A flexural isostasy model for the Pleistocene evolution of the Barents Sea bathymetry

Source at: http://doi.org/10.17850/njg97-1-01 The topographic relief of the Barents Sea was subjected to major changes during the past 1.5 million years mostly due to sediment redistribution driven by glacial activity. This paper addresses the problem of Pleistocene bathymetric evolution of the southern Barents Sea using a numerical modelling approach that considers the influence of regional isostasy on relief development. The model presented in this work shows that most of the bathymetric features were initiated prior to the first documented, shelf-edge glaciations at around 1.5 Ma. During the Early Pleistocene (Calabrian), the Barents Sea shelf was close to sea level with some areas elevated to about 300 m. Most of the shelf experienced up to 200 m topography reduction during the Early to Middle Pleistocene (1.5–0.7 Ma) facilitating bifurcation of the North Atlantic waters into the Barents Sea. Later during the Middle Pleistocene–Present (0.7–0.0 Ma) the relief deepened by 0 to 250 m. Our results demonstrate that the present-day topography of the southern Barents Sea is the consequence of glacial activity influenced by a regional isostatic component, which is the result of selective trough erosion and significant sediment deposition at the Barents Sea margins during the Pleistocene

Seismic geomorphology of Cenozoic slope deposits and deltaic clinoforms in the Great South Basin (GSB) offshore New Zealand

In this study, the Cenozoic sedimentation and infill history of the Great South Basin (GSB), New Zealand, is analysed from a seismic geomorphologic perspective. A suite of sediment types, including mass-transport deposits (MTDs), deltaic clinoforms, contourite-drifts and turbidites, are documented based on high-quality 3-D seismic reflection data and multiple regional 2-D seismic profiles. The MTDs include older, highly compacted and deeper Palaeocene deposits that are markers of late Neogene tectonic reactivation, while the youngerMTDs were translated over slopes eroded by drifts. Possible trigger mechanisms for mass wasting may include oversteepened margins, prolonged fluid dissipation and weak geological layers. Sedimentation from the Eocene to Recent was contemporaneous with regional plate reorganisation and syn-orogenic activity. As a result, three distinct Eocene deltaic systems with variably oriented channels and depositional elements provide evidence for changing plate kinematics during the Eocene. The Eocene deltaic systems are river-dominated and were deposited during relative rise in sea level under variable flow regimes. The passage of the Antarctic Circumpolar Current in the GSB from the Late Eocene to Oligocene led to the deposition of three elongate, detached contourite drifts. In a final phase of basin infill, hemipelagic sedimentation and deposition by turbidity currents dominated late Neogene sedimentation in the GSB. The analyses presented here demonstrate the importance of geomorphology in understanding the sediment infill history, their interactions and temporal organisation, which have wider implications for numerous geoscience disciplines

Seismic, morphologic and scale variabilities of subsurface pipes and vent complexes in a magma-rich margin

Subsurface pipes related to fluid flow are observed in seismic reflection data as vertical to sub-vertical features of low-amplitude reflections, linking chaotic reflections at the base (root zones) of volcanic constructs to their summits which can comprise craters, mounds or eye-shaped vents. To date, uncertainties remain regarding the linear correlation and scaling relationship between pipes and their overlying vent structures. Using 3D seismic reflection data from a magma-rich basin, the Vigrid Syncline in the Vøring Basin (offshore Norway), this study provides a seismic, morphometric and statistical description of forty (40) pipes and their associated structures. These pipes include conical, bifurcated, fault-controlled and columnar types, which are a consequence of the intrusion of two mappable magmatic sills of Early Eocene age. The heights (av. 1098 m), widths (av. 1740 m) and slenderness ratios (i.e. the heights/widths (Ω)) of the pipes (av. 0.6) show low to moderate correlation coefficients with vent parameters such as height (av. 258 m), area (av. 2.3 km2 ) and ellipticity (av. 1.5). The morpho-statistical analyses provided here show that ‘pipe’ formation mechanisms are mutually exclusive and that vent geometries are not particularly systematic in nature

A flexural isostasy model for the Pleistocene evolution of the Barents Sea bathymetry

The topographic relief of the Barents Sea was subjected to major changes during the past 1.5 million years mostly due to sediment redistribution driven by glacial activity. This paper addresses the problem of Pleistocene bathymetric evolution of the southern Barents Sea using a numerical modelling approach that considers the influence of regional isostasy on relief development. The model presented in this work shows that most of the bathymetric features were initiated prior to the first documented, shelf-edge glaciations at around 1.5 Ma. During the Early Pleistocene (Calabrian), the Barents Sea shelf was close to sea level with some areas elevated to about 300 m. Most of the shelf experienced up to 200 m topography reduction during the Early to Middle Pleistocene (1.5–0.7 Ma) facilitating bifurcation of the North Atlantic waters into the Barents Sea. Later during the Middle Pleistocene–Present (0.7–0.0 Ma) the relief deepened by 0 to 250 m. Our results demonstrate that the present-day topography of the southern Barents Sea is the consequence of glacial activity influenced by a regional isostatic component, which is the result of selective trough erosion and significant sediment deposition at the Barents Sea margins during the Pleistocene

The Middle Niger Basin in Nigeria Has a Rift Origin, as Revealed by the Inversion and Modeling of Gravity and Magnetic Data

Abstract The NW‐SE oriented Middle Niger Basin, which is a Campano‐Maastrichtian inland basin has been the subject of debate among geoscientists regarding its origin and development. This paper aims to unravel the basin's origin and evolution by using high‐resolution magnetic, gravity, and topographical data. The integration of aeromagnetic and gravity data provides a means to assess the influence of igneous intrusions during the basin's evolution. The study presents a new perspective on the origin of the basin, suggesting a rift origin where orthogonal extension played a crucial role in its evolution. The research also investigates the relationship between intrusive rocks and the formation of the basin, finding these rocks are solely located within the basement. The magnetic and gravity maps reveal anomalies associated with intrusive structures within the Precambrian crystalline basement. This is a common feature shared with rifted basins on a global scale

Assessment of groundwater vulnerability to leachate infiltration using electrical resistivity method

This aim of this work is to assess the degree of leachate infiltration at a dumpsite in Agbara industrial estate, Southwestern Nigeria using electrical resistivity techniques. Around the dumpsite were 45 vertical electrical sounding (VES) stations and 3 electrical resistivity tomography profiles. Current electrode spread varied from 300 to 600 m for the electrical sounding. Electrode configuration includes Schlumberger and Wenner array for sounding and profiling. The state of leachate contamination was tested using parameters such as aquifer vulnerability index, overburden protective capacity and longitudinal unit conductance (Si) derived from the apparent resistivity values. Four principal geoelectric layers inferred from the VES data include the topsoil, sand, clayey sand, and clay/shale. Resistivity values for these layers vary from 3 to 1688, 203 to 3642 123 to 388, and 67 to 2201 Ω m with corresponding thickness of 0.8–2.4, 2.5–140, 3–26 m and infinity, respectively. The leachate plume occurs at a maximum depth of 10 m on the 2-D inverse models of real electrical resistivity with an average depth of infiltration being 6 m in the study area. The correlation between longitudinal conductance and overburden protective capacity show that aquifers around the dumpsite have poor protective capacity and are vulnerable to leachate contamination. Leachate infiltration is favored by the absence of lithological barriers such as clay which in the study area are either mixed with sand or positioned away from the aquifer

Evolution and morphology of rafted blocks in an ancient deepwater mass transport complex (Exmouth Plateau, offshore North West Australia)

Submarine mass wasting plays a fundamental role in transporting substantial volumes of sediments basinward including gigantic slide blocks. However, the understanding of processes involved in block generation and their associated deformation until flow arrest remains limited, especially in data-starved deepwater settings. Here, 2D and 3D seismic reflection data from the Exmouth Plateau, offshore North West Australia are used to investigate the architecture of large blocks preserved within an ancient mass-transport complex (MTC) and their interaction with the basal shear surface (BSS). The evolution of the investigated MTC (MTC-BDF) is related to instability along the slope and flanks of an underlying bifurcative Miocene canyon. The MTC-BDF spans approximately 75 × 35 km containing at least 32 well-imaged blocks (within the 3D seismic coverage) encapsulated in a well-deformed debrite background. These carbonate blocks interpreted as rafted blocks have lengths ranging from 0.48 to 3.40 km with thicknesses reaching up to 165 m. Interestingly, the blocks are more abundant in a region characterized by moderate- to high-amplitude debrites. Erosional morphologies encompassing a unique groove and other circular- to irregularly shaped depressions mapped along the BSS provide evidence for the erosive nature of the flow. The origin of the groove is related to transported blocks gouging the BSS. Importantly, intrablock deformations are recorded within these blocks as fault and fold systems. This suggests a complex flow regime within MTC-BDF, with the deformations arising either during block transportation or possibly upon arrest of the failed mass while interacting with bathymetric elements. Our findings suggest that inherent deformations within these blocks may serve as high-permeability conduits with implications for deepwater drilling operations within this segment of the Exmouth Plateau and elsewhere in other hydrocarbon-rich deepwater settings

Morphometric analysis of sediment conduits on a bathymetric high: Implications for palaeoenvironment and hydrocarbon prospectivity

Canyons and other sediment conduits are important components of the deep-water environment and are the main pathways for sediment transport from the shelf to the basin floor. Using 3-D and 2-D seismic reflection data, seismic facies and statistical morphometric analyses, this study showed the architectural evolution of five canyons, two slide scars and four gullies on the southern part of the Loppa High, Barents Sea. Morphometric parameters such as thalweg depth (lowest point on a conduit’s base), wall depth (middle point), height, width and base width, sinuosity, thalweg gradient, aspect ratio (width/height) and cross-sectional area of the conduits were measured at intervals of 250-m perpendicular to the conduits’ pathways. Our results show that the canyons and slide scars in the study area widen down slope, whereas the gullies are narrow and short with uniform widths. The sediment conduits in the study area evolved in three stages. The first stage is correlated with a time when erosion and bypass were dominant in the conduits, and sediment transferred to the basin in the south. The second stage occurred when basin subsidence was prevalent, and a widespread fine-grained sequence was deposited as a drape blanketing the canyons and other conduits. A final stage occurred when uplift and glacial erosion configured the entire southern Loppa High into an area of denudation. Our work demonstrates that the morphometric parameters of the canyons, slide scars and gullies generally have increasing linear trends with down-slope distance, irrespective of their geometries. The morphometric analysis of the sediment conduits in the study area has wider applications for understanding depositional processes, reservoir distribution and petroleum prospectivity in frontier basins

Recurrent mass-wasting in the Sørvestsnaget Basin Southwestern Barents Sea: A test of multiple hypotheses

Mass-wasting on the NE Atlantic Margin is generally attributed to Cenozoic glaciations. Using high-quality 2D seismic datasets and two exploration wells, this study investigates the types and driving mechanisms of mass-wasting in the Sørvestsnaget Basin, Southwestern Barents Sea. The methods include seismic interpretation of shelf margin clinoforms, mass-transport deposits (MTDs), submarine channels and V-shaped canyons. The shelf-edge trajectory provided information about sea-level conditions, paleo-sediment routes, and dispersal patterns during the evolution of the basin. In terms of the internal geometry of seismic reflectors, the major depositional units are five sedimentary packages (P1 to P5) characterized by distinct southwest dipping shelf margin clinoforms. Seven identified MTDs have Late Miocene to Pleistocene ages. Miocene and Early Pliocene MTDs in the basin demonstrate a tendency for initial translation through canyons and channels. The youngest MTDs are composed of glaciogenic sediments remobilized by ice streams during large-scale Neogene and Quaternary glaciations. This work shows that mass-wasting has been a recurrent and inherent process in the Sørvestsnaget Basin from the Miocene until recent times. The main triggering mechanisms for slope failure in the basin are interpreted to be increased pore pressure from sea-level fall and high sedimentation rate. Mass-wasting in the study area occurred through progressive, retrogressive and coherent downslope failures

Deep-seated faults and hydrocarbon leakage in the Snøhvit Gas Field, Hammerfest Basin, Southwestern Barents Sea

High-quality 3D seismic data are used to analyze the history of fault growth and hydrocarbon leakage in the Snøhvit Field, Southwestern Barents Sea. The aim of this work is to evaluate tectonic fracturing as a mechanism driving hydrocarbon leakage in the study area. An integrated approach was used which include seismic interpretation, fault modeling, displacement analysis and multiple seismic attribute analysis. The six major faults in the study area are dip-slip normal faults which are characterized by complex lateral and vertical segmentation. These faults are affected by three main episodes of fault reactivation in the Late Jurassic, Early Cretaceous and Paleocene. Fault reactivation in the study area was mainly through dip-linkage. The throw-distance plots of these representative faults also revealed along-strike linkage and multi-skewed C-type profiles. The faults evolved through polycyclic activity involving both blind propagation and syn-sedimentary activity with their maximum displacements recorded at the reservoir zone. The expansion and growth indices provided evidence for the interaction of the faults with sedimentation throughout their growth history. Soft reflections or hydrocarbon-related high-amplitude anomalies in the study area have negative amplitude, reverse polarity and are generally unconformable with structural reflectors. The interpreted fluid accumulations are spatially located at the upper tips of the major faults and gas chimneys. Four episodes of fluid migration are inferred and are linked to the three phases of fault reactivation and Neogene glaciations. Hydrocarbon leakage in the Snøhvit Gas Field is driven by tectonic fracturing, uplift, and erosion. The interpreted deep-seated faults are the main conduits for shallow hydrocarbon accumulations observed on seismic profiles