distribution and significance of novel low molecular weight sterenes in an immature evaporitic sediment from the jinxian sag north china abstract an unusual series of c 22 c 27 monounsaturated sterenes and c 24 c 30 tetracyclic terpanes 17 21 seco hopanes were detected in relatively high concentrations in an immature evaporitic marl sediment of the jinxian sag bohai bay basin north china the site of unsaturation in these novel sterenes is assigned tentatively to the d ring on the basis of mass spectral interpretation which also distinguishes them from reported unsaturated sterenes other hydrocarbon biomarker or stable isotope characteristics are indicative of microbial e g methyl hopanes phytoplankton or higher plant depleted 13 c values of isoprenoids and hopanes inputs and an anoxic carbonate depositional environment hexacyclic hopanes tetracyclic terpanes the hydrocarbon composition showed no obvious biodegradation and the relatively high concentration of unsaturated terpenoids e g gammacerene and low values of other established maturity parameters t s t m 0 23 r o 0 44 t max 417 c are consistent with sediments of low maturity the novel low molecular weight sterenes and the tetracyclic terpanes may be early diagenetic products of microbial sources in a carbonate environment

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

mercury evidence from the sino korean block for emeishan volcanism during the capitanian mass extinction a prominent large negative 13 c org excursion and a coeval notable spike in mercury hg total organic carbon ratio are observed in the middle upper permian gohan formation in central korea located in the eastern sino korean block skb which may represent the capitanian mass extinction event the skb was separated from the south china block by the eastern palaeo tethys ocean this finding from the skb supports the widespread hg loading to the environment emitted from the emeishan volcanic eruptions in sw china this study demonstrates that the hg cycle was globally perturbed in association with global carbon cycle perturbation that occurred during the capitanian extinction

the microbial input in carbonate anhydrite facies of a sabkha palaeoenvironment from guatemala a molecular approach abstract nine representative rock samplesincluding four anhydrites an oil stained dolomite and a laminated mudstone source rock from a sabkha type palaeoenvironment la felicidad 1 well guatemala have been compared in order to tentatively characterize each facies by a geochemical signature each sample has been studied by using basic parameters toc rock eval pyrolysis yields and analyses of alkanes and aromatics by computerized gc ms the following families of compounds have been reviewed n alkanes branched and cyclic alkanes n alkylbenzenes benzohopanes monoaromatic steroids d ring aromatic 8 14 secohopanoids alkylnaphthalenes alkylphenanthrenes alkyldibenzothiophenes and triaromatic steroids despite close geochemical relationships of all the sample a more in depth investigation taking into account molecular patterns and semi quantitative data reveals significant differences among the samples anhydrites may be differentiated from carbonates which illustrates the efficiency of organic geochemistry in environmental palaeoreconstruction even in organiccarbon lean sediments toc 0 04 0 08 in anhydrites in these anoxic marginally mature sediments the strong predominance of triterpanes over steranes tt to st 20 associated with other molecular features leads to the conclusion that the main contribution to the organic matter of all facies is by bacteria several prominent components including novel families iso c23 and iso c27 alkanes tetracyclic terpanes d ring aromatic 8 14 secohopanoids 1 phenylpentadecane undecylnaphathalene and their mono and dimethylated counterparts have been interpreted as derived from halophilic bacteria these conclusions may be extended to all crude oils from the same area which may be considered as true bacterially derived petroleums the la felicidad 1 well data are discussed with reference to other palaeosabkha type sequences from the sw aquitaine basin france in which the bacterial input is less important however in these sabkha sequences 1 phenylpentadecane undecylnaphthalene and related structures have also been identified

branched aliphatic alkanes with quaternary substituted carbon atoms in modern and ancient geologic samples a pseudohomologous series of branched aliphatic alkanes with a quaternary substituted carbon atom baqcs specifically 2 2 dimethylalkanes and 3 3 and 5 5 diethylalkanes were identified in warm 65 c deep sea hydrothermal waters and late cretaceous black shales 5 5 diethylalkanes were also observed in modern and holocene marine shelf sediments and in shales spanning the last 800 million years of the geological record the carbon number distribution of baqcs indicates a biological origin these compounds were observed but not identified in previous studies of 2 0 billion to 2 2 billion year old metasediments and were commonly misidentified in other sediment samples indicating that baqcs are widespread in the geological record the source organisms of baqcs are unknown but their paleobiogeographic distribution suggests that they have an affinity for sulfides and might be nonphotosynthetic sulfide oxidizers

paleomagnetic results from the lower mesozoic daedong supergroup in the gyeonggi block korean peninsula an eastern extension of the south china block abstract lower mesozoic lake deposits in the daedong supergroup of the gyeonggi block were collected at 38 sites for paleomagnetic study a remanent magnetization component with unblocking temperatures of 635 660 c component a was isolated from four sites the directions of this component with both normal and reversed polarities yielded positive fold and reversal tests at the 95 confidence level component a is interpreted to be of primary origin of late triassic time the mean direction of component a d 82 2 i 23 1 with 95 4 1 together with previously reported primary directions yields a pole representative for the gyeonggi block at 31 9 n 220 2 e a 95 12 7 the paleomagnetic pole shows good agreement with that for the south china block suggesting that the gyeonggi block has been part of the south china block the gyeonggi block as the eastern part of the south china block is regarded to have thrust to its position at the present korean peninsula during the collision between the north and south china blocks

comment on chemical remagnetization of the upper carboniferous lower triassic pyeongan supergroup in the jeongseon area korea fluid migration through the ogcheon fold belt by y h park s j doh and d suk summary a recent paper published in geophysical journal international reports that the late palaeozoic to early mesozoic sedimentary rocks in the northeastern okcheon belt of korea were remagnetized during the late cretaceous to early tertiary and argues that the remagnetization was triggered by fluids travelling more than 800 km from the subducting slab of the kula pacific plates based on available geological data however we suggest that the remagnetization was caused by thermal effects of a late cretaceous pluton intruding the sedimentary rocks and or associated short range hydrothermal fluids rather than by long range fluids

paleomagnetism of the dewey lake formation late permian northwest texas end of the kiaman superchron in north america the remanent magnetization of red beds of the late permian dewey lake formation from northwest texas was investigated using thermal chemical and alternating field demagnetization after removal of a small present day viscous overprint the dewey lake shows univectorial decay of the remanence revealing a dual polarity characteristic direction of d 152 4 i 11 1 k 39 5 95 5 9 n 16 sites three polarity transitions were observed defining at least four polarity zones the observed polarity zones are roughly layer parallel and may correlate with the illawarra magnetozone at the end of the kiaman if this is so k ar age determinations of an interbedded ash layer kolker and fracasso 1985 suggest that the kiaman superchron ended before 251 4 ma the paleopole located at 51 4 n 126 2 e confirms the reliability of previously reported late permian poles from southwest united states which fall significantly off the late permian segment of the paleomagnetic euler pole pep track of gordon et al 1984 this implies that a more segmented set of small circles is required to model the north american apparent polar wander path diminishing the usefulness of the pep method

a synthesis of cretaceous palaeomagnetic data from south korea tectonic implications in east asia summary tectonic provinces in south korea include the precambrian gyeonggi massif palaeozoic okcheon belt precambrian yeongnam massif and cretaceous gyeongsang basin from northwest to southeast the cretaceous strata mainly occur in the gyeongsang basin as well as in several small basins along the boundaries of the okcheon belt and on the gyeonggi massif this paper reviews and analyses previously published palaeomagnetic data from the cretaceous successions in south korea a total of 23 cretaceous palaeomagnetic poles from 18 studies satisfy more than four standard reliability criteria the palaeomagnetic pole positions from the gyeongsang basin and from small basins in the gyeonggi massif and the okcheon belt are consistent with one another indicating that the korean peninsula has been a single terrane since the cretaceous however based on the comparison of the palaeomagnetic pole positions and the palaeolatitudes of blocks in the gyeongsang basin it was observed that the gyeongsang basin had experienced tectonic adjustments during the cretaceous period within the gyeongsang basin the geographically northern area yeongyang block was rotated counterclockwise by 16 3 4 6 with respect to the southern area milyang and uiseong blocks based on the comparison of palaeomagnetic pole positions between the two areas this palaeomagnetic result and some geological features in the gyeongsang basin collectively indicate that the yeongyang block underwent counterclockwise rotations accompanied by northwestward protrusion into the yeongnam massif during the late cretaceous these relative tectonic movements within the gyeongsang basin were probably due to the northwestward subduction of the proto pacific oceanic plate during the late cretaceous the gradual eastward displacement of the korea s cretaceous palaeopoles from the eurasian pole increases with stratigraphic age indicating that the korean peninsula underwent progressive clockwise rotations with respect to eurasia during the cretaceous period the clockwise rotation of southwest japan with respect to eurasia is ascribed to the miocene opening of the east sea and has no connection with the cretaceous clockwise rotations of the korean peninsula indicating that the korean peninsula and southwest japan may have been independent terranes during the cretaceous period

upper proterozoic supracrustal rocks of north america a brief review abstract well preserved successions of supracrustal rocks of upper proterozoic age are present around the margins of north america but are rare in the continental interior the thickest and most complete assemblage is present in the cordilleran region particularly in the central and northern parts in these regions a three fold subdivision of the supracrustals is possible the oldest assemblage sequence a is older than 1 2 ga the middle assemblage sequence b is between ca 1 2 ga and 0 8 ga and sequence c is between ca 0 8 ga and 0 57 ga the base of the cambrian here upper proterozoic is used as roughly equivalent to sequences b and c sequence a is only briefly considered detailed lithostratigraphic correlation is possible between the rocks of sequences a and b and generally thinner counterparts in the canadian arctic on the northern margins of the canadian shield sequence c is not represented by sedimentary rocks on the northern edge of the continent the break between sequences a and b the racklan orogeny is not recognised in the southern part of the cordillera but there is evidence of widespread mafic igneous activity at about the same time ca 1 2 ga ago upper proterozoic rocks are poorly represented in the continental interior the keweenawan succession provides an exception it rocks fill an intracratonic rift possibly related to early movements during the grenville orogeny the upper proterozoic history of the eastern part of north america is much simpler in that it comprises a single supracrustal assemblage corresponding to sequence c and the upper part of sequence b all formed after the grenville orogeny thus the different tectonic histories of the eastern and western margins of north america resulted in development of different sedimentary accumulations with the exception of the racklan orogeny which affected the northern part of the cordillera the upper proterozoic assemblages of both the eastern and western margins of the north american continent reflect sedimentary accumulation and subsidence that culminated in the opening of phanerozoic oceans

geometric model of conjugate faulting in the gyeongsang basin southeast korea 1 the nne trending dextral yangsan fault system and the wnw trending sinistral gaum fault system comprise a conjugate set that cuts the cretaceous gyeongsang basin along the se margin of the korean peninsula these faults evidently formed under compressional stress accompanied by a progressive 12 block rotation calculated from a geometric model incorporating angles between conjugate fault sets widths of fault domains and measured fault displacements the angle between paleomagnetic declinations in the set of conjugate fault domains increases with age suggesting incremental block rotation that included overall rotation of the entire gyeongsang basin or the korean peninsula with respect to eurasia the model accounts for yucheon group volcanism subsequent caldera subsidence in the uiseong subbasin and volcanism in the miryang subbasin all produced by regional tension the tectonic regime of the gyeongsang basin apparently evolved from compression to extension at 50 ma reflecting india eurasia collision and opening of the sea of japan east sea

early triassic palaeomagnetic results from the ryeongnam block korean peninsula the eastern extension of the north china block greenish sandstones in the early triassic nogam formation of the ryeongnam block korean peninsula were collected at 23 sites for palaeomagnetic study a high temperature magnetization component with unblocking temperatures of 670 690 c was isolated from seven sites and yielded a positive fold test at the 95 per cent confidence level the high temperature component is interpreted to be of primary origin because the folding age is middle triassic the early triassic palaeomagnetic direction for the ryeongnam block after tilt correction is d 347 1 i 23 8 95 5 5 the palaeomagnetic pole 62 5 n 336 8 e a95 4 7 shows good agreement with the coeval pole for the north china block suggesting that the ryeongnam block has been part of the north china block at least since early triassic times a tectonic history of the korean peninsula includes obduction of the eastern part of the south china block onto the central part of the korean peninsula in the permian with the ryeongnam block geographically isolated from the main part of the north china block collision of the north and south china blocks commenced initially at the korean peninsula and suturing of the two blocks progressed westwards

comment on paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present by r j enkin et al

millimeter scale concentration gradients of hydrocarbons in archean shales live oil escape or fingerprint of contamination abstract archean shales from the pilbara in western australia contain biomarkers that have been interpreted as evidence for the existence of cyanobacteria and eukaryotes 2 7 billion years ga ago with far reaching implications for the evolution of earth s early biosphere to re evaluate the provenance of the biomarkers this study determined the spatial distribution of hydrocarbons in the original drill core material rock samples were cut into millimeter thick slices and the molecular content of each slice was analyzed in core from the hamersley group 2 5 ga c alkanes had gradually increasing concentrations from the surfaces to the center of the rock while the abundance of steranes hopanes and c 15 alkanes decreased with distance from the outer surfaces in samples from the fortescue group 2 7 ga hydrocarbons were overwhelmingly concentrated on rock surfaces two mechanisms are proposed that may have caused the inhomogeneous distribution diffusion of petroleum products into the rock contamination model and leaching of indigenous hydrocarbons out of host shales driven by pressure release after drilling live oil effect to test these models the hydrocarbon distributions in the archean shales are compared with artificially contaminated rocks as well as younger mudstones where leaching of live oil had been observed the results show that chromatographic phenomena associated with live oil escape and contaminant diffusion have strong effects on molecular ratios and maturity parameters potentially with broad implications for oil source rock correlation studies and paleoenvironmental interpretations for the archean shales the live oil effect is consistent with some of the observed patterns but only the contamination model fully explains the complex chromatographic fingerprints therefore the biomarkers in the pilbara samples have an anthropogenic origin and previous conclusions about the origin of eukaryotes and oxygenic photosynthesis based on these samples are not valid however the study also identified indigenous molecules the spatial distribution of particular aromatic hydrocarbons suggests they are syngenetic although devoid of biological information these aromatics now represent the oldest known clearly indigenous terrestrial liquid hydrocarbons

sandstone petrology of the pyeongan supergroup taebaeksan region korea implications for the carboniferous triassic tectonic history of east asia abstract sandstones of the pyeongan supergroup vary from quartzose to quartzo feldspathic in composition the introduction of significant amounts of plagioclase and k feldspar in upper formations of the pyeongan supergroup may be related to a change in tectonic stability of the source area from a relatively stable cratonic interior to an uplifted basement the absence of sandstones rich in lithic fragments in the korean peninsula including the pyeongan and daedong supergroups the latter of which is supposedly post collision between the north and south china blocks suggests that a recycled orogen had never been emplaced in korea reference of the tectonic divisions of korea to those of china or japan should be made with substantial care this includes the current attempts to relate the imjingang belt with the qinling dabieshan belt or the ogcheon belt with the hida belt

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

saturated hydrocarbon biomarkers in oils of late precambrian age from eastern siberia abstract large quantities of petroleum derived from source rocks of late precambrian early cambrian age have been discovered in the lena tunguska region of eastern siberia over the last twenty five years we have examined three oils with presumed late precambrian vendian source rocks from this region for c 15 saturated hydrocarbon biomarkers using gas chromatography gc and gas chromatography mass spectrometry gc ms our results show these oils to have many characteristics in common with other oils of similar age from eastern siberia and oman amongst the compounds detected in the three oils analyzed were 1 n alkanes which show a marine derived distribution 2 centrally branched monomethyl alkanes 3 acyclic isoprenoids pr ph 1 4 tricyclic and tetracyclic terpanes 5 hopanes 6 c 29 unrearranged steranes and 7 c 30 nuclear steranes all of these compounds with the exception of the 4 methylsteranes which on current biochemical knowledge are unexpected in oils of this age can be assigned a prokaryotic source this and other evidence such as the lack of diasteranes suggest microorganism were the major contributors to organic matter deposited as part of a carbonate source rock

clockwise rotations recorded in early cretaceous rocks of south korea implications for tectonic affinity between the korean peninsula and north china recent interest has focused on whether south korea may have undergone variable tectonic rotations since the cretaceous in an effort to contribute to the answer to this question we have completed a palaeomagnetic reconnaissance study of early cretaceous sedimentary and igneous rocks from the kyongsang basin in southeast korea stepwise thermal demagnetization isolated well defined characteristic magnetization in all samples the palaeomagnetic directions reveal patterns of increasing amounts of clockwise cw rotation with increasing age for aptian rock units palaeomagnetic declinations indicate clockwise vertical axis rotations of r 34 3 6 9 for the early aptian rock unit r 24 9 10 6 for the middle aptian and r 0 9 11 8 for the late aptian relative to eastern asia the new cretaceous palaeomagnetic data from this study are consistent with the hypothesis that korea and other major parts of eastern asia occupied the same relative positions in terms of palaeolatitudes in the cretaceous an analysis of and comparison with previously reported palaeomagnetic data corroborates this hypothesis and suggests that much of korea may have been connected to the north china block since the early palaeozoic a plausible cause of the rotation is the westward subduction of the kula plate underneath the asian continent which is inferred to have occurred during the cretaceous according to several geological and tectonic analyses

characterization of organic rich material in an evaporitic environment the lower oligocene of the mulhouse basin alsace france evaporitic sediments from the max borehole mulhouse potash basin southern rhine graben were studied over an interval of about 40 m in the vicinity of sylvite beds total organic carbon toc analyses of 450 samples showed that marly layers interbedded within the evaporites have toc values that fluctuate in a rhythmic manner the highest values are found near the top of the clay anhydrite layers and the lowest values are recorded near the top of the halite rich beds geochemical elemental analysis of kerogen gas chromatography of bitumen and palynological studies of 26 samples showed that the organic matter is mainly of algal origin a and b groups a third category of organic material c group may have been derived from a mixture of continental supply and in situ bacterial productivity

geochemical study of macromolecular organic matter from sulfur rich sediments of evaporitic origin messinian of sicily by chemical degradations abstract selective chemical degradations have been performed on sulfur rich macromolecular organic matter from sediments of the messinian of sicily upper miocene italy the biomarkers released upon different desulfurization experiments are much more abundant than the free lipids and display completely different distributions which reflect the selective trapping of poly functionalized molecules by inorganic sulfur species at an early stage of diagenesis the bound biomarker distributions reveal a dominant phytoplanktonic input originating from an upper oxic water layer and a moderate bacterial reworking of the organic matter a contribution from cyanobacteria to the organic matter cannot be excluded the presence of carotenoids typical from photosynthetic sulfur bacteria attests to a stratified water body where an anoxic photic zone occurred lialh4 hydrogenolysis of sulfur rich macromolecules revealed that polysulfide bridges contribute to a large extent in the cross linking the results of deuterium labelling experiments are discussed in terms of sulfur incorporation on functionalized lipids

origin of free and bound mid chain methyl alkanes in oils bitumens and kerogens of the marine infracambrian huqf formation oman the huqf oil from oman and other time equivalent oils are characterized by relatively large contents of mid chain branched monomethyl alkanes the huqf oil the saturated hydrocarbon fractions the desulfurized polar fractions of the bitumens and the kerogen pyrolysates of three potential source rocks from the huqf formation oman were analyzed in order to resolve the origin of these mid chain branched monomethyl alkanes using off line pyrolysis and chemical degradation in combination with compound specific carbon isotope analysis it was assessed that the mid chain branched monomethyl alkanes are not rearrangement products but are derived from a biological source probably from lipids with c28 carbon skeletons and methyl branching at the 12 or 13 position these compounds were incorporated in the kerogen through reactions of sulfur with functional groups at different positions in the precursor lipid s

evidence for ancient halophiles testing biomarker syngeneity of evaporites from neoproterozoic and cambrian strata molecular fossils from evaporites can provide significant insights into the biotic composition of ancient hypersaline ecosystems however hydrocarbon contamination can mask the true nature of this composition and potentially result in misleading interpretations in this study drill core samples of neoproterozoic and cambrian age dolomite anhydrite and halite from the amadeus basin in central australia contain distinctive and varied hydrocarbon signatures the results are consistent with previous studies of ancient hypersaline settings and include elevated concentrations of heptadecane n c17 docosane n c22 a diverse range of acyclic isoprenoids hopanes and steranes including high concentrations of pregnanes furthermore several samples yielded hydrocarbon signatures with high concentrations of mono and dimethylalkanes relative to n alkanes which is characteristic of many cambrian and precambrian bitumens by quantifying the exterior interior concentration differences of biomarkers in these evaporites considerable insight into the syngeneity of these molecules was obtained in most samples the majority of biomarkers were only detected in the exterior demonstrating that they are contaminants and not indigenous to the evaporites these include biomarkers typically assigned to hypersaline environments demonstrating in this case that their presence is not necessarily an indicator of syngeneity we show that even in combination these molecules can have a wide variety of sources that are not necessarily indigenous to the host rocks nevertheless some neoproterozoic evaporites while also marred by contamination contain demonstrably indigenous biomarkers with equal concentrations on the rock exterior and interior we show that the ability to discern biomarker syngeneity in a complex mix of contaminated and indigenous hydrocarbons requires the need for each compound in every sample to be separately evaluated this study provides an example of how to unravel such a complex series of contamination and obtain more accurate insights into biomarkers of ancient evaporites the approach outlined herein can be readily applied to biomarker studies of other ancient settings

high unblocking temperature haematite magnetizations of late palaeozoic red beds from the okcheon zone southern part of the korean peninsula summary the late carboniferous and permo triassic red beds of the pyeongan supergroup in the okcheon zone southern part of the korean peninsula were found to contain three components of remanence these components which are resolved by thermal demagnetization are characterized by high hhc for late carboniferous and hhpc for permotriassic intermediate hm and low hi unblocking temperatures as the maximum unblocking temperature spectra of the hhc hhpt component often overlapped the hm spectra above 680 c 3 o to 5 c steps were needed above 670 c to resolve the hhc hhpt component magnetization the tilt corrected mean direction of the hhc component red beds is d 255 5 i 2 4 a 20 8 and that of the hhpt component is d 271 9 i 33 4 c 16 5 the precisions of mean directions of hhc and hhpt components improve after tilt correction and allow the directions to be distinguished from each another this indicates that both hhc and hhpt component magnetizations were acquired during or shortly after the deposition of the red beds according to micropetrographic observations the haematite in the red beds can be divided into three types detrital specularite a non detrital specularite b and pigmental haematite c type a grains are tens of micrometres in size and many of them are martite the remanent magnetization of type a is possibly depositional remanent magnetization drm post drm or chemical remanent magnetization crm acquired close to the deposition time whereas that of types b and c is of crm origin acquired during and after folding respectively the time of folding is well established as a triassic to jurassic event we believe that the remanent magnetization carried by type a grains is primary and is correlated to hhc or hhpt component magnetization

upper proterozoic evaporites in the amadeus basin central australia and their role in basin tectonics the amadeus basin an isolated intracratonic basin in the center of the australian continent contains an upper proterozoic to mid paleozoic stratigraphic succession of shallow marine sediments that in places exceeds 14 km in thickness the gillen member of the bitter springs formation which occur toward the base of the upper proterozoic succession includes evaporites which are among the world9s earliest 0 8 to 0 7 ga because of their age the evaporites have been cited in discussions of sea water chemistry and have been the focus of scrutiny for early life forms in spite of their importance the evaporites are poorly known particularly from the viewpoint of their depositional and tectonic setting in an attempt to rectify this deficiency more than 6 000 km of seismic data were analyzed in conjunction with a field and well log study of the unit the late proterozoic amadeus basin appears to have consisted of two major poorly circulated anoxic sub basins which perhaps opened to the ocean to the southeast through the adelaide geosyncline data relating to facies are limited but suggest that deposition of the evaporites was cyclic and followed the patterns identified in other major evaporite basins the carbonates and sulfates being closer to the basin margins and later stage halite and possibly potassium salts being toward the basin center the evaporites were deposited in a shallow marine setting at the time of a relative sea level high stand the apparent sea level high may relate to basin dynamics whereas the cyclicity of the evaporites may be due to eustatic sea level controls acting on the barrier to allow intermittent inflow of sea water salt tectonism began shortly after the evaporites were deposited and continued throughout basin development consequently most of the major anticlinal structures have salt cores the geometry of the salt structures suggests that during their growth the mean strain rate was 10 16 s 1 a rate typical of large salt structures growth on these salt structures has played an important role in controlling later sedimentation particularly during the cambrian

tectonic elements with south china affinity in the korean peninsula new early jurassic palaeomagnetic data summary early jurassic sandstones and shales were collected at 14 sites from the kimpo area in the western part of the korean peninsula for a palaeomagnetic study a characteristic remanent magnetization component which passes the fold test was isolated from seven sites this characteristic component is interpreted to be of primary early jurassic origin because the folding age is middle late jurassic the primary directions together with previously reported ones provide a mean direction d 38 1 i 39 7 95 3 8 11 sites and a palaeomagnetic pole 54 1 n 230 2 e a95 4 1 for the kimpo area this palaeomagnetic pole shows good agreement with the coeval poles for the south china block and is significantly removed from that for the north china block suggesting that the kimpo area has been part of the south china block since at least early jurassic times the kimpo area constitutes a part of the imjingang belt which is palaeontologically allocated to the south china block in its origin while all precambrian tectonic blocks that compose the basement of the korean peninsula are interpreted to be of north china origin we conclude that the imjingang belt including the kimpo area is a tectonic extension of the south china block on the korean peninsula the south china elements were obducted onto the north china block at the site of the present korean peninsula during the collision event of the north and south china blocks and hence the korean peninsula is composed of areas with both north and south china affinities

application of biological markers in the recognition of palaeohypersaline environments the hydrocarbon fractions of a marl sample from a messinian basin in the northern appenines and four oils rozel point oil utah and three seep oils from sicily were studied

palaeomagnetic and rock magnetic studies of cretaceous rocks in the gongju basin korea implication of clockwise rotation palaeomagnetic and rock magnetic studies have been carried out for cretaceous non marine sedimentary rocks gongju group and volcanic rocks in the gongju basin located along the northern boundary of the ogcheon belt korea k ar age dating for the volcanic rocks was also performed it is found that the gongju group was remagnetised during the tilting of the strata with the characteristic remanent magnetisation chrm direction of d i 23 9 50 6 k 95 5 9 5 3 9 at 30 per cent untilting of the strata with a maximum value of precision parameter k while the volcanic rocks are revealed to acquire primary remanence with the direction of d i 204 2 43 8 k 36 6 9 5 8 6 after the tilt correction the k ar ages of the volcanic rocks range from 81 8 2 4 to 73 5 2 2 ma corresponding to the campanian stage of the late cretaceous electron microscope observations of samples from the gongju group show authigenic iron oxide minerals of various sizes distributed along the cleavage of chlorite and in the pore spaces indicating that the strata acquired the chemical remanent magnetisation due to the formation of secondary magnetic minerals under the influence of fluids the palaeomagnetic pole positions are at lat long 69 6 n 224 3 e dp 3 5 dm 5 2 calculated for the 30 per cent tilt corrected direction of the gongju group and at lat long 67 2 n 235 3 e a 9 5 8 9 for the volcanic rocks based on the results of this study it is interpreted that the volcanic rocks acquired the primary magnetisation almost at the same time as the remagnetisation of the gongju group in the late cretaceous comparisons of cretaceous palaeomagnetic poles from the korean peninsula with those from eurasia implies that the korean peninsula underwent clockwise rotation of 21 2 5 3 for the middle early cretaceous 12 6 5 4 for the late early cretaceous and 7 1 9 8 for the late cretaceous with respect to eurasia due to the sinistral motion of the tan lu fault

hydrocarbon shows and petroleum source rocks in sediments as old as 1 7 109 years we report the discovery of indigenous live oil in 1 4 gyr old rocks in the mcarthur basin of northern australia previously reported occurrences of indigenous precambrian oil are 1 gyr old1 5 potential petroleum source rocks in the mcarthur basin range in age from 1 4 to 1 7 gyr and were deposited in marine and lacustrine environments in parts of the basin they have been buried sufficiently deeply to have generated hydrocarbons they span the period corresponding to the appearance of eukaryotic organisms and because of their low degree of thermal alteration they provide a valuable resource for the study of primitive biota through their hydrocarbon biomarkers the hydrocarbon composition of the oil is consistent with a derivation from organic matter of prokaryotic origin these results show that exploration of previously ignored mid proterozoic sediments may lead to the discovery of new reserves of oil

the early tertiary chemical remagnetization in the bakjisan syncline korea its geotectonic implications the bakjisan syncline is located in the northwestern part of the taebaeksan basin korea new paleomagnetic data for the upper carboniferous lower triassic pyeongan supergroup from the pyeongchang area on the west limb of the bakjisan syncline have been obtained and synthesized and compared with previous data from the jeongseon area on the east limb of the syncline a total of 350 specimens were collected from 21 sites to clarify the relationship between the spatial distribution of remagnetized areas and the thrust system in the taebaeksan basin the characteristic remanent magnetization chrm isolated from all samples was a remagnetized component acquired after tilting of the strata and carried by various magnetic minerals magnetite hematite and pyrrhotite from rock magnetic studies electron microscope observations and xrd analyses the pervasive remagnetization is interpreted to be associated mainly with a fluid mediated chemical remanent magnetization crm this is consistent with the results of previous work in adjacent areas the paleomagnetic pole position 88 3 e 83 9 n a95 4 9 from the pyeongan supergroup in the bakjisan syncline indicates that the timing of the remagnetization event is early tertiary times i e paleocene to eocene by comparison with reliable paleopoles from the korean peninsula early tertiary crms are also reported from previous studies of an adjacent region within the northwestern part of the taebaeksan basin in contrast a primary remanent magnetization was reported in the southeastern part of the taebaeksan basin this implies that the major thrust system the gakdong thrust which separates the two regions has caused them to experience substantially different geologic histories since deposition of the strata since many thrusts with ns trend are observed in the northwestern part of the taebaeksan basin compared with the southeastern region it appears that the remagnetizing fluids pervasively penetrated the northwestern part of the basin by utilizing the already well developed thrust system

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

hydrothermal fluid controlled remagnetization of sedimentary rocks in korea tectonic importance of pervasive tertiary remagnetization abstract in order to better understand the tectonic environment of the korean peninsula since cretaceous a paleomagnetic study was carried out on the jinan basin located in southwestern korea from the demagnetization of 597 samples we found that remanence is carried by pyrrhotite and or magnetite black siltstone and hematite red siltstone which is a common magnetic mineral assemblage of the rocks remagnetized in early tertiary in korea all the rock units recorded identical ancient geomagnetic field directions in particular paleodirections were better clustered in geographic coordinates indicating a secondary origin the presence of abundant silicates as inclusions within fe oxides and fe sulfides confirms the authigenic origin of the magnetic carriers precipitated by fluid mediated chemical processes compilation of the korean cretaceous and tertiary poles indicates that the jinan basin was remagnetized in the early tertiary age in addition comparison of the korean cretaceous and tertiary poles with those from adjacent major terrains including china and siberia reveals that a dominant feature of tectonic motions in korea was a vertical axis rotation sense of vertical axis rotation was time dependent with clear distinction between clockwise rotation in cretaceous and counter clockwise rotation in early tertiary such differences in the mode of vertical axis rotation might be caused by the activities of basin bounding strike slip faults in korea possibly driven by the changes of subduction regime of the kula pacific plate in early tertiary

composition and syngeneity of molecular fossils from the 2 78 to 2 45 billion year old mount bruce supergroup pilbara craton western australia shales of very low metamorphic grade from the 2 78 to 2 45 billion year old ga mount bruce supergroup pilbara craton western australia were analyzed for solvent extractable hydrocarbons samples were collected from ten drill cores and two mines in a sampling area centered in the hamersley basin near wittenoom and ranging 200 km to the southeast 100 km to the southwest and 70 km to the northwest almost all analyzed kerogenous sedimentary rocks yielded solvent extractable organic matter concentrations of total saturated hydrocarbons were commonly in the range of 1 to 20 ppm g g rock but reached maximum values of 1000 ppm the abundance of aromatic hydrocarbons was 1 to 30 ppm analysis of the extracts by gas chromatography mass spectrometry gc ms and gc ms metastable reaction monitoring mrm revealed the presence of n alkanes mid and end branched monomethylalkanes cyclohexylalkanes acyclic isopre noids diamondoids tri to pentacyclic terpanes steranes aromatic steroids and polyaromatic hydrocarbons neither plant biomarkers nor hydrocarbon distributions indicative of phanerozoic contamination were de tected the host kerogens of the hydrocarbons were depleted in 13 c by 2 to 21 relative to n alkanes a pattern typical of although more extreme than other precambrian samples acyclic isoprenoids showed carbon isotopic depletion relative to n alkanes and concentrations of 2 methylhopanes were relatively high features rarely observed in the phanerozoic but characteristic of many other precambrian bitumens molecular parameters including sterane and hopane ratios at their apparent thermal maxima condensate like alkane profiles high mono and triaromatic steroid maturity parameters high methyladamantane and methyldiaman tane indices and high methylphenanthrene maturity ratios indicate thermal maturities in the wet gas gener ation zone additionally extracts from shales associated with iron ore deposits at tom price and newman have unusual polyaromatic hydrocarbon patterns indicative of pyrolytic dealkylation the saturated hydrocarbons and biomarkers in bitumens from the fortescue and hamersley groups are characterized as probably syngenetic with their archean host rock based on their typical precambrian molecular and isotopic composition extreme maturities that appear consistent with the thermal history of the host sediments the absence of biomarkers diagnostic of phanerozoic age the absence of younger petroleum source rocks in the basin and the wide geographic distribution of the samples aromatic hydrocarbons detected in shales associated with iron ore deposits at mt tom price and mt whaleback are characterized as clearly archean based on their hypermature composition and covalent bonding to kerogen copyright 2003 elsevier ltd

chemical remagnetization of the upper carboniferous lower triassic pyeongan supergroup in the jeongseon area korea fluid migration through the ogcheon fold belt summary palaeomagnetic and rock magnetic investigations have been carried out for the upper carboniferous lower triassic pyeongan supergroup exposed in the jeongseon area in eastern south korea a total of 302 independently oriented core samples were drilled from 24 sites for the study the mean direction in stratigraphic coordinates d i 345 3 38 4 k 4 8 95 18 2 is more dispersed than the mean direction in geographic coordinates d i 354 9 61 5 k 58 0 95 4 7 and the stepwise untilting of the characteristic remanent magnetization chrm reveals a maximum value of k at 0 per cent untilting furthermore authigenic magnetic mineral grains accompanied with altered clays are identified by electron microscope observations these results collectively imply that the chrms of this study were acquired by the formation of authigenic magnetic minerals after tilting of the strata the palaeomagnetic pole position 97 3 e 82 4 n a95 6 8 of the pyeongan supergroup calculated from the site mean directions of the chrms in geographic coordinates is close to those of the late cretaceous and tertiary periods of the korean peninsula the presence of many hydrothermal vein deposits reportedly formed between 94 and 73 ma near the study area and the evidence for extensive alteration of clay minerals under the influence of fluids shown in the x ray diffraction study strongly suggest that the chemical remanent magnetization was acquired by a fluid mediated process during the late cretaceous early tertiary considering the different remagnetization timing of several areas in the ogcheon fold belt which extends from ne to sw diagonally across the korean peninsula it is interpreted that the fluids and magmatism associated with this remagnetization originated from the subduction of the kula pacific plates under the eurasian plate during the cretaceous period the fluids might have migrated northward or northeastward through the fault systems within the ogcheon fold belt

jurassic and triassic paleomagnetism of south korea middle to late jurassic samples have been collected from granitic rocks in three geological subdivisions of south korea from north to south kyonggi massif okchon folded belt and ryongnam massif triassic samples granites and sediments were collected in the ryongnam massif and its border area with the okchon folded belt the jurassic declinations of the two massifs are northeasterly mean d i 39 6 57 6 n 7 sites k 31 95 11 1 whereas the intervening okchon folded belt reveals northwesterly jurassic declinations d i 337 5 47 n 7 sites k 32 95 10 8 reversed polarity directions are rare but have been observed in three localities the widespread occurrence of similar directions in a given province argues against major tectonic tilting of the granites two sites in jurassic sediments provide additional structural control we interpret the direction difference between the okchon belt and the adjacent massifs as due to left lateral shear in an actively deforming continental margin during the late jurassic early cretaceous daebo orogeny the triassic directions from the ryongnam massif and its border area are east northeasterly d i 62 9 35 7 n 5 k 27 95 15 with the sediments showing normal and reversed polarities comparisons with jurassic and triassic paleomagnetic results from adjacent blocks in asia eurasia north korea north and south china are hampered by a paucity of reliable paleopoles what seems clear however is that north and south china and the major part of korea yield jurassic and younger paleopoles that are to first approximation similar the exception is formed by the results from the okchon folded belt the aggregate of the china and korea blocks yields mean paleopoles for this interval that are different from those published for eurasia but this may be due to imperfections in the eurasian reference poles for the triassic the directions and paleopoles of the china blocks and the ryongnam massif of south korea are dissimilar resulting in interpretations of the area in terms of relative motions mainly rotations

palaeomagnetic constraints from granodioritic plutons jiaodong peninsula new insights on late mesozoic continental extension in eastern asia mechanism and kinematics of the late mesozoic continental extension event of eastern asia are still debated in order to better constrain its evolution two granodioritic plutons of the jiaodong peninsula have been chosen as targets for a time constrained palaeomagnetic study indeed plutons are devoid of visible deformation did not experience rotation along horizontal axis and are precisely dated by u pb and 40ar 39ar methods multidomain md magnetite has been identified as the principal magnetic remanent carrier the interpolation of existing and new u pb and 40ar 39ar ages revealed that characteristic remanent magnetisation was acquired in a narrow range of 116 2 ma twenty out of 27 sites present stable magnetic directions calculated from high temperature or high coercive components the observations of the solo normal magnetic polarity for this palaeomagnetic collection and of the magnetic remanent age consistent with the cretaceous normal superchron cns argue that the characteristic magnetic remanence may be considered as primary detailed field observations of the intrusive relationship between the plutons and country rocks and anisotropy of magnetic susceptibility ams study reveal the absence of the subsequent deformation of plutons or rigid rotation of plutons along a horizontal axis two palaeomagnetic poles have been therefore calculated from these plutons among 12 out 15 cretaceous palaeomagnetic poles including the two new poles provided by this study from the jiaodong peninsula and on both sides of tan lu and muping jimo faults are statistically consistent as a result the jiaodong peninsula behaved as a rigid block as internal deformation appears negligible the remaining three derived poles are probably due to the secular variation or and the vicinity of fault zones near of the palaeomagnetic sampling site thus they can not be applied to the peninsula scaled tectonics comparison of these time52 constrained cretaceous palaeomagnetic results of the jiaodong peninsula with those of north china block ncb indicate that the jiaodong peninsula was rigidly attached to ncb since 3 at least the cretaceous as residual difference is clearly insignificant with respect to the error brackets these new palaeomagnetic results confirm that the relative clockwise cw rotation of eastern liaoning korea block elkb with respect to ncb does not affect the jiaodong peninsula as a rigid block nevertheless some tectonic structures have been reactivated since cenozoic and local rotations could be produced this palaeomagnetic study reveals that the late mesozoic extension in eastern asia is heterogeneously expressed in time and space the complete understanding of the mechanism s of this extensional event needs further multidisciplinary investigations

a late cretaceous paleomagnetic pole from koto rhyolite southwest japan implications for eastern margin deformation of asia 1 a paleomagnetic pole was obtained from late cretaceous rhyolitic ash flow tuffs and associated ring dikes which are collectively called the koto rhyolite in the eastern part of southwest japan characteristic remanent magnetizations were isolated from 33 sites through thermal demagnetization normal and reversed polarity magnetizations were found and are mutually antipodal although the magnetization directions become more dispersed after tilt correction the clearly defined polarity sequence and the positive contact test between ash flow tuffs and ring dikes ensure that the characteristic magnetizations of ash flow tuffs predate the intrusion of associated ring dikes since no regional tilting is expected we regard the in situ magnetization directions to represent the late cretaceous 70 ma paleomagnetic field d 84 6 i 57 5 95 5 5 in eastern southwest japan the paleomagnetic pole is not significantly different from the coeval poles of western southwest japan this result gives a further support to a microplate model for the miocene clockwise rotation of southwest japan by canceling out the effect of the miocene rotation we were able to obtain a paleomagnetic pole of 70 ma 219 7 e 63 0 n 95 12 2 for southwest japan when the japan arc was incorporated in the eastern margin of asia paleomagnetic poles of late cretaceous age from korea south china coast and restored southwest japan are statistically indistinguishable from each other but significantly differ from that of the continental interior of east asia the observed rotation of about 20 probably results from shear deformation exerted by northeast trending strike slip faults along the eastern continental margin of asia

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

a molecular and isotopic geochemical study of meso to neoproterozoic 1 73 0 85 ga sediments from the jixian section yanshan basin north china abstract this paper systematically describes the molecular and isotopic characteristics of meso to neoproterozoic 1 73 0 85 ga sediments from the jixian section yanshan basin north china a correlation is made between molecular fingerprints and paleoenvironmental and paleontologic data acquired from these strata the agreement between these parameters suggest that the biomarkers preserved in these proterozoic sediments are good indicators of the evolution of the paleoenvironment and early life in the yanshan basin the fact that extended regular isoprenoids c20 were detected in most of the studied samples suggest a sustained lipid input to sedimentary organic matter from halophiles and other possible archaebacteria through meso to neoproterozoic two dehydroabietin isomers i e 18 and 19 norabieta 8 11 13 trienes were unexpectedly present in these samples which provides evidence suggesting that the compounds with abieta structure could be derived from primitive organisms such as algae the stable carbon isotope characteristics of kerogen and coexisting carbonate show a rapid decline in atmospheric co2 concentration from 1 73 to1 58 ga and a stable concentration afterwards the difference c in isotopic composition between carbonate and associated kerogen lies in zonal variations along the stratigraphic sequence which can be attributed to the alternations of marine transgressions and regressions that occurred in the yanshan basin during the proterozoic the carbon isotope relationships between kerogen and alkanes from these strata are consistent with the hypothesis that before 1 4 ga both n alkanes and isoprenoids had been derived mainly from heterotrophic halophiles and other archaebacteria but after that only isoprenoids originated from archaebacteria whereas n alkanes were possibly derived from photosynthetic organisms changes in the source of n alkanes around 1 4 ga may suggest a decline of heterotrophic reworking to primary lipids which can be related to the formation of a quiet shallow water environment of an epicontinental sea at this stage in the yanshan basin

assessing biomarker syngeneity using branched alkanes with quaternary carbon baqcs and other plastic contaminants biomarker molecules are valuable for the elucidation of ancient microbial ecosystems and the characterization of petroleum source rocks for such studies acquisition of reliable hydrocarbon data and proof of their syngeneity are essential however contamination of geological samples with anthropogenic petroleum products during drilling storage and sampling can be particularly problematic because these hydrocarbons may over print an original indigenous biomarker profile to evaluate the extent of contamination of drill core and outcrop material we studied the distribution of hydrocarbons in 26 rocks from different locations in the world all rocks had petroleum products on their exterior surfaces twenty two samples also contained surficial hydrocarbons derived from polyethylene plastic including branched alkanes with quaternary carbon centers baqcs and alkylcyclopentanes with pronounced even over odd carbon number preference using three examples from the paleoproterozoic tawallah and mcarthur groups in northern australia we show how indigenous biomarkers can be recognized by comparing hydrocarbon distributions between exterior rock surfaces and the rock interior and how infiltration of allochthonous hydrocarbons can be assessed through the spatial distribution of characteristic polyethylene derived hydrocarbons in the rock the methods outlined in this paper give confidence in the interpretation of biomarkers in particularly sensitive applications such as the first occurrences of certain organisms in the geological record and the provenance of organic matter in meteorites

the tectonic setting of the eastern margin of the sino korean block inferred from detrital zircon u pb age and nd isotope composition of the pyeongan supergroup upper palaeozoic lower triassic korea the upper palaeozoic succession pyeongan supergroup in central eastern korea is well correlated with the equivalent successions distributed in north china suggestive of the korean upper palaeozoic being part of the sino korean block detrital zircon u pb ages and sm nd isotope compositions of the pyeongan supergroup in the samcheok coalfield of the taebaeksan basin were analysed a single predominant zircon age peak at c 1 9 ga 70 is marked in all sedimentary units followed by varying amounts of minor late palaeozoic grains up to 30 the rarity of meso to neoproterozoic and silurian aged zircons confirms that sediment influx from the south china and qinling blocks was insignificant the 2 0 1 8 ga dominated zircon age pattern and the nd isotope composition average end 0 15 5 4 0 of the pyeongan supergroup most closely reflect the signature of the yeongnam massif basements which supports a previous hypothesis that the pyeongan supergroup was mostly derived from a palaeo orogen located to the east southeast relatively higher end 0 values 10 1 in the lowermost and the upper parts of the succession are closely matched by the increased occurrence of syn depositional aged zircons which indicates considerable mixing of juvenile materials at c 320 ma and 260 ma both arc related magmatic events are interpreted to have been related to oceanic subduction suggesting that the eastern margin of the sino korean block was an active continental margin during late palaeozoic times

an isotopic biogeochemical study of neoproterozoic and early cambrian sediments from the centralian superbasin australia abstract organic matter from neoproterozoic and early cambrian sediments of the amadeus and officer basins of the centralian superbasin australia has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons these sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the cambrian hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially dominated ocean to the early stages of metazoan radiation in particular carbon isotopic data for n alkyl and isoprenoid lipids presented here and in earlier studies showed a reversal in carbon isotopic ordering between the proterozoic and phanerozoic by comparison with the 13c of kerogen n alkyl lipids from deep water proterozoic sediments were enriched in 13c and appear to be derived mainly from heterotrophs whilst open marine phanerozoic counterparts are 13c depleted and evidently derived mainly from autotrophs data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean possibly aided by the innovation of faecal pellets

magnetic fabric and post orogenic uplift and cooling magnetisations in a precambrian granulite terrain the datong huai an region of the north china shield abstract the polymetamorphic terrain in the datong huai an region of the north china shield records two metamorphic m1 and m2 and associated deformational d1 d3 and d4 episodes in granulite facies the magnetic fabric is dominated by the d3 foliation imparted by emplacement of allochthonous cover rocks onto basement during compression and subsequent collapse and uplift magnetite is present in four generations as 1 discrete grains 2 exsolution lamellae in mafic minerals 3 corona rims formed during regional decompression and 4 a filling of microfractures it is the dominant ferromagnetic phase and carries a stable high blocking temperature remanence of dual polarity linked to magnetite grain sizes and shapes of generations 2 to 4 remanence was acquired during later stages of uplift and cooling after the m2 metamorphism and d4 deformation and during rapid decompression a ne to nw migration of the palaeofield direction during this time is identified palaeomagnetic directions are not constrained to lineation in the older magnetic anisotropy but lie close to the dominant d3 foliation although no satisfactory methods presently exist for correcting remanence for anisotropy qualitative considerations from petrology and comparisons between sites of contrasting ams fabric suggest that palaeodirections are not prominently deflected into the d3 plane the pole positions define a continuous swathe plotting between 50 e 20 s and 170 e 35 s summarised by group mean poles a1 51 e 20 s dp dm 8 15 a2 80 e 33 s dp dm 6 11 a3 106 e 48 s dp dm 7 13 and a4 164 e 40 s dp dm 11 21 they are assigned to the interval ca 2000 1840 ma and extend the apparent polar wander record for the north china shield backwards in time from the record derived from supracrustal successions

the pyeongan supergroup upper paleozoic lower triassic in the okcheon belt korea a review of stratigraphy and detrital zircon provenance and its implications for the tectonic setting of the eastern sino korean block abstract the tectonic setting of the okcheon belt in the korean peninsula has long been regarded as one of the important topics in discussing east asian tectonics the controversial tectonic setting of the okcheon belt before the triassic collision between north and south china limits proper understanding of the late paleozoic tectonics of east asia focusing on the upper paleozoic to lower triassic pyeongan supergroup coeval sedimentary records in different parts of the okcheon belt are reviewed this study has a clear advantage over previous assessments that build upon comparison between meta sedimentary units of unknown age in the region the pyeongan supergroup sediments show high similarity in both stratigraphy and detrital zircon u pb ages throughout the okcheon belt they are distinct from their age equivalents in south china while sharing characteristics with those in north korea and north china critical criteria include marine influence and enrichment of organic materials at each time period and relative proportion of mesoproterozoic silurian components in detrital zircon age population the combined results agree with the view that the entire okcheon belt was a single tectonic unit at least by the late carboniferous the results of this study favor the idea of the sino korean block encompassing the whole korean peninsula and cast doubts on the tectonic models that attribute the southern part of the korean peninsula to the south china block a retroarc foreland basin setting of the okcheon belt with detritus mainly provided from a subduction related orogen in the continent sided japan is inferred from the provenance characteristics of the detrital zircons

branched alkanes from ancient and modern sediments isomer discrimination by gc ms with multiple reaction monitoring abstract linked scanning of a tandem sector mass spectrometer has been used to identify abundant first field free region ffr1 unimolecular fragmentations in branched and isoprenoid hydrocarbons the most intense structure specific reactions were selected to establish multiple reaction monitoring mrm parameters for gc ms analysis this methodology has been used to study the identity of co eluting and closely eluting hydrocarbon biomarkers from modern and ancient sediments anand from extant micro organisms some sediments of cambrian and proterozoic age have been found to contain suites of monomethylalkanes with all possible isomers present and with little apparent preference for the site of branching

the chemical structure of a pronounced series of iso alkanes in south oman crudes gas chromatograms of the saturated hydrocarbon fractions of the south oman crudes are characterised by a striking series of peaks called x peaks throughout this paper eluting between the n alkanes mainly in the c20 c26 range a gs ms study combined with optimised gc resolution shows that each peak is a superposition of subpeaks which correspond to a complex series of monomethylalkanes the x20 peak in the chromatogram for instance is found to be composed of virtually co eluting peaks corresponding to 5 6 7 8 9 and 10 methylnonadecane the larger x22 x23 and x24 peaks are superpositions of a similar set of monomethylalkanes and in addition a series of presumably dimethylalkanes of which the structures are only partly solved the large abundance of these iso alkanes is very specific for south oman crudes and may be caused by their pre cambrian origin or a specific source material

isotopically heavy carbon in the c21 to c25 regular isoprenoids in halite rich deposits from the sdom formation dead sea basin israel abstract a series of miocene pliocene halite deposits with extremely low organic carbon contents from the sdom formation dead sea basin israel have been studied distributions and 13c contents of biomarkers have been determined using gc ms and irm gcms analyses respectively the hydrocarbon fractions consist mainly of pristane phytane and c21 to c25 regular isoprenoids the predominance of c21 regular isoprenoids in the dead sea halites and other hypersaline deposits indicate that these components could be derived from ether bound membrane lipids of halophilic archaea the lack of intact ether bound lipids in the polar fractions indirectly infers that such components have already been released at early stages of diagenesis their 13c contents are enriched in 13c by up to 7 compared to the biomarkers of presumed phytoplanktonic origin i e steranes and hopanes within the same sediment sample in agreement with a source other than algae and cyanobacteria thus tentatively assigned as halophilic archaea based on biomarker distributions 13c contents and mineral compositions these sediments appear to have been deposited in a salinity stratified water body with a bottom water brine continual evaporation and deposition of the higher salts i e carnallites are favourable conditions for the growth of halophilic archaeal communities

a geomagnetic polarity timescale for the carboniferous the geomagnetic polarity pattern for the carboniferous is incompletely known but with the best resolved parts in the serpukhovian and bashkirian hence data from both igneous and sedimentary units are also used in an additional polarity bias evaluation in the tournaisian to mid visean interval polarity is mainly derived from palaeopole type palaeomagnetic studies allowing identification of polarity bias chrons seven polarity bias chrons exist in the mississippian mi1nb to mi4nb with an additional 33 conventional magnetochrons and submagnetochrons mi4r to mi9r the moscovian and gzhelian polarity is best resolved in magnetostratigraphic studies from the donets basin and the southern urals dispute about the reliability of these data is ill founded since an assessment of supporting data from palaeopole type studies suggests that these datasets currently provide the best magnetic polarity data through the pennsylvanian polarity bias assessment indicates a normal polarity bias zone in the kasimovian in the pennsylvanian there are 27 conventional magnetochrons and submagnetochrons pe1n to ci1r and one normal polarity bias chron pe8nb the kiaman superchron begins in the mid bashkirian with clear data indicating brief normal polarity submagnetochrons within the superchron the magnetochron timescale is calibrated using 31 u pb zircon dates and a quantitative bayesian based age scaling procedure

late cambrian biogeography conodont bioprovinces from korea abstract although the collisional belt between the north and south china blocks has been well defined in china the location of its eastward extension in the korean peninsula is highly controversial the cambro ordovician sedimentary rocks in south korea the joseon supergroup accumulated in the ogcheon belt which has been proposed as the suture zone between the north and south china blocks or the block boundary the joseon supergroup comprises five different lithostratigraphic units and may be divided into two tectonic blocks by the honam shear zone hsz in the ogcheon belt based on the affinities of the cambrian trilobite faunas previous studies correlated the yeongweol unit in the western part of the hsz with south china and the duwibong unit in the eastern part of the hsz with north china to test the above geodynamic interpretation this study analyzed and compared the degree of the provinciality of upper cambrian conodonts from the yeongweol and duwibong units and north and south china the quantitative test for the upper cambrian provincialism shows high bioprovincial affinities between the yeongweol and duwibong units and both conodont faunas from the two units display higher bioprovincial affinities with that of north china rather than with that of south china their high conodont faunal similarity suggests that the korean peninsula might have been included in a larger continental block including the north china and the korean peninsula the sino korean block in early paleozoic time this result is supported by recent studies on lower paleozoic biogeography stratigraphy and sedimentology that suggest that the yeongweol unit of the joseon supergroup is more closely correlated with north china than with south china

detrital zircon u pb ages of the jangsan formation in the northeastern okcheon belt korea and its implications for material source provenance and tectonic setting abstract the jangsan formation distributed in the taebaeksan basin central eastern korea is unfossiliferous and is composed of quartz arenite this formation is conventionally believed to be the lowermost stratigraphic unit of the lower paleozoic sequence deposited on the yeongnam massif in south korea corresponding to early cambrian in age u pb dating of detrital zircon grains using a laser ablation inductively coupled mass spectrometer yields ages ranging from archean to middle proterozoic 1738 67 ma to 3058 53 ma detrital zircons show no ages younger than 1 8 ga suggesting that the jangsan formation was deposited at some time after this age but much prior to ca 520 ma the depositional age of the immediately overlying myobong formation this interpretation is supported by the recent report on the presence of the unconformity between the jangsan and the myobong formations kim and lee 2006 zircon ages from jangsan sandstones define two major groups archean age grains with a maximum frequency at about 2 5 ga and paleoproterozoic age grains with maximum frequencies at about 2 1 and 1 8 ga the observed zircon age distribution in the jangsan sandstones may represent that of the yeongnam massif on which the jangsan formation was deposited such an age distribution of the yeongnam massif matches well with that the north china block suggestive of the yeongnam massif being a part of the sino korean craton during the precambrian

palaeomagnetism of the upper palaeozoic lower mesozoic pyongan supergroup korea a phanerozoic link with the north china block summary the upper carboniferous lower triassic pyongan supergroup is exposed in an e w trending syncline comprising the samcheok coalfield in eastern south korea it borders the southern margin of a ne sw trending okcheon zone of upper jurassic lower cretaceous deformation daebo orogeny although a recent field overprint widely recorded in korean rocks is represented here an ancient field component structure is recovered from the red bed facies in this supergroup by detailed thermal demagnetization a prominent upper jurassic cretaceous overprint is widespread diz 56 1 54 8 ags 9 6 palaeopole at 200 4 e 46 7 n and records the magnetic effect of the daebo orogeny within the okcheon belt it is post deformational in origin and appears to have been confined mainly to the cretaceous normal superchron it has been rotated clockwise since these times in common with the main synclinal axis as a consequence of dextral movements along the tan lu fault system components predating this deformation are recovered from the lower triassic diz 1 1 19 4 ags 18 2 palaeopole at 306 1 e 63 2 n permian diz 358 3 11 5 c 6 3 palaeopole at 311 9 e 58 7 n and upper carboniferous diz 34l u 9 2 mgs 7 2 palaeopole at 335 7 e 44 6 n sediments second order small circle dispersions of site palaeopoles record unaccommodated tectonic rotations and are largest in the oldest beds below an upper carboniferouslower permian unconformity however the presence of reversals probably acquired before and after the carboniferous permian reversed superchron defines ancient field axes and identifies an upper carboniferous lower triassic apw path this path correlates with the contemporaneous path from the north china block and is removed from the path from the south china block agreement with north china is enhanced when these results are corrected for the rotation indicated by the cretaceous overprint we therefore identify a first order correlation between the korean peninsula and north china at least since upper palaeozoic times establishment of and movements along the tan lu fault system since mesozoic times have not obscured this palaeomagnetic correlation

eastern asia in the cretaceous new paleomagnetic data from south korea and a new look at chinese and japanese data lower cretaceous continental sediments and volcanic rocks have been sampled in the gyeongsang basin south korea a detailed analysis of 160 specimens reveals two stable components of magnetization a postfolding low temperature lt component with normal polarity and a stable high temperature ht component with both normal and reversed polarities the blocking temperature of the ht component ranges from 540 c up to the neel temperature of hematite this component predates the folding of the series and yields a pole at 68 n 205 e a95 6 the prefolding magnetization indicates that south korea stood at a latitude nearly identical to its present day latitude in the lower cretaceous comparison of korean data with revised paleomagnetic data from north and south china and japan shows that all these blocks of eastern asia occupied the same positions in term of latitude and were probably parts of a single craton since at least the lower cretaceous the paleomagnetic directions of the sino korean block show large discrepancies with respect to the expected directions of the stable eurasian siberian block an interpretation involving significant n s motion 1000 km between either north and south china or between north china and siberia appears to contradict geological data a preferred interpretation is that the siberian data are in serious error and that the combined china korea lower cretaceous pole provides a valid estimate for the eurasian plate as a whole

lipid taphonomy in the proterozoic and the effect of microbial mats on biomarker preservation the pre ediacaran biomarker record has several characteristic features that distinguish it from its phanerozoic counterpart including high concentrations of unresolved complex mixture ucm low concentrations or absence of eukaryotic steranes and a conspicuous carbon isotopic enrichment of n alkyl lipids relative to bulk sedimentary carbon we propose that these derive from a common non actualistic taphonomy based on the pervasive presence of microbial mats prior to the cambrian substrate revolution such mats would have formed a significant mechanical and biochemical barrier to in falling plankton leaving a biomarker record dominated by benthic microbial lipids most of which would have originated from the lower heterotrophically reworked layers of the mat most proterozoic biomarker assemblages studied in this work derive from shallow water sediments where cyanobacteria dominated upper mats represent a focused source of corrosive molecular oxygen this mat seal effect was broken with the onset of bioturbation in the ediacaran and early cambrian at which point the primary source of fossil biomarkers switched from the benthos to the plankton

micro ablation a new technique to remove drilling fluids and other contaminants from fragmented and fissile rock material abstract we present a new methodology micro ablation that can remove sub millimeter layers of contaminated surfaces from pieces of sedimentary rock that are too small or irregularly shaped to be trimmed using a saw recognizing traces of contaminants is crucial when analyzing samples with low indigenous bitumen content or interpreting trace biomarker components in hydrocarbon rich samples quantitative analysis of individual hydrocarbons in the interior and exterior of these rock fragments can then help to distinguish between autochthonous and allochthonous hydrocarbons

tectonic implications of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china 1 a paleomagnetic study has been carried out in the east of the tan lu fault in liaoning province ne china to understand the timing of tan lu fault activity samples aging from early paleozoic to late mesozoic from 51 sites have been analyzed paleozoic and late permian early triassic rocks are remagnetized by the recent geomagnetic field however late cretaceous between 118 and 83 ma red tuffaceous sandstone passes a positive fold test shows no present earth field characteristic remanent magnetization carried by both magnetite and hematite presents a solo normal polarity and thus provides the only reliable paleomagnetic data in this study the paleomagnetic pole calculated from these rocks p 59 4 n p 205 5 e and a95 7 3 is statistically undistinguishable from all available cretaceous paleomagnetic data from eastern liaoning korean peninsula indicating that these areas may belong to a single tectonic unit here named the east liaoning korea elk block at least since the late cretaceous conversely a significant discrepancy between the elk block and chinese block i e north and south china blocks characterized by a differential rotation 22 5 10 2 with a negligible latitudinal displacement 0 8 6 1 is demonstrated this result indicates first that the left lateral displacement along the tan lu fault if any must have occurred before the late cretaceous and second that the korean block can not be considered as a rigid part of north china block sedimentological and structural evidence show that the meso cenozoic triangle shaped plain consisting of songliao xialiaohe sanjiang zeya and other smaller basins developing in northeast china and southeast russia south of the mongol okhotsk belt experienced a heterogeneous rifting from the late jurassic to tertiary the variable amount of extension larger in the northeast 300 km than in the southwest 80 km is probably related to the clockwise rotation of the elk block centered at the south of the bohai bay basin this result shows that a significant segment of the east eurasian margin more than 1000 km long experienced differential rotation in cenozoic times

palaeomagnetism rock magnetism and magnetic fabrics in precambrian metamorphic terranes of the huabei shield china abstract this study has investigated magnetic remanence rock magnetism and anisotropy of magnetic susceptibility ams in granulite and amphibolite grade metamorphic terranes of the huabei shield between inner mongolia in the west and the bohai sea in the east rock magnetic studies identify annealed metamorphic magnetite grains with multidomain properties as the remanence carriers a widely recorded stable remanence was probably fixed by grain shape effects granulite facies terranes are typically between one and two orders more strongly magnetised than amphibolite terranes and ams fabrics correlate mostly with metamorphic mineral fabrics observed in the country rocks progressive thermal demagnetisation identifies a range of two and three component structures resident in magnetite an important component recognised as a partial or complete remagnetisation by late mesozoic tertiary tectonic magmatic activity is present in basement at the southern margin of the outcrop miyun terrane and where extensive granite plutonism has occurred zhunhua terrane these components have directions corresponding to remanence in the yunmeng shan granite 119 114 ma d i 33 58 39 samples a 95 3 5 palaeopole at 201 e 64 n most remanence elsewhere was probably acquired during post tectonic uplift and cooling of the basement between 2200 and 1850 ma because palaeomagnetic directions are removed from the phanerozoic palaeofield path and they are distinct from the palaeomagnetic record in the overlying jixian supergroup deposited at 1840 900 ma these latter magnetisations are considered reliable indicators of the palaeofield during late palaeoproterozoic times because deformation of overlying supracrustal rocks is mostly slight and no prominent deflection of magnetic remanence by magnetic fabrics is observed palaeofield directions and poles attributed to the time of uplift related cooling are qian an terrane d i 215 71 a 95 9 17 samples pole at 99 e 10 n and north qianxi terrane d i 44 45 a 95 4 41 samples pole at 79 e 11 s in addition a more widely preserved shallow northerly component correlates with a nw e swathe of components recorded by uplift related cooling within the datong huan an granulite terrane in the west of the shield a preliminary palaeo mesoproterozoic apparent polar wander path for the huabei shield is defined from the palaeoproterozoic record in the metamorphic basement rocks and the meso neoproterozoic record in the overlying jixian supergroup it incorporates a loop between 2200 and 1850 ma and exhibits a general east to west trend in subsequent times

petroleum geology and geochemistry of the middle proterozoic mcarthur basin northern australia iii composition of extractable hydrocarbons abstract middle proterozoic organic rich sediments from the mcarthur basin in northern australia contain abundant hydrocarbons which are derived from syngenetic kerogen and hence are representative of the organic remains of microorganisms living at that time the major classes of hydrocarbons identified were n alkanes monomethyl branched alkanes cyclohexyl alkanes and acyclic isoprenoids there were also low abundances of pentacyclic triterpanes comprising hopanes and methyl hopanes low concentrations of steranes were present in most samples but like the triterpanes they were only easily detected in the least thermally altered sediments and hence were of limited use in detailed assessments of thermal maturity the presence of steranes in sediments of this age is strong evidence for the existence of eukaryotic organisms as far back as 1690 ma although the relatively high abundances of branched alkanes indicates that most of this primitive organic matter was probably derived from prokaryotes