Paleo-megalake and paleo-megafan in southern Africa

Abstract

The near juxtaposition of the Makgadikgadi Basin (Botswana), the world's largest saltpan complex, with the Okavango Delta, one of the planet's largest inland deltas (technically an alluvial megafan), has intrigued explorers and scientists since the middle of the 19 th century. It was clear from early observations that the Makgadikgadi Basin once contained a huge lake, paleo-Lake Makgadikgadi. Several authors have since speculated that this lake also covered wide regions to the north and west of the Makgadikgadi Basin. Our interpretation of unusually high-quality helicopter time-domain electromagnetic (HTEM) data indicates that paleo-Lake Makgadikgadi extended northwestward at least into the region presently occupied by the Okavango Delta. The total area of paleo-Lake Makgadikgadi exceeded 90,000 km 2 , larger than Earth's most extensive freshwater body today, Lake Superior (North America). Our HTEM data, constrained by ground-based geophysical and borehole information, also provide evidence for a paleo-megafan underlying paleo-Lake Makgadikgadi sediments.

Airborne and ground‐based transient electromagnetic mapping of groundwater salinity in the Machile–Zambezi Basin, southwestern Zambia

“…The general layered Earth model from the TEM measurements indicated an unconfined freshwater aquifer with electrical resistivities in excess of 70 Ωm underlain by salty groundwater with resistivities below 35 Ωm. Podgorski et al (2013a) described the Okavango Delta as an alluvial mega-fan and used airborne TEM data constrained by ground-based TEM seismic data and borehole records to provide additional evidence for an ancient large-scale alluvial fan complex underlying the Makgadikgadi sediments. Their airborne TEM data were a reprocessing of a commercially obtained versatile TEM (VTEM) data set from the Okavango Delta affected by systematic errors and with large uncertainties regarding key system parameters.…”

“…; Kgotlhang ; Podgorski et al . ). Airborne and follow‐up ground‐based TEM data were used in these studies to map potential freshwater aquifers based on their relatively high formation electrical resistivities.…”

“…In the last few decades, TEM has been developed and used extensively around the globe to identify fresh water aquifers, delineate saltwaterfreshwater interfaces, and map the spatial extent of salty groundwater (Guerin et al 2001;Auken et al 2003;Danielsen et al 2007;Levi et al 2008;Boucher et al 2009;Bauer-Gottwein et al 2010;Herckenrath 2012;Nenna et al 2013). Large-scale airborne geophysical mapping in the Okavango Delta, conducted by the Government of Botswana, has played a major role in the understanding of the groundwater system of the Kalahari Basin (Campbell et al 2006;Kgotlhang 2008;Podgorski et al 2013a). Airborne and follow-up ground-based TEM data were used in these studies to map potential freshwater aquifers based on their relatively high formation electrical resistivities.…”

Shaping of modern southern African biomes: Neogene vegetation and climate changes

“…Until c. 3 Ma, Poaceaerich savanna with Mopane trees (Colophospermum mopane) was dominant probably in the eastern hinterland of the Namib Desert. In northern Botswana, which was largely occupied during the Pleistocene by the palaeo-mega lake Makgadikgadi, stretching from the current Makgadikgadi basin up to the Okavango delta (see Figure 1), the late Pliocene Alab dune fields point to rather dry conditions (Moore et al, 2012;Podgorski et al, 2013).…”

Diagenetic transformations and silcrete–calcrete intergrade duricrust formation in palaeo‐estuary sediments

“…The Makgadikgadi Pans sub-basin (MSB) in northern Botswana is a large (~63 000 km 2 ) depression which has been discussed by authors primarily concerned with extended mid-Kalahari palaeo-lake systems and their links to Zambezi-Kwando-Okavango early drainage (Heine, 1982;Butzer, 1984;Lancaster, 1989; Shaw, 1991, 2002;McFarlane and Eckardt, 2006;Moore et al, 2012, Podgorski et al, 2013. Others have considered duricrust related processes ongoing within the MSB boundaries in relation to regional palaeo-environmental interpretations (Cooke and Verstappen, 1984;Ringrose et al, 2005Ringrose et al, , 2009White and Eckardt, 2006;Riedel et al, 2009).…”