monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

the nature of shallow water carbonate lithofacies thickness distributions carbonate lithofacies thickness distributions are of fundamental importance to understanding shallow water carbonate deposystems because they record evidence of the lateral distribution and migration of lithofacies elements as well as evidence for the various other intrinsic and extrinsic controls on stratal geometries and accumulation rates previous analyses of lithofacies thickness data led to the suggestion that exponential distributions are ubiquitous in the ancient record this has been interpreted to indicate deposition by stochastic poisson process lithofacies mosaics to further investigate these ideas statistical analysis of 56 outcrop and core examples was performed the kolmogorov smirnov test was used to identify the degree to which measured lithofacies thicknesses are well represented by a theoretical exponential distribution results from this analysis show that 16 of the 56 examples can be confidently shown to be exponential while 28 are very probably not exponential this indicates that stochastic poisson processes are a plausible explanation for many carbonate successions but they do not explain all of those tested here suggesting that other non poisson processes either stochastic or deterministic in nature or both must also be important thus lithofacies planform geometries and the processes controlling vertical stacking in ancient carbonate platform top deposystems were likely more diverse than has been suggested requiring significant further quantitative analysis and numerical forward modeling to properly understand

late pleistocene and holocene vegetation history of the bale mountains ethiopia abstract a sediment core recovered from garba guracha a glacial lake at 3950 m altitude in the bale mountains of ethiopia at the boundary of the ericaceous and afroalpine vegetation belts provides a 16 700 year pollen record of vegetation response to climatic change the earliest vegetation recorded was sparse and composed mainly of grasses amaranthaceae chenopodiaceae and artemisia indicating an arid climate at 13 400 cal bp amaranthaceae chenopodiaceae pollen declined sharply and cyperaceae increased suggesting a change to moister conditions the younger dryas interval is represented by a small increase in artemisia and reduced cyperaceae indicating aridity just after the start of the holocene 11 200 cal bp the upper altitudinal limit of the ericaceous belt rose and woody ericaceous vegetation extended across the sanetti plateau in response to increased moisture and temperature the marked change from clastic to organic lake sedimentation at this time reflects the increase in woody vegetation cover in the lake catchment accompanied by soil stabilisation and increased leaf litter and soil humus content from about 6000 cal bp and especially after 4500 cal bp mid altitude dry afromontane juniper podocarpus forests developed on the northern slopes of the mountains in response to reduced rainfall in a shortened wet season erica shrub and forest decreased in area and altitude and the afroalpine ecosystem expanded on the plateau podocarpus declined from about 2000 cal bp as juniperus increased to its present dominance at 2500 3300 m altitude human impact on the high altitude afroalpine and ericaceous vegetation has been relatively minor confirming that the endemic biodiversity of the ethiopian mountains is a legacy of natural holocene vegetation change following repeated expansion and contraction of the upland ecosystems during the quaternary

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

late quaternary palynology in marine sediments a synthesis of the understanding of pollen distribution patterns in the nw african setting abstract after a review of the first steps in marine palynology we show that the understanding of the northwest african setting is crucial to evaluate the potential of marine palynological studies elsewhere we studied distribution patterns of pollen grains in recent marine sediments off nw africa and were able to clearly relate patterns to modern pollen source areas vegetation belts and operating transport systems wind belts and ocean currents in particular patterns of quercus artemisia chenopodiaceae amaranthaceae ephedra gramineae and wet forest trees are very indicative of the position of the vegetation belts on the adjacent continent aeolian pollen transport is carried out by the northeast trade winds and the african easterly jet aej in the rain forest belt transport of pollen and fern spores also occurs by rivers a detailed comparison between recent pollen rain samples from terrestrial and marine sites between 21 and 12 n showed that the latitudinal range of vegetation belts is clearly reflected in the pollen samples of both environments a migration of the southern border of the sahara is reflected by the changing ratio between chenopodiaceae amaranthaceae pollen from the desert and gramineae pollen from the savannah belt distribution patterns of pollen for 9000 and 18 000 14 c yr bp last glacial maximum time slices based on pollen records from eleven marine cores between portugal and the gulf of guinea show significant latitudinal migrations of vegetation belts but a stable position of the main wind trajectories the aej had a stable position around 21 n the belt with trade winds had a stable position from morocco southwards changing vigour of the trade winds is clearly reflected by the patterns of isopollen contours and by changes in pollen influx records

controls and predictability of carbonate facies architecture in a lower jurassic three dimensional barrier shoal complex djebel bou dahar high atlas morocco spatial information on lithofacies from outcrops is paramount for understanding the internal dynamics external controls and degree of predictability of the facies architecture of shallow water carbonate platform tops to quantify the spatial distribution and vertical stacking of lithofacies within an outer platform shoal barrier complex integrated facies analysis and digital field technologies have been applied to a high relief carbonate platform exposed in the djebel bou dahar lower jurassic high atlas morocco the outer platform is characterized by subtidal cross bedded coarse grainstone to rudstone grading into supratidal pisoidal packstone rudstone with tepees that together formed a 350 to 420 m wide shoal barrier belt parallel to the margin this belt acted as a topographic high separating a restricted lagoon from the subtidal open marine region low energy tidal flats developed on the protected flank of the barrier facing the lagoon lithofacies patterns were captured quantitatively from outcrop and integrated into a digital outcrop model the outcrop model enabled rapid visualization of field data and efficient extraction of quantitative data such as widths of facies belts in addition the spatial heterogeneity was captured in multiple time slices i e during different phases of cyclic base level fluctuations in general the lateral continuity of lithofacies is highest when relative water depth increased during flooding of the platform top establishing low energy subtidal conditions across the whole platform and when the accommodation space was filled with tidal flat facies heterogeneity increased during deposition of the relief building bar facies that promoted spatial diversification of depositional environments during the initial phases of accommodation space creation cycles commonly are composed of a thin transgressive tidal flat unit followed by coated grain rudstone bar facies lateral to the bar facies pisoidal grainstone beach deposits accumulated these bar and beach deposits were overlain by subtidal lagoonal facies or would grow through the maximum flooding and highstand there the bars either graded into supratidal pisoidal facies with tepees when accommodation space was filled or were capped by subaerial exposure due to a sea level fall modified embedded markov analysis was used to test the presence of common ordering in vertical lithofacies stacking in a stationary interval constant depositional mode analysis of individual sections did not reveal any ordering which may be related to the limited thickness of these sections composite sections however rejected the null hypothesis of randomness the addition of stratigraphically significant information to the markov analysis such as exposure surfaces and lateral dimensions of facies bodies strengthens the verdict of unambiguous preferential ordering through careful quantitative reconstruction of stratal geometry and facies relationships in fully integrated digital outcrop models accurate depositional models could be established that enhanced the predictability of carbonate sediment accumulation 2009 the authors journal compilation 2009 international association of sedimentologists

abrupt return of the summer monsoon 15 000 years ago new supporting evidence from the lower white nile valley and lake albert abstract the last glacial period ended with an abrupt return to warmer and wetter conditions at a number of sites in intertropical africa asia australia and south america 15 000 years 15 ka ago similar abrupt warming is also evident at this time in high latitudes and in air trapped in greenland ice we here report new supporting evidence of this event from a climatically sensitive region in africa the white nile valley of the central sudan and lake albert in the uganda headwaters during the last glacial maximum the white nile valley was even more arid than it is today with desert dunes active as far south as latitude 12 s the sudden overflow of lake victoria in the ugandan headwaters of the white nile 14 5 ka confirmed here by sr isotope statigraphy caused extensive flooding in the lower white nile valley and severe flooding in egypt the volume of fresh water flowing into the eastern mediterranean at this time ultimately resulted in accumulation of highly organic sediments sapropel 1 on the floor of the mediterranean sea flooding in the central sudan attained an elevation of 382 m along a north south distance of 400 km the recessional shoreline of the 382 m white nile is indicated by concentrations of now buried freshwater gastropod shells and beach sands dated respectively by calibrated ams radiocarbon and osl to 15 16 ka this mega flood event marks the abrupt return of the summer monsoon and may reflect a globally synchronous event

vegetation change in equatorial west africa time slices for the last 150 ka abstract drawing on marine and terrestrial palynological data vegetation maps of equatorial west africa are presented for eleven time slices over the last 150 000 years long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale temporal and spatial variation is revealed in relation to global patterns of climate change rain forest was widespread during oxygen isotope stages 1 and 5 but strongly reduced during stages 3 and 4 and especially during stages 2 and 6 when open grass rich vegetation prevailed glacial rain forest refuges are found in the southwest of the guinean mountains and along the eastern coast of the gulf of guinea miombo woodland of the zambezian vegetation zone expanded during stage 5 especially during the first half podocarpus forest had its largest expansion during substages 5d 115 to 105 ka and 5b 95 to 85 ka the last occurrence of podocarpus in the guinean mountains is during stage 5a the distribution of mangrove swamps was extremely reduced during glacial times during stage 6 savanna and open dry forest covered large areas along the northern coast of the gulf of guinea the southern saharan desert reached far to the south and the namib desert far to the north the area of rain forest was restricted mangrove swamps were strongly reduced and the area of podocarpus forest fluctuated during stage 5 large changes in the area of afromontane forest rain forest dry open forest and savanna occurred rain forest was widespread and mangroves were extensive along the coast during the last interglacial substage 5e podocarpus forest area strongly extended during substages 5d and 5b in substages 5c and 5a rain forest reclaimed areas it had lost in the previous substages 5d and 5b respectively mangrove swamps were less widespread in the later substages of stage 5 than during substage 5e during stage 4 the rain forest area was again strongly reduced and recovered only slightly during the following stage 3 also the mangrove swamp area was reduced except along the ivory coast and along the northwestern coast of the gulf of guinea podocarpus forest only occurred in angola and may be in congo during stage 4 again forest was much reduced during stage 2 and open vegetation types covered large parts of equatorial west africa mangrove swamps must have been rare at the beginning of the holocene mangrove swamps had recovered and reached their largest extension also the rain forests area increased in the early holocene and guinean and congolian rain forests were probably not separated by a savanna corridor now existing in togo and benin

modeling carbonate sequence development without relative sea level oscillations standard conceptual models propose that stratal patterns in carbonate depositional sequences are controlled predominantly by relative sea level oscillations even during greenhouse periods when amplitudes of relative sea level oscillations were small however numerical experiments with a two dimensional forward model of carbonate systems suggest that variations in sediment transport rate and carbonate productivity are capable of producing similar parasequence stacking patterns without relative sea level oscillations this result suggests two alternative end member models one driven by relative sea level change the other driven by changes in transport rate and productivity controlled ultimately by climatic factors many carbonate systems may represent some combination of these end member possibilities

post glacial arid episodes in ethiopia have implications for climate prediction several lines of geomorphological and stratigraphical evidence suggest that the widespread early post glacial wet phase in tropical africa between 12 500 and 5 000 yr bp refs 1 2 was interrupted by severe dry episodes during the intervals 11 000 10 000 8 500 6 500 and 6 200 5 800 yr bp refs 3 9 the magnitude of the second event has recently been questioned10 we present new stratigraphical and dating evidence from the ziway shala lake basin ethiopia indicating the severity and timing of dry phases during the interval 12 000 5 000 yr bp our findings have important implications for predictions of the climatic impact of increasing atmospheric levels of co2

palaeobathymetric reconstruction of peritidal carbonates late barremian urgonian sequences of provence se france abstract peritidal platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france tend to be arranged stratigraphically in deepening up or shallowing up sequences seven facies types lithofacies were defined in the studied stratigraphic interval ranging from supratidal to shallow subtidal settings there is a good correspondence between the inferred relative water depth of facies and their average bed thickness cumulative thickness of facies types expresses quantitatively their palaeobathymetric range and provides an estimate of their average water depth calculations show that the palaeobathymetry of supratidal intertidal facies types is from 0 to 40 cm i e a pertaining to a palaeotidal microtidal range the average palaeobathymetry of rudist facies ascribed to subtidal settings fluctuates between 40 cm and nearly 160 cm measuring a large number of beds belonging to both shallowing up and deepening up sequences and averaging the results appear relevant to minimise the effect of compaction pressure solution and synsedimentary progressive or abrupt changes in accommodation which are expected to modify bed thickness and its original palaeobathymetric significance the method proposed here has a good potential for palaeobathymetric reconstruction of ancient peritidal carbonates

numerical forward modeling of carbonate platform dynamics an evaluation of complexity and completeness in carbonate strata abstract it is clear that carbonate strata are complex and incomplete but the nature and origins of the complexity and the origin and distribution of hiatuses remain poorly understood a three dimensional numerical forward model of carbonate platform systems has been used to investigate how variations in complexity and completeness arise in carbonate strata the model includes depth dependent carbonate production occurring as a stochastic mosaic of producing elements across a topographic surface it also includes depth dependent sediment erosion transport and deposition governed by a regional transport direction that can vary stochastically through time and by wave refraction that causes local variations in transport direction combined mosaic production and variable sediment transport create a complex distribution of prograding islands generating self organizing shallowing upward parasequences of variable thickness and variable lateral extent hiatuses occur throughout the parasequences not just at the base and top generated by nondeposition due to mosaic production and by erosional scour this erosion is triggered by variations in water depth and fetch distance created by complex island morphologies preserved strata represent between 15 and 60 of total elapsed time measured at a 2 ky resolution and much of the preserved thickness represents punctuated deposition with depositional events spanning only a few thousand years stratigraphic completeness depends on subsidence rate and sediment transport rate so that completeness generally increases with increasing subsidence rate and decreasing transport rate but shows a nonlinear relationship with subsidence rate this suggests that reliable estimates of completeness of ancient carbonate strata require more than knowledge of subsidence rate and sea level change particularly because the real situation is likely to be considerably more complex than represented in this model the stochastic production mosaic and stochastic variations in regional transport direction create complex strata whereas the self organizing island progradation process creates simpler ordered strata a combination of the two processes creates an intermediate level of complexity producing strata consisting of laterally impersistent parasequences with numerous erosion surfaces and complex stacking patterns and complex thickness distributions this has important implications for parasequence correlation in outcrop and the subsurface

a 30 000 yr record of land ocean interaction in the eastern gulf of guinea abstract a 30 000 yr dinocyst and pollen record from the eastern equatorial atlantic off cameroon has been investigated in order to identify land ocean linkages during the last deglacial transition a strong correlation between the abundance of brigantedinium spp and the ca fe ratio during the last glacial period suggests enhanced marine productivity in association with cool seawater temperatures and nutrient input linked to coastal upwelling and or a proximal river mouth dry conditions are recorded on the adjacent continent with a significant representation of open vegetation indicators and the afromontane taxon podocarpus after 17 cal ka bp these indicators register a sharp decline as a result of a climatic transition from the dry cooler conditions of the last glacial period to the wetter warmer conditions of the deglaciation simultaneously dinocysts show a significant shift from dominant heterotrophs to an increasing abundance of autotrophs reflecting warmer conditions significant changes are observed during the younger dryas with a return to drier conditions and higher salinities the start of the holocene is marked by very low salinity conditions reflecting optimal monsoonal conditions over west equatorial africa the end of the african humid period is observed between 6 and 5 cal ka bp followed by significant fluctuations in both terrestrial and oceanic proxies

high resolution last deglaciation record from the congo fan reveals significance of mangrove pollen and biomarkers as indicators of shelf transgression abstract high abundances of mangrove pollen have been associated with transgressive cycles on tropical margins but the detailed relations between systems tracts and the taphonomy of the pollen are unclear we report here the occurrence and high abundance of rhizophora pollen in association with taraxerol a rhizophora sourced biomarker from a high resolution congo fan core covering the last deglaciation an age model based on 14c dates enables the temporal changes in taraxerol content and the percentage frequencies and flux pollen grains pg cm 2 103 yr 1 of mangrove pollen to be compared quantitatively with the lateral rate of transgression across the flooding surface derived from glacio hydro isostatic model output and the bathymetry of the margin rhizophora pollen concentrations and taraxerol content of the sediment are very strongly positively correlated with the lateral rate of transgression and indicate independently of any sequence stratigraphic context that mangrove pollen spikes are associated with the transgressive systems tract rather than the highstand systems tract or maximum flooding surface lower resolution longer term records from this margin indicate an association between taraxerol concentrations and transgressive rather than regressive phases the flux of these materials to the congo fan is interpreted as a function of the erosion of flooded mangrove swamp on the shelf and less importantly changing extent of mangrove habitat during sea level rise congo river palaeoflood events also result in reworking of mangrove pollen and supply to the fan but this mechanism is subdominant rhizophora pollen has been underestimated in many palynological studies undertaken on cores from the african margin because of inappropriate sieve mesh size used during laboratory preparation

geostatistical earth modeling of cyclic depositional facies and diagenesis in siliciclastic and carbonate reservoirs depositional facies are often described as being organized in cyclic successions that are overprinted by diagenesis most reservoir modelling workflows are not able to reproduce stochastically such patterns herein a novel geostatistical method is developed to model depositional facies architectures that are rhythmic and cyclic together with superimposed diagenetic facies the method uses truncated pluri gaussian random functions constrained by transiograms cyclicity is defined as an asymmetric ordering between facies and its direction is given by a three dimensional vector called shift this method is illustrated on two case studies outcrop data of the triassic latemar carbonate platform northern italy are used to model shallowing upward facies cycles in the vertical direction a satellite image of the modern bermuda platform interior is used to model facies cycles in the windward to leeward lateral direction as depositional facies architectures are modelled using two gaussian random functions a third gaussian random function is added to model diagenesis thereby depositional and diagenetic facies can exhibit spatial asymmetric relations the method is applied in two regions of the latemar carbonate platform that experience two different types of diagenetic transformation syn depositional dolomite formation and post depositional fracture related diagenesis the method can also incorporate proportion curves to model non stationary facies proportions this is illustrated in cretaceous shallow marine sandstones and mudstones book cliffs utah for which cyclic facies and diagenetic patterns are constrained by embedded transition probabilities

spatial patterns of sediment accumulation on a holocene carbonate tidal flat northwest andros island bahamas abstract to characterize spatial patterns of sedimentation and analyze the morphology of part of the modern tidal flats of northwest andros island in the bahamas this study integrated remote sensing geographic information systems gis and carbonate sedimentology the fundamental data are a landsat tm image that has been classified to create a thematic map of eight subfacies interpreted to represent a distinct tidal flat subenvironment such as adjacent marine exposed levee beach ridge pond and algal marsh spatial statistics of the thematic map characterize the patterns of sediment accumulation quantitative analysis highlights several interesting results concerning subfacies character and distribution 1 of the eight mapped subfacies low algal marsh is most widespread representing 27 5 of the total area whereas exposed levee beach ridge is the least widespread accounting for 10 of the area 2 the patches of different subfacies have different shape complexities with low algal marsh high algal marsh and mangrove ponds being the least complex and exposed levee beach ridge being the most complex 3 markov chain analysis suggests that lateral transitions between different subfacies are highly ordered and 4 frequency distribution of subfacies patch area and lacunarity gap size distribution data exhibit power law relationships over several orders of magnitude consistent with fractal characteristics the fractal nature of patch size and gaps between facies illustrate that on this tidal flat neither the size nor the spatial distribution of subfacies has a characteristic scale this statistical behavior is consistent with the presence of self organization or emergence of pattern in the absence of a template or external forcing the statistical self organization on the tidal flat is the cumulative expression of local processes but it becomes apparent only through analysis of the whole system these results are inconsistent with models suggesting that tidal flats include a migrating complex of randomly distributed randomly sized subenvironments ancient successions that include random patterns may reflect the more pronounced influence of forces external to the sedimentary system instead of an absence of those forces

the uncertainties involved in extracting amplitude and frequency of orbitally driven sea level fluctuations from shallow water carbonate cycles in outcrops shallow water carbonates often form thick vertically stacked metre scale exposure bounded depositional packages here called carbonate cycles because the facies within carbonate cycles can be tied precisely to water depths they are considered ideal for reconstructing past sea level changes there is however increasing evidence that these depositional cycles are unreliable recorders of both the frequency and the amplitude of orbitally driven sea level fluctuations carbonate cycles record only a fraction of the amplitude of a sea level cycle a portion of the rise and nothing of the fall cores through the pleistocene cycles on great bahama bank illustrate this shortcoming although the amplitudes of the last nine sea level changes are each a hundred metres or more the thickness of the cycles varies from a few metres to ca 15 m the lack of correlation between sea level amplitude and cycle thickness is not eliminated for cycles deposited during times of lower sea level amplitudes for example the cretaceous upper cretaceous cycles on the maiella platform margin document the irregularly filled accommodation space and the resultant variability in cycle thickness and frequency uncertainties in assessing the frequencies of sea level changes from shallow water carbonate cycles are caused by missed beats and metre scale oscillations of sea level within highstands that potentially produce cycles of very short duration the random amplitude variability during the last 57 glacio eustatic sea level changes illustrates the difficulty of assessing missed beats where a sea level fluctuation is not recorded because the sea level rise does not reach the platform top missed beats are also produced by the depositional topography that is created by irregularly filled accommodation space as a result variable numbers of cycles are deposited across the platform further complicating orbital frequency analyses are decametre scale oscillations of the sea level during highstands the amplitude of these sub orbital sea level oscillations up to 17 m within the last interglacial marine isotope stage 5e are sufficient to expose shallow platforms like great bahama bank and subsequently produce an additional depositional cycle with similar facies successions the combined effects of missed beats and oscillations within highstands are likely to produce cycles and hiatuses of variable duration that are difficult to extract from the rock record consequently estimates of the orbital forcing mechanisms and frequencies from ancient shallow water carbonate cycles carry large uncertainties

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

marine production in the congo influenced se atlantic over the past 30 000 years a novel dinoflagellate cyst based transfer function approach abstract the sediments from the congo deep sea fan contain valuable information about past environmental conditions of the east equatorial atlantic during the transition from the last glacial maximum lgm to present day climatic conditions the high resolution marine organic walled dinoflagellate cysts dinocysts and terrestrial pollen palynological records from two cores off equatorial west africa covering the last 30 000 years document three major phases in surface productivity 1 during the lgm relative sea level was low nutrient enrichment due to seasonal coastal upwelling prevailed off the congo mouth and high aridity prevailed in the catchment area 2 at around 15 2 cal ka bp monsoonal precipitation strengthened over the congo basin generating high river discharges river induced upwelling and increased nutrient flux to the ocean in parallel erosion of shelf sediments during shelf transgression further enhanced nutrient flux 3 at around 9 8 cal ka bp rainforest vegetation inhibited soil erosion depleted nutrient supply and restricted marine productivity to its modern levels the study presents the application of modern analogues and a dinocyst transfer function to the reconstruction of primary palaeoproductivity pp in a region of freshwater influence a database of recent dinocyst assemblages comprising of 208 sites in the equatorial atlantic enabled the reconstruction of sea surface annual pp 1 3 times higher during the lgm and also during the deglaciation between 15 2 and 13 2 cal ka bp the reconstruction is independent of and thus provides corroboration for other biological and geochemical proxies

impacts of rapid sea level rise on mangrove deposit erosion application of taraxerol and rhizophora records we investigated a well dated marine sediment core from the tropical se atlantic covering the last 25 kyr applying taraxerol and rhizophora pollen as organic geochemical and palynological proxies for mangrove respectively taraxerol records are positively correlated with rhizophora pollen records showing an enhanced supply of mangrove materials into deep sea environments during the last deglaciation termination i sedimentation rates peaked during meltwater pulses 1a and 1b which were associated with the maxima of taraxerol and rhizophora pollen this study supports the view that mangrove input was dominantly controlled by erosion of mangrove rich shelf sediments during the transgressions whether reworked materials were penecontemporaneous or from much older deposits formed during previous sea level cycles is discussed copyright 2005 john wiley sons ltd

stratal order in peritidal carbonate sequences abstract speculation on the depositional origins and geological significance of meter scale cycles in peritidal carbonates is becoming an increasingly prominent facet of sequence stratigraphic theory the understanding of which bears directly on their appropriateness as chronostratigraphic entities as well as their usefulness as records of periodic extrabasinal forcing during sediment accumulation in spite of the generally wide acceptance of the stratigraphic importance and interpretational significance of meter scale parasequences little has been done to quantitatively document the stratigraphic nature of regularly recurring lithologic associations or to verify the predominance of such cyclicity in shallow water limestone dolostone sequences in order to determine the statistical extents and stratigraphic scales of stratal order in such sequences we have examined several long sections of peritidal carbonate both with respect to the presence or absence of markovian lithologic transitions and with respect to the upward shallowing character of lithofacies associations in contrast to common wisdom these measures of stratal order suggest that lithologic manifestation of meter scale cyclicity is relatively uncommon all of the several sequences deemed cyclic via qualitative inspection in fact contain relatively few intervals of demonstrable lithologic order and even fewer exhibit any tendency for contained units to shallow upsection in reality most parts of most shallow water carbonate sequences exhibit little more str tal order than would be apparent in random sequences of peritidal lithologies on the basis of these considerations we suggest that discrimination of meter scale cyclicity in epicratonic carbonates is perhaps more perceptional artifact than stratigraphic reality imminent and future efforts intended to fruitfully evaluate the importance of intrabasinal versus extrabasinal processes of sedimentation in shallow low latitude settings should perhaps eschew more generic perceptions of periodic paleoclimatic forcing in favor of a less regimented view toward the importance of stochastic processes of carbonate accumulation

high resolution pollen record from core kw31 gulf of guinea documents the history of the lowland forests of west equatorial africa since 40 000 yr ago abstract pollen data from core kw31 recovered off the mouth of the niger river 3 31 1n 05 34 1e 1181 m water depth provide an exceptional record of vegetation changes in the west african lowlands between 40 000 and 3500 cal yr b p the highly diverse microflora testify for the permanency of rain and secondary forests in the niger river catchment at least as gallery formations along rivers during the last glacial period when dry conditions occurred in relation to enhanced trade wind circulation the direct consequence of the post glacial warming and the correlative increase in monsoon fluxes over west africa was the increase in forest diversity and the expansion of rain and secondary forests on the nearby continent comparison between kw31 pollen record and continental pollen data from 5 s to 25 n allows the evaluation of migration rates of tropical forest populations throughout north west africa at the beginning of the holocene and the vegetation response to the shift toward aridity recorded widely at the end of the african humid period around 4000 cal yr b p

timing of the younger dryas event in east africa from lake level changes the last deglaciation was interrupted by an abrupt cooling event the younger dryas at 11 000 ndash 10 000 yr bp uncalibrated radiocarbon timescale 1 originally recognized in climate records from northwest europe the younger dryas has now been identified in marine and ice core records worldwide2 6 in the tropics a broadly contemporaneous change in climate is recorded by decreases in water levels and increased salinity of lakes7 9 14 indicating a period of arid climate caused by a reduction in ocean to land moisture flux the exact timing of these changes in relation to the younger dryas event in high latitude records has remained unclear however here we present climate records based on analyses of diatom assemblages geochemistry and magnetic mineralogy of radiocarbon dated sequences of laminated lake sediments from lake magadi in the east african rift these records provide a detailed record of climate change in lowland equatorial africa throughout the last deglaciation 12 800 ndash 10 000 14c yr bp we find that lake level and humidity maxima coincide with the most rapid phases of ice melting in the northern hemisphere and that the climate changes including the younger dryas event were synchronous at low and high latitudes thus the effects of abrupt climate change appear to be felt at both high and low latitudes without a significant time lag

environmental control of pollen grain distribution patterns in the gulf of guinea and offshore nw africa the areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes whereas wind transport is much more important than river transport pollen distribution patterns ofpinus artemisia chenopodiaceae amaranthaceae and asteraceae tubuliflorae trace atmospheric transport by the northeast trades pollen transport by the african easterly jet is reflected in the pollen distribution patterns of chenopodiaceae amaranthaceae asteraceae tubuliflorae andmitracarpus grass pollen distribution registers the latitudinal extension of sahel savannas and dry open forests marine pollen distribution patterns of combretaceae melastomataceae alchornea andelaeis reflect the extension of wooded grasslands and transitional forests pollen from the guinean congolian zambezian forest and from the sudanian guinean vegetation zones mark the northernmost extension of the tropical rain forest rhizophora pollen in marine sediments traces the distribution of mangrove swamps only near the continent pollen ofrhizophora mitracarpus chenopodiaceae amaranthaceae and pollen from the sudanian and guinean vegetation zones are transported by the upwelling under current and the equatorial under current where those currents act as bottom currents the distribution of pollen in marine sediments reflecting the position of major climatic zones desert dry tropics humid tropics can be used in tracing climatic changes in the past

west african monsoon variability during the last deglaciation and the holocene evidence from fresh water algae pollen and isotope data from core kw31 gulf of guinea abstract the study of aquatic and mangrove pollen grains and algae from freshwater environments from core kw31 recovered off the mouth of the niger river 3 31 1 n 05 34 1 e 1181 m water depth documents large scale changes in river discharge linked to variations of atlantic monsoon rainfall during the last glacial interglacial transition and the holocene two main taxa dominate the algal record pediastrum which records the strongest river input from 14 500 to 7100 cal b p and botryococcus which indicates surficial runoff in more arid periods particularly at the onset of the deglaciation and during the younger dryas several dry events punctuated the first and more intense phase of the so called african humid period 14 500 cal b p 9800 cal b p during the younger dryas 13 400 12 100 cal b p then around 11 400 11 200 cal b p indicating major climate instability freshwater discharges decreased after 7100 cal b p and definitely dropped to modern values after 3500 cal b p in agreement with land data the microfossil record of core kw31 shows that the increase in freshwater input to the ocean and correlative rainfall over western tropical africa were gradual in response to insolation forcing at the transition from glacial to interglacial situations

distributions and origins of lipid biomarkers in surface sediments from the southern yellow sea abstract this paper reports on the spatial distribution patterns and investigates the controlling mechanisms of phytoplankton biomarkers brassicasterol for diatoms alkenones for haptophytes dinosterol for dinoflagellates and terrestrial biomarkers odd c number long chain c 27 c 29 c 31 n alkanes in surface sediments from the southern yellow sea sys the contents of the phytoplankton biomarkers in the sys surface sediments reveals a clear spatial pattern with low values near the coasts and increased values seaward caused by higher phytoplankton primary productivity and low sedimentation rates in the basin the contents of terrestrial biomarkers show high values in the northern part of the study areas off the shandong peninsula and jiangsu coast caused by inputs of materials from the modern huanghe river and the old huanghe delta respectively the results also indicate that biomarker ratios offer the best approach for reconstructing marginal sea c cycles as these proxies can be used to estimate the contributions of both terrestrial and marine organic matter and to reconstruct paleoproductivity and paleoecological changes in the sys

late holocene sea level rise in tampa bay integrated reconstruction using biomarkers pollen organic walled dinoflagellate cysts and diatoms a suite of organic geochemical micropaleontological and palynological proxies was applied to sediments from southwest florida to study the holocene environmental changes associated with sea level rise sediments were recovered from hillsborough bay part of tampa bay and studied using biomarkers pollen organic walled dinoflagellate cysts and diatoms analyses show that the site flooded around 7 5 ka as a consequence of holocene transgression progressively turning a fresh brackish marl marsh into a shallow restricted marine environment immediately after the marine transgression started limited water circulation and high amounts of runoff caused stratification of the water column a shift in dinocysts and diatom assemblages to more marine species increasing concentrations of marine biomarkers and a shift in the diol index indicate increasing salinity between 7 5 ka and the present which is likely a consequence of progressing sea level rise reconstructed sea surface temperatures for the past 4 kyrs are between 25 and 26 c and indicate stable temperatures during the late holocene a sharp increase in sedimentation rate in the top 50 cm of the core is attributed to human impact the results are in agreement with parallel studies from the area but this study further refines the environmental reconstructions having the advantage of simultaneously investigating changes in the terrestrial and marine environment 2009 elsevier ltd

integrated marine and terrestrial evidence for abrupt congo river palaeodischarge fluctuations during the last deglaciation we present a high resolution reconstruction of tropical palaeoenvironmental changes for the last deglacial transition 18 to 9 cal kyr bp based on integrated oceanic and terrestrial proxies from a congo fan core pollen grass cuticle pediastrum and dinoflagellate cyst fluxes sedimentation rates and planktonic foraminiferal 18o ratios u37k sea surface temperature and alkane alkenone ratio data highlight a series of abrupt changes in congo river palaeodischarge a major discharge pulse is registered at around 13 0 cal kyr bp which we attribute to latitudinal migration of the intertropical convergence zone itcz during deglaciation the data indicate abrupt and short lived changes in the equatorial precipitation regime within a system of monsoonal dynamics forced by precessional cycles the phases of enhanced congo discharge stimulated river induced upwelling and enhanced productivity in the adjacent ocean copyright 2001 john wiley sons ltd

how relevant is the role of macrophytic vegetation in controlling peritidal carbonate facies clues from the upper jurassic of portugal abstract stratigraphic variability in peritidal carbonates is generally interpreted in terms of sea level changes but little consideration is given to the effects of vegetation and of how long term changes in macrophyte evolution have affected carbonate sedimentation in such settings many present day low energy tropical carbonate shorelines are dominated by macrophyte vegetation although several pre jurassic macrophytes have been interpreted to have lived in brackish water zones records of macrophyte dominated carbonate shorelines in the stratigraphic record are apparently rare or even absent which thus is an enigma we use upper jurassic platform interior carbonates from central portugal to emphasize these issues these successions contain both classical tidal flat bearing cyclothems and ones capped by marsh facies with evidence of macrophytes the former having developed in more restricted settings although these late jurassic shorelines were not affected by true mangroves we propose that tidal flat deposits were not developed because the shorelines at least locally were dominated by macrophytes we speculate that the paucity of classical tidal flat bearing peritidal cyclothems in the cainozoic may have been due at least partially to the spread of major macrophyte dominated mangrove communities during the paleogene

late quaternary changes in ecosystems and carbon cycling on mt kenya east africa a landscape ecological perspective based on multi proxy lake sediment influxes abstract the degree to which different lakes within a landscape respond coherently in unison to external drivers such as climate change and soil development is uncertain presentation of multi proxy geochemical and palaeoecological data from individual lakes in the form of fluxes minimizes distortions resulting from variable sedimentation rates and changes in sediment composition we use the accumulation rates of magnetic minerals total organic c and n terrestrial and aquatic biomarkers graminoid epidermis pollen green algae diatoms and diatom c in four small lakes situated between 2350 and 4595 m a s l on the ne flank of mt kenya east africa to reconstruct changes in c cycling over the last 38 ka the results conflict with earlier models of landscape and lake development showing 1 that glacial interglacial changes in vegetation cannot be interpreted as simple altitudinal shifts in the modern vegetation belts and 2 that limnological changes were not coherent rapid variations in climate water level erosion and nutrient input overwhelmed long term successional trends in lake sedimentation and c accumulation since the last glacial maximum the results also reveal previously unrecognized features of the palaeoenvironmental record such as the rapid degradation of organic matter in diatoms and the occurrence of a productive fire prone montane grassland during the highly seasonal monsoonal climate of the lateglacial and early holocene

the signal and the noise forward modeling of allocyclic and autocyclic processes influencing peritidal carbonate stacking patterns recent carbonate sequence stratigraphic models suggest that the degree of order present in successions of carbonate parasequences is determined by temporal variations in eustatic amplitude and by varying levels of autocyclicity ordered parasequence stacking is suggested to occur during greenhouse periods dominated by low amplitude eustatic oscillations conversely disordered vertical successions are said to occur when amplitudes of eustatic oscillations are high or when autocyclic processes dominate and thus drown the periodic external signal these assertions of causal mechanism are tested here by application of a three dimensional stratigraphic forward model the three dimensional model generates parasequences via a ginsburg type mechanism of sediment transport and shoreline progradation parasequence stacking is controlled by a superimposed longer term eustatic oscillation and parasequences generated are analyzed using runs analysis and durbin watson autocorrelation results from the modeling suggest that autocyclic parasequences generated by shoreline progradation form ordered vertical successions when accommodation changes driven by a low amplitude relative sea level oscillation suggesting that partly autocyclic strata may not be inherently any less ordered than entirely allocyclic strata addition of stochastic processes such as mosaic carbonate production and fluctuations in regional sediment transport direction tend to decrease the level of measurable order present in the autocyclic strata increasing the frequency and amplitude of relative sea level oscillations also tends to decrease the measurable order in stacked autocyclic peritidal parasequence thicknesses these results suggest that controls on parasequence stacking patterns are likely to be more complex and varied than suggested by recent sequence stratigraphic models more outcrop and modeling investigation is required with appropriately circumspect interpretations applied

late quaternary cycles of mangrove development and decline on the north australian continental shelf mangrove communities in the australian tropics presently occur as narrow belts of vegetation in estuaries and on sheltered muddy coasts palynological data from continental shelf and deep sea cores indicate a long term cyclical component of mangrove development and decline at a regional scale which can be linked to specific phases of late quaternary sealevel change extensive mangrove development relative to today occurs during periods of marine transgression whereas very diminished mangrove occurs during marine regressions and during rarer periods of relative sea level stability episodes of flourishing mangrove cannot be linked to phases of humid climate as has been suggested in studies elsewhere rather the cycle of expansion and decline of mangrove communities on a grand scale is explained in terms of contrasting physiographic settings characteristic of continental shelf coasts during transgressive and regressive phases in particular by the existence or lack of well developed tidal estuaries copyright c 1999 john wiley sons ltd

climate induced fluvial dynamics in tropical africa around the last glacial maximum abstract the alluvia of the ntem nyong and sanaga fluvial systems in southern cameroon recorded repeated fluvial activity fluctuations during the late pleistocene including the last glacial maximum lgm the beginning of the african humid period and the northern hemispheric bolling allerod we applied a multi proxy approach on alluvial stratigraphies dated between 22 4 and 13 0 cal ka bp including remote sensing sedimentological and morphogenetic methods phytoliths sponge spicules 14c and 13c data a distinct ne sw gradient of landscape and fluvial dynamics around the lgm can be drawn with evidence for the persistence of extended fluvial rainforest refuges only in the ntem catchment the sanaga and nyong catchment areas were characterized by frequent channel migrations floodplain reorganization and unstable vegetation subject to fire including grasslands woodlands and gallery forests with bamboo thickets in spite of increasing rainfall after 16 4 cal ka bp persisting landscape instability played the major role for fluvial system dynamics floodplain transformations and vegetation development until 13 0 cal ka bp before a general landscape stabilization and rainforest expansion set in at the beginning of the holocene

geological prior information and its applications to geoscientific problems geological information can be used to solve many practical and theoretical problems both within and outside of the discipline of geology these include analysis of ground stability predicting sub surface water or hydrocarbon reserves and assessment of risk due to natural hazards in many cases geological information is provided as an a priori component of the solution that is information that existed before the solution was formed and which is incorporated into the solution such information is termed geological prior information the key to the successful solution of such problems is to use only reliable geological information in turn this requires that a multiple geological experts are consulted and any conflicting views reconciled b all prior information includes measures of confidence or uncertainty without which their reliability and worth is unknown and c as much information as possible is quantitative and qualitative information or assumptions are clearly defined so that uncertainty or risk in the final result can be evaluated this paper discusses each of these components and proposes a probabilistic framework for the use and understanding of prior information we demonstrate the methodology implicit within this framework with an example this shows how prior information about typical sequence stacking patterns allows aspects of 2 d platform architecture to be derived from 1 d geological data alone such as that obtained from an outcrop section or vertical well this example establishes how the extraction of quantitative multi dimensional geological interpretations is possible using lower dimensional data the final probabilistic description of the multi dimensional architecture could then be used as prior information sequentially for a subsequent problem using exactly the same method

sequence stratigraphy and cyclicity in the middle eocene of the fayoum ranges western desert egypt implications for regional sea level changes abstract the middle eocene deposits in the fayoum ranges are composed of complex alternative clastic claystone and sandstone and carbonate limestone and dolostone facies and dominated carbonate limestone facies facies are arranged mainly in regression and shallowing upward emergence cycles and sequences field stratigraphic and microfacies analysis of the study area permits recognition of four major sequences reflecting 3rd order cycles depositional sequences and cycles are bounded by subaerial erosive surfaces or caliche deposits ferruginous crust and by their correlative conformities sequence 1 consists of two shallowing upward cycles dominate carbonate facies each of which starts with nummulitic wackestone capped with nummulitic packstone including globigerinatheka subconglobata subconglobata biozone these cycles were deposited under tropical to subtropical conditions as evidenced by the carbonate nature of the rocks and the abundance of nummulites which need warm conditions for their flourishing sequence 2 consists of four emergence cycles based with claystone and capped with wackestone including morozovella lehneri biozone the duration ma of sequence 2 morozovella lehneri zone is 3 05 ma 44 25 ma for the upper of ta3 3 3 to 41 2 ma for the lower of ta3 3 5 sequence 3 includes three rock units includes trucorotaloides rohri biozone the lower unit involves lowstand systems tract the middle unit contains transgressive systems tract and the upper rock unit includes highstand systems tract the lowstand systems tract consists of emergence cycles of mixed clastic carbonate facies clays at the base and capped with wackestone and packstone facies the transgressive systems tract consists of dominant carbonate facies wackestone at the base and capped with packstone facies sequence 4 involves transgressive systems tract the duration of both sequence 3 and sequence 4 has been estimated as 1 8 ma

a 26 000 year integrated record of marine and terrestrial environmental change off gabon west equatorial africa abstract dinoflagellate cysts pollen and charred cuticle fragments from two sediment cores giant piston calypso core md03 2708 and giant gravity casq core md03 2708cq collected off the ogooue river mouth gabon 01 10 33 s 08 19 01 e 920 m water depth have been analysed to identify the direction and timing of marine terrestrial environmental changes over western equatorial africa during the last 26 000 yr changes in the proxy records indicate that both terrestrial and oceanic domains off gabon were impacted synchronously by significant climate changes during the last glacial interglacial transition and holocene leading into and during the last glacial maximum lgm heterotrophic dinoflagellate cysts and ca x ray fluorescence intensity suggest nutrient enrichment off the river mouth while pollen records indicate expansions of open forest savannah woodland and the afromontane forest in the catchment area from the deglaciation to mid holocene however a marked decrease in brigantedinium spp as well as in poaceae cyperaceae and podocarpus pollen reflects a reduction in nutrient supply to the coastal ocean in parallel with a reduction in grassland herbaceous communities and afromontane forest within the catchment a sharp decline or even disappearance of heterotrophic species during this period is almost contemporaneous with an appearance of operculodinium aguinawense reflecting enhanced river influence in the study area a marked increase of rhizophora mangrove pollen during this transition also indicates eustatic sea level rise after the lgm which forced a major expansion of the mangrove ecosystem across the gradually submerging shelf the combination during the late holocene of a reoccurrence of heterotrophic dinoflagellate cysts with increased poaceae cyperaceae and podocarpus pollen indicates enhanced nutrient supply to the ocean concordant with a shift to cooler drier conditions over the gabon basin this appears to be linked to a deterioration of the monsoon system induced by the low sea surface temperatures in the tropical atlantic ocean in association with decreased summer insolation

the late jurassic tithonian a greenhouse phase in the middle jurassic early cretaceous cool mode evidence from the cyclic adriatic platform croatia well exposed mesozoic sections of the bahama like adriatic platform along the dalmatian coast southern croatia reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding late jurassic tithonian shallow platform interior over 750 m thick ca 5 6 myr duration facies within parasequences include dasyclad oncoid mudstone wackestone floatstone and skeletal peloid wackestone packstone shallow lagoon intraclast peloid packstone and grainstone shoal radial ooid grainstone hypersaline shallow subtidal intertidal shoals and ponds lime mudstone restricted lagoon fenestral carbonates and microbial laminites tidal flat parasequences in the overall transgressive lower tithonian sections are 1 4ae5 m thick and dominated by subtidal facies some of which are capped by very shallow water grainstone packstone or restricted lime mudstone laminated tidal caps become common only towards the interior of the platform parasequences in the regressive upper tithonian are dominated by peritidal facies with distinctive basal oolite units and well developed laminate caps maximum water depths of facies within parasequences estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences were generally 4 m and facies show strongly overlapping depth ranges suggesting facies mosaics parasequences were formed by precessional 20 kyr orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles parasequences are arranged in third order sequences that lack significant bounding disconformities and are evident on accommodation fischer plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position modelling suggests that precessional sea level changes were small several metres as were eccentricity sea level changes or precessional sea level changes modulated by eccentricity supporting a global hot greenhouse climate for the late jurassic tithonian within the overall cool mode of the middle jurassic to early cretaceous

strontium isotope evidence for late pleistocene reestablishment of an integrated nile drainage network evidence of late pleistocene closed basin conditions in equatorial african lakes has far reaching implications for the history of the nile river there has been widespread acceptance that overflow of lakes victoria and albert into the nile occurred some time during the terminal pleistocene but recent suggestions that lake victoria remained a closed basin until ca 7 2 ka imply a much longer period of greatly reduced white nile discharge this hypothesis has major consequences for current ideas about the river9s paleohydrology early human exploitation of riverine resources nile delta sedimentation and late quaternary genesis of sapropels in the eastern mediterranean here we resolve the timing of lake victoria9s overflow by using strontium isotopes as a tracer for water from the principal lakes and rivers of the upper nile our data demonstrate that overflow of lakes victoria and albert into the nile drainage network occurred no later than 11 5 14 c ka

modeling past and future alpine permafrost distribution in the colorado front range rock glaciers a feature associated with at least discontinuous permafrost provide important topoclimatic information active and inactive rock glaciers can be used to model current permafrost distribution relict rock glacier locations provide paleoclimatic information to infer past conditions future warmer climates could cause permafrost zones to shrink and initiate slope instability hazards such as debris flows or rockslides thus modeling change remains imperative this research examines potential past and future permafrost distribution in the colorado front range by calibrating an existing permafrost model using a standard adiabatic rate for mountains 0 5 c per 100 m for a 4 c range of cooler and warmer temperatures according to the model permafrost currently covers about 12 per cent 326 1 km2 of the entire study area 2721 5 km2 in a 4 c cooler climate 73 7 per cent 2004 4 km2 of the study area could be covered by permafrost whereas in a 4 c warmer climate almost no permafrost would be found permafrost would be reduced severely by 93 9 per cent a loss of 306 2 km2 in a 2 0 c warmer climate however permafrost will likely respond slowly to change relict rock glacier distribution indicates that mean annual air temperature maat was once at least some 3 0 to 4 0 c cooler during the pleistocene with permafrost extending some 600 700 m lower than today the model is effective at identifying temperature sensitive areas for future monitoring however other feedback mechanisms such as precipitation are neglected copyright 2005 john wiley sons ltd

glacial to holocene changes in sea surface temperature and coastal vegetation in north central chile high versus low latitude forcing abstract north central chile is located at an important climatic transition zone between humid conditions under the influence of the southern hemisphere westerly winds in the south and the extremely dry climate of the atacama desert in the north offshore equatorward flowing cold waters of the peru chile current converge with relatively warmer waters coming from the low latitudes based on terrestrial and marine proxies from the same archive geob 7139 2 30 12 s 71 59 w we show that during the glacial between 33 and 19 kyr cold sea surface temperatures paralleled enhanced humidity with high terrestrial input and abundant vegetation on the adjacent land suggesting a stronger influence of cold waters from the antarctic circumpolar current and the westerly winds while the deglacial sea surface temperature warming started at 19 kyr the humidity decrease occurred around 17 16 kyr bp the early to mid holocene is characterized by extremely warm and dry conditions we suggest that climate changes were driven by fluctuations in antarctic sea ice extent and the circulation of the hadley cell both ultimately linked to insolation changes our records further imply warm and dry conditions in north central chile during the northern hemisphere heinrich events

a dominant tectonic signal in high frequency peritidal carbonate cycles a regional analysis of liassic platforms from western tethys abstract meter scale peritidal carbonate cycles are a common feature of the geological record but debate continues about what processes lead to their formation three conceptual models or a combination thereof are commonly invoked to explain cycle formation eustasy tectonics or autocyclicity these three models are tested with a large new dataset from different early jurassic plate margins from western tethys study of seven logged sections from spain italy greece tunisia morocco and gibraltar enables an analysis of the possible roles of local versus regional patterns and controls on cyclicity within a sinemurian time slice cycle types are diverse and include shallowing upward cycles parasequences but also deepening upward and diagenetic cycles high frequency sequences and subtidal cycles numbers of cycles per section and cycle stacking patterns within this time slice vary from section to section statistical tests runs tests time series and bundling all indicate random stacking of cycles within sections and an absence of any bundling of thicknesses or of facies trends assessment of cycle types by their occurrence and stacking patterns indicates little support for either eustasy or autocyclicity being the dominant cycle forming mechanism however the variability in numbers of cycles per section thickness variations of the sections cycle type variability and randomness of stacking patterns all favor a pulsed tectonic control for the creation and filling of accommodation space this conclusion is further supported by evidence that has largely arisen during the course of this study of syndepositional extensional tectonics in the sinemurian on these rifted tethyan margins although tectonics appears to be the dominant control superimposed eustasy and or autocyclic processes cannot be discounted

the monsoon s past a sediment core from the gulf of guinea provides insights into changes in the african monsoon over the past 155 000 years

sediments facies tracts and variations in sedimentation rates of holocene platform carbonate sediments and associated deposits northern belize implications for representative sedimentation rates full text is not available on soar publisher s website http jsedres geoscienceworld org cgi content abstract 74 4 498 doi 10 1306 012004740498

identifying ordered strata evidence methods and meaning abstract identifying order or pattern in strata on the basis of qualitative interpretation forms the basis for much current sedimentological and sequence stratigraphic analysis order can be usefully defined as some arrangement of facies or unit thickness that has a discernable trend or pattern that is unlikely to occur by chance because it requires some particular systematic process to form coarsening fining thickening or thinning upward trends and arrangement of strata into cycles are examples of order qualitative interpretations of order often demonstrate little more than an implicit assumption of order this paper defines a robust yet simple to apply quantitative method to identify order in strata and to indicate when order cannot be reliably demonstrated the method is based on two calculated metrics the markov metric m derived from analysis of a vertical facies succession and the runs metric r derived from analysis of observed thicknesses of stratal units most importantly both metrics can be compared with equivalent metrics calculated for disordered strata composed of many randomly shuffled versions of the same lithological units probability values can then be calculated from the comparison between observed and randomly shuffled cases and these p values indicate the degree of evidence present for order in the observed strata several test examples using synthetic strata show that the m and r values can define and identify different degrees and types of stratal order and that the metrics are robust for both stationary and non stationary successions with a range of different lengths and numbers of distinct facies analysis of four outcrop examples two siliciclastic and two carbonate demonstrate that ordered facies successions and thickness trends may be less common than typically assumed none of the four examples analyzed show trends in thickness and only the examples from the book cliffs which represent a bedset scale composite of observations show evidence for facies order the examples demonstrate how a quantitative analysis can lead to better understanding of strata either ordered or disordered and can provide better insight into the validity of current stratigraphic interpretations and models absence of order in many of the analyzed 1d vertical successions may also indicate that we need to focus more on longer term trends and analysis of 2d and 3d stratal geometries

cyclostratigraphic reasoning and orbital time calibration cyclostratigraphy postulates that the stratigraphic record cyclically encodes the periodic orbital forcing of terrestrial insolation thus providing a time calibration regular cycles are sought using spectral analysis of lithological data series but there are inherent ambiguities in this method it may detect more cyclicities than conventional orbital forcing allows but only those with the closest correspondence to estimated orbital frequencies are used for time calibration irregular cycles are subjectively defined in terms of non rhythmic repetitions of facies the calibrations assume that they record the spatially distorted sedimentary effects of orbitally forced periodicity in insolation the null hypothesis that such non rhythmic repetitions are autogenic rather than orbitally forced cannot however be rejected both types of cyclicity conform to an expected universe where orbital forcing is reliably and recognisably encoded in the stratigraphic record neither form of cyclicity rules out the presence of hiatuses thus even if orbital in origin neither can provide dependably refined orbitally scaled time calibration

late quaternary sea level changes of the persian gulf abstract late quaternary reflooding of the persian gulf climaxed with the mid holocene highstand previously variously dated between 6 and 3 4 ka examination of the stratigraphic and paleoenvironmental context of a mid holocene whale beaching allows us to accurately constrain the timing of the transgressive highstand and regressive phases of the mid to late holocene sea level highstand in the persian gulf mid holocene transgression of the gulf surpassed today s sea level by 7100 6890 cal yr bp attaining a highstand of 1 m above current sea level shortly after 5290 4570 cal yr bp before falling back to current levels by 1440 1170 cal yr bp the cetacean beached into an intertidal hardground pond during the transgressive phase 5300 4960 cal yr bp with continued transgression interring the skeleton in shallow subtidal sediments subsequent relative sea level fall produced a forced regression with consequent progradation of the coastal system these new ages refine previously reported timings for the mid to late holocene sea level highstand published for other regions by so doing they allow us to constrain the timing of this correlatable global eustatic event more accurately

holocene changes in marine productivity and terrestrial organic carbon inputs into an icelandic fjord application of molecular and bulk organic proxies this study examines the dynamics of organic carbon contributions from different sources to the sediments of a 39 m core from isafjar ardjup fjord northwest iceland throughout the holocene furth

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

paleoceanographic changes in the ulleung basin east japan sea during the last 20 000 years evidence from variations in element composition of core sediments a millennial scale paleoceanographic record of the ulleung basin in the southern part of the east japan sea es for the last 20 000 years was reconstructed based on variations in the element compositions of core sediment most of the elements showed relatively wide content ranges throughout the core largely because of different sediment types their grain size spectra biological components and geochemical conditions i e redox conditions in particular biogenic components ca sr ba and caco 3 and some minor elements cu mn mo u cd zn and v revealed three distinct intervals of major paleoceanographic changes interval 1 similar to 18 9 3 kyr bp is characterized by a rhythmic alternation of dark and light colored sediment bands distinctive differences in the abundance of organic carbon carbonate and redox elements between the dark and light colored sediment layers are probably attributable to especially those associated with bottom water redox variations combined with the enhanced primary productivity and water stratification in the ulleung basin

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

use of insolation as a proxy for high frequency eustasy in forward modeling of platform carbonate cyclostratigraphy a promising approach abstract eustatic oscillations driven by milankovitchian astronomical forcing have been interpreted as sea level drivers for high frequency carbonate depositional cycles in studies dating from the mid 1960s forward modeling of these oscillations with respect to their recorded effects on cyclical stacking patterns has only been attempted using generalized parameters for milankovitchian forcing the development of increasingly advanced forward modeling software coupled with the availability of formulas quantifying insolation incoming solar radiation as a function of composite orbital variations allows for the testing of milankovitchian insolation against measured stratigraphy in this case a series of milankovitchian insolation curves were calculated and used to generate proxy sea level curves for use in the carb3d forward modeling package in order to synthesize a series of stacked carbonate strata these synthetic successions are compared against that of the latemar platform middletriassic northern italy which has been interpreted to contain a record of orbital forcing within its stratigraphy while the timing and nature of periodic drivers that affected latemar stratigraphy have stirred a vigorous debate results from this study indicate that use of milankovitchian insolation as a proxy for high frequency sea level oscillations was successful in modeling latemar like stratigraphy with both pure milankovitchian and mixed milankovitchian sub milankovitchian temporal frameworks

diatom response to oceanographic and climatic changes in the congo fan area equatorial atlantic ocean during the last 190ka bp changes in siliceous productivity in the eastern equatorial atlantic ocean off the western african margin over the last several glacial cycles have been either related to global to regional oceanographic changes upwelling intensity or climate changes precipitation and river discharge based on diatom assemblages in core kzai 02 located to the south of the mouth of the congo river integrated with a selection of geochemical proxies we show that siliceous productivity in the southeastern angola basin responded to non linear interactions between both oceanographic and climate changes over the last 190 000 years high diatom accumulation rates were recorded in the middle part of mis 6 in cold substage mis 5d and in mis 3 2 during these intervals high diatom productivity was sustained essentially by nutrients including dissolved silica injected by the congo river into the ocean the highest productivity was observed during mis 3 when nutrients were sourced both from the river and regional upwelling low diatom accumulation rates were recorded during early and late mis 6 mis 5e early mis 4 and during the holocene these resulted either from low river discharge and overall low nutrient stocks in the angola basin despite evidence for upwelling or from extremely high river discharge in the case of the latter the terrigenous load drastically increased the turbidity of the surface waters in the southeastern angola basin and lowered phytoplankton productivity despite the presence of sufficient dissolved silica

mechanistic controls on diverse fates of terrestrial organic components in the east china sea terrestrial carbon transferred from the land to sea is a critical component of the global carbon cycle a range of geochemical proxies has been developed to fingerprint the fate of terrestrial organic matter tom in marine sediments however discrepancies among different proxies limit our ability to quantify and interpret the terrestrial signals in marine sediments with consequences for the investigation of both the modern carbon cycle and past environmental change to mechanistically understand these discrepancies we examined the distributions of a range of terrestrial proxies and their aquatic counterparts i e marine proxies in the yangtze river east china sea yr ecs shelf system where tom experiences extensive modification during transport and burial tom proxies in the yr ecs system collectively fit a power law model but with distinct attenuation rates the a values for individual molecular proxy groups among a range of tom proxies the modeled a values decrease in the order soil marker bhps triterpenols lignin hmw n alkanols branched gdgts hmw n alkanes for biomarkers and rsoil bit tomiso for proxies tracing tom rapid loss of tom components through dissociation in the narrow estuary followed by oxidation over the wide open shelf are best described by power curves inherent chemical reactivity i e the number of functional groups responses to hydraulic sorting and in situ production regulate the individual attenuation rates of them chemical reactivity plays the most important role on proxy behavior supported by a strong correlation between a values and standard molal gibbs energies both physical protection and chemical reactivity fundamentally control the overall behavior of tom components with the relative importance being setting dependant the former is relatively important in the estuary whereas the later is the primary control over the open shelf moreover regional variation of different marine counterparts is also significant over the river ecs shelf system seemingly regulated by regional nutrient distributions therefore for tom estimates using molecular ratio approaches the specific behavior of individual terrestrial components and marine counterparts and the physical biological and chemical characteristics of depositional settings all need to be considered

a 220 000 year climatic record for the east equatorial atlantic ocean and equatorial africa evidence from diatoms and opal phytoliths in the zaire congo deep sea fan accumulation rates of microfossil associations are independent of each other and in addition to percentages give indispensable information about the significance of micropaleontological data marine diatoms reveal that coastal upwelling in the zaire fan region was strong during glacial stages and weaker during interglacial stages oceanic upwelling was intense in stages 6 and 2 and at the stage 5d 5c transition but not in stage 4 the benguela current did not penetrate into the gulf of guinea during the last 220 000 years the phfd index based on the contribution of freshwater diatoms and phytoliths is a measure of aridity in equatorial africa the production in the low salinity river plume was high in the most humid periods on land and low when the continent was arid on the long term nutrient supply of the zaire river to the ocean was probably larger in humid than in arid periods periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals except in the very humid interval with strong seasonal contrasts 35 000 20 000 years b p

microbial laminite versus rooted and burrowed caps on peritidal cycles salinity control on parasequence development early cretaceous isolated carbonate platform croatia some parasequences in the interior of the early cretaceous isolated carbonate platform croatia which formed under a greenhouse climate lack the typical regressive tidal flat laminites instead these bioturbated emergent parasequences have burrowed and rooted upper parts capped with thin greenish paleo sols and are reminiscent of triassic lofer cycles we propose that the bioturbated cycle tops reflect coastal salinities that are normal marine brackish or metahaline whereas the transgressive rare and abundant regressive tidal flat laminites formed under hypersaline coastal waters thus these features may be used to track gross salinity changes of coastal waters on the platform through time in addi tion we suggest ways to evaluate whether the salinity changes relate to hypersaline embay ments on the platform or changes in the cli mate at the parasequence scale we propose that the bioturbated emer gent parasequences could have formed under semiarid conditions seaward of subtle shallow embayments on the platform con temporaneously in the bayheads micro bial laminites developed these would require time equivalent updip and downdip laminate capped and bioturbated emer gence capped parasequences however the para sequences could also have been con trolled by climate changes the laminite capped parasequences could have resulted from salinity increase with shallowing of the platform interior under semiarid condi tions stable climate in contrast the bio turbated emergence capped parasequences could have formed during times of more humid climate punctuating the overall semi arid climate the humid phase would have favored brackish to normal marine salinities in the coastal zone along with macrophytes and intense animal and plant bioturbation which would suppress development of lami nite caps thus these parasequences provide a means of tracking gross salinity of coastal waters and if climate induced then they have implications for fluctuating climates in greenhouse worlds

paleoclimatic variations in west africa from a record of late pleistocene and holocene lake level stands of lake bosumtwi ghana abstract a detailed investigation of geomorphological evidence of paleoshorelines and exposed stratigraphic sections of lake deposits combined with a chronology based on radiocarbon dated charcoal and in situ 14c dating of wave polished bedrock provide important new constraints on lake level changes of lake bosumtwi ghana thick sequences of laminated silts alternating with transgressive sands and deltaic gravels attest to a long history of climatically controlled lake level variations the post glacial rise in lake level began sometime after 16 3 ka reached stable levels first at 14 5 0 6 ka and then rose again after ca 14 3 ka a significant lake level regression spanned the interval from 12 6 0 3 to 11 6 0 5 ka synchronous with the younger dryas deep lake conditions were reestablished after ca 11 ka at which time the lake overtopped the crater overflow continued until 8 8 0 5 ka when another significant but short lived regression occurred deep but probably not overflowing conditions were again reestablished by 7 2 0 3 ka and continued until around 3 2 0 1 ka when lake level dropped precipitously multicentury late holocene highstands occurred at 2 2 0 1 and 1 7 0 2 ka although these were significantly lower than those registered in the late glacial and early holocene the timing of late glacial events is similar to those recorded elsewhere in africa and the higher latitudes and likely reflects the dominant control of high latitude northern hemisphere conditions on the african tropics during the times of large northern hemisphere ice sheets mid to late holocene variations appear to be less coupled with changes across africa and elsewhere suggesting that regional forcing may be more important during warmer periods

disentangling marine soil and plant organic carbon contributions to continental margin sediments a multi proxy approach in a 20 000 year sediment record from the congo deep sea fan abstract a 20 kyr long sediment sequence from the congo deep sea fan core geob 6518 1 one of the world s largest deep sea river fans has been analysed for bulk and molecular proxies in order to reconstruct the marine soil and plant organic carbon oc contributions to these sediments since the last glacial maximum the bulk proxies applied c n ratio and 13 c org ranged from 10 to 12 5 and from 24 5 to 21 vpdb respectively as molecular proxies concentrations of marine derived alkenones and terrestrial derived odd numbered n alkanes were used which varied between 0 2 and 4 g g dry weight sediment in addition the branched vs isoprenoid tetraether bit index a proxy for soil organic matter input was used which varied from 0 3 to 0 5 in this core application of binary mixing models based on the different individual proxies showed estimates for terrestrial oc input varying by up to 50 due to the heterogeneous nature of the oc application of a three end member mixing model using the 13 c org content the c n ratio and the bit index enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary oc pool the results show that marine oc accounts for 20 to 40 of the total oc present in the deep sea fan sediments over the last 20 kyr and that soil oc accounts for about half 45 on average of the oc present this suggests that soil oc represents the majority of the terrestrial oc delivered to the fan sediments accumulation rates of the plant and soil oc fractions over the last 20 kyr varied by a factor of up to 5 and are strongly related to sediment accumulation rates they showed an increase starting at ca 17 kyr bp a decline during the younger dryas peak values during the early holocene and lower values in the late holocene this pattern matches with reconstructions of past central african humidity and congo river discharge from the same core and revealed that central african precipitation patterns exert a dominant control on terrestrial oc deposition in the congo deep sea fan marine oc accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions these variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind driven upwelling

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

extending the aridity record of the southwest kalahari current problems and future perspectives an extensive luminescence based chronological framework has allowed the reconstruction of expansions and contractions of the kalahari desert over the last 50 ka however this chronology is largely based on near surface pits and sediment exposures these are the points on the landscape most prone to reactivation and resetting of the luminescence dating clock this is proving to be a limiting feature for extending palaeoenvironmental reconstructions further back in time one way to obviate this is to sample desert marginal areas that only become active during significant arid phases an alternative is to find and sample deep stratigraphic exposures the mamatwan manganese mine at hotazel in the sw kalahari meets both these criteria luminescence dating of this site shows the upper sedimentary unit to span at least the last 60 ka with tentative age estimates from underlying cemented aeolian units dating back to the last interglacial and beyond results from mamatwan are comparable to new and previously published data from linear dunes in the sw kalahari but extend back much further analysis of the entire data set of luminescence ages for the sw kalahari brings out important inferences that suggest that different aeolian forms 1 have been active over different time scales in the past 2 have different sensitivities to environmental changes and 3 have different time scales over which they record and preserve the palaeoenvironmental record this implies that future optically stimulated luminescence work and palaeoenvironmental reconstructions must consider both site location and its relationship to desert margins and sediment depositional styles so that the resolution and duration of the aridity record can be optimally understood

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

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

understanding the impacts of late quaternary climate change in tropical and sub tropical regions abstract the understanding of climate impacts on tropical rivers and catchments has developed in part from models developed for temperate landscapes and a common rhythm is often apparent when millennial scale studies are compared at this level issues arising from the complex response of rivers to internal and external factors appear less important than the climate driven signal understanding the fluvial record however depends on the availability and interpretation of other sources of proxy data such as pollen spectra lake levels and ocean cores in many rainforest areas few pollen records exist and many of these reveal a hiatus at the time of the last glacial maximum examples of fluvial archives from africa indonesia and tropical queensland australia are discussed in relation to independent records of vegetation change and inferences are made concerning critical episodes in fluvial history focusing on the transitions from oxygen isotope stage ois 3 towards glacial conditions in ois2 and the pleistocene holocene transition to modern climates links between climate vegetation change and fluvial activity are presented as descriptive models

taraxerol and rhizophora pollen as proxies for tracking past mangrove ecosystems angola basin and cape basin southeast atlantic surface sediments and sediment cores show that maxima in the abundance of taraxerol relative to other land derived lipids covary with maxima in the relative abundance of pollen from the mangrove tree genus rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests together with the observation that rhizophora mangle and rhizophora racemosa leaves are extraordinarily rich in taraxerol this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the se atlantic the proxy environment relations for taraxerol and rhizophora pollen down core show that increased taraxerol and rhizophora pollen abundances occur during transgressions and periods with a humid climate these environmental changes modify the coastal erosion and sedimentation patterns enhancing the extent of the mangrove ecosystem and or the transport of mangrove organic matter offshore analyses of mid pleistocene sediments show that interruption of the pattern of taraxerol maxima during precession minima occurs almost only during periods of low obliquity this demonstrates the complex environmental response of the interaction between precession related humidity cycles and obliquity related sea level changes on mangrove input

advances in permafrost and periglacial research in antarctica a review recently the research on permafrost periglacial morphology and processes had a great stimulus especially from the international polar year permafrost areas of continental antarctica with its extreme dry and cold environment can be considered an analog of extraterrestrial landscapes like those on mars but also preserve much paleoclimatic information of this crucial part of the global climatic system on the other hand maritime antarctica is one of the areas of the world currently affected by the greatest air warming and provides a unique opportunity to understand the impacts of climate change on permafrost and its related ecosystems despite the significant recent progress some gaps on permafrost distribution still remain as the network for permafrost and active layer monitoring needs further enlargement and better standardization ground ice its age and stability over time need further investigation as well as the role of living organisms on the weathering processes within the cryotic rocks the landscape evolution of continental antartica could be improved providing potential implications also for a better understanding and modeling of life and landscape evolution of other planets

characterization lateral variability and lateral extent of discontinuity surfaces on a carbonate platform barremian to lower aptian oman hiati of various duration in carbonates are commonly expressed as discontinuity surfaces the understanding of processes that form and affect these surfaces leads to an improved sequence stratigraphic interpretation a reliable outcrop correlation and better models for reservoir compartmentalization various intraformational discontinuities were analysed and interpreted in a well exposed study window 2 5 km in lateral length and 60 m in height comprising the barremian aptian qishn formation haushi huqf area central oman this study focuses on the lateral extent and morphology of the surfaces the petrography of the underlying rocks and the facies changes and geochemical trends across these discontinuities furthermore the lateral variability of discontinuity surfaces was documented three genetic types of discontinuities are differentiated i erosion surfaces ii omission surfaces hard and firmgrounds and iii composite surfaces with evidence for both subaerial exposure and submarine boring field observations combined with petrographic and geochemical data suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea level fluctuations of regional scale in contrast a large number of laterally limited surfaces 1 km are related to locally active processes such as waves and current erosion the lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity the sea floor topography waves and currents and differential erosion the most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment this variability is caused by spatial variability in the tidal flat environment meteoric alteration and differential erosion this study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces this variability must be kept in mind when interpretations and correlations are based on one dimensional sections or cores 2005 international association of sedimentologists

climatic instability in west equatorial africa during the mid and late holocene abstract millennial scale climatic variations have punctuated the holocene characterised by abrupt changes from warm to cool or wetter to drier conditions amongst these climatic events there is increased evidence for an abrupt multicentennial shift of climatic conditions around 3 8 3 7 kyr bp 4 1 cal kyr bp in mid to low latitude regions which had a profound impact on landscape and population migration in the mediterranean region subtropical tropical and equatorial africa a number of continental proxies lake levels pollen sequences stable isotopes record this abrupt change towards drier conditions however regionalism in climatic conditions is reflected in the vegetation records possibly in relation to orographic conditions and the influence of sea surface conditions hitherto there have been very few marine sequences that record this particular climatic shift at high resolution we present here new data from the congo deep sea fan containing integrated marine and terrestrial proxies around 5 4 cal kyr bp shifts in surface conditions off the congo river mouth are observed with possible establishment of seasonal coastal upwelling and lower sea surface temperatures in parallel pollen data indicate fluctuations of herbaceous afromontane taxa and charred grass cuticles suggesting more open vegetation in the lowland regions and an increase in cloud forest and or afromontane vegetation at higher altitudes within the congolese region

freshwater diatom influx in intertropical atlantic relationships with continental records from africa diatom assemblages from modern west african rivers and from lacustrine sediments subjected to deflation represent the present day sources of continental diatoms to the sea diatom productivity in large rivers is high especially for the genus melosira windblown diatoms derive mainly from the central and northern sahara summer dust plume where saline chloride water assemblages are widespread or from the southern edge of the sahara winter dust plume where melosira rich assemblages of dilute water predominate freshwater diatom peaks in atlantic cores may reflect 1 phases of increased river influx correlated with humid episodes on the continent or 2 phases of enhanced deflation and wind transport during arid episodes the single hypothesis for fine sediments from mid ocean sites genus melosira dominates the freshwater assemblages of many modern and fossil marine samples whatever the transport agent is therefore it is not an accurate paleoclimate indicator by itself but associated taxa may provide information on the environmental and geographical origin of the displaced diatoms this tentative approach shows that freshwater diatoms in atlantic cores may be a good tool for reconstructing paleoclimates and for establishing continent ocean correlations if species analyses are made and if the continental distribution of the taxa encountered is considered

deciphering the history of hydrologic and climatic changes on carbonate lowstand surfaces calcrete and organic matter evaporite facies association on a palimpsest middle jurassic landscape from portugal abstract the unusual occurrence of calcretes and prominent organic matter in the middle jurassic lower bathonian serra de aire formation of the lusitanian basin of western portugal western iberian margin revealed a complex palimpsest exposure record here interpreted as reflecting hydrological changes caused by phases of emergence and immersion it serves as a potential model for understanding stratigraphic development at lowstand surfaces in carbonate successions the exposure dominated facies association grades upwards into peritidal and lagoonal limestones and the interval is assigned to the regressive peak of a transgressive regressive facies cycle 2nd order of the thick middle jurassic carbonate ramp succession the galinha quarry fatima region ne of lisbon a type section for this lowstand assemblage exhibits varied calcretes with black clasts interbedded with and grading into organic rich marly clayey seams and lenses locally with carbonate nodules carbonates with evaporite traces microbial laminites black clast and fenestral limestones some lithofacies are dolomitized the palynofacies contains phytoclasts associated with less refractory more prone to degradation components which suggests natural combustion pyrolysis wild fires the lowstand surface represents a low relief landscape with small depressions ponds bordering a more distal marginal littoral setting the partly subaerial and partly subaqueous settings were subjected to lengthy exposure and to fluctuating very shallow water bodies and water table coeval climatic regime was a seasonally dry wet one with dry semi arid phases dominating over the sub humid as shown by the combined record of intense calcrete development rhizogenic structures microbial mats brecciation desiccation evaporites and wild fire evidence however sea level rise caused changes to shallow sea water influenced restricted lagoonal peritidal settings comparisons and differences with modern and ancient coast marginal carbonates are made to provide a guide to the variability in such lowstand deposystems in the stratigraphic record

susceptibility modelling of hummocky terrain distribution using the information value method deception island antarctic peninsula abstract the hummocky terrains of deception island antarctic peninsula are continuous surfaces with decimetre to metre wide and decimetre depth bumps located mainly in the lower section of sloping lapilli and scoria terrains a detailed study site between cerro caliente and crater lake was selected for the detailed mapping of hummocky terrains and for modelling their spatial distribution according to controlling geographical factors a model of the susceptibility of occurrence of the hummocky terrains was created using the information value method together with five independent variables elevation slope global summer radiation total curvature and lithology success and prediction rate curves were used for model validation and the area under the curve index was used to quantify the levels of performance and prediction the results were of high quality with a success rate of 88 and a prediction rate of 78 the classes of the independent variables with more relevance in the occurrence of hummocky terrains were elevation between 20 30 m and 60 70 m concave or rectilinear flat areas slopes between 8 and 12o tuff cones and maar deposits and global summer radiation between 1 8 and 2 0 tjm 2 the good quality of the modelling results supports its use for assessing the future potential for formation of new hummocky terrain areas or even to estimate the spatial distribution of buried ice within the permafrost environment of deception island

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr