Article

Palynology, ammonites and sequence stratigraphy fromtethyan middle oxfordianto lower kimmeridgian, S-E France comparison with the boreal realm

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  • RJDC GEOLOGICAL CONSULTANT
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Abstract

The results presented in this paper have to be considered as a contribution to an important project whose aim is the geological study and global sequence stratigraphie correlation (multidisciplinary approach) of the Middle Oxfordian to Tithonian of different French areas, from the Sub-Boreal sections of Boulonnais, Normandy, Charente, Quercy, to the Tethyan sections of the Vocontian Trough. The review includes shallow water as well as deep water sections. The concept of this project is similar to the SE France Berriasian study published by the same working group (JAN DU CHÊNE et al., 1993). A dinocyst stratigraphie distribution chart zone is proposed between the Middle Oxfordian Transversarium Zone and the basal Upper Kimmeridgian Acanthicum of the Mesogean deep water reference sections of Vergons and Châteauneuf-d'Oze (Vocontian Trough; SE France). The two sections studied are rich in ammonites and are there-fore easily correctable with other Vocontian Trough sections to propose a sequence stratigraphic break-up primarily based on bed geometry, lithofacies and stratonomic observation, complemented by palynological and geochemical data, such as Mn content. The 3rd order sequences are stratigraphically calibrated using biostratigraphic information based on ammonites and dinocysts. From Sequence Ox 5 to Kim 3, most of the 3rd order sequences proposed by HARDENBOL et al. (1998) are stratigraphically recognised correctly with the exception of Kim 2. Data given by different geological tools as well as from other areas (particularly from the north of the Aquitaine Basin) suggest a double sequence Kim 2. To avoid any confusion with the HARDENBOL et al. cycle chart, the sequences proposed in this paper are called Kim 2' and Kim 2" respectively at the base and at the top of the interval. Correlation with the Boreal and Sub-Boreal realms are also proposed. The correlation takes into account recent papers on ammonite distribution at the Oxfordian-Kimmeridgian boundary. The joint occurrence of both Amoeboceras bauhini(a boreal species common in the base of the Baylei Zone) and Taramelliceras hauffianum (a Mesogean species) in outcrops of South Germany strongly suggests that the base of the Baylei Zone (and consequently the Oxfordian-Kimmeridgian boundary) corresponds to the base occurrence of T. hauffianum in the uppermost part of the Hauffianum subzone in the Tethyan realm. Most of the important dinocyst species have been observed in fairly comparable stratigraphic position to those known in the Boreal and Sub-Boreal realms. Additional information will be given in the near future by integrated studies presently in progress along the Upper Jurassic margins of the Aquitaine Basin (Quercy and Charente) and in Normandy.

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... jurassica and Tubotuberella dangeardii throughout the productive part of the succession mean that this section is no younger than Early Kimmeridgian. The range tops of these forms are Early Kimmeridgian (Lam and Porter, 1977; Riding, 1987; Riding and Thomas, 1988; Barron, 1989; Jan du Chêne et al., 1999). T. dangeardii is especially typical of the earliest Kimmeridgian (Baylei and Cymodoce chronozones ) (Riding and Thomas, 1988). ...
... They are poorly preserved and are mainly related to warm water environmental conditions (Ridding and Hubbard, 1999). The studied section could be correlated with the Tethyan realm and two correlatable events identical to those of Jan du Chêne et al. (1999), were identified (Fig. 3). These are as follow: 1) Cribroperidinium globatum event: This event starts at Mid Oxfordian and ends in Early Kimmeridgian. ...
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... A sequential analysis of the Kimmeridgian has already been established from the Crussol section Ferry and Atrops, 1989) and from the Châteauneufd'Oze section (Jan du Chêne et al., 2000). Moreover, Moussine-Pouchkine et al. (1998a, 1998b display detailed bed-by-bed correlation of the Lothari ammonite subzone. ...
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