patterns of family extinction depend on definition and geological timescale the recent claim1 of an approximate 26 myr periodicity in the pattern of mass species extinction over the past 250 myr has already stimulated much astrophysical speculation and debate on causal mechanisms2 13 however as shown here the evidence for that claim is strongly contingent on arbitrary decisions concerning the absolute dating of stratigraphical boundaries14 the culling of the database and the definition of what is mass extinction as opposed to background extinction this evidence becomes insufficient under other plausible geological timescales and other acceptable definitions of mass extinction analysis of the nonculled database shows that the reliability of identification of mass extinctions and their timing is at present extremely limited it also suggests that the apparent periodicity of mass extinctions results from stochastic processes

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

the devonian lacustrine sediments of orkney scotland implications for climate cyclicity basin structure and maturation history the orcadian basin of northern scotland largely of middle devonian age is a major lacustrine rift basin with the widely correlateable achanarras sandwick lake bed extending for at least 800 km along the rift above this lake bed there are about 540 m of cyclic lacustrine sediments with lake sedimentation terminated by alluvial fan progadation the upper stromness flagstone formation and the rousay flagstone formation making up this lacustrine sequence are given revised and precise definitions within four reference sections from the orkney islands the sequence consists of about 45 first order cycles averaging about 12 m in thickness which resulted from long term climatic fluctuations in rainfall with a cycle time scale of about 25 000 years longer climatic fluctuations of about 100000 and 400000 years are also present these periods correspond to the precession and two eccentricity orbital cycles detailed knowledge of the stratigraphy constrains the structural and maturation history of the basin the basin formed in a series of extensional half graben and the orkney area suffered later inversion the lake sediments first reached the oil window at relatively shallow depths c 2000 m probably in the early carboniferous implying very high geothermal gradients during the early part of the basin history as corroborated by the presence of devonian volcanics in the region in the orkney area uplift probably started in the late carboniferous

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

simplifying the stratigraphy of time comments and reply comment zalasiewicz et al 2004 1 have proposed fundamental changes in the definition and application of stratigraphic terminology involving time rock and geologic time units that fly in the face of widely accepted principles that have been tried and tested in establishing an international unified

cretaceous to cenozoic thermal evolution of the southwestern south carpathians evidence from fission track thermochronology abstract the southwestern south carpathian orogen is composed of various nappe complexes which were assembled during the cretaceous cenozoic orogeny these are from footwall to hangingwall 1 the danubian nappe complex including a cadomian variscan basement 2 the arjana and severin units with jurassic to early cretaceous rift and oceanic sequences and 3 the getic nappe complex with variscan continental basement fission track ft thermochronology on apatite zircon and sphene from samples collected from various units of the south carpathians in conjunction with field constraints and previous geochronology is used to characterise the alpine tectonic events and to restore the pattern and amount of exhumation since the cretaceous zircon from the flysch unit and the danubian liassic cover sequence yields ft ages around 200 ma suggesting cooling of the rift flanks prior to the opening of the severin rift zircon and sphene from the getic and danubian basement units yield ft ages averaging 110 ma and indicating cooling under 240 c of the basement contemporaneous with or postdating thrusting apatite ft ages display a decreasing age trend from the hangingwall 65 ma to the footwall units 30 ma the age data and corresponding horizontal confined track length distributions suggest that exhumation of the nappe pile occurred in two stages the first is related to the late cretaceous nappe stacking and the second one to the final thrusting of the south carpathians onto the top of the moesian platform apatite ft ages along major brittle wrench faults indicate reheating above ca 120 c during fluid flow associated with fault re activation during oligocene and neogene times thus shear zone rocks experienced a higher temperature overprint during cenozoic time than rocks of the unaffected nappe pile temperatures of hydrothermal flow along these zones decreased below 100 c progressively starting with the late oligocene early miocene when the area began to override the moesian platform

three growth in the mesozoic and early tertiary and the reconstruction of palaeoclimates abstract evidence from the distribution and characteristics of fossil wood in the mesozoic and early tertiary indicates that a much warmer global climate prevailed in those times there appears to have been a broad zone of largely non seasonal climate stretching from about 32 n to 32 s palaeolatitudes in addition to this low latitude zone forest growth extended into very high palaeolatitudes where trees cannot grow at the present day a number of theories have been proposed to account for the palaeoclimate responsible for this distribution of forests most notable have been those involving changes in the amount of carbon dioxide in the atmosphere in the positions of the continents or in the obliquity of the earth s axis of rotation evidence from fossil forests indicates that a combination of the effects of an increased quantity of carbon dioxide in the atmosphere and the palaeopositions of the continents in the mesozoic and early tertiary appears at the moment to be the simplest explanation for the climate of those geological times without the need to invoke axial movement

preservation of primary stable isotope signals in dinosaur remains and environmental gradients of the late cretaceous of montana and alberta abstract although the use of stable isotope data from vertebrate remains is becoming common for the cenozoic their application to mesozoic environments has been rare in part due to the perception that diagenesis has obfuscated all potential primary signal in this paper we illustrate how stable isotope data collected from dinosaur and other vertebrate remains can in fact be used to reconstruct paleoenvironmental conditions during the mesozoic carbon and oxygen isotope ratios were measured from tooth enamel of hadrosaur dinosaurs and from scales of freshwater fish that were collected from sites in the two medicine judith river and dinosaur park formations of montana and alberta these formations represent a coastal to upland gradient along the western margin of the late cretaceous inland seaway isotopic comparisons among skeletal components and among taxa are used as evidence that primary paleoenvironmental information as recorded by isotope data is preserved in tooth enamel and freshwater fish scales a comparison of carbon isotope ratios between hadrosaur tooth enamel and sedimentary organic matter indicates that these animals had a larger isotopic offset compared to bulk diet than modern mammals and that all hadrosaurian isotope data are consistent with the existence of c3 only ecosystems higher and more variable carbon and oxygen isotope ratios from animals occupying the coastal judith river region are interpreted to reflect a range of freshwater to brackish water conditions and plants that were undergoing water stress lower and less variable carbon and oxygen isotope ratios from the upland two medicine and intermediate dinosaur park areas are interpreted to reflect a gradual rainout of moisture from air masses moving inland and more uniform environmental conditions overall these results indicate that stable isotopes from dinosaur and other vertebrate remains have the potential to expand our understanding of terrestrial environments and ecosystems during the mesozoic

isotopic variation in rhythmically bedded chalks paleotemperature variation in the upper cretaceous detailed sampling at 2 cm intervals of a rhythmically bedded chalk marl sequence in southeast england has revealed a cyclic variation in oxygen isotopic composition of the carbonate component these changes are most consistent with paleotemperature fluctuations of up to 4 5 c contrary to some recent models chalk horizons are interpreted to reflect periods of warmer temperature and higher primary productivity than those responsible for marl deposition the effects of different faunal content diagenesis and variations in the water chemistry can all be discounted

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

sunspot periods in the late precambrian glacial climate and solar planetary relations cycles conspicuous in late precambrian 680 myr glacial varves in australia reveal strong climatic periods of about 11 22 145 and 290 yr and a weaker period near 90 yr the 11 22 and 90 yr cycles equate with sunspot periods and the longer cycles with solar and climatic periods as indicated by tree ring studies the varve cycles provide clear evidence of 11 and 22 yr climatic periods in the geological record and may carry important implications for solar physics and planetary science

high frequency cyclicity milankovitch and millennial scale in slope apron carbonates zechstein upper permian north east england the upper permian zechstein slope carbonates in the roker formation zechstein 2nd cycle carbonate in north east england consist of turbidites interbedded with laminated lime mudstone studies of turbidite bed thickness and relative proportion of turbidites percentage turbidites in 20 cm of section reveal well developed cyclicities consisting of thinning upward and thickening upward packages of turbidite beds these packages are on four scales from less than a metre up to 50 m in thickness assuming that the laminae of the hemipelagic background sediment are annual allows the durations of the cycles to be estimated in addition counting the number and thickness of turbidite beds in 20 cm of laminated lime mudstone which is approximately equivalent to 1000 years each lamina is 200 m gives the frequencies of the turbidite beds the average thicknesses and the overall sedimentation rates through the succession for 1000 year time slots figures obtained are comparable with modern rates of deposition on carbonate slopes the cyclicity present in the roker formation can be shown to include milankovitch band ca 100 kyr short eccentricity ca 20 kyr precession and ca 10 kyr semi precession cycles and sub milankovitch millennial scale cycles 0 7 to 4 3 kyr eccentricity and precession scale cycles are related to highstand shedding and relative sea level change caused by milankovitch band orbital forcing controlling carbonate productivity the millennial scale cycles which are quasi periodic probably are produced by environmental changes controlled by solar forcing i e variations in solar irradiance or volcanic activity most probable here are fluctuations in carbonate productivity related to aridity humidity and or temperature changes precession and millennial scale cycles are defined most strongly in early transgressive and highstand parts of the larger scale short eccentricity cycles the duration of the roker formation as a whole can be estimated from the thickness of the laminated lithotype as ca 0 3 myr

regular and irregular climatic cycles and the belemnite marls pliensbachian lower jurassic wessex basin time series of carbonate and organic carbon values are reported for 10 5 m of the belemnite marls the light and dark marl beds form decimetre scale couplets and metre scale bundles light marls are carbon poor and carbonate rich whereas dark marls and laminated shales are carbon rich and carbonate poor sediment composition appears to have been indirectly controlled by climate the regular couplets may record orbital precession cycles 20 ka however the bundles cannot be linked to changes in eccentricity rather they apparently record irregular large amplitude climatic variations with periods of a few hundred thousand years it should not be assumed that 100 400 ka cyclicity in climate related sedimentary sequences can be explained only by orbital forcing

influence of the changing lunar orbit on the astronomical frequencies of pre quaternary insolation patterns the sensitivity of the frequencies of the earth s orbital elements involved in the astronomical theory of paleoclimates obliquity and climatic precession to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth is investigated for the last billions of years but the new frequencies have been computed for the last 440 million years only a time interval over which data and a model of the earth were available moreover we consider only the impact of the changing precessional parameter assuming that the fundamental frequencies of the planetary motion are steady at the geological time scale under such hypotheses the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for obliquity and precession a shortening that is larger for longer periods

the analysis and interpretation of stratification cycles beds in carbonate successions often form regular patterns either there is a cyclic repetition of beds with different thicknesses or bundles of beds occur separated from each other by some distinct layer any such group will be called a stratification cycle cycles of this type are from 0 5 m to several meters in thickness and they seem to be present throughout the geological column the analysis of sedimentary cycles involves three stages 1 regional mapping is necessary to understand the facies of the sediment establishing the lateral persistence of bedding eliminates the possibility that bedding is caused by diagenetic processes 2 petrographic examination and in particular analyses of primary structures are used to reconstruct the sedimentation conditions during cycle formation such conditions are extremely important for judging the time content of individual beds 3 the quantitative analysis of vertical sections using power spectral methods can find superimposed cycles and enables one to judge their degree of regularity the latter approach is illustrated using lower carboniferous limestone sections from nw ireland as an example spectral analysis finds a stratification cycle of 1 to 3 m in thickness each cycle consists of between five to seven limestone beds upper jurassic limestone marl successions from southern germany and late cretaceous and early tertiary successions from italy show a very similar cyclic pattern the scale of the cycles and their regularity suggest that they are ultimately caused by variations in the earth s orbit possibly by climatic cycles as was postulated by milankovitch however the exact mechanism which links sedimentation with orbital variations is not known

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

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

topographic height dependence of internal wave generation by tidal flow over random topography internal waves iws generated by tidal flow over the seafloor play a critical role in ocean circulation and climate we determine the dependence of the radiated iw power on topographic parameters in numerical simulations of tidal flow over two dimensional random topographic profiles that have the spectrum of oceanic abyssal hills the iw power increases as the horizontal spatial resolution scale is decreased but below a certain spatial scale the power saturates at a level less than the linear theory prediction for increasing topographic rms height hrms the emergent interference of the tide and the iws from different generation sites leads to a transition in the iw power dependence on hrms from quadratic to linear this transition in the scaling of the iw power depends on the slopes of a valley s nearest neighboring peaks our results should guide the modeling of iw generation by tidal flow over small scale ocean topography

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

the occurrence and preservation of ammonites in the blue lias formation lower jurassic of devon and dorset england and their palaeoecological sedimentological and diagenetic significance abstract more than two thirds of beds in the lowest jurassic blue lias formation lack ammonites which are commonly preserved in irregular or planar bedded bioturbated limestones very rarely in laminated limestones and almost never in laminated black shales ammonites are preserved in 3d in nodular and planar bedded limestones and at any orientation to bedding co occurrence with macrobenthos and absence from beds without benthos suggest that blue lias ammonites were nektobenthonic scour structures and imbrication of ammonites in the best bed imply presence of traction currents lack of epifauna on large cephalopod shells and other fossils implies rapid deposition in event beds blue lias deposition was episodic not slow and continuous as the fine grain size implies undistorted trace fossils uncrushed ammonites and stable isotope values all suggest early cementation of limestone beds from pore waters of a similar composition to contemporary jurassic sea water a clear diagenetic trend exists with limestones having least and laminated black shales most modified stable isotope values contrast between trace fossil fills and host sediment demonstrates that blue lias rhythms are primary but limestone beds have been diagenetically cemented

the cyclic hierarchy of the purbeckian sierra del pozo section lower cretaceous berriasian southern spain the lowermost cretaceous berriasian sierra del pozo formation is divisible into metre scale cycles that are bundled in a four tiered hierarchy of cycles and cyclic sequences at the smallest scale sixth order cycles thought to be the product of precessionally forced sea level fluctuations c 20 ka average less than a metre in thickness shallow upward and are bounded by surfaces where deeper facies abruptly overlie shallower facies bundles of sixth order cycles called fifth order sequences are recognized by two types of asymmetric patterns in facies distribution first more pronounced facies changes occur at sixth order cycle boundaries lower in a sequence whereas smaller facies changes occur at cycle boundaries higher in a sequence secondly subtidal marine limestones i e biomicrites and biosparites are the dominant facies lower in a cyclic sequence whereas more restricted or shallower water facies i e mud cracked microbial laminites dolomites shale and clay are more predominant higher in a cyclic sequence the bundling of sixth order cycles is explained as a product of periodic change 100 ka in the eccentricity of the earth s orbit the degree of orbital eccentricity modulates the magnitude of precessional sea level fluctuations which in turn determine the relative facies contrasts at sixth order cycle boundaries larger scale fourth and third order sequences are defined by similar patterns in facies contrast at successive sequence boundaries and by a change in predominant facies type from bottom to top these patterns are explained as the product of 400 ka and 2 ma periodic variations in the eccentricity of the earth s orbit in summary the strength of the precessional signal varies in consort with periodic changes in orbital eccentricity at three time scales producing a stacked hierarchy of cycles and sequences of cycles change in obliquity of the earth s axis may modulate the effects of the precessional signal and thereby modify patterns of preserved cyclic structure this interpretation of cyclicity in the sierra del pozo section is markedly different from that of

climate record in varved sediments of the eocene green river formation three time series of varves from the eocene green river formation in colorado consisting of 1469 1869 and 4158 annual thickness measurements were analyzed by a variety of statistical techniques to characterize climate variations the analyses reveal that the time series are lognormal after adjustment for a trend moreover the analyses suggest that the time series are generally nonstationary and are noiselike in structure fourier spectra and maximum entropy spectra of the time series are reddish indicating the importance of nonoscillatory changes in varve thickness at time scales ranging from tens to hundreds of years there are no statistically significant peaks in fourier spectra for the entire time series however one segment of one of the three time series displays statistically significant peaks corresponding to periods of 10 8 and 5 4 years overall the time series are suggestive of a nonperiodic and weakly predictive climate during the time periods corresponding to deposition of the varves

reconstruction of mid cenomanian orbitally forced palaeoenvironmental changes based on calcareous dinoflagellate cysts abstract mid cenomanian precession controlled 21 ka chalk marl couplets of the cap blanc nez section anglo paris basin have been studied with focus on the effects which milankovitch cycles have had on the palaeoenvironment in this paper we present micropalaeontological and lithological proxies that enable the reconstruction of both the cycle architecture and the transformation of the orbitally forced signal into the sediment a palaeoecological reconstruction based on changes in calcareous dinoflagellate cysts c dinocysts assemblages was carried out in which two characteristic ecological assemblages of c dinocysts were identified gradual changes in absolute and relative abundance of the cyst species in these assemblages over several couplets depict a bundling pattern which is interpreted to reflect the modulation of the intensity of the precession cycle by the eccentricity cycle 100 ka the stacking pattern in the natural gamma ray signal and the carbonate and toc content has the same period and provides lithological support of the bundling a shelf basin circulation model is proposed to explain the relation between orbitally forced climate change its palaeoenvironmental consequences and the resulting sedimentary cyclicity variations in surface water circulation are reflected in the sediment by the chalk marl couplets the most distinctive couplets ocurring at the base and top of the bundles while the chalks reflect well mixed surface water conditions the marls particularly those at the bundle boundaries can be interpreted as the sedimentary expression of stratified water masses during deposition of these marls reduced oceanic mixing due to low seasonality during strong precession maxima at the eccentricity maxima caused periods of water column stratification that in turn led to nutrient depletion and decreased productivity in the surface water masses

dinosaur bones fossils or pseudomorphs the pitfalls of physiology reconstruction from apatitic fossils abstract a prerequisite to any attempt to reconstruct thermophysiology of ancient animals through analysis of stable isotopes of oxygen is the assumption that apatitic fossils are isotopically unaltered parts of their original skeletons we suggest that sufficient evidence is available to seriously question this assumption because living bones contain about 1 3 by weight of organic matrix mass balance considerations show that at least half of an apatitic fossil must be new material added post mortem furthermore living apatitic skeletons contain almost no rare earth elements and uranium whereas apatitic fossils bear high concentrations of these elements additionally we found that while in living fish correlation between 18o of oxygen in the phosphate and that in the carbonate of apatite is poor these two values are linearly correlated in fossil fish this suggests diagenetic recrystallization has taken place perfect preservation of micro textures such as haversian canals does not prove the pristine condition of a fossil some of the most beautifully preserved fossils are highly silicified most apatitic fossils probably are pseudomorphs replacing original skeletal elements whereas distribution of stable isotopes of oxygen in fossils might provide information about their burial environment it could be misleading in attempts to interpret the organisms physiology this cautionary note is supported by the similarity of 18op in bones of coexisting fossil fish dinosaurs and various other reptiles at different latitudes the overlap of predicted 18op values in fish and mammals living in contact with the same environmental water also weakens the hope that ectotherms can be distinguished from endotherms by the isotopic composition of oxygen in their bones and teeth

stratigraphic correlation of presumed milankovitch cycles in the blue lias hettangian to earliest sinemurian england simple digital filtering methods allow the correlation of patterns of metre scale cycles between outcrop sections and well logs through the hettangian to earliest sinemurian part of the lower lias in southern england the matching of cyclic patterns is sufficiently confident to allow the identification of a significant break in the blue lias section at lyme regis dorset the standard ammonite zones of the hettangian stage are shown to be of quantifiably unequal duration

dynamic sedimentary conditions during periods of enhanced sequestration of organic carbon in the central southern tethys at the onset of the cenozoic global cooling abstract stagnant bottom water conditions e g low and stable redox potential long water residence time is an assumption commonly used to explain the preservation and burial of high amounts of organic carbon c org in marine sediments rather than stagnant conditions the evidence presented here from north central tunisia supports dynamic conditions during formation of variably c org rich outermost shelf carbonates of the early middle eocene the dynamic conditions are inferred by the deposition of four distinct lithofacies in this outermost shelf setting shedding of carbonate i e mud and fragmented bioclasts from the shallower source areas controlled the distribution of all lithofacies with higher amounts of transported benthic debris occurring in the most proximal lithofacies and vice versa this carbonate shedding also controlled the deposition of three orders of lithological cycles from limestone marly limestone couplets grading to cycles made up of groups of couplets bottom water redox potential varied in intensity throughout this depositional setting with moderate oxygen depletion suboxic conditions in the southern sector of north central tunisia and much higher oxygenation in the northern area evidence for suboxic bottom waters in the southern sector higher c org contents is provided by higher trace metal cu ni zn cr mo u and v enrichments than in the northern area regionally heterogeneous primary productivity of surface waters is suggested to have caused a higher c org burial flux in the southern sector compared to the north a situation interpreted to have been related to varying upwelling patterns due to the effects of regional palaeogeography and the dominant wind patterns the deposition of the studied c org rich carbonates spanned part of the calcareous nannofossil zones np13 to np14 50 48 m y ago and coincided with the initiation of the cenozoic global cooling subsequent to the early eocene climatic optimum eeco 52 50 m y ago an implication is that an increased c org burial in north central tunisia could have been part of a major event sequestering atmospheric co 2 in marine sediments that caused climatic cooling immediately after the eeco this implication however is difficult to reconcile with the data available elsewhere other than our tunisian carbonates major c org sequestration in marine sediments of the early middle eocene transition are poorly documented globally if this scenario is confirmed other negative feedbacks such as enhanced continental weathering increased terrestrial carbon stock decreased co 2 outgassing and or changes in ocean circulation would have been more influential to the onset of the cenozoic global cooling

enso and sunspot cycles in varved eocene oil shales from image analysis abstract on the premise that sequential changes in varve thickness offer a proxy for climatic variations we investigated varve thickness in three core segments from the distal lacustrine oil shales tipton and laney members of the green river formation by means of an image analysis program of two strong bimodal periodicities one at 4 8 5 6 years is interpreted as an el nino type enso phenomenon of atmospheric dynamics while the other at 10 4 14 7 years is interpreted as the sunspot cycle originally recognized in this formation by bradley 1929 1931 weaker periodicities may exist at ca 8 and 33 years the latter also recognized by bradley taken in conjunction with the work of bradley 1929 1931 and of crowley et al 1986 this suggests that some but not all of the oil shale of the green river formation is truly varved and can be used to infer climatic time series automated instrumental scans have greatly extended the possibilities of varve studies as approaches to climatic variations in time but careful selection of facies in their geological framework is necessary

mid proterozoic dolomitic varves and microcycles from the mcarthur basin northern australia abstract the middle proterozoic 1 75 ga wollogorang formation of the unmetamorphosed intracratonic mcarthur basin of northern australia contains a dolomitic black shale facies that has distinctive millimetre and sub millimetre scale bedding laminations and microcycles of alternating organic rich mudstone and organic poor dolostone the microcycles are between 1 and 20 mm thick and their internal laminations are arranged rhythmically into a lower subdivision of mainly dolostone with subordinate mudstone laminae and an upper subdivision of mainly mudstone with thin dolostone laminae the microcycles vary systematically in both thickness and character the thinnest laminations visible around 0 2 mm thick are interpreted as chemical varves the microcycles represent bundles of varves deposited over longer periods over these longer periods each microcycle shows a gradual upward decrease in the amount of dolomite precipitated and or preserved this is related in part to original climatic controls in the environment of deposition and also to a secondary but pre lithification process of dissolution similar to that invoked by trendall 1972 1973 for the formation of mesobands in the bif s of the hamersley basin western australia simple statistical calculations of varve thickness variations on about 100 microcycles from a 1 5 m long core indicate the presence of 7 to 11 year and 300 year periods these periods are comparable with those published by williams 1981 for glaciogenic varves from late proterozoic 680 ma rocks in south australia he relates the former to sunspot cycles and the later to longer term climate periods as evident from tree ring studies although nowhere near as conspicuous as the sunspot cycles described by williams 1981 or the double sunspot cycles of trendall 1972 from the latest and earliest proterozoic respectively these microcycles from the middle proterozoic may be due to similar sunspot related processes and therefore add support to their suggestions for long term stability of solar processes

cyclostratigraphic reasoning and orbital time calibration cyclostratigraphy postulates that the stratigraphic record cyclically encodes the periodic orbital forcing of terrestrial insolation thus providing a time calibration regular cycles are sought using spectral analysis of lithological data series but there are inherent ambiguities in this method it may detect more cyclicities than conventional orbital forcing allows but only those with the closest correspondence to estimated orbital frequencies are used for time calibration irregular cycles are subjectively defined in terms of non rhythmic repetitions of facies the calibrations assume that they record the spatially distorted sedimentary effects of orbitally forced periodicity in insolation the null hypothesis that such non rhythmic repetitions are autogenic rather than orbitally forced cannot however be rejected both types of cyclicity conform to an expected universe where orbital forcing is reliably and recognisably encoded in the stratigraphic record neither form of cyclicity rules out the presence of hiatuses thus even if orbital in origin neither can provide dependably refined orbitally scaled time calibration

stable isotope distribution in maastrichtian vertebrates and paleosols from the haţeg basin south carpathians abstract located in the south carpathians in romania the ha eg basin contains a thick sequence of maastrichtian continental deposits yielding a rich dinosaur and mammalian fauna stable isotope analyses of both calcretes and dinosaur crocodilian and turtle remains from two localities tustea and sibisel were integrated in order to reconstruct environmental conditions during maastrichtian time and to gain further insights into the metabolism and behaviour of the vertebrates the large difference observed between the 18o and 13c of the eggshells and the surrounding mudstones as well as the preservation of the 9 difference between the oxygen isotope composition of the telmatosaurus eggshell and tooth enamel indicate that diagenesis has not significantly altered the primary isotopic signal the presence of smectite in the fraction less than 2 m and the preservation of dinosaur eggshell structure also indicate that diagenesis was not significant in the studied outcrops stable isotope compositions of both calcretes and phosphatic remains suggest warmer conditions during the deposition of the tustea sequence mean annual temperature of around 14 c than during the deposition of the sibisel sequence mean annual temperature of 10 c the intra tooth 18o patterns for zalmoxes and allodaposuchus show different magnitudes of isotopic variation with lower values for tustea and higher for sibisel the calculated 18obody water enrichment for kallokibotion bajazidi is similar to that found in living turtle taxa by contrast in the case of allodaposuchus the isotopic enrichment is higher than for recent taxa this suggests that for allodaposuchus the body water was less buffered by a watery environment which probably indicates more time spent outside water i e more terrestrial habit the 18o values for the teeth of telmatosaurus and zalmoxes are similar to those of allodaposuchus suggesting that at the investigated sites the body temperature of both dinosaurs was similar to that of the crocodile the isotopic composition of calcretes teeth and eggshells indicates a c3 vegetation and diet with 13c values between 27 and 29 pdb and the absence of large scale habitat partitioning between the dinosaurs

signals of astronomical climate forcing in the exposure topography of the north polar layered deposits of mars nasa earth and space science fellowship nnx13ao55h nasa s mars reconnaissance orbiter project

lacustrine varve formation through time abstract studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes if the bottom waters of a lake are partly or totally anoxic the seasonally deposited materials are preserved as annual groupings of laminae varves common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin precipitated carbonate minerals diatom frustules iron rich and manganese rich flocs autochthonous organic detritus and autochthonous and allochthonous materials resuspended from the bottom the style of varving has changed over geologic time reflecting changes in biologic evolution and types of materials available precipitated iron rich laminations were common in the middle precambrian graded sets of clastic organic laminations persisted through the precambrian prior to the evolution of bioturbating benthic organisms glaciolacustrine varves appear to have retained their distinctive character through time carbonate rich varves occurred sporadically in the precambrian and phanerozoic with the exception of diatoms major components of modern lacustrine varves were present through the paleozoic and mesozoic and yet varves are rare in strata of these ages and may have accumulated in marine to brackish water environments diatoms were introduced into lacustrine systems in early tertiary time and are common components of varves from then on diatom laminae combined with a greater chance for geologic preservation of younger lake deposits have increased the number of geologically young occurrences of varved sediments however seasonal associations of modern varve components and the processes they represent are present in ancient deposits and provide clues to the interpretation of ancient environments

the significance of metre scale allocycles in the quest for a fundamental stratigraphic unit the major transgressive sequence in the lower helderberg group devonian of new york state and a regressive sequence of similar scale in the first courceyan mesothem carboniferous of south wales are entirely divisible into metre scale allocycles the boundaries of these cycles are produced by non sedimentological processes larger scale stratigraphic events associated with relative sea level fluctuations the existence of these boundaries as basin wide discontinuities precludes the application of walther s law except within cycles thus palaeogeographic reconstructions based on the assumption of contemporaneity of large scale fades tracts formations and members must be abandoned instead stratigraphic interpretation requires the recognition and application of a genetic unit of analysis consistent with the actual internal allogenic fabric of such sequences application of the metre scale allocycle the smallest allogenic unit of stratigraphic accumulation results in fundamentally different interpretations of the helderberg and courceyan sequences rather than being continuously and unidirectionally transgressive or regressive both sequences were discontinuously generated by episodes of rapid deepening and gradual shallowing at more than one scale

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

high resolution rock magnetic cyclostratigraphy in an eocene flysch spanish pyrenees 1 a rock magnetic cyclostratigraphy based on anhysteretic remanent magnetization arm intensity variations was developed for the eocene arguis formation in the spanish pyrenees the arguis formation was sampled for arm cyclostratigraphy rock magnetic and paleomagnetic analyses rock magnetic measurements indicate that the dominant magnetic mineral controlling the arm cyclostratigraphy is depositional magnetite using thermal demagnetization a detailed magnetostratigraphy was developed for the arguis to provide an absolute time framework for the arm cyclostratigraphy the magnetostratigraphy is carried by a combination of depositional magnetite and secondary iron sulfides spectral analysis of the magnetostratigraphically scaled arm time series reveals the presence of significant milankovitch frequencies including eccentricity obliquity and precession the arm time series was tuned to the orbital eccentricity model for the eocene coherency analysis indicates that the eccentricity tuned arm is in phase with october november insolation for this site s paleolatitude varying amounts of terrigenous input delivered by a fluvial source at orbital time scales during the rainy season and diluted by a relatively constant input of marine carbonate is the most likely explanation for the cyclicity of the arm record the absolute age resolution of the arm chronostratigraphy is 1 or less based on an age offset with the reference chronology that was used for the eocene the offset in age between the two chronologies may be due in part to the uncertainty in the chron ages for this part of the eocene the relative age resolution within the arm chronostratigraphy is much better

geophysical records of dispersed weathering products on the frasnian carbonate platform and early famennian ramps in moravia czech republic proxies for eustasy and palaeoclimate abstract an exceptionally high sea level in frasnian times early late devonian changed many peneplained cratonised and tectonically undisturbed continental margins of tropical belts into carbonate platforms which became covered by thick banks of limestone the stages marked by very pure carbonates developed during partial sea level highstands since when the flooding reached its maximum the shoreline was distant and conditions for reef growth were good an increased extension of emerged flat coastal areas was coupled with an opposite situation when oscillating sea level fell to its momentary minimum and the accommodation space available for accumulation of carbonate material was low subaerially exposed surfaces were subject to weathering and the products were dispersed by aeolian or aquatic means to form layers when these weathering materials were trapped in carbonates this overall scenario relating to the trapping of weathering products in pure carbonates was tested at geographically isolated platform with a stable and only slowly subsiding basement eastern moravia czech republic the amounts of weathering products dispersed in limestone were documented using the combined methods of ray logging ray spectrometry and magnetic susceptibility measuring i e according to their radioactivity k th and u and magnetism fe six third order frasnian eustatic cycles have been inferred from the data with an estimated period of 1 ma the late frasnian and especially the frasnian famennian f f transition brought the total destruction or at least a strong overlay on this hypothetical background setting the record of strong sea level fluctuations in the f f interval is shown in strong oscillations and offsets related to pronounced hiatuses and flooding surfaces such rapid sea level fluctuation is typical for glacioeustatic control although the present estimates of the maximum amplitudes are larger than realisable by glaciation events and may be explained in combination with tectonoeustatic models comparison of sections between the centre and periphery of the platform substantiates the concept that oscillating late frasnian shorelines were rapidly prograding very low sea level stages of early famennian times changed the depositionary systems from extensive platforms to narrow carbonate ramps which were positioned out and down on the extinct reef bank slopes the central parts of the eastern moravian and also other frasnian platforms in the world were not normally covered by f f sediments the transgressive onlaps above any crystalline highs were not observed and therefore the drowned frasnian reefs on their periphery although emphasised by many geologists may reflect sliding or tectonic subsidence on the margins of platform blocks rather than eustatic rise of sea level

whither cyclostratigraphy testing the gamma method on upper pleistocene deep sea sediments north atlantic deep sea drilling project site 609 1 abstract gamma analysis a procedure for tuning cyclic sediments in which gamma is defined as 1 sedimentation rate was applied to the upper pleistocene gray scale record of deep sea drilling project site 609 from the north atlantic the spectrum of the gamma tuned time series produces eccentricity obliquity and precession index signals when the primary periodicity is tuned to the precessional beat frequency however the timescales are significantly too long suggesting that some of the primary cycles used in the gamma tuning procedure have higher frequency than the precessional beat by filtering the specmap calibrated time series at i 0 12 kyr the spurious cy cles are removed from the tuning procedure in this case the resulting gamma corrected spectra look much more like that of the specmap tuned time series however the time series remains slightly too long forward modeling is consistent with the results from modeling the core that is the gamma method is quite robust at revealing orbital periodicity in an orbitally controlled re cord for which sedimentation rates are facies dependent however the method does not produce an accurate time series criteria for complete rejection of gamma results are clarified as either 1 least squares results include negative gamma values or 2 the resulting spectrum does not show an or bital signature variation on sedimentation rates greater than 5 result in incorrect time series however variations on sedimentation rates as high as 15 generally reproduce strong orbital spectra and occasionally the method can also generate an orbital spectrum with up to 25 noise the method is not as robust in predicting gamma values or sedimentation rates although it generally distinguishes facies with relatively high sedimentation rates from facies with relatively low sedimentation rates the values predicted may be incorrect by a factor of2 thus while gamma tuning of the time series is an improvement over observed thicknesses the resulting timescale is not correct the implications of these results for cyclostratigraphy are significant the generation of an orbital spectrum from a time series that is demonstrably incorrect casts doubt on cyclicity as a dating tool

oxygen isotopic composition of fossil equid tooth and bone phosphate an archive of difficult interpretation abstract variation in the concentration of the stable isotopes of hydrogen oxygen and carbon have been tested in continental records as tools for quantitative or semi quantitative paleoclimatological studies among the different methods the potential use of oxygen isotopes in mammal bone and tooth phosphate has recently been recognized measurements carried out on fossil mammal bones of holocene age and their paleoclimatological interpretation corresponded well with paleontological and paleobotanical records in the case of considerably older fossils diagenetic processes may change the primary oxygen isotopic composition of phosphate fossil horse bones and teeth principally of the species equus stenonis were studied to ascertain how far back in time fossil mammal remains may be considered reliable material for paleoclimatological studies the samples come from 13 different locations in southeastern spain their age ranging from maspinian late pleistocene to middle villafranchian pliocene apart from the variations of the 18o po43 values which may be related to climatic changes it is apparent that the isotopic composition of bones and teeth from the same deposit are frequently rather different from one another the isotopic differences range from a few tenths of one to several this suggests a strong influence of taphonomy over the measured isotopic values of fossils in each deposit time can be considered neither the only variable nor the most important one responsible for the change of the primary isotopic composition of fossils under these conditions it is rather difficult to establish lower or upper limits for the age of fossils to be studied for reliable paleoclimatological information since the limits are directly related to taphonomic history this in turn is related to local environmental conditions and not only to the age of fossils

cyclostratigraphy of an orbitally driven tithonian valanginian carbonate ramp succession southern mendoza argentina implications for the jurassic cretaceous boundary in the neuquen basin we conducted detailed sedimentological sequence stratigraphic and cyclostratigraphic analyses on four sections of the vaca muerta formation this unit is characterized by a decimetre scale rhythmic alternation of marls and limestones it consists of five facies associations which represent basin to middle carbonate ramp deposits the rhythmic vertical organization shows a well ordered hierarchy of cycles where elementary cycles bundles of cycles and superbundles within the milankovitch frequency band are recognized cyclostratigraphic data allowed us to build a floating orbital scale for the lower tithonian lower valanginian interval in the neuquen basin orbital calibration of these sections is consistent with riccardi s biostratigraphic scheme which places the jurassic cretaceous boundary within the substeueroceras koeneni ammonite zone equivalent to durangites spp jacobi grandis and initial occitanica standard zones

palaeotidal speeds and ranges estimated from cross bedding sets with mud drapes tidally formed cross bedding sets in which mud drapes are spaced out among sandy foresets occur in cretaceous1 4 eocene5 and holocene6 sands deposited subtidally by strongly asymmetrical sand waves a striking feature of some sets4 6 is that the horizontal drape spacing measured in the direction of sand wave advance varies cyclically on a time scale related to the spring neap tidal cycle as indicated by the numbers of drapes each drape forms part of a distinctive lithological couplet consisting of a group of sandy foresets recording avalanching on the steeper side of the sand wave followed by the drape itself typically divided into upper and lower parts by a centrally placed silt sand parting the drapes have been assigned to slack water but the groups of sandy foresets to episodes of vigorous flow the combination suggesting a quantitative model based on the tide here i show how the peak speeds and ranges of ancient tides can be estimated by combining an empirical bedload transport function with appropriate measurements from such cross bedding sets

reflections of surface water seasonality and climate in stable oxygen isotopes from tyrannosaurid tooth enamel abstract patterns of isotopic variation in enamel of eight albertosaurus teeth from the campanian maastrichtian horseshoe canyon formation alberta were measured by serial sampling along the growth axis cycles in the isotopic values appear to correlate to published tooth growth rates for tyrannosaurids tyrannosaurid dinosaur teeth of 50 mm in length provide ideal repositories of terrestrial climatic information as each records a full annual cycle of body water isotopic variation the relatively thin enamel precludes problems associated with time averaging associated with complex growth patterns found in thick mammalian enamel the most consistent and striking pattern associated with all of the teeth are two relatively closely spaced subequal maxima these appear to be associated with onset of a seasonal episode of high humidity after the activation of the amount effect where the influence of ambient temperature on surface water and body water 18 o ends while temperatures remain above 20 c teeth within a single fossiliferous horizon show the same general isotopic pattern and range a notable difference in pattern shape and magnitude of isotopic variation between tyrannosaurid teeth from several stratigraphic intervals of the lower horseshoe canyon formation section indicates a climatic changes from strong seasonality high annual temperature range with distinct precipitation and humidity maxima during each year at the base of the section to milder seasonality at the top

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

episodic accumulation and the origin of formation boundaries in the helderberg group of new york state at any single locality in the helderberg group of new york state most formation and member boundaries coincide with boundaries of punctuated aggradational cycles in each case of coincidence the boundary is a discontinuity that was produced by a rapid rise of relative base level rather than a facies contact representing gradual migration of contiguous paleoenvironments apparently diachronous formation boundaries in the sequence are not single continuous surfaces instead each diachronous boundary is actually a stratigraphic series of isochronous surfaces that are separate punctuated aggradational cycles pac boundaries produced by distinct geologically instantaneous base level rises these conclusions about the origin of formation boundaries suggest that the concept of the formation as a fundamental unit of stratigraphic description and interpretation may need revision if the stratigraphic record accumulated episodically on a small scale

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

proximate environmental forcing in fine scale geochemical records of calcareous couplets upper cretaceous and palaeocene of the basque cantabrian basin eastern north atlantic abstract calcareous couplets are key elements in reconstructing the evolution of a sedimentary basin due to the influence of forcing mechanisms such as climate sea level and tectonism on their depositional patterns proposed forcing mechanisms however are often not mutually exclusive and even constraining the relative importance of different processes is problematic added to the question of discriminating forcing mechanisms a major challenge is to produce high sampling density so that observations lie within temporal resolutions equal to or finer than the timescales on which different forcing operates here we show fine scale 1 sample 2 cm caco3 18o and 13c records and sedimentological observations from three different sites isla de castro sopelana ma and sopelana da with calcareous couplets in the basque cantabrian basin eastern north atlantic to illustrate the potential of fine sampling strategies to help distinguish proximate environmental forcing partial redistribution of carbonate during burial diagenesis has been proposed for these sediments our caco3 18o and 13c data could thus be dismissed as diagenetic signals if only one sample was collected from each bed detailed observations of the fine scale geochemical records however challenge purely diagenetic explanations combined with sedimentology the caco3 18o and 13c values partially altered by diagenesis are interpreted to have resulted from alternating climates the proximate forcing through which alternating climates caused the geochemical patterns though was different in each section due to their specific palaeogeographic positions in the basin and the properties of the seawater masses the proximity of continental areas of high relief to the isla de castro section supported a high continental influence during its deposition the sopelana ma sediments are assigned to a transgressive system tract a condition that is interpreted to have promoted a high influence of oceanic processes in its depositional setting finally a relatively cool oxygen rich water mass with high oxidation potential influenced the geochemical and depositional patterns of sopelana da beyond the climatic and oceanographic dynamics inferred for a basin that linked the western tethys with boreal domains during major marine transgressions of the late cretaceous to palaeocene an implication of our work is that if similar fine scale geochemical records were applied to calcareous couplets spanning major events in earth s history e g ocean anoxic events alternative forcing scenarios leading to and out of these events could be discriminated

the preservation of glacial interglacial climatic signatures in the oxygen isotopes of elephant skeletal phosphate abstract phosphate 18o values 18op of modern elephant bone and teeth are found to vary linearly according to the 18o of local meteoric water 18omw a parameter with close ties to regional and local climatic conditions enamel dentine cementum and bone separates from individual fossil elephant specimens of late pleistocene age have op values which vary by up to elephant specimens the larger spread in the 18op values of the various skeletal phases for the fossil samples is interpreted as evidence for post depositional alterantion of primary 18op signatures of some if not all of these fossil skeletal components in the fossil samples investigated enamel and dentine phases have systematically lower 18o values than associated bone and cementum phases differential re equilibration with soil waters either by the wholesale replacement of primary apatite or by processes of isotopic exchange is suggested as a mechanism to account for the observed spread in the fossil phosphate 18o data

regional to global correlation of lower cretaceous hauterivian barremian shallow water carbonates of the southern apennines italy and dinarides montenegro southern tethyan margin abstract we propose a high resolution regional to global scale correlation of two hauterivian barremian shallow water carbonate platform sections belonging to different palaeogeographic domains of the southern margin of the tethys these successions are now located more than 500 km apart and are represented by 137 m of core drilled at monte raggeto southern apennines italy and by 80 m of well stratified rocks cropping out in the podgorica mountains dinarides montenegro they display three superimposed orders of stratigraphic cyclicity defined by elementary cycles grouped into bundles and superbundles and attributed to orbitally induced composite sea level fluctuations elementary cycles are interpreted as the precession and the obliquity periodicities 20 40 ky while bundles and superbundles correspond to the short 100 ky and long 400 ky eccentricity cycles respectively as both the ratios between the elementary cycles and the bundles and between the bundles and the superbundles do not always reflect the classical 5 1 and 4 1 relationship the sedimentary record of both the studied sections is likely to include omission of bundles or their portion the general evolution of depositional and diagenetic facies the vertical change in thickness of the cyclic units and the interpretation of superbundles as small scale depositional sequences suggest that elementary cycles and their groups are superimposed on lower frequency environmental oscillations these display an upward transgressive regressive trend t rt of the facies and testify to larger scale variations of accommodation potential on the shelf t rts sequence stratigraphic interpretation of the superbundles as well as the common occurrence of the biostratigraphic dated hauterivian barremian boundary in the studied sections support the long distance regional correlation between the successions to be carried out on the 100 ky scale moreover by assuming the maximum flooding intervals of time equivalent superbundles as virtually isochronous intervals we have detected stratigraphic gaps of 1200 and 600 ky in the monte raggeto and in the podgorica mountains sections respectively both sections are formed of 10 complete superbundles each of them testifying to the 400 ky long eccentricity hence the monte raggeto and podgorica mountains successions represent a duration of at least 4 0 my in terms of elapsed time regardless of gaps within the stratigraphic record finally a correlation between the orbitally induced compared sections and both the 3rd order tethyan stratigraphic cycles and the global cycle chart is suggested our study confirms that cyclically organized shallow marine carbonate platform deposits controlled by orbitally induced sea level fluctuations represent a powerful tool for high precision regional and global correlations this can be of fundamental importance for quantification of sedimentary diagenetic and evolutionary processes as well as for the understanding of autocyclic versus allocyclic control on sequence development

punctuated aggradational cycles a general hypothesis of episodic stratigraphic accumulation according to the hypothesis of punctuated aggradational cycles presented here the stratigraphic record consists of small scale 1 5 m thick shallowing upward cycles pacs separated by surfaces marked by abrupt change to deeper facies this motif pervasive in time and environment is produced by relatively long periods tens of thousands of years of base level stability punctuated by geologically instantaneous relative base level rises of at least basin wide extent as basin wide lithologic time stratigraphic units pacs are fundamental to all aspects of stratigraphic analysis including correlation paleoenvironmental interpretation and paleogeographic reconstruction of several possible allogenic mechanisms for a pervasively cyclic stratigraphic record glacial eustasy driven by orbital perturbations is preferred the pac hypothesis is presented as a comprehensive model to be tested and modified by examination of the stratigraphic record from an episodic perspective

late precambrian tidal rhythmites in south australia and the history of the earth s rotation sedimentary rhythmites of siltstone and fine sandstone from late precambrian c 650 800 ma glaciogenic formations in south australia are interpreted as distal ebb tidal deposits that record variability in the velocity and range of palaeo ebb tides variations in lamina thickness encode a full spectrum of palaeotidal cycles including semidiurnal diurnal fortnightly and monthly tidal cycles as well as the lunar apsides perigee and nodal cycles a half yearly oscillation is attributable largely to a beat between the fortnightly tidal cycles of luni solar conjunction and lunar declination the lunar nodal cycle is discernible as an amplitude modulation of this beat oscillation the data allow determination of the earth9s palaeorotation and the past dynamics of the earth moon system with an accuracy previously unattainable for the precambrian the late precambrian c 650 ma year contained 13 1 0 5 lunar months and c 400 20 days and the late precambrian lunar month c 30 5 1 5 days these values suggest an average equivalent phase lag near 3 since late precambrian time rather than the present value of 6 the period of 19 5 0 5 years determined for the lunar nodal cycle c 650 ma ago indicates a lunar distance 96 9 1 7 of the present distance the low rate of lunar recession since late precambrian time revealed by the rhythmite data militates against a close approach of the moon during the proterozoic precambrian sedimentary rhythmites may hold a key to the early history of the earth9s rotation

palaeoenvironments of the dinosaur bearing lameta beds maastrichtian narmada valley central india abstract the maastrichtian lameta beds of central india are intimately associated with the deccan lavas and are critical to determining upper cretaceous palaeoenvironments and palaeogeography of the area in the type jabalpur sub region four mappable units of the lameta beds are recognised the basal green sandstone is interpreted as a braided stream deposit the lower limestone characterised by brecciation and shrinkage cracks is interpreted as a sub aerially exposed palustrine flat with calcrete formation occurring on topographic highs of low relief plains the overlying mottled nodular beds exhibit a variable range of calcrete fabrics and morphologies including circum granular and linear cracks root casts and nodules these are interpreted as pedogenically modified sheet wash deposits of a semiarid alluvial plain the upper sandstone is a sheet flood deposit again pedogenically modified before arrival of the basal lava flows overall the lameta beds are considered to represent a regionally extensive maastrichtian regolith carbon and oxygen isotope analyses of calcareous components are entirely consistent with soil zone environments the 13c values are low typically 8 to 9 pdb demonstrating a strong input of carbon from the decay of terrestrial land plants calcrete 18o values are variable 5 to 10 pdb consistent with precipitation from meteoric water some of which was evaporatively modified in pools on the alluvial palustrine flat the lameta beds are well known for sauropod nesting sites and sedimentological analyses of these sites suggest that the animals selected topographic highs usually in marly or sandy soft sediment multiple nests with similar egg types probably indicate colonial nesting isotopic analyses of eggshell carbonate agree with earlier work suggesting that the sauropods ate a c3 plant food