Spatial and temporal geochemical variability in lacustrine sedimentation in the East African Rift System: Evidence from the Kenya Rift and regional analyses

Abstract

Many previous studies on lacustrine basins in the East African Rift System have directed their attention to climatic controls on contemporary sedimentation or climate change as part of palaeoenvironmental reconstruction. In contrast, this research focuses on the impact of tectonism and volcanism on rift deposition and develops models that help to explain their roles and relative importance. The study focuses on the spatial and temporal variability in bulk sediment geochemistry from a diverse range of modern and ancient rift sediments through an analysis of 519 samples and 50 major and trace elements. The basins examined variously include, or have contained, wetlands and/or shallow to deep, fresh to hypersaline lakes. Substantial spatial variability is documented for Holocene to modern deposits in lakes Turkana, Baringo, Bogoria, Magadi and Malawi. Mio‐Pleistocene sediments in the Central Kenya Rift and Quaternary deposits of the southern Kenya Rift illustrate temporal variability. Tectonic and volcanic controls on geochemical variability are explained in terms of: (i) primary controlling factors (faulting, subsidence, uplift, volcanism, magma evolution and antecedent lithologies and landscapes); (ii) secondary controls (bedrock types, rift shoulder and axis elevations, accommodation space, meteoric and hydrothermal fluids and mantle CO2); and (iii) response factors (catchment area size, orographic rains, rain shadows, vegetation densities, erosion and weathering rates, and spring/runoff ratios). The models developed have, in turn, important implications for palaeoenvironmental interpretation in other depositional basins.

New haplochromine cichlid from the upper Miocene (9–10 MYA) of Central Kenya

“…The Tugen Hills are part of the eastern branch of the East African Rift System (see e.g., [47][48][49][50]). The mountain range extends for about 100 km from north to south [51,52] and its maximum altitude is around 2400 m. Its thick (up to 3000 m) successions of volcanic, fluvial and lacustrine rocks document active volcanism and the development of deep lakes as the result of ongoing rifting activity [53][54][55].…”

The mantle, CO2and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

“…For example, the large, evaporitic, carbonate producing Great Salt Lake rift basin in Utah (USA), receives 66% of its water from run‐off related to snowmelt in nearby mountains, with 31% from direct precipitation and only 3% from groundwater. However, in many balance‐filled and underfilled rift basins groundwater‐fed springs (shallow meteoric or hydrothermal) are common (Owen et al ., 2018). An extreme example of a spring‐filled lake is Nasikie Engida, to the north‐west of Lake Magadi (Kenya) where an estimated 80 to 90% of inflow is from hot springs (Owen et al ., 2018).…”

A multi‐scale approach to laminated microbial deposits in non‐marine carbonate environments through examples of the Cenozoic, north‐east Iberian Peninsula, Spain

“…In fluvial and hydrological open‐lake systems, the effects of evaporation are not as noticeable as in the case of hydrologically closed systems and, therefore, it is possible to estimate or infer variations in water temperature from the δ 18 O values of calcite (Andrews & Brasier, 2005; Arenas et al, 2015a; Brasier et al, 2010; Dabkowski et al, 2015; Kano et al, 2007; López‐Blanco et al, 2016; Osácar et al, 2016). Even with high evaporation, Baringo Lake water remains fresh due to the subsurface water loss through fractures and receives permanent hydrothermal inflows (Owen et al, 2018; Renaut et al, 2002 and references therein). Together these imprint a distinct geochemical composition to the recent microbial deposits, with positive δ 13 C and δ 18 O values.…”