u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

a global sea level curve for the late quaternary the impossible dream abstract in view of the vulnerability of heavily populated low lying coastal areas to sea level rise and marine incursion an improved late quaternary global sea level curve is sorely needed as a gauge for measuring changing sea level positions contrary to the prevailing view it is proposed that such a global sea level curve can be derived from observations compiled in widely diverse continental margin and coastal settings needed are a larger number of more precisely dated elevation points with minimal relation to land motion and climatic variation which can serve as a basis for a curve defining global sea level particularly for the late pleistocene and holocene such a curve will not be made from any one type section or locality but rather from observation of contemporaneous events compiled in widely diverse settings rather than simply defending a contentious view this essay solicits new and more precise data and a reconsideration of viable approaches

influence of the atlantic inflow and mediterranean outflow currents on late quaternary sedimentary facies of the gulf of cadiz continental margin abstract the late quaternary pattern of sedimentary facies on the spanish gulf of cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the atlantic inflow currents flowing southeastward across the cadiz shelf toward the strait of gibraltar an inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10 20 m that extends deeper and obliquely down paleo valleys as a result of southward down valley flow a mid shelf holocene mud facies progrades offshore from river mouth sources but atlantic inflow currents cause extensive progradation along shelf toward the southeast increased inflow current speeds near the strait of gibraltar and the strong mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf at the outer shelf edge and underlying the mid shelf mud and inner shelf sand facies is a late pleistocene to holocene transgressive sand sheet formed by the eustatic shoreline advance the late quaternary pattern of contourite deposits on the spanish gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges coincident with the northwestward decrease in outflow current speeds from the strait there is the following northwestward gradation of contourite sediment facies 1 upper slope sand to silt bed facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins by comparison the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean outflow current the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies radiocarbon ages verify that the inner shelf shoreface sand facies sedimentation rate 7 1 cm kyr mid shelf mud facies maximum rate 234 cm kyr and surface sandy contourite layer of 0 2 1 2 m thickness on the cadiz slope 1 12 cm kyr have deposited during holocene time when high sea level results in maximum water depth over the gibraltar sill and full development of the atlantic inflow and mediterranean outflow currents the transgressive sand sheet of the shelf and the mud layer underlying the surface contourite sand sheet of the slope correlate respectively with the late pleistocene sea level lowstand and apparent weak mediterranean outflow current

sequence architecture during the holocene transgression an example from the great barrier reef shelf australia abstract the application of sequence stratigraphic analysis to post glacial sediments requires the correct identification of sequence boundaries flooding surfaces and systems tracts the nature of coastal sediments deposited during sea level cycles is complex and misinterpretation is easy particularly in ancient sequences for which eustasy is inferred rather than demonstrated a large core seismic and radiocarbon database from cleveland bay in tropical queensland allows detailed analysis of the systems tracts and parasequences developed during the late holocene despite the large database a unique sequence stratigraphic interpretation is not possible because oscillations in the sea level curve apparently occurred at a frequency higher than the resolving power of radiocarbon dating our best estimate is that the final stages of the holocene sea level rise comprise four parasequences each deposited during episodic slowdowns in sea level rise and or a pulse of rapid sediment supply sea level pauses probably occurred at 12 10 m below modern levels at 8 5 ka bp followed by a fall to ca 17 m at 8 1 ka bp a very rapid transgression to ca 10 m at 7 9 ka bp a further transgression to ca 5 m at 6 8 ka bp and a final rise to the holocene highstand at 1 65 m at 5 5 ka bp the stratigraphic record of these sea level rises is complex occurs within the modern shore connected sedimentary wedge and comprises parasequences associated with shorelines at 11 m p11 17 m p17 10 m p10 5 m p5 and 1 65 m p 1 7 each parasequence comprises in ascending order onlapping estuarine shoreline sediment including mangrove mud and beach sand and progradational shallow bay muddy sand across the bay units up to and including the lower parts of the shallow bay mud correspond to the transgressive systems tract tst of the last 18 ka glacial interglacial cycle the particular parasequence represented being dependent upon location especially depth bay mud above this level corresponds to the post 5 5 ka bp highstand systems tract hst which comprises sand cheniers on the coastal plain and bioturbated muddy sand in the shallow bay the junction between the tst and the hst lies within the bay mud and corresponds approximately to the local flooding surface for the p 1 7 parasequence deposited at the 1 65 m shoreline offshore terrigenous tst strata do not occur over most of the middle and outer shelf which instead is veneered with a thin mid cycle shellbed the lower part of this shellbed is time equivalent to the later part of the tst and the upper part is time equivalent to the hst offshore the maximum flooding horizon mfh and peak eustatic sea level horizon pesh of the late pleistocene holocene sea level cycle lie at some level within the mid cycle shellbed nearshore the mfh and pesh lie within the shore connected sediment wedge at levels near the tst hst boundary however at no locality do either the mfh and pesh necessarily correspond to a physical boundary within the stratigraphy

depositional and erosional coastal processes during the last postglacial sea level rise an example from the central tyrrhenian continental shelf italy abstract a transgressive systems tract tst deposit on the inner continental shelf of the south tuscany region central tyrrhenian sea italy formed during the last postglacial sea level rise its small scale stratigraphy has been detailed using high resolution seismic profiles gravity cores and grab samples the tst deposit overlies a lowstand unconformity shows a tabular geometry and comprises three internal architectures of beach facies 1 architecture a present on the outer sector of the study area is made up of only a reworked sand sheet 2 architecture b on the middle sector comprises palustrine bottom washover and the above mentioned reworked sand sheet and 13 architecture c on the inner sector represents the absence or scarcity of deposits reworked sand sheet ov r the unconformity because the lateral distribution of these vertical successions is not random but parallel to the coast each architecture represents an individual sedimentary stage during sea level rise however all architectures were formed via shoreface retreat in response to the landward migration of a beach complex over the unconformity during this migration the beach system was characterized by a source diastem located in the surf zone and by two sediment dispersal systems one moved the eroded sand over the flat back barrier palustrine area by storm washover while the other transported part of this sand to the lower shoreface forming a reworked sand sheet above the older and inactive source diastem ravinement surface the tst architectures originated from a transgressive succession of beach facies differentiated according to the intensity of shoreface retreat architecture a represents a low preservation potential of the original beach complex architecture b relatively high preservation and architecture c no preservation the intensity of erosion and the consequent preservation potential were totally controlled by antecedent topography

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

surface facies and sediment dispersal patterns southeastern gulf of cadiz spanish continental margin abstract grain size of 294 samples and mineralogical analysis of 364 surface samples from the spanish continental shelf and upper slope of the gulf of cadiz delineate four sediment facies that derive mainly from siliciclastic sources the northern area is formed by the mud rich prodelta of the guadalquivir river parallel to the coast and progradational towards the southeast it exhibits a typical bulk mineral association of illite smectite kaolinite chlorite in the north central area there is a smaller coarser grained prodelta in the bay of cadiz linked to the guadalete river which offshore becomes connected to the guadalquivir prodelta its mineral association is quartz illite kaolinite chlorite in the southern area where fluvial input is negligible the characteristic coarse grained facies generally corresponds to relict late pleistocene reworked deposits the typical mineral association is quartz calcite aragonite smectite mixed layer clay minerals the fourth area corresponds to the shelf break and upper slope offshore cadiz bay where a westward grain size coarsening differentiates the deposits of the last low sea level stand and no typical mineral association exists the mineralogy of the terrigenous deposits indicates a source area from paleozoic sequences of the sierra morena to the north and the subbetic units and gibraltar flysch to the east the neogene deposits of the guadalquivir depression are an additional source of shelf sediments the surface sediment distribution on the inner continental shelf is largely determined by the southeastern atlantic water flow the terrigenous input from rivers and the shelf physiography sediment dispersal on the outer continental shelf and upper slope in contrast largely reflects the location of low sea level stand the development of palimpset deposits and the location of the mediterranean undercurrent over the margin

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

evolution and facies architecture of the mesotidal guadiana river delta s w spain portugal abstract the guadiana river estuary and delta is one of the most important mesotidal fluvio marine systems of the southwestern iberian peninsula the river mouth was formed as a narrow channel excavated by fluvial incision during the pleistocene lowstand and then flooded 6500 yr ago during the flandrian transgression holocene the estuary is in an advanced state of sediment infilling in its proximal part due to its narrow morphology which prevents passage of sediment through to the open coast consequently sediment is accumulating in the river mouth causing progradation as response of the interaction between coastal and fluvial processes sedimentation is controlled by the interaction of sediment load delivered by the guadiana river and the active longshore current which also supplies sand eroded from barrier islands and friable cliffs in the portuguese algarve to the west tidal range is mesotidal 2 0 m and mean significant wave height is 0 6 m with an average period of 3 6 s morphological differences exist between the two sides of the river mouth the western side has a large spit separated from the mainland by a marsh and the eastern side shows an array of old barrier islands separated by salt marsh areas a vibracore study allows us to distinguish 12 different depositional facies in the system fluvial delta tidal inlet flood tidal delta washover beach dune estuarine channel lagoon tidal creek channel margin tidal flat and salt marsh furthermore a different architectural scheme of these facies is present on each side to the east there is a longitudinal repetition of the sandy facies corresponding to the barrier islands on the west side there is a transverse growth of a single spit containing eolian dunes these differences result from asymmetric interaction between the tidal and fluvial currents at the river s mouth and the waves and tidal currents of the open coastal zone

snow accumulation variability at altitude of 7010 m a s l in muztag ata mountain in pamir plateau during 1958 2002 summary precipitation over high mountain is significant for glacier development and river runoff in arid tarim basin in the northwest china however a coherent perspective of precipitation variability at high altitude in tarim basin has not been presented until now here a 41 m ice core at altitude of 7010 m a s l was drilled and gotten to determine annual snow accumulation rates at muztag ata mountain in the headwater of tarim river in pamir plateau during summer 2003 using strong seasonally variation of oxygen isotope and radioactivity reference layers the core was dated reliably back to 1958 and resulted in a 45 year record between 1958 and 2002 the mean annual snow accumulation was about 605 mm water equivalent which is almost 10 times than precipitation in piedmont with elevation below 3000 m a s l the snow accumulation is characterized by high values in 1960s and early 1970s followed by a drop in the middle 1970s and a recent decreasing trend further analysis suggests the upstream zonal flow variation as the major mechanism linking the regional snow accumulation fluctuation to macroscale circulation conditions during the high snow accumulation years the westerly winds between 30 and 50 n from the mediterranean sea to pamir plateau are weakened the decreased upstream westerly winds generate anomalous cyclonic flows in the pamir plateau which results in an enhanced advection of moisture from the tropics to the vicinity of muztag ata mountain and is thus consistent with enhanced snow accumulation at the core site during the low snow accumulation years the above processes are reversed on the basis of this high altitude snow accumulation and temperature a linear regression model is established to simulate annual mass balance in muztag ata region results reveal that snow accumulation conditions largely determine the annual mass balance which has stronger impaction on tarim river runoff

stratal architecture of western mediterranean margins as the result of the stacking of quaternary lowstand deposits below glacio eustatic fluctuation base level abstract through a comparison of high resolution seismic stratigraphy of seven western mediterranean margins similarities and differences in stratigraphic architecture were highlighted and a hierarchy of controlling factors was established the areas are northwestern alboran ebro and northern catalonia in the spanish margin rho ne in the french margin and tuscany latium and calabria in the italian tyrrhenian margin despite their different tectonic physiographic and depositional setting the seismic facies and growth pattern of the middle late pleistocene deposits are comparable the margins are in fact the result of the stacking of lowstand systems tracts of 4th order depositional sequences bounded by polygenetic unconforniities on the shelf and condensed sections on the upper slope this lowstand nature results from the high frequency 100 ka high amplitude 100 m asymmetry falling 65 of the time and stationariness between 10 and 120 m with respect to the present of the glacio eustatic sea level curve if eustasy directly controls the types of deposits making up the margins tectonism conditions their growth pattern as it is the only factor accounting for similarities and differences in the external geometry stratal pattern and distribution of the middle late pleistocene depositional sequences an evolutionary model for the quaternary growth of young passive continental margins is proposed in this model tectonics determines the degree of preservation of lowstand deposits because it conditions the accommodation space left below the erosional profile produced by each glacio eustatic cycle thus some of the sequence stratigraphy principles widely used to set up the model have been modified and adjusted to take into consideration the peculiar nature of quaternary glacio eustasy

the holocene transgression into the estuarine central basin of the odiel river mouth cadig gulf sw spain lithology and faunal assemblages abstract six estuarine facies were distinguished recording the holocene history of sea level rise relating according to the start and development of the holocene transgression which flooded the coast of huelva facies 2 gravels facies 3 grey clayey silts facies 5 well sorted sands facies 4 silty sands facies 5 black clayey silts and facies 6 red muds this group overlies neogene sediments facies 1 three faunal assemblages open bay ob central estuary ce and wave domination wd including remains of macrofauna foraminifers and ostracods plus depositional features are identified in a sedimentological log constructed from a borehole with a continuous core sunk in the central basin of the odiel river estuary huela coast sw spain the ob assemblage requires shallow and protected zones controlled by low energy tidal currents the ce assemblage is located within an intertidal zone where reworked marine forms of foraminifers ostracods and scattered macrofauna co exist with small estuarine foraminifers and ostracods the wd assemblage comprises tests of marine macrofauna with fractured shells plus large marine foraminifers and estuarine ostracods during the first stage of continuous sea level rise 8720 260 bp to 5390 155 bp estuarine accretion high energy tidal currents and wave action took place successively allowing the development of the ob ce and wd assemblages the second stage 5390 155 bp to present with a stabilized sea level comprised a vertical decrease of energy with tidal currents favouring deposition in shallow tidal channels and marsh zones leading to less energetic ce assemblages within the estuarine central basin high sediment supply resulted in deposition during this stage which shows a regressive nature

late quaternary sedimentation off new jersey new results using 3 d seismic profiles and cores abstract regional seismic reflection surveys have delineated a wedge of late quaternary sediment extending 150 km south from the hudson apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector r assumed to represent an erosional surface carved during a low stand of sea level probably corresponding to the wisconsinan maximum glaciation a 3 d reflection survey of a 5 0 5 km area of the southern part of the wedge was carried out in october 1989 line spacing was 10 m and shot spacing 2 5 m navigation achieved position accuracies to the survey shows that the outer shelf sediment wedge has a complex internal structure unrelated to the present seafloor morphology the sedimentary sequence appears to have been formed by a series of depositional events related to glacial melting and interrupted by at least one erosional episode marked by a seismic surface that defines a system of meandering channels faunal studies of samples from cores indicate that the sediments were deposited at shallower depths than at present but there is no evidence for deposition in shallower water or closer proximity to land than the modern mid shelf it appears that the history of periglacial marine sedimentation which accompanied the post wisconsinan deglaciation is no less complex than its continental counterpart

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

lowstand terraces on tyrrhenian sea steep continental slopes abstract wave built terraces formed during sea level stillstands at depths lower than present are found along margins with fairly steep morphology and no to ill developed continental shelf for instance the margin of volcanic islands terraces deposits are up to 20 30 m thick and are flat topped with well defined edges they extend up to 1 km in dip section the deposits are composed of intrabasinal sediments mainly bioclastic sand and silt and are probably due to deposition below the storm wave base during large scale energy episodes two areas of the tyrrhenian sea have been analysed one in a volcanic context the pontine archipelago and the other in a highly active structural context the calabrian arch similar wave built terraces were found in both areas with a main terrace placed at a depth of 100 150 m which is thought to be wurmian older terraces are also present emplaced during the preceding lowstands in the late pleistocene a possible present day terrace is found at about 20 m depth in the pontine archipelago a mechanism of subsequent formation below wave base level and removal because of sea level lowering has been hypothesised during long lasting periods of late pleistocene sea level falls terraces are thus thought to preserve only at the minimum lowstand position and to remain relict on the slope during sea level rise and highstand the analysis of the distribution and depths of these terraces allows some neotectonic interpretation for example in the volcanic archipelago whose western sector has probably risen at an average rate of 2 5 mm yr over the last 20 000 years

transgressive sand sheet covering the shelf and upper slope off sendai northeast japan abstract a thin sand sheet deposited during the last major transgression from 14 000 to 6000 yrs b p covers the shelf and upper slope off sendai northeast japan the sand sheet overlies the sediments deposited during the last low sea level stand and is partly overlain by modern offshore muds this sheet is regarded as palimpsest sediment formed during the transgression in water depths of 50 m the sand sheet is 50 150 cm thick and consists of alternations of poorly sorted thin sand layers and mud layers that are several millimeters to a few centimeters thick it bears mixed environment molluscan shells and small amounts of glauconite scour and fill structures are frequently found gravel with shell fragments is common near the base of the sheet

post glacial sea level control and sequence stratigraphy of carbonate terrigenous sediments wanganui shelf new zealand abstract shallow marine mixed carbonate terrigenous sediments have been accumulating in water depths of 20 110 m on wanganui shelf central western new zealand during the latest quaternary post glacial sea level rise since about 18 000 years bp cores show an upward change from coarse mostly terrigenous dominated sands and gravels to shell rich sediments and then to terrigenous dominated muddy very fine sands and sandy muds these post glacial carbonate terrigenous sediments are a modern analogue for similar episodes of cyclothemic shelf deposition that characterise onland plio pleistocene sections in central western new zealand like their ancient counterparts the latest quaternary sediments can be interpreted in a sequence stratigraphic context a transgressive systems tract 4 15 m thick overlies a transgressive erosion surface evident on seismic reflection records and is represented by slightly shelly coarse sands and gravels at the base of several cores and as palimpsest surficial deposits on the modern shallow shelf out to a depth of about 50 m the overlying shelly deposits both shell rich and matrix rich are equivalent to mid cycle or backlap shellbeds described elsewhere they comprise a diverse in situ or locally transported bivalve molluscan and bryozoan biota typical of temperate latitude cool water carbonate shelf facies these condensed section shellbeds are up to at least 1 5 m thick gradationally overlie the transgressive sediments in cores and occur as modern surficial shelf facies between about 25 and 100 m water depth cores are locally capped by up to a few metres of terrigenous sands or muds that represent highstand systems tract deposits fed onto the shelf from opposing onshore and offshore directions in the nearshore region north island derived felsic fine sands are beginning to prograde seawards westwards across the shellbeds while in the offshore zone south island derived micaceous very fine sands and muds are encroaching upon and covering the shellbeds from the west and south

sea level controls on the post glacial development of the great barrier reef queensland abstract the central great barrier reef is situated on a 125 km wide continental shelf with a shallow shelf break at ca 70 m in consequence the earlier post glacial reef tract was confined to a narrow fringing belt along the present upper slope and outer shelf the reef province only started to assume its modern dimensions after ca 10 ky b p when sea level stabilised at depths around 28 m reef growth since 18 ky b p has been controlled by the episodic nature of the post glacial transgression being related to shorelines s8 to s1 developed at estimated eustatic depths and ages of 114 m 18 ky b p 88 m 17 ky b p 75 m 15 ky b p 56 m 12 ky b p 45 m 11 ky b p 39 m 10 ky b p 28 m 9 5 ky b p 23 m 9 ky b p 9 m 7 5 ky b p and 0 m 6 5 ky b p rates of sea level rise as high as 12 m ky 1 occurred between stillstands outpacing coral growth response and resulting in many mid outer shelf reefs being drowned in situ

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

seismic stratigraphy and relict coastal sediments off the east coast of australia abstract during 1989 marine geophysical surveys were conducted in three regions within the territorial sea 1 of new south wales nsw to explore for heavy mineral sand deposits the northern and central nsw coastline is a recognised beach placer province for economic deposits of rutile and zircon economic placer deposits of these minerals occur as spatially discrete lenses within coastal sand bodies exploration for marine placers was previously attempted during the late 1960s however with mixed results in order to improve the recognition of potential host sites for placer minerals in marine environments a custom made acquisition system was developed which resulted in digital real time data acquisition linked to a high resolution seismic system the digital data were recorded onto mass storage media and subsequently digitally processed to reproduce geophysical records a literature search suggested that the possibility of preservation of drowned relict coastal sediments was questionable due to reworking by subsequent marine transgressions the improved resolution of sedimentary structures beneath the seabed afforded by processing digital data and interpreted using seismic sequence analysis shows that relict structures persist some of which display features attributed to beach barrier preservation these structures are commonly draped by an apron of sediments deposited during the post glacial transgression relict drowned coastal deposits show various degrees of preservation in the areas surveyed it is proposed that the degree of preservation of relict structures is not dependent on the present coastal landscape preservation may be dominated by conditions operating at the time of deposition and to post depositional processes which uniquely characterise each location

late pleistocene holocene sediments on the spanish continental shelves model for very high resolution sequence stratigraphy abstract sequence stratigraphy analysis of high resolution seismic profiles geopulse uniboom and 3 5 khz of late pleistocene holocene sediments has been carried out on five sectors of the spanish continental margin four types of depositional settings are distinguished in these sectors 1 low subsident ramps alboran margin cadiz gulf 2 high subsident 2m kyr ramps alicante valencia 3 ria type morphology on the atlantic passive margin ria de muros and 4 fault scarp morphology systems with subsidence balearic margin a type 1 sequence is interpreted in all these sectors being composed of lowstand systems tract transgressive systems tract and highstand systems tract this conforms to the basic concepts of sequence stratigraphy and each systems tract correlates with a particular part of the last eustatic hemicycle characteristic shelf features such as terraces terraces with beach deposits and progradational sediment wedges evidence a complex stacking of lesser sub sequences in all the systems tracts which must be related to very short period sea level stillstands and fall we propose a very high resolution sequence stratigraphy model in which the last sea level hemicycle is punctuated by p cycles 4500 years which give rise to the neo glacial events h cycles 2200 950 years and c cycles 500 50 years these cycles interact with each other thus establishing the placing of the high and low sea levels this attention to detail 1 explains sedimentary evolution on both the shelf and upper slope during late pleistocene holocene time 2 illustrates some departures from the classical sequence stratigraphy model and 3 also demonstrates that the late pleistocene holocene eustatic curve is not one simple transgression but is modulated by three differing period cycle groups below the milankovitch band our model is delimited by fluctuating sea level during pleistocene holocene times such features should be identifiable on any continental margin however localized features occur due to subsidence and continental shelf morphology which determ ine the location and depth of sedimentary bodies generated in each eustatic cycle

volatile element isotopes of submarine hydrothermal mineral deposits in the western pacific the abundance and isotopic compositions of volatile elements trapped in fluid inclusions of submarine hydrothermal mineral deposits in western pacific subduction zones okinawa trough izu bonin arc mariana trough and lau basin and in kuroko ores in northeastern japan are presented the helium isotopic compositions corrected for air contribution of the okinawa and mariana troughs ranging 4 49 7 68 ra are lower than those of the izu bonin and lau basin 7 62 8 91 ra this characteristic might reflect the differences in regional tectonic setting the okinawa and mariana troughs are related to back arc spreading with strong graben sedimentary signature whereas the izu bonin arc is associated with island arc magmatism the arc contribution to the lau basin volcanism is significantly strong even though it is assigned to back arc spreading nitrogen isotopes can also be explained by a similar hypothesis whereas argon and carbon isotopes cannot be used to discriminate tectonic setting 13c co2 3he and 15n n2 36ar diagrams elucidate the source of carbon and nitrogen the mor type mantle contributions to carbon are mostly smaller in the okinawa and mariana troughs ranging 0 06 8 9 with the average of 2 4 than in the izu bonin and lau basin 2 1 25 with the average of 7 7 the sedimentary contributions to nitrogen are larger in the okinawa and mariana troughs 11 65 with the average of 35 than in the izu bonin and lau basin 4 24 with the average of 15 and the kuroko samples agree well with the latter carbon and nitrogen fluxes are again higher in okinawa trough than in izu bonin arc

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