crustal reworking at nanga parbat pakistan metamorphic consequences of thermal mechanical coupling facilitated by erosion within the syntaxial bends of the india asia collision the himalaya terminate abruptly in a pair of metamorphic massifs nanga parbat in the west and namche barwa in the east are actively deforming antiformal domes which expose quaternary metamorphic rocks and granites the massifs are transected by major himalayan rivers indus and tsangpo and are loci of deep and rapid exhumation on the basis of velocity and attenuation tomography and microseismic magnetotelluric geochronological petrological structural and geomorphic data we have collected at nanga parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the indus and tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes the localization of this phenomenon at the terminations of the himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics

petrology of high pressure granulites from the eastern himalayan syntaxis the eastern himalayan syntaxis situated at the eastern terminus of the himalayas is the least known segment of the himalayas recent research in this area has revealed that the syntaxis consists of the gangdise the yarlung zangbo and the himalayan units each of which is bounded by faults the himalayan unit the northernmost exposed part of the indian plate mainly contains amphibolite facies rocks marked by the assemblages staurolite kyanite plagioclase biotite muscovite sillimanite and garnet amphibole plagioclase in the south to the north low to medium pressure granulite grade pelitic gneisses and marbles are present and are characterized by the assemblages garnet sillimanite k feldspar plagioclase or antiperthite biotite quartz spinel cordierite orthopyroxene in gneisses and anorthite diopside wollastonite and plagioclase diopside quartz phlogopite calcite in marbles within this unit the namula thrust system is a series of moderately north dipping structures that displaced the granulite facies rocks southwards over the amphibolite facies rocks high pressure granulites occur as relics within these granulite facies rocks and contain garnet kyanite granulite and garnet clinopyroxenite the peak assemblage of the garnet kyanite granulite includes garnet core part kyanite ternary feldspar quartz rutile sillimanite garnet rim part k feldspar oligoclase ilmenite biotite and spinel albite biotite or spinel cordierite orthopyroxene which are coronas around sillimanite and garnet are retrograde products of this peak assemblage another peak assemblage includes very high ca garnet cao 32 34 wt alm10 grs 80 and diopside cao 22 24 wt scapolite meionite quartz and accessory al bearing titanite al2o3 4 4 5 wt the diopside has kink bands partial or complete breakdown of ca rich garnet during post peak metamorphism produced pseudomorphs and coronas consisting of fine grained symplectic intergrowths of hedenbergite and anorthite thermobarometric estimates in combination with reaction textures mineral compositions and recent experimental studies indicate that these peak assemblages were formed at p c 1 7 1 8 gpa t c 890 c and the retrograde assemblages experienced near isothermal decompression to p 0 5 0 1 gpa t 850 50 c the whole rock compositions indicate that marble and pelite are plausible candidates for the protoliths these facts suggest the following 1 sedimentary rocks were transported to upper mantle depths and equilibrated at those conditions to form these high pressure granulites which were then emplaced into the crust quickly during the rapid exhumation of these rocks the earlier high pressure assemblages were overprinted by the later low to medium pressure assemblages that is the high pressure granulite belt formed in the syntaxis 2 the namula thrust system is an important tectonic boundary in the syntaxis or even in the higher himalaya more generally

miocene jiali faulting and its implications for tibetan tectonic evolution the karakoram jiali fault zone kjfz comprises a series of right lateral shear zones that southerly bound the eastward extrusion of northern tibet relative to india and stable eurasia here we present new 40 ar 39 ar age data from the puqu and parlung faults two easternmost branches of the jiali fault zone which indicate a main phase of the kjfz shearing from v18 to 12 ma thus the tibetan eastward extrusion bounded by principal strike slip fault zones started and was probably most active around the middle miocene an interval marked also by active east west extension in southern tibet the coincidence of these two tectonic events strongly suggests a common causal mechanism which is best explained as oblique convergence between india and asia under the framework of this mechanism the extension in southern tibet is not a proxy for the plateau uplift the kjfz activity was furthermore coincident with right lateral displacements along the gaoligong and sagaing faults in southeast asia this defines a miocene deformation record for the regional dextral accommodation zone that in response to the continuing india asia collision may have accounted for the initiation and prolonged history of clockwise rotation of the tibetan extrusion around the eastern himalayan syntaxis 2002 elsevier science b v all rights reserved

adakites from continental collision zones melting of thickened lower crust beneath southern tibet adakites are geochemically distinct intermediate to felsic lavas found exclusively in subduction zones here we report the first example of such magmas from southern tibet in an active continental collision environment the tibetan adakites were emplaced from ca 26 to 10 ma and their overall geochemical characteristics suggest an origin by melting of eclogites and or garnet amphibolites in the lower part 50 km of thickened tibetan crust this lower crustal melting required a significantly elevated geotherm which we attribute to removal of the tectonically thickened lithospheric mantle in late oligocene time the identification of collision type adakites from southern tibet lends new constraints to not only the himalayan tibetan orogenesis how and when the indian lithosphere started underthrusting asia can be depicted but also the growth of the early continental crust on earth that consists dominantly of the tonalite trondhjemite granodiorite suites marked by adakitic geochemical affinities

ocean continent boundary in the iberia abyssal plain from multichannel seismic data abstract the ocean continent boundary of the west iberia margin is marked by a basement ridge trending n s four segments of this ridge are recognized each of them being progressively offset westward from 40 n to 43 n because the setting and seismic character of the ridge in the iberia abyssal plain are similar to those of the galicia margin ridge which is made of serpentinized peridotite we think that the southern segments of the ridge are also made of the same mantle material the segmentation of the ridge suggests that the northward propagation of the continental break up during the north atlantic opening in early cretaceous times was discontinuous each segment possibly corresponding to a propagation step east of the ridge the basement of the whole iberia abyssal plain consists of highly thinned continental crust locally resting on a seismic reflector that resembles the s reflector previously recognized off galicia by analogy with the galicia margin we propose that the tilted crustal blocks lay on serpentinized peridotite derived from the upper mantle the s reflector corresponding to the contact between crustal rocks and serpentinite

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

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

fossil herbivores and crocodiles as paleoclimatic indicators of environmental shifts from bed i and bed ii times of the olduvai gorge tanzania abstract the radiation and extinction of east african vertebrate fauna have been linked to key climatic changes that occurred around 2 8 1 7 and 0 5 ma this study tests whether vegetation and diet changes were linked to these climatic fluctuations focusing on the climatic event at 1 7 ma by analyzing the stable isotope composition of fossil herbivore teeth from the olduvai gorge s stratigraphic units upper bed i lower bed ii and upper bed ii which span 1 83 1 33 ma in order to detect shifts in herbivore diets from c3 to c4 plants in conjunction with their drinking water isotope geochemistry c4 grass expansion is known to be favored by drier conditions and this study tests whether herbivore diets permanently changed to being c4 dominant at this key time period crocodile teeth are also tested to determine if they may be used as paleoclimatic indicators since large crocodiles prey on terrestrial herbivores in wetland settings vertebrate bioapatite carbon and oxygen isotope compositions are found to show similar trends as those of pedogenic carbonates carbonate nodules or concretions which reflect a drying environment that was changing from c3 woodland dominated habitats to mixed woodlands and grasslands from bed i to lower bed ii times while a return to more humid conditions in upper bed ii might be expected to lead to a reversal to c3 plants herbivores in this study retained mostly the drought resistant c4 plant diet these results indicate that vegetation and ecosystems passed through a threshold to c4 domination that did not revert to c3 despite partial reversals in climate that occurred later crocodile teeth were not useful in tracking c4 plant expansion but the oxygen isotopes from modern crocodiles are able to show seasonal cycles from wet to dry seasons and bed i crocodiles indicate a degree of annual seasonal changes during that time as well

phytoliths pollen and microcharcoal from the baringo basin kenya reveal savanna dynamics during the plio pleistocene transition abstract as part of the hominin sites and paleolakes drilling project hspdp phytoliths pollen and microcharcoal were examined from the 228 m 3 29 to 2 56 ma baringo tugen hills barsemoi drill core btb13 a total of 652 samples were collected at 10 to 32 cm intervals corresponding to sub millennial to millennial scale temporal resolution microcharcoal was well preserved throughout the core and often peaked in abundance 5 kyr before and after insolation peaks phytolith preservation varied between excellent to total dissolution in alternating intervals throughout the core pollen was rarely preserved these combined datasets indicate that prior to 3 1 ma woody cover fluctuated between open savanna 80 cover at typically precessional 19 23 kyr periodicities during the mid piacenzian warm period mpwp 3 26 3 01 ma intervals with exceptionally high microcharcoal abundance suggest that regional turnover from wooded to open habitats was driven in part by fire after 3 1 ma low elevation woody cover likely never exceeded 40 with oscillations between mesic tall grass vs xeric short grass savanna at precessional periodicities mesic c4 tall grass panicoideae peaked in abundance during insolation maxima whereas xeric c4 short grass chloridoideae peaked during insolation minima the onset of northern hemisphere glaciation nhg at 2 75 ma coincided with the appearance of deep lake phases and increases in grass density and fire frequency spectral analysis and intervals with well preserved phytoliths indicate that precession and interhemispheric insolation gradients influenced vegetation via their effects on equatorial precipitation and fire this study fills a crucial gap in pliocene vegetation reconstructions from the east african rift valley and its associated hominin localities it also provides orbitally resolved regional vegetation data useful in paleodata model comparisons for the onset of the mpwp which is often used as an analog for future warming and nhg

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

the flk zinj paleolandscape reconstruction of a 1 84 ma wooded habitat in the flk zinj amk ptk ds archaeological complex middle bed i olduvai gorge tanzania abstract we have analyzed the phytolith content of 37 samples from the paleosol capped by tuff ic dated 1 84 ma within middle bed i at olduvai gorge tanzania samples were obtained from different trenches sampling an area of about 25 ha to document the paleovegetation associated with the abundant faunal remains and hominin artifacts in flk amk ptk and ds sites the analysis reveals the abundance of globular granulate and forest indicator phytoliths from 3 to 86 relative to the total number of phytoliths in the assemblages attributed to woody plants and of short cell grass phytoliths up to 22 the presence of palm phytoliths up to 57 attests for meso haline soils in the area in agreement with the presence of the saline alkaline olduvai paleolake and one or more groundwater discharge areas freshwater springs and or wetland phytoliths provide botanical evidence for a mixed paleovegetation dominated by forest and woodland with patches of open spaces occupied by grasses prior to the deposition of tuff ic the presence of fern phytoliths in some assemblages suggest shaded and humid habitat which supports the presence of freshwater watercourses or springs that might have attracted hominins and other animals yet we have found that our phytolith extractions residues also include micrometric zeolites chabazite clinoptilolite phillipsite which attest that the phytolith signal in the zinj paleosols is certainly affected by dissolution this study completes the spatial analysis of the area and reveals that the wooded area extends north south and west of flk zinj with palm trees preferentially located in the periphery like the zinj amk and ds sites the phytolith inferred distribution of plants does not support the hypothesis that topography was influential in the location of these sites particularly given that trees and or shrubs were dominant all over rather it is the presence of freshwater ponds that seem to have been the attractive factor for hominins at this particular place and time

early pleistocene fossil wood from olduvai gorge tanzania abstract olduvai gorge is a well known east african site for early hominid and faunal remains as well as stone tools and artefacts through the efforts of a multidisciplinary research team olapp olduvai landscape and palaeoanthropology project the sedimentology tephrostratigraphy dating mapping and palaeoclimatic interpretations are being used to put the whole ecosystem into context to achieve a better understanding of hominid occupation and behaviour the palaeolake together with the alluvial fan and wetland environment have shifted and fluctuated under the influence of climatic change tectonic faulting lava flows and ashfalls numerous fossil plants have been recovered from these sediments including sedges grasses twigs pollen phytoliths and wood one sample of fossil wood has been identified as guibourtia coleosperma caesalpiniaceae a relatively uncommon tree which today grows in angola botswana namibia zambia and zimbabwe this species grows on kalahari sands but must have had a wider distribution in the past the occurrence of this tree in lowermost bed ii approximately 1 81 1 78 ma indicates that there were large trees in the close vicinity and that there were periods of wetter climate large trees would have provided some shelter or safety for the hominids from other scavengers

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

palaeoecological significance of palms at olduvai gorge tanzania based on phytolith remains abstract palms are among the most abundant diverse and economically important families of plants in tropical and subtropical regions of the world their number and diversity make them an important part of the ecosystem phytoliths are abundantly produced in palms mainly the spheroid echinate type and although their number decreases notably after their deposition in soils they remain stable for long periods of time palm phytoliths were recovered from sediments at hwkee on the eastern palaeolake margin of the olduvai basin during lowermost bed ii between tuffs if and iia 1 795 1 71 ma their abundance in trench 107 the only freshwater source recognised to date occurs in three stratigraphically consecutive layers the first one located immediately above the incision layer 40 cm above tuff if above these samples there are no palm phytoliths in the fossil record the identification of the type of palms represented will be useful for determining the landscape distribution and nature of hominin activities along the lake margin and alluvial fan of the central olduvai basin here we use morphometric analysis of spheroid echinate phytoliths from fossil and modern palms phoenix reclinata and hyphaene petersiana and their corresponding soils to determine if the differences are significant and can be confidently applied to the fossil samples fossil and modern soil samples were found to be very similar to each other but the spheroid echinates from the fossil soils were bigger than the modern soil samples either the palms from the samples were different or there is a strong bias towards preserving phytoliths from the smaller end of the range if this is the case then the implication would be that the fossil samples are the leaves and inflorescences of phoenix reclinata a wider variety of modern palms needs to be analysed

vegetation landscape at dk locality olduvai gorge tanzania abstract the olduvai gorge palaeoanthropological site in northern tanzania encompasses about two million years of earth history the sedimentary facies of palaeolake olduvai have been used to reconstruct lake transgressions and regressions up to total drying out interpreted to reflect wet dry climate cycles although multidisciplinary research has been conducted during the past decades to reconstruct the palaeoenvironments and palaeolandscapes of the gorge very few focused on the dk site located about 2 km farther east in the gorge we present here a vegetation study at dk for bed i the oldest stratum based upon the phytolith and diatom recovery of the basalt lava to tuff ib stratigraphic interval these results have been analysed in relation to the different facies in which they occur sandy diamictite sandstone sandy waxy claystone waxy claystone and sandy diatomite the phytolith results from diamictite samples indicate a similar vegetation composition during these more arid periods conversely waxy claystone and sandy waxy claystone samples show a higher diversity in the vegetation composition the diatoms were indicative of a fresh water pool environment thus the dk site would have provided plant foods for hominins such as fruits from trees and shrubs and starch rich rhizomes and tubers from sedges and reeds overall the results at dk site present a different vegetation landscape in comparison to previously published phytolith results from other olduvai stratigraphic levels and regions

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

u pb zircon constraints on the tectonic evolution of southeastern tibet namche barwa area the eastern syntaxis of the himalayas is expressed in the crust as a pronounced southward bend in the orogen the change in strike of geologic features coincides with the high topography of the namche barwa region the exposure of granulite grade metamorphic rocks and a 180 degree bend in the yalu tsangpo we have conducted a geochronologic and geochemical investigation of several suites of granitoids collected from the namche barwa massif and subjacent terranes of southeastern tibet ranging from cm scale dikes and sills to larger outcrop scale intrusions u pb shrimp rg zircon ages establish at least five magmatic episodes 400 to 500 ma 120 ma 40 to 70 ma 18 to 25 ma and 3 to 10 ma these episodes broadly correlate to spatial patterns in sample localities as follows 400 to 500 ma ages occur in zircon cores collected from within the massif proper 120 ma granites related to early gangdese arc plutonism are primarily located northeast of namche barwa later 40 70 ma gangdese activity is expressed in granites west of namche barwa 18 to 25 ma granites occur both along the suture zone west of gyala peri and directly north of namche barwa along the area of the jiali fault zone and are attributed both to shearing within the jiali fault zone and to an early miocene gangdese thrust event exceptionally young 10 ma zircon ages are clustered near the core of the massif along the yalu tsangpo gorge trace element geochemical data indicates the presence of both fluid present and fluid absent melts with a fluid absent decompression melting regime dominating near the core of namche barwa

siliceous islands in a carbonate sea modern and pleistocene spring fed wetlands in ngorongoro crater and oldupai gorge tanzania abstract a biogenic mechanism is proposed that produces a diagnostic geochemical signature of perennial spring fed wetlands in arid basins especially the saline and alkaline volcanic basins of east africa respiration by vegetation and decay of organic matter within marshes in ngorongoro crater tanzania locally increases aqueous equation the resulting lowered ph inhibits the precipitation of calcite and decreases the rate of silica dissolution steep geochemical gradients are produced these are represented mineralogically by siliceous biomineralization within the perennial marsh and carbonate precipitation in surrounding ephemeral wetlands mudflats and lacustrine environments as a test of this model of geochemical sedimentation the mineralogy of the early pleistocene siliceous earthy claystone of oldupai gorge is consistent with its interpretation as a paleo spring wetland deposit because such deposits are expressions of the paleo water table this approach has potential applications in many studies of basin paleohydrology paleoclimatology paleoecology and archaeology

tectonic uplift and eastern africa aridification the history of eastern african hominids has been linked to a progressive increase of open grassland during the past 8 million years this trend was explained by global climatic processes which do not account for the massive uplift of eastern african topography that occurred during this period atmosphere and biosphere simulations quantify the role played by these tectonic events the reduced topographic barrier before 8 million years ago permitted a zonal circulation with associated moisture transport and strong precipitation our results suggest that the uplift itself led to a drastic reorganization of atmospheric circulation engendering the strong aridification and paleoenvironmental changes suggested by the data

intraplate tectonics in asia a precise age for large scale miocene movement along the ailao shan red river shear zone china tertiary left lateral movement along the 1000 km long ailao shan red river shear zone appears to have played an important role in absorbing post collisional northward penetration of india into asia crustal strike slip shear along this zone caused the formation of a gneiss belt metamorphosed to amphibolite grade including anatectic melting both metamorphism and melting were induced by ductile deformation yielding the possibility to date the major tectonometamorphic event that shaped the ailao shan red river belt 17 u pb isotope analyses were performed on small size fractions of zircon monazite and xenotime extracted from two different leucogranitic layers the two samples are located about 50 km apart in the central segment of ailao shan in structurally well controlled settings where the melts crystallized within the strongly foliated gneisses during late stages of deformation all mineral u pb analyses had to be corrected for excess or deficit amounts of radiogenic 206 pb originating from initial 230 th disequilibrium in the 238 u decay series in monazite such disequilibrium 206 pb reaches 20 of total radiogenic 206 pb the corrected u pb ages of monazite and xenotime lie between 22 1 and 23 9 ma whereas zircon yields significantly discordant u pb ages between 30 5 and 33 9 ma pointing to precambrian material in the magma source region inherited components could also be detected in monazite the set of u pb data shows that monazite and xenotime formed simultaneously in both localities substantiating an early miocene age of 23 0 0 2ma for late kinematic crystallization of anatectic melts in the metamorphic belt of the ailao shan red river shear zone

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

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

when did the roof collapse late miocene north south extension in the high himalaya revealed by th pb monazite dating of the khula kangri granite th pb ion microprobe measurements made on 12 monazite grains from the khula kangri granite tibet bhutan frontier are interpreted to indicate that crystallization occurred at 12 5 0 4 ma the leucogranite is cut by the gonto la detachment part of the southern tibet detachment system that has allowed upper level north directed extension of the himalayan orogen significant orogen normal extension in southern tibet appears to have continued 8 10 m y later than previously recognized this is the first reported crystallization age for a leucogranite east of the yadong cross structure an apparent 70 km offset of the high himalaya and southern tibet detachment west of the yadong cross structure reliable ages for high himalaya events major main central thrust slip granite generation and emplacement attainment of critical topography and major detachment extension group between ca 24 and 19 ma we interpret the west to east change across the yadong cross structure to be due to either 1 an abrupt 10 m y younging of principal high himalayan events or 2 a deeper thus younger exposed part of the footwall of the southern tibet detachment near khula kangri the southern tibet detachment is cut by the highly oblique yadong gulu rift a manifestation of tibet plateau east west extension integrated estimates of magnitude and rate of detachment displacement suggest that the observed postcrystallization north directed extension lasted for 1 3 m y after which time the yadong gulu rift formed this interpretation is consistent with initiation of east west extension of tibet at ca 8 ma

a late miocene pliocene origin for the central himalayan inverted metamorphism abstract perhaps the best known occurrence of an inverted metamorphic sequence is that found immediately beneath the himalayan main central thrust mct generally thought to have been active during the early miocene however in situ 208 pb 232 th dating of monazite inclusions in garnet indicates that peak metamorphic recrystallization of the mct footwall occurred in this portion of the central himalaya at only ca 6 ma the apparent inverted metamorphism appears to have resulted from activation of a broad shear zone beneath the mct which tectonically telescoped the young metamorphic sequence this explanation may resolve some outstanding problems in himalayan tectonics such why the mct and not the more recently initiated thrusts marks the break in slope of the present day mountain range it also renders unnecessary the need for exceptional physical conditions e g high shear stress to explain the generation of the himalayan leucogranites

the gangdese thrust a phantom structure that did not raise tibet introductioncrustalthickeninganduplifttoestab lish the tibetan plateau during thelate oligocene to early miocene isinferred from abrupt increases in thecoolingratesofrocksinthesouthernlhasa terrane copeland et al 1987 copeland andharrison 1990 harri sonet al 1992 2000 thisinterpret ation is not without controversy andsome other workers prefer a modelinvolvingstepwisegrowthoftheplat eausincetheeocene e g tapponnieret al 2001 mid tertiary uplift wasnonetheless considerable and is con sideredtohavehadaprofounde ecton the evolution of global climaticsystems raymo et al 1988 raymoandruddimann 1992 molnaret al 1993 1997 inadiscussionofscenar ios to explain the mid tertiaryincrease in cooling rate observed forthe eastern gangdese batholith andcrustal thickening in the region yinet al 1994 1999 suggestedtheexist ence of a south directed gangdesethrust system gts in the southernlhasa terrane marginal to the yar lung tsangpo suture zone ytsz fig 1 yin et al 1994 stated that recognition of the gts relegatesother mechanisms climate changeand tectonic denudation by normalfaulting to a supporting role inexplainingthemid tertiarytransitionin cooling rate the existence of thisstructurehassincebecomeanintegralcomponent in tectonic models descri bingtheindia asiacollisionandasso ciated uplift of the tibetan plateau yin et al 1994 1999 quidelleuret al 1997 searle et al 1997 mak ovsky et al 1999 harrison et al 2000 hodges 2000 yin and harri son 2000 reports of a south directed thrustfault in the zedong area that placeslhasa terrane rocks over tertiaryconglomerates yin et al 1994 1999 harrisonet al 2000 are how ever at odds with previously pub lished geological maps and otherliterature badengzhu 1979 1981 zhang and fu 1982 wei and peng 1984 bureauofgeologyandmineralresources of xizang autonomousregion 1993 in which this relation ship is reported as an unconformity given this apparent dichotomy ofinterpretation and the signi cancethatthepostulatedstructurehasbeenaccordedinnumerouspapersdiscuss ingthetectonicevolutionoftibetwedecided to investigate further basedon our own extensive eld investiga abstract

evolutionary model of the himalaya tibet system geopoem based on new modelling geological and geophysical data a two dimensional thermo mechanical laboratory modelling of continental subduction was performed the subducting continental lithosphere includes a strong brittle upper crust a weak ductile lower crust and a strong upper mantle the lithosphere is underlain by a low viscosity asthenosphere subduction is produced by a piston push force and the pull force from the mantle lithospheric layer which is denser than the asthenosphere the lithospheric layers are composed of material whose strength is sensitive to and inversely proportional to temperature throughout the experiment the model surface was maintained under relatively low temperature and the model base at higher temperature the subduction rate satisfied the peclet criterion modelling confirms that the continental crust can be deeply subducted and shows that slab break off delamination and tectonic underplating are fundamental events with drastic consequences on the subsequent evolution of the convergent system combining these results with previous purely mechanical modelling we elaborate a new evolutionary model for the himalaya tibet convergent system the principal successive stages are 1 subduction of the indian continental lithosphere to 200 250 km depth following subduction of the tethys oceanic lithosphere 2 failure and rapid buoyancy driven uplift of the subducted continental crust from ca 100 km depth to some depth that varies along the mountain belt 20 30 km on average 3 break off of the indian subducted lithospheric mantle with the attached oceanic lithosphere 4 subduction underplating of the indian lithosphere under asia over a few to several hundred kilometers 5 delamination roll back and break off of the indian lithospheric mantle 6 failure of the indian crust in front of the mountain belt formation of the main central thrust and underthrusting of the next portion of indian lithosphere beneath tibet for a few hundred kilometers at the beginning of stage 6 the crustal slice corresponding to the crystalline himalayas undergoes erosion activated uplift and exhumation fl 2000 elsevier science b v all rights reserved

an isotopic study of paleosol carbonates from olduvai gorge the isotopic composition of paleosol carbonates from olduvai gorge can be used to give estimates of the paleoclimatic history of east africa during the plio pleistocene oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water while carbon isotopes are indicative of major changes in the fraction of biomass using the hatch slack c4 photosynthetic pathway three major periods of climatic change in this terrestrial setting occurred at about 1 67 1 3 and 0 6 myr these involved major changes in flora as well as major changes in the isotopic composition of meteoric water overall the climate has become warmer and more arid over the past 2 2 myr

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

rb sr geochronology of granites and gneisses from the mount everest region nepal himalaya nineteen samples of granites orthogneisses and paragneisses from the high himalaya basement nappe s of the mount everest region have been dated by the rb sr method the post metamorphic tourmaline leucogranites of the upper imja drangka nuptse lhotse glacier have high initial sr87 sr86 characteristic of an anatectic origin from crustal material a whole rock isochron age of 52 m y early eocene has been obtained for the samples from the granite body of lhotse glacier apparently sr isotopic homogenization was not reached throughout the much larger nuptse granite

the gangotri granite garhwal himalaya laccolithic emplacement in an extending collisional belt the gangotri miocene leucogranite is composed of several laccoliths 6 7 km long 1 5 2 km thick which can be divided into two sets of lenses the southern lenses intruded in the lower part of the high himalaya sedimentary cover and the northern lenses intruded in an older porphyritic biotite bearing granite in both cases the magmatic fabric is commonly weak with no dominant stretching direction although a rough e w trend is present in the northern lenses the magnetic fabric is characterized by the fact that drastic changes in the direction in the magnitude of the magnetic parameters or in the fabric type planar or linear may take place over very short distances measurements of preferred orientations in thin sections indicate that the strain regime was largely dominated by a coaxial component for both sets of lenses in agreement with the large dispersion observed in both the field and magnetic lineations the comparison of the granite and host rock structures shows that the leucogranite emplacement dates the onset of the extensional tectonism in the high himalaya range and is not related to a southward directed thrust event associated with the main central thrust this is exemplified by the vertical attitude of the feeder dikes that intrude the metasedimentary rocks beneath die southern lenses the presence of these dikes indicates in turn that magma ascent occurred by fracture propagation the spatial disposition of the southern lenses could have resulted either from the disruption of a single laccolithic intrusion by crustal scale boudinage due to a northern gravity backslide of the top of the tibetan slab or from the intrusion of independent laccoliths the use of the elastic bending theory of pollard and johnson 1973 shows that in both hypotheses the current laccolith sizes are compatible with a laccolithic mode of magma emplacement however neither the density contrast between the magma and its enclosing rocks nor the lithological boundary between the tibetan slab and the overlying tibetan metasedimentary series controlled the level of magma emplacement rather flat lying collapse structures which intersected the upward propagating magma dikes are the most likely causes of magma arrest such a mechanism was favored by the schist rich lithology of the metasedimentary host rocks in addition field relationships indicate that the melt supply through the dike system was a continuous rather than pulsed process existing numerical treatments on the rates of magma transport through fractures show that in such a case the laccoliths could have been built in less than 100 years this short time of emplacement the small size of the laccoliths and their peripheral disposition relative to the badrinath granite suggest that the gangotri lenses may represent the initial stage of pluton accretion in the high himalaya which ultimately gave rise to a much larger massif such as the manaslu granite

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

a model for the origin of himalayan anatexis and inverted metamorphism the origin of the paired granite belts and inverted metamorphic sequences of the himalaya has generally been ascribed to development of the main central thrust mct although a variety of models have been proposed that link early miocene anatexis with inverted metamorphism recent dating studies indicate that recrystallization of elements of the mct footwall occurred in the central himalaya as recently as 6 ma the recognition that hanging wall magmatism and footwall metamorphism are not spatially and temporally related renders unnecessary the need for exceptional physical conditions to explain generation of the high himalayan leucogranites and north himalayan granites which differ in age petrogenesis and emplacement style we suggest that their origin is linked to shear heating on a continuously active thrust that cuts through indian supracrustal rocks that had previously experienced low degrees of partial melting numerical simulations assuming a shear stress of 30 mpa indicate that continuous slip on the himalayan decollement beginning at 25 ma could trigger partial melting reactions leading to formation of the high himalayan granite chain between 25 and 20 ma and the north himalayan belt between 17 and 8 ma the ramp flat geometry we apply to model the himalayan thrust system requires that the presently exposed rocks of the hanging wall resided at middle crustal levels above the decollement throughout the early and middle miocene late miocene out of sequence thrusting within the broad shear zone beneath the mct provides a mechanism to bring these rocks to the surface in their present location i e well to the north of the present tectonic front and has the additional benefit of explaining how the inverted metamorphic sequences formed beneath the mct we envision that formation of the mct zone involved successive accretion of tectonic slivers of the lesser himalayan formations to the hanging wall and incorporate these effects into the model the model predicts continued anatexis up to 400 km north of the himalayan range consistent with the timing and geochemistry of leucogranites exhumed on the flank of a south tibetan rift

the zedong window a record of superposed tertiary convergence in southeastern tibet determining the timing magnitude and location of deformation due to the indo asian collision is widely acknowledged as an important step in understanding how the lithosphere responds during continental collision a puzzling result of geological investigations of the lhasa block over the past 2 decades has been the apparent lack of significant tertiary deformation there perhaps the most important structural feature of the lhasa block is the south directed gangdese thrust system which developed along its southern edge the thrust system which separates the andean type batholith of southern asia from rocks of indian affinity is obscured at most locations across southeastern tibet by back thrusts of the younger north directed renbu zedong thrust system the best documented site where both thrusts are exposed occurs near zedong zedong window systematic geochronologic analyses were conducted in this area u pb zircon dating of three samples of a synkinematically to postkinematically deformed hanging wall granitoid the yaja granodiorite cut by the gangdese thrust indicates a crystallization age of 30 4 0 4 ma 2 thus placing an upper bound on the initiation of the thrust u pb zircon dating of granitoid samples structurally higher in the gangdese hanging wall yields emplacement ages of 42 5 1 0 ma and 48 9 0 8 ma 2 similar to other magmatic complexes within the gangdese arc geochemical results are consistent with these plutons forming in the same environment as precollisional intrusions within the gangdese batholith suggesting a significant post collisional input of juvenile heat the 40ar 39ar thermochronology of samples from a vertical section through the hanging wall within the yaja granodiorite coupled with results of a numerical thermal model indicate an average slip rate along the gangdese thrust of 7 mm yr between 30 and 23 ma and a minimum displacement of 50 km farther east in the zedong window thermal effects produced by later north directed thrust sheets of the renbu zedong system appear to have obscured thermal history signatures in the gangdese hanging wall related to earlier south directed thrusting thermochronological results from this region indicate that thermal overprinting related to the north directed thrusting occurred between 25 and 10 ma consistent with previous estimates

taphonomy of phytoliths and macroplants in different soils from olduvai gorge tanzania and the application to plio pleistocene palaeoanthropological samples the abundance and types of phytoliths in the fossil record are taphonomically biased and do not correspond with the macroplant record to better understand the bias and improve the interpretation of samples from olduvai gorge tanzania we analysed the phytoliths from three sample sets modern grasses sedges palm and dicots in the area modern soils in the area and the fossil soils from the eastern palaeolake margin in lowermost bed ii fourier transform infrared spectrometry analyses were performed in parallel to compare the mineral composition of both modern soils and fossil soils we found that the abundance of phytoliths is greatly reduced in soil samples compared with modern plant material but the morphotypes can be reliably interpreted dicotyledonous wood bark phytoliths appear to be over represented in the soil types grass phytoliths and sedges to a lesser degree are preserved in the soils but in lower abundances resulting in these groups being under represented the macroplant fossils are fragments of grass and sedge aerial culms and dicotyledonous stems that are preserved in fluvial and lacustrine deposits it is suggested that phytoliths represent the continuous flora whereas macroplant fossils represent the more robust tissues of selected plants preserved under more catastrophic conditions a post depositional model is proposed and the palaeovegetation is reinterpreted as being richer and more complex than indicated by other fossil data

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

northeast african vegetation change over 12 m y intense debate surrounds the evolution of grasses using the c 4 hatch slack photosynthesis pathway and the emergence of african grasslands often assumed to be one and the same here we bring new insights with the combination of plant leaf wax carbon isotopic composition 13 c wax and pollen data from marine sediments of the gulf of aden northeast africa which show that c 4 biomass increases were not necessarily associated with regional grassland expansion we find broadly opposing trends toward more enriched 13 c wax values and decreased grass pollen proportions between 12 and 1 4 ma this apparently contradictory evidence can be reconciled if a greater proportion of the late miocene northeast african landscape were covered by c 3 grasses than previously thought such that c 4 grasses and shrubs replaced a c 3 ecosystem including trees and productive grasslands in addition 13 c wax and pollen both indicate that true rainforests were unlikely to have been extensive in northeast africa at any time in the last 12 m y although seasonally dry forests were a significant component of the regional landscape since the late miocene here we extend regionally integrative marine archives of terrestrial vegetation back to 12 ma and we evaluate them in the context of an updated compilation of pedogenic carbonate 13 c values from east african rift strata we identify two distinct phases of increasing c 4 biomass between 11 and 9 ma with a reversal by 4 3 ma and then a re expansion between 4 3 and 1 4 ma surprisingly neither was associated with grassland expansion

tibet uplift and erosion abstract the 5 km high tibetan plateau is an outstanding topographic feature on the earth today its horziontal extent elevation and location cause significant effects on modern atmospheric circulation and climate so the history of uplift of the surface of tibet is linked to cenozoic climate changes at local regional and perhaps global scales geological and geophysical studies of the plateau are contributing data on the present and past deformation of the tibetan lithosphere that has formed the plateau primarily during the cenozoic the principal of isostasy then can be used to estimate the elevation history of the surface for a given deformation history different parts of tibet probably had different uplift histories but presently available data are not sufficient for distinguishing many contrasts in one scenario cretaceous and early cenozoic north south distributed shortening of tibetan crust and mantle lithosphere probably caused significant uplift of the surface relative to sea level to perhaps half of the present elevation by the early miocene thinning of the high density mantle portion of the lithosphere during the miocene may then have allowed the thick tibetan crust to rise close to its present elevation perhaps higher before 8 ma since then slow east west extension of tibet probably reduced the crustal thickness slightly and may have caused the elevation of the plateau to decrease during the late cenozoic erosion of tibet unlike narrow mountain belts has been unable to match the uplift of a broad plateau orographic precipitation and efficient river networks concentrate erosion on the edges while the interior is protected from significant erosion despite its lofty elevation the southern edge of the plateau the himalaya has suffered a minimum of 25 km of denudation since the miocene while central tibet shows little or no sign of major erosion since that time the gangdese arc in southern tibet was rapidly eroded during the mid miocene when 4 km of rock apparently were removed from the surface as shown by mineral cooling ages this pulse of erosion was probably caused by a combination of local thrust system movement and changes in base level and precipitation due to relative elevation changes between the gangdese and the himalaya to the south the modern long wavelength flatness of tibet is unlikely to have been caused by erosion and indicates viscous flow at some level of the lithosphere has been acting to level the plateau surface

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

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

upb geochronology of gangdese transhimalaya plutonism in the lhasa xigaze region tibet abstract a series of different plutons from the lhasa xigaze segment of the gangdese transhimalaya belt has been studied by high resolution u pb analyses of zircon using zircon fractions of 5 100 grains each selected upon specific grain characteristics for two diorites located east of xigaze dazhuka the zircons yield concordant ages of 93 4 1 0 and 94 2 1 0 m y respectively also concordant ages of 41 1 0 4 and 41 7 0 4 m y have been obtained for two granodiorites collected southwest of lhasa qushui the precision on the ages of two granites from the xigaze and lhasa area is limited by two factors the presence of inherited radiogenic lead and the occurrence of subsequent lead loss however some concordant zircons detected in both granites define approximate ages of about 67 and 53 m y respectively the inherited lead components show that melting of precambrian material was involved in magma genesis the u pb ages substantiate a magmatic activity lasting from mid cretceous cenomanian to eocene lutetian time such a period of plutonism at the southern margin of eurasia as well as the occurrence of magma generation from continental crust suggest that the gangdese range results from the subduction of tethys oceanic lithosphere indian plate underneath eurasia eurasian plate if this model is true the collision of india with eurasia along the lhasa xigaze sector postdates the emplacement of the 41 m y old gangdese granodiorites i e the collision occurred after lutetian time

petrogenetic and tectonic significance of young leucogranites from the northwestern himalaya pakistan in the himalaya of northwestern pakistan small discordant bodies of leucogranite intrude metamorphosed basement of the indian crust as the first step in assessing the tectonic significance of these granites we have used the shrimp ion microprobe to obtain u pb dates on zircon zircons of igneous appearance are scarce in the leucogranites and with one exception are associated with xenocrystic components which occur as discrete grains and as cores rimmed by young zircon zircons of igneous appearance are high in u 5000 to 40 000 ppm low in th u 0 01 to 0 05 and frequently colored a distinct blue xenocrystic components give a range of proterozoic ages consistent with ages previously reported for indian crust in sharp contrast zircons of igneous appearance yield clusters of concordant tertiary ages two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 ma swat and about 50 ma naran together with previously determined 40ar 39ar and fission track cooling ages these ages document immediate and rapid metamorphism and denudation following eocene collision three leucogranite dikes from northern localities within the nanga parbat haramosh massif are very young having emplacement ages of about 2 3 ma 5 ma and 7 ma the formation and emplacement of these leucogranites during the rapid late tertiary denudation of the nanga parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis

did the indo asian collision alone create the tibetan plateau it is widely believed that the tibetan plateau is a late cenozoic feature produced by the indo asian collision however because tibet was the locus of continental accretion and subduction throughout the mesozoic crustal thickening during that time may also have contributed to growth of the plateau this portion of the geologic history was investigated in a traverse through the central lhasa block southern tibet together with earlier studies our mapping and geochronological results show that the lhasa block underwent little north south shortening during the cenozoic rather our mapping shows that 60 crustal shortening perhaps due to the collision between the lhasa and qiangtang blocks occurred during the early cretaceous this observation implies that a significant portion of southern tibet was raised to perhaps 3 4 km elevation prior to the indo asian collision

paleoenvironmental interpretation of lake margin deposits using δ13c and δ18o results from early pleistocene carbonate rhizoliths olduvai gorge tanzania isotope analyses of lake margin rhizoliths from paleo lake olduvai ca 1 75 ma form the basis of a new model proposed here for interpreting stable isotope values of phreatic rhizolith carbonates average 18o and 13c values from rhizoliths formed in transgressive lacustrine waxy claystones are relatively low low 18o averages 5 5 reflect meteoric water values consistent with increased precipitation during wet periods that would increase the outflow of fresh water from subsurface seeps and shift a brackish groundwater zone lakeward low 13c averages 4 1 could indicate little atmospheric exchange high plant decay and or increased groundwater low 13c flow higher averages in 18o 3 6 and 13c 2 0 occur during dry periods and lake regressions earthy claystones when hydraulic head is reduced the lake recedes and water within the wetlands is subjected to intense evaporation and gas exchange with the atmosphere the isotope ratios of the rhizoliths from lowermost bed ii change in response to groundwater hydrology on milankovitch time scales but the isotopes also provide evidence of shorter term decadal to centennial scale climate fluctuations the orbitally driven climate changes are recorded faithfully by lithologic variations and stable isotope patterns

petrologic case for eocene slab breakoff during the indo asian collision the greater himalayan sequence is the metamorphic core of the himalaya and has been a focus of considerable study yet its petrologic evolution remains controversial pre oligocene metamorphism was nearly obliterated by miocene metamorphism and melting which many workers ascribe to shear heating unusually high concentrations of radioactive elements accompanying burial and or several kilometers of miocene exhumation due to extensional faulting sparse oligocene to eocene ages are often assigned to a tectonically unspecified event an alternative slab breakoff model subduction of greater himalayan rocks to 100 km depth in the eocene followed by buoyant extrusion due to decoupling of the oceanic lithosphere has also been proposed based on rare eocene eclogites but without explanation of miocene melting or metamorphic petrogenesis we argue that slab breakoff readily explains the eocene eclogites miocene partial melts and late eocene k rich magmas in southeastern tibet and that metamorphic and plutonic ages help define the timing and rates of breakoff and extrusion this model implies that 1 much of the greater himalayan sequence was subducted to depths greater than commonly considered 2 fluid absent decompression melting at 30 35 km depth was the consequence of as much as 100 km of extrusion rather than radioactive heating or a smaller crustal level extensional or erosional event and 3 eruption of eocene k rich tibetan plateau lavas has no implication for topography of the tibetan plateau

the namche barwa syntaxis evidence for exhumation related to compressional crustal folding abstract geological observation in the eastern end of the himalayas shows that the asia india suture is folded and continues southward into india and burma where the continuation of the transhimalayan plutonic complex can be identified metamorphic rocks derived from india occur structurally below the suture in the core of a regional antiform isotopic and fission track dating are consistent with the geological interpretation in addition they establish cooling exhumation of rocks from c 30 km depth within the last 4 ma rapid exhumation of deep crustal levels in mountain systems is generally related to extension subsequent to thermal softening of a thickened continental lithosphere however in the eastern himalayas we argue that exhumation is caused by c 10 mm yr 1 erosion coeval with crustal scale folding the general history of this syntaxis resembles the evolution of the western himalayas syntaxis in pakistan

modelling vegetation change during late cenozoic uplift of the east african plateaus abstract the present day vegetation in the tropics is mainly characterized by forests worldwide except in tropical east africa where forests only occur as patches at the coast and in the uplands these forest patches result from the peculiar aridity that is linked to the uplift of the region during the late cenozoic the late cenozoic vegetation history of east africa is of particular interest as it has set the scene for the contemporary events in mammal and hominin evolution in this study we investigate the conditions under which these forest patches could have been connected and a previous continuous forest belt could have extended and fragmented we apply a dynamic vegetation model with a set of climatic scenarios in which we systematically alter the present day environmental conditions such that they would be more favourable for a continuous forest belt in tropical east africa we consider varying environmental factors namely temperature precipitation and atmospheric co 2 concentrations our results show that all of these variables play a significant role in supporting the forest biomes and a continuous forest belt could have occurred under certain combinations of these settings with our current knowledge of the palaeoenvironmental history of east africa it is likely that the region hosted these conditions during the late cenozoic recent improvements on environmental hypotheses of hominin evolution highlight the role of periods of short and extreme climate variability during the late cenozoic specific to east africa in driving evolution our results elucidate how the forest biomes of east africa can appear and disappear under fluctuating environmental conditions and demonstrate how this climate variability might be recognized on the biosphere level

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

late pliocene grassland from olduvai gorge tanzania abstract the olduvai fossil plants documented by us in this paper are the first direct evidence for open grassland in the late neogene of africa based on macroplant remains silicified remains of herbaceous ground cover are exceptionally well preserved in situ within late pliocene sediments below the initial pyroclastic ash surge unit of tuff if in the uppermost part of bed i olduvai gorge northern tanzania published radiometric and palaeomagnetic dates place this grass layer between 1 839 0 005 ma and 1 785 0 01 ma exposed at localities on the south side of the gorge this herbaceous ground cover grew on a floodplain developed on a dried out lake bed following pronounced lake retreat of saline alkaline palaeo lake olduvai during a developing dry climatic phase sheathed basal culms rhizomes and roots are interpreted as those of one or more small mat forming grasses or less likely sedges small dicotyledonous herbs were probably also present the proximity of adjacent plants indicates a relatively dense ground cover roots extended at least 8 cm below the ground surface aerial parts of the plants were absent or were not preserved when the weathered basal culms were covered by a thin layer of brown waxy clay followed by fallout of pyroclastic ash both units were mostly eroded away prior to emplacement of a wet cool pyroclastic surge which then buried and preserved in situ remnants of the herbaceous ground cover preservation of the semi woody rhizomes implies well drained soils otherwise the plant material would have quickly rotted collections from discontinuous exposures indicate the grassland covered an area of at least a few hectares this open grassland would have provided grazing for the late pliocene fauna

high temperature metamorphism in a major strike slip shear zone the ailao shan red river people s republic of china abstract petrographic and thermobarometric analysis provides constraints on thept path of the mylonitic gneisses of the left lateral ailao shan red river shear zone which has accommodated the lateral extrusion of indochina during the tertiary two different paragenesis p1 and p2 are coeval with this deformation and correspond respectively to the amphibolite and greenschist facies microprobe analysis reveals that p1 garnets bear a chemical zonation from core to rim this zonation indicates a temperature increase during garnet growth conditions of formation of garnet rims p1b which are estimated using biotite garnet and plagioclase garnet thermobarometers are close to the granitic solidus 710 70 c and4 5 1 5 kbar p2 conditions are estimated to be approximately 500 c and

metamorphism and melting of the lithosphere due to rapid denudation nanga parbat massif himalaya the nanga parbat haramosh massif of the western himalaya has undergone a complex metamorphic and denudational history over the past 1 8 ga metamorphism in the tato region is characterized by a barrovian type metamorphism followed by partial melting and recrystallization along shear zones during nearly isothermal decompression while the massif was still at temperatures 550 c mineralogical and textural evidence for this path includes garnet zoning patterns late stage migmatization abundant cordierite both in schists and leucogranite dikes replacement of high pressure assemblages by low pressure assemblages and abundant low density inclusions thermobarometry on the nonmigmatized gneisses reveals conditions of 540 740 c at 7 1 13 1 kbar thermobarometry in the migmat ized rocks reveals final equilibration at 608 675 c at 3 9 6 8 kbar early fluid inclusions occur in quartz inclusions within garnet porphyroblasts that grew during decompression the last fluid inclusions to be trapped occur in microfrac

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

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

plio pleistocene macroplant fossil remains and phytoliths from lowermost bed ii in the eastern palaeolake margin of olduvai gorge tanzania abstract fossil macroplants and phytoliths occur in the sediments of the palaeoanthropological site of olduvai gorge northern tanzania current research on hominin land use in the basin during the plio pleistocene has a strong palaeoenvironmental emphasis on the palaeovegetation in particular the occurrence of macroplants and phytoliths at olduvai and their usefulness and reliability for palaeovegetation interpretation are assessed here for the first time modern reference collections from analogous environments have been established and used to identify the fossil taxa from the eastern palaeolake margin of lowermost bed ii as the test case for very detailed spatially and temporally constrained vegetation reconstruction fourier transform infrared spectrometry ftir analysis was used to identify the minerals of the fossil sediments modern plants produce more phytoliths than are preserved in the fossil soils but there were sufficient numbers to show diverse and changing vegetation over short time periods silicified macroplant fragments of sedge culms and dicot stems occur with phytoliths but do not always represent the same plant taxa a more complex flora was shown when using both forms of fossil plants during lowermost bed ii times at the locality of flkn monocots and dicots occurred indicating the presence of marshland and grassland after the deposition of tuff if at vek the phytoliths indicate a shift in dominance from dicots to monocots to a mixture of the two and including palms at hwkee initially palms dominated then there was a mixture of palms grasses and dicots the vegetation at mck comprised dicots monocots sedges and grasses this detailed vegetation data complements the more broad scale vegetation interpretations that have been deduced from the pollen isotopes and faunal data sets