distribution and mechanism of neogene to present day vertical axis rotations pacific australian plate boundary zone south island new zealand remarkably little knowledge exists about mechanisms of vertical axis rotation in continental crust steeply dipping basement rocks in south island new zealand provide an opportunity to map the distribution of rotations across the pacific australian plate boundary zone and to delineate boundaries of rotated blocks in unusual detail we synthesize new structural data with new and existing paleomagnetic data with geodetic data and with patterns of neogene quaternary faulting in the strike slip marlborough fault system for the past 20 m y vertical axis rotations have been hinged about two crustal scale boundaries near the east coast the ne hinge accommodated 50 of early middle miocene clockwise rotation which caused deformation of the eastern ends of the alpine wairau and clarence strike slip faults the sw hinge has accommodated a further 30 50 of finite clockwise rotation since 4 ma and deflects active fault traces the locus of rotation has shifted southwestward astride a subduction margin that is lengthening in that direction rotating rocks are pinned to the south against a locked collision zone where the continental chatham rise impinges against the margin slip on inland strike slip faults is transformed seaward across a zone of fault termination into rigid body rotation of a large continental block that has been thrust eastward over the downgoing subducted slab of the pacific plate the rotation mechanism is a migrating hinge which resembles a flexed telephone book strike slip faults are translated through a brecciated hinge region that does not coincide with a fixed material line in the rock

hurricanes and climate in the caribbean during the past 3700 years bp a multiproxy analysis of lacustrine sediments cored in grand case pond at saint martin north of the lesser antilles archipelago reveals three distinct climatic periods for the last 3700 years from 3700 to 2500 yr cal bp and from 1150 yr cal bp to the present carbonate mud deposition occurred in connection with pond lowstands these periods were also punctuated by severe drought events marked by gypsum laminae and hurricane landfalls leading to marine sand inputs into the pond the intermediate time interval from 2500 to 1150 yr cal bp is typified by black organic mud deposition suggesting that hypoxic to anoxic conditions prevailed at the pond bottom these were probably linked with a perennial pond highstand and reflect more uniform and wetter climatic conditions than today the carbon isotopic composition of the ostracod perissocytheridea bisulcata shows that the lowest 13c values are recorded during the hypoxic periods as a consequence of bacterial recycling of isotopically depleted org

late quaternary hydrological dynamics in the middle kalahari forcing and feedbacks the kalahari region has become a major source of quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change one suite of data from palaeolacustrine landforms has recently provided a new record of major hydrological changes in the last 150 ka burrough s l thomas d s g bailey r m 2009 mega lake in the kalahari a late pleistocene record of the palaeolake makgadikgadi system quaternary science reviews in press here we present an improved analysis of the drivers and feedbacks of lake level change utilising information from three main sources data from the lake system itself from analyses of other late quaternary records within the region and from climate modelling simulations using the hadley centre coupled climate model hadcm3 suggest that once triggered the lake body was large enough to potentially affect both local and regional climates surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late quaternary through its capacity to couple middle kalahari environments to distant forcing mechanisms and to itself force environmental change we demonstrate that the existence or absence of megalake makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern africa s summer rainfall zone

magnetic polarity stratigraphy of a plio pleistocene marine sequence of north island new zealand abstract thick sequences of relatively undisturbed plio pleistocene sediments in the wanganui basin north island new zealand consist of well exposed silts clayey silts sandstones rare limestones and several tephras oriented specimens were collected from a section more than 2500 m thick and palaeomagnetic measurements were made using a c demagnetisations in fields up to 35 mt with the aid of tephrochronology the age of the upper sequence is now well established and falls within the matuyama epoch the lower two thirds of the section except for the basal 500 m is predominantly normally magnetised and is interpreted as a very extended sequence of the gauss epoch the lowest 500 m then represents the gilbert epoch the plio pleistocene boundary as defined at vrica italy falls within the upper part of the section studied in the upper nukumaruan stage for the first time a reliable correlation is made with the international boundary using as intermediaries the palaeomagnetic and tephrostratigraphy of deep sea cores from the southwest pacific as a result of the high deposition rate of the order of 1 2 m ky and the apparent lack of unconformities the temporal resolution is high short lived magnetic events are detected especially in the lower matuyama and upper gauss epochs these generally correlate well with events reported from other extended sections

late cretaceous cenozoic tectonic development of the southwest pacific region abstract a new model of the plate tectonic development of the southwest pacific integrates the continental geology of new zealand with the age structure of the surrounding oceanic crust revealed previously from magnetic anomaly lineations the model differs from previous ones in that the onland geology of new zealand is used to constrain the tectonic development in two important ways 1 the modern australia pacific plate boundary did not transect the new zealand sector until 23 million years ago 2 there has been a total of only c 500 km of dextral displacement on the plate boundary through new zealand the model is described with reference to a series of paleotectonic maps drawn to represent the setting at the times of anomalies 32 24 7 and 5 novel interpretations based on these reconstructions include the following during the late cretaceous the campbell fault was a continental transform fault between the tasman sea spreading centre and the bounty rift its 330 km of dextral displacement accompanying 25 of counterclockwise rotation of a campbell plateau block when the eastward propagating southeast indian ridge broke into the south tasman sea 57 million years ago it continued to propagate directly into southern south island and generated late eocene oligocene continental rifting through western new zealand at the same time back arc spreading in the norfolk basin caused continental rifting along a similar trend in western north island the australia pacific plate boundary originated as a transform fault between the southeast indian ridge and the pre existing kermadec trench it developed in response to the sudden cessation of spreading on the segment of the southeast indian ridge east of a fracture zone here named fracture zone z two implications arise from this model regarding the integrity of antarctica 1 1 during the cretaceous marie byrd land was probably no more than 200 km northwest of its present position 2 2 the proposition made in some earlier plate tectonic reconstructions that if the alpine fault did not form until after the late eocene there must be a late cretaceous early tertiary plate boundary within antarctica is most probably valid

preliminary results from tree increment and playa sediment cores from the paroo north western new south wales australia abstract the paroo ecosystem of far north west new south wales is sensitive to enso the paroo is also currently subject to contention for water extraction aquat conserva mar freshwater ecosystems 8 1998 361 in which information about long term ecosystem dynamics may be useful the environmental history of the paroo has not been described despite the existence of potential records in saline lakes dunes and callitris trees geomorphic and pollen analyses are used to determine the duration and nature of the pollen record in both lake and dune deposits a 2 m core recovered from one unnamed lake informally named palaeolake and the slow accumulation of sediment ca 175 years cm 1 shows the record may cover 38 k years discontinuities in the lake sediments are expected to be less than the larger southern salinas and the gaps will be partly recorded in the dune materials in tandem the tree rings from two stands of callitris glaucophylla have been tested to determine the high resolution dendroclimatological record available ring width patterns were matched between trees using skeleton plots the temporal variability of these patterns and the uniform response of the trees indicates that ring width geometry is dependant upon climate preliminary results for organic material mineral magnetic susceptibility and stratigraphy of the playa and dune facies promise a good record of pleistocene climatic change the results show that the lake records give long but temporally discontinuous information whereas tree rings provide short and relatively continuous information together they record climate changes over the last few thousand years and the impact of european management on the vegetation and rates of sediment deposition

tectonic rotations about vertical axes during the last 4 ma in part of the new zealand plate boundary zone the declinations of the primary magnetization of sedimentary rocks in the northern part of the new zealand plate boundary zone after thermal or alternating field cleaning have been used to determine tectonic rotations about vertical axes of rigid crustal blocks the pattern of rotations during the last 4 ma combined with structural style and continuity defines seven structural domains each ca 100 100 200 km across which contain crustal blocks up to 100 km across and 20 km thick large crustal blocks tens of km across in two of these domains have rotated clockwise more than 20 relative to one of the margins of the plate boundary zone in the last 4 ma their behaviour appears to be controlled by the nature of the plate boundaries such as the presence of an underlying subducted slab and the strength of the crust at the back of the overlying crustal wedge small crustal blocks 10 km across may have rotated clockwise through angles greater than 20 during the last 4 ma floating on an underlying zone of more distributed deformation the tectonic rotations of the large crustal blocks and the nature of the deformation at their boundaries combined with an interpolation of the relative plate positions can be used to reconstruct the plate boundary zone at ca 4 ma

widespread remagnetizations and a new view of neogene tectonic rotations within the australia pacific plate boundary zone new zealand 14 ma 1 than the presently observed rate of 3 4 ma 1 which is only likely to be characteristic of the tectonic regime established since 1 2 ma these new results are consistent with both long and short term deformation on the hikurangi margin being driven by realignment of the subducting pacific plate with collision of the hikurangi plateau in the late miocene potentially being key to both the initiation of tectonic rotations and the widespread remagnetization of neogene sediments however accommodating faster more coherent rotation of the hikurangi margin in neogene reconstructions of the new zealand plate boundary region particularly in the late miocene remains a challenge

an integrated method for reconstructing regional palaeoclimates australia 18 000 yr b p abstract archaeological research on human behavioural adaptations to changes in climate environment requires palaeoclimatic reconstruction on a regional scale most often neither proxy data nor numerical modelling alone can adequately meet this requirement in an effort to satisfy this need the author suggests a method based seasonal circulation patterns and calculations of changes in evaporation rates over land and ocean in this paper circulation models for australia at 18 000 yr b p are based on output from ncar s community climate model and evaporation rate changes are calculated for twelve regions within australia as well as eight offshore winter and summer palaeoclimates for each of these areas are retrodicted on the basis of these changes and these retrodictions are tested against the available proxy data while there are clear discrepancies between the data and retrodictions for the southern part of the continent the method performs well in the north this method has proven useful in reconciling apparently contradictory data and in allowing retrodictions on the seasonal level and for providing palaeoclimatic estimates areas where data are scarce

origin of clay films in rock salt abstract it has long been assumed that thin but pervasive clay intercalations in evaporite deposits of salt and potash represent freshening of the brine body i e dilution by fresh or low salinity water however a corresponding amount of coarser clastics is not present sandy halites are extremely rare sandy potash beds are unknown freshening is not necessary to explain the presence of clay laboratory tank experiments and field observations show that the clay spreads out along the interface between the brine and fresher surface water the clays remain at the interface slowly flocculate and then sink they are retarded along microstratification layers within the brine before reaching the bottom their loose flocculated structure contains significant quantities of water which preserves the pore spaces through which epigenetic brines can later move the fresh and brackish water fossils found in the clays are either swept in with the clays or sink upon death from the freshwater layer above

large tectonic rotations in a wide zone of neogene distributed dextral shear northeastern south island new zealand abstract the new zealand plate boundary zone in the northern part of south island new zealand comprises a series of active dextral strike slip faults referred to as the marlborough fault zone mfz which link oblique continental convergence farther south along the alpine fault to subduction of the pacific plate along the hikurangi margin new paleomagnetic data are presented which together with previous studies suggest coherent neogene clockwise rotation up to 130 about a vertical axis of crustal blocks in the mfz starting at 20 ma there is a striking correlation between the amount of observed rotation and the trend of mesozoic basement structures creating this part of the new zealand orocline in a zone of distributed dextral shear about 100 km wide which has persisted for about 20 ma in the southern part of the mfz crustal blocks appear to be on a scale of 1 10 km with boundaries that are subparallel to the basement strike this way deformation is accommodated by a combination of fault slip and rotation in a zone of more pervasive dextral shear resulting in coherent bending of the basement structure in the central part of the mfz this rotation appears to be that of elongate crustal blocks 50 km 10 km in size rotating 80 clockwise at an average rotation rate 4 ma in detail the rotation rate has decreased towards the present from 6 ma at 20 ma to

discussion and reply origin and diagenesis of lacustrine sediments upper oligocene creede formation southwestern colorado discussion finkelstein et al 1999 1 presented an interpretation of lacustrine sediments particularly the carbonate sediments in the oligocene creede formation that differs greatly from other recent contributions larsen 1994a 2 larsen and crossey 1996 3 larsen and smith 1999 4

plio pleistocene lacustrine evaporites of the baza basin betic chain se spain abstract the baza basin the eastern part of the guadix baza basin in se spain underwent a significant evaporitic sedimentation in non marine settings during the plio pleistocene the largest of these settings developed in the central part of the basin as a shallow saline lake system where abundant gypsum deposits occur benamaurel and galera gypsum units this paper studies these deposits from the cartographic stratigraphic sedimentologic petrographic and isotopic points of view all the gypsum has been preserved as primary enabling a good characterization of the environmental conditions of the original precipitates three interconnected subenvironments or zones inner intermediate and marginal are differentiated in this saline lake system in the inner zone shallow to relatively deeper central lake a regular alternation of gypsum and carbonate laminae accumulated suggesting a seasonal regime many of the gypsum laminae display size gradation both reverse and symmetrical indicating free precipitation in a stable brine body in the intermediate zone mosaic of shallow lakes carbonate dolomitic beds formed in association with dark lutite levels gypsum beds and gypsum nodules and micronodules moreover anoxic conditions developed in this zone which resulted in the formation of native sulphur occurrences of economic value in the marginal zone the evaporitic deposits are developed only locally the galera gypsum unit in particular the various gypsum lithofacies in these marginal deposits suggest the presence of a number of shallow to exposed settings saline mudflat saline marsh and gypsiferous pond the isotopic composition 34 s 18 o of the gypsum samples is consistent with a triassic origin of the sulphate as a result of chemical recycling these data also suggest that a similar recycling mechanism operated in the saline lake system where the gypsum sediments from the margins were coevally recycled towards the inner part both the evaporitic mineralogy and the gypsum and carbonate lithofacies suggest that semiarid conditions prevailed in this basin during the accumulation of the evaporite units

reconstructing paleoenvironments and palaeoclimates in drylands what can landform analysis contribute quaternary period palaeoenvironmental and palaeoclimatic reconstructions are based on a wide and diverse array of proxy data sets some of which are geomorphological in nature in drylands where organic proxies may be limited the use of landforms is particularly important but challenging the capacity to establish the age of depositional forms particularly through the use of luminescence dating has advanced the use of landforms in dryland palaeo research though interpretation of these geoproxy records can be complex especially at the nexus of palaeoclimate and palaeoenvironmental interpretations of past conditions in this paper the use of aeolian and lacustrine forms in quaternary research is considered focusing on the relationships between dynamics form and climate and on the essential linkage between process research and palaeoenvironmental research it is concluded that landform analysis is a critical part of dryland palaeoenvironmental climate reconstruction contributing a different set of data compared to other data sources in terms of the elements of past conditions that are revealed five principles are identified to improve the use of geoproxy records in quaternary research 1 greater use of geomorphic process studies by quaternary scientists to better inform palaeolandform interpretation 2 further development of the use of chronometric data especially in terms of interpreting large data 3 interpret landform records in location specific contexts not in general terms 4 capitalise of the complexity of spatially extensive landform records which may offer better representations of real quaternary environmental complexity than at a point proxies 5 establish ways of integrating spatially extensive geoproxy records with other palaeoenvironmental records these challenges are major but not insurmountable and should represent goals for geomorphologists chronologists and quaternary scientists alike copyright 2011 john wiley sons ltd

unusual twinning features in large primary gypsum crystals formed in salt lake conditions middle miocene madrid basin spain palaeoenvironmental implications reply abstract a gypsum formation in the middle miocene saline lake deposits of the madrid basin is composed of large twinned crystals displaying an unusual habit characterised by the twin re entrant angles systematically opening downward such a habit is an exception to the commonly accepted mottura s rule for the growth of large twinned crystals which have been observed in marine derived evaporitic settings the crystals twinned along 100 are composed of elongated sub crystals formed by the intersection of the pinacoid 010 and the hemipyramid 111 field and petrographic evidence indicate a primary origin by subaqueous growth on the bottom ruling out a secondary origin brine composition dominated by ca na so 4 cl can be one of the several factors potentially controlling the selective growth of this habit further observations could indicate that such inverted twinned crystals may be considered diagnostic of gypsum growth in continental settings as such a pattern has not been recognised in marine evaporite formations

the kinematics of a transition from subduction to strike slip an example from the central new zealand plate boundary 1 we develop a kinematic model for the transition from subduction beneath the north island new zealand to strike slip in the south island constrained by gps velocities and active fault slip data to interpret these data we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region convergence related to the hikurangi subduction margin becomes very low offshore of the northern south island indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate as suggested by previous studies this result has implications for understanding the likely extent of subduction interface earthquake rupture in central new zealand easterly trending strike slip faults such as the boo boo fault are the key features that facilitate the transfer of strike slip motion from the northern south island faults further north into the southern north island and onto the hikurangi subduction thrust our results also indicate that the transition from rapid forearc rotation adjacent to the hikurangi subduction margin to a strike slip dominated plate boundary with negligible vertical axis rotation in the south island occurs via a crustal scale hinge or kink in the upper plate compatible with paleomagnetic and structural geological data despite the ongoing tectonic evolution of the central new zealand region our study highlights a remarkable consistency between data sets spanning decades gps thousands of years active faulting data and millions of years paleomagnetic data and bedrock structure

large tectonic rotation of part of new zealand in the last 5 ma abstract detailed paleomagnetic data from the wairoa syncline a middle miocene to the present forearc basin on the east coast of the north island new zealand show that the rate of clockwise rotation for the last 5 ma has been 7 8 ma of which less than 1 5 ma can be explained by apparent polar wander due to motion of the australian or pacific plates this rotation is similar to a present day rate of 7 ma determined from geodetic data between 5 and 20 ma ago the rate of tectonic rotation is poorly determined and may be between 0 and 2 ma the change in the rate of rotation of the wairoa syncline around 5 ma is probably related to a markedly different tectonic style in the new zealand region within the last 5 ma associated with a change in position of the euler poles of rotation for the pacific australian plates

geomorphology and quaternary geology of the dakhla oasis region egypt abstract dakhla oasis 25 5 n 29 e occupies a structurally localized depression at 90 140 m above sea level 1200 km 2 in area below a 300 m escarpment bordering the libyan plateau western desert of egypt semi arid intervals of the quaternary period generated eight sedimentary formations separated by erosion during hyper arid intervals sediments comprise three generations of colluvial fluvial fanglomerates two generations of tabular spring laid clastic and chemical sediments two generations of mound springs and basinal sediments of fluvio lacustrine evaporitic pluvio aeolian and aeolian origins discussion of these sediments is organized according to geomorphic region from north to south plateau scarp and piedmont lowland and cuesta plain chronological evidence is restricted to many radiocarbon dates of holocene cultural material associated with playa sediments 9 4 5 ka a th u isochron age of 62 0 7 6 ka for basinal evaporites and two th u ages of 176 and 170 ka for a boulder of derived travertine the regional quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces it is broadly similar to sequences earlier reconstructed in the topographically similar kharga oasis region 150 km to the east and kurkur oasis 400 km to the south southeast speculations on chronology and driving mechanism are offered in conclusion

tectonic rotation about the termination of a major strike slip fault marlborough fault system new zealand the marlborough fault system comprises a series of major right lateral strike slip faults that link the alpine fault to the hikurangi subduction zone in the pacific australia plate boundary zone in new zealand all of the major active faults of the marlborough fault system have continuous traces except for the clarence fault which terminates abruptly near the ward syncline paleomagnetic data from upper miocene and lower pliocene sedimentary rocks between the marlborough faults indicate a consistent post early pliocene regional clockwise rotation of about 20 an additional rotation of about 10 is evident at many localities near the termination of the clarence fault it is proposed that the additional rotation relative to the rest of the region is caused by a velocity gradient that likely exists between the active awatere fault and the termination of the clarence fault the existence of such a velocity gradient is consistent with inferences from geodetic strain data which suggest that one third of the displacement in the marlborough fault system occurs between the awatere and clarence faults the kinematics of rotation can be modelled by treating the area as a rigid block that pivots about the termination of the clarence fault the block rotation model satisfies field constraints on the styles of deformation observed at the boundaries of the block and is consistent with available paleomagnetic and geodetic data

the celestite problem in gypsum sr geochemistry an evaluation of purifying methods of gypsiferous samples abstract celestite srso 4 is a very common mineral in gypsiferous rocks in order to evaluate the possible influence of celestite occurrence in gypsum strontium analysis sr content different fine grained lithofacies with a high content of enclosed minerals ranging from 5 to 35 of the bulk rock were studied and a series of experiments with artificial reagents were carried out the results showed that even very low concentrations the recommended methodology to prevent celestite contamination in sr content analysis of fine grained gypsum lithofacies involves three basic steps 1 celestite identification 2 celestite elimination and 3 geochemical analyses we found that back scattered electron microscopy is the best method to identify celestite over a wide range of celestite concentrations in the case of celestite occurrence microprobe analysis provided reliable results as the obtained sr values corresponded to the gypsum lattice if a bulk sample analysis is performed celestite must be eliminated or partially separated from the pure gypsiferous sample in order to reduce contamination for this different methods were modified and tested including a heavy liquid dibromomethane separation procedure however because none of these methods were completely satisfactory a new method based on a hcl 2n leaching was developed and tested nevertheless although the celestite content diminished considerably it was not totally eliminated in conclusion the presence of celestite must always be taken into account when gypsiferous samples are analyzed for their sr content or their 87 sr 86 sr ratio in order to avoid seriously biased results and non reliable geochemical and paleoenvironmental interpretations in celestite rich samples it is convenient to separate the celestite before carrying out the analysis

evaporite minerals and geochemistry of the upper 400 m sediments in a core from the western qaidam basin tibet qaidam basin is a tectonically controlled depression on the northern margin of the tibetan plateau in 2008 a long core was drilled in the qahansilatu sub basin in the western qaidam basin the sediment layers in the upper 400 m alternate between evaporite mineral layers and carbonaceous clay layers the detailed mineralogical investigation focused on evaporite minerals including halite gypsum mirabilite thenardite glauberite eugsterite and bloedite gypsum and halite make up the majority of the evaporate minerals environmentally induced variations in the mineralogy and crystal habit of the sulfates have been extensively investigated gypsum has prismatic and pyramid habits such as disc pyramid stubby prismatic slender prismatic visible isolated gypsum and aggregates rosette radial and twins are mostly scattered in carbonaceous clay layers suggesting that secondary gypsum is well developed gypsum may be a precursor mineral of glauberite and thenardite is the precursor of bloedite as a metastable and rare mineral eugsterite does not appear in other tibetan areas it forms at the expense of pre existing gypsum or thenardite in the core at an experimental temperature of higher than room temperature the presence of eugsterite indicates a warm and or hot climate at its deposition time

aeolian landscapes in central australia gypsiferous and quartz dune environments from lake amadeus there are two different dune systems in central australia regional quartz dunefields and transverse gypsiferous dunes associated with playa lakes these two systems especially gypsiferous dunes at lake amadeus the largest playa in central australia provide a sedimentary geomorphological and environmental history of the region during the late quaternary the gypsifierous dunes consist of a surficial gypcrete overlying an aeolian sediment sequence below a mixture of gypsum sand and quartz sand no clay pellets have been found in the dune sequence in significant contrast to the gypsiferous clay dunes in other parts of australia three possible models of the environmental controls of gypsiferous dune formation are discussed the most plausible one suggests simultaneous gypsum precipitation and deflation sandsized gypsum was precipitated in a groundwater seepage zone around the playa margin during seasonally high water tables and these crystals were deflated onto land during dry intervals forming the marginal gypsiferous dunes these processes require conditions of high regional water table strong climatic seasonality and probably a windier and overall wetter climate at least two separate gypsiferous duneforming episodes can be recognized the age of formation of the younger one has been dated by thermoluminescence at 44 54 ka the gypcrete crust capping the dunes is characterized by intergrown microcrystalline gypsum crystals showing evidence of leaching dissolution and recrystallization it is interpreted as a pedogenic product formed during a stable period after accumulation of the gypsiferous dune after the construction of the younger gypsiferous dune there was a major episode of activation of regional quartz dunefields which formed thick quartz sand mantles overlying gypsiferous dunes on both playa margins and the dune islands within the playa an equivalent aeolian sand layer was deposited within the playa soil structures in this unit indicate that the sand sheet over the playa was later colonized by vegetation activation of the regional dunefields suggests a major period of dry climate which although not dated may correlate with the last glacial maximum identified as a period of maximum aridity from 25 to 18 ka at other sites in australia

devonian fluviodeltaic sedimentation in hong kong abstract twenty three distinct sedimentary facies have been distinguished in the devonian bluff head formation exposed around the tolo channel area of northeastern hong kong these facies have been combined into five facies associations channel aeolian sheetflood deltaic and palaeosol with the bulk of the formation belonging to the channel association the lower part of the bluff head formation around plover cove consists of upwards coarsening cycles each typically 3 m thick the basal parts of some cycles contain distinctive marine fossils of early to middle devonian age sedimentation occurred on a marine influenced delta plain with eustatic sea level rises controlling cycle development the middle and upper parts of the formation contrast strongly with the lower part and show a distinct change to alluvial plain sedimentation upward fining cycles each approximately 40 m thick comprise basal multistorey braided conglomerate filled channel deposits at the base passing upwards into finer grained sheetflood aeolian and channel sandstones at the top palaeosols in the higher parts of the cycles indicate periods of non deposition under semi arid climatic conditions these cycles represent repeated abandonments of the fluvial system which we suggest were controlled by tectonic pulses

magnetite dissolution diachronous greigite formation and secondary magnetizations from pyrite oxidation unravelling complex magnetizations in neogene marine sediments from new zealand detailed rock magnetic and electron microscope analyses indicate that the magnetic signature of neogene marine sediments from the east coast of new zealand is dominated by the authigenic iron sulphide greigite the greigite is present as a mixed population of stable single domain and superparamagnetic grains which is consistent with authigenic growth from solution this growth can result from pyritization reactions soon after deposition which also leads to dissolution of most detrital magnetite however where constrained by field tests our data suggest that remanence acquisition can occur 1 myr after deposition and can vary in timing at the outcrop scale strong viscous overprints result from oxidation of the iron sulphides probably during percolation of oxic ground water this process can sometimes destroy any ancient remanent magnetization this complex magnetic behaviour particularly the presence of late forming magnetizations carried by greigite means that the remanence in new zealand cenozoic sediments and in similar sediments elsewhere cannot be assumed to be primary without confirmation by field tests the reversals test should be employed with caution in such sediments as patchy remagnetizations can lead to false polarity stratigraphies

sticky dunes in a wet desert formation stabilisation and modification of the australian desert dunefields independent dating evidence and dune morphology indicate great stability of the australian dunefields most dunefields have seen only minor superficial modification since they were formed up to 1 million years ago despite quite large changes in climate conditions this stability may be partly due to the relatively dense vegetation cover on australian dunes under the marginally arid climate but new studies supported by many older observations suggest that sticky dunes where sand grains are bonded or cemented may form under a broader range of wind climates than widely thought and have greater resistance to reworking new mapping of the australian continental dunefields from satellite imagery shows a previously unrecognised diversity of dune morphologies dune orientation continuity connectedness crest planform crest sharpness spacing and setting all show patterns of variation over the continent these are consistent with the overall low sand supply and variable wind climate that contribute to the dominance of longitudinal dunes but also with only superficial modification of the dunes after their initial formation the longevity of the dunes is likely also partly due to the stabilisation of dune sand by pedogenesis the bonding of sand by pedogenic calcium carbonate gypsum silica and translocated clays the extremely low mobility of the sand dunes has led to preservation of dunes of great age with stacked accretionary units and multiple palaeosols

large tectonic rotations since the early miocene in a convergent plate boundary zone south island new zealand abstract a palaeomagnetic study in part of the new zealand plate boundary zone provides new constraints on the temporal and spatial distribution of neogene and quaternary tectonic rotations thermal demagnetization of samples from cretaceous basaltic dykes palaeocene oligocene micritic limestone and miocene and pliocene siltstones in the marlborough region south island have defined stable high temperature magnetic components which are interpreted as the primary magnetization declination anomalies after tectonic corrections are interpreted as rigid body rotations about a vertical axis of sample sites relative to the pacific plate all palaeomagnetic data from marlborough cluster into three main groups a 60 100 clockwise rotation affected palaeocene to middle miocene sedimentary sequences across marlborough between 18 ma and 8 ma coeval with a phase of low angle thrusting the absence of this rotation in a late cretaceous dyke swarm defines the present western limit of the early rotating zone a regional 20 clockwise rotation occurred in the last 4 ma during the development of the marlborough fault system in a zone of dextral transpression although locally clockwise rotations 40 may have occurred near some of the major dextral strike slip faults however a negligible rotation is observed in the same period in the region to the southeast of the major kekerengu dextral strike slip fault which appears to have acted as a hinge zone accommodating relative rotation by dextral strike slip on an arcuate fault bending and internal deformation the observed tectonic rotations record the overall clockwise rotation of the trend of the southern end of the hikurangi margin from w to nw in the early miocene to ne today determined independently from the long term relative plate motion data for the pacific and australian plates

long and short term hydroclimatic variabilities in the aptian tethys clues from the orbital chronostratigraphy of evaporite rich beds in the apennine carbonate platform mt faito southern italy abstract the stratigraphic signature of the global late aptian cooling episode and sea level lowstand has been investigated in the mt faito section of the apennine carbonate platform apcp of southern italy several meter scale fine grained limestone intervals with abundant quartz pseudomorphs after anhydrite and minor calcite pseudomorphs after gypsum are present in the middle upper gargasian straddling the marly orbitolina level a regional key marker correlative with part of the fallot oceanic anoxic event the evaporite rich intervals were deposited in a mudflat saltern setting and together with frequent transgressive shallow marine interlayers alternate quite regularly with lacustrine paralic or very shallow marine deposits suggestive of overall wetter conditions three to five couplets of cyclic arid wet phases are thus identified their timing and duration determined by an original cyclostratigraphically constrained age model tuned with the astrochronology from deep water tethyan reference sections suggest fluctuating hydroclimatic conditions arid semiarid vs wet phases over time scales as brief as 100 and 400 ky they are considered to reflect astronomically induced latitudinal migrations of intertropical climate belts a secular climate shift from arid to humid conditions supra regionally correlatable across the upper gargasian of the tethyan realm is dated at 118 1 my it corresponds to the onset of persistent lacustrine deposits on the partially emerged apcp and of abundant river borne supply of siliciclastics along the opposing tethyan margin the observed climate fluctuations occurred during a major apcp subaerial exposure which lasted for 4 4 my precise supra regional correlations suggest that the platform exposure was glacioeustatic in origin and coeval with a long lived late aptian cooling episode which interrupted the mid cretaceous greenhouse biostratigraphic and astrochronological tuning from the apcp indicates that the glacioeustatic lowstand terminated in the earliest albian just above the o reicheli key marker

seismic evidence for conjugate slip and block rotation within the san andreas fault system southern california the pattern of seismicity in southern california indicates that much of the activity is presently occurring on secondary structures several of which are oriented nearly orthogonal to the strikes of the major through going faults slip along these secondary transverse features is predominantly left lateral and is consistent with the reactivation of conjugate faults by the current regional stress field near the intersection of the san jacinto and san andreas faults however these active left lateral faults appear to define a set of small crustal blocks which in conjunction with both normal and reverse faulting earthquakes suggests contemporary clockwise rotation as a result of regional right lateral shear other left lateral faults representing additional rotating block systems are identified in adjacent areas from geologic and seismologic data many of these structures predate the modern san andreas system and may control the pattern of strain accumulation in southern california geodetic and paleomagnetic evidence confirm that block rotation by strike slip faulting is nearly ubiquitous particularly in areas where shear is distributed and that it accommodates both short term elastic and long term nonelastic strain a rotating block model accounts for a number of structural styles characteristic of strike slip deformation in california including variable slip rates and alternating transtensional and transpressional features observed along strike of major wrench faults domains of evenly spaced antithetic faults that terminate against major fault boundaries continued development of bends in faults with large lateral displacements anomalous focal mechanisms and differential uplift in areas otherwise expected to experience extension and subsidence since block rotation requires a detachment surface at depth to permit rotational movement low angle structures like detachments of either local or regional extent may be involved in the contemporary strike slip deformation of southern california a block nature of the crust also implies that not only will strains be inhomogeneous and likely concentrated along edge bounding faults but that local stress orientations will largely be responding to local kinematic constraints of block rotation and fault interaction this behavior coupled with the presence of possible regional detachments accounts for some of the precursory changes observed at considerable distances prior to large earthquakes and the triggering of seismicity or slip on nearby faults or around adjacent block edges although fault displacements along secondary structures associated with block rotations remain small they may still influence the nucleation and the characteristic rupture length of large earthquakes a more complete description of what these structures are and how they interact may prove critical to any fundamental understanding of the earthquake process and any realistic assessment of the regional seismic hazard

palaeogroundwater evolution in playa lake environments sedimentary facies and stable isotope record palaeogene almazan basin spain the palaeogene history of the almazan basin is that of a non marine basin sediments derived from fluvial distributary systems and lateral playa lakes the coeval uplifting of the cameros massif and the aragonian branch of the iberian chain during alpine compression exposed triassic evaporites which became the main source of sulphates to the playa lake system as recorded by the bordalba formation this unit exhibits the classical facies distribution of gypsum precipitating playa lakes which can be grouped into two main settings 1 distal alluvial mud flat and 2 saline mud flat ephemeral lake the stable isotope data for gypsum from the distal alluvial mud flat areas 12 2 18osmow 16 5 10 8 34scdt 13 0 lie within the range of values of neighbouring triassic gypsum or are slightly lower for 34scdt this agrees with palaeogeographical interpretations suggesting that the triassic evaporites were the source of gypsum for the almazan basin the slightly lower values could be explained in terms of a minor contribution through the oxidation and dissolution of palaeozoic derived sulphides the isotopic values for gypsum of the saline mud flat ephemeral lake environments 19 8 18osmow 23 82 15 6 34scdt 19 9 are higher than those of the distal alluvial mud flat the higher 18osmow in the saline mud flat ephemeral lake environments is interpreted as being a consequence of the progressive evaporation of shallow groundwaters from proximal to distal areas the heavier values for the 34scdt in the saline mud flat ephemeral lake environments are interpreted as reflecting the activity of sulphate reducing bacteria which is evidenced by spheroidal dolomite aggregates on gypsum crystals and by the grey colours of the gypsum facies

lacustrine sedimentation in the diapir controlled miocene bicorb basin eastern spain abstract the miocene bicorb basin is a small elongated basin developed by normal faulting of a thick jurassic cretaceous carbonate succession and subsequent diapirism of upper triassic mudstones and evaporites the basin fill comprises a sequence over 650 m thick formed by two units the lower alluvial unit consists of a complex alternation of conglomerates sandstones mudstones and minor lacustrine limestones the upper unit comprises marginal alluvial and lacustrine deposits in which seven lacustrine facies associations have been distinguished the inner lacustrine deposits comprise mudstones and carbonates with minor evaporitic deposits at the northeast and southwest basin edges alluvial inputs led to the development of delta and fan delta environments where sandstone and conglomerate deposits dominate the latter stages of the lake evolution are represented by an expansive thick limestone sequence which close to the nw fault bounded margin pass laterally to breccias the hierarchical arrangement of the upper unit shows five different orders of sequences the first order sequence defines a major vertical trend of lake expansion whereas three second order sequences are linked to major flooding expansion episodes all these sequences are related to the tectonic evolution of the diapir metre scale third and fourth order sequences and fifth order sequences which consist of finely laminated rhythmite deposits probably record climatically forced processes the diapir graben system evolution and the climatic variations have exerted major controls on the sequential arrangement and evolution of the lacustrine system both factors have also strongly influenced the changes in the gastropod assemblages

finite element modeling of neotectonics in new zealand 1 thin shell finite element methods that incorporate faults realistic rheology laterally varying heat flow and topography and plate velocity boundary conditions have been used to model the neotectonics of new zealand we find that new zealand s faults have effective friction of 0 17 comparable to that found in other pacific rim regions the long term average slip rate of the alpine fault varies along strike generally increasing northeastward until slip is partitioned among the strands of the marlborough system the average slip rate 30 mm yr when combined with published geodetic results and historical seismicity strongly suggests a high probability of future large earthquakes tectonic deformation of north island is controlled by a balance between differential topographic pressure and traction from the hikurangi subduction thrust the hikurangi forearc is an independent plate sliver moving relative to the pacific and australian plates there is a complicated zone of slip partitioning in the transition from the alpine fault to the puysegur trench an offshore thrust fault the southern segment of which may correspond to the waipounamou fault system parallels to the se coast of south island and needs to be included in seismic hazard estimates

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

reactivation of tectonics crustal underplating and uplift after 60 myr of passive subsidence raukumara basin hikurangi kermadec fore arc new zealand implications for global growth and recycling of continents we use seismic reflection and refraction data to determine crustal structure to map a fore arc basin containing 12 km of sediment and to image the subduction thrust at 35 km depth seismic reflection megasequences within the basin are correlated with onshore geology megasequence x late cretaceous and paleogene marine passive margin sediments megasequence y a similar to 10 000 km 3 submarine landslide emplaced during subduction initiation at 22 ma and megasequence z a neogene subduction margin megasequence the moho lies at 17 km beneath the basin center and at 35 km at the southern margin beneath the western basin margin we interpret reflective units as deformed gondwana fore arc sediment that was thrust in cretaceous time over oceanic crust 7 km thick raukumara basin has normal faults at its western margin and is uplifted along its eastern and southern margins raukumara basin represents a rigid fore arc block 150 km long which contrasts with widespread faulting and large neogene vertical axis rotations farther south taper of the western edge of allochthonous unit y and westward thickening and downlap of immediately overlying strata suggest westward or northwestward paleoslope and emplacement direction rather than southwestward as proposed for the correlative onshore allochthon spatial correlation between rock uplift of the eastern and southern basin margins with the intersection between moho and subduction thrust leads us to suggest that crustal underplating is modulated by fore arc crustal thickness the trench slope has many small extensional faults and lacks coherent internal reflections suggesting collapse of indurated rock rather than accretion of 1 km of sediment from the downgoing plate the lack of volcanic intrusion east of the active arc and stratigraphic evidence for the broadening of east cape ridge with time suggests net fore arc accretion since 22 ma we propose a cyclical fore arc kinematic rock moves down a subduction channel to near the base of the crust where underplating drives rock uplift oversteepens the trench slope and causes collapse toward the trench and subduction channel cyclical rock particle paths led to persistent trench slope subsidence during net accretion existing global estimates of fore arc loss are systematically too high because they assume vertical particle paths citation sutherland r et al 2009 reactivation of tectonics crustal underplating and uplift after 60 myr of passive subsidence raukumara basin hikurangi kermadec fore arc new zealand implications for global growth and recycling of continents tectonics 28 tc5017 doi 10 1029 2008tc002356

petrography and genesis of quaternary coastal gypcrete in north kuwait arabian gulf abstract gypcrete crusts cover late quaternary playa deposits within the northern coastal flat of kuwait bay arabian gulf this study provides insight into the genesis of the gypcrete crust associated with the fluvial playa in an arid coastal area the playa sediments are mostly muddy sand rich in diagenetic gypsum the latter is concentrated at the top part of this playa where the gypcretic crust is developed field investigation megascopic microscopic and nanoscopic examination and xrd analysis revealed the occurrence of several types of gypcretes namely massive hard crust hard clustered gypsum roses gypseous rhyzocrete and powdery crust with the exception of the last type all gypcretes are formed largely of gypsum with subordinate amounts of bassanite two genetic types of bassanite are recognised these are replacive and precipitative replacive bassanite is the most common and is mainly represented by topotactic alteration of gypsum whereas the precipitative mode is mostly restricted to the powdery crumbled crust and root cavity fill the micromorphology of both types of bassanite is discussed it is suggested that the stability of bassanite is attributed to the elevated ambient temperatures in the presence of highly saline brine and organic acids

challenges to carbonate evaporite peritidal facies models and cycles insights from lower cretaceous stromatolite bearing deposits oncala group n spain abstract peritidal carbonate evaporite successions since they are developed in the transition between continental and marine realms provide essential keys for palaeobathymetric and palaeoclimatic interpretations as a result several facies models have been proposed to assist on the interpretation of ancient tidal flat deposits and peritidal successions have been extensively used for cyclicity analyses in this study well exposed lower cretaceous peritidal deposits oncala group cameros basin n spain are analysed and compared with the most commonly used present day analogues from shark bay the arabian gulf and the bahamas and with ancient peritidal successions providing their palaeoenvironmental and palaeoclimatic interpretation assessing the usefulness and limitations of the facies models and evaluating the suitability of these deposits for analysis of decimetre to metre scale cycles the studied peritidal deposits consist of thinly bedded to laminated dolostones dolomitic stromatolites stromatolite breccias flat pebble and edgewise breccias and calcite and quartz pseudomorphs after anhydrite nodules abundant resemblances of the peritidal deposits of the oncala group with those of shark bay including that they are largely composed of microbialites and intraclasts makes the peritidal deposits of the oncala group one of the best fossil analogues of this present day setting however the presence of anhydrite nodules indicates pervasive evaporite precipitation in the supratidal zone which is a feature that does not occur in supratidal flats of shark bay but is characteristic of arid sabkhas of the arabian gulf nevertheless the fact that carbonate evaporite tidal flats of the oncala group were laterally related with siliciclastic tidal flats with large freshwater input and broadly inhabited by dinosaurs suggests that anhydrites precipitated under less arid climates than those of the arabian gulf nowadays pointing to semiarid climatic conditions during deposition moreover the fact that peritidal deposits with anhydrite nodules were exclusively formed in a low subsidence area of the cameros basin suggests that the rate of accommodation space creation also played an important role in their development regarding the comparison with other fossil peritidal sediments the studied deposits show more abundant similarities with proterozoic and cambrian successions composed mainly of stromatolites microbial laminites and intraclasts than with other mesozoic peritidal deposits in which bioclasts and burrowing are usually more abundant this highlights the difficulties for assigning specific features to certain geological ages finally peritidal facies of the oncala group may change laterally and vertically to any other facies showing a patchy lateral distribution of facies and an unsystematic vertical stacking pattern the sedimentary features of the stromatolite breccia and thinly bedded to laminated dolostone facies do not allow their assignment to a unique tidal zone moreover sedimentary features indicative of subaerial exposure such as anhydrite nodules formed in the capillary zone occur within any of the carbonate facies and show limited lateral extent this results in a succession that cannot be clearly subdivided into subsequent shallowing upward cycles not even by using erosive surfaces or the anhydrite nodule layers as marker horizons of the upper part of the cycles because their limited lateral extent prevents reliable correlations similar composite lateral and vertical facies relationships have been documented both in the present day analogues and in ancient successions which suggests that this kind of facies relationships may be common in peritidal successions and highlights the caution that must be taken when trying to perform cyclicity analysis on them

stratigraphy sedimentology chronology and palaeohydrology of quaternary lacustrine deposits at madigan gulf lake eyre south australia abstract madigan gulf is a large bay at the southern end of lake eyre north a major ephemerally flooded playa in arid central australia at the southwestern margin of a vast 1 300 000 km2 internal drainage basin the stratigraphy and chronology of the quaternary sequence in the gulf is described from 8 cores and a cliff exposure at the gulf margin a number of depositional environments are recognised and their distinctive sedimentary components are described facies recognised include deep and shallow water lacustrine environments dominated by surface water processes and dry or ephemerally flooded playa environments dominated by groundwater controlled processes sedimentary components include terrigenous clastics from river inflow and shoreline erosion carbonates of detrital inorganic or biological origin and gypsum and halite evaporites carbonates and gypsum evaporites precipitated within the basin are frequently reworked as clastic components the establishment of a preliminary chronology for the sequence by the application of thermoluminescence uranium thorium disequilibrium amino acid racemization and radiocarbon dating techniques has allowed a reconstruction of the last 130 ka of lake eyre palaeohydrology the wettest phase occurred during the last interglacial early in oxygen isotope stage 5 when an enlarged lake eyre was up to 25 m deep subsequently there has been a number of dry periods separating successively less effective wet phases culminating in the deposition of a substantial halite salt crust around the time of the glacial maximum the dry interludes are characterised by deflation of salts and sediment from the basin a process controlled by lowering of the watertable the record from madigan gulf demonstrates the dramatic and repetitive impact of lake deflation on the quaternary record of lake eyre in the early holocene a minor but mostly perennial lacustrine event was terminated at about 3 4 ka when the modern ephemeral playa regime was established the major catchment of lake eyre is located in the monsoon watered areas of northern australia as demonstrated by large floodings of the modern ephemeral regime major lacustrine episodes must indicate enhanced monsoon precipitation in northern australia in the holocene the lake has not risen to levels achieved during the early stage 5 lacustral phase indicating a marked reduction in the effectiveness of the monsoon in the present interglacial by comparison with its predecessor

bending within the axial tectonic belt of new zealand in the last 9 myr from paleomagnetic data abstract tongaporutuan stage late miocene 11 6 myr sedimentary rocks at two localities within the axial tectonic belt of new zealand have a direction of magnetisation in which the declination is 020 11 and 030 8 d 95 the directions of magnetisation in rocks of similar age outside the belt have a declination like that of the earth s present axial dipole 360 the clockwise deviation of the declination is inferred to indicate bending of the rocks within the zone of deformation between the pacific and indian plates due to the oblique convergence of these plates

dry lake beds as sources of dust in australia during the late quaternary a volumetric approach based on lake bed and deflated dune volumes abstract dust affects earth s climate ecology and economies across a broad range of scales both temporally and spatially and is an integral part of the earth s climate system previous studies have highlighted the importance of inland lake beds to dust emissions both locally and globally this study aims to explore the relative volumetric importance of ephemeral lakes that emit dust to the australian southeastern dust path over the last glacial cycle srtm dems and gis analyses of long term up to 80 ka lake bed deflation volumes and deposition of sand sized sediment onto downwind source bordering dunes were used to derive estimates of transported dust mass a strong power relationship was found between lake area and the mass of deflated lake bed sediments total dust masses for the largest 53 lakes in southeastern australia were derived using the relationship between lake area and dust mass and used to determine an upper value for total dust mass deflated from lake beds in southeastern australia ephemeral lake derived dust was found to represent at most 13 of the dust derived from southeastern australia deposited in the southern pacific over the last 80 ka or 22 over the last 40 ka lake eyre the largest lake has contributed at most 3 of the australian southeast dust plume these results imply that there are significant additional sources of dust in australia over these timescales such as floodplains or dunefields and that modelling must allow for diverse climatic and geomorphic controls on dust production

gypsum ground a new occurrence of gypsum sediment in playas of central australia abstract there are many playas dry salt lakes in arid central australia regional rainfall about 250 mm y and pan evaporation around 3000 mm y highly soluble salts such as halite only appear as a thin several centimetres thick white ephemeral efflorescent crust on the dry surface gypsum is the major evaporite precipitating both at present and preserved in sediment sequences one type of gypsum deposit forms a distinctive surface feature which is here termed gypsum ground it consists of a thick up to 80 cm gypsum zone which rises from the surrounding smooth white playa surface and is overlain by a heaved brown crust the gypsum zone with an average gypsum content above 60 consists of pure gypsum sublayers and interlayered clastic bands of sandy clay the gypsum crystals are highly corroded especially in the direction parallel to the c axis and on the upper sides where illuviated clay has accumulated in corrosion hollows overgrowth parallel to the a and b axes is very common forming highly discoidal habits these secondary changes corrosion and overgrowth are well developed in the vadose zone and absent from crystals below the long term watertable depth around 40 cm these crystal characteristics indicate a rainwater leaching process at lake amadeus one of the largest playas 800 km2 of central australia such gypsum ground occupies 16 of the total area the gypsum ground is interpreted as an alteration of a pre existing gypsum deposit which probably extended across the whole playa before breaking down leaving a playa marginal terrace and several terrace islands within the gypsum ground this pre existing gypsum deposit preserved in the residual islands consists of pure pale sand sized lenticular crystals it is believed to have been deposited during an episode of high regional watertable causing active groundwater seepage and more frequent surface brine in the playa a later fall in watertable probably resulting from climatic change caused the degradation of the gypsum deposit by dissolution and leaching processes the common distribution of the gypsum ground and marginal terraces in the playas of central australia demonstrates the extent of this hydrologic and climatic history

reconstructions of the new zealand region for the neogene abstract the major structural elements of the present day plate boundary zone through new zealand are a subduction zone under the northern half of the country linked by a wide transform zone to the southward extension of the plate boundary through fiordland and the macquarie ridge using finite rotations of the pacific australian plate pair a sequence of reconstructions of the relative positions of the plates is presented reconstructions of the plate boundary zone based on paleomagnetic data involve essentially the same structural elements as today but with large clockwise changes in their trend with time

late pleistocene evolution of salt lakes in the qaidam basin qinghai province china abstract the qaidam basin is a tectonically controlled depression at 2700 m altitude on the northern margin of the qinghai xizang tibet plateau rimmed by the high aljun qilian ranges to the north and kunlun peaks to the south rising above 5000 m the basin floor experiences hyper arid conditions with evaporation precipitation ratios exceeding 100 1 periglacial and glacial conditions prevail on montane peaks with permafrost above 3800 m on the basin floor small waterbodies lie on extensive halite salt flats on the largest the qarhan salt flat 5800 km2 in extent the small lakes dabuxun and taijinier represent contracted remnants of a once expansive water body throughout neogene time a succession of clastic sediments indicates lake depo centre migration from nw to se towards late pliocene evaporitic conditions developed with formation of gypsum halite celestite mirabilite and bloedite continued deformation through pleistocene time has developed a series of nw se trending domes and troughs this setting has continued to exert a controlling influence on basin and brine evolution with progressive development through sulfate to chloride brines as dry conditions intensified in late pleistocene expanded lake conditions qarhan mega lake corresponding to near the 2800 m contour indicate the existence of past climates much more humid than those of today a drilling program has defined the lateral and vertical extent of evaporitic halite deposits freshwater clastics and shell deposits which predate the halite phase indicate humid lacustral conditions until after 40 000 30 000 yr b p desiccation from about 25 000 yr until about 9000 yr b p resulted in deposition of halite to 60 m thick with thin parting muds representing brief returns to more humid environments high lake shorelines with aragonitic ooids surrounding the dry playa kunteyi and high level ostracod rich beach and near shore deposits on xiao qaidam attest to the presence of expanded late pleistocene lacustral conditions on lakes other than qarhan preceding the final evaporite stage clastic sediments associated with the halite are dominated by loessial silts equivalent to the late pleistocene malan deposits of central china simultaneous halite and loess deposition reflect the dry conditions that developed in the qaidam basin during the latter part of the last glaciation and which have persisted ever since the final evolution of brines has resulted in development of extensive potassium rich brines and salts with the mineral carnallite providing the basis for a large potash extraction industry near golmud the hydrologic history documented by the analyses of lake sediments reflects the interaction of tectonic deformation and climatic change in the development of brines to the potash stage

a simple method for estimating the horizontal velocity field in wide zones of active deformation ii examples from new zealand central asia and chile summary lamb 1994 has described a simple method for estimating the horizontal velocity field in a wide zone of active deformation this method is now used to investigate the horizontal velocity or displacement field in part of the new zealand plate boundary zone central asia and southern central chile in each region a range of weighted least squares solutions have been found depending on assumptions about aspects of the internal deformation in the new zealand example observed tectonic rotations are successfully predicted solutions for central asia place constraints on the manner in which the northward convergence of india into eurasia is accommodated horizontal surface displacement fields are determined for the elastic rebound during the 1960 chilean great earthquake based on available retriangulation data and assumptions about the slip vector on the fault these solutions suggest but do not prove a nearly pure thrust event for this earthquake

distribution patterns of gypsum and kalistrontite in a dry lake basin of the southwestern kalahari omongwa pan namibia the deposits of the omongwa pan southwestern kalahari namibia are partly gypsiferous and locally contain small amounts of kalistrontite the distribution patterns of gypsum caso4 2h2o and kalistrontite k2sr so4 2 are mainly determined by groundwater depth and by the lithological composition of the deposits the latter determines the hydraulic conductivity for saturated and unsaturated flow and therefore controls the depth of the interval within the deposits where evaporation and mineral precipitation can take place other factors that affect the distribution of the evaporite minerals are the patterns of groundwater flow within the basin and the occurrence of a redistribution of salts during short flooding stages gypsum occurs as crystals of four distinct morphological types which each developed in different conditions prismatic crystals formed both as subaqueous precipitates and as crystals that developed within the sediment matrix of a brine saturated surface layer sub euhedral tabular crystals formed within brine filled macropores hemi bipyramidal crystals formed in a nearly permanently brine saturated part of a subsurface horizon phreatic zone as the product of recrystallization of an older gypsum occurrence and lenticular crystals formed by intrasediment growth in the vadose zone the development of these morphological types of gypsum crystals is marked by differences in the differential inhibition of growth of the various crystal forms the further growth of lenticular crystals which are most strongly affected by differential growth inhibition is still characterized by a difference in degree of inhibition between the 111 and 103 forms expressed as a change in orientation of the plane of flattening copyright 1999 john wiley sons ltd

gypsum nucleation and crystal morphology in analog saline terrestrial environments abstract gypsum crystals were grown in experimental conditions analogous to saline terrestrial environments within bentonite clay gels by diffusion control at three different temperatures four brine salinities and four tannic acid a model terrestrial humic substance concentrations the resulting crystals correspond to natural gypsum formed in terrestrial environments prismatic gypsum typically grew at both high and low temperatures in the absence of the organic additive with increasing organic acid concentrations the prismatic crystals progressively became flattened perpendicular to 001 and two temperature dependent trends developed at low temperatures a hemi bipyramidal habit dominated by 1111 faces developed whereas the lenticular e103 dominated habit forme at higher temperatures with progressively greater concentrations of organic material a 100 penetration twinning developed secondary complex nucleation occurred near the twin interfaces and finally rosette and rosette like aggregates formed higher temperatures generally favored better formed and larger rosettes the presence of 5 and 15 nacl greatly decreased nucleation density and resulted in larger single crystals and crystal aggregates the a 100 penetation twins appear to be diagnostic of gypsum growth in natural terrestrial sediments at a ph greater than 7 5

crust and upper mantle structure of wanganui basin and southern hikurangi margin north island new zealand as revealed by active source seismic data

depositional depth of laminated carbonate deposits insights from the lower cretaceous valdeprado formation cameros basin northern spain the lower cretaceous berriasian valdeprado formation cameros basin northern spain contains more than 900 m of laminated carbonates and pseudomorphs after sulfates traditionally many sedimentary packages of different ages and lithologies have been interpreted as deep water deposits based essentially on the abundance of laminations and the absence of subaerial exposure features in contrast the valdeprado formation provides an example of a shallow water deposit dominated by laminations with scarce evidence of subaerial exposure and gives criteria to solve the challenge of distinguishing shallow water and deep water ancient laminated deposits the two most abundant facies all along the valdeprado formation are a parallel laminated limestone formed by alternating carbonate mudstone and calcite and quartz pseudomorphs after displacive gypsum and b graded laminated limestone consisting of quartz mica ostracodes and pseudomorphs after detrital gypsum grains at the base which changes gradually upwards to carbonate mudstone parallel laminated limestone and graded laminated limestone could have been deposited in either deep or shallow environments as a result of salinity fluctuations driven by alternation of flooding and evaporation and by sediment resuspension processes respectively subaerial exposure features such as desiccation mudcracks are scarce in most of the succession except in a few meter scale stratigraphic intervals where they are very abundant interestingly in these intervals desiccation cracks are present at the tops of several successive laminae up to 25 mudcracked laminae per meter of deposit indicating that at least during those periods of time deposition occurred in shallow water bodies that were desiccated frequently in the upper part of the stratigraphic section parallel laminated and graded laminated limestones are associated with current ripple and wave ripple cross laminated arenites and ostracode mudstone to wackestone with centimeter size pseudomorphs after lenticular gypsum and abundant desiccation mudcracks and tepees which also suggest sedimentation in shallow water environments moreover the laminated carbonates display continuous parallel layering and the same facies along the 40 km long outcropping area these deposits are directly interbedded with and pass laterally to siliciclastic sandy muddy flat deposits in the western area of the basin without clinoforms slump structures or slide masses in between all of these features suggest deposition in shallow perennial carbonate sulfate water bodies and their peripheral mudflats developed in a flat bottomed basin with no marked gradients

age and origin of the new zealand orocline in relation to alpine fault movement the alpine fault and the recurved arc structures orocline in the late palaeozoic mesozoic rangitata orogen are two of the first order structures of the new zealand subcontinent a commonly held view is that the orocline originated as a gigantic drag fold with alpine fault movement in view of the post oligocene age of the alpine fault however this concept involving a single recurved arc cannot reconcile the two published sets of palaeomagnetic data on tectonic rotations within the rangitata orogen and its cover rocks these data indicate at least 62 of dextral rotation during each of the mesozoic rangitata orogeny and the late cenozoic kaikoura orogeny a new model presented here postulates that there are actually two dextral recurved arcs a western arc which lies mainly outside the australia pacific plate boundary zone has a multiple origin having formed chiefly during the late triassic phase of the rangitata orogeny by the subduction accretion of the exotic rakaia terrane an eastern arc coincides with the area of the present plate boundary zone it formed as a mega brittle ductile shear zone with the late cenozoic development of the modern australia pacific plate boundary which includes the alpine fault this solves the problem of the nature and location north of the alpine fault of the relative plate movement evident as 480 km of displacement on the alpine fault a major implication of this model for plate tectonic reconstruc tions of the sw pacific is that only approximately 500 km of dextral displacement has occurred through new zealand during the late cretaceous cenozoic compared with the commonly adopted figure of 1000 km

nodular anhydrite growth controlled by pedogenic structures in evaporite lake formations several nodular gypsum beds exhibiting a remarkable vertical arrangement of individual nodules are present in the miocene continental evaporite formations of the calatayud basin northeastern spain the growth of the gypsum nodules initially anhydrite took place within magnesitic carbonate deposits which display incipient pedogenic features such as rhizoliths and clotted to peloidal textures simultaneous and after the pedogenic modification of the carbonate substratum displacing nodules started to grow their arrangement being closely conditioned by the development of vertical fissuring related to root penetration the transformation of anhydrite to gypsum was probably realized early after little burial of the sulphate carbonate deposits the occurrence of vertically oriented gypsum nodules can be seen as a diagnostic feature for palustrine conditions developed in evaporitic lake settings this peculiar morphology of the sulphate nodules having been strongly controlled by the internal structure of the palustrine palaeosols

neocene and quaternary extent and geometry of the subducted pacific plate beneath north island new zealand implications for kaikoura tectonics abstract the extent and geometry of the obliquely subduced oceanic pacific plate beneath north island new zealand for five million year intervals through the mid miocene to quaternary are presented in a series of maps and cross sections these show that the subducted plate progressively increased its extent from ne to sw beneath the north island and in the more northern regions where it was first emplaced concomitantly increased its dip from 10 to 50 the changing extent and geometry of the subducted slab has been established from the age pattern of orogenic andesites and from the geochemical k 2 o h parameter of depth of magma generation the radiometric dates show a migration of the volcanic front back towards the trench at an average rate of 20 km my the trenchward migration is explained by a model of increasing slab dip which is corroborated by the k 2 o data calibrated against the presently active arc taupo volcanic zone with the exception of northern coromandel peninsula the andesitic magmas were generated at 85 100 km depth the interpretation of the dates adopted here indicates that the subducted slab originated at the ne sw trending kermadec hikurangi trench and implies a different and much simpler evolution of the australia pacific plate boundary in the vicinity of north island than other recent models subduction geometry has been found elsewhere to be a principal influence upon the state of stress and deformational style in an over riding plate the possibility is explored that the timing nature and pattern of the neogene to quaternary kaikoura orogeny in north island is due to this influence apart from the effect of oblique subduction in eastern north island there is an accord between the onset of deformation and the emplacement sequence of the shallow slab beneath north island and between the change in subduction geometry and a progressive north to south change in northern north island from compression to extension

characterisation of aeolian sediments from the strzelecki and tirari deserts australia implications for reconstructing palaeoenvironmental conditions abstract in arid environments dominated by desert dunes aeolian sediments represent a major source of potential palaeoenvironmental information however the extent to which dune sedimentology can be used for past environmental reconstruction is unclear this paper assesses the value of dune sediments as palaeoenvironmental indicators by investigating the sedimentological characteristics of linear dunes in the strzelecki and tirari deserts of central australia we use thin section microscopy particle size analysis and x ray diffractometry xrd mineralogy to characterise the sediments occurring within the dunefields of the region and examine the stratigraphic record in the context of dune preservation and sediment reworking we find that it is rarely possible to reconstruct past environmental change within desert dunefields purely on the basis of sedimentological evidence however limited palaeoenvironmental information is preserved within dune sediments which can be combined with additional arid zone proxies and geochronological techniques to enable the most reliable reconstruction of past conditions paleosols provide the most informative and unambiguous palaeoenvironmental indicators within dune sediments acting as markers of relative environmental stability paleosols are characterised by pedogenic carbonates and gypsum and illuviated clays in the form of intact grain coatings the potential for incomplete stratigraphic preservation within dunes is a critical consideration for reconstructing palaeoenvironments however the preservation of paleosols indicates that the dunes in this region have not been completely reworked grain coatings provide important evidence both for pedogenesis when they are intact and for aeolian reworking when they are partially abraded abraded cutans are ubiquitous across the region studied linear dune mineralogy of the strzelecki and tirari deserts is dominated by quartz with minor feldspar and clay minerals the latter in the form of grain coatings and aggregates the occurrence of intact sand sized aggregates composed of clay and silt particles at several sites indicates incipient rather than peak aridity and may within this geomorphic context indicate reduced stream discharges grain size shows a regional bias although silt sized material is most likely to have been deposited as long travelled dust the regional grain size characteristics combined with local occurrences of rock fragments and high feldspar content suggest that sediments are mostly derived from local sources

cenozoic tectonic evolution of the new zealand plate boundary zone a paleomagnetic perspective abstract new zealand straddles the obliquely convergent boundary between the pacific and australian plates with subduction of pacific plate along the hikurangi margin finite plate reconstructions predict 800 km of relative plate motion since 43 ma with 80 90 clockwise rotation of the hikurangi margin since 20 ma at an average rate of 4 4 5 myr and the short term deformation

palaeohydrological evolution and implications for palaeoclimate since the late glacial at laguna de fuente de piedra southern spain abstract here we present a terrestrial multi proxy record of late quaternary environmental changes in the southern iberian peninsula covering approximately 30 ka this sedimentary record originates from a saline playa lake laguna de fuente de piedra hosted within a complex geological setting dominated by triassic claystones and evaporites jurassic carbonates and miocene deposits leading to a complex hydrogeological setting dissolution of evaporites in the catchment and intense evaporation are responsible for saline waters fluctuating in the basin thus salinity as palaeohydrological proxy requires a decoupling of internal and external hydrogeochemical processes the greatest accumulation of evaporites in the lfp late pleistocene holocene record coincides with a more humid or at least less evaporative period based on multi proxy data we describe five lacustrine lithofacies 2 5 and fluvial deposits 1 from sediment cores the proposed conceptual lake margin model contains three main lake water stages repeated within the sedimentary succession and building up the characteristic lithofacies lake water stages refer to a flooding stage influx outflux high water stage influx outflux and low water stage influx

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

dolomitization gypsum calcitization and silicification in carbonate evaporite shallow lacustrine deposits this paper describes and interprets the mineral and facies assemblages that occur in carbonate evaporite shallow lacustrine deposits considering the importance of the processes pathway i e dolomitizacion gypsum calcitization and silicification the palaeogene deposits of the deza formation almazan basin central northern spain are selected as a case study to determine the variety of physico chemical processes taking place in carbonate evaporite shallow lakes and their resulting diagenetic features dolostones are the predominant lithology and are composed mainly of dolomite with variable amounts of secondary calcite 5 to 50 which mainly mimic lenticular gypsum pseudomorphs five morphological types of dolomite crystal were identified dolomite tubes dolomite cylinders rhombohedral dolomite spheroidal and quasi rhombohedral dolomite and cocoon shaped dolomite the dolomite cylinders and tubes are interpreted as the dolomitized cells of a widespread microbial community the sequence of diagenetic processes started with growth of microlenticular interstitial gypsum in a calcareous mud deposited on the playa margin mudflats and that sometimes included microbial sediments immediately following growth of gypsum dolomite replaced the original calcite aragonite muds the microbial community and the gypsum partial or total replacement of gypsum by dolomite was related mainly to the biomineralization of endolithic microbial communities on gypsum crystals later calcitization took place under vadose subaerial exposure conditions the development of calcrete in distal alluvial settings favoured the release of silica and subsequent silicification on the playa margin mudflats stable isotope compositions of calcite range range from 9 02 to 5 83 13cpdb and 7 10 to 1 22 18opdb for the dolomite these values vary from 8 93 to 3 96 13cpdb and 5 53 to 2 4 18opdb quartz from the cherts has 18osmow values ranging from 27 1 to 31 1 wide variation and relatively high 18osmow values for dolomite indicate evaporitic and closed hydrological conditions increased influx of meteoric waters reigned during the formation of secondary calcite spar this article is protected by copyright all rights reserved

spatially variable sedimentary responses to orbitally driven pluvial climate during marine oxygen isotope stage 5 1 dakhla oasis region egypt abstract pleistocene basinal sediments pbs in the dakhla region of egypt s hyperarid western desert comprise four facies a fluvio lacustrine b mixed lacustrine pluvio eolian c pluvio eolian and d mixed eolian pluvio eolian contiguity of basins containing each facies and their stratigraphic position between two bajada gravel formations p b ii and p b iii confirm their equivalence facies a and b with lacustrine components are attributed to orbitally forced poleward incursion of the intertropical convergence zone itcz resulting in increased summer insolation temperature precipitation facies c and d comprising pluvio eolian and eolian sediments reflect geologic topographic influences overprinted on regional pluvial conditions eliminating lacustrine response a th u age of 62 ka on lacustrine marl within facies b is minimal and an osl age of 110 18 ka on sediments immediately below facies b is maximal since bajada gravels p b iii are the youngest pleistocene formation they must represent the final strong incursion of the itcz into the dakhla region at mis 5 1 80 ka because pbs facies a pass rapidly up into p b iii bajada gravels pbs are assigned to the rising limb of the mis 5 1 insolation temperature precipitation curve slightly younger than 80 ka

the kinematics of the plate boundary zone through new zealand a comparison of short and long term deformations summary surveys of shear strain rates derived from repeated triangulation cover about one quarter of the area of the plate boundary zone through new zealand and are well distributed within it using a method developed by haines relating shear strains to the total strain and velocity fields the dilatational and rotational strain rates and the velocities within the deformed zone are derived the plate boundary zone is shown to be two dimensional for the most part in that gradients of the velocity along the length of the zone are small or zero the shear strain rates are not uniform however they reach a maximum along a central axis and decrease gradually to zero toward the sides nor are the two independent components of strain one involving shortening or extension perpendicular and the other shear parallel to the zone equally developed everywhere there is a clear geographic separation with shortening developed over the subduction thrust and shear developed behind in a zone of wrench faulting time variations in the strain field in part of the region above the subduction interface are related to changes in the degree of coupling across the interface a velocity field is computed the relative velocity of the two plates from this data agree very well with that derived from seafloor spreading data these strain and velocity fields derived from geodetic studies give the short term kinematics of the plate boundary zone the long term kinematics of the zone are estimated from 1 uplift and subsidence data which are related to changes in crustal thickness and hence to dilatational strain and 2 variation in the declination of primary magnetization in rocks of known age related to the rotational strain the rate of rotational strain has increased in time from about 2 to 3 myr 1 10 myr ago to about 9 myr 1 today the increase can be understood as a secondary effect of a developing compressional component increasing the coupling between the plates so that more of the motion parallel to the zone is accommodated by distributed shear and less by aseismic slip the rates of strain averaged over the last 1 myr or so and at a scale length of a few tens of kilometres are closely similar in distribution and magnitude to the strain rates derived from short term kinematics while therefore at scale lengths of a few hundred metres or so faulting is very important and the deformation is discontinuous with unstrained blocks faulted with large but uncertain slip against adjacent blocks the deformation at these longer scale lengths is continuous and regular the two consequences of this study are that 1 strain from geodetic data can be directly related to the average long term deformation and therefore can be an important tool in the study of deformation in regions of current tectonic activity and 2 at scale lengths of a few tens of kilometres the deformation of a region can be described as the deformation of a continuum and we can ignore the effects of faulting

from carbonate sulphate interbeds to carbonate breccias the role of tectonic deformation and diagenetic processes cameros basin lower cretaceous n spain interpreting the origin of carbonate breccias requires a detailed analysis because they may be the result of a wide variety of processes that produce similar features this is the case of the lower cretaceous carbonate breccias of the cameros basin previously interpreted as slump or collapse breccias whose origin is interpreted after performing a detailed sedimentary petrographic and tectonic study the studied carbonate breccias consist of angular carbonate mudstone fragments floating in a matrix of calcite and quartz crystals the breccias are interbedded with and laterally associated to alternating layers of carbonate mudstone and calcite and quartz pseudomorphs after gypsum which show strong similirities to the breccia fragments and matrix respectively suggesting that the brecciated beds were originally composed of identical alternating carbonate mudstone and gypsum layers as the unbrecciated layers the breccias are associated with frequently polyharmonic deformation structures which are similarly oriented as the regional tectonic structures indicating that they are related with the alpine contractional deformation of this area of the cameros basin all these features suggest that the carbonate breccias were formed by tectonic deformation of alternating layers of carbonate mudstone and calcium sulphate which have very different rheological behaviours as a result during tectonic deformation sulphate flowed and carbonate layers were broken and displaced producing a breccia of carbonate fragments within a sulphate groundmass afterwards the sulphate groundmass was replaced by quartz and calcite and the breccia acquired its final composition

trace fossils and rhizoliths as a tool for sedimentological and palaeoenvironmental analysis of ancient continental evaporite successions abstract recognition of evaporite formations from continental tertiary basins of spain provides evidence that trace fossils including rhizoliths can be abundant in some saline lake systems and their study helps in palaeoenvironmental interpretation of ancient continental evaporite sequences six main types of trace fossils have been distinguished and include 1 networks of small rhizoliths 2 large rhizoliths 3 tangle patterned small burrows 4 isolated large burrows 5 l shaped traces and 6 vertebrate tracks rhizoliths were related to both marginal areas of hypersaline lakes and lakes of moderately high saline waters in these settings pedoturbation resulted from colonization by grasses and bushes of distinct lake subenvironments the activity of burrowing invertebrate faunas was especially intense in lakes of moderately concentrated brines from which gypsum was the main evaporite mineral deposited a specific gypsum lithofacies bioturbated gypsum deposits forming thick massive beds has a widespread occurrence in many of the basins tangle patterned small burrows and minor isolated large burrows constitute the typical trace fossil types within the gypsum the traces are interpreted as having been caused by burrowing insect larvae probably chironomids coleopterans and annelids the behaviour of these organisms in recent lake environments yields information about the salinity range of lake waters from which gypsum precipitated concentration values averaging 100 150 g l may be thus deduced though some organisms involved in the formation of the traces can tolerate higher salinities the combined analysis of lithofacies and trace fossils from the lacustrine evaporite sequences contributes to the study of distinct saline lake subenvironments as well as changes in the sedimentary evolution of the lake systems consequently trace fossils can provide valuable insight for palaeoenvironmental analysis of at least some evaporite formations that accumulated in continental settings

the origin of miocene evaporites in the tuz golu basin central anatolia turkey implications from strontium sulfur and oxygen isotopic compositions of the ca sulfate minerals abstract sulfur oxygen and strontium isotope compositions of the sulfate minerals gypsum and anhydride of the miocene evaporites in the tuz golu basin which is the largest closed and inner basin of turkey located in the central anatolia were investigated to evaluate the origin of the sulfates and interpret the precipitation paleoenvironment the isotopic mineralogical and chemical properties and composition of the samples collected from drillings were investigated the 34scdt and 18osmow values of the sulfate minerals range from 18 78 to 35 90 and 7 55 22 57 respectively most of the 34s values are similar to marine messinian water in addition the 87sr 86sr ratios of the minerals vary from 0 707803 to 0 708209 most of the 34s and 18o values and 87sr 86sr ratios of the investigated samples in the tuz golu basin are similar to those of the isotopic values of the messinian marine sulfates indicating that the minerals were precipitated mostly from marine water the 34s and 18o values of some samples are higher than those of the evaporites precipitated from the miocene seawater and indicate that the evolution of the sufates in the basin was also controlled by the recycling dissolution of the predeposited marine sulfates oligocene eocene arid conditions and bacterial sulfate reduction bsr processes additionally the low 18o values and 87sr 86sr ratios with high sr content of some samples other than those of the miocene marine sulfates may have been caused by the influence of volcanic emanations hydrothermal fluid re oxidation of sulfur and partially the contribution of the external or internal nonmarine water to the basin e g meteoric water or groundwater surface water the ca sulfate minerals with high sr contents and low 87sr 86sr ratios may have precipitated under the seawater dominated hydrothermal fluid mixing conditions

shallow water evaporitic environments and their source rock potential in the major evaporitic environments on the world s surface today most organic matter accumulates in shallow subaqueous to seasonally subaerially exposed algal mat sediments given the present depositional setting and the most likely flushing by oxidizing water it is unlikely this organic matter could be preserved to form source rocks however if we place such evaporite deposition into a geologic context then there are times in the past when source rocks could have formed in shallow water settings such settings were characterized by hydrological conditions which allowed the retention of hypersaline anoxic pore waters to depths where the organic material was buried deeply enough to generate hydrocarbons when deep basin shallow water evaporite successions were laid down in basins such as the mediterranean in the late miocene the michigan basin in the silurian and other large saline giants then conditions were right for the formation of source rocks within shallow water and salt flat evaporitic environments the evaporites in these saline giants were deposited under conditions of relatively shallow water 50 m the basin never appears to have dried out but water levels changed quickly nearly equal 10 000 years from shallow to deep continual water saturation coupled with saline pore fluids prevented the inflow of fresh oxidizing groundwater into the basin center of shallow water organic rich evaporites immature hydrocarbons derived from such rocks today drip from the 5 5 m y evaporites of sicily in active salt and sulfur mines organic rich sediments could also be preserved to generate hydrocarbons in rapidly subsiding rift basins in such basins rapid burial has prevented the entrance of fresher oxygenated waters and the associated degradation and destruction of the organic matter the early continental riff stage generates the source rocks the ephemeral streams wadis and dune fields generate the reservoirs and the subsequent evaporite stage seals the reservoir

downstream channel changes on a contracting anabranching river the lachlan southeastern australia abstract downstream trends in flow channel morphology and sediments were investigated over 220 km of the middle and upper alluvial lachlan river in southeastern australia the lachlan is a perennial river that rises from temperate humid highlands and flows inland into a semiarid low gradient plain lacking perennial tributaries long daily stage records were used to calculate flow parameters and flood frequencies in single and anabranching channel reaches of the river morphological trends were based on cross section and height data compiled from new and water authority data and from particle size trends constructed from bed and bank sediment samples mean and peak flows channel size and bed particle size all diminish in a downstream direction in the partially confined piedmont zone channel and floodplain morphology feature large flood effects and large channel dimensions that reflect extreme flow variability on the alluvial plains the unconfined single channel contracts with distance downvalley and anabranches develop at high flow stages the development of a full anabranching pattern is associated with large flood volume losses diminishing flood volumes mean flows and channel dimensions is attributed to storage of flood waters in lakes floodways and lagoons and through transmission losses during overbank flows the frequency of bankfull discharge consistently decreases downstream and may reflect the long duration and lower frequency of floods in the lower reaches of the river particle size of bed sediment fines downstream at rates consistent with those reported from sand bed rivers elsewhere this is attributed to a combination of hydraulic sorting and low rates of sediment supply from the catchment

the nature and significance of variations in gypsum crystal morphology in dry lake basins depressions in semiarid regions with a gypsiferous geological substrate commonly contain highly gypsiferous sediments with gypsum that formed either as a synsedimentary precipitate during perennial or ephemeral lake stages or as a diagenetic precipitate during saline mudflat stages the dry to ephemeral lake basins of the monegros region in northern spain are depressions of this type and provide a unique opportunity to examine whether and how conditions of gypsum formation are reflected by gypsum crystal morphology yielding information that can contribute to a correct interpretation of the depositional environment of gypsum in ancient and modern formations in most lake basins of the study area the sediment fill consists of a similar sequence of three lithological units the lower unit includes fragmented gypsum crystals in some basins recording clastic reworking and in other depressions it contains large lenticular crystals formed as phreatic diagenetic precipitates the middle unit typically contains synsedimentary gypsum with a non lenticular morphology modified by postdepositional processes but it also comprises synsedimentary lenticular gypsum in some basins in the upper unit separated from the underlying interval by a marked hiatus both synsedimentary and diagenetic gypsum are present the former including layered gypsum deposits with features such as grading and variations in crystal morphology the results show that a non lenticular crystal habit of gypsum occurring within the groundmass sediment matrix indicates synsedimentary precipitation in contrast a lenticular crystal habit cannot be used in isolation as an indicator of the environment in which the gypsum initially precipitated unambiguously late diagenetic gypsum includes fine grained precipitates in voids created by soil fauna these infillings consist of initially non lenticular crystals with a tabular prismatic habit recording that conditions promoting lenticular crystal growth do not always prevail outside the groundmass in soil related settings and illustrating the importance of knowing the context of analyzed gypsum occurrences at the scale of a sample

late quaternary lacustrine groundwater aeolian and pedogenic gypsum in the prungle lakes southeastern australia abstract detailed petrographic studies of recent or sub recent evaporites where many critical environmental parameters are defined can help in the analysis of ancient deposits and in the establishment of chemical and environmental models for evaporite formation the prungle lakes are part of the now dry willandra lakes system in semi arid southwestern new south wales the willandra lakes have been a site of cyclic quaternary sedimentation in response to the well documented global climatic fluctuations associated with the glacial interglacial cycle at times of hydrologic stress low lake levels are associated with high salt volumes inherited from evaporative concentration in large shallow lakes upstream and the inflow of saline groundwaters thus at prungle a complex array of concentric shorelines lake floor terraces and lunettes has developed as basin within basin landforms which formed in response to filling and drying cycles sediments associated with these geomorphic units include 1 1 freshwater littoral nearshore and deep water deposited laminated sands and muds with biogenic carbonates chiefly of ostracodal and algal origin 2 2 evaporites comprising interbedded clay and laminated gypsum clay couplets which consist of discrete thin laminae of sugary white euhedral prismatic gypsum separated by detrital clay layers with a high degree of optical orientation primary accessory celestite srso4 occurs as discrete patches within the gypsum laminae 3 3 groundwater pyramidal discoidal or lenticular gypsum crystals grown from supersaturation produced by evaporation at the capillary fringe of the water table these have formed displacively within the sediments and caused considerable disruption of the sediment matrix 4 4 aeolian deposition in irregular transverse ridges of sand sized reworked groundwater gypsum and disrupted lacustrine clays the gypsum crystals are predominantly discoidal pyramidal forms which are conspicuously oriented parallel to bedding well sorted and extensively corroded the clay pellets are well sorted and moderately well rounded higher in the profile bedding is indistinct due to pedogenic processes which include modification of detrital grains and secondary crystallization of gypsum and carbonate a thin gypcrete horizon occurs at the surface the last cycle of sedimentation in the prungle lakes is believed from correlation with lakes higher in the willandra system to have occurred during the period 50 000 16 000 yr b p since then groundwaters have dropped below the zone of interaction with the lake floor and surface water no longer reaches the lakes sedimentation has ceased and soil formation with secondary carbonate and gypsum has continued to the present a range of sedimentary environments is identified which depend on strong seasonal oscillations these environments are virtually absent from the australian continent today and their occurrence during the pleistocene supports the contention of enhanced climatic seasonality at that time the array of sediment types and mineralogies is almost identical to that characteristic of coastal sabkha sequences highlighting the difficulty of relying on unusual evaporative mineralogy to differentiate marine and non marine environments detailed petrographic analyses of the prungle sequence have been made in association with a review of theoretical experimental and observational studies of the environmental controls of calcium sulfate mineralogy and crystal habit this has enabled the correlation at prungle of depositional environment with gypsum petrofacies and associated compositional fabric or structural features these observations are more generally applicable to other evaporite deposits many gypsum evaporites reported in the literature have been compared with this scheme developed at prungle

balancing the plate motion budget in the south island new zealand using gps geological and seismological data summary the landmass of new zealand exists as a consequence of transpressional collision between the australian and pacific plates providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary we interpret gps geological and seismological data describing the active deformation in the south island new zealand by using an elastic rotating block approach that automatically balances the pacific australia relative plate motion budget the data in new zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks we find that most of the plate motion budget has been accounted for in previous geological studies although we suggest that the porter s pass amberley fault zone in north canterbury and a zone of faults in the foothills of the southern alps may have slip rates about twice that of the geological estimates up to 5 mm yr 1 of active deformation on faults distributed within the southern alps 100 km to the east of the alpine fault is possible the role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the south island compared to the north island vertical axis rotation rates of tectonic blocks in the south island are similar to that of the pacific plate suggesting that edge forces dominate the block kinematics there the southward migrating chatham rise exerts a major influence on the evolution of the new zealand plate boundary we discuss a model for the development of the marlborough fault system and hikurangi subduction zone in the context of this migration

the last 25 ma of rotational deformation in part of the new zealand plate boundary zone abstract the marlborough fault system is a zone of dextral transpression in continental crust and marks the southern end of the hikurangi subduction system between the obliquely convergent australian and pacific plates detailed mapping over an area of 100 km2 has revealed a complex history of deformation during the last 25 ma the development of a thrust belt in the miocene referred to as d1 deformation was synchronous with the deposition of a thick submarine fan complex the beginning of d1 deformation may mark the initiation of the subduction zone in this part of the plate boundary zone subsequently in the plio pleistocene the region formed a zone of dextral shear marked by major strike slip faults and zones of distributed deformation referred to as d2 deformation crustal blocks less than 5 km across may have rotated ca 60 clockwise about vertical axes relative to the pacific plate in the last 4 ma the pattern of deformation during the last 10 ka to 100 years is consistent with the long term d2 deformation and suggests that large crustal blocks resting on the subducted pacific plate have rotated clockwise about vertical axes relative to the pacific plate accommodated by dextral shear further to the sw in the marlborough fault system the overall effect of the deformation has been the rotation of the edge of the southern part of the hikurangi margin from a w to nw trend in the early miocene to a ne trend today

oligocene to pliocene palaeogeographic evolution of the cankiri corum basin central anatolia turkey abstract the cankiri corum basin is one of the largest basins of central anatolia to have developed oligocene to quaternary terrestrial environments the basin contains significant raw materials for industry and energy but the determination of their distribution patterns requires a good knowledge of the stratigraphic and spatial distribution of deposits besides evolving tectonic regimes in the basin and the sedimentary sequences controlled by them can play key roles in revealing the regional paleogeography on the basis of a new chronological framework provided by mammalian fossils and sedimentological data ten sedimentary formations have been identified for the oligocene pleistocene time interval from the oldest to the youngest these are the incik guvendik kizilirmak kilcak kumartas hancili bayindir akkasdagi bozkir and degim formations during early oligocene times an alluvial fan and braided and meandering rivers deposits developed at the northern and eastern rims of the basin whereas lacustrine products dominated by evaporitic deposits occurred in vast areas at the center in late oligocene the lake area contracted and dominant floodplains and braided rivers took place in the central area of the basin during early middle miocene large lacustrine areas dominated by organic clastic deposits developed in the northern and middle parts of the basin lake shore facies were formed in northern parts of the basin and on some paleohighs surrounding the lake in the orta and abanozu regions volcanic activity started during the middle miocene and lasted until the beginning of late miocene during late miocene there were different types of lacustrine environments in the northern and southern parts of the basin a hypersaline lake characterized by evaporitic deposits in the north and carbonate rich shallow lakes and swamps in the south a younger evaporitic lake formed in early pliocene in the northern part of the basin and covered vast areas its deposits are as thick as 400 m from late pliocene the thick sedimentary sequences deposited during the oligocene early pliocene interval become fragmented and deformed by a tectonic wedge bounded by a normal fault in the west and a thrust in the east sedimentary products of this tectonic regime are represented by thick alluvial fan sequences of the degim formation

variation of gypsum morphology along deep core sg 1 western qaidam basin northeastern tibetan plateau and its implication to depositional environments abstract the qaidam basin is an arid closed intermontane basin located on the northern margins of the tibetan plateau in china a 938 5 m long core sg 1 dated between 2 8 ma 0 1 ma was obtained from the western qaidam basin gypsum is one of major evaporative minerals in the core a total of 201 gypsum samples were selected and their crystal morphologies were carefully investigated the crystal habits are lenticular prismatic tabular twinned stubby and aggregate prismatic crystals occur in the upper 723 m while lenticular crystals exist almost entirely in the upper 523 m tabular crystals are the most common morphology the total abundance of gypsum crystal including tabular lenticular and prismatic forms tends to increase with decreasing depth the relationship between crystal habits and depositional environments is complex because same morphology can appear in different environments and different morphologies can also occur in the same depositional environment however the occurrence of different morphologies can be attributed to the variable growth rates caused by the inhibition effect of additional cations e g mg 2 na k and sr 2 on particular lattice parameters and the variation in precipitation experiments the lattice parameters of the unit cell of gypsum measured by x ray diffraction method are a 5 854 12 57 a b 9 654 16 231 a and c 5 163 14 024 a 113 54 119 88 volume 601 55 712 65 a 3 the substitution of k na and mg 2 for ca 2 can reduce c axis while sr 2 can reduce a and b axes a c b c a b tend to increase with k na and mg 2 and decrease with sr 2 the mg 2 na k and sr 2 contents in gypsum show significant variability with k ca molar ratios varying from 1 03 10 4 to 32 08 10 4 mg ca molar ratios from 0 0023 to 0 1629 na ca molar ratios from 0 031 to 0 575 and sr ca molar ratios from 5 59 10 4 to 19 67 10 4 sr 2 mg 2 na and k concentrations in gypsum mainly depend on growth rate and brine concentration

textural features of holocene perennial saline lake deposits of the taoudenni agorgott basin northern mali abstract the holocene salt lake deposits of the taoudenni agorgott basin northern mali mainly consist of sediments with a high glauberite na2ca so4 2 content the remainder of the deposits largely consists of salt beds with a bloedite na2mg so4 2 4h2o thenardite na2so4 or halite nacl composition a petrographical study of the deposits demonstrates that they formed in a perennial lake that experienced a gradual decrease in water depth textural features of the glauberite dominated deposits are found to be related to water depth through the control that this factor exerts on the sensitivity of the lake to changes in water supply and to short term variations in evaporation rates in this way layering due to variations in glauberite content and crystal size is inferred to be typical of deposits that formed in shallow water whereas unstratified deposits are the product of high lake level stages halite textures are found to be indicative of the place within the water column where crystal growth occurred along the lake bottom or higher which is mainly determined by water depth and partly by evaporation rates the oldest halite beds are largely unaltered cumulate deposits whereas the youngest layers developed exclusively through bottom growth the basal part of one thick halite bed at a level between these two groups of halite layers developed by an alternation of both types of growth in response to variations in evaporation rates variations in mineralogical composition between and within the salt beds that formed during the earliest periods with a higher salinity up to the first stage with halite formation record a change in lake water chemistry with time but they are in one instance also determined by an early diagenetic mineral transformation

marano volcanic rocks east azarbaijan province iran and associated fe mineralisation there are two main types of economic iron ore deposits in iran 1 magmatic segregation deposits and 2 skarns most of the hydrothermal iron deposits in iran except for the skarns are uneconomic one of these uneconomic hydrothermal deposits is the marano fe deposit located in east azarbaijan province nw iran this deposit is considered to have been formed by an epithermal style of mineralisation related to a volcanic dome there are 5 volcanic domes in the marano area ranging in composition from dacite to rhyolite the volcanic rocks show geochemical evidence of fractionation of biotite hornblende magnetite apatite and feldspars the marano volcanic domes crystallised from an i type magma formed in a volcanic arc setting fe mineralisation has occurred around one of these marano domes ma dome in which the igneous rocks contain more biotite and hornblende and are less fractionated than in the other domes the main fe oxide hematite occurs as veins and disseminations in sedimentary wall rocks alteration of the minerals in the host rocks suggests a s 2 9 5 a o 2 10 34 2 and ph 5 5 the small size and shallow level of emplacement of magma together with the absence of extensive hydrothermally altered zones shows that the hydrothermal system was not voluminous enough to form an economic iron deposit

a new explanation for cyclic deposition in marine evaporite basins meteoric water input abstract one of the least discussed processes affecting the deposition of marine evaporites is the role of meteoric water sand and fine grained clastic sediments deposited from river system in a marginal evaporite basin facies the oxygen isotope record in the carbonate minerals mainly dolomites and the br cl ratios of second cycle salts are some of the evidence for influxes of meteoric water important meteoric water influxes are not limited to sabkha and salina evaporites but may also affect deep water evaporite basins one can see in the oxygen isotope record of carbonate minerals an imprint of meteoric water just as the sulfur isotope record reflects the imprint of the marine water sedimentological characteristics of evaporite sequences could be interpreted as variations in the amount of precipitation in the evaporite basin catchment area rather than as a result of changes in sea level for example the varved structures may reflect seasonal flooding of the basin by meteoric water evaporite facies cycles may be the result of longer term weather variation for example the paradox member cycles pennsylvanian utah could reflect periods of increased precipitation which are associated with glacial interglacial cycles