Edwige Masure

THE END OF A MYTH: ARPYLORUS ANTIQUUS PALEOZOIC DINOFLAGELLATE CYST

Abstract Arpylorus antiquus, erected by Calandra in 1964, was isolated from upper Silurian sedimentary rocks from the Mechiguig 1 borehole in southern Tunisia, with other palynomorphs. The folded vesicle and the quadrangular form of the aperture break down into platelike fragments, resembling the tabulation of dinoflagellates. The presence of these elements has been used to interpret A. antiquus as a dinoflagellate cyst. The morphology and affinity of A. antiquus is reinterpreted herein based on investigation of larger sets of samples, including material from the type locality, together with material of Algeria, Saudi Arabia, and Brazil. More complete specimens than those previously described have been observed using gentle laboratory techniques, showing a large development of a fine membrane at the periphery of vesicles. This element was destroyed using classical palynological treatments, implying that the holotype is an incomplete specimen. The membrane at the periphery of vesicles and dorsoventral differentiation of these vesicles suggest that A. antiquus is a part of a more complex biological structure. We suggest a possible relationship with eurypterids, arthropods related to phyllocarids, represented by abundant fragments in the assemblages. Arpylorus antiquus is possibly a structure of storage. The chemical composition of A. antiquus using a Fourier transform infrared FTIR microspectroscopy analysis, reveals a wall composed of biopolymer that is not consistent with dinosporin. We conclude that Arpylorus antiquus is definitively not a dinoflagellate cyst. Although dinoflagellates may have older Paleozoic or even Proterozoic ancestors as the biomarker record may suggest, the dinoflagellate tabulation evolved only in the early Mesozoic.

Age of the Guatemala breccias around the Cretaceous-Tertiary boundary: relationships with the asteroid impact on the Yucatan

Abstract The upper part of the near K/T boundary limestone breccia deposits which crop out in Guatemala near 16 °N contains impact remains: altered glass spherules (tektites) and elevated concentrations of iridium. This suggests that these deposits could result from the impact of the K/T boundary asteroid on the Yucatan. However, their matrix contains foraminifers of the Eugubina Zone and calcareous nannofossils of the CP1a Zone, an association characterizing Early (but not the earliest) Danian. This unusual assemblage of K/T and Danian components suggests that the upper part of the breccia was reworked several thousands of years after the K/T event.

Les kystes de dinoflagellés du Crétacé moyen de la marge atlantique brésilienne, le bassin de Santos

Resume L’etude des kystes de dinoflagelles en matiere organique du puits petrolier 1-SPS-14A du bassin de Santos se place dans l’intervalle chronostratigraphique de l’Albien au Turonien. C’est pendant cet intervalle que se produit l’ouverture definitive de l’Atlantique equatorial qui met en contact la Tethys atlantique et le proto-Atlantique Sud. Le mega-ensemble sedimentaire du Golfe compose des Formations d’Ariri et Florianopolis ne contient pas de dinoflagelles. Ils sont presents qu’a partir de l’ensemble de la Mer de la Formation Guaruja depose lors de la phase d’expansion oceanique. Les taxa de dinokystes sont semblables a ceux connus en Tethys. Dinopterygium cladoides, Litosphaeridium arundum, Odontochitina rhakodes et Systematophora cretacea datent de l’Albien moyen la base de la plate-forme carbonatee de cette derniere Formation non datee par les autres microfossiles. La base de la Formation Itanhaem est attribuee a l’Albien terminal ou a la base du Cenomanien sur la presence de Palaeohystrichophora infusorioides et Ovoidinium verrucosum. La limite cenomano-turonienne n’a pas ete caracterisee par les dinokystes. Le sommet de la Formation Itajai-Acu a livre Atopodinium iuvene connu au Turonien. Les disparitions evenementielles sont placees en regard des biozones de foraminiferes, de nannofossiles et des palynozones etablies anterieurement. La diversite des associations reste inchangee selon les environnements de depots, seule l’abondance relative des taxa varie. Les Coronifera, Florentinia, Ovoidinium, Spiniferites et Trichodinium dominent en nombre les associations des depots carbonates (Formation Guaruja). Ils cedent la place aux Cribroperidinium et Cyclonephelium dans les sediments detritiques (Formation de Itanhaem). Seule une espece est infeodee a la plate-forme carbonatee : Subtilisphaera guarujaensis n. sp.

Morphology of the dinoflagellate genus Atopodinium Drugg emend., senior synonym of Maghrebinia Below and Bejuia Stover & Williams

Abstract The genus Atopodinium, described by Drugg (1978), is herein emended. Atopodinium is a senior synonym of Maghrebinia Below 1981 emend. Masure 1988 and of Bejuia Stover & Williams 1987. A re‐examination of the holotype and isotypes of the type species Atopodinium prostatum Drugg 1978 emend. and of A. haromense Thomas & Cox 1988, shows that the gonyaulacoid paratabulation is incompletely delineated by ornamental features, and the archeopyle is apical, type (tA)a, with precingular accessory parasutures. Analysis of species previously attributed to Bejuia (Atopodinium polygonalis Beju 1983 nov. emend.), and to Maghrebinia (Atopodinium chleuh (Below 1981) comb, nov., Atopodinium mirabilis (Below 1984) comb. nov., Atopodinium perforatum (Clarke & Verdier 1967) comb. nov.), and here assigned to Atopodinium, suggests that a similar pattern of gonyaulacoid paratabulation can be discerned in each of them. Species of Atopodinium may be distinguished by a large non‐ornamented ventral area. The paratabulation ...

Influence of Palaeoenvironmental Factors on the Encystment of Cretaceous Dinoflagellate Cysts (Ceratiaceae): A Study from Godavari Graben, Southern India

ABSTRACT Muderongia staurota forms with long appendages at the distal end of the apical, lateral and antapical horns have been recovered from the Lower Cretaceous Gangapur Formation of Upper Gondwana sequence from the Chintalapudi Sub-Basin (India). The number of distal appendages reflects the number of plates forming the horns. We include these forms in the new species Muderongia gangapurensis sp. nov. The dinoflagellate cysts recovered suggest a late Berriasian to Valanginian for the lower part and a Hauterivian/Barremian age for the upper part of the studied interval of MJR-11 borehole. Unusual Muderongia and Odontochitina cysts bearing similar long appendages have only occasionally been described or illustrated in the literature from sediments rich in continental organic matter. We suggest that Cretaceous Ceratiaceae bearing such appendages are cysts of thecae that encysted in particular environments, where light, salinity, temperature and chemistry of water masses might have been key to their development. Our conclusion is supported by the high morphological variability of horns in modern Ceratiaceae, which reflects environmental factors. We discuss the plasticity of horns in the fossil record and note that such plasticity is recurring in Ceratiaceae, at least in the Early Cretaceous (145 Ma).