Bruno Granier

The contribution of calcareous green algae to the production of limestones: a review

ABSTRACT Calcareous green algae (CGA) are an artificially united but highly heterogeneous group of large unicellular benthic algae with one character in common: all have the capability of secreting a calcareous coating on the outer side of the cytoplasmic envelope. Today, they are a major contributor to carbonate sedimentation at all scales from clay-sized particles (aragonitic needles) to coarser grains (sand and gravel) and even to plurimetric sedimentary structures. There are fossil analogues to the features listed above. Phycologists know best Halimeda, Penicillus, Acetabularia and Cymopolia; micropaleontologists and carbonate sedimentologists are most knowledgeable about Acicularia, Clypeina, Neoteutloporella, Salpingoporella, Anthracoporella, Boueina, and Eugonophyllum. The CaCO3 precipitated to form the coating is generally aragonite (the orthorhombic form) but there are short periods in the geologic record during which its calcite variant (the rhombohedric form) existed contemporaneously in discrete species. Recent studies on Halimeda have shown that some of the Bryopsidales have the capability to calcify strongly in the lower portion of the euphotic zone (where respiration becomes more important than photosynthesis in the process of mineralization) and to produce positive sedimentary reliefs (bioherms) in situ below the fair-weather wave base. Previous models of paleoenvironments considered the presence of Dasycladales or Bryopsidales to indicate shallow-water, that is the upper euphotic zone (from the sea surface down to -25 m), and predominantly low-energy, protected, lagoonal environments. When the algal remains were found in grain-supported facies, they were taken to have been subjected to dynamic transport and therefore indicative of high-energy environments of deposition. The new deeper-water finds have changed interpretations of the environments ascribed fossil algae. A current conception is that ancestral inarticulated Bryopsidales could have grown at depths as great as -120 m (near the base of the lower euphotic zone). This preliminary review concludes with suggestions about fields for continuing investigations.

Les Algues Dasycladales du Permien et du Trias. Nouvelle tentative d’inventaire bibliographique, géographique et stratigraphique

The present work enlists as comprehensively as possible the Permian and Triassic Dasyclad algae. For each species, localities and stratigraphic positions attached to the quoted specimens are detailed within the synonymy list .

Répartition biostratigraphique des orbitolinidés dans la biozonation à ammonites (plate-forme urgonienne du Sud-Est de la France). Partie 1 : Hauterivien supérieur - Barrémien basal.

The proposed biostratigraphic distribution of orbitolinids from the Upper Hauterivian and the lowermost Barremian of SE France is correlated with the ammonite biozonation. It is based on the detailed study of eight sections which delivered orbitolinids intercalated with or capped by levels with ammonites and, in some cases, echinids and dasycladales. Among the 24 species of orbitolinids present during that period, 3 are restricted to the Late Hauterivian: Praedictyorbitolina busnardoi, Paleodictyoconus beckerae and Valserina primitiva.

Brasiliporella, a new mid-Cretaceous dasycladacean genus: the earliest record of the Tribe Batophoreae

New material collected in Albian and Cenomanian strata from Brazil helps us to better understand the structure of a poorly known dasycladacean alga, Holosporella nkossaensis P. Masse, in Bull Centr Rech Explor-Prod elf aquitaine, 19: 301–317, 1995: each of its fertile laterals, which are regularly arranged in verticils along the cylindrical algal thallus, consists of a distally inflated primary bearing two vesicular ampullae in terminal position. These traits are not known in representatives of the genus Holosporella Pia, 1930 nor in any genera described to date. On this basis, we introduce the new genus Brasiliporella with Brasiliporella nkossaensis emend. nov. comb. as its type-species. We also discuss the systematic affinity of the new taxon: it is ascribed to the Tribe Batophoreae, and in a broader manner the current paleontological ‘interpretation of the concept’ (in French: ‘acception’) of the Order Dasycladales, with the creation of two new families and accordingly with the emendation of two other families.

Albian roveacrinids from the southern Congo Basin off Angola

Abstract Microfacies study of the Albian of the Pinda Formation in Well BAGRE 1 (Block 2, Angola offshore) revealed several echinoderm-rich layers. Contrary to other fossil remains, the echinoderms have not been dolomitized and are therefore potentially useful for stratigraphic purposes. The remains are compared to those found in the Sergipe Basin in Brazil and assigned to the Roveacrinidae, a group of stemless microcrinoids. The following species were identified: Roveacrinus communis Douglas, 1908; Roveacrinus cf. communis Douglas, 1908; Roveacrinus aff. geinitzi Schneider, 1989; Roveacrinus pyramidalis Peck, 1943; Roveacrinus sp. The assemblage provides a relatively precise stratigraphic framework in comparison to previous age determinations. Although some species have a wide stratigraphic range, the occurrence of the genus Roveacrinus and the species R. pyramidalis Peck, 1943 suggests a late Albian age, which makes the Angolan assemblages among the oldest known. The main area of distribution of roveacrinids is the Tethyan realm, so these extremely southern occurrences in Angola appear to support the theory of a seaway through the Gulf of Guinea in the late Albian.

Calcareous algae from Upper Albian - Cenomanian strata of the Potiguar basin (NE Brazil)

Calcareous Albian - Cenomanian strata in the Potiguar basin yield a number of microfossils , among which are calcareous algae (Dasycladales and Corallinales). This data, together with an inventory of previous discoveries, enabled the discussion of their biogeography. These benthic organisms probably came from the early Central Atlantic Ocean through its northwestern neck between Africa and South America and thus reached the early South Atlantic platforms.

Les algues et foraminifères benthiques du Jurassique supérieur et du Crétacé inférieur du Sénégal

Very few data have been published on the microfossil contents of the Upper Jurassic and Lower Cretaceous strata of Senegal. Foraminifera were mentioned (though mostly not illustrated) while Algae were not. Among the latter, two new species (Holosporella senegalensis and Dissocladella sp.) have been identified. On the basis of recent developments in algal taxonomy, new combinations [Actinoporella lucasi (Emberger), Clypeina sulcata (Alth) and Holosporella somalica (Conrad et al.)] are proposed and discussed. With respect to biogeography, fossil algal assemblages from Senegal are very similar to those found in North Africa.

Revision of the Jesse Harlan JOHNSON Collection. Part 1. Some fossil Dasycladales from Guatemala

This first report is a revision of fossil calcareous green algae (Dasycladales) described from the Upper Cretaceous and Paleocene series of Guatemala. Among other things in their 1965 paper J.H. Johnson and H.V. Kaska introduced three new species originally referred to the genera Acroporella, Cylindroporella, and Cymopolia. One species, which has previously been referred to the genus Cylindroporella, is a foraminifer.

Upper Aptian calcareous algae from Padurea Craiului (Northern Apuseni mountains, Romania)

A study of calcareous strata previously assigned to the Barremian-Early Aptian interval in the northwestern part of P?durea Craiului, (Apuseni Mountains), led to the identification of a micropaleontological association indicative of a Late Aptian age. Unequivocal evidence for the Late Aptian assignment of these limestones is the presence throughout the sequence of two orbitolinid species, Mesorbitolina texana (ROEMER) and Mesorbitolina subconcava (LEYMERIE). The most interesting sections are located in the neighbourhood of Subpiatr?, where both outcrops and a quarry facilitated detailed analyses. In this area, the Upper Aptian succession consists basically of three types of macrofacies: 1, limestone with rudists; 2, limestone with Bacinella and 3, limestone with corals, each of them showing several types of microfacies. Bacinella structures are the most common feature in the whole succession, irrespective of the macrofacies. This paper focuses on an algal association that was identified in several levels within the succession. Dasycladalean algae are more frequent, and are commonly found in grain-dominated fabrics (mostly grainstone textures), in association with orbitolinid foraminifera and bioclasts of corals, rudists and gastropods. However, a few species are present only in mud-dominated fabrics (i.e. lower-energy intervals). The dasycladalean association from the Upper Aptian deposits of P?durea Craiului is of special interest, for this group registered a dramatic decline at the Lower Aptian/Upper Aptian boundary, as confirmed by the relative scarcity of the Dasycladales in the Upper Aptian carbonate deposits.

Age des carbonates de plate-forme du Site 392A DSDP (Leg 44), marge Atlantique du continent Nord-Américain

Abstract DSDP Site 392A has been drilled on the shelf edge of Blake Plateau (Blake Nose) in the northwestern Atlantic Ocean. At 98 m sub-bottom, drilling reached the top of a carbonate platform series. A Neocomian? or older age was first ascribed to these limestones. Based on the study of the microfossils, benthic foraminifera and green algae, a Berriasian-early Valanginian age can be ascribed to most of the series. The drowning of the platform, therefore occurred in Valanginian times, and not in the Barremian.