a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

geochemistry of the pliocene red clay formation in the chinese loess plateau and implications for its origin source provenance and paleoclimate change abstract recent field observations and sedimentological studies suggest the eolian origin of the late tertiary red clay formation underlying the pleistocene loess soil sequence in the loess plateau thereby extending the wind blown record from 2 6 ma down to 7 0 ma in north central china to address the source provenance of the red clay major and trace element concentrations were analyzed on the samples from a north south loess transect of the loess plateau and a red clay section at jiaxian results show that there is a good agreement of both major and trace element compositions between the last glacial interglacial loess soil units and the jiaxian red clay record the ree distribution patterns of the loess soil and red clay samples are remarkably similar in shape with enriched lree and fairly flat hree profiles and clear negative eu anomaly the geochemical features of the red clay are also identical to those of upper continental crust these chemical characteristics provide further evidence for eolian sedimentation of the red clay from the relations both between na2o al2o3 and k2o al2o3 ratios and between u pb and th pb ratios the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area the chemical similarity between soil unit s1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern china during the late tertiary comparison of down section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that cao al2o3 sr rb and sr ba are more sensitive to climate changes than magnetic susceptibility and can be used to reconstruct the climate history of the late cenozoic

evolution of chaka salt lake in nw china in response to climatic change during the latest pleistocene holocene abstract the late pleistocene and holocene hydrologic balance of chaka salt lake in the eastern qaidam basin of nw china was studied based on the analysis of lithostratigraphy mineralogy total organic carbon and total nitrogen from a 9 0 m long sediment core an age depth model for the lake sediments is based on eight accelerator mass spectrometry ams 14 c measurements of organic matter and a 1700 year radiocarbon reservoir correction the pitzer model was used to calculate the sequence of minerals precipitated as a function of salinity assuming that the initial lake water was recharged from adjacent rivers and springs lake salinity values were derived from a good match between the calculated and observed mineral sequences our multi proxy based hydrologic reconstruction of chaka lake indicates that it was a clastic dominated freshwater lake between 17 2 and 11 4 cal ka bp which may have resulted from the input of glacial water into the lake at that time during the lateglacial and holocene a warm climatic regime predominated between 13 9 and 12 7 cal ka bp and then a cold climatic regime prevailed between 12 7 and 11 4 cal ka bp these warm and cold periods correlate with the bolling allerod and younger dryas events in the region beginning at 11 4 cal ka bp a saline or hypersaline lake developed which may have resulted from increased summer insolation and temperatures these conditions persisted throughout the holocene modeling indicates that lake salinity fluctuated between 66 and 223 ppt from 11 4 to 7 2 cal ka bp and then increased to 223 322 ppt between 7 2 and 6 0 cal ka bp when most regions of china recorded high moisture availability i e the so called mid holocene climatic optimum lake salinity decreased to 66 223 ppt during a short time period between 6 0 and 5 3 cal ka bp possibly caused by reduced evaporation subsequently salinity values rapidly increased to 223 322 ppt between 5 3 and 5 2 cal ka bp and a hypersaline lake with a salinity higher than 324 ppt similar to modern chaka salt lake became established around 5 2 cal ka bp this establishment may have been related to the weakening of asian monsoon regional comparisons of paleoclimatic records indicate that large temporal and spatial variations exist in the occurrence and intensity of drought over western china since the lateglacial

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

model for turbidite to contourite continuum and multiple process transport in deep marine settings examples in the rock record abstract petrological analysis of geological sections in st croix in the caribbean the niesenflysch in switzerland and the annot sandstone in the french maritime alps sheds light on multiple process transport in deep marine settings a model depicting a turbidite to contourite continuum of stratal types is applied to these three rock units recognition of a diverse suite of bedforms coupled with analysis of paleocurrents helps to better interpret depositional origin and basin paleogeography the st croix strata record emplacement by gravity flows and subsequently by bottom currents flowing parallel to the base of slope these sediments accumulated on a lower slope apron a niesenflysch section in the swiss alps west of adelboden includes turbidites which were deposited at fairly regular intervals beyond the base of slope in a setting more distal than that of the st croix sequences most of these turbidites appear to have been partially reworked by bottom currents related to basin circulation or to density flows from the basin margins in the annot sandstone reworked turbidites termed transitional variants and packets of entirely rippled strata are observed in submarine fan and slope sequences in the peira cava area in contrast to those in st croix and the niesenflysch the current emplaced deposits of the annot sandstone are directly associated with fan valley deposits such rippled strata in channels are deposits of gravity flow origin which were subsequently reworked downslope by currents generated by successive gravity flows they also occur on levees by overbank flow consideration of multiple process transport is of special help to interpret sections which are poorly exposed or which can be examined in cores or which are located in sequences that have been highly deformed structurally

provenance of the lower tertiary murree redbeds hazara kashmir syntaxis pakistan and initial rising of the himalayas abstract the murree supergroup of northern pakistan is represented by an over 6 km thick succession of deltaic redbeds and intercalated impure foraminiferal limestones of latest palcocene to middle eocene ilerdian to lutetian age cropping out in the northern part of the hazara syntaxis and by redbeds of younger age early middle eocene to early miocene cropping out in the southern part of the syntaxis rawalpindi area the quartzolithic composition of the murree redbeds testifies to a collision orogen provenance detritus was derived from a suture belt including thrust sheets of metasedimentary and subordinately sedimentary rocks volcanic or volcaniclastic rocks and ophiolites phyllite rock fragments are most common in the ilerdian sandstones whereas volcanic and carbonate rock fragments are more abundant in the lutetian sandstones minor quantities of chert and serpentineschist indicating contribution from uplifted subduction complex sources as well as siltstone shale and limestone grains are invariably present detrital modes of sandstones and southwestward progradation of tertiary clastic wedges both testify to provenance from the proto himalayan chain located to the north and uplifted since the very first stages of the india asia continental collision at the end of the paleocene the coeval chulung la redbeds of the tethys himalaya instead consisting of volcanic and subordinate ophiolitic detritus testify to exclusive provenance from the obducting trans himalayan are trench system this major petrographic difference may be accounted for by the different structural setting of the chulung la piggy back and murree foreland basins these two distinct collisional basins have been separated probably since the onset of collision by a fold thrust belt beginning to rise in the position occupied today by the high and lesser himalayan structural domains throughout the murree supergroup main petrographic parameters do not vary greatly and volcanic sedimentary low grade metasedimentary and ophiolitic detritus persisted until the early miocene indicating slow progressive growth of the chain only during the middle miocene when the highly metamorphosed rocks of the high himalaya were carried southward along the main central thrust mct the mountain range began to rise to dramatic heights and huge amounts of detritus started to feed the siwalik foreland basin sandstones and the remnant ocean turbidites of the indus and bengal fans

late quaternary palaeolake levels in tengger desert nw china comprehensive field investigations and laboratory analyses show that palaeolakes including the megalake tengger and other semi connected and isolated water bodies during late pleistocene covered an area of more than 20 000 km 2 this is an area more than half the size of the tengger desert in nw china stratigraphic correlations and chronological evidence indicate that the palaeolakes started to develop around 42 000 14 c year bp uncalibrated all throughout the paper but their extent was limited until 37 000 14 c year bp based on the chronology of representative lacustrine deposits it can be deduced that the megalake tengger was established around 35 000 14 c year bp and maintained until 22 000 14 c year bp leading to the formation of the baijian hu terraces which are regarded as firm evidence of the existence of palaeolakes the formation mechanism is unclear and the climate situation at the time is still an open question the holocene palaeolakes started to develop around 12 000 14 c year bp the baijian hu terraces indicate that the high water levels in the area occurred around 8500 5400 5100 3500 and 1860 1370 14 c year bp the extent of the holocene palaeolakes primarily migratory lakes was smaller than that of the late pleistocene palaeolakes d 2004 elsevier b v all rights reserved

sedimentation and diagenesis of chinese loess implications for the preservation of continuous high resolution climate records chinese loess has been extensively utilized to produce continuous and high resolution climate records of the late cenozoic such work assumes uninterrupted loess deposition and limited diagenesis here closely spaced optically stimulated luminescence osl dates are used to characterize the holocene and late pleistocene sedimentation histories of three sites across a nw se transect of the chinese loess plateau the results suggest that sedimentation is episodic at subglacial interglacial time scales with rates rapidly varying within units and between sites unconformities noneolian deposition and mixing of sediments also appear to be common existing understanding of loess deposition therefore requires reexamination while previous reconstructions of rapid climate change not dated using absolute methods should be regarded with caution loess deposits may still yield detailed climate records from specific high sedimentation rate strata and evidence for rapid climate change may yet be obtainable by targeting these units through absolute dating the rapid changes in sedimentation presented here indicate the east asian monsoon has the capacity to vary on millennial scales

middle palaeozoic thrusting in the eastern lachlan fold belt southeastern australia abstract early to middle palaeozoic clastic and volcanic strata in the goulburn bungonia region 150 km southwest of sydney are divided by the n trending yarralaw fault into two domains in the western domain major e w shortening formed folds axial planar cleavage and w dipping contraction faults in all pre upper devonian units this deformation formed an anticlinorium cored by a w dipping thrust system with an overturned e younging limb in the eastern domain upright flattened chevron folds occur in ordovician strata with stratal repetition along steep contraction faults spaced at intervals of 1 km or less zones of tectonic melange occur in the hangingwalls of these faults and have a well developed scaly fabric with a steeply plunging striation overprinting a bedding parallel cleavage in mudstone in interbedded silurian shale and limestone a classical stair step trajectory is recognized for the frome hill fault which duplicates the succession and has undergone back rotation to its present steep dip overall thrusting progressed from east to west with deformation in the eastern domain pre dating intrusion of the early devonian marulan batholith whereas farther west deformation continued into the middle devonian the folds and thrusts in the goulburn bungonia region are part of a major fold thrust zone that extends throughout the eastern lachlan fold belt and which was formed in the middle silurian to middle devonian during a period of plate convergence between gondwana and the palaeo pacific ocean the fold thrust zone is inferred to have an arc frontal arc setting above a w dipping subduction zone and the deformation relates to underthrusting of an allochthonous terrane with major shortening in the hangingwall block

aeolian deposits at the southeastern margin of the tengger desert china implications for surface wind strength in the asian dust source area over the past 20 000years abstract independent dust provenance data play an important role in understanding changes in the atmospheric dust loading over geological time major elemental compositions and grain size characteristics of the aeolian deposits xiangshan xs section at the southeastern margin of the tengger desert in northwestern china demonstrate that the deposits are an intermediate product of the transportation of aeolian materials from the dust source area deserts to the dust depositional regions chinese loess plateau that were likely formed by dust storm processes the 40 m and 63 178 m fractions and the ratio of sio2 tio2 of the xs section were used as proxies to reconstruct the surface wind regime over the last 20 kyr the results show that the surface winds were much stronger and fluctuate acutely from 19 1 to 11 4 kyr the winds gradually attenuated after the beginning of the holocene and reached a minimum between 4 0 and 3 5 kyr bp a sharp increase in surface winds occurred after 2 5 kyr bp the surface winds in the asian dust source area are largely consistent with the changes in winter monsoon strength documented by the chinese loess deposits also the stronger surface winds from 19 1 to 11 4 kyr coincide with the high mineral dust concentration determined from the greenland ice core except for the period of bolling allerod b a when the atmospheric dust may have been washed out by enhanced global hydrological cycles although dust was still emitted from source areas this suggests that the stronger surface winds in dust source areas can enhance the atmospheric dust loadings during the late glacial the weakening surface wind regime during the holocene may have greatly contributed to the decrease in dust concentration of the remote dust records the paleo environmental changes in the study area since 42 5 kyr bp are broadly in agreement with other adjacent records however the possible warm and humid spell of 42 5 19 1 kyr bp still requires verification

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

provenance of early palaeozoic sandstones southeastern australia part 1 vertical changes through the bengal fan type deposit abstract ordovician strata of the lachlan fold belt in southeastern australia are dominated by a turbidite succession that in its undeformed state was comparable in size to the modern day bengal fan the ancient fan was derived from the northern part of the cambrian ross delamerian orogenic belt that formed at a convergent boundary between plates containing gondwanaland and part of the palaeo pacific ocean respectively substrate to the submarine fan consisted of mafic volcanic rocks with an immature island arc affinity similar to the eocene izu mariana bonin system sandstone compositions determined from several stratigraphically constrained sections demonstrate a uniform framework composition dominated by monocrystalline quartz with less abundant feldspar polycrystalline quartz metamorphic rock fragments sedimentary rock fragments and mica these indicate derivation from a low grade metamorphic terrain up sequence variation is limited to decreasing feldspar and lithic fragments and increasing quartz indicating increased weathering and lowering of topography in the source terrain over time 25 of counted sandstones in the late ordovician interval contain a small component of mafic intermediate volcanic rock fragments that accompanied a change in palaeocurrent direction from eastwards to northwards in the early silurian the ordovician sequence was disrupted by the formation of several major deformation zones between these zones developed several deep marine sedimentary basins that contain a continuous succession from the ordovician into the early silurian early silurian sandstone is similar in composition to underlying early ordovician rocks except that the feldspar component is generally absent early silurian sandstone was derived from uplifted portions of the ordovician sequence and includes texturally inverted types with sandstone containing a bimodal mixture of coarse well rounded quartz and fine angular quartz

a paleozoic suture in eastern gondwanaland a new tectonic interpretation of southeastern australia tasmania and north victoria land antarctica is given in which a major n s trending lineament representing a suture zone is recognized separating essentially shallow water shelf and continental deposits of latest cambrian or early ordovician age from deeper water ordovician flysch deposits lateral offset of this lineament which is interpreted as a suture along which thrust telescoping and major strike slip faulting occurred could adequately explain the present distribution of major rock types in the three areas and also removes a number of problems previously encountered in correlation

isotope geochemistry of quaternary deposits from the arid lands in northern china abstract quaternary deposits of various types lacustrine desert sand river loess and loess like deposits from the southwestern tarim basin north tianshan northeast china and the central loess plateau exhibit an nd 0 range from 5 to 12 8 and a 147 sm 144 nd range from 0 110 to 0 140 their nd depleted mantle model ages are between 1 50 and 1 92 ga with a mean value of 1 7 ga th sc ratios vary over a wide range from 0 1 to 2 comparison of these geochemical signatures with those of the old australian shales and modern pacific ocean dust suggests a continuous input of mantle derived material into the crust over geological time the deposits from the north tianshan show clearly different chemical and isotopic features with significantly higher sm nd high 143 nd 144 nd low 87 sr 86 sr and low la lu and th sc ratios relative to those in the deposits from the other areas this indicates a geological control on the local source which has an overall young age and an enrichment of basic components the ce 0 values of two loess samples from the central loess plateau are 1 8 and 3 9 corresponding to depleted mantle model ages of 2 2 and 3 4 ga like the rb sr system the evolution of the la ce isotopic system in the crust may be to some extent decoupled from the sm nd system due to la ce fractionation by sedimentary processes the loess deposits and the desert sand are not distinguishable in isotopic composition but show somewhat different chemical compositions we conclude that the loess can have originated from desert processes since the difference in the chemistry of the desert sand and loess may result from mineral sorting during desert processes and aeolian transportation the loess deposits on the central loess plateau chemically and isotopically resemble the desert loess deposits in the southwestern tarim basin but do not resemble those of the north tianshan accordingly the loess on the plateau may have a source region in the tarim basin but clearly not in the north tianshan

shallow water turbidites an example from the mallacoota beds australia abstract a late ordovician turbidite sequence the mallacoota beds exhibits vertical lithofacies associations that suggest deposition in a fan like environment however there are also features indicating occasional episodic reworking by water currents reworking features include both wave current and unidirectional ripple pavements sharp topped turbidites a difference in current direction between superimposed current rippling and underlying bouma c division ripples lensiodal quartzites and occasional hcs beds comparisons between the mallacoota beds and the depositional products of a variety of open ocean currents would indicate that storm related currents were the most likely reworking mechanism this would indicate that the sequence was deposited within storm wave base depositional depths for part of the sequence are estimated at 90 200 m based on a wave generated ripple model therefore these turbidites may have been produced by storm surge with channeling within the turbidites due to the localisation of rip currents during hurricane conditions a generalised model for the characteristic features of turbidites deposited between fair weather wave base and storm wave base is presented it is suggested that such turbidites will contain only occasional examples of reworking and that the frequency of such reworking events per stratigraphic interval might be used as a relative measure of water depth throughout a sequence moreover those turbidite sequences that have sharp contacts between the sandstones and the overlying mudstones may have been modified by storms and therefore deposited in shallower water than previously thought

excepftonally strong near bottom flows on the continental rise of nova scotia recent current velocity measurements across the lower continental rise of nova scotia show a deep equatorwardflow with speeds maximum 73 centimeters per second among the highest recorded for the deep sea silicate measurements indicate that this flow usually consists of southern source antarctic bottom water these measurements confirm the existence of a second and deeper western boundary flow that was earlier inferredfrom geological observations

seafloor zonation in sediment texture on the nova scotian lower continental rise abstract grain size analyses of surface sediment samples from the continental rise below 4000 m off nova scotia clearly show a slope parallel zonation in textural parameters zones of sediment with high sand content 20 are located between 4800 and 4900 m and below 5000 m a zone rich in clay 40 occurs between 4000 and 4800 m the silt clay ratio increases steadily with depth between 4000 and 5100 m these textural trends suggest predominantly slope parallel sedimentary processes on the modern sea floor and conversely little evidence of downslope processes the textural zonations are thought to result from a zonation of bottom currents which are weak at 3500 m but increase regularly to peak speeds greater than 50 cm s 1 on the lower rise at 5000 m the mean position of the northern edge of the gulf stream lies across the southern part of the continental rise over the 4600 to 4900 m depth contours the clay rich band lies upslope from the gulf stream edge beneath a weak to moderate mean abyssal flow toward the southwest in contrast the sand rich zone lies beneath the region of stronger mean southwest flow and beneath the cold filament mapped by weatherly and kelly 1982 this region is also intermittently occupied by the gulf stream and episodic reinforcement of flow in the mean southwest current by bottom sensing eddies from the gulf stream probably creates intermittent high velocity currents that account for the coarse surface texture

provenance of early palaeozoic sandstones southeastern australia part 2 cratonic to arc switching abstract early palaeozoic strata of the northeastern lachlan fold belt australia consist of an early ordovician sequence adaminaby group of quartz rich turbidites and chert and the conformably overlying late ordovician early silurian coomber formation a mafic volcaniclastic sequence of lithic sandstone and mudstone with mafic volcanic and intrusive rocks analysis of detrital modes from the adaminaby group indicate a uniform quartzose petrofacies q 91 f 2 l 7 composed of deep water quartz and sublithic sandstones derived from the west by contrast the lithic sandstone of the coomber formation represents a volcanolithic petrofacies q 1 f 34 l 65 of mainly intermediate volcanic detritus with a tendency to become more silicic up section these sandstones are considered to be derived from a calc alkaline andesitic basaltic volcanic centre in the eastern lachlan fold belt the change from a quartz rich petrofacies to a volcanolithic petrofacies was sharp with no evidence of mixing this change primarily reflects a rapid outpouring of mafic volcanic material in the late ordovician together with an approximately concurrent eustatic rise in sea level

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

evolution from estuary to delta alluvial plain morphology and sedimentary characteristics of the shoalhaven river mouth southeastern australia abstract the shoalhaven river in southern new south wales nsw drains a catchment of 7000 km2 forming a barrier estuary at its mouth with a prograded strandplain to its north previous coring and dating across the floodplain and adjacent strandplain indicate progressive infill of the estuarine basin over the past 7000 years over this time the system transitioned from a wave dominated estuary to a wave dominated delta the shoalhaven river appears to have initially discharged to the sea at crookhaven heads until it adopted a more direct route through an intermittently open mouth at shoalhaven heads construction of berrys canal in 1822 now permanently links the shoalhaven river to the adjacent smaller crookhaven river airborne lidar reveals details of topography of prominent levees and meander scroll bars that flank the lower reaches of the river and beach foredune ridges to the north sedimentological and mineralogical characteristics of modern sediment samples collected from the river channel the beach and the barrier reveal that the shoalhaven river is dominated by quartz sand along its predominantly straight course through the infilled estuarine plains this is in contrast to the tripartite classification of sedimentary depositional environments comprising sandy fluvial delta central mud basin and sandy marine barrier that characterised the initial wave dominated estuary 7000 years ago and is typical of most barrier estuaries in nsw grain size decreases downstream and sands have a higher feldspar content and angularity than is typical of marine sand that has been reworked in the nearshore this fluvially derived component is delivered to the coast intermittently by floods that re open shoalhaven heads as shown by retrospective analysis of aerial photography and satellite imagery grain size decreases with distance alongshore from the river mouth indicating that these sands are transported north by longshore drift to augment a gradual onshore delivery of sand within this coastal compartment scanning electron microscopy of selected grains implies that this fluvial sand has been contributing to incremental formation of beach ridges for much of the past 3000 years since the estuarine basin has been largely infilled with a slight detectable acceleration in the rate of progradation

contourites associated with pelagic mudrocks and distal delta fed turbidites in the lower proterozoic timeball hill formation epeiric basin transvaal supergroup south africa abstract five genetic facies associations architectural elements are recognised for the epeiric sea deposits preserved in the early proterozoic timeball hill formation south africa basal carbonaceous mudrocks interpreted as anoxic suspension deposits grade up into sheet like laminated graded mudrocks and succeeding sheets of laminated and cross laminated siltstones and fine grained sandstones the latter two architectural elements are compatible with the te td and tc subdivisions of low density turbidity current systems thin interbeds of stromatolitic carbonate within these first three facies associations support photic water depths up to about 100 m laterally extensive sheets of mature cross bedded sandstone disconformably overlie the turbidite deposits and are ascribed to lower tidal flat processes interbedded lenticular immature sandstones and mudrocks comprise the fifth architectural element and are interpreted as medial to upper tidal flat sediments small lenses of coarse siltstone very fine grained sandstone analogous to modern continental rise contourite deposits occur within the suspension and distal turbidite sediments and also form local wedges of inferred contourites at the transition from suspension to lowermost turbidite deposits blanketing and progressive shallowing of the floor of the timeball hill basin by basal suspension deposits greatly reduced wave action thereby promoting preservation of low density turbidity current deposits across the basin under stillstand or highstand conditions a lowstand tidal flat facies tract laid down widespread sandy deposits of the medial klapperkop member within the formation salinity gradients and contemporaneous cold periglacial water masses were probably responsible for formation of the inferred contourites the combination of the depositional systems interpreted for the timeball hill formation may provide a provisional model for early proterozoic epeiric basin settings

sedimentation in the chile trench depositional morphologies lithofacies and stratigraphy the depositional bodies of the chile trench trench fans the axial channel sheeted basins ponded basins and axial sediment lobes control the spatial distribution of modem lithofacies in the basin sheeted basins south of 41 s are presumably fed by closely spaced submarine gullies that approximate a line of source of sediment supply along the base of the slope trench fans 41 s 33 s are built at the mouths of major submarine canyon systems which act as point sources of sediment supply the axial channel follows the northward gravitational gradient draining the distributary networks of trench fans into the longitudinal transport system down gradient northern fan lobes are severely dissected by erosional processes evidently periods of proximal deposition alternate with periods of massive sediment remobilization and progradation of the axial dispersal system into more distal environments channelized basins in the canyon mouth areas yield to sheeted basins depositional surface maintains an axial gradient or ponded basins depositional surface is strictly flat in inter canyon areas tectonic disruption of the oceanic basement can locally augment the axial gradient and stimulate flow channelization or reverse the gradient and induce sediment ponding a large margin parallel sediment lobe is built at the base of a high axial escarpment near 33 s where the axial channel crosses a transverse discontinuity at the convergent plate boundary five lithofacies are defined by q mode factor analysis of sediment textures and hydro dynamic structures in 27 cores from the chile trench the channel facies thick amalgamated sand massive to laminated or cross bedded is deposited by high energy processes within the coarse grained bedload of turbidity currents it forms in distributary and axial channels the levee facies rhythmically bedded internally structureless graded sand and graded silt is deposited from concentrated sediment suspensions that quickly lose momentum during channel spillover it forms on channel flanks although constructional levees are not always present the basin 1 facies more complete bouma sequences both upper and lower flow regime structures forms in ponded basins where flows are confined by a high relief seaward trench wall the basin 2 facies graded and laminated silt lower flow regime structures forms in low energy environments such as interchannel areas distal basins trench walls and elevated topographic features the contourite facies silt and sand laminations winnowed from hemipelagic muds and distal turbidites is best developed in sediment starved basins where geostrophic currents are constricted and accelerated between the steep inner and outer trench walls the trench wedge records a coarsening upward sequence as the oceanic plate migrates toward and into the trench during plate convergence and becomes more proximal to sediment sources along the base of the continental margin near canyon mouths prograding trench fans drive the axial channel seaward into the trench wedge and the coarsening upward sequence is truncated by a time transgressive erosional unconformity abandoned axial channel deposits are carried landward beneath prograding fans to record a fining upward sequence above the basal unconformity channel migration and lobe aggradation may produce fining and coarsening upward sequences on depositional fan lobes but sequences on the erosional lobes are fragmented by numerous truncation surfaces

ordovician terranes of the southeastern lachlan fold belt stratigraphy structure and palaeogeographic reconstruction abstract the ordovician of the southeastern lachlan fold belt lfb is represented by two contrasting provinces the molong volcanic province with shoshonitic basalts and shallow marine sediments in the north and a very extensive but relatively thin quartzose flysch chert and black shale sequence elsewhere this paper concentrates on the latter and reviews its stratigraphy correlation sedimentary facies palaeocurrent directions and structure the molong volcanic province contributed insignificant sediment to the surrounding turbidites and there is no evidence that the rise was a fragmented arc as is postulated by most previous workers the rise may have been a hot spot volcano and the southeastern lfb appears to have been a passive margin in the ordovician within the flysch province two terranes are recognized the melbourne terrane in the west and benambra terrane in the east both showing overall upward and eastward fining in the ordovician the boundary is the mount wellington fault zone along which a post ordovician dextral strike slip of up to 400 km is postulated

ordovician contourites in the lachlan fold belt eastern australia abstract the ordovician sequence in the northeastern lachlan fold belt consists of three lithologic units representing an overall fining upward succession from turbidites to black shale the lowest unit dominated by turbidite beds represents a small segment of an extensive ordovician submarine fan sequence that covered much of southeastern australia the overlying unit consists predominantly of ripple bedded sandstone with beds 3 5 cm thick these beds are texturally mature containing heavy minerals mica and silt concentrated on the cross laminae the ripple bedded unit has a mean palaeocurrent trend to 321 which is at 60 to sole marks and almost normal to the trend of ripple cross bedding in the underlying and associated turbidite beds this unit is here interpreted as a sandy contourite sequence that can be attributed to contour currents moving northwards along the eastern margin of gondwana from areas of subpolar downwelling off southern africa and america the two major fining upward successions in the ordovician sequence in southeastern australia may reflect eustatic sea level rises during the middle and late ordovician and thus provide evidence of interglacial periods in the darrawilian and late gisbornian to bolindian the contourites would have accumulated in the latter stages of the glacial periods after sea level had risen sufficiently to cut off major sediment supply to the submarine fan but before the temperature had risen to the extent of preventing deep thermohaline circulation

a geochemical study of loess and desert sand in northern china implications for continental crust weathering and composition abstract chemical compositional variations of desert sands and loess loess like deposits river deposits and saline lacustrine deposits collected mostly from the southern margin of the taklimakan desert china provide strong constraints on the chemical weathering processes of continental crust and also on the provenance compositions of these quaternary deposits constant but lower concentrations of al relative to the average upper continental crust ucc in these quaternary deposits could be attributed to chemical weathering of al rich minerals such as feldspar and mica and removal of clay minerals by wind and water large variations of mobile na ca mg and sr compared to relatively immobile al k and ba resulted from the chemical weathering of plagioclase and carbonate minerals salinization and carbonation of the arid lands most trace elements are not significantly fractionated their variations in absolute concentration are caused by the dilution of quartz evaporates and carbonate minerals variations in sn concentrations probably depend on relative contents of some heavy minerals high sr ba low th u k cs ratios of the saline lake deposits suggest differences in aqueous chemistry of these elements the occurrence of the m type tetrad effect a ree pattern with four convex curves of ree compositions found mainly in the river deposits is considered the result of water particle interaction during chemical weathering of crustal materials y ho ratios of these samples are significantly higher than those of chondrite and the ucc this suggests different chemical behavior of these two elements and possibly the enrichment of carbonate materials the low lree hree feature of the saline lake deposits can be interpreted as due to the different aqueous chemical behavior of the ree s however it can also be reasonably considered as the result of inheritance from their provenance since lree and lree hree variations may be related to the geological setting of the source according to some elements that are not significantly fractionated the average provenance composition of these quaternary deposits are probably characterized by enrichments of ni cr and v over fe higher la th lower la sc and th sc and lower ta w and nb w ratios compared with the ucc composition

overthrust terranes in the lachlan fold belt southeastern australia the paleozoic history of the lachlan fold belt involves terrane translation and accretion of discrete allochthonous fragments four major terranes developed adjacent to the gondwana continental margin and were overthrust in the middle devonian to form a partly composite crust for southeastern australia

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

bottom current controlled sedimentation a synthesis of the contourite problem abstract an overview of the main items concerning deep bottom current controlled deposits is presented these include the definition of contourites their processes of deposition and facies characteristics contourite drift types and seismic patterns the interplay of turbidity and bottom current processes and the correlation between bottom current processes and global changes in climate sea level from this discussion several of the more significant problems are highlighted which we believe should be priority targets for future research 1 identification of contourites especially in ancient series where they are interbedded with turbidites and other facies 2 refinement of the numerous parameters used as tracers of palaeocirculation patterns 3 understanding the interaction between the different types of bottom currents and also between bottom current and other deep water processes 4 distinction in the sedimentary record between the effects of short time scale bottom current variations due to regional causes like benthic storms and geological scale current fluctuations related to climatic or astronomic control 5 understanding the control of glacial interglacial climatic cycles on the nature and rate of contourite deposition