THE ROLE OF SILICA IN IRON FORMATIONS: TEXTURAL, MINERALOGICAL, AND GEOCHEMICAL COMPARISONS FROM LOW METAMORPHIC GRADE NEOARCHEAN AND PALEOPROTEROZOIC EXAMPLES

2020 ◽  
Author(s):  
Latisha Ashley Brengman ◽  
◽  
Esther K. Stewart ◽  
Danielle Stolze ◽  
Emily Faust ◽  
...  
Keyword(s):  
Metamorphic Grade ◽  
Iron Formations

scholarly journals Microbial processes during deposition and diagenesis of Banded Iron Formations

PalZ ◽  
2021 ◽  
Author(s):  
Carolin L. Dreher ◽  
Manuel Schad ◽  
Leslie J. Robbins ◽  
Kurt O. Konhauser ◽  
Andreas Kappler ◽  
...  
Keyword(s):  
Microbial Reduction ◽  
Iron Cycling ◽  
Banded Iron Formations ◽  
Geochemical Composition ◽  
High Pressure And Temperature ◽  
Microbial Life ◽  
Reducing Bacteria ◽  
Iron Formations ◽  
Chemical Sediments

AbstractBanded Iron Formations (BIFs) are marine chemical sediments consisting of alternating iron (Fe)-rich and silica (Si)-rich bands which were deposited throughout much of the Precambrian era. BIFs represent important proxies for the geochemical composition of Precambrian seawater and provide evidence for early microbial life. Iron present in BIFs was likely precipitated in the form of Fe3+ (Fe(III)) minerals, such as ferrihydrite (Fe(OH)3), either through the metabolic activity of anoxygenic photoautotrophic Fe2+ (Fe(II))-oxidizing bacteria (photoferrotrophs), by microaerophilic bacteria, or by the oxidation of dissolved Fe(II) by O2 produced by early cyanobacteria. However, in addition to oxidized Fe-bearing minerals such as hematite (FeIII2O3), (partially) reduced minerals such as magnetite (FeIIFeIII2O4) and siderite (FeIICO3) are found in BIFs as well. The presence of reduced Fe in BIFs has been suggested to reflect the reduction of primary Fe(III) minerals by dissimilatory Fe(III)-reducing bacteria, or by metamorphic (high pressure and temperature) reactions occurring in presence of buried organic matter. Here, we present the current understanding of the role of Fe-metabolizing bacteria in the deposition of BIFs, as well as competing hypotheses that favor an abiotic model for BIF deposition. We also discuss the potential abiotic and microbial reduction of Fe(III) in BIFs after deposition. Further, we review the availability of essential nutrients (e.g. P and Ni) and their implications on early Earth biogeochemistry. Overall, the combined results of various ancient seawater analogue experiments aimed at assessing microbial iron cycling pathways, coupled with the analysis of the BIF rock record, point towards a strong biotic influence during BIF genesis.

Review Lecture - Ore-deposition through geological time

1978 ◽  
Vol 362 (1710) ◽  
pp. 305-328 ◽  
Keyword(s):  
Mineral Deposits ◽  
Banded Iron Formations ◽  
Geological Time ◽  
The Earth ◽  
Recent Developments ◽  
Changing Role ◽  
Iron Formations ◽  
Ore Deposition

Economic mineral deposits represent abnormal concentrations of metals which must be regarded as records of unusual geological events. The recognition of any long-term changes in styles of mineralization must depend on the identification of anomalies within the geological régimes characteristic of successive stages of the Earth’s history. This question will be discussed in relation to recent developments in the Earth sciences. The recognition of structural and chemical inhomogeneities in the lithospheric mantle suggests that mapping of mantle age-provinces may become possible; such studies bear on the significance of certain metallogenic provinces. Coordinated geochemical, structural and palaeomagnetic studies which are throwing light on the evolution of early tectonic systems should help to illuminate the significance of changes in style of mineralization at the Archaean/Proterozoic boundary, as well as the distribution of some types of Proterozoic deposits. Geochemical evidence concerning the changing rôle of organic processes in sedimentation and diagenesis has a bearing on the origin of sedimentary ores, especially over the controversial period characterized by accumulation of banded iron-formations.

Hematite replacement and oxidative overprinting recorded in the 1.88 Ga Gunflint iron formation, Ontario, Canada

Geology ◽  
2020 ◽  
Vol 48 (7) ◽  
pp. 688-692
Author(s):  
Birger Rasmussen ◽  
Janet R. Muhling
Keyword(s):  
Iron Oxide ◽  
Large Scale ◽  
Iron Oxidation ◽  
Original Model ◽  
Iron Deposition ◽  
Iron Formation ◽  
Drill Core ◽  
The Veil ◽  
Iron Formations

Abstract The 1.88 Ga Gunflint Formation in Ontario, Canada, has played a key role in the development of current models for the deposition of iron formations. The presence of hematite-rich iron formation intercalated with chert stromatolites containing purported cyanobacterial microfossils sparked the idea that biology was the principal driver of Fe2+ oxidation and iron deposition. However, despite the abundance of hematite in the Gunflint Formation, a primary depositional origin has not been established. Here we present evidence for the replacement of Fe-silicate granules by hematite in drill core intersecting the Gunflint Formation. Iron-oxide replacement proceeded inwards from granule boundaries and along intergranular fractures, producing iron oxide–rich rims around Fe-silicate cores. The abundance of organic matter in shaly iron formation implies that the iron-rich mudstones experienced anoxic diagenesis and that coexisting hematite was not depositional but formed after burial. Widespread distribution of the alteration textures indicates that this was a large-scale process and that much of the hematite is not primary. Lifting the veil of oxidative overprinting reveals an iron-rich sediment that was originally more reduced and dominated by Fe(II)-rich minerals. Our results imply that a major assumption underpinning the original model for biological iron oxidation as the driver of iron formation deposition may be flawed, raising broader questions about the origin of hematite in other iron formations and the role of biology in iron deposition in the early oceans.

The role of microaerophilic Fe-oxidizing micro-organisms in producing banded iron formations

Geobiology ◽  
2016 ◽  
Vol 14 (5) ◽  
pp. 509-528 ◽  
Author(s):  
C. S. Chan ◽  
D. Emerson ◽  
G. W. Luther
Keyword(s):  
Banded Iron Formations ◽  
Micro Organisms ◽  
Iron Formations

Role of dactinomycin in the improved survival of children with Wilms' tumor

JAMA ◽  
1966 ◽  
Vol 195 (12) ◽  
pp. 1005-1009 ◽  
Author(s):  
D. J. Fernbach
Keyword(s):  
Wilms Tumor

Role of the allergist in diagnosis and management of patients with uveitis

JAMA ◽  
1966 ◽  
Vol 195 (3) ◽  
pp. 167-172 ◽  
Author(s):  
T. E. Van Metre
Keyword(s):  
Diagnosis And Management

The power of norms to sway fused group members

2018 ◽  
Vol 41 ◽  
Author(s):  
Winnifred R. Louis ◽  
Craig McGarty ◽  
Emma F. Thomas ◽  
Catherine E. Amiot ◽  
Fathali M. Moghaddam
Keyword(s):  
Evolutionary Anthropology ◽  
Normative Systems ◽  
Violent Extremism ◽  
Identity Fusion ◽  
Group Members

AbstractWhitehouse adapts insights from evolutionary anthropology to interpret extreme self-sacrifice through the concept of identity fusion. The model neglects the role of normative systems in shaping behaviors, especially in relation to violent extremism. In peaceful groups, increasing fusion will actually decrease extremism. Groups collectively appraise threats and opportunities, actively debate action options, and rarely choose violence toward self or others.

Elaborating the role of reflection and individual differences in the study of folk-economic beliefs

2018 ◽  
Vol 41 ◽  
Author(s):  
Kevin Arceneaux
Keyword(s):  
Decision Making ◽  
Individual Differences ◽  
Cognitive Processes ◽  
Evolutionary History ◽  
Behavioral Responses ◽  
History Of ◽  
Economic Beliefs

AbstractIntuitions guide decision-making, and looking to the evolutionary history of humans illuminates why some behavioral responses are more intuitive than others. Yet a place remains for cognitive processes to second-guess intuitive responses – that is, to be reflective – and individual differences abound in automatic, intuitive processing as well.

The role of affect in feelings of obligation

2020 ◽  
Vol 43 ◽  
Author(s):  
Stefen Beeler-Duden ◽  
Meltem Yucel ◽  
Amrisha Vaish
Keyword(s):  
Positive Emotions ◽  
The Creation ◽  
Sense Of Obligation

Abstract Tomasello offers a compelling account of the emergence of humans’ sense of obligation. We suggest that more needs to be said about the role of affect in the creation of obligations. We also argue that positive emotions such as gratitude evolved to encourage individuals to fulfill cooperative obligations without the negative quality that Tomasello proposes is inherent in obligations.

Sign in / Sign up

Export Citation Format

Share Document