mid cretaceous oceanic red beds in the umbria marche basin central italy constraints on paleoceanography and paleoclimate abstract detailed studies of the mid cretaceous sedimentary strata in the umbria marche basin in italy revealed that aside from several well known organic rich black shale horizons that record oaes several varicolored mainly reddish horizons indicate oxic conditions at the ocean bottom eight such horizons have been identified in aptian cenomanian sequences in the umbria marche basin the dysoxic oxic beds alternate regularly but not cyclically and seem to be the result of non random processes their occurrence is not a completely random process the duration of deposition of these oceanic red beds orbs varies from 0 13 my orb4 recorded in the ticinella primula zone to 4 54 my for orb1 which spans the globigerinelloides ferreolensis zone to the ticinella bejaouaensis zone in the piobbico core mid cretaceous orbs are not a local phenomenon because they occur in the tethyan deposits in the southern and austrian alps the carpathians the northern caucasus the central north atlantic in northeastern england and in the western himalayas they provide evidence for periodic changes in redox conditions at the ocean bottom such changes could have been caused by changes in bioproductivity basin geometry sedimentation rates paleocirculation and or production of bottom waters with higher content of dissolved oxygen in response to changes in paleoclimate we suggest that the periodic inflow of colder more oxygenated bottom waters was the probable cause of orbs development either as a result of changes in the ocean bottom topography or as a result of brief cool climate periods however reliable proxies for changes in deep ocean circulation are still lacking if orbs were the result of the paleoclimate and therefore indirectly caused by changes in co2 in atmosphere they document the increased sensitivity and instability of the mid cretaceous climate thus changes in ocean dynamics were on a scale of several hundred thousand years to several million years which has not been considered by most theories of co2 cycling mid cretaceous greenhouse paleoclimate and paleocean dynamics

sediment dispersal in the argentine basin evidence from visible light spectra abstract visible light reflectance spectra were determined for each of 236 core top samples from the argentine basin and surrounding areas the spectra were analyzed by taking the first derivative of the raw spectral curves and factor analyzing the first derivative values using wavelengths as variables we used a four factor solution that explains about 90 of the cumulative variance factors were evaluated by comparing factor loadings to first derivative curves from known minerals and mineral combinations by the mapped distributions of the factor scores and by comparison to factors from other areas the four factors represent in order of decreasing variance goethite terrigenous vs pelagic sedimentation organic matter and chlorite the goethite and chlorite factors are useful for interpreting sediment influx and dispersal goethitecomes from the falkland plateau and the argentine continental margin once introduce to the deep ocean goethite appears to be transported primarily by isobath parallel currents chlorite on the other hand is transported into the argentine basin by antarctic bottom water aabw and from the falkland plateau however along the falkland plateau chlorite is transported normal to the slope probably by gravitational processes

turonian oceanic red beds in the eastern alps concepts for palaeoceanographic changes in the mediterranean tethys abstract several transitions of lower to middle turonian pelagic marl limestone cycles into oceanic red beds were studied at high resolution to gain a better understanding of the tethyan marine system before and during red bed initiation and development samples were analysed for mineralogy geochemistry and stable isotope composition in particular carbonate geochemistry of diagenetically largely unaltered calcite was used to explore palaeoceanographic changes in the western tethys principal component analysis of carbonate chemical data showed that the development of red coloured pelagic sediments is accompanied by a shift towards highly oligotrophic conditions in the surface ocean as well as a decrease in hydrothermal activity the formation of red beds is most likely associated with a shift towards more oxic conditions in basins with black shale deposits that eventually resulted in enrichment of thiophile elements in the entire basin depletion in nutrients most likely phosphate and red bed deposition followed the maximum flooding in the early turonian highly productive marsh areas from the proximal european shelf were reworked and supplied nutrients during transgression a gradual nutrient depletion during sea level highstand might be the cause of significantly diminished nutrient availability carbonate production in this low latitude setting was influenced by orbital variation in insolation 20 ka cycle stable carbon isotope stratigraphy reveals low sedimentation rates between 1 and 7 mm kyr and a duration of episodes of cretaceous oceanic red bed deposition between 30 and 360 kyrs

new insights into the carrier phase s of extraterrestrial 3he in geologically old sediments to better understand the composition characteristics of helium diffusion and size distribution of interplanetary dust particles idps responsible for the long term retention of extraterrestrial 3he we carried out leaching stepped heating and sieving experiments on pelagic clays that varied in age from 0 5 ma to 90 myr the leaching experiments suggest that the host phase s of 3he in geologically old sediments are neither organic matter nor refractory phases such as diamond graphite al2o3 and sic but are consistent with extraterrestrial silicates fe ni sulfides and possibly magnetite stepped heating experiments demonstrate that the 3he release profiles from the magnetic and non magnetic components of the pelagic clays are remarkably similar because helium diffusion is likely to be controlled by mineral chemistry and structure the stepped heating results suggest a single carrier that may be magnetite or more probably a phase associated with magnetite furthermore the stepped outgassing experiments indicate that about 20 of the 3he will be lost through diffusion at seafloor temperatures after 50 myrs while sedimentary rocks exposed on the earth s surface for the same amount of time would lose up to 60 the absolute magnitude of the 3he loss is however likely to depend upon the 3he concentration profile within the idps which is not well known contrary to previous suggestions that micrometeorites in the size range of 50 100 m in diameter are responsible for the extraterrestrial 3he in geologically old sediments stuart f m harrop p j knott s turner g 1999 laser extraction of helium isotopes from antarctic micrometeorites source of he and implications for the flux of extraterrestrial 3he flux to earth geochim cosmochim acta63 2653 2665 our sieving experiment demonstrates that at most 20 of the 3he is carried by particles greater than 50 m in diameter the size distribution of the 3he bearing particles implies that extraterrestrial 3he in sediments record the idp flux rather than the micrometeorite flux

paleoceanographic significance of sediment color on western north atlantic drifts ii late pliocene pleistocene sedimentation abstract color variations were interpreted in paleoceanographic terms for the late pliocene pleistocene sediments recovered by odp leg 172 on deep sea drifts at blake bahama outer ridge and northeastern bermuda rise the color derived parameters used in interpretation included predicted carbonate content terrigenous fluxes and hematite content abundance of upper carboniferous spores indicates that the hematite is probably derived from the permo carboniferous red beds of the canadian maritimes in the last 800 kyr sedimentation pattern changes on the blake bahama outer ridge were determined by the sediment delivery to the deep basin as well as circulation changes sediment delivery increased during glacials especially during the last 500 kyr and particularly since stage 6 a fundamental change in the thermohaline circulation occurred at about 500 ka corresponding to the end of the mid pleistocene transition period at the onset of the predominant 100 kyr climate cyclicity sedimentation related to wbuc had intensified at that time and had become more focused at depths below 3000 m changes in hematite content and sedimentation rate show a pulse of sediment via the st lawrence outlet at the pliocene pleistocene boundary suggesting that a likely change in the hydrography physiography of the laurentide ice sheet could have been involved in the climatic and ocean circulation changes at that time

magnetic enhancement is linked to and precedes hematite formation in aerobic soil 1 soil formation usually increases magnetic susceptibility most often by increasing the concentrations of magnetite and maghemite which are two ferrimagnetic iron oxides here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite which is later transformed into hematite the iron oxide that gives red color to soil we show that the maghemite hematite ratio is influenced by the particular environment and the degree of soil development so it constitutes an effective tool for paleoenvironmental and planetary studies

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

evaluating optical lightness as a proxy for carbonate content in marine sediment cores abstract optical lightness is increasingly being used as a proxy for the carbonate content of marine sediment we compared three measurements of optical lightness gray scale brightness and l to carbonate content to test the reliability of these measurements as carbonate content proxies in five piston cores from isotope stages 1 though 6 0 130 ka all measures of optical lightness are reasonable proxies of relative but not absolute changes in carbonate content in contrast in the upper sediments of odp hole 997a which are holocene to pliocene in age lightness values in only the top 10 m of the 180 m analyzed exhibit a strong correlation to carbonate content to better understand which factors control the optical lightness of sediments we analyzed samples in which carbonate content remained constant while the composition of three common clay minerals chlorite illite and kaolinite was varied kaolinite even at a concentration of 20 did not significantly change optical lightness however 20 illite reduced optical lightness by 30 and 20 chlorite reduced lightness by 20 we conclude that regional and temporal changes in the composition of the non carbonate sediment fraction may significantly alter the relationship between lightness and carbonate content we recommend that care must be taken when applying these measures to sediment sequences which span long time intervals or to sediment samples taken over a broad geographical areas

origin of red pelagic carbonates as an interplay of global climate and local basin factors insight from the lower devonian of the prague basin czech republic abstract red pelagic sediments are relatively common in the phanerozoic they are often interpreted as products of sea bottom oxidation during greenhouse climate showing a conspicuous alternation with black shales and thus carrying important palaeoceanographic information the lower devonian pragian carbonate strata of the prague basin czech republic praha formation contain a marked band of red pelagic carbonate up to 15 m thick which can be correlated for several tens of km we investigated seven sections 17 to 255 m thick of the prague basin using the methods of facies analysis outcrop gamma ray logging diffuse reflectance spectroscopy optical microscopy element geochemistry magneto mineralogy and electron microprobe analysis the aim was to find the mineral carriers of the red colour investigate the stratigraphic context of the red carbonates and evaluate the local and global prerequisites for their formation the red pigmentation represents enrichment by hematite with respect to goethite approximately 31 of the total reflectance falling in the red colour band represents a threshold for red coloration the red pigmentation is carried by submicronic hematite dispersed in argillaceous pelagic calcilutite and or inside skeletal allochems gamma ray log correlation indicates that the red carbonate band developed in stratigraphic levels with low sedimentation rates typically from 1 to 7 1 mm kyr which are comparable to the mesozoic rosso ammonitico facies the red beds and the whole praha formation pragian to early emsian are characterized by low toc values

geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the tibetan plateau abstract aeolian sediments are an important archive for palaeoclimate reconstructions on the tibetan plateau the accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases respectively during the last decade the number of osl optically stimulated luminescence ages of aeolian sediments has been rapidly increasing this study summarises the results from more than 300 individual osl ages despite the widespread occurrence of aeolian sediments on the tibetan plateau nearly all osl samples are located on the northeastern and the southern part in most regions the strongest accumulation occurred during the late glacial and in the early holocene this coincides with the strengthening of the asian summer monsoon on the tibetan plateau and wetter climate conditions after the relatively dry glacial times the development of a sufficient vegetation cover acting as a sediment trap seems to be an important requirement for the preservation of aeolian archives short dry periods like the younger dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions the formation of palaeosols occurred mainly during the wet early and mid holocene but the number of ages is relatively small in contrast a second phase of aeolian accumulation during the late holocene was related to the weakening of the asian summer monsoon and drier climate conditions this indicates that the reaction of aeolian accumulation on the tibetan plateau depends on the previous climate state a comparison between the osl ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types while the sand deposits in different basins resemble wet and dry phases loess deposits show no common signal between the analysed areas this indicates an influence of local factors such as varying source areas and erosive processes on the slopes in general the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence

cretaceous oceanic red beds corbs different time scales and models of origin abstract the cretaceous oceanic red bed corb is a newly opened window on global oceanic and climate changes during the cretaceous greenhouse world as a result of the international geoscience programmes 463 494 and 555 2002 2010 corbs have been documented in many places by numerous publications the principle goal of this paper is to summarize scientific advances on corbs including chronostratigraphy sedimentology mineralogy elemental and isotopic geochemistry and their relationship to oceanic anoxic events oaes palaeoclimate and palaeoceanography we propose a new geochemical classification of the corbs using cao al 2 o 3 and sio 2 values which lithologically refer to marly clayey and cherty corbs respectively detailed mineralogical studies indicate that hematite goethite and mn 2 bearing calcite are the minerals imparting the red color of corbs hematite clusters of several to tens of nanometers in the calcite structure are the main cause of the red coloring of limestones and the mn 2 bearing calcite gives additional red color goethite was thought to form originally with hematite and was subsequently transformed to hematite during late diagenesis chronostratigraphic data allow the distinction of two groups of corbs by their durations short term corbs are generally less than 1 myr in duration and seem to be on the scale of milankovitch cycles during the deposition of cretaceous reddish intervals from odp cores 1049 and 1050 low primary productivity and relatively high surface temperature resulted in low organic carbon flux into the sediments which reduced oxygen demand and produced oxidizing early diagenetic conditions in such an oxic environment iron oxides formed imparting the reddish color the long term corbs depositional events lasted longer than 4 myr and may be a possible consequence of the oaes enhanced amounts of organic carbon and pyrite burial during and after the oaes would have resulted in a large and abrupt fall in atmospheric co 2 concentration which probably induced significant global climatic cooling during and after the oaes global cooling would have enhanced formation of cold deep water increasing its oxidizing capacity due to the greater content of dissolved oxygen and would promote formation of oceanic red beds sedimentological mineralogical and geochemical data indicate that corbs were deposited under highly oxic oligotrophic conditions probably at a low sedimentation rate the cretaceous red and white limestones from italy have similar compositions of terrestrial input sensitive elements al ti k mg rb zr higher contents of fe 2 o 3 and depleted redox sensitive elements v cr ni and u and micronutrient elements cu zn indicating similar provenance sources but red limestones were deposited under more oxic conditions at the sediment water interface than white limestones the cretaceous red shales such as those from the north atlantic and tibet have similar mineralogy and geochemistry as the late cenozoic red clays in the pacific ocean and the environment where both are formed was well oxidizing at a very low sedimentation rate we compiled seventeen published stratigraphic examples of phanerozoic oceanic red beds including the late cenozoic red clays in the pacific different hypotheses explain the origin of red pigmentation of limestones and shales including 1 detrital origin of iron derived from continental weathering 2 iron bacterial mediation at the time of sedimentation and 3 iron oxidation in oligotrophic highly oxic environment additional research on phanerozoic oceanic red beds is needed in order to better document their origin and palaeoceanographic and palaeoclimatic significance

paleoceanographic significance of sediment color on western north atlantic drifts i origin of color reflectance spectra collected during odp leg 172 were used in concert with solid phase iron chemistry carbonate content and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color on the western north atlantic drifts sediment color is the result of primary mineralogy as well as diagenetic changes sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and fe 2 fe 3 changes in clay minerals hematite most likely derived from the permo carboniferous red beds of the canadian maritimes is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components various intensities for diagenesis result from changes in organic carbon content sedimentation rates and h2s production via anaerobic methane oxidation iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and or increased reactive iron flux in glacials 7 2002 elsevier science b v all rights reserved

quantitative analysis of iron oxide concentrations within aptian albian cyclic oceanic red beds in odp hole 1049c north atlantic abstract aptian albian sediments in core 12x of hole 1049c odp leg 171b are characterized by high frequency cycles that consist of alternating layers of red and green white clayey chalk and claystone the first derivative curves of diffuse reflectance spectra drs for samples of different colors reveal that red brown and orange samples show clear peaks corresponding to hematite and goethite following treatment using the cbd citrate bicarbonate dithionite procedure the red samples lost their red color and corresponding peaks in the first derivative curve and became greenish or whitish therefore hematite and goethite are the minerals responsible for the reddish change in sample color however these minerals behave differently from each other in terms of determining the color of sediment hematite imparts a red color whereas goethite imparts a yellow color therefore a change in the proportions of hematite and goethite can cause a change in sediment color from orange to brown to obtain the absolute contents of iron oxides in these sediments we performed a quantitative analysis using drs with multiple linear regression the results reveal that the albian brown beds contain 0 13 0 82 hematite average value 0 51 and 0 22 0 81 goethite average value 0 58 the aptian orange beds contain 0 19 0 46 hematite average value 0 35 and 0 29 0 67 goethite average value 0 50 x ray diffraction analysis of the aptian and albian cycles reveals no clear variations in mineral content with sediment color it is suggested that hematite and goethite were derived from oxic environments during the period of deposition and early diagenesis the oxic conditions were probably determined by the low accumulation rate of organic matter and the high content of dissolved oxygen in bottom water

clay mineral sedimentation in high northern latitude deep sea basins since the middle miocene odp leg 151 naag high resolution clay mineralogical investigations and their comparison with other sedimentological data from odp sites 908 and 909 central fram strait were used to reconstruct the paleoclimate and paleoceanography in the high northern latitudes since the middle miocene ice rafting has probably occurred since 15 ma the comparison of sand sized components and clay mineral distribution demonstrate that both were not delivered by the same transport process the input of the clay fraction is related to transport through sea ice and or oceanic currents a provenance change at 11 2 ma is indicated by variations within clay mineral distribution and increased accumulation rates this is interpreted as a result of an increase in water mass exchange through the fram strait decreases of the smectite to illite and chlorite ratio at site 909 suggest a middle miocene cooling phase between 14 8 and 14 6 ma and a further cooling phase between 10 and 9 ma the intensification of glaciation in the northern hemisphere is documented by an increase of illite and chlorite from 3 4 to 3 3 ma which is synchronous to the onset of major northern hemisphere glaciation as indicated by oxygen isotope data

timing of diagenetic haematite growth in red pelagic limestones from gubbio italy abstract magnetite haematite and to a minor extent maghaemite are recognised in the cretaceous and paleocene red pelagic limestones at gubbio the magnetite is detrital or biological whereas the haematite grew during diagenesis from a goethitic precursor thermal and af demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level in the few tens of centimetersbelow a recorded geomagnetic reversal defined by the magnetite magnetization some of the haematite grains are magnetized in the post reversal field the blocking temperature spectra of this haematite fraction with post reversal magnetization are found to shift toward higher temperatures as the reversal boundary is approached the blocking temperature spectra reflect the grain size spectra of the haematite which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth the depth below reversal boundaries to which haematite with post reversal magnetization can occur is estimated to be about 60 cm after compaction and is equivalent to a time of about 105 years for these particular sediments a detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single domain critical volume occurs prior to the mechanical fixation of the detrital or biological magnetite subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite because of their occurrence as pigmentary coatings on larger non magnetic grains

quantitative reassessment of brick red lutites evidence from reflectance spectrophotometry abstract brick red lutites are distinctive bright red sediments deposited in the western north atlantic these unique sediments were derived from permo carboniferous outcrops in the canadian maritime provinces transported out the gulf of st lawrence through the cabot straits and redistributed by the western boundary undercurrent along the north american continental margin in this study we used fourteen cores taken off eastern north america to more precisely examine the input and depositional history of brick red lutites our study differs from previous studies in the manner in which the red sediment was identified unlike previous studies which used color charts to assess the presence of brick red lutites we used visible light reflectance spectrophotometry the primary mineral imparting a red color to brick red lutites is hematite experiments with known quantities of hematite in a matrix mineralogically similar to western north atlantic sediment indicate that the presence of hematite can be detected at weight percentages of less than 0 1 using spectral reflectance data we characterized the distribution of brick red lutites for two broadly defined time levels latest glacial and early holocene as expected the maximum input of brick red lutite was during late glacial time and input decreased reaching a minimum during the early holocene since the early holocene there has been little change in the distribution of this unique red sediment on the north american margin however our reflectance spectra indicate renewed accumulation of hematite rich sediment at the present time in the cabot straits

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

climatic interpretation of the luochuan and lingtai loess sections china based on changing iron oxide mineralogy and magnetic susceptibility abstract hematite and goethite estimated from diffuse reflectance spectra and magnetic susceptibility ms have been determined from both the luochuan and lingtai loess sections of the loess plateau of central china changing concentrations of these iron oxides and ms were used to determine paleoclimatic change based on a model that relates pedogenic production of hematite and magnetite to precipitation we propose two precipitation phases on the loess plateau during the last 2 6 ma from the wucheng red clay boundary up to paleosol s5 mis 13 precipitation on the loess plateau was moderate probably not frequently exceeding 450 mm yr and highly seasonal from s5 to the present precipitation during interglacial times has gradually increased to the present levels of 600 650 mm yr for the localities examined throughout the pleistocene spanning both glacial and interglacial conditions hematite to goethite ratios display a consistent decrease this decrease suggests that precipitation on the loess plateau has been getting less seasonal and or has been occurring during times when temperature was lower in addition to these long term changes it also appears that iron oxide records from the loess plateau exhibit 400 500 ka cycles from the wucheng red clay boundary to s5 these 400 500 ka cycles may be analogous to similar length cycles recorded in 13 c marine records in the south china sea and may be linked through weathering and silica production as a result of the asian monsoon

early triassic oceanic red beds coupled with deep sea oxidation in south tethys abstract carbonate oceanic red beds orbs are unusual in phanerozoic shelf settings but can be widespread during discrete intervals several scenarios have been invoked to explain the origin of these orbs but there remains uncertainty about the process by which the red pigmentation of orbs forms here we propose that the occurrence of orbs at intermediate water depths in shelf regions is controlled by fluctuations in the redox state of deeper waters we have examined early triassic peri gondwana shelf sections in south tibet which show the development of spathian late early triassic orbs at intermediate water depths the red color of these orbs is imparted by randomly dispersed hematite crystals that are microns in size showing weak alteration by late burial diagenesis widespread anoxia in both shelf seas and the oceanic realm was well developed in the early triassic synchronous occurrence of spathian orbs in deep shelf regions is closely related to the improved oxidation in deeper settings from anoxia to dysoxia based on changes in the redox proxy of pyrite framboid sizes it is therefore inferred that prolonged deep water anoxia might serve as source of fe ii for the formation of orbs when intensified upwelling develops the global occurrence of early triassic orbs is coincident with the significant rebound of biodiversity after the permian triassic mass extinction indicating the occurrence of orbs marks the terminal stage of an oceanic anoxic event and orbs can serve as an indicator of the ameliorated marine ecosystem

pedogenetic interpretations of particle size distribution curves for an alpine environment abstract the qilian mountains are generally capped by a productive silty soil layer wherever the environment allows as holocene loess is prevalent across the qilian mountains we assume that at least some of these fine sediments are derived from loess deposition and that soils across the region may be genetically linked to test these hypotheses nine pedons in different landscapes within a typical alpine watershed of the qilian mountains were sampled we also collected fine earth samples from glacier surfaces and crevices of glacial debris in the moraine zone the particle size distribution psd is used as a proxy for identifying aeolian fractions in soils the psd curves of all of the fine earth fractions examined are polymodal although three modal sizes of roughly 16 m 35 m and 80 m are found in almost all sediments in varying proportions these modal sizes have been identified as three sources of aeolian sediments in different transport systems the composition and thickness of loess sediments are related to local site conditions and may be related to the paleoenvironmental history of the site clastic debris and vegetation cover serve as dust traps during different stages of soil formation in this alpine environment and soils grow upward with accumulating loess sediment our study demonstrates that psd curves can be used to determine the origins and especially aeolian origins of soils furthermore this study provides insight into the pedology ecology and paleoenvironmental history of loess affected ecosystems in alpine areas of the qinghai tibetan plateau

impact induced mass wasting at the k t boundary blake nose western north atlantic seismic reflection data combined with results from ocean drilling document regional scale slumping associated with the cretaceous tertiary k t impact event the k t boundary is biostratigraphically complete at three ocean drilling program sites 1049 1050 and 1052 located on blake nose 30 n 75 w off eastern florida in water depths of 1300 2600 m maastrichtian chalk is folded and fractured below the k t boundary at all three sites whereas lowermost paleocene clays and chalks are undeformed deformation is pervasive in maastrichtian at the deepest water site site 1049 whereas at the shallower water sites sites 1050 and 1052 thick intervals of structurally intact maastrichtian chalk are separated by thinner intervals of highly deformed sediments correlation of core to seismic reflection data indicates that the k t boundary immediately overlies seismic facies characteristic of mass wasting that extend across most of the 55 km distance of the depth transect maastrichtian sediments appear to have moved as large slump blocks on the upper part of blake nose but deformed more uniformly in the deeper water parts of the transect we suggest that mass wasting occurred on the blake nose 1600 km from the chicxulub crater in response to the cataclysmic seismicity generated by the impact

maastrichtian foraminiferal and paleoceanographic changes on milankovitch timescales milankovitch scale alternations in maastrichtian hemipelagic strata from ocean drilling program hole 1050c blake nose provide a natural experiment of paleoceanography and foraminiferal paleoecology in a tropical subtropical greenhouse ocean cycles are 30 50 cm thick and thought to reflect the 21 kyr precessional cycle high planktic 18o values are correlated with high planktic but low benthic 13c values indicating that cooler and or more saline surface waters were associated with higher productivity high productivity intervals are also characterized by high ca concentrations enrichment in feldspar and kaolinite and high relative abundance of heterohelix spp globigerinelloides spp and laeviheterohelix glabrans conversely low productivity intervals have low planktic 18o values high fe and ti concentrations enrichment in quartz illite and chlorite and relative increases in globotruncana spp and pseudoguembelina spp potential forcing mechanisms for observed covariation include cyclic variation in water column stratification variation in continental nutrient fluxes and changes in the intensity of upwelling

pleistocene precipitation balance in the amazon basin recorded in deep sea sediments abstract terrigenous sediments from ceara rise in the western tropical atlantic ocean record pleistocene amazon basin climate variability iron oxides and oxyhydroxides in this region originate mainly from chemically leached amazon lowland soils concentrations of goethite and hematite in the terrigenous fraction consistently peak during transitions from glacial to interglacial periods suggesting an increased proportion of erosive products derived from the amazon lowlands compared to the physically weathered highlands lowland amazon basin precipitation changes monitored by the percentage of goethite relative to total iron oxides lead ice age extremes with maximum aridity during ice growth and maximum precipitation during ice melt rapid climate changes over the amazon basin may reflect shifts in the position of the intertropical convergence zone forced by northern hemisphere insolation at precessional 1 23 000 yr 1 and obliquity 1 41 000 yr 1 frequencies variance in the orbital eccentricity bands 1 100 000 and 1 413 000 yr 1 may be explained by nonlinear amplification of insolation forcing at precessional frequencies the early response of amazon precipitation to insolation ahead of high latitude ice volume 18o at all orbital frequencies suggests that tropical aridity is part of the chain of events leading to ice ages rather than a response to glacier oscillations

determining the composition of late quaternary marine sediments from nuv vis and nir diffuse reflectance spectra abstract as the length of marine cores increases and sampling intervals decrease the need for rapid and inexpensive means of determining sediment composition has become apparent in this study we examine one potentially useful technique for assessing compositional changes in marine cores diffuse reflectance spectrophotometry we examined nearultraviolet visible and near infrared reflectance spectra from five data sets each data set consists of calibration samples and test samples the calibration samples spectra were related to a sediment component using multiple linear regression the resulting regression or calibration equations were then evaluated using the test samples calibration equations were written relating spectra to several sediment components including carbonate atlantic and east pacific rise odp site 847 organic carbon content atlantic and east pacific rise and opal content east pacific rise the correlation coefficients for the regression equations ranged from a high of 0 99 for carbonate and opal at odp site 847 to a low of 0 97 for atlantic carbonate indicating that spectral variations are highly correlated to sediment composition all of the equations include a substantial number of variables from shorter visible and longer near ultraviolet wavelengths suggesting that these wavelengths are especially important for devices designed specifically to scan marine cores although equations for estimating organic and carbonate content appear independent of other sediment components the opal equation is strongly dependent on carbonate content indicating that opal concentration is correlated to carbonate content tests of the calibration equations indicated that all our equations reasonably estimate the pattern of changes either down core or in surface sediments where our spectral estimates have difficulty is with absolute values frequently over or underestimating observed values by a substantial amount within these limitations diffuse reflectance spectrophotometry can be a useful tool for characterizing marine cores and as our understanding of the relationship between spectra and mineralogy improves so will estimates of absolute values