radiation. Dolomite stoichiometry was calculated from displacement of the (104) peak using the equation of Lumsden (1979).
Dolomite nodules and layers were systematically sampled onboard the JOIDES Resolution during Leg 201. A comparison sample was taken from the surrounding soft sediment with each dolomite sample. Thin sections were stained for calcite according to the method of Dickson (1966) and analyzed using a petrographic microscope. For description of crystallization textures and fabrics of dolomite, the terminology of Friedman (1965) was used. Additionally, cold cathode luminescence was applied in order to detect different generations of carbonate cements.
Bulk dolomite nodules and surrounding sediment samples were powdered and mineralogically analyzed using a Scintag XDS 2000 X-ray diffractometer (XRD). The samples were scanned continuously at 1°/min from 10° to 70° with CuK radiation. Dolomite stoichiometry was calculated from displacement of the (104) peak using the equation of Lumsden (1979).
Fresh broken surfaces of lithified dolomite, as well as samples of freeze-dried unlithified sediment, were coated with platinum and analyzed by field emission scanning electron microscope (SEM; LEO 1530, 143-eV resolution; LEO Electron Microscopy Ltd., Germany) at the Institute for Material Sciences at ETH Zürich (Switzerland). Phase compositions were measured using energy dispersive X-ray (EDX; Z-MAX 30-UP; Thermo NORAN). The acceleration voltage was set at 5 kV for microscopy and at 10 kV for EDX analysis.
Major elements (Mg, Ca, Fe, Mn, and Sr) in the dolomite phase were quantified by electron microprobe analysis (EMPA). All samples were polished (thin sections, as well as embedded rock pieces) and coated with a 20-nm-thick carbon layer before being analyzed on a Cameca SX 50 electron microprobe at the Institute for Mineralogy and Petrography at ETH Zürich. Acceleration voltage was set to 15 kV. A variety of carbonate standards from the ETH Zürich collection were used: calcite (E001), magnesite (E004), siderite (E006), rhodochrosite (E003), and strontianite (E012). Ca and Mn were analyzed using penta- erythritol (PET) crystal, Mg and Sr using thallium acid phthalate (TAP), and Fe using lithium fluoride (LIF). PET, TAP and LIF are three different crystals with different 2d values used for monochromizing. Textural relationships between the phases were studied using reflected light microscopy. Carbon (as carbonate) was calculated by stoichiometry. A total of 50 measurements were taken from each sample with 7-nA probe current and a spot size of 5 µm. Because of the small grain size of the micritic carbonate, only large crystals were measured.
