Marty, D. & Meyer, Ch.A. 2006 Depositional conditions of carbonate-dominated palustrine sedimentation around the K-T boundary (Faciès Rognacien, northeastern Pyrenean foreland, southwestern France) (original) (raw)

The Faciès Rognacien is a sequence of highly bioturbated and pedogenically modified palustrine carbonates that were deposited under oxic conditions around the Cretaceous-Tertiary (K-T) boundary in the northeastern Pyrenean foreland basin (SW France). The sedimentary structures and early diagenetic features identified (mottling, nodule formation, brecciation, pseudomicrokarst, cracking, charophytes, Microcodium) suggest deposition in a palustrine environment between the subarid and intermediate climate type. Sedimentological and paleoecological analysis enables us to distinguish two facies associations, the lacustrine pond facies and the freshwater marsh facies associations. The majority of the carbonates are attributed to the freshwater marsh facies. The lacustrine pond facies occurs only in isolated paleolows, and is identified on the basis of its paleobiological content (charophytes, ostracodes). This suggests that the palustrine carbonates of the Faciès Rognacien were deposited in a seasonal wetland (carbonate-producing freshwater marsh), rather than in the marginal zone of a large, shallow lake. In this wetland paleoenvironment, all carbonates underwent widespread pedogenesis, and small, ephemeral ponds are of limited distribution, most likely recording deposition in paleolows.