lithospheric structure across oblique continental collision in new zealand from wide angle p wave modeling 1 oblique convergence between the australian and pacific plates in south island new zealand has resulted in crustal thickening and distributed deformation within both plates we measure this thickening and image the deformation with seismic wide angle data along a 600 km long transect that spans the plate boundary p wave arrival times from 34 000 rays are used to construct a two dimensional model for seismic velocity with depth crustal velocities average 6 1 and 6 2 0 23 km s for the australian and pacific sides of the boundary respectively upper mantle velocities average 8 1 0 25 km s distributed deformation is indicated by the following observations a reduction in upper crustal and midcrustal velocities by 4 west of the plate boundary ascribed to flexural bending stresses a velocity reduction of 8 immediately east of the alpine fault linked to high pore fluid pressures 17 km of crustal thickening to form a 44 1 4 km deep crustal root that is offset 10 20 km se of the highest mountains a velocity reversal below the midcrust in the eastern part of the crustal root caused either by heating or an artifact from seismic anisotropy strong thickening of a 7 0 0 4 km s fast lower crust within the crustal root and a low velocity zone in the australian upper mantle due to sampling the slow orientation of upper mantle anisotropy

fission track analysis of the late cenozoic vertical kinematics of continental pacific crust south island new zealand during the late cenozoic the pacific plate has been converging obliquely with the australia plate in south island new zealand a result of this convergence has been the growth of a major mountain range the southern alps at the leading edge of the pacific plate the results of fission track analysis of 140 samples from 13 transects across the alps reported here establish the late cenozoic vertical kinematics amount age and rate of rock uplift of the pacific crust underlying the alps the late cenozoic rock uplift of the pacific crust is asymmetrical with respect to the alpine fault being a maximum 19 km immediately east of the central part of the fault with lesser values at the eastern 3 km northern 10 km and southern 8 km extremities of the alps the age of the start of rock uplift varies spatially across the southern alps the earliest indications from fission track analysis being at 8 ma at the southern end of the alps decreasing to 5 ma at the northern end and 3 ma along the southeastern margin this age variation reflects the longer time over which the southern parts of the alps have been in collision the rate of propagation of rock uplift southeastward into the pacific plate has been 30 mm yr nearly 4 times the late cenozoic average rate of convergence normal to the plate boundary late cenozoic mean rock uplift rates range from a maximum of 2 8 mm yr at the alpine fault to a minimum of 1 0 mm yr in the east and have been sustained for periods of 3 8 m y accompanying denudation has exhumed amphibolite grade rocks immediately east of the alpine fault the rock uplift has been controlled by oblique slip displacement on the alpine fault a continental crustal section at least 19 km thick has been uplifted on the alpine fault comparison of the late cenozoic mean rock uplift rates with uplift rates derived from reset zircon data 2 10 mm yr near the alpine fault shows that uplift has accelerated over time but only significantly since 1 3 0 3 ma the amount of mesozoic uplift ranged from minimal amounts north of arthur s pass to 3 km near mount cook to 10 km in the south at lake wanaka

fossil wood in coal forming environments of the late paleocene early eocene chickaloon formation the early cenozoic chickaloon formation is the main coal bearing sequence in south central alaska coal and associated plant macrofossils are well exposed in the eska premier and jonesville coal groups in the wishbone hill district there is a striking variation in the degree and mode of preservation of fossil trees in a vertical sequence through these coal groups we examined the wood taxonomy mineralogy and geochemistry to elucidate potential cause s for these differences the wood anatomy indicates that the wood is all assignable to the cupressaceae taxodiaceae s str and assignable to the form genus taxodioxylon hartig emend gothan however we found no significant variation in the taxonomy of the wood between stratigraphic layers the wood generally becomes better preserved in the jonesville coal group wood from the stratigraphically lower premier coal group exhibits greater plastic deformation and contains less well preserved wood anatomical features the wood from the overlying jonesville coal group retains most of its original morphology but has suffered from brittle fracture the geochemistry and mineralogy of the wood follow a pattern that corresponds to the degree of preservation the less well preserved wood tends to have a higher concentration of iron carbonate minerals e g siderite and ankerite whereas the better preserved wood contains more calcium carbonate or silica all evidence points to rapid permineralization of the original wood although the least well preserved wood shows evidence of greater organic matter decomposition than the better preserved wood the wood taxonomy and mode of preservation of wood from the upper part of the chickaloon formation is similar to wood from coeval fossil forests that developed at higher polar paleolatitudes

fluid generation and pathways beneath an active compressional orogen the new zealand southern alps inferred from magnetotelluric data 1 forty one wideband magnetotelluric mt soundings were collected in a 150 km long transect across the southern alps of the central south island of new zealand an active compressional orogen decomposed mt impedance tensors vertical magnetic field relations and reconnaissance soundings at two locations off line imply an approximately two dimensional geometry here with average regional geoelectric strike of n40 e similar to surface geologic trends two independent two dimensional inversion algorithms were applied to the mt data and both imply a concave upward u shaped middle to lower crustal conductive zone beneath the west central portion of the island the average conductivity of this zone in the strike direction appears to be much higher than that required across strike and may represent anisotropy or along strike conductive strands narrower than the transverse magnetic cross strike mode mt data can resolve the deep crustal conductor under the southern alps is interpreted to represent mainly a volume of fluids arising from prograde metamorphism within a thickening crust fluid interconnection and electrical conduction are promoted by shear deformation the conductor rises northwestward toward the trace of the alpine fault but attains a near vertical configuration at a depth of 10 km and reaches close to the surface 5 10 km inland of the fault trace itself the transition to vertical orientation at this depth is interpreted to occur as fluids ascend across the brittle ductile transition in uplifting schist and approach the surface through induced hydrofractures the high grade schist becomes resistive after depletion of fluids and continues to extrude toward the alpine fault shallow extensions of the deep high conductivity are coincident with modern hydrothermal veining and gold mineralization interpreted to be of deep crustal provenance to the southeast high conductivity also reaches the surface coincident with a major back thrust fault zone of the doubly vergent southern alps orogen which also exhibits evidence for expulsion of high temperature fluids the higher conductivity inferred along strike possible anisotropy could reflect more efficient fluid interconnection in this higher strain direction as well as possible contributions by sheared fluid deposited graphite conductivity of the uppermost mantle of the south island is low consistent with advection of cold mantle lithosphere into the underlying asthenosphere as suggested by p wave delay studies

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

how wet was the arctic eocene rain forest estimates of precipitation from paleogene arctic macrofloras the eocene was the warmest part of the cenozoic when warm climates extended into the arctic and substantive paleobotanical evidence indicates broadleaf and coniferous polar forests paleontological temperature proxies provide a basis for understanding arctic early paleogene climates however there is a lack of corresponding proxy data on precipitation both leaf physiognomic analysis and quantitative analysis of nearest living relatives of an arctic macroflora indicate upper microthermal to lower mesothermal moist climates mean annual temperature 13 15 c cold month mean temperature 4 c mean annual precipitation 120 cm yr for axel heiberg island in the middle eocene leaf size analysis of paleocene and eocene arctic floras demonstrates high precipitation for the paleogene western and eastern arctic the predicted enormous volume of freshwater entering the arctic ocean as a result of northward drainage of a significant region of the northern hemisphere under a high precipitation regime would have strongly affected arctic ocean salinity potentially supporting arctic ocean azolla blooms high paleogene precipitation around the arctic basin is consistent with high atmospheric humidity which would have contributed significantly to polar and global eocene warming

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

a two dimensional tomographic study of the clipperton transform fault from the marine refraction data recorded on five instruments during the clipperton area seismic survey to investigate compensation classic experiment in 1994 we construct a compressional velocity model for a 108 km long profile across the clipperton transform we apply a new seismic tomography code that alternates between ray tracing and linearized inversions to find a smooth seismic velocity model that fits the observed refraction travel times the solution to the forward ray tracing problem is a hybrid of the graph or shortest path method and a ray bending method the inversion is performed with least squares penalties on the data misfit and first derivatives of the seismic structure starting with a one dimensional compressional velocity model for oceanic crust the misfit in the normalized travel time residuals is reduced by 96 decreasing the median travel time residual from 110 to 25 ms the compressional velocity structure of the clipperton transform is characterized by anomalously low velocities about 1 0 km s lower than average beneath the median ridge and parallel troughs of the transform domain the low compressional velocities can be explained by an increased porosity due to fracturing of the oceanic crust we found crustal thicknesses of 5 6 5 9 km under the transform fault to produce the best fit of the pmp phase arrivals and pg pn crossovers since the crust is not thin beneath the transform parallel troughs and the velocity anomaly is not confined to the median ridge we find uplift by serpentinite diapirs unlikely as an explanation for the relief of the median ridge a median ridge that is the result of brittle deformation due to compression across the transform domain is however compatible with our results the upper crust is thicker to the north of the transform than to the south which is likely a consequence of the contrast in temperature structure of these two spreading segments

cycles in perilacustrine facies of late mesozoic rift basins southeastern mongolia detailed study of 365 meters of core recovered from southeastern mongolia reveals fluvial marginal lacustrine and profundal lacustrine depositional environments in an early cretaceous rift basin multiple examples of cyclic sedimentation are superposed on these large scale facies transitions in fluvial facies more than 20 upward fining successions 2 10 m thick are present these contain cross stratified sandstone units with erosional bases that fine upward to mudstone with root marks and burrows they are interpreted as channel fill successions in a fluvial depositional environment whereas finergrained less erosional intervals with abundant soft sediment deformation and climbing ripples may represent a transition to fluvial deltaic environments at the lake margin coarse fluvial deltaic facies form the most likely hydrocarbon reservoirs as indicated by frequency of oil staining in the core physical transport processes dominate well oxygenated fluvial and marginal lacustrine facies whereas cycles in more distal lacustrine facies mainly reflect biogeochemical processes profundal lacustrine strata include kerogen rich laminated micrite distal turbidite beds and dolomitic breccia reminiscent of lacustrine facies in the green river formation of the western united states evidence for anoxia at the lake floor includes framboidal biogenic pyrite high toc content mainly light amorphous organic constituents and paucity of trace fossils relative to the rest of the core approximately 25 dolomite layers are interbedded with laminated micrite and calcareous siltstone units in poorly defined meter scale cycles these beds typically have brecciated or clotted textures and suggest evaporative concentration of magnesium ions at the lake floor the profundal lacustrine sequence displays a distinctive high resistivity low spontaneous potential log character that is observed in well logs from several fields in the zuunbayan subbasin correlative units can be traced at least 60 km to the northeast and southwest of the zuunbayan field indicating that this is a widespread lacustrine depositional unit these lacustrine strata include the most likely petroleum source facies found to date and are likely contemporaneous with other large lake systems in china and mongolia

downstream dilution of a lahar transition from debris flow to hyperconcentrated streamflow nearly instantaneous melting of snow and ice by the march 19 1982 eruption of mount st helens released a 4 106 m3 flood of water from the crater that was converted to a lahar volcanic debris flow through erosion and incorporation of sediment by the time it reached the base of the volcano over the next 81 km that it traveled down the toutle river the flood wave was progressively diluted through several mechanisms a transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater when the total sediment concentration had decreased to about 78 by weight 57 by volume the hyperconcentrated lahar runout flood wave transporting immense quantities of sand in suspension continued to experience progressive downstream dilution although turbulence was significantly dampened by the extremely high suspended load very large standing waves and antidune waves were observed the hyperconcentrated lahar runout flow deposited an unusual faintly stratified coarse sand which locally contained small isolated gravel lenses very similar deposits in the quaternary stratigraphy of mount st helens and other cascades volcanoes suggest that lahars may be more frequent than previously recognized

warm arctic continents during the palaeocene eocene thermal maximum the palaeocene eocene thermal maximum petm 55 5 ma is a geologically relatively brief episode of extreme warmth both deep and surface ocean temperatures increased by up to 5 c in equatorial waters and up to 8 c in mid and high latitude waters from the continents the annual mean air temperature response during the petm is still largely unknown mainly due to a lack of quantitative temperature proxies and sufficient suitable continuous high resolution records recently a new proxy for continental temperature reconstructions has been proposed based on the distribution of membrane lipids of bacteria in present day soils j w h weijers s schouten j c van den donker e c hopmans j s sinninghe damste 2007 environmental controls on bacterial tetraether membrane lipid distribution in soils geochimica et cosmochimica acta 71 703 713 and shown to reconstruct annual mean air temperature in this study we applied this new proxy in an attempt to reconstruct the air temperature in high latitude continental areas during the petm by analysis of a marine sedimentary sequence obtained from the lomonosov ridge in the central arctic ocean integrated ocean drilling program expedition 302 site 004 hole a the results indicate a warming of 8 c above background values of 17 c this warming is coincident with a similar rise in sea surface temperatures documented earlier our results thus further confirm the warm conditions in the arctic and point to a strongly reduced latitudinal temperature gradient during the petm 2007 elsevier b v all rights reserved

tectonic implications of paleomagnetic poles from lower tertiary volcanic rocks south central alaska we have determined the paleolatitude of lower tertiary volcanic rocks in southern alaska to measure possible poleward translation of the wrangellia and the peninsular terranes after 50 m y ago previous paleomagnetic studies have shown that in triassic and jurassic time these terranes were located near the equator and have moved at least 3000 km poleward relative to the north american craton our sample localities are in the northern talkeetna mountains in mildly deformed andesite and dacite flows 50 4 51 3 53 9 and 56 3 m y by k ar that overlap lower cretaceous flysch lower permian volcanic rocks of wrangellia and upper triassic pillow basalt of the susitna terrane results from 26 cooling units 23 of reversed polarity and 3 of normal polarity give a mean paleomagnetic pole at 69 5 n 179 6 e 95 12 2 stratigraphic sections from opposite limbs of a syncline yield directional paths that pass the fold test satisfying a necessary condition for primary origin of the magnetization the corresponding mean paleolatitude 76 n of the northern talkeetna mountains is 8 10 higher than the latitude predicted from the eocene reference pole for north america therefore northward drift of the talkeetna superterrane which is the amalgamation of the wrangellia and peninsular terranes during and after middle jurassic time was probably complete by 50 m y ago our results are consistent with paleomagnetic poles from uppermost cretaceous and paleocene volcanic sequences in denali national park the lake clark region northern bristol bay region and near mcgrath these poles generally lie south of the cratonic poles suggesting that the region between the kaltag bruin bay and castle mountain faults has rotated counterclockwise relative to north america since the early eocene

the ketavik formation a new stratigraphic unit and its implications for the paleogene paleogeography and paleoclimate of southwestern alaska abstract a new formation the ketavik formation is proposed for paleogene rocks of katmai national park near brooks camp the type section is in an area previously mapped as the jurassic talkeetna formation the proposed formation was deposited in a fluvial environment it is distinct from the coeval copper lake formation on the southeast side of the alaska peninsula volcanic arc and was deposited in a different river system the ketavik formation may include previously mapped undifferentiated tertiary rocks at least some of which are similar in age that are scattered along a belt parallel to and northwest of the present magmatic arc the ketavik formation contains dicot and coniferous leaf and wood fossils that indicate a warm temperate climate

teleseismic p wave delays and modes of shortening the mantle lithosphere beneath south island new zealand a high speed zone in the mantle directly beneath the southern alps of new zealand is required by the recorded pattern of teleseismic p waves two parallel lines of 80 seismographs spaced at 2 km intervals recorded three earthquakes from the western pacific with epicentral distances of 52 53 and 78 azimuthal bearings were all within 15 degrees of the mean trends of the seismograph lines differences between measured delays and those predicted from the crustal structure reach 0 8 s along one line and 1 0 s along the other with the rays for the earliest arriving signals passing the depth of 120 km beneath the center of the island assuming these early arrivals are due to structure within the mantle shallower than 200 km they imply that the core of the high speed zone lies beneath the thickest crust which has been shortened by 100 km of convergence during the past 6 7 myr although the shape and position of the high speed body cannot be fixed uniquely a roughly symmetric body centered about a depth of 120 km 80 100 km wide with a depth extent of 100 km and with a maximum speed advance of 7 satisfies the observations the pattern of residuals does not fit with those predicted by simple models of intracontinental subduction in which crust and mantle lithosphere are detached and one slab of mantle lithosphere underthrusts the other rather the residuals favor thickening of mantle lithosphere by a more homogenous straining of it as if mantle lithosphere beneath continental crust behaved as a continuum an excess mass in the mantle is also required by the observed gravity anomalies once allowance is made for the seismically determined crustal thickness this high density mantle anomaly provides sufficient force per unit length to maintain the crustal root which is approximately twice as thick as that necessary to support the topography

paleoceanography of the south china sea since the middle miocene evidence from planktonic foraminifera late middle miocene to pleistocene planktonic foraminifera pf in fairly continuous hemipelagic sediments recovered at ocean drilling program odp site 1143 from the southern south china sea scs were studied with sampling intervals of 10 to 150 cm a total of 16 pf events are revised for the 516 m long section providing an age model for the last 12 ma at this site on the basis of benthic foraminiferal d 18 o stratigraphy and the smoothed planktonic age model new ages are assigned to three pf events last occurrence lo globorotalia multicamerata sensu lato s l at 2 18 ma first occurrence fo sphaeroidinella dehiscens sensu stricto s s at 3 6 ma and fo globigerinoides conglobatus at 6 6 ma in the south china sea distinct pf faunal transition from globorotalia siakensis g mayeri group to mixed layer species occurred during the early late miocene 9 6 ma the transition reflects a deepened upper water thermocline possibly corresponding to the closure of the indonesian seaway and intensification of equatorial pacific warm currents abundance variations of neogloboquadrina spp indicate a marked shoaling of the thermocline in the northern south china sea after 3 2 5 ma affected possibly by a strengthened asian winter monsoon while a deeper thermocline existed in the southern south china sea since the late miocene characterizing the west pacific bwarm poolq wpwp a deepening thermocline influenced by consistently warm surface water since the late miocene in the southern south china sea is also evidenced by a two stepwise increase of pulleniatina group by a gradually decreasing sphaeroidinella sphaeroidinellopsis spp and abundant globorotalia menardii and related species the fo globigerinoides ruber pink at approximately 1 ma and an abrupt increase in the pink to all ratio of g ruber at 0 4 ma at site 1143 provide two additional pf events for deciphering pleistocene biostratigraphy and paleoceanography d 2004 elsevier b v all rights reserved

the obliquely convergent plate boundary in the south island of new zealand implications for ancient collision zones abstract the alpine fault of new zealand forms the western boundary of a zone of distributed deformation formed by the oblique convergence of continental crust belonging to the pacific and australian plates structural and geodetic data from the alpine fault show that a large proportion of the total plate displacement is accommodated by rapid oblique slip on the fault the remaining displacement is distributed over a 200 km wide zone to the east the collision may be modelled as a two sided deforming orogen with the partitioning of deformation being controlled by erosional differences between the narrow high strain inboard and broad low strain outboard sides in ancient collision zones little evidence may remain of the nature and amount of displacement on the inboard side partitioning of deformation among pre existing structures complicates interpretation of the outboard zone radiometric ages may post date collision by several tens of millions of years and indicate slow isostatic uplift and unroofing collision ages if preserved may be recognized by high uplift rates calculated from muscovite biotite pairs

paleomagnetism of eocene volcanic rocks talkeetna mountains alaska previous paleomagnetic studies of eocene rocks deposited in the talkeetna mountains on the northern edge of the combined peninsular wrangellia and alexander terranes the southern alaska superterrane sas yield a paleolatitude of 76 n while late cretaceous rocks on the southern edge of the sas record a 32 n paleolatitude at face value these drastically different paleolatitudes imply that wrangellia moved 44 to the north in only 20 m y requiring a northward component of velocity of about 24 cm yr alternatively the discrepancy might be explained by postulating an unrecognized tectonic boundary separating the two localities allowing different emplacement ages we have tested the unrecognized tectonic boundary hypothesis allowing post eocene emplacement of the sas by sampling eocene volcanic rocks deposited near the southern edge of the sas in the talkeetna mountains our data set comprises measurements from 97 oriented cores collected from 26 lava flows and two tuffs distributed over a distance of 50 km a primary remanence is indicated by positive fold tests and penecontemporaneous intrusion tests age control is provided by nine new k ar whole rock age determinations ranging from 38 8 to 53 6 ma the mean paleomagnetic pole calculated for this study is not significantly different from the pole derived from the eocene flows to the north and gives a paleolatitude of 78 thus ruling out the hypothesis of an unrecognized suture accommodating major post eocene displacement this result has prompted a reevaluation of the data which suggest rapid movement including the precision of the age control the adequacy of averaging of secular variation and the possibility of sedimentary inclination error the bulk of the evidence suggests northward displacement from lower latitudes however the error limits are such that the dramatic velocities previously postulated are not required

late paleocene early eocene paleosols and a new measure of the transport distance of alaska s yakutat terrane abstractan intensely weathered paleosol representing a nearly isochronous landscape exists at many places in continental late paleocene early eocene strata in north america most commonly a single siderite spherule bearing horizon is found from which 18o values were obtained to construct a paleolatitudinal gradient for late paleocene early eocene north america comparison of the paleosol siderite spherule 18o composition from the displaced yakutat terrane of alaska to the north american paleolatitudinal gradient indicates that during the late paleocene early eocene the terrane existed at 44 paleonorth thus supporting hypotheses for a far traveled terrane history

changing lake dynamics and sequence stratigraphy of synrift lacustrine strata in a half graben an example from the triassic ischigualasto villa union basin argentina well exposed triassic rift strata from the ischigualasto villa union basin nw argentina include a 80 to ca 515 m thick lacustrine dominated package that can be correlated across a half graben using key stratigraphic surfaces sequence boundaries lacustrine flooding surfaces and forced regressive surfaces the characteristics of the synrift lacustrine fill in different parts of the half graben have been examined and the mechanisms controlling sedimentation inferred a variety of sedimentary environments are recognized including volcaniclastic floodplain mildly saline lake and playa lake offshore lacustrine delta front to fluvial dominated and wave dominated deltas distributary and fluvial channel and interdistributary bay the succession can be divided into four stratigraphic sequences ss1 to ss4 the oldest of which ss1 contains volcaniclastic fluvial and saline lake deposits it is thickest close to the western border fault zone reflecting more rapid subsidence here accommodation exceeded sediment and water input during ss1 the second and third sequences ss2 and ss3 mark the onset of widespread lacustrine sedimentation reflecting a balance between accommodation creation and water and sediment fluxes sequences ss2 and ss3 are represented by offshore meromictic lacustrine and deltaic deposits the latter mostly sourced from the flexural and southern axial margins of the half graben the presence of stacked parasequences bound by lacustrine flooding surfaces is related to climatically induced lake level fluctuations superimposed on variable rates of subsidence on the controlling rift border fault zone the youngest sequence ss4 is represented by the deposits of littoral lacustrine and shallow shelf deltas distinguished by a change in lithofacies palaeocurrents and sandstone composition suggesting a switch in sediment supply to the footwall margin to the nw the change in the sediment source is related to reduced footwall uplift the possible presence of a relay ramp and or supply from a captured antecedent drainage network during ss4 the rate of creation of accommodation was exceeded by the sediment and water discharge the stratigraphic evolution of lacustrine strata in the half graben was mainly controlled by tectonic processes including subsidence rate and the growth and evolution of the border fault zone but changing climate inducing changes in water balance and lake level and autocyclic processes delta lobe switching were also important

paleoenvironment and paleoecology of a late paleocene high latitude terrestrial succession arkose ridge formation at box canyon southern talkeetna mountains alaska abstract paleogene sedimentary rocks of the arkose ridge formation talkeetna mountains alaska preserve a record of a fluvial lacustrine depositional environment and its forested ecosystem in an active basin among the convergent margin tectonic processes that shaped southern alaska an 800 m measured succession at box canyon indicates braid plain deposition with predominantly gravelly deposits low in the exposure to sandy and muddy facies associations below an overlying lava flow sequence u pb geochronology on zircons from a tuff and a sandstone within the measured section as well as an ar ar date from the overlying lava constrain the age of the sedimentary succession to between 59 ma and 48 ma fossil plant remains occur throughout the arkose ridge formation as poorly preserved coalified woody debris and fragmentary leaf impressions at box canyon however a thin lacustrine depositional lens of rhythmically laminated mudrocks yielded fish fossils and a well preserved floral assemblage including foliage and reproductive organs representing conifers sphenopsids monocots and dicots leaf physiognomic methods to estimate paleoclimate were applied to the dicot leaf collection and indicate warm temperate paleotemperatures 11 15 4 c mat and elevated paleoprecipitation 120 cm yr map estimates as compared to modern conditions results that are parallel with previously published estimates from the partly coeval chickaloon formation deposited in more distal depositional environments in the same basin the low abundance of leaf herbivory in the box canyon dicot assemblage 9 of leaves damaged is also similar to the results from assemblages in the meander plain depositional systems of the chickaloon this new suite of data informs models of the tectonostratigraphic evolution of southern alaska and the developing understanding of terrestrial paleoecology and paleoclimate at high latitudes during the late paleocene early eocene greenhouse climate phase

crustal deformation during 1994 1998 due to oblique continental collision in the central southern alps new zealand and implications for seismic potential of the alpine fault the positions of 115 ground marks in a 150 100 km area of oblique continental collision in the central southern alps new zealand have been measured by global positioning system gps two to four times between 1994 and 1998 contemporary velocity and strain rate fields derived from these observations are largely invariant along the northeasterly strike of the mountains and alpine fault across strike more than 60 of the strain occurs within a band from 5 km nw to 20 km se of the alpine fault but significant strain continues at least a further 60 km se to near the edge of the southern alps foothills projections of the fault parallel and fault normal components of velocity onto an alpine faultnormal profile show that about 85 of the nuvel 1a model relative plate motion is observed within the gps network the surface displacements in the high strain rate region are well fit by a model in which stable slip or shearing is occurring at 50 70 of the relative plate rate in a region deeper than about 5 8 km on the down dip extension of the se dipping alpine fault material shallower than this is behaving elastically and thus storing elastic strain in the region of the alpine fault the longer wavelength displacements can be modeled either as distributed deformation beneath the southern alps or by localization of elastic strain around the upper end of a discrete nw dipping fault or shear zone that is slipping stably below about 30 km depth and would outcrop near the se boundary of the mountains if extrapolated to the surface strain determined from a small scale survey network crossing the alpine fault indicates no significant near surface aseismic fault slip on the central alpine fault over the past 25 years our results are consistent with independent geological evidence that the central section of the alpine fault is capable of producing large to great earthquakes

subcrustal earthquakes in the central south island new zealand and the root of the southern alps the pukaki microearthquake network has revealed significant earthquake activity deeper than 15 km in the central south island new zealand extending to a depth of 73 km beneath the crest of the southern alps events deeper than 25 km define a planar seismic zone that has a strike of 41 and dips northwest at 19 gravity models suggest that earthquakes in this zone are occurring in a seismogenic uppermost mantle underlying an aseismic lower crustal root to the southern alps the 17 difference in strike of the dipping seismic zone and the alpine fault provides an explanation for the pattern of uplift and crustal thickening seen in the central south island

plate boundary deformation in south island new zealand is related to inherited lithospheric structure abstract the alpine fault is the main active structure in the oblique continental collision zone of south island new zealand it is continuous at the surface for 800 km and accommodates 70 of current plate motion a 460 km offset of basement rocks suggests it has accommodated 50 of plate displacement since 45 ma geophysical geological and contemporary kinematic data are successfully modeled by slip on a narrow alpine fault zone extending into the lower crust the data are consistent with plate boundary deformation occurring on either northwest or southeast dipping shear zones in the upper mantle or with widely distributed strain in the upper mantle we propose that the position of the alpine fault and any associated lithospheric discontinuity is controlled by an eocene passive margin that separated palaeozoic continental lithosphere of the challenger plateau from much younger oceanic lithosphere strike slip motion since 25 ma has translated the passive margin into the continental collision zone resulting in subduction of oceanic lithosphere beneath south island and progressive localisation of shear strain near the alpine fault the eocene rift boundary formed by exploiting cretaceous oceanic transform faults and an older discontinuity within the new zealand continent we propose that a precursor to the alpine fault could be as old as palaeozoic inherited structure has clearly controlled the first order deformation pattern through new zealand since at least 100 ma and demonstrates that ancient faults can play an important role in determining lithospheric scale patterns of deformation at continental plate boundaries

eocene volcanism above a depleted mantle slab window in southern alaska the caribou creek volcanic fi eld lies along the continent side edge of forearc basin rocks in south central alaska and consists of over 1000 m of shallow dipping basalt and andesite lavas with minor mafi c pyroclastic deposits dacite and rhyolite lavas along with shallow intrusions form dome complexes with associated pyroclastic deposits that overlie and crosscut the basalt and intermediate lavas the basalts are tholeiitic and strongly depleted in the light rare earth elements la yb 0 18 1 5 with concentrations of high fi eld strength elements e g zr hf ti y similar to mid ocean ridge basalt and with variable enrichment in fl uid mobile elements e g cs ba and pb intermediate and felsic rocks show enrichment in the rare earth elements and fl uid mobile elements plus rb and k but retain low la yb ratios 0 48 3 6 a few andesite and dacite samples are strongly depleted in the heavy rare earth elements and are geochemically similar to adakites e g sr y up to 52 ten 40 ar 39 ar ages for the caribou creek volcanic rocks range from 49 4 2 2 to 35 6 0 2 ma an adakite like tuff beneath the other volcanic rocks yields an age of 59 0 0 4 ma caribou creek basalts were derived from mid ocean ridge like depleted mantle that was emplaced beneath the southern margin of alaska through a slab window following spreading ridge subduction caribou creek volcanism was coeval with oblique subduction oroclinal bending and right lateral strike slip faulting in south central alaska all of which could have induced crustal extension to allow adiabatic melting of the depleted mantle reservoir to form basaltic magmas the basalts then evolved by fractional crystallization with moderate to high degrees of assimilation of jurassic arc basement rocks to form the intermediate and felsic magmas enrichment of the basaltic parent magmas in fl uid mobile elements occurred by contamination from the jurassic arc rocks and or by contamination with metasomatic mantle remnant from preceding subduction high heat fl ow through the slab window induced partial melting of garnet bearing mafi c parts of the jurassic arc basement to form the adakite like rocks the caribou creek volcanic rocks demonstrate that slab windows can directly infl uence magmatism inboard of accretionary prism and forearc basin settings given a suitable deformation regime e g crustal extension and that the infl uence of a slab window on continental margin magmatism can be long lived 20 m y

oxygen isotope and paleobotanical estimates of temperature and δ18o latitude gradients over north america during the early eocene empirical estimates of climate parameters such as mean annual temperature mat are essential to describe both ancient climate and to ground truth climate model simulations of past climates in terrestrial settings no single proxy record is able to provide detailed temporal yet geographically widespread information and it thus becomes essential that paleoclimatic information obtained from different proxies be comparable as an example of how to compare estimates and to illustrate what can be learned by doing so we measured oxygen isotope ratios of phosphate in the tooth enamel of fossil mammals and the body scales of freshwater fish in order to estimate the mean annual temperature mat in which they lived the samples were collected from paleogene rocks of the bighorn green river and powder river basins of wyoming earliest eocene samples provide mat estimates that are similar to mat estimates for the same times and areas obtained from leaf margin analysis furthermore isotopic data from the paleocene eocene thermal maximum petm which has not yet yielded fossil floras indicate a significantly higher mat of 26 c we also used temperature estimates obtained by both methods to investigate paleoelevation and to reconstruct geographic patterns of mat over north america for the early eocene larger laramide basins have higher temperatures and lower inferred elevations compared to associated volcanic highlands where cooler temperatures are consistent with substantial elevations in turn latitudinal gradients in temperature indicate that warming centered on polar regions played an important role during the eocene hothouse lastly we show that the reconstructed eocene relation between oxygen isotope ratios of precipitation and mat is significantly different from the modern relation between these two variables because the relation has changed over time the modern correlation should not be used to estimate paleo mat from measurements of oxygen isotope ratios in fossil material

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

high resolution stratigraphy of an underfilled lake basin wilkins peak member eocene green river formation wyoming u s a abstract lakes tend to respond noticeably to minor changes in sediment and water balance driven by climatic tectonic or geomorphic processes this unique behavior of lacustrine basins can provide a high resolution record of geologic processes within the continental setting far from the globally averaged record of marine strata the wilkins peak member of the eocene green river formation in wyoming usa is dominated by aggradation of repetitive sedimentary facies successions recording distinct lacustrine expansions and contractions these lacustrine cycles consist of up to four successive facies associations littoral profundal sublittoral palustrine and salt pan because they comprise disparate facies that may never have been simultaneously deposited in the basin wilkins peak member cycles are non waltherian successions that do not readily equate to any established sequence stratigraphic unit the completeness of the stratigraphic record in the wilkins peak member varies continuously across the basin at least 126 cycles are present in the erda white mountain 1 core near the basin depocenter whereas only about one third as many are recognizable 53 km north nearer to the basin margin cycle boundaries terminate northward by gradual amalgamation into palustrine facies reflecting the interplay between varying lake levels and a south dipping deposition gradient evidence for complete desiccation and hiatuses is commonplace even near the basin center a truly complete record may not be present anywhere based on recent 40ar 39ar geochronology of tuffs the average cycle duration in the white mountain 1 core is approximately 10 000 years however the true average duration is shorter due to the presence of lacunae and the time required for deposition of the thinnest cycles may have been less than 1000 years no external driving mechanism is presently known for eocene cycles of such short duration raising the possibility that they are instead autogenic cycles related to geomorphic instability of the surrounding landscape evaporite deposition corresponded closely in time and space to maximum differential subsidence suggesting that tectonic influences on drainage patterns and basin accommodation exerted a primary control differential accommodation was most pronounced during deposition of the lower wilkins peak member and became progressively less so after that time based on structural and stratigraphic observations a period of increased tectonic uplift commenced concurrent with deposition of the lower wilkins peak member

the kanaka creek fossil flora huntingdon formation british columbia canada paleoenvironment and evidence for paleocene age using palynology and macroflora paleogene sediments of the huntingdon formation a correlative to the chuckanut formation of neighbouring washington state usa are exposed in the greater vancouver area british columbia canada

using fossil leaves as paleoprecipitation indicators an eocene example estimates of past precipitation are of broad interest for many areas of inquiry including reconstructions of past environments and topography climate modeling and ocean circulation studies the shapes and sizes of living leaves are highly sensitive to moisture conditions and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations however when tested on extant forests this method has consistently overestimated precipitation we present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set the significant relationship that results in addition to having value for paleoclimatic reconstruction refines understanding of the long observed positive relationship between leaf area and precipitation seven precipitation estimates for the eocene of the western united states are revised as lower than previously published but remain far wetter than the same areas today abundant moisture may have been an important factor in maintaining warm frost free conditions in the eocene because of the major role of water vapor in retaining and transporting atmospheric heat

paleomagnetism of eocene plutonic rocks matanuska valley alaska paleomagnetic analysis of 88 samples from 14 sites in four eocene sills in the matanuska valley south central alaska yields a paleomagnetic pole at lat 72 9 n long 281 1 e precision parameter k 15 4 the paleolatitude of this result suggests that this part of the alaskan crust was at or near its present position relative to north america in the middle tertiary this pole also indicates that the region has been rotated clockwise by approximately 50 these results can be explained by local block rotations of fault bounded blocks in response to regional right lateral shear along both the castle mountain and border ranges faults

role of fluids in the metamorphism of the alpine fault zone new zealand models of fluid rock interaction in and adjacent to the alpine fault in the hokitika area south island new zealand were investigated using hydrogen and other stable isotope studies together with field and petrographic observations all analysed samples from the study area have similar whole rock d values dwr 56 to 30 average 45 n 20 irrespective of rock type degree of chloritization location along the fault or across strike distance from the fault in the garnet zone the green chlorite rich fault rocks which probably formed from australian plate precursors record nearly isothermal fluid rock interaction with a schist derived metamorphic fluid at high temperatures near 450 500 c d of water in equilibrium with the green fault rocks dh2o green 18 d of water in equilibrium with the greyschists and greyschist derived mylonites dh2o grey 19 at 500 c dh2o green 17 dh2o grey 14 at 450 c there is no indication of an influx of a meteoric or mantle derived fluid in the alpine fault zone in the study area the alpine fault zone at the surface shows little evidence of late stage retrogression or veining which might be attributed to down temperature fluid flow it is probable that prograde metamorphism in the root zone of the southern alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the alpine fault up to the surface owing to the combined effects of the fault the disturbed isotherms under the southern alps and the brittle ductile transition such fluids could mix with meteoric fluids to deposit quartz rich possibly gold bearing veins in the region c 5 10 km back from the fault trace these results and interpretations are consistent with interpretations of magnetotelluric data obtained in the south island geophysical transects sight programme

stream dominated alluvial fan and lacustrine depositional systems in cenozoic strike slip basins denali fault system yukon territory canada ancient stream dominated wet alluvial fan deposits have received far less attention in the literature than their arid semi arid counterparts the cenozoic basin fills along the denali fault system of the northwestern canadian cordillera provide excellent examples of stream dominated alluvial fan deposits because they developed during the eocene oligocene temperate climatic regime in an active strike slip orogen the amphitheatre formation filled several strike slip basins in yukon territory and consists of up to 1200 m of coarse siliciclastic rocks and coal detailed facies analysis conglomerate sandstone percentages c s maximum particle size mps distribution and palaeocurrent analysis of the amphitheatre formation in two of these strike slip basins document the transition from proximal to middle to distal and fringing environments within ancient stream dominated alluvial fan systems proximal fan deposits in the bates lake basin are characterized by disorganized clast supported boulder conglomerate and minor matrix mud supported conglomerate proximal facies are located along the faulted basin margins in areas where c s 80 to 100 and where the average mps ranges from 30 to 60 cm proximal fan deposits grade into middle fan channelized well organized cobble conglomerates that form upward fining sequences with an average thickness of 7 m middle fan deposits grade basinward into well sorted laterally continuous beds of normally graded sandstone interbedded with trough cross stratified sandstone these distal fan deposits are characteristic of areas where c s 20 to 40 and where the average mps ranges from 5 to 15 cm fan fringe deposits consist of lacustrine and axial fluvial facies palaeogeographic reconstruction of the bates lake basin indicates that alluvial fan sedimentation was concentrated in three parts of the basin the largest alluvial fan system abutted the strike slip duke river fault and prograded westward across the axis of the basin two smaller coarser grained fans prograded syntaxially northward from the normal faulted southern basin margin facies analysis of the burwash basin indicates a similar transition from proximal to distal stream dominated alluvial fan environments but with several key differences middle fan deposits in the burwash basin define upward coarsening sequences 50 to 60 m thick composed of fine grained lithofacies and coal in the lower part trough cross stratified sandstone in the middle and conglomerate in the upper part of the sequence upward coarsening sequences 90 140 m thick also are common in the fan fringe lacustrine deposits these sequences coarsen upward from mudstone through fine grained ripple laminated sandstone to coarse grained trough cross stratified sandstone the upward coarsening sequences are basinwide facies independent and probably represent progradation of stream dominated alluvial fan depositional systems coal distribution in the amphitheatre formation is closely coupled with predominant depositional processes on stream dominated alluvial fans the thickest coal seams occur in the most proximal part of the basin fill and in marginal lacustrine deposits coal development in the intervening middle and distal fan areas was suppressed by the high frequency of unconfined flow events and lateral channel mobility

late paleocene early eocene climate changes in southwestern wyoming paleobotanical analysis the warmest global temperatures of the cenozoic era occurred in early eocene time following a warming trend that started in late paleocene time the greater green river basin of southwestern wyoming is one of the best areas in the rocky mountains for paleobotanical investigation of the paleocene eocene climatic transition intensive sampling has resulted in the recovery of an estimated 189 species of plant macrofossils from the tiffanian clarkforkian wasatchian and bridgerian land mammal ages the leaf morphologies and taxonomic affinities of these fossils were used in combination with other indicators to evaluate paleocene eocene climates following cool humid conditions in the tiffanian the clarkforkian was humid and subtropical and several plant families with modern tropical affinities appeared however as in the tiffanian clarkforkian floras had low diversity and were dominated by a single species in the birch family mean annual temperature mat rose from an estimated 12 c in the tiffanian to 19 c in the clarkforkian while mean annual precipitation map for the tiffanian and clarkforkian is estimated to have been 130 150 cm little fossil plant material is preserved from the latest clarkforkian or the earliest wasatchian which is thought to have contained an interval of cooling and drying followed by renewed warming by the middle wasatchian the time of the cenozoic thermal maximum the inferred mat was about 21 c and the map was near 140 cm a second influx of plant families with tropical affinities appeared in the area and diversity increased significantly but most plant families known from the clarkforkian persisted species turnover from the clarkforkian to the wasatchian was greater than 80 a second turnover of more than 80 of species but not families from the wasatchian to the early bridgerian accompanied drying and increased seasonality of precipitation the early bridgerian mat is inferred to have been near 20 c and the map to have been about 80 cm except for the tiffanian and possibly portions of the early wasatchian paleoclimates during the study interval were predominantly frost free although the moderating influence of the green river lake system has been suggested as a possible explanation for mild eocene winters in wyoming this study shows that virtually frostfree climates existed in the area prior to and independent of significant lake development

sedimentology facies architecture and chemostratigraphy of a continental high latitude paleocene eocene succession the chickaloon formation alaska abstract the paleocene eocene chickaloon formation of southern alaska represents rapid deposition in a floodbasin setting contains abundant and diverse fossil plant material and spans the paleocene eocene thermal maximum petm sedimentologic lithofacies and chemostratigraphic analyses of exposures of the chickaloon formation were conducted in order to provide a contextual framework for this late paleocene early eocene high latitude sedimentary succession and to test if hyperthermal conditions are recorded in the unit at the main study area in the evan jones coal mine strata represent an alluvial sequence dominated by floodplain channel sandstone crevasse lobe crevasse channel and mire deposition floodplain environments are represented by medium gray commonly nodular and or carbonate cemented shaly siltstone and centimeter scale thick sheet sandstone interbeds most channel sandstone deposits are interpreted to be crevasse channels and are generally small 2 5 m thick rarely coarser than medium grained sandstone and sand grains are commonly coated with fe oxides carbonaceous shale and coal are localized and indicate a high rate of organic carbon accumulation in the area 13c analyses of bulk organic carbon from the succession at the evan jones mine are internally consistent with this interpretation they yield uniformly negative values that are typical of continental organic matter 21 7 to 28 5 x 25 4 fossil plant material is also very common and includes leaves wood seeds and resins from broad leaf angiosperms conifers ferns and sphenopsids considered together lithologic and paleontologic data suggest that these strata represent a floodbasin environment the observed crevasse channels probably originate from a main channel located within several kilometers of the depocenter ash fall tuffs punctuate the studied sequence and contain abundant reworked or recycled zircons indicating that the depocenter was proximal to a volcanic source across all of these chickaloon depositional environments a significant negative isotopic shift 5 8 occurs which we hypothesize to represent a short lived perturbation associated with a global hyperthermal event