Swart, P.K., Eberli, G.P., Malone, M.J., and Sarg, J.F. (Eds.), 2000 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 166 137 1 Swart, P.K., Eberli, G.P., Malone, M.J., and Sarg, J.F. (Eds.), 2000. Proc. ODP, Sci. Results, 166: College Station TX (Ocean Drilling Program). 2 Department of Earth Sciences, University of Queensland, Brisbane, QLD Australia 4072. tfrank@earthsciences.uq.edu.au 13. DATA REPORT: GEOCHEMISTRY OF MIOCENE SEDIMENTS, SITES 1006 AND 1007, LEEWARD MARGIN, GREAT BAHAMA BANK 1 Tracy D. Frank 2 ABSTRACT Total carbon and carbonate contents, quantitative carbonate mineralogy, trace metal concentrations, and stable isotope com- positions were determined on a suite of samples from the Miocene sections at Sites 1006 and 1007. The Miocene section at Site 1007, located at the toe-of-slope, contains a relatively high proportion of bank-derived components and becomes fully lithified at a depth of ~300 meters below seafloor (mbsf). By contrast, Miocene sediments at Site 1006, situated in Neogene drift depos- its in the Straits of Florida and composed primarily of pelagic carbonates, do not become fully lithified until a depth of ~675 mbsf. Diagenetic and compositional contrasts between Sites 1006 and 1007 are reflected in geochemical data derived from sed- iment samples from each site. INTRODUCTION This report provides the results of geochemical analyses per- formed on Miocene sediments recovered during Ocean Drilling Pro- gram (ODP) Leg 166 at Sites 1006 and 1007. Sites 1006 and 1007 are the most distal of five sites along the Bahamas Transect drilled into prograding carbonate sequences along the western margin of the Great Bahama Bank (GBB). Site 1007 is located on the toe-of-slope of the western GBB in ~647 m of water. At Site 1007, a nearly com- plete 900-m-thick Miocene section consisting of a succession of bio- turbated, periplatform limestone (e.g., Schlager and James, 1978) with interbeds of turbiditic packstone, grainstone, and floatstone (Eberli, Swart, Malone, et al., 1997) was recovered. Site 1006, the most distal site along the Bahamas Transect, was drilled ~30 km from the platform edge of the GBB in 658 m of water. Approximately 334 m of middle and upper Miocene sediments were recovered at this site, which is positioned in a nearly continuous sequence of Neogene drift sediments that onlap and interfinger with prograding bank slope de- posits (Eberli, Swart, Malone, et al., 1997). Because of its more distal location, the Miocene section at Site 1006 has relatively few turbid- itic deposits and a significantly higher pelagic component, and it con- sists primarily of nannofossil chalk and limestone. The Miocene section at Site 1007, which contains a relatively high proportion of bank-derived components, has been affected by diagenesis. Sediments are fully lithified below ~300 meters below seafloor (mbsf) and exhibit burial compaction features including anastomosing solution seams at depths greater than ~1120 mbsf. By contrast, Miocene sediments at Site 1006, composed primarily of pe- lagic carbonates, do not become fully lithified until a depth of ~675 mbsf. It is well known that periplatform carbonates undergo acceler- ated rates of diagenesis relative to low-Mg calcite (LMC)-dominated pelagic counterparts, primarily because of the metastable nature of the platform-derived aragonite and high-Mg calcite (HMC) compo- nent in deep, cold seawater (e.g., Schlager and James, 1978; Mullins et al., 1985; Dix and Mullins, 1988, 1992; James and Choquette, 1990). However, to what extent the early onset of lithification in peri- platform carbonates influences further alteration during burial is poorly known. In this regard, the suite of geochemical data derived from the sequences of pelagic and periplatform carbonates at Sites 1006 and 1007, respectively, provide a foundation for the examina- tion of the influence of initial sediment composition on patterns and processes of burial diagenesis in fine-grained, shelf carbonates. Bulk sediment samples (~10–20 cm 3 ) were collected aboard the JOIDES Resolution during Leg 166. A representative range of lithol- ogies from the Miocene sections at Sites 1006 and 1007 was chosen at semi-regular intervals on the basis of core descriptions and visual observations. Approximately one fourth of each bulk sample was powdered and dried in a 75°C oven; in cases where individual sedi- ment samples were lithologically diverse, an equivalent amount of each lithology was prepared. Bulk powders were subsequently ana- lyzed for total carbon and carbonate contents, carbonate mineralogy, trace metal contents, and carbon and oxygen isotope compositions. The selective removal and analysis of individual petrographic com- ponents in Site 1007 samples were commonly precluded by the dense cementation and the fine-grained nature of most lithologies. Howev- er, an absence of cement in intermittent clay-rich intervals at Site 1007 allowed for the disaggregation of selected samples and the iso- topic analysis of individual petrographic components. These samples were disaggregated by soaking in a 5.25% sodium hypochlorite (NaOCl) solution for 24 hr and rinsing repeatedly in deionized water. Disaggregated samples were then washed with deionized water and oven dried at 50°C. Additional carbon and oxygen isotope analyses were performed on individual petrographic components from these separates, which were selected with the aid of a binocular micro- scope. Data for Holes 1006A and 1007C are reported in Tables 1 and 2, respectively. ANALYTICAL METHODS AND RESULTS Carbon Coulometry The coulometrics titration technique measures all of the CO 2 that is liberated by acidifying and heating sediment samples in a closed system and back-titrating to a coulometric end point. To determine carbonate carbon concentrations, ~10 mg of sample was reacted with a 50% phosphoric acid solution in a heated reaction vessel. The per- centage of carbonate in each sample reflects the amount of inorganic carbon (IC) liberated as CO 2 with the assumption that all inorganic carbon is present as calcium carbonate, such that CaCO 3 = IC × 8.332. No corrections were made for the presence of either siderite or dolomite. Total carbon (TC) concentrations reflect the amount of car- bon released as CO 2 during combustion of a ~5-mg sample in oxygen at 1000°C. The amount of organic carbon (C org ) was calculated as the