Quaternary glaciation in Africa: key chronologies and climatic implications

Abstract

Multiple episodes of Quaternary glaciation are evidenced on >10 distinct mountain localities throughout Africa, with the best dated sites from Kilimanjaro and Mt Kenya in equatorial East Africa. A general paucity of radiogenic dates constrains the glacial chronology, and regional sequences have largely been based on correlations by relative weathering of features. Excellent glacial moraine preservation and other features of erosion put limits on the spatial extent of palaeoglaciers, and have facilitated advances in palaeo-equilibrium line altitude (ELA) analyses. All radiocarbon dates (n < 30) provide minimum ages of deglaciation, and are consistent with a widespread synchronous advance during the Last Glacial Maximum (LGM, 21 AE 2 ka). K-Ar dates on Kilimanjaro lava flows initially recognised up to three glaciations prior to the LGM. Over 100 cosmogenic radionuclide (CRN) 36 Cl exposure ages on glacial erratics and bedrock from Kilimanjaro and Mt Kenya date 16 landforms, confirming maximum glacial extent prior to Marine Isotope Stage (MIS) 10. No glacial geological features have been dated to MIS 6. While on Kilimanjaro the CRN ages confirm a clear LGM (MIS 2) maximum, Mt Kenya lacks definitive LGM moraines. Lateglacial advances or stillstands on both mountains are suggested by low-relief moraines dating to 14.6 AE 1.2 ka (two boulders) on Mt Kenya and 16.3 AE 1.9 ka and 15.8 AE 2.5 ka on Kilimanjaro. Multiple moraines upvalley have early Holocene ages ranging from 11.2 AE 0.8 to 8.6 AE 0.2 ka. Isolated and equivocal dates on both mountains also provide speculative evidence that the maximum extent since MIS 5e may have occurred close to 30 ka, similar to sites in South America. New palaeoclimatic understanding from lake and ocean proxies suggests hypotheses for the source of low-latitude climate changes causing the advances that can be tested with improved dates. A high degree of intra-regional variance in ELA is observed, with differences by aspect reflecting precipitation gradients. Future work should include more CRN dates, improved mapping and inverse climate-mass balance modelling.

New observations indicate the possible presence of permafrost in North Africa (Djebel Toubkal, High Atlas, Morocco)

“…1). The Atlas Mountains consist of a series of ranges and plateaus extending from southwest Morocco to northern Tunisia across more than 2400 km (Mark and Osmaston, 2008). In Morocco, the Atlas Mountains include, from north to south, the Middle Atlas (Djebel Bou Naceur, 3340 m), the High Atlas (Djebel Toubkal, 4167 m) and the Anti-Atlas (Djebel Sirwa, 3304 m).…”

“…The area has a typical alpine relief with sharp ridges rising above 3500 m and long deep valleys. The upper catchments show evidence of late Pleistocene glaciation with landforms such as roche moutonées and moraines (Chardon and Riser, 1981;Hannah et al, 2016;Hughes et al, 2011;Hughes and Woodward, 2008;Mark and Osmaston, 2008;de Martonne, 1924). Extensive talus slopes and debris cones, together with widespread evidence of frost shattering, mark the landscape above 3000 m.…”

Timing and nature of late Quaternary mountain glaciation

“…Mountain glacier chronologies from ten major mountains and ranges in Africa are reviewed by Mark and Osmaston (2008). The chronological record of African glaciation remains quite limited, but patterns are emerging with new chronologies.…”

The shape of glacial valleys and implications for southern African glaciation

“…There has been much discussion regarding possible glaciation in southern Africa (see Hall, 2004, In Press;Osmaston and Harrison, 2005;Mark and Osmaston, 2008 for reviews) but recent work by Mills (2006) has provided the first scientific evidence pointing to a possible limited glaciation in parts of the Lesotho-Drakensberg area. Mills (2006) and other workers (e.g.…”