Sedimentary Iron Cycling and the Origin and Preservation of Magnetization in Platform Carbonate Muds, Andros Island, Bahamas

Carbonate muds deposited on continental shelves are abundant and well-preserved throughout the geologic record because shelf strata are difficult to subduct and peritidal carbonate units often form thick, rheologically strong units that resist penetrative deformation. Much of what we know about pre-Mesozoic ocean chemistry, carbon cycling, and global change is derived from isotope and trace element geochemistry of platform carbonates. Paleomagnetic data from the same sediments would be invaluable, placing records of paleolatitude, paleogeography, and perturbations to the geomagnetic field in the context and relative chronology of chemostratigraphy. To investigate the depositional and early diagenetic processes that contribute to magneitzation in carbonates, we surveyed over 500 core and surface samples of peritidal, often microbially bound carbonate muds spanning the last not, vert, similar 1000 yr and deposited on top of Pleistocene aeolianites in the Triple Goose Creek region of northwest Andros Island, Bahamas. Sedimentological, geochemical, magnetic and ferromagnetic resonance properties divide the sediment columns into three biogeochemical zones. In the upper sediments, the dominant magnetic mineral is magnetite, produced by magnetotactic bacteria and dissimiliatory microbial iron metabolism. At lower depths, above or near mean tide level, microbial iron reduction dissolves most of the magnetic particles in the sediment. In some cores, magnetic iron sulfides precipitate in a bottom zone of sulfate reduction, likely coupled to the oxidation of decaying mangrove roots. The remanent magnetization preserved in all oriented samples appears indistinguishable from the modern local geomagnetic field, which reflects the post-depositional origin of magnetic particles in the lower zone of the parasequence. While we cannot comment on the effects of late-stage diagenesis or metamorphism on remanence in carbonates, we postulate that early-cemented, thin-laminated parasequence tops in ancient peritidal carbonates are mostly likely to preserve syn-depositional paleomagnetic directions and magnetofossil stratigraphies

La dégradation des pâturages de la région de N'Djaména (république du Tchad) en relation avec la présence de Cyanophycées psammophiles. Etude préliminaire

Dans la région de N'Djaména, la présence de colonies de Cyanophycées psammophiles (Scytonema sp.) a été relevée sur de nombreux pâturages. Cette présence semble liée à une diminution de la biomasse herbacée par imperméabilisation de l'horizon superficiel. Dans le cadre de cette hypothèse, elle serait à l'origine d'une accélération des processus érosifs, en facilitant le ruissellement d'une part et en diminuant la protection des sols réalisée par les pailles d'autre part. Par ailleurs, il apparaît que la présence de l'algue est liée à un certain appauvrissement du cortège floristique; ce phénomène marquerait donc le début de la dégradation des pâturages sur sable et aurait valeur d'indicateu

Biodiversity and distribution of cyanobacteria at Dronning Maud Land, East Antartica

Biodiversity and distribution of cyanobacteria at Dronning Maud Land, East Antarctica.The current study describes the biodiversity and distribution of cyanobacteria from the natural habitats of Schirmacher land, East Antarctica surveyed during 23rd Indian Antarctic Expedition (2003�2004). Cyanobacteria were mapped using the Global Positioning System (GPS). A total of 109 species (91 species were non-heterocystous and 18 species were heterocystous) from 30 genera and 9 families were recorded; 67, 86 and 14 species of cyanobacteria were identified at altitudes of sea level >100 m, 101�150 m and 398�461 m, respectively. The relative frequency and relative density of cyanobacterial populations in the microbial mats showed that 11 species from 8 genera were abundant and 6 species (Phormidium angustissimum, P. tenue, P. uncinatum Schizothrix vaginata, Nostoc kihlmanii and Plectonema terebrans) could be considered as dominant species in the study area.Biodiversidad y distribución de las cianobacterias de Dronning Maud Land, Antártida Oriental. En este estudio se describe la biodiversidad y distribución de las cianobacterias presentes en los hábitats naturales de Schirmacher, Antártida Oriental, muestreados durante la 23ª Expedición India a la Antártida (2003-2004). Las muestras de cianobacterias fueron georreferenciadas mediante un GPS. Se identificaron 109 especies (91 no heterocistadas y 18 provistas de heterocistes) de 30 géneros y 9 familias; en los tramos de altitud sobre el nivel del mar >100 m, 101-150 m y 398-461 m se detectaron 67, 86 y 14 especies, respectivamente. La frecuencia y densidad relativas de las poblaciones de cianobacterias en los tapices microbianos mostraron que 11 especies de 8 géneros eran abundantes y que 6 especies (Phormidium angustissimum, P. tenue, P. uncinatum, Schizothrix vaginata, Nostoc kihlmanii y Plectonema terebrans) se pueden considerar como dominantes en el área de estudio

Systematic study of the blue green algae of Ceylon kept at the herbarium of the Royal Botanical Gardens, Peradeniya

The collection of blue green algae kept at the herbarium of the Royal Botanical Gardens, Peradeniya, was collected by Ferguson more than 70 years ago. Since then many changes have taken place in the taxonomy of the blue green algae. West (1902), Lemmermann (1907), Wine (1915), Crow (1923), Bharadwaja (1934) and Holsinger (1935) had described some of the blue green algae of Ceylon. While examining the collections of blue green algae kept at the herbarium, the authors found that most of the identifications were incorrect and required revision. In the present paper 20 blue green algae are described. The classification and key to the species are based on the characters given by Desikachary (1959). Blue green algae are important to fisheries since Chanos larvae feed on them

Gene Sequencing-Based Analysis of Microbial-Mat Morphotypes, Caicos Platform, British West Indies

Active carbonate platforms provide modern analogs to study microbial-mat development and taphonomy in the sedimentary record. Microbial-mat descriptions and classifications for tropical tidal-flat environments have focused predominantly on morphological observations. This is exemplified by flat and biscuit-shaped mats, where the mat morphotypes are postulated to reflect different Cyanobacteria communities as the main mat-building taxa. To compare the total microbial communities of these two mat types and test this Cyanobacteria hypothesis, we applied optical microscopy and gene sequencing methods using samples from a tidal algal marsh on Little Ambergris Cay, Turks and Caicos, B.W.I. With gene sequencing we find that total diversity and community composition differs significantly between morphotypes; the biscuit mat is more diverse than the flat mat. Microscopy results support that Cyanobacteria populations colonizing the surface layer of these two mat types are responsible for much of the mat's structural elements; however, genetic data find the Cyanobacteria population is indistinguishable between the two mat types. The recovered Cyanobacteria populations fall predominantly into three taxa: Scytonema, Halomicronema, and Crinalium. We propose that the morphology of these two mat types is not controlled by the Cyanobacteria, but instead reflects a time-integrated microbial response to environmental factors, where the microbial community becomes more diverse with time since environmental disturbance

Additions to the filamentous Myxophyceae of Indiana, Kentucky and Ohio

During the past several years, numerous specimens of the Myxophyceae from Indiana, Kentucky and Ohio have accumulated in the herbaria cited below. Some of these species presumably have not previously been reported for this region and are now placed on record. It is known that many collections of algea, the bases for previous reports, have been lost or are inaccessible. It is the desire of the writer and of other students of the herbarium that all published works on the algae be based only upon permanently preserved specimens

Biodiversity of living, non marine, thrombolites of Lake Clifton, Western Australia

<p>Lake Clifton in Western Australia is recognized as a critically endangered ecosystem and the only thrombolite reef in the southern hemisphere. There have been concerns that increases in salinity and nutrient run-off have significantly impacted upon the thrombolite microbial community. Here we used cultivation-independent molecular approaches to characterize the microbial diversity of the thrombolites at Lake Clifton. The most dominant phyla currently represented are the Proteobacteria with significant populations of Bacteroidetes and Firmicutes. Cyanobacteria, previously invoked as the main drivers of thrombolite growth, represent only a small fraction (∼1–3% relative abundance) of the microbial community. We report an increase in salinity and nitrogen levels at Lake Clifton that may be contributing to a change in dominant microbial populations. This heightens concerns about the long-term health of the Lake Clifton thrombolites; future work is needed to determine if phyla now dominating this system are capable of the required mineral precipitation for continued thrombolite growth.</p

Algunas nuevas citas de cianoprocariotas para Galicia (NW Península Ibérica).

NOGUEROL-SEOANE, A. &amp; TEMES-CASAS, M. 2001. Algunas nuevas citas de cianoprocariotas para Galicia (NW Península Ibérica). Bot. Complutnesis 25: 141-154. Se presentan en este trabajo 13 nuevas referencias de cianoprocariotas para Galicia (NW Península Ibérica), de las que ocho se incluyen en el O. Chroococcales Wettstein [Aphanothece nidulans Richter, Aphanothece saxicola Nägeli, Chamaesiphon confervicolus A. Braun, Chroococcus submarinus (Hansgirg) Kovácik, Chroococcus tenax (Kirchner) Hieronymus, Gloeothece rupestris (Lyngbye) Bornet, Merismopedia mediterranea Nägeli y Xenotholos kerneri (Hansgirg) Gold-Morgan et al.]; una de las citas pertenece al O. Oscillatoriales Elenkin [Phormidium irriguum (Kützing ex Gomont) Anagnostidis et Komárek]; tres están incluidas en el O. Nostocales (Borzì) Geitler [Microchaete sp., Nostoc verrucosum Vaucher ex Bornet et Flahault, Rivularia biasolettiana Meneghini, Scytonema cincinnatum Thuret ex Bornet et Flahault]; y una especie se incluye en el O. Stigonematales Geitler [Stigonema minutum (Agardh) Hassall ex Bornet et Flahault]. Todo el material procede de la cuenca del río Lourido y se recogió durante los años 1997-1999.NOGUEROL-SEOANE, A. &amp; TEMES-CASAS, M. 2001. Some new records of Cyanoprokaryota for Galicia (NW Iberian Peninsula). Bot. Complutensis 25: 141-154. Thirteen new records of Cyanoprokaryota for Galicia (NW Iberian Peninsula) are reported; eight of them belong to the O. Chroococcales Wettstein [Aphanothece nidulans Richter, Aphanothece saxicola Nägeli, Chamaesiphon confervicolus A. Braun, Chroococcus submarinus (Hansgirg) Kovácik, Chroococcus tenax (Kirchner) Hieronymus, Gloeothece rupestris (Lyngbye) Bornet, Merismopedia mediterranea Nägeli and Xenotholos kerneri (Hansgirg) Gold-Morgan et al.]; another one belongs to the O. Oscillatoriales Elenkin [Phormidium irriguum (Kützing ex Gomont) Anagnostidis et Komárek]; three of them are included in the O. Nostocales (Borzì) Geitler [Microchaete sp., Nostoc verrucosum Vaucher ex Bornet et Flahault, Rivularia biasolettiana Meneghini, Scytonema cincinnatum Thuret ex 141 A. Noguerol-Seoane &amp; M.a Temes-Casas Algunas nuevas citas de cianoprocariotas.... Bornet et Flahault] and one species is included in the O. Stigonematales Geitler [Stigonema minutum (Agardh) Hassall ex Bornet et Flahault]. The samples were collected in the Lourido´s river basin from 1997 to 1999

Survival of microorganisms in desert soil exposed to five years of continuous very high vacuum

Microorganism survivability in desert algal soil crust under continuous very high vacuu