paleovegetation simulations of lowland amazonia and implications for neotropical allopatry and speciation paleovegetation modeling simulations of the lowland amazon basin were made to assess the relative importance of glacial climate and atmospheric co2 for altering vegetation type and structure as well as to explore the potential physiological mechanisms underlying these ecosystem level responses modeling results support the view that widespread invasion of grasslands into the amazon lowlands during the last glaciation was not likely glacial cooling was probably responsible for maintaining glacial forest cover via its effects in reducing photorespiration and decreasing evapotranspiration which collectively improve plant carbon and water relations modeling results confirm that leaf area index lai a common proxy for canopy density is highly sensitive to independent and interactive changes in climate and low concentration of atmospheric co2 and the results show considerable region to region variation during the last glaciation heterogeneous variations in glacial vegetation lai may have promoted allopatric speciation by geographically isolating species called vicariance in the forest sub canopy the proposed vicariance hypothesis incorporating spatial variations in canopy density conforms to many of the essential tenets addressed by previous neotropical speciation models but also helps to overcome some of their inconsistencies c 2001 university of washington

practical application of the sequential balancing technique an example from the irish variscides the process of sequential restoration presented by cooper trayner 1986 is applied to a n s cross section through the irish variscides to demonstrate that this approach improves the accuracy of thin skinned structural modelling and allows the progressive deformation of a marginal belt to be examined the principles and methods of sequential restoration are illustrated the cross section is restored in four steps and gives a bulk shortening of 52 in this model the fold belt evolved as the basal decollement migrated northwards and considerable ductile shortening by folding and cleavage formation preceded faulting although faulting gradually became more important towards the north the section is divided into four structural domains based upon different deformation histories each is restored independently by removing the ductile strain before restoring the faulting from this example it is clear that many models derived from single step balancing especially those through ductile deformed areas should be re examined

persistent millennial scale climatic variability over the past 25 000 years in southern africa abstract data from stalagmites in the makapansgat valley south africa document regional climatic change in southern africa in the late pleistocene and holocene a new tims u series dated stalagmite indicates speleothem growth from 24 4 to 12 7 ka and from 10 2 to 0 ka interrupted by a 2 5 ka hiatus high resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated 17 ka was interrupted by cooling probably associated with the antarctic cold reversal and was followed by strong warming after 13 5 ka the early holocene experienced warm evaporative conditions with fewer c4 grasses cooling is evident from 6 to 2 5 ka followed by warming between 1 5 and 2 5 ka and briefly at ad 1200 maximum holocene cooling occurred at ad 1700 the new stalagmite largely confirms results from shorter holocene stalagmites reported earlier the strongest variability superimposed on more general trends has a quasi periodicity between 2 5 and 4 0 ka also present are weaker 1 0 ka and 100 year oscillations the latter probably solar induced given similarities to the antarctic records the proximate driving force producing millennial and centennial scale changes in the makapansgat record is postulated to be atmospheric circulation changes associated with change in the southern hemisphere circumpolar westerly wind vortex

decay constant errors in u pb concordia intercept ages abstract although almost universally ignored the effect of errors in the uranium decay constants on u pb concordia intercept ages and pb pb ages are significant and not equivalent to those of simple u pb ages equations are derived for concordia intercept age errors that take decay constant errors into account

irish carboniferous conodonts record maturation levels and the influence of tectonism igneous activity and mineralization organic maturation patterns in the lower carboniferous of ireland have been determined from conodont colour alteration indices cai for some 750 localities onshore ireland conodonts record increasing maturation in the carboniferous rocks from the oil window rocks of the north east southwards to the greenschist meta argillite regime of the munster basin in detail the caledonoid trend has a marked influence in the midlands whilst in the south sharp variations in cai are interpreted as being caused by thrusting of the variscan orogeny in the south east low maturities in the wexford half graben indicate that the region was shielded from orogenic stresses probably by the leinster massif igneous centres such as the carlingford complex and croghan hill produce local sites of increased palaeotemperature significant cai variations have also been noted in proximity to major base metal orebodies the cai results highlight north east ireland and the wexford half graben as areas with hydrocarbon potential

earth s precession cycle and quaternary climatic change in tropical africa high abundances of the freshwater diatom melosira spp reflecting eolian input from dry lake beds in tropical africa occur in deep sea sediments of the equatorial atlantic at discrete times during the late quaternary1 2 we report here an approximately 260 kyr record of melosira accumulation in an equatorial atlantic sediment core and demonstrate significant influence of the earth s precessional cycle on the climate of tropical africa

importance of the indian ocean for simulating rainfall anomalies over eastern and southern africa the relative contributions of the indian ocean and pacific ocean sea surface temperatures ssts to the rainfall variability over eastern central and southern africa during the austral spring summer are examined the variability of african rainfall is statistically related to both oceans but the variability in the two oceans is also related to separate the effects of the indian and pacific oceans a suite of numerical model simulations is presented goga the atmosphere is forced by observed ssts globally ioga the atmosphere is forced by observed ssts only in the indian ocean basin and poga the atmosphere is forced by observed ssts only in the tropical pacific basin while the sst variability of the tropical pacific exerts some influence over the african region it is the atmospheric response to the indian ocean variability that is essential for simulating the correct rainfall response over eastern central and southern africa analyses of the dynamical response s seen in the numerical experiments and in the observations indicate that the pacific and indian oceans have a competing influence over the indian ocean african region this competition is related to the influence of the two oceans on the walker circulation and the consequences of that variability on low level fluxes of moisture over central and southern africa finally given the high correlation found between sst variability in the indian and pacific oceans with the pacific leading by 3 months we speculate on an approach to long lead dynamical climate prediction over central east and southern africa

stable isotopic composition of fossil mammal teeth and environmental change in southwestern south africa during the pliocene and pleistocene abstract the past 5 million years mark a global change from the warmer more stable climate of the pliocene to the initiation of glacial interglacial cycles during the pleistocene marine core sediment records located off the coast of southwestern africa indicate aridification and intensified upwelling in the benguela current over the pliocene and pleistocene however few terrestrial records document environmental change in southwestern africa over this time interval here we synthesize new and published carbon and oxygen isotope data of the teeth from large mammals 6 kg at langebaanweg 5 million years ago ma elandsfontein 1 0 0 6 ma and hoedjiespunt 0 35 0 20 ma to evaluate environmental change in southwestern africa between the pliocene and pleistocene the majority of browsing and grazing herbivores from these sites yield enamel 13c values within the range expected for animals with a pure c3 diet however some taxa have enamel 13c values that suggest the presence of small amounts c4 grasses at times during the pleistocene considering that significant amounts of c4 grasses require a warm growing season these results indicate that the winter rainfall zone characteristic of the region today could have been in place for the past 5 million years the average 18o value of the herbivore teeth increases 4 4 between langebaanweg and elandsfontein for all taxa except suids this increase may solely be a function of a change in hydrology between the fluvial system at langebaanweg and the spring fed environments at elandsfontein or a combination of factors that include depositional context regional circulation and global climate however an increase in regional aridity or global cooling between the early pliocene and mid pleistocene cannot explain the entire increase in enamel 18o values spring fed environments like those at elandsfontein may have provided critical resources for mammalian fauna in the mid pleistocene within an increasingly arid southwestern africa ecosystem

dissolved gas paleotemperatures and 18o variations derived from groundwater near uitenhage south africa abstract under the near ideal hydrologic conditions provided by the uitenhage artesian aquifer reliable estimates of paleotemperatures were obtained by measurement of the dissolved n2 and ar in groundwater confidently dated in the range 28 000 yr b p to the present using 14c the mean annual air temperature in this area during the last glaciation is calculated to have been on average 5 1 2 c lower than during the holocene the change in the 18 o 16 o ratio of the groundwater corrected for changes in ocean water amounted to 0 4 per c

what is the timing of orbital scale monsoon changes abstract a major but little noted divergence of opinion has developed among climate scientists over the orbital scale periodicity and phasing of tropical monsoon variations kutzbach 1981 monsoon climate of the early holocene climate experiment with earth s orbital parameters for 9000 years ago science 214 59 61 proposed that monsoons are driven by northern summer insolation at the precession period but clemens and prell 1990 late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments paleoceanography 5 109 145 2003 a 350 000 year summer monsoon multi proxy stack from the owen ridge northern arabian sea marine geology 201 35 51 inferred a more complicated response tied to latent heat transfer from the southern hemisphere because tropical monsoons affect climate over a vast area resolving this divergence is an important task for the climate community the purpose of this note is to highlight definitive evidence from high resolution dating of speleothem calcite that provides unambiguous support for the kutzbach hypothesis

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

high and low latitude orbital forcing of early hominin habitats in south africa abstract reconstructions of african palaeoenvironments are essential for a full understanding of early hominin evolution but they are often hampered by low resolution or discontinuous climatic data here we present high resolution oxygen 18 o and carbon 13 c isotope time series for the pliocene early pleistocene 1 99 to 1 52 ma of south africa derived from the buffalo cave flowstone deposit the 18 o data are dominated by variations at the orbital precession period 18 23 ka as is typical for records of sub tropical monsoon rainfall the 13 c data indicate the proportion of savannah grasses c 4 plants compared to trees and shrubs c 3 plants and this signal is dominated by an obliquity periodicity 40 ka commonly associated with high latitude ice sheet dynamics a rapid increase in savannah grass proportions between 1 78 and 1 69 ma coincides with a pulse in african mammal turnover and lends support to an adaptive link between the appearance of african homo erectus and the increasingly savannah dominated environment

a chronology of foreland deformation ultra violet laser 40ar 39ar dating of syn late orogenic intrusions from the variscides of southwest ireland abstract the upper palaeozoic sedimentary rocks of the munster and south munster basins southern ireland lie within the rhenohercynian zone of the european variscan orogeny this foreland region accommodated shortening during the asturian phase of variscan deformation at the end of the carboniferous by the development of kilometre scale and lower order folding high angle reverse faulting and regional fabric development at the southwestern extremity of the belt lies the black ball white ball heads area of the beara peninsula where high level igneous intrusions locally exhibit a close relationship with both the ductile and late brittle phases of variscan deformation 40 ar 39 ar ultra violet laser analysis of phlogopite crystals from these intrusions principally trachytic dykes has yielded ages that when combined with structural field relationships help to constrain the timing of variscan deformation in southern ireland these ages include 314 44 1 00 ma for a penetratively deformed lamprophric pipe on black ball head 301 98 1 47 298 08 0 61 ma for dyke material associated with later stage brittle deformation and a date of 296 88 0 60 ma for an undeformed post orogenic dyke on white ball head

isotopic evidence for plio pleistocene environmental change at gona ethiopia abstract a 4 5 ma record of fluvial and lacustrine deposits is well exposed at gona in the afar depression of ethiopia we use isotopic values of pedogenic carbonate and fossil teeth to reconstruct plio pleistocene environmental change at gona an increase in 13c values of pedogenic carbonates since 4 5 ma points to a shift from woodlands to grassy woodlands in the early pliocene 10 4 to 3 9 vpdb to more open but still mixed environments in the late pleistocene 3 0 to 1 4 vpdb this pattern is also seen in isotopic records elsewhere in east africa however at 1 5 ma the higher proportion of c4 grasses at gona is largely a result of a local facies shift to more water limited environments the wide range of 13c values of pedogenic carbonate within single stratigraphic levels indicates a mosaic of vegetation for all time intervals at gona that depends on depositional environment elements of this mosaic are reflected in 13c values of both modern plants and soil organic matter and plio pleistocene soil carbonate indicating higher amounts of c4 grasses with greater distance from a river channel in both the modern and ancient awash river systems 18o values of pedogenic carbonates increase up section from 11 9 in the early pliocene to 6 4 vpdb in the late pleistocene the wide range of 18o values in paleovertisol carbonates from all stratigraphic levels probably reflects short term climate changes and periods of strong evaporation throughout the record based on the comparison between 18o values of plio pleistocene pedogenic carbonates and modern waters we estimate that there has been a 6 5 increase in mean annual 18o values of meteoric water since 4 5 ma 18o values of pedogenic carbonate from other east african records indicate a similar shift increasing aridity and fluctuations in the timing and source of rainfall are likely responsible for the changes in 18o values of east african pedogenic carbonates through the plio pleistocene

orbital forcing of climate over south africa a 200 000 year rainfall record from the pretoria saltpan late pleistocene variations in rainfall in subtropical southern african are estimated from sediments preserved in the pretoria saltpan a 200000 year old closed basin crater lake on the interior plateau of south africa we show that south african summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession as predicted by orbital precession geometry berger 1978 this south african record is out of phase with north african palaeomonsoon indices street and grove 1979 rossignol strick 1983 mcintyre et al 1989 the amplitude of the rainfall response to insolation forcing agrees with climate model estimates prell and kutzbach 1987 these results document the importance of direct orbital insolation forcing on both subtropical north and south african climate as well as the predicted antiphase sensitivity to precessional insolation forcing

500 000 year stable carbon isotopic record from devils hole nevada the record of carbon 13 delta 13 c variations in dh 11 vein calcite core from devils hole nevada shows four prominent minima near glacial terminations glacial interglacial transitions v to ii the delta 13 c time series is inversely correlated with the dh 11 oxygen isotope ratio time series and leads it by as much as 7000 years the delta 13 c variations likely record fluctuations in the delta 13 c of dissolved inorganic carbon of water recharging the aquifer how such variations are transported 80 kilometers to devils hole without obliteration by water rock reaction remains an enigma the record may reflect i global variations in the delta 13 c of atmospheric co 2 and hence the delta 13 c of continental biomass or ii variations in extent and density of vegetation in the southern great basin in the latter case delta 13 c minima at 414 334 246 and 133 thousand years ago mark times of maximum vegetation

precise dating of low temperature deformation strain fringe analysis by 40ar 39ar laser microprobe pyritized graptolites from the welsh basin united kingdom slate belt acted as rigid bodies during cleavage formation and epizonal white micas formed within the resulting strain shadows orthogonal to the principal stress orientation although the quantities of mica are small they are a pure synkinematic mineral and have been dated by ar 40 ar 39 infrared laser microprobe as a means to dating cleavage four samples of strain fringe mica from different hand samples yielded ages ranging from 394 4 3 1 to 397 8 1 8 ma 2sigma with a mean age of 396 1 1 4 ma 2sigma by focusing on minerals that are unequivocally synkinematic this technique provides a novel solution to the problems of isotopically dating slaty cleavage previous studies have predominantly relied on dating whole rock slate samples or separated illite grains by ar 40 ar 39 techniques problems encountered included 1 separating the effects of isotopic contamination by detrital phases 2 ar 39 loss during the irradiation of illite mineral separates and 3 thermally induced ar 40 loss in nature from fine grained minerals by circumventing these problems this new method provides the first unequivocal and high precision age data for acadian deformation in the well characterized welsh basin slate belt with such precision the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent continent collision

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

co2 and temperature controlled altitudinal shifts of c4 and c3 dominated grasslands allow reconstruction of palaeoatmospheric pco2 abstract during the pleistocene the vegetation changes in the high colombian andes included changes from c3 to c4 plants this is inferred from 13c values of the c31 n alkane from the funza 2 sedimentary record taken from the high plain of bogota at 2550 m elevation the environmental factors thought to be responsible for these changes were investigated using a single point simulation of the biome3 vegetation model including changes in precipitation temperature and atmospheric co2 concentrations the model shows that changes are for a major part caused by these latter two factors the isotopic signature of the n alkanes of several extant c3 and c4 grasses from the area were determined to calibrate the interpretation of the isotopic record from the geochemical record we estimated the altitudinal distribution of c3 and c4 plants using present grass distribution patterns based on floristic data as a template this information in combination with palaeotemperature estimates enabled the reconstruction of atmospheric co2 concentrations the reconstructed co2 concentrations follow the trends of the vostok antarctic ice core through three glacial and two interglacial stages the lowest calculated co2 concentration is ca 210 ppmv for the glacial maxima and within the range of lowest values from vostok our highest value 310 ppmv is for interglacial mis 7 this represents a new method to reconstruct palaeoatmospheric pco2 it is less accurate than measurements from ice cores but has potential to be used for sediments that are much older than the ice cores

a new structural model for the sw irish variscides the variscan front of the nw european rhenohercynian abstract the variscan front of nw europe has been drawn in the past from belgium across southern england and southern wales towards southern ireland but the term variscan front is not well defined and means different things to different people a tectonic front should represent the outcrop of a frontal thrust or the tip line of the basal detachment in fact such a tectonic front cannot be traced along the so called variscan front in ireland field based studies of the western part of the irish variscides show that the fold and thrust belt continues north of the so called variscan front but deformation decreases gradually therefore we suggest supported by seismic data a detachment which ends as a blind thrust far to the north the tip line of this basal detachment represents the true tectonic front of the variscides in sw ireland shear indicators show locally a dextral shear component near major faults and 3d microstructural strain analyses show varying x axes and oblate deformation indicating transpression during the tectonic evolution of the western irish variscides therefore a thin skinned model associated with dextral shearing and transpression in the hanging wall of the basal detachment is suggested the evolution of the variscan fold and thrust belt in nw europe is related to the west european indentation model but also to pre variscan basement structures as the leinster wales and london brabant massifs finally an attempt is made to outline the variscan front along the entire nw european rhenohercynian fold and thrust belt ftb

el nino s tropical climate and teleconnections as a blueprint for pre ice age climates 1 at 2 7 million years ago the warm equable climates of early and middle pliocene time used here to mean from 5 to 2 7 ma were replaced by recurring ice ages most attempts to explain the change appeal either to changes in co2 in the atmosphere or reduced heat transport by the atlantic ocean the sources of the strongest teleconnections in the current climate however lie in the tropics and such connections occur by transport of heat and moisture by the atmosphere the most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial pacific el nino southern oscillation enso variations with warm and dry or cool and wet anomalies in extratropical climates we show that in most cases early and middle pliocene climate both in equatorial regions and in the extratropics differ from present day climates with the same spatial pattern as that associated with enso for instance not only was canada warmer during early pliocene time than at present as it is during el nino but the region surrounding the gulf of mexico appears to have been cooler and a bit wetter as it commonly is during el nino a virtually permanent el nino like state appears to have characterized pre ice age climates suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth accordingly cooling and the growth of recurring ice sheets in the northern hemisphere resulted from the development of a strong walker circulation and a weakening of the hadley circulation

contemporaneous faulting and the eruption and preservation of the lough guitane volcanic complex co kerry interbedded with the clastic fluvial sediments of the munster basin the lough guitane volcanic complex represents a rare volcanic episode in the upper devonian of sw ireland from three distinctly separate volcanic centres an exclusively rhyolitic suite of thick lava flows and tuffs were erupted the largest of the centres possessed a system of contemporaneous faults producing a subcircular depressed area itself enclosed within a graben 1 5 km across these faults lead to rapid thickness variations in many volcanic units and a pooled lava flow reaches a thickness of 300 m the site of a major elongate vent lies along one such fault and rapid erosion of its poorly lithified walls generated coarse sandstone boulder agglomerates and is related to the absence throughout the complex of normal air fall tuffs unmixed with terrigenous sand the containment of the bulk of the volcanics by contemporaneous faults and subsequent rapid burial by terrigenous sediments has led to preservation of the volcanic succession virtually intact

structural evolution of the irish variscides the effects of the variscan orogeny on the upper palaeozoic succession are recognizable throughout central and southern ireland the deformation can be zoned using structural styles and trends which illustrate a northward decrease in deformation intensity coupled with increasing control by pre variscan structures in the basement the most intense deformation occurs to the south of the dingle dungarvan line where shortening approaches 50 as a result of layer parallel shortening followed by buckling and finally thrusting the deformation is considered to have developed above a shallow dipping sole thrust which has been located offshore by the swat seismic reflection profiles cross faults which are common throughout the orogen resulted from n s shear couples this is consistent with their origin as accommodation structures due to differential shortening along strike the original shape of the munster basin has exerted a control on the distribution and overall facing of the major structures the sole thrust extends to the north of the dingle dungarvan line and the structural zonation of the orogen is due to variations in the stratigraphic level of this thrust the leinster massif is considered to be essentially autochthonous slip on the sole thrust decays towards the massif which acted as a rigid passive block and was partially responsible for the arcuate trend of the orogen

speleology and magnetobiostratigraphic chronology of the buffalo cave fossil site makapansgat south africa speleological stratigraphic paleomagnetic and faunal data is presented for the buffalo cave fossil site in the limpopo province of south africa speleothems and clastic deposits were sampled for paleomagnetic and mineral magnetic analysis from the northern part of the site where stratigraphic relationships could be more easily defined and a magnetostratigraphy could therefore be developed for the site this is also where excavations recovered the fossil material described a comparison of the east and south african first and last appearance data with the buffalo cave fauna was then used to constrain the magnetostratigraphy to produce a more secure age for the site the magnetostratigraphy showed a change from normal to reversed polarity in the basal speleothems followed by a short normal polarity period in the base of the clastic deposits and a slow change to reversed directions for the remainder of the sequence the biochronology suggested an optimal age range of between 1 0 ma and 600 000 yr based on faunal correlation with eastern and southern africa a comparison of the magnetobiostratigraphy with the gpts suggests that the sequence covers the time period from the olduvai event between 1 95 and 1 78 ma through the jaramillo event at 1 07 ma to 990 000 yr until the bruhnes matuyama boundary at 780 000 yr the faunal bearing clastic deposits are thus dated between 1 07 ma and 780 000 yr with the main faunal remains occurring in sediments dated to just after the end of the jaramillo event at 990 000 yr

the structural evolution of the western irish variscides an example of obstacle tectonics abstract detailed mesostructural and strain analysis investigations across the killarney mallow fault i e the traditional variscan front in southwest ireland reveal that this structural line separates two distinct tectonic regimes north of the killarney mallow fault bulk shortening orthogonal to orogenic strike is estimated to be 12 all of which is accounted for by late stage buckling microscopic strain analysis reveals that there is only local development of a tectonic fabric south of the front bulk shortening is 40 due to combined layer parallel shortening lps buckling and faulting variscan deformation is presented as being essentially coaxial the regional finite strain pattern outlined above is thought to be primarily controlled by the combined effect of a buried basement obstacle in eastern iveragh and increased sedimentary pile thickness at the western end of the orogen

transgressive facies in the south munster basin ireland this paper describes the sedimentation style associated with the basal carboniferous transgression in southern ireland and the influence which this event had on the palaeogeography of the region the transgression as marked by the base of the carboniferous succession is shown to represent one of several genetically related transgressive pulses which commenced during the late devonian at this time an east west trending graben the south munster basin developed in southern ireland this was initially a non marine depositional site in which sediment was derived from the north and west subsidence and eustatic sea level rise resulted in a marine transgression which proceeded in a rhythmic style resulting in a number of transgressive stillstand pulses the first transgressive pulse t1 advanced in a westerly direction along the basin axis resulting in the development of an epicontinental like sea the shoreline remained essentially static along the northern basin margin initially until a second transgressive pulse t2 resulted in expansion of the marine area the latter proceeded by gradual northward erosive advance of a barred coastal area as far as the northern basin margin where the stability of the bounding platform halted its progress erosion of the barrier shoreface was insufficient to destroy all the backbarrier lagoonal deposits which are preserved as a thin transgressive diachronous unit which grades northwards to a coastal alluvial plain immediately preceding the basal carboniferous transgression t3 a shallow wave dominated storm influenced shelf sea occupied the basinal area two sublittoral sand bar complexes developed on the shelf under the influence of shore parallel current regimes apparently derived from source areas located on either side of the epicontinental sea the basal carboniferous transgression took place in two pulses the first t3a resulted in a rapid reduction in sand supply to the shelf and deposition of clay the barrier shoreline responded by erosively retreating across the lagoon leaving a transgressive lag in its wake its northwards advance was however limited due to the relative stability of the northern platform sand supply to the shelf was completely terminated in the second pulse t3b and the barrier rapidly migrated erosively across the northern platform for a considerable distance such that the coastal plain is overlain by a thin transgressive lag this transgressive phase was immediately followed by shoreline stillstand and progressive shallowing of the shelf an open sandy shelf developed on which offshore sand bars accumulated under a storm and wave dominated regime clay deposition continued in the deeper part of the basinal area but was eventually terminated as the shelf sands prograded centripetally into the basin the main factor that controlled the style of the overall transgression was an interplay between eustatic sea level rise and basin subsidence the rate of relative sea level rise together with the effect of differential subsidence and fluvial input from the north appear to have diminished with time the rate at which successive transgressive pulses advanced northwards shows an overall progressive increase

biomarker records of late neogene changes in northeast african vegetation open savannah grasslands dominated by c4 plants became a significant component of northeast african vegetation during the late neogene we present molecule specific carbon isotopic mea surements of terrestrial plant biomarkers preserved in marine sed iments off northeast africa that allow reconstruction of orbital scale vegetation changes in short time windows over the past 9 4 m y the biomarker data show large amplitude vegetation vari ability as early as 3 8 ma with the greatest c4 expansion occurring after 3 4 ma we sampled orbital scale oscillations of up to 5 almost as large as the observed late neogene range of 7 sug gesting that large and repeated oscillations between more open and more closed landscapes were an important aspect of northeast af rican vegetation change during the past 4 m y

isotopic age determinations of crystalline rocks of the upper harz mountains germany dating of crystalline rocks occurring in the upper harz mountains was carried out by means of u pb isotope investigations on zircons and sphene as well as by rb sr isotope measurements on whole rock samples and biotites

flexural shear in a periclinal fold from the irish variscides abstract periclinal folds occur in a structural culmination in the centre of the irish variscan fold belt the culmination marks a zone of enhanced shortening which is associated with a locally attenuated stratigraphy and an anomalous deformation sequence with respect to the remainder of the orogen originally vertical burrows have been used along with cleavage fold relations to study both the three dimensional evolution of the periclinal folding and the temporal relationship between folding and cleavage as well as cleavage forming flattening strains the burrows record along strike shear related to the propagation of the periclinal folds a comparison with strain measurements made outside the culmination zone shows that the galley head area suffered higher strains integration of field data with published analyses of plasticine modelling of periclinal folds yields models for the propagation of a pericline and for the geometry of its lateral terminations

effects of deep co 2 on petroleum and thermal alteration the case of the huangqiao oil and gas field abstract the co2 rich natural gas from the huangqiao oil and gas field of the subei basin is produced along with crude oil the co2 content ranging from 80 56 to 99 30 and the 3he 4he ratio of 0 94 10 6 to 4 67 10 6 indicates that this includes a substantial fraction of mantle derived co2 in the huangqiao region although the positive carbon isotopic series of alkane gases i e 13c1 the crude oil of the huangqiao region is light or condensate oil with low densities of 0 7933 0 8255 g cm3 saturated hydrocarbons comprise 90 06 97 37 the crude oil while the aromatic non hydrocarbon and asphaltene fractions are very small the n alkanes range from c13 to c34 with highest abundances at c16 and c17 the gas chromatogram of the crude oil shows an unresolved hump or unresolved complex mixture ucm distribution of a complete n alkane series non odd even predominance and major n alkane peaks on the highest positions of the ucm distribution this may indicate that deep mantle derived co2 fluid extracted and accumulated the oil now found in the reservoirs or source rocks

subpolar link to the emergence of the modern equatorial pacific cold tongue the cold upwelling tongue of the eastern equatorial pacific is a central energetic feature of the ocean dominating both the mean state and temporal variability of climate in the tropics and beyond recent evidence for the development of the modern cold tongue during the pliocene pleistocene transition has been explained as the result of extratropical cooling that drove a shoaling of the thermocline we have found that the sub antarctic and sub arctic regions underwent substantial cooling nearly synchronous to the cold tongue development thereby providing support for this hypothesis in addition we show that sub antarctic climate changed in its response to earth s orbital variations from a subtropical to a subpolar pattern as expected if cooling shrank the warm water sphere of the ocean and thus contracted the subtropical gyres

pliocene pleistocene evolution of eastern tropical pacific surface water circulation and thermocline depth we evaluated the response of eastern equatorial pacific upper water column hydrography to the panama seaway closure and the initiation of large scale northern hemisphere glaciation the 18o gradient between globorotalia tumida and globigerinoides sacculifer indicates a general shoaling of the thermocline between 4 2 and 3 0 ma which may be related to a recorded decrease in southeast trade wind strength the 13c gradients suggest that surface water nutrient concentrations have increased during the last 5 myr and that upwelling intermediate waters began to change sources at 3 2 ma changes in the trans pacific east west temperature and nutrient gradients at 4 0 and 1 5 ma are coincident with the seaway closure and a major phase of northern hemisphere glaciation changes in the sensitivity of surface circulation to milankovitch forcing 18o records linearly related to orbital variations only after 3 2 ma are associated with the seaway closure pleistocene initiation of 100 and 41 kyr cycles in the thermocline depth proxy may suggest that the hydrographic response to milankovitch forcing is enhanced by air sea interactions which maintain the relatively steep pleistocene trans pacific gradients the 13c records are dominated by the 41 kyr period and are usually coherent with high latitude climate suggesting that associated changes in the global carbon reservoir dominate the tropical 13c signals

a window into africa s past hydroclimates the sisal_v1 database contribution africa spans the hemispheres from temperate region to temperate region and has a long history of hominin evolution although the number of quaternary palaeoclimatic records from the continent is increasing much of the history of spatial and temporal climatic variability is still debated speleothems as archives of terrestrial hydroclimate variability can help reveal this history here we review the progress made to date with a focus on the first version of the speleothem isotopes synthesis and analysis sisal database the geology of africa has limited development of large karst regions to four areas along the northern coast bordering the mediterranean eastern africa and the horn of africa southwestern africa and southern africa exploitation of the speleothem palaeoclimate archives in these regions is uneven with long histories of research e g in south africa but large areas with no investigations such as west africa consequently the evidence of past climate change reviewed here is irregularly sampled in both time and space nevertheless we show evidence of migration of the monsoon belt with enhanced rainfall during interglacials observed in northeast africa southern arabia and the northern part of southern africa evidence from eastern africa indicates significant decadal and centennial scale rainfall variability in northwestern and southern africa precession and eccentricity influence speleothem growth largely through changing synoptic storm activity

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

extremely large variations of atmospheric 14c concentration during the last glacial period a long record of atmospheric 14c concentration from 45 to 11 thousand years ago ka was obtained from a stalagmite with thermal ionization mass spectrometric 230th and accelerator mass spectrometric 14c measurements this record reveals highly elevated 14c between 45 and 33 ka portions of which may correlate with peaks in cosmogenic 36cl and10be isotopes observed in polar ice cores superimposed on this broad peak of 14c are several rapid excursions the largest of which occurs between 44 3 and 43 3 ka between 26 and 11 ka atmospheric 14c decreased from 700 to 100 per mil modulated by numerous minor excursions carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle

stable isotopes in east african precipitation record indian ocean zonal mode observational stable isotope data and model simulations show that the 18 o composition of precipitation in east africa is closely related to the coupled ocean atmosphere system over the indian ocean during the rainy seasons 18 o is a very sensitive recorder of the indian ocean zonal mode iozm the link between 18 o and the iozm is established through adjustments in the large scale overturning circulation over the indian ocean and associated changes in convective activity and precipitation over east africa the iozm is recorded as significant departures in 18 o not only over east africa but as a dipole mode with opposite sign to the east and west of the indian ocean

geochemistry of precambrian carbonates iv early paleoproterozoic 2 25 0 25 ga seawater in an effort to narrow down the first and second order variations in isotopic composition of the early paleoproterozoic 2 25 0 25 ga seawater we report a comprehensive study of mineralogy chemistry and isotopic composition of the malmani dolomite transvaal supergroup south africa duck creek dolomite wyloo group australia and bruce limestone member of the espanola formation huronian supergroup canada based on trace element data their diagenetic rank increases in the order duck creek bruce malmani the interpolation of alteration trends to best values yields an estimate of 0 70550 for 87sr86sr comparable to our previously published value of 0 70496 for 13c the measured range of 0 1 5 pdb is similar to that observed for phanerozoic marine carbonates in contrast the best 18o value for dolostones is 5 pdb depleted in 18o relative to phanerozoic counterparts but comparable to the estimates obtained by similar approach for archean facies the isotope geochemistry and mineralogy of bruce limestone member is consistent with the proposition that the sequence may have been deposited in a lacustrine environment possibly related to the recession of the brace glaciers if such interpretation proves unacceptable from a sedimentological standpoint the origin of the unusual isotopic signatures must be sought despite the above trace element interpretation in as yet unspecified post depositional alteration phenomena in contrast to phanerozoic carbonates the early paleoproterozoic as well as the previously described archean counterparts are enriched in mn and fe

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

orbital precession modulates interannual rainfall variability as recorded in an early pleistocene speleothem interannual variability of african rainfall impacts local and global communities but its past behavior and response in future climate projections are poorly understood this is primarily due to short instrumental records and a lack of long high resolution palaeoclimate proxy records here we present an annually resolved 91 000 year early pleistocene record of hydroclimate from the early hominin bearing makapansgat valley south africa changes in speleothem annual band thickness are dominated by precession over four consecutive orbital cycles with strong millennial scale periodicity the frequency of interannual variability 2 0 6 5 yr oscillations does not change systematically yet its amplitude is modulated by the orbital forcing these long term characteristics of interannual variability are reproduced with transient climate model simulations of water balance for south africa from the late pleistocene to recent based on these results we suggest that the frequency of interannual variations in southern african rainfall is likely to be stable under anthropogenic warming but that the size of year to year variations may increase we see an orbitally forced increase in the amplitude of interannual climate variability between 1 8 ma and 1 7 ma coincident with the first evidence for the acheulean stone tool technology

east african climate change and orbital forcing during the last 175 kyr bp abstract variations in the temporal and spatial distribution of solar radiation caused by orbital changes provide a partial explanation for the observed long term fluctuations in african lake levels the understanding of such relationships is essential for designing climate prediction models for the tropics our assessment of the nature and timing of east african climate change is based on lake level fluctuations of lake naivasha in the central kenya rift 0 55 s 36 20 e inferred from sediment characteristics diatoms authigenic mineral assemblages and 17 single crystal 40ar 39ar age determinations assuming that these fluctuations reflect climate changes the lake naivasha record demonstrates that periods of increased humidity in east africa mainly followed maximum equatorial solar radiation in march or september interestingly the most dramatic change in the naivasha basin occurred as early as 146 kyr bp and the highest lake level was recorded at about 139 133 kyr bp this is consistent with other well dated low latitude climate records but does not correspond to peaks in northern hemisphere summer insolation as the trigger for the ice age cycles the naivasha record therefore provides evidence for low latitude forcing of the ice age climate cycles

physiological significance of low atmospheric co2 for plant climate interactions abstract methods of palaeoclimate reconstruction from pollen are built upon the assumption that plant climate interactions remain the same through time or that these interactions are independent of changes in atmospheric co 2 the latter may be problematic because air trapped in polar ice caps indicates that atmospheric co 2 has fluctuated significantly over at least the past 400 000 yr and likely the last 1 6 million yr three other points indicate potential biases for vegetation based climate proxies first c 3 plant physiological research shows that the processes that determine growth optima in plants photosynthesis mitochondrial respiration photorespiration are all highly co 2 dependent and thus were likely affected by the lower co 2 levels of the last glacial maximum second the ratio of carbon assimilation per unit transpiration called water use efficiency is sensitive to changes in atmospheric co 2 through effects on stomatal conductance and may have altered c 3 plant responses to drought third leaf gas exchange experiments indicate that the response of plants to carbon depleting environmental stresses are strengthened under low co 2 relative to today this paper reviews the scope of research addressing the consequences of low atmospheric co 2 for plant and ecosystem processes and highlights why consideration of the physiological effects of low atmospheric co 2 on plant function is recommended for any future refinements to pollen based palaeoclimatic reconstructions

diachronous variscan tectonothermal activity in the nw iberian massif evidence from 40ar 39ar dating of regional fabrics abstract multigrain concentrates of hornblende and muscovite together with whole rock slate phyllite samples have been dated 27 analyses using 40ar 39ar incremental release methods along a systematic traverse across the various lithotectonic structural elements which comprise northwestern sectors of the variscan iberian massif hornblende concentrates from amphibolites in the allochthonous ordenes complex yield plateau isotope correlation ages of 425 ma and 377 ma muscovite concentrates and whole rock slate phyllite from this and the cabo ortegal complex yield plateau ages which range from 367 ma to 295 ma analyses of similar material from the relative autochthon yield plateau ages between 359 ma and 275 ma muscovite concentrates from three late to post kinematic granitic stocks yield plateau ages between 309 ma and 274 ma at least seven of the 40ar 39ar analyses from metamorphic rocks record variable thermal rejuvenation of intracrystalline argon systems associated with emplacement of proximal granitic stocks the remaining analyses may be used to constrain the local age of various variscan tectonothermal events the oldest fabric ages are recorded in allochthonous units whereas the youngest fabric ages occur along the boundary between internal and external zones middle devonian ages are recorded in the allochthon and suggest a chronological continuity with deformational events in the relative autochthon where variscan deformation initiated in the upper devonian and diachronously prograded eastward the first deformational events recorded in the limit within the internal and external zones occured ca 20 25 ma later lower namurian variscan deformation systematically prograded diachronously eastward across the orogen as new crustal material was added along the front of the developing orogenic wedge however the entire orogen remained tectonically active with different structural features forming at different times and at different places an average propagation rate of ca 5 km m y is suggested by consideration of a 20 25 ma difference in correlative fabric ages and present separations

assessing the paleoenvironmental potential of pliocene to holocene tufa deposits along the ghaap plateau escarpment south africa using stable isotopes the tufa deposits of the ghaap plateau escarpment provide a rich yet minimally explored geological archive of climate and environmental history coincident with hominin evolution in south africa this study examines the sedimentary and geochemical records of ancient and modern tufas from buxton norlim limeworks groot kloof and gorrokop to assess the potential of these sediments for providing reliable chronologies of high resolution paleoenvironmental information chronometric dating demonstrates that tufa formation has occurred from at least the terminal pliocene through to the modern day the stable isotope records show a trend toward higher more variable 18o and 13c values with decreasing age from the end of the pliocene onwards the long term increase in 18o values corresponds to increasingly arid conditions while increasing 13c values reflect the changing proportion of c3 c4 vegetation in the local environment analysis of the thabaseek tufa in particular provides valuable evidence for reconstructing the depositional and chronological context of the enigmatic taung child australopithecus africanus collectively the results of the present study demonstrate the potential of these deposits for developing high precision records of climate change and ultimately for understanding the causal processes relating climate and hominin evolution

diachronous and independent histories of plutonism and mineralization in the cornubian batholith southwest england concordant u pb dates of magmatic monazites in the dominant coarse grained biotite muscovite granites of the late variscan cornubian batholith demonstrate that the emplacement of the six main plutons was diachronous ranging from 293 1 1 3 ma carnmenellis to 274 5 1 4 ma land9s end southern lobe 40 ar 39 ar age spectra for magmatic muscovites confirm that cooling to about 320 c at the present level of exposure was accomplished within 4 to 5 ma in each intrusion moreover age spectra for hydrothermal muscovites show that development of the major sn cu lodes of the south crofty mine commenced before 286 ma only 2 to 3 ma after cooling of the hosting cam brea granite a satellite of the carnmenellis pluton the older plutons had therefore approached ambient temperatures and had even experienced intense hydrothermal activity before emplacement of the youngest

late pleistocene records of speleothem stable isotopic compositions from pinnacle point on the south african south coast highly resolved well dated paleoclimate records from the southern south african coast are needed to contextualize the evolution of the highly diverse extratropical plant communities of the greater cape floristic region gcfr and to assess the environmental impacts on early human hunter gatherers we present new speleothem stable oxygen and carbon isotope ratios 18 o c and 13 c from two caves at pinnacle point south africa covering the time between 330 and 43 ka composite 18 o c and 13 c records were constructed for staircase cave and pp29 by combining all stable isotope analyses into a single time series and smoothing by a 3 point running mean 18 o c and 13 c values record changes in rainfall seasonality and the proportions of c3 and c4 plants in the vegetation respectively we show that in general increased summer rainfall brought about a wider spread of c4 grasses and retreat of the c3 plant dominated gcfr communities the occurrence of summer rainfall on the southern coast of south africa was linked to total rainfall amounts in the interior region through tropical temperate troughs these rainfall systems shifted the southern coastal climate toward more summer winter rainfall when precession was high low and or the westerlies were in a northern southern position

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

taphonomic interpretations of the haasgat hgd assemblage a case study in the impact of sampling and preparation methods on reconstructing south african karstic assemblage formation abstract the haasgat fossil bearing karstic system is situated within the skurweberg mountain range in the northeastern portion of the fossil hominids of south africa unesco world heritage site in south africa as is the case for the nearby gondolin hominin locality haasgat occurs in an area of substantial modern topographic relief that contrasts with the low relief landscape of the southwestern extent of the world heritage site surrounding the blauubank stream valley sites e g sterkfontein swartkrans kromdraai bolt s farm this suggests differential landscape formation processes during the neogene and potentially novel palaeoecosystems and taphonomic processes governing karstic fossil assemblage composition across even a small geographic region this is particularly critical given the overall paucity of taphonomic data from the region the substantial cercopithecoid primate assemblage that is uniquely dominated by the basal baboon species papio angusticeps and the recent announcement of the first hominin specimen from haasgat here we provide the first comprehensive taphonomic analysis of the haasgat hgd faunal assemblage that was developed from ex situ calcified sediment blocks in the 1990s there is direct evidence for biotic activity e g large bodied carnivores and porcupines mediating the formation of parts of the hgd faunal assemblage including at least part of the primate craniodental and postcranial sample there is minimal evidence for pre depositional element uv exposure and weathering or winnowing of the assemblage but there is abiotic distortion and crushing of elements our analysis has equally found that taphonomic data from the hgd assemblage is compromised by a modern overprint of damage through mechanical preparation and a lack of documentation generated during sampling processing and initial curation nearly half the cortical surfaces and many dental specimens in the assemblage exhibit evidence of substantial preparation damage rendering many purported biotic modifications ambiguous or suspect element proportions may be artificially skewed towards craniodental specimens and more reflective of block selection and or selective processing rather than original deposition composition as a result the haasgat hgd sample provides only limited data on the depositional processes mediating karstic assemblage formation in the region and ultimately serves as a cautionary tale of the impacts of palaeontological sampling strategies on subsequent analysis and research

dead carbon in stalagmites carbonate bedrock paleodissolution vs ageing of soil organic matter implications for 13c variations in speleothems twenty one 14c accelerator mass spectrometric analyses were obtained for three holocene stalagmites from the uamh an tartair cave sutherland scotland in order to estimate the past dead carbon proportion dcp results show that the dcp increases from 22 to 38 from 3780 years ago to the present because 13c variation is small within each sample it is concluded that this dcp increase is the product of the ageing of soil organic matter related to peat bog development above the cave that produced older soil co2 and not from a more intense dissolution of the surrounding carbonates which would have led to a 13c increase comparison with samples from other sites in europe shows no intersite correlation between dcp and 13c but a relatively good intersite correlation is observed between dcp and average site temperature thus temperature may be a major factor controlling the production of old soil organic matter co2 and therefore the dead carbon content of seepage water in contrast to the scotland stalagmites two other holocene samples from sites in southern france and belgium exhibit a good correlation between 13c and dcp which can be explained in terms of variations in the intensity of limestone dissolution consequently 13c variations observed in stalagmites are not always due to changes in the vegetation type c3 c4 as has been commonly assumed 13c 12c variations in speleothem calcite may also be controlled by the soil organic matter age and in some cases by the intensity of the limestone dissolution conversely a largely constant speleothem 13c signal as observed for the scotland stalagmites does not necessarily imply that surface climate and vegetation conditions were stable since the dcp variations in this case are clearly related to the peat bog development during stalagmite growth

the 41 kyr world milankovitch s other unsolved mystery 1 for most of the northern hemisphere ice ages from 3 0 to 0 8 m y global ice volume varied predominantly at the 41 000 year period of earth s orbital obliquity however summer or summer caloric half year insolation at high latitudes which is widely believed to be the major influence on high latitude climate and ice volume is dominated by the 23 000 year precessional period thus the geologic record poses a challenge to our understanding of climate dynamics here we propose that variations in the insolation gradient between high and low latitudes control high latitude climate and ice volume during the late pliocene and early pleistocene the differential heating between high and low latitudes driven by obliquity controls the atmospheric meridional flux of heat moisture and latent energy which may exert the dominant control on high latitude climate on milankovitch timescales in the two dimensional zonal energy balance models typically used to study the long term evolution of climate the meridional atmospheric moisture flux is usually kept fixed the hypothesis that insolation gradients control the poleward energy fluxes precipitation and ice volume at high latitudes has never been directly examined within the context of an ice sheet model in light of what we know about modern energy fluxes and their relative influence on high latitude climate this possibility should be examined

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