Marine Anoxia Research Articles

The Lilliput effect in the aftermath of the end-Permian extinction event

Early Triassic animal body fossils and trace fossils are small relative to those in older and younger intervals. Size decreases sharply through the end-Permian extinction event and Permian/Triassic boundary, and the smallest sizes are encountered in the parvus and isarcica Zones of the earliest Induan. Animals appearing within these two zones are also exceedingly small, compared to younger congenerics and conspecifics. Temporary, dramatic size decrease of surviving taxa in the immediate aftermath of the extinction event is an example of the Lilliput effect (coined by [Urbanek, A., 1993. Biotic crises in the history of Upper Silurian graptoloids: a palaeobiological model. Historical Biology 7, 29–50.]). Body size increases somewhat from the carinata Zone (mid-Induan) but remains depressed for the duration of the Early Triassic, and pre-extinction sizes are not commonly recorded until at least the Middle Triassic. Marine and terrestrial faunas appear to be similarly affected. The Lilliput effect and longer term size reduction could be the result of several factors. Environmental parameters such as marine anoxia, due to low atmospheric concentrations of oxygen at this time coupled with sluggish ocean circulation in a greenhouse world, and food shortage are the likely proximal causes for the Early Triassic Lilliput effect. No single cause can explain all the observations, and a combination of factors are likely to be involved.

A new supercontinent self-destruct mechanism: evidence from the Late Triassic–Early Jurassic

We present a new conceptual model where supercontinents, by focusing subduction on narrow areas of the 670 km mantle discontinuity, trigger superplume events and initiate their own fragmentation. This supercontinent-triggered superplume mechanism for continental break-up is examined in light of the Mesozoic fragmentation of Pangaea–Gondwana. We summarize the evidence for a superplume event that occurred between 227 and 183 Ma ago, during the Late Triassic–Early Jurassic break-up of Pangaea–Gondwana. The evidence reviewed includes flood magmatism, kimberlite emplacement, plate reorganization and tectonism (including ophiolite obduction events), reversal rate frequency of the geomagnetic field, marine anoxia, deposition of carbon-rich sediments, including oil source rocks and coal, the carbon isotope record, major mass extinctions, and global sea levels. This Late Triassic–Early Jurassic superplume event was comparable in scale with those in the late Proterozoic ( c . 800 Ma) and during Cretaceous times ( c . 120–80 Ma). Similar to the mid-Cretaceous event, an extended phase of plume magmatism is implicated, with two oceanic and three continental large igneous provinces being emplaced.

Nitrogen cycling during the Cretaceous, Cenomanian‐Turonian Oceanic Anoxic Event II

Low δ15N 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 δ15N could suggest a predominance of terrestrially derived organic matter or a diagenetic control on δ15N variability shifting bulk δ15N 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 δ15N. 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 δ15N values in this study reflect primary changes in the nitrogen cycle. The δ15N 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 δ15N values, which are significantly lower than bulk δ15N 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 δ15N values is observed. This shift possibly reflects greater utilization of 15N‐depleted ammonium during a chemocline upward excursion (CUE). Dominance of low δ15N values from other periods of more widespread marine anoxia is likely the result of similar processes.

Evidence for recurrent Early Triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations

Carbon cycle disturbance associated with mass extinction at the end of the Permian Period continued through the Early Triassic, an interval of approximately 5 million years. Coincidence of carbon cycle stabilization with accelerated Middle Triassic biotic recovery suggests a link between carbon cycling and biodiversity, but the cause of Early Triassic carbon isotope excursions remains poorly understood. Previous modeling studies have focused exclusively on the initial negative excursion in δ 13C across the Permian–Triassic boundary and have not addressed the cycles of positive and negative excursions observed through the Early Triassic. This study uses a simple carbon cycle box model to investigate potential causes underlying the series of Early Triassic carbon isotope excursions and to assess possible relationships between isotope excursions and coeval patterns of carbonate deposition. According to the model, introduction of carbon with the isotope composition of volcanic CO 2 produces small negative carbon isotope excursions followed by larger and more protracted positive excursions. Positive excursions result because increased pCO 2 causes warming, enhancing marine anoxia and associated regeneration of phosphate and thus allowing greater productivity. In addition, carbonate weathering is more sensitive than organic carbon weathering to changes in atmospheric pCO 2 and climate, causing an increase in the overall δ 13C composition of weathered carbon. Therefore, the full Early Triassic record of negative and positive carbon isotope excursions can only be accounted for within the model by several pulses of carbon release characterized by varying mixtures of organic and mantle isotope compositions. Thermal metamorphism of coal and carbonate rocks in the crust of the Siberian craton during eruption of the Siberian Traps flood basalts provides the most plausible mechanism for such a carbon release scenario. If multiple episodes of CO 2 release account for Early Triassic carbon cycle instability (regardless of their precise trigger), then cessation of CO 2 release is likely to explain acceleration of biotic recovery early in the Middle Triassic.

Anomalous hopane distributions at the Permian–Triassic boundary, Meishan, China – Evidence for the end-Permian marine ecosystem collapse

Molecular and carbon isotopic geochemistry of hopanes in marine sediments of the Meishan section in Changxing County, Zhejiang Province of China, were studied to reveal biotic and environmental changes across the Permian–Triassic boundary (PTB) and the Wuchiapingian–Changhsingian boundary (WCB). The hopane distribution at the PTB is characterized by high ratios of moretane/hopane, Tm/Ts, Tm/C 30 hopane, C 31/C 32 hopane and hopane/sterane. This hopane distribution is anomalous for these marine sediments, but it is typical of coal measure strata and soils. Two possible genetic mechanisms for such an anomaly are suggested: (1) these hopanes were terrigenous and most probably originated from acidified soil and peat. This mechanism implies that the marine primary production and aerobic bacteria production at the PTB were extremely low. (2) This hopane distribution was possibly caused by freshening and acidification of the upper water column during the end-Permian to Early Triassic marine stagnation and stratification. This hopane anomaly, which coincides with the end-Permian mass extinction and carbon-isotope excursion, may signal the end-Permian mass extinctions and marine and terrigenous ecosystem collapse. The 13C-enriched hopanes with the fingerprint of typical anoxic marine shales, coupled with an n-C 15– n-C 17-dominated distribution of n-alkanes, strongly indicate that the organic matter around the WCB at Meishan originated mainly from cyanobacteria. The corresponding positive δ 13C carbonate, and higher total organic carbon and hydrocarbon index (HI) values, strongly suggest that high marine primary production and marine anoxia caused by intermittent cyanobacterial blooms, resulted in the local mass extinction at Meishan.

Response of the marine infauna to Triassic–Jurassic environmental change: Ichnological data from southern England

The trace fossil record through the Triassic–Jurassic boundary interval is examined at three sites in central and southern England (St. Audrie's Bay, Somerset; Pinhay Bay, Devon; and Long Itchington, Warwickshire). The lower ‘Pre-Planorbis Beds’ of the Blue Lias Formation record low ichnotaxonomic diversity, low bioturbation intensity, small burrow diameters, and an absence of deep tier bioturbation. The stepwise reappearance of ichnotaxa following this interval is similar at the three sites, suggesting similar rates of recovery in the benthic marine ecosystem and highlighting the potential contribution of these trace fossils to stratigraphic correlation. Mass extinction in the Late Triassic is increasingly linked to the emplacement of the Central Atlantic Magmatic Province (CAMP). Timing of the onset of CAMP volcanism in the UK is currently imperfectly known, but potentially occurred within either the Westbury Formation or the Lilstock Formation. If the onset of CAMP was within the Lilstock Formation, the modestly diverse trace fossil assemblage of the Langport Member of the Lilstock Formation suggests that emplacement of CAMP had little lasting effect on the marine benthos in central and southern England. The decline in benthic activity recorded in the ‘Pre-Planorbis Beds’ appears to be unrelated to the onset of CAMP and any associated environmental change. It is more likely related to an episode of marine anoxia. An episode of marine anoxia also provides a suitable causal mechanism for the reduction of infaunal tiering.

The fate of the homoctenids (Tentaculitoidea) during the Frasnian–Famennian mass extinction (Late Devonian)

ABSTRACTThe homoctenids (Tentaculitoidea) are small, conical‐shelled marine animals that are among the most abundant and widespread of all Late Devonian fossils. They were a principal casualty of the Frasnian–Famennian (F‐F, Late Devonian) mass extinction, and thus provide an insight into the extinction dynamics. Despite their abundance during the Late Devonian, they have been largely neglected by extinction studies. A number of Frasnian–Famennian boundary sections have been studied, in Poland, Germany, France, and the USA. These sections have yielded homoctenids, which allow precise recognition of the timing of the mass extinction. It is clear that the homoctenids almost disappear from the fossil record during the latest Frasnian ‘Upper Kellwasser Event’. The coincident extinction of this pelagic group, and the widespread development of intense marine anoxia within the water column, provides a causal link between anoxia and the F‐F extinction. Most notable is the sudden demise of a group, which had been present in rock‐forming densities, during this anoxic event. One new species, belonging to Homoctenus is described, but is not formally named here.

Changes in the extent of marine anoxia during the Early Jurassic: Evidence from molybdenum isotopes

Changes in the extent of marine anoxia during the Early Jurassic: Evidence from molybdenum isotopes

Preservation of primary REE patterns without Ce anomaly during dolomitization of Mid-Paleoproterozoic limestone and the potential re-establishment of marine anoxia immediately after the "Great Oxidation Event"

Comparison of shallow-water limestone and silicified dolomite from the Mid-Paleoproterozoic Mooidraai Formation, Transvaal Supergroup, South Africa, shows that the primary rare earth element (REE) distribution of these pure marine sedimentary carbonates has been preserved during dolomitization and silicification. Both lithologies display REE (and Y) patterns closely resembling those of present-day seawater, i.e. they show enrichment of the heavy relative to the light REE, positive anomalies of La, Gd and Lu, and super-chondritic Y/Ho ratios. However, these shallow-water carbonates lack any Ce anomalies, indicating that in the Mid-Paleoproterozoic the redox-level of surface water in the Griqualand-West sub-basin of the Kaapvaal Craton did not allow for oxidation of Ce(III). The absence of Ce anomalies from shallow water Mooidraai carbonates indicates a return to marine anoxia immediately after large amounts of marine sedimentary Mn oxides had been deposited in a highly oxygenated marine environment in the underlying Hotazel Formation. This suggests that the “Great Oxidation Event” in the Paleoproterozoic was a transition period characterized by strong fluctuations of the redox level of the Earth’s surface ocean.

Geochemical significance of the relative enrichment of pristane and the negative excursion of δ13CPr across the Permian-Triassic Boundary at Meishan, China

Changes in the distribution of isoprenoid hydrocarbons and in δ13Ckero or δ13CPr across the section from the Changxing Formation to the lower Yinkeng Formation at Meishan (the GSSP of PTB) are studied, in which a relative enrichment of pristane and a sharp shift in both δ13Ckero and δ13Cmole near the boundary are revealed. A possible mechanism for the abnormal accumulation of pristane near PTB is suggested: Lipids in some marine animals and their metabolites, rich in pristane, can be preserved and accumulate in some suitable depositing facies under certain special conditions, such as the catastrophic death of animals and/or developing of an anoxic water column, and thus the pristane enrichment occurs in the sediment. The occurrences of isoprenoid enrichment and high Pr/Ph ratios have been found in other typical marine anoxic sediments accompanied by mass extinction in various extent during the most important geological periods, such as Late Ordovician, end of Devonian, Early Jurassic and Late Cretaceous. These occurrences support to a certain extent the above mechanism that interprets the genesis of a high Pr/Ph ratio in some typical marine anoxic sediments. The synchronous sharp negative shifts in δ13Cmole, δ13Ckero and δ13Ccarb from Beds 24 to 26 of the Meishan profile indicate that a sudden and strong variation of carbon source in the atmosphere-ocean system occurred during the quick but equable evolution from the end-Permian to Early Triassic, and the coupling between the pristane enrichment and negative shift in δ13Ckero and δ13CPr may well indicate the importance of the release of methane hydrates and marine anoxia in the end-Permian mass extinction.

Basaltic volcanism and mass extinction at the Permo-Triassic boundary: Environmental impact and modeling of the global carbon cycle

The Siberian Traps represent one of the most voluminous continental flood basalt provinces on Earth. The mass extinction at the end of the Permian was the most severe in the history of life. In the present paper, these two major concurrent events that occurred are analysed and a geochemical model coupled with an energy balance model is used to calculate their environmental impact on atmospheric CO 2, oceanic δ 13C, and marine anoxia. The latitudinal temperature gradient is reduced relative to today, resulting in warmer temperatures at high latitudes. The warmer climate and the presence of fresh basaltic provinces increase the weatherability of the continental surfaces, resulting in an enhanced consumption of atmospheric CO 2 through weathering. First, the eruption of the Siberian traps is accompanied by a massive volume of 13C depleted CO 2 degassed from the mantle and added to the ocean through silicate weathering, thus lowering marine δ 13C. Second, the rapid collapse in productivity induces a strong decrease in the global organic carbon burial. This too tends to increase the proportion of light carbon in the ocean. These two effects can explain the low δ 13C values across the PT boundary, and methane release need not be invoked to explain the δ 13C fluctuations. It is proposed that the phosphorus cycle, which drives primary production in the model, plays an important role on the recovery of productivity and the δ 13C variations.

Unique marine Permian‐Triassic boundary section from Western Australia

A unique marine Permian‐Triassic boundary section containing rich oil source rocks has been continuously cored in a petroleum borehole from the Perth Basin of Western Australia. Such sequences, which provide a biostratigraphic and environmental record at the time of the largest extinction event of the past 500 million years, are globally rare, and this is the first to be documented in Australia. Throughout geological history there have been periods of global marine anoxia that commonly resulted in the widespread deposition of petroleum source rocks, most notably in the mid‐Cretaceous and Late Jurassic. An apparent paradox is that, previously, source rocks have not been recognised in association with the Permian‐Triassic boundary, despite widespread marine anoxia at this time. The Perth Basin source rocks contain abundant and unusual biomarkers, apparently related to the highly specialised and limited biota that flourished in the aftermath of the end‐Permian extinction event. Local conditions may have favoured source‐rock development, either due to higher productivity resulting from coastal upwelling or through enhanced preservation under strongly anoxic conditions.

Extent and duration of marine anoxia during the Frasnian–Famennian (Late Devonian) mass extinction in Poland, Germany, Austria and France

The intensity and extent of anoxia during the two Kellwasser anoxic events has been investigated in a range of European localities using a multidisciplinary approach (pyrite framboid assay, gamma-ray spectrometry and sediment fabric analysis). The results reveal that the development of the Lower Kellwasser Horizon in the early Late rhenana Zone (Frasnian Stage) in German type sections does not always coincide with anoxic events elsewhere in Europe and, in some locations, seafloor oxygenation improves during this interval. Thus, this anoxic event is not universally developed. In contrast, the Upper Kellwasser Horizon, developed in the Late linguiformis Zone (Frasnian Stage) in Germany correlates with a European-wide anoxic event that is manifest as an intensification of anoxia in basinal locations to the point that stable euxinic conditions were developed (for example, in the basins of the Holy Cross Mountains, Poland). The interval also saw the spread of dysoxic waters into very shallow water (for instance, reefal) locations, and it seems reasonable to link the contemporaneous demise of many marine taxa to this phase of intense and widespread anoxia. In basinal locations, euxinic conditions persisted into the earliest Famennian with little change of depositional conditions. Only in the continental margin location of Austria was anoxia not developed at any time in the Late Devonian. Consequently it appears that the Upper Kellwasser anoxic event was an epicontinental seaway phenomenon, caused by the upward expansion of anoxia from deep basinal locales rather than an ‘oceanic’ anoxic event that has spilled laterally into epicontinental settings.

Rapid marine recovery after the end-Permian mass-extinction event in the absence of marine anoxia

A new Early Triassic marine fauna is described from the Central Oman Mountains. The fauna is Griesbachian in age, on the basis of abundant conodonts and ammonoids, and was deposited in an oxygenated seamount setting off the Arabian platform margin. It is the first Griesbachian assemblage from a well-oxygenated marine setting and thus provides a test for the hypothesis that widespread anoxia prevented rapid recovery. The earliest Griesbachian (parvus zone) contains a low-diversity benthic fauna dominated by the bivalves Promyalina and Claraia. A similar level of recovery characterizes the immediate postextinction interval worldwide. However, the middle upper Griesbachian sedimentary rocks (isarcica and carinata zones) contain an incredibly diverse benthic fauna of bivalves, gastropods, articulate brachiopods, a new undescribed crinoid, echinoids, and ostracods. This fauna is more diverse and ecologically complex than the typical middle to late Griesbachian faunas described from oxygen-restricted settings worldwide. The level of postextinction recovery observed in the Oman fauna is not recorded elsewhere until the Spathian. These data support the hypothesis that the apparent delay in recovery after the end-Permian extinction event was due to widespread and prolonged benthic oxygen restriction: in the absence of anoxia, marine recovery is much faster.

Permian–Triassic boundary interval in the Abadeh section of Iran with implications for mass extinction: Part 1 – Sedimentology

The uppermost Permian strata of the Abadeh section in Iran consist of 56 m of skeletal limestone (Abadehian), that grades upward into 18 m of grey, bioturbated lime mudstone (Djulfian), which in turn grades upward to 18 m of red, nodular wackestone (Dorashamian) containing an abundant pelagic fauna. The overlying lowermost Triassic includes two enigmatic layers at its base. Immediately above the boundary is a 1-m-thick layer of inorganically precipitated synsedimentary carbonate cement. The cement is composed of 10–20-cm-long crystals oriented either perpendicular to the bedding or as dome-shaped features resembling botryoids. About 0.5 m of wackestone overlies the cement layer. The second layer is a 1.5-m-thick grainstone overlying the cement horizon and consists of recrystallised spherical grains (ooids or peloids). The remainder of unit ‘A’ is composed of 100+ m of grey, bioturbated to nodular lime mudstone. The lithofacies succession of the uppermost Permian is interpreted to represent deposition under increasing water depth, related to rising of relative sea level, which led to drowning of the carbonate platform to below storm wave base. Sedimentologic characteristics, lithology, wide distribution, and slow sedimentation rates indicate that strata immediately below the Permian–Triassic (P–T) boundary (Dorashamian interval) were deposited in deep, oxygenated waters. The enigmatic lowermost Triassic synsedimentary carbonate cement and grainstone layers are interpreted to have been deposited in shallow waters, indicating a rapid and major drop in relative sea level at the end of Permian time in this area, followed by a relative sea-level rise during the earliest Triassic. Precipitation of synsedimentary cement immediately above the P–T boundary in Iran and elsewhere (South China) suggests a global change in ocean chemistry. One possible explanation is that dissolved calcium and bicarbonate concentrations in seawater increased sufficiently to promote spontaneous carbonate precipitation, a rare event in the Phanerozoic but common during Precambrian time. Alternatively, a massive heating event could have resulted in CO 2 degassing and decreases in oceanic carbonate solubility, both leading to inorganic, synsedimentary carbonate precipitation. Inorganic precipitation of synsedimentary carbonate cement may indicate that biochemical production of carbonate was halted due to the P–T boundary events. Our study indicates that shallow and moderately deep waters during the latest Permian were well oxygenated in the open ocean setting of the central Tethys Sea in Iran. Therefore, P–T mass extinction scenarios that invoke upon widespread marine anoxia should be viewed with caution.

A palynological investigation of the Lower and lowermost Middle Jurassic strata (Sinemurian to Aalenian) from North Yorkshire, UK

SUMMARY A palynological investigation of the Lower and lowermost Middle Jurassic (Sinemurian to Aalenian) strata of North Yorkshire has been undertaken which incorporates material from the BGS Brown Moor Borehole, near Acklam and the coastal outcrops between Staithes and Robin Hood’s Bay. The resulting dataset is an additional contribution to the Jurassic dinoflagellate cyst biostratigraphy of northern England. Two distinctive variants of Liasidium variabile appear to have biostratigraphical significance in the Upper Sinemurian of North Yorkshire. Specimens of L. variabile from the Caenisites turneri Ammonite Zone, the Eparietites denotatus Ammonite Subzone and the Oxynoticeras simpsoni Ammonite Subzone have short apical and antapical horns. Forms from the overlying uppermost Oxynoticeras oxynotum Ammonite Zone, however, are characterized by elongate apical horns and rounded hypocysts. The regional dinoflagellate cyst diversity increase in the late Pliensbachian and the disappearance of many dinoflagellate cysts in the Lower Toarcian are both interpreted as being related to eustatic fluctuations. The paucity of dinoflagellate cysts close to the Dactylioceras tenuicostatum-Harpoceras falciferum Ammonite zonal transition in the Lower Toarcian was caused by the spread of widespread marine anoxia during the Lower Toarcian maximum flooding event. A new species of dinoflagellate cyst, Nannoceratopsis symmetrica , is described.

Palaeoenvironmental interpretation of a Triassic-Jurassic boundary section from Western Austria based on palaeoecological and geochemical data

A section spanning the Triassic-Jurassic boundary is described from near the village of Lorüns in the Vorarlberg region of western Austria. At Lorüns, the uppermost Triassic is characterised by bedded carbonates of the Kössen Formation supporting a stenotopic fauna indicative of a shallow sub-tidal environment of normal marine salinity. The Triassic-Jurassic boundary may be represented as a sequence boundary developed on top of a 1.1 m thick red mudstone of the lower Schattwald Shale, which is interpreted to have been deposited in a marginal marine environment, possibly a mud flat. Above the boundary beds, the upper Schattwald Shale is characterised by thin-bedded marl and dark limestone beds with an earliest Hettangian macrofauna dominated by epifaunal filter-feeding bivalves, including ostreids, mytilids and oxytomids, which suggest a shallow, subtidal, salinity-controlled environment typical of an interplatform lagoon. Carbonate production rejuvenated in the later Early Hettangian with development of the Lorüns oolite, a shallow subtidal oolitic and oncolitic unit bearing echinoderms indicative of normal marine conditions. Low ThU ratios from the remainder of the section are a result of reduced thorium in carbonate-rich sediments and not from authigenic uranium in anoxic sediments. In the boundary beds evidence for marine anoxia (or dysoxia) is absent where ThU values, determined by gamma-ray spectrometry, are above 5. The negative excursion in δ13C and positive excursion in δ18O in the boundary beds may be due to secondary geochemical effects, due to organic diagenesis or the precipitation of caliche during paleosol development. Alternatively, the excursions may reflect a primary geochemical signal recording short-term decline in primary productivity. Comparison in δ18O and δ13C values between the Kössen Formation and Lorfüs oolite indicate no significant long-term geochemical changes are evident in the section and suggest that any environmental perturbations were restricted to the boundary beds and possible sequence boundary.

Carbon and sulfur isotope anomalies across the Frasnian-Famennian extinction boundary, Alberta, Canada

Stable isotopes of carbonate and organic carbon from two Upper Devonian sections in Alberta, Canada, indicate a “heavy carbon event” across the Frasnian-Famennian (F-F) boundary and a negative δ 13 C shift at the boundary. At Cinquefoil Mountain, δ 13 C values in carbonate are anomalously high (3.5‰ to 4.5‰ PDB [Peedee belemnite]) within an interval (10 m below to 23 m above the F-F boundary) representing about 1 m.y. (two standard conodont zones), compared to background values of ∼1‰ above and below this interval. Superimposed on this positive excursion is a marked δ 13 C decrease of about 1‰ at precisely the F-F boundary. At Medicine Lake, a similar δ 13 C excursion in organic carbon, from a background of −29‰ to a high of −26.5‰, is recorded across the F-F boundary. The δ 34 S data for iron sulfide in these sections show unusually high values (as much as 15‰ to 20‰ CDT [Canon Diablo troilite]) in the F-F boundary interval. These data, together with those from other areas, indicate a period of major global changes (e.g., greenhouse and marine anoxia) that took place well before and after the sudden biomass killing event at the F-F boundary. Existing evidence suggests that the F-F mass extinction was probably caused by a large extraterrestrial impact on Earth at a time when the global ecosystem was already severely stressed.

Application of the Ce anomaly as a paleoredox indicator: The ground rules

Much attention has been paid, in recent years, to the potential application of the Ce anomaly, measured in various marine phases, as a paleoceanographic indicator of widespread marine anoxia. In this paper we present and discuss results from recent studies of present‐day rare earth element (REE) distributions (and hence Ce anomaly distributions) in the marine environment which are particularly pertinent to paleoceanography. Subsequently, we review and discuss the validity of the recent literature in which Ce anomalies have been employed as paleoredox indicators.

Cenomanian-Turonian Organic Facies Onshore and Offshore, Israel: Prognosis for Petroleum Exploration: ABSTRACT

The Cenomanian-Turonian marine sediments of Israel are rich in organic matter: black shales and bituminous marls. They accumulated in a north-south oriented chain of basins located along the paleoshoreline separating the broad platform in the east and the open sea in the west. A detailed biostratigraphy based on planktonic foraminifers, ostracods, and organic composition and content is presented. The range of these organic levels is centered across the Cenomanian-Turonian boundary (Whiteinella archeocretacea zone) extending to early-middle Turonian (Helvetoglobtruncana helvetica zone). These new data contribute to the central Tethy record and corroborate the wide distribution of organic-rich sedimentation induced by marine anoxia. The paleo-oceanography and economic implications of this anoxic event are discussed. Upwelling and an expanded oxygen-depleted zone coupled with regional tectonovolcanism controlled production and preservation of organic matter. Primary production was stimulated by enhanced upwelling and nutrient derived from the Carmel volcanism. As the platform was progressively flooded, the anoxic column moved from slope to shelf basins, reaching the structural high of the Carmel only by the middle Turonian. These organic-rich beds associated with eustatic rise could be potential source rocks if thermally matured. Such sediments might occur in the offshore Pleshet basin, where middle Cretaceous organic deposits aremore » covered by 4 to 5 km-thick sediments. Appropriate structures and sealing (evaporites, shales) provide the required conditions for entrapment and conservation of the in-situ generated hydrocarbon, minimizing loss by migration.« less