elastic flexure and distributed deformation along australia s north west shelf neogene tectonics of the bonaparte and browse basins neogene collision between australia and the banda arc modified the adjacent bonaparte and browse basins of the north west shelf of australia modification comprised both continuous long wavelength amplification of permo carboniferous basement topography and flexure and normal faulting of triassic recent sedimentary cover deformation was continu ous across the browse and bonaparte basins despite the basins beings separated by a rupture barrier style accommodation zone the browse bonaparte transition the degree of basement control and mechanisms of fault linkage vary significantly across this transition and reflect differences in the structural relief amplitude and depth of rifted basement either side of the transition neogene collision amplified the architectural divide amplification of basement topography over wavelengths of several hundred kilometres was associated with negligible horizontal length change the transcurrent component of neogene deformation was partitioned outboard of any continuous flexural amplification

on the suitability of baked clay for archaeomagnetic studies as deduced from detailed rock magnetic studies summary extensive rock magnetic investigations have been carried out on baked clays from four kilns two from bulgaria and two from switzerland found in archaeological sites of different age knowledge of the magnetic characteristics of the grains responsible for the archaeomagnetic signal enables us to determine which baked clays have the stablest magnetization and why this is so this is important in directional studies but even more so in painstaking palaeointensity studies that require a very careful evaluation of the suitability of the burnt clay material the proposed rock magnetic experiments enable the identification of the carriers responsible for the remanence and an adequate interpretation of the experimental results connected with the palaeointensity evaluation the experimental methods employed are illustrated with the particular results obtained from each of the four kilns studied the preliminary elucidation of the magnetic mineralogy of the archaeological samples helps first by obtaining a more reliable palaeointensity result and secondly by explaining some of the discrepancies in the palaeodirectional results examples of successful and failed palaeointensity experiments are given in relation to the magnetic properties previously established for each oven the burnt clay materials in this present study satisfy the essential condition of carrying a thermoremanence in spite of that it is shown that there are many factors that can produce undesirable magnetic properties and thus restrict the suitability of these materials for archaeomagnetic analysis the most important factors influencing the magnetic behaviour during magneto diagnostic experiments are the degree of heating in antiquity the initial composition of the unbaked material and the burial conditions the large difference in heating temperatures within a particular archaeological feature is a major cause of variation in magnetic behaviour amongst individual specimens and so preventing a successful pre selection of specimens for palaeointensity experiments nevertheless the study has shown a very good coincidence between the determined rock magnetic characteristics and the success rate in palaeointensity evaluation

structural style in a young flexure induced oblique extensional system north western bonaparte basin australia abstract in the north western bonaparte basin north west shelf of australia neogene to recent flexure induced extension superimposed obliquely over the mesozoic rift structures thus the area offers a good opportunity to investigate the dynamics and architecture of oblique extension fault systems analysis of basin scale 2d and 3d seismic data along the vulcan sub basin shows that neogene deformation produced a new set of extensional en echelon faults at places accompanied by the reactivation of the mesozoic faults the pre existing mesozoic structures strongly control the distribution of the neogene recent deformation both at regional and local scales main controls on the neogene recent fault style density and segmentation linkage include 1 the orientation of the underlying mesozoic structures 2 the obliqueness of the younger extension relative to the rift inherited faults and 3 the proximity to the timor trough three types of vertical relationships have been observed between mesozoic and neogene recent faults hard linkages seems to develop when both fault systems trend parallel therefore increasing risks for trap integrity it is suggested that the orientation of maximum horizontal stress s hmax relative to the mesozoic faults forming hydrocarbon traps is critical for their potential seal leak behaviour stratigraphic growth across the faults indicates that main fault activity occurred during the plio pleistocene which corresponds to the timing of tectonic loading on timor island and the development of lithospheric flexure synchronism of normal faulting with flexural bending suggests that extensional deformation on the descending australian margin accompanied the formation of the timor trough

observations of gulf stream induced and wind driven upwelling in the georgia bight using ocean color and infrared imagery ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents chlorophyll temperature salinity coastal winds and sea level to study upwelling events in the georgia bight where the gulf stream and continental shelf waters strongly interact these interactions were observed over an 8 day period in april 1980 during which five independent upwellings occurred the upwellings included a nearshore wind driven upwelling enhanced by topographic effects three gulf stream filament induced upwellings and what appears to have been a gulf stream meander induced event the chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore the propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series both techniques yield nearly identical results for the phase speeds of each event there is evidence that one of the filaments accelerated as it entered into the charleston bump area where the gulf stream deflects offshore the other filament exhibited a steady deceleration as it moved past cape canaveral and eventually lost any semblance of wave motion also includedmore are data from april 1979 which offer corroborating evidence of filamentary structure and circulation intercomparisons of field measurements and the nimbus 7 coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0 1 7 0 mg m sup 3 54 references 22 figures 6 tables less

estimate of the magnetic anisotropy effect on the archaeomagnetic inclination of ancient bricks abstract the magnetic fabric of 59 bricks coming from 5 ancient kilns has been studied by measuring the anisotropy of magnetic susceptibility ams and the anisotropy of isothermal airm anhysteretic aarm and thermal atrm remanent magnetization the bricks are characterized by a well developed magnetic fabric that matches their flat shape the shape of the anisotropy ellipsoids is in almost all cases oblate with the maximum and intermediate axes lying parallel to the large face of the brick and the minimum axis perpendicular to it the directions of the principal axes are almost the same irrespectively of the type of anisotropy measured whereas the degree of anisotropy of the airm aarm and atrm is much higher than the ams as the bricks lie horizontally within the kiln the planar magnetic fabric results in an inclination shallowing of the archaeomagnetic direction with respect to that of the earth s magnetic field at the time of their last cooling estimation of this effect on the grounds of atrm measurements yields a shallowing that varies from 4 to 10 for individual samples such inclination difference may significantly bias archeomagnetic dating for the case of the canosa late roman kiln it leads to a dating error of more than two centuries

diachronous rifting drifting and inversion on the passive margin of central eastern north america an analog for other passive margins integration of new data with existing information indicates that the tectonic development of the passive margin of eastern north america between the carolina trough and scotian basin was considerably more complex than the classic two stage rift drift model first the transition from rifting to drifting was diachronous in the southeastern united states the rift drift transition occurred after the late triassic synrift deposition and before eastern north america magmatism in the earliest jurassic 200 ma in maritime canada the rift drift transition occurred after eastern north america magmatic activity and synrift deposition in the early jurassic and before postrift deposition in the early middle jurassic 185 ma second the deformational regime changed substantially after rifting on both the southern and northern segments of the margin generally northwest southeast postrift shortening replaced northwest southeast synrift extension northeast striking reverse faults formed and many of the rift basin boundary faults had reverse displacements in the southeastern united states the change in the deformational regime occurred in the late triassic early jurassic during the rift drift transition simultaneously diabase sills and dikes many striking nearly perpendicular to the trend of the rift basins intruded the continental crust and a massive wedge of volcanic or volcaniclastic rocks developed near the continent ocean boundary in maritime canada the change in the deformational regime occurred during or after the early jurassic and before or during the early cretaceous that is during the rift drift transition or early stages of sea floor spreading

magnetic fidelity of lunar samples and implications for an ancient core dynamo abstract some lunar rocks have stable magnetizations that provide compelling evidence for an ancient lunar core dynamo however a longstanding problem has been interpreting the unstable alternating field af demagnetization behavior observed in the remaining majority of the apollo lunar sample suite similar unstable behavior has also been observed for many meteorites it is unclear whether the behavior of these samples indicates that they formed in the absence of an ancient magnetizing field or whether they simply have poor magnetic recording properties it is necessary to distinguish between these two possibilities in order to determine whether paleomagnetic fields were present on a sample s parent body to address this issue we analyzed five samples whose rock magnetic properties span the full suite of observed demagnetization behaviors mare basalts 15556 15016 12017 10020 and troctolite 76535 we demonstrate that the effects of spurious anhysteretic remanent magnetization arm during af demagnetization in combination with multidomain magnetic carriers and magnetic remanence anisotropy are likely responsible for the apparently poor magnetic behavior of many lunar samples therefore the unstable af demagnetization behavior observed for many lunar samples is not alone sufficient for ruling out the presence of an ancient lunar core dynamo nevertheless spurious arm may explain the observation of surprisingly high 1 t apollo era paleointensity measurements for samples thought to have formed after the cessation of a lunar core dynamo

changes in direction of the remanence of rocks produced by stationary alternating field demagnetization summary a theoretical investigation of the way in which an isotropic rock containing single domain particles acquires both irm and arm or trm has indicated that stationary single axis alternating field af demagnetization with the af axis at an angle to the remanence vector should produce progressive angular changes in a single component remanence as demagnetization proceeds just before the remanence is completely removed it should lie at 90 to the af axis irrespective of the original orientation of the remanence apart from 0 experimental observations on a rock sample support these deductions this analysis has been extended to investigate the way in which arm or trm and irm are demagnetized by static three axis demagnetization methods which are used by some workers in palaeomagnetism theory in conjunction with the use of a numerical model predicts that an arm or trm should not undergo significant direction changes when these methods are applied but an irm should undergo progressive direction changes as demagnetization proceeds usually moving until it makes an angle of cos 1 1 3 with each of the three af axes just before it is removed confirmation that such changes do occur have been obtained by experiments on a rock sample the relative merits of static and tumbling af demagnetization methods are also discussed

a note on the charleston gyre the deflection of the gulf stream caused by a topographic feature the charleston bump located offshore of savannah georgia results in a quasi stationary cyclonic eddy the charleston gyre which is situated over the continental slope east of charleston and cape romain occasionally the upwelling associated with this eddy produces an enhancement in the surface layer primary production that is great enough to be detected by the nimbus 7 coastal zone color scanner czcs in this note a czcs image with simultaneous hydrography current and wind observations is presented that documents an unusual manifestation of the gyre in addition to the czcs image a seasat synthetic aperture radar sar image is included that clearly indicates the presence of the eddy adjacent to the gulf stream front

surface expression of an accommodation zone within the gulf of suez rift egypt the gebel gharamul region in the western gulf of suez offers an excellent outcrop example of the structural geometries associated with an accommodation zone termination the surface expression of the accommodation zone is dominated by a basement promontory which protrudes from the rift shoulder and underlies the junction of oblique ramps from two adjacent half grabens both of which face the gulf of suez the southern half graben represents the breakaway fault of the southwest dipping tilt block domain and the northern half graben represents the collapse of the upper plate above the northeast dipping tilt block domain basement and nubian rocks in the hanging walls above the opposing low angle detachments on either side of the accommodation zone are broken by gulf parallel synthetic normal faults and orthogonal transfer faults which act as block terminations and incrementally accommodate the large scale rotation and displacement between adjacent blocks the prerift and synrift stratigraphic succession is draped over this fault template resulting in a complex and variable distribution of structures the product of an inhomogeneous stratigraphic succession within an accommodation zone

tectonic inheritance and pliocene pleistocene inversion of the algerian margin around algiers insights from multibeam and seismic reflection data 1 the algerian margin has originated from the opening of the algerian basin about 25 30 ma ago the central margin provides evidence for large scale normal faults of oligo miocene age whereas transcurrent tectonics characterizes the western margin a set of nw se oriented dextral transform faults was active during basin opening and divided the 600 km long central margin into segments of 120 150 km the upper miocene plio quaternary and present day tectonic setting is however compressional and supports the occurrence of a margin inversion a process still poorly documented worldwide we show that the central algerian margin represents a rare example of inverted margin where the process of subduction inception is particularly well expressed and helps understand how extensional and transtensive structures are involved in margin shortening using multibeam bathymetry and multichannel seismic reflection sections from the maradja 2003 and 2005 cruises we evidence pliocene pleistocene shortening with contrasting styles along the margin between west khayr al din bank and east boumerdes dellys margin of algiers pre miocene structures such as basement highs and transform faults appear to control changes of the deformation pattern along this part of the margin resulting in different widths geometries and relative positions of folds and faults plio quaternary and active blind thrust faults do not reuse oligo miocene normal and transform faults during inversion but instead grow within the continental margin as testified for instance by the 21 may 2003 mw 6 8 boumerdes zemmouri earthquake at the foot of the continental slope and at the northern sides of basement highs interpreted as stretched continental blocks of the rifted margin the inherited structures of the margin appear therefore to determine this deformation pattern and ultimately the earthquake and tsunami sizes offshore the complex geometry of the fault system along the algerian margin suggests a process of initiation of subduction in its central and eastern parts

implications of paleomagnetic data on miocene extension near a major accommodation zone in the basin and range province northwestern arizona and southern nevada paleomagnetic data from volcanic and crystalline rocks elucidate the evolution of a major miocene accommodation zone in the northern colorado river extensional corridor the accommodation zone is a 10 km wide belt of intermeshing conjugate normal faults that facilitates reversals in the dominant tilt direction of fault blocks and dip direction of major normal fault systems tilt corrected means e g n 28 sites d 353 4 i 61 3 95 6 7 k 17 4 from miocene volcanic strata overlap expected miocene directions at the 95 confidence level these data and geologic relations suggest that at exposed structural levels the accommodation zone did not facilitate distributed strike slip displacement between opposing tilt block domains vertical axis rotations are probably negligible in most of the corridor as the miocene structural grain generally mimics that in the zone discrepancies between characteristic remanent magnetizations chrm in crystalline rocks and expected directions are therefore attributed to rotations about horizontal i e tilting or flexing axes chrms from cretaceous and miocene intrusions suggest 50 90 of tilting of large crystalline terranes on either side of the accommodation zone the magnitude of tilting inferred from the paleomagnetic data is similar to that of tertiary strata in nearby fault blocks implying that these crystalline terranes are parts of highly tilted fault blocks rather than flexed lower plate rocks major low angle normal faults that bound highly tilted parts of these crystalline terranes probably nucleated at steep dips and were rotated to gentle dips by block tilting paleomagnetic data indicative of negligible tilting e g miocene intrusions northern black mountains crystalline terrane n 13 sites d 359 i 55 95 9 k 24 and geologic relations imply that lower plate rocks may surface in both the east and west tilted domains 35 50 km away from the zone the trend toward shallower structural levels with respect to miocene extension and tapering of highly extended terrane toward the accommodation zone imply that the magnitude of upper crustal extension decreases toward the zone temporal patterns of major extension especially an apparently continuous northward younging across both the east and west tilted domains further suggest that the accommodation zone served as a long lived rupture barrier between conjugate normal fault systems rather than as a short term boundary between opposing systems that propagated toward and converged at the zone

controls on the distribution and growth of isolated carbonate build ups in the timor sea nw australia during the quaternary abstract isolated carbonate build ups icbs represent attractive hydrocarbon exploration targets they are often seen as long term transgressive features but their distribution within basins and growth history can be difficult to predict as they respond to the interplay between various tectonic eustatic and oceanographic parameters here we use a 3d seismic megasurvey 18 000 km2 combined with well data to understand the timing and mechanisms of formation of tropical quaternary icbs in nw australia at present the icbs are typically 1 30 km wide and form clusters of 150 build ups developing 2 85 km from the edge of a 650 km wide continental shelf our results demonstrate that the structural evolution of the margin had a major impact on the distribution of the icbs main period of fault activity commenced during the latest miocene early pliocene corresponding to the initial collision of the australian plate with banda arc fault activity increased from late pliocene and peaked during the early pleistocene it was associated with flexural reactivation of structural highs uplift and lows subsidence along the shelf margin seismic evidence of moat channel and drift deposits suggest that contour current activity intensified during the late early pleistocene ca 1 ma bp despite potentially good conditions for carbonate production basement highs and warm water ocean currents icbs did not form until the mid pleistocene ca 0 582 0 8 ma bp this age corresponds to the onset of major sea level fluctuations associated with repeated high amplitude 120 m rapid deglacial rises and slow falls thus we infer that the nw australia icbs formed due to 1 structural shaping of the margin 2 oceanographic changes and most importantly 3 onset of repeated high amplitude transgressions reactivating the carbonate production along isolated highs following 4th 5th order lowstand exposures and allowing catching up carbonate morphologies to develop

coupling of coastal zone color scanner data to a physical biological model of the southeastern u s continental shelf ecosystem 1 czcs data description and lagrangian particle tracing experiments nine coastal zone color scanner czcs images from the southeastern u s continental shelf area during april 1980 were processed and the resulting chlorophyll distributions were analyzed in conjunction with concurrent flow and temperature fields which were obtained from an optimal interpolation of current meter measurements from 17m the chlorophyll distributions obtained from the czcs showed high chlorophyll concentrations over the shelf and low chlorophyll concentrations over the offshore shelf region the variance of the czcs derived chlorophyll distributions was highest at the shelf break region the chlorophyll patterns at the shelf break varied with time and space and showed shapes characteristic of typical gulf stream frontal eddies high chlorophyll bands that were oriented along shelf isolated high chlorophyll patches and simple waveforms each event observed in the chlorophyll patterns corresponded with a gulf stream frontal eddy event that could be identified in the optimally interpolated flow and temperature fields lagrangian particle tracing experiments were also conducted to track the movement of the features observed in the czcs images the particles traced in these experiments showed movement that was consistent with the evolution of the patterns observed in the czcs chlorophyll distributions results of the lagrangian experiments indicate that the optimal interpolation of the current meter measurements reproduced the flow between successive czcs images these experiments provide evidence that the high chlorophyll bands seen in the czcs chlorophyll distributions were produced by the passing of gulf stream frontal eddy events

a theoretical and experimental comparison of the anisotropies of magnetic susceptibility and remanence in rocks and minerals summary susceptibility thermo remanent magnetization trm and isothermal remanent magnetization irm anisotropy ellipsoids have been determined for several rock samples the results indicate that the ellipsoid of initial susceptibility is less anisotropic than the trm and low field irm ellipsoids which are found experimentally to be of identical shape this suggests that palaeomagnetic data for anisotropic rocks may be corrected by using the anisotropy ellipsoid determined from magnetically non destructive low field irm measurements such irm measurements can also be used to obtain anisotropy axes of samples which are inherently anisotropic but which have a susceptibility which is too weak to be accurately measured the results for a series of artificial anisotropic samples containing magnetite particles of different sizes in the range 0 2 90 m were very similar to those for the rocks in contrast a comparison of the susceptibility and irm ellipsoids for anisotropic samples containing particles from a magnetic tape gave very different results in accordance with theory such results imply that susceptibility and irm ellipsoids could be used to determine whether anisotropic rocks contain uniaxial single domain particles magnetization confined to the easy axis or whether the particles are essentially multidomain

trm deviations in anisotropic assemblages of multidomain magnetite anisotropic assemblages of multidomain magnetite particles develop an anisotropy of magnetic susceptibility ams which in turn induces deviations of thermo remanent magnetization trm from the field direction from the theories of multidomain trm acquisition it is shown that the trm anisotropy tensor has its eigenvalue ratios ti related to the principal weak field susceptibility ratios pi by the order of magnitude ti p2i this relation has been experimentally verified on two sets of highly anisotropic rock samples the exponent has been determined to be 1 94 in the samples from a peruvian gabbro and 1 81 in those from the granite of flamanville nw france accounting for experimental difficulties in determining the trm anisotropy tensors these exponents are judged to agree well with the expected one it is therefore stressed that ams measurements provide a good means of evaluating the magnetic field direction from deviated trm directions providing magnetic carriers are mainly multidomain magnetites

oligocene and miocene carbonate platform development in the browse basin australian northwest shelf abstract extensive 2d and 3d seismic reflection data calibrated by wells provide new insights into the lateral extent morphology internal architecture and age of carbonate platforms in the subsurface of the browse basin australian northwest shelf nws the oldest carbonate build ups are interpreted as a giant bryozoan build up complex of oligocene age 34 03 27 8 ma in the late burdigalian tropical reef growth began and numerous reef rimmed carbonate platforms progressively coalesced into an extensive barrier reef from the mid langhian to the early tortonian the browse basin contained an elongate along margin barrier reef system over 500 km long this barrier reef possibly extended in the southwest into the northern carnarvon basin after the early tortonian reefs on top or landward of this major barrier reef system were smaller and less connected this significant reduction in area covered by reef rimmed platforms likely resulted from cooling following the mid miocene climate optimum and relatively high subsidence rates the reef rimmed carbonate platforms that formed between the late burdigalian and the early tortonian are very similar throughout the browse basin platform development after the early tortonian was regionally diverse high subsidence rates in the northern browse basin are interpreted to have promoted the development of thick aggrading platforms lower subsidence in the south led to thinner more widespread platforms recurrently shifting location in response to eustatic change the final phase of reef decline around 6 ma coincides with an increase in current driven drift sedimentation current related winnowing of sediments from the lagoons and slopes of the remaining carbonate platforms likely contributed to their final drowning

correction to observations of gulf stream induced and wind driven upwelling in the georgia bight using ocean color and infrared imagery by c r mcclain et al

kinematics and strain distribution in an orogen scale shear zone insights from structural analyses and magnetic fabrics in the gavarnie thrust pyrenees abstract this work aims to characterize the gavarnie thrust one of the large scale thrusts that define the alpine structure of the west central sector of the pyrenees a detailed comparison of structural analysis and magnetic fabrics is carried out for the paleozoic phyllonites of the gavarnie thrust in order to decipher strain distribution and transport direction the ams at room rt ams and low lt ams temperature and the airm can be correlated with the structural patterns kmin axes are mainly parallel to the pole of the s c or c planes and kmax axes are parallel to the transport direction and related to ductile s c structures furthermore the pj t changes across the shear zone characterize strain variations larger pj and t are found in the basal most deformed part of the shear zone and lower values are found where the interaction between alpine and variscan related petrofabrics is stronger we also interpret the reactivation of variscan inherited fabrics within the alpine shear zone in spite of the heterogeneous strain markers indicate a common top to the south n190e alpine transport direction which contrasts with the strong obliquity of the genetically related structures developed in the southern mesozoic sedimentary cover in this sense our data suggest a complete decoupling between basement and cover units during the alpine compression

early stage orogenesis in the timor sea region nw australia neogene collision between the australian eurasia and pacific plates was coeval with the growth of major depocentres in the timor sea seismic cross sections across these troughs identify a characteristic architecture all three lie inboard of diffuse horst like structural highs and all mimic older depressions in the top permian and upper jurassic surfaces distortion of pre tectonic aptian oligo miocene sequences indicates apparent trough subsidence was coupled to uplift of outboard highs rudimentary cross section restoration identifies negligible strike normal length change we interpret apparent neogene subsidence to reflect amplification of basement topography this was not accommodated by discrete structural inversion rather landward propagation of contractional strain caused continuous vertical amplification of basement topography at shallow levels normal faulting accommodated flexure and thin skinned collapse of detached sedimentary cover permitting it to shed away from structural highs and pond in adjacent troughs we infer that shortening of the north west shelf accommodated oblique convergence between australia and the eurasia pacific arc and speculate that the transcurrent component of this deformation was partitioned well outboard neogene modification is interpreted to reflect the earliest stages of collisional orogenesis