(Table 3) Clay mineralogy and calcium carbonate and organic carbon contents of fabric samples of ODP Leg 117

Calcium carbonate and organic carbon concentrations are from measurements made on board the JOIDES Resolution during Leg 117 (Prell, Niitsuma, et al., 1989, doi:10.2973/odp.proc.ir.117.1989). Values are for samples immdiately adjacent to fabric samples, or for Site 723 within 25 cm of the fabric sample interval. Intervals for which carbon analyses were not performed are represented by values in parenthesis which are from the nearest interval of similar lithology. Organic carbon analyses were not performed for samples below 402 mbsf at Site 731. Analyses performed on similar sediments at Sites 722 and 731 indicate the organic carbon concentration is probably <0.20%.

Mineralogy of ODP Hole 117-722B (Appendix)

Bulk mineralogy of the terrigenous fraction of 99 samples from ODP Site 722 on the Owen Ridge, western Arabian Sea, has been determined by x-ray diffraction, using an internal standard method. The sampling interval, approximately 4.3 k.y., provides a detailed mineralogic record for the past 500 k.y. Previous studies have identified important modern continental sediment sources and the mineral assemblages presently derived from each. These studies have also demonstrated that most of this material is supplied by southwest and northwest winds during the summer monsoon. A variety of marine and terrestrial records and general circulation model (GCM) simulations have indicated the importance of monsoonal circulation during the Pleistocene and Holocene and have demonstrated increased aridity during glacial times and increased humidity during inter glacials. The mineralogic data generated here were used to investigate variations in source area weathering conditions during these environmental changes. Terrigenous minerals present include smectite, illite, palygorskite, kaolinite, chlorite, quartz, plagioclase feldspar, and dolomite. This mineralogy is consistent with the compositions of source areas presently supplying sediment to the Arabian Sea. An R-mode factor analysis has identified four mineral assemblages present throughout the past 500 k.y.: quartz/chlorite/dolomite (Factor 1), kaolinite/plagioclase/illite (Factor 2), smectite (Factor 3), and palygorskite/dolomite (Factor 4). Chlorite, illite, and palygorskite are extremely susceptible to chemical weathering, and a spectral comparison of these factors with the eolian mass accumulation rate (MAR) record from Hole 722B (an index of dust source area aridity) indicates that Factors 1, 2, and 4 are directly related to changes in aridity. Because of these characteristics, Factors 1,2, and 4 are interpreted to originate from arid source regions. Factor 3 is interpreted to record more humid source conditions. Time-series of scores for the four factors are dominated by short-term (10-100 k.y.) variability, and do not correlate well to glacial/interglacial fluctuations in the time domain. These characteristics suggest that local climatic shifts were complex, and that equilibrium weathering assemblages did not develop immediately after climatic change. Spectral analysis of factor scores identifies peaks at or near the primary Milankovitch frequencies for all factors. Factor 1 (quartz/chlorite/dolomite), Factor 2 (kaolinite/plagioclase/illite), and Factor 4 (illite/palygorskite) are coherent and in phase with the MAR record over the 23, 41, and 100 k.y. bands, respectively. The reasons for coherency at single Milankovitch frequencies are not known, but may include differences in the susceptibilities of minerals to varying time scales of weathering and/or preferential development of suitable continental source environments by climatic changes at the various Milankovitch frequencies.

Calcareous nannofossils in Pliocene and Quaternary sediments of ODP Leg 117 holes

A total of 21 calcareous nannofossil datums was found in the upper Pliocene and Quaternary sediments recovered from the ocean floor of the North Atlantic during DSDP Leg 94. These datums were correlated to magnetostratigraphy, and ages were estimated by interpolation between magnetic reversals. Calcareous nannofossil assemblages from 549 samples recovered during ODP Leg 117 were studied in order to estimate the age of the sediments of Sites 720, 721, 722, and 731 drilled at the Indus Fan and the Owen Ridge in the Arabian Sea, Indian Ocean. We also showed that the datums above mentioned can be traced into the Indian Ocean. Two new species, namely Helicosphaera omanica and Reticulofenestra ampla, are described.

Organic compounds in sediments and pore waters of ODP Sites 117-723 and 117-724

Total organic carbon, amino compounds, and carbohydrates were measured in pore waters and sediments of Pliocene to Pleistocene age from Sites 723 and 724 (ODP Leg 117) to evaluate (1) relationships between organic matter in the sediment and in the pore water, (2) the imprint of lithological variations on the abundance and contribution of organic substances, (3) degradation of amino compounds and carbohydrates with time and/or depth, and (4) the dependence of the ammonia concentration in the pore water on the degradation of amino compounds in the sediment. Total organic carbon concentrations (TOC) of the investigated sediment samples range from 0.9% to 8.7%, and total nitrogen concentrations (TN) from 0.1% to 0.5%. Up to 4.9% of the TOC is contributed by hydrolyzable amino acids (THAA) which are present in amounts between 1.1 and 21.3 µmol/g dry sediment and decrease strongly downhole. Hydrolyzable carbohydrates (THCHO) were found in concentrations from 1.3 to 6.6 ?mol/g sediment constituting between 0.1% and 2.0% of the TOC. Differences between the distribution patterns of monomers in Sites 723 and 724 indicate higher terrigenous influence for Site 724 and, furthermore, enhanced input of organic matter that is relatively resistant to microbial degradation. Lithologically distinct facies close to the Pliocene/Pleistocene boundary yield different organic matter compositions. Laminated horizons seem to correspond with enhanced amounts of biogenic siliceous material and minor microbiological degradation. Total amounts of dissolved organic carbon (DOC) in pore waters vary between 11 and 131 mg/L. Concentrations of DOC as well as of dissolved amino compounds and carbohydrates appear to be related to microbial activity and/or associated redox zones and not so much to the abundance of organic matter in the sediments. Distributions of amino acids and monosaccharides in pore waters show a general enrichment in relatively stable components in comparison to those of the sediments. Nevertheless, the same trend appears between amino acids present in the sediments from Sites 723 and 724 as well as between amino acids in pore waters from these two sites, indicating a direct relation between the dissolved and the sedimentary organic fractions. Different ammonia concentrations in the pore waters of Sites 723 and 724 seem to be related to enhanced release of ammonia from degradation of amino compounds in Site 723.

Benthic foraminifera of cores from ODP Leg 117

The relative abundances of benthic foraminifers from the Oman margin have been analyzed from ODP Sites 725 and 726 near the upper boundary of the oxygen-minimum zone (OMZ) and 728 near the lower boundary. The relative abundance pattern of the benthic foraminiferal species in the two shallow sites show synchronous changes, which, together with variations in the faunal composition, may be attributed to changes in the location of the upper boundary of the OMZ during the last 7 million years. At the deeper site, the relative abundance pattern shows considerable variation in the faunal composition during the last 8 million years. The strong dominance of the shallow-water species Ammonia beccarii during the early Pliocene at Site 728 suggests a water depth less than 400 m during the early Pliocene and subsequent subsidence during the middle and late Pliocene to the present > 1400 m water depth.