compositional fractionation of petroleum from reservoir to wellhead in the niobrara shale oil play abstract hydraulic fracturing is routinely used to stimulate unconventional reservoirs in the niobrara shale oil play there are several fracking targets but the actual stimulated rock volume is not well constrained this means that allocating produced oil to specific reservoirs in essence oil reservoir correlation is not straightforward the data presented here support that the chalk units are the principal production zones in the niobrara shale oil play several lines of evidence such as the presence of heavy end n alkanes n c31 consistence in composition of gross fractions the distribution of c27 28 29 diasteranes as well as the pristane to phytane ratio all suggest that oils were produced from the a b chalks particularly from the a chalk during production a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur in particular as regards the n alkanes domain and their carbon isotopic compositions regarding the latter a depletion of 13c in the produced oil s n alkanes by more than three per mil relative to all of those core extracts was observed this finding suggests that compound specific isotope analysis in both oil reservoir and oil source rock correlations cannot be taken at face value i e by simple matching of values besides that fractionation appears to result in the enrichment of rather aliphatic nitrogen containing compounds in crude oils

polydiapirism of the archean mount edgar batholith pilbara block western australia structural analysis of the mount edgar batholith and the enveloping greenstone belt indicates that the batholith and rocks around its margin were subjected to similar deformation events that involved progressive and stepwise diapiric uplift of the batholith these events may be correlated on the basis of fold style orientation and fabric development early recumbent to reclined structures d1 including thrusts were buckled d2 by rounded upright folds prior to shearing d4 along normal faults parallel with the batholith margin d4 deformation was responsible for uplifting the batholith to its present structural position a deep seated linear deformation zone d3 within the batholith did not affect the supracrustal belt syntectonic granite intrusion amphibolite facies metamorphism and migmatisation were associated with d1 in the batholith whereas greenschist facies metamorphism was associated with d1 in the lowermost unit of the greenstone belt the talga talga subgroup amphibolite facies conditions were maintained within the batholith throughout the structural history but this grade was reached in the supracrustal belt only near the batholith margin progressive deformation d1 d2 and metamorphism occurred in response to early massive granite generation and emplacement producing a first order plutonic dome that reached full maturity during d2 solid state diapirism d4 followed producing a gneiss dome of similar dimension restriction of early recumbent folds and thrusts in the supracrustal belt to areas within or adjacent to the batholith is consistent with the model elsewhere deformation is minor the late stage diapirism brought a gneiss complex within the batholith into juxtaposition with lowermost greenschist facies rocks of the pilbara supergroup this complex represents in part sialic material that existed below the pilbara supergroup before diapirism began the complex closely resembles other archean high grade gneiss terranes which suggests that some of these terranes are deeper crustal exposures of granite greenstone terranes

a deep subaqueous fan depositional model for the palaeoarchaean 3 46 ga marble bar cherts warrawoona group western australia the 3 46 ga marble bar chert member of the east pilbara craton western australia is one of the earliest and best preserved sedimentary successions on earth here we interpret the finely laminated thin bedded cherts mixed conglomeratic beds chert breccia beds and chert folded beds of the marble bar chert member as the product of low density turbidity currents high density turbidity currents mass transport complexes and slumps respectively integrated into a channel levee depositional model the marble bar chert member constitutes the oldest documented deep sea fan on earth with thin bedded cherts breccia beds and slumps composing the outer levee facies tracts and scours and conglomeratic beds representing the channel systems

evidence for milankovitch periodicities in cenomanian turonian lithologic and geochemical cycles western interior u s a abstract the limestone marlstone bedding couplets of the bridge creek limestone member cenomanian turonian greenhorn formation were analyzed by applying spectral techniques to high resolution lithologic and geochemical data from a core the results suggest that the bridge creek contains a complex record of orbital cyclicity the dominant signal appears to be obliquity but signals corresponding to precession and eccentricity were also observed the development of the bedding couplets is interpreted to have resulted from a combination of factors including insolation controlled changes in higher latitude precipitation leading to dilution redox cycles and in lower latitude evaporation leading to changes in surface water conditions and productivity cycles in the calcareous plankton the data nterpreted to reflect redox cycles appear to be more strongly influenced by obliquity and show a weak precessional signal in contrast trends in the carbonate record show the opposite response the complex bedding pattern observed in the bridge creek limestone is interpreted to result from the competing influences of different orbital cycles expressed through different pathways of the depositional system and was also affected by changes in sedimentation rates related to relative sea level fluctuations aperiodic dilution by volcanic ash and changes in organic matter production and redox conditions related to a global oceanic anoxic event these factors complicate cycle analysis in the lower part of the member but leave a relatively undisturbed record in the upper bridge creek limes one

granite greenstone terranes in the pilbara block australia as coeval volcano plutonic complexes evidence from u pb zircon dating of the mount edgar batholith the mount edgar batholith in the pilbara block western australia consists in part of a gneiss complex that resembles other archean high grade gneiss terranes the complex is extensively intruded by variably foliated granitoids which also intrude the surrounding greenstone succession the warrawoona group the contact between the greenstone belt and the gneiss complex is tectonic field evidence indicates that the banded gneisses are the oldest part of the batholith zircon u pb ages for three samples are 3429 13ma 3443 10ma and3448 8ma all very similar to the age of zircons in the felsic volcanic rocks near the base of the greenstone succession pidgeon 1978 1 two granitoids representing pre and post tectonic phases respectively give zircon ages of 3304 10ma and3314 13ma thereby constraining the major structural events to be contemporary with granite magmatism consistent with a diapiric model for the tectonic evolution of the batholith collins 1989 2 these ages are similar to the zircon age for terminal volcanism in the warrawoona group pidgeon 1984 3 but are 100ma older than the precisely defined rb sr whole rock ages obtained throughout the batholith collins and gray 1989 4 batholith wide resetting or late closure of rb sr isotopic systems is implied possibly associated with late fluid circulation the temporal coincidence between plutonism and volcanism in the mount edgar region strongly suggests that the greenstone succession contains the extrusive equivalents of both the 3300ma granites and the 3440ma gneisses in the batholith the isotopic evidence combined with the structural data indicates that the granites cannot be derived from the surrounding greenstone belt further there is no compelling evidence for a sialic basement to the greenstone succession

cyclostratigraphy and orbital tuning of the terrestrial upper santonian lower danian in songliao basin northeastern china abstract the songke 1 north sk 1n borehole recovered a continuous 1541 66 m late santonian early danian terrestrial succession in songliao basin sb northeastern china it provides a unique record for improving our understanding of continental paleoclimate and ecological system in cretaceous greenhouse world here we use thorium th logging data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic study on the sk 1n core power spectra evolutionary fast fourier transformation and wavelet analysis all reveal significant decameter to meter scale sedimentary cycles in the nenjiang k 2 n sifangtai k 2 s and mingshui k 2 m formations the ratios of cycle wavelengths in these stratigraphic units are 20 5 2 1 and are interpreted as milankovitch cycles of 405 kyr and 100 kyr eccentricity 38 4 kyr obliquity and 20 kyr precession cycles respectively an astronomical time scale ats is established by tuning filtered 405 kyr eccentricity cycles to a target curve of the astronomical solution la2010d based on the magnetostratigraphic time framework of the sk 1n borehole this ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the cretaceous paleogene k pg campanian maastrichtian santonian campanian boundaries are estimated at core depths of 318 m 752 8 m and 1751 1 m respectively a 3 8 myr long hiatus between the nenjiang k 2 n and sifangtai k 2 s formations occurs from 76 1 to 79 9 million years ago the ages and durations of magnetochrons c33r to c30n are precisely estimated and provide new constraints on the late cretaceous geomagnetic polarity time scale gpts and south atlantic sea floor spreading rates

evaluating late cretaceous oaes and the influence of marine incursions on organic carbon burial in an expansive east asian paleo lake abstract expansive late cretaceous lacustrine deposits of east asia offer unique stratigraphic records to better understand regional responses to global climate events such as oceanic anoxic events oaes and terrestrial organic carbon burial dynamics this study presents bulk organic carbon isotopes 13 c org elemental concentrations xrf and initial osmium ratios 187 os 188 os os i from the turonian coniacian qingshankou formation a 5 ma lacustrine mudstone succession in the songliao basin of northeast china a notable 13 c org excursion 2 5 in organic carbon lean qingshankou members 2 3 correlates to oae3 in the western interior basin wib of north america within temporal uncertainty of high precision age models decreases in carbon isotopic fractionation 13 c through oae3 in the wib and songliao basin suggest that significantly elevated global rates of organic carbon burial drew down pco 2 likely cooling climate despite this os i chemostratigraphy demonstrates no major changes in global volcanism or weathering trends through oae3 identification of oae3 in a lake system is consistent with lacustrine records of other oaes e g toarcian oae and underscores that terrestrial environments were sensitive to climate perturbations associated with oaes additionally the relatively radiogenic os i chemostratigraphy and xrf data confirm that the qingshankou formation was deposited in a non marine setting organic carbon rich intervals preserve no compelling os i evidence for marine incursions an existing hypothesis for generating member 1 s prolific petroleum source rocks based on our results we present a model for water column stratification and source rock deposition independent of marine incursions detailing dominant biogeochemical cycles and lacustrine organic carbon burial mechanisms

tensile and compressive growth structures relationships between sedimentation deformation and granite intrusion in the archaean coppin gap greenstone belt eastern pilbara western australia abstract the coppin gap greenstone belt is composed of an east west striking asymmetric synclinorium between the muccan and mount edgar batholiths along the contact with the muccan batholith the vertical to overturned northern limb is intensely sheared folded and tectonically reduced the southern limb is relatively undisturbed and irregularly intruded by the mount edgar batholith progressive unconformities and sedimentary infilling of growth structures in the gorge creek group record the deformation history the unconformities constrain which of the now steeply dipping shear zones have to be rotated with their cover sequence before they can be interpreted kinematically four mid archaean clastic systems have been recognized the first and third are transgressive littoral quartzose and feldspathic arenites the second and fourth comprise conglomeratic and ferruginous alluvial fan related deposystems east verging thrust tectonics affected the belt after unconformable deposition of the first deposystem on the early archaean warrawoona group in the western extremity of the belt primary tectonic relief was filled with the second deposystem thrust folds were overprinted at right angles by folding sub parallel to the developing belt after truncation the belt was covered by the third and fourth systems in the eastern part of the belt relief created by belt parallel folds affecting the first deposystem was filled by conglomerate overlain by basalts a sequence also assigned to the whim creek group we relate systematic depocentre shifts as observed in the bamboo creek syncline to differential doming of the adjacent batholiths buried thrusts and shear zones may have caused km scale repetition of the underlying sequences the observed relationships place uncertainty on the validity of the existing stratigraphic correlations which now need geochronologic work to resolve part of the thrusting appears to have taken place by inversion on pre existing detachment shear zones in the underlying warrawoona basalts and ultramafic rocks the shear zones descend from a high stratigraphic level in the east towards deeper levels in the west the first motion has been west block down listric normal growth faulting in places accompanied by synsedimentary explosive intrusion of black chert veins mega brecciation and back tilt of fault blocks geometrically these early structures cannot be related to the geometry of batholith doming and are interpreted as the result of either regional tensile stress local caldera collapse or both mechanisms acting synchronously the mid archaean influx of siliciclastic sediments in the coppin gap belt coincides with this change from a tensile to a complex compressive deformation the latter caused by regional thrusting and interbatholith folding late deformation of the belt includes further steepening of the strata and eastward oblique dextral and 060 sinistral strike slip

unraveling the onset of cretaceous oceanic anoxic event 2 in an extended sediment archive from the tarfaya laayoune basin morocco we investigated the onset and development of cretaceous oceanic anoxic event 2 oae2 in a newly drilled core sn degrees 4 from the tarfaya basin southern morocco where this interval is unusually expanded high resolution centimeter scale equivalent to centennial analysis of bulk organic and carbonate stable isotopes and of carbonate and organic carbon content in combination with xrf scanner derived elemental distribution reveal that the ocean climate system behaved in a highly dynamic manner prior to and during the onset of oae2 correlation with the latest orbital solution indicates that the main carbon isotope shift occurred during an extended minimum in orbital eccentricity similar to 400 kyr cycle shorter term fluctuations in carbonate and organic carbon accumulation and in sea level related terrigenous discharge were predominantly driven by variations in orbital obliquity negative excursions in organic and carbonate delta c 13 preceded the global positive delta c 13 shift marking the onset of oae2 suggesting injection of isotopically depleted carbon into the atmosphere the main delta c 13 increase during the early phase of oae2 in the late cenomanian was punctuated by a transient plateau maximum organic carbon accumulation occurred during the later part of the main delta c 13 increase and was associated with climate cooling events expressed as three consecutive maxima in bulk carbonate delta o 18 the extinctions of the thermocline dwelling keeled planktonic foraminifers rotalipora greenhornensis and rotalipora cushmani occurred during the first and last of these cooling events and were likely associated with obliquity paced ocean wide expansions and intensifications of the oxygen minimum zone affecting their habitat space on a global scale

complete archive of late turonian to early campanian sedimentary deposition in newly drilled cores from the tarfaya basin sw morocco an expanded succession of organic rich marlstones and limestones deposited in the tarfaya basin provides an outstanding opportunity to closely retrace climate evolution and sea level changes during the cretaceous greenhouse period we present high resolution x ray fluorescence xrf scanning and bulk carbon and oxygen isotope records from two newly drilled sediment cores in the tarfaya atlantic coastal basin which recovered a continuous upper turonian to campanian succession of 290 m thickness the xrf core scanning records reveal three long term oscillations in the abundance of terrigenous elements increase of al ti k si and fe normalized against ca which correspond to progressive transgressive phases followed by rapid regressions during the coniacian and early santonian sea level highstands during this interval corresponding to the coniacian santonian oceanic anoxic event 3 oae 3 are characterized by overall oxygen depleted to anoxic conditions at the seafloor indicated by the high organic carbon content the presence of laminations and low log mn s high log v ca and high log br ca the upper santonian interval marks the transition from anoxic to oxic bottom water conditions prevalent through the early campanian the composite bulk carbonate 13 c curve exhibits strong similarities to the global stacked 13 c reference curve characterized by negative excursions in the early coniacian navigation and east cliff events and late santonian bracketed by the haven brow and buckle events and by positive excursions in the latest turonian hitchwood event middle coniacian wight fall event and at the santonian campanian boundary during the early campanian enhanced accumulation of fine grained carbonate and clay rich hemipelagic sediments increasing bulk carbonate 18 o and low log br ca and log v ca values indicate climate cooling associated with a substantial improvement in bottom water ventilation two long term 13 c cycles of 2 m y duration probably related to variations in earth s orbital eccentricity are associated with the long term cooling trend initiating the campanian maastrichtian climate transition toward a cool greenhouse state

a 3 dimensional analysis of magnetic anomalies over fracture zones in the cretaceous magnetic quiet zone madeira abyssal plain magnetic anomalies over fracture zones in a magnetic quiet zone are not complicated by reversals in the earth9s magnetic field and thus are easier to interpret showing only the effect of fracture zones as such observations on the kane fracture zone twigt et al 1983 tyro fracture zone slootweg collette 1985 and other fracture zones in the cretaceous magnetic quiet zone all point to an enhanced magnetization over fracture zones mainly situated on the younger side of the fracture zone axis a model which accounts for this relates the asymmetric magnetization to the asymmetric development of topography at the intersection of fracture zone and transform fault the three dimensional analysis of hayes charis and cruiser fracture zones presented in this study leads to a distribution of the magnetization of the oceanic crust which may be interpreted in terms of a varying magnetization intensity or a varying thickness of the magnetic layer on the younger side of the fracture zone axis the magnetization is systematically higher than average up to 6 a m in the intensity model also there are indications that there exists a reduced magnetization on the older side in several places in the study area a few large changes in seafloor spreading direction occur these are accompanied by anomalies which do not conform to the general model evidently the proposed mechanism of emplacement of magnetic bodies may not be effective under these extreme circumstances for the remainder the general validity of the magnetic fracture zone model is confirmed

orbital forcing and sedimentary sequences abstract the variation of eccentricity is connected with the most celebrated attempts to determine a limited portion of geologic time in the elaboration of the theory of the ice age that bears his name croll correlated two important epochs of glaciation with epochs of eccentricity computed to have occurred 100 000 and 210 000 years ago as the analysis of the glacial history progresses these correlations will eventually be established or disproved and should they be established it is possible that similar connections may be made between events far more remote gilbert 1900 p 15 16 but the precessional motion pulses steadily on through the ages like the swing of a frictionless pendulum its throb may or may not be caught by the geological process which obtains in a particular province and in a particular era but whenever the conditions are favorable and the connection is made the record should reflect the persistence and the regularity of the inciting rhythm gilbert 1900 p 18

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

orbital calibration of the late campanian carbon isotope event in the north sea a new record of carbon isotopes nannofossil biostratigraphy gamma ray and fe content variations is presented for the upper campanian of the adda 3 core danish central graben north sea the studied interval provides a revision of previously assigned late coniacian to early santonian ages new biostratigraphic data indicate a late campanian age for the 60 m thick studied interval the late campanian event lce is well recorded by a 1 5 negative excursion in the bulk 13 c along with two stepwise pre excursion negative shifts defining the pre lce the amplitude of the lce appears higher in the north sea than in other areas as seen from the correlation to germany the uk and france this correlation allows identification of a new 0 4 negative excursion defined as the conica event fe and gamma ray variations are used to calibrate the record with cyclostratigraphy fourteen 405 kyr cycles identified in the upper campanian of adda 3 can be correlated to north germany the compilation of previous results from north germany and correlation to adda 3 shows that the boreal upper campanian spans a total of 17 cycles each of 405 kyr that is 6 885 myr the duration of the lce is estimated to be c 1 myr at adda 3 and in north germany supplementary materials calibration of the hh xrf data is available at https doi org 10 6084 m9 figshare c 2134362

astronomically forced variations in multiresolution resistivity logs of lower upper cretaceous cenomanian coniacian terrestrial formations from the songliao basin northeastern china abstract continuous and high resolution well logs from the sk 2 east sk 2e borehole in the songliao basin provide an opportunity to understand the relationship between astronomically forced climate and electrical responses in terrestrial cretaceous strata here we present well logs mud logs and core measurement data of lacustrine deposits in the upper cretaceous qingshankou fm and of fluvial deltaic deposits in the quantou fm the multiresolution resistivity logs used for the cyclostratigraphic analysis include deep laterolog resistivity logs resistivity image logs and array induction logs the results show that the resistivity of strata in quantou fm mainly reflects changes in clay content and that resistivity logs can be used as paleoenvironmental and paleoclimate proxies in cyclostratigraphic studies of the quantou fm for the qingshankou fm formation resistivity is mainly affected by clay minerals which contribute to the overall electrical conductivity as well as nonconductive organic carbon increasing clay and organic carbon contents usually correspond to wetter and warmer climatic conditions the phase relationship between resistivity logs and astronomical cyclicity depends on factors that control resistivity spectral analyses of lithological changes and resistivity logs indicate the presence of eccentricity obliquity and precession cycles throughout the quantou fm this provides strong evidence that climate was the dominant control on cyclic sedimentation in the quantou fm the floating astronomical timescale which was established by calibrating extracted 405 kyr cycles from resistivity logs reveals that the duration of quantou fm was approximately 5 5 myr comparative analysis of power spectra reveals that the sensitivity of resistivity logs with specific resolutions to milankovitch cycles with different frequencies is variable comprehensive analysis of multiresolution resistivity logs is a new method in cyclostratigraphy analysis that has the potential to be effective in detecting signals of milankovitch cycles in terrestrial deposits

duration of the early bajocian and the associated δ13c positive excursion based on cyclostratigraphy the early bajocian about 172 ma ago was a period of tectonic changes a global carbon isotope positive excursion and biological diversification of marine invertebrates e g ammonites radiolarians and coccolithophores unfortunately both the duration of the early bajocian and the associated palaeoenvironmental changes are still poorly constrained we propose here an estimate of the duration of this sub stage based on a cyclostratigraphic analysis of the carbonate content from the chaudon norante section french subalpine basin france the chaudon norante succession has been correlated with les dourbes section using greyscale variations to detect possible local hiatuses the duration estimated here for the entire early bajocian is 4 082 ma two intervals were identified in the positive 13 c excursion an increase of carbon isotope values lasting 1 36 ma and climax isotope values lasting for 2 72 ma a cooling at high latitudes and warming at low latitudes may have enhanced the earth s temperature gradient leading to an increase in humidity which in turn triggered ocean eutrophication at the origin of the 13 c positive excursion supplementary material the complete dataset presented in the paper a colour version of the figure 8 and correlation of 13 c excursions between our studied site and contemporaneous sites are available at www geolsoc org uk sup18555

constraints on the age of the warrawoona group eastern pilbara block western australia abstract zircons from mafic and felsic volcanic rocks in the type area of the warrawoona group the basal archaean greenstone succession of the eastern pilbara block have been dated precisely using the ion microprobe shrimp the results allow two alternative time frames for the duration of the warrawoona group dependent on how the dated zircons are considered to relate to the volcanic rocks our favoured interpretation requires a hiatus of 135 5 ma between the duffer formation at 3 46 ga and the overlying felsic volcanic rocks of the wyman formation and a hydrothermal or later magmatic origin for zircons of age 3 33 ga within one duffer formation sample and the underlying metabasalts the alternative time frame requires a short time for deposition of the entire group less than 15 ma at 3 33 ga and a xenocrystic origin for the 3 46 ga zircons of the duffer formation outside the type area of the warrawoona group the age of an intrusive granodiorite requires that greenstones be older than 3 43 ga and the group formed over an interval of 120 ma visibly different zircons within one of the duffer formation samples were found to be palaeozoic in age and presumably constitute hydrothermal growth of new zircon within the rock at low temperature similar zircons were found within samples from other rock units but with a spread of proterozoic ages

hunting for paleoclimatic periodicities in a geologic time series with an uncertain time scale an 8 m section of a mid cretaceous albian deep sea sediment core from piobbico italy contains 2 cycles m compositional oscillations as postdepositional chemical migration in the core is weak the relative amount of carbonate is a primary indicator of cretaceous paleoclimate variability we report results of spectral analysis of two series caco3 wt measurements taken at roughly 2 cm intervals and a more densely sampled photodensitometer record of light dark variation the uncertainty in the age depth relation i e unknown fluctuations in sedimentation rate hampers a detailed assessment of the suggested eccentricity correlation we fit for long term time scale greater than 75 kyr fluctuations in sedimentation rate by tracking the local frequency modulation of the dominant harmonic in the data series assuming the true input signal to be monochromatic we estimate uncertainty in the observed local frequency by means of a statistical jackknife we fit a smoothed cubic spline to the set of discrete frequency modulation estimates specifying a 2 n misfit criterion where n is the number of frequency estimates from this analysis we infer fluctuations of a factor of two in the sedimentation rate which occur predominately on a time scale of 400 kyr we generate tuned series using several candidate age depth relations from the carbonate and densitometer series the tuned carbonate series returns greater correlation with the modern milankovitch periodicities the 2 cycles m energy resolves principally into two harmonic components whose frequency ratio corresponds to an observational accuracy of 1 2 to that of the 97 0 and 127 6 kyr eccentricity oscillations at frequencies lower than 2 cycles m we find harmonic oscillations whose phase correlates with the beating envelope of the 2 cycles m energy in a manner consistent with the modern milankovitch insolation we also observe a sinusoidal oscillation of lower amplitude with period scaled by those of the presumed eccentricity oscillations of 39 2 1 1 kyr which agrees with the period of the modern obliquity cycle after correction for the effects of tidal friction oscillations corresponding to milankovitch precessional frequencies are not established owing possibly to low signal level and unknown short term deposition fluctuations the tuned densitometer series recovers few new periodic features although its inferred age depth relation correlates well with that of the carbonate series we calibrate the depth variable downcore to the orbital cycles to estimate r 5 0 0 15 m m y as the effective sedimentation rate

geochemical characteristics of archean cherts and other sedimentary rocks in the pilbara block western australia evidence for archean seawater enriched in hydrothermally derived iron and silica abstract geochemical and mineralogical characteristics of archean sedimentary rocks such as cherts banded iron formations bifs shales and sandstones collected from the pilbara block western australia were studied lithologic features of various types of chert occurring within the pilbara supergroup are closely related to their chemical compositions red and brown bands of banded cherts generally show a higher fe 2 o 3 total iron as fe 2 o 3 concentration than do other cherts whereas grey greenish grey and pale yellowish grey cherts are characteristic of relatively higher concentrations of al and ti white cherts are generally composed almost exclusively of sio 2 geochemical characteristics of the cherts suggest that they were precipitated from hydrothermal solutions evidence for the hydrothermal origin includes 1 low mno fe 2 o 3 values 2 low concentrations of heavy metals 3 positive euanomalies 4 low co zn and ni zn values and 5 high concentrations of mn and fe in carbonates positive correlations between fe and heavy metals such as ni and zn imply the intermittent precipitation of fe oxides hydroxides along with these heavy metals in the ancient ocean cherts except for grey greenish grey and pale yellowish grey cherts are highly depleted in detrital materials this may have been caused by rapid precipitation of hydrothermally derived fe and si the archean pilbara ocean is believed to have been enriched in fe and si derived from hydrothermal activity

volcanic degassing hydrothermal circulation and the flourishing of early life on earth a review of the evidence from c 3490 3240 ma rocks of the pilbara supergroup pilbara craton western australia abstract new data gathered during mapping of c 3490 3240 ma rocks of the pilbara supergroup in the pilbara craton show that most bedded chert units originated as epiclastic and evaporative sedimentary rocks that were silicified by repeated pulses of hydrothermal fluids that circulated through the footwall basalts during hiatuses in volcanism for most cherts fossil hydrothermal fluid pathways are preserved as silica barite fe bearing veins that cut through the footwall and up to the level of individual bedded chert units but not above indicating the contemporaneity of hydrothermal silica veining and bedded chert deposition at the end of volcanic eruptive events silica barite fe bearing vein swarms are accompanied by extensive hydrothermal alteration of the footwall to the bedded chert units and occurred under alternating high sulphidation and low sulphidation conditions these veins provided pathways to the surface for elements leached from the footwall e g si ba fe and volcanogenic emissions from underlying felsic magma chambers e g co 2 h 2 s hs so 2 stratigraphic evidence of shallowing upward and subsequent deepening associated with the deposition of warrawoona group cherts is interpreted to relate to the emplacement of subvolcanic laccoliths and subsequent eruption and or degassing of these magmas heat from these intrusions drove episodes of hydrothermal circulation listric normal faulting during caldera collapse produced basins with restricted circulation of seawater eruption of volcanogenic emissions into these restricted basins formed brine pools with concentration of the volcanogenic components thereby providing habitats suitable for early life forms fossil stromatolites from two distinct stratigraphic units in the north pole dome grew in shallow water conditions but in two very different geological settings with different morphologies stratiform and domical stromatolites in the stratigraphically lower c 3490 ma dresser formation of the warrawoona group are intimately associated with barite and chert precipitates from hydrothermal vents suggesting that component microbes may have been chemoautotrophic hyperthermophiles evidence of shallow water to periodically exposed conditions active growth faulting and soft sediment deformation indicates that the volcanogenic emissions were erupted into a shallow water tectonically active caldera and concentrated therein to produce an extreme habitat for early life widespread conical and pseudocolumnar stromatolites in the c 3400 ma strelley pool chert at the base of the unconformably overlying kelly group occur in shallow marine platform carbonates silicification was the result of later hydrothermal circulation driven by heat from the overlying newly erupted euro basalt the markedly different morphology and geological setting of these only slightly younger stromatolites compared with the dresser formation suggests a diversity of microbial life on early earth the biogenicity of putative microfossils from this and younger hydrothermal silica veins in the warrawoona group remains controversial and requires further detailed study

late cretaceous climate changes recorded in eastern asian lacustrine deposits and north american epieric sea strata abstract cretaceous climate data of the long lived cretaceous songliao basin sb in eastern asia is correlated and compared with the western interior seaway wis on the northern american plate in order to understand better the dynamics of the earth s past greenhouse climates nearly continuous late cretaceous terrestrial deposition in the songliao basin is represented by two cores totaling 2431 m in length the turonian maastrichtian age of the section is based on integrated stratigraphy and is comparable in age with upper cretaceous strata in the wis being consistent with global trends the dynamic late cretaceous climates of both the sb and wis gradually cooled from the warmest albian cenomanian time to the end of the maastrichtian with several intervening warm periods as did the global climate however regional differences existed the songliao basin climate was humid to semi humid warm temperate subtropical and the western interior seaway was in the humid warm temperate zone and experienced only moderate climatic changes the shifts of oxygen isotope data in the songliao basin were frequent and abrupt whereas wis records more gradual change affected mainly by fresh water runoff mixing with southern tethyan and northern arctic waters sedimentary cycles of eccentricity obliquity and precession bands are recorded in both the sb and wis basins the sedimentary cycles in the wis and sb are interpreted to be related to variations of the wet dry runoff cycles which indicate that orbital forcing played an important role in global climate change in late cretaceous the most favorable condition for organic carbon burial in both the sb and wis basin was bottom water anoxia regardless of the cause of the anoxia but the organic carbon burial rate was usually much higher in the songliao lake than in the wi epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric co 2 in both basins organic rich deposits formed during a rise in water level and incursion of saline waters the integration of paleoclimate data from cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the cretaceous greenhouse climate change and may provide insights for a future greenhouse world

late cretaceous precessional cycles in double time a warm earth milankovitch response late cretaceous climatic cycles are reflected in lithological and magnetic variations in carbonate sediments from south atlantic deep sea drilling project site 516f at a paleolatitude of roughly 30 s magnetic susceptibility cycles 20 to 60 centimeters in length appear to be controlled by the precession of the equinoxes cyclicity is particularly robust within a 24 meter interval in the lower campanian where overtone spectral peaks are observed as well as secondary susceptibility maxima within individual precession cycles one model for this behavior is that sedimentation in the narrow cretaceous south atlantic was controlled by equatorial climate dynamics with the precessional insolation signal rectified by the large land masses surrounding the ocean basin

orbital tuning as an inverse problem chronology of the early aptian oceanic anoxic event 1a selli level in the cismon apticore 1 orbital tuning the process of fitting sedimentary cycles to orbital periodicities can estimate with high resolution the timing and duration of key events in the geological record we formulate here orbital tuning as the inverse problem of finding the variation in sedimentation rate that matches sediment cycles with orbital periodicities instead of obtaining a single best estimate we apply a bayesian formulation and define a probability distribution of sedimentation rate variations that result in powerful orbital periodicities by sampling this distribution with a monte carlo method we quantify the uncertainty in the inferred sedimentation rates due to uncertainties in the tuning periods and to components of the sedimentary signal that are unrelated to orbital cycles the method is applied to the chronology of a 30 m interval in the cismon apticore borehole southern alps italy that includes the early aptian oceanic anoxic event 1a selli level estimated to last 1 11 0 11 ma 95 interval the 13c record shows a sudden negative shift of about 1 at the base of the selli level 22 47 ka followed by a recovery to preshift values in 240 ka consistent with a scenario where light carbon is quickly added and then flushed out of the ocean atmosphere system

source to sink sediment budget analysis of the cretaceous ferron sandstone utah u s a using the fulcrum approach abstract this paper matches sediment fluxes estimated to have passed through an ancient river system with mapped downstream sediment volumes in a deltaic sink providing a test of the recently developed fulcrum approach to source to sink analysis this paper uses field measurements such as channel depth width and grain size to estimate paleodischarge in an ancient trunk channel of the cretaceous ferron sandstone in central utah the estimates of instantaneous discharge are then integrated over the geological duration of the river to estimate the total sediment volume delivered to downstream deltaic sinks in an attempt to balance the estimated sediment flux with the mapped deltaic deposits in the sink the bankfull channel depths calculated using the scaling relationship between the flow depth and the mean dune height vary from 3 3 to 5 5 m with an average depth of 4 4 m the corresponding bankfull channel width estimates vary from 50 to 80 m with an average value of 65 m calculated using scaling relationship between channel width and the width of accretion surfaces water discharge calculated for these bankfull dimensions vary from 2 7 10 2 m 3 s to 8 6 10 2 m 3 s also indicating that these rivers were routinely capable of generating hyperpycnal flows the instantaneous sediment discharge reaching the fulcrum was calculated using established sediment transport equations these instantaneous discharge values were first converted to mean annual sediment volume using the bankfull event durations recurrence intervals and a factor for the proportion of the total annual sediment load transported during the bankfull period based on empirical relationships from modern climate analogs and then projected over the average time duration of individual parasequences in the ferron notom clastic wedge which is approximately 14 kyr the mass balance across the fulcrum reveals that the average bedload sediment volume derived from the source about 3 km 3 matches with that deposited in the sink within a factor of two however underestimation of the bedload volume in the sink suggests sediment escape beyond the limits of currently mapped sink area previous models for the ferron indicate significant se deflection of sediment due to wave reworking which may account for the missing sandy sediment it is also possible that there is an overestimation of time duration for individual valleys resulting in higher sink volume estimation and larger source to sink mass imbalance monte carlo simulations based on probabilistic estimation were used to test the sensitivity of key parameters used in converting bankfull discharge to mean annual discharge the p10 p50 median and p90 values for the average annual bedload volume q mas are 9 1 10 4 m 3 1 7 10 5 m 3 and 3 7 10 5 m 3 respectively a q mas value between p50 and p90 yields a source to sink balance for bedload volume the current study establishes a mass balance across the fulcrum with a reduced range of uncertainty for the various parameters used uncertainty associated with bankfull channel dimensions has been reduced through inclusion of detailed outcrop data the uncertainty in estimating average annual sediment volume q mas from bankfull events is less than a factor of three this uncertainty can be further reduced by incorporating a more robust global discharge dataset from modern analog river systems despite many assumptions and uncertainties our study shows that the fulcrum method appears to be capable of balancing sediment budgets to within at least an order of magnitude in deep time sedimentary systems

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

astronomical calibration and global correlation of the santonian cretaceous based on the marine carbon isotope record high resolution records of bulk carbonate carbon isotopes have been generated for the upper coniacian to lower campanian interval of the sections at seaford head southern england and bottaccione central italy an unambiguous stratigraphic correlation is presented for the base and top of the santonian between the boreal and tethyan realms orbital forcing of carbon and oxygen isotopes at seaford head points to the boreal santonian spanning five 405 kyr cycles sa1 to sa5 correlation of the seaford head time scale to that of the niobrara formation western interior basin permits anchoring these records to the la2011 astronomical solution at the santonian campanian sa ca boundary which has been recently dated to 84 19 0 38 ma among the five tuning options examined option 2 places the sa ca at the 84 2 ma 405 kyr insolation minimum and appears as the most likely this solution indicates that minima of the 405 kyr filtered output of the resistivity in the niobrara formation correlate to 405 kyr insolation minima in the astronomical solution and to maxima in the filtered 13c of seaford head we suggest that variance in 13c is driven by climate forcing of the proportions of caco3 versus organic carbon burial on land and in oceanic basins the astronomical calibration generates a 200 kyr mismatch of the coniacian santonian boundary age between the boreal realm in europe and the western interior due either to diachronism of the lowest occurrence of the inoceramid cladoceramus undulatoplicatus between the two regions or to remaining uncertainties of radiometric dating and cyclostratigraphic records

early tectonic dewatering and brecciation on the overturned sequence at marble bar pilbara craton western australia dome related or not cataclastic breccias and hydrothermal fault arrays of likely c 3400 ma timing are well developed and exceptionally well exposed in the marble bar chert member of the pilbara craton brecciation involved centimetre to metre scale clast transport distances in breccia zones up to 5 m wide cutting the c 60 m thick chert in a series of right lateral fault zones our observations of downward facing pillow basalts the geometry of the breccias and oxygen isotope data for rocks and the breccia matrix suggest the rocks were at least steeply overturned on this flank of the mt edgar dome prior to brecciation the breccias are inferred to represent steep conjugate fault zones developed by local transtension the history of overturning and brecciation predates the formation of dome related regional foliation and metamorphism and therefore occurred between 3460 and 3320 ma the established ages for deposition of the underlying duffer formation and intrusion of the mt edgar batholith respectively local overturning of the marble bar sequence prior to both brecciation and the main phase of dome formation suggests a protracted deformation history for this segment of the pilbara craton the transtensional movement along the breccias may be representative of strain accommodation accompanying an early doming phase or could be a deformation event that developed independently of doming fluids involved in brecciation were most likely formation waters expelled from the cherts and basalts in response to overpressuring induced by the overturning and progressive burial

effects of climate tectonics and sea level changes on rhythmic bedding patterns in the niobrara formation upper cretaceous u s western interior regional correlation of interbedded pelagic hemipelagic limestones and calcareous shales of the fort hays limestone member of the niobrara formation confirms development of at least two levels of cyclicity occurrence of time parallel rhythmically deposited beds that can be correlated over distances exceeding 800 km lends strong support to the hypothesis that these cycles were induced by milankovitch type climatic forcing however visual observation and fourier analysis of variations in shale and limestone thickness demonstrate that the pattern of fort hays cyclicity lacks regional uniformity complications in the cyclic pattern may have resulted from the influence of orbital parameters having differing periodicities additionally departures from simple cyclical patterns resulted from sedimentary effects of the sevier orogeny and from erosional events associated with sea level changes documentation of thickness variations within the regionally persistent fort hays bedding sequence furnishes a basis for fine scale analysis of cretaceous crustal movements within the western interior seaway

extensional structures during deposition of the 3460 ma warrawoona group in the eastern pilbara craton western australia abstract structures in the granite greenstone terrain of the eastern pilbara were mapped in both the coongan belt greenstones and shaw batholith granitoids important structures that are coeval with an early magmatic event in both the granitoids and the greenstones were identified in the coongan greenstones a brittle extensional fault array is syn kinematic with felsic volcanics of the duffer formation dated at 3452 16 ma pidgeon 1978a in the underlying shaw batholith a major ductile shear zone was mapped at the contact with the coongan belt although the foliation in the shear zone forms part of a domal structure the stretching lineations constantly plunge to the ene the sense of shear as recorded in the shear zone is consistently east up with subsidiary sinistral strike slip movement on the e w trending part and dextral movement on the n s trending part a wedge shaped granitoid intruded into the shear zone during deformation this granitoid is part of the north shaw suite which has been dated at 3467 6 ma mcnaughton et al 1988 the structures in the greenstones and in the batholith have therefore formed during the same event at different crustal levels the structural kinematic magmatic metamorphic and geochronological data are consistent with a model in which these structures represent the downdip part of a dome with a core complex type of geometry in turn this implies that the domal geometry of the shaw batholith was initiated at mid crustal levels at a very early stage namely during deposition of the warrawoona group in the evolution of the pilbara craton as extension occurred during intrusion and extrusion of large volumes of magma the original distribution and thickness of granitoid bodies and greenstones were probably largely determined by the extensional geometry the initial domal shape of the shaw batholith has been enhanced during later deformation phases which caused steepening of n s trending structures

integrated paleoenvironmental analysis of the niobrara formation cretaceous western interior seaway northern colorado abstract this study presents a regional chronostratigraphic framework and paleoenvironmental reconstruction of the niobrara formation in northern colorado based upon multidisciplinary biostratigraphic and lithostratigraphic data a local biostratigraphic zonation is described for the coniacian to earliest campanian of this region of the western interior seaway based primarily upon the distribution of calcareous nannofossils three key paleoenvironmental packages are also identified and linked to the evolution of regional sedimentary facies during the early to late coniacian tethyan water masses interacted with boreal surface currents to produce regional upwelling along tectonically controlled bathymetric highs a well mixed relatively well oxygenated water column with warm surface water temperatures and high fertility sustained a rich microflora fauna and promoted higher carbonate production enhanced fluvial input and a weakening of tethyan influence during the early santonian mark the onset of a regional environmental shift this period of transition extends through the middle santonian and is characterized by pulses of transported material and relatively frequent turnover of faunal associations increased terrigenous runoff likely produced eutrophic surface waters and intensified water column stratification leading to a general deterioration of the bottom water environment in a progressively dysoxic setting continued strengthening of fluvial input during the late santonian to early campanian resulted in surface water freshening and sustained primary productivity this surface water environment in conjunction with stifled vertical mixing promoted the development of a stagnant and intensely stratified water column the basin was therefore severely dysoxic possibly anoxic and corrosive with chemically reducing bottom waters and an expanded oxygen minimum zone thereby limiting biotic development and causing the deposition of finely laminated mud rich carbonate poor seciments

astrochronology of the middle jurassic buqu formation tibet china and its implications for the bathonian time scale abstract the buqu formation in qiangtang basin in china was formed during the bathonian stage of the middle jurassic the subject of this study is the formation at well qz11 at a depth of from 34 to 591 m located in the southern depression of qiangtang basin the optimal accumulation rate from the result of asm analysis was used as the target to tune the gr gamma ray and dlr double lateral resistivity series in qz11 power spectra analysis in tuned gr and dlr series demonstrate the existence of a series of prominent astronomical periods within the buqu formation in the qiangtang basin then 100 kyr bandpass filtered curve was used to establish a floating astronomical time scale for the buqu formation and the maximum and minimum sedimentation rates without considering the factor of formation compaction were 150 m myr and 395 m myr respectively using this scale the lower limit for the duration of the formation is estimated to be approximately 2 09 myr this duration can serve as a reference for temporal and chronological calibrations of the bathonian stage

evidence for multiphase deformation in the archean basal warrawoona group in the marble bar area east pilbara western australia abstract the results of a structural analysis of the marble bar greenstone belt in the mcphee reward area of the eastern pilbara block in western australia indicate that the area has undergone a multiphase deformation on shears which approximately parallel the trace of stratigraphy cf primary igneous layering around the talga talga anticline early extensional movements were associated with the formation of the warrawoona group chiefly the duffer formation and indicate a wnw ese extensional direction similar to the syn warrawoona extension found in the area of the north shaw batholith extension was followed by thrusting with transport to the east the talga talga anticline is a culmination which formed during this event by thrust stacking a major shear in the area the duffada shear was reactivated during granodiorite emplacement with transport to the ne in their present geometry the shears have thrust movements on the south side of the talga talga anticline but normal movements on the north side after the reactivation came a nw se shortening which was accompanied by conjugate shear activity on north trending sinistral and west trending dextral shears and constrained to 2950 ma in the north shaw area the final movements were associated with a n s shortening which resulted in an e w trending thrust which cuts the northern flank of the talga talga anticline and nw and ne trending conjugate faults there is no evidence of radially oriented stretching lineations or slickensides which would be expected if the granitoid bodies which make up the mount edgar batholith were emplaced by a solid state diapiric process the net result of deformation was tectonic disruption of the stratigraphic stacking within the type ara of the talga talga subgroup in the warrawoona group this may offer an additional explanation for anomolously young dates of the talga talga subgroup with respect to the duffer formation and also indicates that the type section for the talga talga subgroup is a lithotectonic sequence

tectonic and eustatic impact on depositional features in the upper cretaceous austin chalk group of south central texas usa abstract the upper cretaceous austin chalk group in south central texas usa displays vertical and lateral variations in thickness and facies resulting from an irregular paleotopography of the seafloor and variable preservation of 3rd order sea level cycles during the coniacian to early campanian the tectonic evolution of the san marcos arch a prominent basement feature in the study area impacted facies and sequence architecture within the austin chalk group outcropping sections of the austin chalk group along the margin of the edwards plateau in south central texas stratigraphically transition between inner and outer ramp environments the cyclic stacking pattern of facies is recorded in vertical stratigraphic succession as 3rd order cycles separated by discontinuity surfaces and condensed deposits inner ramp facies consist of thalassinoides burrowed bivalve wackestone to packstone with minor occurrences of skeletal grainstone outer ramp facies comprise planolites burrowed foraminiferal chalk and marl with fine skeletal debris condensed facies associated with transgressive re working are characterized by glauconitic packstone with high concentrations of coarse skeletal debris and lithoclasts gamma ray profiles of outcrops investigated in the study area are correlated to subsurface wireline logs of wells drilled along the outcrop and subsurface trend in order to construct a stratigraphic framework across the san marcos arch this stratigraphic framework is biostratigraphically well constrained and correlated to the type section of the austin chalk group farther north in the vicinity of austin the integration of sedimentological and stratigraphic information enables the identification of four regional 3rd order depositional sequences within the austin chalk group thickness maps of each depositional sequence illustrate the tectonic evolution of the san marcos arch and its influence on the deposition of the austin chalk group which is judged as negligible during most of the lower austin chalk group coniacian and started to trigger lateral thickness variations and pinch outs in the santonian and early campanian syndepositional tectonic movement played an active role in the geometry of austin chalk depositional sequences and should be accounted for in sequence stratigraphic models developed in chalk depositional settings to explain the occurrence of coarser and cleaner facies

assessing pelagic palaeoenvironments using foraminiferal assemblages a case study from the late campanian radotruncana calcarata zone upper cretaceous austrian alps abstract two upper campanian sections in the austrian alps representing the north western tethyan biogeographic realm from either sides of the penninic ocean alpine tethys have been examined aiming at a high resolution assessment of foraminiferal assemblages the postalm section from the northern calcareous alps southern active margin and the oberhehenfeld section from the ultrahelvetics northern passive margin this study focuses on plankton biostratigraphy and foraminiferal palaeoecology of the radotruncana calcarata total range zone the postalm section displays cyclic red deposits with marls and marly limestones while we find uniform grey marls at oberhehenfeld the oberhehenfeld section from the ultrahelvetics can be correlated stratigraphically to the postalm section using foraminifera calcareous nannoplankton and stable isotope stratigraphy and provides a point of comparison from the northern margin of the penninic ocean the two sections show minimal difference in faunal composition and few distinct local stratigraphic signals palaeoenvironmental trends from the late campanian can be recognised relating the two sections from the austrian alps the depositional water depth can be reconstructed as some 500 800 m plankton assemblages show a remarkable stability despite the sudden appearance and disappearance of r calcarata hinting at the late campanian as a time interval of general foraminiferal stasis without significant evolutionary events we speculate that the origin and extinction of r calcarata are related to the prolonged evolution of ocean stratification during the campanian from the mid cretaceous sluggish hothouse during a time of general slow greenhouse climate decline

obliquity pacing of the hydrological cycle during the oceanic anoxic event 2 abstract the oceanic anoxic event 2 oae2 ca 93 5 ma represents a major phase of environmental change during the mesozoic and is associated with a pronounced positive excursion in the carbon isotope record short term climate oscillations within the oae2 are recorded as milankovitch cycles which have been used to establish a precise temporal framework for the oae2 however few studies discuss the sedimentary expression of milankovitch cycles during the oae2 and its paleoenvironmental implications here we present carbonate and organic carbon isotope data from a biostratigraphically well dated organic rich oae2 interval in a sedimentary succession outcropping in the brianconnais domain at roter sattel fribourg prealps switzerland we sampled the oae2 interval 4 28 m for proxies of detrital sediment quantification al ti magnetic susceptibility at ultra high resolution 1 cm time series analysis of multiple detrital proxies permits the construction of an orbital timescale for the oae2 based for the first time on the stable 173 kyr s3 s6 obliquity modulation cycle the resulting oae2 orbital timescale at roter sattel is consistent with previous timescales obtained in the western interior basin and in southern tibet china our cyclostratigraphic results show an unusually strong obliquity signal during the initiation of oae2 previous studies have demonstrated that the onset of oae2 was associated with magmatic pulses coupled with increases in atmospheric pco2 followed by an overall gradual drawdown of co2 accordingly we suggest that detrital input during the oae2 was the result of intensified continental weathering related to magmatic activity the substantially release of greenhouse gases and an accelerated hydrological cycle modulated by obliquity cycles

theory of chaotic orbital variations confirmed by cretaceous geological evidence variations in the earth s orbit and spin vector are a primary control on insolation and climate their recognition in the geological record has revolutionized our understanding of palaeoclimate dynamics and has catalysed improvements in the accuracy and precision of the geological timescale yet the secular evolution of the planetary orbits beyond 50 million years ago remains highly uncertain and the chaotic dynamical nature of the solar system predicted by theoretical models has yet to be rigorously confirmed by well constrained radioisotopically calibrated and anchored geological data here we present geological evidence for a chaotic resonance transition associated with interactions between the orbits of mars and the earth using an integrated radioisotopic and astronomical timescale from the cretaceous western interior basin of what is now north america this analysis confirms the predicted chaotic dynamical behaviour of the solar system and provides a constraint for refining numerical solutions for insolation which will enable a more precise and accurate geological timescale to be produced

late cretaceous orbitally paced carbon isotope stratigraphy from the bottaccione gorge italy abstract a refined astronomical tuning of the upper albian lower campanian is proposed from the bottaccione reference section gubbio central italy long term eccentricity cycles filtered from a high resolution 13c record were tuned to the highly stable 405 kyr cycles of the new la2010 astronomical solution for the earth s orbital elements the achieved orbital tuning provides a new precise and accurate age model for dating biostratigraphic magnetostratigraphic and carbon isotope events through a 23 myr long record cycles of 8 0 4 7 3 4 and 2 4 myr modulate the entire 13c record thus extending their detection from the cenozoic to 100 ma and represent primary and stable long term oscillation modes of earth s climate ocean system although an ultimate driver of these long term periodicities is lacking we speculate that specifically the periodicity at 4 7 myr represents a homologue of the present eccentricity grand cycles evolved by the chaotic behaviour of solar system planets during the mesozoic the long term periodicities potentially reflect an unexplored expression of the low frequency response of the carbon cycle to global biogeochemical dynamics of major nutrients particularly phosphorus associated with modulation of inputs to the ocean in turn triggered by high order marine transgressions and formation of highly productive shelf seas this very long term eccentricity control modulated by periodic low energy cycles is suggested to play a crucial role in carbon cycling controlling a chain of climate sensitive global biogeochemical processes on the earth finally these grand cycles provide a potential tool for geological correlation and provide a robust constraint for accurate calculation of the orbital evolution of the solar system

geologic characterization of the type cored section for the upper cretaceous austin chalk group in southern texas a combination fractured and unconventional reservoir a rock based geologic characterization was completed on a continuous core through the austin chalk group section an active exploration target in southern texas because this core located in the pearsall field is continuous and includes both lower and upper contacts it can be used as the type cored section for the southern texas austin chalk several general lithofacies are defined two lithofacies lithofacies 1 and 2 are highly bioturbated and have low to moderate organic matter content and are poor to moderate source rocks two other lithofacies lithofacies 3 and 4 are laminated lithofacies 3 containing some burrows and lithofacies 4 containing no burrows both lithofacies are good source rocks organic matter in the laminated lithofacies 3 and 4 and some of the organic matter in the bioturbated lithofacies 2 are dominated by type ii kerogen suggesting the section can be self sourcing a general trend is observed whereby lithofacies that were deposited under more oxygenated conditions increase in abundance up section and is related to a decrease in total organic carbon and hence source rock quality the primary oil and gas production is from fractures with possible later production from the nano to microporous matrix after pressure drawdown pore types are predominantly interparticle nano to micropores and lesser intraparticle nanopores as defined by loucks et al 2012 porosity is less than 8 and permeability is less than 0 05 md and ranges down into the nanodarcy range the type cored section adds to the understanding of the southern texas austin chalk by providing a geological description of lithofacies stacking patterns source rock quality characterization and reservoir quality the type core can be used as a comparison section to other cored sections of the austin chalk

a critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for late cretaceous global correlation abstract climate variability is driven by a complex interplay of global scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter regional correlation which in most cases cannot be obtained with biostratigraphic methods alone chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high resolution correlation over large distances but complications arise from a multitude of possible influences from local differences in biological diagenetic and physico chemical factors on individual 13c records that can mask the global signal to better assess the global versus local contribution in a 13c record it is necessary to compare numerous isotopic records on a global scale as a contribution to this objective this paper reviews bulk sediment 13ccarb records from the late cretaceous in order to identify differences and similarities in secular 13c trends that help establish a global reference 13c record for this period the study presents a global scale comparison of twenty 13c records from sections representing various palaeo latitudes in both hemispheres and different oceanic settings from the boreal tethys western interior indian ocean and pacific ocean and with various diagenetic overprinting the isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute 13c values and variation in amplitude between the sites these differences reflect the varying local influences e g from depositional settings bottom water age and diagenetic history whereas the concordant patterns in 13c shifts might represent 13c fluctuations in the global seawater dissolved inorganic carbon the latter is modulated by variations in organic matter burial relative to re mineralization in the global scale formation of authigenic carbonate and in partitioning of carbon between organic carbon and carbonate sinks these variations are mainly controlled by changes in climate and eustasy additionally some globally synchronous shifts in the bulk 13ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and thus can be globally synchronized by fluctuations in eustasy atmospheric and oceanic oxygen levels or in large scale oceanic circulation because the influence of early diagenetic cements on the bulk 13ccarb signal can but need not be synchronized chemostratigraphy should not be used as a stand alone method for trans continental correlation and especially minor isotopic shifts have to be interpreted with utmost care nevertheless the observed consistency of the 13c correlations confirms global scale applicability of bulk sediment 13c chemostratigraphy for the late cretaceous including sediments that underwent lithification and burial diagenesis such as the sediments from the himalayan and alpine sections limitations arise from increased uncertainties 1 in sediments with very low carbonate content 2 from larger 13c variability in sediments from very shallow marine environments 3 from unrecognized hiatuses or strong changes in sedimentation rates and 4 in sections with short stratigraphic coverage or with few biostratigraphic marker horizons the combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes facies or provincialism of key fossils by using an iterative approach to stepwise increase precision of the correlations isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested which helps to improve biostratigraphic zonations to assess zonal boundary ages and to identify useful criteria for defining late cretaceous stage boundaries many of which are still not formally defined the presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid cretaceous sea level high whereas diachroneity appears to be more pronounced during the late campanian and maastrichtian global sea level fall a similar pattern is observed for trans continental consistency in the 13c shifts graphic correlation of isotopic shifts magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo and magnetostratigraphy finally an attempt of a global average 13c stack is presented for the turonian through maastrichtian

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

factors controlling source and reservoir characteristics in the niobrara shale oil system denver basin this paper clarifies the controls of oil retention in the niobrara formation denver basin in the western united states sweet spots have been recognized using a total of 98 core samples from 5 wells with maturities covering the oil window oil retention in the source rock samples carbonate content 30 wt is controlled by carbonate content which is positively related to the amount of retained oil petrographic features indicate that oil or bitumen is stored in porous calcite fossils i e coccolith and foraminifera which provide additional space for petroleum storage chalk samples carbonate 85 wt are characterized by anomalously low tmax values caused by the influence of heavy petroleum or bitumen the amount of this bitumen is higher than the initial petroleum potential of kerogen in a and b chalks and thus must have been emplaced here the most likely sources are juxtaposed organic rich marl layers thus sweet spots occur where carbonate content is either low high toc or high low toc whereas production of petroleum from the pore space of presumably brittle chalk seems more attractive than production from organic and clay rich rocks

cenomanian to campanian carbon isotope chemostratigraphy from the western interior basin u s a abstract late cretaceous carbon isotope curves generated for localities in europe asia and the deep sea records have provided the foundation for development of a contiguous intercontinental chemostratigraphic framework despite the development of carbon isotope records from selected stratigraphic intervals in the western interior basin however a comprehensive 13c record comparable to those developed in europe and asia and from odp sites had not yet been completed this study reports a new high resolution cenomanian to campanian carbon isotope record for the central western interior basin of north america that makes a key contribution to the intercontinental correlation the curve is correlated to the well developed molluscan biostratigraphic framework for the western interior basin as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the 13c data were derived the new 13c record reflects not only major perturbations in the global carbon cycle such as the mid cenomanian event and the cenomanian turonian ocean anoxic event 2 but also smaller excursions that have been recognized in records from europe and asia this shows that the western interior shallow epeiric sea was not isolated for any appreciable part of cenomanian to early campanian time it consistently recorded changes in the global marine carbon cycle observed elsewhere a critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised late cretaceous time scale assignment of revised ages to western interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the western interior where similar carbon isotope records have been generated this chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested

model for the development of kyanite during partial convective overturn of archean granite greenstone terranes the pilbara craton australia restricted occurrences of early syn and late kinematic kyanite adjacent to large domal batholiths in the archean granite greenstone terrane of the east pilbara craton australia are considered to result from partial convective overturn of the crust the analogue models of dixon summers 1983 and thermo mechanical models of mareschal west 1980 involving gravitionational overturn of dense greenstone crust that initially overlay sialic basement successfully explain the geometry dimension kinematics and strain patterns of the batholiths and greenstone rims application of these models suggests that andalusite and sillimanite are the stable aluminosilicate polymorphs in domal crests and rims where prograde clockwise p t t paths with small pressure changes should be recorded both aluminosilicates are predicted to overprint kyanite which is observed locally around the east pilbara domes kyanite is the predicted aluminosilicate polymorph in the deeper parts of domal rims and within sinking greenstone keels reflecting rapid near isothermal burial the narrow zones of kyanite bearing schists adjacent to some batholiths in the pilbara craton are metamorphosed highly strained equivalents of altered felsic volcanic rocks in the low grade greenstone succession dragged to mid crustal depths 6 kbar during greenstone sinking the schists rebounded as an arcuate tectonic wedge along the southern mount edgar batholith rim during the later stages of doming and were juxtaposed against regional greenschist facies low strain greenstones thus kyanite was preserved if the walls had remained at depth it would have been overprinted by the higher temperature aluminosilicate polymorphs during thermal recovery kyanite growth in the pilbara craton is unlikely to have resulted from ballooning of plutons mantled gneiss doming metamorphic core complex formation or early crustal overthickening the typical subvertical foliations and lineations of the tectonic wedge suggest that subvertical fabrics extended to mid crustal depths c 20 km before rebound providing a three dimensional glimpse of archean dome and keel structures the general occurrence of large granitoid domes in archean granite greenstone terranes restriction of rare kyanite to the adjacent high strain batholith margins and its absence from the batholiths suggest that partial convective overturn of the crust may have been a common process at this early stage of earth history

pioneer nannofossil assemblages from the initial transgression of the niobrara seaway in the turonian san juan basin new mexico usa abstract nannofossils of the north american late cretaceous western interior seaway have been extensively studied but these investigations have primarily focused on the diverse communities of the niobrara and greenhorn sea level highstands we lack a firm understanding of the nature of early nannofossil communities from the initial stages of the transgression and of how the diverse assemblages of the coniacian santonian became established we investigated nannofossils in a core from the san juan basin new mexico with concentrated sampling across this transgression we then compared nannofossil assemblages from the initial transgression of the seaway to the more established cosmopolitan assemblages of the niobrara highstand the initial stages of transgression were characterized by unusual low diversity assemblages dominated by holococcoliths and seldom reported and previously undescribed species of hetero and holococcoliths herein we describe five new species and one new genus from these assemblages ahmuellerella frankiae sp nov gartnerago waszczakii sp nov orastrum schollei sp nov pharus clarescopoli sp nov and wisea sanjuanensis gen et sp nov these initial assemblages transitioned to more cosmopolitan higher diversity assemblages coincident with an unconformity that likely represents subaqueous erosion or prolonged non deposition above this unconformity the nannoplankton were abundant diverse and characterized by open marine cosmopolitan taxa that persisted through the coniacian and santonian x ray fluorescence data collected from the core show a high abundance of the detrital elements al and ti in the section indicating substantial detrital clay input into the area coincident with deposition of the holococcolith dominated assemblages the detrital influence lessened as cosmopolitan nannoplankton became more abundant in the area we suggest that the initial holococcolith rich assemblages are representative of a shallow marine potentially hyposaline turbid or unstable environment such assemblages have been observed from the late turonian elsewhere in northern new mexico and may represent typical pioneer nannofloras of the late cretaceous western interior marine transgressions our integrated investigation of nannofossils and x ray fluorescence geochemistry adds to the meager knowledge base of pioneer nannofloral communities in the initial phases of continental marine transgression

upb zircon geochronology of archaean felsic units in the marble bar region pilbara craton western australia abstract archaean supracrustal rocks that are well exposed in the marble bar region pilbara craton have been assigned to the warrawoona group and younger sequences the predominantly volcanic warrawoona group previously dated at 3300 to 3500 ma is largely basaltic with locally intercalated thick felsic volcanic units the supracrustal rocks have been folded and are distributed around the margins of large roughly circular to ovoid granitic gneissic batholiths a u pb zircon geochronology study was undertaken to obtain precise age constraints for some of the ore deposits in the area especially the big stubby north pole barite and miralga creek zn pb cu au deposits in support of efforts to improve archaean lead isotope models the results also help significantly in interpreting stratigraphic relationships and crustal evolution in the area the new conventional zircon u pb data indicate that most of the warrawoona group from the duffer formation upwards was deposited over a period of 20 ma from 3470 ma to 3450 ma the age of the duffer formation is closely constrained by results of 3471 5 ma and 3465 3 ma and the age of the upper salgash subgroup appears to be established at 3454 1 ma the panorama formation at the southern margin of the north pole dome is 3458 1 9 ma unless the duffer formation was deposited over a period of at least 10 ma this casts doubt on a previously suggested panorama duffer correlation the age of the lower part of the north pole succession is greater than 3458 ma consistent with the correlation of the basal greenstones at north pole with the talga talga subgroup the north pole chert barite unit which is well known for its preservation of early archean stromatolites microfossils and evaporite sediments is clearly older than 3458 ma the 3325 ma age now established for the wyman formation shows that this unit must be excluded from the warrawoona group the age of the talga talga subgroup remains uncertain a felsic schist in the mount ada basalt which has been dated at 3449 3 ma is interpreted to be a sill probably related to the 3450 ma granitoid bodies an age 3724 ma for a zircon xenocryst in the panorama formation is the oldest obtained so far for zircon from the pilbara granite greenstone terrane and indicates the existence of pre pilbara supergroup sialic basement ages of 3465 3 ma and 3449 2 ma applied to previous pb isotope data for the big stubby and miralga creek deposits respectively in combination with comparable data for other syngenetic archaean sulphide deposits yield a general single stage pb evolution model with the parameters t0 4560 ma a0 9 0818 b0 9 9002 and c0 29 343 this gives model ages in accord with known constraints for many archean deposits a model lead age of 3490 ma for the north pole deposit which is older than 3457 ma may be too great but attempts to directly date this deposit have not yet succeeded there are striking parallels between the warrawoona group ages reported here and those recently obtained for the barberton region kaapvaal craton south africa the talga talga subgroup and lower onverwacht tjakastad subgroup sequences have approximately equivalent constraints and an age for the upper salgash subgroup agrees closely with those for the hoogenoeg formation of the upper onverwacht group geluk subgroup

petrology of smoky hill member niobrara chalk upper cretaceous in type area western kansas the smoky hill member of the niobrara chalk is composed primarily of olive gray well laminated to nonlaminated impure chalk which is mostly foraminiferal pelmicrite with packstone or wackestone texture the rock is characterized by well stratified grain fabric ubiquitous constituents include coccolith rich fecal pellets mostly well preserved tests of planktonic forams wisps and silt sized grains of black organic matter fish bones and scales and minute framboids of pyrite or its oxidized equivalent inorganic detritus is common in all samples but only sparse grains of angular quartz silt are detected commonly in thin sections scattered through the member are thick to very thin beds of lighter colored bioturbated probably microbioturbated and granular chalk these are mostly foraminiferal and pelletal micritic wackestones which lack well stratified grain fabric in thin sections fecal pellets are less obvious than in well stratified chalks organic matter is much less common and pyrite framboids are less common in the matrix diagenetic features of smoky hill stratified chalks include compactional deformation of fecal pellets forams burrow structures and macroinvertebrate remains dissolution of aragonitic skeletal material incipient microstylolites sparry calcite cement in foram chambers interstitial calcite cement and secondary calcite overgrowths on coccoliths especially in the matrix bioturbated and granular beds are less well compacted than the stratified chalks and have greater amounts of secondary calcite as interstitial cement and overgrowths on coccoliths in these chalks lithification was initiated earlier than in the stratified chalks bioturbation of these and related kansas chalk deposits produced textures similar to those ascribed by others to deep burial diagenesis and extensive sol tion transfer thin section and scanning electron microscope sem data suggest that most reduction of original porosity to the present average of 38 was accomplished by gravitational compaction the remainder of porosity reduction resulted from the limited addition of secondary calcite which was derived mainly from dissolution of abundant aragonitic skeletal remains and in small part from pressure solution the smoky hill chalk is a pelagic deeper water outer shelf deposit which was laid down mostly as a soft perhaps mostly soupy coccolith rich ooze on a nearly flat sea floor under conditions of normal or nearly normal salinity and generally poor bottom water circulation at irregularly spaced intervals deposition of purer ooze furnished substrates suitable for a burrowing endobenthos which bioturbated sediments and helped to initiate earlier lithification than in nonbioturbated deposits

the floating astronomical time scale for the terrestrial late cretaceous qingshankou formation from the songliao basin of northeast china and its stratigraphic and paleoclimate implications abstract the upper cretaceous qingshankou formation k 2 qn in the songliao basin slb of northeast china consists of up to 550 m thick lacustrine mudstone and shale that constitute one of the most important source rocks of the daqing oil field a high resolution cyclostratigraphic analysis of the natural gamma ray logging from 10 wells of the qingshankou formation k 2 qn reveals orbital cycles of precession 20 ka obliquity 40 ka and eccentricity 100 ka and 405 ka providing strong evidence for astronomically driven climate changes in the late cretaceous terrestrial environments floating astronomical time scales ats are established for all sections which demonstrate variable durations of k 2 qn across the basin 1 09 ma 5 20 ma and strong diachroneity of the lacustrine strata four periods of high depositional rates can be identified in the central parts of the basin possibly recording deposition during times of sustained wet climate and high chemical weathering an ats established from well m206 in the central depression zone of the basin where the most complete and stable milankovitch cycles are present suggests that the maximum duration of the k 2 qn is 5 20 ma from 94 27 ma to 89 07 ma late cenomanian to early coniacian the lacustrine anoxic event 1 lae1 at the cenomanian turonian boundary lasted 210 310 ka during which the most prolific petroleum source rocks in slb were deposited the onset 94 21 94 18 ma and duration 210 310 ka of lae1 in slb are comparable to those of the oceanic anoxic event 2 oae2 onset at 94 21 ma and duration of 320 900 ka suggesting that the same trigger mechanism such as increased atmospheric co 2 from large scale igneous activity may have initiated high primary productivity and organic carbon burial in both marine and terrestrial systems

protracted fluid rock interaction in the mesoarchaean and implication for gold mineralization example from the warrawoona syncline pilbara western australia abstract oxygen isotopic and geochemical analyses on whole rock and quartz veins are combined with structural observations in order to constrain the fluid circulation history within the mesoarchaean warrawoona syncline of the north pilbara craton western australia the plumbing system which is the focus of this study is localized in the so called fielding s find shear zone ffsz a km scale shear zone formed during the burial of greenstones and coeval exhumation of granitic complexes this shear zone runs parallel or close to the axial plane of the syncline it involves a prominent quartz vein network and is lined with strongly hydrothermally altered mafic felsic and sedimentary rocks towards the ffsz felsic and mafic volcanic rocks become intensely silicified with an increase in bulk rock 18 o values from 10 8 to 25 1 for altered felsic volcanics and from 7 1 to 18 3 for altered mafic volcanics geochemical modelling ascribes the silicification to a dissolution precipitation process ree and most other trace elements are strongly depleted in the silicified units with the exceptions of elements such as v cr ni and co which are enriched throughout the warrawoona syncline vein quartz 18 o data are within a small range of 13 2 2 significantly lower than their silicified host rocks these data are interpreted as the result of two main paleo fluid circulation stages intense silicification and 18 o enrichment represent alteration driven by low temperature hydrothermal convection probably involving archaean seawater in contrast the quartz veins network is related to the infiltration of metamorphic and or magmatic fluids during a later deformation episode these quartz veins represent the event responsible for the bulk of economic lode gold formation in the area the protracted fluid rock interaction history in the warrawoona syncline may have played a major role in setting the stage for the late mineralizing event the early hydrothermal circulation could have formed an efficient plumbing system characterized by high permeability low reactivity and possibly au enrichment upgrading the au endowment to the late hydrothermal fluids

cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences over the past 25 yr the science of stratigraphy has evolved to include time correlative data from vastly disparate components of the earth system not least of these is the global signal afforded by cyclostratigraphy which has recorded the evolution of earth s astronomical milankovitch forcing of insolation and the paleoclimate system fossil astronomical signals are collected from cyclic sedimentary sequences by detailed sampling and study of facies geochemistry mineralogy rock magnetism color etc in step with the documentation of astronomically forced paleoclimate from ever older older geologic times innovations in computational science have provided ever longer high accuracy astronomical model targets that can be used for time scale calibration the earth s orbit is affected by motions of other planets notably the orbital perihelia of venus and jupiter which impose a dominant 405 k y eccentricity cycle on earth s orbital evolution the large mass of jupiter stabilizes this cycle over hundreds of millions of years the cyclostratigraphic record of 405 k y cycles is therefore often used to correct chronologies affected by variable sedimentation earth s shape and rotation rate are influenced by tidal dissipation and climate friction these effects affect earth s precession rate through time thus a record of earth moon evolution is also embedded in cyclostratigraphy the geochronologic value of cyclostratigraphy has been affirmed through intercalibration with high precision radioisotope dating which today has the potential to define the ages of stratigraphic horizons with 2 uncertainties at the scale of a precession cycle precession index phasing relative to that of the obliquity elucidates the seasonal nature of astronomical forcing of the paleoclimate system cyclostratigraphy contributes to our knowledge of planetary dynamics for times prior to the current ca 50 ma limit of accurate astronomical solutions and it will guide our future understanding of solar system evolution and the evidence for chaotic diffusion astronomical modeling is undergoing its own revolution with development of new numerical integrators to extend accuracy further back in time finally space exploration has revealed prominent sedimentary bedding and ice stratigraphy on the surface of mars with patterns suggestive of astronomical forcing analogous to earth

paleomagnetism of the marble bar chert member western australia implications for apparent polar wander path for pilbara craton during archean time abstract the archean biosphere drilling project abdp drilled a continuous 270 m long oriented core from the towers formation which includes the marble bar chert member 3456 1 3476 0 ma in the pilbara craton northwestern australia a paleomagnetic study of 261 discrete specimens collected from a 158 5 to 182 0 m section of the marble bar chert member revealed two distinct magnetic components lt and mt the mt component yields seven different mean paleomagnetic directions clustered as mb1 to mb7 these together with the published paleomagnetic poles of early archean rocks from the pilbara craton draw a continuous paleomagnetic pole path which likely to be regarded as the early to late archean apparent polar wander path apwp for the pilbara craton the apwp implies that the pilbara craton underwent a latitudinal drift of about 21 during the interval when the magnetization of the marble bar chert member was acquired the estimated speed of the lateral drift is 12 112 cm yr 120 1120 km myr which is large compared with current plate motion velocities suggesting that continents might have moved during the archean faster than in the phanerozoic

silica alteration zones in the barberton greenstone belt a window into subseafloor processes 3 5 3 3 ga ago abstract silicification of volcanic rocks ranging from komatiitic to dacitic in composition is a common phenomenon of the 3 5 to 3 2 ga old volcano sedimentary succession of the barberton greenstone belt silica enrichment occurs in zones several tens of metres thick at the top of volcanic sequences that are capped by sedimentary chert horizons sio2 contents increase upsection from the original igneous value up to 92 silicification is associated with a depletion of most elements commonly mobile during water rock interaction while k2o rb and ba are enriched in these zones some transition metals sc v and cr were immobile whereas ni and co and some other metals cu zn were mobile and are depleted the 18o values of volcanic rocks show a positive linear relationship with silica content and range from 9 0 to 17 3 the element depletion enrichment patterns and oxygen isotope data indicate low temperature c 100 150 c hydrothermal processes for the origin of the alteration zones the loss of most elements coupled with the addition of sio2 as well as ree systematics indicate high water rock ratios and a fluid ree composition typical of archaean seawater that had a 18o value of 0 hydrothermal activity is attributed to heat derived from cooling of volcanic rocks and a high regional heat flow in an oceanic plateau like setting and resulted in the establishment of shallow subseafloor convection cells diffuse venting of hydrothermal fluids over broad areas of the ancient ocean floor provided an ideal environment for both seafloor and subsurface biota 3 5 ga ago

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

stratigraphic continuity and early deformation of the central part of the coppin gap greenstone belt pilbara western australia abstract this article focuses on the discrepancy between the often advocated stratigraphic continuity of greenstone belts in the pilbara craton australia on the one hand and the observations of syndepositional deformation and other tectonic disturbance on the other hand the coppin gap greenstone belt of the east pilbara consists predominantly of mafic intermediate and felsic rocks with minor amounts of silicified sedimentary rocks of the early archaean warrawoona group several well defined zones subparallel to the bedding show intense brittle to ductile deformation testifying to differential movements of the tectono stratigraphic slices they delimit these deformation zones were at least partly related to west block down normal faults and accommodated upper block to the west transport however new u pb zircon dates geochemical analyses and detailed field observations show that the overall stratigraphic succession in the coppin gap greenstone belt has not been fundamentally disturbed the normal faults occur in several irregularly superposed arrays of km spaced faults part of which were active during deposition normal faults also occur throughout the entire belt combined the early deformation structures indicate east west extension over a minimum period of 20 ma from 3469 ma onwards likely the extension took place over an even longer period of time during much of the time of deposition of the warrawoona group from 3490 ma onwards syndepositional extension of the warrawoona group was geometrically unrelated to the doming of granitoid batholiths surficial i e uppermost crustal gravitational collapse during or shortly after deposition may have caused the apparent contradictory co existence of deformation zones and stratigraphic continuity although the deformation has not caused major disruptions of the stratigraphic succession the precision of the u pb shrimp ages is insufficient to rule out excisions or duplications of stratigraphy on the order of a few million years

lower maastrichtian cyclostratigraphy of the bidart section basque country sw france a remarkable record of precessional forcing abstract cyclostratigraphic analysis of the maastrichtian limestone marl alternations of bidart sw france allows the hypothesis of orbital control on lithological cycles to be evaluated magnetic susceptibility ms oxygen and carbon isotope measurements sampled at a high resolution are analyzed using various cyclostratigraphic tools a statistically significant orbital signal is detected with a remarkable record of the precession corresponding to the limestone marl couplets this well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the ms and 13 c records based on the 100 kyr eccentricity cycle the total duration of the section is estimated at 1 44 0 22 myr correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled bidart 13 c record to the astronomically calibrated 13 c signal of odp hole 762c shows that the studied section extends from 71 5 to 70 ma covering the upper part of chron c32n 1n and 2 3 of chron c31r oxygen isotope data suggest a 2 c cooling of sea surface temperatures during the studied interval when placed on the long term 18 o trend of the bidart section this interval is here recognized as the onset of the early maastrichtian cooling event with its excellent record of the precessional forcing the bidart section along with other sections of the basque country is a useful tool for the refinement of the maastrichtian timescale

review short term sea level changes in a greenhouse world a view from the cretaceous abstract this review provides a synopsis of ongoing research and our understanding of the fundamentals of sea level change today and in the geologic record especially as illustrated by conditions and processes during the cretaceous greenhouse climate episode we give an overview of the state of the art of our understanding on eustatic global versus relative regional sea level as well as long term versus short term fluctuations and their drivers in the context of the focus of unesco iugs igcp project 609 on cretaceous eustatic short term sea level and climate changes we evaluate the possible evidence for glacio eustasy versus alternative or additional mechanisms for continental water storage and release for the cretaceous greenhouse and hothouse phases during which the presence of larger continental ice shields is considered unlikely increasing evidence in the literature suggests a correlation between long period orbital cycles and depositional cycles that reflect sea level fluctuations implying a globally synchronized forcing of eustatic sea level fourth order depositional sequences seem to be related to a 405 ka periodicity which most likely represents long period orbital eccentricity control on sea level and depositional cycles third order cyclicity expressed as time synchronous sea level falls of 20 to 110 m on 0 5 to 3 0 ma timescales in the cretaceous are increasingly recognized as connected to climate cycles triggered by long term astronomical cycles that have periodicity ranging from 1 0 to 2 4 ma future perspectives of research on greenhouse sea level changes comprise a high precision time scale for sequence stratigraphy and eustatic sea level changes and high resolution marine to non marine stratigraphic correlation

cyclostratigraphy of the reference section for the cretaceous white chalk of northern germany lagerdorf kronsmoor a late campanian early maastrichtian orbital time scale new carbonate records of the upper campanian lower maastrichtian white chalk of northern germany at lagerdorf kronsmoor represent a continuous succession suitable for time series analysis the boreal chalk succession is characterized by several intervals of reduced carbonate content in the basiplana spiniger polyplocum upper langei and upper grimmensis granulosus to pseudoobtusa boreal macrofossil zones which are mainly related to periods of increased detrital supply results of spectral analysis on the carbonate time series allow the detection of the periodicities of long and short eccentricity the long eccentricity signal can be extended to the entire upper campanian comprising a total of 15 25 long eccentricity cycles a minimum time span of 6 2 ma and an age of 77 5 0 4 ma for the lower upper campanian boundary the long eccentricity cycles detected from chalk carbonate contents correlate with long eccentricity cycles detected in self potential logs of boreholes proving their significance within different depositional settings and rates of subsidence in the north german basin the biostratigraphic consistent occurrence of long eccentricity cycles provides evidence for the completeness of the sedimentary record the long term intervals of increased detrital supply are the expression of increased progradation of clay minerals related to a long term sea level fall with superimposed short sea level falls within a 2 5 million year interval spanning the campanian maastrichtian boundary it cannot be decided from the present state of knowledge if this signal is controlled by increased erosion due to uplift of inverted structures by eustatic sea level fall or a combination of both the detection of the long eccentricity suggests an orbital forcing superimposed on a long term regressive trend

testing the astronomical time scale for oceanic anoxic event 2 and its extension into cenomanian strata of the western interior basin usa the development of integrated astronomical and radioisotopic time scales from rhythmic strata of the western interior basin wib has played a fundamental role in the refi nement of late cretaceous chronostratigraphy in this study x ray fl uorescence xrf core scanning is utilized to develop a new elemental data set for cyclostratigraphic investigation of cenomanianturonian strata in the wib using material from the aristocrat angus 12 8 core northcentral colorado the xrf data set yields the fi rst continuous 5 mm resolution analysis of lithogenic biogenic and syngeneticauthigenic proxies through the uppermost lincoln limestone member the hartland shale member and the bridge creek limestone member including oceanic anoxic event 2 oae 2 the 40 ar 39 ar ages from ashes in three biozones including a new age from the dunveganoceras pondi biozone uppermost lincoln limestone member provide geochronologic constraints for the cyclostratigraphic analysis astrochronologic testing of the 5 mm resolution xrf weight percent caco3 data via average spectral misfi t analysis yields strong evidence for astronomical infl uence on climate and sedimentation results from the bridge creek limestone member are consistent with the previously published astrochronology from the u s geological survey 1 portland core central colorado and identifi cation of an astronomical signal in the underlying hartland shale member now permits extension of the wib astrochronology into the earlier cenomanian prior to oae 2 high rates of sedimentation in the angus core during the interval of oae 2 initiation as compared to the portland core allow recognition of a strong precessional control on bedding development as a consequence the new results provide a rare high resolution chronometer for the onset of oae 2 and the timing of proposed hydrothermal trace metal enrichment as observed in the 5 mm xrf data

astrochronology of the early turonian early campanian terrestrial succession in the songliao basin northeastern china and its implication for long period behavior of the solar system abstract the first complete early turonian early campanian lacustrine succession has been recovered from the sk i south sk is borehole in the songliao basin slb northeastern china we conducted a detailed cyclostratigraphic study of natural gamma ray gr log thorium th log and magnetic susceptibility ms data from this core spectral analysis of the upper quantou formation k 2 q 3 4 qingshankou formation k 2 qn yaojia formation k 2 y and lower nenjiang formation k 2 n 1 2 reveals a hierarchy of meter to decameter scale cycling in the data the wavelength ratios of the cycles in these stratigraphic units are 20 5 2 1 corresponding with those of milankovitch cycle periods of 405 kyr long eccentricity 100 kyr short eccentricity 37 kyr obliquity 20 kyr precession indicating astronomical control on sedimentation an astronomical time scale ats was established by tuning interpreted 405 kyr cycles to a 405 kyr orbital eccentricity target curve and to four sims u pb zircon radioisotope ages this absolute ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the ages of the c33r c34n geomagnetic polarity boundary in k 2 n 2 and three short reversal events in k 2 y are estimated as 83 633 ma 84 819 84 862 ma 84 982 85 092 ma and 85 240 85 629 ma respectively long period amplitude modulations in the obliquity and eccentricity bands of the 405 kyr tuned gr th series provide strong evidence that long period orbital forcing influenced climate change and depositional processes in the slb the extracted amplitude modulations provide evidence that the orbits of earth and mars were not in secular resonance and were undergoing chaotic interactions during this time although the modulations do not match those of recent astronomical models

integrated quantitative stratigraphy of the cenomanian turonian bridge creek limestone member using evolutive harmonic analysis and stratigraphic modeling abstract secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata in this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation the method exploits a moving window fourier technique that we designate evolutive harmonic analysis eha we calibrate this methodology to a specific set of geologic conditions i e changes in bulk sedimentation using a series of stratigraphic models and then apply the technique to the cenomanian turonian greenhorn formation of the western interior basin application of eha to strata that preserve a record of orbital forcing allows the reconstruction of a high resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified using the data on bulk sedimentation rate rates of accumulation for geochemical proxies representing detrital biogenic and authigenic contributions to the sediment can be calculated by integrating these quantitative assessments of siliciclastic dilution primary production and depositional redox conditions within a high resolution chronostratigraphic framework we are able to deconvolve secular trends in hemipelagic sedimentation during the late cenomanian early turonian in the western interior basin this integrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the western interior basin during the interval representing oceanic anoxic event ii

cyclostratigraphy of the upper cretaceous niobrara formation western interior u s a a coniacian santonian orbital timescale abstract the turonian campanian niobrara formation of the western interior basin u s a is characterized by decimeter scale rhythmic alternations of chalk and marl beds and decameter scale oscillations of chalky and marly facies this study applies recent advances in quantitative cyclostratigraphic analysis to high resolution geophysical records in order to test for an orbital signal we studied records of the entire formation 85 m from two wells in colorado 40 17 n 104 38 w 40 14 n 104 41 w the study utilized high resolution time series of borehole resistivity measured from formation microimager tools fmi advanced spectral techniques indicate the presence of eccentricity obliquity and precession periodicities throughout the study interval deviations of bundling ratios in the lower fort hays member from those predicted by simple eccentricity modulation of precession previously reported in the literature are likely due to the influence of obliquity deconvolution and frequency tracking of orbital components were used to reconstruct sedimentation rates for the niobrara formation and thus develop a high resolution orbital timescale which permits calculations of accumulation rates for sedimentary components and the duration of inclusive stages substages and in some cases biozones the niobrara formation in the studied cores appears to be hiatus free and therefore provides a continuous record of rhythmic deposition for astronomical timescale development the relationship between carbonate content and sedimentation rate throughout the niobrara formation indicates that the decameter scale oscillations of chalk and marl are dominantly driven by variations in siliciclastic flux dilution the duration derived from the orbital timescale between the turonian coniacian and coniacian santonian boundaries is 3 40 0 13 myr which is generally consistent with radiometric estimates for the coniacian the orbitally derived duration of the santonian stage is 2 39 0 15 myr which is very similar to estimates based on curve fitting between radiometric dates development of high resolution orbital chronometers provides excellent time resolution in intervals that lack radiometric time control or where control points are widely spaced

testing late cretaceous astronomical solutions in a 15 million year astrochronologic record from north america abstract astronomically forced insolation cycles milankovitch cycles serve as a primary control on climate and when preserved in the stratigraphic record they provide a high resolution in situ chronometer these celestial rhythms derive from the fundamental frequencies of the solar system and earth s precession constant the fundamental frequencies of earth and mars presently define a secular resonance of 2 1 2 4 myr to 1 2 myr and are hypothesized to have undergone a transition between 50 100 ma due to the chaotic behavior of the solar system in this study a 15 myr long cyclostratigraphic record from the mid latitude western interior seaway wis spanning 82 97 ma is assembled to quantify eccentricity amplitude modulation am and obliquity am which could reveal the 2 1 resonance when present ten high precision radioisotopic dates from the study interval permit a rigorous anchoring of the floating astrochronologies for comparison with theoretical astronomical models the analysis is complimented by the construction of an astronomically tuned 13 c org composite for the early cenomanian early campanian which allows a new assessment of linkages between million year scale astronomical forcing and perturbations of the late cretaceous carbon cycle evaluation of the la2004 model reveals a switch of eccentricity modulation from 2 4 myr cycles to a 1 2 myr cycle from 90 to 86 5 ma followed by a return to a 2 4 myr cycle in younger strata compatible with observations from the wis composite these two resonance transitions are absent in the la2010d and la2011 models among 11 solutions calculated by zeebe 2017 some show resonance transitions during this period but none of them match the geological record with respect to the observed long eccentricity modulation the results of this study also suggest that positive carbon isotope excursions are closely related to obliquity power minima but this interpretation will require further analysis for full confirmation

astronomical dating in the 19th century abstract today astronomical tuning is widely accepted as numerical dating method after having revolutionised the age calibration of the geological archive and time scale over the last decades however its origin is not well known and tracing its roots is important especially from a science historic perspective astronomical tuning developed in consequence of the astronomical theory of the ice ages and was repeatedly used in the second half of the 19th century before the invention of radio isotopic dating building upon earlier ideas of joseph adhemar james croll started to formulate his astronomical theory of the ice ages in 1864 according to which precession controlled ice ages occur alternatingly on both hemispheres at times of maximum eccentricity of the earth s orbit the publication of these ideas compelled charles lyell to revise his principles of geology and add croll s theory thus providing an alternative to his own geographical cause of the ice ages both croll and lyell initially tuned the last glacial epoch to the prominent eccentricity maximum 850 000 yr ago this age was used as starting point by lyell to calculate an age of 240 million years for the beginning of the cambrium but croll soon revised the tuning to a much younger less prominent eccentricity maximum between 240 000 and 80 000 yr ago in addition he tuned older glacial deposits of late miocene and eocene ages to eccentricity maxima around 800 000 and 2 800 000 yr ago archibald and james geikie were the first to recognize interglacials during the last glacial epoch as predicted by croll s theory and attempted to tune them to precession soon after frank taylor linked a series of 15 end moraines left behind by the retreating ice sheet to precession to arrive at a possible age of 300 000 yr for the maximum glaciation in a classic paper axel blytt 1876 explained the scattered distribution of plant groups in norway to precession induced alternating rainy and dry periods as recorded by the layering in holocene peat bogs he specifically linked the exceptionally wet atlantic period to the prolonged precession minimum at 33 300 yr ago and further related basic stratigraphic alternations to precession induced climate change in general such a linkage was also proposed by grove karl gilbert for cyclic alternations in the marine cretaceous of north america extrapolating sedimentation rates he arrived at an astronomical duration for part of the cretaceous that was roughly as long as the final estimate of william thomson for the age of the earth assuming that orbital parameters directly affect sea level karl mayer eymar and blytt correlated the well known succession of tertiary stages to precession and eccentricity respectively remarkably blytt like croll before him used very long period cycles in eccentricity to establish and validate his tuning understandably these studies in the second half of the 19th century were largely deductive in nature and proved partly incorrect later nevertheless this fascinating period marks a crucial phase in the development of the astronomical theory of the ice ages and climate and in astronomical dating it preceded the final inductive phase which started with the recovery of deep sea cores in 1947 and led to a spectacular revival of the astronomical theory by a century the first half of the 20th century can best be regarded as an intermediate phase despite the significant progress made in both theoretical aspects and tuning

the detection and illustration of regular sedimentary cycles using walsh power spectra and filtering with examples from the lias of switzerland power spectral analysis provides an objective method for the detection of regular cyclicity in data recording some oscillating parameter or time series digitization of measured stratigraphic sections is a convenient method for generating long time series during the examination of pelagic sequences for cyclicity related to orbital variations or milankovitch cycles the application of walsh power spectral analysis to stratigraphic sections is outlined and band pass filtering using the walsh transform introduced it is shown that variations in sedimentation rate hiatuses bioturbation and variations in compaction have the effect of damping or destroying spectral peaks the wavelength ratios of spectral peaks are often used during studies of milankovitch cycles to decide which orbital cycles are involved however in some circumstances hiatuses are able to alter wavelength ratios averaged walsh power spectra were generated for three liassic limestone shale sequences from breggia gorge switzerland the 21 000 year 21 ka precession cycle was detected in all three cases the 100 ka eccentricity cycle in two cases and the 41 ka obliquity cycle in one filtering revealed that the supposed 21 ka sedimentary cycles are grouped into packets of four or five small and large amplitude cycles the packets reflect the 100 ka modulation of the 21 ka precession cycle local disruption of the packaging can be used to locate hiatuses in pelagic strata

marine carbon burial flux and the carbon isotope record of late cretaceous coniacian santonian oceanic anoxic event iii abstract episodes of widespread distribution of organic rich marine facies within relatively narrow stratigraphic intervals have been interpreted as oceanic anoxic events oaes there are a number of such intervals in the upper cretaceous some of which also exhibit significant positive excursions in carbon isotope records as a result a general model of the relationship between enhanced organic carbon burial and positive c isotope shifts has emerged carbon isotope stratigraphy has therefore developed the dual utility of a chronostratigraphic tool and a means to help identify and define intervals of exceptional organic matter burial and preservation however variations in regional carbon isotope records of globally documented events suggest that the relationship between organic carbon burial flux and magnitude of carbon isotope excursion may not be entirely straightforward for example strata of coniacian santonian age have long been recognized for enhanced organic content in many areas but the designation of oceanic anoxic event iii for this interval has been rather equivocal in the literature mostly due to the weak positive 13 c excursion 0 5 yet in some areas organic carbon accumulation rates for coniacian santonian strata are roughly double that of the older oae ii which is marked by a 2 4 shift in 13 c interestingly the burial flux of carbonate which leads to depletion rather than enrichment of the c isotope signal is also significantly elevated during coniacian santonian time in this study the role of variations in organic carbon and carbonate accumulation rates on carbon isotopic expression are explored through application of data on the composition accumulation rate and areal distribution of end member facies types to the development of a global carbon isotopic mass balance model the results are used to explore the hypothesis that net organic carbon burial during oae iii was not accurately represented in the carbon isotopic record these results have important implications for interpretation of c isotope records related to past perturbations of the global carbon cycle

cyclostratigraphic analysis of magnetic records for orbital chronology of the lower cretaceous xiagou formation in linze northwestern china abstract in this study we report a tuned astronomical time scale for a sedimentary formation in early cretaceous the lower linze section located in the zhangye basin of the central hexi corridor northwestern china based on detailed field investigations we identified this sediment as the xiagou formation which is widely distributed in the region a thick prominent limestone layer crops out in the middle portion of the linze section and can be correlated to a similar limestone layer in the liupanshan group which has been dated via high resolution magnetostratigraphy this correlation places an age constraint of around 114 ma for the top of the underlying strata a total of 1245 samples were collected from the 474 m thick lower linze section for magnetic susceptibility measurements and cyclostratigraphic analysis spectral and continuous wavelet analyses were applied to the low frequency magnetic susceptibility series and the percentage frequency dependent magnetic susceptibility series as well as to specific subsections exhibiting visible rhythmic bedding a hierarchy of sedimentary cycles was identified with wavelengths of 21 5 37 0 m 7 5 9 5 m 2 1 4 4 m and 1 4 1 7 m the ratios between these lengths correspond well to the ratios between the durations of earth s orbital long eccentricity short eccentricity obliquity and precession cycles we interpret these sedimentary cycles to reflect the effects of orbital forcing on sedimentary processes using band pass filtering to specifically extract eccentricity cycles we established a tuned astronomical time scale for the xiagou formation in the lower linze section with a total duration of about 6 1 myr 114 1 ma to 120 2 ma based on this timescale the sedimentation rate of the xiagou formation is estimated to be in the range of 62 105 m myr with most intervals yielding rates in the 70 80 m myr range

organic geochemical characterization of santonian to early campanian organic matter rich marls sondage no 1 cores as related to oae3 from the tarfaya basin morocco abstract in addition to previously analyzed sediments of cenomanian to santonian age in the tarfaya sondage no 2 well this study presents the results of a stratigraphically younger interval of santonian to early campanian age in the adjacent well tarfaya sondage no 1 this interval is part of the oceanic anoxic event 3 oae3 which occurred mainly in the atlantic realm due to known high quality source rocks related to oaes i e cenomanian turonian the investigated sample section was tested for the quality quantity and kind of organic matter om describing also the depositional environment the study was carried out by means of i elemental analysis c org caco 3 ts ii rock eval pyrolysis iii vitrinite reflectance measurements iv gas chromatography flame ionization detection gc fid and v gc mass spectrometry gc ms total content of organic carbon c org values for the hydrogen index hi mainly in the range 500 700 mg g c org and s 2 values 10 40 mg g rock support the assumption of a high petroleum generation potential in these upper cretaceous sediments ts c org ratios as well as pristane phytane ratios indicate variable oxygen contents during sediment deposition representing a typical depositional setting for the late cretaceous and are in good agreement with previously analyzed data in the tarfaya basin phyto and zoo plankton were identified as marine sourced all of the investigated early campanian and santonian samples are immature with some tendencies to early maturation these results are based on vitrinite reflectance 0 3 0 4 vr r t max values 409 425 c production indices pi s 1 s 1 s 2 n alkane ratios i e carbon preference index as the deposition of these sediments is time related to oae3 the depositional environment was characterized by oxygen deficiency or even anoxic bottom water conditions this situation was favored during the cretaceous greenhouse climate by limited oxygen solubility in the then warmer ocean water furthermore local factors related to nutrient supply and primary bioproductivity led to the exceptionally thick upper cretaceous organic matter rich sedimentary sequence of the tarfaya basin

high resolution sequence stratigraphy and implications for cretaceous glacioeustasy of the late cretaceous gallup system new mexico u s a

hematite replacement of iron bearing precursor sediments in the 3 46 b y old marble bar chert pilbara craton australia the history of atmospheric oxygen prior to the great oxidation event 2 45 2 2 ga is not well understood hematite in the marble bar chert from a nasa funded drill hole abdp1 in the pilbara craton australia has been cited as evidence for an oxygenated ocean 3 46 b y ago however isotopic data from the same drill hole have been used to argue for an anoxic ocean it is generally agreed that the hematite is primary representing either a direct hydrothermal precipitate or a dehydration product of iron oxyhydroxides that formed during anoxygenic photosynthesis here we present new petrographic evidence from the marble bar chert in drill hole abdp1 that shows that hematite in jasper bands formed via mineral replacement reactions the hematite mostly occurs as sub micron sized inclusions within chert so called dusty hematite that are typically arranged into polygonal clusters surrounded by a rim of clear quartz resembling shrinkage structures the lateral transition from laminated chert enclosing minute inclusions of greenalite siderite and magnetite to chert dominated by dusty hematite provides evidence for in situ replacement of iron bearing minerals the presence of hematite rich bands containing octahedral crystals with residual cores of magnetite indicates that some of the hematite was derived from the replacement of magnetite this interpretation is supported by the widespread occurrence of magnetite in jasper displaying progressive stages of replacement from unaltered octahedral inclusions in quartz to hematite pseudomorphs along quartz grain boundaries the occurrence of dusty hematite in fractures sedimentary laminae and the outer margins of polygonal clusters containing greenalite is consistent with fluid mediated oxidation of iron rich precursor minerals the presence of syn sedimentary chert breccias comprising rotated fragments of laminated chert indicates that the precursor sediment was silicified shortly after deposition the abundance of dusty greenalite inclusions which are texturally the earliest components of the laminated chert suggests that the precursor sediment contained an iron rich clay mineral our results show that hematite has replaced ferrous rich minerals after deposition and provide a mechanism to explain the origin of hematite in the marble bar chert which is consistent with the origin of hematite in adjacent basalts a secondary origin for hematite invalidates arguments for an oxygen bearing ocean 3 46 b y ago and provides a viable explanation for the formation of archean jasper bands our findings show that misinterpretations about the origin of hematite in early precambrian cherts could lead to false conclusions about the chemistry of the ancient ocean and atmosphere

hierarchy of high frequency orbital cycles in cretaceous carbonate platform strata abstract lower cretaceous valanginian hauterivian carbonate platform strata which are well exposed in the matese mountains of the southern apennines italy have been analyzed on a microstratigraphic cm scale to exemplify the high frequency cyclic nature of the mesozoic shallow water sedimentation in southern italy based on the vertical organization of lithofacies and their early diagenetic signature 46 metre scale cycles are recognized these elementary cycles are hierarchically organized into groups bundles and superbundles the elementary cycles are prevalently formed by subtidal deposits and show emersion related features at the top suggesting repeated sea level fluctuations the number of elementary cycles compared to time as constrained by biostratigraphy and their grouping into sets implying higher order complexity in the environmental oscillation suggest an orbital control on sedimentation spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity which is characterized by lithofacies thickness periodicities of 1271 391 159 124 and 69 cm linear correlation of the relative ratio set rrs of these periodicities with the corresponding rrs of the orbital perturbation periodicities shows that 1271 and 391 cm fit the 404 220 and 94 890 year cycles of early cretaceous orbital eccentricity 159 and 124 cm fit the 49 010 and 38 030 year cycles of the earth s axial obliquity whereas 69 cm corresponds to the precession periodicity thus the san lorenzello section required not less than 1 6 ma to form at an average rate of 26 mm ka each 400 ka cycle can be viewed as a depositional sequence in which sequence boundaries maximum flooding surfaces and system tract equivalents have been recognized the microstratigraphic approach is very promising for understanding the fine structure of climate related environmental fluctuation recorded by the 3000 m thick carbonate platform successions of the southern apennines over a time span of about 150 ma upper triassic upper cretaceous and for deriving a more precise chronostratigraphy for global correlation

integrating 40ar 39ar u pb and astronomical clocks in the cretaceous niobrara formation western interior basin usa this study revises and improves the chronostratigraphic framework for late turonian through early campanian time based on work in the western interior u s and introduces new methods to better quantify uncertainties associated with the development of such time scales building on the unique attributes of the western interior basin which contains abundant volcanic ash beds and rhythmic strata interpreted to record orbital cycles we integrate new radioisotopic data of improved accuracy with a recently published astrochronologic framework for the niobrara formation new 40ar 39ar laser fusion ages corresponding to eight different ammonite biozones are determined by analysis of legacy samples as well as newly collected material these results are complemented by new u pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry ages from four biozones in the study interval when combined with published radioisotopic data from the cenomanian turonian boundary paired 206pb 238u and 40ar 39ar ages spanning cenomanian to campanian time support an astronomically calibrated fish canyon sanidine standard age of 28 201 ma stage boundary ages are estimated via integration of new radioisotopic data with the floating astrochronology for the niobrara formation the ages are determined by anchoring the long eccentricity bandpass from spectral analysis of the niobrara formation to radioisotopic ages with the lowest uncertainty proximal to the boundary and adding or subtracting time by parsing the 405 k y cycles the new stage boundary age determinations are 89 75 0 38 ma for the turonian coniacian 86 49 0 44 ma for the coniacian santonian and 84 19 0 38 ma for the santonian campanian boundary the 2 uncertainties for these estimates include systematic contributions from the radioisotopic measurements astrochronologic methods and geologic uncertainties related to stratigraphic correlation and the presence of hiatuses the latter geologic uncertainties have not been directly addressed in prior time scale studies and their determination was made possible by critical biostratigraphic observations each methodological approach employed in this study new radioisotopic analysis stratigraphic correlation astrochronology and ammonite and inoceramid biostratigraphy was critical for achieving the final result

rapidly changing styles of subsidence revealed by high resolution mudstone allostratigraphy coniacian of sweetgrass arch area southern alberta and northern montana marine mudstone of the coniacian muskiki member was deposited by storms on a shallow marine ramp across southern alberta and northern montana the rocks range from the c crassus crassus zone of the upper lower coniacian to the s depressus zone of the upper coniacian however upper coniacian strata are only a few metres thick at kevin montana and appear to be thin to absent beneath parts of the adjacent alberta plains probably because of minimal contemporaneous subsidence the muskiki member is partitioned into three packages by subtle bevelling unconformities cut during regional tectonic tilting the lower package indicates flexural subsidence in the nw whereas the middle package indicates subsidence in the sw the rotation of the axis of subsidence may indicate an along strike shift of the region of active thickening in the orogenic wedge the upper package is dominated by a nw trending region of stratal thickening forming a trough shaped rock body 100 km wide 250 km long and up to 50 m thick

new perspectives on orbitally forced stratigraphy this survey of the current status of research into earth s orbitally forced paleoclimatic record summarizes recent developments in the theory of earth s orbital parameters and reviews how various techniques of data collection and analysis have fared in the search and recovery of orbital signals in ancient stratigraphy the emerging significance of the quasi periodicity of earth s orbital variations as a prin cipal tool in the analysis of orbitally forced stratigraphy is discussed in detail five case studies are presented that illustrate new directions in research a time series analysis of discontinuous strata b measurement of ultra high resolution stratigraphic signals c new perspectives on the 100 kyr pleistocene glaciation problem d strati graphic evidence for solar system resonance modes and e evaluating phanerozoic length of day from orbitally forced stratigraphy the study of how earth s orbital parameters came to be recorded in ancient stra tigraphy has recently moved into a new phase of scientific inquiry and discovery notable advances in celestial mechanics and in the analysis of stratigraphic data have given rise to new ways of solving old problems and have uncovered new problems for the first time new tools have facilitated the recovery of extended high resolution orbital signals from stratigraphy advanced analytical techniques have now been fully incorporated into the field an updated theory of earth s orbital parameters provides an accurate ephemeris for the past 16 million years for precision correlation between earth s orbital parameters and orbitally forced stratigraphy some orbital eccentricity modes can be used for orbital stratal cal ibrations to several hundred million years ago these breakthroughs have transformed the study of orbitally forced stratigra phy into an applied field that addresses long standing problems in disciplines as far ranging as geochronology geodynamics and astrodynamics orbital signals provide the framework for a high resolution orbital chronostratigraphy as far back

redox controlled preservation of organic matter during oae 3 within the western interior seaway during the cretaceous widespread black shale deposition occurred during a series of oceanic anoxic events oaes multiple processes are known to control the deposition of marine black shales including changes in primary productivity organic matter preservation and dilution oaes offer an opportunity to evaluate the relative roles of these forcing factors the youngest of these events the coniacian to santonian oae 3 resulted in a prolonged organic carbon burial event in shallow and restricted marine environments including the western interior seaway new high resolution isotope organic and trace metal records from the latest turonian to early santonian niobrara formation are used to characterize the amount and composition of organic matter preserved as well as the geochemical conditions under which it accumulated redox sensitive metals mo mn and re indicate a gradual drawdown of oxygen leading into the abrupt onset of organic carbon rich up to 8 deposition high hydrogen indices hi and organic carbon to total nitrogen ratios c n demonstrate that the elemental composition of preserved marine organic matter is distinct under different redox conditions local changes in 13c indicate that redox controlled early diagenesis can also significantly alter 13corg records these results demonstrate that the development of anoxia is of primary importance in triggering the prolonged carbon burial in the niobrara formation sea level reconstructions 18o results and mo total organic carbon ratios suggest that stratification and enhanced bottom water restriction caused the drawdown of bottom water oxygen increased nutrients from benthic regeneration and or continental runoff may have sustained primary productivity

mixed siliciclastic carbonate upward deepening cycles of the upper cambrian inner detrital belt of laurentia abstract high resolution sedimentological and biostratigraphic data recently recovered from upper cambrian strata in the northern rocky mountain and central appalachian regions reveal that meter scale cycles of very different character developed synchronously during deposition of the basal subzones of the ibexian series in both the carbonate facies belt and the distal part of the inner detrital mixed siliciclastic carbonate facies belt of the laurentian paleocontinent a typical mixed siliciclastic carbonate cycle in the snowy range formation of wyoming and montana consists of the following lithofacies in ascending order shale shale with very thin grainstone interbeds grainstone with subordinate thin shale interbeds flat pebble conglomerate and in some cycles thrombolitic bioherms internal transitions between the constituent lithofacies are mostly gradational but cycle boundaries are sharp with shale directly overlying flat pebble conglomerate and or thrombolitic boundstone we postulate that these mixed siliciclastic carbonate cycles developed in response to different depositional dynamics than meter scale cycles developed in carbonate belt facies specifically cycles in the carbonate belt were produced largely by temporal variation in accommodation space and associated filling of that space through progradation of the carbonate system and aggradation to sea level in contrast cyclic deposition within the inner detrital belt was controlled by variations in terrigenous sediment input and resulting effects on carbonate productivity in this case enhanced delivery of siliciclastic mud by rivers was triggered by regression and or a shift to more humid climatic conditions an upward increase of carbonate in the main part of the cycles reflects enhanced carbonate production in response to the reduction of terrigenous clay supply during shoreline retreat widespread cementation of fine grainstone substrates led to deposition of extensive beds of flat pebble conglomerate possibly in association with elevated sea surface temperatures and enhanced storm intensity thrombolites formed at times of maximum transgression as microbial communities thrived in the absence of turbidity colonizing the irregular surfaces of flat pebble conglomerate beds we thus interpret these wholly subtidal cycles to record full changes in paleobathymetry with the bulk of the cycles recording upward deepening rather than shoaling associated with regression comparison with age equivalent shoaling cycles of the conococheague formation of the carbonate belt of the appalachian mountains highlights the different depositional dynamics in the mixed siliciclastic carbonate systems and underscores the peril in extrapolation of depositional models derived from carbonate systems to mixed systems regardless of age or paleogeographic setting