an early carboniferous paleomagnetic pole for gondwanaland new results from the mount eclipse sandstone in the ngalia basin central australia paleomagnetism of fourteen diamond drill cores from the uppermost devonian lower carboniferous mount eclipse sandstone in the ngalia basin central australia has been studied the samples were oriented using the borehole directions bedding planes identified in the drill cores and regional bedding attitudes three magnetic remanent components have been revealed 1 a drilling induced low to moderate temperature remanence c1 from all the drill cores which is oriented parallel to the drill cores and is most likely a combination of isothermal remanent magnetization and piezoremanent magnetization 2 a moderate to high temperature syndeformational overprint c2 d 226 7 i 82 3 95 6 2 k 68 9 in 65 samples from nine drill cores which was probably acquired during the mid to late carboniferous mount eclipse movement and 3 a moderate to high temperature likely primary remanence c3 d 057 1 i 36 9 95 9 6 k 29 6 from 64 samples in nine drill cores which exhibits a positive fold test c2 and c3 are found only in reddish siltstones and sandstones whereas c1 is best developed in grey reduced sandstones and siltstones a palynological examination gives an early to mid visean early carboniferous age of deposition for samples carrying the interpreted primary component c2 gives a mid to late carboniferous pole at 32 1 s 119 5 e with a95 11 9 which is in agreement with results of a previous study on surface outcrops c3 when combined with results from one drill core in a previous study gives a visean pole at 37 6 s 52 6 e with a95 8 7 this pole suggests a south polar position for central africa during the early carboniferous and therefore indicates the existence of a large ocean between gondwanaland and laurussia at that time the paleo south pole shifted from central africa in the early carboniferous 340 5 ma to east antarctica in the mid to late carboniferous 310 10 ma with a minimal continental drifting rate of 15 20 cm yr

authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

ichnological record of deep sea palaeoenvironmental changes around the oceanic anoxic event 2 cenomanian turonian boundary an example from the barnasiowka section polish outer carpathians abstract trace fossil assemblages including planolites thalassinoides palaeophycus taenidium chondrites and trichichnus have been determined in the upper cenomanian turbiditic deep water succession corresponding to the pre oae 2 interval in the barnasiowka ostra gora section the skole nappe polish outer carpathians these assemblages indicate that oxygenation within sediment fluctuated from oxic to dysoxic zone the overlying uppermost cenomanian organic rich facies bonarelli equivalent horizon corresponding to the main interval of the oae 2 contains black shale layers devoid of trace fossils representing anoxic euxinic events and green shales that include chondrites planolites and thalassinoides recording dysoxic intervals three subintervals phases within the oae 2 sediments have been distinguished in the barnasiowka section based on trace fossil diversity ichnofabrics and chemical redox indices these phases correspond to intervals with various intensity of sea floor oxygenation ichnofabrics within the oae 2 succession was also controlled by consistency of sediment post oae 2 interval recorded by the earliest turonian red and green siliceous manganiferous shales and two fe mn layers represent sediments deposited in well oxygenated conditions under extremely low sedimentation rate most of the shales are parallel laminated and they do not include any benthic microfossils and trace fossils however some of the red and green layers display cryptic bioturbation these features are related to food scarcity cessation of gravity flows unfavorable characteristics of bottom water and a low consistency of substrate

ice age at the middle late jurassic transition a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine invertebrate fauna ammonites and isotopic thermometry 18o values of shark tooth enamel indicates a severe cooling at the middle late jurassic transition mljt about 160 ma ago the magnitude of refrigeration 1 3 c for lower middle latitudes and its coincidence in time with an abrupt global scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time ice sheets may have developed over the high latitude mountainous regions of far east russia the drastic cooling just post dated the middle late callovian widespread deposition of organic rich marine sediments e g northwestern europe central atlantic and arabian peninsula this thermal deterioration can thus be ascribed to a downdraw in atmospheric co2 via enhanced organic carbon burial which acted as a negative feedback effect i e the inverse greenhouse effect the glacial episode of the mljt climaxed in the late callovian lasted about 2 6 myr and had a pronounced asymmetrical pattern composed of an abrupt 0 8 myr temperature fall opposed to a long term 1 8 myr stepwise recovery the glacial conditions at the mljt reveal that atmospheric co2 levels could have dropped temporarily to values lower than 500 ppmv during mesozoic times

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

oroclinal bending of the southern sierra nevada batholith structural magmatic and isotopic features of the southern sierra nevada batholith are deflected clockwise with respect to its central and northern parts directions of magnetization at three localities in the southern sierra nevada are progressively deflected this is consistent with the hypothesis that the region was tectonically rotated in an orocline no paleomagnetic deflection was observed northwest of the white wolf kern canyon fault system oroclinal bending ofa block bounded by the san andreas garlock and white wolf kern canyon faults may have occurred before about 16 x l06 years ago the deformation may have been a response to shear at the western boundary of the north american plate caused by oblique subduction

mesozoic paleomagnetism and northward translation of the baja california peninsula paleomagnetic data from cretaceous igneous and sedimentary rocks of the peninsular ranges and continental borderland of the baja california peninsula yield an average pole position of 83 n 344 e a95 3 4 suggesting that the peninsula as a whole has moved northward 11 and rotated 32 clockwise with respect to the north american craton since cretaceous time only a small portion of this movement is due to the neogene opening of the gulf of california results from stratified rocks giving both positive and negative fold tests are included in the average cretaceous pole the rocks that fail fold tests have been deformed and remagnetized by nearby intrusives that are only slightly younger unconnected directions from these sites closely match corrected directions from sites where the fold tests are positive oceanic rocks were also sampled in the continental borderland from upper triassic and upper jurassic tectonostratigraphic terranes which are apparently allochthonous with respect to the western baja peninsula and each other these oceanic rocks show magnetizations indicating low paleolatitudes although the hemisphere of origin is presently unknown the cretaceous rocks of the baja california peninsula may have originally formed adjacent to the now truncated continental margin along the northern middle america trench northward transport of the peninsula probably occurred by transcurrent faulting associated with oblique subduction of the farallon plate beneath western north america between late cretaceous and late miocene time

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

δ18o po43 and δ18o co32 from belemnite guards from eastern europe implications for palaeoceanographic reconstructions and for the preservation of pristine isotopic values abstract the oxygen isotopic composition of coexisting carbonate and phosphate from belemnite rostra was measured according to well established techniques in 42 samples of early and middle jurassic age and in five samples of oyster shells most of the samples come from various locations in the western carpathians of slovakia and ukraine and from central poland three samples come from the isle of skye the phosphate content of belemnite rostra though variable is systematically very low consistently lower than about 0 3 however this phosphate concentration is close to that found in shells of modern marine organisms including pelecypods gastropods and sepia cuttlebones which in some way could be considered the modern belemnite counterpart the measured oxygen isotopic composition of carbonate is within the normal range of values obtained from these fossils ranging from about 1 3 to about 0 6 pdb 1 with the exception of three samples the 13 c values range from about 0 8 to about 2 8 pdb 1 with the single exception of one sample from the isle of skye the oxygen isotopic composition of phosphate from belemnite rostra ranges from 19 8 to 24 9 v smow 22 of the samples measured showing 18 o values equal to or heavier than 23 0 in contrast the oyster values are considerably lighter in the case of both carbonate and phosphate 18 o enriched values can hardly be related to diagenetic processes that normally cause an oxygen isotope shift towards light values if deposition temperatures are calculated from the heavily enriched values by means of the equation of longinelli and nuti earth planet sci lett 19 1973 373 376 and assuming the 18 o of jurassic ocean water to be equal to 1 taking into account the lack of ice caps during the jurassic the obtained temperatures range from about 8 c to about zero these temperatures are obviously unreliable when mesozoic palaeoceanographic conditions and palaeoclimate are taken into account two different hypotheses are suggested to explain these results other hypotheses being rejected as unreliable 1 phosphate derived from the decaying organic matter of belemnites might have been introduced into belemnite rostra by early diagenetic fluids if the phosphate of belemnite organic matter was isotopically heavy as happens nowadays in the flesh of molluscs the inflow of this phosphate into the rostra could be responsible for the very positive 18 o values shown by many belemnite rostra this hypothesis is suggested by h w 2 previous oxygen isotope measurements on upper cretaceous belemnites yielded 18 o values very close to the most positive values obtained from lower tertiary pelecypods and fish teeth which are known to precipitate their phosphate under isotopic equilibrium conditions with seawater these data suggest the possibility that the phosphate in belemnite rostra is primary phosphate so that the very positive data reported here can be considered the result of good preservation of the pristine isotopic composition of primary phosphate consequently the only way to explain the very positive 18 o values is to consider the oxygen isotopic composition of jurassic ocean water to be more positive than nowadays by at least 3 this hypothesis is suggested by a l and a d m

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

palaeoceanography and biogeography in the early jurassic panthalassa and tethys oceans abstract a first conceptual palaeoceanographic model for the early jurassic panthalassa and tethys oceans is outlined in the present paper the new palaeoceanographic model uses fundamental physic oceanographic principles known from the modern world and a global palaeogeographic reconstruction for the early jurassic to examine the long term response of the panthalassic and tethyan fossil invertebrate faunas to the proposed surface ocean circulation analysis of palaeobiogeographical data ostracods ammonites brachiopods and bivalves has enabled circulation changes to be reconstructed over the studied period in some detail panthalassic circulation pattern shows an almost hemispherical symmetric pattern with the development of the two large subtropical gyres that rotates clockwise in the northern hemisphere and anti clockwise in the southern hemisphere surface circulation in the tethyan ocean is dominated by monsoonal westerly directed equatorial surface currents that reached its western corner and droved them off to the north along the northern side of the tethys ocean during summer and in opposite direction during the winter

drilling induced remanence in carbonate rocks occurrence stability and grain size dependence summary a strong grouping of the directions of natural remanent magnetization in a collection of ordovician limestones and dolomites prior to correction for the in situ orientation of the samples led us to suspect the presence of a substantial spurious magnetization acquired during sample collection and preparation a close correspondence between the directions of the remanence vectors and the direction of the ambient magnetic field during sawing and drilling of the samples suggested that the remanence was dominated by a component acquired during cutting of the samples ten specimens of the camp nelson limestone and shakopee dolomite were demagnetized to 100 mt given an anhysteretic remanence along their axes and then sawed again a substantial magnetization parallel to the ambient field during cutting was acquired by all of the specimens and the resultant directions deviated by 7 70 from the direction of the anhysteretic magnetization stepwise alternating field and thermal cleaning to 60 mt and 400 c respectively failed to remove preferentially the cutting induced magnetic contamination since the fraction of magnetite grains cut during drilling and sawing must be a linear function of grain size modified lowrie fuller tests were carried out and the results are interpreted to indicate the presence of a multidomain magnetite fraction in the shakopee dolomite camp nelson limestone and oregon dolomite ratios of initial to anhysteretic susceptibility dxarm correlate well with the angular deviation of magnetic directions produced by sawing this indicates that acquisition of drilling induced remanence is a function of magnetite grain size compatible with the notion that the drillinginduced component resides in large magnetite grains which have been cut

drilling induced isothermal remanent magnetization the recovery of core samples is important in petroleum exploration mineral exploration and scientific drilling projects and often complete orientation of the samples azimuth and plunge is desirable recovered cores are usually not azimuthally oriented because of the costs associated with deployment and operation of downhole orientation tools inexpensive paleomagnetic orientation methods have been used with considerable success in the borehole environment van der voo and watts 1978 kodama 1984 bleakly et al 1985a b evans and mailol 1986 layer et al 1988 mcwilliams and pinto 1988 in some cases the technique has been hampered by secondary magnetizations associated with the drillstring and or coring tool magnetizations which have partially or completely overprinted the primary and secondary magnetizations used for orientation

the behaviour of manganese in atlantic carbonate sediments abstract manganese porewater and solid phase data are considered from two different atlantic carbonate sediments both with good geochemical characterisation the first case is a continuously accumulated alternating pelagic marl carbonate ooze where there is a correlation in post oxic conditions between mn ii porewater levels and an acetate leachable mn fraction of the sediment this leachable mn appears to have an association with calcite and in this example the leached residue mn content approximates to that of shale in the second case a very recent compositionally homogeneous calcareous turbidite is underlain by mn oxyhydroxide at the former sediment surface which is now acting as a source of mn ii by reduction sorption of mn by the turbidite sediment and shale like leached residue mn levels in anoxic conditions are again observed as mn ii diffuses towards present oxic conditions although no unique equilibrium is achieved similar older buried turbidites have concentration decreases in solid phase mn content preserved from bottom to top as relict evidence that this process has occurred in these turbidites 54 64 of the total mn is leachable by the acetate method and therefore presumed to be sorbed by calcite the oldest example has persisted for 125 kyr it is suggested that the slow breakdown of metastable mn oxyhydroxide and sorption of mn ii to calcite surfaces are important controls on the behaviour of mn in pelagic carbonates in mildly reducing conditions where accumulation fluctuations occur these processes act together with accumulation to limit overall mn migration and to prevent the large mn enrichments seen near the sediment surface in more reducing environments

pliocene shallow water paleoceanography of the north atlantic ocean based on marine ostracodes abstract middle pliocene marine ostracodes from coastal and shelf deposits of north and central america and iceland were studied to reconstruct paleotemperatures of shelf waters bordering portions of the western boundary current system including the gulf loop current florida current gulf stream and north atlantic drift factor analytic transfer functions provided pliocene august and february bottom water temperatures of eight regions from the tropics to the subfrigid the results indicate 1 meridional temperature gradients in the western north atlantic were less steep during the pliocene than either today or during late pleistocene isotope stage 5e 2 tropical and subtropical shelf waters during the middle pliocene were as warm as or slightly cooler than today 3 slightly cooler water was on the outer shelf off the southeastern and mid atlantic coast of the u s possibly due to summer upwelling of gulf stream water 4 the shelf north of cape hatteras north carolina may have been influenced by warm water incursions from the western edge of the gulf stream especially in summer 5 the northeast branch of the north atlantic drift brought warm water to northern iceland between 4 and 3 ma evidence from the iceland record indicates that cold east greenland current water did not affect coastal iceland between 4 and 3 ma 6 middle pliocene north atlantic circulation may have been intensified transporting more heat from the tropics to the arctic than it does today

geologic setting and lithologic column of the cajon pass deep drillhole the cajon pass deep drillhole penetrates a late tertiary basin developed on crystalline basement in the sw mojave desert 4 km from the san andreas fault cores continuous cuttings and geophysical logs from phase i show great diversity in rock types structure and alteration the hole encountered cajon formation arkoses granodiorite tonalite unusual megacrystic granite and augen gneiss granitic and pelitic gneisses with quartzite quartzofeldspathic orthogneiss cut by sheets of hornblende gabbro and interlayered mafic and quartzofeldspathic orthogneisses with rare calcsilicate intervals foliation and compositional layering have low dips throughout the column and layered gneisses contain 10 cm scale recumbent folds faults and alteration zones bound several rock units with low apparent dips basement cores are typically cut by steep fractures 1 mm wide that contain zeolites calcite or chlorite epidote fractures and faults decrease in abundance with depth

57fe mossbauer spectroscopic analysis of deep sea pelagic chert effect of secondary alteration with respect to paleo redox evaluation abstract chemical states of iron in the pre jurassic pelagic deep sea cherts are used as one of redox indicators of lost deep oceans e g the permian triassic boundary case primarily red hematite bearing cherts were often altered secondarily into greenish gray cherts we examined the pattern of secondary change in chemical state of iron associated with color change in the middle triassic chert beds at hisuikyo in central japan by 57fe mossbauer spectroscopy three sets of chert bed with the lateral color change from red to greenish gray were analyzed the analyses confirmed that the red cherts contain hematite paramagnetic fe3 and paramagnetic fe2 whereas the greenish gray cherts contain paramagnetic fe3 and paramagnetic fe2 without hematite the greenish gray parts contain larger amounts of paramagnetic fe2 component of amorphous siderite like mineral in contrast to the red parts have lesser amounts these results confirmed that the primary hematite has changed into paramagnetic fe2 bearing minerals in accordance with the color change by the secondary alteration further comparison with the pyrite bearing primary black to dark gray cherts was discussed with respect to the evaluation for primary redox change in the past oceans

redox condition of the late neoproterozoic pelagic deep ocean 57fe mossbauer analyses of pelagic mudstones in the ediacaran accretionary complex wales uk abstract we report geological and geochemical analysis of neoproterozoic pelagic deep sea mudstones in an accretionary complex in lleyn wales uk ocean plate stratigraphy at porth felen nw lleyn consists of mid ocean ridge basalt 4 m bedded dolostone 2 m black mudstone 5 m hemipelagic siliceous mudstone 1 m and turbiditic sandstone 15 m in ascending order the absence of terrigenous clastics confirms that the black and siliceous mudstone was deposited in a pelagic deep sea based on the youngest u pb age 564 ma of detrital zircons separated from overlying sandstone the deep sea black mudstone was deposited in the late ediacaran the 5 m thick black mudstone contains the following distinctive lithologies i black mudstone with thin pyritic layers 0 8 m ii alternation of black mudstone and gray dark gray siliceous mudstone 2 4 m iii thinly laminated dark gray shale 1 m and iv black mudstone with thin pyritic layers 1 m 57 fe mossbauer spectroscopy confirms that these black mudstones contain pyrite without hematite in contrast red bedded claystones no younger than 542 ma in the neighboring braich section contain hematite as their main iron mineral these deep sea mudstones in the lleyn peninsula record a change of redox condition on the pelagic deep sea floor during the ediacaran the black mudstone at porth felen shows that deep sea anoxia existed in the late ediacaran the eventual change from a reducing to an oxidizing deep sea environment likely occurred in the late ediacaran ca 564 542 ma

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

paleomagnetism of the roskruge and gringo gulch volcanics southeast arizona paleomagnetic data were obtained from nine cooling units of the late cretaceous 72 ma roskruge volcanics and from 25 flows in the lower paleocene gringo gulch volcanics both from southeastern arizona alternating field demagnetization successfully erased the infrequent secondary components of magnetization the paleomagnetic pole position obtained from the roskruge volcanics is at 73 6 n 176 0 e with dp 6 2 and dm 8 8 the gringo gulch volcanics pole position is at 77 0 n 201 0 e with dp 1 2 and dm 1 7 in conjunction with other recently published paleocene and eocene paleomagnetic poles these data provide details of north american apparent polar wander during the laramide orogeny 80 to 40 ma an episode of rapid apparent polar wander from the cretaceous pole position in the bering strait to the eocene pole position near the present rotation axis occurred during that interval of time the initiation of this episode of apparent polar wander appears to be coincident with the major plate reorganizations which occurred at the onset of the laramide orogeny

palaeowind patterns during the latest jurassic earliest cretaceous in gondwana evidence from aeolian cross strata of the botucatu formation brazil abstract the direction of sediment transport in the aeolian sandstones of the botucatu formation latest jurassic earliest cretaceous of the parana basin has been interpreted on the basis of cross strata dip directions which allowed the reconstruction of regional wind patterns in midwestern gondwana regionally cross strata dip directions indicate variations of palaeowind directions across the outcrop area of the botucatu palaeoerg the northern portion of the palaeoerg was characterized by palaeowinds blowing from the nne whereas the southern portion was under the influence of palaeowinds coming from the sw a wind convergence zone occurred at palaeolatitudes around 24 to 26 s the identified wind pattern agrees with general circulation models for the late jurassic which predict that during the summer months december through february strong monsoonal winds to the s existed at low latitudes in gondwana southerly winds converged at the itcz at around 24 s with winds blowing toward the northeast

palaeoceanographic and palaeoclimatic reorganization around the middle late jurassic transition abstract a middle to upper jurassic succession of submarine hardgrounds overlain by nodular limestones is exposed in the jura mountains and in the helvetic of the swiss alps these sediments were accumulated along the northern shelf of the east west trending tethys seaway submarine hardgrounds and nodular limestones were also formed on the brianconnais high today outcropping in the middle penninic nappe pile of the alps hardgrounds record strong and persistent current activity along the northern tethys shelf and on the brianconnais high during the callovian and early oxfordian the transition from hardgrounds to nodular limestones corresponds to a major reorganization of tethys oceanography the change occurred in plicatilis ammonite zone middle oxfordian carbon isotope stratigraphy calibrated against an ammonite dated reference section in the french subalpine basin serves as a correlation tool between ammonite dated sections and successions with poor biostratigraphic resolution correlation demonstrates that the end of hardground formation was synchronous over wide parts of the northern tethys the change in shelf sedimentation coincides with a positive carbon isotope excursion with an amplitude of 1 5 the change in c isotope stratigraphy indicates that observed reorganization of current patterns along the northern tethys shelf was coupled with global change in oceanography and climate we propose that the change in northern tethys sedimentation was caused by opening of new seaways at a time of progressive collapse of pangaea

atlantic water flow pathways revealed by lead contamination in arctic basin sediments contaminant lead in sediments underlying boundary currents in the arctic ocean provides an image of current organization and stability during the past 50 years the sediment distributions of lead stable lead isotope ratios and lead 210 in the major arctic ocean basins reveal close coupling of the eurasian basin with the north atlantic during the 20th century they indicate that the atlantic water boundary current in the eurasian basin has been a prominent pathway that contaminant lead from the laptev sea supplies surface water in the transpolar drift and that the canadian and eurasian basins have been historically decoupled

paleomagnetism of sedimentary rocks from and near the dosecc cajon pass well southern california as part of a larger study of the geologic and tectonic history of the cajon pass area we conducted paleomagnetic studies on sedimentary rocks recovered from the cajon pass dosecc well and adjacent surface exposures from unit 5 of the late early to middle miocene cajon fm a comparison of the magnetic polarity stratigraphy of the surface and the core sections suggests that they do not match well which may imply that the rocks at depth have been deformed so that simple extrapolation from the surficial geology to depth is not possible although tectonic rotation cannot be inferred from the samples from the core a clockwise rotation of 30 8 9 was found in unit 5 of the cajon fm near the well site at the surface which is consistent with the results from the same unit 2 km to the west in contrast the early late to late early miocene crowder fm across the squaw peak fault and the youngest unit unit 6 of the cajon fm at the northwestern end of the formation have not been rotated the rotation of unit 5 near the squaw peak fault is thus probably local caused by drag associated with the fault

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

correlation of reefal oxfordian episodes and climatic implications in the eastern paris basin france oxfordian reefal episodes of lorraine and burgundy have a long time been considered as contemporaneous biostratigraphic data and sequential evolutions peculiar to each region indicate their structural autonomy during oxfordian times a north south oriented well logging transect shows that during the middle oxfordian a shallow reefal platform developed in lorraine while thin deeper deposits occurred in burgundy in spite of their different ages reefal episodes of middle oxfordian in lorraine and upper oxfordian in burgundy exhibit a broadly similar vertical evolution of coral communities during the late oxfordian the contemporaneous occurrence of a diversified assemblage in the burgundy region a colder coral assemblage characterized by eurytopic genera and the decrease in seawater isotopic temperatures in lorraine can be explained by a shift in trophic conditions a climatic change related to structural rearrangements in this strategic place and a modification of oceanic circulations between the arctic and the tethyan regions

paleoclimatic control of biogeographic and sedimentary events in tethyan and peri tethyan areas during the oxfordian late jurassic abstract the paleobiogeographical distribution of oxfordian ammonites and coral reefs in northern and central europe the mediterranean area north and east africa and the middle east and central asia is compared with the distribution in time and space of the most important lithofacies interest in the oxfordian is focused on changes in facies and in biogeographical patterns that can be interpreted as the results of climatic events paleotemperature trends inferred from oxygen isotopes and paleoclimatic simulations are tested against fossil and facies data a late callovian early oxfordian crisis in carbonate production is indicated by the widespread absence of lower oxfordian reefal formations there is a gap hiatus in deposition on epicontinental platforms with middle oxfordian deposits resting paraconformably on upper callovian while shales accumulated in adjacent intracratonic basins simultaneously in mediterranean tethys radiolarites accumulated in deep troughs while rosso ammonitico facies formed on pelagic swells however deposition on swells was also discontinuous with numerous gaps hiatuses and sequences that are much reduced in thickness middle callovian deposits are generally overlain by middle oxfordian limestones the dearth of carbonates is consistent with a cooling event lasting about 1 my by the middle oxfordian a warming leading to greenhouse type conditions is suggested on the basis of both biogeographical mostly coral reef distribution and geochemical data carbonates spread onto an extensive european platform while radiolarites reached a maximum development in the mediterranean tethys two distinct latitudinal belts with seemingly different accumulation regimes are therefore inferred similar latitudinal belts were also present in the late oxfordian when carbonates were widespread the distribution of reefal facies in the late oxfordian early kimmeridgian fits relatively well with gcms simulations that imply low rainfall in the tethyan mediterranean area and slightly higher precipitation in central and northern europe local salinity variations reflecting more arid or humid conditions may bias the paleotemperature signal inferred from 18o values biogeographical and facies distributions combined with 18o values unravel the ambiguity and support a late callovian early oxfordian cooling followed by warming in the later oxfordian

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

trace elements in natural metallic iron from disko island greenland the largest occurrence of natural metallic iron on earth is on the island of disko greenland metallic iron is found there in a variety of different types from small metal particles in basalts to large meter sized blocks we have studied three different types of metallic iron small metal spherules 300 m in basaltic magma larger metal grains 300 m 3 mm often composed of aggregates of smaller particles in similar host rocks and massive iron lumps up to several tons analytical data for 13 siderophile elements in samples from these three types are presented all metals analysed have a distinctly crustal pattern of siderophile elements high co ni re ir or w ir ratios clearly demonstrate that a meteoritic origin for the metallic iron must be excluded since the co ni and re ir ratios are approximately chondritic in the upper mantle of the earth a mantle origin for the disko metals can also be ruled out this supports earlier petrological and geological evidence that the metallic iron was formed through reduction of basaltic magma by carbon derived from tertiary shales and coals significant differences in absolute and relative abundances of siderophile elements occur among the three kinds of metals the strongly siderophile elements e g ir re ni increase in concentration from the small metal spherules through the larger grains to the massive iron lumps the contents of less strongly siderophile elements p w ga decrease in the same sequence evidence is presented that the small metal spherules are formed by in situ reduction larger iron metal grains and massive iron lumps are composed of small spherules accumulated by gravitational settling in a magma reservoir these metal cumulates have extracted highly siderophile elements from a larger volume of basaltic melt

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

preservation of delta 18 o and delta 13 c in belemnite rostra from the jurassic early cretaceous successions stratigraphic collection of 263 belemnite rostra guards from jurassic to lower cretaceous sediments in the moscow area of russia northern germany england new zealand and morocco were analyzed to determine temporal variations in their delta 18 o and delta 13 c as a proxy for isotopic composition of surface seawater internal structures of the rostra were studied using cathodoluminescence and sem techniques their trace element fe mn mg and sr and the stable carbon and oxygen isotope compositions the average stratigraphic resolution is about 1 ma these samples represent a broad range of paleolatitudes and paleoceanographic settings ranging from 42 degrees n to 82 degrees s covering boreal to subtropical brackish to open marine shelf paleoenvironments the rostra originally contained domains enriched in organic matter that were later replaced by luminescent diagenetic calcite thereby generating an impression of seasonal growth rings diagenetic calcite accounts for up to 6 8 percent of the rostrum the trace element content of the rostra range from 227 to 3935 ppm for mg 379 to 1514 ppm for sr and up to 305 and 3662 ppm for mn and fe respectively however selective drilling of only primary calcitic domains resulted in 90 percent of all analyzed samples to fall within the range of trace element values typical for modern low mg calcite shells the chemical and textural data suggest that the primary calcite of the rostra is well preserved as is its isotopic signature the delta 13 c and delta 18 o measurements define oscillating temporal bands of about 3 to 4 per mil width around more or less modern marine values of 2 and 1 per mil respectively oxygen isotopes in the well preserved rostra most likely reflect temperature variations within a approximately 14 or 8 degrees c range the observed 3 to 4 per mil spread of values between contemporaneous specimens which is comparable to the scatter of data reported for modern low mg calcitic brachiopod shells probably reflects the diversity of local ecosystems although some of the spread may be due to real short term temporal variations within single biozones the delta 13 c values of the rostra define a band similar to that of the oxygen isotopes and the temporal oscillations of both isotope curves are commonly in phase the above dataset complemented by the results of jones jenkyns and hesselbo 1994 and jones and others 1994 yields a composite delta 18 o and delta 13 c variations in belemnite guards for the entire jurassic early cretaceous interval for delta 18 o the oscillating band indicates that the most negative values occur at times of independently postulated global and or regional anoxic events such as those in the toarcian and kimmeridgian as well as the aptian these oaes appear to be characterized by up to 10 degrees c higher seawater temperatures than the intervening background times the delta 13 c record shows 13 c depletion for the kimmeridgian event but enrichment for the other two suggesting that the delta 13 c temporal oscillations and oaes are not simply a reflection of surficial productivity due to operation of the biological pump but rather of changing oceanic circulation patterns due to variations in latitudinal surface temperature gradients

trace fossil model for reconstruction of paleo oxygenation in bottom waters recognition of fluctuations in the degree of paleo oxygenation of bottom waters recorded in fine grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions general sedimentary fabric composition of trace fossil assemblages and burrow size and crosscutting relationships have been incorporated into a trace fossil tiering model that permits detailed reconstruction of changes in paleo oxygenation of bottom waters applications of this model to the miocene monterey formation california and the cretaceous niobrara formation colorado indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body fossil information

the shifting biogeography of reef corals during the oxfordian late jurassic a climatic control until recently the jurassic was thought to have been a period characterised by a predominantly warm and equable climate during the oxfordian a time span of six million years in the late jurassic the distribution of tropical coral reefs was limited to about 35 n and near to 25 s however in middle oxfordian time coral reefs were abundant only at higher latitudes and almost entirely missing near the equator during that time the area of maximum reef development had shifted poleward to a belt lying between 20 n and 35 n leaving hardly any coral formations at the lower inner tropical latitudes after demise towards the end of middle oxfordian time the low latitude reefs recovered during the late oxfordian accompanied by a southward migration of reef corals in the northern hemisphere as suggested by stable isotope and palynological data the faunal migration can be correlated with a significant rise in seawater temperature during the middle oxfordian

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

uranium diagenesis in sediments underlying bottom waters with high oxygen content we measured u in sediments both pore waters and solid phase from three locations on the middle atlantic bight mab from the eastern margin of the united states a northern location on the continental shelf off massachusetts oc426 75 m water depth and two southern locations off north carolina en433 1 647 m water depth and en433 2 2648 m water depth these sediments underlie high oxygen bottom waters 250 270 m but become reducing below the sediment water interface due to the relatively high organic carbon oxidation rates in sediments en433 1 212 mol c cm2 y oc426 120 10 mol c cm2 y en433 2 33 mol c cm2 y pore water oxygen goes to zero by 1 4 1 5 cm at en433 1 and oc426 and slightly deeper oxygen penetration depths were measured at en433 2 4 cm all of the pore water profiles show removal of u from pore waters calculated pore water fluxes are greatest at en433 1 0 66 0 08 nmol cm2 y and less at en433 2 and oc426 0 24 0 05 and 0 13 0 05 nmol cm2 y respectively solid phase profiles show authigenic u enrichment in sediments from all three locations the average authigenic u concentrations are greater at en433 1 and oc426 5 8 0 7 nmol g and 5 4 0 2 nmol g respectively relative to en433 2 4 1 0 8 nmol g this progression is consistent with their relative ordering of reduction intensity with greatest reducing conditions in sediments from en433 1 less at oc426 and least at en433 2 the authigenic u accumulation rate is largest at en433 1 0 47 0 05 nmol cm2 y but the average among the three sites on the mab is 0 2 nmol cm2 y pore water profiles suggest diffusive fluxes across the sediment water interface that are 1 4 1 7 times greater than authigenic accumulation rates at en433 1 and en433 2 these differences are consistent with oxidation and loss of u from the solid phase via irrigation and or bioturbation which may compromise the sequestration of u in continental margin sediments that underlie bottom waters with high oxygen concentrations previous literature compilations that include data exclusively from locations where o2 bw 150 m suggest compelling correlations between authigenic u accumulation and organic carbon flux to sediments or organic carbon burial rate sediments that underlie waters with high o2 bw have lower authigenic u accumulation rates than would be predicted from relationships developed from results that include locations where o2 bw 150 m

oscillating redox conditions in the middle late jurassic alpine tethys insights from selected geochemical indices and 57fe mossbauer spectroscopy abstract the middle late jurassic greenhouse conditions included co2 levels that have been estimated to be four to five times higher than they are presently by analysing the pattern of selected trace elements as redox proxies v u and mo and the variations in the chemical state of iron using 57fe mossbauer spectroscopy we demonstrate the occurrence of major changes in sediment redox conditions from the late bajocian through the late oxfordian in the pelagic environment of the alpine tethys in its carpathian domain our interpretation is based on analysis of siliceous limestones rich in radiolarians intercalated with red nodular limestones of ammonitico rosso type facies from the kri na nappe in the eastern part of the tatra mountains poland the presented redox potential eh values shows its changeable pattern along the section from 0 74 v to 0 16 v the low values of eh from 0 74 v to 0 4 v create the long term ca 7 myr trend of the medium scale fluctuations comprising the upper bajocian through the lower oxfordian interval of predominately grey and green radiolarian siliceous limestones this interval comprises the three short term less than 0 5 myr periods of slightly increasing eh from 0 35 v to 0 17 v observed in the uppermost bajocian lower bathonian and lower callovian as well as the significant changes in sediment redox conditions from oxic to dysoxic in the upper bajocian the overlying succession corresponding to the middle upper oxfordian ca 4 myr is characterized by red radiolarian siliceous limestones with positive eh values that indicate deposition under more oxic conditions than those during any other period in the study section the negative values of eh attributed to the upwelling periods coincide with the decreasing sea surface water temperature sst and increasing organic matter flux the largest negative shift is noted in the upper callovian which coincided with the cool climatic phase the positive eh values indicate oxic conditions due to the lowering of organic matter input coinciding with an increased sst caused by surface water stratification based on the observed long term variation in the redox we postulate thermally driven east west atmospheric circulation along the equatorial tethys ocean caused by the sharp contrast in sea surface temperature similar to the walker circulation operating across the modern pacific this phenomenon would have been the dominant periodical mode over the tropics and subtropics regions of the nw tethys during the middle late jurassic global warming reduces the long term strength of the mean tropical atmospheric circulation leading to sea water stratification near the surface and consequently lowering the organic matter flux however additional seaways of heat transport could also exist as they are associated with the opening closing of the hispanic corridor

nd isotope evidence for the evolution of the paleocurrents in the atlantic and tethys oceans during the past 180 ma the nd isotopic composition of atlantic and tethys seawater as deduced from marine phosphorites varied considerably during the past 180 ma the early tethys and central atlantic seawater from 180 to 160 ma ago early middle jurassic had a nd isotopic signature identical to that of the pacific end 6 suggesting that pacific seawater entered the newly forming tethys basin however with time continental runoff draining into the young basin became more important and led to a decrease in the nd isotopic composition and finally a decoupling from the pacific ocean during the late early cretaceous 120 90 ma ago atlantic and tethys seawater reached continental crust like nd isotopic composition values end 10 which could reflect high weathering rates induced by the warm and humid climate at that time in the time span between 80 and 50 ma late cretaceous early tertiary the nd isotopic composition of both tethys and atlantic seawater strongly increased towards pacific seawater values in the case of the atlantic ocean this change has been correlated with the opening of the south atlantic which enabled the more radiogenic pacific seawater to travel westwards around the southern edge of africa into the south and finally the north atlantic in the case of tethys seawater we have to assume that during this period large masses of pacific seawater entered the tethys again directly through the indian tethys seaway the renewed importance of this seaway might be related to the late cretaceous early tertiary first order global sea level highstand the most abrupt change towards lower more crust like values occurred in the early miocene 25 17 ma ago in the south and north atlantic as well as in the tethys during this period the143nd 144nd isotope ratios dropped from 0 5124 end 4 2 down to 0 5122 end 8 this change indicates a diminishing influx of pacif seawater into the atlantic and tethys oceans and can be correlated with the breakdown of the circum equatorial circulation patterns of the world oceans due to plate tectonics from 20 to 17 ma ago miocene the nd isotopic composition of the atlantic ocean increased again and reached values as high as 0 5123 end 6 6 whereas tethys seawater remained at low values this decoupling can be correlated with the incipient complete isolation of the tethys the nd isotopic composition was henceforth controlled by the continental runoff from surrounding land masses the major increase in the nd isotopic composition observed in the atlantic can be related to the opening of the drake passage and establishment of the circum antarctic current system this allowed pacific seawater to enter directly the south atlantic around antarctica a renewed drop in the nd isotopic composition of atlantic seawater during the late miocene can be related to the onset of north atlantic bottom water formation and its subsequent upwelling

paleomagnetic results from granitic basement rocks in the cajon pass scientific drillhole natural remanent magnetizations in granitic rocks intersected by the cajon pass scientific drillhole are a composite of two superimposed magnetizations one magnetization is a primary trm acquired in late cretaceous times upon initial cooling while the other is an irm induced by the coring device coring induced irm has obscured any pre coring vrm and thus core orientation using recent vrm was not possible primary inclinations are internally consistent and agree with expected values derived from the adjacent sierra nevada and southern california batholiths