vegetation history and climate in the savanna biome south africa since 190 000 ka a comparison of pollen data from the tswaing crater the pretoria saltpan and wonderkrater abstract the long term quaternary vegetation and climate history in south africa s savanna biome since ca 190 000 yr bp is elucidated by the palynological record of lake sediments in the tswaing crater the pretoria saltpan and spring deposits from wonderkrater despite hiatuses in both sequences palaeotemperature trends from the two places are presented by means of principal components analysis pca of pollen data allowing a new regional palaeoenvironmental reconstruction correlation in the older sections of the sequences beyond radiocarbon dating is tentative suggesting that the wonderkrater sequence is roughly 4 times younger than the tswaing sequence combined temperature indications from the two sites suggest cooling at ca 14 000 yr bp and slight warming at ca 15 000 yr bp although no data are available between ca 15 000 and 21 000 and 25 000 and 31 000 yr bp generally cool conditions are suggested between ca 11 000 and 33 000 yr bp between ca 33 000 and an extrapolated age of ca 80 000 yr bp at least three warmer pulses of varying intensity occurred no data are available between ca 80 000 and 150 000 yr but between 150 000 and ca 190 000 yr bp two cool and two moderately warm phases are suggested

late quaternary hydrological dynamics in the middle kalahari forcing and feedbacks the kalahari region has become a major source of quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change one suite of data from palaeolacustrine landforms has recently provided a new record of major hydrological changes in the last 150 ka burrough s l thomas d s g bailey r m 2009 mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system quaternary science reviews in press here we present an improved analysis of the drivers and feedbacks of lake level change utilising information from three main sources data from the lake system itself from analyses of other late quaternary records within the region and from climate modelling simulations using the hadley centre coupled climate model hadcm3 suggest that once triggered the lake body was large enough to potentially affect both local and regional climates surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late quaternary through its capacity to couple middle kalahari environments to distant forcing mechanisms and to itself force environmental change we demonstrate that the existence or absence of megalake makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern africa s summer rainfall zone

siderophile trace elements in alh84001 other snc meteorites and eucrites evidence of heterogeneity possibly time linked in the mantle of mars we report neutron activation analyses including radiochemical determination of trace siderophile elements au ge ir ni os and re for three snc martian meteorites and os and re results for numerous eucrites ratios such as ga al in the snc orthopyroxenite alh84001 confirm its martian affinity its many distinctive characteristics most notably its near primordial age notwithstanding to the list of alh84001 s idiosyncrasies can now be added extraordinarily low concentrations of au ni and especially re 17 pg g for a martian meteorite we consider several possible origins for the anomalously low re content in alh84001 including metasomatism or alteration the pyroxene cumulate nature of this rock probably does not account for its low re content other snc meteorites are also cumulates an examination of re nd variations among terrestrial basalts and komatiites suggests that re is compatible with mantle minerals in general and only incompatible with olivine however olivine dominates the mantle residuum especially during komatiite genesis our preferred model is that the alh84001 parent melt formed in a mantle source region that was far more re depleted and or at a substantially lower oxygen fugacity than the sources of the young snc meteorites such a contrast is consistent with models that replenish siderophile elements in planetary mantles by gradual admixture of late accreting matter and similarly derive most planetary water which serves as an oxidant very late in accretion according to this model alh84001 formed before the siderophile rich matter and water had been mixed well into the martian interior possibly the martian mantle never became generally as re rich and or oxidized as the source region s of the younger sncs

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

a high resolution 15 600 year pollen and microcharcoal record from the cederberg mountains south africa abstract the cederberg mountains western cape province south africa are located within the fynbos biome which exhibits some of the highest levels of species richness and endemism in the world the region s post glacial vegetation history however remains largely unknown presented here are high resolution pollen and microcharcoal records spanning the last 15 600 years obtained from the de rif rock hyrax midden from the driehoek valley of the central cederberg in this region previous pollen studies have shown muted variability in vegetation community composition during periods of globally marked climatic variability e g the last glacial interglacial transition in our record however significant changes in vegetation composition are apparent most notably they indicate a shift from ericaceous restioid fynbos present from 15 600 to 13 300 cal yr bp to a brief but prominent development of proteoid fynbos at the beginning of the holocene around 11 200 cal yr bp this vegetation shift is associated with increased moisture at the site and coincides with reduced fire frequency as indicated by the microcharcoal record at 10 400 cal yr bp there is a marked reduction in protea type pollen which is replaced by thicket characterised by dodonaea which became the dominant arboreal pollen type this shift was likely the result of a long relatively fire free period coupled with warmer and wetter climates spanning much of the early holocene a brief but marked decrease in water availability around 8500 8000 cal yr bp resulted in the strong decrease of dodonaea pollen the vegetation of the mid to late holocene is characterised by the increased occurrence of asteraceae and succulent taxa suggesting substantially drier conditions these data give unprecedented insight into the vegetation dynamics across a period of substantial rapid climate change and while they confirm the presence of fynbos elements throughout the last 15 600 years the results highlight significant fluctuations in the vegetation that were triggered by changes in both climate and fire regimes

late quaternary vegetation dynamics and hydro climate in the drakensberg south africa abstract a multi proxy study of a sediment sequence from braamhoek wetland covering the last c 16 000 years reveals a record of regional climate and vegetation dynamics in the drakensberg region south africa including signals from both the organic sediment fraction fossil pollen charcoal n alkane abundance n alkane 13c toc and the inorganic fraction mineral magnetic properties the reconstruction supported by a robust chronology indicates two major periods of increased regional wetness during the late pleistocene to early holocene phase c 13 800 12 600 cal yr bp c 10 200 8500 cal yr bp and one during the late holocene c 2000 cal yr bp to present drier conditions are recorded during the younger dryas c 12 600 11 300 cal yr bp and mid holocene c 7000 2000 cal yr bp a major decline in fynbos vegetation during the early holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern south africa from c 8500 cal yr bp comparison with records from interior of south africa show relatively high inter site variability however the braamhoek moisture proxies do co vary with the speleothem isotope records from makapansgat suggesting a similar hydro climate evolution in eastern and interior parts of the summer rainfall region during the studied period on multi millennial time scales an inverse hydro climatological pattern is evident between these two south african records and reconstructions from tropical locations in southeast africa such a rainfall dipole between eastern tropical and southern africa has previously been identified on shorter time scales i e on inter annual to millennial scales the braamhoek study suggests that a similar dipole pattern is acting also on a multi millennial perspective these long term precipitation anomalies are tentatively coupled to teleconnections from multi millennial changes in the dynamics of the indian ocean dipole iod and el nino southern oscillation enso

tectonosphere of the earth upper mantle and crust interaction abstract the endogenic geological processes which include tectonic magmatic and metamorphic processes form regular combinations called endogenic regimes these regimes are geosynclinal orogenic platform rift tectonic magmatic activation diwa taphrogenic plateau basalt oceanic basins and mid oceanic ridges the endogenic regimes are connected with the peculiarities of the structure composition and state of the entire tectonosphere i e not only of the crust but of the upper mantle as well heat flow is a major factor controlling the type of the regime the other conditions are the temperature distribution in the tectonosphere and the degree and type of penetrability of the tectonosphere to melts and fluids there is a certain regular succession of regimes the structural evolution of the tectonosphere and the transformation of the matter in it are in close relationship the main trend in the development of the tectonospheric material is directed towards geochemical depletion of the upper mantle by fractioning at the initial stages fractioning occurred mostly by degassing and under these conditions the continental crust was formed rich in non compatible elements at that stage the calc alkaline magmas prevailed as the upper mantle was depleted and began to lose its volatiles the mechanism of fractioning changed degassing was substituted for selective melting and in this environment most of the tholeiitic magmas were formed this change in magma composition and in fractioning mechanism was combined with the destruction of the continental crust and the formation of the oceanic crust the diwa regime and the rifts were the first steps in the destruction of continental crust the stages that followed were represented by taphrogenic regimes at various levels these kinds of regimes were manifested in deep continental and marine depressions compensated and not compensated by sediments taphrogenic regimes are advancing from the east and west onto the eurasian continent in the east they form marginal seas and cause subsidence of the eastern parts of the chinese platform in the west they produce collapses of the crust in the mediterranean area the major crisis occurred between the palaeozoic and mesozoic and since that time the process of substitution of the continental crust by the oceanic crust has proceeded over increasingly large territories the evolution of the tectonosphere instigated by the changes in its matter was further complicated by temporal and spatial irregularities in deep heat escape which caused the alternation of excited and quiescent endogenic regimes tectonomagmatic periodicity and their co existence the combination of all these phenomena creates the structural inhomogeneity of the earth s crust at any stage of its history

petrogenesis of the zagami meteorite inferences from synchrotron x ray sxrf microprobe and electron microprobe analyses of pyroxenes abstract the zagami meteorite is a shergottite a basalt rich in pigeonite augite and maskelynite glass shocked plagioclase it is one of the snc meteorites which are inferred to have formed on mars major and minor element abundances in pyroxene principally pigeonite from newly available unm samples were determined by electron microprobe abundances of trace elements ni cu zn and ga were obtained by synchrotron x ray sxrf microprobe many pigeonite grains have normally zoned rims and reversely zoned cores so that the most magnesian pigeonite forms rings or annuli in thin section view in three dimensions the most magnesian pigeonite may form tubes or hourglass shapes the cores commonly contain magmatic inclusions other pigeonites have irregular or multiple magnesian regions with magmatic inclusions among and between them abundances of ni and cr in the magnesian zones and cores are partially decoupled from abundances of other compatible mg and incompatible fe ti elements the textures chemical zoning and element decouplings in the pigeonites are consistent with igneous crystal growth at moderate cooling rates not isothermally or near equilibrium from element partitioning and mass balance the unm zagami is estimated to contain 20 5 or less cumulus pyroxene half augite and half pigeonite half the proportion suggested by equilibrium distribution of fe mg between pigeonite and melt this inconsistency may be resolved if all pigeonite melt element partitioning was affected by the rapid growth of the pigeonites the composition of the parental magma for the unm zagami calculated by mass balance on bulk and pyroxene compositions is similar to the 1170 c melt of the bmnh zagami not the 1140 c melt inferred as parental by other workers the inference that the pyroxene zoning patterns reflect only magmatic events is consistent with an igneous age of 180 m y for zagami

quantitative reconstructions of annual rainfall in africa 6000 years ago model data comparison precipitation are based on 85 pollen sites 14 c dated at 6000 500 years b p and distributed over the whole of africa to improve the reliability of the pollen based climate reconstruction two methods are used the modern analogues technique mat and the plant functional types pft methods we then conduct a model data comparison for five distinct regions allowing an evaluation of model outputs the sahara sahel the eastern sahara western equatorial africa east africa and madagascar the pollen inferred reconstructions are compared with 21 mid holocene simulations yielded by atmospheric general circulation models agcms and coupled ocean atmosphere vegetation models oavgcms the large scale feature of the hydrological changes is shown to be well captured by most of the models data show that during the mid holocene the sahara was considerably wetter than today 200 to 700 mm yr the results reinforce the conclusion that the agcms significantly underestimate this precipitation increase in the sahara whereas the oavgcm simulations are in accordance with the data our results show that vegetation and ocean feedbacks do not have a strong impact in the intertropical zone and that models fail to properly reproduce the climatic conditions in east africa and madagascar the model data comparison also suggests that the lengthening of the dry season during boreal winter in the west equatorial region is a robust feature although the pollen based reconstruction shows no change or only slight drying there

geotectonic significance of gneissic amphibolites from the vema fracture zone equatorial mid atlantic ridge a large collection of gneissic amphibolites was recovered by two close dredge hauls from the deepest part of the north facing slope of the transverse ridge forming the south wall of the vema fracture zone serpentinites and various types of gabbroic rocks ranging from undeformed slightly uralitized gabbros and norites to flaser and mylonitic gabbros were associated with the gneissic amphibolites in the shallowest of the dredge hauls petrological studies indicate that the amphibolites were derived from similar gabbroic rocks that reequilibrated under stress in the conditions of the amphibolite facies on the other hand the associated meta gabbros display sequences of secondary minerals indicating complex cooling and cataclastic histories without reaching metamorphic equilibrium we tentatively suggest that the gneissic amphibolites and associated metagabbros formed in a vertical shear zone generated in oceanic layer 3 by tectonism associated with the vema fracture zone hydrothermal circulation of seawater along the highly permeable shear zone was activated by magmatic intrusions k ar dating suggests within relatively large analytical uncertainties that the amphibolite metamorphism took place 10 m y ago i e at a time when the dredging sites were located in the vicinity of the spreading center

formerly emerging crustal blocks in the equatorial atlantic abstract anomalous crustal topographic highs exceeding the level predicted by the thermal contraction model by up to 2 3 km are observed along the romanche transform zone in the equatorial atlantic previous studies of shallow water reef limestones recovered from one of the shallowest sites on these crustal highs indicated that this site was at or above sea level 5 million years ago and subsided since at an average rate one order of magnitude faster than the subsidence estimated by thermal contraction of the crust seismic reflection profiles obtained across the romanche transform zone suggest that the anomalous highs are capped by reef limestones not only where limestones were actually sampled but also at other locations these findings support the idea that long segments of crust reached close to sea level in the past along the romanche transform zone the vertical crustal motions are probably caused by tectonism typical of long offset transforms inasmuch as the romanche has been a ridge ridge transform since the earliest stages of the opening of the equatorial atlantic it is likely that intense vertical tectonic motions occurred along it throughout the evolution of the atlantic support for this hypothesis is provided by the recovery during dsdp leg 4 of shallow water reef limestone of the eocene age from the summit of the north brazilian ridge along the western extension of the romanche fracture zone the presence of shallow or emergent crust across the equatorial zone during the early stages of opening had probably important consequences upon the water circulation between the north and the south atlantic and may even have provided land bridges for faunal migrations between africa and south america in early cenozoic times after the two continents had already separated

holocene climate change in southernmost south africa rock hyrax middens record shifts in the southern westerlies abstract south africa s southern coastal margin is recognised as being a highly dynamic climatic region that plays a critical role in both regional and global atmospheric and oceanic circulation dynamics our understanding of the past dynamics of this system however has been limited by the number and nature of datasets available that can be used to infer changes in key climatic parameters in the region in this paper we present new high resolution 13c and 15n data from two independently dated rock hyrax procavia capensis middens from seweweekspoort in south africa s groot swartberg mountains these data provide information regarding both past vegetation and hydroclimatic change and allow a regional integration of available data that explore the long term dynamics of mid latitude circulation systems in the african sector of the southern hemisphere combined a negative relationship is apparent between temperature and humidity in this area of the southern cape and these changes can for the first time be clearly linked to variations in antarctic sea ice extent and shifts in the southern westerly storm track this dynamic is particularly evident between 5 and 7 cal kbp when a reduction in sea ice extent and a southward shift of the westerlies are manifested regionally by increased temperatures and a phase of marked aridity

coastal paleo environment and sea level change at macassa bay southern mozambique since c 6600 cal bp changes in holocene coastal paleo environment and sea level variations have been recorded in estuary sediments from macassa bay southern mozambique methods include analysis of fossil diatoms sediment stratigraphy mineral magnetic properties stable carbon and nitrogen isotope composition and carbon and nitrogen content the chronology based on six ams c 14 dates suggests a basal age of the sediment core of c 6600 cal bp calibrated years before present the multi proxy dataset implies two phases when the site was experiencing marine conditions and tentative sea level high stands 1 between c 6600 6300 cal bp which is contemporary with the last phase of the global transgression and the holocene climatic optimum and 2 between c 4700 1000 cal bp a period when sea level curves from the region suggest occasional minor sea level high stands between these phases c 6300 4700 cal bp the environment within the macassa bay estuary was less influenced by marine processes and studied proxies indicate a freshwater phase associated with relatively low sea levels after c 1000 cal bp a terrestrial environment prevailed at the site probably as a result of a combined effect of sea level lowering and high accumulation of organic peat within the estuary c 2011 elsevier ltd and inqua all rights reserved

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

tectonic setting of the bela ophiolites southern pakistan abstract the bela ophiolites consist of a 3 5 km thick sequence of basaltic pillow lava inter flow sedimentary rocks chert argillite limestone and diabase gabbro sills debris of serpentinite up to kilometer sized blocks serpentinite carbonate breccia and less commonly of basalt gabbro peridotite pelagic limestone and their metamorphic equivalents occur throughout the ophiolite sequence and may form extensive horizons the age of the ophiolites as indicated by pelagic microfauna is aptian early maestrichtian the lava flows belong to a spilite keratophyre basaltic andesite suite of tholeiites enriched in fe tio 2 and other trace elements the lava flows although similar to the e type morb differ in details such as la ta ratio ranges 9 62 18 04 for the bela lavas versus 10 15 for the morb the diabase gabbro sills are similar to the associated lava flows however due to their relative enrichment in certain elements e g fe ti hf th and ta etc they may represent more fractionated late melts a comparison of the stratigraphic and structural features of the bela ophiolites with modern oceanic environments reveals that these ophiolites probably originated in a large oceanic fracture zone leaky transform this is based on lithotectonic features such as the common occurrence of debris of foliated serpentinite and serpentinite carbonate breccia bearing rocks in the ophiolite sequence and on geodynamic considerations the fracture zone ancestral to the bela ophiolites probably acted as a boundary between the indian and the neo tethys plates during the cretaceous analogous to the present day owen fracture zone which separates the indian and the arabian plates this ancestral fracture zone was destroyed when transform movement gave way to oblique convergence culminating in the ophiolite obduction in paleocene early eocene time the ophiolite obduction on the west indian continental margin was preceded by alkaline wpb type volcanism which is represented by the porali basalts the bibai lavas and the deccan basalts

from high plateaux to marginal basins the active role of the mantle current geodynamic models pose many serious problems for the description of continental tectonic processes serious difficulties arise also in the description of some of the ocean basins deformation of the earth s crust appears to be concentrated along several mobile megashear belts it is proposed that these could be the surficial expression of mantle chimneys which extend to great depths within these structures post orogenic high plateaux form and as time passes these develop a central depression enclosed within arcs or indeed full scale rings of mountains the enlargement and deepening over time of the back arc depression occurs in concert with the radial migration of a topographic wave in this respect the following structures represent different phases in an evolutionary sequence a the tibetan plateau b the north american cordillera and c the tyrrhenian basin and calabrian arc the development of this succession reflects a particularly high degree of activity in the mantle in which diapiric rising of asthenospheric matter elevates the land and causes tensional rifting the resulting centrifugal movement of the mantle melt results in crustal foundering and engulfment of the area behind the arc which thus becomes susceptible to the subsequent processes of com pressional deformation

a late quaternary pollen record from the transvaal bushveld south africa pollen spectra from cores of organic spring deposits from the transvaal provide evidence for the climatic evolution of the province during the last 35 000 yr b p or more the past climatic phases are derived from palynological reconstructions of past vegetation types by comparison of fossil pollen data with modern surface pollen spectra from various localities evidence is provided for an early moist cool phase with relatively mesic bushveld and expanded montane forest in the central transvaal followed by a drier period with drier bushveld which probably lasted until approximately 25 000 yr b p during the next phase which at the latest ended about 11 000 yr b p the temperatures were probably 5 6 c cooler than at present at that time bushveld vegetation in the central transvaal was replaced by open grassland with macchia elements climatic amelioration came and semiarid savanna returned to the plains at first gradually and then developing into a warm kalahari thornveld type vegetation after 6000 yr b p it apparently became slightly wetter and a more broad leafed bushveld developed about 4000 yr b p it again became cooler and slightly wetter and the bushveld vegetation on the central and northern plains was comparable to present open upland types after 2000 yr b p conditions gradually became warner until about 1000 yr b p when the modern climate of the central transvaal bushveld originated

mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system abstract a distinct series of beach ridges marking the former shorelines of large inter connected lacustrine basins in the kalahari can be clearly identified from landsat imagery and shuttle radar topography mission srtm data these basins which form the terminal sump of the okavango system in northern botswana are now almost completely dry during the quaternary they were intermittently occupied by large stable lake bodies and are thought to have periodically filled to a point of coalescence inundating an area that at its largest extent encompassed 66 000 km 2 poor chronological control has previously limited the utility of this important palaeo archive as part of a region wide lake palaeo shoreline research programme a systematic optically stimulated luminescence osl dating programme has utilised a lightweight hydraulic auger to take samples at depth from relict shoreline features twenty drill sites have generated 140 samples for dating establishing a firm chronology for multiple lake full phases in all three component basins ngami mababe and makgadikgadi of this mega lake this paper presents the final set of ages in the programme derived from four cores from the western and north eastern shorelines of makgadikgadi and uses these ages to establish a chronology of mega lake high stands during the last 300 ka providing a rare directly dated long terrestrial record of positive hydrological excursions within the southern hemisphere

southeast african records reveal a coherent shift from high to low latitude forcing mechanisms along the east african margin across last glacial interglacial transition abstract late quaternary climate variability in the southern african subtropics is still only poorly resolved with significant complexity and apparent contradictions in the regional dataset to more effectively interpret and synthesize key regional records we reanalysed the data from 13 pollen sequences from the summer rainfall zone of south africa spanning the last 45 000 years obtaining directly comparable quantitative reconstructions of mean annual temperature and summer rainfall temperature reconstructions from across the region provide consistent results with all sites reflecting trends observed in southwest indian ocean sea surface temperatures in the adjacent mozambique channel precipitation reconstructions are more heterogeneous with two distinct subregions being identified in the northeast long term trends in precipitation are determined by sea surface and continental temperature trends revealing a positive relationship between temperature and rainfall this long term pattern appears to be primarily driven by high northern latitude mechanisms with direct local insolation being subordinate their relative impact reversed during terminal glacial period early holocene at which time direct insolation forcing became the main driver of rainfall variability further south in central south africa precipitation variability appears also to be influenced by the latitudinal position of the southern hemisphere westerlies which combine with tropical flow to create tropical temperate trough advecting moisture into the interior in this region periods of maximum precipitation coincide with periods of elevated ssts and equatorward expansions of the westerly storm track this study allows for a fully constrained understanding of climate dynamics along the eastern african margin for the last 45 000 years linking dynamics to drivers and describing how the climate systems evolved across the last glacial interglacial transition

terminology for layered intrusions the terminology of igneous cumulates was originally formulated on the concept that the rocks were concentrations of minerals accumulated by crystal settling it is now well established for several major intrusions that plagioclase that had been typed as cumulus should in fact have floated in its parental magmatic liquid nevertheless the terminology has been valuable in the classification of the rocks of these and other intrusions and it has been useful in certain aspects of their genetic interpretation the name cumulate is therefore redefined so that crystal settling is a possible but not essential process in the origins of the rocks to which it is applied the overall nomenclature of layered intrusions is then reviewed and definitions of names are refined and systematized to clarify their applications careful distinction is made between descriptive and genetic names a cumulate is defined as an igneous rock characterized by a framework of touching mineral crystals and grains that evidently were concentrated through fractional crystallization of their parental magmatic liquids a layer is a sheetlike unit of cumulate that is a distinctive entity in its compositional and or textural features a lamina is a thin 2 5 cm sharply defined layer igneous lamination is a general name for planar structure that is pervasive through cumulates on the scale of their grain size layering is the overall structure and fabric manifest through combinations of layers laminae and lamination the difference between layers and layering is essentially the difference between individuals and a population and the terms that describe one are not necessarily appropriate to the description of the other but the fundamental variants of all of layering lamination grading in layers and layer contacts can essentially be described by one or more of the four modifiers grain size modal textural and cryptic where the last refers to cumulus miner al compositions a system for subdividing layered intrusions is proposed in which distinction is made between general divisions ranked as series zones and subzones and prominent units that are called groups members rhythmic units and cyclic units applications to the skaergaard bushveld muskox stillwater and other intrusions are briefly described

a late quaternary pollen sequence from mfabeni peatland south africa reconstructing forest history in maputaland abstract this paper documents a continuous 44 000 yr pollen record derived from the mfabeni peatland on the maputaland coastal plain a detailed fossil pollen analysis indicates the existence of extensive podocarpus abundant coastal forests before 33 000 cal yr bp the onset of wetter local conditions after this time is inferred from forest retreat and the development of swampy conditions conditions during the last glacial maximum 21 000 cal yr bp are inferred to have been colder and drier than the present as evidenced by forest retreat and replacement of swampy reed sedge communities by dry grassland forest growth and expansion during the holocene altithermal 8000 6000 cal yr bp indicates warm relatively moist conditions previous records from maputaland have suggested a northward migration of podocarpus forest during the late holocene however we interpret a mid holocene decline in podocarpus at mfabeni as evidence of deforestation forest clearance during the mid holocene is supported by the appearance of morella serrata suggesting a shift towards more open grassland savanna possibly due to burning these signals of human impact are coupled with an increase in acacia indicative of the development of secondary forest and hence disturbance

rock hyrax middens a palaeoenvironmental archive for southern african drylands abstract like many of the world s subtropical regions southern africa is highly sensitive to changes in the earth s climate system but a dearth of reliable palaeoenvironmental records means that relatively little is known about how regional environments have been affected over centennial to multi millennial timescales to a large extent this sensitivity is a function of the position of these regions at the interface between temperate and tropical circulation systems the resulting seasonality and irregularity of rainfall have limited the development of suitable archives such as lakes and wetlands for the preservation of palaeoenvironmental proxies this paper reviews and evaluates the value of rock hyrax middens as novel palaeoenvironmental archives in southern africa considered are 1 the contemporary taxonomy distribution and ecology of hyraxes 2 the mechanisms of hyrax midden development their physical and chemical structure rates of accumulation and age and 3 the palaeoenvironmental proxies preserved within hyrax middens including fossil pollen stable isotopes and biomarkers the interpretive constraints and opportunities offered by these various midden characteristics are assessed with a view to demonstrating the potential of these deposits widespread as they are through arid and semi arid southern africa in providing a more detailed and chronologically resolved view of late quaternary palaeoenvironments across the subcontinent

igneous processes and closed system evolution of the tharsis region of mars a quantitative petrologic model for the formation of the tharsis rise of mars has been developed that is consistent with global gravity and topography data partial melting of the mantle underlying the tharsis plateau results in the depletion of basaltic chemical components in the source region iron is partitioned preferentially into the basaltic liquid so that the density of the source region is lowered relative to surrounding unmodified mantle basalt is erupted to the surface and or intruded at shallow levels in the crust where it solidifies to low pressure mineral assemblages or perhaps glass these low pressure materials are less dense than their mantle equivalents hence the net volume of the tharsis crust mantle system is increased resulting in the prominent topographic rise with no net gain or loss of mass the distribution of densities with depth is quantitatively consistent with the isostatic models of sleep and phillips 1979 1985 typical values of parameters that are constrained by the gravity and topography data are 150 km crustal thickness 250 km elastic mantle thickness 26 partial melting in the mantle source region and 32 addition of intrusive material to the crust this closed system petrologic process is strictly constructional in nature but shallow intrusion of magma into the crust can cause uplift of overlying strata as advocated by r j phillips and n h sleep submitted manuscript 1987

late quaternary dynamics of southern africa s winter rainfall zone abstract variations in the nature and extent of southern africa s winter rainfall zone wrz have the potential to provide important information concerning the nature of long term climate change at both regional and hemispheric scales positioned at the interface between tropical and temperate systems southern africa s climate is influenced by shifts in the intertropical convergence zone the westerlies and the development and position of continental and oceanic anticyclones over the last glacial interglacial cycle substantial changes in the amount and seasonality of precipitation across the subcontinent have been linked to the relative dominance of these systems central to this discussion has been the extent to which the region s glacial climates would have been affected by expansions of antarctic sea ice equatorward migrations of the westerlies more frequent intense winter storms and an expanded wrz this paper reviews the developing body of evidence pertaining to shifts in the wrz and the evolution of ideas that have been presented to explain the patterns observed dividing the region into three separate axes along the western and southern margins of the continent and across the interior into the karoo and the kalahari a range of evidence from both terrestrial sites and marine cores is considered and potential expansions of the wrz expansions are explored despite the limitations of many of the region s proxy records a coherent pattern has begun to develop of a significantly expanded wrz during phases of the last glacial period with the best documented being between 32 17 ka while more detailed inferences will require the recovery and analysis of longer and better dated records this synthesis provides a new baseline for further research in this key region

holocene palynology and palaeoenvironments in the savanna biome at tswaing crater central south africa abstract a radiocarbon dated pollen and microscopic charred particle record from the holocene section of the tswaing crater in the savanna biome of south africa give new evidence for environmental changes during the period c 9400 1800 cal years bp pollen grains are scarce or absent in layers dating from before 9400 cal years bp but deposits rich in pollen occur in overlying layers the section dated between 9400 cal years bp and c 7200 cal years bp contains grass asteraceae and dry savanna pollen types that suggest fluctuating but generally dry moisture conditions later between c 7200 and 1800 cal years bp broad leaved savanna woodland elements and local swamp pollen indicate relatively stable vegetation and wetter mildly fluctuating climatic conditions which is consistent with previously published biomarker analysis between c 6200 and 5500 cal years bp the numbers of charred particles increased slightly this indicates burning activity which can probably be attributed to dry season ignition of denser fuel under relatively moist conditions a decrease of local swamp pollen between c 3600 and 3500 cal years bp suggests that conditions became briefly drier again as pollen of woody elements declined in favour of open grassland pollen a comparison between the tswaing pollen profile and various other sequences within the central interior of south africa suggests generally similar conditions over the central interior of the sub continent during the holocene deviating from sequences further afield along the coastal areas of southern africa between 9400 cal years bp and ca 7200 cal years bp the western and southern coasts were probably controlled by different atmospheric and oceanic circulation regimes under the influence of a strong westerly winter rain system while the north eastern area where tswaing is situated experienced weaker precession and less summer rain from the intertropical convergence zone

petrogenesis of the snc shergottites nakhlites chassignites meteorites implications for their origin from a large dynamic planet possibly mars abundances of major minor and trace elements were determined in the whole rock and mineral separates of the two distinct lithologies present in the antarctic achondrite elephant moraine a eeta 79001 via sequential instrumental inaa and radiochemical neutron activation analysis rnaa additional chalcophile siderophile and volatile trace elements are reported for the shergottites alha 77005 shergotty and zagami the rare earth element ree abundances of each of the lithologies of eeta 79001 a and b exhibit chondritic normalized patterns similar to alha 77005 the close relationship of the antarctic shergottites indicates that alha 77005 is a residual source produced by incongruent melting of a source similar in bulk composition to eeta 79001a and that eeta 79001b and the interstitial phases in eeta 79001a are the melts produced by such melting episodes incorporating previous isotopic studies and our chemical data we suggest that either fractionation of or contamination by feldspar could account for the different shergottite sources the large ion lithophile lil trace element abundances of the shergottites require variable but extensive degrees of nonmodal melting of isotopically constrained parent sources the extreme extent of such melting is hypothesized to be represented by alha 77005 as a residual composition derivation of a pre 1 3 ae 109yr fractionation sequence is suggested in which ol ol opx opx cpx and opx cpx plag sequentially produce residual liquids capable of accounting for the precursor sources for the snc meteorites on the basis of chemical isotopic and petrologic considerations we conclude that the snc sources are consistent with their derivation by extensive fractionation of a primitive magma initially produced from a source having chondritic refractory lil trace element abundances fe fe fe mg atomic 0 3 and a mineralogy primarily of ol and pyx our model dependent deductions suggest that this magma could be derived without plagioclase or garnet left in the residuum petrogenetic and age relationships among snc meteorites suggest a single complex provenance on a dynamic planet not unlike the earth considering that each of these meteorites possesses chemical isotopic and petrologic features consistent with data presently available from mars we conclude that a martian origin is quite probable

review of oceanic transform activity and development oceanic transforms generally have a complex morphology and structure and they do not conform to the ideal concept of simple fractures that exactly follow small circles centered on euler poles of relative plate motions it is proposed that the special properties of transforms arise because they are inherently leaky i e new plate area forms along them as transforms have finite widths the adjacent ridge tips are at different distances from the euler poles and the plate boundaries along transforms are slightly oblique to the direction of plate motions such that new plate area forms along them however along transforms the normal process of seafloor spreading is interrupted and new plate area forms by a different process transforms are underlain by crust consisting of variable proportions of a material emplaced in the transform domains and b stretched ridge generated crust the transform structure is further modified by shearing deformation related to irregularities of lateral faults and because of propagation of adjacent ridges transform leakiness is not considered to result merely from changes of plate motions though such changes will influence transform structure but it reflects the segmented structure of mid oceanic ridges the persistence of transforms and their migration in the absolute reference frame with a component perpendicular to their strikes shows that the ridge structure is decoupled from flow in deeper levels thermal anomalies along transforms especially enhanced heat losses stabilize the segmented ridge structure

late quaternary highstands at lake chilwa malawi frequency timing and possible forcing mechanisms in the last 44 ka the extensive shoreline deposits of lake chilwa southern malawi a shallow water body today covering 600 km2 of a basin of 7500 km2 are investigated for their record of late quaternary highstands osl dating applied to 36 samples from five sediment cores from the northern and western marginal sand ridges reveal a highstand record spanning 44 ka using two different grouping methods highstand phases are identified at 43 7 33 3 ka 26 2 21 0 ka and 17 9 12 0 ka total error method or 38 4 35 5 ka 24 3 22 3 ka 16 2 15 1 ka and 13 5 12 7 ka finite mixture model age components with two further discrete events recorded at 11 01 0 76 ka and 8 52 0 56 ka highstands are comparable to the timing of wet phases from other basins in east and southern africa demonstrating wet conditions in the region before the lgm which was dry and a wet lateglacial which commenced earlier in the southern compared to northern hemisphere in east africa we find no evidence that wet phases are insolation driven but analysis of the dataset and gcm modelling experiments suggest that heinrich events may be associated with enhanced monsoon activity in east africa in both timing and as a possible causal mechanism

ice sheets and sea level of the last glacial maximum this paper outlines the general issues regarding ice sheets and sea level of the last glacial maximum lgm which formed the basis of an epilog project workshop papers in this special issue of quaternary science reviews provide a comprehensive assessment of these issues from the perspective of geological reconstructions of ice sheet extent records of sea level change ice sheet modelling geophysical models of glacial isostatic adjustment and geochemical proxies of ice volume this new assessment has substantially narrowed the uncertainties in the total changes in ice sheets and sea level and their proxies suggesting a net decrease in eustatic sea level at the lgm ranging from 120 to 135 m r 2001 elsevier science ltd all rights reserved

a tectonic model for ridge transform ridge plate boundaries implications for the structure of oceanic lithosphere abstract the first order geologic and morphologic relationships at along and proximal to ridge transform ridge plate boundaries are used to construct an empirical and speculative tectonic model the distinctive but variable morphotectonic fabric and crustal structure of the transform domain are the product of a tectonic continuum that ranges from very slow rates of strain associated with very thick edges of lithosphere slowly slipping ridge transfrom ridge plate boundaries to extremely high rates of strain associated with very thin edges of lithosphere fast slipping ridge transform ridge plate boundaries the geometry of a ridge transform intersection necessitates the juxtaposition of a relatively cold thick edge of lithosphere against the truncated end of an accreting plate boundary the cold face of lithosphere cools the adjacent wedge of asthenosphere rising beneath the axis of accretion and restricts the amount of partial melting thus attenuating the volume of basaltic melt segregated from the asthenosphere per unit time the shallow level manifestation of this cold edge effect is a thinner oceanic crust at depth the evolving lithosphere thickens rapidly as the cold edge is approached creating changes in the properties of the young lithosphere and forming a weld of upper mantle material against the cold edge of truncating lithosphere the ridge transform weld of upper mantle material creates a shear couple in the lithosphere underlying the intersection resulting in the progressive reorientation of the maximum tensile stress from normal to the ridge axis at some distance from the ridge transform intersection to an oblique angle near the boundary the brittle carapace of oceanic crust that overlies the mantle weld will deform accordingly with the development of oblique dip slip faults the model predicts that the geologic expressions of this cold boundary effect will become more dramatic with increasing thickness of the truncating edge at very slow rates of accretion 100 km juxtapose thick 30 50 km edges of lithosphere against the accreting plate boundary all but nullifying the processes that lead to the emplacement of normal oceanic lithosphere in this environment a relatively strong mantle weld will form at the ridge transform intersection and the thick edges of opposing lithosphere along the length of the transform will tend to confine the strike slip tectonism to a relatively narrow and temporally stable principal transform displacement zone in contrast at very fast rates of accretion large offset transforms 100 km place relatively thin edges of lithosphere

morphology and crustal structure of the kane fracture zone transverse ridge the kane fracture zone kfz transverse ridge is an anomalously shallow ridge which parallels the kfz for over 200 km east of its intersection with the mid atlantic ridge rift valley sea beam bathymetry and gravity data have been used to determine the morphology and density structure of the ridge and travel time data from two seismic refraction experiments have been modeled to constrain its seismic velocity structure the transverse ridge first appears on older lithosphere opposite the eastern ridge transform intersection it rises to a maximum height of about 2000 m above the bordering kfz trough 40 km east of the intersection area although bathymetry data along the western limb of the kfz are relatively sparse a ridge of similar dimensions is not present the kfz transverse ridge has a decidedly flexural shape in cross section with a high steep south facing wall and a gently sloping northern side the grain of the ridge parallel topography north of the kfz continues undisrupted across the transverse ridge suggesting that the ridge has formed by vertical uplift of this crust seismic ray tracing and gravity analyses indicate that the kfz transverse ridge is not locally compensated by an overthickened crust but is underlain by crustal thicknesses and velocities similar to that of normal oceanic crust on either side of the kfz anomalously thin crust is only present immediately beneath the kfz trough and along the south facing wall of the transverse ridge these constraints and the formation of the kfz transverse ridge on the older plate preclude several previously proposed models for its origin including flexural bending due to differential subsidence across the fracture zone constructional volcanism and serpentine diapirism although no single mechanism provides a completely satisfactory explanation for the origin of the kfz transverse ridge the most likely mechanism appears to be a combination of thermal and viscodynamic forces operating near the ridge transform intersection

vertical crustal movements at the vema fracture zone in the atlantic evidence from dredged limestones abstract a crustal block shallower by over 3 km than the level predicted by the thermal contraction model for the ocean crust is located on the southern side of the vema transform in the atlantic lithology magnetic and gravity data suggest the anomalous block is an uplifted piece of crust and upper mantle and not a constructional volcanic feature the crest and upper slopes of the anomalous block are capped by shallow water reef limestones determination of paleofacies and ages of samples of these limestones suggest that 1 a the crest of the anomalous crustal block reached sea level and was exposed subaerially in middle pliocene time about 3 m y ago and subsequently sank to its present depth at an average rate of about 0 3 mm year that is a rate one order of magnitude faster than that predicted by the thermal contraction model for crust of the same age 2 b the anomalous block reached at or above sea level either continuously or intermittently throughout the late miocene from roughly 10 m y ago 3 c paleocene sediments dated at about 55 58 m y have been recovered from the uplifted block where assuming a spreading rate of 1 1 cm year the crust should not be more than about 35 m y old vertical crustal movements at the vema transform provide an example of vertical tectonism in the large oceanic transform fracture zones

east african mid holocene wet dry transition recorded in palaeo shorelines of lake turkana northern kenya rift abstract the wet early to mid holocene of tropical africa with its enhanced monsoon ended with an abrupt shift toward drier conditions and was ultimately replaced by a drier climate that has persisted until the present day the forcing mechanisms the timing and the spatial extent of this major climatic transition are not well understood and remain the subject of ongoing research we have used a detailed palaeo shoreline record from lake turkana kenya to decipher and characterise this marked climatic transition in east africa we present a high precision survey of well preserved palaeo shorelines new radiocarbon ages from shoreline deposits and oxygen isotope measurements on freshwater mollusk shells to elucidate the holocene moisture history from former lake water levels in this climatically sensitive region in combination with previously published data our study shows that during the early holocene the water level in lake turkana was high and the lake overflowed temporarily into the white nile drainage system during the mid holocene 5270 300 cal yr bp however the lake water level fell by 50 m coeval with major episodes of aridity on the african continent a comparison between palaeo hydrological and archaeological data from the turkana basin suggests that the mid holocene climatic transition was associated with fundamental changes in prehistoric cultures highlighting the significance of natural climate variability and associated periods of protracted drought as major environmental stress factors affecting human occupation in the east african rift system

wet and arid phases in the southeast african tropics since the last glacial maximum plant leaf wax carbon isotopes provide a record of c 3 versus c 4 vegetation a sensitive indicator of aridity from the southeast african tropics since the last glacial maximum wet and arid phases in southeast africa were in phase with conditions in the global tropics from 23 to 11 ka but at the start of the holocene these relationships ended and an antiphase relationship prevailed the abrupt switch from in phase to out of phase conditions may partially be attributed to a southward displacement of the intertropical convergence zone itcz during the last glacial southward displacements of the itcz are also linked to arid conditions in southeast africa during the younger dryas and the little ice age

thrusting in oceanic crust during continental drift offshore niger delta equatorial africa 1 two and three dimensional 3 d seismic reflection data acquired over oceanic crust in the deepwater west niger delta reveal convincing evidence for compressional tectonics during oceanic crustal spreading using the 3 d seismic data set we describe numerous inclined seismic reflections that dissect the entire oceanic crust from the top of the crust to the level of the moho that are interpreted as thrusts thrust propagation results in the development of associated hanging wall anticlines and footwall synclines these structures are orthogonal to and clearly postdate normal faults that formed during the accretion of oceanic crust during continental drift and strike at right angles to them the charcot ridge is located 140 km south of these thrusts and is a significantly larger structure it is a triangular shaped uplifted region of oceanic crust measuring 80 by 150 km and is located along the ne sw oriented charcot fracture zone two interpretations are possible for the role of the fracture zone in the development of the charcot ridge 1 a thin skinned model whereby the oceanic crust west of the fracture zone has been thrust southeastward with detachment occurring close to the level of the moho the ridge forms as a result of translation and folding above a crustal scale ramp flat thrust geometry 2 a thick skinned model where there is no detachment close to the moho with the thrust fault being much steeper penetrating the crust and probably the mantle lithosphere in this interpretation the structure formed owing to the compressional reactivation of the fracture zone approximate dating of onlapping reflections on either side of the ridge constrains the timing of its formation as between 25 and 120 ma ago the charcot ridge represents one of the largest thrust structures to be identified in a passive margin setting many other compressional folds with the same orientation formed to the northeast in the benue trough probably during the santonian as a result of a change in the spreading direction during south atlantic rifting we speculate that the same causal mechanism applies for the formation of the charcot ridge

a 19 5 kyr vegetation history from the central cederberg mountains south africa palynological evidence from rock hyrax middens abstract in arid and semi arid areas such as southern africa rock hyrax procavia capensis middens represent an exceptionally valuable source of late quaternary palaeoenvironmental information pollen and stable isotope data derived from two rock hyrax middens extracted from de rif in the cederberg mountains of the southwestern cape casts new light on climatic changes that occurred across the last glacial interglacial transition lgit and the holocene 19 5 0 7 cal kbp and how the region s vegetation responded to these changes significant changes in vegetation community composition would be expected in response to environmental changes characteristic of the contrast between glacial and interglacial climates however the pollen assemblages in general indicate that mountain fynbos remained dominant throughout the record and that most of the pollen taxa exhibited only muted frequency variations this finding could be considered to be inconsistent with indications of marked climatic variations recorded in the stable isotope records for the same midden an analysis of the geological setting and the bioclimatic affinities of the taxa suggest that the explanation for this inconsistency may lie in the dominating influence of sandstone substrates and the relative resilience of mountain fynbos vegetation to climate change

quantification of climate change for the last 20 000 years from wonderkrater south africa implications for the long term dynamics of the intertropical convergence zone abstract in southeast africa a region for which few palaeoenvironmental records are available the fossil pollen record from the wonderkrater spring mound has contributed substantially to our understanding of past vegetation change since the last glacial maximum lgm 21 ka multivariate analysis of the pollen data by scott and thackeray 1987 provided environmental reconstructions suggesting relatively mesic lgm conditions with warm and dry conditions during the early holocene 11 6 cal kbp this conforms to predicted patterns of precipitation change in the southern african tropics in response to northern hemisphere cooling and orbital forcing subsequent data from the cold air cave speleothems and a sea surface temperature record from the mozambique channel however indicate that conditions during the early to mid holocene may have been wetter than present in the wonderkrater region to explore this question further we have created a series of botanical climatological transfer functions based on a combination of modern climate and plant distribution data from southern africa applying these to the wonderkrater fossil pollen sequence we have derived quantitative estimates for temperatures during the cold and warm quarters as well as precipitation during the wet and dry quarters in addition a species selection method based on bayesian statistics is outlined which provided a parsimonious choice of likely plant species from what are otherwise taxonomically broad pollen types we do not propose that our findings invalidate the previous principal component analyses but they do have the advantage of being based more clearly on the relationship between modern plant distributions and individual climatic variables results indicate that temperatures during both the warm and cold seasons were 6 2 c colder during the lgm and younger dryas and that rainy season precipitation during the last glacial maximum was 50 of that during the mid holocene our results also imply that changes in precipitation at wonderkrater generally track changes in mozambique channel sea surface temperatures with a steady increase following the younger dryas to a period of maximum water availability at wonderkrater 3 7 ka these findings argue against a dominant role of a shifting intertropical convergence zone in determining long term environmental trends and indicate that the northern and southern tropics experienced similar climatic trends during the last 20 kyr

geochemical records of palaeoenvironmental controls on peat forming processes in the mfabeni peatland kwazulu natal south africa since the late pleistocene the mfabeni peatland is the only known sub tropical coastal fen that transcends the last glacial maximum lgm this ca 10 m thick peat sequence provides a continuous sedimentation record spanning from the late pleistocene to present basal age c 47 kcal yr bp we investigated the paleaeoenvironmental controls on peat formation and organic matter source input at the mfabeni fen by 1 exploring geochemical records mass accumulation rate total organic carbon carbon accumulation rate delta c 13 delta n 15 and c n ratio to delineate primary production organic matter source input preservation and diagenetic processes and 2 employ these geochemical signatures to reconstruct the palaeoenvironmental conditions and prevailing climate that drove carbon accumulation in the peatland we established that the mfabeni peat sediments have undergone minimal diagenetic alteration the peat sequence was divided into 5 linear sedimentation rate lsr stages indicating distinct changes in climate and hydrological conditions isr stage 1 c 47 to c 32 2 kcal yr bp predominantly cool and wet climate with c4 plant assemblages interrupted by two short warming events lsr stage 2 c 32 2 to c 27 6 kcal yr bp dry and windy climate followed by a brief warm and wet period with increased c4 sedge swamp vegetation lsr stage 3 c 27 6 to c 20 3 kcal yr bp initial cool and wet period with prevailing c4 sedge plant assemblage until c 23 kcal yr bp then an abrupt change to dry and cool glacial conditions and steady increases in c3 grasses lsr stage 4 c 203 to c 10 4 kcal yr bp continuation of cool and dry conditions and strong 0 grassland signature until c 15 kcal yr bp after which precipitation increases lsr stage 5 c 10 4 kcal yr bp to present characterised by extreme fluctuations between pervasive wet and warm to cool interglacial conditions with intermittent abrupt millennial scale cooling drying events and oscillations between c3 and c4 plant assemblages in this study we reconstructed a high resolution record of local hydrology bulk plant assemblage and inferred climate since the late pleistocene which suggest an anti phase link between southern african and the northern hemisphere most notably during heinrich 5 to 2 and younger dryas events

a record of rapid holocene climate change preserved in hyrax middens from southwestern africa the discovery of sensitive paleoenvironmental proxies contained within fossilized rock hyrax middens from the margin of the central namib desert africa is providing unprecedented insight into the region s environmental history high resolution stable carbon and nitrogen isotope records spanning 0 11 700 cal calibrated yr b p indicate phases of relatively humid conditions from 8700 7500 6900 6700 5600 4900 and 4200 3500 cal yr b p with a period of marked aridity occurring from 3500 until ca 300 cal yr b p transitions between these phases appear to have occurred very rapidly often within 200 years of particular importance are 1 the observed relationship between regional aridifi cation and the decline in northern hemisphere insolation across the holocene and 2 the signifi cance of suborbital scale variations in climate that covary strongly with fl uctuations in solar forcing together these elements call for a fundamental reexamination of the role of orbital forcing on tropical african systems and a reconsideration of what factors drive climate change in the region the quality and resolution of these data far surpass any other evidence available from the region and the continued development of this unique archive promises to revolutionize paleoenvironmental studies in southern africa

nonlinear viscoelasticity and the formation of transverse ridges transverse ridges are regions of anomalously high uplift that run parallel to many of the transform fattits at mid ocean ridges previous models of the formation of these ridges generally fail to explain the magnitude of uphft between 1 and 8 km or account for geophysical observations which indicate that the ridges are dynamically uphfted by neutral or heavy but not buoyant material however the potentially large maxwell relaxation time of the lithosphere and the high strain rates and finite deformation of transform faults imply that nonlinear viscoelasticity may play an important role in the formation of these ridges we present simple theoretical and experimental models of viscoelastic flow beneath a transform fattit to show that the purely horizontal motion of the fattit can generate vertical uplift typical of transverse ridges the theoretical model is of an infinite half space of fluid driven from above by two plates moving parallel and in opposite directions to one another the constitutive relation for the viscoelastic rheology is for a second order fluid i e nonlinear viscoelastic effects are treated as perturbations to newtonian purely viscous flow the theoretical model not only predicts the two transverse ridges that are often observed on either side of the transform fault but the central transform valley that separates them as well for typical hthospheric flexural rigidity and deformation associated with transverse ridges the viscoelastic effect provides sufficient vertical stress to produce the observed uplift further the dynmnic uplift is a purely mechanical effect i e it does not involve buoyant materim which corresponds to geophysical observations the experimental model is comprised of a viscoelastic fluid 2 aqueous solution of high molecular weight carboxymethylcellulose driven by a rotating plate this is analogous to a t ransk rm fattit because the boundary of a spiroting circular tectonic plate surrounded by stationary plates is one continuous transform fattit the experiment produces a large ridge of fluid along the edge of the plate with a shght trough outside of the ridge this result is qualitatively described by a cyhnch ical version of of the above theoretical model in conclusion both experimental and theoretical models show that when nonlinear

reconstruction of environmental and climate changes at braamhoek wetland eastern escarpment south africa during the last 16 000 years with emphasis on the pleistocene holocene transition abstract a paleo environmental record covering the last 16 ka 16 000 cal yrs bp from the eastern areas of the summer rainfall region in south africa is presented this area is until now sparsely investigated due to the lack of well preserved natural archives for this study we used a peat section from a wetland situated close to the drakensberg escarpment where the high annual rainfall amounts supported a continuous peat accumulation since c 16 ka one peat core was analysed in terms of fossil pollen composition carbon and nitrogen content isotope composition 13c 15n and microscopic charcoal concentration the greatest degree of temporal resolution was achieved from the late pleistocene and early holocene section where proxy records indicate relatively dry conditions between ca 16 13 7 ka 12 8 10 5 ka 9 5 8 2 ka and wet conditions between c 13 7 12 8 ka and 10 5 9 5 ka a weak moisture signal is also evident at c 8 2 7 5 ka the late pleistocene to early holocene period was relatively cool while conditions became generally warmer after 11 8 ka the interpretation of the mid and late holocene sequence is limited due to a slow accumulation and low sample resolution but the available data suggest relatively dry conditions until c 1 5 ka followed by more humid conditions until c 0 5 ka we suggest that the millennial scale variability within the record can be attributed to shifts in the circulation systems dominating the region i e the latitudinal movements of the inter tropical convergence zone itcz and the dynamics of the mid latitude low pressure belts

oscillatory spreading explanation of anomalously old uplifted crust near oceanic transforms rocks significantly older than their theoretically predicted age have been recovered in the vicinity of some atlantic transform zones rocks of palaeocene 55 58 myr and possibly even of cretaceous age are found near the vema transform on tectonically uplifted crust which should not be older than 30 myr we present here a model which might explain the presence of uplifted anomalously old crust near the vema transform zone tz the proposed model involves axial rift propagation and reorientation and migration of the transform as a result of a change in the regional stress field during transform migration a crustal wedge formerly part of the african plate is transferred to the south american plate the ensuing oscillatory spreading can explain the anomalous age of the uplifted crustal block compression resulting from rift propagation and transform migration provides a mechanism for crustal uplift

transform migration and vertical tectonics at the romanche fracture zone equatorial atlantic the romanch transform offsets the mid atlantic ridge mar axis by about 950 km in the equatorial atlantic multibeam and high resolution multichannel seismic reflection surveys as well as rock sampling were carried out on the eastern part of the transform with the riv akademik strakhov as part of the russian italian mid atlantic ridge project primar morphobathymetric data show the existence on the northern side of the transform of a major 800 kin long aseismic valley oriented 10 o to 15 o from the active valley it disappears about 150 km from the western mar segment the aseismic valley marks probably the former location of the romanche transform paleoromanche that was active up to roughly 8 10 ma when the transform boundary migrated to its present position a temporary microplate developed during the migration and reorientation of the transform this microplate changed its sense of motion as it was transferred from the south american to the african plate a prominent transverse ridge extends for several hundred kilometers parallel to the transform on its northern side reaching its shallowest part shallower by over 4 km than the predicted thermal contraction depth in a zone opposite the eastern mar axis transform intersection rti flat top peaks on the summit of the transverse ridge are capped by acoustically transparent weakly stratified shallow water platform lagunal reef limestones this limestone unit is a few hundred meters thick and overlies igneous basement evaluation of the seismic reflection data as well as study of samples of carbonates ventifact basaltic pebbles and gabbroic peridofitic and basaltic rocks recovered at different sites on the transverse ridge suggest that 1 the summit of the transverse ridge was above sea level at and before about 5 ma 2 the transverse ridge subsided since then at an average rate 1 order of magnitude faster than the predicted thermal contraction rate its summit was flattened by erosion at sea level during subsidence 3 the transverse ridge is an uplifted sliver of lithosphere and not a volcanic construcfional feature and 4 transtensional and transpressional tectonics have affected the transverse ridge hypotheses on the origin of the romanche transverse ridge include 1 lateral heat conduction across the rti 2 shear heating 3 lithospheric flexure due to thermal stresses in the cooling lithosphere 4 viscoelastic deformation of the lithosphere 5 hydration dehydration of mantle peridotites and 6 longitudinal flow of melt and igneous activity across the rti these processes cannot by themselves explain the transverse ridge although some of them could contribute to its formation to a small extent vertical tectonics due to transpressional and transtensional events related to a nonstraight transform boundary and to regional changes in ridge transform geometry is probably the primary process that gave rise to the uplift of the transverse ridge and to its recent subsidence uplift may have been caused primarily by thrust faulting induced by transpression related to the oblique impact of the lithospheric plate against the former paleoromanche and the younger transform boundaries before and during the transition to the present boundary after migration of the transform boundary to its present position transpression was replaced by transtension and by subsidence of the transverse ridge an aseismic axial rift valley impacting against the transform valley about 80 km west of the present rti suggests eastward ridge jumping that probably followed transform migration localized transtension or transpression due to bends in the orientation of the transform may have caused intense although localized vertical movements such as those that formed an ultradeep 7800 m pull apart basin along the transform valley

late quaternary environmental changes from a pollen and diatom record in the southern tropics lake tritrivakely madagascar abstract a pollen and diatom study of a 40 m sedimentary sequence from lake tritrivakely in the central highlands of madagascar provides evidence for climatic and environmental changes during the late pleistocene and the holocene the major features of the modern regional climate and vegetation distribution and the hydrological characteristics of the lake basin are first summarized lithological units and specific methods used to establish the pollen and the diatom biozones are then presented the chronology of the upper 13 m of the sequence 0 41 kyr is supported by ams radiocarbon dates it has not been possible to acquire absolute ages for the lower 27 m of the core however a tentative age model based on comparisons between the terrestrial pollen and the vostok d isotopic temperature records suggests an age of about 150 kyr for the core base the vegetation primarily responded to variations in temperature six major cold warm cycles are identified during the cold phases ericaceous bush surrounded the site assuming that the age model is correct cold phases prior to 143 115 110 94 88 75 69 and 22 17 kyr coincide with periods of high local summer insolation the warm phases are of different amplitude they show first the development of a wooded grassland under a dry climate which may coincide with periods of low summer insolation around 125 100 83 60 and 10 5 kyr and then the growth of mid latitude trees under wetter conditions the diatom record primarily documents changes in the precipitation minus evaporation balance p e in the lake catchment which appear consistent with orbitally induced changes in p and seasonal contrasts as suggested by our pollen based age model and the 14c dated section of the record an overall trend from a relatively deep nutrient rich lake to a shallow oligotrophic peat marsh is partly attributed to the basin infilling however wet dry oscillations are superimposed over this trend the two first lake high stands before 143 and around 115 kyr if the age model is correct and low stands around 125 and 105 kyr match pollen inferred cold and warming phases respectively later periods of low p e also fit cold phases and occur apparently every 12 10 kyr summer rain during phases of high summer insolation was not heavy enough to compensate for the large evaporation evapotranspiration losses during warm summers and dry winters especially during the cold last glacial maximum which was drier than today

evidence for progressive holocene aridification in southern africa recorded in namibian hyrax middens implications for african monsoon dynamics and the african humid period abstract presented here are stable nitrogen isotope data from a rock hyrax procavia capensis middens from northwestern namibia that record a series of rapid aridification events beginning at ca 3800 cal yr bp and which mark a progressive decrease in regional humidity across the holocene strong correlations exist between this record and other terrestrial and marine archives from southern africa indicating that the observed pattern of climate change is regionally coherent combined these data indicate hemispheric synchrony in tropical african climate change during the holocene with similar trends characterising the termination of the african humid period ahp in both the northern and southern tropics these findings run counter to the widely accepted model of direct low latitude insolation forcing which requires an anti phase relationship to exist between the hemispheres the combined dataset highlights 1 the importance of forcing mechanisms influencing the high northern latitudes in effecting low latitude climate change in africa and 2 the potential importance of solar forcing and variations in the earth s geomagnetic shield in determining both long term and rapid centennial scale climate changes identifying a possible mechanism for the variations marking the ahp termination in both the southern and northern tropics

interhemispheric dynamics of the african rainbelt during the late quaternary abstract the spatial pattern of precipitation variability in tropical and subtropical africa over the late quaternary has long been debated prevailing hypotheses variously infer 1 insolation controlled asymmetry of wet phases between hemispheres 2 symmetric contraction and expansion of the tropical rainbelt and 3 independent control on moisture available in southern africa via sea surface temperatures in the indian ocean in this study we use climate model simulations covering the last glacial cycle 120 kyr with hadcm3 and the multi model ensembles from pmip3 the palaeoclimate model intercomparison project to investigate the long term behaviour of the african rainbelt and test these simulations against existing empirical palaeohydrological records through regional model data comparisons we find evidence for the validity of several hypotheses with various proposed processes occurring concurrently but with different regional emphasis e g asymmetric shifts at the seasonal extremes and symmetric expansions contractions towards west equatorial regions crucially variations in rainfall are associated with multiple forcing mechanisms that vary in their dominance both spatially and temporally over the glacial cycle an important consideration when interpreting and extrapolating from often relatively short palaeoenvironmental records

old continent derived metasedimentary rocks in the equatorial atlantic an acoustic basement outcrop along the fossil trace of the romanche transform fault at 6 30 w abstract the last known acoustic basement outcrop along the eastern fossil extension of the romanche fracture zone is located at about 06 30 w and 02 00 n and lies 250 km west of the southwestern tip of the ivory coast ghana ridge between the sierra leone abyssal plain and the guinea basin i e in the oceanic domain the easternmost basement outcrop was surveyed by seabeam during the 1988 equamarge ii cruise of the r v jean charcot and rock samples were collected both by one dredge haul during the latter cruise and by the submersible nautile during the 1992 equanaute cruise this paper presents the morphostructural interpretation of the seabeam survey the observations from the submersible and the results of the petrological study of the rock samples the latter appear to be detrital sediments which were subjected to a low grade metamorphism in the greenschist facies conditions and a strong multiphase cataclasis the rock samples derived from observed taluses and breccias are clasts of mainly meta arkoses with a few quartzites and meta siltstones the meta sedimentary rocks are exotic to the oceanic environment where they presently outcrop they do not belong the pelagic domain of the serria leone abyssal plain nor that of the gulf of guinea they are probably derived from a wheathered continental granitic crust which predates the opening of the atlantic ocean during the albian aptian ages the granitic arena could have then been eroded and transported by rivers to small marginal basins where the detrital sediments were deposited as fluviatile cones as the proto atlantic was opening according to francheteau and le pichon 1972 the marginal basins are associated with the large transform faults and appeared during the opening of the atlantic the sedimentary rocks were probably transported to the present location in the abyssal province at a later date by the transcurrent movements of the romanche fracture zone as the ocean widened they would thus represent allochthonous klippe left behind by the transform fault the dynamometamorphism which affected the sedimentary rocks the brecciation and the uplift which made them crop out are probably also related to relatively recent activity of the romanche fracture zone the outcrop of meta sedimentary rocks forming the easternmost known acoustic basement can be regarded as an intermediate data point along the path of the romanche fracture zone between its presently active oceanic portion about half way between africa and brazil and its formerly active continental segment now represented by the ivory coast ghana ridge

evolving southwest african response to abrupt deglacial north atlantic climate change events abstract climate change during the last deglaciation was strongly influenced by the bipolar seesaw producing antiphase climate responses between the north and south atlantic however mounting evidence demands refinements of this model with the occurrence of abrupt events in southern low to mid latitudes occurring in phase with north atlantic climate improved constraints on the north south phasing and spatial extent of these events are therefore critical to understanding the mechanisms that propagate abrupt events within the climate system we present a 19 400 year multi proxy record of climate change obtained from a rock hyrax midden in southernmost africa arid anomalies in phase with the younger dryas and 8 2 ka events are apparent indicating a clear shift in the influence of the bipolar seesaw which diminished as the earth warmed and was succeeded after 14 6 ka by the emergence of a dominant interhemispheric atmospheric teleconnection

the tethys sea and the alpine himalayan orogenic belt mega elements in a new global tectonic system abstract analysis of meso cainozoic palaeomagnetic data for africa india and eurasia has led to the development of a new mobilistic alpine plate tectonic model characterized by a hierarchical system of plates in relative rotation the new model which discounts seafloor spreading implies that there have been no significant palaeogeographic changes in the overall distribution of continental and oceanic regions the mid oceanic ridges are interpreted as transpressive tectonic features caused by rotation of megaplates containing both continental and oceanic crust the isostatic uplift due to crustal lithospheric thickening giving rise to the general ridge topography as well as to the ridge parallel structural grain the new plate tectonic theory gains strong support from a variety of geophysical geological and palaeoclimatological evidence and several observations that have remained enigmatic or awkward within the context of the orthodox model can be readily accounted for in the new tectonic framework the model maintains the tethys as a relatively narrow epicontinental sea which during its maximum extent stretched latitudinally from the caribbean across the central atlantic to se asia the alpine himalayan orogenic belt developed along the boundary of two megaplates in relative rotation which provided a transpressive tectonic regime the location of the plate boundary to the north of the mediterranean has important implications for discussion of mediterranean microplates for example it now seems that italy has been subjected to 10 15 of clockwise microplate rotation previous conclusions in favour of 30 40 of anticlockwise rotation are regarded as artefacts which arise from incorrectly linking the mediterranean region to the european palaeomagnetic frame instead of to the african one the model suggests further that the indo pakistani plate was closely tied to eurasia this challenges the conventional view that the peninsula was part of an alleged gondwanaland the new pre drift configuration implies that the indo pakistani plate rotated 135 clockwise at around the cretaceous tertiary boundary before redocking with asia in approximately its present relative orientation

climatic changes in eurasia and africa at the last glacial maximum and mid holocene reconstruction from pollen data using inverse vegetation modelling in order to improve the reliability of climate reconstruction especially the climatologies outside the modern observed climate space an improved inverse vegetation model using a recent version of biome4 has been designed to quantitatively reconstruct past climates based on pollen biome scores from the biome6000 project the method has been validated with surface pollen spectra from eurasia and africa and applied to palaeoclimate reconstruction at 6 cal ka bp calendar years the climate was generally wetter than today in southern europe and northern africa especially in the summer winter temperatures were higher 1 5 c than present in southern scandinavia northeastern europe and southern africa but cooler in southern eurasia and in tropical africa especially in mediterranean regions summer temperatures were generally higher than today in most of eurasia and africa with a significant warming from 3 to 5 c over northwestern and southern europe southern africa and eastern africa in contrast summers were 1 3 c cooler than present in the mediterranean lowlands and in a band from the eastern black sea to siberia at 21 cal ka bp a marked hydrological change can be seen in the tropical zone where annual precipitation was 200 1 000 mm year lower than today in equatorial east africa compared to the present a robust inverse relationship is shown between precipitation change and elevation in africa this relationship indicates that precipitation likely had an important role in controlling equilibrium line altitudes ela changes in the tropics during the lgm period in eurasia hydrological decreases follow a longitudinal gradient from europe to siberia winter temperatures were 10 17 c lower than today in eurasia with a more significant decrease in northern regions in africa winter temperature was 10 15 c lower than present in the south while it was only reduced by 0 3 c in the tropical zone comparison of palaeoclimate reconstructions using lgm and modern co2 concentrations reveals that the effect of co2 on pollen based lgm reconstructions differs by vegetation type reconstructions for pollen sites in steppic vegetation in europe show warmer winter temperatures under lgm co2 concentrations than under modern concentrations and reconstructions for sites in xerophytic woods scrub in tropical high altitude regions of africa are wetter for lgm co2 concentrations than for modern concentrations because our reconstructions account for decreased plant water use efficiency

late pleistocene holocene rise and collapse of lake suguta northern kenya rift abstract the late pleistocene to middle holocene african humid period ahp was characterized by dramatic hydrologic fluctuations in the tropics a better knowledge of the timing spatial extent and magnitude of these hydrological fluctuations is essential to decipher the climate forcing mechanisms that controlled them the suguta valley 2 n northern kenya rift has recorded extreme environmental changes during the ahp extensive outcrops of lacustrine sediments ubiquitous wave cut notches shorelines and broad terrace treads along the valley margins are the vestiges of lake suguta which once filled an 80 km long and 20 km wide volcano tectonic depression lake suguta was deep between 16 5 and 8 5 cal ka bp during its maximum highstand it attained a water depth of ca 300 m a surface area of ca 2150 km2 and a volume of ca 390 km3 the spatial distribution of lake sediments the elevation of palaeo shorelines and other geomorphic evidences suggest that palaeo lake suguta had an overflow towards the turkana basin to the north after 8 5 cal ka bp lake suguta abruptly disappeared a comparison of the lake suguta water level curve with other reconstructed water levels from the northern part of the east african rift system shows that local insolation which is dominated by precessional cycles may have controlled the timing of lake highstands in this region our data show that changes of lake levels close to the equator seem to be driven by fluctuations of spring insolation while fluctuations north of the equator are apparently related to variations in summer insolation however since these inferred timings of lake level changes are mostly based on the radiocarbon dating of carbonate shells which may have been affected by a local age reservoir alternative dating methods are needed to support this regional synthesis between 12 7 and 11 8 cal ka bp approximately during the northern hemisphere high latitude younger dryas the water level of lake suguta fell by ca 50 m suggesting that remote influences also affected local hydrology

a carbon and nitrogen isotope study of zagami samples from the two major lithologies fine and coarse grained in zagami have been analyzed for the abundance of carbon and nitrogen and their isotopic compositions using the technique of stepped combustion it was possible to evaluate the distribution of carbon and nitrogen within different species organic carbonate nitrate etc in the samples separates of shock produced glass and pigeonite were also analyzed for carbon the majority of the carbon and nitrogen in each sample arises from contaminants organic materials absorbed gases etc however carbon and nitrogen of magmatic origin is released above 600 c 13c 24 15n 5 the glass separates contain a minor contribution from trapped martian atmospheric co2 in addition to the magmatic component zagami appears to contain two generations of carbonate an isotopically light end member with minimum 13c around 23 plus a more 13c enriched carbonate the latter is typical of martian carbonates formed from fluid in contact with martian atmospheric co2 while the former might represent a more primitive source of carbon and possibly emanate from the carbonate anion present within silicates or phosphates the spread in 13c values of carbonates in martian meteorites clearly points to the operation of at least two processes each imparting a characteristic carbon isotopic signature these processes are interpreted within the framework of models that describe the evolution of zagami type basalts on mars

geologie und bau des sithonia ophioliths chalkidiki ne griechenland anmerkungen zur bildung ozeanischer krusten der oberjurassische sithonia ophiolith der chalkidiki ne griechenland bietet die moglichkeit die an der bildung fossiler ozeanischer krusten beteiligten prozesse ausfuhrlich zu untersuchen

zagami product of a two stage magmatic history abstract large specimens of the zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths we document the presence of whitlockite and of melt veins and pockets of shock origin pyroxene crystals have homogeneous mg rich pigeonite and augite cores overgrown by fe rich zoned pyroxene mostly pigeonite rims amphibole bearing magmatic melt inclusions occur exclusively in the cores we conclude that zagami experienced a twostage crystallization history the first stage occurred in a deep seated slowly cooling magma chamber there the homogeneous mg rich cores of the pyroxenes crystallized during relatively slow cooling the deep seated origin of the cores is also indicated by the presence of amphibole within them which requires pressures of formation equivalent to crystallization at depths 7 5 km on mars modest abundance of homogeneous mg rich cores 15 20 indicates that crystal settling did not play a significant role in this part of the magma chamber during the second stage the mg rich pyroxenes were entrained into a magma that either intruded to the near surface and cooled in a relatively thin dike or sill or extruded to the surface and crystallized in a lava flow 10 m thick again without indications for crystal settling this scenario is suggested by estimates of cooling rates of 0 1 0 5 c h based on sizes of the plagioclase maskelynite crystals and of 0 02 c h based on the width of pyroxene exsolution lamellae brearley 1991 irregular shapes of the mg rich cores result from resorption and possible solid state diffusion and the shapes and sizes of the pyroxenes after crystallization of fe rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores the finer grained areas of the rock inherited smaller and more numerous mg rich pyroxene cores from the first stage than did the coarser grained areas crystallization of both augite and pigeonite cores at depth but mostly pigeonite rims in the nearsurface environment may be the result of a phase boundary shift and expansion of the pigeonite stability field at lower pressures the estimated depth of the magma chamber for zagami of 7 5 km and thickness of the putative lava flow of 10 m are consistent with calculations and observations of volcanic constructs and flows in the tharsis region of mars

alha 81005 meteorite chemical evidence for lunar highland origin based on the well established characteristic lunar and meteoritic ratios of feo mno cr2o3 v and k la and ree patterns alha 81005 meteorite is undoubtedly of lunar highland origin the alha 81005 meteorite is an anorthositic gabbro 72 pl and matches closely in chemical composition to apollo 15 15418 and luna 16 21013 highland rocks the rock is a non kreepy and vlt type the siderophiles au ni and ir content is high 1 5 cl equivalent and similar to other lunar highland breccias the clast has a different ancient meteorite component than the bulk and matrix the meteorite has a young terrestrial age implying a recent lunar cratering event therefore during major lunar basins formation in early eons the earth must have received a significant amount of lunar material which is now mixed in the crust the finding of a lunar meteorite lends credibility to the suggestion that snc achondrites may come from mars

late quaternary vegetation history of southeast africa the molecular isotopic record from lake malawi abstract accurate reconstructions of past hydrological variability are essential for understanding the climate history of the tropics in tropical africa the relative proportion of vegetation utilizing the c3 vs c4 photosynthetic pathway is mainly controlled by precipitation and thus past hydrological changes can be inferred from the vegetation record in this study biomarkers of terrestrial plants lignin phenols and plant leaf wax carbon isotopes are examined from a well dated sedimentary record from lake malawi to provide a vegetation aridity record of the past 23 cal ka from southeast africa we suggest that the ratio of cinammyl to vanillyl c v lignin phenols in lake malawi sediments mainly reflects inputs of c3 trees woody tissue vs c4 grasses non woody tissue and find that changes in the c v ratio generally support variability noted in the n alkane carbon isotope record together these records provide evidence for increased c4 vegetation grasses surrounding lake malawi during last glacial maximum lgm the younger dryas in the early holocene and from 2 cal ka to the present suggesting drier conditions at these times elevated inputs of c3 vegetation are noted in the intervals from 17 13 6 cal ka and 7 7 2 cal ka indicating wet conditions in southeast africa a relationship is noted between the n alkane average chain length acl and temperature with longer acls associated with higher temperatures higher n alkane carbon preference index cpi values correlate with higher mass accumulation rates of biogenic silica and may result from periodic increased northerly winds over lake malawi which enhance upwelling and diatom productivity while simultaneously increasing erosion and transport of plant leaf waxes to the lake the molecular data produced in this study suggest that the carbon isotopic signature of bulk sediment 13ctoc in lake malawi is primarily a reflection of terrestrial inputs c3 vs c4 vegetation and may not mainly reflect changes in algal productivity as previously thought

climatic patterns in equatorial and southern africa from 30 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract as part of a wider study of last glacial and deglacial climates in the southern hemisphere continents we here review terrestrial and near shore marine records from equatorial and southern africa between 30 000 and 10 000 years ago 30 10 ka this time interval covers the lead up to the last glacial maximum lgm 21 2 ka the lgm proper and the ensuing deglacial records selected for review needed to meet three requirements continuity or near continuity over the period a well established chronology and at least one but preferably several unambiguous proxy ies we aim to show how regional climates of the sub continent have responded to orbital forcing as opposed to other global glacial interglacial boundary conditions and how they are related to high latitude climates sea and land surface conditions positions of the intertropical convergence zone itcz and of the westerly belt evidence of past climates derived from many independent proxies is given from west to southwest africa moisture from the atlantic ocean then from equatorial east africa to the southern subtropical summer rainfall domain moisture mainly from the indian ocean the lgm was cooler than today and generally drier in the tropics north of 8 9 s glacial to holocene increase in monsoonal precipitation primarily related to orbitally induced summer insolation in the northern hemisphere occurred by steps of increasing amplitude 17 16 14 5 11 5 ka major wet dry spells coincide with abrupt warm cold events in high northern latitudes and related itcz migrations in the southern tropics the main post glacial increase in tropical rainfall generally appears more gradual and in phase with antarctic warming data suggest a restricted northward migration of the itcz and concentration of tropical rainfall well south of the equator during the lgm and the younger dryas drier glacial conditions prevailed in southeastern africa while parts of southwestern africa point to enhanced humidity during the lgm suggesting that the winter westerly belt was either stronger than today or displaced further north possibly as a result of more extensive antarctic sea ice inferred african climatic fluctuations show the competing influences of tropical and high latitude climates of both hemispheres and suggest changes in both meridional and zonal circulation modes this review also reveals major geographical and methodological gaps and a number of unresolved issues providing pointers for future research

vegetation history inferred from pollen in late quaternary faecal deposits hyraceum in the cape winter rain region and its bearing on past climates in south africa abstract pollen analysis shed light on vegetation community structure over the last 23 000 year in the western cape the pollen from dated hyrax faecal accumulations hyraceum relates to the evolution of climate and contributes to proxy records in southern africa principal components analyses of the pollen data and 13c values of the hyrax dung samples show millennial and shorter scale temperature moisture and seasonality variations in the winter rain region the moisture availability at times do not parallel that in previously studied proxy records in the summer rain region showing an asynchronous moist event in the early holocene and drier conditions in the middle holocene anomalies in climate between the two regions may depend on the degree of northward or southward shifting of winter and summer rain circulation systems scenarios with winter rain or cool growing seasons mostly typify the dung sequence but do not exclude the possibility of southward displacement of the westerly belt under precessional strength with slight summer rain increases during the last glacial maximum limited southward displacement is also possible during the mid holocene

thermal implications for the evolution of the spitsbergen transform fault abstract heat flow taken between svalbard and greenland reveal three thermal provinces 1 1 the molloy ridge within the spitsbergen transform 2 2 the yermak plateau 3 3 the northeastern margin of svalbard nordaustlandet the molloy ridge is a short spreading segment and the average heat flow is much above the sclater et al 1971 cooling curve but agrees with values from the norwegian greenland sea an additional zone of intrusion identified by heat flow lies to the northwest of the molloy ridge it straddles both the visible fracture zone and part of the yermak plateau a thermal boundary lies between the warm western segment of the yermak plateau and the shelf off nordaustlandet if the thermal subsidence of the western yermak plateau can be traced to the latest heating episode then it is likely that the crust is similar to oceanic in composition and not older than 13 m y approximately 20 m y younger than the northeastern segment of the plateau plate rotation shows that there was no room for the western segment of the plateau prior to anomaly 7 we postulate that the original transform is associated with the hornsund fault zone in response to deviatoric stress across the oblique ridge transform system the nansen ridge propagated southwestward aborting the old transform trace and shifted to its present position it is suggested that this propagation and migration of the ridge transform system across a zone of extensional deviatoric stress allowed the massive intrusion of basalt forming the western yermak plateau the propagation phenomenon coincides with large scale tertiary volcanic activity on svalbard readjustment and migration of the oblique transform is still taking place as the transform ridge system is liberated from continental constraints the migration rate will diminish as orthogonality is approached

a long range side scan sonar gloria survey of the romanche active transform in the equatorial atlantic abstract a long range side scan sonar survey along the westernmost 720 km of the active section of the romanche fracture zone shows a narrow lineament which can be traced eastwards almost continuously along the north wall of the romanche trough until it cuts across the trough at its deepest point vema depth this lineament is inferred to be the presently active trace of the romanche transform fault the almost continuous ponded floor along the deep axis of the romanche trough was also mapped in detail as were tectonic trends to the north and south of the trough estimated poles of rotation based on both the active fault trace and the sediment pond show considerable differences between the poles describing the motions between north america and africa and between africa and south america the transform motions near the equator therefore do not appear to be simply coupled to the movement of the bordering continental blocks the location of the active transform fault along the younger northern flank of the romanche trough surveyed here is consistent with a gravimetric model that indicates that the plate boundary should be located under the younger flank of the fracture zone trough alternatively should the active fault be shown in future surveys not to cross over to the southern younger flank of the trough east of vema depth then some shift in the transform motions is indicated

snc meteorites clues to martian petrologic evolution the shergottites nakhlites and chassigny snc meteorites are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body the mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks although their ratios of fe fe mg and certain incompatible elements and their oxygen isotopic compositions are distinctive all have crystallization ages of 1 3 b y or younger and formed from magmas produced by partial melting of previously fractionated source regions isotope systematics suggest that the snc parent body had a complex and protracted thermal history spanning most of geologic time some meteorites have been severely shock metamorphosed and all were ejected from their parent body at relatively recent times possibly in several impact events late crystallization ages complex petrogenesis and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet trapped gases in shergottite shock melts have compositions similar to the composition measured in the martian atmosphere ejection of martian meteorites may have been accomplished by acceleration of near surface spalls or other mechanisms not fully understood if snc meteorites are of martian origin they provide important information on planetary composition and evolution the bulk composition and redox state of the martian mantle as constrained by shergottite phase equilibria must be more earthlike than most current models planetary thermal models should benefit from data on the abundances of radioactive heat sources the melting behavior of the mantle and the timing of planetary differentiation calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years concentrations of volatile elements indicate that the snc parent body was not volatile depleted and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing by providing comparisons for spectral reflectance data and viking soil analyses these meteorites may also constrain surface mineralogy and weathering mechanisms

numerical simulation of crystal fractionation in shergottite meteorites cumulus clinopyroxenes in the shergotty and zagami meteorites suggest crystal fractionation occurred possibly by gravitative settling numerical models of this process in a nonconvecting environment argue that the small phenocrysts can segregate only under extreme conditions of cooling time or gravitational field strength since textures indicate that cooling time was not excessive a large planetary g is required by these models in agreement with other suggestions that the shergottite parent body may be mars other calculations indicate that it is extremely difficult to produce the observed textures in a convecting environment unless crystal setting occurred in a quiescent zone at the bottom of the magma chamber

geochemistry of sediments from the romanche fracture zone equatorial atlantic abstract a suite of sediment samples from the romanche fracture zone in the equatorial atlantic has been subjected to bulk and partition chemical and mineralogical analyses together with radiometric dating in order to study the main controls on composition and origin the interelement relationships in the sediments revealed by geostatistical analysis indicate that 1 ca sr and p 2 al fe ti v zn li be and k 3 mn co ni and cu and 4 mg cr and ni are associated partition chemical data suggest that these element associations represent respectively biogenic terrigenous igneous and hydrogenic phases of the sediment surface and downcore sediment data indicate that the distribution of the biogenic component of the sediment is influenced by water depth the distribution of the igneous component is largely controlled by a contribution from ultramafic sources and shows the influence of subsea erosion on the surface sediments the distribution of the hydrogenic component is influenced by contribution from the water column sediment accumulation rate data indicate that these sediments have accumulated fairly rapidly bottom topography and turbidity current activity are probably the main factors controlling their accumulation metal accumulation rate data indicate that there is no significant hydrothermal contribution to the deposits as has been suggested by other workers

influence of tropical easterlies in southern africa s winter rainfall zone during the holocene abstract south africa s southwestern cape occupies a critical transition zone between southern hemisphere temperate winter and tropical summer moisture bearing systems in the recent geological past it has been proposed that the relative influence of these systems may have changed substantially but little reliable evidence regarding regional hydroclimates and rainfall seasonality exists to refine or substantiate the understanding of long term dynamics in this paper we present a mid to late holocene multi proxy record of environmental change from a rock hyrax midden from katbakkies pass located along the modern boundary between the winter and summer rainfall zones derived from stable carbon and nitrogen isotopes fossil pollen and microcharcoal these data provide a high resolution record of changes in humidity and insight into changes in rainfall seasonality whereas previous work concluded that the site had generally experienced only subtle environmental change during the holocene our records indicate that significant abrupt changes have occurred in the region over the last 7000 years contrary to expectations based on the site s location these data indicate that the primary determinant of changes in humidity is summer rather than winter rainfall variability and its influence on drought season intensity and or length these findings are consistent with independent records of upwelling along the southern and western coasts which indicate that periods of increased humidity are related to increased tropical easterly flow this substantially refines our understanding of the nature of temperate and tropical circulation system dynamics in sw africa and how changes in their relative dominance have impacted regional environments during the holocene