dating loess up to 800 ka by thermoluminescence thermoluminescence tl ages agreeing with expected ages have been obtained for 13 loess samples spanning the age range from 20 to 800 ka our samples are from alaska and north island new zealand and are unusual in tl dating studies of loess older than 80 100 ka by having independent age assignments that are generally well constrained from ages of associated tephra beds with the polymineral fine silt sized 4 11 m grains the partial bleach tl technique yielded expected ages up to about 350 ka whereas the total bleach method gave accurate ages in the range 100 to 800 ka thus the much disputed upper age limit of 100 150 ka for the tl dating of loess now appears to be sample and worker dependent rather than a global property of the tl signals in the tl dominant feldspars

late pliocene and quaternary glaciations of new zealand abstract evidence of late pliocene glaciations is fragmentary the ross glaciation in northwest south island is correlated with the first marine faunal evidence of marked cooling in the wanganui basin in southern north island it is inferred to be in the 2 6 2 4 ma age range the porika glaciation in a separate area of northwest south island is younger judged by palynology and is correlated with a cooling 2 2 2 1 ma bp inferred from stratigraphic evidence of lowered sea level in the wanganui basin a gap of 1 5 ma in the record of glaciations is largely filled by wanganui basin marine sediments although an unconformity cuts out the record between ca 1 45 and 1 0 ma bp since then the many sedimentary cycles caused by sea level changes are presumed to be glacio eustatic in origin uplifted interglacial marine terraces back to marine oxygen isotope stage 17 and river terraces formed by cold climate aggradation are linked into the cyclic sequence through loess and tephra in their cover beds east of the south island cores from the dsdp site 594 in the southwest pacific record the earliest glaciation and higher in the core nine periods of south island glaciation in the last 0 7 ma onshore because of uplift and erosion only the last four glaciations assigned to oxygen isotope stages 10 8 6 and 4 2 are identified being named nemona waimaunga waimea and otira glaciations they are best known in north westland northwest south island where the relations of glacial outwash and interglacial shoreline deposits are displayed the late otira glaciation stage 2 is radiocarbon dated as beginning somewhat before 22 3 ka bp culminating ca 18 ka bp and ending at ca 14 ka bp when rapid deglaciation began a relatively small advance at ca 12 ka bp may have been followed by little change until after 8 6 ka bp recession was then followed by a period of advance from ca 5 ka bp until recent centuries and a subsequent recession that still continues

the last glacial maximum in central and southern north island new zealand a paleoenvironmental reconstruction using the kawakawa tephra formation as a chronostratigraphic marker abstract kawakawa tephra formation comprising oruanui ignimbrite flow member and aokautere ash airfall member represents the products of an exceptionally large and widespread volcanic eruption from taupo volcanic centre in the north island of new zealand the eruption occurred during the last glacial maximum and is radiocarbon dated at c 22 6 ka b p thermoluminescence ages are in broad agreement with the radiocarbon age the presence of aokautere ash in loess deposits in alluvial gully fills on river terraces and its absence from unstable sites permits a detailed assessment of geomorphic activity during the last glacial maximum widespread erosion of regolith aggradation of river valleys and deposition of loess particularly in the period following eruption of the kawakawa point to a cold dry variable climate a collation of pollen data for sediments containing aokautere ash and those 14c dated in the range 17 23 ka shows that tall forest was highly restricted in the central and southern parts of the north island an apparently subalpine grassland shrubland was present at sites from present sea level to over 800 m elevation suggesting that factors other than lower temperatures such as exposure to wind and frost fire and reduced rainfall were important in controlling vegetation patterns we conclude that the interval 23 13 ka b p broadly equivalent to oxygen isotope stage 2 represents the period of greatest environmental change in the north island

towards a climate event stratigraphy for new zealand over the past 30 000 years nz intimate project it is widely recognised that the acquisition of high resolution palaeoclimate records from southern mid latitude sites is essential for establishing a coherent picture of inter hemispheric climate change and for better understanding of the role of antarctic climate dynamics in the global climate system new zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the southern hemisphere westerly circulation zone a critical transition zone between subtropical and antarctic influences new zealand has mountainous axial ranges that amplify the climate signals and consequently the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions since 1995 intimate has through a series of international workshops sought ways to improve procedures for establishing the precise ages of climate events and to correlate them with high precision for the last 30 000 calendar years the nz intimate project commenced in late 2003 and has involved virtually the entire new zealand palaeoclimate community its aim is to develop an event stratigraphy for the new zealand region over the past 30 000 years and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from northern hemisphere records e g last glacial maximum lgm termination i younger dryas an initial outcome of nz intimate has been the identification of a series of well dated high resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal yr bp to the present day high resolution records for the last glacial coldest period lgcp including the lgm sensu stricto and last glacial interglacial transition lgit from auckland maars kaipo and otamangakau wetlands on eastern and central north island marine core md97 2121 east of southern north island speleothems on northwest south island okarito wetland on southwestern south island are presented discontinuous fragmentary records comprising compilations of glacial sequences fluvial sequences loess accumulation and aeolian quartz accumulation in an andesitic terrain are described comparisons with ice core records from antarctica epica dome c and greenland gisp2 are discussed a major advantage immediately evident from these records apart from the speleothem record is that they are linked precisely by one or more tephra layers based on these new zealand terrestrial and marine records a reasonably coherent regionally applicable sequence of climatically linked stratigraphic events over the past 30 000 cal yr is emerging three major climate events are recognised 1 lgcp beginning at ca 28 000 cal yr bp ending at termination i ca 18 000 cal yr bp and including a warmer and more variable phase between ca 27 000 and 21 000 cal yr bp 2 lgit between ca 18 000 and 11 600 cal yr bp including a lateglacial warm period from ca 14 800 to 13 500 cal yr bp and a lateglacial climate reversal between ca 13 500 and 11 600 cal yr bp and 3 holocene interglacial conditions with two phases of greatest warmth between ca 11 600 and 10 800 cal yr bp and from ca 6 800 to 6 500 cal yr bp some key boundaries coincide with volcanic tephras copyright 2007 john wiley sons ltd

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

geological history of the north eastern ring plain of ruapehu volcano new zealand abstract continuous exposures along the upper waikato stream provide new insights into the north eastern ring plain of ruapehu volcano extending the known stratigraphy beyond 22 6 ka time control in the sequence is provided by five rhyolitic tephra units erupted from central north island volcanoes comprising kawakawa okaia omataroa hauparu and rotoehu tephras the sequence is dominated volumetrically by diamictons and fluvial deposits resulting both from volcanic events and periods of instability on the flanks of ruapehu within the sequence are 60 individual andesitic lapilli units derived primarily from ruapehu volcano via mostly sub plinian eruption mechanisms an average eruption rate of more than one lapilli eruption per 1000 years is estimated for the ca 60 ka record the style of deposition on the ring plain changes over time and appears to reflect climate change over the last glacial period in periods of severe climatic conditions during marine 18 o stage 4 porewan stadial and the last glacial maximum of marine 18 o stage 2 ohakean the north eastern ring plain aggraded rapidly with deposition of thick continuous diamicton sequences the other recognized cool period in the southern north island the stadial of late 18 o stage 3 ratan did not appear to induce major aggradation on the north eastern ring plain during periods of mild climate within the last glacial deposition on the north eastern ring plain was dominated by fall accession of either tephra or material reworked from other parts of the ring plain by aeolian processes

chronology of palaeoclimatic change at the end of the last glaciation analysis of sediments recorded in a piston core located east of southern north island new zealand gives a detailed record of climate change at the end of the last glacial accumulation rates1 of both detrital quartz and biological carbonate and biogenic silica components of the sediment are much higher during glacial than post glacial time and they all show a synchronous rapid decline at 14 700 yr bp we attribute this to a decline in intensity of the strong glacial westerly winds in the new zealand region as the polar winds contracted to their present latitudes2 6 the greatest rate of quartz accumulation occurs between 16 200 and 14 700 yr bp and is not matched by any change in carbonate or silica accumulation we believe this reflects accelerated fluvial transport of detritus out of the mountain ranges and consequently increased aeolian dust transport before the decline of the polar westerlies

the post glacial downcutting history in the waihuka tributary of waipaoa river gisborne district implications for tectonics and landscape evolution in the hikurangi subduction margin new zealand abstract determining the spatial and temporal deliveries of sediment from the waipaoa river catchment in the post glacial period is a major goal of integrated source to sink landscape evolution studies in the region in a 2 2 km long section of the waihuka tributary 217 km 2 of the waipaoa river 2150 km 2 in eastern north island new zealand a sequence of at least ten fluvial terraces and abandoned meanders up to 45 m above the present river records rates and times of post glacial downcutting dateable organic and tephra horizons in the terrace and meander infill stratigraphy indicate that downcutting at this location on the waihuka tributary was dominated by a short lived event in the early holocene from 10 8 ka bp when as much as half of the downcutting was accomplished in only 10 15 of post glacial time the large downcutting event is interpreted to record the passing of a succession of major knickpoints or a knickzone through this tributary the initiation of knickpoint retreat in the catchment was primarily a consequence of reduction in sediment supply at the end of mis 2 based on the timing of rapid downcutting in the waipaoa river mainstem we estimate that the rate of knickpoint retreat along the waihuka tributary was about 2 km kyr in the period before and after rapid downcutting in the waihuka tributary modest incision rates averaging 1 2 mm yr probably represent the regional tectonic uplift rate

submergent shorelines in the sw pacific evidence for an episodic post glacial transgression high resolution seismic profiles supported where possible by radiocarbon dates and regional stratigraphic data indicate that the last post glacial transgression in the sw pacific was episodic comprising major stillstands punctuated by rapid rises in sea level on the terrigenous continental shelf east of south island new zealand a succession of shorelines s8 s1 are recognized as follows s8 c 113 m 18 000 yr bp s7 c 88 m 17 000 yr bp s6 c 75 m 15 000 yr bp s5 c 56 m 12 000 yr bp s4 c 46 m 11 000 yr bp s3 c 28 m 9 500 yr bp s3a c 24 m 9 000yr bp s2 c 9 m 7 500yr s1 0 m 6 500yr bp with the exception of s8 and possibly s2 the shorelines are associated with wedges of sediment the size and presence of which imply that 1 sea level stabilized at some shorelines for a considerable period of time up to i 2 000 yr and 2 the intervening rises of sea level estimated to have been at least 10 12 m lo3 yr were too rapid to allow the reworking of the wedges into a transgressive sediment sheet as favoured in some current models on the great barrier reef shelf off queensland australia shorelines s8 sl have also been recognized with a further shoreline feature s4a occurring at c 39 m shorelines sla 0 m o yr bp slb 2 3 m 6 000 yr bp and slc 0 m 6 500 yr bp are recognized as discrete aspects of the post 6 500 yr bp sea level behaviour in north eastern australia the rapid rise in sea level at least between shorelines s5 12 000 yr bp and 53 9 500 yr bp is known to have outpaced reef growth causing in situ drowning of reefs located along the deeper shorelines all modern reefs so far drilled and dated began their development at or above s3 28 m 9 500 yr bp some of the shorelines particularly s5 appear to correlate between the northern and southern hemispheres on the basis of age succession and general depth of occurrence suggesting 1 that they may be global features controlled by the post glacial pattern of ice sheet decay and 2 that hydro isostatic adjustment may exert only a minor control on the depth of particular shorelines at least during the earlieg parts of the post glacial transgression

dust accumulation in the new zealand region since the last glacial maximum abstract loess is widespread in new zealand deposits 1 m thick cover 10 of the land area it has mainly been derived from dust deflated from river floodplains during the last glacial maximum lgm dust accumulation continues today downwind of major river floodplains most loess is quartzofeldspathic having its origins in mesozoic and neogene rocks of the axial ranges and hill country in the central north island there are deposits of volcanic loess derived from aeolian reworking of tephras loess morphology and properties vary greatly due to diverse parent materials post depositional climates and drainage conditions the widespread 26 170 cal yr kawakawa tephra provides a datum for calculating mass accumulation rates mars rates are mostly within the range 70 150 g m 2 yr 1 but enhanced deposition at one site gave a rate of 360 g m 2 yr 1 contemporary mars of 40 100 g m 2 yr 1 were determined for distances of 1 75 0 4 km downwind of the rakaia river lgm mars of quartz for two marine cores p69 q858 drilled 100 300 km east of new zealand are 40 70 g m 2 yr 1 the mar of the aeolian component of p69 is estimated to be ca 15 g m 2 yr 1

hillslope response to climate modulated river incision in the waipaoa catchment east coast north island new zealand quantifying how hillslopes respond to river incision and climate change is fundamental to understanding the evolution of uplifting landscapes during glacial interglacial cycles we investigated the interplay among uplift river incision and hillslope response in the nonglacial waipaoa river catchment located in the exhumed inner forearc of an active subduction margin on the east coast of the north island of new zealand new high resolution topographic data sets light detection and ranging lidar and photogrammetry combined with field mapping and tephrochronology indicate that hillslopes adjusted to rapid latest pleistocene and holocene river incision through the initiation and reactivation of deep seated landslides in the erodible marine sedimentary rocks of the waipaoa sedimentary system postincision deep seated landslides can occupy over 30 of the surface area the ages of tephra cover beds identified by electron microprobe analysis on 80 tephra samples from 173 soil test pits and 64 soil auger sites show that 4000 5000 yr after the initiation of river incision widespread hillslope adjustment started between the deposition of the ca 14 000 cal yr b p waiohau tephra and the ca 9420 cal yr b p rotoma tephra tephrochronology and geomorphic mapping analysis indicate that river incision and deep seated landslide slope adjustment were synchronous between main stem rivers and headwater tributaries hillslope response in the catchment can include the entire slope measured from river to ridgeline and in some cases the interfluves between incising subcatchments have been dramatically modified through ridgeline retreat and or lowering using the results of our landform tephrochronology and geomorphic mapping we derive a conceptual time series of hillslope response to uplift and climate change induced river incision over the last glacial interglacial cycle

ignimbrite morphology and the effects of erosion a new zealand case study ignimbrite morphology previously generalised using aspect ratios is here quantified as the relationships between the various thicknesses of material forming an ignimbrite and the areas and volumes represented by those thicknesses the morphology can be measured for the deposit in its present day eroded condition or reconstructed for the original deposit the reconstructed morphology of the 22 500 year bp ca 11 500 km2 ca 300 km3 oruanui ignimbrite in new zealand is documented to illustrate the latter approach the oruanui ignimbrite is an intermediate aspect ratio deposit and shows broadly linear relationships between 1 in thickness and the cumulative area occupied by that thickness or less of material and 2 thickness and the volume represented by that thickness or less of material two theoretical morphologies one where thicknesses exponentially decay with distance from a maximum and the other of uniform thickness slab are compared with the oruanui data limited comparative data suggest that low aspect ratio violently emplaced ignimbrites will show upward concave curves at one extreme following the exponential decay model and high aspect ratio gently emplaced ignimbrites downward concave curves with the slab model as an extreme when plotted on diagrams where the oruanui data show linear trends the effects of erosion on oruanui and model ignimbrite morphologies are modelled using two theoretical erosion scenarios 1 material is evenly removed from the land surface and 2 thinner non welded material is preferentially removed for the oruanui ignimbrite data area is lost much more rapidly in the first instance than volume for example 5 m of erosion is sufficient to remove 50 area whereas 40 m scenario 1 or 120 m scenario 2 of erosion is required to remove 50 volume in old ignimbrites volume estimates may be reasonably accurate even after strong erosion provided the original thicknesses of ponded landscape forming material can be inferred but estimates of original area and aspect ratio will be inaccurate an envelope enclosing all known outcrops of an ignimbrite will give a better estimate of original area and aspect ratio than simply summing the areas of known outcrops

arsenic movement and traces in the groundwater from the hetao area inner mongolia in the hetao area of inner mongolia quaternary alluvial aquifers used for the water supply are contaminated by naturally occurring arsenic which heavily affects the health of 200 000 local residents this study on the isotopes of strontium and relevant elements contained in the groundwater as well as the arsenic in the groundwater and residents hair indicates that the arsenic originally derives from the upper reaches of this area where arsenic levels are high in groundwater rock and soil over respectively 44 km work line aa and 36 km work line bb away from there the levels of arsenic in the water corresponding to the trend of the residents arseniasis decrease along the direction of the flow from 0 251 to 0 05 mg l and 0 232 to 0 036 mg l the result of this research suggests that long term strategies to deal with this arseniasis should involve finding hydrous terrains uncontaminated by water from the upper reaches and developing routes to prevent water from taking arsenic

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

relative instability of colluvium filled bedrock depressions regolith landslides commonly occur in colluvium filled bedrock depressions rather than on ridges spurs or sites with planar bedrock surfaces drained direct shear tests of colluvium from bedrock depressions in wellington new zealand indicate the presence of cohesion in all samples suggesting that thickness of accumulated deposits may become a limiting factor for stability critical depths for a range of slope angles were calculated assuming conditions of infinite limiting equilibrium and compared to the depth angle relationships for depression and interdepression regolith occurring in the field the results indicate that under saturated conditions interdepression regolith is not thick enough to permit the development of landslides colluvium filled bedrock depressions on the other hand generally exceed critical depth and must be considered susceptible to landsliding in the absence of any significant root cohesion the age of deposits and the abundance of unfailed colluvium filled bedrock depressions suggest that they have been inactive for most of post glacial time stability analysis verified by observing the occurrence of landslides indicates that recent instability has been brought about by deforestation

a 28 000 7600 cal yr bp pollen record of vegetation and climate change from pukaki crater northern new zealand a pollen record of vegetation and climate change representing the interval ca 28 000 7600 cal yr bp was obtained from a 52 5 m sediment core taken from a volcanic explosion crater at present sea level in auckland new zealand 36 59 s this provides one of the few continuous terrestrial records covering marine isotope stage 2 and part of stage 1 from the mid latitudes of the southern hemisphere chronology of the record is underpinned by eight distal taupo volcanic zone rhyolitic tephra of known age augmented by thirteen ams radiocarbon dates the last glacial maximum cooling extended from at least c 28 000 cal yr bp to ca 18 000 cal yr bp when vegetation apparently consisted of patches of beech dominated forest embedded within shrubland and grassland forest patches were probably larger or more widespread than those in central north island to the south but less extensive than further to the north in northland climate warming commenced ca 18 000 cal yr bp marked by the replacement of beech by conifers and angiosperms and by the expansion of forest at the expense of shrubland and grassland no clear late glacial climatic reversal is evident at this site early holocene forest is characterised by the replacement of the dominant forest tree prumnopitys taxifolia by dacrydium cupressinum following breach of the crater rim ca 7600 cal yr bp by rising sea level the maar was rapidly infilled with marine sediments over a period of ca 1000 years

a new 14 c age for the oruanui wairakei eruption new zealand the oruanui eruption was the largest known outburst of taupo volcano new zealand and is among the larger quaternary eruptions documented the eruption deposits are variously known as the oruanui wairakei kawakawa tephra or aokautere ash formations and represent a bulk volume probably exceeding 500 km 3 four new 14 c age determinations on carbonized vegetation in the non welded oruanui ignimbrite are combined to give a conventional age of 22590 230 yr b p compared with the previously accepted figure of 20000 yr b p this new age resolves the anomaly of apparently older 14 c ages being obtained from a demonstrably younger new zealand deposit and strengthens correlation of this eruption with an antarctic ice core acid anomaly the trace of this eruption has great potential as a time plane marker in the antarctic just prior to the last glacial maximum the close similarity in ages between the oruanui and a comparable sized eruption ito aira tn in japan suggests that this period of activity may represent the best chance of resolving any linkages between large scale explosive silicic volcanism and climate changes

climate of the last glaciation in new zealand based on aerosolic quartz influx in an andesitic terrain abstract on western north island new zealand a record of climatic change during the last glaciation is preserved in a terrestrial coverbed sequence of dominantly andesitic provenance here a succession of five loess like andisol units postdates the global high sea level stand of oxygen isotope substage 5e

tl dating studies of tephra loess and lacustrine sediments abstract a brief review is presented of my efforts to improve the accuracy of dating unheated sediments by tl and of the development of a new tephrochronometer specific applications to known age deposits are outlined as are studies of the depositional environment of subaqueous sediments removal of anomalous fading in loess by storage at 75 c for 8 days is demostrated throughout for unheated sediments the preferential use of the partial bleach r gamma or r beta technique is emphasized especially in situations where the growth curves are sublinear contrary to a widespread misconception sublinearity does not invalidate the partial bleach method furthermore examples are given of tl sensitivity or efficiency changes occurring with the regeneration technique changes that are variable and seemingly sample dependent

500 000 year paleomagnetic record from new zealand loess abstract a paleomagnetic record of secular variation has been obtained from a 17 4 m long core drilled from loess in north island new zealand three dated rhyolitic tephra occur in the loess core at depths of 1 5 3 4 and 13 0 m with ages of 22 500 42 000 and 370 000 years respectively the base of the core is estimated to be 500 000 years old which makes this the longest continuous loess sequence yet described from the southern hemisphere two periods of anomalously low inclination in the core are correlated with the mungo event ca 35 000 years ago and the emperor event ca 490 000 years ago the blake event ca 115 000 years ago is not recorded

geomagnetic field control of 14c production over the last 80 ky implications for the radiocarbon time scale we have used a recent estimate of the geomagnetic dipole field strength over the last 80 ky to examine the extent to which changes in geomagnetic field intensity have affected the radiocarbon time scale the magnetic record was converted into a 14c production signal which was then used to produce a synthetic atmospheric 14c record using a two box model for the carbon cycle this calibration suggests that the geomagnetic field has been the main factor governing the production of cosmogenic 14c atoms over the period of time considered and that 14c changes due to other causes such as climatic changes have been of lesser importance the results indicate that the radiocarbon ages are 2 to 3 ky younger than true age in the interval 18 40 ky b p in good agreement with recent u th and 14c age comparisons moreover the results predict that a negligible difference between true and 14c ages should be observed around 45 50 ky

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

cyclostratigraphy and the early jurassic timescale data from the belemnite marls dorset southern england time series based on determinations wt of calcium carbonate and total organic carbon have been generated for the entire lower jurassic hemipelagic belemnite marls dorset southern britain this formation was deposited during early pliensbachian time at a paleolatitude of about 35 n in an epicontinental sea that was largely enclosed by the supercontinent of pangea the sequence contains compositionally diverse light and dark marl bedding couplets the thicknesses of which are notably reduced in the upper third of the section the regularity of the couplets in segments of the sequence combined with a regular amplitude modulation indicates an origin that is related to the orbital precession cycle i e one of the milankovitch parameters a timescale is developed by assigning a duration of 20 k y per couplet and this suggests that the entire formation represents at least 1 78 m y using the new timescale bundles of bedding couplets are shown to have periods consistent with the 123 k y component of the orbital eccentricity variations the amplitude of the couplets varies at the same frequencies as the bundle cycles in accordance with the interpretation that the couplets record precession and the bundles record eccentricity however despite having the same frequency of variation there is no consistent relationship coherence between the variations in amplitude of the couplet cycle and the bundle cycles as would be predicted by the eccentricity precession relationship this mismatch can be explained in terms of nonlinear behavior of a climatic system characterized by a varying response time or nonlinear response of the sedimentary system itself the data contain no evidence for orbital obliquity cycles because the obliquity cycle affects insolation principally at high latitudes the climatic factors that indirectly controlled the sedimentary cyclicity must have arisen at relatively low latitudes the belemnite marls timescale indicates highly variable minimum durations for ammonite zones and subzones true durations cannot be determined because it is possible that the succession is incomplete as a result of undetected erosion and or nondeposition a combination of the new results with cyclostratigraphic data from yorkshire northeast england and the southern alps switzerland indicates based on cycle counts that the pliensbachian stage lasted at least 4 82 m y marine sr isotope ratios appear to have decreased linearly from the start of jurassic time until the end of pliensbachian time the rate of decrease in 87 sr 86 sr established using the belemnite marls timescale was 0 000042 m y or less if the main part of the formation is incomplete using this rate with the observed changes in sr isotope ratios gives minimum durations of 2 86 m y for hettangian time 7 62 m y for sinemurian time and 6 67 m y for pliensbachian time

multiple glacial advances in the rangitata valley south island new zealand imply roles for southern hemisphere westerlies and summer insolation in mis 3 glacial advances stratigraphic evidence and extensive optically stimulated luminescence osl geochronology from an 18 km long reach of the middle rangitata valley south island new zealand provide evidence for at least six distinct glacial advances during the last glacial cycle these include four well constrained marine oxygen isotope stage mis 3 and 2 advances at ca 38 ka ca 27 ka ca 21 ka and at 18 ka as well as less well constrained advances in mis 4 and or early mis 3 ice occupied a farther downvalley reach of the rangitata from 38 ka to after 18 ka indicating that near full glacial conditions persisted for most of the last 20 ka of the last glaciation though the glacier still fluctuated significantly as reflected by the numerous distinguishable advances global or regional cooling alone cannot explain the persistence of near maximum glacial conditions for this extended period nor can it explain the occurrence of the largest advances ca 32 ka instead we invoke the northward expansion of the westerlies during mis 3 as the cause for the early widespread glaciation wherein enhanced westerly flow under moderate cooling maximised glacial extents local insolation favoured extended mis 3 glaciation until ca 32 ka increasing summer insolation gradually reduced glacial extents after ca 28 ka