the infiltration of fine matrices into coarse grained alluvial sediments and its implications for stratigraphical interpretation traps designed to simulate the framework gravel of natural streams and installed in a coarse grained channel allow the identification and differentiation of the processes governing the infiltration of fines into bed interstices vertical patterns of matrix distribution reflect the relative importance of variables acting at both the surface of the channel bed and within the bed sediments differences in grain size and therefore pore size of the framework exercise a strong controlling influence an armour layer of coarse particles superimposed on comparatively finer sub surface bed material common to many coarse grained rivers is shown to encourage the clogging of near surface pores with matrix fines below the obstruction interstices may be protected from incursion and the gravel framework is often left open this is the reason for patchy concentrations of matrices often reported in the stratigraphical literature in contrast a uniform size grading of the bed sediment or an upwards fining leads to a more uniform packing of the interstices with matrix flood history is shown to be an important determinant of both the size distribution and the spatial distribution of matrices and is useful in providing a dynamic explanation of the variability of matrices observed from place to place in ancient deposits

preferential flow in a sandy vadose zone 2 mechanism and implications abstract field experiments conducted at the hancock agricultural research station during the 1987 growing season showed that preferential flow paths were the dominant flow pattern in the central sand area of wisconsin csaw the observed preferential flow was different from other preferential flow patterns mentioned in the literature e g short circuiting flow and fingering flow this paper presents a detailed discussion of the mechanism of this preferential flow and its influence on groundwater contamination soil solution sampling and solute transport modeling four factors that will determine the occurrence of a funneled flow are a conductivity of the upper finer layer k b slope of the inclined layer sin c retention potential of the upper finer layer 2 r and d ponding potential g l

application of theoretically derived rock physics relationships for clastic rocks to log data from the wilmington field ca relationships between porosity and shear modulus are applied to logs recorded in the miocene upper terminal formation of the wilmington field ca to predict porosity from shear wave velocity data recorded through casing using a dipole sonic logging tool a relationship based on a modified hashin shtrikman lower bound appropriate for the unconsolidated nature of the formation allows determination of porosity from the shear modulus the results are similar to those obtained using standard log analysis in sands standard logs predict higher porosities in smectite bearing wackes because of the inclusion in the standard analysis of bound water or micro porosity in the clays which is not included in the porosity value derived from the shear wave velocity

some isotopic constraints on the evolution of the granulite and upper amphibolite facies terranes in the eastern musgrave block central australia abstract the central to eastern musgrave block central australia consists of the meso to neoproterozoic fregon and mulga park subdomains that are separated by a zone of mylonites and pseudotachylytes known as the woodroffe thrust the subdomains were previously considered to have undergone different geological histories but the differences relate mainly to metamorphic grade the fregon subdomain attained at least transitional granulite facies metamorphic conditions and the mulga park subdomain reached upper amphibolite facies felsic gneisses from both the fregon and mulga park subdomains contain zircons that are structured with euhedral centres overgrown by round elongate rims ion microprobe u pb analyses of the cores yield ages of 1557 24 and 1554 28 ma respectively and are interpreted to represent the time of igneous crystallization these ages place a maximum age constraint on the deposition or emplacement of the gneiss precursor high grade metamorphism grading from upper amphibolite to granulite facies took place between 1200 and 1150 ma and prior to the intrusion of several granitoid suites at around 1150 ma the kulgera adamellite and ayers ranges adamellite granitoid suites of the fregon subdomain yield ion microprobe u pb crystallization ages of 1150 12 and 1152 11 ma respectively a concordant u pb isotope dilution analysis on the ayers ranges adamellite yields a more precise age of 1152 3 ma the porphyritic suite intruding the mulga park subdomain yield an ion microprobe u pb magmatic age of 1159 20 ma these emplacement ages indicate extensive grenvillian felsic magmatism not previously recognized in australia the woodroffe thrust formed during a period of substantial crustal shortening the petermann orogeny 550 ma when the fregon subdomain was thrust onto the mulga park subdomain synkinematic muscovite and biotite record k ar and rb sr ages between 560 and 520 ma this petermann event is not recorded in the fregon subdomain due to confinement of the strain and associated mineral recrystallization to the underlying mulga park subdomain we suggest that the granulites were not exposed prior to the petermann orogeny as the basal quartzites of the amadeus basin occur only on the amphibolite facies mulga park subdomain

scour chain employment in gravel bed rivers abstract the dynamics of river beds can be assessed fromscour and fill data obtained from scour chains chains have not been used extensively in gravel bed rivers due to a variety of employment difficulties chain insertion anchoring and relocation can be determined with minimal manpower by utilising a set of tested employment methodologies these are decribed in sufficient detail to allow fluvial geomorphologists ecologists and river engineers to more commonly utilise chains in studies of river stability and river response

yardea dacite large volume high temperature felsic volcanism from the middle proterozoic of south australia the yardea dacite is a large volume felsic volcanic unit from the middle proterozoic gawler range volcanics of south australia it has been previously described as an ignimbrite however some samples contain no petrographic evidence for a pyroclastic origin but have characteristics compatible with final crystallization from a nonfragmented magma these samples may have erupted as lavas but others are likely to be extremely densely welded ignimbrites suggesting a compound nature for the unit geothermometry and phase equilibria indicate that the yardea dacite originated from a high temperature 1000 c felsic magma with a low water content 2 the yardea dacite is not associated with a known caldera of the valles type and shares many characteristics of recently described cenozoic felsic volcanic rocks from the western united states interpreted as rheoignimbrites or as unusually extensive lavas

mapping lithofacies and pore fluid probabilities in a north sea reservoir seismic inversions and statistical rock physics reliably predicting lithologic and saturation heterogeneities is one of the key problems in reservoir characterization in this study we show how statistical rock physics techniques combined with seismic information can be used to classify reservoir lithologies and pore fluids one of the innovations was to use a seismic impedance attribute related to the vp vs ratio that incorporates far offset data but at the same time can be practically obtained using normal incidence inversion algorithms the methods were applied to a north sea turbidite system we incorporated well log measurements with calibration from core data to estimate the near offset and far offset reflectivity and impedance attributes multivariate probability distributions were estimated from the data to identify the attribute clusters and their separability for different facies and fluid saturations a training data was set up using monte carlo simulations based on the well log derived probability distributions fluid substitution by ga

diagnosing high porosity sandstones strength and permeability from porosity and velocity nonuniqueness in relating velocity to porosity in core and well log data complicates interpretation of sonic and seismic measurements one reason for this nonuniqueness in sandstones is clay e g han 1986 another reason is textural variability among samples dvorkin and nur 1996 examine two relatively clay free sandstone groups in the same porosity range but whose velocities significantly differed figure 1a by comparing the data with effective medium theories they interpret this velocity difference as resulting from the difference in the position of diagenetic cement the explanation is that in the fast oseberg rocks contact cement is located predominantly at the grain contacts whereas in the slow troll rocks noncontact cement is located predominantly away from these contacts

geochronology of early to middle proterozoic fold belts in northern australia a review abstract this geochronological review integrates geologically relevant isotopic data from the several early to middle proterozoic fold belts of northern australia a number of firm chronological benchmarks largely established by means of u pb zircon studies now provide a time framework within which to better quantify the tectonostratigraphic history of many of these terranes the apparent worldwide dearth of crustal events in the earliest proterozoic between 2500 and 2000 ma was broken in northern australia with the advent of a major crust forming episode between 1880 and 1850 ma ago these rocks may have evolved from an initial mantle or lower crustal melting and fractionation process about 400 300 ma earlier that is evidenced from sm nd model ages the extent involvement and or degree of assimilation of any pre existing archaean crust is small but whether or not it is negligible or zero is not satisfactorily known the 1880 1850 ma event the barramundi orogeny is well represented in northern australia both lithologically and analytically and the rocks that pre and post date it have a similar tectonic setting over very wide areas of the continent two consistent and widespread elements of this tectonism are regional metamorphism and deformation of the first cycle of supracrustals barramundi orogeny and crystallization of i type k rich felsic magmas closely following and in some cases overlapping with deformational processes in the halls creek inlier the ages of this rapid deep crustal to supracrustal tectonic transition cannot be distinguished within the range 1860 1850 ma this major yet short lived tectonism is mirrored in other fold belts such as pine creek tennant creek and mount isa in which u pb zircon ages give slightly older constraints of 1885 1870 ma 1920 1870 ma and 1885 10 ma respectively the ensuing felsic magmatism in these latter terranes continued for a few tens of millions of years with the crystallization and emplacement of comagmatic volcanic plutonic pairs throughout in the interval 1870 1860 ma in the georgetown and arunta inliers direct evidence of this otherwise ubiquitous event if present is masked by younger high grade metamorphism in the latter however metamorphic crustal components having approximate protolith ages of this order can be inferred from their evolved isotopic signatures the geochronological and geochemical coherency of the extensive early proterozoic 1870 ma magmatism contrasts with that of post 1800 ma magmatism which is less extensive generally anorogenic commonly bimodal in character and varies in age from one terrane to another several major sedimentary basins were being filled at this time major igneous events at 1790 1740 ma 1670 ma and 1500 ma are recognized elongate sublinear volcanic and plutonic belts 1790 1740 ma old are present at mount isa in high grade granitic gneisses of the arunta inlier a few u pb zircon ages and extrapolated rb sr protolith ages are coincident at about 1760 1750 ma indicating that this event may be important in the development of the division 2 sequences of that fold belt the platformal hart dolerite and oenpelli dolerite two of the largest mafic intrusions in the world were emplaced at 1762 25 ma and 1688 13 ma younger felsic plutonism and volcanism gave rise to rapakivi type granites in the mount isa tennant creek and the granites tanami inliers at 1670 ma a time close to that of the aileron deformational metamorphic event in central australia further at 1650 ma there is growing evidence of an unexpectedly coherent hydrothermal episode that reset or disturbed many rb sr ages gave rise to pegmatites and was possibly associated with mineralization in the davenport and eastern arunta inliers discrete middle proterozoic deformational events between 1610 and 1470 ma punctuate the tectonostratigraphic history in the arunta mount isa and georgetown fold belts where they are best documented

grenvillian aged reworking of late paleoproterozoic crust of the southern north australian craton central australia implications for the assembly of mesoproterozoic australia abstract la icp ms u pb monazite and zircon geochronology from metapelites and migmatitic orthogneiss along the central southern margin of the north australia craton nac central australia reveal the presence of a regional scale grenvillian aged ca 1130 ma deformation system grenvillian aged deformation extends over a strike length of over 110 km from the southern aileron province in the vicinity of alice springs to the teapot granite complex within the warumpi province there is also evidence for grenvillian aged migmatisation and resetting of monazite further west in the mount liebig area which may extend the grenvillian aged footprint to a strike length of at least 250 km deformation associated with grenvillian aged reworking produced map scale east west trending folds and strongly foliated steeply dipping shear zones that define the structural architecture of the interface region between the aileron and warumpi provinces shallow westerly plunging folds associated with partial melting have evolved into shear zones and mylonites that record south side up movement phase equilibria modelling of age constrained garnet biotite sillimanite cordierite bearing metapelites from the southern aileron and warumpi provinces suggest grenvillian aged metamorphism reached temperatures in the range of 775 820 c and pressures of 5 5 5 kbar corresponding to thermal gradients of 130 165 c kbar 1 the extensive grenvillian aged system reworks and overprints late paleoproterozoic ca 1650 1630 ma high grade metamorphic rocks the grenvillian aged system occurs above a south dipping lithospheric scale interface that has been geophysically imaged to depths of at least 200 km this feature was interpreted to represent a fossil subduction zone of late paleoproterozoic age however the presence of regional scale grenvillian aged deformation in the crust above this feature suggests that it may instead be grenvillian aged if that is the case deformation along the southern margin of the nac may record suturing of the nac with the grenvillian aged musgrave province to the south this would effectively place the long lived late mesoproterozoic ultrahot orogen that is the musgrave province in southern central australia in an upper plate tectonic setting linked to the convergence of the nac with the south australian craton

preferential flow in a sandy vadose zone 1 field observation abstract field experiments of water movement in the lower portion of an unsaturated zone i e vadose zone are far more difficult to conduct than those in the root zone thus our concept of the transport mechanism in the vadose zone is still primitive and mainly an extrapolation of our understanding of transport in the root zone recent results from field experiments conducted at the hancock agricultural research station indicated that water and solute applied uniformly to soil surfaces did not flow through the entire vadose zone by using dye tracing and profile excavation field experiments were conducted during the 1987 growing season to examine water flow patterns in the unsaturated zone of the central sand area of wisconsin csaw the results confirmed that preferential flow paths constitute the dominant flow pattern at this location water flowing through the root zone was funneled into concentrated flow paths that occupied only a small portion of the soil matrix in the vadose zone yet accounted for most of the transport the observed phenomena of preferential flow in a sandy vadose zone are discussed in this paper the mechanism and implications of preferential flow are presented in a companion paper

ecogeomorphology in the australian drylands and the role of biota in mediating the effects of climate change on landscape processes and evolution

scour fill and burial depth of coarse material in gravel bed streams scour fill and burial depths of coarse particles were examined in two ephemeral streams using magnetically tagged particles and scour chains the burial depth varied within a bedform and from one bedform to another the maximum burial depth was recorded in bars but differences in the mean burial depth in the pools bar and thalweg were insignificant mean burial depth was three to six times the median size of material on bar surfaces and ten to thirty times that in the pools and thalweg more than eighty per cent of the tagged particles which were located on or close to the bed surface moved in each event although previously buried particles were moved by flood events others which were initially exposed remained stationary on the surface or were buried in situ the data indicate that the mean burial depth was intermediate between the mean depths of scour and fill deeply buried particles probably reflect the development of scour holes during flood flows aggradation and degradation changed the recorded burial depth relative to the local bed surface of stationary tracer particles these observations indicate that scour and fill processes during a flow event are sporadic and change with water discharge

geological and palaeomagnetic significance of the kulgera dyke swarm musgrave block nt australia summary the kulgera dyke swarm consists of olivine tholeiites which have intruded late proterozoic transitional granulite gneisses and granites of the eastern musgrave block in central australia preliminary rb sr results suggest that the dolerites were emplaced at 1054 f 14ma in addition a rb sr age of 1060 f 10ma on a biotite from a pegmatite indicates thermal resetting of the country rock minerals during dyke emplacement palaeomagnetic investigations of the dykes yield a primary thermoremanent magnetization direction corresponding to a palaeomagnetic pole at 17 s 266 e ag5 12 in addition to this primary magnetization an overprint component was present in many of the samples providing a palaeomagnetic pole at 30 s 138 e ags 24 which is similar to previous results from other central australian rocks affected by the alice springs orogeny the results extend the area of influence of the carboniferous alice springs orogeny southward into the musgrave block further the results provide no evidence for an earlier late proterozoic petermann orogeny affecting the musgrave block in the kulgera region however the possibility that a petermann orogeny thermal overprint has been erased by the alice springs orogeny cannot be dismissed

alluvial paleosols and pedofacies sequences in the permian lower beaufort of the southwestern karoo basin south africa abstract three types of paleosol profiles are described as representative of the range of soil types that developed on the ancient alluvial plains of the southwestern karoo basin during the late permian continuous 3 dimensional exposures of the lower beaufort adelaide subgroup strata allow detailed sedimentological taphonomic and paleopedological observation of thick floodplain sequences that contain numerous stacked paleosol profiles various floodplain strata contain characteristic paleosol profiles that are regulated by the periodicity and competence of overbank flooding both of which decrease with increasing distance from the contributing channel paleosols developed in levee or channel bank deposits are immature calcic entisols displaying evidence of early carbonate translocation but without well developed horizonation proximal floodbasin paleosols at the foot of the meanderbelt slope are mature calcic vertisols with more fully developed profiles containing zones of both carbonate and clay illuviation as well as some groundwater calcretes slickensided stress argillans in the b horizons are indicative of multiple cycles of wetting and drying distal floodbasin paleosols are dominated by hydromorphic and evaporitic processes as a result of their axial position in the floodbasin sheet like networks of mudcrack casts composed of calcretized aeolian sand and silt suggest that dust was a major source of calcium carbonate to the e soils the paleosols are interpreted as having formed under warm to hot semi arid climatic conditions with a strongly seasonal rainfall of 500 to 800 mm per annum and a mean annual moisture deficiency the geomorphic setting was similar to the holocene indo gangetic alluvial plain vertebrate burrow casts in the proximal floodbasin facies indicate a minimum depth to watertable of 150 cm the distribution of rooted horizons reflects dense vegetation flanking major drainage channels and sparse cover in the distal floodbasin a simple stratigraphic sequence of once laterally continuous paleosols is termed a pedofacies stacked sequences of pedofacies within approximately 20 50 m thick and 100 250 m thick stratigraphic successions reflect second and first order sedimentary cycles respectively both scales of cyclicity are attributed to autocyclically controlled avulsions of differentially aggrading channels in the first instance and of complete drainage networks in the second

smnd mineral isochron ages of late proterozoic dyke swarms in australia evidence for two distinctive events of mafic magmatism and crustal extension two distinctive events of widespread dyke intrusion have been identified in central southern australia crystallization ages of the dykes were determined using sm nd mineral isochrons obtained by splitting clinopyroxene and plagioclase into different magnetic and density fractions respectively the stuart dyke swarm in the southern arunta inlier and the kulgera dyke swarm in the eastern musgrave inlier define essentially identical crystallization ages of 1076 33 and 1090 32 ma respectively marking the first episode of post orogenic mafic magmatism in the region two samples from the gairdner dyke swarm in the stuart shelf yield sm nd mineral isochron ages of 867 47 and 802 35 ma respectively whilst two samples from the amata suite in the central musgrave inlier 790 40 and 797 49 ma these four ages represent the second episode of mafic magmatism in central southern australia these ages allow new constraints to be placed on the timing of large scale crustal extension and formation of intracratic depositional basins in the region initial nd values of 7 8 to 6 6 for the stuart dykes and 0 7 for the kulgera dykes suggest they were derived from different mantle sources with the stuart dykes being produced from strongly enriched sources in contrast positive and relatively uniform initial nd values of 2 5 to 4 1 for the younger amata suite and gairdner dykes indicate that they were derived from relatively depleted and homogeneous mantle sources the 1076 33 ma sm nd age of the stuart dyke swarm is significantly older than its rb sr mineral isochron age of 897 9 ma previously reported suggesting mobility of rb and or sr and partial resetting of rb sr isotopic systematics this study demonstrates that reliable and relatively precise sm nd ages can be obtained for precambrian dykes despite the limited number of mineral phases available in the dykes

south arunta block the internal zones of a proterozoic overthrust in central australia a detailed structural and microstructural analysis indicates that the chewings range area south arunta block was deformed during a north directed shearing event the chewings range quartzite and metasediments together with their granitic basement were involved in a proterozoic ductile deformation event responsible for a flat lying foliation axial planar to n s trending isoclinal folds within the foliation a n s oriented lineation developed parallel to a plane strain shearing or constrictive stretching direction in all rock types a ductile stretching of 100 150 was achieved during this strain history shear criteria observed in the gneisses are consistent with the asymmetric pattern of quartz c axis fabrics in the quartzite and indicate a south over north shear component strain is concentrated in narrow high strain zones which delineate a stack of complexly folded thrust sheets these results provide a new interpretation for the early to middle proterozoic of central australia the south arunta block may represent the internal zones of a north directed proterozoic overthrust correlation between structural elements of the south arunta block and the granulite belt to the north is unclear until this problem is resolved by careful dating it is suggested that d2 did not develop in the granulitic rocks owing to an intracrustal detachment above them

shrimp ionprobe dating of short lived proterozoic tectonic cycles in the northern arunta inlier central australia structural and metamorphic evidence from low p high t metamorphic terranes within the northern arunta inlier central australia indicates that two discrete tectonic cycles affected the region each cycle was associated with compressive deformation coincident with peak granulite facies metamorphism and granite intrusion shrimp u th pb analysis of zircons from early syn and late tectonic granitoids allows the age of the two tectonic cycles to be directly measured the age of the first cycle d1 is determined by emplacement of the mount stafford granite dated at or before 1818 15 ma after the first two foliations of the cycle had formed but before the axial plane cleavage associated with later upright folding the regional extent of this tectono magmatic event is confirmed by an emplacement age of 1818 8 ma measured on the large discordant harverson granite 40 km away the second cycle d2 consisted of four distinct deformation stages d2a 2d the ages of which are constrained by 1785 1775 ma old early syn and late tectonic granitoids the warimbi granite emplaced at or before 1785 22 ma and the granitic protolith to the napperby gneiss inferred to be 1780 10 ma pre date or formed during the earliest foliation s2a zircon considered to have grown at peak granulite facies metamorphic conditions during generation of the dominant s2b foliation gives an age of 1774 6 ma in the possum creek charnockite leucogranite in the napperby gneiss which post dates s2b and large scale upright nw se trending f2d folds yields an age of 1775 12 ma and confirms that the entire tectonic cycle d2a 2d formed in a rapid 10 ma period younger zircons which formed at 1659 6 ma in the napperby gneiss cannot be related to any local structural event but are similar in age to a major magmatic metamorphic episode in the southern arunta black and shaw 1992 150 km away they may be the peripheral manifestation of that event further zircon growth at 1600 ma in the napperby gneiss and possum creek charnockite was caused by hydrothermal fluid fluxing associated with post tectonic pegmatite emplacement these dykes were deformed by amphibolite facies retrograde shear zones ion probe dating of zircon stratigraphy from the granitoids has confirmed the discrete successive tectonic cycles identified by earlier structural and metamorphic studies for the northern arunta inlier at least those cycles or orogenies are associated with short lived 10 ma thermal pulses related to granite magmatism not prolonged thermal perturbations spanning 100 ma or more cf dirks and wilson 1990 dirks and hand 1991 such short lived pulses are intimately associated with granite intrusion and may be a general feature of low p high t metamorphism

fluvio pedogenic processes in an ephemeral stream channel nahal yael southern negev israel abstract a detailed stratigraphic survey conducted in the alluvial fill of the channel of nahal yael a small catchment in the southern negev desert indicates the existence of a continuous compacted red colored unit at an average depth of 50 cm beneath the surficial grey non cohesive alluvium granulometric distinction between the grey and the red alluvium is evident only within the fine

structural and metamorphic controls on the distribution of zircon in an evolving quartzofeldspathic migmatite an example from the reynolds range central australia three types of zircon occur in a complexly deformed and variably migmatized quartzofeldspathic gneiss from the reynolds range central australia the oldest type is inherited from the granitic precursor of the gneiss and is overgrown by a second group of zircon grains that formed during prograde granulite facies metamorphism partial melting of the gneiss resulted in solution of both the inherited and metamorphic zircon no new zircon growth accompanied crystallization of the partial melt suggesting loss of zirconium rich residual fluids hydrous amphibolite facies retrogression of the gneiss and its migmatized variants during late shearing produced new idiomorphic zircon in both the shear zone and its wall rocks important implications of this study are that i zircon has a tendency to dissolve if it comes into direct contact with a melt produced from anhydrous biotite breakdown in a quartzofeldspathic granulite ii melt crystallization is not necessarily accompanied by zircon growth and iii euhedral zircon can grow from a hydrous fluid phase under subsolidus amphibolite facies conditions e g within shear zones

climatic influences on continental deposition during late stage filling of an extensional basin southeastern arizona climatic rather than tectonic influences on continental deposition are recorded in the late stage fill of a neogene extensional basin in south eastern arizona regional geomorphic relations low sedimentation rates and stratigraphic overlap of the principal basin bounding structures identified in a gravity anomaly profile indicate that the plio pleistocene st david formation accumulated in the san pedro valley during a period of tectonic quiescence stable isotopic composition of paleosol calcite is placed within a magnetostratigraphic framework that provides an interpretive record of variable arid to semiarid climate in the valley before 3 4 ma the valley was hydrologically closed and experienced an arid climate with seasonal precipitation drainage integration at ca 3 4 ma corresponds with a transition to wetter conditions less seasonally variable precipitation and a rising water table indicated by hydromorphic paleosols and pond deposits gradually increasing seasonality of precipitation after 2 8 ma and further decrease in winter rainfall after 2 2 ma led to establishment of a dry monsoonal climate between 1 6 and 0 6 ma the change in climate at ca 1 6 ma coincides with abrupt appearance of sheet flood dominated fan gravels above earlier vertically aggraded fluvial channel and interfluve flood plain deposits this change in facies is interpreted as the result of climatic change rather than an example of subsidence driven gravel progradation sedimentation rates were greatest when climate was relatively wet with dominant winter rainfall and about equally low for relatively dry with dominant summer rain and relatively wet but nonseasonal conditions contrary to past model simulations channel flood plain facies ratios and sedimentation rate varied directly ribbon as opposed to sheet channel bodies were favored by relatively wet climatic conditions and were less commonly formed during dry strongly seasonal times precise process response interpretation of this correlation of sedimentological variability to changing climate is limited by the restricted interpretation of paleosolisotope paleoclimate data and the poor understanding of sedimentological response to climate change during 10 5 to 10 6 yr time intervals the results of this study suggest however that caution be applied to a priori interpretations of stratigraphic variations within thick syntectonic basin fills as responses to varying subsidence rates only

shrimp u_pb zircon geochronology of granites in the arunta inlier central australia implications for proterozoic crustal evolution abstract new shrimp u pb zircon isotopic ages are reported for ten granitic suites in the eastern arunta inlier these data combined with previous u pb zircon studies in the region constrain the timing of major palaeoproterozoic igneous events within the arunta inlier and establish a geochronological framework for understanding lithostratigraphic relationships tectonic events and geochemical and isotopic evolution of the granites in the region most granites in the arunta inlier including both syn tectonic and post tectonic types yield zircon ages in the range of 1770 1710 ma which are significantly younger than the 1880 1850 ma orogenic barramundi igneous association recognised throughout many other proterozoic terrains in northern australia no rocks of the barramundi association have been identified in this study the previously proposed barramundi type suites including the jervois and dneiper granites yield ages of 1771 6 and 1771 15 ma respectively many of the granite suites contain inherited zircons with ages in the range of 1890 1830 ma similar to the age of the barramundi association this and the age of the atnarpa igneous complex zhao and cooper 1992 which is coeval with but geochemically distinct from the barramundi association suggest that the 1880 1850 ma orogenic event affected the arunta inlier but has been obscured by the younger tectonic events the youth of tectonic events in the arunta inlier as compared with other proterozoic terrains of northern australia may have resulted from the inlier being located on the southern margin of the northern australian orogenic province during the palaeoproterozoic with the generation of granites in the arunta inlier possibly being related to subduction the combined data indicate that major granitic activity occurred at 1880 1850 1820 1770 1750 1730 1710 1660 1650 and 1615 1590 ma this result is broadly consistent with earlier summaries of the other proterozoic terrains in northern australia although the intensity of each episode varies in different regions

observations of desert flood bores flood bores have been measured in desert stream floods the bores were steep and small pebbles were observed to be pushed ahead bore velocity changed downstream and was controlled by local channel geometry in narrow reaches the bore advanced at rates twice those of wide reaches mean bore velocity was about 50 per cent of that of mean flow at peak flood discharge the surfaces of shallow bores were covered by air foams this was not the case in deeper faster examples

discrete proterozoic structural terranes associated with low p high t metamorphism anmatjira range arunta inlier central australia tectonic implications structural overprinting relationships indicate that two discrete terranes mt stafford and weldon occur in the anmatjira range northern arunta inlier central australia in the mt stafford terrane early recumbent structures associated with d1a 1b deformation are restricted to areas of granulite facies metamorphism and are overprinted by upright km scale folds f1c which extend into areas of lower metamorphic grade structural relationships are simple in the low grade rocks but complex and variable in higher grade equivalents the three deformation events in the mt stafford terrane constitute the first tectonic cycle d1 d2 deformation in the weldon terrane comprises the second tectonic cycle the earliest foliation s2a was largely obliterated by the dominant reclined to recumbent mylonitic foliation s2b produced during progressive non coaxial deformation with local sheath folds and w to sw directed thrusts locally d2d tectonites have been rotated by n s trending upright f2c folds but the regional upright fold event f2d also evident in the adjacent reynolds range rotated earlier surfaces into shallow plunging nw se trending folds that dominate the regional outcrop pattern the terranes can be separated on structural metamorphic and isotopic criteria a high strain d2 mylonite zone produced during w to sw directed thrusting separates the weldon and mt stafford terranes 1820 ma megacrystic granites in the mt stafford terrane intruded high grade metamorphic rocks that had undergone d1a and d1b deformation but in turn were deformed by s1c which provides a minimum age limit for the first structural metamorphic event 1760 ma charnockites in the weldon terrane were emplaced post d2a and metamorphosed under granulite facies conditions during d2b constraining the second tectonic cycle to this period each terrane is associated with low p high t metamorphism characterized by anticlockwise p t t paths with the thermal peaks occurring before or very early in the tectonic cycle these relations are not compatible with continental style collision nor with extensional tectonics as the deformation was compressional the preferred model involves thickening of previously thinned lithosphere at a stage significantly after 50 ma the early extensional event compression was driven by external forces such as plate convergence but deformation was largely confined to and around composite granitoid sheets in the mid crust the sheets comprise up to 80 of the terranes and induced low p high t metamorphism including migmatization thereby markedly reducing the yield strength and accelerating deformation of the country rocks mid crustal ductile shearing and reclined to recumbent folding resulted followed by upright folding that extended beyond the thermal anomaly thus thermal softening induced by heat focusing is capable of generating discrete structural terranes characterized by subhorizontal ductile shear in the mid crust localized around large granitoid intrusions

an assessment based on u_pb zircon data of rb_sr dating in the arunta inlier central australia abstract the chronology of the arunta inlier was originally based mostly on rb sr dating although some of the ages derived from that technique are now shown to be erroneous those which were constrained by structural observations and which relied only on whole rock and not mineral analyses have proven to be remarkably realistic ion microprobe data show that even conventional multigrain u pb zircon analysis is not a particularly appropriate dating technique in a region of this complexity three new u pb zircon ages and others previously derived from the same isotopic system date three of the main tectonic events that were imposed on the arunta inlier the widespread strangways orogeny of the northern and central provinces occurred at 1760 1750 ma the argilke event is not older than 1680 ma demonstrating that the southern province is the youngest in the inlier the dominantly thermal ormiston event is dated at 1140 ma

the role of fungal biomineralization in the formation of early carboniferous soil fabrics paleosols in the lower carboniferous limestones of south wales commonly contain needle fibre calcite which is an unusual form of calcite recently shown to form by the calcification of fungal hyphae in present day soils the needle fibre calcite occurs in two associations in the paleosols as coatings on sediment grains and as rhizocretions the former can be compared with the microbial grain coatings of quaternary calcretes the latter represent the sites of fungal coats on roots and are interpreted as probable ectomycorrhizae a symbiotic fungal sheath root association these findings suggest that biomineralization was important in the formation of soil fabrics during the carboniferous as it is in present day soils

the simpson strzelecki and tirari deserts development and sand provenance abstract sands of the simpson strzelecki and tirari deserts central australia can be divided into two main groups on the basis of their physical and chemical characteristics colour grainsize heavy minerals quartz oxygen isotope composition zircon u pb ages the first group encompasses the strzelecki tirari and southeastern simpson deserts while the second occupies the northern and the western simpson desert the boundary between the two groups corresponds approximately to the northern most extent of the kallakoopah lakes several lines of evidence suggest derivation of the sands mainly from local bedrock with very little subsequent aeolian transport ultimate protosources for the sands in order of importance are for the southeastern simpson tirari and strzelecki deserts the tasman orogenic system new england and lachlan fold belts georgetown inlier musgrave and arunta blocks gawler and curnamona cratons and for the north and western simpson desert arunta musgrave and mount isa blocks and tennant creek inlier sediment from the tasman orogenic system includes an additional exotic component from palaeozoic sediments probably derived mainly from antarctica sediment transport from these protosources across the several hundred kilometres to the surficial sedimentary basins was dominantly by fluvial not aeolian means quaternary aeolian transport or reworking has been minimal serving only to form the dunes by vertical corrasion of underlying sedimentary rocks or residual products of local basement weathering the deserts have received some recent localised sediment input from modern fluvial systems

u_pb zircon dating of tectonomagmatic events in the northern arunta inlier central australia abstract the mount doreen area of the northern arunta inlier has a proterozoic magmatic and tectonic history that extends over 300 ma the oldest unit the turbiditic lander rock beds lrb was folded and metamorphosed from greenschist to granulite grade during the yuendumu tectonic event a u pb zircon age of 1880 5 ma for the late tectonic ngadarunga granite provides a minimum age for this event and supports its correlation with the widespread barramundi orogeny of northern australia two subsequent major deformations the hardy and the wabudali tectonic phases considered to represent discrete phases of the strangways orogeny are tentatively placed at around 1770 ma the hardy tectonic phase locally retrogressed the lrb and produced strong foliations in some granites including one of the carrington suite dated at 1779 6 ma the wabudali tectonic phase formed high strain zones in places more than 2 km wide within which the sedimentary reynolds range group was tightly folded and the lrb were refolded and retrogressed felsic volcanics and arenites of the fault bound nicker beds and patmungala beds dated at 1772 5 ma and 1799 10 ma respectively were also tightly folded during the strangways orogeny juxtaposition of low grade and high grade lrb took place during faulting that occurred after the 1770 ma tectonism but prior to post tectonic granites which may be indirectly related to the 1600 ma chewings orogeny of the southern arunta inlier one post tectonic granite 1635 9 ma is associated with a mafic to intermediate intrusive complex and another 1567 11 ma is part of an extensive megacrystic suite that intrudes folded reynolds range group zircon inheritance was found in five of the six analysed samples with ages ranging from 1 85 to 3 45 ga

the palaeozoic history of an unusual intracratonic thrust belt in central australia based on 40ar 39ar k ar and fission track dating intraplate thrusting involving reactivation of a mid proterozoic province boundary within the basement metamorphic rocks of the arunta block occurs at the northern margin of the late proterozoic to mid palaeozoic amadeus basin in central australia earlier geological and geophysical studies show that the thrust system referred to as the alice springs orogen is 9thick skinned9 in the central part of the thrust belt and was dominated by the crust cutting redbank thrust zone several episodes of thrusting defined stratigraphically began about 400 ma ago analysis and modelling of 40 ar 39 ar age spectra on k feldspar from the basement rocks combined with regional geological constraints point to cooling rates of 3 10 c ma and moderate overall exhumation rates of 100 400 m ma during the alice springs orogeny without appreciably increased heat flow however final uplift along the thrust front at 300 320 ma was rapid as the time of final closure of small domains in k feldspar approximates apatite fission track ages by using 40 ar 39 ar age data as a constraint together with available geological and geophysical data crustal shortening across the thrust belt is thought to be approximately 20 to 30 overall convergence rates of 0 6 3 km ma are slow compared with rates of 5 km ma for continent continent collision zones

the age of the ormiston pound granite implications for mesoproterozoic evolution of the arunta inlier central australia the ormiston pound granite southern arunta inlier intruded during the terminal stages late to post d2 of a major n directed overthrust event called the chewings orogeny which deformed supracrustal rocks of the simpsons and chewings assemblages ion probe zircon u pb analysis of the granite indicates an emplacement age of 1603 10 ma more than 500 ma older than the rb sr isochron age timing of emplacement is confirmed by an age of 1575 20 ma for zircon mantles from a gneissic xenolith in the granite zircon cores from the xenolith yield an age of 1678 14 ma which is taken to represent the protolith age of the surrounding gneisses the shrimp age is similar to but more precise than the 1586 69 ma rb sr isochron age for the chewings orogeny determined by marjoribanks and black 1975 penecontemporaneous 1600 ma magmatism is evident as pegmatites and associated fluid flow zones in the anmatjira and reynolds ranges northern arunta inlier 1100 1030 ma rb sr mica ages from the 1600 ma ormiston pound granite coeval pegmatites and 1680 ma host rock gneisses are similar to a sm nd isochron age for the mafic stuart dyke swarm of the southern arunta inlier and the contemporaneous alcarra dyke swarm in the musgrave inlier some 500 km farther south the rb sr mica ages reflect isotopic resetting by a thermal perturbation either associated with regional crustal extension during 1080 ma dyke intrusion or with the 1150 ma magmatic event in the southern arunta cf black and shaw 1992 irrespective the 1050 900 ma ormiston event described by shaw et al 1984 as granite intrusion associated with high grade metamorphism migmatization and folding needs to be re defined or abandoned

reddening of dune sands evidence from southeast india thin section sem and tem analyses have indicated that the red teri sands of southeast india have formed from weathering in situ of coastal dune sands the data does not support a detrital origin for the red sands c14 dates indicate that dune deposition and weathering to a maximum depth of 10 m leading to the formation of a hematite koalinite and illite rich matrix has taken place rapidly over the past 25 000 years it is postulated that garnet was a major source of hematite ferric oxide

zircon u pb chronometry of the pressure and temperature history of granulites in the musgrave ranges central australia ion microprobe u pb measurements of zircon in the musgrave ranges of central australia date the emplacement of a charnockite which is cut by a shear zone containing a garnet clinopyroxene assemblage m2 pt conditions 11 kb and 720 c at 1200 ma veinlets of a post m2 adamellite cut an m4 assemblage pt conditions 6 kb and 670 c contained in a metadolerite inclusion suggesting that the adamellite was emplaced during or after m4 igneous and metamorphic zircons in the adamellite however grew at about 1200 ma indicating that m2 and m4 were synchronous at the level of precision of our data the time interval between the growth of the two assemblages can not have been more than 20 ma we interpret the pressure temperature and time ptt path obtained by combining our thermobarometric data and zircon u pb ages in terms of magmatic heat input in a thickened crustal segment followed by rapid possibly technically driven uplift of the lower part of the thickened crust to a depth of 15 20 km

porosity and consolidation limits of sediments and gassmann s elastic wave equation the elastic framework properties of sediments relate to porosity porosity relates to the state of consolidation of sediments the full range of quasi static elastic moduli vs porosity behavior can be incorporated into gassmann s 1951 equations i review the atterberg 1911 limits to establish a basis for discussing the precompaction porosity 0 which corresponds approximately to the atterberg plastic limit this porosity is about 0 36 0 40 for sands and sandstones the ratio of the dry frame moduli to the effective mineral moduli is 1 0 i incorporate this ratio into gassmann s equations which operate from 0 0 when sediments have a solid elastic frame for s 0 when sediments no longer have a solid elastic frame gassmann s equations reduce to reuss 1929 isostress average for the solid fluid mixture

nd isotope study of granites from the arunta inlier central australia constraints on geological models and limitation of the method abstract three chemically distinct types of granite high sr low y calc alkaline palaeoproterozoic normal and enriched are present in the palaeoproterozoic arunta inlier of central australia twenty one representative samples were selected for nd isotopic analysis to complement geological and geochemical data most samples analysed have depleted mantle nd isotope model ages tdm following mcculloch 1987 of 2 3 to 2 1 ga similar to most of palaeoproterozoic granites of northern australia mcculloch 1987 these ages do not show a younging trend from the northern to southern provinces although some post 1750 ma granites from the central and southern provinces with typical felsic crust 147 sm 144 nd ratios 0 09 0 11 have younger model ages less than 2 0 ga post 1700 ma normal type granites from the southern province have chemical compositions similar to older granites 1880 1760 ma of the same suite even though they have younger model ages 1960 1930 ma this implies an increase in a younger component within southern source regions through melting of new underplate and or additional mantle input the syn or post tectonic granites 1720 1140 ma of the enriched type high heat producing granites rich in th u and k have similar tdm model ages to older granites of the normal type from the same areas the enriched type granite from the teapot granite complex of the southern province are characterised by low cs sr and high rb cs 30 50 th u 7 20 ratios and high y contents these chemical characteristics are consistent with magma being formed through anatexis of normal type granite sources in contrast an 1820 ma s type granite from the harverson suite in the northern province has an older tdm model age 2 32 ga than the tdm 2 18 ga age of the nearby aileron metamorphics suggesting that the source rock of the granite may contain a significant archaean component the nd isotope data when integrated with geological and chemical information are compatible with the recycling of archaean crustal material such a process might have taken place very early in the history of the arunta inlier through subduction along a continental margin made up of a stretched dismembered thin archaean basement magmatic underplating may have taken place shortly before 1850 ma and continued episodically during subsequent tectono thermal events crustal melts of mixed source rocks formed during these events could contain different amounts of an archaean component

geochronological constraints on orogenic events in the arunta inlier a review early workers subdivided the arunta inlier central australia into three major tectonic provinces classified the principal tectonostratigraphic units into three divisions and separated the tectonomagmatic history into five discrete events ranging in age from 1800 ma to 300 ma a review of the evidence for tectonic boundaries within the arunta inlier suggests that no major structural discontinuity exists between the northern and central tectonic provinces but that the redbank thrust zone is at least in part a province boundary the tectonostratigraphic division concept also requires revision as division 3 rocks of the northern and southern arunta cannot be time equivalents division 1 rocks grade into division 2 in the northern region and division 3 of the northern region may be equivalent to division 1 in the central region rocks originally assigned to divisions are better grouped into a larger number of lithological assemblages until better stratigraphic and isotopic correlations can be made compilation of rb sr and 40ar39ar age determinations obtained before 1984 indicate an almost complete age spectrum from 1800 ma to 1000 ma but age clusters exist at 1400 ma 1100 ma and 400 300 ma which have geological significance subdivision of older ages into discrete tectonic events was not justified from this data alone but more recent u pb isotopic analysis of zircons in rocks designated to particular structural metamorphic events has revealed a complex tectonic history in the 1880 1600 ma interval the northern and central provinces underwent major tectonism between 1780 1730 ma but much of the southern province was not deformed until 1600 ma the revised tectonic history nomenclature is proposed for the arunta inlier following deposition of a widespread turbiditic unit at or before 1880 ma possibly on thinned archaean crust the northern and central provinces underwent localized tectonism magmatism at 1880 ma yuendumu tectonic event and 1820 ma stafford tectonic event prior to the widespread strangways orogeny which is subdivided into an early phase at 1780 1770 ma and late phase at 1745 1730 ma it is not clear whether the strangways orogeny is a single arunta wide event or a series of separate short lived smaller scale events although the major deformation in all areas appears to have involved w to sw directed thrusting in the southern province the major events occurred at 1680 ma argilke tectonic event and 1600 ma chewings orogeny the latter involving n directed thrusting that was penecontemporaneous with post tectonic pegmatite intrusion in the northern province suggesting linkage of both regions at this stage the younger history of the inlier is characterised by several stages of uplift and isolated thermal magmatic events major mesoproterozoic crustal exhumation anmatjira uplift phase has been interpreted from widespread 1500 1400 ma ages including regional scale closure of 40ar 39ar systems in hornblende from mafic granulite outcrop scale rb sr total rock isotopic systems in mylonitized granitoids and sm nd garnet hornblende pairs in mylonitized amphibolites a 1150 ma thermal event in the southern part of the inlier teapot magmatic event is recorded by intrusion of granite pegmatites and the alkaline mordor igneous complex and by isotopic resetting of rb sr mineral systems dolerite dyke injection at 1050 ma reflects limited extensional tectonism that may have related to formation of the amadeus basin the second major uplift event was the alice springs orogeny at 400 300 ma an unusual intracratonic thick and thin skinned thrust event that involved limited retrograde amphibolite facies but extensive greenschist facies metamorphism and restricted pegmatite intrusion

flood frequency of the mojave river and the formation of late holocene playa lakes southern california usa perennial lakes lasting several decades occupied silver lake playa the terminus of the mojave river as recently as 390 90 and 3620 70 bp flood routings from the mojave river headwaters to its terminal playa and water balance calculations for the resulting lakes indicate that floods comparable in magnitude to the largest floods in the modern record must occur almost annually to generate and maintain perennial lakes in contrast the modern floods of this magnitude have recurrence intervals greater than 18 years such an increase in flood frequency is required even if lake evaporation is reduced by as much as 50 modern extreme floods of the mojave river are related to meridional atmospheric circulation and a southeastward shift in the winter low pressure center over the north pacific ocean causing vigorous storms over the headwaters in the san bernardino mountains of southern california this winter pattern probably occurred more frequently to induce the large number of storms and floods needed

ultrasonic velocities in sands revisited ultrasonic compressional and shear wave velocities of isotropic sands are shown to be dependent on their mineralogy their porosity their fluid content and their state of consolidation under fixed temperature and pressure conditions this leads to a distinction between two broad classes of sands those that are well consolidated and those that are loosely consolidated changes in elastic velocities reflect changes in the ratio of bulk and shear moduli to density in response to lithologic variations we decouple the two effects by examining changes in elastic moduli with respect to changes in lithology and we observe three main points 1 for consolidated sandstones the effects of mineralogy and porosity can be approximated both empirically and theoretically by a modified isostrain theory the dry bulk and shear moduli of the rock aggregate follow a mixing law being linear combinations of the respective moduli of the individual constituents the dry elastic moduli of families of clean sands and s

compressional and shear wave logging in open and cased holes using a multipole tool we have found in field observations that the multipole sonic logging tool can effectively measure formation p wave and s wave data in a cased hole the multipole tool containing both monopole and quadrupole source receiver systems was originally designed to log p and s waves directly in all lithologies for an open borehole the monopole source receiver system p wave operates at 7 10 khz as compared with 15 25 khz for a conventional sonic tool while the quadrupole source receiver system s wave operates at 3 7 khz these lower operating frequencies enable the signals to penetrate the well casing and cement more effectively than signals from a conventional sonic tool as a result the formation p and s waves recorded by the multipole tool are generally much stronger than the unwanted waves which travel along the well casing and cement formation arrivals can be easily identified and separated from the casing arrivals for a wide range of lithologies logs run before and after the wells were cased

age geological setting and paragenesis of heavy rare earth element mineralization of the tanami region western australia metasedimentary rock hosted heavy rare earth element hree mineralization occurs as numerous orebodies distributed across a large district of the tanami region of central australia close to a regional unconformity between archean metasedimentary rocks of the browns range metamorphics brm and overlying proterozoic birrindudu group sandstones the orebodies consist predominantly of quartz xenotime and minor florencite and occur along steeply dipping structures within a stockwork of hydrothermal veins and breccias paragenetic stages of the mineralization include 1 a pre ore stage of a greenschist facies overprint of detrital minerals including quartz alkali feldspar plagioclase and muscovite aligned in the premineralization foliation 2 syn ore quartz and white mica alteration associated with a multistage mineralization of the ore minerals primarily in breccias and veins and 3 a post ore stage of veining and brecciation forming several generations of quartz plus hematite barite anhydrite and pyrite in situ u pb dating of xenotime from several deposits prospects yielded an age range for mineralization of 1 65 to 1 60 ga this timeframe lacks local magmatism or orogeny and is significantly younger than the ca 1 72 ga 40ar 39ar age of the pre ore muscovite far field stresses associated with the distal isan and liebig orogenies are invoked as drivers of large scale fluid flow and fault re activation in the region we propose that ore formation was achieved via fluid leaching of ree from the brm followed by fluid mixing in fault zones especially in the vicinity of the unconformity between the brm and overlying birrindudu group sandstones this mineralization style shares many features with unconformity related u deposits and there is significant potential for discovery of further ree orebodies of this style especially in the vicinity of regional unconformities in intercontinental sedimentary basins

the role of downhole measurements in marine geology and geophysics during the last 25 years downhole measurements have been increasingly used for scientific applications in marine geology and geophysics particularly in deep sea drilling operations used mostly by the oil industry to map promising formations for exploration and production of hydrocarbons a variety of instruments have been developed that can be lowered down drill holes to extract information about the subsurface geology in the last decade advances in computers software and data transmission have greatly increased the amount and quality of data that such instruments can provide relatively new instruments that image the borehole wall with high resolution can reveal layers and faults that previously could be seen only in core sections downhole measurements play a crucial role in linking core data with regional geophysical surveys and in providing data where core sections could not be obtained examples of recent scientific applications and approaches are presented that address previous problems with data quality and changes in properties over time after a hole is drilled the role of downhole measurements is discussed for two broad areas of research the structure and composition of the earth s crust most of which is formed at mid ocean ridges and past changes in earth s environment recorded in the deep sea sediments overlying the crust finally new emerging technologies and experiments that promise significant advantages over current methods for downhole measurements in marine geology and geophysics are discussed