the white stone band of the kimmeridge clay formation an integrated high resolution approach to understanding environmental change the kimmeridge clay is a jurassic mudrock succession that shows milankovitch band climatic cyclicity a key issue is to determine how the subtle changes that define this cyclicity result from climatic change using material from the natural environment research council rapid global geological events rgge kimmeridge drilling project boreholes the white stone band was investigated at the lamination scale using backscattered electron imagery and quantitative palynofacies fabric analysis shows the lamination to represent successive deposition of coccolith rich and organic matter rich layers individual laminae contain unsorted palynological debris with a consistent ratio of marine and terrestrial components such mixed organic matter input is interpreted as the result of storm transport linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria as the photic zone extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and subsequently became preserved through sulphurization with greatly increased sequestration of carbon this was significantly increased by late season storm driven mixing of euxinic water into the photic zone increased frequency of storm systems would therefore dilute the coccolith input to give an oil shale hence climatically induced changes in storm frequency would progressively vary the organic content of the sediment and generate the climate cycle signal

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

the enigma of high latitude paleoclimate abstract the geological record of paleontology paleobotany and oxygen isotope determinations show conclusively that the mesozoic and early tertiary paleoclimates of arctic and antarctic latitudes were far warmer than that of the present observations indicate that temperate to subtropical conditions existed in these regions in the past the problem is just as cogent for the paleogeaphic reconstructions of north america and antarctica that are based on studies of rock magnetism temperatures computed by the application of a thermodynamic climate model to paleogeography which verify well for the present and most of the past are very discrepant for high latitude observations tentative explanations of the climate problem that involve changes in solar luminosity earth s axial tilt and ocean currents appear to be untenable another tentative and somewhat heretical proposal is offered here that paleogeography as related to former pole positions determined from rock magnetism may have gross errors due to a long term bias between the rotational and dipole pole locations as a consequences erroneous high paleolatitude locations would be assigned to regions whose fauna flora and paleolatitudes all suggest lower latitude locations

large scale forcing of summertime monsoon surges over the gulf of california and the southwestern united states synoptic forcing of the gulf of california summertime low level wind field is described using a nested regional modeling system under appropriate synoptic conditions strong surge events develop that are characterized by persistent vertically extensive 1 2 km southerly flow extending along the entire gulf of california and into arizona california and even southern nevada these surge periods are initiated either by tropical cyclone activity to the south of baja california or by the westward propagation of lower tropospheric troughs from over the sierra madre occidental to the eastern pacific the flow over the gulf is primarily geostrophic and is associated with the presence of these low pressure centers to the south and west of baja california

intraseasonal teleconnection between north american and western north pacific monsoons with 20 day time scale abstract based on a recently released high resolution reanalysis dataset for the north american region the intraseasonal variability isv with a time scale of about 20 days of the north american monsoon nam is examined the rainfall signals associated with this phenomenon first emerge near the gulf of mexico and eastern pacific at about 20 n they subsequently migrate to the southwestern united states along the slope of the sierra madre occidental the rainfall quickly dissipates upon arrival at the desert region of arizona and new mexico aznm the enhanced rainfall over aznm is accompanied by strong southeasterly low level flow along the gulf of california this pattern bears strong resemblance to the circulation related to gulf surge events as documented by many studies the southeasterly flow is associated with an anomalous low vortex over the subtropical eastern pacific ocean off california and a midlatitude anticyclone over the central united states in the lower troposphere this flow pat

evidence for annual records of phytoplankton productivity in the kimmeridge clay formation coccolith stone bands upper jurassic dorset uk the upper jurassic kimmeridge clay formation is a c org rich sequence of mudrocks that was deposited in a dysoxic basin which served unusually to preserve primary coccolithophorid proportions strikingly contrasting within this dark coloured formation are the white coccolith stone bands which contain pristinely preserved coccolithophorid assemblages preserving potentially primary coccolithophorid abundances with minimal diagenetic alteration using methodology described herein scanning electron microscopy sem observation of mum scale laminae within selected stone bands has revealed five distinctive types of microlamina type 1 being barren clay type 2 comprising coccoliths associated with varying amounts of clay or amorphous organic matter type 3 being purely coccolithic type 4 being of putative microbial origin and type 5 containing frequent calcispheres these are all described and illustrated here illustrated sequences of these are discussed with reference to an hypothetical model sequence based on modem records representing a kimmeridgian year of coccolithophorid productivity annual signals are thus interpreted based on the observations presented here and including summaries of the palynomorph records from the stone bands we comment on watznaueriacean palaeoecology and particularly the interpretation of watznaueria fossacincta barnesiae as an opportunistic growth maximising taxon c 2004 elsevier b v all rights reserved

the origin and nature of seismic reflections of sharp based shoreface deposits upper jurassic siliciclastics northern france in order to advance understanding of the relationship between geological properties and their physical expression in reflection images this study has focused expertise in reflection geophysics petrophysics and sedimentology on the same geological object in this case a succession of upper jurassic sharp based shoreface deposits embedded in offshore marine shales in northern france this integrated approach to determine firstly the origin and nature of seismic reflections calibration and secondly to provide a means of extracting geological information from seismic imagery inverse calibration was built on the following analytical steps firstly detailed and extensive petrophysical analyses of outcrop plug samples continuous core and sonic well logs in combination with a quantification of mineralogical and textural properties allowed a direct conversion of acoustic properties impedance into sedimentological properties resulting in a quantitative physical sequence stratigraphic model secondly the integration of scale dependent acoustic measurements ranging from 0 01 m and 320 khz on cores up to the wavelength of field seismic data was established using an averaging algorithm an effective medium theory type as an upscaling approach this alternative to a vsp or check shot allows an optimized depth time conversion and hence determination of the origin of the seismic reflections with previously unattainable accuracy finally the shape and scale dependence of impedance contrasts were integrated into so called singularity parameters that directly link depositional changes with information from seismic reflections depositional changes in the shallow water domain are generally characterized by step functions whereas those in more distal depositional environments are represented by spiky functions this approach allows the recognition of the associated reflection events and vice versa it provides a unique opportunity to extract the character of impedance changes and thus changes in depositional environment from seismic reflection records in general

late jurassic palaeoclimatic change from clay mineralogy and gamma ray spectrometry of the kimmeridge clay dorset uk abstract the late jurassic was a time of increasing aridity in nw europe here a new clay mineral dataset is presented from a 600 m thick composite core through the kimmeridge clay formation southern england clay mineral assemblages comprise mainly illite and kaolinite with minor randomly interstratified illite smectite mixed layer clays sem observations indicate that clay minerals are mainly detrital except in silty strata of late tithonian age which contain abundant pore filling kaolinite aggregates th k ratios determined from gamma ray spectrometry mirror palaeoclimatically significant variations in kaolinite illite ratios with notable exception where diagenetic kaolinite occurs comparison with age equivalent strata identifies regional cyclic variations in clay minerals at the 100 300 m scale small scale 10 20 m variations in clay minerals and th k also occur it is proposed that the region experienced progressively intense humidity through the kimmeridgian followed by a return to more arid conditions during the early tithonian following a mid tithonian peak in aridity the hudlestoni event9 more humid climatic conditions returned prior to the development of latest tithonian intense aridity late jurassic climate was apparently subject to synchronously cyclic changes across a broad area of the laurasian continent such changes could not have resulted from mountain building or continental rotations supplementary material clay data are available at http www geolsoc org uk sup18376

mechanisms of interannual variability of the southwest united states summer rainfall maximum abstract the mid summer rainfall singularity of the southwest united states principally arizona exhibits marked variations on interannual and decadal time scales examination of the synoptic mechanisms involved in these variations is undertaken here in particular associations between the rainfall the dominant latitude of the summertime mid tropospheric subtropical ridge str over the southwest united states and the sea surface temperatures ssts of the equatorial and north pacific region are documented the analysis utilizes a composite approach for sets of extreme years chosen on the basis of the rainfall and circulation anomalies it is found that northward southward displaced seasonal str is associated with wetter drier summers in arizona further these extremes have tended to follow winters characterized by positive negative phases of the pacific north america pna teleconnection pattern the latter association arises at least in part from the memory imparted to the atmosphere by th

simulation of a north american monsoon gulf surge event and comparison to observations abstractgulf surges are transient disturbances that propagate along the gulf of california goc from south to north transporting cool moist air toward the deserts of northwest mexico and the southwest united states during the north american monsoon they have been shown to modulate precipitation and have been linked to severe weather and flooding in northern mexico and the southwest united states the general features and progression of surge events are well studied but their detailed evolution is still unclear to address this several convection permitting simulations are performed over the core monsoon region for the 12 14 july 2004 gulf surge event this surge event occurred during the north american monsoon experiment which allows for extensive comparison to field observations a 60 h reference simulation is able to reproduce the surge event capturing its main characteristics speed and direction of motion thermodynamic changes during its passage and strong northward moisture flux while the ti

relationship between tropical easterly waves and precipitation during the north american monsoon abstract relationships between tropical easterly waves tews and precipitation over mexico and the united states are examined during the north american monsoon nam the national centers for environmental prediction national center for atmospheric research reanalysis data are used to identify 137 tews that cross mexico north of 20 n after monsoon onset over a 31 yr period from 1975 to 2005 mean precipitation anomalies over two day periods both before and after tew passage are determined using climate prediction center daily precipitation analyses results indicate that positive precipitation anomalies occur along the west coast of mexico and extending into the west central united states in association with tew passage negative precipitation anomalies are found in the south central united states these precipitation anomaly patterns share many similarities to precipitation anomaly patterns previously defined in association with gulf surge events on longer time scales correlations between the total nu

comparison between high resolution seismic and sequence stratigraphic approaches applied to the upper jurassic deposits of the dover strait area northern france abstract this study is an attempt to interpret very high resolution seismic data usually devoted to shallow marine surveys in terms of very high resolution seismic and sequence stratigraphy at the scale of the reservoir seismic data are compared with outcrop based observations in order to discuss the geometrical relationships between rock bodies and the nature of the seismic reflections in terms of seismic facies related to type lithologies two high resolution seismic surveys using a sparker were performed in the dover strait area some 100s of metres away from the boulonnais coastal cliffs the aim was to look to the 130 m thick mixed siliciclastic carbonate deposits of upper jurassic age kimmeridgian tithonian cropping out at the sea floor and to compare them to the coastal cliffs exposures the 100 m apart seismic profiles exhibit a 100 m deep penetration and 1 m in vertical resolution upper 30 ms part of the profiles four seismic facies are recognised on the seismic profiles they comprise ten seismic units which can be grouped into three broad families group 1 has a parallel aggradational reflection configuration and conformable boundaries which may correspond to the transgressive and highstand systems tracts the seismic facies exhibit either a high continuity high amplitude corresponding to clayey mudstone lithologies of the mid ramp environment or a high continuity low amplitude corresponding to shaly lithologies of the outer ramp environment group 2 has a sigmoid progradational reflection configuration bounded at the base by a downlap surface and at the top by a toplap surface these boundaries correspond respectively in the field to a marine regressive surface of erosion and a marine transgressive surface of erosion the seismic facies is cross layered and exhibits a moderate continuity low to moderate amplitude and moderate frequency group 2 corresponds to the bioclastic sand prone facies of the inner ramp environment it is interpreted as lowstand sharp based shorefaces group 3 exhibits a progradational complex to chaotic configuration it lies on an erosional unconformity with paleogullies the seismic facies shows discontinuous reflections with moderate amplitude and high to moderate frequency it corresponds in the field to cross bedded sandstones in channel fill arrangements of fluvial origin wealdian deposits marking the top of the section the different systems tracts sequence boundaries and depositional sequences identified onshore can be recognised as well on the seismic profiles but the comparison demonstrates that seismic data complement the onshore sequence stratigraphic analysis by providing the geometrical relationships between systems tracts onlap downlap toplap that cannot be observed onshore the maximum flooding surfaces however present no specific seismic signature on such a low angle ramp profile it can only be identified precisely in the field which also help to relate lithologies to seismic facies this study represents one of the first attempts to interpret very high resolution seismic data at the outcrop scale it will be improved again in the future by the collection of impedance logs and synthetic seismic traces from cored sections on the coastal cliffs for comparison with the seismic data

quartz silt in mudrocks as a key to sequence stratigraphy kimmeridge clay formation late jurassic wessex basin uk sequence stratigraphic interpretation of mudrocks is often carried out using proxy indicators for grain size or by consideration of other aspects of lithology thought to relate to sea level change such as organic matter content an alternative stratigraphic analysis based on direct estimation of quartz silt content was carried out on a major late jurassic mudrock and oil source rock the kimmeridge clay formation of the wessex basin dorset uk the new data generated by backscatter sem x ray and image analysis show decametrescale stratigraphic patterns that are incompatible with many previous sequence stratigraphic interpretations based on gamma ray logs or visual lithofacies and biofacies description correlation with a basin margin section in the boulonnais northern france indicates that silt rich intervals in basinal facies are coeval within the limits of biostratigraphic resolution with shallow water sand rich packages on the margin variation in silt content in the kimmeridge clay therefore appears to be a record of relative sea level change of at least regional extent it is suggested that analysis of silt content offers the most reliable basis for generation of a regional sequence stratigraphy in basinal mudrocks a revised relative sea level curve for the wessex basin kimmeridgian and early tithonian is presented based on this premise

δ18o po43 and δ18o co32 from belemnite guards from eastern europe implications for palaeoceanographic reconstructions and for the preservation of pristine isotopic values abstract the oxygen isotopic composition of coexisting carbonate and phosphate from belemnite rostra was measured according to well established techniques in 42 samples of early and middle jurassic age and in five samples of oyster shells most of the samples come from various locations in the western carpathians of slovakia and ukraine and from central poland three samples come from the isle of skye the phosphate content of belemnite rostra though variable is systematically very low consistently lower than about 0 3 however this phosphate concentration is close to that found in shells of modern marine organisms including pelecypods gastropods and sepia cuttlebones which in some way could be considered the modern belemnite counterpart the measured oxygen isotopic composition of carbonate is within the normal range of values obtained from these fossils ranging from about 1 3 to about 0 6 pdb 1 with the exception of three samples the 13 c values range from about 0 8 to about 2 8 pdb 1 with the single exception of one sample from the isle of skye the oxygen isotopic composition of phosphate from belemnite rostra ranges from 19 8 to 24 9 v smow 22 of the samples measured showing 18 o values equal to or heavier than 23 0 in contrast the oyster values are considerably lighter in the case of both carbonate and phosphate 18 o enriched values can hardly be related to diagenetic processes that normally cause an oxygen isotope shift towards light values if deposition temperatures are calculated from the heavily enriched values by means of the equation of longinelli and nuti earth planet sci lett 19 1973 373 376 and assuming the 18 o of jurassic ocean water to be equal to 1 taking into account the lack of ice caps during the jurassic the obtained temperatures range from about 8 c to about zero these temperatures are obviously unreliable when mesozoic palaeoceanographic conditions and palaeoclimate are taken into account two different hypotheses are suggested to explain these results other hypotheses being rejected as unreliable 1 phosphate derived from the decaying organic matter of belemnites might have been introduced into belemnite rostra by early diagenetic fluids if the phosphate of belemnite organic matter was isotopically heavy as happens nowadays in the flesh of molluscs the inflow of this phosphate into the rostra could be responsible for the very positive 18 o values shown by many belemnite rostra this hypothesis is suggested by h w 2 previous oxygen isotope measurements on upper cretaceous belemnites yielded 18 o values very close to the most positive values obtained from lower tertiary pelecypods and fish teeth which are known to precipitate their phosphate under isotopic equilibrium conditions with seawater these data suggest the possibility that the phosphate in belemnite rostra is primary phosphate so that the very positive data reported here can be considered the result of good preservation of the pristine isotopic composition of primary phosphate consequently the only way to explain the very positive 18 o values is to consider the oxygen isotopic composition of jurassic ocean water to be more positive than nowadays by at least 3 this hypothesis is suggested by a l and a d m

multiscale diagnosis of the north american monsoon system using a variable resolution gcm abstract the onset and evolution of the north american monsoon system during the summer of 1993 were examined from regional to large scales using the national aeronautics and space administration nasa goddard earth observing system geos stretched grid gcm the model s grid spacing for the dynamical core ranges from 0 4 0 5 in latitude longitude over the united states to about 2 5 3 5 at the antipode and the physical package is solved on an intermediate 1 1 uniform grid a diagnostic analysis of the monsoon s onset reveals the development of a positive potential temperature anomaly at the surface that favors a lower level cyclonic circulation while a negative potential vorticity pv anomaly below the tropopause induces an upper level anticyclonic circulation ignoring diabatic effects this pattern is consistent with the superimposition of idealized pv and anomalies as previously discussed in the literature the inclusion of the smaller scale features of the core monsoon in the mod

principal component analysis of the summertime winds over the gulf of california a gulf surge index a principal component analysis of the summertime near surface quick scatterometer quikscat winds is used to identify the leading mode of synoptic scale variability of the low level flow along the gulf of california during the north american monsoon season a gulf surge mode emerges from this analysis as the leading eof with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence this index is used as a reference time series for regression analysis and compositing meteorological fields of interest to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon as well as the manifestation of these transient events in the large scale circulation it is found that although seemingly mesoscale features confined over the gulf of california gulf surges are intimately linked to patterns of large scale variability of the eastern pacific itcz and greatly contribute to the definition of the northward extent of the monsoonal rains

diurnal cloud to ground lightning patterns in arizona during the southwest monsoon abstract cloud to ground cg lightning shows great variability across arizona from one year to the next as well as from one day to the next availability of moisture location of the subtropical ridge axis transitory troughs in both the westerlies and easterlies and low level moisture surges from the gulf of california can affect thunderstorm occurrence which in turn will affect lightning production diurnal cg lightning patterns in arizona are also determined by daily heating cycles and topography six years of bureau of land management cg flash data are used in this investigation in arizona lightning usually starts first on a daily basis in the plateau region and extends in an arc from the white mountains of eastern arizona westward across the mogollon rim and then northward onto the kaibab plateau of northern arizona flash activity moves in a more or less continuous fashion off the plateau south and westward down the topography gradient and enters the lower desert by early evening at the

environmental cycles in the late jurassic northwest european epeiric basin interaction with atmospheric and hydrospheric circulations abstract despite the large size and the heterogeneity of the northwest european late jurassic kimmeridgian lower tithonian epeiric basin the sedimentary environment was rather uniform in general deposition of mudstones and the microlaminated organic rich sediments took place under low oxic to anoxic conditions detailed environmental analysis clearly points to a seasonal alternation of aerobic with anaerobic conditions in substrate and bottom water resulting in one year life cycles in the benthic environment the widespread uniformity of facies and the seasonal alternation in the oxygen budget of the benthic environments are best explained by a summer to winter change in the atmospheric circulation of the northern hemisphere this change strongly influenced the oceanographic situation in the northwestern european epeiric basin superposed on this one year cyclicity three more hierarchical levels of cycles are stratigraphically recorded they reflect a complex history of orbital forced and non orbital forced climatic changes and or eustatic sea level fluctuations in the late jurassic

late cretaceous paleogene paleogeography and paleocirculation evidence of north polar upwelling abstract quantitative determination of biogenic silica in late cretaceous and paleogene deep sea sediment cores from the central arctic ocean provides evidence of open ocean polar upwelling the timing of polar upwelling coincides with periods of a weakened meridional thermal gradient suggesting that heat transport to the poles by oceanic circulation may have been important the timing of biogenic silica deposition in the arctic precedes its deposition in both the norwegian greenland sea of the north atlantic and he bering sea of the north pacific tectonic events may be resposnible for the timingg and sitting of sites of deposition of biogenic silica in high northern latitudes particularly the tectonic evolution of sites of deep water exchange between the arctic and the world ocean we outline three phases in the post mid cretaceous history of silica deposition in high northern latitudes during phase i the arctic is a silica sink with deep water formation but with no deep water outflow the transition to phase ii is brought about by opening of the svalabard greenland strait to deep water outflow from the arctic to the norwegian greenland sea the transition to phase iii is initiated by submergence of the faroe iceland ridge and deep water outflow from the arctic to the north atlantic climatic conditions in the arctic during late cretaceous and paleogene time are predicted to have favored open ocean upwelling due to a circulation pattern dominated by cyclonic conditions resulting from the establisment of a semi permanent atmospheric low over the alpha ridge bathymetry of the alpha ridge may have intensified paleo upwelling

the portland purbeck junction portlandian berriasian in the weald and correlation of latest jurassic early cretaceous rocks in southern england ammonites and palynology are described at the portland purbeck junction in the weald a major disconformity exists between glaucolithus zone portland beds and the overlying basal purbeck facies the basal purbeck beds of the weald are correlated with the middle purbeck strata of dorset the cinder bed of dorset and wiltshire is described as one of several marine incursions entering wessex from further south in the anglo paris basin not from the spilsby basin the use of cinder bed as a convenient jurassic cretaceous portlandian ryazanian boundary is critically reviewed as is the placing of the base of the berriasian stage in the type purbeck section the rival biostratigrahic schemes based on ostracods and palynology are discussed and the discrepancies between the two schemes in southern england are examined

cyclostratigraphy orbital tuning and inferred productivity for the type kimmeridge clay late jurassic southern england three independently measured variables magnetic susceptibility photoelectric factor and total gamma ray obtained from throughout the type kimmeridge clay fm in dorset southern england were used to identify regular metre scale sedimentary cycles spectral analysis demonstrates that for long stratigraphical intervals the cycles are expressed as large amplitude cycles of 1 87 4 05 m wavelength and smaller amplitude cycles of around half that wavelength these cycles are interpreted to record orbital obliquity and precession respectively the much larger amplitude of the inferred obliquity cycles compared with the precession cycles may indicate a high latitude climatic forcing transferred to lower latitudes via sea level variations orbital tuning indicates that the early kimmeridgian sensu anglico lasted at least 3 6 ma 95 longer wavelength cycles and the late kimmeridgian at least 3 9 ma 103 longer wavelength cycles the first detailed productivity estimates for the kimmeridge clay fm on a cycle by cycle calculation indicate that average productivity of the type kimmeridge clay 220 g m 2 a 1 was less than the average productivity on modern continental shelves the high average organic carbon content of the type kimmeridge clay 3 8 total organic carbon cannot be attributed to high average productivity however the average organic carbon content is consistent with low siliciclastic mineral dilution of organic matter and or elevated preservation linked to reduced bottom water oxygenation

annual layering in the upper jurassic kimmeridge clay formation uk quantified using an ultra high resolution sem edx investigation abstract this paper reports the results of an ultra high resolution investigation of the geochemistry of the late jurassic kimmeridge clay formation kcf using scanning electron microscope energy dispersive x ray analysis sem edx sub millimetre banding is revealed in which each band approximately 112 m thick comprises a couplet of coccolith rich and coccolith poor sediment major element analysis reveals that regularly spaced peaks in the relative amount of calcium are associated with coccolith rich bands it is argued that each couplet represents an annual layer the calcium peaks corresponding to an annual bloom of coccolithophorids there is also a broad correlation between the calcium aluminium ratio and the ratios of sodium aluminium phosphorus aluminium and potassium aluminium to calcium aluminium ratios we tentatively suggest that there may be a link here sodium phosphorous and potassium today being key nutrients for coccolith productivity aluminium is taken as representing the background terrigenous clay fraction if each banded couplet is indeed annual and if the thickness of such bands were to be representative of the kcf as a whole then the post compactional thickness is broadly in agreement with sedimentation rates of 100 m per year calculated by oschmann 1990 this study confirms the view that the kcf in southern england accumulated in a predominantly anoxic environment that favoured the preservation of organic material within the bottom sediment bundles of bands clustering in groups of about 8 10 are tentatively related to short term changes in insolation possibly sun spot cycles

dynamics of a simulated north american monsoon gulf surge event abstractgulf surges are transient disturbances that propagate along the gulf of california goc from south to north transporting cool moist air toward the deserts of northwest mexico and the southwest united states during the north american monsoon they have been shown to modulate precipitation and have been linked to severe weather and flooding in northern mexico and the southwest united states the general features and progression of surge events are well documented but their detailed dynamical evolution is still unclear in this study a convection permitting simulation is performed over the core monsoon region for the 12 14 july 2004 gulf surge event and the dynamics of the simulated surge are examined initially convection associated with the tropical easterly wave precursor to tropical cyclone blas creates a disturbance in the southern goc on early 12 july this disturbance is a precursor to the gulf surge on 13 july and is a kelvin shock internal bore under the influence of rotation that diss

tethyan carbonate carbon isotope stratigraphy across the jurassic cretaceous boundary an indicator of decelerated global carbon cycling the carbon isotope record in four pelagic carbonate sections from the southern alps northern italy across the jurassic cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy the carbon isotope curve from bulk carbonates shows a decrease from kimmeridgian to early tithonian cm24 cm22 values of 13c 2 07 0 14 to late tithonian and berriasian cm18 cm14 values of 13c 1 26 0 16 the change in the carbon isotope record coincides with changes in tethyan calcite and silica accumulation rates with a drop in the calcite compensation depth in the atlantic and tethys oceans and with changes in organic carbon burial along the eurasian margin of the tethys reduced surface water productivity due to diminished transfer rates of biolimiting elements into the atlantic and tethys oceans can explain these observations the decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the tethys and atlantic oceans the proposed changes in tithonian berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles

the relationship between tropical easterly waves and surges over the gulf of california during the north american monsoon abstract coastally trapped disturbances which occur over the gulf of california and are commonly referred to as gulf surges are an important mechanism in the transport of low level moisture into the southwestern united states to determine whether or not gulf surges develop in association with the passage of tropical easterly waves as hypothesized in previous studies standard surface observations and european centre for medium range weather forecasts reanalysis data during the months of july and august over a 14 yr period are examined results indicate that tropical easterly wave troughs often cross western mexico 1 3 days prior to surge onset at yuma arizona indicating a strong correlation between these two events this analysis documents yet another mechanism by which the tropics influences convection in the midlatitudes

climate forcing primary production and the distribution of holocene biogenic sediments in the gulf of california abstract the gulf of california is a marginal seaway under the influence of a monsoon climate that produces cool dry winters and warm humid summers winds tidal mixing and coastal trapped waves forced by climate and the pacific ocean control nutrient advection and primary productivity pp strong northwest winds from the subtropical east pacific high pressure system begin in november and last until april and drive coastal upwelling along the mainland margin especially in the central and southern gulf in the northern gulf particularly around the midrift island tidal mixing and turbulence occurs year round advecting nutrients into the mixed layer and high productivity during summer and early fall months winds are variable of less intensity and mainly blow cross basin except in the most northern gulf summer pp is generally low in the central and southern gulf except along the mainland where coastal trapped waves associated with tropical surges and hurricanes generate mixing over the continental shelf mesoscale eddies or gyres often associated with jets and filaments extend to depths of 1000 m and transport nutrient enriched upwelled waters and plankton detritus across the gulf the largest and most persistent gyres rotate in an anti cyclonic direction east to west and are a principal source of the plankton export to the peninsula margin two major biogenic sediment patterns are present in core top sediments hemipelagic biosiliceous rich muds are accumulating beneath upwelling areas of high productivity in the central gulf and along the mainland margin calcium carbonate and organic carbon rich oc sediments are concentrated along the peninsula margin generally beneath lower productivity waters with the highest oc content in areas with the lowest productivity the high uniform biosiliceous content in guaymas basin extending southward into carmen basin reflects the redistribution by mesoscale gyres of phytoplankon debris produced in mainland coastal upwelling and tidally forced areas around the midrift islands holocene biogenic patterns are similar to the present day with the major difference in rates of accumulation phytoplankton production prior to about 8200 yr bp was significantly higher in the central and southern gulf decreased though the mid holocene and has been reasonably steady for the past 2500 yr the strong north south and east west gradients in present day phytoplankton productivity patterns are also reflected in the holocene sediment record a series of depositional cycles occur in the biogenic record with the strongest peaks of variability at about 150 144 18 200 198 5 and 350 350 40 yrs longer periodicities are present prior to 3200 yr bp but the 350 yr cycle dominates in the late holocene where it is best expressed as productivity dissolution cycles in the carbonate record

enhancement of accumulation and anoxic degradation of organic matter controlled by cyclic productivity a model abstract the aim of the study is to determine the relative influences of the genetic sources the export efficiency and the anaerobic degradation of organic carbon as factors controlling short term cyclic organic rich sedimentation in areas of high marine productivity a cyclic organic sequence of the kimmeridge clay formation of yorkshire u k was studied as an example of ancient sedimentation this formation outcropping in the cleveland basin near marton is known as a lateral equivalent of the major oil source rock unit of the north sea on the basis of petrographic and geochemical results a new model is proposed to explain the short term cyclic sedimentation of organic carbon under continuously anoxic bottom conditions the model assumes that the cyclicity is primarily controlled by variations of mineral free phytoplanktonic productivity such variations are thought to induce changes in carbon recycling in the photic zone so that the export efficiency of the metabolizable organic matter is modified a high sulphate reduction intensity relative to the organic matter flux is observed for the highest productivity periods which also reflects an enhancement of export efficiency as the redox conditions did not change significantly such variations in sulphate reduction intensity must be attributed not only to quantitative variations in the export productivity but also to its qualitative variations with more metabolizable organic matter reaching the anoxic domain during high productivity periods biosedimentary processes depending on productivity such as aggregation are thought to play an important role in reducing the transit time of metabolizable organic matter to the sediment finally the model implies that the amplitude of export productivity variations probably were larger than that of toc variations recorded in sediment which are mainly due to biologically refractory organic matter from plankton

a role for organic petrology in integrated studies of mudrocks examples from devonian black shales of the eastern us abstract over the years the study of mudrocks has lagged far behind that of other lithologies a circumstance that is in part due to their fine grained nature and in part due to economic realities yet within petroleum systems mudstones are usually the main source of hydrocarbons and typically are also important as hydrocarbon seals recent work on late devonian mudstones from the eastern us shows that much progress can be made through an integration of outcrop study macro and micropaleontology ichnofossils gamma ray spectroscopy microscopic examination of thin sections in transmitted and reflected light electron microscopy sem bse electron microprobe carbon and sulfur isotopes and organic geochemistry erosion surfaces within this black shale succession have been traced over large distances and provide the foundation for a sequence stratigraphic re interpretation of these rocks evidence of storm wave reworking of the seabed as well as the realization that benthic colonization was much more widespread than previously believed suggest that anoxic conditions in the water column were not a controlling factor in the accumulation of the large quantities of organic matter found in these shales these distal devonian shales accumulated slowly and allowed accumulation of large proportions of organic matter in modern settings of abundant organic matter accumulation the original material is broken down by bacteria within a matter of months into a mass of largely unidentifiable organic particles and extracellular bacterial slime although one can still find identifiable material within this mass slime and amorphous material strongly dominate after burial and maturation this material turns into the various organic macerals that organic petrologists are accustomed to describe one might wonder in this context how much information about the origin of a given mudstone unit can we hope to extract through organic petrology in order to illustrate how organic petrology of mudrocks can contribute to their better understanding late devonian black shales of the eastern us will be examined from a sedimentological perspective combining sedimentologic and geochemical data with basic observations on organic petrology illustrates how the latter can contribute to more realistic scenarios of black shale genesis

sequence analytical approach to the upper kimmeridgian lower tithonian storm dominated ramp deposits of the boulonnais northern france a landward time equivalent to offshore marine source rocks an interdisciplinary approach based on high resolution physical stratigraphy biostratigraphy organic matter analysis and clay mineralogy has been applied to the mixed siliciclastic carbonate kimmeridgian tithonian deposits of the boulonnais north western france these rocks are the age equivalents of some of the offshore marine source rocks of the north sea and were deposited in an overall storm dominated homoclinal ramp setting which may represent one of the most shore proximal sediments of this age cropping out in north western europe comparison with data from the yorkshire dorset lorraine and aquitaine areas allows the discrimination of three major transgressive regressive sediment packages with disconformities of interregional extent 1 from the baylei zone to top eudoxus zone 2 from the autissiodorensis zone to base scitulus zone 3 from the upper scitulus zone to the pectinatus zone the lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the eudoxus zone and the top of the autissiodorensis zone formed by high frequency relative sea level variations during the periods of maximum transgression of the platform the latter disconformity the p1 nodule bed reflects a major tectonically induced reorganization of the north west european intrashelf sedimentary basin characterized by a shift in both the location of the main depocentre and the sources of sediment production

dynamic mechanisms of the gulf surge 1 the gulf surge is a summertime phenomenon associated with the north american monsoon that transports moisture from the gulf of california into western portions of the united states this phenomenon has been acknowledged operationally and by researchers for over 30 years the surge is typically linked to the presence of some sort of low pressure system such as an easterly wave mesoscale convective system or hurricane located near the southern end of the gulf of california proposed mechanisms for the gulf surge are gravity currents ageostrophic flows kelvin or rossby edge waves the purpose of this paper is to describe the fundamental dynamics of each of these mechanisms and assess their plausibility through scale analyses and idealized numerical simulations and to suggest signatures that may appear in data and output of more sophisticated numerical models

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

a 20 year varve record of siliceous phytoplankton variability in the central gulf of california abstract year to year variability in the structure of the preserved siliceous phytoplankton assemblage is reconstructed from a box core retrieved from the varved sediments along the guaymas slope of the gulf of california a 20 year record from 1953 through 1972 is obtained from interpretation of the varve stratigraphy supported by 210 pb and 228 th dating ecological time series derived from microfossil analysis show a strong coherence with interannual sea level anomalies indicating a response to large scale climatic variability associated with the el nino southern oscillation phenomenon el nino periods are generally marked by increases in preserved abundances of the total siliceous assemblage and in particular by greater numbers of individuals within species whose distribution is limited to tropical and subtropical waters

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

new aspects on the formation of hydrocarbon source rocks episodic volcanism favors as shown by examples from europe the usa and brazil the formation of organic rich sediments hydrocarbon source rocks the examples examined from europe comprise the lower carboniferous oil shale group scotland upper carboniferous coal measures western germany upper jurassic kimmeridge shale north sea area lower cretaceous blattertonstein northwest germany and eocene messel oil shale rheingraben examples from the usa are devonian mississippian gas shales permian phosphoria shale middle cretaceous mowry shale eocene green river shale and miocene monterey shale examples from brazil are permian irati oil shale and oligocene paraiba valley oil shale volcanism is reflected during sedimentation 1 by exhalation of so2 and or co2 2 volcanic ashfalls 3 by generation of anoxia and preservation of organic matter and 4 by halmyrolytic alteration of volcanic ashes into highly surface active clay minerals montmorillonite

integration of sedimentology and ground penetrating radar for high resolution imaging of a carbonate platform ground penetrating radar has not been applied widely to the recognition of ancient carbonate platform geometries this article reports the results of an integrated study performed on an upper jurassic outcrop from the south east paris basin where coral bioherms laterally change into prograding depositional sequences ground penetrating radar profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop a ground penetrating radar profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled the excellent penetration depths of the ground penetrating radar 20 m with a monostatic 200 mhz antenna images the carbonate platform geometries ranging between outcrop workscale a few metres and seismic scale several hundreds of metres this study supports recent evidence of icehouse conditions and induced sea level fluctuations controlling the upper jurassic carbonate production

the low level circulation of the north american monsoon as revealed by quikscat five years 1999 2003 of near surface quikscat ocean winds over the gulf of california and northeast pacific ocean are used to characterize the changes in the low level circulation associated with the north american monsoon our analysis shows that the onset of the summer season is accompanied by a seasonal reversal of the flow along the gulf of california with the establishment of a time mean southerly wind throughout the gulf this reversal not evident in the global reanalysis products occurs in late spring and precedes the onset of the monsoonal rains in the core of the monsoon the time mean flow is found to be modulated by transient events namely gulf surges detected in the near surface wind field as periods of enhanced southerly flow which typically originate at the southern end of the gulf and propagate northward the histogram of the summertime along shore winds identifies these surges as a distinct population of events readily distinguishable from the background flow

the principal mode of interannual variability of the north american monsoon system nonseasonal behavior of the north american monsoon system nams during the summer months june september is investigated based on monthly mean satellite data and the national centers for environmental prediction national center for atmospheric research reanalyses for the period 1979 97 the leading principal component of the monthly mean precipitation over the domain 58 358n 808 1258w is used as a reference time series the associated variations in fields other than the rainfall are identified based on linear regression analysis the reference time series is highly correlated with summer rainfall averaged over this broadly defined nams domain and is therefore referred to as the spatially integrated precipitation index ipi it is also correlated with hurricane activity over the tropical and subtropical northeast pacific in its positive polarity the ipi is characterized by an intensification and northward expansion of the itcz toward the mexican coast with enhanced rainfall throughout mexico but particularly in the south and in a relative sense in the semiarid northwest it has a well defined sea level pressure and surface wind signature with negative sea level pressure anomalies to the northwest of the region of enhanced rainfall and westerly wind anomalies converging into the region from the west along 108 208n these features extend upward to the 500 hpa level and are overlaid by weak anomalies of opposing sign in the upper troposphere there are indications of an associated deep barotropic planetarywave signature over the united states but the geopotential anomalies are only weakly correlated with the ipi the ipi is only weakly correlated with summer rainfall over the southwestern united states with enso and with sst anomalies within the nams domain

surges over the gulf of california during the mexican monsoon abstract northward surges of relatively cool moist maritime air from the tropical pacific into the southwestern united states occur via the gulf of california every summer during the mexican monsoon season these surges advect large amounts of moisture northward and promote increased convective activity in arizona mesoscale model output from 32 successive 24 h simulations are used to examine both the large scale and mesoscale features associated with surge events model data are compared to high resolution aircraft measurements on two days showing clearly that the model is capable of reproducing many of the detailed structures found in the observations results from a large scale analysis indicate that strong surges are produced in the model when a midlatitude trough is in the proper phase relationship with a tropical easterly wave weak surges occur when this relationship is missing

kimmeridge clay sedimentation a new cyclic model abstract the kimmeridgian upper jurassic fine clastic sequences of the boulonnais northern france and dorset southern england represent oxygen controlled environments five facies types with increasingly deteriorating living conditions ranging from normal shelf environments to submarine lifeless desert have been distinguished the widespread occurrence of this facies in the late jurassic north atlantic shelf sea and the palaeogeographic situation require a large scale model to explain the kimmeridge clay sedimentation anoxic conditions are generally explained by one of three models none of which applies directly to the kimmeridge clay a new model derived from the overall palaeogeographic and palaeoclimatic situation is therefore proposed in this model water mass stratification and anoxic bottom conditions refer to a high latitude monsoonal type wind circulation causing a water current and counter current system in the north atlantic shelf sea and the arctic ocean variations in the amount of oxygen in the bottom waters allow recognition of four different cycles with periods ranging from seasonal to 3 107 years they influenced the counter current system and the resulting anoxic conditions

infrasound data inversion for atmospheric sounding summary the international monitoring system ims of the comprehensive nuclear test ban treaty ctbt continuously records acoustic waves in the 0 01 10 hz frequency band known as infrasound these waves propagate through the layered structure of the atmosphere coherent infrasonic waves are produced by a variety of anthropogenic and natural sources and their propagation is controlled by spatiotemporal variations of temperature and wind velocity natural stratification of atmospheric properties e g temperature density and winds forms waveguides allowing long range propagation of infrasound waves however atmospheric specifications used in infrasound propagation modelling suffer from lack and sparsity of available data above an altitude of 50 km as infrasound can propagate in the upper atmosphere up to 120 km we assume that infrasonic data could be used for sounding the atmosphere analogous to the use of seismic data to infer solid earth structure and the use of hydroacoustic data to infer oceanic structure we therefore develop an inversion scheme for vertical atmospheric wind profiles in the framework of an iterative linear inversion the forward problem is treated in the high frequency approximation using a hamiltonian formulation and complete first order ray perturbation theory is developed to construct the frechet derivatives matrix we introduce a specific parametrization for the unknown model parameters based on principal component analysis finally our algorithm is tested on synthetic data cases spanning different seasonal periods and network configurations the results show that our approach is suitable for infrasound atmospheric sounding on a regional scale

the shiveluch volcanic eruption of 12 november 1964 explosive eruption provoked by failure of the edifice abstract restudy of deposits at shiveluch in comparison with other data has shown that the sequence of eruptive events at shiveluch volcano on 12 november 1964 was the following edifice failure involving 1 154 km3 of material at 07 07 a m phreatic explosion with ejection of resurgent ash with a volume of 0 01 km3 plinian activity between 07 20 and 07 47 a m during which andesitic juvenile tephra with a volume of 0 3 km3 erupted during the final stage of the eruption between 07 47 and 08 22 a m pyroclastic flows with a volume of 0 3 0 5 km3 were erupted in this sequence there was no catastrophic directed blast with generation of a destructive pyroclastic density current like those that took place at bezymianny volcano in 1956 and at mount st helens in 1980 the absence of a directed blast is attributed to the fact that the 1964 eruption occurred before magma had enough time to intrude into the edifice and build a cryptodome the failure of the edifice depressurized only a hydrothermal system that existed around the old domes this appears to have been insufficient for the generation of a catastrophic directed blast the case history of volcanic activity at shiveluch before 1964 suggests that if the edifice of the young shiveluch had been stronger and had not failed by landsliding the eruption of 1964 might have consisted of prolonged dome extrusion with relatively weak explosive activity

molecular organic geochemistry of a proposed stratotype for the oxfordian kimmeridgian boundary isle of skye scotland the composition of the soluble organic matter of the oxfordian kimmeridgian flodigarry shale member isle of skye scotland is presented for the first time a continuous succession of silty clays and nodular limestone beds is exposed on a rocky shore to the north of staffin bay this succession is proposed as a potential stratotype of the boundary between the oxfordian and kimmeridgian stages this paper points out the exceptional preservation and very low thermal degradation of the organic matter indeed the molecular composition is characterized by the abundance of unsaturated biomarkers hopenes and diasterenes as well as undamaged bioterpenoids ferruginol and sugiol the abundance of long chain n alkanes characterized by an odd over even predominance reveals a dominant continental contribution this is also attested to by the relatively high amounts of plant biomarkers e g ferruginol sugiol cadalene and retene which suggest a palaeovegetation largely composed of pinophytes especially cupressaceae taxodiaceae and cheirolepidiaceae on the nearest emerged lands the water column of the depositional environment was oxic in its upper part and rather dysoxic in its lower part the composition of the organic matter does not significantly change along the flodigarry shale member in other words no evolutionary events or drastic change in palaeoenvironments can be deduced from the molecular content of these sedimentary rocks and it does not allow us to support a precise location for the oxfordian kimmeridgian boundary in the succession

analysis of 2002 and 2003 warm season precipitation from the north american monsoon experiment event rain gauge network analyses of rainfall characteristics and their linkage to physiographic features are made from the north american monsoon experiment name event rain gauge network nern in northwest mexico the findings are based on the network configuration for the 2002 and 2003 warm seasons despite the relatively short record used a clearer structure of core region monsoon rainfall is beginning to emerge in agreement with earlier coarser scale studies the seasonal precipitation maximum overlies the western slope of the sierra madre occidental but does not strictly parallel a particular elevation band it is shown that the distance to the gulf of california and potentially the configuration of the terrain profile may also play an important role in determining where the axis of maximum precipitation lies the diurnal cycles of precipitation frequency and intensity are shown to have distinct relationships to terrain elevation that are qualitatively similar to those observed over the front range of the rocky mountains in the central western united states the relationship between precipitation and gulf surge events occurring during the summer of 2003 is also explored

sequence stratigraphical interpretation of organic facies variations in marine siliciclastic systems general principles and application to the onshore kimmeridge clay formation uk

palaeoecology of the triassic black shale bivalve daonella new insights into an old controversy abstract several modes of life have been proposed for bivalves of the genus daonella taphonomic studies revealed that most taphocoenoses containing lumachellas shellbeds and butterflied preserved specimens are allochthonous articulated specimens with closed valves and well orientated sagittal planes are interpreted to be in situ autochthonous assemblages show a population structure dominated by subadults and adults monospecific and paucispecific taphocoenoses with daonellids are not due to preservational biases but reflect the former biocoenoses most species show a dependence on facies some are restricted to dysoxic milieus others are only known from normoxic facies but all preferred soft soupy sediments morphological examination does not support the presence of byssus gland in adult stages of daonellids which suggests that they could not be attached to floats proposed life habits such as semi infaunal mud stickers epibenthic chemosymbionts holonekton holoplankton or byssal attached pseudoplankton conflict with taphonomical constraints distribution and morphology daonellids are herein interpreted as epibethic pleurothetic bivalves showing adaptive features to dysoxic milieus like subcircular flat thin shelled valves daonellids were well adapted to soft soupy substrates the use of lighter calcite in place of aragonite the thin shell and the general form of the shell qualified them to float on soft sediments snow shoe strategists

sulphur incorporation in jurassic marine mudrocks and their bitumens at low thermal maturity cleveland basin england abstract the distribution of sulphur between pyrite kerogen elemental sulphur and the aromatic fraction of mudrock bitumens has been quantitated in two cored sections of immature marine kimmeridgian strata which have experienced different levels of thermal stress strata in the two boreholes ebberston and reighton were deposited in different basinal settings basinal marine and platform respectively and occasional euxinic laminated horizons are present at ebberston otherwise dysoxic deposition was the norm at both localities pyrite the dominant sulphur carrier in all the mudrocks has a sulphur isotopic composition consistent with mineralisation in a system mainly open to sulphate diffusion kerogens are mostly low sulphur atomic s c and account for between 5 and 10 of rock sulphur although occasionally up to 30 kerogen sulphur is closely correlated with toc and highest in laminated mudrocks consistent with most effective sulphurization of kerogen under anoxic conditions although kerogen compositions in both cores vary with organic richness no systematic differences in organic input between the borehole localities are recognised geochemically some thermal effects on sulphur geochemistry are therefore interpreted from a comparison of stratigraphically equivalent sections from the two cores bitumen yields and abundances of aromatic sulphur in the more thermally stressed ebberston section although variable are generally much higher than in the reighton section and are partly related to kerogen sulphur content this is tentatively attributed to thermal release of additional extractable bitumen from macromolecules elemental sulphur s0 in bitumen is unrelated in abundance to other sulphur species and isotopically heavier than coexisting pyrite overprinting of minor preserved diagenetic s0 by secondary oxidation of pyrite appears likely the distributions of individual sulphur aromatic compound classes have features related both to maturity and stratigraphy

synchrotron tomographic quantification of strain and fracture during simulated thermal maturation of an organic rich shale uk kimmeridge clay analyzing the development of fracture networks in shale is important to understand both hydrocarbon migration pathways within and from source rocks and the effectiveness of hydraulic stimulation upon shale reservoirs here we use time resolved synchrotron x ray tomography to quantify in four dimensions 3 d plus time the development of fractures during the accelerated maturation of an organic rich mudstone the uk kimmeridge clay with the aim of determining the nature and timing of crack initiation electron microscopy em both scanning backscattered and energy dispersive was used to correlatively characterize the microstructure of the sample preheating and postheating the tomographic data were analyzed by using digital volume correlation dvc to measure the three dimensional displacements between subsequent time heating steps allowing the strain fields surrounding each crack to be calculated enabling crack opening modes to be determined quantification of the strain eigenvectors just before crack propagation suggests that the main mode driving crack initiation is the opening displacement perpendicular to the bedding mode i further detailed investigation of the dvc measured strain evolution revealed the complex interaction of the laminar clay matrix and the maximum principal strain on incipient crack nucleation full field dvc also allowed accurate calculation of the coefficients of thermal expansion 8 10 5 c perpendicular and 6 2 10 5 c parallel to the bedding plane these results demonstrate how correlative imaging using synchrotron tomography dvc and em can be used to elucidate the influence of shale microstructure on its anisotropic mechanical behavior

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

response of the north american monsoon to regional changes in ocean surface temperature 1 the north american monsoon nam an onshore wind shift occurring between july and september has evolved in character during the holocene largely due to changes in northern hemisphere insolation published paleoproxy and modeling studies suggest that prior to 8000 cal years bp the nam affected a broader region than today extending westward into the mojave desert of california holocene proxy sst records from the gulf of california goc and the adjacent pacific provide constraints for this changing nam climatology prior to 8000 cal years bp lower goc ssts would not have fueled northward surges of tropical moisture up the goc which presently contribute most of the monsoon precipitation to the western nam region during the early holocene the north pacific high was further north and ssts in the california current off baja california were warmer allowing monsoonal moisture flow from the subtropical pacific to take a more direct northwesterly trajectory into an expanded area of the southwestern u s west of 114 w a new upwelling record off southwest baja california reveals that enhanced upwelling in the california current beginning at 7500 cal year bp may have triggered a change in nam climatology focusing the geographic expression of nam in the southwest usa into its modern core region east of 114 w in arizona and new mexico holocene proxy precipitation records from the southwestern u s and northwestern mexico including lakes vegetation pollen and caves are reviewed and found to be largely supportive of this hypothesis of changing holocene nam climatology

carbon and oxygen isotope composition of oxfordian early kimmeridgian belemnite rostra palaeoenvironmental implications for late jurassic seas abstract stable isotope analyses have been undertaken on oxfordian early kimmeridgian belemnite rostra derived from three palaeogeographic provinces of europe 1 the boreal subboreal province isle of skye in scotland 2 the submediterranean province central poland and southern germany and 3 the mediterranean province pieniny klippen belt in the western carpathians the samples have been screened for possible diagenetic alteration by using cathodoluminescence and trace element analyses and have been found to be largely well preserved calculated palaeotemperatures 10 15 c and analyses of belemnite habitats suggest that the boreal subboreal belemnites were living in a relatively shallow sea not deeper than 100 150 m while the other belemnites possibly inhabited deeper neritic environments despite the influence of a vital effect the 13c values of belemnite rostra are interpreted to reflect primary variations in the oceanic carbon isotope signal the fairly uniform submediterranean 13c values indicate a similar isotope composition of dissolved inorganic carbon dic in the area of sedimentation of sponge megafacies in the deep tethyan shelves the slightly lowered 13c values of some mediterranean belemnites might occur due to upwelling providing 12c enriched bottom waters onto the area of the czorsztyn ridge in the oxfordian the discernibly more positive 1 2 5 13c values of boreal subboreal belemnites are related to a high biologic productivity and a high organic matter burial in the partly isolated boreal sea the stated differentiation in carbonate 13c values distinctly exceeds present day differences in isotope composition of seawater dic

a molecular and carbon isotope biogeochemical study of biomarkers and kerogen pyrolysates of the kimmeridge clay facies palaeoenvironmental implications abstract structures and carbon isotopic compositions of biomarkers and kerogen pyrolysis products of a dolomite a bituminous shale and an oil shale of the kimmeridge clay formation kcf in dorset were studied in order to gain insight into i the type and extent of water column anoxia and ii changes in the concentration and isotopic composition of dissolved inorganic carbon dic in the palaeowater column the samples studied fit into the curve of increasing 13 c of the kerogen 13 c toc with increasing toc reported by huc et al 1992 their hypothesis that the positive correlation between toc and 13 c toc is the result of differing degrees of organic matter om mineralisation in the water column was tested by measuring the 13 c values of primary production markers these 13 c values were found to differ on average by only 1 among the samples implying that differences in the extent of om mineralisation cannot fully account for the 3 difference in 13 c toc the extractable om in the oil shale differs from that in the other sediments due to both differences in maturity and differences in the planktonic community these differences however are not likely to have significantly influenced 13 c toc either all three sediments contain abundant derivatives of isorenieratene indicating that periodically euxinia was extending into the photic zone the sediments are rich in organic sulfur as revealed by the abundant sulfur compounds in the pyrolysates the prominence of c 1 c 3 alkylated thiophenes over n alkanes and n alkenes is most pronounced in the pyrolysate of the sediment richest in toc this suggests that sulfurisation of om may have played an important role in determining the toc 13 c toc relationship reported by huc et al 1992

glacial reduction of the north american monsoon via surface cooling and atmospheric ventilation nsf ags 1204011 ocn 1304910 oce 1651034 david and lucile packard foundation fellowship in science and engineering

a new approach to an absolute timescale from measurements of orbital cycles and sedimentary microrhythms when the sedimentary microrhythms of two groups of jurassic zones forming part of the chronostratigraphical scale are analysed against recent radiometric age scales there is good agreement with present day cycles resulting from the obliquity of the ecliptic sedimentary microrhythms resulting from orbital forcing can be used to establish either the relative or the true length of chronostratigraphical zones and thus provide a new approach towards an absolute timescale such a scale will be powerful in the analysis of other cycles and perturbations in the geological record

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

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

the upper jurassic boulder beds and related deposits a fault controlled submarine slope ne scotland during the late jurassic kimmeridgian rifting in the north sea large scale normal faults developed to form relatively deep marine basins the north western margin of one of these basins defined by the helmsdale fault is described to show the nature of sedimentation associated with a submarine fault scarp subsidence to the se of the helmsdale fault led to a fault scarp down which various sediment mass flows moved including debris flow rockfall high and low concentration turbidity currents and possible storm surge wash over deposits redeposition by soft sediment sliding was important as a slope accretion process deep channels were incised into the slope and infilled by coarse grained elastics contemporaneous small scale submarine fans located farther off in the present north sea may have developed as a result of slope bypassing sediment flows down such channels the succession is characterized by extreme sediment heterogeneity compared to many deep water environments and it may be part of an ancient fan delta the main influences upon slope accretion were the synsedimentary movements on the helmsdale fault and the nature of the available sediment input such that the succession represents structurally controlled and sedimentologically modified slope development

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

the context of lowstand events in the kimmeridgian late jurassic sequence stratigraphic evolution of the wessex weald basin southern england abstract a depositional sequence stratigraphic framework for the kimmeridgian stage of the wessex weald basin southern england is applied in the investigation of the sedimentary and erosional response to proposed lowstand events this framework recognises 13 sequence boundaries km1 km13 and is based on the integrated assessment of geophysical sedimentological palaeontological and geochemical data changes in the nature and continuity of kimmeridgian unconformity surfaces record the effect of the reorganisation of the onshore basins in response to eustasy and tectonic movements during the earliest kimmeridgian the basin geometry was such that falls in relative sea level generated widespread unconformities associated lowstand events are recorded in marginal areas by a number of sand units derived from a variety of local sources a tectonically enhanced deepening event during the late early kimmeridgian eudoxus zone led to unconformities being confined in their distribution to the basin margins as sea level fell during the latest kimmeridgian a progressive reduction in the depositional area led to an amplification of the effects of lowstand processes at the basin margins where unconformity surfaces are amalgamated on the most positive areas these surfaces are overprinted by a major interregional hiatus the late cimmerian unconformity the timing and effects of kimmeridgian lowstand events were intimately linked to the tectonic evolution of the wessex weald basin thus at times when rates and amounts of eustatic change are small i e during greenhouse times the tectonic signature of a basin will be the primary signal recorded in sedimentary successions

dynamics of the intertropical convergence zone of the east pacific abstract the dynamical factors controlling the mean state and variability of the east pacific intertropical convergence zone itcz and the associated cross equatorial boundary layer flow are investigated using observations from the east pacific investigation of climate epic2001 project the tropical east pacific exhibits a southerly boundary layer flow that terminates in the itcz this flow is induced by the strong meridional sea surface temperature sst gradient in the region away from the equator and from deep convection it is reasonably well described on a day to day basis by an extended ekman balance model variability in the strength and northward extent of this flow is caused by variations in free tropospheric pressure gradients that either reinforce or oppose the pressure gradient associated with the sst gradient these free tropospheric gradients are caused by easterly waves tropical cyclones and the madden julian oscillation convergence in the boundary layer flow is often assumed to be r

hydrological changes and paleoproductivity in the gulf of california during middle and late holocene and their relationship with itcz and north american monsoon variability abstract this study investigates changes in precipitation patterns and variations in paleoproductivity in the tropical pacific region associated with the north american monsoon intertropical convergence zone itcz latitudinal migration and changes in insolation during the middle and late holocene major and trace element records al ba c k si and ti and zr al and ba al ratios in a core from alfonso basin southern gulf of california are used as proxies of terrigenous input and bio productivity records reveal an increase in precipitation and low bio productivity ca 6200 to 2400 cal yr bp associated with the strengthening of monsoonal precipitation and northward shift of the itcz mean position in the eastern tropical pacific a multi centennial drought from ca 2400 to 1900 cal yr bp and a dry and cold interval ca 700 and 500 cal yr bp are characterized by strong aeolian input and enhanced productivity associated with diminution of the summer monsoonal precipitation and reduced insolation in the northern hemisphere and more southerly itcz position correlation of alfonso basin records with other records in the gulf of california and the pigmy and cariaco basins in the gulf of mexico and central atlantic provides constraints on nam itcz migration and insolation driven changes

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

eddy mediated regime transitions in the seasonal cycle of a hadley circulation and implications for monsoon dynamics in a simulation of seasonal cycles with an idealized general circulation model without a hydrologic cycle and with zonally symmetric boundary conditions the hadley cells undergo transitions between two regimes distinguishable according to whether large scale eddy momentum fluxes strongly or weakly influence the strength of a cell the center of the summer and equinox hadley cell lies in a latitude zone of upper level westerlies and significant eddy momentum flux divergence the influence of eddy momentum fluxes on the strength of the cell is strong the center of the cross equatorial winter hadley cell lies in a latitude zone of upper level easterlies and is shielded from the energy containing midlatitude eddies the influence of eddy momentum fluxes on the strength of the cell is weak mediated by feedbacks between eddy fluxes mean zonal winds at upper levels and the mean meridional circulation the dominant balance in the zonal momentum equation at the center of a hadley cell shifts at the transitions between the regimes from eddies dominating the momentum flux divergence in the summer and equinox cell to the mean meridional circulation dominating in the winter cell at the transitions a feedback involving changes in the strength of the lower level temperature advection and in the latitude of the boundary between the winter and summer cell is responsible for changes in the strength of the cross equatorial winter cell the transitions resemble the onset and end of monsoons for example in the shift in the dominant zonal momentum balance rapid shifts in the latitudes of maximum meridional mass flux and of maximum convergence at lower levels rapid changes in strength of the upward mass flux and changes in direction and strength of the zonal wind at upper and lower levels in the monsoonal regime the maximum upward mass flux occurs in an off equatorial convergence zone located where the balance of the meridional geopotential gradient in the planetary boundary layer shifts from nonlinear frictional to geostrophic similar dynamic mechanisms as at the regime transitions in the simulation mechanisms that can act irrespective of land sea contrasts and other inhomogeneities in lower boundary conditions may be implicated in large scale monsoon dynamics in earth s atmosphere

geochemical study of organic matter rich cycles from the kimmeridge clay formation of yorkshire uk productivity versus anoxia abstract in this contribution we study two meter scale cycles from the kimmeridge clay formation cored near marton yorkshire which shows cyclic organic matter om distribution our aim is to try to understand the factors responsile for om accumulation the first cycle called lower cycle shows a total organic carbon toc content between 1 and 10 whereas the second called upper cycle shows a toc content varying between 5 and 35 the geochemical composition major elements and trace elements the organic geochemistry toc hi palynofacies and mineralogy of the sediments have been determined in both cycles the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic matter constituents furthermore dilution effects by inorganic components of the sediment cannot account for the toc cyclicity for lower cycle the mo v and u content is low and little variable as is the intensity of the oxidation which om suffered from this indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions in the upper cycle cyclicity also appears to depend on productivity but variations in the concentration of mo v and u and in the oxidation state of the om suggest the environment was temporarily more reducing it is proposed that larger amounts of h 2 s were released into marine bottom waters as a result of initial om decomposition forced the oxic anoxic boundary to rise in the water column and thus favoured om storage the main driving force for variations in the om concentration was the productivity of organic matter walled phytoplankton redox conditions of the depositional environment could have had a positive action but only by acting as a positive feedback effect

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

kerogen facies and maturity of the kimmeridge clay formation in southern and eastern england abstract the upper jurassic kimmeridge clay formation of southern and eastern england was deposited under anoxic or dysaerobic conditions in a stratified shelf sea anoxic conditions developed in the intra shelf weald and central channel basins of southern england and the cleveland basin of eastern england with generally dysaerobic conditions in the flanking shelf areas only in the basin margins such as in northern scotland were oxic bottom water conditions prevalent the maturity and distribution of the kerogen facies which can be explained in terms of the palaeogeography and burial history of the upper jurassic of southern and eastern england are discussed along with the effects of their variation on commonly used geochemical parameters relationships to clay mineralogy are also examined kerogens are largely type ii amorphous sapropels of marine origin with variable amounts of terrestrially derived type iii material type iii kerogens predominate in the basin margin areas whereas type ii kerogens are restricted to the basin centres over the intermediate shelf areas mixed type ii type iii kerogens are prevalent both the sedimentation rate and differential organic matter preservation can be demonstrated to be the major controls on the kerogen facies of the kimmeridge clay formation variations in the kerogen facies appear to be responsible for the often spurious and scattered maturity measurements from the kimmeridge clay formation using vitrinite reflectance spore coloration and rock eval pyrolysis parameters the results often conflicting with geological models for the post jurassic burial history this appears to be due to the highly variable content of terrestrial and recycled type iii kerogens from older sediments in the mudstones causing the conventional maturity indices to often not reflect the true maturity of the autochthonous marine type ii kerogens

organic petrography and pore structure characterization of low mature and gas mature marine organic rich mudstones insights into porosity controls in gas shale systems analyses of both type ii organic rich low mature mudstones from the kimmeridge clay formation yorkshire england and gas mature mudstones from the vaca muerta formation argentina were performed using petrographic and sem observations to characterize the organic and inorganic components of the rocks and their relationship with porosity the porosity analyses using nitrogen adsorption measurements and mercury intrusion porosimetry were then evaluated as a function of both composition and thermal maturity despite the absence of variation in the pore size distribution and the total pore volume with maturity which is controlled by total organic carbon content toc this study demonstrates that the pore network of these marine mudstones varies considerably with thermal maturity contrary to low mature samples whose porosity depends essentially on mineral interparticle pores the porosity of thermally mature rocks is mainly influenced by organic matter hosted pores located within secondary solid bitumen organic matter om porosity which is rare in the low mature stage appears to increase during thermal maturation in response to the thermal cracking of kerogen and oil to become predominant in gas mature rocks it can therefore be considered that thermal maturation is a major process for the development of the om porosity however the om of high toc 5 5 wt gas mature samples contains smaller pores than gas mature low toc mudstones probably due to a difference in the original om composition between these high and low toc samples by analogy with the kimmeridge clay formation which is often considered as time equivalent in terms of om composition uliana et al 1999 the high toc vaca muerta samples appear to have originally contained greater proportions of oil prone amorphous om and thus a better om intrinsic quality for oil generation this difference of om composition and petroleum potential between vaca muerta marine mudstones appears to have dramatically influenced the om hosted pore genesis during maturation consistent with other studies these results show that thermal maturity is not the only process that can explain om hosted pore genesis in gas shale systems the om composition can greatly influence the evolution of this porosity during maturation organic composition and om thermal maturity may therefore have a complementary effect explaining the diversity of trends observed on porosity in natural formations

seasonality of the transitional region of the california current system off baja california hydrographic data collected over the period 1997 2013 are analyzed to investigate the seasonality of hydrographic features and associated geostrophic flows off the baja california peninsula the upper ocean in the region was found to be homogeneous in winter and spring but subdivided into two regions in the summer and autumn in the first case the system typically shows relatively low temperature and salinity waters which give it a subarctic character in the second only the region north of punta eugenia 28 n maintains subarctic characteristics while the southern region receives an inflow of tropical and subtropical waters that results from the weakening of northwesterly winds which allows the poleward advection of surface waters also during this period a positive wind stress curl promotes the zonal advection of north pacific s eastern edge waters into the coast and to the north as a surface coastal flow average seasonal patterns of geostrophic flow at 200 dbar revealed that the differentiation into provinces is also evident at that depth with two clearly defined cyclonic structures in summer and autumn both separated at the latitude of punta eugenia the analyses conducted also showed a clear continuity of the california undercurrent along the shelf break with more diffuse currents in the winter poleward flows were observed throughout the water column especially in summer and autumn although the origin of the surface flow does not necessarily involve a surfacing of the california undercurrent

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

control of the preservation of organic matter by productivity and sulphate reduction in kimmeridgian shales from dorset uk abstract the kimmeridgian shales of dorset uk have a very wide range of total organic carbon toc content and hydrogen index hi these cyclic changes of organic carbon accumulation are usually interpreted in terms of biomass changes induced by variations in productivity the influence of such variations on the intensity of sulphate reduction and consequently on the preservation of organic carbon were studied the pyrite content does not reflect the full extent of sulphate reduction for sediments with a toc content greater than 10 when easily reducible iron is no longer available h 2 s is preferentially fixed as organic compounds in algal bodies a sulphate reduction index sri initial c org residual c org was calculated for each sediment on the basis of the sulphate reduction reaction stoichiometry and a drastic change in sulphate reduction intensity was seen for toc contents of about 10 above this value the sri is low and decreases with increasing toc content the sediments are rich in organic carbon composed of well laminated stacked algal bodies and were probably deposited at an oxygen depleted water sediment interface in this instance the quality and the amount of organic matter buried depends directly on the organic fluxes towards the redox interface it is assumed that the high relative input of organic matter which can be metabolized exceeds the availability of sulphate in the pore waters so that part of it escapes sulphate reduction and is probably degraded by other processes methanogenesis for toc contents less than 10 the sri is higher and variable the sediments show traces of burrowing and the depositional conditions are thought to be dysaerobic it is proposed that under such conditions bioturbation brings both sulphate and reducible iron into the sediment and that sulphate reduction mainly expressed by the presence of pyrite consumes all the available organic matter which can be metabolized the strong variability in the intensity of sulphate reduction depends on various parameters such as the genetic type of planktonic organic matter the method of transportation to the sediment and possibly the earlier oxic degradation during transportation