Chitinozoans and acritarchs from earliest Tremadocian strata in southern Tunisia

VECOLI, MARCO; RUBINSTEIN, CLAUDIA V.; DE LA PUENTE, G. SUSANA; SERVAIS, THOMAS B.

Sheffield

Congreso; PalAss, 50th Annual Meeting; 2006

The Palaeontological Association (PalAss)

Although there is a general agreement on the earliest Ordovician as the time of origin for chitinozoans, their biostratigraphic utility in early and middle Tremadocian strata is problematical. Gondwanan Tremadocian chitinozoan biozones are not sufficiently constrained by independent chronostratigraphical evidence, and recent investigations highlight inconsistencies between graptolite, acritarch and chitinozoan biostratigraphic correlation. We report a chitinozoan assemblage from the early Tremadocian strata of borehole Tt-1 in southern Tunisia, occurring together with abundant and well preserved acritarch suites. The acritarchs indicate a basal Tremadocian age, demonstrated by the occurrence of index taxa such as Acanthodiacrodium angustum, Ooidium rossicum, Vulcanisphaera africana, Saharidia fragilis. This age attribution is confirmed by the co-occurrence of brachiopods and phyllocarid crustaceans. Enigmatic microfossils such as Virgatasporites and Attritasporites are also present, for which a non-marine origin is inferred.Chitinozoans are poorly preserved and occur in low abundance and low taxonomic diversity. Nonetheless, a preliminary systematic assessment of the microfauna permits the identification at the generic level of specimens of Lagenochitina sp. and Eremochitina sp.A similar and age-equivalent chitinozoan suite was described from the Algerian Sahara by Combaz (1967). The present data show that biostratigraphically significant chitinozoans occur since the lowermost Tremadocian in the peri-Gondwanan palaeogeographic domain.