Abstract
Abstract. Research carried out on the Upper Jurassic dinoflagellate cyst assemblages of the Sub-Tethyan marine realm, show that populations of the dinoflagellate cysts Subtilisphaera? inaffecta and S.? paeminosa are predominant in shallow water marginal marine or brackish environments. The distribution of groups of dinoflagellate cysts, micrhystridid acritarchs and variations of terrestrial inputs represented by phytoclasts are presumed parameters of the salinity balance during such Late Jurassic depositional environments. In this context, the shagreenate to faintly granulate S.? inaffecta appears to be an opportunistic taxon with an ability to prosper in brackish environments. In contrast, the coarsely granulate to pustulate paeminosa form is seemingly less eurytopic and flourishes with success in shallow, marginal marine, environments. SEM studies reveals that the two morphotypes possess transapical archaeopyle sutures on what is usually considered the antapex. Following these observations the cysts are interpreted in a reverse sense. Consequently, the attribution to the genus Subtilisphaera becomes inappropriate. The two morphotypes, interpreted as variants of a single species, are attributed to the genus Corculodinium Batten & Lister, 1988 for which a new emendation is proposed. The specific epithet inaffecta is considered legal over paeminosa.
Highlights
Paeminosa are predominant in shallow water marginal marine or brackish environments
Research carried out on the Kimmeridgian and Tithonian dinoflagellate cyst assemblages in the Sub-Tethyan (SubMediterranean) marine realm, record populations of Subtilisphaera specimens that are commonly predominant
Phytoclast particles are dominant in the Kimmeridgian samples and amorphous organic matter (AOM) is occasionally abundant in the Tithonian samples
Summary
Research carried out on the Kimmeridgian and Tithonian dinoflagellate cyst assemblages in the Sub-Tethyan (SubMediterranean) marine realm, record populations of Subtilisphaera specimens that are commonly predominant. 1, 2), (Eudo.xus section for the phytoclasts (Fig. 3) and for the sporomorphs; Ammonite Zone), the Subtilisphaera population reaches a the opposite hypothesis of a hypersaline environment maximum of 40?'0 (expressed as the total of organic niicro- has been assumed (Bernier & Courtinat, 1979; Kunz, 1990) The Solen well The Tithonian samples examined from the Solen Well (Gigas Ammonite Zone; Quercy; Figs 1, 2) yielded low diversity assemblages of dinoflagellate cysts and sporomorphs plus large amounts of phytoclast particles (mainly abundant in pure limestones) and amorphous organic matter (AOM; abundant in marly limestones). Variable distribution of groups of dinoflagellate cysts, micrhystridid acritarchs and prasinophytes are associated with variations of terrestrial inputs represented by phytociasts that are supposed parameters of the salinity balance prevailing during the Eudoxus Ammonite zone at Loches section and the Gigus Ammonite Zone of the Solen well
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