compositions sources and depositional environments of organic matter from the middle jurassic clays of poland abstract the comprehensive biomarker characteristics from previously undescribed middle jurassic clays of poland are presented the molecular composition of the organic matter om derived from clays of aalenian to callovian age has not changed significantly through time high relative concentrations of many biomarkers typical for terrestrial material suggest a distinct dominance of om derived from land plants increasing concentrations of c29 diaster 13 17 enes towards the northern part of the basin indicate an increase in terrestrial input this terrestrial material would have originated from the enhanced transport of organic matter from land situated at the northern bank of the basin i e the fennoscandian shield the organic matter was deposited in an oxic to suboxic environment as indicated by relatively low concentrations of c33 c35 homohopanes moderate to high pr ph ratio values an absence of compounds characteristic for anoxia and water column stratification such as isorenieratane aryl isoprenoids and gammacerane as well as common benthic fauna and burrows 18o measurements from calcitic rostra of belemnites suggest that the mean value of the middle jurassic sea water temperature of the polish basin was 13 1 c it is suggested that this mirrored the temperature of the lower water column because belemnites are considered here to be necto benthic the organic matter from the middle jurassic basin of poland is immature this is clearly indicated by a large concentration of biomarkers with the biogenic configurations such as hopanes hop 13 18 enes hop 17 21 enes diasterenes and sterenes the identification of preserved unaltered biomolecules like ferruginol 6 7 dehydroferruginol and sugiol in protopodocarpoxylon wood samples from these sediments present particularly strong evidence for the presence of immature om in the middle jurassic sediments moreover the occurrence of these polar diterpenoids is important due to the fact that they are definitely the oldest known natural products detected in geological samples

solar forcing of florida straits surface salinity during the early holocene 1 previous studies showed that sea surface salinity sss in the florida straits as well as florida current transport covaried with changes in north atlantic climate over the past two millennia however little is known about earlier holocene hydrographic variability in the florida straits here we combine mg ca paleothermometry and stable oxygen isotope measurements on the planktonic foraminifera globigerinoides ruber white variety from florida straits sediment core knr166 2 jpc 51 24 24 70 n 83 13 14 w 198 m deep to reconstruct a high resolution 25 yr sample early to mid holocene record of sea surface temperature and d 18 osw a proxy for sss variability after removing the influence of global d 18 osw change due to continental ice volume variability we find that early holocene sss enrichments are associated with increased evaporation precipitation ratios in the florida straits during periods of reduced solar forcing increased ice rafted debris in the north atlantic and the development of more permanent el nino like conditions in the eastern equatorial pacific when considered with previous high resolution reconstructions of holocene tropical atmospheric circulation changes our results provide evidence that variations in solar forcing over the early holocene had a significant impact on the global tropical hydrologic cycle

paleoceanography of surface waters in the gulf of mexico during the late quaternary abstract late quaternary paleotemperatures and paleosalinities of surface waters of the gulf of mexico were estimated using a multivariate statistical analysis of census data of planktonic foraminifera two climatic extremes were selected for detailed basinwide study the climatic optimum 125 000 yr ago and the glacial maximum 18 000 yr ago in addition patterns of climatic change were examined in seven piston cores from 127 000 yr ago to the present day during the climatic optimum 125 000 yr ago temperature distributions in surface waters were similar to those of the present the 22 c winter isotherm trended northeastward across the central basin and paleotemperatures decreased northward summer distributions were nearly homogeneous and ranged between 28 and 29 c winter salinities were 1 fresher than present values in the northmost gulf and 0 4 fresher in the central basin summer salinities were similar during both times in contrast during the last glacial maximum temperatures were 1 to 2 c cooler in winter and 1 c cooler in summer and isotherms formed a circular pattern in the gulf during both seasons salinity was 0 3 fresher in winter than at present but 0 6 saltier in summer conditions deteriorated from the climatic optimum to the glacial maximum in the mexico basin winter temperatures were 2 c cooler from 75 000 to 45 000 yr ago y6 to y3 subzones summer temperatures reached a minimum 3 c cooler 32 000 yr ago y2 y3 boundary and seasonality reached minimal values 5 c from 45 000 to 15 000 yr ago all three parameters became similar in value to those in the straits of florida from 45 000 to 15 000 yr ago suggesting that the exchange of surface waters was enhanced at this time between the two regions summer salinities remained similar to present conditions in the mexico basin whereas winter salinities increased 2 by 32 000 yr ago and then fell 0 5 until the glacial maximum ended the westerlies may have migrated southward over the mexico basin in winter from 32 000 to 15 000 yr ago

alkenone molecular stratigraphy in an oceanic environment affected by glacial freshwater events the sedimentary record of a ratio uk37 of long chain c37 unsaturated alkenones is a useful indicator of glacial interglacial climatic change in the late quaternary northern gulf of mexico where a planktonic foraminiferal 18o caco3 record is complicated by meltwater and or fluvial events williams and kohl 1986 application of a laboratory temperature calibration of the uk37 ratio prahl and wakeham 1987 to a pigmy basin hydraulic piston core record deep sea drilling project core 619 suggested that the minimum glacial surface mixed layer sml temperature was 8 1 c colder than the holocene high sml temperature of 25 6 0 5 c this predicted glacial interglacial temperature difference was significantly larger than the differences predicted by either the foraminiferal 18o or foraminiferal assemblage temperature methods 0 8 2 0 c this large difference may be caused by local prymnesiophyte assemblage changes in response to climatically induced hydrographic changes interglacial periods may be dominated by pelagic prymnesiophyte assemblages while glacial periods may be dominated by neritic assemblages a combined mechanism of both climatically varying prymnesiophyte species assemblage and depth of alkenone biosynthesis may account for the large difference between the temperature methods

textural elemental and isotopic variations among constituents in middle devonian limestones north america abstract biogenic components brachiopods crinoids and corals in middle devonian limestones were manually separated from their enclosing matrix and analyzed by textural elemental and isotopic methods in order to assess the preservational state of these components in general brachiopods in these rocks are better preserved texturally than other constituents as determined by sem and cathodoluminescence observations elemental variations among the major components are compatible with a differential response to diagenesis governed by the relative stability of the original mineralogy of the component however among the most stable low mg calcite brachiopods the relationship between textural preservation and trace element content is complex this apparent complexity may be due at least par ially to our method of textural characterization of whole brachipod samples the nonluminescent portions of a set of well preserved brachipods have textural characteristics and elemental contents which are virtually indistinguishable from modern representatives consequently their 18o values 3 7 0 2 are assumed to represent primary biogenic calcite these 18o values are in the heavy end of the range of values from texturally well preserved whole brachiopods 6 6 to 2 5 texturally altered whole brachiopods 6 7 to 3 7 and texturally altered crinoids and cora s 6 7 to 2 7 this comparison suggests that marine derived pore waters were a predominant component during the principal phase of diagenesis the relatively low l8o values of well preserved brachiopods compared with modern representatives implies that middle devonian seawater was either warmer by about 10 c or depleted in 18o by about 2 3 relative to modern seawater

a review of the biogeography of cretaceous belemnites abstract a pattern of boreal and tethyan marine faunal realms was initiated in the jurassic and continued into the cretaceous the belemnites first display this pattern in the early jurassic and from the middle jurassic to earliest cretaceous two morphologically distinct suborders the belemnitina and the belemnopseina were restricted to the boreal shelf seas and the tethyan and gondwanan shelf seas respectively an austral marine realm was notably lacking during this interval significant change occurred in the late barremian to early aptian when the belemnitina died out leaving the belemnopseina initially the belemnopseidae but followed by the belemnitellidae to invade their niches an austral realm was initiated at this time with the first appearance of a gondwanan belemnopseine family the dimitobelidae the tethyan belemnite realm cannot be recognised after the cenomanian although the belemnitellidae and dimitobelidae defined boreal and austral belemnite realms throughout the late cretaceous climatic zonation remains the most often cited prime cause of provinciality in belemnites however examination of diversity patterns and faunal distributions reveals that palaeogeographic and palaeoceanographic factors were as important if not more so in determining cretaceous provincial boundaries

a palaeoclimate model for the kimmeridgian abstract most attempts at using numerical general circulation model gcm to simulate mesozoic climates have studied the late cretaceous and have focused on the enigmaof apparently equable global climates however this climate regime lasted throughout the mesozoic and it is of interest to examine other periods we present the results of an integration for the late jurassic using a relatively detailed and high resolution model there is generally good agreement between the model climate and the existing geological data in particular the simulation predicts no permanent ice cover near either pole arid conditions over the southwestern usa seasonally arid climate over southern europe and winter storminess over europe and australia however the surface temperatures over siberia and southeastern gondwanaland drop below zero for a significant part of the winter

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

matrix micrite δ13c and δ18o reveals synsedimentary marine lithification in upper jurassic ammonitico rosso limestones betic cordillera se spain abstract matrix micrites are a commonly used carbonate archive for the reconstruction of past environmental parameters but one that is submitted to known limitations main reasons for the often ambiguous value of many micrite based isotope data sets are the unknown origin of the micrite components and their poorly resolved diagenetic history here we present carbon and oxygen isotope data retrieved from oxfordian to tithonian ammonitico rosso nodular micrites sampled from three sections in the betic cordillera southern spain all three sections were correlated and sampled using a rigorous biostratigraphic framework a noteworthy feature is that analyzed matrix micrites are more conservative in terms of their isotopic composition than other carbonate materials commonly considered to resist diagenetic alteration under favourable circumstances remarkably this refers not only to 13 c ratios which reflect the typical late jurassic global trend but also to 18 o ratios that range around 0 3 the 18 o enriched oxygen isotope ratios are considered to represent diagenetic stabilization of carbonate ooze under the influence of marine porewaters within the sediment water interphase i e the immature sedimentary section usually submitted to biogenic activity this interpretation agrees with the very early lithification of micrite nodules with cements precipitated from marine porewaters enriched by the dissolution of aragonite skeletals i e ammonite shells according to the model proposed low sedimentation rates as well as rapid early marine differential cementation under the influence of currents and seawater pumping affected the sediment water interphase of epioceanic swells where deposition resulted in early lithified ammonitico rosso facies the data obtained show that special care must be taken to prevent oversimplified interpretations of carbonate archives particularly in the context of epioceanic settings

orbital and internal forcing of climate on the yucatan peninsula for the past ca 36 ka abstract a 19 6 m sedimentary sequence from lake quexil guatemala is presented as a proxy record of climatic change on the low lying yucatan peninsula over the last ca 36 ka long term climatic fluctuations are attributed to orbital forcing of insolation while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled gcms simulating meltwater cooling of the gulf of mexico may predict some but not all climatic responses in the circum caribbean lake quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones q lg 1 and 2 which were drier only in comparison with holocene conditions q lg 1 appears to have been colder than expected based on insolation alone and is contemporary with the younger dryas event between meltwater pulses 1a and 1b thus other feedbacks also may have cooled surface temperatures in the gulf of mexico such as unique late glacial circulation patterns increased albedo for the florida and yucatan peninsulas or surface temperatures on the north american continent additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub regional climatic variability in the circum caribbean

spatial geochemistry of upper jurassic marine carbonates iberian subplate abstract chemostratigraphy applied to ancient marine carbonates is commonly based on one dimensional stratigraphic sections or core data as demonstrated from modern oceans this approach underestimates the spatial complexity of physico chemical seawater properties here a several hundred kilometer long transect consisting of seven upper jurassic sections from settings ranging from proximal neritic middle shelf to the epioceanic distal fringe across the southern and eastern palaeomargins of the iberian sub plate reveals variability in sedimentologic stratigraphic and geochemical records the comparison of isotopic and elemental data from different carbonate materials matrix micrite carbonate cements in veinlets belemnite rostra and ammonite shells reveals differential diagenetic pathways microfacies cathodoluminescence and geochemical data retrieved from biostratigraphically well constrained sections reveal that epioceanic matrix micrite geochemical data provide valuable proxies for palaeo seawater properties our data are reviewed in the context of published late jurassic records the outcome shows a higher level of complexity including the potential admixture of marine continental and diagenetic geochemical signals in the epicontinental record the stratigraphic trend in carbon isotopes of epioceanic sections agrees upon that of upper jurassic reference sections from the northern tethyan margins while oxygen isotope ratios are relatively 18o enriched palaeo seawater temperatures across the transect investigated were estimated using 18o as tentative proxy for interpreting distance from shore differences in water masses relative depth variations and potential local forcing factors palaeoenvironmental conditions evaluated through the combined record of isotope 18o elemental mn and skeletal content contrast with relative fluctuations in sea level site specific changes in palaeoceanographic parameters such as water depth seawater temperature salinity and upwelling are considered in comparison to examples from ancient and modern oceans

contrast comparison of differential diagenetic pathways of lower tithonian carbonate materials from the betic cordillera s spain evidence for physico chemical paleo seawater properties abstract the reconstruction of paleoenvironmental conditions is based on the study of ancient rock materials for this purpose skeletal materials are often assumed to have higher preservation potential sometimes favored over the use of matrix micrite however factors such as ecology depositional setting mineralogy and diagenetic processes may obscure original geochemical signals and care must be taken when reading such an intricate record this work provides a thorough comparison between geochemical signatures of different carbonate materials interpreted in the light of their paleoenvironmental significance burial and diagenetic processes are taken into account contextualized by ammonite and belemnite ecology two sections deposited in epioceanic tethyan areas and corresponding to the same lower tithonian ammonite biozone are under scope a condensed pelagic and cephalopod rich limestone the alamedilla sector intercalated in thick mafic rocks piles and a typical ammonitico rosso facies the cardador section in contrast to depositional and taphonomic histories typical for a tethyan top swell site i e rather calcareous ammonitico rosso events of carbonate mud deposition rapid burial and early lithification synsedimentary sliding and over imposition of firmground horizons characterize pelagic cephalopod rich limestones differential taphonomy of carbonate skeletals agrees with differential preservation favoring inner cast preservation in ammonitico rosso and shell preservation neomorphic calcite in pelagic cephalopod rich limestones stable carbon and oxygen isotope data together with trace element data sr mg fe mn are presented for a wide range of carbonate materials matrix micrite neomorphic ammonite shells belemnite rostra and carbonate cements optical inspection including cathodoluminescence imaging and geochemical data suggest a fair preservation of the above mentioned materials except for diagenetic marine burial carbonate cements carbon isotope values fall within the typical tethyan late jurassic range ca 2 except data from belemnite rostra which are depleted around 1 which is interpreted as resulting from metabolic fractionation oxygen isotope values are more variable but the clustering of different carbonate materials within a narrow range of values between 1 and 1 is consistent with conservative diagenesis warmer burial fluids explain lower values in later diagenetic carbonate cements no evidence of pervasive diagenetic imprint is revealed by elemental composition the increased abundance of mg fe and especially mn up to 1500 ppm is recognized as hydrothermal contamination proximity to hydrothermal sources the mid subbetic volcanic ridge accords with higher mn concentration at the alamedilla site interestingly the timing of the mineralogical stabilization of each carbonate material reveals a potential record of a post sedimentary geochemical event the obtained information demonstrates the complexity of ancient carbonate records and encourages future research focused on the preservation potential of geochemical proxies throughout time the studied case hopes to be a representative example to approach the interpretation of potential past and present rare analogs

storm deposits and storm generated coarse carbonate breccias on a pelagic outer shelf south east basin france uppermost jurassic limestones of the south east basin france are organized into four facies associations that were deposited in four distinct zones 1 peritidal lagoonal limestones 2 bioclastic and reefal limestones 3 pelagic lime mudstones 4 lime mudstones calcarenites coarse breccias calcarenite deposits of zone 4 exhibit sedimentary structures that are diagnostic of deposition under wave induced combined flow in subzone 4a both vertical and lateral transitions from lime mudstone calcarenite to breccia indicate in situ brecciation under wave cyclic loading breccias were produced by heterogeneous liquefaction of material previously deposited on the sea floor deposits in subzone 4a record relatively long periods 400 kyr of sedimentation below wave base alternating with periods of deposition under wave induced currents and periods of in situ deformation in this zone storm waves were attenuated by wave sediment interaction and wave energy was absorbed by the deformation of soft sediment with reference to present day wave attenuation water depths in this zone ranged between 50 and 80 m landwards of the attenuation zone in zone 3 storm waves were reduced to fair weather wave heights storm wave base was not horizontal and became shallower landwards as a consequence water depth and wave energy were not linearly related on a small area of the seaward edge of subzone 4a cobbles were removed by traction currents and redeposited in subzone 4b there they formed a 100 m thick wedge which prograded over 3 km and was built up by the stacking of 5 to 20 m thick cross stratified sets of coarse breccia this wedge records the transport and redeposition of cobbles by a high velocity unidirectional component of a combined flow the increase in flow velocity in a restricted area is proposed to result from flow concentration in a channel like structure of the downwelling in the gulf formed by the basin in more distal subzone 4c the hydrodynamic effect of wave induced currents was quasi permanent and brecciation by wave sediment interaction occurred only episodically this indicates that seawards of the attenuation zone hydrodynamic storm wave base was deeper than mechanical storm wave base uppermost jurassic carbonates were deposited and soft sediment deformed on a hurricane dominated ramp of very gentle slope and characterized by a zone of storm wave degeneration located seawards of a zone of sedimentation below wave base

palaeogeography of the western pelagonian continental margin in beotia greece during the cretaceous biostratigraphy and isotopic compositions δ13c δ18o of calcareous deposits the palaeogeography of beotia greece during the cretaceous is outlined on the basis of biostratigraphic evidence derived predominantly from the distribution of rudist bivalves and planktonic foraminifera observed facies trends are evaluated together with carbon and oxygen isotopic compositions of limestones and rudist shells the interaction between global sea level fluctuations and gradual subsidence of the pelagonian continental margin controlled facies distribution during most of the cretaceous the sedimentary record begins with berriasian flysch type deposits that accumulated during incipient eohellenian orogenic movements barremian deposits with similar sedimentological characteristics probably belong to the same tectonostratigraphic unit during aptian cenomanian times terrigenous clastics with a few intercalated marine limestones accumulated in south beotia the fossil content of patch reefs presents important biostratigraphic marks in this terrigenous sequence carbon and oxygen isotopic compositions recorded unstable marine environments and subsequent decrease of continental influx continuous subsidence and rising sea levels are evident in the late turonian onlap of rudist limestones on the eohellenian basement of the ptoon mountains as well as in the interfingering of calcareous slope deposits and basinal globotruncana mudstones of south beotia during late coniacian early santonian a marked regression finally led to a regional emersion and the development of a karst relief this regression is predated by heavy oxygen isotopic compositions in the coniacian limestones which probably resulted from isolation of a larger marine embayment from oceanic circulation the subsequent late santonian campanian transgression flooded all of beotia its sediments lie over allochthonous laterites extended rudist biostromes developed as soon as continental influx ceased as indicated both by the stable isotope compositions of rudish shells and embedding limestones during the late campanian the rather uniform platform type depositional environments differentiated and pelagic sedimentation recurred in south beotia whereas depositional environments to the north remained shallow incipient tectonics movements were responsible for a late maastrichtian emersion of north beotia while basinal conditions persisted in the south the onset of flysch type sedimentation occurred simultaneously during the late paleocene in north beotia as well as in the adjacent parnassus and pindos zones however this important facies transition has not yet been precisely dated in south beotia

early detection and in depth analysis of deformation phenomena by radar interferometry the spaceborne differential interferometric sar dinsar technique may play an important role in the measurement of land deformation phenomena especially in urban suburban and industrial areas in order to fully exploit its capabilities and increase its operational use this paper proposes two complementary levels of analysis the first one is a comprehensive low cost screening in order to detect unknown subsidence phenomena over large areas this analysis which provides a first estimation of deformations has to be performed using a limited set of sar images the second level includes an in depth quantitative analysis based on large image stacks which requires more image acquisition and data processing resources this type of analysis can be typically used to study deformation phenomena of special relevance where an effective support to the decision makers requires a fully quantitative estimation of deformations the two levels of analysis were proved over a test area of about 2100 km2 located in catalonia spain without any a priori information seven deformation phenomena were detected using a reduced set of interferograms furthermore the quantitative analysis of a subsidence of small spatial extent which was based on ascending and descending datasets confirmed the capability of dinsar to quantitatively assess deformation phenomena

evidence of the younger dryas in central america abstract three sites provide records that address whether the younger dryas was manifest in central america marine records from barbados and the cariaco basin are discussed as well as possible climatic forcing mechanisms sequences from montane la chonta bog costa rica and lowland lake quexil guatemala record a temperature decline of 1 5 2 5 c dated between 11 070 10 400 14c years bp and ca 12 000 10 300 14c years bp respectively the record from lake la yeguada panama does not include cooling although significant reorganization of local communities occurred during the younger dryas chronozone colder tropical ssts throughout deglaciation contributed to sub regional climatic variation more intense monsoonal activity and cooler air temperatures however the temperature reversals are not associated with the coldest tropical ssts which occurred during meltwater pulses the temperature reversals appear to be a response to extra tropical conditions presumably in the north atlantic which suggests that younger dryas cooling extended as far south as costa rica in panama monsoonal conditions may have blocked cooler temperatures precipitation continued to increase throughout deglaciation due to strong forcing by seasonal solar insolation in central america while desiccation events occurred to the north and south

palaeoclimatic and chronostratigraphic interpretations from strontium carbon and oxygen isotopic ratios in molluscan fossils of quaternary seoguipo and shinyangri formations cheju island korea abstract palaeotemperatures and chronostratigraphies of the quaternary seoguipo and shinyangri formations cheju island south korea were investigated in terms of the strontium oxygen and carbon isotopic compositions of carbonate mollusc shells the 87sr 86sr ratios of mollusc shells from the seoguipo formation range from 0 70911 to 0 70914 which yield carbonate ages of 0 5 1 2 ma early to middle pleistocene using the linear equation between ages and 87sr 86sr ratios of quaternary seawater the 87sr 86sr ratio 0 70917 of aragonitic shells from the shinyangri formation provide late pleistocene ages 0 04 ma based on ams 14c dates of mollusc fossil shells from the shinyangri formation the depositional age of the formation has been extended to 1570 yr bp palaeotemperatures calculated on the basis of the oxygen isotopic composition of the calcitic mollusc shells from the seoguipo formation give a range of values from 12 6 to 19 1 c which is lower than the present day shallow seawater temperature 14 9 25 5 c in the vicinity of the seoguipo coast aragonitic mollusc shells from the shinyangri formation provide oceanic temperatures ranging from 22 5 to 29 8 c which is higher than present day seawater temperatures 14 1 23 2 c the calculated palaeotemperatures of the seoguipo and shinyangri formations are inferred to reflect cold and warm currents flowing over cheju island during the pleistocene to holocene

thermomechanical forcing of deep rock slope deformation 1 conceptual study of a simplified slope 1 thermo elastic rock slope deformation is often considered to be of relatively minor importance and limited to shallow depths subject to seasonal warming and cooling in this study we demonstrate how thermomechanical tm effects can drive rock slope deformation at greater depths below the annual thermal active layer here in part 1 of two companion papers we present 2d numerical models of a simplified slope subject to annual surface temperature cycles the slope geometry and discontinuity sets are loosely based on the randa instability considered in detail in part 2 results show that near surface thermo elastic stresses can propagate to depths of 100 m and more as a result of topography and elasticity of the rock mass shear dislocation along discontinuities can have both a reversible component controlled by discontinuity compliance and provided that the stress state is sufficiently close to the strength limit an irreversible component i e slip induced slip increments are followed by stress redistribution resulting in the propagation of slip fronts thus deformation and progressive rock slope failure can be driven solely by thermomechanical forcing the influence of tm induced stress changes becomes stronger for increasing numbers of critically stressed discontinuities and is enhanced if failure of discontinuities involves slip weakening the net tm effect acts as a meso scale fatigue process involving incremental discontinuity slip and hysteresis driven by periodic loading

radiolarian diversity patterns in the latest jurassic earliest cretaceous abstract the global diversity patterns of latest jurassic earliest cretaceous tithonian berriasian radiolarian faunas were analyzed based on samples from the european alps oman philippines and antarctica and an extensive literature survey several measures of diversity were applied to faunas from tropical oman mexico pacific subtropical alps california philippines japan and subpolar antarctic peninsula new zealand northern russia localities original diversity patterns are obscured by taxonomic sedimentological and preservational biases qualitative and quantitative corrections of these biases indicated a significant diversity gradient from tropical subtropical to subpolar latitudes but no significant difference between tropical and subtropical assemblages the latitudinal diversity gradient was apparently asymmetrical being steeper in the northern hemisphere than in the southern hemisphere in the southern hemisphere the diversity gradient was similar to the one observed in modern radiolarian sedimentary assemblages considering the more equable climate of the tithonian berriasian it appears unlikely that temperature was the only control of the observed diversity patterns the results substantiate the notion of latitudinal diversity gradients as a time invariant feature of the earth possibly driven by gradients in biome size

evidence for seasonal low salinity surface waters in the gulf of mexico over the last 16 000 years oxygen isotopic analyses of individual orbulina universa from orca basin core en32 pc6 document the presence of low salinity surface waters in the northern gulf of mexico over the past 16 kyr isotopic data from an interval immediately following the younger dryas event indicate the rapid decrease in 18o values at the conclusion of the younger dryas was due to a year round return of meltwater to the gulf of mexico data indicate periodic or seasonal low salinity waters existed over the region of the orca basin prior to the initiation of the meltwater spike estimates suggest o universa grew its shell in salinities at least 4 5 below ambient since o universa may have calcified deep in the mixed layer during periods of low salinity surface salinities could have been even lower comparison of the average of individual o universa oxygen isotopic values with data from multiple shell samples of white gs ruber from the same core samples demonstrates that the two species record similar values during the late holocene in contrast o universa records lower oxygen isotopic values during the late glacial deglacial intervals possibly due to differences in seasonal distribution or shell ontogeny between the two species

belemnite taphonomy upper jurassic western tethys part i biostratinomy abstract a detailed taphonomic analysis was performed on 188 belemnites and 56 thin sections from the pozo canada section external prebetic as well as 101 belemnites and 31 thin sections from the rio segura internal prebetic both from the upper oxfordian lower kimmeridgian this manuscript is focused on biostratinomic features and a second part is focused on fossildiagenetic aspects the belemnites correspond to hibolithes and less commonly belemnopsis biostratinomic features including size fragmentation corrasion microboring and encrustation were analysed in each specimen using petrographic conventional cathodoluminescence epifluorescence and scanning electron microscopy techniques fragmentation affects the phragmocone and the rostrum cavum and is usually transversal and rarely longitudinal through the apical line isolated fragments of epirostrum are common corrasion produces irregular surfaces microborings are very common represented by a fungal hyphae b fascichnus dactilus like and scolecia filosa like borings cyanobacteria c entobia sponges d large microborings with y shaped branching diameter 100 500 m subparallel to rostrum surface e large cylindrical to ellipsoidal borings related to cirripeds and f palaeconchocelis starmachii rhodophyte microbes and sessile foraminifera vinelloidea bullopora tolypammina thurammina placopsilina and subdelloidina are the main encrusters microbial films are composed of dense micrite or clotted peloidal microfabrics the biostratinomic features analysed in the belemnite rostra are clearly influenced by the lithofacies and shelf setting the intensity of corrasion microborings and encrustation by indicating time exposure help establish which lithofacies shows the highest sedimentation rate the belemnites from internal prebetic lithofacies that is the outer shelf deposits lumpy limestone and lumpy oncolitic limestone present high values of corrasion microboring and encrustation thereby indicating long time exposure in sharp contrast belemnites from the lithofacies of the external prebetic represent deposition in mid shelf environments spongiolithic limestone spongiolithic marl peloidal limestone and marl limestone rhythmite featuring higher clay content

isotopic evidence for late jurassic early cretaceous climate change abstract strontium oxygen and carbon isotope ratios have been determined from late jurassic early cretaceous belemnites from the volga basin russia and kawhia harbour new zealand 87sr 86sr ratios derived from well preserved belemnites from the volga basin support a middle tithonian age derived from the analysis of the endemic ammonite fauna the kawhia harbour section records a gradual rise in 87sr 86sr values and in comparison with the published 87sr 86sr curve suggests that the lower part of the section is latest oxfordian in age whilst the upper part of the section correlates well with the biostratigraphic correlation suggestion of an early middle tithonian age although the published strontium calibration curve shows a degree of scatter our new data confirm the uniform rise in 87sr 86sr values from the late jurassic into the early cretaceous such an increase may result from either a decrease in mid oceanic ridge spreading and or an increase in weathering rates and flux of radiogenic strontium although a eustatic drop in sea level and concurrent western cordillera uplift suggests that weathering may have been the controlling factor of late jurassic seawater strontium isotope composition palaeotemperatures derived from the well preserved belemnite 18ocarb values from the volga basin indicate that the middle volgian late kimmeridgian was warm 14 20 c followed by a slight cooling and a subsequent gradual increase to the jurassic cretaceous boundary the 18ocarb values from new zealand located at a palaeolatitude of 80 s if interpreted in terms of palaeotemperature indicate a high degree of variability such variability may not be related to palaeotemperature but to changes in oceanic chemistry resulting from the formation and dissolution of an ice sheet and or snow during the oxfordian kimmeridgian carbon isotope trends for the late jurassic show a fall in values from the oxfordian with lowest values occurring in the early middle tithonian before rising but without reaching values obtained in the oxfordian the overall low 13ccarb may be related to a global increase in continental weathering and or upwelling of cooler oceanic water enriched in oxidised organic carbon 12c enriched

late cretaceous terrestrial vegetation a near polar temperature curve quantitative estimates of terrestrial paleotemperatures near the north pole were derived from the physiognomy of the vegetation including leaf margin analysis from rocks of latest albian and late cretaceous age of the north slope of alaska during the latest albian and cenomanian mean annual temperature was approximately 10 3 c during the coniacian mean annual temperature may have been 2 3 c warmer than during the albian cenomanian but no higher than 13 c during the campanian and maastrichtian mean annual temperature would have been about 2 8 c although the ranges for the individual estimates overlap differences among the floras indicate that the relative changes in mean annual temperature did occur

a middle wisconsin pollen record from hay lake arizona abstract the lower part of a 5 m core from hay lake 34 n 109 25 w at 2780 m in east central arizona provides a pollen record for the middle wisconsin identification of fossil pines is based on a key modified from hansen and cushing 1973 geological society of america bulletin 84 1181 1200 pinus edulis and p monophylla are similar in size and morphology but are significantly different from p flexilis haploxylon pines dominate the pollen record the abundance of pinyon pines during the middle wisconsin is interpreted as indicating that this group was widespread at lower elevations the local vegetation was mixed conifer forest consisting of picea p aristata p flexilis and or p strobiformis and with p ponderosa and or p contorta after about 26 000 yr b p tree line was above the elevation of hay lake the middle wisconsin climate is inferred to have been cooler than today and is marked by more available moisture that permitted pinyon pines to grow at low elevations

jurassic septarian concretions from nw scotland record interdependent bacterial physical and chemical processes of marine mudrock diagenesis septarian concretions in the staffin shales formation kimmeridgian isle of skye allow controls on concretion rheology and septarian cracking to be investigated stratabound concretions consist of anhedral ferroan calcite microspar enclosing clay and minor pyrite intergranular volumes range from 77 to 88 and calcite 13c and 18o values in most concretion bodies range from 10 0 to 17 3 and 0 3 to 0 6 respectively consistent with rapid and pervasive cementation in marine pore fluids septarian rupture occurred during incipient cementation with a sediment volume reduction of up to 43 crack lining brown fibrous calcite records pore fluid re oxygenation during a depositional hiatus followed by increasing fe content and 13c related to bacterial methanogenesis brown colouration results from an included gel like polar organic fraction that probably represents bacterially degraded biomass a new hypothesis for concretion growth and septarian cracking argues that quasi rigid proto concretions formed via binding of flocculated clays by bacterial extracellular polysaccharide substances eps this provided rheological and chemical conditions for tensional failure subcritical crack growth volume contraction calcite nucleation and incorporation of degraded products into crack lining cements bacterial decay of eps and syneresis of host muds provided internal stresses to initiate rupture at shallow burial development of septarian shrinkage cracks in muds is envisaged to require pervasive in situ bacterial colonization and to depend on rates of carbonate precipitation versus eps degradation and syneresis subsequent modification of septarian concretions included envelopment by siderite and calcite microspar hydraulic fracturing associated with cretaceous shallow burial or palaeogene uplift and cementation by strongly ferroan yellow sparry calcite that records meteoric water invasion of the host mudrocks an abundance of fatty acids in these spars indicates aqueous transport of organic breakdown products and 13c data suggest a predominantly methanogenic bicarbonate source however the wide 18o range for petrographically identical cement 1 3 to 15 6 is difficult to explain

new aragonite 87 sr 86 sr records of mesozoic ammonoids and approach to the problem of n o c and sr isotope cycles in the evolution of the earth abstract new sr isotope data from well preserved aragonite ammonoid shell material from the mesozoic are compared with that from a living nautilus shell the prominent negative sr isotope excursions known from the middle permian jurassic and cretaceous probably have their origins in intensive plate tectonic activity followed by enhanced hydrothermal activity at the mid ocean ridges mantle volcanism which supplied low radiogenic sr to seawater the maximum positive radiogenic shift in the lower mesozoic sr isotope curve lower triassic peak was likely caused by a significant expansion of dry land surfaces dabie sulu triassic orogeny and their intensive silicate weathering in conditions of extreme warming and aridity in the very end of the smithian followed by warm and humid conditions in the late spathian which apparently resulted in a significant oceanic input of radiogenic sr through riverine flux the comparatively high 87sr 86sr ratio obtained from the living nautilus shell is probably a function of both the alpine orogeny which was accompanied by significant continental weathering and input of radiogenic sr to the oceans and the weakening of mantle volcanism

mesozoic echinoid diversity in portugal investigating fossil record quality and environmental constraints on a regional scale several analyses of diversity through geological time use global synoptic databases and this practice often makes it difficult to distinguish true signals in changing diversity from regional scale sampling and or geological artefacts here we investigate how echinoid diversity changed through the mesozoic of the lusitanian basin in portugal based on a comprehensive revised database and seek to distinguish biological signal from geological or environmental constraints the observed diversity pattern is far from having a defined trend showing many fluctuations that appear to be linked with gaps in the geological record this study revealed that independently of the method used whether correlation tests or model fitting the diversity signal is not completely explained by the studied sampling proxies among the different proxies marine facies variation in combination with outcrop area best explains the palaeodiversity curve

a view on some hydrological triggering systems in landslides abstract in this paper different types of hydrological triggering systems for debris flows shallow and deeper landslides are described the generation of surface run off and high peak discharges in first order alpine catchments is an important triggering mechanism for debris flows failure conditions in shallow landslides can occur when at a critical depth which is determined by the cohesion of the soil and the slope angle the moisture content in the soil becomes close to saturation resulting in a considerable reduction of soil strength deeper landslides 5 20 m depth are in most cases triggered by positive pore pressures on the slip plane induced by a rising ground water level the assessment of meteorological threshold conditions for shallow landslides 1 2 m needs more detailed meteorological information than for deeper landslides in the analyses of the hydrological triggering systems of deeper landslides the presence of a permeable top layer and fissures has to be taken into consideration

the oxygen isotope composition of tropical ocean surface water during the last deglaciation evidence of abrupt climate change in each of the tropical oceans can be found in high deposition rate sediments from the continental margins new ams 14 c dated sediments from the arabian sea reveal a two step depletion of surface ocean 18 o 16 o during the last deglaciation with a return to more enriched values approximately 10 5 ka bp the two step depletion can be correlated among isotope records derived from foraminifer calcite in the arabian sea the gulf of mexico the sulu sea and gulf of california confirming the existence of the two step depletion and 18 o enriched event at 10 5 ka bp in at least three tropical sites outside the north atlantic to determine whether the isotopic enrichment at 10 5 ka bp was caused by local cooling of the surface ocean we estimated sea surface temperatures over this interval using quantitative paleo ecological techniques there is no evidence for cooling in the arabian sea sulu sea or gulf of mexico consistent with the hypothesis that the enrichment at 10 5 ka bp is related to a change in the isotopic composition of the tropical surface ocean and not change in the temperature of calcification we conclude that the cooling at higher latitudes that occurred at 10 5 ka bp did not extend southward to the tropical ocean more cores from high sedimentation rate sites in the tropics are needed to identify the cause and extent of the 18 o signal however these preliminary results are consistent with two meltwater pulses during the deglaciation that distributed isotopically depleted water into each of the tropical oceans with a slow down in meltwater flux at 10 5 ka bp the most likely transport route for the isotopically depleted water from the melting northern hemisphere ice sheets to these isolated tropical ocean basins is via the relatively fast circulation of the atmosphere although other pathways are possible

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

geochemical analysis of nautilus pompilius from fiji south pacific abstract nautilus pompilius from fiji exerts a biological fractionation effect on the sr2 and na contents of its aragonite shell the sr2 content is lower while the na content is greater than that for aragonite precipitated in chemical equilibrium with ambient seawater the oxygen isotope values of nautilus pompilius suggest that its shell aragonite was precipitated in equilibrium with ambient seawater isotope calculations suggest water temperatures of 9 18 c this limits the habitat range of nautilus pompilius during shell formation to water depths of 250 500 m

carbon isotope stratigraphy and pelagic biofacies of the middle upper jurassic transition in the tethys central atlantic connection abstract a bulk carbon isotope stratigraphy based on high resolution sampling of five stratigraphic ammonite dated sections from pelagic swells of the subbetic basin external zones of the betic cordillera southern spain is presented the studied sections are characterized by callovian oxfordian stratigraphic successions located in the south iberian palaeomargin a key area connecting the central atlantic to the tethys oceans the rocks are mainly nodular limestones with common extreme condensation rosso ammonitico facies discontinuities with hiatuses of variable duration submarine hardgrounds fe mn ooids limonite crusts and neptunian dykes are observed around the callovian oxfordian boundary the stratigraphic record although very time averaged allows for a consistent and accurate ammonite chronostratigraphy the carbon isotopes of marine carbonates show a marked trend towards high 13c values from lower oxfordian to the middle oxfordian 4 3 near the plicatilis transversarium boundary the isotopic values stand between 2 7 and 3 0 at the upper oxfordian bifurcatus and hypselum zones and lowermost kimmeridgian bimammatum zone afterward 13c values decrease and reach a relative minimum 2 3 2 5 in the lower kimmeridgian bimammatum planula boundary finally isotopic values increase again 2 6 2 7 in the lower kimmeridgian mid part of the planula zone comparison of carbon isotope stratigraphy between subbetic and other tethyan areas shows similar trends the replacement of thin shelled bivalves by planktonic foraminifers and radiolarians that took place in the callovian oxfordian boundary can be associated to the widening of the trans pangaean seaway this in turn triggered the global warming which increased nutrients concentration in upper water column due to intensified nutrient input by river plumes these phenomena are concomitant with the major oxfordian 13c positive excursion and with a transgressive cycle

the role of bacterial sulfate reduction during dolomite precipitation implications from upper jurassic platform carbonates the early diagenetic formation of dolomite in modern aquatic environments is limited mostly to evaporitic and marine anoxic organic rich sediments dominated by bacterial sulfate reduction bsr in such environments bacterial activity lowers the energy barriers for the nucleation and growth of dolomite and thus promotes the formation of non stoichiometric highly disordered and metastable proto dolomite although the boundary conditions for the formation of modern proto dolomites are considered to be generally understood the role of bsr during limestone dolomitization in ancient marine environments remains questionable herein we present a study about the physicochemical conditions and processes which led to the formation of partly dolomitized limestone and dolostone in the presence of bsr on a stable carbonate platform during the upper jurassic at oker northern german basin the dolomite textures the spatial trace elemental patterns of the dolomite and of the surrounding limestone and the results of 18o and 13c isotope analyses reveal that the oker dolomite has been formed by the early diagenetic replacement of magnesian calcite precursors at temperatures between 26 c and 37 c we interpret the mineralizing fluids responsible for dolomitization as pristine marine to slightly evaporitic and reducing seawater being modified during shallow seepage reflux and or evaporitic tidal pumping the elevated 34scas values 17 9 to 19 7 v cdt of the oker dolomite compared to ambient upper jurassic seawater indicate that bsr facilitated dolomite formation for the first time we show that a linear anti correlation exists between decreasing carbonate associated sulfate cas contents in dolomite and increasing ordering ratio of the dolomite lattice structure with the degree of cation order in dolomite to be given by degree of cation order dol 0 018 cas dol 68 3 r2 0 98 this correlation implies that the cas content of sedimentary dolomite can be used as a measure for dolomite maturity the relationships between the ambient paleo environmental controls the resultant dolomitization pathways and subsequently the structure and the composition of the precipitating dolomite are presented and discussed in relation to the stability of modern and ancient proto dolomites throughout burial diagenesis

warm palaeotemperatures from high late jurassic palaeolatitudes falkland plateau ecological environmental or diagenetic controls abstract oxygen and carbon isotopes have been determined from late jurassic oxfordian tithonian belemnites and inoceramid bivalves from two deep sea drilling project dsdp sites located on the falkland plateau mean belemnite 18o values derived from well preserved skeletal material were 1 29 from dsdp site 330 and 1 45 from dsdp site 511 assuming a seawater smow value of 1 0 mean palaeotemperatures calculated from the oxygen isotopic composition are 17 2 c and 17 9 c respectively the inoceramid bivalves yielded much lighter 18o values mean 3 58 petrographic and geochemical evidence points to the inoceramid bivalves being altered by diagenesis which accordingly accounts for the observed differences in isotopic values vital effects or the importation of belemnites or inoceramids from another area are considered not to account for the observed isotopic trends the palaeotemperatures interpreted from the belemnites are significantly warmer than other recent estimates of late jurassic temperature from oxygen isotope studies and climate model predictions from similar southern palaeolatitudes we suspect our apparent warmer temperatures are because of a combination of increased freshwater runoff depleting surface waters with respect to 18o and related to the semi enclosed nature of the depositional basin retaining warmth relative to the open ocean of similar latitudes

glacial interglacial climatically forced δ 13 c variations in sedimentary organic matter sedimentary organic geochemical properties have long been used to characterize sedimentary organic matter sources1 8 but the characterizations are often not unique there are at least four plausible mechanisms to account for the large 3 6 glacial to interglacial climatic variations in the sedimentary organic carbon isotopic composition 13corg in the northern gulf of mexico they are temperature dependent c isotopic fractionation by phytoplankton mixing of c3 photosynthetic terrigenous and marine organic matter mixing of c3 and c4 photosynthetic organic matter and diagenetic alteration of the originally sedimented material in a 208 7 m deep sea drilling project hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico we find that paired analyses of 13corg and n c are consistent with the hypothesis that the sedimentary organic carbon in the pigmy basin is a glacial interglacial climati cally determined mixture of c3 photosynthetic terrigenous and marine organic matter9 confirming the model of sackett5

palaeotemperatures indicated by upper jurassic kimmeridgian tithonian fossils from mallorca determined by oxygen isotope composition abstract the oxygen and carbon composition of calcite has been determined for belemnites ammonite aptychi and the matrix surrounding these fossils from the kimmeridgian tithonian of mallorca petrography cathodoluminescence and trace element analyses indicate that both ammonite aptychi and matrix has been diagenetically altered whereas the belemnites have been undergone minimal or no modification the belemnites give the heaviest oxygen isotope values of 0 04 to 0 99 pdb and lighter values of 0 71 to 3 98 pdb come from the ammonite aptychi and matrix the carbon isotopic compositions obtained from all the fossils are positive and are similar to those derived from modern marine shallow water skeletons palaeotemperatures calculated on the basis of the oxygen isotopic composition of the belemnites give a range of values from 13 6 to 16 c these results agree with late jurassic palaeotemperatures from similar palaeolatitudes

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

strontium and carbon isotope stratigraphy of the late jurassic shallow marine limestone in western palaeo pacific northwest borneo abstract strontium and carbon isotope stratigraphy was applied to a 202 m thick shallow marine carbonate section within the late jurassic bau limestone at the ssf quarry in northwest borneo malaysia which was deposited in the western palaeo pacific strontium isotopic ratios of rudist specimens suggest that the ssf section was formed between the latest oxfordian 155 95 ma and the late kimmeridgian 152 70 ma which is consistent with previous biostratigraphy the 13 c carb values of bulk carbonate range from 0 10 to 2 28 and generally show an increasing upward trend in the lower part of the section and a decreasing upward trend in the upper part of the section a comparable pattern is preserved in the 13 c org isotope record limestone samples of the ssf section mainly preserve the initial 13 c carb values except for the interval 84 92 m where an apparent negative anomaly likely developed as a result of meteoric diagenesis comparing with the tethyan 13 c carb profile a negative anomaly in the lower ssf section can be correlated with the lowered 13 c values around the oxfordian kimmeridgian boundary in addition 13 c carb values of the bau limestone are generally 1 lower than the tethyan values but comparable with the values reported from scotland and russia located in boreal realm during the late jurassic this suggests that either the tethyan record or the other records have been affected by the 13 c values of regionally variable dissolved inorganic carbon dic the late jurassic 13 c dic values are thought to have been regionally variable as a result of their palaeoceanographic settings this study shows that 13 c chemostratigraphy of the palaeo pacific region contributes to an improved understanding of global carbon cycling and oceanography during this time period

the sources and deposition of organic matter in the late quaternary pigmy basin gulf of mexico abstract the concentration and carbon isotopic composition 13c of sedimentary organic carbon corg n c ratios and terrigenous and marine 13corg endmembers form a basis from which to address problems of late quaternary glacial interglacial climatic variability in a 208 7 m hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico while interpretations of sedimentary 13corg time series records are often not unique paired analyses of 13corg and n c are consistent with the hypothesis that the corg in the pigmy basin is a climatically determined mixture of c3 photosynthetic terrigenous and marine organic matter confirming the earlier 13corg model of sackett 1964 a high resolution 1 4 2 9 ka sample 13corg record shows that sedimentary organic carbon in interglacial oxygen isotope sub stages 1 and 5a b are enriched in 13c average 1 values are 24 2 1 2 o and 22 9 0 7 o relative to pdb respectively while glacial isotope stage values 2 are relatively depleted 25 6 0 5 concentrations of terrigenous and marine sedimentary organic carbon are calculated for the first time using 13corg and corg measurements and empirically determined terrigenous and marine 13corg endmembers the net accumulation rate of terrigenous organic carbon is 4 3 2 6 times higher in isotope stages 2 4 than in sub stages 1 and 5a b recording higher erosion rates of terrigenous organic material in glacial times the concentration and net accumulation rates of marine and terrigenous corg suggest that the nutrient bearing plume of the mississippi river may have advanced and retreated across the pigmy basin as sea level fell and rose in response to glacial interglacial sea level change

tepexpan palaeoindian site basin of mexico multi proxy evidence for environmental change during the late pleistocene late holocene the tepexpan palaeoindian skeleton was discovered in 1947 close to the former lake texcoco margin in the basin of mexico the find has been the object of considerable interest and discussion over the last 60 years regarding its real age and archaeological interpretation here we report new ams radiocarbon dates associated with the sedimentary succession at tepexpan with ages between 19 110 90 and 612 22 14c years bp and a new uranium series date for the skeleton with an age of 4700 200 years bp that indicates a mid holocene age the sedimentary succession was studied in detail using stable isotopes diatoms organic geochemistry and tephrochronology the multi proxy evidence suggests large changes around the margins of lake texcoco in terms of the balance between aquatic and terrestrial plants c3 and c4 plants saline alkaline and freshwater conditions volcanic activity marginal reworking of lake sediments and input from the drainage basin through the late pleistocene late holocene these changes had large impacts on the prehistoric human populations living by the lake shores since the late pleistocene in the basin of mexico

climate change in the circum north atlantic region during the last deglaciation a survey of new and published palaeoclimate data indicates that both the high and low latitude north atlantic regions were characterized by at least three synchronous periods of abrupt climate change during the last glacial to interglacial transi tion climate model results suggest that changes in the melting history of the laurentide ice sheet may explain much of this nonlinear response of the climate system to astronomical milankovitch forcing

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

causative mechanisms of rainfall induced fill slope failures slope failures in fill slopes formed by loosely compacted completely decomposed granite in hong kong occur commonly during intense tropical rainstorms the stress path greatly influences the shear strength of the soil mass and is therefore crucial to the identification of slope failure mechanisms the soil mass in this case is largely unsaturated in situ hydrologic response to rainstorms indicates that soil suction is reduced by rainfall infiltration which often becomes the triggering factor in initiating slope instability the constant dead load tests on unsaturated loosely compacted completely decomposed granite appropriately simulate the field stress path of rainfall induced fill slope failure by reducing suction the tests indicate that matric suction contributes to the dilative or contractive behavior of the unsaturated soils the anisotropically consolidated undrained triaxial tests demonstrate the consistently contractive behavior of the specimens on this basis we delineate the in situ stress conditions leading to the initiation of rainfall induced fill slope failure and the stress paths of the transformation from local failures to flowage based on a systematic study of fill slope case records in hong kong implications of such mechanisms on fill slope stability are given

paleoclimate of the kimmeridgian tithonian late jurassic world ii sensitivity tests comparing three different paleotopographic settings moore g t sloan l c hayashida d n and umrigar n p 1992 paleoclimate of the kimmeridgian tithonian late jurassic world ii sensitivity tests comparing three different paleotopographic settings palaeogeogr palaeoclimatol palaeoecol 95 229 252 topography and location of continents largely determine present day climate we conclude that in the geologic past paleotopographic expression was equally important however in the geologic record paleotopography is difficult to assess and compile because it is largely a self destructive environment without record and is rarely addressed in the literature an objective of this study is to test the sensitivity of paleoclimate to paleotopography by comparing three different late jurassic scenarios paleotopography influences many paleoclimate parameters to varying degrees to test the sensitivity of paleoclimate to modeled paleotopography for simulations incorporating a late jurassic reconstruction we ran three simulations using the same boundary conditions of paleogeography land and ocean and atmospheric co2 concentration 4x the pre lndustrial level 1120 ppm one simulation contained mountain ranges of variable height to 3 kin in another all the mountain ranges were reduced to 1 km highlands the third simulation used a constant 500 m height for all land grid cells the sensitivity tests indicate that paleotopography is an important boundary condition without realistic paleotopography flat or idealized continents surrounded by bodies of water do not produce realistic pateoclimate results we conclude that in paleogeographic reconstructions the location and extent of mountain ranges and highlands should be recognized and given suitable elevations consistent with their plate tectonic origins settings and geologic ages

millennial to century scale variability in gulf of mexico holocene climate records of the intertropical convergence zone itcz related to orbital forcing the d 18 o of the surface dwelling planktic foraminifer globigerinoides ruber show negative excursions between 14 and 10 2 ka radiocarbon years that reflect influx of meltwater into the western gom during melting of the laurentide ice sheet the relative abundance of the planktic foraminifer globigerinoides sacculifer is related to transport of caribbean water into the gom maximum transport of caribbean surface waters and moisture into the gom associated with a northward migration of the average position of the itcz occurs between about 6 5 and 4 5 ka in addition abundance variations of g sacculifer show century scale variability throughout most of the holocene the gom record is consistent with records from other areas suggesting that century scale variability is a pervasive feature of holocene climate the frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability indicating that at least some of the century scale climate variability during the holocene is due to external solar forcing index terms 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic 3030 marine geology and geophysics micropaleontology

belemnite taphonomy upper jurassic western tethys part ii fossil diagenetic analysis including combined petrographic and geochemical techniques abstract fossil diagenetic features were analyzed on 56 belemnite rostra from the pozo canada section external prebetic as well as 31 belemnite rostra from the rio segura internal prebetic both from the upper oxfordian lower kimmeridgian they mainly correspond to hibolithes and secondarily to belemnopsis fossil diagenetic processes were analyzed in each specimen using petrographic conventional cathodoluminescence epifluorescence and scanning electron microscopy and geochemical elemental and stable isotopes techniques the most common fossil diagenetic processes are dissolution calcite cementation and recrystallization of the apical zone and outer growth rings of belemnite rostra these processes may appear enhanced by fracturing and stylolite formation petrographic study also reveals that the alternation of cloudy and clear concentric growth areas displayed by many belemnite rostra corresponds to an early diagenetic feature in origin however an original concentric growth pattern is also observed under epifluorescent microscopy and bsem this growth pattern fits with changes in the mg and s content of the rostra although fossil diagenetic processes typically make specimens non suitable for paleoenvironmental interpretations microsampling of petrographically altered and non altered areas from the same specimens performed directly from thin sections after petrographic study allowed us to obtain excellent geochemical results suitable for paleoenvironmental interpretations these geochemical analyses moreover demonstrates that caution should be taken if elemental analyses are used as the most significant criteria for discriminating diagenetically altered and non altered belemnite samples

high paleolatitude late cretaceous paleotemperatures new data from james ross island antarctica oxygen isotope analysis of well preserved macrofossils from the santonian campanian of james ross island and the maastrichtian of vega island antarctica indicates that cool high paleolatitude temperatures prevailed during the late cretaceous and suggests that cooling occurred between the santonian campanian and the maastrichtian although more than 50 of the material showed diagenetic alteration 52 unaltered aragonite and calcite samples were analyzed mean delta sup 18 o and calculated paleotemperature values were minus 0 23 per thousand and 13 6 c respectively for the santonian campanian and 0 66 per thousand and 11 7 c respectively for the masstrichtian in conjunction with recent late cretaceous paleoclimatic data from high northern paleolatitudes these data indicate the presence of cool polar regions with broad climatic zonation during the late cretaceous this may have partly controlled faunal distributions

late quaternary paleoclimates and biotic responses in eastern north america and the western north atlantic ocean abstract broad scale late quaternary paleoclimatic changes are interpreted from palynological records across eastern north america and from assemblages of marine foraminifera in the western north atlantic ocean quantitative reconstructions of past dominance for major tree taxa at eight fossil pollen sites located south of the maximum glacial extent in the southeastern united states illustrate dramatic responses of tree populations to climatic change during the transition from pleistocene to holocene conditions a series of maps depicting changes in inferred boundaries of predominant airmasses during the late quaternary are based upon paleoclimatic interpretation of paleovegetation maps for eastern north america and climap maps of winter sea surface temperatures for the western north atlantic ocean in the eastern united states at 18 000 b p strong zonal circulation resulted in a fixed position of the atmospheric polar frontal zone along 33 n latitude the pacific airmass extended from 33 n latitude north to the southern margin of the laurentide ice sheet with the maritime tropical airmass dominating south of 33 n across the gulf coastal plain the gulf of mexico and the equatorial atlantic ocean the oceanic polar frontal zone extended northeastward from cape hatteras to 37 n in the western north atlantic ocean late glacial climatic amelioration was first reflected in vegetational changes south of the laurentide ice sheet beginning at 16 500 b p late glacial weakening in zonal atmospheric flow resulted in the penetration of the maritime tropical airmass farther to the north during the summer season increased summer warmth and rain produced substantial melting of the southern flank of the laurentide ice sheet the early holocene interval from 12 500 to 8 000 b p bracketed the time of maximum seasonality of solar radiation ca 11 000 b p during the early holocene enhanced meridional air flows resulted in increased seasonality of temperatures by 10 000 b p the oceanic polar frontal zone was displaced northward from the gulf stream anomalously cold maritime climatic conditions persisted along the central atlantic coast reflecting the position of the cold marine labrador current between the atlantic seaboard and the gulf stream during the mid holocene or hypsithermal interval from 8 000 to 4 000 b p prevailing westerlies expanded the midcontinental region of warmth and aridity for the last 4 000 years the modern climatic regime has been characterized by increased meridional flow

palaeobiogeography of the early cretaceous corals abstract a compilation of the geographical distribution of about 1000 species of corals from the early cretaceous valanginian to cenomanian is presented after the reefal regression during the latest jurassic no corals appear in the berriasian and only a few species are known from the valanginian and hauterivian in many regions it is impossible to distinguish pre barremian stages many of the pre barremian corals reported are hauterivian in age the pre barremian displays an explosion of the scleractinia more than 300 species extended through europe africa and north and south america during the aptian and albian coral distribution was about the same as during the pre barremian but during the albian the number of species decreased and the proportion of ahermatypic forms increased because of pronounced endemism during the albian faunal similarity no longer existed between the americas and europe during the cenomanian the madreporaria nearly disappeared from north america but were still well represented in europe half of the known cenomanian coral species are ahermatypic and they appear to be distributed on the two sides of the hermatypic buildup along the tethyan realm

record of the north american southwest monsoon from gulf of mexico sediment cores summer monsoonal rains the southwest monsoon are an important source of moisture for parts of the southwestern united states and northern mexico improved documentation of the variability in the southwest monsoon is needed because changes in the amount and seasonal distribution of precipitation in this semiarid region of north america influence overall water supply and fire severity comparison of abundance variations in the planktic foraminifer globigerinoides sacculifer in marine cores from the western and northern gulf of mexico with terrestrial proxy records of precipitation tree ring width and packrat midden occurrences from the southwestern united states indicate that g sacculifer abundance is a proxy for the southwest monsoon on millennial and submillennial time scales the marine record confirms the presence of a severe multicentury drought centered ca 1600 calendar cal yr b p as well as several multidecadal droughts that have been identified in a long tree ring record spanning the past 2000 cal yr from west central new mexico the marine record further suggests that monsoon circulation and thus summer rainfall was enhanced in the middle holocene ca 6500 4500 14 c yr b p ca 6980 4710 cal yr b p the marine proxy provides the potential for constructing a highly resolved well dated and continuous history of the southwest monsoon for the entire holocene

deposition of a muddy sediment drift in the southern straits of florida during the late quaternary abstract bottom currents associated with the florida current in large part control deposition of muddy biogenic sediments in the constricted deep sea passage of the southern straits of florida the unit is similar to muddy contourite drifts based on sediment structures changing thickness of biostratigraphic zones and distribution of biogenic sands in twenty piston cores current activity affected deposition more during the last glacial period than during the present and penultimate interglacial periods of the last 127 000 years based on the presence of an erosional regional unconformity that ended in the upper part of the glacial interval and on the change in pattern of silt and clay accumulation rates in the glacial interval relative to interglacial intervals

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

the younger dryas cool episode in the gulf of mexico data are presented from orca basin piston core en32 pc4 in the gulf of mexico that confirm the existence of surface water cooling during the younger dry as chronozone 11 10 ka late glacial planktonic foraminiferal species made a reappearance between 11 4 and 9 8 ka an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer globigerinoides ruber the presence of the younger dryas event in the gulf at 27 n demonstrates that surface water cooling extended to mid latitude regions in the north atlantic the cool surface water interval is bracketed by rapid shifts in 18o related to changes in the influx of meltwater to the gulf of mexico a chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a 500 year period and ended in less than 200 years these results are among the first deep sea sediment data documenting the climatic transitions bracketing the younger dryas with a rapidity observed in ice core records a rapid decrease in 18o values measured in the white form of gs ruber at 10 2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures surprisingly a similar decrease is not observed in the pink form of gs ruber a summer surface water dweller in the gulf this discrepancy may be explained by continued meltwater influx throughout the younger dryas during the summers only such that there was no change in the 18o of the pink form at the end of the episode an additional possibility is that warming at the end of the younger dryas raised year average temperatures and summer temperatures remained constant the coincidence of rapid shifts in 18o with the younger dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the younger dryas cooling based on changes in the routing of laurentide glacial meltwater

paleoceanographic changes during the early cretaceous valanginian hauterivian evidence from oxygen and carbon stable isotopes we investigated valanginian hauterivian bulk rock and belemnite samples from vocontian basin sections in southeastern france for their stable carbon and oxygen isotope signature firstly because these sections permit calibration with high resolution biostratigraphy based on ammonites and secondly because detailed isotope studies for the hauterivian are lacking the results show that 13c values for bulk rock decrease during the late valanginian early hauterivian with 1 and increase again during the late hauterivian with 1 the 18o signal for bulk rock samples is mostly disturbed by diagenesis the belemnites show carbon and oxygen isotope values that are lower and higher than bulk rock samples respectively we explain this as the result of the belemnites recording a deeper water signal with lighter 13c values and heavier 18o values implicating colder water at greater depth the overall preservation of the belemnites is very good and permits the construction of a paleo temperature trend this trend shows warm deeper water temperatures during the late early valanginian 15 c and progressively cooler temperatures during the late valanginian and early hauterivian 11 c during the late hauterivian temperatures increase again 13 c we relate this cooling trend for deeper water to a second order sea level rise which allowed for the exchange of cold boreal and warm tethyan water masses the influx of cold nutrient rich water had a profound effect on carbonate producing biota along the northern margin of the tethys during the hauterivian leading to prolonged phases of condensation and platform destruction during the early hauterivian the carbonate system along the northern tethyan margin shifted into a green water mode of carbonate production high rates of carbonate production under mesotrophic conditions also observed in other parts of the world meant that the global carbon cycle became buffered shown by the stable trends in carbon isotopes

late quaternary vegetational dynamics and community stability reconsidered abstract defining the spatial and temporal limits of vegetational processes such as migration and invasion of established communities is a prerequisite to evaluating the degree of stability in plant communities through the late quaternary the interpretation of changes in boundaries of major vegetation types over the past 20 000 yr offers a complementary view to that provided by migration maps for particular plant taxa north of approximately 43 n in eastern north america continual vegetational disequilibrium has resulted from climatic change soil development and species migrations during postglacial times between 33 and 39 n stable full glacial vegetation was replaced by a relatively unstable vegetation during late glacial climatic amelioration stable interglacial vegetation developed there after about 9000 yr b p late quaternary vegetation has been in dynamic equilibrium with a relatively constant flora south of 33 n on upland interfluves along the northern gulf coastal plain peninsular florida and west central mexico

observation and modelling of the saint etienne de tinee landslide using sar interferometry abstract six different interferograms of the la clapiere landslide were derived from ers 1 sar images during the period aug 20 sept 4 1991 the coherence of the associated images is shown to remain significant over most of the surface of the landslide during the two weeks of the survey the interferograms are remarkably similar and indicate steady state displacements over at least 12 days the displacement field derived from the interferograms is shown to be characterized by a non uniform displacement gradient from top to bottom and reveals a significantly faster motion of the western part of the landslide the amplitude of the motion deduced from interferometry is shown to be in good agreement with ground measurements finally sar interferometry is shown to be able to evidence small scale instabilities which may not be observed with discrete ground measurements

distributed acquisition characterization and process analysis of multi field information in slopes the slope is a multiphase composite system including solid liquid and gas phases slope stability changes under the actions of stress temperature and seepage slopes will be very prone to landslide if in an unstable state in this paper considering the contributions of different fields to the landslide the distributed acquisition characterization and stability analysis of multi field information from slopes was studied systematically using distributed fiber optic sensing dfos technology a sensing system based on dfos was designed and developed for multi field information monitoring including stress temperature seepage and deformation the corresponding methods for data processing identification and methods for characterization description are also proposed on this basis the evolution of the slope is analyzed finally monitoring results of the dfos system from the majiagou landslide are shown as a case study for verification

sedimentological and micropaleontological detection of turbidite muds in hemipelagic sequences an example from the late pleistocene levee of monterey fan central california continental margin abstract undetected turbidite muds in hemipelagic sequences confound biostratigraphic and paleo oceanographic interpretation of continental margins we show that turbiditic muds can be distinguished from hemipelagic muds sedimentologically based on recognition of grading in mean silt particle size coarseness of silt mean size and particle size frequency distributions of the silt fraction further we show that the fossil assemblages in turbidite muds are hydraulically sorted and subtly altered lastly we demonstrate that inclusion of sorted fossil faunas in high resolution biostratigraphy and paleo oceanography leads to incorrect interpretation ten mg samples were taken at one cm intervals from beneath to above the megascopic portion of the five turbidites from the western levee of monterey fan of the central californian continental margin the silt fraction was analyzed in an electronic particle counter to determine the particle size distribution four turbidites grade upward from visually distinct well sorted silt layers bouma t d through megascopically unrecognizable fining upward turbiditic muds ranging from 5 2 to 6 4 in mean diameter to an ungraded hemipelagic interval that ranges in mean size from 6 4 to 6 7 hemipelagic mud directly overlies the turbiditic silt of one turbidite foraminifers were picked from three samples taken from bottom to top of each turbidite unit the specimens were measured for length of long intermediate and short axes to determine shape and size results indicate that benthonic and planktonic foraminifers are hydraulically sorted in turbiditic muds hemipelagic muds contain benthonic tests that are large and variable in size whereas turbiditic muds and silts contain specimens that are small and similar in size planktonic foraminifers also are sorted by size in turbiditic samples the sorting subtly alters the relative species frequencies in turbiditic assemblages compared to those in hemipelagic muds biostratigraphic samples in a piston core from the fan levee were tested using silt size parameters to determine if any samples lay within undetected turbiditic muds we recognized seven such turbiditic samples and successfully resolved two latest pleistocene datums after rejecting the sorted fossil faunas

geochemical evidence for sediment provenance in mudstones and fossil poor wackestones upper jurassic majorca island terra nova 24 437 445 2012 abstract the notion that diagenetic imprint on ancient carbonates significantly compromises palaeoenvironmental interpretations is revealed as an oversimplification the enigmatic case at the core of this research is an extended homogeneous macrofossil poor deposit showing distinctive dark brown colour and very fine grain size aumedra fm majorca island this markedly contrasts with standard ammonitico rosso ar facies known from jurassic epioceanic swells geochemical analysis of matrix micrite carbonate cements and belemnite rostra are used to interpret the aumedra carbonates stable carbon and oxygen isotopes and elemental abundance are compared with data from under and overlying deposits and coeval sections conspicuously higher than expected c and o isotope signature together with strontium enrichment and a typically low iron and manganese concentrations favour a distant shallower probably aragonitic sedimentary supply modern and ancient examples of carbonate deposition are integrated with possible hydrodynamic conditions justifying transport over the studied area a potential ne source is envisaged terra nova 00 1 9 2012

new insights into geochemical behaviour in ancient marine carbonates upper jurassic ammonitico rosso novel proxies for interpreting sea level dynamics and palaeoceanography elemental concentrations in phanerozoic sea water are known to fluctuate both in time and space with regard to carbonates precipitated from marine fluids elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non equilibrium as well as post depositional alteration processes to assess the potential of carbonate elemental chemostratigraphy seven upper jurassic sections were investigated along a proximal to distal transect across the south east iberian palaeomargin the aim was to explore stratigraphic and spatial variations in calcium strontium magnesium iron and manganese elemental abundances the epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint in contrast the epioceanic geochemical record agrees with reconstructed open marine sea water values reflecting a moderate degree of syn depositional to early marine pore water diagenesis establishing a fair degree of preservation of matrix micrite a thorough statistical approach was applied and elemental associations tested for their environmental significance principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium iron and strontium abundances processes related to early diagenetic nodulation in ammonitico rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice the clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the late jurassic the investigation of potential time fluctuation of geochemical patterns was approached through variogram computation the observed temporal behaviour is most likely to be forced by relative sea level dynamics reflecting late jurassic palaeoceanographic conditions and potential planetary interactions the data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors

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