Chert intervals in DSDP and ODP sites (Table 1)

Radiolarian cherts in the Tethyan realm of Jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates. However, the widespread occurrence of cherts in the Eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones. In a new survey of the global spatio-temporal distribution of Cenozoic cherts in Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sediment cores, we found that cherts occur most frequently in the Paleocene and early Eocene, with a peak in occurrences at ~50 Ma that is coincident with the time of highest bottom water temperatures of the early Eocene climatic optimum (EECO) when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity. Cherts occur less commonly during the subsequent Eocene global cooling trend. Primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation. This timing of peak Eocene chert occurrence, which is supported by detailed stratigraphic correlations, contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and/or volcanism in a supposedly sluggish ocean of the EECO, followed during the subsequent middle Eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification, with the formation of chert as a result of biosilica transformation during diagenesis. Instead, we suggest that basin-basin fractionation by deep-sea circulation could have raised the concentration of EECO dissolved silica especially in the North Atlantic, where an alternative mode of silica burial involving widespread direct precipitation and/or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling-deficient conditions of the EECO. Cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones.

(Table T1) Fluid inclusions in siltstone and sandstone grains from ODP Hole 210-1276A

Twenty samples of siltstones and sandstones were taken from Ocean Drilling Program Site 1276 during Leg 210 for fluid inclusion studies. With the exception of one sample of vein calcite, all inclusions were in quartz grains. The results of fluid-inclusion petrology and microthermometry indicate the presence of three fluid inclusion types (Types 1, 2, and 3). Type 1 fluid inclusions are two-phase (liquid + vapor) aqueous inclusions, and Type 2 inclusions are monophase fluid inclusions (liquid or vapor). These are common in all samples and are formed either as primary isolated inclusions or as secondary inclusions as trails along annealed fractures in the grain. Type 3 fluid inclusions are three-phase (liquid + vapor + solid) inclusions. Type 3 inclusions are rare and are observed as isolated inclusions or in a cluster with other types (i.e., Types 1 and 2). The predominant population throughout the different units sampled is two-phase (liquid + vapor) aqueous fluid inclusions (i.e., Type 1). The temperature of homogenization (TH) bivariate plots for Type 1 inclusions shows dominance throughout the hole of low- to medium-salinity fluids with minimum trapping temperatures between 150° and 400°C.

Mineral chemistry of primary and secondary phases in basaltic rocks

Primary magmatic phases (spinel, olivine, plagioclase, clinopyroxene, amphibole, and biotite) and secondary phyllosilicates (smectite, chlorite-smectite, and celadonite) were analyzed by electron microprobe in alkalic and tholeiitic dolerites and basalts from Ocean Drilling Program Sites 800, 801, and 802. Aphyric alkalic dolerite sills (Hole 800A) and basalt flows (Holes 801B and 801C) share common mineralogical features: matrix feldspars are strongly zoned from labradorite cores to discrete sodic rims of alkali feldspar with a high Or component, which overlaps that of quench microlites in glassy mesostasis; little fractionated clinopyroxenes are Ti-rich diopsides and augites (with marked aegirine-augite rims at Site 801); rare, brown, Fe**3+-rich amphibole is winchite; and late biotites exhibit variable Ti contents. Alkalic rims to feldspars probably developed at the same time as quenched mesostasis feldspars and late-stage magmatic biotite, and represent the buildup of K-rich hydrous fluids during crystallization. Phenocryst phases in primitive mid-ocean ridge tholeiites from Hole 801C (Mg numbers about 70) have extreme compositions with chrome spinel (Cr/Cr + Al ratios about 0.2-0.4), Ni-rich olivine (Fo90), and highly calcic plagioclase (An90). Later glomerophyric clumps of plagioclase (An75-80) and clinopyroxene (diopside-augite) are strongly zoned and probably reflect rapidly changing melt conditions during upward transport, prior to seafloor quenching. In contrast, phenocryst phases (olivine, plagioclase, and clinopyroxene) in the Hole 802A tholeiites show limited variation and do not have such primitive compositions, reflecting the uniform and different chemical composition of all the bulk rocks. Replacive phyllosilicates in both alkalic and tholeiitic basalts include various colored smectites (Fe-, Mg-, and Al-saponites), chlorite-smectite and celadonite. Smectite compositions typically reflect the replaced host composition; glass is replaced by brown Fe-saponites (variable Fe/Mg ratios) and olivine by greenish Mg-saponites (or Al-rich chlorite-smectite).

Geochemistry of primary and secondary mineral phases in ODP Leg 209 sediments

Primary and secondary mineral phases from Holes 1268A (11 samples), 1272A (9 samples), and 1274A (12 samples) were analyzed by electron microprobe in Bonn and Cologne (Germany). Bulk rock powders of these samples were also analyzed geochemically, including major and trace elements (Paulick et al., 2006, doi:10.1016/j.chemgeo.2006.04.011). Ocean Drilling Program (ODP) Leg 209 Holes 1268A, 1272A, and 1274A differ remarkably in alteration intensity and mineralogy, and details regarding their lithologic characteristics are presented in Bach et al. (2004, doi:10.1029/2004GC000744) and Shipboard Scientific Party (2004, doi:10.2973/odp.proc.ir.209.101.2004). Because of the least altered character of peridotite in Hole 1274A, abundant clinopyroxene, orthopyroxene, olivine, and spinel were analyzed at this site. In Hole 1272A, primary silicates are rare and analyses were restricted to some samples that contain traces of olivine and orthopyroxene. Because of the intensity of alteration, Hole 1268A is devoid of primary phases except spinel. Commonly, alteration is pseudomorphic and serpentinization of olivine and orthopyroxene can be distinguished. Accordingly, compositional variations of the alteration minerals with regard to the precursor minerals are one of the issues investigated in this data report.

Chemistry of primary and secondary phases in intraplate basalts and volcaniclastic sediments at DSDP Leg 89 Holes

Electron microprobe data are presented for clinopyroxenes, plagioclases, palagonites, smectites, celadonites, and zeolites in Hole 462A sheet-flow basalts and Site 585 volcaniclastic sediments. Glomerocrystic clinopyroxenes in Hole 462A are predominantly Ti-poor augites with minor fractionation to ferroaugites in rim portions. Quenched plumose clinopyroxenes show considerable variation from Ca-rich to Ca-poor augites, although all are characterized by being Tirich and Cr-poor relative to the glomerocrysts. Two differentiated series of Site 585 pyroxene compositions, calcic augite and diopside-salite, demonstrate the coexistence, in the vitric and lithic clasts, of tholeiitic and alkali basalt types, respectively. Plagioclase compositions in all samples are mainly labradorites, although some zoned Hole 462A glomerocrysts range from An73 to An20 and are characterized by high Mg and Fe contents in the more calcic varieties. The K content of the plagioclases is highest in the more sodic crystals, although the overall higher orthoclase component of Site 585 plagioclases reflects the generally higher bulk-rock K content. The compositions of both secondary smectites and celadonites are similar irrespective of the alteration location (glass, matrix, vesicles, etc.), although brown smectites replacing interstitial glass have marginally higher total Fe contents than pale green and yellow smectites. Analyzed zeolites are mainly phillipsites with variable alkali content, and, together with associated celadonite, represent late-stage alteration repositories for K under mildly oxidizing conditions. The compositions of both early and late secondary minerals are typical of those formed by the submarine alteration of basaltic rocks at low temperatures.