strain partitioning in the transition area between oblique subduction and continental collision hikurangi margin new zealand spatial differences in late quaternary structural style and deformation rates indicate a complex pattern of strain partitioning within the transition area from oblique subduction beneath southern north island to oblique continental collision in northern south island new zealand the late quaternary structure of the offshore southern hikurangi margin is determined here using seismic reflection profiles mr1 side scan sonar swath images em12dual multibeam swath bathymetry and backscatter images and sediment core and dredge samples where oblique 50 subduction of the oceanic hikurangi plateau is occurring beneath southern wairarapa region the steep dissected upper margin consists of a wedge of rocks that are being deformed by strike slip and reverse faults beneath the lower margin an accretionary wedge of quaternary age has developed rapidly by frontal accretion of a thick succession of turbidites on the pacific plate estimates of late quaternary geological strain rates have been made on two margin perpendicular transects across southern north island and the offshore margin to budget the predicted nuvel 1a plate motion more than 33 55 of the total plate motion is expressed in the offshore part of the upper plate above the subduction detachment in the central hikurangi margin between 40 s and 41 s this offshore deformation could potentially include margin parallel fault slip of up to 14 15 mm yr across the upper plate strain is partitioned into zones of folding and thrust faulting and possibly more than one zone of strike slip faulting but the partitioning may be incomplete with oblique slip thrusting an important component of the deformation the wide distribution of deformation within the upper plate partially reflects strong coupling between the subducting oceanic plateau and the leading edge of the overriding plate this coupling increases toward the southwest where the continental part of the subduction zone beneath marlborough may now be inactive or very strongly coupled toward the southwest the transpressive deformation style of the upper wairarapa margin continues into the upper marlborough margin and onshore into the strike slip marlborough fault system of northern south island in contrast the accretionary wedge narrows to the southwest and terminates in southeastern cook strait approximately above the transition from subducted oceanic crust to subducted continental crust of the pacific plate farther southwest beneath the lower marlborough margin low strain folding and thrust faulting is occurring but the style of deformation is not typical of the accretionary wedge this shortening results either from a small amount of subduction slip beneath marlborough and or from contractional strain partitioned to the southeast of the continental transpression zone whereas the initial onset of continental collision occurs in marlborough the surface expression of deformation of the pacific plate occurs south of 42 30 s normal faulting of the northwestern margin of the continental chatham rise possibly reflects flexural extension of the pacific plate crust at the southern end of the subduction zone whereas folding and thrust faulting of the north canterbury coastal region results from nw se contraction of the delaminated upper crust entering the southern alps collision zone

holocene palaeoclimate and sea level fluctuation recorded from the coastal barker swamp rottnest island south western western australia abstract the holocene palaeoclimatic history of south western western australia swwa has received little attention compared to south eastern australia and this has resulted in conflicting views over the impact of climate variability in the region we present here a well dated high resolution record from two overlapping sediment cores obtained from the centre of barker swamp rottnest island offshore perth the records span the last 8 7 ka with the main lacustrine phase occurring after 7 4 ka this site preserves both pollen and several ostracod taxa the pollen record suggests a long term shift from the early mid holocene to the late holocene to drier conditions with less shrubland and more low ground cover and less fire activity a salinity transfer function was developed from ostracod faunal assemblage data and trace metal ratios mg ca sr ca and na ca and stable isotopes 18 o and 13 c analysed on selected ostracod valves these provide a detailed history of evaporation precipitation e p differences that clearly shows that the swwa region was subjected to significant climatic shifts over the last 7 4 ka with a broad shift towards increased aridity after 5 ka the swamp ranged from fresh to saline as recorded in the ostracod valve chemistry and the independently derived salinity transfer function the ostracod record also indicates that a sea level highstand occurred between ca 4 5 and 4 3 ka with probable step wise increases at 6 75 6 2 and 5 6 ka with the last vestiges of salt water intrusion at ca 1 ka after about 2 3 ka the fresh groundwater lens that underlies the western portion of the island intersected the swamp depression influencing the hydrology of the swamp the broad climatic changes recorded in barker swamp are also compared with data from southern south africa and it is suggested that the southern annular mode appears to have been the dominant driver in the climate of these regions and that the indian ocean dipole is of little importance in the southern regions of the south western cape of africa and south western western australia

history of stage 5 sea level in bermuda review with new evidence of a brief rise to present sea level during substage 5a abstract oxygen isotope substage 5e is represented by the devonshire formation in bermuda the occurrence of these coastal marine deposits to about 5 m indicates pleistocene sea level data in bermuda do not need tectonic corrections a few published u series coral dates suggest that a conglomerate spencer s point formation may have formed during substage 5c geologic mapping however indicates that the eolianite beneath the conglomerate is pre rather than post devonshire formation in age as was previously thought and the aminostratigraphy of marine sheels also confirms the correlation of the spencer s point and devonshire formations substages 5c and 5a are represented by the southampton formation large eolianites comprise the bulk of this formation they are onlapped by a few small younger marine 1 m and eolian deposits aminostratigraphy confirms that these late southampton age deposits are significantly younger than the devonshire formation and u series dates indicate a substage 5a age the setting of some of these deposits along a protected shoreline precludes discounting their position as anomalous due to large storms this evidence that sea level in bermuda was at about present datum late in substage 5a agrees with interpretations of neotyrrhenian deposits of mediterranean shorelines but not with inferences from the deep sea oxygen isotope record or with data from uplifted coral reefs

wedge geometry mechanical strength and interseismic coupling of the hikurangi subduction thrust new zealand the hikurangi subduction thrust interface east coast north island new zealand exhibits along strike variations in seismic style the southern segment is interseismically locked while the plate boundary thrust slips aseismically in the north the geometry of the offshore accretionary prism is also heterogeneous changing from small to large taper angle fault dip plus surface slope from south to north along strike variations in accretionary prism geometry generally reflect changes in coulomb wedge critical taper angle such variations are controlled by the relative strengths of the subduction megathrust and the wedge material in the southern hikurangi margin the small taper angle indicates a relatively weak subduction thrust interface where strong interseismic locking is inferred in the northern margin high taper angle reflects a strong shallow decollement relative to the south thus based on critical coulomb wedge theory the shallow megathrust appears relatively weak in the locked segment and stronger in weakly coupled regions

landward and seaward directed thrusting accompanying the onset of subduction beneath new zealand a short 5 m y episode of deformation accompanied the onset of the present phase of subduction beneath northern and eastern new zealand in the earliest miocene at many places along the continental margin the structures produced were dominated by subhorizontal thrust sheets with tens of kilometres of displacement thrusting was directed both landward with or without involvement of the upper part of the downgoing plate and seaward the structures are different in style from those typical of active trench slopes which are predominantly seaward directed imbricate thrusts and associated folds the structures show that delamination of the downgoing plate occurred at some places and suggest that a high degree of coupling between upper and lower plates occurred at others

sea level records at 80 ka from tectonically stable platforms florida and bermuda studies from tectonically active coasts on new guinea and barbados have suggested that sea level at 80 ka was significantly lower than present whereas data from the atlantic and pacific coasts of north america indicate an 80 ka sea level close to that of the present we determined ages of corals from a shallow submerged reef off the florida keys and an emergent marine deposit on bermuda both localities are on tectonically stable platforms distant from plate boundaries uranium series ages show that corals at both localities grew during the 80 ka sea level highstand and geologic data show that sea level at that time was no lower than 7 9 m below present florida and may have been 1 2 m above present bermuda the ice volume discrepancy of the 80 ka sea level estimates is greater than the volume of the greenland or west antarctic ice sheets comparison of our ages with high latitude insolation values indicates that the sea level stand near the present at 80 ka could have been orbitally forced

revision of the late pleistocene stratigraphy of bermuda the quaternary stratigraphy of bermuda is one of the world s most complete sedimentary records of interglacial highstands representing at least the past million years yet in terms of the last interglacial rocky bay formation marine isotope substage mis 5e only scanty deposits are preserved in contrast mis 7 generally regarded as a diminutive interglaciation exposes widespread emergent subtidal deposits of the belmont formation indicating a prolonged sea level highstand at ca 2 5 0 3 m this belmont paradox has prompted a reexamination of the geology of key sites along the south shore of bermuda this revision of the late quaternary stratigraphy of bermuda is based on geological field observations primarily the questionable origin of red soil like deposits it is concluded here that there is no physical evidence of the exposure of the upper belmont surface for a full glacial cycle 70 100 ka and that interbedded reddish soil like lenticular deposits are the result of colluvial activity during mid mis 5e reexamination of previously published uranium series u th ages indicates that several 3 m notches contain a mix of ca 125 ka and older coral ages contrary to previous works this study favors an early mis 5e interpretation of the coral ages from the 2 5 m belmont shoreline which is further supported by amino acid racemization aar ratios on whole rock poecilozonites glycymeris and brachiodontes samples from shore and notch deposits an updated aar kinetic model demonstrates that the bulk of epimerization occurred during warm interglacial intervals between 130 and 80 ka and the last 10 ka of the holocene this revised stratigraphy of bermuda now falls into accordance with a more general view of middle and late pleistocene sea level history

role of the shale tectonics on the evolution of the eastern venezuelan cenozoic thrust and fold belt this paper presents a structural and stratigraphic analysis of the foreland fold belt of the eastern venezuelan basin and the main conclusions about shale tectonic mechanisms in the area the deformation of the foreland fold belt has been investigated analyzing the growth strata architecture preserved on the structure fold limbs three contractional episodes are proposed for the eastern venezuelan basin 1 oligocene to middle miocene 2 late miocene to pliocene and 3 pleistocene the first episode produced contractional listric faults inside the shale and long displacement blind thrusts in the underlying cretaceous units the second episode produced the deformation of the cenozoic strata into overlapping east west trending convex northward anticlines that covers more than 200 kilometers in length and 40 kilometers wide break through normal faults product of a high sedimentary load that overcomes contraction and the formation of short displacement blind thrusts in the underlying cretaceous units the last episode is related to an oblique compression and the formation of high angle extensional faults with dextral movement and nw se strike the role of the shale tectonics in the evolution implies that shale deforms in two stages 1 folding and 2 normal faulting of the crest of the anticline break through normal faulting folding controlled the sediment distribution during most of the neogene strata while the normal faulting of the anticlines represent basin potential for hydrocarbon the best potential hydrocarbon plays in the basin are related to oblique collision restricted basins and controlled by break through normal faults and the presence of nw se strike faults that connect the hc source with the reservoirs results from this research imply that the role of sedimentation is fundamental for the overburden sand distribution and tectonic constrain of the folds

aeolianite calcrete microbialite and karst in southwestern australia as indicators of middle to late quaternary palaeoclimates abstract the mid late pleistocene and holocene aeolianites of the tamala limestone on the northern swan coastal plain in southwestern western australia consist of six members that show cyclic deposition of coastal aeolianite overlain by calcrete microbialite karstified surface and palaeosol field work combined with mineralogical chemical stable isotope analysis and uranium thorium u th and optically stimulated luminescence osl dating provides an insight into the repetitive glacial and interglacial climatic periods over the past 500 kyr deposition of the carbonate aeolianites occurred during interglacial episodes marine isotope stage mis 1 5 7 9 11 and possibly 13 due to migration of coastal dunes under the influence of strong southerly to southwesterly winds rainfall was insufficient to support vegetation cover on the dunes and so was probably limited or seasonal the transition from interglacial to glacial climates was characterised by higher effective rainfall accompanied by aeolianite dissolution and karstification during the colder climates and less effective rainfall of the glacial periods there was no carbonate sand deposition instead laminated microbialite and or laminar calcrete formed followed by palaeosol formation the oxygen isotope composition of the microbialites indicates average temperatures during glacial periods 4 c 8 c lower than today and 13 c values demonstrate a higher proportion of c4 plants and therefore a drier or more seasonal climate data from individual members of the tamala limestone show that the wettest interglacial period was mis 5 when extensive karstification and pinnacle development occurred and rainfall was probably higher than at any other time in the past 500 kyr of the glacial periods mis 10 was relatively wet or less seasonal whereas mis 8 and the last glacial maximum lgm were relatively dry and windy the low rainfall during the peak of the glacial periods was probably intensified by colder water offshore due to weakening of the leeuwin current and its replacement by the cold north flowing west australian current

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

whole rock aminostratigraphy of the coorong coastal plain south australia towards a 1 million year record of sea level highstands the coorong coastal plain in southeastern south australia preserves a long quaternary record of cool water temperate carbonate sedimentation in the form of high wave energy barrier shoreline deposits and associated back barrier lagoon facies that formed during successive sea level highstands whole rock samples of bioclastic skeletal carbonate sand with subordinate quartz were collected from aeolian facies modern and relict foredunes of a holocene embayment fill and from ten pleistocene barriers across the coastal plain in a transect from robe to naracoorte the extent of leucine racemization total acid hydrolysate and free amino acids in the pleistocene skeletal carbonate sand 63 500 m increases monotonically with age and is consistently higher than for entire fossil molluscs from the same allostratigraphic units reflecting the lengthy residence time for bioclasts in this high wave energy environment and sediment recycling from the erosion of older barriers the extent of racemization in the whole rock samples conforms with a model of apparent parabolic racemization kinetics and the calculated ages largely agree with previously determined luminescence ages apart from a possible reinterpretation of the significance of the west naracoorte range the coastal plain succession indicates that interglacial sea levels did not deviate by more than 6 m of present sea level for the mid and late pleistocene thus providing an important framework for quantifying ice volume during sea level highstands and calibrating the oxygen isotope record

pliocene pleistocene coastal events and history along the western margin of australia coastal deposits along the western coastal margin of australia a region of relative tectonic stability record plio pleistocene events and processes affecting the inner shelf and adjacent hinterland tectonic deformation of these deposits is more apparent in the carnarvon basin and rather less so in the perth basin the most complete record comes from the perth basin where units of pliocene and pleistocene ages are well represented in the perth basin the predominantly siliciclastic yoganup formation ascot formation and bassendean sand represent a complex of shoreline inner shelf and regressive dune facies equivalents the deposition of which began at an undetermined stage of the pliocene through to the early pleistocene the deposition of this sequence closed with a major regression and significant faunal extinction bioclastic carbonates characterize the middle and late pleistocene of the perth and carnarvon basins fossil assemblages include a distinct subtropical element unknown from the ascot formation and suggesting a strengthening of the leeuwin current the estuarine arcoid bivalve anadara trapezia characterizes assemblages of oxygen isotope stages 5 and 7 in the perth and carnarvon basins where it is now extinct deposits of substage 5e perth basin also record a southerly expansion of warm water corals and other fauna consistent with shelf temperatures warmer than present new uranium series ages on corals from marine sequences of the tantabiddi member of the bundera calcarenite of the western cape range are consistent with the double peak hypothesis for levels of substage 5e but the evidence remains less than conclusive initial uranium series dates from the bibra and dampier formations of shark bay indicate that both derive from the late pleistocene these numerical ages contradict previous interpretations of relative ages obtained from field studies the age relationship of the units requires further investigation

stratigraphy and timing of eolianite deposition on rottnest island western australia over 100 whole rock amino acid racemization aar ratios from outcrops around rottnest island 32 0 s latitude near perth indicate distinct pulses of eolian deposition during the late quaternary whole rock image alloisoleucine image isoleucine a i ratios from bioclastic carbonate deposits fall into three distinct modal classes or aminozones the oldest aminozone e averages 0 33 0 04 n 21 red palaeosol and thick calcrete generally cap the aminozone e deposits a younger aminozone c averages 0 22 0 03 n 63 comprising two submodes at 0 26 0 01 n 14 and 0 21 0 02 n 49 multiple dune sets of this interval are interrupted by relatively weak brown to tan protosols a dense dark brown rendzina palaeosol caps the aminozone c succession ratios from holocene dune and marine deposits aminozone a center on 0 11 0 02 n 15 comprising submodes of 0 13 0 01 9 and 0 09 0 01 6 calibration of a i averages from aminozones e and a are provided by u th and 14c radiometric ages of 125 000 yr marine oxygen isotope stage mis 5e and 2000 6000 14c yr b p mis 1 respectively the whole rock a i results support periodic deposition initiated during mis 5e continuing through mis 5c and then peaking at the end of mis 5a about 70 000 80 000 yr ago oceanographic evidence indicates the area was subjected to much colder conditions during mis 2 4 10 000 to 70 000 yr ago greatly slowing the epimerization rate eolianite deposition resumed in the mid holocene not vert similar6000 yr ago up to the present the a i epimerization pathway constructed from rottnest island shows remarkable similarity to that of bermuda in the north atlantic 32 n latitude these findings suggest that like bermuda the eolian activity on rottnest occurred primarily during or shortly after interglacial highstands when the shoreline was near the present datum rather than during glacial lowstands when the coastline was positioned 10 20 km to the west

high precision u series dating of corals from western australia and implications for the timing and duration of the last interglacial abstract u series ages using methods of thermal ionisation mass spectrometry tims are reported for last interglacial fossil reefs along the stable coastal margin of western australia thorium isotope ratios were measured with superior precision using methods of charge collection high levels of precision in the measurement of both uranium and thorium isotopes has reduced the age uncertainty due to analytical errors excluding the uncertainty in the decay constants by a factor of four over the precisions reported by many earlier tims workers uncertainties in 234u t determined from both 230th 238u and 234u 238u are also significantly smaller than previously reported allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified strict criteria were adopted to screen the new western australian data reliable ages range from 127 to 122 ka published tims observations from other localities have been assessed using the same strict criteria when these are combined with glacio hydro isostatic sea level models they indicate that the last interglacial period occurred from at least 130 to 117 ka however these age constraints are largely determined from single data points and need to be verified with additional ages before considering them to be robust estimates for the timing of onset and termination of the last interglacial globally the main episode of reef growth appears to be confined to a narrow interval occurring from 127 to 122 ka in direct agreement with the narrow range in ages obtained from the western australian sites this may indicate that the last interglacial was of short duration extending from 127 to 122 ka only alternatively this interval may reflect a major reef building event in the middle of a longer duration 130 117 ka interglacial interval

tracking repeated subduction of the hikurangi plateau beneath new zealand abstract the hikurangi plateau has been subducted beneath new zealand twice firstly at ca 100 ma during n s convergence with gondwana and currently during e w convergence between the pacific and australian plates here we use a nationwide 3 d seismic velocity model derived from seismic tomography studies and seismicity relocated with this model to determine the location of the subducted western and southern edges of the plateau in the hikurangi subduction zone in the north island and northern south island we identify the western edge in the 37 140 km depth range based on the distribution of seismic velocities in the top of the subducted pacific plate changes in the thickness of the dipping seismic zone and steepening of the subducted plate downdip of the buoyant plateau in the central south island where the hikurangi plateau is subducting for a second time the plateau dips less steeply its southern edge is well defined by the collision of the delaminated lower crust of the plateau with the northern fiordland subduction zone where it bends the younger subducted australian plate to vertical the hikurangi plateau was originally rifted from the ontong java plateau and the subducted portions of the hikurangi plateau identified here fill a gap in reconstructions of this large igneous province

subtropical carbonates in a temperate realm modern sediments on the southwest australian shelf the southwestern continental margin of australia 19 degrees s 22 degrees s in the western indian ocean is transitional between cool water and warm water carbonate realms it comprises the incipiently rimmed flat topped steep fronted rottnest shelf in the south the uniform subtropical starved carnarvon ramp off shark bay and the ningaloo fringing reef in the north the margin is strongly influenced by the poleward flowing warm nutrient poor leeuwin current which promotes overall downwelling and strong summer equatorward blowing winds which generate local seasonal upwelling the structurally quiescent northern part of the rottnest shelf with minimum accommodation is characterized by luxuriant stands of sea grasses and macrophytes growing on coralline encrusted hardgrounds and rooted in sediments rich in coralline algae and larger symbiont bearing foraminifers together with abundant cool water elements such as bryozoans molluscs and small foraminifers halimeda is poorly calcified and does not contribute to the sediment azooxanthellate corals although present are not common such a sediment pattern has many analogs in the geologic record especially the early cenozoic the incipient rim is a morphologically complex linear ridge system interpreted to be a buried mid pleistocene barrier reef or beach dune complex the northern part of the ridge complex is capped by the houtman abrolhos reef platforms subphotic sediments on the deep outer shelf and upper slope affected by seasonal upwelling are typical cool water poorly sorted bryozoan dominated deposits rich in small foraminifers and sponge spicules the inner part of the more structurally active carnarvon ramp ranges from steep eolianite cliffs to hypersaline environments of shark bay to the ningaloo fringing reef mid ramp sediment especially off shark bay is mostly relict or stranded and foraminifer dominated sand with abundant mg calcite cemented intraclasts these sediments accumulating on a relatively barren seafloor likely represent attenuated carbonate production brought about by downwelling and episodic incursions of saline shark bay derived waters onto the ramp the outer ramp is either planktic foraminiferal sand sorted by strong bottom currents or spiculitic mud such sedimentation patterns should typify the western margins of large ocean basins during those periods in geologic history when circumglobal equatorial circulation was active and equatorial gateways narrow in contrast to eras of supercontinents when cool water carbonate sedimentation and upwelling prevailed in similar settings furthermore because low latitude trade winds relax during glacial epochs and the cool water upwelling belt moves equatorward into otherwise tropical realms temperate and subtropical sedimentation patterns in these regions should oscillate at the 100 ky scale in the stratigraphic record

geomorphic evidence of major sea level fluctuations during marine isotope substage 5e cape cuvier western australia abstract a detailed geomorphologic and morphostratigraphic investigation of raised marine terraces at cape cuvier western australia reveals two morphologically distinct units a lower well developed accretional reef terrace between 3 and 5 5 m above mlws mean low water springs hereafter denoted as represents an extended interval of stable sea level an upper erosional terrace and incipient coralgal rim between 8 5 to 10 5 m represents a brief sea level stillstand at this higher elevation these features suggest the lower and upper terraces developed during discrete sea level events in an attempt to better define the timing of emplacement of each marine unit 20 coral samples collected along vertical and lateral reef growth axis from both terraces were analysed with u series dating unfortunately all coral samples exhibited elevated 234 u initial values suggesting that pervasive uptake of 234 u enriched uranium and 230 th thorium had occurred despite the shortcomings of absolute dating a succession of events can be resolved though morphostratigraphic relationships comparison of the facies relationships coral growth and morphostratigraphic features between the lower and upper terraces indicates that an early to mid mis 5e stillstand at 3 to 5 m was followed by a late rise to 8 5 to 10 5 m this agrees with an emerging global view of mis 5e sea level history derived from stable carbonate platforms rejecting the hypothesis that these higher sea level benchmarks are an artefact of localized tectonic processes

the distribution of carbonate eolianite abstract carbonate eolianite forms distinctive coastal landforms on many mid latitude continents and islands numerous studies of extensive continental and smaller island deposits in both hemispheres have shown the eolianites are predominantly pleistocene in age the coorong coastal plain of south australia contains the world s longest record of eolianite deposition revealing that major phases of carbonate accumulation occurred during interglacial and some interstadial sea level highstands throughout the quaternary similarly the well studied eolianite islands of bermuda and the bahamas record a close match between dune accretion and sea level highstands since the middle pleistocene several other eolianite deposits appear to have formed at least partially during glacial periods the glacial age deposits are eolian reworked relict shelf or coastal sediments or remnants of former highly mobile coastal dunes sourced from low sea level shorelines the distribution and bioclastic composition of large scale eolianite deposits suggests carbonate production on shallow shelves and banks is the ultimate control on the formation of eolianite the bulk of the carbonate comprising those eolianites is heterozoan being produced where there is low terrigenous sediment input in dominantly temperate cool water and subtropical carbonate provinces quaternary cyclical movements of sea level have also controlled the form and rate of coastal carbonate deposition with repeated pulses of sedimentation during highstands forming laterally coalesced vertically stacked or composite dune successions major unconformities within the deposits are marked by paleosols which record hiatuses in coastal sedimentation in several regions major eolianite units overlie coastal deposits of terrigenous sediment those successions suggest that the trend towards aridity and reduction in the supply of terrigenous sediment to shelves during the quaternary has enhanced the production of carbonate and the deposition of eolianite

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

current controlled sediment deposition from the shelf to the deep ocean the cenozoic evolution of circulation through the sw pacific gateway the circulation of cold deep water is one of the controlling factors of the earth s climate forty percent of this water enters the world ocean through the southwest pacific as a deep western boundary current dwbc flowing northwards at bathyal to abyssal depths east of the new zealand microcontinent south of latitude 50 s the dwbc is intimately linked with the antarctic circumpolar current acc which is the prominent force for the shallow water circulation the pacific dwbc is presently the largest single contributor of deep ocean water and deciphering its evolution is of fundamental importance to understanding ocean and climate history and global ocean hydrography the evolution of the dwbc system and of related circum antarctic currents has taken place since 30 25 ma when plate movements created the first oceanic gaps south of australia and south america the stratigraphic record preserved in sediment drifts of the southwest pacific in eastern new zealand is the best available for deciphering the neogene history of southern ocean water masses and of the circulation of the acc dwbc and their precursor systems major current activity commenced on the new zealand margin in the late eocene or early oligocene hoiho drift early acc and was widespread by the mid late oligocene marshall paraconformity and weka pass limestone drift acc during the neogene the eastern south island continental shelf built seawards by accretion at its outer edge of large miocene current drifts up to tens of kilometres long and hundreds of metres thick canterbury drifts also commencing in the mid cenozoic but in depths 2000 m the dwbc emplaced large deep water sediment drifts rates of drift deposition accelerated considerably in the late neogene when climatic change and particularly glacial sea level falls caused the delivery of large volumes of turbiditic sediment into the path of the dwbc via the bounty and hikurangi channels

evidence from middle ordovician paleosols for the predominance of alkaline groundwater at the dawn of land plant radiation atmospheric carbon is estimated to have been 500 times more abundant in hadean time than at present and its concentration has been gradually decreasing since then due to its storage in sedimentary rocks consequently rain ph has been gradually increasing through geologic time leading to the common assumption that groundwaters are less acidic today than they were in the distant past however this assumption overlooks the fact that root forming land plants increase the carbonic acid concentration in soils by one or two orders of magnitude in the absence of rooted land plants reactions between minerals and rainwater are known to promote alkalinity it is hypothesized that groundwater ph must have been on average highest shortly before the late ordovician to silurian proliferation of root forming land plants to verify this hypothesis we studied the mineralogy and geochemistry of the youngest known pre silurian paleosols to have developed on primary rocks and provide evidence that they have evolved in predominantly alkaline groundwaters despite warm and humid paleoenvironmental conditions today a lush vegetation cover would thrive in such a climate and the system would be necessarily acidic due to large inputs of organic acids paired with previous observations indicating that early paleozoic sedimentary rocks are especially rich in detrital illite and k feldspar there is now enough evidence to believe that there was a greater tendency for alkalinity during this time period than during previous and subsequent geologic periods

facies architecture and controlling factors induced depositional model of the quaternary carbonate eolianites in the northwestern mediterranean coast of egypt

biogeographic impact of the leeuwin current in southern australia since the late middle eocene abstract the leeuwin current can be tracked from the western margin of the australian continent to the southern margin by the record of fossilized organisms typical of warm water marine environments this transport smudges the normal latitudinal asymmetry in the biotas of opposing oceanic and continental margins in which the eastern margins of oceans are cooler than the western margins and warmer biotas are restricted to lower latitudes in the east the most comprehensive record is in the large benthic foraminifera although fossils of benthic invertebrates nektonic nautiloids and planktonic protists are also informative in addition organic biomarker hydrocarbons in stranded bitumens and resins demonstrate that they have travelled the same route from their ultimate sources in cenozoic sedimentary basins and modern tropical rainforests of the indonesian archipelago the earliest spoor of the current is in the later middle eocene at which time the part deflection of counter gyral circulation in the indian ocean to the southeast was stimulated by the accelerated opening of the oceanic gap between australia and antarctica thus the origin of the leeuwin current is twice the age of the previously suggested origin in the miocene the current turns on and turns off in the great australian bight during the late quaternary in concert with the interglacials and the glacials at scales of 10 5 yr the switch can be seen in the faunal succession of planktonic foraminifera which are consistent with the neritic benthic faunas of the central gulfs both communities show that at the warm peak of the last interglacial the current transported biota across the bight more strongly than it has during the holocene the cenozoic record of the past 40 ma is in the same mode at 10 6 yr scales the relevant fossils are found concurrently at major marine transgressions and warming reversals of the overall fall in global temperature however the fossil pattern is due to transport on the activated leeuwin current not merely to general warming and the spread of friendly environments to higher latitudes

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

whole rock aminostratigraphy and quaternary sea level history of the bahamas abstract the surficial geology of the tectonically stable bahamian archipelago preserves one of the most complete records of middle to late quaternary sea level highstand cycles in the world however with the exception of deposits from marine isotope substage mis 5e fossil corals for radiometric dating of this rich stratigraphic sequence are rare this study utilizes the previously published independent lithostratigraphic framework as a testing ground for amino acid racemization in whole rock limestone samples at least six limestone soil couplets provide a relative age sequence of events that encompass as many interglacial glacial cycles d alloisoleucine l isoleucine data fall into six clusters or aminozones on the basis of independent dating and the inferred correlation with global mis the ages of several aminozones are known while the ages of others are calculated from calibrated amino acid geochronology this study demonstrates the utility of the whole rock aminostratigraphy method for dating and correlating widespread emergent marine deposits constitutes the first regional geochronological framework for the bahamas and highlights major sea level events over the past half million years

sahke geophysical transect reveals crustal and subduction zone structure at the southern hikurangi margin new zealand 1 the seismic array hikurangi experiment sahke investigated the structure of the forearc and subduction plate boundary beneath the southern north island along a 350 km transect tomographic inversion of first arrival travel times was used to derive a well resolved 15 20 km deep p wave image of the crust the refracted phases and migrated reflection events image subducting slab geometry and crustal structure in the west australian plate moho depth decreases westward across the taranaki fault system from 35 to 28 30 km in the east subducted pacific plate oceanic crust is recognized to have a positive velocity gradient but becomes less distinct beneath the tararua ranges where the interface increases in dip at about 15 km depth from 15 this bend in the subducted plate is associated with vertical clusters in seismicity splay fault branching and low velocity high attenuation material that we interpret to be an underplated subduction sedimentary channel we infer that a step down in the decollement transfers slip on the plate interface at the top of a subduction channel to the oceanic crust and drives local uplift of the tararua ranges reflections from the wairarapa fault show that it is listric and soles into the top of underplated sediments which in turn abut the moho of the overriding plate at 32 km depth near the downdip end of the strongly locked zone the change in dip of the hikurangi subduction interface is spatially correlated with the transition from geodetically determined locked to unlocked areas of the plate interface

chronology of quaternary coastal aeolianite deposition and the drowned shorelines of southwestern western australia a reappraisal abstract aeolianite successions of low gradient continental margins commonly show complex records of coastal dune deposition linked to a wide range of sea level positions and climatic periods of the middle and late pleistocene recording both regional and broader scale drivers of sediment production coastal dune development and landform preservation to better characterise the general pattern of sedimentation that occurs over quaternary glacial interglacial cycles on low gradient temperate carbonate continental shelves we examine the morphology stratigraphy and age of aeolianite deposits in the perth region western australia this includes an analysis of well defined drowned coastal landforms preserved on the adjacent shelf new and previously published optical ages provide a preliminary timeframe for the deposition of aeolianite in the perth region and on rottnest island 17 km offshore an extensive aeolianite ridge near perth representing a former barrier has optically stimulated luminesence osl ages that range from 120 12 to 103 10 ka mis 5e 5a in the context of associated age uncertainties osl ages for an exposure in the same ridge 2 5 km inland record the onlap of much older aeolianite osl age 415 70 ka by shell rich estuarine beds osl age 290 30 ka a further 5 5 km inland from the coast two thick aeolianite units separated by a well developed palaeosol have stratigraphically consistent osl ages of 310 30 and 155 20 ka in contrast aeolianite units that form the northern coast of rottnest island have osl ages of 77 12 ka and 27 5 ka the new osl ages and previously reported tl and u th ages indicate that the bulk of the island comprises dunes deposited around the end of the last interglacial sensu lato mis 5a 4 and during the last glacial mis 4 2 accumulating over a last interglacial coral reef and basal calcarenite drowned barrier and dune landforms preserved on the adjacent continental shelf reveal that barriers were formed during periods of intermediate sea level e g mis 3 and significant dune mobility occurred when the shelf was subaerially exposed the pattern of shelf sedimentation discernible in the perth region large scale coastal carbonate dune deposition during periods of high and intermediate sea level and reactivation during glacial lowstands is largely consistent with published stratigraphic and age data for large scale aeolianite deposits on other low gradient carbonate shelves based on these data a general model is proposed for the cycle of quaternary sedimentation and landform evolution that occurs on these shelves which are dynamic sedimentary environments with coastal landforms and sedimentary successions that are very sensitive to erosion and sediment reworking

climatic cycles inferred from the aminostratigraphy and aminochronology of quaternary dunes and palaeosols from the eastern islands of the canary archipelago aminochronological and aminostratigraphical methods have been used to study the quaternary a e o l i a n deposits f r om the islands located east of the canary archipelago fuerteventura and lanzarote islands and la graciosa montana clara and alegranza islets t h e extent of racemisation epimerisation of four amino acids isoleucine aspartic acid phenylalanine and glutamic acid was measured in land snail shells of the genus theba the age calculation algorithms of these amino acids h a v e b e e n determined to permit t he numerical dating of these deposits eight a m i n o z o n e s e a ch defining dune palaeosol formation episodes have been distinguished and dated at 4 8 6 6 4 42 5 6 0 37 8 4 6 29 4 4 8 22 4 4 5 14 9 3 6 11 0 4 0 and 5 4 1 1 ka b p t h e first f i ve of t h em defining c y c l e s of 5 7 ka the alternation of palaeosols and a e o l i a n deposits w h i c h are related to abrupt transitions from humid to arid conditions are t he reflection of globally induced changes in north africa palaeoenvironmental conditions linked to the effect of african palaeomonsoons on the trade w i n d s and the saharan air layer probably these a eolian cycles with a recurrence neriod of 5 7 ka are t he expression of multiples of the 2 4 ka solar cycle

late cenozoic evolution and earthquake potential of an active listric thrust complex above the hikurangi subduction zone new zealand in the center of the frontal wedge of the hikurangi subduction zone new zealand mahia peninsula and its submarine continuation lachlan ridge are being uplifted and folded above an active landward dipping thrust fault complex that is 80 km long high quality marine seismic reflection profiles reveal complex deformation of a cretaceous to holocene sedimentary section and enable a detailed analysis of the stratigraphy structural evolution deformation rates and future earthquake potential the structural analysis is facilitated by uplifted marine terraces on mahia peninsula and by 14 submarine unconformities in the hanging wall sequence five of which are correlated across the eroded crest of lachlan ridge and into the footwall basin the ages of the unconformities are determined by seismic ties to an offshore exploration well onshore outcrops on the peninsula and seabed samples dated by pollen coccolith nannoflora and foraminifera biostratigraphy nine regional quaternary unconformities which developed in response to eustatic fluctuations in sea level and are not older than ca 1 ma are correlated with oxygen isotope stages in equatorial pacific ocean drilling project core 677 the ages of fault growth strata and progressive restorations of deformed stratigraphy indicate that lachlan ridge developed during three phases of deformation since subduction of the pacific plate commenced beneath the australian plate in the early miocene these include an initial phase of thrust faulting a subsequent phase dominated by extensional faulting and the current mainly pleistocene to holocene phase of structural inversion reactivated listric thrust faulting and folding early to middle miocene thrusts in the deeper core of the complex developed out of sequence by sequentially stepping up into the hanging wall section creating an imbricate fan with emerging thrust tips now buried within the forelimb basin in the middle miocene early pliocene listric extensional faults developed in the active thrust wedge possibly as a result of substantial relief on the subducted pacific plate and controlled the development of lachlan basin to the west of the ridge the principal active thrust is the lachlan fault a listric extensional detachment reactivated to accommodate thrust movement and consisting of at least three right stepping segments depth converted seismic profiles indicate that the fault dips westward at 15 20 6 8 km beneath the western flank of lachlan ridge and steepens to 55 70 or even steeper in the upper 1 2 km of section beneath the eastern flank syninversion pleistocene fault growth strata on both flanks of the associated anticline provide an exceptional record of progressive fold limb rotation resulting from the listric fault geometry a geometric analysis of the fault growth strata and deformed terraces was used to derive a maximum dip slip displacement rate of as fast as 3 0 6 5 mm yr the implied shortening rate of 2 6 6 3 mm yr represents 8 20 of the total 31 mm yr of orthogonal plate convergence across this part of the upper plate of the hikurangi subduction zone the top of the pre fault growth paleogene section reveals as much as 5 8 1 5 km of vertical separation in the north decreasing to 30 50 of this value in the south temporal 10 3 10 6 yr and spatial 10 3 10 4 m of strike length variations in vertical deformation rate have occurred during the past 1 m y maximum rates occurred in the holocene and middle quaternary a long term increase in vertical separation rate on all segments during the pleistocene largely reflects a change in thrust kinematics associated with structural inversion the relatively greater increase in uplift rate on the northern part of the fault during the past 1 m y could be related to the possibility that a subducted seamount lies 10 km beneath the peninsula estimates of earthquake source parameters incorporating paleoseismic uplift data from mahia peninsula indicate a potential moment magnitude of up to m w 7 6 8 0 for an earthquake that ruptures all three segments of the lachlan fault the average recurrence interval for such events is estimated to be 615 2333 yr which is consistent with a mean recurrence interval of 1062 yr for four late holocene earthquakes thus the uplift and folding of mahia peninsula and lachlan ridge results from coseismic displacements on a major listric thrust fault that ruptures the upper plate frequently in association with large magnitude earthquakes

aminostratigraphy and ages of pleistocene limestones of bermuda the pleistocene stratigraphy of bermuda offers important information for sea level history corals are rare in bermuda pleistocene carbonates and so many deposits are not appropriate for u series dating we have extended the geochronological base in bermuda by determining the extent of isoleucine epimerization a i ratios in 1 marine shells glycymeris and others from deposits of sea level high stands 2 land snails poecilozonites from protosols associated with the eolianites that comprise the bulk of bermuda and 3 whole rock samples of bioclastic calcarenites the three distinct types of samples provide independent aminostratigraphies aminozones c e f g h j and k that are mutually consistent and in agreement with the mapped lithostratigraphy correlation of the amino acid ratios with ages based on previously published u series coral dates verifies the utility of the apparent parabolic kinetics model for estimation of amino acid racemization ages extrapolation of ages based on the model to deposits beyond the range of u series dating reveals that a significant middle pleistocene section is present in bermuda

u series and amino acid racemization geochronology of bermuda implications for eustatic sea level fluctuation over the past 250 000 years abstract bermuda is a stable mid oceanic carbonate platform for which a particularly complete record of late pleistocene eustatic sea level fluctuation has been reconstructed from a detailed study of geological field relationships combined with an extensive programme of u series and amino acid racemization geochronology only twice in the past 250 000 yr has sea level in bermuda been above its present level once at approximately 200 k y when it stood at about 2 m and most recently at 125 4 k y when it stood at 5 1 m these times of interglacial high sea level are characterized by the development of patch reefs and marine calcarenites at elevations above present sea level episodes of lower sea stand onto the bermuda platform at elevations higher than 20 m are observed within the two interglacial periods and are characterized by the deposition of eolianites by contrast glacial periods are times of residual soil formation and deposition of speleothems in caves at elevations below present sea level excellent correlation is observed between the bermuda glacio eustatic sea level record and other marine and terrestrial paleoclimate records

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

pleistocene holocene environmental change in the canary archipelago as inferred from the stable isotope composition of land snail shells abstract the isotopic composition of land snail shells was analyzed to investigate environmental changes in the eastern canary islands 28 29 n over the last 50 ka shell 13c values range from 8 9 to 3 8 at various times during the glacial interval 15 to 50 ka moving average shell 13c values were 3 higher than today suggesting a larger proportion of c4 plants at those periods shell 18o values range from 1 9 to 4 5 with moving average 18o values exhibiting a noisy but long term increase from 0 1 at 50 ka to 1 6 1 8 during the lgm 15 22 ka subsequently the moving average 18o values range from 0 0 at 12 ka to 0 9 at present calculations using a published snail flux balance model for 18o constrained by regional temperatures and ocean 18o values suggest that relative humidity at the times of snail activity fluctuated but exhibited a long term decline over the last 50 ka eventually resulting in the current semiarid conditions of the eastern canary islands consistent with the aridification process in the nearby sahara thus low latitude oceanic island land snail shells may be isotopic archives of glacial to interglacial and tropical subtropical environmental change

variation in syn subduction sedimentation patterns from inner to outer portions of deep water fold and thrust belts examples from the hikurangi subduction margin of new zealand

pleistocene aeolianites at cape spencer south australia record of a vanished inner neritic cool water carbonate factory aeolianites are integral components of many modern and ancient carbonate depositional systems southern australia contains some of the most impressive and extensive late cenozoic aeolianites in the modern world pleistocene aeolianites on yorke peninsula are sculpted into imposing seacliffs up to 60 m high and comprise two distinct imposing complexes of the late pleistocene bridgewater formation the lower aeolianite complex which forms the bulk of the cliffs is a series of stacked palaeodunes and intervening palaeosols the diagenetic low mg calcite sediment particles are mostly bivalves echinoids bryozoans and small benthic foraminifera this association is similar to sediments forming offshore today on the adjacent shelf in a warm temperate ocean by contrast the upper aeolianite complex is a series of mineralogically metastable biofragmental carbonates in a succession of stacked lenticular palaeodunes with impressive interbedded calcretes and palaeosols bivalves geniculate coralline algae and benthic foraminifera together with sparse peloids and ooids dominate sediment grains fragments of large benthic foraminifera including marginopora vertebralis a photosymbiont bearing protist are particularly conspicuous palaeocean temperatures are interpreted as having been sub tropical somewhat warmer than offshore carbonate factories in the region today the older aeolianite complex is tentatively correlated with marine isotope stage 11 whereas the upper complex is equivalent to marine isotope stage 5e marine isotope stage 5e deposits exposed elsewhere in southern australia glanville formation are distinctive with a subtropical biota including marginopora vertebralis thus in this example palaeodune sediment faithfully records the nature of the adjacent inner neritic carbonate factory by inference aeolianites are potential repositories of information about the nature of long vanished marine systems that have been removed due to erosion tectonic obliteration or are inaccessible in the subsurface such information includes not only the nature of marine environments themselves but also palaeoceanography

thermoluminescence dating of aceolianites from lord howe island and south west western australian abstract views differ as to how the deposition of aeolianites correlate with glacial interglacial cycles this study evaluates the potential of thermoluminescence tl dating to determine the timing of aeolianite deposition at two australian sites the study areas are rottnest island and the fremantle coastline in western australia and lord howe island in the tasman sea the chronostratigraphy of aeolianite on lord howe island has been comprehensively examined by brooke 1999 whereas the depositional chronology of western australian aeolianite is known only from dating at one or two key sites tl dating provides a chronological framework for both sites and reveals that the timing of deposition of these aeolianites is probably related to sediment supply dune and minor associated marine deposits of lord howe island appear to have been emplaced mainly during sea level highstands when the shelf surrounding the island was flooded and beach sediments accumulated in contrast the aeolianites upon rottnest island and along the adjacent western australian coastline seem to have been deposited during periods of both high and low sea level indicating a more continuous supply of shallow marine sediments

significance of aeolian limestone lenses in quartz sand formations an interdigitation of coastal and continental facies perth basin southwestern australia abstract in the quaternary of the perth basin of southwestern australia the transition from coastal dune ridges to continental siliciclastic sand hinterland is a zone of calcareous sand or limestone lenses on or within siliciclastic sand in the holocene sequences the transition is a zone of landward extended and detached parabolic dunes which in section appear as lenses of calcareous sand resting on pleistocene quartz sand and limestone in the pleistocene sequences aeolian limestone lenses are common in thick sections of yellow quartz sand using the holocene coast to hinterland transition as an analogue the limestone lenses are interpreted to be buried outliers of attenuated parabolic calcareous dunes that migrated inland over an undulating plain of yellow quartz sand from a pleistocene coastal zone these dunes were later buried by influxes of aeolian yellow quartz sand during glacial age desert phases of the pleistocene in section these buried dunes form a zone of limestone lenses within aeolian quartz sand formations thus in a given time interval limestone lenses represent the transition between coastal and hinterland continental desert environments and record the extent that coastal dunes penetrated inland the pleistocene stratigraphic model of aeolian limestone lenses set within a sequence of aeolian siliciclastic sand is a distinctive style of coastal to continental transition which can be used to unravel similar sequences in the stratigraphic record where coastal aeolian calcareous facies interdigitate with desert aeolian siliciclastic facies

optically stimulated luminescence dating of holocene relict foredunes guichen bay south australia abstract optically stimulated luminescence osl dating of quartz sand 106 150 or 150 200 m in bioclastic carbonate quartz sediments sampled from coastal relict foredunes beach ridges was undertaken to evaluate the utility of the osl method for studies of dune dynamics and to quantify rates of coastal progradation twelve sediment samples from a 4 km transect across a holocene embayment fill at guichen bay south australia were measured for their luminescence characteristics apart from one age inversion attributed to recent disturbance associated with mining the osl ages are in sequential order when considered in the context of their associated error terms the osl ages indicate an extremely rapid initial phase of sedimentation i e 1600 m within a few hundred years approximately 5 ka ago followed by a constant rate of progradation for the past 4 ka of 0 39 m a with a high level of association between distance across the embayment fill and luminescence age for this time interval an average rate of dune development of one dune every 80 yr from 3900 yr ago to the present day is apparent the osl ages for the late holocene indicate that the present beach state is largely in equilibrium with sediment supply

tectonic and geological framework for gas hydrates and cold seeps on the hikurangi subduction margin new zealand the imbricated frontal wedge of the central hikurangi subduction margin is characteristic of wide ca 150 km poorly drained and over pressured low taper not vert similar 4 thrust systems associated with a relatively smooth subducting plate a thick trench sedimentary sequence not vert similar 3 4 km weak basal decollement and moderate convergence rate not vert similar 40 mm yr new seismic reflection and multibeam bathymetric data are used to interpret the regional tectonic structures and to establish the geological framework for gas hydrates and fluid seeps we discuss the stratigraphy of the subducting and accreting sequences characterize stratigraphically the location of the interplate decollement and describe the deformation of the upper plate thrust wedge together with its cover sequence of miocene to recent shelf and slope basin sediments we identify approximately the contact between an inner foundation of deforming late cretaceous and paleogene rocks in which widespread out of sequence thrusting occurs and a 65 70 km wide outer wedge of late cenozoic accreted turbidites although part of a seamount ridge is presently subducting beneath the deformation front at the widest part of the margin the morphology of the accretionary wedge indicates that frontal accretion there has been largely uninhibited for at least 1 2 myr this differs from the offshore hawkes bay sector of the margin to the north where a substantial seamount with up to 3 km of relief has been subducted beneath the lower margin resulting in uplift and complex deformation of the lower slope and a narrow 10 20 km active frontal wedge five areas with multiple fluid seep sites referred to informally as wairarapa uruti ridge omakere ridge rock garden and builders pencil typically lie in 700 1200 m water depth on the crests of thrust faulted anticlinal ridges along the mid slope uruti ridge sites also lie in close proximity to the eastern end of a major strike slip fault rock garden sites lie directly above a subducting seamount structural permeability is inferred to be important at all levels of the thrust system there is a clear relationship between the seeps and major seaward vergent thrust faults near the outer edge of the deforming cretaceous and paleogene inner foundation rocks this indicates that thrust faults are primary fluid conduits and that poor permeability of the cretaceous and paleogene inner foundation focuses fluid flow to its outer edge the sources of fluids expelling at active seep sites along the middle slope may include the inner parts of the thrust wedge and subducting sediments below the decollement within anticlinal ridges beneath the active seep sites there is a conspicuous break in the bottom simulating reflector bsr and commonly a seismically resolvable shallow fault network through which fluids and gas percolate to the seafloor no active fluid venting has yet been recognized over the frontal accretionary wedge but the presence of a widespread bsr an extensive protothrust zone 200 km by 20 km in the hikurangi trough and two unconfirmed sites of possible previous fluid expulsion suggest that the frontal wedge could be actively dewatering there are presently no constraints on the relative fluid flux between the frontal wedge and the active mid slope fluid seeps article outline

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

neogene history of the deep western boundary current at rekohu sediment drift southwest pacific odp site 1124 abstract odp site 1124 located 600 km east of the north island of new zealand records post middle oligocene variations in the pacific deep western boundary current dwbc and new zealand s climatic and tectonic evolution sediment parameters such as terrigenous grain size flux magnetic fabric and non depositional episodes are used to interpret dwbc intensity and antarctic climate interpretations of dwbc velocities indicate that the antarctic circumpolar current reached modern intensities at 23 ma as the tectonic seaways expanded completing the thermal isolation of antarctica periods of more intense bottom water formation are suggested by the presence of hiatuses formed under the dwbc at 22 5 17 6 16 5 15 and 14 11 ma the oldest interval of high current intensity occurs within a climatically warm period during which the intensity of thermohaline circulation around antarctica increased as a result of recent opening of circum antarctic gateways the younger hiatuses represent glacial periods on antarctica and major fluctuations in the east antarctic ice sheet whereas intervals around the hiatuses represent times of relative warmth but with continued current activity the period between 11 to 9 ma is characterized by conditions surrounding a high velocity dwbc around the time of the formation and stabilization of the west antarctic ice sheet the increased terrigenous input may result from either changing antarctic conditions or more direct sediment transport from new zealand the pacific dwbc did not exert a major influence on sedimentation at site 1124 from 9 ma to the present the late miocene to pleistocene sequence is more influenced by the climatic and tectonic history of new zealand despite the apparent potential for increased sediment supply to this site from changes in sediment channeling increasing rates of mountain uplift and volcanic activity terrigenous fluxes remain low and constant throughout this younger period

timing and warmth of the last interglacial period new u series evidence from hawaii and bermuda and a new fossil compilation for north america abstract the timing and duration of the last interglacial period have been controversial with some studies suggesting a relatively short duration that is orbitally forced and others suggesting a long duration that is at most only partly related to orbital forcing new high precison thermal ionization mass spectrometric tims u series ages of last interglacial corals from hawaii and bermuda test these competing hypotheses waimanalo formation corals from slowly uplifting oahu hawaii range in age from 134 to 113 ka with most ages between 125 and 115 ka combined with published u series ages from nearby lanai the data suggest a long last interglacial period that may have occurred from 136 to at least 115 ka the results indicate that orbital forcing may not have been the only control on ice sheet growth and decay because sea level would have been high at times of relatively low northern hemisphere summer insolation on tectonically stable bermuda deposits from the 200 ka penultimate interglacial period 120 ka peak last interglacial period and 80 ka late last interglacial period high sea stands have been newly dated fossil corals on bermuda are derived from patch reefs that likely were catch up responses to sea level rise it is expected that u series ages of last interglacial corals on bermuda should overlap with but not be as old as the range of corals on oahu last interglacial corals on bermuda give a range of 125 113 ka which supports this hypothesis a large number of emergent marine deposits on hawaii bermuda and along coastal north america have now been dated to the last interglacial period both oahu and bermuda have marine invertebrate faunas with a number of extralimital southern species of mollusks suggesting warmer than present waters during the last interglacial period warmer waters are also suggested for last interglacial localities around most of north america from florida to canada and greenland and baja california to alaska these observations are consistent with similar warm water faunas of last interglacial age reported from japan the mediterranean basin and western australia it is likely that significant changes in ocean currents took place during the last interglacial period with a movement of relatively warm waters to higher latitudes than is the case today

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

large scale reorganization of ocean currents offshore western australia during the late quaternary abstract the history of coastal surface currents in the eastern indian ocean over the last 130 kyr has been studied through the application of the fi 2 transfer function to planktic foraminifera in deep sea cores in a n s transect offshore western australia the concept of sea surface temperature sst gradient residuals is the amount by which the sea surface temperature gradient of a given time differs from that in the modern sea the sst gradient residuals for several episodes of climate extremes in the late quaternary the last glacial maximum 20 kyr b p the last interglacial maximum 122 120 kyr b p and at the end of the penultimate glaciation 130 kyr b p indicate that areas north of 18 s off western australia have changed very little during the extremes in climate over the last 130 kyr while south of 18 s there have been significant changes in surface water temperatures large areas of anomalously cool surface water were established off north west cape 22 s 24 s during both glacial and interglacial extremes these reflect the increased influence of the west australian current on the surface water circulation during the last glacial maximum and at the end of the penultimate glaciation cold sea surface temperature anomalies were established near to the coast indicating that the leeuwin current did not warm the coastal zone as it does today during the last interglacial maximum the leeuwin current flowed as an intensified current in a narrow zone close to the coast but did not significantly warm surface waters offshore as far as 20 25 s where a zone of cold water was maintained

the enigma of 3400 years bp coastal oolites in tropical northwest western australia why then why there oolites crop out along the northwestern coast of western australia at port smith about 80 km swof broome an oolitic coastal ridge truncated by marine erosion exposes subtidal intertidal and supratidal aeolian facies the deposits are firmly indurated and composed of about 75 tangentially and moderately thickly layered aragonitic ooid grains with over 90 quartz nuclei subtidal sedimentary structures are exposed about a metre above the present high tide mark hinting that sea level may have been somewhat higher when the shoreline was formed however the macrotidal range of up to 7 m and the possibility of cyclonic surges along the coast precludes unequivocal determinations on this point whole rock amino acid racemisation aar geochronology epimerisation of isoleucine d alloisoleucine l isoleucine or a i on each facies of the oolite outcrop averaged 0 106f0 013 n 10 the modern beach contains fewer ooids 30 and nearly half of these are stained brown grey or black perhaps as a result of burial reduction and or mineralization a higher older mean and large standard deviation in whole rock amino acid ratio of 0 145f0 067 n 2 supports our inference that ooids on the modern beach were reworked from fossil deposits reverse phase chronostratigraphy rpc on individual ooid grains holds tremendous promise in this preliminary study rpc results show a narrow variation of d l values cv 6 11 and yield nearly identical d l asp means from light coloured fossil ooids 0 307f0 018 n 17 light 0 323f0 026 n 12 and dark coloured ooids 0 298f0 027 n 10 from the active beach face when compared to a i ratios from 14 c dated mid holocene ooids in the bahamas the mean a i from port smith reflects an age of ca 3500 4500 years that is in agreement with a calibrated ams 14 c age of 3370f50 calendar years bp on the same material thus the ooids were formed transported emplaced strongly cemented and largely eroded from the beach ridge in only 3400 years the environmental conditions that underlie a pulse of ooid deposition during a brief period of the mid holocene almost certainly involve extensive tidal inlets in the area a possible mid holocene oscillation 1 2 m above present and a subsequent fall to present level that terminated the process apparently a unique combination of factors produced ooids here and in only a handful of other sites in australia and the indian ocean d 2005 elsevier b v all rights reserved

neogene evolution of lower trench slope basins and wedge development in the central hikurangi subduction margin new zealand detailed analysis of the stratigraphic architecture and deformation of lower trench slope sedimentary basins permits the tectonic evolution of subduction margins to be constrained this study utilises offshore seismic reflection profiles and onshore outcrop data to examine the entire lower trench slope of the hikurangi subduction margin in the eastern north island new zealand our results constrain the main spatial and temporal changes of facies and sedimentary units since about 25 ma we demonstrate that the geometries and locations of miocene to quaternary sedimentary basins are controlled by tectonic activity and reflect stages of subduction wedge development four types of sedimentary basins have been recognized 1 flysch basins with local olistostromes at the front of seaward propagating thrust sheets 2 5 10 km wide turbidite rich trench slope basins between uplifting structural ridges i e anticlines associated with shortening within 100 km of the subduction front at the seafloor 3 30 40 km wide trench slope basins associated with an upslope increase in thrust and ridge spacing and 4 mixed siliciclastic carbonate shelves formed in association with margin uplift after filling of the wider 30 40 km trench slope basins the lateral and vertical successions of basin geometries and sedimentary infill are consistent with the overall progressive uplift of the subduction wedge formation of some of the wide trench slope basins may be accompanied by significant local subsidence and normal faulting synchronous with active shortening at the subduction front margin wide normal faulting during the middle late miocene may have formed due to upslope collapse related to tectonic erosion all of the basins studied contain major unconformities at their base and top with basin strata deposited over about 2 8 myr the short life span of these lower trench slope sedimentary basins is consistent with a succession of short paroxysmal tectonic episodes rather than continuous deformation for the duration of subduction stratigraphic discontinuities within basins e g facies changes and reversal of paleo currents also record short term tectonic events c 1 2 myr on the basin bounding structures and attest to the episodic nature of upper plate deformation in response to continuous subduction beneath the active margin

global sea level fluctuations during the last interglaciation mis 5e the geomorphology and morphostratigraphy of numerous worldwide sites reveal the relative movements of sea level during the peak of the last interglaciation marine isotope stage mis 5e assumed average duration between 13072 and 11972 ka because sea level was higher than present deposits are emergent exposed and widespread on many stable coastlines correlation with mis 5e is facilitated by similar morphostratigraphic relationships a low degree of diagenesis uranium thorium u th ages and a global set of amino acid racemization aar data this study integrates information from a large number of sites from tectonically stable areas including bermuda bahamas and western australia and some that have experienced minor uplift 2 5 m 100 ka including selected sites from the mediterranean and hawaii significant fluctuations during the highstand are evident at many mis 5e sites revealed from morphological stratigraphic and sedimentological evidence rounded and flat topped curves derived only from reef tracts are incomplete and not representative of the entire interglacial story despite predictions of much different sea level histories in bermuda the bahamas and western australia due to glacio and hydro isostatic effects the rocks from these sites reveal a nearly identical record during the last interglaciation the last interglacial highstand is characterized by several defined sea level intervals slis that include sli 1 post glacial mis 6 5e termination ii rise to above present before 130 ka sli 2 stability at 2 to 3 m for the initial several thousand years 130 to 125 ka during which fringing reefs were established and terrace morphology was imprinted along the coastlines sli 3 a brief fall to near or below present around 125 ka sli 4 a secondary rise to and through 3 4 m 124 to 122 ka followed by sli 5 a brief period of instability 120 ka characterized by a rapid rise to between 6 to 9 m during which multiple notches and benches were developed and sli 6 an apparently rapid descent of sea level into mis 5d after 119 ka u th ages are used to confirm the last interglacial age of the deposits but unfortunately in only two cases was it possible to corroborate the highstand subdivisions using radiometric ages sea levels above or at present were relatively stable during much of early mis 5e and the last 6 7 ka of mis 1 encouraging a comparison between them the geological evidence suggests that significant oceanographic and climatic changes occurred thereafter midway through and continuing through the end of mis 5e fluctuating sea levels and a catastrophic termination of mis 5e are linked to the instability of grounded and marine based ice sheets with the greenland gis and west antarctic wais ice sheets being the most likely contributors late mis 5e ice volume changes were accompanied by oceanographic reorganization and global ecological shifts and provide one ominous scenario for a greenhouse world r 2007 elsevier ltd all rights reserved

scale and structure of time averaging age mixing in terrestrial gastropod assemblages from quaternary eolian deposits of the eastern canary islands abstract quantitative estimates of time averaging age mixing in gastropod shell accumulations from quaternary the late pleistocene and holocene eolian deposits of canary islands were obtained by direct dating of individual gastropods obtained from exceptionally well preserved dune and paleosol shell assemblages a total of 203 shells of the gastropods theba geminata and t arinagae representing 44 samples stratigraphic horizons from 14 sections were dated using amino acid isoleucine epimerization ratios calibrated with 12 radiocarbon dates most samples reveal a substantial variation in shell age that exceeds the error that could be generated by dating imprecision with the mean within sample shell age range of 6670 years and the mean standard deviation of 2920 years even the most conservative approach monte carlo simulations with a non sequential bonferroni correction indicates that at least 25 of samples must have undergone substantial time averaging e g age variations within those samples cannot be explained by dating imprecision alone samples vary in shell age structure including both left skewed 17 out of 44 and right skewed distributions 26 out of 44 as well as age distributions with a highly variable kurtosis dispersion and shape of age distributions of samples do not show any notable correlation with the stratigraphic age of samples suggesting that the structure and scale of temporal mixing is time invariant the statistically significant multi millennial time averaging observed here is consistent with previous studies of shell accumulations from various depositional settings and reinforces the importance of dating numerous specimens per horizon in geochronological studies unlike in the case of marine samples typified by right skewed age distributions attributed to an exponential like shell loss from older age classes many of the samples analyzed here displayed left skewed distributions suggestive of different dynamics of age mixing in marine versus terrestrial shell accumulations