Analogue modelling of the interplay between gravity gliding and spreading across complex rift topography in the Santos Basin

The Santos Basin presents a complex and controversial evolution and distribution of salt tectonics domains. The controversies revolve mainly around the kinematically- linked Albian Gap and São Paulo Plateau. The Albian Gap is a ~450 km long and 60 km wide feature characterized by a post-Albian counter-regional rollover overlying depleted Aptian salt and in which the Albian is absent. The São Paulo Plateau is defined by a pre-salt structural high with significant base-salt topography and overlain by ~2.5 km thick salt. Another prominent feature is the Merluza Graben, a rift depocentre that underlies the southern portion of the Albian Gap and displays significant (3-4 km) of base-salt relief. Two competing hypotheses have been proposed to explain the origin and kinematics of these provinces. One invokes post- Albian extension within the Albian Gap and contraction in the Sao Paulo Plateau. The other invokes post-Albian salt expulsion in the Albian Gap and salt inflation in the São Paulo Plateau without significant lateral deformation. A recent study shows these processes contribute equally to the evolution of these domains, also demonstrating the importance of the previously neglected base-salt relief. We apply 3D physical modelling to test these new concepts and understand the interplay between laterally- variable base-salt relief, gliding and spreading on salt tectonics. Our results show a remarkably-similar salt and post-salt evolution and architecture to the Santos Basin as proposed in recent studies. They improve the understanding on the distribution and interaction of salt-related structural styles and gravity-driven processes, being also applicable to other salt-bearing margins.

Utilization of structural high entropy alloy for CO oxidation to CO2

The nanoengineered high entropy alloy (HEAs) catalysts have attracted the attention of the scientific community due to their exceptional characteristics; wide range of compositional tunability and the utilization of low-cost transition metals. During various electrochemical reactions, the oxidation of carbon-mono-oxide (CO) is an intermediate and it acts as a poison to reduce the efficiency of the reactions. A nanocrystalline HEA catalyst (CoFeNiGaZn) is prepared by easily scalable cast-cum-crush method, providing pristine catalyst surfaces. It is capable of catalyzing the CO-oxidation to CO2 with high conversion efficiency (99.8%). DFT calculations show that the high activity of the HEA can be attributed to the presence of a considerable amount of filled states of dxz and dyz orbital near the Fermi level for Ni atoms over the surface. Due to the favourable transfer of electrons from this orbital to the LUMO of reactant molecules, the endothermicity of the rate-determining step is 1.13 eV.

Joint inversion of surface wave and gravity data reveals subbasin architecture of the Congo Basin

We investigated the architecture of the greater Congo Basin, one of the largest and least-well-studied sedimentary basins on any continent. Seismograms from a large number of M > 4.5 earthquakes within and surrounding the African plate were used to make event-to-station Rayleigh wave group velocity measurements between periods of 5 and 100 s. Group velocities for discrete periods across the basin, obtained by inverting the event-station measurements, were jointly modeled with gravity data to obtain a three-dimensional S-wave and density model of the basin. The model corroborates the existence of two previously suggested subbasins, one to the north and one to the south, each ~8 km deep and separated by an east-west structural high. Our results favor a salt tectonics origin for the structural high but cannot rule out uplifted basement rock. The northern subbasin is offset to the west from the southern subbasin, consistent with previous studies suggesting sinistral motion along basement faults during periods of transpressional tectonics in late Neoproterozoic–early Paleozoic times.

Opportunistic magnetotelluric transects from 3D CSEM surveys in the SW Barents Sea

<p>Magnetotelluric (MT) data allow for electrical resistivity probing of the earth’s subsurface. Integration of resistivity models in passive margin studies could help disambiguate non-unique interpretations of crustal lithologies from seismic and potential field data. In this contribution, we present the first marine MT data in the Barents Sea, derived from industrial controlled-source electromagnetic (CSEM) surveys and characterize its quality, dimensionality and depth penetration to elaborate a modelling strategy. This MT database consists of 337 receivers located along 7 regional transects, emanating from ~70,000 km<sup>2 </sup>of 3D CSEM surveys acquired for hydrocarbon exploration from 2007 to 2019. High-quality MT data are extracted for periods ranging from 0.5 s to 5000 s with no apparent contamination by the active source, nor effects related to large time-gaps in data collection and variable solar activity. Along receiver profiles, abrupt lateral variations of apparent resistivity and phase trends coincide with major structural boundaries and underline the geological information contained in the data. Dimensionality analysis reveals a dichotomy between the “western” domain of the SW Barents Sea, dominated by a single N-S electromagnetic strike, and the “eastern” domain, with a two-fold, period-dependent strike. 35 receivers show 3D distortion caused by nearby bathymetric slopes, evidenced by elevated skew angle values. We delimit geographical areas where the 2D assumption is tenable and lay the foundation for future 2D and 3D MT modelling strategies in the SW Barents Sea. We performed 2D MT inversion along one of the regional transects, a ~220 km-long, E-W profile encompassing a major structural high and distal basin approaching the continent-ocean boundary. The resistivity model shows low crustal resistivity values (1-10 Ω.m) beneath the sedimentary cover in western distal basins, in stark contrast with high resistivity values (1000 - 5000 Ω.m) of the thick crystalline crust in the proximal domain on the structural high. We interpret this abrupt lateral resistivity variation as a crustal necking zone with a rapid transition to a hyperextended continental crust. In the proximal domain, a 50-100 Ω.m and 20 km-wide, intra-crust vertical contact hints at a plausible paleo-plate suture. Integration of resistivity with velocity, density and magnetic susceptibility models will further refine these tectonic models and related processes in the SW Barents Sea margin. Our methodology is applicable globally where 3D CSEM surveys are acquired and has a large potential for harvesting new knowledge on the electrical resistivity properties of the lithosphere.</p>

Reexamination of CSEM inversion at the Lona Prospect, Orphan Basin Canada

In 2010 an exploration well was drilled in the Lona prospect in the Orphan Basin, Canada, whose location was based primarily on a structural high at the base of a Cretaceous unconformity. Additionally, three-dimensional (3D) inversion of controlled-source electromagnetic (CSEM) data collected in 2007 and 2009 indicated elevated resistivities that roughly correlated with the structural high, indicating the possibility of hydrocarbon-saturated sediments. The well did not encounter hydrocarbons and the results were considered a false positive. In an effort to better understand the geological significance of the elevated resistivity anomaly, we re-examine the original interpretation of the Lona prospect by using a seismic image-guided inversion algorithm to analyze CSEM data from both a synthetic model and the field data and correlate those results with lithology predictions from seismic amplitude versus angle inversions (AVA). We conclude that the anomalously high resistivities seen are due to high volumes of cemented sand lithology and not to the presence of hydrocarbons. We speculate that if the results shown here had been available at the time, CSEM would not have provided support to the decision to drill.