geological perspectives on the monte verde archeological site in chile and pre clovis coastal migration in the americas discovery of the monte verde archeological site in chile overturned the previous consensus that the first americans into the new world from asia were the makers of clovis projectile points and rejuvenated the hypothesis that migration through the americas occurred largely on portions of the pacific continental shelf exposed by pleistocene drawdown in eustatic sea level the postulate of travel along a paleoshoreline now hidden underwater is an attractive means to posit pre clovis human movement southward from beringia to chile without leaving traces of migration onshore geologic analyses of the pleistocene paleoenvironment at monte verde and of the morphology of the potential migration route along the continental shelf raise questions that have not been fully addressed the periglacial setting of monte verde may call its antiquity into question and the narrowness of the pacific continental shelf of the americas makes it unlikely that people could travel the length of the americas without impacting ground still onshore and no farther inland than monte verde itself geological perspectives on monte verde and coastal migration jointly suggest that the clovis first hypothesis for peopling the new world may have been abandoned prematurely

late quaternary sea levels and crustal movements coastal british columbia late quaternary sea level fluctuations on the british columbia coast have been established from studies of terrestrial and marine sediments and landforms these studies indicate that the sea level history of mainland british columbia and eastern vancouver island is very different from that of the queen charlotte islands and western vancouver island specifically in the former areas there was a rapid rise of submerged coastal lowlands between about 13 000 and 10 000 years ago emergence culminated about 6000 9000 years ago depending on the locality when the sea relative to the land was 12 m or more lower than at present in some areas during middle and late holocene time relative sea level rose on the mainland coast and at least locally on eastern vancouver island resulting in inundation of coastal archaeological sites and low lying terrestrial vegetation tidal records and precise levelling suggest ongoing submergence of at least part of this region in contrast shorelines on the queen charlotte i

late quaternary relative sea level changes and the role of glaciation upon continental shelves sea levels of the past 20 kyr are largely determined by the response of the earth to the last ice age consequently sea level indicators are an important source of information about the interaction between cryosphere and hydrosphere and the solid earth based on the material presented at a recent european science foundation conference the present paper pin points some of the topics currently under discussion with respect to sea level evidence found on continental shelves these topics include possible effects of erosion and changes in palaeotidal ranges on indicators of former relative sea levels as well as the problems involved in the determination of palaeo water depth in addition to former sea levels more evidence is being gathered for substantial small scale patterns in the sea level changes at or nearby to the former ice margins these patterns are not reproduced by the available geophysical models which reconcile on first order level only the large scale pattern

late pleistocene coastal paleogeography of the queen charlotte islands british columbia canada and its implications for terrestrial biogeography and early postglacial human occupation molluscs sediment lithology and published sub bottom profiles are used to deduce sea levels outline the influence of glacially induced crustal displacement and reconstruct the paleoenvironment of the northeast pacific late quaternary coastline geo spatial modelling shows subaerially exposed land that could have been inhabited by plants and animals and also coastally migrating early north american peoples ice free terrain present by at least 13 790 150 14 c years bp a land bridge and edible molluscs are identified queen charlotte islands qci late pleistocene coastal paleogeography may assist in explaining the biogeography of many terrestrial plant and animal species along the broader northeastern pacific margin and provide evidence for researchers seeking late pleistocene early holocene glacial refugia late pleistocene early holocene coastlines that are not drowned and that may harbour early archaeological sites are identified along the western qci where migrants probably first travelled and the westernmost british columbia mainland where the effects of glacial ice were reduced

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

rise of atmospheric oxygen and the upside down archean mantle 1 the establishment of an oxygen rich atmosphere dramatically altered the evolution of life on earth most of the recent discussion of the topic has been focused on the timing of the event rather than on its mechanism here we draw upon recent developments in the understanding of earth s interior to propose that the rise of oxygen followed a geologically abrupt period of mantle overturn and or intense plume activity near the archean proterozoic transition 2470 2450 million years ago the magmatic event has already been linked to the widespread deposition of oxide facies banded iron formation and the rise of oxygen has been implicated as the trigger for iron deposition and earth s first major glaciation we argue that these events are all related to a change in redox state of volcanic gases brought about by deep seated late archean and earliest paleoproterozoic magmatism

late pleistocene terrestrial deposits on the continental shelf of western canada evidence for rapid sea level change at the end of the last glaciation a paleosol with in situ rooted plant remains has been found in a core at a water depth of 95 m on the central continental shelf of british columbia fluvial sediments associated with the paleosol are sharply overlain by lagoonal or shallow pond sediments these in turn are overlain by shallow marine ediments radiocarbon dates on wood fragments and root recovered from the cored sediments indicate that relative sea level was at least 95 m lower 10 500 yr b p and that the core site was rapidly transgressed by the sea shortly thereafter this rapid transgression was contemporaneous with an equally rapid regression at the heads of fiords on the british columbia mainland to the east the two are probably genetically linked and a result of late pleistocene deglaciation and the migration and collapse of a glacial forebulge our evidence indicates that large areas of the british columbia continental shelf were subaerially exposed 11 10 ka this may have facilitated the southward migration of early humans from beringia into mid continental north america at the end of the pleistocene

late glacial vegetation dynamics of the queen charlotte islands and adjacent continental shelf british columbia canada abstract ams radiocarbon dates and paleoecological analyses of sediments from the continental shelf between the queen charlotte islands and the british columbia mainland confirm that portions of the shelf were subaerially exposed and ice free between at least 14 330 and 12 860 14c years bp 17 370 14 570 cal years bp pollen analysis suggests that cyperaceae likely formed the dominant plant cover on the exposed shelf at dogfish bank and fossil pediastrum algae confirm the presence of freshwater pollen accumulation rates suggest low plant density on the exposed shelf although this is uncertain due to over and under representation of some pollen types in relation to vegetation abundance on the landscape paleoecological analyses of late glacial sediments at west side pond on the southern queen charlotte islands demonstrate succession from herb tundra dominated by cyperaceae at 13 750 14c years bp 16 830 cal years bp to dwarf shrub tundra with salix and empetrum nigrum after 13 500 14c years bp 16 400 cal years bp pteridophytes increased in abundance during the transition to pinus contorta woodland ca 13 000 14c years bp 15 600 cal years bp fossil conifer stomata suggest that p contorta grew locally as early as 13 040 305 14c years bp alnus crispa was co dominant by 11 500 14c years bp 13 500 cal years bp and picea sitchensis or its hybrids were present as early as 11 400 14c years bp 13 400 cal years bp in the south moresby area

oxygen isotopic record of silicate alteration in the shergotty nakhla chassigny meteorite lafayette samples from a suite of shergotty nakhla chassigny snc meteorites were analyzed for their o isotopic ratios by a modified version of the laser fluorination technique measured isotopic ratios 17o 16o and 18o 16o from bulk samples of the shergottites eeta79001 shergotty and zagami the nakhlite lafayette and chassigny are similar to those reported in the literature as are those from olivine and pyroxene mineral separates from lafayette iddingsite a preterrestrial alteration product of lafayette was measured for the first time as a separate phase oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum 18o of 14 4 for a 90 separate based on these measurements end member iddingsite has a 18o of 15 6 which places it among other 18o enriched secondary phases carbonate and silica observed in snc meteorites the relatively large difference in 18o between iddingsite and the olivine and pyroxene it replaces 11 is typical of low temperature alteration products a range of crustal fluid 18o values can be interpreted from the 18o for end member iddingsite assuming isotopic equilibrium was achieved during low temperature hydrous alteration 100 c treiman et al 1993 the calculated range of values 15 to 5 depends on many factors including 1 the modal mineralogy of iddingsite 2 potential isotopic exchange among other o bearing phases such as host silicate and carbonate and 3 exchange with evolved or exotic o reservoirs on mars despite the lack of constraints the calculated range is consistent with isotopic exchange and possibly equilibria among components of the co2 carbonate iddingsite h2o system at low temperature the snc meteorite samples in this study have 17o values that are indistinguishable from bulk mars 0 30 except for a single small sample of iddingsite that has an anomalous 17o of 1 4 while analytical difficulties make isotopic measurements for this sample problematic the 17o is similar in direction to 17o reported for waters extracted from bulk samples of lafayette karlsson et al 1992 if the 17o for iddingsite is confirmed it can be concluded that evolved or exotic fluids on mars have contributed volatiles to the o reservoir from which iddingsite formed 130 to 700 ma ago

rapid sea level change and coastal evolution on the pacific margin of canada a rapid regression occurred off the northern pacific margin of canada approximately between 14 600 and 12 500 14c years b p contemporary with the deglaciation of the continental shelf primarily due to the rapid isostatic rebound sea level had reached a maximum lowering of greater than 150 m and remained low until approximately 12 400 14c years b p after which a rapid transgression occurred at 12 500 14c years b p the shelf tilt across the northern pacific margin of canada ranged between 50 m of submergence at prince rupert on the british columbia mainland to greater than 150 m of emergence on the western edge of the queen charlotte islands this regressive transgressive cycle lasted only from 5200 to 5500 14c years a result of the development and collapse of a glacioisostatic forebulge sediment supply wave action and tidal current energy are the primary factors that controlled the coastal response to these late quaternary relative sea level changes plate tectonics on the other hand played a secondary role in coastal evolution during deglacial regression extensive glacial outwash and glaciomarine deposition occurred except on the outer coast where sediment was transferred to the shelf break during the transgression of the shelf the sediment supply was primarily restricted to the erosion of the previously deposited deglacial deposits resulting in the formation of drowned wave cut terraces spit platforms and modification of estuarine environments as the sea level rose in steps the present unconsolidated coastline is mostly erosional during the most recent enso event the sea level rise of up to 0 4 m resulted in as much as 12 m of coastal retreat

triple oxygen isotope composition of dissolved o2 in the equatorial pacific a tracer of mixing production and respiration 1 as a contribution to the study of equatorial pacific biogeochemistry we measured the o2 ar ratio and the triple isotope composition 18o 17o and 16o of o2 along six meridional lines in the equatorial pacific 8 n 8 s at 95 w 110 w 125 w 140 w 155 w and 170 w o2 ar ratios and 18o were close to equilibrium values within the mixed layer and followed the general trend of increasing 18o with decreasing o2 ar at greater depths the 17 17o 0 5 18o constrains the fraction of photosynthetic o2 17 was slightly elevated with respect to equilibrium within the mixed layer due to local photosynthetic production in aphotic zone waters above 250 m depth the average 17 values were higher than in the mixed layer there are four sources of this photosynthetic signal in the dark ocean production in the euphotic zone prior to subduction in the distant source regions production below the mixed layer during travel to the equatorial zone diapycnal mixing with shallower waters bearing photosynthetic o2 and accumulation of photosynthetic o2 produced at very low rates below the 1 light level our results also constrain biological production rates within the mixed layer at several locations along 95 w and 110 w our average rate of 14c production 53 34 mmol c m 2 d 1 agreed well with other estimates in the equatorial pacific while our average rate of net c production 6 9 6 2 mmol c m 2 d 1 and f ratio 0 12 0 11 were somewhat lower than other estimates adding 18o and 17 as tracers to three dimensional biogeochemical ocean gcms and comparing results with observations will extend our understanding of metabolic rates in the study region

late quaternary geology and geochronology of the central continental shelf of western canada piston cores and high resolution seismic profiles from queen charlotte sound have yielded new information on the late quaternary history of this part of the western canada continental shelf cores in three major troughs goose island mitchell s and moresby up to 130 km apart sample a similar sedimentary sequence this sequence comprises five units the lowest unit a which is up to 40 m thick is a laminated to massive mud containing coarse ice rafted debris deposited between pre 13 6 ka and 12 9 ka during deglaciation of queen charlotte sound this unit is overlain by a sequence of stratified sediments units b1 b3 up to 20 m thick deposited during the transition from the pleistocene to the holocene unit b1 directly overlies and is similar to unit a but lacks ice rafted detritus unit b2 is sandy mud locally gravelly deposited during a period of lagging and winnowing from about 12 9 to 10 2 ka when sea level in queen charlotte sound was lower relative to the land than it is today unit b3 is a laminated to massive mud similar to unit b1 deposited when water depths in queen charlotte sound rapidly increased at the end of the pleistocene due to the combined effect of eustatic sea level rise and forebulge collapse the sedimentary sequence is capped by up to 10 m of mud unit c which is more organic rich and contains more clay than any of the other units it was accumulating under present day conditions as early as 9 7 k y ago

paleoecology of late glacial terrestrial deposits with in situ conifers from the submerged continental shelf of western canada extensive portions of the continental shelf off the coast of british columbia were subaerially exposed during late wisconsinan deglaciation due to lowering of relative sea level by as much as 150 m paleoecological analyses were conducted at two sites on the emergent continental shelf where terrestrial surfaces with in situ conifers are preserved the woody plant remains confirm that during the latest period of subaerial exposure terrestrial vegetation was established on the continental shelf microscopic identification of fossil wood and analyses of pollen and plant macrofossils from the associated paleosols and overlying shallow pond sediments indicate that productive pinus contorta dominated communities with abundant alnus crispa and ferns grew on the shelf adjacent to and on the queen charlotte islands around 12 200 14c yr b p dwarf shrubs including salix and empetrum and herbaceous plants such as heracleum lanatum and hippuris vulgaris were also important components of the shelf vegetation near northern vancouver island mixed coniferous forests dominated by pinus contorta with picea tsuga spp alnus spp and ferns occupied the shelf at 10 500 14c yr b p

paleogeography glacially induced crustal displacement and late quaternary coastlines on the continental shelf of british columbia canada abstract subsequent to the last glacial maximum lgm complex isostatic adjustments resulted from deglaciation eustatic sea level change tectonic faulting and a relatively thin flexible lithosphere in the queen charlotte islands qci region a geostatistical interpolation model charts the sequence of evolving landscapes and displays temporal changes in the magnitudes and extent of crustal flexure that accompanied forebulge development on the late quaternary northeast pacific continental shelf between 14 2 and 8 7 ka bp wavelength and forebulge amplitude are consistent with thermal modeling implying low upper mantle viscosity and thin elastic lithospheric thickness beneath queen charlotte qc sound and hecate strait glacial ice 690 m thick began retreating from dixon entrance after 14 5 ka bp 14c years ago and prior to 12 6 ka bp permitting over 100 m of crustal uplift in northern hecate strait a forebulge persisted in hecate strait and qc sound from 13 2 until after 9 7 ka bp implying fixed glacial ice on the british columbia bc mainland until 10 ka bp paleogeographic reconstructions show two emergent ice free terrains one extending eastward from the qci and the other in qc sound by 11 7 ka bp a landbridge connected the bc mainland and the qci

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

post glacial sea levels on the western canadian continental shelf evidence for rapid change extensive subaerial exposure and early human habitation grounded piedmont type glaciers inundated and isostatically loaded the deep troughs which indent the western canadian continental shelf as far west as the shelf edge glaciers do not appear to have covered the offshore banks east of the queen charlotte islands haida gwaii ice retreated from the shelf at approximately 13 500 14c yr b p rapid emergence of the crust followed the ice retreat and resulted in a relative fall of sea level at 10 400 14c yr b p relative sea level on the continental shelf was more than 100 m below that of today and large areas of the queen charlotte basin were subaerially exposed eustatic sea level rise coupled with subsidence of a glacioisostatic forebulge allowed sea levels to rise very rapidly and reach the present shoreline on the queen charlotte islands haida gwaii by about 9100 14c yr b p dated shoreline deposits shells submerged wood remnants and barnacles on stone tools at elevations between 110 m and 14 m suggest a sea level rise of 6 3 cm per year between 12 200 and 11 000 calender years our reconstructions of the paleogeography and paleoenvironments suggest a hospitable environment for human habitation existed in areas that are now submerged stone tools excavated from intertidal deposits support this interpretation significant local variations in the depth of synchronous shorelines are described and attributed to localized differences in isostatic load the documented rates of crustal adjustment are much greater than those used in conventional geophysical forebulge models regional high resolution seismic reflection data 3400 line km shows little evidence for post glacial faulting and suggest that most crustal adjustments appear to have been isostatically rather than tectonically driven subaerial exposure and subsequent sea level transgression were the dominant post glacial processes that determined the morphology texture and paleoenvironment of the western canadian continental shelf

surficial geology of hecate strait british columbia continental shelf four surficial geological units are defined geophysically for hecate strait on the northern british columbia continental shelf they consist of tertiary bedrock unit 1 unconformably overlain in much of the strait of glacial till unit 2 which is in turn overlain below 200 m water depth by thick silts unit 4 and above 200 m by quaternary sands and gravels unit 3 except in areas where till or tertiary bedrock is at or near surface glacial ice covered most of the strait at some time in the pleistocene but evidence for a late wisconsinan advance is more prevalent in the principal troughs of the strait sea level was as low as the present day 180 m isobath during the late tertiary or early quaternary and possibly as low as 100 m at the end of the pleistocene based on the presence of drainage channels wave cut terraces and both shore oblique and shore parallel sand ridges sedimentary bedforms found ubiquitously above 100 m appear to be in equilibrium with the present hydrodynamic conditions and t

late quaternary glaciation and postglacial stratigraphy of the northern pacific margin of canada abstract areas of southeastern alaska and the queen charlotte islands of the northwestern pacific coast of north america were considered to be ice free during the late wisconsinan glaciation and glacial refugia existed however a glacier extended from mainland north america to the shelfbreak in dixon entrance separating alaska and the queen charlotte islands glacial retreat to the east began sometime after 15 000 to 16 000 14 c yr b p and ice had completely left dixon entrance by 13 500 to 13 000 14 c yr b p a rapid sea level regression occurred soon after deglaciation began due to isostatic rebound with relative sea level falling to approximately 150 m below present in central dixon entrance decreasing the size of the inlet by about 30 percent by 12 400 14 c yr b p the late quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older pleistocene sediments and tertiary bedrock a late wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14 400 and 13 000 14 c yr b p contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the queen charlotte islands to a present depth of 150 m during the sea level lowstand and subsequent transgression a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m the unit is exposed at the seafloor over much of the region suggesting that seabed hydrodynamic energy levels were high after 13 000 14 c yr b p and remain so today

east antarctic ice core sulfur isotope measurements over a complete glacial interglacial cycle 1 both sulfur and oxygen isotopes of sulfate preserved in ice cores from greenland and antarctica have provided information on the relative sources of sulfate in the ice and their chemical transformation pathways in the atmosphere over various time periods the mass independent fractionation in the oxygen isotopes of sulfate from the vostok ice core from east antarctica suggests that gas phase oxidation by the hydroxyl radical oh was relatively greater than aqueous phase oxidation by o3 and h2o2 during the last glacial period than during the eemian and preindustrial holocene the complete sulfur isotopic composition 33s 34s 36s from the same vostok ice core samples along with 34s measurements from the dome c east antarctic ice core from this study lend support to these conclusions and reveal significant isotopic fractionation of 34s during chemical transformation and transport to east antarctica these findings reveal that conservation of sulfur isotopic signatures upon transport cannot be assumed for the east antarctic plateau over the time periods considered

the oxygen cycle of the terrestrial planets insights into the processing and history of oxygen in surface environments physical and chemical processes that operate at low temperature in earth s surface environments and in other planetary settings have left an indelible record of the evolution and interactions of planetary surface and near surface reservoirs this chapter reviews the chemistry of oxygen elemental and isotopic in lunar planetary and earth surface reservoirs the discussion begins with a brief review of the relative abundances of oxygen isotopes in planetary materials including lunar samples the snc martian meteorites and components that are inferred to come from martian surface pools this is followed by a brief largely historical account of the development of oxygen isotope geochemistry in earth surface materials the discussion then transitions using an earth systems perspective into an overview of developments in oxygen isotope geochemistry of atmospheric compounds this treatment includes recent studies that 1 use high precision measurements of 17 o and 18 o to characterize atmospheric oxygen 2 apply information about isotopically substituted species isotopologs for characterizing the position dependent isotopic fractionations of some oxygen bearing atmospheric species and 3 investigate non mass dependent isotopic fractionations in ozone and other atmospheric species the discussion then examines the evidence and models that point to change in the oxygen cycle and oxidation chemistry in earth surface environments over the course of geologic time we use the subdivisions of the earth systems the hydrosphere geosphere and biosphere as a basis for examining these changes this record is explored in the context of hypotheses and data that relate to the nature of the changes and transformations in the oxidation state of these different components of the earth s surface environments we conclude with a brief accounting of areas of research where scientifi c inquiry is presently very active

submerged late quaternary terrestrial deposits and paleoenvironment of northern hecate strait british columbia continental shelf canada abstract stratigraphic and paleoenvironmental analyses of sediments recovered from cores on the western canadian continental shelf indicate that areas of the north central shelf were subaerial and supported terrestrial vegetation during the regional late wisconsinan deglaciation paleoecological analyses of now submerged shelf sediments reveal a late quaternary treeless environment locally covered by wet sedge tundra samples from a coeval onshore section on eastern graham island indicate that a dwarf shrub tundra with mosses and willows also occupied lowland areas on the queen charlotte islands between 13 and 14 ka ice free subaerial conditions persisted for a period of at least 3200 years on some parts of the emergent shelf between 13 2 and 10 ka during the same time period clay rich glaciomarine sediment with ice rafted debris was accumulating in the troughs of the shelf low relative sea levels during deglaciation on the continental shelf adjacent to the eastern queen charlotte islands suggest that late wisconsinan ice was thin and limited in extent in this area the presence of a habitable lowland environment during this time interval strengthens the view that a coastal migration of humans from beringia was possible along portions of the exposed continental shelf

new volcanological and volatile data provide strong support for the continuous existence of galapagos islands over the past 17 million years the first systematic rock sampling of volcanoes along the galapagos hotspot tracks the aseismic cocos carnegie malpelo and coiba ridges and adjacent seamounts in the area between the galapagos islands and central and south america was carried out on r v sonne cruise 144 3 guyot shaped seamounts paleo beach or intertidal wave cut platform deposits the structure and texture of volcanic rocks and low sulfur contents of fresh glasses dredged at these volcanoes imply that ocean islands existed continuously above the galapagos hotspot for at least the past 17 million years these new data significantly extend the time period over which the unique endemic galapagos fauna could have evolved providing a complete solution to the long standing enigma of the evolution of galapagos land and marine iguanas

late quaternary paleoenvironments of northwestern north america implications for inland versus coastal migration routes abstract although the long held normative view of new world colonization relies on entrance through an interior ice free corridor by terrestrially adapted big game hunters a recently demonstrated human presence in southern chile dating prior to the existence of the corridor route implies different colonization scenarios which must be seriously considered a renewed focus of archaeological and paleoecological research on early post glacial landscapes in northwestern north america has revitalized the ice free vs coastal corridor controversy geological findings from glacial geology and paleo sea levels support the possibility of coastal migration from beringia to the pacific northwest between about 14 000 and 10 000 bp and preliminary paleoecological data suggest that the coastal landscape was in part vegetated and probably able to support a terrestrial fauna including humans the same cannot be said about the ice free corridor

paleoecology and ice limits of the early fraser glaciation marine isotope stage 2 on haida gwaii british columbia canada

time of maximum late wisconsin glaciation west coast of canada new data from a deep sea core in the eastern north pacific ocean indicate that the western margin of the late wisconsin cordilleran ice sheet began to retreat from its maximum position after 15 600 yr b p ice rafted detritus is present in the core below the 15 600 yr b p level and was deposited while lobes of the cordilleran ice sheet advanced across the continental shelf in queen charlotte sound hecate strait and dixon entrance the core data are complemented by stratigraphic evidence and radiocarbon ages from quaternary exposures bordering hecate strait and dixon entrance these indicate that piedmont lobes reached the east and north shores of graham island part of the queen charlotte islands between about 23 000 and 21 000 yr b p sometime thereafter but before 15 000 16 000 yr b p these glaciers achieved their greatest late wisconsin extent radiocarbon ages of late glacial and postglacial sediments from queen charlotte sound hecate strait and adjacent land areas show that deglaciation began in these areas before 15 000 yr b p and that the shelf was completely free of ice by 13 000 yr b p

late quaternary geology of eastern graham island queen charlotte islands british columbia a reconnaissance study of quaternary sediments exposed in coastal bluffs on eastern graham island has revealed the presence of two major till units each of which is underlain by glaciomarine stony mud outwash sand and gravel and laminated to massive silt and sand of undetermined origin sediment units below the surface drift are older than the radiocarbon dating limit sediments above this drift provide a nearly continuous record of geologic events from before 16 000 years bp until the present stratigraphic evidence and radiocarbon dates indicate that 1 late wisconsin glaciation of the coastal lowlands of graham island was weak and of short duration and 2 a period of low sea levels during late pleistocene time was followed by a transgression that culminated about 7500 8000 years ago when the sea was about 15 m higher relative to the land than at present marine regression during middle and late holocene time produced wave cut scarps wave cut benches overlain by littoral sediments bars spits and beach and dune ridges

mass dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles abstract sulfur isotope studies of post archean terrestrial materials have focused on the ratio 34s 32s because additional isotopes 33s and 36s were thought to carry little information beyond the well known mass dependent relationship among multiple isotope ratios we report high precision analyses of 33s and 36s values defined as deviations of 33s and 36s from ideal mass dependent relationships for international reference materials and sedimentary sulfides of phanerozoic age by using a fluorination technique with a dual inlet isotope ratio mass spectrometer measured variations in 33s and 36s are explained as resulting from processes involve branching reactions two or more reservoirs formed or mixing irreversible processes in closed systems rayleigh distillation amplify the isotope effect we outline how this new isotope proxy can be used to gain new insights into fundamental aspects of the sulfur biogeochemical cycle including additional constraints on seawater sulfate budget and processes in sedimentary sulfide formation the isotope systematics discussed here cannot explain the much larger variation of 33s and 36s observed in archean rock records furthermore phanerozoic samples we have studied show a characteristic 33s and 36s relationship that differs from those measured in archean rocks and laboratory photolysis experiments thus high precision analysis of 33s and 36s can be used to distinguish small non zero 33s and 36s produced by mass dependent processes from those produced by mass independent processes in archean rocks and extraterrestrial materials

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved