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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]

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]

The interactions between arc-continent collision and subduction zones are still poorly understood. Here, we use 2D seismic data to document upper plate deformational features and identify different structural styles along the New Guinea Trench, western Pacific, and discuss their broader significance. In the western section, normal faults and negative flower structures occur within the strata of the upper plate. An unconformity represents the signal of tectonically driven subsidence. In the eastern section, both thick-skinned and thin-skinned thrusting are found within the frontal upper plate. In the central section, rare extensional or shortening deformation is identified within the forearc basement and overlying strata. Horizontal, thick sedimentary sequences within the Caroline subbasin have been subducted beneath the upper plate. This suggests that Miocene subduction in the eastern section led to the formation of a thrust-deformed ophiolitic basement in the upper plate. Since the Miocene, strike-slip tectonic processes dominated in the upper plate, causing compressional deformation in the strata in the eastern section and extensional to transtensional deformation in the strata in the western section. The strike-slip tectonic processes might have been weakened in the upper plate in central section due to the incoming Eauripik Rise. Over geologic time, arc-continent collision processes and related changing of regional tectonic forces can have a long-lived influence on shaping and deforming subduction systems. • Miocene subduction in the eastern section of the New Guinea Trench induced the thrust-deformed basement in the upper plate • Since the Miocene, strike-slip tectonic processes in the western section deforming the strata in the upper plate • Strike-slip tectonic processes have been weakened in the central section due to incoming Eauripik Rise [ABSTRACT FROM AUTHOR]

The 85°E Ridge is a prominent linear structure in the northeastern Indian Ocean. Its nature and origin are still controversial due to the coverage of thick Bengal Fan sediments. Here we present a newly collected 400-km-long 2-D seismic reflection profile which crosses the 85°E Ridge near 11°N and shows the basement morphology and internal structures of the ridge. The ridge has a thickened crust characterized by two basement highs rising up to ~2–3 km above the surrounding oceanic crust and a Moho depression with amplitude of ~3–4 km. Typical volcanic structures formed by hotspot volcanism are identified in the ridge. Deep-rooted faults played important roles in the formation of the 85°E Ridge. They acted as the preferred conduit for the upwelling of hotspot melts, but their syn - and post-volcanic reactivations induced the collapse of volcanic sequences and the relative uplift of the East Ridge. These observations support that the 85°E Ridge near 11°N having formed by hotspot magmatism drained along a leaky fracture zone. Combined with previous results, a new single-hotspot formation model of the 85°E Ridge is proposed, in which the entire 85°E Ridge was formed by a weak and pulsating mantle plume acting on the northward drifting Indian Plate. Its along-strike variations in location, morphology, and structure in different segments are interpreted to reflect different elastic strength of the oceanic lithosphere and the existence of a pre-existing fracture zone which laterally redistributed the shallow melts. • The 85°E Ridge at 11°N is characterized by basement uplift and Moho depression. • The ridge is separated into the West and East Ridges by a deep-rooted fault. • Typical volcanic structures are identified in the ridge. • Hotspot volcanism along a leaky fracture zone contributes the formation of the ridge. • The entire 85°E Ridge was formed by a single hotspot acting on the Indian Plate. [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]