Search

Abstract: A scanning and transmission electron microscopy-based ultrastructural study of Arcellites humilisVillar de Seoane and Archangelsky, 2008, from the Kachaike Formation and Piedra Clavada Formation (Albian-Cenomanian) from several localities in Patagonia (Argentina), is presented in this paper. TEM-photographs of thin-sectioned specimens show a thick spore body wall composed of three layers: a thin and dense exine, an inner granular perine sublayer with irregularly disposed small channels and lacunae, and an outer alveolate perine sublayer with channels perpendicular to the external surface. Transverse sections of the A. humilis wall are compared with fossil and extant species of Marsileaceae. We show that the wall ultrastructure is similar in A. humilis, A. santacrucensis, A. disciformis, A. stellatus and Regnellidium upatoiensis. However, the body wall and acrolamella of A. humilis are more similar to those of R. diphyllum Lindman than to those of the Marsilea L. or Pilularia L. species. Water ferns such as members of the Marsileaceae played an important role in aquatic or semi-aquatic niches in Patagonian Cretaceous floras, suggesting that high humidity and temperature prevailed during the Albian-Cenomanian in this region of Argentina. [Copyright &y& Elsevier]

Abstract: Palynomorph assemblages have been recovered from the upper levels of the Río Mayer Formation and the basal levels of the Kachaike Formation exposed at the Puesto El Moro Creek, southwest of Santa Cruz Province, Argentina. Forty-five spore species and 25 pollen taxa (including six angiosperms) have been identified. The palynological assemblages of the upper levels of Río Mayer Formation are dominated by pteridophytic spores, while Classopollis is a common element. In the Kachaike Formation, the angiosperm pollen grains are more diverse and abundant than in the underlying unit, and Cheirolepidiaceae pollen continues to dominate. The presence of scarce angiosperm pollen, represented by Clavatipollenites sp., allows reference of the assemblage recorded in the upper levels of the Río Mayer Formation to the Aptian Antulsporites-Clavatipollenites Zone. In addition, the lower levels of the Kachaike Formation are referred to the late Aptian–early Albian, based on the presence of Asteropollis asteroides, Pennipollis peroreticulatus, Clavatipollenites sp. and scarce tricolpate pollen. From the three major stages of the early angiosperm evolution in southern South America that have been previously recognized, the palynoflora of the upper levels of the Río Mayer Formation can be referred to Stage I (late Barremian–Aptian), whereas the assemblages recognized in the Kachaike strata are comparable to Stage II (latest Aptian– earliest Albian). [Copyright &y& Elsevier]

Abstract: The schizaeaceous extant genus Mohria has a distribution restricted to South Africa and Madagascar area. Its cicatricose spores are characterised by their large size and muri with hollow longitudinal channels unknown in other schizaeaceous genera. Fossil spores that sometimes have been referred to Mohria lack this typical character and therefore the determinations were discarded. Early Cretaceous (Albian) sediments from Patagonia, referred to the Piedra Clavada Formation of the Austral Basin, contain spores that have the characters now found in Mohria. These fossils are hereby assigned to the new genus Palaeomohria that includes several morphological types. The paleogeographical proximity of South Africa and Patagonia in Southwestern Gondwana persisted from the Permian to the Early Cretaceous, during a time when floras of both regions had significant similarities. In this context, the finding of Mohria-like spores in Patagonia suggests that the distribution of this fern was more extended in the past and became restricted while the continents shifted apart during the Cretaceous/Tertiary. The two living Mohria species may then represent relict taxa of a much more varied and rich group that flourished during the Early Cretaceous in SW Gondwana. [Copyright &y& Elsevier]

Abstract: Megaspores from the Kachaike and Piedra Clavada formations of Albian and ?Cenomanian age in Santa Cruz Province, Argentina, are described and illustrated by scanning electron micrographs. These include six new species: Arcellites humilis, A. pentagonalis, A. sp. A, Erlansonisporites verrucatus, Minerisporites aequatus and Striatriletes areolatus. Striatriletes reticulatus (Zerndt) Sweet and Trileites cf. T. murrayi (Harris) Marcinkiewicz are recorded for the first time from Argentina. Another eight species that were previously recorded in Patagonia are also described based on specimens found in new localities. Comparison with similar megaspore taxa from other palaeofloristic regions suggests that the megaspores in these formations are of Albian age (perhaps extending into the Cenomanian), confirming previous data obtained from other studies of marine and terrestrial fossils from these formations. The botanical affinities of the megaspores with heterosporous lycopsids (Isoetaceae and Selaginellaceae) and water ferns (Marsileaceae and Salviniaceae) suggest that a warm, humid climate and abundant water bodies prevailed during the Albian in Patagonia. The stratigraphic distribution of all known Early Cretaceous Patagonian megaspores allows recognition of three separate assemblages, M1–M3, each characterized by several exclusive taxa. M1 spans the Berriasian–Barremian, M2 is Aptian, and M3 is Albian–?Cenomanian. [Copyright &y& Elsevier]

Abstract: Pollen grains characteristic of tropical Northern Gondwana (Schrankipollis, Brenneripollis and Pennipollis peroreticulatus) have been recorded from the Cretaceous of Patagonia. They were recovered from the Late Albian–Cenomanian Kachaike Formation in Santa Cruz Province, southern Argentina. The palynological assemblages are dominated by gymnosperm pollen and bryophyte-pteridophyte spores, whereas angiosperms are poorly represented. The angiospermoid type Schrankipollis has not been reported previously from Argentina, and a new species S. kachaikensis is described. Two species of Brenneripollis (of uncertain affinity) and Pennipollis peroreticulatus (related to the Alismatales) are also reported. The first appearances of Pennipollis peroreticulatus are clearly diachronous from north to south, ranging from the Barremian in tropical regions to the Coniacian–Santonian in Antarctica. S. kachaikensis and P. peroreticulatus show restricted stratigraphic distributions through the Kachaike Formation and may be stratigraphically useful markers. A tetrad of Walkeripollis (related to modern Winteraceae) is also recognized. This is the oldest record of Winteraceae in the southern temperate region where the family lives today. Evidence for migration of Winteraceae from tropical Gondwana to Antarctica and Australia throughout South America, is provided by this new finding. The presence of tropical elements in the austral margin of South America gives support to previous studies on the expansion of warm temperatures towards high latitudes during the mid Cretaceous. [Copyright &y& Elsevier]

Abstract: A palynological review of cingulate spores having affinities with the fern family Pteridaceae found in Lower Cretaceous assemblages of Patagonia, Argentina, is presented. The new genus Sotasporites, with three species is defined: S. triangularis sp. nov., S. elegans (Archangelsky and Gamerro) comb. nov. and Sotasporites sp. Comparisons with spores of extant members of the family show close similarities in shape and sculpture with the products of taxa living in the southern Andes. Muricingulisporis annulatus Archangelsky and Gamerro, originally defined from the Aptian Baqueró Group of Patagonia, is maintained in its original combination after the revision of the types. The differences from Cyatheacidites of the family Lophosoriaceae, to which this species was assigned elsewhere, are underscored. Finally, three species of Contignisporites, viz. C. cooksoniae (Balme) Dettmann, C. glebulentus Dettmann and C. burgeri Filatoff and Price are described and reviewed. It is concluded that the Pteridaceae played an important role in Patagonia and were represented by several taxa during the Early Cretaceous. [Copyright &y& Elsevier]

Abstract: A new araucarian pollen cone Alkastrobus peltatus gen. et sp. nov. is described from the Anfiteatro de Ticó Formation (Baqueró Group) of Aptian age in Santa Cruz province, Argentina. The pollen cones are mostly compressions and their microsporangia contain the well-known Cyclusphaera Elsik pollen. The morphology, anatomy and ultrastructure of the pollen cones along with the pollen grains were examined under light, scanning and transmission electron microscopy. An affinity with the Araucariaceae is established on the basis of microsporophyll anatomy and morphology, and comparison of Cyclusphaera with other araucarian pollen grains. In Patagonia during the Cretaceous Period, plants producing Araucariacites, Balmeiopsis and Cyclusphaera pollen lived together. All three types of pollen are found inside microsporangia. Araucariacites, the only type that has survived to the present day, is found in the extant genera Araucaria and Agathis. The new genus confirms the broad diversity that Araucariaceae attained during the Early Cretaceous within western Gondwana. [Copyright &y& Elsevier]

Three new species of the cycadean pollen cone Androstrobus, viz. A. munku, A. patagonicus, and A. rayen, are described. All specimens are represented by microsprophylls or fragmentary cone pieces, and they have been found in the same fossil bed at the locality Bajo Grande, in Santa Cruz province, Argentina, which is referred to the Anfiteatro de Ticó Formation of Aptian age. This is the first record of the genus in Argentina and South America. The good preservation of the material allowed the study of cuticles and pollen with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is noted that Androstrobus is a poorly defined genus that needs a revision of the type material as well as new specimens from the type locality to certify the presence of pollen. Comparisons with other Androstrobus species are made, especially with those that have been described with cuticular characters and structure of pollen. Attention is paid to the similarity of the alveolate pollen ultrastructure of the Patagonian fossils with some extant cycads, especially with genera of the Zamiaceae and Cycadaceae. The variety of pollen cones found in the same bed agrees with the presence of different vegetative organs, leaves, and fronds found previously at the same place, and that were referred to the cycads on the base of their cuticular structure. The abundance of cycads during the mid-Cretaceous in southern Argentina is a contrasting evidence with the present-day absence of the group in southern South America. [Copyright &y& Elsevier]

Abstract: The record of Cycadales in Patagonia begins in the Triassic and extends up to the Oligocene. In this region the group is highly diversified and includes several taxa represented by trunks, leaves and pollen cones. A new cycadalean genus and species, Restrepophyllum chiguoides, form the Aptian Anfiteatro de Ticó Formation, Santa Cruz province, Argentina, is described here. The fossil is a leaf compression with well-preserved cuticle. Its morphology, anatomy and ultrastructure are studied by means of light and electron microscopy. The leaf is lanceolate, serrate, and possesses a prominent midvein and decurrent laterals showing an open, simple or dichotomous venation. The leaf is hypostomatic, and the abaxial cuticle is thinner than the adaxial one. The stomata are irregularly distributed and indistinctly oriented between veins. They are monocyclic to imperfectly dicyclic (haplocheilic); the suprastomatal aperture is raised over the epidermis and the guard cells are sunken. Scattered trichomes and crystalliferous idioblasts are also present. The cuticle is composed of three layers: the outer and inner layers are lamellate, while the middle one is granulate. This new cycad leaf is compared with similar fossil leaves from Gondwana and Europe/North America, and also with similar extant cycad leaves. Based on the general morphology and the main characters of the cuticle, R. chiguoides is assigned to the family Zamiaceae; moreover it is more closely related to the living Zamia (Chigua) restrepoi (D. Stevenson) Lindstrom than to any other member of the Cycadales. Paleophytogeographic evidence suggests a South American origin of Zamia/Chigua and a further migration to northern latitudes. This new type of leaf also suggests the putative existence of a Chigua clade that may be traced back to the Early Cretaceous when two cycadalean families, Zamiaceae and Stangeriaceae, were already well-established in Patagonia. [Copyright &y& Elsevier]

An understanding of paleonvironmental and paleoceanographic evolution of the Southwestern Atlantic Ocean during the Palaeogene is prevented by the lack of precise tools to date and correlate the sedimentary units. Palynological samples collected in the upper portion of the Man Aike Formation, which crops out southern Lago Argentino area, in the southwest of the Austral Basin (50°21′45″S–72°14′30″W), contain well preserved marine organic dinoflagellate cysts, which are potentially important biostratigraphic and paleoenvironmental indicators. Herein we describe the composition of the Man Aike Formation's dinoflagellate cyst assemblages and compare them to similar assemblages collected in the same basin in the upper member of the Río Turbio Formation using Compositional Statistical Analysis. The dinoflagellate cyst assemblages from the upper part of the Man Aike Formation are highly correlated to the assemblages from the upper member of the Río Turbio Formation from outcropping sections (51°31′13″S–72°15′11″W) and with the lower part of sediment cores drilled by Yacimientos Carboníferos Fiscales in the Río Turbio Formation area. These dinoflagellate cyst assemblages show a very low correlation with the assemblages from the upper part of the Yacimientos Carboníferos Fiscales's cores. The comparison of our results with the high-resolution Southern Pacific Ocean dinoflagellate cyst zonation for the late Palaeocene to late Eocene allow us to date some of the dinoflagellate events recorded in formations of southwestern Patagonia. The assemblages from the Man Aike Formation and the lower part of the upper member of the Río Turbio Formation relate to the zones SPDZ11 and SPDZ12 and are assigned to the mid-middle Eocene (late Lutetian to early Bartonian). The biostratigraphy proposed herein constrains the age of the Man Aike Formation and equivalent units based on calcareous microfossil data, mollusks affinities and 87Sr/86Sr isotopic values to an age ranging between ∼42 and 39 Ma. The assemblages from the upper part of the upper member of the Río Turbio Formation relate to the SPDZ13 Zone, which corresponds to the late Eocene (early Priabonian). The dinoflagellate cyst assemblages indicate that they were under the influence of relatively warm, marine open waters in an inner-shelf environment for the lower part of the sections. In the upper part of the sections, the assemblages suggest shallow marine waters associated with coastal areas and high trophic levels, possibly as a result of freshwater inputs. [ABSTRACT FROM AUTHOR]