Early rift sedimentation in the Turkana basin, northern Kenya

Abstract

Summary The ‘Turkana Grit’ deposits of northern Kenya are a thick sequence of immature arkosic sediments of pre-Plio-Pleistocene age. Originally described by Murray-Hughes in the 1930s, these sediments have been variously considered as of either Mesozoic or Miocene age by subsequent authors. These extremely immature, tectonically controlled sediments clearly reflect intense local deformation; their age is of considerable interest, as they clearly signal the onset of significant tectonic activity in the central sector of the East African rift. A regional survey of the Turkana Grits as currently known, coupled with recently available information from the hitherto unmapped Kajong area in the SE Turkana basin, clearly indicates that these sediments represent two distinct episodes of local tectonism and deposition. On the basis of available radiometric and biostratigraphic evidence, the earlier of these episodes appears to be of Cenomanian-basal Palaeocene age, while the later episode dates from the mid-Miocene. These observations suggest that significant tectonic activity in East Africa commenced in the late Mesozoic rather than—as generally assumed—in the mid-Cenozoic. The earliest (late Mesozoic) episode of clastic deposition in the Kajong area was initially controlled by a set of major E-W trending transform faults; these deposits are primarily preserved in associated fault-wedge basins. The documentation of a major transform element in the Kajong area has important implications for the early development of the African Rift as a whole. We suggest here the possibility that the enigmatic distribution of the late Mesozoic rift sediments—which are restricted to the southern sector of the Western Rift and the northern sector of the Eastern Rift—reflects the fact that the original late Mesozoic rift consisted of a single graben. The southern and northern portions of this graben have been subsequently displaced by a major E-W trending dextral transform system, extending some 500 km from the SE Turkana basin to the present northern termination of the Western Rift on the Uganda-Sudan border.

Stratigraphy, sedimentology and diagenetic evolution of the Lapur Sandstone in northern Kenya: Implications for oil exploration of the Meso-Cenozoic Turkana depression

“…Macroscopic observations on hand specimens and microscopic studies on thin sections were performed at the Petrography Lab- Murray-Hughes (1933), outcropping in the northern and central segments of the Kenya Rift (redrawn from Tiercelin et al, 2004). These formations are, from north to south, respectively: (1) the Lubur Series (Arambourg, 1935(Arambourg, , 1943 (here named the Lapur Sandstone; Thuo, 2009) at the northwest end of Lake Turkana; (2) the Muruanachok Sandstone to the west of Lake Turkana (Walsh and Dodson, 1969;Morley et al, 1992Morley et al, , 1999dWescott et al, 1993;Thuo, 2009;Tiercelin et al, 2011); (3) the Lokone Sandstone and Auwerwer Sandstone to the southwest of Lake Turkana (Lokichar Basin) (Boschetto et al, 1992;Morley et al, 1999d;Tiercelin et al, 2004;Vincens et al, 2006;Ducrocq et al, 2010); (4) the Lariu sandstones and the Mount Porr Sandstone (also known as the Sera Iltomia Formation) at the southwest and southeast ends of Lake Turkana, respectively (Savage and Williamson, 1978;Williamson and Savage, 1986;Wescott et al, 1993;Tiercelin et al, 2004); (5) the Kimwarer and Kamego Formations in the Kerio and Baringo Basins in the central Kenya Rift (Walsh, 1969;Lippard, 1972;Chapman et al, 1978;Ego, 1994;Renaut et al, 1999;Tiercelin et al, 2004Tiercelin et al, , 2011. oratory of the FRE 3298 CNRS ''Géosystèmes'', Lille 1 University, France.…”

Hydrocarbon potential of the Meso-Cenozoic Turkana Depression, northern Kenya. I. Reservoirs: depositional environments, diagenetic characteristics, and source rock–reservoir relationships

“…In the Lapurr Range/Lokitaung Gorge at the northwest end of Lake Turkana (Fig. 3), dinosaur bones and angiosperm wood were found in a 400 m-thick series of arkosic sandstones and conglomerates (the Labur or Lubur series of Arambourg (1935)), suggesting a Cenomanian-basal Palaeocene age (Arambourg, 1943;Arambourg & Wolff, 1969;Fuchs, 1939;Williamson and Savage, 1986). Similar arkosic but often unfossiliferous sandstones are also known from discontinuous exposures on the southeast and west sides of Lake Turkana, in the Mount Porr area (Morley et al, 1992;Wescott et al, 1993;Williamson & Savage, 1986) and at the Lariu Range and Muruanachok, respectively (Walsh & Dodson, 1969;Wescott et al, 1993) (Fig.…”

“…(Savage & Williamson, 1978). Both unconformably overlie crystalline basement rocks (mainly gneisses and amphibolites) of Proterozoic age, and are in turn overlain by lower Miocene sediments and basalts (dated at 18.5^0.45 Ma) forming the Loiyangalani Formation, and by Pliocene basalts dated at 3.38^0.25 Ma, respectively (Williamson & Savage, 1986). On the basis of the lack of any volcaniclastic component in the Sera Iltomia sandstones and the discovery of angiosperm fossil wood, a late Mesozoic -basal Palaeocene age is proposed for the Sera Iltomia Formation (Savage & Williamson, 1978;Williamson & Savage, 1986).…”

“…From field and cartographic evidence, the composite Kajong fault network appears to be capped by the Loiyangalani Basalts and thus assumed to be pre-lower Miocene in age (Williamson & Savage, 1986) (Fig. 7B).…”

Thermal and mechanical development of the East African Rift System

“…The Mozambiquian (Pan-African) orogeny (600-900 Ma) produced north-south trending folds and metamorphic fabrics in the eastern part of the region, and these northsouth trends often overprint Ubendian rocks . (Arambourg, 1933;Spence, 1954;Dixey, 1956;Williamson and Savage, 1986). Late Jurassic/Early Cretaceous carbonatites are found along northwest-southeast trending faults that extend northwest of Lake Rukwa to the eastern shore of Lake Tanganyika Coetzee, 1964).…”