GRSG Conference 2022: Orbit to Outcrop
Title: Integrated remote sensing and geological mapping in the Kwanza Basin, Angola
Author: Mike Oehlers
Much of the geological mapping in Angola was carried out between the ‘50s to ‘70s by governmental surveys with important inputs, in isolated pockets, by industry geologists, whether mining or hydrocarbon-related. Much of this data was compiled into incomplete 1:100,000 and 1:250,000 scale geological map series that used poorly controlled (compared to present abilities) aerial photographic data that predated the use of the Landsat series and prior to cloud-penetrating Radar data.
This paper details work completed by Tectosat Ltd in association with Trois Geoconsulting and DDMS to re-map the Kwanza basin, Angola in early 2021. Digital Landsat, SRTM (Shuttle Radar Topography Mission) DEM, PALSAR radar and ASTER image data – all free to download – were acquired to perform a re-evaluation of the surface geology of the onshore Kwanza Bains, Angola, all with accuracies measured in 10’s of m, not kms…
The project was set up to accompany and integrate data collated in the field by Obrangol prior to 2015, when Obrangol published their new map of Angola at 1:250,000 scale. The new interpretation was undertaken at 1:25,000 scale in order that a detailed 1:50,000 scale final map could be produced. The detailed mapping and findings enabled
- Thorough re-evaluation of the structure and litho-stratigraphic map of the region
- Definition of structural provinces within the onshore part of the Kwanza Basin
- The mapping specifically revealed:
- Many faults are rooted in and emanate from the Precambrian basement, especially strike slip faulting within the basin
- The development of a pronounced inverted extensional domain adjacent to Precambrian basement
- The delineation of rafted and pre-rafted elements within the coastal and central basinal domains respectively
- Previously recognised onshore transforms and/or transfer faults are less well-developed at the surface
- Radar mapping of the Quaternary Quelo Fm. reveals hidden structure below
- Evidence for major river capture of the modern day Bengo River by the Kwanza River, with implications for sediment distribution into the offshore domains
These tools are a gift to geologists wishing to analyse areas previously and often only generally mapped – or extrapolated – in inaccessible or inhospitable terrain at higher scales, down to 1:50,000 scale.