fluid flow equations governing primary oil migration as a separate phase abstract a mathematical model of primary oil migration as a separate phase out of compacting shales is presented during burial and oil generation source rock porosity decreases and oil saturation increases until residual oil saturation is reached at this stage oil is expelled out by capillary and excess fluid pressure gradients the model is a system of differential equations which relate changes in oil and water saturation in time to water and oil flow out of the source rock during burial an additional set of equations for periods of erosion of overburden are also provided the equations can be numerically solved by finite difference method if oil and water flow is to be simulated during oil generation then at each time step changes by oil generation in oil and water saturations and porosity must be calculated the solution procedure is briefly outlined

incised channels and gully erosion in northern iberian peninsula controls and geomorphic setting abstract gully erosion has scarcely been reported in the cantabrian cordillera northern iberian peninsula even though this phenomenon is relatively frequent in this mountain range a total of 133 permanent channels with evidences of gully erosion have been mapped in a 71 8 km2 study area on the northern slope of this mountain range the underlying ordovician unit comprises quartzite sandstone and slate which are partially mantled by different surficial deposits the relief is fairly steep with average slopes of 27 and hillsides with level drops of the order of 700 m and generally vegetated by atlantic heaths a result of the degradation suffered by the natural vegetation following forest fires the mapped channels present different morphological features shallow and deep channels some of them with associated ravines and are usually related to headcut in first and second order pre existing channels although some of them are located on unchanneled hillsides with no evidence of pre existing channels moreover lower reaches of first and second order channels are often incised into bedrock a field description and morphometric study has been carried out on channels affected by gully erosion based on their cartography digital terrain models and several layers of thematic mapping this study describes some of the relations between relief factors the type of substratum and the development of gully erosion i there are robust correlations between morphometry relief and erosion intensity and ii gullying is strongly influenced by the presence of a deep regolith the erosion forms observed and the described relations suggest that gully development is associated to landsliding processes which are ultimately controlled by ground water movement through a porous regolith regional uplift and deforestation are argued to be the most likely causes of channel incision and gullying

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

a centennial scale record of vegetation and climate variability from 312 to 240 ka marine isotope stages 9c a 8 and 7e from tenaghi philippon ne greece abstract based on a new centennial scale resolution pollen record from the terrestrial site of tenaghi philippon ne greece we report a series of high amplitude millennial scale forest expansion events during the interval from 312 to 240 ka equivalent to isotopic substages c a of marine isotope stage mis 9 mis 8 and the onset of mis 7e pollen based indices support the climatic interpretation of the forest expansion events as indicators of abrupt increases in temperature and moisture availability in the mediterranean region long term changes in vegetation cover and composition during the studied interval permit the definition of glacial substages early middle and late analogous to the glacial substages of the last climatic cycle within this framework forest expansion events occurred during the early glacial equivalent to mis 9c a and the later part of the middle glacial mid to late mis 8 but are absent from the early part of the middle glacial early mis 8 forest expansion events are also detected during the lateglacial and onset of mis 7 associated with a millennial scale climate oscillation across the glacial interglacial transition i e termination iii t iii a peak for peak match between forest expansion events and antarctic temperature maxima suggests interhemispheric coupling of millennial scale climate variability via global oceanic circulation change and synergistic variability in atmospheric circulation consistent with the bipolar see saw the resolution of our record mean 290 yr also permits the characterisation of climate evolution over the course of interstadial episodes following forest expansion events and highlights differences in the characteristics of early and middle glacial interstadials saw tooth vs plateau profile these differences point to an influence of long term boundary conditions especially global ice volume on the characteristics of millennial scale events

morphology of hydrocarbon droplets during migration visual example from the monterey formation miocene california in this paper we describe the various morphologies of hydrocarbon residue found in the miocene monterey formation in california scanning electron microscope photomicrographs clearly show various shapes of hydrocarbon droplets in microchannels in the monterey formation and hence provide insight not only into the shape of hydrocarbon droplets during migration but also about the migration pathways themselves the small 5 10 m diameter droplets are observed to have various shapes that include spherical droplets amalgamated droplets sausage shaped droplets and elongate rod shaped droplets observations suggest that hydrocarbon droplets move through the rock matrix into microchannels where they coalesce into larger droplets and then move into larger fractures dif erent morphologies are simply a result of amalgamation of simple droplets during migration

geomorphic changes in a complex gully system measured from sequential digital elevation models and implications for management high resolution digital elevation models dems were derived from sequential aerial photography of an active uvio mass movement gully complex in new zealand s north island east coast region to measure geomorphic changes over approximately one year the gully showed a complex behaviour combining uvial and mass movement erosion deposition and reworking of materials stored in an active debris fan during the measurement period 5200 1700 m3 of material were eroded from the 8 7 ha gully complex and 670 180 m3 from the 0 8 ha depositional fan giving a total of 5870 1710 m3 for the entire gully complex fan system the results provide a high resolution description of gully behaviour over a short time period and also demonstrate that mass movement slumping and debris ows accounted for almost 90 per cent 4660 200 m3 of the sediment generated this erosional response is described in terms of gully evolution by comparing the gully complex to other systems in the region in various stages of development the effect of gully evolution on geomorphic coupling between the gully complex and channel system is described and coupling is also shown to vary with the magnitude and frequency of rainfall events from a land management perspective the success of strategies such as tree planting to mitigate against gully erosion depends on the stage of gully development particularly on whether or not mass movement erosion has begun in contrast to gully rehabilitation efforts elsewhere basin wide afforestation in the early stages of gully incision is favoured over riparian planting given that mass movement assisted by excessive groundwater pressure is the main process leading to uncontrollable gully expansion to protect land effectively against continuing gully erosion of headwater catchments and resulting downstream aggradation it is necessary for land managers to understand the spatial and temporal variability of gully development fully so that mitigation efforts can be targeted appropriately copyright 2003 john wiley sons ltd

gully morphology hillslope erosion and precipitation characteristics in the appalachian valley and ridge province southeastern usa this study investigates gully erosion on an east tennessee hillslope in a humid subtropical climate the study area is deeply gullied in ultisols acrisol according to the world reference base for soil with thirty years of undisturbed erosional history with no efforts to correct or halt the erosion the objectives are 1 to examine how different gully morphologies channel sidewall and interfluve behave in response to precipitation driven erosion and 2 to identify an appropriate temporal scale at which precipitation driven erosion can be measured to improve soil loss prediction precipitation parameters total accumulation duration average intensity maximum intensity extracted from data collected at an on site weather station were statistically correlated with erosion data erosion data were collected from erosion pins installed in four gully systems at 78 locations spanning three different morphological settings interfluves channels and sidewalls kruskal wallis non parametric tests and mann whitney u tests indicated that different morphological settings within the gully system responded differently to precipitation p 0 00 for channels and sidewalls regression models relating erosion and precipitation parameters retained antecedent precipitation and precipitation accumulation or duration r2 0 50 p 0 00 for channels r2 0 28 p 0 00 for sidewalls but precipitation intensity variables were not retained in the models for interfluves less than 20 of variability in erosion data could be explained by precipitation parameters precipitation duration and accumulation including antecedent precipitation accumulation were more important than precipitation intensity in initiating and propagating erosion in this geomorphic and climatic setting but other factors including mass wasting and eolian erosion are likely contributors to erosion high correlation coefficients between aggregate precipitation parameters and erosion indicate that a suitable temporal scale to relate precipitation to soil erosion is the synoptic time scale this scale captures natural precipitation cycles and corresponding measurable soil erosion

prediction of concentrated flow width in ephemeral gully channels empirical prediction equations of the form w d aq b have been reported for rills and rivers but not for ephemeral gullies in this study six experimental data sets are used to establish a relationship between channel width w m and flow discharge q m 3 s 1 for ephemeral gullies formed on cropland the resulting regression equation w d 2 51 q 0 412 r 2 d 0 72 n d 67 predicts observed channel width reasonably well owing to logistic limitations related to the respective experimental set ups only relatively small runoff discharges i e q 0 02 m 3 s 1 were covered using field data where measured ephemeral gully channel width was attributed to a calculated peak runoff discharge on sealed cropland the application field of the regression equation was extended towards larger discharges i e 5 10 4 m 3 s 1 q 0 1m 3 s 1 comparing w q relationships for concentrated flow channels revealed that the discharge exponent b varies from 0 3 for rills over 0 4 for gullies to 0 5 for rivers this shift in b may be the result of i differences in flow shear stress distribution over the wetted perimeter between rills gullies and rivers ii a decrease in probability of a channel formed in soil material with uniform erosion resistance from rills over gullies to rivers and iii a decrease in average surface slope from rills over gullies to rivers the proposed w q equation for ephemeral gullies is valid for sealed cropland with no significant change in erosion resistance with depth two examples illustrate limitations of the w q approach in a first example vertical erosion is hindered by a frozen subsoil the second example relates to a typical summer situation where the soil moisture profile of an agricultural field makes the top 0 02 m five times more erodible than the underlying soil material for both cases observed w values are larger than those predicted by the established channel width equation for concentrated flow on cropland for the frozen soils the equation w d 3 17 q 0 368 r 2 d 0 78 n d 617 was established but for the summer soils no equation could be established copyright 2002 john wiley sons ltd

lateglacial and holocene vegetation dynamics in the aegean region an integrated view based on pollen data from marine and terrestrial archives to elucidate the vegetation dynamics in the aegean region during the last 20 kyr we have studied terrestrial palynomorphs in marine core geotu sl152 mount athos basin northern aegean sea at centennial scale 125 to 300 yr resolution the robust chronology of the core allows us to reliably date signals of short term vegetation change in the aegean region for the pleniglacial interval until 14 6 kyr bp our data document steppe vegetation suggesting dry climatic conditions in the borderlands of the aegean sea subaerially exposed parts of the shelf were probably colonized by pinus dominated vegetation until shelf areas were flooded during lateglacial sea level rise the final rapid decrease of pinus pollen percentages between 14 and 13 kyr bp appears to be connected to meltwater pulse mwp 1a the lateglacial interstadial complex ie meiendorf bolling and allerod is characterized by the spread of oak trees but also by the continuous presence of steppe elements indicating only slightly increas

late quaternary paleoclimate in the eastern mediterranean region from stable isotope analysis of speleothems at soreq cave israel abstract the eastern mediterranean continental paleoclimate during the past 25 000 years was determined by a high resolution petrographic stable isotopic and age study of speleothems from soreq cave israel 18o 13c trends indicate that all speleothems older than 7000 yr formed under conditions that differ from those of today the period from 25 000 to 17 000 yr b p was characterized by the highest 18o and 13c values which indicate deposition at temperatures of 12 16 c annual rainfall of 300 450 mm and vegetation typical of a mixed c3 c4type from 17 000 to 10 000 yr b p deglaciation in northern europe 18o values dropped progressively correlative with warming 2 3 c and a gradual increase in precipitation a simultaneous decrease in 13c gives a range expected for c3 type vegetation this period also shows significant 18o and 13c spikes which are correlatable with global events e g heinrich events and the younger dryas stade the speleothems that grew between 10 000 and 7000 yr b p have a unique petrography showing irregular thin laminae of various colors and much detritus they have the lowest 18o corresponding to 1000 mm rain coupled with the highest 13c caused by flooding events which stripped the soil cover from 7000 to 1000 yr b p conditions became closer to those of today this study demonstrates that global events which were recognized in northern europe and north africa are also evident in the eastern mediterranean and are reflected principally by large changes in the rainfall rate

development and controlling factors of gullies and gully complexes east coast new zealand sequential aerial photographs of a small headwater catchment in the waiapu basin east coast region north island new zealand were interpreted to measure and analyse temporal changes in active area of gullies and gully complexes for a longer time span 1939 2003 and with higher temporal resolution compared to previous studies we focus on the conditions leading to the development of gullies and gully complexes under pasture and forest by using topographic thresholds slope area relationships of catchments for the initiation of gullies and gully complexes in addition the influence of two different lithologies as well as the occurrence of major rainfall events was related to gully activity twenty gullies and four gully complexes occupying 62 5 ha or 12 5 per cent of the catchment area occurred in the study catchment between 1939 and 2003 however the majority of these were not active at all of the dates studied gullies developed in the sandstone dominated tapuwaeroa formation tended to attain their maximum size by 1957 with a mean catchment area of 2 1 ha gullies developed in mudstone of the whangai formation attained their maximum size in 1939 with a mean catchment area of 4 31 ha exceptions are gullies which developed into mass movement deposits or into an earth flow deposit as well as gullies developed under indigenous forest topographic threshold values for gullies under pasture and indigenous forest show that values for gullies under forest plot far above the threshold line of gullies under pasture indicating that the topographical threshold for gully development under forest is higher compared to under pasture a threshold value of 9 4 ha in catchment area is needed for the development of gully complexes under pasture all located in the whangai formation and with the same orientation as the strike of the mudstones gully complex area and dominance of mass movement erosion increased with larger catchment area a decreasing distance to the threshold line for gullies under pasture indicates a later development for gully complexes no gully complexes developed under indigenous forest indicating that the threshold value for gully complex development is higher than for gully complexes under pasture and was not reached in the study area a model of shifting topographical threshold for gully development for a given catchment is developed which depends on land use when a catchment has an indigenous forest cover the topographical threshold is very high after conversion to pasture threshold values decrease drastically with the invasion of scrub the threshold slowly increases and returns to a similar level to that under indigenous forest after reforestation development of gullies and gully complexes is a highly dynamic phenomenon and phases of expansion and inactivity indicate that models describing only unidirectional advancing stages without periods of inactivity are not suitable therefore this study adds more phases to models of gully and gully complex development in the east coast region the threshold line for gully initiation under pasture and a value of 9 4 ha in catchment area for gully complex initiation permits one to predict which catchments under similar environmental settings develop gullies and gully complexes on a physical basis this enables land managers to implement sustainable land use strategies to reduce erosion rates of gullies and gully complexes copyright 2006 john wiley sons ltd

hydrocarbon expulsion model and its application to niigata area japan a one dimensional process response type model has been set up to simulate geologic processes of compaction heat transfer source rock maturation and hydrocarbon generation and expulsion during a basin s development the model can be used to calculate the quantity of oil and or gas expelled from a source rock under certain conditions although the model simplifies chemical and physical conditions within sedimentary rocks it may be used as a first approximation in geologic reconstructions of sedimentary basins when applied to the niigata area japan the model predicted the most significant parameters associated with hydrocarbon expulsion including the rate of burial and the quantity of hydrocarbons generated the model also revealed that the time of hydrocarbon expulsion varied from place to place even within the small northern niigata basin major petroleum fields formed when expulsion favorable timing coincided with the development of structure thus a realistic estimate of the timing of expulsion is a key to hydrocarbon exploration

reconstruction of late glacial and holocene climate evolution in southern china from geolipids and pollen in the dingnan peat sequence we have carried out a multi proxy analysis of a radiocarbon dated peat core that records the history of paleoclimate change dating from 18 ka in the dingnan region of southern china fatty acid and hydrocarbon distributions total organic carbon toc concentrations pollen assemblages and sediment lithology reveal a succession of three major paleoclimate intervals plant waxes are the predominant origin of the n alkanoic acid and n alkane compositions of this sedimentary sequence contributions of these geolipid components vary relative to toc and with changes in lithology and help to refine a pollen based reconstruction of local paleoclimate evolution a period of cool and fairly wet climate 15 630 10 450 cal abp follows accumulation of coarse fluvial sediments under relatively dry deglacial conditions the second period 10 450 6040 cal abp experienced the warmest climate and the highest precipitation indicated by a minimum c18 1 c18 0 ratio together with the low cpi values of n alkanes and high acl values the third time interval 6040 3800 cal abp was a moderately dry and cool period the climate record of the most recent period 3800 cal abp is obscured by agricultural disturbance the younger dryas 12 900 11 600 cal abp appears in this record as a period of variable and very wet climate during the interval 10 450 6040 cal abp both temperature and the precipitation evaporation ratio maximized therefore we consider this period to represent the holocene optimum which coincides with that of the northern hemisphere moreover our results do not fit the spatially asynchronous pattern of the east asian monsoon holocene optimum in china suggested by previous studies they instead parallel the pattern of global paleoclimate change and consequently show that the evolution of holocene paleoclimate in southern china is consistent with changes in northern hemisphere solar radiation

quantifying historical gully erosion in northern bavaria the wolfsgraben is one of many ravines that cut into the silty sandy material of the triassic benchlands of northern bavaria germany within the research area a gully several meters in depth has carved in to a bluff 500 m west of the upper main valley an analysis of 17 exposures and 30 drillings was conducted within the gully and its colluvial fan in order to reconstruct the soil formation extreme rainfall events and land use changes throughout history detailed field studies chemical soil analysis dating methods of charcoal and pottery as well as written documents were combined to produce a high resolution stratigraphy nine main phases of landscape evolution caused by extreme rainfall runoff and soil erosion in agriculturally used areas have been identified since the medieval period the highest amount of soil loss occurred during 14th 18th and 19th centuries a result of intensive land use climate changes affected the intensity of rainfall and the magnitude of soil loss during these periods d 2003 elsevier science b v all rights reserved

threshold conditions for initiation of valley side gullies in the middle veld of swaziland abstract gullied and ungullied catchments in four areas of deeply weathered saprolite in the middle veld of swaziland can be successfully separated p

a model for archaeologically relevant holocene climate impacts in the aegean levantine region easternmost mediterranean abstract a repeating pattern of multi centennial scale holocene climate events has been widely globally documented and they were termed rapid climate change rcc events non seasalt potassium ion k series in greenland ice cores provide well constrained timings for the events and a direct timing relationship has been inferred between these events and the frequency of northerly cold polar continental air outbreaks over the eastern mediterranean sea through gaps in the mountain ranges along the northern margin of the basin there also appears to be a remarkable timing agreement with major archaeological turnover events in the aegean levantine region yet no physically consistent assessment exists for understanding the regional climatic impacts of the events around this critical region we present a simple 2 dimensional lagrangian model which yields a broad suite of physically coherent simulations of the impacts of frequency changes in winter time northerly air outbreaks over the aegean levantine region we validate this with existing reconstructions from palaeoclimate proxy data with emphasis on well validated sea surface temperature reconstructions and a highly resolved cave speleothem stable oxygen isotope record from lebanon given that the rccs were clearly marked by negative sea surface temperature anomalies in the region we find that the predominant climatic impacts of this winter time mechanism were cold and wet in contrast with intercalated warmer and more arid conditions of non rcc periods more specifically the rccs are found to be periods of highly variable conditions with an overall tendency toward cold and wet conditions with potential for flash flooding and for episodic snow cover at low altitudes at least in the lower altitude lower 1 1 5 km regions of crete and the levant the modelled winter anomaly process cannot address underlying longer term astronomically forced trends or the relatively warm and arid anomalies in between rccs the latter require further study for example with respect to potential summer time extension of evaporative subtropical conditions over the region finally our results imply that the amount effect observed in levantine cave 18o and precipitation or drip water 18o may not reflect the conventional concept related to temperature dependent fractionation and rayleigh distillation instead it appears to arise from a complex and somewhat counter intuitive mixing in shifting proportionalities between advected external and evaporated mediterranean moisture

the cycle of instability stress release and fissure flow as controls on gully head retreat gully head and wall retreat has commonly been attributed to fluvial scour and head collapse as a result of soil saturation sapping or piping the empirical evidence to substantiate these conceptual models is sparse however and often contradictory this paper explores the hydrological and mechanical controls on gully head and wall stability by modelling the hydrology stability and elastic deformation of a marl gully complex in granada province south east spain the hydrological and slope stability simulations show that saturated conditions can be reached only where preferential fissure flow channels water from tension cracks into the base of the gully head and that vertical or subvertical heads will be stable unless saturation is achieved owing to the high unsaturated strengths of marl measured in this research failure in unsaturated conditions is possible only where the gully head wall is significantly undercut head retreat thus requires the formation of either a tension crack or an undercut hollow finite element stress analysis of eroding slopes reveals a build up of shear stress at the gully head base and a second stress anomaly just upslope of the head wall although tension cracks on gully heads have often been attributed to slope unloading this research provides strong evidence that the so called sapping hollow commonly found in the gully headwall base is also a function of stress release although further research is needed it seems possible that pop out failures in river channels may be caused by the same process the hydrological analysis shows that once a tension crack has developed throughflow velocity in the gully headwall will increase by an order of magnitude promoting piping and enlargement of this weakened area it is therefore possible to envisage a cycle of gully expansion in which erosion channel incision or human action unloads the slope below a gully head leading to stress patterns that account for the tension crack and a stress release hollow the tension crack promotes faster throughflow encouraging hollow enlargement and piping which undercut the gully head the tension crack permits the development of positive pore water pressures behind the gully head leading either to failure or contributing to toppling finally the debris may be eroded by fluvial action unloading a new section of slope and completing the cycle of gully head retreat copyright 2001 john wiley sons ltd

stonelines and landscape development on the laterized craton of madagascar in madagascar stonelines horizons of quartz pebbles in laterites are buried colluvial and alluvial lag gravels that outline former hill and valley surfaces their fabrics especially rare multiple stone layers identify the stonelines as old surface lags and the immature geochemical compositions of their over burdens relative to their substrates demonstrate burial by colluvium hill mantling stonelines are convex upward and less well developed whereas those lining valleys are concave to irregular thicker deeper better packed and sorted and have more rounded stones local differences in position between former and modern landforms demonstrate that in a complexly and tightly folded metamorphic terrain hills and valleys are likely to shift as the landscape is lowered by weathering thus implying that the landscape is held at a relatively submature stage of development

controlling factors of the size and location of large gully systems a regression based exploration using reconstructed pre erosion topography abstract the role of different factors potentially affecting the size and location of large gully systems is explored in two tributary basins of the tagus river s portugal the hillslopes of these basins corresponding to tertiary sedimentary formations are affected by hundreds of large gully systems varying in extent from somewhat 2 to 3 ha a study set of 90 gully systems were vectorized from aerial ortophotos and analysed in relation to a set of potential control variables obtained by reconstructing the pre erosion topography multiple linear regression and logistic regression were combined in order to investigate controls over the general morphometry of these landforms area perimeter and sinuosity and their location in the respective basins results indicate that gully systems initiated as bank gullies in response to an incision by the drainage network in both basins and then evolved as a function of upslope contributing area developing progressively more sinuous outlines as a result of headcut bifurcation pre erosion topographic form was shown to have only a marginal effect with results suggesting gully systems have grown essentially through mass movements in headcuts and sidewalls influenced by subsurface water

environmental influences over the last 16 ka on compound specific δ13c variations of leaf wax n alkanes in the hani peat deposit from northeast china compound specific carbon isotope ratios 13c of leaf wax n alkanes c21 c33 odd carbon numbered n alkanes were measured in the hani peat sequence from northeast china these data were compared with lipid biomarker compositions to assess changes in local vegetation and paleoclimate for the last 16 ka the 13c values of n alkanes range between 36 6 and 30 7 showing that the compounds originate from c3 plants much larger variations 5 4 in the n alkane 13c values than those of atmospheric co2 during the last 16 ka 0 5 indicate that the isotopic values were affected by environmental factors in addition to the postglacial 13c variations in the atmospheric reservoir the stratigraphic records of 13c reveal decoupled fluctuations among the individual n alkanes particularly between 15 5 and 11 4 ka synchronous excursions in the 13c offsets among individual n alkanes 13c and lipid biomarker paleoplant proxies paq and c23 c31 and c27 c31 from 14 9 to 13 2 ka and 12 7 to 11 6 ka suggest that vegetational changes are the most likely causes for the decoupled 13c variations parallel fluctuations of the 13c values of terrestrial higher plant derived c29 and c31n alkanes and the n alkane average chain length acl from 11 to 6 ka indicate that the 13c variations responded to net evaporation changes negative shifts in the n alkane 13c values coinciding with the acl decreases at 10 5 9 3 ka and 8 1 ka indicate the short term onset and fluctuations of the summer monsoon strength in eastern china during the early holocene

a typical calanchi landscape on the eastern apennine margin atri central italy geomorphological features and evolution abstract the surroundings of the town of atri abruzzo region central italy situated about 10 km from the adriatic shoreline can be considered as representative of most part of the italian seaward peninsular landscape the subject of this research the calanchi landscape often generally considered as badlands by non italian authors is in fact made up of many singular landforms each of which calanco corresponds to a more or less extended hydrographic unit the dynamics are mainly the result of the action of the particularly aggressive climatic factors such as the mediterranean rainfall regime on weak substrata clay silt and sand of the plio pleistocene marine cycles the morphogenetic activity is not only limited to channel erosion but it is also due to repeated superficial slides so that it should in fact be better to consider the calanco as the result of a combined erosion process sensu zachar d 1982 soil erosion elsevier amsterdam since the mechanism regulating this process remains unclear this work wants to offer a contribution to this research field multitemporal geomorphological analysis has helped us to distinguish the different areas in which the calanchi evolution has been more or less important in the past in such a way it has been possible to characterize the landscape evolution as a function of the parameters that influence soil loss especially in areas such as that of atri where calanchi like landforms are highly developed moreover this analysis coupled with the processing of 40 years rainfall data also taking into account the concurrent land use changes has clearly shown that the areas affected by calanchi erosion on the eastern apennine margin still tectonically active are progressively diminishing

permeability controls on aquathermal pressuring aquathermal pressuring refers to fluid pressures in excess of the hydrostatic which have been created by fluid thermal expansion against a less expansive sediment matrix two commonly stated objections to this mechanism are 1 hydraulic gradients and the finite but very low permeabilities now existing in the gulf of mexico are sufficient to dissipate aquathermal pressures and 2 the increasing temperatures decrease fluid viscosity at a rate so that hydraulic conductivity increases fast enough to dissipate these pressures evaluation of the momentum transport equations in the eulerian frame of reference indicates the first objection is not applicable because it treats the problem as steady flow and not transient flow furthermore existing data indicate that under no mal diagenetic conditions the decrease in intrinsic permeability caused by consolidation is greater than the viscosity effect therefore the two commonly stated objections to aquathermal pressuring do not by themselves prove the mechanism is ineffective in settings such as the gulf of mexico permeability increases by fracturing and faulting may however be sufficient to bleed off aquathermally produced excess pressures the measured very low permeabilities of gulf coast fine grained sediments indicate that aquathermal pressuring is a potentially important mechanism if the fine grained sediments do control the hydraulic response

the role of sidewall processes in gully development some n s w examples little attention has been paid to the role of sidewall processes in gully development simple estimates of linear incision sidewall erosion ratios at two localities in new south wales australia suggest that sidewall erosion is responsible for more than half the gully volume studies at three localities where overland flow and throughflow are limited to only one sidewall indicate that these processes are responsible for 10 30 per cent of gully volume these observations have important implications for gully management

paleohydrological changes in the eastern mediterranean region during the early to mid holocene recorded in plant wax n alkane distributions and δ13ctoc new data from tenaghi philippon ne greece abstract holocene climate dynamics have strongly influenced precipitation patterns in the eastern mediterranean region this holds particularly true for the 8 2 kyr bp climatic event arguably the strongest perturbation of early to mid holocene climate here we present a biomarker record of leaf wax derived n alkane distributions and stable isotopic composition of total organic carbon 13 c toc along with palynological data from the fen peat archive of tenaghi philippon tp ne greece spanning the interval from 8 7 to 7 5 kyr bp our record documents the response of in situ vegetation within the philippi peatland to changing hydrological conditions and addresses the applicability of organic proxies such as the aquatic index p aq average chain length acl and 13 c toc as indicators of peat surface moisture conditions at the study site the long chain n alkanes n c 27 n c 29 and n c 31 typical of vascular terrestrial plants dominated the peat sequence a period of relatively dry surface conditions indicated by low values of p aq and elevated acl values in concert with elevated 13 c toc values preceded the 8 2 kyr bp climatic event from ca 8 7 to 8 2 kyr bp slightly wetter more humid conditions suggested by an increase in p aq as well as reduced acl and 13 c toc values characterized the interval of the 8 2 kyr bp climatic event notably the increase in surface wetness as indicated by the biomarker record coincided with a marked rise in fern spore proportion as well as increasing proportion of pollen from aquatic taxa following the 8 2 kyr bp event a distinct change in paleohydrology at tp became apparent from ca 7 9 kyr bp onward an increase in the abundance of the mid chain length n alkanes n c 23 and n c 25 indicative of an increased contribution from aquatic plants to the sediment together with a steep increase in p aq and a decrease in acl as well as variation in 13 c toc imply considerably elevated surface moisture levels likely caused by the increased activity of the karstic system of the surrounding mountains collectively the biomarker proxies and pollen data reveal a concise picture of changing moisture conditions at tp in response to the 8 2 kyr bp climatic event

a north to south transect of holocene southeast atlantic continental margin sediments relationship between aerosol transport and compound specific δ13c land plant biomarker and pollen records 1 we examined near surface late holocene deep sea sediments at nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s along the southwest african continental margin contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 are indicators of land plant vegetation of different biosynthetic types which can be correlated with concentrations and distributions of pollen taxa in the same sediments calculated clusters of wind trajectories and satellite aerosol index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites this multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent dust and smoke aerosols are mainly derived from the western and central south african hinterland dominated by deserts semi deserts and savannah regions rich in c4 and cam plants the northern sites congo fan area and northern angola basin which get most of their terrestrial material from the congo basin and the angolan highlands may also receive some material from the chad region very little aerosol from the african continent is transported to the most southerly sites in the cape basin as can be expected from the present position of the phytogeographic zones the carbon isotopic signatures of the n alkanes and n alkanols both become isotopically more enriched in 13c from north to south the results of the study suggest that this combination of pollen data and compound specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

n alkane parameters from a deep sea sediment transect off southwest africa reflect continental vegetation and climate conditions abstract an isobathic transect of marine surface sediments from 1 n to 28 s off southwest africa was used to further evaluate the potential of the chain length distribution and carbon stable isotope composition of higher plant n alkanes as proxies for continental vegetation and climate conditions we found a strong increase in the n c 29 33 weighted mean average 13 c values from 33 near the equator to around 26 further south additionally c 25 35 n alkanes reveal a southward trend of increasing average chain length from 30 0 to 30 5 the data reflect the changing contribution of plants employing different photosynthetic pathways c 3 and c 4 and or being differently influenced by the environmental conditions of their habitat the c 4 plant proportions calculated from the data ca 20 for rivers draining the rainforest to ca 70 at higher latitude correspond to the c 4 plant abundance in continental catchment areas postulated by considering prevailing wind systems and river outflows furthermore the c 4 plant contribution to the sediments correlates with the mean annual precipitation and aridity at selected continental locations in the postulated catchment areas suggesting that the c 4 plant fraction in marine sediments can be used to assess these environmental parameters

plant wax δd values record changing eastern mediterranean atmospheric circulation patterns during the 8 2 kyr b p climatic event abstract throughout the holocene the climate of the mediterranean region has been strongly influenced by variability in the atmospheric circulation of the high and low latitudes a prominent example for such holocene climate perturbations is the 8 2 kyr b p climatic event reorganization of northern hemisphere atmospheric circulation patterns resulted in variations of temperature and precipitation distribution across the mediterranean the effects of changing high and low latitude atmospheric circulation on mediterranean climate in relation to the 8 2 kyr b p climatic event are however not well understood here we present a high resolution record of stable hydrogen isotope composition of plant wax n alkanes dwax across the 8 2 kyr b p climatic event from the tenaghi philippon peat deposit ne greece in order to characterize patterns of precipitation and changes in atmospheric circulation in the eastern mediterranean region our record reveals pronounced changes in dwax that correlate closely with previously published palynological data a long term decline in dwax values characterizes the lower part of the section the 8 2 kyr b p climatic event itself is connected to two distinct positive dwax excursions a minor shift in dwax around 8 2 kyr b p and a major shift in dwax between ca 8 1 and 8 0 kyr b p the upper part of the section shows a progressive trend towards higher dwax values we link shifts in dwax to changes in mediterranean air mass trajectories supplying precipitation to ne greece caused by variations in the relative contributions of northerly derived d depleted moisture and southerly derived d enriched moisture possible control mechanisms for alternating air mass trajectories include changes in the influence of the siberian high and differences in the influence of the african and asian monsoon circulation on anticyclonic conditions in the mediterranean region as well as regional inflow of moist air masses from the aegean sea

early and middle holocene in the aegean sea interplay between high and low latitude climate variability changes in the orbital parameters solar output and ocean circulation are widely considered as main drivers of the holocene climate yet the interaction between these forcings and the role that they play to produce the pattern of changes observed in different domains of the climate system remain debated here we present new early to middle holocene season specific sea surface temperature sst and d 18 oseawater results based on organic walled dinoflagellate cyst and planktonic foraminiferal data from two sediment cores located in the central sl21 and south eastern lc21 aegean sea eastern mediterranean today this region is affected by high to mid latitude climate in winter and tropical subtropical climate in summer the reconstructed d 18 o seawater from lc21 displays a marked w1 3 negative shift between 10 7 and 9 7 ka bp which represents the regional expression of the orbitally driven african monsoon intensification and attendant freshwater flooding into the eastern mediterranean a virtually contemporaneous shift of the same sign and magnitude is apparent in the d 18 ospeleothem record from soreq cave northern israel an important part of which may therefore reflect a change in the isotopic composition of the moisture source region aegean and levantine seas our sst reconstructions show that aegean winter ssts decreased in concert with intensifications of the siberian high as reflected in the gisp2 nss k record specifically three distinct sea surface cooling events at

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

badass gullies fluvio mass movement gully complexes in new zealand s east coast region and potential for remediation abstract this paper reviews gully erosion in the east coast region of new zealand s north island and conceptualises fluvio mass movement gully complexes as badass gully systems tectonic setting and lithological control with steep slopes and a climate influenced by tropical cyclones predispose hill country in the east coast region to gully erosion the clearance of indigenous forest since the late 1800s has dramatically increased catchment erosion and paved the way for development of large scale fluvio mass movement gully complexes these features are a composite of fluvial and mass movement processes they are conceptualised as badass by not conforming to any existing gully model and by generating disproportionate results in east coast catchment sediment cascades their remediation is discussed but their nature means that prevention is better than a cure

carbon isotope constraints on the deglacial co2 rise from ice cores the stable carbon isotope ratio of atmospheric co2 13catm is a key parameter in deciphering past carbon cycle changes here we present 13catm data for the past 24 000 years derived from three independent records from two antarctic ice cores we conclude that a pronounced 0 3 per mil decrease in 13catm during the early deglaciation can be best explained by upwelling of old carbon enriched waters in the southern ocean later in the deglaciation regrowth of the terrestrial biosphere changes in sea surface temperature and ocean circulation governed the 13catm evolution during the last glacial maximum 13catm and atmospheric co2 concentration were essentially constant which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then

rapid atmospheric co2 changes associated with the 8 200 years b p cooling event by applying the inverse relation between numbers of leaf stomata and atmospheric co2 concentration stomatal frequency analysis of fossil birch leaves from lake deposits in denmark reveals a century scale co2 change during the prominent holocene cooling event that occurred in the north atlantic region between 8 400 and 8 100 years b p in contrast to conventional co2 reconstructions based on ice cores from antarctica quantification of the stomatal frequency signal corroborates a distinctive temperature co2 correlation results indicate a global co2 decline of 25 ppm by volume over 300 years this reduction is in harmony with observed and modeled lowering of north atlantic sea surface temperatures associated with a short term weakening of thermohaline circulation

theoretical constraints to gully erosion research time for a re evaluation of concepts and assumptions gullies are conceptualized in the literature as essentially fluvial forms with dimensional boundaries arbitrarily defined between rills and river channels this notion is incompatible with the existing variability of form and process as mass movements frequently exert a fundamental control on gully initiation and expansion to the point of features outgrowing their original contributing area the inability of a conceptual framework to incorporate existing observations inevitably constrains methodologies and research results in this commentary several examples of published results are contrasted with the prevailing assumption of an essentially fluvial nature with the purpose of encouraging discussion on the need for a revised conceptual framework in gully erosion research copyright 2011 john wiley sons ltd

late postglacial paleoenvironmental change in the northeastern mediterranean region combined palynological and molecular biomarker evidence three gravity cores collected from the ne mediterranean nemr across a transect from the northern aegean sea north skyros basin to the south cretan margin scm were investigated for pollen and terrestrial biomarkers derived from epicuticular waxes of vascular plants during the last 20 ky pollen data show diversified mixed temperate forest in the northern borderlands and enhanced mediterranean vegetation in the southern areas documenting an n s climatic trend terrestrial plant biomarkers and their diagnostic geochemical indices exhibit latitudinal patterns which are interpreted in terms of the different delivery pathways fluvial runoff vs atmospheric transport resulting from the climate conditions during different periods during the late glacial and early deglaciation periods 20 14 ka bp relatively increased humidity h index is recorded in the north aegean sea while in the south drier climate was the limiting factor for vegetation development during this interval terrestrial n alkanes showed increased accumulation rates suggesting massive transport of terrestrial organic matter through runoffs and rivers followed by weaker input after 14 ka bp after 11 ka bp a major expansion of forest cover is evidenced in the nemr accompanied by a higher h index because of the climatic amelioration the forest vegetation exhibited regionally different characteristics with cool temperate taxa being more abundant in the aegean cores while the scm record is being featured by mediterranean elements at the onset of the holocene and throughout the holocene climatic optimum the delivery of terrestrial biomarkers increased and became more significant in the aegean sites compared to the scm site within the holocene the average chain length acl of long chain n alkanes exhibits lower values in the northern aegean than in the southeastern aegean and scm indicating the predominance of warmer species southwards finally the h index records a conspicuous humidity increase between 5 4 and 4 3 ka bp in the south aegean that coincides with an increase in the terrestrial biomarker supply and the deposition of a distinct sapropel like layer smh sapropel mid holocene similar trends in t temperature and h indices are slightly delayed and attenuated in the northern aegean and are accompanied by an increase in the acl index a noticeable increase in the accumulation rates ars of terrestrial biomarkers and the hpa index values during this period are clearly recorded in all three cores indicative of enhanced terrigenous inputs of organic matter along with higher in situ preservation

climate dynamics in the borderlands of the aegean sea during formation of sapropel s1 deduced from a marine pollen record abstract to unravel the climatic and environmental dynamics in the borderlands of the aegean sea during the early and middle holocene and notably for the interval of sapropel s1 s1 formation we have analysed terrestrial palynomorphs from a marine core in the northern aegean sea the qualitative results were complemented by quantitative pollen based climate reconstructions a land sea correlation was established based on pollen data and sediment lightness measurements from the same core and previously published benthic foraminifer data from a nearby core the borderlands of the aegean sea underwent a transition from an open vegetation to oak dominated woodlands between 10 4 and 9 5 ka cal bp a coeval increase in winter precipitation suggests that moisture availability was the main factor controlling holocene reforestation the 50 higher winter precipitation during s1 formation relative to pre sapropelic conditions suggests a strong contribution from the borderlands of the aegean sea to the freshwater surplus during s1 formation the humid and mild winter conditions during s1 formation were repeatedly punctuated by short term climatic events that caused a partial deforestation and a reorganisation within the broad leaved arboreal vegetation in the marine realm these events are documented by improved benthic oxygenation the strongest event represents the regional expression of the 8 2 ka cold event and led to an interruption in s1 formation except for the interval of s1 formation the pollen derived winter temperatures correlate with the smoothed gisp2 k series they support the previously published marine based concept that the intensity of the siberian high strongly controlled the winter climate in the aegean region during s1 formation in the aegean sea however climate conditions in the borderlands were more strongly affected by the monsoonally influenced climate system of the lower latitudes

effects of land use changes in vegetation cover and sidewall erosion in a gully head of the penedes region northeast spain the present research addresses the effects of land use changes in the evolution of vegetation cover on gully erosion in the penedes region of northeast spain the contribution of vegetation cover to gully wall stabilization is also discussed the catchment area of the gully is 60 2 ha and is mainly composed of vineyards in this area large gullies have developed on tertiary marls and unconsolidated sandstones detailed aerial photographs 1 5000 and 1 7000 scale of three dates 1975 1995 and 2002 were ortho rectified to derive land use information in the catchment gully vegetation cover and height information to construct detailed digital elevation models land use and gully vegetation cover mapping of the most recent period was assisted by means of fieldwork and a photo interpretation key constructed to help map the older dates soil loss in the catchment was estimated for the 1975 and 2002 scenarios to determine the relations between land use changes to vegetation cover changes and gully sidewall erosion the revised universal soil loss equation was applied for that purpose sidewall mass movements were determined by subtraction of digital elevation models 1 m resolution of each period the results show important land use changes in the catchment due to field reorganization for the plantation of mechanized vineyards it increased soil loss from agricultural fields by 26 5 which influenced vegetation cover dynamics on gully walls with an important development of scrubland to forest and gully erosion with sidewall retreat at rates of 0 025 to 0 50 ha y 1 and mass movements at rates of 16 to 63 2 mg ha 1 y 1 these results indicate that vegetation cover on gully walls although suggesting an improvement with respect to wall protection against splash sheet and rill erosion did not affect sidewall retreat and mass movements copyright 2009 john wiley sons ltd

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

the initiation and growth of gullies in madagascar are humans to blame abstract lavaka madagascar s unusual gullies require thick lateritic regolith on smoothly convex hills and they are initiated locally by a variety of cultural and natural proximate causes such as paths roads defensive trenches around hillforts steep fields unchanneled to slightly concentrated storm run off springs mass movements etc growth continues by rain attack incision by run off earthfalls caused by wetting and drying cycles and especially basal sapping by diffuse groundwater flow above bedrock somewhat in that order lavaka are less directly permitted and promoted by 1 hardening of exposed laterite surfaces which creates a hard soft hard profile from bedrock to laterite which favors incision relative to lateral erosion 2 the superimposition of concave run off profiles onto convex hills and locally 3 re equilibration of watersheds after stream piracy and faulting run off and hardening are interrelated with devegetation because hardening results from exposure following devegetation because both hardening and devegetation increase run off relative to infiltration and because hardening rain attack and run off impede vegetation devegetation is certainly worsened by harmful human activities such as range burning forest cutting and or overgrazing but tectonism and natural climatic aridification are probably ultimately more important given that many lavaka are simply a natural part of the landscape s evolution and that some lavaka clearly predate primary uncut rain forest

the marine isotope stage 1 5 cryptotephra record of tenaghi philippon greece towards a detailed tephrostratigraphic framework for the eastern mediterranean region abstract the iconic climate archive of tenaghi philippon tp ne greece allows the study of short term palaeoclimatic and environmental change throughout the past 1 3 ma to provide high quality age control for detailed palaeoclimate reconstructions based on the tp archive crypto tephra studies of a peat core tp 2005 have been carried out for the 0 130 ka interval the results show that the tp basin is ideally positioned to receive tephra fall from both the italian and aegean arc volcanic provinces two visible tephra layers the santorini cape riva y 2 c 22 ka and the campanian ignimbrite ci y 5 c 39 8 ka tephras and six primary cryptotephra layers namely the early holocene e1 tephra from the aeolian islands c 8 3 ka the campanian y 3 c 29 ka and x 6 tephras c 109 5 ka as well as counterpart tephras tm 18 1d c 40 4 ka tm 23 11 c 92 4 ka and tm 33 1a c 116 7 ka from the lago grande di monticchio sequence southern italy were identified along with repeatedly redeposited y 2 and ci tephra material bayesian modelling of the ages of seven of the primary tephra layers 60 radiocarbon measurements and 20 palynological control points have been applied to markedly improve the chronology of the tp archive this revised chronology constrains the age of tephra tm 18 1d to 40 90 41 66 cal ka bp 95 4 range several tephra layers identified in the tp record form important isochrons for correlating this archive with other terrestrial e g lago grande di monticchio sulmona basin and lake ohrid and marine e g adriatic sea core prad 1 2 and aegean sea core lc21 palaeoclimate records in the mediterranean region

the high resolution palaeoclimatic and palaeoceanographic history of the last 24 000 years in the central aegean sea greece abstract the palaeoclimatic and palaeoceanographic history of the n skyros basin central aegean sea was studied based on the planktonic foraminifera and the stable isotopes obtained from the sediments of a sediment core selected in this area the data were further supported by pollen and dinoflagellate cyst data the data correspond to a mean sampling interval of about 170 yrs and cover the last 24 000 yrs the variations in almost all of the records showed synchronicity suggesting the occurrence of a series of climatic changes the most pronounced climatic changes during the last glacial and late glacial periods are as follows i a brief relatively warm and humid event at 19 5 kyr ii two cold spells at 17 ka and 15 8 ka iii the climatic oscillation during the gi 1 event and iv the development of the younger dryas gs 1 event in two phases during the holocene epoch five brief cold and or arid phases occurred at around 10 5 ka 8 2 ka 7 ka to 6 ka 5 0 ka and 3 0 ka the most warm and humid holocene events correspond to the time of the deposition of the two sapropel sublayers s1a and s1b almost all of these brief climatic changes are coeval with equivalent changes in high northern latitude areas and with changes in the intensity of the siberian high suggesting a climatic link between the studied area and the high latitude areas the prevalence of holocene arid events which coincide with equivalent events recorded in north eastern africa and the middle east suggests a climatic link between the eastern and south eastern regions of the mediterranean sea

massive perturbation in terrestrial ecosystems of the eastern mediterranean region associated with the 8 2 kyr b p climatic event the climatic perturbation at ca 8 2 kyr b p is the strongest short term climate anomaly within the holocene it is generally attributed to a meltwater induced slowdown of the thermohaline circulation in the north atlantic model simulations and available proxy data suggest that it was strongest in the high to middle latitudes around the north atlantic based on new pollen data from tenaghi philippon northeastern greece we provide evidence for a massive climate induced turnover in terrestrial ecosystems of the aegean region associated with the 8 2 kyr b p event the reconstructed winter temperature decline of 4 c is much stronger than suggested by model simulations and proxy data from more northern latitudes of europe although the latter provide a direct downstream response to a north atlantic thermohaline circulation slowdown we attribute this discrepancy to mesoclimatic effects a stronger influence of the siberian high during the 8 2 kyr b p event may have enhanced the katabatic air flow from the mountains bordering the study site via a larger longer persisting snow cover our data demonstrate that high amplitude temperature anomalies and increased seasonality connected to the 8 2 kyr b p event may also have occurred in the lower mid latitudes much farther south than previously thought the magnitudes of these anomalies appear to have been strong enough to have seriously affected neolithic settlers in the northeastern mediterranean region

quantitative modeling of organic matter connectivity in source rocks using fractal geostatistical analysis abstract numerical modeling of hydrocarbon expulsion requires accurate assessment of the 3 d geometry and connectivity of hydrocarbon pathways such as pore systems organic matter networks fractures and stylolites in source rocks in this paper a method combining scanning electron microscopy sem digital image analysis fractal geostatistical analysis and a renormalization algorithm is developed to determine the 3 d geometrical properties defined as organic matter connectivity factor ocf of these pathways in source rocks the method is applied to derive fractal geostatistical models and the ocfs of organic matter networks omn of fourteen source rocks with wide variation in total organic carbon toc content and texture the results show that the connectivity of the omns is affected by both the amount and distribution of organic matter in source rocks uniformly distributed omns lose 3 d connectivity when the toc content is below approx 6 whereas omns with preferred orientation may maintain lateral connectivity at 4 and perhaps lower toc content thus in shales such as the bakken in which vertical omn connectivity may not exist the fracture systems may provide not only primary migration pathway but hydrocarbon reservoirs that are recharged through the laterally connected omns the method developed in this paper can be used to quantify geological models and average geological properties over a wide range of scales and thereby provide reliable geometric parameters for basin modeling using a numerical technique

erosion thresholds and suspended sediment yields waipaoa river basin new zealand characteristics of the suspended sediment load in the waipaoa river new zealand and in two of its tributaries mangatu and te arai rivers are examined for evidence of different dominant erosion processes in the basins upstream different shapes of the suspended sediment concentration water discharge relations lead to differences in long term average yield event yield magnitude frequency relations and relative importance of large flows and rare events in the mangatu river frequent runoff events 2 1 are relatively more important to the long term yield 11 540 t km yr half of the long term average load is transported by events with return periods less than 1 year and there is little evidence of an erosion threshold limitation on sediment supply this is consistent with the predominance in the mangatu basin of hillslope erosion processes that involve scour by surface and channelized runoff particularly gully erosion this contrasts with the te arai river where sediment concentration tends to be much lower at low and moderate flows frequent runoff events transport less of the long term yield 4600 t km 2 yr than do rarer large magnitude flood events event sediment yields are an order of magnitude lower during events with subannual return periods and half of the long term average load is transported during events with a return period of 2 years some of these characteristics appear to result in part from two populations of runoff events in the te arai basin nonetheless they are consistent with field evidence that most of the sediment supplied to the te arai stream network is generated by shallow landslides which are activated once a rainfall threshold is exceeded

holocene atmosphere ocean interactions records from greenland and the aegean sea we compare paleoclimate proxy records from central greenland and the aegean sea to offer new insights into the causes timing and mechanisms of holocene atmosphere ocean interactions a direct atmospheric link is revealed between aegean sea surface temperature sst and high latitude climate the major holocene events in our proxies of aegean sst and winter spring intensity of the siberian high gisp2 k record follow an 2300 year spacing recognised also in the 14c record and in worldwide holocene glacier advance phases suggesting a solar modulation of climate we argue that the primary atmospheric response involved decadal centennial fluctuations in the meridional pressure gradient driving aegean sst events via changes in the strength duration and or frequency of northerly polar continental air outbreaks over the basin the observed natural variability should be accounted for in predictions of future climate change and our timeframe for the aegean climate events in addition provides an independent chronostratigraphic argument to middle eastern archaeological studies

impact of lateglacial cold events on the northern aegean region reconstructed from marine and terrestrial proxy data marine palynomorph data paired with other indicators of sea surface hydrography planktic foraminiferal assemblages and oxygen isotopes were used to decipher the impact of cold events on the northern aegean region during the last glacial to interglacial transition the data which were derived from marine sediment cores geotusl152 and geotusl148 point to a strong impact of the heinrich 1 and younger dryas cold events on surface water conditions in the northern aegean sea shifts in marine palynomorph assemblages correlate with changes in terrestrial vegetation and climate i e precipitation and temperature reconstruc tions based on pollen assemblages in the northern borderlands of the aegean sea the climate responses of the aegean region to heinrich event 1 h1 ca 17 5 to ca 15 7 cal ka bp and younger dryas ca 12 6 to ca 11 7 cal ka bp events appear similar in magnitude with mean annual temperatures between 6 and 108c and mean annual precipitation between 300 and 450 mm however the annual temperature decline during the h1 relative to the preceding already cold conditions was minor 38c the transition from the relatively warm and humid local equivalent of the allerod interstadial to the younger dryas on the other hand witnessed an annual temperature decline of 68c and an annual precipitation decrease of 300 mm the latter occurring abruptly within only ca 150 a the return to warmer conditions in the northern aegean region after the younger dryas was completed at ca 11 6 cal ka bp copyright 2011 john wiley sons ltd

relationships between thermal maturity indices calculated using arrhenius equation and lopatin method implications for petroleum exploration thermal maturity can be calculated with time temperature indices tti based on the arrhenius equation using kinetics applicable to a range of types ii and iii kerogens these ttis are compared with tti calculations based on the lopatin method and are related theoretically and empirically via vitrinite reflectance to the petroleum generation window the ttis for both methods are expressed mathematically as integrals of temperature combined with variable linear heating rates for selected temperature intervals heating rates control the thermal maturation trends of buried sediments relative to arrhenius ttis lopatin ttis tend to underestimate thermal maturity at high heating rates and overestimate it as low heating rates complex burial histories applicable to a range of tectonic environments illustrate the different exploration decisions that might be made on the basis of independent results of these two thermal maturation models

lipid biomarkers in the zoige hongyuan peat deposit indicators of holocene climate changes in west china abstract lipid biomarkers extracted from a peat core obtained from the northeast edge of the tibetan plateau have provided a 13 kyr record of regional climate change a period of warmer climate corresponding to the holocene optimum between 9 ka and 5 ka is evident in greater alteration of n alkanoic acids and n alkanols and in the appearance of biomarkers indicative of greater microbial activity concomitant increases in local precipitation that raised the water level of the peat bog are recorded by increases in the proportions of c23 and c25 n alkanes that are mainly derived from submerged floating plants alternations in submergent and emergent plant n alkane proxies reveal multi decimeter scale rises and falls in the bog water level that relate to variation in precipitation on the tibetan plateau during the holocene major low water level events occurred around 12 6 11 3 10 7 9 4 8 3 6 0 4 5 3 1 2 1 and 1 0 ka these events correlate well with cold dry events recorded in same region from other climatic proxies that reflect millennial scale holocene instability in the asian monsoon system our biomarker results also indicate that peat accumulation and preservation on the tibetan plateau are more sensitive to variability in monsoonal precipitation than in annual temperature

stress fields a key to oil migration a coherent oil migration model based on geomechanical considerations includes both the high molecular kerogen structure and the capillary properties of source rocks oil is squeezed from kerogen by compaction following oil generation this squeezing effect should be created by the differential stress maximum compressive stress minus least compressive stress acting on the kerogen which has been chemically broken up by oil formation in sedimentary bodies whose water is at hydrostatic pressure the migration of oil seems to involve two processes 1 lateral transfer by channeling into the more coarsely microporous layers of the source rocks from the oil generation site toward the geologic structure or lower pressured zone and 2 vertical transfer from source rock to eservoir by the opening or reopening of vertical fractures in the few areas such as structural tops where the least compressive stress is slightly greater than or equal to the pore pressure and where the capillary pressure increment 2 ggr r of oil in the microporosity exceeds the tensile strength of the rock in sedimentary bodies whose water is overpressured the pore pressure should be governed by the least compressive stress and thus migration should begin by oil transfers in a system of small open fractures and eventually in larger fractures the theory demonstrates the impossibility of oil being transferred to the reservoir under true tensile conditions negative effective compressive stress and thus explains the large asphaltic veins of southeastern turkey and the well known bitumen veins of the uinta basin

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

paleoclimate variability in central taiwan during the past 30 kyrs reflected by pollen δ13ctoc and n alkane δd records in a peat sequence from toushe basin abstract a total of 233 samples from the upper 16 m of the toushe peat core retrieved in central taiwan were measured for toc and 13ctoc values from these samples 17 selected samples with large 13ctoc fluctuations were analyzed for n alkane and d of the c27 and c29 n alkanes combining with the detailed high resolution pollen and geochemical records this study reveals more detailed climatic variations in terms of temperature and precipitation as well as abrupt climatic events during the past 30 kyrs before the last glacial maximum lgm climate was cold and damp with predominantly woodland vegetation in toushe basin and turned to cold and dry after 25 kyr bp climatic conditions there were the worst during lgm over the past 30 kyrs especially around 23 and 18 kyr bp when the woodland was diminished and c4 grass was dominated although short durations of relatively wet conditions could be found at 17 16 and 14 kyr bp cold and dry climates were prevailing during 29 5 28 24 22 17 15 and 13 11 5 kyr bp corresponding to heinrich h events 3 2 1 and younger dryas yd respectively during the early holocene dry climate occurred at 11 10 9 7 9 2 and 8 kyr bp whereas wet condition appeared at 10 3 9 8 9 7 5 kyr bp in the middle holocene climate kept warm and moderate wet in the first half period but many dry events existed in the second half following a cold and dry event at 6 kyr bp after a sharply warm peak at 5 2 kyr bp the climate in toushe turned to cold quickly and tree shrub vegetation disappeared completely with the replacement of c3 grasses in the late holocene climate was relatively wetter with predominant c3 grasses in the basin our climatic interpretations based on the peat records agree well with the greenland ice core and chinese speleothem records on millennium time scales during the last glacial period dry climates corresponding to weakening of the east asian summer monsoon easm during the heinrich events and younger dryas in central taiwan and eastern china demonstrate the climatic forcing on such long time scales in concert with regional monsoon climate however the discrepancies exist between our peat record and the dongge hulu stalagmite record on 1 the age of h2 2 climate intensities of lgm and h1 and 3 wetness condition during holocene these observations call for further study on high resolution climatic changes especially on moisture budget in the east asian monsoonal region

shakedown in madagascar occurrence of lavakas erosional gullies associated with seismic activity erosion via lavaka formation is widespread in madagascar but controls on why and where lavakas occur are not understood geographic information system analysis reveals a spatial correlation between lavaka abundance and the frequency of seismic events most lavakas occur in or near areas where recorded earthquakes magnitude 0 5 5 6 are most frequent this correlation explains the unevenness of lavaka distribution in the malagasy highlands and highlights the importance of natural factors in lavaka formation seismic activity appears to precondition the landscape to lavaka formation although the mechanism by which this happens is not yet known recognizing the connection however allows us to pinpoint areas prone to future lavaka development in zones of active deforestation areas with the greatest frequency of seismic events are most at risk for high density lavaka development

organic geochemical evidence of late glacial holocene climate instability in the north aegean sea sedimentary molecular biomarker compositions organic carbon and caco3 concentrations and bulk organic 13c and total 15n values document a series of paleoclimatic changes that have affected organic matter production and sedimentation in the north aegean sea from the termination of the latest glacial maximum through the middle holocene continental environmental conditions have been inferred from land plant biomarkers paleoproductivity patterns of diatoms prymnesiophytes dinoflagellates and nannoplankton were discerned from marine derived biomarkers although organic matter is predominantly marine variations in the proportion of marine and land contributions and in its general preservation are evident rapid changes in the eastern mediterranean thermohaline circulation evidently occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation accompanied cold intervals in the late last glacial the younger dryas and during an interruption of deposition of the s1 sapropel probably in response to strengthening of north winds over the region in contrast decreased thermohaline circulation occurred during the warm interval associated with the s1 sapropel during this period increased freshwater inputs diminished ventilation of deep water masses and enhanced organic matter production and preservation intriguing fluctuations in sea surface temperatures and the concentrations of marine and terrestrial biomarkers within the sapropelic layer most prominently in the interruption from 8 2 to 7 8 calibrated radiocarbon conventional kyr bp support the hypothesis that several distinct events of deep water reoxygenation occurred in the north aegean sea during deposition of the s1 sapropel these events reflect centennial excursions to the more common low productivity and well ventilated conditions of the mediterranean that may possibly be related to north atlantic oscillation cycles

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

late glacial holocene climate variability at the south eastern margin of the aegean sea abstract new micropaleontological palynological and geochemical results from a relatively shallow 500 m sediment core ns 14 in the south eastern aegean sea provide a detailed picture of the regional expression of sapropel s1 formation in this sub basin of the eastern mediterranean sea specifically freshwater input during 10 6 10 0 ka bp has preceded the deposition of s1 further decrease in surface water salinity is evidenced between 10 0 and 8 5 ka bp at the lower part of s1a which in respect to s1b is featured by warmer 19 5 c and more productive surface waters associated with dysoxic bottom conditions a series of coolings detected within the s1 depositional interval may be linked to outbursts of cold northerly air masses and relevant pulses in the deep intermediate water ventilation that caused the s1 interruption between 7 9 and 7 3 ka bp and culminated during the deposition of s1b with the decline of deep chlorophyll maximum dcm at 6 5 ka bp the climate instability and the relevant absence of anoxia weakened the organic matter preservation in the shallow south eastern aegean margin during the s1 times ns 14 record provides evidence for a distinct mid holocene warm up to 25 c and wet phase associated with the deposition of the sapropel like layer smh sapropel mid holocene between 5 4 and 4 3 ka bp the smh layer could represent evidence of on going albeit weak african monsoon forcing only expressed at the south eastern edge of the aegean sea its end is associated with the 4 2 ka bp northern hemisphere mega drought event and the termination of the african humid period at 3 8 ka bp

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

medium term gully headcut retreat rates in southeast spain determined from aerial photographs and ground measurements this paper deals with gully retreat rates at different time scales whereby the short term time scale may span a time interval of 1 5 years the medium term time scale a time interval of 5 50 years and the long term time scale a time interval of more than 50 years an analysis of high altitude aerial photographs in combination with ground measurements allowed us to quantify volumetric gully head retreat rates for 12 permanent gullies in southeast spain guadalentin and guadix study areas over a 40 43 year time interval medium term time scale this resulted in an average retreat rate ve of 17 4 m3 year 1 a power relationship between drainage basin area a and medium term volumetric gully head retreat rate ve 0 069a0 380 r2 0 51 n 21 was found by combining the gully head retreat rates obtained in this study with those obtained by a dendrochronological method the exponent b and the coefficient of determination r2 of the power relationships ve aab increases from the short term to the long term time scale expressing the increasing importance of drainage basin area in gully development with time considerable differences between gully head retreat rates measured at the short and medium term time scales at individual gullies showed the importance of land use changes and unsuccessful management practices on gully head retreat and the episodic nature of gully head retreat when piping and tension cracking are involved higher gully head retreat rates are obtained at the medium term time scale compared to the short term time scale but the differences are not significantly different at 10 the medium term methods tend to measure proportionally more high gully retreat rates but less extreme values compared to the short term method this is explained by a more equal distribution of extreme rainfall events both in space and time at a longer term time scale and hence a higher probability of measuring the average effect of both small and extreme rainfall events at each gully

gully position characteristics and geomorphic thresholds in an undisturbed catchment in northern australia gullying is a significant process in the long term dynamics and evolution of both natural and rehabilitated i e post mining landscapes from a landscape management perspective it is important that we understand gully initiation and development as it is well recognized that catchment disturbance can result in the development of gullies that can be very difficult to rehabilitate this study examines gully position using geomorphic statistics relating to features such as depth width and length in a catchment undisturbed by european activity in the northern territory australia the results demonstrate that gullying occurs throughout the catchment and that a slope area threshold does not exist and that gully position broadly follows the catchment area slope relationship simple relationships relating catchment area and slope to gully depth width and length provide poor results despite these relationships having been found to apply for ephemeral gullies in cropland the results suggest that gully initiation thresholds are low as a result of an enhanced fire regime a threshold model for gully position that uses catchment area and slope to switch between gully and hillslope was evaluated and found broadly to capture gully position copyright 2006 john wiley sons ltd

patterns of development of lavaka madagascar s unusual gullies lavaka madagascar s abundant gullies show a complex pattern of development fourteen independent measures of size and shape in 93 lavaka were investigated by principal components analysis and discriminant function analysis typical lavaka start either as wounds and raw patches on mid hillside that develop step like head scarps or as toe slopes collapsed by seepage slumping or undercutting they become deep raw vertical sided teardrop to heart shaped gashes that may be deepest and broadest uphill as the walls retreat slump and become overgrown lavaka become longer broader gentler and partly filled concavities they can grow to reach from the valley floor to the hill crest or even beyond the crest before healing over unless excessive erosion creates tors and inselbergs they heal over and end up as unremarkable hillside reentrants and side valleys

gully head erosion processes on a semi arid valley floor in kenya a case study into temporal variation and sediment budgeting a three year monitoring programme of gully head retreat was established to assess the significance of sediment production in a drainage network that expanded rapidly by gully head erosion on the low angled alluvio lacustrine njemps flats in semi arid baringo district kenya this paper discusses the factors controlling the large observed spatial and temporal variation in gully head retreat rates ranging from 0 to 15 m a 1 the selected gullies differed in planform and in runoff contributing catchment area but soil material and land use were similar the data were analysed at event and annual timescales the results show that at annual timescale rainfall amount appears to be a good indicator of gully head retreat while at storm event timescale rainfall distribution has to be taken into account a model is proposed including only rainfall p and the number of dry days dd between storms which explains 56 per cent of the variation in retreat rate of the single headed gully of lam1 a detailed sediment budget has been established for lam1 and its runoff contributing area rca by measuring sediment input from the rca the sediment output by channelized flow and linear retreat of the gully head for nine storms it can be seen that erosion shifts between different components of the budget depending on the duration of the dry period dd between storms sediment input from the rca was usually the largest component for the smaller storms the erosion of the gully head occurred as a direct effect of runoff falling over the edge ghwaterfall and of the indirect destabilization of the adjacent walls by the waterfall erosion and by saturation ghmass storage the latter component ghmass storage was usually much larger that the former ghwaterfall the sediment output from the gully was strongly related to the runoff volume while the linear retreat because of its complex behaviour was not overall the results show that the annual retreat is the optimal timescale to predict retreat patterns more detailed knowledge about relevant processes and interactions is necessary if gully head erosion is to be included in event based soil erosion models copyright 2001 john wiley sons ltd

the 8 2 kyr bp event simulated by a global atmosphere sea ice ocean model seven freshwater perturbation experiments were performed with a global atmosphere sea ice ocean model to study the mechanism behind the 8 2 kyr bp holocene cooling event these experiments differed in initial state and duration of the applied freshwater pulse while the amount of freshwater was kept constant 4 67x10 14 m 3 one of the scenarios with freshwater added to the labrador sea at a rate of 0 75 sv during 20 years resulted in weakening of the north atlantic thermohaline circulation during 320 years and surface cooling varying from 1 to 5 degreesc over adjacent continents this result is consistent with proxy data suggesting that a meltwater induced weakening of the thermohaline circulation caused the event moreover our results indicate that the time scale of the meltwater release and the initial state are important as both have a strong effect on the magnitude and duration of the produced model response

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

medium term evolution of a gully developed in a loess derived soil field surveys in the belgian loess belt revealed the presence in many forested areas of large permanent gully systems most of which are currently inactive in cultivated areas such gullies can only be observed in cross sectional soil profiles through hollows as virtually all such large gullies are currently infilled with colluvium little is known about the spatial distribution initiation and temporal evolution of these large permanent gully systems on loess derived soils therefore the medium term evolution of a gully initiated in a cultivated area on loess derived soils southwest of leuven belgium in may june 1986 was studied over 13 years two intense rainfall events created this ephemeral gully which was not erased by subsequent tillage between june 1986 and the december 1999 eight field surveys were conducted to measure gully dimensions during two surveys topographic indices e g slope and drainage area were also measured daily rainfall for the measuring period were obtained from a rainfall station located some 10 km southwest of the gully analysis of rainfall data showed that no extreme rainfall event was required to initiate such large permanent gullies as observed in forested areas and through cross sectional profiles in cultivated fields in the belgian loess belt return periods of the event that caused the gully varied between 1 year and 25 years depending on the assumptions used for defining event rain intensity once established length surface area and volume of the studied gully evolved with time cumulative rainfall or cumulative runoff following a negative exponential relation this accords with observations reported for gullies in australia and the usa this study shows that a degressive increase of gully extension can be largely explained by the evolution of a slope drainage area factor s a which is proportional to stream power with time while gully length and gully surface area asymptotically evolve towards a final value gully volume decreased at a given point in time from this it is inferred that sediment deposition will potentially infill the gully to such an extent that the farmer can drive across it from this moment on the combined effect of water and tillage erosion in the gully drainage area will lead towards rapid infilling this expected evolution of a gully in cultivated fields accords with observations of large infilled gully systems in cultivated areas in eastern belgium the permanent gullies observed under forest are attributed to the fact that after severe gully erosion this area was reforested or abandoned therefore the sediment source was cut off and the gully was not filled in by sediment deposition

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

effect of lake evaporation on δd values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany compound specific hydrogen isotope ratio values of lacustrine n alkanes from two contrasting ecosystems the semiarid to arid nam co central tibet and the humid holzmaar germany were compared in order to assess whether or not these environmental conditions are recorded in the isotopic signatures of biomarkers increased evaporation of lake water at nam co is recorded by the n alkanes of aquatic origin hence isotopic enrichment results in a di erence between terrestrial and aquatic n alkanes in the opposite direction 68 from that known for humid climate conditions 30 predominating at holzmaar based on this isotopic di erence between terrestrial and aquatic n alkanes evaporation to inflow ratio e i values were estimated and suggest that the isotopic di erence is indicative of the general hydroclimatic characteristics of a lake system moreover the comparison with e i values calculated with actual stable water isotope data showed that the dd values of aquatic and terrestrial lacustrine n alkanes serve as a proxy for the relative isotopic di erences between lake and inflow waters and can be used to assess the proportion of water undergoing evaporation relative to the inflow and thus to reconstruct the lake water balance in the past 2008 published by elsevier ltd

gully erosion impacts factors and control gully erosion attracts increasing attention from scientists as reflected by two recent international meetings poesen and valentin eds catena 50 2 4 87 564 li et al 2004 gully erosion under global change sichuan science technology press chengu china 354 pp this growing interest is associated with the increasing concern over off site impacts caused by soil erosion at larger spatial scales than the cultivated plots the objective of this paper is to review recent studies on impacts factors and control of gully erosion and update the review on dgully erosion and environmental change importance and research needst poesen et al 2003 catena 50 2 4 91 134 for the farmers the development of gullies leads to a loss of crop yields and available land as well as an increase of workload i e labour necessary to cultivate the land gullies can also change the mosaic patterns between fallow and cultivated fields enhancing hillslope erosion in a feedback loop in addition gullies tend to enhance drainage and accelerate aridification processes in the semi arid zones fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion in this respect tracers such as carbon nitrogen the nuclear bomb derived radionuclide 137 cs magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment recent studies conducted in australia china ethiopia and usa showed that the major part of the sediment in reservoirs might have come from gully erosion gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess european belt chinese loess plateau north america and sandy soils sahelian zone north east thailand or in soils prone to piping and tunnelling such as dispersive soils most of the time the gullying processes are triggered by

modeling the occurrence of overpressures on the scotian shelf offshore eastern canada many wells on the scotian shelf offshore from nova scotia have drilled into overpressured zones in particular the wells comprising the venture gas field have all encountered overpressures at depths below 4 5 km the characteristics of the overpressure zones in the venture field vary in some important details from overpressured zones on the u s gulf coast in the venture field the shales in the overpressured zones are observed to be normally compacted and interbedded with layers of overpressured sandstones this is in contrast to the gulf coast where the shales in the overpressure zone are undercompacted resistivity logs sonic logs and bulk density logs all provide some indications of overpressures in the venture field but are not as unequivocal indicators of overpressure as they are on the gulf coast theoretical investigations of the causes of overpressures in an environment such as the venture field show that overpressures are unlikely to be caused by loading of sediments the most probable cause of overpressures is recent and continuing fluid generation which is related to the transformation of kerogen to hydrocarbons limits are placed on the average permeabilities and fluid generation rates which are required if overpressures are to be produced by fluid generation

controlling factors of gullying in the maracuja catchment southeastern brazil hundreds of gullies vocorocas of huge dimensions up to 400 500 m long 150 m wide and 50 m deep are very common in the small maracuja catchment in southeastern brazil these erosional features which occur with an uneven intensity throughout the area started due to bad soil management practices at the beginning of european settlement at the end of the 17th century and nowadays are still evolving but at a slower rate as surface soils are usually very resistant to erosion the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning an analysis of well known erosion controlling factors was performed aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution data shows that geology and mainly geomorphology are the main controlling factors since gullies tend to be concentrated in basement rock areas with lower relief domain 2 of maracuja catchment mainly at the fringes of broad and flat interfluves at the detailed scale 1 10 000 gullies are more common in amphitheatre like headwater hollows that frequently represent upper quaternary gullies paleogullies which demonstrate the recurrence of channel erosion so gullies occur in areas of thicker saprolites domain 2 in places with a natural concentration of surface and underground water hollows saprolites of the preserved non eroded hollows are usually pressurized confined aquifer due to a thick seal of quaternary clay layer in a similar configuration to the ones found in hollows of mass movement mudflow sites in southeastern brazil therefore the erosion of the resistant soils by human activities such as road cuts and trenches valos or their mobilization by mudflow movements seem to be likely mechanisms of gullying initiation afterwards gullies evolve by a combination of surface and underground processes such as wash and tunnel erosion and falls and slumps of gully walls copyright 2005 john wiley sons ltd

carbon cycle perturbation and stabilization in the wake of the triassic jurassic boundary mass extinction event 1 the triassic jurassic boundary mass extinction event t j 199 6 ma is associated with major perturbations in the carbon cycle recorded in stable carbon isotopes two rapid negative isotope excursions in bulk organic carbon 13corg occur within the immediate boundary interval at multiple locations and have been linked to the outgassing of 12c enriched co2 from the central atlantic magmatic province in british columbia a positive 13corg excursion of 5 vienna peedee belemnite v pdb spans part or all of the subsequent hettangian stage here we examine the significance of these carbon isotope excursions as records of global carbon cycle dynamics across the t j boundary and test the link between carbon cycle perturbation stabilization and biotic extinction recovery patterns a combination of 13corg and palynological analyses from the late triassic to early jurassic in the mingolsheim core germany suggests that organic carbon isotope variations are best explained as the result of both compositional changes in terrestrial versus marine input and disturbance and recovery patterns of major terrestrial plant groups across the t j boundary a new high resolution 13ccarb record from the val adrara section in the southern alps italy spanning from the uppermost rhaetian through lower sinemurian does not exhibit a negative excursion at the t j boundary but does record a large positive 13ccarb excursion of 4 v pdb in bulk carbonate that begins at the t j boundary and reaches a local maximum at the early late hettangian boundary values then gradually decrease reaching 0 5 at the hettangian sinemurian boundary and remain relatively constant into the early sinemurian complementary 13ccarb data from 4 more sections that span the hettangian sinemurian boundary support carbon cycle stabilization within the upper hettangian our analyses suggest that isotope changes in organic carbon reservoirs do not necessarily require a shift in the global exogenic carbon reservoir and that the positive excursion in the carbonate carbon isotope record is best explained as the combined result of an increase in atmospheric pco2 leading to accelerated carbon cycling decreased skeletal carbonate production and increased organic carbon burial lasting several hundred thousand years the termination of the positive inorganic carbon isotope excursion coincides with the recovery of marine skeletal carbonate producers and coeval changes in terrestrial vegetation and reflects the gradual reduction in pco2 and the stabilization of the global carbon cycle during the sinemurian

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

development of badlands and gullies in the sneeuberg great karoo south africa abstract the study aims to examine the origin and development of land degradation with particular emphasis on badland and gully systems in the sneeuberg uplands of the great karoo this is an area of semiarid extensive stock farming where land degradation in the form of rill and gully erosion has accompanied the replacement of grassland by shrub vegetation species diversity has declined and ground cover has been reduced leading to a positive feedback loop which exacerbates the degradation many foot slopes developed in shales clays and colluvium have extensive incipient badland development with closely spaced gullying up to 1 5 m deep in valley bottom and valley side depression locations gullies up to 8 m deep have developed usually cut to bedrock through valley fills of mainly holocene colluvium both badlands and gullies appear to have developed since european settlement and to be part of the same hydrological system with extensive areas of bare ground badlands feeding water to incising gullies experiments using simulated rainfall throw some light on current processes badland areas are active under high frequency low magnitude rainfall events major gullies are likely to be the result of occasional high magnitude events but these have not been observed overgrazing in the past is the most likely cause of the degradation

molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction a 40 cm deep sphagnum dominated peat monolith from bolton fell moss in northern england was systematically investigated by lipid molecular stratigraphy and compound specific 13c and d analysis using gas chromatography gc gc mass spectrometry gc ms gc combustion isotope ratio ms gc c irms and gc thermal conversion irms gc tc irms techniques 210pb dating showed the monolith accumulated during the last ca 220 yr a period encompassing the second part of little ice age while the distributions of lipids including n alkan 1 ols n alkan 2 ones wax esters sterols n alkanoic acids alkandioic acids and hydroxy acids display relatively minor changes with depth the cooler climate event was recorded in the concentrations of n alkanes and organic carbon cpi values of n alkanes and n alkanoic acids and the ratio of 5 n alkylresorcinols sterols superimposed on the fossil fuel effect the relatively cooler climate event was also recorded by 13c values of individual hydrocarbons especially the c23n alkane a major compound in certain sphagnum spp the d values of the c29 and c33n alkanes correlated mainly with plant composition and were relatively insensitive to climatic change in contrast the c23n alkane displayed variation that correlated strongly with recorded temperature for the period represented by the monolith agreeing with previously reported deuterium records in tree ring cellulose spanning the same period in scotland germany and the usa with more negative values occurring during the second part of little ice age these biomarker characteristics including the compound specific 13c and d records provide a new set of proxies of climatic change potentially independent of preserved macrofossils which will be of value in deeper sections of the bog where the documentary records of climate are unavailable and humification is well advanced

soil development over mud rich rocks produces landscape scale erosional instabilities in the northern gabilan mesa california in soil mantled landscapes the length of hillslopes is set by the relative efficiency of hillslope transport processes and incision by channelized flows in cases where rapid channel incision exposes less weathered more resistant rocks incision should slow creating a damping feedback that prevents runaway channel expansion we present observations from the northern gabilan mesa central coast ranges california which is underlain by mud rich rocks that provide less resistance to erosion than the soils produced from them this strength inversion arises because unconfined mud rich units of the pancho rico formation undergo a process called slaking in which pervasive fractures spaced centimeters apart develop when subjected to wet dry cycles in contrast consecutive wetting and drying cycles have produced a cohesive regolith with higher tensile strength than the slaked bedrock exposure of the relatively weak bedrock may create a positive feedback where the acceleration of erosion within the bedrock undermines the cohesive regolith and allows channels to expand headward at the expense of hillslopes geomorphic mapping reveals numerous channelized features that have incised deeply into bedrock and crosscutting relationships and topographic analyses indicate that these features have consumed regions of the landscape previously occupied by hillslopes however these features are only present in south flowing drainages where soil is thinnest and therefore bedrock is most likely to be exposed by increases in erosion rate preferential headward expansion of these south flowing channels has established a profound topographic asymmetry where south flowing tributaries occupy 75 of drainage basin width these results suggest that processes operating at the scale of the critical zone which may be unique to certain rock types conspire to produce an instability that shapes the morphology of drainage basins

postglacial climate change record in biomarker lipid compositions of the hani peat sequence northeastern china abstract the peat sequence at hani in northeastern china accumulated over the past 16 cal kyr in a percolation mire in which rain water and ground water seeped through the peat system the molecular compositions of n alkanes n alkanols and n alkanoic acids extracted from the hani peat sequence reveal different responses to the progressive evolution of climate and changes in the nature of the peat forming vegetation long chain length components that originate from the waxy coatings of subaerial vascular plants dominate the n alkane distributions throughout the hani peat sequence the paleoclimate integrity of these biomarker molecules appears to be well preserved most of the n alkanol distributions are similarly dominated by long chain components that indicate their origins from subaerial plants in contrast n alkanoic acid distributions are dominated by secondary components that record the importance of post depositional microbial activity in this peat sequence which evidently can be extensive in a percolation mire elevated n alkane paq values and c23 c29 ratios which are both molecular proxies for water loving plants record an especially moist local climate in the bolling allerod 14 5 to 12 9 ka younger dryas 12 9 to 11 5 ka and pre boreal 11 5 to 10 5 ka portions of the hani peat sequence depressed paq values and c23 c29 ratios and larger n alkane average chain length values indicate that the holocene climatic optimum 10 5 to 6 ka was a period of warmer climate with lower effective precipitation which contrasts with evidence of wetter climates in most of east asia

alluvial gully erosion an example from the mitchell fluvial megafan queensland australia considerable attention has been focused on the role of gullies as a contributor to contemporary sediment loads of rivers in australia in southern australia rapid acceleration of hillslope gully erosion has been widely documented in the post european period last 200 years in the northern australian tropics however gully erosion processes operating along alluvial plains have not been well documented and can differ substantially from those gullies eroding into colluvium on hillslopes aerial reconnaissance surveys in 2004 along 13 500 km of the main stem rivers that drain into the gulf of carpentaria goc identified extensive areas of alluvial lands that have been impacted by a pervasive form of gully erosion more detailed remote sensing based mapping within the 31 000 km2 mitchell river fluvial megafan has identified that active gullying into alluvium occupies 0 4 129 km2 of the lower mitchell catchment these alluvial gullies are concentrated along main drainage channels and their scarp heights are highly correlated to the local relief between the floodplain and river thalweg while river incision into the megafan since the pleistocene has developed the relief potential for erosion other factors such as floodplain hydrology soil dispersibility and vegetation also influence the distribution of gullies in this paper we present a conceptual model of alluvial gullies and contend that they represent a distinct end member in the continuum of gully forms that have been described in the geomorphic literature an understanding of the processes driving this form of alluvial gullying can only be gained when they are differentiated from widely described colluvial hillslope gully models and theories we present evidence of type examples of alluvial gullying in the mitchell and through analysis of their distribution and morphology at different scales highlight some of the key mechanisms that are potentially initiating these features and driving their expansion copyright 2009 john wiley sons ltd

holocene seasonality changes in the central mediterranean region reconstructed from the pollen sequences of lake accesa italy and tenaghi philippon greece this study presents pollen based climate reconstructions of holocene temperature and precipitation seasonality for two high resolution pollen sequences from the central lake accesa central italy and eastern mediterranean tenaghi philippon greece regions the quantitative climate reconstruction uses multiple methods to provide an improved assessment of the uncertainties involved in palaeoclimate reconstructions the multimethod approach comprises partial least squares regression weighted average partial least squares regression the modern analogues technique and the non metric multidimensional scaling generalized additive model method we find two distinct climate intervals during the holocene the first is a moist period from 9500 to 7800 cal bp characterised by wet winters and dry summers resulting in a strongly seasonal hydrological contrast stronger than today that is interrupted by a short lived event around 8200 cal bp this event is characterised by wet winters and summers at accesa wh