pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

sea level changes in a back arc foreland transition the late carboniferous permian karoo basin of south africa abstract the late carboniferous to early permian succession in the karoo basin consists in ascending stratigraphic order of diamictites mudrocks greywackes and immature sandstones the diamictites are interpreted as glacigene deposits laid down by a marine ice sheet on a shelf post glacial suspension settling of predominantly mud occurred on the basin floor during open marine and later brackish conditions basin floor fan deposits accumulated in the foredeep whereas deltaic mud silt and sand finally infilled the basin glacigene sedimentation occurred in a back arc basin during the late carboniferous and early permian the post glacial succession accumulated in a foreland basin in which the rising orogenic belt was the predominant sediment source relative sea levels following the major namurian regression apparently remained low during the extensive gondwana glaciation marine ice sheets are highly sensitive to sea level fluctuations and minor sea level rises probably climatically controlled were recorded as interglacials when parts of the marine ice sheet collapsed final collapse of the marine ice sheet was associated with a major transgression post glacial mudrock deposition was characterised by relatively high sea levels except for the period of basin floor fan deposition when there was a sea level lowstand final infilling of the basin by prograding deltas was accompanied by a major regression the late carboniferous to early permian sea level fluctuations in the karoo basin show correspondence with global eustatic cycles reflecting low tectonic interference with sea level patterns however late permian sea levels were predominantly tectonically controlled as a result of foreland basin evolution possible global eustatic events complemented apparent sea level changes within the basin during this period

cenozoic ice volume history development of a composite oxygen isotope record to view cenozoic ice volume and ocean temperature history a composite 18 o time series was constructed for tropical shallow dwelling planktonic foraminifers and for deep water benthic foraminifers we conclude that cenozoic benthic 18 o primarily reflect considerable deep ocean temperature variation and that tropical planktonic 18 o afford the best record of cenozoic ice volume the planktonic composite indicates the presence of a significant ice budget for the past 40 m y the difference between the benthic and planktonic 18 o composites suggests that low latitude production of warm saline bottom water dominated tertiary thermohaline circulation

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

controls on early permian shelf deglaciation in the karoo basin of south africa abstract the late carboniferous to early permian glacigene dwyka group has at its top three types of transitions from diamictite to postglacial mudrock in the southern karoo the type 1 transition sequence consists of clast poor carbonate rich diamictite having a sharp contact with the overlying mudrocks this diamicton accumulated slowly by rain out and sediment gravity flow processes during sedimentation the polar ice front was stabilised by a possible ice shelf collapse of the ice shelf caused rapid ice margin retreat the type 2 transition sequence consists of clast poor diamictite with sandstone bodies overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites deposition of the diamictite facies occurred during oscillations of a subpolar ice front with short stable periods of surface melting of the ice resulting in the formation of small subaqueous outwash fans the type 3 transition sequence consists of bouldery diamictite interbedded with massive or sandstone bearing diamictite overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites the sequence represents highly unstable ice front conditions and fluctuating sea levels with periods of rapid deposition probably by collapsing ice streams climatic conditions may have alternated between polar and subpolar the type 1 transition sequence is predominant in the western part and the type 3 sequence in the eastern part of the karoo basin long term controls on deglaciation was climatic warming as gondwana drifted over the pole as well as changes in land sea configuration superimposed on these were local controls such as relative sea level changes presence of deformable substrate and meltwater production

lateglacial and holocene environmental changes in portuguese coastal lagoons 2 microfossil multiproxy reconstruction of the santo andre coastal area benthic foraminiferal ostracod calcareous nannoplankton and diatom assemblages have been analysed from the 25 45 sedimentary succession of a borehole drilled in the santo andre lagoon southwestern portugal the zones and subzones recognized according to their microfossil content have been used to define six palaeoenvironmental stages extending from the lateglacial to the present stage a and the lower part of stage b 14 2 to 10 0 ka represent a postglacial terrestrial environment when sea level was below present following eustatic sea level rise a normal marine open bay environment established during the upper part of stage b 10 0 to 5 4 ka before 5 4 ka a coastal lagoon developed as a consequence of a sandy barrier formation since then natural variation in the permeability of the detrital barrier through time has been the primary control of the physical chemical and biological features of the lagoonal environment during stage c 5 4 to 3 6 ka as a freshwater dominated lagoon stage d 3

the effect and mechanism of episodic sea level events the record preserved within late wisconsinan holocene incised valley fill sequences abstract late wisconsinan holocene sea level curves have been considered as regional phenomena mainly because geoidal and hydro isostatic effects cause worldwide sea level changes to be non uniform in spite of this observation recent sea level curves suggest a global pattern of episodic sea level rises occuring throughout the last post glacial transgression evidence from the northern gulf of mexico continental shelf supports an episodic model these episodic eustatic rises must have had a profound impact on the evolution of coasts and estuaries episodic sea level rises are manifested in the sedimentary record as rapid translations of the shoreline displacement of estuaries generation of shelf sand bodies and discontinuities within incised valley fill sequences recently gathered evidence from the antarctic continental shelf indicates that late wisconsinan ice sheets were formerly grounded at the shelf edge and that retreat of these ice sheets from the shelf was rapid and sporadic the subsequent draw down of marine ice sheets and the associated eustatic rise in sea level during any single event was probably on the order of 16 to 33 feet 5 to 10 meters in a few centuries on a low gradient shelf such as the north texas shelf the shoreline would translate up to 15 miles 25 kilometers landward during a rise of this magnitude several episodic eustatic events are believed to have occurred during the late wisconsinan holocene deglaciation and were probably instrumental in isolating shelf sandbodies the shoal banks on the north texas shelf which have been interpreted as former shorelines are likely the result of rapid overstepping events sea level reconstructions based on the position of and dates from these banks may be inaccurate due to later reworking of the banks a more complete and continuous sedimentary record of the transgession is preserved within the incised valley fill sequences by applying high resolution seismic stratigraphic techniques to incised valley fill sequences episodic sea level events manifested as discontinuities in estuarine evolution can be accurately dated and related to shelf sand deposits banks the results of drilling on the antarctic continental shelf indicate that marine ice sheets have existed in antarctica since at least early oligocene time so the episodic glacial eustatic mechanism has been operative for at least that long while the processes responsible for delivering sands to the offshore environment may not have changed over geologic time the frequency and rate of eustatic variation has changed and surely has been influential in controlling sand body geometry and distribution on the shelf this implies that the size shape and orientation of shelf sand bodies may differ for glacial versus non glacial periods of geologic time

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

middle holocene sea level rise and highstand at 2 m central texas coast new data suggest a revised picture of middle holocene sea level change for the texas gulf of mexico coast and suggest reevaluation of coastal evolution first brackish marsh facies with calibrated radiocarbon ages of 7 7 to 7 8 ka have been recovered from depths of 8 5 to 9 m in a core from the ancestral colorado river delta and are interpreted to represent a sea level pinning point second a series of ridges along the copano bay margin farther south consist of shelly mud and fine sand with subtidal foram assemblages occur at elevations of 1 95 m above the modern intertidal zone and have produced calibrated radiocarbon ages on foram tests of ca 6 8 to 4 8 ka these ridges are interpreted to represent relict shallow subtidal to intertidal spits that provide minimum sea level positions for the middle holocene and are now emergent because of later sea level fall in aggregate these data show rates of sea level rise during this time period that are very comparable to or even lower than published eustatic rates and suggest a middle holocene sea level highstand for this non uplifting non rebounding and very slowly subsiding part of the north american coastline

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

evidence for a late wisconsin glaciation of the weddell sea the huge ice shelves in west antarctica the ross and filch ner ronne ice shelves have probably extended out on the continental shelf during the late wisconsin1 previous discussions which have focused on the ross sea have suggested 1 that the ice extended across the whole continental shelf2 3 or 2 that there was only a minor expansion4 here we present sedimentological data from the weddell sea fig 1 which suggest that a late wisconsin grounded ice sheet extended to the shelf edge the evidence includes a recent thicker ice in ellsworth mountains at the head of the filchner ronne ice shelf5 this thickening would lead to an expansion of the inland ice sheet over the continental shelf filling up the weddell sea embayment

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

submergent shorelines in the sw pacific evidence for an episodic post glacial transgression high resolution seismic profiles supported where possible by radiocarbon dates and regional stratigraphic data indicate that the last post glacial transgression in the sw pacific was episodic comprising major stillstands punctuated by rapid rises in sea level on the terrigenous continental shelf east of south island new zealand a succession of shorelines s8 s1 are recognized as follows s8 c 113 m 18 000 yr bp s7 c 88 m 17 000 yr bp s6 c 75 m 15 000 yr bp s5 c 56 m 12 000 yr bp s4 c 46 m 11 000 yr bp s3 c 28 m 9 500 yr bp s3a c 24 m 9 000yr bp s2 c 9 m 7 500yr s1 0 m 6 500yr bp with the exception of s8 and possibly s2 the shorelines are associated with wedges of sediment the size and presence of which imply that 1 sea level stabilized at some shorelines for a considerable period of time up to i 2 000 yr and 2 the intervening rises of sea level estimated to have been at least 10 12 m lo3 yr were too rapid to allow the reworking of the wedges into a transgressive sediment sheet as favoured in some current models on the great barrier reef shelf off queensland australia shorelines s8 sl have also been recognized with a further shoreline feature s4a occurring at c 39 m shorelines sla 0 m o yr bp slb 2 3 m 6 000 yr bp and slc 0 m 6 500 yr bp are recognized as discrete aspects of the post 6 500 yr bp sea level behaviour in north eastern australia the rapid rise in sea level at least between shorelines s5 12 000 yr bp and 53 9 500 yr bp is known to have outpaced reef growth causing in situ drowning of reefs located along the deeper shorelines all modern reefs so far drilled and dated began their development at or above s3 28 m 9 500 yr bp some of the shorelines particularly s5 appear to correlate between the northern and southern hemispheres on the basis of age succession and general depth of occurrence suggesting 1 that they may be global features controlled by the post glacial pattern of ice sheet decay and 2 that hydro isostatic adjustment may exert only a minor control on the depth of particular shorelines at least during the earlieg parts of the post glacial transgression

tidal wetland record of holocene sea level movements and climate history abstract paleontological geochemical and lithological indicators of former marine and nonmarine influence are correlated between 13 cores from a tidal wetland wolfe glade on the southeast coast of delaware bay twenty new radiocarbon dates are used to establish the chronostratigraphy of marsh facies sediment iron content weight loss on ignition and remains of plants diatoms and foraminifera known to tolerate specific tidal inundation cycles are used to describe cored facies originating from supratidal intertidal and subtidal salt marsh subenvironments pollen assemblages are used to infer local holocene climate fluctuations and to reconstruct paleoenvironments during marsh evolution the record of paleoclimatology suggests the atlantic chron was warm with variable humidity in the region whereas the subboreal was dominated by cool and humid conditions the subatlantic was warmer and initially dryer with a cool humid phase prior to about 1 ka returning to warmer humid conditions in the last several centuries local relative sea level movements are characterized by five rapid short term episodes when the rate of sea level rise accelerated relative to the rate of marsh aggradation these episodes are recorded by transgressive facies contacts at 5 3 0 2 ka 4 4 0 2 ka 3 25 0 2 ka and 1 8 0 2 ka sidereal years an earlier transgressive facies contact dated 6 9 0 2 ka is probably not the product of a true sea level movement sea level movements are recorded throughout the marsh as palustrine or high marsh peats or peaty overlain by lower intertidal or subtidal marine deposits several features suggest that these episodes are local relative transgressions produced by short term accelerations in the rate of sea level rise relative to marsh aggradation the contemporaneity and apparent suddenness of marine inundations the sequence of facies indicating marine drowning the presence of similar events in marshes elsewhere in delaware bay and the marsh wide extent of indicative facies transitions we propose that the rapid and frequent sea level movements observed in wolfe glade are the result of surges and relaxations in the gulf stream and associated spin up and partial collapse of the north atlantic gyre in response to winds generated by changes in the north atlantic atmospheric thermal gradient associated with holocene climate fluctuations

sea level changes in the holocene over the last 30 years the emphasis in studies of the recovery from low last glaciation sea levels has changed significantly the search for a eustatic sea level curve having global relevance has ended studies into the rheology of the earth s crust and recognition that the geoid has not remained stable over time have resulted in the recognition that there must have been regional differences in eustatic response to deglaciation as a part of this re appraisal there has been a growing appreciation that crustal isostatic response to the removal of the weight of ice sheets has been accompanied by a consequential hydro isostatic response particularly in the areas of the shelf seas in the later part of the post war period attention has additionally been focussed on the much greater potential for error over the whole field of palaeoenvironmental reconstruction in the holocene including not only errors in dating but also a large number of possible sources of errors in heighting as a result of this an increasing number of scientists are withholding judgement on the nature of sea level rise and more particularly on the problem of higher than present late holocene eustatic sea levels the problems outstanding in the early 1960s have not yet been resolved but the bases of uncertainty have changed

effect of cenozoic ice sheet fluctuations in antarctica on the stratigraphic signature of the neogene stratigraphic successions from the gulf of mexico offshore alabama northeast java indonesia ross sea antarctica and several other continental margins have been examined all are characterized by very similar neogene stratal geometries in seismic profiles and well log cross sections from these areas a large mid oligocene i e latest early oligocene earliest late oligocene basinward shift in coastal onlap is followed by a major early miocene transgression and aggradation which is in turn followed by early middle miocene transgressions and late middle and late miocene progradational episodes the succession culminates in plio pleistocene high frequency progradations and transgressions the interregional character of the neogene stratal signature and its similarity to the stratal geometry found in seismic data from the ross sea continental shelf antarctica suggest that the neogene stratal signature is a manifestation of glacioeustatic fluctuations a review of the literature and an analysis of recently acquired and published data indicate that the first major ice sheet grounding event in the ross sea occurred during middle to late oligoce time the ross sea is the repository for ice flowing from a major portion of the continental interior thus the glacial record of the ross sea should serve as a gage of ice volume changes on the continent that were large enough to influence global eustasy the ice advance onto the ross sea continental shelf during middle to late oligocene time may have been the result of a decrease in the rate of shelf subsidence as rifting in the ross sea slowed or ceased advance of the ice sheet resulted in widespread erosion of the continental shelf and shelf overdeepening it is hypothesized that metastable marine based ice sheets have waxed and waned on the antarctic continental shelf since at least the oligocene and that the these waxing and waning events were responsible for the development of a global neogene stratigraphic signature

late quaternary glacial history of the south orkney plateau antarctica abstract piston cores from the south orkney plateau penetrated overcompacted diamictons in water depths of up to 250 m detailed textural and petrological analyses of these diamictons indicate that they are basal tills seismic records from the plateau show a widespread surface of glacial erosion and provide additional evidence of an ice cap grounded to a depth of 250 m piston cores from the slope of the plateau penetrated diatomaceous muds resting directly on poorly sorted muds with very little to no biogenic material the ice rafted debris in these glacial marine sediments is composed almost exclusively of material derived from the south orkney islands this implies deposition beneath an ice shelf as opposed to iceberg rafting in contrast diatomaceous muds contain relatively abundant exotic iceberg rafted material and reflect a glacial maritime setting similar to that of today the sharp contact separating diatomaceous surface sediments from basal tills and sub ice shelf deposits indicates that the ice cap and ice shelf retreated from the plateau rapidly radiocarbon dates for diatomaceous muds from a glacial trough on the plateau indicate that the ice cap and ice shelf retreated from the plateau prior to 6000 to 7000 years ago the homogeneity of surficial diatomaceous sediments suggests that sea ice conditions over the plateau have not changed radically since that time

stable isotopes in late middle eocene to oligocene foraminifera oxygen and carbon isotope ratios in eocene and oligocene planktonic and benthic foraminifera have been investigated from atlantic indian and pacific ocean locations the major changes in eocene oligocene benthic foraminiferal oxygen isotopes were enrichment of up to l in 18o associated with the middle late eocene boundary and the eocene oligocene boundary at locations which range from 1 to 4 km paleodepth although the synchronous eocene oligocene 18o enrichment began in the latest eocene most of the change occurred in the earliest oligocene the earliest oligocene enrichment in 18o is always larger in benthic foraminifera than in surface dwelling planktonic foraminifera a condition that indicates a combination of deep water cooling and increased ice volume planktonic foraminiferal 18o does not increase across the middle late eocene boundary at our one site with the most complete record deep sea drilling project site 363 walvis ridge this pattern suggests that benthic foraminiferal 18o increased 40 m y ago because of increased density of deep waters probably as a result of cooling although glaciation cannot be ruled out without more data stable isotope data are averaged for late eocene and earliest oligocene time intervals to evaluate paleoceanographic change average 18o of benthic foraminifera increased by 0 64 from the late eocene to the early oligocene 18o maximum whereas the average increase for planktonic foraminifera was 0 52 this similarity suggests that the eocene oligocene boundary 18o increase was caused primarily by increased continental glaciation coupled with deep sea cooling by as much as 2 c at some sites average 18o of surface dwelling planktonic foraminifera from 14 upper eocene and 17 lower oligocene locations when plotted versus paleo latitude reveals no change in the latitudinal 18o gradient the oligocene data are offset by 0 45 also believed to reflect increased continental glaciation at present there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from eocene to oligocene time using oxygen isotopes

glacial marine sedimentation and quaternary glacial history of marguerite bay antarctic peninsula abstract marguerite bay situated between the subpolar glacial regime of the northern antarctic peninsula and the polar glacial regime of west antarctica is ideally located to test various models of glacial and glacial marine sedimentation and specific scenarios of late wisconsin ice sheet expansion piston cores and single channel seismic reflection data were collected during the deep freeze 85 and 86 expeditions to determine the late quaternary history of the area seismic data in the bay show a rugged seafloor with numerous deep troughs and a very thin layer of sediment over crystalline basement or older sediments glacial erosion is important in modifying existing features although the ultimate repository of the eroded material is not known it is not found within the bay the piston cores are topped by diatomaceous muds which are underlain by terrigenous muds and muddy gravels that imply deposition beneath an ice shelf basal tills were penetrated at three sites reflecting deposition by a grounded marine ice sheet a reconstruction of the glacial history of marguerite bay since the last glacial maximum shows grounded ice filling the bay in late wisconsin time rising sea level caused an uncoupling of the ice sheet and slow retreat of an ice shelf throughout the holocene

millennial scale instability of the antarctic ice sheet during the last glaciation records of ice rafted detritus ird concentration in deep sea cores from the southeast atlantic ocean reveal millennial scale pulses of ird delivery between 20 000 and 74 000 years ago prominent ird layers correlate across the polar frontal zone suggesting episodes of antarctic ice sheet instability carbon isotopes 13 c of benthic foraminifers a proxy of deepwater circulation reveal that south atlantic ird events coincided with strong increases in north atlantic deep water nadw production and inferred warming interstadials in the high latitude north atlantic sea level rise or increased nadw production associated with strong interstadials may have resulted in destabilization of grounded ice shelves and possible surging in the weddell sea region of west antarctica

glaciological studies on rutford ice stream antarctica rutford ice stream drains part of the west antarctic ice sheet into ronne ice shelf much of the drainage basin has a bed well below sea level and is therefore an area which could undergo substantial change if a climatic warming were to cause sustained thinning of ronne ice shelf snow accumulation data suggest that an accumulation rate of 0 51 0 12 mg m 2 yr 1 is required for balance an extensive ice movement survey network was established across the grounding line in 1978 1980 and was extended for more than 100 km upstream in 1984 1986 velocities at five sites have been calculated using doppler satellite position measurements when the velocities are combined with cross sectional areas of the ice stream measured by radio echo sounding mass flux figures show that drag at the sidewalls and on the base must decrease downstream toward the grounding line the increasing influence of buoyancy forces on ice stream motion is also shown by the steady rise in the ratio of bedrock depth to ice thickness going downstream along the network below the grounding line that was found to cross the middle part of the earlier network is a zone stretching for a further 100 km where it can now be shown that the ice stream is intermittently grounded in these grounded areas the glacier bed is raised with respect to the surrounding seabed and forms eskerlike features surface elevations over the grounded areas are less than 30 m above those needed for hydrostatic equilibrium

marine saline ponds as sedimentary archives of late holocene climate and sea level variation along a carbonate platform margin lee stocking island bahamas a 1500 year late holocene history of coastal and lacustrine carbonate sedimentation is preserved in shallow ponds on lee stocking island exuma cays bahamas details of environmental change have been extracted by integrating lithostratigraphy biostratigraphy macrobiota foraminifers ostracodes and chemical stratigraphy c o isotopes of foraminiferal and molluscan skeletal carbonate mgo wt of ostracode calcite with a well defined 14 ca ms radiocarbon chronology carbonate deposition began within physically restricted euryhaline coastal embayments with several pronounced changes in salinity defined by biotic and calculated salinity variation from mgo wt in shells of cyprideis americana by about 700 740 yr b p embayment closure occurred possibly related to changed longshore deposition associated with sea level rise and or regional change in climate previously documented with closure the initial euryhaline foraminifer assemblage was replaced by a predominant hypersaline biofacies e g triloculina sp with progressive basin fill ostracode assemblages calculated salinities and variation in abundance of the gastropod cerithidea sp may resolve higher order and some extreme salinity fluctuations throughout the remaining history of saline pond development foraminiferal isotope stratigraphy is compatible with that expected for hydrologically closed lake basins carbonate accumulation was effectively shut down 200 years ago replaced by stromatolitic growth present day salinities vary according to water balance governed by rainfall and evaporation a centuries scale 300 400 year flux of abraded reworked marine derived bioclasts admixed with skeletal remains of indigenous biota is also preserved in these ponds allochthonous sediment was transported by hurricane storm surges or related to abrupt transgressive events superimposed on an overall gradual rise in global sea level we discuss evidence for both as controls on sedimentation our study illustrates that saline ponds on bahamian islands are excellent sedimentary archives of local regional and possibly global paleoclimatic events of late holocene age 1999 elsevier science b v all rights reserved

human influence in geomorphology abstract the human influence in geomorphology has a long history and major contributions have for example been made by shaler mcgee gilbert and marsh however in the last two decades concern with global environmental change has brought the role of anthropogeomorphology into sharper focus global warming if it occurs will have important implications for many geomorphological processes and phenomena as a result of the direct effects of warming as a consequence of other related climatic changes e g precipitation change and as a result of climatically moderated changes in major geomorphologically significant variables e g vegetation cover large uncertainties exist with respect to such matters as hydrological response the frequency of tropical cyclones the speed and degree of permafrost degradation the response of glaciers and ice caps the extent of sea level rise the reaction of beaches to rising sea levels and the state of wetlands deltas and coral reefs other human activities may serve to compound the effects of global geomorphological proccesses given the uncertainties of so many of the environmental changes there is a great need to obtain a greater understanding of the rates and mechanisms of landform response geomorphologists need inter alia to establish long term study sites that will generate base line data to monitor the location and rate of change using sequential cartographic and remote sensing materials to determine information on natural background levels and long term trends by means of data gained from cores to gain a more profound understanding of the operation of geomorphological systems particularly with regard to sensitivities and thresholds and to appreciate the consequences of deliberate manipulation of environmental systems by humans

late mid holocene sea level oscillation a possible cause abstract sea level oscillated between 5500 and 3500 years ago at murrells inlet south carolina chezzetcook and baie verte nova scotia and montmagny quebec the oscillation is well constrained by foraminiferal marsh zonations in three locations and by diatoms in the fourth one the implications are 1 there was a eustatic sea level oscillation of about 2 10 m in the late mid holocene on the southeast coast of north america south carolina to quebec that is not predicted by present geophysical models of relative sea level change 2 this oscillation coincides with oceanographic cooling on the east coast of canada that we associate with melting ice and 3 this sea level oscillation climatic event coincides exactly with the end of pyramid building in egypt which is suggested to have resulted from a climate change i e drought cooling this sea level climatic change is a prime example of feedback where climatic warming in the mid holocene promoted ice melt in the arctic which subsequently caused climatic cooling by opening up arctic channels releasing cold water into the inner labrador current that continued to intensify until 4000 years ago this sea level event may also be the best way of measuring when the final ice melted since most estimates of the ages of the last melting are based on end moraine dates in the arctic which may not coincide with when the last ice actually melted out since there is no way of dating the final ice positions

morpho sedimentary characteristics and holocene evolution of the emergent part of the ombrone river delta southern tuscany abstract the holocene evolution of the ombrone river delta has been investigated using morphological and sedimentological evidence the delta had a lagoon like prehistoric evolution while seawards the growth occurred mainly in historical times the data obtained together with the available historical and archeological documentation enable a quantitative evaluation of the volume of the emerged part of the delta to be made moreover for the apical area it has been possible to calculate the annual average increase in the volume of deposition during etruscan and roman times as well as during the middle ages and since the renaissance up to now it has been possible to estimate the periods during which wind exerted a more important role in shaping the delta morphology the volume of sediments deposited during the last 6000 years has been estimated at 1766 10 6 m 3 a combination of climatic conditions littoral dynamics and human action appears to have driven the dynamics of the delta growth which however was not continuous but active especially during the last 3000 years during this period about the 80 of the whole delta volume seems to have deposited high rates of sedimentation occurred between the 16th and the 19th centuries a cold and moist period coinciding with the little ice age when the delta took the typical shape of microtidal wave dominated deltas

bottom currents sedimentation and ice sheet retreat facies successions on the mac robertson shelf east antarctica abstract measurements of water turbidity currents seafloor sediment samples and geophysical data document the sedimentary processes and the late quaternary sedimentary history of a continental shelf valley system on the east antarctic continental margin the valley is up to 1200 m in depth and strikes across the shelf it is interpreted as having formed by glacial erosion processes on the outer shelf sill of the valley northwestward offshore currents with speeds of up to 0 47 m s referenced to 100 cm above the seabed were recorded over a 10 month period such currents are competent to initiate bedload transport of medium sand and formation of small ripple sized bedforms which explains the occurrence of ripple cross bedding observed in some x radiographs of cores a nepheloid layer with concentrations of up to 3 5 mg l was noted at two stations and the available evidence suggests that density flows resulting from the sea ice brine rejection mechanism are competent to entrain shelf bottom sediments episodically sediment cores taken from this environment document the succession of facies resulting from retreat of glacial ice from the shelf during the holocene transgression under low sea level glacial conditions the ice sheet is interpreted to have been grounded on the outer shelf where it deposited a grounding line moraine rising sea level and global warming caused the ice shelf to retreat leaving a sub ice shelf glacial marine mud this is overlain by a laminated to massively bedded ice rafted debris rich facies interpreted as being deposited at the glacial calving front above this is a siliceous mud and ooze facies having a basal age of about 10 000 years bp characterising modern open marine conditions two types of iceberg keel marks on the outer part of the shelf valley are recognised from sidescan sonographs one relict arcuate type formed during the retreat of the ice shelf prior to 10 000 years bp and a second modern elongate type that is presently being formed near the shelf break by iceberg grounding processes this facies succession has been described from other antarctic shelf environments and is probably representative of facies deposited during holocene glacial retreat from the antarctic shelf

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

physical stratigraphy and sedimentology of the late pleistocene holocene tiber delta depositional sequence the tiber delta lies on the passive continental margin of central western italy the tiber delta is a late pleistocene holocene sedimentary succession and constitutes an incomplete high frequency depositional sequence 4th or 5th order which developed from the last post glacial rise in sea level to the present stillstand it is bound by a type 1 basal unconformity which cuts pleistocene deposits five depositional systems have been identified 1 coastal barrier lagoon 2 shelf transition 3 fluvial braided 4 tiber lagoonal deltas t1 t2 t3 and 5 tiber wave dominated delta the first four systems constitute the transgressive system tract tst which is characterized by a retrogradational parasequences set while the fifth system represents the highstand system tract hst characterized by only one parasequence progradational the evolution of these depositional systems has been mostly controlled by sea level rise which was not continuous but punctuated by eight minor stillstands and rapid rises this mechanism of sea level change led to the formation of parasequences that developed within the depositional systems from a palaeogeographical point of view the present tiber delta area was mainly characterized by a coastal barrier lagoon and tiber lagoonal deltas t1 t2 t3 which migrated landwards during the sea level rise throughout the time of the present stillstand the t3 lagoonal delta prograded rapidly into the lagoon reaching the coastal barrier and the lagoon was replaced first by marshes and then by the alluvial plain finally the tiber river overcame the littoral barrier supplying the coast giving rise to the present wave dominated delta

late quaternary coastal and inner shelf stratigraphy apalachicola delta region florida abstract since the beginning of the tertiary the sedimentology of the gulf of mexico basin has been dominated by the depositional activity of the mississippi river the sedimentologic influence of the mississippi diminishes with distance east or west of the louisiana shelf however the texas and northwest florida shelf margins for example are characterized by a series of smaller deltas in the inner and mid shelf areas of these regions the near surface sedimentary units include infilled stream channels and small deltas such features are commonly observed in sub bottom seismic records from the middle and inner shelf of the northeastern gulf along the apalachicola river coast of northwest florida the apalachicola river is the principal source of clastic sediment to the northeastern gulf of mexico during the late holocene virtually all of the river s sediment load has been deposited in the modern apalachicola delta and in the river s estuary apalachicola bay which has been filling rapidly during late quaternary lowstands prior to the development of the modern estuary the river traversed the present day inner and mid shelf incising a network of channels based on seismic records many of these buried shelf channels were considerably larger than their modern counterparts during lowstands the apalachicola river also deposited coarse sediment on the shelf as deltaic and associated river mouth sediments these deposits comprise the modern near surface sediments of the inner and middle shelf an investigation of subsurface sedimentary features observed in seismic profiles provides details on the late quaternary development of the northeastern gulf of mexico shelf seismic reflection profiles obtained on the inner and mid shelf regions of northwest florida reveal an approximately 50 m thickness of late quaternary sediments comprised of two and sometimes three discrete clastic sequences two lower fluvial sequences total as much as 40 50 m in thickness a transgressive marine sand deposit overlies the older features in some places varying in thickness from 0 to 5 m identification of seismic facies combined with stratigraphic data from a suite of coastal boreholes enables correlation of offshore seismic stratigraphic units with late tertiary and quaternary coastal stratigraphy

marine ice sheet decoupling as a mechanism for rapid episodic sea level change the record of such events and their influence on sedimentation abstract unlike terrestrial ice sheets marine ice sheets display more sensitivity to sea level than to climate and they are capable of rapid mass wasting this mass wasting involves ice shelf decoupling from the sea floor and rapid collapse followed by drawdown of the ice sheet glaciologists argue that the marine ice sheet decoupling mechanism could cause sea level rises of a few meters within several hundred years information regarding late wisconsinan holocene glacial history suggests that ice sheet deterioration did not occur at a steady rate studies of the antarctic continental shelf indicate ice sheets grounded over large portions of the shelf during the late wisconsinan glacial maximum and that their retreat from the continental shelf was rapid a study of the trinity sabine incised valley of the texas continental shelf yields a continuous record of holocene sedimentation and sea level change paired upper bay and tidal inlet estuarine systems reflect periods when relative sea level was either at a still stand or slowly rising the flooding surfaces of back stepping parasequences reflect periods of rapid sea level rise large sand bodies on the adjacent shelf used to derive previous sea level curves for the region may represent former shoreline deposits but they also show extensive reworking therefore the curves generated from studies of these sand bodies are inaccurate marine ice sheets have existed in antarctica since at least the late eocene so this mechanism for rapid sea level rise has been active throughout much of cenozoic time as well as during older glacial episodes

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

dual sensor streamer technology used in sleipner co2 injection monitoring co2 has been injected into the saline aquifer utsira fm at the sleipner field since 1996 in order to monitor the movement of the co2 in the sub surface the seventh seismic monitor survey was acquired in 2010 with dual sensor streamers which enabled optimal towing depths compared to previous surveys we here report both on the time lapse observations and on the improved resolution compared to the conventional streamer surveys this study shows that the co2 is still contained in the subsurface with no indications of leakage the time lapse repeatability of the dual sensor streamer data versus conventional data is sufficient for interpreting the timelapse effects of the co2 at sleipner and the higher resolution of the 2010 survey has enabled a refinement of the interpretation of nine co2 saturated layers with improved thickness estimates of the layers in particular we have estimated the thickness of the uppermost co2 layer based on an analysis of amplitude strength together with time separation of top and base of this layer and found the maximum thickness to be 11 m this refined interpretation gives a good base line for future time lapse surveys at the sleipner co2 injection site

paleoclimatic constraints on the maintenance of possible ice shelf cover in the norwegian and greenland seas we examine the controversial issue of whether or not an integrated ice shelf existed in the norwegian and greenland seas during glacial events of the pleistocene our method consists of testing for equilibrium ice shelf configurations with the use of a finite element model that predicts ice shelf evolution under a variety of atmospheric and oceanic forcing conditions ice flow at the margins of the simulated hypothetical ice shelf is determined from one of denton and hughes 1981 reconstructions of continental glaciation applicable to the last glacial maximum our results suggest that the existence of the ice shelf and possibly surrounding marine based ice sheets depends most sensitively on oceanic heat flux a heat flux of approximately 4 80 j m 2 s 1 corresponding to an area average basal melting rate of 0 50 m a 1 ice equivalent is near the upper limit allowing ice shelf equilibrium greater heat flux is found to cause an initial 450 m thick ice shelf to rapidly collapse the equilibrium ice shelf configurations examined provide effective buttressing support for the marine ice sheet grounded in the barents sea 18 kyr b p tests confirming the existence of ice shelf cover in the norwegian and greenland seas are possible through a comparison of the sedimentary record of ice rafted debris with ice shelf flow patterns deduced from our simulations