Influence of Seabed Morphology and Substrate Composition On Mass-Transport Flow Processes and Pathways: Insights From the Magdalena Fan, Offshore Colombia

Although the effects of interactions between turbidity currents and the seabed have been widely studied, the roles of substrate and bathymetry on the emplacement of mass-transport complexes (MTCs) remain poorly constrained. This study investigates the effect of bathymetric variability and substrate heterogeneity on the distribution, morphology, and internal characteristics of nine MTCs imaged within a 3D seismic volume in the southern Magdalena Fan, offshore Colombia. The MTCs overlie substrate units composed mainly of channel–levee-complex sets, with subsidiary deposits of MTCs. MTC dispersal was influenced by tectonic relief, associated with a thin-skinned, deep-water fold-and-thrust belt, and by depositional relief, associated with the underlying channel–levee-complex sets; it was the former that exerted the first-order control on the location of mass-transport pathways. Channel–levee-complex sets channelized, diverted, or blocked mass flows, with the style of response largely controlled by their orientation with respect to the direction of the incoming flow and by the height of the levees with respect to flow thickness. MTC erosion can be relatively deep above channel-fill deposits, whereas more subtle erosional morphologies are observed above adjacent levee units. In the largest MTC, the distribution of the seismic facies is well imaged, being influenced by the underlying bathymetry, with internal horizontal contraction occurring updip of bathymetric highs, erosion and bypass predominating above higher gradient slopes, and increased disaggregation characterizing the margins. Hence, bathymetric irregularities and substrate heterogeneity together influence the pathways, geometries, and internal characteristics of MTCs, which could in turn influence flow rheology, runout distances, the presence and continuity of underlying reservoirs, and the capacity of MTCs to act as either hydrocarbon seals or reservoirs

Influence of Seabed Morphology and Substrate Composition On Mass-Transport Flow Processes and Pathways: Insights From the Magdalena Fan, Offshore Colombia

Although the effects of interactions between turbidity currents and the seabed have been widely studied, the roles of substrate and bathymetry on the emplacement of mass-transport complexes (MTCs) remain poorly constrained. This study investigates the effect of bathymetric variability and substrate heterogeneity on the distribution, morphology, and internal characteristics of nine MTCs imaged within a 3D seismic volume in the southern Magdalena Fan, offshore Colombia. The MTCs overlie substrate units composed mainly of channel–levee-complex sets, with subsidiary deposits of MTCs. MTC dispersal was influenced by tectonic relief, associated with a thin-skinned, deep-water fold-and-thrust belt, and by depositional relief, associated with the underlying channel–levee-complex sets; it was the former that exerted the first-order control on the location of mass-transport pathways. Channel–levee-complex sets channelized, diverted, or blocked mass flows, with the style of response largely controlled by their orientation with respect to the direction of the incoming flow and by the height of the levees with respect to flow thickness. MTC erosion can be relatively deep above channel-fill deposits, whereas more subtle erosional morphologies are observed above adjacent levee units. In the largest MTC, the distribution of the seismic facies is well imaged, being influenced by the underlying bathymetry, with internal horizontal contraction occurring updip of bathymetric highs, erosion and bypass predominating above higher gradient slopes, and increased disaggregation characterizing the margins. Hence, bathymetric irregularities and substrate heterogeneity together influence the pathways, geometries, and internal characteristics of MTCs, which could in turn influence flow rheology, runout distances, the presence and continuity of underlying reservoirs, and the capacity of MTCs to act as either hydrocarbon seals or reservoirs

Global analysis of DNA methylation in early-stage liver fibrosis

<p>Abstract</p> <p>Background</p> <p>Liver fibrosis is caused by chemicals or viral infection. The progression of liver fibrosis results in hepatocellular carcinogenesis in later stages. Recent studies have revealed the importance of DNA hypermethylation in the progression of liver fibrosis to hepatocellular carcinoma (HCC). However, the importance of DNA methylation in the early-stage liver fibrosis remains unclear.</p> <p>Methods</p> <p>To address this issue, we used a pathological mouse model of early-stage liver fibrosis that was induced by treatment with carbon tetrachloride (CCl₄) for 2 weeks and performed a genome-wide analysis of DNA methylation status. This global analysis of DNA methylation was performed using a combination of methyl-binding protein (MBP)-based high throughput sequencing (MBP-seq) and bioinformatic tools, IPA and Oncomine. To confirm functional aspect of MBP-seq data, we complementary used biochemical methods, such as bisulfite modification and <it>in-vitro</it>-methylation assays.</p> <p>Results</p> <p>The genome-wide analysis revealed that DNA methylation status was reduced throughout the genome because of CCl₄treatment in the early-stage liver fibrosis. Bioinformatic and biochemical analyses revealed that a gene associated with fibrosis, <it>secreted phosphoprotein 1 </it>(<it>Spp1</it>), which induces inflammation, was hypomethylated and its expression was up-regulated. These results suggest that DNA hypomethylation of the genes responsible for fibrosis may precede the onset of liver fibrosis. Moreover, <it>Spp1 </it>is also known to enhance tumor development. Using the web-based database, we revealed that <it>Spp1 </it>expression is increased in HCC.</p> <p>Conclusions</p> <p>Our study suggests that hypomethylation is crucial for the onset of and in the progression of liver fibrosis to HCC. The elucidation of this change in methylation status from the onset of fibrosis and subsequent progression to HCC may lead to a new clinical diagnosis.</p

Quantitative analysis of a footwall‐scarp degradation complex and syn‐rift stratigraphic architecture, Exmouth Plateau, NW Shelf, offshore Australia

Interactions between footwall‐, hangingwall‐ and axial‐derived depositional systems make syn‐rift stratigraphic architecture difficult to predict, and preservation of net‐erosional source landscapes is limited. Distinguishing between deposits derived from fault‐scarp degradation (consequent systems) and those derived from long‐lived catchments beyond the fault block crest (antecedent systems) is also challenging, but important for hydrocarbon reservoir prospecting. We undertake geometric and volumetric analysis of a fault‐scarp degradation complex and adjacent hangingwall‐fill associated with the Thebe‐2 fault block on the Exmouth Plateau, NW Shelf, offshore Australia, using high resolution 3D seismic data. Vertical and headward erosion of the complex and fault throw are measured. Seismic‐stratigraphic and seismic facies mapping allow us to constrain the spatial and architectural variability of depositional systems in the hangingwall. Footwall‐derived systems interacted with hangingwall‐ and axial‐derived systems, through diversion around topography, interfingering or successive onlap. We calculate the volume of footwall‐sourced hangingwall fans (VHW) for nine quadrants along the fault block, and compare this to the volume of material eroded from the immediately up‐dip fault‐scarp (VFW). This analysis highlights areas of sediment bypass (VFW > VHW) and areas fed by sediment sources beyond the degraded fault scarp (VHW > VFW). Exposure of the border fault footwall and adjacent fault terraces produced small catchments located beyond the fault block crest that fed the hangingwall basin. One source persisted throughout the main syn‐rift episode, and its location coincided with: (a) an intra‐basin topographic high; (b) a local fault throw minimum; (c) increased vertical and headward erosion within the fault‐scarp degradation complex; and (d) sustained clinoform development in the immediate hangingwall. Our novel quantitative volumetric approach to identify through‐going sediment input points could be applied to other rift basin‐fills. We highlight implications for hydrocarbon exploration and emphasize the need to incorporate interaction of multiple sediment sources and their resultant architecture in tectono‐stratigraphic models for rift basins

The role of mass-transport complexes in controlling channel avulsion and the subsequent sediment dispersal patterns on an active margin: The Magdalena Fan, offshore Colombia

Submarine channel avulsion is a fundamental process in the evolution of submarine fans that records abrupt changes in the sediment dispersal patterns, and the development of sand-rich splay deposits. On passive margins, changing flow conditions have been invoked to explain the location and timing of channel avulsion. On tectonically active basin margins, processes such as seismic activity, seabed faulting and folding and emplacement of mass-transport complexes (MTCs) are additional triggers. This study is based on the detailed mapping and interpretation of the first 1000 m below seabed of a 1900 km2 3D seismic volume in the southern Magdalena Fan, offshore Colombia, a tectonically-active margin. The emplacement of a large MTC deposit (>400 km2 in area and 200 m in thickness) is interpreted to have controlled the avulsion node of a major channel-levee complex-set and influenced the evolution of the subsequent avulsion lobe complex-set. The basal surface of the MTC is highly erosional resulting in net degradation of the seascape. Substrate entrainment by the MTC left behind a narrow erosional remnant ridge that formed a bathymetric anomaly upon which a channel-levee complex-set developed. The irregular levee geometries above the remnant ridge led to instability and levee collapse prior to channel avulsion. Map view geometries and seismic amplitude extractions suggest that the initial avulsion lobes were mud-prone and relatively erratically distributed, and evolved to form well-defined sand-prone lobes. The distribution, morphology and evolution of the avulsion lobe complexes were strongly influenced by the bathymetric anomalies on the MTC top surface which, are generally coincident with protruding megaclasts. The role of MTC emplacement in triggering submarine channel avulsion and the development of sand-prone deposits in proximal locations has important implications for hydrocarbon exploration and production. This study serves as a high-resolution, shallow-subsurface analogue for less well-imaged avulsion cycles on tectonically-active basin margins that are prone to MTCs

Time-transgressive Confinement on the Slope and the Progradation of Basin-floor Fans: Implications for the Sequence Boundary of Deep-water Deposits

Observations from outcrop and subsurface datasets indicate that key stratigraphic surfaces in ancient submarine slope successions are diachronous and form during periods of seascape degradation and sediment bypass. Evidence for time transgressive confinement of submarine channel–levee systems includes composite basal erosion surfaces, cut-off bends and hanging valleys, and external levees overlying lobe deposits. After the onset of a sediment supply cycle, progressive confinement will develop on the submarine slope, through a combination of incision and external levee construction, such that sequential sediment gravity flows will maintain their downslope energy farther into the basin. This way, frontal lobe deposits are incised by channel systems and overlain by external levee deposits as the channel–levee system becomes more entrenched and propagates farther into the basin. The stratigraphic response on the related basin floor is fan growth and net progradation until a maximum basinward extent is reached, which corresponds to the time of maximum through-channel sediment transfer (bypass). At this time a maximum regressive surface forms, although in reality this is challenging to identify in the rock record. Conceptually, this basinfloor process response to progressive slope confinement at a point could be autocyclic, but would be amplified with an allogenically driven waxing-then-waning sediment supply cycle. The coupled progressive confinement of the submarine channel–levee system and basin-floor fan growth will result in a diachronous lithological basal surface to the system. This challenges the idea of the deep-water sequence boundary being isochronous and passing into a single correlative conformity at the base of the basin floor fan, or that there is temporal distinction between deposition by high- and low-density turbidity currents

Entrainment and abrasion of megaclasts during submarine landsliding and their impact on flow behaviour

Many mass transport complexes (MTCs) contain up to kilometre-scale (mega)clasts encased in a debritic matrix. Although many megaclasts are sourced from the headwall areas, the irregular basal shear surfaces of many MTCs indicate that megaclast entrainment during the passage of flows into the deeper basin is also common. However, the mechanisms responsible for the entrainment of large blocks of substrate, and their influence on the longitudinal behaviour of the associated flows, have not been widely considered. We present examples of megaclasts from exhumed MTCs (the Neuquén Basin, Argentina and the Karoo Basin, South Africa) and MTCs imaged in three-dimensional seismic reflection data (Magdalena Fan, offshore Colombia and Santos Basin, offshore Brazil) to investigate these process–product interactions. We show that highly sheared basal surfaces are well developed in distal locations, sometimes extending beyond their associated deposit. This points to deformation and weakening of the substrate ahead of the flow, suggesting that preconditioning of the substrate by distributed shear ahead of, and to the side of, a mass flow could result in the entrainment of large fragments. An improved understanding of the interactions between flow evolution, seabed topography, and the entrainment and abrasion of megaclasts will help to refine estimates of run-out distances, and therefore the geohazard potential of submarine landslides

Regional controls in the distribution and morphometry of deep-water gravitational deposits along a convergent tectonic margin. Southern Caribbean of Colombia

Deep-water fold and thrust belts often develop in convergent tectonic margins, creating irregular slope profiles that control the distribution of deep-water gravity deposits. However, in areas with high sediment supply, the erosion and sedimentation can minimize structural relief and smooth the slope. Using multibeam bathymetry with 3D seismic data, we analyze the distribution of deep-water gravity-driven deposits along the convergent margin of the southern Caribbean of Colombia, comparing areas with different continental sediment supply, slope profile, and shelf width. We identify three geomorphological zones: The Northern, Central and Southern Zones. The Northern Zone is characterized by a gentle slope topography, high sediment supply, and large (>100 km length) channel-levee systems traversing the slope and basin floor. In this zone, shelf-attached mass-transport deposits erode and smooth sea-floor topography. The Central Zone is characterized by low sediment supply and steep and irregular slope topography. Here, short-runout mass-transport deposits sourced from the crests and steep flanks of emergent anticlines are common. The irregular relief created by tectonic deformation forms barriers for sediment transport, leading to tortuous sediment-flow pathways. Submarine canyons incise the thrust-cored anticlines, transporting sediment through interconnected, adjacent piggyback sub-basins. Finally, the Southern Zone is characterized by steep slope and moderate sediment supply. Here, tectonic deformation has been smoothed by numerous shelf-attached mass-transport deposits. The erosional scours carved by mass flows merge downslope and evolve into submarine canyons that can deliver mass-transport deposits more than 80 km into the basin. We analyze the impact of slope profile, sediment input and shelf width on the distribution and morphology of deep-water deposits along the southern Colombian Caribbean margin, and present a predictive model for the depositional patterns more likely to develop in other continental margins affected by deep-water fold and thrust belts. © 2020 Elsevier Lt

Entrainment and abrasion of megaclasts during submarine landsliding and their impact on flow behaviour

Many mass transport complexes (MTCs) contain up to kilometre-scale (mega)clasts encased in a debritic matrix. Although many megaclasts are sourced from the headwall areas, the irregular basal shear surfaces of many MTCs indicate that megaclast entrainment during the passage of flows into the deeper basin is also common. However, the mechanisms responsible for the entrainment of large blocks of substrate, and their influence on the longitudinal behaviour of the associated flows, have not been widely considered. We present examples of megaclasts from exhumed MTCs (the Neuquén Basin, Argentina and the Karoo Basin, South Africa) and MTCs imaged in three-dimensional seismic reflection data (Magdalena Fan, offshore Colombia and Santos Basin, offshore Brazil) to investigate these process–product interactions. We show that highly sheared basal surfaces are well developed in distal locations, sometimes extending beyond their associated deposit. This points to deformation and weakening of the substrate ahead of the flow, suggesting that preconditioning of the substrate by distributed shear ahead of, and to the side of, a mass flow could result in the entrainment of large fragments. An improved understanding of the interactions between flow evolution, seabed topography, and the entrainment and abrasion of megaclasts will help to refine estimates of run-out distances, and therefore the geohazard potential of submarine landslides

Entrainment and abrasion of megaclasts during submarine landsliding and their impact on flow behaviour

Many mass transport complexes (MTCs) contain up to kilometre-scale (mega)clasts encased in a debritic matrix. Although many megaclasts are sourced from the headwall areas, the irregular basal shear surfaces of many MTCs indicate that megaclast entrainment during the passage of flows into the deeper basin is also common. However, the mechanisms responsible for the entrainment of large blocks of substrate, and their influence on the longitudinal behaviour of the associated flows, have not been widely considered. We present examples of megaclasts from exhumed MTCs (the Neuquén Basin, Argentina and the Karoo Basin, South Africa) and MTCs imaged in three-dimensional seismic reflection data (Magdalena Fan, offshore Colombia and Santos Basin, offshore Brazil) to investigate these process–product interactions. We show that highly sheared basal surfaces are well developed in distal locations, sometimes extending beyond their associated deposit. This points to deformation and weakening of the substrate ahead of the flow, suggesting that preconditioning of the substrate by distributed shear ahead of, and to the side of, a mass flow could result in the entrainment of large fragments. An improved understanding of the interactions between flow evolution, seabed topography, and the entrainment and abrasion of megaclasts will help to refine estimates of run-out distances, and therefore the geohazard potential of submarine landslides