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Seismic migration algorithms are often used to reveal subsurface structures and can be roughly divided into stacking methods, pre-stack time migration methods and pre-stack depth migration methods. In theory, pre-stack depth migration methods can provide the most accurate subsurface images. However, these methods are sensitive to the accuracy of the migration velocity model, and thus the creation of a precise migration velocity model is one of the most important steps in seismic processing. We applied the tomographic travel-time inversion and the method of pre-stack Kirchhoff depth migration-based migration velocity analysis (MVA) to certain South China Sea data, in which we iteratively inverted the precise, high-resolution migration velocity model. We selected travel-time differences from the offset-domain common image gathers of the pre-stack Kirchhoff depth migration and inverted the travel-time differences for velocity updating. After several iterations, both the precise migration velocity model and the corresponding pre-stack depth migration image were obtained. The comparisons with Normal Move-out stacking and pre-stack Kirchhoff time migration confirm that the tomographic MVA and corresponding pre-stack Kirchhoff depth migration provide the best image quality and highest-resolution subsurface images from the South China Sea data. [ABSTRACT FROM AUTHOR]

Ciliates (protozoa) are ubiquitous components of plankton community and play important roles in aquatic ecosystems in regards of their abundance, biomass, diversity and energy turnover. Based on the stratified samples collected from the northern Beibu Gulf in August 2011, species composition, abundance, biomass, diversity and spatial pattern of planktonic ciliates were studied. Furthermore the main environmental factors controlling ciliate communities were determined. A total of 101 species belonging to 44 genera and 7 orders (i.e., Oligotrichida, Haptorida, Euplotida, Sessilida, Pleurostomatida, Scuticociliatida and Tintinnida) were identified. The variation of ciliate communities was significant at horizontal level, but that was not at vertical level. Based on cluster analysis, ciliate communities were divided into three main groups. Redundancy analysis (RDA) revealed that Group A, existing in the waters with higher concentration of phosphorus and nitrogen, was dominated by Tintinnidium primitivum. Group B in the waters with lower temperature and chlorophyll-a concentration, was dominated by Leegaardiella ovalis. Group C, existing in the waters with higher temperature and chlorophyll-a concentration, was dominated by large Strombidium spp. and Mesodinium rubrum. Combining multiple analytic methods, our results strongly supported that phosphorus, nitrogen and chlorophyll-a were the most significant factors affecting the ciliate communities in the northern Beibu Gulf in summer. Concentration of phosphorus and nitrogen primarily influenced ciliate biomass, implying a potential impact of eutrophication on ciliate growth. The correlation with chlorophyll-a concentration, on one hand indicate the response of ciliates to the food availability, and on the other hand, the ciliates containing chloroplasts or endosymbionts may contribute greatly to the chlorophyll-a. [ABSTRACT FROM AUTHOR]

The South China Sea is rich in oil and gas resources. With the increasing exploration of oil and gas resources in the northern South China Sea and the increasing demand for energy in the world, The central‐southern South China Sea have become important constituencies for oil and gas resources. The central‐southern basins of South China Sea can be divided into three types of basin groups, namely, the southern basin group (Zengmu Basin, Brunei‐Sabah Basin), the western basin group (Wan'an Basin, Zhong jiannan Basin) and the Central Basin Group (Liyue Basin, Beikang Basin, Nanweixi Basin and Palawan Basin). At present, the degree of exploration is relatively low, and the source rock has not yet formed a understanding of the system. The main source rock development time, source rock characteristics, hydrocarbon generation potential and control factors of each basin group are still unclear, which seriously restricts the exploration of oil and gas. Based on the sedimentary facies distribution and sedimentary filling evolution, combined with the geoche mical characteristics of the source rocks, the source age, organic matter type, hydrocarbon generation potential and main controlling factors of the basins in the central‐southern basins are discussed. By the detailed research on delta scale, provenance system, paleoclimate conditions, ancient vegetation development and hydroca rbon generation parent material, the main controlling factors of hydrocarbon generation potential of source rocks in each basin group are revealed. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS), one of the largest marginal seas in West Pacific, has experienced two marginal sea tectonic cycles, the pro‐SCS and Neo‐SCS, forming a tectonic trend of "compression in the south, extension in the north, subduction in the east and strike in the west", with various kinds of sedimentary basins developed. The Central and Southern South China Sea (CSSCS) mainly has Zengmu, Brunei‐Sabah, Wanan, Zhongjiannan, Nanwei, Beikang, Reed, Palawan and Nansha Trough basins (Fig. 1). Since the exploration in the early 20th century, hundreds of oil and gas fields have been discovered in the CSSCS, making it one of giant oil and gas provinces in the world. However, the oil and gas potential of the CSSCS varied a lot, even among adjacent basins. Oil and gas resources in the southern Zengmu and Brunei‐Sabah basins are huge in scale, with recoverable reserves of nearly 5.3 billion tons of oil equivalent, which is ten times of that the Wanan basin in the west. The oil and gas discoveries in the Beikang basin on the Nansha block are only one three‐hundredth of Zengmu basin. No commercial discoveries have been made in the Reed and Nanwei basins. Although several studies have focused on the petroleum geology of separate basins, no systematical comparison has been made among various basins to reveal their differences and gain an overall perspective, largely due to limited datasets. The present study aims to investigate these aspects, using 90,000‐km 2D seismic profiles, 34 well logs, three cores, 36 outcrops, as well as paleontology, gravity and magnetic data. [ABSTRACT FROM AUTHOR]