Yoshimichi Kajiwara

End-Permian catastrophe by a bolide impact: Evidence of a gigantic release of sulfur from the mantle

Our studies in southern China have revealed a remarkable sulfur and strontium isotope excursion at the end of the Permian, along with a coincident concentration of impact- metamorphosed grains and kaolinite and a significant decrease in manganese, phosphorous, calcium, and microfossils (foraminifera). These data suggest that an asteroid or a comet hit the ocean at the end of Permian time and caused a rapid and massive release of sulfur from the mantle to the ocean-atmosphere system, leading to significant oxygen consumption, acid rain, and the most severe biotic crisis in the history of life on Earth.

Development of a largely anoxic stratified ocean and its temporary massive mixing at the Permian/Triassic boundary supported by the sulfur isotopic record

Systematic sulfur isotope data for whole-rock sulfides have been obtained from the chert-dominated, continuous, pelagic sedimentary sequences spanning the Permian/Triassic (P/Tr) boundary at Tenjinmaru in the Chichibu Terrane and at Sasayama in the Tanba Terrane in Japan. The P/Tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed Cretaceous/Tertiary (K/T) boundary claystone. The observed data clearly demonstrate a significant bimodalism. The 34S/32S ratios with respect to CDT are generally low throughout the Middle Permian (ca.−39 to −25%0) and show a remarkable increase beginning in the lower Upper Permian and persisting into the Lower Triassic (ca.−20 to −2%0), with a temporary and drastic negative shift, down to roughly the same isotopic level as in the Middle Permian, just at the suspected P/Tr boundary (ca.−41 to −23%0). Interestingly, the mode of isotopic excursion across the P/Tr boundary is in striking contrast to that across the K/T boundary which was recently described at Kawaruppu in Hokkado, Japan. The apparent extent of fractionation, with respect to contemporaneous seawater sulfate, in the high 34S/32S group lies within the range of −25 ± 10%0, which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction, and that in the low 34S/32S group mostly exceeds this range, giving the values typically in the range of −45 ± 10%0, which is similar to what is generally observed in the present-day oceanic sediments. The present data would provide strong evidence for the development of a largely stagnant, anoxic, stratified ocean, which presumably began to form in the lower Upper Permian and persisted into the Lower Triassic, and for a brief episode of its temporary massive mixing just at the suspected P/Tr boundary. Such an oceanic oxic-anoxic history may account to some extent for the relatively high enrichments of chalcophile elements in basal Triassic sediments in the world and add a significant constraint to the current arguments on the cause and consequence of the terminal Permian mass extinction.

Latest Paleocene benthic foraminiferal extinction and environmental changes at Tawanui, New Zealand

A major extinction of intermediate-water (500–1000 m) benthic foraminiferal species coincided with a major decrease in δ13C (2.8‰) of terrestrial organic matter (n-C29 alkane) and δ34S (20‰) of whole rock sulfide in a continuous siltstone sequence in the Tawanui Section (46°S paleolatitude) along the Akitio River, southeastern North Island, New Zealand, in the middle part of the uppermost Paleocene nannofossil zone (CP8). The benthic extinction (25% of species) occurred over ∼3 kyr at ∼55.5 Ma. Increases in kaolinite/illite and kaolinite/smectite ratios and in terrestrial organic carbon percentages started ∼3 kyr before the major benthic extinctions, lasted over ∼40 kyr, and probably reflect warmer climate and increased rainfall. The productivity of planktonic foraminifera and calcareous nannoplankton decreased ∼3 kyr prior to the major extinctions and recovered at the time of benthic extinctions. These events that started ∼3 kyr before the extinction can be best explained by warming, increased rainfall, reduced salinity of surface waters, and increased influence of warm saline deep water (WSDW). Benthic foraminiferal oxygen indices indicate a strong decrease in dissolved oxygen levels within the intermediate water from low oxic (1.5–3.0 mL/L O2) to suboxic (0.3–1.5 mL/L O2) conditions coinciding with the benthic extinctions. Increases in total organic carbon (TOC) and in the hydrocarbon-generating potential of kerogen (measured as the hydrogen index (HI)) agree with the interpretation of decreased dissolved oxygen levels of the intermediate water. The lowest oxygen conditions lasted ∼40 kyr and coincided with a decrease in calcareous benthic foraminiferal productivity, highest TOC levels, and lowest δ13C of terrestrial organic carbon. Dominant formation of WSDW or sluggish intermediate-water circulation caused by warming and high rainfall in high-latitude areas most likely led to the ∼3-kyr time lag between events on land and in surface waters preceeding the extinction and the development of dysaerobia in the sea, coinciding with the major benthic extinction and decrease in δ13C and δ34S in New Zealand. Global warming of deep and intermediate waters may have caused decomposition of methane hydrate in sediments, resulting in a strongly decreased δ13C of marine carbonates, promoting dysaerobia in the ocean, and warming global climate by increased methane concentrations in the atmosphere. Upwelling of WSDW, occurring soon after it became dominant in high-latitude areas, is likely responsible for the recovery of normal salinity and the concomitant recovery of planktonic foraminifera and calcareous nannoplankton productivity in high-latitude surface waters. Minor benthic foraminiferal extinctions (9% of species) occurred ∼40 kyr after the major extinctions, lasted ≤ ∼6 kyr, and coincided with the initiation of environmental recovery.

LATE PERMIAN TO MIDDLE TRIASSIC RADIOLARIAN FAUNAS FROM NORTHERN THAILAND

Abstract Moderately well-preserved Late Permian to Middle Triassic radiolarians are identified in chert beds that occur in the Shan-Thai Block of northern Thailand. These radiolarians are identical to the faunas of the Late Permian Neoalbaillella ornithoformis and N. optima Assemblage Zones and the Triassic Parentactinia nakatsugawaensis and Triassocampe coronata Assemblage Zones reported in chert sequences of Japan. We discovered the radiolarian faunas, apparently indicating Late Permian and Early Triassic ages, in almost continuous sequences of chert and shale exposed in the north of Chiang Mai. The occurrence of these radiolarian faunas provides important data to solve the P/T (Permian/Triassic) boundary in pelagic sequences. Our present discovery also furnishes significant data to reconstruct the paleobiogeography of Mainland Thailand during Late Permian to Middle Triassic times. Fifty species belonging to 35 genera, including three unidentified genera, are investigated taxonomically. Four new species Pseudospongoprunum? chiangdaoensis, Cenosphaera igoi, Cenosphaera? rugosa, and Tlecerina? apsornae are described.

Oceanic primary productivity and dissolved oxygen levels at the Cretaceous/Tertiary Boundary: Their decrease, subsequent warming, and recovery

Thirty-six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the Cretaceous/Tertiary (K/T) boundary exposed at Caravaca, Spain. A rapid reduction in the gradient between δ13C values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus (a proxy for organic carbon) and calcium were recorded in sediments 0–0.5 cm above the K/T boundary. These trends imply that an abrupt mass mortality occurred among pelagic organisms, leading to a significant reduction in the flux of organic carbon to the seafloor. In addition, variations in sulfur isotope ratios, the hydrocarbon-generating potential of kerogen (measured as the hydrogen index), and foraminiferal indices of dissolved oxygen level all imply that a rapid decrease in dissolved oxygen was coincident with the δ13C event. Evidence of the low oxygen event has also been recognized in Japan and New Zealand, suggesting that intermediate water oxygen minima were widely developed during earliest Danian time. A threefold increase in the kaolinite/illite ratio and a 1.2‰ decrease in δ18O (carbonate fine fraction) were recorded in the basal 0.1–2 cm of Danian age sediments. These trends suggest that atmospheric warming and an increase in surface water temperature occurred 0–3 kyr after the δ13C event. Recovery in the difference between δ13C values in the carbonate fine fraction and in benthic foraminiferal calcite as well as increases in phosphorus and calcium contents occur at the base of planktonic foraminiferal Zone Pla, implying that an increase in primary productivity commenced some 13 kyr after the K/T boundary. Tables A1-A3 are available on diskette or via Anonymous FTP from kosmos.agu.org directory APENO (Username = anonymous, Password = guest). Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009 or by phone at 800-966-2481;

Sulfur isotope records around Livello Bonarelli (northern Apennines, Italy) black shale at the Cenomanian-Turonian boundary

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Oceanic anoxia at the Cretaceous/Tertiary boundary supported by the sulfur isotopic record

Sulfur isotope ratios for carbonate-hosted sulfate show a rapid increase (+6‰ to +9‰/m.y.) across the Livello Bonarelli black shale (Marche-Umbrian Apennines of Italy), which was deposited at the Cenomanian-Turonian boundary in the middle Cretaceous (93.5 Ma). The increase suggests that rates of pyrite burial increased substantially over the event, resulting in a decrease of 9%–27% in the oceanic reservoir of SO 4 2− . The enhanced pyrite burial may have significantly increased the flux of oxygen to the atmosphere (9–27 × 10 18 mol/m.y.). Furthermore, removal of the large amount of iron associated with this process might have had a profound effect on iron cycle.

Strontium isotopic compositions and paleoceanographic implication of fossil manganese nodules in DSDP/ODP cores, Leg 1–126

Abstract A temporary and drastic increase in 34S/32S ratio of whole rock sulfide has been recognized just at the Cretaceous/Tertiary boundary within the continuous marine sedimentary sequence of the Kawaruppu section in eastern Hokkaido, Japan: the apparent extent of fractionation, with respect to inferred contemporaneous seawater sulfate, in the anomaly zone which includes the “boundary claystone” at the bottom lies in the range of −25 ± 10‰ whereas that in the lower and upper siltstone strata is roughly twice as much, giving the values in the range of −49 ± 10‰ . The former is quantitatively equivalent in magnitude with the range of kinetic isotope effect in bacterial dissimilatory sulfate reduction and the latter with the typical variation range as observed in sedimentary-diagenetic sulfides in ordinary oxic marine basins. The present data would strongly support the temporary occurrence of an aerobe-free, anoxic, oceanic sedimentary environment beginning just at the Cretaceous/Tertiary boundary and continuing for approximately 70,000 years, probably as a consequence of a certain catastrophic event responsible for the terminal Cretaceous mass extinction.

Strontium isotope constraint on the genesis of crude oils, oil-field brines and Kuroko ore deposits from the Green Tuff region of northeastern Japan

Abstract Strontium isotopic compositions of acetic acid (HOAc) leachate fractions of eight manganese oxide deposits from the modern seafloor, and of twenty-one buried manganese nodules from Cretaceous to Recent sediments in DSDP/ODP cores were measured. 87Sr/86Sr ratios of HOAc leachates in all modern seafloor manganese oxides of various origins are identical with present seawater. The 87Sr/86Sr ratios of the HOAc leachates of buried nodules from DSDP/ODP cores are significantly lower than those of nodules from the modern seafloor and are mostly identical with coeval seawater values estimated from the age of associated sediments. It is suggested that the buried nodules in DSDP/ODP cores are not artifacts transported from the present seafloor during the drilling process, but are in situ fossil deposits from the past deep-sea floor during Cretaceous to Quaternary periods. The formation of deep-sea fossil nodules prior to the formation of Antarctic Bottom Water (AABW) indicates that the circulation of oxygenated deep seawaters have activately deposited manganese oxides since the Eocene Epoch, or earlier.

The Bilimoia gold deposit, Kainantu, Papua New Guinea: A fault-controlled, lode-type, synorogenic tellurium-rich quartz-gold vein system

Abstract Crude oils from Akita to northern Niigata oil fields in the Green Tuff region of northeastern Japan have distinctly uniform 87 Sr 86 Sr ratios (0.7080–0.7082), while those from the southern Niigata oil field contain more radiogenic strontium (0.7095–0.7102). The regional variation in the strontium isotopic composition of crude oils is also reflected in their sulfur contents and sulfur isotopic compositions, and may be attributed to the regional heterogeneity of marine organic sediments from which the crude oils were ultimately derived. The 87 Sr 86 Sr ratios of most oil-field brines (0.7061–0.7084), however, are different from and vary more locally than those of the accompanying crude oils. This finding supports the view that strontium, and by inference some other dissolved solutes in the brines, may have evolved during diagenesis by reaction of a connate and/or a meteoric water with rocks in the Green Tuff region. Barites in the sulfide ore and anhydrites and gypsums in the sulfate (sekko) ore from the Fukazawa and Kosaka Kuroko deposits in the Hokuroku district are divided by the 87 Sr 86 Sr ratio of 0.7081 (±0.0001), which is identical to that of crude oils from nearby oil fields. This similarity in ratios lends support to the conclusion that the Kuroko base metal deposits and crude oil deposits were ultimately derived from a common organic sediment named PUMOS (Primitive Undifferentiated Metalliferous Organic Sediments).