climatic and tectonic controls on sedimentation of a mesozoic lacustrine sequence the purbeck of the western cameros basin northern spain abstract the purbeckian rupelo formation of the western cameros basin comprises a sequence of lacustrine carbonates and intercalated distal alluvial sediments up to 200 m thick the vertical succession of facies is interpreted as reflecting the combined effects of variation in climate and clastic supply with time areal facies and thickness distributions show strong tectonic control and reflect the pattern of differential subsidence

jurassic smectite and kaolinite trends of the east european platform implications for palaeobathymetry and palaeoclimate clay minerals cannot only give information on sedimentary depositional environment but also the climate regime under which sediment was weathered the successions of non marine to marine middle and late jurassic strata of the east european platform show upwards increasing contents of smectite and decreasing contents of kaolinite there is also an increasing smectite vs kaolinite ratio laterally in a basinward direction within individual formations vertical smectite and kaolinite content curves coincide broadly with the sahagian and jones eustatic sea level curve all this implies differential settling of smaller smectite particles offshore and larger kaolinite particles onshore smectite formation preservation and supply were further enhanced as the eastwards expanding late jurassic arid zone of laurasia influenced weathering conditions in the sediment source areas to the north and east of the east european platform

the barremian aptian arid phase in western europe abstract evidence is presented from nine areas in western europe speeton yorkshire southern north sea channel and weald basins southern england jeanne d arc lusitanian and aquitanian basins of the north atlantic continental margins lower saxony basin north germany the paris basin and southern france for a phase of aridity which began during the hauterivian middle barremian and continued to dominate the climate of the region until the mid aptian although conditions during this period were not uniformly dry throughout criteria for recognising arid environments include the occurrence of evaporites abundances of carbonate rich sediments red beds firmgrounds carbonate nodules and pyrite concretions depletion of kaolinite spore assemblages of limited morphological diversity and the presence of numerous coniferalean and cheirolepidiacean pollen grains the change from generally humid to dry climates during the barremian is thought to have been linked to a lowering of sea level the arid phase clearly falls within the time span of the first cretaceous oceanic anoxic event

latest jurassic early cretaceous events and the late cimmerian unconformity in north sea area each of several regional or local unconformities may have been identified locally as the late cimmerian unconformity a supposed major break at the base of the valhall formation or roedby formation over most of the north sea the base of the valhall formation is isochronous and conformable with underlying sediments it is detected on seismic reflection profiles because it represents a widespread facies change marking the late ryazanian transgression most of the unconformities are of eustatic origin and the effects of eustatic sea level changes were never completely masked by local tectonics thus in the modeling of individual oil fields the possibility of sedimentary breaks occurring can be predicted in part by reference to regional or eustatic events modified journal abstract

paraglacial gullying of sediment mantled slopes a case study of colletthogda kongsfjorden area west spitsbergen svalbard this paper evaluates the paraglacial evolution of a sediment mantled slope in a polar maritime environment the intensity of paraglacial processes is estimated through quantifi cation of erosion and dating of fi eld sectors with the help of photographic archives gully erosion has been estimated using morphometric parameters and by surveys of vegetation cover the rapid melting of dead ice cores controls gully formation this leads to slope form modifi cation gully profi le gradients are reduced from a mean of 35 to a mean ranging between 10 and 15 profi le evolution results from the collapse of glacier lateral moraine all data mean slope angle of individual gullies frequency distribution of slope angles fractional distance to the apex gullying index volume of debris mobilized vertical erosion rate tend to increase with increasing deglaciation age and the duration of paraglacial activity vegetation colonization is a response to stabilization of the ground surface and the drying up of the ground surface due to dead ice melting the full sequence of paraglacial slope adjustment gully incision stabilization may occur rapidly at the study site i e within two decades finally a lateral morphogenic sequence is proposed showing the importance of paraglacial processes at the onset of the deglaciation

trends cycles and nonstationarities in isotope signals of phanerozoic seawater abstract the new set of 87 sr 86 sr 18 o and 13 c experimental data for phanerozoic seawater the bochum ottawa isotope dataset has been tested by wavelet discontinuity and sliding window correlation dimension analyses for cyclicities and nonstationarities in the isotope signal the tests indicate discontinuities in the strontium isotope signal at 500 340 288 210 65 and 28 ma while for the oxygen and carbon isotopes they are at 500 385 290 210 and 65 ma these discontinuities often coincident with major stage boundaries reflect mostly single likely tectonic events that do not affect the structure of the underlying system the two most pronounced nonstationarities in all isotope systematics are at 65 and 210 ma respectively that is at the k t and norian rhaetian transitions wavelet analysis for all three isotope systems yields a long term quasi periodicity at 94 125 ma best developed during the paleozoic with superimposed intermittent 48 57 and 29 35 ma oscillations all likely a reflection of plate reorganizations within the caledonian hercynian and alpine tectonic cycles

aspects of climatic influence on the clay mineralogy and geochemistry of soils palaeosols and clastic sedimentary rocks climate strongly influences soil clay mineralogy and bulk chemical composition in humid climates chemical weathering is at its most intense and virtually all primary bedrock minerals suffer complete breakdown they are replaced by authigenic hydrated oxides of fe and al together with halloysite and kaolinite in deep profiles these minerals develop where the residence time of water in the soil is slight longer residence times lead to higher solute concentrations and the stabilization of smectite authigenic palygorskite and sepiolite may form in highly saline alkaline soils the stability of these precipitated minerals is problematic they may be metastable or even unstable all other clays found in soils are unstable being incomplete solid state hydrolysis products of substrate minerals the balance between stable metastable and unstable minerals and the rate of profile development are both much influenced by temperature rainfall and activities of soil biota themselves reflecting climate bedrock influence is greatest under conditions of low to moderate precipitation where unstable minerals persist local topography however also strongly influences both the rate and products of chemical weathering quite independently of climate on the grand scale tectonic factors may constrain the time available for profiles to develop hence the extent to which bedrock minerals survive or are altered mountain soils reflect local climate and bedrock composition much more than latitude the sediments delivered to major basins today do not reflect global soil distribution patterns the bulk composition of suspended sediment entering the indian ocean for example is rather similar to that entering the arctic ocean sediment dispersal patterns can also confuse climatic signals a problem not encountered with palaeosols authigenic clays formed within sedimentary basins and post depositional burial alteration of both sediments and buried soil profiles must lead to interpretational ambiguities climatic signals are likely to survive best in bulk compositional data although diagenetic reactions at depths in excess of about 2 km do not appear to be isochemical and in the distribution of more stable yet climatically sensitive minerals kaolinite as opposed to illite chlorite

major erosion surfaces in the basal wealden beds lower cretaceous south dorset the transition from evaporitic and lagoonal purbeck beds into the fluviatile basal wealden beds ryazanian valanginian has in the past been interpreted as a continuous regressive succession mupe bay and bacon hole in south dorset are the only localities in the wessex basin of southern england at which the transition strata are well exposed and not extensively faulted on the basis of facies analysis the lowermost wealden beds are interpreted as a regressive transgressive regressive package environments fluctuated between lagoon inner lagoonal shoreline and fluvial flood plain the overlying succession is remarkable for the presence of two major erosion surfaces which based on field geometries and facies relationships are interpreted as unconformities the lower unconfor mity is overlain at mupe bay by sediments of lagoonal or lacustrine origin the upper unconformity is expressed as the celebrated mupe bay palaeo oilseep an oil cemented conglomeratic sand overlain by a thick succession of fluvial sediments a level near the basal sand and the two erosion surfaces are treated as candidate sequence boundaries wbl wb3 with the thin intervening lagoonal deposits representing peaks of transgression the pattern of one minor conformable sequence boundary followed by two major unconformable sequence boundaries bears a strong resemblance to the early cretaceous sequence stratigraphy suggested in recent global cycle charts however biostratigraphical calibration of the sections is currently inadequate to allow close correlation with candidate sequence boundaries in other areas

constraining the timing of brittle deformation and sedimentation in southern finland implications for neoproterozoic evolution of the eastern fennoscandian shield abstract sheared sedimentary clay was found in a faulted fracture in crystalline bedrock in a tunnelling site at 60 m depth in southern finland brittle faults are numerous in the fennoscandian palaeoproterozoic bedrock but only some of them have relative age constraints while absolute ages are nearly lacking sedimentary rocks altogether are uncommon in finland and only sparsely dated by micropaleontological studies this study reports k ar data of fresh non weathered authigenic illite and constrains a time framework for the local faulting and sedimentation the neoproterozoic tonian to cryogenian ages derived from the grains in diminishing grain size order are c 967 947 809 and 697 ma results indicate that the formation of the extension fracture is related to the collapse of sveconorwegian orogeny c 1000 ma clay and mature quartz sand were deposited in this extension fracture in shallow water in an intracratonic basin followed by early diagenetic processes and neocrystallization of illite around 967 947 ma the neoproterozoic 1000 700 ma sedimentation documented in this study is rare in the fennoscandian shield as a whole neocrystallization of authigenic illite in the finest 0 4 and

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

palaeoclimate control on sequence stratigraphic patterns in the late jurassic to mid cretaceous with a case study from eastern england abstract sediment supply is a fundamental control on the architecture of sedimentary sequences in clastic depositional environments the volume of sediment being transported into the basin of deposition is strongly dependent on both the nature of the weathering regime in the hinterlands and on runoff during arid low sea level phases in the late jurassic and early mid cretacwous clastic supply was reduced and long hiatuses became common at sequence boundaries or during maximum flooding these hiatuses amalgamated where sediment starvation produced strongly condensed super condensed sections in intervening humid higher sea level phases clastic supply was more abundant hence thick sediment packages separate sequence boundaries downlnpping surfaces should be apparent on seismic sections and condensed sections become rare where carbonate deposition dominates over clastic sediment formation is largely intrabasinal and the effects of palaeoclimate on sequence stratigraphy are less obvious knowledge of palaeoclimates may lead us to search for certain sequence stratigraphic patterns connected to changes in sediment supply

the influence of a sudden climatic change on marine deposition in the kimmeridgian of northwest europe a sudden change from humid style to semi arid style deposition markedly affected the accumulation of the upper kimmeridge clay in southern england many of the changes appear to be related to a change in sedimentation rate at this time thus softground faunas are replaced by firmground faunas diagenetic dolostones formed in the methanogenic zone are replaced by sulphate reduction zone carbonate nodules and depositional gradients recorded by lateral biofacies changes becomes steeper the evidence available is in accord with a decline in offshore sedimentation rates during this interval other changes such as a decline in kaolinite abundance were more directly controlled by the drying out of the hinterland similar changes elsewhere in the marine geological record could be used as climatic indicators the climatic change is part of a wider northern hemisphere dry event which affect a broad area in the late jurassic the kimmeridge clay of southern england was one of the last depositional environments to be influenced by the climatic change at this latitude

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

siliciclastic sequence stratigraphic patterns in foreland ramp type basins stratal patterns within shelf depositional sequences are dependent on tectonically controlled subsidence rates and their regional patterns in active tectonic basin settings regional subsidence patterns can be very different from passive continental margin settings resulting in substantial modifications of the basic sequence stratigraphic model in ramp type foreland basins on the tectonically active side subsidence rates decrease seaward in contrast with passive continental margins where the opposite subsidence pattern exists analysis of the interplay between eustasy and subsidence suggests the existence of two tectono stratigraphic zones occurring proximally and distally with respect to the basin margin zone a is defined as the region within which the rate of subsidence always exceeds the rate of eustatic fall consequently relative sea level rises continuously during a eustatic cycle albeit at varying rates zone b is defined as the region within which the rate of eustatic fall periodically exceeds the rate of subsidence resulting in an interval of relative sea level fall during a eustatic cycle on the tectonically active sides of foreland basins zone a lies on the landward side of the basin margin proximal to the orogenic belt and zone b lies seaward off zone a away from the orogenic belt where subsidence rates are lower on passive continental margins because of the opposite subsidence patterns zone a lies seaward of zone b where subsidence rates are greater the location of the shoreline relative to these zones determines the stacking patterns and stratal discontinuities within a depositional sequence if the shoreline remains in zone a then only type 2 sequence boundaries will occur if sufficient sediment flux is available allowing the shoreline to prograde into zone b then type 1 sequence boundaries can occur in foreland basins these type 1 sequence boundaries would become type 2 sequence boundaries updip in zone a the pattern of seaward decreasing subsidence on the tectonically active sides of foreland basins results in characteristic longitudinal facies and stratal patterns when the two zones occur the updip region of the basin proximal to the orogenic belt is characterized by nearly continuous nonmarine deposition albeit at varying rates the downdip region is characterized by forced regressions and deposition primarily of lowstand and transgressive systems tracts a transitional region containing deposits of all three systems tracts commonly occurs between the updip and downdip areas

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

do fossil plants give a climatic signal the agreement in the pattern of major biomes with that of climatic zonation of the earth gives a strong indication that climate is the overriding influence controlling the distribution of plant communities three aspects of plants which may be preserved in the fossil state give a signal of the climatic conditions under which they grew 1 the present climatic association of their 9nearest living relative9 2 leaf physiognomy of arborescent plants 3 the character of their secondary xylem 9wood9 of ordinary usage reflecting by the presence or absence of growth rings the seasonality or lack of it in their environment and the potential for tree growth that it offered the significance and limitations of these 9palaeoclimatic signals9 as they may be read from the fossil plant record are reviewed and evaluated the recent demonstration that stomatal frequency of leaves is responsive to changes in ambient carbon dioxide partial pressure offers promise for direct palaeobotanical evidence for past changes in the level of this climatically significant atmospheric constituent

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

ostracoda marine nonmarine and palaeoclimate history in the upper jurassic of central europe and north america abstract the role of ostracoda in determining climate developments in the upper jurassic of central europe and north america is reviewed based upon two different studies the late jurassic is a period of time for which a change from a humid to a more arid climate has been suggested for several parts of the world however a correlation though almost logical between the arid phase in the middle and late tithonian and a generally cooler climate combined with a sea level lowstand and lower water temperatures has only been demonstrated in very few papers this study intends to seeks palaeoclimatic evidence for the late jurassic by the use of ostracoda development of marine ostracod palaeobiogeography in central and western europe parallels a suggested cooling trend during the oxfordian kimmeridgian tithonian and berriasian a growing diversification of marine ostracod biogeography and an increase in the degree of endemism can be observed in addition there is a gradual southward migration of many species from the subboreally influenced areas in the northwest towards the margin of the tethys in the southeast mainly from the kimmeridgian into the tithonian moreover the genus cytherelloidea which has a long tradition despite some recent contradictions as an indicator for relatively warm water temperatures shifts its northern boundary of occurrence towards the south during the kimmeridgian tithonian and berriasian this occurs independently from the general change of facies because conditions principally suitable for cytherelloidea salinity water depth have at times also existed in some northern basins during the tithonian berriasian these data are in correspondence with a suggested increase in the influx of cold boreal waters into central europe with the beginning of the tithonian leading to slightly colder water temperatures in the shallow seas reduced atmospheric moisture cool arid conditions on the neighbouring continents and also to the diversification of biogeographic regions as a reaction to the conflicting boreal increased and tethyan still steady influences for the kimmeridgian tithonian nonmarine morrison formation in the western interior basin usa both temporal and latitudinal trends from warm climates in the south and near the base of the formation to slightly cooler climates in the north and in the upper parts of the sections have been detected on the basis of the charophyte floras monospecific 18o isotope data from charophytes and ostracods have revealed a trend towards lighter compositions towards the top of the formation this might be interpreted as a general cooling but other interpretations must also be discussed from preserved vital effects and 18o 13c plots of charophyte ostracod associations showing coherent groupings similar to those from modern lakes it is likely that the calcite shells have preserved a high degree of isotopic fidelity different scenarios to explain the observed patterns are discussed a global change towards colder temperatures and arid conditions near the end of the jurassic period is in good correspondence with all the results more local factors however would also be able to explain the data

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic