|
Ancient Shelf Anoxia |
Laboratoire de Géologie, Faculté des Sciences, Parc de Grandmont, F 37200 Tours, France
The formation of mid-Cretaceous glaucony-rich beds on the margins of the Vocontian (SE France) is correlated with the black shales intervals in the adjacent basinal facies. These black shales are a local expression of widespread oceanic anoxic events during the late Lower Aptian, Lower and Middle Albian, and late Upper Albian. An interfingering of glaucony-rich beds and black shales may be seen in some Lower Albian sections in outer shelf facies. Furthermore, one of the most important black shale horizons (the Paquier Level) contains numerous thin layers rich in glaucony grains that often developed at the expense of in situ faecal pellets. This autochthonous origin implies a direct relationship between the laminated black shale facies deposited under anoxic conditions, and glaucony as a subsequent diagenetic product formed under the influence of slightly oxygenated waters. Mineralogical and chemical data acquired on green grains characterize ‘evolved’ assemblages rich in micaceous glauconite, suggesting that the Paquier Level represents a condensed interval. These observations may have considerable significance for mid-Cretaceous sequence stratigraphy and palaeoceanographic investigations.
This article has been cited by other articles:
 |
|
 |
|
  A. AMOROSI and M. C. CENTINEO Glaucony from the Eocene of the Isle of Wight (southern UK): implications for basin analysis and sequence-stratigraphic interpretation Journal of the Geological Society, 1997; 154: 887 - 896. [Abstract] [PDF]
|
|
