Impact of tectonic rafts' gravitational instability on fault reactivation and geometry

The downslope gravitational instability of tectonic rafts can deform large volumes of supra-salt strata on continental margins. Detailed mapping of fault throw and geometry using three-dimensional (3D) seismic reflection data from the salt-rich Espírito Santo Basin (SE Brazil) shows that the complex fault geometries observed are primarily due to downslope gravitational instability of tectonic rafts. Three main tiers of faults were identified and their geometry analysed in detail. Tier 1 faults are associated with the initial stage of fragmentation of supra-salt strata into individual blocks, or rafts, which are separated by listric (roller) faults and associated minibasins. These faults comprise closely spaced normal faults that resulted from outer-arc stretching of strata overlaying discrete tectonic rafts. The faults accommodate a significant part of the bending strain occurring in the hanging-wall blocks of roller faults, thus forming a curved-polygonal planform geometry adjacently to large roller faults. Tier 2 faults are associated with a renewed stage of downslope gravitational gliding of tectonic rafts. The progressive bending of overburden strata during this stage led to the progressive faulting of overburden strata by these faults. The faults comprise closely spaced normal faults with a restricted range in fault strikes, forming a rectangular-polygonal planform geometry over rollover anticlines. Tier 3 faults are associated with a later stage of diachronous grounding of tectonic rafts. Differences in the degree of diachronous grounding of tectonic rafts are responsible for the development of these faults and subsequent shortening of the overburden strata. These faults comprise densely spaced set of normal faults with diverse range of fault strikes, forming an irregular-polygonal planform geometry over rollover anticlines. The interpreted fault tiers show fault throw maxima ranging from 50 m to 60 m, spacings of 180–420 m and trace lengths of 120–650 m. The interpreted fault tiers were reactivated and their growth is characterized by fault segment linkage. The diachronous downslope translation and grounding (welding) of tectonic rafts on sub-salt strata was an important process controlling the degree of deformation off Espírito Santo. Successive episodes of fault reactivation, and the subsequent generation of salt welds below tectonic rafts, potentially formed large conduits favouring fluid migration and the generation of hydrocarbon traps in supra-salt strata

Effect of tectonic inversion on supra-salt fault geometry and reactivation histories in the Southern North Sea

High-resolution 3D seismic and borehole data in the Broad Fourteens Basin, Southern North Sea, are used to investigate the relationship between lithology and fault throw distribution, as well as to understand the reactivation and growth histories of faults developed due to tectonic inversion. Two (2) distinct tiers of faults are identified, and their geometry analysed in detail. Tier 1 faults comprise closely spaced sets of normal faults that resulted from the progressive buckling and stretching of Upper Mesozoic strata during Late Cretaceous to Paleogene tectonic inversion. They have been reactivated, but still show net normal throw separations, even though they were formed during a period of regional compression. Tier 2 faults comprise densely spaced sets of normal faults in Paleogene strata with a broad range of strikes, forming a polygonal pattern. These faults relate to early diagenesis but still record the effect of the Paleogene inversion episode. An important characteristic is that Tier 1 faults are highly segmented, and show differences in throw distribution between shale-rich and sandy intervals. These faults are more segmented with relatively small throw maxima of 14 ms (17.7 m) in shale-rich intervals, while sandy intervals are less segmented with larger throw maxima of 32 ms (40.3 m). Discrepancies in fault throw distribution and segmentation increase the chances of compartmentalisation or localised fluid flow through fault linkage zones, presenting at the same time significant risks when injecting CO2 in subsurface traps. Recognising the effect of tectonic inversion on supra-salt fault geometry, and reactivation histories, can be crucial to the characterisation of faulted hydrocarbon and carbon capture and storage (CCS) reservoirs in tectonically inverted basins such as the Southern North Sea

Dry Matter Accumulation and Uptake of Cations in Roselle (Hibiscus sabdariffa L.) as influenced by Nitrogen, Phosphorus and Farmyard manure rates in the Northern Guinea Savanna zone of Nigeria

ABSTRACT An investigation was conducted durin

Shallow fault systems of thrust anticlines responding to changes in accretionary prism lithology (Nankai, SE Japan)

Three-dimensional (3D) pre-stack depth migrated seismic data are used to analyse the geometry and growth of shallow faults associated with tectonic shortening in four (4) prominent thrust anticlines off Nankai, SE Japan. The four thrust anticlines show a trenchward increase in horizontal shortening and deform the seafloor at present. They shortened the overburden strata by 7143 m in the Late Quaternary, reflecting a horizontal shortening of 32.9% in response to plate subduction. A significant number of closely spaced and segmented fault arrays is observed in their hinge regions. Vertically segmented fault arrays with local throw maxima between 5 and 14 m relate to the existence of more competent (strong) intervals, or layers. Incompetent (weak) intervals record relatively small throw values between 2 and 5 m. We show that the presence of closely spaced, segmented fault arrays at shallow stratigraphic levels can have a significant impact on local stress distribution, controlling near-seafloor strain in accretionary prisms as Nankai's. The observed mechanical layering is likely to continue at depth to control the accumulation of tectonic stress in faults posed to reactivate during seismic events

Conservation status of marine biodiversity of the Western Indian Ocean

The Western Indian Ocean is comprised of productive and highly diverse marine ecosystems that are rich sources of food security, livelihoods, and natural wonder. The ecological services that species provide are vital to the productivity of these ecosystems and healthy biodiversity is essential for the continued support of economies and local users. The stability of these valuable resources, however, is being eroded by growing threats to marine life from overexploitation, habitat degradation and climate change, all of which are causing serious reductions in marine ecosystem services and the ability of these ecosystems to support human communities. Quantifying the impacts of these threats and understanding the conservation status of the region’s marine biodiversity is a critical step in applying informed management and conservation measures to mitigate loss and retain the ecological value of these systems. This report highlights trends in research needs for species in the region, including priorities for fundamental biological and ecological research and quantifying trends in the populations of species. The assessments and analyses submitted in this report should inform conservation decision-making processes and will be valuable to policymakers, natural resource managers, environmental planners and NGOs

Correlation and path coefficient analysis of yield characters of bambara (Vigna subterranea L. Verdc.)

No Abstrac

Competative Behaviour of Groundnut in Sesame-Groundnut Intercropping System under Varying Poultry Manure Rates and Planting Arrangement

Field experiment was conducted during the rainy seasons of 2011 and 2012 at the Teaching and Research Farm of the Faculty of Agriculture, Nasarawa State University, Keffi-Lafia Campus to study the competitive behaviour of groundnut in Sesame-groundnut intercropping system. The experiment consisted of four rates of poultry manure (0, 3.0, 6.0 and 9 t ha-1) and two planting arrangement (single alternate row and double alternate row planting arrangement). The eight treatment combinations were laid out in a randomized complete block design with four replications. The results obtained in both the years showed that sesame when grown with groundnut under different rates of poultry manure and planting arrangement appeared to be a dominant crop as indicated by its higher values of Land equivalent ratio, competitive ratio, higher and positive values for aggressivity and area time equivalent ratio. Application of 6 t ha-1 of poultry manure and double alternate row planting arrangement produced the highest values for all the competition indices measured respectively