2016 Vol. 38, No. 11
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2016, 38(11): .
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2016, 38(11): .
Abstract:
Seasonal variation of the volume, heat and salt transport in the East China Sea and adjacent regions
2016, 38(11): 1-19.
doi: 10.3969/j.issn.0253-4193.2016.11.001
Abstract:
In this paper, based on a nested high resolution reginal ocean modeling system, the relatively complete system of the circulation structure in the East China Sea is constructed. By comparing the model results with the existing estimates based on measurements, the numerical model results show agreement with the observation well. The results indicate that the water exchange in the East China Sea exhibit pronounced seasonal variations. From the view of the volume transport, the Taiwan Strait, the sections east of Taiwan and the section between Iriomote Island and Okinawa Island are the main sections flow into the East China Sea, however, the section between Okinawa Island and Amami Island, Tokara Strait, the Osumi Strait, the section east of Cheju Island, and the section between East China Sea and Yellow Sea are the main sections flow out of the East China Sea. The annual mean volume transport through these sections are 1.06×106 m3/s、20.49×106 m3/s、3.2×106 m3/s、-0.92×106 m3/s、-20.59×106 m3/s、-0.30×106 m3/s、-2.37×106 m3/s and -0.37×106 m3/s (inflow is positive). Comparison of these transports (volume, heat and salinity) indicate that these transport in the East China Sea have similar trends, the maximum flux often appeared in summer (July or August), and the minimum often appeared in winter (January or February). The calculation of volume balance indicates that from July to November that the East China Sea has a net outflow, however, from December to June it has a net inflow. The East China Sea flow into the Yellow Sea throughout the year, the annual mean value of the volume, heat and salt transport are 0.37×106 m3/s,0.027×1015 W and 12.7×106 kg/s respectively.
In this paper, based on a nested high resolution reginal ocean modeling system, the relatively complete system of the circulation structure in the East China Sea is constructed. By comparing the model results with the existing estimates based on measurements, the numerical model results show agreement with the observation well. The results indicate that the water exchange in the East China Sea exhibit pronounced seasonal variations. From the view of the volume transport, the Taiwan Strait, the sections east of Taiwan and the section between Iriomote Island and Okinawa Island are the main sections flow into the East China Sea, however, the section between Okinawa Island and Amami Island, Tokara Strait, the Osumi Strait, the section east of Cheju Island, and the section between East China Sea and Yellow Sea are the main sections flow out of the East China Sea. The annual mean volume transport through these sections are 1.06×106 m3/s、20.49×106 m3/s、3.2×106 m3/s、-0.92×106 m3/s、-20.59×106 m3/s、-0.30×106 m3/s、-2.37×106 m3/s and -0.37×106 m3/s (inflow is positive). Comparison of these transports (volume, heat and salinity) indicate that these transport in the East China Sea have similar trends, the maximum flux often appeared in summer (July or August), and the minimum often appeared in winter (January or February). The calculation of volume balance indicates that from July to November that the East China Sea has a net outflow, however, from December to June it has a net inflow. The East China Sea flow into the Yellow Sea throughout the year, the annual mean value of the volume, heat and salt transport are 0.37×106 m3/s,0.027×1015 W and 12.7×106 kg/s respectively.
Thermohaline structure and ecological characteristics of the Zhanjiang Bay and its estuary in autumn
2016, 38(11): 20-31.
doi: 10.3969/j.issn.0253-4193.2016.11.002
Abstract:
The analysis on the thermohaline structure and ecological characteristics of the Zhanjiang Bay and its estuary in autumn was based on the investigations of Chl a concentration, salinity and water temperature in October 2015. The study showed that the horizontal distribution of the salinity in the Zhanjiang Bay increased gradually from inner bay to outside bay, the Chl a concentration decreased gradually from inner bay to outside bay, the water temperature is higher in shallow area, and that in the bottom of estuary there was a "high salinity, low temperature and low chlorophyll" relatively stable structure of cold water mass. The formation of the water mass was due to the unique terrain structure of estuary. This characteristic promotes the regional water stratification. At the same time, the low transparency of the bottom water body confine the growth of phytoplankton at the bottom of estuary.
The analysis on the thermohaline structure and ecological characteristics of the Zhanjiang Bay and its estuary in autumn was based on the investigations of Chl a concentration, salinity and water temperature in October 2015. The study showed that the horizontal distribution of the salinity in the Zhanjiang Bay increased gradually from inner bay to outside bay, the Chl a concentration decreased gradually from inner bay to outside bay, the water temperature is higher in shallow area, and that in the bottom of estuary there was a "high salinity, low temperature and low chlorophyll" relatively stable structure of cold water mass. The formation of the water mass was due to the unique terrain structure of estuary. This characteristic promotes the regional water stratification. At the same time, the low transparency of the bottom water body confine the growth of phytoplankton at the bottom of estuary.
2016, 38(11): 32-42.
doi: 10.3969/j.issn.0253-4193.2016.11.003
Abstract:
The temporal variability and vertical distribution of barotropic tides, internal tides and near-inertial internal waves (NIW) were investigated on the basis of 3-month moored acoustic Doppler current profiler observations on the continental slope in the northwestern South China Sea in 2006. The diurnal baroclinic constituents are found to be more prominent than the semidiurnal baroclinic ones at mooring site, which are same with the barotropic tides, and amplitudes of the internal tides are stronger in the thermocline, and then decreases with depth. Almost all the major axes of the internal tidal ellipses are perpendicular to the local isobaths, that is, along the southeast-northwest direction approximately. Spring-neap oscillations of about 14 days can be seen at mooring site during observational periods. The coherent diurnal (semidiurnal) internal tidal motions could explain 70% (53%) of the total energy in the diurnal (semidiurnal) tidal band. Further analysis demonstrates that the semidiurnal internal tides are dominated by the first mode, whereas the diurnal internal tides show a variable multimodal structure:the third mode plays a secondary role and is comparable to the first mode. During the passage of Typhoon, the NIW became more energetic. Mesoscale warm eddies are the chimneys through which the near-inertial wind work penetrates rapidly into the deep ocean, and then cold eddies could probably inhibit the downward propagation of the near-inertial wind work.
The temporal variability and vertical distribution of barotropic tides, internal tides and near-inertial internal waves (NIW) were investigated on the basis of 3-month moored acoustic Doppler current profiler observations on the continental slope in the northwestern South China Sea in 2006. The diurnal baroclinic constituents are found to be more prominent than the semidiurnal baroclinic ones at mooring site, which are same with the barotropic tides, and amplitudes of the internal tides are stronger in the thermocline, and then decreases with depth. Almost all the major axes of the internal tidal ellipses are perpendicular to the local isobaths, that is, along the southeast-northwest direction approximately. Spring-neap oscillations of about 14 days can be seen at mooring site during observational periods. The coherent diurnal (semidiurnal) internal tidal motions could explain 70% (53%) of the total energy in the diurnal (semidiurnal) tidal band. Further analysis demonstrates that the semidiurnal internal tides are dominated by the first mode, whereas the diurnal internal tides show a variable multimodal structure:the third mode plays a secondary role and is comparable to the first mode. During the passage of Typhoon, the NIW became more energetic. Mesoscale warm eddies are the chimneys through which the near-inertial wind work penetrates rapidly into the deep ocean, and then cold eddies could probably inhibit the downward propagation of the near-inertial wind work.
2016, 38(11): 43-48.
doi: 10.3969/j.issn.0253-4193.2016.11.004
Abstract:
Based on the China Academy of Space Technology airborne spectrometer test data and the ECMWF wind data, the average backscattering cross sections, asymmetry and anisotropy changed with the incidence angle under different wind speed conditions, and the reason of wave backscatter asymmetry and anisotropy were preliminary analyzed. The results showed that at low incidence angle, the average backscattering cross section decreased as the incidence angle increased and reached a stable value at 18°,after essentially unchanged;wave backscatter asymmetry and anisotropy increased as incidence angle increased, reached a stable value at 18°, after essentially unchanged; under small winds speed conditions, waves asymmetry and anisotropy were related with wind speed, and the anisotropy and asymmetry were more obvious as wind speed increased.
Based on the China Academy of Space Technology airborne spectrometer test data and the ECMWF wind data, the average backscattering cross sections, asymmetry and anisotropy changed with the incidence angle under different wind speed conditions, and the reason of wave backscatter asymmetry and anisotropy were preliminary analyzed. The results showed that at low incidence angle, the average backscattering cross section decreased as the incidence angle increased and reached a stable value at 18°,after essentially unchanged;wave backscatter asymmetry and anisotropy increased as incidence angle increased, reached a stable value at 18°, after essentially unchanged; under small winds speed conditions, waves asymmetry and anisotropy were related with wind speed, and the anisotropy and asymmetry were more obvious as wind speed increased.
2016, 38(11): 49-59.
doi: 10.3969/j.issn.0253-4193.2016.11.005
Abstract:
Using global positioning system (GPS) and tide gauge (TG) data surround the South China Sea during the period 1989 to 2014, the characteristics of relative sea level change and the effects of the 2004 Sumatra earthquake is analyzed. The research shows that relative sea level is rising surrounding the South China Sea with the rate (4.53±0.20) mm/a which is higher than globally averaged sea level rise, and this trend has been intensified after 2004. Surrounding the South China Sea there are six categories of relative sea-level changes, each has its own style. Corresponding with the plate tectonics, four regions with typical characteristics in sea-level rising have formed:southeast coast of China and Vietnam coast, the Malay Peninsula, the northern part of Kalimantan Island and the Philippine Islands. The earthquake stopped the crustal arise and made Malay Peninsula, Nansha and Xisha in China sink violently, accelerating the rate of relative sea level rising,but has little impact on Chinese southeastern coast and the Philippines, the impact on the northern region of Kalimantan Island and Vietnam coast need follow-up study.
Using global positioning system (GPS) and tide gauge (TG) data surround the South China Sea during the period 1989 to 2014, the characteristics of relative sea level change and the effects of the 2004 Sumatra earthquake is analyzed. The research shows that relative sea level is rising surrounding the South China Sea with the rate (4.53±0.20) mm/a which is higher than globally averaged sea level rise, and this trend has been intensified after 2004. Surrounding the South China Sea there are six categories of relative sea-level changes, each has its own style. Corresponding with the plate tectonics, four regions with typical characteristics in sea-level rising have formed:southeast coast of China and Vietnam coast, the Malay Peninsula, the northern part of Kalimantan Island and the Philippine Islands. The earthquake stopped the crustal arise and made Malay Peninsula, Nansha and Xisha in China sink violently, accelerating the rate of relative sea level rising,but has little impact on Chinese southeastern coast and the Philippines, the impact on the northern region of Kalimantan Island and Vietnam coast need follow-up study.
2016, 38(11): 60-72.
doi: 10.3969/j.issn.0253-4193.2016.11.006
Abstract:
The impacts of assimilation of radial velocity (Vr) data for the application of analyses and forecasts for Hurricane Ike (2008) are investigated using the framework of Weather Research and Forecasting (WRF) V3.7 and its three-dimensional variational data (3DVAR) assimilation system developed by the U.S. National Center for Atmospheric Research (NCAR). To evaluate the impact of using the high spatial and temporal resolution of the radar data on the forecast of Hurricane Ike, Vr observations from two coastal radars are pre-processed with quality control procedures before they are assimilated using 3DVAR. Results show that, it is necessary to tune the background error length scale factor to better spread out observations for hurricane radar data assimilations. It is found that Vr data are able to adjust the hurricane's thermal and dynamic structure significantly. With smaller length scale factor, a much clearer cyclonic circulation wind increment around the observed hurricane center can be observed, providing effective meso-and micro scale information for the analysis, which can further improve the hurricane track and intensity forecast.
The impacts of assimilation of radial velocity (Vr) data for the application of analyses and forecasts for Hurricane Ike (2008) are investigated using the framework of Weather Research and Forecasting (WRF) V3.7 and its three-dimensional variational data (3DVAR) assimilation system developed by the U.S. National Center for Atmospheric Research (NCAR). To evaluate the impact of using the high spatial and temporal resolution of the radar data on the forecast of Hurricane Ike, Vr observations from two coastal radars are pre-processed with quality control procedures before they are assimilated using 3DVAR. Results show that, it is necessary to tune the background error length scale factor to better spread out observations for hurricane radar data assimilations. It is found that Vr data are able to adjust the hurricane's thermal and dynamic structure significantly. With smaller length scale factor, a much clearer cyclonic circulation wind increment around the observed hurricane center can be observed, providing effective meso-and micro scale information for the analysis, which can further improve the hurricane track and intensity forecast.
2016, 38(11): 73-89.
doi: 10.3969/j.issn.0253-4193.2016.11.007
Abstract:
Satellite altimetry is one of the important way to monitor significant wave height, this paper uses space-time matching method comparing SWH data of radar altimeters on board six satellites that are T/P, Jason-1, Envisat, Jason-2, Cryosat-2 and HY-2A with SWH data from NDBC buoys, and calibrates SWH data from radar altimeters. All radar altimeters data are chose from September 25, 1992 to September 1, 2015 for a period of 24 a. Matching result yields 53 NDBC buoys, including 7 oceanic buoys, evaluation of accuracy indicates RMSE between 0.4 m and 0.5 m, except T/P, after calibration, RMSE has significantly decreased, a maximum decline is 13.82%; the evaluation result of RMSE in 0.20-0.28 m for oceanic buoys, the evaluation of accuracy is better than all NDBC buoys; after calibration for SWH, there is a little bias between HY-2A satellite radar altimeter data and other 5 foreign satellite radar altimeter data.
Satellite altimetry is one of the important way to monitor significant wave height, this paper uses space-time matching method comparing SWH data of radar altimeters on board six satellites that are T/P, Jason-1, Envisat, Jason-2, Cryosat-2 and HY-2A with SWH data from NDBC buoys, and calibrates SWH data from radar altimeters. All radar altimeters data are chose from September 25, 1992 to September 1, 2015 for a period of 24 a. Matching result yields 53 NDBC buoys, including 7 oceanic buoys, evaluation of accuracy indicates RMSE between 0.4 m and 0.5 m, except T/P, after calibration, RMSE has significantly decreased, a maximum decline is 13.82%; the evaluation result of RMSE in 0.20-0.28 m for oceanic buoys, the evaluation of accuracy is better than all NDBC buoys; after calibration for SWH, there is a little bias between HY-2A satellite radar altimeter data and other 5 foreign satellite radar altimeter data.
2016, 38(11): 90-96.
doi: 10.3969/j.issn.0253-4193.2016.11.008
Abstract:
The HY-2A radar altimeter effective measurements of the sea surface height (SSH) were selected using the IGDR editorial criteria. The crossover points of HY-2A satellite SSH data from cycle 18 to 23 and Jason-2 data within 5 days were determined. The erroneous measurement orbits were removed based on crossover statistics of HY-2A and Jason-2. The quality of the HY-2A SSH data is evaluated using statistics of crossover difference analysis. The cross calibration results show that the number of HY-2A data points removed by the editorial criteria is about 12% of the total HY-2A SSH observations. It is found in this study the standard deviation of SSH between HY-2A satellite and Jason-2 is 7.0 cm for the HY-2A cycles used in this study, and the accuracy of SSH measurements of HY-2A meets the requirements of sensor design.
The HY-2A radar altimeter effective measurements of the sea surface height (SSH) were selected using the IGDR editorial criteria. The crossover points of HY-2A satellite SSH data from cycle 18 to 23 and Jason-2 data within 5 days were determined. The erroneous measurement orbits were removed based on crossover statistics of HY-2A and Jason-2. The quality of the HY-2A SSH data is evaluated using statistics of crossover difference analysis. The cross calibration results show that the number of HY-2A data points removed by the editorial criteria is about 12% of the total HY-2A SSH observations. It is found in this study the standard deviation of SSH between HY-2A satellite and Jason-2 is 7.0 cm for the HY-2A cycles used in this study, and the accuracy of SSH measurements of HY-2A meets the requirements of sensor design.
2016, 38(11): 97-104.
doi: 10.3969/j.issn.0253-4193.2016.11.009
Abstract:
Based on regional tectonic fracture system and gradually shape the canyon area high resolution 3D seismic data of fine resolution, realize the central valley of Qiongdongnan Basin formation mechanism in addition to the late Miocene tectonic changes, large-scale sea level falling, adequate supply source and groove type ancient topography and other related factors, there is another very important factor:the existence of early concealed fault zone at the bottom of the canyon. Research shows that parallel to the development in the central depression belt in Qiongdongnan Basin shelf slope break large-scale deep canyon, at the bottom of the canyon development large strike-slip faults and strike-slip faults to derive a series of secondary fault formation strata fracture zone, to realize the formation of the canyon, scale and distribution direction are affected by faults. Accordingly, the filling and evolution of the canyon, sea level change, is also the source of gravity flow function of the process of interaction and mutual superposition of many factors. To study experienced chasmic stage and basin evolution process is formed during the subsidence stage of the basin is of important guiding significance for large canyon.
Based on regional tectonic fracture system and gradually shape the canyon area high resolution 3D seismic data of fine resolution, realize the central valley of Qiongdongnan Basin formation mechanism in addition to the late Miocene tectonic changes, large-scale sea level falling, adequate supply source and groove type ancient topography and other related factors, there is another very important factor:the existence of early concealed fault zone at the bottom of the canyon. Research shows that parallel to the development in the central depression belt in Qiongdongnan Basin shelf slope break large-scale deep canyon, at the bottom of the canyon development large strike-slip faults and strike-slip faults to derive a series of secondary fault formation strata fracture zone, to realize the formation of the canyon, scale and distribution direction are affected by faults. Accordingly, the filling and evolution of the canyon, sea level change, is also the source of gravity flow function of the process of interaction and mutual superposition of many factors. To study experienced chasmic stage and basin evolution process is formed during the subsidence stage of the basin is of important guiding significance for large canyon.
2016, 38(11): 105-116.
doi: 10.3969/j.issn.0253-4193.2016.11.010
Abstract:
The sedimentary characteristics of Neogene submarine fan in deep-water area of Qiongdongnan Basin was studied through integrated utilization of drilling, well core, slice and laboratory test data. The results show that these submarine fans were formed by transportation of sandy slumps, which featured multi-period. The lithology and physical properties of the submarine fans vary significantly under the control of different sediment sources. The sedimentary structures show characteristics of sandy slump, debris flow, turbidity currentand deep-water underflow alternations. Seismic reflecting amplitudeand frequency reflect changes of sedimentary microfacies, sandstone thickness, sand-shale ratio and sand-shale spatial distributions. Using new 3D seismic data collected in deep-water area, the spatial distribution of submarine fans are depicted by techniques of fine well-seismic calibration, multi attribute, slice and 3D sand hollow. It was found that these submarine fans, stacked vertically and laterally, were cut by muddy channels latterly to form several lithological traps. In conclusion, the submarine fans is with huge exploration potential forming large scalelithological gas reservoirs based on its fine hydrocarbon source rock, good reservoir-cap combination and traps.
The sedimentary characteristics of Neogene submarine fan in deep-water area of Qiongdongnan Basin was studied through integrated utilization of drilling, well core, slice and laboratory test data. The results show that these submarine fans were formed by transportation of sandy slumps, which featured multi-period. The lithology and physical properties of the submarine fans vary significantly under the control of different sediment sources. The sedimentary structures show characteristics of sandy slump, debris flow, turbidity currentand deep-water underflow alternations. Seismic reflecting amplitudeand frequency reflect changes of sedimentary microfacies, sandstone thickness, sand-shale ratio and sand-shale spatial distributions. Using new 3D seismic data collected in deep-water area, the spatial distribution of submarine fans are depicted by techniques of fine well-seismic calibration, multi attribute, slice and 3D sand hollow. It was found that these submarine fans, stacked vertically and laterally, were cut by muddy channels latterly to form several lithological traps. In conclusion, the submarine fans is with huge exploration potential forming large scalelithological gas reservoirs based on its fine hydrocarbon source rock, good reservoir-cap combination and traps.
2016, 38(11): 117-124.
doi: 10.3969/j.issn.0253-4193.2016.11.011
Abstract:
Based on the use of drilling and core data, combined with the identification of casting thin sections, scanning electron microscopy, capilllary pressure experiment and so on, we analyze the reservoir characteristics and controlling factors of Huangliu Formation in the central canyon of Qiongdongnan Basin. The research shows that the finely granular lithic quartz-sandstone is dominated in the Huangliu Formation, and the sorting degree of sandstone is good, indicating the high maturity of rock composition and structure. Primary intergranular pore is the dominant reservoir space type, and the pore texture of sandstone is characterized by medium pore and fine throat at large. The reservoir propertity has the characterise of medium-ultrahigh porosity and medium-ultrahigh permeability. Sedimentary facies and diagenesis are the main factors on reservoir property. The channel sandstone of deep-water turbidity current deposits is the precondition of the development of high-quality reservoir, and the special water depth and temperature-pressure condition are the important factors that affect the diagenesis of reservoir. Because of deep seawater and shallowly buried stratum, the reservoir of Huangliu Formation is in the environment of low temperature and normal pressure in general, so that the diagenesis is generally not strong. But the differences of reservoir porosity and permeability is mainly controlled by compaction. From the west to the east in the central canyon, the depth of seawater increases gradually and the buried depth of stratum gets shallower, the compaction in the west is stronger than the east of central canyon, so the porosity and permeability of reservoir in the east is relatively high, as also as the gas saturation.
Based on the use of drilling and core data, combined with the identification of casting thin sections, scanning electron microscopy, capilllary pressure experiment and so on, we analyze the reservoir characteristics and controlling factors of Huangliu Formation in the central canyon of Qiongdongnan Basin. The research shows that the finely granular lithic quartz-sandstone is dominated in the Huangliu Formation, and the sorting degree of sandstone is good, indicating the high maturity of rock composition and structure. Primary intergranular pore is the dominant reservoir space type, and the pore texture of sandstone is characterized by medium pore and fine throat at large. The reservoir propertity has the characterise of medium-ultrahigh porosity and medium-ultrahigh permeability. Sedimentary facies and diagenesis are the main factors on reservoir property. The channel sandstone of deep-water turbidity current deposits is the precondition of the development of high-quality reservoir, and the special water depth and temperature-pressure condition are the important factors that affect the diagenesis of reservoir. Because of deep seawater and shallowly buried stratum, the reservoir of Huangliu Formation is in the environment of low temperature and normal pressure in general, so that the diagenesis is generally not strong. But the differences of reservoir porosity and permeability is mainly controlled by compaction. From the west to the east in the central canyon, the depth of seawater increases gradually and the buried depth of stratum gets shallower, the compaction in the west is stronger than the east of central canyon, so the porosity and permeability of reservoir in the east is relatively high, as also as the gas saturation.
2016, 38(11): 125-139.
doi: 10.3969/j.issn.0253-4193.2016.11.012
Abstract:
The dolomitization of carbonate rocks is a controversial scientific problem. During the 2012-2013, the Zhanjiang branch of CNOOC drilled the Well Xike-1. The core of well is 1 268.02 m long and 0-1 257.52 m carbonate rocks interval has 7 dolomite tiers. This paper discusses the dolomitization of reefs in the Xisha Islands based on mineral composition, major elements, trace and rare earth elements of sample of well Xike 1. It turned out that the cause of formation of 7 dolomite tiers is not relevant to buried depth and compaction diagenesis and the distribution of dolomite tiers has a close relationship with sea level falling. According to characteristics of element geochemistry of dolomite tiers, the dolomite diagenetic fluid is concentrated high salinity seawater. The paper proposes the hypersaline brine seepage backflow dolomitization pattern in reefs lagoon environment. With the rise and fall of sea level, the reefs are in the loop of submersion and exposure. The descending of sea leval leads to the formation of the lagoon. Because the evaporation capacity is more than precipitation in the Xisha sea area, the salinity of seawater in lagoon is increased and Mg-rich brine is formed. With the infiltration of the Mg-rich brine in mushy reefs, the Mg replaces the Ca formed in CaCO3 in early stage and the dolomite is formed. The cycles of submersion and exposure of reef cause several dolomite tiers formed. The sea level fluctuation controls the development of reefs carbonatite and dolomitization. The changes of paleoclimate leading to the sea level fluctuation play an important role in the formation and development process of reef islands.
The dolomitization of carbonate rocks is a controversial scientific problem. During the 2012-2013, the Zhanjiang branch of CNOOC drilled the Well Xike-1. The core of well is 1 268.02 m long and 0-1 257.52 m carbonate rocks interval has 7 dolomite tiers. This paper discusses the dolomitization of reefs in the Xisha Islands based on mineral composition, major elements, trace and rare earth elements of sample of well Xike 1. It turned out that the cause of formation of 7 dolomite tiers is not relevant to buried depth and compaction diagenesis and the distribution of dolomite tiers has a close relationship with sea level falling. According to characteristics of element geochemistry of dolomite tiers, the dolomite diagenetic fluid is concentrated high salinity seawater. The paper proposes the hypersaline brine seepage backflow dolomitization pattern in reefs lagoon environment. With the rise and fall of sea level, the reefs are in the loop of submersion and exposure. The descending of sea leval leads to the formation of the lagoon. Because the evaporation capacity is more than precipitation in the Xisha sea area, the salinity of seawater in lagoon is increased and Mg-rich brine is formed. With the infiltration of the Mg-rich brine in mushy reefs, the Mg replaces the Ca formed in CaCO3 in early stage and the dolomite is formed. The cycles of submersion and exposure of reef cause several dolomite tiers formed. The sea level fluctuation controls the development of reefs carbonatite and dolomitization. The changes of paleoclimate leading to the sea level fluctuation play an important role in the formation and development process of reef islands.
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