evidence for interaction of a spreading ridge with the outer california borderland abstract the southward passage of the rivera triple junction and its effect on the north american plate are primary controls on the miocene tectonic evolution of the outer borderland of california detrital modes of sand shed off the patton ridge and cored by the deep sea drilling project provide evidence of progressive tectonic erosion of the patton accretionary prism and near trench volcanism volcanic glass in the sediment is predominantly calcalkaline rhyolite and andesite typical of subduction related volcanism but also includes minor low k2o tholeiitic basalt we attribute these compositional features to interaction with a spreading ridge associated with a possible trench ridge trench triple junction along the patton escarpment from 18 to 16 ma this study suggests that evidence of ridge trench interaction may be commonly preserved along submerged plate margins in contrast to its more limited recognition and discussion in the literature based on exposed examples in chile japan and alaska

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

sea surface temperatures of the western arabian sea during the last deglaciation 1 in this study we present a sea surface temperature sst record from the western arabian sea for the last 20 000 years we produced centennial scale d 18 o and mg ca sst time series of core niop929 with focus on the glacial interglacial transition the western arabian sea is influenced by the seasonal ne and sw monsoon wind systems lowest ssts occur during the sw monsoon season because of upwelling of cold water and highest ssts can be found in the low productivity intermonsoon season the mg ca based temperature record reflects the integrated sst of the sw and ne monsoon seasons the results show a glacial interglacial sst difference of 2c which is corroborated by findings from other arabian sea cores at 19 ka b p a yet undescribed warm event of several hundred years duration is found which is also reflected in the d 18 o record a second centennial scale high sst low d 18 o event is observed at 17 ka b p this event forms the onset of the stepwise yet persistent trend toward holocene temperatures highest mg ca derived ssts in the niop929 record occurred between 13 and 10 ka b p interglacial sst is 24c indicating influence of upwelling the onset of arabian sea warming occurs when the north atlantic is experiencing minimum temperatures the rapid temperature variations at 19 17 and 13 ka b p are difficult to explain with monsoon changes alone and are most likely also linked to regional hydrographic changes such as trade wind induced variations in warm water advection

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

reconstruction of sea surface temperature variations in the arabian sea over the last 23 kyr using organic proxies tex86 and u37k well established u37 0 based on long chain unsaturated ketones synthesized by haptophyte algae and the newly proposed tex86 derived from the membrane lipids of crenarchaeota comparison of niop905 and 74kl core top data with present day sst 0 10 m values indicates that both proxies yield temperatures similar to local annual mean ssts however tex86 and u37 0 sst down core records derived from the same cores differ in magnitude and phasing the alkenone sst record of niop905 shows small changes in sst 0 5 c over the last 23 kyr while that of core 74kl shows a 2 c increase from the last glacial maximum lgm 23 19 calendar cal kyr b p through the holocene the last 11 5 cal kyr b p synchronous with changes in the northern hemisphere in contrast the tex86 records of both cores show a large increase in sst from 22 23 c in the lgm to 28 30 c during termination i 19 11 5 cal kyr b p decreasing to present day annual means of 26 c a cold phase between 14 5 and 12 cal kyr b p that may correspond to the antarctic cold reversal is also observed this implies a southern hemisphere control on tropical sst reconstructed by the tex86 possibly related to sw monsoon our results suggest that the application of both tex86 and u37 0 give different but complementary information on sst developments in past marine environments

holocene aridification of india 1 spanning a latitudinal range typical for deserts the indian peninsula is fertile instead and sustains over a billion people through monsoonal rains despite the strong link between climate and society our knowledge of the long term monsoon variability is incomplete over the indian subcontinent here we reconstruct the holocene paleoclimate in the core monsoon zone cmz of the indian peninsula using a sediment core recovered offshore from the mouth of godavari river carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the cmz and document a gradual increase in aridity adapted vegetation from 4 000 until 1 700 years ago followed by the persistence of aridity adapted plants after that the oxygen isotopic composition of planktonic foraminiferglobigerinoides ruberdetects unprecedented high salinity events in the bay of bengal over the last 3 000 years and especially after 1 700 years ago which suggest that the cmz aridification intensified in the late holocene through a series of sub millennial dry episodes cultural changes occurred across the indian subcontinent as the climate became more arid after 4 000 years sedentary agriculture took hold in the drying central and south india while the urban harappan civilization collapsed in the already arid indus basin the establishment of a more variable hydroclimate over the last ca 1 700 years may have led to the rapid proliferation of water conservation technology in south india

red sea outflow during the last glacial maximum abstract the red sea is connected to the gulf of aden and hence to the arabian sea via the strait of bab el mandab which is only about 20 km wide and 300 m deep the shallowest part of the passage however lies about 140 km further basin inward near greater hanish island that passage is only 137 m deep while the channel deeper than 120 m is only 11 km wide foraminiferal and isotopic studies suggest that the inflow outflow salinity contrast at bab el mandab was about 10 during the last glacial maximum lgm compared with 3 1 at present calculation of maximal outflow during the lgm suggests that it was about 14 of the present day value while the density of this outflow was around 1035 kg m 3 compared to the modern value of about 1029 kg m 3 therefore it seems very likely that this outflow played no role of importance in the intermediate water ventilation of the arabian sea during the lgm the persian gulf influence on this ventilation may be excluded as well since the very shallow persian gulf was completely above sea level during the lgm it is anticipated that among other influences lgm curtailment of these sources for intermediate depth ventilation should be reflected in the intensity and extent of the oxygen minimum zone omz in the arabian sea other sources may have become important such as northward penetration of antarctic intermediate water the institute for paleoenvironment and paleoclimate utrecht has recently participated in the 1992 netherlands indian ocean expedition with the intention to determine late quaternary variations in the intensity and extent of the arabian sea omz in transects of cores recovered across its lower dept limit

a solar irradiance trigger for millennial scale abrupt changes in the southwest monsoon 1 marine sedimentary records of the last glacial from tropical monsoon latitudes indicate climate fluctuations comparable to rapid changes in 18o recorded in greenland synchronizing two high resolution sedimentary records from the oman and pakistan margins we resolve millennial scale reversals in sea surface temperature sst gradient sst across the arabian sea which directly correspond with the majority of dansgaard oeschger d o events for the last 65 kyr the relative amplitude of individual monsoon and d o events appears comparable suggesting coupled and at least hemispheric forcing to explore this quasi cyclic forcing we compare alkenone based geologic data with modern satellite derived sst estimates between sites interstadial conditions fall within the range of monsoons during the holocene but stadial conditions have no analogs following published associations between eurasian winter snow cover ewsc and monsoon rainfall and el nino southern oscillation enso events and anomalous ewsc we find a good correlation between the southern oscillation index soi and arabian sea sst throughout the modern data set an apparent 11 year cyclicity in the soi reveals an association between the monsoon soi and solar output variability the soi primarily tracks solar total irradiance but the soi monsoon linkage becomes nonlinear during excursions of the soi associated with el nino events strong el ninos coincide precisely with minimum solar irradiance during the solar cycle which we attribute to threshold behavior in tropical pacific ssts and associated trade wind strength we propose that both short term interannual decadal and long term centennial millennial changes in solar output are consistent with records of enso variability monsoon intensity and d o event timing

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

the effects of source lithology transport deposition and sampling scale on the composition of southern california sand the transverse ranges of southern california represent an uplifted and variably dissected mesozoic magmatic arc and mesozoic to holocene sedimentary and volcanic strata deposited in convergent and transform tectonic settings modern sand within part of the western transverse ranges represents first order sampling scale of the santa monica and the san gabriel mountains second order sampling scale of the santa clara river draining both mountain ranges and third order sampling scale of the beach system between the mouth of the santa clara river and the eastern santa monica mountains and turbidite sand of the hueneme mugu submarine fan source lithology includes plutonic and metamorphic rocks of the san gabriel mountains and sedimentary and volcanic rocks of the santa monica mountains first order sands have large compositional variability sand from local coastal drainage of the santa monica mountains ranges from basaltic feldspatholithic to quartzofeldspathic sand of the san gabriel mountains local drainages has three distinct petrofacies ranging from metamorphiclastic feldspatholithic to mixed metamorphi plutoniclastic and plutoniclastic quartzofeldspathic second order sand is represented by the main channel of the santa clara river the sand has an abrupt downstream compositional change from feldspathic to quartzofeldspathic third order sand beaches and deep sea turbidite samples of the santa monica basin is quartzofeldspathic beach sand is more quartz rich than is santa clara river sand whereas turbidite sand is more feldspar rich than is beach sand deep sea sand has intermediate composition with respect to second order samples of the santa clara river and third order samples of the beach system suggesting that 1 the santa clara river is the main source of sediments to the marine environment and 2 local entry points from canyons located near local drainages may generate turbidity currents during exceptional flood conditions petrologic data of modern sand of the study area are highly variable at first and second order scale whereas third order sand is homogenized the homogenized composition of deep marine sand is similar to the composition of most ancient sandstone derived primarily from the mesozoic dissected magmatic arc of southern california this study of the western transverse ranges illustrates the effects of source lithology transport depositional environment and sampling scale on sand composition of a complex system which provides insights regarding actualistic petrofacies models

planktonic foraminifera of the northern indian ocean distribution and preservation in surface sediments in the northern indian ocean planktonic foraminiferal tests accumulate in a wide variety of surface water environments and depositional settings this variability enables us to isolate the effects that surface water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples foraminiferal abundance varies from 0 to 104 whole foraminifera in the greater than 150 m fraction per gram dry sediment values 10 characterize the three deep basins of the equatorial indian ocean and the western bay of bengal foraminiferal tests are most abundant on carbonate covered ninety east and carlsberg ridges absolute abundance patterns are mainly controlled by non ecological processes variations in dissolution resistant species rsp with water depth reveal that the foraminiferal lysocline fl varies regionally the fl is deepest 3 800 m in the equatorial region rises abruptly to 3 300 m in the arabian sea and varies from 2 600 m to near 2 000 m moving northward in the bay of bengal deep samples with anomalously low rsp 30 suggest redeposition systematic geographic and depth related variation is observed for the 17 most abundant foraminiferal species dissolution resistant species g menardii g tumida g dutertrei p obliquiloculata generally exhibit a rapid and continuous increase in relative abundance at and below the fl susceptible species g ruber g bulloides g glutinata for example exhibit a rapid and continuous decrease in relative abundance at and below the fl moderately susceptible species g conglobatus g aequilateralis g conglomerata for example rapidly increase in abundance at the fl and systematically decrease with depth below the fl principal components analysis pca of faunal data from minimally dissolved 30 rsp samples reveals important ecologically related species intercorrelations the major biogeographic gradient is the negative covarying relationship between ag bulloides g glutinata species pair and a grouping ofg sacculifer g conglobatus g aequilateralis andg ruber pca of all samples demonstrates how differential dissolution alters this and other species relationships species groupings that incorporateg ruber g menardii andg dutertrei are particularly affected by dissolution comparison of average faunal data from minimally dissolved samples in the northern indian ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean for example g bulloides g falconensis andg hexagona are significantly more abundant in northern indian ocean surface sediments while such species asg ruber g sacculifer g dutertrei andp obliquiloculata dominate in other tropical regions

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

three stage evolution of the los angeles basin southern california we propose that an episode of transtension dominated development of the los angeles basin area from 12 to 6 ma following middle miocene transrotation and prior to the modern transpressional regime transtension resulted from the releasing bend of the san gabriel chino hills cristianitos fault which acted as the primary transform boundary in southern california during this episode such an interpretation implies that significant transform motion did not occur on the southern san andreas fault prior to 6 ma and that the gulf of california has opened primarily since 6 ma we propose a three stage model for evolution of the los angeles basin and vicinity within the evolving transform fault system transrotation 18 12 ma transtension 12 6 ma and transpression 6 0 ma timing of these stages correlates with microplate capture events which occurred during conversion from a convergent margin to a transform margin

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

tectonics of the san gabriel basin and surroundings southern california the sangabriel basin is a pliocene pleistocene transverse ranges structure bounded by the san gabriel mountains on the north the san jose and puente hills on the east and the repetto and montebello hills on the west a basement boundary between gneissoid rocks of san gabriel mountains aspect and peninsular ranges rocks strikes east across the basin and connects with the san jose fault this boundary may represent the eastward continuation of the canton fault a middle miocene precursor of the san gabriel fault system with up to 30 km of right slip canton fault displacement is largely canceled by 22 5 km of left slip on a precursor to the raymond fault such that an oligocene dacite in the san jose hills and clasts derived from it show little evidence of large horizontal displacement between the san gabriel mountains and puente hills clockwise rotation in the middle miocene probably influenced the distribution of lateral slip the fill in the northeast trending pliocene pleistocene san gabriel basin is a basal shallow marine sequence overlain by the nonmarine duarte conglomerate in contrast to the deep water fernando formation of the los angeles basin the paleoslope trends south in the direction of the repetto and puente hills evidence that uplift of these hills postdated deposition the triangular san gabriel basin is currently a stable block bounded by the right slip northwest striking east montebello fault on the west and the left slip northeast striking walnut creek fault on the east farther east the san jose and puente hills are underlain by an east trending active fold belt including the san jose reverse fault and anticline the walnut anticline and the puente hills anticline adjacent to the right lateral whittier fault the east montebello fault is bounded on the west by the elysian park anticlinorium a fold belt in downtown los angeles the left slip holocene raymond fault joins the sierra madre reverse fault at its segment boundary marked by the clamshell sawpit fault the triangular stable block between east trending fold belts is bounded on the south by the puente hills blind thrust and on the north by the sierra madre fault documenting north south quaternary convergence east west extension is also indicated although not confirmed by geodetic measurements

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

seasonal sea surface temperature contrast between the holocene and last glacial period in the western arabian sea ocean drilling project site 723a modulated by monsoon upwelling 1 annual summer and winter sea surface temperatures ssts in the western arabian sea were reconstructed through the last 22 kyr using artificial neural networks anns based on quantitative analyses of planktic foraminifera down core sst estimates reveal that annual summer and winter ssts were 2 1 2 and 2 6 c cooler respectively during the last glacial period than in the holocene a 2 5 c sst increase during termination 1a hereinafter referred as glacial to holocene transition in the western arabian sea the study reveals a strong seasonal sst contrast between winter and summer from 18 to 14 calendar kyr owing to the combined effect of weak upwelling and strong cold northeasterly winds minor or no seasonal sst changes were noticed within the holocene period which is attributed to the intense upwelling during the summer monsoon this causes a lowering of sst to values similar to those of the winter season in analogy with the present day a 3 c rise in winter ssts during the glacial to holocene transition coincides with a strengthening of the monsoon suggesting a link between winter sst and monsoon initiation from the beginning of the holocene strikingly annual summer and winter ssts show a cooling trend from 8 ka to the present day implying tropical cooling in the late holocene

sea surface temperature pattern reconstructions in the arabian sea from throughout the arabian sea for four distinct time intervals 0 ka 8 ka 15 ka and 20 ka with the aim of understanding the history of the indian monsoon and the climate of the arabian sea region this was accomplished through the use of paired mg ca and d 18 o measurements of the planktonic foraminifer globigerinoides ruber by analyzing basin wide changes and changes in cross basinal gradients we assess both monsoonal and regional scale climate changes sst was colder than present for the majority of sites within all three paleotime slices furthermore both the indian monsoon and the regional arabian sea mean climate have varied substantially over the past 20 kyr the 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2 5 3 5 c attributable in part to the influences of glacial atmospheric co2 concentrations and large continental ice sheets the elimination of the cross basinal sst gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength changes in d 18 ow that are smaller than the d 18 o signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing ssts throughout the arabian sea were still cooler than present by an average of 1 4 ci n the 8 ka time slice these cool ssts along with lower d 18 ow throughout the basin are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation the results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling

a 300 kyr record of upwelling off oman during the late quaternary evidence of the asian southwest monsoon in the northwest arabian sea upwelling occurs each summer driven by the strong sw monsoon winds upwelling results in high biological productivity and a distinctive assemblage of plankton species in the surface waters off oman that are preserved in the sediments along the oman continental margin creating a geologic record of monsoon driven upwelling sediments recovered from the oman continental margin during ocean drilling program leg 117 provide an opportunity to examine how upwelling has varied during the late quaternary spanning a longer interval than piston cores recovered prior to the odp cruise variations in foraminifer shell accumulation and in the relative abundance of globigerina bulloides indicate dominant cycles of variation at 1 100 kyr the dominant frequency of glacial interglacial variations and at 1 23 kyr the frequency of precessionally driven cycles in seasonal insolation the strongest monsoon winds indicated by increased upwelling occurred during interglacial times when perihelion was aligned with the summer solstice an orbital change that increased the insolation received during summer in the northern hemisphere during glacial times upwelling was reduced and although the precessional cycles were still present their amplitude was smaller at both frequencies the upwelling cycles are in phase with minimum ice volume evidence that glacial interglacial climate changes also include changes to the climate system that influence the low latitude monsoon we attribute the decrease in the monsoon winds observed during glacial times to changes in bare land albedo over asia and or to changes in the areal extent and seasonal cycle in asian snow cover that decrease the summer land sea temperature contrast other mechanisms may also be involved these new upwelling time series differ substantially from previous results however the previous work relied on cores located farther offshore where upwelling is less intense and other physical mechanisms become important our results support the observations derived from atmospheric general circulation models of the atmosphere that indicate that both glacial boundary conditions and the strength of summer insolation are important variables contributing to cycles in the monsoon winds during the late quaternary

planktonic foraminiferal and alkenone records of the last deglaciation from the eastern arabian sea the oxygen isotope record of planktonic foraminifera from tropical core md77194 eastern arabian sea exhibits a clear two step deglaciation with a brief 18o transient event in the tropics this 18o maximum could correspond to a cooling or to a change in the 18o content of sea water in this study past sea surface temperature sst and primary production pp are reconstructed from foraminiferal transfer functions and compared to values estimated from alkenone measurements sst and pp records from both proxies indicate a 1 5 2 5 c deglacial warming coupled with a pp decrease and a 0 5 1 c cooling during the younger dryas yd a detailed comparison between independent micropaleontological and geochemical proxies helps us identify potential biases and thus strengthen the paleo reconstructions

glacial to interglacial contrasts in the northern indian ocean differences between the 18o 16o ratios of planktonic foraminifera deposited during the last glacial maximum about 18 000 yr ago and those deposited during the holocene show that in the indian ocean the south west monsoon was weaker than today but that the north east monsoon was stronger the upwelling observed in modern conditions along the southern coast of arabia had disappeared because of the low speed of the southwestern winds during glacial summers the reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the bay of bengal and along the western coast of india increased precipitation fell on the sea south of 10 n while strong evaporation over the northernmost arabian sea produced an enhanced salinity gradient in that area

the transition from roman to late antique glass new insights from the domus of tito macro in aquileia italy abstract the present paper focuses on the archaeological chemical and isotopic characterisation of glass finds from the domus of tito macro former domus dei fondi cossar in aquileia italy dated between the 1st and the 7th century ad the assemblage comprises both vessels and glassworking residues including a few chunks aims of the study are the identification of the main glass compositions and their contextualisation in roman and late antique reference groups and of provenance of primary glass chemical analyses were conducted by xrf and epma all the analysed fragments are silica soda lime glasses produced with natron as a flux and are compositionally similar to the roman coloured intentionally and unintentionally and colourless antimony manganese and antimony manganese decoloured groups and to the late antique groups himt serie 3 2 and levantine 1 specific compositional traits of himt glass circulating in the north adriatic area and a scarcity of levantine 1 glass are evidenced the presence of rare hit blue glasses including a chunk suggests that colouring took place also at primary stage of production sr and nd isotopic analyses performed on a selection of samples confirmed the eastern mediterranean origin of the glasses although with minor internal differences depending on the compositional group chemical and isotopic data suggest a continuity between the roman and late antique glassmaking in terms of sand deposits and sand flux ratio although with a major change in the decolouring technique after the 4th century ad the prompt reception of the late antique glass compositions took place in aquileia alongside the persistence of earlier compositions probably with the aim of satisfying different segments of the glass market

the oxygen isotope composition of tropical ocean surface water during the last deglaciation evidence of abrupt climate change in each of the tropical oceans can be found in high deposition rate sediments from the continental margins new ams 14 c dated sediments from the arabian sea reveal a two step depletion of surface ocean 18 o 16 o during the last deglaciation with a return to more enriched values approximately 10 5 ka bp the two step depletion can be correlated among isotope records derived from foraminifer calcite in the arabian sea the gulf of mexico the sulu sea and gulf of california confirming the existence of the two step depletion and 18 o enriched event at 10 5 ka bp in at least three tropical sites outside the north atlantic to determine whether the isotopic enrichment at 10 5 ka bp was caused by local cooling of the surface ocean we estimated sea surface temperatures over this interval using quantitative paleo ecological techniques there is no evidence for cooling in the arabian sea sulu sea or gulf of mexico consistent with the hypothesis that the enrichment at 10 5 ka bp is related to a change in the isotopic composition of the tropical surface ocean and not change in the temperature of calcification we conclude that the cooling at higher latitudes that occurred at 10 5 ka bp did not extend southward to the tropical ocean more cores from high sedimentation rate sites in the tropics are needed to identify the cause and extent of the 18 o signal however these preliminary results are consistent with two meltwater pulses during the deglaciation that distributed isotopically depleted water into each of the tropical oceans with a slow down in meltwater flux at 10 5 ka bp the most likely transport route for the isotopically depleted water from the melting northern hemisphere ice sheets to these isolated tropical ocean basins is via the relatively fast circulation of the atmosphere although other pathways are possible

provenance and stratigraphy of the eocene tejon formation western tehachapi mountains san emigdio mountains and southern san joaquin basin california abstract the eocene tejon formation of the western tehachapi and san emigdio mountains of california provides a unique east west trending outcrop belt of otherwise deeply buried strata that underlie the san joaquin basin to the north its stratigraphy and framework mineralogy have been used to define offsets along the san andreas fault a major neogene plate boundary transform fault that has translated coastal california northward more than 300 km by right slip the tejon formation was deposited directly on crystalline basement rocks as a result of an eastward transgression of at least 45 km from the early to the late middle eocene followed by a major regression in the late middle eocene the basal uvas conglomerate member consists entirely of coarse grained transgressive system tract tst deposits characterized by abundant current formed sedimentary structures it is overlain by offshore marine shales of the liveoak shale member which consist of lower tst deposits overlain by highstand system tract hst deposits the overlying regressive metralla sandstone member consists mostly of highly bioturbated fine grained shallow marine hst sandstones with local thin bedded turbidites present in some western exposures the quartzofeldspathic sandstones grand mean qm51 12f42 12lt7 4 of the tejon formation suggest a provenance consisting of plutonic metamorphic and volcanic rocks such as those present in the basement of the san emigdio and techachapi mountains northwestern mojave desert and southern sierra nevada petrologic parameters however suggest variable contributions from these source areas through time three distinctive petrofacies coincide with the three principal lithostratigraphic subdivisions the shallow marine tst sandstones from the uvas conglomerate member are more quartzose than those of the hst metralla sandstone member possibly because higher energy deposition preferentially preserved quartz thin bedded turbidites in the western exposures of the metralla sandstone in contrast have more abundant feldspar and volcanic lithic fragments than the uvas and liveoak members the composition of the tejon formation suggests derivation from a basement uplift provenance with progressive upsection changes from qm60 f33 lt8 uvas to qm46 f44 lt10 liveoak and qm 43 f52 lt5 metralla the composition and provenance of the tejon formation is different from that of the coeval butano sandstone and point of rocks sandstone submarine fan deposits to the north and west

the oligocene ophiolite derived breccias and sandstones of the val marecchia nappe insights for paleogeography and evolution of northern apennines italy abstract ophiolite derived debrites microbreccias and olistoliths are interbedded in the monte morello and argille varicolori formations of the val marecchia nappe constituting the highest tectonic unit of the north eastern apennines and usually considered as having originated from the external ligurian domain the ophiolite derived clastic rocks were supplied exclusively by an oceanic sequence consisting of peridotite gabbro basalt radiolarite pelagic limestone and shale they are interbedded within a succession made up of fine grained carbonate and siliciclastic turbidites and of pelagic claystones petrographic and sedimentological features of the ophiolite derived breccia and sandstone units testify to an intrabasinal source area for these clastic rocks rather than an extrabasinal origin from subaerially exposed oceanic crust forming the inner flank of the basin as previously suggested due to their oligocene earliest miocene age the deposits in which debrites and olistoliths occur are related to early neo alpine tectonic events that caused reactivation and or inversion of old normal transform faults unstable fault escarpments provided a preferential path for submarine landslide and turbidite emplacement debrites microbreccias and olistoliths therefore were added to the basin fill of fine grained turbidite and pelagic deposits this study suggests that the val marecchia nappe succession was deposited on an oceanic substratum stratigraphy and age of the succession of this nappe can be well framed only in the evolution of the sub ligurian domain whereas they conflict with the interpretation of the val marecchia nappe as a nappe originated from the external ligurian domain as suggested previously by most authors this interpretation also requires an oceanic substratum for the sub ligurian domain i e the existence of an oceanic belt external to the ligurian domain which was deformed only in the early miocene the sub ligurian domain therefore would be an eastern branch of the central tethys and would represent the extension in the northern apennines of the maghrebian lucanian oceanic realm as recognized in the betic cordillera maghrebian chain and southern apennines

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

sandstone petrology and provenance of the siwalik group northwestern pakistan and western southeastern nepal abstract the siwalik group consists of a neogene sedimentary succession 5 8 km thick deposited as the himalayan foreland basin developed following collision between the indian and eurasian continents it consists of fluvial deposits composed of shale siltstone and sandstone in the lower part and thick sandstone and conglomerate in the upper part this paper presents new petrologic data on the sandstone composition of two coeval petrofacies of siwalik group in two areas the potwar plateau of northwestern pakistan and the surai khola and bakiya khola localities of western and southeastern nepal in both regions detrital modes reflect a collisional orogen provenance petrologic parameters indicate derivation from mid crustal rocks and overlying sedimentary strata ascribed to different tectonostratigraphic units of the high himalaya and tibetan zone the siwalik sandstones of the potwar plateau nw pakistan are composed of low to medium grade metamorphic and sedimentary detritus and subordinately of ophiolitic and volcanic detritus abundant metamorphic detritus consists of phyllite fine grained schist lithics and coarse grained gneiss derived from the high and or lesser himalaya sedimentary detritus is represented by abundant limestone radiolarian chert siltstone shale very fine grained quartzarenite and other sandstone grains the siliciclastic grains probably were eroded from older terrigenous sequences belonging to the tethys himalayan and lesser himalayan zones uplifted during the india eurasia collision ophiolitic volcanic lithic grains and radiolarian chert reflect a provenance from the indus suture and tran himalayan belt the sandstones of western and southeastern nepal surai khola and bakiya khola sections have higher quartz and lower feldspar contents than those of northwestern pakistan and contain sedimentaclastic western nepal and metamorphiclastic sandstones southeastern nepal comparison of the data presented here with previous work on pre and post siwalik sandstones of the himalaya range and of the remnant ocean basins along both sides of the indian peninsula also derived from the himalayan suture belt suggests abundant quartzolithic detritus from the eocene to the present varying proportions of lithic populations in time are related to rapid uplift of the himalayas and intense unroofing of sedimentary metasedimentary and deeper terranes

petrology and diagenesis of the eocene butano sandstone la honda basin california the lower and middle eocene butano sandstone at least 1500 m and possibly as much as 3000 m thick was deposited as a submarine fan in a narrow restricted continental borderland setting its quartzofeldspathic composition suggests a local provenance from plutonic and metamorphic rocks of the salinian terrane it crops out in three belts of which the middle belt in the central part of the basin was buried the deepest and underwent the most significant diagenetic changes the central belt made up of middle fan deposits contains higher amounts of quartz and lower amounts of feldspar than the more proximal southern inner fan deposits and more distal northern outer fan deposits the presence of authigenic albite laumontite and pore filling kaolinite and chlorite suggests that decreases of feldspars mainly plagioclasej are related mainly to dissolution of plagioclase it is possible that at least 20 25 of the plagioclase with respect to total feldspar has been diagenetically dissolved in the butano sand

variations of the monsoon regime during the upper quaternary evidence from carbon isotopic record of organic matter in north indian ocean sediment cores abstract the 13 c 12 c ratios and contents of organic carbon in deep sea sediment cores of the north indian ocean have been compared for the different climatic stages as determined by oxygen isotope stratigraphy using the differences in the 13 c values between marine and terrestrial organic matter the terrestrial contribution to the eastern gulf of bengal and the andaman sea has been determined for modern and glacial times the geographical distribution of the terrestrial organic carbon linked to sea surface circulation shows that during the last glacial period the ne monsoon circulation was the dominant feature the organic carbon abundance within the sediment which is related to local productivity was greater during glacial times in the areas where production depends on the ne monsoon strength coast of north india in the arabian sea and andaman sea suggesting its reinforcement

coupled sea surface temperature seawater δ18o reconstructions in the arabian sea at the millennial scale for the last 35 ka two sediment cores from the western 905 10 46 9 n 51 56 4 e water depth 1586 m and eastern sk17 15 15 n 72 58 e water depth 840 m arabian sea were used to study past sea surface temperatures sst and seawater 18o 18ow variations for the past 35 ka we used coupled mg ca 18o calcite variability in two planktonic foraminiferal species globigerinoides ruber which thrives throughout the year and globigerina bulloides which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing ssts in both areas based on mg ca in g ruber were 3 to 4 c lower during the last glacial maximum lgm 21 ka than today and the holocene period the sst records based on g bulloides also indicate general cooling down to 18 c in both areas ssts in the western arabian sea based on g bulloides were always lower than those based on g ruber indicating the presence of strong seasonal temperature contrast during the holocene and lgm we interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling sw monsoon and winter convective mixing ne monsoon in the western arabian sea in the eastern arabian sea g bulloides based ssts were slightly lower about 1 c than g ruber based ssts during the holocene indicating the almost absence of a seasonal temperature gradient similar to today however a large seasonal temperature contrast occurred during the lgm which favors the assumption that strong ne monsoon winds forced winter upwelling or convective mixing offshore goa sst and 18ow reconstructions reveal evidence of millennial scale cycles particularly in the eastern arabian sea here the stadial periods northern hemisphere cold periods such as younger dryas and heinrich events are marked by increasing ssts and salty sea surface conditions relative to those during the interstadial periods indeed the 18ow record shows evidence of low saline surface waters during interstadial periods indicating increased freshwater runoff from the western ghats as a consequence of enhanced sw monsoon intensity

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

interpretation of neovolcanic versus palaeovolcanic sand grains an example from miocene deep marine sandstone of the topanga group southern california despite abundant data on volcaniclastic sand stone the compositional spatial and temporal distribution of volcanic detritus within the sedimentary record is poorly documented one of the most intricate tasks in optical analysis of sand stone containing volcanic particles is to distinguish grains derived by erosion of ancient volcanic rocks i e palaeovolcanic noncoeval grains from grains generated by active volcanism subaqueous and or subaerial during sedimentation neovolcanic coeval grains deep marine volcaniclastic sandstones of the middle topanga group of southern california are interstratified with 3000 m thick volcanic deposits both subaqueous and subaerial lava and pyroclastic rocks ranging from basalt andesite to dacite these rocks overlie quartzofeldspathic sandstones petrofacies 1 of the lower topanga group derived from deep erosion of a mesozoic magmatic arc changes in sandstone composition in the middle topanga group provide an example of the influence of coeval volcanism on deep marine sedimentation volcaniclastic strata were deposited in deep marine portions of a turbidite complex volcaniclastic apron built onto a succession of intrabasinal lava flows and on the steep flanks of subaerially emplaced lava flows and pyroclastic rocks distinctive petrofacies 2 5 directly overlying basalt and basaltic andesite lava flows petrofacies 2 is a pure volcanolithic sandstone including vitric microlitic and lathwork volcanic grains and neovolcanic crystals plagioclase pyroxene and olivine the abundance of quenched glass palagonite fragments suggests a subaqueous neovolcanic provenance whereas sandstones including andesite and minor basalt grains suggest subaerial neovolcanic provenance this petrofacies probably was deposited during syneruptive periods testifying to provenance from both intrabasinal and extrabasinal volcanic events deposited during intereruptive periods impure volcanolithic petrofacies 3 includes both neovolcanic 85 and older detritus derived from plutonic metamorphic and palaeovolcanic rocks during post eruptive periods the overlying quartzofeldspathic petrofacies 4 and 5 testify to progressive decrease of neovolcanic detritus 48 14 and increase of plutonic metamorphic and palaeovolcanic detritus the upper topanga group calabasas formation conformably overlying the middle unit has dominantly plutoniclastic sandstone petrofacies 6 neovolcanic detritus is drastically reduced 4 whereas palaeovolcanic detritus is similar to percentages of the lower topanga group petrofacies 1 the middle topanga group sandstones are vertically organized into four

new evidence on the sequence of deglacial warming in the tropical indian ocean transition from the last glacial maximum to holocene has undergone a sequence of fluctuations which exhibit large spatial and temporal variations in different regions of the world here we show that deglaciation warming in the northen indian ocean was initiated 19 ka which is contemporary to the deglaciation warming in the antarctica and southern ocean a gradual warming occurred during the glacial to holocene transition in the northern indian ocean unlike two step warming noticed in the greenland and north atlantic synchronous deglacial warming 19ka in the antarctica and northern indian ocean suggest a strong connection in propagating climate signals between antarctica and the indian ocean probably through the indonesian through flow and or sub antarctica mode water

petrofacies and provenance of the puente formation middle to upper miocene los angeles basin southern california implications for rapid uplift and accumulation rates abstract the puente formation is a middle upper miocene clastic unit lying unconformably on the lower middle miocene el modeno volcanics and topanga group in the los angeles basin the puente formation about 3900 m thick is composed of conglomerate sandstone and mudrock deposited as a submarine fan at bathyal depths several intrabasinal discordances suggest tectonic activity during deposition the succession consists of two main upward thickening and coarsening megacycles reflecting submarine fan progradation the puente formation is characterized up section by 1 thin bedded sandstone and shale la vida member grading to thick bedded sandstone and conglomerate soquel member 2 thin bedded mudrock and sandstone yorba member grading to thick to very thick bedded sandstone and conglomerate sycamore canyon member sandstones of the puente formation are quartzofeldspathic qm35f54lt11 their compositions suggest local provenance from the plutonic volcanic and metamorphic rocks of the san gabriel mountains and surrounding areas petrologic parameters however suggest variable contribution of these source rocks through time four petrofacies with distinctive parameters coincide with the lithostratigraphic subdivisions coarse grained plutonic rock fragments are abundant throughout the succession and consist of plagioclase rich plutonic rocks probably sourced in part from the lowe granodiorite lathwork microlitic to felsitic volcanic lithic grains are also present in the lower and middle part in the la vida petrofacies there is also an intrabasinal cont ibution intraclasts and bioclasts from shelfal areas in the yorba petrofacies there is a local increase of volcanic detritus lv l 0 81 represented by coarser volcanic lithics and abundant volcaniclastic matrix metamorphic detritus is not very abundant the sycamore canyon petrofacies is dominantly plutoniclastic rg r 0 90 hornblende bearing plutonic rock fragments including very abundant hornblende grains the plutonic detritus is dominantly plagioclase orthoclase biotite bearing in the lower part and hornblende bearing in the upper part suggesting unroofing of the lowe granodiorite complex as a key element of uplift of the san gabriel mountains other neogene sandstones deposited in the los angeles basin also consist dominantly of plutoniclastic detritus related to the unroofing of arc related plutonic rocks dissected magmatic arc for example the up section increase in plutonic detritus is consistent with the composition of the upper miocene lower pliocene capistrano formation qm50f47lt3 which has a composition identical to the sycamore canyon petrofacies there is consistent provenance signal in spite of complex transrotational tectonics responsible for opening of the los angeles basin and later transpressional processes which are still active detailed provenance study of the puente formation and related units provides important constraints on paleogeographic and paleotectonic reco structions of southern california basins and uplifts

detrital modes and provenance of miocene sandstones and modern sands to the southern apennines thrust top basins italy abstract the cilento group lower middle miocene the monte sacro conglomerate upper miocene the gorgoglione formation upper miocene and the crati submarine fan holocene are four turbidite sequences deposited in northwest southeast trending thrust top basins of the southern apennines italy foreland region the corigliano basin is a part of the modern taranto gulf foredeep basin that developed since the late pleistocene sandstone detrital modes of the miocene turbidite units are quartzofeldspathic petrofacies 1 2a 4 5 8 q62f25l13 quartzolithic petrofacies 2b q60f16l24 and arkosic petrofacies 7 q50f45l5 reflecting a collisional orogenic provenance volcanolithic sandstones petrofacies 3 q23f11l66 suggest an important contribution also from a volcanic source area related to the convergent continental margin volcanism connected with the collisional tectonic regime that affected the western mediterranean e g sardinia volcanic arc individual carbonatoclastic beds hybrid arenite biocalcarenite and mudstone are interbedded with sandstone units of the ilento group they have siliciclastic content of about 35 and are quartzofeldspathic petrofacies 6 q53f23l24 these beds 0 10 65 m thick record impulsive gravitational collapses of the carbonate platform passive margin to the east and southeast the petrologic parameters show a temporal evolution from metasedimentary to granitic gneissic provenance ascribed to different tectonostratigraphic units of the calabrian arc nine miocene petrofacies suggest dynamic evolution of the source terranes from laughian to tortonian time facies dispersal patterns and petrologic parameters of the miocene sandstones suggest a provenance from the northern and western margins of the basins comparison between the holocene crati fan petrofacies 9 q54f24l22 and miocene detrital modes suggests that the sandstones of the cilento group the monte sacro conglomerate and the gorgoglione formation were derived from unroofing of the thrusted basement block transported by torrential type fluvio deltaic systems and then funneled into a major turbidite dispersal system analogous to the modern crati submarine fan of the corigliano thrust top basin

western mediterranean sand deposits as a raw material for roman glass production abstract during the late roman and byzantine period natron glass was made from its raw materials in a limited number of primary production centres in egypt and syro palestine for the earlier hellenistic and roman period no primary furnaces have been found and the location of primary production during this era remains unclear ancient authors such as strabo and pliny the elder suggest that glassmaking sands were found near the river belus israel in egypt near the mouth of the volturno river italy and also in spain and france however primary production in the western part of the mediterranean is not supported by any direct archaeological evidence and possible sand raw materials from these regions have never been evaluated for their suitability to produce glass in this study 178 modern beach sands from spain france and italy were analysed for their major and minor elemental compositions by calculating the composition of the glasses that can be produced with these sediments after the addition of pure natron and comparison with the composition of typical roman natron glass we were able to judge whether or not these sands are suitable for roman glass production the results indicate that good glassmaking sands are rather rare only a very limited number of the 178 analysed beach sands would produce a glass with major and minor elemental compositions within the ranges of roman imperial natron glass the rest of the analysed sands are unsuitable for glass production in their present form due to their insufficient sio 2 high al 2 o 3 and fe 2 o 3 and either too low or too high cao contents if the sand raw material was too low in cao extra lime could be added to the glass batch in the form of shell or limestone this was taken into account in a second calculation overall we were able to define six limited areas where suitable sand raw materials would have been available to the roman glassmaker good glassmaking sands occur in the basilicata and puglia regions se italy and tuscany w italy after the addition of an extra source of lime also sands from the huelva province sw spain the murcia region se spain and from the provence se france would produce glasses with a typical roman composition

considerations on the provenance determination of plant ash glasses using strontium isotopes abstract strontium isotopic analysis has been proposed as a suitable method to determine the primary production location of ancient plant ash glasses the technique is based upon the assumption that sr enters this glass type with the plant ash used as a flux material and that the 87sr 86sr ratio of the resulting glass reflects the geological provenance of that flux in such case the bulk sr isotopic composition of the bedrock should be inherited unchanged in the plants growing on that bedrock different types of plant ash glasses have been shown to have widely differing 87sr 86sr compositions in this study the 87sr 86sr composition of several plant species growing on different bedrock types is measured and compared to the bulk sr isotopic composition and petrology of that bedrock the paper shows that the 87sr 86sr ratio of these plants is a function not only or even mostly of the local geology but also of the sr isotopic composition of the total water consumed by that plant this is highly likely to be both plant species dependent and dependent on the small scale hydrology of the area immediately surrounding the plant in this way no definite relation between the isotopic composition of a geological outcrop and the plants growing on this bedrock can be inferred hence the isotopic composition of a plant ash made from such plants is uncertain and moreover species dependent though groups of plant ash glasses can certainly be compared in time and space using sr isotopes it may prove difficult to ascertain a plant ash glass type to a specific geographical geological region

roman and late roman glass from north eastern italy the isotopic perspective to provenance its raw materials in this study the strontium neodymium and oxygen isotopic composition of roman 1st 3rd century ad and late roman glass 4th 6th century ad from adria and aquileia two of the most important archaeological sites of north eastern italy is discussed the majority of glass analysed independent from age shows values of strontium isotope ratios close to that of modern seawater indicating that the source of lime in the glass was marine shell and likely coastal sands were used in its production the nd signature of all late roman glasses from aquileia and of the majority of the roman ones from adria independent from their chemical composition is homogeneous and higher than 6 end supporting the hypothesis of an eastern mediterranean origin probably located on syro palestinian coast however the composition of late roman samples with himt signature with lower 87sr 86sr values correlated to higher contents in fe2o3 tio2 mgo and lower contents in cao suggests an area of origin for this glass on the egyptian coast in addition the different nd signatures of two adria roman glasses end 7 suggest their primary production in western mediterranean oxygen isotopes proved to be a further diagnostic method to discriminate natron and soda plant ash glass and different silica sources in the case of the soda plant ash glass the combination of isotopic and chemical data supports the hypothesis of an eastern mediterranean origin for late roman glass which may be produced in few primary workshops on the syro palestinian and egyptian coast although not necessarily in the same ateliers as have been identified so far in the case of the roman glass investigated although the majority of data suggests an eastern mediterranean origin on the basis of nd isotopes and chemical compositions the existence of other primary glass producers located in the western mediterranean can be suggested

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

high resolution holocene monsoon record from the eastern arabian sea through stable oxygen and carbon analyses of rapidly accumulating sediment cores from the eastern arabian sea we show that the excess of evaporation over precipitation e p steadily appears to have decreased during the last 10 000 to 2000 years most probably due to an increasing trend in the summer monsoon rainfall contrary to the land based paleoclimatic data from this region which indicate onset of aridity around 4000 years ago our results are consistent with the hypothesis that significant spatial variability in the monsoon rainfall observed today was persistent during most of the holocene alternatively the trend can be seen as an adjustment between two phases one between 10 000 and 6000 years ago of increasing precipitation and another between 3500 and 2000 years ago after the arid episode we also report a significant 700 year periodicity similar to that reported recently from the south china sea indicating that the centennial millennial scale response of the indian and chinese monsoons to high latitude forcing may be alike

combined tectonic sediment supply driven cycles in a lower carboniferous deep marine foreland basin moravice formation czech republic the lower carboniferous moravian silesian culm basin mscb represents the easternmost part of the rhenohercynian system of collision related deep water foreland basins culm facies the upper visean moravice formation mf of the mscb shows a distinct cyclic stratigraphic arrangement two major asymmetric megacycles bounded by basal sequence boundary each about 500 to 900 m thick have been revealed the megacycles start with 50 to 250 m thick basal segments of erosive channels overbank successions and slope apron deposits interpreted as lowstand turbidite systems up section they pass into hundred metre thick fine grained low efficiency turbidite systems palaeocurrent data show two prominent directions basin axis parallel ssw nne directions which are abundant in the whole mf and basin axis perpendicular to oblique w e to nw se directions which tend to be confined to the basal parts of the megacycles or channel lobe transition systems in their upper parts based on the facies characteristics palaeocurrent data sandstone composition data and trace fossil distribution data we suggest a combined tectonics sediment supply driven model for the mf basin fill periods of increased tectonic activity resulted in slope oversteepening probably combined with increased rate of lateral w e sediment supply into the basin producing the basal sequence boundary and the subsequent lowstand turbidite systems during subsequent periods of tectonic quiescence the system was filled mainly from a distant southern point source producing the thick low efficiency turbidite systems consistently with the previous models our own sediment composition data indicate a progressively increasing sediment input from high grade metamorphic and magmatic sources up section most probably related to an uplift in the source area and progressive unroofing of its structurally deeper crustal parts the first occurrence of the cruziana nereites ichnofacies in sand rich turbidite systems in the youngest parts of the mf go el to go spi zone supported by rapidly increasing quartz concentrations in sandstones is thought to indicate a transition from generally underfilled to generally overfilled phase in evolution of the mscb basin this transition may be linked to the onset of upper visean phase of northward basin fill progradation assumed by previous authors

monsoon upwelling effects on test size of some planktonic foraminiferal species from the oman margin arabian sea variation in upwelling may be monitored using various micropaleontological indices such as the relative abundance or accumulation rate of the planktonic foraminiferal species globigerina bulloides or mass accumulation rate of planktonic foraminifera we have analyzed the relationships between the upwelling history and mean test size variations in the planktonic foraminiferal species globigerinoides ruber globigerinita glutinata g bulloides and neogloboquadrina dutertrei through the last 19 000 years in ocean drilling program hole 723 a from the oman margin arabian sea the study reveals that these species were larger on average between 11 and 5 ka which coincides with a period of strong upwelling on the other hand these species showed smaller mean test sizes during the last glacial period and late holocene when upwelling was weaker mass accumulation rates of these species are linearly proportional to their mean test sizes indicating that both mean size and productivity of individual species are related to the upwelling intensity therefore we propose that the size variations in g ruber g glutinata g bulloides and n dutertrei can be used as an additional micropaleontological index of upwelling intensity in the arabian sea

timing cause and consequences of mid holocene climate transition in the arabian sea abstract we reconstruct centennial scale quantitative changes in surface seawater temperature sst evaporation precipitation from mg ca and 18o of surface dwelling planktic foraminifera productivity from relative abundance of globigerina bulloides carbon burial from caco3 and organic carbon corg and dissolved oxygen at sediment water interface covering the entire holocene from a core collected from the eastern arabian sea from the multi proxy record we define the timing consequences and possible causes of the mid holocene climate transition mhct a distinct shift in evaporation precipitation e p is observed at 6 4 ka accompanied by a net cooling of sst the shift in sst and e p is synchronous with a change in surface productivity a concurrent decrease is also noted in both the planktic foraminiferal abundance and coarse sediment fraction a shift in carbon burial as inferred from both the caco3 and corg coincides with a change in surface productivity a simultaneous decrease in dissolved oxygen at the sediment water interface suggests that changes affected both the surface and subsurface water a similar concomitant change is also observed in other cores from the arabian sea as well as terrestrial records suggesting a widespread regional mhct the mhct coincides with decreasing low latitude summer insolation perturbations in total solar intensity and an increase in atmospheric co2

organic carbon accumulation rates in the holocene and glacial arabian sea implications for o2 consumption in the deep sea and atmospheric co2 variations variations in the deep sea carbon reservoir have been invoked to explain the observed atmospheric carbon dioxide co2 changes during glacial interglacial cycles in order to distinguish between the quantity of organic matter remineralized in the deep sea and that permanently removed into sediments we compared the bulk and organic carbon accumulation rates in holocene and glacial sediments deposited below the oxygen minimum layer with total and organic carbon fluxes to the deep arabian sea from continuous sediment trap deployments this comparison shows that the mass of organic carbon remineralized at the sediment water interface is mainly a function of the bulk sediment flux the oxygen consumed by the organic carbon remineralization is of the order of the observed oxygen deficiency of the modern deep arabian sea water we use the evidence from the northern indian ocean to speculate on the possible effect of abiogenic mineral flux on the removal of organic carbon from upper layers of the world ocean to the deep sea we assume that if the bulk accumulation rate not primary productivity influences the flux of organic carbon that is fixed from the atmosphere by marine organisms then mineral matter flux will exert a significant control over atmospheric co2 contents model calculations incorporating transient changes in global bulk flux caused by natural or anthropogenic changes show that significant proportions of the observed changes in atmospheric co2 contents can be explained by this mechanism

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

synchroneity of oxygen minimum zone intensity on the oman and pakistan margins at sub milankovitch time scales abstract in this paper we present evidence for sub milankovitch variability in monsoon intensity from the oman and pakistan margins northern arabian sea a new high resolution geochemical record from the oman margin combined with microfossil data shows high frequency variations in sea surface productivity caused by changes in the intensity of summer monsoon induced upwelling the local oxygen minimum zone omz which presently impinges on the oman margin was reconstructed using laminations redox sensitive elements and aragonite preservation comparison with a pakistan margin record shows that omz intensity varied synchronously across the basin omz intensity varies together with summer monsoon strength being weakest during periods of minimum summer monsoon intensity correlating the pattern of summer monsoon variability with that of the winter monsoon inferred from proxy records in the northeastern arabian sea suggests a reversed relationship between summer and winter monsoon strength furthermore the oman and pakistan margin records confirm earlier results suggesting a link between high northern latitude climate as reconstructed from greenland ice cores and monsoonal climate

deglaciation in the tropical indian ocean driven by interplay between the regional monsoon and global teleconnections abstract high resolution climate records of the ice age terminations from monsoon dominated regions reveal the interplay of regional and global driving forces speleothem records from chinese caves indicate that glacial terminations were interrupted by prominent weak monsoon intervals wmi lasting a few thousand years deglacial wmis are interpreted as the result of cold temperature anomalies generated by sea ice feedbacks in the north atlantic most prominently during heinrich events recent modeling results suggest however that wmis reflect changes in the intensity of the indian rather than the east asian monsoon here we use foraminiferal trace element mg ca and ba ca and stable isotope records from a sediment core off the malabar coast in the southeastern arabian sea with centennial scale resolution to test this hypothesis and to constrain the nature and timing of deglacial climate change in the tropical indian ocean the malabar deglacial sst record is unique in character and different from other tropical climate records sst at the last glacial maximum was 2 7 0 5 c colder than pre industrial sst deglacial warming started at 18 6 95 ci range 18 8 18 1 kyr bp within error of the onset of warming at other tropical sites as well as in antarctica and the southern ocean and either coeval with or up to 1 kyr before the atmospheric co 2 rise warming took place in two steps separated by an interval of stable sst between 15 7 16 2 14 9 and 13 2 13 9 12 0 kyr bp the 18 o water record and the ba ca record which is a measure of indian sub continent riverine runoff indicate that the last ice age termination was marked by a prominent weak indian monsoon interval interrupted by an intense monsoon phase as seen in speleothem records and predicted by modeling a strong correspondence between the timing of the malabar 18 o sw record and the hulu cave monsoon record suggests that deglacial 18 o changes in both localities dominantly reflect compositional changes in precipitation likely driven by changes in the north atlantic

microfossil evidence for changing salinity patterns in the bay of bengal over the last 20 000 years the monsson climate characterizing the northern indian ocean produces salinity gradients that are large compared with those in other open ocean areas these gradients are substantially independent of thermal and other ecologically important gradients this situation makes it possible not only to isolate the effect of salinity on sea bed distribution patterns of planktonic foraminifera but also to investigate past salinity changes along a north south transect of piston cores in the bay of bengal analysis of 152 surface sediment samples reveals that at least three factors other than salinity are important in controlling foraminiferal distribution sea bed dissolution surface productivity and surface temperature of these dissolution is the most important therefore in order to reconstruct past salinity patterns in the bay of bengal faunal indices need to be developed that isolate the effect of salinity we have developed two independent approaches the first uses ternary diagrams of the three dominant dissolution resistant species globoquadrina dutertrei globorotalia menardii pulleniatina obliquiloculata high values of g dutertrei are associated with low surface salinities the second approach uses dissolution buffered salinity transfer functions based on the total foraminiferal fauna in the 152 surface samples from the northern indian ocean applied to downcore samples these methods show the same basic historical pattern of salinity variation which is in turn consistent with independent inferences based on preliminary oxygen isotope data duplessy 1980 historical changes in the bay of bengal salinity are reconstructed along a north south transect of seven cores at 90 e the stratigraphy of the transect is controlled by oxygen isotope profiles that are similar to the generalized patterns observed in other areas over the past 20 000 yr salinity gradients are reconstructed for three time intervals 1 the last glacial maximum lgm 2 the mid termination mt and 3 the holocene during the lgm interval salinity was highger in the bay of bengal particularly in the north thus reducing the north south salinity gradient during the mt the middle of the transition from glacial to interglacial global climatic regimes northern bay of bengal surface salinity was considerably reduced while salinity to the south was generally similar to today thus the salinity gradient between 10 n and 15 n was considerably steeper than today in contrast the holocene gradient was approximately the same as the modern gradient with absolute values along the transect being slightly but uniformly higher these changes in the pattern of salinity are explained in terms of changes in the local patterns of precipitation and river run off during the lgm the salinity pattern probably results from decreased precipitation and decreased run off by the ganges brahmaputra river system during the mt decreased salinity in the northern bay of bengal is caused by increased precipitation and run off rather than by the influx of glacial meltwater the steeper mt salinity gradient in the central bay of bengal suggests increased eastward advection of equatorial surface waters by a southwest monsoon current somewhat more vigorous than today these patterns can be correlated with faunal evidence from the western arabian sea that suggest decreased upwelling during the lgm and increased upwelling during the mt this coupling of events may be associated with changes in the pattern or intensity of circulation during the southwest monsoon decreased intensity at the lgm 18 000 b p and increased intensity at the mt 10 500 to 12 500 b p