dynamics of turbidity current with reversing buoyancy in nature and industry there are many situations in which dense sediment laden currents are overlain by fluid of density intermediate between that of the bulk suspension and of the interstitial fluid an experimental investigation of such horizontally spreading turbidity currents at a constant inflow rate has been conducted if the bulk density of such currents is initially larger than the ambient density an underflowing gravitational turbidity current results however once the sediment in the suspension settles out the current releases buoyant interstitial fluid through the interface between the current and the overlying ambient fluid this settling of the sediment and the detrainment of buoyant interstitial fluid decreases the spreading velocity of the turbidity current until the current stops and lifts off the bed the rising interstitial fluid accumulates at the free surface to form a new buoyant surface overflow in this study simple spreading relationships based on experimental observations are

scavenging of 230th in the sulu sea abstract thorium 230 concentrations were determined in the sulu sea a small 5000 m deep basin surrounded by the philippine and malaysian islands and the south china sea the mid water of south china sea flows into the sulu sea through the mindoro strait sill depth 420 m thorium 230 concentrations in deep waters at two stations pa 1 in the sulu sea and pa 11 in the south china sea are considerably lower than those in the open ocean average concentrations below sill depth 0 49 dpm m 3 pa 1 0 79 dpm m 3 pa 11 the low concentration and homogeneity of 230 th in deep water below sill depth are consistent with the trend of other semi closed basins such as the japan sea we also measured 232 th concentration in the sulu sea from these data terrigenous 230 th was calculated to be 19 of the measured 230 th in the basin the most probable explanation for the 230 th deficit in the deep water of the sulu sea is an enhanced scavenging effect by the particles supplied from the seafloor using a simple box model the amount of 230 th scavenged by particles supplied from the seafloor is calculated to be 0 052 dpm m 3 y

sulfur carbon ratios and extractable organic matter of the middle proterozoic nonesuch formation north american midcontinent rift abstract the nonesuch formation ca 1 1 ga host to the white pine copper deposit is a generally organic rich unit of relatively wide extent selected strata away from mineralization were analyzed for their organic carbon and total sulfur contents and for the amount and composition of extractable organic matter sulfur to carbon ratios are covariant but the ratios of total sulfur to organic carbon are generally higher than those found for marine phanerozoic black shales deposited under oxic bottom water conditions the sulfur to carbon ratios and the intimate association fo framboidal pyrite and organic matter are suggested to be the result of bacterial sulfate reduction in the nonesuch sediments activity of sulfate reducing bacteria requires a supply of sulfate in the water column and implies that the depositional environment was not a low sulfate aqueous environment a marine embayment dominated more by sea water than riverine input is suggested as the environment of deposition based on the correlation of total sulfur and organic carbon the relatively high total sulfur content and on the absence of sedimentologic and geochemical criteria for saline lacustrine environments deposition of highly reactive organic matter in low concentrations coupled with high concentrations of reactive iron and the absence of bioturbation resulted in unusually efficient pyrite formation extractable organic matter in unmineralized nonesuch strata is interpreted to be autochthonous in origin homologous series of n alkanes and cyclohexyl alkanes regular isoprenoids and monomethyl branched alkanes were identified by gas chromatography ratios of pristane phytane pristane n c17 and phytane n c18 suggest relatively low thermal maturity for the overall unit with a slight increase in the level of thermal maturity from michigan westward to wisconsin the aliphatic character and high extractability of organic matter indicate that the petroleum potential of the nonesuch formation will be good to excellent if the organic rich facies thicken down dip under lake superior or into the southern extension of the rift

signature of the gold cove event 10 2 ka in the labrador sea abstract one of the least known catastrophic meltwater and sediment release events of the laurentide ice sheet during the early holocene is the so called gold cove proglacial lake outbursts a drainage event through the hudson strait this event may have disturbed circulation in the labrador sea by releasing freshwater here we report data from four sediment cores and re analysis of six published records spatially covering 2000 km from the mouth of hudson strait to the northeastern sohm abyssal plain abundant detrital carbonate dc and less positive 18o values in neogloboquadrina pachyderma sinistral suggest a short lived meltwater event in the hudson strait region this discharge transported detrital carbonate rich sediment and shallow water benthic forams southward along the labrador margin mixing with the north atlantic current near the grand banks sediments associated with this event were guided through the deep labrador sea from the mouth of hudson strait and the northwest atlantic mid ocean channel namoc to the sohm abyssal plain furthermore we report less positive 13c values in the epibenthic foram cibicidoides wuellerstorfi from the southern labrador sea during this event our twenty one 14c ams dates in addition to earlier published radiocarbon dates from the labrador margin suggest that this dc event was coeval with the gold cove proglacial lake outbursts related to re advance of the laurentide ice sheet

paleomagnetism of 1 09 ga lake shore traps keweenaw peninsula michigan new results and implications we report paleomagnetic data from a new section of the 1 09 ga lake shore traps exposed on silver island 10 flows and on the adjacent mainland two flows along the northwestern coastline of the

evidence in pre 2 2 ga paleosols for the early evolution of atmospheric oxygen and terrestrial biota the loss of fe from some pre 2 2 ga paleosols has been considered by previous investigators as the best evidence for a reduced atmosphere prior to 2 2 ga i have examined the behavior of fe in both pre and post 2 2 ga paleosols from depth profiles of fe 3 ti fe 2 ti and fe ti ratios and fe 3 ti vs fe 2 ti plots this new approach reveals a previously unrecognized history of paleosols essentially all paleosols regardless of age retain some characteristics of soils formed under an oxic atmosphere such as increased fe 3 ti ratios from their parental rocks the minimum oxygen pressure p o 2 for the 3 0 2 2 ga atmosphere is calculated to be about 1 5 of the present atmospheric level which is the same as that for the post 1 9 ga atmosphere the loss of fe common in paleosol sections of all ages was not due to a reducing atmosphere but to reductive dissolution of ferric hydroxides formed under an oxic atmosphere this reductive dissolution of ferric hydroxides occurred either 1 after soil formation by hydrothermal fluids or 2 during and or after soil formation by organic acids generated from the decay of terrestrial organic matter terrestrial biomass on the early continents may have been more extensive than previously recognized

mindoro strait and sibutu passage transports estimated from satellite data 1 this study investigates the mindoro strait and sibutu passage transports using remotely sensed sea surface height ssh and ocean bottom pressure obp data the analysis reveals the existence of a persistent baroclinic pressure gradient that drives a deepwater overflow from the south china sea into the sulu sea the application of hydraulic theory combined with the geostrophic control formula yields a mean transport estimate of about 2 4 sv 1 sv 106 m3 s 1 through the mindoro strait and about 2 8 sv through the sibutu passage most of this water enters the sulu sea through the bottom layer of the mindoro strait and exits the sulu sea in the upper layer of the sibutu passage the analysis also provides the first satellite based observational evidence on the seasonal and interannual variation of the mindoro strait and sibutu passage transports for the period from january 2004 to december 2007

sediment driven downslope flow in submarine canyons and channels three dimensional numerical experiments abstract the role of submarine canyons and channels in sediment driven downslope flow sediment plumes is examined using a three dimensional rotational numerical model that couples the hydrodynamics and sediment transport the model domain consists of a bottom ocean layer of constant height coupled with an essentially inert upper ocean the model equations are cast in a rotated bottom following coordinate system in which vertical grid spacing is independent of the ocean depth and bathymetry can be resolved accurately this allows for tracing bottom attached sediment plumes decameters in height from shallow water into great depths of the ocean the calculations reproduce morphologic features related to the occurrance of sediment plumes such as the formations of 1 localized deposition areas of sediment off the mouth of submarine canyons and 2 levees at both sides of submarine channels furthermore it is demonstrated that sediment plumes are not only important for the transport of littoral sedimen

a giant late archean lake system the meentheena member tumbiana formation fortescue group western australia abstract the 2720 ma old meentheena member of the tumbiana formation fortescue group is a 30 50 m thick succession of alternating siliciclastic and limestone beds that crop out intermittently over a distance of 680 km across the pilbara craton western australia limestones of the member consist of flat pebble intraformational conglomerate oolite grainstone calcisiltite and calcilutite siliciclastics consist of shale siltstone and sandstone and many of these are tuffaceous sedimentary structures include abundant symmetrical ripples ripple cross stratification desiccation cracks teepee structures and planar to wavy lamination the member is superficially similar in appearance wherever it crops out however the correlation of individual beds and units over distances greater than 15 km is problematic there are no regional marker beds radiometric ages from tuffaceous units young to the west by a few million years four lithofacies are defined a flat pebble conglomerate b ripple cross laminated oolite grainstone c planar to wavy laminated calcilutite calcisiltite and d shale siltstone stromatolites are found in all three of the limestone facies evaporites are rare and include halite pseudomorphs the four lithofacies are generally found in a vertical succession that characterizes a lithofacies association and reflects a deepening upward succession associations may not have all four lithofacies but do reflect the same deepening upward pattern the uppermost portions of shale siltstone facies commonly contain symmetrical ripples and desiccation cracks indicating subaerial exposure measured sections contain as many as 25 of these parasequences indicating fluctuating water levels limestone lithology and facies commonly change abruptly laterally at the meter and greater scale and vertically centimeter to meter scale the sedimentary structures differences and abrupt changes in lithofacies patterns the inability to correlate confidently between regions and the differences in age from east to west suggest a complex diachronous depositional system of fluctuating water levels in separate bodies of water the limestone is dominated by sedimentary structures indicative of shallow water within wave base however it is devoid of evidence of any tidal influence possibilities for depositional environments include a tideless sea or a lacustrine system 87sr 86sr values from limestone differ from known archean marine carbonates ree patterns are decidedly non marine as well a lacustrine system is favored for the meentheena member based on sedimentary structures the abruptness of lithologic and facies changes the facies association lateral gradation into fluvial deposits the inability to correlate many units and beds for more than a few to several kilometers geochemical data stromatolites and comparisons with younger lacustrine basins as well as marine successions there is no single line of evidence that unequivocally establishes a lacustrine origin however multiple lines of evidence are collectively consistent with a lacustrine origin the meentheena member would therefore represent the oldest known carbonate rich lacustrine system which we call the meentheena lakes system

morphological record of oxygenic photosynthesis in conical stromatolites conical stromatolites are thought to be robust indicators of the presence of photosynthetic and phototactic microbes in aquatic environments as early as 3 5 billion years ago however phototaxis alone cannot explain the ubiquity of disrupted curled and contorted laminae in the crests of many mesoproterozoic paleoproterozoic and some archean conical stromatolites here we demonstrate that cyanobacterial production of oxygen in the tips of modern conical aggregates creates contorted laminae and submillimeter to millimeter scale enmeshed bubbles similarly sized fossil bubbles and contorted laminae may be present only in the crestal zones of some conical stromatolites 2 7 billion years old or younger this implies not only that cyanobacteria built proterozoic conical stromatolites but also that fossil bubbles may constrain the timing of the evolution of oxygenic photosynthesis

the 1100ma sturgeon falls paleosol revisited implications for mesoproterozoic weathering environments and atmospheric co2 levels abstract during the active rifting stage of the 1100 ma midcontinental rift in north america alluvial sediments were deposited intermittently between basalt flows on the north and south shores of present day lake superior at times of depositional quiescence paleosols developed in both areas on the alluvial sediments and on the antecedent basalt new results from the sturgeon falls paleosol in michigan characterizing the weathering processes at the time of its formation indicate moderate maturity high degrees of hydrolysis and leaching and a low degree of salinization geochemical provenance indices indicate a homogeneous source for the paleosols and in contrast to earlier work there is little evidence for k metasomatism as a result atmospheric co 2 levels of 4 6 pre industrial atmospheric levels were calculated using a mass balance model this result is consistent with previous calculations from nearly contemporaneous paleosols from the other side of the keweenawan rift and from the 100 ma younger sheigra paleosol in scotland the calculated co 2 values are also consistent with the calculated weathering environment proxies that indicate weak to moderate weathering at this time frame and suggest that the higher greenhouse gas loads indicated by paleoproterozoic paleosols had dissipated by the mid late mesoproterozoic

the submarine delta of the ganges brahmaputra cyclone dominated sedimentation patterns the ganges brahmaputra belongs to the world s largest rivers in terms of sediment discharge but little is known yet about the processes controlling sediment distribution on the shelf and the documentation of these processes in large and small scale sedimentary structures for this study the submarine delta of the river system was investigated by high resolution seismic reflection profiles and piston and gravity coring logged physical properties of the cores were combined with visual core description grain size analysis and radiography sedimentation rates were estimated by 210pb and 137cs gamma spectrometry and cross checked with evaluation of seismic profiles the data reveal that the broad delta topset 20 m waterdepth is formed by a thick layer of sand silt highest sedimentation rates about 10 cm a 1 occur at the centre of clinoform delta foreset beds where about 20 of the total riverine sediment load is deposited and thus cause an annual progradation of the subaqueous delta front by about 15 m the foreset beds consist of graded sand silt layers which are thought to be deposited by sediment laden flows generated during the surge of tropical cyclones tempestites interbedded with silty clay layers the head of a canyon the swatch of no ground that deeply incises into the shelf forms a sediment trap along the westward cyclonic transport path where sedimentation rate increases to about 50 cm a 1 episodically earthquakes or storms destabilize especially the rapidly accumulated foreset beds in the eastern delta creating up to 8 m thick mass flows on the outer shelf in water depth beyond 80 m no holocene sediment is deposited

dramatic local environmental change during the early eocene climatic optimum detected using high resolution chemical analyses of green river formation stromatolites abstract the eocene green river formation represents a system of lakes that covered parts of what is now wyoming colorado and utah and captures the early eocene climatic optimum eeco 52 50 million years ago or ma the warmest period of the cenozoic era and a period associated with very high levels of atmospheric co2 lakes especially closed basin lakes can respond dramatically to environmental change because of their sensitivity to precipitation and evaporation in this study stromatolites from the rife bed of the green river formation are used as fine scale records of terrestrial paleoenvironmental change during a global hothouse climate and to investigate how the environmental dynamics within the lake system affected the growth of stromatolites the stromatolites are composed of branching microdigitate columns laminated on the 10 100 m scale laminae are grouped in cm scale layers that alternate between calcite fan micritic and mixed microstructures the fan layers are depleted in 18o na and mg ca the micrite layers in contrast are comparatively enriched in 18o na and mg ca the 13c and 18o are strongly positively correlated suggesting the stromatolites formed in a closed basin lake consistent with the regional stratigraphy additionally clumped isotope analyses provide the first quantitative values for water temperatures in lake water from the green river formation 35 c for micrite layers and 28 c for fan layers changes in 18o and sodium ion concentration are likely related to periods of evaporation and recharge and thus can be used to estimate lake volume change during stromatolite growth two models one using sodium ion concentrations in a conserved system the other using rayleigh fractionation and mixing equations to explain changes in oxygen isotopes converge upon similar results for lake volume changes revealing multiple episodes of meter scale lake level rise and fall during the accretion of the 30 cm thick stromatolite because of the broad flat bathymetry of the lake such lake volume and depth changes would have been accompanied by shoreline shifts on the order of tens of kilometers while the stromatolites were actively growing challenging the view of a single stromatolite paleoenvironment in the lake therefore the fan microfabric interpreted here as abiogenic in nature formed in cooler waters when the lake was deeper possibly below a thermocline in contrast the micrite microfabric for which there is evidence of biogenicity formed when the lake was shallow and warm the alternation between biogenic and abiogenic microfabrics present in the rife bed stromatolites is hypothesized to result from dramatic changes in lake level influencing the microbiology and chemistry of the waters in which the stromatolites formed indicating that stromatolite growth can occur under disparate conditions and therefore does not necessarily represent a single facies

comparative precambrian stratigraphy and structure along the mid continent rift the mid continent rift is a geophysically identified tectonic structure that has been traced from kansas northeastward into the lake superior district a related arm has been identified by gravity as extending from eastern lake superior southeastward into the lower peninsula of michigan this rift is of precambrian keweenawan age and began developing approximately 1 1 b y b p for most of its extent this continental class rift system is buried below phanerozoic strata outcrops are found only in east central minnesota northwestern wisconsin and the upper peninsula of michigan the most accepted tectonic model of the mid continent rift is that of a central horst partly covered by clastic rocks bounded by high angle faulting and flanked by basins filled with clastic rocks this model was developed in conjunction with field studies in the southwestern lake superior area and generally has been adopted for minnesota iowa nebraska and kansas a comparable model has yet to be presented for the related arm extending into southern michigan in the lake superior outcrop belt the oldest recognized rifted rocks are layered basalts of middle keweenawan age overlying these basalts is an upper keweenawan thick sedimentary sequence composed of the oronto older and bayfield younger groups these sedimentary rocks are almost entirely clastic with texture ranging from conglomerate to shale mudstone rock colors are principally reds and browns with secondary shades of green and white the oronto group is more immature mineralogically and texturally and more complex structurally than the bayfield group the oronto group also is differentiated by one of its units the nonesuch formation which contains organic shales that bleed liquid hydrocarbons from subsurface fractures and vugs in a michigan copper mine conditions of eposition for both groups are closely allied with an aquatic continental environment specific paleogeography ranged from alluvial fan and plain to deltaic flood plain fluvial and lacustrine southwest and southeast of the lake superior outcrop belt stratigraphic relationships are known principally from fewer than a dozen significant wells drilled into the precambrian within the mid continent rift trend analysis of the proposed upper keweenawan red clastic sedimentary rock column within these wells suggests that the lake superior stratigraphy can be provisionally correlated throughout the mid continent rift trend

transport and dynamics of the panay sill overflow in the philippine seas abstract observations of stratification and currents between june 2007 and march 2009 reveal a strong overflow between 400 and 570 m depth from the panay strait into the sulu sea the overflow water is derived from approximately 400 m deep in the south china sea temporal mean velocity is greater than 0 75 m s 1 at 50 m above the 570 m panay sill empirical orthogonal function analysis of a mooring time series shows that the flow is dominated by the bottom overflow current with little seasonal variance the overflow does not descend below 1250 m in the sulu sea but rather settles above high salinity deep water derived from the sulawesi sea the mean observed overflow transport at the sill is 0 32 106 m3 s 1 the observed transport was used to calculate a bulk diapycnal diffusivity of 4 4 10 4 m2 s 1 within the sulu sea slab 575 1250 m ventilated from panay strait analysis of froude number variation across the sill shows that the flow is hydraulically controlled a suitable hydraulic control model

microbenthic distribution of proterozoic tidal flats environmental and taphonomic considerations silicified carbonates of the late mesoproterozoic to early neoproterozoic society cliffs formation baffin island contain distinctive microfabrics and microbenthic assemblages whose paleo environmental distribution within the formation parallels the distribution of these elements through proterozoic time in the society cliffs formation restricted carbonates including microdigitate stromatolites laminated tufa and tufted microbial mats consist predominantly of synsedimentary cements these facies and the cyanobacterial fossils they contain are common in paleoproterozoic successions but rare in neoproterozoic and younger rocks less restricted tidal flat facies in the formation are composed of laminated microbialites dominated by micritic carbonate lithified early yet demonstrably after compaction these strata contain cyanobacteria that are characteristic in neoproterozoic rocks within the formation the facies dependent distribution of microbial populations reflects both the style and timing of carbonate deposition because of the strong substrate specificity of benthic cyanobacteria a reasonable conclusion is that secular changes in microbenthic assemblages through proterozoic time reflect a decrease in the overall representation of rapidly lithified carbonate substrates in younger peritidal environments as well as concomitant changes in the taphonomic window of silicification through which early life is observed

response of western pacific marginal seas to glacial cycles paleoceanographic and sedimentological features abstract this paper reviews the recent progress in late quaternary studies in five northwestern pacific marginal seas especially the south china sea as an example a series of marginal seas separate asia from the pacific ocean and significantly modify the material and energy flux linkage between land and sea during glacial cycles the sea level induced environmental signal was amplified in the marginal seas giving rise to drastic changes in areas and configurations of these seas and to reorganization of sea water circulation in basins since most of the western pacific marginal seas are influenced by monsoon circulation and some of these are located within the western pacific warm pool the glacial geographic changes have produced a profound impact on regional and global climate for example the decrease of sea area and sea surface temperature sst in the marginal seas was one of the factors responsible for the enhanced aridity of inland china during the glaciation glacial intensification of the winter monsoon and increased seasonality of sst in marginal seas might explain at least partly the apparent discrepancy between the tropical paleotemperature estimations based on terrestrial and open ocean records in this region as the western pacific marginal seas trap terrigenous material supplied by east asia the deep water sedimentation rates there can be one to two orders of magnitude higher than in the open ocean down slope sediment transport is more active when the sea level changes particularly during the deglaciation at least four types of carbonate cycles have been recognized in the western pacific marginal seas and each of those contains environmental signals from the surface and deep sea water as well as from the drainage basin

the late pleistocene history of surface water δ13c in the sulu sea possible relationship to pacific deepwater δ13c changes a reconstruction of late pleistocene surface water carbon isotopic 13c variability is presented from ocean drilling program odp site 769 in the sulu sea in the western tropical pacific the sulu sea is a shallowly silled back arc basin with a maximum sill depth of 420 m site 769 was drilled on a bathymetric high in 3643 m of water and has average late pleistocene sedimentation rates of 8 5 cm kyr the oxygen isotope record 18o of globigerinoides ruber at site 769 shows a strong correlation with the specmap stacked 18o record attesting to the continuity of sediment archive at the site surface 13c displays consistent glacial interglacial variability which averages 0 9 and has varied from 0 75 to 1 1 over the last 800 kyr comparison to surface water 13c records in the south china sea and western tropical pacific suggests that the glacial interglacial surface 13c variability is regional in scale planktonic 13c data from odp site 677 in the eastern pacific is also coherent with the site 769 additionally we have found that the site 769 surface 13c record is coherent at periods of 100 and 41 kyr with deepwater 13c records from the pacific the highest correlation occurs with the deep eastern pacific where benthic 13c data from cores rc13 110 and odp site 677 closely match the sulu sea surface water record we evaluate several possible controls of surface water 13c in the sulu sea that may explain the coherent timing with pacific deepwater 13c records these include variations in terrestrial organic matter flux to the basin the upwelling of subsurface water and productivity changes and the influx of western pacific intermediate water to the sulu sea our preferred explanation involves a region of upper intermediate water upwelling in the far western pacific which has been shown to outgas co2 from subsurface waters into surface waters upwelling also occurs in the area of panama basin site 677 these equatorial upwelling zones could potentially provide a route by which pacific intermediate water can modulate the 13c composition of certain pacific surface water locations future reconstructions of late pleistocene surface water 13c variability in the western pacific and indonesian seas will be required to further evaluate the source of the glacial interglacial surface water 13c change

dual overflows into the deep sulu sea 1 the sulu sea isolated from the neighboring ocean below 570 m is nearly isothermal below 1250 m but with a marked salinity increase with depth the source of the deep sulu sea water has been attributed to south china sea water overflowing the 570 m topographic sill of panay strait however the panay overflow estimated as 0 32 106 m3 sec is an unlikely source for the saltier water sulu sea deep water we propose that deep sulu sea ventilation is derived from the south from the sulawesi sea through sibutu passage sulawesi sea water between 245 to 527 m is mixed and heaved over the sibutu passage 234 m sill by the energetic tidal environment oxygen concentrations within the deep sulu sea suggest that the sulawesi overflow is 0 15 106 m3 sec with a residence time of sulu sea deep water of 60 years the deep tropical sulu sea has the unique distinction of being ventilated from two separate sources whose ratio may fluctuate across a range of temporal scales associated with regional thermocline depth changes

ocean response to a hurricane part i observations abstract the response of the ocean to hurricanes was investigated using aircraft deployable expendable current profilers axcp the goals were to observe and separate the surface wave and surface mixed layer sml velocities under the storms and to map the across track and along track velocity and temperature response in the mixed layer and thermocline custom instrumentation was prepared including slower failing axcps and the axcp equipment was installed on noaa wp 3d aircraft research flights were made into two 1984 hurricanes norbert in the eastern pacific off baja california 19 n 109 w and josephine off the east coast of the united states 29 n 72 w thirty one probes were deployed in each hurricane and about half the axcps provided temperature and velocity profiles most velocity profiles exhibited strong surface wave contributions slablike velocities in the sml strong shears beneath the sml and only weak flows in the upper thermocline separation of the surface gravity wave velociti

geochemical implications for the mechanism of deep convection in a semi closed tropical marginal basin sulu sea abstract in 1996 and 2002 we measured the vertical profiles of potential temperature salinity dissolved oxygen nutrients tritium only in 1996 and helium isotopes only in 2002 in the sulu sea a small semi closed tropical marginal basin west of the philippines with a maximum depth of 5000 m judging from these data in combination with those for the south china sea adjacent to the sulu sea we conclude that the deep convection in the sulu sea is controlled by a combination of the following three processes i quasi steady inflow of the south china sea intermediate water through the mindoro strait sill depth 420 m ii occasional inflow of denser intermediate water through the mindoro strait from the south china sea when the thermocline in the south china sea is uplifted and iii formation of less dense bottom water by means of geothermal heating which in turn causes overturning of the sulu sea bottom water below a depth of 3000 m from 1996 to 2002 the bottom water of the sulu sea was stagnant its temperature increased by 0 003 c and its dissolved oxygen concentration decreased by 5 8 mol kg 1 the 6 years study results show that the temperature increase can be attributed to the terrestrial heat flow from the seafloor

remarkably preserved prokaryote and eukaryote microfossils within 1ga old lake phosphates of the torridon group nw scotland abstract the 1000 ma torridon group of northwest scotland are here shown to contain a rich diversity of organic walled microfossils preserved in exceptional detail within sedimentary phosphate the phosphatic nodules and bands in which they occur are autochthonous as are the organic fossils they contain the associated sedimentology of this phosphate is shown to be consistent with a lacustrine setting informal taxonomic treatment of the microfossils allows statistical assessment of the relative abundances of different morphotypes across a range of lacustrine environments exceptional preservation of pristine organic walled eukaryotes and prokaryotes together with a taphonomic spectrum in both physicochemical and biological degradational conditions allows a picture to be built of the earliest lacustrine ecological communities

the mesoproterozoic midcontinent rift system lake superior region usa abstract exposures in the lake superior region and associated geophysical evidence show that a 2000 km long rift system developed within the north american craton 1109 1087 ma the age span of most of the volcanic rocks this system is characterized by immense volumes of mafic igneous rocks mostly subaerial plateau basalts generated in two major pulses largely by a hot mantle plume a new ocean basin was nearly formed before rifting ceased perhaps due to the remote effect of the grenville continental collision to the east broad sagging subsidence combined with a system of axial half grabens separated along the length of the rift by accommodation zones provided conditions for the accumulation of as much as 20 km of volcanic rocks and as much as 10 km of post rift clastic sediments both along the rift axis and in basins flanking a central post volcanic horst pre rift mature quartzose sandstones imply little or no uplift prior to the onset of rift volcanism early post rift red bed sediments consist almost entirely of intrabasinally derived volcanic sediment deposited in alluvial fan to fluvial settings the exception is one gray to black carbon bearing lacustrine unit this early sedimentation phase was followed by broad crustal sagging and deposition of progressively more mature red bed fluvial sediments with an extra basinal provenance

deep water renewal by turbidity currents in the sulu sea the ventilation of the intermediate and deep layers of the ocean is governed by convection dense water formed at the sea surface through air sea interaction processes mainly at high latitudes sinks to great depths convection determines the heat salt and dissolved gas budgets of the ocean s interior and therefore exerts a significant influence on the earth s climate convective processes can also be initiated by the flow of dense water over submarine sills separating ocean basins with water masses of different buoyancy here we report the observation of relatively light deep water in the overflow region near the sill in the northern part of the 5 000 m deep sulu sea because of its buoyancy this water could not have reached the sea floor of its own accord turbidity currents induced by changes in water density that result from sediment influx occur in this region at intervals of several decades as indicated by the frequent deposition of graded sequences of silty mud on the abyssal plain we suggest that such turbidity currents combined with the effects of classical hydrological plume convection are capable of bringing light water to large depths in tropical regions where normal oceanic convection is relatively weak this mechanism may contribute significantly to the ventilation of deep basins

the ecology of living stained deep sea benthic foraminifera from the sulu sea the distribution of living rose bengal stained deep sea benthic foraminifera was determined in the upper 20 cm of sediments of eight soutar box cores taken from two depth transects 510 4515 m in the thermospheric 10 c sulu sea despite the uniformity of bottom water temperatures salinities and dissolved oxygen levels below 1000 m significant faunal differences exist at different depths in the low oxygen 1 25 ml l below 1000 m basin the shallowest site 510 m is dominated 10 of the calcareous fauna by cibicidoides uvigerina 150 m and bolivina 63 m while siphonina is codominant with cibicidoides and uvigerina in the 1005 m core the 2000 m cores are dominated by cibicidoides gyroidinoides and oridorsalis while cibicidoides bradyi and oridorsalis umbonatus dominate the 3000 and 4000 m cores infaunal assemblages of valvulineria mexicana are found in the sediments of the 4515 m core relatively low bottom water oxygen values do not necessarily yield typical low oxygen taxa such as bolivina uvigerina chilostomella bulimina and globobulimina changes in the abundances of these taxa in fossil assemblages have been used as indicators of changes in ancient bottom water oxygen levels but may instead reflect organic carbon contents of the sediments an examination of the vertical distributions of foraminiferal assemblages from the 63 m and 150 m fractions reveals that taxa have microhabitat preferences similar to those observed in other regions taxa found in the upper 0 to 1 cm interval epifaunal include cibicidoides wuellerstorfi and hoeglundina elegans while taxa such as chilostomella and globobulimina reach maximum abundances in subsurface sediments and have infaunal microhabitat preferences cibicidoides bradyi and o umbonatus live in sediment depths from 0 to 4 cm and have transitional preferences with both epifaunal and infaunal occurrences intrageneric differences in test morphologies including pore distribution rounded peripheries and variable spire height are observed in cibicidoides and gyroidinoides and are suggested to be related to microhabitat preferences vertical distributions of a number of taxa found in both the 63 to 150 m and 150 m fractions are similar suggesting that juveniles and adults live under similar microhabitat conditions ontogenetic changes in microhabitat preferences of most species are not observed in this study and therefore would not be expected to account for isotopic vital effects reported for some taxa in previous studies

herringbone calcite petrography and environmental significance abstract herringbone calcite is a previously undescribed carbonate cement and sea floor precipitate that is common in archean carbonates but rare in proterozoic and phanerozoic rocks it is abundant in the 2520 ma campbellrand malmani platform south africa where field relationships such as erosional truncation of layers of herringbone calcite and interbedding of herringbone calcite with grainstones demonstrate that it precipitated from ambient marine water this interpretation is supported by depositional relationships in the 2 6 ga huntsman limestone of the bulawayo greenstone belt zimbabwe the 2 6 ga carawine dolomite australia the 1 90 ga rocknest formation and the 1 8 1 2 ga dismal lakes group canada the ordovician porterfi ld carbonate buildup virginia and various silurian carbonate buildups in the midcontinent united states each of these occurrences is associated with anaerobic depositional environments or organic rich sediments herringbone calcite consists of alternating light and dark crenulated bands each light dark pair is 0 5 1 0 mm thick microscopically each pair of bands consists of a row of elongate crystals with their long axes aligned perpendicular to banding and along the growth direction of the cement the bases of the crystals are optically unoriented but upwards in each crystal the optical c axis rotates until it is perpendicular to crystal elongation the tops of the elongate crystal are thus optically aligned and length slow the light bands of herringbone calcite correspond to the optically oriented parts of the elongate crystals whereas the dark bands correspond to the optically unoriented lower parts of the elongate crystals microspar crystals are also present in some dark ba ds a mg calcite precursor for herringbone calcite now preserved as low mg calcite or dolomite is supported by the presence of micro dolomite inclusions and textural differences between herringbone calcite and textures interpreted as neomorphosed former aragonite or low mg calcite precipitation of herringbone calcite may be consistent with a diffusionally controlled growth model involving branching growth of fibrous crystals and diffusion of a precipitation inhibitor away from the crystallization surface since herringbone calcite is associated with anaerobic depositional environments the inhibitor promoting precipitation of herringbone calcite may be present only in poorly oxygenated sea water thus the stratigraphic distribution of herringbone calcite may be an important indicator of the abundance of oxygen in carbonate depositional environments through time

observations of exchange between the south china sea and the sulu sea 1 the velocity and transport with thermohaline properties are determined from simultaneous moored time series within mindoro tablas and panay straits that connect the south china sea scs and sibuyan sea to the sulu sea these passages provide the only pathway for the scs throughflow below thermocline depths and play a critical role in regulating the heat and freshwater balance within the philippine archipelago the upper layer in mindoro strait has a distinctly seasonal cycle with northward flow during the boreal summer southwest monsoon and southward flow during the winter northeast monsoon in contrast upper layer flow in panay and tablas straits is intraseasonal extraordinarily strong pulses that begin at intermediate depth in the fall transition and shoal toward the sub thermocline during the northeast monsoon are found in mindoro and panay straits these southward flows are strongly correlated to the scs large scale circulation and remote wind forcing off vietnam temperature and salinity in mindoro support the scs source of this subtropical water southward benthic flow in mindoro and panay act to ventilate the deeper sulu sea bottom temperatures suggest the cooler mindoro overflow mixes with the warmer benthic waters from tablas before exiting panay strait into the sulu sea the 2008 mean annual total depth transports were very small o 0 1 sv although individual transport estimates of 1 2 sv were observed in all depth layers over the year the mooring deployment coincided with a strong la nina when the pacific inflow into the scs is expected to be weaker and subsequently transports are lower

new evidence from the south china sea for an abrupt termination of the last glacial period abrupt changes in climatic conditions have been seen at high latitudes in the north atlantic1 and the antarctic2 3 at 13 kyr bp it is important to determine whether this abrupt change was confined to high latitude regions or whether it was global here we present results demonstrating an abrupt change in the rate and character of sedimentation in the south china sea at the close of the last glacial period radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes

early non marine life evaluating the biogenicity of mesoproterozoic fluvial lacustrine stromatolites abstract the record of life on land or in non marine environments during the precambrian is sparse limiting our ability to understand life outside of marine settings before the advent of animals stromatolites from such environments are known but demonstrating stromatolite biogenicity remains difficult as stromatolite growth can be controlled by a spectrum of biologic chemical and biologically mediated processes stromatolites from the mesoproterozoic 1 09 ga copper harbor conglomerate an alluvial fan fluvial and lacustrine deposit offer an interesting test for the presence and nature of microbial life in shallow mesoproterozoic non marine settings stromatolites from a siltstone facies are interpreted as biogenic as they contain detrital rich laminae likely indicative of trapping and binding by microbes and fenestral fabrics suggestive of desiccation or lift off structures in mats via the presence of gas perhaps o2 from photosynthesis or other gases from mat decay the stromatolites formed as microbial mats grew over a mudflat or sandflat with carbonate filled desiccation cracks on an erosive topography and thus provide evidence for life in a very shallow predominantly desiccated environment stromatolites from a conglomerate facies are microdigitate and record both isopachous laminae with radial fibrous calcite fans and botryoids typically considered abiogenic in origin as well as wavy conical laminations likely indicative of the former presence of microbial mats the conglomerate facies stromatolites are interpreted to have formed in a flooded braidplain setting with restricted circulation this study supports the suggestion that microbial communities were abundant in non marine environments in the midcontinent rift during the mesoproterozoic it also highlights how variable environmental factors can influence stromatolite growth even in similar depositional settings and with a consistent microbial presence

erosion of a stable density gradient by sedimentation driven convection stable density gradients are common in the world s oceans and lakes and play a crucial part in their physical chemical and biological evolution it has recently been suggested1 that turbidity currents provide an indirect mechanism for eroding this stratification in these currents light ambient fluid that has been mixed by cyclones with dense suspended sediment is transported to greater depths where it convectively erodes the gradient as the sediment settles here i present experimental results which show that in these circumstances the density gradient is eroded in a number of cycles of decreasing intensity and increasing duration in each cycle some of the sediment settles to the base of a stagnant region of unimpeded sedimentation while the rest is mixed into an overlying region that is vigorously convecting my experimental observations agree with a simple physical model that predicts the rate and extent of vertical mixing as well as the variation of particle sizes in the resulting turbidite

could meltwater pulses have been sneaked unnoticed into the deep ocean during the last glacial the lack of climatic imprint l eft by t he meltwa t er pulse 1a 14 5 ka bp equivalent to a sea level rise of 14 to 20 meters is puzzling recent studies sugge st the event might have occurre d as a hyperpycnal flow i n t he gulf of me xico preve nting its detection in oc eanic records throughout the north atlantic we present a suite of simula tions with the loveclim climate model which mimic th e e ffect of h yperp ycnal f low u nder lgm conditions in a first attempt to constrain its climatic effects analysing the ocean dynamics associated with the anomalous freshwater input we show that the proposed mechanism is capable of sneaking a signif i cant propo rtion of the mwp into the ocean 6 meters equivalent sea level rise using our model under lgm boundary cond itions we also de monstrate t hat in our model the meridional circulati on i s more sensitive t o such inputs i n t he arctic ocean than in the gulf of mexico

230th in the andaman sea rapid deep sea renewal 1 230th activities were determined in seawater collected from the bay of bengal and the andaman sea the andaman sea is a semi closed basin that is isolated from the bay of bengal by the andaman nicobar ridge the noticeable trend in the vertical distribution of 230th activity in the andaman sea is its uniformity below 1250 m depth we applied the scavenging mixing model to this vertical profile in the andaman sea and estimated the upper limit of renewal time to be 6 yr we compared 210pb 226ra ratios among deep waters of various oceanic basins to constrain the application of 230th as a tracer of deep water renewal the 210pb 226ra ratios were almost identical for the deep water of the andaman sea and the inflow water from the bay of bengal suggesting that the deep water in the andaman sea is replaced rapidly without bottom scavenging effects on the 210pb 226ra ratio

the precambrian nonesuch formation of the north american mid continent rift sedimentology and organic geochemical aspects of lacustrine deposition abstract the precambrian keweenawan trough in the lake superior region of north america is part of a failed intractonic rift that is filled with a thick sequence of volcanic and sedimentary rocks one unit in this sequence the none such formation is composed of black to green siltstones and shales and is conformable with the underlying alluvial copper harbor conglomerate and the overlying fluvial freda sandstone the formation is exposed as a lens in northern michigan and wisconsin and attains a maximum thickness of 200 m based on the integration of outcrop and core data nine facies have been recognized in the formation each has been assigned to one of three genetic facies assemblages a marginal lacustrine assemblage characterized by interbedded lithic sandstones siltstones mudstones and sandstone shale couplets is interpreted as a record of deposition on a sandflat mudflat complex a lacustrine assemblage is characterized by massive to well laminated dark shaly siltstones carbonate laminites shales siltstones and mudstones these sediments were probably deposited in a progressively shallowing perennial lake bottom conditions were anoxic and became increasingly more oxic as lake regression progressed a gradual transition from a lacustrine environment to a fluvial environment is represented by the red to brown massive horizontally laminated and rippled fine sandstones siltstones and mudstones of the fluvial lacustrine assemblage interactions among rates of subsidence rates of sedimentation fluctuations in lake level possible changes in climate and differences in tectonic setting controlled sedimentation in the nonesuch lake and resulted in variable vertical facies sequences total organic carbon toc analyses show a strong correlation between organic richness and the shale facies lacustrine assemblage and mudstone facies marginal lacustrine assemblage detailed petrographic analysis using incident white light and reflected blue light fluorescence revealed two prevalent organic petrographies which could be distinguished using combined pyrolysis gas chromatography mass spectrometry py gc ms and to a limited extent by stable carbon isotope mass spectrometry the geographic and stratigraphic distribution of rocks containing the two organic petrographies suggests that differential preservation e g microbial degradation accounts for the difference rather than maturity or variable source input

seasonal upper circulation in the sulu sea from satellite altimetry data and a numerical model eight years of absolute dynamic topography from satellite altimetry data are used to study the seasonal variability of the circulation in the sulu sea ss through empirical orthogonal function eof analysis it is revealed that first seasonal eof mode shows a basin scale anticyclonic cyclonic circulation in summer winter and second seasonal eof mode shows a weak basin scale anticyclonic cyclonic meander flow from the mindoro strait to the sibutu passage and the typical surface circulation structure in the ss is shown as a basin scale anticyclonic cyclonic circulation or meander centered at about 120 8 degrees e 8 6 degrees n in august and december according to the numerical experiments by a connected single layer and two layer model it is shown that the upper circulation in the ss is closely related to the outflow via the sibutu passage and seasonal local wind stress either an outflow via the sibutu passage or the summer monsoon may cause an anticyclonic circulation in the ss while the winter monsoon may cause a cyclonic circulation either an outflow via the sibutu passage or the winter monsoon would push the water out of the ss via the balabac strait but bring the water into the ss via the mindoro strait while the summer monsoon would bring the water into the ss via the balabac strait but push the water out of the ss via the mindoro strait thus in summer the induced anticyclonic circulation with the negative relative vorticity is stronger in the ss but the water transports via the mindoro and the balabac straits are less while in winter the induced cyclonic circulation with the mainly positive relative vorticity is weaker but the water transports via the mindoro and the balabac straits are larger the inflow via the mindoro strait is also significant since the outflow via the sibutu passage is mainly compensated by the inflow via the mindoro strait the western strengthening near the palawan island and the asymmetry of the circulation in the ss is caused by the beta effect the transport via the mindoro strait is generally much larger than that via the balabac strait an inflow into the ss via the dipolog strait contributes little to the circulation in the ss except for the current field near this strait a stronger lower layer current than the upper layer one near the mindoro strait is also discussed

biogenic structures in modern slope to deep sea sediments in the sulu sea basin philippines abstract slowly accumulated slope and rise sediments 5 20 cm 1000 yr are totally bioturbated as compared to only 10 30 in rapidly deposited abyssal plain sediments 100 200 cm 1000 yr in contrast to a decrease in degree of bioturbation biogenic trace diversity increases with water depth all ichnocoenoses are clearly influenced by the low oxygen content of the bottom water caused by minimal circulation and restricted water exchange oxygen deficiency and relatively high sedimentation rates have created nutrient rich sediments thus there is no need for optimal fractionation into individual ecological niches and behavioral programs are not highly developed 1 in slope and rise sediments animal traces are associated with biodeformational structures 2 in slope to abyssal plain sediments trace assemblages are dominated by burrows with open tubes for circulation of respiration water 3 in abyssal plain sediments small diameter biogenic traces common in turbidite sequences graphoglyptids e g paleodictyon are absent this may be due to rapid sedimentation leading to inefficiency of graphoglyptid behavior where graphoglyptids are lacking ichnocoenoses are dominated by forms like phycosiphon in slope and rise sediments graphoglyptids may have been destroyed by deeper burrowing organisms

manganese cerium and iron in the sulu celebes and philippine seas this study was undertaken to investigate trace metals in southeast asian seas that have different hydrographic settings the philippine the celebes and the sulu seas results reveal characteristics of dissolved and leachable manganese dissolved cerium and leachable iron in the water column remarkable increases of mn ce and fe exist at the bottom layer of the water column in the celebes sea the ce mn molar ratios in the bottom waters of the celebes sea are identical to those in the porewaters of the underlying sediment both ce and mn show similar geochemical cycles in these deep waters of the celebes sea in the sulu sea s deep waters the leachable particulate fractions are dominant for fe and mn the residence time of fe in the sulu sea is estimated as 12 years this residence time estimate is very similar to the particle residence time in the water column implying that resuspension of sediment derived particles affects leachable fe distributions in the sulu sea

life on land in the proterozoic evidence from the torridonian rocks of northwest scotland the stoer group and diabaig formation of the torridonian succession in northwest scotland are late mesoproterozoic to early neoproterozoic ca 1200 1000 ma features preserved on the top surfaces of fine to medium grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures these include wrinkle structures remnants of apparent microbial crusts and indications of original cohesiveness and pliancy in sand sized sediment the surfaces on which the microbial structures formed were exposed subaerially abundant deep desiccation cracks and locally pedogenic structures in alluvial interfluve and lacustrine margin settings and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels thus these features indicate that earth9s biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the phanerozoic

precambrian non marine stromatolites in alluvial fan deposits the copper harbor conglomerate upper michigan laminated cryptalgal carbonates occur in the precambrian copper harbor conglomerate of northern michigan which was deposited in the keweenawan trough an aborted proto oceanic rift this unit is composed of three major facies deposited by braided streams on a large alluvial fan complex coarse clastics were deposited in braided channels predominantly as longitudinal bars whereas cross bedded sandstones were deposited by migrating dunes or linguoid bars fine grained overbank deposits accumulated in abandoned channels gypsum moulds and carbonate filled cracks suggest an arid climate during deposition stromatolites interstratified with these clastic facies occur as laterally linked drapes over cobbles as laterally linked contorted beds in mudstone as oncolites and as poorly developed mats in coarse sandstones stromatolites also are interbedded with oolitic beds and intraclastic conglomerates stromatolitic microstructure consists of alternating detrital and carbonate laminae and open space structures radialfibrous calcite fans are superimposed on the laminae the laminae are interpreted as algal in origin whereas the origin of the radial fibrous calcite is problematic the stromatolites are inferred to have grown in lakes which occupied abandoned channels on the fan surface standing water on a permeable alluvial fan in an arid climate requires a high water table maintained by high precipitation or local elevation of the water table possibly due to the close proximity of a lake occurrence of stromatolites in the upper part of the copper harbor conglomerate near the base of the lacustrine nonesuch shale suggests that these depositional sites may have been near the nonesuch lake

weathering and paleosol formation in the 1 1 ga keweenawan rift abstract at 1 1 ga the north american craton began to rift resulting in flood style basaltic volcanism during the phase of active tectonism some of that basalt was weathered and redistributed by fluvial processes new observations near the northwestern shore of lake superior have also revealed the presence of seven paleosols formed on weathered immature sediments derived from the basalt that are described here for the first time only three other paleosols have previously been described from this part of the geologic record so these new paleosols represent a significant new discovery the paleosols are weakly developed and exhibit physical and chemical characteristics similar to phanerozoic entisols in contrast to many precambrian paleosols the keweenawen paleosols have been subject to minimal post burial alteration among the paleosols three distinct pedofacies are recognized 1 waterlogged gleyed fluvial proximal paleosols 2 dry fluvial distal paleosols and 3 cumulative fluvial proximal paleosols despite these facies differences using a combination of physical and chemical measures of weathering it is found that the paleosols are all derived from the same parental basalt with one of the paleosols showing an additional extra basinal rhyolitic component by considering the mass balance behaviour of a variety of alkali and alkaline earth elements it is possible to rule out significant potassium metasomatism suggesting that these paleosols may be particularly useful for paleoatmospheric and paleobiologic reconstructions and that they form an important new source of data about mesoproterozoic weathering

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

distribution of bioactive trace metals fe co ni cu zn and cd in the sulu sea and its adjacent seas abstract here we present the first vertical distribution of dissolved d and acid dissolvable ad bioactive trace metals fe co ni cu zn and cd in the sulu sea and the south china sea together with those observed previously by the same method in the western north pacific at a depth of 50 75 m concentration minima of some trace metals were observed in the sulu sea d zn cu and fe and the south china sea d zn which coincided with the chl a maximum indicating scavenging of these metals including biological uptake above 150 m in the south china sea elevated concentrations of d co and cu were observed which could result from fluvial coastal waters and or shelf sedimentary sources in the surface mixed layer in the sulu sea d fe concentrations were high 2 nm presumably due to the flowing of waters across the philippine archipelago except for fe concentrations of d and ad species at each corresponding depth were not significantly different concentrations of ad fe 6 8 17 nm below 500 m in the sulu sea were much higher than those of d fe 0 2 1 7 nm indicating that particulate fe is abundant in the basin probably coming from nearby sedimentary sources the vertical distributions of d ni cu zn and cd in the south china sea were nutrient like and deviated slightly from those in the western north pacific this is caused by a rapid flushing of waters from the philippine sea coupled with vertical mixing within the south china sea the distribution of these metals in the sulu sea was more uniform below 500 m the average concentrations of d ni cu zn and cd in the deep water of the sulu sea were 6 1 1 5 3 3 and 0 5 nm significantly lower than those of the western north pacific 9 6 2 8 10 1 and 1 0 nm respectively we also found lower d cd po4 ni po4 and zn si oh 4 ratios in the sulu sea than those of the pacific the depletion of these concentrations and the d cd po4 and ni po4 ratios in the sulu sea is probably because the deep water of the basin is rapidly exchanged with shallow waters but isolated from nutrient rich deep waters derived from the north pacific due to the surrounding topographic barriers including the islands and the shallow sills while subsurface waters were flowing along density surfaces sigma t values of 26 from the south china sea to the sulu sea the concentrations of macronutrients d ni cu zn and cd increased due to the regeneration from biogenic particles the increases in the concentrations of bioactive elements relative to that of po4 were n p si ni cu zn cd 15 1 40 2 4 10 3 0 6 10 3 2 7 10 3 0 03 10 3 in a molar unit

the antiquity of oxygenic photosynthesis evidence from stromatolites in sulphate deficient archaean lakes the tumbiana formation about 2700 million years old was largely deposited in ephemeral saline lakes as judged by the unusual evaporite paragenesis of carbonate and halite with no sulfate stromatolites of diverse morphology occur in the lacustrine sediments some with palimpsest fabrics after erect filaments these stromatolites were probably accreted by phototropic microbes that from their habitat in shallow isolated basins with negligible sulfate concentrations almost certainly metabolized by ozygenic photosynthesis

on convection and mixing driven by sedimentation the sedimentation of small particles from a suspension and the concomitant release of light interstitial fluid may constitute a buoyancy source for the development of convective motions when the dense suspension is emplaced beneath a stratified fluid an intermediate convecting layer between the sedimenting front and the density gradient above gradually grows in depth by erosion of the overlying stratified fluid novel laboratory experiments involving sedimentation below a two layer stratified region show that turbulent mixing and entrainment across the top density interface is significant for a broad range of the richardson number a simple theoretical model predicting the rate of erosion of the stratification above the convecting layer agrees well with these experiments the model is then extended to include the case of an overlying continuous density gradient and compared successfully with both new experimental data and the original data of kerr 1991 owing to the effects of dispersion of grain sizes small particles in the convecting fluid may lower the efficiency of the interfacial mixing by the turbulent eddies our model calculations suggest that turbulent mixing and entrainment driven by sedimentation may be significant in the atmospheric and oceanic contexts in both of which stratification is weak such mixing may also occur in molten magma chambers following the sedimentation of suspended crystals and in this case it may suppress large scale overturning events

sediment induced slope convection two dimensional numerical case studies the potential role of sediment in oceanic slope convection is examined by means of a rotational numerical model applied in a vertical ocean slice the model couples the hydrodynamics with transport settling deposition and resuspension of fine grained silty muds sediment plumes turbidity currents descending on an idealized continental slope with constant bottom slope are driven from an initial density anomaly caused by an assumed suspension of sediment in shelf water a number of case studies were conducted in order to understand the effects of 1 different suspended sediment concentrations in shelf water as compared to an equivalent salinity anomaly salt brine release 2 different oceanic density stratifications and 3 resuspension of bed sediment it is demonstrated that sediment plumes may account for a downslope transport of water which once void of its sediment load becomes lighter than water above then sedimentation along the slope with a maximum adjacent to the foot of the slope drives vigorous upward convection parameterized in the model stirring slope water over a depth range of several hundred meters this is in agreement with field observations from a tropical ocean detrainment associated with sediment settling constitutes an important mechanism inherent in sediment plumes it not only induces upward convection but also prevents the rapid increase in plume thickness caused by entrainment as compared to water mass plumes owing to a balance between entrainment and detrainment the sediment plume while descending on the slope attains constant height and bed shear velocities in order to facilitate the detection of sediment plumes in historical or future field data we describe their simulated traces in terms of water mass properties and flow anomalies

calcium carbonate cement caliche in keweenawan sedimentary rocks 1 1 ga upper peninsula of michigan abstract a complex caliche profile and numerous widespread zones of carbonate cement occur in a thick sequence of fluvial siliciclastic sandstones and conglomerates that were deposited in the lake superior basin during and after continental basaltic volcanism as interflow conglomerates of the portage lake volcanics and as the oronto group in conglomerates the carbonate cement forms discontinuous zones up to 60 cm thick and several meters in length consisting of up to 25 vol carbonate whereas the caliche horizon at the centennial mine shows typical upward grading features characteristic of pedogenic caliche the widespread sparry carbonate cement is less diagnostic it is interpreted also as caliche for the following reasons 1 it predates regional epidote metamorphism 2 a caliche profile has been described from the same strata 3 textures characteristic of caliche such as carbonate rimmed pebbles pendulose calcite on pebbles sand grains floating in a carbonate matrix and exfoliated chlorite 4 possible vadoids 5 the carbonate rich zones are widespread stratigraphically and geographically in basinward inclined alluvial fans and 6 the distribution of these zones and the total quantity of contained carbonate requires other than a point source for the origin of the carbonate several lines of evidence suggest that the prevailing climate may have been arid with a fluctuating perhaps seasonal rainfall pattern required for caliche 1 a paleolatitude about 30 north 2 carbonate filled shrinkage cracks denoting high evaporation 3 intermittent flashy or ephemeral streams recorded locally in fluvial beds by numerous superimposed horizons of mud chip conglomerate enormous previously cemented mudstone rip ups and desiccation cracked mud drapes interpretation of the cement as vadose caliche is compatible with a sedimentation model for the region as a semi arid intermontane basin flanked by alluvial fans and with a central saline lake

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

morphology water characteristics and sedimentation in the silled sulu sea southeast asia during 1977 rv valdivia recovered 46 cores occupied two hydrographic stations and ran eleven bathymetric profiles in the roughly rectangular sulu sea which trends northeast and covers about 250 000 km2 the sulu sea deep in the southeast is separated from the shallower palawan depression in the northwest by the northeast trending cagayan ridge the maximum sill depth between the sea and the open ocean is about 400 m and the water column is layered cutting off the deep water which is homogeneous warm 10 c and oxygen deficient 1 6 ml ml o2 from normal oceanic water the shelves are generally broad and covered with calcareous sand and gravel except in the east and southeast where they are narrow and covered with muddy sand and gravel the shelf carbonates give way to bathyal oozes and the muddy sands grade into varied silts dominated by volcanic and sedimentary debris the smooth abyssal plain of the sulu sea deep is at a depth of 4800 5000 m and northwest of it is an plain at 4000 4200 m turbidites characterize both plains the aragonite and calcite compensation depths are at about 1400 m and 4500 m respectively the turbidite beds average 5 10 cm thick with all bouma s divisions recognizable apart from a the southern turbidites station 14224 are of two types calcareous and terrigenous the calcareous turbidites characterized by shell debris including shallow water foraminifera were derived from the upper slopes flanking the broad shelves the terrigenous turbidites characterized by sedimentary and volcanic rock fragments apparently originated from the slopes off mindanao the eastern turbidites station 14233 are finer grained characterized by sedimentary rock fragments and came from the narrow muddy shelves further east off panay negros and mindanao radiocarbon dating suggests that depositional rates for the turbidite sequences ca 100 cm 1000 yr are an order of magnitude greater than the rates for bathyal oozes organic carbon contents in the surface sediments are highest between 500 m and 1200 m water depth exceeding 2 off mindanao station 14226 and reaching 1 82 on the palawan slope station 14206 the lowest contents are at the palawan shelf edge 0 11 at station 14204 where the proportion of carbonate sand is very high and in the bathyal oozes of the central sulu sea 1 where sedimentation rates are low and mineralisation of organic matter is effective contents average 1 below 4500 m in the sulu sea deep the colour of the surface sediment appears to be related to the organic carbon content olive colours above 1200 m and below 4500 m and brown colours between the surficial sediments are characterized by living shelly faunas and intense bioturbation above 150 m and by intense bioturbation and absence of a shelly fauna down to 3000 m bioturbation decreases below 3000 m and in the sulu sea deep is confined to a few zoophycos granulites and cosmorhaphe burrows the faunal changes are apparently related to bottom water oxygen concentrations

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

the copper harbor conglomerate a late precambrian fining upward alluvial fan sequence in northern michigan the keweenawan copper harbor conglomerate exposed in northern michigan is part of a thick succession of volcanics and terrigenous clastics deposited in the keweenawan trough a failed intracontinental rift it is a fining upward wedge of volcanogenic conglomerate and sandstone deposited as proximal to distal braided stream and sheet flood facies on coalesced alluvial fans and sand flats this unit along with the lower portion of the overlying nonesuch shale consists of an alluvial fan shallow lake sequence that filled the rift during and following volcanic activity the fining upward nature of the sequence reflects a waning sediment supply probably due to lowering of the source area following faulting the copper harbor conglomerate exhibits attributes of both arid fan and humid fan alluvial models coarse grained facies are lithologically similar to alluvial fan units deposited in modern humid regions conversely finer distal copper harbor facies exhibit numerous features indicating flashy discharges and desiccation processes typical of deposition in modern arid regions ambiguity of sedimentary features useful for climatic inference probably reflects the limited applicability of holocene models to more ancient alluvial sequences because precambrian hydraulic regimes developed under various climatic settings may have differed from their holocene counterparts

sterane and triterpane biomarkers in the precambrian nonesuch formation north american midcontinent rift abstract molecular fossils and organic matter from microbial communities living around 1 1 ga ago are well preserved in the nonesuch formation of the us midcontinent rift system although some compound classes of biological markers have been recognized repeatedly in previous studies of nonesuch rocks and associated petroleums steranes and triterpanes have not been detected failure to detect these compounds was due primarily to instrumental limitations and the relatively high thermal maturity of samples collected within zones of copper mineralization our analyses of nonesuch samples from the white pine mine and nonmineralized localities in michigan and wisconsin reveal suites of c 26 c 30 steranes and c 27 c 35 pentacyclic triterpanes similar to those found in phanerozoic oils and sedimentary rocks of marine origin stereoisomeric distributions in the nonesuch samples are consistent with moderate thermal maturity except in the mineralized zone near white pine

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes

anoxia in the terrestrial environment during the late mesoproterozoic a significant body of evidence suggests that the marine environment remained largely anoxic throughout most of the precambrian in contrast the oxygenation history of terrestrial aquatic environments has received little attention despite the significance of such settings for early eukaryote evolution to address this we provide here a geochemical and isotopic assessment of sediments from the late mesoproterozoic nonesuch formation of central north america we utilize rhenium osmium re os geochronology to yield a depositional age of 1078 24 ma while os isotope compositions support existing evidence for a lacustrine setting fe s c systematics suggest that the nonesuch formation was deposited from an anoxic fe rich ferruginous water column thus similar to the marine realm anoxia persisted in terrestrial aquatic environments in the middle to late proterozoic but sulfidic water column conditions were not ubiquitous our data suggest that oxygenation of the terrestrial realm was not pervasive at this time and may not have preceded oxygenation of the marine environment signifying a major requirement for further investigation of links between the oxygenation state of terrestrial aquatic environments and eukaryote evolution

the midcontinent rift system one of the most prominent features on gravity and aeromagnetic maps of the united states is a series of major generally linear anomalies that extend from central kansas to lake superior and then turn southward into central michigan figures 1 2 this system of anomalies clearly reflects major geological features and as such it must represent a very significant episode in the history of the north american continental lithosphere the geologic features associated with these anomalies particularly axial basins filled with basalt and immature clastic rocks along with evidence of crustal extension indicate that the episode was probably one of incipient rifting