identification of permian palaeowind direction from wave dominated lacustrine sediments lodeve basin france lacustrine environments are an excellent indicator of continental palaeoclimate in particular the sedimentary record of waves in lakes may be used to constrain atmospheric palaeocirculation wave ripples have been identified in a permian lacustrine basin the salagou formation 260 250 ma lodeve basin located in the southern french massif central part of the western european hercynian mountain chain wave ripple patterns are interpreted with regards to hydrodynamics and water palaeodepth it is shown that in the case of the salagou formation wave ripple orientations were controlled by the direction of the prevailing palaeowind the late permian wind blew from between north and 20 east of north possibly over several millions of years and certainly throughout the period of deposition of about 2000 m of strata in the lodeve basin permian lacustrine sedimentation is widespread and well preserved on the earth s surface and so wave ripple data may help constrain numerical modelling of the earth s past climates especially with regards to permian times outside of desert regions

observations of turbulence in a tidal beam and across a coastal ridge during a microstructure survey off california in monterey bay we found a midwater beam of strong turbulence emanating from the shelf break along the ray path of the semidiurnal m2 internal tide within the 50 m thick beam the turbulence kinetic energy dissipation rate e exceeded 10 6 w kg 1 and the diapycnal eddy diffusivity k was 0 01 m2 s 1 the beam extended 4 km off the shelf break several factors suggest that this beam of strong turbulence resulted from the breaking of semidiurnal internal tides the beam appeared to originate from the shelf break which is a potential generation site for semidiurnal internal tides the beam closely followed the ray path of the semidiurnal internal tide the average e off the shelf break varied by a factor of 100 with a semidiurnal tidal periodicity the isopycnal displacement confirmed the presence of semidiurnal internal tides processes associated with the breaking of internal tides are intermittent and sporadic at the same location we also observed equally intense turbulence in a 100 m thick layer of stratified water across the ridge of a sea fan this layer of strong turbulence was separated from the bottom and was clearly not generated by bottom friction although less well resolved in time the strong turbulence above the bottom seemed to vary with the semidiurnal tide and existed at the lee of the ridge where the isopycnal surface dipped and rebounded in a pattern resembling that of internal hydraulic jumps on the basis of the behavior of the density field we believe that the deep mixing was most likely produced by the across ridge current of internal tides the breaking of internal tides at middepth where the richardson number is close to the critical value is likely due to shear instability the presence of the coastal ridge provides an alternative pathway for converting energy from internal tides to turbulence via internal hydraulics multiplying the average e in the midwater beam by the length of the global coastline gives 31 gw only a small fraction of the estimated 360 gw dissipated globally by m2 internal tides our observations suggest that either most internal tides are generated away from shelf breaks or most internal tides generated at shelf breaks propagate away from their generation sites rather than dissipate locally and eventually contribute to pelagic mixing

late pliocene to recent planktonic foraminifera from the north atlantic dsdp site 552a quantitative palaeotemperature analysis

flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

the influence of whitecapping waves on the vertical structure of turbulence in a shallow estuarine embayment abstract the vertical distribution of the turbulent kinetic energy dissipation rate was measured using an array of four acoustic doppler velocimeters in the shallow embayment of grizzly bay san francisco bay california owing to the combination of wind and tide forcing in this shallow system the surface and bottom boundary layers overlapped whitecapping waves were generated for a significant spectral peak steepness greater than 0 05 or above a wind speed of 3 m s 1 under conditions of whitecapping waves the turbulent kinetic energy dissipation rate in the upper portion of the water column was greatly enhanced relative to the predictions of wind stress wall layer theory instead the dissipation followed a modified deep water breaking wave scaling near the bed bottom 10 of the water column the dissipation measurements were either equal to or less than that predicted by wall layer theory stratification due to concentration gradients in suspended sediment was identified as the likely cause for t

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

mudstone petrology of the mesoproterozoic unkar group grand canyon u s a provenance weathering and sediment transport on intracratonic rodinia abstract the synthesis of mudstone petrology and interbedded sandstone detrital zircon geochronology provides insights into the provenance weathering regime hydrodynamic effects and diagenesis of the mesoproterozoic unkar group unkar mudstones were derived largely from the grenville orogen go of southwest texas and the adjacent yavapai mazatzal ym and southern granite rhyolite sgr terranes detrital zircon data indicate distinct pulses of go derived sediment during hakatai and dox formation deposition whereas shinumo sediment contains a larger component of ym and sgr material an increase in plagioclase and biotite abundances in the dox further suggest an orogenic pulse bulk chemistry including elevated cr and ni abundances and ree systematics implicate a heterogeneous provenance for unkar sediment best approximated by a mix of granite or granodiorite with some basalt weathering of unkar sediment as determined from mudstone and crystalline source bulk chemical trends is characterized as moderate cia values between 55 and 70 indicative of a temperate climate in an orogenic setting small less than 10 wt amounts of detrital kaolinite and chlorite are consistent with a moderate temperate weathering regime illite the dominant clay mineral in the unkar group is largely the 2m1 polytype and detrital in origin however it is estimated that 7 of the k in the escalante creek member results from k metasomatism and may form up to 15 wt authigenic 1m or 1md illite the clay size fraction and zircon are the chief contributors to the ree budget in unkar mudstones lithostratigraphic variations in the hree distributions can be attributed partially to variable zircon abundance in the silt size fraction a likely function of hydrodynamic sorting age constraints on the duration of unkar group sedimentation range from 30 to 100 my for the 1100 m conformable shinumo dox succession and result in compacted sedimentation rates of between 1 0 and 3 6 cm 103 yr these rates are comparable to mesozoic foreland basin settings

an interpretation of boron contents within a palaeoproterozoic volcano sedimentary succession pretoria group transvaal supergroup south africa abstract boron contents of sedimentary rocks were measured in three profiles through the palaeoproterozoic pretoria group enhanced boron values occur at a number of stratigraphic levels across much of the preserved basin and only these anomalies are considered significant evaluation of the various possible factors controlling these high boron concentrations suggests that inherited boron sedimentation rate detrital tourmaline silica and carbonate dilution metamorphism and evaporitic borates were relatively unimportant a major role is indicated for the preferential uptake of boron by clay minerals and for both andesitic volcanic and related hydrothermal activity as a source of boron the dilution of boron concentrations due to organic coating of clay minerals may also be important in the case of the pretoria group stratigraphically expressed boron anomalies which cannot be explained by these various factors are inferred to represent enhanced palaeosalinity of the waters of deposition the suggested marine transgression is supported by sedimentological data

paleoenvironmental reconstruction of challenger mound initiation in the porcupine seabight ne atlantic the understanding of the paleoenvironment during initiation and early development of deep cold water coral carbonate mounds in the ne atlantic is currently a focus of international research the integrated ocean drilling program iodp expedition 307 drilled the 155 m high challenger mound in the porcupine seabight sw off ireland in order to investigate for the first time sediments from the base of a giant carbonate mound in this study we focus in high resolution on 12 m of sediments from site 1317 encompassing the mound base the mound initiation and start up phase coincide with the intensification of the northern hemisphere glaciation inhg at around 2 7 ma further carbonate mound development seems to be strongly dependent on rapid changes in paleoceanographic and climatic conditions at the pliocene pleistocene boundary especially characterized and caused by the interaction of intermediate water masses the mediterranean outflow water mow the eastern north atlantic water enaw and the influence of southern component water scw this study is based on well established proxies such as 18o and 13c of planktonic globigerina bulloides and benthic foraminifera fontbotia wuellerstorfi discanomalina coronata lobatula lobatula lobatula antarctica and planulina ariminensis as well as grain size parameters to identify the paleoenvironmental and paleoecological setting favourable for the initial coral colonization on the mound stable oxygen and carbon isotope records of benthic foraminiferal species indicate that l lobatula provides a reliable isotopic signature for paleoenvironmental reconstructions in particular 18o values of l lobatula indicate that initial mound growth started in a glacial mode with moderate excursions in 18o values carbon isotope values of d coronata are significantly offset compared to other epibenthic species this offset may be related to vital effects bottom water temperatures calculated using standard equations based on 18o of foraminiferal tests range between 7 and 11 c consistent with the known temperature range conducive for cold water coral growth and development bottom currents transporting intermediate water masses of southern origin mediterranean and bay of biscay enhanced at 2 6 ma supporting first coral settlements with the inhg the benthic 13c and the sortable silt records indicate that the early pleistocene hydrodynamic regime was characterized by weaker current intensities associated with vertical movements of mow or its replacement by scw at intermediate depth after these sluggish phases enhanced mow flow dominated again and led to stronger current intensities and most probably sediment erosion on challenger mound erosion in combination with early diagenetic oxidation processes overprinted the sediment layers as indicated by dissolved coral skeletons the increase in ca content and sediment density minimum 13cplanktonic values as well as the occurrence of gypsum and pyrite implying a careful evaluation of original and overprinted geochemical signals we conclude that the challenger mound development was already influenced by short term variability of water masses from southern origin and possible erosional events comparable to the late pleistocene setting

the 8 2 ka event abrupt transition of the subpolar gyre toward a modern north atlantic circulation 1 climate model simulations of the 8 2 ka event show an abrupt strengthening of the atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early holocene the freshwater outburst from proglacial lakes and the onset of labrador sea water formation the 8 2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the north atlantic region about 8200 years before present it coincides with a meltwater outburst from north american proglacial lakes that is believed to have weakened the atlantic meridional overturning circulation and northward heat transport followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries marine proxy data however date the onset of deep water formation in labrador sea to the same time the subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease although similarities in timing are compelling a mechanism to reconcile these apparently contradictory events was missing our simulations show that an abrupt and persistent strengthening of the atlantic subpolar gyre provides a plausible explanation the intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation stabilized by internal feedbacks and persistent after the cessation of the perturbation as a direct consequence deep water formation around its center intensifies this corresponds to the modern flow regime and stabilizes the meridional overturning circulation possibly contributing to the holocene s climatic stability

paleoclimatic implications of late pleistocene sediment yield rates for the bonneville basin northern utah abstract climate factors such as precipitation and temperature as well as climate driven geomorphic processes such as glaciation affect rates of erosion and the amount of sediment supplied from a drainage basin sediment yield thus sediment yield rates provide paleoclimatic implications although very little work has been published on ancient sediment yield rates late pleistocene lake bonneville utah idaho and nevada with its well documented lake level history and well preserved deltaic sequences provides a unique opportunity to estimate ancient sediment yield rates two end member delta systems coarse grained gravel classic gilbert type deltas and fine grained sand silt and clay deltas are exposed along the eastern margin of paleolake bonneville one example of each end member delta is examined in this study american fork and weber river deltas the established bonneville hydrograph can be used to determine time of deposition for a given package of sediments because these shoreline deltaic sediments were deposited in shallow water the geomorphic expressions of these deltas are well preserved and their sediment volumes can be determined river drainage basin area can be combined with time constraints and delta volumes to estimate sediment yield rates sediment yield rate estimates for the coarse grained american fork and fine grained weber river deltas are 478 m 3 km 2 yr 1 34 and 705 m 3 km 2 yr 1 15 respectively the similarity of these values is somewhat surprising due to the large difference in drainage basin sizes american fork 160 km 2 and weber river 3328 km 2 however this similarity suggests that precipitation may be the dominant control on sediment yield using sediment yield precipitation regression equations developed for similar modern basins in the southern alps of new zealand a first order approximation of paleoprecipitation is 1 6 m yr 14 for american fork delta and 1 9 m yr 7 for weber river delta these paleoprecipitation value are comparable to modern precipitation values of 0 4 1 5 m yr range of mean values over both drainage basins a maximum late pleistocene precipitation increase of 33 over the modern day value is suggested this is determined by the difference between the highest paleoprecipitation rate 1 9 m yr 7 of the weber river delta and the modern value 1 5 m yr previous climate models and this 33 paleoprecipitation increase suggest a maximum decrease in basin floor paleotemperature of approximately 13 c this paleotemperature decrease is consistent with previous estimates of late pleistocene temperatures using amino acid epimerization rates and periglacial wedges in the bonneville basin and adjacent areas these estimates suggest that although late pleistocene precipitation rates may have been slightly higher than present up to 33 higher late pleistocene temperature and evaporation rates were more important in the development of lake bonneville and associated glaciers

facies architecture and sequence stratigraphy of fine grained lacustrine deltas along the eastern margin of late pleistocene lake bonneville northern utah and southern idaho this study documents the effects of changing lake level limnostasy tectonics sediment yield and basin physiography on the facies architecture sequence stratigraphy and reservoir quality of three fine grained deltas deposited along the eastern margin of late pleistocene lake bonneville analysis of facies architecture indicates that the weber and spanish fork deltas were strongly wave modified because they were situated along openly exposed portions of the shoreline the bear river delta nestled in a relatively isolated northeast arm of the lake records both fluvial and wave processes these fine grained deltas were fed by low gradient rivers that drained large regions that were sparsely glaciated whereas other contemporaneous coarse grained gilbert deltas were fed by steep gradient rivers that drained local source areas that were strongly influenced by glaciers limnostasy tectonics and sediment yield were similar for all three fine grained deltas implying that the most influential forcing parameter on sequence stratigraphy is basin physiography basin physiography specifically ramp length and accommodation most strongly controlled the external and internal geometry of the lowstand systems tract of each delta potential hydrocarbon reservoir quality e g grain size and sorting is largely a product of drainage basin size and stream gradient relative differences in ramp lengths seemed to determine thickness and lateral continuity of delta front deposits relative differences in accommodation appeared to determine the internal geometry of the delta front deposits especially in the lowstand systems tract these deltas can serve as analogs for lacustrine exploration and production where many forcing parameters typically are unknown

intratidal variations in stratification and mixing in the hudson estuary this study represents a detailed examination of intratidal variations in boundary layer structure in a relatively narrow straight section of the hudson river estuary during high river discharge the presence of active mixing is inferred from estimates of the richardson number the maximum height above bed to which mixing occurs is comparable during flood and ebb however the regions of mixing differ in density structure during the flood active mixing is confined to a well mixed near bed layer whereas during the ebb active mixing occurs throughout regions of significant stratification tidal straining maintains stratification during the ebb while it promotes the growth of a uniform bottom mixed layer during the flood in general maximum and minimum near bed stratification occur during late ebb and flood respectively reflecting the dominant role played by tidal straining in determining intratidal variation vertical stretching was also found to be an important term in the stratification balance during the ebb

on the reflection of internal wave groups from sloping topography abstract strong interactions often leading to wave breaking and mixing are known to occur between a train of internal waves incident on a plane sloping ocean boundary and its reflection propagating away from the slope intermittent processes of internal wave generation at the sea surface or ocean floor however produce packets or groups of internal waves the size of the volume within which an internal wave group of narrow bandwidth overlaps with its reflection from a plane boundary depends on the finite dimensions of the group the height above a slope within which interactions can occur is calculated as a function of the direction of approach of the incident group to the plane wave groups traveling with positive downslope group velocity components such as internal tidal rays generated at the shelf break produce relatively thicker interaction regions than do groups of equal dimensions and frequency approaching a slope from deep water in some regions the thickness of layers of enhanced mixing ove

measurements of turbulence in the upper ocean mixing layer using autosub abstract the rate of dissipation of turbulent kinetic energy has been measured with airfoil probes mounted on an autonomous vehicle autosub on constant depth legs at 2 10 m below the surface in winds up to 14 m s 1 the observations are mostly in an area limited by fetch to 26 km where the pycnocline depth is about 20 m at the operational depths of 1 55 15 9 times the significant wave height hs and in steady winds of about 11 6 m s 1 when the wave age is 11 7 17 2 dissipation is found to be lognormally distributed with a law of the wall variation with depth and friction velocity breaking waves leaving clouds of bubbles in the water are detected ahead of the autosub by a forward pointing sidescan sonar and the dissipation is measured when the clouds are subsequently reached bands of bubbles resulting from the presence of langmuir circulation are identified by a semiobjective method that seeks continuity of band structure recognized by both forward and sideways pointing sidescan sonars the times

the late carboniferous glacial to postglacial transition facies and sequence stratigraphy western paganzo basin argentina abstract namurian early westphalian glacial postglacial deposits have been documented in the paganzo basin argentina but integrated sequence stratigraphic and sedimentological analyses of the glacial postglacial transition are rare in the cuesta de huaco section the glacial postglacial transition encompasses the lower sequence of the existing schemes glacioeustatic changes in sea level controlled the architecture and vertical arrangement of facies the basal sequence boundary is coeval with the onset of glaciation when sea level fell contemporaneous with glacial erosion and bypass of sediment the upper sequence boundary is a high frequency sequence boundary the basal deposits are interpreted as an early transgressive systems tract etst initiated during glacial retreat the interval fines upward contains current reworked diamictites conglomerates and sandstones deposited in a subglacial to proglacial environment facies i ii and ice rafted glaciomarine rhythmites facies iii postglacial brackish marine black shales facies iv represent the late transgressive systems tract ltst micritic limestone beds were deposited during a period of sediment starvation coeval with the maximum marine inundation in the basin mfz it marks a turnaround in the stacking pattern that became coarsening and thickening upward during the overlying highstand systems tract hst it consists of fine grained turbidites facies v and classical turbidites with wave reworked beds at the top facies vi deposited in a shallow deltaic systems intervening postglacial brackish deposits contain an ichnofauna dominated by trackways of arthropods and minor grazing traces preserved in bedding planes that resemble nonmarine ichnocoenoses and differ from the archetypal brackish ichnofaunas even when palynological data support the saline depleted environment

on the vertical structure of wind driven sea currents abstract the vertical structure of wind driven sea surface currents and the role of wind wave breaking in its formation are investigated by means of both field experiments and modeling analysis of drifter measurements of surface currents in the uppermost 5 m layer at wind speeds from 3 to 15 m s 1 is the experimental starting point of this study the velocity gradients beneath the surface are found to be 2 to 5 times weaker than in the wall boundary layer surface wind drift identified via drift of an artificial slick with respect to 0 5 m depths is about 0 7 which is even less than the velocity defect over the molecular sublayer in the wall boundary layer at a smooth surface to interpret the data a semiempirical model describing the effect of wave breaking on wind driven surface currents and subsurface turbulence is proposed the model elaborates on the idea of direct injection of momentum and energy from wave breaking including microscale breaking into the water body momentum and energy tran

the vertical structure of turbulent dissipation in shelf seas abstract the free fall fly profiler has been used to determine the variation in energy dissipation in the water column over a tidal cycle at mixed and stratified sites in the irish sea it was found that exhibits a strong m4 variation with a pronounced phase lag that increases with height above the bed in mixed conditions this m4 signal which extends throughout the water column is reasonably well reproduced by turbulent closure models of the vertical exchange in the summer stratified situation the m4 signal in is confined to about 40 m above the seabed with phase delays of more than 4 h relative to the seabed the lowest levels of dissipation 10 5 w m 3 measured in the pycnocline are significantly above the system noise level and much higher than predicted by a model using the mellor yamada level 2 closure scheme my2 0 however when allowance is made for the diffusion of tke the model my2 2 simulates the depth time distribution of dissipation in the stratified case satisfactorily if

the contribution of salt fingers to vertical mixing in the north atlantic tracer release experiment abstract the north atlantic tracer release experiment natre was performed in an area moderately favorable to salt fingers however the classic finger signature of a distinct thermohaline staircase caused by upgradient density flux was absent this is likely because mixing by turbulence was sufficiently strong to disrupt the formation of permanent step and layer systems despite the lack of a staircase optical shadowgraph profiles revealed that small scale tilted laminae previously observed in a salt finger staircase were abundant at the natre site using microstructure observations the strength of salt finger mixing has been diagnosed using a nondimensional parameter related to the ratio of the diffusivities for heat and buoyancy the dissipation ratio by examining the dissipation ratio in a parameter space of density ratio r and richardson number ri the signal of salt fingers was discerned even under conditions where turbulent mixing also occurred while the model for turbulence descr

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

were non avian theropod dinosaurs able to swim supportive evidence from an early cretaceous trackway cameros basin la rioja spain a fundamental question remaining unanswered in dinosaur behavior is whether they had the ability to swim we report the discovery of an exceptional swimming dinosaur trackway with 12 consecutive footprints in lacustrine nearshore sediment from the early cretaceous cameros basin la rioja spain the singular morphology of these footprints strongly suggests a fl oating animal clawing the sediment as it swam diagnostic traits of theropod dinosaur footprints are identifi able in these peculiar elongated s shaped ichnites paleoenvironmental reconstruction indicates an upper shoreface setting with a maximum water depth of 3 m substantiating the swimming hypothesis ichnological analysis of the trackway shows that this theropod used a pelvic paddle motion similar to that of modern bipeds and swam with amplifi ed asymmetrical walking movements to maintain direction into a leftward water current after recent hints of swimming dinosaurs this new evidence persuasively demonstrates that some non avian theropod dinosaurs were swimmers

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

ripple marks in quartz arenites of the hurwitz group northwest territories canada evidence for sedimentation in a vast early proterozoic shallow fresh water lake abstract supermature quartz arenites of the whiterock member deposited in the early proterozoic intracratonic hurwitz basin have a maximum thickness of 400 m and a minimum areal extent of 100 000 km2 the unit is unusual in that it is virtually devoid of other rock types and displays sedimentary structures that consist almost entirely of short spaced ripple marks and parallel stratification both formed by oscillatory flow the ripples have spacings that are consistently small average

from tides to mixing along the hawaiian ridge the cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing we investigated this cascade along the hawaiian ridge using observations and numerical models a divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models large internal tidal waves with peak to peak amplitudes of up to 300 meters occur on the ridge internal wave energy is enhanced and turbulent dissipation in the region near the ridge is 10 times larger than open ocean values given these major elements in the tides to turbulence cascade an energy budget approaches closure

recent developments in the study of ocean turbulence abstract this review describes the changes in the understanding of turbulence and mixing in the upper layers of the ocean the abyssal ocean and in continental shelf seas that have come in the past 25 years largely through advances in instruments and methodology

evidence for enhanced boundary mixing in the santa monica basin transients in the heat content in santa monica and san pedro basins imply a basin wide diapycnal eddy diffusivity greater than 1 cm sup 2 s this is significantly larger than the value for sf sub 6 of 0 25 0 08 cm sup 2 s determined for the interior of santa monica basin for september 1985 to february 1986 by ledwell and watson however the exodus of sf sub 6 from santa monica basin after february 1986 by which time the tracer had mixed to the boundaries of the basin was fast enough to be consistent with a greatly enhanced vertical flux since the kinetic energy in the basin had not changed significantly it is unlikely that a temporal increase in forcing resulted in enhanced fluxes in the interior of the basin the most likely interpretation is that diapycnal fluxes in the basin are dominated by processes in the boundary regions temperature and sf sub 6 profiles from near the edges of the basin do not give conclusive evidence either for or against such enhanced mixing 20 refs 19 figs 5 tabs

tides and the climate some speculations abstract the important role of tides in the mixing of the pelagic oceans has been established by recent experiments and analyses the tide potential is modulated by long period orbital modulations previously loder and garrett found evidence for the 18 6 yr lunar nodal cycle in the sea surface temperatures of shallow seas in this paper the possible role of the 41 000 yr variation of the obliquity of the ecliptic is considered the obliquity modulation of tidal mixing by a few percent and the associated modulation in the meridional overturning circulation moc may play a role comparable to the obliquity modulation of the incoming solar radiation insolation a cornerstone of the milankovic theory of ice ages this speculation involves even more than the usual number of uncertainties found in climate speculations

the potential of morphometrically based phylo zonation application of a late cenozoic planktonic foraminiferal lineage phylo zonations or lineage zonations are based upon morphological changes within individual evolutionary lineages these zonations although potentially of use for stratigraphic subdivision and correlation often suffer from a lack of quantitative exactness in the definitions of chronospecies thus exact reproducibility is hindered for stratigraphic determinations the potential of morphometrically defined phylo zonations is demonstrated on a temperate south pacific late cenozoic lineage of planktonic foraminifera globorotalia conoidea through intermediate forms to globorotalia inflata in dsdp site 284 exhibiting phyletic gradualism our sampling interval is about 0 1 m y during the last 8 m y changes in the number of chambers in the final whorl test conicalness percentage of keeled forms and test roundness or inflatedness are used to quantitatively define the following five chronospecies g conoidea late miocene 6 1 8 3 m y g conomiozea latest miocene 5 3 6 1 m y g puncticulata sphericomiozea earliest pliocene 4 5 5 3 m y g puncticulata puncticulata early middle pliocene 2 9 4 5 m y and g inflata late pliocene quaternary 0 2 9 m y this phylo zonation is directly applicable to temperate cool subtropical southern hemisphere areas where the evolution took place kennett 1967 1973 scott 1979 it is still not known if the lineage occurs elsewhere thus the applicability of the phylo zonation over broader areas is still uncertain trends in general size and aperture shape seem to be climatically controlled and thus may be only of local stratigraphic utility the practical applications of morphometric phylo zonation for stratigraphy is to a large extent dependent upon the amount of time and effort required to statistically define the trends experiments with large numbers of subsamples from this lineage demonstrate that accurate stratigraphic determinations are possible from measurements on only 15 specimens per sample except for those very close to chronospecies boundaries

fluvial channel belts floodbasins and aeolian ergs in the precambrian meall dearg formation torridonian of scotland inferring climate regimes from pre vegetation clastic rock records abstract the interpretation of climate regimes from facies analysis of precambrian clastic rocks has been challenging thus far hindering full reconstructions of landscape dynamics in pre vegetation environments yet comparisons between different and co active sedimentary realms including fluvial channelised floodplain and aeolian hold the potential to shed further light on this thematic this research discusses a fluvial aeolian record from the 1 2 ga meall dearg formation part of the classic torridonian succession of scotland tentatively considered to date as a braided fluvial deposit this unit is here reappraised as the record of fluvial channel belts floodbasins and aeolian ergs fluvial deposits with abundant transitional to upper flow regime structures mostly cross beds with tangential sets and plane antidunal beds and simple low relief sediment bars indicate a low sinuosity ephemeral style floodbasin deposits consist of plane and cross beds ubiquitously bounded by symmetrical ripples and rare sediment bars related to the progradation of splay complexes in temporary flooded depressions aeolian deposits occur nearby basement topography and are dominated by large scale pin stripe laminated cross beds indicative of intermountain ergs neither ephemeral fluvial nor intermountain aeolian systems can be considered as reliable indicators of local climate since their sedimentary style is respectively controlled by catchment size and shape and basin topography relative to groundwater tables contrarily the occurrence of purely clastic rather than carbonate or evaporitic floodplain strata can be more confidently related to humid regimes in brief this study provides new insight into an overlooked portion of the torridonian succession of scotland and discusses climate inferences for precambrian clastic terrestrial rocks

surface manifestation of internal tides generated near hawaii analysis of topex poseidon satellite altimetry reveals short wavelength fluctuations in the ocean surface tide that are attributable to internal tides a significant fraction of the semidiurnal internal tide generated at the hawaiian ridge is evidently phase locked to the astronomical potential and can modulate the amplitude of the surface tide by 5 cm the internal tide is thus easily mapped along satellite groundtracks and it is found to be spatially coherent over great distances with waves propagating well over 1000 km from the hawaiian ridge before decaying below noise level both first and second baroclinic modes are observed in both the m 2 lunar and s 2 solar tides the high space time coherence is in sharp contrast to what is often inferred from current meter observations but it confirms recent speculations from an acoustic experiment north of hawaii

quasi steady exchange flow in the bosphorus current meter moorings and high resolution surveys in the bosphorus reveal important details of the exchange flow during early september 1994 the flow was quasi steady and demonstrated strong mixing particularly in the surface layer after it entered the principal contraction of the strait composite froude numbers in the contraction are lower than expected consistent with recent modeling that shows friction producing significant deviations from predictions of inviscid two layer hydraulic theory

effect of velocity hiatuses in oscillatory flow on migration and geometry of ripples wave flume experiments a series of wave flume experiments was conducted to closely look at characteristics of geometry and migration of wave generated ripples with particular reference to the effect of velocity hiatuses during which the near bed flow velocity becomes much smaller than the threshold of sediment movement three types of wave patterns were generated two types for simulating waves with intervening velocity hiatuses and regular waves for comparison purposes in the former two types two different wavelengths of water waves were generated alternately in the course of a wave test the wave with a longer wavelength was set large enough to mobilize the bottom sediment whereas the wave with a shorter wavelength was set too small to mobilize the sediment the former two types were designed to be different in sequence of convexity and concavity of wave patterns the sequence with the convex concave longer wave and successive convex concave shorter wave was described as a zero up crossing wave pattern and the inverse sequence was described as a zero down crossing wave pattern the ripples developed under oscillatory flow with intervening hiatuses manifested the following characteristics in geometry and migration i the morphological characteristics of ripples namely wavelength height and the ripple steepness are unaffected by the intervening hiatuses of velocity ii the directions of ripple migration under the zero up crossing and zero down crossing wave patterns corresponded well with the directions of the flow immediately before onset of the hiatuses iii the observation of sand particle movement on the ripple surface indicated that under the zero up crossing waves the velocity hiatus prevents the entrained sediment cloud from being thrown onshore and thus the sediment grains thrown onshore are fewer than those thrown offshore as a result of the sediment movement over one wave cycle the net sediment transport is directed offshore under the zero up crossing wave pattern iv the velocity of ripple migration was highly correlated with acceleration skewness under most of the zero up crossing zero down crossing wave patterns flow acceleration skewed negative positive and ripples migrated offshore onshore

initiation of 2 45 2 1 ga intracratonic basin sedimentation of the hurwitz group keewatin hinterland northwest territories canada continental to shallow marine rocks of the hurwitz group exposed as outliers across the hearne province in northern canada were deposited between 2 45 and 2 11 ga on a 3 3 2 6 ga granite greenstone basement initiation of the hurwitz basin was characterized by low relief and rates of subsidence that never progressed beyond the intensity of regional sagging during stage 1 polymictic conglomerate lower noomut formation was deposited in palaeovalleys cut into archaean basement and subarkose to quartz arenite quartz pebble conglomerate upper noomut formation was deposited on a low relief sand plain abundant first cycle quartz rich sandstones are attributed to intense humid climate weathering in low relief source areas and at sites of temporary storage as well as to repeated fluvial and eolian reworking interbedding of pyritic palaeoplacers and continental redbeds denotes fluctuating levels of atmospheric oxygen disappearance of pyritic palaeoplacers upsection signifies ultimate changeover to an atmosphere with sustained free oxygen stage 2 padlei formation was marked by a climatic shift toward cold glacial conditions as indicated by dropstones greywacke till pellets and possible ikaite pseudomorphs in lacustrine rhythmites stage 3 kinga formation represents a return to wet warm conditions with fluvial eolian deposition of subarkose and quartz arenite on a low relief sand plain maguse member and deposition of supermature quartz arenite in a vast 100 000 km2 minimum shallow water lake or series of lakes whiterock member local chert beds at the top of the kinga formation hawk hill member formed by spring discharge due to regional gravity driven convective groundwater flow an intracratonic setting is implied by 1 a symmetric basin centred fill 2 absence of features indicating a shelf slope break 3 absence of rift rocks 4 a prolonged slow subsidence history 5 likely correlation with other continental to shallow marine deposits scattered across the keewatin hinterland and 6 positioning 1000 2000 km away from closest coeval passive margin sequences we speculate that hurwitz basin formed due to lithospheric stretching related to a large scale mantle upwelling during the protracted breakup of an earliest palaeoproterozoic supercontinent kenorland

convectively driven turbulent mixing in the upper ocean abstract two experiments were performed to study the characteristics of turbulence in convective mixed layers in the upper ocean in the first a diurnal convective mixed layer developed in the bahamas under the influence of the cycle of daytime solar heating and nighttime evaporative cooling the mixed layer reached as deep as 100 m each night and restratified each day in the second the mixed layer of a warm core gulf stream ring deepened from less than 50 m to more than 150 m in a little more than a day when subjected to rapid cooling during a cold air outbreak although individual profiles of the rate of viscous dissipation of turbulent kinetic energy had considerable spatial and temporal variability the mean dissipation profiles were similar to those in convecting atmospheric boundary layers the is established by the surface buoyancy flux jb0 jb0 0 61 and 0 72 in the bahamas and ring data respectively compared with 0 64 in convecting atmospheric mixed layers the mean profiles decre

model estimates of m2 internal tide energetics at the hawaiian ridge 1 a primitive equation model is used to examine the structure and energetics of m 2 internal tides generated at the hawaiian ridge recent estimates based on altimeter data suggest that 20 gw of barotropic tidal dissipation occurs at the ridge with conversion to internal tides believed to be the dominant dissipation mechanism the model simulates an internal tide that accounts for 9 7 gw of radiated energy away from the ridge in the northeast and southwest directions the strongest generation occurs at three sites where enhanced barotropic currents flow across elongated topographic features the depth integrated baroclinic energy flux and energy densities at these sites are on the order of 10 4 w m 1 and 10 4 j m 2 respectively a modal decomposition indicates that 62 of the outgoing energy flux is accounted for by the first internal mode 15 is accounted for by the second mode and less than 5 is accounted for by each subsequent higher mode the tidal dissipation due to bottom friction along the ridge is estimated to be 0 1 gw the level of turbulent dissipation near the ridge owing to tidal energy conversion remains to be determined to assess fully the barotropic baroclinic energy budget

stratigraphy sedimentology and physical volcanology of the henik group central ennadai rankin greenstone belt northwest territories canada late archean paleogeography of the hearne province and tectonic implications abstract extensive areas of the hearne and rae provinces are underlain by archean metavolcanic and metasedimentary rocks in the rae province supracrustal sequences with prominent continental to shallow water quartz arenites have been interpreted by others as rift and passive margin deposits in the hearne province to the southeast the ennadai rankin greenstone belt is exposed in an area ca 700 200 km forming the second largest greenstone belt in canada it comprises mainly greenschist facies grade mafic and felsic volcanic siliciclastic chemogenic and volcaniclastic rocks stratigraphic sedimentologic and physical volcanologic data based on 1 50 000 scale mapping in the central part of the belt indicate deposition in a subaqueous mafic volcanic plateau slope basin system that was well removed from a continental influence water depth was below storm wave base as indicated by preservation of delicate lamination in pelitic and iron formation units absence of features suggestive of subaerial exposure oscillatory flow or tidal currents and lack of interfingering rocks that could represent laterally adjacent shelf coastal or continental environments reconnaissance level regional geologic and geochronologic data indicate an overall pattern of supracrustal deposition in the hearne province consisting of a large mafic volcanic plain isolated felsic volcanic centres with lenses and belts of deep water sedimentary rocks at least two speculative yet testable tectonic models are consistent with the inferred paleogeography for both the rae province is considered to be the western continental hinterland to the ensimatic hearne province the rae and hearne provinces may record late archean continental extension sea floor spreading oceanic volcanic arc growth diachronous back arc spreading and collapse and arc continent collision with thrusting of oceanic rocks on to attenuated rae crust alternatively the hearne province may represent northwestward accretion of multiple volcanic arc trench pairs

sedimentation earthquakes and tsunamis in a shallow muddy epeiric sea grinnell formation belt supergroup ca 1 45 ga western north america

regional gold enrichment of conglomerates in paleoproterozoic supergroups formed during the 2 45 ga rifting of kenorland abstract we describe the presence of witwatersrand type gold mineralization in paleoproterozoic strata indicating this style of deposit is not confined to the archean the discovery of basal and intraformational conglomerate hosted gold mineralization in the huronian supergroup s mississagi formation near sudbury ontario has indicated potential for witwatersrand type gold mineralization to occur also in early paleoproterozoic basin fills on the hearne wyoming and karelian cratons the paleoproterozoic hurwitz snowy pass and karelian supergroups located on these cratons are similar to the huronian supergroup on the superior craton in terms of sequence and litho stratigraphy and maximum age of deposition a review of the stratigraphy and past gold exploration from each supergroup has revealed each basin to contain similar fluvial poly to oligomictic pyritic conglomeratic strata with locally anomalous gold and or uranium concentrations at stratigraphic levels that correlate to those of the mississagi and matinenda formations of the huronian supergroup examination of gold and gold enriched pyrite from the mississagi formation conglomerates suggests that specific point sources existed for most of the gold therein each of the above basins forms part of a larger contiguous continental rift system prior to the breakup of the supercontinent kenorland at around 2480 ma as each basin fill was displaced to different geographic positions following this continental breakup and then subjected to separate orogenic and metamorphic overprints the gold and uranium mineralization in each of the basins is unlikely to be of a common post depositional hydrothermal origin but in all likelihood of a paleoplacer origin it is suggested that this period of gold enrichment is the result of truncation and reworking of underlying stratigraphically older units and or from former gold deposits occurrences and gold enriched greenstone dominated hinterlands the omnipresence of detrital and or syn depositional pyrite in conglomerates of each basin reinforces the idea that a lack of atmospheric oxygen at the time of kenorland rifting existed during their deposition and prior to the great oxidation event our comparative analysis of kenorland rift graben fills reveals that gold potential which can be determined by the presence of detrital pyrite as observed at the pardo project should exist in all stratigraphic equivalents of the mississagi and matinenda formations where preferentially reworked fluvial conglomerates rest on an erosional unconformity and where a corresponding au enriched archean hinterland existed

possible evidence for episodic epeiric marine and fluvial sedimentation and implications for palaeoclimatic conditions c 2 3 1 8 ga kaapvaal craton south africa abstract the debate on palaeoproterozoic atmospheric composition climate and the timing and nature of the postulated great oxidation event possibly at c 2 3 ga remain matters of debate within precambrian geology this paper contributes to the debate through examination of physical sedimentary structures preserved within two separate groups of sedimentary deposits from the central and northern portions of the kaapvaal craton south africa within the c 2 3 2 1 ga pretoria group study of epeiric marine sandstones and mudrocks magaliesberg and silverton formations c 2 1 ga suggests that fluvial input was predominant over low energy reworking by waves winds and tides this together with extensive evidence for microbial mat growth within the littoral sandstones of the magaliesberg formation points to strongly episodic sedimentation by both marine and fluvial processes within two younger basins belonging to the c 2 05 1 8 ga waterberg group anomalously high palaeoslopes calculated according to standard palaeohydrological methods combined with direct field evidence for sediment gravity flows and sheetflood deposition within an overall braided fluvial setting again suggest episodic sedimentation strongly episodic sedimentation can most easily be reconciled with a greenhouse palaeoclimate at least for that part of kaapvaal at that time taken together these data sets point to the postulate that the generally accepted change from a palaeoproterozoic greenhouse through a great oxidation event c 2 3 ga to less extreme climatic conditions may have been gradational and even diachronous across the earth s cratons at that time

the cycle of turbulent dissipation in the presence of tidal straining in regions of large horizontal density gradient tidal straining acts to produce a periodic component of stratification that interacts with turbulent mixing to control water column structure and flow a 25 h series of measurements of the rate of dissipation of turbulent kinetic energy e in the liverpool bay region of freshwater influence rofi have revealed the form of this interaction and indicate substantial differences from regions where horizontal gradients are weak in the rofi system there is a pronounced difference between flood and ebb regimes during the ebb the water column stratifies and strong dissipation is confined to the lower half of the water column by contrast during the flood stratification is eroded with complete vertical mixing occurring at high water and high values of dissipation 3 mw m23 extending throughout the water column the cycle of dissipation is therefore predominantly semidiurnal in the upper layers whereas near the bottom boundary the principal variation is at the m4 frequency as observed in regions of horizontal uniformity toward the end of the flood phase of the cycle tidal straining produces instabilities in the water column that release additional energy for convective mixing confirmation of increased vertical motions throughout the water column during the late flood and at high water is provided by measurements of vertical velocity and the error velocity from a bottom mounted acoustic doppler current profiler

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

paleoproterozoic stromatolites hurwitz group quartzite lake area northwest territories canada decimetric to metric domal stromatolites with constituent ministromatolites characterize reddish 13c enriched dolostones in the watterson formation of the quartzite lake area west of hudson bay they provide paleontologic support for a correlation with the only other known early paleoproterozoic stromatolite occurrences in north america the kona formation of michigan and the nash formation in southern wyoming they also are similar to stromatolites in probable coeval jatulian carbonates in karelia on the baltic shield and possibly to stromatolites in the hutuo group in china

a tracer study of mixing in the santa cruz basin a tracer release experiment to study diapycnal and isopycnal mixing was performed in santa cruz basin in 1988 1989 approximately 1450 g of sulfur hexafluoride were injected close to an isopycnal surface at 1500 m depth in may 1988 this depth is midway between the bottom of the basin at 1920 m and the sill at 1084 m the diapycnal dispersion measured during the first few months while the tracer was still mixing to the walls of the basin yielded a diapycnal eddy diffusivity of 1 0 cm2 s 1 within a factor of 1 5 this is approximately 4 times larger than the diffusivity found by ledwell and watson 1991 in the interior of santa monica basin where the buoyancy frequency was 5 times greater the tracer was well mixed to the walls 6 months after the injection and at that time the diapycnal spread of the tracer was greater near the walls than in the interior the rate of diapycnal dispersion of the tracer increased dramatically after the tracer had mixed to the walls of the basin indicating enhanced boundary mixing an effective basin wide diapycnal diffusivity of 10 cm2 s 1 would be required to support the fluxes of tracer observed a one dimensional model for tracer and heat diffusion does not simulate the results very well however probably because of the finite mixing time between the boundary region and interior and because of the complexity of the processes in the boundary region

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

observations of enhanced diapycnal mixing near the hawaiian ridge profiles of potential density obtained from ctd casts at two stations at different distances from the hawaiian ridge are examined for evidence of diapycnal turbulent mixing as indicated by density inversions and internalwave vertical strain results from independent casts are used to produce ensemble averaged vertical distributions for the number of inversions and the thorpe scale both parameters were found to be higher over the slope of the topography at 2500 m depth than in the deep ocean 110 km to the north thorpe scale based estimates of the rate of dissipation of turbulent kinetic energy and turbulent vertical diffusivity are elevated by an order of magnitude over the slope relative to deep ocean background levels the vertical distributions of these mixing parameters are nonuniform and exhibit signs of locally enhanced dissipation possibly due to internal tides generated at the ridge at the deep station turbulence is at background levels from the surface down to 2000 m below this a localized zone of enhanced mixing is observed within which the dissipation rate is o 1029 w kg21 and turbulent diffusivity is greater than o 1024 m2 s 21 perhaps due to an internal tide ray originating at the ridge the full depth topographical enhancement of mixing near the ridge also appears in the vertical strain field estimates of dissipation rate and turbulent diffusivity based on an internal wave wave interaction model give results similar to direct thorpe scale methods except in weakly stratified environments where both methods are subject to uncertainty near the topography the variation in mixing intensity observed between casts is sensitive to sporadic large mixing events which are triggered by internal waves associated with the spring tide the upper portion of the water column stronger stratification is more responsive to the tide than the deep regions

controls on spatial and temporal distribution of precambrian eolianites abstract inversely graded stratification generated by the migration of wind ripples and adhesion structures permit unequivocal identification of precambrian eolianites these criteria in combination with scale of cross beds angle of inclination of foresets geometry of depositional units and associated non eolian facies are used to discriminate between precambrian dune draa dune plinth sand sheet and interdune deposits that formed in inland and coastal settings based on an analysis of published literature fundamental conclusions can be drawn on the spatial and temporal distribution of precambrian eolianites the oldest reported eolianites are from the ca 2 1 ga deweras group in zimbabwe and hurwitz group in canada and numerous examples of eolianites are reported from the 1 8 ga and younger rock record lack of archean and early paleoproterozoic eolianites and their widespread development after 1 8 ga are examined with respect to absence of vegetation crustal growth and tectonic setting relative sea level fluctuations unfavorable atmospheric and or climatic change and non recognition the lack of pre 2 2 ga eolianites may be related to reworking by braided rivers combing across non vegetated floodplains reworking of coastal eolianites during transgression or their non recognition in the early precambrian record the temporal concentration of eolianites at 1 8 ga may best be related to the early stages of breakup and the assembly phases of supercontinents

architectural elements from lower proterozoic braid delta and high energy tidal flat deposits in the magaliesberg formation transvaal supergroup south africa abstract three architectural elements are identified in the lower proterozoic magaliesberg formation pretoria group transvaal supergroup of the kaapvaal craton south africa 1 medium to coarse grained sandstone sheets 2 fine to medium grained sandstone sheets and 3 mudrock elements both sandstone sheet elements are characterised by horizontal lamination and planar cross bedding with lesser trough cross bedding channel fills and wave ripples as well as minor desiccated mudrock partings double crested and flat topped ripples due to the local unimodal palaeocurrent patterns in the medium to coarse grained sandstone sheets they are interpreted as ephemeral braid delta deposits which were subjected to minor marine reworking the predominantly bimodal to polymodal palaeocurrent trends in the fine to medium grained sandstone sheets are inferred to reflect high energy macrotidal processes and more complete reworking of braid delta sands the suspension deposits of mudrocks point to either braid delta channel abandonment or uppermost tidal flat sedimentation the depositional model comprises ephemeral braid delta systems which debouched into a high energy peritidal environment around the margins of a shallow epeiric sea on the kaapvaal craton braid delta and tidal channel dynamics are inferred to have been similar fine material in the magaliesberg formation peritidal complexes indicates that extensive aeolian removal of clay does not seem applicable to this example of the early proterozoic

dynamical processes of transfer at the sea surface abstract this review describes the dynamical processes of transport from and immediately below the sea surface particularly those which involve convergence and the separation of flow and which result in the renewal of surface water at horizontal scales ranging from millimeters to hundreds of meters turbulence at or near the sea surface derives from several processes breaking waves and the bubbles they may produce precipitation and spray langmuir circulation and thermal convection and turbulence which is internally generated by shear interest in the subject derives from the requirements to predict air sea fluxes of heat momentum and gases to develop climate models to interpret satellite images of the sea surface including those of ship wakes and to predict upper ocean structure including mixing layer depth in models of phytoplankton blooms and acoustic propagation the general effect of subsurface turbulence on the sea surface and the effects of surfactants is described and each process is discussed in turn laboratory experiments and theoretical studies have contributed particularly to the understanding of the interaction of vortices and turbulence with the surface and to the consequences of breaking waves they point to the development of instability in the flow ahead of steep waves carrying parasitic capillary waves which may contribute to the onset of flow separation on the leading face of the waves and the development of a rotor or roller below the wave crest shown most clearly in the pattern of streamlines in a frame of reference moving forward with the wave the conditions near the flow separation line on the wave surface ahead of the rotor may be similar to those produced by vortices approaching a free surface detailed observation of breaking waves at sea is lacking but some progress has been made using acoustics to detect the clouds of subsurface bubbles formed by the larger breakers and the depth to which they penetrate the possible importance of three dimensional effects in breaking waves is discussed and a conjectural sketch of the surface flow field and the surface separation and reattachment pattern following a plunging breaker is described recent observations show elevated levels of turbulence close to the sea surface the depth of the layer in which this occurs is shown to be consistent with information derived from sonar studies of the depth of bubble clouds the observed frequency of breaking waves and laboratory observations of breaking waves rain is known to knock down the sea reducing the frequency and intensity of breaking waves the precise mechanics of the phenomena are uncertain but an enhancement of near surface turbulence and the damping of short surface gravity waves has been observed in laboratory experiments langmuir circulation temperature ramps and convection all associated with coherent structures are processes which mix the upper ocean although their relative importance is unknown connections between studies with quite disparate motivations are found to help provide descriptions of the upper ocean processes and estimates of the time scale of surface renewal associated with each of the processes identified many quantities being transferred across the sea surface appear to be transported by dynamical processes of scale much smaller than that of the dominant surface waves although their subsequent diffusion in the mixing layer may be strongly influenced by the larger scale processes further careful measurements in the laboratory and at sea are required to quantify the fluxes associated with the processes and to relate them to external parameters such as wind speed

the generation of internal tides at the hawaiian ridge previous analyses of altimeter and acoustic data indicate that the hawaiian ridge is a significant generation site for semidiurnal m2 period internal waves owing to tidal flow over topography such waves likely play an important role connecting the dissipation of tidal energy to ocean mixing here a primitive equation numerical model with realistic stratification bathymetry and tidal forcing is used to simulate the generation of these waves in a manner consistent with altimeter sea surface observations the highest amplitude waves originate at three generation sites located at both the island and seamount portions of the chain these sites have in common both enhanced flows across ridge shaped topography and maxima in model calculated body force which couples barotropic and baroclinic motions the model vertical structure suggests the presence of multiple dynamical modes within 100 km of the ridge and not just the lowest modes that have been detected at the sea surface

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

isolation extinction and migration within late pliocene populations of the planktonic foraminiferal lineage globorotalia globoconella in the north atlantic abstract quantitative records of globorotalia puncticulata and globorotalia inflata the last two members of the globorotalia globoconella lineage obtained from north atlantic sediments collected at dsdp site 552 odp site 659 and odp site 665 are used to examine fluctuations in the biogeographic distribution of these species in the late pliocene between 3 and 2 ma abundance data indicate that prior to the expansion of northern hemisphere glaciation at about 2 5 ma gr puncticulata was an important component of the planktonic foraminiferal fauna and had a geographic distribution ranging from 2 n to at least 56 n in the north atlantic a previously undescribed 6 chambered variant of gr puncticulata is found at both sites 659 and 665 the stratigraphic distribution of this morphotype is restricted first occurring at 2 9 ma and then disappearing when glacial intensity increased at 2 75 ma isotope stage 110 similar declines in gr puncticulata abundances occurred during glacial isotope stages 102 100 and 98 immediately prior to the extinction of gr puncticulata during glacial isotope stage 96 it appears that this extinction event was latitudinally diachronous within the north atlantic occurring earliest in the north at site 552 2 453 ma then at site 659 2 443 ma and later still in the site 665 equatorial record 2 438 ma at site 665 the first record of gr inflata occurs during glacial isotope stage 94 2 416 ma shortly after the extinction of gr puncticulata in the mid latitude north atlantic there was a 340 000 year period following the disappearance of gr puncticulata when the globoconella lineage was absent the gr inflata gap the gr inflata population found in the equatorial atlantic must therefore have been introduced from the south atlantic probably by the south equatorial current faunal records from sites 552 and 659 show that it was not until glacial isotope stage 78 2 10 ma that gr inflata became widely established in the north atlantic prior to this large scale migration event there were two limited colonisation events during glacial isotope stages 86 and 82 when gr inflata populations reached as far as site 659 in the eastern north atlantic these incursions are believed to be reflect the entrainment of gr inflata within south atlantic central water and the northward subsurface transport of individuals to the coastal upwelling zone off northwest africa it seems likely that the same mechanism was responsible for the re establishment of the globoconella lineage in the north atlantic at 2 10 ma but in this instance additional factors such as enhanced glacial circulation patterns and ecological changes within planktonic foraminiferal faunas resulted in the successful expansion of gr inflata across the north atlantic and the mediterranean

facies and depositional sequence of the mesoproterozoic rohtas limestone eastern son valley vindhyan basin abstract paleogeography and process related facies analysis of the shelf originated rohtas limestone of early mesoproterozoic age has been attempted lithology structure microfabric and toc are the mainstay of facies classification the rohtas limestone consists of seven facies out of which the organic rich black shale and the crinkle laminated limestone facies dominates the basal part reveal distinctive fabric of microbial mat origin and represents outer shelf products with gradual shoaling the crinkle laminated limestone facies gains importance and locally turns into the nodular limestone facies through early diagenetic modification the grey shale facies poor in organic content replaces them further upward the other three facies viz the thinly laminated heterolithic facies typified by close alternations between black shale and limestone the planar laminated limestone facies and the wavy laminated limestone facies alternate with the grey shale facies progressively dominating the top part of the succession while the heterolithic facies records deposition across the paleochemocline the planar laminated and the wavy laminated limestone facies document deposition in shallow agitated shelf confined between a condensed zone below and an unconformity above the overall coarsening upward rohtas limestone records development of a hst

internal tides in monterey submarine canyon abstract the m2 internal tide in monterey submarine canyon is simulated using a modified version of the princeton ocean model most of the internal tide energy entering the canyon is generated to the south on sur slope and at the head of carmel canyon the internal tide is topographically steered around the large canyon meanders depth integrated baroclinic energy fluxes are up canyon and largest near the canyon axis up to 1 5 kw m 1 at the mouth of the upper canyon and increasing to over 4 kw m 1 around monterey and san gregorio meanders the up canyon energy flux is bottom intensified suggesting that topographic focusing occurs net along canyon energy flux decreases almost monotonically from 9 mw at the canyon mouth to 1 mw at gooseneck meander implying that high levels of internal tide dissipation occur the depth integrated energy flux across the 200 m isobath is order 10 w m 1 along the majority of the canyon rim but increases by over an order of magnitude near the canyon head where internal ti

suspected microbial mat related crack like sedimentary structures in the palaeoproterozoic magaliesberg formation sandstones south africa abstract the occurrence of patchy preservation of ripples and of palimpsest ripples on many sandstone bed surfaces of the c 2 1 ga magaliesberg formation pretoria group transvaal supergroup south africa suggests that microbial mats grew within the upper parts of sandy deposits of the braid deltaic tidally controlled epeiric marine coastline palaeoenvironment inferred for this stratigraphic unit recently limited occurrences of petee ridges cracked sand layers elephant skin textures wrinkle structures and manchuriophycus like cracks have been found substantiating the envisaged role for microbial mats binding sandy sediment and providing cohesion during active sedimentation by fluvial and tidal processes ripple marks associated with most of these biogenic sedimentary structures enable evaluation of genetic processes for the ripples currents waves wind as well as estimation of wave heights and water depths cf tanner w f 1967 ripple mark indices and their uses sedimentology 9 89 104 tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 the petee ridges are interpreted as reflecting spring low tidal desiccation which cracked the mats followed by disruption of sand beneath the mat due to loading from incoming tides or subsequent deposits slightly sinuous sand cracks on ripple crests are related to a similar combination of low tidal desiccation and formation of wind ripples with subsequent high tides providing the deeper water conditions and larger wave heights calculated from the tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 formula synaeresis cracking is inferred for both elephant skin cracks and manchuriophycus structures these inferred suspect microbial sedimentary structures when studied in relation to data derived from associated ripples thus enable better estimation of depositional conditions within the magaliesberg palaeoenvironment and indicate minimum epeiric tidal ranges of c 112 cm in general these structures are found associated with evidence for shallower water and higher energy conditions which probably protected the microbial mats from degradation by heterotrophic bacteria through fast burial a possible association of such mat related structures with epeiric marine or passive margin coastline conditions may be pertinent for much of the precambrian clastic record

near boundary mixing above the flanks of a midlatitude seamount fine scale velocity and density profile data with concurrent turbulent velocity and temperature dissipation estimates obtained above the flanks of fieberling guyot a seamount in the eastern north pacific ocean are examined for evidence of near bottom boundary mixing fine scale shear and strain spectral levels were elevated over the flanks of the seamount in a 500 m thick stratified layer above the bottom the velocity shear was horizontally isotropic clockwise and counterclockwise with depth shear spectral levels were comparable and no significant correlation between shear and strain was observed above the steepest bottom slopes near the seamount summit rim excess vertical strain relative to shear was observed as compared to the background internal wave field suggesting the presence of high frequency internal waves these signals may have been the product of wave reflections from the steep flanks of the seamount and or wave generation from tidal currents flowing over the rough bottom associated with the enhanced shears and strains were more frequent occurrences of low 10 m richardson number events increased overturning scales and larger estimated turbulent eddy diffusivity relative to observations 15 km or more from the seamount in particular turbulent diffusivity estimates increased from o 0 1 10 4 m2 s 1 in the ocean interior to 1 5 10 4 m2 s 1 within 500 m vertically 1 3 km horizontally of the seamount flank a simple geometric scaling argument suggests that boundary mixing of this intensity has relevance to the large scale circulation at abyssal depths where a large fraction of the ocean waters is in close proximity to the bottom

carbon isotope record for the onset of the lomagundi carbon isotope excursion in the great lakes area north america carbonate units of the chocolay group in the lake superior area usa and the gordon lake formation of the correlative upper huronian supergroup ontario canada were deposited after the last paleoproterozoic glacial event and an episode of intense chemical weathering the huronian supergroup contains at the base 2 45 ga volcanics and is intruded by the 2 22 ga nipissing diabase dykes and sills while the chocolay group is bracketed in age between 2 29 and 2 20 ga the lomagundi 2 22 2 1 ga carbon isotope excursion started after the paleoproterozoic glacial epoch and before a plume breakout event at 2 22 ga therefore the chocolay and upper huronian carbonates were deposited either before or during the onset of the lomagundi event notably thin carbonates of the basal gordon lake formation and thick carbonate succession of the kona dolomite in the northeastern exposures of the chocolay group record 13 c values as high as 9 5 versus v pdb similar to other successions deposited during the lomagundi event both units contain pseudomorphs and molds after sulfates this observation suggests that seawater sulfate contents rose dramatically in association with the onset of the lomagundi event and the rise of atmospheric oxygen carbonates in the western and southern exposures of the chocolay group randville and bad river dolomites and saunders formation previously assumed to be equivalent to the gordon lake formation and kona dolomite have carbon isotope values close to 0 based on basin analysis we infer that these carbonate units were deposited during a negative carbon isotope excursion after the lomagundi event started and are slightly younger than the kona dolomite and gordon lake formation this interpretation implies that the carbonate platform in the great lakes area transgressed to the west over shallow marine and fluvial deposits the negative carbon isotope excursion in the lake superior area might correspond to similar 13 c values of the mooidraai dolomite in the griqualand west basin south africa supporting correlation between paleoproterozoic successions of north america and south africa and the notion of three global glaciations in the paleoproterozoic era carbonates of the mille lacs group trout lake glen township and denham formations in minnesota have 13 c values ranging from 1 2 to 2 5 combined with geochronologic constraints these data suggest that these units were deposited after the lomagundi excursion and are related to the rifting event that led to development of the so far unrecognized 2 0 ga passive margin in the lake superior area 2006 elsevier b v all rights reserved

northeastern atlantic and arctic faunal provinces based on the distribution of recent ostracod genera the benthonic ostracod communities of 93 recent northeast atlantic shallow marine sites have been studied the ostracod assemblages from 76 of these sites were previously undescribed while an additional 17 sites predominantly from british stations were assessed from the available literature excluding mesohaline genera a total of 102 podocopid ostracod genera were recognized on the northeast atlantic shelf between the niger delta and the barents sea using both semi quantitative most northerly and southerly occurrences of genera and quantitative q mode analysis site site methods it becomes apparent that ocean currents and water mass temperature exact a considerable control on the spatial latitudinal distribution of benthonic ostracoda at the generic level it has been demonstrated that the majority of northeast atlantic shelf ostracoda are restricted to one or several zoogeographical regions or provinces nigerian most southerly liberian sierra leonian guinean mauritanian moroccan lusita

eolian aqueous interactions in the development of a proterozoic sand sheet shikaoda formation hosangabad india abstract a 40 m thick eolian sand sheet deposit characterizes the upper part of the proterozoic shikaoda formation near hosangabad it sharply overlies shoreface deposits and comprises wind ripple strata 50 adhesion strata 17 and subaqueous strata 33 each stratification type defines stratal packages tens of centimeters thick and few meters wide that are superposed upon one another in a nearly random fashion the eolian facies is inferred to have been deposited in a low gradient sandy supratidal setting the subaqueous deposits of the sand sheet also reflect a tide affected westward opening coastal setting with an approximately north south shoreline abundance of aqueous and adhesion strata coupled with the absence of granule rich coarse grained layers corrugated erosion surfaces and evaporites are the typical features of the shikaoda eolian sand sheet these features indicate that in spite of abundant sand supply from the coastal sources and a net aggradational setting repeated flooding and high surface moisture were the principal factors that inhibited dune building processes and favored the growth of a flat bedded eolian sand sheet in the shikaoda sandstone numerous subhorizontal nearly flat bounding surfaces split the sand sheet succession into tabular sediment bodies 50 100 cm thick each of the bounding surfaces can be traced for a few tens of meters and can be correlated to an event of aqueous flooding vertical stacking of tabular sandstone bodies implies that long term sediment aggradation rate in the low lying supratidal region kept pace with that of basin subsidence the sedimentological features of the shikaoda sand sheet facies when compared with known modern and ancient sand sheet deposits suggest that the shikaoda sand sheet developed independent of an erg in a comparatively wet climatic setting the sub humid coastal eolian sedimentary system of padre island texas is probably the closest modern analogue of the shikaoda sand sheet facies

three dimensional nature of flow near a sill velocity and density sections across knight inlet british columbia demonstrate that lateral recirculations are a first order feature of the flow in the lee of the sill the flow over this sill has been used as a typical example of two dimensional hydraulics with a lower layer that thins and accelerates as it moves downstream below an almost stagnant layer that widens downstream creating a distinctive wedge shape however we find that rather than being stagnant the velocity in this wedge shaped layer is actually quite large consisting of a swiftly recirculating dipole vortex during flood tide and a monopole vortex during ebb tide though we may have missed the matching half of a dipole with our sampling during ebb the recirculations during flood tide carry an amount of water equal to 25 of the tidal flux while the monopole during ebb tide carries 20 of the tidal flux these recirculations bias along channel estimates of volume flux especially in the middle wedge shaped layer and demonstrate that accurate volume fluxes in the lee wave are only possible if three dimensional surveys are made our three dimensional survey shows that there is a net isopycnal convergence of water in the middle layer at a rate adequate to close the volume budget of the flow without recourse to diapycnal fluxes we also calculate the strength of the vorticity in the recirculations observed during flood tide and attribute their formation to boundary layer separation

sedimentation patterns during the precambrian a unique record abstract although the similarities between depositional processes and products as well as the analogous controls on basin filling and evolution appear to have enjoyed great uniformity throughout the sedimentary rock record a noticeable distinction exists in the rates and intensities of a broad range of geological processes in the precambrian epoch this paper searches for distinctiveness in the precambrian sedimentary record both siliciclastic and carbonate through an extensive though not exhaustive review of the relevant literature augmented by new observations while differences in precambrian deltaic aeolian glacial and possibly also lacustrine deposits and settings appear to have been small their large scale development was controlled largely by a combination of temporal and geodynamic influences essentially of global compass in this regard the onset of the supercontinent cycle and major perturbations in palaeo atmospheric composition appear to have been significant marine environments provide a poor platform for precambrian phanerozoic comparisons of sedimentation patterns as those from the former period are preserved almost exclusively in epeiric settings an environment essentially lacking on modern earth for the shallow marine carbonates biological mediation of chemical sediment deposition changed radically from dominance by microbial biota in the precambrian to a combination of metazons protozoans and algae for the skeletal carbonates of the phanerozoic despite it being widely recognized that precambrian channel systems were braided in all environments deltaic tidal alluvial fluvial as a consequence of the lack of vegetation and poor development of soils the fluvial setting has some enigmatic aspects amongst these is evidence for ponding of muddy detritus in apparently sandstone bed load dominated braided systems with effects on local palaeoslopes which have resulted in unusual palaeohydraulic parameters for precambrian fluvial systems this is perhaps a field of research which holds greater promise when investigating sedimentation patterns prior to the phanerozoic

turbulence characteristics and dissipation estimates in the coastal ocean bottom boundary layer from piv data abstract turbulence characteristics in the coastal ocean bottom boundary layer are measured using a submersible particle image velocimetry piv system with a sample area of 20 20 cm2 measurements are performed in the new york bight at elevations ranging from 10 cm to about 1 4 m above the seafloor recorded data for each elevation consists of 130 s of image pairs recorded at 1 hz after processing the data at each elevation consist of 130 instantaneous spatial velocity distributions within the sample area the vertical distribution of mean velocity indicates the presence of large scale shear even at the highest measurement station the flow also undergoes variations at timescales longer than the present data series spatial spectra of the energy and dissipation are calculated from individual vector maps the data extend well beyond the peak in the dissipation spectrum and demonstrate that the turbulence is clearly anisotropic even in the dissipation range the vector maps are also patched together to

calculating earth moon system parameters from sub yearly tidal deposit records an example from the carboniferous tradewater formation abstract the secular evolution of the earth moon system remains poorly constrained largely because there are few continuous tidal rhythmite or foreset bundle sequences that preserve deposition over more than several neap spring tidal cycles deposits recording less than one year of deposition do not facilitate direct calculation of past lunar distance directly from kepler s laws but may prove necessary to reconstruct lunar orbital evolution because they are far more common than longer records a method is demonstrated to make use of shorter tidal deposit sequences by utilizing conservation of angular momentum between the earth and moon and estimating the solar component of tidal deposition while assuming a constant moment of inertia for earth since the proterozoic the precision and accuracy of spectral estimates obtained from short records are considered as are the limitations of subsequent calculations of earth moon parameters the late carboniferous abbott sandstone of the tradewater formation in the illinois basin preserves just over 6 apparently continuous neap spring cycles in its semidiurnal deposits the quality of these data as assessed via sedimentological evidence and statistical time series properties produces spectral estimates that are likely within at least 5 of the actual underlying periodicity 90 accuracy to test the usefulness of such records we assessed the possible scenarios of 90 and 95 accuracy at 90 accuracy the error bounds on earth moon parameter estimates become rather large and render individual data sets to be of limited use at 95 accuracy very general inferences about the evolution of the earth moon system may be made calculated mean lunar orbital distance at 315 ma is 3 798 10 8 m with error bounds of 0 086 10 8 m and 0 046 10 8 m we conclude that short sequences of cyclic tidal deposits offer rather limited resolution of lunar distance estimates utilizing multiple sub yearly data of similar age in ensemble may prove necessary if further investigations of secular changes in earth moon parameters are to proceed

cold water coral carbonate mounds as unique palaeo archives the plio pleistocene challenger mound record ne atlantic through the interplay of a stabilising cold water coral framework and a dynamic sedimentary environment cold water coral carbonate mounds create distinctive centres of bio geological accumulation in often complex continental margin settings the iodp expedition 307 drilling of the challenger mound eastern porcupine seabight ne atlantic not only retrieved the first complete developmental history of a coral carbonate mound it also exposed a unique early pleistocene sedimentary sequence of exceptional resolution along the mid latitudinal ne atlantic margin in this study a comprehensive assessment of the challenger mound as an archive of quaternary palaeo environmental change and long term coral carbonate mound development is presented new and existing environmental proxy records including clay mineralogy planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts planktonic foraminifer oxygen isotopes and siliciclastic particle size are thereby discussed within a refined chronostratigraphic and climatic context overall the development of the challenger mound shows a strong affinity to the plio pleistocene evolution of the northern hemisphere climate system albeit not being completely in phase with it the two major oceanographic and climatic transitions of the plio pleistocene the late pliocene early pleistocene intensification of continental ice sheet development and the mid pleistocene transition to the more extremely variable and more extensively glaciated late quaternary mark two major thresholds in challenger mound development its late pliocene 2 74 ma origin and its middle late pleistocene to recent decline distinct surface water perturbations i e water mass polar front migrations productivity changes melt water pulses are identified throughout the sequence which can be linked to the intensity and extent of ice development on the nearby british irish isles since the earliest pleistocene glaciation induced shifts in surface water primary productivity are thereby proposed to fundamentally control cold water coral growth which in turn influences on mound sediment accumulation and hence coral carbonate mound development throughout the pleistocene as local factors such as proximal ice sheet dynamics and on mound changes in cold water coral density significantly affected the development of the challenger mound they can potentially explain the nature of its palaeo record and its offsets with the periodicities of global climate variability on the other hand owing to this unique setting a regionally exceptional high resolution palaeo record of early pleistocene ca 2 6 to 2 1 ma environmental change including early british irish ice sheet development broadly in phase with the 41 ka paced global climate system is preserved in the lower challenger mound all in all the challenger mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic continental margin environments

patterns of sedimentation in the precambrian abstract the principle of uniformitarianism may be applied to precambrian basin evolution and to the sedimentary record as a whole the major difference in the precambrian eon lay in variability of rates and intensities of processes controlling weathering erosion transport deposition lithification and diagenesis this paper examines precambrian sedimentation patterns within the larger framework of earth evolution pre rock record sedimentation probably comprised deep water oceanic realms within which meteoritic and cometary impact events generated very large tsunamis resulting in very coarse volcaniclastic detritus combined with fine dust settling out of suspension all reworked by marine current systems and localised turbidites from c 4 to 3 2 ga greenstone belts provided the predominant settings for the thin passive margin carbonates bif stromatolitic evaporites pelites and quartzites and lesser synorogenic turbidites conglomerates and sandstones that accompanied the volcanic and volcaniclastic rocks typical of these settings common palaeoenvironments were high gradient alluvial fans low sinuosity braided rivers and relatively shallow marine settings subject to wave and tidal action and turbidity currents although continental crustal growth continued largely through greenstone belts until c 2 7 ga the witwatersrand basin c 3 0 2 7 ga kaapvaal craton south africa reflects initial stabilisation of the oldest craton with an epeiric sea accumulating largely fluvial detritus subject to tidal inland and storm wave craton marginal reworking within a retroarc foreland basin setting neoarchaean palaeoproterozoic sedimentation is discussed within a framework of two global superevents at c 2 7 ga and 2 2 1 8 ga each encompassing major changes in earth s evolution related to the supercontinent cycle mantle superplumes peaks in crustal growth rates and significant biochemical changes within the atmosphere hydrosphere system concomitant globally raised sea levels led to chemical and clastic epeiric seas within which the first giant carbonate platforms developed and deposition of iron formation peaked globally at c 2 5 ga the first global glaciation at c 2 4 2 2 ga provides little support for the snowball earth theory but does suggest a negative feedback loop model whereby intraglacial co 2 related warming and synglacial decreases in weathering alternated up to three times models for palaeo atmospheric and oceanic evolution are mutually exclusive but by c 1 8 ga the existence of large landmasses and free oxygen in earth s atmosphere enabled erg development and red bed sedimentation globally the full spectrum of phanerozoic modern sedimentary environments was thus present on earth a third postulated superevent at c 0 8 0 6 ga essentially recreated conditions experienced at c 2 2 1 8 ga with additionally at least three global refrigeration events

shallow marine and coastal eolian quartz arenites in the neoarchean palaeoproterozoic karutola formation dongargarh volcano sedimentary succession central india abstract the neoarchean palaeoproterozoic karutola formation a 200 m thick supermature quartz arenite occurs interlayered between two thick units of intermediate to basic volcanic rocks of the dongargarh group despite metamorphism and deformation detrital texture and sedimentary structures are well preserved allowing detailed process based facies analysis the facies recognised include 1 inner shelf 2 shoreface 3 delta mouth lower delta plain 4 tidal flat and 5 foreshore backshore a coastal sand sheet dominated by adhesion structures and consisting of alternating eolian and foreshore aqueous deposits records eolian processes operative in the karutola coastal area textural characteristics hint at a significant eolian contribution to the shallow marine sand overall palaeocurrent indicates a nw se shoreline trend with hinterland to the west of the present outcrop belt a surface indicating an abrupt increase in the water depth divides the formation into two units the lower part encloses inner shelf to foreshore backshore deposits and the upper part of the succession records deposition from the shoreface to lower deltaplain environment a tidal flat sandstone mudstone unit is developed only in the north western end of the study area a granite gneiss source terrain cropping out to the west and a hot humid climate appears to have supplied the abundant quartz sand to the karutola shoreline and the sand population attained textural maturity through eolian and aqueous reworking it is postulated that the aqueous eolian interaction inferred for the karutola sand should be common in sandy depositional environments that lacked land vegetation

grenville magmatism in west texas petrology and geochemistry of the red bluff granitic suite zone of regional extension as suggested by recent geophysical and the red bluff granitic suite rbgs underlies part of the franklin petrological studies mountains in west texas it was emplaced into a middle proterozoic shelf sequence at 1120 35 ma the suite is predominantly metaluminous it consists of early granitic to quartz syenitic sills a main mass of alkali feldspar granite small bodies of alkali feldspar syenite leucogranitic dikes and late stage peralkaline