sea level fall and coastal water cooling during the late holocene in southeastern brazil based on vermetid bioconstructions abstract the relative sea level variation curve obtained by dating and leveling vermetid shells from northern santa catarina state 26 3 s presents fall trend during all the last 4 0 cal ka bp which matches previous results based on the same kind of indicator for the brazilian coast between 3 s and 28 s chemical and isotopic analyses of 50 vermetid bioconstructions from distinct localities of south southeastern brazilian coast indicate possible changes in the coastal water temperature these changes may have been caused by oscillations in the strength of brazilian coastal current which carries la plata plume northward being therefore responsible for the penetration of cold and less saline water masses in the study area this is a reasonable explanation for the scarcity of vermetid biolithites around 3 4 2 6 cal ka bp and 0 5 0 cal ka bp

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

sea level change along the italian coast during the holocene and projections for the future published and new sea level data are used to provide projections of sea level change in italy for the year 2100 by adding new isostatic and tectonic component to the ipcc and rahmstorf projections comparison of the observations from more than 130 sites with different geomorphological and archaeological sea level markers with the predicted sea level curves provides estimates of the vertical tectonic contribution to the relative sea level change the results are based on the most recent anu model for the ice sheets of both hemispheres including an alpine deglaciation model on the basis of the eustatic tectonic and isostatic components to the sea level change projections are provided for marine inundation scenarios for the italian coastal plains for the year 2100 that today are at elevations close to current sea level

deep rooted thick skinned model for the high atlas mountains morocco implications for the structural inheritance of the southern tethys passive margin a re interpretation of the deep structure of the high atlas is presented through integration of geophysical and geological data highlighting the architectural significance of the southern tethys palaeomargin previous crustal models suggest the occurrence of a flat intra crustal detachment at a depth of 20 km a zone where surface thrusts merge and below which the lower high atlas crust appears continuous however within this study seismic refraction data electrical resistivity surveys and gravity modelling all appear to detect a jump in crustal thickness between the high atlas and the northern plains we interpret these data as penetration by thrusts within the south atlasic fault zone through the lower crust to offset the moho in accordance with a deep rooted thick skinned tectonic model the south atlasic fault zone corresponds to a series of crustal scale structures inherited from a series earlier orogenic events pan african hercynian and atlasic and thus is sufficiently weak to create separate crustal blocks in the northern part of the stable african plate this structural configuration was achieved during cenozoic plate collision between africa and europe culminating in tectonic inversion of mesozoic extensional basins linked to the development of tethys and opening of the atlantic the inherited structures typically comprise normal faults and tilted blocks affecting the upper crust and crustal scale detachments affecting the lower crust 2006 elsevier ltd all rights reserved

hydrological changes related to the variability of tropical south american climate from the cabo frio lagoonal system brazil during the last 5000 years from west to east the fluminense coastline composed of two series of lagoons presents an aridity gradient induced by a local upwelling that is controlled by trade winds coming from the south atl

reconstruction of southwestern atlantic sea surface temperatures during the last century cabo frio continental shelf brazil modern sea surface temperatures ssts were estimated from uk 37 values of ten core top sediment samples collected under the cabo frio upwelling system and validated by comparison with satellite derived ssts uk 37 ssts were found to reflect annual sst means in the offshore area and seasonal means winter spring in the inshore and central areas the latter areas are mainly influenced by upwelling processes whereas the offshore area is under the influence of the thermal front of the brazil current bc sst variability during the last century was then reconstructed from three short sediment cores the record showed a general cooling trend in the inshore and central areas suggesting intensification of the upwelling process the trends at the offshore area reflected oscillations of the bc thermal front with piling up of warmer bc waters closer to the coast since ca 1950

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

the reef builder gastropod dendropoma petreaum a proxy of short and long term climatic events in the eastern mediterranean abstract high resolution 18 o and 13 c records obtained from seven cores were drilled from ledges of the reef builder gastropod dendropoma petreaum and used to reconstruct variations in the levantine basin sea surface temperature hydrology and productivity during the past 500 years the 18 o of the aragonite shell of living d petreaum indicate that skeletal deposition occurs under isotopic equilibrium and faithfully record the temperature and surface water 18 o during summer and autumn the mean down core 18 o record clearly captures global and local climatic events such as the little ice age lia and the recent warming of surface waters in the eastern mediterranean comparison to the western mediterranean vermetid 18 o record reveals changes in the freshwater evaporation budgets of the two basins during cold and warm periods the eastern basin had lower surface temperatures and excess evaporation during the lia and experienced a relatively larger warming and or a decrease in freshwater evaporation during the past 70 years the d petraeum 13 c is strongly related to 13 c of dissolved inorganic carbon and to the primary productivity of the surface water the mean down core 13 c record exhibits enrichment during the lia maximum and a strong depletion trend during the last century the lia 13 c enrichment is attributed to an increase in primary production and high nutrient levels which resulted from increased vertical mixing and upwelling the last century 13 c depletion is mostly related to the increased anthropogenic emissions of 13 c depleted carbon dioxide and to a certain decrease in primary production the data indicate that d petraeum isotopic signatures are unique proxies for last 500 years high resolution reconstruction of paleo oceanographic environments in the mediterranean and potentially in the sub tropical atlantic regions

coseismic extension from surface cracks reopened by the 2014 pisagua northern chile earthquake sequence the a d 2014 pisagua earthquake sequence reactivated ancient surface cracks along the entire rupture length in the northern chilean forearc these subtle brittle strain features that are 50 km above the subduction zone interface in the hyperarid atacama desert record deformation from the single earthquake sequence in this study we document how ancient cracks formed during thousands of plate boundary earthquake cycles were reopened during the 2014 earthquake sequence we show that crack orientations along the rupture length reflect deformation from the m w 8 1 mainshock and from an m w 7 7 aftershock 100 km to the south as documented by displacements calculated from continuous geodetic observations we suggest that cracks form during the passage of surface waves and repeated opening and closing enhance crack aperture the orientation and opening of the oldest cracks in the forearc are indicative of the modal or most common rupture area of major megathrust earthquakes in the region while the long term preservation of cracks may be limited to northern chile similar features likely form during strong earthquakes at other subduction zones and represent permanent forearc deformation

a newly discovered orogenic event in morocco neoproterozic ages for supposed eburnean basement of the bou azzer inlier anti atlas mountains abstract the bou azzer inlier within the anti atlas orogenic belt of morocco exposes a dismembered ophiolite long considered to mark a late neoproterozoic suture between the west african craton wac in the south and neoproterozoic arcs to the north southern parts of the bou azzer inlier include meta igneous units paragneiss schist and muscovite bearing granite that have until now been regarded as the c 2 ga eburnean wac basement onto which the ophiolite was obducted an example of supposed paleoproterozoic basement occurs at tazigzaout the main units within this complex are metagabbro augen granite gneiss finely banded granite gneiss and variably sheared syn tectonic leucogranite all of which are intercalated within a complex sub vertical upper greenschist facies ductile dextral shear zone the meta igneous rocks are crosscut by a sheeted muscovite biotite granite pluton three concordant u pb analyses of zircon from an augen granite gneiss provide a date of 753 1 2 ma zircon from a nearby metagabbro provide an indistinguishable date of 752 2 2 4 ma both dates are considered best estimates of the crystallization ages of their igneous protoliths analyses of zircon from two crosscutting leucogranite bodies provide younger dates of 705 2 3 ma and 701 2 1 ma the initial nd values of all lithological units in the complex range from 4 9 to 6 0 with depleted mantle model tdm ages of 890 790 ma the high positive nd values for all of these igneous units is indicative of an isotopically juvenile source such as depleted mantle derived material and precludes substantial interaction with old evolved crustal sources these data demonstrate that the basement rocks of the tazigzaout complex are neoproterozoic intrusions not c 2 ga eburnean units as found in more southerly anti atlas inliers the structural relationships and u pb ages are interpreted as recording dextrally transpressive deformation of c 755 ma juvenile crust after c 750 and before 700 ma this neoproterozoic deformation occurred as much as 100 ma prior to the top to the north thrusting of the meta igneous units over units of the ophiolite and arc and provides strong evidence for two discrete pan african events in morocco

post paleocene cooling in the southern canadian atlantic region evidence from apatite fission track models the traditional view of the geomorphic evolution of the southern canadian atlantic margin is one of gradual exhumation and peneplanation following triassic jurassic rifting thermal modelling of apatite fission track data from pre carboniferous granitic basement in nova scotia and from permian and triassic sandstones from nova scotia new brunswick and prince edward island suggest a more complex thermal evolution of the onshore part of the margin models clearly indicate significantly elevated regional paleotemperatures during jurassic time and as much as 30 c of post paleocene cooling model predicted paleogeothermal gradients for granitic samples from the digby d 1 well are normal ranging from 15 to 20 c km post paleocene cooling may be attributable to the combined effects of 13 c of exhumational cooling from erosion of approximately 700 m of post aptian sediments caused by decreased eustatic sea levels and 8 17 c of cooling from the propagation to depth of a 10 20 c decrease in paleo mean ann

quantitative analysis of intraspecific variations in the carbon and oxygen isotope compositions of the modern cool temperate brachiopod terebratulina crossei abstract this study unravels intraspecific variations in the carbon isotope 13 c and oxygen isotope 18 o compositions of shells of the modern cool temperate brachiopod terebratulina crossei collected at a water depth of 70 m in otsuchi bay northeastern honshu japan brachiopod shells have been used as proxies of the 13 c values of dissolved inorganic carbon dic 13 c dic and seawater temperature 18 o 18 o sw values to reconstruct the evolution of phanerozoic oceans to identify more reliable shell portions as the proxies we conducted a rigorous time series comparison of 13 c and 18 o values between the brachiopod shells and calcite precipitated in isotopic equilibrium with ambient seawater equilibrium calcite 13 c ec and 18 o ec values respectively samples were collected from the outer and inner surfaces of the secondary shell layer along the maximum growth axis ontogenetic series and inner series samples respectively the ontogenetic series 13 c values which showed regular annual and irregular non annual cycles partly fell in but were mostly less than the range of the 13 c ec values the 13 c cycles were often associated with one or two minor negative peaks the peaks were likely resulted from an increased incorporation of respiration derived 12 c due to elevated metabolic activity during spawning the ontogenetic series 18 o values showed distinct seasonal variations and were mostly within the range of 18 o ec values the amplitude of the 18 o profiles was relatively large during the younger fast growth stage and decreased during the senescent slow growth stage the inner series 13 c and 18 o values of individual shells varied within narrow ranges the inner series 13 c values were close to the minimum 13 c ec values the inner series 18 o values were in the upper range of the 18 o ec values kinetic isotope fractionation effects were evident but its degree varied among different shells we identified the shell portions reliably recording past ocean environments the best estimates of annual average 13 c dic values were obtained from ontogenetic series 13 c values near the anterior shell edge and from inner series 13 c values those of the annual average seawater temperature were obtained from ontogenetic series 18 o values from the entire transect and from the fast growth stage

a critical review of mid to late holocene sea level fluctuations on the eastern brazilian coastline abstract the eastern coast of brazil is 7000 km long and has been the subject of systematic paleo sea level investigations for more than 35 years more than 1000 samples have been radiocarbon dated and paleo sea level trends have been determined for 14 coastal sectors these trends have in common a mid holocene sea level maximum pmt above present sea level and a subsequent fall to the present time the time and elevation of the pmt the time when relative sea level rose above present mean sea level and the nature of late holocene sea level fall can however differ significantly discrepancies are observed not only between neighboring coastal sectors but also between different studies in a same coastal sector this paper discusses all the key radiocarbon dated samples used to establish regional trends in relative sea level on the eastern coast of brazil it is concluded that although many of the key sea level indicators are imprecise in time and space there is widespread evidence 30 of the data set for a progressive decline possibly with uneven rates of relative sea level since the end of the pmt

multiproxy assessment of holocene relative sea level changes in the western mediterranean sea level variability and improvements in the definition of the isostatic signal abstract a review of 917 relative sea level rsl data points has resulted in the first quality controlled database constraining the holocene sea level histories of the western mediterranean sea spain france italy slovenia croatia malta and tunisia we reviewed and standardized the geological rsl data points using a new multi proxy methodology based on 1 modern taxa assemblages in mediterranean lagoons and marshes 2 beachrock characteristics cement fabric and chemistry sedimentary structures and 3 the modern distribution of mediterranean fixed biological indicators these rsl data points were coupled with the large number of archaeological rsl indicators available for the western mediterranean we assessed the spatial variability of rsl histories for 22 regions and compared these with the ice 5g vm2 gia model in the western mediterranean rsl rose continuously for the whole holocene with a sudden slowdown at 7 5 ka bp and a further deceleration during the last 4 0 ka bp after which time observed rsl changes are mainly related to variability in isostatic adjustment the sole exception is southern tunisia where data show evidence of a mid holocene high stand compatible with the isostatic impacts of the melting history of the remote antarctic ice sheet our results indicate that late holocene sea level rise was significantly slower than the current one first estimates of gia contribution indicate that at least in the northwestern sector it accounts at least for the 25 30 of the ongoing sea level rise recorded by mediterranean tidal gauges such contribution is less constrained at lower latitudes due to the lower quality of the late holocene index points future applications of spatio temporal statistical techniques are required to better quantify the gradient of the isostatic contribution and to provide improved context for the assessment of 20th century acceleration of mediterranean sea level rise

dendropoma lower intertidal reef formations and their palaeoclimatological significance nw sicily abstract most carbonate rocky shores of nw sicily are marked by a coalescence of shells of the gastropod dendropoma in a construction that is variably developed as a response to wave impact here we review all the available information on these constructions and find that the fossil reefs are reliable sea level indicators the thickness of the reef samples never exceeds 30 40 cm below sea level whereas all 14 c dates fall within a range of few centuries some small fragments ejected by violent sea storms date back to 2500 years cal bp no samples older than 6200 years cal bp have been detected so far the present distribution of mediterranean vermetid platforms should result from a northward migration related to the long term effect of the holocene sea surface temperature sst warming some consideration on the morphology of the reefs and the comparison with the available data point out that dendropoma reefs are excellent biological indicators of sea level fluctuations especially when detected and sampled in tectonically stable areas as those in nw sicily

warmer or cooler late holocene marine palaeoenvironments interpreting southeast australian and brazilian sea level changes using fixed biological indicators and their δ18o composition abstract relic inter tidal assemblages of sessile organisms which are referred to as fixed biological indicators fbis are shown to be useful proxies for late holocene climatic and environmental changes as well as direct indicators of short term fluctuations in sea level a detailed comparison of change in the inter tidal assemblages of two southern hemisphere sites at comparable latitudes port hacking new south wales south east australia and the laguna imbituba region of southern brazil indicates periods of marked similarities in the timing and nature of changes at 5200 3800 cal years bp and differences after 2400 cal years bp there is sufficient concurrence of cooling phases and falling sea levels to strongly suggest that in some cases global rather than regional forcing factors are at work the value of inter tidal organisms as indicators of changed environments is developed by identifying the past and present distributions of the common marker species tubeworms barnacles and mussels the 18 o content of these extant specimens at port hacking confirmed changes in ocean water temperature and associated sea level behaviour corresponding to invasion or extinction of temperature sensitive species a similar pattern is repeated although in a less marked fashion in the laguna imbituba region of southern brazil

effects of holocene sea level changes on subtidal palaeoecosystems southeastern brazil abstract southeastern brazilian marine coastal deposits provide an excellent opportunity to investigate environmental changes such as sea level and trophic variability during the holocene period in this study we present a sediment record from arraial do cabo bay rio de janeiro state in order to improve the understanding of the upper subtidal palaeoecosystem evolutionary dynamics of this bay we provide a microfacies analysis of holocene carbonate and mixed siliciclastic carbonate deposits cropping out today from the supratidal to the subtidal zones the age depth model is based on 14 c dating and revealed a basal age of 7000 cal years bp in the six distinguished microfacies the biogenic components are dominated by vermetids and coralline algae a number of subordinate components are also present including the microfacies determining thin shelled bivalves fossil vermetids are represented by monospecific clusters of overgrowing petaloconchus varians coralline red algae are represented by lithophyllum pustulatum spongites fruticulosus spongites yendoi mesophyllum engelharti and unidentified geniculate corallines the microfacies analysis revealed that the substrate of the benthic community in the upper subtidal ecosystem of the bay changed according to the relative sea level 1 during the rapid sea transgressive trend it was coarse soft substrate 2 after the postglacial sea level maximum succeeding a slow decline to present sea level it changed into fine soft substrate at 7000 years ago the coarse soft substrate was characterised by fruticose corallines and composed of quartz grains from continental run off input after the postglacial sea level maximum the highstand elevation along with the established upwelling system brought about a predominantly carbonate deposition vermetids and corallines along with thin shelled bivalves thrived in a low sedimentation rate setting and high nutrient level environment

recent unprecedented warming and oligotrophy of the eastern mediterranean sea within the last millennium the mediterranean region is a climatic transitional zone between the subtropical monsoon regime and the temperate westerlies and is subject to forces acting upon the global climate system much knowledge about its climate over the last millennium is derived from terrestrial records whereas changes in sea surface temperatures ssts and in the dissolved inorganic carbon pool dic are poorly known we present continuous high resolution reconstructions of sst and 13cdic in the eastern mediterranean em sea as inferred from oxygen and carbon isotope records from the skeletons of the reef builder gastropod dendropoma sp spanning the past millennium the sst reconstruction reveals a 250 year persistent warming trend during which the twentieth century was the warmest on record coupled with a distinct trend of 13cdic depletion and superimposed upon decreased primary production this climate reconstruction reflects a new state of the em over the anthropocene era that exceeds the natural variability of the last millennium

holocene oscillations of southwest atlantic shelf circulation based on planktonic foraminifera from an upwelling system off cabo frio southeastern brazil the brazil current bc is a relevant feature in the atlantic meridional overturning circulation amoc its behavior during slowdown or intense amoc remains poorly known because of the lack of pal

from rifting to passive margin the examples of the red sea central atlantic and alpine tethys abstract evolution of the red sea gulf of suez and the central atlantic rift systems shows that an initial transtensive rifting phase affecting a broad area around the future zone of crustal separation was followed by a pre oceanic rifting phase during which extensional strain was concentrated on the axial rift zone this caused lateral graben systems to become inactive and they evolved into rift rim basins the transtensive phase of diffuse crustal extension is recognized in many intra continental rifts if controlling stress systems relax these rifts abort and develop into palaeorifts if controlling stress systems persist transtensive rift systems can enter the pre oceanic rifting stage during which the rift zone narrows and becomes asymmetric as a consequence of simple shear deformation at shallow crustal levels and pure shear deformation at lower crustal and mantle lithospheric levels preceding crustal separation extensional denudation of the lithospheric mantle is possible progressive lithospheric attenuation entails updoming of the asthenosphere and thermal doming of the rift shoulders their uplift provides a major clastic source for the rift basins and the lateral rift rim basins their stratigraphic record provides a sensitive tool for dating the rift shoulder uplift asymmetric rifting leads to the formation of asymmetric continental margins corresponding in a simple shear model to an upper plate and a conjugate lower plate margin as seen in the central atlantic passive margins of the united states and morocco this rifting model can be successfully applied to the analysis of the alpine tethys palaeo margins such as rif and the western alps

40ar 39ar ages and duration of the central atlantic magmatic province volcanism in morocco and portugal and its relation to the triassic jurassic boundary the central atlantic magmatic province camp is the world s largest known continental igneous province and is 15 contemporaneous with the triassic jurassic t j boundary that marks one of the five largest biological extinctions in the last 16 600 ma although constraints on the duration of the camp volcanism remain yet poorly defined the assumption that the camp 17 may have had a causal relationship with the climatic and biotic crisis was suggested marzoli a bertrand h knight k cirilli 18 s buratti n verati c nomade s renne p r youbi n martini r allenbach k neuwerth r rapaille c zaninetti l 19 bellieni g 2004 synchrony of the central atlantic magmatic province and the triassic jurassic boundary climatic and biotic 20 crisis geology 32 973 976 in this paper we present new 40ar 39ar ages on basaltic flows from moroccan central high atlas 21 oujda and argana and portuguese algarve and santiago do cacem basins where camp lava flows are interlayered with t j 22 sedimentary sequences 23 in the moroccan basins where the basalts were erupted across the t j boundary well defined 40ar 39ar plateau ages n 12 24 for more than 90 of the total erupted volume of camp basalts range from 197 8 0 7 ma to 201 7 2 4 ma and display a main 25 restricted peak at 199 1 1 ma providing a precise estimate of the 40ar 39ar age of the t j boundary concordant with the current 26 u pb age 199 6 0 3 ma palfy j mortensen j k carter e s smith p l friedman r m tipper h w 2000 timing the 27 end triassic mass extinction first on land then in the sea geology 28 39 42 the topmost lava flows recurrent unit yield a 28 significantly younger mean age of 196 6 0 6 ma highlighting late episodic eruption of camp magmas these late basalts 29 represent a small magma volume b10 of the total which was erupted most likely due to asthenospheric upwelling and 30 lithospheric extension within the t j central high atlas basins 31 in the portuguese basins stratigraphical and palynological studies of the associated continental sedimentary sequence 32 underlying the volcanic units suggest an age close to the t j boundary for the camp basaltic flows this is confirmed by new 33 40ar 39ar data for the portuguese basalts which provide the first accurate radio isotopic ages for lava flows in the european 34 camp with two plateau ages yielding a mean value of 198 1 0 4 ma these plateau ages plus three concordant mini plateau 35 ages suggest synchronous rifting and volcanism both in south western europe and morocco central high atlas and oujda basins in summary the eruptive history of the camp with an early extremely widespread and intense peak at 199 1 ma and a tail of 37 episodic eruption events until 196 6 ma is consistent with the biotic turnover at the t j boundary which was likely caused by 38 devastating effects of extensive volcanic eruptions

structural and geochronological constraints on the evolution of the bou azzer neoproterozoic ophiolite anti atlas morocco abstract the bou azzer ophiolite in the moroccan anti atlas represents the suture of the neoproterozoic pan african orogen the bou azzer inlier includes from ne to sw three main geological units a volcanic arc an ophiolite and a continental platform several subduction related plutons intrude the ophiolite and the volcanic arc and syn to late orogenic deposits unconformably cover the three terranes the eburnean 2 ga continental basement observed in other inliers of the anti atlas appears not to crop out at bou azzer where rocks traditionally attributed to that old basement are in fact neoproterozoic rocks either metagranitoids of the continental margin or ophiolitic metagabbros the age of a metagabbro of the ophiolite is reported here for the first time as 697 8 ma shrimp u pb on zircons u pb geochronological data are also presented for two syn kinematic subduction related plutons which together with previous data establish a time span of ca 655 635 ma for these arc type rocks moreover the oumlill granite previously attributed to the eburnean basement has been dated as 741 9 ma the earliest tectonometamorphic event affecting the ophiolite is recorded as a relic foliation and a garnet rutile metamorphic assemblage which might attest to an early peak pressure exceeding the 5 6 kbar medium pressure reported so far thus we suggest a first stage of ophiolite underthrusting below a volcanic arc followed by ophiolite exhumation and the concomitant development of the main low grade planar linear tectonic fabric the ages of the calc alkaline syn kinematic subduction related plutons 655 635 ma might be taken as the end of subduction and the beginning of the ophiolite exhumation obduction the author s work in the bou azzer region supports the ophiolite continental platform interpretation of leblanc 1975 and leblanc and moussine pouchkine 1994 rather than the tectonic melange interpretation proposed by saquaque et al 1989b and others a recumbent anticlinal and the basal thrust of the ophiolitic terrane are the main macrostructures formed during the obduction stage characterized by top to the w sw kinematics this deformational event is also recorded in the rocks of the underlying continental platform a syn orogenic unit namely the tiddiline formation unconformably overlies the arc volcanics the ophiolite and the continental platform further collisional deformation affected the tiddiline sediments giving way to ese wsw striking upright folds and oblique reverse faults the latest structures in this neoproterozoic suture were left lateral strike slip faults pointing to an increase in the left lateral component of the continental collision

holocene reef growth in the tropical southwestern atlantic evidence for sea level and climate instability the holocene epoch offers a potential analogue for understanding future sea level variability as both sst s and global mean sea levels gmsl were at times higher than observed today however gmsl can differ significantly from relative sea level rsl even at far field sites remote from margins of former ice sheets much of this spatial variability has been shown to be consistent with the predictions of glacial isostatic adjustment gia models whilst it is generally accepted that rsl at far field sites reached its maximum during the mid holocene there have been many interpretations of sea level fall following the highstand from 6 ka here we present a rsl history from several tectonically stable far field sites in eastern brazil derived from 17 microatoll and 45 fossil reef flat ages our results show evidence for two periods of rsl instability during the holocene which differ from gia predictions including a hiatus in reef growth 3 7 2 5 ka these results are broadly synchronous with several other locations in the southern hemisphere suggesting global rather than regional climatic forcing mechanisms are responsible variations in sst and southern hemisphere ice sheet dynamics are proposed as possible controlling mechanisms for the observed rsl oscillations beginning at 3 7 ka and 2 ka respectively we suggest that these global processes combined with increased precipitation and higher sediment flux from several regional climatic forces created inhospitable conditions for reef growth contributing to the observed hiatus and reduced reef flat accretion during the late holocene 2 ka to present

kinematic and thermal evolution of the moroccan rifted continental margin doukkala high atlas transect 1 the atlantic passive margin of morocco developed during mesozoic times in association with the opening of the central atlantic and the alpine tethys extensional basins formed along the future continental margin and in the atlas rift system in alpine times this system was inverted to form the high and middle atlas fold and thrust belts to provide a quantitative kinematic analysis of the evolution of the rifted margin we present a crustal section crossing the atlantic margin in the region of the doukkala basin the meseta and the atlas system we construct a post rift upper crustal section compensating for tertiary to present vertical movements and horizontal deformations and we conduct numerical modeling to test quantitative relations between amounts and distribution of thinning and related vertical movements rifting along the transect began in the late triassic and ended with the appearance of oceanic crust at 175 ma subsidence possibly related to crustal thinning continued in the atlas rift in the middle jurassic the numerical models confirm that the margin experienced a polyphase rifting history the lithosphere along the transect preserved some strength throughout rifting with the effective elastic thickness corresponding to an isotherm of 450 c a mid crustal level of necking of 15 km characterized the pre rift lithosphere

apatite fission track analyses on basement granites from south western meseta morocco paleogeographic implications and interpretation of aft age discrepancies abstract this work is based on apatite fission track analysis of samples mostly granites from the basement of the cretaceous tertiary phosphate and ganntour plateaus exposed in the jebilet and rehamna massifs western meseta morocco this basement belongs to the carboniferous early permian variscan belt and the earlier marine onlap is late triassic in age however the aft ages are post triassic and different in the jebilet 186 203 ma and rehamna 148 153 ma track length modelling support the occurrence of moderate heating events during the jurassic and the eocene respectively with cooling during the permian and cretaceous intervals these results are partly accounted for by considering a moderate subsidence during the late triassic liassic which is a noticeable change in the regional paleogeographic concept of west moroccan arch however the discrepancies between the aft results from the studied massifs make necessary to explore further explanation we interpret the observed discrepancies by the difference in age and depth of crystallization of the sampled granites in the variscan orogen i e 330 ma 5 6 km in the jebilet versus 300 ma 8 10 km in the rehamna the importance of the late jurassic early cretaceous uplift and erosion of the entire meseta and that of its late eocene burial are emphasized

echinoderm skeletal preservation calcite aragonite seas and the mg ca ratio of phanerozoic oceans abstract the alternation between abiotic calcite and aragonite precipitation in shallow seawater and the oscillation of seawater mg ca ratio throughout the phanerozoic are both popular hypotheses echinoderms with well preserved stereom provide new empirical evidence that supports both these hypotheses analyses are reported from 29 specimens cambrian to eocene age containing ossicles preserved either as mg calcite 3 3 to 8 mole mgco3 or as mixed calcite and dolomite 5 to 12 5 mole mgco3 echinoderms with high mole mgco3 occur in the early cambrian and late carboniferous to triassic low values come from the silurian and jurassic to cretaceous the average composition of echinoderms with preserved stereom does not fall below 3 5 mol mgco3 during the phanerozoic and reaches its highest mean value of 16 0 mol mgco3 today an empirical partition coefficient of 0 03182 for modern tropical echinoids is used to indicate the mg ca ratio of ancient seawater from the mg ca ratio of fossil stereom some assumptions are involved and a likely error is calculated from the mg2 variation of modern echinoids high mean seawater mg ca ratios are calculated for early cambrian 3 3 and the late carboniferous to triassic 2 3 but never reached today s value of 5 2 low mg ca ratios 1 1 are indicated from jurassic to cretaceous echinoderms the 29 echinoderm samples plot close to first order mg ca seawater oscillations derived from geochemical models and mg ca ratios determined from fluid inclusions but considerable discrepancies exist when shorter 106 myr time intervals are considered further data and improved understanding of mg partitioning is required before accurate secular variation in the mg ca of seawater can be determined from echinoderms however they are an underused resource in this context and provide an excellent seawater archive

controls of subsurface temperature variability in a western boundary upwelling system 1 the mechanisms controlling subsurface temperature variability on the outer shelf in a western boundary upwelling system are quantified using observations from a mooring deployed off cabo frio brazil results from a multiple linear regression analysis reveal that in addition to low frequency variations associated with the seasonal evolution of temperature the dominant mechanisms controlling temperature variability are wind stress curl driven upwelling cross isobath transport the proximity of the brazil current to the shelf break and perhaps changes in the strength of tidal mixing associated with the spring neap cycle the influence of the proximity of the brazil current decreases strongly with depth being restricted to the top 80 m regression coefficients indicate that the relative contributions from the different forcings are roughly similar and that no single process has a dominant role explaining temperature variability near the shelf break these suggest that successful modeling efforts in the region must adequately represent each of those processes

post variscan tectonics in eastern anti atlas morocco new field data integrated by fission track ft analysis unravel an innovative scenario for the post variscan evolution of the eastern anti atlas this area unaffected by meso cenozoic tectonics according to most workers is crosscut by crustal faults bearing evidence of a polyphase deformation history apatite ft ages ranging between 284 and 88 ma point to fast neogene exhumation and unravel contrasting cooling paths across major faults results show that the study area was buried beneath 2 km of allochthonous variscan units now eroded the eastern anti atlas acted as the southern shoulder of the atlasic rift in the mesozoic and underwent a dextral transpressional structuring of neogene age followed by sub meridian shortening the southern front of atlasic deformation is therefore located inside the anti atlas region and it is still active

response of the great barrier reef to sea level and environmental changes over the past 30 000 years previous drilling through submerged fossil coral reefs has greatly improved our understanding of the general pattern of sea level change since the last glacial maximum however how reefs responded to these changes remains uncertain here we document the evolution of the great barrier reef gbr the world s largest reef system to major abrupt environmental changes over the past 30 thousand years based on comprehensive sedimentological biological and geochronological records from fossil reef cores we show that reefs migrated seaward as sea level fell to its lowest level during the most recent glaciation 20 5 20 7 thousand years ago ka then landward as the shelf flooded and ocean temperatures increased during the subsequent deglacial period 20 10 ka growth was interrupted by five reef death events caused by subaerial exposure or sea level rise outpacing reef growth around 10 ka the reef drowned as the sea level continued to rise flooding more of the shelf and causing a higher sediment flux the gbr s capacity for rapid lateral migration at rates of 0 2 1 5 m yr 1 and the ability to recruit locally suggest that as an ecosystem the gbr has been more resilient to past sea level and temperature fluctuations than previously thought but it has been highly sensitive to increased sediment input over centennial millennial timescales

cenozoic uplift of nuussuaq and disko west greenland elevated erosion surfaces as uplift markers of a passive margin remnants of a high plateau have been identified on nuussuaq and disko central west greenland we interpret the plateau as an erosion surface the summit erosion surface formed mainly by a fluvial

climate variability and sea level change during the holocene insights from an inorganic multi proxy approach in the se brazilian continental shelf abstract two sediment cores collected in the shelf off rio de janeiro rj13 01b 10 8 cal kyr bp and rj13 02b 4 7 cal kyr bp were investigated in high resolution to evaluate changes in sedimentary processes and paleoclimatic and paleoceanographic variability during the holocene in the southeastern brazil information from inorganic proxies of continental input al ca and fe ca redox sensitive elements fe al v al and mn al paleoproductivity sr al cd al and ba al as well as data for grain size geophysical properties p wave velocity gamma ray density acoustic impedance magnetic susceptibility and porosity si total organic carbon and calcium carbonate were considered the data revealed three main periods of sediment accumulation i from 10 8 cal kyr bp to 7 6 cal kyr bp the sediment was coarse si content was high 27 the magnetic susceptibility was low and the presence of shell fragments all suggest a period of low continental input and the deposition site was shallow i e lower sea level ii from 7 5 cal kyr bp to 4 6 cal kyr bp the elevated ratios of al ca 0 69 0 08 fe ca 0 27 0 04 sr al 31 57 4 47 10 4 cd al 0 09 0 03 10 5 and ba al 0 70 0 16 10 4 are consistent with a period of maximum sea transgression and elevated influence of the nutrient rich south atlantic central water sacw iii from 4 5 cal kyr bp to the present events of higher fluxes of toc ni cu and zn were observed from ca 3 2 cal kyr bp to 3 4 cal kyr bp in both cores related to humid climate overall the multi proxy approach shed light on the effects of climate and oceanographic variability on sediment input and accumulation in a less studied portion of the brazilian shelf which are consistent with other shelf areas and with changes in regional climate systems like the intertropical convergence zone itcz south american monsoon systems sams and south atlantic convergence zone sacz

from central atlantic continental rift to neogene uplift western anti atlas morocco terra nova 23 35 41 2011 abstract to put constraints on the mesozoic to recent growth of the anti atlas system we investigated the temperature time history of rocks by applying extensive low temperature thermochronological analysis to three precambrian inliers along the coast and 250 km into the interior bedrocks yield old u th he ages on zircon 248 193 ma and apatite 150 50 ma and also fission track ages of 173 121 ma on apatite these datasets are interpreted as recording passive margin upward movements from central atlantic rifting until the early cretaceous a phase of sedimentary burial was evidenced for the cretaceous eocene the extension of this thin 1 5 km basin is loosely constrained but can be extended to the western regions of northern africa effects of the existing thermal perturbation of lithospheric origin 100 km below the atlas show that the 120 60 c isotherms are not much deflected large scale uplift has possibly occurred in the western anti atlas since c 30 ma and is associated with a mean denudation rate of 0 08 km ma 1

the south western branch of the variscan belt evidence from morocco abstract this work is based on the compilation and re evaluation of the most significant data either personal or from the literature concerning the moroccan variscides the latter constitute the only moderately disturbed or even undisturbed part of the south western branch of the variscan belt facing directly nw gondwana they include two orogenic segments namely the northern mauritanides and the meseta domain exposed in the saharan and atlas meseta regions respectively and a foreland belt cropping out essentially in the anti atlas the eastward thrust units of saharan morocco oulad dlim mostly originate from the west african craton wac border in an area of thin palaeozoic sedimentation thin skinned fold thrust foreland arcs develop progressively northward zemmour at the expense of the increasingly thick palaeozoic series whereas thick skinned deformation characterizes the inverted proximal paleomargin in the anti atlas domain as suggested by the meseta and anti atlas stratigraphic similarities the meseta domain corresponds to a collage of moderately displaced thinned crustal blocks from the distal gondwana paleomargin variscan deformation is dominated by nw verging thrusts and metamorphism developed in the thickened tectonic prism in relation with crustal anatexis at depth the meseta anti atlas boundary is a major ene trending transpressional dextral fault referred to as the south meseta fault smf discussing the correlations between the variscan segments of morocco and sw iberia allows us to suggest that a latitudinal transform zone similar to the smf separated these segments during the late palaeozoic subduction of the rheic ocean crust would have been directed se ward along both the iberian and moroccan meseta and nw ward south of the smf i e along the wac

late holocene palaeotemperatures and palaeoenvironments in the southeastern brazilian coast inferred from otolith geochemistry abstract holocene palaeoceanography and climatic reconstructions were evaluated based on proxy analyses of fish otoliths from shellmounds located along the coast of rio de janeiro state brazil modern coastal seasonal upwelling is associated with the ascension of a deep and cold water mass as a consequence of persistent ne winds that affect the climate in southeastern brazil however this seasonal influence and the effect of the holocene palaeoenvironment on shallow water are poorly known in this work coastal palaeotemperatures were estimated based on the geochemical analyses of otolith the results of the 18o and 13c analyses from holocene otoliths obtained from coastal shellmounds separated by a distance of almost 200 km show two distinctive otolith derived palaeotemperature signals in a coastal region under upwelling influence additionally this analysis suggests that the fish lived in marine waters showing similar microchemistry values composition when compared with modern marine otoliths

the anti atlas chain morocco the southern margin of the variscan belt along the edge of the west african craton abstract broadly synchronous circum atlantic variscan alleghanian orogenic belts developed during the late palaeozoic gondwana laurentia collision in the northern part of the west african craton wac the variscan orogeny produced basement controlled structures in the anti atlas which represents the pericratonic foreland now located south of the variscan domains of morocco and north of the mauritanides belt new structural field observations document the strong involvement of the basement and the inversion and folding of the palaeozoic sedimentary basins at the edge the wac two contrasting domains differently responding to regional nw se shortening are recognized 1 a narrow belt along the atlantic coast characterized by thin skinned folding and ese vergent thrusting para autochthonous anti atlas 2 a large area between the wac sensu stricto and the south atlas front showing huge basement uplifts amidst a folded palaeozoic cover with upright polyharmonic folds autochthonous anti atlas the structural trend of the basement inliers is inherited at least in some case from previous proterozoic fractures compressional reactivations led to basement uplift and concomitant folding of the palaeozoic cover cover series are horizontally shortened by mostly upright symmetrical buckle folds of various wavelengths in response to thickness variations between abundant incompetent silt and shale horizons and rare competent carbonate and quartzite beds deformation is greatest near the borders of and between closely spaced basement uplifts regionally deformation intensity decreases either abruptly or progressively towards the se and it vanishes within the undeformed tindouf basin

thick dyke emplacement and internal flow a structural and magnetic fabric study of the deep seated dolerite dyke of foum zguid southern morocco 1 knowledge on forced magma injection and magma flow in dykes is crucial for the understanding of how magmas migrate through the crust to the earth s surface because many questions still persist we used the long thick and deep seated foum zguid dyke morocco to investigate dyke emplacement and internal flow by means of magnetic methods structural analysis petrography and scanning electron microscopy we also investigated how the host rocks accommodated the intrusion regarding internal flow 1 important variations of the rock magnetic properties and magnetic fabric occur with distance from dyke wall 2 anisotropy of anhysteretic remanent magnetization reveals that anisotropy of magnetic susceptibility ams results mainly from the superposition of subfabrics with distinct coercivities and that the imbrication between magnetic foliation and dyke plane is more reliable to deduce flow than the orientation of the ams maximum principal axis and 3 a dominant upward flow near the margins can be inferred the magnetic fabric closest to the dyke wall likely records magma flow best due to fast cooling whereas in the core the magnetic properties have been affected by high temperature exsolution and metasomatic effects due to slow cooling regarding dyke emplacement this study shows that the thick forceful intrusion induced deformation by homogeneous flattening and or folding of the host sedimentary strata dewatering related to heat as recorded by thick quartz veins bordering the dyke in some localities may have also helped accommodating dyke intrusion the spatial arrangement of quartz veins and their geometrical relationship with the dyke indicate a preintrusive to synintrusive sinistral component of strike slip

holocene sea surface temperatures and related coastal upwelling regime recorded by vermetid assemblages southeastern brazil arraial do cabo rj abstract in places where ocean currents cause upwelling nearshore sea surface temperatures sst are often cooler than nearby offshore waters in the arraial do cabo bay coast upper holocene aragonitic vermetids are represented by monospecific clusters of overgrowing petaloconchus varians occurring in supratidal intertidal carbonate and mixed siliciclastic carbonate deposits based on stable isotope composition 13c 18o of fossil vermetid shells radiocarbon ages and altimetric survey the upper holocene upwelling system of the cabo frio area southeastern brazil rio de janeiro is assessed in the studied region at 3700 cal years bp the maximum relative sea level rsl was 4 0 m with a sst of 20 7 c subsequently vermetid based sst decreased from 22 8 to 17 c at 3300 cal years bp with the coldest temperatures recording a strong upwelling event at around 2000 cal years bp when the rsl was at 2 m the intensification in upwelling water masses is identified by the 13c enrichment along with higher 18o in the vermetid shells the decreasing sst trend assessed from 3300 to 2000 cal years bp can be related to more frequent south atlantic coastal water intrusions on the surface layer in the mid shelf increasing the nutrient concentration in the upper layer from 1900 to 1300 cal years bp a higher sst up to 21 c occurred during the continuous sea level fall

smooth or oscillating late holocene sea level curve evidence from the palaeo zoology of fixed biological indicators in east australia and beyond abstract the nature of late holocene sea level change has important palaeo environmental implications for the understanding of past and present coastal oceanic and climatic systems this study develops a fixed biological indicator fbi method based on tubeworm barnacle assemblages in order to construct a late holocene sea level curve for south east australia it also compares changes within and between mid latitude regions of the southern hemisphere using the palaeo biology of inter tidal sub fossils that have provided time elevation data covering the past 5000 years five sites from around the mouth of the port hacking estuary 29 km south of sydney are described in detail the results suggest that rather than relative sea level describing a stable or smoothly falling pattern from a maximum of 1 0 m above present over the last 5000 years on the southeast australian coast there have been complex movements from a maximum of over 1 5 m with at least one marked fall between 3500 and 3400 yr bp and the possibility of a small positive oscillation around 1900 yr bp furthermore changes in the inter tidal species at our sites suggest that there was a period between 4300 and 2800 years where ocean temperatures were warmer than present our port hacking findings are compared with other studies from the east coast of australia as well as the pacific islands and brazil evidence from each location suggests a broad similarity in the timing of environmental events and marine fluctuations across an expanse of the southern hemisphere are such similarities coincidental or part of mechanisms common to mid latitude southern hemisphere regions

post variscan evolution of the anti atlas belt of morocco constrained from low temperature geochronology the anti atlas belt of morocco extends ene wsw over more than 600 km from the atlantic margin in the west to the interior of the african plate in the east it exhibits precambrian rocks outcropping as basement inliers and surrounded by marine ediacaran cambrian sequences around the axis of the mountain range the belt which has for a long time been interpreted as of variscan age is now revealed to have experienced major vertical movements through mesozoic and cenozoic times thereby the anti atlas domain appears to be affected by two episodes of exhumation separated by an episode of subsidence the initial episode occurred in the late triassic and led to the exhumation of 7 5 10 5 km of crustal rocks by the end of the middle jurassic ca 160 150 ma the following phase resulted in 1 3 km of basement subsidence and occurred during the late jurassic and most of the early cretaceous the basement rocks were then slowly brought to the surface after experiencing 2 3 5 km of exhumation throughout the late cretaceous and the cenozoic the timing of these episodes of exhumation and subsidence coincides with major tectonic and thermal events in relation with the evolution of the atlantic and tethys oceans indicating that the effects of their rifting and drifting extended beyond their presumed margins

planktonic foraminifera in the sediment of a western boundary upwelling system off cabo frio brazil abstract the distribution of planktonic foraminifera in box core tops under the influence of a western boundary upwelling system along the southeastern brazilian continental margin was examined to evaluate the similarity percentage simper and to create a biofacies model for paleoenvironmental applications species associated with warm and oligotrophic water were distributed in the rio de janeiro sector of the campos basin while productive water species were most abundant in the rio de janeiro sector of the santos basin and cold water species were most abundant in the cabo frio upwelling system cfus four major biofacies are associated with the oceanographic setting of the cfus one from the campos basin a brazil current front one from the santos basin b mixture of coastal and oceanic waters and two associated with the cabo frio high in the northern biofacies c and southern biofacies d the distribution of biofacies c and d was associated with temperature differences biofacies c represents a mixture of upwelling and tropical waters while biofacies d represents a mixture of cold nutrient rich and santos basin waters these biofacies were also defined in core cf10 01b in which six main paleoceanographic phases were characterized during the last 9 cal kyr predominantly showing alternating dominance between biofacies c and d from 9 0 to 5 0 cal kyr before the present bp the system was dominated by biofacies c between 4 0 and 3 5 cal kyr bp biofacies d was dominant between 3 5 and 2 5 cal kyr bp a strong influence of coastal waters and weakened upwelling activity were indicated by the dominance of biofacies b c d the last 2 5 cal kyr was dominated by biofacies d the sst in this core was reconstructed using the modern analog technique mat which revealed 0 35 c of variability indicating no sst changes during the holocene the weak sensitivity of the mat was due to the interplay among different oceanographic features

fish bone diagenesis in southeastern brazilian shell mounds and its importance for paleoenvironmental studies abstract brazilian shell mounds are relicts of prehistoric settlements characterized as distinct features on the sandy coastal plain sandy bars of coastal lagoons and rocky island they are composed of shells of edible marine mollusks fish remains and wildlife bones intermixed with sand in the coastal lagoon region of the rio de janeiro state these shell mounds range in age between 5100 and 1300 cal bp in this study we analyzed the geochemistry of the bones of the whitemouth croaker that primarily offers insight on the nature of bone diagenesis and its use for radiochronology and as isotope paleo thermometer the x ray diffractograms of bones from the tarioba shell mound exhibit elevated calcite profiles in contrast to a reduced hydroxyapatite concentration two peaks of quartz and the presence of feldspar provide evidence of exogenous materials e g sand or silt particles infilling hollow spaces within the fish bones the beirada and the ponte do girau shell mounds are characterized by the highest peaks of apatite relative to calcite which is clearly different from the result obtained for tarioba the manitiba profile is similar to the tarioba profile except for calcite peaks that are approximately three times lower than those for tarioba at a depth of 25 cm in the tarioba shell mound the redox sensitive index of diagenetic alteration reaches its maximum value suggesting a zone of accumulation in the soil horizon redox condition the 18o derived temperatures profile based on mollusks showed a consistent range from 18 1 to 24 1 c indicating seasonal events of intense upwelling of the south atlantic central water breaking the mean warm surface conditions of the brazil current diagenetic imprints of tarioba shell mound suggest humid burial conditions with the loss of hydroxyapatite and the enrichment of exogenous calcite drier depositional environmental conditions are indicated in the ponte do girau and the beirada shell mounds while intermediary depositional environmental conditions characterize the manitiba shell mound in the period represented by the shell mound samples the sea level exhibited significant oscillations and portions of the inner shelf were exposed which may have resulted in an anomalous derived temperature records these results are compatible with events of anomalous temperatures occurring in the sea level during the time span of occupation of these shell mounds

relative sea level changes in the last 5500 years in southern brazil laguna imbituba region santa catarina state based on vermetid ages abstract twenty six new radiocarbon dates from vermetid shells collected in the southernmost sector of the brazilian rocky coast presented dates ranging from 5410 80 to 190 65 years b p with associated paleosea levels varying from 2 10 m to 0 20 m above present sea level the overall suggested trend of the relative sea level rsl declining until at least 190 years b p is somewhat contradictory to a proposed rsl rise in the last 1000 years in southern brazil the data also seem to undermine a more widely accepted rsl trend that suggests that at least two negative rsl oscillations occurred between 4100 and 3800 years b p and between 3000 and 2700 years b p the maximum elevation of the rsl in the holocene in southern brazil was possibly lower than that observed in most of the brazilian eastern coast discrepancies between ancient sea levels of similar ages are attributed to coincidental methodological problems to imprecisions in determining past relative sea levels and to possible changes in the geomorphology and wave climate close to shore during the last 5000 years a general trend of increasing 18 o with a reduction in age in the studied samples may suggest a gradual reduction of water temperature in the region during the same period

the analysis of last interglacial mis 5e relative sea level indicators reconstructing sea level in a warmer world the last interglacial mis 5e 128 116 ka is among the most studied past periods in earth s history the climate at that time was warmer than today primarily due to different orbital conditions with smaller ice sheets and higher sea level field evidence for mis 5e sea level was reported from thousands of sites but often paleo shorelines were measured with low accuracy techniques and in some cases there are contrasting interpretations about paleo sea level reconstructions for this reason large uncertainties still surround both the maximum sea level attained as well as the pattern of sea level change throughout mis 5e such uncertainties are exacerbated by the lack of a uniform approach to measuring and interpreting the geological evidence of paleo sea levels in this review we discuss the characteristics of mis 5e field observations and we set the basis for a standardized approach to mis 5e paleo sea level reconstructions that is already successfully applied in holocene sea level research application of the standard definitions and methodologies described in this paper will enhance our ability to compare data from different research groups and different areas in order to gain deeper insights into mis 5e sea level changes improving estimates of last interglacial sea level is in turn a key to understanding the behavior of ice sheets in a warmer world

post variscan exhumation of the central anti atlas morocco constrained by zircon and apatite fission track thermochronology the origin of the anti atlas relief is one of the currently debated issues of moroccan geology to constrain the post variscan evolution of the central anti atlas we collected nine samples from the precambrian basement of the bou azzer el graara inlier for zircon and apatite fission track thermochronology zircon ages cluster between 340 20 and 306 20 ma whereas apatite ages range from 171 7 ma to 133 5 ma zircon ages reflect the thermal effect of the variscan orogeny tectonic thickening of the ca 7 km thick paleozoic series likely enhanced by fluid advection apatite ages record a complex mesozoic cenozoic exhumation history track length modelling yields evidence that i the precambrian basement was still buried at ca 5 km depth by permian times ii the central anti atlas was subjected to erosional exhumation during the triassic early cretaceous then buried beneath ca 1 5 km thick cretaceous paleogene deposits iii final exhumation took place during the neogene contemporaneously with that of the high atlas

the inverted triassic rift of the marrakech high atlas a reappraisal of basin geometries and faulting histories the high atlas of morocco is an aborted rift developed during the triassic jurassic and moderately inverted during the cenozoic the marrakech high atlas with large exposures of basement and triassic early syn rift deposits is ideal to investigate the geometries of the deepest parts of a rift constituting a good analogue for pre salt domains it allows unraveling geometries and kinematics of the extensional and compressional structures and the influence that they exert over one another a detailed structural study of the main triassic basins and basin margin faults of the marrakech high atlas shows that only a few rift faults were reactivated during the cenozoic compressional stage in contrast to previous interpretations and emphasizes that fault reactivation cannot be taken for granted in inverted rift systems preserved extensional features demonstrate a dominant dip slip opening kinematics with strike slip playing a minor role at variance to models proposing a major strike slip component along the main basin bounding faults including faults belonging to the tizi n test fault zone a new middle triassic paleogeographic reconstruction shows that the marrakech high atlas was a narrow and segmented orthogonal rift sub perpendicular to the main regional extension direction which was nw se in contrast to the central and eastern segments of the atlas rift which developed obliquely this difference in orientation is attributed to the indented ouzellarh precambrian salient part of the west african craton which deflected the general rift trend in the area evidencing the major role of inherited lithospheric anisotropies in rift direction and evolution as for the cenozoic inversion total orogenic shortening is moderate 16 and appears accommodated by basement involved large scale folding and by newly formed shortcut and by pass thrusting with rare left lateral strike slip indicators triassic faults commonly acted as buttresses

paleoproductivity changes during the holocene in the inner shelf of cabo frio southeastern brazilian continental margin benthic foraminifera and sedimentological proxies abstract sedimentological and benthic foraminifera analyses carried out on a core length 4 15 m collected at 22 56 31 s and 41 58 48 w at a water depth of 43 m sampled from the inner shelf of cabo frio southeastern brazilian continental margin allowed identification of different hydrodynamic and productivity regimes related to sea level fluctuations and or climatic changes during the last 9 4 ka cal bp prior to 7 0 ka cal bp a less intense hydrodynamic and lower productivity regime occurred at lower sea levels and under drier climatic conditions between 7 0 and 5 0 ka cal bp relatively stronger local oceanic circulation and relatively high productivity were observed in a scenario of rising sea levels and more humid conditions from 5 0 to 3 0 ka cal bp bottom currents weakened and input of nutrients increased with productivity levels similar to the previous phase at lower sea level and in a drier climate from 3 0 ka cal bp up to the present stronger hydrodynamic conditions and a higher productivity regime are linked to the establishment of the upwelling process in cabo frio from 2 5 ka cal bp to the present upwelling enhancement has been recognized resulting from the combined action of ne winds and the intensification of the meandering pattern of the brazil current bc

the moroccan anti atlas the west african craton passive margin with limited pan african activity implications for the northern limit of the craton abstract the moroccan anti atlas region located south of the south atlas fault has been viewed traditionally as containing two segments separated by the anti atlas major fault these two segments are said to consist of a 600 700 ma pan african segment located in the northeast and b 2 ga eburnian segment situated to the southwest on the basis of observations in the zenaga and saghro inliers and of a recent literature review we suggest that this subdivision is inappropriate in that eburnian and pan african materials occur throughout the anti atlas region the entire anti atlas is underlain by eburnian crust unconformably overlain by a lower neoproterozoic passive margin allochthonous pan african ocean crustal slices were thrust onto the west african craton wac passive margin sequence 685 ma ago as a result of pan african accretion tectonics high level high k calc alkaline and alkaline granitoids locally intruded the anti atlas sequence as a whole at the end of the pan african orogeny at 585 560 ma the intervening 100 m y interval was marked by quiescence this succession of events can be related to the behaviour of one single rigid cratonic passive margin during an orogeny and correlated to the pan african events that occurred to the east in the tuareg shield and to the north in avalonian terranes this model implies that the actual northern limit of the wac is located at the south atlas fault saf and not at the anti atlas major fault aamf we propose that the aamf corresponds to the southwestern boundary of an aulacogen that formed along the northern margin of the wac during early neoproterozoic times this is consistent with the development of the gourma aulacogen on the eastern side of the wac this model further suggests that the northeastern boundary of the wac occurs north and not south of ougarta algeria support for this model is provided by geological and geophysical evidence

the brazilian sea level curves a critical review with emphasis on the curves from the paranaguaand cananeia regions abstract relative sea level curves for the mid to late holocene have been proposed for eight different sectors along the brazilian coast this paper aims to review the data used to construct the curves proposed for two sectors the paranaguaand cananeia regions in southeast brazil more specifically we analyze the palaeo sea level indicators vermetid tubes shells wood fragments and shell midden deposits related to 1 the sea level maximum of the mid holocene and 2 the two secondary oscillations that would have occurred between 4100 3800 years b p and 3000 2700 years b p the sedimentary deposits of the coastal plain as well as vermetid datings suggest a mid holocene sea level maximum between 3 5 and 4 m the great majority of the indicators used to infer the secondary oscillations in previous studies were derived from shell middens besides being unreliable palaeo sea level indicators these data also showed inconsistencies that undermine the existence of such oscillations the plot of all the data derived from vermetid samples found along the brazilian coast also indicate a rather smoother sea level fall in the last 5100 years

variability of the brazil current during the late holocene abstract our understanding of the centennial scale variability of the brazil current bc during the late holocene is elusive because of the lack of appropriate records here we used the mg ca and oxygen isotopic composition of planktonic foraminifera from two marine sediment cores collected at 27 s and 33 s off southeastern south america to assess the late holocene variability in the upper water column of the bc our results show in phase fluctuations of up to 3 c in sea surface temperatures sst and 0 8 in oxygen isotopic composition of surface sea water a proxy for relative sea surface salinity sss time series analyses of our records indicate a cyclicity with a period of ca 730 yr we suggest that the observed cyclicity reflects variability in the strength of the bc associated to changes in the atlantic meridional overturning circulation amoc positive negative sst and sss anomalies are related to a strong weak bc and a weak strong amoc moreover periods of peak strength in the bc occur synchronously to a weak north brazil current negative sst anomalies in the high latitudes of the north atlantic and positive negative precipitation anomalies over southeastern south america equatorial africa further corroborating our hypothesis this study shows a tight coupling between the variability of the bc and the high latitudes of the north atlantic mediated by the amoc even under late holocene boundary conditions