reconstructing past seawater mg ca and sr ca from mid ocean ridge flank calcium carbonate veins proxies for past seawater chemistry such as mg ca and sr ca ratios provide a record of the dynamic exchanges of elements between the solid earth the atmosphere and the hydrosphere and the evolving influence of life we estimated past oceanic mg ca and sr ca ratios from suites of 1 6 to 170 million year old calcium carbonate veins that had precipitated from seawater derived fluids in ocean ridge flank basalts our data indicate that before the neogene oceanic mg ca and sr ca ratios were lower than in the modern ocean decreased ocean spreading since the cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early tertiary may explain the recent rise in these ratios

a scenario of mesozoic cenozoic ocean circulation over the blake plateau and its environs after the continental breakup of north america africa and europe a sluggish wind driven circulation gyre probably formed in the juvenile north atlantic basin surface flow in the western atlantic ocean during the early cretaceous likely was northward along the seaward edge of an extensive reef that flourished offshore of north america sometime during the late cretaceous the surface circulation in the gulf of mexico had evolved into a clockwise rotary pattern as the exchange of water with the pacific ocean diminished by latest cretaceous time a vigorous easterly current flowed through the suwannee strait of southern georgia and northern florida injecting copious amounts of water and sediment into the western blake plateau basin this flow pattern apparently persisted into paleocene time during late paleocene and early eocene time strong northerly flow through the straits of florida and across the blake plateau was established this represented the onset of gulf stream circulation over the blake plateau the position of the gulf stream shifted repeatedly across the northern and central plateau during the tertiary and quaternary periods the westernmost track was located along the inner blake plateau parallel to the florida hatteras slope the easternmost track was 500 m lower bathymetrically and crossed the central plateau and continental slope just north of the blake spur the gulf stream apparently shifted in response to changes in water depth on the blake plateau that accompanied global fluctuations of sea level during rises of sea level the gulf stream drifted westward until it impinged on the florida hatteras slope and outer shelf during lowerings of sea level the gulf stream was deflected progressively eastward across the central plateau by the charleston bump a prominent bathymetric bulge of the northern blake plateau

stratigraphic framework and petroleum potential of northeastern baltimore canyon trough mid atlantic outer continental shelf geologic data from 29 wells in the baltimore canyon trough were released to the public as of 1982 and provide sufficient information for establishing upper jurassic through cenozoic rock stratigraphic units most of the units are lithologically similar to formations on the scotian shelf and are therefore considered in this study to be the scotian shelf homotaxial equivalents the oldest rocks penetrated by exploratory wells in the baltimore canyon trough are of late jurassic age and are correlative to the scotian shelf mohawk mic mac and abenaki formations the mohawk sandstone and mic mac shale equivalents in the baltimore canyon trough represent lower delta plain to predominantly prodelta environments and the abenaki equivalent limestone represents a shelf margin carbonate buildup delta progradation continued during the early cretaceous and lower delta plain and delta front sand and shale equivalent to the scotian shelf missisauga formation were deposited a destructional phase of the delta is represented by the naskapi equivalent a calcareous shale inundation by the sea was incomplete however and channel and distributary mouth bar sands logan canyon equivalent were deposited a final marine transgression began during the late cretaceous and resulted in the deposition of mudstone which is considered equivalent to the sco ian shelf dawson canyon formation marine conditions prevailed through much of the remainder of the cretaceous and cenozoic in both the scotian shelf and baltimore canyon trough areas lithologic similarities between cenozoic units of the scotian shelf and baltimore canyon trough are less significant although both basins exhibit an upward increase in sand content the scotian shelf cenozoic strata are more sandy than those in the baltimore canyon trough in ascending order the baltimore canyon trough cenozoic section consists of the uppermost dawson canyon equivalent a chalk unit a mudstone unit an unconsolidated sand unit and an uppermost clay unit stratigraphic traps may be present in the baltimore canyon trough upper jurassic and lower cretaceous deltaic sandstones and shelf margin carbonates the deltaic units contain channel and distributary mouth bar sandstones which may be potential reservoirs seals may be formed by lateral and vertical contacts against the prodelta interdistributary bay and marine shales the abenaki stratigraphic reef trend provides another potential target source rocks reservoir rocks and traps may be associated with the trend but its potential can only be defined by future drilling

40ar 39ar age of detrital muscovite within lower ordovician sandstone in the coastal plain basement of florida implications for west african terrane linkages detrital muscovite was concentrated from a core of lower ordovician sandstone recovered from 1282 m in the sun oil company h t parker no 1 well marion county florida the concentrate records a 40ar 39ar plateau age of 504 1 2 1 ma the paleozoic sedimentary section penetrated in this well is part of an extensive subsurface lower ordovician middle devonian sedimentary succession characterized by gondwanan paleontological affinities the succession has been correlated with sequences of similar age in the bove basin of west africa which unconformably overlie metamorphic units of the bassaride and rokelide orogens in senegal and guinea muscovite within these metamorphic rocks records ca 500 510 ma postmetamorphic 40ar 39ar cooling ages and was likely a proximal source for the lower paleozoic clastic detritus represented in the pre mesozoic sedimentary sequences beneath the southeastern united states coastal plain

stratigraphic and palaeoenvironmental summary of the south east georgia embayment a correlation of exploratory wells a continental offshore stratigraphic test cost well and six exploratory wells have been drilled in the south east georgia embayment the oldest rocks penetrated are weakly metamorphosed lower ordovician quartz arenites and silurian shales and argillites in the transco 1005 1 well and upper devonian argillites in the cost ge 1 well these marine strata which are equivalent to the tippecanoe sequence in florida underlie the post rift unconformity and represent part of a disjunct fragment of gondwana that was sutured to the north american craton during the late palaeozoic alleghanian orogeny the palaeozoic strata are unconformably overlain by interbedded non marine jurassic bajocian and younger sandstones and shales and marginal marine lower cretaceous sandstones calcareous shales and carbonates which contain scattered beds of coal and evaporite together these rocks are stratigraphically equivalent to the onshore fort pierce and cotton valley formations and rocks of the lower cretaceous comanchean provincial series the abundance of carbonates and evaporites in this interval which reflects marine influences within the embayment increases upwards eastwards and southwards the upper cretaceous part of the section is composed mainly of neritic calcareous shales and shaley limestones stratigraphically equivalent to the primarily marginal marine facies of the onshore atkinson cape fear and middendorf formations and black creek group and to limestones and shales of the lawson limestone and peedee formations cenozoic strata are primarily semiconsolidated marine carbonates palaeocene to middle eocene strata are commonly cherty middle miocene to pliocene strata are massive and locally phosphatic and glauconitic quaternary sediments are dominated by unconsolidated carbonate sands the effects of eustatic changes and shifts in the palaeocirculation are recorded in the upper cretaceous and tertiary strata

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

mesozoic stratigraphy and paleoenvironments of the georges bank basin a correlation of exploratory and cost wells abstract the exxon 975 1 conoco 145 1 and mobil 312 1 hydrocarbon exploratory wells and the continental offshore stratigraphic test cost g 1 and g 2 wells were drilled in the southeastern part of the georges bank basin we used drill cuttings and logs from these wells to describe and correlate the dominant lithostratigraphic units and to document lateral changes in the depositional environments the strata penetrated by the exxon 975 1 and cost g 1 wells are much more terrestrial than at the seaward downdip cost g 2 conoco 145 1 and mobil 312 1 wellsites oldest rocks penetrated by the exploratory wells represent a middle jurassic carbonate evaporite sequence that correlates to the iroquois formation the iroquois records nonmarine to marginal marine sabkha tidal flat and restricted lagoonal paleoenvironments in the exxon 975 1 and cost g 1 wells but progressively changes to inner neritic littoral and lagoonal paleoenvironments at the mobil 312 1 wellsite the nonmarine deltaic siliciclastics of the overlying mohican formation misaine shale and mic mac mohawk formations are thicker and the marine carbonates of the scatarie and bacarro limestones are usually thinner in the jurassic strata of the exxon 975 1 and cost g 1 wells than at the other wellsites similarly lower delta plain and delta front facies of the early cretaceous missisuaga and logan canyon formations at the exxon 975 1 and cost g 1 wellsites reflect a greater terrestrial influence than the laterally equivalent shallow marine to delta front facies present at the downdip wellsites

gulf trough the atlantic connection analyses of seismic reflection profiles and stratigraphic data indicate a continuation of the gulf trough trend across eastern south carolina and offshore between cape fear and cape hatteras north carolina seismic profiles show a linear northeast trending zone of nondeposition and erosion and areas of chaotic deposition in the eocene and oligocene sections the character of deposition and erosion along this trend is similar to that produced by bottom currents under the core of the present gulf stream the trend separates deep water from shallower water deposits indicating that the erosion was produced by strong marine currents flowing through the gulf trough in the high sea levels of middle eocene through early oligocene time

cenozoic seawater sr ca evolution records of seawater chemistry help constrain temporal variations in geochemical processes that impact the global carbon cycle and climate through earth s history here we reconstruct cenozoic seawater sr ca sr casw using fossil conus and turritellid gastropod sr ca combined with an oxygen isotope paleotem perature record from the same samples the gastropod record suggests that sr casw was slightly higher in the eocene 11 4 3 mmol mol than today 8 54 mmol mol and remained relatively stable from the mid to late cenozoic we compare our gastropod cenozoic sr casw record with a published turritellid gas tropod sr casw record and other published biogenic benthic foraminifera fossil fish teeth and inorganic pre cipitate calcite veins sr casw records once the uncertainties with our gastropod derived sr casw are taken into account the sr casw record agrees reasonably well with biogenic sr casw records assuming a seawater ca history derived from marine evaporite inclusions all biogenic based sr casw reconstructions imply decreasing seawater sr through the cenozoic whereas the calcite vein sr casw reconstruction implies increasing sr through the cenozoic we apply a simple geochemical model to examine the implications of divergence among these seawater sr reconstructions and suggest that the interpretation and uncertainties associated with the gastropod and calcite vein proxies need to be revisited used in conjunction with records of carbonate depositional fluxes our favored seawater sr ca scenarios point to a significant increase in the proportion of aragonite versus calcite deposition in shelf sediments from the middle miocene coincident with the proliferation of coral reefs we propose that this occurred at least 10 million years after the seawater mg ca threshold was passed and was instead aided by declining levels of atmospheric carbon dioxide

sr mg ratios of modern marine calcite empirical indicators of ocean chemistry and precipitation rate holocene biotic and abiotic marine calcite have a similar range of mg contents 0 to 22 and 4 to 21 mol mgco3 respectively yet biotic calcite has sr2 concentrations that are consistently 1250 ppm higher than those of abiotic calcite as in laboratory experiments a positive linear relation is observed between dsr and calcite mg content this produces two distinct linear trends on a plot of sr2 vs mg2 concentrations principal axes of variation for both trends have similar slopes yet distinctly different sr2 concentration intercepts biotic y 0 024x 1298 r2 0 70 abiotic y 0 027x 47 r2 0 77 the similar slopes of these trends reflect the constancy of mgca and srca ratios of modern seawater equations describing the dependence of dsr on calcite mg content are derived from both trends biotic dsr 3 16 x 10t 6 ppm mg 0 169 abiotic dsr 3 52 x 10 6 ppm mg 0 0062 characterization of sr mg trends for holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater mgca and srca ratios the relatively high sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms calcites precipitated from seawater in laboratory experiments have dsr values that are similar to those of biotic marine calcite suggesting that both precipitate at approximately the same rate our estimates of surface area normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded ph stat experiments we conclude that the dsr values for biotic and experimental marine calcite are kinetically controlled whereas the lower precipitation rates of abiotic marine calcite yield dsr values that approximate equilibrium conditions experimentally derived equations describing the relation between dsr and calcite precipitation rate indicate that the offset in sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates however observations of naturally occurring marine cements suggest that the five order of magnitude offset best represents natural system processes

offshore extent of gondwanan paleozoic strata in the southeastern united states the suwannee suture zone revisited abstract the recognition of the suwannee terrane in southeastern north america was a critical step in advancing our current understanding of the tectonic evolution of ocean basins unfortunately further clarification of the boundaries of the suwannee terrane has proven difficult due to the thick coastal plain cover limited well log analyses and a paucity of seismic reflection data onshore we present the results from a new compilation and analysis of legacy marine seismic reflection refraction and well data from offshore the southeastern united states which reveals in the subsurface a previously unmapped lower paleozoic sedimentary section spanning the continental shelf from florida to north carolina previously only identified in two deep offshore wells cost ge 1 and transco 1005 1 this paleozoic platform sequence is identified in seismic reflection profiles as a package of low frequency sub horizontal laterally continuous reflectors which are clearly discordant with and distinct from the overlying mesozoic and cenozoic stratigraphy above the post rift unconformity pru the inferred base of the paleozoic sequence is marked by the downward diminution of parallel seismic reflectors as well as an increase in seismic velocities to 6 km s observed on numerous offshore seismic refraction surveys while clearly deformed in some areas these paleozoic strata are generally sub horizontal range in thickness from 4 to 6 km and can be mapped continuously over an area in excess of 130 000 km 2 similar sedimentary rocks have been recognized from onshore exploration wells in florida since the 1930s and were subsequently identified to be part of the suwannee basin within the larger exotic suwannee terrane of gondwanan affinity recognition of the presence and extent of these gondwanan strata offshore implies 1 the inferred position of the suwannee suture zone offshore lies 200 km further north approximately along the boundary between the carolina terrane and the charleston terrane 2 previously identified terranes brunswick charleston suwannee northern florida are likely distinct crustal blocks but their amalgamation predates deposition of the overlying paleozoic section of the suwannee basin 3 collectively this crust represents the gondwanan continent based on the size and presence of a stable platform stratigraphy nominally doubling the size of the last sutured terrane the suwannee terrane

coccolith sr ca as a new indicator of coccolithophorid calcification and growth rate 1 polyspecific coccolith separates from core top sediments in the eastern equatorial pacific show variations of 15 in sr ca ratios across the equatorial upwelling zone with sr ca highest at the equator and decreasing off axis these variations cannot be due to changes in the sr ca of seawater which varies by less than 2 in the surface ocean variations in sr ca of coccolith sediments are similar to variations in primary productivity and alkenone estimated coccolithophorid growth rates in overlying surface waters and to caco3 rain rates measured in sediment traps because of these relationships and because calcification rate exerts a strong control on sr ca in abiogenic calcites we suggest that the observed sr ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates although temperature may also influence coccolith sr ca to a lesser degree changes in dissolution intensity and coccolith assemblages appear to exert a minor influence if any on coccolith sr ca in these sediment core tops if further work confirms relationships between coccolith sr ca and coccolithophorid productivity sr ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon an important control on deep ocean ph and partitioning of co2 between the atmosphere and ocean in addition coccolith sr ca might provide an independent record of past changes in coccolithophorid growth rates which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved co2 in the surface ocean

empirical partition coefficients for sr and ca in marine barite implications for reconstructing seawater sr and ca concentrations 1 a robust record of fluctuations in seawater sr and ca concentrations is critical for understanding the long term global carbon cycle as it is influenced by the history and location of carbonate precipitation chemical weathering and hydrothermal activity such a record is also necessary for interpretation of paleoceanographic records temperature productivity derived from carbonate sources e g sr ca mg ca li ca marine barite an inorganic phase preserved in oxic deep sea sediments may record seawater sr and ca concentrations using core top barite samples we have derived the partition coefficients for sr dsr 2 9 10 5 ca dca 1 9 10 8 and sr ca dsr ca 1 6 103 in barite the natural variability of core top marine barite sr ca sr ba and ca ba ratios selected from different ocean basins is 10 1 15 0 and 16 3 respectively since estimates of cenozoic fluctuations in seawater sr ca ratios are large possibly greater than 80 relative to the variability recorded in core tops marine barite may be used to reconstruct seawater sr ca ratios and sr and ca concentrations using empirically derived partition coefficients

a biomineralization model for the incorporation of trace elements into foraminiferal calcium carbonate measurements of srca of benthic foraminifera show a linear decrease with water depth which is superimposed upon significant variability identified by analyses of individual foraminifera new data for cdca support previous work in defining a contrast between waters shallower and deeper than 2500 m measured element partition coefficients in foraminiferal calcium carbonate relative to sea water d have been described by means of a one box model in which elements are extracted by rayleigh distillation from a biomineralization reservoir that serves for calcification with a constant fractionation factor such that d 1 f 1 f where f is the proportion of ca remaining after precipitation a modification to the model recognises differences in element speciation the model is consistent with differences between dsr dba and dcd in benthic but not planktonic foraminifera depth variations in d for sr and ba are consistent with the model as are differences in depth variation of dcd in calcitic and aragonitic benthic foraminifera the shallower depth variations may reflect increasing calcification rates with increasing water depth to an optimum of about 2500 m observations of unusually lower dcd for some deep waters not accompanied by similar dsr or dba may be because of dissolution or a calcification response to a lower carbonate saturation state

rift basins of the long island platform four buried early mesozoic rift basins on the long island platform region of the united states atlantic continental margin were mapped using seismic reflection magnetic and gravity data low angle normal border faults and high angle cross faults control the structure of three of the basins and some of these faults can be traced deep into the crust faulted basement blocks characterize the fourth basin adjacent basins form pairs in which the border faults dip toward each other and may have acted to localize crustal thinning two phases of rifting took place an early stage characterized by widespread faulting leading to basin formation and a late stage characterized by uplift and erosion near the hinge zone and subsidence seaward of the hinge zone the new york bight basin at the western end of the platform may be an offshore extension of the hartford basin paleozoic tectonic and structural trends are inferred to be the primary controls on the location of these basins although our data are not specific enough to address local structural details

rise and demise of the bahama grand banks gigaplatform northern margin of the jurassic proto atlantic seaway abstract an extinct 5000 km long jurassic carbonate platform and barrier reef system lies buried beneath the atlantic continental shelf and slope of the united states a revised stratigraphic framework a series of regional isopach maps and paleogeographic reconstructions are used to illustrate the 42 m y history of this bahama grand banks gigaplatform from its inception in aalenian early middle jurassic time to its demise and burial in berriasian valanginian time early early cretaceous aggradation progradation rates for the gigaplatform are comparable to those of the familiar capitan shelf margin permian and are closely correlated with volumetric rates of siliciclastic sediment accumulation and depocenter migration siliciclastic encroachment behind the carbonate tracts appears to have been an important impetus for shelf edge progradation during the early cretaceous sea level changes combined with eutrophication due to landward soil development and seaward upwelling and the presence of cooler upwelled waters along the outer shelf appear to have decimated the carbonate producers from the carolina trough to the grand banks this allowed advancing siliciclastic deltas to overrun the shelf edge despite a notable reduction in siliciclastic accumulation rates however upwelling did not extend southward to the blake bahama megabank so platform carbonate production proceeded there well into the cretaceous subsequent stepwise carbonate abatement characterized the blake plateau basin whereas the bahamas have maintained production to the present the demise of carbonate production on the northern segments of the gigaplatform helped to escalate deep water carbonate deposition in the early cretaceous but the sudden augmentation of deep water carbonate reservoirs in the late jurassic was triggered by other agents such as global expansion of nannoplankton communities

quality assessment of potable water in the town of kolasib mizoram india the potable water for the residents of the town of kolasib in mizoram state india is supplied by the public health engineering department phed of the government of mizoram without any notable treatment the source of water is the tuichhuahen river flowing from north to south in the area water samples were analyzed for their physicochemical and bacteriological characteristics in order to obtain the current quality level of the potable water in the twon the samples were collected from two different sources i e the supply from the government agency phed and from the naturally occurring springs tuikhurs the results suggest that the water supplied by the phed is better than that from the tuikhurs however the quality of water from both sources which are used for drinking and domestic purposes were found to be more or less within the tolerance limits

florida a jurassic transform plate boundary magnetic gravity seismic and deep drill hole data integrated with plate tectonic reconstructions substantiate the existence of a transform plate boundary across southern florida during the jurassic on the basis of this integrated suite of data the pre cretaceous florida bahamas region can be divided into the pre jurassic north american plate jurassic marginal rift basins and a broad jurassic transform zone including stranded blocks of pre mesozoic continental crust major tectonic units include the suwannee basin in northern florida containing paleozoic sedimentary rocks a central florida basement complex of paleozoic age crystalline rock the west florida platform composed of stranded blocks of continental crust the south georgia rift containing triassic sedimentary rocks which overlie block faulted suwannee basin sedimentary rocks the late triassic jurassic age apalachicola rift basin and the jurassic age south florida bahamas and blake plateau marginal rift basins the major tectonic units are bounded by basement hinge zones and fracture zones fz the basement hinge zone represents the block faulted edge of the north american plate separating paleozoic and older crustal rocks from jurassic rifted crust beneath the marginal basins fracture zones separate mesozoic marginal sedimentary basins and include the blake spur fz jacksonville fz bahamas fz and cuba fz bounding the blake plateau bahamas south florida and southeastern gulf of mexico basins the bahamas fz is the most important of all these features because its northwest extension coincides with the gulf basin marginal fault zone forming the southern edge of the north american plate during the jurassic the limited space between the north american and the south american african plates requires that the jurassic transform zone connecting the central atlantic and the gulf of mexico spreading systems was located between the bahamas and cuba fz s in the region of southern florida our plate reconstructions combined with chronostratigraphic and lithostratigraphic information for the gulf of mexico southern florida and the bahamas indicate that the gulf was sealed off from the atlantic waters until callovian time by an elevated florida bahamas region restricted influx of waters started in callovian as a plate reorganization and increased plate separation between north america and south america africa produced waterways into the gulf of mexico from the pacific and possibly from the atlantic

what do we know about the evolution of mg to ca ratios in seawater 1 although most reconstructions of the evolution of the mg to ca ratio in seawater conclude that it has increased during the course of the cenozoic they disagree widely regarding the magnitude of this change on the basis of fluid inclusion and caco3 mineralogy observations the increase was at least threefold on the basis of mg content of foraminifera shells it was only a factor of 1 7 a recently published reconstruction based on the mg content of calcite fillings of voids in ridge flank basalts lends support to the conclusion that the change was severalfold but as it is very difficult to come up with a plausible geologic scenario which could account for such a large change we lean toward the smaller estimate based on the magnesium content of foraminifera shells

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

new cocorp profiling in the southeastern united states part i late paleozoic suture and mesozoic rift basin new cocorp profiling in the southeastern united states has revealed a broad zone of dipping reflections that extends downward through the crust beneath the coastal plain in western georgia the zone is over 50 km wide and most of the reflections dip moderately steeply toward the south regional considerations suggest that this feature marks the late paleozoic suture between north america and africa where crossed by the cocorp survey the suture occurs beneath the north flank of the triassic early jurassic south georgia basin the main depocenter of the south georgia basin occurs about 90 km to the south and is formed by a large half graben containing more than 5 km of rift basin fill farther south the paleozoic suwannee basin sequence beneath northern florida is poorly imaged on the cocorp profiles however weak reflections suggest that these strata including basal felsic volcanics may have an aggregate thickness of about 6 km in north central florida at the northwest end of the cocorp traverse a prominent horizon imaged in the upper crust beneath the inner piedmont probably marks the southern appalachian detachment the detachment appears to be cut off by the towaliga fault implying that the towaliga fault is in part a down to the north normal fault intermittent moho reflections occur at 11 12 s two way time along the length of the cocorp survey indicating that the crust in the region has a roughly uniform thickness of about 33 36 km assuming an average crustal velocity of 6 km s

strontium to calcium ratios in the marine gastropod conus ermineus growth rate effects and temperature calibration here we investigate the potential of sr ca ratios in the marine gastropod conus ermineus for reconstructing seawater temperatures we present annually resolved records of sr ca and 18o for four shells collected alive from the flower garden banks national marine sanctuary in the gulf of mexico our results show that variations in sr ca and 18o covary with the in situ seasonal temperature cycle sr ca and temperature are positively correlated in contrast with the inverse relationship found in inorganically precipitated aragonite the seasonal sr ca variability is superimposed on a long term trend of increasing sr ca with age both the seasonal and long term ontogenetic changes in sr ca are associated with variations in growth rate defined here as the shell linear extension rate ler the seasonal variability in ler is superimposed on a long term decrease with ontogeny thus the covariance of sr ca ratios with temperature and ler suggests that sr incorporation is likely driven by temperature influence on growth rate rather than by thermodynamic effects unlike the seasonal variability the ontogenetic effect is characterized by inverse covariation between sr ca and ler suggesting that sr ca variability is not controlled by growth rate alone but probably by two different biomineralization mechanisms one related to temperature and the other related to age we use the seasonal sr ca signal of four shells to construct a temperature calibration to minimize the ontogenetic effects we separate the records into juvenile and adult growth stages and calculate the sr ca temperature t relationships juvenile sr ca mmol mol 1 0 042 0 008 t c 0 24 0 21 r2 0 66 adult sr ca mmol mol 1 0 072 0 014 t c 0 05 0 34 r2 0 68 applying the calibration to a single specimen provides mean annual temperature estimates within 1 c of the in situ temperature record but resolves the seasonal variability only within 3 5 c the large error in the seasonal estimates reflects the high variability among specimens to reduce the uncertainty on seasonal temperatures we propose combining records from multiple shells to generate an average temperature record the potential of this approach needs however to be validated in other locations

the relationship between shell size and mg ca sr ca δ18o and δ13c of species of planktonic foraminifera the relationship between shell size and mg ca sr ca 18o and 13c of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions mg ca increases and sr ca decreases with increasing size except for two globorotaliid species which show the opposite trend the changes in mg ca broadly follow 18o calcification temperatures except that surface and near surface dwelling species show larger changes in mg ca than can be accounted for by differences in calcification temperature derived from 18o the increases in mg ca and decreases in sr ca vary linearly with the well established increase in 13c with size this is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition it appears that variations in calcification rate affect mg and sr shell chemistry the observations may account for part of the temporal variability in foraminiferal sr ca within a single size fraction that has been attributed to changes in seawater sr ca