Isotopic stratigraphy suggests Neoproterozoic ages and Laurentian ancestry for high-grade marbles from the North-Central Norwegian Caledonides

2002 ◽  
Vol 139 (4) ◽  
pp. 375-393 ◽  
Author(s):  
V. A. MELEZHIK ◽  
M. GOROKHOV ◽  
A. E. FALLICK ◽  
D. ROBERTS ◽  
A. B. KUZNETSOV ◽  
...  
Keyword(s):  
Late Ordovician ◽  
Time Interval ◽  
Low Grade ◽  
High Grade ◽  
North Central ◽  
The North ◽  
Strontium Isotope Stratigraphy ◽  
Dolomite Marble ◽  
Isotope Stratigraphy ◽  
Norwegian Caledonides

Carbon and strontium isotope stratigraphy has been applied to constrain the depositional ages of high-grade marble sequences in the Ofoten district of the North-Central Norwegian Caledonides. Two marble formations hosted by diverse schists from the Bogen Group, all previously correlated over long distances with a Late Ordovician–Early Silurian, low-grade, fossiliferous succession, have been studied for carbon, oxygen and strontium isotopes. The least altered 87Sr/86Sr ratios ranging between 0.7062 and 0.7068, and the best preserved δ13C values falling between +5.0 and +6.5‰ obtained from two marble formations, are consistent with a seawater composition in the time interval 700–600 Ma. The results obtained do not support the previously proposed correlation of the Bogen Group with an Ordovician–Silurian lithostratigraphic succession further north. The apparent depositional ages suggest that the tectonostratigraphic succession studied is inverted and that the tectonostratigraphy of the region requires revision. The Neoproterozoic depositional ages combined with the palaeogeographic position of Baltica imply that carbonates were initially accumulated in seas on a continental shelf, probably Laurentia, and were tectonically transported onto Baltica during Early Silurian, Scandian collision, at c. 425 Ma. Prospecting for new dolomite marble deposits of the Hekkelstrand type and carbonate-hosted manganese–iron ores should be restricted to 700–600 Ma sequences in the Uppermost Allochthon of the Norwegian Caledonides.

New age constraints on the duration and origin of the Late Ordovician Guttenberg δ13Ccarb excursion from high-precision U-Pb geochronology of K-bentonites

2020 ◽  
Author(s):  
J. Garrecht Metzger ◽  
Jahandar Ramezani ◽  
Samuel A. Bowring ◽  
David A. Fike
Keyword(s):  
High Precision ◽  
Carbon Isotopic Composition ◽  
Late Ordovician ◽  
Environmental Drivers ◽  
Time Interval ◽  
Driving Mechanism ◽  
Ionization Mass ◽  
Mass Extinctions ◽  
Carbon Isotopic ◽  
The North

Perturbations to the global carbon cycle as recorded in the isotopic compositions of marine deposits have been commonly associated with major shifts in the climate and/or biologic activity, including mass extinctions. The Late Ordovician Guttenberg isotopic carbon excursion (GICE) is a large, globally correlative positive shift (∼3‰) in the carbon isotopic composition of marine carbonates (δ13Ccarb), but its driving mechanism(s) remains ambiguous. This is in large part due to uncertain correlations among Late Ordovician records, as well as complex and poorly constrained temporal relationships of abundant K-bentonite (altered volcanic ash) marker beds deposited in this time interval. Here, we provide new, high-precision U-Pb zircon geochronology by chemical-abrasion−isotope-dilution−thermal ionization mass spectrometry for K-bentonites bounding the GICE in the North American Midcontinent, including robust 206Pb/238U ages (reported with 2σ analytical uncertainty) for two important regional markers: the Deicke (453.35 ± 0.10 Ma) and Millbrig (453.36 ± 0.14 Ma) K-bentonites. The new data from these K-bentonites directly constrain the duration of the GICE to less than 400 k.y. at two well-studied locations in eastern Missouri, United States. The abruptness of the GICE precludes relatively gradual tectonic mechanisms as possible drivers of the excursion and suggests more rapid environmental drivers, such as changes in eustatic sea level associated with pre-Hirnantian glacial activity.

Isotopic evidence for a complex Neoproterozoic to Silurian rock assemblage in the North-Central Norwegian Caledonides

2002 ◽  
Vol 114 (1-2) ◽  
pp. 55-86 ◽  
Author(s):  
V.A Melezhik ◽  
D Roberts ◽  
I.M Gorokhov ◽  
A.E Fallick ◽  
K.B Zwaan ◽  
...  
Keyword(s):  
North Central ◽  
Isotopic Evidence ◽  
The North ◽  
Norwegian Caledonides

scholarly journals Reconstructing past variations in environmental conditions and paleoproductivity over the last  ∼ 8000 years off north-central Chile (30° S)

2020 ◽  
Vol 17 (22) ◽  
pp. 5763-5785
Author(s):  
Práxedes Muñoz ◽  
Lorena Rebolledo ◽  
Laurent Dezileau ◽  
Antonio Maldonado ◽  
Christoph Mayr ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Primary Productivity ◽  
Environmental Conditions ◽  
Time Interval ◽  
Coastal Zones ◽  
Moisture Index ◽  
Subtropical Anticyclone ◽  
North Central ◽  
The North ◽  
Lower Productivity

Abstract. The aim of this project was to establish past variations in the main oceanographic and climatic features of a transitional semiarid ecosystem on the north-central Chilean coast. We analyzed recent sedimentary records retrieved from two bays, Guanaqueros and Tongoy (30∘ S), for geochemical and biological analyses, including the following: sensitive redox trace elements, biogenic opal, total organic carbon (TOC), diatoms and stable isotopes of organic carbon and nitrogen. Three remarkable periods were established with different environmental conditions and productivities: (1) > 6600 cal BP, (2) 4500–1800 cal BP and (3) 140 cal BP to the present (2015 CE). The first period was characterized by a remarkably higher productivity (higher diatom abundances and opal) in which large fluxes of organic compounds were also inferred from the accumulation of elements, such as Ba, Ca, Ni, Cd and P, in the sediments. Meanwhile, significantly reduced conditions at the bottom of the bays were suggested based on the large accumulation of Mo, Re and U, showing a peak at 6600 cal BP, when sulfidic conditions could have been present. According to the pollen moisture index (PMI), this was also identified as the driest interval. These conditions should be associated with an intensification of the Southern Pacific Subtropical Anticyclone (SPSA) and stronger southerly western winds, emulating La Niña-like conditions, as has been described for the SE Pacific during the early Holocene and part of the mid-Holocene. During most of the second period, lower productivity was observed; however, a small increase was identified between 3400 and 4000 cal BP, although lower amounts of diatom (valves g−1) and nutrient-type metal accumulations were evident. Anoxic conditions at the bottom of the bays changed to an almost stable suboxic condition during this time interval. The third period was marked by intense oxygenation after 1800 cal BP, as observed by a drastic change in the accumulation of U, Mo and Re. This was followed by a return to more reduced conditions over the past 2 centuries, characterized by a small productivity rise after ∼140 cal BP, as suggested by the opal accumulations. Overall, lower primary productivity, lower reduced conditions at the bottom and higher-humidity conditions were established after 6600 cal BP to the present. We suggest that the oxygenation might be associated with a weak effect from the oxygen minimum zone over the shelf and intensified El Niño activity, introducing oxygenated waters to the coastal zones through the propagation of equatorial waves and establishment of conditions that reduced the primary productivity from the mid-Holocene toward the beginning of the modern era.

A probable glacio-marine deposit of Late Ordovician—Early Silurian age from the north central Newfoundland Appalachian Belt

1974 ◽  
Vol 111 (6) ◽  
pp. 549-564 ◽  
Author(s):  
A. M. McCann ◽  
M. J. Kennedy
Keyword(s):  
North Atlantic ◽  
Late Ordovician ◽  
Mobile Belt ◽  
North Atlantic Region ◽  
Upper Ordovician ◽  
Atlantic Region ◽  
North Central ◽  
Marine Deposits ◽  
Lower Silurian ◽  
The North

SummaryConglomerate beds occur in an Upper Ordovician—Lower Silurian clastic sequence on the northeastern side of the Newfoundland Central Paleozoic Mobile Belt. They contain scattered pebbles and cobbles dispersed in a finely laminated sandstone and siltstone matrix. Laminations are generally 5–20 mm thick and the clasts 10–300 mm across. The laminations are locally disrupted by the clasts. These laminations have subsequently been tectonically flattened into augen around the clasts and locally disrupted by boudinage. It is concluded that these conglomerate beds represent icerafted glacio-marine deposits interbedded with turbidites which were probably deposited in a locally restricted marine environment. The deposits are interpreted on the basis of scattered fossil localities as being of Late Ordovician–Early Silurian age. They are compared with deposits of similar age elsewhere in the North Atlantic region.

Environmental and genetic effects on birth weight in graded-up goat kids

1994 ◽  
Vol 74 (3) ◽  
pp. 397-400 ◽  
Author(s):  
F. Sánchez G. F. ◽  
H. Montaldo V. ◽  
A. Juárez L.
Keyword(s):  
Birth Weight ◽  
Key Words ◽  
Fixed Effects ◽  
Genetic Factors ◽  
Genetic Group ◽  
Low Grade ◽  
High Grade ◽  
Feeding System ◽  
The North ◽  
Genetic Groups

A linear model analysis was carried out to study the effect of sex, litter size, age of dam, year, birth period and genetic group on birth weight in goats. Genetic groups consisted of graded-up goats from backcrosses of local goats with Alpine, Granadina, Nubian, Saanen and Toggenburg sires, classified as low grade (from 1/2 to 3/4 of exotic genes) and high grade (over 3/4 of exotic genes). Heritabilities were also obtained for low- and high-grade kids. The data concern 4623 records from a farm under a stall feeding system in the north of Mexico. All of the main fixed effects but only the genetic group × birth period interaction were significant (P < 0.05). Males were heavier than females and singles were heavier than double and multiple-born kids. Birth weight means increased as dam age increased. Birth weight means for high and low grade kids were, respectively, 3.3 and 3.2 kg in Alpine kids, 3.1 and 3.2 in Nubian, 2.7 and 2.9 in Granadina, 3.3 and 3.3 in Saanen and 3.3 and 3.1 in Toggenburg. Heritability estimates were 0.40 ± 0.14 and 0.44 ± 0.18 in high and low grade kids, respectively. Key words: Goat kids, birth weight, Alpine, Granadina, Nubian, Saanen, Toggenburg, crossbreds, heritability, non-genetic factors

Mélange development in the Boones Point Complex, north-central Newfoundland

1981 ◽  
Vol 18 (3) ◽  
pp. 433-442 ◽  
Author(s):  
K. Douglas Nelson
Keyword(s):  
Debris Flow ◽  
Late Ordovician ◽  
The South ◽  
Upper Ordovician ◽  
North Central ◽  
Clastic Rocks ◽  
The North ◽  
Volcaniclastic Rocks ◽  
Acadian Orogeny

The Boones Point Complex in north-central Newfoundland is a narrow mélange belt separating Roberts Arm terrain volcanic and volcaniclastic rocks to the north from Upper Ordovician westerly derived clastic rocks to the south and east. The mélange has a sedimentary matrix and contains a polymict assemblage of blocks. Limestone blocks have yielded Llanvirn–Llandeilo conodont faunas. Sedimentologic and structural analyses indicate that the complex is composed of subaqueous debris flow deposits, which are the proximal facies equivalent of the Late Ordovician clastics to the south. This debris flow material was tectonically deformed prior to the Medial Devonian 'Acadian' orogeny, probably as a result of earlier 'Taconic' thrusting.

Structural analysis of the Velardeña mining district, Mexico: a faulted Au–Ag-rich hydrothermal system

2009 ◽  
Vol 46 (2) ◽  
pp. 123-138 ◽  
Author(s):  
Nicolas Pinet ◽  
Alain Tremblay
Keyword(s):  
Hydrothermal System ◽  
Vertical Displacement ◽  
Basin And Range ◽  
Normal Faults ◽  
Mining District ◽  
Low Grade ◽  
High Grade ◽  
Normal Faulting ◽  
North Central ◽  
Epithermal Au

Epithermal Au–Ag veins of the Velardeña mining district (north-central Mexico) correspond to narrow, fault-controlled, high-grade structures that are continuous along strike for several kilometres. The veins converge toward the Guardarraya intrusion where carbonate-hosted deposits are found at the contact with surrounding limestones. The mineralized structures are cut by Basin and Range normal faults showing apparent vertical displacement up to 320 m. Paleostress reconstructions in the Velardeña mining district suggest that mineralized structures formed during a NNE-directed extensional event that predated the Basin and Range faulting event (ENE-directed). Basin and Range normal faulting is responsible for surface exposures of various Au–Ag mineralizations formed at different crustal depths, thus enabling studies of the entire hydrothermal system—from low-grade breccia zones in the volcanic cover rocks to deeper base-metal-rich deposits.

Klinische Wertigkeit der Positronen-Emissions-Tomographie (PET) bei onkologischen Fragestellungen: Ergebnisse einer interdisziplinären Konsensuskonferenz

1996 ◽  
Vol 35 (02) ◽  
pp. 42-52 ◽  
Author(s):  
R. Bares ◽  
U. Bull ◽  
A. Guhlmann ◽  
E. Moser ◽  
M. F. Wannenmacher ◽  
...  
Keyword(s):  
Low Grade ◽  
High Grade ◽  
Klinische Anwendung ◽  
Wissenschaftliche Studien

Zusammenfassung Ziel: Es ist das Ziel der vorliegenden Arbeit, an Hand bisher publizierter Studienergebnisse eine Beurteilung des klinischen Stellenwertes von PET in der Onkologie zu erarbeiten. Methoden: Im Rahmen einer interdisziplinären Konferenz mit namhaften Experten wurde eine Wertung des gegenwärtigen Stands von PET in der Onkologie an Hand der in der Literatur dokumentierten Studienergebnisse erarbeitet. Angestrebt wurde eine differenzierte Bewertung von PET für die klinische Anwendung in fünf Klassen (1a, 1b, 2a, 2b, 3) von »angemessen« (1a), »akzeptabel« (1b), »hilfreich« (2a), »noch keine Bewertung möglich« (2b), »ohne Nutzen« (3). Ergebnisse: Für den klinischen Einsatz in der Onkologie ist 2-F18-Fluorodeoxyglukose (FDG) das Radiopharmakon der Wahl. PET ist klinisch in der Patientenversorgung zur Rezidivdiagnostik von high-grade Gliomen (FDG), low-grade Gliomen (C-11 Methionin oder F-18 Tyrosin), für die Dignitätsdiagnostik des peripheren Lungenrundherdes bei Risikopatienten sowie für die Diagnostik des Pankreaskarzioms indiziert (Indikation 1a). PET kann in der Patientenversorgung bei folgenden Indikationen (1b) eingesetzt werden: »low-grade« Gliome, Suche nach unbekanntem Primärtumor bei Kopf-Hals-Tumoren, Rezidivdiagnostik des nicht kleinzelligen Bronchialkarzinoms sowie des Rektumkarzinoms, Lymphknotenstaging beim nicht kleinzelligen Bronchial-Karzinom, Pan-kreas-Karzinom, muskelinvasiven Blasen-Karzinom und Hoden-Karzinom. Staging bei M. Hodgkin (Stad. I/II versus III), frühe Therapiekontrolle bei Resttumor und Rezidivdiagnostik bei M. Hodgkin und hochmalignen Non-Hodgkin-Lymphomen, Lymphknoten-Staging und Fern-metastasensuche beim malignen Melanom (Breslow >1,5 mm), Lymphknoten- und Fernmetastasen-Nachweis beim Schilddrüsen-Karzinommit erhöhtem hTg und nicht radiojodspeichernden Metastasen. Zahlreiche weitere Indikationen zeichnen sich bereits jetzt ab, sind jedoch noch weniger gut durch wissenschaftliche Studien belegt. Für die meisten Indikationen außerhalb wissenschaftlicher Studien ist eine individuelle Kosten-Nutzen-Betrachtung durch den verantwortlichen Arzt geboten. Schlußfolgerungen: Die metabolische Bildgebung von PET besitzt für eine Vielzahl onkologischer Fragestellungen prinzipielle Vorteile gegenüber der anatomisch-morphologisch orientierten Schnittbilddiagnostik. Für die klinische Indikationsstellung ist allerdings eine differenzierte Betrachtung der spezifischen Leistungsfähigkeit von PET geboten.

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