Geosciences

This study contributes to the growing complexity of the impala fossil record through a morphological description and analysis of Aepyceros fossils from late Pleistocene deposits in Kenya's Lake Victoria Basin. We show that the Lake Victoria impala belongs to an extinct species that differs from modern impala and its fossil predecessors by a combination of exceptionally deep mandibles and teeth characterized by greater hypsodonty and occlusal lengths. Whereas modern impala (A. melampus) displays substantial ecological flexibility, these traits in the extinct species suggest a more dedicated adaptation to grazing in open and dry environments. Previous phylogeographic observations indicate that A. melampus was extirpated from East Africa, perhaps during the middle-to-late Pleistocene, and later recolonized from southern Africa. The Lake Victoria impala raises the possibility that the evidence interpreted as extirpation may instead reflect speciation, with A. melampus giving rise to a novel East African species while persisting unchanged in southern Africa. Increased rainfall and rising atmospheric CO 2 concentrations at the end of the Pleistocene may have played a role in the disappearance of the extinct form via habitat loss and possibly competition with the more versatile A. melampus.

The effect of changing palaeoclimate and palaeoenvironment on human evolution during the
Pleistocene is debated, but hampered by few East African records directly associated with
archaeological sites prior to the Last Glacial Maximum. Middle to Late Pleistocene deposits on
the shoreline of eastern Lake Victoria preserve abundant vertebrate fossils and Middle Stone Age
artefacts associated with riverine tufas at the base of the deposits, which are ideal for palaeoenvironmental reconstructions. New data from tufas identified on Rusinga Island and on
the mainland near Karungu, Kenya are provided from outcrop, thin-sections, mineralogical,
stable isotopic and U-series dating analyses. Tufa is identified at four sites: Nyamita (94.0 ± 3.3
and 111.4 ± 4.2 ka); Kisaaka, Aringo (455 ± 45 ka); and Obware. The age ranges of these tufa
deposits demonstrate that spring-fed rivers were a recurrent, variably preserved feature on the
Pleistocene landscape for ca 360 kyr. Poor sorting of clastic facies from all sites indicates flashy,
ephemeral discharge, but these facies are commonly associated with barrage tufas, paludal
environments with δ13C values of ca 10‰ indicative of C3 plants and fossil Hippopotamus, all of
which indicate a perennial water source. Other tufa deposits from Nyamita, Obware and Aringo
have a mixed C3/C4 signature consistent with a semi-arid C4 grassland surrounding these springfed
rivers. The δ18O values of tufa from Nyamita are on average ca 1‰ more negative than
calcite precipitated from modern rainfall in the region, suggesting greater contribution of
depleted monsoonal input, similar to the Last Glacial Maximum. Microdebitage and surface
collected artefacts indicate that early modern humans were utilizing these spring-fed rivers. The
presence of spring-fed rivers would have afforded animals a reliable water source, sustaining a
diverse plant and animal community in an otherwise arid environment.

The effect of changing environment on the evolution of Homo sapiens is heavily debated, but few data are
available from equatorial Africa prior to the last glacial maximum. The Karungu deposits on the northeast coast
of Lake Victoria are ideal for paleoenvironmental reconstructions and are best studied at the Kisaaka site near
Karunga in Kenya (94 to N33 ka) where paleosols, fluvial deposits, tufa, and volcaniclastic deposits (tuffs) are exposed
over a ~2 km transect. Three well-exposed and laterally continuous paleosols with intercalated tuffs allow
for reconstruction of a succession of paleocatenas. The oldest paleosol is a smectitic paleo-Vertisol with saline and
sodic properties. Higher in the section, the paleosols are tuffaceous paleo-Inceptisols with Alfisol-like soil characteristics
(illuviated clay). Mean annual precipitation (MAP) proxies indicate little change through time, with an
average of 764 ± 108 mm yr−1 for Vertisols (CALMAG) and 813 ± 182 to 963 ± 182 mm yr−1 for all paleosols
(CIA-K). Field observations and MAP proxies suggest that Karungu was significantly drier than today, consistent
with the associated faunal assemblage, and likely resulted in a significantly smaller Lake Victoria during the late
Pleistocene. Rainfall reduction and associated grassland expansion may have facilitated human and faunal dispersals
across equatorial East Africa.

The cichlid fishes of the East African Great Lakes are the largest extant vertebrate radiation identified to date. These lakes and their surrounding waters support over 2,000 species of cichlid fish, many of which are descended from a single common ancestor within the past 10 Ma. The extraordinary East African cichlid diversity is intricately linked to the highly variable geologic and paleoclimatic history of this region. Greater than 10 Ma, the western arm of the East African rift system began to separate, thereby creating a series of rift basins that ...

Olduvai Gorge, Tanzania contains a rich record of Pleistocene paleoclimate and paleoenvironment, as well as an abundance of paleontological and archaeological data. The 2.2 Ma of volcaniclastic infill can be divided into time-slices using dated tuffs. Sediments were deposited in a semi-arid, closed rift basin containing a shallow salineealkaline lake until w1.75 Ma. Four trenches in uppermost Bed I sample a w20 ka time-slice between Ng'eju Tuff (base, 1.818 AE 0.006 Ma) and Tuff IF (top, 1.803 AE 0.002 Ma). They form a w1 km transect of the lake margin flat that contains both stacked and cumulative paleosols that are interpreted as a heterogeneous paleocatena. Closer to the lake, paleosols are thinner, vertically stacked, and separated by thin tuffs or tufa. Further from the lake margin, there is additional volcaniclastic input, and paleosols are thicker and cumulative. Macroscale and micromorphological features identify these clay-rich paleosols as paleo-Vertisols. Abundant pedogenic slickensides and a variety of ped shapes were observed in the field, as well as micro-ped structures and stress cutans in thin section. Although weakly developed, these paleo-Vertisols also have distinct horizons defined by soil color changes, differing ped shapes, and bulk geochemistry and are indicative of monsoonal precipitation seasonality.

Olduvai Gorge, Tanzania is known for its fossil and cultural record of early hominins. The archaeological records are typically found within pedogenically modified sediments, thus the interpretation of paleosols provides important paleoenvironmental context information. The Gorge contains a rich and diverse record of paleosols that vary spatially and temporally, however the stratigraphy can be divided into time slices using dated tuffs and studied in a paleolandscape context. Sediments were deposited in a semi-arid closed rift basin containing paleo Lake Olduvai, with volcanoes supplying volcaniclastic material to an alluvial fan system on the eastern side and quartzofeldspathic fluvial sediments derived from weathered basement rocks on the western side. The shallow saline-alkaline lake in the basin center and groundwater levels in the surrounding uplands fluctuated with Milankovitch-driven climatic (precession) cycles of w20,000 years. The rift basin paleolandscape (at w1.8 Ma) is reconstructed using sedimentology, stratigraphy and paleopedology. Standard field descriptions of physical and biogenic paleosol structures are combined with stable isotope ratios of carbonates, and whole rock geochemistry of sediments, to reveal diversity of paleosols within the basin. There are at least three distinct types of paleosols that record a paleocatena related to both landscape and drainage differences. Red tephra-rich Andisols developed on the volcaniclastic alluvial fan to the east of the paleolake, calcium-carbonate-rich, silty Aridisols developed on the interfluves and floodplain of the fluvial plain on the west, whereas clay-rich paleosols (Vertisols) developed on the lake margin and lake in the center of basin. Variances in geomorphology, depositional environment, parent material, and depth to the water table are reflected in the development of distinctly different soil types that can provide key data needed for high-resolution reconstruction of the landscape known to be utilized by early hominins.

The multi component FLK North archaeological site was discovered over 50 years ago, and its interpretation has been highly controversial since. Explanations of the dense bone and stone tool accumulation range from a site on a featureless lake margin that is dominantly anthropogenic in origin to a site near a freshwater wetland that is dominated by carnivore activity (e.g. felids and hyenas). FLK North occurs stratigraphically between the Ng'eju Tuff (1.818 AE 0.006 Ma) and Tuff IF (1.803 AE 0.002 Ma), and is composed of 9 distinct levels. Analysis of newly recovered fossil bones and artifacts has shown that the bones of large animals are largely the product of felid hunting and feeding behavior, followed by hyena gnawing and breakage of some bones. The expanded sample of felid prey remains is significant for understanding the contrasts between the mortality profiles of fossil assemblages produced by carnivores and those produced by hominins. Geologic mapping in the environs of the site has revealed rich sedimentological and paleoecological records and a thin, but persistent tuff (here named Kidogo Tuff) that is w1.5 m below Tuff IF. Electron microprobe analyses of the tuff mineralogy revealed a unique geochemical fingerprint that permits its use for correlation of widely separated outcrops and facilitates the high resolution reconstruction of the landscape at the time of site formation. The 9 archaeological levels comprise a relatively continuous record through a Milankovitch precession cycle (dry-wet-dry). As the lake receded into the central basin during the dry part of the cycle, surface water supplies dwindled and groundwater-fed springs and wetlands became the dominant freshwater supply. The FLK North archaeological record essentially ended when level 1 was covered with 0.4 m of Tuff IF in a violent volcanic eruption of nearby Mt. Olmoti. However, the overlying Bed II sediments contain scattered archaeological material and a freshwater carbonate deposit that is similar to those found associated with other Bed II archaeological sites, e.g. VEK, HWK and HWKE. The recognition of the ecological association of springs, wetlands and archaeological remains is a powerful predictive tool for locating new archaeological sites in this region that is known for hominin remains.

The multi component FLK North archaeological site was discovered over 50 years ago, and its interpretation has been highly controversial since. Explanations of the dense bone and stone tool accumulation range from a site on a featureless lake margin that is dominantly anthropogenic in origin to a site near a freshwater wetland that is dominated by carnivore activity (e.g. felids and hyenas). FLK North occurs stratigraphically between the Ng'eju Tuff (1.818 AE 0.006 Ma) and Tuff IF (1.803 AE 0.002 Ma), and is composed of 9 distinct levels. Analysis of newly recovered fossil bones and artifacts has shown that the bones of large animals are largely the product of felid hunting and feeding behavior, followed by hyena gnawing and breakage of some bones. The expanded sample of felid prey remains is significant for understanding the contrasts between the mortality profiles of fossil assemblages produced by carnivores and those produced by hominins. Geologic mapping in the environs of the site has revealed rich sedimentological and paleoecological records and a thin, but persistent tuff (here named Kidogo Tuff) that is w1.5 m below Tuff IF. Electron microprobe analyses of the tuff mineralogy revealed a unique geochemical fingerprint that permits its use for correlation of widely separated outcrops and facilitates the high resolution reconstruction of the landscape at the time of site formation. The 9 archaeological levels comprise a relatively continuous record through a Milankovitch precession cycle (dry-wet-dry). As the lake receded into the central basin during the dry part of the cycle, surface water supplies dwindled and groundwater-fed springs and wetlands became the dominant freshwater supply. The FLK North archaeological record essentially ended when level 1 was covered with 0.4 m of Tuff IF in a violent volcanic eruption of nearby Mt. Olmoti. However, the overlying Bed II sediments contain scattered archaeological material and a freshwater carbonate deposit that is similar to those found associated with other Bed II archaeological sites, e.g. VEK, HWK and HWKE. The recognition of the ecological association of springs, wetlands and archaeological remains is a powerful predictive tool for locating new archaeological sites in this region that is known for hominin remains.

The opening and closing of the equatorial East African forest belt during the Quaternary is thought to have influenced the biogeographic histories of early modern humans and fauna, although precise details are scarce due to a lack of archaeological and paleontological records associated with paleoenvironmental data. With this in mind, we provide a description and paleoenvironmental reconstruction of the Late Pleistocene Middle Stone Age (MSA) artifact-and fossil-bearing sediments from Karungu, located along the shores of Lake Victoria in western Kenya. Artifacts recovered from surveys and controlled excavations are typologically MSA and include points, blades, and Levallois flakes and cores, as well as obsidian flakes similar in geochemical composition to documented sources near Lake Naivasha (250 km east). A combination of sedimentological, paleontological, and stable isotopic evidence indicates a semi-arid environment characterized by seasonal precipitation and the dominance of C 4 grasslands, likely associated with a substantial reduction in Lake Victoria. The well-preserved fossil assemblage indicates that these conditions are associated with the convergence of historically allopatric ungulates from north and south of the equator, in agreement with predictions from genetic observations. Analysis of the East African MSA record reveals previously unrecognized northesouth variation in assemblage composition that is consistent with episodes of population fragmentation during phases of limited dispersal potential. The grassland-associated MSA assemblages from Karungu and nearby Rusinga Island are characterized by a combination of artifact types that is more typical of northern sites. This may reflect the dispersal of behavioral repertoiresdand perhaps human populationsdduring a paleoenvironmental phase dominated by grasslands.

The multi component FLK North archaeological site was discovered over 50 years ago, and its interpretation has been highly controversial since. Explanations of the dense bone and stone tool accumulation range from a site on a featureless lake margin that is dominantly anthropogenic in origin to a site near a freshwater wetland that is dominated by carnivore activity (e.g. felids and hyenas). FLK North occurs stratigraphically between the Ng'eju Tuff (1.818 AE 0.006 Ma) and Tuff IF (1.803 AE 0.002 Ma), and is composed of 9 distinct levels. Analysis of newly recovered fossil bones and artifacts has shown that the bones of large animals are largely the product of felid hunting and feeding behavior, followed by hyena gnawing and breakage of some bones. The expanded sample of felid prey remains is significant for understanding the contrasts between the mortality profiles of fossil assemblages produced by carnivores and those produced by hominins. Geologic mapping in the environs of the site has revealed rich sedimentological and paleoecological records and a thin, but persistent tuff (here named Kidogo Tuff) that is w1.5 m below Tuff IF. Electron microprobe analyses of the tuff mineralogy revealed a unique geochemical fingerprint that permits its use for correlation of widely separated outcrops and facilitates the high resolution reconstruction of the landscape at the time of site formation. The 9 archaeological levels comprise a relatively continuous record through a Milankovitch precession cycle (dry-wet-dry). As the lake receded into the central basin during the dry part of the cycle, surface water supplies dwindled and groundwater-fed springs and wetlands became the dominant freshwater supply. The FLK North archaeological record essentially ended when level 1 was covered with 0.4 m of Tuff IF in a violent volcanic eruption of nearby Mt. Olmoti. However, the overlying Bed II sediments contain scattered archaeological material and a freshwater carbonate deposit that is similar to those found associated with other Bed II archaeological sites, e.g. VEK, HWK and HWKE. The recognition of the ecological association of springs, wetlands and archaeological remains is a powerful predictive tool for locating new archaeological sites in this region that is known for hominin remains.

Olduvai Gorge, Tanzania is known for its fossil and cultural record of early hominins. The archaeological records are typically found within pedogenically modified sediments, thus the interpretation of paleosols provides important paleoenvironmental context information. The Gorge contains a rich and diverse record of paleosols that vary spatially and temporally, however the stratigraphy can be divided into time slices using dated tuffs and studied in a paleolandscape context. Sediments were deposited in a semi-arid closed rift basin containing paleo Lake Olduvai, with volcanoes supplying volcaniclastic material to an alluvial fan system on the eastern side and quartzofeldspathic fluvial sediments derived from weathered basement rocks on the western side. The shallow saline-alkaline lake in the basin center and groundwater levels in the surrounding uplands fluctuated with Milankovitch-driven climatic (precession) cycles of w20,000 years. The rift basin paleolandscape (at w1.8 Ma) is reconstructed using sedimentology, stratigraphy and paleopedology. Standard field descriptions of physical and biogenic paleosol structures are combined with stable isotope ratios of carbonates, and whole rock geochemistry of sediments, to reveal diversity of paleosols within the basin. There are at least three distinct types of paleosols that record a paleocatena related to both landscape and drainage differences. Red tephra-rich Andisols developed on the volcaniclastic alluvial fan to the east of the paleolake, calcium-carbonate-rich, silty Aridisols developed on the interfluves and floodplain of the fluvial plain on the west, whereas clay-rich paleosols (Vertisols) developed on the lake margin and lake in the center of basin. Variances in geo-morphology, depositional environment, parent material, and depth to the water table are reflected in the development of distinctly different soil types that can provide key data needed for high-resolution reconstruction of the landscape known to be utilized by early hominins.

Here we report our recent discovery of a new obsidian source in central Armenia. Using portable XRF, we were able to chemically identify Ptghni obsidian as a previously unrecognized source on the same day that we first encountered it during our field surveys. Obsidian was found in alluvial-lacustrine sediments exposed within the Hrazdan Gorge, where it had been deposited after having eroded from an upstream source. These sediments were covered by mafic lavas and later exposed by downcutting of the Hrazdan River. Based on the stratigraphy of the gorge, the lava flows -- and, therefore, the sediments sandwiched between them -- predate 441 ka. The composition of Ptghni obsidian does not fit into the chemical trends of known sources in the Gegham and Tsaghkunyats ranges, so its precise volcanic origin remains unknown. Comparisons to unidentified artifacts in the literature revealed no matches, but obsidian sourcing work in Armenia has largely focused on the Holocene, when the Ptghni source might no longer have been accessible. The discovery of Ptghni obsidian is crucial for research into early hominin expansions given that it was an obsidian source available for use as toolstone by hominins during the Early and/or Middle Pleistocene.

A B S T R A C T Here we report our recent discovery of a new obsidian source in central Armenia. Using portable XRF, we were able to chemically identify " Ptghni " obsidian as a previously unrecognized source on the same day that we first encountered it during our field surveys. Obsidian was found in alluvial-lacustrine sediments exposed within the Hrazdan Gorge, where it had been deposited after having eroded from an upstream source. These sediments were covered by mafic lavas and later exposed by downcutting of the Hrazdan River. Based on the stratigraphy of the gorge, the lava flows – and, therefore, the sediments sandwiched between them – predate 441 ka. The composition of Ptghni obsidian does not fit into the chemical trends of known sources in the Gegham and Tsaghkunyats ranges, so its precise volcanic origin remains unknown. Comparisons to unidentified artifacts in the literature revealed no matches, but obsidian sourcing work in Armenia has largely focused on the Holocene, when the Ptghni source might no longer have been accessible. The discovery of Ptghni obsidian is crucial for research into early hominin expansions given that it was an obsidian source available for use as toolstone by hominins during the Early and/or Middle Pleistocene.