Geological controls on the evolution of submarine channels in the Espírito Santo Basin, SE Brazil

Submarine channels are conduits that transfer sediment from continental shelves to the deep sea. They can form important hydrocarbon reservoirs when filled with sand-prone deposits and are, consequently, one of the most important hydrocarbon prospects on continental margins around the world. In this thesis, a 3D seismic volume from offshore Espírito Santo (SE Brazil) was used to analyse submarine channel systems near the modern sea floor. The aim of the thesis was to investigate the key controlling factors on variations in the morphology and architecture of submarine channel systems, at the same time, providing an analogue for modern and ancient depositional systems on continental slopes around the world. This work shows significant variations in morphology and architectures along the investigated submarine channel systems. The spatial variations in both channel and valley morphology documented here suggest an important role of local factors (e.g. mass-wasting events, tributaries, substrate lithology and salt tectonics) in the development of channel systems. It also records in great detail the nature of the interaction between mass-transport deposits and turbidity currents at the early stages of channel evolution. Basal scars created by mass-wasting events can capture turbidity currents and facilitate flow channelisation, which is a key process for submarine-channel initiation. In addition, the replacement of MTDs by channel-fill deposits has profound implications for reservoir volumes and net-to-gross ratios in channel systems. Spatial variations in channel sinuosity observed in this work are interpreted as reflecting substrate erodibility beneath the channel system. Submarine channels will show higher sinuosity when encountering resistant substrates, and lower sinuosity when the substrate is more erodible. Temporal changes in channel sinuosity resulted from enhanced sediment discharge from tributaries. This work stresses the role of lateral channel migration as an important mechanism responding to factors such as sediment supply and ultimately, controlling the evolution of submarine channel systems

Quantitative seismic geomorphology of a submarine channel system in SE Brazil (Espírito Santo Basin): scale comparison with other submarine channel systems

Detailed morphological analyses of a Pleistocene-Holocene submarine channel system in terms of its hierarchical framework, were carried out using a 3D seismic volume from offshore Espírito Santo, SE Brazil. The channel morphology shows marked variations, with five segments (Segments a to e) being identified along its full length. For example, the cross-sectional area of the channel decreases by a factor of 70 from Segment a to Segment c, and is then followed by a nearly four-fold increase from Segment c to Segment d. The significant changes in channel morphology relate to temporal and spatial variations in flow volume within the channel. In the same channel system, the valley reveals three distinct segments (Segments A to C), with similar aspect ratios but marked variations in morphology along the valley distance. Valley morphological changes are chiefly affected by erosional processes. Segment B is characterised by the largest valley-base width, valley width, and cross-sectional area compared to the other two segments. Valley enlargement in Segment B results from relatively high degrees of lateral channel migration and associated cut bank erosion, leading to the widening of the valley, especially the valley base. In Segment C, the valley is characterised by inner bank erosion in the form of shallow-seated mass failures, which only enlarged the upper part of the valley wall. The spatial variations in both channel and valley morphology documented here suggest an important role of local factors (e.g. salt diapirs, tributaries, overbank collapse) in the development of channel systems. Hence, the morphological analyses developed in this work provide an effective tool for studying channels and valleys on continental slopes around the world

The role of mass wasting in the progressive development of submarine channels (Espírito Santo Basin, Se Brazil)

A Pliocene–Quaternary submarine channel system, influenced by localized mass wasting, is investigated using high-resolution 3D seismic data from offshore Espírito Santo Basin, SE Brazil. Three abandoned channels, a channel belt, and a mass-transport deposit (MTD) are recognized in the channel system in a confluence region confined by salt diapirs. In this confluence region, the cross-sectional area (CSA) of the channel system can be up to 1.2 km2, i.e., 4 to 10 times larger than other parts of the study area. These significant changes in the architecture and morphology of the channel system resulted from the interaction between mass-wasting processes and turbidity flows. We postulate that a basal erosional scar created by mass-wasting processes was later filled with an MTD. This basal scar was then used as a preferential pathway for turbidity flows, which were captured by its headwall and lateral margins. The interpreted data show that the captured turbidity flows greatly widened the basal scar but caused only small modifications in scar height. This predominance of widening processes over channel incision occurred because part of the MTD in the basal scar was removed downslope by turbidity flows and replaced by channel-fill deposits. This paper shows that important flow-capture processes can predominate in channel-confluence regions of continental slopes. Basal scars can capture turbidity flows and facilitate flow channelization, which are key processes for submarine-channel initiation. Importantly, the replacement of MTDs by channel-fill deposits has profound implications for reservoir volumes and net-to-gross ratios in channel systems and partly depends on the properties of the turbidity flows, such as their erosive ability and frequency. The more erosive and frequent flows are captured by the basal scar, the larger is the accommodation space created for subsequent sand-prone turbidites

Data-Driven Adaptive Tracking Control of Unknown Autonomous Marine Vehicles

This paper is concerned with data-driven adaptive tracking control for unknown autonomous marine vehicles (AMVs) with uncertainties and disturbances. By deploying the data-driven technique and observer design, an equivalent data model of the AMV is firstly established. Based on the proposed data model, a novel data-driven adaptive tracking controller is designed, and the corresponding stability analysis for the closed-loop AMV system is presented theoretically. Finally, simulation studies are given to demonstrate the validity of the main results

Bedform evolution along a submarine canyon in the South China Sea: New insights from an autonomous underwater vehicle survey

Traditional mapping of bedforms in submarine canyons relied on vessel-mounted and towed sensors, but their fine-scale geomorphology and shallow structure requires higher resolution datasets. This study utilizes a high-resolution dataset obtained from an autonomous underwater vehicle, combined with seismic reflection profiles and sediment cores, to analyze bedform sets within a 25.6 km long submarine canyon (canyon C14) in the northern South China Sea. A train of crescent-shaped axial steps, indicative of cyclic steps formed by supercritical turbidity currents, is imaged along the canyon. Axial steps in the upper course show erosional truncations and sub-horizontal reflectors on the lee and stoss sides, respectively, pointing to erosional–depositional cyclic steps formed by confined flows with high erosional capacity. This is facilitated by canyon narrowness and steeper axial gradient. After a transition segment, the lower course widens, with a gentler axial gradient, resulting in increased asymmetry and wavelength of axial steps. Backset bed deposits on the stoss sides of these steps indicate depositional cyclic steps with higher aggradation. Sediment filling, almost padding each cyclic step associated scour suggests the reworking of previously formed bedforms by gravity flows fed by destabilization processes on the canyon sidewalls and upstream lee faces and, possibly, by shelf-edge and uppermost slope spillover into the canyon. At the lowermost course, cyclic steps transition to a furrow field, likely associated to flow velocity reduction facilitated by canyon floor widening and a further decrease in slope gradient. Flow braiding and re-convergence, related to the erosion of fine-grained deposits within the canyon floor, should have played a role to produce furrows under supercritical conditions. This work enhances our understanding of the detailed morphology and shallow relief configuration of bedforms in deep-water submarine canyons, providing insights into their causative processes and evolution

Seismic architecture of Yongle isolated carbonate platform in Xisha Archipelago, South China Sea

This study presented recently reprocessed multi-channel seismic data and multi-beam bathymetric map to reveal the geomorphology and stratigraphic architecture of the Yongle isolated carbonate platform in the Xisha Archipelago, northwestern South China Sea. Our results show that the upper slope angles of Yongle carbonate platform exceed 10° and even reach to ∼32.5° whereas the lower slope angles vary from .5° to 5.3°. The variations of slope angles show that margins of Yongle Atoll belong to escarpment (bypass) margins to erosional (escarpment) margins. The interior of carbonate platform is characterized by sub-parallel to parallel, semi-continuous to continuous reflectors with medium-to high-amplitude and low-to medium-frequency. The platform shows a sub-flat to flat-topped shape in its geometry with aggradation and backstepping occurring on the platform margins. According to our seismic-well correlation, the isolated carbonate platform started forming in Early Miocene, grew during Early to Middle Miocene, and subsequently underwent drowning in Late Miocene, Pliocene and Quaternary. Large-scale submarine mass transport deposits are observed in the southeastern and southern slopes of Yongle Atoll to reshape the slopes since Late Miocene. The magmatism and hydrothermal fluid flow pipes around the Yongle Atoll have been active during 10.5–2.6 Ma. Their activity might intensify dolomitization of the Xisha isolated carbonate platforms during Late Miocene to Pliocene. Our results further suggest that the Yongle carbonate platform is situated upon a pre-existing fault-bounded block with a flat pre-Cenozoic basement rather than a large scale volcano as previously known and the depth of the basement likely reached to 1400 m, which is deeper than the well CK-2 suggested

Potential of Core-Collapse Supernova Neutrino Detection at JUNO

JUNO is an underground neutrino observatory under construction in Jiangmen, China. It uses 20kton liquid scintillator as target, which enables it to detect supernova burst neutrinos of a large statistics for the next galactic core-collapse supernova (CCSN) and also pre-supernova neutrinos from the nearby CCSN progenitors. All flavors of supernova burst neutrinos can be detected by JUNO via several interaction channels, including inverse beta decay, elastic scattering on electron and proton, interactions on C12 nuclei, etc. This retains the possibility for JUNO to reconstruct the energy spectra of supernova burst neutrinos of all flavors. The real time monitoring systems based on FPGA and DAQ are under development in JUNO, which allow prompt alert and trigger-less data acquisition of CCSN events. The alert performances of both monitoring systems have been thoroughly studied using simulations. Moreover, once a CCSN is tagged, the system can give fast characterizations, such as directionality and light curve

Detection of the Diffuse Supernova Neutrino Background with JUNO

As an underground multi-purpose neutrino detector with 20 kton liquid scintillator, Jiangmen Underground Neutrino Observatory (JUNO) is competitive with and complementary to the water-Cherenkov detectors on the search for the diffuse supernova neutrino background (DSNB). Typical supernova models predict 2-4 events per year within the optimal observation window in the JUNO detector. The dominant background is from the neutral-current (NC) interaction of atmospheric neutrinos with 12C nuclei, which surpasses the DSNB by more than one order of magnitude. We evaluated the systematic uncertainty of NC background from the spread of a variety of data-driven models and further developed a method to determine NC background within 15\% with {\it{in}} {\it{situ}} measurements after ten years of running. Besides, the NC-like backgrounds can be effectively suppressed by the intrinsic pulse-shape discrimination (PSD) capabilities of liquid scintillators. In this talk, I will present in detail the improvements on NC background uncertainty evaluation, PSD discriminator development, and finally, the potential of DSNB sensitivity in JUNO