late magmatic mineral assemblages with siderite and zirconian pyroxene and amphibole in the anorogenic mt gibraltar microsyenite new south wales australia and their petrological implications abstract the mt gibraltar intrusion near mittagong and bowral in new south wales australia lat 34 27 54 s long 150 25 44 is a small intrusive body of hypersolvus microsyenite emplaced into the triassic hawkesbury sandstone of the sydney basin in jurassic time possibly related to extensional faulting the rock itself consists of intermediate alkali feldspar with minor titanomagnetite and interstitial pyroxene ranging from nearly pure hedenbergite to hd 34 aeg 65 in composition it is crosscut by an irregular system of late magmatic veins consisting of homogeneous alkali feldspar ab 50 or 50 clinopyroxene evolving from sodic hedenbergite to zirconium rich aegirine arfvedsonite and siderite during postmagmatic evolution of the veins microcrystalline or amorphous silica precipitated together with calcite filling miarolitic cavities the late magmatic mineral assemblage of the veins indicate crystallisation at assumed 700 bar pressure at t 650 670 c log f o2 22 this corresponds to conditions very close to the magnetite wustite curve zirconium bearing pyroxene has a restricted stability field in the system sio 2 zro 2 feo feo 1 5 nao 0 5 ho 0 5 at moderately elevated peralkalinity and intermediate silica activity under such conditions pyroxene and amphibole will act as effective sinks for zr preventing crystallisation of magmatic zircon or more exotic zr silicates the mt gibraltar microsyenite is therefore a rare example of an igneous rock in which zirconium is camouflaged in pyroxene and amphibole rather than forming its own minerals

synchronizing terrestrial and marine records of environmental change across the eocene oligocene transition records of terrestrial environmental change indicate that continental cooling and or aridification may have predated the greenhouse icehouse climate shift at the eocene oligocene transition eot by ca 600 kyr in north america marine terrestrial environmental change asynchronicity is inferred from a direct comparison between the astronomically tuned marine eot record and published 40ar 39ar geochronology of volcanic tuffs from the white river group wrg sampled at flagstaff rim wyoming and toadstool geologic park nebraska which are type sections for the chadronian and orellan north american land mammal ages we present a new age model for the wrg underpinned by high precision 206pb 238u zircon dates from 15 volcanic tuffs including six tuffs previously dated using the 40ar 39ar technique weighted mean zircon 206pb 238u dates from this study are up to 1 0 myr younger than published anorthoclase and biotite 40ar 39ar data calibrated relative to fish canyon sanidine at 28 201 ma giving consideration to the complexities strengths and limitations associated with both the 40ar 39ar and 206pb 238u datasets our interpretation is that the recalculated 40ar 39ar dates are anomalously old and the 206pb 238u zircon dates more accurately constrain deposition 206pb 238u calibrated age depth models were developed in order to facilitate a robust intercomparison between marine and terrestrial archives of environmental change and indicate that i early orellan terrestrial cooling recorded at toadstool geologic park was synchronous with the onset of early oligocene antarctic glaciation and ii the last appearance datums of key chadronian mammal taxa are diachronous by ca 0 7 myr between central wyoming and nw nebraska

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

the late crystallization stages of low ti low fe tholeiitic magmas insights from evolved antarctic and tasmanian rocks abstract examples of the latest stages of crystallization in evolved tholeiitic rocks can be found in the low ti low p ferrar magmatic province in antarctica e g thern promontory and archambault ridge and tasmania e g the red hill intrusion and mount wellington sill evolved rocks of this magmatic province include a rocks of basaltic andesite composition containing plagioclase augite pigeonite and interstitial fe ti oxides b rocks of andesitic composition with plagioclase as a liquidus phase a single fe rich subcalcic clinopyroxene and fe ti oxides and c rocks of dacitic composition displaying granophyric texture containing sodic plagioclase alkali feldspar ferrohedenbergite fayalite fe ti oxides quartz and accessory phases the latest crystallization stages are thus characterized by the striking chemical convergence of subcalcic fe augite and fe pigeonite followed by more evolved rocks that preserve quartz alkali feldspar cotectic granophyric relationships lack subcalcic clinopyroxene and contain coexisting olivine and calcium rich clinopyroxene these features are consistent with crystallization at or below the quartz fayalite magnetite oxygen buffer at temperatures close to 800 c the trace element geochemistry of coexisting pyroxenes feldspar and fe ti oxides are entirely consistent with magmatic evolution caused by fractional crystallization of the observed phases similarities and differences with other silicic volcanic rocks elsewhere are also described there is no evidence for liquid immiscibility

global cooling accelerated by early late eocene impacts at ocean drilling program site 689 maud rise southern ocean 18o records of fine fraction bulk carbonate and benthic foraminifers indicate that accelerated climate cooling took place following at least two closely spaced early late eocene extraterrestrial impact events a simultaneous surface water productivity increase as interpreted from 13c data is explained by enhanced water column mixing due to increased latitudinal temperature gradients these isotope data appear to be in concert with organic walled dinoflagellate cyst records across the same microkrystite bearing impact ejecta layer in the mid latitude massignano section central italy in particular the strong abundance increase of thalassiphora pelagica is interpreted to indicate cooling or increased productivity at massignano because impact induced cooling processes are active on time scales of a few years at most the estimated 100 k y duration of the cooling event appears to be too long to be explained by impact scenarios alone this implies that a feedback mechanism such as a global albedo increase due to extended snow and ice cover may have sustained impact induced cooling for a longer time after the impacts

the burgess shale and associated cambrian formations west of the fossil gully fault zone on mount stephen british columbia west of the fossil gully fault zone on mount stephen the three lowest members only of the burgess shale formation are preserved the kicking horse shale the yoho river limestone and the campsite cliff shale the formation rests unconformably upon the takakkaw tongue formation whose dark basinal limestones conformably overlie paler shelf like limestones of the mount whyte formation mapping has resolved a long standing problem and shown that the stratigraphical position of the famous mount stephen trilobite beds lies within the campsite cliff shale it has also revealed some of the complexities of the fossil gully fault zone among which different periods and directions of component fault movements are indicated faunal evidence shows that the plagiura kochaspis to albertella and albertella to glossopleura zonal boundaries lie within the takakkaw tongue sequence within the burgess shale three distinct soft bodied communities occur at different stratigraphical levels on this mountain slope the oldest

eocene oligocene global climate and sea level changes st stephens quarry alabama we integrate upper eocene lower oligocene lithostratigraphic magnetostratigraphic biostratigraphic stable isotopic benthic foraminiferal faunal downhole log and sequence stratigraphic studies from the alabama st stephens quarry ssq core hole linking global ice volume sea level and temperature changes through the greenhouse to icehouse transition of the cenozoic we show that the ssq succession is dissected by hiatuses associated with sequence boundaries three previously reported sequence boundaries are well dated here north twistwood creek cocoa 35 4 35 9 ma mint spring red bluff 33 0 ma and bucatunna chickasawhay the mid oligocene fall ca 30 2 ma in addition we document three previously undetected or controversial sequences midpachuta 33 9 35 0 ma shubuta bumpnose lowermost oligocene ca 33 6 ma and byram glendon 30 5 31 7 ma an 0 9 18 o increase in the ssq core hole is correlated to the global earliest oligocene oi1 event using magnetobiostratigraphy this increase is associated with the shubutabumpnose contact an erosional surface and a biofacies shift in the core hole providing a fi rst order correlation between ice growth and a sequence boundary that indicates a sea level fall the 18 o increase is associated with a eustatic fall of 55 m indicating that 0 4 of the increase at oi1 time was due to temperature maximum 18 o values of oi1 occur above the sequence boundary requiring that deposition resumed during the lowest eustatic lowstand a precursor 18 o increase of 0 5 33 8 ma mid chron c13r at ssq correlates with a 0 5 increase in the deep pacifi c ocean the lack of evidence for a sea level change with the precursor suggests that this was primarily a cooling event not an ice volume event eocene oligocene shelf water temperatures of 17 19 c at ssq are similar to modern values for 100 m water depth in this region our study establishes the relationships among ice volume 18 o and sequences a latest eocene cooling event was followed by an earliest oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall

reducing disparity in radio isotopic and astrochronology based time scales of the late eocene and oligocene a significant discrepancy of up to 0 6 myr exists between radio isotopically calibrated and astronomically tuned time scales of the late eocene oligocene we explore the possible causes of this discrepancy through the acquisition of high precision 206pb 238u dating of zircons from 11 volcanic ash beds from the umbria marche sedimentary succession which hosts the global stratotype section and point for the base of the oligocene our results indicate that the four 40ar 39ar dates from the umbria marche succession which underpin the late eocene oligocene portion of the paleogene geomagnetic polarity time scale in the 2012 edition of the geological time scale are anomalously old by up to 0 5 myr conversely when integrated with the established magnetic polarity record of the umbria marche succession 206pb 238u zircon data from this study result in oligocene magnetic reversal ages that are generally equivalent to those obtained through the tuning of ocean drilling program odp site 1218 equatorial pacific furthermore our results indicate that the late eocene tuning of odp site 1218 and international ocean discovery program iodp sites u1333 1334 equatorial pacific to the 405 kyr eccentricity signal is accurate at least back to 36 ma propagating the full uncertainty of our radio isotopic data set and where appropriate taking into account locally derived astronomical time scales we arrive at an age of 34 09 0 08 ma for the eocene oligocene boundary and 28 11 0 17 ma for the base of the chattian

accuracy and precision of the late eocene early oligocene geomagnetic polarity time scale an accurate and precise geomagnetic polarity time scale is crucial to the development of a chronologic framework in which to test paleoclimatic and paleoenvironmental interpretations of marine and terrestrial records of the eocene oligocene transition eot the magnetic polarity patterns of relatively continuous marine and terrestrial records of the eot have been dated using both radioisotopic techniques and astronomical tuning both of which can achieve a precision approaching 30 k y for much of the paleogene however the age of magnetic reversals between chrons c12n and c16n 2n has proved difficult to calibrate with discrepancies of up to 250 k y between radio isotopically dated and astronomically tuned marine successions rising to 600 k y for comparisons with the 206pb 238u dated terrestrial record of the white river group in north america in this study we reevaluate the magnetic polarity pattern of the flagstaff rim and toadstool geologic park records of the white river group c12n c16n 2n our interpretation of the flagstaff rim polarity record differs significantly from earlier studies identifying a previously unreported normal polarity zone correlated to c15n which eliminates discrepancies between the wrg and the 206pb 238 dated marine record of the rupelian global stratotype section and point in the italian umbria marche basin however residual discrepancies persist between u pb dated and astronomically tuned records of the eot even when stratigraphic and systematic uncertainties associated with each locality and dating method are taken into account which suggests that the uncertainties associated with astronomically tuned records of the eot may have been underestimated

cyclostratigraphy and astronomical tuning during the oligocene in the jizhong depression bohai bay basin northeastern china abstract the dongying formation ed and the first member of the shahejie formation es1 in the central raoyang sag cover about 1705 m long sedimentary series of terrestrial lacustrine infill we employed the gamma ray gr log data as a paleoclimatic and paleoenvironmental proxy to conduct the high resolution cyclostratigraphy research in well w33 and w62 prominent sedimentary cycles in decameters and meters were revealed by multi taper mtm power spectra evolutionary fast flourier transformation fft and correlation coefficient analyses in the es1 and ed intervals the 405 kyr long eccentricity 125 kyr and 100 kyr short eccentricity 40 kyr obliquity and 23 kyr precession can be recognized with a wavelength ratio of approximately 20 5 2 1 respectively by tuning the 405 kyr filter output in well w33 to the orbital target curve of la2010d astronomical solution we established an astronomical time scale ats that provided absolute age controls during the oligocene and shed light on the event correlation among isolated depressions in the bohai bay basin sediment accumulation rates sars were derived from the extracted 405 kyr long eccentricity and were tested with an average of 17 cm kyr age boundaries of ng ed1 ed1 ed2 ed2 ed3 ed3 es1 and es1 es2 are 23 03 ma 24 34 ma 25 53 ma 29 05 ma and 33 10 ma respectively based on the ats and sars we discussed the depositional evolution within age boundaries cause of high sars and origin of formation overpressure after the largest lake transgression shallow water deltas and fluvial plains transitionally dominate the central raoyang sag with shallowing water depth thin interlayers of mudstones and sandstones originate from shallow water deltaic systems with low sand to mud ratios under high sars enhanced by mountain uplift and low sand to mud ratios formation overpressure results mainly from high porosities in under compacted mudstone intervals

chemical evolution of granitic rocks in the east antarctic shield with particular reference to post orogenic granites granitic intrusives of the east antarctic shield range in age from early archaean 3930 ma to cambrian and show systematic variations in chemical and isotopic characteristics many archaean orthogneisses are of tonalitic to granodioritic composition and represent new continental crust derived from the mantle by a two stage process involving hydrous melting of mafic crustal rocks syn orogenic granitic rocks are generally of more potassic composition and were derived by intracrustal melting under lower ph2o conditions they are mostly of more typical i type derived from igneous source materials but there is an increasing proportion of s types derived by melting of sedimentary materials with time late and post orogenic intrusives are mostly granites s s with a type anorogenic affinities and were derived by melting of relatively anhydrous granulite facies lower crustal rocks they are characterised by marked enrichment of y zr nb la and ce relative to p ti and sr and commonly have high f femg znfe and gaal plagioclase apatite and ti minerals were probably residual phases during partial melting as well as being involved in fractional crystallisation whereas other minor phases such as zircon were apparently relatively soluble in the high temperature melts emplacement of a type granites at about 500 ma may have been associated with internal fracturing of gondwanaland before eventual break up

magnetostratigraphy of eocene oligocene boundary sections in italy no evidence for short subchrons within chrons 12r and 13r abstract the marine magnetic polarity record shows many small scale anomalies that could be due to short normal polarity subchrons within chrons 12r and 13r new examination of published magnetostratigraphic results from a section near gubbio shows that suspected short chrons in this section are probably not real the eocene oligocene boundary in the stratotype section at massignano lies just above a tentatively identified normal magnetozone that might correlate with a possible short normal subchron within chron 13r in a new investigation of the weathered marlstones in this section acquisition and thermal demagnetization of irm reveal a magnetic mineralogy dominated by magnetite with minor amounts of maghemite and hematite vector analysis of the natural remanent magnetization discloses a complex structure in some samples at least two and up to four components were isolated the magnetostratigraphy based on a magnetite component correlates well to the main features of the chron 13n 16n polarity sequence no short polarity subchrons are found although the resolution is inadequate to exclude the possibility that they exist in particular we did not find a short normal polarity magnetozone previously located close to the eocene oligocene boundary the results of this study favour the interpretation that low amplitude magnetic anomalies represent geomagnetic intensity fluctuations rather than unresolved short polarity intervals

the derwent hunter submarine volcano the product of a long defunct subduction zone abstract the derwent hunter volcano 31 s 156 e is one of a 1400 km long chain of oligocene miocene undersea volcanoes that transect the tasman abyssal plain it developed some 15 16 ma ago and the rocks it contains form an abbreviated differentiation sequence that range in composition from olivine tholeiite to either mugearite or basaltic andesite these rocks generally contain normative hypersthene but do not contain significant quantities of either normative quartz or normative nepheline and their trace element abundances generally lie in the area of overlap between the subalkali and alkali rock series the more primitive rocks contain spinels 36 cr 2 o 3 olivines fo 81 83 plagioclases an 63 70 and less commonly augite set in a glassy mesostasis some specimens contain xenocrysts of anorthitic plagioclase an 85 94 and calcic salite en 36 fs 12 wo 52 the volcano is part of the tasmantid volcanic chain and the latter is one of a number of parallel volcanic chains of oligocene miocene age that arise in eastern australia and the tasman sea both the onshore and offshore volcanoes contain rocks that belong to a transitional petrographic series that comprises tholeiitic transalkalic and alkalic members with one exception the ages of the volcanoes across the various chains are similar for the same latitudes the exception is the easternmost chain i e lord howe where the ages of the individual volcanoes lag behind their counterparts at similar latitudes when considering the origin of these parallel volcanic chains the fundamental problems are 1 a what processes occurred within the asthenosphere to create a volcanic focus that extends for 1000 km in an east west direction and has been active for circa 40 ma 2 b why are the ages of the lord howe seamounts not synchronous with the other volcanic chains 3 c what processes and materials are required to generate the geochemically diverse and complex magmas needed to construct these intraplate volcanoes it is proposed that these magmas evolved from a line of diapirs within the asphenosphere the diapirs began forming at a depth of 650 km as the result of the heating and partial melting of pressure transformed materials that had originally been subducted after traversing the asthenosphere individual diapirs impinged on the base of the lithosphere where they reactivated pre existing fractures and produced extensional rock failure this resulted in the extraction of batches of magma from the diapirs and the composition of each batch was substantially controlled by the degree of partial melting and the ambient pressure at the source of magma extraction intratelluric fractional crystallization limited assimilation of crustal materials high level magmatic differentiation and the mixing of different batches of magma all assisted in the evolution of the more differentiated magmas the diapirs developed along a trend parallel to the long axis of a long defunct subduction zone it is proposed that this subduction zone was linear along most of its length but in the east it terminated in a section that was displaced northwards by a transform fault and the materials subducted by this displaced segment triggered the string of diapirs that eventually produced the lord howe seamount chain

u th he dating of volcanic phenocrysts with high u th inclusions jemez volcanic field new mexico we measured u th he ages of fayalite and hedenbergite phenocrysts with britholite and chevkinite inclusions from the 1 6 ma otowi lower member of the bandelier tuff jemez volcanic field u and th the major parent nuclides of radiogenic 4 he are concentrated in britholite and chevkinite inclusions and are essentially absent from the host grains we analyzed 36 fayalite 21 non abraded 15 abraded and 13 hedenbergite 7 non abraded 6 abraded phenocrysts and applied alpha ejection corrections assuming uniform intracrystalline distributions of inclusions and parent nuclides in the phenocrysts a subset of phenocrysts was subjected to abrasion to remove the alpha ejection affected regions the alpha ejection correction factors ft of the non abraded samples range between 0 90 and 0 96 whereas those of the abraded samples are virtually unity the fayalite and hedenbergite crystals yield mean ages of 1 60f0 10 ma s d and 1 69f0 13 ma respectively the overall mean age of 1 62f0 11 ma s d is indistinguishable from previously published 40 ar 39 ar ages of 1 61f0 01 ma 1j our results suggest that other inclusion

delayed climate cooling in the late eocene caused by multiple impacts high resolution geochemical studies at massignano italy abstract high resolution studies 13c 18o and elemental abundances were done in rocks at and below the gssp for the eocene oligocene e o boundary at massignano italy in addition to an earlier known ir anomaly at 5 61 m which is possibly linked to the popigai impact event we confirm the presence of two additional ir anomalies in the intervals from 6 00 to 6 40 m and from 10 00 to 10 50 m with maximum values of 259 32 ppt at 6 17 m and 149 24 ppt at 10 28 m respectively the lower ir anomaly might be derived from the chesapeake bay impact event whereas for the other one no impact event is known similar 13c and 18o trends related to the two ir anomalies indicate that the ir anomaly at 10 28 m might be also derived from an impact into a continental shelf similar to the chesapeake bay impact event 18o values decrease in the high ir layers to 1 16 and 1 17 respectively which together with the negative shifts in 13c in the ir rich levels indicate a warm pulse superimposed on a general late eocene cooling trend that is characterized by 18o values ranging between 0 6 and 0 4 the release of methane hydrate after an impact in a continental shelf or seafloor or impacts of 12c rich comets during a 2 2 million year long comet shower respectively could produce these more negative carbon and oxygen excursions compared to the continuously decreasing trend over the whole late eocene massignano section

middle eocene to early oligocene magnetostratigraphy of odp hole 711a leg 115 western equatorial indian ocean oceandrillingprogram odp site711 locatedinthewesternequatorialindianocean near the seychelles archipelago on madingley rise is an important site for studying middle eocene to early oligocene climatic evolution this site is ideal for studying the impact of neo tethyan gateway closure on indian ocean currents and circulation to further understand global climatechangesthroughthe greenhousetoicehouse transition middleeocene to lower oligocene strata recovered within hole 711a cores 711a 14x to 21x primarily consist of clay bearing nannofossil oozes chalks with layers rich in radiolarians here we report a high resolution mag netostratigraphic recordanda new integratedagemodel forthemiddleeocene to lower oligocene sectionof hole 711a correlationof thepolaritypattern tothe geomagnetic polarity timescale pro vides a record from chron c19r middle eocene to c12r early oligocene our results extend the existing polarity record down into the middle eocene and confirm published results from the lower oligocene section of the hole overall these new results from hole 711a have important impli cations foridentifyinganddating global climatechange events and for reconstructing calcitecom pensation depth history at this site supplementary material magnetostratigraphicdata usedfor construction of age modelsforhole

geochemistry and rb sr geochronology of associated proterozoic peralkaline and subalkaline anorogenic granites from labrador anorogenic granites of middle to late proterozoic age in the davis inlet flowers bay area of labrador are subdivided on the basis of petrology and geochemistry into three coeval suites two of these are high temperature anhydrous hypersolvus granites a peralkaline aegirine sodic calcic to sodic amphibole bearing suite and a non alkaline fayalite pyroxene bearing suite the third is a group of non alkaline subsolvus hornblende biotite bearing granites associated with the hypersolvus peralkaline suite is a group of genetically related syenites and quartz syenites the granites cut ca 3 000 ma old archaean gneisses as well as elsonian layered basic intrusions of the nain complex one of these a crudely layered mass which ranges in composition from gabbro to diorite and monzonite appears to be related to the syenites the peralkaline granites and some of the syenites are extremely enriched in the high field strength elements such as y zr nd as well as rb ga and zn and have low abundances of ba sr and most of the transition elements in contrast the non alkaline hypersolvus and subsolvus granites do not show the same degree of enrichment concentration of the highly charged cations in the peralkaline suite is believed to be the result of halogen rich fluid activity during fractionation of the magma the sodic evolution trend in the peralkaline suite is reflected mineralogically by the development of aegirine and aegirine hedenbergite solid solutions and by a spectacular amphibole compositional range from katophorite through winchite richterite riebeckite to arfvedsonite and ferro eckermannite accessory phases which are ubiquitous in these rocks include aenigmatite astrophyllite fluorite monazite and zircon the non alkaline hypersolvus granites typically contain iron rich phases such as fayalite eulite ferrosilite hedenbergite and annite rich biotite in the subsolvus granites amphiboles range in composition from edenite through common hornblende to actinolite and also coexist with annite rich biotite

eocene oligocene paleoceanographic changes in the stratotype section massignano italy clues from rock magnetism and stable isotopes 1 we have conducted high resolution paleomagnetic and rock magnetic studies in addition to stable isotope analyses of the massignano sedimentary section which is the global stratotype section and point gssp for the eocene oligocene boundary our research builds upon the many past studies of the massignano section in seeking to understand the timing and nature of the paleoenvironmental variations that occurred during the transition for the earth s climate system from greenhouse to icehouse the new paleomagnetic results provide a refined magnetostratigraphy of the section and new age for the eocene oligocene boundary at 33 7 ma abrupt and large alternations in magnetic concentration composition and grain sizes that occur in the high resolution rock magnetic record are interpreted to be the result of rapid bimodal shifts in deep sea circulation that affect sediment sources or transport we speculate that currents flowing through the gateway between the atlantic and indo pacific oceans may have turned on and off as the gateway was progressively closing resulting in the deposition of two different assemblages of magnetic minerals at massignano finally stable isotope 18o and 13c data collected on ostracod valves also suggest significant changes in sea bottom circulation in the neo tethys ocean at and about 2 m y before the eocene oligocene boundary

geochemistry of intrusive rocks associated with molybdenite mineralization kigom complex northern nigeria abstract the kigom igneous complex of northern nigeria is a small intrusive complex made up of peralkaline arfvedsonite granite riebeckite biotite granite and riebeckite aegirine granite the granites show coherent major element chemistry typical of that of the nigerian younger granites and are enriched in rb li zr nb th y f and ree and depleted in ba and sr compared to the world average for rocks of similar composition the riebeckite aegirine granite exhibits a two to three fold increase in the concentration of zr nb li f th zn and ree over comagmatic granites concentrations of the highly charged cations in these granites are believed to be the result of halogen alkali rich fluid activity during the fractionation of the magma corresponding trace element increases in the granites in areas of alkali metasomatism albitization support this argument and reflect the partial confinement of this alkali volatile phase within the high level magma chambers it is important to recognize that the chemical signatures of this liquid state fractionation process may be explanatory mechanisms in the formation of some kinds of lithophile ore deposits the degree of peralkalinity maintained miscibility in the residual fluid between silicate and aqueous phase to low temperatures so that mineralizing components continuously accumulated together the interaction between this phase and early formed minerals led to mo mineralization the well known classification of granites into sedimentary protolith s type igneous protolith i type and a type indicates that the granites studied here have typical a type features an origin by partial melting of lower crustal material probably granulite facies under a high flux of mantle derived volatiles is suggested for these rocks as a result of mixing of crustal and mantle derived fluids a syenitic magma was produced which then experienced selective contamination as a result of further reaction melting during fractionation and ultimately produced a peralkaline differentiate

middle eocene late oligocene climate variability calcareous nannofossil response at kerguelen plateau site 748 a major deterioration in global climate occurred through the eocene oligocene time interval characterized by long term cooling in both terrestrial and marine environments during this long term cooling trend however recent studies have documented several short lived warming and cooling phases in order to further investigate high latitude climate during these events we developed a high resolution calcareous nannofossil record from odp site 748 hole b for the interval spanning the late middle eocene to the late oligocene 42 to 26 ma the primary goals of this study were to construct a detailed biostratigraphic record and to use nannofossil assemblage variations to interpret short term changes in surface water temperature and nutrient conditions the principal nannofossil assemblage variations are identified using a temperate warm water taxa index twwt from which three warming and five cooling events are identified within the middle eocene to the earliest oligocene interval among these climatic trends the cooling event at 39 ma cooling event b is recorded here for the first time variations in fine fraction 18o values at site 748 are associated with changes in the twwt index supporting the idea that significant short term variability in surface water conditions occurred in the kerguelen plateau area during the middle and late eocene furthermore odp site 748 calcareous nannofossil paleoecology confirms the utility of these microfossils for biostratigraphic paleoclimatic and paleoceanographic reconstructions at southern ocean sites during the paleogene

integrated magnetobiostratigraphy of the middle eocene lower oligocene interval from the monte cagnero section central italy the monte cagnero sedimentary section which crops out in the northeastern apennines near urbania in the umbria marche basin italy contains well exposed strata spanning the middle eocene to lower oligocene interval we use an integrated magnetobiostratigraphic approach to generate a high resolution age model for the monte cagnero section with the goal of obtaining a reliable chronostratigraphic framework for studying eocene oligocene palaeoceanographic changes during the switch from greenhouse to icehouse conditions the studied sediments consist of alternating reddish and greenish limestones and marlstones a new integrated age model for the section is based on high resolution palaeomagnetic analyses combined with detailed planktonic foraminiferal and calcareous nannofossil biostratigraphic results rock magnetic measurements show that the magnetic mineralogy is dominated by a mixture of highand low coercivity minerals probably representing a combination of hematite and magnetite a robust magnetostratigraphic signal together with the identification of key planktonic foraminiferal and nannofossil biostratigraphic events allows construction of a detailed age model for the section based on these results we infer that the section spans a continuous interval within magnetochron resolution from the middle eocene to lower oligocene c 41 27 ma chrons c18r c12r the monte cagnero section therefore represents a sequence that is suitable for studying the impact of the neo tethyan gateway closure on subtropical eocene circulation and determining the nature and timing of palaeoceanographic changes in the tethys through the late middle eocene to early oligocene interval the cenozoic era which represents the last 65 million years myr from the end of the cretaceous to the present is a transformational time in the evolution of earth s palaeoclimate benthic foraminiferal oxygen isotope do records from all major ocean basins indicate a cooling trend over the past 50 myr since the early eocene climatic optimum c 53 51 ma e g zachos et al 2001 2008 the middle eocene to early oligocene was a key interval for earth s transition from warmer greenhouse to cooler icehouse conditions this interval is characterized by the expansion of antarctic large ice sheets to 50 the size of the present day volume e g zachos et al 1996 lear et al 2000 coxall et al 2005 katz et al 2008 coxall wilson 2011 culminating in the eocene oligocene from jovane l herrero bervera e hinnov l a housen b a eds 2013 magnetic methods and the timing of geological processes geological society london special publications 373 79 95 first published online march 25 2013 http dx doi org 10 1144 sp373 13 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics 2013 at universita degli studi di urbino carlo bo on july 29 http sp lyellcollection org downloaded from

a restudy of utahcaris orion euarthropoda from the spence shale middle cambrian utah usa utahcaris orion conway morris robison 1988 from the lower middle cambrian series 3 stage 5 spence shale member situated in utah usa is redescribed based on a restudy of the original material newly recognized features including ventral lateral eyes trunk appendages and a bulbous cephalic shield with subtriangular extension reinforce similarities with sanctacaris uncata from the middle cambrian burgess shale both are assigned to the new family sanctacarididae sanctacaridids represent the oldest chelicerates their ecology and that of their nearest non chelicerate relatives indicate that chelicerata were plesiomorphically predatory

the mineralogy and chemistry of the anorogenic tertiary silicic volcanics of s e queensland and n e new south wales australia the late oligocene early miocene volcanism of this region is chemically strongly bimodal the mafic lavas volumetrically dominant comprise basalts hawaiites and tholeiitic andesites while the silicic eruptives are mainly comendites potassic trachytes and potassic high silica rhyolites the comendites and rhyolites have distinctive trace element abundance patterns notably the extreme depletions of sr ba mg mn p cr v and eu and the variable enrichment of such elements as rb zr pb nb zn u and th the trachytes exhibit these characteristics to lesser degrees the comendites are distinguished from the rhyolites by their overall relative enrichment of the more highly charged cations e g lree nb y and especially zr and zn the phenocryst mineralogy of the trachytes and rhyolites comprises various combinations of the following phases sodic plagioclase albite andesine calcic anorthoclase sanidine quartz ferroaugite ferrohedenbergite ferrohypersthene fayalitic olivine ilmenite titanomagnetite and rarely biotite near annite and fe hastingsitic amphibole accessories include apatite zircon chevkinite ferrohedenbergite bearing rhyolites only and allanite amphibole and botite rhyolites only the comendites generally contain ca poor anorthoclase sanidine quartz fluorarfvedsonite aegirine and aegirine augite zr bearing aenigmatite and ilmenite coexisting fe ti oxides are absent in the comendites and relatively uncommon in the rhyolites and trachytes where present they indicate equilibration temperatures of 885 980 c and fo2 between qfm and wm buffers the magmas are thus interpreted to have been strongly water undersaturated during phenocryst equilibration which is also consistent with the general paucity of pyroclastics the rarity of hydrous mineral phases and the extreme fe enriched ferromagnesian phenocryst compositions the chemical and mineralogical data are interpreted to indicate the operation of extreme fractionation processes controlling the development of the silicic magmas and the comendites trachytes and certain trachyte rhyolite series are considered to have evolved from a mafic parentage the available oxygen sr and pb isotopic data however point to some modification of the magnas through crustal equilibration processes the remaining high silica rhyolites are considered to most likely represent crustal partial melts but are again modified by extensive fractionation

the middle cambrian burgess shale and its relationship to the stephen formation in the southern canadian rocky mountains the burgess shale has been an anomalous geologic unit ever since walcott named it in 1911 as the geographic equivalent of the ogygopsis shale in the middle cambrian stephen formation of southeastern british columbia but it has never been recognized outside of its type locality so its status relative to the stephen formation remained uncertain the geologic setting of the burgess shale was determined by aitken and fritz in 1968 when they recognized the cathedral escarpment and divided the stephen formation into a thin platformal succession on top of the escarpment and a thick basinal succession which included walcott s burgess shale in front fieldwork by royal ontario museum parties between 1982 and 1997 has now demonstrated that the thin and thick stephen successions lie within different facies belts and should be regarded as separate formations the stephen shale formation is part of the middle carbonate belt succession whereas the name burgess shale formation is applied to the thick basinal

40ar 39ar step heating ages of north american tektites and of impact melt rock samples from the chesapeake bay impact structure abstract this study presents 40ar 39ar step heating ages of four north american tektites three bediasites and one georgiaite and of two groundmass samples extracted at different depths from clast rich impact melt rocks cb w61 and cb w84 recovered by the usgs icdp eyreville b drill core about 9 km from the centre of the chesapeake bay impact structure radiometric age determination on both north american tektites and impact melt rocks from within chesapeake bay crater offers the first possibility to confirm the origin of these tektites for this aim argon isotopic data from 13 samples aliquots of tektite rims cores and bulk and 4 samples aliquots from two impact melt rocks were obtained over 15 to 26 step heating extractions age spectra of all tektite samples show plateaux comprising 62 98 of the 39ar release over consecutive intermediate and high temperature heating steps few low temperature extractions indicate excess 40ar inverse isochron 40ar 36ar intercepts of tektite samples are indistinguishable from air 295 5 however impact melt rock spectra presented complex ar release affecting primarily the low temperature heating steps inverse isochrones indicate excess argon from which the 40ar 36ar intercept was used to correct the age calculation cb w61 and cb w61 2 40ar 36ar intercepts are 354 5 2 5 and 327 2 6 3 respectively and those for cb w84 and cb w84 2 are 332 0 7 3 and 329 6 5 6 respectively the inverse isochron weighted mean age according to currently suggested k decay constants revisions by schwarz et al 2011 and renne et al 2011 for all four tektites is 34 86 0 25 ma mswd 0 96 p 0 41 n 4 and for the two impact melt rocks is 37 16 3 65 ma mswd 0 83 p 0 36 the combined tektite and impact melt rocks isochron mean age of 34 86 0 23 0 32 ma mswd 0 87 p 0 43 is slightly though not significantly higher than the plateau mean age of 34 55 0 27 0 36 ma mswd 0 66 p 0 62 placing this age in the global stratotype section and point gssp marine section exposed at massignano italy it falls below the eocene oligocene e o boundary overlapping with the 10 28 m ir anomaly these results agree within errors with previously reported ages of 35 20 0 54 ma especially those derived from k ar and ar ar total fusion analysis an age of 34 86 0 32 ma sets the chesapeake bay impact event close to the youngest of the three ir anomalies at 35 0 ma in the case the impactor was ir rich e g a chondrite primitive achondrite stony iron or iron meteorite the concordance with the e o boundary at 33 9 ma seems only marginally possible and only if the ir contribution from the ejecta were potentially due either to its small amount becoming diluted in the geologic record or the impactor being ir poor e g of differentiated achondritic composition this study also brings to front the need to re establish the stratigraphic and palaeo magnetic correlations across the globe for the ir anomalies and the magneto stratigraphy during the mid to late eocene and early oligocene and the need to re evaluate the markers for the eocene oligocene boundary

magma evolution of the sete cidades volcano sao miguel azores the sete cidades volcano sao miguel azores is situated at the eastern end of the ultraslow spreading terceira rift axis the volcano comprises several dominantly basaltic pre caldera eruptions a trachytic caldera forming stage and a post caldera stage consisting of alternating trachytic and basaltic eruptions the post caldera flank lavas are more primitive 5 wt mgo than the pre caldera lavas implying extended fractional crystallization and longer crustal residence times for the pre caldera shield building lavas thermobarometric estimates show that the ascending alkali basaltic magmas stagnated and crystallized at the crust mantle boundary similar to 15 km depth whereas the more evolved magmas mainly fractionated in the upper crust similar to 3 km depth the caldera forming eruption was triggered by a basaltic injection into a shallow trachytic magma chamber lavas from all stages follow a single continuous liquid line of descent from alkali basalt to trachyte although slight differences in incompatible element e g ba nb la nb and sr isotope ratios imply some heterogeneity of the mantle source major and trace element data suggest similar partial melting processes throughout the evolution of the volcano slight geochemical differences between post and pre caldera stage lavas from the sete cidades volcanic system indicate a variation in the mantle source composition with time the oxygen fugacity increased from the pre caldera to the post caldera stage lavas probably as a result of the assimilation of crustal rocks this is supported by the presence of crustal xenoliths in the lavas of the flank vents the lavas from the sete cidades volcano generally have low sr isotope ratios however rocks from one post caldera vent on the western flank indicate mixing with magmas resembling the lavas from the neighbouring agua de pau volcano having higher sr isotope ratios the different magma sources at sete cidades and the adjacent agua de pau volcano imply that despite their close proximity there is only limited interaction between them

the mobility of zirconium and other immobile elements during hydrothermal alteration abstract development of zircon and other zr phases in hydrothermal deposits indicates that zr can be highly mobile in these systems mobility is most common in but not restricted to f rich hydrothermal systems related to alkalic f rich igneous suites these suites can range from peralkaline through metaluminous to peraluminous a few examples are neither alkalic nor f rich three locations in the trans pecos magmatic province texas u s a demonstrate this hydrothermal zr mobility all three igneous systems are alkalic and f rich but vary in alkali al ratios peralkaline rhyolites and trachytes in the christmas mountains contain as much as 2100 ppm zr mostly in aegirine or arfvedsonite zircon is rare or absent fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38 000 ppm zr occurring as small disseminated zircons the deposits also are enriched in a variety of incompatible elements including be rare earth elements ree y nb mo hf pb th and u the sierra blanca intrusions a series of mildly peraluminous f rich rhyolite laccoliths contain as much as 1000 ppm zr mostly as zircon hydrothermal zircon occurs as overgrowths on magmatic grains as veinlets connected to overgrowths and in fluorspar replacement bodies in adjacent limestone the highest zr concentrations in fluorspar are 200 ppm metaluminous quartz monzonite from the infiernito caldera contains 400 600 ppm zr mostly as zircon euhedral zircon in quartz fluorite veins in the quartz monzonite indicates mobility of zr zirconium concentrations in the veins are unknown but the paucity of zircon suggests little zr enrichment relative to the host zircon and more rarely zirconolite occur in skarn in the ertsberg district of irian jaya indonesia unlike in texas related igneous rocks are metaluminous and the hydrothermal system was f poor worldwide hydrothermal zircon other zr phases and ti and al bearing phases occur in skarn epithermal precious metal veins volcanogenic massive sulfide deposits and mylonites we propose that differences in zr mineralogy of igneous source rocks is an important factor in determining the availability of zr to hydrothermal fluids although zr concentrations in the sierra blanca and christmas mountains rhyolites are similar zr enrichment in fluorspar was much greater in the christmas mountains we suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release zr but that zircon was only moderately attacked therefore far more zr was available for transport and subsequent deposition in the christmas mountains than at sierra blanca availability of other trace elements probably is also governed by their mineral host although zr mobility is most common in f rich hydrothermal systems related to alkalic and f rich igneous systems mobility at ertsberg may have been promoted by sulfate complexing

evaluation of the astronomical time scale for the paleocene and earliest eocene abstract the astronomical tuned time scale is rapidly extended into the paleogene but due to the existence of an eocene gap different tuning options had to be presented for the paleocene these options differ both in number and tuning of 405 kyr eccentricity related cycles and are only partially consistent with recalculated 40 ar 39 ar constraints for the cretaceous paleogene k pg and paleocene eocene p e boundaries in this paper we evaluate the cyclostratigraphic interpretation of records from odp leg 198 and 208 sites and the zumaia section to solve the problem of the different tuning options we found that the interval between the k pg boundary and the early late paleocene biotic event elpe comprises 17 instead of 16 405 kyr eccentricity related cycles as previously proposed while the entire paleocene contains 25 405 kyr cycles starting from 40 ar 39 ar age constraints for the k pg boundary a new tuning to 405 kyr eccentricity is presented for the paleocene and earliest eocene which results in ages of 66 0 and 56 0 ma for the k pg and p e boundaries respectively this tuning introduces considerable differences in age for a number of nannofossil events at odp sites 1209 and 1262 in the interval between 61 and 63 ma but eliminates large and abrupt changes in the seafloor spreading rate the tuning seems further consistent with recalculated 40 ar 39 ar ages for ash layer 17 of early eocene age however despite this apparent consistency with existing radio isotopic constraints an alternative 405 kyr younger or less likely older tuning cannot be excluded at this stage

insights into deposition and deformation of intra caldera ignimbrites central nevada abstract magnetic studies together with structural and 40 ar 39 ar age analyses were used to investigate the development and deformation of ignimbrites of the caetano tuff formation in central north nevada magnetic susceptibility susceptibility anisotropy ams and magnetic remanence approaches were used to decipher events accompanying emplacement and subsequent deformation of that tuff for both intracaldera tuffs and outflow deposits 40 ar 39 ar ages both those presented here and previously published ages indicate about 33 8 ma for the age of caetano ignimbrites approximately at the eocene oligocene boundary although extensive faulting associated with regional extension of the great basin region has dissected these deposits the thickness of the intra caldera ignimbrites has been estimated at 3 5 km or more thermal modeling for cooling of a caldera filling of 3 5 km thickness indicates acquisition of remanent magnetization can persist up to 25 ka sufficient to average secular variation this contrasts with rapid cooling and remanence acquisition in outflow ignimbrites typically only tens of meters thick a 750 m thick reference section was selected for more detailed study about 10 km to the west of the type area this reference section fault bounded at both base and top represents the upper part of the formation its lower member includes the uppermost 250 m of the lower massive resistant unit of ignimbrites a middle member of 375 m of well stratified pyroclastic deposits vitrophyres and sediments and an upper member of about 125 m of recessive ignimbrite and thin bedded clastic and pyroclastic deposits structural and magnetic remanence measurements suggest 13 eastward tilting of the caldera floor occurred early during deposition of the middle member flow directions inferred from ams k max axes in the middle member diverge about 45 relative to those in the underlying member and suggest a change in vent source accompanying the deposition of the middle member correcting for e w extension the outflow ignimbrites reached approximately 20 km to the west and south of the caldera north of the caldera ignimbrites formerly assigned to the caetano tuff but now assigned to the tuff of cove mine exhibit variable flow directions from an indeterminate source significantly however the intracaldera ams magnetic lineations conventionally used as proxies for flow lines trend mainly wnw parallel to a proposed major paleodrainage which stretches from the southern cortez range through 40 km to the tobin range caetano tuff magnetic remanence is entirely reversed and corresponds to magnetization acquired in the younger part of magnetochron 13r the magnetic remanence directions of both the intra caldera and outflow ignimbrites are similar d 151 i 60 significantly different from those predicted by a coeval reference pole for north america raising the possibility of a regional counterclockwise rotation of the sampling area of 15 6 presumably this began during faulting and major regional extension about 16 ma ago during the middle miocene and possibly continued later

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

astronomical calibration of the middle eocene contessa highway section gubbio italy abstract the eocene climatic system experienced an important transition from warm paleocene greenhouse to icehouse oligocene conditions this transition could first appear as a long term cooling trend but at an up close look this period is a complex combination of climatic events and for most of them causes and consequences are still not fully characterized in this context a study has been carried out on the middle eocene sedimentary succession of the contessa highway section central italy which is proposed as the global stratotype section and point gssp for the lutetian bartonian boundary at the top of the chron 19n with an astronomically calibrated age of 41 23 ma through a cyclostratigraphic analysis of the rhythmic sedimentary alternations and combination with the results of time series analysis of the proxy record we provide an orbital tuning of the middle eocene and astronomical calibration of the bio magnetostratigraphic events particularly for the c19n c18r chron boundary recognized at the contessa highway section

orbitally forced paleoenvironmental and paleoclimate changes in the late postevaporitic messinian of the central mediterranean basin paleoenvironmental and paleoclimate changes that occurred during the late postevaporitic stage of the mediterranean basin in the messinian foreland domain of the adriatic region offer a new perspective on the relationship between orbital forcing and climate response the magnetic susceptibility record of the fonte dei pulcini a section maiella mountains italy allows us to orbitally tune the record between 5 394 and 5 336 ma and to temporally constrain the paleoenvironmental and paleoclimate changes evidenced by quantitative paleontological palynomorphs ostracods and calcareous nannofossils stable isotope 18 o and 13 c and x ray diffraction xrd analyses the base of the fonte dei pulcini a section is characterized by paratethyan ostracods and dinocysts which point to the late messinian lago mare biofacies loxocorniculina djafarovi zone of the mediterranean messinian stratigraphy from paleontological and geochemical 18 o analyses there is no evidence of a marine incursion in the fonte dei pulcini a section the major changes in terms of paleodepth paleosalinity evaporation versus precipitation aridity versus humidity and reworking processes occurred in the upper part of the fonte dei pulcini a section during the last messinian insolation cycle i cycle 511 512 which is characterized by high amplitude oscillations in contrast the lower part of the fonte dei pulcini a section which was deposited during relatively low amplitude insolation cycles is characterized by more stable environmental conditions comparing summer insolation with the paleoenvironmental changes at the fonte dei pulcini a section we identify delays of several thousands of years between orbital forcing and climate response

the eocene oligocene boundary and the psychrospheric event in the tethys as recorded by deep sea ostracods from the massignano global boundary stratotype section and point central italy abstract latest eocene earliest oligocene deep water ostracods from the massignano global boundary stratotype section and point gssp central italy were studied from a palaeoecological perspective to investigate the psychrospheric event in the tethys although quantitative analyses were hampered by the low incidence of fauna the high resolution sampling used in this study 148 samples distributed over a 23 m thick succession spanning 3 m y allowed the following inferences 1 overall features e g abundance diversity composition of the assemblages suggest a middle lower bathyal environment with no significant palaeobathymetrical changes 2 today a similar fauna notably characterised by the common occurrence of the genus agrenocythere would likely be encountered in upper psychrospheric conditions water masses beneath the permanent thermocline with a temperature range of 4 10 c 3 although no noticeable faunal turnover has been recognised throughout the succession minor faunal changes seem to occur in the first part of the section probable appearance of legitimocythere presequenta and to a lesser extent also across the eocene oligocene boundary the presumed appearance of l presequenta latest eocene correlates quite well in timing and possible significance with the faunal changes observed in other microfossil groups foraminifers and dinocysts this event is possibly linked to a cooling pulse which might have been caused by the arrival or increasing advection of cold bottom waters in the study area faunal evolution across the eocene oligocene boundary is thought to be consistent with an intensification of the cooling trend and an increase of primary productivity which fits fairly well with the 13c record relationships between the subtle ostracod faunal changes observed in the massignano gssp and the main late eocene early oligocene psychrospheric event can be only speculative nevertheless we found no evidence that precludes the possibility of interpreting the massignano ostracod pattern as a subdued local expression of this major event although speculative this is a reasonable hypothesis because the investigated area is situated in western tethys far from the main circulation of deep ocean waters

new eocrinoids from the burgess shale southern british columbia canada and the spence shale northern utah usa the family lyracystidae n fam and genus lyracystis n gen are proposed for the holotype and one paratype of the middle cambrian eocrinoid gogia radiata sprinkle the burgess shale arms from the same unit and many additional partial and more complete specimens of this eocrinoid collected from the burgess shale since 1975 a second species lyracystis reesei n gen and n sp is described from a single partly complete specimen from the similar aged spence shale of northern utah lyracystis has three wide v shaped arms bearing numerous long straight brachioles in the notch a partly organized theca having larger and smaller ridged plates with epispires and a very long multiplated stalk made up of rounded or spiny small plates lyracystis is the longest stalked suspension feeding echinoderm known from the middle cambrian the three remaining paratypes of gogia radiata and four new specimens with possible branched brachioles from the burgess shale are renamed gogia stephenensis n sp

astronomical forcing in late eocene marine sediments we use an x ray fluorescence xrf core scanner to obtain records of elemental concentrations in sediment cores from ocean drilling program odp leg 171b site 1052 blake nose atlantic margin of northern florida this record spans the middle to late eocene as indicated by bio and magnetostratigraphy and displays cyclicity that can be attributed to the orbital forcing of a combination of climate ocean circulation or productivity we use the xrf counts of iron and calcium as a proxy of the relative contribution from calcium carbonate and terrestrial material to construct a new composite depth record this new composite depth record provides the basis to extend the astronomically calibrated geological time scale into the middle eocene and results in revised estimates for the age and duration of magnetochrons c16 through c18 in addition we find an apparent change in the dominance of orbitally driven changes in obliquity and climatic precession at around 36 7 ma on our new time scale long term amplitude modulation patterns of eccentricity and obliquity in the data do not seem to match the current astronomical model any more suggesting the possibility of new constraints on astronomical calculations

iron and titanium solution properties in peraluminous and peralkaline rhyolitic liquids the saturation surface of pseudobrookite fe2tio5 was determined for melts in the system sio2 al2o3 k2o feo fe2o3 tio2 at 1400 c and 1 atm the variation in concentrations of fe2o3 tio2 and fe2tio5 in liquids can be used to infer relative changes in activity coefficients of these components with changing k2o k2o al2o3 of the melts saturation concentrations of these components are low and relatively constant in the peraluminous melts and increase with increasing k2o k2o al2o3 in peralkaline liquids the activity coefficients of fe2o3 and tio2 and fe2tio5 therefore are higher in peraluminous liquids than in peralkaline liquids in this system in addition the iron redox ratio was measured as a function of k2o k2o al2o3 for liquids just below the saturation surface f text o text 2 was fixed so all variations in redox ratio are entirely due to changes in melt composition the redox ratio from unsaturated liquids was applied to saturated liquids where redox analysis of the glass is impossible the homogeneous equilibrium experiments indicate that the activity coefficient of fe2o3 relative to that of feo is significantly greater in peraluminous melts than peralkaline melts both the heterogeneous and homogeneous equilibria suggest that in peralkaline liquids k in excess of that required to charge balance tetrahedral al 3 is used to stabilize both fe 3 and ti 4 calculations show that ferric iron and titanium compete equally effectively for charge balancing potassium but neither can outcompete aluminum the observed changes in solution properties of fe2o3 and tio2 in the synthetic melts are used to explain variations in fe ti oxide stabilities in natural peraluminous and peralkaline rhyolites and granites since the activity coefficients of both ferric iron and titanium are significantly higher in peraluminous liquids than in peralkaline liquids fe ti oxides should occur earlier in the crystallization sequence in peraluminous rhyolites than in peralkaline rhyolites in addition iron will be reduced in peraluminous granites and rhyolites relative to peralkaline ones under comparable p t and f text o text 2 finally observed crystallization patterns for minerals containing highly charged cations other than ferric iron and titanium are evaluated in the context of this and other experimental studies

chemical weathering processes in the great artesian basin evidence from lithium and silicon isotopes variations in lithium and silicon isotope ratios in groundwaters of the great artesian basin in australia and the causes of these variations have been explored the chemistries of li and si in groundwater are influenced by the dissolution of primary phases the formation of secondary minerals and the reaction of solid phases with dissolved constituents while isotopic variations are generated by uptake into clays which preferentially incorporate the light isotopes the lithium isotopic composition expressed as view the mathml source li7 of the groundwaters ranges from 9 to 16 16 and clearly reflects changes in aquifer conditions reaction transport modelling indicates that changes in li concentrations are principally controlled by the ratio of the weathering rate of primary minerals to the precipitation rate of secondary minerals whereas view the mathml source li7 is affected by the extent of isotope fractionation during secondary mineral formation which is dependent on mineralogy the patterns of groundwater si concentrations and view the mathml source si30 values versus flow distance suggest that si is at steady state in the aquifer the view the mathml source si30 value of most of the groundwater samples is close to 1 1 which is significantly lower than the view the mathml source si30 value of the reservoir rocks 0 0 since precipitation of clays preferentially removes the light si isotopes from solution the most plausible explanation for these low groundwater view the mathml source si30 values is addition of si by dissolution of isotopically light secondary minerals these data together with model calculations show that li isotopes are extremely sensitive to changes in the chemical and physical conditions in the aquifer whereas si is not importantly the model suggests that even in large aquifers with long fluid residence times where steady state would be expected to be reached the concentrations and isotopic fractionation of trace elements are not controlled by li adsorption the model developed here provides a basis for using li isotopes measured in groundwaters and surface waters to constrain weathering processes

astronomical forcing and sedimentary noise modeling of lake level changes in the paleogene dongpu depression of north china abstract challenges in interpreting continental sequence stratigraphy and typically uncertain geochronology hinder the understanding of paleolake evolution and hydrocarbon exploration in terrestrial basins the dongpu depression in north china is a lacustrine basin with abundant hydrocarbon resources an accurate chronology for the paleogene stratigraphy in the dongpu depression is lacking and the mechanism of lake level variation remains unclear in this study we utilize high resolution gamma ray logs to conduct a cyclostratigraphic analysis of the shahejie formation which is a paleogene succession in the dongpu depression characterized by sandstones and dark mudstones interbedded with thin salt rocks time series analysis reveals evidence for 405 kyr eccentricity cycles in the gamma ray series which is supported by statistical modeling of optimal sedimentation rates tuning of the gamma ray data to this 405 kyr eccentricity cyclicity enables a 14 7 myr long astronomical time scale to be constructed this astrochronology is anchored to the astronomical age of the dongying formation shahejie formation boundary 28 86 ma in the bohai bay basin thus providing an absolute timescale for the studied interval that extends from 28 86 ma to 43 59 ma using this anchored astrochronology we show that a recently established sedimentary noise model for inferring sea level change in marginal marine settings can be used to similarly infer lake level fluctuations in terrestrial basins in particular sedimentary noise modeling of the tuned gamma ray series reveals high resolution changes in sedimentary noise that are indicative of lake level variations linked to million year scale i e 4 8 myr 2 4 myr and 1 2 myr astronomical forcing these inferred changes in lake level are supported by previously published sequence stratigraphic interpretations moreover an evolutionary correlation coefficient ecoco analysis of the gamma ray series also indicates recurrent distortions in sedimentation that may be linked to lake level changes this study provides new methods for the assessment of paleolake level variations as well as insights into the connection between astronomical forcing and lake evolution across long timescales in terrestrial basins

environmental magnetic record of antarctic palaeoclimate from eocene oligocene glaciomarine sediments victoria land basin summary the onset of continent wide glaciation in antarctica is still poorly understood despite being one of the most important palaeoclimatic events in the cenozoic the eocene oligocene boundary interval has recently been recognized as a critical time for antarctic climatic evolution and it may mark the preglacial glacial transition magnetic susceptibility intensity of natural and artificial remanences hysteresis parameters and magnetic anisotropy of the lower half late eocene early oligocene of the ciros 1 core from mcmurdo sound antarctica reveal alternating intervals of high and low magnetic mineral concentrations that do not correspond to lithostratigraphic units in the core pseudo single domain magnetite is the main magnetic mineral throughout the sequence and sharp changes in magnetite concentration match changes in clay mineralogy beneath and at the eocene oligocene boundary the detrital magnetite originated from weathering of the ferrar group which comprises basic extrusive and intrusive igneous rocks weathering processes and input of magnetite to the victoria land basin were intense during periods when the antarctic climate was warmer than today but during intervals when the climate was relatively cool chemical weathering of the ferrar group was suppressed and input of detrital magnetite to the victoria land basin decreased our results also indicate that a cold and dry climate was not established in antarctica until the eocene oligocene boundary with major ice sheet growth occurring at the early late oligocene boundary some earlier cold intervals are identified which indicate that climate had begun to deteriorate by the middle late eocene boundary

visual identification and quantification of milankovitch climate cycles in outcrop an example from the upper ordovician kope formation northern kentucky

biotic response of tethyan bathyal ostracodes through the eocene oligocene transition the composite faunal record from the massicore and massignano global stratotype section and point east central italy abstract the eocene oligocene transition eot is marked by a double stepped positive 18 o excursion of 1 3 and a deepening of the calcium compensation depth ccd interpreted to represent marked antarctic glaciation and global ocean atmosphere cooling i e oi 1 event a 0 5 m 55 70 kyr resolution ostracode faunal study of the massicore drilled up section from the italian massignano quarry containing the eocene oligocene global stratotype section and point gssp revealed a relative increase in krithe and decreases in faunal evenness and shannon index correlative to the oi 1 event these transient faunal changes may reflect local water column changes e g export production or intensified thermohaline flow of cooler deep waters through the paleotethyan seaway comparison of these massicore ostracode faunal data to previously published massignano quarry ostracode faunal data reveals similar relative abundances among common taxa where the study intervals overlap and thereby provide a more complete tethyan ostracode record spanning all of c13n and the broader eot at the gssp locality

geologic constraints on the chaotic diffusion of the solar system the correlation of earth s orbital parameters with climatic variations has been used to generate astronomically calibrated geologic time scales of high accuracy however because of the chaotic behavior of the solar system two initially close calculations of earth s orbit diverge exponentially and have a large uncertainty beyond several million years in the past this chaotic behavior is related to a combination of angles in the precession motion of the orbits of earth and mars which currently is in resonance how long stays in libration critically depends on the dynamical model and initial conditions for the solar system here we show that geologic data can differentiate between astronomical solutions that do and do not exhibit a transition in since 40 ma and that sediments can thus provide a history for the evolution of we find that the chaotic transition of from libration to circulation did not occur after ca 30 ma we can thus constrain the chaotic diffusion of the solar system in the past and our results provide new and challenging constraints for astronomical models

the ree ti mineral chevkinite in comenditic magmas from gran canaria spain a syxrf probe study the ree ti silicate chevkinite has been recognised previously in miocene ignimbrites from gran canaria and in correlative offshore syn ignimbrite turbidites we have estimated the partition coefficients of ree y zr and nb for chevkinite and co existing peralkaline rhyolitic comendite glass using synchrotron xrf probe analyses syxrf in order to evaluate the role of this mineral in the ree budget of felsic peralkaline magmas the zr nb ratio of the chevkinite is 1 55 1 7 strongly contrasting with zr nb of 6 5 in the associated glass zr shows a three fold enrichment in chevkinite relative to the residual melt whereas nb is enriched by a factor 10 the enrichment of ce and la in chevkinite is even more significant namely 19 wt ce and 12 wt la compared to 236 ppm ce and 119 ppm la in the glass chevkinite glass ratios are 988 30 for la 806 30 for ce 626 30 for pr 615 40 for nd 392 50 for sm 225 30 for eu 142 25 for gd 72 20 for dy for trace elements we derived kdte of 74 25 for y 8 for hf 50 for th 15 5 for nb and 3 55 0 4 for zr mineral glass ratios for co existing titanite are 28 10 for la 86 20 for ce 98 30 for pr 134 35 for nd 240 50 for sm 50 20 for eu 96 25 for gd 82 25 for dy 99 30 for y 45 10 for nb and 3 0 5 for zr based on these data the removal of only 0 05 wt of chevkinite from a magma with initially 300 ppm ce would deplete the melt by 93 ppm to yield 207 ppm ce in the residual liquid chevkinite thus appears when present to be the controlling mineral within the lree budget of evolved peralkaline magmas

punctuated evolution of global climate cooling during the late middle to early late miocene high resolution planktonic foraminiferal and oxygen isotope records from the mediterranean high resolution planktonic foraminiferal and oxygen isotope records are presented from a mediterranean deep marine succession dated astronomically between 12 12 and 9 78 ma planktonic and benthic oxygen isotope records are punctuated by two episodes of 18o increase which have astronomical ages of 11 4 and 10 4 ma and correspond to the mi5 and mi6 events of miller et al 1991a these ice growth events coincide with low amplitude variations in the 1 2 myr obliquity cycle and are accompanied by significant faunal changes in the mediterranean such as the arrival of neogloboquadrinids the increase in abundance of the g apertura g obliquus group and the areal differentiation between n atlantica and n acostaensis short term variations in the planktonic foraminiferal and oxygen isotope records correspond to dominantly precession controlled sedimentary cycles features of the sapropel grey marl layers indicate that the short term astronomically controlled circum mediterranean climate changes remained basically the same over the last 12 myr

the spence shale lagerstatte an important window into cambrian biodiversity the spence shale member of the langston formation is a cambrian miaolingian wuliuan lagerstatte in northeastern utah and southeastern idaho it is older than the more well known wheeler and marjum lagerstatten from western utah and the burgess shale from canada the spence shale shares several species with these younger deposits yet it also contains a remarkable number of unique species because of its relatively broad geographical distribution and the variety of palaeoenvironments and taphonomy the fossil composition and likelihood of recovering weakly skeletonized or soft bodied taxa varies across localities the spence shale is widely acknowledged not only for its soft bodied taxa but also for its abundant trilobites and hyoliths recent discoveries from the spence shale include problematic taxa and provide insights about the nature of palaeoenvironmental and taphonomic variation between different localities supplementary material a generic presence absence matrix of the spence shale fauna and a list of the spence shale localities are available at https doi org 10 6084 m9 figshare c 4423145

petrogenetic evolution of felsic volcanic sequences associated with phanerozoic volcanic hosted massive sulphide systems the role of extensional geodynamics abstract felsic volcanic hosted massive sulphide deposits form in many different geotectonic environments usually associated with episodes of extension however empirical geochemical links between felsic volcanism geotectonic environment and extensional geodynamics have not been adequately documented so as to distill the fundamental relationships between these features and formation of volcanic hosted massive sulphide vhms mineralization which is important considering most vhms deposits are hosted in felsic volcanic bearing sequences using felsic geochemical data from six different vhms mineralized phanerozoic geotectonic settings it seems that the felsic geochemical data are consistent with the overall geotectonic interpretations for these areas which in turn helps in stratigraphic and geotectonic interpretations for detailed vhms exploration in extensional geodynamic settings bimodal volcanism is common compared to the continuum of compositions observed under compressional to neutral high stress regimes in calc alkaline arc building environments the empirical geochemical metallogenic vhms relationships evident in the archean felsic volcanic rocks in particular the low zr y n yb n 2 o conditions in different source areas and geotectonic environments they seem to be the predominant controls on the compositional evolution of felsic magmas in extensional settings because of the limited degree of assimilation and fractional crystallization afc affecting their compositions with rapid intrusion into the uppermost crust to positions were they achieve neutral buoyancy in the volcanic to subvolcanic environment within plate felsic or a type anorogenic type and anomalous ocean ridge or type felsic magmas that have tholeiitic affinities relatively low alkali elements are common within parts of the volcanic sequences hosting massive sulphide deposits reflecting in part a relationship to extension the high contents of high field strength elements zr ga lree hree y nb etc and other lines of evidence indicate they are relatively high temperature relatively reduced magmas probably derived from previously dehydrated granulitic or melted oceanic simatic or continental sialic crust low p granulites or amphibolites but also in some cases possibly mantle rocks such that they are significantly water undersaturated during melting i e a h 2 o 1 reduced viscosities typical of high temperature melts enable rapid intrusion to higher levels diking vs diapirism higher rates of heat advection from mantle mafic magmas into the thickened oceanic and or continental crust during lithospheric extension are needed to facilitate melting of these rock to form a type and or or type partial melts tholeiitic felsic this usually results in bimodal magmatism as magma mixing is not favored in extensional settings especially at high magma production intrusion and extrusion rates i e high heat flow this would inhibit ferromagnesian phase in particular hornblende and magnetite fractionation especially at low f o 2 in the felsic magmas that would deplete the melt in y hree as well as ore related elements particularly zn which is 2 to 3 times higher in a type and or type rocks compared to other magma types therefore the empirical felsic igneous geochemical metallogenic relationships observed by others low zr y n yb n

a climate driven model and development of a floating point time scale for the entire middle devonian givetian stage a test using magnetostratigraphy susceptibility as a climate proxy abstract here we propose an approach to establish a preliminary age chronology for complete stages within the phanerozoic by applying cyclostratigraphic methods that employ high resolution data sets this requires use of geochemical or geophysical data known to serve as a cyclic climate proxy to demonstrate the method we use the magnetostratigraphic susceptibility technique as the basis for fitting a climate model to the givetian stage of the middle devonian system we show a milankovitch eccentricity climate zonation for the givetian that is pinned to time series analyses from outcrop samples from its upper givetian frasnian france and lower eifelian givetian morocco stage boundaries using these data sets we construct a uniform cyclicity model designed to conform to a 405 kyr cyclicity with a duration corresponding to the published duration for the givetian of 4 4 myr kaufmann 2006 to this model we fit two well established conodont zonation schemes thus allowing time estimates for conodont ranges for the givetian indicating a range from 1 8 myr to 100 kyr before extinction of an individual conodont species we then test and adjust the model using independent data sets from the eastern united states adjustments to the initial model yield a duration of 28 climate half cycles zones for the givetian stage and an increased age to 5 6 myr these zones allow high correlation among sections to better resolve timing of major bio events and provide a floating point time scale to which absolute ages can be applied

taphonomy palaeoecological implications and colouration of cambrian gogiid echinoderms from guizhou province china based on rich material 381 specimens examined from two cambrian echinoderm faunas the early cambrian balang fauna and middle cambrian kaili fauna in guizhou province south china the taphonomy of gogiid echinoderms is described in detail and the preservation of stereomic microstructure and organic remains of cambrian gogiid echinoderms is reported here for the first time taphonomic considerations include entombment patterns decay sequences individual specific diagenetic histories unusual burial postures selective disarticulation patterns and postmortem elongation in particular five categories of gogiid entombment patterns are proposed to describe the multi directional orientations recorded at the burial time of articulated gogiids gogiid bearing slabs of guizhou material primarily 70 display the type 2 entombment pattern articulated gogiids preserved with fan shaped brachioles thus most guizhou gogiids were buried with brachioles preserved in feeding posture during obrution events balang gogiid faunas contain the oldest evidence of palaeoecological interactions among echinoderms and other indigenous taxa in addition to pre burial and post burial decay other potential causes for unusual disarticulation patterns exhibited by the gogiids from the lower cambrian balang formation include pre burial bio disturbance and post burial bioturbation based on ichnogenera including rusophycus and planolites chemical analyses reveal that carbon calcium manganese and iron are the major elements responsible for the variety of colours exhibited by guizhou gogiids three dimensional stereomic microstructure mean stereom pore size 8 4 8 7 m average trabecular thickness 4 5 4 6 m occurs on the external surfaces of thecal plates in two gogiid species stereom preservation in calcite suggests that the dissolution of calcareous echinoderm plates yielding characteristic mouldic preservation is sub recent after lithificaiton and exposure of gogiid bearing marine sedimentary successions on or near the land surface

the relationship between a type granites and residual magmas from anorthosite evidence from the northern sherman batholith laramie mountains wyoming usa abstract anorthosite complexes commonly are spatially and temporally associated with a type granite batholiths but their genetic relationship if any has been difficult to determine this study focuses on the northern portion of the 1 43 1 44 ga sherman batholith which is located adjacent to the 1 44 ga laramie anorthosite complex laramie mountains wyoming usa the northern sherman batholith is an ideal place to resolve the relationship of a type granite with anorthosite because of the age of the crust into which it is emplaced most a type granites are intruded into crust only slightly older than the granites themselves and there is little isotopic contrast between potential mantle and crustal source rocks the northern sherman batholith intrudes archean crust that by 1 44 ga had developed nd sr and pb isotopic compositions that differed greatly from contemporaneous mantle the northern sherman batholith is an iron enriched metaluminous alkalic to alkali calcic batholith most of the batholith is composed of fayalite granite with minor volumes of monzodiorite and olivine gabbro hypabyssal dikes of these compositions crop out in the highest structural levels exposed in the area the northern sherman batholith is less differentiated and has assimilated less felsic crust than the southern portions which intrude more fertile proterozoic crust northern sherman batholith rocks are compositionally and isotopically very similar to monzonitic and dioritic rocks of the laramie anorthosite complex none of these rocks have isotopic compositions similar to their archean host rocks precluding derivation solely from such sources instead northern sherman batholith granites like laramie anorthosite complex rocks are related to mantle derived tholeiitic magmas emplaced at the base of the crust the tectonic environment and magmatic processes that lead to the formation of massif anorthosite are also conducive to the formation of voluminous a type granite of which the northern sherman granite is a prime example

biotic signals from nannoflora across the iridium anomaly in the upper eocene of the massignano section evidence from statistical analysis abstract strong evidence for a major late eocene impact including an iridium rich layer and shocked quartz has been found in the massignano section central italy stratotype of the eocene oligocene boundary quantitative calcareous nannofossils analyses have been performed and classical and multivariate statistical techniques have been applied to assess the paleonvironmental effect of this impact on the nannoflora abundance patterns indicate 1 a warming episode just above the iridium layer 2 a subsequent slight cooling trend probably related to the global cooling during late eocene to early oligocene 3 marked fluctuations in the trophic resources and an increase in near shore taxa in the upper part of the interval 4 increase in low nutrient taxa in biotite rich layers just above the iridium level possibly related to lowered productivity linked to volcanic activity all these signals appear most likely to be the result of long term climatic changes rather than to short term effects of extraterrestrial impact in addition cluster analysis was performed on the assemblage data this delineated similarities among different taxa and grouped samples with similar assemblages several groups related to temperature trophic and unknown preference conditions have been distinguished a consistent difference in the abundances of the taxa and in their correlation has been detected between samples above and below the iridium level this change appears to be related to two important sedimentary features which are found in the interval above the iridium occurrence 1 the presence of biotite rich layers linked to increasing volcanism and 2 a conspicuous color transition from reddish to greenish related to changes in sedimentary environments e g variations in trace element abundance these environmental changes rather than the impact may have affected the nannoflora assemblages

astronomic calibration of the late eocene early oligocene massignano section central italy we present an astronomically tuned polarity timescale for the late eocene early oligocene based on a cyclic limestone marls sedimentary succession exposed at massignano italy gssp for the eocene oligocene boundary here we applied spectral analysis techniques to the high resolution magnetic susceptibility record the results provide clear evidence of a regular and cyclic signal that allows us to discard a stochastic mechanism as controlling these fluctuations conversely these outcomes reveal the presence of stable and notable periodicities that are in tune with those associated with orbital forcing through a cyclostratigraphic analysis of the rhythmic sedimentary alternations and combination with the results of time series analysis of the proxy record we refine the late eocene portion of the gpts through astronomical tuning of the rhythmic sedimentary alternations to recent astronomically calculated variations of earth s orbit we recalibrated the polarity boundaries ages and the main stratigraphic events recognized throughout the sedimentary record among these an age of 33 714 ma is proposed for the e o boundary

testing high resolution magnetic susceptibility and gamma radiation methods in the cenomanian turonian upper cretaceous gssp and near by coeval section abstract low field mass specific magnetic susceptibility and gamma radiation spectra grs field and laboratory data sets for two upper cretaceous marine sedimentary sequences representing the cenomanian turonian c t boundary in the western interior seaway in central colorado have been measured sections including the c t global boundary stratotype section and point gssp and a one kilometer distant co eval sequence the s section it has previously been established that both and grs data sets are controlled by detrital eolian fluxes into the marine environment although the effect of weathering if any on these parameters when exposed in outcrop is not well documented in addition these parameters are controlled by differing detrital eolian components that may be derived from different sources or be differentially concentrated within the marine system of great interest is 1 how well these data sets record climate cycles 2 how the and grs data are affected by weathering and 3 how well the two methods support each other reported here are the results of a number of field and laboratory experiments designed to evaluate instruments and how and grs data sets co vary and to test their usefulness as correlation tools in stratigraphy results show that both and 40k data sets from laboratory measurement on samples collected in the field where rocks are relatively fresh are generally well correlated respond closely to climate and the corresponding detrital eolian flux into the marine environment and can be used for a rough proxy for each other however weathering appears to affect the 40k data by removing 40k thus reducing correlation potential although does not appear to suffer as badly in more weathered sections and good correlations between sections remain field grs measurements produce a broadly smoothed data set that regionally can be very useful for correlation although potential global correlations are not tested here using data reported here and comparing these data to a 100 kyr cyclic eccentricity e1 climate model for the upper cretaceous at 93 9 ma shows that and 40k data measured in the laboratory can be used to build floating point time scales that produce essentially equivalent results as do other studies using absolute dates

precise timing of the upper taghanic biocrisis geneseo bioevent in the middle upper givetian middle devonian boundary in northern spain using biostratigraphic and magnetic susceptibility data sets abstract the ability to correlate with high precision among geological successions is critical in evaluating the global coincidence and therefore magnitude and duration of geological events this is a difficult problem given resolution uncertainties and ambiguities in biostratigraphic data sets the magnetostratigraphy susceptibility mss method based on low field bulk magnetic susceptibility ms measurements of closely spaced samples provides a well established abiotic high resolution correlation tool in stratigraphy that when combined with bio chemostratigraphic and other geophysical techniques offers ways to resolve correlation problems in addition such data sets lend themselves to time series analysis where developing high resolution timing of events becomes possible this paper examines the final episode equivalent to the geneseo bioevent in the appalachian basin of the important taghanic biocrisis known from globally distributed middle devonian geological sections the geneseo bioevent is important because the extinction of some major fossil groups occurred during this time while other groups declined significantly including many benthonic groups however the maxima of extinctions does not appear to have occurred everywhere simultaneously to help resolve timing of this bioevent results are reported for two middle devonian successions from northern spain the s huergas de gordon and punta boletos sections both showing the final taghanic biocrisis geneseo interval and correlate these successions to the same interval within an independent global database time series analyses of the mss data sets from the spanish sections was performed using multi taper mtm and fourier transform ft methods and have extracted well defined milankovitch bands from the primary ms data from each section using ft and mtm values for eccentricity at 400 kyr and 100 kyr a floating point time scale was developed for the two spanish sections that provides age resolution to 50 kyr for these successions the results show that the geneseo bioevent in northern spain occurred within a narrow time window estimated to have lasted for 70 kyr this time window fall s within the polygnathus ansatus uppermost part ozarkodina semialternans conodont zones just at the middle upper givetian boundary of the middle devonian in what appears to be the upper regressive phase of t r cycle iia

alkali and alkaline earth element geochemistry of los humeros caldera puebla mexico abstract results of the measurements of alkali k rb and cs and alkaline earth ba and sr elements on seven pre caldera and twenty post caldera samples of los humeros volcanics pliocene to recent are described these data are interpreted in terms of the known solid liquid partition coefficients it appears that fractional crystallization is a dominant petrogenetic process and is controlled by the observed modal phases namely plagioclase olivine and clinopyroxene in decreasing importance and perhaps in addition biotite and titanomagnetite in the later stages of the differentiation sequence the available major element chemistry and mass balance calculations support these conclusions sr and nd isotopic data further suggest that these magmas were generated in the underlying mantle fractionated in a shallow level magma chamber and underwent very insignificant sialic contamination before eruption

volcanic clasts in silurian conglomerates of the midland valley hagshaw hills inlier scotland and their meaning for caledonian plate tectonics 34 igneous clasts of predominantly rhyolitic composition of the parishholm and hareshaw conglomerate silurian hagshaw hills inlier midland valley scotland have been analysed for major and trace element contents the geochemical composition of the clasts indicates different source areas firstly some clasts are derived from rhyolites of a within plate setting peralkaline rhyolites of oceanic islands or continental rifts and secondly other clasts are derived from calc alkaline to high k rhyolites such rhyolites erupt mainly above convergent plate boundaries but occur also in continental areas of crustal extension both conglomerates were shed from the direction of the southern uplands into the midland valley since no calc alkaline rhyolites are known in the southern uplands a volcanic terrane should have been situated during the silurian in the area where the southern uplands lie now the geotectonic character of this terrane cannot unequivocally be identified with the help of the trace element data of the clasts therefore several models are discussed

marine biotic signals across a late eocene impact layer at massignano italy evidence for long term environmental perturbations the eocene oligocene transition marks the passage from greenhouse conditions to an icehouse state with progressive global cooling starting in the early middle eocene the late eocene presents substantial evidence for extraterrestrial impacts whose effects on living organisms and climatic changes are still not completely clear a high resolution microfloral and faunal investigation has been carried out in a 4 m thick segment of the massignano global stratotype section and point for the eocene oligocene boundary the studied interval includes a late eocene 35 7 0 4 myr old impactoclastic layer containing several cosmic signatures the impact event recorded at massignano had no abrupt dramatic effects on marine biota in terms of extinction however significant quantitative changes in the calcareous plankton and dinoflagellate cyst assemblages occurred 60 kyr after the impact event the observed pattern is intepreted as reflecting a long term re organization of water structure

environmental magnetic record of paleoclimate change from the eocene oligocene stratotype section massignano italy 1 a high resolution environmental magnetic study of the massignano section italy global stratotype section and point for the eocene oligocene boundary has been performed to test whether a clear magnetic signature associated with climatic change is recognizable in this record our results reveal the existence of alternating intervals with high and low magnetic mineral concentrations similar to the pattern of rock magnetic property variations observed from an environmental magnetic study of the ciros 1 sediment core from antarctica these results suggest that an external forcing mechanism drove the sedimentary response to global climate change prior to the major oi 1 cooling event at the eocene oligocene boundary

lower palaeozoic volcanism of the eastern alps and its geodynamic implications a geodynamic model for the lower palaeozoic evolution of the eastern alps upper ordovician to middle devonian gurktal nappe styrian greywacke zone palaeozoic of graz is discussed based on new field work and numerous geochemical analyses of volcanic rocks it is suggested that in the upper ordovician there existed on the one hand a passive continental margin or continental rift flooded by the sea where mildly alkaline basalts erupted magdalensberg series carinthia kaser series gurktaler alpen on the other hand a convergent plate boundary in the form of an active continental margin or island arc or in the form of an orogen formed by continent continent collision which can be recognized by the eruption of calc alkaline volcanic rocks probably also existed in the upper ordovician blasseneck porphyroid styrian greywacke zone nockseries gurktaler alpen in the lower silurian a reorganization of the plate boundaries took place resulting in the disintegration of the upper ordovician collision zone along deep reaching faults further extensional movements during the silurian and devonian led to the disintegration of a broad shelf platform and to the eruption of alkaline within plate basalts the extensional movements were responsible for the thinning of the continental crust and a general subsidence which probably lasted until lower carboniferous time

long periodic variations in the earth s obliquity and their relation to third order eustatic cycles and late neogene glaciations abstract evolutive spectra of four high resolution climatic proxy records reveal that the spectral power in the obliquity frequency band increases during five well defined intervals in the last 5 3 million years these intervals correspond to periods of high amplitude variations in the tilt obliquity of the earth s axis connected with a 1 2 myr cycle and to sea level lowstands of third order eustatic cycles in the haq et al 1987 curve this implies that the development of major plio pleistocene glaciations proceeded episodically and that third order cycles are glacio eustatically controlled in at least two of these intervals sinistrally coiled neogloboquadrinids entered the mediterranean at times of glacial periods one interval starts around 2 8 ma and is characterized by the first occurrence of n atlantica s another interval begins at the plio pleistocene boundary around 1 8 ma and is characterized by the common occurrence of sinistrally coiled n pachyderma also during the late miocene third order cycles correlate well with the 1 2 myr cycle of obliquity a significant drop in the third order eustatic curve starting at the tortonian messinian boundary for instance coincides with a period of high amplitude variations in the obliquity time series connected with the 1 2 myr cycle

integrated stratigraphy magneto bio and chronostratigraphy and geochronology of the palaeogene pelagic succession of the umbria marche basin central italy

the cambrian substrate revolution and the early evolution of attachment in suspension feeding echinoderms abstract the cambrian characterized by the global appearance of diverse biomineralized metazoans in the fossil record for the first time represents a pivotal point in the history of life this period also documents a major change in the nature of the sea floor neoproterozoic type substrates stabilized by microbial mats were replaced by unconsolidated soft substrates with a well developed mixed layer the effect of this transition on the ecology and evolution of benthic metazoans is termed the cambrian substrate revolution csr and this is thought to have impacted greatly on early suspension feeding echinoderms in particular according to this paradigm most echinoderms rested directly on non bioturbated soft substrates as sediment attachers and stickers during the cambrian epoch 2 as the substrates became increasingly disturbed by burrowing forming a progressively thickening mixed layer echinoderms developed new strategies for attaching to firm and hard substrates to test this model we evaluated the mode of attachment of 83 cambrian suspension feeding echinoderm species attachment mode was inferred based on direct evidence in fossil specimens and interpretations of functional morphology these data were analyzed quantitatively to explore trends in attachment throughout the cambrian in contrast to previous studies the majority of cambrian clades eocrinoids helicoplacoids helicocystoids isorophid edrioasteroids and solutes are now interpreted as hard shelly substrate attachers only early edrioasteroids attached directly to firm substrates stabilized by microbially induced sedimentary structures contrary to the predictions of the csr paradigm our study demonstrates that cambrian echinoderms were morphologically pre adapted to the substrate changes that occurred during the cambrian allowing them to fully exploit the appearance of hardgrounds in the furongian we find no support for the claim that the csr explains the peak in echinoderm diversity during cambrian epochs 2 3 or that it caused the extinction of helicoplacoids

oligocene climate dynamics a planktonic and benthic foraminiferal stable isotope stratigraphy of the oligocene equatorial pacific ocean drilling program site 1218 was generated at 6 kyr resolution between magnetochrons c9n and c11n 2n 26 4 30 ma on a newly developed astronomically calibrated timescale our data allow a detailed examination of oligocene paleoceanography the evolution of the early cryosphere and the influence of orbital forcing on glacioeustatic sea level variations spectral analysis reveals power and coherency for obliquity 40 kyr period and eccentricity 110 405 kyr orbital bands with an additional strong imprint of the eccentricity and 1 2 myr obliquity amplitude cycle driving ice sheet oscillations in the southern hemisphere planktonic and benthic foraminifera 18o are used to constrain the magnitude and timing of major fluctuations in ice volume and global sea level change glacial episodes related to obliquity and eccentricity variations occurred at 29 16 27 91 and 26 76 ma corresponding to glacioeustatic sea level fluctuations of 50 65 m alteration of high latitude temperatures and antarctic ice volume had a significant impact on the global carbon burial and equatorial productivity as cyclic variations are also recorded in the carbon isotope signal of planktonic and benthic foraminifera the water column carbon isotope gradient and estimated percent carbonate of bulk sediment we also investigate the implications of a close correspondence between oxygen and carbon isotope events and long term amplitude envelope extrema in astronomical calculations during the oligocene and develop a new naming scheme for stable isotope events on the basis of the 405 kyr eccentricity cycle count

a climate driven model using time series analysis of magnetic susceptibility χ datasets to represent a floating point high resolution geological timescale for the middle devonian eifelian stage

the emu bay shale konservat lagerstatte a view of cambrian life from east gondwana recent fossil discoveries from the lower cambrian emu bay shale ebs on kangaroo island south australia have provided critical insights into the tempo of the cambrian explosion of animals such as the origin and seemingly rapid evolution of arthropod compound eyes as well as extending the geographical ranges of several groups to the east gondwanan margin supporting close faunal affinities with south china the ebs also holds great potential for broadening knowledge on taphonomic pathways involved in the exceptional preservation of fossils in cambrian konservat lagerstatten ebs fossils display a range of taphonomic modes for a variety of soft tissues especially phosphatization and pyritization in some cases recording a level of anatomical detail that is absent from most cambrian konservat lagerstatten