mutvei s solution an ideal agent for resolving microgrowth structures of biogenic carbonates accretionary hard parts of many organisms provide excellent archives of past climate and environmental conditions or life history traits variable growth rates function as environmental and physiological proxies and growth increments as calendars recognition of growth structures is thus a prime necessity for sclerochronological studies here we present a new handy easy to use and time efficient technique that resolves annual and sub annual growth structures in skeletons of a wide range of different organisms mutvei s solution simultaneously etches biogenic carbonates and calcium phosphates fixates the soluble and insoluble organic matrices and fibers and stains mucopolysaccharides it produces a filigreed three dimensional relief of etch resistant ridges growth lines and etched depressions growth increments and stains skeletal growth structures in shadings of blue growth lines stand out as crisp darker blue stained lines reflected optical light microscopy axial and oblique illumination and scanning electron microscopy can be used to analyze the microgrowth structures we demonstrate the use of the technique on hard tissues of various marine and freshwater bivalves a coral a sclerosponge a barnacle gastropods a cephalopod a fish otolith and a whale s ear bone this technique may be of interest for paleoclimatologists geochemists and biologists it can significantly expand the use of biogenic hard parts as environmental and physiological indicators because it reveals microgrowth structures of biogenic skeletons that potentially form on a periodic basis and thus function as calendars

clay mineral evolution changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4 567 ga of planetary evolution in our solar system reflect evolving tectonic geochemical and biological processes clay minerals were absent prior to planetesimal formation 4 6 billion years ago but today are abundant in all near surface earth environments new clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in earth s evolution notably the formation of a mafic crust and oceans the emergence of granite rooted continents the initiation of plate tectonics and subduction the great oxidation event and the rise of the terrestrial biosphere the changing character of clay minerals through time is thus an important part of earth s mineralogical history and exemplifies the principles of mineral evolution

the sandstone derived provenance record of the gualala basin northern california u s a abstract detrital zircon u pb ages and pb isotope compositions of detrital feldspars from the late cretaceous eocene gualala basin in northern california indicate that the basin received sediments from the southern sierra nevada the mojave block and the salinian block mesozoic detrital zircon age components and pb isotope compositions of detrital feldspars from the basin are similar to u pb zircon ages and pb isotope compositions from previously studied coeval conglomerate clasts the detrital zircons and feldspars however also include additional age and pb isotope components that are unobserved or poorly represented in the conglomerate based provenance record these new data suggest a more complex provenance history than that inferred from previously studied conglomerate clasts and strongly imply a connection to the mojave desert provenance evolution of the sediments in the basin indicates that significant contribution of sediment from the mojave desert began during the paleocene when it is inferred that the drainage network expanded eastward from its previous extent the presence of mojave derived late permian zircons as well as feldspars that have high 208pb 204pb ratios in the eocene age german rancho formation indicates that the basin remained in the vicinity of the mojave desert until the eocene this result demonstrates that the gualala basin had undergone very little northward motion at that time and consequently requires that no significant northward translation took place prior to 50 ma the results of this study highlight the value of additional provenance constraints combined with age distributions when identifying sediment source terranes

atmospheric oxygenation caused by a change in volcanic degassing pressure around two and a half billion years ago following the end of the archaean eon the atmosphere turned from anoxic to weakly oxic in what is known as the great oxidation event using a model of volcanic degassing gaillard et al demonstrate that a preceding period of continental crust formation may have been the trigger they propose that as continents emerged and volcanoes became increasingly subaerial rather than submarine magmatic volatiles were degassed at lower pressures leading to a progressive oxidation of the gases released this shift to a release of sulphur as sulphur dioxide rather than as hydrogen sulphide could then have fed marine sulphate reduction and the eventual oxygenation of earth s atmosphere the precambrian history of our planet is marked by two major events a pulse of continental crust formation at the end of the archaean eon and a weak oxygenation of the atmosphere the great oxidation event that followed at 2 45 billion years ago this oxygenation has been linked to the emergence of oxygenic cyanobacteria1 2 and to changes in the compositions of volcanic gases3 4 but not to the composition of erupting lavas geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3 5 billion years ago5 6 here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation using thermodynamic calculations simulating gas melt equilibria in erupting magmas we suggest that mostly submarine archaean volcanoes produced gases with so2 h2s 1 and low sulphur content emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late archaean then led to widespread subaerial volcanism which in turn yielded gases much richer in sulphur and dominated by so2 dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere

paleoproterozoic increase in zircon δ18o driven by rapid emergence of continental crust abstract numerous geologic proxies for earth system processes track dramatic changes at the atmosphere lithosphere or atmosphere ocean interface during the early paleoproterozoic era the presence of a geodynamic driver for these changes and how this might have affected the deeper lithosphere is more cryptic here we present temporally constrained 18o and ehf in detrital zircon from paleoproterozoic sedimentary successions in western australia and canada that chart a rapid change in the oxygen isotopic composition from

oligocene and miocene paleogeography of central california and displacement along the san andreas fault recently completed sedimentologic and petrologic studies of oligocene and miocene strata in the temblor range san joaquin basin and santa cruz mountains la honda basin permit detailed reconstructions of paleogeography as well as new estimates of displacement along the san andreas fault during the oligocene and miocene the san joaquin and la honda basins were contiguous the southwestern margin of the san joaquin la honda basin was tectonically unstable and paleogeographically complex with several small deep sea fans fed by sediment derived from nearby subaerial uplifts of franciscan and granitic basement one of these deep sea fans represented by the temblor formation of the southern temblor range and the vaqueros sandstone of the central santa cruz mountains apparently has been displaced about 315 to 320 km by post early miocene post zemorrian about 23 ma right lateral slip along the san andreas fault this new estimate of displacement places an additional constraint on interpretations of san andreas slip history but ambiguities remain the time of initiation of san andreas displacement is poorly known and available data do not permit discrimination between a history of relatively continuous slip versus a history of episodic slip

the effects of source lithology transport deposition and sampling scale on the composition of southern california sand the transverse ranges of southern california represent an uplifted and variably dissected mesozoic magmatic arc and mesozoic to holocene sedimentary and volcanic strata deposited in convergent and transform tectonic settings modern sand within part of the western transverse ranges represents first order sampling scale of the santa monica and the san gabriel mountains second order sampling scale of the santa clara river draining both mountain ranges and third order sampling scale of the beach system between the mouth of the santa clara river and the eastern santa monica mountains and turbidite sand of the hueneme mugu submarine fan source lithology includes plutonic and metamorphic rocks of the san gabriel mountains and sedimentary and volcanic rocks of the santa monica mountains first order sands have large compositional variability sand from local coastal drainage of the santa monica mountains ranges from basaltic feldspatholithic to quartzofeldspathic sand of the san gabriel mountains local drainages has three distinct petrofacies ranging from metamorphiclastic feldspatholithic to mixed metamorphi plutoniclastic and plutoniclastic quartzofeldspathic second order sand is represented by the main channel of the santa clara river the sand has an abrupt downstream compositional change from feldspathic to quartzofeldspathic third order sand beaches and deep sea turbidite samples of the santa monica basin is quartzofeldspathic beach sand is more quartz rich than is santa clara river sand whereas turbidite sand is more feldspar rich than is beach sand deep sea sand has intermediate composition with respect to second order samples of the santa clara river and third order samples of the beach system suggesting that 1 the santa clara river is the main source of sediments to the marine environment and 2 local entry points from canyons located near local drainages may generate turbidity currents during exceptional flood conditions petrologic data of modern sand of the study area are highly variable at first and second order scale whereas third order sand is homogenized the homogenized composition of deep marine sand is similar to the composition of most ancient sandstone derived primarily from the mesozoic dissected magmatic arc of southern california this study of the western transverse ranges illustrates the effects of source lithology transport depositional environment and sampling scale on sand composition of a complex system which provides insights regarding actualistic petrofacies models

petrofacies and provenance of late mesozoic forearc basin northern and central california data from the great valley group sequence represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc this information is useful in documenting tectonic and magmatic events within the arc and related terranes and forms the basis for the establishment of petrostratigraphic units for mapping and correlation sandstone and conglomerate compositions are controlled by changes in provenance many of which were basinwide and synchronous clay mineral composition is controlled primarily by burial metamorphism careful attention to sample collection sample preparation and petrographic techniques is essential for uniform results seven petrographic parameters p f lv l m qp q q f and l listed in decreasing importance to petrofacies discrimination define eight petrofacies stony creek platina lodoga grabast boxer cortina los gatos and rumsey listed in approximate order of decreasing age the upper jurassic lower cretaceous petrofacies stony creek platina and lodoga contain higher lithic contents supracrustal sources whereas the upper cretaceous petrofacies especially the rumsey contain higher proportions of plutoniclastic components quartz feldspar and micas the proportion of potassium feldspar increases from near zero in the upper jurassic to nearly 50 of all feldspars in the uppermost cretaceous the lower part of the great valley group upper jurassic and lower cretaceous contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes tectonic highlands formed by the arc arc collision nevadan orogeny that occurred prior to initiation of the franciscan great valley sierra nevada arc trench system the klamath mountains area provided a major proportion of this detritus ophiolite and serpentinite detritus was deposited locally near the base of the great valley group as a result of deformation along the east side of the growing franciscan subduction complex volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the sierra nevada area during the cretaceous as the volcanic cover was stripped off plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin crustal components were more continental in the southern sierra nevada and more oceanic in the northern sierra nevada as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south by the middle of the late cretaceous extensive batholithic terranes provided potassium feldspar rich arkosic detritus to the entire forearc basin by the paleogene arc magmatism had migrated eastward sufficiently that deeper levels of the california part of the arc were exposed by erosion tectonic activity decreased in the forearc basin and the basin was filled to sea leve in most parts

paleolatitude of the butano sandstone california and its implications for the kinematic histories of the salinian terrane and the san andreas fault the lower to middle eocene butano sandstone of the santa cruz mountains california is part of the central portion of the salinian terrane a slivered granitic fragment west of the san andreas fault the butano sandstone has been correlated with the point of rocks sandstone across the san andreas fault approximately 315 km to the southeast the magnitude of this offset is the same as the amount of neogene san andreas fault offset documented in other studies thus the correlation of these two eocene units implies that no pre san andreas system motion of the butano sandstone has occurred paleomagnetic studies indicating large northward translations of cretaceous and paleocene rocks of coastal california however raise the possibility of continued northward motion of the salinian terrane during or after deposition of the butano sandstone to better our understanding of the eocene position of the salinian terrane the paleolatitude of the butano sandstone was determined by paleomagnetic analysis of azimuthally unoriented cores from exploratory oil wells specimens from 30 core intervals from the top to the middle or lower parts of the formation were subjected to alternating field and thermal demagnetization the resulting paleolatitudes group better when bedding is horizontal than in their drill hole attitudes providing a positive fold test several magnetic polarity zones are present the mean paleolatitude 34 6 2 5 is significantly lower than that expected if the rocks were deposited in their present day location on an underformed north american craton when neogene slip on the san andreas and on smaller inboard faults is restored however the measured paleolatitude does not differ significantly from that expected this result supports the correlation of the butano and point of rocks sandstones and implies that the salinian terrane experienced no significant motion between deposition of the butano sandstone and establishment of the neogene san andreas dextral fault system

constraints and deception in the isotopic record the crustal evolution of the west musgrave province central australia abstract the hf and nd isotopic evolution of the musgrave province central australia is used to constrain the timing of crust formation and lithospheric organisation of proterozoic australia the dataset from this region challenges two widely held tenets of hf and nd isotope systematics namely that crust formation events can only be identified as periods when crystallisation ages correspond to model ages and that linear hf evolution arrays away from depleted mantle along crustal lu hf or sm nd slopes reflect reworking of the same source hf isotopes in musgrave province zircon crystals indicate two major crust formation events at c 1900 ma and at 1600 1550 ma although no juvenile rocks or crystals are known from c 1900 ma radiogenic addition into the crust at this time is required to account for consistent nd and hf evolution patterns which show no indication of an initially heterogeneous source oxygen isotopes in zircon grains confirm that much of the c 1900 ma hf isotopic signal is not compromised by mixtures furthermore the correspondence between mantle extraction and the commencement of reworking of archean material supports new crust generation at c 1900 ma and a coupling between lower and upper crustal processes the c 1900 ma timing of juvenile addition is dissimilar to that in the albany fraser and arunta orogens and may reflect continental arc development on the margin of a southern continent the general hf isotopic evolution trend of the musgrave province apparently reflects reworking from a dominant c 1900 ma source with some additional unradiogenic and radiogenic input through time however in the 1220 1050 ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle derived material intracontinental rifts and other regions with sustained very high temperature crustal recycling processes generate magmatic provinces with extreme hfse enrichment this can have a profound influence on isotopic evolution trends suppressing typical juvenile addition patterns isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within hfse enriched magmas without diverging isotopic signatures from apparent reworking trends in the musgrave province the crust had become so hfse enriched during the prolonged musgrave orogeny 1220 1150 ma that it was insensitive to mantle input which is estimated to have been as much as 85 during this event

holocene climate variability in europe evidence from δ18o textural and extension rate variations in three speleothems time series o isotope profiles for three u th dated stalagmites have revealed that for much of the holocene a site on the atlantic seaboard sw ireland exhibits first order 18o trends that are almost exactly out of phase with coupled 18o curves from two southern european sites se france and nw italy in the irish stalagmite cc3 from crag cave sw ireland low 18o at 10 000 cal yr bp reflects cool conditions by the early to mid holocene 9000 6000 cal yr bp 18o had increased reflecting the onset of warmer conditions on the atlantic seaboard this shift to higher 18o was accompanied by a marked increase in the stalagmite extension rate reinforcing our interpretation that this was a period of relative warmth except for an episode of increased extension rate about 5500 yr ago 18o in the crag stalagmite exhibits a gradual decrease accompanied by declining extension rates between 7800 and 3500 cal yr bp interpreted as a cooling trend there is evidence for increases in both 18o and stalagmite extension rate in the period from 3500 cal yr bp to the present day suggesting a return to warmer conditions on the atlantic seaboard in the stalagmite from nw italy er76 grotta di ernesto trentino province the early holocene c 9200 7800 cal yr bp is characterised by high 18o probably indicative of warm and or dry conditions exceptionally low 18o from 7800 to 6900 cal yr bp at this site reflects a well defined wet phase cerin wet phase in the last three millennia this stalagmite exhibits a shift to lower 18o interpreted as some combination of cooler and or wetter conditions unlike the irish stalagmite the italian sample does not show a correlation between 18o and extension rate instead its extension rate correlates roughly with 13c presumably reflecting a climate driven vegetation change in the early holocene 18o in the french stalagmite cl26 grotte de clamouse herault province se france was low relative to its holocene average for much of the period since c 3500 cal yr bp this stalagmite exhibits higher 18o than in the early holocene suggesting warmer conditions like the irish stalagmite the french sample exhibits a well defined correlation between 18o and extension rate had drip water availability been the dominant control on 18o at this semi arid site then higher 18o would have been accompanied by lower not higher extension rates this suggests strongly that temperature rather than rainfall amount was the dominant control at this site while conclusions regarding the patterns of climate variability on a continent scale must remain tentative because of the limited number of stalagmites studied we argue that early holocene warm conditions on the atlantic seaboard irish site coincided with relatively cool conditions at the clamouse site by c 3500 yr ago the pattern appears to have been reversed

late holocene annual growth in three alpine stalagmites records the influence of solar activity and the north atlantic oscillation on winter climate annual growth rates and the ratio of dark to light colored calcite within single annual laminae in three contemporaneously deposited holocene speleothems from grotta di ernesto an alpine cave in northern italy respond to changes in surface temperature rather than precipitation based on monitoring of present day calcite growth and correlation with instrumental data for surface climatic conditions we interpret a higher ratio of dark to light colored calcite and the simultaneous thinning of annual laminae as indicative of colder than present winters such dark and thin laminae occur in those parts of the three stalagmites deposited from ad 1650 to 1713 and from ad 1798 to 1840 as reconstructed through lamina counting these periods correspond to the well known maunder and dalton minima of solar activity an 11 yr cyclicity in growth rate coupled with reduced calcite deposition during the historic minima of solar activity is indicative of a solar influence on lamina thickness spectral analysis of the lamina thickness data also suggests that the north atlantic oscillation variability influenced winter temperatures based on the present day controls on cave calcite formation we infer that high frequency changes in solar activity modulated the seasonal duration of soil co2 production

extreme δ18o signatures in zircon from the saglek block north atlantic craton document reworking of mature supracrustal rocks as early as 3 5 ga

high pressure granulites at the dawn of the proterozoic abstracthigh pressure metamorphism is uncommon in the ancient geo logical record kanja malai in the salem crustal block southern india contains high pressure kyanite garnet bearing felsic granu lites that equilibrated at 14 16 kbar and 820 860 c laser abla tion inductively coupled plasma mass spectrometry u pb zircon and in situ monazite geochronology indicate that these assemblages grew ca 2490 ma these pressure temperature time constraints pro vide a rare record indicating that thickened crust and low apparent thermal gradient conditions existed during the archean proterozoic transition a period of earth history for which the rock record com monly preserves evidence for comparatively high apparent thermal gradients the thermal regimes required to generate these metamor phic conditions are typical of collisional orogenesis and suggest that the continental lithosphere was capable of supporting crustal thick ening to 45 50 km such crustal thickening provides supporting evi dence that tectonic regimes similar to modern earth style tectonics were in operation at the archean proterozoic transition introduction

a paleoclimate record of the last 17 600 years in stalagmites from the b7 cave sauerland germany abstract petrographical and geochemical parameters of stalagmites from the b7 cave in iserlohn letmathe northern rhenish massif nw germany record late and postglacial climate changes temperature and or precipitation fabrics and microfacies of the stalagmite profiles lead to a differentiation of four hierarchies of rhythms clastic layers in the stalagmites are caused by flooding events and are time markers twenty four tims th u age dates provide a time calibration of stalagmite growth phases one stalagmite reveals an early growth period between 17 6 and 16 7 ka bp between 9 6 and 5 5 ka bp atlantic episode of the holocene the growth rate of the stalagmites was higher than before and after this time with dominant light porous microfacial laminae and high 18 o and 13 c values representing partly kinetic fractionation effects this part of the holocene is interpreted as a mainly warm episode with frequent interruptions of dripping within the past 4 ka the profiles with predominant dark compact facies reveal low isotopic values which may be interpreted as a temperature proxy record the stalagmite records resemble records from an irish stalagmite correlation with the 14 c record from european tree rings suggests that colder periods in the north atlantic were accompanied by drier winters in central europe

why was flood volcanism on submerged continental platforms so common in the precambrian abstract many archean and proterozoic greenstone belts contain volcanic rocks that erupted subaqueously but interacted with continental crust on their way to the surface this points to emplacement in a tectonic setting that was rare to absent throughout the phanerozoic the eruption of flood basalts onto submerged continental platforms to explain the situation requires that sea levels were high during periods of flood volcanism perhaps because the ocean basins were partially filled by extensive active and high standing oceanic ridges or by oceanic plateaus the common preservation of crust contaminated submarine basalts even in the oldest supracrustal sequences may indicate that continental crust was voluminous even at an early stage in earth history

extreme oxygen isotope zoning in garnet and zircon from a metachert block in melange reveals metasomatism at the peak of subduction metamorphism

oxygen isotopes in subducted oceanic crust a new perspective from siberian diamondiferous eclogites 1 there are three methods of investigating the oxygen isotope composition of oceanic crust 1 data from drilling obtained samples 2 study of obducted ophiolites and 3 from crustal derived xenoliths however each approach has limitations drilling capabilities are limited to the upper 1 3 km of the oceanic crust ophiolites are segments of oceanic crust and underlying mantle exposed at the earth s surface but their origin and emplacement are still debated nonetheless the study of ophiolite sequences has enabled many of the fundamental observations regarding ancient oceanic crust and the oxygen isotope signature of the upper mantle analyses of ophiolite sequences e g samail reveal 18o variations ranging from isotopically enriched in relation to morb 18o morb to isotopically depleted low 18o morb interpreted to show the effects of seawater interaction at different temperatures mantle derived xenoliths also display compelling geochemical evidence suggesting they are remnants of subducted ocean crust and may in fact be more representative samples some kimberlite hosted diamondiferous eclogite xenoliths with crustal protoliths reveal a marked oxygen isotope disparity between oceanic crust and the upper mantle i e a bimodal distribution of both mantle like 18o 5 6 and isotopically enriched oxygen 18o 6 8 the isotopically high 18o values are often observed in eclogite xenoliths with ultramafic protoliths which form beyond the low temperature alteration zone this finding is in contrast to traditional oxygen isotope versus depth curves of ophiolite sequences here we present a compiled data set from siberian eclogites and pyroxenites that illustrates this bimodality using magnesium number mg as a depth proxy and investigate the conditions that could potentially result in the observed abnormal oxygen isotope variations

strengths and limitations of zircon lu hf and o isotopes in modelling crustal growth abstract the robust nature of the mineral zircon combined with our analytical ability to readily acquire in situ uranium lead u pb lutetium hafnium lu hf and oxygen o isotopic data has resulted in a rapid rise in the use of zircon isotopic datasets for studying both the generation of continental crust and its growth through earth history in such studies there has been a strong focus on developing methods to determine the timing and or proportion of juvenile magmatic addition to the continental crust one widespread approach to determine the timing of crustal growth has been the construction or fitting of reworking arrays to regional hf isotopic datasets simple stochastic models are presented which highlight that in many cases apparent reworking arrays are much more likely to represent a process of on going dilution and refertilisation of ancient crust consistent with hot zone models of granitoid generation and the need to refertilise lower crustal reservoirs to maintain magmatism a new compilation of magmatic rock zircon lu hf and o isotope data is used to demonstrate that the use of mantle like o isotope data as a screening tool for meaningful hf model ages is also unlikely to be reliable with independently constrained data indicating that as few as 14 of hf model ages provide a meaningful indicator of the timing of crustal growth the limitations of hf model ages are discussed with regard to existing approaches for continental growth and we demonstrate that popular inverse modelling approaches suffer from a bias created by both the use of model ages and numerical artefacts in an effort to address some of the limitations within existing models we develop stochastic models based on joint calibration of multiple datasets which allow for more unique solutions

increased subaerial volcanism and the rise of atmospheric oxygen 2 5 billion years ago the hypothesis that the establishment of a permanently oxygenated atmosphere at the archaean proterozoic transition approximately 2 5 billion years ago occurred when oxygen producing cyanobacteria evolved is contradicted by biomarker evidence for their presence in rocks 200 million years older to sustain vanishingly low oxygen levels despite near modern rates of oxygen production from approximately 2 7 2 5 billion years ago thus requires that oxygen sinks must have been much larger than they are now here we propose that the rise of atmospheric oxygen occurred because the predominant sink for oxygen in the archaean era enhanced submarine volcanism was abruptly and permanently diminished during the archaean proterozoic transition observations are consistent with the corollary that subaerial volcanism only became widespread after a major tectonic episode of continental stabilization at the beginning of the proterozoic submarine volcanoes are more reducing than subaerial volcanoes so a shift from predominantly submarine to a mix of subaerial and submarine volcanism more similar to that observed today would have reduced the overall sink for oxygen and led to the rise of atmospheric oxygen

provenance and stratigraphy of the eocene tejon formation western tehachapi mountains san emigdio mountains and southern san joaquin basin california abstract the eocene tejon formation of the western tehachapi and san emigdio mountains of california provides a unique east west trending outcrop belt of otherwise deeply buried strata that underlie the san joaquin basin to the north its stratigraphy and framework mineralogy have been used to define offsets along the san andreas fault a major neogene plate boundary transform fault that has translated coastal california northward more than 300 km by right slip the tejon formation was deposited directly on crystalline basement rocks as a result of an eastward transgression of at least 45 km from the early to the late middle eocene followed by a major regression in the late middle eocene the basal uvas conglomerate member consists entirely of coarse grained transgressive system tract tst deposits characterized by abundant current formed sedimentary structures it is overlain by offshore marine shales of the liveoak shale member which consist of lower tst deposits overlain by highstand system tract hst deposits the overlying regressive metralla sandstone member consists mostly of highly bioturbated fine grained shallow marine hst sandstones with local thin bedded turbidites present in some western exposures the quartzofeldspathic sandstones grand mean qm51 12f42 12lt7 4 of the tejon formation suggest a provenance consisting of plutonic metamorphic and volcanic rocks such as those present in the basement of the san emigdio and techachapi mountains northwestern mojave desert and southern sierra nevada petrologic parameters however suggest variable contributions from these source areas through time three distinctive petrofacies coincide with the three principal lithostratigraphic subdivisions the shallow marine tst sandstones from the uvas conglomerate member are more quartzose than those of the hst metralla sandstone member possibly because higher energy deposition preferentially preserved quartz thin bedded turbidites in the western exposures of the metralla sandstone in contrast have more abundant feldspar and volcanic lithic fragments than the uvas and liveoak members the composition of the tejon formation suggests derivation from a basement uplift provenance with progressive upsection changes from qm60 f33 lt8 uvas to qm46 f44 lt10 liveoak and qm 43 f52 lt5 metralla the composition and provenance of the tejon formation is different from that of the coeval butano sandstone and point of rocks sandstone submarine fan deposits to the north and west

freshwater bivalves tell of past climates but how clearly do shells from polluted rivers speak abstract freshwater bivalves margaritifera margaritifera linnaeus and unio crassus philipsson from rivers in sweden 79 specimens and england one specimen were used to study the effects of human induced pollution on shell growth table 1 we analyzed variations in annual and daily shell growth rates of 80 specimens from unpolluted and polluted ph

tectonic evolution of the southern apennines thrust belt italy as reflected in modal compositions of cenozoic sandstone the composition of sandstones derived from erosion of the southern apennines orogen provides constraints for cenozoic tectonic evolution clastic wedges were derived mainly from the strongly deformed calabrian arc allochthon this key tectonic element is interpreted as a thrust sheet of european crust moved about 300 400 km eastward during the paleogene to neogene toward the adria foreland during the paleogene to early miocene the liguride complex oceanic terrane was deposited in a remnant ocean basin east of the calabrian arc related to northwestward subduction of ligurian oceanic lithosphere beneath the european margin upper paleogene quartzofeldspathic and volcanolithic liguride sandstones testify to provenance from the subduction complex to the magmatic arc respectively upper oligocene to lower miocene quartzolithic sandstone suggests a recycled orogen provenance i e metasedimentary rocks in the growing accretionary calabrian arc final closure of the liguride remnant ocean basin and onset

petrology and diagenesis of the eocene butano sandstone la honda basin california the lower and middle eocene butano sandstone at least 1500 m and possibly as much as 3000 m thick was deposited as a submarine fan in a narrow restricted continental borderland setting its quartzofeldspathic composition suggests a local provenance from plutonic and metamorphic rocks of the salinian terrane it crops out in three belts of which the middle belt in the central part of the basin was buried the deepest and underwent the most significant diagenetic changes the central belt made up of middle fan deposits contains higher amounts of quartz and lower amounts of feldspar than the more proximal southern inner fan deposits and more distal northern outer fan deposits the presence of authigenic albite laumontite and pore filling kaolinite and chlorite suggests that decreases of feldspars mainly plagioclasej are related mainly to dissolution of plagioclase it is possible that at least 20 25 of the plagioclase with respect to total feldspar has been diagenetically dissolved in the butano sand

bedrock geology of the san francisco bay area a local sediment source for bay and coastal systems abstract local watersheds may contribute over half of the sediment load coming into san francisco bay today the bedrock underlying these watersheds is the ultimate source for most of this sediment this paper outlines the geologic history of this bedrock which records the complex tectonic history of the san francisco bay area over the last 200 ma the jurassic to eocene franciscan complex in the bay area is the most widespread bedrock the local franciscan can be broken into nine tectonic terranes that represent pieces of seafloor that were accreted to the north american margin in over a 100 myr period of subduction each terrane has a unique age range sequence of seafloor rocks and metamorphic history the franciscan rocks were thrust eastward under the great valley complex the great valley complex reflects a forearc basin comprised of jurassic ocean crust the coast range ophiolite and overlying jurassic and cretaceous turbidite dominated sedimentary rocks of the great valley group by the beginning of the cenozoic era shallowing of the angle of subduction along the continental margin led to uplift and infilling of the forearc basin to shelf depth recorded at this time are sedimentary sequences governed by eustatic sealevel changes and evidence of the first unroofing of franciscan rocks marine sedimentary rocks dominate the region through the miocene and unconformities within the early tertiary sedimentary record reflect periods of tectonic activity and uplift middle to late miocene sedimentary rocks are extensively deposited throughout the bay area in the late miocene the mendocino triple junction passed northward through the area and transform tectonism commenced a slab window developed behind the triple junction resulted in volcanic activity that produced the sonoma volcanics in the north bay and volcanics of the east bay hills by pliocene time terrestrial sedimentary rocks were being deposited in many parts of the bay area faulting associated with the san andreas system led to the development of small basins the displacement of local bedrock blocks and the transport of the salinian complex from the southern sierra to the western margin of the bay area the modern topography of the region started emerging by about 6 ma to 4 ma when compression across the san andreas system increased and uplift of the coast ranges began the first estuarine influence in san francisco bay is recorded in 600 ka rocks about the same time as the modern sacramento river system started flowing through the san francisco estuary valley today s local san francisco bay watershed is comprised of numerous small stream systems around the bay with headwaters in the surrounding hills and mountains active tectonism produces relief in these watersheds of typically 500 m or more with the ridgelines typically supported by more resistant bedrock units steep topography leads to rapid bedrock erosion particularly of the finer grained sedimentary rocks landslides provide a significant portion of the sediment carried by the streams and several of the bedrock units are more prone to landslides particularly the central and novato quarry terranes of the franciscan complex and finer grained units of both the great valley group and tertiary rocks many of the larger streams have dammed reservoirs that trap much of their sediment load before it can reach the bay

a reappraisal of the early slip history of the san andreas fault central california usa the modern san andreas fault system california united states is widely considered to have formed in response to the initiation of pacific north american plate interaction ca 27 ma although there is general consensus on the magnitude and timing of neogene displacement along the san andreas system its paleogene history remains unresolved in particular 100 km of right lateral offset between mid cretaceous plutonic rocks of the northern salinian block and the western edge of sierra nevada basement remains unaccounted for after restoration of neogene displacement along strike slip faults of the san andreas system our detrital zircon data invalidate a key paleogene piercing point by demonstrating that displaced portions of the hypothesized middle eocene butano point of rocks submarine fan were never contiguous across the san andreas fault we instead show that the eocene provenance characteristics exhibited by northern salinian strata closely match those of the southern sierra nevada and northwestern mojave desert this implies that the northern salinian block was located at least 75 50 km farther south in eocene time than previously recognized our data require 1 pre 23 ma dextral slip along the san andreas fault in central california and or 2 slip along a predecessor fault that formed prior to pacific north american plate interaction this previously undocumented slip may indicate that significant pacific north american plate interaction propagated from the plate margin into the continental interior much earlier than conventionally believed alternatively late paleogene slip could predate the development of the modern plate boundary and represent inboard dextral strike slip displacement along the eastern margin of the salinian block similar to the deformation that occurs today along the strike slip sumatra fault system

petrofacies and provenance of the puente formation middle to upper miocene los angeles basin southern california implications for rapid uplift and accumulation rates abstract the puente formation is a middle upper miocene clastic unit lying unconformably on the lower middle miocene el modeno volcanics and topanga group in the los angeles basin the puente formation about 3900 m thick is composed of conglomerate sandstone and mudrock deposited as a submarine fan at bathyal depths several intrabasinal discordances suggest tectonic activity during deposition the succession consists of two main upward thickening and coarsening megacycles reflecting submarine fan progradation the puente formation is characterized up section by 1 thin bedded sandstone and shale la vida member grading to thick bedded sandstone and conglomerate soquel member 2 thin bedded mudrock and sandstone yorba member grading to thick to very thick bedded sandstone and conglomerate sycamore canyon member sandstones of the puente formation are quartzofeldspathic qm35f54lt11 their compositions suggest local provenance from the plutonic volcanic and metamorphic rocks of the san gabriel mountains and surrounding areas petrologic parameters however suggest variable contribution of these source rocks through time four petrofacies with distinctive parameters coincide with the lithostratigraphic subdivisions coarse grained plutonic rock fragments are abundant throughout the succession and consist of plagioclase rich plutonic rocks probably sourced in part from the lowe granodiorite lathwork microlitic to felsitic volcanic lithic grains are also present in the lower and middle part in the la vida petrofacies there is also an intrabasinal cont ibution intraclasts and bioclasts from shelfal areas in the yorba petrofacies there is a local increase of volcanic detritus lv l 0 81 represented by coarser volcanic lithics and abundant volcaniclastic matrix metamorphic detritus is not very abundant the sycamore canyon petrofacies is dominantly plutoniclastic rg r 0 90 hornblende bearing plutonic rock fragments including very abundant hornblende grains the plutonic detritus is dominantly plagioclase orthoclase biotite bearing in the lower part and hornblende bearing in the upper part suggesting unroofing of the lowe granodiorite complex as a key element of uplift of the san gabriel mountains other neogene sandstones deposited in the los angeles basin also consist dominantly of plutoniclastic detritus related to the unroofing of arc related plutonic rocks dissected magmatic arc for example the up section increase in plutonic detritus is consistent with the composition of the upper miocene lower pliocene capistrano formation qm50f47lt3 which has a composition identical to the sycamore canyon petrofacies there is consistent provenance signal in spite of complex transrotational tectonics responsible for opening of the los angeles basin and later transpressional processes which are still active detailed provenance study of the puente formation and related units provides important constraints on paleogeographic and paleotectonic reco structions of southern california basins and uplifts

detrital modes and provenance of miocene sandstones and modern sands to the southern apennines thrust top basins italy abstract the cilento group lower middle miocene the monte sacro conglomerate upper miocene the gorgoglione formation upper miocene and the crati submarine fan holocene are four turbidite sequences deposited in northwest southeast trending thrust top basins of the southern apennines italy foreland region the corigliano basin is a part of the modern taranto gulf foredeep basin that developed since the late pleistocene sandstone detrital modes of the miocene turbidite units are quartzofeldspathic petrofacies 1 2a 4 5 8 q62f25l13 quartzolithic petrofacies 2b q60f16l24 and arkosic petrofacies 7 q50f45l5 reflecting a collisional orogenic provenance volcanolithic sandstones petrofacies 3 q23f11l66 suggest an important contribution also from a volcanic source area related to the convergent continental margin volcanism connected with the collisional tectonic regime that affected the western mediterranean e g sardinia volcanic arc individual carbonatoclastic beds hybrid arenite biocalcarenite and mudstone are interbedded with sandstone units of the ilento group they have siliciclastic content of about 35 and are quartzofeldspathic petrofacies 6 q53f23l24 these beds 0 10 65 m thick record impulsive gravitational collapses of the carbonate platform passive margin to the east and southeast the petrologic parameters show a temporal evolution from metasedimentary to granitic gneissic provenance ascribed to different tectonostratigraphic units of the calabrian arc nine miocene petrofacies suggest dynamic evolution of the source terranes from laughian to tortonian time facies dispersal patterns and petrologic parameters of the miocene sandstones suggest a provenance from the northern and western margins of the basins comparison between the holocene crati fan petrofacies 9 q54f24l22 and miocene detrital modes suggests that the sandstones of the cilento group the monte sacro conglomerate and the gorgoglione formation were derived from unroofing of the thrusted basement block transported by torrential type fluvio deltaic systems and then funneled into a major turbidite dispersal system analogous to the modern crati submarine fan of the corigliano thrust top basin

neoarchean lithospheric strengthening and the coupling of earth s geochemical reservoirs this paper explores the secular evolution of the height of an isostatically balanced collisional mountain belt in the context of ongoing convergence we show that until the neoarchean continents were unable to sustain topography 2500 m during the neoarchean the continental lithosphere evolved through a rheological threshold allowing for the development of signifi cant topography the consequence of the strengthening of the continental lithosphere is fundamental for the coupling of the earth s geochemical reservoirs the neoarchean was a period of global changes during which exogenic envelopes recorded major shifts in composition toward modern values we propose that during the neoarchean the exogenic envelopes which were until then coupled to the mantle through hydrothermal processes and volcanism also became coupled to the continental crust through reliefgenerating tectonics processes and erosion hence changing the balance between mantle versus crustal interaction with the exogenic earth

crustal thickening and clay controls on o isotope variation in global magmatism and siliciclastic sedimentary rocks new compilations of global o isotope data from zircon and siliciclastic sedimentary rocks highlight an increasing range in 18o values in both systems since the late archean this is consistent with an increased clay component in sedimentary rocks and subsequent incorporation into igneous rocks each of these factors can arguably be achieved by increased crustal thickening in the late archean resulting in greater burial and melting of supracrustal rocks and increased chemical weathering and recycling of upper crustal rocks despite the suggested change in tectonic regimes in the late archean stochastic modelling in this study demonstrates that 18o data do not provide evidence for a secular decrease in the proportion of mantle derived magmas in granitoid rocks instead best fit models indicate that juvenile input and reworking of supracrustal material vary with respect to the short term 100 200 myr tectonic cycles preserved in the continental crust hence major step changes in global tectonic regimes in the post hadean such as the initiation of subduction in the mid to late archean are not supported by global zircon o isotope datasets and instead minor progressive changes are indicated for earth s tectonic regimes

episodic earth evolution abstract u pb ages of zircons from precambrian granitoids and major rivers are grouped into a series of major peaks at about 2 7 2 5 2 1 1 9 and 1 1 ga recently these peaks have been interpreted as times of enhanced preservation of the continental crust associated with the assembly of supercontinents an older interpretation which we support is that they correspond instead to periods of accelerated crustal growth related to episodic convection of the mantle in this paper we use fluid mechanics experiments to develop a new model of mantle convection and crustal growth a dense layer at the base of the mantle persists until 2 7 ga when it destabilizes and generates large domes that rise into the upper mantle there they cause a large increase in the rate of subduction which leads to enhanced granite magmatism at convergent margins and thus to a pulse of crustal growth the domes heat the upper mantle which partially melts at mid ocean ridges to produce thick oceanic crust that resists subduction the subsequent period of subdued plate motion is broken by the next generation of mantle domes before and after the archean proterozoic period of episodic crustal growth plate tectonics operated quasi continuously

selective alteration of arkose framework in oligo miocene turbidites of the northern apennines foreland impact on sedimentary provenance analysis

an archean yellowstone evidence from extremely low δ18o in zircons preserved in granulites of the yilgarn craton western australia we report the discovery of archean 2980 2670 ma zircons from the yilgarn craton in western australia that record unusually low delta o 18 signatures to 0 5 these zircons occur in cordierite orthopyroxene granulites that retain the geochemical signature of intense premetamorphic hydrothermal alteration we propose a model whereby the low delta o 18 zircons crystallized within protoliths that record multiple stages of high temperature interaction and hydrothermal exchange between shallow crustal material and o 18 depleted meteoric fluids in a setting analogous to that of the yellowstone caldera burial and subsequent granulitefacies metamorphism of this crust led to the crystallization of zircon which acquired and preserved the extremely o 18 depleted signature of the whole rock the apparent absence of strongly o 18 depleted archean zircons has been a puzzling feature of the global zircon record but we suggest this is an artifact of poor preservation potential our findings suggest that long lived shallow crustal magmatic hydrothermal systems similar to those operating in modern caldera complexes were also a feature of archean earth

evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon

a change in the geodynamics of continental growth 3 billion years ago models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout earth s history the oxygen isotopic composition of zircons for which uranium lead and hafnium isotopic data provide age constraints is a key archive of crustal reworking we identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time growth of continental crust appears to have been a continuous process albeit at variable rates a marked decrease in the rate of crustal growth at 3 billion years ago may be linked to the onset of subduction driven plate tectonics

offset along the san andreas fault of eocene strata from the san juan bautista area and western san emigdio mountains california analyses of eocene strata that rest on gabbroic basement rocks in the western san emigdio mountains and northernmost gabilan range indicate that the 2 sequences have been offset right laterally 305 320 km along the san andreas fault in both areas basal shallow marine conglomerate of penutian age grades upward into shale of ulatisian and narizian age that was deposited at bathyal water depths in a basin with access to open ocean additional similarities in the upper eocene and oligocene stratigraphic units suggest original contiguity of the depositional basins the inferred offset indicates that the salinian block was attached to western california by at least early eocene time the longer distances of northward transport of the salinian block that are suggested by preliminary paleomagnetic data from upper mesozoic granitic rocks and upper cretaceous and paleocene strata must have occurred during paleocene or earlier time

eoarchean to paleoproterozoic crustal evolution in the north china craton evidence from u pb and hf o isotopes of zircons from deep crustal xenoliths abstract granulite facies xenoliths entrained within igneous rocks shed a light on poorly understood yet critical questions about age origin and history of the lower continental crust here we present the first coupled in situ u pb lu hf and o isotope data for the precambrian zircons from fourteen deep crustal xenoliths from the north china craton the geochronological data demonstrates that the oldest lower crustal remnants formed at 3 82 ga and related magmatism continued until 3 55 ga the eo paleoarchean zircons with exception of one analysis have subchondritic initial hf isotopes with negative ehf t and are characterized by normal mantle to elevated 18o values 5 37 6 90 indicating a development of a low lu hf reservoir and hydrosphere crust interactions in the early earth magmatic zircons from lower crustal xenoliths of north china define a strongly episodic distribution of ages at 3 82 3 55 ga 2 7 ga 2 5 ga and 1 95 1 85 ga and a non linear hf isotope age array for nearly 2 gyr indicating episodic crustal generation and reworking through time the lower crustal xenoliths record a change in zircon o isotope compositions from a restricted range at 3 8 2 6 ga to more variable after 2 5 ga both heavier 18o up to 10 25 and lighter 18o low to 2 16 o isotope compositions than the normal mantle are observed in 2 5 ga magmatic zircons the secular change in zircon o isotopes documents an increase in recycling rate of surface derived materials including high 18o sediments weathered and altered rocks and low 18o altered oceanic crust into magma sources at the end of archean which in turn is possibly linked to modern style subduction processes and maturation of the crust at that time

north atlantic oscillation dynamics recorded in shells of a long lived bivalve mollusk existing reconstructions of the winter north atlantic oscillation wnao are based on terrestrial proxies and historical documents no direct high resolution long term rec ords from marine settings are available for this major climate dictating phenomenon which severely affects a variety of economic aspects of our society here we present a 245 yr proxy wnao index based on shells of the long lived marine bivalve mollusk arctica islandica variations in annual rates of shell growth are positively correlated with wnao related changes in the food supply maximum amplitudes in frequency bands of 7 9 and 5 7 yr fall exactly within the range of instrumental and other proxy wnao indices these estimates were obtained for specimens collected live 2000 km apart in the central north sea and on the norwegian shelf hence the wnao influences hydrographic regimes of large regions of the ocean our study demonstrates that a islandica can reliably reconstruct wnao dynamics for time intervals and regions without instrumental records our new tool functions as a proxy for the wnao index prior to the twentieth century greenhouse forcing and has the potential to further validate other proxy based wnao records

a lithologic control on active meandering in bedrock channels topographic evidence requires that some rivers actively meander in bedrock yet the way in which rivers can erode laterally and meander within bedrock banks is not well understood lateral channel migration and especially lateral channel migration via active bedrock meandering is commonly responsible for the preservation of unpaired strath terraces a process level understanding of lateral channel migration and active meandering in bedrock rivers is key to interpreting the climatic and tectonic significance of unpaired strath terraces and the planform shape of bedrock rivers in this study we compare erosional processes in two adjacent bedrock channels in the santa cruz mountains california the main differences between these channels are that pescadero creek actively meanders within mudstone while butano creek is straight and incises sandstone laboratory rock strength and slake durability tests show that while the two lithologies have similar tensile strengths before drying the meander supporting mudstone loses strength dramatically when dried and rewet slakes while the sandstone does not the slaked mudstone bank rock was easily detached without the need for bed load tools during in situ erosion tests while mudstone that had not dried and sandstone were not detachable the depth of bank rock detached solely from rewetting of previously dried mudstone ranges between 1 and 8 mm which is well in excess of annual background erosion in the santa cruz mountains in addition hand samples of the mudstone rapidly disintegrated upon wetting and drying in the laboratory whereas sandstone hand samples remained intact in the meandering stream there is a consistent pattern of scoured bedrock exposed to drying and slaking along the outside cutbank of meander bends and forced bars that grade into soil and vegetation which protect the bedrock from slaking along the inside of bends additionally in the meandering stream subaerially exposed mudstone clasts are often found to be disintegrating on the surface of bars taken together these observations suggest that slaking allows for bedrock meandering in two fundamental ways first by rapidly disintegrating coarse hillslope derived sediment that is deposited in the channel slaking suppresses the negative feedback on lateral channel migration that would otherwise result from the buildup of talus along a retreating bedrock valley wall on the outside of a meander bend second at cutbanks where scour exposes bare bedrock to drying slaking weakens a layer of bank rock to the point where it can be eroded by clear water flows in these ways slaking enables erosion into bedrock banks in response to curvature driven fluid shear stress perturbations as in alluvial rivers

proterozoic onset of crustal reworking and collisional tectonics reappraisal of the zircon oxygen isotope record a global u pb and 18o zircon database shows temporal changes in the magmatic record related to changes in the degree of crustal reworking the 18o composition of bulk sediment remains relatively constant through geologic time with a mean value of 14 9 in contrast the 18o values in magmatic zircons vary from relatively low values averaging 6 in the archean to increasingly higher and scattered values defining a series of peaks and troughs in post archean data the degree of crustal reworking increases at times of supercontinent assembly therefore we attribute the pattern of post archean 18o values recorded by magmatic zircons to a significant increase in the incorporation of high 18o sediment in response to enhanced crustal thickening and reworking associated with the onset of collisional tectonics especially during formation of supercontinents