Numerous elongated mounds and channels were found at the top of the middle Miocene strata using 2D/3D seismic data in the Liwan Sag of Zhujiang River Mouth Basin (ZRMB) and the Beijiao Sag of Qiongdongnan Basin (QDNB). They occur at intervals and are rarely revealed by drilling wells in the deepwater areas. Origins of the mounds and channels are controversial and poorly understood. Based on an integrated analysis of the seismic attribute, palaeotectonics and palaeogeography, and drilling well encountering a mound, research results show that these mounds are dominantly distributed on the depression centres and/or slopes of the Liwan and Beijiao sags and developed in a bathyal sedimentary environment. In the Liwan and Beijiao sags, the mounds between channels (sub) parallel to one another are 1.0–1.5 km and 1.5–2.0 km wide, 150–300 m and 150–200 m high, and extend straightly from west to east for 5–15 km and 8–20 km, respectively. Mounds and channels in the Liwan Sag are parallel with the regional slope. Mounds and channels in the Beijiao Sag, however, are at a small angle to the regional slope. According to internal geometry, texture and external morphology of mounds, the mounds in Beijiao Sag are divided into weak amplitude parallel reflections (mound type I), blank or chaotic reflections (mound type II), and internal mounded reflections (mound type III). The mounds in Liwan Sag, however, have the sole type, i.e., mound type I. Mound type I originates from the incision of bottom currents and/or gravity flows. Mound type II results from gravity-driven sediments such as turbidite. Mound type III is a result of deposition and incision of bottom currents simultaneously. The channels with high amplitude between mounds in the Beijiao and Liwan sags are a result of gravity-flow sediments and it is suggested they are filled by sandstone. Whereas channels with low-mediate amplitudes are filled by bottom-current sediments only in the Beijiao Sag, where they are dominantly composed of mudstone. This study provides new insights into the origins of the mounds and channels worldwide.

Analysis of 3D seismic data and well log data from the Rovuma Basin in East Africa reveals the presence of a late Eocene channel-lobe complex on its slope. The first two channels, denoted as channel-1 and channel-2, are initiated within a topographic low on the slope but come to a premature end when they are blocked by a topographic high in the northwest region of the basin. New channels migrate southeastward from channel-1 to channel-6 due to the region’s sufficient sediment supply and stripping caused by bottom currents. The primary factors controlling the development of the channel complex include its initial paleo-topographic of seafloor, the property of gravity flows, the direction of the bottom current, and the stacking and expansion of its levees. The transition zone from channel to lobe can also be clearly identified from seismic sections by its pond-shaped structure. At a certain point, thest systems record a transiton from erosive features to sedimentary features, and record a transition from a confined environment to an open environment. Channels and lobes can be differentiated by their morphologies: thick slump-debris flows are partly developed under channel sand sheets, whereas these slump-debris flows are not very well developed in lobes. Well log responses also record different characteristics between channels and lobes. The interpreted shale volume throughout the main channel records a box-shaped curve, thereby implying that confined channel complexes record high energy currents and abundant sand supply, whereas the interpreted shale volume throughout the lobe records an upward-fining shape curve, thereby indicating the presence of a reduced-energy current in a relatively open environment. Within the Rovuma Basin of East Africa, the average width of the Rovuma shelf is less than 10 km, the width of the slope is only approximately 40 km, and the slope gradient is 2°–4°. Due to this steep slope gradient, the sand-rich top sheet within the channel also likely contributes to the straight feature of the channel system. It is currently unclear whether the bottom current has any effect on its sinuosity.

In the present study, the coal-rock organic facies of Oligocene Yacheng Formation of the marginal basin in the South China Sea were classified and divided. In addition, through the correlations of the large-scale coal-bearing basins between the epicontinental sea and the South China Sea, it was concluded that the coal forming activities in the South China Sea presented particularity and complexity. Furthermore, the coal forming mechanisms also presented distinctiveness. The marginal basins in the South China Sea consist of several large and complex rift or depression basins, which are distributed at different tectonic positions in the South China Sea. Therefore, the marginal basins in the South China Sea are not simple traditional units with onshore continental slopes extending toward the deep sea. The marginal basins are known to consist of multi-level structures and distinctive types of basins which differ from the continental regions to the sea. During the Oligocene, the existing luxuriant plants and beneficial conditions assisted in the development of peat. Therefore, the Oligocene was the significant period for the formation and aggregation of the peat. However, the peat did not form in unified sedimentary dynamic fields, but instead displayed multi-level geographical units, multiple provenance areas, instability, and nonevent characteristics. As a result, the marginal basins in the South China Sea are characterized by non-uniform peat aggregation stages. In another words, the majority of the peat had entered the marine system in a dispersive manner and acted as part of the marine deposits, rather than during one or several suitable coal-forming stages. These peat deposits then became the main material source for hydrocarbon generation in all of the marginal basins of the South China Sea. The study will be of much significance for the hydrocarbon exploration in the marginal basins of the South China Sea.

Through the analysis of the faults and their internal structure in Zhu I Depression, it is found that the internal structure of the late fault is obviously segmented vertically. It develops unitary structure (simple fault plane) in shallow layers, binary structure (induced fracture zone in hanging wall and sliding fracture zone in footwall) in middle, layers and ternary structure (induced fracture zone in hanging wall and sliding fracture zone in middle, and induced fracture zone in footwall) in deep layers. Because the induced fracture zone is a high porosity and permeability zone, and the sliding fracture zone is a low porosity and ultra-low permeability zone, the late fault in middle layers has the character of “transporting while sealing”. The late fault can transport hydrocarbon by its induced fracture zone in the side of the hanging wall and seal hydrocarbon by its sliding fracture zone in the side of the footwall. In deep layers, the late fault has the character of “dual-transportation”, induced fracture zones in both sides of hanging wall and footwall can transport hydrocarbon. The early fault that only developed in the deep layers is presumed to be unitary structure, which plays a completely sealing role in the process of hydrocarbon migration and accumulation due to inactivity during the hydrocarbon filling period. Controlled by hydrocarbon source, early/late faults, sand bodies and traps, two reservoir-forming models of “inverted L” and “stereo-spiral” can be proposed in middle layers, while two reservoir-forming models of “cross fault” and “lateral fault sealing” are developed in the deep layers of Zhu I Depression.

Taiwan Island’s outcropping strata can provide important insights into the sedimentary environment and source development of the southeast China margin. This research is based on the Eocene–Miocene strata of the Tsukeng area in the central Western Foothills, northeast shoreline of Taiwan Island and two sites of the East China Sea Shelf Basin (ECSSB), using petrology and detrital zircon U-Pb age for the analysis. Results show that central and northeast Taiwan Island experienced a transformation from continental to marine facies during the Eocene–Miocene, and the sandstone maturity changed with time. Source analysis shows that sediments from the Eocene–early Oligocene strata mainly originated from near-source Mesozoic rocks, whose zircon age is consistent with the igneous rock in the surrounding area and coastal Cathaysia, showing 120 Ma and 230 Ma peaks in the age spectrum diagram. Since the late Oligocene, peaks of 900 Ma and 1 800 Ma are seen, indicating that deposition of matter from the old block began. The sediments could be a mixture of the surrounding Mesozoic volcanic and fewer pre-Cambrian rocks sourced from the coastal river and sporadic old basement in the ECSSB instead of long-distance transportation.

In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, “V”-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples, the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.

Previous studies of gas hydrate in the Dongsha area mainly focused on the deep-seated gas hydrates that have a high energy potential, but cared little about the shallow gas hydrates occurrences. Shallow gas hydrates have been confirmed by drill cores at three sites (GMGS2 08, GMGS2 09 and GMGS2 16) during the GMGS2 cruise, which occur as veins, blocky nodules or massive layers, at 8–30 m below the seafloor. Gas chimneys and faults observed on the seismic sections are the two main fluid migration pathways. The deep-seated gas hydrate and the shallow hydrate-bearing sediments are two main seals for the migrating gas. The occurrences of shallow gas hydrates are mainly controlled by the migration of fluid along shallow faults and the presence of deep-seated gas hydrates. Active gas leakage is taking place at a relatively high-flux state through the vent structures identified on the geophysical data at the seafloor, although without resulting in gas plumes easily detectable by acoustic methods. The presence of strong reflections on the high-resolution seismic profiles and dim or chaotic layers in the sub-bottom profiles are most likely good indicators of shallow gas hydrates in the Dongsha area. Active cold seeps, indicated by either gas plume or seepage vent, can also be used as indicators for neighboring shallow gas hydrates and the gas hydrate system that is highly dynamic in the Dongsha area.

To better monitor the vertical crustal movements and sea level changes around Greenland, multiple data sources were used in this paper, including global positioning system (GPS), tide gauge, satellite gravimetry, satellite altimetry, glacial isostatic adjustment (GIA). First, the observations of more than 50 GPS stations from the international GNSS service (IGS) and Greenland network (GNET) in 2007–2018 were processed and the common mode error (CME) was eliminated with using the principal component analysis (PCA). The results show that all GPS stations show an uplift trend and the stations in southern Greenland have a higher vertical speed. Second, by deducting the influence of GIA, the impact of current GrIS mass changes on GPS stations was analysed, and the GIA-corrected vertical velocity of the GPS is in good agreement with the vertical velocity obtained by gravity recovery and climate experiment (GRACE). Third, the absolute sea level change around Greenland at 4 gauge stations was obtained by combining relative sea level derived from tide gauge observations and crustal uplift rates derived from GPS observations, and was validated by sea level products of satellite altimetry. The results show that although the mass loss of GrIS can cause considerable global sea level rise, eustatic movements along the coasts of Greenland are quite complex under different mechanisms of sea level changes.

Conventional retrieval and neural network methods are used simultaneously to retrieve sea surface wind speed (SSWS) from HH-polarized Sentinel-1 (S1) SAR images. The Polarization Ratio (PR) models combined with the CMOD5.N Geophysical Model Function (GMF) is used for SSWS retrieval from the HH-polarized SAR data. We compared different PR models developed based on previous C-band SAR data in HH-polarization for their applications to the S1 SAR data. The recently proposed CMODH, i.e., retrieving SSWS directly from the HH-polarized S1 data is also validated. The results indicate that the CMODH model performs better than results achieved using the PR models. We proposed a neural network method based on the backward propagation (BP) neural network to retrieve SSWS from the S1 HH-polarized data. The SSWS retrieved using the BP neural network model agrees better with the buoy measurements and ASCAT dataset than the results achieved using the conventional methods. Compared to the buoy measurements, the bias, root mean square error (RMSE) and scatter index (SI) of wind speed retrieved by the BP neural network model are 0.10 m/s, 1.38 m/s and 19.85%, respectively, while compared to the ASCAT dataset the three parameters of training set are –0.01 m/s, 1.33 m/s and 15.10%, respectively. It is suggested that the BP neural network model has a potential application in retrieving SSWS from Sentinel-1 images acquired at HH-polarization.