in the eastern Changchang Depression might have been accentuated by deposition of sediments and vertical growth along the canyon flanks, where collapse deposits were widely developed. Corresponding to the segmentation of the CCS, the forming mechanisms of the canyon between the three segments would be different. The turbidite channel in the head area had likely been triggered by the abundant sediment supply from the northwestern source together with the fault activity at about 5.7 Ma of the RRF. The formation and evolution of the canyon in the western segment were caused by combined effects of the turbidite channel from the northwestern source, the MTC from the northern continental slope, and the paleo-seafloor geomorphology. In the eastern segment, the canyon was constrained by the tectonic transformation occurring at approximately 11.6 Ma and the insufficient sediment supply from the wide-gentle slope.展开更多
文摘The condensates from the Yacheng Gas Field, Ying-Qiong Basins, have unusual chemical characteristics, with distribution dominated by terpanes and steranes derived from higher-plants. Pr/Ph ratios (6-11) are very high. Drimane, cadinanes and homocadinanes exist in high concentration. Anomalously abundant 18α(H)-oleanane and remarkably abundant bicadinanes are present in Yacheng condensates, while 17α(H)-hopanes are in extremely low concentration. Taraxastane and significantly abundant 17α(H)-diahopanes occur in the condensates. In addition, a number of C 29 and C 30 unknown pentacyclic triterpanes were monitored in the condensates, some of which are abundant. The unknown compounds may be terrestrial biomarkers or their occurrence may suggest a sub-oxic (dyacrobic) clay-rich depositional environment. C 29 homologues are relatively predominant in regular and rearranged steranes. The concentration of diasteranes is markedly higher than that of regular steranes. The characteristics of Yacheng condensates are indicative of terrestrial source input. Based on condensate-condensate and condensate-rock correlations, combined with results of studies on sedimentary facies. Yacheng condensates may be sourced from Yacheng and Lingshui Formations in the Qiongdongnan Basin. The maturity of Yacheng condensate is relatively high, at late oil window stage (corresponding to 0.9%-1.3% R 0), based on sterane and terpane maturity parameters.
文摘This paper aims to explore whether paleo-suture zone exists in the pre-Cenozoic basement of South China Sea (SCS). By taking advantage of integrated geophysical surveying data, including multi-channel reflection seismicity, oceanic bottom seismicity, gravity and magnetic data as well as paleomagnetism and drilling information, a comprehensive analysis on sedimentary stratigraphy, seismic stratigraphy, magmatic and metamorphic petrology, geochemistry, gravity study, magnetics, paleogeomagnetics as well as geotectonics was carried out, and the results clearly indicate that a pre-Cenozoic suture zone, i.e. “Qiongnan (south Hainan Island) suture zone”, does exist on the north margin of SCS. This suture zone starts in the west from the Jiusuo-Lingshui fault zone in the south of Hainan Island, extends eastward across the continental slope to the north of SCS, and links with Shoufeng fault in Taiwan. It is inferred that the Qiongnan suture zone was sutured approximately in Indosinian (Triassic) Epoch and is actually the vestige of “Qiongnan ocean basin”, the extension of the main paleo-Tethys ocean basin in SCS. The formation of Qiongnan suture zone marked the collision-accretion of the Qiongnan Block toward the Qiongzhong Block. The Qiongnan suture zone is linked to the west with the southward extension of the principal suture zone of the Paleo-Tethys at Bitu-Changning-Menglian-Bentong-Raub, across the southern segment of the Red River-East Vietnam-Wanna strike-slip fault zone, and connected to the east with the suture zone emplaced into the south margin of the Oki-Hida Pre-Jurassic terranes in southwest Japan, across the northerni2 e segment of the Manila trench fault zone in the northeast side of Taiwan Island. The discovery of this suture zone is believed to be potentially significant toward study of the pre-Cenozoic geotectonic pattern of SCS, the temporal and spatial distribution of the east paleo-Tethys structural domain in SCS and the relationship of recombination and superimposition between the east paleo-Tethys structural domain and the west Pacific structural domain, in addition to the oil/gas geological potentials in the pre-Cenozoic marine vestige-superimposed basin in the study area.
基金supported by the Major Research Plan of the National Natural Science Foundation of China(Grant No.91028009)the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.41002031)the Foundation of State Key Laboratory of Petroleum Resource and Prospecting,China University of Petroleum(Grant No.PRP/open-1205)
文摘Based on an integrated analysis of high-resolution 2D/3D seismic data and drilling results, this study analyzes the tectonic- sedimentary evolution of the Qiongdongnan Basin （QDNB） since the late Miocene, and discusses the controlling factors on the formation and development of the Central Canyon System （CCS）. The sediment failures caused by the relative sea level falling might have discharged deposits from the slope to the canyon. The two suits of the infillings, i.e., turbidites and mass transport complex （MTC）, were derived from the northwestern source and northern source, respectively. The sediment supplies, which differ significantly among different areas, might have led to the variations observed in the internal architectures. Tectonic transformation around 11.6 Ma had provided the tectonic setting for the CCS and formed an axial sub-basin in the central part of the Changchang Depression, which could be called the rudiment of the CCS. The tectonic activity of the Red River Fault （RRF） at about 5.7 Ma might have strengthened the hydrodynamics of the deposits at the junction of the Yinggehal Basin （YGHB） and the QDNB to trigger a high-energy turbidity current. The MTC from the northern continental slope system might have been constrained by the Southern Uplift, functioning as a barrier for the infillings of the CCS. Thanks to a sufficient sediment supply during the Holocene period and the paleo-seafloor morphology, the relief of modern central canyon with the starving landform in the eastern Changchang Depression might have been accentuated by deposition of sediments and vertical growth along the canyon flanks, where collapse deposits were widely developed. Corresponding to the segmentation of the CCS, the forming mechanisms of the canyon between the three segments would be different. The turbidite channel in the head area had likely been triggered by the abundant sediment supply from the northwestern source together with the fault activity at about 5.7 Ma of the RRF. The formation and evolution of the canyon in the western segment were caused by combined effects of the turbidite channel from the northwestern source, the MTC from the northern continental slope, and the paleo-seafloor geomorphology. In the eastern segment, the canyon was constrained by the tectonic transformation occurring at approximately 11.6 Ma and the insufficient sediment supply from the wide-gentle slope.
