Charophytes from the Upper Jurassic-Lower Cretaceous of the northern Aquitaine Basin (SW France)
Résumé
Upper Jurassic and Lower Cretaceous charophyte assemblages
of three sites from the northern part of the Aquitaine Basin (SW
France) are studied. It allows to understand paleoecological,
paleobiogeographical and biostratigraphic features of this area
during this time, where Early Cretaceous deposits are scarce in
comparison to others European basins. The presence of Latochara
latitruncata (PECK, 1937) MÄDLER, 1955 in Chassiron
represents the most southern occurrence of this genus during Upper
Jurassic. The presence of Nodosoclavator bradleyi (HARRIS,
1939) GRAMBAST, 1969 is noticed for the first time in the assemblage
of Chassiron, and allowed the observation of the structured
layer features. The presence of Porocharacean, in association with
Clavatoracean and scarce Characean, in Cherves-de-Cognac and
Angeac-Charente is relevant concerning the hypothesis of brackish
environments. The association of charophytes with abraded specimens
of marine taxa (i.e. bryozoans) in Angeac-Charente An2-SA
and An1-SA is similar to assemblages found in deltaic-estuarine
facies from Iberian basins (Spain). The presence in the same
populations of Clavator grovesii var. grovesii (HARRIS, 1939)
MARTÍN-CLOSAS, 1996 along with C. grovesii var. discordis
(SHAÏKIN, 1976) MARTÍN-CLOSAS, 1996 and intermediate in
Cherves-de-Cognac and Angeac-Charente strata is of stratigraphic
relevance, since they have been recognised in the Maillardii, Incrassatus
and Nurrensis charophytes biozones which represent the
Berriasian. In the case of Angeac-Charente, this result differs
from the previous study of this site, which gave a Hauterivian-
Barremian age to this site, considering the charophyte as reworked
material. This result is relevant for the study of the sedimentary
history of the northern part of the Aquitaine Basin, while there is
no Latest Berriasian to Latest Albian deposits discovered in this
area.
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