paleosol carbonates from the omo group isotopic records of local and regional environmental change in east africa abstract pliocene and pleistocene sedimentary rocks from the omo turkana basin in east africa are well known for fossil and archeological evidence of human evolution and provide a unique opportunity to study four million years of environmental change in a rift basin this study uses carbon and oxygen isotope ratios of pedogenic carbonates to examine environmental variability across 5000 km 2 within the omo turkana basin an expanded isotopic dataset including the first isotopic data on pedogenic carbonates from the shungura formation and new data from the nachukui and koobi fora formations is compared to published isotopic records from both the omo turkana basin and the lower awash basin ethiopia regionally the carbon isotope record indicates a steady increase of c 4 vegetation in floodplain environments for the past 4 million years the oxygen isotopic record indicates that the isotopic composition of rainfall was depleted in 18 o relative to today s waters and that both basins likely received more rainfall in the pliocene than today a shift to higher 18 o values in paleosol carbonate after 2 ma in the omo turkana basin but not in the lower awash basin suggests that the ecology and hydrology in these two rift basins were influenced by different climatic regimes in addition to regional trends pedogenic carbonates sampled from different parts of the basin show that the distribution of c 4 vegetation and soil water 18 o values varied with proximity to the axial river system and specifically that c 3 vegetation was more dominant in soils of the shungura formation compared with coeval sediments downstream in the nachukui and koobi fora formations this large isotopic dataset from pedogenic carbonates provides the opportunity to examine how terrestrial systems responded to global climate change during the last 4 million years from both local and regional perspectives the isotopic data indicate that local basin and climate dynamics strongly influenced the impact of large scale environmental change in east african rift basins

precessional forcing of lacustrine sedimentation in the late cenozoic chemeron basin central kenya rift and calibration of the gauss matuyama boundary the fluviolacustrine sedimentary sequence of the chemeron formation exposed in the barsemoi river drainage tugen hills kenya contains a package of five successive diatomite fluvial cycles that record the periodic development of freshwater lakes within the axial portion of the central kenya rift the overwhelming abundance in the diatomite of planktonic species of the genera aulacoseira and stephanodiscus and the virtual absence of benthic littoral diatoms and detrital material indicate areally extensive deep lake systems a paleomagnetic reversal stratigraphy has been determined and chronostratigraphic tie points established by 40 ar 39 ar dating of intercalated tuffs the sequence spans the interval 3 1 2 35 ma and bears a detailed record of the gauss matuyama paleomagnetic transition the 40 ar 39 ar age for this boundary of 2 589 0 003 ma can be adjusted to concordance with the astronomical polarity time scale apts on the basis of an independent calibration to 2 610 ma 29 kyr older than the previous apts age the diatomites recur at an orbital precessional interval of 23 kyr and are centered on a 400 kyr eccentricity maximum it is concluded that these diatomite fluvial cycles reflect a narrow interval of orbitally forced wet dry climatic conditions that may be expressed regionally across east africa the timing of the lacustrine pulses relative to predicted insolation models favors origination of moisture from the northern africa monsoon rather than local circulation driven by direct equatorial insolation this moisture event at 2 7 2 55 ma and later east african episodes at 1 9 1 7 and 1 1 0 9 ma are approximately coincident with major global climatic and oceanographic events

east african lake evidence for pliocene millennial scale climate variability late cenozoic climate history in africa was punctuated by episodes of variability characterized by the appearance and disappearance of large freshwater lakes within the east african rift valley in the baringo bogoria basin a well dated sequence of diatomites and fluviolacustrine sediments documents the precessionally forced cycling of an extensive lake system between 2 70 ma and 2 55 ma one diatomite unit was studied using the oxygen isotope composition of diatom silica combined with x ray fluorescence spectrometry and taxonomic assemblage changes to explore the nature of climate variability during this interval data reveal a rapid onset and gradual decline of deepwater lake conditions which exhibit millennial scale cyclicity of 1400 1700 yr similar to late quaternary dansgaard oeschger events these cycles are thought to reflect enhanced precipitation coincident with increased monsoonal strength suggesting the existence of a teleconnection between the high latitudes and east africa during this period such climatic variability could have affected faunal and floral evolution at the time

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

sedimentology and stable isotopes from a lacustrine to palustrine limestone deposited in an arid setting climatic and tectonic factors miocene pliocene opache formation atacama desert chile abstract field relations petrography gis and geochemistry of a late miocene pliocene limestone the opache formation calama basin atacama desert chile shows that depositional facies diagenetic histories and isotopes differ from eastern to western parts of the basin we recognize two facies lacustrine characterized by ostracod diatom mudstone and wackestone and palustrine characterized by both shallow water and pedogenic features gis analysis of the basin topography reveals an intrabasinal low in the eastern area and steeper hydrological gradients to the west with the calama constriction restricting flow between east and west petrography and geochemical results confirm that the calama constriction influenced depositional parameters ponding groundwater to the east forming a shallow lake and creating palustrine conditions to the west our analyses indicate that lake waters were less enriched in 13c or 18o than palustrine waters even though petrologic studies show that the lacustrine carbonates have a complex diagenetic history derived from groundwater rich in dissolved minerals this seemingly contrary observation can be reconciled if an important source of water for the western carbonates was sourced from the pacific ocean and was less evolved whereas eastern limestones precipitated from water which had become depleted in 18o during transport from the east today moisture from the pacific very rarely if ever reaches inland as far as calama indicating that during the late miocene mid pliocene breakdown in the temperature inversion due to weakened or absent upwelling in the cold coastal pacific current allowed moisture from the pacific to reach inland this changing atmospheric circulation pattern may have also affected upper level airflow that today blocks eastern sourced moisture from crossing the andes allowing it to reach farther westward into the atacama region during the late miocene pliocene together these moisture sources were sufficient to produce carbonate rich palustrine and lacustrine environments in the calama basin

chemical sedimentology and paleoenvironmental history of lake olduvai a pliocene lake in northern tanzania lake olduvai was a saline highly alkaline closed basin lake in which lacustrine sediments of bed i and lower bed ii of olduvai gorge were deposited between ca 1 92 and 1 70 ma the lake consisted of a lacustrine area the central basin cb surrounded by lake margin terrain that was alternately flooded and dried the lacustrine deposits consist largely of authigenic clay and carbonate minerals zeolites k feldspar chert and pyrite claystones of the cb and most of the eastern lake margin elm terrain consist chiefly of mg rich authigenic illite smectite and interlayered illite smectite i s these clays were formed penecontemporaneously with detrital clay deposition by interaction of the detrital clays with the saline highly alkaline water the lake olduvai clays average 65 70 mg 2 sio 2 and alkali ions from lake water and the remaining 30 35 is detrital clay lacustrine clays of the elm indicate that this area was flooded by saline water for substantial periods of time hominids occupied the elm at times of lower lake levels when the clays were dried calcite is the most abundant carbonate mineral and occurs chiefly as sand size euhedral crystals dispersed in claystone and less commonly as calcite crystal limestones and nodules the sand size calcite crystals were formed diagenetically at shallow depths possibly from a gaylussite and or micritic calcium carbonate precursor dolomite occurs chiefly in the form of dolostones some of which are probably of replacement origin the oxygen isotope composition of lake water and pore fluid of the cb varied over 11 as determined from calculated delta 18 o h 2 o values of authigenic minerals clay minerals were formed chiefly in the more saline waters sand size calcite crystals were generated mostly from less saline pore fluids and limestone nodules were formed chiefly from dilute pore fluid dolostones were formed from fluids of varying salinity hydrogeology of the central basin was complex and postdepositional fluid movements are documented by differing delta 18 o h 2 o values for different authigenic minerals of the same samples pore fluids moved within the lake deposits for a considerable period of time after deposition as shown by 18 o values of quartz and k feldspar formed at different times downward flow of lacustrine fluids is indicated by zeolitic alteration of the underlying tuffaceous alluvial deposits lake olduvai became overall shallower during the deposition of bed i and the subaerial exposure increased leading to occasional playa conditions these changes very likely resulted from increasing aridity and tectonic activity the lake that deposited lower bed ii was larger than that responsible for upper bed i and episodes of wetter climate alternated with drier periods in which salinity and probably temperatures were higher than in the bed i lake

a spring and wooded habitat at flk zinj and their relevance to origins of human behavior the 1959 discovery of the hominin fossil zinjanthropus boisei brought the world s attention to the rich records at olduvai gorge tanzania subsequent excavations of archaeological level 22 flk zinj bed i uncovered remains of homo habilis and a high density collection of fossils and oldowan stone tools the occurrence of this unusual collection of bones and tools at this specific location has been controversial for decades we present paleoecological data that provide new insights into the origin of flk zinj our recent excavations 200 m north of the site uncovered a 0 5 m thick tufa mound draped by tuff ic in the same stratigraphic horizon as level 22 stable isotope analyses indicate that the carbonates were deposited by a freshwater spring phytolith analysis of the waxy clay under tuff ic revealed abundant woody dicotyledon and palm phytoliths indicating that the site was wooded to densely wooded the time equivalency and close physical proximity of the two environments indicate the two are related this study has provided the first documented evidence of springs in bed i and these data have important implications for the interpretation of hominin behavior in meat acquisition and the ongoing debate on scavenging versus hunting

lake level changes and hominin occupations in the arid turkana basin during volcanic closure of the omo river outflows to the indian ocean in the east african rift the western margin of lake turkana northern kenya exposes mio plio pleistocene lake sediments with dated volcanic horizons constraining basin dynamics at the astronomical time scale since the late pliocene coastal archaeological sites have formed within the lacustrine dynamics here lake levels are reconstructed from 2 4 to 1 7 ma using sedimentary facies and water depth controlled sediment association the lacustrine stratigraphy is measured with a total station and cyclostratigraphy is derived from tephrochronology the water depths are evaluated from paleochemical properties of lake sediments analyzed by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry our reconstruction highlights that lake turkana rose during 100 ka insolation eccentricity maxima periods in response to higher monsoonal inputs of the omo river however lake turkana also expanded through an insolation minimum at 2 17 1 95 ma this asynchronous lake phase coincides with volcanic closure of the omo river and lake turkana outflow sill to the east and the indian ocean an archaeological hiatus occurs during this endorheic lake phase and alkalinity increases at the beginning of the hiatus the lake rose again during insolation eccentricity maxima at 1 9 1 7 ma and a new outflow sill opened to the west and the nile basin hominin coastal occupations return during this exorheic freshwater lake phase

response of the east african climate to orbital forcing during the last interglacial 130 117 ka and the early last glacial 117 60 ka variations in the temporal and spatial distribution of solar radiation caused by changes in earth9s orbit provide a partial explanation for observed long term fluctuations in african lake levels the understanding of causal links between insolation changes and lake level fluctuations is essential for the design of models predicting future changes in the hydrological budgets and water supply in africa here we present a record of climate change in east africa between 175 and 60 ka this time span includes the last interglacial the eemian 130 117 ka which may provide the closest analogue to the present interglacial assessments of the nature and timing of east african climate changes are based on lake level fluctuations of lake naivasha kenya inferred from sediment characteristics diatom assemblages and 40 ar 39 ar dating our results show dramatic alternation between deep freshwater and shallow highly alkaline lake conditions the lake naivasha record demonstrates that periods of increased humidity in east africa mainly follow precessional insolation forcing in spring causing more intense april may rains every 23 k y

facies model of a semiarid freshwater wetland olduvai gorge tanzania the sedimentology and stratigraphy of a freshwater wet land in early pleistocene 1 75 ma volcaniclastic deposits olduvai gorge tanzania are characterized using texture mineralogy micro fossils and stratigraphic description to create a depositional facies model the freshwater wetland was located on the margin of a semi arid closed basin containing a playa lake the lake margin deposits are dominated by two distinct lithologies waxy claystones and earthy sediments waxy sediments are olive green dense claystones that con tain authigenic minerals such as trona and represent a fluctuating saline alkaline lake hay 1976 earthy sediments are beige friable siltstones that contain siliceous microfossils bone fragments and minor pebbles they represent the freshwater wetland microfossils from the earthy sediments and diatomites indicate freshwater marsh biota with some rare salt tolerant species associated lithofacies are diatomite carbonate and sandstone interpretation of vertical and lateral lithofacies variations in the 2 km 2 wetland based on 50 excavations identified seven distinct sub environments spring deposits perennial marsh pool ephemeral wet land fringing wetland wetland channel and ephemeral stream the stratigraphic sequence estimated to represent an 40 50 kyr long interval indicates that persistent 10 3 yr wet periods prevailed dur ing the deposition of thick waxy clays when the lake expanded and flooded the wetlands and equally long intervening dry periods caused the lake to contract allowing the flourishing of wetlands and accretion of earthy sediment the lithofacies associations in the olduvai paleo wetland provides an important first step in the development of a de positional environmental model for freshwater wetlands that can be tested elsewhere particularly in arid and semiarid settings

freshwater limestone in an arid rift basin a goldilocks effect abstract the olduvai basin 3 s situated just west of the east african rift system in northern tanzania contains a two million year record of paleoclimate and paleoenvironmental change as well as a rich archive of vertebrate paleontology including hominins milankovitch precession cycles 20 kyr regulate the mean annual precipitation 250 700 mm yr and the 2500 mm yr evapotranspiration results in a negative hydrologic balance despite persistent aridity extensive deposits of freshwater limestone punctuate the stratigraphic record between 2 and 1 ma lake olduvai occupied the basin and its sediments are a proxy for climate driven cycles three limestones 1 84 1 80 and 1 36 ma in age which formed within lake margin floodplains adjacent to the lake were studied to determine their depositional environment using field relations sedimentary structures fossils petrography and stable isotope and major element geochemistry the three limestones are similar in that they contain peloidal micrite siliciclastic detrital grains and rhizoconcretions abundant faunal remains gastropods ostracods charaphytes and fish indicate that ponded water was relatively fresh and alkaline geochemical and stable isotope data indicate two types of groundwater sourced carbonate producing waters a deeper sourced fluid that was enriched in iron and manganese due to extended water rock interactions and a shallower groundwater that traveled through alluvial fan deposits regional faults tapped the deeper groundwater producing carbonate at spring sites while seeps associated with basinward changes in alluvial fan slopes drew on shallower groundwater sources isotope compositions indicate that fault related waters experienced some evaporation as water moved away from the spring sites while compositions of the seep related carbonate remained relatively constant pedogenic alteration and meteoric calcite cementation affected the carbonate when the spring and seep sites dried out secondary strontium rich dolomite precipitated within the limestones during burial under paleo lake olduvai sediments and fluids during periods of lake expansion integrating these data within the geological context of regional paleoclimatic and local environmental change indicates that the freshwater carbonates formed periodically when the conditions were just right i e a goldilocks effect carbonates near the basin center formed from groundwater flowing under a hydraulic head from faults or fractures during the falling limbs of milankovitch cycles when the lake was in recession carbonates near the basin margin formed from an increased rate of groundwater seepage that occurred only on the rising limbs of cycles in both contexts the continuous flow of groundwater with surface evaporation and co2 degassing optimizes the conditions for limestone formation in this arid environment these results help explain the formation of freshwater limestones in the rift basin link the carbonates to specific portions of milankovitch cycles and document that localized sources of potable water were present for use by hominins in olduvai gorge during an important period of human evolution

paleoenvironmental reconstruction of a paleosol catena the zinj archeological level olduvai gorge tanzania abstract paleosols record paleoclimatic processes in the earth s critical zone and are archives of ancient landscapes associated with archeological sites detailed field micromorphologic and bulk geochemical analysis of paleosols were conducted near four sites at olduvai gorge tanzania within the same stratigraphic horizon as the zinjanthropus paranthropus boisei archeological site paleosols are thin

seismic imaging of the olduvai basin tanzania abstract a 5 6 km long line of refraction and reflection seismic data spanning the pliocene pleistocene fill of the olduvai basin tanzania is presented the line is oriented along a northwest southeast profile through the position of olduvai gorge coring project ogcp borehole 2a our aims are to 1 delineate the geometry of the basin floor by tracing bedrock topography of the metaquartzitic and gneissic basement 2 map synsedimentary normal faults and trace individual strata at depth and 3 provide context for the sequence observed in ogcp cores results with refraction tomography and poststack migration show that the maximum basin depth is around 405 m 25 m in the deepest portion which quadruples the thickness of the basin fill previously known from outcrops variations in seismic velocities show the positions of lower density lake claystones and higher density well cemented sedimentary sequences the bed i basalt lava is a prominent marker in the refraction seismic results bottom most sediments are dated to 2 2 ma near where borehole 2a bottoms out at the depth of 245 m however the seismic line shows that the basin fill reaches a maximum stratigraphic thickness of around 380 m deep at borehole 2a in the western basin where the subsidence was greatest this further suggests that potential hominin palaeoenvironments were available and preserved within the basin fill possibly as far back as around 4 ma applying a temporal extrapolation using the average sediment accretion rate

paleovegetation changes accompanying the evolution of a riverine system at the bk paleoanthropological site upper bed ii olduvai gorge tanzania abstract paleovegetation studies are essential to ecologically frame hominin evolution the analysis of the phytolith content of 22 paleosol samples collected along the vertical sequence of the channel containing the bk bell s korongo archaeological levels provided evidence of the paleovegetation that accompanied the evolution of the riverine system that formed this site 1 353 million years ago when climate was particularly arid the analysis reveals the abundance of forest indicator phytoliths 46 to 92 of the assemblages rare grass silica short cells and sedges phytoliths up to 15 of assemblages and palms up to 10 of the phytolith assemblages the vegetation of the bk fluvial system was therefore characterized by abundant woody plants it did not vary significantly diachronically in the period of time under scrutiny the alluvial paleovegetation corresponds well to the fluvial dynamic that formed bk including the presence of sterile samples recovered in areas where the water traction changed the soils frequently this spot of dense paleovegetation together with the fluvial watercourse in a paleolandscape likely dominated by sparse open vegetation could have been attractive seasonally for animals and hominins

paleoclimatic and paleoenvironmental framework of flk north archaeological site olduvai gorge tanzania abstract 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 0 006 ma and tuff if 1 803 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 1 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

orbital rhythms monsoons and playa lake response olduvai basin equatorial east africa ca 1 85 1 74 ma the lithostratigraphy at the pliocene pleistocene boundary exposed in olduvai gorge east africa was used to determine the duration and cause of climate variations wet dry periods the area has rich paleontological and archaeological records and the time interval is a critical period in human evolution five episodes of lake expansion and contraction can be interpreted from a stratigraphic interval defined by tuffs between ca 1 85 and 1 74 ma suggesting precession controlled cyclicity the geochronometry of the sequence was determined using the paleomagnetic record top of subchron cn2 1 785 ma the ages of two tuffs tuff ib and tuff if and sedimentation rates insolation w m 2 variations calculated as a function of eccentricity and precession predict five cycles of varying insolation 10 between 2 0 and 1 5 ma rainfall would have increased by one third between dry and wet portions of each 21 000 k y cycle this study represents the first dated terrestrial record at the pliocene pleistocene boundary with sufficient resolution to link lake cycles a climate proxy to astronomic forcing the wet dry climate pendulum may have been a factor in the natural selection processes of hominin evolution and the first wave of hominin migrations out of africa 1 8 ma

sedimentary geology and human origins a fresh look at olduvai gorge tanzania abstract recent field work at olduvai gorge tanzania using sedimentary geology in particular high resolution paleoenvironmental reconstruction and isotope geochemistry has revealed that freshwater was in proximity to a number of the rich fossil sites in beds i and ii 2 0 1 0 ma this paper presents the first geological evidence for springs associated with archaeological sites in this semiarid rift basin the springs appear to be limited to a small area within the basin and were likely connected to faults that acted as conduits for groundwater tufas associated with ten archaeological sites have stable isotope signatures occurring in a cluster bounded by 18o ratios from 6 to 1 and the 13c ratios from 5 to 2 the 18o values cluster around 4 that of precipitation in the region indicating a meteoric source the longevity of the spring record reflects a hydrologic system that apparently persisted for hundreds of thousands of years previous landscape reconstructions depicted the archaeological sites on the lake margin of paleo lake olduvai as an alkaline playa the discovery of springs at or near the archaeological sites provides fresh insights for interpreting hominin behavior during this key time in evolution with respect to procuring food water and materials for stone tools as well as hominin adaptation to climate change and paleoenvironmental change the idea that spring deposits may be in proximity to archaeological sites could lead to discovery of new sites at other hominin fossil localities in the east african rift system ears

plio pleistocene marine continental correlation using habitat indicators from olduvai gorge tanzania abstract reconstructions of plio pleistocene habitats and lake levels from a brief interval 200 000 yr of hominid bearing sediments from bed i and lower bed ii olduvai gorge tanzania are for the first time integrated with climatic data from the deep sea in order to examine the effect of largescale climatic events in east africa the period of densely vegetated habitats and wet conditions at olduval at 1 82 myr shows a best fit with a period of northern hemisphere warming as evidenced by oxygen isotopes from deep sea core v28 239 from the western pacific this environmental response is similar to that witnessed in east africa during the period of warming climates associated with deglaciation at 10 000 8 000 yr

an astronomically tuned climate framework for hominins in the turkana basin understanding the influence of orbital climate cycles on hominin evolution remains a key challenge in paleoanthropology the two major unresolved issues are the absence of a climate proxy yielding highresolution b20 kyr terrestrial climate records and the lack of age control on hominin fossil occurrences at sufficiently high resolution here we present a novel climate proxy strontium isotope ratios 87sr 86sr of lacustrine fish fossils from the turkana basin that solves these issues by recording orbitally forced variation in summer monsoon intensity over the ethiopian highlands we successfully applied the climate proxy to a 150 kyr time interval of 2 million year old paleolake deposits containing hominin fossils existing age control of the studied interval was improved by a new magnetostratigraphic record precisely locating the base of the olduvai chron c2n near the bottom of the sequence spectral analysis demonstrates that 87sr 86sr variability is primarily determined by precession which enables us to place hominin fossils in an astronomically tuned climate framework the sr climate proxy is potentially applicable to all homininbearing lake deposits in the turkana basin ranging in age from 4 2 to 0 8 million years ago ma our results demonstrate that between 2 and 1 85 ma the turkana basin remained well watered and inhabited by hominins even during periods of precession maxima when summer monsoon intensity was lowest this is in contrast to other basins in the east african rift system ears that were impacted heavily by precessionforced droughts we hypothesize that during lake phases the turkana basin was an aridity refugium for permanent water dependent fauna including hominins over the precessional climate cycles

biogeochemical evidence from ogcp core 2a sediments for environmental changes preceding deposition of tuff ib and climatic transitions in upper bed i of the olduvai basin abstract sediment cores recovered by the olduvai gorge coring project ogcp in 2014 afford the opportunity to examine the coupling of biogeochemical evidence for climatic and environmental change within the context of hominin evolution at this renowned east african locality investigations of elemental total organic carbon toc or corg wt carbon to nitrogen ratio c n molecular source specific biomarkers and isotopic 13corg 2hnc31 compositions of organic matter provide evidence for temporal changes in sedimentary materials derived from terrestrial plants c3 c4 and aquatic producers algae sponges cyanobacteria and in precipitation the 13 kyr record of upper bed i immediately preceding tuff ib extends high resolution stratigraphic profiles of precession scale alternations of wetter and drier conditions to encompass the entire interval from the bed i basalt to tuff ib the second wetter interval designated w2 records local influences on climate and water supply consistent with evidence for discrete sediment sources based its physical properties e g gamma radiation magnetic susceptibility compared with the overall sequence the 13ctoc values for wetter interval w2 reveal two millennial scale 2 5 kyr drier episodes followed by a shift in the dominance of c3 over c4 plants accompanying the transition to a drier climate d3 moreover biogeochemical data for upper bed i show that changes from drier to wetter conditions occur more rapidly 900 yr than wetter to drier transitions 2 6 kyr based on interpolated ages in addition biomarker profiles indicate that aquatic plants primarily algae and macrophytes may have been subject to more profound and faster fluctuations than variations in terrestrial vegetation expressed in terms of the relative proportions of woodland and grassland settings thus environmental and climatic changes not only influenced the availability of resources of food and shelter for hominins within the olduvai region but also led to their variation on centennial to millennial to precessional timescales

elastic wave attenuation in fluid saturated berea sandstone in a previous publication o hara 1985 i presented detailed measurements on the attenuation of elastic waves in fluid saturated berea sandstone these measurements were used in a systematic empirical study of the frequency dependence of attenuation as a function of external pressure applied to the sandstone pore fluid pressure and the saturated sandstone temperature two pore fluids were used in the study a brine solution and n heptane i measured the attenuation of the extensional and torsional rod modes of cylindrical specimens of the sandstone at identical conditions of pressure and temperature for each of the two fluids

paleopedology and paleohydrology of a volcaniclastic paleosol interval implications for early pleistocene stratigraphy and paleoclimate record olduvai gorge tanzania abstract a cumulative red paleosol interval developed on volcaniclastic parent material under semiarid conditions in olduvai gorge tanzania it contains a complex history of pedogenesis that was affected by 1 episodic pyroclastic and debris fan processes and 2 episodic expansions and contractions of an adjacent alkaline lake and the associated fluctuations in the water table the paleosol interval is 130 320 cm thick represents 25 ka of the 50 kyr duration of lowermost bed ii and is defined by early pleistocene 1 75 ma tuffs if and iia the paleosol interval records a paleocatena related to both landscape and drainage the slope position on a pyroclastic fan relative to an alkaline lake the proximity to freshwater wetlands and the position of water table biogenic paleosol structures include grass and sedge root traces zeolite rhizocretions and soil fauna termite and ant traces abundant pedogenic features sensitive to soil moisture conditions including redoximorphic mottles in the paleosol matrix fe oxide glaebules grain and pore coatings illuviated clay grain and pore coatings and vadose siliciclastic and zeolite crystal silt record episodic water table fluctuations the geochemistry of whole rock samples distinguishes two parent materials early low ti zr weathered volcaniclastic sediment and late high ti zr tuffaceous sediment which represent two distinct pedogenic phases the lower paleosol developed at both sites whereas the upper paleosol developed only at the upslope site mass balance calculations indicate greater weathering higher eh and ph and greater zeolite precipitation at the upslope site than at the downslope site these relationships are compatible with the upslope site having had a lower overall water table and better drained conditions than the downslope site which had a higher water table and poorly drained conditions the lower paleosol provides evidence of a fluctuating water table consistent with a wetter climate followed by a prolonged arid period the upper paleosol began to form after a return to wetter conditions and ended under arid conditions the position of the olduvai subchron c2n 1 942 1 785 ma in bed i directly beneath the paleosol interval is used to make a tentative correlation at 1 75 ma with global climate dust records wet dry cycles

palaeovegetation changes recorded in palaeolake olduvai ogcp core 2a 2 09 2 12 ma naibor soit formation olduvai gorge tanzania abstract for five decades olduvai gorge has been a key site to reconstruct and understand the relationship between environmental and landscape conditions and use of affordances by early african hominin populations following the first olduvai gorge coring project ogcp during 2014 a multiproxy microbiological analysis which includes phytoliths pollen diatoms sponge spicules and chrysophyte cysts was undertaken on samples collected from various borehole cores the aim of the study is to better understand palaeoenvironmental and palaeovegetation conditions and changes through time and their relationship to hominin presence and evolution this study details the first palaeobotanical and palaeoenvironmental study of borehole 2a at olduvai gorge it represents the as yet oldest known sedimentary sequence in the olduvai basin for a portion of the pre bed i naibor soit formation this is a unit that is not accessible in any natural exposures in olduvai gorge and has only recently been encountered by drilling here we present the results from a particularly phytolith prone portion between 2 09 ma and 2 12 ma phytolith results indicate a savannah environment dominated by grasses where poaceae were a key component and where the c3 pooideae grasses were mostly dominant alternating with c4 grasses oscillations between grass subfamilies c3 pooideae c4 chloridoideae and c4 panicoideae to lesser degrees indicate five substantial climatic shifts varying between more humid and arid conditions associated with phytoliths freshwater indicators such as diatoms sponge spicules and chrysophyte cysts were also identified suggesting the presence of wetlands in the lake catchment area pollen is extremely rare in the sediments but when present comprises fungal spores and poaceae pollen thus supporting the wetland and grassland reconstructions respectively these results offer for the first time a whole picture of the palaeovegetation and associated palaeoenvironments for this pre bed i period together with previous results from other areas and chronological periods they improve our understanding of the evolution and adaptation of early hominins and their close relationship to the surrounding landscape

isotopic records of climate seasonality in equid teeth abstract we investigate how oxygen isotopes in equid teeth can be used as a record of seasonality first we use in situ laser ablation and conventional microsampling techniques to understand time averaging of environmental signals in intra tooth isotope profiles in modern feral horse teeth n 5 from mongolia where there is a large seasonal gradient in the oxygen isotopic composition of precipitation we demonstrate that laser ablation can be used to sample inner middle and outer enamel layers in large mammalian herbivore teeth the inner enamel layer records less attenuated isotopic signals than other layers as predicted by the mineralization patterns but intra tooth signal amplitude is similar for laser and conventional sampling methods second we use modern zebra teeth n 21 collected in eastern africa to evaluate how intra tooth oxygen isotope variation relates to rainfall patterns in the tropics we show that the intra tooth isotopic range increases with intra annual precipitation isotopic range which in turn relates to aridity in the equatorial bimodal rainfall region but is influenced by other hydroclimate processes in the region as a whole finally we address isotopic seasonality during the early pleistocene in eastern africa using oxygen isotopes in fossil equid teeth from southwestern kenya n 11 and northern tanzania n 5 we find variable isotopic seasonality in the past similar to present day eastern africa consistent with the notion that hominins and other mammals were able to accommodate environmental variability on intra annual scales in addition to well documented orbital cycles

wetland sedimentation and associated diatoms in the pleistocene olorgesailie basin southern kenya rift valley abstract the olorgesailie basin in the southern kenya rift valley contains a variety of lacustrine wetland and terrestrial facies that were laid down during the last 1 2 million years this study integrates diatom ichnofossil and rhizolith silica and carbonate evidence in order to identify and characterize shallow wetland deposition at the top member 14 ca 493 ka of the olorgesailie formation a key feature of these deposits is the presence of facies with aquatic indicators diatoms that are overprinted by ichnofossils and rhizoliths that suggest drier conditions diatom floras include several fresh water aulacoseira spp and saline indicators such as thalassiosira rudolfi t faurii cyclotella meneghiniana and anomoeoneis sphaerophora the main indicators of shallow fresh to mildly saline waters include epithemia argus rhopalodia gibberula encyonema muelleri and synedra spp three main suites of ichnofossils indicate varying water table depths during their formation these consist of 1 horizontal tunnels that suggest saturated substrates 2 vertical burrows formed in substrates with relatively lower water tables and 3 termite hymenopteran and beetle ichnofossils that indicate dry substrates member 14 of the olorgesailie formation also contains carbonate and siliceous rhizoliths which occur both together and separately four possible models are suggested to explain the silica and carbonate rhizolith formation 1 a complex of spring fed marshes and dry areas 2 ephemeral wetlands and floodplains 3 wetlands with abundant organic decay and 4 initial carbonate rhizoliths that were replaced by silica preservation of cellular structures and the reworking and incorporation of rhizoliths in overlying younger strata suggest that they formed early during diagenesis

reconstruction of a pleistocene paleocatena using micromorphology and geochemistry of lake margin paleo vertisols olduvai gorge tanzania abstract 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 saline alkaline lake until 1 75 ma four trenches in uppermost bed i sample a 20 ka time slice between ng eju tuff base 1 818 0 006 ma and tuff if top 1 803 0 002 ma they form a 1 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 paleosols and parent materials were analyzed for bulk geochemistry of major rare and trace elements geochemical proxies reveal changing hydrology not definitively identifiable in the field or micromorphology molecular weathering ratios show increased weathering and mass balance calculations indicate greater translocations positive and negative through time lower soil moisture due to a drier climate likely created better drained conditions allowing for increased pedogenesis the records of femn oxides and zeolites precipitated in rhizoliths are further evidence for changing redox conditions and water chemistry redox sensitive elements such as fe and mn were mobilized during saturated soil conditions and precipitated during drier conditions as the hydrology changed due to increased aridity zeolites precipitated as rhizoliths due to capillary rise and evaporative pumping of saline alkaline water the fluctuating hydrology identified in the paleo vertisols deposited between 1 79 and 1 81 ma is indicative of a precession cycle and consistent with records from olduvai gorge and throughout east africa this 20 ka time slice of the 2 ma drying trend identified in africa coincides with the first hominin migrations out of africa at 1 8 ma and suggests that hominins were living in a water stressed environment with annual precipitation seasonality and large variations in precipitation due to precession

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

paleoenvironmental and paleoecological reconstruction of a freshwater oasis in savannah grassland at flk north olduvai gorge tanzania the records of early hominins are commonly localized both temporally and spatially even in archaeologically rich basins like olduvai gorge tanzania the flk north site was discovered in 1960 but the reason for the exact location of this dense concentration of fossils and stone tools on a lake margin flat has not been explained we present new geological and geochemical information from six excavations in upper bed i which revealed up to 1 4 m thick carbonate deposits attesting to the presence of freshwater springs in the area surrounding flk north the 18o signatures of the tufa are typical for meteoric water that has evolved during evaporation tuff if that caps the sequence was deposited on uneven topography with the highest area a low relief ridge between two faults at the archaeological site and lowest areas being sites of groundwater discharge the model proposed here is that rainfall on adjacent highlands was transported to the basin where faults acted as conduits for water similar hydrogeological settings at modern lakes manyara and eyasi currently support lush groundwater forest and woodland despite arid climate flk north may have been an oasis offering freshwater and shelter for consuming meat by both carnivores and hominins

hominin evolution in settings of strong environmental variability abstract investigations into how climate change shaped human evolution have begun to focus on environmental dynamics i e the nature and tempo of climate and landscape variability an approach that de emphasizes static reconstructions of early hominin habitats the interaction among insolation cycles is especially apparent in the paleoenvironmental records of the east african rift system where the longest records of human evolution are preserved however environmental indicators such as deep sea oxygen isotopes terrestrial dust flux paleosol carbon isotopes and lake sediments do not point consistently to any simple trend or climate driver of evolutionary change comparison of environmental indicators cautions against an exclusive focus on any given end member of environmental fluctuation driest or wettest warmest or coolest and argues for the impact of the entire range of variability in shaping evolutionary change a model of alternating high and low climate variability for tropical africa further implies that specific environmental indicators reflect different aspects of east african environmental dynamics the model may thus help reconcile some of the conflicting interpretations about the environmental drivers of hominin evolution first and last appearances of hominin lineages benchmark biogeographic events and the emergence of key adaptations and capacities to alter the surroundings are consistently concentrated in the predicted longest intervals of high climate variability the view that emerges is that important changes in stone technology sociality and other aspects of hominin behavior can now be understood as adaptive responses to heightened habitat instability

hominin use of springs and wetlands paleoclimate and archaeological records from olduvai gorge 1 79 1 74 ma abstract an interdisciplinary study of the geologic and archaeological records of a 50 ky year period at the plio pleistocene boundary in olduvai basin tanzania revealed that a small groundwater fed wetland was a consistent focus of hominin activity during periods of climate change wet dry cycles paleoenvironmental analysis of sedimentary records from 33 excavations in lowermost bed ii lmb ii olduvai gorge 3 s revealed evidence of significant climate fluctuations that produced two and one half lake cycles between 1 79 and 1 74 ma the region experienced wet dry cycles in response to combined astronomical forcing effects of eccentricity 100 ky cycle and precession of the equinox 19 and 23 ky cycles rhythmic variability of the monsoon system produced wet periods followed by a transition into dry periods followed by a transition back into wet climate a high resolution study of the stratigraphy documented a groundwater fed wetland complex 1 km2 that flourished during low lake levels dry periods and was drowned during high lake levels wet periods stratigraphic analysis temporal changes of 916 artifacts from 13 excavations selected from a landscape transect across alluvial fan spring wetland and lake margin environments showed no notable differences in artifact type frequency and raw material type when comparing wet periods as a group and dry periods as a group however a lateral shift of hominin activity on the landscape did occur between wet and dry periods the oldowan tool kit did not vary at spring sites between wet and dry periods whereas the tool kit did vary at other lake margin sites between wet and dry periods both analyses suggest that climate affected the location of an activity not type of activity these data suggest that oldowan hominins adapted their land use patterns to exploit spring wetland resources available during dry periods a switch from wet to dry conditions likely altered surface and groundwater systems affecting food and potable water availability forcing hominins to adjust their subsistence patterns

palaeosalinity and palaeoclimatic geochemical proxies elements ti mg al vary with milankovitch cyclicity 1 3 to 2 0 ma ogcp cores palaeolake olduvai tanzania abstract the analysis of geochemical palaeoclimate and palaeosalinity proxy elements ti mg and al derived from x ray fluorescence xrf scans of olduvai beds i and ii from olduvai gorge coring project ogcp borehole cores 2a and 3a provides a record of cyclic variation between 1 3 ma and 2 0 ma the boreholes were drilled into the depocentre of the olduvai basin between fifth and flk faults where palaeolake olduvai was most persistent and deepest during most of bed i the lake was particularly deep and probably meromictic preserving high toc contents and commonly preserving fine lamination due to lack of bioturbation accretion rates were also high during bed i when rates of basinal subsidence were maximal due to crustal stretching associated with basaltic volcanism towards the end of bimodal ngorongoro volcanism basaltic magma effusive activity is manifested as tuffs scoriaceous layers and the bed i basalt complex lava flows a magnesium anomaly is recorded in the claystone geochemistry at this time and deposition of dolomite and limestone beds are restricted to this syn volcanic phase of basin history during bed i deposition accretion rates 0 23 mm yr were high enough to permit recognition of cycles with an average periodicity of 22 3 kyr corresponding to the earth s precession only the high values during the mg anomaly are adequate for the application of the palaeosalinity proxy element ratio mg al but ti counts provide a cyclic record in both bed i and bed ii during bed ii deposition the accretion rate was much slower 0 058 mm yr and cyclicity averaged 40 4 kyr corresponding to earth s orbital obliquity the bed ii interval corresponds to mis stages 40 to 64 coincidence of precessional and obliquity minima at 1 8 ma explains the superdrought that affected the basin at the time of emplacement of tuff if when the lake was dried out the aridity of the sequence containing tuff ia is also associated with a precessional minimum the cyclic record suggests that three bed i basalt flows were extruded at 1 94 ma during a time span lasting between 6 kyr and 15 kyr

phytoliths infer locally dense and heterogeneous paleovegetation at flk north and surrounding localities during upper bed i time olduvai gorge tanzania the phytolith content of 10 samples collected immediately under tuff if similar to 1 785 ma at flk n and other surrounding localities similar to 2 km 2 provides a direct botanical evidence for woody vegetation in the eastern margin of olduvai gorge during uppermost bed i time observation and counting of 143 phytolith types 5 to 150 mu reveal dense but heterogeneous woody cover similar to 40 90 of unidentified trees and or shrubs and palms associated to the freshwater springs surrounding flk n and more open formation presumably similar to 25 70 woody cover in the southeast at localities vek hwk w and hwk e the paleovegetation is best described as groundwater palm forest woodland or bushland which current analogue may be found near lake manyara in similar hydrogeological context freshwater springs near saline alkaline lake re evaluating the published pollen data based on this analogy shows that 70 of the pollen signal at flk n may be attributed to thicket woodland acacia groundwater woodland gallery and groundwater forests while 30 is attributed to swamp herbage and grasslands micro botanical isotopic and taphonomical studies of faunal remains converge on the same conclusion that the area surrounding flk n which attracted both carnivores and hominins in the early pleistocene was densely wooded during uppermost bed i time

the role of pollution versus natural geological sources for lead enrichment in recent lake sediments and surface forest soils this paper assesses the role of airborne pollution and natural geological sources for lead enrichment in lake sediments and in surface soils of boreal forests this assessment is based on analyses of stable lead isotopes 206pb and 207pb and lead concentrations in sediment cores 30 lakes ombrotrophic peat and soil samples in sweden the 206pb 207pb ratio and concentration profiles in the sediment cores change synchronously over the last 3 000 years in different lakes temporal concentration changes in sediments and peat deposits are very consistent and these temporal concentration changes coincide well with the history of lead production in europe the 206pb 207pb ratio is almost the same in all soil mor samples 1 152 0 009 n 94 and similar to values recorded in aerosols despite very high and different 206pb 207pb ratio of the mineral soil in the c horizon 1 3 1 7 this study provides evidence that lead enrichment in recent sediments and peat and in the mor layer are caused by deposition of pollution lead and not natural processes

early pleistocene lake formation and hominin origins in the turkana omo rift abstract prior research has correlated the formation of plio pleistocene lakes in east africa to global regional climate changes and interpreted the lacustrine basins as significant settings of hominin evolution paleo lake lorenyang from the turkana omo rift is important to these issues as its marginal deposits contain some of if not the earliest currently known specimens of acheulian stone tools and african homo erectus magnetostratigraphic and sedimentological evidence indicates that the oldest preserved paleo lake lorenyang deposits are dated at 2 148 2 128 ma and derive from the nw turkana basin predating those from the omo basin by 100 kyr and the ne turkana basin by 190 kyr apparently the lake expanded asynchronously in the rift potentially due to a volcano tectonic influence on the location of drainage networks depositional slopes or topographic elevation differences within and between the basins at the time of flooding the onset of the lake temporally coincides with the eruption of basalt lava flows dated to 2 2 2 0 ma that blocked the southeast outlet of the turkana basin this provides a plausible mechanism for hydrologic closure and lacustrine basin formation through volcano tectonic impounding it also points to a non climatic cause for the initial formation of paleo lake lorenyang at 2 14 ma first appearances for african h erectus 1 87 ma and acheulian tools 1 76 ma in the turkana omo rift postdate the lake s initial formation by about 270 kyr and 380 kyr respectively such timing differences contrast with studies that correlate all three to the 400 kyr eccentricity maximum at 1 8 ma although the turkana omo rift is just one example it does provide alternative insights to views that link climate hominin evolution and lake formation in east africa

whole rock geochemistry tracks precessional control of pleistocene lake salinity at olduvai gorge tanzania a record of authigenic clays the paleoclimatic framework of human evolution is central to the study of human origins olduvai gorge tanzania has a rich paleontological record including four hominin species we analyzed 177 mudstone samples from a lacustrine section supported by a new high resolution geochronology to track changes in paleolake water chemistry six peaks in al 2 o 3 mgo indicate freshening events occurring over a generally saline and alkaline environmental background five of the six events occurred at peak climatic precession correlating with december insolation at 20 s the southern monsoon therefore may have been more effective at delivering moisture to east africa than today peak amplitude of geochemical variation preceded the ca 1 84 ma eccentricity maximum by 20 k y suggesting that eccentricity modulation was unexpectedly weak in this interval or that other factors affected the water balance or geochemical record this study demonstrates that authigenic clay geochemistry determined through whole rock analyses can preserve a record of astronomically forced environmental change and documents paleohydrologic changes in tropical africa at a time when zonal walker circulation increasingly affected global climate new stone technologies emerged and the genus homo spread beyond africa

environment and climate of early human evolution evaluating the relationships between climate the environment and human traits is a key part of human origins research because changes in earth s atmosphere oceans landscapes and ecosystems over the past 10 myr shaped the selection pressures experienced by early humans in africa these relationships have been influenced by a combination of high latitude ice distributions sea surface temperatures and low latitude orbital forcing that resulted in large oscillations in vegetation and moisture availability that were modulated by local basin dynamics the importance of both climate and tectonics in shaping african landscapes means that integrated views of the ecological environmental and tectonic histories of a region are necessary in order to understand the relationships between climate and human evolution

vegetation of northern tanzania during the plio pleistocene a synthesis of the paleobotanical evidences from laetoli olduvai and peninj hominin sites abstract more than 40 years of scientific investigations of the hominin bearing plio pleistocene sediments of northern tanzania have provided a number of paleobotanical data which taken as a whole provide today a way to investigate vegetation changes between 4 and 1 ma at a time when our early ancestors emerged here i have integrated the data from all vegetation proxies obtained for the paleontological sites of laetoli olduvai and peninj i e macroscopic plant remains pollen and phytolith assemblages carbon and oxygen isotopic ratios measured on carbonates and organic biomarkers this important yet discontinuous botanical record suggests some similarities between past and present day vegetation at the regional scale afromontane forests with olea podocarpus juniperus hagenia abyssinica in the highlands and wooded grasslands with grasses and drought adapted acacia commiphora capparidaceae and chenopodiaceae and or amaranthaceae in the lowlands were present in the southern serengeti crater highlands region since 4 ma grasses of the c 4 photosynthetic type made their first appearance in the record at 3 7 ma i e during the mid pliocene 700 ky before major p co 2 and temperature decline c 4 grasses became dominant in the vegetation soon after 3 66 ma probably in response to reduced precipitation at 2 6 ma phytolith and isotope indicate grassland with abundant c 4 xerophytic grasses that document strong aridity during the intensification of northern hemisphere glaciation period 2 7 2 5 ma after 2 ma the detailed and diverse record at olduvai indicates complex vegetation patterns linked to oscillating precipitation varying lake levels and the presence of geological faults hence despite low basin averaged reconstructed paleo precipitation amounts of 250 700 mm y c 4 grasslands closed woodlands wetlands and palm groves co occurred on short spatial scales near saline lake olduvai freshwater wetlands and palm rich woodlands occurred in highly localized areas on the lake margins where aquifer barriers and or outcrops caused by geologic faults allowed groundwater discharge botanical evidence of paleo springs at laetoli olduvai and peninj includes the marked presence of typha cattail and hyphaene palm tree in association with acacia pollen grains and at olduvai abundant forest indicator phytoliths and organic and isotopic biomarkers at olduvai freshwater wetlands were most developed when lake level and fluvial competence where low i e during dry periods when wet dry climate variability was extreme in east africa 1 9 1 7 ma freshwater springs may therefore have offered a sustainable habitat i e refuge for several species including hominins and favored hominin and artifact concentration at these specific places particularly during environmentally stressful times