mid cretaceous sequence stratigraphy and sedimentary cyclicity in the western paris basin abstract cenomanian and turonian depositional patterns of the western paris basin are interpreted in terms of sequence stratigraphy a system tract analysis of the epicontinental normandie basin with pelagic chalks and of the maine platform covered by clastics provides evidence for relative changes in coastal onlap various minor uncomformities are related to these changes of sea level the four global cycles uza or zc 2 2 2 5 of haq et al 1987 1988 are recognised while an additional one is proposed for the geslinianum zone in addition periodic rhythmic cycles are commonly registered within the chalk expressed by the repitition of various facies enhanced both by biosedimentary processes and diagenetic alteration these elementary climatic cycles allow accurate lithostratigraphic correlations during this period when the sea level peaked on the tectonically passive border of the armorican block the paris basin appears to record a detailed set of events which can be correlated with those in the atlantic boreal and tethyan provinces

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

geochronology and calibration of global milankovitch cyclicity at the cenomanian turonian boundary new 40 ar 39 ar geochronology and global cyclostratigraphic calibration provide high resolution insights into the timing of geochemical fluctuations across oceanic anoxic event ii oae ii five new 40 ar 39 ar data from a single section in western canada suggest an age of 96 4 1 ma for the cenomanian turonian c t boundary this is 3 m y older than previously dated time series analysis e g wavelet transform reveals that oae ii was synchronously deposited worldwide over a period of 320 k y the preservation and stationarity of milankovitch cyclicity in sections across the atlantic indicates that no major fluctuations in sedimentation rate occur across the oae ii except for a minor short term decrease in the rate just before the c t boundary a 13 c org increase of 2 took place at the beginning of oae ii over a period of 110 k y and likely represents a period of worldwide excessive organic carbon burial during transgression leading to a 12 c depletion of seawater and sedimentation this interval was followed by a three step decrease to pre oae ii 13 c values

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

the early toarcian and cenomanian turonian anoxic events in europe comparisons and contrasts two intervals of mesozoic time are demonstrably of sufficient geological brevity to qualify readily for the term anoxic event the earlyfalciferum zone orexaratum subzone of the toarcian and thewhiteinella archaeocretacea interval zone that straddles the cenomanian turonian boundary both periods of time saw regional deposition of anomalously organic rich strata black shales accompanied by a positive 2 pdb carbon isotope excursion in coeval biogenic carbonates and significant faunal change the duration of both events was probably less than half a million years and both were preceded by regional erosion and possible upwelling coincident sea level rise and transgression is likely a european view of these events however spotlights some significant differences whereas thefalciferum zone organic matter is generally more concentrated and more hydrogen rich on the palaeo european shelf than on the tethyan continental margins the reverse holds true for the black shales formed during thewhiteinella archaeocretacea interval zone furthermore the carbon isotope composition offalciferum zone organic matter from both north european and tethyan sites is anomalously negative compared to that developed in thewhiteinella archaeocretacea interval zone differing planktonic organisms may have been involved and their possible diverse ecological requirements may go some way to explaining the nature and distribution of facies deposited during these two events

geologic structure and neotectonics of the north african continental margin south of sicily abstract marine geological and geophysical data together with drilling information indicate that the north african passive continental margin has been subjected to extension and wrenching after it collided with the northern part of sicily the area of the tripolitania basin jarrafa trough melita and medina bank and the ragusa malta plateau has formed part of a sinking passive margin since the dispersal of gondwanaland at about 180 my ago as observed from geohistory diagrams a record of rifting in a nw se direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data the rifting started during the neocomian and lasted until the eocene when activity became minor a pre middle miocene period of northward subduction of oceanic crust is inferred from the geology in ne sicily uplift of the northern part of the african margin after collision in the middle miocene is seen in wells in southern sicily after the messinian a rift and dextral shear zone established itself across the african margin from the strait of sicily to the medina ridge in the lonian basin the zone is marked by up to 1 7 km deep grabens narrow active wrench faulted channels volcanic fissures and local uplifted keilhorsts such as malta this zone which varies in width from 100 to 35 km forms the southern boundary of a microplate which includes sicily we speculate that the present motion of this microplate is partly due to the eastward movement of the calabrian arc with the sicilian block over the last remaining oceanic lithosphere in the eastern mediterranean

radium mobility and the age of groundwater in public drinking water supplies from the cambrian ordovician aquifer system north central usa abstract high radium ra concentrations in potable portions of the cambrian ordovician c o aquifer system were investigated using water quality data and environmental tracers 3h 3hetrit sf6 14c and 4herad of groundwater age from 80 public supply wells psws groundwater ages were estimated by calibration of tracers to lumped parameter models and ranged from modern 1 myr in the most downgradient confined portions of the potable system more than 80 and 40 percent of mean groundwater ages were older than 1000 and 50 000 yr respectively anoxic fe reducing conditions and increased mineralization develop with time in the aquifer system and mobilize ra into solution resulting in the frequent occurrence of combined ra rac 226ra 228ra at concentrations exceeding the usepa mcl of 185 mbq l 5 pci l the distribution of the three ra isotopes comprising total ra rat 224ra 226ra 228ra differed across the aquifer system the concentrations of 224ra and 228ra were strongly correlated and comprised a larger proportion of the rat concentration in samples from the regionally unconfined area where arkosic sandstones provide an enhanced source for progeny from the 232th decay series 226ra comprised a larger proportion of the rat concentration in samples from downgradient confined regions concentrations of rat were significantly greater in samples from the regionally confined area of the aquifer system because of the increase in 226ra concentrations there as compared to the regionally unconfined area 226ra distribution coefficients decreased substantially with anoxic conditions and increasing ionic strength of groundwater mineralization indicating that ra is mobilized to solution from solid phases of the aquifer as adsorption capacity is diminished the amount of 226ra released from solid phases by alpha recoil mechanisms and retained in solution increases relative to the amount of ra sequestered by adsorption processes or co precipitation with barite as adsorption capacity and the concentration of ba decreases although 226ra occurred at concentrations greater than 224ra or 228ra the ingestion exposure risk was greater for 228ra owing to its greater toxicity in addition 224ra added substantial alpha particle radioactivity to potable samples from the c o aquifer system thus monitoring for ra isotopes and gross alpha activity gaa is important in upgradient regionally unconfined areas as downgradient and gaa measurements made within 72 h of sample collection would best capture alpha particle radiation from the short lived 224ra

stratigraphic sequences and their chronostratigraphic correlation abstract the exxon sequence models of posamentier and coworkers incorporate two concepts which i question they suggest that rivers grade to a bayline but evidence from modern major rivers indicates that they do not they also proposed that fluvial sedimentary accomodation space is generated by the seaward shift in equilibrium profiles during sea level fall but this is too simplistic a model based on the use of schematic continental margin configurations which do not incorporate real slope and relief data in most cases a fall in base level leads to deltaic progradation and upstream fluvial incision most coastal plain fluvial wedges result from two processes sea level rise with the drowning and filling of estuaries and active source area tectonism major tectonic events adjacent to foreland basins such as terrane collisions lead to the development of sequences of third order type duration approximately 1 15 m y changes in intraplate stress regimes resulting from changes in regional plate kinematics have a similar episodicity and can be shown to be responsible for some third order cycles on extensional continental margins examination of the chronostratigraphic basis of the mesozoic cenozoic cycle chart of haq and coworkers reveals internal inconsistencies and an unrealistic downplaying of the built in potential for error this chart is not an approved global standard and it should be used with extreme caution

petroleum geology of tunisia recent discoveries and important oil shows have proven the existence of hydrocarbons in newly identified depocenters and reservoirs in general except for some areas around the producing fields tunisia is largely underdrilled the national company etap has decided to release data and to publish a synthesis on the petroleum geology of tunisia the geology of tunisia provides a fine example of the contrast between alpine folding which typifies northern tunisia and the african craton area of the saharan part eastern tunisia corresponds to an unstable platform forming plains or low hills and extending eastwards to the shallow pelagian sea there are a wide variety of basins central and northern tunisia represents a front basin the saharan ghadames basin or the chott trough are sag basins the gulf of gabes was formed as a distension margin the gulf of hammamet is a composite basin and several transversal grabens cut across the country including offshore and are rift type basins all these features are known to be oil prolific throughout the world two large fields and many modest size pools are known in tunisia oil and gas fields in the surrounding countries namely the saharan fields of algeria and libya the large bouri fieldmore offshore tripolitania and discoveries in the italian part of the straits of sicily suggest a corresponding potential in tunisia exposed paleogeographic and structural maps balanced sections and examples of fields and traps will support an optimistic evaluation of the future oil exploration in tunisia less

organic rich sedimentation at the cenomanian turonian boundary in oceanic and coastal basins in the north atlantic and tethys one of the most striking results of the deep sea drilling project is the proof that organic rich sediments have a widespread geographical distribution during the period from upper cenomanian to middle turonian such sediments were drilled at north atlantic dsdp sites 105 135 137 138 367 398 551 603 they are also present from outcrops or oil wells on the shelf of the african continental margin senegal tarfaya and agadir basins in the tethys former alboran block southern spain algeria tunisia and umbrian apennines italy and in the north sea although these sediments have different lithologies and depositional environments from shelf areas to the deep sea their study mainly based on organic geochemistry with additional data on sedimentology biostratigraphy and palaeo bathymetry suggests that a unique pulse of organogenic accumulation characterizes the cenomanian turonian boundary event ctbe the content and type of organic matter are related to the depositional environment and organic preservation the organogenic accumulation is distributed according to various trends off the african continental margin the organic content increases from onshore areas to the shelf casamance area and moreover increases also in deep sea areas with a gradual transition from terrestrial type iii to marine type ii the best preservation of the organic matter being in the deepest areas i e site 367 off the american continental margin site 603 shows the same toc and type of organic matter as at site 105 the ctbe is also well recorded in the northern part of the atlantic celtic margin north sea by a drastic lithological change black shales within chalks but the type of organic matter is mainly terrestrial in the tethyan area the organic matter is of marine origin and well preserved results are compared with those of pratt 1984 from the western interior basin of the usa different hypotheses to explain this synchronous widespread accumulation of organic matter are discussed 1986 the geological society

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

paleooceanography of the mesogean sea based on ostracods of the northern tunisian continental shelf between the late cretaceous and early paleogene a new method analysis used in the study of the el kef section north western tunisia led to the paleooceanographic reconstruction of the mesogean between late cretaceous and early paleogene several changes observed are in fact worthy of particular mention paleobathymetrically the area changed from an upper bathyal environment of about 400 m deep to an outer shelf domain of 100 50 m furthermore the oxygen minimum zone o m z became highly intense at a the cretaceous tertiary transition catastrophic event b the p1 p2 boundary intense thermic stratification and c between p4 and p6 very active paleoproductivity in this last episode the continental shelf environment was subjected to intense upwelling responsible for the formation of a prephosphatic environment at water sediment interface the paleooceanographic history of phosphates in the gafsa metlaoui basin is in fact in perfect stratigraphic and paleoenvironmental agreement with the paleobathymetric evolution of the kef region finally paleooceanographic communication between the mesogean and the north atlantic was at this period highly free because of lack of hydrologic relations between the north atlantic and the norwegian sea

basement control in the development of the early cretaceous west and central african rift system abstract the structural framework of the precambrian basement of the west and central african rift system wcars is described in order to examine the role of ancient structures in the development of this early cretaceous rift system basement structures are represented in the region by large pan african mobile belts built at ca 600 ma surrounding the 2 ga west african congo and sao francisco cratons except for the small gao trough eastern mali located near the contact nappe of the pan african iforas suture zone along the edge of the west african craton the entire wcars is located within the internal domains of the pan african mobile belts within these domains two main structural features occur as the main basement control of the wcars 1 an extensive network of near vertical shear zones which trend north south through the congo brazil nigeria niger and algeria and roughly east west through northeastern brazil and central africa the shear zones correspond to intra continental strike slip faults which accompanied the oblique collision between the west african congo and sao francisco cratons during the late proterozoic 2 a steep metamorphic nw se trending belt which corresponds to a pre pan african ca 730 ma ophiolitic suture zone along the eastern edge of the trans saharian mobile belt the post pan african magmatic and tectonic evolution of the basement is also described in order to examine the state of the lithosphere prior to the break up which occurred in the earliest cretaceous after the pan african thermo tectonic event the basement of the wcars experienced a long period of intra plate magmatic activity this widespread magmatism in part relates to the activity of intra plate hotspots which have controlled relative uplift subsidence and occasionally block faulting during the paleozoic and the early mesozoic this tectonic activity was restricted to west of the hoggar west of air and northern cameroon during the late jurassic early cretaceous the st helena mantle plume may have had an important effect in weakening the lithosphere across a broad zone from brazil to sudan however causes of extension and stretching are likely to be found in a plate tectonic framework at that time the opening of both the indian and atlantic oceans were the dominant forces which favoured the development of the wcars and its propagation by strike slip movements and extensional displacements along pre existing pan african lithospheric zones of weakness

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

climatically influenced distribution of gymnodinium catenatum during the past 2000 years in coastal sediments of southern norway abstract dinoflagellate cyst analysis of cored late holocene sediments from the norwegian coast of the skagerrak and northern north sea confirms the conclusions of previous studies from the kattegat that climate influenced the quantitative distribution of gymnodinium catenatum graham 1943 these studies provide some of the first data on the effect of small scale climatic changes on one component of the phytoplankton during the past 2000 years in core 9310 from the skagerrak as in previous cores from the kattegat g catenatum cysts increase proportionally from about ad 0 to peak amounts at about ad 900 1200 and 1450 corresponding to periods of relatively warmer climate proportional decreases in g catenatum correspond to periods of cooler climate in the 900s and 1300s and to the colder climate of the little ice age climax in the 1600s in the site of core 9307 from the north sea coast higher proportions of g catenatum 15 were probably reached between 300 and 1000 years later than in the other cores due to the location of this site being closer to the biogeographic limit for high proportions of the species new results also suggest that high proportions of the species 2 58 were confined to open coastal waters south of bergen norway living and fossil cysts of g catenatum in this region are small compared with reported sizes elsewhere 24 40 vs 37 60 m and may not be conspecific with g catenatum irrespective of their taxonomy the quantitative distribution of these cysts is influenced by climatic changes and they are a reliable indicator of warmer water in more open coastal waters of scandinavia during the late holocene

relationship between zn pb ore and oil accumulation processes example of the bou grine deposit tunisia abstract the bahloul formation of cenomanian turonian age combines qualities of a potential source rock for oil and of a rich lead zinc mineralization in the bou grine area on the border of the lorbeus massif diapir tunisian atlas analysis of 46 core samples from 7 boreholes drilled within or outside the mine area revealed the richness in organic matter of the bahloul formation 4 5 toc its low maturity t max 423 c and marine planktonic origin hi 600 mg hc g 1 toc abnormally high values of the oil production index up to about 30 indicate the presence of migrated oil in the mine and in samples from the northeast boreholes this information is confirmed by other observations high relative amounts of hydrocarbons in the bitumen extracts high pr ph ratios and high amounts of light naphthenic hydrocarbons the abundance of the latter components observed in chromatograms where n alkanes are nearly absent may indicate the development of a biodegradation process during migration however this biological activity may have exerted the greatest intensity at the expense of indigenous organic constituents in the mine area where considerable amounts of hopanes and steranes were observed all these data supported by geological observations allow us to propose the following genetic model for the bou grine deposit the bahloul formation which associates high amounts of organic matter zinc and lead on a regional scale zn pb 0 5 2 and a high porosity could have served as a source for the migrated oil and for the metals necessary to the mineralization as well as a conduit for the oil and metal bearing brines an intense biological activity developed at the expense of the organic content of the bahloul formation and of the sulfate from the adjacent triassic diapir may have produced the hydrogen sulfide responsible for ore deposition

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

oil window in the gulf of suez basin egypt petroleum in the gulf of suez is multisourced mainly by restricted marine cretaceous to eocene beds the campanian carbonates of the sudr formation and the turonian shales of the abu qada formation are high quality sources other proven sources are carbonate and shale intervals within other sub miocene formations geothermal modeling calibrated by maturation measurements suggests that the organic rich lower miocene marls may not be mature enough to expel hydrocarbons north of the morgan amal fields area but are mature to the south this could be related mainly to a gradual increase in thermal gradient from north to south 20 55 degree c km a few anomalies do exist however thermal gradients are generally higher in areas where oil accumulated the depth of peak generation ranges between 5 200 m to the north and 3 300 m to the south the geographic variations in heat flow maturation depths and age of source rocks are not reflected in the timing of hydrocarbon migration during the middle miocene a short lived salinity crisis resulted in the deposition of massive thick evaporites that form the ultimate seal in the gulf the accompanying rapid burial of the underlying sub miocene potential source intervals caused them all to sequentially enter the oil window within a verymore short time soon after the evaporites accumulated this timing was perfect for hydrocarbon preservation after seal deposition and major disturbing regional tectonic events the almost simultaneous migration from all the source beds resulted in mixed multisourced hydrocarbon accumulations less

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

micropalaeontological and geochemical evidence of mid cretaceous dysoxic anoxic palaeoenvironments in the sergipe basin northeastern brazil

the stratigraphic and palaeogeographic setting of the late cenomanian anoxic event the late cenomanian carbon isotope excursion can be shown to be synchronous over most areas of the globe where micropalaeontological data are adequate the sedimentological variations seen in these different areas are thought to be due to palaeobathymetry the relationship between this anoxic event and the major faunal change in the late cenomanian is described

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

palaeogeography of africa during the cretaceous period abstract a first attempt is made to synchronize the major palaeogeographical events of the african cretaceous where recognizable palaeoclimatological interpretations are given an overview of the nature of the continental margins and the plate tectonic setting for africa during the cretaceous provides a convenient backdrop for presenting the palaeogeographical development of the continent lacustrine deposits occur along the line of south atlantic rifting late jurassic oceanic crust in the south atlantic dates from the valanginian with continental volcanism adjacent to the walvis ridge continuing until the albian locally there was a barremian incursion in southeast africa the falkland plateau and walvis ridge areas created shallow water barriers in the aptian which facilitated the massive accumulation of salt tectono eustatic transgressions took place in the middle to late albian cenomano turonian late turonian to coniacian and campano maastrichtian anoxic conditions prevailed during the late jurassic agulhas bank falkland plateau aptian albian the cenomanian turonian and the coniacian these are relatable to the epicontinental transgressional maxima and the heavy influx of organic debris however there was no campano maastrichtian anoxic event

integrated depositional model for the cenomanian turonian organic rich strata in north africa abstract during the late cenomanian early turonian c t oceanic anoxic event oae2 organic rich strata was deposited in rift shelf basins and slopes across north africa and in deep sea basins of the adjacent oceans based on a review of published and unpublished information this paper documents the distribution and organic richness of c t strata across the whole region within a palaeogeographic framework and systematically analyses the conditions and processes which controlled their deposition previously the c t in north africa has been most intensively studied in southern morocco tarfaya and tunisia only little data is availabe for other parts of north africa namely algeria libya and egypt because distribution of c t corg strata there becomes more patchy a general decrease in peak organic richness and black shale thickness occurs from west to east partly as a result of upwelling along the moroccan atlantic coast and the absence of upwelling in the eastern mediterranean area furthermore in the confined central atlantic the oxygen minimum zone omz in many places reached down to the deep sea floor 3 4 km while the lower limit of the omz along the north african tethys was much shallower and underlain by oxic water masses as documented by high resolution biostratigraphic and chemostratigraphic data c t black shale deposition in most areas outside the upwelling zone are restricted to a strong eustatic latest cenomanian transgressive phase triggered by this sea level rise the omz impinged onto the north african continental shelf and the margins of intrashelf basins which mostly formed during the early cretaceous as halfgrabens important units containing c t organic rich strata in the region are the atlantic tarfaya black shales morocco western sahara black shales and phtanites in the moroccan and algerian atlas the bahloul fm in the se constantine basin and in northern and central tunisia the etel fm in the sirte basin the al hilal fm in cyrenaica libya the abu roash fm in the abu gharadig and fayium basins western desert egypt the daliyya fm along the ne sinai palestine isreal coast and the shueib fm in west central jordan

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

organic facies of middle cretaceous black shales in deep north atlantic the middle cretaceous black shales of the deep north atlantic consist of alternating layers of sediment rich in total organic carbon toc that contains abundant amorphous types of organic matter and sediment poor in toc that contains mostly woody and coaly types of organic matter the amorphous materials are derived mostly from marine organisms in the eastern north atlantic off africa in the caribbean and on the demerara rise off surinam and from higher land plants in the western north atlantic and off europe marine amorphous material is important off africa because this was an area of upwelling and highly productive surface water amorphous marine organic matter was deposited across the entire north atlantic basin in the cenomanian in response to an ocean wide upwell ng event connected with the opening of the equatorial atlantic the difference between the toc rich and background toc layers reflects deposition of the former under reducing conditions which allowed the preservation of labile amorphous materials of marine and terrestrial orgin and of the latter under oxidizing conditions when nearly all that was preserved was refractory organic material

cretaceous synsedimentary tectonics in the atlas system of central morocco cretaceous sediments in central morocco were deposited in various depositional environments and comprise an undetermined lower cretaceous base up to maastrichtian the sedimentary columns show a similar facies evolution basal unconformities conglomeratic layers and significant differences in thicknesses reflect pre and synsedimentary vertical tectonic movements these tectonic movements took place along large ne sw striking fault systems one of the major features of the present tectonic framework permanent displacement of the subsidince maxima in time and space indicate the development of small tectonic blocks which were tilted and or compressed between the fault zones high sedimentation rates in areas of strong subsidence however prevented the evolution of intraplatformbasins although tectonic influence was important eustatic sea level changes ruled the whole sedimentary regime

organic geochemical characteristics of atlantic ocean cretaceous and jurassic black shales abstract organic rich black shales have been observed in mesozoic strata penetrated by the deep sea drilling project dsdp these black shales represent a major carbon sink in the geologic record of paramount importance in establishing the origin of the black shales is the character and level of preservation of the organic matter within the north and south atlantic sample suite three types of organic matter were identified well preserved marine organic matter moderately well preserved terrestrial material and severely altered and or recycled organic matter the spatial and temporal distribution of the three types of organic matter suggest that the organic rich shales are not of a single origin these shales have developed as a result of high continental runoff from regions rich in sedimentary carbon and or elevated terrestrial productivity or high marine productivity and preservation in part due to rapid deposition by turbidity currents or mass slumping a detailed analysis of individual and closely spaced dsdp sites further documents that anoxia was probably not the result of synchronous major expansions of anoxic bottom water masses but represents isolated occurrences

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

cretaceous palaeogene sedimentation patterns and structural evolution of the tunisian shelf offshore the pelagian islands central mediterranean abstract the late jurassic palaeogene structural evolution of the eastern tunisian platform exerted a significant control on the depositional architecture of the 4 5 km thick carbonate marl succession that was deposited on this african plate margin throughout this period widespread jurassic platform carbonates nara fm underwent extension and subsidence throughout the early cretaceous this extension resulted in the formation of a system of nw se trending normal faults coupled with minor antithetic structures flanking half grabens up to 20 km wide these subsiding basins hosted the deposition of shallow water carbonates interfingered with marls and fine grained siliciclastics this succession which is up to 2 5 km thick is interpreted to have been deposited during a syn rift episode which continued until the mid aptian overlying basinal marls and carbonates seal the nw se syn rift extensional faults thus marking a post rift stage that extends up to the eocene post rift sedimentation ends in the middle upper eocene with the deposition of platform carbonates relating to the halk el menzel formation which lies unconformably above different stratigraphic levels of the underlying basinal carbonates this is capped by an erosional surface of regional extent from the latest cretaceous onwards compressional activity occurred on this part of the pelagian block partially reactivating lower cretaceous extensional structures thrusting and folding generated uplift and associated erosion leading to the development of local unconformities and hiatuses at different levels in the stratigraphic column this compressional event marks the onset of convergence between the african and european plates and thus the transition from a passive margin to a foreland in this area the structural history of this part of the african plate margin displays similar evolutionary trends to other tethyan passive margins which were established during the jurassic and early cretaceous times when extensional events split pre existing carbonate platforms

petroleum geology of east central tunisia the tectonic features of tunisia are complex and include folds all types of faults evaporite diapirs and the saharan flexure which separates a stable paleozoic province on the south from a subsidence zone of mesozoic and cenozoic strata of the offshore ashtart and tripolitania basins the remainder of the offshore region is mostly stable shelf of the pelagian craton which also extends onshore the present study focused on this shelf where two carbonate intervals contain proven hydrocarbon reservoirs the metlaoui formation of earliest eocene ypresian age and the zebbag formation of late cretaceous turonian age regionally well defined belts of metlaoui carbonates trend northwest on the northeast are open marine deep water micrites and marls with abundant planktonic foraminifers thick bars of nummulitid packstone grainstone were deposited in shallow water at an angle to the paleoshelf the reservoir is confined largely to the bars and visible effective porosity is best developed in those areas among the foraminifers filled with sand size nummulitid debris where secondary solution enlargement has occurred this lithology tested oil in two recent wildcat wells and is a commercial reservoir at sidi el itayem and ashtart fields distribution of zebbag carbonates is more complex a northwest trending platform was bounded on three sides by deep water where shale and micrite with planktonic foraminifers were deposited predominately back reef and lagoonal foraminifer rudist wackestones and packstones occur in narrow belts apparently controlled at least locally by block faulting they tested oil in two recent discoveries the most significant porosity is interparticle generally enlarged by solution in foraminifer packstones but intraparticle voids in foraminifers and rudists commonly contribute to the porosity analyses of surface and subsurface samples identified the bahloul basal turonian and bou dabbous ypresian formations as source rocks fluorescence spectra of several oils were compared with extracts from these samples and indicate the bahloul to be the source of oils in recent metlaoui and zebbag discoveries

the cenomanian turonian anoxic event in europe an organic geochemical study received 14 october 1988 revised 14august 1989 accepted 31 august 1989 thirty two sediment samples mainly black shales from cenomanian turonian organic rich sequences in europe and tunisia were examined by organic geochemical techniques the results of molecular analyses indicate that all the black shales are dominated by marine derived organic matter from both algal and bacterial sources with only a minor terrestrial component oxygen deficient conditions prevailed during the deposition of the black shales although interbedded non laminated organic lean horizons indicate that oxygen deficiency was intermittent at some sites the presence of 17cx h 18c h 211 h 28 30 bisnorhopane in some black shale samples from shallow shelf areas may be evidence for severely oxygen depleted conditions possibly in association with upwelling and an oxygen minimum layer overall the organic geochemical data are in agreement with a depositional model whereby an oxygen minimum layer developed in response to high surface productivity this oxygen minimum layer may have extended over a considerable thickness of the water column 1000 m in some areas we report the first observation of an a ring methylated c29 hopane namely methyl 17e h 18 h 211 h 28 30 bisnorhopane the environmental significance of this compound cannot yet be assessed although in the sample in which it occurs the direct parallel between the carbon number distribution of the hopanes and that of the methylhopanes suggests either that they have the same biological origin or that methylation of hopanoids may have occurred possibly during diagenesis

chemostratigraphy versus biostratigraphy data from around the cenomanian turonian boundary a detailed isotopic profile is presented for a stratigraphically expanded cenomanian turonian boundary section in chalk facies exposed at eastbourne sussex and compared with data from pueblo colorado in both sections macro and micropalaeontological markers first appearances and disappearances are well constrained and their relative positions and relationship to the structure of the carbon isotope curve are identical this consistent relationship between two independent phenomena one geochemical the other biostratigraphical is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon isotope excursion in these two areas this interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon isotope excursion in europe and north america

global correlation of cenomanian upper cretaceous sequences evidence for milankovitch control on sea level we have investigated the sequence stratigraphy of two widely separated marine cenomanian successions in southeast india and northwest europe and used high resolution ammonite biostratigraphy to demonstrate that sea level changes are globally synchronous and therefore must be eustatically controlled sequence scale sea level changes in the cenomanian were driven by the long eccentricity cycle 400 k y in the milankovitch band we hypothesize that during pre quaternary time the third order sequences of vail and haq are essentially a sediment response to sea level changes driven by the 400 k y cycle construction of a relative sea level curve for the marginal marine succession in india demonstrates that the short term sea level changes are rapid 10 100 m m y and have a magnitude of 2 20 m glacioeustasy is a possible but unproven driving mechanism

palaeoenvironmental evolution of the late cretaceous sequence in the tarfaya basin southwest of morocco abstract the late cretaceous sedimentary evolution of the tarfaya basin is reviewed based on late albian campanian outcrops and two cored exploration wells s13 and s75 with a stratigraphic range from the early cenomanian to the late turonian standard sedimentological and micropalaeontological methods were used together with clay mineralogy and organic geochemistry two distinct depositional environments were found the first is late albian early middle cenomanian in age and dominated by terrigenous silici and bioclastic sediments containing primarily terrestrial organic matter with a low organic content abundant illite and chlorite eroded from crystalline rocks outcropping in the anti atlas mountain and mauritanides is present as is abundant kaolinite reworked from soils surrounding the tarfaya basin the second environment comprises late cenomanian campanian sediments characterized by pelagic marls and limestones with a high organic content and a abundant pelagic macro and microfauna these sediments which were probably deposited in an upwelling system are characterized by higher contents of smectite