the cowichan fold and thrust system vancouver island southwestern british columbia the cowichan fold and thrust system is a southwest verging linked thrust system formed by northeast southwest large scale crustal contraction involving the upper cretaceous nanaimo group and its wrangellian basement the geometry of the thrust system from plan and profile perspectives illustrates its thick skinned structural style the thrust system is interpreted to be a leading imbricate fan thrusting was most likely in sequence creating an estimated minimum 20 30 shortening at the basement cover interface both fault propagation and fault bend folding are evident the former being more common kinematic indicators and the geometry of the thrust system show no evidence of significant transpressional or transtensional displacement fields contraction postdates deposition of the nanaimo group and is indirectly dated as late eocene the sole fault of the thrust system is interpreted to rise from northwest to southeast on a series of deep lateral to oblique ramps and merge with the san juan fault system this explains the rapidly westward thickening wedge of thrusted wrangellian basement in the study area in the east the sole fault is interpreted to have locally permitted the nanaimo group to overthrust the san juan terrane investigation of the cowichan fold and thrust system reveals how shortening during westward progressing terrane accretion is accommodated in a forearc region dominated by a large slab of rigid semicontinental crust

obducted nappe sequence in the san juan islands northwest cascades thrust system washington and british columbia the san juan islands northwest cascades thrust system in washington and british columbia is composed of previously accreted terranes now assembled as four broadly defined composite nappes stacked on a continental footwall of wrangellia and the coast plutonic complex emplacement ages of the nappe sequence are interpreted from zircon ages field relations and lithlogies to young upward the basal nappe was emplaced prior to early turonian time 93 ma indicated by the occurrence of age distinctive zircons from this nappe in the sidney island formation of the nanaimo group the emplacement age of the highest nappe in the thrust system postdates 87 ma detrital zircons within the nappe the nappes bear high pressure low temperature hp lt mineral assemblages indicative of deep burial in a thrust wedge however several features indicate that metamorphism occurred prior to nappe assembly metamorphic discontinuities at nappe boundaries absence of hp lt assemblages in the footwall to the nappe pile and absence of significant unroofing detritus in the nanaimo group a synorogenic relationship of the thrust system to the nanaimo group is evident from mutually overlapping ages and by conglomerates of nanaimo affinity that lie within the nappe pile from the foregoing relations and broader cordilleran geology the tectonic history of the nappe terranes is interpreted to involve initial accretion and subduction zone metamorphism south of the present locality uplift and exhumation orogen parallel northward transport of the nappes as part of a forearc sliver and finally obduction at the present site over the truncated south end of wrangellia and the coast plutonic complex

applications of geochemistry in tsunami research a review abstract much progress has been made since the first published studies of tsunami deposits nearly 30 years ago geochemistry is now a much more widely used proxy in tsunami research mainly due to its increasingly recognised value in the identification of historical and or prehistorical deposits at times even providing the conclusive proof when other proxies are missing or equivocal but also its significance in environmental impact assessments following recent tsunamis the rapid advance in analytical techniques has also made it a more approachable and popular method as it is now often faster and cheaper here we provide a review of the applications of geochemistry including the techniques used as well as a database of studies that used chemical proxies in their investigation of recent and old events including onshore and offshore tsunami deposits chemical signatures are often used as markers of marine inundation either as salinity indicators where they can also allow the identification of the limit of tsunami inundation or tracers of the incorporation of marine sourced carbonates their applications as indicators of source material are nevertheless expanding thereby potentially providing additional information on the hydrodynamic processes associated with tsunami inundation although they are largely site specific the effects of post depositional changes in different climatic regimes are examined with a particular emphasis on water leachable components and implications for post event recovery of coastal ecosystems we demonstrate the usefulness of chemical proxies in studies of the geological record of tsunamis extending back thousands of years suggest new approaches and discuss limitations and existing knowledge gaps

stable isotopes reveal human influences on southern new zealand soils abstract a multi isotopic soil study across a southern new zealand transect has been undertaken as part of a geochemical baseline survey to identify human impacts on new zealand s landscape and characterise different land uses and anthropogenic effects carbon nitrogen and sulphur isotopes from two soil depths 0 30 and 50 70 cm were acquired across a variety of land uses including pristine national parks urban centres intensively farmed pastoral land climates dry 6000 mm annual rainfall altitude sea level to 2300 m above sea level and soil parent material lithology sandstone schist basalt detrital organic matter accumulated more in lowlands than at higher altitudes with higher carbon and nitrogen contents found in river valleys carbon isotopes clearly differentiated between drier higher altitude or open pastoral sites more positive values and wetter forested sites more negative values nitrogen isotopes reflect anthropogenic human influence with elevated values around urban and intensively farmed sites and lower values characterising indigenous forests and pristine sites sulphur isotopes either show more positive values typical of fertilisers rain or sea spray in open pastoral sites or more negative values consistent with weathered geological sources such as metamorphic sulphides found in schist in some river valley sites the study demonstrates that regional isotope studies are a potential tool to understand the long and short term impacts on landscapes and may be useful for future mineral exploration urban health studies agricultural site remediation and land use control and regulation

stratigraphy age and paleogeography of the eocene chuckanut formation northwest washington the eocene chuckanut formation of washington s north cascades comprises as much as 6000 m of alluvial strata and is one of the thickest nonmarine sequences in north america it is exposed in several disconnected outcrop belts that are remnants of what was probably an extensive fluvial system in western washington in this study seven stratigraphic members are defined in the main outcrop belt of the chuckanut formation near the town of bellingham their ages based on fission track zircon dates palynologic studies and correlation by mapping extend from the early to the late eocene three types of fluvial systems contributed to the chuckanut formation and are distinguished on the basis of their lithology sedimentology and petrology the first comprises fine load meandering river deposits of the lower eocene bellingham bay member and the middle eocene slide member sandstones are arkosic and had their main source in rapidly uplifted high grade metamorphic terranes in eastern washington the second type

detrital zircon constraints on terrane ages and affinities and timing of orogenic events in the san juan islands and north cascades washington detrital zircon geochronology of this report pertains to cretaceous orogeny in northwest washington an event that involved blueschist metamorphism and emplacement of nappes in the san juan islands northwest cascades thrust system and continental arc magmatism and associated barrovian metamorphism in the neighboring coast plutonic complex structurally low in the thrust system quartzose gneiss of the yellow aster complex yields an entirely precambrian suite of detrital zircons with an age pattern that is similar to that of ordovician miogeoclinal rocks and the outboard yukon tanana yreka and shoo fly terranes elsewhere in the cordillera midway in the nappe pile of the northwest cascades sandstone in the bell pass melange has a zircon age population of 110 ma an age that together with the spectrum of exotic materials associated with the sandstone suggests the melange was a major zone of dislocation during mid cretaceous nappe emplacement at a high level in the thrust system are nappes of the fida

observations on the nature and origin of fusain abstract evidence for a wildfire origin of fusain is examined charcoal produced by natural fires and artificial charring resembles fossil fusain both in physical size and shape and in optical reflectance artificially charred leaves and naturally burnt wood are illustrated using the sem reflectance studies on modern charcoals suggest that much semifusinite may be produced by pyrolysis the ecological implications of a wildfire origin of fusain are discussed and it is concluded that fires have been a feature of terrestrial ecosystems from at least the late devonian

exploring the joint compositional variability of major components and trace elements in the tellus soil geochemistry survey northern ireland abstract the complexity of modern geochemical data sets is increasing in several aspects number of available samples number of elements measured number of matrices analysed geological environmental variability covered etc hence it is becoming increasingly necessary to apply statistical methods to elucidate their structure this paper presents an exploratory analysis of one such complex data set the tellus geochemical soil survey of northern ireland ni this exploratory analysis is based on one of the most fundamental exploratory tools principal component analysis pca and its graphical representation as a biplot albeit in several variations the set of elements included only major oxides vs all observed elements the prior transformation applied to the data none a standardization or a logratio transformation and the way the covariance matrix between components is estimated classical estimation vs robust estimation results show that a log ratio pca robust or classical of all available elements is the most powerful exploratory setting providing the following insights the first two processes controlling the whole geochemical variation in ni soils are peat coverage and a contrast between mafic and felsic background lithologies peat covered areas are detected as outliers by a robust analysis and can be then filtered out if required for further modelling and peat coverage intensity can be quantified with the br in the subcomposition br rb ni

measurements of the cretaceous paleolatitude of vancouver island consistent with the baja british columbia hypothesis a previously unsampled outcrop of gently dipping or flat lying upper cretaceous sedimentary strata in the vancouver island region which contains unaltered aragonitic mollusk fossils yielded a stable remanent magnetization that is biostratigraphically consistent with cretaceous magnetochrons 33r 33n and 32r these results characterized by shallow inclinations indicate an upper cretaceous paleolatitude of about 25 3 degrees north which is equivalent to that of modern day baja california these findings are consistent with the baja british columbia hypothesis which puts the insular superterrane well south of the oregon california border in the late cretaceous

controls on the chemical variability of peat types in a domed peat deposit baram river area sarawak malaysia pyrolysis gc ft ir fid and pyrolysis gc ms studies have been conducted on peat samples from the margin and central portions of a tropical domed peat deposit in the baram river area sarawak malaysia in order to determine the chemical variability of peat types found within the deposit in an effort to unmix the chemical variability of the samples an extended qmodel program was utilized which produced a series of 4 end members these end members composed of various proportions of each of the 49 pyrolysis products monitored in this study are combined in various proportions to reproduce the composition of each of the 32 samples comparison of the chemical data with previous petrographic and megascopic analysis reveals parallel trends between the input from the end members and the makeup and degree of degradation of each of the peat types from this analysis it can be concluded that the 4 end members produced in this analysis represent input from a guaiacyl lignins b lignin biodegradation products c cellulosic derived products and d syringyl lignins the inputs from the 4 end members can be traced to the type of plants and the degree of degradation in addition comparison of the spatial distribution of the 4 end members reveals that the samples in the central portion of the deposit have much more chemical variability than the highly degraded samples on the margin of the deposit

kinematic analysis of the san juan thrust system washington shear related fabric in the middle to late cretaceous san juan thrust system washington is observed in imbricated blocks and in fault zones a few millimeters to tens of meters thick foliation and lineation are defined in tectonic blocks by alignment of 1 newly grown muscovite and chlorite and 2 flattened and stretched radiolaria mineral porphyroclasts and rock fragments thin argillaceous shear zones bear a pronounced lineation defined by lithologic streaks and slickenside corrugations the slickenside and stretching lineations show a well defined preferred orientation in a horizontal northwest southeast direction widespread s c fabrics asymmetric pressure shadows fault drag features and asymmetric folds in the x z plane yield a sense of tectonic transport at most localities of upper plate to the northwest aragonite prehnite lawsonite pumpellyite and rare na amphibolite and na pyroxene characterize the metamorphism during the thrusting the findings of this study indicate north west orogen parallel transport of the san juan thrust system we suggest that this structure is a large step over zone transferring dextral strike slip from the western cascades to the oceanward side of wrangellia

a 7300 year record of environmental changes in a coastal wetland moawhitu new zealand and evidence for catastrophic overwash tsunami abstract three sedimentary sequences from a coastal wetland behind a sand barrier on the west coast of d urville island new zealand were examined using a multi proxy approach including sedimentological geochemical and microfossil diatom analyses with the chronology established using radiocarbon and 210pb dating data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in moawhitu this was followed by periods of alternating wetland encroachment and open water displaying spatial variations until a peatland was established about 1300 cal yr bp the wetland was then partially drained in the early 1900s leading to compaction of the peat near the surface a coarse layer containing gravel sand and shells with a sharp lower contact in the northern area of the wetland is attributed to an overwash about 2500 3000 yr bp most probably a tsunami generated by the rupture of a local or regional fault the high resolution continuous record obtained with xrf core scanning revealed a geochemical signature ca and s for the overwash 600 m inland in the middle area of the wetland while it was absent from the southern site 1 1 km from the shore this suggests that except at the northern end of moawhitu the sand dune acted as an effective barrier preventing any sediment from overtopping 2500 3000 yr bp with only a geochemical evidence marking the extent of seawater inundation no sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in moawhitu as recounted in m ori oral tradition p r kau although pebbles at the surface of the dune are likely to be linked to this event thus the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century however our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years it also shows that a high resolution continuous xrf record can provide the evidence for short term changes catastrophic or not that did not leave any clear sedimentological signature thus providing a better insight of environmental changes in any depositional environment

comparisons of central appalachian carboniferous coal beds by benches and a raised holocene peat deposit abstract three carboniferous age coals from southern west virginia u s a were examined at bench level and compared to a holocene peat deposit the snuggedy swamp south carolina u s a data for all deposits consisted of coal or peat thickness ash content and petrographic composition as well as parting or overlying clastic sediment thickness comparison of coal and parting thickness showed an inverse relationship in all cases bimodal distribution patterns for coal peat thickness versus area indicate that the transition between areas of extensive thick coal peat and extensive thin coal peat was rapid in the coal deposits at bench level both ash and organic inert content increased toward the transition to thin coal the areas of thick coal contained the highest vitrinite reactive contents and lowest ash values volumetrically this is similar to the distribution of low ash well preserved thick peat occurring in the central raised areas of the snuggedy swamp surrounded by areas of high ash decomposed peat subject to flooding although the depositional environments interpreted for each of the three coal beds and the snuggedy peat deposit differ widely the deposits themselves show similar distribution trends in thickness ash content and petrographic composition

multi proxy evidence for trans pacific tsunamis in the hawai ian islands abstract the origin of two sand layers buried in polol wetland on the northeast coast of the island of hawai i was investigated using a multi proxy approach including radiometric dating sedimentology geochemistry micropalaeontology palynology and historical records based on 210 pb 137 cs and pollen data the lower sand unit extending 250 to 350 m inland is attributed to the 1946 aleutian tsunami while the upper sand unit was laid down by the 1957 aleutian tsunami chronological information does not appear to support any link between these deposits and historical storm events furthermore sedimentological geochemical diatom and pollen results suggest deposition of marine and near beach sediments under high energy conditions typically associated with tsunami inundation this work presents the first conclusive sedimentary evidence for distantly generated tsunamis on the hawai ian islands opening the way for more comprehensive historical and palaeotsunami studies indeed a brief review of archaeological data suggests that the hawai ian coast may have experienced similar large magnitude events in the past from both local and distant sources

apatite fission track dating of the cowichan fold and thrust system southern vancouver island british columbia the cowichan fold and thrust system on southern vancouver island comprises a linked system of folds and thrust faults in crystalline and sedimentary rocks of the wrangellia terrane and its sedimentary cover the upper cretaceous nanaimo group and upper paleocene to lower eocene sandstones of the chuckanut formation apatite fission track analysis indicates that cooling below the closure temperature of fission track retention in apatite 100 20 c for both the island plutonic suite from the wrangellian basement and the nanaimo group occurred at 50 40 ma middle eocene thrusting is interpreted to have occurred immediately prior to this time in the middle eocene but after post cretaceous regional burial of the turonian to maastrichtian nanaimo group and deposition of upper paleocene and lower eocene sandstones which are involved in the deformation these timing constraints support the hypothesized temporal linkage between contraction and uplift of wrangellia during the middle eocene and continued margin normal contraction of the pacific rim terrane the crescent terrane at 45 ma

paleomagnetism and tectonic significance of albian and cenomanian turbidites ochoco basin mitchell inlier central oregon 1 understanding continental growth and convergent margin dynamics associated with terrane accretion and modification of the cordilleran margin of north america is prevented by conflicts in paleogeographic models for major terranes oceanic plates and the north american margin we present new paleomagnetic data suggesting that the blue mountains superterrane located at an inboard portion of the cordilleran margin has undergone substantial northward translation and clockwise rotation relative to north america since mid cretaceous time positive baked contact conglomerate and fold tests provide evidence that the magnetization of these rocks dates from their deposition these results yield a mean direction of d 10 8 i 58 5 k 127 95 4 1 and n 11 comparison of magnetic inclinations and magnetic fabrics shows no evidence for inclination error a paleolatitude of 39 2 4 8 4 3 n is obtained indicating a paleolatitude anomaly of 15 9 4 1 northward translation of 1760 460 km and cw rotation of 37 7 3 with respect to north america since circa 93 ma application of an ad hoc 5 inclination error yields translation of 1200 460 km through comparison with other units in the western cordillera we infer that the mitchell inlier was located adjacent to the sierra nevada arc during mid cretaceous time and that the blue mountains province may correlate with the intermontane superterrane in british columbia other interpretations such as large inclination errors or an independent displacement history for the mitchell inlier are possible but unlikely more work is needed to fully test these hypotheses and resolve major questions of cordilleran tectonics

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

the coast belt thrust system evidence of late cretaceous shortening in southwest british columbia the coast belt thrust system cbts is the leading edge of a west vergent contractional belt that formed along the inboard margin of the insular superterrane in late cretaceous time the foreland of this contractional belt comprises a system of east dipping frontal thrusts that imbricate jurassic and early cretaceous supracrustal arc sequences and related plutonic suites of the western coast belt wcb these faults root eastward into an imbricate zone of folded thrusts and out of sequence reverse faults across which the metamorphic gradient has been structurally inverted to the east and structurally above the imbricate zone is a folded stack of high pressure thrust sheets comprising metamorphosed island arc and oceanic rocks of the central coast belt ccb these rocks represent the exhumed crustal root of the cbts metamorphosed volcanic and volcaniclastic rocks that occur in thrust sheets of the imbricate zone yield u pb zircon dates which support a correlation with lower plate jurassic and early cretaceous arc sequences of the wcb structural and geochronologic data indicate a two stage history of late cretaceous shortening during the early stage of shortening supracrustal arc and related basin sequences along the inboard margin of the insular superterrane were structurally imbricated and accreted to the toe footwall of a westward prograding accretionary complex made up of previously assembled terranes of the ccb these early stage structures are represented by folded thrusts in the imbricate and hinterland zones of the cbts the timing of this early stage thrusting is bracketed by the emplacement of synorogenic plutonic suites which yield u pb zircon dates of 97 1 ma and 96 6 3 ma late stage shortening involved both thin skinned thrusting and folding of jura cretaceous arc sequences in the wcb foreland and out of sequence thrusting of higher grade thrust sheets in the imbricate and hinterland zones of the cbts in the foreland this episode of deformation is bracketed by late and postkinematic plutons which yield u pb zircon dates of 94 2 ma and 91 4 3 ma respectively in the imbricate zone this episode of deformation is bracketed by the emplacement of synkinematic and postkinematic plutons which yield u pb zircon dates of 96 6 3 ma and 94 6 5 ma respectively the development of thick skinned out of sequence thrusts in the imbricate and hinterland zones of the cbts signals a northeastward migration of the deformation front in late cretaceous time this shift in the locus of thrusting resulted in southwestward telescoping and structural inversion of the metamorphic hinterland and may account for the complex stacking order and thermal history of the southern coast belt

chemical signatures of palaeotsunamis a forgotten proxy article i nfo article history a range of diagnostic criteria are required to help identify palaeotsunami deposits although chemical signatures have long been used as indicators of palaeosalinity in sedimentary sequences their use in the studies of palaeotsunami deposits is rarely applied and is yet to be widely recognised the chemical composition of interstitial water in coastal ponds and sedimentary sequences in coastal marshes and lagoons has been used successfullyasanindicatoroftsunamiinundation chemicalsignaturescanalsoprovidecluesaboutthelandward limit of runup of a tsunami beyond the area of sediment deposition like most palaeotsunami proxies however the preservation of chemical signatures varies with environmental conditions

geomorphology and accommodation space as limiting factors on tsunami deposition chatham island southwest pacific ocean abstract chatham island in the southwest pacific ocean is exposed on all sides to potential tsunami impact in historical time tsunamis are known to have inundated the coast on several occasions with the largest event in 1868 coastal dunes along the northeast coast of chatham island preserve sedimentary evidence of this and possibly earlier tsunami events as localised gravel lags however these deposits lack a clear stratigraphic context and establishing their age is difficult this study examines the sediment record in a freshwater wetland at okawa point located directly landward of the dunes where apparent tsunami gravels occur sediment descriptions pollen foraminifera chemical data and radiocarbon dates from cores are used to reconstruct the environmental history of the wetland the record extends from ca 43 ka to the present and incorporates glacial post glacial and human influenced phases throughout this time the wetland appears to have remained isolated from catastrophic marine inundation the only evidence for saltwater intrusion is observed in the historic period via geochemical grain size and pollen data which record a marine inundation event that forced the transport of a thin cm thick deposit of dune and beach sand into the seaward edge of the wetland this is interpreted as the signature of the 1868 tsunami the lack of more widespread physical evidence for this and other tsunami events in the wetland is attributed to the morphological roughness afforded by coastal dunes and limited accommodation space for holocene deposits

the skipjack island fault zone an active transcurrent structure within the upper plate of the cascadia subduction complex abstract the skipjack island fault zone has been mapped in the san juan islands between vancouver island canada and the washington state mainland usa a decade ago interpretation of multibeam sonar seafloor imagery revealed that skipjack island an east west striking sedimentary bedrock outcrop was a fault controlled structural feature a major fault separates skipjack island from a deformed sedimentary bedrock outcrop on the seafloor to the north recently the skipjack island fault zone s morphology and extent have been explored both to the west and east of the island using multibeam echosounder bathymetry seismic reflection profiles and sediment cores the character of the skipjack island fault zone is well defined locally by the interpreted seismic reflection profiles which show active faults that displace sediments deposited since the last glacial maximum the central part of the fault zone near skipjack island appears as a near vertical structure in the shallow subsurface that has been subjected to left lateral motion as evidenced by a bedrock exposure on the seabed north of the island where folded strata bend eastward against the fault the result of drag from fault motion interpretations of recent geophysical data suggest an extension of the skipjack island fault zone farther to the west where it trends towards and possibly connects with the fulford fault on vancouver island and to the east where it either terminates north of lummi island or continues eastward onto the mainland the skipjack island fault zone is interpreted to be the northern boundary of the san juan archipelago with the devils mountain fault zone being the southern boundary both fault zones represent the longest continuous faults of the san juan archipelago this newly mapped fault zone and its zone of deformation to the north may represent the northern boundary of the cascadia forearc potential sesimicity of the skipjack island fault zone and its proximity to the steep unstable northeastern side of orcas island and the southern front of the fraser river delta poses a geohazads problem in the form of earthquakes landslides submarine slides and tsunamis

slaty cleavage development and magnetic anisotropy fabrics the shale to slate transition preserved in the ordovician martinsburg formation at the lehigh water gap pennsylvania provides an opportunity to study the relationship between magnetic anisotropy fabrics and the development of slaty cleavage our previous work has indicated that anisotropy of magnetic susceptibility ams does not record changes in finite strain associated with cleavage development in these rocks but instead measures the degree of dissolution and new growth of ehlorite additional ams data presented in this paper lend further support to this conclusion conversely anhysteretie remanent magnetization anisotropy arma which is not affected by paramagnetie ehlorite accurately reflects the strain induced rock fabrics associated with cleavage formation arma results show that magnetite dimensional orientations vary from bedding parallel in shale samples to cleavage parallel in samples with well developed slaty cleavage samples with weak and pencil cleavage display scattered arma orientations which lie in between bedding and cleavage these intermediate orientations may be due to either passive rotation of magnetite from bedding parallel to cleavage parallel or re crystallization of magnetite if rotation occurred grain rotation was highly heterogeneous in the samples with incipient cleavage the intermediate arma orientations may also reflect the varying contribution of two magnetite preferred orientations a depositional orientation parallel to bedding and a new growth orientation parallel to cleavage

petrologic evolution and paleogeography of the late cretaceous nanaimo basin washington and british columbia implications for cretaceous tectonics systematic variations in sandstone petrofacies of the upper cretaceous nanaimo group are related to basin evolution and uplift of surrounding tectonic provinces a subaerially exposed horst partially separated southern and northeastern portions of the nanaimo basin volcaniclastic and arkosic sediment was derived from this horst the horst subsided below wave base during very early evolution of the nanaimo basin but it controlled sediment dispersal throughout basin development lower units of the nanaimo group in the southern nanaimo basin are chert rich and were derived largely from terranes of the san juan islands and north cascades basaltic and plutonic debris from the insular belt was deposited into the northwestern nanaimo basin during early basin development minor deposition of arkosic debris from the coastal plutonic belt also occurred upper units of the nanaimo group contain abundant plagioclase rich sediment derived from the coastal plutonic belt rocks along the southeastern margin of the basin however reflect continued sedimentation from terranes of the san juan islands and north cascades arkosic and dacitic debris from insular belt sources is recognized in the northwestern nanaimo basin the nanaimo basin may have developed as a pull apart basin within a broad zone of normal and transcurrent faulting in response to oblique convergence or transform faulting between the kula plate and the pacific margin of washington and british columbia

spatial variability in modern tropical peat deposits from sarawak malaysia and sumatra indonesia analogues for coal petrographic and chemical variability in two tropical low ash domed peat deposits of similar age and physiographic setting but different external morphology were examined as modern analogues for coal both occur in microtidal alluvial to deltaic plain settings support similar arborescent vegetation and have accumulated in the past 5 000 years one deposit is an extremely convex mature done with a surface that rises 10 m above river level the other is a low gradient dome rising only 3 m above river level but with a concave base up to 6 m below both deposits have been eroded by adjacent rivers yet peat in the mature dome has accumulated remote from persistent flooding and exhibits distinctive internal stratigraphy decomposed sapric peat floors the deposits and is overlain by increasingly better preserved woody hemic and a cap of coarse fibrous peat derived from less arborescent vegetation consistent flooding in the low gradient dome has maintained conditions for the accumulation of predominantly woody hemic peat which interfingers with and is overlain by oxidised sapric peat and levee derived clastic sediments peat types in both deposits exhibit distinctive polymodal textures and organo chemical signatures that correspond to botanical input and degree of decay due to the abundance of pre huminite vitrinite macerals in all peat types from these deposits megascopic and microscopic texture is a better discriminator for comparison to ancient coal types it is suggested that the upward vertical sequence of decreasing woodiness and increasing lightness in colour observed in the mature dome might best be compared to sequences observed in tertiary brown coals this typical sequence can be modified or overprinted due to flooding in the burial process

late miocene remagnetization within the internal sector of the northern apennines italy abstract paleomagnetic and geologic evidence indicates that upper jurassic radiolarian cherts of both the tuscan cherts formation continental margin tuscan units and the monte alpe cherts formation oceanic crust ligurian units were remagnetized during miocene orogenesis of the northern apennines of italy characteristic overprint magnetizations with reversed polarities have been found over a large area within the internal sector of the northern apennines including eastern liguria elba island and the thyrrenian margin and west of the middle tuscan ridge the reversed polarity overprint average direction d 177 i 52 95 15 was most likely acquired during late miocene uplift and denudation of the orogenic chain and thermochemical remagnetization was a probable consequence of increased circulation of orogenic fluids similarly mostly reversed polarity directions of magnetization have been found by other workers in overlying post orogenic messinian sediments d 177 i 57 95 3 which show little counterclockwise ccw vertical axis rotation with respect to stable europe 8 5 the monte alpe cherts sampled at sites in the external sector of the northern apennines close to major tectonic features have normal polarity overprint directions with in situ w sw declinations since the overlying post orogenic messinian sediments have not been substantially rotated about vertical axes the evidence points to an earlier pre late miocene remagnetization in the external parts of the orogenic chain

paleomagnetic evidence for poleward transport of upper jurassic rocks in the decatur terrane san juan islands washington the san juan islands are underlain by a west vergent late cretaceous thrust and nappe system part of a larger thrust belt exposed in the northwest cascades of washington and the southwestern coast mountains of british columbia published paleomagnetic data from cretaceous plutons for example the coast plutonic complex intruding the thrust belt suggest that it has been displaced northward by as much as 2400 km since 90 100 ma this study focuses on the preintrusive travel history of the decatur terrane one of the units involved in the san juan thrusting the decatur terrane is of special interest because it may be correlative with the coast range ophiolite cro and great valley sequence of the southern california coast ranges we report new paleomagnetic data from the james island formation an upper jurassic preintrusive turbidite unit and from the obstruction formation a terrigenous sandstone unit deposited on the decatur terrane in the late cretaceous nine sites in the obstruction formation yield a single remanence direction grand mean d 90 7 i 67 9 that is clearly a postfolding overprint possibly of late cretaceous age the six site mean remanence directions from the james island formation cluster well only after restoring the beds to horizontal by a scheme that takes account of their complex structure this positive fold test and the presence of two polarities provide evidence that the remanence is primary the mean paleolatitude corresponding to the corrected remanence direction from the james island formation is 0 9 2 the data thus corroborate equatorial paleolatitudes derived from parts of the cro by others and suggest that the decatur terrane and cro represent fragments of a larger terrane originally located near the jurassic equator unlike the cro however the decatur terrane was still near the equator at 145 ma if the plutons intruding the san juan north cascades thrust belt formed 2400 km to the south then the paleomagnetism of the decatur terrane suggests it moved 20 farther poleward in the interval 145 ma to 97 ma than did an equivalent site on north america a much smaller amount of pre late cretaceous motion is allowed by error limits on the paleolatitudes but more is required if tilting is partly responsible for the shallow paleomagnetism of the cretaceous plutons

hydraulic reversals and episodic methane emissions during drought cycles in mires reversals in hydraulic head and extensive methane losses were identified during a drought cycle from changes in hydraulic head and dissolved methane profiles in peat glacial lake agassiz peatlands northern minnesota united states during the summer 1990 drought regional groundwater discharged from the mineral soil underlying the peat to raised bogs concentrations of dissolved ch sub 4 in pore water showed that much of the peat column was supersaturated with respect to a reference standard of 1 atm partial pressure ch sub 4 by the summer of 1991 the severity of the drought lessened and the upper peat column was resaturated with precipitation derived water groundwater flow was then controlled by local precipitation driven recharge flow systems and the regional groundwater that was discharged affected only the peat immediately above the mineral soil peat interface in contrast during the summer of 1991 concentrations of dissolved ch sub 4 in pore water were all undersaturated with respect to 1 atm partial pressure ch sub 4 23 refs 5 figs

expanding the proxy toolkit to help identify past events lessons from the 2004 indian ocean tsunami and the 2009 south pacific tsunami article i nfo some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 indian ocean tsunami and the 2009 south pacific tsunami and a revised toolkit provided the new application of anisotropy of magnetic susceptibility ams to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences together with data from grain size analysis are presented the value of chemical proxies as indicators of saltwater inundation associated marine shell and or coral high energy depositional environment and possible contamination is demonstrated and issues of preservation addressed we also provide new findings from detailed studies of heavy minerals new information gathered during the unesco international oceanographic commission ioc international tsunami survey of fine onshore sediments following the 2009 south pacific tsunami is presented and includes grain size chemical diatom and foraminifera data the tsunami deposit varied ranging from fining upward sand layers to thin sand layers overlain by a thick layer of organic debris and or a mud cap grain size characteristics chemical data and microfossil assemblages provide evidence for marine inundation from near shore and changes in flow dynamics during the tsunami

paleomagnetism of the methow region north central washington structural application of paleomagnetic data in a complexly deformed variably remagnetized terrane jurassic through paleocene rocks of the methow pasayten belt were studied in order to use paleomagnetic directions to resolve the question of cretaceous northward transport in the end circumstanc

a test for the analogy of tropical domed peat deposits to dulling up sequences in coal beds preliminary results abstract megascopic and microscopic characteristics of a domed peat deposit in sarawak malaysia were examined to test their analogy to dulling up sequences in low ash coal beds preliminary petrographic results show high concentrations 95 of vitrinite precursor material for all peat types but that fibrous peats in the upper central portion of the deposit contain more preserved plant material than peats toward the base and margins which although more decomposed contain large fragments 5 150 cm of wood these results present contradictory evidence in support of a dulling up model and suggests that modern tropical peat domes are perhaps poor petrographic analogues for dulling up sequences this deposit would produce an all bright coal seam with bright vitrain bands of variable thickness and amount set in bright high vitrinite matrix

discordant paleomagnetic poles from the canadian coast plutonic complex regional tilt rather than large scale displacement stratigraphic petrologic and isotopic data indicate that parts of the coast plutonic complex and the north cascade range have been tilted northeast side up by angles of approximately 30 degree about north northwest trending axes these tilts can account for discordant paleomagnetic directions observed in mid cretaceous plutons from these regions without large scale displacement relative to north america

structural geology and accretionary history of the northwest cascades system washington and british columbia pre tertiary rock units on the western flank of the cascades in washington and southern british columbia constitute the northwest cascades system nwcs this litho tectonic package is characterized by predominantly oceanic lithologies subjected to high p t metamorphism and structurally mixed to form a regional melange although the focus of this report is on rocks of the nwcs as originally defined survey of the regional geology suggests broadening of the limits of this system to include the san juan islands the pacific rim complex and pre tertiary rocks on the western flank of the central and southern washington cascades the shuksan metamorphic suite a relatively coherent and broadly exposed unit of the nwcs contains a regionally consistent stretching lineation which provides evidence of east northeast directed underthrusting subduction during the early cretaceous blue schist metamorphism metamorphic f2 folds are approximately normal to the stretching lineation and appear to have developed late in the same deformational event the melange structure postdates the high pressure regional metamorphism it is characterized by a tectonic assemblage of diverse and unrelated rock units occurring as fragments as much as 10 or more kilometres in breadth and separated by a network of low to high angle north northwest striking faults pre fault restoration is impossible argillaceous or serpentinitic material commonly occurs in deformation zones between more competent lithologies mylonite zones as much as several metres thick are widely developed and display stretched clast lineations indicating a north northwest south southeast transport direction for both low and high angle faults the high angle faults are therefore strike slip in nature shear sense indicators are mixed in thrust fault zones but many indicate dextral movement for the strike slip faults k ar whole rock ages of mylonites range from 20 127 ma but two late cretaceous ages of 87 and 91 3 ma are considered as best representing the time of faulting the inferred shift in direction of tectonic transport from east northeast west southwest during early cretaceous metamorphism to north northwest south southeast during late cretaceous faulting and melange formation is correlated with a mid cretaceous change in plate interaction between the north american and farallon kula plates from high to low angle convergence the nwcs melange is interpreted to have formed during large dextral transform motion along the continental margin and to have reached final emplacement by thrusting against the southern end of wrangellia and the coast plutonic complex

remagnetization during cretaceous normal superchron in eastern san juan islands wa implications for tectonic history abstract the eastern san juan islands expose an island arc ophiolite sequence and one or more ocean floor terranes cover rocks of the former including red radiolarian tuff and arc derived sandstone have no penetrative fabric and lack high pressure minerals in contrast pillow basalts and ribbon cherts of the latter are strongly deformed and the overlying metagraywacke is folded with a penetrative axial plane cleavage all ocean floor rocks have aragonite in veins indicative of higher pressure conditions than experienced by the island arc rocks a downward magnetization is common to the ocean floor rocks consistent with widespread remagnetization during the cretaceous normal superchron this magnetization is carried by magnetite and in red rocks by hematite fluid flow during or after deformation and high p metamorphism likely facilitated remagnetization at low temperature the magnetic directions are somewhat scattered but most are moderately to steeply down to the southeast they are far from directions expected with or without northward transport of baja bc rotation of observed directions into agreement with those expected for either present or more southerly locations also rotate structural elements in the host rocks three alternative rotation histories explored here all produce structural reconstructions that differ considerably from the present structure a tectonic history of the eastern san juan islands based on any of these reconstructions would be superior to one based on present attitudes of structures this is because at least a constraint that the restored paleomagnetic directions match a paleomagnetic field direction is satisfied choices among alternative reconstructions would become clearer with better understanding of relative ages of specific structures and their magnetizations improved geologic understanding of the regional setting where the rocks could have been deformed and remagnetized would also help

reconciliation of two sided thrusting burial metamorphism and diachronous uplift in the cascades of washington and british columbia several recently published data sets have shed new light on many of the fundamental kinematic aspects of mid cretaceous orogeny in the cascades of northwestern washington and southwestern british columbia specifically a it is now clear that contractional deformation associated with this orogeny affected rocks east of the crystalline core of the range to a greater degree than had previously been suspected and b geobarometric data from the crystalline core of the range now permit a quantitative reconstruction of the crustal thickening event responsible for core metamorphism to be attempted i propose a new kinematic model for mid cretaceous orogeny that reconciles these data with previously collected data sets that focused on deformation in the northwest cascades san juan islands thrust system the model derived from this analysis suggests that the cascades underwent a minimum of between 400 and 500 km of east west shortening between about 115 and 85 ma owing to the collision of the greater insular terrane which probably included rocks of the chilliwack nooksack terrane with the western edge of the greater intermontane terrane which included the methow basin and bridge river hozameen terrane on the basis of their relative and absolute times of uplift i assign the deepest part of the metamorphic core the skagit gneiss to the greater insular terrane and the structurally higher carapace of the core the settler nason metapelites and the cogburn creek mad river metabasalt metachert to the westernmost intermontane terrane the contact between the skagit gneiss and the overlying assemblages must represent a fault or suture across which at least 120 km of displacement took place this fault is also the root zone from which many of the nappes in the northwestern cascades and san juan islands were derived i concur with previous workers who suggested that the collisional event was not precipitated by the closure of a several thousand kilometer wide ocean but was rather due to a short lived margin normal convergence event that both followed and was followed by periods during which the continental margin was highly influenced by oblique subduction and strike slip faulting

the behaviour of major and trace elements in complete vertical peat profiles from three sphagnum bogs the distribution of major elements al ca k mg na in peat profiles from two contrasting ombrotrophic sphagnum bogs is interpreted in respect to the abundance and mineralogical composition of ash atmospheric deposition plant bioaccumulation and leaching high concentrations of ca are found in the minerotrophic peats from a continental bog underlain by calcareous sediments luther bog ontario aluminum is more abundant in the minerotrophic peats from a coastal bog in a siliceous terrain barrington bog nova scotia the peats at the coastal site contain an average of 3 times as much na and mg as the peats from the continental bog because of sea spray potassium is highly enriched in the surface peats at both sites because of plant bioaccumulation the behaviour of trace metals cr cu fe mn ni pb u v zn in peat profiles is explained in terms of the abundance and distribution of mineral matter plant bioaccumulation the response of metals to acidic anaerobic conditions and anthropogenic atmospheric deposition the distribution of ni v and cr in the peats from a third bog galbraith bog ontario follows that of mineral matter content and the metals are highly correlated with ash relative to the mean composition of the underlying mineral sediments clays collected at 30 other sites the peats are neither significantly 2 times enriched nor depleted in ni v and cr manganese is strongly enriched in surface and near surface peat layers because of plant bioaccumulation in contrast fe and mn are relatively depleted in subsurface peats due to their enhanced solubilities in acidic anaerobic waters the opposite is true for cu and u which accumulate in peats because of their diminished solubilities in anaerobic environments enrichments of zn and pb also occur but these are restricted to surface peats and are due to anthropogenic metal deposition

paleodepositional environments and tectonosedimentary controls of the postglacial permian coals karoo basin south africa abstract coal deposits of the karoo basin in south africa are contained within an 80 250 m thick clastic sequence designated the vryheid formation this formation constitutes part of the ecca group of the karoo sequence and contains several mineable bituminuos coal and anthracite beds and sporadic coking coal seams the sedimentary succession was deposited during the early permian following the late carboniferous dwyka ice age paleoclimate initially influenced the paleodepositional environments which for the lowermost stages comprised glaciofluvinal outwash braided plain deposits overlying minor deltaic and glaciolacustrine fill the early permian floral assemblages attest to a cool temperature climatic regime in the extreme northern parts of the basin the lowermost coals frequently directly overlie dwyka diamictite or pre karoo basement paleodepositional systems associated with the coals above the glaciogenic succession consisted predominantly of regressive fluviodeltaic facies assemblages in the northern regions regressive deltaic lobes prograded rapidly basinward across the relatively shallow intracratonic platform in the northeast areas greater subsidence rates were accompanied by multiple stacking of regressive deltaic cycles in several areas of the coalfields peat accumulation was associated with the bed load braided fluvial systems these subsequently modified the underlying deltaic deposits by intense and deep erosion that removed portions of the underlying stratigraphy smaller scale syndepositional anastomosed rivers which were contemporaneous with certain peat swamps locally controlled seam distribution and adversely affected coal seam quality coal distribution was directly controlled a the tectonic setting b the nature of the pre karoo basement lithologies c the basement paleotopography and d the paleodepositional systems associated with and following peat formation the coalfields are restricted to a relatively small area in the northern and northeastern parts of the karoo basin where a stable intracratonic shelf provided a suitable tectonic setting for peat accumulation resistant basement lithologies orthoquartzite and felzite produced positive topographic relief while easily weatehred archean granite basement terrain left residual topographic depressions that were later extensively filled by sediment differential compaction of fine sediment mud and silt deposited over the diverse basement topography provided further subtle controls on coal seam thickness sediments and coal overlying basement highs compacted significantly causing thinning and a draping effect of the sedimentary cover in contrast paleovalleys contained substantial thickness of sediment and host some of the thickest seams these coals can however thin and shale out against the adjacent elevated valley flanks the paleovalley coals were further affected by multiple seam splits produced by fluvial channels that contemporaneously occupied the lowland areas

origin of the zalesi u ni co as ag bi deposit bohemian massif czech republic fluid inclusion and stable isotope constraints the zalesi vein type deposit is hosted by early paleozoic high grade metamorphic rocks on the northern margin of the bohemian massif the mineralization is composed of three main stages uraninite arsenide and sulfide the mineral assemblages formed at low temperatures 80 to 130 c locally even lower and low pressures 100 bars the salinity of the aqueous hydrothermal fluids 0 to 27 wt salts and their chemical composition vary significantly early fluids of the oldest uraninite stage contain a small admixture of a clathrate forming gas possibly co2 salinity correlates with oxygen isotope signature of the fluid and suggests mixing of brines 18o around 2 relative to standard mean ocean water smow with meteoric waters 18o around 4 smow the fluid is characterized by highly variable halogen ratios molar br cl 0 8 10 3 to 5 3 10 3 molar i cl 5 7 10 6 to 891 10 6 indicating a dominantly external origin for the brines i e from evaporated seawater which mixed with iodine enriched halite dissolution brine the cationic composition of these fluids indicates extensive interaction of the initial brines with their country rocks likely associated with leaching of sulfur carbon and metals the brines possibly originated from permian triassic evaporites in the neighboring polish basin infiltrated into the basement during post variscan extension and were finally expelled along faults giving rise to the vein type mineralization cenozoic reactivation by low salinity low 18o around 10 smow fluids of mainly meteoric origin resulted in partial replacement of primary uraninite by coffinite like mineral aggregates

observing tilts in midcrustal rocks by paleomagnetism examples from southeast british columbia metamorphic core complexes that originated in the middle crust have been exposed by uplift and extension indicators of paleohorizontal planes are few or absent thus it is difficult to determine the degree of tilting that might have accompanied this process however if aberrant paleomagnetic directions paleodirections are observed in core complexes or their associated intrusive rocks and if large scale rotation and translation can be excluded then these paleodirections can be used to calculate the sense and magnitude of tilting we describe paleodirections from mid crustal rocks in southeastern british columbia where uplift and extension occurred in eocene time about a central culmination aligned north south several large extensional faults dip both to the west and to the east of this central culmination the eocene granby pluton 49 3 n 118 5 w situated to the west of the main culmination has a mean direction of magnetization d i 309 41 63 7 the standard error and paleopole at 44 n 138 e a63 7 to the east of the main culmination a 20 km long section of altered eocene syringa dikes and associated metadiorite 49 3 n 117 7 w has a mean direction of 56 47 63 3 and paleopole at 56 n 319 e a63 3 the paleopoles are very different from one another and from those calculated from contemporaneous 53 to 49 ma rocks of the north american craton to the east they also differ from those observed from coeval bedded volcanic rocks to the west of the sampling area hence these large aberrancies cannot be caused by translations we suggest that they are caused by tilting which occurred during the extension process the tilts are in opposite senses on either side of the central culmination they are estimated to be down 38 8 at 99 e for the granby pluton and down 41 4 at 270 w for the dikes and metadiorite these tilts are consistent with the wernicke model for simple extensional shear

the geology botany and chemistry of selected peat forming environments from temperate and tropical latitudes abstract peat has been studied in several geologic settings 1 glaciated terrain in cold temperate maine and minnesota u s a 2 an island in the atlantic ocean off the coast of maine where sea level is rising 3 the warm temperate u s atlantic and gulf coastal plains where sea level has changed often and 4 the tropical coast of sarawak malaysia and the tropical delta of the batang hari river sumatra indonesia most of these deposits are domed ombrotrophic or partly ombrotrophic bogs in which peat accumulation continued above the surface of the surrounding soil however the bogs of the u s atlantic and gulf coastal plains are comparatively not as domed and many have almost level surfaces in some bogs aquatic or semi aquatic plant materials accumulated replaced water in the depressions and formed a surface on which marsh or swamp vegetation could subsequently live die and accumulate in others the plant materials accumulated initially on level silt or sand surfaces supporting marshes or swamps as the peat dome formed plants growing on it changed from luxuriant ones near the base of the dome where nutrients were brought into the bog by surface and ground water to stunted ones at the top of the dome where the raised bogs are fed by nutrient poor precipitation the physical and chemical changes that take place in the sequence of environments from the pond stage of deposit development through the grassy marsh stage through the forested swamp stage and finally through the heath dome stage can be measured in terms of acidity and ash volatile matter carbon hydrogen nitrogen sulfur and oxygen contents as well as in the kind and distribution of trace elements the organic and inorganic contents of the deposits relate to geomorphology and geomorphology relates to their settings as models of coal formation some domed peat deposits may help in solving problems of distribution and character of ancient coal beds but clearly not all peat deposits are precursors of coal most holocene peat deposits are subject to destruction by erosion fire and decomposition through microbial and chemical oxidation before burial the best environments for coal precursors have biomass accumulation a continuously rising water table within the mass and minimum influx of clay and silt until preservation by burial the most suitable settings for future economic coal deposits are domed bogs that accumulate thick widespread peat having low ash and low sulfur contents the ombrotrophic peat deposits of tropical sarawak and sumatra are thick and extensive contain low ash and low sulfur peat and have high heating values they are considered to be the best tropical coal analogs because of their extent and chances of preservation the base of the peat is below adjacent river levels and chemical and structural conditions are favorable for accumulation

geochemical signatures up to the maximum inundation of the 2011 tohoku oki tsunami implications for the 869 ad jogan and other palaeotsunamis abstract the geochemical signature of the tohoku oki tsunami deposit and underlying soil was assessed two months five months and seven months after the 11 march 2011 tsunami inundated the sendai plain the extent of the recognisable sand deposit was traced up to 2 9 km inland while a mud deposit was found up to 4 65 km inland representing 60 and nearly 95 of the maximum tsunami inundation respectively the limit of tsunami inundation was identified 4 85 km from the shore using geochemical marine markers s and cl two months after the tsunami in the absence of any sedimentological evidence concentrations of other geochemical markers k ca sr indicative of the marine incursion and associated minerals were found to decrease landward 13 c and 15 n and c n ratios suggested a mixture of terrestrial and marine organic sources in the sediment while 34 s of sulphate reflected the marine source of water soluble salts the chemical composition of the 869 ad jogan tsunami sand deposit was characterised by high sr and rb concentrations and was comparable to that of the tohoku oki tsunami deposit suggesting that the sources of sediment may be similar marked decreases in s and cl with time indicated that rainfall resulted in the leaching of salts from the sandy sediments however both s and cl markers as well as sr were still well preserved in the muddy sediments and underlying soil beyond the limit of the recognisable sand deposit seven months after the tsunami this suggests that geochemical indicators may well be useful in identifying the extent of historical and palaeotsunamis by determining the marine origin of fine grained sediments beyond the limit of recognisable sand deposition in particular when marine microfossils are sparse or lacking as is the case on the sendai plain this would allow researchers to redraw palaeotsunami inundation maps and re assess the magnitude of events such as the jogan tsunami and other palaeotsunamis not only on the sendai plain but also elsewhere around the world this has important implications for tsunami risk assessment hazard mitigation and preparedness

contribution of ductile flow to exhumation of low temperature high pressure metamorphic rocks san juan cascade nappes nw washington state the san juan cascade sjc nappes were subducted to a depth of 18 km metamorphosed under low temperature high pressure conditions and then exhumed all within 16 m y during exhumation penetrative deformation by solution mass transfer smt resulted in a widespread spaced cleavage strain directions were determined for 27 sandstone samples and absolute strain measurements for a subset of 19 samples z directions generally plunge moderately to the ne and x and y directions are scattered in the plane perpendicular to z smt deformation is constrictional at the local scale but the tensor average indicates plane strain uniaxial shortening at the regional scale with sx sy and sz equaling 1 01 0 91 and 0 58 respectively the average flattening plane xy dips 30 to the ne and the average x direction plunges 20 to the north the large shortening in z was compensated by a mass loss volume strain of 47 we present a simple one dimensional model that illustrates the relationship between finite strain and ductile exhumation for a steady state convergent wedge assuming depth dependent ductile flow and no reversal of principal strain rates with depth this model indicates that ductile thinning of the sjc nappes accomplished only 13 of the total exhumation despite a vertical shortening strain of 36 there is no evidence that normal faulting contributed significantly to exhumation we conclude that erosion operating at an average rate of 1 1 km m y 1 was the dominant exhumation process

discordant 14c ages from buried tidal marsh soils in the cascadia subduction zone southern oregon coast peaty tidal marsh soils interbedded with estuarine mud in late holocene stratigraphic sequences near coos bay oregon may have been submerged and buried during great m 8 subduction earthquakes smaller localized earthquakes or by nontectonic processes radiocarbon dating might help distinguish among these alternatives by showing that soils at different sites were submerged at different times along this part of the cascadia subduction zone but comparison of conventional 14c ages for different materials from the same buried soils shows that they contain materials that differ in age by many hundreds of years errors in calibrated soil ages represent about the same length of time as recurrence times for submergence events 150 500 yr this similarity precludes using conventional 14c ages to distinguish buried soils along the southern oregon coast accelerator mass spectrometer 14c ages of carefully selected macrofossils from the tops of peaty soils should provide more precise estimates of the times of submergence events

revised ages of blueschist metamorphism and the youngest pre thrusting rocks in the san juan islands washington new ages of rocks in the san juan islands northwest washington significantly change our understanding of the evolution of the san juan islands thrust system re examination of foraminifera bearing mudstones at richardson on lopez island indicates a late aptian 112 115 ma not late albian 100 ma age as currently presented in the literature the age brackets of thrusting marked by these pre thrusting mudstones and 84 ma post thrusting sedimentary rocks span a much longer period than previously thought diminishing controls on rates of displacement in the thrust system and the timing of regional deformation in western washington new 40 ar 39 ar plateau ages of phengite in blueschist facies meta volcanic rock also at richardson are 124 0 7 ma 2 late barremian these blueschist facies volcanic rocks are in fault contact with the fossiliferous mudstones therefore the blueschist facies metamorphism at richardson previously inferred to be associated with the thrusting now appears to have occurred prior to thrusting further the ar ages demonstrate that blueschist facies fabric formed earlier than the thrust event and is therefore not directly useful in analyzing the thrusting kinematics the richardson 40 ar 39 ar age is similar to isotopic ages found in the eastern san juan islands and in the shuksan blueschist terrane in the northwest cascades and thus fits into an emerging regional age pattern of blueschist facies metamorphism during late jurassic early cretaceous up to barremian but not late albian cenomanian if this pattern is more broadly confirmed for the san juan islands all the blueschist facies metamorphism can be regarded as having formed in subduction zones elsewhere along the continental margin rather than in the anomalous setting of an on land thrust system as in the san juan islands resume de nouveaux ges pour les roches des iles san juan dans le nord ouest de l etat de washington changent profondement notre comprehension de l evolution du systeme de chevauchement san juan un reexamen des mudstones foraminiferes a richardson sur l ile lopez indique un ge aptien tardif 112 115 ma et non albien tardif 100 ma tel qu indique actuellement dans la litterature les plages d ges pour le chevauchement marquees par ces mudstones precedant le chevauchement et des roches sedimentaires 84 ma posterieures au chevauchement couvrent une periode beaucoup plus grande que stipulee anterieurement diminuant les controles sur les taux de deplacement dans le systeme de chevauchement et le moment de la deformation regionale dans l ouest de l etat de washington de nouveaux ges plateaux 40 ar 39 ar de la phengite dans des roches volcaniques au facies des schistes bleus aussi a richardson datent

a comparison of temperate and boreal peats from ontario canada possible modern analogues for permian coals abstract peat profiles were sampled from a raised bog and an interior fen located in the boreal james bay lowlands northern ontario and a cold temperate swamp and a cold temperate bog in the great lakes st lawrence lowlands southern ontario an examination of the micromorphology and maceral compositions of the peats indicates that considerable differences exist between environments the boreal bog and fen both consist predominantly of relatively unaltered textinite commonly sphagnum derived with higher liptinite contents in the fen profile attributable to the more diverse vegetation both the cold temperate swamp and bog show high levels of humification at the surface possibly partially attributable to recent climatic warming trends causing a decline in water table elevation in all profiles funginite was persistent ranging from 2 to 10 of the total maceral content indicating that aerobic conditions generally prevailed at the surface at the time of deposition the influence of depositional environment and vegetation type on the resulting peat was born out in plots of tissue preservation index vs gelification index the petrographic study also demonstrated that none of the profiles contained high inertodetrinite semifusinite contents comparable to those within cold climate cratonic permian gondwana coals since the oxidation processes leading to the formation of inertinite are considered to take place at the peat stage if the peats studied were to contain a similar maceral assemblage upon coalification inertinite precursors may be present in the peat the lack of petrographic similarity between the holocene peats and the permian coals may be related to a number of factors the decrease in water table elevation possibly responsible for the inertinization of the permian coals may have occurred following the cessation of peat formation not concurrently with accumulation and is potentially attributable to long term factors such as climatic warming the change in the peat forming vegetation from permian glossopteris and gangamopteris dominated communities to holocene sphagnum and coniferous vegetation alters the characteristics of the initial botanical starting materials and some aspects of the ecology particularly trophic and ph conditions which control the post depositional alteration of the plant materials and the resulting maceral assemblages

paleomagnetism of 122 ma plutons in new england and the mid cretaceous paleomagnetic field in north america true polar wander or large scale differential mantle motion a paleomagnetic study of cretaceous white mountains plutonic complexes in new hampshire and vermont yields high unblocking temperature dual polarity magnetizations in different types of igneous rocks the resulting pole position for three plutons 71 9 n 187 4 e a95 6 9 age 122 5 ma agrees with previously published mid cretaceous poles for north america which together give a mid cretaceous standstill reference pole slightly revised from globerman and irving 1988 at 71 2 n 194 1 e a95 3 7 n 5 studies we argue on the basis of the wide geographic distribution of these studies the variety in tectonic settings and rock types positive reversal tests and an overall reversal pattern consistent with geomagnetic polarity time scales that this mean pole represents the north american mid cretaceous reference field for nominally 36 m y 124 to 88 ma the standstill pole limits to within 4 the motion of the north american plate relative to the earth s spin axis during the same mid cretaceous interval the new england hotspot track 124 ma monteregian hills 122 5 ma cretaceous white mountains and 103 to 84 ma new england seamounts requires 11 4 of north poleward motion of north america in direct conflict with the paleomagnetic standstill a similar 13 discrepancy is independently demonstrated between the spin axis and the tristan da cunha hotspot track on the african plate during the mid cretaceous interval the hotspot spin axis discrepancies ended by 90 ma when it is shown that both atlantic hotspots agree with north american and african dipole paleolatitudes and present day locations nondipole fields are an unlikely explanation of the uniform motion of these two widely separated hotspots with respect to the spin axis leaving as possible interpretations true polar wander and large scale but differential mantle motion the southerly motion of the mid cretaceous louisville hotspot relative to the spin axis is ostensively at odds with what would be predicted under the true polar wander interpretation and points to differential mantle kinematics the motions of the three widely separated mid cretaceous hotspots with respect to the spin axis may be related to the recently proposed increase in global oceanic lithosphere production rates which gave rise to the mid cretaceous superplume

arc parallel extension and fluid flow in an ancient accretionary wedge the san juan islands washington structural analysis of the lopez structural complex a major late cretaceous terrane bounding fault zone in the san juan thrust system reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics after formation of regional ductile flattening and shear related fabrics the area was crosscut by brittle structures including 1 southwest vergent thrusts 2 extension veins and normal faults related to northwest southeast extension and 3 conjugate strike slip structures that record northwest southeast extension and northeast southwest shortening aragonite bearing veins are associated with thrust and normal faults but only rarely with strike slip faults high pressure low temperature hp lt minerals constrain the conditions for brittle deformation to 20 km and

lake mire deposition earthquakes and wildfires along a basin margin fault ronne graben middle jurassic denmark abstract regional uplift of structural highs took place in the greater north sea region in early middle jurassic times resulting in a change from marine shelf deposition in the early jurassic to widespread emergence erosion and localized deposition in grabens the middle jurassic baga formation exposed on the island of bornholm in the baltic sea was deposited in the ronne graben which forms a dog leg pull apart basin linking the northern and southern branches of the tornquist zone the studied succession is situated on the hanging wall immediately adjacent to the main eastern graben margin fault and the footwall consists of deeply weathered granite it is the only locality along the northern branch of the tornquist zone where active tectonic influence on middle jurassic deposition can be demonstrated in outcrop small alluvial fans composed of poorly sorted washout sands and muddy debris flows with weathered granite boulders fringed the footwall scarp syn depositional soft sediment deformation and chaotic bedding structures interpreted as seismites caused by earthquake shocks are characteristic at several levels on the hanging wall further away from the active fault the depositional environment was dominated by shallow freshwater lakes with deposition of clay lake deposition outpaced subsidence and open oxygen deficient freshwater mires were formed during periods of no or only incremental fault movement the mires were only occasionally isolated from clastic input due to doming and dense vegetation resulting in accumulation of pure peat beds the content of spores and pollen shows that the mires were covered by a vegetation of arborescent and herbaceous filicopsida ferns lycopsida club mosses cycadales bennettitales ginkgoales caytoniales taxodiaceae or cupressaceae and araucariaceae wildfires were common in the mires and also on the footwall probably followed by episodes of increased run off and erosion of the upland the presence of common washout sands debrites seismites and abundant lacustrine flooding surfaces indicating sudden drowning of the mires was caused by abrupt movements on the fault with associated earthquakes the succession thus provides an example of temporal changes in deposition in response to changes in tectonic conditions the study illustrates how regional uplift of structural highs caused a restriction of deposition to narrow grabens like the ronne graben facies patterns changed dramatically from laterally extensive uniform packages controlled by sea level changes in the early jurassic to strongly localized deposition with marked facies changes controlled by faulting and earthquakes in the middle jurassic the succession thus serves as an excellent example of tectonically controlled deposition under humid conditions in a continental graben

late mesozoic and possible early tertiary accretion in western washington state the helena haystack melange and the darrington devils mountain fault zone the helena haystack melange hh melange and coincident darrington devils mountain fault zone ddmfz in northwestern washington separate two terranes the northwest cascade system nwcs and the western and eastern melange belts wemb the two terranes of paleozoic and mesozoic rocks superficially resemble each other but record considerable differences in structural and metamorphic history the hh melange is a serpentinite matrix melange containing blocks of adjacent terranes but also exotic blocks of schistose metavolcanic rocks and jurassic tonalite and associated amphibolite the hh melange must have formed between early cretaceous and late middle eocene time because it contains tectonic clasts of early cretaceous shuksan greenschist and is overlain by late middle eocene sedimentary and volcanic rocks less certain constraints on its age are a tectonic clast of metarhyolite that yields 90 ma metamorphic ages and the presumption that the melange was emplaced before the outboard olympic terrane arrived at about 50 ma the apparent continuity of the hh melange and the decatur terrane of the san juan islands suggests that the melange is the strongly tectonized equivalent of the fidalgo ophiolite the out crop pattern suggests that the hh melange overlies rocks of the nwcs and it may have formed when the wemb terranes were thrust over rocks of the nwcs much of the exposed belt of the hh melange is overlain by late middle eocene feldspathic sandstone and volcanic rocks of the barlow pass volcanics of vance 1957a which are cut by numerous faults of the ddmfz paralleling the melange the barlow pass volcanics appear to overlie the straight creek fault without large offset but a displaced exotic block of amphibolite with attached early or early middle eocene sandstone in the melange suggests that strike slip movement along the ddmfz was synchronous with movement on the straight creek fault and stretched cobbles in the conglomerates of the barlow pass volcanics suggest post straight creek movement the possible continuation of the ddmfz to the northwest as the san juan and the west coast faults on vancouver island suggests that the structure has had a major role in the emplacement of all the westernmost terranes in the pacific northwest this major suture is strongly bowed to the northeast opposite the great oroclinal bend of the olympic terrane suggesting that the emplacement of that terrane may have deformed a once straighter strike slip zone

fission track dating of the tectonic development of the san juan islands washington the san juan islands of washington state form a geologically complex province located between the north cascades vancouver island and the olympic peninsula we have obtained 53 fission track dates from the san juan islands province that help constrain its late paleozoic to early cenozoic tectonic and sedimentary history and its relationship to neighboring geologic terranes the san juan islands can be divided into two main blocks separated by the haro fault south of the haro fault complexly deformed metamorphosed and probably exotic early paleozoic to early late cretaceous rocks form four imbricate thrust plates separated by south and east dipping late early to late cretaceous thrust faults reset zircon fission track dates indicate that thrusting may have produced an upside down geothermal gradient in the uppermost plate the decatur terrane if present this gradient was probably produced by conductive or frictional heating associated with a now eroded overlying thrust fault and hot thrust plate

geochemical and petrographical characteristics of a domed bog nova scotia a modern analogue for temperate coal deposits a freshwater domed bog in nova scotia canada was investigated for its petrographic mineralogical and geochemical characteristics three cores were taken from the lagg zone margin and centre to examine different stages of evolution in a fen to domed bog sequence based on this study a model was developed which shows the relationship between factors controlling peat geochemistry and petrography all of them being dependent on trophic conditions the bog may represent a modern analogue for temperate coal deposits and thus can be used to help understand spatial variability within coal beds rheotrophic conditions in the early stages of mire development result in the formation of high ash highly humified carex dominated peat while the evolution toward ombrotrophic conditions is reflected in a progressive replacement by low ash and well preserved sphagnum dominated peat the associated decrease in ph reflects a decrease of groundwater influence which is also supported by the mineralogical assemblage and petrographic data decrease in reflectance and change in maceral composition except for cl br i and se which are associated with the organic fraction variations in elemental composition can be explained in terms of mineral matter abundance i e decrease upward and with increasing distance from the margin sea spray is the most probable origin for halogen enrichment in the peat

polyphase brittle and ductile deformation of late jurassic ophiolitic basalt argillite matrix melange and stratigraphic overlap sequence northwestern washington state abstract a belt of jurassic to cretaceous ophiolitic rocks borders the western margin of the u s cordillera and stretches from central california to northwestern washington state the northern end of this belt lies between the san juan islands and the northwest cascades within this region ophiolitic rocks consist of a succession of oceanic and arc affinity igneous and sedimentary rocks which form a sedimentary melange and sedimentary overlap sequence which is imbricated during the mid cretaceous the melange contains blocks and olistoliths of peridotite plagiogranite chert basalt and volcanoclastic conglomerate which range in size from a meter to over 1 km and are contained within a matrix of argillite and volcanoclastic breccia and conglomerate peridotites were exposed to the sub aqueous surface along serpentinized shear zones prior to their incorporation into the melange and the sedimentary matrix of the melange underwent brittle deformation during the earliest stages of its structural history melange rocks are overlain in angular unconformity by a jura cretaceous arc sourced sedimentary succession which is at least 500 meters thick and passes upward from a basal breccia containing clasts of plagiogranite gabbro tonalite chert and basalt into argillite containing late jurassic radiolarians the argillite is overlain by poorly sorted greywacke and conglomerate with clast populations similar to those of the basal breccia the conglomerate fines upward into a massive to bedded feldspathic lithic arenite and greywacke that yields mid cretaceous detrital zircons the overlap succession and the melange are deformed by two generations of highly penetrative structures d1a and d1b which produced north to east vergent tight to isoclinal folds and axial planar pressure solution cleavages all units are further deformed by three generations of penetrative structures the successively younger nne to nw ne and e w to wnw trending folds have foliations that cross cut the earlier structural fabrics and faults formation of the melange required differential elevations during the time of deposition and the presence of rocks which are sourced from both arc and oceanic crust extension within the forearc provides a mechanism to exhume peridotites and generate differential topography for arc and oceanic affinity rocks to erode and be incorporated into the melange as part of olistostromal deposits

underplating process from melange formation to duplexing example from the cretaceous shimanto belt kii peninsula southwest japan accretionary complexes are considered to form through off scraping and underplating which results in the lateral and vertical growth of an accretionary prism accretion of the upper part of the oceanic crust and the formation of melange are important components of the accretionary process although the origin of melange is considered controversial in order to better understand the origin of melange and its role in accretion in particular during underplating we have studied the relationship between the formation of melange and duplexing in the miyama assemblage here the melange is composed dominantly of shale basalt chert and sandstone this study stresses the following features 1 the structure of the miyama assemblage appears to be a composite suite of landward and seaward dipping duplexes 2 the melange fabric displays a systematic asymmetry which may have resulted through shearing along the decollement and 3 facing of horses within duplexes changes from north to south coinciding with a change in the sense of shear inferred from the melange fabric which suggests that it formed prior to duplexing

sulphur low temperature ash and minor elements in humid temperate peat of the fraser river delta british columbia recent peat deposits of the fraser delta have accumulated in a variety of depositional settings and from a wide range of vegetation studies of these deposits have enabled evaluation of some factors that control the distribution of sulphur ash and minor elements in coal brackish peat of the lower delta plain is characterized by high total sulphur up to 5 6 low c n 12 5 c s sphagnum peat organic s is the main s form in all peat 70 of s carbon bonded s comprises 28 88 and ester sulphate 6 40 of total s pyritic s elemental s and soluble sulphate s are minor whereas hydrogen sulphide occurs in trace amounts silicon is the most abundant element 2 8 28 followed by al 334 ppm 6 4 or fe 357 ppm 5 0 na 43 ppm 2 3 ca 404 ppm 1 1 mg 217 ppm 1 2 and ti 40 580 ppm all the minor elements are correlated with low temperature ash on an ash basis brackish and freshwater clay facies have higher al and k and lower ca contents than organic facies and brackish facies have twice the fe and na content of freshwater facies the abundance of total s and the ash content of the peat reflects the depositional environment and the peat facies the higher ph of brackish peat has facilitated bacterial reduction of seawater sulphate leading to higher s peat the higher kaolinite content of freshwater peat reflects the acid conditions ph 3 4 5 of the peat bogs and the in situ formation of kaolinite there is no evidence for formation of pyrite which reflects the low ph that has inhibited microbial mobilization of organic sulphur the minor element abundance is a product of the distribution of detrital and authigenic ash the lower total polysaccharides c and c n ratios of brackish facies reflects the greater degree of decomposition in this facies

the petrology and diagenesis of middle jurassic clastic sediments ravenscar group yorkshire the petrology of non marine clastic sediments from the middle jurassic ravenscar group was investigated to identify and to assess the significance of possible controls on diagenesis diagenetic modifications took place in three broad regimes within the depositional groundwater eogenesis during burial mesogenesis and during uplift and erosion telogenesis eogenesis involved the initial interaction of the original sedimentary assemblage with its depositional pore waters eogenetic processes were influenced strongly by bacterial degradation of organic matter present in the finer grained sediments this bacterial activity caused a lowering of pore water ph and subsequently reduced eh feldspar dissolution and alteration of muscovite to kaolinite occurred quartz overgrowths and vermiform kaolinite precipitated in sands with oxygenated and mildly acidic pore waters whereas chlorite and quartz overgrowths formed in sands with anoxic and neutral pore waters this caused complete reduction of porosity in both finer grained and texturally less mature floodplain facies sandstones channel facies sandstones were cemented only with a thin veneer of quartz overgrowths creating a rigid but still porous quartzose framework bacterial ferric iron reduction throughout the water table subsequently established more ubiquitous conditions raised ph and caused rhombic siderite cementation within the remaining porosity mesogenetic modifications of the mineralogy formed at the surface occurred when pore water composition changed during burial bicarbonate saturated solutions migrated through the surviving porosity precipitating replacive poikilotopic ferroan calcite carbonate dissolution occurred subsequently carbonate dissolution was possibly caused by the same solutions which then precipitated dickite and further authigenic quartz telogenetic modifications took place during uplift and exposure groundwater reactions and subaerial exposure probably caused further carbonate and feldspar dissolution as well as alteration of chlorite to interstratified chlorite vermiculite it is concluded that the diagenesis of these non marine clastic sediments reflects various factors the complex interrelationship of which precludes the identification of any single factor as wholly controlling their diagenesis eogenetic modifications involved the interaction of the sediments and their pore waters as a result of the metastability of the mineral assemblage established at this time these modifications can still be recognized despite the sediments subsequent history

a reflected light petrographic technique for peats although our method is quite similar to early reflected light studies we modified the preparation in three ways first we quick froze the peat by immersing it in liquid nitrogen and then freeze drying it in a vacuum the second modification was to prepare larger 5 x 7 cm blocks of peat to permit reliable size estimates for woody peats finally we used an automated polisher instead of hand polishing the blocks because of the superior and consistent quality of preparation from authors

evolution and paragenetic context of low δd hydrothermal fluids from the panasqueira w sn deposit portugal new evidence from microthermometric stable isotope noble gas and halogen analyses of primary fluid inclusions abstract the evolution paragenetic context and origin of remarkably low d hydrothermal fluids from the hercynian panasqueira w sn cu ag deposit have been investigated through a combined microthermometric stable isotope halogen and noble gas fluid inclusion study large variations in d between 60 and 134 have been observed in primary fluid inclusions from growth zones in a quartz crystal pa66 paragenetically constrained to the main sulfide stage mss of ore formation the same fluids exhibited relatively constant fluid inclusion homogenisation temperatures 254 to 260 c salinities 7 4 to 8 7 wt nacl equivalent and calculated fluid 18o 3 8 to 4 4 all the fluids exhibited 40ar excesses mean molar br cl and i cl ratios varied from 2 3 10 3 4 2 10 3 and 8 10 4 10 10 4 respectively with the more br rich fluids being associated with the more deuterium depleted fluids the low palaeolatitude of panasqueira throughout the main stages of ore formation and the overwhelming predominance of meteoric fluids in the main late and post ore mineralising fluids with d of 40 to 65 lends little support for any models involving low d palaeometeoric water the limited range of 40ar cl ratios 1 1 10 5 1 6 10 5 also precludes boiling during the mss or mixing of meteoric water with highly fractionated deuterium depleted magmatic waters as viable mechanisms for producing the low d fluids the high br cl and i cl of the mss fluids indicate significant fluid interactions with organic rich sediments or metasediments in particular regionally abundant carboniferous coals or coaly sediments that are inferred to be depleted in deuterium by around 85 compared to palaeometeoric water the large range of d observed in the mss fluids may be explained by isotopic exchange of palaeometeoric water with these coals at varying water rock wt wt ratios between 0 02 and 0 002 with fluid oxygen isotopic compositions controlled by exchange with the beira schists such a model is consistent with the requirements that any satisfactory model must take into account viz i the relative constancy of temperature salinity 40ar and fluid 18o during excursions to low d ii the high i cl and br cl ratios observed and iii the coincidence of these low d fluids with the onset of precipitation of polymetallic sulfides and phosphates under reducing conditions the model indicates that meta sedimentary sources of ore forming components became increasingly important during the evolution of the panasqueira sn w deposit and accounts in part for the observed progression from oxide dominated to base metal sulfide dominated parageneses

the changuinola peat deposit of northwestern panama a tropical back barrier peat coal forming environment abstract a large 82 km 2 thick 8 m low ash low sulfur peat deposit has formed on the northwestern coast of panama its low ash and low sulfur contents can be attributed partly to 1 doming 2 the occurrence of a relatively continuous marine blocking beach barrier shoreline feature and 3 leaching of the mineral matter this deposit is roughly rectangular in shape and oriented with its longest axis parallel to the beach barrier shoreline it would produce an economic coal bed that is bright and finely banded in its thickest central region and more coarsely banded at its margins its northwestern margin would be characterized by interfingering of coal with sandstone and siltstone of the changuinola river flood plain whereas its southeastern boundary would be characterized by truncation of the upper part of the seam by marine to brackish shales siltstones and carbonates that were derived from almirante bay total sulfur was found to be very low less than 0 2 dry wt except in a few places in these rare cases nearly all of the sulfur was pyritic and the total sulfur content was anomalously high 14 although the general tendency was for total sulfur to increase wherever the deposit was influenced by marine conditions one case was found where sulfur was high at the base of an inland freshwater peat core which suggests either a hidden marine influence or the need for some new mechanism to explain sulfur enrichment in such an anomalous case differences in inherent fixed carbon contents and calorific values due to changes in peat type and analytical uncertainties tended to mask seamwide trends in these parameters however fixed carbon contents and calorific values showed a slight tendency to increase with depth especially if plotted for single peat types vitrinite reflectance within the hypothetical changuinola coal bed would be expected to increase as follows 1 toward the margins of the deposit 2 toward the bottom and top of the bed and 3 toward stream channels or tidal inlets

stratigraphy depositional setting and tectonic significance of the clastic cover to the fidalgo ophiolite san juan islands washington the san juan islands of northwest washington state comprise a diverse assemblage of paleozoic and mesozoic terranes amalgamated during a regional cretaceous orogenic event detailed tectono stratigraphy of the sedimentary cover to the fidalgo complex indicates the presence of several stratigraphically distinct units which are described and formalized in this paper the fidalgo complex and its sedimentary cover are the structurally highest rocks in the san juan thrust system the fidalgo complex is a highly disrupted middle to upper jurassic ophiolite with arc related intrusives volcanics and sediments the trump unit is an informally named sequence of siliceous sediments volcanic graywacke and minor volcanics that occurs at the stratigraphically highest portion of the fidalgo complex complex facies lithologies and provenance indicate that deposition of this oxfordian to upper tithonian unit occurred in an arc proximal setting the upper tithonian and younger lummi group elevated here lies depos

was the oligocene miocene a time of fire and rain insights from brown coals of the southeastern australia gippsland basin abstract lithotype cycles ranging from 10 to 30 m thick in the brown coals of the latrobe valley gippsland basin australia display well developed lightening upward trends cycle tops are characterized by abrupt and unconformable boundaries with the overlying cycle geological geochemical palynological and macrofossil evidence is consistent with a relative drying terrestrialization upward depositional model for the cycles the abundance of charcoal in dark lithotypes near the cycle bases is explained by the fire prone and highly flammable nature of the herbaceous reed wetlands in common with similar modern wetlands in modern australasia in which the dark lithotypes are suggested to have formed this together with the greater preservation potential of charcoal in subaqueous environments results in the wettest facies of the latrobe valley coals having the highest charcoal contents despite prevailing warm wet climate conditions and the predominance of rainforests that are suggested to have characterized the cenozoic of southern australia some swamp taxa were clearly already pre adapted to tolerate fire and are likely to have been the ancestors of the fire adapted floral communities of modern arid australia

mid cretaceous thrusting in the southern coast belt british columbia and washington after strike slip fault reconstruction a major thrust system of mid cretaceous age is present along much of the coast belt of northwestern north america thrusting was concurrent and spatially coincided with emplacement of a great volume of arc intrusives and minor local strike slip faulting in the southern coast belt 52 to 47 n thrusting was followed by major dextral slip faulting which resulted in significant translational shuffling of the thrust system in this paper we restore the displacements on major dextral slip faults of the southern coast belt and then analyze the mid cretaceous thrust system two reconstructions were made that use dextral faulting on the yalakom fault 115 km castle pass and ross lake faults 10 km and fraser fault 100 km the reconstructions differ in the amount of dextral offset on the straight creek fault 160 and 100 km and how much the ne part of the cascades crystalline core expanded 30 km and 0 km during eocene extension reconstruction a produces the best match of lithotectonic units and thrust systems our synthesis shows that the southern coast belt thrust system was 250 180 km wide after thrusting the thrust system was mainly southwest vergent but had a belt of northeast vergent back thrusts on the northeast side associated with the tyaughton methow basin which may indicate large scale tectonic wedging thrust faults are commonly low to moderate angle but high angle faults also occur especially as late stage out of sequence structures involving plutons the amount of thrust displacement across the system is unknown but must be at least 100 km and may be many hundreds of kilometers most thrusting occurred from 100 to 80 ma and did not migrate systematically until after 90 ma when thrusting and magmatism shifted to the northeast for a few million years widespread thrusting occurred both near plutons and where there are no or small plutons which strongly suggests that thrust faulting was caused by regional to plate scale forces such as rapid plate convergence and or arc continent collision

composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics housen b a richter c and van der pluijm b a 1993 composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics tectonophysics 220 1 12 magnetic fabrics from rocks with multiple mineral preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and or orientations of the individual mineral fabrics and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks these criteria include 1 the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics and 2 the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases composite magnetic fabrics are observed in the shales and slates of the martinsburg formation lehigh gap pennsylvania modeling of the ams anisotropy of magnetic susceptibility and arma anhysteretic remanent magnetization anisotropy behavior constrains the relative degree of anisotropy of the bedding parallel and cleavage parallel fabrics in particular arma model results allow a good estimate of magnetite fabric strength we conclude that in the presence of composite magnetic fabrics quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric such determinations require knowledge of the mineral s that are responsible for the measured magnetic fabric and their behavior during deformation

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

petrographyof some fraser river delta peat deposits coal maceral and microlithotype precursors in temperate climate peats abstract peat deposits on the recent lobe of the fraser river delta british columbia have accumulated in a variety of depositional settings the study of the decomposition of the plant components associated with each depositional area has enabled prediction of the occurrence and distribution of the precursors of the loal macerals and microlithotypes on inactive portions of the distal lower delta plain thin sedge grass peats ave developed these peats were influenced by marine conditions near the base and freshwater conditions higher in the section a high ratio of cellulose to lignin in marsh plants and limited exposure of these tissues to desiccation and oxidation prodcue primarily desmocollinite smaller amounts of cernite cutinite and alganite origginate from algal and sedge lipids in the transition to freshwater peats oxyfusinite pyrofusinite and micrinite partially replace former exinite and vitrinite group maceral precursors subsequent transgression by marine waters has further promoted decomposition of the peat laterally extensive but thin and discontinouus coal seams which would develop from such peat will contain vitrite bands near the base and grade upsection into interlamlaminated durite and vitrinertite peats deposited between the upper and lowerdelta plain originate from brackish water as such earliest peat horizons contain similar maceral compositions to thoce encountered in distal delta plain deposits crevasse and fire splays disrupt gradational changes in fabric upsection and along channel margins flooding by oxygenated neutral ph waters followed by extended periods of desicaation result in increases of inertodetrinite macrinite sclerotinite and oxyfusinite interlaminated durites and vitrinertites will form common microlithotypes interbedded bands of telinite cutinite and cerinite are produced by later freshwater sedge grass peat accumulations in this biofacies clarite replaces durite after colonization by sphagnum lignin rich tissues from ericaceous shrubs and pinus contorta provide precurssors for subernnite telocollinite and telinite stumps of massive telinite interrupt these banded macerals coal seams originating from such peats would be thick laterally extensive and characterized by vitrite with laminae of liptite and lenses of clarite in the upper part

relationship between peat geochemistry and depositional environments cranberry island maine abstract the heath great cranberry island maine offers a unique locality for studying lateral and vertical relationships between radically different peat types within 1 km 2 the majority of the heath is a sphagnum moss dominated raised bog surrounding the raised bog is a swamp marsh complex containing grass sedge sphagnum moss alder tamarack and skunk cabbage swamp marsh deposited peat occurs both around the margins of the heath and under sphagnum dominated peat which was deposited within the raised bog a third peat type dominated by herbaceous aquatics is present underlying the swamp marsh dominated peat but is not present as a dominant botanical community of the heath the three peat types have major differences in petrographic characteristics ash contents and associated minerals sulfur contents range from a low of 0 19 wt dry within the raised bog to a high of 4 44 wt dry near the west end of the heath where swamp marsh peat occurring directly behind a storm beach berm has been influenced by marine waters the presence of major geochemical variations within a 1 km 2 peat deposit suggests the need for in depth characterization of potential peat resources prior to use

the nature and influence of fire in carboniferous ecosystems fusain occurs widely in carboniferous coals and sediments it is now recognised to represent charcoal and be the product of wildfire the occurrence of fire is partly constrained by atmospheric oxygen levels availability and nature of fuel and by aspects of climate rainfall and seasonability in particular the majority of fires in the carboniferous were probably started by lightning strikes or by volcanic activity experiments on the charring of modern plants has shown that the reflectance of charcoal and hence fusain is directly related to temperature of formation different fire types may yield fusain assemblages of differing reflectance spectrums but it may be significant that many modern charcoal assemblages yield only semifusinites as seen by reflectance microscopy the significance of these findings is assessed in relation to the use of fusinites and semifusinites as depositional indicators as interpreted from coal petrology fires may have a dramatic effect on ecosystems not only causing changes in vegetational succession but also severe erosion can occur following a major fire which can be traced in depositional systems in this paper we document three major carboniferous sedimentary systems affected by fire clastic sedimentary systems using extensive fusain deposits in mid lower carboniferous near shore sediments in donegal ireland volcanic systems using late early carboniferous volcaniclastic sequences in the midland valley of scotland and coal and coal bearing sequences in the upper carboniferous westphalian b of the pennine basin england in the later settings the influence of fire in peat formation and succession is assessed in addition data on the vegetational composition of charcoal assemblages is considered it is concluded that fire plays a major role in many carboniferous ecosystems

chapter 22 paleomagnetism of continental north america implications for displacement of crustal blocks within the western cordillera baja california to british columbia

multiple bench architecture and interpretations of original mire phases examples from the middle pennsylvanian of the central appalachian basin usa abstract coal seams often exhibit lateral and vertical variability in composition when sampled as a whole seam this variability is masked but if a seam is subdivided into correlateable components this variability can be tested and better understood herein an architectural approach is used to divide seams into intra seam components clastic splits and mineral partings as well as persistent fusain and durain layers can be used as intra seam bounding units to subdivide a seam into subdivisions called benches regional examination of lower and middle pennsylvanian age coal seams shows that many contain laterally persistent bounding surfaces that can be used to define multiple benches of coal within each seam inter bench analyses from some of the most extensively mined seams in the central appalachian basin show that individual benches often have different spatial and quality trends hence some component of whole seam variability is a function of changes in the relative contribution of these different benches to the seam as a whole many coal benches also exhibit intra bench variation in coal parameters intra bench variation can be analyzed in terms of parameters such as sulfur content and ash yield in order to address changes in coal quality for regional resource evaluation intra bench variation can also be analyzed in terms of a combination of palynologic petrographic and geochemical parameters termed compositional groups in order to better understand the development of the original mire systems compositional groups are defined by ranges of multiple criteria which are inferred to owe their origin to the mire type in which they formed vertical changes in compositional groups within coal benches can be used to infer paleo edaphic conditions during peat accumulation if seam thickness is a product of bench configuration and trends in compositional groups occur in benches then trends in quality can be marginally predicted based upon seam thickness and inferred bench architecture additionally changes in inter bench and intra bench thickness and compositional profiles can be used to infer original depositional controls such as paleotopography syndepositional structural movement and syndepositional clastic influx for more accurate reserve estimates

a tsunami ca 6300 years bp and other holocene environmental changes northern hawke s bay new zealand abstract sediment cores collected in a coastal lagoon a few kilometres east of wairoa northern hawke s bay new zealand were examined using sedimentological geochemical palynological and micropaleontological analyses a distinct short lived catastrophic saltwater inundation csi about 6300 years bp and possibly other minor marine incursions are preserved in the coastal estuarine to lagoonal freshwater sedimentary sequences which have been deposited in the last 6500 years the csi is characterised by a gravel unit that thins landward and decreases in particle size to sand within a sequence consisting mainly of brackish estuarine muds diatom assemblages indicate a marked change from the shallow brackish estuarine muds to marine gravels and sands to brackish estuarine muds the marine influence in the gravel and sand is also shown by the presence of marine dinoflagellates and a peak in na rb sedimentological chemical and paleontological in particular diatoms evidence indicates it is a csi we conclude that this was a tsunami and propose the most likely propagating mechanisms marine influence decreases upcore and totally freshwater conditions are evident in the upper section of the cores the geochemistry of the sediments mainly reflects the change in stratigraphy with distinct signatures for tephra na fe cr organic rich and peat units as br and the coarse gravel sand csi unit na rb cr fe but it is also indicative of changes in depositional environment the change in chemistry na rb in the csi event is indicative of a saltwater influence whereas a marked change in s content suggests a sudden change from brackish to freshwater conditions shortly after 4800 years bp another peak in s and br content about 3200 years bp may indicate another temporary change to brackish conditions

regionally extensive mid cretaceous west vergent thrust system in the northwestern cordillera implications for continent margin tectonism the intermontane insular superterrane boundary zone represents a fundamental crustal boundary separating the two largest allochthonous crustal fragments in the north american cordillera structural stratigraphic and geochronologic relations along this boundary indicate that substantial west vergent compression and concomitant crustal thickening occurred there in mid cretaceous time this orogenic zone extends for more than 1200 km along strike length between southern southeast alaska and northern washington in southern southeast alaska and northwest british columbia rocks of the insular superterrane were imbricated along a series of west to southwest vergent thrust faults in northern washington and southwestern british columbia a wide zone encompassing the margins of the two superterranes as well as numerous intervening smaller fragments was shortened principally along west vergent thrusts known geologic relations do not discriminate among existing tectonic models that explain the origin of the mid cretaceous thrust system

multi proxy records of regionally sourced tsunamis new zealand abstract a multi proxy study of sediment cores from kaituna bay mimiwhangata in northern new zealand has produced a record of three palaeotsunamis dated to around 6500 cal yr bp 2800 cal yr bp and 1450 ad these events punctuate a coastal palaeoenvironmental history spanning the last 8000 years or more in which the site progressed from a semi open lagoon to a freshwater swamp proxies used included stratigraphy geochemistry palynology diatoms foraminifera geomorphology and a regional palaeotsunami synthesis the identification of tsunamigenic sources for these events is tentative we propose that the two oldest events are associated with a source in the tonga kermadec trench region with the most recent possibly associated with the kuwae caldera collapse in 1452 1453 ad palaeotsunami deposits contemporaneous with the estimated age of the three events identified in this study were used to assist in identifying possible source regions the development of regional and national palaeotsunami databases is in its infancy but as more data become available the ability to determine the source magnitude and frequency of past events will improve this will greatly enhance our understanding of the regional risk from tsunamis

effect of permafrost on geochemistry in a canadian peat plateau bog permafrost is a common feature in the canadian subarctic resulting in the development of distinctive wetland forms such as peat plateaux which are perennially frozen peatlands the geochemistry of a peat plateau bog in east little bear river valley northwest territories is discussed including variations in botanical and mineralogical composition and the influence of permafrost the riparian margin of the plateau bog is unfrozen but permafrost occurs at 0 68 m depth 10 m inland cores taken in these 2 sites exhibit variations in peat stratigraphy but possess a similar c shape ash distribution in the core not affected by permafrost most elements studied al ba cr fe k mg na si th ti v also display a c shape distribution and their concentration can be explained in terms of mineral matter abundance and variety halogens cl i br on the other hand are mainly associated with the organic fraction whereas ca and se appear to be associated with both the organic and inorganic fraction in the permafrost affected core all elements independently of their organic or inorganic affinity exhibit a substantial enrichment immediately above the permafrost table whereas they are depleted immediately below this is inferred to be the result of solute redistribution linked with ice formation caused by upward permafrost growth and downward seasonal freezing

paleomagnetism and tectonics of the cretaceous mt stuart batholith of washington translation or tilt abstract the mt stuart batholith is a composite pluton of late cretaceous age that intrudes the crystalline north cascades terrane of northwestern washington its paleomagnetic direction d 10 0 i 45 5 95 4 9 is markedly different from the direction expected for cretaceous rocks from northwestern washington d 330 5 i 73 0 which means that the mt stuart batholith either has moved relative to the north american interior or has been tilted through a substantial angle or both since it acquired its magnetism either tilt or translation are possible geometrically but translation is more likely because 1 local geology apparently does not support tilt in the required direction 2 it probably is not possible for a panel of rock the size of the mt stuart batholith to tilt through the necessary angle ca 35 after its deeper parts have cooled sufficiently to retain remanent magnetization 3 the sense of paleomagnetic discordance found in the mt stuart batholith clockwise rotation of declination flattened inclination is identical to that found in nearly every other allochthonous terrane in the western north american cordillera including every other cretaceous batholith studied except the sierra nevada

petrology and organic geochemistry of peat samples from a raised bog in kalimantan borneo abstract two peat cores from the margin and centre of a tropical raised bog from the sebangau river near palangkaraya in kalimantan indonesia were investigated to illustrate the changes during peatification using coal petrographic and organic geochemical techniques these methods included a maceral analysis on polished peat blocks under reflected white and blue light excitation using the brown coal maceral nomenclature soxhlet extraction was carried out and an estimate of the humic composition was undertaken on the residues gc and gc ms analysis of the alkane and aromatic fractions were also made to identify biomarkers present in the peat results of this study show that peats from the margin of the raised bog were more decomposed than peats from the centre tissue content extract yield and alkaline insoluble acid soluble humic acid fraction support these results not only were there differences between the two locations of the peat cores but also differences arose with respect to depth in both cores the basal peats were more decomposed than the peats from the upper layers this was a result of their differing environments of deposition i e the basal peats were deposited under relative mesotrophic conditions and a more seasonal climate whereas the peats from the upper layers were deposited under acidic and oligotrophic conditions the biomarker composition of the alkane fraction included long chain n alkanes from n c 23 to n c 35 with an odd over even predominance and interestingly n alkanes from n c 36 to n c 40 with an even over odd predominance peaking at n c 38 pentacyclic triterpenoids were mainly represented by 17 21 h homohopane and hop 17 21 ene biomarkers in the aromatic fraction included polyaromatic triterpenoids derived from and amyrin