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

postapocalyptic greenhouse paleoclimate revealed by earliest triassic paleosols in the sydney basin australia the permian triassic boundary in the sydney basin of australia is coincident with a pronounced decrease in 13 c isotopic values of organic carbon the last coals anywhere in the world for all of the early triassic ca 6 m y time and extirpation of the glossopteris flora at the top of the illawarra and newcastle coal measures coal bearing paleosols of the latest permian represent extensive swamplands of the seasonally deciduous glossopteris flora in a humid cold temperate lowland southwest of an andean style volcanic arc stone rolls large ribs of floor rock up into the coal within some of the uppermost coals of the permian coal measures can be interpreted as string bogs of a kind now found in cold climates at latitudes of 68 70 which is compatible with a paleomagnetically estimated paleolatitude of 65 85 s for the sydney basin paleolatitude was not much different for earliest triassic time but paleosols of that age include inceptisols and entisols showing substantial chemical and textural weathering more like soils now forming at latitudes of 40 58 than those within polar circles this anomalous high latitude warmth set in at the permian triassic boundary sedimentation rates increased at the boundary marked by geochemically unusual acidification of clay and a dramatic carbon isotopic excursion these changes in environments and ecosystems can be explained by soil erosion following deforestation implied by the plant extinctions and abundant fungal remains at the permian triassic boundary evidence from paleosols can now be added to that from paleontological and isotopic studies showing that disruption of the carbon cycle at the permian triassic boundary resulted in a co 2 or ch 4 post apocalyptic greenhouse paleoclimate

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

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

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

changing fluvial environments across the permian triassic boundary in the karoo basin south africa and possible causes of tetrapod extinctions abstract the karoo supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern gondwana the strata record 100 million years of almost continuous sediment accumulation from the permo carboniferous 300 ma through to the early jurassic 190 ma under a range of climatic regimes and within several tectonically controlled sub basins alluvial sediments dominate the succession from the late permian onwards fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten fold biostratigraphic subdivision of these strata the permian triassic boundary in the karoo succession is marked by a major extinction of the herbivorous dicynodonts which co incides with a rapid change in fluvial facies this study uses field observations of the sedimentary facies palaeosols and in situ fossils of well exposed p tr boundary sequences in the southern karoo basin to provide evidence of environmental changes that may have caused the tetrapod extinctions in the main karoo basin below the p tr boundary sequence the sediments comprise drab greenish grey mudrocks with a few thick 3 12 m multistoried laterally accreted fine grained sandstone bodies the mudrocks host hydromorphic palaeosols with palustrine carbonate horizons and mostly disarticulated skeletal remains of dicynodon assemblage zone fauna above a transition zone of approximately 20 m thickness these strata change into reddish brown mudrocks with numerous thin 0 5 5 m ribbon sandstone bodies and more continuous sheet sandstones calcic palaeosols with rhizocretions nodular horizons and pervasive calcareous encrustation of articulated skeletons of lystrosaurus and associated fauna of the lystrosaurus assemblage zone within a 20 m thick interval of the transitional strata fossils of dicynodon and lystrosaurus occur together the facies transition that co incides with the latest permian dicynodont extinction is interpreted as a change in fluvial style from meandering to low sinuosity channels with general drying of the floodplain habitats and redistribution of vegetation belts the horsetails in particular became significantly reduced in areal distribution the changes in fluvial style in the karoo basin at the end of the permian were triggered by a pulse of thrusting in the southerly source area dated at 247 ma 2 ma which brought about rapid progradation of a large sandy braided fan system the katberg sandstone fm into the central parts of the basin a concomitant basinward migration of depositional environments allowed the lystrosaurus communities that were adapted to dry floodplains to colonise the entire basin to the detriment of most of the wet floodplain dicynodon fauna that lived there

depth to pedogenic carbonate horizon as a paleoprecipitation indicator comment and reply royer 1999 1 has recently used a large data set from the u s natural resources conservation service nrcs to reexamine the relationship between mean annual precipitation and depth to the calcic horizon in soils the extremely poor correlation between these variables in his nrcs data r2 0

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

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

stable isotope geochemistry of organic matter alteration in animikie basin sediments within the thermal aureole of the duluth ccomplex abstract we have determined total organic carbon toc total carbonate carbon tcc and 13 c values for toc in samples from the early proterozoic animikie basin sediments virginia and biwabik iron formations that have been variably metamorphosed by the duluth complex toc values for the variably metamorphosed virginia formation show no systematic variation with distance from the intrusion toc from 0 06 to 2 54 in the biwabik iron formation samples outside the thermal aureole of the intrusion have toc generally below 1 compared to 1 7 6 2 for samples within the thermal aureole this enrichment may reflect extensive remobilization of organic carbon within the thermal aureole however 13 c org values measured for both the virginia and biwabik iron formations within the thermal aureole are not significantly different from those outside the thermal aureole it thus appears that in the iron formation the thermal shock caused by the intrusion induced migration of labile organic carbon that was isotopically similar to the residual kerogen the relatively low tcc in samples within the thermal aureole of the intrusion appear to indicate decarbonation of the iron formation also occurred

equation for compaction of paleosols due to burial existing empirically derived compaction curves for marine sediments fail to estimate the compaction of paleosols flood plain sediments and peats as indicated by deformation of clastic dikes dinosaur footprints and sandstone paleochannels yet compaction estimates are vital to reconstructing paleoclimate and geochemical profiles of paleosols to modeling sediment accumulation rates of nonmarine rocks and to tectonic flexural modeling of molasse facies this paper presents a compaction equation and physically derived constants that make geologically realistic estimates of compaction of paleosols and other nonmarine sediments a protocol for the application of the equation is suggested that would allow the following equation to solve for burial compaction c as a fraction of original thickness given depth of burial d in km as c s i f e d k 1 this equation can be applied to nonmarine sedimentary rocks or paleosols given appropriate empirical data on the physical constants in the equation such as initial solidity s i initial porosity f and the corresponding curve fitting constant k data on physical constants useful for this equation are compiled here for a range of paleosol and nonmarine sediment types

pattern of vertebrate extinctions across an event bed at the permian triassic boundary in the karoo basin of south africa the extinction of vertebrates around the time of the permian triassic boundary has long been regarded as a gradual event occurring over millions of years our new field investigations of fluvial strata in the central and southern karoo basin of south africa have revealed the presence of an event bed coinciding with a mass extinction of terrestrial fauna and flora the bed is in a sedimentary sequence that is marked by a reddening of flood plain mud rocks and a change from high to low sinuosity river channel systems here we show that the pattern of vertebrate taxa disappearing below this boundary and the subsequent appearance of new taxa above the boundary are consistent with a relatively sudden possibly catastrophic event perhaps of 50 000 yr duration or less

stable carbon and oxygen isotope shifts in permian seas of west spitsbergen global change or diagenetic artifact we performed petrographic cathodoluminescence electron microprobe and isotopic analyses of brachiopod shells from the permian kapp starostin formation in west spitsbergen to reevaluate the 9 negative shift in 13c and 18o values reported in 1989 by m gruszczynski s halas a hoffman and k malkowski the 13c and 18o values within shells typically decrease with increasing luminescence indicating diagenesis nonluminescent nl shell 13c and 18o values are 4 3 and 6 2 higher respectively than those of associated cements and matrix for the same stratigraphic interval 13c and 18o values of the nl shells are equal to or substantially greater than those reported by gruszczynski et al for the interval where those authors saw a 10 13c shift our mostly nl spiriferella polaris shells only yield a 1 5 shift gruszczynski et al reported a 9 18o shift whereas we observe almost none our results strongly suggest that the 9 isotopic shifts reported in gruszczynski et al are diagenetic artifacts on the other hand their kazanian tatarian 13c maximum of 7 5 is substantiated by our data this late permian 13c maximum represents the highest spiriferid brachiopod 13c values in the phanerozoic and within stratigraphic uncertainty correlates with the whole rock 13c maximum in east greenland and northwestern europe the 13c shift may reflect changes in global storage of organic carbon indicated by coal volume changes in the late permian

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

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

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

the terminal paleozoic fungal event evidence of terrestrial ecosystem destabilization and collapse because of its prominent role in global biomass storage land vegetation is the most obvious biota to be investigated for records of dramatic ecologic crisis in earth history there is accumulating evidence that throughout the world sedimentary organic matter preserved in latest permian deposits is characterized by unparalleled abundances of fungal remains irrespective of depositional environment marine lacustrine fluviatile floral provinciality and climatic zonation this fungal event can be considered to reflect excessive dieback of arboreous vegetation effecting destabilization and subsequent collapse of terrestrial ecosystems with concomitant loss of standing biomass such a scenario is in harmony with predictions that the permian triassic ecologic crisis was triggered by the effects of severe changes in atmospheric chemistry arising from the rapid eruption of the siberian traps flood basalts

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

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

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

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

alluvial sandstone composition and paleoclimate i framework mineralogy abstract systematic variations in compositional maturity of first cycle fluvial sandstones are found in the cutler formation permian and fountain formation permian pennsylvanian in colorado and in the gondwana supergroup permian triassic of peninsular india these variations reflect changing climate during deposition climate is considered to be the critical factor affecting maturity because source rocks granite granite gneiss and tectono environmental setting alluvial systems associated with basement cored block uplifts were similar and remained relatively unchanged throughout deposition of all three of the units the roughly 3 200 m thick gondwana succession consisting of five sandstone petrofacies is characterized by the following sequence of change oldest to youngest in compositional maturity expressed in q f r percentages 54 42 4 88 10 2 62 34 4 82 16 2 99 1 0 this sequence is a function of the changing paleoclimate glacial arid temperate humid warm semiarid warm semihumid warm humid associated with the overall global limatic change and the changing latitudinal location of india as it moved from a location close to the south pole northward during the interval of time represented by gondwana deposition lithologic and fossil evidence indicates that during deposition of the fountain formation climate gradually changed from relatively wet and warm to at least semiarid and warm this climatic change is the main factor responsible for the difference in compositional maturity of the older fountain sandstone q f r 65 26 9 relative to the younger q f r 54 36 10 cutler sandstone was deposited in an arid climate and has maximum compositional immaturity q f r 49 44 7 a log log plot of the ratio of total quartz to total feldspar plus rock fragments against the ratio of total polycrystalline quartz to to al feldspar plus rock fragments is a sensitive discriminator of first cycle sandstones with differing climatic heritage bulk chemical composition data support interpretation of climate from framework mineralogy but by themselves are not sensitive enough to be unequivocal indicators the same is true for the ztr index and observations of degree and abundance of solution pits embayments on detrital quartz results of this study support the conclusion of earlier empirical and theoretical analyses which suggest that the optimum conditions for the production and preservation of a distinctive climatic signature on sand composition are met in extensional plate tectonic settings such settings are characterized by coarse grained crystalline parent rocks short transport distances in low order streams deposition in nonroutine environments and shallow burial diagenesis however even in such optimum settings only rarely will climate be a more important determinant of sandstone composition than the tectonic setting itself

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

altered river morphology in south africa related to the permian triassic extinction the permian triassic transition in the karoo basin of south africa was characterized by a rapid and apparently basin wide change from meandering to braided river systems as evidenced by preserved sedimentary facies this radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die off of rooted plant life in the basin evidence from correlative nonmarine strata elsewhere in the world containing fluvial permian triassic boundary sections suggests that a catastrophic terrestrial die off of vegetation was a global event producing a marked increase in sediment yield as well as contributing to the global 13 c excursion across the permian triassic boundary

methane driven oceanic eruptions and mass extinctions focusing on the permian triassic boundary ca 251 ma i explore the possibility that mass extinction can be caused by an extremely fast explosive release of dissolved methane and other dissolved gases such as carbon dioxide and hydrogen sulfide that accumulated in the oceanic water masses prone to stagnation and anoxia e g in silled basins the mechanism of the explosive release is the same as in the lake nyos disaster of 1986 i e a water column eruption caused by the interplay of buoyancy forces and exsolution of dissolved gas the eruption brings to the surface deep anoxic waters that cause extinctions in the marine realm terrestrial extinctions are caused by explosions and conflagrations that follow the massive release of methane the air methane mixture is explosive at methane concentrations between 5 and 15 and by the eruption triggered floods this scenario accounts well for the available data and may be relevant to other phenomena

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

rapid and synchronous collapse of marine and terrestrial ecosystems during the end permian biotic crisis a newly studied permian triassic p tr boundary section in jameson land east greenland contains an abundant and well preserved marine fauna as well as terrestrial palynomorphs for the first time it is possible to compare the biotic crises of the marine and terrestrial realms using the same samples from the same section the sediments record a negative excursion in 13 c carb values of 8 9 and in 13 c org values of 10 11 the presence of the conodont hindeodus parvus combined with the 13 c carb record enables correlation with the proposed global stratotype section at meishan this shows that the greenland section is the most expanded p tr section known collapse of the marine and terrestrial ecosystems took between 10 and 60 k y it took a further few hundred thousand years for the final disappearance of permian floral elements collapse of the terrestrial and marine ecosystems began at the same stratigraphic level and preceded the sharp negative excursion in the 13 c record

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

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

δ13c depth profiles from paleosols across the permian triassic boundary evidence for methane release stable carbon isotopic analyses of organic carbon 13 c in individual paleosol profiles from permian triassic sequences of antarctica reveal systematic isotopic variations with profile depth these variations are in many cases analogous to those in modern soils which are functions of redox conditions soil development and degree and type of microbial decay in modern soils these isotopic depth functions develop independently from vegetation changes c 3 versus c 4 vegetation and can be diagnostic of soil orders this study shows that soil intrinsic functions can be preserved in the 13 c values of paleosols as old as 260 ma and constitute valuable data for paleoecological interpretations a large carbon isotopic offset of as much as 10 in whole paleosol profiles across the permian triassic boundary indicates significant changes in the soil biogeochemistry and the soil atmosphere system early triassic paleosols are distinctive in their extremely low 13 c values to 42 and often show an anomalous 13 c depth distribution compared to both permian paleosols and modern soils highly depleted 13 c values as the ones in early triassic paleosols are suggested to be associated with microbial methane oxidation methanotrophy this hypothesis implies increased methane concentrations in the early triassic soil atmosphere system increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the permian triassic boundary

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

calcified root cells in miocene pedogenic carbonates of the madrid basin evidence for the origin of microcodium b abstract calcified root cells forming microspar and pseudospar mosaics of calcite and or dolomite crystals constitute a major component of calcretes and dolocretes from the miocene of the madrid basin the calcified cells occur in massive nodules or fill root tubes in the calcrete dolocrete profiles the arrangement of the cells within the mosaics and their internal features together with the isotopic data clearly indicate that the crystals formed through the calcification of root cells and not through recrystallization or dolomitization calcified root cells formed in a favourable microenvironment caused by biochemical phenomena associated with plant growth in these examples the calcification is incomplete as only in the innermost part of the root the cells were totally calcified whereas in the root cortex only the cell walls were calcified the distribution of the calcified cells within the roots was controlled by the different ionic environments which prevail within an active root system in the inner part the ionic conditions were mostly controlled by the cellular activity of the root creating a suitable microenvironment for the biomineralization of the cells this differs notably from most published examples of calcified root cells in which it is usual for the cortical cells of roots to be completely calcified the calcified root cells of the madrid basin resemble unequivocally the problematic microcodium b which suggests that this type of microcodium formed through calcification of root cells

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

a pedotype approach to latest cretaceous and earliest tertiary paleosols in eastern montana a pedotype approach to the study of paleosols emphasizes individual profiles it is an alternative approach to the study of geosols which are laterally extensive suites of paleosols or pedofacies which are pedogenically distinctive sedimentary facies this is the first pedotype study of paleosols across the cretaceous tertiary boundary in eastern montana pedotypes allow assessment of sedimentation and fossilization the sequence of paleosols across the cretaceous tertiary boundary at bug creek is one of high temporal resolution because most available geological time can be accounted for by differing degree of development inferred for each pedotype paleosols at bug creek include pedotypes that preserve plant fossils well but were unfavorable for preservation of fossil vertebrates pedotypes also allow reassessment of ecosystem change despite indications of catastrophe at the cretaceous tertiary boundary the array of paleocene and cretaceous pedotypes are not strikingly different the upper cretaceous hell creek formation includes pedotypes interpreted as gleyed alfisols inceptisols and entisols probably formed under seasonally water logged forest and mean annual rainfall of the order of 900 1200 mm most paleosols of the lower paleocene tullock formation were histosols but some can be interpreted as gleyed inceptisols and entisols probably formed under bald cypress swamps in a humid climate with 1200 mm mean annual rainfall broadly comparable pedotypes were present before and after the cretaceous tertiary boundary although paleocene flood plain forest lived in paleosols chemically a little more oligotrophic than cretaceous paleosols this modest difference supports the idea that change to coaly facies in the earliest paleocene was a local shift in sedimentary environment such local changes do not begin to account for profound disruption in specific composition of plant and animal communities at the cretaceous tertiary boundary in eastern montana

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

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

long quaternary record in eastern washington u s a interpreted from multiple buried paleosols in loess loess that is from a few meters to 75 m thick covers an area of more than 20 000 km2 on the columbia plateau in washington idaho and oregon the region of deepest loess is in eastern washington and is called the palouse the palouse is downwind of the channeled scabland through which massive outburst floods from glacial lake missoula flowed repeatedly during glacial stages of the pleistocene the deepest stratigraphic section yet studied is in a remnant of the once continuous loess cover that is surrounded by scabland channels a normal over reverse magnetic polarity zonation in this section supports an age of more than 790 000 yr but 15 35 m of loess may be present beneath this section so a total of 1 5 2 million yr is possible upward fining of texture in some layers in the loess at this site and stratigraphic evidence at nearby sites suggest that at least some pulses of loess deposition were triggered by episodes of cataclysmic floods nineteen or more individual paleosols can be recognized in 26 m of section based on field morphology physical and chemical properties and micromorphology the paleosols consist of calcic petrocalcic and duripan horizons many of which are associated with cambic horizons less strongly developed soils in this and other sections have been obscured by partial overlap of soil development in an episodically rising loess landscape paleosols in the loess at other sites reflect a dry to moist climatic gradient from west to east across the region during the pleistocene that was grossly similar to today s accumulation of pedogenic carbonates and silica dominates in a western zone where the present day mean annual precipitation is less than about 450 mm translocation of silicate clays and leaching of carbonates dominate in a central steppe zone where precipitation is between 450 and about 700 mm fragipans are common in an eastern zone along the steppe forest transition at present day precipitation of over 700 mm reconnaissance study suggests that these climatic pedogenic zones have been somewhat stable during many of the episodes of soil development preserved in the loess although some paleosols have different features from the majority of the paleosols in that zone e g paleosols with fragipans in a sequence of paleosols with argillic horizons which suggests that some episodes of soil development took place under different climatic conditions

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

geochemical and organic carbon isotope studies across the continental permo triassic boundary of raniganj basin eastern india abstract organic carbon isotope and geochemical changes across a continental interior permo triassic boundary section from the raniganj basin india indicate a 9 drop in organic carbon 13c in the early triassic and synchroneity of this event throughout the pangea the study demands a common causative mechanism for the perturbation of the global carbon reservoir and not a combination of multiple causes a global sea level fall and oxidation of marine gas hydrates possibly increased the 12co2 input in the ocean atmosphere system which caused a climatic shift from humid to warm semi arid type and consequent extinction of land plants simultaneous increase in erosion from near barren lands change in the erosional base level and provenance deposited the boundary sandstone with positive europium anomaly and debris flow type matrix rich conglomerate no extraterrestrial source therefore is needed to explain this eu anomaly the response of the terrestrial plant community to this perturbation of the carbon reservoir was however sluggish and the 13c drop took place slowly being maximal in the early triassic only

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

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

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

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

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

vertebrate extinction across permian triassic boundary in karoo basin south africa distinct assemblages of paleosols above and below the permian triassic boundary in the karoo basin of south africa are evidence for reorganization of ecosystems following this greatest of all mass extinctions the permian triassic boundary is recognized from the last appearance of dicynodon and from a series of negative excursions in the isotopic composition of carbon within therapsid tusks pedogenic carbonate nodules and organic matter the boundary is also marked by laminated beds with very weakly developed paleosols a change from purple 10r to brownish red 2 5yr paleosols and a thin 10 cm claystone breccia of reworked soil clasts paleoclimatic changes include a shift from arid and highly seasonal paleoclimate inferred from diffuse and shallow calcareous nodules in permian paleosols to semiarid and less seasonal paleoclimate inferred from deep and well focused calcic horizons in triassic paleosols an earliest triassic shift to warmer and wetter paleoclimate is also indicated by increased chemical weathering abundance of lycopsids and diversity of labyrinthodonts permian paleosols have root traces comparable to those of open shrubland and riparian woodland whereas triassic paleosols have root traces and profile forms like soils of open woodland this is a significant paleoenvironmental change but not as dramatic a change as would be expected from the devastating extinctions of 88 of fossil vertebrate genera latest permian therapsid reptiles were diverse and ecologically specialized in contrast the principal earliest triassic therapsid lystrosaurus was a burrower with no specific habitat preference its short internal nares barrel chest and high neural spines would have given it greater aerobic scope than preexisting therapsids and may have been an advantage under conditions of hypercapnia and hypoxia these adaptations and associated ecosystem changes are compatible with widespread vertebrate mortality by acidosis and pulmonary edema in a post apocalyptic greenhouse created by the voluminous release of methane from shallow marine and permafrost clathrates

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

tempo of the end permian event high resolution cyclostratigraphy at the permian triassic boundary the permian triassic p t boundary is marked by the most severe mass extinction in the geologic record high resolution cyclostratigraphy on a 10 4 yr scale across the p t boundary in a core from the carnic alps austria revealed significant cycles in the ratio 40 10 4 7 2 3 m identified with milankovitch cycles of 412 100 40 20 k y eccentricity 1 and 2 obliquity and precession wavelet analysis indicates continuity of deposition across the boundary with an average accumulation rate of 10 cm k y the dramatic faunal changes at the p t boundary can be constrained within an interval of 60 k y possibly 8 k y with the accompanying sharp negative global carbonisotope shift within 30 k y suggesting a catastrophic cause

paleoclimate and the global distribution of paleosols a theoretical model is developed for the relationship between paleoclimate and paleosols for the time interval following the widespread appearance of vascular land plants the model defines four paleoclimatic zones 1 a wet equatorial zone primarily characterized by oxisols and secondarily by argillisols and histosols 2 a subtropical dry zone containing calcisols and less commonly gypsisols and vertisols 3 a moist mid latitude zone with argillisols spodosols gleysols and histosols and 4 a polar zone featuring protosols and gleysols the model is general in nature and its application to the geologic past will be affected by variability through time in paleogeography and paleoclimatic parameters

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery

phyllotheca the pastures of the late permian abstract the association between some herbivorous dicynodonts and the plants they depended on in the late permian of southern gondwana is examined in the light of recent palaeobotanical work the ecological restrictions that the flora placed on the herbivores are examined such restrictions indicate that the dicynodonts were not specialised herbivores as previously thought but generalised and opportunistic a reconstruction of a plant which was certainly at times on the dicynodont menu is presented the morphologies and the preferred habitats of both animals and plants were complimentary

permo triassic fluvial systems in the southeastern karoo basin south africa abstract a prominent clastic wedge of latest permian to early triassic age katberg sandstone prograded northwestwards into the main karoo basin from a southerly source area as a sedimentary response to renewed tectonism associated with the cape fold belt proximal to distal relationships within this clastic wedge and its relationships with underlying and overlying formations reveal a variety of stream types which reflect changing tectonic and climatic conditions towards the close of permian times the depositional area of the southeastern karoo basin was crossed by meandering river channels cutting through earlier formed floodplain deposits balfour formation tectonic rejuvenation of the source area in early triassic times led to steeper gradients and a sharp increase in the supply of coarser grained detritus as a result alluvial fans developed in areas adjacent to the source terrane and the river channels became braided depositing only sands katberg sandstone with muds and silts being carried down into the most distal parts of the floodplain burgersdorp formation subsequent denudation of the source area gradually reduced slopes and allowed the source ward shift of the distal facies until it eventually overstepped the earlier formed braided stream deposits accompanying the changes in tectonic conditions was a change in climatic which also influenced stream type the late permian to early triassic period records a general change to warmer climatic conditions following the widespread glaciation of the early to middle permian thus the lowest beaufort group sediments were probably deposited in warm temperate to humid conditions with later deposits being laid down under an increasingly arid regime

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

search for evidence of impact at the permian triassic boundary in antarctica and australia life on earth was almost destroyed some 250 m y ago in the most profound of all known mass extinction events we investigated the possible role of impact by an extraterrestrial bolide through chemical and mineralogical characterization of boundary breccias search for shocked quartz and analysis for iridium in permian triassic boundary sections at graphite peak and mount crean antarctica and wybung head australia thin claystone breccias at the isotopically and paleobotanically defined boundary at all three locations are interpreted as redeposited soil rather than impact ejecta the breccias at all three locations also yielded shocked quartz but it is an order of magnitude less abundant 0 2 vol and smaller only as much as 176 micrometers m diameter than shocked quartz at some cretaceous tertiary boundary sites faint iridium anomalies were detected up to 134 pg g 1 these values are an order of magnitude less than iridium anomalies at some cretaceous tertiary boundary sites furthermore peak iridium values are as much as 1 m below the isotopically and paleobotanically defined boundary the idea that impact caused the extinctions thus remains to be demonstrated convincingly

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