(Appendix) Oxygen isotope record and carbonate mineralogy of the top part of ODP Hole 101-633A

Hole 633A was drilled in the southern part of Exuma Sound on the toe-of-slope of the southeastern part of Great Bahama Bank during ODP Leg 101. The top 55 m, collected as a suite of six approximately 9.5-m-long hydraulic piston cores, represents a Pliocene-Pleistocene sequence of periplatform carbonate ooze, a mixture of pelagic calcite (foraminifer and coccolith tests), some pelagic aragonite (pteropod tests), and bank-derived fine aragonite and magnesian calcite. A 1.6-m.y.-long hiatus was identified at 43.75 mbsf using calcareous nannofossil biostratigraphy and magnetostratigraphy. The 43.75-m-thick periplatform sequence above the hiatus is a complete late Pliocene-Quaternary record of the past 2.15 m.y. The d18O curve, primarily based on Globigerinoides sacculifera, clearly displays high-frequency/low-amplitude cycles during the early Pleistocene and low-frequency/high-amplitude cycles during the middle and late Pleistocene. Variations in aragonite content in the fine fraction of the periplatform ooze show a cyclic pattern throughout the Pleistocene, as previously observed in piston cores of the upper Pleistocene. These variations correlate well with the d18O record: high aragonite corresponds to light interglacial d18O values, and vice versa. Comparison of the d18O record and the aragonite curve helps to identify 23 interglacial and glacial oxygen-isotope stages, corresponding to 10.5 aragonite cycles (labeled A to K) commonly established during the middle and late Pleistocene (0.9 Ma-present). Strictly based on the aragonite curve, another 11 aragonite cycles, labeled L to V, were identified for the early Pleistocene (0.9 to 1.6 Ma). Mismatches between the d18O record and the aragonite curve occur mainly at some of the glacial-to-interglacial transitions, where aragonite increases usually lag behind d18O depletion. When one visually connects the minima on the Pleistocene aragonite curve, low-frequency (0.4 to 0.5 m.y.) supercycles seem to be superimposed on the high-frequency cycles. The timing of this supercycle roughly matches the timing of the Pleistocene carbonate preservation supercycles described in the Pacific, Indian, and Atlantic oceans. Mismatches between aragonite and d18O cycles are even more obvious for the late Pliocene (1.6 to 2.15 Ma). Irregular aragonite variations are observed for the late Pliocene, although after the onset of late Pleistocene-like glaciations in the North Atlantic Ocean 2.4 m.y. ago the d18O record has shown a mode of high-frequency/low-amplitude cycles. Initiation of climatically induced aragonite cycles occurs only at the Pliocene-Pleistocene transition, 1.6 m.y. ago. After that time, aragonite cycles are fully developed throughout the Quaternary. The 11-m-thick periplatform sequence below the hiatus represents a lower Pliocene interval between 3.75 and 4.45 Ma. The bottom half (4.25-4.45 Ma) has a fairly constant, high aragonite content (averaging 60%) and high sedimentation rates (28 m/m.y.) and corresponds to the end of the prolonged early Pliocene interglacial interval (4.1-5.0 Ma), established as a worldwide high sea-level stand. The second half (3.75-4.25 Ma), in which aragonite content decreases by successive steps, paralleled by a gradual 5180 enrichment in Globigerinoides sacculifera and low sedimentation rates (10 m/m.y), corresponds to the climatic deterioration established worldwide between 4.1 and 3.8 Ma, to a decrease of carbonate preservation observed in the equatorial Pacific Ocean, and to a global sea-level decline. Dolomite, a ubiquitous secondary component in the lower Pliocene, is interpreted as being authigenic and possibly related to diagenetic transformation of primary bank-derived fine magnesian calcite. Transformation of the primary mineralogical composition of the periplatform ooze was evidently minor, as the sediments have retained a detailed record of the Pliocene-Pleistocene climatic evolution. Clear evidence of diagenetic transformations in the periplatform ooze includes (1) the disappearance of magnesian calcite in the upper 20 m of Hole 633A, (2) the occurrence of calcite overgrowths on foraminiferal tests and microclasts at intermittent chalky core levels, and (3) the ubiquitous presence of authigenic dolomite in the lower Pliocene.

Calcium carbonate, total and organic carbon and accumulation rate characteristics at DSDP Leg 78A Holes

Bulk sediment accumulation rates and carbonate and carbonate-free accumulation rates corrected for tectonic tilting have been calculated for Leg 78A sediments. These rates are uniformly low, ranging from 0.1 to 6.8 g/(cm**2 x 10**3 yr.), reflecting the pelagic-hemipelagic nature of all the sediments drilled in the northern Lesser Antilles forearc. Rates calculated for Sites 541 and 542 [0.6-6.8 g/(cm**2 x 10**3 yr.)], located on the lower slope of the accretionary prism, are significantly greater than the Neogene rates calculated for oceanic reference Site 543 [0.1-2.4 g/(cm**2 x 10**3)]. This difference could be the result of (1) tectonic thickening of accretionary prism sediments due to folding, small-scale faulting, and layer-parallel shortening; (2) deposition in shallower water farther above the CCD (carbonate compensation depth) resulting in preservation of a greater percentage of calcareous microfossils; or (3) a greater percentage of foraminiferal sediment gravity flows. Terrigenous turbidites are not documented in the Leg 78A area because of (1) great distance from South American sources; (2) damming effects of east-west trending tectonic elements; and (3) location on the Tiburon Rise (Site 543). This lack of terrigenous material, characteristic of intraoceanic convergent margins, suggests that published sedimentation models for active continental convergent margins with abundant terrigenous influxes are not applicable to intraoceanic convergent margin settings.

(Table 1) Mineralogy of DSDP Leg 65 sediments

During Leg 65, four sites were drilled near the mouth of the Gulf of California where high sedimentation rates made it possible to sample young oceanic crust near the ridge crest. The oldest sediments cored were upper Pliocene siltstones (Site 483); the samples at the other sites (482, 484, and 485) were all Quaternary in age. A series of 80 sediment samples, most of them hemipelagic clays, were examined by semiquantitative X-ray diffraction and Carbonate Bomb techniques to determine their mineralogy and carbonate contents. The results of this study may be used to determine their provenance and diagenesis.

Organic carbon, calcium carbonate and carbon/nitrogen ratio at DSDP Leg 93 sites

A large number of samples of nonlithified and lithified sediments from Leg 93 sites were analyzed for their contents of organic carbon and calcium carbonate. An average of two samples was selected from every core for carbonate determination; organic carbon was measured in most of these samples. Nearly all of these analyses were performed on board Glomar Challenger for samples from Sites 603 and 604. Site 605 samples, plus some of the deeper samples from Hole 603B, were analyzed at the University of Michigan. The procedures used in both cases were virtually the same, and their results compared well. Organic carbon analyses were done using a Hewlett- Packard 185-B CHN Analyzer. Portions of samples selected for calcium carbonate determinations were treated with dilute HC1 to remove carbonate, washed with deionized water, and dried at 110°C. A Cahn Electrobalance was used to weight 20-mg samples of sediment for CHN analysis. Samples were combusted at 1050°C in the presence of an oxidant, and the volumes of the evolved gases determined as measures of the C, H, and N contents of sediment organic matter. Areas of gas peaks were determined and compared to those of rock standards of known carbon and nitrogen contents. These values were used to standardize instrument response so that C/N atomic ratios could be reported. Organic carbon concentrations were calculated on the basis of sediment dry weight. Hydrogen elemental analysis with the procedure used is untrustworthy because of the variable amounts of clay minerals and their hydrates, hence hydrogen values are not reported for samples analyzed by this method.