neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

extension controls quaternary tectonics geomorphology and sedimentation of the n appennies foothills and adjacent po plain italy abstract in the middle pleistocene thrusting in the n apennine fold and thrust belt came to an end and foredeep sedimentation in the adjacent po plain basin ceased a new tectono sedimentary regime was installed extensional faults were activated in the foothills and are limited to the northeast by a major sw dipping normal fault the bologna fault for which a vertical displacement of 1000 m is estimated the region northeast of the fault i e its footwall was progressively tilted towards the po plain the sw sectors of the tilting region were progressively uplifted above sea level subjected to erosion thereby feeding a deltaic system which prograded towards the northeast in the subsiding regions compressional structures without major deformation are recorded in the zone of maximum curvature all these features are explained by the onset of extensional deformation along the bologna fault and consequent flexural unloading of its footwall the evidence therefore shows that the transition region between the n apennine foothills and po plain has been under a tensional stress regime since the middle pleistocene

kaolinitic paleosols in the south west of the iberian peninsula sierra morena region spain paleoenvironmental implications abstract this paper studies the physical and chemical characteristics of eight different soil profiles with paleohorizons rich in kaolinites and developed on different lithologies along the southern border of the hercinian iberian peninsula sierra morena region the paleohorizons of four of these soils are defined by low ph levels desaturation of the exchange complex and proportions of kaolinite of over 75 these characteristics are associated with subtropical pedogenic conditions during the pliocene period a further two soil profiles are contemporary and defined by the following features they occupy depression areas the clay fraction is dominated by kaolinites and smectites the exchange complex is saturated and the ph is above neutral values the last two soil profiles are developed on pliocene continental deposits and have more moderate pedogenic features their kaolinite levels are around 50 and their evolution is associated with shorter periods of exposure to these subtropical alteration conditions

pliocene lower pleistocene chronostratigraphy a re evaluation of mediterranean type sections the pliocene pleistocene stages defined for the mediterranean region are generally used as the standard chronostratigraphic units for the upper neogene and quaternary the recently developed calcareous plankton bio chronology based on results from ocean drilling program leg 107 and numerous outcrop sections provides the necessary time control for evaluating the ages and stratigraphic relationships for the various pliocene pleistocene stages and their associated stratotypes our results indicate that the currently accepted stratotypes do not provide a continuous stratigraphic representation for all of pliocene early pleistocene time on the basis of these findings we propose a revised chronostratigraphic scheme for this time period a tripartite subdivision is proposed for the pliocene series the zanclean stage is retained for the lower pliocene representing the interval from the miocene pliocene boundary ca 4 93 ma to ca 3 5 ma the middle pliocene is represented by the piacenzian stage and it incorporates strata deposited from ca 3 5 to 2 5 ma none of the currently used pliocene stages fully represents the upper pliocene ca 2 5 to 1 6 ma as a result late pliocene time lacks an adequately defined chronostratigraphic unit the selinuntian stage appears to be the most appropriate stage for the lower pleistocene ca 1 6 to 0 8 ma it can be divided into three stratigraphically continuous substages santernian emilian and sicilian the calabrian stage which is commonly used to designate the lowest part of the pleistocene should be abandoned because its stratotype does not include a record of the first 500 000 yr of pleistocene time

a genetic model of hydrocarbon derived carbonate chimneys in shelfal fine grained sediments the enza river field northern apennines italy abstract methane derived authigenic carbonate mdac concretions have been recently exposed in the pleistocene argille azzurre fm outcropping along the enza riverbanks northern apennines foothills italy the relations between the sediment deposition the coeval tectonic deformation and the mdac concretions have been investigated to unravel the mechanism of methane migration through the sediments and the processes leading to mdac occurrence the biogenic methane responsible for the formation of mdac chimneys and slabs has been generated in the organic rich pliocene sediments located in the po plain subsurface the gas migrated up dip towards the northern apennines foothills the mdac cements are mainly composed of dolomite whose precipitation requires thousand years and the absence of so 4 in the pore fluids according with the sedimentation rates of the mdac hosting pleistocene succession the sulphate methane transition zone migrated upwards faster than time required for dolomite precipitation therefore the connate water migrating together with the methane could have acted as second dic source allowing the mdac formation also in the methane rich zone

neoproterozoic paleozoic and mesozoic granitoid magmatism in the qinling orogen china constraints on orogenic process abstract the qinling orogen is one of the main orogenic belts in asia and is characterized by multi stage orogenic processes and the development of voluminous magmatic intrusions the results of zircon u pb dating indicate that granitoid magmatism in the qinling orogen mainly occurred in four distinct periods the neoproterozoic 979 711 ma paleozoic 507 400 ma and early 252 185 ma and late 158 100 ma mesozoic the neoproterozoic granitic magmatism in the qinling orogen is represented by strongly deformed s type granites emplaced at 979 911 ma weakly deformed i type granites at 894 815 ma and a type granites at 759 711 ma they can be interpreted as the products of respectively syn collisional post collisional and extensional setting in response to the assembly and breakup of the rodinia supercontinent the paleozoic magmatism can be temporally classified into three stages of 507 470 ma 460 422 ma and 415 400 ma they were genetically related to the subduction of the shangdan ocean and subsequent collision of the southern north china block and the south qinling belt the 507 470 ma magmatism is spatially and temporally related to ultrahigh pressure metamorphism in the studied area the 460 422 ma magmatism with an extensive development in the north qinling belt is characterized by i type granitoids and originated from the lower crust with the involvement of mantle derived magma in a collisional setting the magmatism with the formation age of 415 400 ma only occurred in the middle part of the north qinling belt and is dominated by i type granitoid intrusions and probably formed in the late stage of a collisional setting early mesozoic magmatism in the study area occurred between 252 and 185 ma with the cluster in 225 200 ma it took place predominantly in the western part of the south qinling belt the 250 240 ma i type granitoids are of small volume and show high sr y ratios and may have been formed in a continental arc setting related to subduction of the mianlue ocean between the south qinling belt and the south china block voluminous late stage 225 185 ma magmatism evolved from early i type to later i a type granitoids associated with contemporaneous lamprophyres representative of a transition from syn to post collisional setting in response to the collision between the north china and the south china blocks late mesozoic 158 100 ma granitoids located in the southern margin of the north china block and the eastern part of the north qinling belt are characterized by i type i to a type and a type granitoids that were emplaced in a post orogenic or intraplate setting the first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process these suggest that the tectonic evolution of the qinling orogen is very complicated

carbonate platform growth and demise offshore central vietnam effects of early miocene transgression and subsequent onshore uplift abstract miocene carbonate platforms cover a large part of the central vietnamese south china sea margin early carbonate deposition took place on two regional platforms separated by a narrow depression developed along the trace of the east vietnam boundary fault zone west of the east vietnam boundary fault zone the tuy hoa carbonate platform fringes the continental margin between da nang and nha trang here platform growth initiated during the early miocene and continued until middle miocene time when regional uplift led to subaerial exposure termination of platform growth and karstification east of the fault zone the triton carbonate platform was also initiated during the early miocene carbonate growth thrived during early and part of middle miocene time and a thick clean lower and middle miocene carbonate succession cover the triton horst and the qui nhon ridge during the middle miocene partial drowning resulted in the split up of the triton carbonate platform repeated partial drowning events throughout the middle and late miocene resulted in westwards retreat of platform growth and eventual platform drowning and termination of carbonate deposition modern carbonate growth continues on isolated platforms hosting the paracel islands farther seawards the onset of widespread carbonate deposition largely reflects the early miocene transgression of the area linked with early post rift subsidence and the opening of the south china sea the mid neogene shift in carbonate deposition is interpreted as a consequence of regional uplift and denudation of central and south indochina starting during middle miocene time when the tuy hoa carbonate platform became subaerially exposed stressed carbonate growth conditions on the triton carbonate platform probably resulted from increased inorganic nutrient input derived from the uplifted mainland possibly enhanced by deteriorated climatic conditions and rapid sea level fluctuations promoting platform drowning

revision of the plio pleistocene cycles and their application to sequence stratigraphy and shelf and slope sediments in the gulf of mexico abstract the ages cycles and correlation of the pliocene and pleistocene have been discussed and argued for decades the revision of the pliocene pleistocene sequence chronostratigraphy presented in this paper is based on data obtained from more than 100 wells in the south additions and deepwater areas offshore louisiana and texas gulf of mexico the high resolution biostratigraphic data combined with well log sequence stratigraphic interpretations and correlations of the seismic record sections through a two way time log or synthetic seismogram permits the pliocene and pleistocene series to be divided into 14 fourth order sequences and seven third order sequences we have discussed and illustrated the most important events that have led up to this detailed revision of the plio pleistocene this documentation is very important because most of these papers have been published in journals that have not been readily available to most geologists and geophysicists

neoproterozoic tectonic evolution of south qinling china evidence from zircon ages and geochemistry of the yaolinghe volcanic rocks abstract the south qinling terrain is located at the northern margin of the yangtze block neoproterozoic volcanic sedimentary sequences of the yaolinghe group play the most significant role in studying the tectono magmatic evolution of the south qinling based on temporal and spatial geochemical variations the yaolinghe group can be divided into three volcanic cycles basaltic lavas of cycle 1 crystallized at 847 8 ma and exhibit typical island arc basalt characteristics with enrichment of liles th u and lrees depletion of hfses nb ta zr hf ti and homogeneous initial 143nd 144nd ratios ranging from 0 51162 to 0 51172 corresponding to initial nd values of 1 6 to 3 5 these features suggest that they were derived from a depleted mantle source during a subduction period volcanic rocks of cycle 2 show a complete lithological evolution from basalt through andesite to rhyolite without a significant gap of sio2 content they formed between 731 11 ma and 768 7 ma and display trace element signatures similar to arc volcanics with positive lile and negative hfse anomalies these basalts have lower initial 87sr 86sr ratios from 0 7030 to 0 7052 and higher initial 143nd 144nd ratios from 0 51172 to 0 51194 with positive initial nd values ranging from 0 9 to 5 3 whereas intercalated felsic rocks show lower initial 143nd 144nd ratios from 0 51150 to 0 51177 with initial nd values varying from 4 5 to 1 9 suggestive of metasomatic alteration of lithospheric mantle by slab derived fluids melts cycle 3 lavas show undepleted hfses nb ta zr hf and slightly enriched liles th u and ti concentrations they were generated in a rift related setting between 680 ma and 650 ma geochronological and geochemical evidence from lavas of the yaolinghe group suggest that the panxi hannan arc system extended to northern south qinling and the magmatism in the northern margin of the yangtze block evolved from arc to rift magmatism during the neoproterozoic

pliocene sequence stratigraphy climatic trends and sapropel formation in the northern apennines italy abstract the pliocene stratigraphy of the romagna northern apennines foredeep has been reconstructed through mapping and measuring the different lithostratigraphic units the physically correlated sedimentary bodies have been chronologically calibrated through biostratigraphic analyses analysis of facies and fossil content allowed reconstructing the main depositional systems and their evolution the co occurrence of shallow to deep water environments and carbonate to siliciclastic systems allowed understanding fully the role of eustasy and climate vs continuous tectonic deformation controlling the accommodation and basin morphology following a limited sea level lowering at 4 2 ma associated with the first signal of cooling in the early pliocene a fast growing subtropical type carbonate platform developed in response to warm and oligotrophic surface waters furthermore a significant drop in sea level at 3 75 ma points to an important pliocene continental glaciation in the northern hemisphere during the subsequent transgression warm and possibly humid climate favoured the deposition of the first pliocene sapropel around 3 3 ma the growth of a second generation of carbonate platform between 3 3 and 3 042 ma suggests a renewed warm period and limited runoff at the top of this highstand thick sapropels developed which can easily be correlated across the mediterranean the platform abruptly drowned was overwhelmed by bio erosion and was covered by iron phosphate crusts whereas in the adjacent basins numerous sapropel layers occurred rich of biosiliceous forms documenting the shift from ccarb to corg deposition strong oscillations of climate due to precessionally controlled seasonality and increased precipitation and runoff are considered as the main causes of the increase of surface water fertility after the 2 87 ma sea level drop again very significant the sapropel rapidly disappears in conjunction to the development of the lowstand wedge after this cold period which ended around 2 6 ma carbonate platforms never recovered due to the enduring cooler surface waters and the onset of an active drainage on the apenninic range this study documents the role of the eustatic variations on the pliocene deposition of the actively deforming northern apennines foredeep the abrupt lithostratigraphic changes appear also controlled by palaeoproductivity variations associated with climate and runoff

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

a short term cooling event 4 205 million years ago in the ptolemais basin northern greece abstract a distinct clay rich layer in the otherwise regular succession of alternating lignites and marls of the early pliocene ptolemais formation reveals an equally distinct palynomorph assemblage only in this layer fresh water dinoflagellate cysts spiniferites cruciformis and gonyaulax apiculata are encountered these co occurring dinoflagellate species may be taken to indicate that surface water temperatures must have been remarkably low for early pliocene mid latitudes contrasting other indications that overall warm humid climates prevailed at this time a multi component study of this so called dinolayer with an astrochronologically derived age of 4 205 0 01 ma was undertaken to further investigate the apparently contrasting climatic signals integrated sedimentological micropaleontological palynological and geochemical data indicate that the dinolayer was deposited in a shallow fresh water lake the pollen record points to slightly cooler conditions during deposition of the dinolayer in comparison with conditions just below and above an anomalously low winter temperature is proposed as a possible cause for the recorded phenomena

3 d architecture and plio quaternary evolution of the paola basin insights into the forearc of the tyrrhenian ionian subduction system

compositional polarity of triassic granitoids in the qinling orogen china implication for termination of the northernmost paleo tethys abstract the qinling orogen was formed from the closure of the northernmost paleo tethys sea and the tectonic suturing of the yangtze and north china cratons the timing of this collision and the tectonic framework are debated the widely developed triassic granitoids in the western qinling orogen offer a key to understand the tectonic evolution of this region here we compile the geological geochemical and geochronological data of the triassic granitoids from the qingling orogen and conclude that the granitoids north of the mian lue suture were emplaced in an active continental margin related to the northward subduction of the mian lue oceanic plate during 248 200 ma the granitoids can be classified into i and s types with the former constituting the major variety northward from the mian lue fault an s type granite belt appears followed by and locally overlapping with an i type granite belt the i type granite belt can be subdivided into four sub belts from south to north with increasing contents of k2o k2o na2o sio2 th and u and the ratios of k2o na2o rb sr and 87sr 86sr i but decreasing contents of na2o al2o3 mg and ehf t except for the northernmost belt which occurs in the huaxiong block of the north china craton this geochemical polarity of i type granitoids and the zoned distribution of s and i types granitoids cannot be explained through continental collision orogeny including syn to post collision but can be well interpreted by considering the progressive subduction of the northernmost branch of the paleo tethys as represented by the mian lue ocean thus the termination of the northernmost paleo tethys and the onset of the continental collision between the yangtze and the north china plates are considered to have occurred at about 200 ma during the transition from triassic to jurassic our model is also supported by the available data from other studies and provides a revised framework for the timing and tectonics of assembly of the yangtze and the north china cratons

middle pliocene sea surface temperatures a global reconstruction identification and analyses of pliocene marine microfossils from 64 globally distributed stratigraphic sequences have been used to produce a middle pliocene sea surface temperature reconstruction of the earth this reconstruction shows little or no change from current conditions in low latitude regions and significant warming of the ocean surface at mid and higher latitudes of both hemispheres this pattern of warming is consistent with terrestrial records and suggests a combination of enhanced meridional ocean heat transport and enhanced greenhouse effect were responsible for the middle pliocene warmth

source diagenesis and fluxes of particulate organic carbon along the western adriatic sea mediterranean sea article i nfo in this study we investigated the modern organic carbon oc cycling along the clinoform shaped deposit that developed after the attainment of the modern sea level in the adriatic sea 5 5 kyr cal bp newly acquired data were combined with published results to characterize the i origin ii diagenesis and iii fluxes of oc along the adriatic clinoform 13 c 14 c and lignin phenols were used to constrain the composition of oc accumulating in surface sediments sediment cores collected at different water depths were used to describe the early diagenesis during burial in different regions in addition on the basis of an extensive number of accumulation rates and oc data we assessed the flux of oc to the seabed and its burial our results showed that terrigenous oc is the dominant oc source in the po prodelta mainly in the form of pre aged soil derived oc and vascular plant fragments along the clinoform both 14c and the concentration of lignin derived phenols decreased with increasing distance from the po prodelta indicating the influence of an additional pool of aged oc that gradually becomes more important because of its selective preservation during the sediment transport as a result degradation rates k decreased along the clinoform as a function of the sediment oxidative history the calculated half life of reactive oc t1 2 was 14 6 yrs in the po prodelta whereas topset forest deposits south of this region exhibited higher values 100 yrs indicating the presence of refractory material in the distal bottomset region the t1 2 was particularly high ranging from 255 to 912 yrs because of the significant southward component of the sediment transport the oc deposition in the southern surface sediments exceeded the local oc input via rivers ratio deposition input 1 2 conversely the northern adriatic was characterized by a marked imbalance ratio deposition input 0 3 0 5 according to our calculations the oc flux to the seabed along the clinoform was 309 gg of c per year whereas the oc burial was 180 gg of c per year corresponding to an overall burial efficiency of 59

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

role of sea level forced sedimentary processes on the distribution of organic carbon rich marine sediments a review of the late quaternary sapropels in the mediterranean sea abstract the 124 ka to present sapropel s5 s1 series in the eastern mediterranean sea correspond to the last glacial interglacial period and permit detailed investigation of 5th order sedimentary frequencies the sapropel layers are clustered in high frequency milankovian cycle that occur within sequence stratigraphic 4th order cycles of late pleistocene holocene sea level oscillations the sea level changes had an amplitude exceeding 120 m and have been correlated to the glacial interglacial cycles modulated by the 100 ka eccentricity using published data we examined occurrences of the complete s5 s1 series in the mediterranean sea and then we focussed on two stratigraphic sequences in the central adriatic shelf and middle adriatic depression where sapropels s5 and s1 were deposited during periods of sea level rise recorded by the transgressive systems tract marine isotopic stage 5 and 1 respectively sapropels s4 and s3 were deposited during the highstand systems tract that developed throughout mis 5 of the late pleistocene sequence sapropel s2 should have been deposited during the warm mis 3 3 and followed the mis 4 sea level drop when sediment supply was enhanced during the late highstand and falling stage of sea level of the late pleistocene sequence the pronounced mis 2 cold stage led to a lowstand and to the regional erosional surface sequence boundary we also compared the adriatic sapropel s5 s2 sequence 4th order to the mid pliocene cluster o sequence 3rd order in both cases sapropels are well formed before the increase of sediment supply due to progradation of the shelf wedge that occurs in the late high stand and initial falling stage in sea level finally we considered the influence of sea level lowering which could cause a weakening of north adriatic deep water formation therefore influencing the mediterranean deep water circulation this condition would favour oxygen depletion but it does not correspond to a well developed sapropel as in the case of s2 based on the assumption that productivity increases related to insolation play a dominant role in their sedimentation sapropel s2 is the result of low amplitude insolation maxima that were unable to generate a productivity increase leading to the burial of conspicuous amount of organic matter therefore in the adriatic sea the absence of the s2 sapropel is correlated to the high sedimentation rate diluting the signal whereas in the eastern mediterranean basin this sapropel is virtually absent because of a weak orbital forcing combined with oxidation that erased its record

productivity generated annual laminae in mid pliocene sapropels deposited during precessionally forced periods of warmer mediterranean climate abstract paleoproductivity estimates for a sequence of five mid pliocene mediterranean sapropels illustrate the importance of insolation maxima in enhancing organic carbon accumulation well laminated sapropelitic intervals in the northern apennines have been studied by a combination of sedimentological and micropaleontological analysis detailed electron microscope description bulk chemical composition carbon isotopic composition and elemental ratios each sapropel formed during precessional minima lasted 7 5 to 10 kyr which is the same duration calculated for coeval counterparts in odp sites in the eastern mediterranean the organic carbon mass accumulation rates of the studied sapropels show the same values of those calculated in the coeval mediterranean sapropels suggesting that the same productivity conditions were controlling sapropel formation in the whole mediterranean despite the differences in depositional setting and the strong variations in sedimentation rate mat forming diatoms play an important role in increasing the settling velocity allowing rapid sinking of organic matter and preventing bacterial remineralization in the water column the consequent partial oxygen depletion at the seafloor increases preservation which is therefore considered an effect rather than a cause of the organic carbon accumulation

u pb and lu hf isotopes in detrital zircon from neoproterozoic sedimentary rocks in the northern yangtze block implications for precambrian crustal evolution abstract a combined study of lu hf isotopes and u pb ages for detrital zircons from sedimentary rocks can provide information on the crustal evolution of sedimentary provenances and comparisons with potential source regions can constrain interpretations of paleogeographic settings detailed isotopic data on detrital zircons from neoproterozoic sedimentary rocks in the northern part of the yangtze block suggest that these rocks have the maximum depositional ages of 750 ma and share a similar provenance in their source area units of late archean 2 45 to 2 55 ga to paleoproterozoic 1 9 to 2 0 ga u pb ages made up the basement and were overlain or intruded by magmatic rocks of neoproterozoic u pb ages 740 to 900 ma hf isotopic signatures of the detrital zircons indicate that a little juvenile crust formed in the neoarchean reworking of old crust dominates the magmatic activity during the archean to paleoproterozoic while the most significant juvenile addition to the crust occurred in the neoproterozoic only the neoproterozoic zircon u pb ages can be matched with known magmatism in the northern yangtze block while other age peaks cannot be correlated with known provenance areas similar zircon u pb ages have been obtained previously from sediments along the southeastern and western margins of the yangtze block thus it is suggested that an unexposed old basement is widespread beneath the yangtze block and was the major contributor to the neoproterozoic sediments this basement had a magmatic activity at 2 5 ga similar to that in north china but zircon hf isotopes suggest significant differences in the overall evolutionary histories between the yangtze and north china

magnetic stratigraphy and biostratigraphy of pliocene argille azzurre northern apennines italy abstract an integrated biomanetostratigraphic chronology for the mediterranean pliocene has been developed in the last five years mainly from land sections in southern italy calabria and sicily and odp leg 107 tyrrhenian sea cores in this paper the chronology is applied to terrigenous sediments from the northern apennine foredeep where reworking as well as sedimentation rate and facies variations limit the resolution of biostratigraphy and physical stratigraphy the integrated chronology gives improved stratigraphic control for a messinian to upper pliocene section exposed on the banks of the stirone near parma northern italy and for a short lower pliocene section located nearby at sant andrea bagni the sections are in the vicinity of stratotype sections for the tabianian lower pliocene and piacenzian upper pliocene and the chronology gives new insights into the complex pliocene sedimentation history in the northern apennine foredeep at this time at the stirone section the base of the pliocene record is in a normal polarity chronm correlated to the thvera subchron indicating a hiatus at the miocene pliocene boundary and the absence of the mpl1 foraminiferal zone at sant andrea bagni mpl1 is also missing in contrast to previous reports we conclude that this biozone is probably absent throughout the northern apennines where post messinian flooding appears to have occurred at the onset of mpl2 time during the gilbert chron sedimentation rates at stirone reached 104 cm kyr as nearly 300 m of argille azzurre blue clay were deposited in less than 0 5 myr very sporadic sedimentation is apparent from the late nunivak to the top of the section late gauss chron with a number of hiatuses being recognized within chron 2ar late gilbert and in the early gauss this interruption of sedimentation at about 4 1 ma is associated with a widely recognized early pliocene tectonic event involving thrusting and migration of the depocenter of the northern apennine foredeep

metallogeny during continental outgrowth in the columbia supercontinent isotopic characterization of the zhaiwa mo cu system in the north china craton abstract the eastern qinling molybdenum belt eqmb in central china represents the largest mo province in the world located at the southern margin of the north china craton this mo province is largely associated with mesozoic granitoids here we report re os isochron age of 1761 33 ma 2 mswd 2 9 from molybdenite in the recently discovered zhaiwa porphyry mo cu system within the eqmb this age coincides with the peak eruption period 1 78 1 75 ga of the xiong er group volcanic rocks which unconformably overlie the taihua supergroup and are interpreted to have developed on a continental arc the re concentrations 1 to 43 ppm of the zhaiwa molybdenites are similar to those of typical porphyry cu mo au systems developed on continental arcs the 34 s values of the zhaiwa ores 2 7 7 3 average 5 2 suggest that the sulfur was mainly sourced from a magmatic system the sulfides from the ores yield sr i average of 0 70533 similar to that of the xiong er group 0 70547 albeit higher than that of the kuanping group 0 70334 and lower than the taihua supergroup 0 70763 suggesting a mixed source the average e nd 1 76 ga of the sulfides from the ores 0 9 falls between the averages of the taihua supergroup ca 6 8 and the kuanping group ca 7 4 the pb isotope ratios of the ores are similar to but slightly higher than those of the taihua supergroup reflecting preferential leaching of radiogenic pb from the taihua supergroup by magmatic fluids integrated data and interpretations constrain the zhaiwa mo cu deposit to be a porphyry mineral system developed within a ca 1 76 ga continental arc related to oceanic plate subduction beneath the southern margin of the north china craton a correlation between tectonic settings and metallogenic types clearly indicate that the xiong er group was formed in a volcanic arc confirming paleo mesoproterozoic continental outgrowth along the margins of the columbia supercontinent the isotopic characterization of the zhaiwa deposit provides new insights into the enigma of the widespread distribution of large and super large mo deposits of eqmb along the southern margin of the north china craton

triassic mineralization with cretaceous overprint in the dahu au mo deposit xiaoqinling gold province constraints from shrimp monazite u th pb geochronology abstract the xiaoqinling terrane in central china is the second largest gold producing area in china previous application of age constraints has yielded ages for the gold mineralization ranging from paleoproterozoic through triassic indosinian to jurassic and cretaceous yanshanian shrimp u th pb dating of hydrothermal monazite in a mo mineralized quartz vein from the dahu au mo deposit in the northern xiaoqinling terrane identifies two mineralization episodes hydrothermal monazite intergrown with molybdenite yields an initial precipitation age of 216 5 ma which is identical to but more precise than the molybdenite re os isochron age of 218 41 ma a younger generation of monazite is distinguished by data falling on a mixing array it is inferred that the younger monazite was formed at the expense of the older ones during the yanshanian probably during a single event that occurred at 125 ma combining these results with available geochronological data and geological evidence we conclude that molybdenum mineralization accompanied by monazite deposition took place in the indosinian followed by a yanshanian tectono hydrothermal event that resulted in large scale gold mineralization in the xiaoqinling terrane our observation demonstrates that monazite is sensitive to hydrothermal overprint and thus is useful for dating fluid infiltration event

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

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

timing of the yuchiling giant porphyry mo system and implications for ore genesis the yuchiling mo deposit is a recently discovered giant porphyry system in the east qinling mo belt china its apparent causative intrusion i e the yuchiling granite porphyry is the youngest intrusion phase 4 of the heyu multiphase granite batholith which was emplaced between 143 and 135 ma new robust constraints on the formation of the yuchiling porphyry mo system are provided by combined zircon u pb biotite 40ar 39ar and molybdenite re os dating zircon grains from the mo mineralized granite porphyry yield weighted 206pb 238u age of 134 0 1 4 ma n 19 2 error mswd 0 30 magmatic biotite from the same sample yield a 40ar 39ar plateau age of 135 1 1 4 ma 2 error and an inverse isochron age of 135 6 2 0 ma n 7 2 error mswd 10 8 which are effectively coincident with the zircon u pb age within analytical error three pulses of mineralization can be deduced from the molybdenite re os ages namely 141 137 and 134 ma which agree well with the zircon u pb ages of granitic phases 1 2 and the yuchiling porphyry phase 4 respectively these well constrained temporal correlations indicate that mo mineralization was caused by pulses of granitic magmatism and that the ore forming magmatic hydrothermal activity responsible for the yuchiling porphyry mo system lasted about 8 ma the yuchiling mo deposit represents a unique style of porphyry mo system formed in a post collision setting and associated with f rich high k calc alkaline intrusions which differ from convergent margin associated porphyry mo deposits

pb sr nd isotope constraints on the fluid source of the dahu au mo deposit in qinling orogen central china and implication for triassic tectonic setting abstract the dahu au mo deposit is a structure controlled lode system occurring in the northern xiaoqinling terrane huaxiong block qinling orogen this paper reports a new sr nd pb isotope dataset obtained for ore sulfides and the hostrocks within the taihua supergroup in an attempt to constrain the source of the ore forming fluids from a new dimension 16 sulfide samples yield i sr ratios of 0 70470 0 71312 with an average of 0 70854 e nd t values between 13 5 and 18 1 with average of 15 1 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios of 17 033 17 285 15 358 15 438 and 37 307 37 582 with averages of 17 162 15 405 and 37 440 respectively 5 gneiss samples from the taihua supergroup yield i sr ratios of 0 70947 0 73201 averaging 0 72294 e nd t values of 20 0 to 31 1 averaging 25 1 and 206 pb 204 pb i 207 pb 204 pb i 208 pb 204 pb i ratios of 17 127 18 392 15 416 15 604 and 37 498 37 814 with averages of 17 547 15 470 and 37 616 respectively these data show that the ore sulfides have less radiogenic sr nd pb isotope systematics than the hostrocks and suggest that the ore forming fluids which interacted with the wallrocks to form ores must be sourced from a depleted mantle or a depleted subducted oceanic slab in combination with the spatial scenario and geochemical signatures of the triassic magmatites and mineral systems we argue that in the triassic the mianlue ocean was not completely closed and that the northward oceanic plate subduction still survived along the mian lue suture which caused the late triassic magmatism and associated mineralization in qinling orogen including the au mo dahu deposit

constraints on strike slip motion from seismic and gravity data along the vietnam margin offshore da nang implications for hydrocarbon prospectivity and opening of the east vietnam sea

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

paleoproterozoic positive δ13ccarb excursion in the northeastern sino korean craton evidence of the lomagundi event abstract the 2 33 2 06 ga positive 13 c carb excursion associated with environmental change and the breakup of the kenorland or superia supercontinent is called the lomagundi or jatulian event or great oxidation event and has been reported in many early precambrian cratons but not yet in the sino korean craton the guanmenshan formation of the liaohe group occurs in the northeastern part of the sino korean craton 13 c carb and 18 o values in 42 samples from this formation range from 3 5 5 9 v pdb and 15 4 24 8 v smow respectively showing a clear positive 13 c carb excursion that characterizes the lomagundi event thirty five of the 42 samples with less hydrothermal alteration have higher 13 c carb and 18 o carb values than the other 7 samples obviously affected by fluid flow confirming that it was fluid flow that reduced the 13 c carb and 18 o carb values this positive 13 c carb excursion places deposition of the guanmenshan formation within the age range of 2 33 2 06 ga

constraining the role of the qinling orogen in the assembly and break up of rodinia tectonic implications for neoproterozoic granite occurrences abstract new shrimp and id tims dating results in this study reveal that the widespread early neoproterozoic granites in the qinling orogen were emplaced mainly between 960 and 900 ma major elements mineral compositions and trace elements data also indicate that all these early neoproterozoic granites are characterized by the features of crust derived and typical continent continent syn collisional granites this imply that continent continent collisional event could have occurred in the qinling orogen during the period of 960 to 900 ma which was closely related to the formation of rodinia thus our study argues that the final assembly of rodina occurred at 900 ma on the other hand k feldspar granite dq05 a type granite and granodiorite dq07 from the study area are dated at 711 11 and 717 10 ma respectively and are considered to have generated in an extensional setting this extensional tectonic regime originated from 810 ma when large scale continental bimodal volcanic rocks were formed in south qinling and lasted at least until the time of 710 ma which is consistent with the break up of rodinia this study also suggests that the north china craton did not collide and join together with the south china craton in the neoproterozoic and both of them were probably far away from each other

u pb ages and lu hf isotopes of detrital zircons from the southern qinling orogen implications for precambrian to phanerozoic tectonics in central china abstract the qinling orogen central china was constructed during the mesozoic collision between the north china and yangtze continental plates the orogen includes four tectonic units from north to south the huaxiong block reactivated southern margin of the north china craton north qinling accretion belt south qinling fold belt or block and songpan fold belt evolved from the northernmost paleo tethys ocean separating the gondwana and laurentia supercontinents here we employ detrital zircons from the early cretaceous alluvial sediments within the qinling orogen to trace the tectonic evolution of the orogen the u pb ages of the detrital zircon grains from the early cretaceous donghe group sediments in the south qinling fold belt cluster around 2600 2300 ma 2050 1800 ma 1200 700 ma 650 400 ma and 350 200 ma corresponding to the global kenorland columbia rodinia gondwana and pangaea supercontinent events respectively the distributions of ages and ehf t values of zircon grains show that the donghe group sediments have a complex source comprising components mainly recycled from the north qinling accretion belt and the north china craton suggesting that the south qinling fold belt was a part of the united qinling north china continental plate rather than an isolated microcontinent during the devonian triassic the youngest age peak of 350 200 ma reflects the magmatic event related to subduction and termination of the mian lue oceanic plate followed by the collision between the yangtze craton and the united qinling north china continent that came into existence at the triassic jurassic transition the interval of 208 145 ma between the sedimentation of the early cretaceous donghe group and the youngest age of detrital zircons was coeval with the post subduction collision between the yangtze and the north china continental plates in jurassic

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

the mediterranean messinian salinity crisis an apennine foredeep perspective abstract owing to its expanded stratigraphic sections the apennine thrust belt offers the opportunity to better understand the evaporitic and post evaporitic messinian events a physical stratigraphic framework of messinian deposits based on facies analysis and basin wide correlation of key surfaces and sedimentary cycles is presented it is shown that the messinian apennine foredeep had marginal basins with shallow water primary evaporites and deeper basins where resedimented evaporites accumulated under relatively deep water conditions like many other mediterranean examples primary shallow water evaporites of apenninic marginal basins show evidence for subaerial exposure and erosion however the development of such an erosional surface does not correspond to the deposition of primary evaporites in the deepest part of the basin s here the unconformity can be traced towards the base of resedimented evaporites or to a level within them implying that the deeper basins of the apennine foredeep never underwent desiccation during the messinian salinity crisis but rather received the eroded marginal evaporites this fact usually overlooked raises important questions about the deep desiccation model of the mediterranean

carbonate deposition in restricted basins a pliocene case study from the central mediterranean northwestern apennines italy abstract carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness because of their significance in petroleum geology however spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic dominated or mixed carbonate siliciclastic systems pliocene successions of tuscany and the tyrrhenian shelf northern apennines italy record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation this study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves analyses of the extension composition facies and sequence stratigraphic architecture of the studied piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data which document the slightly diachronous development of the carbonates within mediterranean planktonic foraminifera subzones mpl4b and mpl5a and magnetic polarity chron c2an the carbonate units are part of a regionally defined tectonically controlled sequence and represent the first transgressive unit overlying the basal sequence boundary but are also found in the regressive portion of the sequence collectively the units document the establishment of a shallow marine carbonate factory dominated by calcareous red algae the larger benthic foraminifer amphistegina and heterozoan skeletal components along the margins of a complex archipelago like coastal domain a review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by a spatial discontinuity b an overall skeletal association consistent across separate basins but with local variability in dominant skeletal components c preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems d predominance of low to moderate energy facies e preferential onset of deposition during transgression with possible development of mixed carbonate siliciclastic facies and f differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins these observations built upon the study of mid piacenzian carbonate units from the central mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis

ree geochemistry of carbonates from the guanmenshan formation liaohe group ne sino korean craton implications for seawater compositional change during the great oxidation event abstract the worldwide 2 33 2 06 ga positive 13 c carb excursion has been correlated with the great oxidation event goe and termed as the lomagundi event the 2 3 1 85 ga guanmenshan formation in the liaohe group of the northeastern sino korean craton is characterized by positive 13 c carb excursion and is a potential candidate to evaluate the lomagundi event using rey rare earth element and yttrium ree y chemical fingerprints here we present major and trace element analysis of 42 samples from the guanmenshan formation which are pure marine chemical sediments and use the data to trace the seawater composition during 2 3 1 85 ga 15 least altered dolomicrite samples 600 m strata have ree values of 0 739 4 175 ppm 2 414 1 184 ppm and the y ho ratios of 34 5 56 6 44 1 5 7 they show uniform positive la sn la sn 1 04 0 27 and gd sn gd sn 1 64 0 40 anomalies and notable lree depletions indicated by nd sn yb sn values of 0 24 0 92 average 0 56 0 19 these features are consistent with the geochemistry of well oxygenated shallow ambient seawater and suggest that these samples provide a robust record of the primary rey signature of seawater during the lomagundi event the rey patterns of 15 silicified dolomites marbles locally with veinlets from the pb zn mining camps in the region with average eu cn eu cn 1 56 0 95 are identical to those of high temperature hydrothermal fluids 250 c characterized by a flat pattern and marked positive eu anomalies indicating that these rocks were subjected to metasomatism by hydrothermal fluids the guanmenshan formation shows average ce sn ce sn of 0 93 0 09 and sm cn yb cn of 1 which are higher than those of the archean 2 33 ga chemical sediments generally f o 2 and p co 2 the rey in the dolomicrite were mainly sourced from fluxes of solutes from terrestrial weathering and also from seafloor hydrothermal processes on a subordinate scale the guanmenshan dolomicrites have eu sn eu sn values of 1 34 2 55 i e around 1 53 indicating that they were deposited during 2 33 2 06 ga as the eu sn eu sn 1 53 can be used as a proxy for the 2 33 2 06 ga marine chemical sediments our study shows that the guanmenshan formation was formed at a critical turning point in earth history when the global atmosphere hydrosphere system witnessed a dramatic change from reducing to oxidizing conditions

detrital zircon u pb geochronological and lu hf isotopic constraints on the precambrian magmatic and crustal evolution of the western yangtze block sw china abstract in situ u pb geochronological and lu hf isotopic studies of detrital zircon from a variety of precambrian strata along the western margin of the yangtze block of south china show that the rocks have maximum depositional ages of ca 1000 740 ma all of the strata probably formed in a subduction related tectonic setting the kunyang group heishantou formation and huili group tongan formation have maximum depositional ages of 960 1000 ma and contain zircons whose ages are dominantly paleoproterozoic 2500 2300 1900 1700 and 1650 1500 ma the yanbian group has a zircon population ranging mainly from 860 to 1000 ma different from that of the bikou group with ages from 745 to 890 ma ages of zircons from the lieguliu and guanyinya formations range from 740 to 900 ma the paleoproterozoic detrital zircons commonly have negative or slightly positive hf values from 8 0 to 2 3 whereas most of the 1000 740 ma zircons have moderately to significantly high positive hf values from 0 3 to 13 0 the new detrital zircon u pb and lu hf isotopic dataset suggests four major episodes of magmatism in the region 2500 2300 1900 1700 1650 1500 and 1000 740 ma and the presence of widespread archean basement of the western yangtze block the data also suggest an important period of juvenile magmatism at 1000 740 ma our results favor a model in which continuous subduction 1000 740 ma along the western margin of the yangtze block lasted for 260 million years

fluid evolution of the yuchiling porphyry mo deposit east qinling china the yuchiling mo deposit east qinling china belongs to a typical porphyry mo system associated with high k calc alkaline intrusions the pure co2 pc co2 bearing c aqueous h2o naci w and

palinspastic restoration and paleogeographic reconstruction of the peri tyrrhenian area during the neogene abstract this paper presents the results of research carried out on the paleogeographic and geodynamic post collisional evolution of the peri tyrrhenian area from the southern alps to sicily during this post collisional evolution a back arc area thrust belt foredeep system developed in which the following tectono sedimentary zones can be distinguished from the external to the internal ones the foreland zone connected to the foredeep through a slope generally controlled by normal faults the foredeep an assymmetric depression with strong subsidence related to the compressional activity of the thrust zone the chain whose outward migration from the late oligocene onward was discontinuus with important stages of crisis partially connected to the mechanical response of different crustal thicknesses existing in the foreland the discontinuous satellite basins developed within the thrust belt the back arc basins developed in the inner part of the chain where the superposition of the extensional tectonics over previous compressional domains causes the fragmentation of the thrust belt leading to its destruction according to this model seven palinspatic maps are discussed regarding the following time intervals late oligocene 25 24 m y burdigalian 22 20 m y langhian 17 16 m y serravallin 15 13 m y tortonian 10 9 m y late messinian 5 5 5 3 m y and early pliocene 5 3 4 6 m y during five of these time intervals significant geodynamic modifications occurred in the whole peri tyrrhenian area leading to paleogeographic changes in any case the geodynamic evolution of the whole area seems clearly controlled by the activity of important bundles of tectonic lines transversal to the chain which in the same time interval in the outermost part of the thrust belt separated areas with different values of shortening and in tthe most internal zones separated segments having different amount of extension these tectonic lines certainly have a crustal significance and have probably acted along previous formed discontinuities

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

u pb dating of baddeleyite and zircon from the shizhaigou diorite in the southern margin of north china craton constrains on the timing and tectonic setting of the paleoproterozoic xiong er group abstract the xiong er volcanism marks an important thermal event in the southern margin of the north china craton during the paleoproterozoic precise u pb ages of zircon and baddeleyite from the shizhaigou diorite which intruded the majiahe formation of the upper part of the xiong er group were determined in this study by multi collector sims the mean 207 pb 206 pb ages are 1789 3 5 ma for baddeleyite and 1780 11 ma for zircon from shizhaigou diorite respectively the major and trace elements and sr nd isotopic compositions indicate an em i mantle type signature and crustal contamination features combining with previous chronological data it is proposed that the age of the xiong er volcanism is between 1770 ma and 1800 ma with a peak at 1780 ma our result supports the view that the xiong er volcanic rocks formed in an extensional rift environment

zircon u pb ages and geochemistry of the wenquan mo bearing granitioids in west qinling china constraints on the geodynamic setting for the newly discovered wenquan mo deposit abstract east qinling is the largest porphyry molybdenum province in the world these mo deposits have been well documented in west qinling however few mo deposits have been discovered although granitic rocks are widespread recently the wenquan porphyry mo deposit has been discovered in gansu province which provides an insight into mo mineralization in west qinling in this paper we report pb isotope compositions for k feldspar and sulfides s isotope ratios for sulfides the results obtained from petrochemical study and from in situ la icp ms zircon u pb dating and hf isotopes the granitoids are enriched in lile and lree with ree and trace element patterns similar to continental crust suggesting a crustal origin the mg 40 05 to 56 34 and cr and ni contents are high indicating a source of refractory mafic lower crust the e hf t values of zircon grains from porphyritic monzogranite range from 2 9 to 0 6 and from granitic porphyry vary from 3 3 to 1 9 the zircons have t dm2 of 1014 to 1196 ma for the porphyritic monzogranite and 954 to 1224 ma for the granitic porphyry implying that these granitoids were likely derived from partial melting of a late mesoproterozoic juvenile lower crust the pb isotope compositions of the granitoids are similar to granites in south china showing that the magma was sourced from the middle lower crust in the southern qinling tectonic unit the pb isotopic contrast between the mo bearing granitoids and ores shows that the pb in the ore forming solution was derived from fractionation of a triassic magmatic system 34 s values of sulfides are between 5 02 and 5 66 similar to those associated with magmatic hydrothermal systems la icp ms zircon u pb dating yields crystallization ages of 216 2 1 7 and 217 2 2 0 ma for the granitoids consistent with a previously reported molybdenite re os isochron age of 214 4 7 1 ma this suggests that the mo mineralization is related to the late triassic magmatism in the west qinling orogenic belt in view of these geochemical results and known regional geology we propose that both granitoid emplacement and mo mineralization in the wenquan deposit resulted from the triassic collision between the south qinling and the south china block along the mianlue suture since triassic granitoid plutons commonly occur along the qinling orogenic belt the triassic wenquan mo bearing granitoids highlight the importance of the triassic tectono magmatic belt for mo exploration in order to apply this metallogenic model to the whole qinling orogen further study is needed to compare the wenquan deposit with other deposits

u pb zircon and sm nd isotopic study of the huangtuling granulite dabie sulu belt china implication for the paleoproterozoic tectonic history of the yangtze craton sims data demonstrate archean 2 9 to 2 7 ga and paleoproterozoic 1991 43 ma ages for rounded detrital zircon cores and unzoned rims respectively in a graulite sample collected from huangtuling dabie sulu orogenic belt china the granulite rocks in this locality have pelitic compositions and represent an exposure of the northern margin of the yangtze craton the rounded zircon cores show oscillatory zoning and have th u ratios 0 17 0 78 systematically higher than those of the unzoned luminescent rims 0 005 0 03 the age of the detrital zircon cores and whole rock nd isotope model age suggest that the huangtuling granulite was possibly derived from a provenance dominated by archean rocks similar to the kongling complex exposed 200 km in the southwest multiple phases of metamorphism have been identified for the granulites with the dominant granulite facies mineral assemblage defining an early clock wise metamorphic p t path orthopyroxene plagioclase and whole rock material define a linear trend in a 147sm 144nd 143nd 144nd diagram corresponding to an age of 1926 146 ma this result and the u pb data for the zircon rims suggest that a collisional event may have occurred along the northern margin of the yangtze craton at 2 0 ga inviting further study on whether the yangtze craton was involved in the assembly of the recently proposed paleo mesoproterozoic supercontinent columbia

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

chronostratigraphic distribution of cetaceans in the pliocene of northern apennines italy palaeoecological implications abstract a large number of cetacean fossils have been recovered through the time from the pliocene deposits in northern apennines thrust belt on both the padan adriatic and the tyrrhenian side in this work the cetaceans of castell arquato basin padan adriatic side have been placed within a high resolution chronostratigraphic framework available for this area this results in a better assessment of their evolutionary history and of the palaeoecologic factors controlling their diversity and abundance through the time our results document a greater diversity between 3 1 and 2 7 ma time interval likely due to the development of eutrophic conditions during precessionally driven insolation maxima at 400 ka eccentricity maxima which are recorded in deeper depositional settings by sapropel clusters eutrophic conditions kept a complex trophic chain as currently observed in the ligurian sea corsican ligurian provencal basin an area characterized also by upwelling a reduction in both number and ecological diversity of cetacean taxa is observed along the pliocene pleistocene transition this trend related to the onset of the quaternary icehouse conditions appears in good agreement with the recently recognized extinction event that affecting the marine megafauna at the end of the pliocene

shrimp and la icp ms zircon geochronology of the xiong er volcanic rocks implications for the paleo mesoproterozoic evolution of the southern margin of the north china craton the paleo mesoproterozoic xiong er volcanic rocks along the southern margin of the north china craton are lithologically and geochemically similar to those formed in subduction related continental margin volcanic arcs the volcanic rocks are primarily composed of basaltic andesites and andesites with minor dacites and dacitic rhyolites traditionally the xiong er volcanic rocks have been divided from lower to upper into the xushan jidanping and majiahe formations but the ages of volcanic rocks in these formations have not been well constrained which has hindered further understanding the tectonic significance of the xiong er volcanic belt at the southern margin of the north china craton shrimp and la icp ms u pb zircon analyses combined with cathodeluminescence cl images have enabled resolution of xenocrystic and magmatic zircons that can be directed toward determination of the ages of the xiong er volcanic rocks shrimp and la icp ms u pb analyses on magmatic zircons from two basaltic andesite samples one dacite sample and one rhyolite sample of the xushan formation known as the lowest sequence of the xiong er volcanic rocks indicate that the volcanic eruption of this formation occurred at 1 78 ga but most xenocrystic inherited zircons in these samples yielded 207pb 206pb ages ranging from 2 55 ga to 1 91 ga of three samples collected from the jidanping formation two rhyolite samples 05xe015 and 05xe100 yielded weighted mean 207pb 206pb ages of 1778 5 5 ma and 1751 14 ma respectively similar to the ages of the volcanic rocks in the xushan formation whereas one dacite sample 05xe066 gave a weighted mean 207 pb

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

sedimentary and biological response to sea level and palaeoceanographic changes of a lower middle jurassic tethyan platform margin southern alps italy abstract the sediment succession formed at the platform to basin transition along the western margin of a jurassic tethyan carbonate platform records a cyclicity in the order of 3 10 my these cycles are interpreted as due to sea level fluctuations associated to palaeoceanographic changes of the surface waters as inferred by the evolutionary dynamics of the calcareous nannofossils overimposed to these variations the skeletal composition of the platform succession records a longer term order of 50 my trend of progressive environmental deterioration related to the break up of pangea our case study deals with the venetian platform margin and the lombardian basin of the southern alps italy a lower to middle jurassic platform basin system of the western tethys four depositional sequences have been recognized in the lower to middle jurassic the local sea level curve derived from sequence analysis records a short lived on the venetian platform the skeletal sediment composition of the carbonate platform changed from sinemurian domerian photozoan to toarcian heterozoan assemblages dominated by suspension feeders this change appears due to increased trophic resources the older event of platform demise correlates to the sea level drop of the latest domerian the final drowning of the venetian platform occurred after the early aalenian drop in the sea level among the basin biota calcareous nannofossils represent the major pelagic carbonate producer since the beginning of the jurassic nevertheless the sinemurian bajocian deep sea carbonates of the lombardian basin consist mainly of allochthonous mud exported off platform with a low nannoplanktonic contribution moreover the platform demise correlates with condensation gaps and mass flows in the basin this relationship suggests that the growth history of the carbonate platform directly controlled the carbonate sedimentation in the adjacent basin the nannofloras recorded in the lower and middle jurassic successions of the lombardian basin consist of two different taxonomic groups the genus schizosphaerella a group of uncertain systematic affinity and several genera of coccolithophorids an inverse correlation between the abundance of schizospheres and coccoliths has been recorded throughout the whole interval investigated moreover during periods of platform and sea level fall schizosphaerella spp dropped in abundance whereas rates of coccolith diversification calculated according to roth s equations reached peak values our evidence shows that schizospheres could be oligotrophic forms while coccolithophorids on the contrary probably diversified during periods of increased nutrient resources the observed sea level falls are in phase with increased trophic resources and holds on up to the transgressive interval the biological response includes a dramatic drop of the platform carbonate productivity and increased corg accumulation on the sea floor the long term evolution of the sedimentary system records increasing eutrophication from liassic to dogger as reflected by the compositional changes of the carbonate producers

taxonomic diversity and stratigraphic distribution of mediterranean pliocene bivalves abstract the mollusc disappearance extinction events throughout the mediterranean pliocene suggest the definition of four faunistic units mediterranean pliocene molluscan units mpmus the bivalve taxonomic diversity the paleobiogeographic significance and the chronological classification of each unit are analyzed in detail the boundaries of the mpmus approximate the major climatic changes of the northern hemisphere respectively at 3 0 2 5 and 2 1 ma on the whole the molluscan fauna changes 356 species of shallow water bivalves have been considered record the transition from a tropical unit mpmu1 to a biogeographic unit mpmu4 comparable with that of the recent mediterranean

growth and reworking of the early precambrian continental crust in the north china craton constraints from zircon hf isotopes abstract we synthesize more than 2600 hf isotope data on the archean paleoproterozoic zircons from the north china craton ncc recalculation of the data based on single stage and two stage hf model ages of the eastern block of the ncc shows peak ages of 3902 13 ma and 3978 18 ma respectively and also small peaks at 3 5 4 0 ga the majority of zircon ehf t values are positive suggesting the possibility of the crust and the mantle differentiation at ca 3 9 4 0 ga in the eastern block of the ncc most magmatic zircons from the whole of ncc have their hf model age range of 2 4 2 9 ga and the single stage model ages is cluster at 2698 4 ma whereas the two stage model ages concentrate at 2714 5 ma implying that the protoliths were juvenile crustal rocks the most prominent peak at 2 7 ga indicates that this period marks the most important stage of the crust mantle differentiation and crust formation of the ncc the widespread 2 5 ga rocks in the ncc and the absence of the 2 5 ga peaks in hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2 5 ga furthermore the 2 5 1 7 ga zircon hf isotope features are also related to the reworking of the crustal rocks our results from the integration of a large database suggest that the eastern block and the trans north china orogen have undergone similar crust mantle differentiation and magmatism leading to the conclusion that the essential cratonization of the north china took place at the end of neoarchean

geochemistry and habitat of natural gases in po basin northern italy three types of natural gases can be distinguished in the po basin 1 bacterial gases dgr13cch4 60 ppt dgrdch4 180 to 200 ppt c2 0 2 which are found predominantly in pliocene pleistocene reservoirs 2 mixed gases dgr13cch4 60 to 50 ppt dgrdch4 180 to 200 ppt c2 0 2 to 5 which are predominantly in reservoirs of messinian upper miocene age but also in a few places in older and younger reservoirs 3 thermogenic gases dgr13c 50 ppt dgrd 200 to 150 ppt c2 5 which commonly are associated with oil and are produced predominantly from miocene and mesozoic reservoirs a quantitative assessment of gas in place for these three gas types is 1 80 2 10 and 3 10 respectively the areal distribution and amount of the three gas types are controlled strictly by geologic factors synsedimentary tectonics and turbidite sedimentation are the best conditions for the trapping of biogenic gas in the southeastern part of the area where 70 of the bacterial gas in place is produced here bacterially formed methane is produced from depths of up to 4 500 m 15 000 ft and is the deepest bacterial gas so far reported in the literature in the pedealpine homocline lower sedimentation rates and a weak deformation of pliocene pleistocene sediments prevented appreciable accumulations only 15 of the bacterial gas in the basin is produced in this area thermogenic gases are found in the vicinity of the apennines where strong tectonic movements have favored its migration from deeper mesozoic sources into tertiary reservoirs or into deep mesozoic carbonate reservoirs of the pedealpine homocline

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

geodynamic settings and tectonic model of skarn gold deposits in china an overview seventy skarn type gold deposits including 1 super large 19 large and 24 medium sized are known from different geotectonic units of china they contain a total resource of approximately 1000 t of gold 625 t in south china and account for 20 of china s gold reserves these skarn deposits are sited in collisional orogenic belts fault controlled magmatic belts and reactivated cratonic margins all of the chinese skarn gold provinces were affected by phanerozoic collisional orogenesis the timing of the metallogenic events and the spatial temporal distribution of the chinese skarn gold deposits indicates that they were formed during ore forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen and not to subduction systems as is commonly advocated for porphyry copper systems around the pacific rim

a major change in the sedimentation regime in the crotone basin southern italy around 3 7 3 6 ma abstract the lower pliocene succession of the crotone basin calabrian arc southern italy is mainly comprised of blue grey marly clay with good magnetic properties here the bio magnetostratigraphic data indicate a mean sedimentation rate of about 12 15 cm kyr around 3 7 3 6 ma a major change in the sedimentation regime occurred the blue grey hemipelagic marls grade rapidly into silty marls with a significant increase in the terrigenous fraction and with abundant siliceous remains throughout the whole interval magnetic properties of these sediments are very poor but an integrated calcareous plankton biostratigraphy foraminifera and nannofossils infers a high average sedimentation rate about 50 60 cm kyr the abrupt onset of this sedimentation regime in the crotone basin is contemporaneous with a major unconformity already recognized in the northern sector of the basin part of a major reorganization phase in the whole apenninic maghrebid chain known as globorotalia puncticulata event reports of coeval siliceous sediments in other marginal basins of the apennines southern calabria southern and northern apennines suggest that this siliceous event might have been regionally extensive having important palaeoceanographical implications we infer that the siliceous event is characterized by a combined tectonic and climate induced change in palaeoceanographic conditions the tectonic triggering factors may have been linked to two synchronous events in the tyrrhenian apennine system 1 the shortening event also known as g puncticulata event and 2 the coeval opening of the vavilov basin in the tyrrhenian sea which yielded profound influences in terms of physiography and characteristics of the crotone basin the consequent uplift of the southern apennines would have increased sediment supply and availability of silica resulting in eutrophication and enhanced silica preservation strong winter mixing and possibly upwelling conditions could have increased primary productivity during heavy isotope stages gi4 gi2 and mg8 at the onset of the siliceous event this important event lasting from ca 3 6 ma to ca 3 2 ma would have recorded a peculiar transitional period before further climatic deterioration and more drastic palaeoceanographic changes occurred around 3 1 ma leading to cyclic sapropel deposition in the whole of the mediterranean sea

first dated human occupation of italy at 0 85 ma during the late early pleistocene climate transition abstract a candidate for the oldest human occupation site in italy is monte poggiolo where the lithic tool bearing levels are currently dated to 1 ma based on electron spin resonance esr the low analytical precision of 30 at 2 makes it unclear whether the date actually conflicts with a recent reassessment of age constraints on key hominin sites from italy france and spain pointing to a uniformly young timing for the earliest habitation of southern europe during the late early pleistocene climate transition within reverse magnetic polarity subchron c1r 1r 0 988 0 781 ma our new magnetostratigraphic and biostratigraphic results show a sequence of stable normal and reverse polarities in a regional lithostratigraphic context that indicate the monte poggiolo tool bearing site post dates the jaramillo normal polarity subchron most probably occurring at 0 85 ma immediately after the pronounced cooling that culminated with marine isotope stage 22 when the associated regression may have opened new migration routes through the po valley for large mammals and hominins

speleogenesis in highly geodynamic contexts the quaternary evolution of monte corchia multi level karst system alpi apuane italy abstract the mt corchia karst system is one of the most important and famous caves in the world different from many other large caves here the geological structure has had only a minor role on the vertical multi level pattern of the cave a detailed geomorphic and morphometric analysis of the cave and a preliminary study of cave sediments along with new datings of speleothems allow us now to depict the multistage evolution of this cave which produced at least three major paleo phreatic levels related to different base level stages the analysis of the directions of cave passages shows that the three main phases have different orientations which can be attributed to the different surface morphology during speleogenesis in former times chronological constraints and geomorphic features suggest that the upper part of mt corchia cave developed during the end of pliocene in a stage of favourable climatic conditions and with a moderate tectonic uplift rate the morphological features and the nature of sediments in the upper paleo phreatic level at 1350 1450 m above present sea level apsl imply the occurrence of a wide allogenic catchment area this drainage pattern persisted also in the following stage during a significant but slow lowering of the base level which allowed the formation and the intense vadose rearrangement of the epi phreatic network around 1100 1250 m apsl an uplift stage in the early pleistocene caused the capture of the basins and the loss of allogenic feeding a third epi phreatic level was formed at around 900 m apsl when the catchment area was reduced to the present extent of carbonate rock more than 1 ma ago the recent evolution is due to rapid uplift and to the progressive incision of surrounding basins which led to the lowering of the local base level and to a readjustment of the cave system in order to adapt to a new equilibrium with the present elevation of the springs

fluid inclusion geochemistry and ore genesis of the longmendian mo deposit in the east qinling orogen implication for migmatitic hydrothermal mo mineralization abstract the 1 85 ga longmendian mo deposit in east qinling is the oldest mo system recognized in china it is unique for three reasons 1 quartzofeldspathic orebodies are away from any intrusion or fault 2 it is closely associated with migmatitic rocks and 3 it has remarkably high re content in molybdenite 504 to 1660 ppm the origin of the deposit is poorly constrained in the longmendian deposit strong mo mineralization is always associated with hydrothermally altered migmatitic amphibolites to probe into ore genesis detailed fluid inclusion studies are carried out on both mineralized migmatitic amphibolites and ore barren rocks four compositional types of fluid inclusions are observed including co 2 ch 4 pc type co 2 h 2 o c type daughter mineral bearing s type and h 2 o nacl w type quartz in mesosome and melanosome of mineralized migmatitic amphibolites contains all of the four types of inclusions measurements of immiscible inclusion assemblages in the ores constrain the mo mineralization temperatures and pressures to be 225 390 c and 114 265 mpa respectively primary fluid inclusions in barren migmatitic gneisses are dominated by s type and minor of c and pc types which are identical to those in the leucosome of migmatitic amphibolites these inclusions yield lower homogenization temperatures than those in the mineralized mesosome and melanosome of migmatitic amphibolites suggesting that the ore causative injected melts should have higher temperatures and originated from depths such features of the ore forming fluids indicate that the longmendian deposit was a migmatitic hydrothermal system caused by high temperature melt injection this interpretation can also be supported by the observations below 1 tourmaline is abundant in melanosome but absent in mesosome 2 the consistent quartzofeldspathic composition of leucosome is independent of mesosome 3 leucosome in migmatitic amphibolite crosscuts each other 4 halite bearing fluid inclusions are prevalent in studied samples which is the feature of granitic rocks instead of the scenarios of in situ migmatites and 5 the trapping temperatures of fluid inclusions in mineralized migmatitic amphibolite are much lower than those required for partial melting but higher than those obtained from barren migmatitic rocks

petrogenesis and geodynamics of late archean magmatism in eastern hebei eastern north china craton geochronological geochemical and nd hf isotopic evidence abstract the eastern part of the north china craton contains large volumes of late archean hornblenditic tonalitic dioritic granodioritic and granitic rocks la icpms zircon u pb dating of three plutons from eastern hebei eastern north china craton record emplacement ages of 2526 2515 ma and metamorphic ages of 2500 2490 ma for the diorite granodiorite and monzogranite and 2440 ma for the k feldspar granite hornblendites have high mgo 8 6 10 6 wt cr 674 1126 ppm ni 125 159 ppm and v 224 315 ppm at low basic silica contents sio2 45 7 49 0 wt they are enriched in light rare earth elements lrees and large ion lithophile elements liles and depleted in high field strength elements hfses with positive nd t values 1 2 to 2 0 indicating they were derived from an enriched mantle source the monzogranites have high sr and ba contents and sr y and la yb ratios low y and hrees abundances and positive nd t and zircon hf t values with nd and hf model ages less than 3 0 ga reflecting that they were derived from partial melting of a juvenile lower crust at high pressure however the k feldspar granites with low sr and ba concentrations and high hree and y contents are considered to have originated from partial melting of juvenile crustal materials at shallow crustal levels the diorites and granodiorites have variable major and trace element concentrations magmatic zircons from these rocks have heterogeneous hf t values but record uniform homogeneous u pb ages indicating they resulted from mixing of mafic and felsic magmas coupled with fractional crystallization because of the widespread distribution of late archean magmatism and evidence for magma mixing possibly related to mafic magma underplating it appears likely that this event in the eastern north china craton may relfect mantle plume activity that resulted in significant growth of continental crust during the late archean

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

ca 2 5 billion year old coeval ultramafic mafic and syenitic dykes in eastern hebei implications for cratonization of the north china craton abstract a group of extremely rare coeval ultramafic mafic and syenitic dykes was discovered in the eastern hebei region of the north china craton these dykes intrude the 3 8 2 55 ga old caozhuang complex an olivine gabbro dyke and syenite dyke yield respectively shrimp zircon u pb ages of 2516 26 ma and 2504 11 ma interpreted as the magmatic crystallization age their zircons have single stage hf model ages 2677 ma and 2705 ma the olivine gabbros have mg values of 59 63 similar to high magnesian tholeiitic basalt they show relatively lree enriched patterns without eu anomalies la yb n 9 28 9 78 gd yb n 2 8 eu 0 96 1 00 with enrichment in liles and depletion in hfses they also contain high cr and ni and have zr hf and nb ta ratios similar to those of the primitive mantle the syenites are alkaline in composition with 8 67 8 88 wt na 2 o k 2 o and show high total ree contents 543 854 ppm and strong lree enriched patterns with minor eu negative anomalies la yb n 50 101 gd yb n 5 2 5 3 eu 0 80 0 82 trace element diagrams show strong lile enrichment relative to hfse zr hf and nb ta ratios are 47 49 and 26 76 respectively which are much higher than those of primitive mantle and higher than the average nb ta ratio of post archean continental crust the petrological and geochemical features indicate that these dykes were derived from a deep subcontinental lithospheric mantle source which implies that the ncc probably had continental crust of considerable thickness at this time combined with evidence for 2 5 ga granite intrusion and metamorphism in the eastern hebei region and adjacent areas we propose that the ncc has been a present scale craton at the end of archean

geological evolution regional perspectives and hydrocarbon potential of the northwest phu khanh basin offshore central vietnam abstract seismic stratigraphic and structural analyses of the northwest phu khanh basin offshore central vietnam based on 2 d seismic data indicate that the initial rifting began during the latest cretaceous or palaeogene controlled by left lateral transtension along the east vietnam boundary fault zone evbfz and northwest southeast directed extension east of the evbfz rifting stopped due to transpression during middle oligocene times but resumed by left lateral transtension during the late oligocene thick sequences of lacustrine and alluvial sediments were deposited during the palaeogene rift periods the late oligocene rifting ended due to inversion triggered by right lateral wrenching near the palaeogene neogene boundary following the onset of this inversion regional uplift and volcanism took place in the southern half of the study area and contemporaneous subsidence and transgression took place farther north leading to widespread carbonate deposition as the right lateral wrenching decreased during the early neogene thermal subsidence and siliciclastic sedimentation became dominant resulting in the buildup and southward propagation of the shelf slope sediment accumulation and subsidence rates increased after the middle miocene times due to eastward tilting of central vietnam and the adjacent offshore area potential direct hydrocarbon indicators dhis in the phu khanh basin include common amplitude anomalies gas chimney like features and seafloor gas seeps in addition oil seeps are found at dam thi nai immediately landward of the basin geochemical analyses of the oil seeps indicate the existence of at least two early to peak mature source rocks maturation modelling combined with the seismic analysis suggests the likely presence of oil kitchens 40 50 km downdip in the basin and a fairly simple oil migration route the basin is probably charged from lacustrine syn rift mudstones humic coals and fore reef marls potential reservoirs are turbidite lowstand delta shelf and coastal sandstones as well as platform and reef carbonates and fractured basement various structural and stratigraphic traps formed during the palaeogene and early neogene prior to the main stage of petroleum generation

eustatic signals in deep marine sedimentary sequences recovered at odp site 978 alboran basin western mediterranean sea abstract a continuous section of pliocene marine sediments was recovered at ocean drilling program site 978 located in the alboran sea between spain and morocco three pliocene subunits have been defined at site 978 the lowermost subunit ic 129 2 m thick is characterized by alternating beds of lighter more calcareous and darker less calcareous claystone with bioturbated upper and lower contacts type 1 cycles the middle subunit ib 67 1 m thick is composed of relatively homogeneous nannofossil claystone and the uppermost subunit ia 211 6 m thick contains abrupt based darker terrigenous layers interpreted as turbidites that are interstratified with lighter nannofossil claystone type 2 cycles the rhythmically bedded light and dark layers in subunit ic correlate with those in the rosello composite section of sicily a global reference standard for the pliocene time scale these sedimentary cycles are products of variations in precession and resulting continental runoff missing cycles occur during eustatic highstands the shift to more homogeneous sedimentation in subunit ib is represented in similar aged sequences throughout the mediterranean which display evidence of submarine mass wasting mediterranean wide slope degradation was likely a response to rapid sea level change at approximately 3 ma this change in sedimentation style was accompanied by an upsection increase in sediment accumulation rates associated with turbidite influx in subunit ia turbidite frequency throughout the pliocene section can be linked to eustatic changes in sea level with turbidite maxima corresponding with mid sequence downlap surfaces and their associated condensed sections

further evidence for 1 85 ga metamorphism in the central zone of the north china craton shrimp u pb dating of zircon from metamorphic rocks in the lushan area henan province abstract this paper reports shrimp zircon u pb dating of precambrian supracrustal and granitic rocks from the lushan area henan province in the southern portion of the central zone also referred to as the trans north china orogen of the north china craton a graphite garnet sillimanite gneiss sample tw0006 1 of the shangtaihua group gives a range of inherited zircon ages from 2 73 to 2 26 ga and a metamorphic zircon age of 1 84 0 07 ga a garnet bearing gneissic granitoid sample twj358 1 which is considered to intrude the shangtaihua group gives a magmatic zircon age of 2 14 0 02 ga and a metamorphic zircon age of 1 87 ga the metamorphic zircon ages of 1 87 1 84 ga obtained in this study indicate that an important tectonothermal event occurred at the end of the paleoproterozoic in the lushan area this supports the southern continuation of a central zone in the north china craton that workers have recently considered to result from continent continent collision it is also evident that the shangtaihua group was formed during the paleoproterozoic between 2 26 and 2 14 ga and not during the archean as previously considered

the meta gabbroic complex of fushui in north qinling orogen a case of syn subduction mafic magmatism abstract sims zircon geochronology and oxygen isotopes as well as la icpms zircon lu hf isotopic analyses were carried out on a suite of rocks from the fushui complex to probe its origin and tectonic significance for the evolution of the qinling group in the north qinling orogenic belt the fushui complex comprises several phases of meta gabbros the dominant rock type is light colored meta gabbro followed by mica bearing and dark colored meta gabbros with abundant dark gabbroic enclaves with different sizes and shapes and occasional occurrence of mica bearing gabbroic pegmatite dikes age determination shows that the magmatic intrusion began at about 500 ma and surged at 490 480 ma with the latest zircon crystallized at about 476 ma this age spectrum is remarkably coeval with the peak metamorphism 500 480 ma of the surrounding qinling group metamorphic rocks dated by zircons from eclogites retrograded eclogites hp mafic granulites and uhp felsic gneisses representing syn subduction mafic magmatism these late cambrian to early ordovician zircons display a slightly enriched hf isotopic feature with a limited range in ehf t 5 to 2 and yield uniform tdm age 1 15 1 38 ga they also show a relatively small variation in 18o 6 69 0 44 2 8 75 0 34 2 much higher than the normal mantle value the isotopic feature suggests that the fushui complex was originally derived from enriched lithospheric mantle which was metasomatized by melts from ancient continental sediments and altered morb basalts the carboniferous zircons dominantly occurring as rims of early ordovician cores display very similar hf tdm ages 1 19 1 27 ga and oxygen isotopes as their counterparts corresponding to their recrystallization at 335 ma during amphibolite facies metamorphism when exhumed our study on the fushui complex together with the recently reported zircon u pb age data on the surrounding hp uhp metamorphic rocks demonstrates that the qinling group preserves a complete cycle of tectonic evolution in an orogenic belt from an oceanic basin spreading and mini continent formation to deep subduction of mini continent and multiple stage exhumations