provenances of the mesozoic sediments in the ordos basin and implications for collision between the north china craton ncc and the south china craton scc abstract to constrain the provenance of the ordos basin and the evolution history of the qinling orogen belt from the triassic to the jurassic 10 samples from the dongsheng area and 28 samples from the yan an area were analyzed for u pb ages and lu hf and sm nd isotopic compositions the results indicate that middle jurassic sediments in the dongsheng area were derived from the khondalite belt langshan mountain and the yinshan terrane mesozoic sediments in the yan an area consist of two parts one part is derived from the north china craton ncc which has u pb age groups of 1 8 ga and 2 5 ga and hf model ages of 2 8 ga the other part is derived from the qilian qinling orogenic belt which has u pb age groups of 600 1500 ma and 100 500 ma and nd and hf isotopic model ages of less than 2 2 ga combining the u pb ages with the hf and nd isotopic model ages mesozoic detrital zircons with u pb age groups of 1 8 ga and 2 5 ga in the yan an area are found to also be derived from the khondalite belt langshan mountain and the yinshan terrane not from the trans china orogen belt from the late late triassic sediments of the yan an area the low average values of the hf 2 03 ga and nd 2 03 ga model ages and the characteristic age population of 600 1500 ma reveal that the main collision or continental subduction between the ncc and the south china craton scc occurred in the late late triassic after the main collision or continental subduction the proportion of sediments from the qinling qilian orogenic belt began to decrease recorded in the early jurassic samples which may be in response to the gradual slowing of the uplift speed of the qinling orogenic belt in the early middle jurassic the sediments have a main u pb age population of 100 500 ma low detrital zircon hf model ages average value is 1 17 ga and low whole rock nd model ages average value is 1 13 ga which suggests that the qilian qinling orogenic belt may have a fast uplift history in the early middle jurassic

ice age at the middle late jurassic transition a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine invertebrate fauna ammonites and isotopic thermometry 18o values of shark tooth enamel indicates a severe cooling at the middle late jurassic transition mljt about 160 ma ago the magnitude of refrigeration 1 3 c for lower middle latitudes and its coincidence in time with an abrupt global scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time ice sheets may have developed over the high latitude mountainous regions of far east russia the drastic cooling just post dated the middle late callovian widespread deposition of organic rich marine sediments e g northwestern europe central atlantic and arabian peninsula this thermal deterioration can thus be ascribed to a downdraw in atmospheric co2 via enhanced organic carbon burial which acted as a negative feedback effect i e the inverse greenhouse effect the glacial episode of the mljt climaxed in the late callovian lasted about 2 6 myr and had a pronounced asymmetrical pattern composed of an abrupt 0 8 myr temperature fall opposed to a long term 1 8 myr stepwise recovery the glacial conditions at the mljt reveal that atmospheric co2 levels could have dropped temporarily to values lower than 500 ppmv during mesozoic times

plio pleistocene palaeogeography of the southern north sea basin 3 75 0 60 ma abstract palaeogeographical maps are presented for the southern north sea basin from approximately 1 w to 7 e and 51 55 n for the period from approximately 3 75 0 60 ma reconstructions centre on 3 75 ma coralline cragbrunssumian 2 55 ma red crag brielle ground reuverian 2 40 ma red crag westkapelle ground praetiglian early tiglian 2 00 ma norwich crag smith s knoll and ijmuiden ground middle tiglian 1 75 1 70 ma cromer forest bed paston winterton shoal late tiglian eburonian 1 40 ma kesgrave yarmouth roads waalian 1 15 ma kesgrave yarmouth roads menapian and 0 60 ma cromer forest bed west runton yarmouth roads cromerian complex from 3 75 2 40 ma the basin is mainly a marine area fringed to the east and south by fluviatile deposition and broadly open via the southwest to the atlantic following marked marine regression and cooling at around 2 40 ma the period from 2 00 1 70 ma is mainly one of renewed marine transgression and warmer conditions during which a great european delta built out fed mainly from the east and south into the southern north sea from 1 40 0 60 ma marine waters were almost entirely excluded from the area and temperate intervals alternated with increasingly glacial episodes whilst the great european delta continued to expand northwards into the northern north sea

thermal origin of continental red beds in se china an experiment study abstract the origin of continental red beds in se china is the result of high diagenetic temperatures rather than an arid climate during their deposition here we present results from an experimental study where black mud was heated to demonstrate the formation of red beds diffuse reflectance spectroscopy drs of heated samples enables determination of the relative proportion of goethite and hematite iron in black mud is predominantly in the form of goethite that has an initial dehydration temperature of ca 150 c increasing temperature or prolonged heating time is accompanied by decreasing goethite and organic content increasing hematite and red colouration heat provided to subsiding red bed basins is supplied by cooling of an intracrustal granitic magma layer the thermal model can explain vertical colour temperature redox and mineral zonation in red bed sequences from red hematite bearing through green yellow cu zn v sulphide mineralization to grey black hydrocarbon halite bearing sediments the model can also be used to help prospect for hydrocarbon and halite deposits in the se china red bed basins

thames river sediments of the british early and middle pleistocene abstract the thames drainage system contains the most complete record of fluvial sediments in the british quaternary the kesgrave sands and gravels form the main body of this sediment having been deposited over an interval that spans the later part of the early pleistocene and most of the middle pleistocene conventional stages pre pastonian a through to early anglian ca 1 2 ma this deposit provides a stratigraphic context for related bio morpho and pedostratigraphic evidence and for the recognition of pre anglian pre oi stage 12 upland glaciation in the welsh mountains and intense periglaciation in lowland england it also facilitates correlation with the stratigraphy of northern europe and the global pattern of orbitally forced climatic change this paper describes the first catchment wide correlation of thames river sediments and proposes a formal redefinition of the lithostratigraphic units concerned the scheme outlined here is based on two lithologically distinctive formations defined at type areas reflecting significant changes in catchment dimensions the earlier sudbury formation was formed when the thames catchment extended into wales and drained northwards across east anglia the later colchester formation was formed after the upper catchment had been reduced in extent to that of the present river but continued to flow across east anglia the whole sediment body is now named the kesgrave group

the south china block indochina collision where when and how this study uses new field observations and existing studies to shed new light on the origin and significance of two nw se striking orogens in nw and ne vietnam we conclude that the architecture of each belt is a stack of ne directed nappes formed either under deep ductile synmetamorphic conditions or under shallow depth in the sw and ne parts respectively the song ma zone and song chay ophiolitic melange represent two ophiolitic sutures however the late permian song da and babu mafic rocks are not ophiolites but intraplate basalts related to the emeishan plume a late triassic unconformity the 225 205 ma postorogenic plutonism and the 250 230 ma syntectonic metamorphism support an early to middle triassic age for these tectonic events both nw and ne belts are due to sw directed subduction with arc magmatism ocean closure and continental collision though two contemporary s dipping subduction zones might explain the structural evolution of the two belts a single convergent system offset by the tertiary red river fault is preferred as this s directed subduction better accounts for the late permian intraplate magmatism this scenario is discussed in the general geodynamic framework of se asia

stratigraphical and palaeobiogeographical significance of fossil wood from the mesozoic khorat group of thailand fossil wood from the poorly dated jurassic cretaceous continental sediments of the khorat group northeastern thailand isan is described the khorat group is widely distributed laos cambodia and thailand and despite its poorly known age stratigraphy and palaeoecology is of importance in understanding the sibumasu indochina collision the systematics of wood assemblage and palaeobiogeographical analysis reveal strong relationships with indochina especially vietnam and suggest an age in the range middle jurassic to early cretaceous according to wood taphonomy the corresponding trees grew alongside streams under a rather arid climate although this became wetter during the deposition of the upper formations of the khorat group

xenoxylon a boreal fossil wood in the mesozoic redbeds of southeast asia potential for the stratigraphy of the khorat group and the palinspatic reconstruction of southeast asia abstract the fossil wood genus xenoxylon is reported in situ for the first time in thailand it originates from the indosinian terrane from the mesozoic continental redbeds of the phu kradung formation khorat group palinspatic reconstruction palaeobiogeography and correlation with other occurrences of the genus in southern china as well as in vietnam suggest a middle to late jurassic age for the phu kradung formation level yielding the fossil wood the dating of this formation is still controversial and thus our data is an important step towards a better understanding of its geological history and palaeoecology as well as of the southeast asia mesozoic continental redbeds significance for the evolution of the vertebrates

identification of an anastomosing river system in the early cretaceous khorat basin northeastern thailand using stratigraphy and paleosols abstract the phu kradung and phra wihan formations of the early cretaceous khorat group were investigated to characterize the depositional system and paleoclimate based on stratigraphy paleosol features paleosol profiles and reworked deposits the sediments of both formations are classified into 12 facies on the basis of their primary depositional attributes such as bedding grain size texture and sedimentary structures furthermore these facies are grouped into eight architectural elements based on stratigraphic relationships and outcrop scale macroforms the proportions of each architectural element indicate that the depositional system was that of an anastomosing river the anastomosing river system in the studied section is characterized by a high rate of vertical floodplain aggradation and the development of a relatively stable crevasse channel paleosols are developed mainly in floodplain deposits and are characterized by the development of calcretes a semi arid to sub humid paleoclimate is deduced from the occurrence of the calcretes in addition their microstructures suggest that these calcretes were formed under several different conditions with micritic carbonate precipitating under relatively arid climates and alveolar septal structures under semi arid to sub humid conditions using the thicknesses of the calcrete horizons we conclude that the difference in the amount of precipitation between the wet and dry periods was highly variable without any order during deposition of the studied section the thicknesses of intervals between successive calcrete horizons indicate that the inflow of fine materials occurred randomly across the floodplain partly superimposed multiple calcrete horizons were developed during periods of low sediment supply a random deposition of floodplain sediments appears to characterize the anastomosing river system of the khorat basin

early and middle pleistocene river systems in eastern england evidence from leet hill southern norfolk england pleistocene sediments at leet hill southern norfolk are examined in terms of their sedimentary structures palaeocurrent indicators clast and heavy mineral lithology and litho and morphostratigraphic position colour of the quartzite and vein quartz clasts is used to differentiate the bytham and the kesgrave sands and gravels with the bytham sands and gravels having a significantly higher proportion of coloured material the kirby cane sands and gravels are the lower sedimentary unit and were deposited by the bytham river which drained a catchment extending into central england at leet hill erosion of the kesgrave sands and gravels by the bytham river has given the kirby cane sands and gravels a distinctive lithological assemblage trace clast lithologies suggest that the kesgrave sands and gravels in the region of leet hill were deposited in a coastal location with an input from northern sources as well as southern and welsh sources diagnostic of the thames catchment the glaciofluvial leet hill sands and gravels were deposited by outwash from the anglian scandinavian ice sheet initially the flow direction of the outwash was determined by the bytham river valley but this changed to a southerly direction once the valley had been infilled this paper provides the first indication of the location of the boundary early pleistocene coastline between the fluvial kesgrave sands and gravels and the marine equivalent reworked by coastal processes and demonstrates the way the pre glacial relief initially controlled patterns of glaciofluvial sedimentation during the early part of the anglian glaciation copyright 1999 john wiley sons ltd

wood decay of xenoxylon yunnanensis feng sp nov from the middle jurassic of yunnan province china abstract a permineralised gymnosperm wood xenoxylon yunnanensis feng sp nov is described from the middle jurassic shaximiao formation in huize county yunnan province southwest china the pycnoxylic wood consists of thick walled tracheids and thin walled rays it is characterised by uniseriate contiguous compressed bordered pits on the radial walls of tracheids and one large simple pit in each cross field growth rings exhibit narrow latewood the mean sensitivity of analysis of 25 growth rings is 0 2 suggesting that a climate with abundant rainfall and weak seasonality could have prevailed in yunnan at least locally during the middle jurassic the outer portion of the wood is largely decayed and shows poorly preserved cells lacking details decayed tracheids displaying various features including removal of middle lamellae separations of secondary walls presence of thickened corners and appositions are recognised as cell reactions to fungal activity irregularly distributed micro cavities are formed by complete decomposition of tracheids and rays in the wood abundant fungal remains occurring in the wood generally consist of multiple branched hyphae these fungal hyphae are either confined to individual cell lumens or extend through adjacent cells although the probable reproductive structure and typical clamp connection are very rarely observed with few septate hyphae the affinities of these fungal hyphae are somewhat obscure nevertheless our study sheds light on the palaeoecology of middle jurassic terrestrial ecosystems of southwest china

s wave velocity structure of the taiwan chelungpu fault drilling project tcdp site using microtremor array measurements the taiwan chelungpu fault drilling project tcdp drilled a 2 km deep hole 2 4 km east of the surface rupture of the 1999 chi chi earthquake mw 7 6 near the town of dakeng geophysical well logs at the tcdp site were run over depths ranging from 500 to 1 900 m to obtain the physical properties of the fault zones and adjacent damage zones these data provide good reference material for examining the validity of velocity structures using microtremor array measurement therefore we conduct array measurements for a total of four arrays at two sites near the tcdp drilling sites the phase velocities at frequencies of 0 2 5 hz are calculated using the frequency wavenumber f k spectrum method then the s wave velocity structures are estimated by employing surface wave inversion techniques the s wave velocity from the differential inversion technique gradually increases from 1 52 to 2 22 km s at depths between 585 and 1 710 m this result is similar to those from the velocity logs which range from 1 4 km s at a depth of 597 m to 2 98 km s at a depth of 1 705 m the stochastic inversion results are similar to those from the seismic reflection methods and the lithostratigraphy of tcdp a borehole comparatively these results show that microtremor array measurement provides a good tool for estimating deep s wave velocity structure

kalasinemys a new xinjiangchelyid turtle from the late jurassic of ne thailandh tong et al new xinjiangchelyid turtle from ne thailand a new xinjiangchelyid turtle kalasinemys prasarttongosothi n gen n sp is described on the basis of skull and shell material from the upper jurassic phu kradung formation at phu noi locality kalasin province in ne thailand this second xinjiangchelyid turtle from phu noi is distinct from phunoichelys thirakhupti by the smooth shell surface the presence of a cervical notch and vertebral 1 narrower than nuchal the skull presents an arterial system characteristic of the xinjiangchelyidae basal eucryptodira and its outline is similar to that of annemys spp known from the middle late jurassic of china and mongolia but distinct from the latter mainly by the wider triturating surface smaller foramen palatinum posterius and the shape of the prefrontal and frontal as well as that of the basisphenoid and basioccipital based on the turtle assemblages the correlation with mainland asia further supports a late jurassic age for the lower part of the phu kradung formation where phu noi site is located stratigraphically our study provides new insight on the evolution of the basal eucryptodiran turtles in asia

the palaeolatitudinal distribution of fossil wood genera as a proxy for european jurassic terrestrial climate the potential of using the latitudinal distributions of fossil wood genera as a proxy for jurassic terrestrial climate conditions in western laurasia was tested using a database of 386 entries the fossil wood genera brachyoxylon protaxodioxylon and simplicioxylon are southern taxa which have only occasionally extended north of 45 n all latitude references are to palaeolatitudes conversely protocedroxylon and xenoxylon are mostly found at high latitudes the standard deviation of the data on the palaeolatitudes of the northern genera is however much larger than that of the southern genera this is interpreted as resulting from brief periodic southward extensions of the protocedroxylon and xenoxylon distributions while the southern genera remained confined south of 40 n the interval during which the northern genera replaced the southern genera at mid latitudes can be hypothesized to be times of global terrestrial climate cooling or increased rainfall comparisons between the spatiotemporal distributions of these northern taxa and independent climate sensitive indicators clay mineral assemblages oxygen isotopes and neritic carbonate distribution suggest that these genera were adapted to more humid conditions characterizing the mid latitudes of the northern hemisphere accordingly southward migrations of this climatic zone occurred during the early and late pliensbachian early toarcian and early middle oxfordian time intervals these reconstructions are limited by the low resolution and restricted spatial coverage of the wood record therefore further sampling at the ammonite zone level is needed nevertheless the present study suggests that wood taxa distribution represents an underexploited but potentially powerful record of terrestrial environmental changes during the jurassic period

the pliensbachian toarcian paleoclimate transition new insights from organic geochemistry and c h n isotopes in a continental section from central asia the taskomirsay section south kazakhstan is a unique pliensbachian toarcian sequence of lignites clayey layers and silty sandstones deposited in a fluvial lacustrine environment with nearby swampy areas this period characterized by a drastic climate change has been particularly studied in western tethyan marine environments whereas very few studies focused on continental settings paleoflora analyses associated with a multi isotope approach based on well preserved type iii bulk organic nitrogen isotopes a15norg and hydrogen isotopic composition a2h of n alkanes were developed to document paleoclimatic changes in the area sporomorph associations and fossil woods revealed a globally warm to cool temperate climate characterized by xenoxylon a conifer morphogenus biogeographically related to cool humid settings apart from slightly less humid and warmer conditions in the early toarcian warmer conditions are supported by reconstructed mean annual air temperatures maats based on the first branched glycerol dialkyl glycerol tetraethers brgdgts ever recorded in the early jurassic nevertheless no drastic changes were recorded in the a15norg values its signal being attributed to tenuous equilibrium between water and nutrient availability via intense n recycling based on n alkane distributions sources of organic matter were separated in two pools i a purely terrestrial n c27 and ii an aquatic pool n c23 constituted of vegetation that thrived under almost permanent water supply the n alkane a 2h values 248 to 151 as well as their amounts and average chain lengths acl are in agreement with cool temperate conditions in the pliensbachian and less humid warmer conditions in the early toarcian the isotopic difference between a2h values of n c27 and n c23 2hter aq suggests enhanced seasonality during the pliensbachian toarcian transition and low seasonality in the early toarcian in agreement with temperate climate regime finally contrasted response to paleoclimate changes between markers suggests different spatial integration of those proxies the role of sea level variations for a2h values might also resolve this contrasted response

environment and ecology of east asian dinosaurs during the early cretaceous inferred from stable oxygen and carbon isotopes in apatite abstract during the cold late barremian early albian interval terrestrial environments in east asia were populated by rich and diverse vertebrate faunas characterized by a strong provincialism the latitudinal gradient of temperature and the existence of geographic barriers likely accounted for some aspects of this heterogeneous distribution of faunas other factors however such as local environmental conditions and interactions within vertebrate communities which could have influenced their distribution have not yet been fully identified and understood therefore new and published oxygen and carbon isotope compositions of apatite from chinese and thai reptiles dinosaurs crocodilians and turtles have been analyzed and interpreted in terms of ecology local air temperature and precipitation amounts differences in carbon and oxygen isotope compositions between various groups of sympatric plant eating dinosaurs sauropods ornithopods and ceratopsians indicate food resources partitioning among them most likely to avoid competition mid latitude environments where the jehol biota flourished were submitted to cool temperate climatic conditions with mean air temperature mat of 10 4 c and mean annual precipitations map of about 600 mm yr compatible with the existence of forest environments by contrast sub tropical regions characterized by mat of about 20 25 c were either submitted to high amounts of seasonal precipitations of about 1200 mm yr in thailand or to significant aridity map of about 400 mm yr in south china this difference in precipitation regime between thailand and south china may be attributed to the occurrence of the coastal cordillera extending along the east margin of the south china block these mountain ranges likely prevented humid air masses from the pacific to penetrate some parts of south china thus generating a rain shadow effect mosaic environments characterizing east asia during the late early cretaceous may have acted as a cradle for the origination of advanced dinosaur taxa that subsequently radiated over eurasia and north america during the late cretaceous

palaeocurrent direction estimated in mesozoic redbeds of the khorat plateau lao pdr indochina block using anisotropy of magnetic susceptibility mesozoic redbeds in the western part of central and southern laos are the most abundant rocks of the khorat plateau in earlier studies palaeocurrent directions of the mesozoic redbeds in the khor

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

peat forming materials and evolution of swamp sequences case analysis of a jurassic inland coal basin in china abstract a case analysis was conducted in the yima coal mine which is located in a jurassic inland basin located in the henan province of central china using data from palynological ecology plant residues coal petrography and some geochemical characteristics the plant community during this coal forming period and the precursors of the coal forming peat were determined the peat forming paleoenvironment and evolutionary sequences within the swamp were reconstructed according to the differences in the spore pollen complex of the coals in the yima mine seven kinds of palynofacies each characterized by predominant species occured within the relative beds seven different types of ecological characteristics are indicated the different stages are represented by the corresponding floral facies six diagnostic properties of the coal facies were determined by studying the petrographic characteristics of each coal and seven different kinds of ancient peat forming swamp paleoenvironments are indicated by the coal facies a genetic model of formation development and evolutionary sequences of the coal forming swamp in the jurassic of central china is proposed

oxygen isotopes of east asian dinosaurs reveal exceptionally cold early cretaceous climates early cretaceous vertebrate assemblages from east asia and particularly the jehol biota of northeastern china flourished during a period of highly debated climatic history while the unique characters of these continental faunas have been the subject of various speculations about their biogeographic history little attention has been paid to their possible climatic causes here we address this question using the oxygen isotope composition of apatite phosphate from various reptile remains recovered from china thailand and japan values indicate that cold terrestrial climates prevailed at least in this part of asia during the barremian early albian interval estimated mean air temperatures of about 10 4 c at midlatitudes 42 n correspond to present day cool temperate climatic conditions such low temperatures are in agreement with previous reports of cold marine temperatures during this part of the early cretaceous as well as with the widespread occurrence of the temperate fossil wood genus xenoxylon and the absence of thermophilic reptiles such as crocodilians in northeastern china the unique character of the jehol biota is thus not only the result of its evolutionary and biogeographical history but is also due to rather cold local climatic conditions linked to the paleolatitudinal position of northeastern china and global icehouse climates that prevailed during this part of the early cretaceous

new record of fossil wood xenoxylon from the late triassic in the sichuan basin southern china and its paleoclimatic implications abstract fossil wood is one of the significant proxies for terrestrial paleoclimate and paleogeographical reconstruction in earth history abundant and diversified mesozoic fossil woods are well recorded in china however triassic fossil wood is very scarce here we report a new fossil wood from the late triassic xujiahe formation norian to rhaetian in guangyuan of northern sichuan basin southwestern china the fossil wood material consists of two well preserved specimens yielding secondary xylem with distinct growth rings bordered pits on the radial tracheid walls are mostly contiguous biseriate alternate locally uniseriate and strongly flattened cross fields show a large window like pore this anatomy is typical for the important fossil wood morphogenus xenoxylon gothan and based on a novel combination of radial and cross field pitting type and ray height a new species xenoxylon guangyuanense sp nov is recognized the finding of this new fossil wood taxon contributes to a better understanding of the yet poorly documented xenoxylon early radiation during the late triassic as well as of the origin of x meisteri group a peculiar endemic group which diversified in far east asia from the triassic to the early cretaceous xenoxylon is a paleobiogeographically significant genus being bound to cooler and or wetter climates of northern hemisphere throughout its late triassic late cretaceous range the occurrence of xenoxylon in the sichuan basin of southern china may indicate a short term cooling event sandwiched within a period during which warm and wet climate conditions largely prevailed over lower latitude regions of the northern hemisphere such a cooling event in the sichuan basin which was located at a low paleolatitude on the eastern rim of tethys may be in accordance in time with the temperature decline event in norian rhaetian boundary uncovered by oxygen isotope 18 o record in italy of the western rim of tethys