Journal ArticleDOI
Iron silicate microgranules as precursor sediments to 2.5-billion-year-old banded iron formations
Reads0
Chats0
TLDR
In this paper, the authors suggest that the precursor mineral was an iron-rich silicate that formed either in the water column or on the seafloor, and the microgranular textures are preserved only where early diagenetic silica prevented the compaction of lamina sets.Abstract:
Banded iron formations (BIFs) are chemical sedimentary rocks comprising alternating layers of iron-rich and silica-rich minerals that have been used to infer the composition of the early Precambrian ocean and ancient microbial processes. However, the identity of the original sediments and their formation is a contentious issue due to postdepositional overprinting and the absence of modern analogues. Petrographic examination of the ca. 2.5 Ga Dales Gorge Member of the Brockman Iron Formation (Hamersley Group), Western Australia, reveals the presence of abundant silt-sized microgranules composed of stilpnomelane. The microgranules are most common in the least-altered BIF where they define sedimentary laminations, implying a depositional origin. We suggest that the precursor mineral was an iron-rich silicate that formed either in the water column or on the seafloor. The microgranular texture may have developed due to clumping of amorphous mud, forming silt-sized floccules. The microgranules were resedimented by dilute density currents and deposited in lamina sets comprising a basal microgranular-rich lamina overlain by amorphous mud with dispersed microgranules. The lamina sets collectively define plane-lamination structure, probably of the lower flow regime. The microgranular textures are preserved only where early diagenetic silica prevented the compaction of lamina sets. Episodic resedimentation of iron silicates alternating with periods of nondeposition and seafloor silicification provides an explanation for some of the characteristic banding in BIF. We propose that for most of the early Precambrian, the persistence of ferruginous oceans with elevated silica concentrations favored the widespread growth of iron silicate minerals, which in environments starved of continental sediments formed extensive deposits of the precursor sediment to iron formation.read more
Citations
More filters
Journal ArticleDOI
Iron Isotope Systematics
TL;DR: The distribution of these three oxidation states is markedly stratified in the Earth as discussed by the authors, and the distribution of the three states is very different in different regions of the world, as shown in Figure 1.
Journal ArticleDOI
An authigenic origin for Precambrian greenalite: Implications for iron formation and the chemistry of ancient seawater
TL;DR: In this paper, experimental evidence is presented showing that Fe 2+ and SiO 2 (aq) in anoxic seawater-derived solutions promote rapid nucleation of a hydrous Fe(II)-silicate gel at 25 °C.
Journal ArticleDOI
Reverse weathering as a long-term stabilizer of marine pH and planetary climate
Terry T. Isson,Noah J. Planavsky +1 more
TL;DR: Elevated rates of reverse weathering within silica-rich oceans led to enhanced carbon retention within the ocean–atmosphere system, promoting a stable, equable ice-free climate throughout Earth’s early to middle ages.
Journal ArticleDOI
Biogenic Fe(III) minerals: From formation to diagenesis and preservation in the rock record
TL;DR: In this article, the role of Fe(II)-oxidizing bacteria in the deposition of ancient banded iron formations (BIF) is discussed, with the main challenge of separating biogenic from abiogenic processes over deep time.
Journal ArticleDOI
Biomass recycling and Earth’s early phosphorus cycle
TL;DR: It is proposed that the size of the marine phosphorus reservoir was instead constrained by muted liberation of phosphorus during the remineralization of biomass, contributing to the delayed rise of atmospheric oxygen.
References
More filters
Book
The chemical evolution of the atmosphere and oceans
TL;DR: Holland et al. as mentioned in this paper reconstruct the chemical evolution of the Earth's atmosphere and oceans using data from a wide spectrum of fields to trace the history of the ocean-atmosphere system.
Journal ArticleDOI
Some Precambrian banded iron-formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origins
TL;DR: Banded iron-formations (BIFs) occur in the Precambrian geologic record over a wide time span as mentioned in this paper and are part of Archean cratons and range in age from about 3.5 until 2.5 Ga.
Journal ArticleDOI
Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes
Andrey Bekker,Bryan Krapež,John F. Slack,Noah J. Planavsky,Axel Hofmann,Kurt O. Konhauser,Olivier Rouxel +6 more
TL;DR: In this article, it was shown that occurrences of BIF, GIF, Pherozoic ironstones, and exhalites surrounding VMS systems are linked to diverse environmental changes.
Journal ArticleDOI
The silica cycle in the Precambrian
TL;DR: In this paper, it was shown that the Neoproterozoic silica cycle was dominated by inorganic reactions among dissolved silica, clay and zeolite minerals, and organic matter.
Journal ArticleDOI
Accretion of Mudstone Beds from Migrating Floccule Ripples
Juergen Schieber,Juergen Schieber,John B. Southard,John B. Southard,Kevin Thaisen,Kevin Thaisen +5 more
TL;DR: Using flume experiments, it is found that the bedload transport and deposition of clay floccules occurs at flow velocities that transport and deposit sand, which suggests an underlying universal process.