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

surface current measurements using airborne visible image time series abstract measurements of nearshore water currents are important for a number of reasons including understanding sediment transport and beach erosion planning and evaluation of littoral construction projects and military operations in very shallow water because direct measurements are difficult and expensive to make remote sensing techniques are of great interest a digital camera system has been used to remotely measure ocean surface currents from an aircraft by estimating the doppler shift of gravity waves navigational data are used to map each of a sequence of images to a geodetic reference frame at the level of the mean ocean surface the 3 d frequency wave number spectrum of the luminance modulations in subsets of these mapped data exhibits the dispersion relation for surface gravity waves and the 2 d velocity vector is retrieved by estimating the doppler shift of the higher frequency waves in this spectrum wavelengths in the band of about 5 30 m the relationship of this technique to that of tracking visible surface features between image pairs is examined with examples current retrievals in shallow water outside the surf on a quasi linear beach and in an exposed tidal inlet channel are favorably compared with simultaneous in situ current measurements with errors of 10 in magnitude and 5 in direction

late mesozoic and cenozoic palaeomagnetism of australia i a redetermined apparent polar wander path summary palaeomagnetic measurements have been carried out on one cretaceous and five cenozoic sedimentary sequences of australia of those one is in the carnarvon basin of north western australia and the others are in the otway basin of south eastern australia the new results are used together with those published previously to define a revised late mesozoic cenozoic apparent polar wander path for australia this path differs from earlier basalt derived paths by the absence of a large westward excursion and zig zag irregularities it is characterized instead by a substantially straight cenozoic trajectory a sharp bend in the late cretaceous and a non uniform rate of apparent polar wander the early tertiary segment of the new path lies north of the original paths thus eliminating a discrepancy that has been noted previously between the indian and australian palaeomagnetic data luyendyk rennick peirce and klootwyk peirce a re examination of the original data suggests that this discrepancy as well as two others in the australian results may have been caused principally by incomplete time averaging of remanence directions because the volcanics on which the results were based had been extruded episodically

timing trace and origin of basaltic migration in eastern australia eastern australian cenozoic volcanism includes a prominent southward migration of activity varied explanations have invoked hotspot or linear magma sources in the asthenosphere the movement of australia over old seafloor spreading zones with direct or delayed response in volcanism or changes in stress fields the present appraisal using new data contradicts some ideas and favours volcanism triggered directly by passage of lithosphere over initial sites of coral sea spreading the conclusions suggest that eastern australia has a major complex hotspot trail established for the past 65 myr it forms an independent and key continental reference to the hawaiian emperor oceanic trail it raises the notion that both continental and oceanic trails can mark the ghosts of former spreading sites

viscous magnetization archaeology and bayesian statistics of small samples from israel and england 1 certain limestones remagnetize viscously and noticeably over archaeological time intervals after their reorientation into monuments the laboratory demagnetization temperatures tub for the vrm increase with the installation age with rates of 0 07 c0 year for israel chalk and 0 1c0 year for english chalk the empirical relationship may be used to date enigmatic buildings or geomorphological features e g land slips such correlations also give some insight into the viscous remagnetization process over time intervals 4000 years which are unobtainable in laboratory studies the tub age relationship for the viscous remagnetization appears to follow a power law linearized as log10 b log10 tub different pelagic limestones follow different curves and whereas conventional regression estimates the power law exponent b the small sample size recommends a bayesian statistical approach from sites constructed with pelagic chalk from eastern england precise prior information b 0 761 is compared with less precise information for much more ancient sites in northern israel b 0 873 the collective posterior correlation shows a generalized power law exponent b 0 849 that regression explains 84 9 of the collective variance in age r2 0 849 of course site specific calibration is required for archaeological age determinations

middle permian paleomagnetism of the sydney basin eastern gondwana testing pangea models and the timing of the end of the kiaman reverse superchron abstract paleomagnetic and geochronologic data from the eastern margin of gondwana have been obtained from the gerringong volcanics in the southern sydney basin australia the corresponding paleomagnetic pole at 56 9 s 154 8 e n 131 a95 9 1 has a 40ar 39ar plagioclase plateau age of 265 05 0 35 0 46 ma from the bumbo latite and overlaps with recent radio isotopic and paleomagnetic results published from western gondwana the long documented inconsistency between middle permian eastern and western gondwanan paleomagnetic datasets is most likely an artefact of a lack of reliable paleomagnetic data from eastern gondwana for this period a number of well dated and recently published ca 265 ma paleomagnetic results from gondwana and laurussia are shown to be consistent with the wegenerian pangea a configuration with a loose n s fit of the continents for the middle permian the lack of crustal overlap negates the need for a pangea b configuration which if valid must have been assembled to pangea a by ca 265 ma the reverse polarity bumbo latite was sampled from the kiaman type section located in the southern sydney basin three cases of normal polarity were detected in the overlying saddleback dapto and berkeley latites previously assigned to the kiaman reverse superchron krs we review krs aged magnetostratigraphic data and propose that an age assignment of 265 ma most likely represents the termination of the non reversing field with longer stable intervals of normal polarity recorded and able to be correlated globally

ocean wave dispersion surface measured with airborne ir imaging system image sequences of the ocean have been collected at long range and low grazing angle with an airborne infrared system the images are geographically registered and 3d frequency wavenumber spectra are calculated and shown to have a strong 2d dispersion surface that is characteristic of wind waves and swell wave directions compare well with in situ measurements and their speeds are consistent with the water depth the authors conclude that temporal sequences of ir images acquired from long distance can provide information for extracting surface wave parameters

marine magnetic anomalies palaeomagnetism and the drift history of gondwanaland abstract the results of palaeomagnetic surveys of mesozoic and tertiary rocks from gondwanaland can be reconciled with the results of modelling the evolution of oceanic floors from analyses of marine magnetic anomalies previous inconsistencies were mainly due to errors apparent in the australian cenozoic palaeomagnetic data an alternative tertiary apparent polar wander path apwp has been constructed from an analysis of all published laterite and weathered profile data palaeomagnetic results for africa antarctica australia india madagascar and south america are compared for rotations corresponding to marine magnetic anomalies 16 22 28 34 and m1 and for fit india has been selected as the reference continent since it provides the most detailed apwp having drifted about 50 of latitude since breakup

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

middle miocene climate and vegetation models and their validation with proxy data abstract the miocene is a relatively recent epoch of the earth s history with warmer climate than today particularly during the middle miocene climatic optimum mmco approximately 17 15 ma although the cause of the warming is probably not only attributable to co2 but also to changes in orography and configuration of ocean gateways this time interval represents an ideal case study to test the ability of climate models to simulate warm climates comparable to those that the earth may experience in the near future however even with higher than present day co2 concentrations the mmco warming inferred from terrestrial proxy data has been difficult to reproduce in climate models since fossil flora do not provide direct information on climate but on flora and vegetation climate model results are generally compared to climate reconstructions obtained from the fossil flora in this study we apply an alternative method by simulating palaeovegetation from the outputs of the climate model using a dynamic vegetation model model vegetation reconstruction can then be compared to the vegetation cover indicated by the fossil flora record at the various localities provided that a common classification of plant functional types pfts is used for the data and the model here we reconstruct the vegetation of the middle miocene with the global dynamic vegetation model caraib using the climatologies derived from five atmospheric general circulation models the reliability of the simulations is examined on a presence absence basis of pfts by comparison of vegetation reconstructions to palaeoflora data recorded in the northern hemisphere and the tropics this comparison provides an overall agreement around 60 between model and data when all sites and tree types are considered three model simulations out of five show to be better at predicting the absence than the presence the presence of warm temperate mixed forests in the middle latitudes dominated by broadleaved deciduous warm temperate and subtropical trees is generally well reproduced in caraib simulations however poor agreement is obtained for the presence of tropical pfts out of the tropics and for warm pfts at latitudes northward of 50 n where climate models remain too cold to produce assemblages of trees consistent with the data nevertheless the model data comparison performed here highlights several mismatches that could result not only from missing feedbacks in the climate simulations but also from the data the results of the likelihood analysis on presence absence of pfts illustrate the uncertainties in the pft classification of the neogene floral records the coexistence of some pfts in the palaeovegetation data is impossible to reproduce in the vegetation model simulations because of the climatic definition of the modern pfts this result indicates either a bias in the identification of modern analogues for fossil plant taxa or a possible evolution of environmental requirements of certain plants

magnetic overprinting in southeastern australia and the thermal history of its rifted margin the magnetizations of many rock units in southeastern australia have been severely overprinted interpretation of early work was hindered by this and one of the aims of the current research is to ascertain the nature of the overprint mechanism its geological significance and its regional extent results from three igneous bodies from the sydney basin which have been studied previously in a reconnaissance fashion have provided a new insight into the reason for such widespread magnetic overprinting the hornsby breccia hb and milton monzonite mm yield similar magnetic signatures both containing discrete high and low temperature magnetizations with directions of dec 72 inc 83 95 4 and dec 13 inc 76 95 2 respectively for hb and dec 60 inc 78 95 4 and dec 348 inc 79 95 6 respectively for mm the corresponding pole positions are 29 s 166 e a95 7 and 59 s 139 e a95 4 for hb and 22 s 171 e a95 7 and 55 s 158 e a95 11 for mm the paleomagnetic direction and pole from the third body studied the mogo hill basalt mh are dec 241 inc 81 95 5 and 41 s 130 e a95 9 this pole position and the two low temperature overprint pole positions from hb and mm are consistent with ages ranging from 100 m y to approximately 70 m y when compared to the late mesozoic apparent polar wander path we relate the overprinting to uplift erosion and rapid supracrustal cooling of the southeastern margin of australia associated with initial phases of marginal rift development prior to seafloor spreading in the tasman sea the temperatures of rocks now exposed may have reached 200 c or higher before the rapid cooling blocked and stabilized the overprint magnetizations

palaeomagnetism of the dundas fossey trough tasmania oroclinal rotation and late cretaceous overprinting abstract the dundas fossey trough a curved belt of early palaeozoic rocks in western and northern tasmania is hypothesised to have developed as an orocline driven by asthenospheric flow behind a rapidly retreating subduction zone on the east gondwana margin rocks of the wurawina supergroup from the trough were sampled for a palaeomagnetic test of this hypothesis rock magnetic analysis identifies both magnetite and hematite remanence carriers hematite carries a normal polarity overprint which was acquired at relatively low temperature thermal demagnetisation over the magnetite unblocking range reveals a linear trend that defines component a which displays both normal and reversed polarity component a passes a modified version of the fold test indicating that it is pre deformational the declination of component a correlates linearly with regional strike thus passing the orocline test a palaeomagnetic pole for the cambrian owen group after correction for oroclinal rotation is displaced from the gondwana polar wander path suggesting that the western limb of the trough may have been rotated anticlockwise by about 40 prior to the development of the orocline presumably during known early to middle ordovician deformation adjustment of the palaeomagnetic declination data to account for this earlier phase of rotation improves the fit parameters of the orocline test the palaeomagnetic results are consistent with the orocline model for the dundas fossey trough and support the inference that the trough extends beneath later cover in southeastern tasmania overprint component b yields a mean pole in broad agreement with other overprints previously observed both in tasmania and the eastern seaboard of the australian mainland and like them appears to have been acquired during the late cretaceous normal polarity superchron we speculate that magnetic overprinting in tasmania is related to enhanced oxidation by meteoric water driven by regional uplift

paleomagnetism and paleothermometry of the sydney basin 1 thermoviscous and chemical overprinting of the milton monzonite the early triassic 245 ma milton monzonite of the sydney basin australia has four distinct components of natural remanent magnetization nrm with only slightly overlapping ranges of unblocking temperatures the low temperature lt component the first to be thermally demagnetized is thought to be a late cretaceous 100 ma thermoviscous overprint acquired in slow cooling during uplift the high temperature ht component the second to be demagnetized is probably the primary thermoremanent magnetization trm of the milton intrusion but could possibly be a jurassic overprint lt and ht are usually carried by magnetite and occasionally by pyrrhotite samples from nine sites have a further nrm component which unblocks at higher temperatures than ht but below the magnetite curie temperature of 580 c this component is argued to be a chemical remanent magnetization crm because of its discrete range of high unblocking temperatures above those of the thermal components ht and lt and is called crm1 crm1 has almost the same direction as lt and is likely carried by authigenic magnetite produced during uplift 100 ma samples from five sites have a fourth nrm component with a direction resembling that of ht but carried by hematite this fourth component could be a primary trm but is more likely a crm and is therefore called crm2 the ht crm2 mean direction is d 50 i 75 5 defining a paleopole at 16 s 172 e the ht crm2 paleopole falls near 150 ma on the australian apparent polar wander path but is a considerable distance from paleopoles of permian and early triassic age there is no known tectonic or other remagnetizing event in the sydney basin around 150 ma for this reason we propose that the ht crm2 paleopole defines a new triassic segment of the australian polar wander path the lt crm1 mean direction is d 348 i 79 with a paleopole falling at 56 s 1580 e near 100 ma on the polar wander path this age is consistent with uplift and cooling related to initial rifting of the tasman sea

hf radar comparisons with moored estimates of current speed and direction expected differences and implications the validation of estimates of ocean surface current speed and direction from high frequency hf doppler radars can be obtained through comparisons with measurements from moored near surface current meters acoustic doppler current profilers or drifters expected differences between current meter cm and hf radar estimates of ocean surface vector currents depend on numerous sources of errors and differences such as instrument and sensor limitations sampling characteristics mooring response and geophysical variability we classify these sources of errors and differences as being associated exclusively with the current meter as being associated exclusively with the hf radar or as a result of differing methodologies in which current meters and hf radars sample the spatially and temporally varying ocean surface current vector field in this latter context we consider three geophysical processes namely the stokes drift ekman drift and baroclinicity which contribute to the differences between surface and near surface vector current measurements the performance of the hf radar is evaluated on the basis of these expected differences vector currents were collected during the high resolution remote sensing experiment ii off the coast of cape hatteras north carolina in june 1993 the results of this analysis suggest that 40 60 of the observed differences between near surface cm and hf radar velocity measurements can be explained in terms of contributions from instrument noise collocation and concurrence differences and geophysical processes the rms magnitude difference ranged from 11 to 20 cm s 1 at the four mooring sites the average angular difference ranged between 15 o and 25 o of which about 10 o is attributed to the directional error of the radar current vector estimates due to the alignment of the radial beams

paleomagnetism of mesozoic and tertiary rocks from east el owenat area southwest egypt ten sites 310 samples from alkali syenite at east el oweinat 23 2 n 29 5 e yield a stable mean direction of magnetization d 340 3 i 19 9 with 95 12 1 k 13 4 n 10 after alternating field cleaning resulting in a pole at 67 8 n 268 8 e with a95 8 6 this pole position agrees with the other upper cretaceous pole positions of africa from seven sites 82 samples from upper cretaceous nubian sandstone at east el oweinat a mean direction d 349 9 i 27 1 with 95 10 1 k 37 8 mixed polarity was obtained after thermal demagnetization combined with previous investigations on nubian sandstone at other localities schult et al 1978 1981 this yields a pole at 80 8 n 238 9 e with a95 3 2 k 435 9 n 30 five sites from tertiary basalt yield a mean direction d 12 4 i 23 9 and 95 9 2 k 46 6 after alternating field cleaning which yield a paleopole position at 74 1 n 159 8 e with a95 6 0 k 107 8 n 5 the paleopole positions of east el oweinant rocks confirm the apparent polar wander path of africa established in previous papers hussain et al 1980 schult et al 1981 more comparisons with rotated south american and australian pole positions after proper reconstructions to africa show agreements with the present results

shallow water bathymetry derived from an analysis of x band marine radar images of waves image sequences of surface gravity waves are readily produced by standard marine x band radars these image sequences contain a great deal of information regarding wave parameters and their variation over an area by approaching the analysis of such data using image analysis techniques it is possible to map the variations in wave behaviour in a shallow water area wave celerity and direction can be mapped and inversion algorithms based on linear wave theory used to infer the underlying bathymetry knowledge of the period of the waves is necessary for the analysis and this can also be calculated from the radar data although there is some discrepancy between the figures derived from radar data and from an offshore s4dw instrument these discrepancies are investigated and the results presented three days of data from the holderness ii deployment during 1995 have been analysed and estimates of the bathymetry produced the calculated depths show a mean water level comparable to that read off an admiralty chart for the area and a tidal signal is also clearly superimposed on the data giving confidence in the water depths derived using this technique

comparison of the coe thellier thellier and microwave palaeointensity techniques using high titanium titanomagnetites results from a tertiary basaltic intrusion from the sydney basin new south wales abstract conventional thellier and microwave mw palaeointensity experiments accompanied by rock magnetic tests were conducted on samples from an early tertiary ca 49 ma basaltic intrusion the peats ridge pr basalt from the sydney basin thermomagnetic and low temperature susceptibility measurements suggest that the dominant magnetic mineral is ti enriched titanomagnetite tm65 tm50 and hysteresis results indicate that the majority of samples exhibit psd like behaviour some samples show evidence of alteration during laboratory heating but only at temperatures in excess of 400 c no alteration is observed in the dominant temperature range 70 300 c used for calculation of palaeointensities stepwise thermal demagnetisation studies reveal single component after removal of a small viscous reverse polarity magnetisations in all samples with a mean characteristic remanence chrm direction of d i 197 60 95 5 k 62 coe thellier thellier ctt experiments yielded a high success rate with 68 of samples conforming to standard acceptance criteria microwave mw palaeointensity experiments predominantly using the perpendicular applied field technique produced a greater success rate of 82 mean palaeointensities of 27 1 4 4 t n 21 and 27 4 4 0 t n 28 were obtained from the ctt and mw techniques respectively these means could not be distinguished statistically and the respective quality indicators were similar these results suggest that the new microwave technique for calculating palaeointensities is in this case equivalent to the well established ctt technique this is an intuitive outcome given that rock magnetic analyses suggest that alteration does not occur below the curie temperature of the samples our results therefore provide a positive test for the equivalence of the mw and ctt techniques the virtual dipole moment vdm value for the intrusion is 4 7 0 7 10 22 am 2 suggesting that the dipole field was approximately 59 of the present day value at ca 49 ma this provides a valuable data point from the southern hemisphere for a sparsely covered time period in the global palaeointensity database

comments on cretaceous climatic equability in polar regions recently we examined the apparent contradiction of the former occurrence of extensive biota at very high palaeolatitudes as evidenced principally by the cretaceous flora and fauna of the gippsland and otway basins of victoria douglas and williams 1982 our study was prompted by new palaeomagnetic data which indicated near polar palaeolatitudes for southeastern australia during the cretaceous supplementary evidence of floras and faunas at high northern palaeolatitudes supported the conclusion that in view of the apparent respiration requirements of the flora reasonable equability of light day night cycle throughout the year is indicated for polar regions during the late mesozoic and earliest cenozoic we further suggested that a reduced obliquity of the ecliptic may have been the cause of such equability it should be pointed out that we offered no explanation of the relatively temperate climate of polar regions during the cretaceous compared with polar regions today a reduction in obliquity would increase equability of light and insolation at high latitudes but cannot account for overall polar warming axelrod 1984 reviewed alleged palaeopolar biota including our cretaceous forms and explained them by the nature of the thermal environments in polar regions and by the physiological responses of plants and animals allied to those that lived there he questioned the necessity for equability of light and the idea of a reduced obliquity we find his thesis unconvincing however and emphasize the following points 1 it is clearly established that in southeastern australia during the early cretaceous forests comprising a diverse partly evergreen flora ranging from cryptogams to large trees were extant these forests afforded habitats for a wide range of animal life including dinosaurs 2 the mesozoic apw path for australia schmidt and embleton 1981 ndicates that this biotic community existed at very high to polar palaeolatitudes ca 70 85 s the australian palaeomagnetic data are supported by apw paths for other gondwana continents after reconstruction or

an interpretation of cretaceous and tertiary biota in polar regions abstract rich fossil floras and vertebrate faunas lived within the arctic and atarctic circles during the cretaceous and paleogene these occurrences seem explicable by the nature of the thermal environments in polar regions and by the physiological responses of plants and animals allied to those that lived there there seems no need to invoke a lower tilt to the earth s axis to provide greater warmth and light in polar regions to account for these fossil records

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

application of the linear dispersion relation with respect to depth inversion and remotely sensed imagery remote sensing methods have been developed to estimate bathymetry through the use of a theoretical relationship between wave speed and water depth known as the linear finite depth dispersion equation for surface gravity waves the authors describe a validation effort encompassing several hundred observations of wavenumber magnitude for sea swell frequencies obtained over a wide variety of conditions to investigate possible error sources resulting from the practical application of this relationship these wavenumber estimates were computed from pressure gauge signals using signal processing algorithms that can be equivalently applied to measurements of wave phase as imaged through remote sensors the major goal was to determine the accuracy of the dispersion relation while attempting to minimize errors associated with sensor positioning tidal variations and doppler shifts due to mean currents for water depths outside the surf zone the linear dispersion relation is highly accurate with average depth estimation errors on the order of 3 9 of the observed depth in shallower regions nominally less than 4 m for this field site where wave breaking is evident and nonlinear shoaling effects are more pronounced normalized depth errors of over 50 were commonly observed with most predictions being deeper than observations strong correlation between these bias errors and measured wave heights emphasizes the importance of accounting for wave amplitude in the calculation of shallow water phase speeds for depth estimation a simple depth correction is provided to allow for bathymetry estimation within the surf zone

palaeomagnetic dating of late cretaceous to early tertiary weathering in new england n s w australia abstract palaeomagnetic dating of australia s regolith is becoming more refined with advances in techniques and better definition of the late mesozoic and cenozoic apparent polar wander path of australia the suspected great antiquity of parts of the regolith is being confirmed through the application of palaeomagnetic dating to authigenic iron oxides which form during weathering earlier palaeomagnetic investigation tentatively suggested that deeply weathered volcanics in the new england area formed in the mesozoic implying that ideas regarding the palaeoenvironment of new england may need considerable revision published dates for other unweathered volcanics from this area are k ar ages of 21 8 ma 32 8 ma and 25 1 ma the earlier palaeomagnetic conclusions were based on results from only one the sugarloaf of the seven separate localities nine sites originally sampled these results being the only results that were internally consistent follow up work using a high sensitivity cryogenic magnetometer has now yielded consistent results from the six other localities which support those from the sugarloaf but a revised weathering age of about 60 ma seems more likely this age is virtually identical to that determined for the morney profile in southwestern queensland

viscous remanent magnetization model for the broken ridge satellite magnetic anomaly a range of crustal models for the interpretation of the broken ridge satellite magnetic anomaly have been constructed from bathymetric data the source magnetizations were assumed to be constant in direction throughout the source region and parallel to the present earth s field at the center of the source region the model calculations were made at the observation points of a selected set of magsat investigator b passes with a variable magnetic field direction calculated from the mgst 4 81 field model the horizontal perimeter of all the models was defined by the departure of the broken ridge bathymetry from an average oceanic depth of 4 5 km a topographic model with an upper surface defined by the bathymetry of the ridge and a lower surface defined by the average oceanic depth requires a magnetization of 42 a m to account for the observed anomaly amplitude an airy type isostatic model with an upper surface defined by the bathymetry of the ridge and a lower surface predicted from the bathymetry requires a magnetization of 6 a m to account for the observed anomaly amplitude a midcrust model with an upper surface at the average oceanic depth and a lower surface at the average oceanic moho requires a magnetization of 13 a m to account for the observed anomaly amplitude a comparison of the locations of the model and observed anomaly peaks shows that the broken ridge anomaly can be modeled assuming present field directions there is not sufficient sensitivity in the data to distinguish between the models on the basis of anomaly location the model magnetizations vary from 6 a m where the whole crust is uniformly magnetized to 42 a m where the topographic expression of the ridge is the source of the anomaly the strength of the required magnetization contrasts cannot be accounted for by induced magnetization if normal oceanic crustal materials are assumed to be the source for the observed anomaly measured and modeled remanent magnetizations of seafloor rocks are typically within the lower part of the range of required values but the higher magnetizations are associated with very young rocks and dredge samples it is concluded that the source magnetizations have been enhanced by the development of a viscous remanence effect since the last reversal of the earth s field

palaeomagnetic cleaning strategies abstract cleaning is a term used in palaeomagnetism to refer to laboratory methods designed to demagnetize preferentially the less stable components of magnetization although the diversity of methods suggests that there is a wide choice available this is illusory except in simple cases the wrong cleaning strategy may yield misleading results cleaning methods include thermal magnetic alternating field or a f low temperature chemical shock and microwave cleaning a cleaning strategy involves one or more cleaning methods applied in a specific sequence the design of a strategy is made easier with the a priori knowledge of magnetic mineralogy and granulometry or in other words rock magnetic properties although not a substitute for other rock magnetic experiments the variation of low field susceptibility with temperature k t not only provides information on magnetic mineralogy and granulometry but it also draws attention to chemical alteration that may occur during thermal cleaning apart from the rapid though reversible decrease of k associated with curie temperatures other diagnostic k t features include the low temperature about 140 c peak typical of multidomain md magnetite the high temperature hopkinson peak typical of fine grained magnetite and other magnetic minerals and the classic lepidocrocite maghemite haematite profile which is irreversible examples are given where the remanence caused by lightning can be effectively eliminated only by applying a f or low temperature lt pre treatment such remanence may be an isothermal remanent magnetization irm or a combination of irm and anhysteretic remanent magnetization arm as the unblocking temperature of relatively low coercivity md grains may extend to high temperature it is often desirable to suppress md remanence an example is given of palaeointensity determination with the without lt pre treatment the nature of the lt transition is briefly addressed in the light of a rare double low temperature peak which may reflect both the isotropic point and the verwey transition

on the accuracy of hf radar surface current measurements intercomparisons with ship based sensors high frequency hf radar systems can provide periodic two dimensional vector current estimates over an area approaching 1000 km as the use of these hf systems has gained wider acceptance a number of attempts have been made to estimate the accuracy of such systems however comparisons of hf radar current estimates with in situ sensors are difficult to interpret since hf systems measure currents averaged over an area of 1 km 2 and to a depth of only 50 cm while in situ sensors measure currents at a point and somewhat greater depths 1 to 10 m previous studies of the accuracy of hf radar technology have thus attributed the differences observed between hf radar and in situ sensors to an unknown combination of vertical shear horizontal inhomogeneity in situ instrument errors and hf radar system errors this study examines the accuracy of hf radar current measurements using data from the 1993 high resolution remote sensing experiment conducted off cape hatteras north carolina data from four shipborne in situ current meters are compared with data from an ocean surface current radar oscr a commercial current measuring radar we attempt to discern the predominant sources of error in these data by using multiple simultaneous measurements from different sensors and by examining the variation of observed current differences as a function of location the results suggest an upper bound on the accuracy of the oscr derived radial currents of 7 to 8 cm s the measurement of near surface currents in the coastal environ ment is an important problem

depth inversion in shallow water based on nonlinear properties of shoaling periodic waves abstract two depth inversion algorithms dia applicable to coastal waters are developed calibrated and validated based on results of computations of periodic waves shoaling over mild slopes in a two dimensional numerical wave tank based on fully nonlinear potential flow fnpf theory in actual field situations these algorithms would be used to predict the cross shore depth variation h based on sets of values of wave celerity c and length l and either wave height h or left right asymmetry s2 s1 simultaneously measured at a number of locations in the direction of wave propagation e g using video or radar remote sensing techniques in these dias an empirical relationship calibrated for a series of computations in the numerical wave tank is used to express c as a function of relative depth koh and deep water steepness koho to carry out depth inversion wave period is first predicted as the mean of observed l c values and ho is then predicted either based on observed h or s2 s1 values the celerity relationship is finally inverted to predict depth h the algorithms are validated by applying them to results of computations for cases with more complex bottom topography and different incident waves than in the original calibration computations in all cases root mean square rms errors for the depth predictions are found to be less than a few percent whereas depth predictions based on the linear dispersion relationship which is still the basis for many state of the art dias have rms errors 5 to 10 times larger

australian antarctic depression from the mid ocean ridge to adjacent continents a morphotectonic depression some 15 106 km2 in area and centred on the australia antarctic discordance1 extends across the southern half of australia through the south east indian ocean to wilkes land in antarctica fig 1a b the depression is co extensive with a negative satellite free air gravity anomaly2 which suggests that the region is underlain by downward convecting asthenosphere here i outline the depression and explore its age in a pre breakup 55 myr reconstruction fig 1c the eastern highlands of australia and the transantarctic mountains are colinear because the eastern highlands were notably high during the late cretaceous and shared with the transantarctic mountains a history of volcanism in the jurassic both highlands probably constituted the eastern flank of the past depression in the centre of which thick 8 km late cretaceous sediment in the ceduna saddle3 and a possible mirror image in offshore antarctica mark its depocentre a broad area of late carboniferous marine sediments in southern australia4 may represent the earliest sign of the depression

a review of indian phanerozoic palaeomagnetism implications for the india asia collision abstract an overview is presented of the indian apparent polar wander path apwp for the phanerozoic and in particular for post late palaeozoic times this apwp is compiled on basis of data available at october 1981 from peninsular and extrapeninsular indo pakistan and from dsdp cores from the indian plate one of the more important and newly recognized features of this apwp is a large scale triassic jurassic loop this loop indicates a changeover from a late palaeozoic early mesozoic northwards and counter clockwise rotational movement with greater india reaching moderately low southern latitudes into a southwards and clockwise rotational movement during the early to middle jurassic recognizable likewise in apwp s from other gondwana continents this loop reflects the opening of the neotethys studies of extrapeninsular regions up to and north of the indus tsangpo suture zone have shown wide spread presence of magnetic overprints which delineate two regionally confined age groups younger overprints 20 40 m y predominate in the more external thrust zones older overprints 50 60 m y in contrast are found in the more internal zones both north and south of the indus tsangpo suture zone the latter are interpreted to reflect a late phase of relaxation in the early tertiary collision of greater india with south central asia or off shore island arcs which occurred at equatorial to low northern palaeolatitudes 0 10 n subsequent northwards movement over 2500 3000 km or more and impingement of greater india into southern asia resulted into large scale underthrusting of greater india along the main central thrust beneath southern tibet and to clockwise rotation of thrust units in the western himalaya a discrepancy between indian palaeomagnetic data and results available todate from southern tibet is discussed

palaeomagnetism of the early permian mount leyshon intrusive complex and tuckers igneous complex north queensland australia summary this study provides reliable precisely defined and well dated early permian 286 6 ma palaeomagnetic poles for australia from the mount leyshon intrusive complex mlic and the tuckers igneous complex tic both complexes are associated with prominent negative magnetic anomalies indicating the presence of rocks carrying stable remanence of reverse polarity with a koenigsberger ratio greater than unity the characteristic remanence carried by the intrusive phases and by locally remagnetized contact metamorphosed host rocks is always of reverse polarity consistent with acquisition during the permo carboniferous kiaman reverse superchron the corresponding palaeopoles confirm that australia occupied high latitudes in the early permian the pole positions are mlic lat 43 2 s long 137 3 e dp 6 0 dm 6 4 q 6 tic lat 47 5 s long 143 0 e dp 6 0 dm 6 6 q 6 permian palaeomagnetic overprinting is detectable at considerable distances from the mlic 2 3 km well beyond the zone of visible alteration the primary nature of the early permian palaeomagnetic signature is established by full baked contact aureole tests at both localities other new data from australia are consistent with the poles reported here comparison of the australian african and south american apparent polar wander paths apwp suggests that mean permian and triassic poles from west gondwana particularly from south america are biased by remagnetization in the jurassic cretaceous and that the late palaeozoic mesozoic apwp for gondwana is best defined by australian data the australian apwp exhibits substantial movement through the mesozoic provided only that the time averaged palaeofield was zonal the early triassic palaeomagnetic data from australia provide an important palaeogeographic constraint that the south geographic pole was within or very close to se australia around 240 ma the new early permian poles are apparently more consistent with pangaea b type reconstructions of gondwana and laurussia than with the pangaea a2 configuration this may be partly an artefact of reconstruction problems within gondwana as systematic differences between approximately coeval apparently reliable permo carboniferous poles from africa south america and australia are evident in standard gondwana reconstructions these discordances require a tighter fit of the southern continents suggesting that some attenuation of continental margins not accounted for in the reconstructions has occurred during breakup of gondwana or that the fit between east and west gondwana needs to be substantially modified if stretching of continental margins during breakup of supercontinents is a general phenomenon it may help to ameliorate but not solve the long standing controversy regarding pangaea reconstructions although alternative pangaea reconstructions such as pangaea b may reconcile poles from laurussia with australian poles in the late carboniferous early permian no plausible reconstruction can bring the early triassic poles into agreement this suggests that persistent departures from a pure dipole field may have been present in the early triassic lesser but still significant non dipole effects may also have been present during the late carboniferous and permian and may help resolve the pangaea a versus b controversy without requiring substantial attenuation of continental margins or intracontinental deformation we suggest that the most parsimonious interpretation of the palaeomagnetic and geological information is that laurussia and gondwana remained in a pangaea a2 type configuration through the permian and triassic discordance between the apwps for these two supercontinents is attributable mainly to persistent non dipole components of the geomagnetic field which were most important in the early triassic

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

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

late mesozoic and cenozoic palaeomagnetism of australia iii bias corrected pole paths for australia antarctica and india summary palaeomagnetic results from part i of this study and their analysis in part ii are combined to eliminate bias from the cenozoic apparent polar wander path for australia a bias due to non dipole components in past geomagnetic fields or for poles calculated from hot spot data due to the motion of hot spots relative to the earth s rotational axis this path is extended in approximately bias free form to the late mesozoic and indicates a significant change in the drift direction of the continent between 26 and about 60 ma the bias corrected australian path is used first with seafloor spreading data for the southern ocean to derive a corresponding late mesozoic cenozoic pole path for antarctica the latter shows that the antarctic drift direction reversed in the early tertiary it is suggested that the early tertiary directional changes of both australia and antarctica are part of a global reorganization of plates during the eocene postulated by rona richardson cande mutter and patriat achache next the australian path is compared with hot spot data from the african and australian plates indicating a movement of the hot spots relative the earth s rotational axis during the cenozoic the direction of this movement is found to be consistent with previous results from other parts of the world finally the australian path is used together with non dipole components in the geomagnetic field to explain a prominent westward displacement of the mid and late cenozoic poles of india relative to those of australia because of uncertainties in the original poles and in the analysis the present results are likely to contain appreciable errors nevertheless their consistency with independent findings supports the dipole quadrupole model of part ii for mid and late cenozoic geomagnetic fields

paleoclimate and polar wander abstract fossil faunas floras and 18 o temperatures indicate that weak or no meridional temperature gradients existed over the continents from triassic to eocene for much of this time tropical pacific 18 o temperatures were some ten degrees colder than at present while arctic and antarctic regions apparently enjoyed warm temperate to semitropical climates polar wander involving displacement of the poles to what are now tropical marine latitudes is offered to explain this uniformly warm paleoclimate this hypothesis is supported by a theoretical model which is discussed

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

the kiaman reversed polarity superchron at kiama toward a field strength estimate based on single silicate crystals abstract we present the first geomagnetic paleointensity measurements on single plagioclase crystals from lavas formed during the 262 318 ma permo carboniferous reverse polarity superchron commonly known as the kiaman rock magnetic experiments suggest that feldspar crystals separated from two lavas of the kiaman superchron type area near kiama australia carry pseudo single domain low ti magnetic inclusions capable of faithfully retaining a primary paleointensity signal thellier paleointensity experiments yield virtual dipole moments of 8 5 0 2 1022 am2 and 9 3 0 3 1022 am2 for these crystals furthermore these results lack the alteration problems that prohibit paleointensity and sometimes paleodirection determination using whole rock lava samples from the type area the derived field strengths are 5 6 times higher than some other virtual dipole moment vdm values of kiaman age derived from whole rock igneous samples this suggests either high paleointensity variability during the kiaman superchron or that unrecognized non ideal magnetic behavior has compromised some prior paleointensity results reported from whole rocks elsewhere

paleomagnetism and paleothermometry of the sydney basin 2 origin of anomalously high unblocking temperatures the milton monzonite of southeastern australia was thermoviscously remagnetized as a result of cretaceous burial and uplift thermal demagnetization separates the low unblocking temperature lt overprint from the high unblocking temperature ht primary remanence with a relatively sharp junction between lt and ht components in vector projections for single domain grains the junction temperature tl between two such vectors corresponds to the maximum blocking temperature tr reactivated in nature apart from a correction for the difference between natural and laboratory timescales however measured tl values are distributed over an implausibly wide range 250 c for burial remagnetization of an untilted intrusion like the milton monzonite furthermore many tl values are anomalously high compared to the predictions of single domain theory multidomain grains are the cause of these anomalies samples pretreated before thermal demagnetization by zero field cycling to liquid nitrogen temperature so as to erase multidomain remanence and isolate single domain remanence do have the theoretically expected tl values in these samples realistic remagnetization time and temperature tr tr conditions in nature are predicted using the t t contours of pullaiah et al 1975 the anomalously high tl values before low temperature treatment are due to multidomain grains which carry 50 of the lt overprint the lt thermal demagnetization curve in samples dominated by multidomain grains is quasi exponential in shape with a high temperature tail extending almost to the curie point as predicted by multidomain theory these high lt unblocking temperatures which are much greater than plausible remagnetization temperatures reached in nature overlap and mask the lower part of the ht unblocking temperature spectrum driving up tl values and leading to inflated estimates of tr although multidomain remanence is a sufficient explanation of anomalously high unblocking temperatures of thermoviscous overprints in the milton monzonite chemical overprinting may be a factor in other lithologies and tectonic settings

long term landscape evolution of the northparkes region of the lachlan fold belt australia constraints from fission track and paleomagnetic data abstract apatite fission track thermochronology aftt and paleomagnetic pm results have been used to constrain the late paleozoic to cenozoic landscape evolution of the lachlan fold belt lfb around the northparkes copper gold deposit in east central new south wales the present day landscape of this region of the lfb is relatively flat with little expression of the underlying rock and has previously been interpreted to indicate long term stability of the region since the end of lfb orogenesis in the early carboniferous this was presumably borne out by pm analyses from thick weathered horizons within open pits at the mine which suggested that significant periods of weathering and hence relative landscape stability prevailed during the early to middle carboniferous and at some time during the cenozoic results from aftt analyses however indicate that the region must have experienced significant episodes of cooling denudation during the mid permian to mid triassic and during the early cenozoic as

southern polar forests the early cretaceous floras of victoria and their palaeoclimatic significance abstract a diverse fossil flora including cryptogams pteridosperms cycadales bennettitales ginkgoales coniferales and angiosperms occurs in early cretaceous fluvial and lacustrine strata in the otway and gippsland basins in southern victoria both evergreens e g araucarians cycads ferns and deciduous or semi deciduous forms e g certain pteridosperms and ginkgoales seem to have been represented certain ferns ginkgos and conifers grew to a large size overall the assemblages are typical of early cretaceous floras the associated fauna includes dinosaurs hypsilophodontids allosaurs lepidosaurs chelonians birds fish including the lungfish ceratodus and insects the evidence of the biota as a whole suggests a warm to cool temperate relatively equable climate of moderate seasonality with no widespread winter freezing the complex mesozoic apparent polar wander path apw indicated for australia places victoria in high to polar palaeolatitudes ca 70 85 s during the early cretaceous this apw path is supported by paths for other gondwana continents the existence of the victorian early cretaceous forest and biotic communities through polar nights of about two to five months duration is difficult to accept evergreen species would have required relative equability of light whatever the temperature the dinosaurs foliage throughout the year and the lungfish warm to temperate conditions without freezing in view of the consistency of mesozoic palaeomagnetic results for gondwanaland and the enigmatic presence of mesozoic and early cenozoic fossil floras and faunas in very high northern palaeolatitudes the possibility of a reduced obliquity of the ecliptic in mesozoic early cenozoic time should be considered

accuracy of bathymetry and current retrievals from airborne optical time series imaging of shoaling waves a sequence of visual images of shoaling ocean waves collected from an aircraft can be used to retrieve maps of water depth and or currents the data are mapped to rectilinear coordinates on the mean ocean surface and three dimensional 3d cubes of these data typically 2 min dwell and 256 m spl times 256 m square area are fourier transformed to provide the 3d frequency wavenumber spectrum of the modulations the spectrum is fitted by the theoretical two dimensional dispersion surface for linear gravity waves with the depth and current vector as free parameters and the errors determined by comparison with simultaneously collected in situ data very little attention has been focused on the limitations and inherent errors in this approach for retrieving these parameters in the past this paper examines the dependence of these errors upon various instrumental and collection geometry parameters in order to estimate the achievable retrieval accuracy and provide collection guidelines significant errors occur when the mapping is inaccurate and when the data cubes are too small either spatially or temporally data cubes of the size given above or larger are required to contain the relative errors within 5 to 10 of the ground truth values the spatial resolution and temporal sampling rate are less critical and pixel sizes of spl sim 3 4 m and framing rates of spl sim 0 5 hz for depth and 1 2 hz for currents are sufficient for providing adequate results with the data examined here finally we show that the covariance matrix from the functional fit provides a quantitative measure of the retrieval accuracy independent of in situ data

paleothermometry of the sydney basin evidence from overprinting of magnetizations of late permian and mesozoic rocks and from the rank of permian coals and mesozoic phytoclasts coal particles suggests that surface rocks in the sydney basin eastern australia have been raised to temperatures of the order of 200 sup 0 c or higher as vitrinite reflectance an index of coal rank or coalification is postulated to vary predictably with temperature and time estimates of the paleotemperatures in the sydney basin based on observed vitrinite reflectance measurements can be made in conjunction with reasonable assumptions about the tectonic and thermal histories of the basin these estimates give maximum paleotemperatures of present day surface rocks in the range 60 249 sup 0 c depending on factors such as location in the basin the thickness of the sediment eroded and the maximum paleogeothermal gradient higher coal rank and consequently larger eroded thicknesses and paleogeothermal gradients occur along the eastern edge of the basin and may be related to seafloor spreading in the tasman sea on the basin s eastern margin a theory of thermal activation of magnetization entailing the dependence of magnetic viscosity on the size distribution of the magnetic grains is used to obtain an independent estimate of the maximum paleotemperaturesmore in the sydney basin this estimate places the maximum paleotemperature in the range 250 300 sup 0 c along the coastal region both coalification and thermal activation of magnetization models provide strong evidence of elevated paleotemperatures which in places exceed 200 sup 0 c and the loss of sediment thicknesses in excess of 1 km due to erosion less

eustatic and palaeoenvironmental assessment of the mid cretaceous bathurst island group of the money shoals platform northern australia abstract the cretaceous system of the money shoals platform consists of the bathurst island group which is extensively developed on the continental borderland of northern australia the platform experienced a simple post cretaceous tectonic history and in its southern part the bathurst island group is nonconformable on precambrian basement an ideal circumstance for evaluating eustacy and palaeoenvironmental succession the group records a long term sea level cycle of late aptian mid turonian age its lowest part represents a transgressive systems tract developed on a pediment surface of very low local and regional relief compositionally mature glauconitic sandstone and radiolarian mudstone are characteristic facies indicative of terrigenous sediment starvation for the shallow transgressive sea which received wind driven plankton bearing currents from the shelf edge 400 km to the north a district scale nodular phosphorite horizon and associated highly condensed section capping the transgressive suite represents the culmination of deepening it is succeeded by a shelfal mudstone succession comprising the bulk of the bathurst island group and interpreted as a highstand systems tract clay mineralogy of this and the underlying radiolarian mudstone is uniform and dominated by smectite mixed layer species of poor crystallinity the clay assemblage is attributed to a pedigenic origin associated with weathering of moderate intensity on a poorly drained low relief landscape the upper part of the group comprises bioturbated glauconitic and quartzose sandstone displaying sedimentary evidence of high energy depositional conditions consistent with regression it is viewed as a prograding aggrading shelf margin systems tract which accumulated under circumstances of declining accommodation a disconformity at the top of the group cut on strata of mid turonian age completed the sedimentary cycle calculated sedimentation rates indicate a major change in detrital sediment supply broadly coincident with the passage from transgressive to highstand systems tract and unrelated to eustacy the change is attributed to mid cretaceous landscape rejuvenation it is also reflected in the late albian cenomanian sedimentary record of the epicontinental great artesian basin where enhanced sediment supply likewise overprinted and obscured the eustatic signature mid cretaceous landscape rejuvenation reflected in the sedimentary record broadly correlates with evidence of uplift in eastern and southern australia now recognised from fission track studies it also correlates with a widely recognised palaeomagnetic overprint attributed to a mid cretaceous thermal event affecting the crust of southern and eastern australia although short term third order sea level cycles are not apparent for the bathurst island group three eustatic episodes related to global patterns can be recognised late aptian transgressive onlap early albian maximum flooding and late turonian regression

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

estimation of wave phase speed and nearshore bathymetry from video imagery a new remote sensing technique based on video image processing has been developed for the estimation of nearshore bathymetry the shoreward propagation of waves is measured using pixel intensity time series collected at a cross shore array of locations using remotely operated video cameras the incident band is identified and the cross spectral matrix is calculated for this band the cross shore component of wavenumber is found as the gradient in phase of the first complex empirical orthogonal function of this matrix water depth is then inferred from linear wave theory s dispersion relationship full bathymetry maps may be measured by collecting data in a large array composed of both cross shore and longshore lines data are collected hourly throughout the day and a stable daily estimate of bathymetry is calculated from the median of the hourly estimates the technique was tested using 30 days of hourly data collected at the sandyduck experiment in duck north carolina in october 1997 errors calculated as the difference between estimated depth and ground truth data show a mean bias of 35 cm rms error 91 cm expressed as a fraction of the true water depth the mean percent error was 13 rms error 34 excluding the region of known wave nonlinearities over the bar crest the accuracy of the technique improved and the mean rms error was 20 cm 75 cm additionally under low amplitude swells wave height h 1 m the performance of the technique across the entire profile improved to 6 29 of the true water depth with a mean rms error of 12 cm 71 cm

time temperature relations for the remagnetization of pyrrhotite fe7s8 and their use in estimating paleotemperatures abstract paleotemperature controls the maturation of coal and hydrocarbons in sedimentary basins and is also important in determining paleogeothermal gradient and hence tectonic style in exhumed metamorphic terrains one method of estimating paleotemperature analyses the partial remagnetization of a rock due to heating in thick volcanic or sedimentary sequences over subcrustal heat sources such as plumes or at convergent plate margins the overprinted natural remanent magnetization nrm of a rock records both the age and the paleotemperature of remagnetization but a temperature correction from laboratory to geological time scales is required using theoretical time temperature relations time temperature relations are well known for magnetite fe 3 o 4 but are reported here for the first time for pyrrhotite fe 7 s 8 another common nrm carrier data for each mineral separately yield independent estimates of paleotemperature if geologically reasonable estimates of heating time can be made paleotemperature can be estimated without geological input if data for both minerals are combined together with the age of remagnetization determined from the paleomagnetic pole of the nrm overprint these paleotemperature estimates can be used to infer the history of heating and uplift following burial as a test case we examine thermally acquired nrm overprints carried by pyrrhotite fe 7 s 8 and magnetite fe 3 o 4 in the milton monzonite of southeastern australia these overprints record a heating event about 100 ma ago probably thermal doming prior to rifting of the tasman sea that upgraded coal rank in the sydney basin extrapolating from laboratory to geological times using the new time temperature contours for pyrrhotite we estimate that the presently exposed sydney basin in the vicinity of the milton monzonite was remagnetized by heating to 165 30 c for 100 ka assuming a paleogeothermal gradient of 70 c km appropriate for young or incipient rifts the depth of burial at the time of remagnetization is estimated to have been 2 3 0 4 km this figure is in excellent agreement with independent estimates based on reflectance data for the coal accessory mineral vitrinite

water depth and surface current retrievals from airborne optical measurements of surface gravity wave dispersion visible images of nearshore ocean waves obtained from an aircraft have been utilized to estimate the surface currents and water depth below the waves a digital framing camera was mounted in a motion stabilized turret and used to obtain temporal sequences of high quality optical images of shoaling ocean waves data on the position and attitude of the camera turret were used to map the image data to a rectilinear coordinate system at the level of the surface effectively separating the spatial and temporal modulations due to the waves the resulting three dimensional 3 d space time data sets were fourier transformed to obtain frequency wave number spectra of these modulations these spectra contain information on the propagation characteristics of the waves such as their wavelengths and frequencies and their directions and speeds of propagation the water depth and current vector have been estimated by choosing these parameters so that a best fit is obtained between the theoretical dispersion relation for linear gravity waves and these 3 d wave spectra image data sets were acquired during the shoaling waves experiment showex along the quasi linear coastline in the vicinity of the army corps of engineers field research facility frf near duck on the north carolina outer banks summary wave parameters and bathymetry and current retrievals are typically within 10 of contemporaneous in situ measurements though outliers occur

pangea in permian to jurassic time the apparent polar wander paths apwps for the northern and southern continents have been redetermined using revised time scales and data when plotted on the conventional pangea pangea a the paths are distinct but essentially linear and parallel from late carboniferous to late permian time both paths then undergo a sharp change in direction and converge so as to overlap in early to middle jurassic time if the permo triassic magnetic field was an axial dipole then paleomagnetic data show that pangea was mobile during most and possibly all of the mid triassic to mid jurassic interval because of the uncertainties in pole ages and positions and errors in measurements the new apwps are consistent with a range of pangeas in particular the data are compatible with two paleomagnetic pangeas a2 and a new class of pangea here named the d pangeas these resemble morel and irving s 1981 pangea b and the c pangeas of smith et al 1981 unlike the a2 pangeas the b c and d pangeas all require large 2000 km relative motion between the northern and southern continents geological data require the transition from an earlier pangea to pangea a to take place along a transform zone here named the pangea transform zone or ptz the ptz is considered to be technically analogous to the great glen fault of scotland four types of possible ptz are examined passing through either the western or eastern end of the brunswick magnetic anomaly of eastern north america or north and south of iberia the geological data suggest that those pangeas that require large displacements on ptzs that pass east of the brunswick magnetic anomaly are improbable b and c pangeas are snapshots giving precise paleomagnetic reconstructions d pangeas fit long stretches of the apwps as well as possible a2 pangeas fit the apwps moderately well but also require the geological displacement to be smaller the differences in displacement between the d and a2 pangeas reflect geometrical relationships between euler poles ptz curvature and the apwps the general geological evidence suggests that d pangeas are less probable than a2 pangeas but that they cannot be rejected transition from a2 to a is most likely to have occurred via a sequence of rotations about different poles rather than a single rotation in detail the conventional pangea requires modification africa must be broken into at least two fragments along the benue trough and its northern continuation northwest africa then fits more tightly into northern south america which modifies the apwps and reduces the gap between them by including the effects of continental extension and using detailed geological data the gap can be reduced to one in which the a63 circles touch or overlap non dipole fields or an expanding earth need not be invoked to explain the mismatch of the apwps on the conventional pangea the finite rotation required for the older pangea to pangea a is very close to van der voo and french s 1974 single rotation for a2 to a but is actually the sum of three smaller rotations that reflect the modification to pangea a continental extension and the postulated ptz displacement of the possible ptzs a ptz parallel to the west african continental magnetic anomaly with a displacement of about 170 km gives a better fit of this anomaly to the east coast magnetic anomaly of north america further refinements to pangea a2 will depend on a better knowledge of stretching factors on the passive continental margins of the modified pangea a and incorporation of rotations due to major faults such as the south atlas fault in morocco

palaeomagnetism of the ejecta bearing bunyeroo formation late neoproterozoic adelaide fold belt and the age of the acraman impact abstract a new palaeomagnetic study has been conducted on haematitic shales and siltstones of the late neoproterozoic bunyeroo formation in the adelaide fold belt geosyncline south australia which host an extensive horizon of shock deformed rock fragments and microtektite like material of probable impact origin thermal step demagnetisation of 116 samples of red shale and siltstone from six sections sites revealed a high temperature component with a bedding corrected site mean direction of remanence of d 56 6 i 29 3 95 10 7 that gives a pole at 18 1 s 16 3 e dp 6 5 dm 11 8 the high temperature component provides a positive tectonic fold test 99 level of confidence the bunyeroo high temperature remanence direction is near the remanence direction d 50 i 40 indicated by modelling the subsurface magnetic source of the central high amplitude anomaly at acraman australia s largest confirmed meteorite impact structure 220 350 km west of the adelaide fold belt and also is close to the mean direction d 48 3 i 54 7 95 5 2 determined for surface melt rock from acraman statistical tests show that the virtual geomagnetic poles indicated by the directions for the subsurface central magnetic source and surface melt rock at acraman may be regarded as subsets of the bunyeroo palaeomagnetic pole position indicating that the three pole positions are statistically indistinguishable the results imply that the subsurface magnetic source and surface melt rock acquired their remanence in the ambient geomagnetic field during cooling after the impact when structural disturbance had ceased while the bunyeroo formation was accumulating the agreement among the various remanence directions argues strongly that the ejecta horizon in the bunyeroo formation was derived from acraman the present findings confirm that the acraman impact occurred in the late neoproterozoic about 590 ma which is the age of the bunyeroo formation provided by rb sr whole rock shale dating of equivalent and contiguous strata in the adelaide fold belt region the bunyeroo palaeomagnetic data give a palaeolatitude of 15 indicating a low palaeolatitude for the acraman impact and supporting other findings that the adelaide fold belt occupied low to equatorial palaeolatitudes during the late neoproterozoic