multicentury scale records of carbonate hydrographic variability on the northern iceland margin over the last 5000 years the waters off northern iceland are subjected to extreme hydrographic variability on annual to decadal timescales in years when cold low salinity water moves coastward and sea ice is prevalent i e the late 1960s marine productivity of surface waters is low because the water column is well stratified in the opposite oceanographic mode warm salty atlantic water dominates the shelf and vertical mixing results in high productivity we track these two contrasting modes by measuring the carbonate content of marine sediments a proxy for productivity in three cores from northern iceland the fjord record b997 328pc is anchored by eleven 14c ams dates and has a resolution of one sample every 50 yr thirteen oscillations occurred over the last 4800 cal yr with an average length of 370 yr these are superimposed on a long term decrease in net carbonate accumulation the little ice age is marked by the largest decrease in carbonate content and in flux with smaller minima at 2300 and 3000 cal yr b p marked peaks in carbonate optima occurred at 2000 and 3800 cal yr b p the carbonate record from b997 328pc can be correlated with records on the inner shelf b997 330pc and midshelf b997 327pc indicating that significant regional changes in oceanography occurred at the southern margin of the norwegian greenland sea the marine carbonate fluctuations closely track temperature reconstructions from the greenland summit site for the last 2000 cal yr and show similar but slightly offset oscillations between 2000 and ca 4800 cal yr b p

jurassic evolution of the arabian carbonate platform edge in the central oman mountains the jurassic sahtan group exposed in northern oman was deposited in shallow marine environments at the edge of the arabian platform facing the neo tethys hamrat duru basin the upper sahtan group is made up of a mixed siliciclastic carbonate unit overlain by pure carbonate deposits assigned to a bathonian and early callovian age on the basis of brachiopods and foraminifers these carbonate depositional systems were composed of outer oolitic shoals that underwent subaerial exposure and a deeper somewhat restricted gently dipping shelf interior oolitic material was shed off the platform edge into the deep sea depositional complex of the guweyza formation the sahtan group is affected by an important thickness reduction towards northeastern jabal akhdar the angular unconformity 0 2 at the top of the sahtan group is shown to result from tilting and top truncation of genetic sequences this unconformity is overlain by the rayda formation a veneer that shows an onlap pattern including a gradual deepening upwards facies evolution the minimal time span of the stratigraphic hiatus is mid callovian kimmeridgian oxfordian and kimmeridgian sequences were probably never deposited in this area because of lack of accommodation space and or because of subaerial exposure it is proposed herein that the unconformity was shaped by subaerial carbonate dissolution during a steady tectonically driven exhumation of the platform edge during the tithonian a major eustatic sea level rise caused transgression of the rayda formation upon the platform edge and normal shelf marine conditions resumed in the eastern arabian peninsula

development of microporosity in a micritic limestone reservoir lower cretaceous middle east abstract abundant intercrystalline microporosity is developed within the matrix of micritic limestones over several hundreds of meters of section in the thamama group lower cretaceous at sajaa field eastern u a e sediments in the upper shuaiba formation uppermost tamama group include muddy rudist algal coralgal and orbitolina dominated lithofacies matrix is composed of euhedral to subhedral micro rhombic low mg calcite crystals with average diameters of about 5 m microporosity development was not related to leaching chalkification of lithified micrite during post depositional emergence of the shuaiba formation features diagnostic of emergence are lacking in core below the upper contact of the unit matrix microporosity is believed to have been an early developed property of micritic limestones trace element compositions of matrix reflect a diagenetic process that involved conversion of a calcitic lime mud into micro rhombic micrite and microspar using a closed system geochemical model the observed matrix oxygen isotope compositions 18 o of 4 to 5 pdb are compatible with dissolution of aptian lime mud 18 o of 2 pdb and reprecipitation of calcite in fluids of marine composition under conditions corresponding to burial depths of 550 800 m porosity of 30 50 at 40 50 c closed system conditions are consistent with textural constraints for limited or arrested cementation in the matrix chemical compaction was responsible for partial occlusion of matrix microporosity as microporosity is decreased in zones of intense stylolitization slight corrosion of matrix crystals and leaching of peloids and orbitolina postdated cementation and chemical compaction during deep burial

environmental changes and the rise and fall of civilizations in the northern horn of africa an approach combining δd analyses of land plant derived fatty acids with multiple proxies in soil the domains of the ancient polities d mt and aksum in the horn of africa s highlands are a superior natural system for evaluating roles of environmental change on the rise and fall of civilizations to compare environmental changes of the times of the two polities we analyzed stable hydrogen isotopic ratios d of land plant derived fatty acids n c26 30 and other proxies from soil sequences spanning the holocene from the region three results suggest that trends in d values unambiguously reflect changes in rainfall first increases in d coincide with dry periods inferred from studies of eastern african lakes second changes in d values were parallel among sections during overlapping time intervals third consideration of vegetation history did not alter directions of trends in d values over time by unambiguously recording precipitation the d values also enhanced interpretations of proxies that are affected by both climate and land clearing both d mt ca 2750 2350 cal y bp and the aksumite ca 2100 1250 cal y bp rose during wetter intervals of the drier part of the holocene after ca 6000 cal y bp analyses of charred matter indicated that fire had been a common agent of land clearing in all sites the influence of climate on fire varied however prior to the emergence of d mt d values were correlated with c4 c3 plant ratios estimated from 13c values there are no c4 trees and precipitation may have been the main influence on canopy openness after ca 4300 cal y bp there was no significant relationship between d and c4 c3 plant ratios suggesting that factors such as fire influenced canopy openness regardless of climate furthermore the impact of land clearance differed between sites and between d mt and the aksumite s times in one site the interval from 3550 cal y bp to the decline of d mt had several anomalies that suggested dramatic increases in thermal severity of fire and human impact among these were a large contribution of charred matter to a high total organic carbon that low hydrogen and oxygen indices suggest was severely altered by other factors than humification these results support hypotheses about the rise of civilizations being favored by specific climatic conditions but suggest that patterns of land clearing differed during the declines of d mt and the aksumite

cenomanian early turonian carbonate platform of northern oman stratigraphy and palaeo environments abstract the jebel akhdar and adam foothills outcrops in northern oman arabian peninsula offer the opportunity to study in detail the lateral and vertical changes of a cenomanian early turonian carbonate platform formed by the natih formation wasia group eleven sections with less than 5 km offset were logged to express metre scale lithological and biostratigraphical vertical changes the first rudist zonation is established complementing classical benthonic foraminifer and ammonite biozones typical cenomanian rudist association caprinids and radiolitids occur in the natih e c d a lower part whereas lower turonian hippuritid rudists are represented in the upper part of the natih a a sedimentological and palaeoecological approach leads to identification and interpretation the facies and discontinuities of the natih carbonate platform and to a reconstruction of its spatial organization application of the concepts of sequence stratigraphy allows interpretation of the units of the natih in terms of systems tracts an attempt is made to correlate the sequence stratigraphical model to eustatic sea level changes and regional tectonic events three palaeoenvironmental models taking into account bio and lithofacies are proposed

late holocene ca 4 ka marine and terrestrial environmental change in reykjarfjordur north iceland climate and or settlement core b997 328pc is from the landward side of a 100 m deep basin in reykjarfjordur a small fjord on the north coast of the northwest peninsula of iceland this is an area that can be severely affected by incursions of polar sea ice but has not suffered marked land erosion during the settlement period the core is 422 cm in length and consists principally of fine grained muds with in situ molluscs eleven ams 14c dates on molluscs indicate a constant sediment accumulation rate of ca 1 cm 10 yr 1 for the last 4280 50 yr bp we measured and derived a variety of proxies for indications of changes in the nearshore environment these included physical properties and grain size mass accumulation rates micropalaeontology pollen and foraminifera multivariate analysis and constrained clustering were used to define major changes in the proxies in several parameters the major change in the fjord environment occurred close to 1000 14c yr ago thus approximately coincident with the onset of the settlement of iceland other changes are noted at around 1600 and 3400 14c yr ago betula pollen disappears from the record ca 1500 yr bp and there are peaks in marine productivity occurring ca 2 and 3 4 ka a major decline in carbonate accumulation and a sharp increase in the cold water benthic foraminifer elphidium excavatum forma clavata 400 yr ago represents the local marine signature of the little ice age none of the changes in our data can be explained adequately by a simple call to land use practices and an increase in land to sea transport but both the pollen and foraminiferal records indicate a decrease and even loss of warm elements in both flora and fauna over the past 4 kyr copyright 2001 john wiley sons ltd

early cretaceous platform margin configuration and evolution in the central oman mountains arabian peninsula the hajar supergroup middle permian lower cretaceous of northeastern oman records rifting and development of a passive margin along the edge of the arabian platform facing neo tethys the jurassic and lower cretaceous part comprising the sahtan kahmah and wasia groups was deposited during the maximum extent of the broad epicontinental sea landward of this margin these limestone units reach a total of 1500 m in thickness and they correlate with the principal hydrocarbon reservoirs of the arabian peninsula the trace of the jurassic and cretaceous margin in northeastern oman followed a zigzag series of rift segments resulting in promontories and reentrants that changed in position through time in response to the configuration and differential motion of underlying rift blocks in an overall extensional regime synsedimentary normal faulting with 600 m of throw occurred locally during the middle jurassic whereas during the late jurassic the margin was subjected to erosion from variable uplift of up to 300 m before subsiding to below storm wave base this uplift may have been caused by compression from oceanic crust that obducted along the southeastern side of the platform subsequently lower cretaceous strata document varying rates of block subsidence the lower cretaceous succession in the central oman mountains and adjacent subsurface began with regional drowning around the jurassic cretaceous boundary the succession in the east saih hatat records a single regressive sequence culminating in the progradation of the shallow water carbonate platform by the cenomanian however the succession in the west jebel akhdar and interior is dominated by shallow water carbonate facies but punctuated by a second regional drowning in the late aptian a third late cretaceous drowning terminated deposition of the wasia group in the turonian and was caused by convergence of oceanic crust and foreland basin formation although previously ascribed to eustatic sea level rises the two early cretaceous drowning events can be explained as consequences of the tectonic behavior of the platform the earlier event rayda formation occurred when first uplift tilted the eastern side of the platform and induced a relative sea level stillstand and widespread evaporative conditions in the interior hith anhydrite and then the eastern side subsided rapidly to below storm wave base forming a broad embayment starved of periplatform sediment by contrast the second drowning nahr umr formation was due to detrital influx generated by uplift on the west side of the platform both tectonic episodes led to a reduction in the calcium carbonate generating capacity of the epicontinental sea causing shallow water fa ies to be abruptly overlain by deeper water facies the effects from these two drownings eventually diminished and shallow water environments reestablished themselves the overall succession appears independent of eustatic sea level change

influence of climate and dolomite composition on dedolomitization insights from a multi proxy study in the central oman mountains abstract dedolomitization is an important diagenetic process that can yield information on the history of paleo fluids in a given aquifer or outcrop and by extension it offers a window into past hydrologic conditions dedolomitization is also relevant economically as it can alter the porosity and permeability of carbonates thus affecting reservoir quality despite considerable research the process of dedolomitization is still not entirely understood here new findings from the central oman mountains highlight the importance of dolomite chemistry and fluctuating climate on dedolomitization petrographic mineralogical and geochemical data from both altered and pristine dolomite hosted in jurassic carbonate rocks from the sahtan group and outcropping at wadi mistal in the jebel akhdar tectonic window reveal two dolomite bodies with different characteristics stratabound and fault related dolostone the ferroan dolomite crystals are larger in the fault related dolostone whereas the non ferroan dolomite crystals are smaller in the stratabound dolostone petrography reveals a complex suite of alteration textures including pristine dolomite recrystallized dolomite and calcitized dolomite dedolomite iron oxides are present pervasively in the altered rocks and different alteration textures co occur in the same sample relative to unaltered dolomite in this outcrop the recrystallized dolomite is characterized by similar positive carbon isotope values but less negative oxygen isotope values and the calcitized dolomite is characterized by even less negative oxygen isotope values and more negative carbon isotope values based on field data and petrography two phases of alteration are evident an earlier dedolomitization event affecting the stratabound dolomite only and a more pervasive pleistocene holocene alteration phase associated with surface weathering that affected both the fault related dolomite and to a lesser extent the stratabound dolomite stable isotope results further suggest that the more recent subaerial weathering phase happened under two alternating climate regimes dedolomitization was triggered by meteoric fluids that interacted with soil related carbon during humid climatic period s whereas recrystallization of ferroan fault related dolomite happened during more arid climatic period s with less developed soils and lower fluid rock interaction these results suggest that weathering of ferroan fault related dolomite can lead to formation of goethite and recrystallized non stoichiometric dolomite with a reset stable oxygen isotope signature and sometimes to dedolomitization

late holocene high frequency east asia winter monsoon variability inferred from the environmentally sensitive grain size component in the distal shelf mud area east china sea the b2 b2g and i4 sediment cores recovered from the centre of the distal mud area of the east china sea ecs were analysed for grain size distribution proxies for environmentally sensitive grai

reconstructing mid to high latitude marine climate and ocean variability using bivalves coralline algae and marine sediment cores from the northern hemisphere quantifying the role and contribution of the world s oceans in past present and future global change is an essential goal in climate paleoclimate and environmental studies although the global oceans interact and influence climate greatly the marine environment is substantially under represented in key climate assessment reports especially during the last millennium ipcc 2007 see palaeoclimate chapter 6 6 the last 2000 years the under representation of marine records in key climate documents likely results from the often imprecise chronologies associated with many marine based archives which greatly hinders singular climate comparisons lag lead phasing relationships with well dated and or annually resolved archives however several marine archive records have excellent chronological constraint in particular many marine bivalve taxa and coralline algae have annual increments that form within their carbonate framework that can be used to establish an absolutely dated chronology via cross dating techniques from the marine environment additionally in some cases where sedimentation rates are high and alternative chronological dating methods exist e g tephrochronology other than radiocarbon measurements often greater than 40 years uncertainty sediment archives can provide continuous sub decadal records of environmental change for centuries to millennia this brief introductory article and accompanying special issue will focus on the utilization of bivalves coralline algae and high resolution marine sediment cores in paleoclimate and environmental studies within the most recent millennium with a focus on the northern hemisphere

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

the influence of regional factors in the expression of oceanic anoxic event 1a oae1a in the semi restricted organya basin south central pyrenees spain abstract the global occurrence of oxygen deprived conditions in the ocean characterizes the early aptian hence the hallmark of that time interval is the accumulation of organic rich sediments during an episode of severe oxygen deficiency known as oceanic anoxic event 1a oae1a as seen elsewhere in the tethyan domain an overall change in facies marked by increased input of terrigenous material distinguishes the lower aptian in the study area but the nature of the lithologies associated with the organic carbon rich deposits remain dominated by carbonate sediments and are expressed differently with respect to other areas where the occurrence of black shales characterizes oae1a this comparison indicates that significant spatial heterogeneity occurred in sub tethyan basins coeval with the global oceanic event the present work provides a high resolution multi proxy study petrography total inorganic carbon tic total organic carbon toc carbon isotope 13corg clay mineralogy and biomarkers of the upper 155 m of the el pui section organya basin including the record of oae1a the results reveal that oxygenic conditions fluctuated throughout the studied interval with episodes of oxygen depletion that concurred with toc values 1 however petrographic observations molecular biomarkers and redox sensitive trace elements rstes indicate that full anoxia was not achieved the results also provide the first high resolution 13corg profile for the el pui section that replicates in greater detail the carbon isotopic signature reported for the tethyan domain the upper 155 m of the el pui section include expanded and well defined trends of the carbon isotope segments c2 upper part c3 c4 c5 and c6 partial which correlate with other tethyan sections and allow for the recognition of the lower aptian oae1a in the uppermost 40 m of the section such improved high resolution chemostratigraphic curve could contribute to a more precise chronostratigraphic correlation of aptian events in a broader scale

a platform to basin transition for lower aptian carbonates shuaiba formation of the northeastern jebel akhdar sultanate of oman abstract the platform to basin transition of the lower aptian shuaiba carbonate platform throughout a large part of the arabian peninsula has hitherto mainly been documented from subsurface data and has widely been regarded as having been progradational in northeastern jebel akhdar however the shuaiba platform did not prograde and was scarp bounded early lithification accounts for the rigid nature of the scarp a biological framework being nearly absent early exposure surfaces neptunian dykes sills internal breccias and other sediment features as well as the geographic coincidence of the platform scarp with older and younger scarps suggest a tectonic control of margin morphology and dynamics a contemporaneous peak of allodapic sediments and reactivation of older basement structures in adjacent basins also tends to indicate the importance of structural influence on platform margin organization

geology and reservoir characteristics of carbonate buildup in giant bu hasa oil field abu dhabi united arab emirates bu hasa field in abu dhabi was the first giant oil field in the arabian gulf to produce from the lower cretaceous shuaiba formation aptian the field has a productive area of about 155 673 ac 63 047 ha and 12 6 billion bbl of oil reserves the formation is composed mainly of rudistid and algal sediments rudistid mounds having overlain and built up the topography of an algal platform the position and elevation of the platform edge combined with rising eustatic sea level created a tendency toward both vertical and lateral growth and regulated the form and distribution of the rudist accumulation the shuaiba formation has good reservoir quality ranging in porosity from 18 25 and with average permeability exceeding 100 md nine reservoir units a i classified by their porosity permeability and lithology can be clearly defined from the logs eleven main lithofacies have been defined in the shuaiba from detailed core descriptions these lithofacies were deposited in three main phases the earliest phase consisted of chalky mud supported sediment with some algal colonies followed by a middle phase characterized by a thick algal platform during this stage of deposition a shallow water carbonate platform developed over the south and central part of the field grading into deeper open marine sedimentation toward the north the late phase was characterized by rudistid buildups mainly caprinids and caprotinids the growth of the thick algal platform in the south and central areas controlled the initial distribution of the main rudistid buildup toward the north small rudistid reefs are sparsely developed and present only n the latest stage on high energy shoals

timing and mechanisms of surface and intermediate water circulation changes in the nordic seas over the last 10 000 cal years a view from the north iceland shelf abstract the north iceland shelf bears essential components of the present surface and intermediate circulation of the northern north atlantic instrumental and historical data give evidence of the sensitivity of this domain to broad regional scale oceanic and atmospheric anomalies our investigation of the paleohydrological variability off northern iceland throughout the last 10 000 cal yr suggests that atmospheric forcing alone through combined changes in strength of the wind stress curl and sea level atmospheric pressure pattern over the nordic seas is sufficient to explain the recorded changes in origins and dynamics of surface and intermediate water masses our biotic proxies coccoliths and benthic foraminifera were extracted from a giant piston core md99 2269 collected in a shelf trough where sediment accumulated at an excess rate of 2 m kyr the mid holocene from 6 5 to 3 5 cal kyr bp was a time of peaked carbonate production and subsequent sedimentation and strong water column stratification with a thick layer of cold fresh arctic surface water overlapping an enhanced flow of irminger atlantic intermediate water applying conditions triggering present time carbonate plankton blooms in the studied area we infer that a lowered cyclonic activity associated with decreased winter storms and reduced production of arctic intermediate water in the iceland sea were conductive of the recorded mid holocene water column structure the opposite situation warm atlantic surface water low vertically integrated inflow of irminger water abutment of arctic intermediate water in deep shelf troughs characterized the early holocene as well as a shorter late holocene period centred at 2 cal kyr bp the little ice age ca 0 2 0 6 cal kyr bp and a short event at around 3 cal kyr bp stand as times of extreme advection of polar waters and extended sea ice development a comparison of the recorded long term holocene evolution of water column structure off northern iceland with climate and hydrological changes in the north eastern atlantic suggests that the strength of atlantic inflow into the nordic seas was subjected to a balance between the irminger and the norwegian branches this balance is thought to be mostly related to changes in the intensity and location of westerly winds and associated atmospheric pressure gradients in the north atlantic

holocene climate variability at multidecadal time scales detected by sedimentological indicators in a shelf core nw off iceland a holocene sediment record is presented from the djupall trough situated on the inner shelf northwest of iceland the paleoclimatic development has been interpreted on the basis of mass accumulation rate carbonate content mean grain size sediment petrology and 29 radiocarbon dates the results demonstrate in the early holocene 10 000 8000 cal year bp high sediment accumulation rates attributable to the effect of enhanced sediment mobilisation under influence of a relatively low sea level and remobilisation of glacial sediments on the sparsely vegetated vestfirdir peninsula the data suggest that a general southward displacement of the polar front commenced around 5000 4000 cal year bp a new proxy for holocene climatic variability is presented by the basalt plagioclase ratio in the 63 100 mum fraction high basalt plagioclase values are primarily related to periods of increased storminess and bottom current energy which enhanced the transport of basaltic sediment from the coastal zone towards the outer shelf advection of polar waters containing basalt rich ird from the eastern greenland blosseville kyst basalt province may also have contributed to increased basalt plagioclase ratios the correlation between basalt plagioclase ratios and proxies of solar activity c 14 production and be 10 flux was explored and suggests that some of the centennial scale peaks in colder climate could be related to increased nuclide production in the upper atmosphere in addition it was found that the medieval warm period c 1100 700 cal year bp was characterised by strong cyclone activity over the iceland region intense atmospheric circulation during this period has been confirmed also by other studies in the northern north atlantic region less

depositional system and reservoir potential of the middle cretaceous wasia formation in central eastern arabia abstract stratigraphy and depositional facies of the middle cretaceous wasia formation in central eastern arabia were studied in detail using subsurface data we also investigated the effects of depositional environmental changes and other geological parameters on the petroleum and groundwater reservoir potentials of the formation in the subsurface the wasia formation is divided into seven members composed mostly of siliciclastic deposits in the lower part and fine grained siliciclastic and carbonate sediments in the upper part five different facies which depict vertical and horizontal variations have been recognized changes in facies may be related partly to changing depositional environment from non marine fluvial and transitional in the lower part to very shallow and open marine shelf in the upper part interpretation of directions of increasing thickness and clastic percentage and of areas for potential stratigraphic traps shows that the lower siliciclastic part seems to have the highest probability to become petroleum and water reservoirs further the calculated average porosity of different members indicates that both sandstones and limestones of the wasia members are porous enough to be potential petroleum reservoirs and that the shales would have sufficient sealing capacity however the chances that large structural traps exist are low mature source rocks are not present nearby and unless a long distance migration of petroleum took place in the past the petroleum potential of the wasia in the study area appears very remote the wasia formation is a potential groundwater aquifer as far east as the arabian coastal area high yields with excellent hydraulic properties as well as large volumes of abstractable water in storage have been reported from the study area the regional differences of the parameters such as thickness porosity and permeability of the wasia aquifer in this area are mainly due to changes in depositional system the presence of fresh groundwater in the wasia formation of central arabia could have a damaging effect on the quality of petroleum if it is present any hydrocarbons which remained would be heavy viscous and immobile and could not be easily produced

catastrophic soil erosion in iceland impact of long term climate change compounded natural disturbances and human driven land use changes abstract this study examines the interplay between long term climate changes compounded natural disturbances and human driven land use changes on catastrophic soil erosion of the heathland ecosystem of haukadalshei i south iceland soil erosion was catastrophic for three centuries 1660 1960 ad and was characterized by almost total loss of vegetation and underlying soil soil erosion resulted in a desertified barren landscape that had no resemblance to the original heathland ecosystem soil erosion was spatially reconstructed in a chronological order using information on the average progress of eroding fronts anecdotal and historical evidence along with tephrochronological information the progress of the fastest eroding front was rapid 29 7 m yr 1 human driven land use changes played a role in the heathland degradation relentless free range grazing by livestock resulted in decreased resistance of heathland communities to soil erosion adverse climate change during little ice age lia 1550 1850 ad intensified the effect of grazing the catastrophic soil erosion was triggered by a massive sand encroachment 1660 ad from three outwash sand plains along the glacial river far the sand drift was sustained by dry northern glacial katabatic winds that drove the soil erosion long term climate change resulted in glacier fluctuation that caused changes in water discharge in the river far sand drift was intense during periods of no water discharge 1660 1708 ad and 1800 1929 ad and following glacial river floods 1708 1884 1902 1929 and 1939 ad also sand drift was intense due to unusually frequent volcanic tephra fallouts 1693 1721 and 1766 ad information on factors that increase the risk of soil erosion and trigger and drive soil erosion is critical in understanding catastrophic soil erosion

the cretaceous sequence stratigraphy of the socotran platform the republic of yemen outcrop studies combined with subsurface seismic and well data enable a detailed sequence stratigraphic analysis of the socotran platform during the cretaceous palaeogeographic reconstructions for the barremian aptian qishn formation albian cenomanian fartaq formation and maastrichtian sharwayn formation are presented the palaeogeographic maps have been constrained by data from outcrop studies on socotra and the adjacent islands of samhah and abd al kuri as well as the samhah 1a well which lies 60 km to the southwest of samhah island two major sequences can be recognised in the qishn formation and can be further subdivided into systems tracts an upper qishn highstand systems tract has been identified on a north south seismic line with coastline parallel facies belts an interpretation of the reservoir facies and porosity development of the highstand systems tract is attempted using the good quality seismic data in the socotran platform three major sequences can be recognised in the fartaq formation and one in the sharwayn formation which are illustrated on a second east west seismic line

formation and emplacement ages of the masirah ophiolite sultanate of oman hornblende separates from gabbros and biotite separates from crosscutting potassic granites of the masirah ophiolite have been analyzed by conventional k ar techniques the gabbros have late jurassic early cretaceous ages 126 158 ma and the granites have broadly similar ages 124 146 ma because the gabbros are likely to give ophiolite formation ages and the granites ophiolite emplacement ages it can be concluded that the masirah ophiolite was emplaced very soon after formation the late jurassic early cretaceous ages contrast with the middle cretaceous ages 90 95 ma of the semail ophiolite confirming earlier suggestions that the masirah ophiolite cannot simply be a right laterally displaced fragment of the semail ophiolite but is instead an uplifted block of indian ocean crust the formation and emplacement of the masirah ophiolite are discussed in the context of the late mesozoic evolution of the western indian ocean

late jurassic to cretaceous evolution of the eastern tethyan hawasina basin oman mountains remnants of a mesozoic continental margin can be studied today in the nappe pile of the oman mountains successions of the arabian carbonate platform and the adjacent deep hawasina basin are preserved in the nappe pile and in the foothills of this mountain range the jurassic cretaceous sediment successions of the hawasina basin sumeini and hamrat duru group are focus of this study these basinal archives contain information on the response of an eastern tethyan equatorial ocean system to multiple perturbations of the carbon cycle and of climate during the cretaceous turbiditic continental slope and basinal successions formed near the calcite compensation depth are difficult to date with biostratigraphy and sequence stratigraphy the available stratigraphic framework for the hawasina successions was not sufficient for tracing palaeoceanography through the time window of interest in this study therefore existing sequence stratigraphy and biostratigraphy are complemented by additional biostratigraphic data and with a newly established carbon and strontium isotope chemostratigraphy the hawasina basin was affected by sea level variations by changes in oceanography and also by regional tectonics a first major modification of oceanography occurred at the end of the jurassic when pelagic maiolica type sediments were accumulated in the deep basin and on adjacent submarine highs lower member of huwar and sid r formations pelagic to hemipelagic conditions existed until the valanginian marked by a major carbon isotope excursion pelagic sediments were afterwards replaced by a succession of fine to coarse grained turbidites of hauterivian to aptian in age the transition into the mid cretaceous is marked by a sudden shift to fine grained siliceous or chert deposits at a time when sediments enriched in organic carbon were accumulated in the western tethys and atlantic oceans the continental slope as well as the hawasina basin seemed to have been well ventilated during early and mid cretaceous time siliceous limestones and chert are indicator of well mixed and nutrient rich surface water while absence of black shales suggests young and oxygenated deep water with a possible source on the vast arabian platform these peculiar oceanographic conditions were most pronounced during the onset of the extreme greenhouse episodes of the oceanic anoxic event 1a this article is protected by copyright all rights reserved

temperature reconstructions for sw and n iceland waters over the last 10 cal ka based on δ18o records from planktic and benthic foraminifera abstract we have obtained 18 o carb data from planktic n pachyderma s and benthic foraminifera c lobatulu s m barleeanu s from eight cores between 40 and 500 m water depth along the sw core b997 347 and n iceland margins cores b997 321 324 327 328 329 330 and 332 that span the last 10 cal ka sampling resolution varies between centuries to millennial scales over this time range changes in 18 o carb in foraminifera are the product of changes in the global ice volume and the temperature and salinity of the water at the level in which the foraminifera live in order to evaluate the relative roles of these variables we investigate 1 the salinity s and 18 o water values for present day waters off iceland and 2 the present day relationships between 18 o carb or calcite values of foraminifera and water column temperature and salinity data we estimate the average error in the temperature estimate to be 0 3 c based on a monto carlo simulation of the various error terms we argue that around iceland the variations in 18 o carb of both benthic and planktic species over the last 10 cal ka are principally controlled by temperature variations while salinity changes prove less important spatial and temporal changes are examined for both bottom water and 50 m water temperature reconstructions based on six and four cores respectively reconstructed temperatures for sites around sw n iceland indicate that surface and seafloor water temperatures were warmest in the early holocene 10 6 cal ka beginning at 6 cal ka surface and seafloor temperatures began to cool in n iceland and to become less stratified in sw iceland over the last 5000 yrs sea surface temperature variations have been 1 c for 50 of the observations with a maximum range of 2 5 c a profound decrease in temperature of 1 5 c is recorded in our fjord site b997 328 during the little ice age an abrupt earlier cold event is well expressed in at least three n iceland cores around 5 cal ka

temporal changes in holocene δ18o records from the northwest and central north iceland shelf the region of north iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts in this study we present total carbonate and 18o records of benthic and planktic foraminifera from nine sediment cores from the north iceland shelf the results of this work indicate that the deglaciation of the vestfirdir peninsula was completed by 10 200 cal yr bp the 8200 cal yr bp cold event is present only as a minor isotopic event and seems not to have had much of a cooling effect on the bottom waters of the northwest iceland shelf the holocene maximum warmth attributed to a stronger north icelandic irminger current occurred between ca 7800 and 6200 cal yr bp over the past 4500 cal yr bp a general cooling trend has occurred on the north iceland shelf and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf relatively cooler waters were present at 4200 4000 cal yr bp 3200 2900 cal yr bp 2500 2350 cal yr bp and 600 200 cal yr bp whereas relatively warmer waters were present on the shelf at 3750 3450 cal yr bp 2800 2600 cal yr bp and 1700 1000 cal yr bp copyright 2004 john wiley sons ltd

middle cretaceous carbonate reservoirs fahud field and northwestern oman reservoir facies in fahud field and throughout northwestern oman are in shallow shelf carbonates of the middle cretaceous mishrif and mauddud formations interparticle porosity formed in the mishrif as sand aprons of lithoclast and skeletal grainstones surrounding fault block islands and less commonly in the mauddud as biostromes of rudist packstones moldic porosity after fine rudist debris is more common than interparticle porosity and occurs in thicker stratigraphic units interpreted to have formed locally in meteoric water lenses associated with islands and regionally during subaerial exposure associated with sea level lows

solar and tropical ocean forcing of late holocene climate change in coastal east asia abstract in this study paleoclimate signals were extracted from high resolution sediment records very recently produced from the mulyoungari swamp on jeju island south korea and examined to determine the main factors driving late holocene climate change in east asia the high resolution of the mulyoungari records allows the detection of multidecadal to centennial scale climate change with various cycles this enables comparisons with important paleoclimate proxies such as total solar irradiation tsi and sea surface temperatures ssts in the western tropical pacific wtp spectral analyses of pollen and magnetic susceptibility ms data identify significant periodicities of 780 470 135 145 and 50 70 years the mulyoungari swamp responded sensitively to global climate change during the holocene showing well known holocene cycles in the results our tree pollen index of warmness tpiw shows important late holocene cold events associated with low sunspot periods such as oort wolf sporer and maunder minimum comparisons among standard z scores of filtered tpiw tsi and other paleoclimate records from central and northeastern china off the coast of northern japan southern philippines and peru all demonstrate significant relationships this suggests that solar activity drove holocene variations in both east asian monsoon eam and el nino southern oscillation enso in particular the latter seems to have predominantly controlled the coastal climate of east asia to the extent that the influence of precession was nearly muted during the late holocene

sr ca profile of long lived tridacna gigas bivalves from south china sea a new high resolution sst proxy abstract high resolution 18o and sr ca ratio profiles of a modern live caught and a fossil dead collected giant bivalve shell tridacna gigas from northern south china sea were analyzed the high resolution 18o profiles as documented in most of previous studies showed pronounced seasonal cycles and recorded the combined influence of seawater 18o and sea surface temperature the sr ca ratio profiles derived from icp oes had well defined annual cycles and significant and negative correlation with sea surface temperature while the sr ca profiles derived from la icp ms did not reveal clear annual cycles this difference was likely caused by the organics contents in t gigas shells which had a chemical composition different than caco3 crystals and a heterogeneous distribution across the shell the sampling methods and the experimental errors two calibration equations between sr ca ratios determined by icp oes of modern t gigas shell and instrumental sst were calculated based on all monthly and extremum sst data and the equation from extremum data produced better sst predictions these results suggested that the high resolution icp oes derived sr ca ratios of t gigas in the south china sea had the potential of providing a good proxy of historical sst

two millennia of north atlantic seasonality and implications for norse colonies 18o values of mollusks recovered from near shore marine cores in northwest iceland quantify significant variation in seasonal temperature over the period from 360 b c to a d 1660 twenty six aragonitic bivalve specimens were selected to represent intervals of climatic interest by using core sedimentological characteristics carbonate powder was sequentially micromilled from shell surfaces concordant with growth banding and analyzed for stable oxygen 18o and carbon 13c isotope values because 18o values record subseasonal temperature variation over the lifetime of the bivalves these data provide the first 2 000 year secular record of north atlantic seasonality from ca 360 cal yr b c to cal yr a d 1660 notable cold periods 360 b c to 240 b c a d 410 and a d 1380 to 1420 and warm periods 230 b c to a d 140 and a d 640 to 760 are resolved in terms of contrast between summer and winter temperatures and seasonal temperature variability literature from the viking age ca 790 to 1070 during the establishment of norse colonies and later in iceland and greenland permits comparisons between the 18o temperature record and historical records thereby demonstrating the impact of seasonal climatic extremes on the establishment development and in some cases collapse of societies in the north atlantic

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

do paleoclimate proxies agree a test comparing 19 late holocene climate and sea ice reconstructions from icelandic marine and lake sediments geochemical mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments modern spatial calibrations or down core comparisons with instrumental climate data multi proxy studies provide another means of evaluating interpretations of proxies this paper presents a multi proxy assessment comparing 19 sub centennially resolved late holocene proxy records covering the period 300 1900 ad from seven icelandic marine and lacustrine core sites we employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and ultimately their utility as proxies for regional climate proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera abundance of the sea ice biomarker ip25 allochthonous quartz in marine sediments a proxy for drift ice around iceland marine carbonate abundance total organic carbon concentration chironomid assemblages lacustrine biogenic silica and carbon nitrogen ratios in lake sediments most of the examined proxy records including temperature and sea ice proxies correlate strongly with each other over multi centennial timescales and thus do appear to record changes in regional climate copyright 2011 john wiley sons ltd

cretaceous flexural history of northern oman mountain foredeep united arab emirates an important feature of the middle cretaceous arabian continental margin was the regional upwarping in the foreland of the northern oman mountains we interpret this upwarp as an early expression of a cratonward migrating peripheral swell associated with the emplacement of the semail ophiolite onto the margin subsurface stratigraphic data indicate that the swell was expressed during the cenomanian and attained its maximum relief during the turonian by the santonian further downflexure of the margin took place around an axis west of the study area burying the then inactive turonian swell beneath the deposits of the westward expanding foreland basin we suggest that establishment of the later more cratonward flexural regime took place abruptly rather than as a continuo sly migrating wave the middle cretaceous swell axis paralleled the present day axis of the oman mountains the upwarp was slightly asymmetric to the east and loosely constrained estimates of its width and height are 150 km and 244 93 mi and 800 ft respectively the dimensions suggest an anomalously low flexural rigidity 1022 n m for the middle cretaceous continental lithosphere we attribute this low apparent rigidity to the combined effects of remnant thermal and mechanical processes of an earlier rifting event and compression of the margin during the cretaceous emplacement of the semail ophiolite the small dimensions of the middle cretaceous swell suggest that other continental margins with similar geologic histories may also have narrow extinct swells buried beneath foreland deposits such swells may have significant impact on the entrapment of hydrocarbons as we propose for the sajaa margham trend

relative sea level changes and sedimentary facies development of the lowermost cretaceous berriasian valanginian cycles in the north of ar riyad city saudi arabia abstract a new high resolution stratigraphic framework for the thick and well exposed lower cretaceous rocks of saudi arabia has been provided the studied successions consist mainly of carbonates with minor interbedded siliciclastics forming the silayy yamamah and buwaib formations in the study area north of ar riyad city based on the integrated sedimentary facies analysis a relative sea level curve for the berriasian valanginian interval has been established including stacking pattern of the different facies cycles two transgressive regressive facies cycles have been identified and documented in the studied sections the first cycle started during the middle berriasian 143 ma comprising the silayy and yamamah formations it terminated at the yamamah buwaib formational contact during the early valanginian 138 ma characterized by a friable brownish ferruginous sandstone bed at the base of the buwaib formation the second transgressive regressive cycle encompasses the entire lower valanginian buwaib formation a major unconformity surface formed during the early late valanginian 136 ma marking the end of the second cycle and characterized by a distinctive hardground condensation the correlation and dating of the recognized cycles identified in central saudi arabia shows a contemporaneity to equivalent surfaces globally and thus strongly supports an isochronous formation of berriasian valanginian facies cycles by eustatic sea level changes

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

a centennial scale variability of tropical north atlantic surface hydrography during the late holocene abstract sea surface temperature sst and sea surface salinity sss fluctuations in the northeastern caribbean have been reconstructed through the last 2000 yr using an artificial neural network and 18 o analyses of planktonic foraminifera a warmer period prevailed in the ne caribbean from ad 700 950 which may reflect the occurrence of stronger and or more frequent el nino events a 2 c cooling of winter ssts from ad 1400 to 1550 coincides with the occurrence of reduced solar output the sporer event episodes of lower ssss with marked minima at the onsets of the dark ages in europe ad 500 600 and little ice age ad 1400 are cyclically recurrent at intervals of 200 400 yr and coincide with drier periods in mexico this may indicate that the tropical atlantic evaporation precipitation budget and ssss are affected by a centennial scale modulation involving the freshwater export import from into the atlantic ocean coeval changes recorded in the deep north atlantic circulation indicate that low latitude sss anomalies may be advected polewards by the north atlantic current system thus affecting deep ocean convection and strength of the thermohaline circulation

internally generated decadal cold events in the northern north atlantic and their possible implications for the demise of the norse settlements in greenland we attribute and describe the governing mechanisms of decadal cold excursions in the subpolar north atlantic of similar amplitude and duration to cold events reconstructed from climate proxies during the last millennium detected in an ensemble of three transient and one unperturbed climate simulation the cold events are attributed to internal regional climate variability with varying external forcing increasing their magnitude and frequency the underlying general mechanism consists of a feedback loop initiated by a weakening of the north atlantic subpolar gyre which induces persistent colder and fresher surface conditions in the labrador sea and eventually a deep convection shutdown we thus exclude a hemispheric climate reorganization or a weak ocean overturning circulation as necessary trigger for such events an associated northeastward atmospheric cold advection over the labrador sea deteriorates local living conditions on south greenland essential for the sustainability of the norse settlements

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

sea surface temperature variability in southern okinawa trough during last 2700 years 1 most of the temperature reconstructions for the past two millennia are based on proxy data from various sites on land here we present a bidecadal resolution record of sea surface temperature sst in southern okinawa trough for the past ca 2700 years by analyzing tetraether lipids of planktonic archaea in the odp hole 1202b a site under the strong influence of kuroshio current and east asian monsoon the reconstructed sst anomalies generally coincided with previously reported late holocene climate events including the roman warm period sui tang dynasty warm period medieval warm period current warm period dark age cold period and little ice age however the medieval warm period usually thought to be a historical analogue for the current warm period has a mean sst of 0 6 0 8 c lower than that of the roman warm period and sui tang dynasty warm period despite an increase since 1850 ad the mean sst in the 20th century is still within the range of natural variability during the past 2700 years a close correlation of sst in southern okinawa trough with air temperature in east china intensity of east asian monsoon and the el nino southern oscillation index has been attributed to the fluctuations in solar output and oceanic atmospheric circulation

transition from subduction to exhumation related fabrics in glaucophane bearing eclogites oman evidence from relative fabric chronology and 40ar 39ar ages abstract controversy over the age of peak metamorphism and therefore the tectonic evolution of the arabian margin relates to the polydeformed and polymetamorphosed nature of glaucophane bearing eclogites from the saih hatat window beneath the allochthonous samail ophiolite in ne oman these eclogites contain relicts of earlier fabrics structures and metamorphic assemblages and provide a record of change from subduction to exhumation the eclogites are part of a mafic layer that was disrupted into boudins up to 0 5 km in length within a lower plate shear zone as sifah shear zone the megaboudins not only preserve the relicts of the highest grade of metamorphism but also an early ene trending lineation and sheathlike isoclines enveloped by the flat lying schistosity the boudin bearing layer is isoclinally folded with calc schist mafic schist and quartz mica schist where the regional folds have axes parallel to the ne trending stretching lineation a type folds textural evidence suggests multiple growth events for garnet and clinopyroxene requiring polymetamorphism of the mafic layers that formed the eclogite megaboudins the surrounding calc schist and quartz mica schist are both intensely deformed with transposition foliation containing an ne trending lineation in phengite and asymmetric shear indicators such as c type shear bands and asymmetric pressure shadows around garnets that give top to the ne sense of shear although consistent ene trending lineations in all the boudins suggest that they have largely acted as passive nonrotating rigid bodies the presence of ne vergent asymmetric mesofolds extensive dynamic recrystallisation multiple generations of phengites and a range of 40ar 39ar apparent ages within the megaboudins suggest however that they have not acted entirely passively during the later deformation phengites isolated from the high p low t fabrics show groupings in 40ar 39ar apparent ages interpreted as distinct metamorphic cooling intervals at 140 135 120 98 and 92 80 ma microstructural relations suggest that age groupings younger than 100 ma reflect phengite growth during exhumation with the top to the ne shearing the older ages 120 110 ma from fabrics that give top to the s shear sense may reflect growth during the subduction phase the combination of groupings of apparent argon ages older than the crystallisation age of the samail ophiolite the suggestion of different geothermal gradients and superposed metamorphism suggest that the eclogites and garnet blueschists formed as a result of underthrusting along a break that was not directly related to the metamorphic sole of the ophiolite the glaucophane eclogites are interpreted as having formed at different times under varying pressure temperature conditions during underthrusting with variations in the rate of underthrusting allowing thermal equilibration and or rapid cooling at different crustal levels

quantitative controls on the regional geometries and heterogeneities of the rayda to shu aiba formations northern oman using forward stratigraphic modelling abstract the complex geometry of carbonate systems is influenced by a multitude of physical as well as biological processes the lower cretaceous carbonates of northern oman are characterised by a variability of regional scale geometries with expected vertical and lateral facies variations the main environmental and tectonic controls acting on the depositional processes of the lower cretaceous ramps and platforms through space and geological time in 4 dimensions are only partially understood in this study we use a 4d dionisosflow forward stratigraphic modelling fsm approach to explore the role of i eustasy ii subsidence iii initial paleobathymetry and iv wave energy to generate carbonate stacking patterns and heterogeneities carbonate production was maintained constant through deposition multi disciplinary and multi scale datasets were used i e seismic well and field data to constrain the fsm input parameters and sensitivity analysis was carried out to validate or refute some depositional model hypotheses results show that basement topography and eustasy have the greatest influence on the progradational geometries and the lateral continuity of clinoform architectures during the tithonian to valanginian second order super sequence in the valanginian to aptian super sequence subsidence was the primary control for the observed aggradational stacking pattern lateral and vertical stacking of carbonate lithologies textures as well as facies are thus apprehended through this fsm approach leading to a better assessment of petroleum systems elements as reservoir seal and trap

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

high frequency cycles in the upper aptian carbonates of the organya basin ne spain high frequency cycles in upper aptian carbonates have been studied on the carbonate ramp of organya southeastern pyrenees the depositional area comprises a shallow marine to deeper marine transect a detailed facies model is developed subdividing the transect into an inner ramp area above fairweather wave base a mid ramp area between fairweather wave base and storm wave base and an outer ramp area below storm wave base

stratigraphic organization of carbonate ramps and organic rich intrashelf basins natih formation middle cretaceous of northern oman the middle cretaceous carbonate deposits in the middle east are among the most productive oil bearing stratigraphic intervals in the world containing numerous giant fields in for instance the united arab emirates mauddud and mishrif formations iran sarvak formation and oman natih formation one of the main reasons for this concentration of hydrocarbons is a geological factor the coexistence of both reservoir facies and source rocks in the same depositional sequences due to the repeated creation of organic rich intrashelf basins this is demonstrated in a high resolution sequence stratigraphic study of the natih formation in oman which shows distinct and predictive patterns in the distribution and geometries of reservoir source rock and seal facies the sequence stratigraphic model presented here may serve as a reference for time equivalent deposits in the middle east the sedimentological analysis showed that the natih formation was formed by the alternation of two types of depositional systems 1 a flat bedded mixed carbonate clay ramp dominated by benthic foraminifera and 2 a carbonate dominated ramp bordering an intrashelf basin with abundant rudists in the mid ramp environment and organic rich basinal facies three fully developed third order sequences are distinguished showing a similar evolution of the depositional system with a mixed carbonate clay ramp system at the base followed by a carbonate dominated ramp system in the upper part variations occur on this pattern however depending on the relative influence of eustasy environmental factors and tectonism the late albiannearly cenomanian sequence i shows an evolution from a mixed flat ramp to a carbonate dominated ramp and organic rich intrashelf begin page 22 basin and sedimentation is predominantly controlled by eustatic sea level in the middle cenomanian sequence ii the evolution from a mixed ramp to a carbonate ramp is also observed but no intrashelf basin topography was developed in the studied area this may be due to the high influx of clay that influenced the environment in this sequence inhibiting the carbonate production probably in combination with the lack of sufficient creation of accommodation space the late cenomaniannearly turonian transgressive part of sequence iii shows a similar evolution to that observed in sequence i with the development of an organic rich intrashelf basin during highstand however a tectonically controlled sedimentation pattern is observed with the development of forced regressive wedges due to the flexural bulge of the foreland basin intrashelf basin formation occurred twice in the transgressive part of the third order depositional sequences of the natih formation our study shows that this is mainly the result of differential sedimentation rates that is the dynamics of the carbonate sedimentary system itself in response to rapid rises in relative sea level probably of eustatic origin tectonism was only a minor factor in the creation of the basin topography possibly through the creation of small initial relief the accumulation of the organic matter is not only a result of the creation of a sufficiently deep water column to guarantee dysaerobic conditions for its preservation the late albian and late cenomaniannearly turonian were also periods of generally favorable conditions worldwide for high organic matter productivity the time lines and stratigraphic architecture of the third order sequences presented here have an application potential at the scale of the arabian plate the general sedimentation pattern is predicted by our model but modifications due to different local conditions are likely to occur

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

holocene multidecadal to millennial scale variations in iceland scotland overflow and their relationship to climate the nordic seas overflows are an important part of the atlantic thermohaline circulation while there is growing evidence that the overflow of dense water changed on orbital time scales during the holocene less is known about the variability on shorter time scales beyond the instrumental record here we reconstruct the relative changes in flow strength of iceland scotland overflow water isow the eastern branch of the overflows on multidecadal millennial time scales the reconstruction is based on mean sortable silt ss from a sediment core on the gardar drift 60 19 n 23 58 w 2081 m our ss record reveals that the main variance in isow vigor occurred on millennial time scales 1 2 kyr with particularly prominent fluctuations after 8 kyr superimposed on the millennial variability there were multidecadal centennial flow speed fluctuations during the early holocene 10 9 kyr and one prominent minimum at 0 9 kyr we find a broad agreement between reconstructed isow and regional north atlantic climate where a strong weak isow is generally associated with warm cold climate we further identify the possible contribution of anomalous heat and freshwater forcing respectively related to reconstructed overflow variability we infer that ocean poleward heat transport can explain the relationship between regional climate and isow during the middle to late holocene whereas freshwater input provides a possible explanation for the reduced overflow during early holocene 8 10 kyr

marine reservoir age variability and water mass distribution in the iceland sea abstract lateglacial and holocene tephra markers from icelandic source volcanoes have been identified in five sediment cores from the north icelandic shelf and correlated with tephra layers in reference soil sections in north iceland and the grip ice core land sea correlation of tephra markers that have been radiocarbon dated with terrestrial material or dated by documentary evidence provides a tool for monitoring reservoir age variability in the region age models developed for the shelf sediments north of iceland based on offshore tephrochronology on one hand and on calibrated ams 14c datings of marine molluscs on the other display major deviations during the last 4500 years the inferred temporal variability in the reservoir age of the regional water masses exceeds by far the variability expected from the marine model calculations the observed reservoir ages are generally considerably higher by up to 450 years than the standard model ocean it is postulated that the intervals with increased and variable marine reservoir age reflect incursions of arctic water masses derived from the east greenland current to the iceland sea and the north icelandic shelf

masirah graben oman a hidden cretaceous rift basin reflection seismic data well data geochemical data and surface geology suggest that a cretaceous rift basin exists beneath the thrusted allochthonous sedimentary sequence of the masirah graben oman the masirah graben is located east of the huqf uplift parallel to the southern coast of oman the eastern side of the northeast trending huqf anticlinorium is bounded by an extensional fault system that is downthrown to the southeast forming the western edge of the masirah graben this graben is limited to the east by a large wedge of sea floor sediments and oceanic crust that is stacked as imbricate thrusts these sediments ophiolites were obducted onto the southern margin of the arabian plate during the collision of the indian afghan plates at the end of the cretaceou most of the masirah graben is covered by an allochthonous sedimentary sequence which is complexly folded and deformed above a detachment this complexly deformed sequence contrasts sharply with what is believed to be a rift sequence below the ophiolites the sedimentary sequence in the masirah graben was stable until further rifting of the arabian sea gulf of aden in the late tertiary resulting in reactivation of earlier rift associated faults wells drilled in the masirah graben in the south penetrated reservoir quality rocks in the lower cretaceous natih and shuaiba carbonates analyses of oil extracted from infracambrian sedimentary rocks penetrated by these wells suggest an origin from a mesozoic source rock

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

stratigraphy and tectonosedimentary evolution of a late aptian albian carbonate margin the northeastern jebel akhdar sultanate of oman abstract upper aptian albian shallow water carbonates with rudists large foraminifera and calcareous algae are described from northern oman in the northeastern part of the parautochton of jebel akhdar the corresponding lithostratigraphic unit the al hassanat formation is partly a time equivalent of the nahr umr shales of albian p p age which have a wide extent on the arabian craton the al hassanat platform developed in two main phases first during the late aptian early albian the platform was fringing an emerged area central jebel akhdar with a limited extent basinward then during the middle albian the flooding of the central jebel akhdar resulted in an extensive development of the platform and a connection with the nahr umr shelf this sedimentary evolution and its palaeogeographic expressions were mainly controlled by structural patterns extensive uplift and block faulting to the edge of the antecedent early aptian platform with a significant differential subsidence then a sag of the arabian promontory this tectonosedimentary dynamics was related to the migration of the oceanic adjacent tethyan plate and took place during the global geodynamic albian revolution

seismic stratigraphy of a lower cretaceous prograding carbonate platform oman and implications for the eustatic sea level curve the lower cretaceous of northern oman consists of a large carbonate platform that prograded over a distance of 280 km 174 mi in approximately 23 m y the seismic stratigraphic interpretation of this system based on a regional three dimensional survey 40 000 km2 15 400 mi2 revealed a complicated organization of nested clinoforms with changing depositional dips the tectonic setting and stratal patterns suggest that different orders of sea level fluctuations ranging from 20 to 150 m 66 492 ft in amplitude have controlled the overall sedimentation the lower cretaceous lekhwair habshan and salil formations form the lithofacies of this carbonate platform that prograded in a northeastward direction from the united arab emirates and oman to northern oman filling in the rayda basin the majority of this system is documented in seismic and well data whereas the final part of the progradation is visible on outcrops in the oman mountains cored wells and outcrops have been dated with calpionellids echinoids and calcareous algae biostratigraphy 14 sequences have been identified and are grouped into four sequence sets based on their seismic stratigraphic organization the differences in stratal patterns between the sets are interpreted to be caused by variations in the amplitude of sea level fluctuations the sequence sets indicate a general increase of the amplitude of sea level fluctuations to a maximum of 150 m 492 ft in the early valanginian followed by a general highstand and low amplitude fluctuations 20 m 66 ft in the late valanginian the oman relative sea level curve shows similarities with the one proposed for the vocontian basin in france providing strong evidence for the eustatic nature of these fluctuations a glacio eustatic control is invoked to explain this global trend

calciclastic submarine fans an integrated overview abstract calciclastic submarine fans are rare in the stratigraphic record and no bona fide present day analogue has been described to date possibly because of that and although calciclastic submarine fans have long intrigued deep water carbonate sedimentologists they have largely been overlooked by the academic and industrial communities to fill this gap we have compiled and critically reviewed the existing sedimentological literature on calciclastic submarine fans thus offering an updated view of this type of carbonate slope sedimentary system calciclastic submarine fans range in length from just a few to more than 100 km three different types can be distinguished 1 coarse grained small sized most calciclastic submarine fans were formed on low angle slopes and were sourced from distally steepened carbonate ramps subjected to high energy currents under these conditions shallow water loose grainy sediments were transferred to the ramp slope and eventually funnelled into the submarine fan by sediment gravity flows these conditions seem to have been more easily met on leeward margins in which the formation of reefs was hampered by cool waters nutrient enrichment or oligophoty another circumstance that contributes to the transfer of shallow water sediments to the distal ramp slope is a low sea level forcing the carbonate factory closer to the slope break and destabilizing sediments by increased pore water pressure however the most important factor controlling the development of calciclastic submarine fans was the existence of an efficient funnelling mechanism forcing sediment gravity flows to merge downslope and build up a point sourced sedimentary accumulation in most cases this occurred through a major slope depression associated with tectonic structures an inherited topography or large scale mass failures

facies variation diagenesis and exploration potential of the cretaceous rudist bearing carbonates of the arabian gulf the cretaceous rudist bearing carbonates of the arabian gulf region are proven exploration targets for hydrocarbons and form the reservoirs of a number of giant fields including bu hasa fateh fahud idd el shargi rumaila shaybah and shah rudist buildups occur in three principal formations 1 aptian shuaiba 2 cenomanian mishrif and 3 maastrichtian simsima a regional subaerial unconformity marks the upper boundary of each of these formations associated with the rudists that dominate the shuaiba formation are calcareous algal crusts foraminifera and echinoid plates which accumulated in mudstone packstone and carbonate sands these rudists are mainly caprinids with a lesser number of caprotinids monopleurids and requienids deposited in a normal marine shallow shelf setting the mishrif formation contains mollusk fragments bioclastic packstones to grainstones miliolid and nonrudist bivalves in muddy limestones and rudist mainly radiolitids and caprinids conglomeratic floatstones with fragmented rudists mixed with wackestone lithoclasts the mishrif sediments accumulated as a progradational low energy leeward margin formed in marginal slope shoal backshoal and lagoonal settings the simsima formation consists of bioclastic grainstone to packstone and dolomitic lime mudstones to wackestone these are rich in bioclastic grains loftusia rudist and rudist debris coral and foraminifera deposited on a restricted to semirestricted shallow marine shelf that was exposed to moderate energy conditions the excellent reservoir porosity and permeability of the rudist deposits and their associated sediments are the products of primary and secondary diagenesis freshwater leaching during post aptian post cenomanian and post maastrichtian erosion enhanced the secondary moldic porosity fracturing locally improved porosity and permeability other porosity types that occur include interparticle intraparticle vuggy growth framework shelter intercrystalline and karstic because of their favorable depositional and postdepositional conditions the cretaceous succession of rudists in this region contains many giant oil fields

pairwise comparisons to reconstruct mean temperature in the arctic atlantic region over the last 2 000 years existing multi proxy climate reconstruction methods assume the suitably transformed proxy time series are linearly related to the target climate variable which is likely a simplifying assumption for many proxy records furthermore with a single exception these methods face problems with varying temporal resolutions of the proxy data here we introduce a new reconstruction method that uses the ordering of all pairs of proxy observations within each record to arrive at a consensus time series that best agrees with all proxy records the resulting unitless composite time series is subsequently calibrated to the instrumental record to provide an estimate of past climate by considering only pairwise comparisons this method which we call paico facilitates the inclusion of records with differing temporal resolutions and relaxes the assumption of linearity to the more general assumption of a monotonically increasing relationship between each proxy series and the target climate variable we apply paico to a newly assembled collection of high quality proxy data to reconstruct the mean temperature of the northernmost atlantic region which we call arctic atlantic over the last 2 000 years the arctic atlantic is a dynamically important region known to feature substantial temperature variability over recent millennia and paico allows for a more thorough investigation of the arctic atlantic regional climate as we include a diverse array of terrestrial and marine proxies with annual to multidecadal temporal resolutions comparisons of the paico reconstruction to recent reconstructions covering larger areas indicate greater climatic variability in the arctic atlantic than for the arctic as a whole the arctic atlantic reconstruction features temperatures during the roman warm period and medieval climate anomaly that are comparable or even warmer than those of the twentieth century and coldest temperatures in the middle of the nineteenth century just prior to the onset of the recent warming trend

relative sea level changes during the cretaceous in israel detailed lithologic microfaunal and biometric investigations using relative abundances diversity indexes and duration charts of ostracods and foraminifera allowed the recognition of sea level changes during the cretaceous of israel three major transgressive regressive sedimentation cycles occur on the northwest margins of the arabian craton these cycles are the neocomian aptian which is mostly terrigenous sediments the albian turonian which is basin marls and platform carbonates and the senonian which is uniform marly chalks the cycles are separated by two major regional unconformities the aptian albian and turonian coniacian boundaries the sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes the paleodepth curve il ustrates the gradual sea level rise reaching its maximum during the late cretaceous with conspicuous advances during the late aptian late albian cenomanian early turonian early santonian and early campanian major lowstands occur at the aptian albian cenomanian turonian turonian coniacian and campanian maastrichtian boundaries this model for israel agrees well with other regional and global sea level fluctuations four anoxic events black shales accompanying transgressions correspond to the cretaceous oceanic record we hypothesize the presence of mature oil shales in the present day eastern mediterranean basin close to allochthonous reef blocks detached from the cretaceous platform

decadal to millennial scale periodicities in north iceland shelf sediments over the last 12 000 cal yr long term north atlantic oceanographic variability and solar forcing giant piston core md99 2269 recovered 25 m of sediment in hunafloaall a deep trough on the north iceland margin fronting the iceland sea and the site of a shelf sediment drift the rate of sediment accumulation is 2 m kyr 5 yr cm the core terminated in the vedde tephra v12 cal ka the sediment was sampled at between 5 and 50 yr sample including rock magnetic grain size and sediment properties data reduction was carried out using principal component analysis two pc axes for the 5 yr sample magnetic data are strongly correlated with measures of coercivity arm20 mt arm and magnetic concentrations karm in turn arm20 mt arm is highly correlated negatively with grain size and the mean size of the sortable silt fraction analyses of the two pc axes with mtm spectral methods indicate a series of significant s 99 periodicities at millennial to multidecadal scales including those at v200 125 and 88 yr which are associated with solar variability we also document a strong correlation between the sediment magnetic properties and the d 18 o on benthic foraminifera on the north iceland inner shelf we hypothesize that the links between variations in grain size magnetic concentrations and solar forcing are controlled by atmospheric and oceanographic changes linked to changes in the relative advection of atlantic and polar waters along the north iceland margin today these changes are associated with variations in the deep convection in the greenland and iceland seas the precise linkages are however presently elusive although a combination of coarser sediments and low d 18 o values define a holocene thermal maximum between v8 and 6 cal ka 2003 elsevier science b v all rights reserved

an ocean facing aptian albian carbonte margin oman a high energy aptian albian platform margin in northern oman fronted onto an open oceanic basin making the area a valuable analogue for coeval guyot margins most similar aged carbonate margins described in the literature faced either intracratonic or minor oceanic basins the studied margin is characterized by a stabilized outer rim which although it did not rise discernibly above the adjacent lagoonal deposits flanked a steep upper slope 32 40 basinwards with a relief of at least 30 m two main facies provided the rigidity of the outer margin lithocodium boundstones that constituted up to 50 of the rock volume and marine fibrous cements that occluded up to 35 of primary pore space in contrast coral rudist patches and other shelly sessile benthos were distributed irregularly and the rudist bioherms of the outer margin were often disrupted with shells being transported and redeposited the inner margin is characterized by wedge shaped storm layers that radiate from the platform top lagoonwards where they interdigitate with carbonate sands and small rudist bioherms polygenetic discontinuity surfaces that bear evidence of both marine hardground and subaerial exposure stages are prominent features of the margin throughout the latest aptian to middle albian the platform succession recorded some 30 relative sea level falls of which seven reached amplitudes of many tens of metres these seven high amplitude falls in sea level are recorded across the entire south eastern portion of the arabian craton and are probably of eustatic origin

gulf of maine shells reveal changes in seawater temperature seasonality during the medieval climate anomaly and the little ice age article i nfo in this study we use subannually resolved oxygen isotope values of fossil dead collected and modern live caught bivalve shells arctica islandica l from the northwestern atlantic gulf of maine usa to reconstruct past seasonal changes in seawater temperature our results indicate decreased seasonal temperature amplitude of about 1 6 c or 21 during medieval times ca ad 1033 1062 compared to shells from the early little ice age ca ad 1321 1391 and during the late 19th century ad 1864 1886 additionally seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the gulf of maine during the 11th century compared to summers and winters in the 14th century and the late 19th century the inferred decreased seasonality during medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures as seawater cooled during the little ice age we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle