| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2005: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2004: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
Bioturbation effects of the feeding behavior of fishes and its paleontological significance throughout the geologic age are discussed in this research. In particular, biogenic sedimentary structures produced by the feeding behavior of rays are treated for the evaluation of bioturbation and biogenic mixing process of the sediments. Such the structures are well known as the trace fossil, Piscichnus waitemata. Field observations from the paleoecologic and sedimentologic viewpoints have carried out for the post-Paleogene P.waitemata-bearing strata.
The research results are summarized as the follows :
(1)The oldest record of occurrence of Piscichnus waitemata represents that from the post-Cretaceous marine sediments. However, no occurrence record has been known from the Paleogene strata. In this research, the investigator found the trace fossil from the Oligocene shallow marine sediments, the Misaki Formation distributed in the Toi Peninsula, southernmost part of Miyazaki Prefecture, Japan. T
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he data on morphology, size-dimensions, and mode of occurrence of the Oligocene Piscichnus strongly suggest that the structure was produced by a peculiar excavating mechanism, water-jetting manner.
(2)According to the previous data, the occurrence of Piscichnus waitemata was restricted to the sandy sediments of shallow marine origin. Based on the data obtained from the Plio.-Pleistocene deep-sea sediments of the Boso Peninsula and other localities (Yonaguni-jima : Okinawa, Hamada : Shimane, Toi-Peninsula : Miyazaki), the investigator leveled that the producers of P.waitemata have already invaded to the bathyal environments until the early Pleistocene. This fact implies that the habitats of the Piscichnus-animals have expanded from the shallow to the deep-sea settings during the latest Tertiary.
(3)According to observations on the Recent feeding excavations produced by rays, while the single feeding activity of a ray may be carried out during a very short interval of time, the substrate at the feeding area may sustain intense and deep sediment reworking. Considering to this fact and the new data obtained from this research project, it reveled that the effects of feeding behavior of rays are very important for the biogenic sediment mixing process, bioturbation, not only the shallow-marine but also the deep-sea sediments. Less
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