the impact of hurricane diana on the north carolina continental shelf abstract intense storms including hurricanes are believed to have an important impact upon the biota and sediment cover on the continental shelf hurricane diana crossed onslow bay north carolina during september 1984 and provided an opportunity to examine its effect on the sea floor an area in the bay transited by the hurricane had been surveyed previously by side scan sonar 3 5 khz echosounding and underwater television we re surveyed the area in november 1984 with the same techniques and collected box cores for sedimentary structure analysis the post hurricane survey yielded no unequivocal evidence of hurricane impact on the sea floor and surprisingly showed an abundance of seemingly delicate benthic organisms thriving on the impacted area sedimentary structures in the box cores included rip up clasts and cross laminations that are indicative of a dynamic sedimentary environment but they could have formed during non hurricane storm conditions the lack of a dramatic signature on the sea floor from hurricane diana is attributed to the low sediment influx and frequent occurrence of intense storms on the north carolina shelf these factors result in an armored depositional environment that shows little response to the passage of each successive storm

blake plateau control of miocene sedimentation patterns by large scale shifts of the gulf stream axis the distribution of buried channel networks within cenozoic sequences of the blake plateau and their correlation with global sea level oscillations indicate that the gulf stream axis shifted landward against the florida hatteras slope during sea level high stands and seaward across the central blake plateau during sea level lowstands a sedimentation model incorporating axial shifts of the gulf stream successfully predicts the miocene stratigraphy of the florida hatteras slope and blake plateau as defined by seismic and drill hole data

an integrated stratinomic model for the genesis and concentration of small shelly fossil style phosphatic microsteinkerns in not so exceptional conditions abstract carbonate fluorapatite filled millimeter scale microsteinkerns are a key element of the small shelly fossil ssf fauna generally associated with the late proterozoic cambrian the purported disappearance of these fossils and this style of phosphatic preservation during the cambrian stage 2 botomian extinction has been linked to changes in ocean chemistry and or changes to the physical environment due to the evolution of metazoans as well to the changing role of metazoans in the marine environment through a qualitative meta analysis of existing literature we document a broader temporal distribution for ssf style preservation than previously recognized we examine these occurrences for common patterns of depositional conditions and we offer a conceptual model for both the origin of the phosphatic microsteinkerns and their eventual concentration in certain sediments based on known biogeochemical diagenetic processes of authigenic calcium fluorapatite precipitation phosphogenesis and subsequent concentration of phosphatic sedimentary particles this polycyclic phosphogenic condensation ppc model makes predictions as to how and where this form of preservation might occur in cambrian and non cambrian marine strata alike

hiatal duration of correlative sequence boundaries from oligocene pliocene mixed carbonate siliciclastic sediments of the south florida platform abstract sequence boundaries defined by regional unconformities in mixed carbonate siliciclastic sediments have a variable duration from the margin to the interior of the florida platform factors controlling the timing and duration of these unconformities include a combination of global eustatic and regional mechanisms sediment supply current intensification integrated chronostratigraphies developed from a transect of continuous cores in the south central interior to the southern margin of the florida platform show an increase in duration of the hiatal gaps along correlative sequence boundaries toward the platform edge two sequence boundaries are correlated across the south florida platform and mark formation contacts the lower sequence boundary sb a marks the suwannee limestone arcadia formation contact and is of significantly less duration in the platform interior southwest peninsular florida 2 0 m y than at the south platform margin middle florida keys 8 1 m y the hiatal gap along the upper sequence boundary sb b marking the arcadia formation overlain by miocene pliocene sediments that vary in age and composition regionally records the same increase from the central part of the platform southwest florida arcadia fm peace river fm 1 6 m y to the south platform edge lower florida keys arcadia fm stock island fm 11 5 m y eustatic fluctuations affected the relative sedimentation rates of the mixed sediments in the platform interior and at the margin most notably the large eustatic fall at the end of the early oligocene terminated carbonate deposition of the suwannee limestone sb a sediment accumulation on the platform interior was more temporally continuous than at the margin because of greater siliciclastic input from the north the strengthening of marine currents beginning in the middle miocene limited sediment accumulation across the southern platform margin sb b and possibly caused erosion of the margin carbonates increasing the duration of the hiatal gap on top of the arcadia formation

a specimen based approach to reconstructing the late neogene seabird communities of california abstract california has experienced major climate change from the early miocene 23 ma to the present fossil seabirds are useful for studying marine faunal responses to these changes because they are numerous in museum collections and easily identified to the family level from fragmentary remains because extant seabirds respond quickly to environmental changes we hypothesize that the fossil record of crown group miocene seabirds will reflect past environments previous studies of fossil seabird diversity through the cenozoic of the north pacific relied mainly on literature records to describe the appearance and disappearance of seabird species and correlated these patterns to geologic and climatic events our study uses an empirical specimen based approach to describe the seabird response to climate and tectonic change during 12 million years of coastal california s geologic history middle miocene to early pliocene the foundation of our dataset is 242 fossil seabird specimens from orange county the strata from orange county form the basis for delineating chronostratigraphic bins used for studying 285 additional seabird fossils from other parts of california for a total of 527 seabird fossils examined our results show a relationship between pelagic seabirds and offshore facies as well as a clear increase of pan alcid abundance and decline of sulid abundance through time this pattern may be the result of taphonomic bias combined with the effect of shallower facies preserved through time the increase in pan alcid abundance is also coincident with global climatic and tectonic changes and with enhanced and stable nutrient upwelling upwelling through this time also helps to explain morphological changes in salmon and speciation rates in marine mammals the specimen based methodology used here can be applied to contemporaneous taxa such as marine mammals to quantitatively analyze diversity during the late neogene and further explore the relationship between physical drivers and faunal change

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

lithology based sequence stratigraphic framework of a mixed carbonate siliciclastic succession lower cretaceous atlantic coastal plain this study presents a lithology based sequence stratigraphic framework and depositional model for lower cretaceous mixed siliciclastic carbonate sediments of the mid atlantic coastal plain eastern united states lithologic data from cores and cuttings were integrated with wireline logs and two dimensional seismic data to document lithofacies variability and stacking patterns across the albemarle basin of eastern north carolina ten facies associations are defined which are variably present within siliciclastic and carbonate dominated depositional profiles interpreted to extend from onshore lowland coastal plain to deep shelf depositional environments three depositional sequences 0 1 2 were identified each with component upward shoaling parasequences seismic reflectors typically coincided with key sequence stratigraphic surfaces which guided correlations between wells parasequences are grouped into parasequence sets with progressive progradational or retrogradational highstand and transgressive systems tracts respectively stacking patterns transgressive parasequences are thinner uniform in thickness and tend to be more dominated by molluskan carbonate facies highstand parasequences have more variable thickness are siliciclastic dominated and tend to be progradational on seismic data late highstand deposits of sequence 1 are dominated by restricted carbonate facies that likely reflect increased aridity lowstand deposits were not recognized from onshore well and seismic data the sequence stratigraphic framework developed documents the complex spatial and temporal facies relationships within a wave dominated mixed carbonate siliciclastic passive margin succession the strata studied document the complex interplay of lithofacies within a transition zone between near shore carbonate dominated strata to the south southeast georgia embayment and siliciclastic dominated marginal marine successions to the north baltimore canyon trough it also provides a useful stratigraphic calibration set for coeval offshore sediments that have been identified as potential areas for hydrocarbon exploration

role of temperature and nutrients in extinction of turritelline gastropods cenozoic of the northwestern atlantic and northeastern pacific abstract turritelline gastropods mesogastropoda turritelline are common to abundant components in many fossil cretaceous cenozoic and recent marine benthic communities but the environmental factors affecting their evolution and extinction are poorly understood this is in large part because today they occur most abundantly in cooler waters associated with upwelling or other high nutrient conditions but thermal tolerances and preferences are unclear for extinct turritelline species turritellines were diverse and abundant throughout the new world for much of the cenozoic beginning in the early neogene through both extinction and range contraction however they started to disappear from higher latitudes on both atlantic and pacific coasts of north and central america the highest rate of extinction took place in the western atlantic in the plio pleistocene when almost all turritelline species in this area became extinct preliminary comparison of the available stratigraphic record suggests that this paleobiogeographic pattern is not an artefact of the record this biogeographic shift coincides with a postulated regional mass extinction among all marine mollusks in the western atlantic at around the same time causes for turritelline extinction however appear to be more complex than the decline in temperature that is cited most often as the probable cause of the western atlantic molluskan extinction event neogene turritellines in the western atlantic appear to have been adversely affected by collapse and or major reorganization of oceanic productivity associated with the formation of the isthmus of panama nutrients thus may have been more important than temperature change in controlling extinction probability in this group

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

mineralogy geochemistry and genesis of the ferromanganese ores from hazara area nw himalayas northern pakistan abstract ferromanganese ores occur in hazara area near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate in pakistan the hazira formation of cambrian age is a relatively thin unit up to 150 m thick which consists of either thin ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite or thicker evenly bedded reddish brown siltstone it has a conformable lower contact with the abbottabad formation cambrian and an unconformable upper contact with the samana suk limestone jurassic the ferromanganese ores of the hazara area were studied in terms of their mineral and geochemical composition mineralogically a variety of mn and fe phases have been noticed in kakul galdanian and chura gali ferromanganese ores bixbyite is the principal mn phase while pyrolusite hollandite partridgeite and braunite occur in lesser amounts hematite however is the only fe phase in these ores gangue minerals include carbonates cryptocrystalline quartz iron clay and variable amounts of apatite plumbogummite and barite glauconite occurs in traces textural features suggest remobilization and subsequent precipitation of early diagenetic mn and fe phases along the fractures and interstices of the gangue minerals during later metamorphism chemical analyses show that the mn fe ratio in the ores is highly variable and ranges from 0 46 to 5 25 these ores exhibit a line of descent from lree to hree with a small positive ce anomaly their ree is higher than the hydrothermal mn deposits and lower than the hydrogenous crust the petrochemical characteristics suggest a mixed hydrothermal hydrogenetic source for the ferromanganese ores which have formed in shallow water or continental shelf environment due to the upwelling of anoxic deep seated water

bacterial origin of east australian continental margin phosphorites many models of the origin of marine phosphorites require a sediment rich in organic matter which by decomposition releases phosphorus for the precipitation of carbonate fluorapatite1 7 this concept is useful in explaining contemporary phosphorite in areas of very high productivity off the coasts of peru chile and south west africa8 10 where there are high organic matter fluxes to the sea floor4 7 11 it does not explain the origin of marine phosphorite deposits which formed in regions of limited oceanic upwelling and productivity12 14 the east australian continental margin an area of phosphogenesis throughout the late pleistocene and holocene13 14 is a modern analogue of an east coast phosphogenic province15 17 with low productivity over the upper slope region where the most recent phosphorites have been found18 evidence is reported here for the carbonate fluorapatite in the east australian phosphorites being located within bacterial cellular structures and a model proposed for the origin of these deposits through the slow bacterial assimilation of phosphorus from seawater in an area of restricted sedimentation

distribution texture and composition of modern phosphate pellets in peru shelf muds abstract textural analysis including estimates of concentrations of authigenic phosphate pellets were made for eight sediment cores from the peru continental margin phosphatic pellets separated from these modern organic rich sediments are black spherical ovoidal in shape and in thin section often display a concentric structure around a nucleus consisting of inorganic mineral grains some pellets have a gray white exterior coating which appears to be secondary diagenetic calcite phosphatic pellets account for upwards of 80 of the sediment mass in some cores pellets concentrate in specific size classes generally between 125 and 500 m in diameter and occur within a poorly sorted sediment

eocene eustatic sea level changes evidence from western sinai egypt abstract a major horizon of reworked material lies within the thebes formation near the top of the upper part of the lower eocene planktonic foraminiferal zone p9 the thebes formation is well exposed in western sinai and this reworked horizon lag deposit has been found to be widely distributed and coeval with similar deposits in israel and jordan when examined in detail it is found to consist of concentrated phosphatic nodules coprolites phosphatic grains and polished benthic and planktonic foraminifera the thebes formation has generally been described as a deep water basinal deposit however the presence of this lag deposit indicates an important period of shallow water deposition before the return to deeper water conditions in which the upper 20 m of this formation and the beds of the overlying darat formation were laid down a second but less pronounced phase of shallowing both in terms of concentration of lag deposits and its geographic distribution occurred at the top of the middle eocene khaboba formation top of zone p14 the shallowings are attributed to eustatic sea level falls and not to tectonic movements the eocene period in sinai was one of general tectonic stability and the effect of movements associated with the syrian arc folds are not detectable south of hammam faraun the two horizons of reworked material coincide stratigraphically with two global low sea level stands

phosphogenesis and organic carbon preservation in the miocene monterey formation at naples beach california the monterey hypothesis revisited the middle part of the miocene monterey formation at naples beach west of santa barbara california is predominantly composed of organic rich mudstone interstratified with phosphatic laminae minor lithologies include volcanic ash dolomite porcelanite and chert and condensed phosphatic beds sediments dated as 14 3 13 5 ma have average total organic carbon toc values around 8 5 wt and organic carbon oc accumulation rates are around 565 mg cm2 k y sediments dated as 13 5 13 ma are characterized by average toc values of 12 6 wt and oc accumulation rates of around 1130 mg cm2 k y the interval between 13 and 10 6 ma is marked by condensation average toc values are around 8 6 wt and oc accumulation rates diminished to around 55 mg cm2 k y the last interval studied is dated as 10 6 9 4 ma and average toc values are around 6 wt whereas oc accumulation rates rose again to 320 mg cm2 k y the presence of erosional surfaces angular unconformities and reworked clasts and nodules suggests that bottom current activity and gravity flow deposition have been instrumental in sediment accumulation the phosphatic laminae were precipitated at a very early stage of diagenesis during periods of nonsedimentation they formed less permeable sedimentary lids and may as such have contributed to enhanced oc preservation between 13 and 10 6 ma the thus formed phosphatic laminae were frequently subjected to subsequent sediment winnowing and reworking resulting in the formation of condensed phosphatic beds calculated p c molar ratios suggest that 1 the measured section is highly enriched in phosphorus p relative to oc 2 regeneration of organic p from organic matter decomposition was negligible and 3 the source of p was external likely upwelled bottom water rich in inorganic p in spite of good preservation conditions and correspondingly high toc contents the overall oc accumulation rates are moderate in comparison to those of actual high productivity areas which is mainly due to the episodic character of depositional processes and the intervening long periods of nondeposition and sediment reworking they preclude this section and by extrapolation the monterey formation in general from being an important oc sink during the middle miocene alternatively large oc sinks were probably created on the continent lignite deposits and in sedimentary depocenters which received increasing amounts of detrital sediments due to a combination of climate change spreading of grasslands and the increasing importance of mountain chains such as the himalaya the associated high nutrient fluxes may have been involved in the backstepping and drowning of carbonate platforms and in the generation of widespread phosphat rich deposits during the late early and early middle miocene

the genesis mineralization and stratigraphic significance of phosphatic glauconitic condensed limestone unit in the manavgat basin sw turkey abstract a condensed hemipelagic limestone unit with glauconite and phosphate separates a drowned late burdigalian carbonate platform from overlying langhian pelagic mudstones marls and calcarenitic tempestites within the neogene manavgat basin of southwestern anatolia turkey the unit consists of coeval lenticular limestone bodies between 1 cm and 15 m in thickness ranging from 10 m to 3 km in lateral extent the p2o5 content of this limestone ranges from 0 2 to 10 by weight and the iron oxide clay and other metal oxide contents of this unit substantially exceed those of the underlying and overlying rocks this condensed stratigraphic unit was deposited on the southwesterly outer shelf portions of drowned horsts that directly faced upwelling currents the unit displays three main facies 1 glauconitic phosphate crusts associated with hardgrounds 2 bedded glauconitic phosphatic limestones and 3 glauconitic phosphatic limestones interbedded with resedimented limestones facies 1 forms the thinnest units whereas facies 3 is the thickest since the thickness and spatial distribution of this facies are related to environmental contrasts caused by block faulting of the underlying carbonate platform this lithostratigraphic unit of hemipelagic glauconite phosphate deposition represents an interval of maximum flooding in tectonically active situations and depositional hiatus on submarine highs that separate the carbonate transgressive systems tract from the overlying terigenic tempestite highstand systems tract this appears to be the sole condensed unit within the miocene manavgat basin and is here ascribed to a third order 2 3 eustatic rise in sea level comprising the maximum flooding of the first order cycle this is also the time for early mid miocene major changes in mediterranean climate from tropical to temperate

oxygen and carbon isotope composition of structural carbonate in weathering apatites from laterites southern brazil and western senegal abstract the oxygen 18 o c and carbon 13 c c isotope compositions of the structural carbonate group co 3 in apatites from lateritic profiles were investigated the weathering profiles located in southern brazil and in western senegal are developed on three different types of apatite rich parent rock carbonatite metamorphosed marine phosphorite and sedimentary marine phosphorite the parent rock apatites are of magmatic hydrothermal metamorphic and sedimentary origins the in situ formation of apatite of weathering origin in the profiles is well documented petrographically and geochemically the overall range of measured 18 o c and 13 c c values of apatites of weathering origin 22 to 27 smow for 18 o c and 15 to 10 pdb for 13 c c is much smaller than the range of measured and or published isotope compositions of parent rock apatites 4 35 for 18 o c and 11 to 1 for 13 c c in any profile the apatites of weathering origin can exhibit lower similar or higher 18 o c values than parent rock apatites in contrast their 13 c c values are systematically and significantly lower than those of the parent rock apatites apatites formed as a result of weathering in laterites can therefore be readily distinguished from apatites of other origin on the basis of their isotope composition assuming that apatite co 3 fractionates o in a way similar to calcite co 3 the structural carbonate group of the apatites of weathering origin appears to form in approximate isotopic equilibrium with the weathering solutions the very low 13 c c values exhibited by these apatites indicate that the dominant sources of dissolved co 2 in the soil water are organic the isotope composition of structural carbonate in apatite of weathering origin in lateritic profiles may provide useful information for paleoenvironmental studies

distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix abstract to investigate the potential of mo and as as possible geogenic contaminants three sediment cores were examined to evaluate their mineralogical association distribution and mobility the cores were described and analyzed for total organic carbon toc ca mg si al p sr as mo fe and s content except in the uppermost segment limestone was the main lithology with the occasional presence of dolomite and clay that change in lithology was also observed in the bulk chemical composition where ca mg and sr concentrations increased with depth while si al and p concentrations decreased with depth minor minerals included pyrite fes 2 powellite camoo 4 and ferrihydrite the minimum maximum median and standard deviations for all analyzed elements including as and mo were comparable for all three cores molybdenum and as however varied significantly with depth and median as and mo values were above their respective crustal averages of approximately 1 1 mg kg and 1 5 mg kg the median values for as were 1 9 mg kg in core dep 1 3 3 mg kg in dep 2 and 1 mg kg in dep 5 the median values for mo were 2 3 mg kg in core dep 1 2 5 mg kg in dep 2 and 2 5 mg kg in dep 5 maximum concentrations for as were 101 9 mg kg 47 5 mg kg and 56 2 mg kg in cores dep 1 dep 2 and dep 5 respectively maximum concentrations for mo were 880 mg kg 123 mg kg and 225 mg kg in cores dep 1 dep 2 and dep 5 respectively electron microprobe analyses of individual minerals revealed variable concentrations of as ranging from approximately 300 to 9000 mg kg in pyrite and up to 17 600 mg kg in powellite camoo 4 the mo concentration in pyrite was consistently below the detection limit of approximately 100 mg kg in powellite the mo concentration was up to 42 wt a subset of 10 samples from different stratigraphic sections and with different as and mo concentrations was further investigated to assess as and mo mobility under changing physicochemical conditions leaching the aquifer matrix with a 1 m naoac solution at a ph of 8 1 removed more than 70 mo in 8 of the 10 samples the maximum value was 97 in contrast to mo as was mobilized to a lesser degree in 8 of the samples less than 30 were removed and the maximum was only 50 molybdenum which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix while as on the other hand should be much less mobile because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite thus it is advisable to include mo in the analytical program whenever elevated as concentrations are encountered in groundwater

sr and nd isotopic analysis of phosphorite sedimentation through one miocene high frequency depositional cycle on the north carolina continental shelf abstract a well developed seismic litho and biostratigraphic data base with good models for the formation and deposition of phosphate rich sediments exist for the upper cenozoic sediments on the north carolina continental margin this provides a unique opportunity to evaluate the potential of utilizing strontium and neodymium isotopic analyses to help unravel a complex genetic history of phosphate formation and deposition thirty one samples from three vibracores in onslow bay supplied hand picked concentrate subsamples of five phosphate grain types and thirty one concentrate subsamples of phosphate peloids for stratigraphic analysis all subsamples were analyzed for their sr isotope composition while only thirteen were analyzed for nd isotopes the 31 peloid samples represent three different stratigraphic units and include 1 holocene surficial sands with highly variable concentrations and types of reworked phosphate 2 pleistocene moldic carbonates with minor concentrations of black peloidal phosphate and 3 miocene mid burdigalian frying pan sequence unit 1 fps 1 of the pungo river formation with very high concentrations of multiple types of phosphate grains that decrease upsection and change grain types with changing lithofacies the latter unit represents deposition during one high frequency sea level cycle stratigraphic analysis utilized one grain type phosphate peloids for comparative purposes with the depositional model of riggs and mallette 1990 the sr and nd data cluster into significant categories that are coincident with these three major stratigraphic units sr and nd isotope compositions of selected phosphate grains from three phosphate rich depositional sequences are utilized to 1 date the initial miocene transgression of unit fps 1 of the pungo river formation 2 decipher processes of formation and deposition of major phosphate grain types through one miocene sea level cycle including the processes of in situ formation versus reworking 3 develop a sr and nd chronostratigraphy for evaluating changing patterns of continental margin sedimentation through high frequency depositional cycles 4 determine effects of reworking and weathering on the isotope signals between miocene pleistocene and holocene sediments 5 evaluate the suitability of utilizing sr and nd isotopes for detailed chronostratigraphic analysis of phosphorite sedimentation and 6 refine our understanding of the upper cenozoic evolutionary history of north carolina s continental margin

stratigraphic framework of sediment starved sand ridges on a mixed siliciclastic carbonate inner shelf west central florida abstract seismic reflection profiles and vibracores have revealed that an inner shelf sand ridge field has developed over the past few thousand years situated on an elevated broad bedrock terrace this terrace extends seaward of a major headland associated with the modern barrier island coastline of west central florida the overall geologic setting is a low energy sediment starved mixed siliciclastic carbonate inner continental shelf supporting a thin sedimentary veneer this veneer is arranged in a series of subparallel shore oblique and to a minor extent shore parallel sand ridges seven major facies are present beneath the ridges including a basal neogene limestone gravel facies and a blue green clay facies indicative of dominantly authigenic sedimentation a major sequence boundary separates these older units from holocene age organic rich mud facies marsh which grades upward into a muddy sand facies lagoon or shallow open shelf seagrass meadows cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies ravinement or sudden termination of seagrass meadows the shelly sand facies grades upward to a mixed siliciclastic carbonate facies which forms the sand ridges themselves this mixed siliciclastic carbonate facies differs from the sediment on the beach and shoreface suggesting insignificant sediment exchange between the offshore ridges and the modern coastline additionally the lack of early holocene pre ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively radiocarbon dating has indicated that these sand ridges can form relatively quickly 1 3 ka on relatively low energy inner shelves once open marine conditions are available and that frequent high energy storm dominated conditions are not necessarily required we suggest that the two inner shelf depositional models presented open shelf vs migrating barrier island may have co existed spatially and or temporally to explain the distribution of facies and vertical facies contacts

uranium series and ams 14c studies of modern phosphatic pellets from peru shelf muds recent sediments and separated phosphate pellets 125 500 m in diameter from the peru shelf have been analyzed for uranium decay series isotopes and 14c in order to determine age relationships and mineralization rates uranium series ages of pellets separated from one box core are significantly higher than ams radiocarbon ages determined for the same pellets these differences appear to be a consequence of mixing of an older generation of pellets with ones which are more recently formed postdepositional adsorption of reactive elements such as thorium and protactinium onto pellet surfaces may also contribute to the observed discordancy with radiocarbon ages sediment radiocarbon and 210pb sediment results as well as some trends in the uranium series data suggest that high concentrations of phosphate pellets have accumulated in some peru shelf sediments without extensive reworking individual pellets apparently form very quickly on time scales of a few years estimated authigenic uptake rates of phosphorus into pellets ranges from 0 5 to 9 40 mol p cm 2 yr 1 somewhat higher than rates measured for nodules from the same area this is consistent with observations that pelletal morphologies predominate over nodular forms within ancient phosphorite deposits

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

geochemistry and petrology of a middle tithonian limestone marl rhythmite in the neuquen basin argentina depositional and burial history

source rock potential of the phosphorite bituminous chalk marl sequence in jordan abstract the phosphorite and the overlying oil shale succession in central and eastern jordan has been studied for its organic matter composition maturation hydrocarbon potential and sedimentological implications pristine phosphorite was authigenically precipitated from interstitial solutions in ventilated environments later they were reworked and winnowed to produced the granular phosphorites possibly as wave or storm sand bodies the oil shale was deposited in the same basins where restricted water circulation and subsequent hypersalinity led to more reducing conditions and better organic matter preservation both facies represent a high bio productivity regime associated with paleo upwelling on the shallow southern epicontinental shelf of the tethys ocean the organic matter is dominantly amorphous and the extractable part is high kerogen is type ii s to type iii all maturity parameters investigated proved it to be immature e g r0

electron spin resonance optical dating of marine estuarine and aeolian sediments in florida usa abstract for the first time electron spin resonance optical dating esrod has been conducted on littorally transported and aeolian siliciclastic sediments in florida esrod utilizes light sensitive radiation sensitive defects at silicon sites that have been replaced by aluminum and titanium atoms to give rise to a time dependant signal these defects saturate at higher levels of radiation dose compared to optically stimulated luminescence and therefore extend the optical dating range back into the millions of years our results show that the trail ridge sequence is a multi depositional unit that began deposition around 2 2 ma and continued until 6 ka the osceola cape of the effingham sequence was deposited around 1 5 ma and the chatham sequence was a multi depositional terrace with at least three events preserved

miocene phosphate accumulation in the cuyama basin southern california abstract middle and upper miocene phosphatic strata in the cuyama basin of southern california contain approximately 6 4 10 9 metric tons 2 1 10 14 mol of phosphorus p that accumulated in slope and shelf strata at rates between 0 9 and 3 8 mol p cm 2 year 1 from 15 5 to 10 8 ma an estimated 63 of all phosphorus lies in a single third order sequence deposited between 14 8 and 13 ma the main impetus for this brief phosphogenic event was a 200 m relative sea level rise that resulted from strike slip faulting immediately east of the basin minor element and petrologic analyses suggest the overall increase in phosphorus accumulation correlates with less reducing conditions in the shallowly buried marine sediments on the slope and the expansion of phosphogenesis to the outer shelf both events were probably related to landward shifts of the pacific oxygen minimum zone and coastal upwelling centers during the relative sea level rise whereas these tectonic events were apparently local the phosphatic deposits of the cuyama basin clearly demonstrate that tectonism can strongly influence phosphate accumulation rates in marginal marine environments

paleoceanographic model of neogene phosphorite deposition u s atlantic continental margin the neogene stratigraphic section of the southeastern u s continental shelf coastal plain system is characterized by i a series of major regional phosphogenic episodes ii a strong spatial relationship between the structural or topographic framework and phosphate deposition and iii distinct cyclical and regional patterns of deposition of the terrigenous carbonate and phosphate lithofacies the complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea level fluctuations associated changes in climate and the dynamics of the gulf stream in response to the bathymetric configurations of the continental margin during the past 20 million years

phosphogenesis around the proterozoic phanerozoic transition there was a very significant and widespread phosphogenic event around the proterozoic phanerozoic transition this is reflected in the occurrence of many major and minor latest proterozoic and cambrian phosphate deposits phosphorites in asia australia africa and south america as well as minor occurrences in many other parts of the world the major peak in phosphogenesis was in the tommotian with lesser events in the ediacaran and the lenian bracketed by other minor though significant events recent evidence on the timing of proterozoic phosphogenesis does not now support the suggestion of a phosphogenesis glaciation link these peaks in phosphogenesis are taken as evidence that there was a marked increase in the phosphate content of the shallow seas at about this time possibly as a result of the circulation of deep phosphorus rich ocean waters into the photic zone not only was this responsible for the formation of phosphorites but it also had a profound effect on the biota and may have been a driving mechanism for the cambrian faunal explosion and the initiation of biomineralization

44ca 42ca and 143nd 144nd isotope variations in cretaceous eocene tethyan francolites and their bearing on phosphogenesis in the southern tethys measurements of 4 4 ca 4 2 ca and 1 4 3 nd 1 4 4 nd isotope ratios in carbonate fluorapatite cfa through the aptian eocene section of the negev israel together with quantified rates of p and ca accumulation and bulk sedimentation permit an examination of the relationships of these five factors to tethyan phosphogenesis the data provide an aptian eocene ca 70 ma record of the ca isotope composition of 35 cfa samples 24 of which were also analyzed for nd isotopes representing 11 time stratigraphic phosphate horizons within the sequence the 4 4 ca values are significantly lower in the aptian albian samples 4 4 ca 0 11 to 0 06 than in the campanian eocene samples 4 4 ca 0 22 to 0 42 whereas the e n d values increase from continental crust like in the aptian albian e n d t 10 9 to more radiogenic pacific like e n d t 6 6 to 6 1 in the campanian both peaks of 4 4 ca and e n d t in the campanian coincide with the peak of tethyan phosphogenesis in the negev which is marked by a sharp increase of p accumulation rates from 200 mol cm 2 k y 1 in pre campanian time to 1700 mol cm 2 k y 1 in the campanian and a decrease in rates of ca accumulation and bulk sedimentation the coincident increases of 4 4 ca and e n d t values and p accumulation rates in the negev area during the campanian suggest that they are related in this time interval and were induced by the global late cretaceous sea level rise and increasing circumequatorial tethyan flow

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

polarimetric radar measurements of a forested area near mt shasta the authors present the results of an experiment using the nasa jpl dc 8 airsar aircraft synthetic aperture radar over a coniferous forest near mt shasta california in 1989 calibration devices were deployed in clearings and under the forest canopy and passes at 20 degrees 40 degrees and 55 degrees incidence angles were made with the airsar a total of eight images at differing incidence angles have been processed and calibrated the multipolarization multifrequency data were examined and it was found that the c band cross section averaged over like and cross polarizations is the best parameter for distinguishing between two stands with differing forest biomass the average cross section at p and l bands is useful only for smaller incidence angles parameters describing the polarization behavior of the scattering were primarily useful in identifying the dominant scattering mechanisms for forest backscatter

taphofacies models for epeiric sea environments middle paleozoic examples abstract skeletonized organic remains display various modes of occurrence which may be used to better understand the sedimentary dynamics of strata within which they occur aspects of skeleton biostratinomy and early diagenesis are distributed nonrandomly within the stratigraphic record and therefore are useful in discriminating taphonomic facies for purposes of taphonomic comparisons skeletonized marine taxa are reduced to five generally defined types massive arborescent univalved bivalved and multielement different skeletal types display different attributes which reflect specific responses to physical chemical and or biological processes the taphonomic properties of disarticulation reorientation and sorting fragmentation corrosion and abrasion skeletal dissolution and early diagenesis display patterns which are predictable with respect to a variety of inter related physico chemical parameters these can be quantified through indices which evaluate relative frequencies of occurrence sedimentary events alter the temporal and spatial homogeneity of processes which generate background taphofacies and superimpose event related properties thereby generating composite taphofacies such events produce taphonomic signature which in themselves correspond to specific environmental conditions i e water depth and event intensity indeed background and event related processes interact to generate complex but nonetheless diagnostic facies attributes useful in reconstructing paleoenvironments the comparison of standard indices among beds should allow the recognition of stratigraphic patterns and facilitate the diagnosis of systematic gradients among taphonomic properties deductively derived taphofacies models corroborated by empirical data from paleozoic strata illustrate the distribution of taphonomic properties with respect to environmental energy turbulence background sedimentation rate and sediment oxygenation these parameters also indirectly influence other less obvious factors including bioturbation and sediment chemistry trends in the distribution of taphonomic properties taphonomic gradients permit us to map otherwise unrecognized trends in these environmental parameters across a hypothetical onshore offshore transect within a generalized epeiric sea setting taphofacies models provide the quantifiable basis by which evolution of taphofacies may be gauged and then related to biotic and abiotic phenomena moreover taphofacies models evaluate the preservability of skeletal remains in different environmental settings and therefore provide information important in paleoecological studies

sedimentology geochemistry and origin of phosphatic chalks the upper cretaceous deposits of nw europe santonian lower campanian and lower maastrichtian phosphatic chalks in northern france southern england and belgium are europe s largest sedimentary phosphatc deposits the stratigraphy sediment ology petrography mineralogy and geochemistry of the lithofacies are reviewed and new data presented depositional and diagenetic models for phosphatic chalk deposits are developed using published experimental work and from observations of modern high and low productivity phosphogenic systems it is concluded that phosphatic chalks were deposited in well oxygenated current swept environments phosphatization required a delicate balance to be maintained between moderate organic carbon and carbonate sedimentation rates reduced bulk sediment accumulation rate and an enhanced rate of bioturbation precipitation of carbonate fluorapatite francolite accompanied the bacterially mediated decomposition of organic matter occurring within centimetres of the sediment seawater interface and taking place preferentially within microbial bodies and coatings in addition to the organically derived component pore water phosphate levels were enhanced by phosphate absorbed on ferric oxyhydroxides which was liberated during iron reduction mineralization was probably a dominantly post oxic process but occurred in a thick sediment mixed layer in which marine organic matter was undergoing intense mixed aerobic and anaerobic microbial degradation phosphogenesis occurred predominantly on the ne margins of the anglo paris basin where shallower sea floors and suitable palaeoceanographic conditions prevailed phosphogenic episodes were limited by sea level fluctuations which controlled the effectiveness of the erosional currents that formed and maintained the phosphatic basins and may have stimulated local productivity

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

subtropical to temperate facies from a transition zone mixed carbonate siliciclastic system palaeogene north carolina usa palaeogene passive margin sediments on the us mid atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate siliciclastic shelves this study utilizes well cuttings outcrop core and seismic data to document temporal and spatial variations in admixed bryozoan rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone this zone was situated between north flowing warm waters of the ancestral gulf stream carbonate dominated settings and south flowing cold waters of the ancestral labrador current siliciclastic dominated settings some degree of mixing of carbonates and siliciclastics occurs in all facies however siliciclastic prone sediments predominate in nearshore settings while carbonate prone sediments are more common in more open marine settings of the inner shelf break and deep shelf a distinctive dual break shelf depositional profile originated following a major late cretaceous to palaeocene transgression that drowned the earlier shallow platform this profile was characterized by prominent mid shelf break dividing the shallow shelf from the deep shelf and a major continental shelf slope break incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin storm wave base also contributed to the preservation of the dual break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid shelf break sediment fines in deep shelf facies were produced in place transported downdip from the shallow shelf by storm ebb currents and boundary currents and reworked from adjacent areas of the deep shelf by strike parallel boundary currents regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf with warmer waters and more humid climates favouring carbonate deposition and cooler more arid conditions favouring glaucony and siliciclastic dominated deposition continuous wave and current sweeping of the shallow shelf favoured deposition of mud lean facies across much of the shallow shelf skeletal components in much of the carbonate rich strata formed in warm nutrient rich subtropical waters as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages these indicators of warm water deposition within the bryozoan mollusk rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage such facies generally are associated with cooler water depositional settings

a review of apatites iron and manganese minerals and their roles as indicators of biological activity in black shales abstract biological contribution to the formation of minerals has become more than a descriptive area in geological thought and research mechanisms of specific mineral accumulation and deposition in oceancs lakes and even desert environment are studied using interdisciplinary approaches and applied in the interpretation of earth processes phosphorus iron and manganese are and probably were essential elements in life forms the common minerals of these elements apatite and magnetite for example can be found in a variety of sedimentary environments both ancient and modern where they could be useful indicator minerals to interpret geologic environments the crystal morphological structural and chemical including isotopic attributes of these usually fine grained minerals can be compared with bulk chemical and stratigraphic information to augment our understanding of the mechanisms of formation and diagenesis in sediments such as black shales

evolution of the cape fear terrace a complex interaction between the gulf stream and a paleo shelf edge delta abstract a high resolution seismic stratigraphic study of the cape fear terrace outer continental shelf off cape fear north carolina combined with bio lithostratigraphic data have yielded a complex chronostratigraphic framework of the quaternary sequences that comprise this portion of the north american continental margin the cape fear terrace is one of six terraces protuberances that form significant topographic irregularities along the south carolina and north carolina shelf slope break the cape fear terrace is situated upon an anomalous point source prograding shelf margin feature which has protruded out onto the upper slope throughout much of the quaternary this upbuilding outbuilding followed a period of active submarine erosion in which the ancestral gulf stream and or associated meanders cut an erosional path beneath the present shelf margin during the early pliocene the protuberance was originally constructed during a relative lowstand of sea level as a shelf edge delta severe modification of this deltaic lobe occurred during a relative highstand of sea level as gulf stream activities began to more effectively modify the margin the anomalous thick accumulation of shelf edge sediments acted as a barrier to flow inducing complex flow patterns of the gulf stream causing preferential erosion on its downstream side subsequent deposition may have resulted during more elevated highstands of sea level as evidenced by the presence of active sand waves in the terrace protuberance region today once this shelf edge bathymetric irregularity had been established the gulf stream acted as a dynamic force inducing cellular flow structures within the shelf environment and enabling sediments to be transported seaward along the paleo shoals complex

paleoecology of miocene crocodylians in florida insights from stable isotope analysis abstract fossils from late miocene localities in north florida offer new information about the paleoecological relationships between sympatric alligatorine and tomistomine crocodylians large robust tomistomines traditionally referred to gavialosuchus americanus outnumber alligator fossils at localities representing coastal estuarine depositional environments stable isotope analysis of carbon 13 c and oxygen 18 o values in fossil crocodylian tooth enamel carbonate co 3 provides evidence for niche partitioning between these two taxa which may have co inhabited estuarine paleoenvironments our isotopic results imply that alligators procured prey from primarily freshwater or terrestrial sources whereas tomistomines fed mainly on marine based prey items as indicators of saltwater paleoenvironments the fossil tomistomines may therefore be informative for tracking miocene sea level change

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

origin and age of phosphorite from the south central florida platform relation of phosphogenesis to sea level fluctuations and δ13c excursions abstract francolite carbonate fluorapatite from predominantly peloidal phosphorite grains in the miocene hawthorn group from the babcock deep core southwestern florida is highly substituted with an average composition of ca4 61na0 22mg0 14k0 05sr0 02 po4 2 23 co3 0 62 so4 0 12 f 1 04 13c values of 1 0 7 8 pdb of the francolite co3 indicate a substantial contribution of c from an organic source the sulfur isotopic composition of francolite so4 is depleted to slightly enriched relative to miocene seawater and suggests that phosphogenesis occurred during early burial diagenesis in organicrich sediments above or in the zone of sulfate reduction the uniformly high sr na mg so4 and co3 contents of the francolite the 18o values of the francolite co3 0 2 4 2 pdb and the inclusion of pyrite and organic matter in phosphorite grains suggest that the francolite has had minimal chemical alteration since its formation phosphorite from the babcock deep core has sr 87 86 ratios that range from 0 708148 0 708880 and sr derived ages that range from late oligocene 25 6 0 7 ma to early late miocene 9 2 1 4 ma the sr derived ages of relatively fragile calcareous benthic foraminifers are consistently younger than associated hard tightly cemented phosphorite and support textural evidence of extensive reworking the age of the host sediment ranges from early miocene to pliocene and its depositional history is related to sea level fluctuations approximately three quarters of the total phosphorite in the babcock deep core formed during or within 2 my before the major early to mid miocene positive 13cshift as recorded at dsdp site 588 southwest pacific one third of the total phosphorite formed just prior to the carbon shift in the short interval between 21 9 and 20 4 ma these results indicate that reworked phosphorite deposits may provide a proxy of organic carbon cycling on continental shelves that correspond to sealevel fluctuations and to variations in the 13crecord

phosphorus accumulation rates in a miocene low oxygen basin the monterey formation pismo basin california abstract phosphorus p limits oceanic productivity on long time scales and therefore determining changes in oceanic p accumulation through time is important for modeling oceanic paleoproductivity we determined p concentrations and accumulation rates at shell beach california a section of phosphatic rich marine sedimentary rocks which includes the widespread phosphatic and siliceous facies of the monterey formation phosphorus concentrations had wide ranges in the major lithologies found in these facies with values in phosphatic shales ranging from 0 36 to 3 9 wt compared to 0 02 to 0 42 wt in dolomitic and siliceous strata phosphorus accumulation rates in mol p cm 2 yr 1 for all values reported here showed significant variability with both sample lithology and position in the section phosphorus accumulation rates were much higher in phosphatic shale strata 1 5 29 than in dolomitic and siliceous strata 0 1 3 1 in both facies furthermore p accumulation rates were generally higher in phosphatic shale strata of the upper siliceous facies 3 1 29 compared to the lower phosphatic facies 1 5 14 mean p accumulation rates calculated using linear sedimentation rate models for each facies and observations of the relative amount of phosphatic shale dolomite and siliceous strata are comparable between the portions of phosphatic and siliceous facies studied this indicates that the two facies with their faunal and sedimentological characteristics considered to reflect major oceanic and climatic changes during the middle miocene are similar in terms of p burial total p accumulation rates are also comparable to other phosphogenic miocene and modern environments we modeled variable sedimentation rates to examine the sensitivity of mean p accumulation rates to the linear sedimentation rate assumption increasing shale sedimentation rates to values above those estimated by linear models yields higher mean p accumulation rates in both facies though they remain comparable in terms of net p burial modeling also revealed that for increased shale sedimentation rates in each facies siliceous sedimentation must be about three times faster than dolomitic strata sedimentation

dating phosphogenesis with strontium isotopes authigenic and replacement francolites in modern phosphorite have values of sup 87 sr sup 86 sr within error of that of modern marine sr 0 70916 plus minus 2 during the phosphatisation of carbonate sr is not inherited from the carbonate but is totally exchanged with sr in ambient water the sup 87 sr sup 86 sr in shallow marine pore waters is indistinguishable from the value for modern marine sr so authigenic francolite which precipitates from pore water accurately records the isotopic ratio of contemporary marine sr by comparing the sup 87 sr sup 86 sr in francolite with published curves for the isotopic evolution of tertiary marine sr we have dated phosphogenetic events affecting the chatham rise 4 90 plus minus 0 35 ma the nambian margin 1 15 plus minus 0 25 ma and 4 70 plus minus 0 35 ma and the sechura desert peru 11 8 plus minus 0 5 ma

nd isotope evidence for the evolution of the paleocurrents in the atlantic and tethys oceans during the past 180 ma the nd isotopic composition of atlantic and tethys seawater as deduced from marine phosphorites varied considerably during the past 180 ma the early tethys and central atlantic seawater from 180 to 160 ma ago early middle jurassic had a nd isotopic signature identical to that of the pacific end 6 suggesting that pacific seawater entered the newly forming tethys basin however with time continental runoff draining into the young basin became more important and led to a decrease in the nd isotopic composition and finally a decoupling from the pacific ocean during the late early cretaceous 120 90 ma ago atlantic and tethys seawater reached continental crust like nd isotopic composition values end 10 which could reflect high weathering rates induced by the warm and humid climate at that time in the time span between 80 and 50 ma late cretaceous early tertiary the nd isotopic composition of both tethys and atlantic seawater strongly increased towards pacific seawater values in the case of the atlantic ocean this change has been correlated with the opening of the south atlantic which enabled the more radiogenic pacific seawater to travel westwards around the southern edge of africa into the south and finally the north atlantic in the case of tethys seawater we have to assume that during this period large masses of pacific seawater entered the tethys again directly through the indian tethys seaway the renewed importance of this seaway might be related to the late cretaceous early tertiary first order global sea level highstand the most abrupt change towards lower more crust like values occurred in the early miocene 25 17 ma ago in the south and north atlantic as well as in the tethys during this period the143nd 144nd isotope ratios dropped from 0 5124 end 4 2 down to 0 5122 end 8 this change indicates a diminishing influx of pacif seawater into the atlantic and tethys oceans and can be correlated with the breakdown of the circum equatorial circulation patterns of the world oceans due to plate tectonics from 20 to 17 ma ago miocene the nd isotopic composition of the atlantic ocean increased again and reached values as high as 0 5123 end 6 6 whereas tethys seawater remained at low values this decoupling can be correlated with the incipient complete isolation of the tethys the nd isotopic composition was henceforth controlled by the continental runoff from surrounding land masses the major increase in the nd isotopic composition observed in the atlantic can be related to the opening of the drake passage and establishment of the circum antarctic current system this allowed pacific seawater to enter directly the south atlantic around antarctica a renewed drop in the nd isotopic composition of atlantic seawater during the late miocene can be related to the onset of north atlantic bottom water formation and its subsequent upwelling

geochemistry of ferromanganese crusts and nodules from the south tasman rise southeast of australia abstract eighteen samples of ferromanganese oxide crusts up to 15 cm thick and nodules have been dredged or cored from elevated parts of the seafloor south of tasmania ferromanganese deposits overlie a variety of basement rocks nodules are dominantly ellipsoidal and mononucleate and range up to 13 cm in diameter surface textures for both crusts and nodules range from smooth to rough gritty or botryoidal typically internally laminated the ferromanganese deposits are dominantly ferruginous vernadite while quartz plagioclase fluorapatite phillipsite goethite and in five samples todorokite are minor phases both crusts and nodules show enrichment of fe co and pb and depletion of mn ni cu and zn to be expected with a vernadite dominated mineralogy cobalt and pb content increase with decreasing water depth with highest values in the range 1 2 km the mineralogy chemistry and physical appearance of the deposits indicate a hydrogenetic origin probably in an environment swept by strong erosive and oxygenated bottom currents the samples analyzed are similar in composition to seamount and ridge crusts and nodules from elsewhere in the southwest pacific they are markedly different to those described from the north pacific and in particular are generally much lower in co one co rich crust from a seamount on the south tasman rise water depth 1700 m does not fit in the distribution of co in ferromanganese deposits of the southern pacific and may reflect a local zone of oxygen depletion associated with the subtropical convergence its significant enrichment in co 0 8 1 0 suggests a detailed survey may be warranted to fully assess the economic potential of this material

relationship between phosphogenesis and sequence architecture sequence stratigraphy and biostratigraphy in the middle ordovician of the armorican massif nw france abstract in the armorican massif nw france the middle ordovician formations contain abundant phosphatic p beds associated with terrigenous sediments laid down on a storm dominated shelf facies analysis and sequence stratigraphy carried out on sections located in the crozon peninsula w armorican massif allow us to distinguish four p facies 1 beds with p nodules and crusts contained within sediments laid down on the distal and median parts of the inner shelf 2 amalgamated beds with p nodules and crusts and 3 beds with lingulid brachiopods heavy minerals and p clasts associated with retrogradation phases 4 p clast bearing conglomerates associated with progradation phases the genesis of these facies and their location in the depositional sequences are controlled by the fluctuation of terrigenous inputs during sea level changes sediment volume partitioning we propose a genetic model integrating the superposition of very high frequency vhf and high frequency hf eustatic signals in this model the amalgamated beds and beds with lingulid brachiopods heavy minerals and p clasts result from the superposition of several sea level rise episodes of vhf cycles occurring within the retrogradation phase of a hf cycle the lateral extension of p facies was investigated in the eastern part of the armorican massif benioc domfront les tanneries and st aubin du cormier sections several early darriwilian transgressive events associated with phosphogenesis episodes are dated through high resolution chitinozoan studies some of these transgressive events are at least of regional scale e g ornensis and protocalix transgressive events the topmost calix transgressive event is clearly identified over the northern gondwanan and avalonian domains and may reflect a global eustatic signature

late cretaceous to miocene phosphatic sediments in the georges bank basin u s north atlantic outer continental shelf abstract phosphorite and phosphatic sediments are present in the georges bank basin in marine late cretaceous to miocene strata equivalent to the dawson canyon formation and banquereau formation of offshore nova scotia the late cretaceous to paleocene phosphorite occurs predominantely as sand and gravel sized pellets and as cement in conglomeratic aggregates the eocene and miocene phosphate occurs mainly as fine very fine sand size spheroidal avoidal pellets in unconsolidated clayey silts the older phosphorites form intraformational conglomerates that are the result of a winnowed finer grained matrix leaving lag deposits of phosphorite we present evidence that most of the eocene and miocene phosphate is primary and formed during marine trangressions our observations extend the geographic and temporal limits of the major phosphogenic system of the western north atlantic northward and through time however compared to the well known phosphorite deposits along the southeastern margin of the u s a these northern deposits are not of commercial scale due to a high terrigenous input and the lack of a mechanism capable of driving persistant upwelling

mixed carbonate siliciclastic sequence stratigraphy of a paleogene transition zone continental shelf southeastern usa abstract the sequence stratigraphy and facies of the paleogene in the subsurface of the albemarle basin north carolina was defined using 1600 thin sections of plastic impregnated well cuttings from 24 wells wireline logs biostratigraphic data and seismic data the facies formed in the transition zone between warm subtropical and temperate conditions on a swell wave dominated open shelf exposed to major boundary current activity the shelf has a distinctive seismic profile consisting of a shallow inner shelf inner shelf break deep shelf depths in excess of 200 m and the continental slope the inner shelf was characterized by distinctive quartz sand and sandy mollusk facies inshore passing seaward into a broad wave swept abrasional shelf and then into storm influenced bryozoan echinoderm limestones to depths of several tens of meters argillaceous lime mud marl deposition was widespread across the deep shelf extending onto the inner shelf during major highstands sediment thickness trends were controlled by greater differential subsidence of crustal blocks within the albemarle basin which considerably modified but did not obliterate the effects of eustatic sea level changes in this passive margin setting five supersequences were identified on seismic and in wells each consisting of multiple regionally identifiable sequences the paleocene supersequence is dominated by widespread marl deposition reflecting shelf flooding into the late paleocene thermal maximum this warming corresponds with widespread inner shelf skeletal carbonate deposition from the late paleocene through the middle eocene the two eocene supersequences identified are dominated by bryozoan echinoderm rich carbonates that formed a seismically definable sediment buildup 50 km wide by 100 m thick across the deepest inner shelf during the lower to early middle eocene middle to upper eocene supersequence highstand sequences indicate increased progradation and greater mixing of shelf carbonates with nearshore siliciclastics likely in response to lowering sea levels and cooling climate the two oligocene supersequences identified are dominated by coarse siliciclastic sand that is heavily admixed with mollusk foraminifer dominated carbonates rapid flooding followed by extensive progradation of shallow shelf sediments in oligocene sequences reflects continued eustatic lowering driven by the onset of icehouse climatic conditions increased incision and reworking of deep shelf sediments during oligocene supersequence highstands resulted from increased ancestral gulf stream boundary current activity during icehouse times key elements controlling facies distribution through time include significant wave energy which controls the width and distribution of inner shelf facies belts through the degree of water bottom abrasion and winnowing boundary currents also are capable of large scale reworking of deep shelf sediment they also provide a mechanism for widespread inner shelf hardground development during major transgressions in addition boundary currents play a major role in stabilizing local climate by buffering seasonal temperature variations directly influencing which carbonate grain producers can thrive in this transition zone setting

pacific pelagic phosphorus accumulation during the last 10 m y as a limiting nutrient to marine life phosphorus p is an effective tracer of today s marine productivity the distribution of p in marine sediments likewise tracks the history of marine productivity because of its relative insolubility in seawater caco3 biogenic opal terrigenous sediment and total p have been measured in cores from nine pacific sites deep sea drilling project dsdp 65 66 310 77 62 572 463 586 and gpc 3 and one subantarctic dsdp 266 site these sites were specifically chosen to provide information on biota burial flux changes with time for sedimentary sinks that represent key oceanographic variables i e rate of upwelling water depth and carbonate dissolution gradient the accumulation rates of these components for the last 10 ma were then calculated from determined core age versus depth plots core bulk density and porosity data the accumulation of p weakly correlates with that of caco3 moderately with that of total sediment and very strongly with carbonate free accumulation two prominent peaks for all components occur at 2 3 ma and 5 6 ma and record the chemical loading of dissolved caco3 sio2 and p from glacially emergent continental shelves these results indicate that continental shelf phosphorites form during interglacially high sea levels and correspond to low deep sea p accumulation rates whereas glacially lowered sea levels allow for shelf bypassing and greater deep sea p accumulation rates

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites