Lower Silurian (Aeronian) megafaunal and conodont biofacies of the northwestern Michigan Basin

1997 ◽  
Vol 34 (6) ◽  
pp. 753-764 ◽  
Author(s):  
Rodney Watkins ◽  
Jeffrey J. Kuglitsch
Keyword(s):  
Tidal Flat ◽  
Continental Margins ◽  
Michigan Basin ◽  
Siliceous Sponge ◽  
Lower Silurian ◽  
The North ◽  
Conodont Biofacies ◽  
Shallow Subtidal ◽  
Sponge Spicules ◽  
Water Depths

Lower Silurian (Llandovery: Aeronian) carbonates of the Burnt Bluff Group, northwestern Michigan Basin, represent a transect along a southward-dipping ramp that extends from tidal-flat to basin environments. Benthic megafaunas include an ostracod biofacies (tidal flat), stromatoporoid–coral biofacies (very shallow subtidal), pentamerid, crinozoan, and crinozoan–stromatoporoid biofacies (deeper subtidal), and a crinozoan–sponge biofacies (distal ramp and basin). The crinozoan–sponge biofacies, which includes diverse, small crinozoan ossicles, 19 types of siliceous sponge spicules, and at least 65 other taxa, has a biota that is similar to those of Silurian continental margins. Megafaunal biofacies indicate an Early Silurian gradient going from a shoreline in the north to water depths of perhaps 60 m in the south. The Burnt Bluff Group contains conodonts of the Icriodella discreta – Icriodella deflecta zone as an onshore biofacies with Panderodus, Kockelella, Ozarkodina, Icriodella, and Oulodus, and an offshore biofacies with Panderodus, Walliserodus, and Aspelundia.

Stressed from above and stressed from below: dissolved oxygen fluctuations in Lough Hyne, a semi-enclosed marine lake

2020 ◽  
Vol 77 (6) ◽  
pp. 2106-2117
Author(s):  
Caitlin Q Plowman ◽  
Cynthia D Trowbridge ◽  
John Davenport ◽  
Colin Little ◽  
Luke Harman ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Current Flow ◽  
Benthic Communities ◽  
Marine Reserve ◽  
South Basin ◽  
Seagrass Meadows ◽  
The North ◽  
Shallow Subtidal ◽  
Lough Hyne ◽  
Water Depths

Abstract Dissolved oxygen (DO) concentrations of the fully marine Lough Hyne, SW Ireland, were sampled in biologically different habitats between 2014 and 2019 to investigate the declining water quality in the marine reserve and the severity of oxidative stress on benthic communities. DO was measured above and below shallow subtidal rocks, in the Rapids connection to the Celtic Sea, in seagrass meadows (Zostera marina), and at various water depths (1–15 m) in the South Basin. DO values above rocks were normoxic to hyperoxic in daytime (7.8–17.3 mg l−1); below rocks were often hypoxic (0.24–2 mg l−1). South Basin sites experienced hypoxia less often than the North Basin, except for the Goleen, presumably due to differential current flow. DO fluctuations occurred in spring (before ephemeral macroalgae proliferate), summer (when algal mats smother the benthos), and autumn (when macroalgae decay). While the Rapids were normoxic, the seagrass meadows below them exhibited periodic DO stress. Labhra Cliff (9–14.5 m) was normoxic to hyperoxic in autumn but experienced suboxic and hypoxic events in summer. Many organisms in Lough Hyne are experiencing periods of hypoxia below their published sublethal limits, the effects of which could be exacerbated by periodic hyperoxia.

scholarly journals Upper Ordovician and Silurian carbonate shelf stratigraphy, facies and evolution, eastern North Greenland

1984 ◽  
Vol 148 ◽  
pp. 1-73
Author(s):  
J.M Hurst
Keyword(s):  
Deep Water ◽  
Carbonate Rocks ◽  
Upper Ordovician ◽  
Carbonate Production ◽  
Lower Silurian ◽  
The North ◽  
Lithostratigraphic Units ◽  
Shallow Subtidal ◽  
North Greenland

A new lithostratigraphic scheme is erected for the uppermost Ordovician and lower Silurian shelf carbonate rocks of Peary Land and Kronprins Christian Land, eastern North Greenland. All carbonate rocks were deposited on a fairly stable shelf which was bordered to the north and east by deep-water basins. The shelf foundered in the latest LIandoverian, terminating carbonate production. Five formations and two members are defined and extend from the uppermost Ordovician (Cincinnatian) to the uppermost LIandoverian, or possibly lowermost Wenlock in the Silurian. Lithostratigraphic units include: Turesø Formation (new) composed of alternating light and dark grey peritidal to shallow subtidal laminated or massive dolomites, cryptalgal laminites and fenestral lime mudstones – uppermost Ordovician (Richmondian, Cincinnatian) to Lower or Middle Llandoverian; Ymers Gletscher Formation (new) composed of light grey peritidal lime mudstones, fenestral lime mudstones and cryptalgal laminites 0150 Lower to Middle Llandoverian; Odins Fjord Formation (new) composed of shallow to deep subtidal dark lime mudstones, wackestones and commonly floatstone and rudstone biostromes – Middle (possibly Lower) to Upper Llandoverian; Melville Land Member (new) composed of light grey peritidal lime mudstones, fenestral lime mudstones and cryptalgal laminites – Middle (possibly Lower) Llandoverian; Bure lskappe Member (new) composed of drowned shelf, dark grey to black laminated lime mudstone with terrigenous mudstone interbeds – Upper Llandoverian; Samuelsen Høj Formation (new) composed of light grey to white reef limestones – uppermost Llandoverian; Harefjeld Formation (new), a faulted, folded and cleaved black lime and terrigenous mudstone unit in eastern Kronprins Christian Land – Ordovician to Silurian (Llandoverian).

RENDIMENTO DE CULTIVARES DE CAUPI (Vigna unguiculata L Walp.) SUBMETIDAS À DIFERENTES LÂMINAS DE IRRIGAÇÃO

Irriga ◽  
1999 ◽  
Vol 4 (3) ◽  
pp. 139-144 ◽  
Author(s):  
Gianini Peixoto Bezerra Lima ◽  
José Vanglesio de Aguiar ◽  
Raimundo Nonato Távora Costa ◽  
Vital Pedro da Silva Paz
Keyword(s):  
Vigna Unguiculata ◽  
Irrigation System ◽  
Northeast Brazil ◽  
Marginal Product ◽  
Applied Water ◽  
Cowpea Cultivars ◽  
The North ◽  
Significant Difference ◽  
Caixa Postal ◽  
Water Depths

RENDIMENTO DE CULTIVARES DE CAUPI (Vigna unguiculata L Walp.) SUBMETIDAS À DIFERENTES LÂMINAS DE IRRIGAÇÃO1       Gianini Peixoto Bezerra Lima José Vanglesio de Aguiar Raimundo Nonato Távora Costa Universidade Federal do Ceará – Departamento de Engenharia Agrícola. Campus do Pici. Bloco 804. CEP 60455-760 – Fortaleza-CE Vital Pedro da Silva Paz Escola Superior de Agricultura Luiz de Queiroz – Departamento de Engenharia Rural, bolsista da FAPESP. Av. Pádua Dias, 11 – Caixa Postal 11. 13418-900 – Piracicaba-SP       1 RESUMO       O caupi é um dos cultivos mais tradicionais do Norte e Nordeste do Brasil, constituindo alimento básico nestas regiões. Com este trabalho foi possível estabelecer relações entre a quantidade de água aplicada e produtividade de grãos, para três variedades de feijão caupi submetidas a diferentes lâminas de água. Para caracterização das lâminas de água foi utilizado um sistema de irrigação por aspersão convencional em linha. O controle da irrigação foi realizado a partir de tensiômetros instalados à 15 cm de profundidade. Os resultados mostraram que: i) a cultivar João Paulo II apresentou melhores resultados de produtividade para as lâminas de água aplicadas que variaram de T1 = 291,8 mm a T5 = 141,2 mm; ii) sob condições de reduzida disponibilidade de água, ou seja, menor lâmina aplicada, não ocorreu diferença estatística  para a produtividade entre as cultivares estudadas; e iii) para as condições do estudo, a cultivar Setentão apresentou a menor taxa de redução do produto marginal.       UNITERMOS: caupi, irrigação, função de produção       LIMA, G. P. B., AGUIAR, J. V., COSTA, R. N. T., PAZ, V. P. S. Responses OF cowpea cultivars (Vigna unguiculata L Walp) at differents irrigation deficits     2 ABSTRACT       The caupi is one of the most traditional cultivation of the north and northeast - Brazil, constituting a basic food in these areas. With this work it was possible to establish relationships between the amount of water applied and productivity of grains, for three caupi varieties submitted to different irrigation sheets. To diferentiate water depths in the irrigation system, the aspersion in line was used. The control of the irrigation was accomplished using tensiometers installed to 15 cm of depth. The results showed that: i) the João Paulo II variety presented better productivity for the applied water depths; ii) under reduced conditions of water avai lability for study conditions, these was no significant difference in the productivity reached among the cultivars studied; and iii) for the conditions of the study, the variety Setentão presented the smallest rate of reduction of the marginal product.       KEYWORDS: cowpea, irrigation, production function  

scholarly journals I.—Microscopic Structure of Irish Granites. No. 2. Granite of Aillemore, Co. Mayo

1874 ◽  
Vol 1 (1) ◽  
pp. 1-2
Author(s):  
Edward Hull
Keyword(s):  
The Other ◽  
Microscopic Structure ◽  
South Side ◽  
North West ◽  
Fine Grained ◽  
Lower Silurian ◽  
The North ◽  
Geological Map ◽  
Vertical Walls ◽  
Dark Green

This granite forms an isolated mass, rising into two eminences a few miles south of Louisburg, called Corvock Brack (1287 feet) and Knockaskeheen (1288 feet). It is a greyish granite—generally fine—grained—consisting of quartz, two felspars,—one orthoclase, the other triclinic, probably oligoclase—and dark green mica. In some places there are patches in which the felspar assumes the appearance of “graphic granite.” Numerous boulders of this granite are strewn over the district to the north-west, and on the south side of Knockaskeheen; the rock is traversed by regular joints ranging N. 10 W., along which it splits off into nearly vertical walls. The position of the granite is shown on Griffith's Geological Map of Ireland, and it is surrounded by schistose beds, generally metamorphosed, and probably of Lower Silurian age. The granite itself is of older date than the Upper Llandovery beds, which lie to the southward.

Definition of tectono-sedimentary elements for rifted continental margins of the Norwegian and Greenland seas

2021 ◽  
pp. M57-2021-31
Author(s):  
Harald Brekke ◽  
Halvor S. S. Bunkholt ◽  
Jan I. Faleide ◽  
Michael B. W. Fyhn
Keyword(s):  
Lower Jurassic ◽  
Passive Margin ◽  
Continental Margins ◽  
Axial Line ◽  
Continental Breakup ◽  
The North ◽  
Tectonic Development ◽  
Definition Of ◽  
Conjugate Margins ◽  
Greenland Margin

AbstractThe geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.

Landscape development in western and central Dronning Maud Land, East Antarctica

2001 ◽  
Vol 13 (3) ◽  
pp. 302-311 ◽  
Author(s):  
Jens-Ove Näslund
Keyword(s):  
Large Scale ◽  
High Elevation ◽  
Continental Margins ◽  
Landscape Development ◽  
Ice Streams ◽  
The North ◽  
Ice Stream ◽  
Dronning Maud Land ◽  
Break Up

Large-scale bedrock morphology and relief of two key areas, the Jutulsessen Nunatak and the Jutulstraumen ice stream are used to discuss glascial history and landscape development in western and central Dronning Maud Land, Antarctica. Two main landform components were identified: well-defined summit plateau surfaces and a typical alpine glacial landscape. The flat, high-elevation plateau surfaces previously were part of one or several continuous regional planation surfaces. In western Dronning Maud Land, overlying cover rocks of late Palaeozoic age show that the planation surface(s) existed in the early Permian, prior to the break-up of Gondwana. A well-develoment escarpment, a mega landform typical for passive continental margins, bounds the palaeosurface remnants to the north for a distance of at least 700 km. The Cenozoic glacial landscape, incised in the palaeosurface and escarpment, is exemplified by Jutulsessen Nunatak, where a c. 1.2 km deep glacial valley system is developed. However, the prominent Penck-Jutul Trough represents some of the deepest dissection of the palaeosurface. This originally tectonic feature is today occupied by the Jutulstraumen ice stream. New topographic data show that the bed of the Penck-Jutul Trough is situated 1.9±1.1 km below sea level, and that the total landscape relief is at least 4.2 km. Today's relief is a result of several processes, including tectonic faulting, subaerial weathering, fluvial erosion, and glacial erosion. It is probable that erosion by ice streams has deepened the tectonic troughs of Dronning Maud Land since the onset of ice sheet glaciation in the Oligocene, and continues today. An attempt is made to identify major events in the long-term landscape development of Dronning Maud Land, since the break-up of the Gondwana continent.

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