an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

deep structures and surface boundaries among proto tethyan micro blocks constraints from seismic tomography and aeromagnetic anomalies in the central china orogen abstract the qinling qilian orogen preserves the records of early paleozoic convergence among the proto tethyan micro blocks in this study we analyze the seismic velocity structure and the aeromagnetic anomalies in the qinling qilian orogen and its adjacent areas showing that the northernmost boundaries of these proto tethyan micro blocks are defined by the guyuan longshoushan fault in the qilian orogen and by the luonan luanchuan fault in the qinling orogen respectively the lithosphere north of the qinling qilian orogen subducted southward under the qinling qilian orogen the boundaries of the micro blocks in the qinling qilian orogen of the proto tethys domain are mostly ew or ne trending combined with early paleozoic geological records our results indicate that the south dipping low velocity anomaly under the alxa block and the south dipping high velocity ones under the north qilian orogen and the north china block might indicate that the alxa block the north qilian oceanic slab and the north china block subducted southward the south dipping high velocity anomaly under the north qilian orogen is interpreted as the remnant of the proto tethys ocean in that area however the north dipping low velocity anomaly under the south qinling and the north qinling orogens the qaidam block and the north dipping high velocity one under the yangtze and the bikou blocks suggest that the south qinling and the north qinling orogens the qaidam the yangtze and the bikou blocks subducted northward the present spatial framework of the qinling qilian orogen is related to early paleozoic convergence among the proto tethyan micro blocks

alpha and beta diversity of encrusting foraminifera that recruit to long term experiments along a carbonate platform to slope gradient paleoecological and paleoenvironmental implications abstract the spatial and temporal distribution and diversity of sediment dwelling foraminifera are reasonably well known but encrusting hard substrate dwelling foraminifera are little studied encrusting foraminifera are common in the world s oceans attached to floating debris or marine animals in the water column to living on rocks sand grains and organisms in benthic environments from shallow to deep marine regions with projected ocean acidification and warming conditions these important calcifying protists that comprise beaches buffer sediments and contribute to complex food webs are potentially in peril results indicate that calcifying foraminifera were the first to colonize experimental molluscan substrates within the first year in shallow habitats with colonization offshore in subsequent years agglutinated foraminifera become more common after one year species richness diversity remained relatively similar throughout the study but species turnover diversity was greatest within the first year and between the shelf slope break and deeper water following the thermocline and photic zone regions the equivalent of the shannon entropy index provided important information on diversity and community structure paleobathymetric distributions can be resolved after six years into four distinct foraminiferal distributional zones shallow shelf 15 m outer shelf 33 m shelf slope break 73 88 m and slope depths 213 m to 267 m some encrusting foraminifera are invasive settling in high numbers within the first year and increasing their abundance through the duration of the experiment a foraminiferan discorbis bertheloti was discovered to bioerode carbonate and is a potentially excellent paleobathymetric indicator for 15 33 m depths results differ from previously reported pioneer and climax foraminiferal communities documented for caribbean coral reefs because long term experiments reveal the spatial and temporal development and distribution of carbonate producing encrusting foraminifera in these climatically sensitive regions

shallowly buried enigmatic seismic stratigraphy on the new jersey outer shelf evidence for latest pleistocene catastrophic erosion chirp seismic profiles reveal a prominent seismic facies boundary 0 20 m below the seafloor within an 8 6 10 2 km area of the new jersey outer shelf this irregular boundary separates seismically transparent facies from underlying stratified facies the irregularities form two populations of incisions trending northeast and east northeast stratified blocks within the transparent facies occasionally within presumed incisions together with lithologic evidence indicate that some of the transparent facies was formed by disruption of the stratified facies preservation of steep 50 90 incision flanks implies that deposition of the transparent facies closely followed disruption catastrophic erosion and redeposition following the multiple breaching of glacial lake dams to the north ca 19 12 ka constitute the likeliest mechanisms both for producing facies boundary incisions and emplacing the transparent facies implying that local forcing can generate erosional unconformities on periglacial shelves in the absence of base level change this facies boundary adds complexity to the already complex shallowly buried stratigraphic record of the last glacio eustatic cycle on the new jersey continental shelf long considered typical of periglacial shelves worldwide

tracking the last sea level cycle seafloor morphology and shallow stratigraphy of the latest quaternary new jersey middle continental shelf seafloor geomorphology and surficial stratigraphy of the new jersey middle continental shelf provide a detailed record of sea level change during the last advance and retreat of the laurentide ice sheet 120 kyr b p to present a nw se oriented corridor on the middle shelf between water depths of 40 m the mid shelf paleo shore and 100 m the franklin paleo shore encompasses 500 line km of 2d huntec boomer profiles 500 3500 hz an embedded 4 6 km2 3d volume and a 490 km2 swath bathymetry map we use these data to develop a relative stratigraphy core samples from published studies also provide some chronological and sedimentological constraints on the upper 5 m of the stratigraphic succession the following stratigraphic units and surfaces occur from bottom to top 1 r a high amplitude reflection that separates sediment 46 5 kyr old by ams 14c dating from overlying sediment wedges 2 the outer shelf wedge a marine unit up to 50 m thick that onlaps r 3 channels a reflection sub parallel to the seafloor that incises r and appears as a dendritic system of channels in map view 4 channels fill the upper portion of which is sampled and known to represent deepening upward marine sediments 12 3 kyr in age 5 the t horizon a seismically discontinuous surface that caps channels fill 6 oblique ridge deposits coarse grained shelly units comprised of km scale shallow shelf bedforms and 7 ribbon floored swales bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits we interpret this succession of features in light of a global eustatic sea level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr the morphology of the new jersey middle shelf shows a discrete sequence of stratigraphic elements and reflects the pulsed episodicity of the last sea level cycle r is a complicated marine non marine erosional surface formed during the last regression while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum wisconsin lowstand i e marine oxygen isotope stage 3 1 channels is a widespread fluvial subarial erosion surface formed at the late wisconsin glacial maximum 22 kyr b p the shoreline migrated back across the mid shelf corridor non uniformly during the period represented by channels fill oblique ridges are relict features on the new jersey middle shelf while the ribbon floored swales represent modern shelf erosion there is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession

ultramafic impact melt sheet beneath the south pole aitken basin on the moon 1 the spectral profiler onboard the japanese lunar explorer kaguya conducted the first hyperspectral survey around the south pole aitken basin spa on the moon that is one of the largest impact structures in the solar system the radiative transfer modeling revealed that fresh crater central peaks inside spa are commonly composed of an ultramafic assemblage dominated by magnesium rich orthopyroxene suggesting a homogeneous layer buried under spa the extensive ultramafic layer could be a relic of a gigantic impact melt pool produced by the spa forming impact the preponderance of orthopyroxene could have resulted from significant fractional crystallization of the lunar magma ocean prior to the onset of plagioclase floatation

sediment transport in the new york bight north american atlantic shelf vincent c e swift d j p and hillard b 1981 sediment transport in the new york bight north american atlantic shelf mar geol 42 369 398 aanderaa current meter data collected during the course of noaa s new york bight project are sufficiently extensive in time 135000 observation hours and space 41 stations to permit an estimate of the sediment transport in this area the analysis is based on mean flow observations the role of wave oscillatory currents in resuspending sediment is considered but not explicitly included in the sediment transport calculations an estimate of the potential sediment transport rate qb at each station for three different threshold velocities uth 12 16 and 20 cm s 1 were made using a bagnoldtype transport equation qb const uc uth 3 for uc uth qb 0 for uc uth where uc is the mean current speed comparison was made between the results from this simple equation and other bedload and suspended load transport rates which include wave data for a limited subset of the bight data this comparison indicates that the bagnold results are reasonable for the along isobath transport estimates but are not reliable for the cross isobath transport in the cross isobath direction waves appear to play a dominant role in determining the transport rate the comparison also indicates that the bagnold approach tends to overestimate transport in deep water in shallow water resuspension of sand and rotor pumping of current meters both may become important and sediment transport calculations may not be accurate fine sediment suspended transport is approximately double the potential bedload transport for fine sand 0 02 cm but does not dominate the total transport as is believed to occur on the washington shelf smith and hopkins 1972 the data show that the new york bight is a storm dominated shelf with the general southwestward drift of water 6 cm s 1 modulated by more intense storm induced flows the transport calculations indicate that the bulk of sediment transport occurs during the winter months when wind stress is at a maximum and the water column is well mixed two major transport provinces are present a the hudson shelf valley and b the rest of the shelf the shelf valley acts as a sink and a barrier to the continuity of the mainly southwestward transport of sediment 104 g cm 1 yr 1 along the shelf within the valley the potential transport of material is of the order of l05 g cm 1 yr 1 along the valley axis progressive vector transport paths for fine sediment indicate that removal of sediment out of the ends of the valley can occur rapidly however consider ation of the finesediment budget for the whole hudson shelf valley and of the attenua tion of wave activity with depth show that these results are not inconsistent with the presence of high mud concentrations in the valley up valley sediment rates predominate during the period for which data are available

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

strataform overview of its design and synthesis of its results abstract the strata formed on continental margins record the history of both marine and terrestrial events occurring on earth the strataform program was created to develop a better understanding of relationships between these events and margin stratigraphy in order to obtain the maximum information from strata they are being examined simultaneously on various temporal and spatial scales and their formation is being studied where events and accumulation are known to be active the general objectives of strataform are to add geological perspective to studies of sedimentary processes to constrain stratigraphic interpretations better and to develop numerical models relating processes and stratigraphy this research is being undertaken on margins off northern california and new jersey which provide unique opportunities for investigation of short term and long term stratigraphy respectively this volume and paper focus upon studies undertaken off northern california north of cape mendocino this area is tectonically active with a coastal mountain range narrow shelf and input of sediment primarily from the eel river recent estimates indicate that 1 to 3 10 7 t yr of mud silt and clay are supplied to the continental shelf sand accumulates on the inner shelf 70 reaches the continental slope or deeper during the previous lowstand of sea level sediment discharge was 25 greater and probably led to hyperpycnal debris and other flows transporting sediment down the slope on the eel shelf flood and storm events combine to create normally stratified fine grained layers with basal sand and much terrestrial organic debris these layers are modified through time but some can be buried and preserved subsurface flood layers seem to impact observations of acoustic backscatter on the middle shelf and subsurface fluids gas freshwater affect electromagnetic measurements on the inner shelf budgets of eel river mud accumulation for the past century indicate 20 trapped on the adjacent shelf and 20 on the upper slope 150 600 m the remaining 60 is dispersed to more distal locations over holocene time scales eel river sediment has built a small sandy subaqueous delta and a subtle bulge of muddy sediment on the middle shelf north of the river gullies have been eroded on the open slope during lowstands of sea level and have accreted upward during highstands a massive failure has formed the humboldt slide due to earthquake activity and unstable substrates possibly from excess pore pressures and gas the tectonic setting has impacted margin stratigraphy from small scales fluid expulsion pockmarks to large scales spatial variation of late cenozoic sedimentation the broad dispersal of eel sediment demonstrates the three dimensional character of the resulting stratigraphy including the large scale clinoform structure developed on the shelf upper slope the rollover point topset foreset boundary for this feature is the shelf break i e below sea level which is important information for stratigraphic interpretations of sea level change

high resolution 3d seismic reflection and coring techniques applied to late quaternary deposits on the new jersey shelf studies of variable small scale features typical of quaternary glacimarine environments require an interdisciplinary approach precisely navigated high resolution 3d seismic surveys nested within a regional 2d seismic framework and integrated with a precisely navigated coring program designed to sample specific shallow acoustic facies we illustrate this approach with examples from continuing studies of sediments on the new jersey continental shelf surficial stratigraphy associated with the latest pleistocene holocene deglaciation has been imaged twice in true 3d using the huntec dts system a deep towed high frequency 500 3500 hz boomer source in both cases nominal profile spacing was 10 m 2 5 m shot points penetration of 40 ms 30 m was achieved seismic facies in the upper 5 m have been interpreted using differential gps navigated vibra cores accuracy of position of both seismic profiles and core locations approaches 5 m much smaller than the wavelengths of the geologic features being imaged sampled survey results show multiple sediment filled channels buried beneath the modern outer shelf meandering south and southeast in the general direction of the shelf edge channels are typically a few meters deep and 100 200 m across lateral continuity between the channeled surfaces within the outer shelf wedge and the mid shelf cannot be demonstrated because of later erosion but both sets of channels incise reflector r believed to be a pre late wisconsinan exposure surface ams14c dates on benthic foraminifers from cores show that channels on the midshelf are cut into sediment 45 000 yrs old and filled with muddy sediment as young as 12 500 yrs whereas channels on the outer shelf are filled with coarser and perhaps older sediment both sets of filled channels are buried beneath a surficial sand layer the integrated approach described here can remove some uncertainties and considerably sharpen the quaternary stratigraphic picture without the perspective obtained from 3d seismic surveys and equally precise sampling interpretations based on broader regional seismic surveys and spot coring are inevitably constrained by the potential for mismatching shallow acoustic and sedimentary facies

sequence stratigraphy of the burdigalian rudeis formation in ras el ush oil field gulf of suez application of gamma ray analysis and biostratigraphy abstract the rudeis formation represents one of the most important oil producing reservoirs in the gulf of suez this formation exhibits conspicuous lateral facies changes and therefore presents a complex exploration target due to tectonic activity in the study area it is composed largely of shale with a few limestone interbeds but so far composed of fine grained marl and sandstone here we interpret the sequence stratigraphy of the rudeis formation at two onshore wells ras el ush 7 and ras el ush 8 in the southernmost western shore of the gulf of suez via the integration of gamma ray log and biostratigraphic data in order to develop a high resolution sequence stratigraphic model of these syn rift rocks and determine their viability for hydrocarbon exploration using new biostratigraphic analysis of calcareous nannoplankton and planktic foraminifera we verified the ages of the rudeis successions our results suggest the occurrence of three burdigalian depositional sequences sq1 sq2 and sq3 along with six stratigraphic surfaces delineating sedimentation cycles and were mainly deposited in inner shelf to upper slope settings each of the sequences typically contains a transgressive systems tract bounded above by a maximum flooding surface and a highstand systems tract bounded above by a sequence boundary we further demonstrate that the variable timing in deposition and erosion of these depositional sequences were controlled by either local tectonism associated with gulf of suez rifting or eustatic sea level changes

paleoenvironmental evidence for latest pleistocene sea level fluctuations on the new jersey outer continental shelf combining high resolution sequence stratigraphy and foraminiferal analysis foraminiferal assemblages in vibracored sediments within 5 m of the seafloor document high resolution sea level fluctuations and confirm the complex quaternary depositional history of the new jersey margin biostratigraphic data have been integrated with ongoing 2 d 3 d high resolution seismic analyses to interpret paleoenvironments of surficial stratigraphy beneath the modern middle to outer shelf cluster analysis of foraminiferal assemblages sampled every 20 cm average define four sample groups a d dominated by benthic species group a characterized by cibicides lobatulus is a middle to outer shelf assemblage 60 100 m water depths group b is composed of middle shelf species 30 60 m water depths and is characterized by low abundances and a fairly uniform distribution of foraminifera which suggests reworking and or a high rate of sediment accumulation group c dominated by elphidium excavatum is an inner to middle shelf assemblage 10 40 m water depths group d present in only one core and dominated by ammonia beccarii represents marginal marine environments 0 10 m water depths with fluctuations in salinity in general the modern sedimentary veneer i e the upper 20 cm is characterized by the deeper water fauna of group a sediments below these modern deposits are characterized by groups b and c reflecting shallower water depths and variable sediment accumulation rates on the inner and middle shelf taken together the group succession in the cores suggests an overall se to nw landward transgression in these latest pleistocene holocene deposits seismic analysis indicates that one core 27 penetrates the flank of a buried channel including its fill and the pre channel section within the channel three alternations of groups c and d suggest fluctuations between marginal marine and middle shelf paleoenvironments high frequency perhaps very small 10 m changes in base level are indicated using previously published ams 14c dates these fluctuations can be constrained as having occurred between 45 000 yr b p channel incision and 12 500 yr b p channel filling suggesting the non uniform nature of the last wisconsinan deglaciation

island arc volcanic rocks in the north qaidam uhp belt northern tibet plateau evidence for ocean continent subduction preceding continent continent subduction abstract a suite of early paleozoic island arc volcanic rocks consisting mainly of basaltic lavas and some intermediate silicic rocks crops out in the north qaidam basin northeastern tibet plateau these rocks have been extensively metamorphosed under greenschist facies conditions and hence differ from the older proterozoic intermediate mafic volcanic rocks which have generally experienced amphibolite facies metamorphism the early paleozoic volcanic rocks are divided into three groups based on their geochemical characteristics 1 vtg i consists of island arc tholeiitic basalts basaltic andesites and andesites that crop out in jilusu and shuangkoushan 2 vtg ii which are high al alkaline and sub alkaline basalts in jilusu and 3 vtg iii an assemblage of highly depleted morb type basalts andesites and dacites that occurs mostly in shuangkoushan groups vtg i and ii are considered to be the products of mature island arcs produced in two stages in the first stage following initiation of ocean continent subduction the island arc tholeiites were generated by partial melting of the subsiding oceanic crust and mantle wedge beneath the island arc as subduction progressed and accelerated calc alkaline and high al basalts were formed and the crust beneath the island arc was thickened the highly depleted morb type lavas vtg iii have boninitic affinities and are believed to have been generated from depleted mantle material modified by subduction zone fluids possibly in the fore arc region the island arc tholeiites are dated at 514 2 8 5 ma whereas uhp eclogite in the north qaidam belt has been dated at 494 ma these ages suggest that ocean continent subduction took place in the north qaidam basin in the early paleozoic and was followed shortly by continent continent collision and subduction which produced the uhp rocks

seabed characterization on the new jersey middle and outer shelf correlatability and spatial variability of seafloor sediment properties abstract nearly 100 collocated grab samples and in situ 65 khz acoustic measurements were collected on the new jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data and more recently with chirp seismic reflection profiling eighteen short cores were also collected and probed for resistivity based porosity measurements the combined data set provides a basis for empirically exploring the relationship among the remotely sensed data such as backscatter and reflection coefficients and directly measured seabed properties such as grain size distribution velocity attenuation and porosity we also investigate the spatial variability of these properties through semi variogram analysis to facilitate acoustic modeling of natural environmental variability grain size distributions on the new jersey shelf are commonly multi modal leading us to separately characterize coarse 4 mm fine

the sedimentary record of the post glacial transgression on the gulf of cadiz continental shelf southwest spain abstract four seismic units ta to td have been identified from the analysis and interpretation of high resolution seismic profiles in a sector of the gulf of cadiz shelf they constitute a composite seismic unit attributed to the transgressive systems tract tst of the last depositional sequence the earliest transgressive unit was deposited on the outer shelf and represents the distal facies of a coastal deposit a process of shelf partitioning seems to have occurred during the formation of the three later transgressive parasequences the shelf sector offshore from the guadiana river mouth was a high energy environment dominated by storm events by contrast the shelf sector offshore from the donana national park was a low gradient shelf where large barrier island and lagoon systems were formed the sparse occurrence of marine deposits within the tst is a consequence of the episodic nature of the sea level rise the generation and preservation of these transgressive deposits results from the interaction of the following controlling processes 1 relative sea level rise the formation of coastal transgressive deposits is related to intervals of reduced sea level rise or stillstands within a period of continuous sea level rise those sea level changes were probably driven by short term periods of colder climate during the late pleistocene holocene deglaciation the younger dryas interval is the most widely recognised climatic event of this type but probably other events of similar characteristics had the same effect on the glacio eustatic sea level rise 2 sediment supply changes short lived climatic events probably also involved changes in the sediment supply to the continental shelf due to changes in erosion rates and river regimes of the river basin hinterlands 3 effect of the paleophysiography paleogeography the sedimentary environments differentiation processes are associated to the formation of an exposed coastal promontory offshore from the guadiana river mouth and a semi protected embayment offshore from donana national park this coastal configuration was controlled by previous tectonic evolution and influenced the non uniform landward migration of the coastline

are the oroclines of the variscan belt related to late variscan strike slip tectonics terra nova 23 241 247 2011 abstract early variscan structures and magnetic anomalies delineate four oroclines along the variscan belt the arcs bend the lithostratigraphic zones of the autochthon and the allochthonous terranes which include ophiolites of the rheic suture and units of gondwanan derivation subducted on both sides of the rheic ocean a transcurrent model dominated by right lateral motion explains the genesis and evolution of the oroclines and a simple plate tectonics scenario links late variscan dextral strike slip movements in the variscides to a broad intracontinental shear zone kinematically equivalent to a transform fault terra nova 00 1 7 2011

quantitative reconstruction of paleoenvironmental conditions in the gulf of suez during the burdigalian langhian early to middle miocene using benthic foraminifera abstract in this study we examine a 750 m thick section of lower to middle miocene sediments penetrated by an exploration well named arm 36 drilled in the central eastern part of the gulf of suez we used the planktic foraminiferal biostratigraphy of this section to classify these sediments into four previously established planktic foraminiferal biozones m2 m3 m5 and m6 we then employed benthic foraminifera to describe the paleoenvironmental conditions in the gulf of suez and to correlate the results with other successions e g alpine foreland basin molasse basin altdorf section and the austrian part in the central paratethys the correlation indicates that similarities exist between the main paleoenvironmental events in the gulf of suez and central paratethys even though they were located in different climatic zones and were controlled by different tectonic events the similarities may be related to global climatic conditions consequently we applied several indices paleodepth proxies and multivariate statistics on 316 ditch samples containing 72 benthic species to reconstruct the paleoenvironmental conditions during this time interval analyses of benthic foraminifera and their ecological preferences indicate that these sediments were deposited in inner shelf to upper slope environments that were characterized by oxic bottom waters and normal marine salinity during the investigated interval

pleistocene climatic history reflected in planktonic foraminifera from odp site 1073 leg 174a new jersey margin nw atlantic ocean abstract abundance records of planktonic foraminifera 150 m from the upper 520 m of odp site 1073 hole 1073a leg 174a 639 m water depth have been integrated with specmap derived isotope stratigraphy percentage of calcium carbonate and coarse sediment fraction data in order to investigate the pleistocene climatic history of the new jersey margin six planktonic taxonomic groups dominate the foraminiferal assemblage at site 1073 neogloboquadrina pachyderma d mean 33 8 turborotalita quinqueloba 18 5 n pachyderma s 18 4 globigerina bulloides group 11 4 globorotalia inflata group 9 4 and globigerinita glutinata 4 1 based on the distributions of these six foraminiferal groups the pleistocene section can be divided into three paleoclimatic intervals interval i intermediate corresponds to the quaternary sediments from sequence boundary pp1 to the seafloor 79 5 0 mbsf emiliania huxleyi acme 85 ka at 72 mbsf interval ii warm occurs between sequence boundaries pp3 and pp1 325 79 5 mbsf last occurrence of pseudoemiliania lacunosa 460 ka at 330 mbsf and interval iii coldest occurs between sequence boundaries pp4 and pp3 520 325 mbsf calcareous nannofossils and dinocysts in proximity to pp4 indicate that the sedimentary record for 0 9 1 7 ma is either missing altogether or highly condensed within the basal few meters of the section neogloboquadrina pachyderma d displays eight peaks of abundance which correlate for the most part with depleted 18o values increases in calcium carbonate percentages low coarse fraction percentages increased planktonic fragmentation greater dissolution and low n pachyderma s abundances these intervals are interpreted as representing warmer interglacial conditions neogloboquadrina pachyderma s displays seven peaks of abundance which correlate for the most part with 18o increases decreases in calcium carbonate percentages increases in coarse fraction percentages and low n pachyderma d abundances these intervals are interpreted as representing cooler glacial conditions in interval iii a faunal response to relative changes in sea surface temperature is reflected by abundance peaks in neogloboquadrina pachyderma d followed by turborotalita quinqueloba and then n pachyderma s proceeding from warmest to coolest respectively this tripartite response is consistent with the oxygen isotope record and although not as clear also occurs in intervals i and ii six peaks peak intervals of globigerina bulloides abundance are closely matched by peaks in globigerinita glutinata and occur within oxygen isotope stage ois 2 latter part 3 4 5 8 9 13 14 and 15 we speculate that these intervals reflect increased upwelling and nutrient levels during both glacials and interglacials eight peak intervals of globorotalia inflata show a general inverse correlation with g bulloides and may reflect lowered nutrient and warmer surface waters

seaward branching coastal plain and piedmont incised valley systems through multiple sea level cycles late quaternary examples from mobile bay and mississippi sound u s a abstract most incised valleys become more organized seaward through tributaries merging with the main trunk valley late quaternary incised valleys on the mississippi and alabama inner continental shelf branch seaward although they do coalesce towards the shelf break where they feed shelf edge deltas to link fluvial systems with their associated previously mapped incised valleys on the shelf and evaluate the contribution of small coastal plain valley systems to the lowstand systems tract high resolution seismic data and cores were collected from mobile bay eastern mississippi sound and the mobile bay head delta these data show four unconformity bounded stacked units and this study focuses on the upper two regionally mappable units the upper two unconformities were sampled in core as exposure surfaces and on the basis of stratigraphic position depth of incision and 14c dates are interpreted as sequence boundaries the shallowest sequence boundary a formed in response to the oxygen isotope stage 2 sea level lowstand while the underlying sequence boundary b formed in response to an earlier lowstand stage 6 a map of sequence boundary b shows a network of seaward branching valleys 20 35 m deep and 0 6 7 7 km wide that extend across mobile bay and mississippi sound these valleys which are bounded by well developed terraces are extensions of the piedmont mobile fluvial system and the coastal plain fowl and la batre fluvial systems a map of the stage 2 sequence boundary shows that all systems generally reoccupied their previous valley positions and are separated by interfluve plateaus valley fill between sequence boundary b and the stage 2 sequence boundary is generally composed of a basal unit of alluvial sediments overlain by bay head delta deposits however stage 2 to 1 valley fill is composed entirely of central basin sediments the presence of bay head delta deposits on the inner shelf indicates this depositional environment backstepped across the estuaries to modern positions backstepping likely occurred as the low gradient paleovalleys were inundated resulting in rapid rates of transgression fluvial gradients measured on sequence boundary b and the stage 2 sequence boundary below the modern mobile bay head delta plain and the estuaries are very low 1 3 0 3 m km the mobile bay head delta and upper mobile bay are confined by steep topography which opens basinward into the low gradient shorelines surrounding lower mobile bay and mississippi sound during falling sea level channel branching likely occurred as the low gradient fluvial systems extended basinward beyond the confined topography these channels incised as sea level fell below the steeper shelf break during the lowstand stage 2 valley morphology is partially influenced by the position of the underlying stage 6 valleys both coastal plain and piedmont valley systems exhibit compound fill indicating that differentiation between these types of incised valleys cannot be based on valley fill architecture alone

late quaternary sedimentation on the outer and middle new jersey continental shelf result of two local deglaciations high resolution seismic profiles show two prominent late quaternary sediment wedges on the outer and middle new jersey continental shelf an extensive wedge along the outermost shelf and upper slope up to 50 m thick appears to have been deposited on the hudson apron during an early melting of the late wisconsin laurentide ice sheet subsequent southward transport of this sediment occurred during sea level regression still stand and transgression a mid shelf sediment wedge which forms the fortune shore probably was deposited during a second melt event 11 to 12 ka as sea level was transgressing over the shelf

measuring the shallow porosity structure of sediments on the continental shelf a comparison of an electromagnetic approach with cores and acoustic backscatter we validate estimates of shallow sedimentary porosities made on the continental shelf by electromagnetic methods through a comparison with those measured directly in cores specifically we show that an electromagnetic surveying system we have used to measure sediment resistivity in a number of seafloor locations returns porosity depth profiles that are related to those measured in cores and that our data have good sensitivity to the structure within the uppermost few tens of centimeters of seafloor we then consider inferences of sediment type made by observations of acoustic backscatter in the light of our porosity measurements our results suggest that electromagnetic methods provide complementary information that can be used to improve grain type estimates at and just below the seafloor especially when combined with acoustic backscatter data because the system is pulled along the seafloor data can be quickly collected from a large area of seafloor and can be used to interpolate facies conditions between core locations

the northern boundary of the proto tethys ocean constraints from structural analysis and u pb zircon geochronology of the north qinling terrane abstract the north qinling terrane including the kuanping erlangping and qinling groups is located in the northern part of the qinling orogen here we present results from structural analyses of the north qinling terrane and its surrounding regions three episodes of deformation d 1 d 2 and d 3 are recognized the d 1 deformation is characterized by nne dipping and ssw dipping penetrative foliations s 1 the s 1 foliations are mainly marked by a strong preferred orientation of hornblende crystals and they were subsequently overprinted by the d 2 deformation the d 2 deformation is marked by tight asymmetric folds with nne dipping and ssw dipping axial plane foliations s 2 we propose that the d 1 and d 2 deformations mainly occurred during 440 400 ma after the peak ultra high pressure metamorphic event 520 480 ma and so these two deformation events could constrain the collision and exhumation processes of the north qinling terrane which probably indicates the closure of the kuanping ocean located between the north qinling terrane and the north china block in the early paleozoic these two deformations are overprinted by the d 3 deformation characterized by ene trending upright open folds two detrital zircon age spectra for the kuanping group with the youngest zircon of 640 ma and 510 ma respectively are different from those recorded for the north china block which may reveal the continuous southward subduction of the kuanping ocean during the neoproterozoic to early paleozoic interval we propose that the kuanping ocean marks the northern boundary of the proto tethys ocean in the study area

buried paleo channels on the new jersey continental margin channel porosity structures from electromagnetic surveying abstract we report on a marine electromagnetic em survey across two portions of the new jersey continental margin that have been previously shown to contain buried paleo channels the em method used provides bulk porosity estimates to depths of around 20 m below the seafloor and is thus able to place porosity constraints on the nature of the channel infill and the contrast in physical properties across the channel boundaries our data show that a key condition for the channels to have an electrical signature is that they incise an underlying regional unconformity r thought to represent a subaerially eroded surface exposed during the late wisconsinan glaciation channels that cut r are seen through increases in apparent porosity another seismically imaged channel sequence which lies within the outer shelf sediment wedge sequence above r does not have an electrical signature indicating that the sediments above and below the channel boundaries have similar physical properties

clastic sequences developed during late quaternary glacio eustatic sea level fluctuations on a passive margin example from the inner continental shelf near barnegat inlet new jersey analysis of 100 km of seismic reflection geopulse profiles from a 47 km 2 grid on the new jersey low mesotidal inner continental shelf near barnegat inlet reveals that the upper 30 m is composed of 3 unconformity bounded units vibracores 1 6 m long recovered from 12 sites contain several lithofacies reflecting a variety of depositional environments that existed during late quaternary glacioeustatic sea level fluctuations on this slowly subsiding passive margin with low sediment supply environments include rivers during glacial and stadial lowstands of the sea and a barrier island lagoon complex as well as pro barrier ebb tidal delta shore attached and detached ridges and below storm wave base shelf during interglacial or inter stadial highstands following the last major interglacial 125 ka sea level fell and rivers eroded a planar seaward dipping surface r1 by early wisconsinan time 70 ka as sea level rose during the mid wisconsinan 55 ka a barrier island system migrated to within 0 2 1 7 km of the modern barrier shoreline leaving a 4 to 6 m thick record depositional sequence i maximum highstand of the mid wisconsinan sea level was 20 m below present sea level fell again during the late wisconsinan 20 ka and rivers again flowed across the exposed shelf creating an unconformity r2 a barrier lagoonal system developed under rising sea level by at least early middle holocene time based on peats 8810 170 yr b p cored from 12 m the mid wisconsinan 55 ka barrier system was preserved under these early holocene transgressive sediments lower unit of depositional sequence ii lower transgressive tract the modern barrier and inner continental shelf deposits upper unit of depositional sequence ii upper transgressive tract are relatively thin average 3 4 m pebbly sands overlying a prominent unconformity a transgressive surface r3 formed by marine erosion during the holocene sea level rise both the ebb tidal delta and shore attached linear sand ridges act as partial shields to wave and tidal current erosion of the muddy sub strate below r3 in the nearshore area this shielding is creating a transgressive surface marine unconformity of relatively high relief 3 7 m

cenozoic evolution of the pamir plateau based on stratigraphy zircon provenance and stable isotopes of foreland basin sediments at oytag wuyitake in the tarim basin west china abstract the pamir salient is the western expression of mountain growth related to indo eurasian convergence though a rough framework has emerged describing the tectonic evolution of the pamir detailed knowledge of the spatial and temporal evolution of cenozoic deformation is necessary to determine how strain progressed through the orogenic belt here we present new stratigraphic zircon provenance and stable isotope data from jurassic to miocene strata along the pamir s northeastern margin near the town of oytag wuyitake in the tarim basin west china prominent 40 ma peaks in oligocene to early miocene detrital zircon grains record the erosion of an eocene belt of shoshonitic rocks in the central to southeastern pamir this is roughly coincident with an 4 shift in the oxygen isotopic composition 18o of carbonates during the eocene and or oligocene from an average of 8 7 to 12 6 suggesting a reorganization of atmospheric circulation during that time this could have been caused by uplift of tarim basin bounding ranges and or retreat of the paratethys sea a subsequent change from eocene to jurassic aged detrital zircon grains in the early to middle miocene indicates provenance shifted from source rocks in the central and or se pamir to the hanging wall of the main pamir thrust mpt coincident with prograding facies at that time this suggests deformation progressed outward toward the northeast margin of the pamir plateau in the early to middle miocene our results corroborate outward advancement of himalayan deformation affecting all margins of the tarim basin by the middle miocene

early paleozoic orocline in the central china orogen abstract the altun qilian kunlun orogen as a western segment of the central china orogen has experienced a tectonic evolution of the proto tethys ocean and the early paleozoic orogenic movement to produce multiple stage early paleozoic structures and rocks the corresponding ophiolites metamorphic rocks and granites in the orogen show some similarities in petrology and geochemistry especially isotopic geochronology this indicates that they should be under the same subduction accretion system during the early paleozoic while there is diachronism of evolutionary time along strike combined with the paleomagnetic data and plate reconstruction the north qinling central qilian central altun oulongbuluke qaidam east kunlun and west kunlun micro continents from gondwana made up a chain like superterrane within the northern proto tethys ocean based on the detailed structural analysis and spatial and temporal distribution of the main rocks the proto tethys ocean subducted southward and formed a nearly linear subduction zone the tarim qaidam micro continent was likely to have drifted as a unit and mostly rotated relatively counterclockwise in the early paleozoic under the southward oblique subduction collision some large scale dextral strike slip faults developed and the relative displacement and rotation of continents micro continents and tectonic belts also took place in the region making the subduction zone bent to form a s shaped pattern in plan view in this paper we suggest that they are coupled oroclines and put forward a kinematic evolution model the shangdan ocean likely closed no earlier than the formation of the oroclines generating a curved suture zone bypassing east qaidam further linked southward to the central kulun suture although the coupled oroclines was displaced and destroyed by subsequent superimposed structures especially in the west of the altun orogen and east of the qaidam areas the early paleozoic tectonic unconformity and depositional systems developed in the tarim basin and the s shaped pattern of the paleostructures and hydrocarbon reservoirs provide evidence for its existence

magmatic history of the northeastern tibetan plateau 1 the northeastern margin of the tibetan plateau is underlain by the qaidam and qilian terranes which consist primarily of mid proterozoic through lower paleozoic oceanic and arc type assemblages that have been accreted to the southern margin of the tarim sino korean craton most previous models suggest that these assemblages formed along a northeast dipping subduction system constructed along the margin of the tarim sino korean craton during early paleozoic time the main components are interpreted to have formed either as an archipelago of volcanic arcs and back arc basins or as a broad expanse of accretionary complexes our geochronologic data support a model suggested by sobel and arnaud 1999 in which the qaidam and qilian terranes are separated from the tarim sino korean craton by a mid paleozoic suture that closed along a southwest dipping subduction zone the basement to these terranes consists of oceanic assemblages that were amalgamated into a coherent crustal fragment prior to emplacement of 920 930 ma granitoids early paleozoic arc type magmatism occurred between 480 and 425 ma apparently sweeping southwestward across much of the qilian and qaidam terranes accretion related magmatism along the inboard margin of the qilian terrane occurred between 423 ma and 406 ma following silurian devonian accretion the region has experienced late paleozoic and mesozoic uplift and erosion and has been severely overprinted by tertiary thrusting uplift and strike slip motion along the altyn tagh fault correlation of geologic features and magmatic histories between the altun shan and the nan shan suggests that the eastern altyn tagh fault has a total left lateral offset of 375 km

discovery of early paleozoic eclogite from the east kunlun western china and its tectonic significance abstract eclogites discovered in the eastern part of the east kunlun mountains western china are primarily composed of garnet omphacite quartz rutile the garnets show end member components of 48 55 almandine 1 2 spessartine 19 29 grossularite and 16 29 pyrope and the omphacite has a jadeite content of 21 63 the peak metamorphic assemblage of eclogites records a p t condition of 1 6 gpa and 590 c 650 c zircon u pb dating of the inherited magmatic zircons from fine grained eclogite reveals a neoproterozoic age of 934 ma representing the protolith age of the eclogite zircons from the coarse grained eclogite contain inclusions of garnet omphacite and rutile and yield a weighted mean age of 428 ma indicating the metamorphic age of eclogite the eclogites together with the late cambrian 508 ma high pressure granulite to the west constitute an early paleozoic high pressure metamorphic belt in the east kunlun

magnitude and timing of episodic sea level rise during the last deglaciation a succession of elevated ridge deposits on the south florida margin was mapped using high resolution seismic and side scan sonar imaging in water depths ranging from 50 to 124 m the ridges are interpreted to be subtidal shoal complexes and paleoshorelines eolian dune or beach formed during the last sea level transgression oolitic and skeletal grainstones and mixed skeletal peloidal ooid packstones were recovered using a research submersible all of the grains are of shallow water or intertidal origin and both marine and nonmarine cements were identified formation and preservation of these features are attributed to episodic and rapid changes in the rate of the deglacial sea level rise at the onset of the termination 1a 18o excursion this high resolution record of sea level change appears to be related to deglacial processes operating on submillennial time scales and supports increasing evidence of rapid episodic fluctuations in ice volume climate and ocean circulation patterns during glacial interglacial transitions

recent and modern marine erosion on the new jersey outer shelf abstract recent chirp seismic reflection data combined with multibeam bathymetry backscatter and analysis of grab samples and short cores provide evidence of significant recent erosion on the outer new jersey shelf the timing of erosion is constrained by two factors 1 truncation at the seafloor of what is interpreted to be the transgressive ravinement surface at the base of the surficial sand sheet and 2 truncation of apparently moribund sand ridges along erosional swales oriented parallel to the primary direction of modern bottom flow and oblique to the strike of the sand ridges these observations place the erosion in a marine setting post dating the passage of the shoreface ravinement and the evolution of sand ridges that form initially in the near shore environment also truncated by marine erosion are shallowly buried fluvial channel systems formed during the last glacial maximum and filled during the transgression and a regional reflector r that is 40 kyr depths of erosion range from a few meters to 10 m the seafloor within eroded areas is often marked by ribbon morphology seen primarily in the backscatter data as areas of alternating high and low backscatter elongated in the direction of primary bottom flow ribbons are more occasionally observed in the bathymetry where observed crests exhibit low backscatter and troughs exhibit high backscatter sampling reveals that the high backscatter areas of the ribbons consist of a trimodal admixture of mud sand and shell hash with a bimodal distribution of abraded and unabraded sand grains and microfauna the shell hash is interpreted to be an erosional lag while the muds and unabraded grains are in this non depositional environment evidence of recent erosion at the seafloor of previously undisturbed strata the lower backscatter areas of the ribbon morphology were found to be a well sorted medium sand unit only a few 10 s of cm thick overlying the shelly muddy sandy material concentrations of well rounded gravels and cobbles were also found in eroded areas with very high backscatter and at least one of these appears to be derived from the base of an eroded fluvial channel seafloor reworking over the transgressive evolution of the shelf appears to have switched from sand ridge evolution which is documented to 40 m water depth to more strictly erosional modification at greater water depths we suggest that this change may be related to the reduction with water depth in the effectiveness of sediment resuspension by waves resuspension is a critical factor in the grain size sorting during transport by bottom currents over large bedforms like sand ridges otherwise we speculate displacement of sand by unidirectional currents will erode the seafloor

seismic geomorphology of buried channel systems on the new jersey outer shelf assessing past environmental conditions abstract quantitative geomorphologic analysis of shallowly buried dendritic channel systems on the new jersey shelf provides estimates of paleo hydrologic parameters needed to link channel morphology to the former hydrodynamic setting these channels observed in 1 4 khz deep towed chirp seismic data formed presumably as fluvial systems when the shelf was exposed during the last glacial maximum lgm the presumed fluvial origin of these channels is supported by their incision into underlying pleistocene strata a chaotic seismic fill unit at their bases which may be indicative of non marine gravel lag and measured stream junction angles that are consistent with a riverine origin the channels would also have been subjected to estuarine tidal environments during ensuing sea level rise we employ empirically derived hydraulic equations for modern rivers and estuaries to estimate paleo discharges velocities and maximum shear stresses using the preserved and interpolated paleo channel geometries as a guide generally trunk main channels have box like symmetric cross sections with width depth ratios of 100 whereas smaller tributary channels have more v shaped asymmetric cross sections with width depth ratios of 40 70 the high width depth ratios along with low sinuosities 1 1 and slopes

lower pleistocene to present structural deformation and sequence stratigraphy of the continental shelf offshore eel river basin northern california seismic stratigraphic sequences and deformational features are mapped beneath the continental shelf of the offshore eel river basin of northern california using a closely spaced high resolution multichannel seismic grid geometries of sequences and morphologies of bounding unconformities reflect competing tectonic and glacioeustatic influences producing shifting sedimentation patterns in the offshore basin during the last v1 myr estimated timing of unconformity formation correlates generally with a deep ocean global n 18 o curve both before and after a v500kyr transition from 41 kyr to 100 kyr dominated cycles we suggest that glacioeustatic fluctuations are the dominant control on unconformity formation basinwide however regional tectonic influences on sequence development are also observed folding associated with gorda north america plate convergence ended progressively from south to north between v1 0 ma and v500 ka in response to northward migration of the mendocino triple junction mtj since v500 ka continued encroachment of the mtj produces rotation of preexisting structures uplift of the table bluff anticline tba related periods of channel incision south of the tba and generally reduced sediment preservation across the shelf mtj related uplift may also have induced formation of eel canyon over the past v1 0 myr a dominant northern sediment source becomes progressively less important a southern source probably the paleo eel river has become dominant since v750 ka seismic unconformities fall into two categories 1 irregular surfaces of limited mappable extent interpreted as incision exposure surfaces forming during relative sea level lowstands and 2 smooth laterally extensive regional unconformities interpreted as ravinement surfaces that erode lowstand surfaces in all but deeply incised areas during sea level transgressions a sequence stratigraphic model for sediment deposition and preservation on the eel river shelf predicts that preserved sediment on the eel margin is dominated by fluvially derived highstand silts and muds deposited by longshore directed currents and waves lowstand sediments are preserved only in fluvial channels infilled during late lowstand early transgression preserved transgressive sediments are likely limited to a thin veneer of well sorted coarse sediment or shell debris deposited above the transgressive ravinement future deep coring will be required to confirm these predictions 2002 elsevier science b v all rights reserved

the last glacial insights from continuous coring on the new jersey continental shelf abstract sedimentation on the pleistocene new jersey nj shelf is complex and results from the interaction of processes chiefly driven by glacioeustatic change erosion non deposition downcutting and infilling combine to produce a complicated set of reflectors and sedimentary units that are best interpreted in the shallow subsurface with the aid of high resolution seismic reflection profiling the highly variable lithology on the shelf has historically been an impediment to significant core recovery in this challenging environment coring using the ahc 800 drilling system provided continuous downcore recovery at three sites on the outer shelf the sites targeted fluvial incisions channel fill and exposure surfaces associated with glacial lowstands the exceptional cores were analyzed using an integrated approach textural and benthic foraminiferal data were evaluated to determine the environment of deposition and estimate paleodepth carbon dating of wood and shell material provides the temporal framework for interpretation and k ar dating of hornblende crystals provides insights into the source region of sediments our integrated analysis indicates the nj shelf was a dynamic environment from at least 45 ka estimates of sea level from this study are consistent with other studies from the pleistocene nj margin the oldest sediments 36 k y recovered by drilling came from below site 3 and above site 1 r a time transgressive regional unconformity best estimates are for formation of r on the mid shelf between mis3b and the mis3b a transition 45 ka under neritic conditions channels were incised during late mis2 between 30 and 16 ka channel infill was focused in a narrow time frame during latest mis 2 16 14 ka shortly after the shoreline began to migrate landward rates of 1 2 cm yr are consistent with modern fluvial estuarine sedimentation rates reinvigoration and infilling of the channels around 14 ka is associated with meltwater pulse 1a we find no evidence at our study area for jokelhlaup deposition associated with the intra allerod cold period 13 ka regional deposition channel infill and interfluvial regions was underway by latest mis2 early mis1 as sea level transgressed the shelf the uppermost sediments are of holocene to recent age and are routinely and likely rapidly reworked eroded and mixed by shelf processes the sediment source during mis3 as determined by hornblende age dates was bimodal older sediments were derived from the reading prong nj highlands and younger sediments were sourced from along the hudson river delivery to the study area was through a more southerly paleo hudson position that may have resulted in formation of the outer shelf wedge through deltaic sedimentation during at least mis 3b 3a

basal inflection controlled shelf edge wedges off new jersey track sea level fall a key marker for examining the latest pleistocene history of the new jersey margin is the high amplitude long recognized r horizon reflector this time transgressive surface was formed 47 33 ka and represents the integrated topographic and bathymetric surface developed during the complicated sea level oscillation associated with the regression that preceded the last glacial maximum lgm from landward to seaward across the outer shelf the r reflector changes from subhorizontal in most locations 9 m beneath the modern seafloor to seaward dipping forming the base of two offlapping sediment wedges the previously described outer shelf wedge and a deep shelf wedge seaward of it this transition occurs across two inflection zones where the dip of the r reflector steepens seaward that can be traced for tens of kilometers along strike and mark the landward limits of these wedges these inflection zones are possibly former wave dominated shorefaces these represent the primary topographic elements present during the last regression we speculate that these inflections dictated both the locations for deposition of the two prograding offlapping wedges that developed during the complex sea level fall prior to the lgm and their successive erosion before and after the lgm we suggest that such inflection zones and their associated wedges are important markers of regression in clastic dominated outer shelf settings along passive margins

drainage of late wisconsin glacial lakes and the morphology and late quaternary stratigraphy of the new jersey southern new england continental shelf and slope abstract we propose that late wisconsin deposition and erosion hudson shelf and block island valleys on the shelf and slope from new jersey to southern new england were a consequence of the catastrophic drainage of glacial lakes behind terminal moraine systems and the huge volume of water stored beneath the laurentian ice sheet and subsequent erosion of the lake sediments by flash floods the morphology imparted by glaciation regulated the discharge associated with the ablation of the glaciers associated with the deposits west of hudson shelf valley are the remains of mammoth and mastodon which were transported from their living habitats along the lake shores to their present burial sites on the shelf the floods also triggered gravity flows on the upper continental slope which made possible the transportation of coarse debris over hundreds of km into the deep sea that these catastrophic flood morphologies can still be recognized on the middle to outer shelf suggest that much of its surface was little modified during the late pleistocene holocene transgression thus the late pleistocene holocene transgression may have been characterized by short periods when sea level rose rapidly allowing for the preservation of relict features

a cold early palaeozoic subduction zone in the north qilian mountains nw china petrological and u pb geochronological constraints the north qilian high pressure hp low temperature lt metamorphic belt is composed mainly of blueschists eclogites and greenschist facies rocks it formed within an early palaeozoic accretionary wedge associated with the subduction of the oceanic crust and is considered to be one of the best preserved hp lt metamorphic belts in china here we report new lawsonite bearing eclogites and eclogitic rocks enclosed within epidote blueschists in the north qilian mountains five samples contain unaltered lawsonite coexisting with omphacite and phengite as inclusions in garnet indicating eclogite facies garnet growth and lawsonite pseudomorphs were observed in garnet from an additional 11 eclogites and eclogitic rocks peak pressure conditions estimated from lawsonite omphacite phengite garnet assemblages were 2 1 2 4 gpa at temperatures of 420 510 c in or near the stability field of lawsonite eclogite and implying formation under an apparent geothermal gradient of 6 8 c km 1 consistent with metamorphism in a cold subduction zone shrimp u pb dating of zircon from two lawsonite bearing eclogitic metabasites yields ages of 489 7 ma and 477 16 ma respectively cl images and mineral inclusions in zircon grains indicate that these ages reflect an eclogite facies metamorphism an age of 502 16 ma is recorded in igneous cores of zircon grains from one lawsonite pseudomorph bearing eclogite which is in agreement with the formation age of early ordovician for some ophiolite sequences in the north qilian mountains and may be associated with a period of oceanic crust formation the petrological and chronological data demonstrate the existence of a cold early palaeozoic subduction zone in the north qilian mountains

u pb zircon geochronology of coesite bearing eclogites from the southern dulan area of the north qaidam uhp terrane northwestern china spatially and temporally extensive uhp metamorphism during continental subduction coesite bearing eclogites from 100 km 2 in the southern dulan area north qaidam mountains nqm of western china contain zircon that records protolith crystallization and ultra high pressure uhp metamorphism sensitive high resolution ion microprobe mass spectrometer and laser ablation inductively coupled plasma mass spectrometry u pb analyses from cathodoluminescence cl dark zircon cores in a coesite bearing eclogite yield an upper intercept age of 838 50 ma and oscillatory zoned cores in a kyanite bearing eclogite gave a weighted mean 206 pb 238 u age of 832 20 ma these zircon cores yield steep heavy rare earth element hree slopes and negative eu anomalies that suggest a magmatic origin thus c 835 ma is interpreted as the eclogite protolith age unzoned cl grey or bright zircon and zircon rims from four samples yield weighted mean ages of 430 4 438 2 446 10 and 446 3 ma flat hree patterns without eu anomalies and contain inclusions of garnet omphacite rutile phengite and rare coesite these ages are interpreted to record 16 5 myr of uhp metamorphism these new uhp ages overlap the age range of both eclogite and paragneiss from the northern dulan area suggesting that all uhp rock types in the dulan area belong to the same tectonic unit our results are consistent with slow continental subduction but do not match oceanic subduction and diapiric exhumation uhp model predictions these new data suggest that similar to eclogites in other hp uhp units of the nqm and south altyn tagh protoliths of the eclogites in the dulan area formed in a continental setting during the neoproterozoic and then subducted to mantle depth together with continental materials during the early palaeozoic

an ultrahigh resolution 3 d survey of the shallow subsurface on the continental shelf of new jersey regional seismic surveys have identified a wedge of late quaternary sediment extending 150 km south from the hudson river apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector that is assumed to be an erosional surface carved during a lowstand of sea level probably corresponding to the wisconsin maximum glaciation about 18 000 years ago an extremely high resolution 3 d seismic reflection survey of the southern part of the wedge figure 1 was carried out in 1993 as part of the strataform strata formation on margins initiative funded by the u s office of naval research