Neoproterozoic strata of the southern Canadian Cordillera and the isotopic evolution of seawater sulfate

Ross, Gerald M.; Bloch, John; Krouse, H. R.

doi:10.1016/0301-9268(94)00072-y

Cited by 118 publications

(74 citation statements)

References 85 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At the time of initial publication, the stratigraphic trends reproduced in Figure 3 were viewed as evidence for temporal variation in the strength of the local marine connectionwith the lowest δ 34 S values refl ecting the most open conditions. In subsequent years, we have observed that large and often-systematic δ 34 S variations over relatively short stratigraphic intervals within single sedimentary units are not unusual for Proterozoic sulfi de accumulations (Ross et al, 1995;Strauss, 1997Strauss, , 2002, including SEDEX mineralization (Carr and Smith, 1977;Smith et al, 1978;McGoldrick et al, 1999), and that these patterns may have global implications Lyons et al, 2004).…”

Section: Sulfur Isotope Trendsmentioning

confidence: 90%

Proterozoic sedimentary exhalative (SEDEX) deposits and links to evolving global ocean chemistry

Lyons¹,

Gellatly²,

McGoldrick³

et al. 2006

Evolution of Early Earth's Atmosphere, Hydrosphere, and Biosphere - Constraints From Ore Deposits

View full text Add to dashboard Cite

Sedimentary exhalative (SEDEX) Zn-Pb-sulfi de mineralization fi rst occurred on a large scale during the late Paleoproterozoic. Metal sulfi des in most Proterozoic deposits have yielded broad ranges of predominantly positive δ 34 S values traditionally attributed to bacterial sulfate reduction. Heavy isotopic signatures are often ascribed to fractionation within closed or partly closed local reservoirs isolated from the global ocean by rifting before, during, and after the formation of Rodinia. Although such conditions likely played a central role, we argue here that the fi rst appearance of signifi cant SEDEX mineralization during the Proterozoic and the isotopic properties of those deposits are also strongly coupled to temporal evolution of the amount of sulfate in seawater.The ubiquity of 34 S-enriched sulfi de in ore bodies and shales and the widespread stratigraphic patterns of rapid δ 34 S variability expressed in both sulfate and sulfi de data are among the principal evidence for global seawater sulfate that was increasing during the Proterozoic but remained substantially lower than today. Because sulfate is produced mostly through weathering of the continents in the presence of oxygen, low Proterozoic concentrations imply that levels of atmospheric oxygen fell between the abundances of the Phanerozoic and the defi ciencies of the Archean, which are also indicated by the Precambrian sulfur isotope record. Given the limited availability of atmospheric oxygen, deep-water anoxia may have persisted well into the Proterozoic in the presence of a growing sulfate reservoir, which promoted prevalent euxinia. Collectively, these observations suggest that the mid-Proterozoic maximum in SEDEX mineralization and the absence of Archean deposits refl ect a critical threshold in the accumulation of oceanic sulfate and thus sulfi de within anoxic bottom waters and pore fl uids-conditions that favored both the production and preservation of sulfi de mineralization at or just below the seafl oor. Consistent with these evolving global conditions, the appearance of voluminous SEDEX mineralization ca. 1800 Ma coincides generally with the disappearance of banded iron formations-marking the transition from an early iron-dominated ocean to one more strongly infl uenced by sulfi de availability. 170 T.W. Lyons et al.

show abstract

Section: Sulfur Isotope Trendsmentioning

confidence: 90%

Proterozoic sedimentary exhalative (SEDEX) deposits and links to evolving global ocean chemistry

Lyons¹,

Gellatly²,

McGoldrick³

et al. 2006

Evolution of Early Earth's Atmosphere, Hydrosphere, and Biosphere - Constraints From Ore Deposits

View full text Add to dashboard Cite

show abstract

“…Canfield & Teske (1996) used biological 'clock' arguments for the origin of the sulphide-oxidizing organism Beggiatoa, which requires atmospheric oxygen .0.05 present atmospheric level by 750 Ma. The variability of sulphur isotopic values of pyrite and trace levels in carbonate becomes as great as in the Phanerozoic after the Marinoan, suggesting oxidation of the sulphide pool and significant microbially mediated sulphate oxidation of organic matter throughout the ocean (Ross et al 1995;Kah et al 2005). The volumetrically insignificant Banded Iron Formations found in association with a few Neoproterozoic glacial occurrences are likely to reflect local conditions in which deep-water anoxia may have been enhanced by ice cover (or by hydrothermal activity), rather than reflecting evidence for a global condition (see Tajika (2003Tajika ( , 2004, combined with Phanerozoic PCO 2 curve of Berner (1994) supplemented in the Ordovician and Precambrian by inferred variations in greenhouse forcing consistent with the glacial record.…”

Section: Neoproterozoic Glaciation In Earth Historymentioning

confidence: 99%

Neoproterozoic glaciation in the Earth System

Fairchild

Kennedy

2007

JGS

216

116

View full text Add to dashboard Cite

The Neoproterozoic contains severe glacial intervals (750–580 Ma) including two extending to low palaeomagnetic latitudes. Paucity of radiometric dates indicates the need for chronostratigraphic tools. Whereas the marine 87 Sr/ 86 Sr signatures show a steady rise, δ 13 C fluctuates, the most reproducible variations being negative signatures in carbonate caps to glacial units, but more diagenetic work is needed. Four conceptual models for the icehouse conditions are contrasted: Zipper-Rift Earth (diachronous glaciation related to continental rift margins), High-tilt Earth (high-obliquity and preferential low-latitude glaciation), Snowball Earth (extreme glaciation related to runaway ice–albedo feedback) and Slushball Earth (coexistence of unfrozen oceans and sea-level glaciers in the tropics). Climate models readily simulate runaway glaciation, but the Earth may not be able to recover from it. The Slushball state requires more extensive modelling. Biogeochemical models highlight the lack of CO 2 buffering in the Neoproterozoic and the likely transition from a methane- to a CO 2 -dominated climate system. Relevant processes include tropical weathering of volcanic provinces, and new land biotas stimulating both clay mineral formation and P delivery to the oceans, facilitating organic C burial. Hence a step change in the Earth System was probably both facilitated by organisms and responsible for moderating Phanerozoic climate.

show abstract

“…The Windermere Supergroup extends from northwestern Canada to northern Mexico and preserves the late Precambrian rift-drift history of the Cordilleran margin of Laurentia (Ross, 1991;Ross et al, 1995). It consists of a continental-margin wedge succession that accumulated during late Neoproterozoic time on the northwestern and western margin of Laurentia and crops out along an arcuate part of the Foreland Fold and Thrust Belt of the northern Canadian Cordillera (Fig.…”

Section: Windermere Supergroupmentioning

confidence: 99%

“…600-543 Ma) represents a critical time in earth history, marked by the end of the Proterozoic "snowball" glaciations (Hoffman et al, 1998), appearance of the oldest (Ediacaran) metazoans (Glaessner, 1984;Narbonne, 1998;Narbonne and Gehling, 2003) and profound changes in the isotopic composition of seawater (Kaufman and accessible region in the northern Cordillera, has not previously been studied in the same detail as the Mackenzie Mountains. The late Neoproterozoic succession of northwestern Canada, the Windermere Supergroup, was deposited during the breakup of Rodinia and the opening of the proto-Pacific (Ross, 1991;Ross et al, 1995;Dalrymple and Narbonne, 1996). Rifting likely occurred in several phases, with events at 780 Ma (Harlan et al, 2003), 740 and 723 Ma (geochronological constraints for deposition of basal Windermere strata reviewed by Ross et al, 1995), and 570 Ma (Colpron et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…The late Neoproterozoic succession of northwestern Canada, the Windermere Supergroup, was deposited during the breakup of Rodinia and the opening of the proto-Pacific (Ross, 1991;Ross et al, 1995;Dalrymple and Narbonne, 1996). Rifting likely occurred in several phases, with events at 780 Ma (Harlan et al, 2003), 740 and 723 Ma (geochronological constraints for deposition of basal Windermere strata reviewed by Ross et al, 1995), and 570 Ma (Colpron et al, 2002). The top of the supergroup is the sub-Cambrian unconformity (Fig.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Integrated Ediacaran chronostratigraphy, Wernecke Mountains, northwestern Canada

Pyle

Narbonne

James

et al. 2004

Precambrian Research

View full text Add to dashboard Cite

Terminal Neoproterozoic (Ediacaran, ca. 600-543 Ma) strata of the upper part of the Windermere Supergroup are well-exposed in the Mackenzie Mountains and the Wernecke Mountains of northwestern Canada. Windermere strata in the Mackenzie Mountains contain an exceptional Ediacaran biostratigraphic and isotopic (C and Sr) record, while the sequence stratigraphic record is subtle throughout this predominantly deep-water succession. Coeval strata in the Wernecke Mountains can be correlated with the succession in the Mackenzie Mountains on a formational level. In contrast to the deep-water setting of the Mackenzies succession, the Werneckes succession preserves a predominantly shallow-water succession amenable to detailed sequence stratigraphy. Integrated lithostratigraphy, chemostratigraphy, biostratigraphy and sedimentology partitions the Wernecke Mountains succession into five depositional sequences and constrains correlation with strata in the Mackenzie Mountains. The siliciclastic and carbonate sediments, deposited along the margin of the proto-Pacific Ocean, record accumulation in continental slope, neritic, and terrestrial paleoenvironments. Distinctive temporal chemostratigraphic and biostratigraphic attributes allow these strata to be correlated with other Ediacaran successions worldwide. Integrating sequence stratigraphy with these attributes is a robust, yet under-utilized correlation tool and is a step toward erecting a more detailed working Neoproterozoic chronostratigraphy.

show abstract

Neoproterozoic strata of the southern Canadian Cordillera and the isotopic evolution of seawater sulfate

Cited by 118 publications

References 85 publications

Proterozoic sedimentary exhalative (SEDEX) deposits and links to evolving global ocean chemistry

Proterozoic sedimentary exhalative (SEDEX) deposits and links to evolving global ocean chemistry

Neoproterozoic glaciation in the Earth System

Integrated Ediacaran chronostratigraphy, Wernecke Mountains, northwestern Canada

Contact Info

Product

Resources

About