stable organic carbon isotope stratigraphy across oceanic anoxic event 2 of demerara rise western tropical atlantic ocean drilling program odp leg 207 recovered expanded sections of organic carbon rich laminated shales on demerara rise western tropical atlantic high resolution organic carbon isotope and total organic carbon toc records are presented which span the cenomanian turonian boundary interval ctbi including the oceanic anoxic event oae 2 from four sites oriented along a nw striking depth transect these records represent the first high resolution carbon isotope records across oae 2 from the south american margin of the tropical atlantic due to the scarcity of age significant fossils the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the ctbi across the depth transect and to tie this to biostratigraphically well defined sections in the western interior basin pueblo usa boreal shelf seas eastbourne england and western tethys oued mellegue tunisia all four sections studied document a 6 increase of 13corg values at the base of the ctbi which is followed by an interval of elevated 13corg values and a subsequent decrease our results supply an important stratigraphic base for subsequent paleoceanographic studies on late cenomanian to early turonian sediments from demerara rise and elsewhere

organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

reconstruction of water column anoxia in the equatorial atlantic during the cenomanian turonian oceanic anoxic event using biomarker and trace metal proxies abstract the occurrence of the biomarker lycopane and the enrichment patterns of redox sensitive trace metals in black shales from demerara rise western tropical atlantic reveal that bottom waters were anoxic during the upper cenomanian and lower turonian at this location bottom waters were clearly oxygen depleted already before oceanic anoxic event 2 oae 2 and continued to be so afterwards furthermore the presence of fossil derivatives of isorenieratene and chlorobactene pigments derived from green sulfur bacteria demonstrates that the waters at the base of the photic zone occasionally contained sulfide i e were euxinic before and after oae 2 low concentrations of derivatives of these pigments are present while much higher concentrations occur within the oae 2 section stratification of the water column must have been strong to sustain euxinic conditions in the photic zone for prolonged periods a substantial drop in the concentrations of isorenieratene and chlorobactene derivatives demonstrates that this stratification temporarily broke down during oae 2 a simultaneous decrease in sea surface temperatures suggests that local ventilation was instrumental in this re oxygenation event a rapid decrease in seawater derived trace metal burial rates at demerara rise occurring in phase with the onset of the anoxia related to oae 2 suggests an approximately synchronous onset of oae 2 in the proto north atlantic

modification of clast shape in high arctic glacial environments abstract clast shape data from a range of different glacial environments at several high arctic valley glaciers in svalbard are presented these data add to the growing body of reference information about clast shape in modern glacial environments and is used to explore the role of lithology in clast morphogenesis and to evaluate the different methodological approaches to the analysis of clast shape data the following conclusions are drawn 1 it is possible to distinguish clasts transported subglacially from those moved supraglacially 2 it is not possible to differentiate among different types of subglacial sediment or to distinguish them collectively from glaciofluvial samples 3 lithology has some influence on clast shape although not as much as previously suggested and 4 covaria t plots of the ra percentage of angular and very angular clasts versus c40 percentage of clasts with c to a axial ratio 0 4 index give superior data visualization and discriminate more effectively among different glacial sediments than sphericity and roundness plots

errata neogene fjordal sedimentation on the western margin of the lambert graben east antarctica the lambert graben is occupied by the world s largest fjord system through which flows the lambert glacier the amery ice shelf and their tributaries along the western margin of the graben in the northern prince charles mountains remnants of uplifted miocene and pliocene strata of the glacigenic fjordal pagodroma group total more than 800 m in thickness these sediments provide evidence for a dynamic east antarctic ice sheet during the neogene period each of the four pagodroma group formations defined from this region rests unconformably on either proterozoic or permo triassic rocks the unconformity surfaces represent parts of the walls and floors of neogene fjords for these surfaces to have been eroded the ice must have been grounded out as far as the continental shelf in prydz bay the pagodroma group was deposited by wet based glaciers discharging into a fjordal setting and includes lithofacies that are quite different from those produced by modern antarctic ice masses the principal lithofacies are massive diamicts and soulder gravels deposited both close to a calving grounded glacier terminus and from icebergs the few stratified diamicts are the product of more distal iceberg sedimentation an ice transported gravel lithofacies includes rockfall debris derived from palaeofjord walls and mixed with subglacially derived diamicts some lithofacies contain evidence of subaquatic slumping and gravity flowage volumetrically minor lithofacies include laminites with some exposures exhibiting large ice rafted clasts the laminites represent less proximal mainly ice free fjordal sediments resulting either from tidal current sorting of suspended sediment originating from subaquatic glaciofluvial discharge or from turbidity currents derived from unstable subaquatically deposited glacigenic sediment the pagodroma group provides a record of multiple glaciation by dynamic sliding glaciers carrying large amounts of both basal and supraglacial debris the closest modern analogues in terms of the thermal and dynamic characteristics of the neogene lambert glacier appear to be the fast flowing tidewater glaciers of east greenland these glaciers originate from the interior ice sheet and discharge large volumes of icebergs the resulting lithofacies are predominantly diamicts

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

n2 fixing cyanobacteria supplied nutrient n for cretaceous oceanic anoxic events the abundance of specific membrane lipids 2 methylhopanoids indicates that cyanobacteria played a key role in the seemingly global deposition of black shales during the early aptian ca 120 5 ma and late cenomanian ca 93 5 ma oceanic anoxic events organic matter rich sediments deposited during these events are characterized by a 15n content typical of newly fixed n2 indicating that cyanobacterial n2 fixation was the main source for nutrient n we propose that denitrification and anaerobic ammonium oxidation effectively cut off the return of nutrient n from the anoxic deep waters to the photic zone in the oceans giving n2 fixing cyanobacteria a competitive advantage over algae during these oceanic anoxic events

cenomanian turonian and δ13c and δ18o sea level and salinity variations at pueblo colorado stable isotopes of the surface dwelling planktic foraminifera hedbergella planispira its abundance variations and mineralogical analysis of the cenomanian turonian at pueblo co reveal cyclic variations in surface salinity due to changes in precipitation freshwater influx marine incursions and long term sea level fluctuations hedbergella planispira is a proxy for salinity variations as indicated by 2 4 more negative 18o values in intervals of peak abundances as compared to intervals with reduced populations negative 18o values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods accompanied by increased clastic transport more positive 18o values reflect more normal marine salinities as a result of arid periods and or marine incursions and correlate with intervals of increased biogenic carbonate deposition the magnitude of salinity variations during the low sea level of the hartland shale is twice that during the sea level transgression of the bridge creek limestone the rapid positive 13c shift that marks the onset of oceanic anoxic event 2 oae 2 at pueblo occurred over a period of about 100 ky 93 90 94 00 ma and coincided with the major sea level transgression that culminated in the deposition of the basal bridge creek limestone a positive 13c shift also occurred in the rotalipora cushmani zone prior to oae 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter the likely cause for oae 2 is depletion of 12c in the water column as a result of high primary productivity whereas an earlier r cushmani zone event was primarily caused by increased input of terrigenous organic matter both 13c events are associated with enhanced organic matter preservation and anoxic or dysoxic bottom waters

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

the early toarcian early jurassic and the cenomanian turonian late cretaceous mass extinctions similarities and contrasts abstract the early toarcian eto and cenomanian turonian c t mass extinctions are comparable from a wide range of scales and perspectives from a broad standpoint their similarities include virtually identical extinction intensity at the familial and generic levels widespread basinal facies deposited during sea level highstands an overall greenhouse climate and anoxia as an important causal mechanism the high resolution macroinvertebrate data analyzed here consisting of stratigraphic ranges diversity and abundance point to smaller scale similarities the two events resulted in significant ecological disruption and in both cases the biotic responses were very similar taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and in the eto belemnites in addition epifaunal taxa adapted to low oxygen conditions such as the buchiids posidoniids and inoceramids flourished in the post extinction environment during the survival interval as conditions ameliorated the biota became more diverse and gradually began to resemble pre extinction biotas furthermore the 13c curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions this points to the potential application of 13c as a tool for determining the repopulation modes and timing for other mass extinctions

a case for sirius group alpine glaciation at mount fleming south victoria land antarctica a case against pliocene east antarctic ice sheet reduction the sirius group comprises a suite of consolidated glacial deposits that are widespread in the transantarctic mountains some of the deposits contain pliocene marine diatoms because of the interpretation that the sirius group tills and the marine diatoms were deposited by the east antarctic ice sheet it has been inferred that the east antarctic ice sheet was much reduced in area and volume during the pliocene these interpretations were evaluated by studying sirius group lodgment tills on mount fleming in the dry valleys sector of the transantarctic mountains we infer that the sirius group lodgment tills at mount fleming do not support the hypothesis that the east antarctic ice sheet was much reduced during the pliocene we demonstrate that sirius group lodgment tills on mount fleming were deposited by alpine ice this conclusion is founded on ice flow directions inferred from rattails gravel fabric and the orientation of bullet boulders as well as on sediment and gravel characteristics of the tills only a very few unidentifiable diatom fragments were recovered better preserved identifiable pliocene marine diatoms occur in moderate abundances in a 5 10 cm thick unconsolidated and discontinuous drift that caps the lodgment tills on the basis of the decline in diatom preservation with depth into the till we dismiss transport of the better preserved diatoms by the ice that deposited the underlying sirius group lodgment till instead we attribute diatom presence to eolian deposition and recycling into lodgment tills at a later stage

repeated anoxia extinction episodes progressing from slope to shelf during the latest cenomanian abstract oceanic anoxic event 2 oae 2 during the cenomanian turonian c t transition caused stepwise marine extinctions using organic compounds stable carbon and oxygen isotopes and foraminifera from three depth transect sections in northern spain this study revealed repeated anoxic euxinic events coinciding with warming and stepwise extinctions of planktonic and or benthic foraminifera within intermediate to surface waters in the proto north atlantic during the c t transition those short duration euxinic events occurred four times at 93 95 ma marked by the extinction of rotalipora greenhornensis at 93 90 ma marked by the extinction of rotalipora cushmani at the mid time maximum of the plateau of the 13 c of carbonates 93 70 ma and at the time of the c t boundary 93 55 ma furthermore the main benthic foraminiferal extinctions occurred during the first and second euxinic events in the upper slope during the second and third euxinic events in the outer to middle shelf and during the third and fourth events in the middle shelf the main euxinic events in each section also showed a progression to the shallow shelf the main anoxia extinction events occurred in the upper slope and outer shelf then moved to the middle shelf the shallowest section had relatively weak anoxia and a proportionally low extinction rate these new findings indicate that foraminiferal extinctions started from the intermediate water and the continental slope and then moved to the continental shelf this was the result of the repeated progression of euxinic anoxic water from the upper slope to the middle shelf on the eastern continental margin of the proto north atlantic four times during a 400 kyr period to the end of the cenomanian

nitrogen isotopic composition of sediments from the eastern tethys during oceanic anoxic event 2 abstract low nitrogen isotopic compositions 15n have been reported in deposits from the proto north atlantic and western tethys during oceanic anoxic event 2 oae2 at the cenomanian turonian c t transition it has been proposed that the low 15n values may have resulted from enhancement of n2 fixation and or incomplete assimilation of the upwelled ammonium due to expansion of anoxic euxinic conditions however few 15n measurements are available for the sediments from the eastern tethys and the pacific and therefore the global significance of the n cycle and its environmental implications remains to be tested here we present 15n data from oae2 deposits in the gongzha section in the tingri area of southern tibet which was located on the southern margin of the eastern tethys during the mid cretaceous the 15n data reveal a large perturbation of the n cycle during oae2 the pronounced negative shift in 15n prior to oae2 as well as the persistent low 15n values during oae2 imply the significant contribution of n2 fixation the changes in the marine n cycle suggest that the expansion of an anoxic environment may also have occurred in the southern continental margin areas of eastern tethys the coincidence of the marine faunal turnover and the perturbation of the n cycle suggests that the expansion of anoxic water masses may have played an important role in the extinction of marine organisms across the c t boundary in eastern tethys

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

provenance of the sirius group and related upper cenozoic glacial deposits from the transantarctic mountains antarctica relation to landscape evolution and ice sheet drainage abstract this study uses bulk x ray diffraction xrd heavy mineral analysis and analysis of detrital modes of the sirius group and related upper cenozoic deposits to evaluate their provenance the data suggest that deposition of the sirius group occurred as a result of long term glacial denudation of the transantarctic mountains such a conclusion is in contrast with the traditional view of deposition on a pre existing high relief glacial topography during one relatively short term phase of glacial expansion by the east antarctic ice sheet two petrofacies are distinguished which have different geomorphological settings and paleo ice flow directions one petrofacies includes much material from the higher elevated sedimentary sequences of the transantarctic mountains and represents overriding of the mountains and deposition of part of the sirius group during or after the late oligocene to early miocene the second petrofacies is characterized by a large input from crystalline basement sources and represents active erosion and deposition in glacial troughs during the neogene the second petrofacies of the sirius group shows similarities to the record from dry valley drilling project core 11 dvdp 11 which indicates that east antarctic ice was last flowing through the dry valleys in the late miocene to early pliocene

evolutionary trends of tropical calcareous nannofossils in the late neogene abstract examination of middle late miocene sediments recovered during odp leg 154 in western equatorial atlantic has led to identification of evolutionary transitions in some groups of late neogene calcareous nannofossils through analyses of high resolution samples 10 cm sample interval equivalent to average interval of 6 kyr we were able to document the origin of the genera catinaster amaurolithus and ceratolithus and the nannofossil species discoaster berggrenii and d quinqueramus the presence of intermediate morphotypes between end members representing distinct species sheds new light on phylogenetic relationships and or confirms relationships suggested in previous studies the mode and timing of the evolutionary transitions described are discussed successive branching from triquetrorhabdulus rugosus is demonstrated for amaurolithus primus amaurolithus amplificus and ceratolithus acutus a new genus is therefore established nicklithus type species nicklithus amplificus n comb a new species is described ceratolithus larrymayeri n sp the genera triquetrorhabdulus amaurolithus nicklithus and ceratolithus all belong to the family ceratolithaceae

a marine and terrestrial sirius group succession middle beardmore glacier queen alexandra range transantarctic mountains antarctica a succession of sirius group glacigene sediments which crop out along the western margins of the beardmore valley between cherry icefall and hewson glacier below the cloudmaker is designated as the stratotype of the cloudmaker formation this new formation overlies a multiply glaciated pavement dominion erosion surface cut into the precambrian goldie formation and is disconformably overlain by the meyer desert formation sirius group the cloudmaker formation comprises bedded and massive diamictons bedded sands and silts and laminated clays assemblages of foraminifera occur throughout the cloudmaker formation and indicate that these basal sirius group sediments were deposited in brackish glacial marine environments the general absence of diatoms suggest these marine waters were ice covered similar marine assemblages are also present in basal sirius group sediments at oliver bluffs dominion range recycled marine diatom assemblages in the sirius group at the latter locality indicate that the host sediments have an age of 3 8 ma pliocene the cloudmaker formation is placed in the pliocene although a latest miocene age for the basal sediments cannot be ruled out stratigraphie sedimentologic and paleontologic evidence suggests that beardmore valley was occupied by a fjord and tidewater glacier system that extended at least 165 km through the transantarctic mountains from the southwestern ross sea the stratigraphy of the cloudmaker formation consists of a succession of members separated by disconformities it is hypothesised that these strata were deposited by a dynamic valley glacier system that underwent a history of glacier advance and grounding alternating with glacier retreat and flotation over a marine water column a combination of fjord basin sediment filling and sea level oscillations may also have influenced the pattern of glacier ice advance and retreat within beardmore paleofjord the marine cloudmaker formation is overlain by the terrestrial diamicton dominated meyer desert formation at oliver bluffs the meyer desert formation diamictons are interbedded with fluvial and lacustrine sediments successions that contain in situ vascular plant fossils principally the southern beech nothofagus mosses and beetle remains a magellanic type flora and fauna occupied the coastal margins of the beardmore paleofjord the vertical transition from the basal marine cloudmaker formation to terrestrial meyer desert formation provides a sea level datum that can be used to assess the extent of post sirius group tectonic uplift uplift rates at the cloudmaker section 90 km inland from the transantarctic mountain front or rift shoulder margin in the queen alexandra mountain block are determined to be 429 or 350 m myr this assumes a total uplift of 1331 m for the uppermost marine sediments of the cloudmaker formation and maximum diatom based ages for the sirius group of 3 1 ma or 3 8 ma gross similarities in stratigraphy and interpreted paleoenvironments are apparent between the cloudmaker succession beardmore paleofjord and the upper miocene pliocene successions at the mouth of taylor paleofjord 800 km to the north contrasting present day elevational settings for these two widely separated marine successions indicates the post sirius rate of tectonic uplift for the transantarctic mountains has been significantly greater in the queen alexandra block

a review of nitrogen isotopic alteration in marine sediments key points use of sedimentary nitrogen isotopes is examined on average sediment 15n 14n increases approx 2 per mil during early burial isotopic alteration scales with water depth abstract nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record however bulk sedimentary nitrogen isotope ratios which can be determined routinely and at minimal cost may be altered during burial and early sedimentary diagenesis particularly outside of continental margin settings the causes and detailed mechanisms of isotopic alteration are still under investigation case studies of the mediterranean and south china seas underscore the complexities of investigating isotopic alteration in an effort to evaluate the evidence for alteration of the sedimentary n isotopic signal and try to quantify the net effect we have compiled and compared data demonstrating alteration from the published literature a 100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that at sites located off of the continental margins an increase in sediment 15n 14n occurs during early burial likely at the seafloor the extent of isotopic alteration appears to be a function of water depth depth related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of n isotopic alteration moreover the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global n cycle

a euxinic southern north atlantic ocean during the cenomanian turonian oceanic anoxic event abstract during mid cretaceous times large amounts of organic carbon corg became sequestered in black shales possibly due to oceanic anoxic events characterized by the development of an extended oxygen minimum zone omz here we provide the first direct evidence for an open ocean omz in the cenomanian turonian c t southern north atlantic and in fact show that the base of the photic zone was euxinic as revealed by molecular fossils from photosynthetic green sulfur bacteria in c t black shales this together with evidence for bottom water anoxia and accumulation of redox sensitive trace metals and hydrogen rich organic matter indicates a continuously euxinic water column concurrent with the high corg accumulation rates which are 15 150 times greater in the southern than in the northern north atlantic and the low biological productivity this suggests that preservation controlled the accumulation of corg in c t black shales

cenozoic prograding sequences of the antarctic continental margin a record of glacio eustatic and tectonic events abstract sedimentary sections up to 6 14 km thick lie beneath many areas of the antarctic continental margin the upper parts of the sections contain up to 6 km of cenozoic glacial and possibly non glacial sequences that have prograded the continental shelf up to 85 km we describe the cenozoic sequences using two general categories based on their acoustic geometries type ia sequences which account for most prograding of the antarctic continental shelf have complex sigmoidal geometries and some acoustic characteristics atypical of low latitude margins such as troughs and mounds lying parallel and normal to the shelf edge and high velocities 2 0 2 6 km s for flat layers within 150 m of the seafloor type iia sequences which principally aggrade the paleoshelf lie beneath type ia sequences and have mostly simple geometries and gently dipping reflections the prograding sequences are commonly located near the seaward edges of major mesozoic and older margin structures relatively rapid cenozoic subsidence has occured due to the probable rifting in the ross sea thermal subsidence in the antarctic peninsula and isostatic crustal flexure in wilkes land in prydz bay and the weddell sea prograding sequences cover mesozoic basins that have undergone little apparent cenozoic tectonism grounded ice sheets are viewed by us and others as the principal mechanism for depositing the antarctic prograding sequences during the initial advance of grounded ice the continental shelf is flexurally overdeepened the inner shelf is heavily eroded and gently dipping glacial strata are deposited on the shelf i e type iia sequences the overdeepened shelf profile is preserved a during glacial times by grounded ice sheets episodically crossing the shelf eroding sediments from onshore and inner shelf areas and depositing sediments at the front of the ice sheet as outer shelf topset banks and continental slope foreset aprons i e type ia sequences and b during interglacial times like today by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge thereby creating troughmouth fans and sheet like prograding sequences i e type ia sequences numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the antarctic ice sheet the available drilling and seismic interpretations provide the following history 1 cenozoic ice sheets have existed in places near the continental shelf since middle to late eocene time 2 a grounded antarctic ice sheet first expanded to the continental shelf edge with probable overdeepening of the outer shelf in late eucene to early oligocene time in prydz bay possibly in early miocene time in the ross sea and at least by middle miocene time in the weddell sea 3 the relative amounts of shelf prograding and inferred ice volume variations and related sea level changes have increased since middle to late miocene time in the eastern ross sea prydz bay and possibly weddell sea our analysis is preliminary further acoustic surveys and scientific drilling are needed to resolve the proximal antarctic record of glacio eustatic climatic and tectonic events recorded by the prograding sequences

classification of poorly sorted sedimentary rocks abstract the classification and nomenclature of sandstones has evolved over the years into a system which is now generally accepted as standard however no equivalent system exists for the poorly sorted sedimentary rocks which include grain sizes from clay to gravel a descriptive classification is proposed based on an earlier system but using updated nomenclature and lithological fields such a scheme is needed to clearly define lithological terms currently used in the description of sedimentary sequences

interpretation of the nitrogen isotopic composition of precambrian sedimentary rocks assumptions and perspectives nitrogen isotope compositions in sedimentary rocks d 15 n sed are routinely used for reconstructing cenozoic n biogeochemical cycling and are also being increasingly applied to understanding the evolution of ancient environments here we review the existing knowledge and rationale behind the use of d 15 n sed as a proxy for the precambrian n biogeochemical cycle with the aims of i identifying the major uncertainties that affect analyses and interpretation of nitrogen isotopes in ancient sedimentary rocks ii developing a framework for interpreting the precambrian d 15 n sed record iii testing this framework against a database of precambrian d 15 n sed values compiled from the literature and iv identifying avenues of focused research that should increase confidence in interpreting precambrian d 15 n sed data this review highlights the intrinsic complexity of the d 15 n sed proxy and the significant effort that remains to realize its potential specifically it is crucial to gain a better understanding of how and when diagenesis and metamorphism affect the d 15 n of bulk and kerogen bound nitrogen ultimately more data are required to apply statistics to interpreting d 15 n sed variability within given geological time intervals finally numerical modeling of the d 15 n sed variability expected in different environments under varying redox scenarios is necessary to establish a predictive template for interpreting the ancient nitrogen isotope record in spite of the challenges facing the application of this proxy to the precambrian the existing d 15 n sed record shows several features possibly related to the stepwise oxygenation of the surface environment underlining the potential for nitrogen isotopes to reveal clues about the evolution of early earth

cenomanian to campanian carbon isotope chemostratigraphy from the western interior basin u s a abstract late cretaceous carbon isotope curves generated for localities in europe asia and the deep sea records have provided the foundation for development of a contiguous intercontinental chemostratigraphic framework despite the development of carbon isotope records from selected stratigraphic intervals in the western interior basin however a comprehensive 13c record comparable to those developed in europe and asia and from odp sites had not yet been completed this study reports a new high resolution cenomanian to campanian carbon isotope record for the central western interior basin of north america that makes a key contribution to the intercontinental correlation the curve is correlated to the well developed molluscan biostratigraphic framework for the western interior basin as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the 13c data were derived the new 13c record reflects not only major perturbations in the global carbon cycle such as the mid cenomanian event and the cenomanian turonian ocean anoxic event 2 but also smaller excursions that have been recognized in records from europe and asia this shows that the western interior shallow epeiric sea was not isolated for any appreciable part of cenomanian to early campanian time it consistently recorded changes in the global marine carbon cycle observed elsewhere a critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised late cretaceous time scale assignment of revised ages to western interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the western interior where similar carbon isotope records have been generated this chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

influence of lateral particle advection and organic matter degradation on sediment accumulation and stable nitrogen isotope ratios along a productivity gradient in the canary islands region abstract we compare total and biogenic particle fluxes and stable nitrogen isotope ratios 15n at three mooring sites along a productivity gradient in the canary islands region with surface sediment accumulation rates and sedimentary 15n higher particle fluxes and sediment accumulation rates and lower 15n were observed in the upwelling influenced eastern boundary region ebc compared to the oligotrophic sites north of gran canaria european station for time series in the ocean canary islands estoc and north of la palma lp the impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi year flux record at the estoc remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0 8 and total nitrogen preservation of about 0 4 of the estimated export production higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50 of the particulate matter at the estoc was derived from allochthonous sources low 15n values in the lower traps of the estoc and lp point to a source region influenced by coastal upwelling we conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources this could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions

cyanobacteria proliferation in the cenomanian turonian boundary interval of the apennine carbonate platform immediate response to the environmental perturbations associated with oae 2

nitrate reduction sulfate reduction and sedimentary iron isotope evolution during the cenomanian turonian oceanic anoxic event onset of the oae in italy have unusually low bulk d 57 fe values unlike those found in the black shale livello bonarelli deposited during the oceanic anoxic event itself these latter conform to the phanerozoic norm for organic rich sediments pyrite formation in the pre oae black shales has apparently taken place via dissimilatory iron reduction dir within the sediment a suboxic process that causes an approximately 2 fractionation between a lithogenic fe iii oxide source and fe ii aq in contrast bacterial sulfate reduction bsr at least partly in the water column characterized the oae itself and was accompanied by only minor iron isotope fractionation this change in the manner of pyrite formation is reflected in a decrease in the average pyrite framboid diameter from 10 to 7 mm the gradual albeit irregular increase in fe isotope values during the oae as recorded in the italian section is taken to demonstrate limited isotopic evolution of the dissolved iron pool consequent upon ongoing water column precipitation of pyrite under euxinic conditions given that evidence exists for both nitrate and sulfate reduction during the oae it is evident that redox conditions in the water column were highly variable in both time and space

spatial extent and degree of oxygen depletion in the deep proto north atlantic basin during oceanic anoxic event 2 massive organic matter burial due to widespread ocean anoxia across the cenomanian turonian boundary event 94 ma resulted in a major perturbation of the global carbon cycle the so called oceanic anoxic event 2 oae2 the characteristics and spatial distribution of the oae2 deposits that formed in the deep basin of the proto north atlantic remain poorly described however here we present proxy data of redox sensitive trace elements e g mo fe al corg ptot and mn for oae2 sediments from five deep sea drilling project and ocean drilling program sites located in the deep proto north atlantic basin our results highlight that bottom waters in the entire deep proto north atlantic were anoxic during most of oae2 furthermore regressions of mo with total organic carbon content toc previously shown to document the degree of water mass restriction confirm that the water circulation in the proto north atlantic basin was severely restricted during oae2 comparison of these values to mo toc ratios in the present day black sea suggests a renewal frequency of the deep proto north atlantic water mass of between 0 5 and 4 ka compared to a maximum of 200 years for the present day northern atlantic the plenus cold event a cooler episode during the early stages of oae2 hypothesized to be caused by declining pco2 due to extensive burial of organic matter appears to have led to temporary re oxygenation of the bottom water in the deep proto north atlantic basin during oae2

short term euxinia coinciding with rotaliporid extinctions during the cenomanian turonian transition in the middle neritic eastern north atlantic inferred from organic compounds oceanic anoxic event 2 oae2 which occurred during the cenomanian turonian c t transition and lasted 1 m y is characterized by a positive global carbon isotopic excursion and stepwise extinctions in marine biota to examine temporal variations in the dissolved oxygen content of the water column shallow marine c t sediments from northern spain were analyzed for concentrations of dibenzothiophenes which are indicators of euxinic depositional environments and 2 3 6 trimethylarylisoprenoids which probably indicate photic zone euxinia the positive excursion in 13 c values of carbonates is accompanied by short term 10 3 10 4 yr and long term 10 5 yr increases in dibenzothiophene and 2 3 6 trimethylarylisoprenoid concentrations suggesting that the bottom water and photic zone of the eastern marginal sea of the north atlantic ocean were euxinic two of the short term increases in organic compound concentrations took place just after the last occurrence of the planktonic foraminifers rotalipora greenhornensis and r cushmani these transient maxima indicate that the extinction of both planktonic foraminifers was due to short term oaes lasting 10 3 10 4 yr

styles of sedimentation beneath svalbard valley glaciers under changing dynamic and thermal regimes glacier beds provide crucial information concerning past and present ice dynamics and thermal regime in this paper we present structural and sedimentological data from four valley glaciers austre lovenbreen midtre lovenbreen vestre lovenbreen and austre broggerbreen on broggerhalvoya nw spitsbergen the main focus of this paper is midtre and austre lovenbreen two typical high arctic land based polythermal valley glaciers the former has a long record of documentation regarding its response to twentieth century climatic warming structural mapping on the glacier surface and analysis of sediments in the proglacial area of midtre lovenbreen indicate that the dynamic regime and thermal structure of the glacier have changed through time dynamically midtre lovenbreen was once heavily crevassed and relatively fast moving but now is virtually crevasse free and slow moving the sedimentary record indicates that extensive areas of this glacier were wet based when it was in a more advanced state probably at its neoglacial maximum late nineteenth early twentieth centuries during this advance a thin deforming layer of diamicton commonly fluted was draped over the existing morphology in the presently exposed proglacial area this morphology consisted of large streamlined ridges aligned parallel to ice flow erosion of the underlying bedrock appears to have been limited radio echo soundings of the glacier show that at present it is characterized by a polythermal basal thermal regime with wet based subglacial conditions only beneath its thicker parts modification of the bed is limited under this thermal regime and as a result the supraglacial environment dominates modern sedimentation comparative studies on austre lovenbreen which also is probably polythermal indicate similar sedimentary characteristics and facies associations although here there are much more extensive areas of striated bedrock indicative of former basal sliding in contrast both austre broggerbreen and by analogy vestre lovenbreen are known to be predominantly cold based collectively these four glaciers suggest a trend of glacier recession and thinning accompanied by a change in thermal regime from predominantly wet based through partly frozen to completely frozen this study suggests that svalbard valley glaciers have several dynamic modes and that glaciers switch between these modes largely as a reaction to changes in mass balance

beware intercepts interpreting compositional ratios in multi component sediments and sedimentary rocks the corganic ntotal ratio and the hydrogen index hi are commonly used to describe the bulk composition the sources and the post depositional alteration of sedimentary organic matter data from modern sediments and sedimentary rocks frequently show significant intercepts and strong linear relationships in plots of corganic vs ntotal and of s2 vs corganic for many different data sets demonstrating that the ratios are not constant across the range of organic matter contents the presence of such intercepts whose causes are well understood means that changes in corganic ntotal and hi as corganic changes cannot be used to infer different organic matter sources and or post depositional alteration or degrees of organic matter preservation of different sediment fractions moreover the strong linear regressions in such x y plots imply that the organic fraction of sediments and sedimentary rocks in any given setting or stratigraphic section generally has a uniform composition

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

the neogene east antarctic ice sheet a dynamic or stable feature abstract this paper is a review of the history and behaviour of the east antarctic ice sheet during the late neogene and is a response to the publication of sugden et al 1993a the case for a stable east antarctic ice sheet in geografiska annaler 75a 4 the antarctic ice sheet is a critical factor in the global climate and oceanographic system knowledge of its historical development is critical to understanding global palaeoceanographic and palaeoclimatic systems and their development the webb harwood hypothesis proposes that the ice sheet while being present in antarctica for more than 40 ma was until recently ca 2 5 ma a dynamic feature waxing and waning under a more temperate climatic and glaciologic regime the stabilistic hypothesis proposes that the current ice sheet has existed in its present cold and polar form for at least the last 14 ma the case for a stable east antarctic ice sheet is the clearest statement of the stabilistic argument to date the authors find support for their viewpoint by presenting evidence from several geologic data bases that does not support their own null meltdown hypothesisr which they deem to be equivalent to the webb harwood hypothesis thereby they conclude supporting the stabilistic hypothesis however their conclusions are weakened by failure to reject their null hypothesis conflict between the meltdown and webb harwood hypotheses infraction of geological laws and poor application of stratigraphic principles several issues are highlighted here as important for direction of future research and discussion concerning late cenozoic antarctic glacio climatic history

neogene glacial record from the sirius group of the shackleton glacier region central transantarctic mountains antarctica neogene glacigenic strata collectively referred to as the sirius group are widely distributed throughout the transantarctic mountains the group is particularly well exposed near the head of shackleton glacier 858109 to 858409s on roberts massif and at bennett platform these deposits are critical for examining the nature of former ice flow from the east antarctic ice sheet into the ross embayment the sirius group rests on a glacially grooved and striated pavement named herein the shackleton erosion surface the sub sirius group surface on roberts massif was of low relief and glaciogenic sediment was deposited on it as a sheet of uniform thickness at bennett platform stratigraphic sections attain a thickness of 110 m thick and are subdivided into the shackleton glacier formation maximum thickness 98 m and the overlying bennett platform formation 44 m separated by an unconformity a third older lithified diamictite containing wood fragments occurs as clasts within these formations and as boulders in the modern lateral moraines of shackleton glacier the dominant facies massive diamict is interpreted primarily as lodgement till other facies indicate glaciofluvial and glaciolacustrine deposition facies associations suggest deposition either by sliding temperate or by polythermal glaciers under much warmer conditions than those of today widespread large and small scale faulting has affected the sirius group and underlying rocks to the extent that inland exposures are over 500 m higher than those to the north over a distance of 30 km thus at the time of deposition of the sirius group the mountains were probably lower and the ice sheet was much thinner

the expression of the cenomanian turonian oceanic anoxic event in tibet the gongzha section of tibet china is located at the northern margin of the indian plate se tethys and is characterized by hemipelagic grey marls and marly limestones light grey limestones and silty limestones but no organic rich sediments high resolution biostratigraphy reveals an expanded cenomanian turonian ct boundary interval and the 13c record includes the main features of the classical positive carbon isotope excursion that characterizes the ct oceanic anoxic event the biotic response inferred from the foraminifera suggests that oxic to dysoxic conditions prevailed except for a short interval marked by peak abundance of heterohelix that indicates a significantly dysoxic environment during the 13c b peak excursion the overall decreasing trend in redox sensitive trace elements rste during the maximum 13c excursion confirms the absence of significant longer lasting anoxia in the gongzha section enrichments in rste are linked to phases of increased detrital input chemical weathering indices suggest that the upper cenomanian sediments accumulated under an increasingly hot and humid climate that culminated near the ct boundary in the early turonian lower weathering indices suggest a warm drier climatic regime with reduced continental runoff phosphorus mass accumulation rates show a significant peak at the onset of the positive 13c excursion followed by a decrease up to the basal turonian this pattern is positively correlated with the long term decrease in detrital index as also observed in numerous other ct boundary sections e g eastbourne pueblo and whadi el ghaib sinai long term phosphorus accumulation in the gongzha section is therefore associated with changes in detrital input the overall decreased detrital input can be explained by the increasingly remote continental sources due to the major transgression at the end of cenomanian coupled with changes in continental weathering intensity linked to increasingly more arid climate conditions

nitrogen cycling during the cretaceous cenomanian turonian oceanic anoxic event ii low 15n values ranging from 1 2 to 3 9 and atomic carbon nitrogen c n ratios of 25 50 are characteristic of black shales deposited during the cenomanian turonian boundary interval and oceanic anoxic event ii oae ii an observed antithetic relationship between c n ratios and 15n could suggest a predominance of terrestrially derived organic matter or a diagenetic control on 15n variability shifting bulk 15n values lower however hydrogen indices hi generally 450 and a positive correlation of hi with c n mitigates against a significant terrestrial organic matter fraction high c n values are likely the result preferential degradation of labile n rich compounds during early diagenesis and loss of n as ammonium from sediments through time a hypothetical model that considers the degradation of a 15n enriched labile protein fraction yields only small 1 2 negative shifts in 15n however 15n depletion during diagenesis is contrary to normal isotope kinetics which should result in 15n enrichment of bulk organic matter therefore we conclude that the bulk 15n values in this study reflect primary changes in the nitrogen cycle the 15n data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient nitrogen poor phosphorus replete waters during oae ii and from the mid cenomanian to santonian at demerara rise the low 15n values which are significantly lower than bulk 15n values in modern regions where nitrogen fixation is known to be important probably result from a more significant fraction of dissolved inorganic nitrogen being produced by nitrogen fixation during the peak of oae ii a marked shift to lower 15n values is observed this shift possibly reflects greater utilization of 15n depleted ammonium during a chemocline upward excursion cue dominance of low 15n values from other periods of more widespread marine anoxia is likely the result of similar processes

patterns of local and global redox variability during the cenomanian turonian boundary event oceanic anoxic event 2 recorded in carbonates and shales from central italy careful evaluation of the local geochemical conditions in past marine settings can provide a window to the average redox state of the global ocean during episodes of extensive organic carbon deposition these comparisons aid in identifying the interplay between climate and biotic feedbacks contributing to and resulting from these events well documented examples are known from the mesozoic era which is characterized by episodes of widespread organic carbon deposition known as oceanic anoxic events this organic carbon burial typically leads to coeval positive carbon isotope excursions geochemical data are presented here for several palaeoredox proxies cr ti v mo zn mn fe speciation i ca and sulphur isotopes from a section exposed at furlo in the marche umbrian apennines of italy that spans the cenomanian turonian boundary here oceanic anoxic event 2 is represented by a ca 1 m thick radiolarian rich millimetre laminated organic rich shale known locally as the bonarelli level iron speciation data for thin organic rich intervals observed below the bonarelli level imply a local redox shift going into the oceanic anoxic event with ferruginous conditions i e anoxic with dissolved ferrous iron transiently developed prior to the event and euxinia i e anoxic and sulphidic bottom waters throughout the event itself pre oceanic anoxic event enrichments of elements sensitive to anoxic water columns were due to initial development of locally ferruginous bottom waters as a precursor to the event however the greater global expanse of dysoxic to euxinic conditions during the oceanic anoxic event greatly reduced redox sensitive trace metal concentrations in seawater pyrite sulfur isotopes document a positive shift leading into the oae carbonate i ca ratios were generally low suggesting locally reduced bottom water oxygen conditions preceding the event and relatively increased o2 concentrations post event combined the furlo geochemical data suggest a redox stratified water column with oxic surface waters and a shallow chemocline overlying locally ferruginous bottom waters preceding the event globally widespread euxinic bottom waters during the oceanic anoxic event followed by chemocline shallowing but sustained local redox stratification following the event this article is protected by copyright all rights reserved

the cenomanian turonian extinction and oceanic anoxic event evidence from southern tibet deep shelf locations on the perigondwanan margin of southern tibet record a major extinction of foraminifera and calcareous nannoplankton in the latest cenomanian top of the rotalipora cushmani zone this is followed by a low diversity survival interval that straddles the cenomanian turonian boundary whiteinella archaeocretacea zone during which only low diversity surface water dwelling foraminifera and nannoplankton and microfilaments are present rapid recovery in the early turonian saw the appearance of new species the reappearance of many lazarus species and the reestablishment of a diverse community of planktonic foraminifera that included a range of shallow to deep water column dwellers the extinction and survival intervals coincide with the development of dysaerobic facies characterised by small sized burrows and moderately large sized framboid pyrite populations at no time does the water column appear to have become sulfidic this study indicates that the end cenomanian oceanic anoxic and extinction events were also manifested in moderately high southerly palaeolatitudes on the southern margin of the tethyan ocean thereby increasing the known extent of this global event albeit with the proviso that the anoxic event was a dysoxic one

the nitrogen isotope composition of sediments from the proto north atlantic during oceanic anoxic event 2 sediment records of the stable isotopic composition of n 15n show light 15n values at several sites in the proto north atlantic during oceanic anoxic event 2 oae 2 at the cenomanian turonian transition 94 ma the low 15n during the event is generally attributed to an increase in n2 fixation and incomplete uptake of 4 for phytoplankton growth a compilation of all reliable data for the proto north atlantic during oae 2 demonstrates that the most pronounced negative shift in 15n from pre oae 2 to oae 2 occurs in the open ocean but with 15n never lower than 3 using a box model of n cycling for the proto north atlantic during oae 2 we show that n2 fixation is a major contributor to the 15n signal especially in the open ocean incomplete uptake of 4 for phytoplankton growth is important in regions dominated by downwelling with lateral transport of 4 acting as a major source in the southern proto north atlantic where bottom waters were euxinic the light 15n signature is largely explained by upwelling of 4 our study provides an overview of regional differences in 15n in the proto north atlantic and highlights the role of lateral exchange of water and nutrients in addition to local biogeochemical processes in determining 15n values of oae 2 sediments

on the sedimentological origin of down core variations of bulk sedimentary nitrogen isotope ratios 1 the bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the south china sea site 17940 and ocean drilling program odp site 1144 differs by up to 2 during the last glacial period given their close proximity both core sites are located in the same biogeographic zone and nutrient regime and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions in an attempt to resolve this offset we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary 15n namely the variable contribution of inorganic n to bulk n in the sediment and the grain size dependence of bulk 15n we find that neither effect singly or in combination is sufficient to explain the significant 15n offset between the two down core records by elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site this study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts such as odp site 1144

c isotope stratigraphy and paleoenvironmental changes across oae2 mid cretaceous from shallow water platform carbonates of southern mexico the stratigraphic and geochemical record of the mid cretaceous cenomanian turonian oceanic anoxic event 2 oae2 has been studied in numerous tethyan and proto atlantic hemi pelagic pelagic successions but little data comes from nearshore carbonate successions from the proto pacific region here we present the results of a combined stratigraphic and 13c study of c t platform carbonates from southern mexico which were deposited within the proto pacific two scales of sedimentary cyclicity are recognized high frequency peritidal and subtidal cycles 0 4 8 m display little evidence of cycle capping subaerial exposure and are not correlative between sections these relationships suggest that the amplitudes of high frequency sea level changes were minimal during the peak mid cretaceous greenhouse longer term transgressive regressive sequences 18 40 m are correlated between sections and using 13c trends can be correlated with sequences developed in northern europe and india the mexican successions were sampled at a high resolution 10 ky for stable isotopes inorganic organic carbon and oxygen total organic carbon insoluble residues and trace metals the 13ccarb curve matches global trends including 6 distinct isotopic stages permitting identification of oae2 despite the lack of characteristic anoxic facies using the 13ccarb trends we tie the previously identified ammonite planktonic foram and nannofossil biostratigraphy from england and the western interior seaway of colorado into the mexican sections the initiation of oae2 defined by an abrupt positive 3 4 13c shift coincides with a long term sea level rise though the sedimentary expression of the deepening is no greater than that observed for any of the other sea level events across the studied interval oae2 termination transition from gradually decreasing to background 13c values is not associated with a particular sea level trend stratigraphic changes in insoluble residues proxy for continental sediment discharge across oae2 are not correlative between sections and do not show consistent systematic relationships with 13c or sea level variations therefore do not support the hypothesis that oae2 was associated with increased continental derived nutrient influx two peaks in trace metal concentrations coincide with the abrupt increase in 13c ratios onset of oae2 and during the transition from elevated to decreasing 13c values near the c t stage boundary these trends are similar to those recorded in coeval deposits of the western interior seaway and are consistent with the hypothesis that oae2 development was related to the release of reduced metals during the short lived 1 my caribbean oceanic plateau basalt eruption in this scenario oxidation of the metals depleted the existing low dissolved o2 concentrations and thermally buoyant plumes of seawater enriched in biolimiting elements mixed with surface waters stimulated primary productivity and further reduced o2 concentrations leading to widespread anoxia and a large positive 13c shift

upper cretaceous carbon and oxygen isotope stratigraphy of hemipelagic carbonate facies from southern tibet china a high resolution carbon isotope curve derived from upper cretaceous hemipelagic sediments cropping out at tingri southern tibet shows similarities to patterns established on other continents notably in the presence of a well defined positive excursion across the cenomanian turonian boundary where 13 c values exceed 3 5 from the upper turonian to the lower campanian 13 c values generally decline apart from a minor positive excursion in the middle coniacian a trend that departs from that recorded from europe relatively low 13 c values c 1 at the santonian campanian and campanian maastrichtian boundaries in tibet define a prominent broad positive excursion centred in the middle campanian and terminated by an abrupt fall towards the close of the stage when compared with data from europe and north africa the 13 c values of the tibetan section are generally lower by c 1 5 except for the middle campanian positive excursion where values 13 c c 2 are comparable with those documented from europe and north africa these differences are interpreted as reflecting variable mixing of water masses carrying different carbon isotope signatures such that areas close to the major sinks of marine organic carbon recorded higher 13 c values than those located in more distal regions oxygen isotope ratios albeit affected by diagenesis may record a palaeotemperature signal

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

fluctuations of the oxygen minimum zone at the end of oceanic anoxic event 2 reflected by benthic and planktic fossils the latest cenomanian to early turonian late cretaceous section at vallecillo mexico contains a continuous and highly fossiliferous sedimentary record across the late oceanic anoxic event oae 2 and shows similar distributions of benthic inoceramids and planktic foraminifers during this period of an expanded oxygen minimum zone omz we suggest that these synchronous abundance changes result from similar environmental vulnerability of planktotrophic larval stages of inoceramids and deeper dwelling planktic foraminifers and that these synchronous changes reflect the expansion of the omz the abundances of ammonites and fishes used as independent control groups do not correlate and rule out a preservational bias ammonites fishes and their hatchlings thus populated shallower water depths than inoceramid gametes and planktic foramininifers the improving conditions at the end of oae 2 resulted in the dispersal of new inoceramid and foraminiferal morphotypes

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

heterogeneous oxygenation states in the atlantic and tethys oceans during oceanic anoxic event 2 abstract the cenomanian turonian boundary ca 93 5 ma is marked by an episode of profound environmental change including a major perturbation of the carbon cycle and an oceanic anoxic event oae 2 here we present molybdenum mo isotope variations within the oae 2 interval for four sections from the western tethys furlo and la contessa and the north atlantic odp site 1276 and dsdp site 367 the main target of this study is to investigate the extent of reducing conditions truly global in extent or restricted to poorly ventilated restricted deep basins with particular reference to the relationship between the change in the oxygenation state of the ocean and the link to global perturbations of the carbon cycle recorded in carbon isotopes all four sections show fluctuations in the redox sensitive trace metal rste distribution suggesting rapid variations in local redox conditions ranging from anoxic to euxinic the rste enrichment factors efs also suggest different depositional conditions and paleoceanographic processes in the western tethys versus the north atlantic whereas the north atlantic sites show evidence of weak watermass restriction associated with the action of a particulate shuttle within the water column the efs of the tethyan sections are characteristic of unrestricted marine systems mo isotopes show surprisingly negative values through the tethyan sections at the onset of oae 2 an increasing trend in mo 98 is observed with values ranging from 0 6 to 0 6 during the second half of oae 2 the mo 98 curve shows a progressive shift towards more negative values in the north atlantic mo 98 signatures from odp site 1276 show a similar behaviour as observed in the western tethys at dsdp site 367 mo isotopes are generally heavier during oae 2 fluctuating around an average value of 1 1 this is consistent with fully euxinic conditions and the black shales deposited may have recorded the seawater signature during oae 2 the mo isotope signature is lighter than the modern ocean value 2 3 and suggests a higher proportion of bottom water euxinia 10 although this estimate is greater than the euxinic fraction in the modern ocean our results challenge the suggestion of a globally euxinic deep waters during oae 2 the variations in mo toc ratios within the north atlantic and tethys oceans are in good agreement with a general drawdown of mo within the oae interval suggesting a general increase in anoxic conditions during oae 2 our results highlight the role of local parameters in the development of euxinia even during period of widespread anoxia such as oaes

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

further evidence for the development of photic zone euxinic conditions during mesozoic oceanic anoxic events periods in earth history characterized by extensive organic carbon deposition so called oceanic anoxic events oaes are the subject of considerable scrutiny insight into the extent of anoxic conditions in the water column has been provided by the reported occurrence of derivatives of isorenieratene a carotenoid found only in green sulphur bacteria and thus indicative of photic zone euxinia i e a water column containing free h 2 s in north atlantic deep sea sediments deposited during the cenomanian turonian boundary oae2 bonarelli event in this study we have used the distributions of chlorophyll and bacteriochlorophyll degradation products maleimides 1 h pyrrole 2 5 diones and high molecular weight porphyrins to examine further the cenomanian turonian boundary oae2 as well as other oaes of the early toarcian posidonienschiefer event and early aptian selli event in particular methyl isobutyl me i bu maleimide on structural grounds appears to be diagnostic of green sulphur bacteria this compound occurs in five of seven examined marls that record the early toarcian oae marche umbria italy further expanding the geographical range of toarcian sediments where evidence for photic zone euxinic conditions has been found me i bu maleimide occurs in three of six black shales spanning the livello selli marche umbria italy the type locality for the aptian oae1a providing the first evidence for photic zone euxinic conditions during this event with respect to the cenomanian turonian oae maleimide evidence for photic zone euxinic conditions was found in all the north atlantic sites investigated including those characterized by relatively organic lean sediments several tethyan sites and one site off western australia these data indicate that euxinic conditions were common in the water column during mesozoic oceanic anoxic events

20 my of nitrogen fixation during deposition of mid cretaceous black shales on the demerara rise equatorial atlantic ocean abstract thick sequences of dark colored organic carbon rich finely laminated santonian cenomanian claystones and homogeneous albian siltstones were recovered from ocean drilling program sites 1257 1258 and 1260 on the demerara rise in the western equatorial atlantic ocean total organic carbon toc concentrations vary from 2 to over 20 wt in the sequences of black shales that were deposited over a period of 20 million years similarly long periods of elevated marine productivity implied by the high toc concentrations are uncommon in the geological record and must have required unusual paleoceanographic conditions the importance of nitrogen fixing bacteria to sustaining the amplified export production of organic matter is indicated by 15n values that remain between 4 and 0 a range that is notably less positive than the average of 5 for modern ocean sediments although containing mostly marine organic matter the black shales have toc tn molar ratios between 20 and 40 that mimic those of land plant organic matter the anomalously large toc tn ratios suggest selective organic matter degradation probably associated with low oxygen conditions in the water column that favored preservation of nitrogen poor forms of organic matter relative to nitrogen rich components deposition of black shales on the demerara rise was likely a consequence of the mid cretaceous warm and wet greenhouse climate that strengthened thermohaline stratification of this part of the atlantic ocean which in turn encouraged bacterial nitrogen fixation enhanced primary production magnified organic matter export and ultimately established anoxic conditions at the seafloor that improved preservation of organic matter for much of the 20 my period represented by these thick sequences

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

age and paleoenvironment of the cenomanian turonian global stratotype section and point at pueblo colorado biostratigraphy and stable isotopes indicate that the global stratotype section and point gssp at pueblo contains an essentially complete sedimentary record across the global ocean anoxic event oae 2 and the cenomanian turonian boundary the oae 2 d 13 c shift occurred over a period of about 90 ky and was accompanied by a major sea level transgression which at its peak was marked by an incursion of oxygen rich waters creating a benthic oxic zone that lasted about 100 ky a mid cenomanian d 13 c shift sea level transgression and faunal turnover occurred about 2 my before oae 2 d 18 o values of the planktic foraminifer hedbergella planispira and its relative abundance changes reveal cyclic variations in surface salinity due to alternating freshwater influx and marine incursions whereas dominance by the low oxygen tolerant heterohelix species indicates a well developed oxygen minimum zone omz for most of the middle to late cenomanian and early turonian profound faunal changes accompanied these oceanographic events including the extinction of 30 of the species assemblage and an equal gain in evolutionary diversification though the overall combined relative abundances of outgoing and incoming species were less than 2 and 4 respectively of the total assemblages the faunal turnover began with the sea level transgression and rapid increase in d 13 c values and accelerated with the influx of oxygen rich deep water increased water mass stratification and competition during the benthic oxic zone the incursion of oxygen rich deep waters at this time was also observed in morocco and may represent a global event of a still unknown source d 2003 elsevier b v all rights reserved

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

the landform and sediment assemblage produced by a tidewater glacier surge in kongsfjorden svalbard abstract this paper describes the landform and sediment assemblage produced by a surge in 1948 of the kongsvegen kronebreen tidewater glacier complex in northwest spitsbergen the main geomorphological products of this advance are two large thrustmoraine complexes on opposite sides of the fjord and a system of geometrical ridges revealed on glacier decay the thrust moraines are composed largely of diamicton sandy and muddy gravel gravelly sand sand and mud with minor laminites all of these appear to be derived from the fjord floor and represent both fine fjord basin sediments and coarse grounding line fan deposits thrusting was the principal mode of emplacement of the sediment onto the adjacent land areas during the 1948 advance however the geomorphology of the thrust moraine complexes on either side of the fjord is quite different reflecting a transpressive regime on the southwest side mainly long ridges and a normal compressive regime on the northeast side short ridges and pinnacles of a hummocky nature the advance which produced the moraine complex has previously been attributed to a surge of kongsvegen but the glaciological and geomorphological evidence suggests that the advance involved both kongsvegen and kronebreen comparison of the landform assemblage produced by this event with that produced by other tidewater glacier surges demonstrates the diverse range of landform assemblages associated with glacier surges or other episodes of rapid flow within glaciomarine environments

late neogene sirius group strata in reedy valley antarctica a multiple resolution record of climate ice sheet and sea level events late neogene sirius group strata from tillite spur and quartz hills in the reedy glacier area antarctica demonstrate the variability in sirius group facies and contrasts sirius group strata deposited at high and low paleo elevation respectively the tillite spur and quartz hills formations pliocene are formally defined here the tillite spur formation type section crops out on the edge of the wisconsin plateau overlooking tillite spur it comprises 32 m of alternating coarse gray conglomerate and muddy olive brown diamictites the quartz hills formation type section crops out above the western margin of reedy glacier in a pre existing cirque towards the southern end of the quartz hills it comprises c 100 m of alternating massive diamictites and rhythmically interbedded sandstone and laminated mudstones which were deposited close to sea level and subsequently rapidly uplifted 500 m myr 1 to their present elevation at c 1500 m three orders of paleoclimatic variability are recorded in the sirius group strata from reedy valley 1 recycled marine microfloras in glacial diamictites indicate intervals of marine incursion into the antarctic cratonic interior co occurring with reductions in the east antarctic ice sheet 2 an advancing and retreating paleo reedy glacier deposited a glacial interglacial sequence alternating on a 10 100 kyr scale 3 centimeter and millimeter stratification in strata of the quartz hills formation record annual kyr scale variability

changes in ocean denitrification during late carboniferous glacial interglacial cycles rates of denitrification below some oceanic upwelling zones reach a maximum during periods when sea level rise was fastest throughout the pleistocene glacial cycles nitrogen isotope data from north american shales deposited 300 million years ago during palaeozoic glaciations are indicative of a similar pattern

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

nitrogen and carbon cycle perturbations through the cenomanian turonian oceanic anoxic event 2 94 ma in the vocontian basin se france abstract oceanic anoxic event 2 spanning the cenomanian turonian boundary was an episode of major perturbations in global biogeochemical cycles characterized by the widespread burial of organic carbon in both oceans and epicontinental basins in the vocontian basin se france this event was expressed by the deposition of the niveau thomel a succession of interbedded dark shales grey marls and bioturbated carbonates as observed in the lambruisse section analyses of the total organic carbon toc content combined with the concentrations of redox sensitive trace elements revealed that conditions fluctuated from oxic to suboxic anoxic during the deposition of the niveau thomel transient periods of deoxygenation were related to perturbations in nutrient cycling reflected by near zero to negative 15n signatures indicative of increased diazotrophy the development of deoxygenated conditions in the vocontian basin was likely preconditioned by hydrographically restricted conditions as confirmed by mo vs u enrichments reducing bottom water ventilation associated with water column stratification intervals of reoxygenation were likely linked to climate induced changes in particular a phase of regional or global cooling associated with a drop in pco2 called the plenus cold event pce resulted in vigorous reoxygenation of the vocontian basin

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

end cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the northwestern pacific ocean abstract the second largest cretaceous extinction event coincided with an oceanic anoxic event at the cenomanian turonian c t boundary this high resolution analysis of upper bathyal benthic foraminifera in central hokkaido japan indicates that the extinction event occurred in the latest cenomanian over a period of 0 2 m y 93 6 93 4 ma analysis of the dissolved oxygen index based on calcareous benthic foraminiferal wall thickness size and morphology shows that low oxygen 0 1 1 5 ml l conditions developed during a period of 0 15 m y before the c t boundary and 1 5 m y after the minimum oxygen condition 0 1 1 ml l prevailed twice during this interval similarly benthic foraminiferal extinctions occurred twice in concert with initiation of the two minimum oxygen levels coincidence of the two extinction horizons with developemt of low oxygen conditions suggests that the main cause of the extinctions was formation of dysoxic intermediate water this report suggests that the global c t boundary extinction event occurred in a stepwise fashion during the latest cenomanian 0 2 0 5 m y due to development of widespread oceanic anoxic dysoxic conditions within intermediate water masses

astronomical constraints on global carbon cycle perturbation during oceanic anoxic event 2 oae2 abstract oceanic anoxic event 2 oae2 was a major disturbance in global carbon cycling and transient climate disruption triggered by a pulse of volcanic co2 although this well studied perturbation to the ocean atmosphere system offers a unique opportunity to better understand abrupt climate change in response to co2 forcing the origin evolution and duration of the event are still debated due in large part to the temporal resolution of existing oae2 records and uncertainty over the duration of the overall perturbation and c cycle shifts within it here we report coupled magnetic susceptibility ms and carbon isotope time series of 2 5 to 5 0 5 kyr resolution from an expanded oae2 interval from southern tibet china ms cyclicity indicates short eccentricity modulation permitting the construction of a high precision orbital timescale which when integrated with the high resolution 13 c carb record fully constrains the timing and nature of onset through recovery of oae2 revealing finer scale structure than previously recognized abrupt coupled shifts in 13 c carb and ms and changing phase relationships in step with transitions between high and low long eccentricity indicate orbitally linked changes in marine carbon cycling and monsoon dynamics superimposed on repeated wholesale oceanographic changes in particular the high resolution tibetan record reveals dynamic shifts in the phasing relationship of ms and 13 c which suggests that the initiation of ocean anoxia was probably not orbitally forced this finding is in sharp contrast with the paradigm of orbitally forced ocean anoxia conversely the new record suggests that termination of anoxia was likely orbitally forced and superimposed on a dramatic oceanographic change

enhanced productivity rather than enhanced preservation led to increased organic carbon burial in the euxinic southern proto north atlantic ocean during the cenomanian turonian oceanic anoxic event three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes