relation between depositional environment and the elemental composition of early diagenetic siderite early diagenetic siderites from marine and fresh water depositional environments are characterized by distinctive compositional trends siderite from fresh water environments is often relatively pure i e greater than 90 mol feco sub 3 and commonly attains end member composition siderite from marine environments however is always extremely impure and has extensive substitution of mg up to 41 mol and to a lesser extent ca up to 15 mol for fe in the siderite lattice in addition marine siderite generally contains less mn and has a higher mg ca ratio than fresh water siderite this compositional variation appears to result from differences in the chemistry of early marine and meteoric pore waters inasmuch as early marine pore waters generally have a higher mg sup 2 ca sup 2 ratio and contain less mn sup 2 and fe sup 2 and more ca sup 2 and mg sup 2 than meteoric waters

evidence for increased latent heat transport during the cretaceous albian greenhouse warming quantitative estimates of increased heat transfer by atmospheric h2o vapor during the albian greenhouse warming suggest that the intensified hydrologic cycle played a greater role in warming high latitudes than at present and thus represents a viable alternative to oceanic heat transport sphaerosiderite d 18 o values in paleosols of the north american cretaceous western interior basin are a proxy for meteoric d 18 o values and massbalance modeling results suggest that albian precipitation rates exceeded modern rates at both mid and high latitudes comparison of modeled albian and modern precipitation minus evaporation values suggests amplification of the albian moisture deficit in the tropics and moisture surplus in the mid to high latitudes the tropical moisture deficit represents an average heat loss of 75 w m 2 at 108n paleolatitude at present 21 w m 2 the increased precipitation at higher latitudes implies an average heat gain of 83 w m 2 at 458n at present 23 w m 2 and of 19 w m 2 at 758n at present 4 w m 2 these estimates of increased poleward heat transfer by h2o vapor during the albian may help to explain the reduced equator to pole temperature gradients

the paleohydrology of lower cretaceous seasonal wetlands isle of wight southern england abstract the floodplain deposits of the wealden group lower cretaceous of the isle of wight southern england were formed in a seasonal wetland setting a type of environment widespread today along higher order tropical and subtropical river systems but rarely identified in the geological record the unit consists of four main lithofacies sheet sandstones with dinosaur footprint casts green gray mudstones with vertebrate remains abundant lignite pyrite and siderite spectacularly color mottled mudstones with goethite and locally pseudo anticlines and red mudstones with pseudo anticlines hematite and carbonate nodules the sheet sandstones are interpreted as crevasse deposits the green gray mudstones were deposited in shallow ponds on the floodplain which acted as sinks for debris released by local floods following wildfires the mottled mudstones represent surface water gley soils formed in seasonally waterlogged areas and the red mudstones resemble present day vertisols that formed on topographically elevated areas only intermittently flooded these mudstones show vertical transitions from one to another and although they could be interpreted as components of simple catenas the absence of associated facies changes implies that topographic differences were not the only control it is proposed that these three mudstone types formed as seasonal wetland catenas in which differences in soil drainage conditions resulted from variations in the flooding hydroperiod affecting areas with minor relief differences rather than drainage variability simply reflecting static topographic differences such seasonal wetland systems are rarely documented in the stratigraphic record despite being a widespread environment in present day tropical regions and the wealden deposits are used to identify criteria for the recognition of this important environment in the rock record these southern english wetlands are compared with other lower cretaceous wetlands from northern spain enabling hydrological factors which controlled deposition to be recognized

constraints on palaeoenvironments in the lower cretaceous wealden of southern england from the geochemistry of sphaerosiderites abstract sphaerosiderites are millimetre scale concretions of feco 3 that form predominantly in waterlogged environments and are of use in palaeoenvironmental and palaeohydrological studies we present petrographic elemental and stable isotopic 13 c 18 o data from sphaerosiderites collected from the lower cretaceous wealden sediments of southern england the sphaerosiderites are composed of very pure feco 3 with only small amounts of ca mg and mn present suggesting that they are well preserved and were precipitated from fresh groundwater 13 c values display a relatively large range from about 5 to 30 vpdb in contrast 18 o values are relatively invariant 1 0 83 with an average of 3 01 vpdb the relationship between carbon and oxygen suggests that the sphaerosiderites faithfully record palaeo groundwater 18 o likely 18 o values for groundwater were calculated using a published experimentally derived siderite water fractionation equation and plausible assumed values for palaeotemperature the average estimate was 4 9 smow the wealden sphaerosiderite oxygen isotope values are comparable with other early cretaceous data from similar palaeolatitudes but lower than estimated holocene values for equivalent latitudes this observation may indicate greater rainfall at 30 n during the cretaceous relative to the holocene and also suggests relative stability of palaeoclimatic conditions during the early cretaceous at this palaeolatitude

an early cretaceous lacustrine record organic matter and organic carbon isotopes at bernissart mons basin belgium abstract the early cretaceous bernissart lake deposits mons basin belgium constitute an important historical site in the field of palaeontology in this study we focus on the organic matter om content of the 50 m long borehole core ber 3 drilled at bernissart organic data rock eval palynofacies c n ratios and carbon isotope measurements on bulk om and selected isolated wood fragments were collected the om distribution exhibits two total organic carbon toc cycles 12 m and 38 m thick respectively that are stacked in a lower frequency cyclic pattern a general increase of in situ aquatic production and preservation of om through time is evidenced within the freshwater masses a spectral analysis of a high resolution gamma ray record demonstrates that the sedimentation was controlled by orbitally induced climatic changes precession obliquity and short and long term eccentricity cycles are recognized the 12 m thick and the 38 m thick toc cycles fit well with a 100 kyr short term and a 400 kyr long term eccentricity cycle respectively long term organic fluctuations are interpreted as resulting from orbitally induced fluctuating lake levels through time carbon isotope evolution of bulk om is thought to reflect firstly two local patterns of sedimentation 1 the changing contribution of in situ amorphous organic matter versus terrestrial om and 2 the possible influence of enhanced productivity the negative 13 c wood trend recorded at bernissart seems equivalent to published coeval 13 c wood and 13 c carb in the upper barremian to lower aptian this trend noted at bernissart is thus regarded as reflecting changes of the carbon isotope ratios of atmospheric co 2 previous presented palynological data suggest a middle barremian to lowermost aptian stratigraphic range for the succession at bernissart according to this new dataset we refine the age assignment for bernissart the duration of deposition is now estimated to range between 0 55 and 2 2 myr in the upper barremian to lowermost aptian

collisionless encounters and the origin of the lunar inclination the moon is generally thought to have formed from the debris ejected by the impact of a planet sized object with the proto earth towards the end of planetary accretion models of the impact process predict that the lunar material was disaggregated into a circumplanetary disk and that lunar accretion subsequently placed the moon in a near equatorial orbit forward integration of the lunar orbit from this initial state predicts a modern inclination at least an order of magnitude smaller than the lunar value a long standing discrepancy known as the lunar inclination problem here we show that the modern lunar orbit provides a sensitive record of gravitational interactions with earth crossing planetesimals that were not yet accreted at the time of the moon forming event the currently observed lunar orbit can naturally be reproduced via interaction with a small quantity of mass corresponding to 0 0075 0 015 earth masses eventually accreted to the earth carried by a few bodies consistent with the constraints and models of late accretion although the encounter process has a stochastic element the observed value of the lunar inclination is among the most likely outcomes for a wide range of parameters the excitation of the lunar orbit is most readily reproduced via collisionless encounters of planetesimals with the earth moon system with strong dissipation of tidal energy on the early earth this mechanism obviates the need for previously proposed but idealized excitation mechanisms places the moon forming event in the context of the formation of earth and constrains the pristineness of the dynamical state of the earth moon system

the mid cretaceous water bearer isotope mass balance quantification of the albian hydrologic cycle a latitudinal gradient in meteoric n 18 o compositions compiled from paleosol sphaerosiderites throughout the cretaceous western interior basin kwib 34 75 n paleolatitude exhibits a steeper more depleted trend than modern predicted values 3 0x 34 n latitude to 9 7x 75 n lighter furthermore the sphaerosiderite meteoric n 18 o latitudinal gradient is significantly steeper and more depleted 5 8x 34 n to 13 8x 75 n lighter than a predicted gradient for the warm mid cretaceous using modern empirical temperature n 18 o precipitation relationships we have suggested that the steeper and more depleted relative to the modern theoretical gradient meteoric sphaerosiderite n 18 o latitudinal gradient resulted from increased air mass rainout effects in coastal areas of the kwib during the mid cretaceous the sphaerosiderite isotopic data have been used to constrain a mass balance model of the hydrologic cycle in the northern hemisphere and to quantify precipitation rates of the equable greenhouse albian stage in the kwib the mass balance model tracks the evolving isotopic composition of an air mass and its precipitation and is driven by latitudinal temperature gradients our simulations indicate that significant increases in albian precipitation 34 52 and evaporation fluxes 76 96 are required to reproduce the difference between modern and albian meteoric siderite n 18 o latitudinal gradients calculations of precipitation rates from model outputs suggest mid high latitude precipitation rates greatly exceeded modern rates 156 220 greater in mid latitudes 2600 3300 mm yr 99 greater at high latitudes 550 mm yr the calculated precipitation rates are significantly different from the precipitation rates predicted by some recent general circulation models gcms for the warm cretaceous particularly in the mid to high latitudes our mass balance model by no means replaces gcms however it is a simple and effective means of obtaining quantitative data regarding the mid cretaceous hydrologic cycle in the kwib our goal is to encourage the incorporation of isotopic tracers into gcm simulations of the midcretaceous and to show how our empirical data and mass balance model estimates help constrain the boundary conditions

extension of berner s new geochemical classification of sedimentary environments to ancient sediments using stable isotopes of carbon and oxygen in siderite nodules and lithology of host shales one can recognize geochemical environments proposed by berner in devonian carboniferous sediments of the appalachian basin his oxic post oxic and sulfidic diagenetic environments are well represented sediments of the methanic environment may be present but the evidence is equivocal the sulfidic sediments can be further subdivided into well laminated and bioturbated corresponding to the presence of h 2 s in the overlying water in the first case but confined to the sediment pore waters in the second journal abstract

distinguishing base level change and climate signals in a cretaceous alluvial sequence we present the results of oxygen isotope and electron microprobe analyses of sphaerosiderites obtained from cretaceous paleosols in iowa the sphaerosiderite d 18 o values record creta ceous meteoric groundwater chemistry and an overall waning of brackish groundwater inundation during alluvial plain aggrada tion and soil genesis we focus on horizons that precipitated from freshwater in which d 18 o values ranging from 23 3 to 26 8 relative to the peedee belemnite standard are interpreted to record variations in the cretaceous atmospheric hydrologic cycle during relative sea level highstands moisture was derived from the cre taceous western interior seaway whereas during lowstands when the seaway narrowed and occasionally withdrew from the midcon tinent the dominance of hemispheric scale atmospheric moisture transport initiated in the tropical tethys ocean led to decreased precipitation rates these processes did not operate like a switch but rather as a continuum of competing moisture sources and mechanisms of transport between the nearby epicontinental sea and the distant tropics the sphaerosiderite data demonstrate 1 temporal variation in the intensity of hemispheric scale atmospher ic moisture transport and 2 long term amplification of the global hydrologic cycle marked by extreme 18 o depletion at the albian cenomanian boundary

pore water evolution during sediment burial from isotopic and mineral chemistry of calcite dolomite and siderite concretions abstract coal measures often contain concretions segregations of diagenetic minerals originally formed within unconsolidated sediments three different types calcite pyrite dolomite pyrite and siderite occurring spatially quite close together in the central pennine region of england vary widely in carbon isotope composition 10 35 13c 21 49 and in major cation chemistry ca mg fe mn within some siderite concretions very high mn fe ratios were found in central subsamples these were also most enriched in 13c the fe mg ratio decreases systematically from centre to edge early shallow to deeper later precipitation the calcite pyrite and dolomite pyrite concretions developed completely prior to significant burial both have high mn fe ratios but negative 13c values calcite 21 49 dolomite 8 67 to 10 48 all of these patterns can be equated precisely with theories of pore water evolution developed on the basis of geochemical investigations of modem sediments microbial processes sulphate reduction methanogenesis contributed significantly as did thermal decarboxylation to siderite precipitated at considerable burial depth mn iv and fe iii acted differentially as oxidants producing co2 and increasing alkalinity the interplay of fresh and marine depositional waters is seen most obviously in the presence or absence of sulphate reduction this controlled mineral type iron sulphide or carbonate as well as isotopic and mineral chemistry

a comparison of methods used to estimate the height of sand dunes on mars the collection of morphometric data on small scale landforms from other planetary bodies is difficult we assess four methods that can be used to estimate the height of aeolian dunes on mars these are 1 stereography 2 slip face length 3 profiling photoclinometry and 4 mars orbiter laser altimeter mola results show that there is good agreement among the methods when conditions are ideal however limitations inherent to each method inhibited their accurate application to all sites collectively these techniques provide data on a range of morphometric parameters some of which were not previously available for dunes on mars they include dune height width length surface area volume and longitudinal and transverse profiles the utilization of these methods will facilitate a more accurate analysis of aeolian dunes on mars and enable comparison with dunes on other planetary surfaces

fossil wood carbon isotope stratigraphy of the non marine wealden group lower cretaceous southern england fossil wood carbon isotope data are presented for the wessex formation a non marine unit within the lower cretaceous valanginian barremian wealden group of the isle of wight and dorset southern england the carbon isotope values have a range 13 c c 26 6 to 19 8 that is consistent with that expected for mesozoic c 3 plants consideration of the isle of wight fossil wood carbon isotope data together with data from dorset allows construction of a composite fossil wood carbon isotope curve for almost the entire wealden group the new carbon isotope curve is in smooth continuity with data previously published from the overlying lagoonal vectis formation and marine lower greensand group of aptian age a tentative correlation with a tethyan reference carbon isotope curve allows the provisional application of stage level chronostratigraphy to the wealden group correlations suggest that the wealden group sediments are dominantly of hauterivian and barremian age and that the valanginian is either condensed or partially missing the carbon isotope data presented indicate that even during times of relative carbon cycle quiescence atmosphere co 2 faithfully tracks the carbon isotopic composition of the oceanic reservoir

stability and facies association of early diagenetic mineral assemblages an example from a jurassic ironstone mudstone succession u k abstract sedimentological and petrographic data from two lower liassic ooidal ironstones the frodingham and pecten ironstones and associated mudstones from eastern england have been collected within these ironstones early diagenetic berthierine siderite and minor glauconite have a limited lateral extent associated with an intrabasinal high the market weighton swell this mineral assemblage passes laterally and vertically into mudstones and silty mudstones within which pyrite is the dominant early diagenetic iron mineral the ironstones are stratigraphically condensed having experienced low net sediment accumulation rates and shallow high energy conditions thermodynamic considerations indicate that berthierine and siderite should be stable in anoxic environments where sulfide activity is negligible pyrite is rare within the ironstones suggesting that sulfate reduction was a negligible process during ironstone formation where pyrite is present it postdates berthierine and siderite indicating that sulfate reduction may have been a later process in some beds we propose that berthierine and siderite were precipitated during suboxic diagenesis where sulfate reduction was inhibited and iron reduction was the dominant process of organic matter oxidation suboxic diagenesis resulted from the extended periods of physical and biological sediment reworking during ironstone deposition which favored the oxidation of iron minerals and aerobic egradation and loss of organic matter berthierine formed during early suboxic diagenesis at the expense of detrital clays and iron oxides during later suboxic diagenesis pore water bicarbonate activities increased leading to siderite precipitation early glauconite also formed in places and it seems likely that it formed close to the oxic suboxic interface the predominance of pyrite in the mudstones indicates that sulfate reduction was the major process of organic matter oxidation during early diagenesis

atmospheric pco2 and depositional environment from stable isotope geochemistry of calcrete nodules barremian lower cretaceous wealden beds england abstract nodular soil carbonates calcretes are present in overbank facies of lower cretaceous non marine wealden beds wessex formation of southern england field evidence suggests that these calcretes formed mostly under semi arid mediterranean type climatic conditions typical calcrete fabrics identified petrographically include floating detrital grains corroded grain margins and circumgranular cracks defining peds localized alteration of primary micrites is mainly associated with large cracks where early non ferroan diagenetic cementation and neomorphism was focused diagenetic ferroan calcites occur as void fills and yield relatively light carbon isotope and oxygen isotope compositions 13 c 15 0 18 o 6 3 compared to well preserved micrite 13 c 10 2 18 o 4 0 precise definition of 13 c values for well preserved micrites allow estimation of partial pressure of atmospheric co 2 p co 2 for the early barremian of 560 ppmv using a published diffusion reaction model the data suggest that atmospheric co 2 was low during the mid early cretaceous before rising to a previously defined mid cretaceous high data from calcretes in the weald clay highlight the need for selection of appropriate material and careful evaluation before p co 2 calculations are attempted the weald clay samples come from marshy palaeoenvironments where ingress of atmospheric co 2 into the soil zone was either reduced or prevented

effect of bacteria on the elemental composition of early diagenetic siderite implications for palaeoenvironmental interpretations many ancient early diagenetic siderite concretions are thought to have been precipitated by microbially mediated reactions and their trace element chemistry has been used to infer palaeoenvironments of formation e g marine versus freshwater in this study pure cultures of the microorganism geobacter metallireducens were used to precipitate siderite in the laboratory at a range of temperatures 18 40 c magnesium and calcium in three different ratios 3 1 as in seawater 1 1 and 1 3 as in freshwater or manganese were added to some cultures at each incubation temperature to study trace element incorporation the siderite produced exhibited the rhombohedral crystal form typical of concretionary siderite however this microbial siderite did not simply retain the trace element chemistry of the water from which it precipitated as is assumed in palaeoenvironmental interpretations instead manganese and calcium incorporation were found to be inversely proportional to the rate of microbial activity which itself is dependent upon the nutritional status of the microorganisms magnesium incorporation was found to be rate independent and at high mg ca ratios it caused inhibition of calcium incorporation in short the influence of microorganisms on the trace element composition of early diagenetic siderite must be taken into account in order to produce valid palaeoenvironmental interpretations

isotopic composition of siderite as an indicator of depositional environment compilation of available oxygen and carbon isotopic data for siderites from different depositional environments indicates that marine and continental siderites are characterized by distinctive compositional fields the most notable difference between the fields is the generally higher 13 c values of continental vs marine siderites this difference appears to reflect the fact that marine sediments generally undergo a more extensive period of sulfate reduction than do the continental sediments in which siderite forms analysis of siderite geochemistry may assist in determination of depositional environment in cases where the available sedimentological evidence is ambiguous

general circulation model simulation of the δ18o content of continental precipitation in the middle cretaceous a model proxy comparison we use the genesis atmospheric general circulation model gcm with water isotopic transport and fractionation capabilities to quantify the influence of atmospheric co 2 sea level and elevation of the western cordillera on the 18 o of middle cretaceous precipitation the model predicts a systematic increase of nearly 3 in the 18 o of north american precipitation due to warming associated with an increase in co 2 from 2 to 12 times pre industrial levels in contrast the specification of lowstand conditions and a high ancestral western cordillera reduces the 18 o of north american precipitation locally by as much as 6 and 8 we compare the simulated 18 o of precipitation with the 18 o of paleosol siderite spherules and find good agreement only when the model includes lowstand conditions and a high ancestral western cordillera our results imply either that cretaceous high latitude paleosol 18 o was influenced by orographic precipitation and the western interior seaway or that the gcm9s hydrological cycle is deficient at high p co 2 additional paleosol data are needed to resolve this issue

spherulitic siderites in the holocene coastal deposits of korea eastern yellow sea elemental and isotopic composition and depositional environment abstract siderite concretions are recovered from both freshwater unit ii and tidal unit i deposits in the holocene macrotidal flat of kyunggi bay west coast of korea siderites from both units show a spherulitic and well rounded texture and well developed equant rhombs on the external surfaces the size of the concretions in unit ii 50 150 m in diameter is normally larger than that in unit i 10 20 m the siderites in unit ii are chemically pure and highly enriched in fe whereas those of unit i are relatively impure and distinctly zoned demarcating high mn up to 69 1 mol in the core and high fe up to 75 9 mol in the margin within siderites of unit i substitution for fe by ca and mg reaches up to 20 3 mol mean 15 1 mol and 16 1 mol mean 12 6 mol respectively bulk 18 o values 0 7 to 1 3 peedee belemnite pdb for siderites in unit i are relatively higher than those 7 1 to 0 5 pdb in unit ii regardless of units siderite 13 c values 21 3 to 11 2 pdb are persistently low indicating microbially mediated precipitation at shallow burial depth extensive mn ca and mg substitution coupled with enrichment of 18 o in the siderites of unit i seems to reflect marine influence during the holocene transgression the occurrence of early diagenetic siderites provides supporting evidence on the depositional environment marine vs non marine of the holocene muddy coastal deposits of korea eastern yellow sea

eogenetic siderites in lacustrine oil shales from queensland australia a stable isotope study abstract tertiary lacustrine oil shales from the lowmead and duaringa basins in queensland australia contain siderite as a ubiquitous minor phase and in ironstone bands within the sequence there are two distinctive types of siderite in the ironstone bands sphaerosiderites and finely crystalline siderites petrological evidence indicates that the sphaerosiderites in the ironstone bands formed eogenetically by growing displacively within the soft sediment the geological setting of the basin and the sedimentological evidence indicate a lacustrine environment the deposition of siderite is therefore considered to be controlled by processes in the lacustrine water body and sediments the maximal burial depth is estimated to be 1400 m and consequently the oil shales have not undergone any advanced thermal alteration stable oxygen and carbon isotope analysis of the siderites show a wide compositional range 18o 12 8 to 2 4 vs pdbg and 13c 5 5 to 12 9 vs pdb for the lowmead basin 18o 9 6 to 1 2 vs pdb and 13c 18 6 to 16 4 vs pdb for the duaringa basin the oxygen isotope compositions indicate that the siderite formed in a to 16 4 vs pdb for the duaringa basin the oxygen isotope compositions indicate that the siderite formed in a freshwater environment but generally show a range more negative than the expected equilibrium composition with coeval meteoric waters the carbon isotope composition may reflect deposition within the bacterial oxidation and fermentation zones the shallow lake setting with high productivity results in siderite precipitation under high ph either at the water sediment interface or within the sediment the 13c of the dissolved carbonate will be elevated by intense photosynthesis under these conditions of co2 depletion high ph isotopic disequilibrium during siderite formation will result in 13c and 18c lower than the equilibrium composition in agreement with the recorded isotopic data

middle cretaceous greenhouse hydrologic cycle of north america we present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid latitude north america based on the oxygen isotopic composition of sphaerosiderites found in middle cretaceous wetland paleosols our reconstructed middle cretaceous d 18 o values of precipitation are 4 less than values from comparable modern low elevation coastal settings free of monsoons the data fit a conceptual model in which the precipitation source for the eastern margin of the cretaceous western interior seaway of north america is an 18 o enriched oceanic coastal jet in this subtropical tropical setting midcretaceous precipitation rates are interpreted to range from 2500 to 4100 mm yr

late paleozoic tropical climate response to gondwanan deglaciation coupled climate biome model simulations of the late paleozoic were developed to determine the response of pangean tropical climate to gondwanan deglaciation the model simulations predict substantial changes over equatorial pangea including continental drying a reversal of equatorial winds warming heavier 18 o values of meteoric precipitation and the expansion of deserts and the contraction of forests the magnitude of these tropical responses is sensi tive to the extent of gondwana continental ice and the deglacial rise in atmospheric pco 2 boundary conditions that are not well known for the late paleozoic nonetheless the model predictions are consistent with climatic and environmental trends determined from terrestrial proxy data implying that the deglaciation of gondwana was a transformational climate event in tropical pangea

microbial influence on the oxygen isotopic composition of diagenetic siderite abstract numerous early diagenetic siderite concretions previously described have been interpreted as the results of microbially mediated reactions interpretation of oxygen isotope data for such material requires an understanding of the effect of temperature on fractionation processes however whilst equilibrium fractionation of oxygen isotopes between siderite and water has been measured down to 33 c extrapolation to lower temperatures may be invalid furthermore inorganic measurements may not be applicable to microbial systems the specific iron reducing microorganism geobacter metallireducens has been cultured anaerobically in the laboratory using acetate as an organic substrate and amorphous feooh as an electron acceptor the acetate is oxidised to co2 with concurrent iron reduction and extracellular siderite precipitation rhombohedral siderite crystals up to 25 m in size have been precipitated over a range of temperatures 18 40 c stable isotopic analysis of these crystals and the solutions from which they precipitate shows that this microbial precipitation of siderite has an associated isotopic fractionation different from the published equilibrium and which is not simply a function of temperature in all cases 18o values of siderite are lower than predicted by inorganic equilibrium fractionation data this may explain the numerous anomalously low 18o values reported for early diagenetic marine siderites and previously attributed to mechanisms such as mixing with meteoric water sediment water interaction recrystallisation or variable isotopic fractionation despite a lack of supporting evidence

precipitation rates and atmospheric heat transport during the cenomanian greenhouse warming in north america estimates from a stable isotope mass balance model stable isotope mass balance modeling results of meteoric 18o values from the cenomanian stage of the cretaceous western interior basin kwib suggest that precipitation and evaporation fluxes were greater than that of the present and significantly different from simulations of albian kwib paleohydrology sphaerosiderite meteoric 18o values have been compiled from the lower tuscaloosa formation of southwestern mississippi 25 n paleolatitude the dakota formation rose creek pit fairbury nebraska 35 n and the dunvegan formation of eastern british columbia 55 n paleolatitude these paleosol siderite 18o values define a paleolatitudinal gradient ranging from 4 2 vpdb at 25 n to 12 5 vpdb at 55 n this trend is significantly steeper and more depleted than a modern theoretical siderite gradient 25 n 1 7 65 n 5 6 vpdb and a holocene meteoric calcite trend 27 n 3 6 67 n 7 4 vpdb the cenomanian gradient is also comparatively steeper than the albian trend determined for the kwib in the mid to high latitudes the steep latitudinal trend in meteoric 18o values may be the result of increased precipitation and evaporation fluxes amount effects under a more vigorous greenhouse world hydrologic cycle a stable isotope mass balance model has been used to generate estimates of precipitation and evaporation fluxes and precipitation rates estimates of cenomanian precipitation rates based upon the mass balance modeling of the kwib range from 1400 mm yr at 25 n paleolatitude to 3600 mm yr at 45 n paleolatitude the precipitation evaporation p e flux values were used to delineate zones of moisture surplus and moisture deficit comparisons between cenomanian p e and modern theoretical siderite and holocene calcite latitudinal trends shows an amplification of low latitude moisture deficits between 5 25 n paleolatitude and moisture surpluses between 40 60 n paleolatitude the low latitude moisture deficits correlate with a mean annual average heat loss of 48 w m2 at 10 n paleolatitude present 8 w m2 at 15 n the increased precipitation flux and moisture surplus in the mid latitudes corresponds to a mean average annual heat gain of 180 w m2 at 50 n paleolatitude present 17 w m2 at 50 n the cenomanian low latitude moisture deficit is similar to that of the albian however the mid latitude 40 60 n precipitation flux values and precipitation rates are significantly higher albian 2200 mm yr at 45 n cenomanian 3600 mm yr at 45 n furthermore the heat transferred to the atmosphere via latent heat of condensation was approximately 10 6 that of the present at 50 n the intensified hydrologic cycle of the mid cretaceous greenhouse warming may have played a significant role in the poleward transfer of heat and more equable global conditions paleoclimatological reconstructions from multiple time periods during the mid cretaceous will aid in a better understanding of the dynamics of the hydrologic cycle and latent heat flux during greenhouse world conditions