petrology and geochemistry of neoproterozoic volcanic arc terranes beneath the atlantic coastal plain savannah river site south carolina the piedmont of south carolina and georgia is a complex mosaic of exotic terranes of uncertain provenance farther south and east these terranes form the basement beneath several kilometers of cretaceous and cenozoic sedimentary rocks commonly referred to as the atlantic coastal plain the distribution and geologic history of this hidden crystalline basement can be inferred only on the basis of limited exposures at the margins of the coastal plain onlap aeromagnetic lineaments that define basement trends in the subsurface and core data from wells that penetrate basement during the past 40 years basement cores aggregating more than 6 miles 10 000 m have been recovered from 57 deep wells at the department of energy s savannah river site these cores provide the only known samples of basement terranes that lie southeast of the fall line in central south carolina cores from the 57 deep wells along with structural trends defined by aeromagnetic lineaments allow us to define four distinct units within the basement beneath the coastal plain 1 the crackerneck metavolcanic complex greenstones and felsic

geochemistry and skeletal structure of diploria strigosa implications for coral based climate reconstruction abstract geochemical tracers incorporated into the skeleton of reef building corals are ideal proxies for reconstructing environmental parameters of ambient seawater such as temperature and salinity at subseasonal resolution however validation concerns of these environmental proxies due to the complex skeleton of some tropical atlantic corals have hindered such coral based environmental reconstructions in this region compared to the tropical pacific in order to identify complications associated with the complex skeletal architecture of the massive brain coral diploria strigosa we performed microsampling experiments along and across individual skeletal elements we demonstrate that the mesoscale heterogeneity of sr ca 18o and 13c is a systematic feature of d strigosa and is linked to different vital effects between skeletal elements the thecal wall is significantly depleted in sr 18o and 13c compared to the adjacent septa and columella and differences between apparent temperature signatures of several degrees are greater for sr ca suggesting that this temperature proxy is more sensitive to skeletal mixing than 18o parallel subseasonal microsampling experiments performed along individual skeletal elements of a single corallite of a d strigosa coral which grew at a rate of 0 65 cm year allow for investigating potential biases associated with its complex skeletal mesoarchitecture highest correlation between sr ca and 18o from skeletal material retrieved from the centre of the thecal wall suggests that microdrilling the theca provides the best environmental signal compared to adjacent microsampling profiles moreover based on monthly mean climatology the temperature dependence of sr ca for this profile is comparable to previous calibrations published from faster growing d strigosa based on these results we conclude that accurate microsampling along the centre of the thecal wall of d strigosa is a prerequisite for generating robust climate reconstructions from its skeleton

the effect of rock content on nutrients in a sierra nevada forest soil abstract the effects of rock content on nutrient concentrations and contents kg ha 1 in a skeletal soil derived from andesite were investigated rock content to a 60 cm depth ranged from 8 to 69 among 20 quantitative soil pits within a 10 ha area on average rocks contained 9 of total soil c 19 of total soil n 3 of total ecosystem c and 12 of total ecosystem n percent rock content also appeared to cause increases in organic matter concentrations rock content was significantly positively correlated with total c and total n concentrations in the fine earth 2 mm fraction soil c was organic no carbonates were present percent rock content was also significantly positively correlated with fine earth c n ratio suggesting that organic matter in rockier soils was in an earlier stage of decomposition at any given depth other consistent correlations with rock content included bray p positive and exchangeable mg 2 negative the decrease in fine earth mass with increasing percent rock content offsets the increase in c concentration such that there was no correlation between percent rock content and either fine earth or total soil fine earth plus rock c content kg ha 1 percent rock content was significantly negatively correlated with total n bray p inorganic n exchangeable k ca 2 and mg 2 contents however the results of this study show that high rock content can affect soil c and nutrient pools not only because of the contributions of the rocks themselves but also because high rock content appears to cause higher concentrations in the fine earth fraction

40 ar 39 ar ages from subsurface crystalline basement of the wiggins uplift and southwesternmost appalachian piedmont implications for late paleozoic terrane accretion during assembly of pangea

reconstructing twentieth century sea surface temperature variability in the southwest pacific a replication study using multiple coral sr ca records from new caledonia 1 coral based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation analytical expense and time constraints coral sr ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of amedee island new caledonia different sampling resolutions were examined in coral sr ca fortnightly and monthly and 18o fortnightly monthly and seasonally as well as similar scale subsampling of the daily in situ sea surface temperature sst record the mean coral sr ca 18o and sst values do not change as a function of sampling resolution the coral sr ca signal is highly reproducible the average absolute offset between coeval monthly sr ca determinations between any two coral time series is 0 035 0 026 mmol mol 1 0 65 c which is less than twice the analytical precision of the coral sr ca measurements the stack average of the monthly coral sr ca variations and monthly anomalies are significantly correlated with monthly in situ sst 1967 1992 r 0 96 and 0 64 respectively p 0 05 and n 302 and 1 grid monthly sst data product 1900 1999 r 0 95 and 0 56 respectively p 0 05 and n 1198 the coral sr ca sst reconstruction exhibits interannual and decadal timescale fluctuations that exceed those observed in the gridded sst record which may reflect true differences between sst at a shallow reef site and those averaged over a 1 grid box or inadequacies in the methodology used to create the gridded sst product when few observations are available a warming trend of 0 6 c is observed in the twentieth century coral sr ca sst record

improving sst reconstructions from coral sr ca records multiple corals from tahiti french polynesia we reconstruct sst from coral sr ca ratios measured at three coral cores taken from the lagoon of tahiti french polynesia two coral cores were drilled from the same coral colony one horizontally and one vertically and a third core was drilled vertically from another coral growing at a different site we evaluate several sr ca records as proxies for regional sst variations 1 the three single core records from tahiti 2 an average sr ca record computed from the two cores drilled from the same coral colony 3 an average sr ca record computed from all three tahiti cores and 4 an average sr ca record computed from the three tahiti cores and a fourth core taken from a different island rarotonga on a monthly scale the average sr ca record including the four coral cores from tahiti and rarotonga shows the best correlation with regional sst the variance of the sst reconstruction is very realistic and the residual sst is low this suggests that reconstructing sst from average proxy records gives a better representation of regional sst variations of the three tahiti cores the one that was drilled horizontally shows the best correlation with grid sst on an annual mean scale all three tahiti corals show much larger interannual sst variations than that indicated by grid sst

a further study of the tropical western hemisphere warm pool abstract variability of the tropical western hemisphere warm pool whwp of water warmer than 28 5 c which extends seasonally over parts of the eastern north pacific the gulf of mexico the caribbean and the western tropical north atlantic tna was previously studied by wang and enfield using the da silva data from 1945 93 using additional datasets of the ncep ncar reanalysis field and the ncep sst from 1950 99 and the levitus climatological subsurface temperature the present paper confirms and extends the previous study of wang and enfield the whwp alternates with northern south america as the seasonal heating source for the walker and hadley circulations in the western hemisphere during the boreal winter a strong hadley cell emanates northward from the amazon heat source with subsidence over the subtropical north atlantic north of 20 n sustaining a strong north atlantic anticyclone and associated northeast ne trade winds over its southern limb in the tna this circulation including the ne

comment on a snapshot of climate variability at tahiti at 9 5 ka using a fossil coral from iodp expedition 310 by kristine l delong terrence m quinn chuan chou shen and ke lin 1 the integrated ocean drilling program iodp expedition 310 recovered drill cores from the drowned reefs around the island of tahiti 17 40 s 149 30 w many of which contained samples of massive corals from the genus porites herein we report on one well preserved fossil coral sample a 13 6 cm long porites sp dated by uranium series techniques at 9523 33 years monthly 18o and sr ca determinations reveal nine clear and robust annual cycles coral 18o and sr ca determinations estimate a mean temperature of 24 3 c 3 2 c colder than modern for tahiti at 9 5 ka however this estimate is viewed with caution since potential sources of cold bias in coral geochemistry remain to be resolved the interannual variability in coral 18o is similar between the 9 5 ka coral record and a modern record from nearby moorea the seasonal cycle in coral sr ca is approximately the same or greater in the 9 5 ka coral record than in modern coral records from tahiti paired analysis of coral 18o and sr ca indicates cold wet warm dry interannual anomalies opposite from those observed in the modern instrumental record

trace element variations in fossil corals from tahiti collected by iodp expedition 310 reconstruction of marine environments during the last deglaciation 15 to 9 ka abstract climate responses and changes in marine environments during the last deglaciation have been controversial and few paleoceanographic data are available from the tropical south pacific though this region is crucial in the investigations of ocean atmosphere interactions integrated ocean drilling program expedition 310 was conducted to establish the time course of the postglacial sea level rise at tahiti in the south pacific a principal objective of this expedition was to examine the variation of marine environments during the last deglaciation as fossil porites coral is ideal for assessing past marine environments we selected only porites specimens from the many coral specimens retrieved examined them by xrd and dated them by the 14c method in all we obtained 17 pristine porites specimens composed of only aragonite with ages from 15 to 9 ka then we measured mg ca ba ca and u ca ratios and cd contents as proxies for upwelling and sea surface temperature higher ba ca ratios and cd content together with lower reconstructed ssts using u ca ratios in the coral specimens between 12 6 and 9 8 cal ka compared to around 15 cal ka suggest that upwelling and or entrainment of subsurface water into mixed layer was enhanced around tahiti during this period this finding is consistent with previous reports and supports the idea that the south pacific was characterized by la nina like conditions at least from 12 6 to 9 8 cal ka

strontium calcium ratios in modern porites corals from the great barrier reef as a proxy for sea surface temperature calibration of the thermometer and monitoring of enso high precision sr ca ratios are reported for porites corals from davies reef at 19 s on the midshelf of the great barrier reef australia skeletal growth parameters were also determined from coral slabs using x ray photographs and densitometry measurements a calibration of the sr ca thermometer has been obtained using in situ measured sea surface temperatures which gives sr ca 10 10 48 0 01 0 0615 0 0004 t wheret is in c this calibration applies to different species of porites and a large range of annual extension and calcification rates provided sampling follows a major growth axis biases of 1 2 c have been observed in the low density margins where growth is hampered by interfering fans of corallites the analytical and the long term reproducibility of sr ca derived temperatures are both better than 0 3 c 2 coral growth parameters such as the extension rate or density generally appear to respond to environmental changes such as rainfall but do not affect the sr ca partitioning between coralline aragonite and seawater no correlation has been found between calcification rate and sr ca variations consistent with sr ca being mainly controlled by temperature in the great barrier reef the interannual variability in sst is primarily related to the el nino southern oscillation phenomenon and is typically marked by a cold anomaly during the winter preceding the mature warm phase instrumental records show that the surface waters of the coral sea around 19 s have experienced a significant cooling associated with the el ninos of 1965 1972 and 1982 1983 which the porites corals record faithfully the coral derived temperatures for the period from 1965 to 1993 show an increase of 1 3 c which has occurred mainly since 1979 this warming is larger in magnitude but consistent with the trend for the southern hemisphere land and marine temperature records which shows an increase of around 0 4 c

chronology of the central atlantic magmatic province implications for the central atlantic rifting processes and the triassic jurassic biotic crisis abstract the central atlantic magmatic province camp is among the largest igneous provinces on earth emplaced synchronously with or just prior to the triassic jurassic t j boundary ca 200 ma in great part due to the controversial connection between the occurrence of camp and the events of the t j boundary the demand for better constraints on the duration and eruptive chronology of this province has increased more than 100 new 40 ar 39 ar ages have been published in the last 15 years with more than half of these in the last 3 years a careful review and selection of available ages as well as the publication of 16 new ages from the carolinas newark basin usa french guyana and morocco are presented judicious selection yields a total of 58 accepted age determinations for camp magmatism ranging from 202 to 190 ma covering every part of the camp a more complete picture develops with intrusive camp magmatism commencing as early as 202 ma extrusive activity initiated abruptly 200 ma reaching peak volume and intensity around 199 ma on the african margin the main period of camp magmatism is confirmed as brief but is suggested to consist of at least two phases over 1 5 ma with magmatism commencing along the africa north american margins and slightly later along the south american margin two volumetrically minor but distinctive magmatic peaks centered at 195 and 192 ma are mirrored in data from all three continents and highlighted by our statistical approach models describing rifting and thermal input and magma production on these timescales are explored despite significant advances in our understanding of the chronology of camp more data of better quality and broader geographical coverage are needed to completely characterize the evolution of the camp and infer its geodynamic origin in addition lack of a well defined t j boundary age as well as the absence of a relevant basis for comparison between u pb and 40 ar 39 ar data for this time period remain limiting factors to unambiguously linking camp in time with the events of the t j boundary

reply to comment by cahyarini et al on a snapshot of climate variability at tahiti at 9 5 ka using a fossil coral from iodp expedition 310

constraints on the structure and tectonic development of the early mesozoic south georgia rift southeastern united states seismic reflection data processing and interpretation seismic reflection data collected by the consortium for continental reflection profiling cocorp over the buried triassic jurassic south georgia rift reprocessed in order to improve the upper 5 s of reflection time provide a window into the regional deep structure of the rift and delineate variations in basin structure and depositional styles located at the southernmost extent of the north american east coast early mesozoic rift system the structure of the south georgia rift basin has previously been known only from scattered drilling and potential field interpretation leaving the internal and boundary as well as the deep structure unknown the reflection data reveal that the south georgia basin consists of a broad complex terrane of isolated synrift grabens with intervening structural highs in contrast with earlier concepts of a single narrow trough or an amorphous sag basin two main subbasin depocenters are observed in west and west central georgia the largest of which is more than 100 km in width and the deepest at least 7 km at its inferred base analysis of the reflection data indicates that the distinct structural and seismic stratigraphic character of the reflection packages is analogous to other better studied extensional provinces e g north american basin and range the reprocessing of the reflection data provides a view of contrasting styles of faulting and subsidence within the rift the structural style of the subbasins varies drastically along strike changing from 1 a narrow asymmetric graben bordered by a planar and more deeply penetrating normal fault to 2 a broad and roughly symmetric graben bordered by a shallower dipping possibly listric fault along which extension may have been accommodated at depth by a low angle detachment or by a more complex system of high angle faults only limited crustal extension is suggested by the narrower graben and planar fault 1 whereas much greater extension would be expected from the wider graben bordered by a listric low angle fault 2 such a dual style of basin formation is predicted by segmented plate models of variable extension along continental margins and intracratonic rifts and may imply a significant change in crustal rheology along the developing rift integration of the interpretation of the regional structure of the south georgia basin with that of the deeper crustal structure as inferred from the 16 s reflection time cocorp data indicates that the synrift basins developed mainly over the upper plate of the alleghanian late paleozoic suture between north america and west africa the major subbasin border faults dip northward in an antithetic relation to the predominantly northward vergence of the suture zone the border faults thus do not appear to have reactivated antecedant structure although the development of the south georgia rift appears to have approximately coincided with early mesozoic thinning of the crust in the southeastern united states no horizontally layered or laminated lower crust is observed as has been associated with other more fully rifted terranes e g north american basin and range continental shelf around british isles however the moho discontinuity appears to have formed as a dynamic feature superimposed on late paleozoic compressional structure probably associated with early mesozoic rifting these findings thus support the interpretation that the south georgia rift developed as a major early mesozoic depocenter and possible incipient spreading center associated with the initial formation of the central atlantic ocean

climate change on the yucatan peninsula during the little ice age we studied a 5 1 m sediment core from aguada x caamal 20 36 6 n 89 42 9 w a small sinkhole lake in northwest yucatan mexico between 1400 and 1500 a d oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2 2 and the benthic foraminifer ammonia beccarii parkinsoniana appeared in the sediment profile indicating a hydrologic change that included increased lake water salinity pollen from a core in nearby cenote san jose chulchaca showed a decrease in mesic forest taxa during the same period oxygen isotopes of shell carbonate in sediment cores from lakes chichancanab 19 53 0 n 88 46 0 w and salpeten 16 58 6 n 89 40 5 w to the south also increased in the mid 15th century but less so than in aguada x caamal climate change in the 15th century is also supported by historical accounts of cold and famine described in maya and aztec chronicles we conclude that climate became drier on the yucatan peninsula in the 15th century a d near the onset of the little ice age lia comparison of results from the yucatan peninsula with other circum caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the lia at that time sea surface temperatures cooled and aridity in the circum caribbean region increased

contrasting accreted terranes in the southern appalachian orogen basement beneath the atlantic and gulf coastal plains and west african orogens abstract a variety of lithostratigraphic units may be outlined within the pre mesozoic crystalline basement of the atlantic and gulf coastal plains these include 1 a group of metamorphic rocks of variable grade together with deformed and retrogressed granite in southwestern alabama and southeastern mississippi wiggins uplift hornblende and biotite within higher grade units record 40ar 39ar post metamorphic cooling ages of 310 300 ma 2 a suite of contrasting igneous rocks granite basalt and agglomerate and serpentinite which occurs along the brunswick altamaha magnetic anomaly in southwestern alabama and 3 an extensive apparently coherent tectonic element the suwannee terrane comprised of undeformed granite in which biotite records 40ar 39ar post magmatic cooling ages of 530 525 ma low grade felsic metavolcanic rocks a suite of high grade metamorphic lithologies st lucie metamorphic complex in which hornblende yields 40ar 39ar post metamorphic cooling ages of 515 510 ma and a succession of lower ordovician middle devonian sedimentary rocks characterized by gondwanan fauna the west african orogens mauritanides bassarides and rokelides record a locally complex polyphase tectonothermal evolution the earliest event corresponded to westward rifting of a continental fragment from the west african craton at 700 ma this led to development of a rift facies lithotectonic succession which included sedimentary units and intracontinental igneous sequences rifting was limited and a western ensialic arc began to develop by 680 ma the associated convergence culminated in an episode of folding and metamorphism at 650 ma pan african i orogenesis following widespread deposition of late paleozoic glacial and flyschoid sediments a second tectonothermal event occurred between 550 and 500 ma pan african ii orogenesis the west african orogens were marked by general tectonic quiescence throughout most of the early and middle paleozoic late paleozoic 300 ma collision of gondwana and laurentia resulted in eastward translation of previously tectonized mauritanide units over their foreland and emplacement at highest structural levels of previously imbricated nappes which include sequences with uncertain palinspastic origins the late paleozoic hercynian transport was largely intracontinental and only westernmost portions of the exposed mauritanides record an associated penetrative tectonothermal overprint characteristics of pre mesozoic basement units which comprise the suwannee terrane in the florida subsurface suggest they represent extensions of the bassaride rokelide orogen there is no apparent record of paleozoic tectonothermal activity in the suwannee terrane this contrasts markedly with penetrative late paleozoic reworking of basement units in the wiggins uplift this suggests that a major dextral transcurrent fault was active during the late paleozoic and that proximal basement units were directly involved in collisional aspects of pangea assembly the various basement units of the coastal plain are not correlative with any of the non laurentian terranes exposed in the southern appalachian orogen e g carolina terrane of the eastern piedmont which accreted in the ordovician devonian to exterior positions along the eastern margin of the north american craton these exotic appalachian terranes were transported into their present structural positions during late paleozoic collision of gondwana and laurentia they are separated from gondwanan elements of the suwannee terrane by a suture approximately marked by the brunswick altamaha magnetic anomaly

empirical assessment of coral sr ca and mg ca ratios as climate proxies using colonies grown at different temperatures 1 coral strontium calcium sr ca and magnesium calcium mg ca ratios might be useful for reconstructing past sea surface temperature sst in tropical oceans where instrumental data are limited however the link between coral skeletal trace elements and sst is disputed and biological factors such as skeletal growth rate may also affect trace elements in a coral we studied the relationships between growth rate and sst and sr ca and mg ca ratios using corals porites spp cultured in thermostated tanks sr ca was controlled primarily by sst while mg ca mainly reflected the growth rate with negligible contribution from species on both the variations these relationships are consistent with modeled results of cation partitioning during aragonite crystal formation

oscillations in the southern extent of the indo pacific warm pool during the mid holocene the indo pacific warm pool ipwp is thought to play a key role in the propagation and amplification of climate changes through its influence on the global distribution of heat and water vapour however little is known about past changes in the size and position of the ipwp in this study we use a total of 48 modern and fossil coral records from the mentawai islands sumatra indonesia and muschu koil islands papua new guinea to reconstruct oscillations in the extent of the ipwp since the mid holocene we show that reliable estimates of mean sea surface temperature sst can be obtained from fossil corals by using low resolution sr ca analysis of a suite of corals to overcome the large uncertainties associated with mean sr ca sst estimates from individual coral colonies the coral records indicate that the southeastern and southwestern margins of the ipwp were cooler than at present between similar to 5500 and 4300 years bp similar to 1 2 degrees c 0 3 degrees c and were similarly cool before similar to 6800 years bp this mid holocene cooling was punctuated by an abrupt short lived shift to mean ssts that were warmer than at present between similar to 6600 and 6300 years bp similar to 1 3 degrees c 0 3 degrees c while similarly warm conditions may have also existed after similar to 4300 years bp we suggest that mid holocene cooling at our study sites was related to contractions of the southeastern and southwestern margins of the ipwp associated with the more northerly position of the inter tropical convergence zone itcz that accompanied mid holocene strengthening of the asian summer monsoon conversely intervals of abrupt warming appear to correspond with widespread episodes of monsoon weakening and accompanying southward migrations of the itcz that caused the ipwp to expand beyond our coral sites intervals of a strengthened asian monsoon and cooling in the southwestern ipwp during the mid holocene appear to correspond with a more positive indian ocean dipole iod like mean configuration across the tropical indian ocean suggesting that the asian monsoon iod interaction that exists at interannual time scales also persists over centennial to millennial scales associated mean changes in the pacific enso modes may have also occurred during the mid holocene the dynamic and inter connected behaviour of the ipwp with tropical climate systems during the mid holocene highlights the fundamental importance of the warm pool region for understanding climate change throughout the tropics and beyond c 2009 elsevier ltd all rights reserved

rock fragments evolution and nutrients release in vineyard soils developed on a thinly layered limestone tuscany italy abstract this work dealt with two groups of vineyard soils developed from a thinly layered limestone in central italy so as to evaluate the evolution of the rock fragments and their capability to release nutrients one group consisted of five soils at 1 2 years after plantation of vines renewed soils while the other group was represented by five soils at 20 29 years from plantation aged soils soils were sampled by horizons on a volume basis fine earth rock fragments classed according to the degree of alteration and fresh rock were analyzed for mineralogy porosity ph total nh 4 n and extractable ca mg and k results indicated that the rock fragments of the aged soils were less and appeared more altered than those of the renewed soils this fact was ascribed to weathering processes that progressively transformed rock fragments into fine earth weathering of rock fragments was promoted by the calcite dissolution and the mechanical works made to break up the soil and for routine soil management because of this rock fragments increased porosity and exposed new mineral surfaces to soil solution with consequent reduction of their size and increasing of their friability and release of nh 4 n ca mg and k

late triassic and early jurassic palaeogeography of the world abstract a new version of global and regional palaeogeographic maps is presented for two time intervals these maps depict the plate tectonic configuration palaeoenvironment and lithofacies during the late triassic carnian norian and early jurassic hettangian toarcian time the individual maps illustrate the general conditions present during the maximum marine transgressions of higher frequency cyclicity within the absaroka sequence of sloss during triassic time pangaea began to stretch initiating the rifting and future break up of the supercontinent the continued northward drift of the cimmerian continent corresponded with the progressive closure and consumption of palaeotethys oceanic crust and the opening of the neotethys ocean the most significant late triassic convergent event was the indosinian orogeny occurring as a result of the consolidation of south china and north china blocks also indochina and indonesia were sutured to south china at the same time the qiangtang block approached the eurasian margin the consolidation of the north chinese and amurian blocks left open a large embayment of panthalassa between amuria and laurasia the so called mongol okhotsk ocean active subduction existed along the margin of this ocean dipping cratonwards towards east siberia the last collisional events of the uralian orogeny took place during the triassic and early jurassic time the conclusion of the uralian orogeny was accompanied by uplift of the adjacent areas of eastern europe and western siberia during the early jurassic the palaeotethys ocean was finally closed and the cimmerian continent collided with asia causing the cimmerian orogeny the time around the triassic jurassic boundary marked an important biotic extinction event plate tectonic activity caused palaeogeographic and palaeoclimatic change which may have contributed to the mass extinction from the plate tectonic and palaeogeographic point of view the following events could have influenced the extinction 1 the closure of palaeotethys and assembly of the asian part of pangaea 2 the break up of pangaea in the future central atlantic area and transition from rifting to drifting and 3 the very extensive basaltic volcanism of the central atlantic magmatic province

a coral oxygen isotope record from the northern red sea documenting nao enso and north pacific teleconnections on middle east climate variability since the year 1750 a 245 year coral oxygen isotope record from the northern red sea ras umm sidd egypt 28 n in bimonthly resolution is presented the mean annual coral 18o signal apparently reflects varying proportions of both sea surface temperature and 18oseawater variability in conjunction with instrumental observations of climate the coral record suggests for interannual and longer timescales that colder periods are accompanied by more arid conditions in the northern red sea but increased rainfall in the southeastern mediterranean whereas warmer periods are accompanied by decreased rainfall in the latter and less arid conditions in the northern red sea a 70 year oscillation of probably north atlantic origin dominates the coral time series interannual to interdecadal variability is correlated with instrumental indices of the north atlantic oscillation nao the el nino southern oscillation enso and north pacific climate variability the results suggest that these modes contributed consistently to middle east climate variability since at least 1750 preferentially at a period of 5 7 years

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

the carnian pluvial event in western europe new data from iberia and correlation with the western neotethys and eastern north america nw africa regions abstract at the beginning of the late triassic a period of increased precipitation occurred over large tracts of central pangea the carnian pluvial event it was a short lived event 1 ma coeval with a marked sea level fall and active rifting new and classical sections of carnian age in the iberian peninsula have been studied and a new correlation scheme is proposed for the iberian domain integrating field data and subsurface electric log data this is the first time that the portuguese and spanish late triassic carnian sediments are correlated the carnian pluvial event is identified in the iberian peninsula as a continental clastic wedge manuel fm and coeval sediments in between marine evaporite formations during a marked sea level drop event its age is considered to be julian early carnian by palynological and paleogeographic considerations a new correlation of the late triassic sediments of the iberian peninsula with coeval sediments of western europe nw africa and eastern north america is proposed and a new paleogeographical map of central eastern pangea for this period is presented in order to demonstrate that the geographical extent of the siliciclastic sediments related to the carnian pluvial event was much larger than accepted before

lithospheric sources of north florida usa tholeiites and implications for the origin of the suwannee terrane abstract sr nd and pb isotopic data for mesozoic tholeiites from six drillholes in northern florida suwannee terrane indicate derivation of the magmas from a source that was slightly incompatible element enriched with respect to bulk earth probably continental lithospheric mantle variably contaminated by more enriched crust initial isotopic compositions of the florida tholeiites show a considerable range 87 sr 86 sr 0 7059 to 0 7097 end 4 6 to 0 1 206 pb 204 pb 18 30 to 18 65 207 pb 204 pb 15 57 to 15 66 and 208 pb 204 pb 38 22 to 38 35 these compositions are distinctly different from those of mesozoic alkali basalts from the subsurface of southwestern florida heatherington a l mueller p a 1991 geochemical evidence for triassic rifting in southwestern florida tectonophysics 188 291 302 it is suggested that the north florida tholeiites were derived from within the continental lithosphere in contrast with mesozoic volcanic rocks from southwestern florida which have been previously suggested to be related to a mantle plume sm nd isotope systematics suggest derivation of the tholeiites from a 1 ga source a similar age to that proposed by pegram pegram w j 1990 development of continental lithospheric mantle as reflected in the chemistry of the mesozoic appalachian tholeiites usa earth and planetary science letters 97 316 331 for the source of tholeiitic basalts within the carolina terrane this supports proterozoic tectonic models which suggest that both the suwannee and carolina terranes had affinities with south american portions of gondwana containing 1 ga crust specifically the sunsas rondonian province nance murphy 1996 mueller p a kozuch m heatherington a l wooden j l offield t w koeppen r p klein t l nutman a p 1996 evidence for mesoproterozoic basement in the carolina terrane and speculations on its origin in nance r d thompson m d eds avalonian and related peri gondwanan terranes of the circum north atlantic gsa special paper 304 pp 207 218

pigment distribution in the caribbean sea observations from space abstract the caribbean is a semi enclosed tropical sea which is generally considered oligotrophic but that is influenced by nearly 20 of the annual discharge of the world s rivers amazon and orinoco rivers and by seasonal upwelling along the southern margin to investigate the role of these nutrient sources on the productivity of the region we mapped the distribution of pigments in the eastern caribbean east of 80 w using a series of coastal zone color scanner czcs images collected between november 1978 and december 1982 five additional images were examined for the period 1983 1986 the images revealed a seasonal cycle in the spatial structure of near surface pigment during january may there were high pigment concentrations 0 5 mg m 3 along the continental margin south of 14 n where upwelling occurred very little pigment 3 105 km2 this plume reached puerto rico around september october and drifted westward slowly losing its color signature we estimate that the discharge of the orinoco contributes 2 12 of the daily nitrogen requirements of the phytoplankton growing in the river plume and leads to the fixation of 7 29 105 tons of carbon per year the rest of the nitrogen demand appears to be met by nitrogen cycling the large scale 100 km pigment distribution patterns in the caribbean sea seem to be controlled by wind stress flux of water through the basin and river discharge westward advection of atlantic water probably dominates the flow during the first half of the year restricting the dispersal of blooms to the southern half of the caribbean while flushing the central and northern portions as the influx of atlantic water decreases in the second half of the year local ekman transport driven by the trade winds becomes dominant and surface waters drift northwestward throughout the basin the seasonal sequence of changes in pigment distribution patterns was consistent from year to year except in 1980 and 1984 when wind conditions in the caribbean were anomalous close scrutiny of the 4 years of czcs images did not reveal any evidence of large scale 300 km eastward flowing currents in the central caribbean this supports the view that previous observations of countercurrents were based on partial sampling of eddies of 100 250 km diameter

pangea s complex breakup a new rapidly changing stress field model over the years numerous proposals have been presented describing the relationship between the central atlantic magmatic province camp and the break up of pangea recent proposals have focused on refuting the original proposal of a mantle plume origin for the large igneous province and attendant dikes and instead propose an upper mantle or passive cause for the break up and camp in this paper we examine the fundamental assumption that the multiple dike orientations associated with the break up are geographically or temporally delimited new mapping and compilations of older local maps demonstrate that multiple dike orientations ranging from nw to ne trending were intruded throughout the western carolinas and are not geographically limited further new plagioclase 40 ar 39 ar dates indicate that all three orientations observed were emplaced within a 2 ma period c a 199 197 ma based on this information we propose that a rapidly rotating stress field must be responsible for the emplacement of multiple dike orientations in the carolinas and the break up of pangea and go on to propose several new tectonic models to account for this rotating stress field d 2005 elsevier b v all rights reserved

thermal and mechanical aspects of magma emplacement in giant dike swarms we consider the thermal history and dynamics of magma emplacement in giant feeder dikes associated with continental flood basalts for driving pressure gradients inferred for giant dike swarms thicknesses of 10 m would enable dikes to transport magma laterally over the distances observed in the field up to thousands of kilometers without suffering thermal lock up using time dependent numerical solutions for the thermal evolution of a dike channel under laminar and turbulent flow conditions in the presence of phase transitions we investigate the possibility that the observed dike thicknesses of the order of 100 m result from thermal erosion of the country rocks during dike emplacement this implies that the observed range of dike widths in giant dike swarms may reflect variations in the source volume and not the excess magma pressure it is found that the total volume of intruded magma required to produce an order of magnitude increase in dike width via wall rock melting broadly agrees with the estimated volumes of individual flows in continental flood basalts the presence of chilled margins and apparently low crustal contamination characteristics of some giant dikes may be consistent with turbulent magma flow and extensive melt back during dike emplacement in this case measurements of the anisotropy of magnetic susceptibility most likely indicate magma flow directions during the final stages of dike intrusion shear stresses generated at the dike wall when the dike starts to freeze strongly decrease with increasing dike width which implies that thicker dikes may have less tendency to produce consistent fabric alignment our results suggest that if the dike was propagating downslope off a plume related topographic swell the mechanism responsible for flow termination could possibly have been related to underpressurization and collapse implosion of the shallow magma plumbing system feeding the intrusion radial dikes that erupted at the periphery of the topographic uplift might have increased rather than decreased extensional stresses in the crust within the topographic uplift upon their solidification

a description of coads surface meteorological fields and the implied sverdrup transports for the atlantic ocean from 30 s to 60 n abstract using coads data spanning 1947 1988 we describe the regional nature of the atlantic ocean wind driven circulation between 30 8 and 60 n and its annual and interannual variability the sverdrup streamfunction defines the circulation gyres our focus is on three central gyres the northern hemisphere anticyclonic subtropical gyre the cyclonic tropical gyre just north of the equator and the clockwise equatorial gyre straddling the equator this rendition of the sverdrup streamfunction computed with constant drag coefficient and air density compares favorably with that from other climatologies in the straits of florida analyses suggest that differences between the annual cycle in sverdrup transport and observations may be due to regional winds farther north in the tropical gyre the sverdrup circulation argues against a continuous western boundary current transporting water from the equatorial region into the caribbean in boreal winter bringing to question the mechanisms for the known interh

sst artifacts in coral proxy records produced by early marine diagenesis in a modern coral from rabaul papua new guinea 1 we investigated the effects of early marine diagenesis on the skeletal geochemistry of a porites coral collected live offshore of rabaul papua new guinea the lowermost 14 cm of the 1 9 m coral core contains physical evidence of alteration which is clearly visible in x radiograph sem and petrography images abrupt and significant increases in coral 18o and sr ca and decreases in coral mg ca occur at the transition from unaltered to altered skeleton all of which imply significant sst cooling if the altered nature of the coral skeleton went unrecognized screening for the effects of early marine diagenesis should become a standard procedure in coral climate studies

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

new cocorp profiling in the southeastern united states part ii brunswick and east coast magnetic anomalies opening of the north central atlantic ocean new cocorp profiles on the coastal plain of georgia and northern florida support the hypothesis that the brunswick anomaly marks a late paleozoic suture they do not support the alternate view that this anomaly is caused by a mesozoic rift basin the trend of the brunswick anomaly relative to the appalachian gravity gradient indicates that in westernmost georgia and adjacent alabama african basement suwannee terrane is in proximity to autochthonous north american basement grenville farther east one or more paleozoic accreted terranes intervene between the north american and african sides of the orogen offshore the brunswick anomaly closely parallels the east coast magnetic anomaly this relationship implies that the east coast magnetic anomaly marks not only the present continental oceanic crustal transition but also the northward continuation of the late paleozoic suture between north america and africa transitional crust beneath the carolina trough baltimore canyon trough and correlative parts of the african atlantic margin is thus likely to have formed within a preexisting suture zone the dramatic change in character of the u s atlantic margin southward from the carolina trough to the blake plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

a snapshot of climate variability at tahiti at 9 5 ka using a fossil coral from iodp expedition 310 1 the integrated ocean drilling program iodp expedition 310 recovered drill cores from the drowned reefs around the island of tahiti 17 40 s 149 30 w many of which contained samples of massive corals from the genus porites herein we report on one well preserved fossil coral sample a 13 6 cm long porites sp dated by uranium series techniques at 9523 33 years monthly 18o and sr ca determinations reveal nine clear and robust annual cycles coral 18o and sr ca determinations estimate a mean temperature of 24 3 c 3 2 c colder than modern for tahiti at 9 5 ka however this estimate is viewed with caution since potential sources of cold bias in coral geochemistry remain to be resolved the interannual variability in coral 18o is similar between the 9 5 ka coral record and a modern record from nearby moorea the seasonal cycle in coral sr ca is approximately the same or greater in the 9 5 ka coral record than in modern coral records from tahiti paired analysis of coral 18o and sr ca indicates cold wet warm dry interannual anomalies opposite from those observed in the modern instrumental record

emplacement age of post tectonic granites in southern guinea west africa and the peninsular florida subsurface implications for origins of southern appalachian exotic terranes the coyah granite of guinea intruded western portions of the rokelide orogen following a tectonothermal event at ca 550 ma it records a biotite muscovite plus whole rock rb sr isochron age of 533 7 m y mswd 1 6 which is interpreted to closely date crystallization the osceola granite represents a major lithotectonic element in the pre cretaceous crystalline basement of peninsular florida five biotite concentrates from cuttings recovered from four wells penetrating the pluton record 40ar 39ar plateau ages ranging between 527 4 1 9 m y and 534 6 2 0 m y petrographic characteristics of the four samples suggest relatively rapid post magmatic cooling and the plateau ages are interpreted to closely date emplacement of the pluton similarities in age and petrographic characteristics combine to suggest that the coyah and osceola granites were initially part of a sequence of plutons emplaced along the northwestern margin of the gondwana continent portions of this terrane amalgamated with laurentia during late paleozoic assembly of pangea various exotic lithotectonic terranes which had previously accreted or were at least proximal to the north american craton were transported to their present structural position in the southern central appalachian orogen during this collision

paleoclimate proxy perspective on caribbean climate since the year 1751 evidence of cooler temperatures and multidecadal variability 1 annually resolved coral 18o and sr ca records from southwestern puerto rico are used to investigate caribbean climate variability between 1751 and 2004 c e mean surface ocean temperatures in this region have increased steadily by about 2 c since the year 1751 with sr ca data indicating 2 1 0 8 c and 18o data indicating 2 7 0 5 c coral geochemical records from across the tropics demonstrate that regional variability is important for understanding climate variations at centennial time scales a strong multidecadal salinity signal in the oxygen isotope data correlates with observed multidecadal temperature variations in the northern hemisphere instrumental wind and precipitation data indicate that the most recent coral isotopic variations are caused by expansion and contraction of the steep regional salinity gradient forced by trade wind anomalies through meridional ekman transport the timing of the fluctuations suggests that the multidecadal scale wind and surface circulation anomalies might play a role in atlantic temperature variability and meridional overturning circulation but further work is needed to confirm this suggestion

reconstructing seawater δ18o from paired coral δ18o and sr ca ratios methods error analysis and problems with examples from tahiti french polynesia and timor indonesia we compare several statistical routines that may be used to calculate delta o 18 and sss from paired coral sr ca and delta o 18 measurements typically the delta o 18 coral sst relationship is estimated by linear regression of coral delta o 18 vs sst if this method is applied evidence should be given that at a particular site sst and sss do not co vary in the tropical oceans sst and delta o 18 sw sss often co vary and this will bias the estimate of the regression slope of delta o 18 coral sst using a stochastic model we show that covariance leads to a bias in the coefficients of the univariate regression equations as the slope of the delta o 18 coral sst relationship has known we propose to insert this value for gamma 1 in the regression models this requires that the constants of the regression equations are removed to omit the constants we propose to center the regression equations i e to remove the mean values from the variables the statistical error propagation is calculated to assess our ability to resolve past variations in delta o 18 sw sss at tahiti we find that the combined analytical uncertainties of coral delta o 18 and sr ca equal the amplitude of the seasonal cycle of delta o 18 sw sss therefore we cannot resolve the seasonal cycle of sss at tahiti at timor the error of reconstructed delta o 18 sw sss is lower than the magnitude of seasonal variations of delta o 18 sw sss and the seasonal cycle of delta o 18 sw sss can be resolved c 2008 elsevier ltd all rights reserved

refining gondwana and pangea palaeogeography estimates of phanerozoic non dipole octupole fields summary reliable phanerozoic paleopoles have been selected from the stable parts of the gondwana continents and upon appropriate reconstruction have been combined in an apparent polar wander apw path which can be compared with a previously compiled path for laurussia this comparison once again confirms that pangea a reconstructions for late palaeozoic and early mesozoic times cannot be reconciled with the available paleomagnetic data unless these data are corrected for latitudinal errors caused by non dipole octupole field contributions or by inclination shallowing because the discrepancies persist even when only paleopoles from igneous rocks are used inclination shallowing cannot be the sole cause of the problem there is an apparent decrease in the percentage of octupole field contributions needed as a function of time for mesozoic and younger time gondwana laurussia comparisons require on average lower ratios of octupole dipole fields than for palaeozoic time however the gondwana paleopoles for the palaeozoic include a much greater proportion of results derived from sedimentary rocks than do those for the mesozoic so that this apparently diminishing octupole field contribution may be an artefact we have also examined whether the clustering of coeval gondwana poles improves with optimal g3 contributions but found that while there are improvements they are not systematic and not statistically significant a combined apw path has been constructed for pangea for times since the mid carboniferous which accounts for octupole fields or equivalently inclination shallowing we argue that this global path is an improvement over previous constructions as it represents a self consistent plate tectonic model and does not violate widely accepted pangea a reconstructions

reproducibility of geochemical and climatic signals in the atlantic coral montastraea faveolata 1 monthly resolved 41 year long stable isotopic and elemental ratio time series were generated from two separate heads of montastraea faveolata from looe key florida to assess the fidelity of using geochemical variations in montastraea the dominant reef building coral of the atlantic to reconstruct sea surface environmental conditions at this site the stable isotope time series of the two corals replicate well mean values of 18o and 13c are indistinguishable between cores compare 0 70 versus 0 68 for 13c and 3 90 versus 3 94 for 18o mean values from the sr ca time series differ by 0 037 mmol mol which is outside of analytical error and indicates that nonenvironmental factors are influencing the coral sr ca records at looe key we have generated significant 18o sea surface temperature sst r 0 84 and sr ca sst r 0 86 calibration equations at looe key however these equations are different from previously published equations for montastraea variations in growth parameters or kinetic effects are not sufficient to explain either the observed differences in the mean offset between sr ca time series or the disagreement between previous calibrations and our calculated 18o sst and sr ca sst relationships calibration differences are most likely due to variations in seawater chemistry in the continentally influenced waters at looe key additional geochemical replication studies of montastraea are needed and should include multiple coral heads from open ocean localities complemented whenever possible by seawater chemistry determinations

an evaluation of quantitative reconstruction of past precipitation records using coral skeletal sr ca and δ18o data abstract coupled records of 18o and sr ca in porites coral have been used to derive hydrological conditions by removing the sr ca inferred temperature component from the 18o signal nanwan a semi enclosed bay in southern taiwan provides an opportunity to demonstrate the feasibility of quantitatively reconstructing past precipitation history recurrence of seawater 18o offsets between wet and dry seasons in the early 1990s is well correlated with the precipitation record even though the hydrological signal only accounts for 20 of the total annual coral 18o variation of ca 1 offsets can be found in the residual 18o of modern corals after removing the thermal effect which contributes to the other 80 the observed timing and amplitude of the seasonal seawater 18o offsets in nanwan and their correlation with precipitation are reproduced by hydrological models in the mid holocene the seasonal anomaly of residual 18o was twice that of the modern value based on the 9 yr sr ca 18o data recorded in a 6 73 ka porites coral hydrological models suggest an annual rainfall of 1800 3000 mm yr at the window during mid holocene 20 higher than that of the average of 30 yr modern instrumental records of 1500 2500 mm consistent with the qualitative pollen record from lake sediments the seasonal decrease of residual 18o in 5 of 9 yr was earlier than the increase of the coral sr ca inferred temperature which implies that these rainy seasons probably occurred from the early mid spring to mid summer earlier than that from late spring to late summer today the driving force may be related to the changes of solar insolation and the east asian monsoon it is cautioned that the variability of hydrographic conditions imposes restrictions on a precise calculation of the amount of paleo precipitation the dynamic nature of local tectonics monsoons and water circulation should be further addressed to precisely quantify precipitation over the past 10 000 yr from coral geochemical records

is the brunswick magnetic anomaly really the alleghanian suture the southeastern margin of the united states presents a complex picture of accreted paleozoic terranes and a rift related mesozoic overlap assemblage buried by a thick veneer of coastal plain sediments basement terranes have been defined on the basis of drilling and geophysical data their relationship to each other and to plate tectonics is in debate the brunswick magnetic anomaly in georgia has been cited as the location of the late paleozoic suture between north america and a continental fragment with african affinities known from the northern florida subcrop this paper poses a new plate model for this region based upon the following assumptions 1 that deep well tests furnish a reasonable data set for the discrimination of various basement rock types across the region and 2 that the brunswick anomaly is the outboard limit of the north american piedmont avalon terrane we propose that the area between the northwest limit of african rocks and the trace of the brunswick anomaly is a region of crustal overlap as african related rocks were overthrust to the northwest the original irregular outline of the north american continental margin and the landward extensions of oceanic fracture zones are intimately related to the kinematics of suspect terranes in the appalachian orogen the implications of the model suggest that differential shortening during collision and differential extension during subsequent rifting accommodate movements on repeatedly activated transforms

crustal structure across the brunswick magnetic anomaly offshore georgia from coincident ocean bottom and multi channel seismic data we present results from a coincident wide angle and deep penetrating multichannel reflection seismic experiment conducted on the continental shelf of the southeast georgia embayment over 5000 air gun shots were recorded by a 6 km long towed streamer and six ocean bottom seismic instruments along a 250 km north south profile crossing the brunswick magnetic anomaly bma these data indicate a transition in seismic properties across the bma including higher seismic velocities south of the bma particularly in the upper crust 7 15 km depth and a transition from reflective to transparent crust from north to south we interpret this transition to indicate an increased mafic content in crust south of the bma magnetic modeling based on our seismic results indicates that the bma may be explained as an edge effect anomaly of the more mafic upper crust we suggest that the increased mafic content toward the south is due to rift related mafic intrusion an alternative interpretation is discussed in which the seismic transition across the bma is related to an alleghanian suture athough there is no direct indication in the data for the association of the bma and an alleghanian suture along our profile such an association cannot be ruled out the southern portion of the profile crosses the margin hinge zone where we observe seaward dipping reflectors similar to those observed along the northern blake plateau basin and carolina trough hinge zones which have been interpreted as volcanic sequences our seismic data include no evidence for very high velocity 7 0 km s mid crust to lower crust inboard of the hinge zone such as is observed in the carolina trough outboard of the hinge zone this indicates that the volume of emplaced mafic material changes dramatically across the hinge zone and suggests that rift related magmatic processes along the margin were highly focused

evaluation of sampling resolution in coral stable isotope records a case study using records from new caledonia and tarawa we have generated a 40 year long monthly stable isotope record from a porites lutea coral collected offshore of amedee new caledonia 22 s 167 e to investigate the relation between sampling resolution in coral isotope studies and retrieval of sea surface environmental information we interpret the high correlation between our oxygen isotope record and a twenty year long sea surface temperature record at the monthly timescale r 0 88 to indicate that our coral isotope record is an accurate monitor of environmental conditions offshore of amedee the character of the signal and the percent variance explained in the record at the annual band at the quasi biennial oscillation band qbo 2 0 2 4 years and at the el nino southern oscillation band enso 3 8 years changes little in response to a reduction in sampling density from monthly to bimonthly to quarterly similar results have been obtained in a reanalysis of a coral isotope record from tarawa kiribati our results indicate that a significant amount of the information obtained from high density sampling can also be retrieved from lower density sampling in particular bimonthly sampling yields virtually no drop off in variance explained and quarterly sampling is satisfactory for resolving interannual and decadal scale trends in time series the proposed sampling approach may enable a more rapid filling in of numerous spatial holes in coral sampling sites needed for reconstruction of long term decadal scale variations in climate

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

melt generation at volcanic continental margins no need for a mantle plume melt generation in a rifting environment is studied using a dynamic 2 d finite element model the lithosphere is extended to large realistic thinning factors assuming a mantle temperature of 1333 c the focussing of deformation results in a distribution of thinning factors along the margin at breakup time consistent with observations the timing of melt production late synrift and the amounts of melt are consistent with observations at volcanic margins the dynamical processes related to lithospheric rifting enhance the produced melt volumes sufficiently to explain the sometimes enigmatic melt volumes found at volcanic margins

a 1400 year high resolution record of atmospheric circulation over the north atlantic and asia major ion series developed from new subannual scale sampling of an ice core from central greenland are calibrated with instrumental series of atmospheric sea level pressure recording major marine icelandic low and terrestrial siberian high atmospheric circulation systems to provide proxy records of atmospheric circulation over the past 1400 years examination of the proxy records reveals major changes in behaviour of these systems c ad 1400 multidecadal and centennial scale periodic components characterization of mean sea level pressure anomaly fields during the little ice age and the mediaeval warm period the potential role of solar forcing coupled ocean atmosphere associations and a perspective within which the characteristics of instrumental era climate can be assessed

the effect of rock fragments on wheat biomass production under highly variable moisture conditions in mediterranean environments abstract the effects of soil properties that affect water availabilty to plants such as soil depth rock fragments parent material and degree of erosion on biomass production of rainfed wheat were studied on hilly soils under different weather conditions total above ground biomass production tagbp of wheat was measured along catenas of marl and shale sandstone formations in two successive growing periods during the first growing period which was extremely dry total amount of rainfall r 95 mm versus 370 mm in an average year the soils on marl free of rock fragments produced an average tagbp of 1100 kg ha 1 despite their great soil depth whereas on shoulders and footslopes of the stony soils on shale sandstone formations tagbp values of 4620 and 11 100 kg ha 1 were measured respectively the opposite occurred the following growing period which was exceptionally wet r 663 mm soils on marls were more productive due to the higher fertility status than the soils on shale sandstone formations rock fragments more responsible for the lower exploitable soil volume and the generally lower biomass production under wet climatic conditions play an important role on soil water conservation under dry climatic conditions

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

annual to interannual temperature variability in the caribbean during the maunder sunspot minimum we reconstruct caribbean seawater temperatures from sclerosponge sr ca ratios using a specimen of ceratoporella nicholsoni that grew at 20 m below sea level in a reef cave at jamaica we sample the time interval from 1620 to 1745 a d with almost monthly resolution this interval includes the maunder sunspot minimum one of the coldest periods of the little ice age reconstructed annual temperature amplitudes are on the order of about 1 c the mean growth rate calculated from the annual sr ca variations corresponds perfectly with u th based growth rates we find that the interannual climate variability is determined by el nino southern oscillation and by a decadal signal most likely originating from the tropical north atlantic on a multidecadal timescale the maunder minimum is characterized by a 1 2 c cooling and reduced amplitudes of the interannual and decadal temperature variations

an 8 century tropical atlantic sst record from the cariaco basin baseline variability twentieth century warming and atlantic hurricane frequency 1 we present the first direct comparison and calibration of a downcore foraminiferal mg ca record to historical instrumental sea surface temperature sst mg ca measured on the planktic foraminifer globigerina bulloides from a cariaco basin sediment core strongly correlate with spring march may instrumental ssts between a d 1870 and 1990 a mg ca sst equation is derived and a paleo sst record is presented spanning the last 8 centuries an interval that includes the end of the medieval warm period and the little ice age the long term record displays a surprising amount of variability the temperature swings are not necessarily related to local upwelling variability but instead represent wider conditions in the caribbean and western tropical atlantic the mg ca sst record also captures the decadal and multidecadal variability observed in records of global land and sea surface temperature anomalies and atlantic tropical storm and hurricane frequency over the late nineteenth and twentieth centuries a divergence between the sst proxy record and atlantic storm frequency around 1970 appears to reflect a fundamental change in atlantic hurricane behavior noted in historical data on average twentieth century temperatures are not the warmest in the entire record but they do show the largest increase in magnitude and fastest rate of sst change over the last 800 a

atmospheric and oceanic evidences of el nino southern oscillation events in the south central pacific ocean from coral stable isotopic records over the last 137 years we measured 18o and 13c in porites lutea collected in the moorea lagoon where the instrumental records show that an el nino southern oscillation enso event implies both a cloud cover decrease and a weak sea surface temperature sst increase two proxies allow an enso record to be reconstructed at moorea the annual 13c anomaly associated with the south pacific convergence zone motion and an annual 18o anomaly showing increased sst the frequency bands exhibited by the singular spectral analysis ssa and the multitaper method of the annual 18o and 13c records are centered on 2 5 and 5 2 years and 2 4 and 3 2 years respectively which are the main enso modes we used ssa to reconstruct enso events at moorea over the past 137 years results indicate that climate variability at this site is strongly affected by enso events

an assessment of the sr ca ratio in shallow water hermatypic corals as a proxy for sea surface temperature the high precision measurement of the sr ca ratio in corals has the potential for measuring past sea surface temperatures at very high accuracy however the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the sr ca ratio of seawater and that kinetic effects such as the calcification rate can affect the sr ca ratio of corals and produce inaccuracies of the order of 2 4 c in the present study a number of cores of the massive hermatypic scleractinian coral porites from the central great barrier reef have been analyzed for sr ca at weekly to monthly resolution results from a 24 year record from myrmidon reef show an overall variation from 22 7 c to 30 4 c the record shows a warming cooling trend with maximum warming centred on the 1986 1987 summer while some bleaching was reported to have occurred at myrmidon reef in 1982 the sr ca record indicates that subsequent summer temperatures were much higher the 4 5 year record from stanley reef shows a maximum sst of 30 c during the 1997 1998 el nino event the calibrations from myrmidon and stanley reefs are in excellent agreement with previously published calibrations from nearby reefs while corals do not calcify in equilibrium with seawater due to physiological control on the uptake of sr and ca into the lattice of coralline aragonite it can be argued that provided only a single genus such as porites sp is used and that the coral is sampled along a major vertical growth axis then the sr ca ratio should vary uniformly with temperature similarly objections based on the spatial and temporal variability of the sr ca activity ratio of seawater can be countered on the basis that in most areas where coral reefs grow there is a uniformity in the sr ca activity ratio and there does not appear to be a change in this ratio over the growth period of the coral evidence from several corals in this study suggest that stress can be a major cause of the breakdown in the sr ca sst relationship thermal stress resulting from either extremely warm or cool temperatures can produce anomalously low sr ca derived ssts as a result of the breakdown of the biological control on sr ca fractionation it is considered that other stresses such as increased nutrients and changes in light intensity can also lead to a breakdown in the sr ca sst relationship two of the main issues affecting the reliability of the sr ca method are the calibration of the sr ca ratio with measured sst and the estimation of tropical last glacial maximum lgm palaeotemperatures instead of producing a constant calibration just about every one published so far is different from the others what is obvious is that for most calibrations while the slope of the calibration equation is similar the intercepts are not while the cause for this variation is still unknown it would appear that corals from different localities around the world are responding to their own particular environment or that certain types of environments exert a control on the corals physiology sr ca derived sst estimates for the lgm and deglaciation of 5 c 6 c cooler than present are at odds with estimates of 2 c 3 c cooling by other climate proxies the apparent lack of reef growth during the lgm suggests that ssts were too cold in many parts of the tropics for reefs to develop this would lend support to the idea that tropical ssts were much cooler than what the climap data suggests

the influence of inherited structures on dike emplacement during gondwana breakup in southwestern africa abstracta kinematic analysis of cretaceous and pre cretaceous structures was carried out along the west coast of southern africa extending from the cape town area into namibia with the aim of investigating whether inherited structural discontinuities controlled gondwana breakup and the associated opening of the south atlantic in the cretaceous this was augmented by map and satellite image analyses of mainly cretaceous mafic dikes exposed from sw angola to the southern tip of africa the combined results provide consistent evidence of e w to ne sw directed extension during the cretaceous e w extension dominated from southern angola to the namibian south african border and ne sw directed extension occurred in an area extending from west central namibia to the southwestern coast of south africa these two extension directions overlap from west central namibia to southernmost namibia the kinematic analysis of pan african structures provides evidence of ene wsw directed shortening in the western saldania

a high resolution calibration of sr ca thermometry using the caribbean coral montastraea annularis 1 a relationship has been established between the sr ca ratio in the skeleton of the scleractinian coral montastraea annularis and sea surface water temperature in south florida in order to obtain this correlation specimens of montastraea annularis were transplanted to a site at a local reef where every two to three months throughout a 2 year period the corals were stained with alizarin red s and where water temperature which annually ranges between 20 and 30 c was continually monitored at the end of the experimental period the coral skeleton was sampled at a rate of 50 samples per year each sample corresponding to only around 20 g of calcium carbonate for the 2 5 year period the sr ca ratio exhibited excellent correlation in the first year r2 0 83 sr ca mmol mol 10 11 0 0452 sst c but a rather poorer correlation in the second year r2 0 68 sr ca mmol mol 10 09 0 0406 sst c averaging the data into monthly values for year 1 we determined a relationship of sr ca mmol mol 10 165 0 0471 sst c on the basis of the excellent correlation between temperature and sr ca we feel that this relationship is the most accurate discrepancies in the second year are suggested to arise from slight sampling errors relative to the stain lines

magmatic rifting of pangaea linked to onset of south american plate motion abstract the causes of the transition from amagmatic to magmatic rifting during continental break up are not always clear and have been often linked to the break through of a plume however stress fields recorded in the crust may offer new insights into the relationship between changes in the stress field and the onset of magmatism in this paper stress fields recorded in the crust of north america are used to test possible causes of the break up of pangaea and the transition from amagmatic to magmatic rifting finite element models reveal that the most likely scenario for the break up involves the initial northwest motion of north america at 230 ma followed by a south southeast motion of south america at 200 ma with the initiation of magmatism and finally a weakened area between north and south america sometime soon after 200 ma which resulted in north america being dominated by northwest motion once again it was also determined that plate boundary structure and orientation play a large part in the recorded stress fields and must be taken into consideration when modeling continental break ups and rifting

influence of continental roots and asthenosphere on plate mantle coupling the shear tractions that mantle flow exerts on the base of earth s lithosphere contribute to plate driving forces and lithospheric stresses we investigate the sensitivity of these tractions to sub lithospheric viscosity variations by comparing shear tractions computed from a mantle flow model featuring laterally varying lithosphere and asthenosphere viscosity with those from a model with layered viscosity lateral viscosity variations generally do not change the direction of shear tractions but deeply penetrating continental roots increase traction magnitudes by a factor of 2 5 compared to 100 km thick lithosphere a low viscosity asthenosphere decreases traction magnitudes by a smaller amount and is important only if 100 km thick increased plate mantle coupling beneath thick continental lithosphere may increase plate driving forces surface deformation and mantle derived lithospheric stresses in these regions by contrast a low viscosity asthenosphere does not decouple the lithosphere from mantle flow highlighting the geological importance of mantle tractions on the lithosphere

florida current surface temperature and salinity variability during the last millennium surface water d 18 ow near dry tortugas increased 0 4 during the course of the little ice age lia 1200 1850 a d equivalent to a salinity increase of 0 8 1 5 on the great bahama bank where surface waters are influenced by the north atlantic subtropical gyre d 18 ow increased by 0 3 during the last 200 years although a portion 0 1 of this shift may be an artifact of anthropogenically driven changes in surface water sco2 the remaining d 18 ow signal implies a 0 4 1 increase in salinity after 200 years b p the simplest explanation of the d 18 ow data is southward migration of the atlantic hadley circulation during the lia scaling of the d 18 ow records to salinity using the modern low latitude d 18 ow s slope produces an unrealistic reversal in the salinity gradient between the two sites only if d 18 ow is scaled to salinity using a high latitude d 18 ow s slope can the records be reconciled variable atmospheric 14 c paralleled dry tortugas d 18 ow suggesting that solar irradiance paced centennial scale migration of the inter tropical convergence zone and changes in florida current salinity during the last millennium citation lund d c and w curry 2006 florida current surface temperature and salinity variability during the last millennium paleoceanography 21 pa2009 doi 10 1029 2005pa001218

rock fragments and soil hydrological processes significance and progress abstract in this review we explore the significance of rock fragments in studies of soil hydrological processes because according to research the effects of rock fragments on soil hydrological processes are inconsistent positive negative rock fragments play a critical role in the biosphere as the primary filter for water and solutions containing contaminants and heavy metals rock fragments have a complex influence on soil hydrological processes e g soil erosion runoff generation water infiltration solute transport and water flow and are highly relevant in a typical system in the soil plant atmosphere continuum cracks related to rock fragments provide preferential flow paths through which pollutants are transported into groundwater in this paper the published literature is reviewed concentrating on rock fragments and their effects on soil hydrological processes systematic studies and examples illustrate the effects of rock fragments architecture i e coverage content size position spatial heterogeneity morphology weathering and topography on soil hydrological processes methods and models applied to evaluate the effects of rock fragments on soil hydrological processes are examined in detail we conclude that the relationship between rock fragments and soil hydrological processes is complicated and requires more international research efforts this review concludes with a discussion of perspectives on areas of research that can improve understanding of the effects of rock fragments on soil hydrological processes with insights and suggestions also being provided regarding potential research trends requirements and solutions

palaeozoic to early jurassic history of the northwestern corner of gondwana and implications for the evolution of the iapetus rheic and pacific oceans abstract the palaeozoic to mesozoic igneous and metamorphic basement rocks exposed in the merida andes of venezuela and the santander massif of colombia are generally considered to define allochthonous terranes that accreted to the margin of gondwana during the ordovician and the carboniferous however terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains a general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the merida andes and the santander massif we present new zircon u pb icp ms data from 52 igneous and metamorphic rocks which we combine with whole rock geochemical and pb isotopic data to constrain the tectonic history of the precambrian to mesozoic basement of the merida andes and the santander massif these data show that the basement rocks of these massifs are autochthonous to gondwana and share a similar tectono magmatic history with the gondwanan margin of peru chile and argentina which evolved during the subduction of oceanic lithosphere of the iapetus ocean the oldest palaeozoic arc magmatism is recorded at 500 ma and was followed shortly by barrovian metamorphism peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at 477 ma and the intrusion of synkinematic granitoids until 472 ma subsequent retrogression resulted from localised back arc or intra arc extension at 453 ma when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement continental arc magmatism dwindled after 430 ma and terminated at 415 ma coevally with most of the western margin of gondwana after pangaea amalgamation in the late carboniferous to early permian a magmatic arc developed on its western margin at 294 ma as a result of subduction of oceanic crust of the palaeo pacific ocean intermittent arc magmatism recorded between 294 and 225 ma was followed by the onset of the andean subduction cycle at 213 ma in an extensional regime extension was accompanied by slab roll back which led to the migration of the arc axis into the central cordillera of colombia in the early jurassic

the geological history of northwestern south america from pangaea to the early collision of the caribbean large igneous province 290 75ma abstract northwestern south america preserves a record of the assembly of western pangaea its disassembly and initiation of the far western tethys wilson cycle subsequent pacific margin magmatism and ocean plateau continent interaction since the late cretaceous numerous models have been presented for various time slices although they are based on either spatially restricted datasets or dates that are inaccurate estimates of the time of crystallisation here we review a very large quantity of geochronological geochemical thermochronological sedimentological and palaeomagnetic data that collectively provide tight constraints for geological models these data have been collected over a trench pacific parallel distance of 1500 km colombia and ecuador and reveal important temporal trends in rifting and subduction the temporal framework for our model constraints are obtained from robust concordant zircon u pb ages of magmatic rocks during 290 75 ma the late cretaceous thermal history of the margin

a jurassic granite from southern georgia u s a silicic extension related magmatism along the southeastern coastal plain abstract ion microprobe shrimp u pb dating of single zircon grains extracted from granite cuttings from the subsurface of southeastern georgia pierce co yields a well defined crystallization age of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 159 pm 3 end document ma 2 confirming the presence of mesozoic silicic magmatism in the northern suwannee terrane revision of suwannee terrane subcrop age province boundaries is required by these data the granite is 20 40 m yr younger than subsurface diabases in the same r

the temperature relationship in coralline aragonite influence of variability in and skeletal growth parameters this paper provides an evaluation of two of the most likely pitfalls of sr ca thermometry i e the effect of biogenic cycling of sr vs ca in the surface ocean and the effect of variable extension rate on sr incorporation in coralline aragonite the authors also report calibration of the sr ca temperature relationship for three coral species porites lobata pocillopora eydouxi and pavona clavus collected for the hawaiian and galapagos islands analyses of seawater samples show significant spatial and depth variability in the sr ca ratio the uncertainty introduced by this effect is estimated to be 0 2 degrees c for corals located in tropical oligotrophic waters and potentially larger for corals located in upwelling areas sr ca along two different growth axes of a galapagos pavona clavus with annual extension rates of approximately 6 and 12 mm y respectively indicate an offset of 1 2 degrees c with higher sr ca values associated with slower extension rates the offset observed between the two growth axes may be the result of variations in extension and or calcification rate these results are important in determining past sea surface temperatures for reconstruction of paleoclimates

coral oxygen isotope records of interdecadal climate variations in the south pacific convergence zone region 1 the south pacific convergence zone spcz a region of high rainfall is a major feature of subtropical southern hemisphere climate and contributes to and interacts with circulation features across the pacific yet its past temporal variability and forcing remain only partially understood here we compare coral oxygen isotopic 18o series spanning a d 1997 1780 and a d 2001 1776 from two genera of hermatypic corals in fiji located within the spcz to examine the fidelity of these corals in recording climate change and spcz interdecadal dynamics one of these coral records is a new 225 year subannually resolved 18o series from the massive coral diploastreaheliopora diploastrea s use in climate reconstructions is still relatively new but this coral has shown encouragingly similar interannual variability to porites the coral genus most commonly used in pacific paleoclimate studies in fiji we observe that interdecadal 18o variance is also similar in these two coral genera and diploastrea contains a larger amplitude interdecadal signal that more closely tracks instrumental based indices of pacific interdecadal climate change and the spcz than porites both coral 18o series record greater interdecadal variability from 1880 to 1950 which is consistent with the observations of folland et al 2002 who reported higher variability in spcz position before 1945 these observations indicate that diploastrea will likely provide a significant new source of long term climate information from the spcz region

40ar 39ar constraints on chronology of augusta fault zone movement and late alleghanian extension southern appalachian piedmont south carolina and georgia

integration of cocorp deep reflection and magnetic anomaly analysis in the southeastern united states implications for origin of the brunswick and east coast magnetic anomalies integration of magnetic anomaly analysis with cocorp deep reflection data from the southeastern united states provides three new constraints on the interpretation of the brunswick and east coast magnetic anomalies as well as on the reflection data these are as follows 1 the source of the brunswick anomaly lies within the deep crust this anomaly is not caused by a mesozoic rift basin as proposed by some workers 2 a simple seaward dipping high susceptibility slab model can explain both the brunswick and east coast magnetic anomalies the along strike change in character of the two anomalies results largely from a change in azimuth of the source body 3 beneath the southeastern united states this source body dips south lies immediately on the south flank of the prominent southward dipping reflective zone revealed on cocorp surveys and was previously associated with the alleghanian suture between north america and africa these results imply that a dipping highly magnetized zone in the upper plate of the alleghanian suture is responsible for both the brunswick and east coast magnetic anomalies the high susceptibility material responsible for these anomalies might be mafic lower continental or oceanic crust thrust upward during alleghanian continental collision or mafic igneous material intruded into the upper plate of the suture zone during subsequent mesozoic rifting or both the latter hypothesis implies that the alleghanian suture acted as a zone of weakness a repository which was reactivated to control the site of ultimate atlantic rifting and possibly initial sea floor spreading

stability of dike intrusion along preexisting fractures we investigate the ability of magma to propagate along preexisting fractures oblique to the least compressive stress relaxation of the preexisting shear stress to zero over the portion of the fracture dilated by magma the dike results in slip for some distance along the closed portion of the fracture ahead of the dike tip and a stress concentration near the dike tip this could lead to the production of new tensile cracks oblique to the parent dike that could capture the flow if the shear stress resolved on the fracture plane is perpendicular to the fracture front mode i ii the front may deviate along its entire length if the shear stress is parallel to the fracture front mode i iii the front may splay into segments for mode i ii dikes the maximum tensile stress occurs at the dike tip and is parallel to the dike if the effective tensile stress exceeds the rock tensile strength then the intruding magma rather than dilating the existing fracture is expected to propagate into a self generated crack analogous to the wing cracks observed to form at the tips of pure mode ii fractures for mode i iii dikes the maximum tensile stress lies within the plane of the dike and is oriented at some angle that depends upon the far field boundary conditions even if the magma pressure exceeds the ambient normal stress it appears to be very difficult for dikes to intrude into preexisting fractures unless one or more of the following conditions is satisfied 1 the fracture is nearly perpendicular to the least compressive stress 2 the resolved shear stress on the fracture is small compared to the excess magma pressure i e the ratio of shear to opening of the dike walls is small 3 the effective ambient dike normal stress is small compared to the rock tensile strength this indicates that it may be quite difficult for dikes emerging from midcrustal to lower crustal depths to follow faults

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

characterisation of triassic rifting in peru and implications for the early disassembly of western pangaea abstract triassic igneous and sedimentary rocks exposed within the basement of the andes were deposited in a series of rifts and may record the early disassembly of western pangaea these rocks are sporadically exposed along almost the entire length of western south america although reliable geochronological and isotopic data are sparse we combine new geochronological zircon u pb isotopic hf nd and geochemical data with stratigraphic observations to constrain the age and tectonic setting of the mitu rift of southern peru the peruvian mitu rift is compared with other triassic rifts in colombia and ecuador palanda rift 240 225 ma bolivia mitu rift triassic bolivia chile and argentina e g cuyo basin 246 230 ma and conclusions are reached regarding the relationship between triassic extension along the western margin of pangaea and the eventual formation of the proto caribbean and central atlantic oceans the mitu rift peru was active during 245 240 to 220 ma and was synchronous with rifting along the pacific margin of colombia and ecuador along the chilean margin and western argentina and probably rifting within bolivia rifting north of the huancabamba deflection was accompanied by subduction and led to seafloor spreading whereas rifting along the peruvian and chilean margins mainly occurred in the absence of subduction and terminated prior to the formation of extensive transitional crust extension within peru and chile probably occurred via a combination of transtension steepening and detachment of an arrested slab we propose that plate tectonic forces initiated the early break up of pangaea by attenuating its margins and enhancing mantle upwelling prolonged extension may have propagated along pre existing weak zones that extended into the continental interior captured melts derived from the upwelled mantle forming a lip e g central atlantic magmatic province became hot and weak and eventually lead to the formation of a juvenile ocean e g central atlantic

changes in wind driven upwelling during the last three centuries interocean teleconnections based u37 0 paleothermometer yielded high resolution records of sea surface temperatures sst from 1700 to 2000 ad the trends in the u37 0 index reveal steady sst increases of 1 to 2c at both sites since the end of the little ice age higher frequency changes in sst indicate a decoupling in the relative intensity of wind driven upwelling at the two sites periods of enhanced upwelling in guaymas correspond to periods of decreased upwelling in cariaco and vice versa we propose that these contrasts reflect regional differences in the upwelling response of upwelling to changes in the positioning of the inter tropical convergence zone itcz and the subtropical high sh under current climate conditions citation goni m a r c

u sr and mg in holocene and pleistocene corals a palmata and m annularis abstract mg sr and u concentrations are reported for living holocene dead and pleistocene montastrea annularis and acropora palmata in an effort to characterize starting materials and identify diagenetic effects in unrecrystallized skeletal aragonite the data indicate that skeletogenesis of minor elements is a taxa specific process yielding different mg sr and u values for each species during diagenesis sr concentrations increase and mg concentrations decrease in both species u diagenesis appears to be affected by skeletal structure establishment of u concentration ranges for modern corals provides a criterion for selecting samples for dating concentration changes in mg and sr during diagenesis limit their usefulness as paleo environmental indicators

juxtaposed mesozoic diabase dike sets from the carolinas a preliminary assessment aeromagnetic anomaly maps of the north carolina piedmont provide confirming evidence of juxtaposed mesozoic diabase dike sets dikes in north carolina may be divided into four domains on the basis of dike orientations most dikes are olivine normative but there are apparent systematic differences in chemical compositions that are reflected in different orientations and ages two orientations dominate northwest and north south the northwest trending set dominates in the south carolina piedmont and the north south set extends through much of the central virginia piedmont and under the coastal plain in south carolina the north south dikes are part of a set that converges near charleston and georgetown south carolina and diverges northward into virginia preliminary information suggests that the north south dikes are younger than the more common northwest trending dikes current models proposed for stress regimes associated with the breakup of pangea can accommodate the northwest set but not the north south convergent set this convergent set may be evidence for crustal deformation above a mantle plume centered near charleston and georgetown in middle jurassic time it is possible that presumed mafic plutons under the coastal plain near charleston regional seismicity patterns and orientations of the diabase dikes are all related to an intersection of zones of crustal weakness inherited from mid mesozoic time the western margin of northwest trending dikes may be related to tectonic features inherited from pre mesozoic time

sr ca sea surface temperature calibration in the branching caribbean coral acropora palmata 1 we measured sr ca ratios by thermal ionization mass spectrometry in radial and axial growth of modern caribbean acropora palmata corals comparison of our results with sea surface temperature sst allows radial and axial sr ca sst calibrations of sr ca mmol mol 11 30 0 07072 sst c and sr ca mmol mol 11 32 0 06281 x sst c respectively application of the calibrations to fossil acropora palmata from the last glacial maximum in barbados guilderson et al 1994 imply 7 c cooler conditions than the present much larger than the 1 1 5 cooling suggested by modern analog technique foraminifera based estimates trend staid and prell 2002 if the foraminifera based estimates are correct then the excess cooling suggested by the barbados corals could be explained by a 5 shift in the marine sr ca ratio or an addition of 20 abiotic secondary aragonite

thermal evolution of the central atlantic passive margins continental break up above a mesozoic super plume a near synchronous early jurassic 200 ma magmatic event along the north american and west african passive continental margins can be explained by the upwelling of a large scale mantle plume super plume beneath the west african craton lateral deflection of the outflow from the plume to the ne by the ambient sub lithospheric mantle flow could account for tholeiitic basaltic magmatism extending over a distance of nearly 5000 km from brazil to southern spain continental break up is considered to occur above the stagnation streamline along which cooler material eroded from the base of the continental lithosphere by the plume is returned to the convecting mantle the dynamic model is a scaled version of that recently proposed for the hawaiian plume and satisfactorily explains the apparent lack of involvement of thermally anomalous mantle in the generation of central atlantic oceanic crust

crustal structure of the southeast georgia embayment carolina trough preliminary results of a composite seismic image of a continental suture and a volcanic passive margin new deep penetration multichannel seismic reflection data combined with refraction results and magnetics modeling support a hypothesis that the carolina trough is a mesozoic volcanic passive margin exhibiting a seaward dipping wedge and associated underplating the structure of carolina platform continental crust is consistent with the late paleozoic continental collision that produced the appalachians but imbrication has had no obvious effect on shallower structures produced by mesozoic extension and volcanism the origin of prominent magnetic anomalies crossing the southeast georgia embayment can be explained by processes attending mesozoic separation of africa and north america and is not related to a paleozoic continental suture as previously postulated

conservation of soil moisture by different stone covers on alpine talus slopes lassen california abstract this study reports on the influence of stone covers with different clast sizes on the soil moisture of alpine talus slopes in lassen california fifteen four plot sets were sampled in the dry season july 1990 in sandy areas and in talus covered with pebbles cobbles or blocks between 2740 and 2775 m three depths 0 5 5 10 10 15 cm were sampled field moisture content increased gradually with depth in all soil profiles and also in plots covered by increasingly larger rocks surface soils in sand areas were very dry but under rocks had water contents 6 to 14 times greater differences among plots decreased with depth but subsoil samples in sand were still drier than those beneath any stone cover at similar depths blocks were most effective in conserving moisture water content below them was higher than even in deep 10 15 cm sand soils soil temperatures were recorded in sand and under blocks for an 11 day period minima were not significantly different but average maxima were 5 6 c lower under blocks than in sand which reached highs 4 4 c lower than the air differences in soil moisture among talus types are ascribed to lower evaporation losses under stones due to both disruption of capillarity by the coarse particles which prevented water flow to the talus surface and to their efficient reduction of maximum temperatures an irrigation experiment was conducted at 2110 m on a steep talus on the chaos crags from july 18 to aug 2 1993 four 100 75 cm plots with the same surface types than at lassen received 22 5 mm water moisture content was then periodically sampled watering produced similar water distributions among soil depths and talus types to those in lassen evaporation occurred quickly in bare soils due to high air and soil temperatures the sand surface was already dry 2 days after watering but stone covered plots remained moist until day 15 when soils under blocks still retained 77 97 of the water content percent by weight at the start of the test

concentrated flow erosion rates as affected by rock fragment cover and initial soil moisture content abstract concentrated flow experiments using a small hydraulic flume and a constant flow discharge and bed slope have been conducted in order to investigate the effects of rock fragment cover rc on sediment yield for an initially wet and an initially air dry loamy topsoil the experimental results indicate that rc reduces concentrated flow erosion rates e in an exponential way i e e e brc which is similar to previously reported relations for other water erosion processes such as interrill erosion and sheet rill erosion measured on runoff plots the decay rate b of this exponential relationship increased throughout the experiments because of scour hole development and bed armouring the concentrated flow erosion rates and b values also depend on the initial moisture content of the topsoil depending on rc mean concentrated flow erosion rates were 20 to 65 less on initially wet compared to initially air dry topsoils the mean value for b was 0 032 for the initially wet but only 0 017 for the initially air dry topsoil indicating that a rock fragment cover is less efficient in reducing concentrated flow erosion rates when the topsoil is initially air dry than when it is initially wet the results help explain the data scatter in reported relationships between rc and interrill rill erosion rates they also indicate that a given surface rock fragment cover will offer more protection to wet topsoils than to dry topsoils which are very common in mediterranean environments event based water erosion models should incorporate effects of antecedent soil moisture content as well as those of rc on concentrated flow erosion rates

the effect of colony topography on climate signals in coral skeleton the stable oxygen isotope composition of the aragonitic skeleton of hermatypic corals is a potential archive of paleotemperature and rainfall data biological processes also influence coral 18o although it has been difficult to determine which processes are involved and whether or not they dominate the stable isotope signal we show here that colony topography or surface bumpiness is associated with significant differences in 18o 13c and the timing of high density band formation between same age corallites in the central and fastest growing region of a coral colony these differences reflect changes experienced by individual corallites as they grow from the summit of a bump toward the bottom of a valley corallites on the bump record isotopic temperatures more than 1 c higher and accrete high density skeleton about 2 months earlier than their valley counterparts just 20 mm away we propose that these changes are not caused by corallite aging but rather by changes in the overall rate and timing of light enhanced calcification which is lower and occurs later in shaded valleys than it does on exposed bumps although we conclude that sea temperature is the dominant influence on 18o values in our coral our results show that significant isotopic variations may be expected over a small surface area in a single colony the production of accurate and reproducible coral based climate records thus requires an understanding of the complexities of coral growth processes and incorporation of this knowledge into sampling strategies and interpretation of data