a proton and electron microprobe study of gallium nickel and zinc distribution in chromian spinel abstract chromian spinels from a number of localities were analyzed by proton and electron microprobes to examine the variation of trace elements in different geological environments chromian spinels studied include those representing ophiolitic complexes layered intrusions in continental areas alaskan type complexes komatiitic subvolcanic sills ni sulfide ores and metamorphosed mafic and ultramafic rocks nickel concentrations range from 30 to 4690 ppm proton microprobe with a mean value of 943 ppm nickel favouring the octahedral sites in the spinel structure displays an overall increase with a decrease in the cr cr al fe 3 ratio nickel partitioning between chromian spinel and mantle silicates appears to be primarily dependent upon the major element composition of the chromian spinel zinc concentrations range from 230 to 9810 ppm proton microprobe with a cluster around 500 ppm ophiolitic chromian spinels display the lowest overall zn values zinc levels appear to discriminate between chromian spinels in chromitite samples from those occurring as accessory chromian spinel in dunites or other rock types chromian spinels that are enclosed in or adjacent to sulfide grains display higher concentrations of zn zinc strongly favouring the tetrahedral sites displays a crude negative correlation with the mg mg fe 2 ratio and appears to vary as a function of temperature all the chromian spinel grains analyzed contain measurable quantities of ga by proton microprobe ranging from 10 to 208 ppm there is a reciprocal relationship between the ga concentration and the cr cr al fe 3 ratio and a crude positive correlation between the ni and ga concentrations measured ga concentrations in chromian spinel and whole rock samples are supportive of the experimental mineral melt partition coefficient of malvin and drake 1987 similar to the peridotite xenoliths mid ocean ridge basalts and oceanic island basalts ga correlates well with al 2 o 3 in the case of the ophiolitic chromian spinels and most of those representing layered complexes the ophiolitic chromian spinels seem to have crystallized from melts whose compositions are similar to those of partial melts of the upper mantle

a new skeleton of phuwiangosaurus sirindhornae dinosauria sauropoda from ne thailand a new skeleton of a sauropod dinosaur has been discovered in the early cretaceous sao khua formation at ban na khrai in changwat kalasin ne thailand all sauropod bones from ban na khrai share all their characteristics with the type specimen of phuwiangosaurus sirindhornae martin buffetaut suteethorn 1994 the 60 complete skeleton is very well preserved and includes cranial elements a tooth a frontal a postorbital a squamosal both quadrates and the braincase whereas the type specimen is only 10 complete and consists of postcranial bones only the material from ban na khrai belongs to a single subadult individual of phuwiangosaurus as attested by the unfused neurocentral sutures of the vertebrae which are firmly fused and larger in size in the holotypic specimen

the norian plateosaurus bonebeds of central europe and their taphonomy abstract plateosaurus is probably the single most common dinosaur in the late triassic known from over 40 localities in the norian knollenmergel mudstones of central europe in addition it is also one of the best known triassic dinosaurs due to the discovery of many complete skeletons these complete skeletons as well as the majority of all other material are actually derived from only a handful of localities three of which are compared here to one another in detail frick northern switzerland trossingen southwestern germany and halberstadt central germany are recognized as the result of the same taphonomic processes and can all be described with the term plateosaurus bonebed this type of bonebed is characterized by its large size measured in thousands of square meters the large number of incomplete and complete plateosaurus skeletons and the lack of other vertebrate fossils with the exception of the primitive turtle proganochelys the uniformly upright carcass position precludes post mortem transport and strongly argues for in situ death shallow depressions in the thick floodplain muds of the knollenmergel must have formed efficient traps for the heaviest animal at that time plateosaurus the animals became mired and were scavenged upon by small theropods whose shed teeth are always present in plateosaurus bondebeds miring explains the deep position of the feet and hindquarters and in combination with scavenging and weathering the bias towoards bones of the posterior body region the lack of juvenile individuals is due to their lower foot pressure which was below the threshold for becoming mired

genesis and taphonomic biases of quaternary tank deposits of northeastern brazil abstract a taphonomic comparison among ten quaternary tank deposits bearing megafauna remains in northeastern brazil allowed the identification of four regional scale taphonomic aspects controlled by climate seasonality differential preservation of mega mammal bones poor physical integrity spatial resolution local and time averaging 104 years sedimentary aspects such as the high degree of packing of fossiliferous layer indicate conditions of low clastic detrital sediment input in arid conditions the correlation among geochronological data of tank deposits and paleoclimatic curves of northeastern brazil suggest that the climate was arid semi arid characterized by seasonality between dry and rainy periods thus we postulate the succession of the two paleoenvironmental and paleoecological scenarios during the late quaternary affecting the formation of fossiliferous tank deposits i the intensity and duration of arid periods led animals to search for water and food and consequently concentration and death near these water sources and ii in the rainy season carcasses disarticulated and fragmented bones around these water sources were transported and accumulated through high energy tractive flows reworking previously buried skeletal material

unveiling the taphonomy of elusive natural tank deposits a study case in the pleistocene of northeastern brazil abstract fossiliferous natural tanks are a singular type of sedimentary deposit restricted to northeastern brazil which usually preserves a diversified late pleistocene vertebrate fauna their fossil assemblages are taxonomically well known but their taphonomy is poorly understood this work presents a detailed taphonomic analysis of a tank deposit from jirau site ceara state northeastern brazil to improve understanding of the processes that influenced fossil deposition and preservation in natural tanks and to shed light on paleoecological and paleoenvironmental aspects related to the late pleistocene vertebrate fauna from northeastern brazil tank deposits from different localities were also compared to figure out potential taphonomic patterns among them additionally comparisons with other brazilian pleistocene deposits and other debris flow deposits bearing vertebrates were undertaken the study revealed the predominance of the megamammal eremotherium laurillardi in the deposit which we attributed to its abundance in late pleistocene biocoenosis as well as bone resistance scarcity of non mammalian vertebrates is likely related to their paucity in late pleistocene biocoenosis time averaging was evidenced by the co occurrence of different weathering petrographic and color patterns and may have affected the ontogenetic profile of the accumulation relative to the original biocoenosis analyses of weathering stages tooth and trample marks indicate wide exposition of the thanatocoenosis before burial abrasion and petrographic patterns allow reworking in the assemblage to be inferred permineralization and substitution are the fossilization processes observed taphonomy indicates that floods deposited clasts and bioclasts in the tank under an arid or semiarid climate in a debris flow regime comparison with other tank deposits revealed several similar taphonomic features and differences related to sedimentology and stratigraphy taphonomic similarities suggest rather homogeneous environmental conditions in the northeastern brazil during the late pleistocene as previously suggested by taxonomic studies comparison with other brazilian pleistocene deposits shows that tanks have more temporal fidelity than caves coastal and some fluvial deposits the jirau vertebrate accumulation was produced by the reworking and transport of skeletal elements accumulated in a nearby thanatocoenosis and is similar to other better known debris flow hosted vertebrate accumulations

paleomagnetism of the cambrian moore hollow group texas evidence for a primary magnetization carried by detrital magnetite petrographic and paleomagnetic studies of the cambrian moore hollow group texas establish the presence of three magnetic minerals and several components of magnetization hematite is the dominant carrier of the magnetic remanence in most samples and is primarily a diagenetic replacement of preexisting fe bearing phases hematite dominant samples have characteristic directions which range from shallow easterly to shallow southerly this distribution suggests multiple components of magnetization acquired at various times in the paleozoic the paleopole obtained for an unmineralized breccia 135 7 e 15 4 n represents either a chemical remanent magnetization of middle ordovician to early silurian age or a vector addition of two or more cambrian through silurian components mineralized breccias at the silver creek mississippi valley type deposit yield a permian direction 117 0 e 51 6 n because hematite in this deposit predates mineralization the permian age represents a maximum age for the mineralization at silver creek many samples contain goethite as a replacement of fe dolomite glauconite and pyrite the direction of magnetization carried by goethite is near the present geomagnetic field or in a minority of samples antipodal to it rounded ti magnetite was identified by sem in magnetic extracts from siliciclastic poor facies irm acquisition and thermal demagnetization confirms the presence of magnetite in these samples some samples contain an apparent modern viscous remanent magnetization the dominant component 72 samples 10 sites has a site mean declination of 93 8 and inclination of 14 5 with an 95 8 5 corresponding to a pole position at 163 0 e 0 6 s the presence of detrital magnetite polarity changes lack of evidence for prolonged burial and the proximity of this pole position to other late precambrian cambrian poles suggest that this component of magnetization indeed reflects the late cambrian paleopole for cratonic north america

first report of cisuralian early permian charcoal layers within a coal bed from baode north china with reference to global wildfire distribution abstract fossil charcoal is reported for the first time from a cisuralian coal bed of the shanxi formation in the qiaotou section baode shanxi north china based on anatomical characteristics these charcoal fragments consist of coniferous or cordaitalean xylem unidentified primary xylem and cordaitalean and possible fern leaves these charcoal fragments represent the evidence of palaeowildfire taking place in tropical peat swamps during the cisuralian in cathaysia the palaeowildfire is most likely to be a surface fire and burning litter and shrubby vegetation fire frequency for this early permian peat swamp might have been on the order of 176 294 588 1429 years close to modern values compared with modern analogues the north china block during the cisuralian was probably wet in general but could be occasionally seasonally dry for short time intervals previous charcoal and inertinite records moreover indicate that palaeowildfires were globally common during the cisuralian overall more wildfire evidence was found in the artinskian kungurian than the asselian sakmarian except in the euramerican realm probably due to more suitable regional climate vegetation to fuel fires and taphonomic circumstances

preservation of primary stable isotope signals in dinosaur remains and environmental gradients of the late cretaceous of montana and alberta abstract although the use of stable isotope data from vertebrate remains is becoming common for the cenozoic their application to mesozoic environments has been rare in part due to the perception that diagenesis has obfuscated all potential primary signal in this paper we illustrate how stable isotope data collected from dinosaur and other vertebrate remains can in fact be used to reconstruct paleoenvironmental conditions during the mesozoic carbon and oxygen isotope ratios were measured from tooth enamel of hadrosaur dinosaurs and from scales of freshwater fish that were collected from sites in the two medicine judith river and dinosaur park formations of montana and alberta these formations represent a coastal to upland gradient along the western margin of the late cretaceous inland seaway isotopic comparisons among skeletal components and among taxa are used as evidence that primary paleoenvironmental information as recorded by isotope data is preserved in tooth enamel and freshwater fish scales a comparison of carbon isotope ratios between hadrosaur tooth enamel and sedimentary organic matter indicates that these animals had a larger isotopic offset compared to bulk diet than modern mammals and that all hadrosaurian isotope data are consistent with the existence of c3 only ecosystems higher and more variable carbon and oxygen isotope ratios from animals occupying the coastal judith river region are interpreted to reflect a range of freshwater to brackish water conditions and plants that were undergoing water stress lower and less variable carbon and oxygen isotope ratios from the upland two medicine and intermediate dinosaur park areas are interpreted to reflect a gradual rainout of moisture from air masses moving inland and more uniform environmental conditions overall these results indicate that stable isotopes from dinosaur and other vertebrate remains have the potential to expand our understanding of terrestrial environments and ecosystems during the mesozoic

gregarious behaviour among non avian theropods inferred from trackways a case study from the cretaceous cenomanian candeleros formation of patagonia argentina abstract gregarious behaviour among dinosaurs has been inferred from several lines of evidence monospecific bonebeds skeletal morphology phylogenetic inferences comparison with modern ecosystems and parallel trackways with particular characteristics but is relatively poorly documented for non avian theropods here we report five parallel theropod trackways of large track size average length of 28 cm in the cretaceous cenomanian candeleros formation from northwestern patagonia argentina the tracks are provisionally assigned to aff asianopodus pulvinicalx and considering the autopod morphology of the theropod taxa documented in the candeleros formation abelisaurid theropods are suggested as trackmakers the trackways possess similar stride speed estimation direction and preservational features and track show uniform depth and do not overlap physical barriers i e large fluvial channels or perennial lake that could influence the direction of the theropod trackmaker gaits were not recognized in the section taking into account these considerations a gregarious behaviour for the abelisaurid theropod trackmakers is proposed the tracks are preserved as shallow undertracks in a medium grained sandstone bed deposited in a floodplain setting the tracking surface is interpreted as the overlaying layer of muddy siltstone the occurrence of swelling clays and microbial mats in the track bearing level could have contributed to the substrate stabilization and their role in the preservation is discussed

taphonomic and paleoecologic investigations of the late cretaceous santonian iharkut vertebrate assemblage bakony mts northwestern hungary abstract the iharkut vertebrate locality an open pit mine in the bakony mountains western hungary has provided a rich and diverse assemblage of late cretaceous santonian continental vertebrates the isolated and associated remains represent 31 different taxa including fish amphibians turtles lizards pterosaurs crocodilians non avian dinosaurs and birds sedimentologic investigations suggest that the iharkut depositional environment was represented by the floodplain of a very low gradient river the 10 50 cm thick bonebed of site sz 6 is the most important fossiliferous layer in the open pit mine and analysis of this site indicates alternating energy conditions during the bone accumulation which resulted in fossils of different states of preservation being deposited together the vertebrate assemblage of site sz 6 includes three main different subsets with widely different taphonomic history the characteristics and the preservation mode high rate of abrasion and the spherical shape of the bone pebbles suggest that this type of the isolated bones was more exposed to abrasion and probably the remains were transported from farther away than the other isolated bones the second group includes 88 of the iharkut collection containing most of the identified isolated bones and teeth and represents polytypic attritional remains transported and deposited by high density flow during ephemeral flood events meanwhile the monospecific ankylosaur skeletal material from iharkut site sz 6 may represent a mass death assemblage because seven skeletons of hungarosaurus were discovered from an area of approximately 400 m 2 and in many cases close to each other in the same layer the iharkut vertebrate assemblage is dominated by bones of aquatic semi aquatic animals while the number of terrestrial animal remains is subordinate the taphonomic analysis of the ankylosaur material from iharkut locality further strengthens the previously suggested hypothesis that some of the ankylosaurs preferred wetland habitats e g areas along fluvial systems while the other two herbivorous dinosaur groups from iharkut ornithopods and ceratopsians were probably living in distal habitats

changes of mesozoic vegetation and the extinction of dinosaurs abstract the structure of mesozoic vegetation is outlined as consisting of evergreen brachyphyllous forests deciduous forests dominated by phoenicopsis and then by parataxodium cycadophyte sclerophyllous shrublands and fern marshes warm warm temperate and temperate zones are indicated for successive periods dinosaur localities are situated mostly in the warm and warm temperate zones but a few of them fall in the temperate zone feeding habits of dinosaurs are inferred from combined evidence of depositional environments surrounding vegetation and stomach contents it is suggested that dinosaurs were associated mainly with open vegetation such as shrublands and marshes capable of supporting large populations of herbivores the shrubland and marsh dinosaur communities are provisionally indicated the latter comprising diplodocids stegosaurs and hadrosaurids replacements of dinosaur communities were concomitant with major vegetational changes forestation at the end of cretaceous time might have played an important role in the final extinction

the record of triassic charcoal and other evidence for palaeo wildfires signal for atmospheric oxygen levels taphonomic biases or lack of fuel abstract as wildfires are today important sources of disturbance in many terrestrial ecosystems it is of great interest to understand how different environmental parameters and fire activity interacted during past periods of the earth history fossil charcoal inertinites and pyrogenic polycyclic aromatic hydrocarbons pahs represent the only direct evidence for the occurrence of such palaeo wildfires in the present study a review of published data together with new data on the occurrence of fossil charcoal for the permian and the triassic is presented for a long time it has been speculated that an assumed lack of evidence for palaeo wildfires during the triassic should be explained by a large drop in atmospheric oxygen concentration following or during the end permian mass extinction event preventing the occurrence of wildfires however evidence for palaeo wildfires is relatively common in many middle and late triassic strata whereas such evidence is almost totally lacking from early triassic sediments the interpretation of this charcoal gap or depression is difficult as many factors e g atmospheric oxygen concentration taphonomical biases lack of sediments suitable for the preservation of macroscopic charcoal lack of fuel and ignorance of scientists may have influenced not only the production but also the preservation and recovery of evidence for palaeo wildfires during this period thus it is not clear whether this early triassic charcoal gap can also be seen as evidence for an assumed wildfire gap or not without any doubt further investigations on the early triassic record of charcoal and other evidence for palaeo wildfires will be necessary before this problem can be solved in fact it can be expected that the number of published records of early triassic evidence for palaeo wildfires will increase in the future as more and more scientist working on sediments of this age may become aware of the interest in fires from this time this will certainly make it possible to give a much better picture of the temporal and regional distribution of wildfires during this period in the future

taphonomy and preservation of a monospecific titanothere assemblage from the washakie formation late eocene southern wyoming an ecological accident in the fossil record abstract more than twenty partial skeletons all cf mesatirhinus sp were discovered in overbank deposits associated with sandstone channels within the adobe town member of the washakie formation washakie basin southwest wyoming taphonomic and sedimentologic data indicate a mass mortality event with reduced post mortem transport of the carcasses such a mass death assemblage of a large mammal taxon is a rare occurrence for the paleogene record accordingly position and orientation of all the bones were recorded to make possible an accurate detailed map of the deposit the remains principally include disarticulated skeletons of both sexes from juveniles to old adult some axial portions and limbs remained articulated others suggest partial articulation the collected remains were scattered in loose associations within an area of about 7 5 9 m recent erosion sheetwash has destroyed an unknown extent of the original mass burial to the east and south of the excavation but the 68 oriented bonebearing blocks collected represent about 50 of the exposed site the skeletal remains occurred within a single unit of poorly sorted but generally upward fining quartz grit with a basal mudflake conglomerate the bones are not abraded but have suffered from severe compaction damage and recent freeze thaw action the sediment represents a mass flow accumulation deposited during the waning stages of a flash flood the large number of individuals of a single taxon suggests that part of a herd of titanotheres was killed in a single mass mortality event the cause of death is not known but it is likely that the accumulation represents a small fraction of a large herd that was crossing a flooded river the carcasses drifted downstream to be left as a carcass jam on the flood plain as the floodwaters withdrew it follows that the assemblage represents a close approach to a single taxon slice from a terrestrial biocoenosis and allows interpretations to be made about the autecology social behavior age composition and community structure of titanotheres decomposition of the integument and other tissues of partially buried carcasses may have been a factor contributing to the pockety nature of the sediment

taphonomy of the prosauropod dinosaur sellosaurus and its implications for carnivore faunas and feeding habits in the late triassic abstract the stubensandstein upper triassic norian is a complex system of fluvial deposits in southwest germany and yields one of the most diverse records of fossil vertebrates from the european continental triassic taphonomic data from 17 partial skeletons of the prosauropod dinosaur sellosaurus gracilis are presented with emphasis on a recently rediscovered field sketch of one particular specimen the preservational states and burial postures of individuals forming a practically monospecific prosauropod assemblage indicates in situ preservation of single specimens most likely by miring in unconsolidated fluvial sands covered by floodplain deposits shed teeth of carnivores and the mode of preservation suggest that one of the prosauropod carcasses was scavenged at least two different types of predators several individuals of a large indeterminate primitive archosaur and a phytosaur left traces of their activities during scavenging on the carcass the prosauropod carnivore tooth assemblage provides the first evidence that deep snouted phytosaurs with heterodont dentitions were capable of manipulating and feeding on large terrestrial prey moreover scavenger prey assemblages in the norian of central europe support the hypothesis that large carnivorous basal archosaurs as represented for example by rauisuchians were replaced by theropod dinosaurs in the late triassic

paleomagnetism of the callander complex and the cambrian apparent polar wander path for north america the 7 km2 circular callander alkaline complex was emplaced into anorthositic and granitic gneisses of the grenville province in the canadian shield about 575 5 ma ago at the start of the cambrian the complex has not been subsequently metamorphosed or tilted detailed alternating field and thermal step demagnetization of 252 specimens from 29 sites led to the identification of a characteristic a magnetization component with a direction of d 82 2 i 82 7 95 3 1 k 83 n 26 sites in 5 sites of mesocratic to leucocratic syenite from the core of the complex in 5 sites of fenitized host rock from its aureole and in 16 sites of lamprophyre from radiating dikes isothermal remanent magnetization tests show that the a component is retained by both magnetite and hematite in a complete spectrum of domain sizes a reversals test suggests and a contact test shows the a component to be primary its pole position at 46 3 s 121 4 e dp 5 9 dm 6 1 does not fall on published but poorly defined

on gregarious behavior in albertosaurusthis article is one of a series of papers published in this special issue on the theme albertosaurus one century ago a field party from the american museum of natural history discovered a bonebed in the upper cretaceous horseshoe canyon formation of alberta canada excavations by that museum th

sandstone body and shale body dimensions in a braided fluvial system salt wash sandstone member morrison formation garfield county utah excellent three dimensional exposures of the upper jurassic salt wash sandstone member of the morrison formation in the henry mountains area of southern utah allow measurement of the thickness and width of fluvial sandstone and shale bodies from extensive photomosaics the salt wash sandstone member is composed of fluvial channel fill abandoned channel fill and overbank flood plain strata that were deposited on a broad alluvial plain of low sinuosity sandy braided streams flowing northeast a hierarchy of sandstone and shale bodies in the salt wash sandstone member includes in ascending order trough cross bedding fining upward units mudstone intraclast conglomerates single story sandstone bodies basal conglomerate abandoned channel fill multistory sandstone bodies and overbank flood plain heterolithic strata trough cross beds have an average width thickness ratio w t of 8 5 1 in the lower interval of the salt wash sandstone member and 10 4 1 in the upper interval fining upward units are 0 5 3 0 m thick and 3 11 m wide single story sandstone bodies in the upper interval are wider and thicker than their counterparts in the lower interval based on average w t linear regression analysis and cumulative relative frequency graphs multistory sandstone bodies are composed of two to eight stories range up to 30 m thick and over 1500 m wide w t 50 1 and are also larger in the upper interval heterolithic units between sandstone bodies include abandoned channel fill w t 33 1 and overbank flood plain deposits w t 70 1 understanding w t ratios from the component parts of an ancient sandy braided stream deposit can be applied in several ways to similar strata in other basins for example to 1 determine the width of a unit when only the thickness is known 2 create correlation guidelines and maximum correlation lengths 3 aid in interpreting the controls on fluvial architecture and 4 place additional constraints on input variables to stratigraphic and fluid flow modeling the usefulness of these types of data demonstrates the need to develop more data sets from other depositional environments

taphonomy of the late cretaceous dinosaur bearing beds of the lano quarry iberian peninsula abstract the lano quarry located in the northern part of the iberian peninsula basque cantabrian region has yielded a diverse continental vertebrate assemblage from the late cretaceous late campanian to early maastrichtian the fossil assemblage consists of almost 40 species including bony fish amphibians lizards snakes turtles crocodilians dinosaurs pterosaurs and mammals lano is the most productive european vertebrate locality hitherto known from the late cretaceous the sedimentology of the lano section shows that the three associated fossiliferous beds known as l1a l1b and l2 were deposited in an alluvial system composed primarily of fluvial sands and silts the sedimentary structures are consistent with channel areas within an extensive braided river the l1a level was excavated in detail and mapped following a square metre grid system the main features of the multispecies vertebrate assemblage are as follows wide range of body size including microfossils large proportion of adult individuals rare articulated skeletal parts size sorting and dominance of small elements high spatial density long bones showing some preferential orientation variable dip variable degree of breakage and large proportion of splintering wide range of weathering and abrasion no evidence of predatory activity or chemical alteration on the basis of these features we suggest that the lano association lies between the taphonomic modes for attritional vertebrate assemblages in fluvial channels though it tends more toward the channel fill than the channel lag mode the l1a sample of lano is a heterogeneous assemblage of elements ranging from isolated bones and teeth to articulated skeletons with allochthonous and para autochthonous characteristics it consists of a mixture of vertebrates from different palaeocommunities and includes aquatic or semi aquatic elements and remains transported from a variety of habitats on the alluvial plain the dinosaur bones are commonly broken and show a greater degree of abrasion than those of freshwater vertebrates indicating that they may be allochthonous however actinopterygians amphibians pleurodiran turtles and eusuchian crocodilians are interpreted as being para autochthonous palaeobatrachid frogs bothremydid turtles and alligatoroid crocodilians are the most relatively abundant vertebrates of the lano fossil assemblage the occurrence of pelomedusid turtles and crocodilians is indicative of an intertropical warm climate

early and late paleozoic remagnetization of the cambrian peerless formation colorado abstract the upper cambrian peerless formation in central colorado contains two secondary components of magnetization the dominant component was removed during initial af demagnetization of specimens whereas a weaker component was removed during subsequent thermal demagnetization irm acquisition experiments suggest that the dominant component has low coercivity whereas the weaker component has high coercivity the latter component has southeasterly and shallow directions and the corresponding pole position is located at 40 0 n 134 5 e the high coercivity blocking temperatures over 600 c and petrographic evidence suggest this component resides in diagenetic hematite the magnetization is interpreted as a crm acquired in the late paleozoic the low coercivity component directions fall on a great circle that passes through the modern field direction and two modes at 107 e 10 and 287 e 10 this component is interpreted as a vector sum of two antipodal crms and a modern vrm the pole position 10 n 150 e suggests acquisition in the early paleozoic and the remanence resides either in maghemite or in diagenetic magnetite

taphonomic modes in the maastrichtian continental deposits of the haţeg basin romania palaeoecological and palaeobiological inferences abstract the uppermost cretaceous continental deposits of the ha eg basin sw romania have yielded a high diversity vertebrate assemblage including the dwarf insular dinosaurs of nopcsa in 1902 franz nopcsa was the first to comment on the preservation patterns of vertebrate fossils suggesting that the most important fossil accumulations which he simply referred to as fossiliferous pockets were the result of the predatory activity of crocodilians crocodilian feeding grounds recent investigations of the fossil occurrences within the ha eg basin revealed a much wider range of taphonomic modes from microfossil bonebeds to isolated partially articulated skeletons than previously believed the survey of the vertebrate accumulation types and their sedimentary context documents a wide range of processes responsible for their genesis operating within a fluvial dominated upland setting study of the individual fossil accumulations yields important information on the palaeoecology composition of local biocenoses trophic interactions and palaeobiology social behaviour habitat preferences of the ha eg fossil assemblage

paleomagnetism of the catoctin volcanic province a new vendian cambrian apparent polar wander path for north america the vendian cambrian segment of the lauretian apparent polar wander path apwp has been poorly constrained and the subject of some controversy the catoctin volcanic province in central virginia is well dated at 570 35 ma rb sr and 597 18 ma u pb and therefore presented an excellent paleomagnetic target for resolving the laurentian vendian cambrian apwp a total of 206 samples from 32 sites were collected from the catoctin basalts feeder dikes and sills the study revealed three ancient directions of magnetization the youngest c component fails the fold test and yielded a characteristic in situ direction of d 147 i 44 k 21 95 9 the corresponding paleopole falls along the middle ordovician segment of the laurentian apwp and we consider this component to be the result of a taconic remagnetization the second component the b component is carried by hematite exhibits dual polarities and passes a fold test the tilt corrected b component characteristic direction is d 92 i 17 k 16 95 13 the corresponding paleopole at 4 s 193 e falls near a well established late cambrian 505 ma pole for laurentia and we consider this component to be a remagnetization during a late cambrian tectonic event in the central appalachians the third component isolated in the catoctin basalts the a component yields a tilt corrected mean of d 68 i 84 k 59 95 9 this component passes a fold and reversal test a suite of samples was collected from two catoctin feeder dikes and surrounding country rocks that yield a positive baked contact test the a pole at 43 s 128 e falls significantly away from previously proposed vendian poles for laurentia a reevaluation of previous paleomagnetic studies from coeval rock units reveals similarly steep directions and leads us to propose a new apwp this new apw track indicates that laurentia was located near the pole during the interval 615 580 ma and drifted rapidly 16 cm yr 1 toward its late cambrian equatorial position

taphonomy of jack s birthday site a diverse dinosaur bonebed from the upper cretaceous two medicine formation of montana jack s birthday site is a diverse vertebrate assemblage from the upper two medicine formation of western montana age is roughly 74 ma the site covers roughly 3000 m2 and excavations over 140 m2 a large bone sample 1600 skeletal elements allowed statistical evaluation of the preservational and compositional variation within the site evidence including sedimentary facies plant and invertebrate fossils and bone orientation and condition indicates jack s birthday site represents part of a small shallow floodplain lake lithologies and fossil preservation vary from northwest to southeast over a distance of 50 m this variation represents a transition from lake through shoreline to marginal shoreline floodplain environments containing ten dinosaur taxa and a variety of non dinosaurs jack s birthday site provides one of the best single faunal samples of the region the vertebrate assemblage includes two taphonomic fractions the first consisting of attritional predominantly isolated and allochthonous elements represents a time averaged assemblage the other consists of associated parautochthonous remains restricted to a single horizon taxa represented by associated remains include three iguanodontoids hypacrosaurus prosaurolophus and gryposaurus and the theropod troodon associated individuals of these taxa have non random distributions within the site fisher s exact test p 0 01 and observed taxonomic clustering may reflect group behavior and or event mortality the four or more troodon represent the first described multi individual troodontid occurrence the diversity and spatial complexity of the parautochthonous fraction of the birthday site assemblage is difficult to explain discussion of possible event mortality mechanisms focuses on three drought botulism and cyanobacterial toxicosis these share an ability to act over an ecologically significant period of time affect a variety of species and concentrate mortality along water sources aspects that may have been important in generating the birthday site assemblage evidence at the site favors drought or perhaps a drought botulism hypothesis however taxonomic clusters could represent completely separate events with a variety of causes

preservation of exceptional vertebrate assemblages in middle permian fluviolacustrine mudstones of kotel nich russia stratigraphy sedimentology and taphonomy the kotel nich locality in european russia has long been a rich source of high quality tetrapod fossils including pareiasaurs dicynodonts gorgonopsians and theriodonts the age of the kotel nich locality has been debated but it corresponds to early severodvinian in the russian stratigraphic scheme equivalent to the late capitanian late middle permian on the international time scale remarkably the majority of specimens are complete quite unlike those from most russian permo triassic red bed localities commonest of all are 1 2 metre long pareiasaur skeletons of the genus deltavjatia preserved in hollows on top of a consolidated palaeosol horizon previous taphonomic scenarios in the russian literature have included suggestions that the animals were overwhelmed beneath sand dunes mired in soft fluviatile sediments caught at the bottom of a deep lake trapped in burrows or dumped in fluviatile scours it is probable that the pareiasaurs were searching for water in a time of catastrophic aridification and died weakened in shallow hollows in this case we also emphasise the importance of floodplain microtopography in creating the sedimentary conditions necessary for the preservation of exceptional vertebrate assemblages in a slowly aggrading fluviolacustrine setting

compositions of chromite associated minerals and parental magmas of podiform chromite deposits the role of slab contamination of asthenospheric melts in suprasubduction zone environments abstract podiform chromitites in the mantle sections of ophiolites belong to either high cr metallurgical or high al refractory varieties their highly variable compositions are reflected by different cr s 100cr cr al and cr2o3 and al2o3 contents of the chromite falling in the boninitic and morb fields respectively parental magmas of high cr chromitites have higher sc mn co and ni and lower ti v zn and ga concentrations than morb melts their trace element patterns are similar to those of boninites except for ni and zn in contrast high al chromitites have parental magmas characterized by generally flat morb normalized patterns showing slight enrichments in v mn and co and depletion in ni and zn regardless of their compositions both types of chromitites have chondrite normalized platinum group element pge patterns showing enrichment in ipge and depletion in ppge a variety of platinum group minerals are typically present in both types occurring either as euhedral inclusions or along fractures in chromite grains these minerals have a wide span of re os isotopic compositions reflecting a variety of origins there is a diversity of unusual minerals and mineral inclusions associated with podiform chromitites the presence of these minerals suggest that grains of amphibolite plagioclase amphibole and zircon and eclogite coesite kyanite and garnet were present in the magmas from which chromite crystallized multiphase mineral inclusions demonstrate that podiform chromitites form from hydrous mafic magmas in suprasubduction zone environments ssz we propose a new model in which chromitite formation was involved in intra oceanic subduction zones initiated in closing oceanic basins continued subduction carries oceanic and possibly continental crustal materials to deep levels where they are metamorphosed under greenschist amphibolite and eclogite facies conditions the tearing and breakoff of the subducted slab possibly along the transitional contact between amphibolites and eclogites create a slab window through which the underlying asthenosphere rises and melts to generate cr rich mafic magmas these upward migrating magmas pass through the subduction zone and assimilate the subducted slab as a result of slab contamination these magmas become more siliceous more oxidized and more hydrous rapidly triggering chromite crystallization minute grains of chromite are suspended in the upward moving magmas as they migrate through the overlying metasomatized mantle wedge such chromite bearing magmas eventually deposit chromite in magma conduits in the uppermost mantle close to the moho where the upward flow changes from vertical to subhorizontal and velocity is greatly reduced highly reduced and ultrahigh pressure minerals including diamonds are reported in literature both in podiform chromitites and host peridotites of ophiolites some of these minerals in association with host peridotites may have been brought by the uprising asthenosphere at mid oceanic ridges due to the mantle convection it is also possible that some diamonds may have formed in the subducted slab below about 150 km some minerals of subducted slabs are preserved because they are encapsulated in chromite grains where they are protected from the ssz melts some of these ssz mantle wedges are emplaced on land to become podiform chromitite bearing ophiolites

paleomagnetic and petrographic evidence for early magnetizations in successive terra rosa paleosols lower pennsylvanian black prince limestone arizona an early synsedimentary chemical remanent magnetization crm is found in and below terra rosa paleosols which cap regressive carbonate cycles in the pennsylvanian morrowan black prince limestone in southeastern arizona authigenic hematite occurring in fractures between soil nodules in liesegang bands and replacing allochems is abundant in specific horizons and is related to soil forming processes paleomagnetic analysis of many specimens from the paleosol horizons reveals both northwesterly and shallow and southeasterly and shallow directions these unidirectional northwesterly and southeasterly magnetizations are interpreted to be antipodal equivalents and show a stratigraphic distribution with at least three reversals the mean direction declination 308 inclination 9 corresponds to a pole position at latitude 34 n longitude 143 e similar to other pre kiaman carboniferous poles some specimens also contain multicomponent magnetizations those with dual polarities or with curved thermal demagnetization trajectories and are interpreted to be the result of remagnetization after a reversal in the earth s field demagnetization and rock magnetic results for the reddened rocks confirm that hematite is the primary magnetic carrier in contrast to the paleosol zones the magnetization in the interbedded gray marine limestones resides in magnetite and does not exhibit stable decay terra rosa paleosols are likely to have preserved the hematite and associated magnetizations that formed as a result of soil forming processes these paleosols therefore may contain data that are useful in determining pole positions and validating polarity zonations

marine transgressions and the evolution of cretaceous dinosaurs fluctuations transgressions and regressions of intercon tinental sea ways during the mesozoic era affected the habitat area of coastal plains by alternately restricting the space during transgressive phases and expanding the space during regressive phases in western north america a coastal plain stretched along the eastern front of the young rocky mountains during most of the late cretaceous here we report results of a six year field study of the sediments and dinosaur remains from this coastal plain in montana that provide evidence that anagenesis characterized dinosaur evolution at this time and that the evolutionary pulse coincided with a marine transgression

vegetation climatic and floral changes at the cretaceous tertiary boundary the western interior of north america has the only known non marine sections that contain the iridium rich clay interpreted as the cretaceous tertiary k t boundary1 7 because vegetation and climate can be directly inferred from physiognomy of leaves8 15 and because leaf species typically represent low taxonomic categories studies of leaf floras in these sections provide data on the effects of a terminal cretaceous event on the land flora vegetation and climate a previous study based on detailed sampling of leaves and their dispersed cuticle16 in the raton basin provides a framework for interpretation of other leaf sequences over 20 degrees of latitude we conclude that at the boundary there were 1 high levels of extinction in the south and low levels in the north 2 major ecological disruption followed by long term vegetational changes that mimicked normal ecological succession 3 a major increase in precipitation and 4 a brief low temperature excursion which supports models of an impact winter

40ar 39ar age and correlation of the nonmarine two medicine formation upper cretaceous northwestern montana u s a the age of the nonmarine two medicine formation of northwestern montana is currently based upon correlations with k ar dated western interior ammonite zones 40ar 39ar dating of biotite and plagioclase separated from four bentonites and one crystal rich tuff permits for the first time direct determination of the age of two medicine strata biotite and plagioclase from a bentonite 10 m below the top of the two medicine formation yield concordant 40ar 39ar ages of 74 ma while biotite and plagioclase from two bentonites and a crystal rich tuff from approximately 100 m above the base of the formation cluster in age around 80 ma the total duration of two medicine deposition is estimated using these new radio isotopic ages via extrapolation of an average rock accumulation rate the new 40ar 39ar ages facilitate regional correlation of the dinosaur dominated paleofauna recovered from the two medicine formation and help constrain the timing of the claggett and bearpaw transgressions the ages support correlatio

volcanic associated nickel deposits from around the widgiemooltha dome western australia volcanic peridotitc associated nickel sulfide deposits occur in archean komatiitic flow sequences around the widgiemooltha dome in the eastern goldfields region of western australia the deposits are typically small shoots 40 volatile free al 2 o 3 2 content of metamorphic fluids and the timing of fluid access to the rocks along the eastern side of the widgiemooltha dome host rocks have undergone serpentinization and variable but generally extensive prograde talc carbonate alteration e g redross dordie rocks north and widgiemooltha 3 deposits in the north munda deposit they have experienced serpentinization with minor carbonate alteration and in addition prograde metamorphic reconstitution to forsteritc talc rich assemblages dunitic units in the west wannaway and wannaway north deposits escaped prograde serpentinization talc carbonate alteration and significant metamorphic reconstitution but have been retrogressively serpentinized sulfides from the different alteration environments show systematic mineralogical and compositional differences at all deposits peak metamorphic temperatures 550 degrees 600 degrees c resulted in reversion of sulfides to a dominant fe ni co cu bearing monosulfide solid solution accompanied by pentlanditc or fe cu intermediate solid solution in some cases most of the present ore mineralogies and textures relate to exsolution of low temperature sulfides from metamorphic monosulfide solid solution with reequilibration and recrystallization during slow postmetamorphic cooling deformation produced a tectonite fabric in the ores characterized by preferred orientation of sulfide grains and mineral layering breccia ores were formed in response to brittle deformation in host rocks and continued ductile behavior in the sulfides deformation also affected the overall configuration of the ore shoots and led to significant sulfide mobilization and ore shoot distension after allowing for the metamorphic imprint a number of primary features of the ore environment can be isolated and there is strong evidence for the prior existence of magmatic sulfides the association of ores with early formed largely dunitic units similar bulk ni cu and ni co ratios for ores from different deposits precious metal data low s se ratios and distinctive magmatic spinels in the sulfides all point to a magmatic control on the ores strong positive correlation between ni and mgo in host units and similar ni mgo ratios in both mineralized and unmineralized units suggest that sulfide liquids formed and equilibrated with the parent magma at depth before being extruded as part of olivine rich crystal mushes

vertebrate preservation in fluvial channels abstract two taphonomic modes for attritional vertebrate assemblages in channels are proposed based on the sedimentary context of the vertebrate remains and taphonomic features of the bones themselves the channel lag mode includes bones that are buried with coarse lithologies near the bases of active channels the channel fill mode occurs in fine grained to mixed fills of abandoned channels the extreme for a channel lag assemblage would be a cluster of allochthonous abraded unidentifiable fragments and the extreme for a channel fill assemblage would be a cluster of autochthonous unbraded complete skeletons between these extremes there is a broad spectrum of possible taphonomic histories for bones in channels but distinct channel lag vs channel fill modes can be recognized in fluvial deposits in different tectonic and climatic settings throughout the phanerozoic physical and biological processes that affect the different modes produce different samples of vertebrate paleocommunities with bones in the channel lag mode representing transported remains from a variety of habitats whereas channel fill assemblages are more autochthonous and habitat specific channel facies channel pattern and alluvial architecture are used to develop hypotheses concerning how the taphonomic modes relate to different scales of fluvial processes fluvial systems with numerous abandoned channels provide more sites for preservation of relatively complete fossil vertebrates in channel fills while systems that continually rework sediments by lateral migration preserve more vertebrate remains as channel lags large scale physical controls on channel pattern and fluvial architecture probably have had significant effects on the quality and quantity of the vertebrate record throughout the history of land vertebrates taphonomic modes provide a basis for comparing faunas with similar preservational histories throughout the geologic record and they can help to minimize biases in important paleobiological parameters such as diversity estimates and the timing of appearance and extinction events

biogenic magnetite from surface holocene carbonate sediments great bahama bank magnetic separates and rock magnetic tests from holocene carbonate surface sediments of the bahamas indicate that fine grained magnetite maghemite is common at or near the sediment water interface and forms a major portion of the magnetic fraction magnetite crystals range from 400 to 1000 a in diameter as observed under the transmission electron microscope tem and often occur as elongate chains or multi grain clusters crystals are very similar in dimension and grain habit to those of known biogenic origin mainly bacteria all measured grains are within the single domain stability field for magnetite based on crystal dimensions coercivity distributions are fairly broad 5 100 mt or greater likely the result of partial oxidation of the magnetic minerals no large multidomain grains were observed in the tem study individual grains occur in several shapes in the microscope image mainly hexagonal and cuboidal prismatic widespread occurrence of single domain magnetite in this isolated carbonate setting suggests that biogenic precipitation is a major contributor of early in situ depositional magnetization a contribution of magnetite from authigenic precipitation during burial has not been documented in these near surface environments

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

the plant debris beds of the early cretaceous barremian wessex formation of the isle of wight southern england their genesis and palaeontological significance abstract the early cretaceous barremian wessex formation of the isle of wight primarily represents high sinuosity fluvial but also lacustrine and terrestrial deposition on a low relief floodplain occupying half grabens with active normal faults immediately to the north plant debris beds form a very small proportion of the succession but are the main source of vertebrate fossils including dinosaurs these conspicuous but thin grey units are distributed randomly throughout the wessex formation and are of limited lateral extent the lower part of most plant debris beds comprises a poorly sorted matrix supported conglomerate the upper part of most consists of structureless mudstone which usually grades up into colour mottled but predominantly red and purple floodplain mudstones the plant debris beds contain an unusual mixture of freshwater molluscs diverse aquatic and terrestrial vertebrates and mainly terrestrial plants with a variable quality of preservation we conclude that each plant debris bed represents a locally generated sheetflood which was then transformed on the floodplain into a debris flow by the acquisition of surface material the debris flows surged into and were deposited in depressions on the alluvial plain including abandoned chute and cut off channels oxbows and ponds these units are therefore intrabasinal and interfluvial and the fossils that they contain are locally derived similar deposits of palaeontological significance have not been reported elsewhere in the literature in view of this their origin and sedimentology their palaeontological significance and the taphonomy of the flora and fauna they contain are discussed

early permian depositional environments and pond bonebeds in central archer county texas abstract the lower permian redbeds of north texas contain the oldest abundant non aquatic vertebrate fauna in the past collecting of fossils and study of their paleozoology has been emphasized with the exception of the pioneering work of olson 1958 1977 little attention was paid to sedimentological paleoecological and taphonomical aspects of the fauna this study focuses on the sedimentary framework paleoenvironment fossil content and taphonomy of the most common type of fossil occurrence the pond bonebed five sedimentary facies are recognized meanderbelt sandstones large straigt channel fill sandstones small straight channel fill sandstone interbedded facies and floodplain mudstone these are the components of small meandering river systems with local tributaries and crevasse splays pond bonebeds occur as gray claystone lenses in red floodplain mudstones deposited in oxbow lakes or swamps the fauna is largely aquatic orthacanthus ectosteorhachis paleoniscoids sagenodus or semiaquatic eryops trimerorachis archeria edaphosaurus with subordinate terrestrial elements diadectes dimetrodon fossil plants found as impressions petrifactions and charcoal are indicative of swamps psaronius and well drained soils conifers all of the organic debris accumulated gradually by biological and physical processes occasional isolated but complete vertebrate skeletons are found in the floodplain mudstones

north america s largest dinosaur trackway site implications for morrison formation paleoecology little known exposures of the upper jurassic morrison formation from the purgatoire valley of southeastern colorado have yielded the world s largest continuously mapped assemblage of dinosaur trackways body fossils include plant invertebrate and vertebrate remains indicative of predominantly fresh water conditions the tracks occur in a lacustrine sequence characterized by 1 shallow water shales 2 micritic shoreface limestones with ooids intraclasts ripple marks mud cracks and 3 minor quartzose sandstone with salt crystal casts analysis of these sedimentary facies suggests that in southeastern colorado lakes were larger and longer lived than in other morrison paleoenvironments trackway orientations and footprint depth contours pinpoint the location of the paleoshoreline at successive levels in the section detailed mapping of 1 300 footprints in bed 2 has revealed more than 100 trackways which testify to the activity of both quadrupedal and bipedal dinosaurs the respective ratio based on trackway counts is 40 60 the quadrupedal tracks are attributed to sauropods and represent the first ever discovered in north america they also exhibit the first known manus claw impressions and are in need of formal description more than 90 of the bipedal tridactyl prints lack claw impressions and are tentatively therefore referred to the ornithopoda cf gypsichnites possibly a camptosaurus the small proportion with distinct claw impressions may represent allosaurus resulting estimates of species diversity 5 and predator prey ratio 1 30 are in general agreement with the estimates of other authors based on skeletal remains and they suggest that the purgatoire river tracks may accurately reflect the composition of the dinosaur fauna distinctive groupings of parallel non overlapping trackways suggest gregarious behavior among sauropods and tridactylous forms

differentiation of the cuthbert lake ultramafic dikes and related mafic dikes in the cuthbert lake region of north central manitoba northeasterly trending ultramafic mafic dikes part of the molson dike swarm show a range of composition from gabbro to olivine hornblende pyroxenite to hornblende peridotite the major dike which is ultramafic in composition is 60 m thick olivine and chromian spinel were the earliest cumulus phases formed in a subcrustal magma chamber before the emplacement of the dikes orthopyroxene and clinopyroxene were formed following emplacement at about 1120 c plagioclase and hornblende were the latest phases to crystallize from the intercumulus melt mineralogical and chemical variations across the major dike are interpreted to have resulted from flow differentiation of multiple injections of magma carrying suspended olivine crystals olivine phenocrysts changed their compositions from about fo87 to values ranging from fo80to fo73 as a function of the amount of intercumulus melt the composition of this melt is estimated to have been basaltic a mafic dike about 10 m thick and occurring about 20 m away from the main ultramafic dike is believed to have been formed from magmas that were tapped from an upper layer overlying the olivine rich zone in a subcrustal magma chamber separation must have occurred when clinopyroxene and plagioclase appeared on the liquidus

existence of a marginal basin within the circum superior belt geochemical evidence from the churchill superior boundary in manitoba canada mafic volcanic rocks incorporated within the churchill superior boundary zone at ospwagan lake moak lake assean lake and the fox river belt constitute part of the circum superior belt major and trace element data have been obtained from mafic and ultramafic volcanic rocks from four localities the data provide a means of comparing and contrasting the geochemistry of the rocks from the portion of the circum superior belt surrounding the archean superior province in manitoba with other units from elsewhere in the belt and with rocks from the adjacent proterozoic churchill province major element geochemical data are consistent with the rocks having originally formed in a oceanic environment trace element and rare earth element data suggest that the environment was a marginal basin al2o3 tio2 ratios indicate that the magmas were derived from a mantle source by small degrees of partial melting high field strength element patterns show that the mantle source region giving rise to the rocks was relatively uniform in composition trace element mid ocean ridge basalt morb and chondrite normalized patterns indicate similarities in alkali element enrichment for the rocks at asean and ospwagan lakes virtually all the rocks have ti zr nb y and p levels morb which is consistent with the mantle source region having undergone a small degree of partial melting zr p ratios for the rocks from the fox river belt are consistently lower than those from the other localities and the assean lake rocks show slight enrichment in light rare earth elements which may suggest local compositional variability in the mantle source regions supplying the magmas to the fox river belt and the ospwagan assean and moak lake areas

minimal insect herbivory for the lower permian coprolite bone bed site of north central texas usa and comparison to other late paleozoic floras abstract an examination of 598 leaves from the lower permian late sakmarian coprolite bone bed cbb site in north central texas usa reveals low herbivory levels based on analyses of foliar surface area removed 0 25 and frequency of herbivorized leaves 15 6 these values contrast with a similar study from a somewhat younger mid artinskian nearby site where analogous values are 2 55 and 31 8 respectively as at the younger site when compared to all other co occurring plant taxa cbb pteridosperms were overwhelmingly herbivorized particularly the peltasperm autunia cf conferta and the medullosan odontopteris cf lingulata the latter preserving an exceptionally high herbivory level of 3 31 these two host plant taxa accounted for 96 8 of all herbivorized leaves and 96 4 of all leaf surface area removed by insects for the bulk flora four subgroups of feeding were documented margin feeding 70 1 of all occurrences hole feeding 24 1 and minor skeletonization earliest occurrence and galling distinctive gall types one on the midveinal region of a cf conferta and the other on a branchlet of walchia piniformis also occurring in the european early permian add to an existing but depauperate insect gall record for the pennsylvanian and permian emerging evidence indicates that herbivory intensity was spatiotemporally heterogeneous across fluvially associated landscapes during the early permian in both western euramerica texas usa and western gondwana parana basin brazil differing by an order of magnitude within each of these areas localities with the highest percentages of bulk leaf surface area removed by herbivores in both realms ranged from 2 39 to 2 97 this range approximates about a third of modern surface area removal values by insect herbivores in both subtropical to tropical floras

a sauropod skeleton associated with theropod teeth in the upper jurassic of thailand remarks on the taphonomic and palaeoecological significance of such associations abstract the association of a partial sauropod skeleton with carnosaur teeth is described from the late jurassic sao khua formation of northeastern thailand this association is reminiscent of similar instances reported from the upper jurassic of western north america and east africa and can best be explained by dismemberment of a sauropod carcass by carnosaurs this type of evidence does not indicate whether the sauropod was killed by carnosaurs or whether the carnosaurs merely acted as scavengers the sauropod skeleton carnosaur teeth association can be used as a taphonomic indicator of a lack of post mortem transportation this in turn can lead to palaeogeographical conclusions as exemplified by the case of the damparis dinosaurs late jurassic of france the occurrence of which indicates in situ immersion

the biostratigraphic importance of conchostracans in the continental triassic of the northern hemisphere conchostracans or clam shrimp order conchostraca sars are arthropods with a carapace consisting of two chitinous lateral valves triassic conchostracans range in size from 2 to 12 5 mm long and are common in deposits that formed in fresh water lakes isolated ponds and brackish areas their dessication and freeze resistant eggs can be dispersed by wind over long distances therefore many conchostracan species are distributed throughout the entire north ern hemisphere in the late permian to middle triassic interval several of these forms are also found in gondwana many wide ranging conchostracan species have short stratigraphic ranges making them excellent guide forms for subdivision of triassic time and for long range correlations the stratigraphic resolution that can be achieved with conchostracan zones is often as high as for ammonoid and conodont zones found in pelagic marine deposits this makes con chostracans the most useful group available for biostratigraphic subdivision and correlation in continental lake deposits upper triassic gondwanan conchostracan faunas are different from conchostracan faunas of the northern hemisphere in the norian some slight provincialism can be observed even within the northern hemisphere for example the sevatian redondestheria seems to be restricted to north america and acadiestheriella n gen so far has been found only in the sevatian deposits from the fundy basin of southeastern canada here we establish a con chostracan zonation for the changhsingian late permian to hettangian early jurassic of the northernhemispherethat forthemostpart isverywellcorrelatedwiththemarinescale thiszona tion is especially robust for the changhsingian to early anisian late ladinian to cordevolian and rhaetian to hettangian intervals for most of the middle and upper triassic this zonation is still preliminary five new genera six new species and a new subspecies of conchostracans are described that are stratigraphically important half of the eight stage boundaries of the triassic have been defined by a bio event within a marine global stratotype and point gssp locality and these definitions have been accepted by both the international subcommission on triassic stratigra phy and the international commission on stratigra phy the remaining four stage boundaries are nearing final definition in the lower triassic both the base of the induan priority brahmanian stage base of triassic and the base of the next younger olenekian stage have been firmly defined in the middle triassic there is wide agree ment that the defining species for the base of the anisian stage should be chiosella timorensis in the gssp candidate site at desli caira romania but there has not yet been a formal vote on this the base of the overlying ladinian stage however has been firmly defined in the upper triassic the base of the carnian has been firmly likewise defined but there is not yet a final defi nition for the boundaries of the overlying norian and rhaetian stages a consensus has not been reached on a defining species for the base of the norian or its gssp locality but all of the different proposals under consideration do at least fall within a rather narrow stratigraphic interval for the base of the rhaetian misikella posthernsteini kozur mock has been chosen as the defining species by the international working group on the rhaetian stage and the gssp candidate locality at steinbergkogel austria has been studied in detail by a group under the leadership of l krystyn vienna and presented to the participants of the international conference on upper triassic sub divisions zonations and events in bad goisern in the autumn of 2008 the base of the overlying hettangian stage base of the jurassic has been defined so far only by a working group as the fad first appearance datum of psiloceras spelae guex taylor rakus bucher the final definition of the triassic stages within marine gssp sections will be completed in the near future but more than 50 of known triassic rocks are of continental origin therefore the main task of triassic stratigraphers in thefuture will besubdivid ing and correlating terrestrial strata both between

a theropod dinosaur feeding site from the upper jurassic of the junggar basin nw china abstract direct evidence for theropod feeding behaviour is rare in the fossil record and mainly limited to bite marks on bones here we describe a dinosaur assemblage from the lower part of the early late jurassic qigu formation at liuhuanggou gorge southern junggar basin nw china which has yielded fragmentary remains of a large sauropod as well as four teeth of large sized theropods and one tooth of a small sized theropod the sauropod bones show numerous bite marks that can be confidently linked to the large sized theropod probably a metriacanthosaurid the abundance of the theropod bite marks on a single skeleton indicates that the sauropod carcass was probably fed on extensively some bones are completely crushed and occur in patches of hundreds of tiny individual fragments indicating that they were trampled repeatedly by large dinosaurs both the feeding traces and the trampling suggests that the sauropod carcass was exposed for a substantial amount of time before it was finally buried within the deposits of a well drained floodplain the traces and the distinct preservation of the sauropod remains offer valuable insights into the feeding behaviour of large sized theropods within late jurassic continental ecosystems

hadrosaurid and lambeosaurid bone beds from the upper cretaceous two medicine formation of montana taphonomic and biologic implications numerous dinosaur bone beds have been found in the upper cretaceous two medicine formation taphonomy and size frequency profiles for the most common skeletal elements of six predominantly hadrosaurid and or lambeosaurid assemblages were compared all six localities are single highly concentrated bone horizons within silty mudstones most are monospecific with some degree of skeletal association parautochthonous and likely the result of mass mortality four are associated with small lacustrine or waterhole environments and may be the result of drought related mortality within the two medicine formation drought was apparently a common mechanism for generating fossil assemblages both hadrosaurids and lambeosaurids appear to have been gregarious lack of association between small total length 3 m and larger individuals suggests either that juvenile growth rates were as rapid as large ungulates or less likely that juveniles had a period of noninteraction with adults perhaps dwelling in strictly ju

taphonomy of debris flow hosted dinosaur bonebeds at dalton wells utah lower cretaceous cedar mountain formation usa abstract a taphonomic study of the lower cretaceous dalton wells dw dinosaur bonebeds near moab utah provides insight into the origins preservational biases and paleobiological significance of one of the richest and most diverse early cretaceous dinosaur sites known the bonebeds occur in a stacked succession of debris flows at the base of the yellow cat member of the cedar mountain formation which was deposited in a seasonally dry alluvial lacustrine setting although only 5 of the locality has been collected more than 4200 bones were recovered representing an assemblage overwhelmingly dominated by dinosaurs with a minimum of 67 individuals that represent at least eight genera the assemblage also includes eight elements from four non dinosaurian reptiles the dinosaur fauna is sauropod dominated mni minimum number of individuals 41 a basal macronarian mni 15 venenosaurus mni 3 a camarasaurid mni 2 and a large number mni 21 of generically unassigned sauropod elements other dinosaurs include the theropods utahraptor mni 9 nedcolbertia mni 2 a possible ornithomimid mni 2 plus a large iguanodontid mni 4 and the ankylosaurid gastonia mni 9 patterns of skeletal articulation and clustering ontogenetic representation and bone surface modification indicate that the assemblage accumulated and was exposed for more than a year as the result one or more multiple mass mortality events likely droughts that culled large numbers of subadults from the biocoenose carcasses and disarticulated elements were reworked then later transported a short distance and buried by a succession of debris flows skeletal representation data patterns of sorting breakage burrows abrasion and scratch marks provide evidence for sorting trampling and scavenging prior to debris flow reworking pre debris flow sorting is attributed to earlier hydraulic winnowing of easily transported elements the intensity and thoroughness of breakage involving 97 of the elements suggest highly focused high load impacts compatible with trampling by sauropods and iguanodontids lightly abraded and vertically displaced elements indicate episodes of trampling in soft mud trampling occurred before and after debris flow transport theropod tooth marks are uncommon but bone scavenging by osteophagous insects was common and severe resulting in substantial damage to articular surfaces comparisons of dw and other debris flow hosted bonebeds indicate that there are few consistent patterns among fossil assemblage and bone modification data however there are numerous similarities in the geological and spatial taphonomy datasets from these sites resulting from the similar physico hydraulic conditions under which elements were transported reworked and buried geologically and taphonomically dalton wells is similar to the blagoveshchensk monodominant hadrosaur bonebed in the udurchukan formation of eastern russia which also is interpreted as a debris flow hyperconcentrated flow deposit dalton wells also shares geologic and taphonomic characteristics with four bonebeds southeast of the town of green river utah and all occur at the base of the yellow cat member the uniform stratigraphic occurrences of the dalton wells blagoveshchensk and the green river sites resting on an unconformity and their shared sedimentologic and taphonomic features indicate that these sites originated in response to similar tectonic depositional and biostratinomic factors

petrogenesis of ultramafic and mafic rocks of the thompson nickel belt manitoba abundant sill like bodies of serpentinized ultramafic rocks with associated nickel sulfide deposits are found on the western side of the thompson nickel belt near the moak lake setting lake cataclastic fault zone the ultramafic rocks range in composition from dunite to orthopyroxenite and feature variable alteration chemical variation across the bodies is suggestive of in situ differentiation controlled mainly by olivine and orthopyroxene relative abundances of some elements incompatible for olivine and orthopyroxene suggest a parental liquid of komatiitic affinity ultramafic and mafic rocks are petrogenetically linked a high degree of partial melting of mantle material and subsequent low pressure crystal fractionation are responsible for the spectrum of composition from ultramafic to mafic

observations on elephant mortality and bones in water holes an unusually severe drought in 1982 led to a temporary die off of elephants at a natural water source in hwange national park zimbabwe compared to living populations the age structure of the animals killed by drought is strongly biased toward 2 to 8 year old animals however the fresh carcasses of these young elephants were commingled with weathered remains of adults that had died earlier creating a mixed skeletal sample whose age structure was much closer to that of living populations observations of elephant bones that have accumulated due to natural mortality at water holes might provide analogs for paleoecological interpretations of fossil proboscidean assemblages

vertebrate taphonomy and paleoecology in an upper pleistocene tank deposit of paraiba brazil taphonomic modes evidence of temporal and spatial resolutions and paleoecological patterns of the brazilian intertropical region abstract curimatas paleontological site cps preserved one of the most iconic fossil assemblages of late pleistocene vertebrates of brazil fossils were collected in a tank deposit a singular type of quaternary vertebrate bearing deposit of south america in this work a detailed taphonomic study of the tank assemblage of cps is presented this analysis also provides taphonomic and paleoecological data obtained through the application of common multivariate techniques and provides estimates of time and spatial resolution for tank deposits the results show that although the cps assemblage has experienced an array of taphonomic processes the long distance transport was the main process controlling the taphonomic pathway of the thanatocoenosis during the biostratinomic phase and was responsible for the co occurrence of other processes such as abrasion fragmentation and bioclastic sorting the origin of the taphonomic modes of vertebrates in the tank deposit of cps may have been controlled by three major taphonomic phenomena i a taphonomic bias towards the large bodied size ii long time span of transportation towards the final burial environment and iii some degree of reworking furthermore the analysis of these taphonomic modes supports a previous hypothesis although taphonomic biases affect the origin of tank assemblages paleoecological patterns can be preserved with considerable fidelity the time resolution in tank accumulations is of the order of 10 3 to 104 years and their spatial resolution seems to be from local to regional

theropod trackways associated with a gallimimus foot skeleton from the nemegt formation mongolia abstract a theropod tracksite was discovered in the nemegt formation maastrichtian at bugiin tsav mongolia by the korea mongolia international dinosaur project in 2009 a total of 67 tracks 14 trackways one didactylous 13 tridactylous and 12 isolated tracks belonging to four ichnomorphotypes were mapped on a single horizon this indicates at least four different theropod trackmakers lived in the same area at the same time this tracksite consists of laminated gray mudstone yellowish brown siltstone couplets interbedded with eolian yellowish brown sandstone deposited on a distal floodplain abundant footprints with v shaped profiles cross section within in the vertical section indicate that dinosaurs repeatedly walked across in this area before the discovery of the tracks the site was illegally excavated by fossil poachers a widespread problem in the gobi desert during excavation of the track horizon a clenched inclined gallimimus foot skeleton was found in the mudstone extended down 20 cm below the track bearing sandstone layer the occurrence of tracks closely associated with body fossils is unusual and taphonomically intriguing it is possible that the foot skeleton represents an animal that died in its tracks however the depth of the foot in mud is probably too shallow for the animal to have been mired sedimentological and taphonomic evidence also suggests that the pes of gallimimus may have passed straight through the track bearing sandstone layer the inclined right pes indicates that the body lay on its left side on the substrate during decomposition in the mud all digits were flexed but the distal phalanges were stuck and anchored in the stiff lower mud consequently as more proximal phalanges were able to accommodate flexing they were pulled away and dislocated from the anchored distal phalanges subsequent trampling by dinosaurs in the track bearing sandstone would have further distorted the underlying foot

the dinosaur fauna of the sao khua formation of thailand and the beginning of the cretaceous radiation of dinosaurs in asia abstract the most abundant and most diverse dinosaur remains hitherto found in thailand come from the sao khua formation now considered pre aptian early cretaceous in age this assemblage includes theropods the early and primitive tyrannosaurid siamotyrannus isanensis an early but relatively advanced ornithomimosaur the enigmatic siamosaurus suteethorni and possibly another very small theropod and sauropods phuwiangosaurus sirindhornae and another poorly known taxon the sao khua fauna which includes neither psittacosaurus nor iguanodontids seems to be older than any of the vertebrate assemblages from the gobi basin several of the dinosaurs from the sao khua formation may be close to the origin of groups that later played an important part in the dinosaur faunas of asia nemegtosaurid sauropods or both asia and north america tyrannosaurids ornithomimids

absolute dating of dedolomitization and the origin of magnetization in the cambrian morgan creek limestone central texas goethite associated with dedolomite in the morgan creek limestone in central texas carries a chemical remanent magnetization crm the pole position 88 n 96 w k 67 95 2 7 which is close to that of the modern pole and the fact that only normal directions are present suggest that the component is a post brunhes 700 000 yr crm dedolomite is common in the morgan creek and consists of calcite rhombohedra with relict dolomite goethite occurs surrounding the rhombs and in rhombic zones within the crystals the goethite precipitated when iron was released from ferroan dolomite during the dedolomitization process the paleomagnetic data therefore date the dedolomitization process as modern dedolomitization is probably related to surface weathering of the morgan creek in addition to goethite associated with dedolomite the morgan creek contains hematite replacing fossils and glauconite and detrital hematite the morgan creek also contains three other magnetic components one of these components is a viscous remanent magnetization aligned with the present magnetic field another component is a triassic jurassic crm residing in hematite a fourth component in the morgan creek is an early paleozoic magnetization residing in hematite and minor magnetite and represents the vector addition of a detrital remanent magnetization and one or more crms the results of this study demonstrate that paleomagnetic and petrographic techniques can be used to date a diagenetic event and also illustrate the complex nature of magnetization in a sedimentary unit

growth interruptions in silicified conifer woods from the upper cretaceous two medicine formation montana usa implications for palaeoclimate and dinosaur palaeoecology abstract taphonomic studies suggest that most dinosaur bone assemblages in the upper cretaceous campanian two medicine formation of montana originated from drought induced mass mortalities on the floodplain this hypothesis is tested further by studying intra annual growth patterns in silicified woods of cupressaceous taxodiaceous conifers found in association with dinosaur bone material at a palaeolatitude of 48 n true growth rings are completely absent but growth interruptions characterised by concentric variably persistent zones 1 8 latewood cells wide are common interruptions are irregularly spaced so that for example four interruptions may occur along a radius of only 25 cells in one specimen whilst in another specimen a radius more than 650 cells wide may completely lack interruptions irregular growth patterns like this occur in upper cretaceous woods across a broad latitudinal belt in the us western interior demonstrating that they resulted from regional climatic forcing rather than localised phenomena growth interruptions record the occurrence of short term aperiodic disturbances to tree growth under an equable megathermal climate that was otherwise favourable for continuous year round cambial activity the only probable cause of growth interruption formation were drought induced fluctuations in the water table and resultant water stress growth patterns suggest that sufficient water for uninhibited growth was continuously available for years at a time but when water stress did occur it did so repeatedly over a very few months comparison with present day east africa where trees show very similar growth patterns implies that the equable but erratically humid environment of the late cretaceous western interior was exactly the kind of setting where mass mortalities amongst megafauna might be expected like east africa this environment would have had sufficient carrying capacity to permit large herds of megafauna to develop under normal conditions but when repeated phases of droughts struck such populations would have been highly vulnerable

circum iapetus paleogeography of the precambrian cambrian transition with a new paleomagnetic constraint from laurentia abstract the paleogeography of the precambrian cambrian transition is still poorly known but is fundamental for understanding late neoproterozoic climate extremes and the spatial associations of the rapidly evolving ediacaran and cambrian fauna this period has also been proposed to host unusual geodynamic events such as rapid plate motions and or the bulk tumbling of the earth with respect to its spin axis called true polar wander tpw new paleomagnetic and 40ar 39ar geochronologic results have been obtained from a pair of shallowly emplaced syenitic intrusions in western quebec the mont rigaud and the chatham grenville stocks are related to a failed rift arm of the iapetus ocean both intrusions bear hornblendes which provide overlapping 40ar 39ar plateau ages of 533 2 1 1 ma mont rigaud and 531 4 3 4 ma chatham grenville corresponding to early cambrian nemakit daldynian time characteristic paleomagnetic reversed directions from both intrusions are easterly and shallow d 89 3 i 30 1 95 6 2 k 38 8 n 15 sites and the mont rigaud intrusion also carries antipodal normal polarity directions the combined result yields a north paleopole at location 11 9 s 184 6 e dp 3 8 dm 6 9 placing the montreal region at 16 4 s paleolatitude in the early cambrian in good agreement with late ediacaran and middle to late cambrian paleomagnetic results from laurentia laurentia likely resided at low southerly paleolatitudes throughout the cambrian ruling out a major inertial interchange tpw event for early to middle cambrian time a comparison of late ediacaran to middle cambrian paleomagnetic results from laurentia baltica siberia and elements of west gondwana implies that by early cambrian time a large paleolatitudinal gap existed between laurentia and its presumed conjugate rift margins thus placing a wide iapetus ocean between them the position of baltica within the circum iapetus paleogeography is contentious due to differing interpretations of the few paleomagnetic results during ediacaran time laurentia underwent large apparent polar wander that is manifested as motion from low latitude at 615 ma to the south polar region at 590 575 ma and then rapidly back to low latitude by 565 550 ma the large and perhaps rapid apparent polar wander of laurentia and other continents in the ediacaran remains enigmatic and controversial

stratigraphic framework of upper pennsylvanian and lower permian marine to continental transition wichita falls lawton and sherman quadrangles north central texas approximately 1 900 ft 580 m of continental rocks of latest virgilian wolfcampian and early leonardian age are exposed in an area of about 3 800 mi2 9 900 km2 between the brazos and red rivers of north central texas the stratigraphic complexity of these strata has impeded internal correlation and mapping since the rocks were first described by w f cummins in the late 19th century precise correlation of this discontinuously stratified fluvial sequence with well defined limestone bounded fluvial deltaic and marine formations to the south has been hampered because of 1 the pronounced change in lithology that accompanies this marked facies transition 2 a shift in strike of approximately 65 that coincides with a change in facies t act thus amplifying the stratigraphic complexity of the region and 3 generally poor exposure of the gently inclined strata the continental sequence is composed of approximately 25 major and numerous minor upward fining principally fluviogenic cycles sandstone units 5 60 ft or 1 5 18 m thick mark the bases of these cycles and occur as regionally persistent zones with multistory and multilateral geometry these generally resistant cuesta forming units interfinger with limestone bearing strata or are separated from them along strike by intervening zones of red mudstone the fine grained upper portion of the cycles 10 to 100 ft or 3 to 30 m thick is predominantly concretionary red mudstone although gray and variegated claystone lenses thin siltstone and sandstone beds and lenticular and channel fill conglomerates are characteristic precise mapping of sandstone units and correlation with prominent limestone pinch outs have permitted a stratigraphic tie with the marine section of the colorado and brazos river valleys continental rocks are divided into the bowie and wichita groups equivalent marine strata are divided into the cisco and albany groups formations have been defined in each group to allow a maximum degree of intergroup correlation end of article last page 145

direct dating of ultramafic sills and mafic intrusions associated with ni sulfide mineralization in the thompson nickel belt manitoba canada the paleoproterozoic thompson nickel belt a segment of the northwest margin of the archean superior craton in manitoba is one of the largest nickel producing regions in the world and the second largest ni cu pge platinum group elements mining camp in canada after sudbury the nickel sulfide ores are hosted in or associated with ultramafic sills of komatiitic affinity that were emplaced into sulfur rich metasedimentary rocks of the ospwagan group and subsequently strongly deformed and metamorphosed amphibolite to granulite facies during the trans hudson orogeny a u pb zircon age of 1880 2 1 4 ma for a metaperidotite olivine orthopyroxenite from the upper part of a boudinaged ultramafic sill at the pipe 2 deposit is interpreted as the age of crystallization of the intrusion the first age from an ultramafic sill containing mined nickel sulfide in the thompson nickel belt this age confirms a direct petrogenetic relationship between ni cu pge mineralization and widespread mafic ultramafic magmatic activity molson igneous events at ca 1 88 ga along the superior province craton margin e g thompson nickel belt fox river belt cape smith belt new quebec orogen at the south pit of the thompson mine a u pb zircon age of 1860 7 0 7 ma for a composite mafic intrusion garnet amphibolite to layered metagabbro identifies a new age of mafic magmatic activity in the thompson nickel belt that is unrelated to nickel sulfide mineralization the thermal effects of the trans hudson orogeny are recorded by a range of zircon dates and ca 1760 ma metamorphic titanite from the south pit intrusion and are consistent with interpretations that regional metamorphism occurred as a single progressive event the results of this study open up the possibility of using the high precision u pb geochronology of mineralized ultramafic rocks to precisely constrain the duration of mafic ultramafic magmatism in the thompson nickel belt and assess potential age differences between ultramafic sills across and along strike of this world class nickel metallotect

taphonomy of the lower permian geraldine bonebed in archer county texas abstract lower permian admiral formation redbeds in north texas are famous for their vertebrate fauna this paper provides a detailed taphonomic analysis of the geraldine bonebed in central archer county texas one of the most important fossil vertebrate occurrences in the region the geraldine bonebed is situated in the floodbasin facies red and gray mudstones with abundant psaronius roots of a small meandering river system such basins were covered with a dense swamp forest with a high diversity of vertebrates the geraldine bonebed has yielded from an area of 30 m 2 44 partly articulated skeletons of four genera of tetrapods and the remains of another eight vertebrate taxa the bones lie on a layer of fern and conifer foliage and wood intermingled with fossil charcoal the sediment the occurrence of wasserleichen and the skeleton orientation indicate post mortem transportation and deposition in water a single mass death event which could have been a forest fire drove the animals into a pond where they perished carcasses floating in water together with plant debris were concentrated by wind induced drift into this exceptional fossil deposit a recent example of this process of bonebed formation after mass death was described by weigelt 1927 from the texas gulf coast

lacustrine varve formation through time abstract studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes if the bottom waters of a lake are partly or totally anoxic the seasonally deposited materials are preserved as annual groupings of laminae varves common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin precipitated carbonate minerals diatom frustules iron rich and manganese rich flocs autochthonous organic detritus and autochthonous and allochthonous materials resuspended from the bottom the style of varving has changed over geologic time reflecting changes in biologic evolution and types of materials available precipitated iron rich laminations were common in the middle precambrian graded sets of clastic organic laminations persisted through the precambrian prior to the evolution of bioturbating benthic organisms glaciolacustrine varves appear to have retained their distinctive character through time carbonate rich varves occurred sporadically in the precambrian and phanerozoic with the exception of diatoms major components of modern lacustrine varves were present through the paleozoic and mesozoic and yet varves are rare in strata of these ages and may have accumulated in marine to brackish water environments diatoms were introduced into lacustrine systems in early tertiary time and are common components of varves from then on diatom laminae combined with a greater chance for geologic preservation of younger lake deposits have increased the number of geologically young occurrences of varved sediments however seasonal associations of modern varve components and the processes they represent are present in ancient deposits and provide clues to the interpretation of ancient environments

revisiting the equable climate problem during the late cretaceous greenhouse using paleosol carbonate clumped isotope temperatures from the campanian of the western interior basin usa abstract greenhouse climates such as the late cretaceous period provide important reference frames for understanding modern anthropogenic climate change upper cretaceous terrestrial climate proxies have been interpreted as evidence for equable climates with reduced seasonal variations in temperature however climate models have largely failed to reproduce these reconstructions unless parameters such as atmospheric co2 concentrations are set to unreasonable values to help resolve such model proxy disagreements we reconstruct mean annual range in temperature mart for the campanian 75 ma kaiparowits south central utah and two medicine northwest montana formations using warmest mean monthly temperature reconstructions from the clumped isotope composition of paleosol carbonate nodules and reconstructions of local mean annual air temperatures from other methods an evaluation of the applicability of bulk elemental soil geochemistry temperature proxies in these deposits supports the use of previous leaf physiognomy based estimates of mean annual temperature for our mart reconstructions we test the validity of several common assumptions made in reconstructing mart in two novel ways first mart is commonly calculated as twice the difference between local mean annual air temperature and warmest mean monthly temperature and we validate this method by estimating modern mart for a range of environments using climate reanalysis data second we constrain the effect of radiative soil heating on our soil carbonate temperature estimates by showing that for most environments likely to be preserved in the geologic record summer soil temperatures are 9 c larger than previous proxy reconstructions of late cretaceous mart these results add to a growing body of literature showing that terrestrial mart during ancient greenhouse periods was not significantly different from modern seasonal temperature variations finally the similarity in mart between the kaiparowits and two medicine formations suggests that latitudinal changes in mart did not contribute to the faunal provincialism that has been proposed by some paleontologists

oxygen and strontium isotopes from fossil shark teeth environmental and ecological implications for late palaeozoic european basins article i nfo fossil shark remains occur in both marine and nonmarine late palaeozoic deposits therefore their palaeo ecology is controversial the oxygen and strontium isotopic composition of biogenic fluorapatite in 179 teeth scales and spines predominantly of hybodontid lissodus and xenacanthiform orthacanthus xenacanthus bohemiacanthus triodus sharks from various late carboniferous moscovian to early permian artinskian basins of europe are used as ecological tracers to decipher diadromous or obligate freshwater lifestyle of the investigated taxa the 18 op values of the different shark teeth range from 11 7 to 20 2 within the different basins with mean values of 16 9 0 5 for the bohemian massif 16 2 0 8 for eastern germany 18 2 1 0 for southwestern germany 18 5 0 7 for southern central spain 17 6 0 4 for