states of paleostress north and south of the periadriatic fault comparison of the drau range and the friuli southalpine wedge this study focuses on the analysis of structures and kinematics of a n s profile along the axis of maximum shortening of the european eastern alps the area includes the southern austroalpine unit in the north and the southalpine unit which is a part of the adriatic indenter the stratigraphically different units are separated by the periadriatic fault the major strike slip fault within the alps in order to assess the kinematics of these units mainly fault slip data from north and south of the periadriatic fault were analyzed we distinguish a succession of five main kinematic groups in both units 1 n s compression 2 nw se compression 3 ne sw compression 3 changes gradually from subvertical to subhorizontal 4 n s compression and 5 nw se compression our study reveals that the deformation sequence on either sides of the paf is similar the mean orientations of the principal stress axes however show small but consistent differences the subhorizontal axes north of the periadriatic fault plunge northward in the south southward a counterclockwise ccw rotation of the southern part in respect to the north is evident and in line with the well known counterclockwise rotation of the adriatic indenter as well as dextral displacement of the n fanning stress field along the periadriatic fault opposing plunge directions are interpreted as a primary feature of the internal stress field within an orogenic wedge further increased during ongoing compression

fe mn cu and zn in interstitial water of near shore sediments abstract the concentrations of fe mn cu and zn were studied in the pore water of reduced muddy sediments off the gironde estuary in the area representing the deposit of the river load fe and mn concentrations were also determined in the intertidal zone in the marennes oleron bay all samples were formed of an oxidized surface layer overlying a reduced sediment the mn data from the pore water support the idea of the recycling of mn by dissolution mobilization migration and reprecipitation fe did not present a depth gradient but surface sediment showed fe depletion relative to the underlying sediment which may represent the boundary between the oxidized surface layer and the reduced underlying sediment where iron can be easily mobilized in the pore water mn and fe concentrations were higher in the pore water off the gironde estuary sediments than in those of the intertidal zone the reasons may be the degree of reducing conditions caused by bacterial activity the tide cycle with alternative oxidations and reduction of the surface sediments of the tidal flats and the association of metal fe or mn in an easily soluble phase under reducing conditions e g the effect of different complexing agents in the two regions or the equilibrium of metals with different mineral phases the cu distribution shows no trend with depth cu concentrations in the different intervals may depend upon the diagenetic reaction and quality of organic matter sulphide concentration and complex formation the zinc concentrations decreased with depth which supports the idea of sulphide precipitation and or decrease of the potential mobilized zinc with depth

coupled manganese and carbon isotopic events in marine carbonates at the cenomanian turonian boundary abstract the boundary interval between the cenomanian and turonian stages of the upper cretaceous shows a positive excursion in the carbon isotopic composition of organic matter and carbonate in many epicontinental and oceanic sections of the atlantic tethyan realm some of the studied epicontinental sections contain an excursion in the manganese content of carbonates coincident with the shift in carbon isotopic values in a key reference section at pueblo colorado the stratigraphic position and magnitude of the manganese excursion are described with respect to the carbon isotopic excursion coincident excursions in manganese contents and carbon isotopic values are verified for a section in normandy france the depositional setting for these two sections is persistently to intermittently we l oxygenated with the accumulation of interbedded chalky and marly sediments no shift in manganese values was detected through the isotopic excursion in a section from northern nebraska where fossils are preserved only as bedding plane impressions due to extensive early diagenetic dissolution of carbonate the carbon isotopic and manganese excursions begin at the same stratigraphic position but manganese contents return to background values within the lower half of the carbon isotopic excursion the relative timing and duration of these signals suggest the existence of a large manganese reservoir that was rapidly mobilized transfer of manganese from deep sea oxides mn4 to epicontinental carbonates mn2 is inferred to have occurred during expansion of oceanic oxygen minimum zones with associated changes in redox gradients and boundaries simultaneous excursions in carbon isotopic values and manganese contents can occur at sites of carbonate accumulation when the carbon and manganese cycles are linked through the reducing potential of widespread oxygen deplete water masses

environmental and climatic control on seasonal stable isotope variation of freshwater molluscan bivalves in the turkana basin kenya abstract we present growth incremental stable isotope records 18o and 13c of modern and 2 ma fossil bivalve shells from the semi arid turkana basin n kenya s ethiopia these data suggest that seasonal cyclicity in 18o and 13c recorded by modern and fossil shells is driven by wet dry seasonal changes in host water chemistry forced by monsoonal rainfall over the ethiopian highlands fully lacustrine shells show lower amplitude or even absent seasonal cyclicity in comparison with deltaic or riverine shells because of the buffering effect of the large water volume in the lake setting riverine shells arguably have the clearest relation to seasonally variable climate parameters riverine molluscs thus provide a potentially valuable proxy for varying rainfall 18o values in the turkana basin catchment cross plots of molluscan 18o and 13c data reveal dominant environmental control on molluscan isotope values with remarkably large isotopic differences between lacustrine deltaic and riverine environments we interpret this isotope pattern to directly result from the different mixing proportions of omo river source water with evaporated lake water in these environments the interpretation of fossil molluscan 18o and 13c data in a palaeoclimatological context is not straightforward since the potential influence of temporal changes in lake water temperature surface evaporation or river discharge on the 18o budget of the lake is smaller than the isotopic shifts caused by shifting facies patterns in the sedimentary record even though it is clear from the rich molluscan faunas that the 2 ma palaeo lake lorenyang must have been significantly less alkaline than modern lake turkana and likely provided good drinking water and abundant availability of food for the different species of hominins inhabiting the region at that time stable isotope values of molluscan bivalves are not suitable to record the difference in alkalinity between these two settings

syndepositional tectonics and extension compression relationships at the front of the taiwan collision belt a case study in the pleistocene reefal limestones near kaohsiung sw taiwan in the kaohsiung area sw taiwan large lenses of pleistocene reef limestones interbedded in clastic layers of the gutingkeng formation cover the crest of the takangshan and panpingshan anticlines tectonic analyses carried out on these limestones provide evidence that these anticlines developed during deposition of the reefs this is supported by synsedimentary normal faulting related to tensional stresses at the hinge of the anticlines this synsedimentary extension is subperpendicular to the local trends of fold axes and parallel to the compression responsible for fold development and which is mainly marked by strike slip faults these observations lead us to propose a model of extension compression relationships and reef development during quaternary folding in the foreland of the taiwan collision belt

inversion of the paleogene chinese continental margin and thick skinned deformation in the western foreland of taiwan abstract new structural data available seismicity data together with mechanical constraints on the eurasian continental lithosphere and reconstruction of paleostress trajectories are combined in order to re assess and discuss the dominant deformation mode thin skinned vs thick skinned in the western fold and thrust belt of the active taiwan collision zone serial balanced cross sections and computed paleostress tensors suggest that structural styles and stress trajectories at the front of the taiwan mountain belt may vary rapidly along strike depending on the presence of pre orogenic paleogene troughs in the chinese continental margin taihsi and tainan basins that are favourably oriented to be reactivated and inverted in localities of the western foreland where basin inversion and thick skinned basement involved shortening predominate the crustal seismic activity is important and characterized by strike slip faulting in these domains of the fold thrust belt the stress deviations with respect to the regional transport direction are also important by contrast in domains of significant syn orogenic subsidence a thin skinned style of deformation may be prominent due to the lack of available pre existing features the seismic activity is limited to few major faulted boundaries such as the active chelungpu sani thrust and the stress deviations are limited the timing of deformation at the belt front seems to be independent of the structural styles so that frontal folds are active since probably 0 5 ma however in inner parts of the western foothills of taiwan where superimposed thick skinned and thin skinned deformation are required out of sequence thrusting occurs to maintain the topographic profile finally we suggest that kinematics and structural styles of the western fold thrust belt are controlled by the mechanics of the eurasian continental margin in agreement with a recent study at the scale of the orogen the limited shortening amounts across the wf and in the central range as well as the absence of continental hp rocks better support a thick skinned collision model for taiwan

influence of paleoenvironmental factors on preservation of organic matter in middle cretaceous greenhorn formation pueblo colorado sedimentological and geochemical studies of the upper cretaceous hartland shale and overlying bridge creek limestone members of the greenhorn formation reveal close associations between abundance of current induced sedimentary structures extent of bioturbation and type of preserved organic matter abundant hydrogen rich organic matter 4 5 wt and low sulfur to organic carbon ratios are characteristic of the laminated facies which lack current induced sedimentary structures sparse hydrogen poor organic matter 0 1 0 5 wt and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies which contain numerous sedimentary structures indicative of currents the concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively by currents rather than by the rate of oxygen consumption by decomposition thus paleoclimatic and paleo oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units it is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen depleted bottom water and high preservation of organic matter thus accounting for the intermittent widespread deposition of organic rich strata during maximum transgression and depth of the greenhorn sea the lateral association of voluminous deltaic deposits with dee water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the hartland shale and bridge creek limestone members

paleoclimate of the past 4000 years at lake turkana kenya based on the isotopic composition of authigenic calcite abstract authigenic calcite was analyzed for 13 c and 18 o in a 12 m long core from lake turkana that spans the last 4200 yr the 18 o record is interpreted to reflect lake level history and indicates high stands prior to 4000 yr b p from 1800 to 2000 yr b p and within the last century this coincides better with the history of lake level change reported for other lakes in africa than did the previous lake level curve for lake turkana based on 14 c dates of exposed shoreline deposits the 13 c curve roughly parallels the 18 o curve and may reflect the influence of the omo river plume both of the isotope records are strongly cyclic with periodicites common to both at 80 120 150 and 225 yr other somewhat longer periodicites are nearly equal in the two records and there is close agreement with previously published cycles based on carbonate and lamination thickness analyses in the same turkana core

quaternary transfer faulting in the taiwan foothills evidence from a multisource approach abstract the major structures of the western foothills of taiwan mainly consist of nne ssw trending folds and imbricated west vergent thrust systems the additional occurrence of n140 e striking oblique structures was revealed through a multisource approach involving a digital elevation model dem a study of drainage network anomalies aerial photographs side looking airborne radar slar images and spot p and landsat images these structures are described from north to south based on new field analyses including stratigraphy and tectonics studies they are also compared to seismic data and geodetic reconstruction in order to evaluate their present day activity these n140 e major morphostructures are interpreted as left lateral transfer fault zones either inherited from the eurasian passive margin and or newly formed in the cover in response to the presence of basement highs within the foreland basin peikang and kuanyin highs the sanyi and the chishan transfer fault zones display a high seismic activity the distribution of earthquakes and the related focal mechanisms confirm the left lateral movement along n140 e directions the chiayi chishan and fengshan fault zones act presently as transfer fault zones as indicated by gps data the associated n70 e to n100 e trending faults result from the reactivation of normal faults of the eurasian passive margin as right lateral strike slip faults in the foothills during the plio quaternary collision in taiwan we conclude that multisource and multiscale geomorphic studies combined with tectonic analysis in the field yield a significant contribution to the understanding of the structural and kinematic development of the western foothills at the front of the taiwan collision belt

preservation of laminated shale in ancient clinoforms comparison to modern subaqueous deltas in phanerozoic fine grained marine sedimentary deposits preservation of physical lamination is commonly presumed to record anoxic benthic conditions lamination may also be preserved however in oxygen rich settings where sediment influx is rapid and as a consequence high levels of turbidity and fluid substrates inhibit colonization by benthic organisms differentiation between these two situations is critical for accurate paleoenvironmental interpretations the recognition of clinoforms which are common in ancient fine grained successions is a key step in making this distinction in the tropic shale and correlative tununk member of the mancos shale of southern utah clinoforms are preserved in two superposed depositional sequences the fourth and fifth sequences in the succession the geometry of the clinoforms indicates that foreset deposits accumulated relatively rapidly and bottomset deposits more slowly in sequence 4 patterns of preservation of lamination in clinoforms resemble those in modern subaqueous deltas these ancient clinoforms evidently prograded into oxygenated waters and preservation of lamination was primarily controlled by the rate of sediment accumulation in sequence 5 however the oxygen level apparently controlled the preservation of lamination

application of sequence stratigraphic concepts to the upper cretaceous tununk shale member of the mancos shale formation south central utah parasequence styles in shelfal mudstone strata

organic rich sedimentation at the cenomanian turonian boundary in oceanic and coastal basins in the north atlantic and tethys one of the most striking results of the deep sea drilling project is the proof that organic rich sediments have a widespread geographical distribution during the period from upper cenomanian to middle turonian such sediments were drilled at north atlantic dsdp sites 105 135 137 138 367 398 551 603 they are also present from outcrops or oil wells on the shelf of the african continental margin senegal tarfaya and agadir basins in the tethys former alboran block southern spain algeria tunisia and umbrian apennines italy and in the north sea although these sediments have different lithologies and depositional environments from shelf areas to the deep sea their study mainly based on organic geochemistry with additional data on sedimentology biostratigraphy and palaeo bathymetry suggests that a unique pulse of organogenic accumulation characterizes the cenomanian turonian boundary event ctbe the content and type of organic matter are related to the depositional environment and organic preservation the organogenic accumulation is distributed according to various trends off the african continental margin the organic content increases from onshore areas to the shelf casamance area and moreover increases also in deep sea areas with a gradual transition from terrestrial type iii to marine type ii the best preservation of the organic matter being in the deepest areas i e site 367 off the american continental margin site 603 shows the same toc and type of organic matter as at site 105 the ctbe is also well recorded in the northern part of the atlantic celtic margin north sea by a drastic lithological change black shales within chalks but the type of organic matter is mainly terrestrial in the tethyan area the organic matter is of marine origin and well preserved results are compared with those of pratt 1984 from the western interior basin of the usa different hypotheses to explain this synchronous widespread accumulation of organic matter are discussed 1986 the geological society

climate variations and the appalachians from the late paleozoic to the present results from model simulations abstract a series of climate model simulations are utilized to examine the climate evolution of the appalachians from the carboniferous to the present through consideration of large scale changes in paleogeography and potential variations in carbon dioxide on long time scales the model simulations predict considerable variations in temperature and precipitation through time in addition a number of shorter time scale phenomena may influence the climatic record of the appalachians in particular milankovitch orbital variations can produce rhythmic climate and weathering particular geographic configurations since the carboniferous tend to promote sensitivity to orbital variations although far from comprehensive the model simulations provide independent predictions of climate which can be utilized to investigate the evolution of the appalachians deductively

isotopic composition of waters from ethiopia and kenya insights into moisture sources for eastern africa 1 oxygen and deuterium isotopic values of meteoric waters from ethiopia are unusually high when compared to waters from other high elevation settings in africa and worldwide these high values are well documented however the climatic processes responsible for the isotopic anomalies in ethiopian waters have not been thoroughly investigated we use isotopic data from waters and remote data products to demonstrate how different moisture sources affect the distribution of stable isotopes in waters from eastern africa oxygen and deuterium stable isotopic data from 349 surface and near surface groundwaters indicate isotopic distinctions between waters in ethiopia and kenya and confirm the anomalous nature of ethiopian waters remote data products from the tropical rainfall measuring mission trmm and national centers for environmental prediction ncep reanalysis project show strong westerly and southwesterly components to low level winds during precipitation events in western and central ethiopia this is in contrast to the easterly and southeasterly winds that bring rainfall to kenya and southeastern ethiopia large regions of high equivalent potential temperatures e at low levels over the sudd and the congo basin demonstrate the potential for these areas as sources of moisture and convective instability the combination of wind direction data from ethiopia and e distribution in africa indicates that transpired moisture from the sudd and the congo basin is likely responsible for the high isotopic values of rainfall in ethiopia

trace metal solubility in an anoxic fjord abstract intermittent anoxia in the saanich inlet water column provides an easily accessible marine o2 h2s interface to study the response of metals to both a steep redox gradient and the availability of reactive reduced sulfur species our study indicates a strong anoxic zone sink for copper and cadmium and the characteristically enhanced solubility of manganese and iron thiosulfate and sulfite are below detection limits 1 m and 0 1 m respectively and thus not important in metal complexation elemental sulfur concentrations are high at the oxic anoxic interface and throughout the anoxic zone indicating the potential for metal complexation by polysulfides a thermodynamic approach employing metal sulfide formation and class specific sulfidic ligand complexation to generate equilibrium profiles adequately describes the solubility of iron copper and cadmium the extension of this scheme to other transition and class b metals in other marine environments with redox fronts is suggested

recurrent depletion of benthic oxygen with 4th order transgressive maxima in the cretaceous western interior seaway abstract a study was designed to investigate the relationship between depletion of benthic oxygen and 4th order sea level change within the cretaceous western interior seaway of north america three 4th order sea level change cycles were studied in strata belonging to the tropic shale and the tununk shale member of the mancos shale in utah these sedimentary deposits accumulated within prodeltaic environments in utah strata belonging to all three 4th order cycles exhibit evidence for depletion of benthic oxygen at times of peak 4th order transgression and development of condensed sections the evidence includes decreased intensities of bioturbation increased cr al ni al and zn al ratios and decreased mn fe ratios the data also suggest that depletion of benthic oxygen in the distal section preceeded that in the more proximal one and thus may reflect episodic expansion of an oxygen depleted water mass es from the pelagic to the prodeltaic environment of the seaway evidence for subsequent increases in benthic oxygen level with the onset of 4th order regressions is interpreted to reflect either aggradation of the seafloor above the oxygen poor water due to sediment accumulation or contraction of the oxygen depleted water mass from the prodeltaic part of the seaway or a combination of the two s organic c ratios of strata interpreted to have been deposited under conditions of depleted benthic oxygen are distinctly below 0 4 and thus were not useful for recognition of paleo oxygen levels in the prodeltaic environment this study highlights the importance of depletion of benthic oxygen as a mechanism for enhancing preservation of organic carbon in condensed sections on a hundred thousand year time scale our results underline the potential for source rock formation in similar prodeltaic deposits of other epicontinental seaways during periods of relatively high sea level and global depletion of benthic oxygen

westward advance of the deformation front and evolution of submarine canyons offshore of southwestern taiwan abstract this study analyzes both 2d and 3d seismic images around the palm ridge area offshore of southwestern taiwan to understand how the deformation front shifted westward and how tectonic activities interact with submarine canyon paths in the transition area between the active and passive margins palm ridge is a submarine ridge that developed on the passive china continental margin by down dip erosion of several tributaries of penghu canyon it extends eastward across the deformation front into the submarine taiwan accretionary wedge the presence of proto thrusts that are located west of the frontal thrust implies that the compressional stress field has advanced westward due to the convergence of the philippine sea plate and eurasian plate since the deformation front is defined as the location of the most frontal contractional structure no significant contractional structure should appear west of it we thus suggest moving the location of the previously mapped deformation front farther west to where the westernmost proto thrust lies high resolution seismic and bathymetric data reveal that the directions of the paleo submarine canyons run transverse to the present slope dip while the present submarine canyons head down slope in the study area we propose that this might be the result of the westward migration of the deformation front that changed the paleo bathymetry and thus the canyon path directions the interactions of down slope processes and active tectonics control the canyon paths in our study area

a mass balance approach to basin sedimentation constraints on the recent history of the turkana basin abstract the turkana basin provides some excellent examples of mass balance constraints on recent basin history high sedimentation rates in the basin imply that major river captures occurred in the recent geologic past the chemistry of the lake is that to be expected for a relatively deep closed basin alkaline lake after several thousand years mass balance in the water budget shows that major changes in lake levels over a short time interval can only result from catastrophic events

detailed facies analysis of the upper cretaceous tununk shale member henry mountains region utah implications for mudstone depositional models in epicontinental seas abstract lower middle turonian strata of the tununk shale member of the greater mancos shale were deposited along the western margin of the cretaceous western interior seaway during the greenhorn second order sea level cycle in order to examine depositional controls on facies development in this mudstone rich succession this study delineates temporal and spatial relationships in a process sedimentologic based approach the 3 dimensional expression of mudstone facies associations and their stratal architecture is assessed through a fully integrative physical and biologic characterization as exposed in outcrops in south central utah sedimentologic characteristics from the millimeter to kilometer scale are documented in order to fully address the complex nature of sediment transport mechanisms observed in this shelf muddy environment the resulting facies model developed from this characterization consists of a stack of four lithofacies packages including 1 carbonate bearing silty and sandy mudstone cssm 2 silt bearing calcareous mudstone scm 3 carbonate bearing silty mudstone to muddy siltstone cms and 4 non calcareous silty and sandy mudstone ssm spatial and temporal variations in lithofacies type and sedimentary facies characteristics indicate that the depositional environments of the tununk shale shifted in response to the 2nd order greenhorn transgressive regressive sea level cycle during this eustatic event the tununk shows a characteristic vertical shift from distal middle shelf to outer shelf cssm to scm facies then from outer shelf to inner shelf environment scm to cms and to ssm facies shifting depositional environments as well as changes in dominant paleocurrent direction throughout this succession indicate multiple source areas and transport mechanisms i e longshore currents offshore directed underflows storm reworking this study provides a rare documentation of the greenhorn cycle as exposed across the entire shelf setting high resolution mapping of genetically related packages facilitate the development of process based depositional models that can be utilized for lateral correlations into the equivalent foredeep strata of the cretaceous interior

pathways of organic carbon oxidation in three continental margin sediments we have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of denmark and norway rates of nh4 and sigma co2 liberation sediment incubations were used with o2 penetration depths to conclude that o2 respiration accounted for only between 3 6 17 4 of the total organic carbon oxidation dentrification was limited to a narrow zone just below the depth of o2 penetration and was not a major carbon oxidation pathway the processes of fe reduction mn reduction and sulfate reduction dominated organic carbon mineralization but their relative significance varied depending on the sediment where high concentrations of mn oxide were found 3 4 wt mn only mn reduction occurred with lower mn oxide concentrations more typical of coastal sediments fe reduction and sulfate reduction were most important and of a similar magnitude overall most of the measured o2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon we suspect that the importance of o2 respiration in many coastal sediments has been overestimated whereas metal oxide reduction both fe and mn reduction has probably been well underestimated

climate change in the turkana basin as deduced from a 4000 year long δo18 record abstract a model of the oxygen isotopic composition of lake turkana waters sheds insight into the paleoclimatic interpretation of a 18 o profile of inorganic calcite from a core taken from the lake the model indicates that high frequency fluctuations seen in the isotopic record are probably due to shifts in lake level while the long term increase of 1 4 seen from 4 to 2 kyr bp cannot be due solely to lake level change it must be due to changes in other climatic parameters such as the isotopic composition of the inflow these findings suggests that the abrupt change observed in lake turkana and many other african lakes at 4 ka was the precursor to a 2000 year long adjustment in the climate over the ethiopian plateau the isotopic record from lake turkana agrees with other paleoclimate records from the basin including the diatom stratigraphy and radiocarbon dates on exposed shoreline deposits

pollen and isotopic records in late holocene sediments from lake turkana kenya abstract a 12 m piston core lt 84 8p taken in the northern basin of lake turkana has been dated by 6 ams radiocarbon dates on large ostracods and analysed for its pollen content during the past 2500 years the pollen assemblages were dominated by chenopodiaceae amaranthaceae cheno am and gramineae representing the local pollen signal of the surrounding vegetation under arid conditions percentage fluctuations of cheno am are interpreted as reflecting lake level variations in good correspondance with oxygen isotope from the same core a rise in lake level is recorded at about 1600 yr b p preceded by a relative lowstand during much of the period from 2500 to 1600 yr b p the top of the core is estimated to be about 600 yr old and shows a shift of unknown duration towards a more humid condition the high lake level documented in this paper roughly coincides with that reconstructed from other cores in the lake based on diatom and carbonate analyses

trends in depth and extent of bioturbation in cambrian carbonate marine environments western united states cambrian carbonate strata of the great basin deposited below fairweather wave base but above mean storm wave base inner shelf and below mean storm wave base but above maximum storm wave base middle shelf were examined for extent and depth of bioturbation data indicate that initial extensive colonization of marine infaunal habitats occurred between tommotian and atdabanian time throughout the remaining 65 m y of cambrian time bioturbation increased although depth of bioturbation remained relatively constant at less than 6 cm during this time the amount of bioturbation in the inner shelf was greater than that in the middle shelf

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

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

rapid deformation rates due to development of diapiric anticline in southwestern taiwan from geodetic observations abstract we adopted 106 campaign mode gps observations and 310 precise leveling measurements between 2002 and 2010 to understand the present day crustal deformation in mudstone area and to estimate the earthquake potential of the hsiaokangshan hksf and the chishan faults chnf in southwest taiwan horizontal velocities east of the chnf are 66 mm yr 270 and gradually decrease westward to 15 mm yr n259 a horizontal velocity gradient of 15 mm yr is shown between the hksf and chnf subsidence rates west of the hksf and east of the chnf are 5 10 mm yr while the uplift is observed between these two faults in the highest elevation with the maximum rate of 18 mm yr the observed deformation patterns are difficult to be fully modeled by 2d kinematic fault model field relationships within the vertical shear zones of the mudstone therefore indicate that the deformation pattern may be also controlled by a relic onshore mud diapir that is still experiencing vertical uplift consistency between the geological and geodetic vertical velocities weak rock strength and no destructive earthquakes over the last 100 years imply that faults hksf within the mudstone area are creeping however the chnf or the associated decollement may still have earthquake potential

geochemical indicators of depositional environment and source rock potential for the upper ordovician maquoketa group illinois basin two depositional cycles are recognized within the upper ordovician maquoketa group of the illinois basin in a core from the new jersey zinc 1 parrish well of fulton county illinois organic carbon corg total sulfur 13c content of the organic carbon dgr13corg hydrogen and oxygen indices hi and oi from rock eval pyrolysis and yields of extractable organic matter eom vary through the cycles dark brown to black laminated shales are present in the lower portion of each cycle and have high values of corg 1 0 3 0 hi 500 1000 mg hydrocarbon hc g total organic carbon toc and eom 500 2500 ppm and more negative dgr13corg values dgr13corg 30 to 30 5 mil gray to greenish gray bioturbated shales are present in the upper portion of each cycle and have low values of corg 1 0 hi 500 mg hc g toc and eom 500 ppm and more positive dgr13corg values 28 5 to 29 5 pmil compared to the laminated shales although thermally immature to marginally mature in this core the laminated shales represent potential source rocks for petroleum because they contain good to excellent quantities of oil prone organic matter and are more deeply buried in other areas of the basin kerogen elemental data and rock eval data suggest that the source of organic matter in the maquoketa was uniform with the notable exception of graptolite rich layers distributions of saturated hydrocarbons for maquoketa samples resemble those derived from amorphous organic matter the organic walled microfossil gloeocapsomorpha prisca was not identified in kerogens of the maquoketa shale and its absence is most likely due to an unfavorable depositional environment and or climate variations in bulk geochemical data and carbon isotopic compositions within the maquoketa group indicate substantial reworking and degradation of organic matter associated with bioturbation and oxygenated depositional conditions organic rich shale was deposited in an environment where circulation of the water column was sluggish and dissolved oxygen concentrations were low resulting in the preservation of organic matter organic poor shale was deposited in an environment where circulation of the water column was strong dissolved oxygen concentrations were high and burrowing organisms thoroughly reworked the sediment resulting in the degradation of organic matter a maximum difference in carbon isotopic ratios of 2 pmil between organic rich and organic poor units of the maquoketa roup suggests that heterotrophic reworking of organic matter was important in the depositional environment the carbon isotopic composition and h c ratio of kerogen for graptolite rich shale suggests that organic productivity may have played an intermittent role in the accumulation of organic matter in the maquoketa shale

carbon sulfur iron systematics of the uppermost deep water sediments of the black sea box cores recovered during leg 4 of the 1988 r v knorr black sea oceanographic expedition from deep water regions of the basin were dominated by coccolith rich microlaminated unit 1 sediment and muddy gray turbidite layers both organic carbon oc and pyrite sulfur values for unit 1 display narrow ranges with mean concentrations of 5 3 1 1 1 wt and 1 3 0 3 wt respectively unit 1 is not enriched in pyrite s relative to sediments deposited under oxygenated bottom waters normal marine sediments with comparable oc concentrations carbon sulfur relationships evaluated on a calcium carbonate free basis to avoid spurious correlations resulting from dilution effects demonstrate that oc and pyrite s are essentially decoupled these observations combined with the persistence of elevated pore water sulfide to depth and a strong correlation between pyrite s and the detrital fe component argue strongly for limitation of pyrite formation in unit 1 by the availability of reactive fe unit 1 fe limitation is further indicated by degree of pyritization dop studies a measure of the extent to which the original potentially reactive fe has been transformed to pyrite these studies show sulfidation of reactive fe ranging from 57 to 78 with dop values independent of oc concentration unit 1 dop profiles suggest that the majority of the pyrite is formed in the sulfidic water column and or very close to the sediment water interface pyrite s concentrations of unit 1 when compared with the particulate reduced sulfur fluxes measured in time series sediment traps are compatible with predominantly water column pyrite formation because of the limitations in the supply of reactive fe associated with the comparatively high supply of oc the microlaminated sediment is characterized by c s ratios greater than those typical of holocene oxically deposited sediments the turbidite muds of the deep basin display high reduced s values relative to holocene normal marine sediments in samples with low oc concentrations low c s ratios this reflects pyrite formation under anoxic sulfidic bottom water conditions in a probable upper slope source region as well as during transport and final deposition intermediate dop values for the turbidites in part a product of their rapid rate of deposition reveal that fe limitation is ultimately not a factor and that further pyrite should form during burial however the very rapid rate at which unit 1 pyrite forms suggests fundamental differences between the overall reactivities of the fe phases associated with the microlaminated and turbiditic sediments the signature of water column anoxia with regard to sedimentary pyrite formation is clearly indicated by the high dop values of unit 1 and the comparatively high levels of s associated with the low concentrations of oc of the turbidite muds this agrees with similar conclusions based on studies of ancient sedimentary rocks

chondrites a trace fossil indicator of anoxia in sediments the trace fossil chondrites a highly branched burrow system of unknown endobenthic deposit feeders occurs in all types of sediment including those deposited under anaerobic conditions in some cases such as the jurassic posidonienschiefer formation of germany chondrites occurs in black laminated carbonaceous sediment that was deposited in chemically reducing conditions in other cases such as numerous oxic clastic and carbonate units throughout the geologic column chondrites typically represents the last trace fossil in a biotutbation sequence this indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters

evaluation of oxygen isotopes in carbonate as an indicator of lake evolution in arid areas the modern qinghai lake qinghai tibet plateau abstract the oxygen isotopic composition of carbonate in lakes has been used as a useful indicator in palaeolimnological research and has made some important contributions to our understanding of lacustrine systems for modern lakes in arid or cold areas however there are few data available to test the effect of lake salinity and temperature on the oxygen isotopic composition of various carbonate sources such as ostracod bulk carbonate and fine grained carbonate for arid high altitude lake qinghai our results suggest that variations in the 18o values of carbonate in lake qinghai are mainly controlled by the oxygen isotope ratio of the lake water changing with water salinity as a secondary effect increasing water depth leads to cooler bottom and surface water which may result in more positive 18o values of ostracod and bulk carbonate

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

environmental oxygen fluctuations and the adaptive response of marine benthic organisms oxygen depletion is widespread in modern and ancient benthic environments most modern examples exhibit a significant cyclic fluctuation in o 2 availability ranging from tidal to seasonal cycles and longer term periods e g el nino in contrast only long term changes have been generally recognized in ancient environments benthic organisms adapt along two pathways 1 to low o 2 values and free h 2 s including chemosymbiosis 2 synchronization of individual life cycles to the o 2 fluctuation cycle by living as planktonic larvae in oxygenated surface waters using oxygenated periods in bottom waters during the adult stage examples of both adaptive pathways can be recognized in the benthic faunas of fossil oxygen controlled environments thus recording short and longer term fluctuations

middle late holocene river terraces in the erhjen river basin southwestern taiwan implications of river response to climate change and active tectonic uplift abstract we reconstruct the holocene river history of the erhjen river area 140 km 2 by correlating river terraces aided by 28 radiocarbon dates multiple terraces developed in the lower erhjen river since the middle holocene they converge downstream to the coastal plain the rates of channel incision into bedrock calculated from these terraces at yuehshihchieh are 7 8 mm year during ca 5 7 2 5 ka 5 cm year during 1 5 1 3 ka and 1 cm year since 1 ka the last is close to the average incision rate since middle holocene meanwhile only a single but wide middle late holocene paleo floodplain was developed in the upper erhjen river it was completely abandoned only after 0 8 ka likely following an episode of base level fall starting from the coastal plain based on the apparent downstream and upstream convergence of these dated terraces we identify a doming structure or anticline within the basin which results in a tilt rate of 10 6 to 10 7 per year in the lower erhjen river valley the major terraces here had different initial long profiles which implies that a critical graded long profile may not be a prerequisite for formation of a wide erosional terrace surface instead we propose that these terraces were initiated by a series of catastrophic rainfall events probably climatic related which brought a large amount of bedload from hillslopes to prevent the channel from incising when valley widening was facilitated by high discharge runoff we find that not only terrace surface formation but also channel incision can be strongly controlled by climatic driven discharge and bedload conditions as suggested by the contrast of bedrock incision rates we observe at yuehshihchieh apparently the climate and its effects on the landscape cannot be regarded as constant during the holocene even in a humid tropical area like taiwan however such a fluctuation of climate could only be recorded in a setting where rivers have a high tendency to incise so that multiple terraces can be created the lower erhjen river that is characterized by active tectonic tilting is an example of this setting

cretaceous rhythmic bedding sequences a plausible link between orbital variations and climate abstract simple oscillation cycles have been recognized in cretaceous pelagic sequences as a marked periodicity in carbonate and or organic carbon content the estimated periodicities of these cycles resemble milankovitch type variations in orbital elements however during warm geologic periods the nature of the link between orbital variations and the sedimentary record has been problematic climate model studies show that the intensity of continental margin precipitation in specific low latitude regions is a function of land sea thermal contrast which is sensitive to orbital variations cretaceous climate model simulations are characterized by regions of intense precipitation the locations of which are controlled by geographic configuration in particular in the model simulation the northern margin of the tethys ocean has all the climatic characteristics necessary to exhibit a sensitivity to orbital variations detailed studies of the biota sedimentology and geochemistry of the bedding rhythms in greenhorn cyclothem in the western interior seaway of north america are best interpreted in terms of variations in precipitation runoff and stable stratification of the seaway combined the geologic and model studies support a link between orbital periodicities variations of intense precipitation associated with specific paleogeographic situations and cretaceous bedding patterns this hypothesis has important implications for the sensitivity of the atmosphere hydrosphere lithosphere system to external forcing

climatic cyclicity and terrigenous sediment influx to the early turonian greenhorn sea southern utah abstract rhythmically alternating beds of limestone and shale in pelagic deposits of the cenomanian turonian north american western interior seaway have been widely attributed to climatic cyclicity in the milankovitch band whether these rhythmic beds record cycles of terrigenous dilution or of productivity remains controversial we present results of a study of early turonian strata of the tropic shale and tununk member of the mancos shale in southern utah aimed at testing the dilution model in a prodeltaic environment within 130 km of the paleoshoreline the study transect consisted of four localities spaced along a 110 km onshore offshore transect in each of the four sections we studied a stratigraphic interval characterized by beds of limestone or marlstone that alternate with beds of marly shale or calcareous shale along the transect content of quartz sand and coarse silt in each of the beds generally decreases and content of calcium carbonate increases in each section quartz sand and coarse silt content varies antithetically with calcium carbonate content these observations suggest that the limestone marlstone beds accumulated during times when rates of terrigenous sediment transport to offshore sites were relatively slow conversely the shaly beds were deposited during times of enhanced terrigenous sediment flux these ob ervations support the hypothesis that limestone shale bedding rhythms record wet and dry phases of climate cycles in utah the limestone marlstone beds contain smaller proportions of mixed layer illite smectite clays than do the shaly beds climatic cyclicity apparently led to cyclic variations in the proportions of clay minerals supplied to the prodeltaic environments or to variation in the loci of accumulation of different clay minerals analysis of intensity of bioturbation and preservation of fecal pellets also indicates that the limestone marlstone beds accumulated under more oxic benthic conditions than did the shaly beds detailed examination of the alternating beds of limestone marlstone and shale in southern utah indicates that the deposits are characterized by a distinctive succession of facies these deposits are better interpreted as bedding cycles composed of three gradational lithologies than as bedding rhythms composed of two alternating lithologies data on grain size and calcium carbonate content suggest that the bedding cycles correspond to shoaling upward parasequences that developed in response to small scale changes in relative sea level our study suggests that climatically modulated changes in fresh water discharge and terrigenous sediment supply were mainly responsible for these sea level changes and for cyclic variations in benthic oxygenation in prodeltaic environments of the earl turonian western interior seaway

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework sequence stratigraphy has been combined with total organic carbon toc analysis from well logs core and cuttings to develop a model of toc accumulation in marine source rocks routine well profiling of toc in marine source rocks has revealed that recurrent patterns in the vertical distribution of toc occur that can be explained with sequence stratigraphic concepts the model assumes that the principle controls on organic carbon accumulation are 1 the presence of low oxygen conditions at the sediment water interface and 2 sedimentation rate under these circumstances toc will vary inversely with terrigenous clastic influx if accommodation is high clastic influx is low in distal locations and the resulting weight percent toc in basinal sediments is increased th maximum toc in a vertical profile through a single marine sequence probably correlates to the maximum flooding surface toc decreases above this surface due to increasing sediment dilution during highstand progradation and decreases below it with the higher sedimentation rate of the older transgressive systems tract commensurate with toc increase towards the maximum flooding surface the organic matter type becomes more marine and therefore increasingly oil prone several marine source rock examples are presented as well as a lacustrine example which also conforms to the marine model

stratigraphical architecture at the muddy margin of the cretaceous western interior seaway southern utah the tropic shale and correlative tununk shale member of the mancos shale accumulated during cenomanian turonian time within prodeltaic environments near the western margin of the western interior seaway of north america stratigraphical and sedimentological analysis has revealed a detailed history of relative sea level change in the thick fine grained succession the tropic and tununk shales were deposited during the greenhorn second order sea level cycle over a time span of about 2 5 million years in southern utah six depositional sequences are superposed upon the record of this long term sea level change the sequences developed during third order relative sea level cycles of hundreds of thousands of years duration and are composed of at least 37 parasequences arranged in retrogradational aggradational and progradational parasequence sets the tropic shale and tununk shale member accumulated just basinward of the axis of maximum subsidence of a foreland basin stratal geometries and facies distribution patterns in the succession indicate that in southern utah the greenhorn cycle was tectonically controlled during the greenhorn transgression and highstand rapid rates of tectonic subsidence trapped terrigenous sediment to the west of the study area in the more proximal foreland at this time hemipelagic facies accumulated at relatively slow rates in southern utah and type 2 sequences developed during third order sea level cycles in contrast during the greenhorn regression rates of thrust induced subsidence in the proximal foreland basin evidently slowed and deltaic clinoforms prograded across the study area at least one forced regression occurred in southern utah at this time and type 1 sequences developed the formation of type 1 sequence boundaries in the upper part of the tropic shale and tununk shale member points to episodes of base level fall and indicates that the six third order sea level cycles recorded in the succession were not the result of changes in sediment supply alone the third order cycles may have been a consequence of episodic tectonism the timing of these cycles however suggests that development of sequences and parasequences in the tropic shale and tununk shale member may have been related to orbital forcing in the milankovitch band glacioeustasy or climatically related fluctuations in the amount of groundwater stored on continents may explain these high frequency sea level changes

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

molluscan biostratigraphy of the koobi fora hominid bearing deposits since the discovery1 of late cenozoic hominid bearing deposits in the koobi fora area north kenya a variety of studies2 9 have been undertaken to provide a chronostratigraphical and palaeoenvironmental context for the important palaeoanthropological and early archaeological discoveries1 10 unfortunately although the exposures are areally extensive 1 000 km2 they are broken up into subareas fig 2 these local sections are often difficult to correlate with one another due to intervening bush cover and faulting here i summarize a molluscan biostratigraphical analysis which demonstrates serious stratigraphical miscorrelations between certain local sections including some previously indicated by vertebrate evidence these miscorrelations require substantial revisions to current stratigraphical interpretation of the koobi fora deposits in particular both the suregei and tulu bor tuff horizons actually represent different levels although the tulu bor is considered to overlie the suregei some exposures currently attributed to the tulu bor are actually older than some units previously mapped as the suregei fortunately the stratigraphical miscorrelations reported here do not significantly affect the relative placement of the mollusc faunas reported in a previous evolutionary analysis15 superpositional relationships in the areas from which these faunas were collected mainly collecting areas 102 103 110 123 202 and 203 are unaffected by the miscorrelations reported here

plate collision and paleostress trajectories in a fold thrust belt the foothills of taiwan abstract field analyses of compressional faulting and folding in the foothills of western taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events two main compressional events have contributed to the present structure of the fold thrust belt stratigraphic data show that these events are plio pliocene in age older normal faulting indicates nnw sse extension across the chinesse passive continental margin during the neogene the two main compressional events of the taiwan collision correspond to similar fan shaped distributions of maximum compressive stress trajectories with a counterclockwise shift of 30 50 between the two events using the relationship between recent stress trajectories and the direction of recent plate motion as a guide we reconstruct the direction of plate convergence for the older event we suspect that the relative motion philippine sea plate eurasia has rotated counterclockwise of at least 35 45 in taiwan during collision this conclusion is in agreement with independent plate tectonic reconstructions several problems provide objectives to further tectonic and paleomagnetic studies including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost taiwan

an anoxic event at the albian cenomanian boundary the fish scale marker bed northern alberta canada abstract the fish scale marker bed fsmb of the shaftesbury formation which marks the albian cenomanian boundary is a regional stratigraphic marker in the western interior of canada at the outcrop studied on the smoky river in northwestern alberta three major shale units can be distinguished in the fsmb and contiguous strata the lowermost shale unit 1 is bioturbated and contains high diversity dinoflagellate and moderate diversity foraminiferal assemblages it has dominantly type iii terrestrial organic matter om and low total organic carbon content toc the unit was deposited in an open marine neritic environment of normal salinity the fsmb unit 2 represents a zone of condensed bioclastic accumulation composed of abundant fish remains the dinoflagellate species diversity is drastically reduced in this unit and it lacks benthonic foraminifera and bioturbation unit 2 is characterized by mainly type ii marine om and high toc values unit 2a contains rippled sandstone related to either a shallowing or to deeper water currents a fish hash conglomerate making up unit 2b can alternatively be interpreted as a bioclastic condensed and winnowed deposit or as a transgressive lag unit 2c consists of black platy shale with abundant fish remains and represents a minor marine trangression during the deposition of fsmb when the bottom waters were dominantly anoxic collectively the features of unit 2 suggest deposition under a stratified water column with moderate productivity of planktonic and nektonic organisms in the upper oxygenated layers but with anoxic bottom waters unit 3 overlying the fsmb consists of blocky shale with reduced concentration of fish remains due to increased rate sedimentation during its deposition the organic rich sediment of unit 3 was progressively diluted by clastic material and there was an increase in the dissolved oxygen content of the bottom waters the anoxic event at the fsmb is related to a relative rise in sea level and possibly to the mixing of waters different salinities and temperatures from the arctic ocean and the gulf of mexico in the western interior seaway

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

deformation history of the southwestern taiwan foreland thrust belt insights from tectono sedimentary analyses and balanced cross sections abstract analysis of the basin scale and local deformation history and estimates of shortening rates are performed in the southwestern foreland thrust belt of the plio pleistocene taiwan orogen timing of deformational events is constrained using both syntectonic unconformities and other markers of syndepositional tectonic activity three cross sections are investigated and balanced intermediate shortening rates are estimated based on balanced and restored cross sections the total amount of shortening along studied balanced sections results from superimposed thin skinned and thick skinned styles a shallow aseismic thick decollement is located to depth of 6 8 km at the base of thick late miocene shales that behaves as ductile layer the occurrence of a deep seismic decollement to depth of 12 15 km is confirmed by seismicity fault plane solutions of focal mechanisms and a seismic reflection profile providing evidence of reactivated and inverted inherited extensional features beneath the coastal plain three major tectonic stages are recognized within the southwestern foothills which are correlated with local thrusting events the first stage begins at 5 ma with the onset of the taiwan collision and ends at 2 1 6 ma it reflects an initial submarine accretionary stage associated with moderate tectonic activity the second major stage occurs during late pliocene early pleistocene this intermediate collision stage sealed the evolution of the southern foreland thrust wedge from submarine to continental environment in relation with exhumation and denudation of the central range the last stage of deformation begins in the middle pleistocene and continues until present it is associated with high rates of sedimentation and most of the thrusts are activated or reactivated at that time and out of sequence thrusting occurs the collision started synchronously near 5 ma throughout the southwestern taiwan total and intermediate shortening rates are more or less constant through time in studied sections that may suggest that long term deformation in the taiwan foreland thrust belt occurred more or less at steady state since 5 ma the southward decrease of rates of shortening from 3 6 to 4 8 mm year in northern sections to 2 2 mm year in southern section might be related to both influence of indentation by the peikang high to the north and southward transition at the scale of the southwestern foothills from collision to subduction setting the effect of the obliquity of the convergence resulting in regional southward migration of the collision cannot be definitely inferred from this analysis our results place new kinematic and time constraints which must be taken into account in forthcoming geodynamic models of the taiwan collision

mechanical twin sets in calcite as markers of recent collisional events in a fold and thrust belt evidence from the reefal limestones of southwestern taiwan stress reconstructions were carried out based on inversion of calcite twin data from slightly deformed quaternary reefal limestones from sw taiwan results demonstrate that twinning reliably recorded the complex quaternary and present day stress fields in a young mountain range undergoing collisional shortening the stress regimes reconstructed at microscopic scale are predominantly compressional and reflect the main stages of the neotectonic evolution of the collision belt no twinning has been observed in a sample collected in the holocene platform of southern taiwan indicating that these formations did not undergo sufficient stress to initiate calcite twinning three different stress regimes have been recorded in the samples collected in pleistocene reef limestones that developed in relation to active fold systems of the western foothills these regimes appear to be homogeneous at the site scale and at the scale of sw taiwan the reconstructed ene and nw trending compressions only present in sw taiwan probably reflect local perturbations of the regional 105 trending compression the perturbation might be due to activation of a set of folded faulted blocks in the studied area a nw se extension also identified in these samples is related to extrados stretching due to fold development the results are consistent with independent stress data i e quaternary faulting borehole breakouts and focal mechanisms of earthquakes the analysis of mechanical twins in calcite rocks constitutes a powerful tool for tectonic analyses in fold and thrust belts

active deformation of taiwan from gps measurements and numerical simulations using a two dimensional distinct element model we evaluate the relationships between plate kinematics and present day deformation in taiwan where active collision occurs in particular the distribution of velocity fields calculated in our models is compared with the actual velocity field revealed by the most recent geodetic data gps obtained in taiwan and the surrounding islands of the philippine sea plate and the eurasian shelf the main aim of this paper is to produce a mechanically consistent 2 d model that accounts for the observed velocity field taken as whole within the limits of acceptable rheological parameters and reasonable boundary displacement conditions we evaluate how the active deformation of taiwan is influenced by the presence of strong and weak zones such as the structural highs in the foreland and subduction zones with accretionary prisms respectively major mechanical discontinuities such as the main fault zones in the mountain belt and the opening of the okinawa trough particular attention is paid to the role of preexisting discontinuities since the presence of mechanical decoupling along major faults strongly affects the distribution of the velocity and stress patterns we show that despite parameter uncertainties several tectonic factors the presence of the strong kuanyin and peikang highs in contrast to the weak subduction zone to the south the weak active regional shear zones and the opening of the back arc okinawa trough concur to provide an acceptable mechanical model for this regional deformation these sources are related not only to the geometry of the plate boundary the direction of plate convergence and the shape of the chinese margin but also to the presence of major zones of relative weakness and mechanical decoupling such as the longitudinal valley fault zone and the western thrust belt of taiwan

geometry and quaternary kinematics of fold and thrust units of southwestern taiwan structural and paleostress analyses provide new insights into the quaternary kinematics of the outermost fold and thrust units of southwestern taiwan foothills the frontal folds are interpreted as fault related folds and their tectonic evolution through space and time is tightly constrained fold development is correlated with reef building on top of the anticlines moreover we provide field evidence that nw se fault zones oblique to the structural grain of the belt probably acted as transfer fault zones during the the quaternary fold thrust emplacement two successive quaternary stress regimes are evidenced in southwestern taiwan a nw se compression followed by a recent nearly e w compression the latter shows an along strike change from pure e w contraction to the north to perpendicular n s extension in the south this southward decrease in n s confinement probably represents the on land signature of the incipient quaternary tectonic escape predicted by analogue and numerical modelling and evidenced at present day by global positioning system data

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

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

mudrock sequence stratigraphy a multi proxy sedimentological paleobiological and geochemical approach devonian appalachian basin abstract delineation of stratigraphic sequences and their component systems tracts in mudrock dominated facies is generally difficult due to the relatively homogenous fine grained nature of the strata in this study we apply a multi proxy analytical approach to a thick devonian mudrock dominated succession through detailed analysis of sedimentologic paleobiologic and geochemical data through 600 m of mudrock rich facies varied combinations of proxies prove to be most useful in delineating sequence development in anoxic dysoxic and oxic dominated mudrock settings and in mixed mudrock carbonate and mixed mudrock sandstone successions these interpretations are tested against an established sequence stratigraphic framework for 11 middle to upper devonian mid eifelian to lower famennian sequences in the appalachian basin the sequences presented here further detail and refine global devonian t r cycles id to iie of the well known johnson sandberg and klapper sea level curve the usefulness of proxies in delineating depositional sequences and systems tracts varies dependent on depositional paleoceanographic paleoecologic and early diagenetic conditions those proxies that show a range of variations in specific settings such as grain size degree of bioturbation and concentrations of toc and elements elemental ratios e g caco3 al ti mg sc si mo ni v si al and ti al may help delineate depositional dynamics related to redox conditions condensation dilution and clastic biologic and or authigenic sediment sources in fine grained anoxic dominated facies interpreted to represent basinal settings sequences and systems tracts are best delineated by anoxic related proxies toc and mo in intermediate dysoxic dominated settings toc mo bioturbation and al remain effective indicators of sequence development in relatively oxygenated mudrock rich and carbonate poor sequences bioturbation may function as the most effective proxy for recognizing systems tracts for mixed fine grained siliciclastic carbonate successions concentration and type of caco3 e g benthic macroskeletal pelagic styliolinid dacryoconarid and micritic calcisilt are useful in identifying position within cycles in more proximal carbonate poor successions fine and coarse grained fractions become increasingly differentiated these can be distinguished by relatively high si al ratios si al ca 5 elemental ratios indicative of coarser clastic input e g si al zr al and ti al are applicable to identifying position with a sequence but they may also be affected by input from eolian volcanogenic or biogenic sources in addition fluxes of siliciclastic carbonate and toc sediment types may dilute the concentration of the others multiple lines of evidence should be examined in interpreting relative depth and position within a sequence