late quaternary paleotemperatures derived from a speleothem from cango caves cape province south africa abstract an oxygen isotope temperature record over a large part of the past 30 000 yr has been obtained for the southern cape province of south africa by combining data on the isotopic composition of a stalagmite from a deep cave with that of a confined groundwater aquifer in the same region results show that temperatures during the last glacial maximum were on average about 6 c lower than those today with peaks up to 7 c lower a detailed analysis of the past 5000 yr suggests multiple fluctuations with generally lower temperatures 1 2 c around 4500 and 3000 yr b p the carbon isotopic composition of the stalagmite indicates significant vegetation changes between the late pleistocene and today and also during the second half of the holocene

the validity of the asteraceae poaceae fossil pollen ratio in discrimination of the southern african summer and winter rainfall zones abstract situated at the transition between the mid latitudes and the sub tropics southern africa has a climatic dichotomy between winter and summer rainfall zones wrz and srz the latitudinal extent of the winter rainfall zone during the late pleistocene remains contentiously debated within the regional palaeoscience literature one method posited to reflect the seasonality of rainfall at a given location throughout late pleistocene records for south africa is the ratio of fossil pollen asteraceae to poaceae although adopted for a range of southern african locations the veracity of this method has not been tested this study explores the extent to which this ratio can discriminate between the srz and wrz and the extent of the region subject to fluctuation during the late quaternary the ratio is found to successfully discriminate regions which are and would have remained during the past 20 000 cal yr bp in the srz and wrz exclusively on the basis of these statistics it appears that wrz conditions can be inferred from ratio scores 0 6 and srz conditions from scores

using the value of the crosscorrelation coefficient to locate microseismic events a procedure to locate seismic events uses the value of the crosscorrelation coefficient between waveforms of different events first an empirical relation between spatial event separation and maximum crosscorrelation coefficient is established for a subset of a priori located reference events then this relation is used to determine the hypocenters of an increasing number of events by a grid search strategy measured arrival time differences between s and p waves also constrain the location although the reference events are located by a standard method using the arrival time measurements at three or more receivers the correlation based location requires only one receiver the method has been applied to microseismic data recorded at a single borehole sensor during the 2004 05 injection experiment at the continental deep drilling site ktb in germany with the approach significantly more weak seismic events were located compared to the number of events recorded by a near surface receiver array and by inversion of arrival times the proposed location method is particularly well suited to locate small magnitude earthquakes within dense event clouds when too few arrival time observations for part of the events are available and standard location methods fail these conditions are frequently met in the case of microseismic monitoring of geothermal or enhanced oil recovery experiments

palynological evidence for late quaternary warming episodes in southern africa abstract polleniferous sediments from southern africa associated with past warm episodes before the last glacial maximum are rare interpretation of environmental conditions during these phases are complicated by difficulties of dating in sediments from the northern areas north of 28 s the prominence of tropical woodland pollen suggests that the period between 7000 and 6500 yr b p was associated with optimal temperatures during the holocene identifying the warmest phase in the southern high lying grasslands and semi arid karoo shrublands south of 28 s is difficult because unlike the savanna areas of the north they do not yield good pollen indicators for changes in temperature such as those of frost sensitive trees however some pollen sequences from further south along the southern coast of africa 34 s and at marion island in the southern ocean 47 s suggest that the holocene temperature optimum occurred at about the same time in the sub antarctic area in the south and the subtropical regions in the north the advent of moister conditions in southern africa during the early to middle holocene is generally recorded earlier ca 7500 6500 yr b p in the north at ca 26 s than around 31 s ca 5000 yr b p this change is provisionally associated with a relative shift in seasonality from a predominance of all season precipitation to a greater proportion of summer rainfall which apparently reached the southern karoo areas two thousand years later than the northern bushveld region

holocene paleo climatic record from the south african namaqualand mudbelt a source to sink approach variations in the sediment input to the namaqualand mudbelt during the holocene are assessed using an integrative terrestrial to marine source to sink approach geochemical and sr and nd isotopic

reflection waveform inversion using local descent methods estimating attenuation and velocity over a gas sand deposit prestack seismic reflection data contain amplitudes traveltimes and moveout information waveform inversion of such data has the potential to estimate attenuation levels reflector depths and geometry and background velocities however when inverting reflection data strong nonlinearities can cause reflectors to be incorrectly imaged and can prevent background velocities from being updated to successfully recover background velocities previous authors have resorted to nonlinear global search inversion techniques we propose a two step inversion procedure using local descent methods in which we perform alternate inversions for the reflectors and the background velocities for our reflector inversion we exploit the efficiency of the back propagation method when inverting for a large parameter set for our background velocity inversion we use newton inverse methods during the background velocity inversions it is crucial to adaptively depth stretch the model to preserve the vertical traveltimes this reduces nonlinearity by largely decoupling the effects of the background velocities and reflectors on the data nonlinearity is further reduced by choosing to invert for slownesses and by inverting for a sparse parameter set which is partially defined using geological reflector picks applying our approach to shallow seismic data from the north sea collected over a gas sand deposit we demonstrate that the proposed method is able to estimate both the geometry and internal velocity of a significant velocity structure not present in the initial model over successive iterations the use of adaptive depth stretching corrects the pull down of the base of the gas sand vertical background velocity gradients are also resolved for an insignificant extra cost the acoustic attenuation parameter q is included in the inversion scheme the final attenuation tomogram contains realistic values of q for the expected lithologies and for the effect of partial fluid saturation associated with a shallow bright spot the attenuation image may also indicate the presence of fracturing

time reversal imaging of seismic sources and application to the great sumatra earthquake the increasing power of computers and numerical methods like spectral element methods allows continuously improving modelization of the propagation of seismic waves in heterogeneous media and the development of new applications in particular time reversal in the three dimensional earth the concept of time reversal hereafter referred to as tr was previously successfully applied for acoustic waves in many fields like medical imaging underwater acoustics and non destructive testing we present here the first application at the global scale of tr with associated reverse movies of seismic waves propagation by sending back long period time reversed seismograms we show that seismic wave energy is refocused at the right location and the right time of the earthquake when tr is applied to the sumatra andaman earthquake 26 dec 2004 the migration of the rupture from the south towards the north is retrieved therefore tr is potentially interesting for constraining the spatio temporal history of complex earthquakes

siliceous microfossils as late quaternary paleo environmental indicators at braamhoek wetland south africa this thesis contributes with information on past climate and environmental changes in south africa s summer rainfall region the study is based on multi proxy analyses on wetland peat cores and analyses of stable isotope composition 13c 18o and wood anatomy in cross sections from subtropical trees breonadia salicina the peat archive covers the last 16 ka ka 1000 cal yrs bp and was analysed in terms of fossil pollen charcoal diatoms phytoliths and stable isotope composition the peat record infers relatively wet climate conditions at c 13 7 12 8 ka 10 5 9 5 ka and 2 5 0 5 ka and drier conditions at c 16 13 7 ka 12 8 10 5 ka and during mid holocene tentatively cooler late pleistocene temperatures shifted towards warmer after c 9 5 ka the study of b salicina demonstrates the paleo climatic value of subtropical trees despite absence of annual tree rings an age model was constructed from radiocarbon dating and calibration by wiggle matching 13c in b salicina shows a co variation with annual rainfall amounts suggesting that it may be considered a regional climate proxy 18o is mainly influenced by local factors but acts as a useful complement when interpreting 13c together with other regional high resolution records the 600 year long 13c record suggests dry climate conditions in northern south africa during the 1700s and mid 1500s ad inferred climate and environmental changes are suggested being a response to expansion contraction and latitudinal shifts of the tropical subtropical and mid latitude atmospheric circulation cells an observed inverse humidity pattern between southern and equatorial africa suggests that enso like teleconnections may be a possible forcing mechanism in a decadal to centennial time perspective

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

a late quaternary record of monsoon variability in the northwest kimberley australia abstract understanding of the late quaternary environment of australia s vast kimberley region has to date been hindered by the region s lack of classic palaeoenvironmental archives such as deep lake sediments however mound spring peat deposits in the region have been found to be a potentially rich archive of palaeoenvironmental data here we present a high resolution record from black springs mound spring in the kimberley s northwest filling some of the current gaps in knowledge of the region s environmental history this builds on a 6000 year record developed from the same site and indicates that since the last glacial interglacial transition the australian summer monsoon has varied greatly in intensity with an increase in monsoonal precipitation from 14 000 yr bp and pronounced drying in the late holocene despite some chronological uncertainties thought to be due to the inclusion of younger microscopic root fragments changes in the record compare well with other records of climatic change from the kimberley and across tropical northern australia

pollen analysis of hyena coprolites and sediments from equus cave taung southern kalahari south africa equus cave in quaternary tufa near taung in the semiarid woodland of the southern kalahari yielded 2 5 m of sediment in which a rich assemblage of bones and coprolites was preserved the fossils were accumulated mainly by hyenas during the late pleistocene and holocene pollen from coprolites reflects diet as well as vegetation over relatively large areas visited by hyenas while pollen from sediments represents more local sources the pollen sequence derived from coprolites and sediments demonstrates how the vegetation evolved from open grassland with small shrubs and occasional trees during the late pleistocene to open savanna with more small shurbs then during the last 7500 yr to modern savanna temperatures were not more than 4 c cooler and it was slightly moister than today during the late pleistocene phase it became gradually warmer but relatively dry before optimal temperature and moisture conditions developed around 7500 yr b p climatic conditions slightly less favorable for woodland occurred during part of the late holocene

a multi proxy analysis of late quaternary palaeoenvironments sekhokong range eastern lesotho the eastern lesotho highlands host an array of periglacial and glacial geomorphic features their analysis has provided past climate interpretations predominantly for cold periods yet no multi proxy temporally continuous palaeoenvironmental records exist this study presents a palaeoenvironmental reconstruction based on sedimentary characteristics fossil pollen and diatoms from an alpine wetland located in the sekhokong mountain range the record commences in the late pleistocene with a wet period from 16 450 to 14 440 cal a bp interrupted by dry conditions from 16 350 to 15 870 cal a bp from 14 150 to 8560 cal a bp drier conditions are inferred slowly transitioning to warmer wetter conditions warmer dry conditions are inferred for 8560 7430 cal a bp followed by cold wet conditions from 7280 to 6560 cal a bp a dry warmer period occurs from 6560 to 3640 cal a bp indicated by pollen diatom and sedimentary records followed by cool wet conditions from 3400 to 1200 cal a bp the period from 1110 cal a bp to the present is characterized by progressive drying pronounced cold events are detected from the diatom record moisture records appear relatively specific to the topographic setting of sekhokong near the great escarpment edge probably driven by orographically constrained synoptic controls

an improved method for hydrofracture induced microseismic event detection and phase picking the ability to detect small microearthquakes and identify their p and s phase arrivals is a key issue in hydrofracture downhole monitoring because of the low signal to noise ratios s n an array based waveform correlation approach matched filter is applied to improve the detectability of smallmagnitudeeventswithmechanismsandlocationssimilar to a nearby master event after detecting the weak events a transformed spectrogram method is used to identify the phase arrivals the technique has been tested on a downhole monitoring data set of the microseismic events induced by hydraulic fracturing it is shown that for this case one event with a s n around 6 db which is barely detectable using an array stacked short time average long time average sta lta detector under a reasonable false alarm rate is readily detected on the array stacked correlation traces the transformedspectrogramanalysisofthedetectedeventsimproves p ands phasepicking

pollen indications of holocene palaeoenvironments at florisbad spring in the central free state south africa mid to late holocene pollen data from florisbad in the central free state south africa reveal a number of moisture fluctuations commencing at c 6500 bp the pollen sequence indicates an arid climate but shows more availability of moisture under grassy conditions from summer rain at c 6300 bp and again at c 4420 bp the interval between these dates is characterized by a dry episode with karroid shrubs some time between 5500 and 4500 bp possibly as a result of less marked summer seasonality after 4220 bp moisture conditions gradually fluctuated in intensity or seasonal availability until c 2100 1700 bp when strong summer evaporation is indicated at the upper end of the sequence the data are complemented by previously published results on environmental change from the nearby deelpan site to the west although some distinct events correlate regionally over south africa summer rains appear to have been significant at florisbad at an earlier stage in the mid holocene than in the karoo to the south

holocene pollen from swamp cave and hyrax dung deposits at blydefontein kikvorsberge karoo south africa abstract pollen analysis of material from a variety of sediment types including those from ponds streams a rock shelter and hyrax dung accumulations in the blydefontein basin 31 09 s 25 05 e fig 1b provide a record of vegetation change in the eastern karoo over the last 10 000 years the pollen composition fluctuated as a result of different taphonomic processes inherent in the various sampled deposits results further demonstrate that long term vegetation changes alternated between karoo shrub and grassland plant communities karoo shrubs suggesting relatively dry conditions were generally prominent in the early holocene until ca 5400 yr bp when more grassy vegetation began to flourish presumably in response to increased summer rain conditions pollen representation of the early holocene is not detailed enough to trace millennial scale variations during this period but more detailed middle to late holocene data show millennial or shorter scale shifts between grassland and drier karroid veld

a 3000 year high resolution stalagmitebased record of palaeoclimate for northeastern south africa high resolution stable isotope variations and growth structure analyses of the last three millennia of a 6600 year stalagmite record at cold air cave makapansgat valley south africa are presented growth layers which are measurable over the last 250 years are shown to be annual the correlation between the width of growth layers and precipitation is strongly positive changes in 18o and 13c are positively correlated and inversely correlated to changes in the colour of the growth layers in the stalagmite variations in colour are directly correlated with mean annual temperature dark colouration is the product of increased temperature and mobilization of organic matter from the soil and is associated with wetter summers and enhanced growth of c4 grasses darker colouring and enriched 18o and 13c reflect a warmer wetter environment whereas lighter colouring and depleted isotopic values are indicative of cooler drier conditions the dominant episode in the 3000 year record is the cool dry 500 year

subaerial debris flow deposition in the upper paleozoic cutler formation western colorado abstract outcrops of the lower part of the cutler formation near gateway colorado contain proximal alluvial fan deposits of two principal lithofacies the diamictite lithofacies d consists of a variety of sharply bounded massive muddy beds which are interpreted as deposits of subaerial debris flows the gravelly sandstone lithofacies s consists of amalgamated beds of laminated and cross bedded conglomeratic sandstones which are interpreted as water deposited sediments clasts in s are rarely larger than 0 5 m in maximum diameter but clasts in d are commonly much larger up to 8 m both normal and inverse grading are visible in d but grading is generally not well developed in either lithofacies imbrication of clasts although more pronounced and more consistent in s is fairly commo in both lithofacies four subfacies of diamictite are distinguishable on the basis of clast packing and grading massive matrix supported dram graded matrix supported dmg inversely graded clast supported dci and massive clast supported dcm given the hydrodynamic and rheologic properties of debris flows as reported by previous workers four debris flow regimes are postulated on the basis of varying water content and clast interaction subfacies dram and drag typify deposits of flows having viscous clast interactions subfacies dci represents deposits of flows having inertial or colliding clast interactions subfacies dram comprises deposits of flows with demonstrably high yield strengths subfacies dcm represents deposits of flows in which yield strength was insufficient to support most clasts this classification specifically recognizes turbulence selective deposition and bedload transport of clasts as essential characteristics of certain dilute debris flows it also accommodates as debris flow deposits some beds which have features usually associated with aqueous deposition including clast frameworks channelization imbrication and normal grading

time reverse modeling of low frequency microtremors application to hydrocarbon reservoir localization 1 time reverse modeling is applied to synthetic and real low frequency microtremors measured at the earth surface with synchronized seismometers in contrast to previous time reverse applications no single event or first arrival time identification is applied for microtremor localization synthetic low frequency microtremors are numerically generated within a small underground area and modeled with a finite difference algorithm simulating two dimensional elastic wave propagation time reverse modeling using synthetic microtremors shows that small underground source areas can be accurately located different source characteristics which emit mainly p waves or s waves vertically influence the localization accuracy time reverse modeling is applied to two real microtremor data sets acquired 16 months apart above known oil reservoirs nearby voitsdorf austria to investigate whether spectral anomalies observed above the reservoirs originate from the reservoirs time reverse modeling indicates that low frequency microtremor signals originate from the reservoir locations and provides a possible method for reservoir localization

palynological analysis of hyrax middens from southern africa abstract hyrax middens in relatively dry parts of africa preserve plant material which includes pollen the bottoms of two stratified hyrax dung middens from blydefontein basin in the karoo shrubland of south africa were dated by radiocarbon to ca 300 yr b p and ca 1130 yr b p comparison of midden pollen spectra with pollen from alluvial sediments near one of the hyrax middens and in modern surface samples indicates that middens contain pollen which reflects local vegetation and that diet probably does not have a major influence on pollen spectra changes in pollen composition probably reflect climatic conditions during the early history of the older midden profile grass dominated spectra suggest moist conditions existed between 1200 and 300 yr b p and an interval of slightly more shrubby karoid vegetation possibly points to a minor dry spell at 1000 yr b p a sharp increase of karoid shrub vegetation and a decrease of grass since 300 yr b p is reflected in both middens the change was apparently triggered by relatively dry conditions and later during the last 150 years it was enhanced by overgrazing from european domestic stock

image domain velocity inversion and event location for microseismic monitoring abstractmicroseismic event locations obtained from seismic monitoring data sets are often a primary means of determining the success of fluid injection programs such as hydraulic fracturing for oil and gas extraction geothermal projects and wastewater injection event locations help the decision makers to evaluate whether operations conform to expectations or parameters need to be changed and may be used to help assess and reduce the risk of induced seismicity however obtaining accurate event location estimates requires an accurate velocity model which is not available at most injection sites common velocity updating techniques require picking arrivals on individual seismograms this can be problematic in microseismic monitoring particularly for surface acquisition due to the low signal to noise ratio of the arrivals we have developed a full wavefield adjoint state method for locating seismic events while inverting for p and s wave velocity models that optimally focus multiple complementary ima

extended wave equation imaging conditions for passive seismic data abstractthe information obtained from seismic monitoring at injection sites is often limited to seismic event properties e g location origin time moment tensor the accuracy of which greatly depends on the assumed or estimated elastic velocity models current traveltime based methods to calibrate velocity models rely on having distinct arrivals in surface seismic monitoring however the signal to noise ratio of arrivals is often too poor for pick based methods and migration techniques are needed wave equation migration can image microseismic sources without the need for picking or knowledge of the onset time by reconstructing the wavefield through the model space and applying an imaging condition we have devised extended imaging conditions for passive seismic wave equation imaging algorithms and we have found that they represent a key step toward verifying and updating elastic velocity models by extending imaging conditions away from zero lag in time and space we can better evaluate the focu

uncertainties in passive seismic monitoring the use of passive seismic techniques to monitor oil field completion and production processes is on the rise stress changes induced by such reservoir activities as hydraulic fracturing water injection or fluid extraction will often result in failure of the rocks with a concurrent release of seismic energy in the form of compressional p and shear s waves passive seismic monitoring is based on recording these emitted waves and then using their arrival times to estimate the location of the failure events

microseismic imaging using a source function independent full waveform inversion method we thank kaust for sponsoring this research we also thank to the team of swag for their help during the research

holocene palaeoenvironments inferred from a sedimentary sequence in the tsoaing river basin western lesotho abstract the paper presents a sedimentological palynological and phytolith record from a 13 m deep holocene sedimentary sequence located in the tsoaing river valley southwestern lesotho six conventional radiocarbon and two ams dates provide a relatively high resolution holocene record for the sedimentary sequence ranging from ca 12 000 to 4000 years bp pollen is absent in the upper section but present in the lower 2 m confirming terminal pleistocene holocene conditions reported in previous published pollen and charcoal records from the region the absence of pollen in the upper layers of ca 9000 years bp and younger suggests that conditions over southwestern lesotho throughout much of the holocene was typified by a seasonal climate that prevented long term preservation of plant remains although other plant material like robust spores microscopic charcoal and phytoliths withstood oxidation sedimentological and phytolith results suggest that the period from ca 8600 to 8450 years bp experienced rapid environmental change towards drier conditions phases of chemical disintegration with organic input including local swamp phytoliths are suggested at ca 7000 years bp and again after 4500 years bp

velocity calibration for microseismic monitoring a very fast simulated annealing vfsa approach for joint objective optimization to accurately locate microearthquakes that are genetically related to hydraulic fracture stimulation a thorough knowledge of the velocity structure between monitoring and fracturing treatment wells is essential very fast simulated annealing vfsa is implemented to invert for a flat layered velocity model between wells using perforation or string shot data a two point ray tracing method is used to find the ray parameter p for a ray traveling from a source to a receiver the original traveltime calculation formula is modified to account for the borehole source receiver geometry vfsa is used as a tool to optimize p and s wave velocities simultaneously unlike previous applications of vfsa two improvements result from a new study 1 both p and s wave arrival time misfits are considered in a joint objective function and 2 p and s wave velocities are perturbed simultaneously during annealing the inverted velocities follow the true values closely with a very small root mean square error indicating the inverted model is close to the global minimum solution whose rms error should be zero for synthetic examples data noise contaminates inverted models but not substantially in synthetic test results a comparison of models inverted using vfsa and occam s inversion technique indicates that inverted models using vfsa are superior to those using occam s method in terms of velocity accuracy