calcretes at sequence boundaries in upper carboniferous cyclothems of the sydney basin atlantic canada abstract nodular and associated groundwater calcretes in coal bearing cyclothems of the sydney basin mark the boundary between underlying marginal marine and overlying alluvial deposits they are inferred to represent lowstand surfaces sequence boundaries the host sediments include both sand siltstones and palustrine limestones microfabrics of calcretes with detrital hosts show evidence of replacement displacement and shrinkage alpha fabrics suggesting that the calcretes formed under relatively arid conditions in contrast microfabrics of nodular calcretes with limestone hosts exhibit predominantly beta fabrics with root induced brecciation and subordinate shrinkage fabrics the calcretes and host limestones are inferred to have formed in topographic lows thick alluvial sediments with red calcic vertisols overlie the calcretes and formed within the transgressive systems tract under conditions of abundant sediment supply coals and associated hydromorphic palaeosols lie near the transgressive maximum and in the highstand systems tract the presence of calcareous palaeosols on lowstand surfaces suggests that the lowstands were times of relative climatic aridity

sequence stratigraphy of the punta ballena member of the jama formation early pleistocene ecuador insights from integrated sedimentologic taphonomic and paleoecologic analysis of molluscan shell concentrations abstract early pleistocene strata are well exposed along the uplifted eastern margin of the esmeraldas caraquez basin particularly on the coastal cliff west of the city of jama a type locality for shallow marine quaternary sedimentary exposures on north central ecuador here at least 180 m of sediments accumulated in inner shelf to subaerial settings are present jama formation this paper is concerned with the middle stratigraphic unit of the jama formation the punta ballena member pbm integrated sedimentologic paleontologic and stratigraphic observations reveal that the pbm is composed of eight disconformity bounded depositional sequences hiatal shell concentrations which formed as a consequence of landward and seaward stratal attenuation are associated with sequence bounding and intrasequence surfaces together with sedimentologic characteristics these fossiliferous levels are important indicators of facies architecture and therefore are useful tools for interpreting sequence stratigraphy according to their taphonomic features and taxonomic composition the hiatal shell concentrations occurring within the pbm may be grouped into two main types each of which occupies a predictable stratigraphic position within the sequences current wave winnowed beds at the cycle base and community shell concentrations in a roughly mid cycle position current wave winnowed beds commonly underlain by thalassinoides burrows that penetrate to depths of as much as 1 5 m below ravinement surfaces are transported skeletal concentrations and formed through physical processes in shallow high energy environments they comprise a time averaged mixture of specimens having different ecologies and states of preservation and accumulated mainly under conditions of total passing of siliciclastic sediment i e terrigenous sediments are delivered to the site as suspended load but owing to the high environmental energy failed to accumulate community shell concentrations occur in sparsely fossiliferous intervals and result from reduced net sedimentation within low energy relatively deeper settings they are composed of matrix supported loosely clustered life oriented and little disturbed fossil assemblages but are packed in excess of likely living densities and are visually dominated by successive generations of the infaunal bivalve raeta undulata which colonized a slowly aggrading muddy seafloor the sedimentological and paleontological evidence presented here not only supports the results of previous studies which demonstrate the value of condensed shell concentrations in the identification of stratigraphically significant surfaces but also provides adds to the distinctive features of these shell beds

anatomy of extremely thin marine sequences landward of a passive margin hinge zone neogene calvert cliffs succession maryland u s a abstract detailed examination of neogene strata in cliffs 25 35 m high along the western shore of chesapeake bay maryland reveals the complexity of the surviving record of siliciclastic sequences 150 km inland of the structural hinge zone of the atlantic passive margin previous study of the lower to middle miocene calvert plum point member and choptank formations documented a series of third order sequences 7 10 m thick in which lowstand deposits are entirely lacking transgressive tracts comprise a mosaic of condensed bioclastic facies and regressive highstand tracts are present but partially truncated by the next sequence boundary smaller scale fourth order cyclic units could not be resolved together these sequences constitute t e transgressive and early highstand tracts of a larger second order miocene composite sequence the present paper documents stratigraphic relations higher in the calvert cliffs succession including the upper miocene st marys formation which represents late highstand marine deposits of the miocene second order sequence and younger neogene fluvial and tidal inlet deposits representing incised valley deposits of the succeeding second order cycle the st marys formation consists of a series of tabular units 2 5 m thick each with an exclusively transgressive array of facies and bounded by stranding surfaces of abrupt shallowing these units which are opposite to the flooding surface bounded regressive facies arrays of model parasequences are best characterized as shaved sequences in which only the transgressive tract survives and are stacked into larger transgressive highstand and forced regression sets biostratigraphic analyses by others indicate that this onshore record contains the same number of third order 1 my duration units as present offshore and so thinning landward of the hinge zone was accomplished not by omission or erosion of entire cycles of deposition but instead by omission of some subsidiary elements e g lowstand tracts by erosional shaving of sequence tops removing the entire regressive tract in some sequences by a reduced number of component high order cycles surviving per larger set and by qualitative changes in the anatomy or composition of elements e g condensed transgressive tracts shaved sequences rather than parasequences all of these differences can be attributed to limited accommodation ut preservation of an onshore record of each baselevel cycle was probably also favored by the large amplitude and rapidity of eustatic fluctuations during the miocene

unraveling tectonic and climatic controls on synorogenic growth strata northern apennines italy we develop a new high resolution stratigraphic age model to unravel the contributions of tectonic and climatic processes on early to late pleistocene synorogenic growth strata we capitalize on excellent continuous exposures along the flank of the po foreland in northern italy to elucidate hydrologic geomorphic and sedimentologic processes that are regularly attributed to but rarely proven to be caused by glacial interglacial climatic changes and unsteady rock uplift we perform our analysis on the enza section a succession of marine and terrestrial strata exposed along the enza river between parma and reggio emilia northern italy bedding in the enza section displays synorogenic growth strata geometry with bedding dips that range from 2 to 55 that becomes progressively shallower upsection we develop an age model that incorporates biostratigraphy magnetostratigraphy rock magnetic cyclostratigraphy cosmogenic radionuclide burial dating and optically stimulated luminescence dating and shows that the enza section spans the interval between 0 04 and 1 65 ma furthermore the age model pins the time of deposition for several lithostratigraphic units of regional significance and shows that sediment accumulation was unsteady ranging from 14 31 cm k y in the marine part of the section to 5 362 cm k y in the overlying littoral and terrestrial part of the section unsteady deposition is most pronounced in the terrestrial deposits where thick fluvial gravel packages accumulated in short 10 15 k y time periods that coincide with quaternary glacial intervals there is direct evidence for a dominant tectonic control in the older marine part of the section here sediment accumulation rates on the limb of the fold growing along this portion of the northern apennine mountain front show that between 1 07 and 1 65 ma repetitive progradation of neritic sand units directly followed pulses of rapid punctuated uplift in contrast the cyclic terrestrial facies variations in the enza section reveal that once the section became emergent at ca 1 ma and uplift slowed climate was the dominant control on sediment production and deposition

inferred glacio eustatic control for high frequency depositional sequences of the plio pleistocene kazusa group a forearc basin fill in boso peninsula japan abstract the plio pleistocene forearc basin fill of the kazusa group as much as 3000 m thick is represented by a series of marine environments ranging from deep sea basin plain to shallow sea it developed during about 2 4 to 0 45 ma and is well exposed in the boso peninsula japan chronostratigraphic resolution of the kazusa group is partly within about 0 05 m y based on the combination of fission track dating of volcanic ash layers and bio and magneto stratigraphy many volcanic ash layers are intercalated in the kazusa group and provide distinct chronostratigraphic surfaces within the heterogeneous lithologies detailed outcrop studies on depositional facies discontinuities and lateral terminations of volcanic ash layers allow high resolution sequence stratigraphic interpretation of the kazusa group seventeen depositional sequences were identified in the kazusa group each depositional sequence was tentatively correlated with the stable oxygen isotope sea level index integrated with the age framework of the kazusa group this correlation indicates that frequencies of the depositional sequences can be estimated to be in the range of 0 2 0 02 m y and are within fourth and fifth order stratigraphic cyclicities depositional sequences constitute third order transgressive and highstand sequence sets and the kazusa group is interpreted to represent a third order composite sequence with a duration of about 1 95 m y development of the third order composite sequence was also controlled by an overall rise and fall of glacio eustatic sea levels overprinted by tectonic events related to fluctuations in oceanic plate motion which occurred at about 2 6 ma and 0 5 ma respectively

plio quaternary uplift rates in the outer zone of the central apennines fold and thrust belt italy abstract geological seismic and borehole data permitted the reconstruction of the plio quaternary uplift subsidence and erosion sedimentation history for the outer sector of the central apennines during the latest contractional stages middle late pliocene the frontal sector of the belt experienced a net subsidence locally compensated by the growth of the fold and thrust system this tectonic uplift was localized at the axial culmination of the anticlines and particularly for the major structures was responsible for exhumation and erosion of the neogene succession and for near flat planation surfaces development on meso cenozoic carbonate rocks at the crest of the anticlines since the early middle pleistocene a regional doming involved the outer part of the belt peri adriatic domain this process interacted with quaternary eustatic sea level fluctuations and caused the basinward migration of shallow marine deposits forming an overall prograding system quaternary shoreline retreat base level drop and climatic changes were mainly associated with valley deepening and fluvial terrace formation the present study outlines that fold thrust growth and regional doming driving processes characterized by different amplitude wavelength and uplift rate amounts are both responsible for the morphological setting of the central apennines external zones

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

multi channel seismic imaging of a crustal magma chamber along the east pacific rise a reflection observed on multi channel seismic profiles along and across the east pacific rise between 8 50 n and 13 30 n is interpreted to arise from the top of a crustal magma chamber located 1 2 2 4 km below the sea floor the magma chamber is quite narrow 4 6 km wide but can be traced as a nearly continuous feature for tens of kilometres along the rise axis

rapid crustal accretion and magma assimilation in the oman u a e ophiolite high precision u pb zircon geochronology of the gabbroic crust 1 new high precision u pb zircon geochronology from the oman united arab emirates u a e ophiolite provides insight into the timing and duration of magmatism and the tectonic setting during formation of the lower crust the new data come from a well preserved and exposed crustal section in the center of the wadi tayin massif single grain and grain fragment 206pb 238u dates from upper level gabbros tonalites trondhjemites and gabbroic pegmatites corrected for initial th exclusion range from 112 55 0 21 to 95 50 0 17 ma with most data clustered between 96 40 0 17 to 95 50 0 17 ma zircon dates from upper level gabbros are most consistent with the ophiolite forming at a fast spreading ridge with half rates of 50 100 km ma dates from tonalites trondhjemites and from a gabbroic pegmatite associated with a wehrlite intrusion overlap with dates from adjacent upper level gabbros suggesting that any age differences between these three magmatic series are smaller than the analytical uncertainties or intrasample variability in the dates three of the dated upper level gabbros and a single gabbroic pegmatite from the base of the crust have 1 ma intrasample variability in single grain dates suggesting assimilation of older crust during the formation or crystallization of the magmas whole rock end t of seven samples including the upper level gabbros with variable zircon dates have tightly clustered initial values ranging from end 96 ma 7 59 0 23 to 8 28 0 31 the end values are similar to those from other gabbros within the ophiolite suggesting that any assimilated material had a similar isotopic composition to primitive basaltic magmas the new dates suggest that the studied section formed at a fast spreading mid ocean ridge between 96 4 95 5 ma the large intrasample variability in zircon dates in some samples is unexpected in this setting and may be related to propagation of a younger ridge into older oceanic lithosphere

high resolution sequence stratigraphy of clastic shelves iii applications to reservoir geology abstract high frequency clastic shelf sequences contain porous deposits consisting of coastal to shallow water sandstones and conglomerates which may represent very good reservoirs and therefore critical targets for exploration and production as well as for fluid hydrocarbon water or co2 storage the study of these reservoirs following a sequence stratigraphic approach is essential to predict their features and distribution within systems tracts forming high frequency sequences which in turn compose higher rank systems tracts and sequences a critical aspect to improve the exploitability of the reservoirs is their heterogeneity which directly affects the volume of the reservoirs and determine internal compartmentalization the heterogeneity can be primary related to depositional processes influencing grain size and facies distribution and secondary related to diagenesis in particular the primary heterogeneity is referred to the facies variability from distal to proximal settings to the accumulation of condensed shell beds and to facies characteristics of bedsets whereas the secondary heterogeneity derives from diagenetic processes at sequence stratigraphic surfaces and facies contacts and within sandbodies both the distribution of reservoirs and their heterogeneity can be predicted following a high resolution sequence stratigraphic approach ultimately the integration of subsurface data with the analysis of outcrop analogs is essential to better understand the features of clastic shelf reservoirs and to develop 3d models of fluid migration

crystallization depth beneath an oceanic detachment fault odp hole 923a mid atlantic ridge oceanic detachment faults are increasingly recognised as playing an integral role in the seafloor spreading process at slow and ultraslow spreading mid ocean ridges with significant consequences for the architecture of the oceanic lithosphere although melt supply is considered to play a critical control on the formation and evolution of oceanic detachments much less well understood is how melts and faults interact and influence each other few direct constraints on the locus and depth of melt emplacement in the vicinity of detachments are available gabbros drilled in odp hole 923a near the intersection of the mid atlantic ridge and the kane transform fault 23 n the mark area represent magmas emplaced into the footwall of such a detachment fault and unroofed by it we here present u pb zircon dates for these gabbros and associated diorite veins which when combined with a tectonic reconstruction of the area allow us to calculate the depths at which the melts crystallized th corrected single zircon u pb dates from three samples range from 1 138 0 062 ma to 1 213 0 021 ma we find a crystallization depth of 6 4 1 7 1 3 km and estimate that the melts parental to the gabbros were initially emplaced up to 1 5 km deeper at 8 km below the seafloor the tectonic reconstruction implies that the detachment fault responsible for the exposure of the sampled sequence likely crossed the ridge axis at depth suggesting that melt emplacement into the footwall of oceanic detachment faults is an important process the deep emplacement depth we find associated with detachment mode spreading at 1 2 ma appears to be significantly greater than the depth of magma reservoirs during the current magmatic mode of spreading in the area suggesting that the northern mark segment preserves a recent switch between two temporally distinct modes of spreading with fundamentally different lithospheric architecture this article is protected by copyright all rights reserved

high precision zircon u pb geochronology of astronomically dated volcanic ash beds from the mediterranean miocene several orbitally tuned miocene sedimentary sequences around the mediterranean contain abundant intercalated volcanic ash beds these sequences provide the rare opportunity to directly compare radioisotopic dating methods with independent and accurate deposition ages derived from astrochronology we present a large data set n 16n 16 n 166n 166 of zircon u pb dates obtained by chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims techniques for ash beds from an almost continuous orbitally tuned messinian to langhian 6 2 15 4 ma sedimentary sequence exposed along the adriatic coast south of ancona italy we use this unique data set to evaluate 1 the accuracy of zircon u pb dates 2 the significance of initial intermediate daughter product disequilibria for zircon u pb geochronology of young rocks 3 the effect of prolonged pre eruption zircon crystallization and zircon recycling on u pb derived ash bed deposition ages and 4 discuss the implications for the intercalibration of radioisotope geochronometers and the calibration of the geologic time scale

accretion and oxidation of a superfast spread axial melt lens tims and sims zircon analyses of the iodp hole 1256d gabbros abstract iodp hole 1256d penetrates a complete section of upper oceanic crust spread from the east pacific rise at a full rate of up to 220 mm yr here we present u pb zircon data from hole 1256d gabbroic rocks using isotope dilution thermal ionization mass spectrometry id tims and secondary ion mass spectrometry sims three gabbro samples yielded th corrected weighted mean 206pb 238u sims dates of 15 03 0 14 ma 15 13 0 35 ma and 15 23 0 12 ma an id tims th corrected weighted mean 206pb 238u date of 15 191 0 040 ma from the first of the three samples provides verification and refinement of the timing of magmatism the u pb dates agree with the predicted age of the crust based on marine magnetic anomalies suggesting the gabbros most likely formed by intrusion and crystallization at or near the ridge axis zircons from two of the studied samples have anomalously high th u ratios likely reflecting oxidation of u prior to or during zircon crystallization the elevated o2 of late stage melts in the axial melt lens may be related to progressive crystallization assimilation of hydrothermally altered sheeted dikes and gabbros and or contamination of the melt lens by seawater derived saline brines

palaeoenvironmental reconstruction of late quaternary foraminifera and molluscs from the enea borehole versilian plain tuscany italy abstract foraminifera and molluscs from the 90 m deep enea borehole versilian plain central italy were studied for paleoenvironmental purposes palaeontological analyses integrated with u th and radiocarbon data helped to recognize late quaternary sea level changes and supplied results on tectonic mobility of the area the study highlighted four sedimentary phases the first phase consists of a shore environment attributed to mis 7 1 a hiatus corresponding to mis 6 is hypothesized at the top of this interval recognition of the paleo shoreline of mis 7 1 at 72 8 m signifies a vertical displacement due to the extensional tectonics of the apennine orogenesis the second phase consists of a transgressive succession with evidence of warm temperatures which was interpreted as part of the transgression leading to the mis 5 5 highstand the third phase includes sub aerial and lacustrine deposits radiocarbon dates and palaeoecological reconstruction led us to attribute this interval to mis 4 mis 3 and mis 2 the fourth phase begins with a lagoon environment attributable to holocene sea level rise and ends with marsh episodes signifying the progradation of the alluvial plain this reconstruction confirms the hypothesis of tectonic stability for the versilian area during the holocene

structural pattern of the galapagos microplate and evolution of the galapagos triple junctions a 13 000 km2 microplate intervenes to prevent the junction of the nazca cocos and pacific plates in the eastern equatorial pacific ocean west of the galapagos islands the microplate is rotating clockwise at 6 m y about an absolute pole 400 km southeast of its center so that although its northern margin has a similar motion to adjacent parts of the cocos plate its southern margin is 50 slower the perimeter of the galapagos microplate is best defined by bathymetry and has been surveyed with sea beam and examined by deep tow two of the three triple junctions on its margins are ridge ridge ridge rrr junctions 160 km apart on the crest of the east pacific rise epr the most like a classic rrr junction is the pacific nazca galapagos intersection at 1 10 n where the epr axis is joined by a narrow volcanic ridge 70 km long and 1 km high the cocos nazca galapagos junction at the west end of the cocos nazca spreading center is inferred to be of the rff type but the transform fault branches are represented by large nontransform offsets lack of stable transform faults is related to rapid westward migration of the junction caused by lengthening of the cocos nazca axis at 60 70 mm yr this rate which was once required to maintain a stable nazca cocos pacific rrr junction has persisted even after birth of the microplate about 1 ma continuing propagation of the cocos nazca axis has opened up the hess deep rift basin in the eastern epr flank in advance of the eruptive propagator tip this rift valley has a relief of more than 3 km from its uplifted rims to the floor where severe attenuation exposes basal layers of the epr crust the similar dietz deep rift basin at the southeastern margin of the microplate 70 km from hess deep was formed when a lengthening galapagos nazca spreading axis rifted through another part of the epr flank

constraints on the magmatic evolution of the oceanic crust from plagiogranite intrusions in the oman ophiolite we present major and trace element as well as sr nd and hf isotope data on a suite of 87 plutonic rock samples from 27 felsic crustal intrusions in seven blocks of the oman ophiolite the rock compositions of the sample suite including associated more mafic rocks range from 48 to 79 wt sio2 i e from gabbros to tonalites the samples are grouped into a ti rich and relatively light rare earth element lree enriched p1 group ce yb n 0 7 resembling the early v1 lavas and a ti poor and lree depleted p2 group ce yb n 0 7 resembling the late stage v2 lavas based on the geochemical differences and in agreement with previous structural and petrographic models we define phase 1 p1 and phase 2 p2 plutonic rocks felsic magmas in both groups formed by extensive fractional crystallization of olivine clinopyroxene plagioclase apatite and ti magnetite from mafic melts the incompatible element compositions of p1 rocks overlap with those from mid ocean ridges but have higher ba nb and th nb trending towards the p2 rock compositions and indicating an influence of a subducting slab the p2 rocks formed from a more depleted mantle source but show a more pronounced slab signature these rocks also occur in the southern blocks with the exception of the tayin block of the oman ophiolite implying that the entire ophiolite formed above a subducting slab initial nd and hf isotope compositions suggest an indian morb type mantle source for the oman ophiolite magmas isotope compositions and high th nb in some p2 rocks indicate mixing of a melt from subducted sediment into this mantle

proximal distal ichnofabric changes in a siliciclastic shelf early pliocene guadalquivir basin southwest spain abstract the lower pliocene deposits cropping out along the atlantic coast of cadiz in the conil cabo roche area formed on a shelf gently deepening towards the w nw up to five types of facies can be recognized distributed in belts from proximal to distal parts of the shelf 1 coarse grained sandstone with trough cross stratification facies on the most proximal parts of the shelf inner shelf deposits 2 medium grained sandstone with low angle planar cross stratification facies deposited in a more distal position due to storm currents transporting sediment offshore this facies intercalates with the previous trough cross bedded sandstone 3 massive fine grained sandstone and siltstone facies laterally and vertically related with the previous facies type and representing sediments formed in the middle shelf close to the storm wave base 4 tabular sandstone bed facies corresponding to storm bed deposits intercalated within the two previous facies 5 greenish bluish shale facies accumulated on the outer shelf below storm wave base three ichnofabrics associated with these facies are recognized 1 the two cross bedded facies are dominated by a macaronichnus ichnofabric characterized by macaronichnus and bichordites traces that represent colonization of a shifting sandy substrate by polychaetes macaronichnus tracemakers and by sea urchins bichordites producers 2 a rosselia ichnofabric consisting of vertical traces of rosselia cross cutting macaronichnus characterizes the interval of massive fine grained sandstone and silt facies and interbedded tabular sandstones this ichnofabric formed under high sedimentation rates with rosselia traces exhibiting stacked patterns that indicate vertical readjustment following deposition 3 massive fine grained sandstone and silt facies are distinguished by a cylindrichnus ichnofabric this fabric was produced by the activity of a moderately diverse community dominated by sessile burrow dwelling probably superficial detritus feeding polychaetes rosselia and cylindrichnus tracemakers and vagile deposit feeding polychaetes planolites producers in addition infaunal deposit detritus feeders producing spreiten structures teichichnus are found in distal areas pervasive indistinct mottling of the sediment of this facies was probably due to the activity of very shallow burrowers in the uppermost sediment tiers this proximal distal replacement of ichnofabrics reflects the change of benthic communities across the shelf this distribution does not fit the traditional seilacherian ichnofacies model for soft ground shallow marine settings in which proximal vertical dwelling burrows of the skolithos ichnofacies dominate high energy environments in the pliocene of cadiz shallow tier burrows of deposit detritus feeders characterize the high energy facies instead which fit better with the cruziana ichnofacies this deviation can be related with the particular palaeoenvironmental conditions thus vagile opportunistic deposit feeders colonized the dune foreset when the dunes were stable and the progradation of the structure favored the preservation of the traces

major controls on architecture sequence stratigraphy and paleosols of middle pleistocene continental sediments qc unit eastern central italy abstract middle pleistocene continental sediments in central italy qc unit record the oldest fluvial accumulation along the uplifting margin of the peri adriatic basin the architecture of the sediment body can be divided into two unconformity bounded fining upward cycles interpreted as genetically related depositional sequences these sequences highlight the systematic adjustment of the fluvial system to changes in the ratio between accommodation space and sediment supply a s ratio and from base to top comprise the following surfaces and stratal components i a regionally correlative sequence boundary resulting from an a s ratio 0 ii a low accommodation systems tract characterized by conglomerate rich amalgamated channel fills and recording an a s ratio 1 and v a mature red argillic paleosol to constrain the climatic signal for paleosols formation the two sequence capping mature paleosols have been investigated the results of these studies suggest that they were developed under humid and warm climatic conditions associated with interglacial phases which have been correlatively attributed to marine oxygen isotope stages 11 and 9

marine and nonmarine deposition in a long term low accommodation setting an example from the middle pleistocene qm2 unit eastern central italy abstract facies anatomy and large scale stratigraphic organization of mid pleistocene strata qm2 unit exposed near the town of ortona eastern central italy have been defined through an integrated outcrop and subsurface dataset and record sedimentation within a long term low accommodation setting the studied interval can be subdivided into nine facies associations reflecting a range of continental marginal marine nearshore and innermost shelf environments and contains a well preserved record of high frequency relative sea level changes in the form of a stack of three unconformity bounded sequences each of the three sequences designated qm23 qm22 and qm21 from oldest to youngest consists of a specific subset of the nine identified facies associations as a function of preserved depositional systems and systems tracts typically the following architectural elements occur in ascending stratigraphic order i a basal unconformity molded by fluvial incision and subaerial exposure during sea level fall and shoreface erosion during subsequent rise ii a maximum regressive surface which is coincident with the sequence boundary iii a transgressive systems tract including braided river conglomerates and floodplain fines within the confines of an incised valley palustrine carbonates and back barrier lagoon mudstones and a deepening and fining upward shoreface to offshore transition facies succession bounded at the base by a wave ravinement surface iv a sharp regressive surface of marine erosion produced by shoreface incision during relative sea level fall and v a prograding downstepping and offlapping sharp based lithofacies assemblage of either beach conglomerates or sandstones ascribed to the falling stage systems tract overlain by a rooted paleosol marking subaerial exposure sequences were deposited on the uplifting palaeo adriatic shelf in response to repeated high frequency and high amplitude eustatic changes in sea level that would promote the creation of accommodation space by subtracting space to deposition the contemporaneous regional uplift of the basin margin may be accounted for the shingled downstepping configuration of individual sequences to form a falling stage sequence set of a larger composite sequence in dip view the erosional contact at the base of the qm2 falling stage sequence set is a composite regressive surface resulting from the downdip convergence and amalgamation of multiple erosional surfaces produced by the progressive basinward translation of successive sequences results from this study have direct implications for the oil and gas field development and exploration when making predictions of reservoir and seal geometries within shallow marine marginal marine and nonmarine sediments emplaced in similar long term limited accommodation settings

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

formation of fast spreading lower oceanic crust as revealed by a new mg ree coupled geospeedometer abstract a new geospeedometer is developed based on the differential closures of mg and rare earth element ree bulk diffusion between coexisting plagioclase and clinopyroxene by coupling the two elements with distinct bulk closure temperatures this speedometer can numerically solve the initial temperatures and cooling rates for individual rock samples as the existing mg exchange thermometer was calibrated for a narrow temperature range and strongly relies on model dependent silica activities a new thermometer is developed using literature experimental data when the bulk closure temperatures of mg and ree are determined respectively using this new mg exchange thermometer and the existing ree exchange thermometer this speedometer can be implemented for a wide range of compositions mineral modes and grain sizes applications of this new geospeedometer to oceanic gabbros from the fast spreading east pacific rise at hess deep reveal that the lower oceanic crust crystallized at temperatures of 998 1353 c with cooling rates of 0 003 10 2 c yr stratigraphic variations of the cooling rates and crystallization temperatures support deep hydrothermal circulations and in situ solidification of various replenished magma bodies together with existing petrological geochemical and geophysical evidence results from this new speedometry suggest that the lower crust formation at fast spreading mid ocean ridges involves emplacement of primary mantle melts in the deep section of the crystal mush zone coupled with efficient heat removal by crustal scale hydrothermal circulations the replenished melts become chemically and thermally evolved accumulate as small magma bodies at various depths feed the shallow axial magma chamber and may also escape from the mush zone to generate off axial magma lenses

a late eocene date for late triassic bird tracks arising from r n melchor s de valais j f genise nature 417 936 938 2002 bird like tracks from northwest argentina have been reported as being of late triassic age1 they were attributed to an unknown group of theropods showing some avian characters however we believe that these tracks are of late eocene age on the basis of a new weighted mean 206pb 238u date isotope dilution thermal ionization mass spectrometry method on zircons from a tuff bed in the sedimentary succession containing the fossil tracks in consequence the mentioned tracks are assigned to birds and its occurrence matches the known fossil record of aves

sequence development during uplift palaeogene stratigraphy and relative sea level history of the outer moray firth uk north sea abstract published models of sequence stratigraphy have been derived from studies of the depositional history of subsiding basins during the palaeogene sediment accumulation in the outer moray firth basin of the north sea coincided with episodes of basin uplift palaeogene trends in coastal onlap and relative sea level in this basin have been estimated directly from seismic data and reveal two long duration cycles of relative sea level fall and rise the first cycle comprising over 800 m fall followed by 500 m rise was initiated in the earliest palaeocene and lasted approximately 9 my the second cycle began in the early eocene and resulted in approximately 70 m fall and 150 m rise in relative sea level over 13 my the duration of both of these cycles can be defined as second order superimposed on both of these long term second order cycles are higher frequency variations in relative sea level with periodicities of around 1 5 my and amplitudes of up to 150 m these shorter cycles are associated with the deposition of sequences identified on the seismic data one of the effects of this superimposition was to either subdue or enhance the development of systems tracts within the sequences enhancement took place where the sea level trends were similar on both the long and the short duration curves e g both rising systems tracts were subdued where sea level trends were opposed in general lowstands and transgressive systems tracts showed significant enhancement within a sequence when the sequence coincided with the steeply falling and steeply rising portions respectively of the long duration relative sea level cycle groups of these skewed sequences are stacked in certain distinct patterns termed sequence sets the pattern type is again dependent on the coincidence of the group of sequences with the second order cycle in general downstepping sequence sets are associated with the steeply falling part of the second order cycle progradational sequence sets with the gently falling to gently rising portion and retrogradational sequence sets with the steeply rising portion these stacking patterns reflect large scale changes in accommodation volume the multi sequence depositional record of a tectonically driven long duration cycle of relative sea level can be considered as a composite sequence where its systems tracts are composed of sequence sets

the stillwater complex integrating zircon geochronological and geochemical constraints on the age emplacement history and crystallization of a large open system layered intrusion a reply to the comment by rais latypov on wall et al j petrology 59 153 190 2018

distributed deformation ahead of the cocos nazca rift at the galapagos triple junction the galapagos triple junction is not a simple ridge ridge ridge rrr triple junction the cocos nazca rift c n rift tip does not meet the east pacific rise epr instead two secondary rifts form the link incipient rift at 2 40 n and dietz deep volcanic ridge the southern boundary of the galapagos microplate gmp at 1 10 n recently collected bathymetry data are used to investigate the regional tectonics prior to the establishment of the gmp 1 5 ma south of c n rift a band of northeast trending cracks cuts epr generated abyssal hills it is a mirror image of a band of cracks previously identified north of c n rift on the same age crust in both areas the western ends of the cracks terminate against intact abyssal hills suggesting that each crack initiated at the epr spreading center and cut eastward into pre existing topography each crack formed a short lived triple junction until it was abandoned and a new crack and triple junction initiated nearby between 2 5 and 1 5 ma the pattern of cracking is remarkably symmetric about c n rift providing support for a crack interaction model in which crack initiation at the epr axis is controlled by stresses associated with the tip of the westward propagating c n rift the model also shows that offsets of the epr axis may explain times when cracking is not symmetric south of c n rift cracks are observed on seafloor as old as 10 5 ma suggesting that this triple junction has not been a simple rrr triple junction during that time

seasonal cycle of velocity in the atlantic north equatorial countercurrent as measured by surface drifters current meters and ship drifts this report describes the general circulation and seasonal variation of currents in the equatorial atlantic concentrating on the north equatorial countercurrent necc using data collected as part of the seasonal response of the equatorial atlantic and programme francais ocean et climat dans l atlantique equatorial experiments plus historical ship drifts during 1983 1985 the lagrangian circulation was studied by launching and tracking 30 freely drifting drogued buoys in the north equatorial countercurrent and 23 in the south equatorial current sec in addition continuously recording current meters were moored for 20 months at depths from 20 to 300 m near the center of the necc at 6 n 28 w these measurements are the longest series ever obtained in this current and provide information about its seasonal and interannual variations and zonal meridional and vertical structure the seasonal cycle of the necc is very regular from year to year each year the necc starts up in may june it flows eastward across the atlantic with surface speeds of up to 143 cm s in the west extending down to 350 m at 28 w and flowing into both the guinea current and north equatorial current it disappears or reverses from about january june west of 18 w some near surface water of the necc is inferred to downwell and flow equatorward toward the equatorial undercurrent the sec flows into the north brazil current which during spring continues up the coast into the caribbean during fall however the whole north brazil current retroflects or turns back on itself between 45 and 50 w forming the western necc the retroflection establishes a meander pattern in the necc that slowly propagates westward during fall at a speed of 4 cm s the meanders have a displacement of about 300 km in latitude a wavelength of 900 km and meridional velocity fluctuations of up to 100 cm s the swift currents and time dependent meanders in the western necc cause a high eddy kinetic energy 2400 cm2 s2 equivalent to that of the energetic part of the gulf stream

hummocky cross stratification from the lower jurassic hasle formation of bornholm denmark abstract the exposed part of the lower pliensbachian hasle formation is composed of coarse siltstone and fine grained sandstone and is hummocky cross stratified throughout the stratification can be described as amalgamated h and or hf divisions the dott bourgeois ideal sequence for hummocky cross stratification is slightly modified so that the basal pebbly lag is extended to include the graded and laminated pebbly portion at the base of the h division the suggestion to include a parallel laminated p division below the h division is not followed the hummocks of the hasle formation are mainly of erosional nature but hummocks representing growing bed forms have been observed the formation was deposited in an open marine shelf 1 2 km from the fault controlled coast lines the hummocky cross stratification was probably formed in depths of 10 40 m by combined flow storm currents representing along coast geostrophic flows storms were frequent and the coastline faced a wide epeiric sea with a fetch towards the west of possibly 1000 km the hettangian of bornholm represents an overall transgressive or deepening sequence passing from lacustrine over fluvial to tidal flat deposits the recognition of hummocky cross stratification in the hasle formation thus indicates that the deepening continued in the pliensbachian this conforms with published curves on eustatic sea level changes

temperature variations in the equatorial atlantic as revealed by drifting buoys from may through september 1983 surface buoys deployed as a component of the focal experiment programme francais ocean et climat dans l atlantique equatorial drifted in the cold waters of the south equatorial current in the equatorial atlantic ocean the surface temperature sst is analysed along the buoy tracks in late may the strong temperature drop near 4 w and 3 s is associated with vertical mixing as cold patches appear near the equator horizontal advection is important in june and july as the cold water tongue expands southwards and westwards it is also important later in the western atlantic south of the equator where the cooling by advection is balanced primarily by heating from the atmosphere

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

zircon dating of oceanic crustal accretion most of earth s present day crust formed at mid ocean ridges high precision uranium lead dating of zircons in gabbros from the vema fracture zone on the mid atlantic ridge reveals that the crust there grew in a highly regular pattern characterized by shallow melt delivery combined with results from previous dating studies this finding suggests that two distinct modes of crustal accretion occur along slow spreading ridges individual samples record a zircon date range of 90 000 to 235 000 years which is interpreted to reflect the time scale of zircon crystallization in oceanic plutonic rocks

the temporal and spatial distribution of magmatism during lower crustal accretion at an ultraslow spreading ridge high precision u pb zircon dating of odp holes 735b and 1105a atlantis bank southwest indian ridge abstract ocean drilling program hole 735b at atlantis bank on the southwest indian ridge sampled 1508 m of plutonic oceanic crust hosted in the footwall of an oceanic detachment fault we present new high precision isotope dilution thermal ionization mass spectrometry id tims u pb zircon dates from samples spanning the length of hole 735b and from the shallower adjacent hole 1105a 158 m the new dates provide the most complete and precise record of both the spatial and temporal distribution of magmatism during accretion of the lower oceanic crust to date whole rock and mineral geochemistry from hole 735b define three main igneous series weighted mean 206pb 238u dates suggest each igneous series intruded beneath the preceding series weighted mean 206pb 238u dates range from 12 175 to 11 986 ma in series 1 11 974 to 11 926 ma in series 2 and 11 936 to 11 902 ma in series 3 0 015 to 0 069 ma weighted mean 206pb 238u dates from hole 1105a range from 11 9745 to 11 9573 ma 0 0082 to 0 0086 ma the hole 1105a dates are coeval with series 2 in hole 735b consistent with previous correlations of fe ti oxide rich layers between the two holes suggesting individual magmatic series formed sheet like bodies that were 250 m thick and extended 1 1 km parallel to the ridge axis e w and 0 48 km in the spreading direction n s the data suggest a total duration of magmatism in hole 735b of 0 214 0 032 ma corresponding to accretion over a horizontal distance of 2 6 0 4 km the crust at atlantis bank was formed during active detachment faulting and the successive underplating of each magmatic unit may have been favored in this environment the combined u pb dates and reported ti in zircon temperatures are consistent with magmatic cooling rates of 10 3 10 4 c ma over the temperature interval of 900 700 c

u th ra disequilibria and the extent of off axis volcanism across the east pacific rise at 9 30 n 10 30 n and 11 20 n there is widespread interest in the distance that mid ocean ridge magmatism extends beyond the neovolcanic zone off axis magmas also provide a means to map out variations across the melting zone we present 238u 230th 226ra data for 35 well characterized samples that extend up to 50 km away from the ridge axis across the east pacific rise at 9 30 n 10 30 n and 11 20 n the 230th 238u ratios range from 1 00 to 1 19 and the 226ra 230th ratios range from 1 to 2 78 the samples have a bimodal 230th 238u distribution with approximately half overlying published axial data on the u th diagram and the remainder lying close to the equiline the u series disequilibria in the majority of the samples can be explained by aging subsequent to eruption in a zone 8 km wide about the neovolcanic zone consistent with visual evidence for sample age nevertheless seven of the samples lie above calculated 230th 238u axial decay curves and or have 226ra excesses implying eruption tens of kilometers off axis these are consistent with evidence from seamounts and seismic interpretations that magmatism can extend up to 20 km off axis the implication is that magma is not as efficiently focused beneath the ridge axis as has generally been believed there is a decrease in initial 230th 238u in both these and published samples inferred to have formed off axis but there is no compelling evidence that this reflects source heterogeneity simple modeling suggests that this could be explained by a decrease in fertility and melt column length as the overlying lithosphere thickens with age and the solidus shallows

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

cyclic changes in lithofacies and molluscan content in the early pleistocene omma formation central japan related to the 41 000 year orbital obliquity abstract eleven cyclothems based on change in sedimentary facies and molluscan fossil associations are identified in the middle part of the omma formation early pleistocene in kanazawa central japan the systematic change in the molluscan fossil associations within individual cycles indicates that the oceanic conditions changed in parallel with water depth fluctuations such that an increase in water depth corresponds to a marine climatic warming these changes in water depth and oceanic conditions exactly coincides with the oxygen isotope fluctuations reported for deep sea sediments the cyclothems identified here in the omma formation can be explained best as the result of glacio eustasy with a period of the 41 000 years which corresponds to the period of orbital obliquity

molluscan palaeoecology and sedimentological features an integrated approach from the miocene meduna section northern italy molluscs were studied to reconstruct the palaeoenvironmental conditions of the miocene sequence of the torrente meduna area friuli northern italy and to compare palaeobiological results with those of an earlier sedimentological analysis the study identifies six fossil communities and relevant individual assemblages and ascribes them to palaeobiocoenoses comparable to modern mediterranean ones introduced by french marine ecologists 1 chlamys praescabriuscula community 2 pecten burdigalensis community 3 loripes dentatus assemblage 4 protoma rotifera community 5 benus ancilla assemblage and 6 venus conus community the palaeobiological analysis demonstrates that the entire miocene sequence up to the late tortonian or very early messinian was deposited within the infralittoral zone at shallow to very shallow depths onto wave influenced bottoms the greatest water depth occurred during early tortonian and was of approximately 25 m palaeobiological and sedimentological methods provide different sets of information which complement each other efficiently general environmental conditions in this case a delta influenced environment can best be reconstructed on the basis of sedimentological data however specific aspects of the environment primarily palaeobathymetry may only be interpreted by means of through palaeobiological analysis

protracted timescales of lower crustal growth at the fast spreading east pacific rise the formation of oceanic crust at mid ocean ridges is a fundamental component of plate tectonics a large fraction of the new crust is created when magmas in the lower crust cool to form gabbroic rocks the duration of magmatism during formation of the new gabbroic crust is expected to vary with plate spreading rate and has been constrained by dating gabbroic rocks at the slow spreading southwest indian ridge and mid atlantic ridge1 2 3 4 here we present high precision u pb dating of zircon minerals from gabbroic rocks formed at the fast spreading east pacific rise and exposed at hess deep we find that the zircons formed between 1 420 and 1 271 0 006 0 081 million years ago within individual samples the zircon minerals exhibit a range in formation dates of up to 0 124 myr consistent with either protracted crystallization from a magma or assimilation into the magma of older zircons from adjacent rocks the variability of zircon dates is comparable to that measured at the slow spreading mid atlantic ridge3 we conclude that the timescales of magmatic processes in the lower crust may be similar at slow and fast spreading ridges implying that the duration of crust formation at mid ocean ridges is not only controlled by spreading rate

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

tectonic development of the samail ophiolite high precision u pb zircon geochronology and sm nd isotopic constraints on crustal growth and emplacement 1 new high precision single grain u pb zircon geochronology and whole rock nd isotopic data provide insight into the magmatic and tectonic development of the samail ophiolite the analyzed rocks can be broadly divided into two groups based on their structural position dates and isotopic composition an older group related to on axis magmatism and a younger group of post ridge dikes sills and stocks on axis gabbros tonalites and trondhjemites yielded th corrected 206pb 238u dates from 96 441 0 062 to 95 478 0 056 ma these dates combined with dates from rioux et al 2012 suggest that most of the ophiolite crust formed at an oceanic spreading center in 1 ma the post ridge intrusions come from all depths in the crust the upper mantle and the metamorphic sole post ridge gabbros tonalites and trondhjemites from the crust and mantle yielded th corrected 206pb 238u dates of 95 405 0 062 to 95 077 0 062 ma a small trondhjemitic pod from the metamorphic sole yielded younger th corrected 206pb 238u dates of 94 90 0 38 to 94 69 0 12 ma isotopic data suggest two distinct sources for the post ridge magmas five of the gabbros and tonalites from the crust have end 96 ma 6 90 0 12 to 7 88 0 16 and two trondhjemites from the upper mantle and metamorphic sole have end 96 ma 7 77 0 08 and 7 01 0 16 the negative end t and u pb dates from the mantle dike require that subduction or thrusting was established below the ophiolite 0 25 0 5 ma after formation of the crust the bimodal isotopic composition of post ridge magmas may reflect coeval decompression and or fluid fluxed melting of the mantle and melting dehydration or assimilation of sediment in the down going plate at this time the new data place temporal constraints on mid ocean ridge and supra subduction zone models for ophiolite formation

near surface current and temperature variability observed in the equatorial atlantic from drifting buoys we examine data from 23 surface drifters which were deployed between june 1983 and july 1984 at 4 w 1 5 4 s the drifters were equipped with a window shade drogue centered at 15 m depth and in most cases a 117 m long thermistor chain drift data indicate a westward south equatorial current with typical speeds of about 20 cm s 1 south of the equator maximum westward flow of 30 40 cm s 1 occurred in june through september of 1983 and 1984 consistent with climatology near zero westward flow which was significantly weaker than was expected from climatology by about 20 cm s 1 occurred from february to april 1984 this probably represents real interannual variability and may be related to the fact that the equatorial atlantic was warmer than usual in the spring and summer of 1984 energetic variations on time scales of o 1 month and less and space scales of o 100 km and less are ubiquitous in the drift and temperature data kinetic energy levels associated with these variations south of the equator are typically 100 cm2 s 2 with slightly higher values in boreal summer energy levels north of the equator are about 500 cm2 s 2 on the basis of data available only during the boreal summer and fall the sources of this energy include inertia gravity waves instabilities of the general circulation and other phenomena for which there is no simple explanation

cracking of lithosphere north of the galapagos triple junction the galapagos triple junction is a ridge ridge ridge triple junction where the cocos nazca and pacifi c plates meet around the galapagos microplate directly north of the large scarps of the cocos nazca rift a 250 km long and 50 km wide band of northwest southeast trending cracks with volcanics at their western ends crosscuts and blankets the north south trending abyssal hills of the east pacifi c rise it appears that the roughly northeast southwest extension of east pacifi c rise generated seafl oor has been accommodated by a succession of minor rifts that during at least the past 4 m y had their triple junctions with the east pacifi c rise at distances of 50 100 km north of the tip of the propagating cocos nazca rift we propose that the rift locations are controlled by stresses associated with the dominant cocos nazca rift and scaled by the distance of its tip to the east pacifi c rise we speculate that similar ephemeral rifts occurred south of the cocos nazca rift and were instrumental in the origin of the rotating galapagos microplate ca 1 5 ma

magma emplacement differentiation and cooling in the middle crust integrated zircon geochronological geochemical constraints from the bergell intrusion central alps abstract u th pb zircon geochronology is an essential tool for quantifying the emplacement differentiation and thermal evolution of crustal magmatic systems however the power of u pb zircon dates can be enhanced through complementary characterization of mineral texture and geochemistry as this permits more detailed interpretations of geochronological datasets than conventionally achieved our approach to better relating zircon dates and geological processes consists of a multi method analytical workflow including cathodoluminescence imaging cl in situ la icpms epma zircon geochemistry u pb zircon id tims geochronology and solution icpms zircon trace element analysis u pb tims tea these methods are here applied to zircon from the bergell intrusion a composite alpine pluton preserving a 10 km mid crustal transect hand samples of tonalite granodiorite and hybridized granitoid each record 250 700 kyr of autocrystic zircon growth bergell zircons are ubiquitously zoned with ca 10 4 10 6 yr growth histories as evidenced by id tims analysis of microsampled fragments from single crystals u pb tims tea data exhibit compositional trends on multiple spatiotemporal scales including the handsample scale representing in situ differentiation at the emplacement level e g th u lithology scale defining trajectories corresponding to the production of tonalitic versus granodioritic magmas lu hf and pluton scale indicating increasingly evolved melts over 1 6 myr of pluton assembly zr hf these absolute tims tea temporal trends are corroborated by relative la icpms epma core to rim geochemistry we compare records of trace element evolution from tims tea bergell whole rock geochemistry and a global compilation of whole rock geochemical data these findings support zircon compositional evolution as a robust indicator of differentiation at local and crustal scales and provide key empirical constraints on melt differentiation and cooling timescales in the middle crust

sedimentology and high frequency sequence stratigraphy of a forearc extensional basin the miocene caleta herradura formation mejillones peninsula northern chile abstract facies and sequence stratigraphic interpretation for the 380 m thick caleta herradura formation miocene are presented based on detailed and comprehensive outcrop data from the caleta herradura half graben mejillones peninsula northern chile the caleta herradura formation contains an array of lithofacies comprising sandstones sandy mudstones diatomites and breccio conglomerates that are interpreted as the products of inner shelf to non marine depositional settings complete exposure allows for recognition of a number of distinct and laterally persistent key stratal surfaces that permitted the identification of twenty five high frequency meter to tens of meters scale sequences based on their internal organization two main motifs of such unconformity bounded depositional packages can be distinguished deepening and deepening to shallowing upwards transgressive and highstand systems tracts were resolved based on such facies stacking patterns the origin of sequences is difficult to decipher and remains somewhat uncertain however several lines of direct and indirect evidence constrain interpretations for both the sequence architecture and bounding unconformities and help to discriminate between the various mechanisms that may have driven their development in essence these demonstrate that neither tectonically driven sea level oscillations nor climatically induced changes in sediment supply can adequately explain the distinctive features of unconformities and the facies architecture of sediments they delimit instead these high frequency changes in relative sea level are best explained as a consequence of glacio eustatic oscillations the contemporaneous deep ocean proxy records appear to support a causal link between the observed stratigraphic cyclicity and glacio eustatic changes in sea level due to modulation of short term milankovitch scale events by longer period astronomical variations however the type of astronomical forcing remains elusive hindered by lack of adequate age controls and a poor understanding of pacing mechanisms of high frequency climate changes during the middle to late miocene

plate tectonics piecing together rifts earth s crust is formed where tectonic plates rift apart and upwelling magma solidifies disparate observations from rifts beneath the oceans and on land provide insights into the dynamics of rifting and opportunities for synthesis

petrochronology of zircon and baddeleyite in igneous rocks reconstructing magmatic processes at high temporal resolution zircon zrsio4 and baddeleyite zro2 are common accessory minerals in igneous rocks of felsic to mafic composition both minerals host trace elements substituting for zr among them hf th u y rees and many more the excellent chemical and physical resistivity of zircon makes this mineral a perfect archive of chemical and temporal information to trace geological processes in the past utilizing the outstanding power and temporal resolution of the u pb decay schemes baddeleyite is a chemically and physically much more fragile mineral it preserves similar information only where it is shielded from dissolution and physical fragmentation as an inclusion in other minerals or in a fine grained or non reactive rock matrix it offers the potential for dating the solidification of mafic rocks with high precision through its crystallization in small pockets of zr enriched melt after extensive olivine and pyroxene fractionation zircon and baddelelyite u pb dates are for an overwhelming majority of cases and where we can assume a closed system considered to reflect the time of crystallization the development of the u pb dating tool ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry since 2005 has led to unprecedented precision of better than 0 1 in 206pb 238u dates bowring et al 2005 increased sensitivity of mass spectrometers and low laboratory blanks due to reduction of acid volumes allow routine u pb age determinations of micrograms of material at sufficiently high radiogenic common lead ratios see schoene and baxter 2017 this volume in situ u pb age analysis using laser ablation or primary ion beam sputtering allows analysis of sub microgram quantities of zircon material from polished internal sections or zircon surfaces with spot diameters ranging from 30 m for laser ablation inductively coupled plasma mass spectrometry la icp ms to 10 m for secondary ion mass spectrometry sims lateral resolutions of 2 5 m for nanosims

characterization of the in situ magnetic architecture of oceanic crust hess deep using near source vector magnetic data marine magnetic anomalies are a powerful tool for detecting geomagnetic polarity reversals lithological boundaries topographic contrasts and alteration fronts in the oceanic lithosphere our aim here is to detect lithological contacts in fast spreading lower crust and shallow mantle by characterizing magnetic anomalies and investigating their origins we conducted a high resolution near bottom vector magnetic survey of crust exposed in the hess deep tectonic window using the remotely operated vehicle rov isis during rrs james cook cruise jc21 in 2008 hess deep is located at the western tip of the propagating rift of the cocos nazca plate boundary near the east pacific rise epr 2 15 n 101 30 w rov isis collected high resolution bathymetry and near bottom magnetic data as well as seafloor samples to determine the in situ lithostratigraphy and internal structure of a section of epr lower crust and mantle exposed on the steep 20 dipping south facing slope just north of the hess deep nadir ten magnetic profiles were collected up the slope using a three axis fluxgate magnetometer mounted on rov isis we develop and extend the vertical magnetic profile vmp approach of tivey 1996 by incorporating for the first time a three dimensional vector analysis leading to what we here termed as vector vertical magnetic profiling approach we calculate the source magnetization distribution the deviation from two dimensionality and the strike of magnetic boundaries using both the total field fourier transform inversion approach and a modified differential vector magnetic analysis overall coherent long wavelength total field anomalies are present with a strong magnetization contrast between the upper and lower parts of the slope the total field anomalies indicate a coherently magnetized source at depth the upper part of the slope is weakly magnetized and magnetic structure follows the underlying slope morphology including a bench and lobe shaped steps imaged by microbathymetry the lower part of the slope is strongly magnetized with a gradual reduction in amplitude from east to west across the slope surface morphology and recent drilling results indicate that the slope has been affected by mass wasting but the observation of internally coherent magnetization distributions within the upper and lower slopes suggest that the disturbance is surficial we attribute the spatial differences in magnetization distribution to the combination of changes in in situ lithology and depth to the source these survey lines document the first magnetic profiles that capture the gabbro ultramafic and possibly dike gabbro boundaries in fast spreading lower crust

structure of uppermost fast spread oceanic crust exposed at the hess deep rift implications for subaxial processes at the east pacific rise the uppermost 2 km of the oceanic crust created at the fast spreading 135 mm yr 1 full rate equatorial east pacific rise epr is exposed for tens of kilometers along escarpments bounding the hess deep rift mosaics of large scale digital images from the remotely operated vehicle rov argo ii and direct observations from the submersible alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units these rock units are characterized by extensive faulting fine scale fracturing and rotations of coherent crustal blocks meters to tens of meters across the uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces through most of the basaltic lava unit however lava flow contacts dip 20 70 w toward the epr and generally increase in dip downward in the section dikes cutting the lavas and in the underlying sheeted dike unit generally dip 90 40 e away from the epr deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units we interpret this upper crustal structure as the result of subaxial subsidence within 1 2 km of the epr that accommodated the thickening of the basaltic lava unit to 500 m variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply these results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the hess deep rift if this type of structure is typical of uppermost oceanic crust generated at the epr these processes may be common along fast spreading mid ocean ridges

integration of channel and floodplain suites ii vertical relations of alluvial paleosols abstract extrachannel sediments of the lower eocene willwood formation which were subdivided into different pedofacies or developmental stages exhibit two well developed orders of pedofacies sequences over which a grosser scale cyclicity is superposed simple sequences with thicknesses measured in meters are comprised of one or more soil profiles that are bounded above and below by pedogenically unmodified crevasse splay deposits on a larger scale compound pedofacies sequences are tens of meters thick and consist of several simple sequences sandwiched between channel sandstones between these sandbodies pedogenic maturity of the multistorey paleosols progressively increases and then decreases upwards in response to episodic avulsion formation of both compound and simple pedofacies seq ences was largely controlled by local patterns of deposition and erosion that produced vertical variability in both rate of sediment accumulation and parent material because paleosol maturity also reflects the effects of extrabasinal factors a pedofacies megasequence which is hundreds of meters thick developed in response to changes in tectonic activity through willwood time comparison between willwood deposits in the northern and central parts of the bighorn basin also reveals that areally differing sediment accumulation rates and thereby basin subsidence rates can be interpreted from large scale pedofacies sequences consequently paleosols are useful in determining changes in relative rates of sediment accumulation that are controlled by both intrabasinal and extrabasinal factors

dating the growth of oceanic crust at a slow spreading ridge nineteen uranium lead zircon ages of lower crustal gabbros from atlantis bank southwest indian ridge constrain the growth and construction of oceanic crust at this slow spreading midocean ridge approximately 75 of the gabbros accreted within error of the predicted seafloor magnetic age whereas 25 are significantly older these anomalously old samples suggest either spatially varying stochastic intrusion at the ridge axis or more likely crystallization of older gabbros at depths of 5 to 18 kilometers below the base of crust in the cold axial lithosphere which were uplifted and intruded by shallow level magmas during the creation of atlantis bank

long waves in the equatorial atlantic ocean during 1983 long waves appeared at a zonally oriented sea surface temperature sst front in the eastern equatorial atlantic during june and july of 1983 the low frequency westward moving long waves 1000 km 24 days are monitored in the noaa 7 satellite infrared images as meridional displacements of the front the long waves observed in the atlantic are similar to the waves previously seen in the eastern equatorial pacific with several exceptions the atlantic long waves have a shorter duration nearly three wave cycles at 15 w and the wave amplitude is limited eastward of longitude 10 w the atlantic equatorial front appears to have a minimum north south displacement between longitudes 5 w and 10 w while westward of 10 w the displacements exceed 400 km several buoys were launched south of the equator at longitude 4 w by the programme francais ocean climat en atlantique equatorial group on june 21 1983 for the first 3 weeks three of the buoys moved westward parallel to the equatorial sst front and measured relatively constant temperatures at 2 m during mid july changes were observed in the buoy temperatures the buoy trajectories and the long wave pattern a comparison of the buoy temperatures at a depth of 2 m and atmospherically corrected satellite estimates of sst show a residual dependence of the satellite data on the zenith angle even when the angle is limited to 45 in general the satellite sst measurements reproduce the trends observed in the buoy measurements but small bias differences occur between buoys and between day and nighttime sst comparisons equatorial cross sections by ship and satellite over a 7 day interval in june 1983 also show that sst trends are comparable in both sets of data

evidence for initial excess 231pa in mid ocean ridge zircons abstract a limiting factor in the accuracy and precision of u pb zircon dates is accurate correction for initial disequilibrium in the 238u and 235u decay chains the longest lived and therefore most abundant intermediate daughter product in the 235u isotopic decay chain is 231pa t1 2 32 71 ka and the partitioning behavior of pa in zircon is not well constrained here we report high precision thermal ionization mass spectrometry tims u pb zircon data from two samples from ocean drilling program odp hole 735b which show evidence for incorporation of excess 231pa during zircon crystallization the most precise analyses from the two samples have consistent th corrected 206pb 238u dates with weighted means of 11 9325 0 0039 ma n 9 and 11 920 0 011 ma n 4 but distinctly older 207pb 235u dates that vary from 12 330 0 048 ma to 12 140 0 044 ma and 12 03 0 24 to 12 40 0 27 ma respectively if the excess 207pb is due to variable initial excess 231pa calculated initial 231pa 235u activity ratios for the two samples range from 5 6 1 0 to 9 6 1 1 and 3 5 5 2 to 11 4 5 8 the data from the more precisely dated sample yields estimated dpazircon duzircon from 2 2 3 8 and 5 6 9 6 assuming 231pa 235u of the melt equal to the global average of recently erupted mid ocean ridge basaltic glasses or secular equilibrium respectively high precision id tims analyses from nine additional samples from hole 735b and nearby hole 1105a suggest similar partitioning the lower range of dpazircon duzircon is consistent with ion microprobe measurements of 231pa in zircons from holocene and pleistocene rhyolitic eruptions schmitt 2007 schmitt 2011 the data suggest that 231pa is preferentially incorporated during zircon crystallization over a range of magmatic compositions and excess initial 231pa may be more common in zircons than acknowledged the degree of initial disequilibrium in the 235u decay chain suggested by the data from this study and other recent high precision datasets leads to resolvable discordance in high precision dates of cenozoic to mesozoic zircons minor discordance in zircons of this age may therefore reflect initial excess 231pa and does not require either inheritance or pb loss

seismic analysis of the axial magma chamber reflector along the southern east pacific rise from conventional reflection profiling the thickness and internal properties of the magma sill located at the top of the axial magma chamber amc along the southern east pacific rise epr have been investigated through a combination of waveform modeling the near vertical incidence reflections from this body and analysis of reflection amplitude variation as a function of source receiver offset or slowness our results show that the amc reflector observed along the southern epr is best modeled by a thin 100 m thick sill of partial melt vs 0 km s sandwiched between higher velocity material and that the thickest sills are generally associated with the lowest p and s wave velocities the comparatively high p wave velocities and nonzero shear wave velocities inferred for this sill indicate that it is filled with partially molten magma which in some locations has a high crystal content this may have important implications for eruption mechanisms and along axis mixing of magma at the epr there is no simple relationship between morphologic indicators of magma supply e g axial depth or volume and sill thickness depth or velocity magma sill properties may be closely tied to the eruption and replenishment cycle of the amc and thus may vary on a much shorter spatial and temporal scale than axial morphology which reflects longer term variations in magma supply to the ridge

dynamic equilibrium among erosion river incision and coastal uplift in the northern and central apennines italy erosion river incision and uplift rates in the northern and central apennines italy since 0 9 ma are determined from new cosmogenic nuclide data beryllium 10 concentrations in modern and middle pleistocene sediments indicate erosion rates from 0 20 to 0 58 mm yr these rates are similar to estimates of sediment yield 0 12 0 44 mm yr river incision 0 35 mm yr and uplift 0 01 1 0 mm yr rates inferred from other methods that integrate landscape process rates since the early pleistocene these rates of landscape change are significantly lower than long term exhumation rates of 1 2 mm yr since ca 4 5 ma inferred from thermochronometry collectively these data suggest that hillslope erosion and river incision rates in the northern and central apennines have balanced local uplift rates for 1 my but that exhumation rates have slowed significantly since emergence of the mountain chain in the pliocene this condition of dynamic equilibrium was potentially achieved within ca 3 ma similar to some model predictions of hillslope and fluvial system adjustment

the petrology geochronology and tectono magmatic setting of igneous rocks in the suckling dayman metamorphic core complex papua new guinea abstract southeastern papua new guinea has hosted magmatism throughout the cenozoic with the latest phase being concurrent with active extension in the woodlark rift there the suckling dayman metamorphic core complex sdmcc has exhumed middle crustal rocks in the past few million years along a still active low angle normal fault the mai iu fault uplift of the sdmcc has exposed metasedimentary and metaigneous rocks of late cretaceous pleistocene age that record an evolution from oceanic spreading to subduction to collision and finally to subduction inversion and extensional exhumation we present new petrographic whole rock geochemical and geochronologic zircon u pb la icp ms data from the sdmcc to reconstruct its long term evolution the dominant footwall lithology of the sdmcc the goropu metabasalt has a morb composition detrital zircons from metasedimentary beds intercalated with these basalts yield u pb based maximum estimates for deposition of 103 and 72 ma suggesting a late cretaceous spreading age of the oceanic protolith bulk compositions of low grade tholeiitic meta gabbroic and tonalitic rocks yau igneous complex that intrude the goropu metabasalt reveal both enriched and depleted light rare earth element patterns zircon u pb ages from the yau igneous complex range between 60 and 57 ma providing a minimum age for the formation of the goropu metabasalt much younger syn extensional granitoids in the mafic footwall of the sdmcc have calc alkaline to high k compositions and u pb ages on zircon between 3 7 and 2 0 ma our data indicate that the mai iu fault had re activated a paleogene thrust as an extensional detachment fault by 3 7 0 2 ma u pb ages of detrital zircons in modern streams draining the footwall of the sdmcc essentially reflect the ages revealed by the paleocene and plio pleistocene intrusions xenocrystic zircons in the plio pleistocene granitoids imply that the crust underlying the metabasaltic carapace of the sdmcc consists chiefly of australian continent derived sedimentary rocks

a fossil melt lens in the oman ophiolite implications for magma chamber processes at fast spreading ridges from seismic evidence we know that a small body of magma is present at mid crustal levels beneath most fast spreading ridges and that this small sill or melt lens overlies a much broader area of hot but largely solid material a crystal mush that constitutes the lower ocean crust beyond this however we have little direct knowledge of the physical and chemical processes that operate in and below the melt lens nor the role the melt lens plays in the storage and aggregation of mid ocean ridge basalts morb we here offer constraints on the processes of melt transport modification and residence beneath fast spreading ridges from a coupled structural and geochemical study through the crustal section of the oman ophiolite concentrating on the uppermost plutonic rocks and transition into sheeted dykes we find that almost the entire oman plutonic suite the layered gabbro and most of the high level gabbro is dominated by cumulate rocks containing very low proportions of trapped interstitial melt the exception to this is the very uppermost part of the section within 150 metres of the base of the sheeted dyke complex at which level the gabbros instead display a marked heterogeneity of structure texture and composition and plutonic rocks of generally basaltic composition occur for the first time associated pegmatitic ferrogabbros formed by in situ fractionation of these liquids this horizon passes up into a more homogeneous microgabbroic facies also of basaltic composition within which isolated asymmetric doleritic chilled margins are found and thence into doleritic sheeted dykes we argue that the thin heterogeneous gabbro horizon is a fossilised melt lens containing pooled liquids of net basaltic composition mg of 65 expelled from the crystal mush beneath existing models have suggested that steep fabrics observed in homogeneous gabbros beneath this horizon formed by subsidence of originally horizontal cumulus layers formed at the base of the melt lens but this is not supported by the field relationships instead we propose that the fabrics record the buoyant ascent of magma through the mush pile probably in part by porous flow and reflect crystallisation essentially in situ without significant vertical transport of the mush low residual melt porosities in the sub melt lens region imply efficient extraction of interstitial liquid and at least episodically high permeabilities in the upper part of the lower crust

seismic structure and indicators of magma budget along the southern east pacific rise in this paper we re examine the relationship between seismically constrained variations in crustal structure along the southern east pacific rise sepr and the segment scale variations in axial depth morphology basalt geochemistry and hydrothermal activity that have often been attributed to along axis differences in the supply of magma to the mid ocean ridge along 800 km of the fast spreading sepr good correlations exist between axial depth ridge cross sectional area mantle bouguer anomaly and the mgo weight percent of basalts recovered from the rise axis these correlations indicate along axis changes in crustal thickness and temperature consistent with variations in magma supply on time scales of 100 000 years in contrast we show that the depth and width of the midcrustal magma sill the thickness of seismic layer 2a and the intensity of hydrothermal venting are poorly correlated with regional variations in ridge depth and cross sectional area we suggest that the emplacement geometry width of the intrusion zone and flow lengths not magma supply controls extrusive layer seismic layer 2a thickness we hypothesize that magma lens properties and hydrothermal activity are closely linked to spreading events dike intrusion eruptions faulting which occur on much shorter timescales 10 100 years than the longer term variations in magma supply reflected in along axis changes in the shape and depth of the ridge axis

protracted construction of gabbroic crust at a slow spreading ridge constraints from 206pb 238u zircon ages from atlantis massif and iodp hole u1309d 30 n mar sensitive high resolution ion microprobe shrimp u pb zircon ages of 24 samples from oceanic crust recovered in integrated ocean drilling program iodp hole u1309d and from the surface of atlantis massif mid atlantic ridge mar 30 n document a protracted history of accretion in the footwall to an oceanic detachment fault ages for 18 samples of evolved fe ti oxide gabbro and felsic dikes collected 40 1415 m below seafloor in u1309d yield a weighted mean of 1 20 0 03 ma mean square of weighted deviates 7 1 however the ages range from 1 08 0 07 ma and 1 28 0 05 ma indicating crustal construction occurred over a minimum of 100 200 ka the zircon ages along with petrologic observations indicate at least 2 major periods of intrusive activity with age peaks separated by 70 ka the oldest ages are observed below 600 mbsf an observation inconsistent with models requiring constant depth melt intrusion beneath a detachment fault the data are most consistent with a multiple sill model whereby sills intrude at random depths below the ridge axis over a length scale greater than 1 4 km zircon ages from broadly spaced samples collected along the southern ridge of atlantis massif yield a detachment fault slip rate of 28 7 6 7 mm a and imply significant asymmetric plate spreading up to 100 on the north american plate for at least 200 ka during core complex formation

seasonal variations of the subsurface thermal structure in the gulf of guinea abstract the subsurface thermal structure in the gulf of guinea is analyzed using the historical hydrographic data file of particular interest is the rapid vertical displacement of the thermal structure from the warm march may season to the cold july august season this displacement field is trapped at the equator with vertical and meridional scales appropriate to a second or third mode baroclinic kelvin wave it has a maximum amplitude between 4 w and 10 w with a node near 2 e south of 4 s no seasonal displacement of the thermocline underlies the seasonal variation in the sea surface temperature along the eastern boundary north of the equator to 3 e the displacement field vanishes thus the coastal upwelling associated with a vertical displacement tightly bound to the northern coast from 2 e to 10 w appears detached from the equatorial regime

tectonic controls on sequence stacking pattern and along strike architecture in the pleistocene mejillones formation northern chile implications for sequence stratigraphic models abstract in the mejillones formation a shallow marine pleistocene succession of northern chile the cyclic stratigraphic record is the result of the complex interaction of regional uplift glacio eustasy local tectonics sediment supply and sedimentary processes stratal geometries characteristics of sedimentary facies and nature of sequence bounding unconformities have been investigated to evaluate the influence of i intrabasinal short term normal faulting on both along strike variations in sequence architecture and genetic complexity of key stratal surfaces and ii long term regional uplift on sequence stacking pattern the stratigraphic succession dissected by small displacement few meters normal faults striking obliquely with respect to the palaeo shoreline trends displays systematic variations in sequence architecture and the nature of bounding surfaces across them indeed depending on position with respect to the fault plane two basic types of internal organisation can be recognised in the examined shallow marine almost clastic starved sequence within grabens it consists of a siliciclastic rich transgressive systems tract tst which is bounded beneath by a transgressively modified glossifungites demarcated sequence boundary sb rs overlain by a mollusc bearing falling stage systems tract fsst the erosional downlap surface that separates the tst from the fsst is the regressive surface of marine erosion rsme on the footwall crests the combination of marine regressive erosion during falls in relative sea level and uplift has resulted in complete removal of the sediments of the tst from these sites leading to the formation of a tectonically enhanced basal unconformity composed of the rsme superimposed onto the previous sb rs sb rs rsme the prominent lateral change in component units systems tracts and nature of bounding surfaces within the studied sequence is directly related to the presence of normal faults and indicates that fault activity had a major impact on the sequence stratigraphic evolution of the mejillones formation enhancing subsidence within the grabens and promoting unconformities in the horsts overall the mejillones formation records a long term sea level fall driven by the contemporaneous regional uplift punctuated by repeated high frequency eustatic sea level changes the effect of this superimposition was that glacio eustatic sequences were displaced progressively downward and basinward and stacked in a distinct downstepping tectonically enhanced falling stage sequence set which reflects basin wide loss in accommodation space the sequence set is underlain by a composite rsme that becomes progressively younger basinward and is made up by the lateral and down dip connection of a series of lower rank sequence boundaries including hanging wall sb rss and footwall sb rs rsmes of successive sequences

propagation of the seasonal upwelling in the eastern equatorial atlantic abstract several mechanisms have been proposed to explain the coastal and equatorial upwelling in the eastern atlantic guinea gulf the most controversial is the mechanism of remote wind forcing in the western equatorial atlantic suggested by moore et al 1978 most of the possible explanations for the upwelling and their relative importance are discussed in view of recent observations detailed analysis of daily sea surface temperature sst collected at 16 coastal stations along the northern coast of the guinea gulf reveals that the upwelling event propagates westward along this coast at a mean speed of 0 7 m s 1 similar analysis of historical monthly mean sst data shows that the coastal upwelling event propagates poleward from 1 s to at least 13 s at the same phase speed furthermore the northern hemisphere and southern hemisphere coastal upwelling signals seem to start at the same time from the equator the same kind of analysis applied to hydrographic data from a station situated 41 km off abid

effects of uplift and tilting in the central northern apennines italy abstract the morphotectonics of the central northern apennines reflect the effects of pliocene pleistocene regional uplift and tectonics high uplift rates and extensional tectonics prevailed in the axial sector while lesser uplifting eastward tilting and gravity sliding affected the periadriatic belt the axial sector has a chocolate slab pattern of blocks with intermontane depressions bounded by normal faults and characterized by differential vertical movements the periadriatic belt is a ne dipping monocline broken by transverse faults into separate blocks with different evolutionary development the evolution of the axial sector can be correlated with that of the periadriatic sector because the unconformities in the marine succession of the periadriatic basin are linked to pulses of uplift in the axial chain the amounts of coarse grained sediments in intermontane depressions and in the periadriatic belt are correlated with the erosion processes affecting the axial sector this morphostructural pattern may be connected with the formation of a long wavelength bulge associated with mantle upwelling

evaluating the temporal link between the karoo lip and climatic biologic events of the toarcian stage with high precision u pb geochronology the karoo large igneous province k lip is considered to have substantially influenced global warming marine anoxia and concomitant marine extinction in the toarcian lower jurassic the sequence and duration of these events has been uncertain thus precluding direct comparison between sedimentary successions and the k lip two relatively narrow time intervals of the early toarcian one approximately within the lower portion of the h falciferum ammonite zone and the other near the pliensbachian toarcian boundary pl to b have received much attention because they are associated with carbon isotope excursions cies and marine extinctions potential causal mechanisms have been proposed such as the release of massive amounts of carbon to the atmosphere via a catastrophic magmatic intrusive episode related to the k lip here we test the timing with four new high precision ca id tims u pb zircon ages from the toarcian stage collected from tephra interstratified with ammonite bearing carbonates in southernmost peru we also present new u pb zircon and baddeleyite data from three sills and one rhyolite of the k lip in south africa our new data permit a substantial reinterpretation of the toarcian timescale the pliensbachian toarcian boundary pl to b a prominent global extinction level must be older than 183 5 ma on the basis of our oldest tephra the h falciferum cie equivalent to the so called toarcian oceanic anoxic event is bracketed by two ash fall bed dates between 183 22 0 26183 22 0 26 and 181 99 0 13 ma181 99 0 13 ma all 2 analytical and tracer errors the cie duration is estimated at approximately 300 ka on the basis of minimum error interpolation of ammonite zone boundaries the base of the h falciferum cie appears to correlate in time with the onset k lip sill emplacement dated by the oldest sill at 183 014 0 072 ma183 014 0 072 ma however sill emplacement appears to have lasted for a minimum of 2 million years at least until 181 31 0 19 ma181 31 0 19 ma which is in disagreement with a short duration of the h falciferum negative cie furthermore our data suggest that the timing of the main volume of the k lip may have been approximately 4 5 ma this prolonged and possibly pulsed magmatic activity of the k lip may be correlated with extinction pulses and climate changes in the middle and late toarcian stage each event occurring within a unique set of global environmental conditions

evidence and implications of crustal magmatism on the flanks of the east pacific rise article i nfo article history formation of oceanic crust along the east pacific rise is thought to be complete within a few kilometers of the rise axis here however we present evidence for magmatism 20 km from the spreading center in 300 ka old crust seismic data reveal an intrusive complex 2 km beneath the seafloor which is limited in lateral extent b5 km and comprises a melt lens underlain by low velocity high attenuation crust the crustal magma body overlies a region of off axis delivery of mantle melt that results from a long lived skew between the axes of mantle upwelling and plate spreading magmatism on the flanks of the epr may be commonplace thus affecting the architecture of oceanic crust and providing the necessary conditions to drive off axis hydrothermal activity

in situ enrichment of ocean crust microbes on igneous minerals and glasses using an osmotic flow through device the integrated ocean drilling program iodp hole 1301a on the eastern flank of juan de fuca ridge was used in the first long term deployment of microbial enrichment flow cells using osmotically driven pumps in a subseafloor borehole three novel osmotically driven colonization systems with unidirectional flow were deployed in the borehole and incubated for 4 years to determine the microbial colonization preferences for 12 minerals and glasses present in igneous rocks following recovery of the colonization systems we measured cell density on the minerals and glasses by fluorescent staining and direct counting and found some significant differences between mineral samples we also determined the abundance of mesophilic and thermophilic culturable organotrophs grown on marine r2a medium and identified isolates by partial 16s or 18s rdna sequencing we found that nine distinct phylotypes of culturable mesophilic oligotrophs were present on the minerals and glasses and that eight of the nine can reduce nitrate and oxidize iron fe ii rich olivine minerals had the highest density of total countable cells and culturable organotrophic mesophiles as well as the only culturable organotrophic thermophiles these results suggest that olivine a common igneous mineral in seawater recharged ocean crust is capable of supporting microbial communities that iron oxidation and nitrate reduction may be important physiological characteristics of ocean crust microbes and that heterogeneously distributed minerals in marine igneous rocks likely influence the distribution of microbial communities in the ocean crust

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

uplifted marine terraces of the akamas peninsula cyprus evidence of climatic conditions during the late quaternary highstands an outcrop study of uplifted marine terraces provides information on the climate of past sea level maxima supplementing existing palaeoclimatological archives the western coast of the akamas peninsula shows several uplifted and intricately stacked quaternary marine terraces this study focuses on the sedimentology petrography and sequence stratigraphy of the last three recent terraces and provides palaeoclimatological reconstruction and chronological framing all three terraces display basically the same stratigraphic succession which consists of regressive sequences ranging from bioturbated storm influenced subtidal high energy sands to subaerial exposure and aeolian deposition each sequence differs in petrography reflecting contemporaneous climatic conditions the first studied sequence marine isotope stage 9 or 11 was deposited in a warm arid climate with oligotrophic water favouring ooid formation the second sequence marine isotope stage 7 displays colder but humid conditions with lower carbonate production and strong detrital input the third sequence marine isotope stage 5e records warm humid conditions with high carbonate production combined with significant detrital input these littoral terraces offer high quality outcrops of glacioeustatic dominated littoral sedimentology together with evidence indicative of the regional climate during the late pleistocene

use of trace fossils in delineating sequence stratigraphic surfaces tertiary venetian basin northeastern italy abstract the lowermost third order sequence of the venetian molasse basin upper chattian lower aquitanian in the belluno syncline is composed of a transgressive systems tract comprising a basal condensed glauconitic sand sheet deepening upwards into finer grained offshore deposits and a highstand systems tract mainly consisting of prograding offshore mudstones capped by very fine sandstones representing offshore transition deposits an integrated sedimentological ichnological and micropaleontological approach has allowed the recognition of the internal organization of the sequence the subdivision into parasequences in absence of an obvious physical expression and the characterization of significant discontinuity surfaces at both sequence and parasequence scales the transgressive surface shows a complex geometry of bored and encrusted cavities produced by erosional undercutting and a system of neptunian dykes and sills with hiatal shell concentrations as infill component parasequences in the texturally homogeneous transgressive sand sheet can be identified on the basis of the preservational state of trace fossil assemblages softground versus firmground conditions and subtle changes in grain size and glauconite content omission surfaces bounding the parasequences are marked by increased glauconite content and densely crowded predominantly vertical or oblique relatively large very distinct thin walled or unwalled and uncompacted burrows the condensed section coincides with highest values in relative abundance of planktic foraminifers and in diversity of benthic foraminifers parasequence bounding flooding surfaces in the muddy offshore portion of the highstand systems tract are recognized as firmground surfaces mantled by thin shell concentrations in a matrix of silty highly burrowed glauconitic sand

an algorithm for u pb isotope dilution data reduction and uncertainty propagation this is the publisher s version also available electronically from http onlinelibrary wiley com