episodic post rift subsidence of the united states atlantic continental margin sediment thickness paleobathymetry and chronostratigraphy from cost wells offshore from georgia and new jersey indicate periods of rapid subsidence superimposed on the slower thermal subsidence of the continental margin rapid subsidence occurred during the coniacian santonian the eocene and in the cost wells off new jersey since the end of early miocene once the maximum effects of water and sediment loading compaction and thermal cooling are removed the residual vertical movements caused by tectonic and sea level fluctuations can be analyzed because no global sea level change can account for all residual movements we propose that tectonism variously amplified by loading is responsible for the observed episodes of rapid subsidence synchroneity of subsidence with sea floor spreading changes in the north atlantic suggests a unified cause for these events recognition of episodic subsidence may have implications for fault timing petroleum potential and global sea level effects on passive margins

silicate weathering rates decoupled from the 87sr 86sr ratio of the dissolved load during himalayan erosion this study establishes that carbonate weathering dominates the supply of sr with elevated 87sr 86sr ratios in the bhote kosi sun kosi river system central nepal a major himalayan tributary to the ganges the dissolved load of the bhote kosi sun kosi displays a rapid increase in the 87sr 86sr ratio in its lower section downstream of the main central thrust a feature common to other himalayan tributaries of the ganges mass balance analysis of the contributing sources to the dissolved load identifies the weathering of palaeoproterozoic impure carbonates comprised largely of dolomite and mica from the lesser himalaya as the most significant lithological control upon elevated 87sr 86sr ratios in situ laser ablation analysis of the dolomite component yields 87sr 86sr ratios of 0 93 to 1 11 indistinguishable from bulk rock this confirms the presence of a highly soluble source of radiogenic strontium and suggests that diffusive exchange during a protracted metamorphic history has homogenised sr isotopes between silicate and carbonate phases within the assemblage weathering of the carbonate component of such rocks has yielded unusually high 87sr 86sr at significant sr fluxes in the dissolved load approximately 60 of the impact of the bhote kosi sun kosi on the marine 87sr 86sr ratio can be traced to weathering of this carbonate since similar lithologies outcrop within the catchments of most himalayan tributaries that feed the ganges and brahmaputra rivers the presence of such radiogenic carbonates undermines the inference that the impact of these rivers on sr isotopes in seawater is indicative of high silicate weathering rates that result from the uplift of tibet and the himalaya

middle miocene serravallian temperate carbonates in a seaway connecting the atlantic ocean and the mediterranean sea north betic strait s spain abstract miocene deposits in the contact area between the prebetic and subbetic domains betic cordillera s spain record the last stages of marine deposition on the southern iberian margin and the final closure of the north betic strait in the early tortonian late miocene serravallian middle miocene shallow water carbonates and mixed carbonate siliciclastics formed on a platform at the southern margin of the north betic strait these shallow water deposits informally termed the la escalera formation onlap an erosion surface carved into underlying miocene and older rocks carbonate components are mainly bryozoans coralline red algae molluscs and benthic and planktonic foraminifers typical of heterozoan lithofacies several facies types can be distinguished based on different grain sizes and sedimentary structures large scale geometries and stratigraphic facies relationships indicate that the la escalera formation was deposited on a homoclinal ramp attached to a deeply eroded emergent relief to the south a beach system developed at the southern margin with backshore lagoons and local incursions of coarse terrigenous sediments seawards of the beach system was a submarine dune belt that extended over several square kilometres at the northeastern end of the la escalera formation longshore currents shifted submarine dunes to the northeast maximum production of carbonate skeletons took place seawards of the dune field from this factory area skeletal debris was moved landwards and incorporated into the dunes and beaches whereas other skeletal particles were transported downslope by storms and fed a facies belt with hummocky and swaley cross stratified sediments the finest grained particles accumulated below a storm wave base along with significant planktic debris carbonate deposits change laterally westwards to terrigenous sediments formed in similar facies belts terrigenous influx limited carbonate production on the western part of the ramp by disturbing the growth of coralline algae and bryozoans vertical variations of facies within the formation depict a major transgressive regressive cycle modulated by up to 10 higher frequency cycles despite its location in an atlantic linked basin the sedimentary model of the la escalera formation shows similarities to the models proposed for neogene mediterranean temperate carbonates which imply a relatively low energy regime on the ramp in comparison with the open ocean platforms this relatively low energy regime can be explained by the position of the north betic strait at the eastern end of the guadalquivir basin however hummocky and swaley cross stratified deposits are significantly more developed in la escalera deposits than in known examples of neogene mediterranean carbonates

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

geographic vectors of human mobility in the andes 34 36 s comparative analysis of minor obsidian sources abstract we have carried out long term comparative in a wide latitudinal range of the andes 29 37 south encompassing selected areas that differ in ecology and biogeography this latitudinal span shows diversity in subsistence modes across time and space ranging from andean agro pastoralists in the north to patagonian hunter gatherers in the south as part of this research a program of geochemical and archaeological characterization of obsidian sources and distributions is being developed attempting to assess connections between different biogeographical contexts this work has allowed recognizing five andean sources with different geological and topographical properties stemming from this macro regional endeavor in this paper we present a comparative analysis of the human use of two sources that based on the intensity of human use on a macro regional scale can be interpreted as minor sources this study is framed on gis least cost models for human circulation across rugged landscapes allowing access to the sources we assess temporal and spatial patterns of human occupation of high altitude andean deserts and neighboring areas comparing two of obsidian sources laguna del diamante 34 s and cerro huenul 36 s the results indicate the existence of asymmetric distributions particularly in the case of laguna del diamante this evidence is used to assess the existence of dominant geographic vectors of human access and use of the andean highlands on this basis we explore the analytical potential of minor sources for the study of human biogeography and organization of technology

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

the belair fault a cenozoic reactivation structure in the eastern piedmont the belair fault zone near augusta georgia oriented approximately n25 e is a fundamentally important structural feature of the southeastern piedmont and adjacent coastal plain geologic studies by prowell and o9connor in 1978 indicated that during the late cretaceous and eocene the belair fault zone was an oblique slip reverse fault that resulted in vertical separations of the barnwell eocene and middendorf upper cretaceous formations of 10 m and 30 m respectively by means of an extensive drilling program prowell and o9connor 1978 determined that the horizontal separation of the late paleozoic augusta fault by the belair fault was 23 km they furthermore suggested that because of an apparent offset of the margin of the atlantic coastal plain in the region much of this displacement may have occurred in post cretaceous time during the past few years we have been engaged in field studies along the projected course of the belair fault zone in the kiokee and carolina slate belts of south carolina these studies indicate that the belair fault zone does not significantly displace rock units laterally in the footwall of the augusta thrust it now appears that the belair fault zone is a tear fault in the upper plate of the augusta thrust and therefore most of the lateral displacement along the belair fault zone probably occurred during the late paleozoic hercynian or alleghanian deformation which has recently been documented in the kiokee belt of south carolina by snoke and others 1980b during the late cretaceous and cenozoic the belair fault zone was reactivated as an oblique slip reverse fault resulting in the displacement of the middendorf and barnwell formations of the atlantic coastal plain

provenance study on prehistoric obsidian objects found in romania eastern carpathian basin and its neighbouring regions using prompt gamma activation analysis abstract macroscopic characteristics such as hardness relatively easy workability transparency translucency and shiny black colour of the carpathian 1 c1 type obsidian which is one significant variety of the carpathian obsidians made it highly valuable in the prehistoric times it was transported several hundreds of kilometres away from the geological source becoming wide spread in the eastern part of the carpathian basin as well seventy two pieces of prehistoric neolithic to bronze age obsidian artefacts tools arrow heads chips and fragments found in different parts of romania transylvania banat and muntenia have been investigated by non destructive prompt gamma activation analyses the aim of the study was to determine the provenance of their raw materials the geochemical composition of the artefacts showed high similarity with that of the obsidian samples collected at outcrops from the slovakian side of the tokaj mountains based on characteristic major and trace element concentrations most of the studied romanian obsidian artefacts are characterized as c1 type obsidians however some archaeological pieces from banat and muntenia have been identified as carpathian 2 c2 tolcsva erd benye and mad type based on the pgaa results any other provenance such as lipari melos sardinia yali antiparos or armenia can be excluded with high significance our results suggest that in parallel with the predominance of the c1 type obsidian raw material in the transylvanian basin simultaneous use of c2 type obsidian raw material can be shown outside transylvania in banat and muntenia and especially during the neolithic this can imply different connections and raw material supply routes from the tokaj mountains to transylvania and to the southern regions during the neolithic and the copper age

chemical characterization of obsidians from different mediterranean sources by non destructive sem eds analytical method the aim of our research is to check the sem eds non destructive analytical method for discriminating and locating the possible sources of obsidian artefacts moreover in order to obtain a significant discrimination of mediterranean obsidians we analysed samples collected from outcrops of the major sources monte arci sardinia and palmarola lipari pantelleria gyali and melos islands all samples were analysed by both xrf whole rock and sem eds glass and microliths microphenocrysts the xrf analysis reveals that major elements discriminate obsidian the discrimination using major elements is very useful because the amount of trace elements is lower than the detection limit of a si li ed detector the major elements particularly sio2 al2o3 cao na2o and k2o of obsidian glass discriminate the six main mediterranean sources our work demonstrates therefore the possibility of discriminating different provenance of obsidian artefacts using sem eds by means of a relatively rapid effective and above all non destructive method

a scenario of mesozoic cenozoic ocean circulation over the blake plateau and its environs after the continental breakup of north america africa and europe a sluggish wind driven circulation gyre probably formed in the juvenile north atlantic basin surface flow in the western atlantic ocean during the early cretaceous likely was northward along the seaward edge of an extensive reef that flourished offshore of north america sometime during the late cretaceous the surface circulation in the gulf of mexico had evolved into a clockwise rotary pattern as the exchange of water with the pacific ocean diminished by latest cretaceous time a vigorous easterly current flowed through the suwannee strait of southern georgia and northern florida injecting copious amounts of water and sediment into the western blake plateau basin this flow pattern apparently persisted into paleocene time during late paleocene and early eocene time strong northerly flow through the straits of florida and across the blake plateau was established this represented the onset of gulf stream circulation over the blake plateau the position of the gulf stream shifted repeatedly across the northern and central plateau during the tertiary and quaternary periods the westernmost track was located along the inner blake plateau parallel to the florida hatteras slope the easternmost track was 500 m lower bathymetrically and crossed the central plateau and continental slope just north of the blake spur the gulf stream apparently shifted in response to changes in water depth on the blake plateau that accompanied global fluctuations of sea level during rises of sea level the gulf stream drifted westward until it impinged on the florida hatteras slope and outer shelf during lowerings of sea level the gulf stream was deflected progressively eastward across the central plateau by the charleston bump a prominent bathymetric bulge of the northern blake plateau

the lami pyroclastic succession lipari aeolian islands a clue for unravelling the eruptive dynamics of the monte pilato rhyolitic pumice cone abstract the lami succession piled up during the explosive activity of the monte pilato on lipari island central aeolian arc italy it comprises a repetitive alternation of fall and pyroclastic density current beds which define 13 units separated by fine ash beds despite the homogeneous rhyolitic composition the juveniles fragments show strong textural heterogeneities from highly vesicular pumice to dense black obsidians the pumice types are termed i tube which shows elongated tubular vesicles ii frothy highly vesicular with large sub rounded vesicles and iii agglomerated and welded two types of obsidian pyroclasts are recognized i aphyric black obsidian and ii grey obsidian showing spherulitic texture all these pyroclastic types occur throughout the stratigraphic succession and mixed in the same bed they account for changing physical conditions along the conduit which is hypothesised to be filled by a melt plug during the eruption of 12 out of 13 units the strong textural heterogeneities of the juvenile fragments testify for the existence of differential shear rates which can be explained though two shear mechanism i simple shear producing horizontal zonation of texture in the conduit with black obsidians along the conduit walls passing to tube and frothy pumice to the centre and ii pure shear producing a vertical zonation in the conduit with black obsidians at the top overlying frothy pumice agglomerated and welded pumice of unit 13 is thought to represent the portion of magma heated by a batch of hotter melt that entered the magma chamber and triggered the eruption the deposits of unit 13 represent a unique case of spatter accretion due to accumulation of hot low viscous rhyolitic pumice fragments emplaced from pyroclastic fountaining

correlation of onshore offshore oligocene through lower miocene strata using 87sr 86sr isotopic ratios north flank of cape fear arch north carolina usa abstract cores from onshore and offshore of the onslow block reveal at least three depositional sequences above the eocene castle hayne limestone and below the miocene pungo river formation through use of 87sr 86sr ratios and their resultant dates these sequences are correlated from onshore to offshore thus clarifying the geologic history of the inner continental shelf of north carolina the oldest depositional sequence consists of calcareous quartz sand and sandy pelecypod mold grainstone updip and yellowish gray very fine to fine calcareous quartz sand with minor clay and silt downdip most of the carbonate in the downdip part of the sequence consists of foraminifers ostracods echinoid spines and other small allochems eight hand picked foraminiferal samples including two replicate analyses from this sequence selected from two onshore cores and one offshore core yield 87sr 86sr ratios from 0 707901 to 0 708006 equivalent to lowess locally weighted regression scatterplot smoother dates ranging from 29 2 to 32 0 ma this indicates this sequence is rupelian early oligocene in age and assignable to either the ta4 4 or ta4 5 global coastal onlap cycle the youngest sequence consists of oyster bearing quartz sand and laterally equivalent clay with mollusks onshore and very fine to fine calcareous quartz sand offshore twelve foraminiferal and one ostracod sample including five replicate analyses from three cores on the inner shelf of onslow bay yield 87sr 86sr ratios from 0 708332 to 0 708386 equivalent to lowess dates ranging from 21 1 to 22 2 ma this indicates the sequence is aquitanian early miocene in age and assignable to the tb1 4 global coastal onlap cycle although chattian late oligocene sequences are recognized onshore in outcrop and core and are projected to continue into onslow bay no cores provided sr samples for analysis interpreted to be late oligocene in age

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

moving obsidian the case of antofagasta de la sierra basin southern argentinean puna during the late middle and late holocene abstract this paper presents the results of an xrf analysis on the provenience of 118 obsidian artifacts from archaeological sites of the antofagasta de la sierra basin catamarca province argentina dating to the late middle and late holocene c 4500 1100 bp the time span considered encompasses a local process of gradual transformation from hunter gatherer early agro pastoral groups to consolidated agro pastoral societies for this study non destructive elemental analysis of obsidian artifacts was conducted using two different x ray fluorescence spectrometers ed xrf this information was then supplemented by previous provenience results undertaken on 59 obsidian archaeological artifacts from the same area a comparative synthesis of chemical and macroscopic characterization of five obsidian sources located in southern argentinean puna is also presented the provenance of archaeological materials was assigned by comparison with twelve presently known argentine sources on this basis late middle and late holocene obsidian regional movement patterns differential distribution and use of this raw material are discussed furthermore this obsidian research lends support to the existence of exchange networks based on the use of different extra regional obsidian sources located in the northern argentinean puna

obsidian provenance determination by back scattered electron imaging obsidian glass is a significant component of the lithic artefact assemblage of primitive cultures the ability to characterize and correlate artefacts with specific sources provides significant information about prehistoric patterns of procurement and exchange1 because visual and light optical microscopic methods have proved ineffective in characterizing obsidian chemical methods such as x ray fluorescence2 xrf and instrumental neutron activation analysis3 inaa are usually used to try to determine provenance here we show that electron microscopy specifically back scattered electron bse imaging may be used to characterize obsidian petrographically the variety and number of bse observable features are generally sufficient to petrographically fingerprint individual obsidian sources sources are also sufficiently homogeneous so that bse characterization can determine provenance for individual artefacts of archaeological obsidian

obsidian use and mobility during the early and middle holocene in the salt puna nw argentina abstract we discuss the use of obsidian as a tool to understand the mobility range of hunter gatherers living in a high elevation desert in the salt puna specifically in the area of antofagasta de la sierra catamarca between ca 9000 and 6000 bp xrf analyses of a vertical sample of obsidian artifacts pertaining to early and middle holocene contexts from three archaeological sites show the use of various sources within a range of 40 95 km respectively from the study area our analyses suggest that mobility patterns during the early colonization phase early holocene of this high elevation region included two sources located in the eastern and northwestern areas of the salt puna and reveal a process of landscape learning by contrast during the phase of effective occupation middle holocene a period coinciding with climatic fluctuations and decreasing rainfall a greater number of obsidian sources were used suggesting increased knowledge of the landscape as well as a pattern of territorial range shifting

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

gulf trough the atlantic connection analyses of seismic reflection profiles and stratigraphic data indicate a continuation of the gulf trough trend across eastern south carolina and offshore between cape fear and cape hatteras north carolina seismic profiles show a linear northeast trending zone of nondeposition and erosion and areas of chaotic deposition in the eocene and oligocene sections the character of deposition and erosion along this trend is similar to that produced by bottom currents under the core of the present gulf stream the trend separates deep water from shallower water deposits indicating that the erosion was produced by strong marine currents flowing through the gulf trough in the high sea levels of middle eocene through early oligocene time

subtropical carbonates in a temperate realm modern sediments on the southwest australian shelf the southwestern continental margin of australia 19 degrees s 22 degrees s in the western indian ocean is transitional between cool water and warm water carbonate realms it comprises the incipiently rimmed flat topped steep fronted rottnest shelf in the south the uniform subtropical starved carnarvon ramp off shark bay and the ningaloo fringing reef in the north the margin is strongly influenced by the poleward flowing warm nutrient poor leeuwin current which promotes overall downwelling and strong summer equatorward blowing winds which generate local seasonal upwelling the structurally quiescent northern part of the rottnest shelf with minimum accommodation is characterized by luxuriant stands of sea grasses and macrophytes growing on coralline encrusted hardgrounds and rooted in sediments rich in coralline algae and larger symbiont bearing foraminifers together with abundant cool water elements such as bryozoans molluscs and small foraminifers halimeda is poorly calcified and does not contribute to the sediment azooxanthellate corals although present are not common such a sediment pattern has many analogs in the geologic record especially the early cenozoic the incipient rim is a morphologically complex linear ridge system interpreted to be a buried mid pleistocene barrier reef or beach dune complex the northern part of the ridge complex is capped by the houtman abrolhos reef platforms subphotic sediments on the deep outer shelf and upper slope affected by seasonal upwelling are typical cool water poorly sorted bryozoan dominated deposits rich in small foraminifers and sponge spicules the inner part of the more structurally active carnarvon ramp ranges from steep eolianite cliffs to hypersaline environments of shark bay to the ningaloo fringing reef mid ramp sediment especially off shark bay is mostly relict or stranded and foraminifer dominated sand with abundant mg calcite cemented intraclasts these sediments accumulating on a relatively barren seafloor likely represent attenuated carbonate production brought about by downwelling and episodic incursions of saline shark bay derived waters onto the ramp the outer ramp is either planktic foraminiferal sand sorted by strong bottom currents or spiculitic mud such sedimentation patterns should typify the western margins of large ocean basins during those periods in geologic history when circumglobal equatorial circulation was active and equatorial gateways narrow in contrast to eras of supercontinents when cool water carbonate sedimentation and upwelling prevailed in similar settings furthermore because low latitude trade winds relax during glacial epochs and the cool water upwelling belt moves equatorward into otherwise tropical realms temperate and subtropical sedimentation patterns in these regions should oscillate at the 100 ky scale in the stratigraphic record

paleobathymetric influence on the development of the late ediacaran yangtze platform hubei hunan and guizhou provinces china abstract a compiled facies map based on 48 sections positioned in three chinese provinces hunan guizhou and hubei and field data emphasize the changes in depositional environments on the shelf of the ediacaran yangtze platform the facies interpretation suggests three depositional environments 1 a deep water basin with a slope facies on its margins maoping and wuhe sections hubei province 2 intertidal or shoals environments subjected to wave energy yangjiaping and zhongling sections hunan province wengan section guizhou province 3 a shallow water subtidal shelf environment subjected to currents xikou section guizhou province during the doushantuo formation time period 635 ma 551 ma condon d zhu m y bowring s yang a jin y g 2005 u pb ages from the neoproterozoic doushantuo formation china science science 308 95 98 the shelf showed an irregular bathymetry interpreted as inherited from the rifting history of the yangtze platform following the break up of rodinia approx 700 ma the tilted blocks influenced the platform development and the facies distribution locally more than the doushantuo formation time period 84 ma has been necessary to compensate the variations of bathymetry inherited of the tilted blocks geometry

the dynamic history of the trans mexican volcanic belt and the mexico subduction zone abstract the trans mexican volcanic belt tmvb is a 1000 km long neogene continental arc showing a large variation in composition and volcanic style and an intra arc extensional tectonics it overlies the rivera and cocos slabs which display marked changes in geometry geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc and the lower crust beneath the arc is partially molten east of 101 w the tmvb is built on a precambrian to paleozoic crust with thickness of 50 55 km west of 101 w the tmvb is underlain by jurassic to cenozoic marine and continental arcs with a 35 40 km thick crust the evolution of the tmvb occurred in four stages 1 from 20 to 10 ma the initial andesitic arc moved inland showing progressively drier melting and eventually slab melting suggesting flattening of the subducted slab 2 since 11 ma a pulse of mafic volcanism migrated from west to east reaching the gulf of mexico by 7 ma this mafic lavas marks the lateral propagation of a slab tear triggered by cessation of subduction beneath baja california 3 thereafter the volcanic front started moving trenchward with a marked phase of silicic volcanism between 7 5 and 3 ma local emplacement of small volume intraplate like basalts since 5 ma and development of extensional faulting these features are related to slab rollback enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust 4 the modern arc consists of a frontal belt dominated by flux and slab melting and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint

a near field sea level record of east antarctic ice sheet instability from 32 to 27 myr 1 fossil facies and isotope analyses of an early high paleolatitude 55 s section suggests a highly unstable east antarctic ice sheet from 32 to 27 myr the waxing and waning of this ice sheet from 140 to 40 of its present volume caused sea level changes of 25 m ranging from 30 to 50 m related to periodic glacial 100 000 to 200 000 years and shorter interglacial events the near field gippsland sea level gsl curve shares many similarities to the far field new jersey sea level njsl estimates however there are possible resolution errors due to biochronology taphonomy and paleodepth estimates and the relative lack of lowstand deposits in njsl that prevent detailed correlations with gsl nevertheless the lateral variations in sea level between the gsl section and njsl record that suggest ocean siphoning and antisiphoning may have propagated synchronous yet variable sea levels

chemical differentiation of obsidian within the glass buttes complex oregon two hundred twenty five source samples from the multi component obsidian source at glass buttes oregon were characterized by neutron activation analysis to determine the number of chemical groups present seven geochemical groups were found within the glass buttes complex an abbreviated neutron activation analysis procedure previously used to differentiate between obsidian sources in mesoamerica was also successful in separating obsidian from different outcrops at glass buttes thirty one artifacts from the robins spring site on glass buttes were also analysed the abbreviated naa procedure was also successful at assigning the artifacts to the different subsources at glass buttes

post glacial seismic stratigraphy central great barrier reef australia a regional programme of continuous seismic boomer profiling in the central great barrier reef province has identified a widespread shallow seismic discontinuity reflector a which is interpreted as the pre holocene surface nine seismic facies units are distinguished primarily on the basis of the seismic records but also with the aid of additional criteria such as location and surface sediment types two units underlie reflector a and are pre holocene these units are interpreted as a permo carboniferous bedrock and b pleistocene tertiary sediments consisting of both shelf wide terrigenous units and carbonate mounds and platforms under present reefs seven units are post glacial and overlie reflector a these units are interpreted as c fluvial estuarine channel fill d relict delta front deposits e relict transgressive veneer f coastal coarse and g fine deposits h modern reef and i reef talus in general post glacial sediment cover is very thin and in many places on the mid shelf the pre holocene units crop out substantial post glacial accumulations are limited to protected coastal embayments and to offshore reef masses

types of mixing and heterogeneities in siliciclastic carbonate sediments abstract mixed siliciclastic carbonate deposits consist of a suite of different types of mixing between the two components from bed core plug to stratigraphic seismic scales producing a high vertical and lateral lithological variability mixed deposits results from the interaction of siliciclastic input and coeval carbonate production controlled by temporal and or spatial factors although mixed deposits are very diffuse in the geological record studies about these deposits are scrappy and not well encoded accordingly mixed deposits represent a labyrinth for researchers who want to investigate them for the first time in this paper different types of mixing compositional versus strata controlled by different allocyclic e g sea level climate and or autocyclic e g depositional processes factors that operate at different scale are documented mixing is recognized and described at three main scales of observation bed core plug scale lithofacies well log scale and stratigraphic seismic scale i compositional mixing reflects the contemporaneous accumulation of the two heterolithic fraction in space and time this type of mixing is observable at lamina to bed scale locally producing depositional structures diagnostic for particular depositional environments ii strata mixing results from the alternation of the two heterolithic fraction in time this type of mixing is observable at lithofacies to stratigraphic scale and can be related to depositional processes climatic variations and or relative sea level changes a correct identification of these different types of mixing and the scale of their occurrence is crucial in revealing i physical processes that control the sedimentation ii environmental factors that influence the carbonate factory related to the siliciclastic dispersal mechanisms and iii internal heterogeneity of the resulting sedimentary deposit furthermore the petroleum industry is interested to unravel new insights about internal properties of mixed siliciclastic carbonate systems e g porosity permeability and to reconstruct predictive 3d models for the related reservoirs the correct prediction of internal heterogeneity and the recognition of lateral and vertical compartmentalization have an important impact on hydrocarbon exploration and exploitation

the southern tyrrhenian subduction zone deep geometry magmatism and plio pleistocene evolution abstract we report on a high resolution vp vp vs and qp model of the southern tyrrhenian subduction zone obtained by the inversion of p and s wave arrival times and t values from intraslab seismicity the arcuate shape of the southern apennines calabrian arc sicilian maghrebides is perfectly mirrored by two rather continuous low and high vp bands lying beneath the belt system at ca 25 and 100 km respectively between 100 and 300 km two independent high vp slabs lie beneath the neapolitan region and the southern tyrrhenian sea separated by unperturbed mantle we suggest that the ca 150 km wide slab window beneath the southern apennines opened after a tear occurring within a composite subduction system formed by the apulian continental lithosphere and the ionian oceanic slab the abrupt slab rupture induced ultrafast southeastward retreat of the ionian slab and the 19 cm yr spreading of the back arc oceanic marsili basin between ca 2 1 and 1 6 ma ago the 25 km low vp zone beneath the arc denotes continental upper crustal rocks below the chain its striking continuity requires a unique orogenic wedge at 25 km depth below the southern apennines the calabrian arc and the sicilian maghrebides the alternative explanation would imply the ubiquitous occurrence of autochthonous lower plate rocks at 25 km depth i e a puzzling autochthonous continental calabria the ionian slab beneath calabria shows high vp high qp and low vp vs anomalies typical of old oceanic lithosphere intermediate depth seismicity is concentrated within its thin oceanic crust suggesting the occurrence of vigorous metamorphism the slab dehydration promotes the melting of the overlying mantle as testified by high vp vs and low qp anomalies between the slab and the aeolian magmatic arc

glass geochemistry of pyroclastic deposits from the aeolian islands in the last 50 ka a proximal database for tephrochronology abstract volcanic ash 1000 analyses provides a basis for proximal distal and distal distal tephra correlations tephra deposits from the different aeolian islands are geochemically diverse with some individual eruptions showing diagnostic geochemical heterogeneity recognised both stratigraphically and or spatially major element glass analyses reveal that vulcano 0 21 ka and stromboli 4 13 ka have erupted potassic shoshonitic and k series tephra with broadly overlapping compositions but data presented here demonstrates that their eruptive products can be distinguished using either tio2 contents or their hfse th ratios whilst individual volcanic sources often produce successive tephra deposits with near identical major and minor element compositions through time i e lipari vulcano trace element glass data can help to decipher successive eruptions changes in lree and th concentrations of volcanic glasses erupted spanning approximately the last 50 ka greatly enhance the potential to discriminate successive eruptive units on lipari the new proximal glass database has been used to verify new ionian sea core m25 4 12 and existing distal occurrences of aeolian island derived tephra enabling the reassessments of past ash dispersals finally proximal and distal data have been used to establish an integrated proximal distal eruptive event stratigraphy for the aeolian islands

reservoir characterization and hydrocarbon accumulation in late cenozoic lacustrine mixed carbonate siliciclastic fine grained deposits of the northwestern qaidam basin nw china abstract late cenozoic lacustrine mixed carbonate siliciclastic sequences in the northwestern qaidam basin nw china are mainly composed of high porosity and low permeability fine grained rocks but have big potentials of oil gas commercial production however how these fine grained rocks generate high quality reservoirs and accumulate hydrocarbons remains poorly known this study focuses on shallow buried shang youshashan formation middle late miocene n22 and shizigou formation late miocene pliocene n23 reservoirs and hydrocarbons in xiaoliangshan area of the northwestern qaidam basin we conduct mineralogy petrography and porosity and permeability analysis for reservoir rocks and biomarker analysis for hydrocarbons and potential source rocks the results indicate that the n22 high quality reservoirs are dominated by fractured marlstones and lime mudstones and constitute structural traps whereas the n23 hydrocarbon reservoirs are mainly composed of siliciclastic dominantly rocks and form stratigraphic lithologic traps similar biomarker ratios between crude oil samples and paleogene organic matter rich rocks reveal that hydrocarbons in the shallow system were likely derived from deep buried source rocks rather than late cenozoic lacustrine fine grained rocks themselves in this case large scale vertical fractures created by kink band structures in the northwestern qaidam basin are supposed to facilitate hydrocarbon migration and accumulation preliminary production data and exploration well oil gas test results demonstrate highest yields and thus large hydrocarbon potentials in the n22 marlstone and lime mudstone reservoirs collectively we suggest that relatively high permeability fractured and carbonate rich reservoirs on structural highs are favorable targets for future oil gas exploration in the northwestern qaidam basin this petroleum system provides a typical and significant example for hydrocarbon exploration and development in mixed carbonate siliciclastic fine grained rocks of nonmarine petroliferous basins

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

coeval versus reciprocal mixed carbonate siliciclastic deposition middle devonian baltic basin eastern europe implications from the regional tectonic development the middle devonian narva succession in the baltic basin represents a significant turnaround in the history of the basin the detailed study of core and outcrop sections and the three dimensional correlations across the baltic basin reveal a carbonate dominated mixed retrogressive succession overlain by a siliciclastic dominated progradational succession the palaeogeographic reconstructions show how the shallow tide influenced basin expanded from south west to north east and later during the transgression also to the north south and east the transgressive portion of the basin fill is dominated by carbonate rich sabkha and supratidal to intertidal deposits on the basin margins and subtidal carbonates in the basin centre siliciclastic material was derived by tidal currents and storm waves from the south west through a tidal inlet and flood tidal delta complex this initial transgressive phase is characterized by the lack of subsidence or even episodic uplifts in the northern north western part of the basin margin shown by convergence of timelines and the thin 30 m transgressive succession in contrast on the southern margin the facies associations stack vertically into a 70 to 80 m thick succession indicating significantly higher subsidence rates the upper part of the transgressive phase indicates subsidence across the whole basin the upper progradational portion of the basin fill is dominated by coarse siliciclastic tide influenced deltaic deposits that rapidly prograded from north west to south east this detailed study on the narva succession shows that siliciclastic and carbonate deposition was coeval and that mixing occurred at different temporal and spatial scales the mixing was controlled by grain size volume and location of siliciclastic input rather than relative sea level changes as suggested in widely used reciprocal mixing models it is suggested that the forebulge of the scandinavian caledonian fold and thrust belt migrated to the north western margin of the baltic basin during the earliest eifelian as indicated by the lack of subsidence and probable uplift in the northern north western margin during the early transgressive phase the forebulge migration ceased although the forebulge had already started to subside during the later stages of the transgressive phase the deltaic progradation is interpreted to be associated with the orogenic collapse and uplift in the scandinavian caledonides that caused the erosion of the foreland basin fill and the coarse sediment transport into the baltic basin

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

the identification of archaeological obsidian sources on kamchatka peninsula russian far east using geochemical and geological data current progress abstract the current state of the art of provenance studies for archaeological obsidian on kamchatka peninsula is presented prehistoric people widely used obsidian as a raw material for making tools and acquired it from several primary sources the exact position of seven sources allowed us to understand the general features of obsidian geochemistry and tectonic position of obsidian bearing volcanic formations this also made it possible to suggest the localization of seven still unknown sources for archaeological obsidian on kamchatka verification of our preliminary conclusions can be made by fieldwork in selected areas

pliocene quaternary volcanism and faulting at the intersection of the gulf of california and the mexican volcanic belt the junction of the western mexican volcanic belt and the gulf of california represents a superposition of subduction and continental rifting tectonic regimes in the late cenozoic subduction of the oceanic rivera plate has caused late cenozoic uplift of western mexico forming the jalisco block this paper addresses three questions where is the northern boundary of the jalisco block how is the continental fracture system related to that offshore and what is the spatial distribution and composition of subduction related lavas 40 ar 39 ar dates on cretaceous to paleogene silicic ash flows show that the northern boundary of the jalisco block may be defined by the abrupt change in basement age from cretaceous to miocene 40 ar 39 ar and k ar dates on faulted lavas from the nayarit region indicate that extension at the edge of the jalisco block has occurred since ca 4 2 ma the least principal stress 3 direction associated with these faults has had two different orientations from 4 2 ma to the present several pliocene to holocene 4 20 1 05 and 0 65 ma lava flows and aligned cinder cones have a n45 w associated least principal stress direction whereas three pliocene 3 36 3 38 and 3 11 ma lava flows are cut by faults indicating a north to north northeast least principal stress direction the two different stress directions may arise either from structural features in the basement of the arc or from changes in offshore plate boundaries e g 2 5 ma when the rivera and mathematicians plates were locked together whole rock major and trace element analyses of lavas from the coastal nayarit region reveal three different lava types an alkali basalt series basaltic andesite and andesite the alkali basalts show feo and tio 2 enrichment and have low ba zr and ba la ratios consistent with derivation from an oceanic island type mantle the basaltic andesites and andesites are both alkaline and calc alkaline contain hydrous phenocrysts and have high sr zr and la nb ratios consistent with a subduction related source among these lavas there is a correlation between sr zr oxygen fugacity and h 2 o contents suggesting that an oxidized hydrous fluid is involved in the genesis of the subduction related lavas the distribution of subduction related volcanic centers in the coastal nayarit region and areas southeast within the jalisco block defines front that parallels the middle america trench and is consistent with a 45 dip on the subducted rivera plate

relict and contemporary influences on the postglacial geomorphology and evolution of a current swept shelf the eastern cape coast south africa abstract few stratigraphic models of continental shelves incorporate the process of geostrophic current sweeping consequently its role in the stratigraphic record is often overlooked we examine the narrow current swept eastern cape shelf of south africa using a combination of geophysical techniques seafloor sampling and video observations and interpret the role of current action on the transgressive stratigraphy of this steep subtropical shelf during the last glacial maximum fluvial valleys incised the acoustic basement rocks during the subsequent transgression two distinct shorelines were formed and preserved at 105 m and 60 m their development and preservation is linked to i high sediment supply from adjacent fluvial sources ii early diagenesis and iii alternating sea level stillstands and periods of rapid sea level rise during melt water pulses 1a and 1b respectively the deeper shoreline formed in a sandy wide coastal plain setting with limited bedrock influence whereas the shallower shoreline comprised alternating rock headlands and embayments like the contemporary coast differences in antecedent topography and geology are responsible for the temporal variability in shoreline type coastal squeeze is exacerbated with increasing bedrock control as the shoreline migrates landward between the two shoreline complexes in the mid shelf the transgressive stratigraphy records initial valley infill by progradation of coast parallel sandy spits these are capped by a stiff lagoonal mud deposited as ongoing sea level rise overspilled the valley interfluves onlapping the adjacent aeolianites the uppermost stratigraphy comprises mounds of rhodoliths which interfinger with a sandy inner to middle shelf highstand wedge after sea level reached its present position ca 7 4 ka yr bp the shelf became subject to reworking by the high energy geostrophic agulhas current this has had the following major effects on the shelf stratigraphy 1 the topographic relief of the cemented palaeo shorelines has been emphasised by removal of the post transgressive cover and 2 the shelf no longer acts as a depocenter instead the seabed consists of rhodoliths gravel streamers bedrock or gravel hash of the wave ravinement surface given the necessary antecedent conditions such as accommodation sediment supply and favourable diagenetic climate prominent shorelines can form and be preserved on the shelf strong current sweeping emphasises these morphological features on subtropical shelves

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

episodic back arc extension during restricted mantle convection in the central mediterranean abstract in the central mediterranean during the last 80 myr africa has been slowly converging toward eurasia with an average relative velocity of less than 1 cm yr 1 for 50 myr this slow convergence led to the build up of the alpine orogenic belt and to the initiation of consumption of the former tethys ocean in the last 30 myr however the whole central western mediterranean has been swept by rapid episodes of trench migration up to 6 cm yr 1 and back arc opening which consumed the whole former tethys ocean we combine plate tectonic history geological timing and laboratory modelling to reconstruct the subduction history and the evolution of the central mediterranean over the last 80 myr we find that the dynamic evolution of the subducting oceanic lithosphere can reconcile the rapid episodic back arc migration with the slow african convergence but only if the subduction process is restricted to the upper mantle

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

role of river suspended material in the global carbon cycle the reaction of ca derived from silicate weathering with co2 in the world s oceans to form carbonate minerals is a critical step in long term climate moderation ca is delivered to the oceans primarily via rivers where it is transported either as dissolved species or within suspended material the relative importance for climate moderation of riverine dissolved ca vs suspended ca transport stems from the total ca flux and its climate dependence data in the literature suggest that within uncertainty global riverine dissolved ca flux is equal to suspended material ca flux to determine how these fluxes depend on temperature and rainfall a 40 yr field study was performed on 4 catchments

quantifying the impact of riverine particulate dissolution in seawater on ocean chemistry the quantification of the sources and sinks of elements to the oceans forms the basis of our understanding of global geochemical cycles and the chemical evolution of the earth s surface there is however a large imbalance in the current best estimates of the global fluxes to the oceans for many elements in the case of strontium sr balancing the input from rivers would require a much greater mantle derived component than is possible from hydrothermal water flux estimates at mid ocean ridges current estimates of riverine fluxes are based entirely on measurements of dissolved metal concentrations and neglect the impact of riverine particulate dissolution in seawater here we present 87sr 86sr isotope data from an icelandic estuary which demonstrate rapid sr release from the riverine particulates we calculate that this sr release is 1 1 7 5 times greater than the corresponding dissolved riverine flux if such behaviour is typical of volcanic particulates worldwide this release could account for 6 45 of the perceived marine sr budget imbalance with continued element release over longer timescales further reducing the deficit similar release from particulate material will greatly affect the marine budgets of many other elements changing our understanding of coastal productivity and anthropogenic effects such as soil erosion and the damming of rivers

late pleistocene to precolumbian behind the arc mafic volcanism in the eastern mexican volcanic belt implications for future hazards an area of widespread alkaline to subalkaline volcanism lies at the northern end of the cofre de perote citlaltepetl pico de orizaba volcanic chain in the eastern mexican volcanic belt mvb two principal areas were active about a dozen latest pleistocene to precolumbian vents form the 11 km wide e w trending cofre de perote vent cluster cpvc at 2300 2800 m elevation on the flank of the largely pleistocene cofre de perote shield volcano and produced an extensive lava field that covers s 100 km 2 more widely dispersed vents form the naolinco volcanic field nvf in the sierra de chiconquiaco north of the city of jalapa xalapa three generations of flows are delineated by cone and lava flow morphology degree of vegetation and cultivation and radiocarbon dating the flows lie in the behind the arc portion of the northeastern part of the mvb and show major and trace element chemical patterns transitional between intraplate and subduction zone environments flows of the oldest group originated from la joya cinder cone radiocarbon ages v42 000 yr bp at the eastern end of the cpvc this cone fed an olivine basaltic flow field of v20 km 2 that extends about 14 km southeast to underlie the heavily populated northern outskirts of jalapa the capital city of the state of veracruz the central cone group ccg of intermediate age consists of four morphologically youthful cinder cones and associated vents that were the source of a lava fields 27 km 2 of late pleistocene or holocene age the youngest group includes the westernmost flow from cerro colorado and a lava flow v2980 bp from the rincon de chapultepec scoria cone of the nvf the latest eruption from the compound el volcancillo scoria cone occurred about 870 radiocarbon years ago and produced two chemically and rheologically diverse lava flows that are among the youngest precolumbian flows in mexico and resemble paired aa pahoehoe flows from mauna loa volcano the el volcancillo eruption initially produced the high effusion rate short duration toxtlacuaya alkaline aa lava flow from the southeastern crater this 12 km long hawaiite average 50 5 sio2 flow was followed by extrusion of the calc alkaline r o naolinco lava flow from the northwestern crater this large volume v1 3 km 3 tube fed basaltic pahoehoe flow average sio2 49 traveled 50 km inferred effusion rates suggest emplacement over a decade long period flows of all three age groups are transected by highway 140 and the railway that form major transportation arteries between jalapa and puebla this area has not previously been considered to be at volcanic risk but volcanism here has continued into precolumbian time future eruptions of similar magnitude and location to those documented here could pose significant hazards to transportation corridors and to densely populated areas in and to the north of jalapa slight

late cenozoic reverse faulting in the fall zone southeastern virginia abstract a set of en echelon reverse faults cut paleozoic metamorphosed igneous rocks of the piedmont and overlying late cenozoic sediments at the old hickory heavy mineral deposit in the fall zone of southeastern virginia diorite of the eastern slate belt was faulted over nearshore to shore face deposits of the pliocene yorktown formation these nw se striking faults experienced oblique dip slip movement with a maximum displacement of up to 6 m on individual faults faults tip out along strike and are overlain by distinct cobble beds suggesting that sediment deposition and faulting were contemporaneous deformation at old hickory may have been formed by reactivation of existing paleozoic structures under a regionally extensive compressional stress field parallel to the modern one

non depositional and erosional offshore bioeroded hardgrounds from the lower cretaceous of the neuquen basin argentina insights into their sequence stratigraphic implications and controls abstract hardgrounds are important surfaces for basin analysis and oil exploration representing in some cases significant markers of the sedimentary basin fill in the neuquen basin bioerosion structures are common on the shell surfaces of benthic organisms but bioeroded hardgrounds are comparatively uncommon in the pilmatue member of the lower cretaceous agrio formation valanginian hauterivian two examples of bioeroded hardgrounds are described in detail allowing to recognize contrasting palaeoenvironmental and sequence stratigraphic contexts and in turn discussing the potential major controlling factors in each example in both cases trypanites isp and gastrochaenolites isp are described interpreted as belonging to a trypanites ichnofacies the two cases are developed in different environmental conditions one in non depositional offshore conditions at the top of a parasequence i e transgressive surface and the other in offshore erosional settings with the omission surface located in an intra parasequence position with no obvious sequence stratigraphic connotation these marked differences in the palaeonvironmental conditions non depositional vs erosive and sequence stratigraphic context inter vs intra parasequence occurrence interpreted for these example allowed us to propose different controlling factors related to the generation of the hardgrounds despite these differences namely long periods of non deposition and low energy conditions vs shorter time and high energy erosive conditions in both cases a trypanites ichnofacies is developed representing an important aspect to be considered in the characterization of the basin evolution based on omission surfaces

paleoceanographic model of neogene phosphorite deposition u s atlantic continental margin the neogene stratigraphic section of the southeastern u s continental shelf coastal plain system is characterized by i a series of major regional phosphogenic episodes ii a strong spatial relationship between the structural or topographic framework and phosphate deposition and iii distinct cyclical and regional patterns of deposition of the terrigenous carbonate and phosphate lithofacies the complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea level fluctuations associated changes in climate and the dynamics of the gulf stream in response to the bathymetric configurations of the continental margin during the past 20 million years

tephrostratigraphy chronology and climatic events of the mediterranean basin during the holocene an overview the identification and characterisation of high frequency climatic changes during the holocene requires natural archives with precise and accurate chronological control which is usually difficult to achieve using only 14c chronologies the presence of time spaced tephra beds in quaternary mediterranean successions represents an additional independent tool for dating and correlating different sedimentary archives these tephra layers are potentially useful for resolving long standing issues in paleoclimatology and can help towards correlating terrestrial and marine paleoclimate archives known major tephras of regional extent derive from central and southern italy the hellenic arc and from anatolia a striking feature of major holocene tephra deposition events in the mediterranean is that they are clustered rather than randomly distributed in time several tephra layers occurred at the time of the s1 sapropel formation between c 8 4 and 9 0 ka bp mercato gabellotto fiumebianco e1 cappadocia and ot

green grey and black a comparative study of sierra de las navajas mexico and lipari italy obsidians abstract sierra de las navajas state of hidalgo mexico and lipari aeolian islands italy were among the most important sources for obsidian trade in mesoamerica and in the mediterranean during the stone age in this paper obsidians from these two localities were compared in terms of their aspect chemical composition microcrystallinity and microvesiculation in sierra de las navajas the typical deep green obsidian with a golden hue has been analyzed together with a less common dark grey porphyritic variety lipari obsidian is commonly black but a light grey variety also occurs obsidian of both varieties was analyzed for this paper microvesicularity was investigated through scanning electron microscope sem observation microporosimetry and for sierra de las navajas green obsidian through a preliminary x ray computed microtomographic study crystallinity and micro or nano crystallinity were investigated through x ray powder diffraction and eds energy dispersion system microanalyses finally the chemical composition in terms of major and trace elements including rare earth elements was determined using x ray fluorescence xrf and inductively coupled plasma mass spectrometry icp ms the comparison of samples of different colors suggests that the characteristic green color of sierra de las navajas obsidians could be related to their relatively high iron content and to the occurrence of many elongated and iso oriented vesicles which may also be responsible for the obsidian s golden hue low iron and an absence of vesicles give lipari obsidian its normal black color the light grey obsidian from lipari probably owes its color and imperfect conchoidal fracture to numerous bubbles of less than 1 m in size and to nano crystallinity sierra de las navajas obsidians show a significant chemical variability in terms of trace elements that can be explained by common evolutionary processes in the magma chamber however this variability is also internal to a single volcanic complex and this makes the trace element contents unsuitable to differentiating between the different sub sources of the same area on lipari our data do not allow us to distinguish between the two sub sources of vallone del gabellotto and canneto dentro on the basis of major and trace elements on the whole our study suggests that caution should be used for both lipari and sierra de las navajas when identifying obsidian sub sources on the basis of trace element contents

provenance of obsidian artifacts from the natural protected area laguna del diamante mendoza province argentina and upper maipo valley chile by la icp ms method abstract by means of inductively coupled plasma mass spectrometry associated with laser ablation la icp ms we analyzed several obsidian artifacts from the natural protected area laguna del diamante mendoza argentina and upper maipo valley chile this analytical method almost non destructive is a powerful tool for the determination of trace elements and is very useful in characterizing and determining the provenance of obsidian fragments of archeological interest although care must be taken to avoid or account for heterogeneities within obsidian such as microcrysts in the macro region of study two types of sources can be differentiated on the basis of their primary location high altitude sources emplaced in the andes range 2500 m a s l including laguna del diamante laguna del maule and las cargas sources and low altitude 1500 m a s l extra andean sources situated on the eastern plains cerro huenul and el peceno in addition while the primary location of arroyo paramillos source is currently unknown we consider it as a sub source of laguna del diamante since its wide archaeological distribution has a main core within laguna del diamante area and in the upper maipo river basin considering this pattern the assignation of provenances presented here improves the basis for assessing the use of high andean environments from both sides of the mountain range in addition we will also improve the geochemical discrimination between the two sources arroyo paramillos and las cargas that based on only previous xrf analysis are chemically overlapping leading to an incorrect interpretation of their pattern of archaeological distribution the better characterization of the obsidian sources of the laguna del diamante and neighboring regions allows discussions of mobility exchange and human use of this lithic resource in the highland of central western argentina central chile

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

evidence for cenozoic tectonism in the southwest georgia piedmont paleocene nonmarine sediment in the georgia piedmont has been isolated from correlative coastal plain deposits by high angle reverse faults and subsequent erosion the reverse faults also offset surficial deposits of probable pliocene age the sediments preserved north of pine mountain in the vicinity of warm spring9s georgia consist of 1 a lower sedimentary sequence herein called the republic mine beds composed mainly of massive locally bauxitic kaolinitic clay and well bedded coarse to fine quartz sand and 2 an upper sequence herein called surficial deposits composed predominantly of clayey quartz sand and quartzite gravel the compositional and textural dissimilarities between the two sequences indicate differences in provenance depositional environment and tectonic setting the orientation of the faults and the sense of fault movement near warm springs indicate that this area of the western georgia piedmont is unlike that of the tectonic regimes previously documented in the atlantic and gulf coastal plains the orientation of some structures and the amount and rate of fault deformation are more similar to features in the gulf coastal tectonic province whereas the involvement of basement rocks in fault zones and the compressional style of deformation are comparable to tectonic features described elsewhere in the eastern united states especially in coastal plain sediments along the fall line of the atlantic coastal plain

long term and short term global cenozoic sea level estimates backstripping analysis of three continuously cored well dated boreholes from the new jersey coastal plain ocean drilling program odp leg 150x indicates a long term 10 8 n10 7 yr eustatic fall of 100 m since 55 ma early eocene and suggests short term 0 5n3 m y eustatic falls of less than 70 m eustatic estimates are calculated from residuals between the decompacted unloaded and paleodepth corrected records and tectonic subsidence assuming a cooling lithospheric plate because the residuals are similar among the three sites we interpret them as an approximation of the eustatic signal

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

the sources and transport of sr and nd isotopes in the baltic sea we have determined the concentration and isotopic composition of sr and nd in waters from the baltic sea the baltic sea is an intracontinental stratified brackish water estuarine like system and the rivers emptying into it drain a suite of terranes ranging from proterozoic archean in the north to phanerozoic in the south the sampled brackish waters range in salinity from seawater sw at 35 289 to a minimum of 2 460 at the surface in the innermost part of the gulf of bothnia the sr concentrations show generally conservative behavior indicating a simple two component mixing however small deviations 3 70 from a perfect mixing line reveal that the imprints from rivers with different sr concentrations are preserved in the blending strontium concentrations from a depth profile across the redoxcline in the baltic proper indicate that vertical particle transport alters the sr concentration in the water our estimated concentration of sr in the average freshwater input to the baltic is 0 03 ppm which is only about 0 4 of the sw concentration the sr isotopic data range from e sr sw 0 in seawater to e sr bw sw 7 8 in the least saline baltic water bw sample in the gulf of bothnia the isotopic composition of sr versus 1 sr in the baltic sea follows an almost perfect mixing line which shows that seawater sr is mixed with much more radiogenic components calculated end member values of e sr sw for each sample show that the riverine input into the gulf of bothnia has e sr sw 120 200 and 10 50 e units in the baltic proper these values are in general agreement with direct measurements of river waters in each region however the calculated values in the gulf of bothnia are lower than the measured river water input in this region which indicates the presence of less radiogenic sr presumably originating from the river waters draining the southern part of the basin which are partially transported northward and mixed with sr from the gulf of bothnia rivers the nd concentration in the baltic sea is not conservative varying between 5 and 45 ppt with the highest concentrations in the bottom waters due to vertical particulate transport a plot of e nd o in baltic water yields a good correlation with the calculated freshwater end member e sr sw the data show that it is possible to unravel the different freshwater sources into the baltic and to identify the zones of particulate removal of both non conservative species such as the ree and of quasi conservative species such as sr the use of isotopic tracers in this estuarine environment may provide a much better insight into mixing and element transport it should also be possible to trace lateral movements of freshwater inputs

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

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

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

on the provenance of prehistoric obsidian artifacts in south korea abstract using a series of geochemical data from obsidian samples taken from unmodified rocks and prehistoric sites we investigated the provenance of some obsidian artifacts found in south korea by using la icp ms and shrimp methods we analyzed rare earth elements rees and lead pb isotopic ratios of obsidian samples from the north korean side of the baekdusan mountain nk and artifacts from a neolithic site in gadeokdo southeast coast of south korea bg published accounts on the elemental correlation of previously analyzed samples were re examined in consideration of their geological compatibility it appears that the prehistoric artifacts from the middle to northern part of south korea have a genetic relationship with obsidians from the baekdusan area whereas those of the southern part are related to kyushu japan ree patterns of the bg and the nk samples demonstrate a prominent contrast between them suggesting their different provenances presumably the bg obsidians are related to the volcanic rocks of kyushu given that pb isotopic ratios are indicative of the relative contribution of crust versus mantle component to the volcanic magma they indicate the addition of a crustal component to the volcanic magma for the baekdusan volcanic rocks and the nk obsidians the kyushu volcanics and the bg obsidians have a relative affinity to the mantle component the geochemical approach adopted in the current research may be regarded as an accurate and effective means to discriminate and isolate obsidian sources helpful for provenance and other archaeological study of obsidian artifacts

paleocene faulting within the beaufort group atlantic coastal plain north carolina postrift faulting in the atlantic coastal plain of the eastern united states is a focus of several recent studies particularly because of seismic activity associated with areas such as charleston south carolina earthquake of 1886 understanding the ancient behavior of fault systems can contribute to increased awareness of earthquake potential where traditional mechanisms of earthquake activity are poorly understood in the coastal plain of eastern north carolina the graingers wrench zone a more recently active northeast southwest trending fault system overprints a paleocene east west fault trend and preserves evidence of episodic activity during mesozoic and cenozoic time the western border of the graingers basin is coincident with a northeast southwest oriented feature delineated on aeromagnetic and gravity maps this northeast southwest trending western border fault records movement that initially occurred during the paleozoic was reactivated during the triassic jurassic and the cretaceous cenomanian and maastrichtian and has been active into the holocene paleocene deformation records a shift in motion from the northeast southwest trend to the east west this shift in direction controls the present day distribution of early to late paleocene strata of the beaufort group stratigraphic relationships between the paleocene and underlying cretaceous units suggest that the fault zone propagated to the southwest during the late danian selandian and into the selandian thanetian post paleocene activity of the northeast southwest trending faults exhibited a down to the east displacement pattern and appears to have a minor component of strike slip which may offset the older east west trending structures preservation of topographic features such as a fault line scarp with as much as 13 m of relief triangular facets and extensive ravinement normal to the scarp orientation suggest holocene movement on the faults historical records indicate seismicity in the area during the latter part of the nineteenth century the combined northeast southwest and east west fabric has geometry similar to those of fault zones in georgia and seismically active areas of south carolina the faults that affect the area were probably formed by interaction of the neuse hinge and the roanoke island goldsboro fault which border the graingers basin to the south and north respectively differential movement on these larger structures may be the result of compression caused by changes in direction of motion of the north american plate

geology of continental shelf onslow bay north carolina as revealed by submarine outcrops lithologic and stratigraphic data from rocks dredged from the continental shelf off onslow bay north carolina provide surface control for seismic studies of the southeastern united states continental margin and help to explain the distribution of potentially economic phosphate rich sediments on this shelf outcropping miocene rocks in this area indicate that the region has long been a positive geologic feature and has received relatively little pliocene and pleistocene sedimentation leached molluscan moldic calcareous quartz sandstones of late oligocene to early miocene age belgrade formation and middle to late miocene age pungo river formation crop out in southwestern and northeastern onslow bay respectively these two areas border a band of highly phosphatic su ficial sediments probably derived from unlithified phosphatic units of the pungo river formation lower pleistocene calcarenites that correlate with the waccamaw formation crop out on the sea floor near cape fear which bounds onslow bay on the south a core on frying pan shoals off cape fear after passing through pleistocene coquina calcareous quartz sandstone and oolitic sand penetrated upper pliocene calcarenites of the bear bluff formation and middle miocene phosphatic argillaceous sandstones of the pungo river formation samples from this core hole show that phosphate increases toward the top of the unindurated pungo river formation section indicating that this formation is probably the source of the high phosphate concentrations in the surficial sediments near cape fear wher the bear bluff calcarenites also crop out upper pleistocene units include oolitic limestones adjacent to the outer shelf calcareous quartz sandstones around cape fear and molluscan coquinas near cape lookout which bounds onslow bay on the north the outer shelf is blanketed by submarine lithified algal limestones and sandstones of holocene age

surficial sediments of the great australian bight facies dynamics and oceanography on a vast cool water carbonate shelf abstract the great australian bight gab the largest sector of the southern australia continental margin is a site of cool water carbonate sedimentation throughout ranging from locally warm temperate inboard to cool temperate outboard surficial sediments are a mixture of calcareous pleistocene skeletal and lithic intraclasts relict grains and holocene biofragments with minor amounts of quartz inboard the inner shelf is an area of abundant macrophytes and seagrasses active carbonate sediment production and accumulation and little relict sediment the huge middle portion is a shaved shelf with active sediment winnowing and mostly relict sediment the outer shelf and upper slope is a variably productive sediment factory characterized by prolific calcareous epibenthic growth on hard substrate subaqueous islands shedding particles into surrounding sands and muds patterns of holocene sedimentation are linked to modern oceanographic parameters in this high energy setting characterized by overall downwelling prolific rhodoliths occur on the nw inner shelf where shallow summer waters are the warmest in the gab these warm saline nutrient depleted waters then drift eastward across the shelf suppressing heterozoan carbonate production on the central and eastern mid shelf this arrested production in the eastern gab is countered locally by summer coastal upwelling along western eyre peninsula with bryozoan rich sediment extending well inboard onto the mid shelf the outer shelf and upper slope is an area of prolific bryozoan growth likely linked to upwelling except in the central gab a region of year round downwelling where the area is one of off shelf fine sediment transport and carbonate mud deposition these patterns in the central gab at least are present in the underlying holocene and pleistocene suggesting that the general modern oceanographic dynamics and resultant carbonate sedimentation have persisted throughout the quaternary

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

an introduction to the application of x ray microtomography to the three dimensional study of igneous rocks imaging rocks in three dimensions through x ray microtomography enables routine visualization of structures in samples which can be spatially resolved down to the sub micron scale although x ray tomography has been applied in biomedical research and clinical settings for decades it has only recently been applied to studies of rocks and few geoscientists realize its value and potential this contribution provides an introduction to the principles and techniques of x ray microtomography to the study of igneous rock textures as well as reviewing the current state of the art we hope that this short review will encourage more geoscientists to apply x ray microtomography in their research and that this will lead to new insights into the processes that occur in magmatic as well as other geological systems

a novel approach in the mineralogy of carpathian mahogany obsidian using complementary methods abstract carpathian obsidians can have various macroscopic features they are typically black or grey and their transparency ranges from clear to opaque the tolcsva source very rarely can yield brown or red mahogany type obsidian archaeological as well as geological pieces of mahogany obsidian were previously identified and characterised using prompt gamma activation analysis pgaa in 2007 the exact location of the red variant s outcrop was identified on the szokolya hill tolcsva the aim of this study was to better understand the possible reasons for the colouring of red obsidian a novel approach was applied using multiple methods for the analysis of the samples for comparison other carpathian type namely black obsidian from tolcsva and red obsidian from bogazkoy anatolia were also studied besides the pgaa measurements of the bulk elemental composition mossbauer spectroscopy and transmission electron microscopy tem were used to study the samples in order to identify the presence of ferrous or ferric iron with the help of small angle neutron scattering sans the bulk nanostructures of the samples have been investigated and their surface or volume fractal dimensions have been determined black obsidians showed isotropy while mahogany samples displayed a considerable anisotropy in the bulk pore orientation according to our results a large amount of the iron is dominantly located in different phases in the case of mahogany and black obsidians based on the summarised results the differences between the red and black variants can be also explained by the different oxidation states of the fe ions which may explain the colour difference

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

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics