cambrian grand cycles a northern appalachian perspective large scale sedimentary cycles or grand cycles are the most obvious features of the port au port group in southwestern newfoundland each cycle is interpreted to represent deposition in outer platform muddy tidal flats lower shaly half cycle and ooid shoal complexes upper carbonate half cycle unpredictable metre scale assemblages of oolite and carbonate laminite constituting the carbonate half cycles are attributed to frequent migration of the shoal complexes in response to hydrographic factors such as tidal fluctuations and storms predictable metre scale shallowing upward cycles of parted limestone and shale in the shaly half cycles were probably controlled mainly by variable rates of carbonate sedimentation a eustatic mechanism however cannot be discounted comparison with other north american grand cycles suggests a eustatic mechanism for grand cycle formation possibly involving variations in the rate of sea level rise the interpreted sequence of formation established on the basis of the port au port group involves 1 a rapid sea level rise which flooded the platform with shoreward derived siliciclastic muds and resulted in the development of muddy tidal flats and 2 the gradual development of ooid shoal complexes which encroached onto the tidal flats with decreasing rates of sea level rise in contrast to western north american examples newfoundland grand cycles are composed almost entirely of peritidal sediments they are also thinner and have a smaller areal extent than do those in the west these differences may be due to such factors as narrower shelves slower rates of sedimentation and lower amplitudes of sea level rise on the present northeastern margin of the north american craton than on the western margin

effects of grand cycle cessation on the diagenesis of upper cambrian carbonate deposits in the southern appalachians u s a abstract the vertical transition from the mainly subtidal alternating shale and carbonate units or grand cycles of the conasauga group middle to upper cambrian to the peritidal dolostone of the knox group upper cambrian to lower ordovician marks a major change in the early paleozoic passive margin sedimentation of the southern appalachians the grand cycles represent an interplay between intrashelf shale basin and carbonate platform deposition the end of grand cycle deposition occurred in response to carbonate platform progradation over the infilled intrashelf basin and is associated with a prominent change in diagenetic patterns observed in the uppermost conasauga group strata the maynardville formation the maynardville records upward shallowing from subtidal shale and limestone into peritidal dolostone this change from a subtidal into a peritidal depositional regime influenced the early diagenesis of the maynardville and in conjunction with the changes in the regional facies distribution at the end of grand cycle deposition extended its influence upon the burial diagenesis of these deposits the subtidal deposits of the maynardville contain a variety of calcite cements dolomite is not abundant in these deposits where it occurs mainly as a fine crystalline ferroan phase associated with argillaceous layers and pressure dissolution features the local source for this dolomite during burial was provided by expulsion of pore fluids from interbedded shale deposits diagenesis of clay minerals and pressure dissolution of carbonates ferruginous coatings on hardgrounds in the subtidal deposits provided an additional local source of iron for the formation of replacement saddle dolomite the subtidal deposits also contain saddle dolomite cement associated with mississippi valley type mvt minerals which indicate the involvement of externally derived fluids during late burial diagenesis of these strata the peritidal deposits on the other hand are extensively dolomitized fine crystalline dolomite most likely represents early diagenetic replacement of tidal flat carbonate sediment coarse crystalline replacement dolomite formed during burial by recrystallization of early dolomite and dolomitization by warm burial brines fenestrae desiccation cracks and evaporite dissolution voids are occluded with dolomite cement which is commonly complexly zoned zoned dolomite precipitated during shallow to intermediate burial and is postdated by saddle dolomite cement saddle dolomite in pore centers dissolutional voids and tectonic fractures formed during late burial from warm fluids associated with the migration of mvt brines the effects of changes in the depositional setting on diagenesis are reflected in similar early diagenesis between the subtidal maynardville and the underlying conasauga group carbonate deposits and between the peritidal deposits of the upper maynardville and the rest of the overlying knox group the depositional environments and early diagenesis also affected the burial diagenesis the changes in regional facies distribution caused by carbonate platform progradation at the end of grand cycle deposition resulted in a decrease in the proportion of siliciclastic components this decrease was accompanied by a decline in the amount of ferroan carbonate in the peritidal deposits the maynardville is conformably overlain by carbonate deposits of the knox group this allowed the maynardville knox succession to behave as a single hydrologic unit for the migration of burial fluids in response to the formation of the ordovician foreland sevier basin to the southeast during the conversion from a passive into a convergent continental margin the nolichucky shale separates the maynardville knox succession from the carbonate deposits of the underlying conasauga group which were in contrast affected by the migration of burial fluids from the cambrian intrashelf shale basin to the west

lake lewis basin central australia environmental evolution and osl chronology abstract lake lewis is the furthest from the coast of australia s salt lakes and lies at the southern edge of influence of the australian monsoon regime the macdonnell ranges south of the lake intercept moist air masses crossing the region and efficiently deliver water and sediment to the lake and its surrounding alluvial plain we describe lacustrine fluvial and aeolian environments of the basin and report optically stimulated luminescence osl dates from representative sediments a long period of generally wetter conditions during most of the pleistocene is represented by thick uniform lacustrine clay beneath and near lake lewis this is overlain by more heterogeneous lacustrine sediments deposited since hydrologic closure of the basin which indicate fluctuating climatic conditions osl results show that dune building in the basin commenced before 95 ka when salinity at the depocentre was high dune building peaked around 23 21 ka osl ages of fluvial deposits show that floods occurred during the last 20 ka following the last phase of maximum aridity in the region

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

carbon oxygen and sulphur isotope variations in concretions from the upper lias of n e england carbon oxygen and sulphur isotope data for transects across two pyrite bearmg carbonate concretions and their host sediments from the upper lias of n e england show symmetrical zonation 13cpdb values of the calcite cement 12 9 to 15 4 indicate that most of it originated from organic matter by bacterial reduction of sulphate augmented with marine and to a lesser extent fermentation derived carbonate organic carbon 13cpdb 26 1 to 37 0 reflects the admixture of allochtho nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation two phases of pyrite are present in each concretion the earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34scd values of 22 to 26 indicating formation by open system sulphate reduction the later euhedral phase is more abundant and reaches values of 2 5 to 5 5 at concretion margins this phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system the 13c and 34s data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface the 18o values of the calcite in one concretion 18opdb 2 3 to 4 8 indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater the other concretion is isotopically much lighter 18opdb 8 9 to 9 9 and large 18o differences between concretions in closely spaced horizons imply that local factors control the isotopic composition of pore waters

initiation of the australian summer monsoon 14 000 years ago abstract definitive evidence for the onset of monsoon moisture in northern australia following the arid phase of the last glacial maximum has been elusive in large part due to the lack of long continuous sediment records here we report new evidence from two separate drainage basins in the kimberley region of monsoonal northwestern australia at both sites radiocarbon ages on basal biogenic materials in flood deposits indicate stream flow as high or higher than maximum historic levels began about 14 cal ka bp these results suggest that the australian summer monsoon was fully active several millennia earlier than previously expected the early onset of the monsoon and the widespread evidence for diminished monsoon activity in the late holocene cannot be reconciled with primary forcing of the australian monsoon by changes in low latitude summer insolation over australia

orbitally paced paleoproductivity variations in the timor sea and indonesian throughflow variability during the last 460 kyr 1 a high resolution 1 2 kyr multiproxy record from the timor sea in the easternmost indian ocean international marine global change images program core md01 2378 latitude 13 04 95 s longitude 121 47 27 e 1783 m water depth closely tracks changes in intermediate water ventilation and paleoproductivity over the last 460 kyr within one of the main outflow passages of the indonesian throughflow spectral analysis of five different flux based productivity proxies indicates spectral power concentrated in the 100 kyr glacial interglacial and the 23 kyr and 19 kyr precessional periods paleoproductivity maxima lead ice volume benthic 18o maxima by 20 to 40 1300 to 2600 years at the precession band the spectral differences in tropical paleoproductivity records from the pacific and indian oceans suggest that local processes wind and circulation patterns driven by insolation are dominant in driving productivity rather than large scale tropical features in the timor sea productivity fluctuations over the last 460 kyr were strongly influenced by monsoonal wind patterns offshore nw australia 23 and 19 kyr and were also modulated by sea level related variations in the intensity of the indonesian throughflow 100 kyr

variations of the northwest australian summer monsoon over the last 300 000 years the paleohydrological record of the gregory mulan lakes system abstract monsoon rains in the kimberley region feed an interconnected chain of lake basins the gregory lakes system in northwestern australia a terminal system surrounded by dunefields of the great sandy desert this semi arid region records a sequence of quaternary climatic changes at times much wetter at times much drier than today a morphostratigraphic sequence defines episodic formation of dunes and related sediments reflecting past hydrologic and climatic changes which caused them thermoluminescence dating provides a broad temporal framework identifying major hydrologic changes of the past 300 ka ancient foreshore dunes define shorelines of mega lake phases the largest of which covered some 6500 km2 with ages near 300 ka later lacustral expansions near 200 and 100 ka reflect wet phases broadly comparable to marine isotope stages 7 and 5 with a trend towards increasing aridity through time longitudinal quartz dune formed within the mega lake confines between successive wet phases with at least two dune building episodes near or just before 230 and 70 ka monsoon activity today produces short lived flood events such as recorded in 1993 climates of the mega lake phases need not be drastically different from today s although a substantial increase in the frequency of high magnitude events was certainly involved

a composite study of onset of the australian summer monsoon abstract onset of the australian summer monsoon is identified each year 1957 87 using the wind and rainfall record at darwin onset is defined as the first occurrence of wet 850 mb westerly winds composites of atmospheric fields at stations in and about the australian tropics are constructed relative to the onset date at darwin the composite onset is accompanied by the development of a convectively driven baroclinic circulation over northern australia upper tropospheric easterlies expand about the equator and the subtropical jet shifts poleward at onset this behavior is interpreted as a transient southerly shift of the local hadley circulation concurrent with the development of an upper level anticyclone over northern australia the composite onset coincides with the arrival of an eastward propagating convective anomaly the anomaly originates in the southern indian ocean propagates eastward at 5 m s 1 and is detectable as far east as the date line an eastward propagating zonal wind anomaly also

gangue mineral 87 sr 86 sr ratios and the origin of mississippi valley type mineralization the 87 sr 86 sr ratio measurements in mississippi valley type gangue minerals and host marine carbonates ranging in age from upper cambrian to mississippian show that in northwestern ohio where the mineralization is sparse the minerals precipitated from fluids in local isotopic equilibrium with the host carbonates in which the minerals were emplaced in contrast most gangue minerals from districts of major mineralization in illinois kentucky virginia and tennessee contain strontium with higher 87 sr 86 sr ratios than the carbonate hosts and appear to have crystallized from fluids containing strontium from silicate minerals in the sedimentary succession no evidence has been found for a magmatie component in the ore fluid strontium data from elmwood tennessee show that the early ore fluids like those of northwestern ohio were in isotopic equilibrium with the host carbonates but that they were mixed with and displaced by introduced fluids containing more radiogenic strontium these findings are consistent with the two fluid mixing model for the mississippi valley mineralization where a fluid indigenous to the host carbonates and containing reduced sulfur was mixed with introduced fluids analogous to metal bearing and low sulfide oil field brines with an extensive history of chemical exchange with clays and other silicate minerals in the sedimentary succession

insolation forcing of the australian monsoon as controls of pleistocene mega lake events 1 during the last c 300 000 years mega lakes with areas an order of magnitude greater than those of today occurred in the monsoon region of northern australia the results of an atmosphere global circulation model agcm sensitivity experiment show that the repeated occurrence of mega lake phases during the pleistocene and the strong monsoon flow that this implies can be related to milankovitch insolation forcing the agcm experiment is centred on the southern hemisphere low latitude summer insolation high of 115 000 years ago the details of the results indicate a strong response of the australian monsoon to the higher insolation at that time with a longer monsoon season increased precipitation and higher resultant runoff than at present

formation temperature estimation by inversion of borehole measurements we describe a new numerical method that uses inverse methods to model thermal stabilization of a borehole after drilling mud circulation has stopped the following five geophysical parameters can be estimated from the method 1 true formation temperature tf 2 mud temperature tm at the time the mud circulation stops 3 thermal invasion distance r into the formation before the formation is at the true formation temperature tf 4 formation thermal conductivity k perpendicular to the borehole and 5 efficiency factor f for heating mud in the borehole after mud circulation has stopped crucial input data for the model are the temperature measurements with shut in time taken at a fixed depth more than two measurements being required and the mud temperature at the surface at the time circulation stops other input data include the radius of the borehole and the densities and specific heats of the drilling mud and of the formation on which the temperature measurements are made applicatio

δ18o values 87sr86sr and sr mg ratios of late devonian abiotic marine calcite implications for the composition of ancient seawater abstract late devonian frasnian abiotic marine calcite has been microsampled and analyzed for 87 sr 86 sr ratios 18o and 13c values and minor element concentrations portions of marine cement crystals from the alberta and canning basins have escaped diagenetic alteration and preserve original marine 18o values 4 8 0 5 pdb 13c values 2 0 to 3 0 pdb 87 sr 86 sr ratios 0 70805 3 and sr mg weight ratios 0 04 to 0 05 marine 87 sr 86 sr ratios are globally consistent and can be correlated within the alberta basin and among the alberta canning and williston basins correlation of isotopic and chemical data strengthen the conclusion that marine cements from the leduc formation preserve original marine 18o values which are 3 to 4 lower than those of modern marine cements these low 18o values are best explained by precipitation from 18o depleted seawater and not by elevated seawater temperature or diagenetic alteration for comparison with devonian data analogous data were collected from holocene mg calcite and aragonite marine cements from enewetak atoll marshall islands mg calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater and mg calcite cements are homogeneous with respect to sr and mg contents empirically derived homogeneous distribution coefficients for mg and sr in modern abiotic mg calcite from enewetak atoll are 0 034 and 0 15 respectively an equation describing the dependence of dsr on mg content was based on a compilation of sr and mg data from holocene abiotic marine calcite dsr 3 52 10 6 ppm mg 6 20 10 3 unlike that derived from experimental data this sr mg relation is consistent over a range of 4 to 20 mol mgco3 and may represent precipitation phenomena which are minimally controlled by kinetic effects comparison of sr and mg contents of analogous devonian and holocene marine cements suggests that the mg ca ratio of late devonian seawater was significantly lower and that the sr ca ratio was significantly higher than that of modern seawater

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

palynology of eastern indonesian marine piston cores a late quaternary vegetational and climatic record for australasia abstract pollen analyses of late quaternary sediments from nine marine piston cores reveal a continuous vegetation and environmental record for eastern indonesia and northern australia on the island of halmahera a montane oak forest largely replaced the tropical lowland vegetation during the last glacial period while fern cover was strongly reduced during its maximum 18 000 yr b p climate was cooler and slightly drier than today around 10 000 yr b p mangrove vegetation expanded following the rising sea level in our western new guinea record at 14 000 yr b p climate grew warmer and slightly wetter until it stabilised around 10 000 yr b p at that time the mid to upper montane forests expanded to their full altitudinal range and fern cover increased while montane oak forest grassland and woodland areas had contracted in our marine pollen records during the last glacial the climate of northern australia was distinctly drier than today grassland vegetation with sedges increased considerably at 38 000 and 24 000 yr b p replacing eucalypt forest and culminating in a maximum grassland cover at the height of the last glaciation 18 000 yr b p the rapid sea level rise allowed the expansion of mangrove forests and salt bush marshes which had become established on the large tidal flats of the drowning sahul shelf around 12 000 yr b p one piston core g6 4 extends to 300 000 yr b p and shows that glacial periods are characterized by high pollen concentrations in marine sediments recording expanding grassland vegetation during interglacial woodland and fern cover increased while pollen concentrations in the sediments were low after 190 000 yr b p a more open vegetation suggests that conditions were in general much more arid than before repeated mangrove vegetation expansions suggest major rises in sea level at around 244 000 220 000 and 130 000 yr b p

quaternary stratigraphy geochronology and evolution of the magela creek catchment in the monsoon tropics of northern australia abstract magela creek a major tributary of the east alligator river in northern australia has left a detailed sedimentary record of a fluvial landscape dominated by climatic and eustatic changes associated with quaternary glacial interglacial cycles uranium series dates from young pisoliths in floodplain deposits indicate that ferruginisation is probably ongoing under present conditions while ferricretes in degraded terraces that flank the lower valley reveal a fluvial history extending back to early pleistocene or tertiary time inset within this older alluvium is a valley fill which from thermoluminescence dates was initiated about 300 kyr ago with each glacial climate change and associated fall in sea level distinct palaeochannels have been eroded into these floodplains infilling later with alluvium when climate and base level conditions were conducive to fluvial deposition radiocarbon dates show that the most recent palaeochannel beneath the modern magela creek last started to fill by downstream progradation and vertical accretion of bedload sand about 8 kyr the palaeochannel filled at an accelerating rate probably as a result of declining stream competence associated with drier conditions in the late holocene augmented by the backwater effects of sea level rise continued aggradation blocked the mouths of tributary valleys along magela creek forming alluvial dammed tributary lakes and deferred junction tributary streams from about 300 kyr cyclic episodes of channel incision and sediment evacuation in this tropical monsoon river valley have become less effective possibly because increasing aridity in the late quaternary has reduced the erosional effectiveness of australia s northern rivers reduced flow regime and rising sea level in the late holocene has resulted in the latest phase of alluvial accretion

sensitivity of the australian summer monsoon to tilt and precession forcing abstract the response of the australian summer monsoon to orbital forcing is studied using a coupled general circulation model gcm with the focus on the relative roles of tilt and precession on the forcing of the northern australian summer monsoon it was found that unlike the northern hemisphere monsoons which are dominated by precession forcing the australian monsoon can be enhanced significantly not only by precession forcing but also by tilt forcing coupled to oceanic feedback the new insights obtained from a series of experiments with differing tilt precession configurations allow an interpretation of the australian late quaternary monsoon record in which insolation forcing plays a significant role

thermal analysis of the southern powder river basin wyoming temperature and geologic data from over 3000 oil and gas wells within a 180 km 30 km area that transect across the southern powder river basin in wyoming u s a were used to determine the present thermal regime of the basin three dimensional temperature fields within the transect based on corrected bottomhole temperatures bhts and other geologic information were assessed using 1 a laterally constant temperature gradient model in conjunction with an l1 norm inversion method and 2 a laterally variable temperature gradient model in conjunction with a stochastic inversion technique the mean geothermal gradient in the transect is 29 c km but important lateral variations in the geothermal gradient exist the average heat flow for the southern powder river basin is 52mw m2 with systematic variations between 40mw m2 and 60mw m2 along the transect extremely high local heat flow values up to 225mw m2 in the vicinity of the teapot dome and the salt creek anticline and low heat flow of 25mw m2 occ

wolfe creek crater a continuous sediment fill in the australian arid zone records changes in monsoon strength through the late quaternary abstract a bolide that impacted nw australia during the late quaternary left a circular depression more than 100 m deep and nearly a kilometer in diameter with a crater rim 30 m above the regional terrain the resultant crater is a window into the regional water table the surface of the contemporary central pan is 25 m below the adjacent terrain coincident with the late holocene regional water table modified by local evaporative processes shielded from aeolian deflation by the crater rim the central depression has slowly filled with dust sand and chemical precipitates estimated to be 20 100 m thick based on geophysical surveys one of the few continuous depocenters in the australian arid zone the nature of the crater s sediment fill is controlled by interactions between the water table primarily in response to changes in summer monsoon rain changes in the delivery of sand and dust to the crater by the prevailing easterly winds and the level of the sedimentary fill surface optically stimulated luminescence osl and 14c dates constrain an age model indicating the upper 10 m of sediment fill recovered from the central pan span the past 60 ka the lowest 3 m consist of clayey sand deposited in perennial water during marine isotope stage mis 3 the water table subsequently dropped rapidly 35 ka and remained more than 7 m below the late holocene level through most of mis 2 during which 2 m of sandy clay was deposited on a dry crater floor confirming a dry and dusty last glacial maximum lgm climate by 14 ka a rising water table intersected the crater surface modifying the upper 50 cm of lgm sediment and syndepositionally modifying another 60 cm of subsequent sandy clay deposition aeolian sediment delivery effectively ceased 13 ka and the upper 4 8 m is a gypsum dominated precipitate which initially accumulated rapidly before equilibrating with the late holocene water table shortly after 6 ka lacustrine carbonate encrustations on rocks at the base of the crater wall and 4 m above the central pan with 14c ages 40 ka document a time when regional groundwater maintained a water body in the crater 3 5 4 5 m above the modern groundwater level the crater wall deflected the prevailing easterly winds creating a horseshoe dune extending westerly on both sides of the crater with an extension rate of 35 m ka 1 an augered hole through the northern dune revealed 10 m of sediment overlying ferricrete the lowest meter is a mixture of broken ferricrete and sand that we interpret to be debris from the bolide impact three osl dates through the dune project an age for the debris dune contact of 120 10 ka changes in physical properties and bulk sediment 13c through the 9 m of aeolian sediment indicate the lowest 1 8 m was deposited during mis 5 120 85 ka under a uniformly wetter climate than present the overlying 4 3 m of sediment was deposited between 85 and 14 ka mis 4 3 2 and exhibits transitional characteristics between the lower unit and the upper 3 8 of sand which was deposited primarily during the holocene large changes in the regional water table occurred over the past 60 ka including an lgm water table persistently 7 m lower than late holocene levels and 3 5 4 5 m higher prior to 40 ka plausibly in mis 5 indicative of a stronger australian summer monsoon than at any time subsequently age models and sediment properties from the two sedimentary records indicate the crater was formed 60 ka and most likely 120 ka more recently than previous estimates

continuous 150 k y monsoon record from lake eyre australia insolation forcing implications and unexpected holocene failure our reconstructed history of lake eyre provides the first continuous continental proxy record of australian monsoon intensity over the past 150 k y this continental record s broad correspondence to the marine isotope record demonstrates that this very large catchment with its hydrology dependent on a planetary scale climate element responds to milankovitch scale climate forcing abrupt transitions from dry phases to wet phases ca 125 and 12 ka coincide with northern hemisphere winter insolation minima rather than southern hemisphere summer insolation maxima indicating that northern hemi sphere insolation exerts a dominant control over the intensity of the australian monsoon stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but within the uncertainties are consistent with northern hemisphere forcing regardless of the hemispheric forcing the low intensity of the early holocene australian monsoon by comparison with the last interglacial and particularly the last high level lacustrine event at 65 60 ka when all forcing elements were modest is an enigma that can be explained by a change in boundary conditions within australia

time slice analysis of the australian summer monsoon during the late quaternary using the fast ocean atmosphere model we use the fast ocean atmosphere model foam to investigate the variation in the australian summer monsoon over the last 55 000 years a synthesis of palaeoenvironmental observations is used to constrain the model for six time slices 55 35 21 11 6 and 0 ka both inter hemispheric forcing and the seasonal timing of local insolation changes play key and interacting roles on the evolution and intensity of the monsoon during the onset to the monsoon a heat low develops to the west of australia over the indian ocean in all time slices but with varying strengths divergent outflow from asia converges with the cyclonic flow to bring increased rainfall to northern australia and the maritime continent the relative importance of a low pressure pull and the high pressure push varies according to the strength of the pressure anomalies only in the middle holocene is the low pressure pull the dominant forcing mechanism at 21 ka the climate shift to colder mean temperatures determines the large scale dynamics of the monsoon the general picture that emerges from these results is consistent with available palaeodata but highlights the importance of a broad regional perspective to ascribe the driving mechanisms at different times copyright 2006 john wiley sons ltd

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

the role of the australian monsoon in the western catchment of lake eyre central australia during the last interglacial abstract relative changes in monsoon intensity can be deduced from palaeoenvironmental data such as lake level records shore line features and aeolian loess deflationary sequences these data can provide assessments of past changes in the nature and timing of monsoon activity the lake eyre basin 1 300 000 km 2 in central australia is a key site for determining the nature and extent of monsoon fluctuations through glacial interglacial cycles a last interglacial high lake level phase some time between 90 130 ka is confirmed by both palaeoenvironmental and computer simulated data this coincides with a time of high sea level and strong orbital forcing of the asian monsoon the primary forcing mechanism for the north australian monsoon the large monsoon fed river systems of the cooper and diamantina are likely to have contributed most of the inflow to fill this megalake phase of lake eyre evidence from the neales river suggests that these smaller and more southerly rivers were also active this paper examines the likelihood that the relative synchroneity in fluvial and lacustrine activity across the basin at this time is the result of a common climate forcing mechanism in examining the role of the monsoon in this western catchment of the lake we present two possible scenarios to explain enhanced fluvial activity during the last interglacial

wetting and drying of australia over the past 300 ka alternately dry and wet climatic episodes across central and eastern australia during the past 300 ka have greatly affected australia9s rivers lakes and dune fields evidence of widespread climate and flow regime changes has been provided by 75 thermoluminescence tl dates and 18 u th dates from alluvial and eolian sediments fluvial conditions dominated part of the last two interglacials stage 5 and 7 resulting in large sand loads in rivers in the present simpson desert and southeastern australia during the last interglacial fluvial activity in central australia peaked at 110 ka stage 5 pluvial probably 5 10 ka behind world temperature and sea level maxima following the last late interglacial wet phase aridity associated with dune building spread from central australia toward its margins achieving greatest intensity during the last glacial maximum a less widespread wet phase identified at about 55 35 ka stage 3 subpluvial is associated with high lake levels and paleochannel activity in southeastern australia this tl record of variable continental aridity in australia correlates well with global changes including the variable eolian dust flux into central china the northern pacific ocean and antarctica

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

glacial interglacial water cycle global monsoon and atmospheric methane changes the causes of atmospheric methane ch4 changes are still a major contention in particular with regards to the relative contributions of glacial interglacial cycles monsoons in both hemispheres and the late holocene human intervention here we explore the ch4 signals in the antarctic epica dome c and vostok ice records using the methods of timeseries analyses and correlate them with insolation and geological records to address these issues the results parse out three distinct groups of ch4 signals attributable to different drivers the first group 80 variance well tracking the marine 18o record is attributable to glacial interglacial modulation on the global water cycle with the effects shared by wetlands at all latitudes from monsoonal and non monsoonal regions in both hemispheres the second group 15 variance centered at the 10 kyr semi precession frequency is linkable with insolation driven tropical monsoon changes in both hemispheres the third group 5 variance marked by millennial frequencies is seemingly related with the combined effect of ice volume and bi hemispheric insolation changes at the precession bands these results indicate that bi hemispheric monsoon changes have been a constant driver of atmospheric ch4 this mechanism also partially explains the holocene ch4 reversal since 5 kyr bp besides the human intervention in the light of these results we propose that global monsoon can be regarded as a system consisting of two main integrated components one primarily driven by the oscillations of inter tropical convergence zone itcz in response to the low latitude summer insolation changes anti phase between the two hemispheres i e the itcz monsoon component and another modulated by the glacial interglacial cycles mostly synchronous at the global scale i e the glacial interglacial monsoon component although atmospheric ch4 record integrates all wetland processes including significant non monsoonal contributions it is the only and probably the best proxy available to reflect the past changes of global monsoon however the utility of ch4 as a proxy of monsoon changes at any specific location is compromised by its bi hemispheric nature

heat flow in the utah wyoming thrust belt from analysis of bottom hole temperature data measured in oil and gas wells bottom hole temperature bht data from oil and gas wells represent a large albeit low quality data base for heat flow determinations a method for analyzing bht data sets that directly addresses the problem of noise in the data is presented and illustrated by application to 303 bhts from the anschutz ranch ar cave creek cc and anschutz ranch east are oil gas fields in the utah wyoming thrust belt located in the middle rocky mountain physiographic province of the western united states correction of raw bht data by means of a horner plot yields 81 corrected bhts an additional 90 bhts not suitable for a horner correction are corrected by means of a new bht correction which may be applied to any single bht for which a depth and time of measurement are known the average geothermal gradient at both ar cc and are is found to be 23 c km although an average gradient analysis fails to explain scatter in the data analysis of corrected bhts through inversion of a layered earth model yields estimates of formation thermal gradients and temperature fields at ar cc and are that are stable and unique with an average precision of 2 to 3 c thermal conductivity measurements were made on 360 drill cutting samples representing 14 thrust belt formations in situ conductivity is estimated using porosity from calibrated well logs heat flow is estimated by comparing temperature calculated by a two dimensional finite element model with temperature estimated from analysis of bht data analysis of bht data from the ar cc area yields an estimated regional heat flow of 60 mw m2 8 mw m2 a similar analysis at are results in an estimate of 58 mw m2 8 mw m2 these estimates are close to values determined for the wyoming basin and the central colorado plateau and imply that a thermal transition from the middle rocky mountains to elevated heat flow characteristic of the basin and range province 80 to 90 mw m2 must take place within 50 km

extending the record of lacustrine phases beyond the last interglacial for lake eyre in central australia using luminescence dating abstract we show with multiple luminescence dating techniques that the sedimentary record for lake eyre australia s largest lake extends beyond 200 thousand years ka to marine isotope stage mis 7 transgressive clayey sand and finely laminated clays overlying the miocene etadunna formation in lake eyre north document the deep lake phases of central south australia in the past until now unresolved chronology has hampered our ability to interpret these sedimentary records which are important for understanding the timing of the wettest phase of central australia s late quaternary climate in this study we apply quartz optically stimulated luminescence osl dating thermally transferred osl tt osl dating and k feldspar post infrared infrared stimulated luminescence pirir dating to lake floor sediments near williams point in madigan gulf to provide new age constraint for the lacustrine sediments of lake eyre methodological studies on quartz and k feldspar demonstrate that these luminescence dating procedures are suitable for the lake eyre lacustrine samples and produce consistent replicate ages a bayesian model applied to the new dating results provides a chronological model of lacustrine deposition and shows that the transgressive clayey sand were deposited 221 19 ka to 201 10 ka and that the deep water sediments were laid down in early mis 6 191 9 ka to 181 9 ka we also find evidence for a potential depositional hiatus in mid mis 6 and the likely formation of a palaeo playa later in mis 6 from 158 11 ka to 143 15 ka in contrast the mis 5 sediments are characterised by oscillating deep and shallow water lacustrine units deposited 130 16 ka to 113 20 ka this study is the first of its kind to provide evidence for a wet desert interior in australia beyond the last glacial cycle using comprehensive numerical dating our results show that past deep lake episodes of central south australia which were previously thought to represent peak interglacial conditions are actually associated with both warm interglacial and cold glacial periods with all the wettest episodes generally coinciding with the intervening periods between the glacial and interglacial maximums we assume from these results that orbital forcing is not a first order control for the long term dynamics of the lake eyre basin and the indo australian monsoon the high lake level events of lake eyre are well correlated with millennial scale cooling events and stadials of the north atlantic and coincide with weakened episodes events for the east asia summer monsoon this may imply an important role for the northern high latitudes in influencing the indo australian monsoon which may be associated with a southward migration of the intertropical convergence zone itcz during cooling periods in the north atlantic

a strontium isotopic study of formation waters from the illinois basin u s a abstract the isotopic composition of sr has been measured in 73 formation water samples from paleozoic strata in the illinois basin 87sr 86sr ratios range from 0 7079 to 0 7108 with the exception of four samples the waters are more radiogenic than corresponding paleozoic sea water values the relatively narrow range of slightly elevated 87sr 86sr rations is uniformly distributed in waters throughout the stratigraphic column and in silurian waters across the basin isotopic analyses of core samples from reservoir rocks show an absence of water rock sr isotopic equilibration basin lithology and analyses of detrital rock units indicate that clay minerals in shales and in quartz sandstone matrices represent the only significant source of radiogenic sr for the waters silurian and devonian water show a two component mixing relation which suggests that they comprise a single hydrogeological system that evolved when radiogenic water from new albany shales entered silurian devonian carbonate rocks and mixed with marine interstitial water regional migration of the waters and associated petroleum within the silurian devonian strata proposed in other studies is consistent with the sr isotopic data under favorable circumstances subsurface waters are capable of retaining a sr isotopic recor of their evolution

deriving geothermal parameters from bottom hole temperatures in wyoming this article describes a method to determine geothermal gradients and formation temperatures using bottom hole temperatures bhts from wireline log headers and then tests the method by applying it to analyses from more traditional sources bottom hole temperatures depths and times since circulation ended were collected from at least one well in every township that had been drilled for petroleum exploration in the state of wyoming using approximately 3500 bhts collected from almost 2000 wells equations were developed for average formation temperatures and geothermal gradients across the state a method of correcting the average data to true formation temperatures in each individual well was also developed the geothermal temperatures so derived very closely match temperatures from production bhts that are the normal industry standard for formation temperatures and suggest that bht information is much more accurate than commonly thought the use of bht measurements to compute temperature gradients was also developed the effects upon formation temperatures of common data recording errors of vertical circulation of groundwater especially above 1700 m 5577 ft depth and of lateral groundwater circulation through deep aquifers are documented the methods developed offer promising avenues for research in the areas of hydrogeology geothermal exploration determining formation temperatures and heat flow

analysis of temperatures in sedimentary basins the michigan basin we develop an analytical and numerical methodology for the analysis of large bottom hole temperature bht data sets from sedimentary basins and test the methodology using temperature stratigraphic and lithologic data from 411 boreholes in the michigan basin least squares estimates of temperature gradients in the formations and lithologies present are calculated as solutions to a large system of linear equations at each borehole the temperature difference between the bottom and top of the hole is represented as a sum of temperature increments through the various formations or lithologies penetrated by the borehole quadratic programming techniques enable bounds to be placed on the gradient solutions in order to suppress or exclude improbable gradient estimates numerical experiments with synthetic data reveal that the estimates of temperature gradients for a given formation or lithology are sensitive to the degree of representation of that unit well represented units have more stable gradient estima

insolation and cross hemispheric controls on australian monsoon variability over the past 180 ka new evidence from offshore southeastern papua new guinea the australian summer monsoon asm is primarily a synoptic feature determined by the differential thermal response to solar insolation between the australian continent and the western pacific warm pool wpwp in austral summer little is known about the process involved in driving long term asm variability here we present a 180 ka record of terrestrial fluxes into offshore southeastern papua new guinea png a prevailing monsoon area in the wpwp terrestrial fluxes were estimated by a 230th normalized method indicating higher terrestrial inputs into the ocean during glacial stages we argue that the higher terrestrial fluxes are mainly fluvial which in turn are linked to stronger asm precipitation on land though the increased terrestrial flux could possibly also be due to the lowstand or glacial erosion of mountain glaciers cross spectral analysis indicates that the asm precipitation maxima are controlled by local summer insolation maxima wpwp sea surface temperature minima and east asian winter monsoon eawm maxima in precession frequency bands 21 ka 1 this result suggests that the 21 ka components of the asm in the past 180 ka are not only insolation driven but also a dynamic component strengthened by cross hemispheric pressure gradient resulted from the precession maxima forcing copyright 2012 john wiley sons ltd

sensitivity of the australian monsoon to insolation and vegetation implications for human impact on continental moisture balance general circulation model experiments test the geologically based correlation of high monsoon rainfall over interior australia with northern hemisphere insolation and evaluate the sensitivity of the australian monsoon to ecosystem change our results suggest that northern hemisphere insolation control on the intensity of the siberian high rather than summer insolation over the australian continent determines the strength of the australian monsoon on millennial time scales unlike a classic monsoon regime additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere atmosphere feedbacks linked to vegetation type and soil properties this sensitivity offers a resolution to the observed failure of the australian monsoon to penetrate the interior in the holocene postulated regular burning practiced by early humans may have converted a tree shrub grassland mosaic across the semiarid zone to the modern desert scrub thereby weakening biospheric feedbacks and resulting in long term desertification of the continent

early to middle miocene monsoon climate in australia the present day australian monsoon delivers substantial moisture to the northern regions of a predominantly arid continent however the pre quaternary history of the australian monsoon is poorly constrained due to sparse and often poorly dated paleoclimate proxy evidence sedimentological and paleontological data suggest that warm humid and seasonal environments prevailed in central and north australia during the miocene though it is unclear whether these were products of the australian monsoon we perform a series of sensitivity experiments using an atmospheric general circulation model combined with an offl ine equilibrium vegetation model to quantitatively constrain the areal extent of the miocene monsoon our results suggest a weaker than modern monsoon climate during the miocene this result is insensitive to atmospheric co 2 although somewhat sensitive to vegetation interactions and the presumed distribution of inland water bodies none of our miocene experiments exhibit precipitation rates greater than modern over north australia in disagreement with paleoclimate record interpretations vegetation modeling indicates that inferred precipitation values from fossil fl ora and fauna could only support miocene vegetation patterns if atmospheric co 2 was twice the modern concentration this suggests that elevated co 2 was critical for sustaining miocene vegetation

orbital time scale circulation controls of the australian summer monsoon a possible role for mid latitude southern hemisphere forcing abstract discussions of the quaternary paleoclimatology of the northwestern australian summer monsoon have emphasized inter hemispheric forcing of the northern australian summer monsoon by the east asian winter monsoon here we draw on the results of general circulation model experiments to examine southern hemisphere circulation characteristics that controlled the australian summer monsoon in response to milankovitch insolation forcing the experiments suggest that during tilt and precession driven southern hemisphere low latitude insolation highs the monsoon regime has the potential to be forced by inflow from the mid latitudes of the southern hemisphere to lend credence to the general circulation model results we employ a simple force balance model to demonstrate the dynamics controlling southern hemisphere inflow into the monsoon region of northwestern australia and draw attention to work that suggests this mechanism may explain recent precipitation trends in the region our findings caution against drawing correlations of stratigraphic events in the east asian australian monsoon records without first having a full appreciation of the dynamics that controlled paleoclimate states