crustal structure of the western part of the southern granulite terrain of indian peninsular shield derived from gravity data abstract the southern granulite terrain sgt is composed of high grade granulite domain occurring to the south of dharwar craton dc the structural units of sgt show a marked change in the structural trend from the dominant north south in dc to east west trend in sgt and primarily consist of different crustal blocks divided by major shear zones the bouguer anomaly map prepared based on nearly 3900 gravity observations shows that the anomalies are predominantly negative and vary between 125 mgal and 22 mgal the trends of the anomalies follow structural grain of the terrain and exhibit considerable variations within the charnockite bodies two dimensional wavelength filtering as well as zero free air based zfb analysis of the geoid corrected bouguer anomaly map of the region is found to be very useful in preparing regional gravity anomaly map and inversion of this map gave rise to crustal thicknesses of 37 44 km in the sgt crustal density structure along four regional gravity profiles cutting across major shear zones lineaments plateaus and other important geological structures bring out the following structural information the bavali shear zone extending at least up to 10 km depth is manifested as a plane separating two contrasting upper crustal blocks on both sides and the gravity high north of it reveals the presence of a high density mass at the base of the crust below coorg the steepness of the moyar and bhavani shears on either side of nilgiri plateau indicates uplift of the plateau due to block faulting with a high density mass at the crustal base the bhavani shear zone is manifested as a steep southerly dipping plane extending to deeper levels along which alkaline and granite rocks intruded into the top crustal layer the gravity high over palghat gap is due to the upwarping of moho by 1 2 km with the presence of a high density mass at intermediate crustal levels the gravity low in periyar plateau is due to the granite emplacement mid crustal interface and the thicker crust the feeble gravity signature across the achankovil shear characterized by sharp velocity contrast indicates that the shear is not a superficial structure but a crustal scale zone of deformation reaching up to mid crustal level

new probable cnidarian fossils from the lower cambrian of the three gorges area south china and their ecological implications abstract lower cambrian assemblages of phosphatic and chitinous tubular fossils of probable cnidarian affinities were recovered from the yanjiahe shuijingtuo and shipai formations in the three gorges area south china terreneuvian cambrorhytium cf c major co occur with an unnamed taxon in the yanjiahe formation they can be compared with specimens from the ediacaran miaohe fauna in the three gorges area the most abundant and diversified cnidarian assemblages including cambrorhytium gracilis n sp cambrorhytium cf major cambrorhytium minor sphenothallus songlinensis sphenothallus taijiangensis sphenothallus kozaki sphenothallus sp byronia sp and mackenzia sp are reported from the overlying cambrian stage 3 4 shuijingtuo and shipai formations these new fossils show previously unknown evidence for cnidarian affinities such as an attachment disk clonal clusters and probable budding structures these diversified assemblages of probable cnidarian fossils further fill major gaps in the cambrian record of stem metazoans and document associated early evolutionary patterns in addition our discovery suggests that along with sponges these tubular fossils represent another important component of benthic ecosystems that colonized often dysoxic deep settings during the cambrian explosion the observed increases of average body size and biomineralization among these probable cnidarians are tentatively linked to oxygenation of deep oceanic settings and appearance of predatory pressure during the ediacaran cambrian transition respectively

the ediacaran cambrian rise of siliceous sponges and development of modern oceanic ecosystems abstract the lack of unequivocal sponge fossils before the cambrian despite their probable deep origin during the cryogenian period has been a conundrum to geologists their impact on the dramatic evolution of ecosystems and the seawater silica cycle during the ediacaran cambrian e c transition is also speculative in this study abundant sponge spicules and spicule like structures that probably represent original sponge fossils were recovered from four sections of the e c boundary interval in the yangtze gorges south china the paleontological and geochemical data presented herein provides evidence for a continuous distribution of relatively abundant sponge spicules some even forming spiculites as well as the earliest biogenic deposition of silica by metazoans in the ediacaran cambrian boundary interval these results further confirm that a biological takeover of oceanic dissolved si co occurred with the evolution of silica biomineralization in the e c interval resulting in the widespread deposition of biogenic chert hydrothermal input in spicule bearing cherts is also observed such hydrothermal activity might have favored the blooming of sponges through significant nutrient supply these results provide the first conjunction of geochemical and paleontological proxies in support of previous models considering that sponges by ventilation filtration and oxygenation of seawater were important ecosystem engineers of the e c bioradiation event and of the related establishment of modern type ecosystems

structural controls on the evolution of the kutai basin east kalimantan abstract the kutai basin formed in the middle eocene as a result of extension linked to the opening of the makassar straits and philippine sea seismic profiles across the northern margin of the kutai basin show inverted middle eocene half graben oriented nne ssw and n s field observations geophysical data and computer modelling elucidate the evolution of one such inversion fold nw se and ne sw trending fractures and vein sets in the cretaceous basement have been reactivated during the tertiary offset of middle eocene carbonate horizons and rapid syn tectonic thickening of upper oligocene sediments on seismic sections indicate late oligocene extension on nw se trending en echelon extensional faults early middle miocene n7 n8 inversion was concentrated on east facing half graben and asymmetric inversion anticlines are found on both northern and southern margins of the basin slicken fibre measurements indicate a shortening direction oriented 290 310 ne sw faults were reactivated with a dominantly dextral transpressional sense of displacement faults oriented nw se were reactivated with both sinistral and dextral senses of movement leading to the offset of fold axes above basement faults the presence of dominantly wnw vergent thrusts indicates likely compression from the ese initial extension during the middle eocene was accommodated on nne ssw n s and ne sw trending faults renewed extension on nw se trending faults during the late oligocene occurred under a different kinematic regime indicating a rotation of the extension direction by between 45 and 90 miocene collisions with the margins of northern and eastern sundaland triggered the punctuated inversion of the basin inversion was concentrated in the weak continental crust underlying both the kutai basin and various tertiary basins in sulawesi whereas the stronger oceanic crust or attenuated continental crust underlying the makassar straits acted as a passive conduit for compressional stresses

an integrated stratinomic model for the genesis and concentration of small shelly fossil style phosphatic microsteinkerns in not so exceptional conditions abstract carbonate fluorapatite filled millimeter scale microsteinkerns are a key element of the small shelly fossil ssf fauna generally associated with the late proterozoic cambrian the purported disappearance of these fossils and this style of phosphatic preservation during the cambrian stage 2 botomian extinction has been linked to changes in ocean chemistry and or changes to the physical environment due to the evolution of metazoans as well to the changing role of metazoans in the marine environment through a qualitative meta analysis of existing literature we document a broader temporal distribution for ssf style preservation than previously recognized we examine these occurrences for common patterns of depositional conditions and we offer a conceptual model for both the origin of the phosphatic microsteinkerns and their eventual concentration in certain sediments based on known biogeochemical diagenetic processes of authigenic calcium fluorapatite precipitation phosphogenesis and subsequent concentration of phosphatic sedimentary particles this polycyclic phosphogenic condensation ppc model makes predictions as to how and where this form of preservation might occur in cambrian and non cambrian marine strata alike

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

comment on terreneuvian small shelly faunas of east yunnan south china and their biostratigraphic implications by b yang et al palaeogeography palaeoclimatology palaeoecology 398 2014 28 58 the recent article by yang et al 2014 provides a very useful summary of the litho and biostratigraphy of the sub trilobitic lower cambrian on the tropical shelf of south china our concern with this article is that it did not draw on or utilize existing reports that followed iugs protocols in the proposal of a gssp horizon and locality for informal stage 2 of the lower cambrian indeed a proposal of an integrated bio and chemostratigraphic signature i e the peak of the l4 carbon isotope excursion within the watsonella crosbyi assemblage zone in south china for the base of stage 10 and the location of a stage 2 gssp 9 m below the top of the dahai member at the laolin roadcut offers the potential for correlation of a stage 2 base across southern china and globally i e into siberla and avalonia

carbon isotope stratigraphy of the precambrian cambrian sukharikha river section northwestern siberian platform a high resolution carbon isotope profile through the uppermost neoproterozoic lower cambrian part of the sukharikha section at the northwestern margin of the siberian platform shows prominent secul

global correlation of the early cambrian of south australia shelly fauna of the dailyatia odyssei zone a lack of well resolved biostratigraphic data has prevented robust regional and global correlation of lower cambrian successions from south australia a new early cambrian biostratigraphy based on data derived from 21 measured stratigraphic sections and drill cores 11 described herein reveals the abundance and diversity of shelly fauna from the arrowie basin and the value of early cambrian small shelly fossils ssf for biostratigraphic studies here we examine shelly fauna associated with the youngest of three recently established biozones the dailyatia odyssei taxon range zone hereafter d odyssei zone and their correlative potential the d odyssei zone features a diverse suite of tommotiids organophosphatic brachiopods bradoriid arthropods molluscs and phosphatic problematica this fauna permits strong correlation often at species level with other major early cambrian terranes particularly antarctica south china and laurentia and suggest a cambrian series 2 stages 3 4 age for the d odyssei zone bradoriids have proven to be useful biostratigraphic tools four new species and three new genera are described herein acutobalteus sinuosus gen et sp nov eozhexiella adnyamathanha gen et sp nov manawarra jonesi gen et sp nov and mongolitubulus descensus sp nov the description of eohadrotreta sp cf zhenbaensis represents the first occurrence of the acrotretoid brachiopod eohadrotreta from australia

ediacarian sponge spicule clusters from southwestern mongolia and the origins of the cambrian fauna carbon and strontium isotopic data are used to show that the earliest sponge spicule clusters and associated phosphatic sediments with anabarites from southwestern mongolia are of ediacarian age spicule morphologies include bundles of oxeas arranged in three dimensional quadrules linked together at junctions by tetracts pentacts hexacts or polyactines all are referred to the phylum porifera class hexactinellida these sponge spicules provide the oldest remains that can be assigned without question to an extant phylum and also the first firm evidence for filter feeding and metazoan silica biomineralization in the fossil record it is suggested that siliceous and phosphatic members of the cambrian fauna may have had their origins in eutrophic and outer shelf facies of the late proterozoic

skeletal faunas of the lower cambrian yu anshan formation eastern yunnan china metazoan diversity and community structure during the cambrian age 3 abstract the lower cambrian stage 3 yu anshan formation in yunnan province south china hosts the chengjiang lagerstatte an exceptional window on the cambrian explosion however skeletal microfossils from this formation have long been neglected owing to the dominance of siliciclastics over carbonates here we characterize a new assemblage of small shelly fossils from the maotianshan shale member of the yu anshan formation the assemblage consists of univalved mollusc hyolith and brachiopod shells trilobite and bradoriid carapaces chancelloriid sclerites sponge spicules and echinoderm ossicles combining this information with taxonomic data previously tabulated for fossil assemblages from three other facies we performed quantitative comparisons of the genus level taxonomic diversity and modes of life and nutrition of four mutually equivalent early cambrian age 3 paleocommunities 1 skeletal faunas of the inner shelf 2 predominantly soft bodied faunas of the intra shelf basin 3 archaeocyathan faunas of the carbonate shelf and 4 sponge dominated faunas of the slope to basin areas the taxonomic and paleoecological distinctness of these four paleocommunities indicate possible low levels of competition within the communities and rapid expansion of habitat ecospace ranges though with similarities in the taxonomic composition of poriferans and arthropods reflecting the rapid migration of these two groups into new habitats the present integrative study provides a more comprehensive portrait of metazoan diversification and paleocommunity evolution during the peak phase of the cambrian explosion than do investigations based on single communities

transitional ediacaran cambrian small skeletal fossil assemblages from south china and kazakhstan implications for chronostratigraphy and metazoan evolution abstract the ediacaran cambrian transition records distinct evolutionary changes of metazoans the ediacaran fossils i e ediacara type biota and tubular fossils are contrasting with the diverse small skeletal fossils ssfs from the early cambrian the apparent dissimilarities hindered studies deciphering their evolutionary relationships this also led to a popular assumption that there exists a mass extinction of the ediacara biota and cloudinids at the precambrian cambrian pc c boundary here we report for the first time a transitional fauna which consists of typical elements of ediacaran i e cloudinids and related tubicolous organisms together with cambrian ssfs including protoconodonts anabaritids and siphogonuchitids from south china and maly karatau kazakhstan the sediments yielding the transitional fauna are characterized by siliceous rocks in both regions and were previously considered to be unfossiliferous their chronostratigraphic assignment in south china has been debated for years based on the new fossil assemblage the siliceous strata of the daibu member northeast yunnan south china and the basal kuanchuanpu formation south shaanxi south china can be assigned to the earliest cambrian ssf biozone anabarites trisulcatus protohertzina anabarica assemblage zone and thus can be considered of early cambrian in age a new subzone of the earliest ssf zone in eastern yunnan south china is proposed herein defined as ganloudina symmetrica rugatotheca typica interval subzone the new fauna demonstrates that the cloudinids originally confined to the late ediacaran persisted into the cambrian fortunian and no major extinction event occurred at the pc c transition

a review on active tectonics and deep crustal processes of the western sichuan region eastern margin of the tibetan plateau abstract one of remarkable geological and geomorphological features in continental china is the presence of a north south trending tectonic zone which separates the seismically active tibetan plateau to the west from the tectonically stable south china and ordos blocks to the east the zone also owns a name of north south seismic belt as a large number of great historical earthquakes occur on it the most recent one the 2008 wenchuan earthquake attests its recent tectonic activity in this review i take the western sichuan region as an example to probe the structural styles and kinematic pattern as well as deep geological process associated with tectonic deformation of the north south trending zone through integrated studies on active faults gps crustal deformation and geophysical structure we show that deformation in the western sichuan is governed by interactions among three crustal blocks songpan chuandian and south china of distinctive rheological properties under the tectonic framework that eastward growth of the soft eastern tibet is blocked by the hard lithosphere of the south china block the left lateral xianshuihe fault continues to the north south trending fault system without crustal shortening to form a bounding fault to limit the northern extend of the magnificent clockwise rotation of crustal material around the eastern himalaya syntax upper crust of the three blocks is dominated by brittle deformation whereas the ductile flow of lower crust would drag the brittle upper crustal blocks to move with respect to each other the relative motions among the brittle upper crustal blocks cause strain accumulations among their bounding faults to generate large earthquakes deformation of the western sichuan region can thus be described in terms of combined model of rigid block movement and continuous deformation we suggest this combined model can be applied to entire continental china

tilt depth method a simple depth estimation method using first order magnetic derivatives aeromagnetic data are routinely presented as contour or color shaded maps of the total magnetic intensity tmi an interpreter s task is to identify features anomalies contained within the map and qualitatively and or quantitatively interpret them into geologic structures at depth if the map contains anomalies that have large magnetic intensities the bodies might be considered to have large magnetizations or to be at shallow depths small amplitude anomalies superimposed on these anomalies could be masked or even missed by an interpreter thus the task of the interpreter is to use the spectral content of the anomalies to try and resolve these ambiguities part of this process is also to obtain estimates of the depth and shape of the body causing the anomalies

chronology of early cambrian biomineralization data on the first appearances of major animal groups with mineralized skeletons on the siberian platform and worldwide are revised and summarized herein with references to an improved carbon isotope stratigraphy and radiometric dating in order to reconstruct the cambrian radiation popularly known as the cambrian explosion with a higher precision and provide a basis for the definition of cambrian stages 2 to 4 the lophotrochozoa and probably chaetognatha were first among protostomians to achieve biomineralization during the terreneuvian epoch mainly the fortunian age fast evolutionary radiation within the lophotrochozoa was followed by radiation of the sclerotized and biomineralized ecdysozoa during stage 3 the first mineralized skeletons of the deuterostomia represented by echinoderms appeared in the middle of cambrian stage 3 the fossil record of sponges and cnidarians suggests that they acquired biomineralized skeletons in the late neoproterozoic but diversification of both definite sponges and cnidarians was in parallel to that of bilaterians the distribution of calcium carbonate skeletal mineralogies from the upper ediacaran to lower cambrian reflects fluctuations in the global ocean chemistry and shows that the cambrian radiation occurred mainly during a time of aragonite and high magnesium calcite seas

sponge spicules from the lower cambrian in the yanjiahe formation south china the earliest biomineralizing sponge record abstract sponges are the earliest metazoans and according to molecular clocks have a deep history back into the cryogenian however the record of their biomineralized elements below the ediacaran cambrian boundary has been controversial here we present the first and earliest indisputable record of hexactinellid spicules in the lowest cambrian terreneuvian below the small shelly fossil anabarites trisulcatus protohertzina anabarica assemblage zone zone i spicules recovered from cherts of the lowest yanjiahe formation in the yichang hubei province south china include monaxons diaxons triaxons and that are all siliceous in composition this earliest record of silica biomineralization by filter feeding metazoan suggests sponges have contributed to the cycling of silica in the oceanic system as early as the beginning of the phanerozoic these results along with a review of previously reported sponge occurrences suggest a two step evolution on sponges of the early cambrian

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

the integration of gravity magnetic and seismic data in delineating the sedimentary basins of northern sinai and deducing their structural controls abstract the sinai peninsula is a part of the sinai sub plate that located between the southeast nubian arabian shield and the southeastern mediterranean northward the main objectives of this investigation are to deduce the main sedimentary basin and its subdivisions identify the subsurface structural framework that affects the study area and determine the thickness of sedimentary cover of the basement surface the total intensity magnetic map bouguer gravity map and seismic data were used to achieve the study aims structural interpretation of the gravity and magnetic data were done by applying advanced processing techniques these techniques include reduce to the pole rtp power spectrum tile derivative and analytical signal techniques were applied on gravity and magnetic data two dimensional gravity and magnetic modeling and interpretation of seismic sections were done to determine the thickness of sedimentary cover of the study area the integration of our interpretation suggests that the northern sinai area consists of elongated troughs that contain many high structural trends four major structural trends have been identified that reflecting the influence of district regional tectonic movements these trends are 1 ne sw trend 2 nnw sse trend 3 ene wsw trend and 4 wnw ese trend there are also many minor trends e w nw se and n s structural trends the main sedimentary basin of north sinai is divided into four sub basins 1 northern maghara 2 northeastern sinai 3 northwestern sinai and 4 central sinai basin the sedimentary cover ranges between 2 km and 7 km in the northern part of the study area

mineral magnetic properties of loess paleosol couplets of the central loess plateau of china over the last 1 2 myr 1 we have conducted a multiparameter investigation of 15 loess paleosol couplets s0 l1 to s14 l15 from the jiaodao section in the central loess plateau of china using environmental magnetic approaches coupled with soil science techniques the magnetic parameters display systematic variations that seem to be closely related to paleoclimate variations and intensity of pedogenesis high temperature susceptibility curves of paleosols show a generally decreasing trend in reversibility from the base of the lishi formation to the holocene black loam possibly indicating a decrease in weathering intensity this may reflect a long term increase in aridity and or a general long term cooling trend of the interior of the asian continent from 1 2 ma to the present several samples display wasp waisted hysteresis loops these are most pronounced in moderately enhanced paleosols less pronounced in the practically unaltered loess and subdued in the well developed paleosols but wasp waistedness reappears in the most developed paleosols this wasp waistedness sequence suggests that the composition concentration and grain size of magnetic minerals all contribute to the hysteresis behavior of samples from the studied loess paleosol sequence but each factor has a different effect at different stages of pedogenesis

facies phosphate and fossil preservation potential across a lower cambrian carbonate shelf arrowie basin south australia abstract the effects of sedimentological depositional and taphonomic processes on preservation potential of cambrian small shelly fossils ssf have important implications for their utility in biostratigraphy and high resolution correlation to investigate the effects of these processes on fossil occurrence detailed microfacies analysis biostratigraphic data and multivariate analyses are integrated from an exemplar stratigraphic section intersecting a suite of lower cambrian carbonate palaeoenvironments in the northern flinders ranges south australia the succession deepens upsection across a low gradient shallow marine shelf six depositional facies sequences are identified ranging from protected fs1 and open fs2 shelf lagoonal systems high energy inner ramp shoal complex fs3 mid shelf fs4 mid to outer shelf fs5 and outer shelf fs6 environments non metric multi dimensional scaling ordination and two way cluster analysis reveal an underlying bathymetric gradient as the main control on the distribution of ssfs unlike groups that produced primary organophosphatic biominerals taxa that built calcareous skeletons are more taphonomically controlled which is further exacerbated by sampling and processing biases a strong facies association with condensed and reworked horizons suggests the stratigraphic occurrence of calcareous groups reflects conditions conducive to preservation phosphogenesis and phosphatization rather than true stratigraphic ranges consequently organophosphatic taxa should take precedence in the erection of biostratigraphic zones for subdivision of lower cambrian successions

seawater carbon and strontium isotope variations through the late ediacaran to late cambrian in the tarim basin abstract the radiation of early animals during the cambrian explosion was accompanied by widespread perturbations in oceanic and atmospheric conditions however the cause effect relationships between evolutionary innovations carbon c cycling and continental weathering are still a matter of debate further paleoenvironmental reconstructions of poorly studied paleo continents covering the precambrian cambrian pc c transition may improve the correlation of the events and their impact on the earth system on a global scale the tarim basin was presumably located proximal to the well studied south china craton during the ediacaran cambrian boundary and is expected to contribute equally to our paleoenvironmental reconstructions here we apply carbon and strontium sr isotope records 13c and 87sr 86sr obtained from well preserved marine carbonates spanning the late ediacaran to the late cambrian from the keping region in the northwestern tarim basin nw china by comparison to other carbonate successions from various paleo continents our obtained seawater 87sr 86sr curve in this study shows a stepwise first order increase to more radiogenic values superimposed by second order presumably regional variations our obtained 13c variations exhibit four prominent negative and three positive excursions identical to the global 13c record based on existing paleontological evidence and our new tarim 13c and 87sr 86sr curves we propose a stratigraphic correlation from the late ediacaran to the late cambrian between the tarim basin and other paleo continents besides our paleoenvironmental reconstruction reveals both regional and global sea level changes that may have controlled the influx of radiogenic sr and presumably the influx of nutrients controlling primary production and the rate of organic carbon burial in the tarim basin at the time of deposition these feedbacks may have ultimately influenced the rapid diversification of metazoans and the oxygenation of the cambrian ocean and atmosphere approaching present po2 levels

possible biogenic structures from the lower cambrian strata in yunnan province south china microbially induced sedimentary structures miss are microbial traces in sandy deposits they have been formed by various modes of microbial behaviour in response to the prevailing physical dynamics in shallow marine environments since early archaean time an association of fossils phosphatic structures and grains stromatolites and microbial laminated levelling structures is documented from the zhongyicun member of lower cambrian strata in the baideng section dated close to 535 ma sem examination demonstrates that microbial laminated levelling structures are the result of the development of microbial mats composed of filamentous structures we propose that there was a short hiatus after the dolomite layer deposited when the dolomite layer was weathered to form centimetre scale valleys firstly and then microbes accumulated in these valleys and formed the microbial laminated levelling structures

an integrated study of the grain size dependent magnetic mineralogy of the chinese loess paleosol and its environmental significance 1 to investigate the grain size dependent properties of the magnetic minerals in chinese loess paleosol samples touxiangdao xining qinghai province china magnetic extracts were divided into two size fractions by gravitational settling on the basis of hysteresis measurements thermal demagnetization of low temperature saturation isothermal remanent magnetization and nonmagnetic studies sem and xrd we identified magnetic phases both in the grain size fractions of the magnetic extracts and in the less magnetic residues to provide more accurate and complete descriptions of all the magnetic components in the bulk natural samples the results show that the oxidation degree nonstoichiometry of magnetic minerals is strongly affected by both grain size and the paleoclimatic environment in which they were deposited and altered in ascending order of the oxidation degree of our samples we find 1 loess coarse particles lc are multidomain md magnetite with slight oxidation 2 paleosol coarse pc particles are also md magnetite but with a higher oxidation degree compared to lc 3 loess fine lf particles are pseudo single domain psd magnetite with a high oxidation degree and 4 paleosol fine pf particles are psd maghemite single domain sd and superparamagnetic sp maghemite mainly stay in the residues further thermomagnetic analysis of pf psd maghemite revealed that this natural maghemite has a curie temperature identical to that of magnetite and that the conversion efficiency of transformation from maghemite to hematite is only about 50 after a 700 c heating cooling cycle these new results identify the sources of multicomponent nrm in chinese loess sequences as well as clarify the paleoenviromental and paleoclimatic controls on the remanence components

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

soft sediment deformation structures from the diexi paleo dammed lakes in the upper reaches of the minjiang river east tibet abstract the north south trending upper reaches of the minjiang river run along the longmen shan min shan fault zone a zone of abrupt topographic change along the eastern margin of the tibetan plateau multiple levels of well preserved soft sediment deformation structures seismites occur in sediments deposited in paleo dammed lakes in the upper part of the minjiang river valley these deformation structures include liquefied convolute deformation water escape structures flame structures pseudonodules ball and pillow structures sedimentary dykes mud lenses and large scale folds several kilometers from the barrier bar of the diexi paleo dammed lakes seven deformed structural layers were identified at different heights in late quaternary stratigraphic sequences near shawan village maoxian county analyses of the deformation structures landforms and the structural environment indicate that these deformation structures were caused by earthquakes slumps and landslides osl optical stimulated luminescence and 14c dating of soft sediment layers from the shawan site indicate that intense earthquakes occurred during the period 25 20 ka b p therefore accurate geological dating of deformed features in dammed lake deposits in high mountains and canyons enables the record of moderate to large magnitude earthquakes to be extended to the late pleistocene holocene upon the eastern tibetan plateau

carbon isotope variability across the ediacaran yangtze platform in south china implications for a large surface to deep ocean δ13c gradient new isotope data obtained from relatively conformable carbonate rich strata of the ediacaran yangtze platform in south china reveal substantial 13 c variability in platform sections four negative 13 c anomalies with a nadir down to 8 pdb are present in the interval between the cap carbonate level 635 ma and the precambrian cambrian boundary 542 ma while in slope and basinal sections 13 c values are negative through the entire doushantuo formation 635 551 ma if these 13 c values are close to their primary seawater signature they imply a strong 10 surface to deep ocean 13 c gradient that is consistent with long term deep ocean anoxia and the presence of a large dissolved organic carbon doc reservoir the two prominent negative 13 c excursions within the doushantuo formation above the cap carbonate level are associated with shoaling and local exposure of the platform the anomalies may thus record remineralization of a large oceanic doc pool via sulfate reduction that transferred 13 c depleted carbon from the oceanic doc reservoir to the surface ocean during regression inconsistencies in ediacaran 13 c profiles globally and variations in south china in particular highlight the need for further evaluation of local departures in 13 c from an inferred average seawater signature

new carbon isotope stratigraphy of the ediacaran cambrian boundary interval from sw china implications for global correlation the yangtze platform preserves relatively thick carbonate successions and excellent fossil records across the ediacaran cambrian boundary interval the intensely studied meishucun section in east yunnan was one of the global stratotype section candidates for the precambrian cambrian boundary however depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified the laolin section located in ne yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the precambrian cambrian boundary however the stratigraphic framework and correlations were controversial we studied and systematically sampled the laolin section and present here new carbon isotope data for this section the laolin section consists of in ascending order the baiyanshao dolostone of the dengying formation the daibu siliceous dolostone zhongyicun dolomitic phosphorite lower dahai dolostone and upper dahai limestone of the zhujiaqing formation and the black siltstone of the shiyantou formation our data reveal a large negative 13 c excursion 7 2 l1 in the daibu member which matches the previously published data for the laolin section and a large positive excursion 3 5 l4 in the dahai member which was not shown in the published data the excursion l1 correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in siberia and mongolia similar magnitude excursions are also known from morocco and oman for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 ma thus confirming a global biogeochemical event near the ediacaran cambrian boundary our data also indicate that deposition was more continuous at the laolin section compared with the meishucun section where there are no records of a comparable negative excursion near the ediacaran cambrian boundary nor any comparable positive excursion in the dahai member therefore the laolin section has proven potential to be a supplementary global stratotype section for the ediacaran cambrian boundary on the yangtze platform

precambrian cambrian boundary global stratotype ratified and a new perspective of cambrian time the precambrian cambrian boundary global stratotype is the base of the phycodes pedum zone at fortune head southeastern newfoundland the initial two stage radiation of the phanerozoic fauna the appearance of phanerozoic aspect trace producers and subsequent origin of diverse skeletalized metazoans was earliest cambrian fossil assemblages with deep complex burrows or originally mineralized skeletal fossils with exception of cloudina are early cambrian or younger correlation into avalon indicates that strata once referred to the proterozoic e g manykaian or nemakit daldynian and rovno stages are lowest cambrian and that the siberian tommotian stage is middle lower cambrian the thick sequence and complex epeirogenic history of the placentian series as compared with the trilobite bearing branchian series suggest that most early cambrian time is represented by the subtrilobitic lower cambrian

marine redox variations and nitrogen cycle of the early cambrian southern margin of the yangtze platform south china evidence from nitrogen and organic carbon isotopes the early cambrian is a crucial interval during which the marine environment encountered significant perturbations alongside key biological innovations the nitrogen isotopic composition of ancient sediments has the potential to record co variation between the marine ecosystem and environmental conditions here we report bulk nitrogen and organic carbon isotopic compositions accompanied by mo concentration data a proxy for redox conditions for a shelf marginal drill core section sancha and a deep basinal outcrop section yuanjia in hunan province south china for the cambrian fortunian stage variable delta n 15 bulk values 4 to 2 parts per thousand and low delta c 13 org values 35 parts per thousand to 33 from the yuanjia section indicate that anoxic waters shoaled into the photic zone with ammonia assimilation competing with anammox in the basinal area in the late cambrian stage 2 low delta n 15 bulk and delta c 13 org values together with high mo bulk concentrations delta n 15 bulk 5 to 0 parts per thousand delta c 13 org 33 5 to 31 0 parts per thousand 100 ppm mo bulk in sancha section and delta n 15 bulk 0 parts per thousand delta c 13 org similar to 33 parts per thousand 100 ppm mo bulk in yuanjia section reflect intense n 2 fixation accompanied by intermittent ammonia assimilation under expanded euxinic condition with shoaling chemocline possibly into the photic zone in the early cambrian stage 3 relatively high delta n 15 bulk values alongside positive delta c 13 org excursions at both sections indicate an increasing contribution from n 15 enriched nitrate assimilation and hence more oxic conditions shelf margin sediments from the middle and late parts of cambrian stage 3 are characterized bylaw delta n 15 bulk values similar to 0 parts per thousand being lowest in the basinal area 3 to 0 parts per thousand in combination with high mo bulk concentration 100 ppm and high mo tocbulk ratios averaging similar to 18 in deep basinal sediments these data suggest that the photic zone became anoxic again but that sulfidic conditions occurred in the basinal area only compared with stage 2 euxinia was less extensive during this interval with photosynthetic biomass dominating over chemoautotrophic biomass at both localities based on a combination of delta n 15 data from this study and published data from studies on contemporaneous sections in yunnan province and the three gorges area it is possible to reconstruct the spatial variability and temporal evolution of redox conditions in the various marine environments along the southern margin of the yangtze platform the basinal area appears to have been dominated by anoxia and intermittent euxinia in the photic zone during most of the early cambrian fortunian stage to stage 3 with the exception of more oxic conditions during early stage 3 on the platform oxygenated shallow water prevailed with the exception of the notable cambrian stage 2 anoxic event the outer shelf area experienced anoxia from stage 2 to stage 3 of the early cambrian although of possibly limited areal extent the high mo bulk concentrations and mo tocbulk ratios suggest that the south china basin was well connected with the considerably oxygenated open ocean and that the mean low delta n 15 bulk values similar to 1 6 parts per thousand from the basin may reflect generally lower delta n 15 composition for seawater nitrate in the early cambrian compared with modern value c 2015 elsevier b v all rights reserved

detrital zircon age and biostratigraphic and chemostratigraphic constraints on the ediacaran cambrian transitional interval in the irkutsk cis sayans uplift southwestern siberian platform

carbonate carbon isotope chemostratigraphy and u pb zircon geochronology of the liuchapo formation in south china constraints on the ediacaran cambrian boundary in deep water sequences abstract the ediacaran cambrian transition was one of the most significant intervals in geological history witnessing the origin of the metazoans and major environmental changes establishing a precise chronostratigraphic framework for the ediacaran cambrian transition has great significance for understanding the geological and evolutionary processes during this transition an integrated study on carbonate carbon isotopes and u pb zircon dating was conducted within the liuchapo formation in the sifangjing section in northeastern guizhou province south china to recognize the ediacaran cambrian boundary in slope facies of the yangtze block a substantial negative carbonate carbon isotope excursion was recognized within the lower part of the liuchapo formation moreover a weighted mean u pb zircon age of 540 7 3 8 6 6 ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion the carbon isotope and age dating results indicate that the ediacaran cambrian boundary within the sifangjing section should be placed in the lower part of the liuchapo formation additionally in the sifangjing section a distribution of horodyskia minor extends up to the basal cambrian while the last appearance datum lad of palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the liuchapo formation this relationship indicates that the lad of the palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the ediacaran cambrian boundary successions in slope and deep water basin settings of the yangtze block

cambrian small skeletal fossil and carbon isotope records of the southern huangling anticline hubei china and implications for chemostratigraphy of the yangtze platform abstract rich small skeletal fossil assemblages are described from the yanjiahe formation and tianzhushan member of southern huangling anticline the anabarites trisulcatus protohertzina anabarica assemblage zone small skeletal fossil zone 1 is recognized in the middle to upper yanjiahe formation while the thin topmost conglomeratic limestone unit yielded a mixed assemblage resulting from reworking and redeposition of source material of small skeletal fossil zones 1 to 3 including anabarites trisulcatus protohertzina anabarica p unguliformis watsonella crosbyi aldanella attleborensis anabarella plana our revised biostratigraphic correlation indicates the existence of longer hiatuses in the yanjiahe formation and between the yanjiahe and shuijingtuo formations the obtained 13ccarb values in our profile deviate in some details from those of some previous reports based on the new biostratigraphic correlation the 13ccarb trend records values oscillating between 3 to 4 4 in the upper anabarites trisulcatus protohertzina anabarica assemblage zone which is unusual for the yangtze platform this interval of positive 13ccarb values in the upper yanjiahe formation and the dahai member of eastern yunnan are here interpreted to reflect the impact of a local aquafacies moreover it is here argued that the selection of a carbon isotope peak as a primary index tool in the laolin section for defining the cambrian stage 2 must be treated with caution as this isotope excursion is influenced by a regional water mass and does not reflect an open marine seawater signature underlining other technical and theoretic concerns on the general application of chemostratigraphy in cambrian shallow water carbonate platforms overall we suggest that chemostratigraphic correlations need to be supported by biostratigraphic tools

river terraces as a response to climatic forcing formation processes sedimentary characteristics and sites for human occupation abstract climate impact on the fluvial processes led to morphological and sedimentological differentiation of a terrace this diversity in the fluvial environment determined how people could adapt to the river although the climatic impact on development and initiation of river terraces seems to be well accepted a number of pertinent questions disturb this simplicity for instance the exact terrace development within a climate cycle is still under debate different kinds of terraces and their sedimentary successions may originate either from aggradation incision or lateral migration is there a typical sedimentary succession below terraces what is the genetic origin of each sedimentary layer what are the relative ages of those layers and erosion phases within a climate driven erosion aggradation cycle the variability in staircase preservation in relation to climatic cyclicity is analysed in three scenarios specific scenarios depend essentially on the preservation of the fluvial deposits dating from the warm periods finally a preliminary inventory is presented of the most favourable sites for human occupation in fluvial valleys as derived from a random selection of archaeological findings generally human occupation in that morphological position seems to be linked with at least temporarily dry conditions climatic conditions do not seem to play the major role the termination of a settlement may have been due to increased risks of flooding apart from other than natural fluvio environmental reasons

rock slope failure and the river long profile this study examines the geomorphic effects of large 10 6 m 3 rock slope failures on long profiles of rivers in the swiss alps and the new zealand southern alps regression of channel slope versus drainage basin area objectively highlights knickpoints separating incised from aggraded reaches that often correspond to locations of large rock slope failures for a fixed concavity index the highest values of the steepness index and erosion index along a given profile spatially coincide with breach channels cut into formerly river damming rockslide debris as old as 10 k y assuming that the knickpoints do not predate slope failure data show that high profile steepness and inferred specific stream power are not always the cause but often a result of large river blocking rock slope failure in mountain basins omission of rockslide data from slope area plots lowers the steepness index and increases the concavity index on average yet only in few cases more than one standard deviation

use of a regional relict landscape to measure vertical deformation of the eastern tibetan plateau 1 field work and topography analysis show that remnant local areas of a low relief landscape or erosion surfaces are geographically continuous across the southeastern tibetan plateau margin we correlate these remnant surfaces as a paleolandscape that formed at low elevation remnants of this paleolandscape are preserved because incision of the fluvial system has been largely limited to major rivers and principal tributaries and has not yet progressed throughout the entire fluvial network the incomplete adjustment of the fluvial system signals initiation of rapid bedrock incision into a developing plateau margin and erosional denudation is concentrated in the major river channels this interpretation contradicts earlier notions that low gradient regional topography is the product of regional elevation reduction by intense landscape dissection due to the presence of several large southeast flowing rivers the modern altitude of the reconstructed paleolandscape or relict landscape constrains the vertical displacement of the plateau surface in response to crustal thickening and subsequent erosion during the lateral growth of the tibetan plateau regional preservation of the relict landscape is consistent with minor surface disruption by late cenozoic thrust faults and folds and supports a model of distributed lower crustal thickening because significant erosion is limited to narrow river gorges an increase in the plateau elevation due to isostatic rebound is minor therefore we propose that the modern elevation of the relict landscape reflects isostatically compensated thickening of the lower crust

geochronological constraint on the cambrian chengjiang biota south china the cambrian chengjiang biota of south china provides compelling fossil evidence for the rapid appearance of metazoan phyla in earth history the cambrian explosion however the timing of the chengjiang biota is poorly constrained owing to lack of datable rock materials within the maotianshan shale that yields the fossils here we integrate secondary ion mass spectrometry sims and chemical ablation isotope dilution thermal ionization mass spectrometry ca id tims u pb analyses of detrital zircons from the maotianshan shale to provide high precision geochronological constraint on the chengjiang biota the youngest group of sims u pb detrital zircon dates yields an age peak at 520 ma six zircons from this group are further dated by the ca id tims u pb technique but suggesting that they were not formed from a single zircon growth event thereby neither the age peak nor the weighted mean age defined by the youngest sims u pb dates could represent the maximum depositional age of the maotianshan shale instead the youngest ca id tims u pb date 518 03 0 69 0 71 ma 2 analytical uncertainty incorporates u pb tracer calibration uncertainty provides the first robust maximum age of the chengjiang biota this new geochronological constraint on the chengjiang biota indicates that the cambrian explosion reached its major phase around 518 03 0 69 0 71 ma demonstrating a protracted process 22 myr for the cambrian explosion supplementary material sims and ca id tims zircon u pb data are available at https doi org 10 6084 m9 figshare c 4024849

evaluating the role of climate and tectonics during non steady incision of the yellow river evidence from a 1 24 ma terrace record near lanzhou china abstract the competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain most of recent studies have attributed terrace formation to climatic changes and held that even in tectonically active settings climate variations control cycles of terrace planation and abandonment based on field investigations of loess paleosol sequences magnetostratigraphy and optically stimulated luminescence osl dating we develop a new chronology for a spectacular flight of terraces along the yellow river near lanzhou china over past 1 24 ma all the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates however the ages of terraces cluster in two relatively short time periods 1 24 0 86 ma and 0 13 ma present during the intervening time between 0 86 ma and 0 13 ma terraces either did not form or were not preserved we suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation preservation thus our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision

glacier and landslide feedbacks to topographic relief in the himalayan syntaxes despite longstanding research on the age and formation of the tibetan plateau the controls on the erosional decay of its margins remain controversial pronounced aridity and highly localized rock uplift have traditionally been viewed as limits to the dissection of the plateau by bedrock rivers recently however glacier dynamics and landsliding have been argued to retard headward fluvial erosion into the plateau interior by forming dams and protective alluvial fill here we report a conspicuous clustering of hundreds of natural dams along the indus and the tsangpo rivers where these cross the himalayan syntaxes the indus is riddled by hundreds of dams composed of debris from catastrophic rock avalanches forming the largest concentration of giant landslide dams known worldwide whereas the tsangpo seems devoid of comparable landslide dams in contrast glacial dams such as river blocking moraines in the headwaters of both rivers are limited to where isolated mountain ranges intersect the regional snowline we find that to first order high local topographic relief along both rivers corresponds to conspicuously different knickzones and differences in the type and potential longevity of these dams in both syntaxes glacier and landslide dams act as a negative feedback in response to fluvial dissection of the plateau margins natural damming protects bedrock from river incision and delays headward knickpoint migration thereby helping stabilize the southwestern and southeastern margins of the tibetan plateau in concert with the effects of upstream aridity and localized rock uplift

source of silica and silicification of the lowermost cambrian yanjiahe formation in the three gorges area south china abstract the rise of siliceous organisms is generally considered to have driven the abrupt decrease of silica in the ocean during the ediacaran cambrian e c interval even if the exact timing and biological triggers of this event are still debated although ediacaran cambrian chert depositions are widely distributed multiple evidences converge to support their hydrothermal origin in this study we provide petrographic study supplemented by elemental concentration sem and raman spectral data on the siliceous rocks from the yanjiahe formation the three gorges area south china in order to ascertain the origin of included silica and discuss the involved processes of silica deposition contrary to most previous studies our analyses suggest that studied cherts mainly resulted from biogenic silica and subsidiary from abiotic precipitation influenced by surrounding hydrothermal activity and from detrital input the deposition model of silica includes direct deposition of siliceous bioclasts secondary replacement of carbonate by dissolved biosilica and microbial induced silicification from seawater the sink of silica recorded in the yanjiahe formation was characterized of a transition from typical precambrian to phanerozoic process in addition micropalaeontological and taphonomical analyses of the yanjiahe formation revealed two pulses of microfossil abundance and diversity in the fortunian and stage 2 respectively they can be correlated with a regression and an enrichment in dissolved phosphate that probably derived from enhanced detrital flux

correlations of fluvial knickzones with landslide dams lithologic contacts and faults in the southwestern annapurna range central nepalese himalaya 1 we investigate the role of landslide dams spatial changes in lithology and rock uplift on faults in the formation of knickzones on bedrock rivers we focus our analysis in the southwestern annapurna range of the central nepalese himalaya where detailed geologic maps topographic data field observations and aerial photographs are available we identified knickzones in our study area from normalized river steepness indices ksn values extracted from river longitudinal profiles derived from a 25 m digital elevation model we interpolated from digitized topographic map contours we compared the location of these knickzones with 1 lithologic contacts and faults from a detailed geologic map of the modi khola valley and 2 inferred ancient landslide dam features mapped from field observations and aerial photographs the steepest location on the modi khola occurs near the same latitude as the steepest reach on the mardi khola located directly to the east potentially highlighting a major topographic transition across the annapurna however we find that landslide dams once blocked the flow of the modi khola and damming followed by incision after landslide breaching can explain the location of these knickzones without the need for active faulting near the main central thrust we also conclude that 1 knickzones do not correlate with any spatial changes in lithology and 2 knickzones generated by rock uplift on unmapped faults cannot be ruled out we emphasize that disentangling the processes responsible for knickzone formation remains challenging even when high resolution geologic and topographic data are available

determination of sedimentary cover and structural trends in the central sinai area using gravity and magnetic data analysis abstract the present study is an attempt to determine the sedimentary cover and structural trends in the central part of sinai peninsula egypt this study has been implemented by the integration of gravity and magnetic methods gravity data has been used for 2d modelling along some profiles perpendicular to the main structural trends of the study area magnetic data will be analyzed to determine the depth to the basement surface the depths obtained from magnetic data will be used as a control points in the gravity modelling in order to minimize the error and facilitate the iteration of the suggested models the basement relief map from magnetic and gravity output has been produced this map indicates that the basement depths generally increases from south to north and from east to west direction of the study area the sedimentary cover is about 1 5 2 km in the southern part and increases to more than 4 km in the northeastern and western parts and changes gradually in the other parts of the study area results of structural trend analysis indicate that the study area is greatly affected by several structural trends n s e w nw se and nne ssw directions these trends are associated with the baltim fault trend tethyan trend gulf of suez and aqaba trend respectively

differential impact of small scaled tectonic movements on fluvial morphology and sedimentology the huang shui catchment ne tibet plateau abstract the aim of this paper is to investigate the morphological implications of the interplay between tectonic movements at different rates timescales and spatial extent in a catchment of intermediate size the huang shui river a main tributary of the yellow river in the ne tibet plateau river incision started from a peneplain like surface that developed in post miocene pliocene times at the end of the tertiary a general tectonic uplift of the tibetan plateau initiated river incision this general uplift also caused local fragmentation of the huang shui catchment into blocks kilometers or maximally a few tens of kilometers of local extent that have subsided and or uplifted relative to one another fluvial deposition of 30 m in the subsiding blocks contrasts with erosion and formation of gorges in the uplifted blocks incision into the former peneplain was not continuous but a staircase of terraces developed under climatic influences terrace deposits are sometimes capped by interglacial soils or soil derived material apparently terrace incision occurred at the transition to the next cold period the different rates of uplift and subsidence of the individual blocks resulted in the simultaneous development of erosion and accumulation terraces of different sizes within the same catchment even within the same tectonic block this makes it impossible to connect the terraces of the different blocks except for the three youngest terraces representing the last 300 000 years thus illustrating the uniform tectonic history of the catchment since that time

implementation of magnetic gravity and resistivity data in identifying groundwater occurrences in el qaa plain area southern sinai egypt abstract el qaa plain is one of the areas that have been proved to be promising as to its soil and groundwater resources in the southwestern part of sinai this study was carried out to study the lateral and vertical variations in the subsurface lithologic properties in el qaa plain area and delineating the subsurface structure that affecting el qaa plain depression gravity magnetic data fifty one 51 vertical electrical sounding ves s and digital elevation model dem map were used two dimensional density modeling analytical signal tilt derivatives euler deconvolution techniques and interpretation of the resistivity data were applied on potential data this study concluded that el qaa plain is a ne sw depression confined by two normal faults and subdivided into five sedimentary units rock fragments and boulders derived to the plain from the surrounding highlands are the main components of the first surface unit that characterized by high resistivity values this layer is overly another unit composed of gravelly sand with thickness ranging between 10 and 140 m the third unit is composed mainly of sand with intercalations of clay with thickness ranging from 2 to 152 m a reefal limestone unit is a fourth unit interpreted from this study the fifth unit is composed of clay the water bearing formations in el qaa plain area are located principally in the second and the third layers finally the depth to the basement surface ranges from 400 m to more than 1 5 km below sea level also there are many minor structural trends interpreted from this study and affecting the el qaa plain are striking in n s e w and ne sw directions

a new lower cambrian shelly fossil biostratigraphy for south australia abstract definition of early cambrian chronostratigraphic boundaries is problematic with many subdivisions still awaiting ratification integrated multi proxy data from well resolved regional scale schemes are ultimately the key to resolving broader issues of global correlation within the cambrian in australia early cambrian biostratigraphy has been based predominantly on trilobites phosphatic shelly fauna have great potential as biostratigraphic tools especially in pre trilobitic strata because they are widespread and readily preserved but they have remained underutilised here we demonstrate their value in a new biostratigraphic scheme for the early cambrian of south australia using a diverse shelly fauna including tommotiids brachiopods molluscs and bradoriids biostratigraphic data are derived from ten measured stratigraphic sections across the arrowie basin targeting hawker group carbonates including the wilkawillina wirrapowie and ajax limestones and the mernmerna formation the stratigraphic ranges of shelly fossils are predictable and repeatable across the arrowie basin allowing three discrete shelly biozones to be identified spanning terreneuvian stage 2 to series 2 stages 3 4 the kulparina rostrata zone new and part of the overlying micrina etheridgei zone new are pre trilobitic predominantly terreneuvian the cambrian series 2 stage 3 dailyatia odyssei zone new features a very diverse shelly fauna and will be described in detail in a separate publication these zones provide robust means to correlate terreneuvian series 2 successions in neighbouring coeval basins in australia particularly the stansbury basin wider correlation is possible throughout east gondwana and especially with south china

further shrimp geochronology on the early cambrian of south china zircon 206pb 238u ages are reported for bentonites from two cambrian sections in south china the meishucun and the fandian the analyzed zircons vary widely in age because of the presence of detrital and altered grains spot ages were corrected for calibration drift during analysis and the age of reference zircon sl13 was calibrated as 580 ma against other standards using sims use of mixture modeling was essential to resolve the different age components and to identify the volcanic ages two age groups occur within the meishucun bed 5 bentonite of which the larger at 518 7 2 5 ma is interpreted as a post depositional zircon growth event and the other at 539 4 2 9 ma as the volcanic age bentonites from the meishucun bed 9 and its fandian equivalent have two age groups 526 5 1 1 ma and 540 2 1 0 ma we interpret the younger of these as the tuff magmatic age and the older as detrital small shelly fossils indicate meischucunian bed 5 is an equivalent of the late nemakit daldynian and its 539 4 2 9 ma age both closely times the base of the cambrian and is a maximum for the basal tommotian the 526 5 1 1 ma for bed 9 and its equivalents approximates the close of the tommotian

delineation of intra crustal horizon in eastern dharwar craton an aeromagnetic evidence abstract a correlative study of two mutually independent geophysical properties like magnetic susceptibility variations and shear wave velocity structure of the crust has been carried out in a part of the eastern dharwar craton of indian peninsular shield analysis of the aeromagnetic anomaly field over an area of 35 000 km 2 comprising the peninsular gneissic basement complex and a part of cuddapah basin has resulted in identification of two distinct magnetic horizons one at a depth of 2 km and the other at a depth of 12 km correlation of these results with the inferences made by the inversion of rayleigh wave phase velocity and other geophysical studies has confirmed the presence of a crustal layer at a depth of 12 km this horizon has been inferred to be the depth to the lower boundary of the upper crust in this region

linking landslides hillslope erosion and landscape evolution this virtual issue highlights 10 recent innovative unconventional or otherwise significant contributions to earth surface processes and landforms that help advance the state of the art in research on linkages between landslides hillslope erosion and landscape evolution the selected studies address this feedback within a temporal spectrum that ranges from the event to the millennial scale thus underscoring the importance of detailed field observations high resolution digital topographic data and geochronological methods for increasing our capability of quantifying landslide processes and hillslope erosion copyright 2009 john wiley sons ltd

paleosols identified by rock magnetic properties indicate dam outburst events of the min river eastern tibetan plateau abstract river terrace sediments are archives of past fluvial processes and they may also reflect a wide range of additional environmental processes detailed studies of river terrace sediments are important for understanding the role of tectonics climate and extreme geomorphological events in fluvial evolution here we present a sedimentary reconstruction using the combination of field description magnetic measurements and optically stimulated luminescence and ams 14c dating of the maoxian mx section in the third terrace of the min river in the eastern margin of the tibetan plateau the section is mainly composed of clastic deposits and spans the interval from the last glacial to late holocene apart from the silt at the bottom and the gravel layer in the middle it is difficult to determine whether other clastic deposits were exposed sub aerially multiple magnetic proxies indicate that the mx section contains three layers of pedogenic production of fine grained magnetite maghemite which correspond to paleosol layers the paleosol layers indicate the occurrence of at least three intervals of exposure to the atmosphere the three paleosol layers were likely caused by dam outburst events the results demonstrate that rock magnetic methods are a useful approach for identifying paleosol layers in fluvial sediments

on reduction of magnetic and gravity data on an arbitrary surface acquired in a region of high topographic relief discussion and reply when attempting to get an overview of continuation of potential fields in exploration geophysics one cannot avoid reading the much quoted article by bhattacharyya and chan hereafter referred to as bc however it is unfortunate that the article is unclear on some fundamental points which this comment attempts to clarify

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

rock magnetic characterization of pedogenesis under high energy depositional conditions a case study from the mio pliocene siwalik fluvial sequence near dehra dun nw himalaya india abstract systematic rock magnetic studies accompanied by field investigations are presented for 51 pedogenic horizons from magnetostratigraphically constrained middle upper siwalik fluvial sequence 9 4 ma near dehra dun in the himalayan foreland basin hfb detailed sedimentologic studies infer predominantly proximal to distal alluvial fan setting with considerably high rate of sedimentation 55 cm ka paleosol profiles in the mohand rao mr section are commonly truncated by channel activity these paleosols display few rootlets diffused color contrast amongst variegated pedogenic horizons rare concretions intense gleying at places and frequent incursions by sand silt layers the mean mass specific magnetic susceptibility lf for pedogenic horizons is 0 95 10 8 m3 kg max 1 4 10 8 m3 kg min 0 5 10 8 m3 kg and the associated non pedogenic layers is 0 82 10 8 m3 kg max 1 2 10 8 m3 kg min 0 4 10 8 m3 kg the low frequency dependence of the susceptibility fd mean 2 and high coercivities bocr mean 425 mt of the pedogenic layers infer the absence of finer pedogenic superparamagnetic sp fraction that might have depleted during post depositional burial processes acquisition of isothermal remanent magnetization irm shows under saturation and gentle upward trend even at high applied fields 4000 mt advocating the predominance of hematite and goethite sympathetic variation in the total organic and inorganic carbon content with iron oxides stable under warm humid oxidative arid and cold restricted conditions confirm the sensitivity of the rock magnetic parameters to ambient climatic condition relative variations in goethite hematite and ferrimagnetic contents have been derived from ratios mainly based upon selective irm saturations and their coercivities these studies are validated by sandstone petrography and clay mineralogy for the same section however the variation in rock magnetic parameters shows a better amplification and allows relative quantification of the ambient climatic conditions the assemblage of iron oxides using the rock magnetic ratios of the pedogenic layers in these high energy conditions broadly infer the prevalence of semi humid to semi arid climate entirely during the late miocene to early pliocene period in the hfb with an increased seasonality during early pliocene the present approach envisages a great scope for quantitative database under the given setup of high energy conditions that are common in the mio pliocene hfb

sediment thicknesses of the western anatolia graben structures determined by 2d and 3d analysis using gravity data abstract western turkey is tectonically one of the most active and rapidly deforming regions of continental crust in the world the most pronounced structural and morphological features of this region are defined by normal faulting in an e w direction which creates the boundaries of the buyuk menderes kucuk menderes and gediz grabens the graben systems may have become active between 11 7 ma and are now deeper than the surrounding topography the gediz and buyuk menderes grabens exhibit negative bouguer gravity anomalies the bouguer gravity anomalies increase towards the center of the aegean sea in a regional sense the grabens are filled with recent sediments giving rise to relative negative gravity anomalies these anomalies were interpreted using 2d and 3d gravity inversion techniques in order to determine the depth to the metamorphic basement inversion of geophysical anomalies implies fitting the observed data to theoretical anomalies possibly produced by subsurface bodies inversion of gravity anomalies is a non linear problem in the sense that body parameters are not linearly related to the anomalies gravity anomalies caused by structures are mostly determined by a 2d model which has an n sided polygonal cross section for non linear problems theoretically it is more suitable to determine the parameters of the structure by a series of juxtaposing prisms or vertical dykes extending to infinity rather than using a single n side polygonal model the depths to the top surfaces of a rectangular prisms with infinite depth represent the relief of the basement the basement relief can be computed on the basis of density contrast if the reference depth is assessed as a result of 3d analysis of the bouguer gravity map the maximum thickness of sedimentary cover appears to be more than 2 0 and 1 5 km for the gediz and buyuk menderes grabens respectively towards the saraykoy kizildere area the sedimentary thickness cover thickens to more than 2 0 km 2d analysis of the bouguer gravity profiles indicate that the maximum thickness of the sedimentary cover is between 2 5 and 3 5 km in the buyuk menderes graben and between 0 5 and 2 0 km in the gediz graben

lowermost cambrian acritarchs from the yanjiahe formation south china implication for defining the base of the cambrian in the yangtze platform the asteridium heliosphaeridium comasphaeridium ahc acritarch assemblage is composed of common organic walled microfossils in the basal cambrian chert phosphorite units in south china indicating that the ahc assemblage can be a useful biostratigraphic tool for the ediacaran cambrian boundary successions in the yangtze platform to test the validity of the ahc acritarch assemblage as a biostratigraphic tool the stratigraphic range of the ahc acritarch assemblage was confirmed and its spatial and temporal relationships to other bio and chemostratigraphic tools were analysed in the yanjiahe formation yangtze gorges area south china the result shows that the ahc assemblage temporally correlates to the anabarites trisulcatus protohertzina anabarica assemblage zone and spatially correlates to the large negative carbon isotope anomaly of the lowermost cambrian bace in the yanjiahe formation this implies that the radiation of phytoplankton occurred slightly before the radiation of the small shelly fossils and the ahc acritarch assemblage can be another important chronological reference to the lowermost cambrian successions in south china and potentially to global correlations

age and extent of a giant glacial dammed lake at yarlung tsangpo gorge in the tibetan plateau many glacier dams on major rivers at the southeastern edge of the tibetan plateau had been previously determined through remote sensing and glacier terminal position calculation it was hypothesized that such damming substantially impeded river incision into the plateau interior investigation on the large glacial dammed lake at the entrance of tsangpo gorge is critical for understanding this hypothesis so far the issues such as age lake surface elevation and stages of this dammed lake are still in debate our field survey of lacustrine deposits and loess distribution along the middle yarlung tsangpo river and its tributary nyang river suggested that the lake surface elevation was at about 3180 m asl the 23 quartz optically stimulated luminescence osl and 4 organic ams 14 c ages all fall into the last glacial period 41 13 ka the osl and 14 c ages are in general agreement with each other where applicable there might be only one long damming event because the ages of lacustrine deposits from 2970 to 3100 m asl are similar and every lacustrine section is sustained for a long time the estimated lake surface area was 1089 km 2 and the volume was 170 km 3 which differ from previous estimations which suggested two stage about early holocene and 1 5 ka lakes and the largest lake surface elevation reached 3500 m

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

a 900 k y record of strath terrace formation during glacial interglacial transitions in northwest china the timing of the development of strath terraces with respect to climatic variability remains equivocal previous studies attribute strath terrace formation to glacial or interglacial climates or to variations in sediment and water fluxes that cause lateral erosion followed by vertical incision a chronology of strath terrace formation spanning similar to900 k y has been generated on the basis of loess paleosol couplets and paleomagnetic thermoluminescence and radiocarbon dating of strath terraces in the qilian shan of northeastern tibet repetitive stratigraphic and geomorphic patterns on each terrace indicate that they formed during glacial interglacial transitions long term bedrock incision rates and inferred rock uplift rates appear steady and unrelated to strath formation over the past 900 k y

magnetic properties as tracers for source to sink dispersal of sediments a case study in the taiwan strait abstract different lithologies between taiwan and southeastern china lead to diverse mineralogical composition for weathering products derived from the two shores of the taiwan strait pyrrhotite and magnetite are respectively the dominant magnetic minerals associated with fluvial sediments from western taiwan and southeastern china while magnetite commonly co exists with pyrrhotite in sediments sourced from taiwan pyrrhotite has not been found in sediments sourced from mainland china associated with such a distinction are vast differences in magnetic properties including magnetic susceptibility sirm hirm and the s ratio which can be used to study the provenances of sediments in the taiwan strait and adjoining marginal seas based on any two of these parameters the magnetic characteristics of much of the taiwan strait sediment can be explained using a two endmember mixing model source to sink dispersal of sediments in the taiwan strait can then be traced from the distribution of these parameters the results not only corroborate an earlier study based on radionuclides and particle size distribution huh et al 2011 but reveal more diagnostic details besides spatial distribution based on a large number 216 of surface sediments we also analyzed temporal variation of magnetic properties in six well dated cores collected at key sites along the sediment source to sink pathways from profiles of these parameters in cores from the middle of the northern taiwan strait it is calculated that sediment supply from taiwan has increased substantially in the past five decades which may very well be related to accelerated land use and increased frequency of intense rainfalls in taiwan during the same period the approach described in this work may be extended to other source to sink systems around the world and through time especially the mountainous islands fringing the pacific and indian oceans in southeastern asia as with taiwan these islands have high denudation rates and pyrrhotite is in all likelihood a mineral characteristic of their metamorphic terrains

uplift driven valley incision and climate controlled river terrace development in the thames valley uk abstract the sequence of terraces of the river thames in southeast england has previously been shown to span the period from the earliest pleistocene to the present this terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary large scale fluvial incision resulting in basin wide terrace formation appears to have been concentrated at the warming limbs of the major climatic glacial interglacial cycles when sediment supply was greatly reduced this incision and subsequent valley floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm cold transitions and during the cold stages when high sediment supply conditions prevailed although the timing of terrace aggradation may be controlled by climate change the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of quaternary climatic change alone and recently developed models suggest that long term incision by the thames has been driven by uplift this paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons superimposed upon these broad changes revealed by the complex internal sedimentary architecture of many terrace sediments are the geomorphological system responses to both higher frequency climate driven changes and more localized intrinsic fluvial system adjustments

correlation of the cambrian evolutionary radiation geochronology evolutionary stasis of earliest cambrian terreneuvian small shelly fossil ssf taxa and chronostratigraphic significance early faunas with watsonella crosbyi with or without aldanella spp have been equated with the siberian tommotian stage uppermost terreneuvian and used to define a proposed cambrian stage 2 base much earlier terreneuvian occurrences are now shown by recovery of these micromolluscs below the i carbon excursion in the siberian nemakit daldynian stage and comparable 13 c excursions in the middle meishucunian china and middle chapel island formation avalonia this 13 c excursion a reliable stage 2 marker lies in a c 10 ma interval in the cambrian radiation in which long ranged small shelly fossil taxa provide limited biostratigraphic resolution

terreneuvian small shelly faunas of east yunnan south china and their biostratigraphic implications the study discusses the detailed composition of terreneuvian small shelly fossil ssf assemblages of eastern yunnan province meishucun xianfeng and huize regions the described sections represent shallow water deposits of the yangtze platform that include a number of stratigraphical hiati the reported ssf assemblages can be assigned to the regional ssf biozones i iii anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone zones ii and iii are slightly redefined based on new data two subzones of zone ii are proposed here namely annelitellus yangtzensis obtusoconus honorabilis subzone and maikhanella cambriana oelandiella korobkovi subzone claviconchella qianyii gen et sp nov and bubiites simplex gen et sp nov are reported here we also provide a critical revision of the ssf distribution for the well known meishucun section the correlation scheme for east yunnan documents the extent and duration of stratigraphical hiati the distribution of ssfs and the lithological characterization indicate three major events of exposure of the carbonate platform resulting in sedimentary breaks and possible karstification this prompts new consideration of the previously described stable isotope stratigraphy of shallow platform strata considering the complexity of the terreneuvian earth history as well as the uniqueness of ssf an integration of sedimentology geochemistry and paleontology is needed for future ssf study

first report of a meishucun type early cambrian stage 2 ichnofauna from the malyi karatau area se kazakhstan palaeoichnological palaeoecological and palaeogeographical implications abstract a trace fossil assemblage from the early cambrian phosphorites of the aktugai and koksu sections chulaktau formation of the lesser karatau area malyi karatau in the following text in se kazakhstan is reported for the first time based on a rich and biostratigraphically significant small shelly fossil ssf record the ichnofauna can be attributed to the basal cambrian terreneuvian uppermost fortunian to stage 2 along with rare vertical burrows the ichnoassemblage yielded abundant simple worm shaped epi and infaunal burrows of various ichnotaxa being associated with branched traces and pre trilobitic arthropod traces the non arthropod ichnofauna consists of hyporeliefs of large straight to slightly meandering traces belonging to palaeophycus isp and psammichnites isp type traces this ichnofauna is accompanied by horizons with short inclined u shaped burrows of the planolites type the evidence of treptichnus pedum like simple branching sub horizontal traces is proved for the koksu section but remains problematic for the aktugai section as they are poorly preserved and could be mixed up with planolites type traces additionally a dark brown coloured phosphoritic sandy dolostone band close to an iron manganese rich stromatolite bed on the base of the ushbas member contains vertical funnel shaped burrows of more than a decimetre in length which could be attributed to dwelling burrows of infaunal lingulid brachiopods lingulichnus several short and larger knob shaped vertical burrows in the surrounding phosphoritic dolostones occasionally display faintly preserved radial running and distally branching probes they resemble star shaped trace fossils from the meishucun and from the younger cambrian stage 4 guanshan sections of south china the arthropod traces can be attributed to rusophycus type traces probably r avalonensis as well as to monomorphichnus type and problematic primitive cruziana type trackways the arthropod traces are concentrated in the massive phosphorites of the karatau member upper chulaktau formation of the aktugai i and the koksu localities some of them are preserved as positive hyporeliefs on the subsurface of an overlaying greenish grey coloured chert band panel a of the fourth figure in this article the ichnotaxonomic inventory the facies the lithology and the depositional regime of the hosting rocks as well as the trace preservation in the massive phosphorites resemble the situation in the some older fortunian stage meishucun ichnofauna of southern yunnan south chinese yangtze platform as well as in some aspects the ichnoassemblage from the much younger stage 4 wulongqing formation of yunnan the here reported type of early cambrian ichnofauna could be characteristic for the abundant basal cambrian phosphorite dominated shelf deposits on the northwestern realm of gondwana