Gombe Group basalts and initiation of Pliocene deposition in the Turkana depression, northern Kenya and southern Ethiopia

2004 ◽  
Vol 141 (1) ◽  
pp. 41-53 ◽  
Author(s):  
BEREKET HAILEAB ◽  
FRANCIS H. BROWN ◽  
IAN McDOUGALL ◽  
PATRICK N. GATHOGO
Keyword(s):  
Basaltic Magma ◽  
Volcanic Eruptions ◽  
Lava Flows ◽  
Southern Ethiopia ◽  
Magmatic Activity ◽  
Lake Turkana ◽  
North Central ◽  
Northern Kenya ◽  
Turkana Basin ◽  
Magmatic Event

A little before 4 Ma ago, deposition of Pliocene and Pleistocene strata described as the Omo Group began in the Turkana and Omo basins of northern Kenya and southern Ethiopia. Soon after, basaltic magma erupted as thin lava flows, and intruded as dykes into the oldest Pliocene strata of the basin. These flows and intrusions are similar petrographically and geochemically, and mark a basaltic magmatic event spanning latitudes from 2° 45′ N to 6° 45′ N at a longitude of about 36° E. By 3.94 Ma, this basaltic magmatic activity had ceased. Previous researchers used these lavas as an important seismic marker in their study of the southern part of the Turkana Basin. Subsequent volcanic eruptions formed North, Central and South islands in Lake Turkana, and the Korath Range in southern Ethiopia. Thus there was a hiatus in basaltic magmatic activity of nearly 4 Ma in the area presently occupied by Lake Turkana and the lower Omo Valley, although volcanism continued on the eastern margin of the basin. Here we review the field occurrences of these basalts, their distinctive petrography, composition, age and significance to Pliocene deposition in the basin.

A quantitative study of five thousand years of volcanism on Sao Miguel, Azores

1978 ◽  
Vol 288 (1352) ◽  
pp. 271-319 ◽  
Keyword(s):  
Quantitative Study ◽  
Basaltic Magma ◽  
Volcanic Eruptions ◽  
Lava Flows ◽  
Explosive Eruptions ◽  
Lateral Movement ◽  
The Past ◽  
Pumice Fall ◽  
Eruptive Fissures ◽  
Fall Deposits

The activity of the three stratovolcanoes on the island of Sao Miguel is documented by tephrochronology, and during the past 5000 years a total of some 57 volcanic eruptions have taken place, mostly of magnitudes 4-6 on Tsuya’s scale. Approximately half were trachytic, and half basaltic. Each stratovolcano has a caldera within which each has had one historic eruption. The trachytic eruptions were predominantly explosive, and most took place from vents situated within the calderas. Isopach and isograde maps of most of the resulting pumice fall deposits are given. The basaltic eruptions produced both lava flows and pyroclastics, and isopach and isograde maps are given for some of the main fall deposits. The Agua de Pau volcano has had particularly large explosive eruptions, several of them (including Fogo A, the largest in the past 5000 years) being of plinian type. The output of the three volcanoes over the 5000 years is equivalent to 4.6 km 3 of dense rock, at which rate the exposed parts of the volcanoes could have accumulated in 150000 years. At least half of the erupted material is trachytic, a proportion typical of the entire accessible parts of the volcanoes. The 50 known eruptive vents of the past 5000 years are distributed in a zone 55 km long by 8 km wide which may lie above a major fracture zone. Some eruptive fissures trend obliquely across this zone, suggesting right-lateral movement along the fracture. Basaltic eruptions were confined to a much smaller area than in the preceding millennia perhaps due to the formation, at the time of the great Fogo A eruption 5000 years ago, of a broad trachytic magma chamber underlying the Agua de Pau and Furnas volcanoes which basaltic magma has since been unable to penetrate.

scholarly journals Orbital Influence on Precipitation, Fire, and Grass Community Composition From 1.87 to 1.38 Ma in the Turkana Basin, Kenya

2021 ◽  
Vol 9 ◽  
Author(s):  
Chad L. Yost ◽  
Rachel L. Lupien ◽  
Catherine Beck ◽  
Craig S. Feibel ◽  
Steven R. Archer ◽  
...  
Keyword(s):  
Environmental Change ◽  
Community Composition ◽  
High Amplitude ◽  
Homo Erectus ◽  
Southern Ethiopia ◽  
Time Interval ◽  
Northern Kenya ◽  
Turkana Basin ◽  
Core Study ◽  
Vegetation Surveys

The Turkana Basin in northern Kenya and southern Ethiopia has yielded hundreds of hominin fossils and is among the most important localities in the world for studying human origins. High resolution climate and vegetation reconstructions from this region can elucidate potential linkages between hominin evolution and environmental change. Microcharcoal and phytoliths were examined from a 216 m (1.87–1.38 Ma) drill core (WTK13), which targeted paleo-Lake Lorenyang sediments from the Nachukui Formation of the Turkana Basin. A total of 287 samples were analyzed at ∼32–96 cm intervals, providing millennial-scale temporal resolution. To better understand how basin sediments record fire and vegetation from the watershed, the paleorecord was compared with nine modern sediment samples collected from Lake Turkana along a transect of increasing distance from the 1978 to 1979 shoreline. This included vegetation surveys and phytolith production data for species from areas proximal to the basin. We found that phytolith and microcharcoal concentrations decreased predictably moving off shore. However, phytoliths from plants sourced in the Ethiopian Highlands increased moving off shore, likely the result of increased exposure to the Omo River sediment plume. In our down-core study, microcharcoal was well-preserved but phytolith preservation was poor below ∼60 m (∼1.50 Ma). Spectral analysis revealed that microcharcoal often varied at precessional (∼21 kyr) periodicities, and through a correlation with δDwax, linked orbitally forced peaks in precipitation with elevated fire on the landscape. Phytoliths revealed that alternating mesic C4 versus xeric C4 grass dominance likely varied at precessional periodicities as well, but that grass community composition was also mediated by basin geometry. Two high eccentricity intervals of particularly high amplitude and abrupt environmental change were centered at ∼1.72 and 1.50 Ma, with the intervening period experiencing high fire variability. With the switch from lacustrine to fluvial-deltaic deposition at the core site by 1.5 Ma, mesic C4 grasses dominated and fire activity was high. This upper interval correlated to the time interval from which Nariokotome Boy (Homo erectus/ergaster) was discovered 3 km east of our drill site. Phytoliths indicated a seasonally wet and open landscape dominated by xeric C4 grasses, sedges, and other herbaceous plants.

The fertile past: the Gabra concept of oral tradition

Africa ◽  
1986 ◽  
Vol 56 (2) ◽  
pp. 193-209 ◽  
Author(s):  
Aneesa Kassam
Keyword(s):  
Oral Tradition ◽  
Southern Ethiopia ◽  
Lake Turkana ◽  
Eastern Province ◽  
Sheep And Goats ◽  
Northern Kenya ◽  
Opening Paragraph

Opening ParagraphThis study on the concept of oral tradition is based on three years of fieldwork, between 1980 and 1983, amongst the Gabra of northern Kenya, an Eastern-Cushitic (Oromo) speaking people who originated in southern Ethiopia and who live today on both sides of the Kenya–Ethiopia border. According to the 1978 national census figures, there are about 30,553 Gabra living on the Kenyan side of the border, mainly in the arid waste of the Eastern Province. In this hostile landscape, in the volcanic, boulder-strewn country on the edge of the Chalbi Desert east of Lake Turkana, the Gabra roam with their herds of cattle, camels, sheep and goats in constant search of pasture for their animals.

scholarly journals Evidence of active magmatic rifting at the Ma’Alalta volcanic field (Afar, Ethiopia)

2021 ◽  
Vol 83 (6) ◽  
Author(s):  
Gianmaria Tortelli ◽  
Anna Gioncada ◽  
Carolina Pagli ◽  
Mauro Rosi ◽  
Laura De Dosso ◽  
...  
Keyword(s):  
Seismic Data ◽  
Volcanic Field ◽  
Lava Flows ◽  
Magmatic Activity ◽  
Magma Storage ◽  
Plumbing System ◽  
Mafic Lava ◽  
Cinder Cones ◽  
Mafic Rocks ◽  
Seismic Networks

AbstractDuring continental rifting, strain and magmatism are believed to localize to narrow magmatic segments, while the rift margin is progressively abandoned. We integrate volcanological, geochemical, petrological and seismic data from the Ma’Alalta volcanic field (MVF) near the western margin of Afar, to show that the MVF is an active magmatic segment. Magmatism in MVF initiated with lava flows and large-volume, caldera-forming ignimbrites from a central edifice. However, the most recent magmatic activity shifted towards mafic lava fields, cinder cones and obsidian-rich silicic domes erupted from vents aligned NNW-SSE, defining a ~ 35-km-long magmatic segment. Along the same area, a NNW-SSE alignment of earthquakes was recorded by two local seismic networks (2005–2009 and 2011–2013). The geochemistry of the mafic rocks is similar to those of nearby axial volcanoes. Inferred magma storage depth from mineral geobarometry shows that a shallow, silicic chamber existed at ~ 5-km depth below the stratovolcano, while a stacked plumbing system with at least three magma storage levels between 9 and 24 km depth fed the recent basalts. We interpret the wide set of observations from the MVF as evidence that the area is an active magmatic segment, showing that localised axial extension can be heavily offset towards the rift margin.

Rock varnish record of the African Humid Period in the Lake Turkana basin of East Africa

The Holocene ◽  
2021 ◽  
pp. 095968362110116
Author(s):  
Tanzhuo Liu ◽  
Christopher J Lepre ◽  
Sidney R Hemming ◽  
Wallace S Broecker
Keyword(s):  
East Africa ◽  
Lake Level ◽  
Drainage System ◽  
Early Holocene ◽  
Lake Turkana ◽  
Moisture Condition ◽  
Turkana Basin ◽  
Rock Varnish ◽  
Geomorphic Features ◽  
Humid Period

Rock varnish is a manganiferous dark coating accreted on subaerially exposed rocks in drylands. It often contains a layered microstratigraphy that records past wetness variations. Varnish samples from latest Pleistocene and Holocene geomorphic features in the Lake Turkana basin, East Africa display a regionally replicable microstratigraphy record of Holocene millennial-scale wetness variability and a broad interval of wetter conditions during the African Humid Period (AHP). Three major wet pulses in the varnish record occurred during the generally wet interval of the early Holocene (11.5–8.5 ka) when the lake attained its maximum high stand (MHS) at 455–460 m. A >23 m drop from the MHS occurred between 8.5 and 8 ka. Subsequently two additional wet pulses occurred during the early to middle Holocene (8–5 ka) when the lake occupied its secondary high stand at 445 m. Collectively, these five wet phases represent an extended wet interval coincident with the AHP in the region. One moderate wet phase occurred during the subsequent climatic transition from the humid to arid regime (5–4.3 ka) after the lake level dropped rapidly from 445 m to <405 m. Five minor wet phases took place during the overall arid period of the late Holocene (4.3–0 ka) when the lake level oscillated below 405 m. These findings indicate that the AHP terminated rapidly around 5 ka in the Turkana basin in terms of lake level drop, but the regional shift in relative humidity from the AHP mode to its present-day condition lagged for about 700 years until 4.3 ka, hinting at a gradual phasing out in terms of moisture condition. These findings further suggest that Lake Turkana overflowed intermittently into the Nile drainage system through its topographic sill at 455–460 m during the early Holocene and has become a closed-basin lake thereafter for the past 8 ky.

Pliocene archaeological occurrences in the Lake Turkana basin

1994 ◽  
Vol 27 (1-3) ◽  
pp. 159-171 ◽  
Author(s):  
Mzalendo Kibunjia
Keyword(s):  
Lake Turkana ◽  
Turkana Basin

scholarly journals Stepwise drying of Lake Turkana at the end of the African Humid Period: an example of forced regression modulated by solar activity?

2016 ◽  
Author(s):  
Alexis Nutz ◽  
Mathieu Schuster
Keyword(s):  
Solar Activity ◽  
Lake Level ◽  
Controlling Factors ◽  
Lake Turkana ◽  
Turkana Basin ◽  
Orbital Precession ◽  
Forced Regression ◽  
Humid Period

Abstract. Although timing of the termination of the African Humid Period (AHP) is relatively well-established now, modes and controlling factors are still being determined. Here, through a geomorphological approach, we characterize the evolution of the final regression of Lake Turkana at the end of the African Humid Period. We show that lake level fall during this period was not constant, yet rather stepwise consisted of five periods marked by rapid rates of lake level fall separated by periods of lower rates of lake level fall. Even the overall regressive trend is associated with regional decreased precipitations due to reduced insolation controlled by orbital precession, we discuss the origin of the five periods of accelerated rates of lake level fall. Finally, we propose that accelerations are associated with periods marked by solar activity minima that locally resulted in the repeated westward displacement of the Congo Air Boundary (CAB), thereby reducing rainfall across the Lake Turkana basin.

A New and Open CoiledValvata(Gastropoda) from the Pliocene Koobi Fora Formation of the Turkana Basin, Northern Kenya

2010 ◽  
Vol 84 (5) ◽  
pp. 996-1002 ◽  
Author(s):  
Henning Scholz ◽  
Matthias Glaubrecht
Keyword(s):  
New Species ◽  
Environmental Stress ◽  
Environmental Conditions ◽  
Lake Level ◽  
Shell Morphology ◽  
Koobi Fora ◽  
Northern Kenya ◽  
Turkana Basin ◽  
High Level ◽  
Stratigraphic Interval

New field collections allow the study and description ofValvata juliaenew species from the Pliocene upper Burgi Member of the Koobi Fora Formation of Kenya. The shell morphology of this species varies from trochospiral to planispiral to open coiled. The species is restricted to a short stratigraphic interval.Valvata juliaeis considered as an invader of the Turkana Basin during a lacustrine transgression event. The open coiling of the species is interpreted as an ecophenotypic response to a high level of environmental stress caused by lake level fluctuations and emergence of delta systems. These environmental conditions broughtValvata juliaeto extinction soon after it invaded the Turkana Basin.

n-Paraffins in the sediments and in situ fossils of the Lake Turkana Basin, Kenya

1982 ◽  
Vol 46 (9) ◽  
pp. 1505-1511 ◽  
Author(s):  
Paul I. Abell ◽  
Marshall J. Margolis
Keyword(s):  
Lake Turkana ◽  
Turkana Basin
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