paleomagnetism of carboniferous strata from the stellarton gap deposition of carboniferous sediments within the stellarton graben of nova scotia was controlled by displacements on the bounding hollow and cobequid fault systems periods of both normal and transcurrent faulting have occurred on both faults as a result models for the development of the stellarton basin have included a pull apart basin and a thermal subsidence basin paleomagnetic study of stratigraphic sequences from within the graben showed evidence for three separate periods of remanence acquisition st3 st2 st1 ordering the acquisition sequence for these three magnetizations is mainly circumstantial being based on the distribution of each remanence phase relative to stratigraphic position and deformation of the strata the oldest magnetization st3 is grossly divergent from previously reported carboniferous results suggesting an early period of large scale clockwise rotation magnetization st2 has a similar pole position to many others from maritime carboniferous basins located within the app

multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

evolution of the ridges of midelt errachidia section in the high atlas revealed by paleomagnetic data new paleomagnetic data 43 sites from mesozoic sediments are contributed in this work verifying the presence of a pervasive syntectonic early cretaceous remagnetization in the easternmost area of the moroccan high atlas using the small circle intersection method we have calculated the characteristic remagnetization direction dec 337 3 inc 38 4 that fits with a 100 ma age according to the apparent polar wander path of africa the paleomagnetic vectors of remagnetization are used to obtain the geometry during the remagnetization stage 100ma of one of the most renowned geological cross sections of the high atlas the midelt errachidia profile the partial restoration of the cross section at 100ma allows us to determine the dips of the beds at the remagnetization stage in five structures ridges or anticlines our results indicate that the five ridges that configure the midelt errachidia profile were initiated to different degrees prior to wholesale compressive deformation during the cenozoic this configuration can be explained according to two different scenarios that we discuss in this paper transpression and diapirism the geological model obtained both at present and at 100ma indicates the existence of a mesozoic cover substantially decolled from the paleozoic basement what strongly contrasts with previously published transects of the same area

palaeomagnetism of nw scotland syenites in relation to local and regional tectonics summary a detailed thermal demagnetization study has been carried out on a number of syenitic intrusions from north of the great glen fault in scotland multicomponent remanences of normal and reversed polarity have been recognized these define a series of palaeomagnetic poles from which an ordovician to silurian apparent polar wander path for northern scotland is deduced comparison of this apparent polar wander path with the established path for britain throws new light on the sequence of thrusting and magmatic activity in the nw highlands and precludes large scale 1500 km movement along the great glen fault later than the ordovician the data emphasize previously published discrepancies between the apparent polar wander paths of britain baltica and laurentia and are consistent with the suggestion that britain was among a set of intracratonic microplates which underwent complicated distinct movements throughout the caledonian orogeny

a paleogene flora from the upper bonnet plume formation of northeast yukon territory canada palaeontological exploration of the bonnet plume basin in northwestern yukon territory canada has revealed a late paleocene to early eocene macrofloral assemblage from a channel fill deposit the flora is typified by cosmopolitan taxa and dominated by deciduous angiosperms with the notable presence of zizyphoides ettingshausenia and corylites floras with a similar composition are known from late cretaceous through early eocene deposits in alaska and the canadian arctic archipelago where they have been interpreted as evidence for warm equable temperatures this collection represents the most diverse known paleogene plant macrofossil assemblage from the yukon territory and helps to expand our knowledge of ancient high latitude floras

a comparison of gcm simulated cretaceous greenhouse and icehouse climates implications for the sedimentary record abstract two general circulation model simulations of mid cretaceous climate are presented one representing a greenhouse and the other representing an icehouse world through a comparison of greenhouse and icehouse palaeoclimates differences in processes which are intrinsically linked with climate such as continental weathering and snow and ice accumulation may be observed a number of conspicuous and discrete climatic differences can be seen between the two simulations which may be translated into a number of identifiable signatures in the sedimentary record the climate at mid high latitudes in the icehouse simulation was more arid than the greenhouse simulation and could result in deposition of smectite dominated clay suites in contrast the climate of low latitudes of the icehouse simulation resulted in a moister climate than the greenhouse simulation which could affect the weathering regimes and result in deposition of kaolin dominated clay suites thus cool climate episodes do not necessarily result in a global increase in aridity the icehouse simulation predicts a small permanent icecap at high latitudes which could account for the origin of dropstones in marine sediments furthermore a sea level fall as a consequence of an accumulation of ice at high latitudes may also increase continentality and surface albedo which may also contribute to the causes of the drier climate at high latitudes hurricanes are likely to be more frequent in greenhouse than icehouse climates mid latitude depressions also important for generating storms are likely to be both intense and frequent during icehouse and greenhouse periods of the middle cretaceous

paleomagnetism of rocks from burin peninsula newfoundland hypothesis of late paleozoic displacement of acadia criticized the posttectonic st lawrence granite 360 5 ma and associated subvertical dikes have two magnetizations n and h n points north with an intermediate upward inclination declination 005 inclination 50 alpha 95 10 paleopole 12 n 120 e we consider n to have been acquired close to the time of initial cooling the h magnetization points south with low inclination h is also the dominant magnetization in the nearby permo carboniferous spanish room formation h is considered to be an overprint acquired chemically during the kiaman reversed superchron late carboniferous and permian the n magnetization corresponds to a paleolatitude of 31 7 s very different from the near equatorial values expected from the commonly accepted late devonian and earliest carboniferous tournaisian reference paleofields for cratonic north america this is generally consistent with the hypothesis of a southerly displaced acadia proposed by kent and opdyke although the displacement is much greater 30 rather than 15 however we show that all inclinations observed from middle to upper devonian and tournaisian rocks from the craton are not significantly different either from the kiaman paleofield or from the h overprints observed from newfoundland some of these cratonic studies are not very detailed but it is noteworthy that the declination observed in the most comprehensive of them catskill red beds also agrees with the kiaman paleofield and with the h overprints from newfoundland declinations in some other cratonic studies show small departures of only a few degrees with one exception based on limited sampling and two from the colorado plateau which may have been rotated which could be caused by experimental inaccuracies moreover the directions obtained from cratonic studies are 97 reversed as they are in rocks with kiaman magnetizations we suggest therefore that the commonly accepted late devonian to earliest carboniferous reference paleofield for north america is either entirely kiaman in age or has been seriously affected by kiaman overprinting consequently the 30 of southerly displacement which the n magnetization of the st lawrence granite apears to indicate and the 15 invoked by kent and opdyke we consider to be illusory three late precambrian rock units 623 to 606 ma have scattered declinations but similar inclinations yielding paleolatitudes of about 35 the scattered declinations presumable were caused by local pre carboniferous relative rotations there is little or no evidence of kiaman overprinting in precambrian rocks indicating that overprinting is comparatively superficial and is probably related to late paleozoic groundwater circulation

synfolding and prefolding magnetizations in the upper devonian catskill formation of eastern pennsylvania implications for the tectonic history of acadia the upper devonian catskill formation was sampled for paleomagnetic study in east central pennsylvania 41on 76ow in one area the dominant component of magnetization se is revealed over a broad spectrum of demagnetization temperatures ranging to at least 660oc a conventional fold test is positive at the 99 confidence level however statistical analysis of dispersion with incremental bedding tilt correction shows a significant peak in the precision parameter after about 3 4 unfolding the magnetization is therefore secondary with a mean direction of d 166 6 o i 1 8 o the

application of paleomagnetism to accretionary tectonics and structural geology the use of paleomagnetism to determine translations and rotations of geologic terranes has contributed to a better understanding of deformation within accretionary complexes shear zones and rifts in this report to the i u g g we review the progress resulting from paleomagnetic studies during the last four years in the cordillera of north america the appalachian orogen and the circum pacific region

kinematic history of the narragansett basin massachusetts and rhode island constraints on late paleozoic plate reconstructions the formation of the narragansett basin of rhode island and massachusetts and the polyphase deformation geometry of the pennsylvanian age basin sediments can be explained by collision and strike slip interactions between an avalonian microcontinent the european north american plate and the african plate during the late paleozoic sinistral movement between an avalonian microcontinent and the european north american plate resulted in formation of pull apart basins subsequently africa moved toward north america along an east west trending dextral megashear zone and collided with the eastern margin of southern north america the narragansett basin is located on the avalonian microcontinent near the suture with the north american continent and in the transition zone between the megashear and the collision tectonic regimes the basin shape stratigraphy and sedimentary relationships can be explained by the coalescence of two composite grabens which formed at different times the thicker northern graben is only affected by one deformation whereas the southern graben shows evidence of four distinct phases of postrifting deformation the first two coaxial folding deformations of the basin sediments are attributed to the closure of the basin complex during collision of africa and north america the third and fourth deformations are interpreted as sinistral r riedal and dextral shears respectively associated with the east west trending megashear system a prograde barrovian metamorphic front started in the western portion of the southern graben slightly after the first deformation and migrated northward and eastward where it is synchronous with the second deformation

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

palaeomagnetism of the early carboniferous deer lake group western newfoundland no evidence for mid carboniferous displacement of acadia early carboniferous visean to possibly earliest namurian sedimentary rocks of the deer lake group of western newfoundland rest unconformably on grenvillian basement rocks of the canadian shield which form the western border of the early palaeozoic appalachian orogen in addition to magnetically soft magnetizations directed along the present field three families of magnetization directions are found two of them referred to as n north and s south are antiparallel and prefolding and were probably acquired during the depositional process n and s are roughly of equal frequency they have a mean direction irrespective of sign of 0 7 35 2 k 40 95 8 9 and a palaeopole 21 5 n 121 8 e 10 3 6 0 corresponding to a palaeolatitude of 20 6 s this agrees with the palaeolatitude 17 5 s determined from the somewhat older early carboniferous tournaisian terenceville formation of the avalon platform on the eastern side of the appalachian orogen in newfoundland the third magnetization referred to as h roughly horizontal has a mean direction 156 8 13 3 k 37 95 10 1 and a palaeopole 45 4 n 140 3 e 10 3 5 3 corresponding to a palaeolatitude of 7 4 n we interpret this to be an early kiaman latest carboniferous to early permian overprint probably acquired chemically the palaeolatitude determined from the h overprint agrees with that determined from early carboniferous rocks of cratonic north america west of the appalachians therefore we argue early carboniferous palaeofield determinations for cratonic north america have been strongly biased by unremoved kiaman overprints because of this and because of the good agreement between early carboniferous palaeolatitudes obtained from opposite margins of the appalachian orogen we suggest that there is at present no palaeomagnetic evidence for the previously proposed 1500 km displacement from the south of an eastern portion of the appalachians acadia relative to cratonic north america during the carboniferous

paleomagnetic evidence for the continuity and independent movement of a distinct major crustal block in the southern appalachians the magnetization of 22 granitic and gneissic southern appalachian rock units with estimated cooling ages of 415 250 m y has been determined included are 842 samples from 114 sites within 19 granites 100 sites and 3 gneisses 14 sites located in north carolina south carolina and georgia data for units which cooled to temperatures 20 000 km sup 2 in size a mean paleopole for this group with corrections for maximum tilt estimates exhibits good precision but has a paleosite latitude of approx 10 sup 0 n without tilt correction the paleopole for group b still exhibits an anomalous paleositemore latitude of approx 4 sup 0 n these data indicate that the group b block elberton sparta crustal block lying to the se has an apparent paleosite latitude corresponding to magnetization at a location to the north of the zone containing group a units less

the geology of gaspra the surface of gaspra can be divided into several facets separated by ridges superimposed on the facets and ridges are two populations of craters type 1 craters are crisply defined and constitute a production function of impact origin type 2 craters are mostly irregular shallow depressions and probably of various origins some of the type 2 craters may have formed by impact and be remnants of a crater population that predates the type 1 population the number of type 1 craters suggests that they started to accumulate 2 107 to 3 108 years ago the freshest craters have a depth diameter ratio of 1 7 as compared with 1 5 typically observed on other bodies the craters appear to have become shallower with age at a rate of 10 6 to 10 7 m year the shallow depth of newly formed craters and the progressive degradation with age are ascribed to downslope movement of poorly coherent surface materials the movement being aided by seismic shaking as a result of impact the surface shows subtle color differences the most prominent differences are observed around craters on ridges where the surface has a stronger 1 m absorption than elsewhere the contrast is not observed around craters on the facets the color differences are attributed to alteration of the materials brought to the surface the unaltered material is estimated to be located at least 50 m below the surface on the facets only on the ridges is unaltered material at a shallow enough depth to be excavated by the observed craters the rate of degradation of craters the rounded form of the ridges the depth of altered material on the facets and the presence of old degraded craters all suggest that gaspra is covered with a regolith a few tens to several tens of meters thick

the formation of inertinite rich peats in the mid cretaceous gates formation implications for the interpretation of mid albian history of paleowildfire abstract image analysis and standard point count petrographic data are used to interpret the amount source and variation of inertinite in coal seams of the mid cretaceous gates formation rocky mountain foothills northeastern british columbia inertinite on average is abundant between 40 60 by seam by volume and higher in some zones and within seams fluctuates cyclically the inertinite is interpreted to be almost exclusively fire derived suggesting that fire was a relatively common occurrence in the original peat forming wetlands inertinite enrichment in the gates coals appears to have resulted from preferential destruction of vitrinite precursors by either low temperature decomposition processes or burning rather than by formation of inertinite by a microbial process the position of the gates formation depositional setting east of the rising canadian cordillera is interpreted to have resulted in overall drier conditions in the region and periodic drought in the wetland settings cyclic variation in inertinite vitrinite composition within some of the seams is primarily attributed to climatic variations although variation in subsidence rates could also have been responsible

paleobotanical evidence for cool north polar climates in middle cretaceous albian cenomanian time mid cretaceous albian cenomanian floras are abundant and diverse on the north slope of alaska the older floras consist of conifers cycadophytes ferns ginkgophytes and sphenophytes horsetails angiosperms appeared in latest albian time and rapidly diversified the preserved floras consist entirely of deciduous plants with the exception of a microphyllous conifer ferns and sphenophytes deciduousness is evidence for strong seasonality which for these floras might be variations in either light or temperature or both cool temperatures are suggested by the prevalence of toothed leaves among the angiosperms and the presence of large leaved conifers the paleobotanical evidence points to a mid cretaceous climate that was no warmer than cool temperate on the north slope of alaska

new paleomagnetic data from carboniferous volcanics and red beds from central new brunswick it has long been argued on the basis of paleomagnetic data derived from devonian carboniferous and permian lithological units from eastern north america that a sinistral megashear of carboniferous age parallels and lies within the faults delimiting the appalachian caledonian chains recent paleomagnetic studies in the northern appalachians have cast doubt on the models of a carboniferous offset the geologic evidence suggests that only a small amount of dextral and not sinistral strike slip has occurred on faults which are parallel with pre acadian paleogeographic realms the purpose of this paleomagnetic study is to test the validity of the proposed left lateral motion at one of the sites of its presumed passage in central new brunswick six sites 80 oriented specimens in carboniferous red beds and volcanics were collected on both sides of the fredericton fault and other parallel faults after af and thermal cleaning the mean direction of magnetization is 158 38 the fold test is indecisive the corresponding paleopole is 135 e 21 n and the paleolatitude 20 s the paleopole positions and paleolatitudes are not significantly different on either side of the fredericton fault and no left lateral motion was detected by paleomagnetic means as no such motion was detected in south central new brunswick and newfoundland it is possible but unlikely that it took place in northern new brunswick and in the western gaspe peninsula this contribution is useful in discussing possible motions of acadia

palaeomagnetism and magnetic anisotropy of carboniferous red beds from the maritime provinces of canada evidence for shallow palaeomagnetic inclinations and implications for north american apparent polar wander summary a palaeomagnetic and magnetic anisotropy study was conducted on the lower middle carboniferous maringouin and shepody red bed formations of the maritime provinces of canada to detect and correct inclination shallowing because of the shallow inclinations commonly observed in red beds and the strong dependence of north america s palaeo mesozoic apparent polar wander apw on red beds inclination shallowing may substantially affect large portions of north america s apw path hematite is the primary magnetic mineral carrier in these red beds accompanied by secondary magnetite maghemite goethite and pigmentary hematite thermal and chemical demagnetization of the shepody fm successfully isolated characteristic remanence directions of d 177 i 20 4 95 6 5 n 19 and d 177 8 i 17 7 95 6 9 n 16 respectively thermal demagnetization of the maringouin fm isolated a characteristic remanence direction of d 178 7 i 24 9 95 14 5 n 9 high field anisotropy of isothermal remanence followed by alternating field and thermal cleaning on leached samples was used to isolate the fabric of hematite individual particle anisotropy was measured directly from magnetic separates using a new technique hematite s magnetic fabric and particle anisotropy were used to apply an inclination correction our inclination corrections indicate up to 10 of inclination shallowing corresponding to corrected palaeopole positions of 27 2 n 118 3 e a95 6 2 and 27 4 n 117 2 e a95 13 1 for the shepody and maringouin formations respectively this correction corresponds to a 6 increase in colatitude for carboniferous north america which translates into approximately a 650 km change in north america s palaeogeographic position the proposed position of north america supports a pangea b type reconstruction

remote sensing of comets and asteroids in the past quadrennium we have observed a fragmented comet collide with jupiter and discovered a population of objects of the order of hundreds of kilometers in diameter beyond the orbit of neptune a probable source region of short period comets we are still in the age of discovery as studies of the solar system continue the discovery of many small asteroids with the same surface composition as the second largest main belt asteroid 4 vesta has opened our eyes to a pathway by which certain meteorites reach earth and by which asteroids collide and their orbits evolve this evidence for delivery of meteorites was found by pushing existing observing techniques to their limits an expanded capability for detecting returned radar echoes from asteroids permits the extraction of basic information about their position shape spin state size and surface texture which is equivalent to that acquired from a flyby of a robotic spacecraft we will never send spacecraft to as many asteroids as can be studied from the ground so the contributions of ground based astronomy at all wavelengths provides insights into the chemical and physical diversity of the asteroids and comets remote sensing is carried out by ground based and earth orbiting telescopic studies and robotic spacecraft traveling through the solar system in the past quadrennium we have viewed data returned from two main belt asteroid flybys missions which represent the transition of asteroids as targets of astronomical study t o subjects of geological study scientists using the galileo spacecraft additionally made the serendipitous discovery of dactyl a satellite of 243 ida the first direct proof that satellites orbit asteroids the significant advances discussed below have occurred because of 1 chance discovery the discovery of comet shoemaker levy 9 and dactyl 2 the interaction between theoretical predictions and observational programs discovery of trans neptunian objects 3 the use of available technology pushed to its limits of sensitivity discovery of small asteroids with the same surface composition as 4 vesta and 4 the consequence of technical upgrading of facilities the latter provides fundamental facts about the diverse physical characteristics of small solar system bodies a prime example is advancing knowledge derived from radar astronomy our new knowledge has generated a modified view of the number and nature of the small bodies in the solar system and how they formed and evolved through time

dual polarity early carboniferous remagnetization of the fisset brook formation cape breton island nova scotia summary red siltstones and volcanic flows of the fisset brook formation of cape breton island nova scotia were folded or tilted in two phases one of late tournaisian and the other of mid namurian age upon thermal demagnetization both rock types yield three components of magnetization herein denoted as l i and h the l component has low unblocking temperatures and a direction conforming to that of the present day geomagnetic field l is inferred to be of recent origin the intermediate i component carried by haematite is of synfolding origin directions could be obtained through vector subtraction for the demagnetization interval of 300 550 c and yield a mean of d i 160 38 k 90 8 ag5 s lo after 39 per cent of the tilt correction is applied the h component has even higher unblocking temperatures which overlap to a large degree with those of the i component but analysis of intersecting great circles appears to yield a best fit direction for h which is nearly antipodal to that of the i component h is also synfolding and yields a mean direction of d i 342 38 k 120 9 ag5 6 9 after 60 per cent of tilt correction both components are interpreted as secondary chemical remanent magnetizations of late tournaisian to early namurian age a comparison of all available carboniferous results from the craton and the northern appalachians indicates that palaeolatitudes for nova scotia changed from about 20 s to about 10 s in the interval between the early and late namurian and that they changed again from about 10 s to 0 between the late namurian and the stephanian declinations show good agreement between newfoundland nova scotia new brunswick and the craton with the exception of the meguma terrain which underwent a counterclockwise rotation with respect to the mainland in the late carboniferous as noted previously by spariosu kent keppie 1984

confirmation of the carolina slate belt as an exotic terrane an assemblage of middle cambrian atlantic faunal province trilobites has been found in the rocks of the carolina slate belt near batesburg south carolina geologic and paleomagnetic data suggest that the carolina slate belt and the adjacent charlotte belt constitute an exotic terrane that was accreted to north america in early to middle paleozoic time

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

palaeomagnetic argument for a stationary spitsbergen relative to the british isles western europe since late devonian and its bearing on north atlantic reconstruction abstract palaeomagnetic results from the devonian of central spitsbergen mimer valley formation billefjorden suggest an average palaeofield direction for the late devonian early carboniferous with declination 227 5 inclination 30 6 corresponding to a relative pole position at lat 24 s long 325 e this magnetization which is post tectonic is regarded as acquired chemically linked with the upper devonian svalbardian phase of deformation this result together with some recent data from central spitsbergen defines a devonian polar wander segment that accords extremely well with corresponding british data we interpret this in terms of no major displacement of central spitsbergen as compared with western europe since devonian time svalbard and the barents sea region have probably formed a fairly stable platform since the early devonian on the balance of available geological and palaeomagnetic evidence from spitsbergen the british isles and newfoundland the north atlantic region does not appear to have been subjected to strike slip motions in the order of thousands of kilometers in or since the late devonian

mid cretaceous floras and climate of the russian high arctic novosibirsk islands northern yakutiya abstract two mid cretaceous floras collected in terrigenous and volcaniclastic deposits of the novosibirsk islands in the russian high arctic were studied these floras are the most poleward mid cretaceous floras known and existed at palaeolatitudes up to 82 85 n these represent our best insight into polar conditions at one of the warmest intervals in earth history an albian flora from the balyktakh formation of the kotel nyi island comprises 40 species of ferns bennettites cycadophytes ginkgoaleans czekanowskialeans conifers and gymnosperms incertae sedis this flora is most similar to the albian buor kemuss flora widespread in the arctic siberia and alaska and to a lesser extent to the aptian silyap flora of siberia a turonian flora from the derevyannye gory formation on the novaya sibir island includes approximately 50 taxa of ferns ginkgoaleans conifers and angiosperms this flora exhibits plants common for the early cretaceous as well as taxa typical for cenomanian senonian which implies that the age of the plant bearing deposits is likely to be turonian the cretaceous climate has often been described as warm with a higher degree of equability than today with the near polar regions in particular being much warmer than today our estimates using clamp and a new global gridded climate calibration demonstrate that for the turonian novaya sibir flora plant physiognomy reflects a humid climate with warm summers and mild frost free winters the mean annual temperature is estimated to have been 9 2 2 2 c the warm month mean temperature 17 2 2 8 c the cold month mean temperature 1 1 3 8 c and the mean growing season precipitation 537 392 mm these temperature parameters indicate that within 900 km of the turonian north pole the climate was similar to that of modern temperate or even warm temperate zones but must have differed considerably in having pronounced high latitude sunlight seasonality the ecology of the late cretaceous arctic plants reflects their adaptation to this climate synchronous shedding of foliage deciduousness was by far the most common strategy and retention of leaves year round evergreenness was also viable for a small number of taxa large deciduous leaves typical for the cretaceous arctic dicots probably reflect the combination of a warm and humid climate with high latitude light regime long days in summer and predominance of relatively weak and mostly diffuse sunlight the large range of leaf size in a given plant species of arctic angiosperms was most probably linked to the seasonal character of annual shoot development

paleomagnetism of fluorite veins in the devonian st lawrence granite newfoundland canada paleomagnetic results are reported from the devonian st lawrence granite and the fluorite veins within the granite or its related porphyry dikes paleomagnetic analysis of 359 specimens from 29 sites shows that there is no statistically significant difference at 95 confidence between the site mean characteristic remanent magnetization chrm directions carried by pyrrhotite and or magnetite of the granite and fluorite veins no post granite metamorphic event is known in the area thus these concordant directions indicate that the granite and fluorite veins are coeval and retain a primary remanence however the mean chrm direction of 25 vein and granite sites yields an early pennsylvanian paleopole of 316 ma on the north american apparent polar wander path at 35 5 n 129 2 e a95 3 4 that is younger than the 374 2 ma devonian u pb zircon age for the granite two intersecting vertical vein sets indicate that the st lawrence granite has not been tilted since emplacement of the fluorite veins t

palaeomagnetism of early cambrian brigus red shale eastern newfoundland abstract studies of the early cambrian brigus br red shale exposed in conception bay yielded a single stable mean remanence direction of d 265 i 58 reverse polarity before tilt correction and d 279 i 48 k 47 95 6 9 forn 7 sites 25 samples after correction for gentle tilt the corresponding north pole palaeopole position is 27 s 51 e dp dm 6 9 this magnetization is characterized by a linear vector trajectory at higher unblocking temperature t ub spectra 400 680 c the magnetization directions at the low t ub range 400 c are more variable from sample to sample although they typically have steep downward inclinations with no evidence of kiaman overprinting marginal but not statistically significant improvement k 44 77 in the grouping of site means after tilt correction suggests that the predominant univectorial westerly remanance was probably acquired after deposition based on both geological and magnetic evidence the brigus shale formation appears to be remagnetized during siluro devonian times the position of the far sided antipole br 27 n 129 w located in the vicinity of the pole for the cambrian morrison river formation mr at 20 n 146 w which is discordant from the younger palaeozoic late ordovician carboniferous poles reported for the avalon zone is fortuitous since the magnetization of br is most likely secondary the magnetization is younger than the iapetus closure date determined geologically late ordovician consequently the displacement of the avalon zone with respect to the north american craton cannot be estimated the width of the proto atlantic ocean cannot be calculated

the direction of the north pole and the control network of asteroid 951 gaspra abstract a control network containing 19 points identified on galileo images obtained during the october 1991 flyby was used to determine the direction of gaspra s north pole we find the right ascension and declination in j2000 coordinates to be o 9 5 o 26 7 1 2 this result agrees with earlier determinations based on telescopic observations of gaspra s lightcurve we confirm that the rotation is prograde but we lack the time base to improve the value of the rotation period of 0 2934197 days determined by lightcurve analysis magnusson et al 1992 we propose a prime meridian 0 longitude that passes through the center of the 630 m diameter crater charax a selection that places the prime meridian close to gaspra s long axis

eocambrian paleomagnetism of the boston basin evidence for displaced terrane a paleomagnetic study of the late precambrian roxbury formation consisting of extrusives and clastic sediments has yielded a steeply downward directed and pre folding characteristic magnetization d i 219 71 95 5 k 311 paleopole at 13 n 267 e n 4 sites which indicates a significantly higher paleolatitude 55 than would be expected if the boston basin were part of the equatorial north american craton in the latest precambrian and earliest paleozoic this characteristic magnetization reveals dual polarities and is further supported by a positive conglomerate test a ubiquitous post folding late paleozoic overprint is present in nine sites d i 183 14 95 8 k 42 with a paleopole at 41 s 285 e the pre folding magnetization resides in hematite which is inferred to have formed during early oxidation of the rocks the high stability of this hematite may have prevented its magnetization from being reset during the late paleozoic chemical event responsible for the magnetic overprint the boston basin has a marked geological similarity to the avalon basement terranes in nova scotia and newfoundland as well as the armorican massif in france and the high paleolatitudes observed for all these terranes suggest a common paleogeographical affinity a likely paleolocation is near the northwestern margin of gondwana which was located at the southpole in the latest precambrian and early cambrian

paleomagnetic evidence for post devonian displacement of the avalon platform newfoundland the possibility that the avalon platform where the avalonian lithotectonic belt is best developed was involved in late paleozoic displacement was tested by paleomagnetic study of red sandstones of the upper devonian terrenceville formation of eastern newfoundland two magnetization directions were identified by thermal demagnetization analysis of 60 oriented samples from 10 sites a high blocking temperature thermally discrete a component of normal and reversed polarity and an intermediate blocking temperature thermally distributed b component of reversed polarity the b component d 185 9 i 3 3 a95 7 2 for n 8 sites is interpreted as a postfolding secondary magnetization and gives a paleomagnetic pole position latitude 43 6 n longitude 117 1 e near early to late permian paleopoles for north america the a component d 181 6 i 28 0 a95 10 1 for n 9 sites is interpreted as the characteristic magnetization possibly dating from near the time of deposition of the terrence ville formation the corresponding paleomagnetic pole position latitude 27 4 n longitude 123 5 e falls within a group of late devonian early carboniferous paleopoles obtained from the acadia displaced terrain encompassing the coastal areas of new england and the canadian maritimes which form another part of the avalonian belt these paleopoles are systematically offset by 15 to 20 in latitude from coeval pole positions obtained from cratonic north america thus the avalonian belt of the northern appalachians which is thought to represent a remnant of a precambrian and early paleozoic microcontinent on tectonostratigraphic considerations appears to correspond to a late paleozoic displaced terrain on the basis of paleomagnetic evidence

paleomagnetism of certain constituents of the bay st george sub basin western newfoundland abstract paleomagnetic studies have been made of certain constituents of the bay st george sub basin specifically results are reported from the spout falls formation tournaisian the jeffreys village member of the robinsons river formation visean and the searston formation namurian westphalian the following magnetizations have been isolated spout falls a tournaisian with d 343 5 i 22 7 k 61 2 95 7 1 and the corresponding pole at 28 6 n 139 5 e 4 5 8 5 spout falls b kiaman with d 166 7 i 12 2 k 51 7 95 10 7 and the corresponding pole at 34 5 s 42 7 w 5 5 10 9 jeffreys village a visean with d 351 2 i 27 3 k 54 0 95 7 6 and the corresponding pole at 26 5 n 130 7 e 4 5 8 3 searston a namurian with d 161 7 i 11 7 k 107 95 7 4 and the corresponding pole at 33 9 s 37 2 w 3 8 7 5 and searston c with d 111 6 i 13 8 k 28 8 95 14 5 and the corresponding pole at 19 6 s 19 0 e 7 6 14 8 after comparison with paleopoles of similar ages derived from eastern and western newfoundland rocks from constituents of the east coast basin and for interior north america it is concluded that 1 it is unlikely that any large scale relative motion took place since the early carboniferous between eastern and western newfoundland 2 it is unlikely that any north south relative motion took place between the east coast basin and the bay st george sub basin and 3 the bay st george sub basin results do not support the earlier proposed displaced terrane hypothesis of the northern appalachians in as much as the motions during the carboniferous are not supported there is evidence of the northward motion of the appalachians and north america as a whole during the carboniferous the magnetostratigraphic horizon marker in the carboniferous separating a dominant normal and reversed magnetization on the older side and an entirely reversed kiaman magnetization on the younger side may be placed in the bay st george sub basin at the base of the searston formation

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

paleomagnetism of the lower devonian traveler felsite and the acadian orogeny in the new england appalachians a suite of felsic extrusive rocks from the lower devonian traveler felsite north central maine 46 1 n lat 68 9 w long was collected for paleomagnetic study 28 samples from 5 sites in the lower pogy member 56 samples from 10 sites in the upper black cat member and 13 samples from 10 cobbles in the basal conglomerate of the overlying trout valley formation characteristic magnetizations based on af demagnetization analyses and supported by thermal studies give a formation mean direction after simple correction for bedding tilt of d 25 2 i 20 2 95 10 6 for 13 sites in the traveler felsite the occurrence of normal and reversed magnetozones under stratigraphic control and the antiparallel directions of the polarity units following the tilt correction indicate an acquisition of remanence near the time of formation of the rock units the mean direction corresponds to a south paleopole position of 29 s lat 262 e long p m 6 11 for the traveler felsite this pole position is in close agreement with poles from two other rock units of similar age from the same lithostratigraphic belt in the northern appalachians the mean of these three poles is distinct from late silurian and middle devonian poles from cratonic north america laurentia and from early devonian results from the acadia displaced terrane suggesting that this area constituted a separate tectonic unit during the early devonian we propose a tectonic model in which a traveler terrane is rotated 20 to 30 while converging with laurentia and undergoing deformation during the early to middle devonian acadian orogeny

evidence against large scale carboniferous strike slip faulting in the appalachian caledonian orogen kent and opdyke1 have argued that during the late devonian and early carboniferous the eastern part of the northern appalachians acadia was situated 1 500 km further south relative to cratonic north america than it is at present and that it moved to its present position sometime later in the carboniferous fig 1 van der voo and scotese2 proposed an even greater displacement of 2 000 km which they attribute to motion between cratonic north america and europe acadia being attached to europe fig 1 the argument is that palaeolatitudes p derived palaeomagnetically from upper devonian and lower carboniferous rocks of cratonic north america are 15 20 more northerly than those of acadia and europe the proposed shear zone passes through central newfoundland using palaeomagnetic results from eastern and western newfoundland we show here that no such motion occurred we also show that kiaman late carboniferous and permian overprinting is widespread in newfoundland and that these secondary magnetizations agree with two exceptions attributed to dextral rotation of the colorado pleateau with observations from late devonian and early carboniferous rocks of the north american craton confirming the proposal3 that magnetizations of the cratonic early carboniferous rocks are kiaman not early carboniferous in age our results also enable us to extend this proposal3 to late devonian rocks of the craton hence the palaeolatitudinal offset of fig 1 is almost certainly not tectonic but is an artefact of the wrong assumption of the equivalence of rock and magnetization ages

a geomagnetic polarity timescale for the carboniferous the geomagnetic polarity pattern for the carboniferous is incompletely known but with the best resolved parts in the serpukhovian and bashkirian hence data from both igneous and sedimentary units are also used in an additional polarity bias evaluation in the tournaisian to mid visean interval polarity is mainly derived from palaeopole type palaeomagnetic studies allowing identification of polarity bias chrons seven polarity bias chrons exist in the mississippian mi1nb to mi4nb with an additional 33 conventional magnetochrons and submagnetochrons mi4r to mi9r the moscovian and gzhelian polarity is best resolved in magnetostratigraphic studies from the donets basin and the southern urals dispute about the reliability of these data is ill founded since an assessment of supporting data from palaeopole type studies suggests that these datasets currently provide the best magnetic polarity data through the pennsylvanian polarity bias assessment indicates a normal polarity bias zone in the kasimovian in the pennsylvanian there are 27 conventional magnetochrons and submagnetochrons pe1n to ci1r and one normal polarity bias chron pe8nb the kiaman superchron begins in the mid bashkirian with clear data indicating brief normal polarity submagnetochrons within the superchron the magnetochron timescale is calibrated using 31 u pb zircon dates and a quantitative bayesian based age scaling procedure

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

paleomagnetism of early cambrian redbeds on cape breton island nova scotia results are reported from steeply dipping red sandstones collected at nine sites 45 samples of the lower cambrian morrison river and maccodrum formations on southeast cape breton island which forms part of the avalon terrane demagnetization studies indicate minimal overlap of stability spectra in thermal alternating field and chemical treatments a stable component hematite with high unblocking temperatures 680 c is dominant at all sites its mean direction corrected for geologic tilt is d 281 i 32 k 97 giving a paleomagnetic pole pole m at 20 n 146 w dp dm 3 6 the corresponding in situ direction is d 147 i 59 k 97 with a pole m at 2 s 39 w dp dm 6 8 poles m and m were compared with published paleozoic poles for the avalon zone and cratonic north america to test whether the magnetization originated before or after the taconic ordovician folding it could have been acquired during deposition or early diagenesis early to middle cambrian in whic

a tectonic model for the late paleozoic of southeastern new england hornblende and biotite sup 40 ar sup 39 ar age spectra from rocks in south central connecticut help define a permian triassic cooling curve for the area together with petrologic and structural information a time temperature pressure strain path is established similar data for the narragansett basin in rhode island and massachusetts allow correlation of the late paleozoic histories of the two areas together these data suggest that in the late paleozoic south central new england was part of a fold thrust belt and the narragansett basin was a retroarc foreland basin nw se compression during the final assembly of pangaea resulted in se directed thrusting causing the development of clastic wedges in adjacent rhode island and massachusetts in the late carboniferous early permian a clockwise rotation of this deformation from nw to nne led to northward underthrusting and concomitant uplift of both eastern connecticut and rhode island in the permian and triassic

late paleozoic tectonic evolution of the norfolk basin southeastern massachusetts the norfolk basin of southeastern massachusetts formed during the pennsylvanian in a tectonically active setting the sedimentary facies in the basin form a wet alluvial fan depositional system constructed primarily by braided streams provenance and other sedimentologic data constrain the amount of offset along proposed strike slip faults located north of the basin left lateral motion previously suggested to have played a major role in the formation of the norfolk and narragansett basins appears to have played a negligible or at most indirect role in the formation of the norfolk basin the basin underwent two episodes of folding with associated development of two axial planar cleavages and episodes of reverse thrust and strike slip faulting during the permian alleghanian orogeny illite crystallinity and other petrologic data demonstrate that the sedimentary rocks were metamorphosed to the lower greenschist facies probably at temperatures between 200 and 300 c these data indicate that the la

first images of asteroid 243 ida the first images of the asteroid 243 ida from galileo show an irregular object measuring 56 kilometers by 24 kilometers by 21 kilometers its surface is rich in geologic features including systems of grooves blocks chutes albedo features crater chains and a full range of crater morphologies the largest blocks may be distributed nonuniformly across the surface lineaments and dark floored craters also have preferential locations ida is interpreted to have a substantial regolith the high crater density and size frequency distribution 3 differential power law index indicate a surface in equilibrium with saturated cratering a minimum model crater age for ida and therefore for the koronis family to which ida belongs is estimated at 1 billion years older than expected