superimposed tectono metamorphic episodes of jurassic and eocene age in the jadeite uplift myanmar as revealed by 40ar 39ar dating abstract the myanmar jadeite uplift forms an important link between the indo burma range and the tagaung myitkyina belt two contrasting ages of jurassic 152 4 1 5 ma of glaucophane from blueschist and eocene 44 8 1 1 and 45 0 1 3 ma of phengitic muscovites from quartz schists in the uplift were yielded using 40 ar 39 ar dating the jurassic age of the glaucophane even older than the forming age of the jadeitite from recent relevant literatures and for the reason of possible excess argon involved is interpreted as the lower limit of the subduction age previous studies correlated this subduction with the woyla intra oceanic arc or the incertus arc to the west the eocene ages of phengitic muscovites are interpreted as the time of an intra continental shearing deformation event against the timing of hp lt metamorphism as previously suggested combined with other studies it is suggested that the tagaung myitkyina belt and the indo burma range belonged to a single belt which has been separated by the sagaing fault leaving the jadeite uplift straddling along the fault between the belt and the range we propose a rapid exhumation model for the myanmar jadeitite at 45 ma coeval with onset of the sagaing fault

synopsis of late palaeozoic and mesozoic terrane accretion within the cordillera of western north america and discussion establishing the paleogeographic origin of most of the terranes within the cordillera remains an ellusive goal despite more than 10 years of multidisciplinary research the home port of any major terrane has not been identified unequivocally even most continental fragments that show affinities to north america cannot be repositioned confidently along the cordilleran margin and some continental fragments e g chulita probably are not north american in origin cordilleran oceanic terranes including island arcs seamounts off ridge islands and scraps of ocean basins are especially difficult to reposition because panthalassa has been destroyed faunal studies with emphasis on palaeobiogeographic affinities are the most useful particularly when coupled with analyses of faunal diversity and endemism such studies suggest that some terranes previously thought to have formed near the cordillerran margin were situated thousands of kilometres to the west and were separated from the continent by broad ocean basins rather than by a narrow marginal sea

late palaeogene quaternary geology of halmahera eastern indonesia initiation of a volcanic island arc the late palaeogene quaternary stratigraphy of halmahera is described and new formation names are proposed based on recent field investigations of the ne and central part of the island this stratigraphic information provides new insights into the neogene history of halmahera and the development of the present island arc the late palaeogene and younger rocks rest unconformably on an ophiolitic basement complex which formed part of a late cretaceous early tertiary fore arc after volcanic arc activity ceased in the eocene the former fore arc terrane was uplifted and deeply eroded in the late palaeogene some of the late palaeogene early miocene river valleys are currently being re excavated by the present rivers slow subsidence began in the mid late oligocene and by the end of the miocene all eastern halmahera was the site of shallow water carbonate deposition there is no evidence for arc volcanism in central halmahera at this time and the reported oligo miocene volcanism in nearby regions is interpreted as volcanism related to the sorong fault system the miocene shallow water region subsided rapidly in the early pliocene and the sedimentary basin formed was filled with marls succeeded by siliciclastic turbidites with increasing amounts of calc alkaline volcanic debris from a pliocene volcanic arc built on the western arms of halmahera probably on the eroded early tertiary arc this phase of rapid subsidence in the pliocene back arc region resulted from the initiation of subduction of the molucca sea lithosphere eastwards beneath halmahera differential subsidence on nw se and ne sw sets of faults in the region immediately behind the active arc led to the formation of deep sediment filled basins adjacent to the eastern arms a major deformation event in the pleistocene resulted in folding and local thrusting at the junction between eastern and western halmahera and volcanism ceased in the pliocene arc the third halmahera arc the quaternary arc currently active in the northern part of the islands began activity within the last 1 ma and is built upon the deformed and partly eroded pliocene arc the pleistocene deformation event and shift in position of the arc are interpreted as the result of the interaction of the eastward dipping molucca sea plate with adjacent plates either with a fragment of the australian continent in the sorong fault zone and or with the philippine sea plate beneath northern halmahera

disassociated feathers in burmese amber shed new light on mid cretaceous dinosaurs and avifauna abstract even in the absence of associated skeletal material isolated feathers in amber remain of high scientific interest the remarkable preservation of these delicate structures in amber implies a potential for significantly improving our knowledge of feather evolution and diversity a large sample set of 150 burmese amber specimens upper cretaceous 99 ma containing feathers is herein described several structural types can be differentiated including flight feathers contour feathers semiplumes and filoplumes in some cases peculiar pigmentation patterns and structural features can be documented additionally different developmental stages have been captured in this assemblage with some examples of erupting feathers or neoptile plumage comparisons with previous studies including skeletal material described in amber show that enantiornithes and non avialan dinosaurs are most likely represented in the assemblage as well as unknown taxa

potential contributions of ancient oceanic islands to evolutionary theory before much was known about the geology of continental margins and the occurrence of oceanic islands in suspect terranes tests of theories related to island biogeography were undertaken mostly by ecologists and in paleontological investigations of non insular biota a significant new source of paleontological data with which to test models for species equilibrium over evolutionary versus ecological time scales and other important problems in evolutionary theory exists within circum oceanic belts where ancient oceanic islands are preserved as allochthonous terranes research on faunas from these areas simplifies attempts to apply the theory of island biogeography to the fossil record and to trace the history of island populations over evolutionary time scales paleontologic data from a paleozoic island arc alexander terrane show significant fluctuations in the taxonomic diversity of brachiopods and thus question one of the main assertions of the dynamic equilibrium model these data also support the con

biogeographic complexity in triassic bivalves of the wallowa terrane northwestern united states oceanic islands not continents provide the best analogues high levels of endemism and complex overlapping biogeographic patterns characterize modern molluscan faunas of the hawaiian islands and the triassic bivalve fauna of the wallowa volcanic arc terrane in hells canyon oregon such biogeographic complexities and high levels of endemism in many modern and mesozoic island settings constrain the use of faunal data as a primary basis for paleogeographic reconstruction of accreted terranes large taxonomically diver samples are required to identify genuine biogeographic patterns in these insular settings selective use of individual species genera or families to reconstruct terrane paleogeography may give misleading results

geochronology and geochemistry of precambrian gneisses metabasites and pegmatite from the tobacco root mountains northwestern wyoming craton montanathis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh t e krogh deceased april 2008 the middle mountain metamorphic domain of the montana metasedimentary terrane northwestern wyoming craton within the northwestern tobacco root mountains mainly comprises migmatized tonalitic gneiss interlayered with amphibolitic hornblende gneiss both of which are cut by metamorphosed mafic rocks together these gneisses are defined as middle mountain gneiss archean tonalitic gneiss from west of and amphibolitic gneiss from east of the bismark fault give from chemically and air abraded zircon grains u pb id tims ages of 3325 5 1 7 and 3340 ma respectively these results reflect primary magmatic ages and show that the middle mountain gneiss extends into the northern area of the central fault block between the bismark and mammoth faults older crustal processes in the tonalitic gneiss are evidenced by inherited grains the oldest of which is 3460 ma a metabasite hosted in tonalitic gneiss in the bismark fault selvage zone yields a zircon age of 2468 ma which is interpreted as the time of

island arc carbonates characterization and recognition in the ancient geologic record abstract carbonates of island arc origin that are preserved in paleozoic mesozoic terranes of the north american cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs this study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities models are developed that show patterns in the long term evolution of shallow marine organisms and the construction evolution and demise of carbonate platforms in island arcs a suite of criteria is identified that may be used to differentiate island arc carbonates from limestones that accumulated in other platform settings biogeographic isolation prolonged subsidence steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism impoverished normal marine faunas complex provincial affinities and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences fringing and barrier reefs at the shelf margin extensive lagoonal deposits and rapid lateral and vertical facies changes although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform and particular facies types may not be represented e g fringing and barrier reefs may be replaced by sand shoals at the platform margin many characteristics have potential value for identifying carbonates of island arc origin in the ancient rock record apart from being associated with calc alkaline volcanic and volcaniclastic assemblages the most valuable suite of features for recognizing island arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities extraordinary thicknesses of platform shallow marine and periplatform carbonates and rapid facies changes between volcanic and carbonate rocks and between shallow and deep water limestones recognizing that an ensemble of features is distinctive within island arc carbonates considerably enhances identification of volcanic arcs in the ancient geologic record and thus improves the likelihood of successfully unraveling the complex geologic history of ocean basins

a new cambrian sphinctozoan sponge from north america its relationship to archaeocyaths and the nature of early sphinctozoans a new early cambrian sponge of sphinctozoan organization named polythalamia americana nov gen et sp is described from nevada and alaska u s a p americana nov gen et sp shows little resemblance to other cambrian reported sphinctozoans but is similar to late palaeozoic to early mesozoic forms from europe and asia e g stylothalamia and amblysiphonella the polyphyletic origin of sphinctozoans based upon spicule criteria from younger examples is therefore corroborated by the varied morphology and clearly widespread palaeogeographic distribution of cambrian forms which were hitherto recognized only from australia p americana nov gen et sp possesses a relatively small globular multi chambered calcareous skeleton with thin but densely perforate walls and a central retrosiphonate perforate spongocoel the skeleton is composed of an irregular microstructure of unknown but probable calcitic original mineralogy there are no spicules or primary internal structures but secondary vesicular filling tissue is present the pore organization however it directly comparable to archaeocyaths e g coscinocyathines and this character is taken to be the only synapomorphy available for taxonomic and phylogenetic purposes indeed p americana nov gen et sp is closely associated with a diverse archaeocyath assemblage and draws attention to morphological similarities between some archaeocyaths and sphinctozoans thus questioning the criteria at present used to distinguish between these groups accordingly a list of nomenclatural synonymies is given to aid comparison coscinocyathine archaeocyaths possess chambered juvenile stages and p americana nov gen et sp is suggested to represent an aspiculate lineage of sphinctozoan grade which may be derived from forms such as clathricoscinus by neoteny it appears that at least three clades of sphinctozoan grade calcified sponges were present by end of early cambrian time and their occurrence in association with island arcs of the palaeopacific rim is confirmed

stable carbon isotopes of c3 plant resins and ambers record changes in atmospheric oxygen since the triassic estimating the partial pressure of atmospheric oxygen po2 in the geological past has been challenging because of the lack of reliable proxies here we develop a technique to estimate paleo po2 using the stable carbon isotope composition d 13 c of plant resins including amber copal and resinite from a wide range of localities and ages triassic to modern plant resins are particularly suitable as proxies because their highly cross linked terpenoid structures allow the preservation of pristine d 13 cs ignatures over geological timescales the distribution of d 13 c values of modern resins n 126 indicates that a resin producing plant families generally have a similar fractionation behavior during resin biosynthesis and b the fractionation observed in resins is similar to that of bulk plant matter resins exhibit a natural variability in d 13 c of around 8 d 13 cr ange 31 to 23 m ean 27 which is caused by local environmental and ecological factors e g water availability water composition light exposure temperature nutrient availability to minimize the effects of local conditions and to determine long term changes in the d 13 co f resins we used mean d 13 c values d 13 c resin for each geological resin deposit fossil resins n 412 are generally enriched in 13 c compared to their modern counterparts with shifts in d 13 c resin of up to 6 these isotopic shifts follow distinctive trends through time which are unrelated to post depositional processes including polymerization and diagenesis the most enriched fossil resin samples with a d 13 c resin between 22 and 21 formed during the triassic the mid cretaceous and the early eocene experimental evidence and theoretical considerations suggest that neither change in pco2 nor in the d 13 c of atmospheric co2 can account for the observed shifts in d 13 c resin the fractionation of 13 c in resin producing plants d 13 c instead is primarily influenced by atmospheric po2 with more fractionation occurring at higher po2 the enriched d 13 c resin values suggest that atmospheric po2 during most of the mesozoic and cenozoic was considerably lower po2 10 20 than today po2 21 in addition a correlation between the d 13 c resin and the marine d 18 o record implies that po2 pco2 and global temperatures were inversely linked which suggests that intervals of low po2 were generally accompanied by high pco2 and elevated global temperatures intervals with the lowest inferred po2 including the mid cretaceous and the early eocene were preceded by large scale volcanism during the emplacement of large igneous provinces lips this suggests that the influx of mantle derived volcanic co2 triggered an initial phase of warming which led to an increase in oxidative weathering thereby further increasing greenhouse forcing this process resulted in the rapid decline of atmospheric po2 during the mid cretaceous and the early eocene greenhouse periods after the cessation in lip volcanism and the decrease in oxidative weathering rates atmospheric po2 levels continuously increased over tens of millions of years whereas co2 levels and temperatures continuously declined these findings suggest that atmospheric po2 had a considerable impact on the evolution of the climate on earth and that the d 13 c of fossil resins can be used as a novel tool to assess the changes of atmospheric compositions since the emergence of resin producing plants in the paleozoic

volcaniclastic and carbonate sedimentation in late paleozoic island arc deposits eastern klamath mountains california the carboniferous baird formation and early permian mccloud limestone eastern klamath mountains california record depositional relations of volcaniclastic and carbonate sediments within an island arc setting pennsylvania parts of the baird include interbedded mudstone sandstone and pebbly sandstone of volcaniclastic composition these beds accumulated by gravity displacement as volcaniclastic submarine fans a locally conformable transition from the baird to the overlying wolfcampian mccloud limestone is marked by limestone conglomerate of debris flow origin interbedded with volcaniclastic sediments and skeletal wackestone this slope related sequence is overlain by skeletal wackestone and interbedded skeletal packstones and the section represents a distally steepened carbonate ramp that prograded over volcaniclastic slope deposits in other areas diachronous bodies of mccloud limestone disconformably overlie upper mississippian volcanics and volcaniclastics of the baird formation laterally variable age relations of the mccloud and baird indicate that platforms developed at different times on elevated arc surfaces prograding locally over relic volcaniclastic slopes and accumulating thick carbonate sequences through platform subsidence

evaluation of solutions for deep constant head boreholes estimation of the field saturated hydraulic conductivity kfs is essential for ground water management and for numerical modeling of ground water flow and contaminant transport the constant head borehole test can be used to measure kfs of deep soils for a deep borehole of ha 10 500 where h is the water height in the borehole and a is the radius the accuracy of the estimated kfs varies depending on the shape factor associated with ha many analytical solutions have been obtained on the basis of approximate boundary conditions available to evaluate the shape factor to find the best solution that provides an accurate shape factor the accuracy of the different solutions was evaluated using a series of numerical simulations that satisfy the pressure boundary condition of the borehole test our comparison on the basis of the analytical and numerical solutions shows that for homogeneous soils the kfs calculated by xiang s solution xiang 1993 eos trans am geophys union 74 43 285 and that by reynolds et al 1983 soil sci 136 250 268 are almost identical to the numerical results xiang s solution however was found to be more accurate for evaluating the flow distribution than was that of reynolds et al

cretaceous cenozoic tectonic events in the western myanmar burma assam region correlation of late mesozoic mafic and ophiolitic rocks suggests that in the late lower cretaceous a northeasterly facing mafic arc was emplaced onto southeast borneo western sumatra western myanmar burma then 1100 km south of its present position the mogok belt of myanmar and the denqen bangong co ophiolite zone in tibet all then situated on the southwestern margin of asia reversal in tectonic polarity and eastward subduction generated a late cretaceous magmatic arc in western myanmar and sumatra and its continuation through the mogok belt into the gandise batholith of tibet magmatism interrupted in the latest cretaceous probably resumed in the western myanmar tibet and sumatra arc segments in the early palaeogene it was again interrupted in the mid eocene when an east vergent ophiolite nappe overrode the indo burman ranges deforming lower eocene turbidites derived from the magmatic arc to the east following renewed northward and eastward subduction of ocean floor in the latest eocene india collided with northern myanmar and with tibet along a suture south of the jurassic triassic flysch and adjacent yarlung ophiolite in the mogok segment of the late cretaceous arc crust thickened in the early cretaceous orogeny underwent extension to form a metamorphic core complex as myanmar west of the sagaing fault moved northward more than half of this northward movement preceded the well documented 450 km of post early miocene dextral displacement on the sagaing fault and related spreading in the andaman sea generation of late cretaceous to early eocene i and s type granites in and east of the mogok belt was related either to crustal shortening or more probably to subsequent extension in the mogok belt

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

plate tectonics and island arcs the plate tectonic concepts that developed rapidly in the late l960s made possible the understanding of island arcs before that time mobilistic concepts evolved slowly hindered particularly in the united states by an obstructionist geoscience establishment the volcanic belts of island arcs form about 100 km above subducting plates convergent plate boundaries evolve complexly with time and at any one time vary greatly along their lengths seismicity defines positions but not trajectories of descending slabs which sink more steeply than they dip and are overridden by advancing upper plates subduction occurs beneath only one side at a time of an internally rigid plate and the common regime in an overriding plate behind a surficial accretionary wedge is extensional except where a collision is underway back arc basin lithosphere is built behind or by migrating island arcs which lengthen and increase their curvatures a collision can involve two active arcs in which case intervening lithosphere sinks beneath both of them or an active margin and a passive one either type of collision generally is followed by the breaking through of new subduction beneath the composite mass of light crust from a new trench on the outside of the aggregate conversely a new subduction system commonly is a by product of collision a strip of back arc basin crust is in many cases left attached to the aggregate in front of the new trench and becomes the basement for a fore arc basin the leading edge of which is raised as melange is stuffed under it sedimentation in trenches is predominantly longitudinal and can be from distant sources accretionary wedges are dynamic being thickened at both toes and bottoms by tectonic accretion and thinned by gravitational forward flow melange is largely a product of tectonic imbrication and flowage driven by these conflicting processes not of submarine sliding high pressure metamorphic rocks form beneath overriding plates not within wedges in front of them arc magmas incorporate much material from the lithosphere through which they rise and vary correspondingly with the evolving composition of that lithosphere arc crust is inflated into geanticlines by intrusive rocks and thermal expansion submarine island arc volcanic rocks are widely spilitized with na enrichment and ca depletion by hydrothermal reaction with sea water the lower crust of mature island arcs consists of granulite facies rocks of mafic intermediate and felsic intermediate compositions the mohorovicic discontinuity may be primarily a constructional boundary representing the shallow limit off crystallization of voluminous rocks of ultramafic composition or plagioclase free mineralogy

comparison of terrane accretion in modern southeast asia and the mesozoic north american cordillera the western part of the north american cordillera has been divided into numerous suspect terranes some of these terranes have traveled hundreds to thousands of kilometres between the time of their formation and their final incorporation into the accretionary belt of the cordillera most of the terranes appear to be relics of island arcs oceanic plateaus and islands continental margin fragments and complex accretionary terranes the latter including melange belts ophiolite fragments and thrust faulted forearc provinces because the terranes have complex histories and diverse stratigraphies it has been difficult to envisage an actualistic setting for the mesozoic cordillera here we propose an analogy with the tectonic setting of the indo pacific region from the tonga trench on the east to eastern indonesia on the west this region comprises several distinct island arcs several large oceanic plateaus numerous accretionary terranes melange zones ophiolite fragments and a variety of continental fragments all moving toward the central collision zone like the cordillera this part of the indo pacific region is undergoing oblique convergence driven by relatively high rates of movement between the oceanic plates and the collision zone also analogous to the cordillera is the formation of a foreland fold and thrust belt developing between the collision zone and the australian continent and a zone of basement rooted foreland folds suggestive of an early laramide style of deformation

multiple alternating forearc and backarc ward migration of magmatism in the indo myanmar orogenic belt since the jurassic documentation of the orogenic architecture of eastern neotethys in se asia abstract we integrated our new data with a review of published work on the indo myanmar orogenic belt imob of the eastern neotethys in myanmar western yunnan china and naga hills india in order to better understand subduction accretion processes of the neotethys ocean in se asia and interactive relationships between the gondwana and laurasia supercontinents from east to west the imob is divided into three geographic units the shan thai plateau myanmar central basin and indo burma range the mogok metamorphic and slate belt is within the shan thai plateau the shan thai plateau and eastern myanmar central basin contain paleozoic sedimentary successions low grade to amphibolitic facies metamorphic rocks and the luxi ultramafic and myitkyina mogok ultramafic diorite belts unmetamorphosed and metamorphosed sediments have similar detrital zircon age peaks of 1000 ma and 700 ma or 500 ma and they are separated by the luxi ultramafic belt whose end 0 and 87sr 86sr i values are similar to surrounding granite diorite and migmatite and the os 4 8 8 8 is indicative of old sub continental lithospheric mantle rather than an oceanic suture zone these data and relations suggest that these regions belong to the cimmerian continental sliver derived from the gondwana supercontinent the myitkyina mogok ultramafic diorite belt located along the eastern margin of the myanmar central basin that was associated with the continental sliver contains peridotite andesite hornblende gabbro diorite granodiorite and plagiogranite all with arc geochemical signatures and ages of 177 166 ma the source region of some of these igneous rocks contains a component of em1 which is close to low 87sr 86sr i ratio of a migmatite in the cimmerian continental sliver as shown by sr nd isotopes values suggesting this belt developed as a jurassic continental margin arc the mogok metamorphic and slate belt contains granodiorite diorite tonalite granite and migmatite extending from the gongshan tengchong and luxi areas in western yunnan china to mandalay kalaw padatchaung and moulmein in myanmar these rocks have arc geochemical character and yield ages of 185 170 ma 128 112 ma 91 ma and 75 45 ma suggesting development of four episodes of arc magmatism along the central axis of the myanmar central basin there are magmatic arc related 106 94 ma diorite granodiorite and tonalite as well as eocene and neogene present 38 0 ma andesite dacite trachyte and rhyolite accretion took place along the central axis of the myanmar central basin towards the indo burma range and westward to the present trench axis on the margin of the indian ocean as shown by westward younging of accretionary complexes and trench slope basins a jurassic accretionary complex located in the hpakan area in the north of the myanmar central basin contains 189 147 ma high pressure metamorphic rocks such as jadeitite garnet mica schist and glaucophane schist in the eastern belt of the indo burma range early cretaceous 119 115 ma accretionary complexes consist of upper plate triassic unmetamorphosed and low grade metamorphic sediments and lower plate amphibolites high pressure metamorphic rocks and jurassic early cretaceous oceanic plate stratigraphy containing morb and oib type basalts and thin bedded radiolarian cherts late early cretaceous 100 ma and late cretaceous to middle eocene 75 45 ma trench slope basin deposits containing abundant fossil plants and shallow water sedimentary structures cover most of the indo burma range where sediments rest with an angular unconformity on older accretionary complexes the presence of earlier magmatic arcs accretionary complexes and trench slope basins suggests that the present trench on the margin of the indian ocean has evolved by continuous eastward subduction since the jurassic the magmatic arc axis migrated eastward landward during some time periods jurassic to early cretaceous and late cretaceous to middle eocene and westward seaward migration during others early cretaceous to late early cretaceous and middle eocene to present during continuous east dipping subduction

zircon upb age constraints on the mid cretaceous hkamti amber biota in northern myanmar abstract hkamti amber contains exquisite fossils but the age of the amber biota is unclear in this study we documented the characteristics of fossils hosted in the amber and we present zircon u pb ages of tuff layers from the kachin and hkamti sites i e the new mine we also present a compilation of arthropod and echinoderm syn inclusions from the mid cretaceous hkamti amber of myanmar indicating a humid tropical or subtropical forest paleo environment zircon analyses n 143 of four tuff samples that host the amber deposit in different pits yielded a weighted mean age of 109 7 0 4 ma zircon rare earth element data demonstrate the zircons are of igneous origin therefore the age of the cretaceous amber biota from hkamti is ca 110 ma this means that the hkamti assemblage should be treated as distinct from other burmese amber collections as it represents a significantly older source within a different depositional environment the commercial sources of burmese amber are variable and encompass multiple mining regions which makes maintaining distinctions between deposits important if their faunal contents are to be studied in a proper temporal or ecological context the refined understanding of amber deposits in myanmar highlights the importance of distinguishing sources but it also offers an opportunity to study a series of deposits from 110 to 72 ma instead of just one snapshot of terrestrial ecology around 99 ma

biogeographic constraints for tectonic reconstructions of the pacific region suspect terranes in western north america contain permian and triassic genera that were endemic to the tethyan region trend surface analysis of modern biogeographic data constitutes a new approach to understanding the origin of these exotic faunas we use the generic diversity of living reef corals together with paleomagnetic results from quaternary lavas to calculate the present locations of easter island hawaii and tahiti the results demonstrate that the eastward decline in coral diversity may be used as a measure of longitude similar data from the fossil record should constrain paleogeographic reconstructions of the pacific region

evolution of a permo triassic sedimentary melange grindstone terrane east central oregon the grindstone terrane in east central oregon is one of the few areas in western north america where large blocks of unmetamorphosed devonian mississippian and permian limestones are inter mixed with permian and lower triassic radiolarian chert and pennsylvanian permian and triassic volcaniclastic rocks although originally described as parts of a coherent succession we interpret the grindstone rocks to be a sedimentary melange composed of paleozoic limestone slide and slump blocks that became detached from a carbonate shelf fringing a volcanic knoll or edifice in late permian to middle triassic time and were intermixed with permian and triassic slope to basinal clastic and volcaniclastic rocks in a forearc basin setting paleogeographic affinities of the grindstone limestone faunas and volcaniclastic debris in the limestone and clastic rocks all indicate deposition in proximity to an island arc system near the north american craton the grindstone terrane deposits are unconformably overlain by upper triassic to middle jurassic sequences of the izee terrane although lithologic and faunal differences indicate that the grindstone and izee terranes together represent a tectonic block separate from the adjacent baker terrane all three terranes were juxtaposed by late triassic or early jurassic time we recommend reduction to informal status for the coffee creek mississippian spotted ridge pennsylvanian and coyote butte permian formations because 1 they cannot be mapped or traced beyond limited areas and 2 these older rocks are chaotically inter mixed with younger chert and volcaniclastic rocks new biostratigraphic data indicate that the bulk of the spotted ridge volcaniclastic rocks represent a part of the triassic vester formation of the izee terrane

island arc sedimentation in the middle devonian kennett formation eastern klamath mountains california the kennett formation is a unit of intra arc sediments which was deposited during the final stages of early to middle devonian island arc construction in the eastern klamath mountains california nearshore bioturbated volcaniclastics with a shallow marine fauna also contain rare debris of land plants indicating island source areas these sediments grade to volcaniclastic turbidites of slope origin which in turn grade to thin bedded siliceous mudstone representing a basin floor environment limestone lenses at the top of the kennett are debris deposits with matrix supported intraclasts and overturned colonial skeletons which were derived from shallow carbonate banks sedimentary facies of the kennett indicate a mature arc topography of islands submerged highs and intra arc basins basins were probably developed by tectonic extension of the arc during the early devonian

regression models for hydraulic conductivity and field test of the borehole permeameter the saturated hydraulic conductivity ks of sediments in the vadose zone is an important parameter in predicting the seepage rates of water and contaminants the borehole permeameter is an in situ technique to test a relatively large sample size at any depth solutions are presented which account for the effects of unsaturated flow these solutions are derived from a regression analysis of results of numerical simulations in which unsaturated hydraulic conductivity is represented by one or two parameters the results of a borehole permeameter test in a uniform sand are compared with field ponding tests and air entry permeameter tests the regression based solutions for the borehole permeameter which account for capillarity provide very good agreement with other permeameter results depending upon the approach used to solve the borehole problem ks values determined by methods which neglected and included capillary effects varied by a factor of only about two for the soil tested

petrographical properties of a semi precious coaly stone oltu stone from eastern turkey abstract oltu stone is a unique black gemstone used commonly as an ornament in turkey the most distinctive characteristics of oltu stone are its strength and its reflective black appearance after polishing it has been widely used since the 18th century as an important material for the production of quality prayer beads this relatively hard stone is found in marine flysch and marl deposits as scattered chunks macroscopically it more closely resembles obsidian than coal many scientists have researched the origins of this stone but until recently its genesis was not well understood its petrographical property is remarkable and quite interesting in order to perform petrographical studies on oltu stone ten samples were taken from two locations a few kilometers from the town of oltu which is northeast of erzurum city in eastern turkey polished briquettes and thin sections were produced from the samples for petrographical examination under a coal microscope sem and eds analyses were also conducted internal cellular structures can clearly be traced in fluorescent mode the great strength of the stone has always incorrectly led to the conclusion that its genesis is unlike the genesis of coal however fluorescent light plainly revealed detailed cellular structures with the aid of fluorescent light suberinite textures and silicate filling of the cell cavities were clearly observed

nd and sr isotopic characterization of the wrangellia terrane and implications for crustal growth of the canadian cordillera nd and sr isotopic data are reported from samples of most of the major lithologic units of the wrangellia terrane exposed on vancouver island and the queen charlotte islands initial epsilon nd values range from 1 0 to 7 3 and initial 87 sr 86 sr ratios range from 0 70323 to 0 70481 these ratios are similar to those of modern island arcs and demonstrate the unevolved juvenile nature of this terrane these data indicate that wrangellia probably resided in an intra oceanic environment until its accretion to north america nd crustal residence ages for clastic sedimentary rocks of wrangellia mean t cr 0 77 pm 0 33 ga t dm 0 57 pm 0 35 ga are much closer to their stratigraphic ages than is the case for the ages of many other phanerozoic sedimentary rocks thus providing strong evidence for phanerozoic crustal addition to north america early proterozoic crustal components cannot comprise more than about 6 of wrangellia therefore the terrane consists of 94 new mantle d

vadose zone permeability tests summary solutions to determine saturated hydraulic above a water table by means of constant head borehole infiltration tests are summarized and critiqued analytical solutions are available for open and partly cased boreholes and deep and shallow water table conditions the formulas are based on various simplifying assumptions pertaining to soil properties and boundary conditions none of the solutions account for capillary effects for identical test conditions values of hydraulic conductivity calculated from these formulas may differ by as much as a few hundred percent

discovery of triassic phylloid algae possible links with the paleozoic triassic phylloid algae have recently been discovered in a reef in the southern yukon these plate like algae are the primary frame builders in a few small patches in the upper section of the reef where they are associated with fossils and sedimentary structures suggesting deposition in very shallow water a vague porous microstructure in some of the algae suggests affinities with paleozoic codiacean phylloid algae but preservation is too poor to permit definite classification nevertheless the indication that phylloid algae did not become extinct at the end of the paleozoic as formerly supposed increases the possibility of finding missing evolutionary links between paleozoic phylloid algae and their modern counterparts

dispersed remnants of a northeast pacific fringing arc upper paleozoic terranes of permian mccloud faunal affinity western u s two fragmentary subparallel belts of terranes within the western north american cordillera contain upper paleozoic rocks and are characterized by contrasting lithotectonic assemblages and contrasting permian faunal affinity these two belts are a volcanic arc related successions of permian mccloud faunal affinity mccloud belt and b subduction related accretionary complexes of permian tethy an faunal affinity cache creek belt this paper supports the hypothesis that the fragmentary terranes of the mccloud belt once constituted parts of a northeast pacific fringing arc system and in constrast to some earlier interpretations concludes that the volcanic arc evolved above an eastward dipping subduction zone the absolute distance between this arc and western north america during the late paleozoic cannot be constrained however there is little evidence to suggest closure of a major 10 km ocean basin or protracted periods of westward dipping subduction parts of devonian to permian volcanic island arc sequences of the western u s cordillera are represented in the northern sierra eastern klamath bilk creek grindstone and chilliwack terranes these scattered volcanic arc remnants share several fundamental characteristics 1 the sequences were constructed across continental affinity basement assemblages 2 they underwent similar tectonic evolution during late paleozoic time such as coeval pulses in volcanism and related depositional histories 3 they contain early permian mccloud type fauna of distinctive biogeographic affinity 4 mccloud belt terranes are spatially and possibly genetically related to westward lying accretionary complexes of the cache creek belt which contain fragments of upper triassic blueschist and permian limestone blocks bearing tethyan permian fusulinids and corals based on the presence of distinctive early permian mccloud fauna the island arc remnants discussed in this paper are referred to as the mccloud belt the similarities between mccloud belt terranes suggest that they were once parts of a long lived late paleozoic volcanic arc complex the stratigraphy of these terranes records the tectonic evolution of the volcanic arc volcanism within the paleozoic arc began as early as the early devonian and was succeeded or accompanied by carbonate and epiclastic sedimentation during the middle and late devonian an influx of detritus derived from sedimentary and metasedimentary rocks during the late devonian and mississippian records the uplift and erosion of arc basement sequences an event that was at least locally accompanied by ongoing volcanism a pulse in volcanism during the pennsylvanian and coeval uplift led to the establishment of shallow marine and deltaic volcanogenic and carbonate sedimentation and locally subaerial exposure which persisted into the early early permian elsewhere during the early permian shallow water carbonate deposition was established with only minor influx of volcanogenic debris during the late permian and locally as early as late early permian a major pulse in volcanism occurred and is now represented by voluminous sequences of volcanogenic debris and lavas most of these sequences are overlain by upper triassic carbonate platformal sequences arc volcanism was recorded at least locally until the middle jurassic paleomagnetic data are used to constrain a schematic pre cretaceous reconstruction of these volcanic arc sequences and their associated subduction assemblages the inferred paleogeography of island arc sequences and the adjacent accretionary terranes suggests that volcanism occurred above an east dipping subduction zone with a long lived paleogeographic relation to north america the current structural position of these terranes is largely the result of mesozoic and locally younger deformation

paleo oceanographic and tectonic settings of early miocene reefs and associated carbonates of offshore southeast asia the late oligocene to early middle miocene was a period of widespread reef and associated carbonate deposition over a wide latitudinal range in the offshore region of southeast asia a generally rising eustatic sea level during this period allowed the accumulation of thick reefal units an expansion of the coral algal regional facies belt north to japan and south to new zealand occurred during the early miocene as the result of a reduced oceanic latitudinal temperature gradient an episode of enhanced organic carbon burial is reflected in a positive dgr13c excursion from 17 5 to 13 5 ma increasing paleo oceanographic equability may have resulted in reduced ocean circulation with the resultant development of an expanded oxygen minimum zone marine oil prone or anic carbon was deposited in silled anoxic basins both bounded by and within island arc systems a combination of tectonic and paleo oceanographic factors therefore created conditions that favored contemporaneous deposition of organic carbon rich source beds and reef reservoirs during the latest early to early middle miocene paleogeographic and facies reconstructions for an 18 m y interval indicate that deposition occurred in three tectonic settings 1 passive continental margins 2 convergent plate boundaries and 3 obliquely convergent plate boundaries in all these settings the vertical motion histories of fault bounded blocks and of larger tectonic elements within which they are contained directly controlled the geographical distribution of carbonate buildups their scal and morphology duration diagenesis and relationship to siliciclastics

early cretaceous wedge extrusion in the indo burma range accretionary complex implications for the mesozoic subduction of neotethys in se asia the indo burma range ibr of myanmar the eastern extension of the yarlung tsangpo neotethyan belt of tibet in china contains melanges with serpentinite greenschist facies basalt chert sericite schist silty slate and unmetamorphosed triassic sandstone mudstone and siltstone interbedded with chert in the east and farther north high pressure blueschist and eclogite blocks in the naga hills melange our detailed mapping of the mindat and magwe sections in the middle ibr revealed a major 18 km antiformal isocline in a melange in which greenschist facies rocks in the core decrease in grade eastwards and westwards symmetrically outwards to lower grade sericite schist and silty slate and at the margins to unmetamorphosed sediments and these metamorphic rocks are structurally repeated in small scale imbricated thrust stacks in the mindat section the lower western boundary of the isoclinal melange is a thrust on which the metamorphic rocks have been transported over unmetamorphosed sediments of the triassic pane chaung group and the upper eastern boundary is a normal fault these relations demonstrate that the ibr metamorphic rocks were exhumed by wedge extrusion in a subduction generated accretionary complex along strike to the north in the naga hills is a comparable isoclinal melange in which central eclogite lenses are succeeded outwards by layers of glaucophane schist and glaucophanite and to lower grade greenschist facies sericite schist and slate towards the margins in the natchaung area from west to east unmetamorphosed triassic sediments overlie quartzites sericite schists actinolite schists and meta volcanic amphibolites derived from morb type basalt which are in fault contact with peridotite olivine in the peridotite has undulatory extinction suggesting deformation at 600 700 c similar to the peak temperature of the amphibolite these relations suggest generation in a metamorphic sole the amphibolites have u pb zircon ages of 119 3 ma and 115 ma which are close to the zircon ages of nearby calc alkaline granite and diorite which belong to an active continental margin arc that extends along the western side of the shan thai block the ibr accretionary complex and the active continental margin arc were generated during early cretaceous 115 128 ma subduction of the neotethys ocean

a field method to determine unsaturated hydraulic conductivity using flow nets a practical new field method is proposed to evaluate hydraulic conductivity in partially saturated media near a water impoundment the new method is an inverse procedure which utilizes a flow net constructed from the steady state total hydraulic head distribution around the water source in the vicinity of constant head sources and downstream along any stream tube wetness and conductivity generally decrease knowing the stream tube geometry and hydraulic gradient from the flow net darcy s law is used to determine unsaturated hydraulic conductivities within the stream tube relative to some segment of the stream tube where conductivity is known this approach was used successfully to predict the unsaturated hydraulic conductivity which was input to two variably saturated numerical models utilizing total hydraulic head fields generated by the models this procedure is also applied to pressure head and water content data collected in the field surrounding a constant head borehole infiltration test originally designed to determine only saturated hydraulic conductivity above the water table for practical purposes the new procedure compares very favorably with 1 results of a field experiment to obtain unsaturated hydraulic conductivity in situ using the instantaneous profile method and 2 values of unsaturated conductivity calculated from field and laboratory measurements of water content and pressure head

a triassic sponge from vancouver island possible holdover from the cambrian tiny cap shaped fossils recovered from silicified residues in upper triassic rocks of vancouver island wrangellia are identified as a calcareous sponge nucha vancouverensis n sp nov the genus nucha pickett and jell was first reported from middle cambrian rocks of australia the triassic example constitutes the first occurrence outside the cambrian system and the continent of australia the absence of representatives in rocks between triassic and cambrian age suggests that it is a long range refugium taxon the occurrence of such a wide ranging holdover organism reinforces the role of refugia in preferential survivorship over long periods of geologic time other holdover taxa are known from volcanic displaced terranes of western american cordillera and their study may help clarify neglected aspects of survival and evolution

structural and tectonic development of the indo burma ranges abstract the indo burma ranges form an enigmatic mountain belt with fragments of evidence for an early accretionary history jurassic jade belt hp lt metamorphism early cretaceous ophiolites highly deformed triassic turbidites pane chaung formation pcf kanpetlet schists it remains uncertain whether this early history involved collision of a microcontinent mt victoria land mvl unconformably sealed by aptian cenomanian limestones or can be explained entirely as an accretionary type ophiolite on the western margin of the west burma terrane wbt complex deformation in the deepwater triassic jurassic late cretaceous and paleogene deepwater sequences is replaced in the late eocene early oligocene by molasse deposition these events mark closure of the neo tethys ocean between india and the ibr wbt and the onset of major dextral translation 2000 km 40 ma recent between the coupled india ibr wbt region and sundaland in the late miocene recent major transpressional deformation affected the ibr and central basin of the wbt the late deformation events sedimentary depocentres and impinging thick crustal regions of the eastern himalayas and shillong plateau have all affected the overall shape wedge taper of the modern ibr with the wedge and retro wedge behaving anomalously compared with typical accretionary prisms all tectonic models proposed for the ibr wbt have weaknesses or ambiguities and there is considerable scope for future research to resolve the many outstanding tectonic metamorphic structural and sedimentary issues these are important tasks because the ibr is a key region for understanding the development of northern gondwana the himalayan orogeny and se asia as well as providing insights into the complex development of highly oblique collisional margins

bivalve bioerosion in cretaceous neogene amber around the globe with implications for the ichnogenera teredolites and apectoichnus abstract amber samples with bivalve borings from six localities around the world ranging in age from hauterivian to miocene have been studied the possible assignment to teredolites or gastrochaenolites is discussed considering the type of substrate as an ichnotaxobase it is proposed to regard amber or similar resins as a variant of xylic substrates and to maintain the separation between the two ichnogenera and their different paleoecological implications the amber borings are assigned to teredolites clavatus leymerie 1842 and apectoichnus longissimus kelly and bromley 1984 respectively the presence of bioglyphs in a few borings suggests a mechanical production process with pholadid bivalves such as martesia preserved inside many of the samples representing the producer in general the amber producing trees mostly grew along a forested coastline where they were occasionally flooded by seawater or even transported from rivers into the sea and later deposited

terpenoid composition and botanical affinity of cretaceous resins from india and myanmar abstract fossil resins from the cretaceous sediments of meghalaya india and kachin myanmar burma were analysed using curie point pyrolysis gas chromatography mass spectrometry and thermochemolysis gas chromatography mass spectrometry to help elucidate their botanical source the major pyrolysis products and methyl esterified thermochemolysis products of both the resins were abietane and labdane type diterpenoids with minor amount of sesquiterpenoids the thermochemolysis products also included methyl 16 17 dinor callitrisate methyl 16 17 dinor dehydroabietate and methyl 8 pimaren 18 oate the latter two from just the myanmarese resin the exclusive presence of both labdane and abietane diterpenoids and the lack of phenolic terpenoids may suggest that the studied cretaceous resins were derived from pinaceae pine family conifers

taphonomy and chemotaxonomy of eocene amber from southeastern australia abstract amber is a complex organic polymer that offers unparalleled utility as a preservation medium providing insights into past organisms and environments however under specific circumstances this information can be compromised through alteration of the amber structure understanding the degradation of amber in the geosphere could improve prospecting techniques and maximise the quality and validity of chemical information from altered samples this study analysed 114 amber samples retrieved from two new eocene australian deposits at strahan tasmania and anglesea victoria using a combination of attenuated total reflectance fourier transform infrared and solid state 13c cross polarised magic angle spinning nuclear magnetic resonance spectroscopy results identified both class ib polylabdanoid and class ii cadinene based amber the presence of class ii amber in australia suggests one of two possibilities 1 a local dipterocarpaceae source the primary producer of class ii resins despite the absence of this family from the australian eocene fossil record or 2 a local unidentified botanical source of cadinene based amber a third alternative that class ii amber was transported to australia from southeast asia via ocean currents is rejected taphonomic analysis revealed four mechanisms of alteration prevalent in amber across the two study regions with evidence of oxidation and metal carboxylate formation both the nature and extent of these alterations were found to vary significantly between classes i and ii suggesting that amber class may play a defining role in determining the chemical pathways by which amber degrades of note was the high proportion of amber that exhibited no significant chemical changes despite extensive visible alteration features suggesting the integrity of palaeobiological and palaeoenvironmental information in these samples may be preserved

stratigraphic evolution of the paleozoic stikine assemblage in the stikine and iskut rivers area northwestern british columbia the stikine assemblage the basement of stikinia extends 500 km along the western flank of the intermontane belt east of younger coast belt plutons four different stratigraphic successions are characteristic of lower to middle devonian carboniferous and permian rocks in the stikine and iskut rivers area west of forrest kerr creek are penetratively deformed lower to middle devonian island arc volcaniclastic rocks coralline limestone and felsic tuff fringing carbonate buildups in an arc setting are best illustrated in the sequence at round lake where lower carboniferous mafic dominated bimodal submarine volcanic rocks grade upward into two distinctive coarse echinoderm limestone units and medial siliceous siltstone and limestone conglomerate conodont colour alteration indices for lower carboniferous rocks near newmont lake indicate an anomalously low temperature thermal history upper carboniferous permian polymictic volcanic conglomerate and lower permian limestone overlie these strata there t

evidence of displaced terranes from permian to jurassic faunas around the pacific margins for the permian to jurassic time interval tethyan marine invertebrate faunas which are generally accepted as having lived at low latitude can be distinguished from less diverse higher latitude faunas displacement of these low latitude faunas to positions of high latitude around the pacific margins therefore provides key evidence for the movement of so called suspect or displaced terranes the fullest story so far has been worked out for the western margin of n america as far north as southern alaska but there is also convincing evidence for the substantial northward movement of continental segments along the ne asian margin as regards the southern hemisphere the torlesse terrane of new zealand appears to have moved a considerable distance southwards but there is no fauna1 evidence of comparable far travelled suspect terranes along the andean margin of south america not only tethyan and boreal but e and w pacific elements are detectable in the faunas and the distribution of these argues for a panthalassia studded with islands of various sizes fringing the adjacent continents rather than for the disintegration of a single continent pacifica

geology and paleobiology of islands in the ordovician iapetus ocean review and implications a history of islands in the iapetus ocean and their destruction is recorded by widespread occurrences of lower to upper ordovician volcanic and epiclastic rocks and some limestone through the axial parts of the appalachian caledonide orogen in north america and northwestern europe assemblages of arenigian and llanvirnian benthic shelly fossils chiefly brachiopods from these rocks constitute the celtic biogeographic province that is distinguished by its endemic genera and by some that are older than in other biogeographic provinces some that are younger than elsewhere and others that have not hitherto been found together evidence from these fossils and from the geology of the rocks pertaining to them suggests that north american terranes that included islands of arenigian llanvirnian age lay at middle to high latitudes both in mid ocean and within the armorican continental margin whereas coeval rocks in west central ireland and norway that have toquima table head shelly fossils were originally part of the laurentian continental margin eradication of the celtic assemblage and the reduction of ordovician faunal provinciality in the appalachian caledonide region coincide with llanvirnian obduction subduction of hundreds of kilometres of iapetus ocean crust late llanvirnian and younger ordovician rocks in the remnant basin including some of peri insular origin have brachiopods of scoto appalachian affinities no discrete islands of ashgillian age have been recognized although fossiliferous volcaniclastic and polymictic conglomerates indicate intermontane basins in some places shelly fossils in these rocks and those in the siltstones and limestones from the gaspe peninsula are like those of ashgillian age elsewhere

geology of an amber locality in the hukawng valley northern myanmar abstract amber burmite from the hukawng valley of myanmar has been known since at least the 1st century ad it is currently being produced from a hill known as noije bum which was first documented as a source of amber in 1836 several geologists visited the locality between 1892 and 1930 all of them believed that the host rocks to the amber are tertiary most said eocene in age and this conclusion has been widely quoted in the literature however recent work indicates a cretaceous age insect inclusions in amber are considered to be turonian cenomanian and a specimen of the ammonite mortoniceras of middle upper albian age was discovered during the authors visit palynomorphs in samples collected by the authors suggest that the amber bearing horizon is upper albian to lower cenomanian the preponderance of the evidence suggests that both rocks and amber are most probably upper albian this determination is significant for the study of insect evolution indicating that the oldest known definitive ants have been identified in this amber american museum novitates 3361 2002 72 this site occurs within the hukawng basin which is comprised of folded sedimentary volcanic rocks of cretaceous and cenozoic age the mine exposes a variety of clastic sedimentary rocks with thin limestone beds and abundant carbonaceous material the sediments were deposited in a nearshore marine environment such as a bay or estuary amber is found in a fine clastic facies principally as disk shaped clasts oriented parallel to bedding a minority occurs as runnels stalactite shaped with concentric layering caused by recurring flows of resin an upper albian age is similar to that of orbitolina limestones known from a number of locations in northern myanmar one of these at nam sakhaw 90 km sw of noije bum has also been a source of amber

oman exotics oceanic carbonate build ups associated with the early stages of continental rifting the so called oman exotic limestones form isolated masses from boulder size to 1 000 m thick of middle to upper permian and upper triassic fossiliferous limestones and crop out within imbricated thrust slices beneath the semail ophiolite in the oman mountains permian exotics are of dominantly reef and forereef facies whereas triassic exotics are more typically of back reef and lagoonal facies they are commonly associated with a substrate of alkalic and transitional tholeiitic basalts and are interpreted as a series of reef associated carbonate buildups deposited in part on oceanic islands or seamounts close to the site of initial rifting of the oman continental margin