22-EPN3-070: Investigation of geomorphic features in Ntwetwe pans, Makgadikgadi Basin, Botswana
January 23, 2024

20-EPN3-70: Investigation of geomorphic features in Ntwetwe pans, Makgadikgadi Basin, Botswana, using Ground Penetrating Radar: implications for Matrial surface landforms

Visit by Mebatseyon Shawel (Addis Ababa University, Ethiopia) to TA1.5 Makgadikgadi Salt Pans (Botswana).
Dates of visit: 06-13 July 2023

The Makgadikgadi Basin in Botswana, covering an area of 16,000 square kilometres, is the largest salt pan in the world. Its formation is related to a tectonic episode in the Tertiary, possibly linked to the East African Rift System (EARS), which caused the subsidence and infilling with water and sediments. Changes in climate and tectonics eventually led to the drying up of the ancient lake, leaving behind the expansive salt pans we see today. The basin consists of two major pans, namely Sua and Ntwetwe, with a combined area of approximately 8,400 square kilometres. These pans are mostly flat but feature distinct geomorphic elements such as mounds and shoreline features that can be easily identified through satellite imagery. In the western part of the Ntwetwe pan, there are numerous mounds with an east-facing convex side and an average height of 5 metres. These mounds are primarily composed of fine-grained sands, calcareous sand, and occasionally contain bivalve shells. While several theories have been proposed regarding their origin, the internal sedimentary structure of these geomorphic features remains unknown.

On Mars, conical mounds are significant morphological features that have been observed and mapped in various regions. The Noachian-Hesperian climate change on Mars resulted in the deposition of crudely layered sediments in the equatorial region, where fluctuations in groundwater played a crucial role. These layered sediments, known as Equatorial Layered Deposits (ELDs), contain numerous mounds that were exposed due to impact craters. The objective of this study is to investigate the mounds in the Ntwetwe pan using geophysical methods, particularly Ground Penetrating Radar (GPR). By employing GPR, we aim to image the internal structure of these mounds and other geomorphic features, with the ultimate goal of understanding the formation and preservation of similar structures on the Martian surface.

Several sites within the Ntwetwe pan were selected for GPR survey, primarily along east-west and north-south profiles. These sites are located in the northwest, northeast, and central parts of the pan. Over a period of six days, approximately 23 kilometres of GPR data were collected. Most of the surveys utilized 50MHz antennas, while three lines were acquired using both 50MHz and 30MHz antennas to attain penetration depth as well as resolution. Preliminary results indicate clear imaging of the top 15 meters over the mounds and delta sites. However, reflections away from these structures appear to be weaker,
possibly due to the high moisture content of clays on the pan floor, requiring further processing works to achieve better results.

Read the full scientific report with kind permission by Mebatseyon Shawel.