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![Overall composite panel diagram for the Oltulelei Formation, looking north, based on information, detailed stratigraphic logs, and correlations in supplementary data DR3 (see footnote 1, text and panel diagrams). Note that horizontal relationships are not to scale; approximate distances between localities are shown below the panel. Olkesiteti Member is indicated by shades of gray plus the red basal unit in Locality G, Oltepesi Member is indicated by shades of brown, and Tinga Member is indicated by light orange. The Oltulelei Tuffs in the Olkesiteti Member are light gray. Heavy green line marks the erosional unconformity on the Olorgesailie Formation, which is also the base of the Oltulelei Formation and the Olkesiteti Member, and the heavy orange and black lines show the lower boundary of the Oltepesi and Tinga Members, respectively. Dashed orange line indicates inferred channel margin. OG—Olorgesailie Fm.; M—Member. See supplementary data DR1 (see text footnote 1), and Deino and Potts (1990, 1992) for information on the geochronology.]()
![Summary diagram showing phases of aggradation and erosion in the Olorgesailie Basin over the past 1.2 m.y. Erosional phases are in dashed lines, and approximate depth of maximum erosion is indicated by the y axis, with valley depths based on the thickness of fill. Gray vertical dotted lines indicate the time interval between the two formations with no sedimentary record. The Olkesiteti Member filled part of the eroded landscape of the Olorgesailie Formation, the Oltepesi Member filled valleys cut into the previous deposits in the lower parts of this landscape, and the Tinga Member in turn filled channels and spread out over the earlier deposits.]()
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![Representative strata and lithologies of the Oltulelei Formation; see also Table DR2 and Figs. DR3A–C (see text footnote 1). Letter and number combinations identify the stratigraphic sections, i.e. G06-08 = Locality G, Year 2006, Section 08 and GOK-1 = Locality G, Archeological Site OK-1. (A) Locality G red soil (phase G-1) and overlying Oltulelei Tuff deposits (phase G-3a; above dashed line) at archaeological site GOK-1. (B) Locality G clays, diatomaceous silts (phase G-2), and a tuff with white, silicified plant stems in growth position; phase G-3a above dashed line. (C) Enlargement of plant stem tuff in B. (D) Step trench section G06-03 showing tufa and associated diatomaceous silts up through clays and a tabular plant stem tuff (top of trench) in phases G-2 and lower G-4. (E) Typical gravels of phase G-6 in section G09-01; yellow bed near section base is the upper plant stem tuff at the top of phase G-5. (F) Phase G-4 at archaeological site GOK-4. (G) Oltulelei Tuffs (gray units) in cliff exposure near section OLT05-02, phases OLT-2a and 2b (below and above dashed line, respectively). Muteti Nume for scale. (H) Oltepesi Member (phases OLT-4 through OLT-6) in Locality OLT at section OLT07-ST4, where it fills and overtops a valley cut through one of the tabular Oltulelei Tuffs (phase OLT-2a) and Olorgesailie Formation Member 13. (I) Oltepesi Member channels in southern Locality C (section C16–1, phase C-1) above an erosional unconformity on Olorgesailie Formation Member 8. (J) Back wall of archaeological excavation BOK-2 showing the disrupted, radiating pattern of a proposed spring vent (within dashed line) in phase B-2, and a clastic dike with pumices, dated at 200 ka (Table 1). (K) Tinga Member boulders of phase B-7 at section B08-04, topping a hill formed by Olkesiteti Member, phase B-2. (L) Tinga Member boulder weighing an estimated 35,000 kg in western Locality B, with Rick Potts for scale.]()
![Perspective diagrams looking NNE, reconstructing middle to late Pleistocene cycles of deposition and erosion of the Olorgesailie rift subbasins, based on detailed information provided in supplementary data DR1–DR3 (see text footnote 1). (A) Inferred extent of the Olorgesailie Formation at the end of lacustrine deposition at 500 ka. (B) Basin topography after lowering of base level to the south and erosion by a drainage system that formed valleys and escarpments (black hashed symbols); inferred time of red soil formation in Locality G. (C) Deposition of the lower part of the Oltulelei Formation (dark-gray shading), with fluvial deposits, volcaniclastics, diatomaceous silts, and tufas filling erosional lows, indicating an elevated water table possibly controlled by a lake in the Koora Graben. (D) Fluvial influx of large volumes of tuff and pumice (Oltulelei Tuffs, indicated in light purple) that filled the northern basin valleys and spilled over into the Koora Graben, creating a sequence of widespread tabular deposits. (E) Lower base level to the southwest and reestablishment of the drainage system, eroding new valleys into the Oltulelei Tuffs and underlying sediments. (F) Inferred fault movement on the west side of Locality B, which temporarily blocked east-to-west drainage, filling valleys and depositing distinctive orange-brown sediment over the Oltepesi Plain with distinctive orange-brown sediments (Oltepesi Member). Following this valley filling, a new drainage formed along the down-thrown side of the Lava Peninsula fault and carried a fresh influx of volcaniclastics from the north. (G) Catastrophic flooding from the north deposited the Tinga fan over the northeast part of the basin, with flood sediment extending past the Scoriaceous Cone. Drainage was reestablished around the eastern and southern margins of the fan, connecting the Olkesiteti and Oltulelei River systems. (H) Present-day erosional phase with the Olkesiteti River and the Oltulelei River draining into the Ol Keju Nyiro River, which has cut eastward across the toe of the Tinga fan to capture the upper part of a drainage that previously joined the Oltulelei River. Note that the escarpment on the southern edge of the white Olorgesailie Formation outcrops has receded north over time, and the Ol Keju Nyiro Gorge is an antecedent channel that originated as a drainage on exposed Olorgesailie Formation paleolake deposits and later cut into the lavas of Mount Olorgesailie. Localities B, C, and OLT are shown in A; for additional names of topographic features and localities, see Figures 1, 2, and 6. Dates and paleogeographic reconstructions are based on information in Table 1, Figure 4, and supplementary data DR3 (see text footnote 1). Note that not all phases of deposition described in the text or shown in Figures 4 or Figures DR3A–C (see text footnote 1) are depicted in these diagrams.]()
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Image
Overall composite panel diagram for the Oltulelei Formation, looking north,... Available to Purchase
in The Oltulelei Formation of the southern Kenyan Rift Valley: A chronicle of rapid landscape transformation over the last 500 k.y.
> GSA Bulletin
Published: 15 March 2018
distances between localities are shown below the panel. Olkesiteti Member is indicated by shades of gray plus the red basal unit in Locality G, Oltepesi Member is indicated by shades of brown, and Tinga Member is indicated by light orange. The Oltulelei Tuffs in the Olkesiteti Member are light gray. Heavy
Image
Summary diagram showing phases of aggradation and erosion in the Olorgesail... Available to Purchase
in The Oltulelei Formation of the southern Kenyan Rift Valley: A chronicle of rapid landscape transformation over the last 500 k.y.
> GSA Bulletin
Published: 15 March 2018
lines indicate the time interval between the two formations with no sedimentary record. The Olkesiteti Member filled part of the eroded landscape of the Olorgesailie Formation, the Oltepesi Member filled valleys cut into the previous deposits in the lower parts of this landscape, and the Tinga Member
Journal Article
The Oltulelei Formation of the southern Kenyan Rift Valley: A chronicle of rapid landscape transformation over the last 500 k.y. Available to Purchase
Journal: GSA Bulletin
Publisher: Geological Society of America
Published: 15 March 2018
GSA Bulletin (2018) 130 (9-10): 1474–1492.
... distances between localities are shown below the panel. Olkesiteti Member is indicated by shades of gray plus the red basal unit in Locality G, Oltepesi Member is indicated by shades of brown, and Tinga Member is indicated by light orange. The Oltulelei Tuffs in the Olkesiteti Member are light gray. Heavy...
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Image
Representative strata and lithologies of the Oltulelei Formation; see also ... Available to Purchase
in The Oltulelei Formation of the southern Kenyan Rift Valley: A chronicle of rapid landscape transformation over the last 500 k.y.
> GSA Bulletin
Published: 15 March 2018
by Olkesiteti Member, phase B-2. (L) Tinga Member boulder weighing an estimated 35,000 kg in western Locality B, with Rick Potts for scale.
Image
Perspective diagrams looking NNE, reconstructing middle to late Pleistocene... Available to Purchase
in The Oltulelei Formation of the southern Kenyan Rift Valley: A chronicle of rapid landscape transformation over the last 500 k.y.
> GSA Bulletin
Published: 15 March 2018
) Inferred fault movement on the west side of Locality B, which temporarily blocked east-to-west drainage, filling valleys and depositing distinctive orange-brown sediment over the Oltepesi Plain with distinctive orange-brown sediments (Oltepesi Member). Following this valley filling, a new drainage formed
