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Anatomy of a Condensed Section: The Lower Cenomanian Glaucony-Rich Deposits of Cap Blanc-Nez (Boulonnais, Northern France)

By
Alessandro Amorosi
Alessandro Amorosi
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Maria Carla Centineo
Maria Carla Centineo
Dipartimento di Science delta Term e Geologico-Ambientali, Via Zamboni 67, 40127 Bologna, Italy
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Published:
January 01, 2000

Abstract:

Detailed examination of the lowermost Cenomanian, glaucony–rich deposits of Cap Blatic–Nez (Northern France) reveals a hierarchy of depositional units within a stratigraphically condensed succession, providing a fundamental tool for its sequence stratigraphic interpretation.

Condensation is obvious in the highly bioturbated basal glaucony–rich unit (Strouanne Formation), where glaucony is predominantly autochtho nous, highly evolved (˂ 8% K20), and generally constitutes 60–90% of the sand fraction. Glaucony concentration decreases markedly upwards (to less than 10%) in the overlying rhythmically bedded marls and chalks (Petit Blanc–Nez Formation), where the green grains are allochthonous and comparatively less evolved (6.0–6.5% K20). Glaucony distribution shows a vertical cyclic pattern within the condensed interval. Maxima of glau cony concentrations are invariably recorded at intensively burrowed omission surfaces, interpreted as bases of either parasequences or parasequence sets.

The characterization of glaucony attributes indicates that a prolonged break in sedimentation, on the order of 0.5–1 Ma, occurred in the study area during the Early Cenomanian. The highly condensed nature of the basal glaucony–rich deposits suggests that either one or two of the third–order Lower Cenomanian depositional sequences recognized in the coeval, less condensed successions of Western Europe are missing at Cap Blanc–Nez. Glaucony maturity in the overlying marl–chalk couplets is consistent with interpretation of these deposits as Milankovitch–scalc cycles.

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SEPM Special Publication

Marine Authigenesis: From Global to Microbial

Craig R. Glenn
Craig R. Glenn
Department of Geology and Geophysics, University of Hawaii
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Liliane Prévôt-Lucas
Liliane Prévôt-Lucas
Centre de Géochimie de la Surface, Strasbourg
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Jacques Lucas
Jacques Lucas
Université Louis Pasteur, Institut des Sciences de la Teree, Strasbourg
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SEPM Society for Sedimentary Geology
Volume
66
ISBN electronic:
9781565761889
Publication date:
January 01, 2000

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