East African lake evidence for Pliocene millennial-scale climate variability

Abstract

Late Cenozoic climate history in Africa was punctuated by episodes of variability, characterized by the appearance and disappearance of large freshwater lakes within the East African Rift Valley. In the Baringo-Bogoria basin, a well-dated sequence of diatomites and fluviolacustrine sediments documents the precessionally forced cycling of an extensive lake system between 2.70 Ma and 2.55 Ma. One diatomite unit was studied, using the oxygen isotope composition of diatom silica combined with X-ray fluorescence spectrometry and taxonomic assemblage changes, to explore the nature of climate variability during this interval. Data reveal a rapid onset and gradual decline of deepwater lake conditions, which exhibit millennial-scale cyclicity of ~1400-1700 yr, similar to late Quaternary Dansgaard-Oeschger events. These cycles are thought to reflect enhanced precipitation coincident with increased monsoonal strength, suggesting the existence of a teleconnection between the high latitudes and East Africa during this period. Such climatic variability could have affected faunal and floral evolution at the time.

Environment and Climate of Early Human Evolution

“…The combination of soil carbonate δ 13 C data, leaf wax δ 13 C data, and faunal records of grasslands in the Shungura Formation is commonly used as evidence for an increase in aridity (e.g., Bobe 2011;deMenocal 2004deMenocal , 2011Maslin et al 2014;Sepulchre et al 2006), but these inferences should be tempered given the highly local nature of the faunal record, the relatively high proportion of reduncine bovids throughout the Omo-Turkana Basin, and the increases in indications of both seasonally arid and wet, open habitats in the Shungura Formation after ∼2 Ma. It is important to emphasize that the presence of open indicators does not necessarily indicate a dry environment; in fact, grasses usually succeed in places and seasons where there is water, particularly in the shallow subsurface.…”

“…Many reviews exist on human evolution and climate, in part because the field is constantly being updated with new fossils, behavioral data from archaeology, environmental and climate proxy data, and theories on how these data can (or should) be related to one another (e.g., deMenocal 2004, Kingston 2007, Maslin et al 2014, Potts 2013. This review aims to synthesize some of the main data sets and narratives that are used to evaluate the environmental and climatic influences on human evolution.…”

Neogene biomarker record of vegetation change in eastern Africa

“…This is based on the proximity to those areas and regional wind patterns (e.g., figure 1 in ref. 83). Provenance studies from nearby marine cores support this interpretation (84,85).…”

The Hominin Sites and Paleolakes Drilling Project: inferring the environmental context of human evolution from eastern African rift lake deposits

“…Its goal was the collection and analysis of high-resolution paleoenvironmental records from paleo-lake drill cores near the depocenters of lacustrine basins of significant paleoanthropological importance in eastern Africa, each of which meets these conditions. As discontinuously exposed outcrops have shown these lakebeds to be commonly laminated (e.g., Wilson et al, 2014) with bedding characteristics often similar to demonstrably annual varves documented in modern African rift lakes (Pilskaln and Johnson, 1991;Cohen et al, 2006) and deposited at high sedimentation rates, their records fulfill the first criterion. The second criterion is fulfilled as each of the drill sites lies in close proximity to rich and diverse fossil vertebrate and archaeological sites, with sediments of the same age, and which collectively span some of the most critical intervals of hominin evolutionary history (e.g., earliest Homo, earliest stone tools, origin of Acheulian and Middle Stone Age technologies, earliest modern H. sapiens), and where new, important fossils and artifacts are still being recovered.…”

“…The stratigraphic interval of the Chemeron Formation targeted here (3.3-2.6 Ma) contains ∼ 100 fossil vertebrate localities, including three hominin sites, providing an opportunity to explore the nature of environmental change associated with shifting insolation patterns (for example, documenting the lacustrine response to changing precipitation patterns at precessional, millennial, and perhaps even shorter timescales; e.g., Kingston et al, 2007;Wilson et al, 2014) and to assess specific terrestrial community responses to pervasive, short-term climatic change through the interval of Northern Hemisphere glacial intensification. At this time in eastern Africa we also observe the diversification of Paranthropus (a group of hominins with robust cranial features and large teeth for a strong bite force) and our own genus Homo, as well as the earliest evidence for stone tool-making in nearby West Turkana (Harmand et al, 2015).…”