geochemical characteristics and depositional environment of paleogene lacustrine source rocks in the lufeng sag pearl river mouth basin south china sea abstract a systematic geochemical analysis of samples from newly drilled wells in the lufeng sag pearl river mouth basin has been carried out to characterize source rock quality determine organic matter input and reconstruct the depositional environment of the enping and wenchang formations total organic carbon toc content ranges from 0 46 to 1 57 wt in the enping formation and from 0 53 to 6 10 wt in the wenchang formation kerogen types i ii were identified in the wenchang formation samples while kerogen types ii iii were identified in the enping formation samples maturity parameters suggest marginally mature to mature levels for most samples with higher maturity for the wenchang formation samples biomarker assemblage and trace element ratios of the wenchang and enping formations are distinctively different indicating predominantly aquatic origin organic matter input under suboixc anoxic water conditions for the wenchang formation and more allochthonous terrestrial organic matter input under oxic water conditions for the enping formation moderate to high primary productivity and temperature drove water stratification together with weak detrital material dilution led to the enrichment of organic matter in the wenchang formation while the low primary productivity poor preservation conditions and high dilution led to the relatively poor source rock quality in the enping formation

observations of variability on synoptic timescales in the east pacific itcz abstract data obtained in the eastern pacific intertropical convergence zone itcz during the tropical eastern pacific process study tepps show a 3 6 day variability the noaa ship ronald h brown collected surface meteorological observations c band doppler radar volumes atmospheric soundings and rainfall data while on station at 7 8 n 125 w from 8 23 august 1997 the 3 6 day variability was a prominent timescale in the meridional wind and humidity data the maxima of the surface to 700 mb meridional wind anomalies were 5 12 m s 1 maxima of the moisture anomalies at the same levels were 1 3 g kg 1 in phase with the low level southerlies while upper level moisture lagged the southerlies by less than a day the radar indicated a close connection between precipitation in the vicinity of the ship and the meridional wind with the precipitation occurring when the surface southerlies were strongest the meridional and zonal wind components had a maximum of 850 450 mb wind shear during the southerly e

response of the eastern tropical pacific to meridional migration of the itcz the generation of the costa rica dome abstract a regional ocean circulation model with fine horizontal resolution has been developed in order to obtain a coherent seasonal picture of the eastern tropical pacific off central america the costa rice dome with a cyclonic circulation grows rapidly in late spring off the gulf of papagayo and matures in summer and early fall in accord with the northward migration of the itcz in winter strong northern converging in the southernmost itcz from three passes in central america excite warm anticyclones nonlinear eddies confined in the upper layer those anticyclones are identified as the intermediate geostrophic eddies by matsuura and yamagata the costa rica dome is eroded in winter and early spring by the westward propagating warm anticyclones but at the same time a new embryo of the dome begins to evolve from the westward propagating cold cyclonic eddy excited off the gulf of papagayo by the northers the costa rica dome can be maintained by the winds with the cyclonic wind stress curl in summer on

wind generated eddy characteristics in the lee of the island of hawaii 1 weekly satellite sea surface height ssh anomaly data are used to clarify the mesoscale eddy characteristics in the lee of the island of hawaii the largest island in the hawaiian island chain the lee eddy variability can be separated into two geographical regions in the immediate lee southwest of hawaii region e eddy signals have a predominant 60 day period and a short life span whereas in the region along 19 n west of 160 w region w the eddy variability is dominated by 100 day signals and extends over a broad region by applying a linear ekman pumping model forced by the weekly quikscat wind data we find that the observed 60 day eddy signals originate in the southwest corner of hawaii and are induced by the local 60 day wind stress curl variability associated with the blocking of the trade wind by the island of hawaii the relationship between the wind forcing and the observed ssh signals demonstrates the role of the ocean as an integrator that responds more effectively to the low frequency synoptic atmospheric forcing 60 days than to the higher frequency forcing 30 days since the large amplitude 60 day ssh anomalies take 1 2 weeks to fully develop it is possible that real time observed wind stress data can be used for the prediction of these anomalies in contrast to the wind induced 60 day eddy signals in the lee of the island of hawaii the 100 day eddy signals in region w are likely generated by the instability of the sheared north equatorial current and hawaii lee countercurrent

the structure and evolution of cold surges east of the rocky mountains abstract northerly surges of cold air often move southward along the eastern side of the rockies from southern canada into mexico the strongest surges which generally develop in midwinter are associated with temperature decreases and pressure rises of 20 30 c and 15 30 mb respectively within 24 h surges are usually accompanied by a meridionally elongated pressure ridge and strong low level ageostrophic winds that parallel the terrain the width of the pressure ridging is approximately 1000 km over the southern plains but decreases to only a few hundred kilometers when the surge enters mexico this paper provides a detailed description of a northerly surge to the east of the rocky mountains that occurred on 12 14 november 1986 using both observational and model data the structural evolution of the surge is analyzed in addition the dynamics of the event is explored by diagnosing the momentum thermodynamic energy and vorticity equations to determine the typical synoptic scale evolution of these

offshore wind forcing in the gulf of tehuantepec mexico the asymmetric circulation since the early surveys carried out by the eastern tropical pacific eastropic and scripps tuna oceanographic research stor projects in the tropical pacific off mexico the northerly winds which blow over the gulf of tehuantepec were described as an important factor controlling the dynamics of this coastal ocean in january february 1989 an international team carried out the experiment tehuano designed to study the response of the gulf to these wind pulses the complete evolution of the coastal ocean after an event of moderate intensity was observed the forcing is characterized by a mostly symmetric fan shaped offshore wind jet which in turn produces a remarkably asymmetric upper ocean response while analytical results based on ekman theory forced by a symmetric offshore wind predict the formation of a symmetric dipolar circulation the observed flow consists mainly of a large 200 km in diameter anticyclonic warm core eddy in the western gulf with only a weak cyclonic counterpart in the eastern gulf intense surface cooling under the wind jet is caused by entrainment of subsurface water into the upper layer the thermocline in the west deepens with the development of the eddy which is formed initially by the advection of warm surface waters from west of the gulf east of the axis of the wind the mixed layer deepens due to wind induced entrainment while at the same time shoaling and compression of the deeper isotherms by curl induced upwelling ekman pumping strengthen the thermocline

a transbasin mode of interannual variability of the central american gap winds seasonality and large scale forcing abstracta transbasin mode tbm is identified as the leading mode of interannual surface wind variability over the intra americas seas across central america based on empirical orthogonal function analysis the tbm is associated with variability in central american gap winds most closely with the papagayo jet but with considerable signals over the gulfs of tehuantepec and panama although el nino southern oscillation enso is the main large scale forcing the tbm features a distinct seasonality due to sea level pressure slp adjustments across the pacific and atlantic during july september enso causes meridional slp gradient anomalies across central america intensifying anomalous geostrophic winds funneling through papagayo to form the tbm during wintertime enso peaks but imparts little anomalous slp gradient across central america with a weak projection on the tbm because of the competing effects of the pacific north american teleconnection and tropospheric kelvin waves besides enso tropical at

hydrocarbon biomarkers of different lithofacies of the salt iv formation of the mulhouse basin france forty nine samples from an 11 m section of the salt iv formation of the tertiary mulhouse basin alsace france covering six different lithotypes marl nodular lenticular laminated and massive anhydrite halite were analysed for hydrocarbon biomarkers the hydrocarbon biomarker assemblages are dominated by acyclic isoprenoids especially phytane 0 13 pr ph 0 52 n alkanes with specific distribution patterns and steranes large differences in their distributions indicate significant changes in the palaeoenvironment the largest changes observed are those in the desmethyl and methylsterane distributions and are probably linked to an occasional reconnection of the evaporite basin with the sea leading to an input of dinoflagellate algae 3 methylsteranes are present in all samples studied and their carbon number distribution mimics that of the 5 desmethylsteranes in line with previous suggestions that they are diagenetic products of sterols with a sugar unit at c 3 biosynthesized from dietary sterols the increase in relative abundance of the 3 methylsteranes during periods of marine incursions suggests that these precursors are biosynthesized by marine organisms variations in biomarker composition between the different lithofacies are minor probably because the organic matter is mainly associated with the marl and all lithotypes contain a marl component detailed subsampling of two marl layers and subsequent analysis indicated that the changes on a small time scale are minor to those on a larger time scale

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

isthmus of tehuantepec wind climatology and enso signal abstract the statistical characteristics of the winds at the isthmus of tehuantepec and their seasonal and interannual variability are studied through the analysis of several datasets and a reconstruction of the winds for a 31 yr period observations show that the long term monthly mean wind speeds and frequency of occurrence of northerly winds have a strong seasonal signal with maximum values during december january minimum during may june and a relative maximum in july the frequency distribution of wind speed is bimodal a feature that is closely related to the wind direction with northerly winds being stronger based on these results and the close relationship between the across isthmus pressure differences and the local winds a statistical model is developed to get a reconstruction of 12 hourly winds through the isthmus of tehuantepec for 1964 95 the model reproduces fairly well the main characteristics of the observed winds the bimodal distribution of the wind speed and the seasonal signal in

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

a census of tehuantepec and papagayo eddies in the northeastern tropical pacific 1 we use a 12 year 1992 2004 time series of satellite altimetry to characterize long lived wind generated anticyclonic eddies originating in the gulfs of tehuantepec and papagayo in the northeastern tropical pacific a total of 42 tehuantepec and 26 papagayo eddies were observed eddy merging usually of a tehuantepec papagayo pair was observed on 16 occasions on average the eddy season began in late october and lasted approximately 250 days until early july with 3 5 tehuantepec and 2 2 papagayo eddies formed each year minimum average eddy lifespan was 143 days and 84 days for tehuantepec and papagayo eddies respectively there was considerable interannual variability in eddy activity with greater fewer number of eddies more intense weaker eddies and a longer shorter eddy season during el nino la nina years eddy intensification was consistently observed at the east pacific rise

biomarker stratigraphy of the lower cretaceous of espirito santo basin brazil abstract this study involves the use of molecular parameters steranes and terpanes and carbon isotopes as stratigraphic correlation markers in a lower cretaceous lacustrine sequence from the espirito santo basin southeast brazil the biomarker variations revealed changes in sedimentary environment that had not been detected by sedimentological paleontological and seismistratigraphic methods additionally the observed variations assumed to have been contemporary for the whole basin could also be used as chronostratigraphic markers the carbon isotope data led to the recognition of two sedimentary sequences the upper sequence 13 c around 26 begins with very low amounts of gammacerane and of a novel c24 tetracyclic alkane apparently with a des a hopane structure a sharp increase in concentration of the c24 compound divided the upper sequence into two stratigraphic subunits the second of which shows an increasing gammacerane concentration with depth the lower sequence 13 c around 28 starts with a distinct drop in abundance levels of the c24 tetracyclic alkane and of methyl steranes gammacerane concentrations attain a maximum at the top of this sequence showing subsequently a decreasing trend with depth but remaining reasonably high throughout the sequence however a second sharp decrease of the c24 tetracyclic alkane shows a modification in sedimentary environment downwards combined all these stratigraphic changes delimitate four depositional cycles which could be easily recognized in wells from the eastern part of the basin showing gradual erosion updip to the west such sedimentary changes could be correlated with independent geochemical information on neighbouring lacustrine sequences of the same age suggesting a dominant freshwater influence in the basal part of the sequence contrasted with a more saline environment in the upper levels the use of these markers has been of great value in redefining stratigraphic correlations in the espirito santo basin and may prove useful to resolve similar difficulties in vicinal areas

satellite observations of mesoscale eddies in the gulfs of tehuantepec and papagayo eastern tropical pacific seawifs high resolution ocean color images and avhrr sea surface temperature were obtained for the period from november 1998 to march 1999 generation of mesoscale eddies was observed for the region between the gulf of tehuantepec and the gulf of papagayo tropical pacific ocean eighteen eddies with diameters ranging between 100 and 450 kmwere identified 14 originated in the gulf of tehuantepec and m ost were cyclonic our results show that the frequency of cyclonic eddy formation is higher than it has been reported and their lifetime can be longer using both ocean color images and daily temporal resolution instead of sea surface temperature alone improved our ability to identify and follow the propagation of these eddies the generation and fate of smaller cyclonic eddies around the periphery of the anticyclonic eddy indicate the importance of the onshore offshore exchange of energy and biological material which has not been considered previously three anticyclonic eddies were generated in the gulf of papagayo these eddies have a common origin and they travel along the main flux of the costa rica coastal current crcc which later turns offshore and joins the north equatorial current this behavior can be seen clearly on seawifs images and suggests that the crcc influences eddy propagation time series of chlorophyll a concentration and sst were obtained fromtwo points at tehuantepec and two at papagayo cross correlation analysis confirms an inverse relationship between these variables showing that a decrease in sst is followed by an increase in chlorophyll a concentration values indicating high growth and primary production rates r 2004 elsevier ltd all rights reserved

planetary and synoptic scale signatures associated with central american cold surges abstract motivated by outstanding issues from a previous case study of a midlatitude cold surge that affected mexico and central america the climatology of central american cold surges is examined in this paper an independently derived listing of 177 cold surge events is employed for which the following properties are tabulated onset date duration time between cold surge events latitude of maximum equatorward penetration min and 48 h maximum surface temperature change at merida mexico t these data show that 75 of the cold surges have durations of 2 6 days the same timescale as mobile disturbances in the westerlies also there does not appear to be any relationship between t and the duration of the event although cold surges that penetrate to low latitudes min 7 10 n have a weak tendency to persist longer than those that do not penetrate to low latitudes min 15 20 n in addition the reding data indicate that the cold surges tend to reach their most equatorward extent where

structure and significance of c30 4 methyl steranes in lacustrine shales and oils abstract the structure of the abundant c 30 4 methyl steranes of ancient freshwater lacustrine sediments and derived oils is of interest as their precursors the 4 methyl and in particular 4 23 24 trimethyl sterols dinosterols are reported to be specific to dinoflagellates this study employs a novel liquid crystal gc phase combined with gc ms and gc ms ms to separate and characterise mixtures of c 30 4 methyl sterane standards not resolvable on non polar phases this technique is then applied to identify the c 30 4 methyl steranes in an ancient freshwater sediment a freshwater lacustrine and a marine derived oil a comparison is also made with the 4 methyl steranes in marine sediments containing varying amounts of dinoflagellate cysts the c 30 4 methyl steranes of the freshwater lacustrine samples have been shown to possess a 4 methyl 24 ethylcholestane structure while both 4 methyl 24 ethylcholestanes and 4 23 24 trimethyl 5 h cholestanes dinosteranes were found in the marine dinoflagellate rich sediments while still indicative of dinoflagellates 4 methyl 24 ethyl sterols are generally not the major dinoflagellate sterol and alternative explanations for the abundance of 4 methyl 24 ethylcholestanes in ancient lacustrine sediments should be considered possibly ancient freshwater dinoflagellates synthesised principally the 4 methyl 24 ethyl form alternatively a source from an unrecognized algal class is possible while a source from bacteria which are known to synthesise certain 4 methylsterols is discussed

unusual biomarker maturation ratio changes through the oil window a consequence of varied thermal history abstract saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas condensate window to high vitrinite reflectances r o 1 16 in mature marine and lacustrine mesozoic clastic samples from a south african basin two of the ratios reverse above r o 0 9 these unusual maturation effects result from isolated periods of high rates of maturation increase the basin cooled regionally after the break up of gondwana but high heating rates prevailed during the late cretaceous early tertiary as africa moved across a hotspot and again in the late tertiary as a result of a possible hotspot and hydrothermal event

rifted margin source rock deposition a carbon isotope and biomarker study of a west african lower cretaceous lacustrine section lower cretaceous passive margin sections penetrated in wells peripheral to the deep basinal development of pre salt sediments of the liawenda ponta vermelha troughs in the lower congo coastal basin revealed sustained source potential kerogen type kinetic ea a and carbon isotopic data plus rock extract biomarker signatures confirmed large systematic organofacies variations within these rift phase sediments an inverse correlation between 25 28 30 trisnorhopane and gammacerane abundances suggested three major depositional regimes reflecting salinity and water depth control 13c depleted basal sediments showing strong gammacerane 4 methyl sterane signatures were segregated by a major isotopic excursion this event represented the transition between saline playa lake to deeper water stratified conditions supporting a high level of anoxia for these intermediate sediments sterane and tricyclic diterpane abundances plus sterane hopane ratios had marine connotations and could be interpreted as the result of intermittent marine incursions fore shadowing irreversible oceanic ingression a resurgence of gammacerane abundance in the uppermost sediments typified littoral shallow marine depositional conditions recognition of a possible non ubiquity in lacustrine depositional conditions during the opening of a rifted margin provides further insight into the complexity and attendant controls on hydrocarbon generation in such habitats

midsummer gap winds and low level circulation over the eastern tropical pacific abstract the low level seasonal and intraseasonal wind variability over the northeastern tropical pacific netp its relationship with other variables and the connection with large and middle scale atmospheric patterns are analyzed using a suite of datasets quick scatterometer quikscat wind data show that the low level circulation over the netp is mainly affected by the northerly trades the southerly trades and the wind jets crossing through the tehuantepec papagayo and panama mountain gaps the seasonal and intraseasonal evolution of these wind systems determines the circulation patterns over the netp showing predominant easterly winds in winter and early spring and wind direction reversals in summer over the central region of the netp during summer when southerly trades are the strongest and reach their maximum northward penetration weak westerlies are observed in june easterlies in july august despite that strong southerlies tend to turn eastward and again westerlies in september octob

enso s impact on the gap wind regions of the eastern tropical pacific ocean abstractthe recently released ncep climate forecast system reanalysis cfsr is used to examine the response to enso in the northeast tropical pacific ocean netp during 1979 2009 the normally cool pacific sea surface temperatures ssts associated with wind jets through the gaps in the central american mountains at tehuantepec papagayo and panama are substantially warmer colder than the surrounding ocean during el nino la nina events ocean dynamics generate the enso related sst anomalies in the gap wind regions as the surface fluxes damp the ssts anomalies while the ekman heat transport is generally in quadrature with the anomalies the enso driven warming is associated with large scale deepening of the thermocline with the cold thermocline water at greater depths during el nino in the netp it is less likely to be vertically mixed to the surface particularly in the gap wind regions where the thermocline is normally very close to the surface the thermocline deepening is enhanced to the south

satellite observations of the wind jets off the pacific coast of central america part i case studies and statistical characteristics measurements of near surface winds by the nasa scatterometer nscat from october 1996 through june 1997 are analyzed to investigate the three major wind jets along the pacific coast of central america that blow over the gulfs of tehuantepec papagayo and panama each jet is easily identifiable as locally intense offshore winds in the lee of low elevation gaps through the sierra madre mountain range the jets have relatively narrow cross stream width but often extend several hundred kilometers or more into the pacific the tehuantepec and papagayo jets sometimes merge with the northeast trade winds of the pacific the tehuantepec jet was highly energetic with characteristic timescales of about 2 days events were triggered by high pressures associated with cold surges into the gulf of mexico that originated over the great plains of north america the papagayo and panama jets were much more persistent than the tehuantepec jets the winds at both of these lower latitude locations exhibited a strong seasonal variation with almost exclusively offshore flow from late november 1996 through late may 1997 and periods of onshore flow in october and november during the late stages of the 1996 central american monsoon season superimposed on this low frequency seasonal variation were events with characteristic timescales of a few days based on nscat data the spatial and temporal evolution of major wind events is described in detail for three representative case studies in december 1996 the jets developed sequentially from north to south consistent with the notion that wind events in the two lower latitude jets are associated with cold air outbreaks that trigger the tehuantepec jet a day or so earlier in november 1996 and march 1997 the papagayo and panama jets were strongly influenced by tropical phenomena that had little apparent association with the tehuantepec jet these latter two case studies together with the distinction between the statistical characteristics of the three jets suggest that the papagayo and panama jets are predominantly controlled by a mechanism that is very different from the across gap pressure gradients associated with high pressure systems of midlatitude origin that control the tehuantepec jet

messel oil shale western germany assessment of depositional palaeoenvironment from the content of biological marker compounds abstract the extractable lipids of two outcrop samples of messel oil shale have been analysed by gc and gc ms both samples contain as major lipids similar distributions of 4 methylsteroids hopanoids and long chain c 28 c 36 alkanediols and 1 hydroxyalkanones compared with other reported distributions of sedimentary alkanediols and 1 hydroxyalkanones those reported herein extend to higher carbon numbers greater variety of mid chain positional isomers and are the oldest the major sterol has been shown to be 4 methyl 24 ethyl 5 h cholestan 3 ol whereas 4 23 24 trimethyl 5 h cholest 22 en 3 ol dinosterol is more abundant than the 24 ethyl structural isomer two novel c 31 4 methylsterols have been recognised and are proposed to have a 23 methyl 24 ethyl 28 side chain desmethylsteroids are of low abundance compared with 4 methylsteroids the two outcrop samples differ principally in their distributions of hydrocarbons whereas sample 1 contains negligible steroidal hydrocarbons sample 2 exhibits abundant desmethylsterenes and 4 methylsterenes such differences illustrate the inhomogeneous nature of the messel deposit in regard to its content of biological marker compounds alkaline hydrolysis of the kerogen of sample 1 releases mainly hydroxy compounds similar in composition to the corresponding extractable lipids together with trace amounts of ketones and hydrocarbons similarly lithium aluminium hydride treatment of the kerogen of sample 1 yields hydroxy compounds but with a different composition to the alkaline hydrolysis products overall the content of biological marker compounds suggests that the major sources of the sedimentary organic matter were dinoflagellates and bacteria especially cyanobacteria the algal assemblage was probably dominated by dinoflagellates of low species diversity with other algal classes in relatively low abundance deposition probably took place into an anoxic hypolimnion supporting a significant population of chlorobium type bacteria

application of organic geochemistry to sequence stratigraphic analysis four corners platform area new mexico u s a abstract the sequence stratigraphic model of sedimentation postulates the existence of a time condensed section deposited at very low sedimentation rates occurring in the uppermost transgressive systems tract and the lowermost highstand systems tract this condensed interval has of often been equated with zones of increased hydrocarbon source potential and invoked as a petroleum source rock often in the absence of supporting geochemical data in this study isotopic molecular lithostratographic and paleontological data are presented for 51 outcrop samples from a cenomanian turonian section at red wash new mexico u s a interpretations are made within a sequence stratigraphic framework ramp model sedimentation rates are estimated in order to define the location of the codensed intervalm for comparison with the zone of best source potential approximately 80 m of section were sampled the interval of maximum flooding and westernmost progression of the cretaceous seaway shoreline as defined by paleontological data is stratigraphically immediately below the occurrence of discontinuities in total organic carbon content hydrogen index and fluoramorphinite concentration in the kerogen the overall transgressive event is accompanied by increases in relative concentrations of 24 n propylcholestane total steranes and rearranged steranes these changes are consistent with a simultaneous decrease in the ratio of terrigenous organic matter to marine algal input as westward flooding proceeded the simultaneous occurrence of discontinuities in kerogen related parameters and continuous trends in bitumen related parameters probably implies mobilization of soluble organic matter across the flooding event boundary sedimentation rate estimates for six intervals in the red wash section show that the best oil source rock potential occurs immediately above the condensed interval and maximum flooding surface within the highstand systems tract previous studies of cretaceous sections in other portions of the western interior basin have located the best source rock potential below the condensed zone we conclude that the equivalence between source rock occurence and condensed sections as applied through the sequence stratigraphic model requires modification before the model may be used to predict the location of oil source rocks in a ramp setting in this respect it is critical that the data in sequence stratigraphic studies be used to define the model and not allow the model to dictate the interpretation of the data

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

equatorial kelvin waves generated in the western tropical pacific ocean trigger mass and heat transport within the middle america trench off costa rica sequences of correlated seafloor temperature current velocity and acoustic backscatter events recorded at ocean drilling program odp sites at 4300 m depth in the middle america trench have been inferred to result from tidally induced turbidity currents generated in the vicinity of the 3300 m deep sill at the southern end of the trench new data from the borehole observatories extend the temperature records to 11 years november 2002 to december 2013 and confirm the highly episodic nature of the events we present satellite altimetry data and ocean circulation model results to show that event timing is correlated with intraseasonal kelvin wave motions in the equatorial pacific the observed temperature events had a mean 1 standard deviation occurrence interval of 61 24 days which spans the periods of the first two baroclinic modes lag times between peak bottom water temperatures at the odp sites and the passage of eastward propagating kelvin wave crests at locations in the eastern equatorial pacific are consistent with the time for mode 1 waves to propagate to the southern end of the trench at a mean phase speed of 2 0 m s 1 findings indicate that kelvin wave currents augment tidal motions in the vicinity of the sill triggering turbidity currents that travel northwestward along the trench axis at mean speeds of 0 1 m s 1 we conclude that mode 1 or possibly mixed mode 1 and mode 2 baroclinic kelvin waves generated by large scale atmospheric processes in the western tropical pacific lead to heat and mass transport deep within middle america trench in the eastern tropical pacific

transient upwelling generated by two dimensional atmospheric forcing and variability in the coastline abstract the present paper deals with two dimensional transient upwelling in a two layer ocean of constant depth motions generated by several two dimensional atmospheric forcings are investigated using asymptotic expansions in time it is shown that the component of the wind parallel to the coast generates an interface elevation which propagates along the coast as an internal kelvin wave front strong horizontal baroclinic motions are linked to this phenomenon the velocity within the deep layer is in the opposite direction to that of the wind on the surface it is found that the spin up time of mean motions is of the order of the coriolis period the motion generated by a wind blowing over a bay is then studied the bay is idealized by a right angle corner two independent cases are considered depending on whether or not the wind is parallel to one coast or the other

evidence for an impact origin of the late ordovician bear swamp structure in upstate new york usa a 3d seismic survey has imaged a complex crater of possible impact origin in the finger lakes region of upstate new york near bear swamp state forest the bear swamp crater is uppermost ordovician 444 ma in age and is completely buried in the subsurface at a depth of approximately 1220 m 4000 ft the nearly circular crater is about 3 5 km 2 2 mi in diameter and contains a central rebound structure with a diameter of about 1 km 0 6 mi two exploration wells were drilled into the crater and core and image log data were obtained the first well tested the central rebound which consisted of steeply dipping beds and heavily brecciated zones as seen on the image logs the second well tested the flank of the central uplift in the roughly 300 m 1000 ft thick annular basin thin sections taken from whole core recovered in the second well revealed planar deformation features pdf in quartz grains within the reworked crater fill sediments minor gas shows were encountered at the base of the crater fill s

inertial wind path and sea surface temperature patterns near the gulf of tehuantepec and gulf of papagayo during the northern hemisphere winter the surface atmospheric pressure on the gulf of mexico side of central america is often higher than that on the pacific side the resultant southward pressure gradient drives strong southward winds through a gap in the sierra madre mountain range at the isthmus of tehuantepec the atmospheric jet is narrow in comparison with the relevant radius of deformation so when it leaves the coast and flows out over the gulf of tehuantepec it is an inertial jet therefore the jet is expected to be deflected into a clockwise inertial circle by the coriolis force a similar process should also occur for central american atmospheric jets through mountain range gaps near the gulf of papagayo satellite measurements of sea surface temperature together with coastal wind data for the first 41 days of 1986 were examined to see if the expected wind path influenced sea surface temperature sst near the gulf of tehuantepec and the gulf of papagayo consecutive daily satellite images when the coastal southward tehuantepec wind increased suggest that the initial development of cold surface water in a clockwise loop is due to the wind mixing the shallow thermocline surface water along its inertial path a simple 1 layer analytical ocean model suggests in agreement with observations that the wind can drive surface quasi geostrophic currents of 1 m s 1 since the wind path is circular the wind actually generates a clockwise rotating ocean eddy with the approximate scale of the wind inertial circle the satellite sea surface temperature measurements also suggest that the wind driven surface ocean current is unstable in addition stronger gradients in sst to the right of the expected wind flow are consistent with advection of sea surface temperature by ocean surface ekman flow

intraseasonal variability of surface salinity in the eastern tropical pacific associated with mesoscale eddies strong variability in sea surface salinity sss in the eastern tropical pacific etpac on intraseasonal to interannual timescales was studied using data from the soil moisture and ocean salinity soil moisture active passive and aquarius satellite missions a zonal wave number frequency spectral analysis of sss reveals a dominant timescale of 50 180days and spatial scale of 8 degrees 20 degrees of longitude with a distinct seasonal cycle and interannual variability this intraseasonal sss signal is detailed in the study of 19 individual etpac eddies over 2010 2016 identified by their sea level anomalies propagating westward at a speed of about 17cm s etpac eddies trap and advect water in their core westward up to 40 degrees of longitude away from the coast the sss signatures of these eddies with an average anomaly of 0 5 pss magnitude difference from ambient values enable the study of their dynamics and the mixing of their core waters with the surroundings three categories of eddies were identified according to the location where they were first tracked 1 in the gulf of tehuantepec 2 in the gulf of papagayo and 3 in the open ocean near 100 degrees w 12 degrees n they all traveled westward near 10 degrees n latitude category 3 is of particular interest as eddies seeded in the gulf of tehuantepec grew substantially in the vicinity of the clipperton fracture zone rise and in a region where the mean zonal currents have anticyclonic shear the evolution of the sss signature associated with the eddies indicates the importance of mixing to their dissipation

the origin and fate of 4 methyl steroids ii dehydration of stanols and occurrence of c30 4 methyl steranes abstract certain features of the distributions of sedimentary 4 methyl steroid hydrocarbons have been investigated i competitive dehydration experiments with stanols adsorbed on a shale suggests a possible explanation for the low abundance of 4 methyl sterenes relative to their desmethyl counterparts in immature sediments ii a 4 methyl spirostene which is a minor product of the backbone rearrangement of 4 methylcholest 4 ene in the laboratory has been tentatively assigned its presence in a toarcian black shale with a second isomer provides further evidence that the sedimentary backbone rearrangement of 4 methyl sterenes is analogous to that of their desmethyl counterparts and iii the major c30 4 methyl steranes in semecourt shale toarcian paris basin differ from those in an eocene lacustrine shale from china this indicates the potential complexity of c30 steroidal alkanes both 4 methyl and desmethyl which can occur in sedimentary organic matter and shows that care must be taken in using m z 217 mass chromatograms alone for routine input and maturity assessment using steroidal alkanes

biomarker paleo reconstruction of the german wealden berriasian early cretaceous in the lower saxony basin lsb during the early cretaceous berriasian wealden 3 4 northwestern germany was covered by an east west elongated tentatively brackish lake in which locally more than 700 m thick black shales were deposited while the distribution of organofacies in the basin is relatively well documented the paleoenvironmental conditions in the basin center e g occurrence and spread of water column stratification and the spatial record of biomarkers in wealden 3 4 shales and coals are rarely known we here present respective data from the entire basin in large areas total organic carbon toc contents are above 5 wt and hi values above 700 mg hydrocarbons hc g toc supporting the high potential of shales in the central basin as petroleum source rocks furthermore bulk geochemical data as well as biomarkers clearly mirror the wealden 3 4 facies distribution with the differentiation of a predominantly terrestrial setting east of the weser river and an aquatic and brackish lake setting in the west certain biomarkers such as isorenieratane specific for green sulfur bacteria indicate that the basin consisted of a permanently stratified water column with a brackish marine deep water body and an oxic anoxic transition zone in the photic zone in the southwestern gate of the lake including the isterberg area and towards the east no water column stratification developed characteristic of wealden 3 4 black shale organic matter are high relative abundances of saturated versus aromatic hydrocarbons most likely due to high botryococcus algal input highly negative 13c values in the extract fractions low isotopic canonical variables sensu sofer in aapg bull 68 31 49 1984 and high gammacerane dinosterane and c35 homohopane relative abundances interpreting those data the different sub facies of the environmental setting can be excellently documented particularly in the western part of the basin wealden 3 4 shales are important petroleum source rocks however an overlap of biomarker signatures with those from jurassic posidonienschiefer formation posidonia shales from the same area shows that oil source rock correlations in this area remain challenging

dinoflagellate origin for sedimentary 4α methylsteroids and 5α h stanols biological marker compounds provide useful tools for evaluating the depositional environments of recent and ancient sediments and petroleums1 largely through established relationships between the organic matter of sediments and source organisms1 2 such relationships are best tested and explored by investigating the lipid components of natural populations of autochthonous biota that can be clearly recognized as contributors to underlying bottom sediments in this context we have studied the lipids of the freshwater dinoflagellate peridinlum lomnickii woloszynska order peridiniales class dinophyceae collected from the waters of priest pot3 a eutrophic lake in the english lake district its distributions of both 4 methylsterols and 4 methylstanones closely resemble those of the underlying bottom sediments demonstrating that dinoflagellates are important contributors of these sedimentary compounds the 4 methylsteroidal hydrocarbons found in ancient sediments and petroleums4 6 are presumably diagenetic products of such 4 methylsteroids and therefore reflect dino flagellate inputs to the original depositional environments furthermore the prominence of 5 h cholestan 3 ol in p lomnickii suggests that dinoflagellates may be the long sought direct biological source of sedimentary 5 h stanols

biological markers in the rhaetian black shales of south west britain abstract in the light of renewed interest in on shore petroleum exploration within the united kingdom we have investigated the aliphatic hydrocarbon distributions of contemporaneously deposited black shales from rhaetian upper triassic westbury formation outcrops and subcrops in the worcester graben and bristol channel trough the aliphatic hydrocarbon compositions of six samples three from each tectonic basin are examined by gas chromatography mass spectrometry although there are close similarities in the hydrocarbon content of the individual members of each sample suite there are significant differences between the two suites most notably the polycyclic components of the worcester graben samples are dominated by 4 methylsteroids thought to be products derived from dinoflagellate 4 methylsterols and also hopanes indeed polycyclic components are generally more abundant in the worcester graben all the samples show evidence of minor terrigenous inputs i e plant waxes from the prominence of the odd numbered higher n alkane components in the range n c 25 n c 35 the distributions of biological marker compounds in the samples indicate that none is sufficiently mature to have generated oil the shales from the bristol channel trough are however more mature than those from the worcester graben

ocean currents evident in satellite wind data satellite mounted radar scatterometers designed to quantify surface winds over the ocean actually measure the relative motion between the air and the ocean surface estimates of the wind stress from conventional surface wind measurements are usually derived neglecting ocean currents however when the relative motion is used the differences in the estimated stress can be as large as 50 near the equator and may even reverse sign during an el nino this assertion is supported by the strong relationship between the surface currents measured by the tropical atmosphere ocean tao array in the pacific ocean and the differences between the winds estimated from scatterometer data and those measured by tao anemometers the fact that the scatterometer measures relative motion and not wind alone makes scatterometer derived stress a more accurate representation of the boundary condition needed for both atmospheric and oceanic models than stress fields derived neglecting ocean currents

mean three dimensional circulation in the northeast tropical pacific abstract historical xbt data are used to construct a mean climatology of the three dimensional geostrophic circulation in the northeast tropical pacific southwest of mexico and central america and are diagnosed based on linear dynamics forced with satellite scatterometer winds unlike the familiar central tropical pacific where the zonal scales are very large and the wind forcing nearly a function of latitude alone the north pacific east of about 120 w is strongly influenced by wind jets blowing through gaps in the central american cordillera the curl imposed by these wind jets imprints on the ocean producing a distinctive pattern of thermocline topography and geostrophic currents that are consistent with the sverdrup balance notably the weakening of the north equatorial countercurrent near 110 w is due to the wind forcing given the observed stratification and wind stress curl planetary vorticity conservation also determines the distribution of vertical velocity in the region with about 3 5 sv

east pacific ocean eddies and their relationship to subseasonal variability in central american wind jets subseasonal variability in sea surface height ssh over the east pacific warm pool off central america is investigated using satellite observations and an eddy resolving ocean general circulation model ssh variability is organized into two southwest tilted bands on the northwest flank of the tehuantepec and papagayo wind jets and collocated with the thermocline troughs eddy like features of wavelength similar to 600 km propagate southwestward along the high variance bands at a speed of 9 13 cm s wind fluctuations are important for eddy formation in the gulf of tehuantepec with a recurring interval of 40 90 days when forced by satellite wind observations the model reproduces the two high variance bands and the phase propagation of the tehuantepec eddies our observational analysis and model simulation suggest the following evolution of the tehuantepec eddies on the subseasonal timescale in response to the gap wind intensification a coastal anticyclonic eddy forms on the northwest flank of the wind jet and strengthens as it propagates offshore in the following two to three weeks an energetics analysis based on the model simulation indicates that besides wind work barotropic and baroclinic instabilities of the mean flow are important for the eddy growth both observational and model results suggest a re intensification of the anticyclonic eddy in response to the subsequent wind jet event off papagayo ocean eddy formation is not well correlated with local wind jet variability in both the gulfs of tehuantepec and papagayo subseasonal ssh variability is preferentially excited on the northwest flank of the wind jet factors for this asymmetry about the wind jet axis as well as the origins of wind jet variability are discussed

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c

characterization of organic matter from a restricted evaporative sedimentary environment late miocene of lorca basin southeastern spain the lorca basin located within the tectonically evolving betic cordillera of southeastern spain developed as a rapidly subsiding basin in an open marine setting during much of the late miocene the basin underwent sporadic phases of circulatory restriction with marked production and preservation of organic matter culminating in evaporative sedimentation latest miocene an organic geochemical study using biomarker analyses clarifies the degree of mixing between inflowing water sources both marine and nonmarine gives clues to the complex and variable circulation within the water and helps determine the extent of basinal hypersalinity as the water in this basin evolved toward evaporative conditions a number of organic rich depositional phases 25 wt toc he e termed pre evaporative took place during the early parts of these phases the upper water is interpreted as nutrient rich and comparatively normal and the bottom water as anoxic this was followed by rising salinities and short phases of evaporite formation such a sedimentary history may serve as a model for understanding of evaporite related source rocks and related hydrocarbons in other areas of the world

sea level variability in the eastern tropical pacific as observed by topex and tropical ocean global atmosphere tropical atmosphere ocean experiment sea surface height measurements from the topex altimeter and dynamic height from tropical ocean global atmosphere tropical atmosphere ocean toga tao moorings are used to explore sea level variability in the northeastern tropical pacific ocean after the annual harmonic is removed there are two distinct bands of variability one band is centered at 5 n to 7 n and extends from 165 w to 110 w and the other band is centered at 10 n to 12 n and extends from 120 w to the coast of central america the correspondence between the two independent observation data sets at 5 n is excellent with correlations of about 90 the variability at 5 7 n is identified as instability waves formed just south of the north equatorial countercurrent during the months of july through march wave amplitudes are largest in the range of longitudes 160 140 w where they can exceed 10 cm the waves disappear when the equatorial current system weakens during the months of march through may the variability at 11 n in 1993 has the form of anticyclonic eddies these eddies propagate westward at a speed of about 17 cm s 1 consistent with the dispersion characteristics of free rossby waves the eddies are shown to have their origin near the coast of central america during northern fall and winter their formation seems to result from intense wind bursts across the gulfs of tehuantepec and papagayo which generate strong anticyclonic ocean eddies the disappearance of the eddies in the summer of 1993 coincides with the seasonal intensification of equatorial currents thus the variability at 11 n has very little overlap in time with the variability at 5 n

phorbin steryl esters in black sea sediment traps and sediments a preliminary evaluation of their paleooceanographic potential abstract the distributions of pyropheophorbide a steryl esters in one year deployments of sediment traps at two locations in the black sea are described in nearly all our trap samples phorbin steryl esters pses contribute a significant portion of the total phorbin flux the relative abundances of sterols esterified to pyropheophorbide a varied throughout the year and we suggest these changes result from the observed seasonal variation of phytoplankton species in the overlying water column the distribution of free sterols in a one year composite sediment trap sample closely approximates the distribution of sterols derived from the hydrolysis of sedimentary pses collected at an adjacent site from these results we suggest that the distribution of sedimentary pse sterols provides a record of sterol deposition to the sediment water interface esterification of sterols to pyropheophorbide a apparently prevents the preferential removal of 4 desmethyl sterols relative to 4 methyl sterols and the reduction of stenols to stanols during degradation analysis of pses in a gravity core covering the last 8 10 kyr shows that the abundance and distribution of pses change with downcore variations in sedimentology detailed analysis of pses in sediments may therefore provide a means to evaluate paleooceanographic changes in phytoplankton community structure and sterol early diagenesis the synthesis nmr ci ms and visible spectroscopic properties of four abundant pses found in the black sea are also described

secular and environmental constraints on the occurrence of dinosterane in sediments abstract the distribution patterns of sedimentary a ring methylated steranes have changed markedly over geological time although dinosterane and its isomer 24 ethyl 4 methylcholestane have been tentatively identified in three proterozoic rock units they are either not detectable or occur in low abundance relative to 3 methyl steranes throughout most of the palaeozoic between permian and middle triassic times 260 220 ma ago 4 methyl sterane abundances in marine sediments increased markedly the presence of dinosterane in some middle triassic marine sediments is contemporaneous with the appearance of fossil cysts of uncontested dinoflagellate affinity 4 methyl steranes including dinosterane or their precursor sterenes and sterols then show a continuous presence often in high abundance in marine sediments from the late triassic through to the present day assemblages of 4 methyl steranes and their precursors but with dinosterane absent or in low relative abundance are often the predominant steroids in lacustrine sediments in the cainozoic dinosterane appears to arise predominantly from marine dinoflagellates and as a consequence is a useful biological marker for mesozoic and cainozoic marine organic matter the isomer 24 ethyl 4 methylcholestane is likely to have multiple origins although its very high abundance in tertiary lacustrine sediments and oils compared to older materials suggests that dinoflagellates could also be the source in these cases

regional source rock potential of lacustrine oligocene kishenehn formation northwestern montana intermontane basins of the northern united states overthrust belt have received only minor attention from petroleum geologists and geochemists in the modern literature despite the common occurrence of oil shales and thick sediment columns in such basins the present study investigates the petroleum source rock potential of the freshwater lacustrine sediments including mudstones oil shales and lignites of the kishenehn basin of northwestern montana and southeast british columbia outcrop samples of the tertiary kishenehn formation include excellent albeit immature petroleum source rocks average total organic carbon contents and hydrogen indices exceed 6 and 500 mg g respectively and numerous samples contain type i kerogen all samples studied are thermally immat re to marginally mature having vitrinite reflectance values of 0 28 to 0 51 ro organic geochemical and petrographic analyses of the kishenehn sediments allow estimates of detailed depositional setting and specific biological input to the sediment column the southernmost sediments in the basin contain the least land plant organic matter input and possess the richest petroleum source potential although vitrinite reflectance values are not particularly sensitive to maturity differences in this sample set molecular geochemical data were found to be useful in evaluating fine maturity distinctions and are used here to establish the order of kishenehn outcrops on the basis of maturity this use of molecular markers as maturation and depositional setting indicators for freshwater lacustrine environments has widespread application in thrust belts the results of this tudy will be useful in exploration of over two dozen intermontane basins throughout the northern extent of the united states overthrust belt

characteristics of wind generated rings in the eastern tropical pacific ocean eddies are generated in the eastern tropical pacific 3 s 23 n 75 105 w by winds blowing through central american mountain passes from the atlantic we used coastal zone color scanner czcs and advanced very high resolution radiometer avhrr satellite imagery complemented with monthly in situ sea surface temperature and wind series from the comprehensive ocean atmosphere data set coads to study these eddies and their effect on pigment concentrations in the region pigment values in the gulf of tehuantepec generally reach higher values in november march before those in the gulf of papagayo the eddies generated in the gulf of tehuantepec are associated with passages of cold fronts across the gulf of mexico from the north while the eddies off papagayo and panama are associated with increases in trade wind intensity czcs images showed larger numbers of eddies per season than have been previously reported on the basis of in situ and avhrr observations or numerical simulations we counted 13 eddies in 1979 1980 8 in 1984 1985 and 6 in 1985 1986 the eddies transfer both energy and biological constituents from the continental margin to the offshore tropical pacific the eddies frequently moved distances in excess of 1500 km from their point of origin both anticyclonic and cyclonic eddies are generated but in general there are more anticyclones anticyclonic eddies generally moved to the southwest some cyclonic eddies moved to the south and southeast along the central american coast and appeared to be trapped by the cyclonic costa rica thermal dome eddies traveled at speeds varying between 9 and 21 cm s 1 and had diameters of 100 500 km phytoplankton concentrations associated with the eddies varied from 2 to 10 mg m 3 within 70 km of the coast to 1 mg m 3 up to 600 km of the coast between late april and october fewer eddies were observed and phytoplankton concentrations were lower 0 25 mg m 3 and more uniform over the region

the relationship between sedimentary organic carbon isotopic composition and organic biomarker compound concentration abstract a study of organic biomarker compounds which could serve as tracers of terrigenous and marine sedimentary organic matter sources was performed on samples from a 208 7 m hydraulic piston core hole dsdp hole 619 from the hemipelagic pigmy basin in the northern gulf of mexico organic carbon normalized concentrations of total long chain c37 c39 alkenones and some individual c27 c29 desmethyl sterols were determined to be useful proportional indicators tracers of preserved marine and terrigenous organic carbon respectively the alkenones whose only known source is marine phytoplankton of the class prymnesiophyceae generally occurred in higher concentrations in interglacial isotope stages 1 and 5a b than in the intervening glacial stages sterols c27 c29 apparently of a dominantly terrigenous origin occurred in lower concentrations during interglacial stages than in glacial stages tracers of both terrigenous and marine organic matter appear to be affected by the differential diagenetic alteration of the biomarker corg ratios as indicated by a simple first order kinetic model the lack of any desmethylor 4a methylsterol which is linearly related to the proportion of marine sedimentary organic matter as scaled by 13corg indicates that either 1 1 sedimentary diagenesis has obscured the biomarker corg vs 13corg record 2 2 phytoplanktonic assemblage changes caused variations in the biomarker corg ratio of the primary input preferential preservation of terrigenous sterols may result in a biased sedimentary record of sterol input which could be misinterpreted as indicating solely terrigenous sterol sources a simple model which characterizes the effects of sedimentary diagenesis on the relationship between corg normalized biomarker ratios and 13corg demonstrates the potential problems of long term differential diagenetic skewing on those tracer records

reconstructing the phytoplankton community of the cariaco basin during the younger dryas cold event using chlorin steryl esters 1 a record of the downcore distribution of chlorin steryl esters cses through the younger dryas was produced from cariaco basin sediments in order to assess the potential use of cses as recorders of the structure of phytoplankton communities through time using an improved high performance liquid chromatography method for the separation of cses we find significant changes in the distribution of cses during the younger dryas in the cariaco basin during the younger dryas enhanced upwelling in the cariaco basin caused an increase in the diatom population and therefore an increase in the relative abundance of cses derived from diatoms in contrast the dinoflagellate population and therefore cses derived from dinoflagellates decreased in response to the climate change during the younger dryas these community shifts agree well with the shifts observed in the present day on a seasonal basis that result from the north south migration of the intertropical convergence zone over the cariaco basin we also identify changes in the abundance of several cses that seem to reflect rapid warming and cooling events this study suggests that cses are useful proxies for reconstructing phytoplankton communities and paleoenvironments index terms 1055 geochemistry organic geochemistry 4267 oceanography general paleoceanography 4855 oceanography biological and chemical plankton keywords younger dryas cariaco basin chlorin steryl esters

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

dynamically balanced absolute sea level of the global ocean derived from near surface velocity observations 1 the 1992 2002 time mean absolute sea level distribution of the global ocean is computed for the first time from observations of near surface velocity for this computation we use the near surface horizontal momentum balance the velocity observed by drifters is used to compute the coriolis force and the force due to acceleration of water parcels the anomaly of horizontal pressure gradient is derived from satellite altimetry and corrects the temporal bias in drifter data distribution ncep reanalysis winds are used to compute the force due to ekman currents the mean sea level gradient force which closes the momentum balance is integrated for mean sea level we find that our computation agrees within uncertainties with the sea level computed from the geostrophic hydrostatic momentum balance using historical mean density except in the antarctic circumpolar current a consistent horizontally and vertically dynamically balanced near surface global pressure field has now been derived from observations

the central american midsummer drought regional aspects and large scale forcing abstract the midsummer drought msd is a diminution in rainfall experienced during the middle of the rainy season in southern mexico and central america as well as in the adjacent caribbean gulf of mexico and eastern pacific seas the aim of this paper is to describe the regional characteristics of the msd and to propose some possible forcing mechanisms satellite and in situ data are used to form a composite of the evolution of a typical msd which highlights its coincidence with a low level anticyclone centered over the gulf of mexico and associated easterly flow across central america the diurnal cycle of precipitation over the region is reduced in amplitude during midsummer the msd is also coincident with heavy precipitation over the sierra madre occidental part of the north american monsoon reanalysis data are used to show that the divergence of the anomalous low level flow during the msd is the main factor governing the variations in precipitation a linear baroclinic model is used to show

waxy bitumen stranding in southern australia a geochemical study of multiple oil families and their likely origins abstract reports of bitumen stranding on the ocean beaches of southern australia date back to the early days of european settlement previous investigations have shown that this coastal bitumen comprises three categories of stranded petroleum waxy bitumen asphaltite and oil slicks all three varieties are physically and chemically distinct from each other and bear no geochemical resemblance to any indigenous australian crude oil this study focuses on the most common variety waxy bitumen which accounted for 90 of the strandings on six south australian beaches repeatedly surveyed during 1991 1992 geochemical analysis of 96 individual specimens collected from these survey sites and other beaches in south australia and western victoria has shown them to be variously weathered high wax crude oils of paraffinic to aromatic intermediate bulk composition elemental isotopic and biomarker differences allow their assignment to at least five oil families with inferred source facies that range from deep freshwater lacustrine through paludal and deltaic to euxinic marine possibly deposited within different sedimentary basins family 1 2 and 3 waxy bitumens all contain biomarkers derived from the freshwater alga botryococcus sp and tropical angiosperms notably dipterocarps similar biomarker assemblages are unknown in australian sedimentary basins but are common in cenozoic crude oils and source rocks throughout western indonesia family 4 waxy bitumens lack these biomarkers but do contain dinosterane and 24 n propylcholestane indicative of a marine source affinity while the carbon isotopic signatures and high pristane phytane pr ph ratios of family 5 waxy bitumens are consistent with their origin from coal rich source rocks deposited in fluvial to deltaic sedimentary successions the majority of these waxy bitumens represent an oceanic influx of non indigenous southeast asian crude oils carried into the waters of southern australia by the leeuwin current although they are likely to originate from natural seepage within the indonesian archipelago it is unknown whether the parent oils emanate from submarine seeps or from inland seepages which are then carried to the sea by rivers the common practice of tanker cleaning operations in the java and banda seas may augment the supply of natural bitumen to the beaches of australia

petroleum geochemistry of the lower and middle jurassic in atlantic margin basins of ireland and the uk potential hydrocarbon source rocks of lower and middle jurassic age have been reported from outcrop shallow boreholes and exploration wells in atlantic margin basins of the uk hebrides west of shetlands and flanking the ne rockall trough and recently in the continuation of this trend offshore ireland slyne erris and porcupine basins previously these organic rich mudrocks were considered to be of little economic importance due largely to their perceived limited areal distribution and low maturity however recent geochemical studies of oils and shales from exploration drilling of these basins shows the lower and middle jurassic to have considerable potential as effective hydrocarbon source rocks supplanting the late jurassic early cretaceous kimmeridge clay formation equivalents as the only viable oil source rock in the region flanking the atlantic margin in the irish and uk sectors rich oil source potential occurs in two transgressive mudrock cycles of lower jurassic age these are the sinemurian pliensbachian interval and the overlying toarcian section present in basins such as the solan minch hebrides slyne north celtic sea st george s channel and central english channel the middle jurassic source rocks have a more limited areal distribution and occur in the faroe shetland solan west lewis west flannan hebrides slyne and north porcupine basins with oil source potential in regressive marginal marine to lacustrine facies mudrocks geochemical studies were undertaken on mudrocks from the lower and middle jurassic sections in atlantic margin basins outcrop shallow borehole core and exploration well cores and cuttings samples and on oils from drill stem test and shows core and cuttings extracts detailed analyses using gc gc ms and carbon isotopes allowed both characterization of the source rocks and oil to source correlation biomarker and carbon isotope studies of oils from the faroe shetland basin foinaven and schiehallion fields the porcupine basin connemara accumulation the wessex basin wytch farm and kimmeridge oil fields and wells in the slyne basin show strong correlations to the various source rock developments in the lower and middle jurassic the mixed biodegraded foinaven and schiehallion oils have a major waxy component and correlate with lacustrine middle jurassic source rocks in the solan and west lewis west flannan basins middle jurassic sourcing of the connemara oils is also suggested while oils in the slyne basin appear to have been largely sourced by the lower jurassic pabba shale formation oils in the wessex basin wytch farm and kimmeridge appear to have been sourced by hettangian sinemurian mudrocks and those in the north celtic sea basin by toarcian source rocks the results from this study in combination with previously published data show that rich effective oil prone source rocks occur in both the lower and middle jurassic of the atlantic margin basins offshore ireland and the uk these source rocks can be correlated with indigenous oils indicating the existence of a previously under evaluated petroleum system

lipid and mineralogical composition of the cretaceous black shale deposits of the fardes formation southern iberian paleomargin betic cordillera south spain black shale type facies 1 3 1 5 toc registering the global cenomanian turonian boundary oceanic anoxic event ctbe in a deep trough on the southern iberian paleomargin fardes formation betic cordillera have been analyzed for their lipid composition and bulk clay mineralogy the bulk mineralogy is composed of phyllosilicates 70 80 quartz 10 30 and feldspar 5 clinoptilolite opal ct calcite dolomite pyrite barite and halite are present in minor amounts dioctahedral smectite 50 85 is the dominant phase among clays concurrently with palygorskite 10 40 illite 10 30 and kaolinite chlorite 5 these mineral associations and other inorganic geochemical features reflect the importance of oceanic bottom circulation for smectite particle transport coming from other neighbouring oceanic realms the study of the solvent extractable organic matter has shown that these black shales result from anoxic depositional events with high microbial reworking of autochthonous and allochthonous inputs distributions of c21 c27n alkanes without odd to even carbon number preference occurring along with c25 c28iso and anteiso alkanes are found in all shales other microbial lipids are more specific of each black shale type hopanoid components namely hopanoid acids are more abundant in the sediments of the cenomanian turonian boundary ctb whereas the underlying cenomanian hemipelagite layers contain a number of acyclic compounds such as phytol derived isoprenoid acids linear methyl ketones 5 6 10 14 trimethylpentadecan 2 one and c23 c26 13 oxofatty acids representing detrital contributions of microbially oxidized lipids archebacterial inputs are re presented by significant amounts of 2 6 10 14 18 22 hexamethyltetracosane in the ctb shales and by dimethylgeranylbenzene and dimethylfarnesylbenzene in the underlying cenomanian hemipelagite sections the latter isoprenoid components are tentatively identified for the first time higher plant components are also found suberin acids namely c22 and c24 mono and dicarboxylic are abundant in the ctb shales and dammarane is a major component of the cenomanian sediments

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

molecular genetic markers and maturity indices in intermontane lacustrine facies kishenehn formation montana abstract molecular markers have considerable promise as thermal maturation indicators in source rocks having a well defined depositional environment this occurs in the kishenehn formation northwest montana and southeast british columbia an oligocene unit comprised of fluvial and lacustrine shales up to 3 km of these non marine sediments were deposited in a 900 sq km elongated half graben atop the precambrian rocks of the lewis thrust sheet specific outcrops of the coal creek member of the kishenehn formation are known to contain excellent potential source rocks including extensive oil shales the source rock potential and molecular marker geochemistry of most of the major kishenehn outcrops have now been investigated and regional results are presented in this paper source rock analysis of a regional suite of kishenehn samples indicates excellent petroleum potential immature type i kerogen throughout the basin several classes of distinctive diagenetic molecular markers occur within the coal creek member of the kishenehn formation including diasterenes spirosterenes methylspirosterenes b ring monoaromatic anthrasteroids hopanes and moretanes molecular markers indicative of non marine deposition include dehydroabietane conifer input and an onocerane recently identified in leaf fossils of miocene lacustrine beds in adjacent idaho triterpane ratios are significantly more sensitive than vitrinite reflectance methods in assessing thermal maturation in the kishenehn and are successfully used in this study to order outcrop locations according to thermal maturity level the systematic variation of specific markers with increasing thermal maturation suggests that molecular correlation is feasible and could provide a method of assessing stratigraphic continuity in the basin

the structure and evolution of gap outflow over the gulf of tehuantepec mexico abstract mesoscale model simulations are used to examine the structure and dynamics of a gap outflow event over the gulf of tehuantepec mexico that was associated with a surge of cold air along the eastern slopes of the sierra madre the simulated gap outflow winds emerged from chivela pass reached a maximum speed of 25 m s 1 and turned anticyclonically as they fanned out over the gulf northerly winds were also able to ascend the mountains east and to a lesser extent west of chivela pass indicating that the movement of cold air across the sierra madre was not confined to the pass a mesoscale pressure ridge was aligned along the axis of the gap outflow jet which was flanked to the west by an anticyclonic eddy and to the east by a weaker cyclonic eddy a model derived trajectory along the axis of the outflow jet traced an inertial path with anticyclonic curvature produced primarily by the coriolis acceleration the cross flow pressure gradient acceleration along this trajectory was negligible be

biomarker evidence for botryococcus and a methane cycle in the eocene huadian oil shale ne china the saturated and unsaturated hydrocarbons of two samples hd 19 and hd 21 from the same section of the middle eocene lacustrine huadian oil shale in ne china were identified and shown to be mainly from algal and bacterial sources comparison of the two samples provided an opportunity to explore the contribution from telalginite to the hydrocarbon profiles cells identified from microscopy as botryococcus in the telalginite of hd 21 were confirmed as belonging to the l race of b braunii from the presence of monoaromatic lycopane derivatives and small amounts of several lycopadienes lycopane was abundant and was probably derived from biohydrogenation of lycopadienes and related lipids on the basis of d 13 c values hopane distributions showed a dominance of those with the biological 17b 21b stereochemistry as expected for an immature shale with low amounts of 17b 21a hopanes moretanes and 17a 21bhopanes two hopenes were also abundant and assigned as c29 and c30 neohop 13 18 enes which occurred together with the c29 and c30 hop 17 21 enes these had depleted carbon isotope values 43 7 to 50 8 indicative of production by methane oxidizing bacteria methanotrophs the high proportion of hopanoids with carbon numbers c32 indicates extensive post depositional diagenetic alteration of bacteriohopanepolyols as well as a direct input of c30 hopanoids the data clearly indicate that there was active utilization of methane in this lacustrine depositional setting but isoprenoid hydrocarbon biomarkers for methanogens such as pentamethylicosane pmi and squalane were in surprisingly low abundance it is possible that these bacterial contributions were present as polar lipids the origins of an unusual c38 isoprenoid alkane assigned as bipristane are uncertain but may be from methanogens steranes and sterenes were relatively minor components but abundant diasterenes and 4 methyldiasterenes were present reflecting significant conversion of the original lipid composition by way of clay catalysed diagenesis the biomarker data suggest that the bottom waters in the original depositional environment had low o2 content but the sediments were probably neither sulfidic nor strongly reducing the high content of organic matter in the shale likely reflects both high but fluctuating productivity due to eutrophic conditions in the overlying water and good preservation in the sediments

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

interannual variability of tehuantepec eddies 1 topex poseidon satellite altimeter observations and the naval research laboratory layered ocean model simulations show interannual variability in the number and intensity of tehuantepec eddies off the mexican southwest coast analysis of the results illustrates that downwelling coastally trapped waves which are generated in the equatorial pacific play a crucial role in the modulation and generation of tehuantepec eddies and a dominant role in tehuantepec eddy interannual variability this introduces a new paradigm in which the generation and modulation of tehuantepec eddies is not exclusively explained in terms of the strong and intermittent tehuantepec wind events in fact the results show anticyclonic eddy formation during periods of calm tehuantepec winds that is specifically exemplified by the formation of two anticyclonic tehuantepec eddies during a 5 month period of weak gulf of tehuantepec winds during summer of 1997 furthermore the satellite observed and nlom simulated proliferation of tehuantepec eddies during el nino years is explained by the corresponding increase in downwelling coastally trapped waves and a lack of increase in the number and strength of tehuantepec wind events during el nino years

organic facies variations in the westbury formation rhaetic bristol channel sw england abstract despite their dark colour laminated fabric and dysoxic character the thermally immature shales of the rhaetic westbury formation of the bristol channel area typically have total organic carbon toc values of only 1 0 1 5 and hydrogen indices hi 200 variations in toc and hi are correlated with the amorphous organic matter aom fluorescence but not the aom suggesting that redox related variations in aom preservation control the organic facies the diameter of equidimensional black wood phytoclasts decreases in intervals with higher toc and hi suggesting an association with lower energy depositional conditions such intervals also show a relative increase in light brown wood probably a reflection of more humid onshore conditions and lower phytoclast oxidation at source phytoc values suggest the input of terrestrial om was relatively low and stable during westbury deposition indicating a distal setting removed from fluviodeltaic sediment sources

kardla hiiumaa island estonia the buried and well preserved ordovician marine impact structure abstract the kardla marine impact structure estonia 58 58 n 22 46 e was formed at 455 ma upper ordovician in a shallow epicontinental sea some tens of kilometres from the land and erosion area the iron rich projectile about 200 m in diameter approached from the west at an angle of 30 45 the impactor penetrated about 50 m thick water layer and the sedimentary cover and exploded in the uppermost part of the crystalline basement a complex crater 4 km wide and about 500 m deep with a central uplift rising 130 m from the crater floor was formed the highest point of the rimwall is 110 m above the target level the rimwall is cut by at least two resurge excavated gullies the variable height of the rimwall obviously results from the obliqueness of the impact outside the crater an elliptical area was revealed 12 15 km in diameter with deformed sedimentary rocks below the target level the elliptical shape of this area may also be due to the oblique impact because the crater and its surroundings were buried directly after the impact the whole complex of impact related sediments is preserved there they are recovered by 160 wells six of which penetrate the entire complex of impact breccias inside the crater

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

molecular fossils and other organic markers as palaeoenvironmental indicators of the messinian calcare di base formation normal versus stressed marine deposition rossano basin northern calabria italy a multidisciplinary study has been carried out on the late miocene messinian calcare di base formation in northern calabria italy with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone the research has been developed through sedimentological microfacies organic petrography and geochemical analyses palynofacies rock eval pyrolysis and gas chromatography mass spectrometry the carbonates studied preserve their original mineralogy aragonite and microstructure the prevailing microfacies consists of clotted peloidal micrite with antigravitative fabric larger and darker cylindrical subcylindrical micritic grains attributable to faecal pellets are more or less randomly dispersed in the peloidal micrite the faecal pellets have been ascribed to copepods because zooclasts of these arthropods were observed in the palynofacies bright epifluorescence characterizes the faecal pellets and peloidal micrite indicating their high content of organic matter detrital and stromatolitic microfacies occur rarely around a few percent the detrital microfacies is characterized by silt sized grains organized in thin sometimes bioturbated graded laminae the stromatolitic microfacies shows planar to gently curved wrinkled laminae organized in dark and light couplets the associated sedimentary organic matter shows low maturity and preserves the original signatures of the source organisms rock eval pyrolysis revealed a transitional composition between type ii and type iii kerogen suggesting a mixture of marine and terrigenous organic matter input the molecular biogeochemical data indicate three main biological signatures algae bacteria and higher plants organic markers together with sedimentary evidence indicate a marine depositional scenario influenced by freshwater input rather than evaporitic concentration we conclude that the most probable bacterial process involved in carbonate precipitation of the calcare di base considering the freshwater input and consequent probable enrichment in organic matter and ca2 ions is ammonification of amino acids in aerobic conditions

air sea interaction over the eastern pacific warm pool gap winds thermocline dome and atmospheric convection high resolution satellite observations are used to investigate air sea interaction over the eastern pacific warm pool in winter strong wind jets develop over the gulfs of tehuantepec papagayo and panama accelerated by the pressure gradients between the atlantic and pacific across narrow passes of central american cordillera patches of cold sea surface temperatures ssts and high chlorophyll develop under these wind jets as a result of increased turbulent heat flux from the ocean and enhanced mixing across the base of the ocean mixed layer despite a large decrease in sst exceeding 38c in seasonal means the cold patches associated with the tehuantepec and papagayo jets do not have an obvious effect on local atmospheric convection in winter since the intertropical convergence zone itcz is located farther south the cold patch of the panama jet to the south on the other hand cuts through the winter itcz and breaks it into two parts a pronounced thermocline dome develops west of the gulf of papagayo with the 208c isotherm only 30 m deep throughout the year in summer when the panama jet disappears and the other two wind jets weaken sst is 0 58c lower over this costa rica dome than the background this cold spot reduces local precipitation by half punching a hole of 500 km in diameter in the summer itcz the dome underlies a patch of open ocean high chlorophyll this thermocline dome is an ocean dynamic response to the positive wind curls south of the papagayo jet which is optimally oriented to excite ocean rossby waves that remotely affect the ocean to the west the meridionally oriented tehuantepec and panama jets by contrast only influence the local thermocline depth with few remote effects on sst and the atmosphere the orographical triggered air sea interaction described here is a good benchmark for testing high resolution climate models now under development

the significance of 24 norcholestanes 4 methylsteranes and dinosteranes in oils and source rocks from east sirte basin libya abstract the present paper involves a detailed evaluation of specific steroid biomarkers by gas chromatography mass spectrometry gc ms and gc metastable reaction monitoring mrm analyses of several crude oils and source rocks from the east sirte basin 24 norcholestanes dinosteranes 4 methyl 24 ethylcholestanes and triaromatic steroids have been identified in both source rocks and crude oils of the east sirte basin diatoms dinoflagellates including those potentially associated with corals and or their direct ancestors are amongst the proposed sources of these biomarkers these biomarker parameters have been used to establish a mesozoic oil source correlation of the east sirte basin hydropyrolysis of an extant coral extract revealed a similar distribution although immature of dinosteranes and 4 methyl 24 ethylcholestanes also observed in the sirte oils and source rocks this is consistent with the presence of dinoflagellates present during the deposition of the mesozoic aged east sirte basin formations a good data correlation for the rock extracts revealed a similar distribution of 3 24 dimethyl triaromatic steroids 3 methyl 24 ethylcholestanes 4 methyl 24 ethylcholestanes and 2 methyl 24 ethylcholestanes observed in one of the oil families and associated source rocks for the east sirte basin

biological marker compounds as indicators of the depositions history of the maoming oil shale abstract the eocene maoming oil shale from guangdong province occurs as a laterally uniform stratigraphic section typically 20 25 m thick from which the aliphatic hydrocarbon constituents of six representative samples were investigated using gc and c gc ms the sediments evaluated included the basal lignite a vitrinite lens from the overlying claystone and four intervals from the massive oil shale bed as expected the lignite and vitrinite differ markedly from the oil shales the lignite is dominated by bacterial hopanoids and components of higher plant origin including c 29 steroids and triterpenoids such as oleanenes visually the oil shale samples show corroded and degraded phytoclasts spores wispy particles of fluorescent organic material attributable to dinoflagellates and especially in the uppermost sample colonial algal bodies the distributions of biological markers in the oil shales show many features in common notably a dominance of dinoflagellate derived 4 methylsteroids and a significant proportion of higher plant derived n alkanes with marked odd over even carbon number predominance overall they exhibit several features that resemble characteristics of the messel shale the hydrocarbons of the lowest shale horizon suggest that there may have been a gradual transition between deposition of the original peat and the subsequent oil shales the aliphatic hydrocarbons of the uppermost shale are dominated by a number of c 31 and c 33 botryococcane homologues and other unusual branched alkanes possibly derived from green algae all of the samples are immature overall molecular and microscopic examination of the stratigraphic succession of the maoming oil shale suggests a shallow lacustrine environment within which peats were deposited this lake subsequently deepened to support abundant algal populations especially dinoflagellates culminating in a dominance of botryococcoid algae

the toarcian black shale event in northern italy abstract during the early toarcian jurassic c 192 ma organic rich sediments were deposited in many areas of europe this paper reports the major findings of the first part of an organic geochemical investigation of the toarcian oceanic anoxic event oae thirty two black shales and associated lithologies were studied from seven localities in the southern alps of northern italy toarcian organic rich sediments up to 4 3 toc were deposited in various palaeoceanographic settings within the lombardy belluno and julian basins and on the trento plateau results of biomarker analyses indicates that in all sections mixed contributions from algae and bacteria dominate a variable but generally minor terrigenous input the preservation of significant quantities of marine derived organic matter and the typically well developed sedimentary lamination suggest that the black shales accumulated under oxygen deficient conditions in all palaeoceanographic settings molecular evidence suggests that the algal derived components of the sedimentary organic matter is partially degraded in many of the basinal samples this observation is here interpreted as being the result of aerobic decomposition of algal debris during transport through the water column other lines of evidence indicate that oxygen depletion intensified during the later stages of the toarcian oae with enhanced preservation of authochthonous organic matter in the light of these results the preferred model for the accumulation of black shales on the tethyan southern margin incorporates anoxic basin bottom waters overlain by a relatively well oxygenated water column

the midsummer drought over mexico and central america abstract the annual cycle of precipitation over the southern part of mexico and central america exhibits a bimodal distribution with maxima during june and september october and a relative minimum during july and august known as the midsummer drought msd the msd is not associated with the meridional migration of the intertropical convergence zone itcz and its double crossing over central america but rather with fluctuations in the intensity and location of the eastern pacific itcz during the transition from intense to weak weak to intense convective activity the trade winds over the caribbean strengthen weaken such acceleration in the trade winds is part of the dynamic response of the low level atmosphere to the magnitude of the convective forcing in the itcz the intensification of the trade winds during july and august and the orographic forcing of the mountains over most of central america result in maximum precipitation along the caribbean coast and minimum precipitation along the pacific

petroleum charge history in the baiyun depression and panyu lower uplift in the pearl river mouth basin northern south china sea constraints from integration of organic geochemical and fluid inclusion data the source thermal maturity and charge history of oil and gas condensate in the baiyun depression and the panyu lower uplift were determined using organic geochemical and fluid inclusion data nearly all the gas condensates and oil in the study area originated from eocene enping formation source rocks whereas the condensate fluids in the eastern area originated from the enping and zhuhai formations the condensate fluids have a relatively low thermal maturity with a calculated vitrinite reflectance equivalent that typically ranges from 0 8 to 1 0 based on the c29 sterane isomerization ratios and aromatic hydrocarbon maturity parameters four types of oil inclusions with various fluorescence colors yellow blue and api gravities 25 44 were recognized in the oligocene and lower miocene reservoir units which suggest multiple oil charging events the homogenization temperatures of the fluid inclusions recorded the oil charge events accompanying large scale hot fluid movement which was most likely caused by the charging of high temperature natural gas from the deeper wenchang formation the trapping pressures of the oil inclusions and the reconstructed burial histories were used to determine the timing of oil charge the main oil charge occurred from 16 7 ma throughout the baiyun depression and panyu lower uplift whereas the panyu lower uplift experienced an additional oil charge from 5 0 ma the natural gas charge occurred during the main oil charging period and may continue to the present day multiple physical processes such as gas injection without gas exsolution gas washing with gas exsolution and migration fractionation have played important roles in gas condensate formation and controlling the petroleum distribution in the baiyun depression and panyu lower uplift

the origin and fate of 4 methyl steroid hydrocarbons i diagenesis of 4 methyl sterenes abstract treatment of 4 methylcholest 4 ene under mild acid conditions at low temperatures gives chemical evidence for certain features seen in the distributions of sedimentary 4 methyl steroid hydrocarbons and further indicates that many low temperature diagenetic reactions of steroids are explicable in terms of acid catalysed rearrangements specifically the results provide i indirect evidence that the 4 ene skeleton is a key intermediate in the dehydration of 4 methyl stanols in sediments ii an explanation for the distribution of 4 methyl sterenes and a nor sterenes in the lacustrine messel shale eocene iii an explanation for the presence of 4 methyl steranes in relatively immature sedimentary rocks despite the precursor stanols having the 4 methyl configuration with increasing maturity in the paris basin shales lower toarcian the less stable 4 methyl steranes decrease gradually in abundance relative to their 4 methyl counterparts at a rate fairly similar to the change in pristane stereochemistry

satellite observations of the wind jets off the pacific coast of central america part ii regional relationships and dynamical considerations abstract satellite estimates of winds at 10 m above the sea surface by the nasa scatterometer nscat during the 9 month period october 1996 june 1997 are analyzed to investigate the correlations between the three major wind jets along the pacific coast of central america and their relationships to the wind and pressure fields in the inter american seas and eastern tropical pacific comparisons with sea level pressure confirm the conventional view that tehuantepec wind variations are driven by pressure variations in the gulf of mexico associated with north american cold air outbreaks the three jets sometimes developed sequentially from north to south statistically however the papagayo and panama jets were poorly correlated with variations of the tehuantepec jet over the nscat observational period the papagayo and panama jets were significantly correlated with each other and were coupled to coherent variations of the trade winds extending from the caribbean sea to the eastern tropical pacific the det