Neoproterozoic iron formation: An evaluation of its temporal, environmental and tectonic significance

Abstract

Neoproterozoic iron formation (NIF) provides evidence for the widespread return of anoxic and ferruginous basins during a time period associated with major changes in climate, tectonics and biogeochemistry of the oceans. Here we summarize the stratigraphic context of Neoproterozoic iron formation and its geographic and temporal distribution. It is evident that most NIF is associated with the earlier Cryogenian (Sturtian) glacial epoch. Although it is possible that some NIF may be Ediacaran, there is no incontrovertible evidence to support this age assignment. The paleogeographic distribution of NIF is consistent with anoxic and ferruginous conditions occurring in basins within Rodinia or in rift-basins developed on its margins. Consequently NIF does not require whole ocean anoxia. Simple calculations using modern day iron fluxes suggest that only models that invoke hydrothermal and/or detrital sources of iron are capable of supplying sufficient iron to account for the mass of the larger NIF occurrences. This conclusion is reinforced by the available geochemical data that imply NIF record is a mixture of hydrothermal and detrital components. A common thread that appears to link most if not all NIF is an association with mafic volcanics.Word Count: 11,011

Geological characteristics and age of the Dahongliutan Fe-ore deposit in the Western Kunlun orogenic belt, Xinjiang, northwestern China

“…The macrobands, mesobands (<2.54 cm) and microbands (0.3-1.7 mm) are usually well preserved, although low-grade greenschist-metagabbro facies metamorphism occurred in most Fe deposits (Trendall and Blockley, 1970;Klein, 2005). In most Neoproterozoic BIFs, iron resides almost exclusively in hematite (Klein and Beukes, 1993;Cox et al, 2013) instead of magnetite (Volkert et al, 2010;Freitas et al, 2011). Accessory minerals include chlorite, quartz and carbonate.…”

“…Manganese is also a significant component of Neoproterozoic BIFs. Detrital material inputs are common, and bands are poorly developed or entirely absent in most Neoproterozoic BIFs (Cox et al, 2013).…”

“…Xu et al (2013Xu et al ( , 2014 Klein and Ladeira, 2004;Halverson et al, 2011) or glaciated rift environment (Young, 2002). Rapitantype BIFs have been widely reported to be related to the prominent Neoproterozoic glacial events (Sturian: 718-660 Ma; Marinoan: 651-635 Ma), such as those in the Rapitan in Canada, Urucum in Brazil, the Adelaide Geosyncline in South Australia, Damara in South Africa, southern Paraguay Belt in Brazil and Jiangnan paleocontinent in South China Block (Tang et al, 1987;Klein and Beukes, 1993;Lottermoser and Ashley, 2000;Klein and Ladeira, 2004;Ilyin, 2009;Babinski et al, 2013;Cox et al, 2013;Li et al, 2014).…”

“…In comparison with Superior-type BIF, the Dahongliutan BIF exhibits similarity in host rocks, mineral assemblages, and banded compositions and structures. The Dahongliutan BIF may represent a case for the reappearance of iron formation during the Neoproterozoic, which reflecting the recurrence of anoxic ferruginous conditions in the Neoproterozoic-Early Cambrian deep sea (Isley and Abbott, 1999; Kump and Seyfried, 2005;Canfield et al, 2007Canfield et al, , 2008Johnston et al, 2010Johnston et al, , 2012Basta et al, 2011;Shields and Och, 2011;Cox et al, 2013 …”

“…Banded Iron Formations (BIFs), typically thin bedded or laminated, are chemical sediments containing >15 wt.% Fe 2 O 3 and composed of intercalated microcrystalline quartz, iron oxides, iron-rich silicates and carbonates (James, 1954;Pickard, 2003;Basta et al, 2011;Cox et al, 2013). The deposition of BIFs requires an anoxic water column to transport ferrous iron to sites of iron precipitation.…”