|
Department of Earth Sciences, The University, Parks Road, Oxford OX1 3PR, UK
Refined biostratigraphic data from India and new data from Iran confirm that several major phosphogenic events took place within the Precambrian-Cambrian boundary interval across southern and central Asia. The palaeoceanographic setting of these event is briefly reviewed with reference to changes in the biosphere, where it is shown to have coincided with a widespread radiation of skeletons of diverse mineralogy (siliceous, apatitic, aragonitic, calcitic). Although a connection between palaeoceanographic changes and biomineralization cannot yet be demonstrated, the possibility that phosphogenesis enhanced the fossil record at this point is tested.
Preliminary criteria are put forward and illustrated for the recognition of primary phosphatic skeletons, secondarily phosphatized organic remains and secondarily phosphatized carbonate skeletons. This latter category comprises a major proportion of phosphatic small shelly fossils in the Chinese and Iranian sequences. Three kinds of phosphatic taphofacies are then distinguished for early skeletal biotas: residual phosphatic, phosphatized carbonate and phosphatized organic facies (i.e. lägerstatten conditions). In several phosphogenic regions, the skeletal fossil record begins with residual phosphatic assemblages, followed by phosphatized carbonate taphofacies. Such diagenesis played an important role in enhancing the fossil record at this time because the first skeletons were thin (5–40 µm) and vulnerable to neomorphism in dolomitic or clastic facies. Phosphatized organic remains appeared locally during the major phosphogenic events, perhaps associated with more anoxic seafloor conditions that supressed the shelly calcareous benthos.
This article has been cited by other articles:
 |
|
 |
|
  S. Clausen and J. J. Alvaro Lower Cambrian shelled phosphorites from the northern Montagne Noire, France Geological Society, London, Special Publications, 2007; 275: 17 - 28. [Abstract] [PDF]
|
|
