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.

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Sulfur isotopic fractionation factors involving pairs of pyrite, pyrrhotite, sphalerite, chalcopyrite, and galena have been determined experimentally over the temperature range 250" C to 600" C.Since chalcopyrite and pyrrhotite are not stable at higher PS2 conditions, buffer assemblages were necessary to control PS2 in experiments with these minerals. Since low PS2 values and low temperatures are unfavorable to rapid isotope exchange, techniques were devised whereby equilibrium constants could be estimated indirectly in systems where direct measurements are not possible because of the time factor.Current data place the sulfide minerals in the following order of 34s enrichment under equilibrium exchange conditions: pyrite > (pyrrhotite N sphalerite) > chalcopyrite > galena in agreement with theoretical predictions. In agreement with theory the equilibrium exchange constant K for a given mineral pair depends upon temperature as follows: 1000 In K = ~1634s = AT-2, where A denotes a constant. The A values for various mineral pairs have been determined with + 10 % uncertainties as follows: 11.0 X 105 (py-gn), 8.0 X 105 (sp-gn), 6.5 X 105 (cp-gn), 4.5 X 105 (py-cp), 3.0 X lo5 (py-sp, py-PO), 1.5 X 105 (sp-cp, po-cp), and " 0 (sp-po).Les facteurs de fractionnement des isotopes de soufre, pour les paires de pyrite, pyrrhotite, chalcopyrite et galbne, ont Ct C CvaluCs expCrimentalement ? I des tempkratures dont I'ordre de grandeur varie de 250" C a 600" C.Vu que la chalcopyrite et la pyrrhotite ne sont pas stables a des conditions de haute PS2, I'utilisation de tampon s'avhe nkessaire pour contrbler la PS2 lors des expCriences avec ces minCraux. De plus, les faibles valeurs de PS2 et de tempkratures n'Ctant pas favorables a un Cchange rapide d'isotope, des techniques ont Ct C mises au point pour Cvaluer indirectement les constantes d'Cquilibre dans les systbmes oh le facteur temps rend les mesures directes impossibles.Les donnCes actuelles rkpartissent I'enrichissement en 34s des sulfures, sous des conditions d'echange a I'Cquilibre, dans I'ordre suivant: pyrite > (pyrrhotite rv sphalhite) > chalcopyrite > galbne.Cela est en accord avec les prCdictions thkoriques. ConformCment A la thCorie la constante K d'kchange a l'kquilibre pour une paire de minCraux donnCs est fonction de la tempCrature selon 1'Cquation suivante: 1000 In K + ~6 3 4 s = AT-2, oh A est une constante. Les valeurs de A pour diffkrentes paires de minCraux ont Ct C dCterminCes avec 10 % d'incertitude, comme suit: 11.0 X 105 (py-gn),8.0 X 105(sp-gn), 6.5 x 105 (cp-gn), 4.5 X IOj(pyxp), 3.0 X lOj(py-sp, py-po), 1.5 X 105(sp-cp, po-cp), et N 0 (sp-po).

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