Age Determinations in the Circum – Ungava Geosyncline and the Evolution of Precambrian Banded Iron-Formations

1972 ◽  
Vol 9 (6) ◽  
pp. 652-663 ◽  
Author(s):  
B. J. Fryer
Keyword(s):  
Large Scale ◽  
Sedimentary Rocks ◽  
Life Forms ◽  
Hudson Bay ◽  
Fold Belt ◽  
Banded Iron Formations ◽  
Unique Nature ◽  
Valuable Marker ◽  
Iron Formations ◽  
Age Determinations

Rb-Sr whole-rock isochron studies on volcanic and sedimentary rocks from the Belcher Fold Belt in Hudson Bay, and sedimentary rocks from the Labrador Trough and the Lake Mistassini area of Quebec, yield ages of 1800, 1870, and 1790 m.y., respectively. These age determinations substantiate previous correlations between these areas based on stratigraphic and structural similarities. Consequently, the concept of a Circum – Ungava Geosyncline appears to be valid on geochronological grounds, with geosynclinal development terminating with the onset of the Hudsonian orogeny at about 1800 m.y.The Circum – Ungava Geosyncline contains banded iron-formations exhibiting shallow-water sedimentary structures which distinguish them from older banded iron-formations. These deposits probably represent the hydrospheric response to the initial large scale introduction of oxygen to the atmosphere by evolving life forms. Because of their probable unique nature these younger banded iron-formations may serve as a valuable marker horizon for global correlations of Proterozoic strata.

scholarly journals Preliminary Rb-Sr age determinations from the North Greenland fold belt, Johannes V Jensen Land, with comments on the metamorphic grade

1981 ◽  
Vol 106 ◽  
pp. 77-84
Author(s):  
N Springer
Keyword(s):  
Sedimentary Rocks ◽  
Metamorphic Grade ◽  
Low Grade ◽  
Fold Belt ◽  
Isotopic Dating ◽  
Field Mapping ◽  
Sedimentary Structures ◽  
The North ◽  
North Greenland ◽  
Age Determinations

This report presents the first Rb-Sr age determinations obtained on low-grade metasediments within the eastern part of the North Greenland fold belt. Samples were collected during the 1979 field mapping in eastem Johannes V. Jensen Land, the results ofwhich have been published elsewhere (Soper et al., 1980). Material selected for this study was taken from moderately folded rocks of the Polkorridoren Group and from the northem part of the fold belt where deformation is intense and sedimentary structures are rarely preserved (fig. 23). The principles and methods of isotopic dating of sedimentary rocks applied in this study have been treated in a recent paper by Clauer (1979).

scholarly journals Photoferrotrophy, deposition of banded iron formations, and methane production in Archean oceans

2019 ◽  
Vol 5 (11) ◽  
pp. eaav2869 ◽  
Author(s):  
Katharine J. Thompson ◽  
Paul A. Kenward ◽  
Kohen W. Bauer ◽  
Tyler Warchola ◽  
Tina Gauger ◽  
...  
Keyword(s):  
Large Scale ◽  
Iron Oxidation ◽  
Coastal Sediments ◽  
Oxygenic Photosynthesis ◽  
Iron Formation ◽  
Banded Iron Formations ◽  
Banded Iron Formation ◽  
Earth’S Climate ◽  
Iron Formations ◽  
Scale Deposition

Banded iron formation (BIF) deposition was the likely result of oxidation of ferrous iron in seawater by either oxygenic photosynthesis or iron-dependent anoxygenic photosynthesis—photoferrotrophy. BIF deposition, however, remains enigmatic because the photosynthetic biomass produced during iron oxidation is conspicuously absent from BIFs. We have addressed this enigma through experiments with photosynthetic bacteria and modeling of biogeochemical cycling in the Archean oceans. Our experiments reveal that, in the presence of silica, photoferrotroph cell surfaces repel iron (oxyhydr)oxides. In silica-rich Precambrian seawater, this repulsion would separate biomass from ferric iron and would lead to large-scale deposition of BIFs lean in organic matter. Excess biomass not deposited with BIF would have deposited in coastal sediments, formed organic-rich shales, and fueled microbial methanogenesis. As a result, the deposition of BIFs by photoferrotrophs would have contributed fluxes of methane to the atmosphere and thus helped to stabilize Earth’s climate under a dim early Sun.

The mid-Paleozoic deformation in the Hazen fold belt, Ellesmere Island, Arctic Canada

1990 ◽  
Vol 27 (10) ◽  
pp. 1359-1370 ◽  
Author(s):  
Eva M. Klaper
Keyword(s):  
Large Scale ◽  
Ellesmere Island ◽  
Small Scale ◽  
Northwestern Part ◽  
Fold Belt ◽  
Southeastern Part ◽  
Lower Paleozoic ◽  
Slip Mechanism ◽  
Fold Belts ◽  
Surface Geology

The mid-Paleozoic deformation of lower Paleozoic subgreenschist-facies sediments of the Hazen fold belt in northern Ellesmere Island is represented predominantly by chevron-style folding. Folded multilayers display cleavage fans suggesting synchronous fold and cleavage formation. Bedding-parallel slip indicates a flexural slip mechanism of folding. The geometry of several large-scale anticlinoria has been interpreted as being due to formation of these structures over detachments and thrust ramps.The constant fold geometry, the parallel orientation of faults and large- and small-scale folds, and the axial-plane foliation are related to a single phase of folding with a migrating deformation front in the Hazen fold belt during the mid-Paleozoic orogeny. The minimum amount of shortening in the Hazen and Central Ellesmere fold belts has been estimated from surface geology to increase from 40–50% of the original bed length in the external southeastern part to 50–60% in the more internal northwestern part of the belts.The convergent, thin-skinned nature of the Hazen and Central Ellesmere fold belts indicates that the postulated transpressive plate motions during the accretion of Pearya did not affect the study area.

scholarly journals Spatial variation and mechanisms of leaf water content in grassland plants at the biome scale: evidence from three comparative transects

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ruomeng Wang ◽  
Nianpeng He ◽  
Shenggong Li ◽  
Li Xu ◽  
Mingxu Li
Keyword(s):  
Spatial Variation ◽  
Water Content ◽  
Large Scale ◽  
Life Forms ◽  
Important Variable ◽  
Leaf Water ◽  
Leaf Water Content ◽  
Desert Grassland ◽  
Large Spatial Scale ◽  
Grassland Plants

AbstractLeaf water content (LWC) has important physiological and ecological significance for plant growth. However, it is still unclear how LWC varies over large spatial scale and with plant adaptation strategies. Here, we measured the LWC of 1365 grassland plants, along three comparative precipitation transects from meadow to desert on the Mongolia Plateau (MP), Loess Plateau, and Tibetan Plateau, respectively, to explore its spatial variation and the underlying mechanisms that determine this variation. The LWC data were normally distributed with an average value of 0.66 g g−1. LWC was not significantly different among the three plateaus, but it differed significantly among different plant life forms. Spatially, LWC in the three plateaus all decreased and then increased from meadow to desert grassland along a precipitation gradient. Unexpectedly, climate and genetic evolution only explained a small proportion of the spatial variation of LWC in all plateaus, and LWC was only weakly correlated with precipitation in the water-limited MP. Overall, the lasso variation in LWC with precipitation in all plateaus represented an underlying trade-off between structural investment and water income in plants, for better survival in various environments. In brief, plants should invest less to thrive in a humid environment (meadow), increase more investment to keep a relatively stable LWC in a drying environment, and have high investment to hold higher LWC in a dry environment (desert). Combined, these results indicate that LWC should be an important variable in future studies of large-scale trait variations.

scholarly journals Iron and Carbon Isotope Constraints on the Formation Pathway of Iron-Rich Carbonates within the Dagushan Iron Formation, North China Craton

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 94
Author(s):  
Xiaoxue Tong ◽  
Kaarel Mänd ◽  
Yuhao Li ◽  
Lianchang Zhang ◽  
Zidong Peng ◽  
...  
Keyword(s):  
Iron Reduction ◽  
Isotope Composition ◽  
Iron Formation ◽  
Banded Iron Formations ◽  
Organic C ◽  
Formation Pathway ◽  
Wide Range ◽  
Dissimilatory Iron Reduction ◽  
O Isotope ◽  
Iron Formations

Banded iron formations (BIFs) are enigmatic chemical sedimentary rocks that chronicle the geochemical and microbial cycling of iron and carbon in the Precambrian. However, the formation pathways of Fe carbonate, namely siderite, remain disputed. Here, we provide photomicrographs, Fe, C and O isotope of siderite, and organic C isotope of the whole rock from the ~2.52 Ga Dagushan BIF in the Anshan area, China, to discuss the origin of siderite. There are small magnetite grains that occur as inclusions within siderite, suggesting a diagenetic origin of the siderite. Moreover, the siderites have a wide range of iron isotope compositions (δ56FeSd) from −0.180‰ to +0.463‰, and a relatively negative C isotope composition (δ13CSd = −6.20‰ to −1.57‰). These results are compatible with the reduction of an Fe(III)-oxyhydroxide precursor to dissolved Fe(II) through microbial dissimilatory iron reduction (DIR) during early diagenesis. Partial reduction of the precursor and possible mixing with seawater Fe(II) could explain the presence of siderite with negative δ56Fe, while sustained reaction of residual Fe(III)-oxyhydroxide could have produced siderite with positive δ56Fe values. Bicarbonate derived from both DIR and seawater may have provided a C source for siderite formation. Our results suggest that microbial respiration played an important role in the formation of siderite in the late Archean Dagushan BIF.

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