regional observation of a nuclear test from a vertical hydrophone array abstract in order to evaluate the potential of water column vertical hydrophone arrays for the measurement of continental events at regional distances ocean acoustic data bases were examined for arrivals from these types of events in 1987 the nuclear test lockney m b 5 7 37 28 n 116 38 w was observed in the deep ocean water column at a range of 900 km by the vertical line array vla at 35 n 126 w although the hydrophone data were contaminated below 10 hz by array suspension noise and ocean acoustic noise adaptive array processing allows us to extract the p and t phases the root mean square rms direct p wave amplitude in the water column is 100 6 db referenced to 1 pa in the 4 to 8 hz band in a 20 sec window which suggests a detection threshold of m b 5 2 in a deep oceanic environment at this range for a single hydrophone the arrival time of the t phase i e the portion of seismic energy that has somehow coupled into and propagated within the deep ocean sound channel aki and richards 1980 is consistent with a p wave conversion at the continental margin assuming a velocity of 6 km sec from nts to the continental margin and acoustic propagation at 1 5 km sec in the water column from the continent to the array

nature of the recent vertical ground movements inferred from high precision leveling data in an intraplate setting ne ardenne belgium yearly high precision leveling surveys have been performed from 1993 to 1998 along a 48 km long local network centered on gileppe lake at the foot of the ardenne massif belgium institut geographique militaire and institut geographique national igm ign levelings of 1948 and 1974 yielded additional information the data were corrected for collimation and thermal errors other sources of error earth tides atmospheric refraction rod miscalibration were estimated and corrections were made when necessary random errors of individual surveys range from 0 15 to 0 74 mm km the recorded elevation changes indicate the existence of tilted segments some 5 to 10 km in length with yearly tilt values amounting up to 2 rads fault movements of a few mm yr are also demonstrated the segment limits are spatially stable from one year to the next but very frequent sense reversals of the vertical motions are observed this explains why the total movement over a 20 to 30 year period is barely higher than the yearly displacements various nontectonic causes of vertical ground movement e g monument instability varying water loading of the lake sediment compaction etc have been considered yielding little satisfactory explanation of the patterns of observed elevation changes we propose that the recorded motions which we call reversible fault creep and reversible tilt respectively are a true tectonic signal reflecting the tectonic noise which accompanies the long term deformation of uplifting areas in intraplate settings such movements are characteristic of fault segments which may occasionally generate earthquakes

fossils or sedimentary structures carbonaceous spheroids from the shale of the cryogenian nantuo formation in shengnongjia area south china abstract black shale of the cryogenian nantuo formation shennongjia area south china contains spheroids which co occur with fossils of macroalgae these three dimensional structures occur sparsely as isolated specimens or abundantly as clusters which show different types of boundaries between individuals they are generally circular on bedding surfaces and elliptical on transecting sections and range up to several millimeters in diameter both petrographic thin sections and scanning electron microscopy sem reveal that these spheroids are mostly organic carbon in composition and exhibit sharp well rounded external margins composed of microcrystalline clay minerals the carbonaceous nature of these spheroids and different elemental abundances between spheroids and matrix are also confirmed by raman spectroscopy and energy dispersive x ray spectroscopy eds organic carbon isotopic values of individual spheroids range from 28 55 to 28 83 with an average of 28 72 which show indistinguishable 13corg values with the surrounding sedimentary matrix but exhibit statistically significant difference to those of contemporaneous macroalgae a range of physical origins for these spheroids including concretions fluid escape structures raindrop impressions or bubble impressions are considered and cannot be entirely rejected alternatively biogenic origin is also a possible interpretation from observations of their morphological mineralogical geochemical and sedimentological characteristics although their nature remains unresolved the documentation of these new carbonaceous spheroids from the nantuo formation of shennongjia area adds to a growing list of fossil like structure records in the cryogenian period

organic walled microfossil assemblages from glacial and interglacial neoproterozoic units of australia and svalbard before the onset of the neoproterozoic snowball earth glaciations eukaryotes had begun diversifying and in their aftermath macroscopic life including both animals and macroalgae became abundant and widespread although glacially driven mass extinctions have been hypothesized little is known about the biosphere during and between these glaciations here we present new data from organic walled microfossil assemblages from five successions in australia and svalbard that collectively span the first sturtian glaciation and interglacial interval and integrate them with data derived from a critical evaluation of the literature to produce a new estimate of eukaryotic diversity from 850 to 650 ma these new glacial and interglacial assemblages consist of only smooth walled spheroids leiosphaerids aggregates of cells and filaments in contrast to the much more diverse organic walled microfossil assemblages found in early neoproterozoic rocks this contrast is not attributed to biases in deposition or preservation but is instead interpreted as reflecting an interval of lowered eukaryotic diversity that spanned the glaciations and that may have begun millions of years prior to their onset

the age of the nantuo formation and nantuo glaciation in south china a u pb sensitive high resolution ion microprobe shrimp age of 654 5 3 8 ma from an ash bed immediately below the nantuo formation in south china provides the lowest age constraint for the nantuo glaciation which has been correlated with the global marinoan glaciation a u pb shrimp age of 636 3 4 9 ma from a fallout tuff within the basal layer of the nantuo formation along with the existing age of 635 2 0 6 ma from its overlying doushantuo cap carbonate suggests that the traditionally defined nantuo formation may have been deposited in a short time period at the end of the nantuo glaciation in combination with available ages globally the data support a relatively short duration and rapid termination of marinoan glaciations

a tonian age for the visingso group in sweden constrained by detrital zircon dating and biochronology implications for evolutionary events detrital zircon u pb ages from samples of the neoproterozoic visingso group sweden yield a maximum depositional age of 886 9 ma 2 a minimum depositional age is established biochronologically using organic walled and vase shaped microfossils present in the upper formation of the visingso group the upper formation correlates with the kwagunt formation of the 780 740 ma chuar group in arizona usa and the lower mount harper group yukon canada that is older than 740 ma mineralized scale microfossils of the type recorded from the upper fifteenmile group yukon canada where they occur in a narrow stratigraphic range and are younger than 788 ma are recognized for the first time outside laurentia the mineralized scale microfossils in the upper formation of the visingso group seem to have a wider stratigraphic range and are older than c 740 ma the inferred age range of mineralized scale microfossils is 788 740 ma this time interval coincides with the vase shaped microfossil range because both microfossil groups co occur the combined isotopic and biochronologic ages constrain the visingso group to between 886 and 740 ma thus tonian in age this is the first robust age determination for the visingso group which preserves a rich microfossil assemblage of worldwide distribution the organic and mineralized microorganisms preserved in the visingso group and coeval successions elsewhere document global evolutionary events of auto and heterotrophic protist radiations that are crucial to the reconstruction of eukaryotic phylogeny based on the fossil record and are useful for the neoproterozoic chronostratigraphic subdivision

forward modeling of the southern apennines forward kinematic modeling has been developed to reconstruct the successive geometries of geological sections the method is tested here on a geological section across the southern apeninnes where syntectonic neogene deposits are of help in determining the timing of the deformation that progressively affected more eastern parts of the apulian margin well known triassic and paleogene decollement levels induced thin skinned tectonics in the mesozoic and cenozoic sedimentary cover but the basement geometry is only poorly revealed by subsurface data two distinct hypotheses have been tested 1 thin skinned tectonics and 2 basement involved tectonics the shortening of the prism is estimated to be between 170 and 210 km whether or not the basement is involved in the imbricated stack of thrust sheets the results are discussed in the light of regional constraints i e regional flexure uplifts etc which favor basement involved structures at depth in addition to the effects of compression other phenomena affected the geometry of the prism and have to be taken into account because of the recent uplift of the belt the inner parts of the apenninic wedge have emerged and undergone erosion part of this eroded material has been simultaneously trapped in piggyback basins which record both the geometric and temporal evolution of the prism normal faulting also affected the western part of the southern apennines reactivating older thrust as detachment surfaces along which block rotation occurred

orienting and locating ocean bottom seismometers from ship noise analysis breakthroughs in understanding the structure and dynamics of our planet will strongly depend upon instrumenting deep oceans progress has been made these last decades in ocean bottom seismic observations but ocean bottom seismometer obs temporary deployments are still challenging and face setup limitations launched from oceanographic vessels obss fall freely and may slightly drift laterally dragged by currents therefore their actual orientation and location on the landing sites are hard to assess precisely numerous techniques have been developed to retrieve this key information but most of them are costly time consuming or inaccurate in this work we show how ship noise can be used as an acoustic source of opportunity to retrieve both the orientation and the location of obss on the ocean floor to retrieve the obs orientation we developed a first method based on a combination of seismic and pressure data through the use of the acoustic intensity this latter can be used to quantify the obs orientation from the ship noise direction of arrival doa which can then be compared with known ship trajectories obtained from the automatic identification system ais to accurately relocate obss we also developed a second method based on the hydrophone data which computes distances of acoustical sources by measuring time differences of arrival tdoa between direct and reverberated phases the obs location is then retrieved by fitting measured ship distances with known ship trajectories in this study a full network of obss deployed in the sw indian ocean was reoriented and a test station was relocated we demonstrate that our new methods may quantify the obs orientation with an accuracy of about one degree and its location with an accuracy of a few tens of metres depending on the number of ships used in the analysis

glacial origin of the cryogenian nantuo formation in eastern shennongjia area south china implications for macroalgal survival abstract the cryogenian period was characterized by global glaciations imposing extreme environmental stresses on early multicellular organisms globally distributed diamictite deposits are the major evidence for these glaciation events but the glacial origin of at least some of these diamictite deposits has been disputed complicating interpretations of the environmental conditions influencing the evolution of life in the cryogenian 720 635 ma in this study we conducted a systematic sedimentological investigation of the marinoan age 650 635 ma nantuo formation in six sections representing a 20 km long east west transect in the eastern shennongjia area of south china the nantuo formation which ranges in thickness from 2 m in the east to 300 m in the west comprises diamictite conglomerate lonestone bearing sandstone green siltstone and black shale facies the eastern sections e g longxi and wushanhu consist mainly of diamictite facies exhibiting micro scaled rotation structures microshear grain stacking grain to grain contacts and water escape structures supporting their deposition in a subglacial setting in contrast the western sections shijiahe liziping and songluo consist of massive and graded diamictite and conglomerate facies consistent with an origin as glacially induced submarine debris flows furthermore the lonestone bearing sandstone facies in these sections contain abundant dropstones and mud pellets within finely laminated turbidites indicating an ice rafted origin with locally reworking by turbidity currents the green siltstone and black shale facies lack glacigenic features and may represent late deglacial deposits based on thickness and facies variations among the study sections we infer that the nantuo formation records glacial sedimentation on a complex paleotopographic surface that was incised into the underlying bedrock with subglacial deposits to the east transitioning into glaciomarine deposits to the west of study area the distal songluo section likely records three cycles of glacial advance and retreat in the form of a facies alternation between diamictite and black shale consistent with a dynamically fluctuating ice margin in summary our sedimentological investigation supports a glacial origin for the nantuo formation in the eastern shennongjia area the occurrence of the benthic macroalgal dominated songluo biota in the black shale facies at songluo suggests that strong glacial retreats provided niches for macroalgal survival in the cryogenian glacial ocean

new record of organic walled morphologically distinct microfossils from the late paleoproterozoic changcheng group in the yanshan range north china abstract eukaryotic life has likely existed since the late paleoproterozoic yet little is known about its early diversity and phylogenetic relationships organic walled microfossils owms with conspicuous morphology provide a unique material to investigate the deep evolution of eukaryotic and prokaryotic microbial clades here we report a diverse assemblage of owms from the lower changcheng group c 1673 1638 ma changzhougou and chuanlinggou formations in the yanshan range north china which consists of 15 species including 2 that are newly described the fossil assemblage is dominated by spheromorphs with less numerous process bearing vesicles as are colonial and filamentous forms among these 6 morphologically complex taxa dictyosphaera 2 species of germinosphaera pterospermopsimorpha simia and valeria are identified as unambiguous unicellular eukaryotes four species cucumiforma navifusa schizofusa and large leiosphaeridia with relatively simple morphology but having large size thick wall and some showing median split excystment structures are of probable eukaryotic affinity however various colonial microfossils could be either eukaryotes or prokaryotes the new record of morphologically disparate owms represents one of the earliest occurrences of eukaryotes in both china and the world and indicates that the eukaryotic life was already well established in the late paleoproterozoic and was of moderate diversity similar to that of the mesoproterozoic

geodynamic evolution of the central dinarides abstract the central part of the dinarides unlike the northwestern and southeastern dinarides shows a consistent pattern in the distribution of the large tectonostratigraphic units from southwest apulia to northeast the following five main units originating in different parts of the mesozoic tethys can be distinguished 1 adriatic dinaridic carbonate platform formations 2 carbonate clastic units flysch bosniaque of the passive continental margin 3 ophiolite bearing formations of the dinaridic ophiolite zone also containing radiolarites greywackes and shales including melange formations and overstepped late jurassic to cretaceous cover sequences 4 active continental margin units represented by upper cretaceous palaeogene trench sediments with blueschists tectonized ophiolite melange alpine medium pressure metamorphic rocks originated from upper cretaceous palaeogene sediments and alpine synkinematic granitoids 5 a nappe consisting of allochthonous palaeozoic triassic formations which is thrust onto the ophiolites and genetically related sedimentary formations the frontal parts of this nappe directly overlie the northeastern margin of the adriatic dinaridic carbonate platform i e the external dinarides the evolution of the central dinarides was controlled by a sequence of tectonic events which took place within the alpine cycle 1 rifting processes lasting some 40 50 ma which started in the late permian and ended in the norian 2 opening of the oceanic dinaridic tethys commenced in the late triassic and persisted for some 70 80 ma until the end of the jurassic 3 subduction processes and emplacement of ophiolites started in late jurassic early cretaceous times during the closing phase of the dinaridic ocean or dinaridic tethys the palaeozoic triassic nappe was emplaced on the ophiolites the thrusting was accompanied by alpine metamorphism 120 100 ma 4 the main alpine deformational event and medium pressure metamorphism with synkinematic granite plutonism took place in late eocene early oligocene times when the ophiolite and palaeozoic triassic nappes were emplaced on the adriatic dinaridic carbonate platform which at the same time was deformed resulting in the development of the external dinarides fold and thrust belt

growth processes and melange formation in the southern apennines accretionary wedge abstract the southern apennines owe their present geometry to the subduction of an apulian continental lithospheric slab and are thus best interpreted as an accretionary wedge southward the apenninic thrust front branches on to the still active ionian wedge which is related to the present calabro sicilian subduction the interpretation of conventional seismic reflection profiles and exploration wells combined with geologic field studies biostratigraphy and structural geology provide constraints for a geodynamic model for the post messinian growth of the apenninic prism our model for the apennines is a good analogy for submerged oceanic accretionary prisms in both instances features such as out of sequence thrusts underplating and duplexes are viewed as processes to explain the thickening of accretionary wedges syntectonic terrigenous deposits have accumulated in the synclines developed above the flats of pliocene thrust faults these depocenters represent piggy back basins younger accretion at the eastern border of the accretionary wedge has led to a progressive uplifting and tilting of the already emplaced thrust sheets including a continous westward migration of the depocenters in the piggy back basins during pliocene and early quaternary times a contrary west to east migration of the depocenters locally occurred where preexisting flats of pliocene thrust faults have been refolded rather than only being rotated dewatering processes and effects of overpressures on undercompacted sediment deformations can also be studied in the southern apennines melanges and broken formations form an important component of the trench apparently restricted to the base of tectonic nappes listric normal faults are a major structural element which preserves in combination with the erosion of topographic highs and resedimentation in the piggy back basins a uniform geometric shape critical taper for the prism the age and location of these distensive or gravitational effects are also discussed

magnetic interpretation related to geo magnetic provinces the italian case history abstract a comparison of the results obtained from the geophysical interpretation with the available information regarding the italian geological situation permitted us to establish our so called geo magnetic provinces the relationship between the magnetic characteristics and the tectonic evolution permitted the identification of each of the four following provinces that exist inside the global tectonic confines 1 1 the sardo corso block which represents the eastern boundary of stable europe this province is characterized by medium wavelength low amplitude anomalies that originate in an outcropping basement hercynian granites s l 2 2 the orogenic belt which constitutes the double alps apennines system from a magnetic standpoint this system is characterized by short wavelength low amplitude anomalies that are due to a paleozoic outcropping and or buried acid crystalline basement these anomalies are found to overlie long wavelength medium amplitude regional anomalies that are related to a deep apenninic basement central northern apennines 3 3 the foreland area which occurs from sicily hyblean plateau and apulia northwards to ancona and the po plain this area is characterized by a crystalline basement which is typically differentiated from the standpoint of basicity 4 4 the rifting zone which is represented by the part of the tyrrhenian sea lying south of the 41st parallel discontinuity the ionian abyssal plain and the pantelleria and linosa troughs in the sicily channel the main characteristic of this province is its extreme basicity differentiation in the crystalline basement which is induced by the geochemical processes connected with the deep geodynamic events these phenomena do not permit the correlation of the semioceanic basement of the rifting zone with the continental basement by means of interactive modeling a structural tectonic picture of the basement of the various italian geo magnetic provinces has been obtained the main result was found to be that the orogenic belt basement is undergoing intense tectonic compression and overlies the structural highs of the foreland area which mainly show tensive events

frontal part of the northern apennines fold and thrust belt in the romagna marche area italy shallow and deep structural styles in this study surface geological data resulting from a detailed field survey including structural and biostratigraphic analysis have been integrated with subsurface seismic lines and well logs data in order to reconstruct the tectonic evolution of the external zones of the northern italian apennines in the romagna marche foothills and adriatic sea areas this integrated analysis shows 1 a late messinian to lower pleistocene progression of structural development from the hinterland to the foreland of the studied sector of the thrust belt 2 relatively limited 20 southward increasing amounts of shortening obtained by the construction of line length balanced and restored geological cross sections 3 a regional deformation style characterized by the presence of backthrusts associated with most foreland vergent thrust ramps leading to quasi symmetric uplift and a low critical taper for the wedge typical of foreland fold and thrust belts with a weak basal decollement triassic anhydrites in the present case 4 an important influence of basement faulting which despite a general basement cover decoupling appears to control stress localization in the latter producing linkage of basement and cover stuctures in a combination of thin and thick skinned tectonic styles and 5 contrasting structural styles characterizing deep features as imaged by seismic reflection profiles and shallow ones deep stuctures consist of growth anticlines bounded by major thrust ramps and back limb back thrusts separated by broader open synclines both involving a mesozoic paleogene mainly carbonate passive margin succession in the crestal zones of major anticlines shallow structures affecting neogene terrigenous foredeep sediments show a complex pattern of upright to recumbent folds of tens to hundreds of meters wavelength related to minor thrusts and backthrusts deformation of the mesozoic paleogene multilayer appears to be dominated by thrust propagation in the cores of early formed anticlines developed by buckling instabilities the overlying neogene deposits are detached from the carbonate substratum along the base of the foredeep succession bedding parallel slip occurring along this detachment level appears to be accommodated by the complex structures in the crests of major anticlines where the thrusts lramp to the surface cutting up section complex shallow structures interpreted to accommodate at shallow structural levels the deep deformation would therefore represent a geometrical requirement for maintaining strain compatibility across the shallow detachment level located at the base of the foredeep succession

energetics of the deep ocean s infrasonic sound field simultaneous measurements of infrasonic 0 5 20 hz acoustic particle velocity and acoustic pressure made by the marine physical laboratory s set of freely drifting swallow floats are analyzed in terms of the energetics of acoustic fields results from a recent deep ocean deployment indicate that the midwater column s acoustic potential and kinetic energy density spectra are equal above 1 7 hz since away from the ocean boundaries the sound field is locally spatially homogeneous near the ocean bottom the vertical spatial inhomogeneity is statistically significant between 0 6 1 4 hz and 7 20 hz in the lower band the pressure autospectrum decreases with increasing distance from the ocean bottom whereas in the upper band it increases due to the deep sound channel s ability to trap acoustic energy at the higher infrasonic frequencies for ship signals the signal to noise ratio in the active intensity magnitude spectrum is 3 6 db greater than in either of the two energy density spectra due to the vector nature of acoustic intensity although smaller than the net horizontal flux above a few hertz a statistically significant net vertical flux density of energy occurs across the whole frequency band from the ocean surface into the bottom the direction of the net horizontal flux density for various discrete sources e g a magnitude 4 1 earthquake a blue whale and commercial ships is discussed the net horizontal flux density of the background sound field between 5 and 12 hz may have been determined by the surrounding ocean bottom topography in one experiment its direction approximately coincides with the center of a topographic window however it also matches the heading toward a 4000 km distant hurricane a third possibility of an unknown broadband source cannot be eliminated with the available data

the survival of benthic macroscopic phototrophs on a neoproterozoic snowball earth the greatest ice ages in earth s history occurred during the 654 635 ma marinoan glaciation when glaciers reached tropical oceans and our planet approached a snowball earth condition paleontological and genomic data suggest that several eukaryotic groups must have survived the marinoan glaciation but their fossil record is scarce and limited to microbes whose ecological and physiological ranges are poorly constrained thus hampering a full understanding of how and where eukaryotic life particularly macroscopic phototrophs survived this snowball earth here we report carbonaceous compression fossils from the marinoan age nantuo formation in south china these fossils are preserved in thin black shales sandwiched between glacial diamictites deposited in inner shelf environments of the mid latitudinal yangtze block some of these fossils are interpreted as benthic macroalgae thus the marinoan glaciation must have been punctuated by episodes of open waters where habitable benthic substrates were available in the photic zone and along the coast of mid latitudinal continents such open waters may have been the refugia where macroscopic phototrophs survived the marinoan glaciation and subsequently diversified in the early ediacaran period

seaweeds through time morphological and ecological analysis of proterozoic and early paleozoic benthic macroalgae abstract benthic marine macroalgae or seaweeds are key ecological players in oceans today and have been since the proterozoic to date however morphological and evolutionary patterns for precambrian macroalgae have been documented only in rather broad terms to refine our understanding in this critical interval we updated a dataset of proterozoic to early paleozoic noncalcified macroalgal fossils preserved as macroscopic carbonaceous compressions the data were analyzed using non parametric multidimensional scaling nmds and functional form group ffg approaches in order to characterize morphological and ecological evolutionary patterns of these macroalgae at the broadest scale the results show progressive increases in thallus size morphospace range and aspects of ecological complexity such as canopy heights surface area volume ratios and functional form groups through time these trends however are not always monotonous in particular significant increases in proterozoic macroalgal morphological diversity and maximum size appear to have occurred in the neoproterozoic tonian and ediacaran periods respectively analysis of ediacaran macroalgal assemblages shows that macroalgae broadly follow the ediacara like fossil assemblages with a significant drop in most studied metrics in the terminal ediacaran stage 550 539 ma the latter event occurs during the kotlinian crisis experienced by ediacara type macro organisms highlighting the possibility that this extinction event during the ediacaran cambrian transition affected both macroalgae and ediacara type macro organisms our analysis also confirms an ordovician increase in the morphological and ecological diversity of macroalgae

ocean chemistry neoproterozoic glass bleeding volcanic eruptions at ocean ridges produce large volumes of glass that is rapidly leached by seawater geochemical calculations suggest that this process helps to explain the deposition of carbonates at the end of extreme ice ages

normal faults in thrust sheets pre orogenic extension post orogenic extension or both abstract in fold and thrust belts that experienced both pre orogenic and post orogenic extension it may be difficult to establish whether observed normal faults pre dated post dated or were synchronous with thrusting geometrical structural patterns may be insufficient to constrain the relative chronology of extensional and contractional deformations the systematic use of kinematic criteria makes it possible to unequivocally define the timing relationships of reverse and normal fault development and hence to correctly unravel complex structural evolutions kinematic analysis in the southernmost umbria marche apennines of italy where both normal and thrust faults are present revealed a history of repeated tectonic inversion characterised by two distinct stages of extension separated by an episode of folding and thrusting structural overprinting relationships observed at thrust normal fault intersections were useful for i removing sequentially younger deformations and hence ii separating and quantifying the effects of orogenic contraction from those of both pre orogenic and post orogenic extension

thick skinned tectonics in the external apennines italy new evidence from magnetic anomaly analysis 1 we discuss the tectonic implications of a new residual magnetic map of the apennine belt adriatic apulian foreland obtained by integrating ground and offshore data sets chiappini et al 2000a negative anomalies are documented over the adriatic apulian foreland areas whereas the external apennine belt is characterized by a ubiquitous low amplitude 30 nt long wavelength positive anomaly in the central northern apennines three 100 km wide more intense 100 200 nt round shaped anomalies are superimposed to the long wavelength feature finally in the tyrrhenian sea and margins high intensity short wavelength positive negative couplets coincide with magmatic outcrops or bodies at shallow depth the low amplitude anomaly pattern over italy suggests that the magnetic basement beneath the triassic evaporites is ubiquitously incorporated in the external belt compressive fronts implying a thick skinned tectonic style for the external apennines the new residual magnetic map resolves the inconsistency between previous aeromagnetic data agip spa italia 1981 which suggested a lack of basement involvement in the apennine belt and recent seismic data which imaged deep reflectors penetrating the basement two magnetic models along ne sw transects in the northern and southern apennines suggest consistent structural styles in the northern apennines positive anomalies roughly coincide with the external compressive fronts although there are local second order differences between the belt front and the edges of the anomaly here the magnetic data show that the basement rises southwestward along the thrust fronts from 6 7 km depth in the adriatic foreland to 2 3 km depth in the axial belt where some exploration wells have penetrated basement within the belt front basement exhumation is inferred to occur along high angle low displacement thrust faults inverting preexisting normal faults in the southern apennines a remarkable positive magnetic anomaly is parallel with and tens of kilometers southwest of the belt front seismic data and oil wells show that the basement surface cannot be shallower in the belt than in the foreland therefore the observed magnetic anomaly is produced by strongly magnetic basement beneath the belt likely an internal crustal wedge tectonically interposed between the apulian carbonate sequences and basement

matched field processing geoacoustic inversion and source signature recovery of blue whale vocalizations matched field processing mfp and global inversion techniques have been applied to vocalizations from four whales recorded on a 48 element tilted vertical array off the channel islands in 1996 global inversions from selected whale calls using as few as eight elements extracted information about the surrounding ocean bottom composition array shape and the animal s position these inversion results were then used to conduct straightforward mfp on other calls the sediment sound speed inversion estimates are consistent with those derived from sediment samples collected in the area in general most animals swam from the east to west but one animal remained within 500 m of its original position over 45 min all whales vocalized between 10 and 40 m depth three acoustic sequences are discussed in detail the first illustrating a match between an acoustic track and visual sighting the second tracking two whales to ranges out to 8 km and the final sequence demonstrating high resolution dive profiles from

quantifying temperature variation between neoproterozoic cryochron nonglacial interlude nanhua basin south china abstract three major late neoproterozoic global cryochrons mark the coldest climate state in earth history with glaciers covering most if not all continents however the terrestrial paleosurface temperature differential between cryochron and nonglacial interlude is unknown time equivalent cryogenian and ediacaran sedimentary successions from south china and oman show multiple negative excursions of the corrected values of their chemical index of alteration ciacorr these excursions reflect climate cooling and correlate with the sturtian marinoan and gaskiers cryochrons based on the na mat transfer function sodium chemical depletion index mean annual temperature we estimate the temperature differential between cryogenian cryochron and nonglacial interlude reached 20 5 4 at around 30 paleolatitude and 12 5 4 temperature difference between the ediacaran cryochron and nonglacial interlude near the equator the fluctuation of ciacorr and mat trends within individual cryochrons likely indicate cold warm climate cycling during the cryogenian cryochron

excellent source rocks discovered in the cryogenian interglacial deposits in south china geology geochemistry and hydrocarbon potential abstract the cryogenian 720 635 ma is characterized by the well known sturtian and marinoan glaciations which plays a key role in understanding remarkable climate and sea level changes and oxygenation events that occurred during the neoproterozoic era however less attention has been paid to the interglacial deposits recently we paid great attentions to the excellent hydrocarbon source rocks toc 2 in the cryogenian interglacial datangpo formation 663 4 ma 654 3 8 ma in south china which mainly consists of black shales with thin manganese interbeds making the interglacial interval a new focus to elucidate their characteristics and depositional environments petrological and geochemical studies were conducted on fresh rock samples collected from six sections gucheng sanlian xiaoxi gaodongyuan xiaochayuan yanglizhang in manganese mining areas at southeastern south china sedimentary reconstructions suggest a transition from restricted to open ocean environment during the deposition of the datangpo formation and this formation records variations from warm and humid to dry and cold climate black shales were deposited in its lowest member during the warm period and showed greatest thicknesses more than 20 m at depocenters microscopic observations of the black shale samples exhibited abundant benthic algae with great diversities indicating a gradual recovery of the ecosystem biomarker analyses further reveal that these algae combined with bacterial microorganisms prosperous in low salinity reducing environments were the dominant organic contributors to the source rocks which were inferred by low pristane pr to phytane ph ratio pr ph low gammacerane high tricyclic terpene and high c27 sterane contents trace element records combined with isotopic data suggest that the deposition of source rocks in datangpo formation were related to a burst in surface water productivity due to warm climate and better preservations resulted from anoxic waters within a stratified water column these findings indicate the cryogenian source rocks may provide a new potential field for future explorations of shale gas and deep oil and gas

the umbria marche arcuate fold belt italy abstract in this paper the structural setting of the umbria marche fold belt is briefly described the basement cover relationships and the primary or secondary origin of the arcuate shape are also discussed mainly on the basis of structural data it is suggested that the umbria marche fold belt can hardly be the result of a thin skinned tectonics under little overburden but one or more deep seated detachment levels must have worked thick skinned tectonics during the mio pliocene transpressional phase furthermore an orocline origin for the arcuate shape of the fold belt resulting from a progressive history of oblique right lateral shearing is suggested during the first deformative stage stage 1a late miocene the cover detached from the basement is deformed by a nw se trending linear fold belt whilst the basement is deformed by oblique right lateral shear then stage 1b the linear fold belt is progressively bent by right lateral dragging in correspondence with the deep seated shear zones during the second deformative stage stage 2 early piocene the cover deforms in connection with the basement the northern and the central sectors of umbria marche apennines undergo a prevailing shortening accomodated by nw se nnw sse dip slip thrusting the southern sector undergoes a prevailing right lateral shearing accommodated by nne ssw oblique thrusting

a complex microbiota from snowball earth times microfossils from the neoproterozoic kingston peak formation death valley usa a thin carbonate unit associated with a sturtian age 750 700 million years ago glaciogenic diamictite of the neoproterozoic kingston peak formation eastern california contains microfossil evidence of a once thriving prokaryotic and eukaryotic microbial community preserved in chert and carbonate stratiform stromatolites oncoids and rare columnar stromatolites also occur the microbial fossils which include putative autotrophic and heterotrophic eukaryotes are similar to those found in chert in the underlying preglacial units they indicate that microbial life adapted to shallow water carbonate environments did not suffer the significant extinction postulated for this phase of low latitude glaciation and that trophic complexity survived through snowball earth times

tracking sperm whales with a towed acoustic vector sensor passive acoustic towed linear arrays are increasingly used to detect marine mammal sounds during mobile anthropogenic activities however these arrays cannot resolve between signals arriving from the port or starboard without vessel course changes or multiple cable deployments and their performance is degraded by vessel self noise and non acoustic mechanical vibration in principle acoustic vector sensors can resolve these directional ambiguities as well as flag the presence of non acoustic contamination provided that the vibration sensitive sensors can be successfully integrated into compact tow modules here a vector sensor module attached to the end of a 800 m towed array is used to detect and localize 1813 sperm whale clicks off the coast of sitka ak three methods were used to identify frequency regimes relatively free of non acoustic noise contamination and then the active intensity propagating energy of the signal was computed between 4 10 khz along three orthogonal directions providing unambiguous bearing estimates of two sperm whales over time these bearing estimates are consistent with those obtained via conventional methods but the standard deviations of the vector sensor bearing estimates are twice those of the conventionally derived bearings the resolved ambiguities of the bearings deduced from vessel course changes match the vector sensor predictions

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

palynology of the huqf supergroup oman extensive subsurface sampling of the huqf supergroup in the sultanate of oman has yielded microfossil assemblages of cryogenian ediacaran and early cambrian age microfossils have been recovered from most stratigraphic units in the huqf including marinoan equivalent horizons of the ghadir manqil formation cryogenian abu mahara group the masirah bay shuram and buah formations of the ediacaran nafun group and the a3 latest ediacaran and a6 early cambrian cycles of the ara group despite the extensive recovery of leiosphaerid acritarchs from the shuram formation there is no indication of the large acanthomorphs typical of other early middle ediacaran assemblages this absence suggests a relatively young post extinction depositional age for the shuram however the signal is complicated by local deep water conditions and the facies specific distribution of proterozoic microfossils a shallower water sequence of undivided nafun group sediments preserves sphaeromorphic acritarchs in association with filamentous microfossils fragmentary vendotaenids and possible vaucheriacean algae

detrital graphite particles in the cryogenian nantuo formation of south china implications for sedimentary provenance and tectonic history abstract the tectonic history of the yangtze block of south china prior to the ediacaran period has been a matter of debate in particular the tectonic history of the shennongjia terrane in the central northern margin of the yangtze block is poorly understood and the tectonic relationship between the shennongjia terrane and the huangling massif exposed in the huangling anticline is unclear previous researchers have reported u pb dates of detrital zircons and nd isotopic compositions of clastic rocks from cryogenian successions in the shennongjia terrane to identify ancient crustal remnants and the provenance of clastic sediments and to constrain the age and crustal evolution of the yangtze block here we describe abundant graphite discs from silty mudstone of the cryogenian nantuo formation in the shennongjia area of the yangtze block these graphite discs are opaque 23 171 m in size and highly reflective most are abraded or rounded although some show hexagonal crystalline morphology their raman spectra are distinct from those of indigenous carbonaceous material cm in the sedimentary matrix from the nantuo formation at the same locality raman cm geothermometric analysis indicates that graphite discs experienced a maximum metamorphic temperature of nearly 600 c which is inconsistent with the relatively low metamorphic grade of the host rock these observations indicate that the graphite discs are of detrital origin most likely derived from high grade metamorphic rocks in the basement of the yangtze block e g the archean paleoproterozoic kongling terrain in the core of the huangling anticline consistent with the hypothesis that the shennongjia region was a part of yangtze block by the end of the cryogenian period

tomographic constraints on the geodynamic evolution of the italian region in this paper we present p wave tomographic images of the mantle beneath italy obtained by inverting 6000 teleseismic p and pkp wave arrival times accurately repicked recorded in the time period 1988 1994 by the stations of the national seismic network of the istituto nazionale di geofisica we pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set the data were inverted with the well established aki christofferson husebye tomographic technique different reference models and residuals computation have been tried to verify the stability of the results the high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the alps and the apennines looking for their lateral and vertical continuity down to 800 km depth the main finding of this study is a continuous high velocity body located between 250 and 670 km depth beneath the entire apenninic system dipping toward the tyrrhenian area which continues upward segmented in two main anomalies in the northern apenninic and the calabrian arcs we interpret this high velocity feature as the subducted oceanic lithosphere between the eurasian and african plates dipping down to the upper lower mantle boundary beneath the tyrrhenian sea the retrieved images of the lithosphere subducting beneath apennines are reliable in terms of thickness about 80 90 km and p wave velocity contrast 2 4 higher than the normal mantle furthermore our tomographic images which focus on the deep geometry and continuity of the velocity structures provide new keys to understanding the geodynamic evolution of the italian region the segmentation of the high velocity slab upward suggests a complex evolution of the arc trench system and the initially continuous subduction of the ionian adriatic plate progressively developed in subordinate arcs probably due to lateral heterogeneity of the subducting lithosphere

globally synchronous marinoan deglaciation indicated by u pb geochronology of the cottons breccia tasmania australia u pb zircon data from the uppermost cottons breccia representing the marinoan glacial postglacial transition on king island tasmania provide the first direct age constraint on the cryogenian ediacaran boundary in australia zircons in four samples from the topmost meter of the cottons breccia dated by sensitive high resolution ion microprobe exhibit two modes ca 660 ma and ca 635 ma the younger component predominates in the uppermost sample a possibly volcanolithic dolomitic sandstone apparently lacking glacially transported debris in the transition to cap carbonate chemical abrasion thermal ionization mass spectrometry ca tims u pb dating of euhedral zircons from that sample yields a weighted mean age of 636 41 0 45 ma equivalence to published tims ash bed dates from cryogenian ediacaran transitional strata in namibia 635 51 0 82 ma within glacial deposit and china 635 23 0 84 ma 2 m above glacial deposit supports correlation of those strata to the australian type sections and globally synchronous deglaciation at the end of the cryogenian period

normal mode composition of earthquake t phases understanding the nature of the coupling between the underwater acoustic field and the land seismic field is important for evaluating the performance of the t phase stations in the international monitoring system for the comprehensive nuclear test ban treaty for upslope propagation in an ocean environment the places where underwater acoustic field energy couples into the land seismic field are determined to first approximation by the local water depth and the normal mode composition of the acoustic energy therefore the use of earthquake generated t phases as natural probes of water to land coupling characteristics is aided by knowledge of their modal composition data collected by a 200 element 3000 m aperture vertical hydrophone array during a 1989 experiment in the deep northeast pacific ocean are used to determine the mode composition of t phase arrivals from two mb 4 1 earthquakes near the w est coast of the u s one occurring offshore and the other on land results from an eigenanalysis approach and conventional mode decomposition for the two events are consistent and show that at 5 hz the offshore event s arrivals have higher order mode content compared to those from the event on land single hydrophone recordings at pt sur of two mb 4 4 hawaiian events in 1996 and 1997 one occurring offshore and the second on land display time frequency arrival structures that are explainable by the dispersion characteristics over the oceanic path although other effects due to complex source time functions and shear wave and dispersive propagation effects along the initial land path cannot be separated with these single element data differences in these two events arrival structures suggest differences in normal mode content consistent with those seen in the pair of 1989 events ocean path dispersion also appears to play a significant role in determining the i n water arrival structure from a 1995 french nuclear test at mururoa recordings of two hawaiian events in 1997 by the t phase station vib and the seismic station at berkeley illustrate that the water land coupling confuses the relative timing between normal modes resulting in apparent loss of information about the source

pulsed iceberg delivery driven by sturtian ice sheet dynamics an example from death valley california the kingston peak formation is a cryogenian sedimentary succession that crops out in the death valley area california usa it is widely accepted to record pre glacial conditions kp1 followed by two glaciations of pan global extent the older sturtian kp2 to kp3 and younger marinoan glaciation kp4 in the type area the kingston range detailed facies analysis of the sturtian succession reveals that a basal diamictite unit and an upper boulder conglomerate were deposited by proglacial subaqueous sediment gravity flows an olistostrome unit punctuating the succession is interpreted to result from tectonically induced downslope mobilization during isostatic rebound triggered by significant ice meltback focussing on strata onlapping the olistostrome this article provides insight into the processes of glacial re advance following an intra sturtian glacial minimum the first 50 m of strata above the olistostrome are thinly bedded turbidites that are devoid of lonestones a trend towards thicker graded beds upsection in concert with the gradual appearance and then abundance of lonestones testifies to the influence of ice rafting and to the resumption of a direct ice sheet influence upon sedimentation stratigraphic organization into thickening and coarsening upward bedsets over a multi metre scale reveals a subaqueous gravity flow dominated succession composed of a spectrum of high to low density turbidites with thick graded boulder conglomerates at intervals the finer grained facies assemblage is heterolithic current ripple cross laminated sandstones intercalated with shales that bear delicate granule to pebble sized dropstones in abundance intervals of dropstone bearing and dropstone free strata are attributable to dynamic oscillation of the ice margin in the hinterland integrating palaeocurrent data with observations from neighbouring outcrop belts allows a detailed palaeogeographic map of the eastern death valley area to be compiled for the first time