Characteristics of Mesozoic fluvio-lacustrine formations of the western Central African Republic (Carnot Sandstones) by means of mineralogical and exoscopic analyses of detrital material
“…Later examples of the palaeogeographic formations include the Carnot-a Mesozoic fluvio-lacustrine detrital formation located in the western part of the CAR and presented by clastic material formed before the end of the Cretaceous [50]. More details on alluvial deposits of Carnot sandstones are given in [51]. Active tectonic movements and volcanic eruptions during the Cretaceous resulted in distribution of the typical morphological bodies of the intrusives igneous rocks-dykes and sills [52].…”
The interactions between the geophysical processes and geodynamics of the lithosphere play a crucial role in the geologic structure of the Earth’s crust. The Bangui magnetic anomaly is a notable feature in the lithospheric structure of the Central African Republic (CAR) resulting from a complex tectonic evolution. This study reports on the coherence in the geophysical data and magnetic anomaly field analysed from a series of maps. The data used here include raster grids on free-air altimetric gravity, magnetic EMAG2 maps, geoid EGM2008 model and topographic SRTM/ETOPO1 relief. The data were processed to analyse the correspondence between the geophysical and geologic setting in the CAR region. Histogram equalization of the topographic grids was implemented by partition of the raster grids into equal-area patches of data ranged by the segments with relative highs and lows of the relief. The original data were compared with the equalized, normalized and quadratic models. The scripts used for cartographic data processing are presented and commented. The consistency and equalization of topography, gravity and geoid data were based using GMT modules ‘grdfft’ and ‘grdhisteq’ modules. Using GMT scripts for mapping the geophysical and gravity data over CAR shows an advanced approach to multi-source data visualization to reveal the relationships in the geophysical and topographic processes in central Africa. The results highlighted the correlation between the distribution of rocks with high magnetism in the central part of the Bangui anomaly, and distribution of granites, greenstone belts, and metamorphosed basalts as rock exposure. The correspondence between the negative Bouguer anomaly (<−80 mGal), low geoid values (<−12 m) and the extent of the magnetic anomaly with extreme negative values ranging from −1000 to −200 nT is identified. The integration of the multi-source data provides new insights into the analysis of crustal thicknesses and the average density of the Earth in CAR, as well as the magnitude of the magnetic fields with notable deviations caused by the magnetic flux density in the Bangui area related to the distribution of mineral resources in CAR.
“…Later examples of the palaeogeographic formations include the Carnot-a Mesozoic fluvio-lacustrine detrital formation located in the western part of the CAR and presented by clastic material formed before the end of the Cretaceous [50]. More details on alluvial deposits of Carnot sandstones are given in [51]. Active tectonic movements and volcanic eruptions during the Cretaceous resulted in distribution of the typical morphological bodies of the intrusives igneous rocks-dykes and sills [52].…”
The interactions between the geophysical processes and geodynamics of the lithosphere play a crucial role in the geologic structure of the Earth’s crust. The Bangui magnetic anomaly is a notable feature in the lithospheric structure of the Central African Republic (CAR) resulting from a complex tectonic evolution. This study reports on the coherence in the geophysical data and magnetic anomaly field analysed from a series of maps. The data used here include raster grids on free-air altimetric gravity, magnetic EMAG2 maps, geoid EGM2008 model and topographic SRTM/ETOPO1 relief. The data were processed to analyse the correspondence between the geophysical and geologic setting in the CAR region. Histogram equalization of the topographic grids was implemented by partition of the raster grids into equal-area patches of data ranged by the segments with relative highs and lows of the relief. The original data were compared with the equalized, normalized and quadratic models. The scripts used for cartographic data processing are presented and commented. The consistency and equalization of topography, gravity and geoid data were based using GMT modules ‘grdfft’ and ‘grdhisteq’ modules. Using GMT scripts for mapping the geophysical and gravity data over CAR shows an advanced approach to multi-source data visualization to reveal the relationships in the geophysical and topographic processes in central Africa. The results highlighted the correlation between the distribution of rocks with high magnetism in the central part of the Bangui anomaly, and distribution of granites, greenstone belts, and metamorphosed basalts as rock exposure. The correspondence between the negative Bouguer anomaly (<−80 mGal), low geoid values (<−12 m) and the extent of the magnetic anomaly with extreme negative values ranging from −1000 to −200 nT is identified. The integration of the multi-source data provides new insights into the analysis of crustal thicknesses and the average density of the Earth in CAR, as well as the magnitude of the magnetic fields with notable deviations caused by the magnetic flux density in the Bangui area related to the distribution of mineral resources in CAR.
“…Figure 14.Alternative hypotheses for the drainage evolution of the palaeo-Congo River. 1 – Northward into the Benue Trough and Chad Basins during the Cretaceous Period (Ziegler & Rowley, 1998) based on micro-diamond provenance and palaeo-current directions in the Albian–Maastrichtian Carnot and Mouka-Ouadda Sandstone formations in the Central African Republic (Giresse, 1982, 1990, 2005; Censier, 1990; Censier & Lang, 1999). 2 – Karner & Driscoll (1999) and Nibbelink & Budihardjo (2002) postulated that the palaeo-Congo River flowed into the palaeo-Ogooue River (probably via the Ivindo catchment) during the Cretaceous Period, in order to explain the large volume of Upper Cretaceous sediment along the northern margin of Gabon (Séranne & Anka, 2005).…”
Palaeogeography is the representation of the past surface of the Earth. It provides the spatial context for investigating how the Earth evolves through time, how complex processes interact and the juxtaposition of spatial information. In hydrocarbon exploration, palaeogeographies have been used to map and investigate the juxtaposition, distribution and quality of play elements (source, reservoir, seal and trap), as boundary conditions for source-to-sink analysis, climate modelling and lithofacies retrodiction, but most commonly as the backdrop for presentations and montages. This paper demonstrates how palaeogeography has been and can be used within an exploration workflow to help mitigate exploration risk. A comprehensive workflow for building palaeogeographies is described which is designed to provide a standard approach that can be applied to a range of tasks in exploration and academia. This is drawn from an analysis of the history of palaeogeography and how it has been applied to exploration in the past and why. Map applications, resolution and content depend on where in the exploration and production (E&P) cycle the map is used. This is illustrated here through three case studies, from the strategic decisions of global new ventures exploration to the more detailed basin and petroleum analyses of regional asset teams evaluating basins and plays. Through this, the paper also addresses three commonly asked questions: (1) How can I use palaeogeography in my workflow? (2) How reliable are the maps? (3) How do I build a palaeogeography?
“…The thickness of the unit is highly variable but has been reported to be as thick as 300 to 400 m in places (Censier, 1990). Heavy mineral and quartz exoscopic analysis (Censier, 1990) demonstrate that the detrital material of the Carnot came from a southerly origin, has similar mineralogical composition throughout the whole infilled basin, and was composed of reworked detrital formations. The Nola and Bolé River series was originally thought to be the source of the reworked material.…”
Section: Carnot Sandstonementioning
confidence: 99%
“…The surface of the original sedimentary basin was much larger than has been interpreted on the basis of current limits of the Carnot Sandstone. The western margin may have extended beyond the CAR and Cameroon border (Censier, 1990).…”
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