Bioturbation in Middle Bathyal, Cenozoic Nannofossil Oozes and Chalks, Southwest Pacific
Bioturbation in Middle Bathyal, Cenozoic Nannofossil Oozes and Chalks, Southwest Pacific
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西南太平洋中深海、新生代超化石软泥和白垩的生物扰动
DOI：
10.2973/dsdp.proc.90.128.1986
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
C. Nelson
中科院分区：
文献类型：
--
作者：
C. Nelson
The high-quality cores obtained on Leg 90 have enabled preliminary qualitative study of the trace fossils in middle to late Cenozoic oozes and chalks at sites from equatorial to subantarctic latitudes in the southwest Pacific. Cores are dominated by a range of biogenic hieroglyphs that are in the main taxonomically nondiagnostic and are identified principally by subtle color contrasts with the host sediment, or by pyritization. Structures include abundant mottles, blebs and spots, common streaks and wisps, and rarer threads, tubes, rinds, halos, rings, and pockets. Planolites-like and possibly Trichichnus burrows occur, and below some critical sub-bottom depth in most holes a Planolites-ChondritesZoophycos ichnofaunal assemblage is developed. The megascopically apparent intensity of bioturbation in cores is summarized on stratigraphic logs for each site, and ranges widely both within and between sites. Controlling factors were unlikely to have been variations in either substrate character or water depth as primary sediments were almost wholly pure (foraminifer-bearing) nannofossil oozes deposited at middle bathyal (1-2 km) depths. Instead, fluctuations in sedimentation rates and in the rate of supply of organic nutrients at the seafloor were probably the influential controls on the degree of sediment bioturbation. Overall increases in both these parameters in the Neogene can explain the upward disappearance of the Planolites-Chondrites-Zoophycos assemblage in cores. Fundamental causes probably relate to the Cenozoic evolution and fluctuations in position and level of productivity of surface and intermediate-depth water masses in the southwest Pacific.
