the roussillon basin s france a case study to distinguish local and regional events between 6 and 3 ma the roussillon basin is a non silled miocene sedimentary basin filling a late oligocene early miocene graben the basin was intensively impacted by the 2 messinian fluvial erosion as evidenced in exposed sections in seismic profiles and in deep boreholes drilled for hydrocarbon exploration as the basin was open to the mediterranean sea the huge drop in sea level at the peak of the messinian salinity crisis is clearly recorded along with the subsequent sudden marine reflooding and the resulting prograding sedimentary filling particularly in gilbert type fan deltas here the messinian erosional surface mes is accurately mapped in a high resolution document which corrects the confusion resulting from the set of 1 50 000 scale regional maps aim of the 3d reconstruction of the mes is to modernize geological mapping a crucial challenge for mediterranean and peripheral areas thanks to a reliable chronostratigraphy provided by planktonic foraminifers calcareous nannofossils micro and macro mammal remains paleomagnetism and a 10 be cosmogenic nuclide derived study our reconstruction is one of the most comprehensive models of changes in sea level from 6 to 3 ma after the marine reflooding of the mediterranean basin at 5 46 ma the fluctuations in sea level recorded in the roussillon basin were forced by global changes following reflooding the prades large olistostrome collapsed prepared by the previous exhumation along the canigou fault the olistostrome is a good example of a local accident resulting from messinian events the exceptional changes in sea level at the peak of the messinian salinity crisis deeply marked the roussillon basin momentarily overprinting the pyrenean orogenesis key words roussillon basin messinian subaerial erosion zanclean sedimentary filling prades olistostrome

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

regional patterns of magnetite authigenesis in the appalachian basin implications for the mechanism of late paleozoic remagnetization we report paleomagnetic and rock magnetic data from sedimentary carbonates of the appalachian basin that have implications for the mechanism of widespread late paleozoic remagnetization in this rock type sampling was accomplished mostly along two across basin transects one in devonian carbonates of new york state and the other in ordovician and mississippian carbonates of tennessee and alabama paleomagnetic investigations of the new york devonian carbonates along a transect from albany to buffalo indicate that these rocks were completely remagnetized in alleghenian time rock magnetic studies show that magnetite concentration varies in a regular fashion along the transect with a local maximum near syracuse and decreasing gradually to the east and west this pattern shows a striking correlation with the degree of diagenetic alteration of clay minerals in a devonian bentonite horizon which took place during alleghenian time we conclude that most of the magnetite present in these carbonates is of authigenic origin and that clay mineral alteration and magnetite authigenesis were coeval late paleozoic events that were controlled by the same diagenetic factors thermoviscous remagnetization processes cannot be ruled out in this setting in light of the observed degree of thermal maturity however our results suggest that chemical factors played a critical role in remagnetization since they allow us to infer that magnetite authigenesis and remagnetization are about the same age we propose a geochemical model for magnetite authigenesis wherein the iron is derived from detrital smectites during diagenetic illitization which is triggered by the introduction of potassium rich brines results from the tennessee transect from nashville to chattanooga show a very different pattern paleomagnetic studies indicate that late paleozoic remagnetization has affected ordovician carbonates of the nashville dome paleozoic carbonates in the overthrust belt near chattanooga also carry the late paleozoic remagnetization however mississippian carbonates between the dome and the overthrust belt are very weakly magnetized and show no evidence for late paleozoic remagnetization samples show only a present field magnetization or at one locality in northwestern alabama a dual polarity magnetization of probable mississippian age rock magnetic studies indicate that higher concentrations of magnetite are present in the remagnetized rocks of the nashville dome and the overthrust belt than in the nonremagnetized mississippian carbonates we therefore conclude that magnetite authigenesis and remagnetization are related events in this setting and that the remagnetization must be due to chemical processes the presence of a remagnetization shadow in the younger rocks now exposed between the fold thrust belt and the flexural arch is attributed to westward flow of magnetite forming aqueous fluids through deep sub carboniferous aquifers during alleghenian time upward migration of the fluids through the mississippian carbonates may have been prevented by the devono mississippian chattanooga shale an impermeable stratum that is present throughout the region

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

deterioration mechanisms of tuffs in midas monument slightly weathered white and pink tuffs of the midas monument have deterioration problems in this study depths and characteristics of the weathering zones developed within the tuffs are investigated through optical microscopy x ray diffractometry xrd chemical analyses scanning electron microscopy sem and some index parameters accelerated weathering tests including wetting drying freezing thawing and salt crystallization are performed and durability assessment methods are used to predict the durabilities of the tuffs the findings are compared with field observations by examining quantitative weathering indices and comparing them with thin section studies it is found that thin section analyses of the crystals loi and wpi are good indicators to quantify the depth of weathering for the tuffs however thin section studies have limited value for fine grained tuffaceous matrix the chemical weathering of the tuffs produces weathered zones that are 4 5 cm thick within the white tuff and 2 5 cm thick within the pink tuff physical weathering causes scaling of outer layers of the tuffs and fracturing of feldspars along their cleavage planes however variations of the index properties of the tuffs due to weathering are not so significant to quantify the weathering depths in the tuffs among the accelerated weathering tests salt crystallization is found to be the most destructive environmental condition pigeon droppings rich in no3 are found to be the main source of soluble salt at the midas monument the salt transported up by capillary rise due to surface water causes spalling of the tuffs in the capillary zone surface water and salt of any kind in the close vicinity of the monument should be totally eliminated for the purpose of conservation field observations and the durability equations reveal that the white tuff is less durable than the pink tuff wet to dry strength ratio yields a better stone durability assessment among various durability methods used in this study d 2002 elsevier science b v all rights reserved

ordovician paleomagnetic results from the st george and table head carbonates of western newfoundland we have studied 85 limestone and dolostone samples from 21 sites of the st george and table head groups lower and middle ordovician on port au port peninsula humber zone their gentle 15 tilt is probably devonian a steep viscous component dominant in the natural remanence is removed by thermal and less efficiently alternating field demagnetization in about 60 of all samples the thermal treatment yielded a southeasterly reverse component a which typically remained blocked to 450 500 c and then decayed to noise mean a component directions calculated from zijderveld plots and referred to bedding are d i 148 5 33 6 for n 9 st george sites and d i 150 0 i 40 7 for n 5 table head sites corresponding antipoles are 17 5 n 152 3 e dp dm 2 8 4 9 and 13 4 n 149 2 e dp dm 2 9 4 7 respectively we interpret these results as representative of the geomagnetic field in the early and mid ordovician in 14 samples mainly from the older st george strata thermal

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

ironstones and green marine clays in the dongjeom formation early ordovician of korea abstract in the sino korean north china block the occurrence of ironstone is reported for the first time from the lower ordovician dongjeom formation korea the dongjeom formation comprises much quartzose sediment deposited on the extensive carbonate platform and is composed of three coarsening upward sequences ironstone beds are distributed on the tops of the lower two sequences suggesting that they mark approximately maximum flooding events during the relative lowstand of sea level when the dongjeom formation was deposited extensive weathering in the source areas coupled with higher order sea level rises resulted in the formation of the dongjeom ironstones the dongjeom ironstones include much green marine clays ironstones of the lowest sequence are characterized by glaucony facies and those of the middle sequence by chamosite facies chemical compositions of dongjeom glauconies reveal that they were originally nascent to slightly evolved 3 to 5 k 2 o wt and that they were affected by illitization after burial their immature compositions suggest that glauconies were formed in about 10 3 to 10 4 years or less on the seafloor the substrates for glauconitization are interpreted as detrital mineral grains regressions after glauconitization introduced iron oxides to the green grains eventually forming the iron oxide rich band under the most oxidizing conditions the distribution of glauconies in limited horizons suggests that the dongjeom glauconies are autochthonous in origin chamosites have granular shapes and are mixed with quartzose sand grains suggestive of reworking during storms the dongjeom chamosites were transformed from the precursor berthierines the occurrence of glauconies in correlative horizons in korea and north china may indicate that glauconitization in the host sediments which were deposited in far northern gondwana occurred under the influence of a coeval transgressive event

quantification of weathering depths in slightly weathered tuffs slightly weathered white and pink tuffs of midas monument have deterioration problems in this study depths of the weathering zones developed in the tuffs are investigated through optical microscopy xrd chemical analyses sem and some index parameters by examining quantitative weathering indices and comparing them with thin section studies it is found that thin section analyses of the phenocrysts loi and wpi are good indicators to quantify the depth of weathering for the tuffs however thin section studies have limited value for fine grained tuffaceous matrix the chemical weathering of the tuffs produces weathered zones that are 4 5 cm thick within the white tuff and 2 5 cm thick within the pink tuff physical weathering causes fracturing of feldspars along their cleavage planes variations of the index properties of the tuffs caused by weathering are not significant enough to quantify the weathering depths in the tuffs

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

controls on fan depositional processes in the schist ranges of the southern alps new zealand and implications for debris flow hazard assessment sixteen morphometric and vegetation cover variables associated with 32 debris flow and 28 fluvial fans and their basins in the schist ranges of the southern alps of new zealand are examined the results show statistically significant differences in the area length planimetric shape relief ratio melton s ruggedness r and forest and total vegetation cover between debris flow and fluvial basins and in the apex and toe elevations area and upper and average axial gradients between debris flow and fluvial fans all of these variables except the apex and toe elevations of the fans reflect differences between debris flow and fluvial processes and environmental controls on them discriminant analysis indicates that the relief ratio and melton s r of the basin and upper and average gradients of the fan axis are able to correctly classify debris flow and fluvial fans with almost equally good results obtained by employing only a pair of variables either basin relief ratio and upper fan gradient or basin melton s r and basin shape the lower thresholds at debris flow sites and upper thresholds at fluvial sites for the relief ratio and melton s r of the basin and upper and average gradients of the fan are identified and these as well as the mean values of these variables show significant differences from fans in nearby sedimentary ranges of the southern alps with important implications for the assessment of debris flow hazard on fans fan gradient is found to be closely associated with basin size area and length at debris flow sites but with basin ruggedness relief ratio at fluvial sites both fan types show a weak association between their size and the size of the contributing basin

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

a quantitative study of the weathering of greywacke abstract geotechnical tests point load los angeles abrasion and shore hardness and field tests of strength schmidt hammer shear vane and penetrometer we of samples from fresh greywacke to greywacke derived soil in a single quarry many samples showed a smaller scale variation essentially an unweathere the variation of strength across such transects was measured and correlated with indices determined from mineralogy and chemical composition this corr of strength of similar rocks in the region which may be used as a cheap alternative to geotechnical testing at least for regional reconnaissance of ag

comment on origin of the highly elevated pyrenean peneplain by julien babault jean van den driessche and stephane bonnet sebastien castelltort and alain crave

defining fault avoidance zones and associated geotechnical properties using masw a case study on the springfield fault new zealand abstract the springfield thrust fault at dalethorpe west canterbury new zealand provides a test case to explore the correlation between shear wave velocities at a range of scales and direct field observations of distributed deformation and outcrop properties the springfield fault ruptures to the surface through hard torlesse greywacke overlain on a flight of late quaternary glacio fluvial terraces by 5 m of gravel fault slip has displaced all but the lowest terraces revealing the geometry and location of faulting we used multi channel analysis of surface waves and meter scale cross hole measurements to map shear wave velocities below the lowest apparently undisplaced terrace we correlated these surveys with geotechnical parameters measured at outcrops and investigated relationships in the laboratory both field and laboratory results indicate that the shear wave velocity of torlesse greywacke declines sharply with increasing fracture density field surveys further indicate that relatively unweathered high velocity greywacke is being exhumed in a bivergent wedge between two opposite facing thrusts the fracturing and low shear wave velocities are focused in a wide low velocity damage zone that has developed in the hanging wall of the main thrust and a smaller but similar feature in the hanging wall of the backthrust this is consistent with the geomorphology of the site our correlations of geomorphic indicators of deformation with fault zone velocity structure provide a useful method with which to characterize the distribution of cumulative strain this type of analysis has utility for land use planning on or close to active faults especially where they are obscured by fluvial deposits

discrepancies between experimental observations in natural and synthetic samples abstract the evidence is reviewed by comparing the data obtained from synthetic samples with those derived from natural samples of magnetic minerals present in rocks it is shown that there are many issues which are still unresolved some suggestions are made concerning the future direction of rock magnetic research such as the need for intensified studies of natural samples the aim of this note is not to disclose anything new but rather to open up some lines of thought and draw attention to questions and ideas that may have been lurking in our minds from the very beginnings of paleomagnetism

in situ gamma ray spectrometric study of weathered volcanic rocks in hong kong in situ gamma ray spectrometry grs measurements were conducted at 35 sites in hong kong where volcanic rocks with varying extent of weathering were exposed elemental analyses using x ray fluorescence spectrometry and inductively coupled plasma mass spectrometry were carried out on samples collected from these 35 plus 22 other locations to assess the feasibility of using the grs method to quantify the extent of weathering the parker weathering index varying within a range of 0 0 0 8 for the samples studied was used as a geochemically based reference scheme for correlating the gamma ray spectrometric results with the extent of weathering for the former 35 sites the concentrations of the three major radioelements k u and th determined by in situ grs were compared to laboratory determined values from the samples the study reveals that no significant change occurs to the contents of the three radioelements during the initial state of weathering but once the rocks become highly weathered further progression of weathering is accompanied by a systematic removal of k and an increased dispersion of u and th the results show that k content which is indicative of the extent of weathering can be retrieved reliably with the gamma ray spectrometry technique the study has given support to the potential use of the downhole spectral gamma method for evaluation of weathering grade and the detection of subsurface clay rich levels copyright 2002 john wiley sons ltd

high elevation of low relief surfaces in mountain belts does it equate to post orogenic surface uplift we present experiments of upraising and relaxing topographies showing that peneplanation can occur above the ultimate base level sea level after active uplift the erosion of a topography bounded by a piedmont generates a final smooth and highly elevated topography smoothing at high elevation is even possible during active uplift if the evolution of topography is disrupted by the deposition of the products of erosion on its piedmont which is the case at the transition from underfilled to overfilled conditions in foreland basins

long lived transfer zone paleovalleys in mountain belts an example from the tertiary of the spanish pyrenees abstract major fluvial valleys located in sediment transfer zones that link hinterland drainage basins with their depositional basins are an important but neglected element of fluvial systems studies of present day examples are limited and to date no examples have been described from the geological record tertiary synorogenic fluvial successions in the spanish pyrenees include regional scale unconformity based linear bodies of conglomerate that are interpreted as the fills of transfer zone paleovalleys these paleovalleys are sited mainly in the external zones of the mountain belt between the internal axial zone on which the drainage basin was largely established and the depositional basins one body here termed the sis conglomerate is preserved in a growth syncline between two th ust related lateral structures growth of the syncline during sedimentation permitted a 1400 m succession of clast supported pebble and cobble conglomerates to accumulate during a c 18 m y period between the middle eocene to oligocene the paleovalley served not one but a series of evolving thrust sheet top and foreland basins during this period the stability of the paleovalley was governed by its location between long lived pre existing structures that were inverted during compressional deformation this example demonstrates that fluvial paleovalleys located in transfer zones can when structurally controlled be long term features capable of accumulating and preserving a significant thickness of strata

reply to comment by yanni gunnell and marc calvet on origin of the highly elevated pyrenean peneplain gunnell and calvet 2006 hereinafter referred to as gc challenge the recent model that we proposed for the origin of the highly elevated pyrenean peneplain by contest ing our morphometric analysis of this chain and the relation we made between the morphological evolution and the piedmont sedimentation their reasoning is as follows 1 according to calvet 1996 on which their comment is largely based the high elevation low relief surfaces in the eastern pyrenees are remnants of a peneplain that devel oped before the pliocene from applanation near to sea level and which was later uplifted by 2000 m during the plio quaternary in other words gc belong to the applanation school whereas we woul d belong to the altiplanation school 2 high elevation low relief surfaces do not exist in the central pyrenees 3 therefore the relationships we made between the morphology of the central pyrenees and the pattern of the detrital sedimentation in the adjacent ebro foreland basin is meaningless 4 contrary to the initial interpretation of calvet 1996 gc recognize that crustal thickening did not develop since the pliocene in the eastern pyrenees so they appeal to another geodynamical process such as extension or lithosphere delamination to explain the supposed uplift

chemical remanent magnetization due to deep burial diagenesis in oolitic hematite bearing ironstones of alabama abstract oolitic hematite bearing ironstones of the silurian red mountain formation of alabama are shown to carry a single component remanence stable enough to have survived major folding of probable permian age nevertheless the remanence direction ten sites yielding a paleopole at 38 0 n 132 4 e with dm 3 6 dp 1 9 its reverse polarity and a negative intraformational conglomerate test show that the remanence was very likely acquired during the pennsylvanian some 130 ma after deposition this remanence is likely a chemical remanent magnetization crm acquired during diagenesis induced by heating due to deep burial under a pennsylvanian clastic wedge two possible mechanisms for acquisition of crm during deep burial diagenesis are considered in hypothesis i the oolitic hematite transformed from original geothite when heated to about 80 c acquiring crm in hypothesis ii the oolitic hematite originated from ferrihydrite and was too fine grained to acquire stable crm until heat raised the solubility of hematite allowing grain growth hypothesis i explains the timing of remanence acquisition better but there is some evidence that oolitic goethites may be stable to considerably more than 80 c hypothesis ii has some difficulty explaining preliminary paleomagnetic results from oolitic hematite bearing ironstones of the silurian clinton group new york state we prefer hypothesis i but both hypotheses remain plausible both hypotheses warn that continental red beds may also acquire crm during diagenesis induced by deep burial heating long after deposition but before folding

paleomagnetism and the evolution of fluids in the proterozoic athabasca basin northern saskatchewan canada in the athabasca basin diagenetic hematite of variable paragenesis occurs throughout the sandstones and underlying paleoregolith this hematite carries three distinct single component magnetizations a d 158 i 62 95 5 n 21 b d 11 i 36 95 7 n 6 and c d 18 i 79 95 3 n 27 in some areas of the sandstones such as near reactivated fault zones the diagenetic hematite has been altered to goethite which yields a very low intensity incoherent d magnetization ages for the a b and c magnetizations inferred from comparisons with paleomagnetic directions in precambrian rocks whose ages are known approximately are 1750 1600 1600 1450 and about 900 ma respectively the a magnetization is carried by the earliest formed hematite and its estimated age compares well with u pb ages of 1650 1700 ma for early diagenetic apatite u pb and rb sr ages of approximately 1500 and 900 ma for uraninite and illite coeval with hematite that carries the b and c magnetiza

geophysical constraints on the deep structure along the ecors pyrenees line the structure of the central part of the pyrenean range traversed by the ecors vertical reflection seismic line is further constrained by a joint interpretation of complementary and reprocessed data wide angle low frequency profiling of moho topography indicates an abrupt termination of the northern european moho at the north pyrenean fault and a range of possible geometries of a deeper iberian moho which does not seem to extend significantly to the north of this fault when reprocessing vertical reflection data to 25 s two way travel time strong clear straight reflections are discovered in the part of the section under the northern foreland long after the moho reflection their strong northward dip indicates that they originate in fact at reflectors at depth beneath the north pyrenean fault which may correspond to the connection between the two levels of moho the reflections then being from the northward inclined limit between the wedge of iberian crust underlying the southern edge of the european mantle a range of possible shapes is allowed by the conjunction of these seismic data which is compatible with the results of a detailed gravity profile this would indicate that the imbrication of european into iberian lithosphere has been of limited extent with respect to the surface trace of the north pyrenean fault provided no strong density contrast in the mantle part of the section contributes significantly to the gravity anomaly

a three dimensional model of the pyrenean deep structure based on gravity modelling seismic images and petrological constraints summary the present study aims at building a 3 d density model of a whole collisional mountain belt at the lithospheric scale the geometry of internal structures is constrained by seismic studies while density values are imposed by petrological considerations the model must fit both the bouguer and geoid anomalies this approach is applied to the pyrenees for which numerous geophysical data are available the crustal structure is constrained from the results of seismic profiles the most important crustal feature is the large moho jump which coincides with the surface expression of the north pyrenean fault considered as the suture between the iberian and eurasian plates the eurasian crust is about 30 km thick whereas the iberian crust is 50 km thick in the central part of the range thick sedimentary basins at the piedmont and two large heavy intracrustal bodies located in the western and central parts of the range are also important features of the crustal model at the lithospheric scale a low velocity strip under the north pyrenean fault down to 80 100 km depth interpreted as the subduction of the iberian lower crust has been revealed by tomographic models the density of this structure has been constrained using petrological arguments which assume that the crustal material is transformed into eclogite at about 12 15 kbar 40 50 km depth an eclogite type density value much higher than the mantle density is thus imposed from 50 to 100 km depth theoretical bouguer and geoid anomalies are computed for this 3 d density model using a summation of density block anomalies a good agreement is found with observations giving strong support to the proposed model the crustal structure as seen by seismic profiles explains most of the observed long wavelength negative bouguer anomaly as well the local anomalies related to the intracrustal bodies a possible mantle origin of these bodies is ruled out on the other hand the transformation of the subducted lower crust into dense eclogite provides a successful fit to the long wavelength positive geoid anomalies in addition the water released during eclogite formation may help to explain the high conductivity zone detected down to 80 km south of the north pyrenean fault the 3 d model proposed here thus reconciles petrological considerations and geophysical data

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

paleomagnetic dating of the transformation of oolitic goethite to hematite in iron ore we show that the oolitic hematite ores of birmingham alabama carry a remanence direction stable enough to have survived major folding nevertheless this remanence was very likely acquired in the

the north maladeta fault spanish central pyrenees as the vielha 1923 earthquake seismic source recent activity revealed by geomorphological and geophysical research abstract the spanish central pyrenees have been the scenario of at least two damaging earthquakes in the last 800 years analysis of macroseismic data of the most recent one the vielha earthquake 19 november 1923 has led to the identification of the north maladeta fault nmf as the seismic source of the event this e w trending fault defines the northern boundary of the maladeta batholith and corresponds to a segment of the alpine gavarnie thrust fault our study shows that the nmf offsets a reference neogene peneplain the maximum observed vertical displacement is 730 m with the northern downthrown sector slightly tilting towards the south this offset provides evidence of normal faulting and together with the presence of tectonic faceted spurs allowed us to geomorphically identify a fault trace of 17 5 km this length suggests that a maximum earthquake of mw 6 5 0 66 could occur in the area the geomorphological study was improved with a resistivity model obtained at pruedo where a unique detritic late miocene sequence crops out adjacent to the nmf the section is made up of 13 audiomagnetotelluric soundings along a 1 5 km transect perpendicular to the fault trace at pruedo and reveals the structure in depth allowing us to interpret the late miocene deposits as tectonically trapped basin deposits associated with normal faulting of the nmf the indirect age of these deposits has been constrained between 11 1 and 8 7 ma which represents a minimum age for the elevated pyrenean peneplain in this part of the pyrenees therefore we propose the maximum vertical dip slip rate for the nmf to be between 0 06 and 0 08 mm a normal faulting in this area is attributed to the vertical lithospheric stress associated with the thickened pyrenean crust

the aksay segment of the northern altyn tagh fault tectonic geomorphology landscape evolution and holocene slip rate 1 millennial slip rates have been determined for the altyn tagh fault atf at three sites near aksay 94 e in northeastern tibet by dating fluvial channels and terrace riser offsets with radiocarbon and 10be 26al surface exposure dating up to nine main surfaces are defined on the basis of morphology elevation and dating the abandonment age of some surfaces is constrained by radiocarbon dating which typically coincides with the youngest cosmogenic ages for a particular surface older surface exposure ages are taken to represent the duration of terrace emplacement cumulative offsets range from 20 to 260 m and fall in distinct groups indicative of climatically modulated regional landscape formation most samples are younger than 14 ka and postdate the last glacial maximum the end of the early holocene optimum marks the boundary between the ages of the two main terrace levels at 5 6 ka at this longitude the atf is divided into a northern and southern branch the northern atf should thus yield a minimum rate for the atf system slip rate estimates using the abandonment age of the overlying level for fill terraces or channels and the emplacement of the underlying level for strath terraces give 30 consistent results yielding an average holocene rate of 17 8 3 6 mm yr it is 9 mm yr less than the long term rate obtained near tura at 87 e 26 9 6 9 mm yr in keeping with the inference of an eastward decreasing rate on the atf due to increased thrusting to the south however it remains twice the rate determined by gps studies

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

origin of the highly elevated pyrenean peneplain 1 peneplanation of mountain ranges is generally considered the result of long term erosional processes that smooth relief and lower elevation near sea level therefore peneplain remnants at high elevation in mountain ranges are used to infer posttectonic surface uplift such an interpretation has been proposed for the pyrenees where high elevation low relief erosional surfaces rose up to more than 2000 m because the pyrenean foreland basins are filled with very thick continental deposits which have buried the early jagged landscape we challenge this hypothesis by pointing out that relief applanation does not necessarily require elevation lowering we propose an alternative interpretation in which piedmont aggradation of detrital sediment that comes from erosion of the high chain induces the rise of the base level of the range therefore reducing strongly the erosive efficiency of the drainage system and resulting in the progressive smoothing of the relief such a process allows a high elevation low relief erosional surface to develop at the scale of the range in the pyrenees occurrence of high elevation low relief erosional surface remnants does not imply a posttectonic uplift but is instead due to the dissection of the initial miocene high elevation low relief surface by the recent drainage system the erosive activity of which has been enhanced by global climate change from the late pliocene onward

the tectonic implications of solundian upper devonian magnetization of the devonian rocks of kvamshesten western norway the allochthonous old red sandstone of kvamshesten western norway records polyphase orogenic deformation and palaeomagnetic results from both the devonian sediments and mylonites associated with the basal thrust define a syn to post tectonic magnetization withd 218 i 3 and 95 9 7 the corresponding pole position lat 21 s long 324 e suggests a late devonian early carboniferous magnetization age solundian and probably dates the time of thrust movements

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

thermodynamic interpretation of weathering indices and its application to engineering properties of rocks abstract weathering indices typified by the miura index w o m that are the ratios of geochemically mobile to relatively immobile elements can be shown to be logarithmically related to the free energy of the weathering reaction this can be demonstrated for silicate minerals other extensive properties such as the moduli of elasticity and rigidity are similarly correlated the mass strength envelope implied by the corresponding o log w plot concurs well with plotted values for rocks suggesting that the correlation is valid for intact rocks as well by a combination of the miura index and an index believed to show not only the state of weathering but also the susceptibility to further weathering the parker index w o p it is possible to obtain estimates of the activation energy for the incongruent aqueous dissolution of minerals which compare favourably with experimental determinations although the engineering behaviour of rocks is generally governed by physical parameters and thus by short term mechanical or physico chemical forces there are some instances where failure has been attributed to the chemistry of the rock itself for these rocks a good correlation is obtained between a chemical weatherability index log w o m w o p and rock durability as measured by the los angeles abrasion test

field characterisation of weathered ankara andesites abstract this paper presents field and some index properties of weathered ankara andesites carried out over a period of 4 years ankara andesites are distributed widely around the city of ankara on which numerous important structures have been founded thus the weathering characteristics of ankara andesites both from the engineering geological and the rock mechanics points of view are important the field work involved assessment of the rock mass weathering grades conduction of simple field tests schmidt hammer and point load tests on the rock materials characterisation of discontinuities and collection of representative samples from each weathering grade for laboratory testing the relationship between the experimentally determined parameters and quantitative engineering geological descriptions provided a simple geological method for the assessment of the design parameters and mapping the distribution of mass weathering grades as a result of the evaluation an idealized weathering profile and the scale of rock mass weathering grades together with their range of thicknesses were proposed some index tests such as effective porosity schmidt hammer value shv point load strength and seismic velocity provided good relations with the degree of weathering

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

origin and depositional environment of ordovician stratiform iron mineralization from zamora nw iberian peninsula the ordovician stratiform iron deposits at zamora nw iberia are arranged in several levels ranging between 0 2 and 1 5 m in thickness which are interstratified in the upper member of the pielgo quartzites formation arenig the sandy nature and trace fossils corresponding to the ichnogenus cruziana and daedalus together with major and trace element contents of this formation suggest an inter and subtidal shallow marine depositional environment which on a global scale formed part of a broad shelf situated in the northern margin of the gondwana continent the iron mineralization displays a foliated and banded structure due to the alternation of quartzitic phosphatic apatite chamositic chamositic biotitic and ferriferous magnetite and hematite beds they have high tio2 ta sc v nb co zn and y contents the magnetite contains unusually large amounts of tio2 v cr and ni there is also a clear depletion in eu and the eu sm cn ratio is 1 the chamosite contains high concentrations of cr and v these results suggest that iron was supplied from the weathering of a continental source in combination with volcanic activity such as within basin basic volcanism or the presence of basic volcanic rocks in the exposed land the physicochemical conditions of iron mineral crystallization calculated from chamosite compositions are the following log f o2 38 8 to 30 7 log f s2 13 2 to 9 5 and t 200 to 330 c these results together with the 18o value 2 of the magnetite suggest that chamosite and magnetite were crystallized during later diagenesis and early low grade metamorphism under redox conditions below the magnetite hematite buffer

schmidt hammer exposure age dating shd of late quaternary fluvial terraces in new zealand schmidt hammer sh r values are reported for surface clasts from numerically dated holocene and pleistocene fluvial terraces in the south island of new zealand the r values are combined with previously obtained weathering rind radiocarbon terrestrial cosmogenic nuclide and luminescence terrace ages to derive sh r value chronofunctions for greywacke clasts from four distinct locations our results show that different weathering rates affect the form of the sh r value versus age curve however a fundamental dependency between the two remains constant over timescales ranging from 102 to 105 years power law scaling constants suggest changes in clast weathering rates are primarily affected by climatic precipitation and temperature and sedimentologic variables source terrane petrology age uncertainties of 22 of the surface age suggest that schmidt hammer exposure age dating shd is a reliable calibrated age dating technique for fluvial terraces copyright 2013 john wiley sons ltd

early silurian paleopole for redbeds and volcanics of the king george iv lake area newfoundland redbeds and felsic and mafic volcanics of the king george iv lake area of the dunnage zone in southwestern newfoundland have been studied paleomagnetically after unfolding both hematite and magnetite carry a consistent direction of magnetization d 29 6 i 1 0 k 19 3 95 11 3 corresponding to a near equitorial paleolatitude 0 5 n 6 and yielding a paleopole at 84 6 e 35 9 n dm 11 3 dp 5 6 a positive fold test shows that the remanence was acquired before devonian deformation a positive conglomerate test and a reversal of the magnetization in a continuous redbed sequence demonstrates that the remanence was acquired at the time of formation which has been assigned to the early silurian on the basis of a u pb zircon date of 431 5 ma no other undisputed primary or pre fold remanence has been reported from atlantic canada for the late ordovician silurian period therefore from paleomagnetic data it is not yet possible to estimate the amount of post silurian movement within

pyrenean orogeny and plate kinematics 1 the evolution of the pyrenees a mountain range between iberia and eurasia has remained the subject of many debates between geologists and geophysicists for a long time by combining the identification of seafloor spreading anomalies a33o to m0 in the bay of biscay with those in the north atlantic we have derived a position of a mean pole of rotation for the entire opening of the bay of biscay four hundred kilometers of shortening took place between the iberian and eurasian plates in the pyrenean domain during the opening of the bay of biscay from chrons m0 to a33o time 118 to 80 ma the deep seismic etude continentale et oceanique par reflexion et refraction sismique ecors profile shot across the pyrenees and teleseismic data show the presence of two distinct slabs which dip to the north the southern slab is linked to the subduction of the neo tethys ocean which was created from late jurassic to early aptian simultaneously elongated back arc basins formed along the future pyrenean domain this slab was active from at least 118 ma early aptian to 100 ma late albian the northern slab active since 85 ma is linked to the subduction of the lower continental crust located south of the pyrenean domain in the upper crust normal faults as well as the north pyrenean fault became reverse faults and former back arc basins were inverted giving rise to the uplift of the pyrenees as a double asymmetrical wedge