Based on specimens collected in Yinggehai, Hainan, China from 2013 to 2016, a stable epiphytic taxon is found on the surface of the individual of marine green alga Cladophora aokii Yamada. According to the morphological characteristics, the taxonomy of Cl. aokii and its epiphytes is carried out. There are some epiphytes attached on Cl. aokii Yamada including Cl. fascicularis (Mertens ex C. Agardh) Kützing, Chaetomorpha pachynema (Montagne) Kützing, Ceramium camouii Dawson, Licmophora abbreviata Agardh, Lyngbya sp. and Chattonella sp.. The formation of the individual of Cl. aokii is dissected and explained, which can help to analyze the adaption in details among this species, its epiphytes and native marine environment. The results reveal the marine macro-epiphytic taxonomy in Hainan, China, and preliminarily explain the adaptive relationship between macroalgae and environment.

The Dongfang1-1 gas field (DF1-1) in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources. The second member of the Pliocene Yinggehai Formation (YGHF) is the main gas-producing formation and is composed of various sedimentary types; however, a clear understanding of the sedimentary types and development patterns is lacking. Here, typical lithofacies, logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling, logging, analysis and testing data. Based on 3D seismic interpretation and attribute analysis, the origin of high-amplitude reflections is clarified, and the main types and evolution characteristics of sedimentary facies are identified. Taking gas formation upper II (IIU) as an example, the plane distribution of the delta front and bottom current channel is determined; finally, a comprehensive sedimentary model of the YGHF second member is established. This second member is a shallowly buried “bright spot” gas reservoir with weak compaction. The velocity of sandstone is slightly lower than that of mudstone, and the reflection has medium amplitude when there is no gas. The velocity of sandstone decreases considerably after gas accumulation, resulting in an increase in the wave impedance difference and high-amplitude (bright spot) reflection between sandstone and mudstone; the range of high amplitudes is consistent with that of gas-bearing traps. The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps, and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps. The study area is a delta front deposit developed on a shallow sea shelf. The lithologies of the reservoir are mainly composed of very fine sand and coarse silt, and a variety of sedimentary structural types reflect a shallow sea delta environment; upward thickening funnel type, strong toothed bell type and toothed funnel type logging facies are developed. In total, 4 stages of delta front sand bodies (corresponding to progradational reflection seismic facies) derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF; these sand bodies are dated to 1.5 Ma and correspond to four gas formations. During sedimentation, many bottom current channels (corresponding to channel fill seismic facies) formed, which interacted with the superposed progradational reflections. When the provenance supply was strong in the northwest, the area was dominated by a large set of delta front deposits. In the period of relative sea level rise, surface bottom currents parallel to the coastline were dominant, and undercutting erosion was obvious, forming multistage superimposed erosion troughs. Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.

Tectonically, the northwestern South China Sea (SCS) is located at the junction between three micro-plates, i.e., the Indochina, South China and Zhongsha-Xisha micro-plates, and involves three basins, i.e., the Yinggehai Basin, the Qiongdongnan Basin and Xisha Trough in the east, and the Zhongjiannan Basin in the south. Since the Pliocene (5.3 Ma), the Yinggehai Basin has experienced repeated accelerating subsidence, high thermal fluid, and widely developing mud-rich overpressure chambers, abundant mud diapers and crust-mantle mixed CO₂. While a large central canyon was developed in the Qiongdongnan Basin, new rift occurred in the Xisha Trough. These characteristics demonstrate a single tectonic unit for the northwestern SCS, for which we have undertaken stress field modeling to understand its plate deformations and sedimentary responses. Our results demonstrate that an extension tectonic event occurred after 5.3 Ma in the Yinggehai-Qiongdongnan-Xisha trough area, which is characterized by thinner crust (<16 000 m), half-graben or graben structural style and thicker sedimentary sequences (>3 500 m). A new rift system subsequently was developed in this area; this event was mainly driven by the combined effects of different movement velocity and direction of the three micro-plates, and the far-field effect of the continental collision between the Indian Plate and the Tibetan Plateau, and subduction of the Pacific Plate underneath the Eurasian Plate.

Natural hydrocarbon seeps in a marine environment are one of the important contributors to greenhouse gases in the atmosphere, including methane, which is significant to the global carbon cycling and climate change. Four hydrocarbon seep areas, the Lingtou Promontory, the Yinggehai Rivulet mouth, the Yazhou Bay and the Nanshan Promontory, occurring in the Yinggehai Basin delineate a near-shore gas bubble zone. The gas composition and geochemistry of venting bubbles and the spatial distribution of hydrocarbon seeps are surveyed on the near-shore Lingtou Promontory. The gas composition of the venting bubbles is mainly composed of CO₂, CH₄, N₂ and O₂, with minor amounts of non-methane hydrocarbons. The difference in the bubbles' composition is a possible consequence of gas exchange during bubble ascent. The seepage gases from the seafloor are characterized by a high CO₂ content (67.35%) and relatively positive δ¹³C_V-PDB values (-0.49×10^-3-0.86×10^-3), indicating that the CO₂ is of inorganic origin. The relatively low CH₄ content (23%) and their negative δ¹³C_V-PDB values (-34.43×10^-3--37.53×10^-3) and high ratios of C₁ content to C_1-5 one (0.98-0.99) as well point to thermogenic gases. The hydrocarbon seeps on the 3.5 Hz sub-bottom profile display a linear arrangement and are sub-parallel to the No. 1 fault, suggesting that the hydrocarbon seeps may be associated with fracture activity or weak zones and that the seepage gases migrate laterally from the central depression of the Yinggehai Basin.

Based on heavy mineral data in core samples from eleven drillings, supplemented by paleontological, element geochemical and seismic data, the evolution of sediment provenance and environment in the Qiongdongnan Basin (QDNB) was analysed. The results show that the basement in the QDNB was predominantly composed of terrigenous sediments. Since the Oligocene the QDNB has gradually undergone transgressions and evolution processes in sedimentary environment from terrestrial-marine transitional to littoral-neritic, neritic, and bathyal roughly. The water depth showed a gradually increasing trend and was generally greater in the southern region than that in the northern region in the same time. With changes in sedimentary environment, provenances of the strata (from the Yacheng Formation to the Yinggehai Formation) showed principal characteristics of multisources, evolving from autochthonous source, short source to distant source step by step. During the Early Oligocene, the sediments were mainly proximal basaltic pyroclastic source and adjacent terrigenous clastic source, afterwards were becoming distant terrigenous clastic sources, including Hainan Island on the north, Yongle Uplift on the south, Shenhu Uplift on the northeast, the Red River System on the northwest and Indochina Peninsula on the southwest, or even a wider region. The Hainan Island provenance began to develop during the Early Oligocene and has become a main provenance in the QDNB since the Middle Miocene. The provenances from Yongle Uplift and Shenhu Uplift most developed from the Late Oligocene to the Early Miocene and gradually subsided during the Middle Miocene. During the Late Miocene, as a main source of sediments filled in the central canyon, the Red River System provenance added to the QDNB massively, whose impact terminated at the end of the Pliocene. The western Yinggehai Basin (YGHB) provenance derived from Indochina Peninsula had developed from the Pliocene on to the Pleistocene. In addition, the material contribution of marine authigenous source to the basin (especially to the southern region) could not be ignored.

In the late Miocene, giant ancient pockmarks, which are fairly rare globally, developed in the Qiongdongnan Basin. In this paper, to determine the sedimentary characteristics and genetic mechanism of these giant ancient pockmarks in the Yinggehai Formation of the Qiongdongnan Basin, based on high-resolution 3D seismic data and multiattribute fusion technologies, we analyzed the planar distribution and seismic facies of the ancient pockmarks and compared the characteristics of the ancient pockmarks with those of channels, craters, and hydrate pits. Moreover, we also discussed the implications of the fluid escape system and paleo-bottom current activity in the ancient pockmark development area and analyzed the influence of the ancient pockmarks on the paleoclimate in this region. Finally, an evolutionary model was proposed for the giant ancient pockmarks. This model shows that the giant ancient pockmarks in the southern Qiongdongnan Basin were affected by both deep fluid escape and lateral transformation of paleobottom currents. In addition, the giant ancient pockmarks contributed to the atmospheric CO₂ concentration in the late Miocene and played a great role in the contemporary evaluation of deepwater petroleum exploration.

Located at the northwest continental slope of the South China Sea, the Qiongdongnan Basin bears valley-shaped bathymetry deepening toward east. It is separated from the Yinggehai Basin through NW-trending Indo-China- Red River shear zone, and connected with NW subsea basin through the Xisha Trough. Along with the rapid progress of the deepwater exploration, large amounts of high resolution geophysical and geological data were accumulated. Scientific researches about deepwater basins kept revealing brand new tectonic and sedimentary discoveries. In order to summarize the structural features and main controlling factors of the deepwater Qiongdongnan Basin, a series of researches on basin architecture, fault activities, tectonic deformation and evolution were carried out. In reference to analogue modeling experiments, a tectonic situation and a basin formation mechanism were discussed. The researches indicate that: the northern boundary of the Qiongdongnan Basin is strongly controlled by No. 2 fault. The overlapping control of two stress fields from the east and the west made the central depression zone extremely thinned. Combined with the changed stress field, the segmentation of a preexisting weakness zone made the sags in the east experiencing different rifting histories from the west ones. The NE-trending west segment of the Qiongdongnan Basin experienced strong rifting during Eocene, while the roughly EW-trending sags in the east segment show strong rifting during late Eocene and early Oligocene. Local structures such as NW-trending basal fault and inherited uplifts controlled the lateral segmentation. So first order factors such as regional stress field and preexisting weakness zone controlled the basin zonation, while the second order factors determined the segmentation from east to west.

A rarely reported middle−late Miocene−Pliocene channel (incised valley fill), the Huaguang Channel (HGC), has been found in the deep-water area of the southwestern Qiongdongnan Basin (QDNB). This channel is almost perpendicular to the orientation of another well-known, large, and nearly coeval submarine channel in this area. Based on the interpretation of high-resolution 3D seismic data, this study describes and analyzes the stratigraphy, tectonics, sedimentation, morphology, structure and evolution of HGC by means of well-seismic synthetic calibration, one- and two-dimensional forward modeling, attribute interpretation, tectonic interpretation, and gas detection. The HGC is located on the downthrown side of an earlier activated normal fault and grew northwestward along the fault strike. The channel is part of a slope that extends from the western Huaguang Sag to the eastern Beijiao Uplift. The HGC underwent four developmental stages: the (1) incubation (late Sanya Formation, 20.4–15.5 Ma), (2) embryonic (Meishan Formation, 15.5–10.5 Ma), (3) peak (Huangliu Formation, 10.5–5.5 Ma) and (4) decline (Yinggehai Formation, 5.5–1.9 Ma) stages. The channel sandstones have a provenance from the southern Yongle Uplift and filled the channel via multistage vertical amalgamation and lateral migration. The channel extended 42.5 km in an approximately straight pattern in the peak stage. At 10.5 Ma, sea level fell relative to its lowest level, and three oblique progradation turbidite sand bodies filled the channel from south to north. A channel sandstone isopach map demonstrated a narrow distribution in the early stages and a fan-shaped distribution in the late stage. The formation and evolution of the HGC were controlled mainly by background tectonics, fault strike, relative sea level change, and mass supply from the Yongle Uplift. The HGC sandstone reservoir is near the Huaguangjiao Sag, where hydrocarbons were generated. Channel-bounding faults and underlying faults link the source rock with the reservoir. A regionally extensive mudstone caprock overlies the channel sandstone. Two traps likely containing gas were recognized in a structural high upstream of the channel from seismic attenuation anomalies. The HGC will likely become an important oil and gas accumulation setting in the QDNB deep-water area.

A few species in the genus Grateloupia (Halymeniaceae, Rhodophyta) have been investigated in detail with respect to morphological observations and molecular analyses. In this study, the authors document the vegetative and reproductive structures of two new species of Grateloupia, G. dalianensis H.W.Wang et D.Zhao, sp.nov. and G. yinggehaiensis H.W.Wang et R.X.Luan, sp.nov. They both have the morphological character that carpogonial ampullae and auxiliary cell ampullae are the simple Grateloupia-type. The two species can be distinguished from other species of the genus by their distinctive morphological features respectively. Based on ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene sequences, the phylogenetic tree obtained in the study indicated that they are both embedded within the Grateloupia clade. G. dalianensis clusters a subclade with G. asiatica, and G. yinggehaiensis forms a single monophyletic subclade with G. hawaiiana.