scholarly journals Transcriptomic and isotopic data reveal central role of ammonium in facilitating the growth of the mixotrophic dinoflagellate, Dinophysis acuminata

Harmful Algae ◽  
2021 ◽  
Vol 104 ◽  
pp. 102031
Author(s):  
Theresa K. Hattenrath-Lehmann ◽  
Deepak Nanjappa ◽  
Huan Zhang ◽  
Liying Yu ◽  
Jennifer A. Goleski ◽  
...  
Keyword(s):  
Isotopic Data ◽  
Dinophysis Acuminata

Rb/Sr geochronology in the Thompson belt, Manitoba: implications for Aphebian crustal development and metallogenesis

1981 ◽  
Vol 18 (5) ◽  
pp. 932-943 ◽  
Author(s):  
C. Brooks ◽  
P. Theyer
Keyword(s):  
Broad Band ◽  
Early Period ◽  
Growth Trajectories ◽  
Isotopic Data ◽  
Depositional History ◽  
Sedimentary Sequences ◽  
Thompson Groups ◽  
Facies Metamorphism ◽  
History Of

The supracrustal metasediments of the Thompson belt (Pipe and Thompson Groups) show pronounced differences in Rb/Sr age (1855–1685 and 1665–1575 Ma, respectively) and initial Sr ratio (0.7096–0.7166 and 0.7203–0.7233). However, they have similar Rb/Sr ratios (0.8–1.2), and the age and isotopic differences are attributed to differing degrees of postdepositional, metamorphic reworking. The Sr-growth trajectories of these metasediments define a broad band on the evolution diagram and indicate a probable (maximum?) age of deposition of ca. 2.0 ± 0.1 Ga. Furthermore, the role of Archean detritus in the depositional history of these sediments is quite limited, based on isotopic data for the basement gneisses and adjoining granulites of the Pikwitonei region.Comparison of these data with those for metagraywackes of the adjacent Kisseynew gneisses (average [Formula: see text]) indicates that there were fundamental differences between the marine environments within which the two Aphebian sedimentary sequences were deposited. The high Rb/Sr in the Thompson belt metasediments is interpreted to reflect a relatively "long" equilibration of authigenic clays with circulating seawater (open ocean?) whereas the lower Rb/Sr of the Kisseynew metasediments reflects rapid sedimentation in an eugeosynclinal environment dominated by juvenile Aphebian material.Combined K/Ar and Rb/Sr ages suggest that the metamorphic reworking of the Thompson belt metasediments had three phases, an early period of folding ([Formula: see text]), followed by cross-folding and amphibolite facies metamorphism corresponding to the main pulse of the Hudsonian Orogeny ([Formula: see text]), and finally, late-stage shearing, faulting, and retrograde metamorphism (1625–1550 Ma). Mafic to ultramafic magmatism and associated nickel mineralization are confined to the interval between the deposition of the Thompson belt supracrustals and the first phase of Hudsonian deformation (i.e., ca. 2.1–1.8 Ga).

Geochemical and Nd-Pb isotopic systematics of late Archean granitoids, southwestern Slave Province, Canada: constraints for granitoid origin and crustal isotopic structure

1999 ◽  
Vol 36 (7) ◽  
pp. 1131-1147 ◽  
Author(s):  
Katsuyuki Yamashita ◽  
Robert A Creaser ◽  
James U Stemler ◽  
Tony W Zimaro
Keyword(s):  
Partial Melting ◽  
Regional Scale ◽  
Crustal Thickening ◽  
Crustal Material ◽  
Isotopic Data ◽  
Metasedimentary Rocks ◽  
Slave Province ◽  
Juvenile Crust ◽  
Direct Input

New geochemical and Nd-Pb isotopic data for ~ 2.62-2.59 Ga granitoids from the southwest Slave Province are used to determine the source(s) of granitoid magmas, to evaluate the role of pre-2.8 Ga basement during this magmatism, and to refine the existing Nd-Pb isotopic structure of the western Slave Province. The Pb isotopic data require crust older than ~3.2 Ga as a granitoid protolith, whereas the Nd isotopic data require input from juvenile crustal material. This discrepancy is explained if the granitoid protoliths are mixtures of ancient basement and ~2.7 Ga juvenile crust in varying proportions. Specifically, granitoids from the southwestern Slave Province require 10-30% basement, whereas granitoids from other parts of the western Slave Province require >50%. Incorporation of basement as a protolith may be achieved indirectly, by assimilation of basement during juvenile ~2.7 Ga magmatism, or directly during ~2.62-2.59 Ga magmatism. The granitoid isotopic data suggest that indirect basement input was important on a regional scale, but direct input may have also taken place in some areas of the western Slave Province, particularly along the ~111°W "isotopic boundary" zone previously recognized. The geochemical characteristics of these granitoids are compatible with an origin by partial melting of dominantly amphibolite and metasedimentary rocks to produce the ~2.61 Ga and ~2.59 Ga magmatism, respectively; partial melting occurred in response to regional crustal thickening at this time.

scholarly journals Siliceous subglacial deposits: archives of subglacial processes during the Last Glacial Maximum

2021 ◽  
pp. 1-8
Author(s):  
Shalev Siman-Tov ◽  
Terrence Blackburn ◽  
Bernard Hallet ◽  
Matthew A. Coble ◽  
Emily E. Brodsky
Keyword(s):  
Isotopic Analysis ◽  
Rock Fragment ◽  
Isotopic Data ◽  
Geologic Time ◽  
Rock Interface ◽  
The Last Glacial Maximum ◽  
Siliceous Deposit ◽  
Detailed Chemical ◽  
The Last Glacial

Abstract We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic bedrock recently exposed by glacier retreat. Whereas a single, <1 μm, Si-rich layer covers the highly polished bedrock on the up-glacier (stoss) surfaces, distinct, lithified deposits commonly occur at the lee of small bedrock protuberances, on a scale <0.1 meter. The deposit is millimeters in thickness and consists of laminae tens to hundreds microns thick that differ from one another in color, rock-fragment abundance and chemical composition. Ca-rich laminae that are sufficiently enriched in uranium (~2–50 ppm) to permit U-series isotopic analysis suggest that the subglacial deposit formed 10–20 ka, much earlier than previously assumed. We conclude that (1) the siliceous deposit persisted for at least 10 000 years despite the intervening erosion and weathering, (2) distinct episodes of formation due to significant changes in hydrology and water chemistry are recorded in the deposit, and (3) a siliceous slurry may have existed at the ice-rock interface and influenced the local friction. This work reinforces earlier findings that subglacial chemical deposits can form and persist on geologic time scales and may have implications for the role of the cryosphere in the Earth's geochemical cycles and climate system.

The wet, the wild and the domesticated: The Mesolithic–Neolithic transition on the west coast of Scotland

2002 ◽  
Vol 5 (2) ◽  
pp. 147-189 ◽  
Author(s):  
Rick J. Schulting ◽  
Michael P. Richards
Keyword(s):  
Stable Isotope ◽  
West Coast ◽  
Isotopic Data ◽  
The West ◽  
Subsistence Economy ◽  
Neolithic Transition ◽  
Marginal Environment ◽  
Ams Dates ◽  
Stable Isotope Data

Models of the Mesolithic–Neolithic transition in Britain in recent years have tended to downplay the role of changes in the subsistence economy, emphasizing a very gradual adoption of new domesticated resources. This view has been particularly pervasive for the west coast of Scotland, which in the context of Britain presents a relatively marginal environment for farming. In this article, we challenge this too-quickly emerging orthodoxy through the presentation and discussion of both new and previously published stable isotope data and AMS dates. The palaeodietary information, while limited, strongly suggests a very rapid and complete change in the subsistence economy coincident with the earliest manifestations of the Neolithic on the west coast of Scotland early in the fourth millennium cal. BC. Whatever explanation is invoked to account for the transition needs to engage with the isotopic data. The possibility of colonization at some level needs to be seriously reconsidered.

The role of CO2 in alkali rock genesis

1976 ◽  
Vol 113 (2) ◽  
pp. 97-113 ◽  
Author(s):  
N. M. S. Rock
Keyword(s):  
Trace Element ◽  
Alkali Basalt ◽  
High Pressures ◽  
Alkaline Rock ◽  
Basalt Magma ◽  
Isotopic Data ◽  
Calcic Plagioclase ◽  
Basaltic Magmas ◽  
Normal Differentiation

SummaryThe extreme rarity of alkaline rock suites bearing both calcic plagioclase and magmatic carbonatites is believed to reflect a fundamental bifold division between Gabbroic and Carbonatitic types, plagioclase being present only in the former and carbonatite only in the latter. Alkali basalt magma may be parental to both lineages, the gabbroic lineage deriving from normal differentiation under low CO2 pressure, and the carbonatitic by suppression of plagioclase crystallization under high pressures of CO2, leading through pyroxene fractionation to a ‘secondary parental’ olivine-poor nephelinite magma. Support for this hypothesis is found in evidence for the suppression of plagioclase in CO2-rich alkali basaltic magmas and for the secondary origin of olivine-poor nephelinites, in the nature of xenoliths and cumulates at carbonatite complexes, in Sr isotopic data, and in major and trace element compositions of the magmas. The possible origin of melilitic rocks at carbonatite complexes is also briefly discussed.

scholarly journals Using global isotopic data to constrain the role of shale gas production in recent increases in atmospheric methane

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Alexei V. Milkov ◽  
Stefan Schwietzke ◽  
Grant Allen ◽  
Owen A. Sherwood ◽  
Giuseppe Etiope
Keyword(s):  
Shale Gas ◽  
Gas Production ◽  
Atmospheric Methane ◽  
Isotopic Data
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