Oxygen-dependent Ichnocoenose in Paleo-pelagic Substrates

JIN Hui-juan; LI Yu-ci; FANG Guo-qing

On the basis of sedimentological and palichnological investigations on the nearly 20 profiles of 9 paleo-pelagic depositional areas in China, some conclusions on the identification of the relationship between ichnocoenose in paleo-pelagic substrates and the oxygen content have been drawn as follows: ①The difference in the relative oxygen content of the pelagic oxygen-depleted substrate produces a different representative ichnofossil association, i.e. the dissolved oxygen content of the oxygen-depleted substrate indicated by Associations A, B and C, which are mainly composed of Megagrapton, Paleodictyon and Protopaleodictyon , of Scalarituba and Phycosiphon , and of Chondrites and Zoophycos , respectively, decreases gradually with different associations; ②The size of ichnofossil burrows usually has a normal relationship with the oxygen content of substrates, namely the diameter of burrows becomes smaller with decreasing of the oxygen content; ③The differentiation of ichnofossils decreases with decreasing of the oxygen content of substrates; ④It should be prudent to apply some individual ichnofossils in identifying the oxygen-depleted environment, for instance, Chondrites and Zoophycos can not be always regarded as an ichnofossil indicator to an oxygen-depleted environment, it is necessary to investigate multiple factors before a conclusion that more accords with the true fact can be drawn.

Lanzhou Institute of Geology, Chinese Academy of Sciences, Lanzhou 730000

Received Date: 2002-12-26

Rev Recd Date: 2003-01-10

Publish Date: 2003-03-10

Key words:

Abstract: On the basis of sedimentological and palichnological investigations on the nearly 20 profiles of 9 paleo-pelagic depositional areas in China, some conclusions on the identification of the relationship between ichnocoenose in paleo-pelagic substrates and the oxygen content have been drawn as follows: ①The difference in the relative oxygen content of the pelagic oxygen-depleted substrate produces a different representative ichnofossil association, i.e. the dissolved oxygen content of the oxygen-depleted substrate indicated by Associations A, B and C, which are mainly composed of Megagrapton, Paleodictyon and Protopaleodictyon , of Scalarituba and Phycosiphon , and of Chondrites and Zoophycos , respectively, decreases gradually with different associations; ②The size of ichnofossil burrows usually has a normal relationship with the oxygen content of substrates, namely the diameter of burrows becomes smaller with decreasing of the oxygen content; ③The differentiation of ichnofossils decreases with decreasing of the oxygen content of substrates; ④It should be prudent to apply some individual ichnofossils in identifying the oxygen-depleted environment, for instance, Chondrites and Zoophycos can not be always regarded as an ichnofossil indicator to an oxygen-depleted environment, it is necessary to investigate multiple factors before a conclusion that more accords with the true fact can be drawn.

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Oxygen-dependent Ichnocoenose in Paleo-pelagic Substrates

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