model for the combined flow origin of hummocky cross stratification many shallow marine sandstones are characterized by gently dipping trough cross stratification there appear to be significant similarities between this low angle cross stratification and typical hummocky cross stratification and it is proposed that much of what is currently recognized as hummocky cross stratification is related to low relief megaripple bed forms that are equilibrium structures for fine grained sand under combined wave surge and unidirectional currents the geometry that obtains when these bed forms migrate is low angle trough cross stratification high rates of sedimentation from incipient suspension and limited lateral migration of individual bed forms promote preservation of convex upward depositional surfaces hummocks between troughs highly unsteady flow leads to abundant internal scour and drape surfaces neither random scour and drape nor oscillatory currents seem sufficient to generate hummocky bed forms

holocene carbonate sedimentation on the west eucla shelf great australian bight a shaved shelf the southern continental margin of australia is a cool water carbonate sedimentary province located in a high energy swell dominated oceanographic setting a vibrocore transect of 14c dated sediments across the centre of the eucla shelf is the first record of holocene shelf deposition in the great australian bight much of the seafloor shallower than 70 m water depth the base of wave abrasion is bare cenozoic limestone in some places encrusted by late pleistocene coral rich limestone that is cemented by high magnesium calcite 12 mole mgco3 the areally extensive 100 km wide hard bored substrate supports an epibiota of coralline algae minor bryozoans and soft algae or is covered by patches of holocene sediment up to 1 5 m thick generally a basal bivalve lag 3 ka overlain by quartzose bioclastic palimpsest sand this pattern of active carbonate production but little accretion on the wave swept mid to inner shelf is similar to that on other parts of the southern australian continental margin the term shaved shelf is proposed for this style of carbonate platform formed by alternating periods of sediment accretion cementation and erosion the palimpsest sand is typically rich in bivalves coralline algae and locally detrital dolomite outer shelf holocene sediment below the base of wave abrasion but inboard of the shelf edge is a metre thick unit of fine microbioclastic muddy sand with minor delicate bryozoans overlying a 9 13 ka rhodolith gravel some of this outer shelf sediment appears to have been resedimented the shelf edge is a sandy and rocky seafloor with active bryozoan growth and sediment production the holocene sediments are enriched in coralline algal particles and conspicuous large foraminifers cf marginopora and depleted in bryozoans as compared to coeval deposits on the lacepede and otway shelves off southeastern australia these differences are interpreted to reflect warmer waters of the leeuwin current and prevalent downwelling in this area as opposed to the general upwelling and colder waters in the east

evolution in the test size of deep sea benthic foraminifera during the past 120 m y evidence is presented for stratigraphic variations in test size of the largest deep water 1500 m water depth calcareous trochospiral benthic foraminifera for eight dominant lineages composed of ten genera over the past 120 m y variations in test size show 1 a general trend of increasing test size during the past 120 m y and 2 fluctuations highlighted by six minima and six maxima that are synchronized among genera the long term increase in size corresponds to an increase in the 18o of deep water benthic foraminifera the minimum and maximum sizes correspond to minima and maxima in the 18o respectively in addition three major minima in test size correspond to distinct low dissolved oxygen events these latter synchronisms indicate that oceanic climate and dissolved oxygen or related factors likely controlled evolution in test size of deep water calcareous trochospiral benthic foraminiferal genera

sequence stratigraphy of the aux vases sandstone a major oil producer in the illinois basin the aux vases sandstone mississippian has contributed between 10 and 25 of all the oil produced in illinois the aux vases is not only an important oil reservoir but is also an important source of groundwater quarrying stone and fluorspar using sequence stratigraphy a more accurate stratigraphic interpretation of this economically important formation can be discerned and thereby enable more effective exploration for the resources contained therein

oceanographic control of diatom abundances and species distributions in surface sediments of the tropical and southeast atlantic abstract this paper is a descriptive account of the diatomaceous component of pelagic sediments from the tropical and southeast atlantic ocean geographic patterns of diatom abundances whole and fragment forms per gram major species relative abundances and diatom assemblages resolved by q mode factor analysis are presented comparisons drawn to sea surface temperature salinity and productivity distributions suggest that i diatom abundances primarily reflect surface productivity with no apparent dissolution effects due to water depth ii relative abundances of major species vary in their ecologic dependence but do reflect major oceanographic features of the surface waters and iii of the five diatom assemblages resolved four finely delineate the complexity of the low latitude oceanography these assemblages in decreasing order of statistical importance are associated with 1 warm waters of moderate to high primary productivity 2 the oceanward margin of the benguela current a region of high primary production with a maximum in austral summer 3 low salinity waters off the mouths of the zaire and niger rivers and 4 subtropical to tropical waters of lower productivity mostly in the western equatorial atlantic the fifth factor represents the equatorward advection of subantarctic to antarctic diatoms by deep ocean currents

lithology based sequence stratigraphic framework of a mixed carbonate siliciclastic succession lower cretaceous atlantic coastal plain this study presents a lithology based sequence stratigraphic framework and depositional model for lower cretaceous mixed siliciclastic carbonate sediments of the mid atlantic coastal plain eastern united states lithologic data from cores and cuttings were integrated with wireline logs and two dimensional seismic data to document lithofacies variability and stacking patterns across the albemarle basin of eastern north carolina ten facies associations are defined which are variably present within siliciclastic and carbonate dominated depositional profiles interpreted to extend from onshore lowland coastal plain to deep shelf depositional environments three depositional sequences 0 1 2 were identified each with component upward shoaling parasequences seismic reflectors typically coincided with key sequence stratigraphic surfaces which guided correlations between wells parasequences are grouped into parasequence sets with progressive progradational or retrogradational highstand and transgressive systems tracts respectively stacking patterns transgressive parasequences are thinner uniform in thickness and tend to be more dominated by molluskan carbonate facies highstand parasequences have more variable thickness are siliciclastic dominated and tend to be progradational on seismic data late highstand deposits of sequence 1 are dominated by restricted carbonate facies that likely reflect increased aridity lowstand deposits were not recognized from onshore well and seismic data the sequence stratigraphic framework developed documents the complex spatial and temporal facies relationships within a wave dominated mixed carbonate siliciclastic passive margin succession the strata studied document the complex interplay of lithofacies within a transition zone between near shore carbonate dominated strata to the south southeast georgia embayment and siliciclastic dominated marginal marine successions to the north baltimore canyon trough it also provides a useful stratigraphic calibration set for coeval offshore sediments that have been identified as potential areas for hydrocarbon exploration

crustal response to continental collisions between the tibet indian south china and north china blocks geochronological constraints from the songpan garze orogenic belt western china we report shrimp u th pb monazite conventional u pb titanite sm nd garnet and rb sr muscovite and biotite ages for metamorphic rocks from the danba domal metamorphic terrane in the eastern songpan garze orogenic belt eastern tibet plateau these ages are used to determine the timing of polyphase metamorphic events and the subsequent cooling history the oldest u th pb monazite and sm nd garnet ages constrain an early barrovian metamorphism m1 in the interval c 204 190 ma coincident with extensive indosinian granitic magmatism throughout the songpan garze orogenic belt a second higher grade sillimanite grade metamorphic event m2 recorded only in the northern part of the danba terrane was dated at c 168 158 ma by a combination of u th pb monazite and titanite and sm nd garnet ages it is suggested that m1 was a thermal event that affected the entire orogenic belt while m2 may represent a local thermal perturbation rb sr muscovite ages range from c 138 100 ma whereas rb sr biotite ages cluster at c 34 24 ma these ages document regional cooling at rates of c 2 3 c myr 1 following the m1 peak for most of the terrane however those parts of the terrane affected by the higher temperature m2 event e g the migmatite zone experienced initially more rapid c 8 c myr 1 cooling after peak m2 before joining the regional slow cooling path defined by the rest of the terrane at c 138 ma regional slow cooling between c 138 and c 30 ma is thought to be the result of post tectonic isostatic uplift after extensive crustal thickening caused by collision of the south and north china blocks the clustering of biotite rb sr ages marks the onset of rapid uplift across the entire terrane commencing at c 30 20 ma this cooling history is shared with many other regions of the tibet plateau suggesting that uplift of the tibet plateau including the songpan garze orogenic belt occurred predominantly in the last c 30 myr as a response to the continuing northwards collision of india with eurasia

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

depositional facies of high energy beach to offshore sequence comparison with low energy sequence a study of the nearshore zone and continental shelf of a high energy coast was made in the ventura port hueneme area of california during the summer of 1974 to investigate depositional facies characteristics and compare them with similar facies from a low energy coastal setting analysis of box cores can cores and vibracores permits recognition of three principal zones 1 nearshore facies backshore to 9 m water depth made up primarily of parallel ripple and cross bedded clean sand bioturbation is only locally significant 2 transition facies 9 to 18 m water depth a zone of fine sand and silty sand characterized by an increase in biogenic over physical sedimentary structures that are commonly preserved as laminated to burrowed beds wave ripple bedding and parallel lamination are important structures in this facies 3 offshore facies 18 m water depth sandy silt is the primary texture and bioturbation is the dominant sedimentary structure remnant parallel lamination is the only physical sedimentary structure present comparison of the results of this study with a previous description of a low energy beach to offshore sequence at sapelo island georgia indicates that the two areas do not differ greatly in their facies or overall vertical sequence of sedimentary structures the principal difference is in the thickness of the three facies the california facies are significantly thicker than their georgia counterparts this difference is in direct response to the role of higher wave energy on the california coast

detrital zircon provenance of the late triassic songpan ganzi complex sedimentary record of collision of the north and south china blocks the majority of the songpan ganzi triassic flysch sequence is believed to have derived from denudation of the dabie and sulu ultrahigh pressure uhp metamorphic belt in eastern china e g nie et al 1994 1 zhou and graham 1996 2 however intense debate still exists on the sources of

late stages of continent continent collision timing kinematic evolution and exhumation of the northern rim aar massif of the alps abstract the alpine front s external crystalline massifs represent exhumation of mid crustal basement during late stage continent continent collision we unravel the geodynamic evolution of the northalpine front aar massif by combining structural and low t thermochronometric data a crustal scale tectonic restoration neogene present and estimation of associated changes in exhumation rates become possible the european continental margin experienced multiple switches from horizontal to vertical and again to horizontal dominated tectonics early thrust related inversion of rift basins is followed by a switch to rapid vertical exhumation with deformation along steep reverse normal faults this vertical tectonics is related to a positive buoyancy force of the european crust induced by lower crustal delamination of the aar massif during an orogenic rollback process of the european lithosphere 22 20 ma differential rock uplift rates of up to 1 3 1 6 km myr resulted which decreased northwards to 0 1 km myr reducing buoyancy forces isostatic compensation led to a horizontal tectonic style again persisting compressional forces induced an orogen scale strain partitioning with dextral transpressive faults in the south and simultaneous crustal scale northwest directed thrusting in the north en bloc exhumation of the entire aar massif in the thrust s hanging wall occurred between 13 5 ma and 5 0 ma at rates of 0 5 0 9 km myr and 0 6 0 8 km myr respectively it is this late stage thrusting in combination with surface erosion which shaped today s prominent northalpine front switches between horizontal and vertical tectonics might generally be relevant for late continent continent collisional stages here buoyancy forces of non thinned continental crust entering the subduction zone cause a strong vertical tectonic deformation style instead of classical thrust tectonics

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

natural long term annealing of the zircon fission track system in vienna basin deep borehole samples constraints upon the partial annealing zone and closure temperature abstract fission track ft analysis of zircon from cretaceous and tertiary sandstone samples in vienna basin boreholes has provided constraints for the thermal stability of the zircon ft system over a geological timescale confined track lengths and ages were measured for samples from depths of 1 5 7 5 km the deepest with a present environmental temperature of 200 c mean track lengths range from 10 3 to 10 8 m indistinguishable within error from the unannealed reference length of 10 7 0 1 m 1 standard error thus showing no sign of systematic downhole reduction central zircon ages are consistently older than stratigraphic ages of parent rocks with no single grain ages significantly younger than their respective stratigraphic ages such ft age and length evidence strongly suggests that the tracks have not been significantly annealed since sediment deposition because the present geothermal regime as well as sample burial depths have been near constant for at least the past 5 m y the lower temperature limit of the zircon ft partial annealing zone is 200 c for a heating duration of the order of 5 10 m y such evidence from long term natural annealing is compatible with a zircon ft partial annealing zone cf 200 350 c derived by the extrapolation of laboratory annealing results based on onfined track length measurements but cannot alone discriminate between different annealing models for the zircon ft closure temperature a perhaps over simplified concept these results are consistent with the oft quoted temperature of 250 c for cooling rates of 10 100 c m y

tectonothermal evolution of the triassic flysch in the songpan garze orogen eastern tibetan plateau abstract low temperature metamorphic indicators were used to investigate the tectonothermal evolution of the triassic flysch in the songpan garze orogen eastern margin of the tibetan plateau iso thermal zones mapped with illite crystallinity kubler index ki describe a complex pattern of the diagenetic anchimetamorphic and epimetamorphic zones from this pattern a general increase in grade toward the longmenshan fault belt is observed and across the longmenshan fault belt greenschist facies and anchizonal rocks on its nw side are juxtaposed to diagenetic rocks in the sichuan basin on its se side this juxtaposition is marked by ki jumps of 0 23 2 in the sw portion of the longmenshan fault through 0 39 2 in the middle and reaching 0 71 2 in the ne of the longmenshan fault thus describing a clockwise rotation of the upper part of the longmenshan fault after metamorphism across the xianshuihe fault the truncated ki zones within the triassic flysch suggest a total offset of roughly 50 60 km due to post metamorphic sinistral strike slip peak metamorphic conditions are estimated at 365 431 c with a pressure facies of low to intermediate type 3 kbar compression at the end of the triassic was induced by the interaction of the south china north china and north tibetan blocks which caused the closure of the paleo tethys ocean and led to the folding of the triassic flysch within the songpan garze basin very low to low grade metamorphism was caused by crustal thickening due to an accretionary wedge setting which led to an increase in the thickness of the triassic flysch to 10 km and resulted in a temperature increase in those rocks due to burial finally the indo asia collision caused the formation of the longmenshan and the xianshuihe strike slip faults in the early tertiary and disturbed the distribution of the metamorphic zones

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

redefinition of the meramecian chesterian boundary mississippian the meramecian chesterian mississippi boundary in the type area is currently defined as the highest occurrence of the crinoid platycrinites penicillus and the lowest occurrence of the crinoid genera agassizocrinus and talarocrinus because these taxa have not been reported outside eastern north america attempts have been made to use conodonts and foraminifera to extend the meramecian chesterian boundary outside the type area unfortunately changes in conodont and foraminiferal assemblages do not coincide with the currently defined meramecian chesterian boundary and use of these fossil groups does not allow exact placement of the boundary outside of eastern north america the authors suggest that the meramecian chesterian boundary be redefined as the boundary between foraminiferal zones 15 and 16i of the mamet scheme irrespective of the occurrence of platycrinites penicillus this change in definition places the ste genevieve limestone genevievian stage in the lowermost part of the chesterian series with which it is biotically and sedimentologically more allied than with the underlying st louis limestone this change provides a sound biostratigraphic base for correlating the meramecian chesterian boundary outside of the type area foraminifera conodonts brachiopods and corals all show significant changes at or slightly below the st louis ste genevieve contact rather than at the genevievian chesterian contact more 52 references less

an early miocene atlantic wide foraminiferal palaeoceanographic event abstract in the lower miocene deep sea record of the atlantic ocean a foraminiferal assemblage dominated by small smooth thin walled bolivinids occurs at several sites in different regions from 20 17 ma no modern deep sea analogues are known but such assemblages are present in modern environments in the upper bathyal zone within the oxygen minimum zone we interpret this as reflecting lowered oxygen conditions in the deep atlantic ocean perhaps resulting from a period of sluggish bottom water circulation in the early miocene ocean this was a period of major change in global 13 c equivalent to the beginning of the monterey carbon excursion

integration of zircon color and zircon fission track zonation patterns in orogenic belts application to the southern alps new zealand an exhumed crustal section of the mesozoic torlesse terrane underlies the southern alps collision zone in new zealand since the late miocene oblique horizontal shortening has formed the northeastern southwestern trending orogen and exhumed the crustal section within it on the eastern side rocks are zeolite to prehnite pumpellyite grade greywacke on the western side rocks they have the same protolith but are greenschist to amphibolite facies of the alpine schist zircon crystals from sediments in east flowing rivers hinterland have pre orogenic fission track ages 80 ma and are dominated by pink radiation damaged grains up to 60 these zircons are derived from the upper f10 km crustal section unreset ft color zone that includes the late cenozoic zircon partial annealing zone both fission tracks and color remain intact and unaffected by orogenesis many zircon crystals from sediments in west flowing rivers foreland have synorogenic ftages and about 80 are colorless due to thermal annealing they have been derived from rocks that originally lay in the reset ftcolor zone and the underlying reset ft colorless zone the reset ft color zone occurs between f250 and 400 jc in this zone zircon crystals have color but reset ft ages that reflect the timing of orogenesis d 2002 elsevier science b v all rights reserved

sedimentary response to mississippian tectonic activity at the east end of the 38th parallel fracture zone carbonate fades of the greenbrier group establish the presence of an east west trending mississippian uplift and record the timing of late paleozoic tectonic movement in the east central appalachian basin at the east end of the 38th parallel fracture zone this fracture zone has been defined by previous workers from the alignment of igneous intrusive and volcanic rocks ore mineralization zones major fault systems and landsat lineaments across eastern and central north america this fracture system is apparently associated with displacement along faults in the precambrian basement rock movement along the fracture zone occurred periodically throughout the phanerozoic the lineament may be distinguished both geomorphically on landsat imagery and side looking airborne radar and stratigraphically mississippian tectonic activity along the eastern section of the fracture zone is indicated by anomalous thinning of sediments facies patterns and stratigraphic relations of uppermost devonian to upper mississippian strata of the eastern appalachian plateau

a zero damage model for fission track annealing in zircon a zircon fission track annealing model is calculated on the basis of annealing experiments from the literature with induced tracks in decay event damage free zircon samples empirically derived parallel and fanning equations for this zero damage model yield an excellent fit to the data with the fanning model providing slightly better statistical parameters a comparison between annealing models with fanning iso annealing lines but different decay event damage densities reveals that annealing temperatures and closure temperatures for the estimated partial annealing zone are highest for the zero damage model compilations of existing geologic constraints on the zircon partial annealing zone on one hand and the zircon closure temperature on the other show that these constraints do not or only partly overlap with curves of proposed models for the zircon partial annealing zone and closure temperature this finding is consistent with the fact that the annealing behavior of zircon from long duration temperature evolutions is increasingly influenced by the accumulated decay event damage zircon samples of young age or low u content show a behavior closest to the predictions of the zero damage model and are in the predicted range of published models with low decay event damage density for thermal events of more than 10 myr duration however constraints from field studies show marked differences from proposed partial annealing zone boundaries of the zero or low damage models the applicability of the zero damage model is threefold 1 it predicts correct closure temperatures in the case of very rapid cooling across the partial annealing zone where basically no decay event damage is accumulated 2 it predicts an uppermost boundary for complete annealing of a mixture of zircon components of different age as found in sedimentary samples and in this case may be used as a thermometer 3 it represents an important reference for the establishment of a more comprehensive model of zircon fission track annealing that also includes the influence of decay event damage for such a model two different equations are discussed however additional detailed experimental and field data are needed for a more robust annealing model that includes the influence of decay event damage annealing

paleoceanographic significance of neogene benthic foraminiferal changes in a southwest pacific bathyal depth transect temporal changes in benthic foraminiferal assemblages were quantitatively examined 63 m fraction in four southwest pacific deep sea neogene sequences in a depth transect between approximately 1300 and 3200 m to assist in evaluating paleoceanographic history the most conspicuous changes in benthic foraminiferal assemblages occurred in association with paleoclimatic changes defined at least in part by oxygen isotopic changes the largest centered at 15 ma early middle miocene is represented by an increase in the relative frequencies ofepistominella exigua which underwent a major upward depth migration at that time this was contemporaneous with the well known positive oxygen isotopic shift in the early middle miocene in sites 588 and 590 most of the increase in relative abundances ofe exigua occurred during the middle to later part of the 18o shift following major growth of the east antarctic ice sheet later assemblage changes occurred at 8 5 and 6 5 ma these associations indicate that the benthic foraminiferal assemblages in this depth transect largely adjusted to changes in deep waters related to antarctic cryospheric evolution in general the neogene benthic foraminiferal assemblages in this region underwent little change during the last 23 million years this faunal conservatism suggests that deep sea environments underwent relatively little change in the southwest pacific during much of the neogene although paleoceanographic changes did occur partly in response to high latitude cryospheric evolution these were not of sufficient magnitude to create major deep sea faunal changes in this part of the ocean the benthic foraminiferal assemblages are dominated by individuals smaller than 150 m most taxonomic turnover occurred in the larger 150 m size fractions

discrimination of local and global effects on upper mississippian stratigraphy illinois basin u s a abstract interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics eustasy tides and climate on upper mississippian middle chesterian stratigraphy in the tectonically active tide dominated illinois basin the cross sections show that five mixed carbonate siliciclastic high frequency sequences in the bethel through glen dean formations can be correlated around the outcrop belt through areas with very different subsidence histories the sequence boundaries are marked by paleosols and incised valleys and can be correlated basin wide within a framework of distinctive marker beds because of its updip position lowstand systems tracts are not preserved in the illinois basin the transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open marine skeletal limestone shallow marine shale and heterolithic siliciclastic tidal flat deposits the maximum flooding surface mfs for the sequences is picked at the base of the deepest water limestone facies highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal flat facies the basin wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea level changes rather than local tectonics or autogenic processes the sequences were likely produced by moderate to high amplitude 30 100 m fourth order 400 ky glacio eustatic sea level changes driven by the transition from the greenhouse conditions of the early mississippian to the icehouse conditions of the late paleozoic the lateral extent and frequency of component parasequences suggests that they were likely produced by fifth order sea level changes 10 100 ky the sequences may be bundled into third order composite sequences but the third order signal is obscured by the magnitude of the fourth order sea level changes a feature typical of ice house stratigraphies the sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the cincinnati arch and the more rapidly subsiding basin interior episodes of high and low differential subsidence occurred every two to three sequences these subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences the occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the appalachian orogenic belt to the east even in this tectonically active setting however it is the eustatic signal that generates basin wide mappable stratigraphic sequences

revealing exhumation of the central alps during the early oligocene by detrital zircon u pb age and fission track double dating in the taveyannaz formation

triassic continental subduction in central tibet and mediterranean style closure of the paleo tethys ocean the qiangtang metamorphic belt qmb in central tibet is one of the largest and most recently documented high pressure hp to near ultrahigh pressure near uhp belts on earth lu hf ages of eclogite and blueschist facies rocks within the qmb are 244 223 ma indistinguishable from the age of uhp metamorphism in the qinling dabie orogen results of a u pb detrital zircon study suggest that protoliths of the qmb include upper paleozoic qiangtang continental margin strata and sandstones that were derived from a paleozoic arc terrane that developed within the paleo tethys ocean to the north we attribute qmb hp metamorphism to continental collision between the qiangtang terrane and a paleo tethys arc terrane this collision and the coeval south china north china collision may have slowed convergence between laurasia and gondwana derived terranes and initiated mediterranean style rollback and backarc basin development within much of the remnant paleo tethys ocean realm

neogene bottom water masses and benthic foraminifera in the ne atlantic ocean modern benthic foraminiferal assemblages show a correlation with oceanic bottom water masses a study of the neogene benthic foraminifera from seven sites to the south and two sites to the north of the azores ridge shows patterns of change which can be interpreted in terms of past water masses an antarctic bottom water aabw influence has been present to the south since the mid miocene but to the north of the azores ridge aabw was present only up to the late pliocene since when it has been absent overlying aabw is north atlantic deep water nadw and north east atlantic deep water neadw the latter shows a spectacular increase in importance from the late pliocene to recent the faunal changes can be correlated with changes in circulation in the late pliocene which heralded the incoming of major glacial events from c 2 4 ma

upper mississippian lower carboniferous carbonate stratigraphy and syndepositional faulting reveal likely ouachita flexural forebulge effects eastern kentucky u s a abstract stratigraphic analysis of late middle to early late mississippian early carboniferous late meramecian early chesterian carbonates in east central and northeastern kentucky u s a shows six unconformity bound sequences the earliest late meramecian st louis sequence shows a relatively uniform distribution and a typical eastward appalachian gradient along the ene trending outcrop belt on the western margin of the appalachian basin however abrupt uplift and exposure of deeper water st louis deposits indicated by erosional thinning and well developed exposure features at the meramecian chesterian transition signal inception of regional early chesterian uplift that intensively altered the nature and distribution of the five overlying early chesterian carbonate sequences uplift was related to the syndepositional reactivation of wnw trending basement faults that broke up the st louis platform and generated a mosaic like distribution of the overlying five sequences due to structurally related erosional incision and paleoslope change to the southwest these early chesterian events coincide with a major phase of northeast directed ouachita orogeny on the southern margin of laurussia and concomitant forebulge migration to the ene modeling of regional stress distribution as well as timing and location during bulge migration strongly indicate that a migrating ouachita bulge reactivated basement structures and generated the noted stratigraphic anomalies in eastern kentucky and nearby areas the likelihood of low amplitude flexural waves like the ouachita bulge migrating across areas where they were not previously considered has major implications for understanding structural stratigraphic and eustatic anomalies in supposedly stable cratonic areas far removed from active tectonism

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

natural long term annealing of the zircon fission track system around a granitic pluton we measured 24 ages and 14 length distributions of fission tracks in zircons separated from basement sandstones around a granitic pluton to investigate natural long term annealing behaviors of the zircon fission track zft system samples were collected from three cretaceous coherent units of the shimanto accretionary complex shikoku japan along an eastward traverse at distances of between 1 6 and 10 6 km from the intrusion contact of 15 ma takatsukiyama granite exposing about 5 km in diameter sampling was carried out around the expected position of the transition zone of track retention i e the fossil partial annealing zone fpaz based on previous regional zft age distributions approaching the contact original zft ages of 100 ma show a continuous reduction to 15 ma at 3 km distance their single grain age distributions accordingly change from widespread multimodal patterns reflecting provenance ages to unimodal ones characterizing the secondary heating by the granite intrusion mean and distributions of zft lengths also show notable variations within the fpaz as a result of mixing both preexistent tracks that were shortened by the miocene heating and unannealed ones having original long lengths that have been formed and accumulated after the cooling of the pluton these facts along with observed track segmentation and annealing anisotropy suggest that the shortening patterns of tracks in nature a heating duration of 105 106 years estimated from thermal modeling are indistinguishable from those previously demonstrated at laboratory timescales this basically validates the conventional approach of extrapolating laboratory based kinetic parameters to geologic timescales the observed fpaz and thermal modeling results in conjunction with laboratory heating data previously reported and recent constraints from an ultradeep borehole favor a relatively narrow temperature range for the partial annealing zone i e 230 to 330 c for a heating duration of 106 years

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

mid miocene isotope stratigraphy in the deep sea high resolution correlations paleoclimatic cycles and sediment preservation mid miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates for example deep sea drilling project sites 289 and 574 the mid miocene carbon isotope records are characterized by an interval of high 13c values between 17 and 13 5 ma the monterey excursion of vincent and berger 1985 upon which are superimposed a series of periodic or quasi periodic fluctuations in 13c values these fluctuations have a period of approximately 440 kyr suggestive of the 413 kyr cycle predicted by milankovitch theory vincent and berger proposed that the monterey excursion was the result of increased organic carbon burial in continental margins sediments the increased 13c values called 13c maxima superimposed on the generally high mid miocene signal coincide with increases in 18o values suggesting that periods of cooling and or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric co2 levels it is likely that during the monterey excursion the ocean atmosphere system became progressively more sensitive to small changes in insolation ultimately leading to major cooling of deep water and expansion of continental ice we have assigned an absolute chronology based on biostratigraphic and magneto biostratigraphic datum levels to the isotope stratigraphy and have used that chronology to correlate unconformities seismic reflectors carbonate minima and dissolution intervals intervals of sediment containing 13c maxima are usually better preserved than the overlying and underlying sediments indicating that the 13c values of tco2 in deep water and the corrosiveness of seawater are inversely correlated this again suggests that the 13c maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric co2 the absolute chronology we have assigned to the isotopic record indicates that the major mid miocene deepwater cooling ice volume expansion took 2 m y and was not abrupt as had been reported previously the cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals the cooling was not monotonic and the 2 m y interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period the increase in 18o values of benthic foraminifera between 14 9 and 12 9 ma was greatest at deeper water sites and at sites closest to antarctica the data suggest that the 18o value of seawater increased by no more than about 1 1 per mil during this interval and that the remainder of the change in benthic 18o values resulted from cooling in antarctic regions of deepwater formation equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0 4 per mil steplike increases in 13c values only one of these increases in planktonic 13c is correlated with any of the features in the mid miocene benthic carbon isotope record

late quaternary productivity changes in the equatorial indian ocean odp hole 716a abstract the equatorial indian ocean is swept by the indian ocean equatorial westerlies iew which intensify in monsoon transitions during april may and october november driving eastward equatorial current eec to the upper ocean the eec brings significant changes in the surface productivity in the equatorial region influencing the life style of the surface and deep sea fauna this study is aimed at understanding 300 kyr record 450 150 kyrs ago of productivity changes linked to variations in iew eec in the equatorial indian ocean using high resolution microfaunal record from integrated ocean drilling program iodp hole 716a maldives ridge in total 451 core samples of 10 cm 3 volume from the 300 kyr long sequence ranging 450 150 kyrs ago were analyzed at every 1 cm interval to generate census data of the benthic foraminiferal fauna factor and cluster analyses using percentages of 53 highest ranked benthic foraminiferal species were run that enabled us to identify five biofacies indicating the varied nature of deep sea environments during the late quaternary the results show a major shift roughly 300 kyr ago across marine isotope stages 9 and 8 mis 9 8 recorded in this study as mid brunhes transition at hole 716a the present study also combines published planktic foraminiferal fauna and pteropod records from hole 716a to understand if the surface to shallow and intermediate water paleoenvironments were coupled with deep water changes during the late quaternary in the maldivian archipelago biofacies robulus nicobarensis trifarina reussi rn tr uvigerina porrecta reussella simplex upo rs and cymbaloporetta squammosa bolivinita sp cs bsp dominate before the mid brunhes transition and document high organic flux with relatively low oxygen paleoenvironment similar to the planktic foraminifer globigerina bulloides population while benthic foraminiferal biofacies hoeglundina elegans miliolinella subrotunda he ms and uvigerina peregrina quinqueloculina seminulum upe qs record high seasonality in food supply with well oxygenated deep water following the mid brunhes climatic transition 300 kyr ago at hole 716a these changes are also recorded in the population of planktic foraminiferal species globigerinoides ruber and neogloboquadrina dutertrei as well as pteropods organic carbon flux linked to changes in the iew eec strength appears to be the most plausible factor controlling faunal assemblages and hence paleoproductivity dynamics in the maldivian region our results suggest that the strength of the iew is inversely related with the indian ocean dipole iod the iod strengthened across mis 9 8 during which time the iew weakened leading to major changes at hole 716a

the enigma of early miocene biserial planktic foraminifera small biserial foraminifera were abundant in the early miocene ca 18 9 17 2 ma in the eastern atlantic and western indian oceans but absent in the western equatorial atlantic ocean weddell sea eastern indian ocean and equatorial pacific ocean they have been assigned to the benthic genus bolivina but their high abundances in sediments without evidence for dysoxia could not be explained apertural morphology accumulation rates and isotopic composition show that they were planktic genus streptochilus living streptochilus are common in productive waters with intermittent upwelling the widespread early miocene high streptochilus abundances may reflect vigorous but intermittent upwelling inducing high phytoplankton growth rates however export production estimated from benthic foraminiferal accumulation rates was low possibly due to high regeneration rates in a deep thermocline the upwelled waters may have been an analog to subantarctic mode waters carrying nutrients into the eastern atlantic and western indian oceans as the result of the initiation of a deep reaching antarctic circumpolar current active agulhas leakage and vigorous vertical mixing in the southern oceans

high resolution sequence stratigraphy in tertiary carbonate rich sections by thin sectioned well cuttings thin sectioned well cuttings provide a low cost yet widely available and underused source of subsurface data that can be used to generate high resolution sequence stratigraphic frameworks in variably consolidated carbonate prone units in basins that lack cores or high quality suites of wire line logs because of the shallow 1 km depths of many cenozoic basins there is limited downhole mixing of cuttings although these carbonate prone basins are widespread globally they generally have not been subject to analyses of high resolution sequence stratigraphy because of the sparsity of outcrop and core data we used plastic impregnated thin sections of unwashed well cuttings from a paleogene carbonate prone succession from the coastal plain of north carolina to define the stacking patterns of the facies in the subsurface this data set along with biostratigraphic wire line log and seismic data was used to generate the framework of regional lithology based sequence stratigraphy systems tracts were determined by correlating vertical changes in the percentages of rock types in the well cuttings sequence boundaries were picked beneath units having the maximum abundance of quartz sandstone cuttings maximum flooding surfaces were picked beneath the units having the most abundant cuttings of deepest marine facies thus despite some downhole mixing thin sectioned well cuttings can be used to generate lithology based sequence stratigraphic frameworks for shallow carbonate prone sedimentary basins which previously were inaccessible except by expensive deep coring programs

central and southern appalachian water and wind gap origins review and new data abstract the origin and evolution of transverse drainage were stumbling blocks to classical historical geomorphologists and many problems still remain decollements that upramp laterally transported at depth tectonic sheets in the central and southern appalachians have produced structural geomorphic fronts that are prominent features often of regional or subregional extent cf blue ridge north mountain allegheny as these structural geomorphic fronts likely were features that developed significant cover relief during the alleghanian orogeny they may hold clues to incipient landscape development during and soon after orogenesis unless buried by thick sediment cover where these fronts are crossed by transverse drainage lines spectacular water gaps that frequently expose complex structural features are produced there are many other transverse water gaps not located across decollement structures in the region these gaps display complex features that shatter bedrock and must also be accounted for in any comprehensive hypothesis of transverse water gap origin lineaments including both cross strike structural discontinuities and disturbed zones are present in the appalachians and coincide with a number of transverse water gaps the positioning of weakened bedrock zones high on structures where downcutting streams had access to them permits a localizing mechanism such as structural ensnarement to operate local sedimentary patterns may also have played roles in drainage localization major unsolved problems include post alleghanian tectonic effects rates and timings of uplift erosion and deposition whether lithotectonic weaknesses are most pronounced in gap areas and establishing a numerical chronology for drainage development whereas lithotectonic influence upon drainage development is stressed in this chapter the importance of other factors e g climate catastrophic events as documented by others in this volume is fully recognized

paleoceanographic changes during the past 1 9 myr at dsdp site 238 central indian ocean basin benthic foraminiferal proxies abstract deep sea benthic foraminifera have been quantitatively analyzed in samples 125 m size fraction from ocean drilling program odp site 238 to understand paleoceanographic changes in the central indian basin over the past 1 9 myr factor and cluster analyses of the 25 highest ranked species made it possible to identify five biofacies characterizing distinct deep sea environmental settings the environmental interpretation of each biofacies is based on the ecology of recent deep sea benthic foraminifera the benthic faunal record indicates fluctuating deep sea conditions in environmental parameters including oxygenation surface productivity and organic food supply these changes appear to be linked to indian summer monsoon variability the main climatic feature of the indian ocean region the benthic assemblages show a major shift at 0 7 to 0 6 ma marked by major turnovers in the relative abundances of species coinciding with an increased amplitude of glacial cycles these cycles appear to have influenced low latitude monsoonal climate as well as deep sea conditions in the central indian ocean basin

three dimensional sequence analysis of a subsurface carbonate ramp mississippian appalachian foreland basin west virginia usa well cuttings wireline logs and limited core and outcrop data were used to generate a regional three dimensional sequence framework for upper mississippian chesterian greenbrier group carbonates in the appalachian foreland basin west virginia usa the resulting maps were used to document the stratigraphic response of the basin to tectonics and to glacio eustasy during the transition into ice house conditions the ramp facies include inner ramp red beds and aeolianites lagoonal muddy carbonates mid ramp ooid and skeletal grainstone shoal complexes and outer ramp wackestone mudstone that grades downslope into laminated silty lime mudstone the facies make up fourth order sequences a few metres to over 90 m 300 ft thick the sequences are bounded along the ramp margin by lowstand sandstones and calcareous siltstones on the ramp sequence boundaries are overlain by thin transgressive siliciclastics and aeolianites and only a few are calichified maximum flooding surfaces on the outer ramp lie beneath deeper water facies that overlie lowstand to transgressive siliciclastic or carbonate units on the shallow ramp maximum flooding surfaces overlie siliciclastic prone transgressive systems tracts that are overlain by highstand carbonates with significant grainstone units interlayered with lagoonal lime mudstones the fourth order sequences are the major mappable subsurface units they are bundled into weak composite sequences which are bounded by red beds in spite of differential subsidence rates across the foreland basin 1 to 3 cm k y up to 25 cm k y eustatic sea level changes controlled regional sequence development thrust load induced differential subsidence of fault blocks coupled with in plane stress controlled the rapid basinward thickening of the depositional wedge whose thickness and facies were influenced by subtle structures such as arches trending at high angles as well as parallel to the margin

sequence development of a mixed carbonate siliciclastic high relief ramp mississippian kentucky u s a abstract the discovery of the supergiant oil fields of the caspian region has focused attention on eustatic tectonic and climatic controls on lower carboniferous facies this paper documents the development of a highly complex mixed carbonate siliciclastic ramp succession of the lower mississippian upper osagean lower meramecian fort payne salem interval kentucky that formed peripheral to an abandoned delta system borden formation following drowning of the paleoshelf during a time of arid climate and tectonic quiescence the antecedent borden deltaic marine paleoshelf stood 100 m above the starved basin plain to the southwest and had marginal slopes of less than 0 5 the succession is a supersequence 0 to 150 m thick approximately 5 to 10 my duration composed of two upper osagean fort payne and two lower meramecian warsaw salem depositional sequences which correlate with the global sea level cycles of ross and ross 1988 the supersequence lowstand systems tract on the basin floor consists of the lower part of a unit of green shale and mounds mound growth appears to have continued during supersequence transgression culminating in some mounds up to 60 m thick on the borden paleoshelf the supersequence transgressive systems tract is a condensed glauconite horizon s the supersequence highstand tract consists of marine quartz sandstone and shale peritidal carbonates high energy crinoidal bryozoan grainstone banks and deep ramp and slope siliceous calcisiltite third order sequences have local lowstand transgressive sand bodies those in sequence 2 are clinoformed strike sand lobes up to 50 m thick while those in the younger sequences are discontinuous sheets dip oriented lobes the siliciclastic units appear to be associated with a paleodrainage system off the borden paleoshelf in upper osagean sequences 1 and 2 third order highstand systems tracts are aggradational on the paleoshelf and prograded to the southwest as a series of clinoforms into the starved basin lower meramecian sequences 3 and 4 highstand systems tracts are relatively layer cake reflecting loss of accommodation during late osagean basin filling and they prograded more to the west into the subsiding reelfoot graben illinois basin the extremely complex facies relations reflect the interaction of the antecedent shelf slope basin topography the mixed carbonate and siliciclastic systems mounded basin floor topography the highly channeled margin morphology eustasy and relatively stable tectonics

short term annealing characteristics of spontaneous fission tracks in zircon a qualitative description abstract thermal annealing behavior of fission tracks ft has not yet been documented under short term

interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data clay mineral crystallinity and crystallite domain size data determined by x ray diffraction xrd are methods extensively used in the characterization of very low grade metamorphic conditions however the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained a consequence of the different machine conditions measurement methods and sample preparations used during analysis a calibration approach to the standardization of data using rock chip standards is presented which allows data sets produced by different research groups to be directly and quantitatively compared a standardized scale the crystallinity index standard cis is proposed with illite crystallinity anchizonal boundary limits of 0 25d 2 and 0 42d 2 and equivalent illite crystallite sizes of 52 and 23 nm respectively determined by the warren averbach method calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments and should improve the accuracy and reliability of correlations made between xrd data and other indicators of very low grade metamorphism hence increasing the value of such clay mineral studies

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

coupling accumulation model with gas bearing features to evaluate low rank coalbed methane resource potential in the southern junggar basin china to reveal the resource potential of low rank coalbed methane lrcbm and determine the favorable area from six different zones in the southern junggar basin in china a new lrcbm assessment methodology was developed this methodology comprises three steps developing the regional accumulation model determining the zone with gas bearing features and exploring for the favorable targets first the coalbed methane cbm generating characteristics the sealing properties of the over and underlying rocks in the cbm reservoir and the hydrogeological characteristics preserved in the reservoir were analyzed by combining these characteristics with the tectonic burial history geothermal history hydrocarbon evolution and cbm gas saturation changes the lrcbm regional accumulation model that illustrates the lrcbm enrichment characteristics of the middle lower jurassic series in the southern junggar basin was derived second the lrcbm gas bearing features of each zone were comprehensively analyzed using a large data set acquired from a coalfield the lrcbm bearing features and the variation of their related parameters in six different zones of the southern junggar basin were presented these parameters relate to features such as coal seam distribution petrology reservoir property coal thermal evolution and coal and gas content characteristics third the favorable targets are explored by calculating the lrcbm resources and intensively evaluating each zone the favorable targets are candidates for further exploration in the southern junggar basin at depths shallower than 2000 m 7000 ft the lrcbm resources in the southern junggar basin are 3054 7 108 m3 10 8 1012 ft3 with resource abundance of 0 42 11 65 108 m3 km2 0 06 1 66 108 ft3 ac thereby demonstrating a significantly good exploitation prospect moreover the favorable and relatively favorable areas for further exploration in the southern junggar basin are zone 4 and 5 respectively

assembly of the lhasa and qiangtang terranes in central tibet by divergent double subduction abstract integration of lithostratigraphic magmatic and metamorphic data from the lhasa qiangtang collision zone in central tibet including the bangong suture zone and adjacent regions of the lhasa and qiangtang terranes indicates assembly through divergent double sided subduction this collision zone is characterized by the absence of early cretaceous high grade metamorphic rocks and the presence of extensive magmatism with enhanced mantle contributions at ca 120 110 ma two jurassic cretaceous magmatic arcs are identified from the caima duobuza rongma kangqiong amdo magmatic belt in the western qiangtang terrane and from the along tso yanhu daguo baingoin daru tso magmatic belt in the northern lhasa terrane these two magmatic arcs reflect northward and southward subduction of the bangong ocean lithosphere respectively available multidisciplinary data reconcile that the bangong ocean may have closed during the late jurassic early cretaceous most likely ca 140 130 ma through arc arc soft collision rather than continent continent hard collision subduction zone retreat associated with convergence beneath the lhasa terrane may have driven its rifting and separation from the northern margin of gondwana leading to its accretion within asia

tectonothermal evolution of the triassic flysch in the bayan har orogen tibetan plateau abstract the bayan har orogen comprises a major part of the qingzang dianxi fold region in western china it preserves important information of the tectono thermal evolution covering the time span from the closure of the paleo tethys ocean up to the formation of the himalayas low temperature metamorphic indicators such as mineral assemblages illite crystallinity ic chlorite crystallinity cc illite polytype b cell dimension of k white micas geothermometry of selected minerals were analyzed the values of kubler index ki of the triassic flysch in the bayan har orogen range from 0 23 1 63 2 while arkai index ai in a range of 0 21 0 60 2 iso thermal zones mapped with ki describe a pair of anchizones and an anchiregion within the bayan har orogen the giant yushu anchizone in the southwest extending 750 km long and 100 km wide the zaling eling lakes anchizone in the center about 150 km long and 40 km wide and the xing tong zhe anchiregion in the northeast covering an area of roughly 60 000 km 2 they are separated by diagenetic zones peak metamorphic conditions are estimated around 280 330 c and a low to intermediate n new hampshire pressure type a slight change with increasing then decreasing pressure was observed from sw to ne the relationship between anchimetamorphic pattern of triassic flysch and large scale folds and faults indicates syn to post structural metamorphism compression at the end of the triassic induced by the interaction of the tarim north china and indian blocks caused the closure of the paleo tethys ocean and led to the folding of the triassic flysch within the paleo tethys ocean basin anchimetamorphism may have been caused by crustal thickening of 10 km due to an accretionary wedge setting and a temperature increase in those rocks due to burial such a regional metamorphic pattern would provide important information for reconstruction of palaeotectonic palaeogeograph and the evolutionary history of tibetan plateau

genetic stratigraphy and depositional systems of the upper devonian lower mississippian price rockwell deltaic complex in the central appalachians u s a abstract rocks of the price and rockwell formations comprise the uppermost devonian lower mississippian deltaic complex in the central appalachians the price formation is dominantly marine and refers to all uppermost devonian lower mississippian rocks above either hampshire group red beds or the marine greenland gap formation and below either the greenbrier limestone group or maccrady formation red beds in the central appalachians the rockwell formation is dominantly non marine and refers to equivalent rocks in south central pennsylvania and the maryland west virginia panhandle region members of the price formation are generally equivalent to discrete genetic events price deposition was initiated in latest devonian time when a regional transgression covered delta and alluvial plain facies of the catskill deltaic complex with protected bay and strandline facies of the oswayo member in west virginia pennsylvania and western maryland farther south these transgressive facies overlie the cloyd conglomerate member a thin regressive transgressive sedimentary wedge and occur in the lower part of the sunbury shale member subsurface berea sandstone deposition corresponded to regional exposure and erosion in the outcrop belt this unconformable surface was overstepped in earliest mississippian time by a major transgression that deposited a variably thick but persistent basal transgressive sandstone during shoreface retreat sandstones that have been referred to the cussewago sandstone in northern west virginia and southwest pennsylvania are part of this basal sandstone eastward these sandstones thicken coarsen and interbed with a polymictic diamictite at the base of the rockwell formation shaly facies of the earliest mississippian transgression overlie the basal sandstone the riddlesburg shale preserves offshore and open bay facies in west virginia that grade eastward to estuarine and restricted back bar lagoon and marsh facies of a barred bay complex in south central pennsylvania and the maryland west virginia panhandle from central west virginia riddlesburg facies grade southward into basinal facies of the sunbury shale member syndepositionally active basement features the west virginia dome and tri state block were structurally positive areas in the foreland basin the tri state block caused truncation of lower mississippian marine facies in western maryland and large scale westward erosional overlap of channel fill sandstones in the upper rockwell formation the west virginia dome was also structurally positive and the basal transgressive sandstone contains phosphatic omission surfaces on the dome crest lack of subsidence caused scour and incision of riddlesburg facies by overlying deltaic facies progradation ensued with fluvial dominant shallow water deltaic systems price rockwell member in northern west virginia and marine dominant deep water deltaic facies farther south a 150 m minimum paleodepth estimate in the foreland basin is based on stratigraphic thickness in southern west virginia following a transgression near the kinderhookian osagean boundary price marine deltaic facies form a coarsening upward sequence to delta plain coals and coastal alluvial plain red beds a 35 m estimate for average storm wave base utilized tempestite proximal distal trends

oligocene miocene biostratigraphy magnetostratigraphy and isotopic stratigraphy of the western north atlantic magnetostratigraphic records from western north atlantic deep sea drilling project dsdp sites 563 and 558 are correlated with the geomagnetic polarity time scale gpts berggren et ai 1984a 1984b using marine magnetic anomalies and selected biostratigraphic datum levels the magnetochronology established is used to make direct magnetobiostratigraphic correlations that agree with previous oligocene early miocene studies however we show that zones nn8 partim and nn9 and associated epoch 11 correlate with magnetic anomaly 5 chron csn this contrasts with previous indirect correlations of epoch 11 with anomaly sa and requires an upward adjustment of 1 5 2 0 m y for middle late miocene calcareous nannofossil zones we correlate the middle late miocene boundary with zone nn8 and earliest chron csn 10 4 ma

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

mesozoic cenozoic tectonothermal evolution of the eastern part of the tibetan plateau songpan garze longmen shan area insights from thermochronological data and simple thermal modelling we present a synthesis of the tectonic and thermochronological evolution of the eastern tibet since the triassic the long term cooling histories obtained on magmatic and metamorphic rocks of the south songpan garze kunlun and yidun blocks are similar showing a very slow and regular cooling during late jurassic and cretaceous confirming the suspected lack of major tectonic events between c 150 and 30 ma the exhumation linked to the tertiary growth of the tibetan plateau initiated around 30 ma and concentrates at the vicinity of the major tectonic structures exhumation rates increased again from about 7 ma in the longmen shan to interpret this very slow cooling rate between late jurassic and early cenozoic from granites of this area we use a simple 1d thermal model that takes into account the thermal properties of both sediments and crust the results suggest that 1 high temperature 500 8c can be kept over a long period of time 2 during cretaceous cooling is mostly controlled by the thermal properties of sediments of continental origin and 3 the initial late triassic rapid cooling rate was caused by the large thermal contrast between the granite body and the sedimentary rocks rather than by a high exhumation rate

updip sequence development on a wave and current dominated mixed carbonate siliciclastic continental shelf paleogene north carolina eastern u s a abstract cores quarry exposures and exploratory wells in the paleogene sediments of the albemarle basin north carolina span the transition between the southern carbonate and northern siliciclastic provinces of the eastern u s continental shelf succession this swell wave and current dominated shelf succession differs from the standard carbonate sequence stratigraphic model because available accommodation is limited by the depth of wave abrasion and scour the study area is on the thin updip part of the shelf which includes the relatively positive cape fear arch onslow block and the slowly subsiding 1 5 cm ky albemarle block to the north the paleogene supersequence set has a basal boundary that is a hardground on cretaceous shoreface shallow shelf mollusc facies it is overlain by a thin paleocene sequence of transgressive deeper offshore glauconitic fine sands to deep marine silt shale five regionally mappable vertically stacked eocene sequences 0 30 m thick contain coastal sands shoreface sandy mollusc rudstone offshore bryozoan grainstone packstone and subwave base fine wackestone packstone and marl eocene sequences commonly are bounded by hardgrounds overlain by thin local lowstand shallow marine sands they consist of a thin transgressive shallow marine unit commonly absent overlain by an upward shallowing highstand marine succession on the arch lowstand and transgressive units may be condensed into lags the lower oligocene succession on the arch has a single marl to fine foram sand dominated sequence whereas downdip two to three siliciclastic rich sequences are developed capped by nearshore sandy molluscan facies the upper oligocene section is dominated by possibly three sequences composed of basal thin sands grading up into variably sandy mollusc rudstone sequence development was influenced by differential movement of basement blocks which influenced localization of fines in lows coupled with increasing third order eustatic sea level changes during later paleogene global cooling this was coupled with swell wave and current sweeping of the shelf that effectively decreased available accommodation by 20 30 m and generated the distinctive hardgrounds at sequence boundaries and variable development of lowstand and transgressive system tracts the well developed highstand deposits reflect maximum accommodation allowing deposition of an upward shallowing succession that terminated at the depth of wave abrasion and current scour on the open shelf the sequence stratigraphic development contrasts markedly with that from tropical shelves which tend to be aggraded to sea level

subtropical to temperate facies from a transition zone mixed carbonate siliciclastic system palaeogene north carolina usa palaeogene passive margin sediments on the us mid atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate siliciclastic shelves this study utilizes well cuttings outcrop core and seismic data to document temporal and spatial variations in admixed bryozoan rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone this zone was situated between north flowing warm waters of the ancestral gulf stream carbonate dominated settings and south flowing cold waters of the ancestral labrador current siliciclastic dominated settings some degree of mixing of carbonates and siliciclastics occurs in all facies however siliciclastic prone sediments predominate in nearshore settings while carbonate prone sediments are more common in more open marine settings of the inner shelf break and deep shelf a distinctive dual break shelf depositional profile originated following a major late cretaceous to palaeocene transgression that drowned the earlier shallow platform this profile was characterized by prominent mid shelf break dividing the shallow shelf from the deep shelf and a major continental shelf slope break incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin storm wave base also contributed to the preservation of the dual break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid shelf break sediment fines in deep shelf facies were produced in place transported downdip from the shallow shelf by storm ebb currents and boundary currents and reworked from adjacent areas of the deep shelf by strike parallel boundary currents regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf with warmer waters and more humid climates favouring carbonate deposition and cooler more arid conditions favouring glaucony and siliciclastic dominated deposition continuous wave and current sweeping of the shallow shelf favoured deposition of mud lean facies across much of the shallow shelf skeletal components in much of the carbonate rich strata formed in warm nutrient rich subtropical waters as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages these indicators of warm water deposition within the bryozoan mollusk rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage such facies generally are associated with cooler water depositional settings

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

carbon oxygen isotope signal of mississippian slope carbonates appalachians usa a complex response to climate driven fourth order glacio eustasy abstract mississippian chesterian ramp slope muds in virginia deposited on the margin of a rapidly subsiding foreland basin were not significantly reset isotopically by regional meteoric aquifer systems that affected units on the adjacent platform carbon and oxygen isotopic ratios of these muds tend to covary at the scale of the twelve 4th order sequences that dominate the platform succession the 13 c values of the slope muds range from 0 5 to 4 pdb and lie in the range of least altered contemporaneous brachiopods from north america indicating little resetting of carbon isotopes by diagenesis there is an approximately 1 to 2 decrease in 13 c in the maximum flooding zone relative to the lowstand followed by a positive shift upward in the highstand before becoming more negative toward 4th order correlative conformities meteoric diagenesis might have reset some sediments just beneath a sequence boundary to lighter values it cannot account for the observed shifts evident throughout the sequences the 13 c enriched values in 13 c profiles could be due to increased productivity during glacial stages the increased productivity during glacial stages was probably due to increased ocean circulation coupled with shallowing which brought the ramp top into waters with more 13 c enriched dissolved inorganic carbon with the opposite effects occurring during deglaciation the 18 o values of muds range from about 2 2 to about 4 6 pdb falling within and beyond the lighter part of the range of contemporaneous north american brachiopods mii h s grossman e l yancey t e 1999 carboniferous isotope stratigraphies of north america implications for carboniferous paleoceanography and mississippian glaciation geol soc am bull 111 960 973 these values likely have been reset by burial diagenesis and perhaps by some meteoric diagenesis just beneath correlative conformities the sequences show negative excursions of 1 to 2 in 18 o in the maximum flooding zone relative to the lowstand and then become more positive upward in the highstand then decrease toward the correlative conformities some of the preserved signal could reflect ice volume changes although this would account for only 0 5 to 1 change the ice volume effect during lowstands plus cooling of ramp top waters and small increases in salinity due to increased aridity in the appalachian basin could account for the remaining 0 5 to 1 5 of oxygen isotope excursions with the opposite effect occurring during high sea levels the 18 o and 13 c of the appalachian ramp slope facies lack the strong 3rd order trends of the mid continental united states and europe the remnant 4th order carbon and oxygen isotope signal is similar in structure to cenozoic deep sea isotope profiles that are due in large part to 4th order glacio eustasy this would be compatible with onset of late paleozoic glaciation of gondwana

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

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

a field based estimate of the zircon fission track closure temperature abstract a field based estimate of the zircon fission track closure temperature is proposed from 13 zircon fission track cooling ages of the gold butte block se nevada using previously published and new thermochronological data the thermal history of the gold butte block is re evaluated resulting in a geothermal gradient estimate of 20 3 c km and a slow cooling rate of 0 55 0 02 c m y from the late jurassic to the early miocene before onset of rapid miocene cooling the rapidly cooled part of the gold butte block provides a slip rate of 10 5 km m y of the hanging wall that caused the miocene exhumation of this crustal section assuming these thermal conditions are correct the closure temperature of the zircon fission track system is determined at 205 18 c which is in good agreement with previous field based estimates because of the variation in zircon fission track annealing behavior with radiation damage field studies are a suitable way to calibrate the closure temperature of the zircon fission track system

late oligocene miocene paleoceanographic evolution of the southeastern indian ocean evidence from deep sea benthic foraminifera odp site 757 abstract we quantitatively analyzed deep sea benthic foraminifera from 125 m size fraction from ocean drilling program odp site 757 to understand deep sea paleoceanographic changes in the southeastern indian ocean during the late oligocene miocene 26 5 5 35 ma we used the knowledge of the ecology of recent deep sea benthic foraminifera for environmental interpretations factor and cluster analyses were run using percentages of 46 highest ranked species that helped identify six biofacies defining six clusters of samples the faunal data document a major shift in deep sea ventilation organic carbon flux and productivity at 8 3 ma coinciding with the major intensification of the indian ocean monsoon system this marks a change from cold and well oxygenated deep waters with low and pulsed organic carbon flux during 26 5 to 8 3 ma to oxygen poor deep waters with sustained flux of organic matter from 15 0 to 7 6 ma the deep sea currents were stronger in the southeastern indian ocean probably due to major expansion of the east antarctic ice sheet and increased production of deep waters and in turn increased deep sea circulation the productivity increased in the indo pacific region in the late miocene and the modern monsoon regime probably established at 8 3 ma

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

sequence stratigraphic analysis using well cuttings mississippian greenbrier group west virginia well cuttings analysis predates modern carbonate facies analysis sequence stratigraphy seismic reflection surveys and advanced geophysical logging techniques these newer methods have resulted in well cuttings becoming less important as a major source of data for high resolution subsurface analysis binocular analysis of well indurated paleozoic well cuttings can be used to construct detailed vertical facies successions in wells when tied to wire line logs facies analysis can then be used to construct higher resolution sequence stratigraphic frameworks and time slice maps this approach was tested on mississippian carbonates in the appalachian basin of west virginia the analysis was done using the washed coarse fraction 1 2 mm 0 04 0 08 in of the cuttings for each sample interval classified according to dunham rock type counted to determine relative abundance and plotted as percent lithology versus depth for each well digitized wire line logs and the cuttings percent logs were adjusted typically 10 ft 3 m or so to consider drilling lag lithologic columns were produced from the combined data and sequences were picked gamma ray markers were used to correlate the sections and sequence stratigraphic cross sections were produced time slice maps were generated that show the thickness of the individual sequences and the distribution of major facies within systems tracts this approach generated a rock based high resolution sequence framework for the reservoir and led to a much better understanding of controls on the distribution and stacking of reservoirs

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

paleogene stratigraphy and sea level history of the north carolina coastal plain global coastal onlap and tectonics abstract coastal onlap of paleogene depositional sequences mapped by stage and compared to curves of global coastal onlap and eustasy facilitate differentiation of the effects of local uplift and subsidence from eustasy on the onslow and albemarle blocks about the neuse hinge in north carolina differential uplift and subsidence of these blocks has controlled the stratal geometries and patterns of relative coastal onlap on each block potential mechanisms to produce the uplift and subsidence include episodic flexural deformation resulting from sediment loading in the salisbury embayment and horizontal compressional deformation resulting from plate motion danian sea level rise produced the initial paleogene siliciclastic sequences ta1 2 and ta1 3 on both blocks after deposition of the danian sequences and prior to thanetian inundation the onslow block was elevated relative to the albemarle block the ypresian ta2 5 2 9 one is generally restricted to the downdip albemarle block has a depositional updip limit and represents a major basinward shift in local coastal onlap at a time when global coastal onlap and long term eustatic curves predict a major landward shift this suggests that both blocks were uplifted during the ypresian lutetian bartonian sequences ta3 3 ta3 5 3 6 represent the most extensive landward shift in coastal onlap during the paleogene in north carolina and show erosional updip limits on both blocks differences in the degree of overstepping on the two blocks reflects post middle eocene uplift but greater relative uplift of the albemarle block the priabonian ta4 1 and either the ta4 2 or ta4 3 has erosional updip limits on both blocks and represents a significant basinward shift in local coastal onlap this shift occurs during a time when global coastal onlap and long term eustasy indicate a landward shift as great as that during the lutetian bartonian therefore both blocks were uplifted but the distribution of the priabonian on the albemarle block indicates greater relative uplift in north carolina the rupelian ta4 4 oversteps the priabonian on both blocks but not as far as predicted by global coastal onlap and eustasy based on the offlapping relationship of the erosional updip limit on both blocks both areas were uplifted prior to rupelian deposition chattian sediments tb1 1 1 4 lower part reflect a downward shift in coastal onlap which is consistent with global coastal onlap and long term eustatic fall

benthic foraminiferal evidence for the existence of an early miocene oxygen depleted oceanic water mass this study presents new data derived from changes in benthic foraminiferal assemblages between 24 and 8 ma in the atlantic and indian oceans which are integrated with published stable isotope and fauna1 records we have identified an intermediate to deep water mass which was lower in oxygen and was restricted to the nw indian atlantic and the tethys mediterranean oceans our interpretations are based on the coeval occurrences 19 5 16 5 ma of high abundances of smooth walled bolivinids in these oceans our observations agree with the interpretations of previous workers for the occurrence of tethys derived intermediate and deep water in the northern indian ocean between 24 and 14 ma and for northern component water production in the atlantic ocean between 20 and 16 ma the water mass defined by these bolivinids formed a southward flowing northern component water in the atlantic ocean and contributed via tethys to the intermediate and deep water input into the indian ocean

timing of granite emplacement and cooling in the songpan garze fold belt eastern tibetan plateau with tectonic implications abstract new u pb and rb sr geochronology on syn and post orogenic granites provide constraints on the timing of major tectonic events in the songpan garze fold belt west sichuan china the ma nai granite was probably syn kinematic with the main deformation and yields an age of 197 6 ma that is interpreted as an upper age limit of the indosinian event zircons and apatites from the post kinematic rilonguan granite also yield jurassic ages 195 6 and 181 4 ma the post orogenic markam massif gives two ages of 188 1 and 153 3 ma both granites are undeformed and cut structures in the triassic sedimentary rocks these results demonstrate that the major deformation and decollement tectonics in the songpan garze fold belt occurred prior to the early jurassic the wide range of ages obtained for post kinematic granites from early jurassic to late jurassic suggests that locally magmatic activity persisted for a long time at least 50 ma after the indosinian compressional tectonism no tertiary ages have been obtained suggesting that these granites were not affected strongly by the india asia collision

environmental distribution of recent benthic foraminifera on the northeast united states continental slope several bathymetrically consistent recent benthic foraminiferal biofacies have been recognized from the continental slope south east of cape cod faunal assemblages are dominated by globobulimina bulimina upper slope less than 1 000 m and uvigerina peregrina lower slope uppermost rise water depths between 1 000 and 2 500 m the globobulimina bulimina assemblage coincides with the oxygen minimum zone this agrees with the occurrence of globobulimina in mediterranean sapropels organic rich sediments deposited under anoxic conditions previous studies have noted the association of u peregrina with bathyal water depths deep water temperatures of 3 to 4 c and water of low oxygen content however correlations between abundance of u peregrina and water depth or temperature are not the same everywhere and no correlation with dissolved oxygen in the water column is seen on the united states continental slope and rise the highest abundances of u peregrina coincide with maxima of organic carbon and silt within the slope sediments this suggests that the distribution of u peregrina in this region may be influenced more by low oxygen in the sediments rather than by low oxygen content of the overlying water

sequence development on a sediment starved low accommodation epeiric carbonate ramp silurian wabash platform usa mid continent during icehouse to greenhouse transition abstract twelve cored wells through the silurian section of the wabash platform indiana u s a and 2 non cored basinal wells with cuttings were studied to define the sequence stratigraphy of a sediment starved ramp within a low latitude epeiric sea during the latest ordovician icehouse to silurian greenhouse transition the wabash platform approximately 200 000 km2 area was bounded to the north by the michigan basin to the east by the appalachian foreland basin and passed to the southwest into the vincennes basin which was open to the ocean facies developed include platform fringing buildups stromatactis wackestone core stromatoporoid skeletal wackestone caps and crinoidal rudstone packstone flank facies and non buildup crinoid grainstone packstone sheets shoals skeletal wackestone variably cherty between fair weather and storm wave base deep lagoon and deep ramp and carbonate mudstone clean to argillaceous sub storm wave base deep lagoon and deep ramp basin the eleven sequences 2 m to 30 m thick and 1 to 4 m y durations average 2 5 m y generally can be correlated to global sea level cycles the lower three sequences are disconformity bounded reflecting moderate ice sheets but the others are relatively conformable the most easily mapped regional surfaces are the transgressive surfaces because the correlative conformities are cryptic the wide well spacing prevented mapping of lowstand system tracts the transgressive systems tracts are upward deepening upward fining carbonate units that become more argillaceous and silty upward the highstand systems tracts are upward coarsening carbonate mudstone to wackestone packstone and rare grainstone barrier bank complexes and isolated buildups aggraded during deposition of the upper 4 sequences to form a discontinuous raised rim 40 m relief to the ramp while the interior of the platform remained sediment starved subsidence rates in the basin were very low 0 6 to 1 2 cm k y but the low platform accumulation rates 0 2 cm k y to 0 8 cm k y prevented the seafloor from building to sea level in all but the lower three sequences and later over barrier banks accumulation rates 2 cm k y parasequence development in high accommodation settings elsewhere in the silurian in north america records transition from moderate ice sheets to an ice free world this is weakly expressed on the wabash platform due to the dominantly deeper subtidal setting the remarkably low sedimentation rates resulted from the epeiric sea being isolated from the open ocean and they likely are typical of the large epeiric seas of the paleozoic

mixed carbonate siliciclastic sequence stratigraphy of a paleogene transition zone continental shelf southeastern usa abstract the sequence stratigraphy and facies of the paleogene in the subsurface of the albemarle basin north carolina was defined using 1600 thin sections of plastic impregnated well cuttings from 24 wells wireline logs biostratigraphic data and seismic data the facies formed in the transition zone between warm subtropical and temperate conditions on a swell wave dominated open shelf exposed to major boundary current activity the shelf has a distinctive seismic profile consisting of a shallow inner shelf inner shelf break deep shelf depths in excess of 200 m and the continental slope the inner shelf was characterized by distinctive quartz sand and sandy mollusk facies inshore passing seaward into a broad wave swept abrasional shelf and then into storm influenced bryozoan echinoderm limestones to depths of several tens of meters argillaceous lime mud marl deposition was widespread across the deep shelf extending onto the inner shelf during major highstands sediment thickness trends were controlled by greater differential subsidence of crustal blocks within the albemarle basin which considerably modified but did not obliterate the effects of eustatic sea level changes in this passive margin setting five supersequences were identified on seismic and in wells each consisting of multiple regionally identifiable sequences the paleocene supersequence is dominated by widespread marl deposition reflecting shelf flooding into the late paleocene thermal maximum this warming corresponds with widespread inner shelf skeletal carbonate deposition from the late paleocene through the middle eocene the two eocene supersequences identified are dominated by bryozoan echinoderm rich carbonates that formed a seismically definable sediment buildup 50 km wide by 100 m thick across the deepest inner shelf during the lower to early middle eocene middle to upper eocene supersequence highstand sequences indicate increased progradation and greater mixing of shelf carbonates with nearshore siliciclastics likely in response to lowering sea levels and cooling climate the two oligocene supersequences identified are dominated by coarse siliciclastic sand that is heavily admixed with mollusk foraminifer dominated carbonates rapid flooding followed by extensive progradation of shallow shelf sediments in oligocene sequences reflects continued eustatic lowering driven by the onset of icehouse climatic conditions increased incision and reworking of deep shelf sediments during oligocene supersequence highstands resulted from increased ancestral gulf stream boundary current activity during icehouse times key elements controlling facies distribution through time include significant wave energy which controls the width and distribution of inner shelf facies belts through the degree of water bottom abrasion and winnowing boundary currents also are capable of large scale reworking of deep shelf sediment they also provide a mechanism for widespread inner shelf hardground development during major transgressions in addition boundary currents play a major role in stabilizing local climate by buffering seasonal temperature variations directly influencing which carbonate grain producers can thrive in this transition zone setting