Sedimentary provenance and maximum depositional age analysis of the Cretaceous? Lapur and Muruanachok sandstones (Turkana Grits), Turkana Basin, Kenya

Abstract

The Turkana Basin of northwestern Kenya is well known for its rich Neogene–Quaternary vertebrate fossil record; however, it also represents one of the few locations in sub-Saharan Africa where Cretaceous vertebrate fossils, including dinosaurs and other archosaurs, are preserved. These Cretaceous deposits are colloquially referred to as the ‘Turkana Grits’, and assumed to be Cretaceous in age based on their limited biostratigraphy. The ‘Turkana Grits’ are overlain by Palaeogene volcanic rocks (<35 Ma), which are widely considered to record the earliest evidence of plume-related volcanism in the East African Rift System. In this study, we present the results of an integrated sedimentary provenance investigation of two units within the ‘Turkana Grits’ called the Lapur and Muruanachok sandstones. Analysis of U–Pb ages and Lu–Hf initial ɛHf(t) values from 1106 detrital zircons demonstrate that sediments are primarily derived from Neoarchaean and Neoproterozoic basement sources, except for six Palaeogene grains from the upper Lapur Sandstone, which are of unknown provenance. Considered together, these data point to the Mozambique Belt, which makes up the nearby rift flanks, as the primary provenance source. This is consistent with palaeocurrent data, and suggests localized sediment input by alluvial fans, which fed into NNW-directed fluvial systems. Perhaps the most surprising finding is the identification of the late Paleocene detrital zircons, which not only demonstrate that the depositional age for the top of the formation is Paleocene rather than Cretaceous, but also provides possible evidence for the oldest Palaeogene volcanic activity within the East African Rift System.

Early syn-rift igneous dike patterns, northern Kenya Rift (Turkana, Kenya): Implications for local and regional stresses, tectonics, and magma-structure interactions

“…37-38 Ma (O'Connor et al, 2011;Tiercelin et al, 2012a). Detrital zircons confirm a Paleogene age for the upper part of the section (Owusu Agyemang et al, 2019). The Turkana Volcanics have previously been dated by Zanettin et al (1983) and McDougall and Brown (2009) as part of a belt that ranges in age between ca.…”

Magma‐Assisted Continental Rifting: The Broadly Rifted Zone in SW Ethiopia, East Africa

“…A 5 to 30‐m‐thick conglomeratic sandstone layer, silicified at the top, is exposed along the margin of the Amaro Horst (Ebinger et al., 1993; WoldeGabriel et al., 1991) but is absent west of the BRZ (Davidson, 1983; Philippon et al., 2014). The age of the sandstone layer is uncertain; however, several authors have correlated the sediments with the petrographically similar lower unit of the Turkana Grits of inferred Cretaceous age in northern Kenya (Levitte et al., 1974; Murray‐Hughes, 1933; Owusu Agyemang et al., 2019; Savage & Williamson, 1978; Walsh & Dodson, 1969). In contrast, Davidson (1983) suggested an early Paleogene depositional age, based on sediment composition and the nature of contact with the overlying Eo‐Oligocene volcanics.…”