reliability of palaeozoic palaeomagnetic poles and apwp of gondwanaland abstract a review of reliable palaeomagnetic data from gondwana palaeozoic rocks supports the apparent polar wander path apwp initially proposed by morel and irving this path or versions of it has recently gained favour with a number of groups the apwp suggests that during the mid palaeozoic gondwanaland was very mobile no palaeomagnetic pole position s has been yet reported that confirms the contentious segment of apwp from the late ordovician to the early silurian the apwp implies that the south pole moved rapidly from north africa in the ordovician to a position off southern south america by the silurian back to central africa by the early carboniferous and across gondwanaland to australia by the late carboniferous the distribution of palaeozoic tillites independently supports such a mobilistic gondwanaland the palaeomagnetic and tectonic evidence are compatible with the lachlan fold belt of australia having been in place since the mid devonian

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

an effect of dissolved nutrient concentrations on alkenone based temperature estimates the ratio of 37 carbon diunsaturated to diunsaturated and triunsaturated alkenones uk 37 produced by some haptophytes is widely used as a proxy for past sea surface temperatures however our isothermal culturing experiments with emiliania huxleyi clone ccmp372 show uk 37 values to also vary with nutrient availability and cell division rate these results provide a reasonable explanation for large isothermal variation in uk 37 values of single coccolithophorid strains grown in culture they also suggest that alkenone based estimates of past sea surface temperatures may have been influenced by dissolved nutrient concentrations as well as by temperature

palaeomagnetism of devonian ring complexes from the bayuda desert sudan new constraints on the apparent polar wander path for gondwanaland summary the approach of gondwana and or microplates derived from its northern margins towards laurentia and the closure of the intervening palaeo tethys is a controlling factor in the geodynamic evolution of the atlantic bordering continents during the early and mid palaeozoic however the currently available palaeomagnetic data for gondwana especially for the geodynamically critical silurian to devonian interval are still rather sparse and are compatible with a number of palaeogeographic scenarios in order to address this issue 114 samples 18 sites have been collected from a series of high level acidic intrusive rocks rhyolitic lavas and tuffs of mid devonian age 377 5 ma rb sr along the southern escarpment of the gilif hills sudan 17 83 n 32 67 e detailed demagnetization experiments revealed the presence of three directionally distinct components of magnetization labelled a b and c the overall mean direction of component a dec 0 9 inc 29 8 95 4 6 k 91 1 n 12 sites is indistinguishable from either the direction of the present field or the geocentric axial dipole field in northern sudan mixed polarities suggest a recent or pleistocene age of this component component b also displays mixed polarities the site mean directions for this component average to 6 5 declination 40 2 inclination with 95 7 0 and k 48 1 based on 10 sites and yield a palaeomagnetic pole at 48 8 s 23 5 e dp 5 1 1 dm 8 4 maghaemite and haematite have been identified to be the predominant magnetic phases in samples which carry component a and or b both a and b are the probable results of low temperature oxidation of magnetite although the age of component b can not be directly determined it is inferred by correlation with published data to reflect a late carboniferous overprint component c identified in 11 sites 39 samples is characterized by a very steep downward magnetization dec 296 2 inc 79 3 95 10 8 k 18 7 n 11 sites which corresponds to a palaeomagnetic pole position in the southwestern corner of libya 25 9 n 11 6 e dp 19 6 dm 20 6 maximum blocking temperatures of component c generally below 580 c are indicative of magnetite as carrier of this remanence the results of thermal remanent magnetization experiments demonstrate that component c is a thermo remanent magnetization probably primary and suggest this component to be representative for the direction of the earth s magnetic field during emplacement of the gilif hills volcanic rocks in mid devonian times the position of the resulting palaeomagnetic pole lends new support to geodynamic scenarios advocating the existence of a wide approx 5000 km pre hercynian ocean during devonian times the simplest reconciliation of component b with the reference apparent polar wander path is achieved by assuming it to be of carboniferous age and by invoking a westward cusp in the carboniferous part of the apparent polar wander path taken at face value the age of this cusp coincides with large scale post orogenic right lateral strike slip movements in hercynian europe and north africa this interpretation does not require the apparent polar wander apw loop and very high rates of plate motion implied by some alternative models however if it is valid it will require reinterpretation of the remanence age of one west african intrusive suite and of some eastern australian palaeozoic rocks

the msissi norite revisited k ar dating petrography and paleomagnetism the msissi norite in morocco 30 93 n 4 71 w from where one of the paleomagnetic reference pole for africa in devonian times has been derived has been revisited and dated petrological examination shows that the rock is an alkaline gabbro teschenite k ar analyses on fresh biotite yield a 136 139 ma age which infirms the supposed devonian age the paleomagnetic study displays several distinct magnetic components

late devonian carbonate magnetostratigraphy from the oscar and horse spring ranges lennard shelf canning basin western australia a b s t r a c t the late devonian was a time of major evolutionary change encompassing the fifth largest mass extinction the frasnian famennian event in order to establish a chronological framework for global correlation before during and following the frasnian famennian mass extinction we carried out a coupled magnetostratigraphic and biostratigraphic study of two stratigraphic sections in the upper devonian carbonate reef complexes of the lennard shelf in the canning basin western australia magnetostratigraphy from these rocks provides the first high resolution definition of the late devonian magnetic polarity timescale a 581 m reference section and an 82 m overlapping section through the marginal slope facies napier formation of the oscar range as well as a 117 m section at horse spring virgin hills formation were sampled at decimeter to meter scale for magnetostratigraphy conodont biostratigraphy was used to correlate both sections and link magnetostratigraphic polarity zones to a globally established biostratigraphy as table characteristic remanent magnetization chrm with dual polarities ne shallowly upward and sw shallowly downward is recovered from 60 of all samples with magnetite inferred to be the chief magnetic carrier from thermal demagnetization characteristics these directions define a geomagnetic pole at 49 5 s 285 8 e and 95 2 4 n 501 placing the canning basin at 9 9 s during the late devonian consistent with carbonate reef development at this time ac onservative interpretation of the magnetostratigraphy shows the recovery of multiple reversals from both sections not including possible cryptochrons and short duration magnetozones field tests for primary remanence include positive reversal tests and matching magnetozones from an overlapping section in the oscar range as trong correlation was found between magnetic polarity stratigraphies of the oscar range and horse spring sections and we correlate 12 magnetostratigraphic packages the relative stratigraphic thicknesses of the isochronous sediments from these two sections indicate that carbonate accumulation was 4 5 faster in the middle slope deposits at oscar range than in the more distal lower slope horse spring deposits for the middle frasnian through famennian the magnetic field during the late devonian underwent a relatively high reversal frequency with good potential for regional and global correlation and should prove useful in deciphering a high resolution chronostratigraphy across the lennard shelf to enable higher confidence examination of reef development across a major biotic crisis

the armorica microplate fact or fiction critical review of the concept and contradictory palaeobiogeographical data abstract the problem of an armorica microplate detached from gondwana and having had during part of the palaeozoic an independent latitudinal evolution is reconsidered in terms of a critical review of the palaeomagnetic data that were the very roots of this concept and through an alternative approach based on palaeoclimatic and palaeobiogeographical data palaeomagnetic data for the silurian and the devonian of the south european regions supposedly constituting the armorica microplate remain rare and ambiguous those from gondwana are more numerous but contradictory enough to give rise to diverging models regarding the latitudinal evolution of this continent consequently the reality of an armorica microplate cannot be considered as established on the contrary lithological indicators of palaeoclimate and palaeobiogeographical data are in total harmony and indicate that in actual fact the southern european regions remained permanently closely connected with gondwana of which they composed the northern margin although repeatedly maintained for more than 20 years the concept of an armorica microplate can thus be considered a fiction this conclusion should lead to the dismissal of geodynamical models proposed for the variscan belt to which this concept was integrated and are contradicted by inescapable palaeobiogeographical constraints

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

ecological and environmental factors affecting alkenone distributions in seawater and sediments 1 the use of alkenones to estimate past sea surface temperatures has gained wide acceptance but there are still some issues that need to be resolved before alkenone proxies can be used confidently in all environmental settings a particular concern is defining what seawater temperature is recorded by the alkenone distributions preserved in sediments does it for example reflect a seasonal average or a snapshot of bloom conditions or some other combination of environmental effects this paper reviews some of the environmental and ecological factors that might affect alkenone distributions and in particular the influence of depth and seasonality on alkenone production in the water column

paleomagnetism of upper devonian reefal limestones canning basin western australia two conflicting models have been proposed for the middle paleozoic position of gondwana with respect to euramerica a pole from morocco msissi norite that may be of late devonian age suggests that a broad ocean 3 000 km separated the northern continents from gondwana whereas results from mauritania gneiguira supergroup indicate that this ocean had closed by devonian time detailed thermal and alternating field demagnetization experiments have been carried out on red and gray limestones from seven sites 89 samples in an essentially undeformed late devonian reef complex northern canning basin western australia after minor tilt correction the site mean characteristic directions average 42 7 28 9 declination inclination with k 61 6 and 95 7 8 these results position northwestern australia at 15 s latitude in the late devonian a paleolatitude consistent with the presence of a well developed reefal sequence an early age is inferred for these magnetizations on the basis of the occurrence of mixed polarities and the fact that no post devonian directions for australia resemble the observed declinations and inclinations if the smith and hallam reconstruction for gondwana is used the paleomagnetic pole calculated for the late devonian of western australia agrees with the msissi norite result from morocco and suggests that an ocean still separated gondwana from euramerica in the late devonian the pole measured from the gneiguira supergroup in mauritania may be based on remagnetizations of late paleozoic age the directions determined from canning basin limestones are similar in inclination to but differ by 40 in declination from paleomagnetic results from the upper devonian comerong volcanics lachlan fold belt southeastern australia canning basin samples are from the stable craton and comerong volcanics samples are from the tasman fold belt the discrepancy between the two australian results may be best explained by tectonic rotation of the comerong volcanics locality

scheck breccias from devonian reef complexes of canning basin western australia abstract late frasnian and early famennian marginal slope deposits of the canning basin reef complexes include distinctive red open framework breccias characterized by red micritic clasts cemented by white calcite spar they closely resemble the adneter scheck breccias in the jurassic adnet limestone of the austrian alps scheck breccias from the canning basin are largely confined to red stromatolitic and terrigenous marginal slope sediments having depositional slopes of 10 14 which were deposited in water depths of some tens to hundreds of meters individual breccias beds are strongly lensoid with concave locally scoured bases they are between 10 and 100 cm 4 and 39 in thick and are composed predominantly of irregular red micritic clasts reworked from associated nodular limestones breccias are clast supported and may be inverse to normally graded normally graded or massive the proposed depositional mechanism began with slumping of muddy sediment containing abundant early cemented nodules this initiated bimodal density modified grain flows nodules were supported by dispersive forces and deposited by frictional freezing as the depositional slope decreased producing clast supported graded sequences the finer sand and mud fractions continued downslope as turbidity currents leaving behind minor perched mud trapped in the open framework breccias early cementation by radiaxial calcite prevented further sediment infilling these devonian scheck breccias are characteristic components of condensed sequences as shown by conodont dating they represent infrequent events only about one bed of breccia was deposited for every 10 m 33 ft of section in about 300 000 years over a vertical section of about 200 m 660 ft end of article last page 495

magnetostratigraphy late devonian iridium anomaly and impact hypotheses paleomagnetism sedimentology and fine scale stratigraphy have been integrated to explain the origin of an iridium anomaly in the late devonian of western australia thermal demagnetization experiments were carried out on 93 specimens of marginal slope limestone form the northern canning basin samples are from a condensed sequence of deep water 100 m frutexites microstromatolites frutexites is a shrublike cyanobacterial organism that probably precipitated hematite or a metastable precursor from sea water when plotted within the microstratigraphic framework for the study area the observed characteristic directions from the sampled interval 14 5 cm thick are in five discrete layer parallel normal and reversed polarity zones the measured northeast southwest declinations and shallow inclinations probably record late devonian magnetostratigraphy on a centimetre scale the frutexites bed studied there occurs close to the frasnian famennian late devonian boundary a time of mass extinction of a wide variety of marine organisms throughout the world anomalously high iridium concentrations observed in the frutexites bed have suggested to some authors that the mass extinction was caused by meteorite impact this study concludes that iridium which is present over the span of five layer parallel magnetic reversals was concentrated over a long period of time by biologic processes thus the canning basin iridium anomalymore may be unrelated to meteorite impact less

alkenone temperature and carbon isotope records temporal resolution offsets and regionality 1 over the last decade the number of paleoceanographic studies presenting and discussing alkenone derived sea surface temperature sst records and carbon isotope ratios of alkenones 13calkenones has increased rapidly this short review paper summarizes the state of knowledge about sst variability determined by alkenone paleothermometry in sediment trap studies and investigations of marine sediments for timescales of single to millions of years in particular from the evaluation of quaternary records characteristic temperature pattern have emerged that mismatch with sst curves estimated by other methods e g foraminiferal stable oxygen isotopes and transfer functions in future studies the spatial distribution of such variance patterns typically observed in alkenone sst curves should be checked in order to better understand their meaning for ocean circulation changes and a possible relationship to global climate change on the other hand certain physical and biological processes have the potential to put the reliability of alkenone sst curves into question accordingly examples for possible effects of bioturbational mixing lateral transport of remote alkenones diagnetic alteration and degradation of alkenone composition biogeographic and temporal diversity changes in alkenone producing algae as well as the influence of changes in salinity and nutrient conditions on the alkenone paleotemperature signal are briefly mentioned highlighting the need for more detailed future studies on these issues finally a short summary on the status of the use of the 13calkenones signal as a proxy for past variations in the carbon dioxide pressure pco2 in ocean surface waters and related problems is given

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

paleomagnetism of the upper devonian reef complexes canning basin western australia paleomagnetism of the upper devonian reef complexes in the canning basin western australia was reinvestigated with a primary aim of testing its magnetization age samples were collected from back reef and reefal limestones basinal red beds syndepositional allochthonous blocks and sediment infillings in syndepositional cracks and voids a characteristic remanence similar to that identified in a previous study was found in six autochthonous sites in outcrop and four diamond drill cores with a mean direction of declination d 27 5 inclination i 19 9 half angle of 95 confidence cone 95 15 2 the primary origin of this remanence was demonstrated by both a syndepositional breccia test and an allochthonous block test the corresponding late devonian pole position 62 0 s 23 2 e with half angle of 95 confidence cone a95 14 6 overlaps with the previously reported paleopole from this reef complex and other late devonian paleopoles from australia the evidence indicates that the spread of late middle to early carboniferous paleopoles from australia is caused by a phase of rapid apparent polar wander rather than the tectonic discordance of southeastern australia in relation to the craton

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

the organic geochemistry of peru margin surface sediments i a comparison of the c37 alkenone and historical el nino records abstract the alkenone u k 37 paleothermometer has potential as a sedimentary marker for el nino southern oscillation enso events in the peru upwelling regime we assessed this potential by comparing the historical enso record with detailed u k 37 profiles for 210 pb dated cores from the peru margin oxygen minimum zone omz sediments with the greatest potential for holding a sedimentary u k 37 record of el nino events are sediments from the center of the omz sectioned at intervals the yearly sedimentation rate the u k 37 signals of individual el nino events were substantially attenuated in the sediments we examined and periods of frequent enso activity e g 1870 1891 were more readily identified than isolated enso events in periods of less frequent enso activity detailed depth profiles of the c 37 alkenones in a core from 253 m o 2 k 37 values for the five 2 mm sections from 0 1 cm suggests that the u k 37 may be unaffected by the alkenone loss correlation between the c 37 alkenone concentration profiles in two cores from 15 s collected nine years apart are consistent with the use of these compounds for molecular stratigraphy

reconstruction of past nutrient utilization in the eastern angola basin based on sedimentary 15n 14n ratios the 15n records of two sediment cores from the angola basin have been used to investigate past changes in nutrient utilization in the surface waters of this highly productive region low 15n 14n ratios in the cores from 3000 m water depth generally correspond to low sea surface temperatures and high sedimentary organic content demonstrating a link between upwelling productivity and the degree of nitrate depletion glacial 15n was lower by 0 5 0 7 and paleoproductivity was elevated by around 30 relative to interglacial periods indicating that although productivity was higher nitrate was less depleted during glacial than interglacial periods more pronounced than the glacial interglacial changes in 15n values of both cores are precession related 23 kyr fluctuations these cyclic 15n variations which are in phase with those of paleoproductivity and sea surface temperature indicate that changes in trade wind driven upwelling intensity and the advection of cold nutrient rich water from the south drive nutrient availability and productivity off the southwest coast of africa no strong evidence was found from sedimentary 15n values for denitrification in the water column in the angola basin during the past 180 kyr

small changes in the sea surface temperature during the last 20 000 years molecular evidence from the western tropical pacific one of the most controversial problems of glacial paleoclimatology is the conservative change in tropical sea surface temperature sst in contrast with the large high altitude temperature change in the western tropical pacific in this report sst was estimated for the last 20 000 years using alkenones preserved in marine sediments recovered from a site 800 km north of new guinea the uk37 unsaturation degree of long chain alkenones synthesized by planktonic prymnesiophyte algae record suggests that sst decreased at most 1 5 c at the last glacial maximum this small changes in sst of the western tropical pacific is concordant with results previously reported in uk37 studies from the eastern equatorial pacific and the equatorial atlantic the uk37 based sst estimates are in good agreement with the climap results and planktonic foraminifera 18o but much smaller than those ca 5 c obtained from coral sr ca and 18o thermometries and glacial vegetation reconstruction

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

late quaternary insolation forcing on total organic carbon and c37 alkenone variations in the arabian sea we here present records of total organic carbon toc and c37 alkenones used as indicators for past primary productivity from the western was and eastern arabian sea eas new data from an open ocean site of the was upwelling area are compared with similar records from ocean drilling program odp site 723 from the continental margin off oman and md 900963 from the eas these records together with other proxies used to reconstruct upwelling intensity indicate periods of high productivity in tune with precessional forcing on the basis of their phase relationship to boreal summer insolation they can be divided into three groups in the was differences between monsoonal proxies 1 and productivity 2 document a combined signal of moderate sw monsoon winds and of strengthened and prolonged ne monsoon winds whereas in the eas phasing indicates maximum productivity 3 at times of stronger ne monsoon winds associated with precession related maxima in ice volume

syn deformational remanent magnetization of the mount eclipse sandstone central australia summary the palaeomagnetism of the latest devonian early carboniferous mount eclipse sandstone in central australia reveals samples from 16 out of 31 sites having a consistent hightemperature component of natural remanent magnetization site mean directions from the two limbs of the most detailed studied syncline attain their best grouping after 75 per cent of unfolding and further unfolding causes a cross over feature mineralogical studies using microscope and electron microprobe show that this remanance is most likely to be carried by secondary haematite formed by alteration of fe rich minerals during the midcarboniferous deformation four different models are examined to reconstruct the palaeohorizontal for the syn deformational remanence the best estimate of the palaeomagnetic south pole position is lat 33 8 s and long 121 2 e dp 19 2 drn 19 7 close to australia this result indicates a rapid polanvard movement of eastern gondwanaland during the first half of the carboniferous we also suggest that the widespread alice springs orogeny related overprints in central australia were acquired during the beginning of the main phase of deformation in the mid carboniferous

upwelling and productivity changes inferred from a temperature record in the central equatorial pacific a series of c37 39 alkenones synthesized by prymnesiophyte algae is commonly preserved in marine sediments and can be used for estimating past sea surface temperatures ssts 1 2 here we present an alkenone analysis of sediments taken from the central equatorial pacific ocean core w8402a 14gc 0 57 n 138 57 w which shows that sst varied slightly 2 c but coherently with milankovitch insolation cycles over the past 250 kyr the in phase response of the sst to the precessional component of insolation indicates that this part of the sst time series may be driven by changes in local trade wind strength and the longer 100 kyr eccentricity component indicates a response to basin wide south pacific winds using a simple heat balance model we use our palaeotemperature record to constrain the upwelling rates that have occurred in the past similar sst records from the eastern pacific could constrain the horizontal advection component of the sst record and allow for better estimates of upwelling upwelling and palaeoproductivity then could be compared to determine whether changes in equatorial nutrient levels actually cause equivalent changes in productivity

linearity spectrum analysis of multi component magnetizations and its application to some igneous rocks from south eastern australia summary a method that enables the objective resolution of almost parallel multi component magnetizations is described and demonstrated a feature distinguishing this method from others is its simultaneous analysis of demagnetization data from a group of specimens rather than the analysis of data from one specimen at a time the only prerequisite is that the specimens are derived from a homogeneous source thus for a formation carrying a simple single component magnetization all specimens from the formation may be simultaneously reduced for a more complicated two component magnetization it is shown that only specimens from a particular site can be considered homogeneous and for a complex three component system each sample often requires undivided attention thus the workload is proportionally increased to achieve analyses of comparable reliability from data of variable quality new pole positions from mesozoic intrusions of the sydney basin nsw are from the marsden park breccia pipe 48 s 127 e a95 6 the st marys breccia pipe 46 s 150 e a95 8 the prospect dolerite 60 s 142 e a95 13 and 53 s 180 e a95 6 and from the dundas breccia pipe 58 s 162 e a95 36 and 31 s 195 e a95 16 the last two formations possess multi component magnetizations these pole positions are consistent with previous results from south eastern australia

paleomagnetic results indicate pre permian counter clockwise rotation of the southern tamworth belt southern new england orogen australia 1 visean ignimbrites from three fault bounded blocks within the southern tamworth belt southern new england orogen australia retain a prefolding high temperature component of remanence carried mainly by magnetite paleomagnetic data indicate that the southern tamworth belt occupied low to moderate paleolatitudes during the early carboniferous normal and reversed polarities with low to moderate inclinations suggest that the steep reverse polarity latest carboniferous to earliest permian overprint is absent from the high temperature component data set the mean characteristic remanence direction of three early to middle visean ignimbrite flows 32 sites from the rouchel block is declination dec 154 2 and inclination inc 38 8 95 12 5 k 98 8 which corresponds to a paleo south pole at latitude 64 9 s longitude 258 1 e dp 5 5 dm 9 2 where dp is the angular length of the semiaxis of the ellipse of confidence of the calculated paleopole that lies along the pole to site great circle and dm is the angular length of the semiaxis perpendicular to dp six middle to late visean ignimbrite flows 29 sites from the gresford block retain a mean remanence of dec 159 6 and inc 54 1 95 13 7 k 24 7 corresponding to a paleo south pole at latitude 72 8 s longitude 228 4 e dp 13 4 dm 19 2 despite widespread overprinting throughout much of the myall block reliable information was obtained from three late visean ignimbrite flows five sites with a mean direction of dec 118 1 and inc 42 5 95 12 0 k 41 6 from which a paleo south pole of latitude 35 7 s longitude 233 4 e dp 9 1 dm 14 7 is calculated the calculated paleo south poles do not fall on the early carboniferous segment of the published apparent polar wander path for australia and suggest that the southern tamworth belt has undergone significant counter clockwise rotation relative to cratonic australia inferred rotations for the rouchel gresford and myall blocks are approximately 80 80 and 120 respectively stratigraphic and geological evidence suggest rotation took place between the mid namurian and latest carboniferous and is thought to have resulted from sinistral strike slip during compression at the eastern margin of australia

atlantic core top calibration of the u37k index as a sea surface palaeotemperature indicator abstract a field calibration of the uk index with sea surface temperature is discussed through analysis of an extensive suite of surface sediments n 109 from the northeastern atlantic 2 s 75 n values of u 37 k are compared with sea surface temperatures for overlying waters measured at different depths and seasons to obtain a correlation suitable for palaeotemperature reconstructions the best fit is obtained using surface 0 m temperatures corresponding to caloric winter and autumn months however the annual average spring and summer surface temperature equations also have high correlation coefficients and are also appropriate for climatic studies the results further validate the general applicability of the u 37 k as a climatic proxy because the calibration equations are valid over a wide range of surface water temperatures 0 28 c for different algal populations and are representative of the average contribution of alkenones to sediments as found in sediment cores

evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions implication for paleotemperature reconstruction abstract the successful reconstruction of sea surface temperatures using alkenone paleothermometry u37k has relied on the premise that there is no significant differential degradation of alkenones with different states of unsaturation during diagenetic processes to test this assumption we conducted a comparative study of contemporary sediments in oxic and anoxic bottom waters from the santa monica basin offshore california long chain alkenones were quantified and sea surface temperature were calculated using the calibrated u37k t relationship of prahl et al 1988 our results show that temperature record from the oxic sediments is higher by as much as 4 c compared to those from time equivalent anoxic sediments as a result of differential degradation of long chain unsaturated alkenones and bioturbation mixing in the oxic sediments the differential degradation of c37 3 vs c37 2 alone could account for up to 2 5 c difference between these two records this finding has significant implication in the interpretation of paleo sea surface temperature data using alkenone paleothermometry

structure paleogeographic inheritance and deformation history of the southern atlas foreland fold and thrust belt of tunisia 1 structural analysis of the southern tunisian atlas was carried out using field observation seismic interpretation and cross section balancing it shows a mix of thick skinned and thin skinned tectonics with lateral variations in regional structural geometry and amounts of shortening controlled by nw se oblique ramps and tear faults it confirms the role of the late triassic early jurassic rifting inheritance in the structuring of the active foreland fold and thrust belt of the southern tunisian atlas in particular in the development of nw se oblique structures such as the gafsa fault the late triassic early jurassic structural pattern is characterized by a family of first order nw se trending normal faults dipping to the east and by second order e w trending normal faults limiting a complex system of grabens and horsts these faults have been inverted during two contractional tectonic events the first event occurred between the middle turonian and the late maastrichtian and can be correlated with the onset of the convergence between africa and eurasia the second event corresponding to the principal shortening tectonic event in the southern atlas started in the serravalian tortonian and is still active during the neogene the southern atlas foreland fold and thrust belt propagated on the evaporitic decollement level infilling the late triassic early jurassic rift the major eocene atlas event described in hinterland domains and in eastern tunisia did not deform significantly the southern tunisian atlas which corresponded in this period to a backbulge broad depozone

depth and seasonality of alkenone production along the california margin inferred from a core top transect alkenone unsaturation indices uk 37 of marine sediment could prove particularly useful on organic rich continental margins where carbonate dissolution hampers the use of other paleoclimatic proxies mccaffrey et al 1990 kennedy and brassell 1992 forty core top samples of recent sediment from a latitudinal transect 23 40 n along the california margin yield uk 37 values that correlate linearly with modern mean annual sea surface temperatures ssts in the range of 12 23 c reproducibility of the unsaturation value in closely spaced cores is near analytical error uk 37 data define a relationship to temperature nearly identical to the prahl et al 1988 laboratory cultures of emiliania huxleyi the close agreement is particularly significant in light of the nannofossil composition of the sediments where the abundance of the coccolith taxon gephyrocapsa oceanica known to synthesize alkenones equals or exceeds that of e huxleyi comparison with seasonal temperature variations at different depths indicates that little if any alkenone production occurs at depths 30 m along the continental margin water depths 2 km sediments in more pelagic locations exhibit small but consistent biases toward winter and or subsurface production similar to previously reported sediment trap and core top data from the oregon margin prahl et al 1993 doose et al 1997

alkenone sea surface temperature in the southern ocean for the last two deglaciations a piston core taken from the tasman plateau in the southern ocean has been studied for organic compounds to reconstruct the late pleistocene marine environments here we report paleo sea surface temperature sst for the last two deglaciations using the unsaturation degree of alkenones u k 37 preserved in the marine sediments the u k 37 record indicates that the sst was at least 4 c lower than the present sst at the last glacial maximum lgm and the amplitude of paleo sst is at most 5 2 c from the penultimate glacial mis 6 to the last interglacial warm period the eemian our results also demonstrate that the eemian warm period in the southern ocean lasted only 3 000 years followed by a sharp cooling at around 120 kyr bp the sharp cooling in the southern ocean seemed to occur a few millennia 2 3 kyrs before the beginning of continental ice sheet growth

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

palaeomagnetism of the brewer conglomerate in central australia and fast movement of gondwanaland during the late devonian summary palaeomagnetic analysis of 11 diamond drill cores from the late devonian brewer conglomerate in the northeastern part of the amadeus basin central australia yields three magnetic components a drilling induced remanence c1 acquired during the industrial drilling process a mid to late carboniferous syndeformational overprint c2 acquired during the alice springs orogeny and a primary remanence c3 c3 passes a fold test and gives a latest devonian pole bc at 47 1ds 041 0de with a95 6 4d the revised apwp for gondwanaland requires west gondwanaland to drift across the south pole during the late devonian with a speed of 20cm yr 1 while east gondwanaland remained at low latitude positions it is suggested that fast plate movement occurred far more often during the palaeozoic than has previously been thought

palaeomagnetism of red beds of the late devonian worange point formation se australia summary gently folded strata of the late devonian merrimbula group along the south coast of new south wales are similar to numerous deposits of late devonian to early carboniferous subaerial to shallow marine quartzose sandstone that are known as the lambie facies of se australia because the lambie sands overlap the early palaeozoic tectonic elements of the lachlan fold belt large displacement since the late devonian of any lachlan terranes with respect to interior australia is precluded we collected oriented core samples from 37 sites primarily in reddish quartzose litharenites of the worange point formation the remanent magnetization is carried by haematite incremental thermal demagnetization reveals a dominant well defined steep upward north component of magnetization that post dates the mid carboniferous folding the south pole position 146 4 e 68 6 s ag5 3 1 derived from the overprinted specimens is close to both the late carboniferous and mid cretaceous reference poles as well as the spin axis of today the overprint is attributed to both viscous partial thermoremanent and chemical remanent magnetization vptrm and crm its exclusively normal polarity is consistent with a mid cretaceous acquisition perhaps related to the rifting of the se australian margin a characteristic component of magnetization is isolated between 660 and 680 c in 30 per cent of the samples although a regional fold test of the overall result is inconclusive because the directions of characteristic magnetization are generally close to the axes of folding two sets of samples from opposite limbs of a local syncline pass a fold test at 90 per cent confidence indicating a pre folding origin of the remanence the presence of both polarities in thin horizons some of which are palaeosols and diagenetic haematite associated with incipient cleavage formed in an early stage of deformation before folding indicates that the acquisition of remanent magnetization occurred over a protracted period an analysis that combines great circle demagnetization paths and set points facilitates the incorporation of more data but gives a biassed result although normal and reverse polarity subsets are roughly antipodal residual post folding components cause the normal subset to fail a fold test a south pole position 19 7 e7 70 8 s ag5 7 1 is derived from the specimens with characteristic component of reverse polarity in which the isolation of a characteristic component is clear the pole position is close to that of a previous palaeomagnetic study from a widely separated occurrence of lambie facies sediments both results are applicable not only to the lachlan fold belt but also to the rest of australia and gondwana as a whole the position of the two poles derived from the lambie facies overlap assemblage in the lachlan fold belt supports the interpretation that the progression

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

pre and post folding magnetizations from the early devonian snowy river volcanics and buchan caves limestone victoria summary multicomponent magnetizations of the snowy river volcanics have been resolved into pre folding dec 340 1 inc 59 2 and post folding dec 10 5 inc 72 3 elements the former is attributed to initial cooling of the volcanics while the latter is probably related to the waning stages of the deformational episode which was presumably accompanied by cooling we argue that the pole position from the pre folding magnetizations lat 74 3 s long 222 7 e represents the australian palaeopole for the early devonian a reassessment of other australian pole positions determined from rocks of about this age suggests that remagnetization during the carboniferous may be common interpretation of the pole path prior to the devonian is equivocal and awaits further study the post folding magnetizations from the volcanics are similar in stability and direction to those from the buchan caves limestone dec 27 8 inc 75 6 which appears to be completely remagnetized the age of this remagnetizing event appears to be mid carboniferous if our interpretation of the pole path for this time is correct it is noted that a much unappreciated attribute of the fold test lies with identifying not just the relative age of magnetization but also the palaeohorizontal only when the palaeohorizontal is established can the calculation of a palaeopole be justified

alkenones as paleoceanographic proxies 1 alkenone derived estimates of temperature and co2 are contributing to our understanding of earth s climate history in order to increase confidence in alkenone based climate proxies we recommend the following actions first the sedimentary component or fraction containing alkenones should be identified in order to assess the impact of horizontal advection and vertical mixing on alkenone derived temperature and co2 estimates second differential mixing rates of alkenone containing particles and sand sized foraminifera should be quantified by independent dating of the two phases until that is accomplished apparent temporal offsets of climate proxies in the two phases should be interpreted cautiously third the stability of the unsaturation ratio and carbon isotopic compositions of alkenones during all phases of diagenesis should be confirmed both field and laboratory observations are required fourth future alkenone investigations should be coupled with other paleoclimate proxy measurements at high deposition rate sites in a variety of oceanographic settings in upwelling regions and in the vicinity of river plumes salinity and nutrient proxies should be measured since changes in these parameters may affect alkenone biosynthesis

molecular record of secular sea surface temperature changes on 100 year timescales for glacial terminations i ii and iv high resolution palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand year timescale1 3 little is known4 however about the variation of climate and of palaeoceanographic conditions throughout the quaternary on timescales of less than 1 000 years at frequencies far greater than those of the milankovitch orbital cycles here we show that such high time resolution is possible from molecular stratigraphic studies based on biomarker organic molecules alkenones we have sampled alkenone stratigraphic records at 70 to 200 yr intervals across glacial terminations i ii and iv in sediment cores from oop site 658 off northwest africa5 sea surface temperatures ssts derived from the alkenone uk37 index6 8vary rapidly beyond the range of analytical noise by up to 2 5 c in 300 yr showing hitherto unknown cycles with about 600 yr periodicities some of the changes parallel similar events in the oxygen isotope stratigraphy sst oscillations may be linked in part to abrupt breakdowns in atlantic deep water ventilation resulting from meltwater events of quaternary glacial terminations3 9 10

paleomagnetism of the hervey group central new south wales and its tectonic implications paleomagnetic work on the hervey group in southeast australia reveals a predeformational magnetization as suggested by the retention of a predeformational compaction produced magnetic fabric and the effect of deformation on both the magnetic fabric and the direction of the magnetic remanence in cleaved rocks the formation mean direction d 29 2 i 19 3 with 95 15 5 gives a latest devonian early carboniferous palaeomagnetic pole at 54 4 s 24 1 e with dp 8 4 dm 16 2 comparing this pole with existing poles from australia and north america it is suggested that 1 the lachlan fold belt of southeast australia has been part of cratonic australia since at least the late devonian and consequently the late palaeozoic palaeomagnetic data from the lfb may be applied to the whole of gondwanaland 2 cratonic australia and the new england fold belt were all in an equatorial position during the early carboniferous 3 there was probably a rapid anticlockwise rotation of gondwanaland during the late devonian around an axis close to australia 4 a v shaped ocean existed between laurussia and the northern margin of western gondwanaland during the late devonian early carboniferous the appalachian hercynian orogenic belt is probably the result of the closure of this ocean

prefolding and premegakinking magnetizations from the devonian comerong volcanics new south wales australia and their bearing on the gondwana pole path palaeomagnetic results from the late middle to early late devonian comerong volcanics in the budawang synclinorium lachlan fold belt lfb new south wales australia satisfy a fold test and support the hypothesis that foliated parts of the lfb have been folded by megakinks during the terminal mid carboniferous orogenic phase the preferred pole position is at 76 9 s 330 7 e a95 7 2 allowing calibration of the australian pole path at around 370 ma ago an alterative pole position at 71 3 s 283 1 e same a95 takes into account a possible rotation of the megakinked terrane by 15 clockwise with respect to the australian craton although there are still problems unravelling previously published results from silurian rocks in the lfb both because of unreliability and uncertainty as to where the lfb crustal units lay in relation to the australian craton there is no geological reason to suspect any large relative movement between the lfb and the craton since the middle devonian and thus the comerong volcanics pole position is representative of the late devonian for australia the new pole requires reassessment of many other poles that have previously been accepted as representing the siluro devonian for australia and gondwanaland we present reasons for believing that the magnetization or remagnetization of many rock units e g mereenie sandstone and mulga downs group australia and the gneigura supergroup africa was later than sedimentation probably during widespread early carboniferous deformation another rock unit msissi norite africa could be of early carboniferous rather than late devonian age

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

assessment of sea surface temperature variations in the central north atlantic using the alkenone unsaturation index u37k abstract a high resolution record of u37k derived sst estimations has been obtained in a core from the central north atlantic ocean su90 08 43 30 n 30 24 w spanning a time period of 280 ky the general trend of the u37k profile parallels closely the 180 signal and represent an independent confirmation that the sst variations in the glacial interglacial time scales are correlated with the northern ice sheets evolution in contrast to the climap 1984 conclusions based on the foraminiferal transfer function technique the sst during the last interglacial period lip isotopic stage 5 5 are 2 3 c warmer than during the holocene this result is in good agreement with many studies based in coastal and continental records that strongly suggest warmer climatic conditions over north america and europe finally the sst estimates during the last glacial maximum lgm 18 ky bp where 4 5 c cooler than during the previous glacial period pgp stage 6 we argue that this difference is caused by a northward position of the polar front during the pgp in the central north atlantic

australian palaeozoic palaeomagnetism and tectonics ii a revised apparent polar wander path and palaeogeography abstract new palaeomagnetic data from mid to late palaeozoic rocks in australia have enabled us to revise the palaeozoic apparent polar wander path apwp this modified australian apwp is supported by data from other parts of gondwanaland the palaeomagnetic poles indicate that during the early and mid palaeozoic australia underwent rapid rotation first clockwise during the mid ordovician to the early silurian then counterclockwise from the mid silurian until the end of the devonian while it remained at low to equatorial latitudes this was succeeded by a rapid southward movement during mid carboniferous times the implications of the palaeomagnetic data for the tectonic relationship between the lachlan fold belt lfb and cratonic australia are consistent with the tectonic evidence that the lfb has been in place since the mid devonian

subtropical north atlantic temperatures 60 000 to 30 000 years ago a reconstruction of sea surface temperature based on alkenone unsaturation ratios in sediments of the bermuda rise provides a detailed record of subtropical climate from 60 000 to 30 000 years ago northern sargasso sea temperatures changed repeatedly by 2 to 5 c covarying with high latitude temperatures that were previously inferred from greenland ice cores the largest temperature increases were comparable in magnitude to the full glacial holocene warming at the site abrupt cold reversals of 3 to 5 c lasting less than 250 years occurred during the onset of two such events greenland interstadials 8 and 12 suggesting that the largest most rapid warmings were especially unstable

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters