vertical magnetic structure of ocean crust determined from near bottom magnetic field measurements consensus on the source of marine magnetic anomaly stripes has remained one of the most elusive aspects of the vine and matthews seafloor spreading model which has been of such fundamental importance to global plate tectonics the first attempt to measure the vertical magnetic structure of oceanic crust exposed at a scarp face using near bottom magnetic measurements is reported along with the theoretical basis for the reduction and analysis of these measurements magnetometers mounted to deep tow and submersible platforms were used to determine the horizontal and vertical variation of crustal magnetization of the upper 2 km of young oceanic crust exposed by a steep submarine escarpment at the blanco fracture zone in the northeast pacific ocean results show a large amplitude magnetic anomaly is consistently found at the extrusive to intrusive transition indicating that the extrusives are strongly magnetized compared to the weakly magnetized intrusive crust profiles also show the systematic presence of more than one polarity with depth indicating the possibility of dipping polarity boundaries within the extrusives forward models find that a dipping polarity boundary model correctly predicts the amplitude and shape of the overlying sea surface anomaly while a block model with vertical polarity boundaries overestimates the amplitude these in situ results are used to directly assess the contribution made by the extrusive section to the overlying magnetic anomaly signal in essence to define the magnetic source layer it is concluded that the extrusive lavas constitute the main magnetic source for magnetic anomalies in oceanic crust less than 2 m y in age

salinity history of the earth s early ocean it is commonly thought that the oceans are becoming saltier with time as sodium and chlorine are weathered out of continental rocks and transported to the sea here we argue that the salinity of the early ocean was 1 5 to 2 times the modern value and that it did not decline significantly until surprisingly late in the earth s history if correct this theory could help explain why the evolution of higher life took so long

the june july 1993 seismo acoustic event at coaxial segment juan de fuca ridge evidence for a lateral dike injection the coaxial segment juan de fuca ridge was the site of an intense swarm of earthquakes that began at 21 43 gmt on june 26 1993 julian day 177 the swarm started near 46 15 n and migrated northward over the next 40 hours to 46 36 n where the majority of 676 events occurred during the following 3 weeks of activity the earthquakes propagated nne at a velocity of 0 3 0 1 m s 1 from the southern to northern swarm sites the activity went undetected by land based seismic networks along the oregon and washington coasts suggesting that the earthquakes were all m 4 0 the character of this earthquake swarm is very similar to dike injections observed at krafla and kilauea volcanoes the earthquake activity and subsequent migration probably represent a lateral dike injection into faults and fissures comprising the coaxial segment the reservoir acting as the dike s source likely resides beneath or to the south of the initial southern swarm of earthquakes the large magma supply at axial volcano cannot be ruled out as the source for the coaxial dike even though axial volcano exhibited no earthquake activity related to the coaxial swarm the t wave earthquake swarm reported here is the first deep ocean observation of volcanic seismicity associated with what most likely was a mid ocean ridge dike injection event

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

observations and models of inertial waves in the deep ocean the structure of the inertial peak in deep ocean kinetic energy spectra is studied here records were obtained from polymode arrays deployed in the western north atlantic ocean 40 w to 70 w 15 n to 42 n the results are interpreted both in terms of local sources and of turning point effects on internal waves generated at lower latitudes in most of the data there is a prominent inertial peak slightly above f however the peak height above the background continuum varies with depth and geographical environment three classes of environment and their corresponding spectra emerge from peak height variations class 1 is the 1500 m level near the mid atlantic ridge with the greatest peak height of 18 db class 2 includes a the upper ocean depth less than 2000 m b the deep ocean depth greater than 2000 m over rough topography and c the deep ocean underneath the gulf stream with intermediate peak height of 11 5 db class 3 is the deep ocean over smooth topography with the lowest peak height of 7 5 db near f the horizontal coherence scale is 0 60 km at depths from 200 m to 600 m and the vertical coherence scale is 0 200 m in the lower part of the main thermocline and 0 1000 m in the deep water the phase difference suggests a downward energy propagation in the lower thermocline and standing waves in the deep water a one turning point model is developed to describe inertial waves at mid latitudes based on the assumption that inertial waves are randomly generated at lower latitudes global generation where their frequency wave number spectrum is given by the model of garrett and munk 1972 1975 using the globally valid wave functions obtained by munk and phillips 1968 various frequency spectra near f are calculated numerically the model yields a prominent inertial peak of 7 db in the horizontal velocity spectrum but no peaks in the temperature spectrum the model is latitudinally dependent the frequency shift and bandwidth of the inertial peak decrease with latitude energy level near f is minimum at about 30 and higher at low and high latitudes the observations of class 3 can be well described by the model a low zonal wave number cutoff is required to produce the observed frequency shift of the inertial peak the differences between the global generation model and the observations of class 1 and class 2 are interpreted as the effects of local sources a locally forced model is developed based on the latitudinal modal decomposition of a localized source function asymptotic eigensolutions of laplace s tidal equation are therefore derived and used as a set of expansion functions the forcing is through a vertical velocity field specified at the top or bottom boundaries of the ocean for white noise forcing the horizontal velocity spectrum of the response has an inertial peak which diminishes in the far field with the forcing located at either the surface or the bottom several properties of the class 2 observations can be described qualitatively by a combination of the global and local models the reflection of inertial waves from a turbulent benthic boundary layer is studied by a slab model of given depth frictional effects are confined to the boundary layer and modeled by a quadratic drag law for given incident waves reflection coefficients are found to be greater than 0 9 for the long waves which contain most of the energy this result suggests that energy containing inertial waves can propagate over great distance as is required by the validity of the model of global generation

seabeam depth changes associated with recent lava flows coaxial segment juan de fuca ridge evidence for multiple eruptions between 1981 1993 after a swarm of earthquakes was detected on the coaxial segment of the juan de fuca ridge in june july 1993 the area was resurveyed with seabeam multibeam sonar to search for depth changes associated with a submarine volcanic eruption quantitative comparison of the 1993 seabeam survey with surveys in 1981 82 and 1991 shows one area of seafloor depth change up to 29 m between 1991 93 exactly where a pristine lava flow was discovered in addition two other depth anomalies up to 37 m and 20 m are identified between 1981 91 evidence that other recent eruptions have occurred along this spreading ridge segment

tectonic and paleoclimatic significance of a prominent upper pennsylvanian virgilian stephanian weathering profile iowa and nebraska usa abstract a virgilian stephanian weathering profile up to 4 m deep containing a paleosol basal rakes creek paleosol in the basal mudstone of the rakes creek member and karstified marine sediments in the ost kenosha and avoca members below is restricted to southeastern nebraska specifically the weeping water valley and the missouri river valley bluffs of adjacent easternmost iowa this weathering profile informally referred to as the weeping water weathering profile disappears farther eastward into the shallow forest city basin in southwestern iowa weeping water weathering profile features are prominent in comparison to other midcontinent pennsylvanian subaerial exposure surfaces indicating prolonged subaerial exposure relatively high elevation and a marked drop in water table along the nemaha uplift in southeastern nebraska eastward on the margin of the forest city basin the basal rakes creek paleosol and underlying karst are thinner and relatively poorly developed paleosol characteristics indicate formation on lower landscape positions comparative pedology the contrasting of paleosol variability morphology and micromorphology between different paleosols in the same regional succession provides a basis for interpreting the larger significance of the basal rakes creek paleosol the stratigraphically older upper lawrence and snyderville paleosols in the same area are significantly different in patterns of lateral variability and overall soil characteristics weaker eustatic control and stronger tectonic activity may explain the greater west east variability and eventual eastward disappearance of the basal rakes creek paleosol differences in soil characteristics between the vertisol like upper lawrence and snyderville paleosols and the non vertisol like basal rakes creek paleosol appear to be due to climate change particularly a shift from more seasonal to more uniform rainfall this climate change hypothesis is compatible with overall virgilian stratigraphic trends in the northern midcontinent outcrop area

magnetic properties of zero age oceanic crust a new submarine lava flow on the juan de fuca ridge a volcanic eruption that occurred in october 1993 on the juan de fuca ridge shows unusually high magnetization when compared with older samples from the off axis juan de fuca ridge and other pacific sites these data plus data from other young oceanic basalts indicate that oceanic crustal magnetization may decay rapidly by 10 in the first year the considerably slower decrease in magnetization for rocks from older off axis sites agrees with previous models of progressive low temperature oxidation of the mineral titanomagnetite the magnetization for newly erupted submarine basalts however is not consistent with the exponential decay predicted from older sites indicating that oxidation may not be the sole process responsible for the short term decay similarly weak field magnetic susceptibility of the younger rocks does not show an obvious corresponding decrease with increasing age as expected for the oxidation of titanomagnetite to titanomaghemite these preliminary results indicate that decay of magnetization of oceanic crustal rocks with time may have two distinct stages with only the later stage being due to the progressive oxidation of the magnetic minerals

detection of changes in ridge crest morphology using repeated multibeam sonar surveys a quantitative analysis method is developed to objectively identify significant bathymetric changes between multibeam sonar surveys of the same seafloor area the technique involves mathematical gridding of bathymetric surveys from different years co registration of grids based on prominent features covered in both surveys calculation of slope weighted depth difference grids and determination of the boundaries of statistically significant differences the resulting difference grids are used in interpreting geological processes and calculating the volume of new material added to the seafloor the method is applied to data from the southern juan de fuca ridge where a seafloor volcanic eruption of 0 05 km3 is inferred to have occurred between 1983 and 1987 camera tow data and submersible observations provide ground truth which confirms the validity of the quantitative analysis method and indicates empirically that the detection limit of the method allows new seafloor landforms measuring 1 105 m2 in area or about 200 300 m in diameter and 5 15 m in thickness to be detected through repeated sea beam bathymetric surveys

alvin magnetic survey of zero age crust coaxial segment eruption juan de fuca ridge 1993 magnetic profiles obtained by deep submersible alvin across a newly erupted lava flow on the juan de fuca ridge jdfr show strong magnetic anomaly fields 20 000 nt and high crustal magnetization 50 a m contrast relative to the surrounding older lavas these results are consistent with previous ideas that extrusive crust is initially highly magnetized within the high amplitude magnetic anomaly over the center of the flow there is a clearly defined deep notch like magnetic low this notch may indicate thermal demagnetization associated with a subsurface feeder dike weakly magnetized intrusives or altered extrusive rock if the former mechanism is active the notch should disappear with time as the dike cools

observations of overturning in the thermocline the context of ocean mixing abstract the time sequence of events that lead to internal wave breaking and ocean turbulence is investigated data are obtained from depths 100 400 m with a repeat profiling ctd and a coded pulse doppler sonar the instruments were deployed from r p flip during february march 1995 while stationed 30 km west of point arguello california as an aspect of the marine boundary layer experiment although the water depth at the site is 1500 m both rms shear and diapycnal diffusivity as inferred from the average rate and size of overturning events increase with depth below 250 m a deep source of wave energy is implied depth time series of 6 4 m shear s 2 m strain n2 n2 where n is the buoyancy frequency 6 4 m gradient richardson number ri n2 s2 and 2 m effective strain rate the depth derivative of ctd inferred vertical velocity are obtained at 4 minute intervals over a 9 day 100 400 m domain the occurrence of overturns static instabilities of vertical scale 2 m in the observed density

biogeochemistry of nautiloids and paleoenvironmental aspects of buckhorn seawater pennsylvanian southern oklahoma abstract sediments in the buckhorn quarry and adjacent outcrops southern oklahoma are shallow water carbonates which are intercalated with coals and minor conglomerates they belong to the boggy formation of the deese group and are desmoinesian pennsylvanian in age strontium concentrations of shell septa and cameral deposits of pennsylvanian cephalopods are variable and fall either in the low range with 0 17 0 22 or the high range with 0 39 0 60 sr ca atomic ratios these values suggest that extrapallial and or cameral fluids responsible for the formation of all three cephalopod macrostructures were in chemical disequilibrium with ambient seawater thus the biological discrimination for sr was well establihed by pennsylvanian time for nautiloids the mg concentrations appear to be controlled at the species genus levels in contrast the na mn and fe contents of nautiloids are influenced and controlled by the physicochemical conditions of the surrounding seawater information obtained from brachiopod and from the least altered cephalopod samples suggest that buckhorn seawater was physiochemically similar to that of modern ocean water and the postulated temperature and salinity values represent the most reasonable intepretations considering paleontological sedimentological and biogeochemical data salinity of the buckhorn sea which was within 5 s of the pennsylvanian equator ranged from 29 to 34 ppt with a mean of 32 ppt this near normal salinity was complemented by an average water temperature of 36 c 34 38 c for the shallower and of 21 c 14 30 c for the deeper parts of the buckhorn sea of southern oklahoma overall water temperatures fluctuated between 14 and 38 c

grain size dependent paleointensity results from very recent mid oceanic ridge basalts 1 we report paleointensity analyses on a suite of four samples from two axial zero age mid oceanic ridge basalt flows from the east pacific rise paleointensity experiments have been performed on several profiles each consisting of a batch of small millimeter scale subsamples going from the rapidly cooled glassy margin to the interior the coe version of the thellier double heating procedure was used with back checks performed after every other heating step most of the samples show very good behavior i e constant ratio between the lost and acquired magnetization through a large temperature range quality factor usually above 10 and positive checks which lead to unambiguous paleointensity determinations paleointensities obtained on glasses reported here and in a previously published study are very consistent and reproducible and in agreement with expected in situ values of earth s magnetic field intensity however results found within the crystalline part of the samples show values that are considerably up to 50 higher than expected these variations seem to be correlated with the cooling history of the samples and appear to be universal since all samples exhibit the same intriguing pattern an extensive study of magnetic properties allows us to link this incongruent behavior to 1 the presence of multidomain effects and 2 the cooling rate difference between laboratory experiments and in situ cooling

geology of the northern cleft segment juan de fuca ridge recent lava flows sea floor spreading and the formation of megaplumes geologic mapping and lava sampling were carried out after the discovery of large bursts of hydrothermal fluids megaplumes over the southern juan de fuca ridge in 1986 and 1987 our investigations of the northernmost section of the cleft segment have discovered 1 semicontinuous low temperature venting and one major high temperature vent site along 17 km of the neovolcanic zone and 2 very glassy lightly sedimented sheet flows and pillow mounds superimposed on older terrain over about 24 km along the northern most part the pillow mounds are documented to have erupted between 1981 and 1987 the occurrence of the megaplumes during this same time period strengthens the hypothesis that megaplumes are caused by sea floor extension events although the basalts from the entire length of the neovolcanic zone of the cleft segment appear to have been derived from the same mantle source a systematic northward increase in mg number along the segment within the neovolcanic zone indicates less shallow level differentiation to the north possibly related to the development of new magma chambers during the recent phase of sea floor spreading that has occurred there

tectonic influences on carbonate deposition and diagenesis buckhorn asphalt deese group desmoinesian arbuckle mountains oklahoma abstract the dry branch section is a mixed siliciclastic carbonate sedimentary sequence containing carbonate rocks that experienced incomplete diagenesis due to early introduction of oil from the oil creek formation ordovician the section is part of the deese group desmoinesian exposed in the western portion of the mill creek graben arbuckle mountains oklahoma the sequence was deposited in shallow marine shelf setting within a tectonically active basin deposition was strongly influenced by adjacent terrigenous coastal depositional environments the section was synclinally deformed by wrench faults to the north which were active soon before and after deposition two of these faults cut both the dry branch section and the underlying oil creek formation a known petroleum reservoir and t e source of fault related oil seeps throughout the central arbuckle region these faults acted as avenues for reservoir fluids to enter section as a result of remigration driven by orogenic stress carbonate rocks which show evidence of diagenesis influenced by reservoir fluids are present in the upper part of the section limited cementation overcompaction and arrested carbonate diagenesis resulted from the effects of interstitial asphalt which formed as a result of intraformational biodegradation of oil creek oil stratigraphic variation in petrologic characteristics suggests that oil introduction into dry branch sediments occurred as a single event within 10 000 years of deposition of uppermost part of section coinciding regionally with the desmoinesian ouachita orogenic pulse dia enesis has resulted in moderate isotopic depletion of altered fossils 418o 3 5 13c relative to unaltered skeletal aragonite 18o 0 to 1 13c 3 7 to 5 0 petrographic and stable isotopic study shows that two phases of early carbonate cementation affected dry branch carbonates 1 early clear spar that is more depleted in 18o 5 than the altered fossils 2 later spar which contains asphalt inclusions microspar and poikilotopic sparry cement present in the upper dry branch are anomalously depleted in 13c 20 this is close to the isotopic compositional range of asphalt in the section indicating that organic carbon derived from oil biodegradation was present in the porewater during diagenesis carbonate geochemical and petrographic evidence and the early post depositional tectonic introduction of oil indicate that subsurface water was a principal diagenetic agent

strong inertial currents and marginal internal wave stability in the central north sea solar insolation stabilizes the water column and suppresses vertical exchange observations from the central north sea clearly show that increased heating in summer is accompanied by enhanced de stabilizing vertical current differences shear surprisingly to such extent that the equilibrium state is marginally stable under calm weather conditions the shear is predominantly generated by near inertial motions while the internal wave spectrum primarily results from nonlinear interaction between the dominating tidal and near inertial motions in terms of the associated enhanced vertical mixing across the largest vertical temperature gradients shelf seas are not different from the abyssal ocean despite the proximity to energy sources near boundaries in the former by the lack of sufficiently strong wind and tidal mixing this internal mixing is considered to be responsible for the diapycnal transport of nutrients leading to the observed increase in near surface values and triggering the late summer phytoplankton bloom

deep sea high resolution hydrography and current measurements using an autonomous underwater vehicle the overflow from the strait of sicily autosub 2 an autonomous underwater vehicle auv developed by the southampton oceanography centre was used for high resolution hydrographic surveys in the sicily strait a combination of seasoar type profiling and terrain following missions were undertaken and velocity and hydrographic measurements taken from autosub 2 were compared with concurrent shipboard hydrographic and velocity profiles even though shipboard stations were separated by just 5 to 8 km along the mission path data from the auv showed small scale variability that was missed by the shipboard sampling in this paper we present the example of an intense jet with maximum speed greater than 0 50 m s 1 less than 4 km wide

stable isotopic studies of nautilus macromphalus sowerby new caledonia and nautilus pompilius l fiji abstract two specimens of nautilus macromphalus sowerby from new caledonia and two specimens of nautilus pompilius l from fiji have been selected for stable isotope analysis of all septa these animals were captured at depths of 80 m and 200 m respectively the early formed septa were also analyzed from three additional specimens of n macromphalus captured in new caledonia at 300 400 m oxygen isotope compositions of septa from both populations are characterized by 1 an abrupt increase in su18o of 1 3 5 from septa 6 to 8 and 2 septum to septum variations in 13 and 18o which are roughly sympathetic and larger for carbon than oxygen septa from the fiji specimens are slightly depleted in 18o relative to those from new caledonia the isotopic step between septa 7 and 8 is interpreted to record the hatching of the embryo after development of the seventh septum marked 18o depletion of septa 1 7 evidently reflect non equilibrium metabolic isotope fractionation during embryonic groth stages or perhaps more likely a difference in the isotopic compositions of nepionic fluid and sea water the oxygen isotope compositions of septa 10 and higher and shell walls appear to closely approach isotopic equilibrium with sea water as demonstrated by a comparison of calculated isotopic and known temperatures for aragonite precipitation by an aquarium grown specimen a slightly warmer average environment of growth is indicated for the fiji samples

internal structure of uppermost oceanic crust along the western blanco transform scarp implications for subaxial accretion and deformation at the juan de fuca ridge 1 the uppermost 2 km of oceanic crust created near the southern end of the juan de fuca ridge 60 mm yr full spreading rate is exposed in a tectonic window created along the north wall of the blanco transform fault a total of 27 submersible dives transect this escarpment over a distance of 30 km corresponding to 1 m y of spreading history in this exposure weakly deformed basaltic lavas grade downward into much more intensely fractured lavas cut by basaltic dikes lava flow surfaces dip persistently to the northwest toward the spreading center and the dikes dip southeast away from the spreading center the underlying sheeted dike complex is composed of subparallel dikes that dip moderately to the southeast discrete faults and more distributed cataclastic deformation zones separate the panels of sheeted dikes from one another disruption of the lava and dike units are interpreted as a result of dramatic subaxial vertical mass transport that created the accommodation space for the accumulation of a thickness of 1000 1500 m of basaltic lava the observed patterns of tilting of lavas and dikes imply subsidence beneath the region of active volcanism 3 km wide that is most rapid near the axis and diminishes quickly off axis deformation that accommodates this subsidence has generated extensive fracture porosity in the subaxial region that could strongly influence upper crustal hydrothermal pathways alteration history seismic properties and the distribution of subsurface biological communities

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

central anomaly magnetization high constraints on the volcanic construction and architecture of seismic layer 2a at a fast spreading mid ocean ridge the epr at 9 30 50 n abstract the central anomaly magnetization high camh is a zone of high crustal magnetization centered on the axis of the east pacific rise epr and many other segments of the global mid ocean ridge mor the camh is thought to reflect the presence of recently emplaced and highly magnetic lavas forward models show that the complicated character of the near bottom camh can be successfully reproduced by the convolution of a lava deposition distribution with a lava magnetization function that describes the variation in lava magnetization intensity with age this lava magnetization function is the product of geomagnetic paleofield intensity which has increased by a factor of 2 over the last 40 kyr and low temperature alteration which decreases the remanence of lava with exposure to seawater the success of the forward modeling justifies the inverse approach deconvolution of the magnetic data for lava distribution and integration of that distribution for magnetic layer thickness this approach is tested on two near bottom magnetic profiles al2767 and al2771 collected using alvin across the epr axis at 9 31 n and 9 50 n our analysis of these data produces an estimate of the relative thickness of the magnetic lava layer which is remarkably consistent with existing multichannel estimates of layer 2a thickness from lines cdp31 and cdp27 the similarity between magnetic layer and seismic layer 2a at the 9 10 n segment of the epr crest provides independent support to the notion that seismic layer 2a in young oceanic crust represents the highly magnetic lava layer and that the velocity gradient at the base of layer 2a is related to the increasing number of higher velocity dikes with depth in the lava dike transition zone the near bottom magnetic anomaly character of the camh is a powerful indicator of the emplacement history of upper crust at mors which allows prediction of the relative thickness and architecture of the extrusive lavas independent of other constraints

zigzag microstructure in rugose corals a possible indicator of relative seawater mg ca ratios low mg calcite lmc and high mg calcite hmc have been identified confidently as original biominerals in different rugose corals devonian tabulophyllum had a lmc skeleton whereas pennsylvanian lophophyllidium had a hmc skeleton zigzag microstructure a diagenetic microstructure in rugose corals may be related to early migration of mg2 ions during transformation of hmc into lmc therefore zigzag microstructure may indicate that the original mineral was hmc even in specimens that subsequently converted to lmc stratigraphically corals with zigzag microstructure are confined to the late paleozoic which is coincident with the aragonite sea of p a sandberg hence fluctuating mg ca ratios may have directly controlled oscillations in marine carbonate chemistry and the mineral composition of rugose corals so that hmc skeletons as indicated by zigzag microstructure formed during intervals with aragonite seas and lmc skeletons e g tabulophyllum formed during intervals with calcite seas

influence of stratification and topography upon internal wave spectra in the region of sills 1 a non hydrostatic model in vertical cross section form is used to examine the role of sill width and buoyancy upon the energy cascade into the internal tidal band and higher frequencies in sill regions power spectra analysis of computed time series show that as sill width is reduced the energy transfer from the baroclinic tide to its higher harmonics is reduced however there is an increase in energy at higher frequencies corresponding to lee wave periods in addition internal mixing on the lee side of the sill increases the addition of small scale topography on the sill slope produces a similar spectral change in the internal wave distribution and mixing for a narrow sill the addition of a surface buoyant layer with a higher buoyancy frequency significantly reduces the energy cascade to higher frequencies with a corresponding reduction in mixing the associated spectra have characteristics resembling wide sill topography

wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison panfish j t and peterson f 1988 wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison in g kocurek editor late paleozoic and mesozoic eolian deposits of the western interior of the united states sediment geol 56 261 282 wind directions for middle pennsylvanian through jurassic time are predicted from global circulation models for the western united states these predictions are compared with paleowind directions interpreted from eofian sandstones of middle permsylvanian through jurassic age predicted regional wind directions correspond with at least three quarters of the paleowind data from the sandstones the rest of the data may indicate problems with correlation local effects of paleogeography on winds and lack of resolution of the circulation models the data and predictions suggest the following paleoclimatic developments through the time interval studied predominance of winter subtropical high pressure circulation in the late pennsylvanian predominance of summer subtropical high pressure circulation in the permian predominance of summer monsoonal circulation in the triassic and earliest jurassic and during the remainder of the jurassic influence of both summer subtropical and summer monsoonal circulation with the boundary between the two systems over the western united states this sequence of climatic changes is largely owing to paleogeographic changes which influenced the buildup and breakdown of the monsoonal circulation and possibly owing partly to a decrease in the global temperature gradient which might have lessened the influence of the subtropical high pressure circulation the atypical humidity of triassic time probably resulted from the monsoonal circulation created by the geography of pangaea this circulation is predicted to have been at a maximum in the triassic and was likely to have been powerful enough to draw moisture along the equator from the ocean to the west

high resolution magnetic signature of active hydrothermal systems in the back arc spreading region of the southern mariana trough high resolution vector magnetic measurements were performed on five hydrothermal vent fields of the back arc spreading region of the southern mariana trough using shinkai 6500 a deep sea manned submersible a new 3 d forward scheme was applied that exploits the surrounding bathymetry and varying altitudes of the submersible to estimate absolute crustal magnetization the results revealed that magnetic anomaly derived absolute magnetizations show a reasonable correlation with natural remanent magnetizations of rock samples collected from the seafloor of the same region the distribution of magnetic anomaly derived absolute magnetization suggests that all five andesite hosted hydrothermal fields are associated with a lack of magnetization as is generally observed at basalt hosted hydrothermal sites furthermore both the pika and urashima sites were found to have their own distinct low magnetization zones which could not be distinguished in magnetic anomaly data collected at higher altitudes by autonomous underwater vehicle due to their limited extension the spatial extent of the resulting low magnetization is approximately 10 times wider at off axis sites than at on axis sites possibly reflecting larger accumulations of nonmagnetic sulfides stockwork zones and or alteration zones at the off axis sites

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

seasonal cycle variations on the supercontinent of pangaea the seasonal cycle of temperatures on pangaea early late permian configuration is simulated with a two dimensional energy balance climate model results indicate that the annual range of temperatures in the southern hemisphere of pangaea was considerably larger than any occurring at present maximum mean monthly summer temperatures are 38 c daytime highs probably exceed 45 c in some regions however summer temperatures in polar regions are considerably lower 0 5 c and are favorable for persistence of ice in eastern australia and glaciation in siberia conditions that receive some support from geologic data these simulations suggest that very high summer temperatures and a large annual range are major features of supercontinent environments such conditions may have significantly influenced the distribution of terrestrial permian biota our results are difficult to reconcile with postulated equable climates for some supercontinent configurations

glacial eustatic base level climatic model for late middle to late pennsylvanian coal bed formation in the appalachian basin abstract late middle late pennsylvanian middle allegheny and lower conemaugh marine units in the appalachian basin represent the distal edges of glacial eustatic marine incursions of the midcontinent sea onto the detrital apron of the appalachian highlands because these marine units typically overlie coal beds the main environment of formation of this type of coal bed appears to have been that of a coastal swamp migrating ahead of transgression as base level rose the water table continually rose and the swamp was further nourished and surrounding vegetation kept thick enough to inhibit detrital influx by rainfall from the expanding nearby source of moisture even in parts of the appalachian cyclic succession with no marine units upper allegheny monongahela dunkard the coal beds rep esent the wettest part of the climate cycle of cecil 1990 sandwiched between detrital units representing seasonal wet dry climates when sediment was most readily mobilized and antipodal to nonmarine limestones representing the driest climates throughout this time the appalachian basin was in the center of the tropical zone of a nearly accreted megacontinent quite distant 4000 km from permanent oceanic sources of moisture climate modeling without considering inland seas or orographic effects on winds shows that the tropical zone of such a large land mass would have suffered from a severe deficit in rainfall and soil moisture although further modeling shows that the appalachian orogenic highlands would have drawn in moisture to ncrease rainfall in their vicinity they also may have impeded the normal westward flow of moisture laden easterly winds the western source for enough moisture to form coal beds was most likely the north american midcontinent sea during major highstand this sea would have covered about 2 million km2 and provided both high base level and abundant nearby moisture for enough continual rainfall to keep the coastal peat swamps widespread fresh and relatively detritus free in the appalachian basin in contrast during major lowstand it would have covered only about 200 000 km2 with its shoreline about 1500 km away and it apparently provided less consistent moisture to the appalachian basin then because most nonmarine limestones and paleosols formed there during the e times contain evidence of drier climates therefore upper allegheny monongahela and dunkard coal beds most probably formed when the midcontinent sea was approaching highstand and stood just west of the presently preserved outcrop thus they likely represent the coastal lowland equivalent of a marine unit at highstand farther west this constrained time of peat formation and preservation in a variety of coastal environments prior to and during marine highstand is responsible for the discrete and widespread nature of the coal bed interval in a typical depositional cycle or cyclothem a pattern that stands in contrast to the complicated relations of overlying and underlying detrital units which reflect the segregation of sand and mud into a complex mosaic of local deltaic and ter estrial subenvironments that developed when sea level rainfall and the water table were lower

variability of sea ice draft off hokkaido in the sea of okhotsk revealed by a moored ice profiling sonar in winter of 1999 1 using a moored ice profiling sonar along with an adcp a spatial section of draft across 855 km of sea ice was obtained for the first time in the southwestern part of the okhotsk sea near hokkaido in winter of 1999 the draft evolved from 0 20 m in mid february to 1 45 m in late march with the overall value of 0 72 m the draft characteristics were quite different between february and march before and after the period of strong winds the increase of the mean draft from february to march was associated with the increase of deformed ice the maximum draft observed was 17 m ice volume was dominated by the contribution from portions of deformed ice especially in march these results suggest that deformed ice dominated in the region of observation and dynamical processes were mainly responsible for the evolution of draft

life history of the pliocene scallop fortipecten based on oxygen and carbon isotope profiles abstract oxygen and carbon isotope profiles from the outer calcite layer of two well preserved specimens of the pliocene scallop fortipecten takahashii exhibit distinct attenuation in their annual ranges throughout the complete growth history of approximately 10 years the segments of oxygen isotope profiles corresponding to winter or summer extremes were compressed suggesting growth retardation during extreme water temperatures these profile compressions correspond well with the positions of growth rings on the outer shell surface one scallop shell which evidently grew in warmer environments based on mean oxygen isotope values developed growth rings in summer while a second shell with colder mean temperature values exhibits winter growth rings a drastic reduction in isotope fluctuation occurred at a shell age of approximately 3 years and possibly is related to the onset of the reproductive phase which may have suppressed shell growth in favor of building up reproductive tissue sexual maturity brought a change in life habit from a swimming to a reclining mode which is clearly shown by the change in shell architecture although scallop shells during the juvenile stage may record a complete seasonal cycle isotopic profiles in the adult stage contain repeated growth breaks as a result using isotope signals as paleoenvironmental proxies must be done carefully at least with scallop shells

timing of volcanism along the northern east pacific rise based on paleointensity experiments on basaltic glasses 1 samples from two adjacent and contrasting ridge segments along the east pacific rise were measured for their magnetic paleointensity in order to further explore the possibilities of dating very young volcanic samples using secular variations in the earth s magnetic field the ridge segment north of the orozco transform fault 15 22 16 20 n is the shallowest and broadest along more than 5000 km of the east pacific rise whereas the adjacent segment to the north 16 16 18 n has a typical morphology for its intermediate spreading rate both ridge segments were densely sampled during the panr01mv cruise and 36 samples of axial lava flows consisting mainly of glasses from the rims of the flows and some fragments of lobate basalts were selected from this collection for paleointensity experiments the coe version of the thellier double heating procedure in air was used twenty seven units provide internally consistent paleointensity estimates leading to precise estimates of the paleofield which range between 8 t and 57 t comparisons with reference paleointensity curves compiled from subaerial flows archeomagnetic data and sedimentary records projected to the sampling site coordinates show that the measured values can be used to constrain the volcanic history of the ridge segments over the past few thousand years a good agreement was found between apparent freshness of the glasses the geochemistry of the lavas and their magnetic paleointensity values the inflated southern segment seems characterized by recent activities as indicated by numerous flows with paleointensities clustering around today s value 39 t or around the high values typical of 2000 3000 years ago 55 t we interpret this distribution to indicate the flooding by effusive lava flows of the entire axial plateau some 2000 3000 years ago followed by a volcanic phase producing smaller volume lava flows confined to the innermost 200 m of the ridge axis the northern ridge segment is characterized by dispersed paleointensity values consistent with a series of small eruptions of diverse ages samples collected at the tips of both ridge segments across the 16 20 n axial discontinuity have the lowest paleointensities and are thus thought to be significantly older consistent with models advocating reduced magmatism near ridge axis discontinuities this study demonstrates the strong potential of paleointensity measurements as a tool to help constrain volcanic history at ridge axes

carbon and oxygen isotope composition of nautilus macromphalus a record of thermocline waters off new caledonia abstract this study investigates the controls on the stable isotope composition of shell nacreous layer of a modern nautilus macromphalus from new caledonia closely spaced samples were taken both along growth lines isochrons and growth axis time series carbon isotope compositions 13 c 0 3 to 1 pdb of the shell decrease in the domains of maximal growth 0 3 and muscle insertion 0 4 maximal 13 c variations of about 1 are recorded in time series a global ontogenetic decrease of 13 c values is observed for both dorsal and ventral areas 0 4 to 0 8 and can be ascribed to a metabolic effect with age or to changes in the food source by contrast oxygen isotope compositions are quite constant 1 1 18 o

acoustic detection of a seafloor spreading episode on the juan de fuca ridge using military hydrophone arrays until recently no practical method has been available to continuously monitor seismicity of seafloor spreading centers the availability of the u s navy s sound surveillance system sosus for environmental research has allowed the continuous monitoring of low level seismicity of the juan de fuca ridge in the northeast pacific on june 22 1993 noaa installed a prototype system at u s naval facility whidbey island to allow real time acoustic monitoring of the juan de fuca ridge using sosus on june 26 2145 gmt a burst of low level seismic activity with accompanying harmonic tremor was observed and subsequently located near 46 15 n 129 53 w on the spreading axis of the juan de fuca ridge over the following 2 days the activity migrated to the nne along the spreading axis with the final locus of activity near 46 31 5 n 129 35 w the nature of the seismicity was interpreted to represent a lateral dike injection with the possibility of eruption on the seafloor based on this interpretation a response effort was initiated by u s and canadian research vessels and both warm water plumes and fresh lavas were subsequently identified at the site

the non tropical coral cladocora caespitosa as the new climate archive for the mediterranean high resolution weekly trace element systematics abstract high resolution weekly laser ablation icp ms trace element analyses b sr u mg ba are reported for the scleractinian coral cladocora caespitosa collected from the northern adriatic sea geochemical ratios sr ca b ca mg ca u ca ba ca were measured in a 38 mm long 10 years growth external coralline portion wall region and generally exhibit a close relationship with the in situ measured weekly fortnightly data on sea surface temperature sst available for the last 6 years in particular b ca ratios tuned to fine scale variations in sst show a high degree of correlation r 0 856 n 136 with sst and indicate that coral calcification only occurs above a minimum temperature threshold of 14 16 c in addition the ranges of trace element variability are larger than those typically recorded in tropical corals consistent with the large seasonal variations in sst of the adriatic this study thus demonstrates the feasibility of extracting and exploiting high resolution geochemical records from non tropical corals such as c caespitosa as a proxy for sst

rapid emplacement of a mid ocean ridge lava flow on the east pacific rise at 9 46 51 n in april 1991 during a submersible diving expedition to the east pacific rise epr crest at 9 46 51 n a new volcanic eruption on the sea floor was discovered here we report results from numerical modeling of that eruption which indicate that 4 106 6 106 m3 of lava was emplaced in 1 2 h with an average eruption rate of 103 106 m3 s 1 comparable to rates observed in hawaii at kilauea s east rift zone if the rapid emplacement of the 1991 epr lava and its short eruption duration are typical of volcanic events at fast spreading mid ocean ridge crests these characteristics have broad implications for our ability to detect monitor and understand the evolution of magmatic and volcanic processes within the axial zone

geochemical analysis of nautilus pompilius from fiji south pacific abstract nautilus pompilius from fiji exerts a biological fractionation effect on the sr2 and na contents of its aragonite shell the sr2 content is lower while the na content is greater than that for aragonite precipitated in chemical equilibrium with ambient seawater the oxygen isotope values of nautilus pompilius suggest that its shell aragonite was precipitated in equilibrium with ambient seawater isotope calculations suggest water temperatures of 9 18 c this limits the habitat range of nautilus pompilius during shell formation to water depths of 250 500 m

variability in the internal wave field induced by the atlantic deep western boundary current at 16 n abstractfive years of continuous mooring data combined with conductivity temperature depth ctd lowered acoustic doppler current profiler ladcp measurements from five cruises are used to investigate the influence of the deep western boundary current dwbc on the internal wave field and associated vertical mixing at the continental slope at 16 n in the western atlantic the mooring data include 2 hourly rotor current meter measurements and temperature conductivity time series with a high temporal resolution of 5 20 min thus the data resolve time scales ranging from the low frequency variability of the large scale dwbc that generates internal waves due to interactions with the topography to frequencies greater than that of internal waves that are associated with vertical mixing estimates of the vertical mixing induced by the breaking of the observed internal waves show elevated diapycnal diffusivities of up to 10 3 0 4 10 3 m2 s 1 in the bottommost 1500 m during times of a strong dwbc maximum ve

shifts in oxygen and carbon isotope signals in marine molluscs from the central paratethys europe around the lower middle miocene transition abstract stable isotope data of mollusc shells from two adjacent time slices karpatian badenian from the central paratethys were investigated to detect differences in environmental parameters and to depict shifts in the isotope signature of the paratethyan seawater around the early middle miocene transition altogether seventeen different gastropod species and one bivalve species from the karpatian korneuburg basin and the badenian northern alpine foreland basin were selected representatives of various ecological guilds yielded different isotope patterns especially in 13c reflecting different original habitats or nutrition although molluscs precipitate their shells in oxygen isotopic equilibrium we preferred to compare isotope data of shells of the same genus of the family turritellidae from the karpatian and badenian the badenian turritella shells from the northern alpine foreland basin yielded distinctly higher 18o and 13c values than the respective karpatian shells from the korneuburg basin as the main factors controlling 18o values in gastropod shells are temperature and 18o of the water during precipitation the differences between the oxygen isotope data of the two time slices can only be explained by these factors good independent palaeotemperature proxies exist for the early to middle miocene of central europe they do not indicate a significant temperature variation therefore different 18o values of the seawater in the different basins of the central paratethys must be responsible for the contrasting 18o values when calculated with commonly assumed 18o seawater values for the miocene badenian turritella shells indicate too cold temperatures these data clearly document the danger of palaeotemperature interpretations based solely on stable isotopes as smaller and marginal marine settings such as the paratethys sea can be seriously influenced by regional differences in the isotope composition of the seawater only a thorough consistent control by other climate proxies e g palaeoecology of molluscs as in this study allows a sensible interpretation

on the behavior of internal waves in the wakes of storms abstract the rossby adjustment process in the wake of a storm is studied with a view to finding within the context of linear theory how wave dispersion in both the vertical and meridional directions spreads energy which is initially confined entirely to the mixed layer comparisons are made between three cases 1 a periodic storm on the f plane where dispersion is purely vertical 2 a bounded storm on the f plane and 3 a bounded storm centered 2700 km from the equator on an equatorial beta plane particular attention is paid to the initial rate of loss of energy from the mixed layer and some simple formulas which work very well in the cases studied are derived these show that the rate of loss goes up when the mixed layer depth is increased and also that the rate scales as the square of the wavenumber values of the rates are sufficient to provide a major source of energy for internal waves below the mixed layer the often observed tendency for phase lines to propagate upward is found in all case

unprecedented pressure increase in deep magma reservoir triggered by lava dome collapse 1 the collapse of the soufriere hills volcano lava dome on montserrat in july 2003 is the largest such event worldwide in the historical record here we report on borehole dilatometer data recording a remarkable and unprecedented rapid 600s pressurisation of a magma chamber triggered by this surface collapse the chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site by analyzing the strain data and using added constraints from experimental petrology and long term edifice deformation from gps geodesy we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 mpa and average radius 1 km pressurisation is attributed to growth of 1 3 of gas bubbles in supersaturated magma triggered by the dynamics of surface unloading recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude

oxygen and stable carbon isotopes from a nautiloid from the middle pennsylvanian late carboniferous impregnation lagerstatte buckhorn asphalt quarry primary paleo environmental signals versus diagenesis abstract two shell fragments one of an undetermined cephalopod and one of an orthoconic nautiloid pseudorthoceratidae gen et sp indet from the pennsylvanian buckhorn asphalt lagerstatte oklahoma were studied to reconstruct paleotemperatures and to explore possible diagenetic alterations for the first time not only parts of the shell of an orthoconic nautiloid but also its cameral deposits were sampled in high resolution the mineralogy geochemistry and microstructure of both shell remains the pseudorthoceratid and the undetermined cephalopod were investigated in detail before high resolution transects for oxygen and stable carbon isotopes were sampled the shell fragment of the undetermined cephalopod showed no or very little diagenetic alteration therefore the measured 18o variation 18o range of 0 68 and the inferred temperature range of 28 to 31 c are interpreted to represent an original signal the temperatures indicate that the specimen lived in shallow warm tropical waters the 13c signal with a 13c range of 3 43 is interpreted to be the consequence of a strong metabolic effect a septum of the phragmocone of the pseudorthoceratid nautiloid was only slightly altered by diagenesis and a largely original 18o signal could be obtained the 18o values exhibit an inferred temperature range of 14 to 15 c indicating that this species lived in deeper and cooler waters the cameral deposits were investigated in detail by energy dispersive x ray edx and by xrd gadds x ray diffraction general area detector diffraction system analyses part of the cameral deposits in the orthoconic nautiloid turned out to originally consist of high mg calcite hmc instead of the estimated aragonite anyhow the massive cameral deposits show signs of strong small scale alteration resulting in a distinct spreading of oxygen values the oxygen and carbon isotope plots show a linear trend for the oxygen carbon correlation this is interpreted as the mixing of two end members with the lightest end members suggesting a meteoric diagenesis with a diagenetic fractionation of the aragonite to low mg calcite lmc respectively the hmc to lmc and dolomite the calculated temperatures of the pseudorthoceratid specimen and the undetermined cephalopod indicate two different paleoenvironments additionally the pseudorthoceratid nautiloid displays the narrow range of temperatures in the deeper parts of the sea and the undetermined cephalopod the more fluctuating temperatures in the shallow areas it is also shown how important a detailed investigation of microstructures and mineralogy of samples with an according cautious interpretation of the achieved dataset is the importance of an intensive examination of samples is pointed out to avoid small scale alterations to be overlooked since this would lead to a misinterpretation of the results

spondylus gaederopus a new mediterranean climate archive based on high resolution oxygen and carbon isotope analyses abstract the presented study evaluates the potential of the mediterranean bivalve spondylus gaederopus linne 1758 as a palaeoclimatic archive its fixosessil life in water depths 18 o and carbon 13 c isotope data obtained from high resolution sampling of a modern s gaederopus from rhodes greece collected alive in 4 m water depth in spring 2002 suggest that the outer calcitic shell layer as well as the inner aragonitic shell layer is precipitated in equilibrium with seawater due to the complexity of the outer calcitic shell layer with its spines and prickles a chronological sampling of this part of the shell is not possible in contrast the inner aragonitic shell layer with its well developed growth bands allows a fast chronologic sampling 18 aragonite growth bands were sampled from the inner shell layer of the studied specimen corresponding to 9 years of growth with 9 10 samples per year carbon stable isotopes 13 c ar yield mean values of 0 70 0 6 and show a remarkable negative shift of about 1 8 from about 1 6 to about 0 2 through time this ontogenetic depletion in 13 c might be related to physiological developments like sexual maturity as it is the case in other bivalves seasonal variations with an average amplitude of 0 85 are superimposed on the observed secular trend these cycles show an increase in amplitude that has not been described before and cannot be explained so far oxygen isotopes 18 o ar exhibit mean values of 1 11 0 5 clearly pronounced seasonal cycles with an average amplitude of 1 45 show the same wavelength as the carbon cycles but run out of phase the 18 o ar correlates well with sea surface temperature and correlation fits best during summer periods deviations between measured and predicted 18 o ar input data sea surface temperature seawater 18 o show that maximal discrepancies occur during winter periods these discrepancies can be best explained by a decrease in local seawater 18 o due to increased freshwater influx on rhodes maxima in precipitation hence river runoff occur during winter months

high resolution bathymetric surveys using scanning sonars lava flow morphology hydrothermal vents and geologic structure at recent eruption sites on the juan de fuca ridge the coaxial and cleft segments of the juan de fuca ridge have isolated chronic high temperature and focused hydrothermal vent sites both segments also have experienced recent volcanic eruptions which produced extensive ephemeral low temperature and diffuse hydrothermal venting to study the geologic setting of these sites high resolution bathymetric surveys at eight locations on the coaxial and cleft segments were collected between 1993 and 1999 two 675 khz scanning sonar systems were used mesotech on the submersible alvin and imagenex on the remotely operated vehicle jason the bathymetry from these surveys can be gridded at a scale of 2 4 m and contoured at 1 m and thus can resolve many fine scale features on the seafloor that are indistinguishable in multibeam bathymetry collected at the sea surface bathymetric data at this resolution are particularly useful for identifying geologic features related to diking faulting and lava flow emplacement for example the high resolution bathymetric maps show that submarine fissure eruptions that form pillow lavas last long enough to become localized and to produce point source constructs along their length and their extrusion rate is low enough that no significant drainback occurs in contrast lobate sheet flows are formed by short lived high effusion rate eruptions in which no localization of output occurs along the eruptive fissure and inflation is quickly followed by drainback resulting in extensive collapse features however if the process of submarine lava flow inflation occurs at a slower rate and over a longer period of time it can create lava rises up to 25 m high with distinctive structure and morphology the scanning sonar data also show that fissures and grabens have formed or reactivated where dikes approach the surface adjacent to recent eruptive sites the fine scale bathymetry establishes that all the hydrothermal vent sites studied at the coaxial and cleft segments are located along prominent volcanic or tectonic extensional structures which provide the physical pathway for fluids from the subsurface to the seafloor furthermore the fine scale morphology of recent lava flows can be used as a qualitative indication of eruption duration

thickness of a submarine lava flow determined from near bottom magnetic field mapping by autonomous underwater vehicle magnetic field surveys obtained near the seafloor can map the boundaries of recent volcanic eruptions and can provide thickness estimates of these lava flow units independent of bathymetry differencing methods magnetic thickness estimation requires knowledge of the intensity of magnetization of the new lava and surrounding terrain but this can be satisfactorily obtained by representative sampling of the various volcanic units while bathymetry differencing requires pre existing data to assess the thickness of new lava eruptions magnetic surveys can be obtained after an eruption has occurred in this study near bottom magnetic surveys were obtained using an autonomous underwater vehicle auv which operates without a tether or human intervention auv technology offers rapid deployment and an efficient surveying approach for remotely mapping recent lava eruption sites on the seafloor

emplacement origins of coarsely crystalline mafic rocks hosted in greenstone belts examples from the 2 7 ga yilgarn craton western australia coarsely crystalline mafic rocks commonly referred to as dolerite and diabase make up a substantial proportion of archean greenstone belts and are hosts to major orogenic gold deposits yet their internal architecture and contact relationships remain poorly documented and their emplacement origins are assumed rather than supported with evidence we present results from drill core logging of several late archean coarsely crystalline packages from the eastern goldfields superterrane of the yilgarn craton western australia including the golden mile dolerite these large mafic bodies comprise mostly medium to coarsely crystalline mafic rocks but also include a variety of other products of differentiation the bodies range from 75 to 460 m thick and extend for tens of kilometers are primarily hosted in mudstones and basalt and appear to be concordant to stratigraphy as such this study excludes mafic dykes and extremely thick and internally complex bodies such as the bushveld complex from base to top the internal stratigraphy generally consists of a lower unit of aphyric basalt dolerite gabbro and peridotite pyroxenite then a voluminous middle dolerite gabbro and an upper quartz dolerite gabbro and a topmost aphyric basalt granophyric veins and domains are common in the upper third of the mafic body contacts are gradational between all lithofacies with the exception of granophric veins which have sharp contacts within this overall stratigraphic framework there is variability in the relative thickness of lithofacies number of lithofacies as well as repetition of some lithofacies several examples also include basalt in the interior in well exposed examples the key evidence for distinguishing intrusions from extrusions is provided by the top contact however the top contact from these examples is ambiguous to overcome this gap we review the character of well studied thick ponded lavas from the literature most aspects of the internal character are not unique to intrusions although the maximum groundmass grain size excluding granophyric veins of the archean examples 3 mm is significantly coarser than that for any known ponded lavas 1 mm the ability to distinguish intrusions from extrusions has important implications for reconstructing archean greenstone stratigraphy and mineral exploration

exploring aberrant bivalve shell ultrastructure and geochemistry as proxies for past sea water acidification throughout much of earth s history marine carbonates have represented one of the most important geological archives of environmental change several pivotal events during the phanerozoic such as mass extinctions or hyperthermal events have recently been associated with ocean acidification nevertheless well defined geological proxies for past ocean acidification events are at best scarce here experimental work explores the response of bivalve shell ultrastructure and isotope geochemistry c 13 o 18 and mg 26 to stressful environments in particular to sea water acidification in this study the common blue mussel mytilus edulis was cultured from early juvenile stages to one year of age at four ph regimes ph nbs 72 to ph 80 shell growth rate and ultrastructure of mainly the calcitic portion of the shells were compared between experimental treatments specimens exposed to low ph environments show patches of disordered calcitic fibre orientation in otherwise well structured shells furthermore the electron backscattered diffraction analyses reveal that under acidified conditions the c axis of the calcite prisms exhibits a bimodal or multi modal distribution pattern similar shell disorder patterns have been reported from mytilids kept under naturally acidified sea water conditions in contrast this study found no evidence that different ph regimes affect shell carbon oxygen or magnesium isotope ratios based on these observations it is proposed that i stressful environments in this case low sea water ph predictably affect bivalve biomineralization patterns and ii these findings bear potential as a novel petrographic proxy for ancient sea water acidification an assessment of the applicability of these data to well preserved fossil shell material from selected time intervals requires additional work

the oxygen and carbon isotope composition of carboniferous fossil components sea water effects the aragonitic molluscs and lime mud of the pennsylvanian buckhorn asphalt deese group of southern oklahoma precipitated calcium carbonate in oxygen and carbon isotopic equilibrium with ambient sea water in addition 18o values indicate that the pelecypods precipitated their shells during the warmer months of the year the coiled nautiloids probably precipitated their shells in the warm surface water and throughout the year for the orthocone nautiloids the 18o values suggest that they precipitated their shells in deeper cooler water the low mg calcite brachiopods of the mississippian lake valley formation of new mexico precipitated shells in oxygen and carbon isotopic equilibrium with ambient sea water the 18o and 13c values of the buckhorn and lake valley faunas in conjunction with other published results suggest that carboniferous sea water was on a average depleted in 18o by 1 5 2 pdb relative to recent sea water however the 13c value of 2 6 2 pdb for average carboniferous sea water is similar to that of recent ocean water early diagenetic alteration of metastable carbonates probably occurs in a meteoric sea water mixing zone in this zone the oxygen and carbon isotopic compositions of these components are increased by about 2 4 pdb over their marine composition

paleointensity record in zero age submarine basalt glasses testing a new dating technique for recent morbs abstract thellier thellier paleointensity experiments were conducted on a collection of glasses from three very recent submarine axial flows two were erupted along the juan de fuca ridge at around 46 n and one along the east pacific rise south at around 18 s the within sample dispersion of paleointensity results from the animal farm flow epr south is very low and leads to a well defined mean value of 35 6 1 t 95 error on the mean based on 11 glass chips from four independent samples today s geomagnetic field intensity in the area is 31 2 t comparing animal farm results with published field model reference curves developed for the past 400 yr suggests an eruptive date estimated between 1880 a d and 1950 a d taking into account different sources of errors this is consistent with qualitative evidence for the age of this flow and constitutes the first precise demonstration of using paleointensity as a dating tool for very recent mid ocean ridge basalts morbs however in the juan de fuca area results show a more erratic pattern with samples varying by up to 30 higher and lower from the expected value of about 55 t the dispersion is attributed to the large local crustal magnetic anomalies in this area that can lead to inconsistent intensity values over the same unit local magnetic anomalies should thus always be checked when doing paleointensity on morb samples which should also be distributed as widely as possible in a flow unit when no significant magnetic anomalies are detected the paleointensity dating tool is anticipated to be especially efficient to investigate the volcanic cyclicity along the epr axis during the last several hundred years

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

gypsum to anhydrite transition in the miocene of southern poland abstract gypsum deposits in the carpathian foredeep of southern poland were altered daring burial to anhydrite this alteration did not completely destroy primary lithologic features different gypsum lithotypes have equivalents in the altered sulfate sections relics of and pseudomorphs after crystalline and sedimentary structures indicate that extensive replacement and cementation occurred early during burial diagenesis the replacement of gypsum by anhydrite was probably initiated in the shallow subsurface by high temperature and or reaction with brines of high salinity accordingly the importance of a deep burial for gypsum diagenesis in the studied area may have been overestimated

doppler sonar observations of internal waves wave field structure abstract during may of 1980 an internal wave measurement experiment was conducted from the research platform flip off the california coast this paper discusses an 18 day sequence of velocity profiles obtained during the experiment using a pair of doppler sonars the sonars profile to a depth of 700 m with approximately 20 m depth resolution plots of the velocity and shear field indicate the dominance of near inertial motions much of the near inertial variance can be ascribed to a few identifiable wave groups the progress of these groups can he tracked for many days the shear at the base of the mixed layer is often dominated by near inertial motions propagating vertically through the thermocline rather than wind forced motions in the mixed layer itself power spectral analysis suggests that the low frequency component of the wave field is dominated by the near inertial and tidal peaks and their harmonics the wisdom in modeling the low frequency wave field as an equivalent continuum is questioned

on the nature of internal wave spectra near a continental slope 1 amongst the most energetic motions in the deep ocean are internal waves supported by stable vertical stratification in density previously these waves were considered freely propagating as described by a smooth continuum internal wave band iwb frequency spectrum we studied details of the iwb using yearlong current observations from the bay of biscay instead of observing continuum iwb spectra near a continental slope we show that at least the first half decade of the iwb is dominated by motions at localized frequencies determined by strong non linear interactions between waves at the fundamental semidiurnal tidal and atmospherically induced inertial frequencies

skeletal aragonite neomorphism in plio pleistocene sandy limestones and sandstones hollywood florida usa abstract the basic mechanics of the neomorphism of aragonitic shells to calcite are generally understood but fundamental questions remain concerning the details of the process completely and partially neomorphosed aragonitic skeletal fragments recovered in cores of plio pleistocene limestones and sandstones from hollywood florida provide some insights into the process skeletal aragonite neomorphism occurred in a volume for volume manner across solution films which resulted in the preservation of ghosts of fine scale microstructures neomorphic calcite crystals that replaced skeletal aragonite in at least some instances inherited their crystallographic orientation from adjoining calcite cement crystals rather than from the host shell microstructure some neomorphic calcite crystals inherited the optical orientation of nearby echinoderm ossicles however host shell microstructure commonly controlled the direction of migration of the neomorphic replacement front anisotropies in shell solubility influenced the directional rates of growth of neomorphic calcite crystals as evidenced by the strong tendency for the boundaries between neomorphic calcite and aragonite to parallel or coinicide with shell microstructural features no examples were observed where neomorphic calcite replaced aragonite along euhedral crystal faces such as commonly occurs during dolomitization and the replacement of limestone by megaquartz

a 220 km2 recently erupted lava field on the east pacific rise near lat 8 s seamarc ii records show a 220 km2 area of unusually high reflectivity on the east pacific rise epr near lat 8 s which we interpret to be a recently erupted lava field this is the only segment of the epr exhibiting high reflectivity over such a large area in our continuous seamarc ii coverage from lat 8 n to 18 n and 3 s to 23 s the lavas appear to issue from the axial neovolcanic zone between lat 8 15 and 8 17 s the lava field extends up to 18km off axis and inundates scarps up to 100 m high on the basis of measurements of scarp heights just outside areas where they are buried we estimate the average thickness of the field to be 70 20 m thus the volume of the lava field is 15 4 km3 in comparison the average annual volcanic budget for the earth is approximately 4 5 km3 and the largest historic basaltic eruption from the icelandic laki fissure in 1783 was approximately 12 3 km3 when did the eruption occur comparative studies of acoustic reflectivity and photographed bottom characteristics elsewhere along the epr suggest that the lava field has little or no sediment cover and is very young this is also one of the only areas on the epr where earthquakes occur that do not appear to be caused by transform faulting if the earthquakes are related to the lava field then major eruptions may have occurred in 1964 1965 and 1969 a large helium plume near lat 13 s may be caused in part by eruptions of the lat 8 s lava field this is consistent with estimates of currents at 2 3 km depth which are such that a plume generated at lat 8 s would eventually appear off axis at lat 13 s our observations suggest that this spreading segment which is bounded by small ridge axis discontinuities at lat 8 05 s and 8 47 s may have been the most volcanically active segment along the epr during the past 25 yr

palaeoenvironmental reconstructions by stable isotopes of middle miocene gastropods of the central paratethys abstract the stable isotopes of carbon and oxygen were used to provide information of mixing of marine and freshwater and subsequently used to determine palaeosalinities in the middle to late miocene st margarethen zollhaus section upper sarmatian mactra zone pannonian a succession of three gastropod assemblages indicates changing environmental conditions from a limnic fluviatile to littoral mudflat and a sublittoral marine environment several shells of the main representatives of the three assemblages potamides hartbergensis hilber granulolabium bicinctum brocchi potamides disjunctus sowerby and additionally shells of lymnaea sp a typical freshwater gastropod and pomatias conicus a terrestrial gastropod were taken for stable isotope analyses oxygen and carbon isotope data of the freshwater endmember are distinctively lower 18 o 4 5 13 c 9 than of the marine endmembers 18 o 2 2 13 c 2 3 in contrast to the expected intermediate isotopic composition between the freshwater and marine environment the shells of supposed brackish environments have higher 18 o values than the shells of the marine environment these higher 18 o values are explained by evaporation which affected the protected areas of riverine to lacustrine environments and small pools on mudflats formerly considered to be the habitats of the brackish assemblages thus the oxygen and carbon isotope data extend the already existing palaeoenvironmental information

submeter bathymetric mapping of volcanic and hydrothermal features on the east pacific rise crest at 9 50 n 1 recent advances in underwater vehicle navigation and sonar technology now permit detailed mapping of complex seafloor bathymetry found at mid ocean ridge crests imagenex 881 675 khz scanning sonar data collected during low altitude 5 m surveys conducted with dsv alvin were used to produce submeter resolution bathymetric maps of five hydrothermal vent areas at the east pacific rise epr ridge2000 integrated study site 9 50 n bull s eye data were collected during 29 dives in 2004 and 2005 and were merged through a grid rectification technique to create high resolution 0 5 m grid composite maps these are the first submeter bathymetric maps generated with a scanning sonar mounted on alvin the composite maps can be used to quantify the dimensions of meter scale volcanic and hydrothermal features within the epr axial summit trough ast including hydrothermal vent structures lava pillars collapse areas the trough walls and primary volcanic fissures existing autonomous benthic explorer abe bathymetry data 675 khz scanning sonar collected at this site provide the broader geologic context necessary to interpret the meter scale features resolved in the composite maps the grid rectification technique we employed can be used to optimize vehicle time by permitting the creation of high resolution bathymetry maps from data collected during multiple coordinated short duration surveys after primary dive objectives are met this method can also be used to colocate future near bottom sonar data sets within the high resolution composite maps enabling quantification of bathymetric changes associated with active volcanic hydrothermal and tectonic processes

two stage neomorphism of jurassic aragonitic bivalves implications for early diagenesis abstract aragonitic bivalves in middle jurassic paralic limestones from lincolnshire eastern england have been neomorphically replaced by inclusion rich calcite spar textural features of neomorphic spar are analogous to examples from other calcitized jurassic molluscs but lincolnshire bivalves show evidence for two distinct stages of replacement staining cathodoluminescence and backscatter scanning electron microscopy reveal an initial volumetrically minor and frequently fabric selective replacement by nonferroan calcite with most of the remaining skeletal aragonite subsequently replaced by ferroan calcite spar stable isotope data from individual bivalves define a negative covariant mixing trend ranging from early relatively 13c depleted and 18o enriched nonferroan calcite d13c 2 pdb to ferroan calcite with composition similar to associated late pore filling cements d13c 2 pdb d1 o 7 pdb the early diagenetic end member precipitated from depositional pore fluids with bicarbonate supplied both from dissolution of skeletal aragonite and bacterial oxidation of organic material in contrast ferroan neomorphic spar precipitated during burial diagenesis and dewatering of shales surrounding the limestone bulk trace element signatures of the bivalves are dominated by late ferroan calcite but electron probe microanalysis and intrinsic blue cathodoluminescence shows that early neomorphic calcite contains negligible amounts of fe mn and mg together with isotopic and fabric data this indicates that early neomorphism occurred at shallow depths and may even have begun at the sediment water interface in the absence of through flowing meteoric waters early replacement did not proceed via an inward migrating neomorphic front instead calcitization was initiated at numerous individual reaction centers throughout the shells and was principally controlled by the distribution of the skeletal organic matrix this contrasts strongly with most previous reports of aragonite neomorphism during arly diagenesis

paleozoic mg calcite preserved implications for the carboniferous ocean modern mg calcite echinoderm skeletons are thought to lose mg so rapidly that no pre pleistocene ossicles retain their original mg concentrations however carboniferous echinoderm skeletons from the imo formation of arkansas and the holder formation of new mexico are reported herein that are still composed of mg calcite 7 8 to 14 5 mol mgco 3 their sr concentration is also high 620 to 3710 ppm the pore system in these echinoderm skeletons is filled with ferroan calcite or siderite that has not grown in optical continuity with the skeleton the discovery of carboniferous mg calcite confirms an interpretation already made from their diagenetic replacements marine mg calcite has been associated with proposed icehouse conditions and although the carboniferous echinoderm skeletons are compatible with this as they formed during gondwana glaciation they are too few to be of significance also they are organic secretions and so can override secular mineral trends based on inorganic precipitates the carboniferous echinoderm skeletons produced in tropical waters have a concentration of mg similar to values for modern echinoderms the simplest explanation for this similarity is that both precipitated by similar processes from oceans of similar composition this does not support predictions based on mass balance modeling that the mg ca ratio of the carboniferous ocean was half that of today9s the sr content of carboniferous echinoderms is less than that for modern echinoderms leading to a prediction of 6 ppm sr concentration for the carboniferous ocean further examples of mg calcite are required to substantiate these interpretations

dating and characterization of polymorphic transformation of aragonite to calcite in pleistocene bivalves from rhodes greece by combined shell microstructure stable isotope and electron spin resonance study absolute dating of diagenesis is a challenging yet significant problem reconstructing the depositional and diagenetic history of a late pleistocene coralligene type red algal reef and overlying maerl red algal sand from the plimiri coastal cliff se island of rhodes greece is enabled using a combination of microstructure stable isotope analyses and electron spin resonance of large bivalve shells partially altered by diagenesis these shells consisting of both original shell aragonite and polymorphic transformed rims now consisting of neomorphic spar provide the opportunity to date the primary age when the shells were precipitated as well as the age of their polymorphic transformation the contamination of samples presented a significant problem for interpreting ages based on data from electron spin resonance esr alone however sample contamination was evaluated with quantitative xrd providing the opportunity to apply corrections which increased reliability of the ages the carbon and oxygen stable isotope values and the neomorphic spar microtexture suggested that the polymorphic transformation at plimiri took place in a meteoric environment with a high and increasing fluid rock ratio the electron spin resonance dates combined with the vertical sedimentary evolution allowed to assign the formation of the red algal reef to the marine isotope stages 6 to 5e transgressive event ca 135 to 120 ka and to identify meteoric diagenetic phases during possibly the marine isotope stage 5d and the upper marine isotope stage 5c to lower 3 the use of electron spin resonance dating of neomorphic spar and age correction for sample contamination is presented herein for the first time and the results suggest that it might provide a useful tool to date late pleistocene diagenesis

high resolution geochemistry and sequence stratigraphy of the hushpuckney shale swope formation eastern kansas implications for climato environmental dynamics of the late pennsylvanian midcontinent seaway abstract the hushpuckney shale member of the swope formation missourian stage eastern kansas is the core shale of a kansas type cyclothem formed during the late transgressive to early regressive phases of a late pennsylvanian glacio eustatic cycle coeval high frequency climato environmental dynamics of the midcontinent seaway are preserved in the kgs orville edmonds no 1a study core as centimeter scale variation in major components organic carbon authigenic sulfides and phosphate detrital siliciclastics organic macerals trace element redox proxies mo u v zn and ichnofabric features benthic o 2 levels declined sharply from the base of the black shale 0 cm went sulfidic at 4 cm and reached a redox minimum at 21 cm above this level redox potential gradually rose fluctuating between sulfidic and nonsulfidic conditions from 35 cm to the black shale gray shale contact at 52 cm onset of dysoxic conditions at that contact allowed establishment of a benthic community of soft bodied organisms comprised of deep tiered tracemakers tolerant of low o 2 conditions trichichnus and shallow tiered tracemakers favoring soupground helminthopsis or firmground substrates the zoophycos phycosiphon schaubcylindrichnus planolites association most geochemical records exhibit a low order cycle spanning the full 52 cm thickness of the black shale submember reflecting a dominant glacio eustatic control the base and top of the black shale submember record lateral migration of the pycnocline across the midcontinent shelf during the transgressive and regressive phases respectively the maximum flooding surface mfs is at 17 23 cm an interval containing the euxinic peak and characterized by high concentrations of illite representing a cratonic siliciclastic flux and terrestrial organic macerals the product of transient increases in humidity weathering rates and the export of coal swamp vegetation associated with the interglacial highstand of the swope cyclothem although a transgressive surface of maximum starvation sms cannot be confidently identified a phosphate rich regressive condensation surface at 28 34 cm records pycnoclinal weakening due to increased aridity associated with renewed southern hemisphere icesheet growth a correlative shift in dominance from terrestrial to marine derived organic macerals reflects increased upwelling of nutrient rich deepwaters and enhanced primary productivity penecontemporaneous paleogeographic and climatic factors e g semirestricted circulation monsoonal precipitation predisposed the midcontinent seaway toward sensitivity to high frequency climato environmental fluctuations which are preserved as 2 to 7 cm thick cycles in the study core the 52 cm thick black shale submember contains 12 such high order cycles which have an estimated average duration of 2 to 9 kyr implying a sub milankovitch band i e millennial scale climatic control the results of this study are relevant to the sequence stratigraphic interpretation of kansas type cyclothems the dynamics of gondwanan ice age glacio eustatic cycles and the development of boundary conditions for late pennsylvanian paleoclimate models

dynamics and navigation of autonomous underwater vehicles for submarine gravity surveying we investigated the effect of autonomous underwater vehicle auv dynamics and navigation on underway submarine gravimetry our research was motivated by the need to obtain spatially dense marine gravity measurements close to the source of subkilometer scale geologic features in the shallow oceanic crust such measurements have been previously obtained for instance with piloted submarines and towed sleds however the high cost and in the case of on bottom measurements poor spatial sampling preclude routine acquisition of these measurements continuous underway gravity surveys with auvs is a compelling cost effective option but this method requires separating the auv accelerations from the measured gravity we show that auvs with a large distance between the center of buoyancy and the center of gravity have lower vertical accelerations than torpedo shaped auvs and consequentially are better suited for underway gravity surveys furthermore state estimators which combine sensor measurements and models of the vehicle s motion provide superior estimates of the vehicle s vertical accelerations than methods used in previous underway submarine gravity surveys we simulated the use of these navigation methods in detecting dike swarms at the east pacific rise analysis showed that we can shorten filters used in reducing gravity data and consequentially provide improved measurements of the free water anomaly with a minimal detectable spatial wavelength approximately 65 lower than previously reported results

gradients in seasonality and seawater oxygen isotopic composition along the early permian gondwanan coast se australia abstract oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater both locally and globally microsampled accretionary calcite from two species of the fossil bivalve eurydesma sowerby and morris 1845 collected from sediments of cisuralian age in high latitude marine sediments along the se coast of australia records cyclic seasonal fluctuations in shell 18 o values during growth demonstrating the primary nature of the isotope signal and thus allowing investigation of early permian seawater isotopic composition and water temperature in the high southern latitudes the mean and seasonal range of 18 o carb decreases poleward across about 10 of paleolatitude 67 s 77 s the presence of co occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near freezing thus permitting calculation of realistic estimates of water composition and summer temperatures summer 18 o carb values indicate water temperatures between 5 c and 12 c with warmer values at lower latitudes the decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the gondwanan coast is much like that observed along high latitude coastlines today calculated 18 o water decreases toward the pole likely associated with an increasing contribution of isotopically light fresh water derived from summer snow melt the gradient in 18 o water is similar to that documented over a similar span of latitude on the modern se greenland coast we infer the presence of a north flowing coastal current of cold o 18 depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole 18 o values in se australia however are about 3 lower than those off greenland suggesting comparatively lower salinity water or more o 18 depleted glacial ice runoff in the permian gondwanan high latitudes perhaps augmented by more depleted negative global average seawater conditions in southeastern australia during the largest of the permian deglaciations were warmer than present day antarctica at similar latitudes but may approximate those of early mid miocene antarctica with frozen winters but summers closer to 10 c

aragonite calcite transformation based on pennsylvanian molluscs a mineralogical microstructural and geochemical approach was used to trace the postdepositional alteration of molluscs and to quantify the biogenic aragonite to calcite transformation in the boggy formation mid desmoinesian of oklahoma the results show that with progressive alteration primary biogenic aragonite was gradually replaced by diagenetic low mg calcite during the initial phase of alteration the nacreous tablets of the shell layers fused and with progressive postdepositional diagenesis they were replaced by either fine or coarsegrained calcite during this diagenetic transformation no significant changes in chemical concentrations were noted for ba cu ni pb and zn whereas mg mn and fe increased by factors of about 14 to 25 relative to their depositional concentrations concurrently na sr 18 o and 13 c concentrations decreased by factors ranging from 2 5 to 10 under similar diagenetic conditions matrix samples were more altered than were contemporaneous fossils and it is postulated that grain size surface area was a major control on the degree of alteration of carbonate grains the matrix of the boggy formation has retained sufficient geochemical information to suggest an original aragonitic limemud precursor of nonmolluscan affinity with the geochemical methods and quantified trends the least altered mollusc samples of the boggy formation consisting of only aragonite can be identified geochemical data of the most altered samples suggest that the diagenetic fluids which affected boggy sediments and fossils were similar in composition to meteoric water moreover the dissolving aragonite through diffusion controlled dissolution determined the elemental as well as isotopic chemistry of the diagenetic calcite in the altered shells it is postulated that similar diagenetic waters and processes affected sedimentary units of the breathitt pennsylvanian kentucky brush creek pennsylvanian pennsylvania ohio lukow jurassic poland bear paw lea park cretaceous western canada and nugssuaq cretaceous greenland formations which contain well preserved aragonitic molluscan faunas