Characterization of insoluble organic matter in sediments at DSDP Site 87-582

Lipids, humic acids, and kerogens were isolated from Site 582 sediment cores. The amount of each organic fraction in the samples taken from 5.6 to 694 m sub-bottom is almost unrelated to depth of the sample. A study of the oxidation of organic matter by the alkaline KMnO4 method reveals that distribution of polymethylene chain lengths of the kerogens and humic acids in the marine sediments differ from those in lacustrine sediments. The order of abundance of these chains in the sediments is: kerogens, 52-66% of total methylene chains; humic acids, 25-33%; and lipids, 8-16%. The results suggest that polyunsaturated fatty acids (>=4 double bonds) may be important in the formation of polymethylene chains of kerogens and humic acids in marine sediments.

Foraminifers from DSDP Leg 87 holes

Leg 87 investigated two sites in the Nankai Trough, off southeastern Japan, and one in the Japan Trench, off northeastern Japan. Several holes at the Nankai Trough sites penetrated mostly Quaternary interbedded sandy turbidites and hemipelagic mud. Foraminifers are common only in certain turbidite sands because both sites are at or just below the carbonate compensation depth. The planktonic assemblages from these sandy layers consist of mixed cool-temperate and warm-water species, and include both solution-resistant and solution-prone species. The benthic assemblages from these same layers are composed of mixtures of shelf to abyssal species. The northward-flowing Kuroshio is important in producing the mixed planktonic faunas, whereas turbidity currents are the primary agents in mixing benthic faunas and in the rapid burial of both planktonic and benthic foraminifers, which protects them from solution. Interbedded hemipelagic muds are barren or contain sparse faunas. Hole 582B penetrated through the trench-fill deposits into hemipelagic sediments that originated in the Shikoku Basin. These muds contain a dissolution facies of solution-resistant planktonic species, partially dissolved tests, and deep bathyal benthic species. Drilling at Site 584, on the landward midslope of the Japan Trench, penetrated a section of dominantly diatomaceous mudstone. This section contains a meager Pliocene calcareous fauna in its upper third and a nearly monospecific assemblage of Martinottiella communis in the lower two-thirds. Diatom biostratigraphy indicates that this change in assemblages occurs near the Miocene/Pliocene boundary. Similar biofacies changes are observed in neighboring sections drilled during Legs 56 and 57. The change from agglutinated to calcareous faunas is probably related to a relative drop in the carbonate compensation depth at the end of the Miocene.