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Highlights • Supplies from rivers cannot explain the supper high sedimentation rate of the RDSD. • Due to Dongsha Uplift since 3 Ma, roughly 1/2 formations since Miocene were denudated. • Annual denudation rate from Dongsha Uplift sine 3 Ma had been about 60 Mt/y. • Sediment denudated from the Dongsha Uplift can be the main source for the RDSD. Abstract The slope of the northern South China Sea (SCS) is one of the world's most active areas of modern marine sedimentary processes. A rapidly deposited sediment drift (RDSD) was identified on the slope near Dongsha Island. The sources of this body have been studied and discussed by several authors, but no consensus has been achieved. Based on multi-channel seismic profiles interpretation and data analysis of long-term observation of bottom currents, we identified that although the amounts of sediments input from the Pearl and Hanjing Rivers, and from Kao-ping and Tseng-Wen Rivers are large, considering the current situation of northern SCS, none of the Pearl River, the Hanjiang River, the Kao-ping River and the Tseng-Wen River can maintain the deposition pattern of the northern SCS margin as the single source, especially to maintain the supper high sedimentation rate at the RDSD area. The Miocene drape formation (MDF) calmly draped over an unconformity after rifting stage resulting in a relatively constant thickness of about 2000 m throughout the overall northern SCS continental margin, and followed by a standard configuration of a clinoform, the Pliocene formation and another clinoform of about another 700 m in total thickness. Due to Dongsha uplift since 3 Ma, roughly 1/2 of MDF and the N 2 formation in the Dongsha area measures 150 km by 200 km were denudated resulting in an average annual denudation rate of 60 × 106 t/y. If these sediments were deposited on a slope region within an area measuring 100 km by 100 km, the sedimentation rate could reach 250 cm/ky. This is clearly an impressive new sediment source that has never been discussed before. Moreover, the RDSD is near the Dongsha Uplift and on the adjacent slope. We believe that this new sediment source should be the main contributor for the RDSD development. [ABSTRACT FROM AUTHOR]

An ancient gully system was revealed in the Northwest South China Sea using high-resolution three-dimensional (3D) seismic data. They are straight, regular, and intensely spaced sediment transporting routines, and are much smaller in size than channels. The gully system was distributed on the margin slope of the peri-carbonate platform in the middle Miocene. Two different types of gullies were identified based on the variation in the seismic response. Among them, most of the gullies are filled by low seismic amplitude reflectors, except a unique one, developed on the east slope of the study area, and is characterised by high seismic amplitude reflectors. The head of this gully reaches the carbonate platform, which provides carbonate clasts to the gully. The other gullies, expressing low seismic amplitude reflectors, develop limitedly on the slope of the carbonate platform and seldom receive source sediments from the carbonate platform. The gullies sit on the polygonal faults of middle Miocene, exhibit same strike with larger-scale linear ones of polygonal faults. These linear polygonal faults elongate from northwest to southeast, perpendicular to the slope contours, and in the same direction as the gullies. The coincidence between gullies and polygonal faults exhibits that the formation of gullies has been triggered mainly by the polygonal fault system (PFS) in the middle Miocene. These findings suggest that the middle Miocene carbonate platform provides favourable fine-grained lithology conditions for the formation of the PFS, while the linear polygonal faults initiate the gully system peri-carbonate platforms. Subsequently, the following gravity flows shape the initial configuration into the final features, while different provenances and different types of gravity flows create various characteristics of gullies. • Ancient gully system around the carbonate platform is characterized using seismic data. • The linear polygonal faults initiated the gully system peri-carbonate platforms. • The diverse filling features imply the western and eastern gullies experienced different synsedimentary geological events. • The entire evolutionary process of gully systems is described. [ABSTRACT FROM AUTHOR]

• Extensive Middle Miocene fining in southward clastic sequences were deposited in the north of East Java. • Two newly identified turbidite fans exhibit opposite source directions based on 3D seismic data. • The formation of the turbidites fans were predominantly controlled by the paleotopography of the Early Miocene and intense regional tectonic events. • East Java was in a laterally neritic to bathyal environments with occasionally exposed volcanoes during the Middle Miocene. East Java, on the southeastern margin of the Sundaland Shelf, is an ideal and pilot location to study paleogeographic changes due to the interactions of the Eurasian and the Indian-Australia plates. Many studies have been conducted; however, some issues remain poorly understood, such as the initial compression stage and associated paleogeography of East Java. Here, we report newly acquired high-resolution seismic data and drilling wells in the area of the Madura Strait. We systematically reconstruct a three-dimensional model on the paleogeography of East Java in the Middle Miocene in combination with others' results. Different depositional environments and characteristics of the related lithofacies observed on both sides of the Middle Miocene volcanic arc imply that weak subaerial and subaqueous volcanism existed in East Java. The extensive Ngrayong fining in the southward clastic sequences, located north of the mentioned volcanic arc, were deposited in a bathyal marine environment, which showed an oversteepening slope and basinal characteristics with outer neritic to bathyal facies within the present-day Kendeng Zone and Madura Strait area. This differs from the northern region of the present-day Rembang-Madura Inversion Zone and the northern offshore region of East Java, which were deposited in a transitional and neritic marine environment. We identified two new turbidite fans showing opposite source directions based on 3D seismic data within the Madura Strait area. Four controlling factors contributed to the formation of the Ngrayong turbidite fans, including the paleotopography of the underlying Kujung Formation, short-term intense regional tectonic events, high rates of sediment supply and occasional volcanic activity. [ABSTRACT FROM AUTHOR]

The Bengal Fan is a mud-rich, deep-water sediment system. A series of recently discovered biogenic gas reservoirs in the northeastern Bay of Bengal are fine-grained. The Pliocene gas discovered in the study area accumulated in the levee element of a deep-water channel complex identified by high-resolution three-dimensional (3D) seismic interpretation integrated with well logs and sidewall cores (SWC). The thickness and porosity of the levee gas reservoir are of good quality, but the permeability is relatively low owing to the high mud content. The discovery of the levee sandstone indicates various reservoirs in this mud-rich sediment system. Moreover, gas discovery implies that the gravity-flow sediment systems "link" the source rock in the study area. Gas reservoirs were discovered in Pliocene gravity-flow sediment systems, where the palaeo-climate experienced significant changes with a dramatic increase in total organic carbon (TOC) from the Miocene to the Pliocene. TOC-rich pelagic mudstones and deep-water gravity sediments act as source rocks for petroleum systems. Therefore, gravity-flow sediment systems have developed self-accumulating petroleum plays that exhibit enormous potential for exploration. Given the structural framework in the northeastern part of the Bay of Bengal, stratigraphic or structure-stratigraphic traps could have developed in the Pliocene deep-water sediment systems in the Bengal Fan. • Fine-grained deep-water turbidite gas reservoirs in upper Bengal Fan. • Bengal Fan is with Pliocene deep-water sediment systems. • Stratigraphic or structure-stratigraphic traps for exploration. • A close relationship between petroleum and deep-water gravity systems. [ABSTRACT FROM AUTHOR]

By using 3D seismic dataset recently acquired in offshore Mozambique, we address the distribution pattern of an Upper Eocene channel-levee-lobe complex in deep-water of Rovuma Basin. The unique levee of this complex asymmetrically developed only on one side of the channel course. We attribute this asymmetric levee development to the interaction between the western slope bottom current from south to north and the gravity flow from west down slope. Due to the winnowing and sorting by the western slope bottom current, the sorted fine grain sediments of the gravity flow was blew and deposited to aside remaining clean sand from the gravity flow deposited within the channel as quality reservoir. The stacking and expanding of the levee forced the channels windward migrated to the south forming channel-1 to 6 from north to south. The corresponding lobe did not keep its feeder channel's axis direction, but bended from northeast to east or southeast, forming a U-turn from the channel to lobe. We believe that in addition to the paleotopography effect, the bottom current in Querimbus Graben might also lead to the bending of the lobe. The Querimbus Graben bottom current in this region flows from north to the south driven by the southward-drifting eddy. We suppose that a southward bottom current also existed at the Eocene time in this region and contributed to the southward bending of the lobes. • Eocene channels migrated from north to south along Rovuma Slope. • Levees only developed at the northern side of the channels. • Northward slope current blowing fine grains and building the levee to a side of the channels. • Southward down deep bottom current bended the lobes from the south. [ABSTRACT FROM AUTHOR]