paleoenvironmental and temporal significance of variably colored paleozoic orthoconic nautiloid cephalopod accumulations abstract accumulations of orthoconic nautiloid cephalopods occur throughout the lower paleozoic from the ordovician to the carboniferous studies focused on unraveling the nature of their formation tend to be restricted both spatially and temporally to localized investigations of either the constituent faunas or the lithological successions within which they occur herein an innovative approach to determining common factors among these particular fossil rich beds is utilized whereby different color and taphonomic groupings are identified and classified for known world occurrences of orthoconic nautiloid cephalopod concentrations these groupings are related to inferred paleosettings and paleoenvironmental gradients those horizons with a predominantly black to gray color generally represent event beds and were frequently deposited together with black shales while those ranging from red brown green beige are prevalently accumulations associated with condensed sequences and discontinuity surfaces the findings are further used to identify time specific changes in orthoconic nautiloid accumulation processes

tectono sedimentary evolution and geochronology of the middle miocene altinapa basin and implications for the late cenozoic uplift history of the taurides southern turkey abstract the tauride range in southern turkey is flanked and overlain by neogene sedimentary basins to the south and on top of the high range these basins are mainly marine whereas poorly studied intramontane basins dominated by continental deposits are exposed to the north in this paper we study the stratigraphy and structure of the continental altinapa basin and provide 40ar 39ar geochronology for volcanic deposits in the stratigraphy the stratigraphy can be subdivided into a lower group displaying 400 m of fining upward fluvio lacustrine sediments unconformably overlain by an upper group with 500 m of lacustrine deposits andesitic lavas and volcaniclastic sediments 40ar 39ar dating of three volcaniclastic samples across the upper group provide 11 8 11 6 ma ages the altinapa basin is an extensional basin which formed predominantly due to n s to ne sw directed stretching the main basin forming phase occurred during deposition of the lower group prior to 11 8 ma paleostress inversion analyses demonstrate uniaxial stress with highly variable extension directions that are consistent with currently observed seismicity patterns the middle miocene extension history of the altinapa basin is consistent with a regional pattern of middle miocene ne sw to nw se extension north of the cyprus subduction zone this suggests that the cyprus subduction zone has been in retreat relative to central anatolia since at least middle miocene time the continental altinapa basin is currently at an elevation of 1 km whereas partly contemporaneous marine sediments in the mut basin that lies on top of the tauride range are elevated to 2 km this shows strong late cenozoic differential uplift in southern turkey with at least 1 km more uplift of the tauride range than of the intramontane basins to the north we conclude that the current high elevation of the taurides is related to late neogene extension and does not result from the late cretaceous to perhaps oligocene folding and thrusting that deformed the rocks in the range

a new late holocene sea level record from the mississippi delta evidence for a climate sea level connection abstract a detailed relative sea level rsl record was constructed for the time interval 600 1600 ad using basal peat to track sea level and containing 16 sea level index points that capture 60 cm of rsl rise the study area is in the mississippi delta where the spring tidal range is 0 47 m the impact of ocean currents on sea surface topography is limited and crustal motions are well constrained age control was obtained by ams 14 c dating and most ages represent weighted means of two subsamples sample elevations were determined by combining differential gps measurements with optical surveying all index points were plotted as error boxes using 2 confidence intervals for the ages plus all vertical errors involved in sampling and surveying as well as the indicative range of the samples a striking clustering of sea level index points between 1000 and 1200 ad suggests a possible acceleration in the rate of rsl rise removal of the long term trend 0 60 mm yr 1 allows for the possibility of a sea level oscillation with a maximum amplitude of 55 cm however given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out comparison of the new rsl record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes including the medieval warm period and the little ice age however given the error margins associated with this reconstruction it is stressed that this causal mechanism is tentative and requires corroboration by high resolution sea level reconstructions elsewhere

deciphering the sardic ordovician and variscan deformations in the eastern pyrenees sw europe detailed geological mapping of the la cerdanya area canigo unit eastern pyrenees provides new data characterizing the different structural styles exhibited by cambrian lower ordovician jujols group and upper ordovician successions their unconformable contact related to the sardic phase ranges from 0 paraconformity to 90 angular discordance the jujols group rocks topped by the unconformity are affected by sardic foliation free open folds the pre sardic succession the sardic unconformity and the lower part of the post sardic succession rabassa conglomerate and cava formations are cut and offset by several late ordovician nne ssw trending synsedimentary extensional faults associated with hydrothermal activity which dramatically affected the thickness of the lower part of the upper ordovician succession we relate 1 the mid ordovician sardic uplift and erosion and 2 a mid to late ordovician upward propagating extensional fault system bounding the outline of half grabens subsequently infilled by alluvial deposits to a thermal doming event about 475 450 ma that led to the uplift and stretching of the ordovician lithosphere thermal doming may be caused by mafic magma underplating and responsible for the coeval calc alkaline magmatic activity broadly developed in the eastern pyrenees we discuss the similarities between the mid ordovician sardic unconformity and other early paleozoic unconformities described in neighbouring areas finally we suggest a geodynamic scenario in which a regional scale thermal event was related to the opening of the rheic ocean that led to the drift of avalonia from the sw european margin of gondwana

a simple model for the skewness of global sea surface winds abstract a strong linear relationship between the mean and skewness of global sea surface winds both zonal and meridional is shown to exist such that where the wind component is on average positive it is negatively skewed and vice versa this relationship is observed in reanalysis satellite and buoy data this relationship between the mean and skewness fields of sea surface winds follows from the nonlinear surface drag predicted for a turbulent boundary layer by monin obukhov similarity theory since forcing perturbations speeding the wind up are subject to a stronger drag force than perturbations slowing it down furthermore it is demonstrated that the results of an empirical fit of observed surface winds to a stochastic differential equation presented in a recent study by sura are consistent with the white noise limit of the momentum equations for a turbulent boundary layer subject to fluctuating forcing albeit with a somewhat different physical interpretation

relative sea level rise and tidal development in the fundy tidal system previous studies of sea level and tidal amplification in the bay of fundy suggested a linear increase of tidal amplitude as relative sea level rose new data presented here are used in a numerical tidal model in an effort to reproduce paleotidal regimes over the last 7000 years five new sea level curves covering the last 4000 years and some previously published data extending the record back to 7000 years before present bp are used as the data base these data when used together with the tidal model indicate that tidal amplitudes increased much more rapidly between 7000 and 4000 years ago than in the period 4000 years ago to present it is also shown that changes in depth within the bay of fundy produce little effect on the tidal amplitudes whereas such variations in water depth on georges bank account for almost all the change this calculation of tidal amplitude changes allows calibration of sea level curves to be made for the bay of fundy using higher high water hhw indicators

catastrophic tidal expansion in the bay of fundy canada tidal models for the bay of fundy canada site of the highest recorded modern tide show that tidal amplification began in the early holocene and by ca 5000 bp the range was almost 80 of the present range empirical data consisting of 146 sea level index points and other observations appear to contradict model results aggregated relative sea level data for chignecto bay and minas basin show that rapid tidal expansion began ca 3400 bp however if we separate these two geographically separate data sets evidence for this rapid late holocene tidal expansion is confined to minas basin we explain this singularity by positing a barrier at the mouth of minas basin at the minas passage that delayed tidal expansion with the rapid breakdown of this barrier and near instantaneous tidal expansion water temperature dropped tidal currents and turbidity increased and the form of the inner estuary was changed from lagoonal mesotidal to macrotidal we argue that the catastrophic breakdown of the barrier is

onset of recent rapid sea level rise in the western atlantic ocean a high resolution record of sea level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2 m thick salt marsh peat sequence at chezzetcook nova scotia canada former mean tide level positions are reconstructed with a precision of 0 055 m using a transfer function derived from distributions of modern salt marsh foraminifera our age model for the core section older than 300 years is based on 19 ams 14c ages and takes into account the individual probability distributions of calibrated radiocarbon ages the past 300 years is dated by pollen and the isotopes 206pb 207pb 210pb 137cs and 241am between ad 1000 and ad 1800 relative sea level rose at a mean rate of 17 cm per century apparent pre industrial rises of sea level dated at ad 1500 1550 and ad 1700 1800 cannot be clearly distinguished when radiocarbon age errors are taken into account furthermore they may be an artefact of fluctuations in atmospheric 14c production in the 19th century sea level rose at a mean rate of 1 6 mm yr between ad 1900 and ad 1920 sea level rise accelerated to the modern mean rate of 3 2 mm yr this acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming 2005 elsevier ltd all rights reserved

the giant lavas of kalkarindji rubbly pāhoehoe lava in an ancient continental flood basalt province the kalkarindji continental flood basalt province of northern australia erupted in the mid cambrian c 511 505 ma it now consists of scattered basaltic lava fields the most extensive being the antrim plateau volcanics apv a semi continuous outcrop c 50 000 km2 reaching a maximum thickness of 1 1 km cropping out predominately in the sw of the apv close to the top of the basalt succession lies the blackfella rockhole member brm originally described as basaltic agglomerate the brm has in recent years been assumed to be explosive tephra of phreatomagmatic origin thus providing a potent vehicle for volatile release to the upper atmosphere our detailed field investigations reveal that this basaltic agglomerate is in reality giant rubble collections 15 20 m thick forming the upper crusts of rubbly p hoehoe lava units 25 40 m thick covering 18 000 72 000 km2 and an estimated volume of 1 500 19 200 km3 these flows rheologically but not chemically distinct from the majority of kalkarindji lavas indicate a fundamental change in eruption dynamics a low volatile content induced high amounts of pre eruptive degassing causing super cooling and an increase in crystal nucleation and viscosity a more viscous lava and a consistently faster rate of effusion analogous to that of laki iceland created the flow dynamics necessary to disturb the lava crust to the extent seen in the brm volatile release is estimated at 1 65 x 104 2 11 x 105 tg total co2 at a rate of 867 tg a 1 and 9 07 x 103 1 16 x 105 tg so2 at 476 50 tg a 1 these masses accounted for 0 5 of cambrian atmospheric conditions whilst limiting factors reduced the effect of volatile delivery to the atmosphere thus any potential global impact caused by these flows alone was minimal

cambrian depositional history of the zanskar valley region of the indian himalaya tectonic implications a well preserved cambrian section in the zanskar valley of northern india has previously been interpreted to record the transition from a passive to an active tectonic margin related to cambrian ordovician orogenesis this interpretation has been used to support the tectonostratigraphic interpretation of other successions across the tethyan himalaya our detailed paleoenvironmental analysis significantly revises the tectonic and depositional history of these cambrian deposits no definitive record of impending cambrian ordovician orogenesis is recorded in these late middle cambrian rocks a critical transition from an 125 m thick stromatolite bearing carbonate deposit the karsha formation into shale and sandstone of the kurgiakh formation was interpreted to represent tectonically induced drowning of a carbonate platform siliciclastic strata of the kurgiakh formation were thought to record deep water flysch deposition in a tectonically active foreland basin next to an arc trench system this interpretation was based on sandstone beds with classic bouma sequences we show that these event beds in the kurgiakh instead contain hummocky cross stratification quasi planar lamination and combined flow ripple stratification all of which reflect deposition in shallow marine storm influenced environments thus although the karsha carbonate platform may have been drowned it did not culminate in deep sea flysch deposition and this in turn eliminates a major line of evidence linking kurgiakh deposition to the onset of cambrian ordovician orogenesis other aspects of cambrian ordovician deposits of northern india also shed doubt on the proposed link between kurgiakh sedimentation and the cambrian ordovician orogenic event first our improved biostratigraphic database suggests that the transition from the karsha carbonate to the kurgiakh formation may have predated the main phase of cambrian ordovician orogenesis as recorded by overlying ordovician molasse by as much as 20 30 my second published data from the ordovician molasse indicate northward paleocurrents which are parallel to those recorded by siliciclastic deposits of the parahio formation below the karsha and thus are at odds with standard models of foreland basin development for the cambrian ordovician event our sedimentological analysis of depositional cycles of the parahio formation indicates that these strata record storm influenced environments from offshore marine to shoreface to fluvial settings this is at odds with previous paleoenvironmental interpretations that ranged from deep sea flysch to intertidal deposits paleocurrent data for marine and fluvial facies of the parahio formation in both zanskar and the spiti valley to the south indicate northeast sediment transport this supports the view that the parahio and overlying carbonate of the karsha formation record the ancient northern passive margin of india during the cambrian and that these strata may be distal equivalents of the younger cambrian deposits of the lesser himalaya

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

melanosclerites from the late ordovician strata of the shiala formation indian gondwana abstract melanosclerites organic walled microfossils of problematic affinity are recorded herein from the lower to middle part of the shiala formation of late ordovician age and is situated below ordovician silurian boundary established previously by acritarchs data the assemblages recovered yielded the melanosclerites taxa melanoporella clava melanoporella bulla melanoporella polonica melanoporella sp 1 melanoporella sp 2 and melanosteus sp the ordovician silurian sedimentary sequence discussed herein was a part of the gondwanan palaeocontinent situated at 25 to 30 s the melanosclerite assemblage recovered herein from the shiala formation is broadly comparable with the ojlemyr cherts of sweden situated at high palaeolatitude and also of late ordovician age melanosclerites have not previously been studied in detail from indian gondwana and published records on this fossil group are rare in general the present findings improve our knowledge on this group

palaeogeography of atlantic canada 13 0 kyr abstract we combine isobase maps with a digital terrain model of atlantic canada to map coastlines from 13 14c kyr bp to the present at 13 14c kyr bp there are ridges of high relative sea level rsl values over newfoundland and the maritime provinces and a re entrant of low values in the gulf of st lawrence this pattern persists well into the holocene and reflects crustal response to the slow wasting of ice caps that persisted in newfoundland and the maritime provinces for up to five millennia after the removal of ice from the gulf of st lawrence by a migrating calving embayment the palaeogeographic reconstructions reveal an archipelago on the outer shelf from grand bank to the continent that persisted from 13 14c kyr bp until ca 8 14c kyr bp much of the magdalen shelf was exposed but the magdalen islands were never connected to the mainland prince edward island was initially separated from the mainland became connected after 11 14c kyr bp and was separated again just before 6 14c kyr bp when northumberland strait formed the reconstructions are highly sensitive to relatively small changes in isobase values especially on the shallow banks on the continental shelf

the armorica microplate fact or fiction critical review of the concept and contradictory palaeobiogeographical data abstract the problem of an armorica microplate detached from gondwana and having had during part of the palaeozoic an independent latitudinal evolution is reconsidered in terms of a critical review of the palaeomagnetic data that were the very roots of this concept and through an alternative approach based on palaeoclimatic and palaeobiogeographical data palaeomagnetic data for the silurian and the devonian of the south european regions supposedly constituting the armorica microplate remain rare and ambiguous those from gondwana are more numerous but contradictory enough to give rise to diverging models regarding the latitudinal evolution of this continent consequently the reality of an armorica microplate cannot be considered as established on the contrary lithological indicators of palaeoclimate and palaeobiogeographical data are in total harmony and indicate that in actual fact the southern european regions remained permanently closely connected with gondwana of which they composed the northern margin although repeatedly maintained for more than 20 years the concept of an armorica microplate can thus be considered a fiction this conclusion should lead to the dismissal of geodynamical models proposed for the variscan belt to which this concept was integrated and are contradicted by inescapable palaeobiogeographical constraints

the tethyan himalaya palaeogeographical and tectonic constraints from ordovician palaeomagnetic data abstract to test whether the tethyan himalaya were part of the northern margin of india in the early palaeozoic we have produced the first primary palaeomagnetic data bedding corrected declination 267 5 inclination 63 0 95 10 pole latitude 20 2 n longitude 28 6 e from low metamorphic grade ordovician red beds in the tethyan himalaya shian formation the palaeomagnetic data are of excellent quality and a statistically positive fold test combined with a comparison with late cambrian ordovician gondwana poles suggests a primary hematite bearing magnetization acquired between 470 and 500 ma this is in excellent agreement with stratigraphic faunal and provenance age estimates and the palaeomagnetic data demonstrate that the tethyan himalaya must have been located in proximity to the indian craton during early ordovician times and are therefore consistent with a continuous margin at that time the shian formation pole overlaps with 470 500 ma gondwana poles but an even better fit can be obtained by invoking a post ordovician clockwise rotation of 13 4 such a rotation is similar in both sense and magnitude to clockwise rotations recorded in primary triassic sequences as well as palaeogene palaeomagnetic overprint data from the tethyan himalaya rotations of the tethyan himalaya compared with cratonic india are thus probably all of post late eocene age triassic and early ordovician data do not imply any crustal shortening between tethyan himalaya and cratonic india however in the early ordovician india was rotated 90 compared with its present orientation and any enlargement of india would not be detected by palaeomagnetic data

new insights on the neogene tectonic evolution of the aksu basin se turkey from the anisotropy of magnetic susceptibility ams and paleostress data abstract the junction between the aegean and cyprus arc in the southern turkey forms a triangular shaped morphological structure so called isparta angle ia in neogene time the inner part of the isparta angle became overlain by sedimentary basins including manavgat koprucay and aksu characterized by marine clastics and carbonates aksu basin one of these marine basins provides geological records about the neogene crustal deformation and stress field in the eastern mediterranean region therefore we kinematically assess if and when tectonic stress fields affected the aksu basin in early miocene to recent times for this purpose anisotropy of magnetic susceptibility ams data ams of cored samples and fault slip data from the brittle mesoscopic faults were collected the 490 oriented samples for anisotropy of magnetic susceptibility measurements were analyzed and two different maximum magnetic lineation s directions are recognized 1 n s magnetic lineation in pliocene and 2 from n s to nw se magnetic lineation in the miocene the results inferred from more than 1000 fault slip data collected from 83 different sites combined with ams results demonstrate that the aksu basin developed under four different tectonic phases 1 e w extensional phase related to basin formation 2 n s compressional lycian phase 3 n e s w compressional aksu phase and 4 n s extensional recent phase

the temporal autocorrelation structure of sea surface winds abstractthe temporal autocorrelation structures of sea surface vector winds and wind speeds are considered analyses of scatterometer and reanalysis wind data demonstrate that the autocorrelation functions acf of surface zonal wind meridional wind and wind speed generally drop off more rapidly in the midlatitudes than in the low latitudes furthermore the meridional wind component and wind speed generally decorrelate more rapidly than the zonal wind component the anisotropy in vector wind decorrelation scales is demonstrated to be most pronounced in the storm tracks and near the equator and to be a feature of winds throughout the depth of the troposphere the extratropical anisotropy is interpreted in terms of an idealized kinematic eddy model as resulting from differences in the structure of wind anomalies in the directions along and across eddy paths the tropical anisotropy is interpreted in terms of the kinematics of large scale equatorial waves and small scale convection modeling the vector w

recent advances in modeling swash zone dynamics influence of surf swash interaction on nearshore hydrodynamics and morphodynamics the role of the swash zone in influencing the whole nearshore dynamics is reviewed with a focus on the interaction between surf and swash zone processes local and global hydromorphodynamic phenomena are discussed in detail and a description of the overall swash zone operation is given the effects of swash zone boundary conditions are highlighted together with the importance of surf zone boundary conditions major emphasis is placed on illustrating the interactions of various hydrodynamic modes which in turn control the swash and surf zone morphology finally methods to account for swash zone processes in coastal models with different temporal and spatial resolutions are proposed

darriwilian shallow marine deposits from the sultanate of oman a poorly known portion of the arabian margin of gondwana the amdeh formation is a 3 4 km stack of sparsely fossiliferous quartzites and shales which crops out in the al hajar mountains near muscat here we describe the uppermost member am5 that can be dated biostratigraphically as darriwilian and which is the outcrop equivalent and probably the seaward continuation of the saih nihayda formation in the ghaba salt basin of northern oman the outcrops at wadi daiqa and hayl al quwasim consist of 690 m of quartzitic sandstones shales and bivalve rich shell beds trace fossils referable to the cruziana and skolithos ichnofacies abound the member comprises storm dominated shelf shoreface and delta deposits a number of new discoveries have been made in the outcrops fragments of the arandaspid fish sacabambaspis ossicles and moulds of the early disparid crinoid iocrinus two new genera of conodont an occurrence of the rare trinucleid trilobite yinpanolithus and palynological and sedimentological evidence of more continuous floian darriwilian deposition than is usual in the region sea levels during middle ordovician time are estimated to have been 50 200 m above present levels and a wide low gradient shelf covered much of arabia similar trace fossils and storm dominated micro tidal sedimentary rocks occur throughout the region small changes of sea level possibly caused by the growth and melting of polar ice sheets could lead to substantial seaward or landward shifts of facies belts the am5 deposits are thick compared to most equivalents in arabia implying active subsidence and a ready supply of sediment

salt marsh aggradation in response to late holocene sea level rise at amherst point nova scotia canada a radiocarbon 14c chronology determined for plant macrofossils in exposed salt marsh sediments at amherst point nova scotia canada shows that the edge of the high salt marsh aggraded 7 5 m since 900 bc equivalent to a mean rate of 25 9 cm 100 yr 1 four phases of rapid aggradation 900 600 bc 100 bc ad 200 ad 700 1100 and ad 1600 to present were interspersed with three phases of slower aggradation 600 100 bc ad 200 700 and tentatively ad 1100 1600 the stepped pattern of marsh aggradation probably resulted from eustatic sea level fluctuations superimposed on background signals of crustal subsidence and tidal range expansion because the rate of high salt marsh aggradation lagged or exceeded the rate of higher high water hhw increase at various times the high salt marsh aggradation trend only approximates the trend of hhw increase the eustatic sea level fluctuations are estimated to have a range of at least 0 8 m

the early palaeozoic geography of europe in the early ordovician three main continents are recognized by faunas in europe laurentia northwest of the closed suture of the iapetus ocean which was tropical baltica north of the general area of the trans european suture zone which was temperate and gondwana south of the tesz which was high latitude as the ordovician progressed various terranes separated and drifted away from the gondwana supercontinent at different times namely avalonia which was probably originally part of gondwana near south america iberia armorica perunica bohemia and various alpine fragments each terrane developed progressively different faunas as time went by avalonia collided with baltica near the end of ordovician confirmed by faunas tectonics and palaeomagnetism and subsequently avalonia baltica collided with laurentia to form laurussia from the mid silurian to the early devonian the ibero armorica perunica and alpine terranes did not join the european collage until the devonian the modern sites of the terrane boundaries bear little direct relationships to the original palaeogeographical boundaries in the early palaeozoic

the postglacial relative sea level lowstand in newfoundland relative sea level in coastal regions of newfoundland fell from late glacial maximum levels to postglacial minima in several phases i an early period of high relative sea level when late wisconsinan ice was at the coast and discharging meltwater plumes into the ocean ii a period of rapidly falling relative sea level during which glaciers retreated inland and iii a period without glacier ice during which relative sea level continued to fall but at decreasing rates falling relative sea level caused fluvial incision of glacial deposits in some coastal embayments and culminated with the construction of lowstand marine deltas these deltas were submerged during the subsequent holocene transgression seismic reflection data from selected deltas show that they comprise wedges of sediment with prograded seaward dipping foreset style internal reflections the depth of the relative sea level lowstand varies spatially and it was diachronous it occurred relatively early and deep in peripheral regio

coordinated biotic and abiotic change during the great ordovician biodiversification event darriwilian assembly of early paleozoic building blocks abstract the ordovician period records an extraordinary biodiversity increase known as the great ordovician biodiversification event gobe which coincided with a series of environmental changes to the earth system notably a cooling global ocean increased oxygenation and increased nutrient supply from volcanism and continental weathering the co evolution of earth and its biota during this interval has been studied in various contexts on multiple paleocontinents emerging patterns depend on the lens of investigation here we summarize the current state of understanding by reviewing and synthesizing the fossil and sedimentary records recent paleontological studies mainly focused on rhynchonelliform articulated brachiopods bryozoa cephalopods trilobites graptolites echinoderms and reef organisms have documented details of diversification body size increase development of ecosystem complexity and intensification of inter continental dispersal from the late cambrian through late ordovician biomass increased markedly between the early and middle ordovician furthermore diversification rates increase statistically during the mid darriwilian age both globally and regionally coincident with these biotic changes geochemical proxies record significant changes to earth s physical system oceanic temperatures decreased and atmospheric oxygen levels increased to near modern levels in concert with the middle ordovician diversification of shelly fauna anoxic pulses ceased and evidence for deep ocean ventilation prevails in middle ordovician strata furthermore a major middle late ordovician change in oceanic strontium isotopic composition indicates increased weathering of juvenile volcanic rocks and delivery of nutrients to marine settings this multi proxy dataset records near simultaneous changes in fossil rich shallow marine environments during exactly the interval of greatest diversification by integrating biotic and geochemical datasets a clear picture of the co evolution of earth and its biota emerges indicating that the darriwilian was the critical interval facilitating increased capacity of ecosystems we therefore recommend restricting the term gobe to indicate this short interval of rapid diversification and ecosystem change and using ordovician radiation when referencing the sum of diversifications that occurred throughout the ordovician period

c3 c4 variations in salt marsh sediments an application of compound specific isotopic analysis of lipid biomarkers to late holocene paleoenvironmental research in salt marshes bulk carbon isotope values reflect organic matter contributions not only from salt marsh plants but also from algal and bacterial inputs as well as allochthonous terrestrial organic matter in the present study compound specific isotope analysis was applied to a core and modern plant samples collected from a machiasport maine salt marsh we sampled 10 plant species common to the marsh including spartina alterniftora spartina patens juncus gerardi solidago sempervirens salicornia europa potentilla anserina atriplex patula plantago maritima suaeda maritima and limonium nashii isolation of two n alkanes c 27 and c 29 present in marsh plant samples allowed for the reconstruction of past plant communities present in the cored deposits for the c 27 and c 29 homologues there is a 3 10 separation in carbon isotopic composition between c3 and c4 species carbon isotopic values down core show a transition from a c4 dominated plant community to a c3 dominated community attributable to the migration of lower marsh zones onto brackish freshwater marsh zones during a late holocene relative sea level rise the two homologues used have the potential to provide paleoenvironmental information in future core work where the sea level variable will be controlled

lower devonian ostracods from the istanbul area western pontides nw turkey gondwanan and peri gondwanan affinities a lower devonian silicified ostracod fauna has been recovered from limestone interbeds in the buyukdere section of the kozyatagi member of the pendik formation forty one species belonging to 33 genera have been recognized twenty three are already known and 15 are described in open nomenclature one genus and three species omerliella rectangulata gen et sp nov microcheilinella istanbulensis sp nov and roundyella goekchenae sp nov are described silicified larval stages of trilobites agglutinated foraminifers and conodonts co occur with the ostracods the ostracod assemblages are mixed faunas between the epineritic eifelian mega assemblage representative of high energy environments and the basinal thuringian mega assemblage representative of low energy environments the conodont faunas of the pendik formation represent the serotinus patulus and partitus biozones of the late emsian earliest eifelian the emsian ostracods of nw turkey show numerous species level links between the western pontides istanbul terrane and assemblages of contemporaneous faunas of the cantabrian mountains spain morocco and thuringia germany and of similar biofacies this supports the notion that the istanbul terrane armorican terrane collage and northern margins of gondwana were in geographical proximity in late early devonian time

a comparison of present sea level linear trends from tide gauge data and radiocarbon curves in eastern canada abstract a comparison is made of the results for determinations of vertical crustal movements by means of two independent sources of data widely used in geodesy and geology tide gauge sea level linear trends and gradients of radiocarbon curves as a reference the map of vertical crustal movements of canada is added which was computed using not only tide gauge data but also geodetic levelling data these results show similar trends computed by both techniques but an average value of 0 1 m century greater for the sea level trends the map of vertical crustal movements is in good agreement with the trends provided by the gradients of radiocarbon curves

calibrated density profiles of caribbean mangrove peat sequences from computed tomography for assessment of peat preservation compaction and impacts on sea level reconstructions oceanic mangroves accumulate peat with sea level rise without terrestrial sediment inputs but fossil peat s elevation as a tide range limited sea level indicator is assumed to be affected by compaction despite assumption of decomposition compression and dewatering pure rhizophora mangle peat appears coarse water saturated and loose even at depth calibrated peat densities from computed tomography ct and petrologic analysis allow quantitative assessment of compaction in continuous peats from florida 6 m thick belize 12 m thick and panama 3 5 m thick pure peat exhibits voids at all depths and 80 water contents ct density does not increase with depth bulk densities are low minimally variable and trend free higher ct density intervals coincide with compositional changes sediment coral ct of peat buried under sediment shows a shift to higher densities ct of air dried continuous peat shows uncompressed fine and coarse roots and voids with negative densities indicative of air in place of interstitial water peat s high water content and hydraulic conductivity prevent dewatering and compaction hypothetically maintaining original sea level indicative elevations at intermediate depths non compacted sediment free offshore peats can provide a continuous proxy for reconstructing the record of sea level rise at any site if depositional disturbance and geochemical and biotic processes affecting 14 c ages are also assessed

a review of tectonics and sedimentation in a forearc setting hellenic thrace basin north aegean sea and northern greece abstract exposure of the forearc region of the north aegean sea greece offers insight into evolving convergent margins the sedimentary fill of the thrace basin during the late eocene to oligocene time provides a record of subduction driven processes such as growth of magmatic arcs and construction of accretionary complexes this large sediment repository received sediment from two sources the southern outboard basin margin reflects the active influence of the exhumed accretionary prism e g pindic cordillera or biga peninsula while the northern inboard margin records the effect of the magmatic arc in the rhodope region the forearc basin sedimentary fills shoal upward into shallow marine strata but are dominated mainly by deep marine facies the depositional trend and stacking pattern are dominated by progradational patterns this trend which is observed in both basin margins is related to tectonic deformation rather than sea level fluctuations additional evidence for this tectonic uplift comes from the backstripping analysis the accretionary complex provided material into the forearc basin this material was transported northeast and formed a sand rich turbidity system that evolved upslope into shallow marine deposits stratigraphic data indicate that this turbidity system exhibits a successive landward inboard migration of the depocenter provenance data utilizing sandstone petrography conglomerate clast composition and bulk rock geochemistry suggest that this system reflects an increased influx of mafic material into the basin volcanic arc derived material was transported south and east and accumulated in deep marine settings both stratigraphic and provenance data indicate a seaward outboard migration of the basin depocenter and a significant increase in felsic detritus into the forearc

marginal faunal belts and their structural implications with examples from the lower palaeozoic fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms on a global scale the identification of exterior oceanic biofacies may be of use in discriminating the course of former continental margins the isograptid graptolite biofacies early to middle ordovician can be distinguished from contemporary epicratonic graptolite biofacies its worldwide occurrence corresponds with continent margins reconstructed from other criteria hence a new isograptid record from irian jaya e new guinea although based on a small sample suggests that there may have been an ordovician oceanic site there on a continental scale the tectonic juxtaposition of different biofacies or of different stratigraphical packages contributes to an understanding of tectonics and can serve to quantify displacement the accretionary prism hypothesis for the southern uplands of scotland is supported and contrasted with the rearrangement of biofacies in the cambro ordovician cow head group of western newfoundland which reveals not only the original shelf margin slope topography now vanished but also provides an estimate of the movement involved in the emplacement of one taconic allochthon on a more local scale faunal evidence is used in assessing the original position of 9suspect9 marginal areas using the simplest possible model this shows for example that anglesey was not greatly separated from gondwana in the early ordovician but strike slip movement cannot be disproved local changes in relative sea level are determinable from sediments and faunas in marginal belts these may differ from the global eustatic curve and when this happens it is a measure of local tectonic activity particular sea level curves may serve to define structurally coherent units within mobile belts new sea level curves are contrasted for a segment of n wales north of the bala fault with that for central sw wales arenig llandovery the s welsh area mostly responded passively to the eustatic curve which can adequately account for shifts in facies and faunas while n wales had a curve often at odds with eustasy and reflecting its structural history

the dynamic evolution of the palaeozoic geography of eastern asia abstract new palaeogeographical reconstructions are presented for eleven time intervals through the palaeozoic of the eastern asia region from the middle cambrian at 510 ma to the end of the permian at 250 ma they centre on the continental blocks of north china south china and annamia indochina and their relationships with northeastern gondwana which was united to form part of pangea from the late carboniferous onwards also shown is the continent of tarim during the lower palaeozoic as well as the hutag uul songliao and khanka jiamasu bureya terranes both of which straddle the russian mongolian and chinese borders today from silurian times onwards we conclude that annamia and south china were united as a single continent throughout the lower palaeozoic and early devonian and were translocated by major strike slip faulting along the northeastern gondwana margin during that period from off afghanistan to outboard of the sibumasu and australian sectors of the superterrane they left the gondwana marginal area together during the lower devonian opening of the palaeotethys ocean but very shortly afterwards they themselves divided into the two separate continental blocks that we recognise today not to reunite until the triassic the various cambrian to permian rocks found in japan largely represent active volcanic arcs which originally lay to the southeast of south china although the carboniferous was more quiescent there the neotethys ocean opened during the permian dividing sibumasu and the tibetan terranes from gondwana and the palaeotethys ocean started to close progressively in the upper palaeozoic as most of the east asian continents and smaller terranes moved towards siberia the positions of the various continents and terranes have been deduced from a mixture of palaeomagnetic and faunal data the positions of large igneous provinces and kimberlites and the need to provide kinematic continuity between maps of successive ages however many uncertainties remain

late eocene evolution of the cicekdagi basin central turkey syn sedimentary compression during microcontinent continent collision in central anatolia abstract the central anatolian crystalline complex cacc exposes metasediment rocks overlain by cretaceous ophiolites and intruded by granitoids following late cretaceous exhumation of its high grade metamorphic rocks the cacc started to collide with the central pontides of southern eurasia in the latest cretaceous to paleocene here we present the sedimentary stratigraphic and tectonic evolution of the cicekdagi basin located in the northwest of the cacc magnetostratigraphic dating supported by 40 ar 39 ar geochronology shows a late eocene basin age the basin fill unconformably overlies metamorphic basement in the south and ophiolites of the cacc in the north it consists of red conglomerates sandstones and siltstones which overlie a sequence of nummulitic limestones in the south these limestones are 10 m thick are underlain by a few meters of conglomerate unit unconformably covering the cacc metamorphics in the north the limestones are underlain by a 200 m thick sequence of volcanics and fine grained clastics intercalating with shallow marine black shales the upper eocene sediments of the cicekdagi basin were deformed into a syn anticline pair progressive unconformities in the northern flank and a rapid and persistent 180 switch in paleocurrent directions from southward to northward in the southern flank of the anticline demonstrate syn sedimentary folding we interpret the folding to result from a southward progression of the cankiri foreland basin as a result of ongoing collision between the cacc and the pontides

salt marshes as archives of recent relative sea level change in west greenland abstract temperate latitude salt marshes are a proven environment from which high precision 0 10 0 20 m relative sea level rsl records can be developed over recent decades and centuries such records provide an important link between millennial histories of rsl change and instrumental records the high latitude salt marshes in greenland have not previously been explored as potential archives of recent rsl change here we develop four diatom based transfer functions using contemporary diatom data collected from three salt marshes located 40 km south of the coastal town of sisimiut west greenland our preferred model has a good fit between observed and predicted elevations r 2 0 94 and a root mean square error prediction of 0 19 m we apply the four models to a short sediment profile collected from one of the marshes that formed between c 600 cal year bp and the present three of the four models predict the same trend in which rsl rose from 0 55 0 19 m mean tide level mtl to 0 05 0 19 m mtl between c 600 and 400 cal year bp at a rate of c 2 7 mm year 1 after 400 cal year bp rsl slowed and remained stable until the present day the results of this study demonstrate that greenland salt marshes are potentially valuable archives of data for developing quantitative estimates of rsl change during the last few centuries thereby bridging the gap between existing millennial scale approaches and more recent direct observations of ice sheet behaviour and associated vertical land motions

sea level climate correlation during the past 1400 yr we present a new mean high water curve for hammock river marsh clinton connecticut obtained by improving the age model for an existing record of relative marsh elevation based on foraminiferal analysis of a 1 8 m long peat core unlike the earlier curve the new curve confirms trend changes in mean high water rise during the past 1400 yr as noted for salt marshes 15 km farther west suggesting a regional cause these trend changes and century scale mean high water variations in the clinton record correlate positively with large scale regional variations in sea surface and summer air temperature indicating a link between sea level and the climate ocean system on the basis of the clinton mean high water curve we conclude that real sea level oscillated centimeters to decimeters on a century time scale over the past 1400 yr was 25 25 cm higher ca a d 1050 medieval warm period than ca a d 1650 little ice age and rose at a mean rate of 1 mm yr 1 over the past 350 yr there was little or no rise during the cool 1800s

seasonal and annual variations in the volumetric sediment balance of a macro tidal salt marsh abstract this paper examines the spatial and temporal variability in the volumetric sediment balance of allen creek marsh a macro tidal salt marsh in the bay of fundy the volumetric balance was determined as the balance of inputs of sediments and organic matter via accretion on the marsh surface and outputs of sedimentary material primarily due to erosion of the marsh margin changes in marsh surface elevation were measured at 20 buried plates and 3 modified sediment elevation tables from 1996 2002 and detailed margin surveys were conducted in 1997 1999 and 2001 using a differential global positioning system changes in surface area were calculated using gis overlay analysis and used in conjunction with accretion and erosion data to derive volumetric estimates of gains and losses of sedimentary material in the marsh system currently the volumetric sediment balance at allen creek marsh is positive however the processes of erosion and accretion demonstrate seasonal annual and spatial variability inputs to the system include deposition on the marsh surface from sediment laden waters and from ice rafting of sediments sediment is deposited onto the marsh surface year round even during the winter when vegetation cover is sparse and the amount of deposition in general is not significantly correlated with the frequency of tidal inundations based on the data from 1996 to 2002 the mid and high marsh zones experience mean accretion rates of approximately 1 4 cm year 1 whereas accretion rates in the low marsh region are statistically significantly lower 0 8 cm year 1 the absolute amount of accretion varies between seasons and from year to year the main loss to the marsh is through erosion of the marsh margin cliffs which can remove a comparatively large volume of sedimentary material in one mass wasting event and which also decreases the vegetated surface area available for deposition from sediment laden waters the volume of material removed from the marsh margin almost tripled between 1997 169 m3 and 2001 502 m3 following breaching of the side of a tidal creek channel altering the patterns of margin erosion and deposition in the marsh system during this time however other sheltered areas of the marsh system such as along the tidal creek banks showed evidence of new vegetation growth increasing the amount of vegetated surface area available for deposition the processes of erosion and deposition on the marsh surface exhibit considerable spatial variability with different regions of the marsh being more or less sensitive to seasonal variability in the dominant controls influencing sediment deposition and erosion in this system namely wave activity vegetation ice and water depths a key factor in predicting how a marsh will evolve and respond to a number of different controls e g sea level rise or reduced sediment supply is to quantify both accretion of the marsh surface and erosion of the marsh margin evaluating the marsh system as a volumetric whole this study demonstrates that a marsh system should be assessed in three dimensions rather than simply as a surface of accumulation this is particularly important for open coastal marshes exposed to the erosive action of waves

the karakorum block in central asia from ordovician to cretaceous abstract the karakorum block records a predominantly marine ordovician to cretaceous sedimentary history six major sedimentary cycles are recognised the oldest sediments early ordovician transgress over a crystalline basement the 1 km thick ordovician silurian mostly shaly succession contains rare carbonate intercalations in the early devonian a wide peritidal platform spread over the craton sedimentation rates were low 10 20 m ma and upper devonian probable lower carboniferous carbonates and clastics rest unconformably on the early devonian carbonates no evidence has been found for either late carboniferous or glaciogenic deposits sedimentation rates increased during the permian up to 50 m ma with thicknesses between 1 and 2 5 km three steps are identified 1 a huge alluvial to marginal marine terrigenous prism aggraded during the asselian sakmarian 2 the artinskian murgabian is characterised by local emergence and erosion linked to extension with block rotations 3 greater differentiation occurred from late permian to middle triassic when a peritidal carbonate flat developed in the southwest facing a deeper basin to the northeast carbonate sediments prevailed throughout the carnian norian the permo triassic evolution is interpreted as the passive margin stage of the karakorum block which previously belonged to the perigondwanian fringe when like mega lhasa it drifted northward on the tethyan transit plate mega lhasa is considered as a collage of blocks possibly separated by thinned crust or short lived seas with ocean crust quartzo lithic sandstones with grains of mafic volcanics and serpentinite overlain with gentle unconformity by pliensbachian toarcian red sandstones with sedimentary and metasedimentary clasts record the eo cimmerian deformation in the karakorum this orogenic episode was over by the aalenian when a shallow water carbonate ramp aggraded onto the previously emergent area the pre barremian upper jurassic and lower cretaceous are poorly documented in post barremian times the sedimentary succession of n karakorum was severely deformed in huge thrust sheets including slabs of crystalline basement a coarse conglomerate of mid cretaceous age sealed the thrust sheet edifice finally isolated campanian pelagic mudstones are recorded anticlockwise rotation of mega lhasa followed the late triassic docking of the iranian spur using the latter as pivot the rotation was completed during the middle jurassic when se pamir shaksgam and karakorum joined the qiangtang more closely assembling mega lhasa as it approached the asian margin

reconciling the geological history of western turkey with plate circuits and mantle tomography abstract we place the geological history since cretaceous times in western turkey in a context of convergence subduction collision and slab break off to this end we compare the west anatolian geological history with amounts of africa europe convergence calculated from the atlantic plate circuit and the seismic tomography images of the west anatolian mantle structure western turkish geology reflects the convergence between the sakarya continent here treated as eurasia in the north and africa in the south with the anatolide tauride block atb between two strands of the neotethyan ocean convergence between the sakarya and the atb started at least 95 90 myr ago marked by ages of metamorphic soles of ophiolites that form the highest structural unit below sakarya these are underlain by high pressure low temperature metamorphic rocks of the tavsanli and afyon zones and the oren unit which in turn are underlain by the menderes massif derived from the atb underthrusting of the atb below sakarya was since 50 ma associated with high temperature metamorphism and widespread granitic magmatism thrusting in the menderes massif continued until 35 ma after which there is no record of accretion in western turkey plate circuits show that since 90 ma 1400 km of africa europe convergence occurred of which 700 km since 50 ma and 450 km since 35 ma seismic tomography shows that the african slab under western turkey is decoupled from the african plate this detached slab is a single coherent body representing the lithosphere consumed since 90 ma there was no subduction re initiation after slab break off atb collision with europe therefore did not immediately lead to slab break off but instead to delamination of subducting lithospheric mantle from accreting atb crust while staying attached to the african plate this led to asthenospheric inflow below the atb crust high temperature metamorphism and felsic magmatism slab break off in western turkey probably occurred 15 myr ago after which overriding plate compression and rotation accommodated ongoing africa europe convergence slab break off was accommodated along a vertical ne trending subduction transform edge propagator step fault zone accelerating southwestward slab retreat of the aegean slab the se aegean slab edge may have existed already since early miocene times or before but started to rapidly roll back along the southeastern aegean step in middle miocene times penetrating the aegean region in the pliocene

refining gondwana and pangea palaeogeography estimates of phanerozoic non dipole octupole fields summary reliable phanerozoic paleopoles have been selected from the stable parts of the gondwana continents and upon appropriate reconstruction have been combined in an apparent polar wander apw path which can be compared with a previously compiled path for laurussia this comparison once again confirms that pangea a reconstructions for late palaeozoic and early mesozoic times cannot be reconciled with the available paleomagnetic data unless these data are corrected for latitudinal errors caused by non dipole octupole field contributions or by inclination shallowing because the discrepancies persist even when only paleopoles from igneous rocks are used inclination shallowing cannot be the sole cause of the problem there is an apparent decrease in the percentage of octupole field contributions needed as a function of time for mesozoic and younger time gondwana laurussia comparisons require on average lower ratios of octupole dipole fields than for palaeozoic time however the gondwana paleopoles for the palaeozoic include a much greater proportion of results derived from sedimentary rocks than do those for the mesozoic so that this apparently diminishing octupole field contribution may be an artefact we have also examined whether the clustering of coeval gondwana poles improves with optimal g3 contributions but found that while there are improvements they are not systematic and not statistically significant a combined apw path has been constructed for pangea for times since the mid carboniferous which accounts for octupole fields or equivalently inclination shallowing we argue that this global path is an improvement over previous constructions as it represents a self consistent plate tectonic model and does not violate widely accepted pangea a reconstructions

a horseshoe crab arthropoda chelicerata xiphosura from the lower devonian lochkovian of yunnan china a single specimen of a new species of the synziphosurine kasibelinurus pickett 1993 is described from the lower devonian lochkovian xiaxishancun formation of yunnan province china the new species k yueya sp nov extends the geographic extent of the family kasibelinuridae from the australian palaeocontinent to the south china palaeocontinent and the stratigraphic range back some 50 ma from late to early devonian

stratigraphic evidence for hirnantian glaciation in the alborz mountain ranges northeastern iran abstract the author examined the high latitude hirnantian diamictites of the ghelli formation and the early silurian olive gray shales of the niur formation exposed in the northeastern alborz mountains iran these 404 m thick glacial deposits can be divided into three progradational retrogradational cycles each potentially controlled by the regional advance and retreat of the hirnantian ice sheet the glaciated source area was west of the study area in the arabian shield region where numerous tunnel valleys have been reported time calibration was performed based on a high quality biostratigraphic control mainly derived from the chitinozoan biozones tanuchitina fistulosa acanthochitina barbata armoricochitina nigerica ancyrochitina merga tanuchitina elongata spinachitina oulebsiri and spinachitina fragili s the land derived miospores present in most chitinozoan assemblages often abundant seem associated with global sea level changes during the late ordovician glaciation the ghelli formation s high abundance of terrestrial miospores and low abundance of marine palynomorphs suggests its deposition in a shallow marine environment additionally rhythmic bedded tidalites of claystone and sandstone indicate the growth of early land plants producing cryptospores on adjacent flooded areas based on marine palynomorphs chitinozoans and acritarchs the northeastern alborz mountains glacial deposits were dated as hirnantian the niur formation was assigned to the earliest llandovery rhuddanian glacial deposits and marine palynomorphs suggest the presence of hirnantian ice caps in the alborz mountains at the margin of the arabian plate and indicate the peripheral extension of the late ordovician ice sheet several biostrome beds forming pelmatozoan bryozoan mud mounds mainly comprising bryozoans echinoderms tentaculites and subordinate trilobites were found in the glacial deposits of the ghelli formation suggesting carbonate deposition during the hirnantian these carbonate beds are not related to the boda warming event which happened over the gondwana landmass in the katian interval the glacial deposits of the alborz mountain ranges are thus not correlated to those of the gondwana paleocontinent climatic amelioration is more likely than local reduction of clastic input to be responsible for the biostrome beds in the glacial member of the ghelli formation namely a short lived episode of global warming during the hirnantian interval the milankovitch cycles four new chitinozoan species namely armoricochitina persianense n sp tanuchitina alborzensis n sp spinachitina iranense n sp and hyalochitina jajarmensis n sp are described and illustrated biometric data are also provided for the iranian s oulebsiri and a nigerica

late holocene sea level changes from grain size data evidence from the gulf of mexico grain size kurtosis of sand in the beach ridge plain of st vincent island florida is numerically reasonably uniform within any one ridge set but changes at important set boundaries where these changes are found there are also differences in air photo and field appearance and in measured ridge set heights sets with low kurtosis 3 0 stand topographically high and sets with higher values 3 6 stand low study of wave energy levels and beach sand grain size kurtosis along modem gulf of mexico beaches shows that kurtosis is an inverse function of surf zone energy density storms and storminess for the study area can be evaluated in the framework of the selective transport model of may 1973 the actual data sequence is greatly different from what is required by the model and therefore storms and storminess cannot be invoked to explain the history of the area instead the data sequence matches results predicted by the model for small sea level changes storms and tectonism do not have appropri

a review of lower and middle palaeozoic biostratigraphy in west peninsular malaysia and southern thailand in its context within the sibumasu terrane abstract fossils from the cambrian to devonian rocks of southern thailand the langkawi islands mainland kedah perlis north perak and central west peninsular malaysia are listed and reviewed and their stratigraphy and correlation reassessed the hitherto anomalous record of the trilobite dalmanitina from malaysia is reviewed and found to be of latest ordovician hirnantian age rather than lower silurian age as previously reported and is considered a probable synonym of the widespread mucronaspis mucronata a new stratigraphical nomenclature is erected for part of the langkawi mainland kedah and perlis area successions in which the term setul limestone which stretched from the ordovician to the devonian is abandoned and replaced by the middle ordovician kaki bukit limestone the late ordovician and early silurian tanjong dendang formation the silurian mempelam limestone and the early devonian timah tasoh formation all underlying the paraconformity with the late devonian langgun red beds there was a single depositional basin in the generally shallow water and cratonic areas of southern thailand langkawi and mainland kedah and perlis in contrast to the deeper water basin of north perak only silurian rocks are dated with certainty within another basin in central west malaysia near kuala lumpur which were also cratonic and shallow water although to the east in west pahang there are basal devonian deeper water sediments with graptolites the area is reviewed in its position within the sibumasu terrane which in the palaeozoic also included central and northern thailand burma myanmar and southwest china part of yunnan province

cambrian stratigraphy and depositional history of the northern indian himalaya spiti valley north central india recent work on himalayan tectonics indicates that prior to the cenozoic collision of india and asia an enigmatic cambrian ordovician event may have strongly infl uenced the regional geology of the himalaya stratigraphic and sedimentological analyses of well preserved cambrian deposits are critical for understanding the nature of this early tectonic event and its infl uence on the later tectonic evolution of the himalaya the parahio formation defi ned herein of the parahio valley spiti region in the tethyan himalaya of india is the best biostratigraphically resolved section of cambrian strata in the entire himalaya this formation consists of 1350 m of dominantly siliciclastic deltaic deposits the formation ranges from uppermost lower cambrian lungwangmiaoan stage to middle middle cambrian hsuchuangian stage representing a time span of 5 10 m y it contains numerous mediumscale shoaling cycles that range from storminfl uenced offshore deposits to thick trough cross bedded fl uvial facies many thin carbonate beds with abundant trilobite fossils directly overlie the fl uvial facies and represent transgressive systems tract deposits the cycles are interpreted to have resulted from delta lobe switching based on a lack of systematic stratigraphic changes in cycle or facies thicknesses this paleoenvironmental reconstruction contradicts previous interpretations of this unit that range from deep sea fl ysch to shallow marine tidalites in addition our paleoenvironmental analysis and paleocurrent data suggest that the uppermost lower to middle cambrian deposits of the lesser and tethyan himalaya are parts of the same ancient northward prograding fl uvial deltaic depositional system of the paleo tethys margin of india an angular unconformity with overlying ordovician conglomeratic rocks has considerable local relief with meter scale scours and a valley fi ll 100 m thick the scours have northeast southwest orientations which parallel both the paleocurrents in the underlying parahio formation as well as published paleocurrent readings from the coarse red beds of the overlying ordovician strata the cambrian ordovician unconformity is of regional extent and our recent biostratigraphic database indicates that the minimum hiatus associated with the unconformity in spiti is 15 m y our sedimentological analysis and associated paleocurrent data from the parahio formation along with additional data from units both above and below the unconformity indicate that published models portraying foreland basin development at this time with southward directed thrusting are problematic an alternate possibility that uplift took place south of the tethyan himalaya is also problematic because no published stratigraphic or structural evidence exists for such an uplift to the south for either the greater or the lesser himalaya lithotectonic zones

the lower palaeozoic of oman and its context in the evolution of a gondwanan continental margin the lower palaeozoic haima group of the sultanate of oman comprises a sequence dominated by siliciclastic rocks up to several kilometres thick and broadly divisible into two groups the sequence is known in outline from subsurface exploration but recent field work on outcrops in the isolated huqf area in east central oman has allowed a more detailed environmental interpretation of the succession at the base coarse continental deposits of the lower haima group rest unconformably on precambrian lower cambrian huqf group sediments mainly carbonates and evaporites the overlying upper haima group comprises from base to top the aeolian dominated amin formation the non marine coastal plain to shallow marine intertidal subtidal sediments of the andam formation the non marine to marginally marine ghudun formation and the complex cyclical deep to shallow water deposits of the safiq formation correlation of the haima group of oman with the lower palaeozoic of the arabian peninsula north africa and iran allows the evolution of the gondwanan margin to be modelled a widespread lower cambrian sequence of coarse alluvium resting on peneplained upper precambrian infracambrian huqf group strata represents the final stage of uplift and basin fill associated with the late proterozoic suturing of arabia and adjacent plates which resulted in the formation of the gondwanan continent the overlying thick sequence of continental fluvial and aeolian sediments was deposited in a series of stable intracratonic basins across the gondwanan landmass in the mid and late cambrian an overall sea level rise led to the repeated development of shallow marine shelf carbonates across the margin the subsequent replacement of this marginal carbonate sequence with a thick marginal to non marine sand dominated sequence may reflect the interplay of several events the drift of gondwana towards more southerly latitudes a phase of strong tectonic rejuvenation during the latest cambrian early ordovician and or a eustatic fall in sea level organic rich marine mudrocks were deposited over much of the gondwanan platform during a series of marked eustatic sea level rises during the mid late ordovician and early silurian in oman no evidence has yet been found for the significant late ordovician glacial event recorded from north africa and saudi arabia

a key extensional metamorphic complex reviewed and restored the menderes massif of western turkey article i nfo this paper provides a review of the structure and metamorphism of the menderes massif in western turkey and subsequently a map view restoration of its neogene unroofing history exhumation of this massif among the largest continental extensional provinces in the world is generally considered to have occurred along extensional detachments with a ne sw stretching direction restoration of the early miocene history however shows that these extensional detachments can only explain part of the exhumation history of the menderes massif and that ne sw stretching can only be held accountable for half or less of the

modeling the contribution of m2 tidal amplification to the holocene rise of mean high water in the gulf of maine and the bay of fundy abstract increase in the m2 principal lunar semi diurnal component of the tidal range is an important contributor to the postglacial rise of the high tide level in the gulf of maine and the bay of fundy in addition to relative sea level rise the increase occurred as the shape of this semi enclosed embayment changed with sea level rise and its natural period approached resonance with the m2 tide a three dimensional tide model 3dens predicts the following m2 tidal ranges averaged for the gulf of maine bay of fundy as a percentage of the present range 54 59 at 7000 yrs b p 73 at 5000 yrs b p 78 at 4000 yrs b p 85 at 3000 yrs b p 94 at 2000 yrs b p and 98 at 1000 yrs b p with a predicted sea level rise of 0 15 0 90 m by the year 2100 m2 tidal range may increase 0 3 1 9

late ordovician glaciation in southern turkey abstract we present a new survey of several palaeozoic sections in both the taurus range and the border folds that documents typical glacial features including a glacial pavement and striated dropstones halevikdere formation and demonstrates the former presence of an ice sheet in southern and south eastern turkey evidence for the late ashgill hirnantian age of this episode is provided by macro and microfossils found within the glacial formation the extension of ice related deposits into the northernmost part of the arabian platform mardin region implies a much wider distribution of the ordovician ice sheet than was previously believed and strongly suggests that southern turkey lay close to egypt during the lower palaeozoic

ordovician paleomagnetism of eastern yunnan china three magnetic components have been isolated in ordovician formations of the yangtze paraplatform south china block two of these daqing a and hongshiya b components yield paleopoles that conform to the carboniferous to triassic segment of the apparent polar wander path for south china and are therefore interpreted as remagnetizations the third component declination inclination 301 degree 66 degree n 5 sites k 21 4 alpha sub 95 17 degree passes the fold test and is interpreted as primary late early ordovician the paleopole at 39 degree s 236 degree e and the paleolatitude of 48 degree s support an ordovician position of south china adjacent to gondwana

linking the indochina block and gondwana during the early paleozoic evidence from u pb ages and hf isotopes of detrital zircons abstract to constrain the paleoposition of indochina within gondwana during the early paleozoic we performed in situ u pb and hf isotope analyses on detrital zircons from three river sediment samples in the truong son belt of the indochina block the age distributions yield dominant neoarchean 2 5 ga mesoproterozoic 1 7 1 4 ga grenvillian 0 95 ga and pan african 0 65 0 5 ga age groups and minor paleo to meso archean zircons hf isotope compositions of zircons for each age group exhibit large ranges of ehf t suggesting that the zircon host rocks have diverse sources the oldest hf model ages for zircons of neoarchean grenvillian and pan african age group yield 3 7 ga or older while those of mesoproterozoic age group show 3 3 ga the remarkable similarity of age distribution and hf isotope compositions among detrital zircons of indochina and those of tethyan himalaya western cathaysia and qiangtang suggests that indochina was located outboard of qiangtang and south of south china in the indian margin of gondwana during the early paleozoic our results are consistent with the paleontological correlations of east gondwana margin during the early paleozoic

late tournaisian conodonts from the taungnyo group near loi kaw myanmar burma implications for shan plateau stratigraphy and evolution of the gondwana derived sibumasu terrane abstract carboniferous conodonts are reported for the first time from myanmar burma conodont faunas representative of the scaliognathus anchoralis and gnathodus typicus protognathodus cordiformis conodont zones date the sampled taungnyo group south of loi kaw kayah state as late tournaisian confirming a mississippian lower carboniferous age for the sampled part of this stratigraphic unit the dated strata are stratigraphically just below the tournaisian visean t v boundary tournaisian strata are thus for the first time unequivocally demonstrated in the shan plateau region of myanmar similar conodont faunas from the t v boundary interval in se asia indicate a complete stratigraphic sequence at this level in shallow marine sequences on intra tethyan cathaysian tectonic blocks south china and in deep marine palaeo tethyan sediments cherts of the inthanon suture zone thailand however in shallow marine sequences on the sibumasu block located on the ne margin of gondwana in the carboniferous they demonstrate a non sequence or unconformity at this level also seen elsewhere in gondwana biogeographic links between upper tournaisian and early visean conodonts on the sibumasu terrane and laurentia and eastern australian gondwana support a nw australian gondwana margin position for sibumasu in the late palaeozoic

temporal filtering enhances the skewness of sea surface winds abstractthe component of the sea surface wind in the along mean wind direction is known to display pronounced skewness at many locations over the ocean a recent study by proistosescu et al found

review of trilobite biofacies distributions at the cambrian ordovician boundary detailed analysis of trilobite assemblages at the cambrian tremadoc transition reveals the presence of four possibly five biogeographic provinces baltic north china southeast china north american and possibly siberian one or more discrete biofacies characterize the transition in each province when plotted palaeogeographically these appear to be largely temperature controlled interdigitation of provincialized trilobite biofacies is recognized by the representation of dominant types of trilobite olenaceans ceratopygaceans remopleuridaceans dikelocephalaceans and leio stegiaceans in particular on key boundary sections these sections at nochixtlan mexico batyrbay southern kazakhstan broken skull river district of mackenzie canada and jiangshan chang shan western zhejiang china permit the correlation of biogeographic provinces globally as a result of the application of trilobite biostratigraphy relatively few problems prevent the maintenance of a cambrian ordovician boundary stratotype section in its traditional baltic biogeographic setting

historical rates of salt marsh accretion on the outer bay of fundy we examine rates of salt marsh accumulation in three marshes of the outer bay of fundy at each marsh we selected a site in the high marsh with similar vegetation and thus similar elevation accretion rates were estimated by 137 cs 210 pb and pollen stratigraphy to estimate rates of change over periods of 30 100 and 170 years respectively these rates are compared with records from the two closest tide gauges saint john new brunswick and eastport maine to assess the balance of recent marsh accretion and sea level change averaged marsh accretion rates have ranged from 1 3 0 4 to 4 4 1 6 mm year 1 over the last two centuries recent rates are similar to the rate of sea level change recorded at eastport maine suggesting that they are in step with recent sea level change but very sensi tive to short term variation in relative sea level based on the pollen stratigraphy in the marsh sediments the marsh ac cretion rate was higher during the late 18th to early 19th century higher rates probably were due to local increases in relative sea level as a result of neotectonic activity and may have been enhanced by increased sediment deposition through ice rafting

stratigraphic evidence for the hirnantian latest ordovician glaciation in the zagros mountains iran abstract high latitude hirnantian diamictites dargaz formation and lower silurian kerogenous black shales sarchahan formation are locally exposed in the zagros mountains the glaciogenic dargaz deposits consist of three progradational retrogradational cycles each potentially controlled by the regional advance and retreat of the hirnantian ice sheet glacial incisions of sandstone packages change laterally from simple planar to high relief

holocene land and sea level changes in great britain analysis of more than 1200 radiocarbon dated samples that constrain relative sea levels in great britain over the past 16 000 yr provides estimates of current land level changes negative of relative sea level change maximum relative land uplift occurs in central and western scotland ca 1 6 mm yr 1 and maximum subsidence is in southwest england ca 1 2 mm yr 1 sediment consolidation arising from autocompaction as the sediment accumulates and from land drainage increases the subsidence in areas with thick sequences of holocene sediments with an average effect equivalent to at least an extra ca 0 2 mm yr 1 land subsidence but more in parts of southeast england 0 5 1 1 mm yr 1 modelled changes in tidal range during the mid to late holocene in eastern england suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified the effect is most significant for large coastal lowlands the fenland and humber ca 0 5 and 0 6 mm yr 1 that were tidal embayments during the mid to late holocene

mid to late holocene relative sea level change in southwest britain and the influence of sediment compaction relative sea level changes in southwest britain are poorly constrained because of limitations in the quality and quantity of existing geological data as a consequence in contrast to most other regions in the uk it is not possible to reliably infer rates of land and sea level change during the last few thousand years furthermore geologically based sea level reconstructions from this area display significant misfits with relative sea level predictions based on a recent global model of the glacio isostatic adjustment process this paper presents a new record of relative sea level change for the last 4000 years derived from radiocarbon dated sea level index points in addition to providing information concerning the pattern and rates of late holocene sea level change these data are used to evaluate the suggestion that the apparent misfits between model predictions and geological reconstructions can be satisfactorily explained as a consequence of the lowering of sea level index points by sediment compaction the results indicate that a simple first order method of decompaction based on the stratigraphic position of sea level index points can eliminate much of the misfit between reconstructions and predictions and substantially reduce vertical scatter in geological data they also suggest that the influence of compaction on sea level data from this region may be larger than previously thought the simple addition of reliable stratigraphic data in combination with targeted sampling has the potential to improve our understanding of the compaction process and increase the utility of existing data this is increasingly important as the partnership between geophysical modelling and geological investigation becomes more commonplace in sea level studies around the world

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

lower palaeozoic stratigraphy and palaeontology karadere zirze area pontus mountains northern turkey lower palaeozoic rocks in the karadere zirze area east of safranbolu pontides northern turkey range from early ordovician to silurian overlying the probably tremadoc bakacak formation are aydos formation quartzites followed conformably by the karadere formation dated as early arenig to early llanvirn by means of graptolites which are assigned to seventeen genera and include three new forms eoglyptograptus bouceki prolasiograptus haplus praecursor and undulograptus mui late arenig trilobites from the karadere formation include bergamia cyclopyge dionidella leioshumardia and seleneceme in the limestone member of the overlying ketencikdere formation uncommon trilobites suggest only a mid to late ordovician age but con odonts with colour alteration index 5 6 indicate the amorphognathus tvaerensis biozone early caradoc macrofossils are rare in the siltstone member but conodonts from the middle of the unit suggest the highest subzone of the a tvaerensis biozone the youngest visible strata are on acritarch evidence at least as high as caradoc but the ashgill is not confirmed and the contact with overlying silurian rocks is unexposed the findikli formation comprises a lower member black argillites with llandovery graptolites and acritarchs and an upper member grey shales with late wenlock graptolites overlain unconformably by devonian rocks the succession differs significantly from contemporaneous deposits in southern turkey and its affinities lie with western europe including the welsh basin

origin and evolution of the tengchong block southeastern margin of the tibetan plateau zircon u pb and lu hf isotopic evidence from the meta sedimentary rocks and intrusions abstract u pb ages and hf isotopic data from detrital zircons of gaoligongshan metamorphic complex and the carboniferous menghong group and igneous zircons from intrusions constrain the origin tectonic affinity east gondwana crustal evolution processes and the properties of regional high grade metamorphic rocks in the tengchong block of southeastern china three granites intruded into the tengchong block at 72 ma 114 ma and 122 ma detrital zircons range in age from archean to late ordovician for both the carboniferous menghong group and the gaoligongshan metamorphic complex analyses for these two units yield similar age clusters at 2 5 ga 1 6 ga 1 17 ga 0 95 ga and 0 65 0 5 ga as well as parallel hf isotopic distributions the protolith of the studied gaoligongshan complex in the tengchong block should deposit in the late paleozoic detrital zircon age distribution patterns of the carboniferous menghong group and the gaoligongshan complex show dominant younger grenvillian age peaks at 0 95 ga indicating the strong paleogeographic connection of the tengchong block with the indian margin the hf isotopic comparison of both detrital and igneous dated zircon shows that the tengchong block can be represented by the post archean indian continental margin after 250 ma the intensive magma events affected the region and considerable juvenile material accreted to the crust of the tengchong block

storms and shoreline retreat in the southern gulf of st lawrence abstract storms play a major role in shoreline recession on transgressive coasts in the southern gulf of st lawrence gsl southeastern canada long term relative sea level rise off the north shore of prince edward island has averaged 0 3 m century over the past 6000 years 0 2 m century over 2000 years this has driven long term coastal retreat at mean rates 0 5 m a but the variance and details of coastal profile response remain poorly understood despite extensive sandy shores sediment supply is limited and sand is transferred landward into multidecadal to century scale storage in coastal dunes barrier washover deposits and flood tidal delta sinks charlottetown tide gauge records show mean relative sea level rise of 3 2 mm a 0 32 m century since 1911 a further rise of 0 7 0 4 m is projected over the next 100 years when differenced from tidal predictions the water level data provide a 90 year record of storm surge occurrence combined with wind wave hindcast and sea ice data this provides a catalogue of potentially significant coastal storms we also document coastal impacts from three recent storms of great severity in january and october 2000 and november 2001 digital photogrammetry 1935 1990 and shore zone surveys 1989 2001 show large spatial and temporal variance in coastal recession rates weakly correlated with the storm record in part because of wave suppression or coastal protection by sea ice large storms cause rapid erosion from which recovery depends in part on local sand supply but barrier volume may be conserved by washover deposition barrier shores with dunes show high longshore and interdecadal variance with extensive multidecadal healing of former inlet and overwash gaps this reflects recovery from an episode of widespread overwash prior to 1935 possibly initiated by intense storms or groups of storms in the latter half of the 19th century with evidence from the storms of 2000 2001 this points to the importance of storm clustering on scales of weeks to years in determining erosion vulnerability as well as the need for a long term large scale perspective in assessing coastal stability the expected acceleration in relative sea level rise together with projections of increasing storm intensity and greatly diminished winter ice cover in the southern gsl implies a significant increase in coastal erosion hazards in future

the panghkawkwo graptolite bed llandovery silurian myanmar and the location of the sibumasu or sibuma terrane in the silurian abstract the panghkawkwo graptolite bed is shown to comprise several graptolitic horizons extending through the aeronian middle llandovery and into the lower telychian upper llandovery graptolite assemblages are diverse indicating an outer shelf or deeper depositional environment they are similar to those of bohemia and saudi arabia peri gondwanan europe and core gondwana respectively but include also taxa agetograptus and species of metaclimacograptus not known from these regions but which characterize lower latitude llandovery graptolite assemblages the evidence for the silurian location of the sibuma su terrane is discussed the presence of monograptus belophorus and cyrtograptus rigidus in the lower sheinwoodian wenlock of western yunnan suggests a non equatorial palaeolatitude the panghkawkwo graptolites suggest a location for sibuma su between gondwana and south china

holocene relative sea level movements along the north norfolk coast uk abstract relative changes in holocene sea level are reconstructed from foraminiferal assemblages in seven cores recovered from the intertidal zone of north norfolk eastern england a total of 33 radiocarbon and infra red stimulated luminescence dates provide a detailed chronological framework for these changes a transfer function approach developed from modern uk foraminiferal datasets establishes a series of 21 new sea level index points for this coastline which are combined with 18 existing index points and a further number of limiting values errors associated with changing tidal ranges through the holocene are reduced by adopting recently developed tidal models for this period this new approach allows the use of foraminiferal assemblages to be extended from the upper saltmarsh environment traditionally used for sea level studies to lower elevations in the tidal frame and include clastic detrital sediments the results confirm the previously observed trend of continuously rising sea levels in this area during the last 10 000 years which is consistent with a glacial isostatic adjustment model relative sea level rsl rises from an observed minimum of approximately 13 50 m od at about 7500 cal bp to approximately 4 0 m at about 5300 cal bp which equates to a mean rise of c 4 3 mm yr 1 subsequently rsl rose gradually to present levels although there is evidence that a minor reverse in this trend occurred between 4000 and 2000 cal bp when sea level fell by about 1 m to c 3 5 m the rate of land subsidence for north norfolk is 0 54 0 03 mm yr 1 inverse of late holocene sea level rise

reinterpretation of past sea level variation of the bay of fundy reports of shifts in rates of aggradation in a salt marsh deposit at amherst point nova scotia have been linked with fluctuations in eustatic sea level crustal subsidence and possibly changes in tidal amplitude however evidence for the most recent fluctuation is an artifact of early acadian land reclamation that occurred in the seventeenth century at amherst point acadian settlers had constructed dikes to prevent regular tidal flooding but probably allowed occasional flooding of the surface by tidal waters thus maintaining the salt marsh signature of the deposit statistical analysis of the pollen assemblage from the uppermost deposit inter preted as a regressive sequence aligns critical depths with pollen assemblages retrieved from modern soils of diked and drained marshes inspection of historical aerial photographs confirms that the dikes persisted on the site until at least 1939 interpretations of earlier fluctuations recorded in deposits below this regressive sequence remain valid it is possible that the bay of fundy experienced a regressive period just prior to acadian diking but future research on unexamined salt marsh deposits here or elsewhere must include an exhaustive search of historical documents to avoid misinterpretation of anthropogenic modifications

paleomagnetic results from the silurian of the yangtze paraplatform gpdyke n d huang k xu g zhang w y and kent d v 1987 paleomagnetic results from the silurian of the yangtze paraplatform in d v kent and m km editors laurasian paleoma etism and tectonics teetonophysics 139 123 132 samples have been collected from sites from three localities located in sichuan and in yunnan provinces the samples were taken from limestones and red siltstones covering most of the silurian of the south china block the results from the limestone sites were disappointing and all the sites that yielded successful results were from red siltstones characteristic high temperature components were successfully isolated from fifteen of these sites the sites from xiushan county sichuan 28 48o n 108 99 0 e successfully pass the fold test at the 99 level indicating that the magnetization was acquired before folding in the mesozoic the direction obtained from this locality is directed toward the east with shallow positive inclinations d 85 6 o i 12 1 cuss 5 33 the results obtained from a single red bed locality from qijiang county sichuan 28 58 n 106 85 e yield a similar direction the results from the upper silurian of yunnan 25 5 n 103 73o e were obtained from only two sites and the isolated directions were towards the west with shallow inclinations this direction is opposed to the characteristic directions obtained from sichuan and are interpreted as a reversed silurian direction the paleomagnetic pole position determined from all sites given equal weight n 15 falls at 4 9 n lat 194 7 e long with ass 5 61 o

crustal evolution of peri gondwana crust into present day europe the serbo macedonian and rhodope massifs as a case study abstract the continental crust of europe west of the trans european suture zone tesz is mostly a collage of peri gondwana cadomian and avalonian terranes that were formed on the late neoproterozoic active margins of the supercontinent rifted from it during consecutive opening of oceanic basins and variably involved in ordovician carboniferous variscan and cretaceous eocene alpine orogenies while in many localities it is possible to study isolated portions of the european geologic history few sites can hold evidence for the entire record in a relatively small area the balkan terranes of the serbo macedonian smm and the rhodope massifs which contain neoproterozoic cadomian remnant basement and were involved in multiple phanerozoic phases of magmatism and metamorphism provide an ideal locality in which we can study the entire crustal evolutionary history of europe west of the tesz here we present new zircon u pb hf and rutile u pb data from basement rocks of the smm and rhodope as well as of beach placers from mouths of the large rivers draining the balkan towards the aegean sea strymon nestos and evros rivers basement igneous rocks of the smm and circum rhodope were dated to the late neoproterozoic 588 ma middle ordovician ca 460 ma carboniferous 300 ma permo triassic 254 ma paleocene 65 ma and miocene ca 23 ma demonstrating the episodic nature of crustal evolution in this terrane assemblage hf in zircon shows these intrusions evolve from negative ehf t values in the ordovician towards positive values in the paleocene zircons in beach placer samples also show distinct age peaks that follow the pulses of igneous activity in the source terranes with the addition of jurassic ca 150 ma zircons the u pb system in rutiles from the beach placer samples was mostly reset and records the final metamorphic phase during alpine orogeny 35 ma with some rutiles preserving eo alpine 80 ma ages in contrast to the igneous samples detrital zircons from the beach placer samples follow a trend bound by evolution lines leading to hf tdm model ages between 0 6 and 1 6 ga as a whole since the late neoproterozoic the balkan crust was the subject of repeated reworking in a series of magmatic orogenic events some extent of juvenile igneous addition on this evolving cadomian substrate brings about the shallow rise in ehf t values we observe in the igneous basement rocks the end result observed in the balkan is of a continental crust comprising a neoproterozoic peri gondwana cadomian core reworked in multiple episodes of phanerozoic orogenies and augmented to some extent by variable mantle derived input we argue that this mode of crustal origin and evolution is also applicable to many peri gondwana terranes of western europe

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

the probability distribution of sea surface wind speeds part i theory and seawinds observations the probability distribution of sea surface wind speeds w is considered daily seawinds scatterometer observations are used for the characterization of the moments of sea surface winds on a global scale these observations confirm the results of earlier studies which found that the two parameter weibull distribution provides a good but not perfect approximation to the probability density function of w in particular the observed and weibull probability distributions share the feature that the skewness of w is a concave upward function of the ratio of the mean of w to its standard deviation the skewness of w is positive where the ratio is relatively small such as over the extratropical northern hemisphere the skewness is close to zero where the ratio is intermediate such as the southern ocean and the skewness is negative where the ratio is relatively large such as the equatorward flank of the subtropical highs an analytic expression for the probability density function of w derived from a simple stochastic model of the atmospheric boundary layer is shown to be in good qualitative agreement with the observed relationships between the moments of w empirical expressions for the probability distribution of w in terms of the mean and standard deviation of the vector wind are derived using gram charlier expansions of the joint distribution of the sea surface wind vector components the significance of these distributions for improvements to calculations of averaged air sea fluxes in diagnostic and modeling studies is discussed

did the amalgamation of continents drive the end ordovician mass extinctions abstract global biodiversity has been punctuated throughout the phanerozoic by extinction events that vary in their degree of intensity and devastation the mass extinction event that occurred at the end of the ordovician period rapidly removed a wide range of species because taxonomic loss occurred during an ice age this is believed to have initiated the extinctions and thus these extinctions have often been viewed as a deep time analogue to the loss in species diversity during the present day glacial interval the current study however indicates that temperature though arguably being a trigger was not the sole reason for the crisis based on a large bibliographic database of rhynchonelliform brachiopods that specifically operates within very narrow time slices where every locality has been precisely georeferenced for the upper ordovician lower silurian interval we show that the extinctions were not uniformly distributed nor was the succeeding recovery here we argue that changing plate tectonic configurations during the ordovician silurian interval may have exerted a primary control on biotic extinction and recovery in particular the proximity and ultimate loss of microcontinents and associated smaller terranes around laurentia may have restricted shelf and slope habitats during the latest ordovician but nevertheless in a contracted iapetus ocean provided migration routes to help drive a diachronous early silurian recovery the conclusion that plate tectonics was a primary factor controlling the extent of the extinctions and the subsequent diversity rebound demonstrates that a reduction in diversity was perhaps the most important manifestation of the end ordovician crisis and further raises the question whether this could be applied to other large phanerozoic perturbations in biodiversity levels

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

further paleomagnetic results from the silurian of the yangtze block and their implications abstract silurian redbeds were sampled at two localities in northeastern guizhou and yunnan provinces of china for paleomagnetic study progressive thermal demagnetization revealed multiple magnetic components from these samples a low unblocking temperature component a of recent origin a post folding middle to high unblocking temperature component b probably acquired during late mesozoic time and a pre folding high unblocking temperature component c two statistically distinguishable groups of directions were further recognized from the c component with one c1 having more easterly declination than the other c2 and both having a of shallow inclination the paleomagnetic pole from the c1 magnetization coincides with a pre folding pole reported from the coeval rocks in neighboring southern sichuan province its relation to the apparent polar wander path apwp for the yangtze block yb suggests that the c1 magnetization was probably acquired during the silurian by the same argument the c2 magnetization was probably acquired sometime between the silurian and carboniferous these results reconfirm the equatorial position for the yb during mid paleozoic time and clockwise rotation of the yb since at least the mid cambrian