Sm-Nd in marine carbonates and phosphates: Implications for Nd isotopes in seawater and crustal ages

Shaw, Henry F.; Wasserburg, G. J.

doi:10.1016/0016-7037(85)90042-0

Cited by 293 publications

(83 citation statements)

References 52 publications

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“…At the end of the Proterozoic (between 6 1 O-550 Ma), seawater Sr isotopic ratio rose rapidly to values of ca. 0.709 ( VEIZER et al, 1983;SHAW and WASSERBURG, 1985;BURKE et al, 1982). This rise is comparable in magnitude to that recorded in marine carbonates from the Cretaceous to present.…”

Section: Introductionsupporting

confidence: 74%

Strontium isotopic variations of Neoproterozoic seawater: Implications for crustal evolution

Asmerom

Jacobsen

Knoll

et al. 1991

Geochimica et Cosmochimica Acta

201

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Section: Introductionsupporting

confidence: 74%

Strontium isotopic variations of Neoproterozoic seawater: Implications for crustal evolution

Asmerom

Jacobsen

Knoll

et al. 1991

Geochimica et Cosmochimica Acta

201

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“…Redox conditions control the conversion and distribution of Cerium (Ce) and to a lesser degree Europium (Eu) (Sholkovitz et al, 1994); hence both elements provide further information on process controlling parameters. The earlier concept that limestone was a poor choice for seawater REE proxy due to the effects of diagenesis in ancient carbonates (e.g., Scherer and Seitz, 1980;Shaw and Wasserburg, 1985), was replaced by the current paradigm, which suggests that diagenesis, particularly meteoric and mixed water, has no effect on the pattern, composition and/or distribution of REEs in carbonates (limestones and dolomites) except in diagenetic systems with extremely large watererock ratios (e.g., Banner et al, 1988;Barton et al, 2006;Webb and Kamber, 2000;Kamber and Webb, 2001;Nothdurft et al, 2004;Webb et al, 2009).…”

Section: Rare Earth Elements (Ree)mentioning

confidence: 99%

Origin of Lower Ordovician dolomites in eastern Laurentia: Controls on porosity and implications from geochemistry

Azomani

Azmy

Blamey

et al. 2013

Marine and Petroleum Geology

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a b s t r a c tThe Catoche Formation of the St. George Group in eastern Laurentia (western Newfoundland) consists of early Ordovician (Arenigian) shallow marine platform carbonates (w160 m thick), which were extensively dolomitized during the course of their diagenetic history. The dolomites occur as both replacement and pore-filling cements and are a major control on porosity distribution in the formation. The origin and diagenetic history of the Catoche dolomites at Daniel's Harbour (western Newfoundland) were analysed in comparison to equivalent successions at Port au Choix (PaC) and Port au Port Peninsula (PaP) to assay the reservoir potential of these dolomites in eastern Laurentia. Petrographic examination identified at least three generations of dolomites in the Catoche Formation, which are: (1) an early replacement sub-to eu-hedral micritic dolomite (<4 mme30 mm, D1), (2) eu-to sub-hedral dolomite (70 mme1 mm) often with cloudy cores and clear rims (D2), and (3) subhedral to anhedral saddle dolomite cement (200 mme3 mm, D3). The micritic dolomite (D1) exhibits a dull cathodoluminescence (CL) under cathodoluminoscope, whereas dolomite D2 exhibits consistent concentric CL zonation. Some subhedral crystals of D3 appear zoned both in plane polarized light and cathodoluminoscope, otherwise D3 exhibits a dull CL. Stoichiometric dolomite occurs in all three generations with D2 as the dominant dolomite by abundance.The low strontium (47 ± 25 ppm) content coupled with depleted d 18 O value of dolomitizing fluids (-10 to -11.2& VSMOW) and near-micritic grain size, suggests an early precipitation of dolomite D1 at low temperatures of near-surface conditions from solutions likely formed by mixing of early Ordovician sea and meteoric waters. In contrast, microthermometric measurements of primary two-phase fluid inclusions in dolomite D2 (homogenization temperatures of 102e168 o C with a salinity range of 19.8e25 eq wt% NaCl) and dolomite D3 (homogenization temperatures of 158e190 o C with a salinity range of 20.2e22.2 eq wt% NaCl), suggest that both dolomite generations were generated in mid to deep burial settings from high salinity, low temperature (<200 o C) hydrothermal fluids likely under suboxic conditions. This is consistent with the low Sr concentrations for D2 (36.4 ± 8 ppm) and D3 (38.7 ± 9 ppm), d 18 O values of dolomitizing fluids for D2 (þ2.1 to þ8.1&, VSMOW) and D3 (þ6 to þ8.1& VSMOW), coupled with Fe contents of D2 (1684 ± 1096 ppm) and D3 (1783.7 ± 618 ppm) as well as the respective Mn (D2 ¼ 131.2 ± 50 and D3 ¼ 197.5 ± 55 ppm) concentrations.SREE and shale normalized (REESN) values of Catoche carbonates indicate enrichment in rare earth element (REE) composition of the earliest calcite (C1) relative to those of Arenig seawater, whereas the REESN profiles of the dolomite generations mimic that of calcite C1. The Ce (Ce/Ce*)SN and La (La/La* ¼ Pr/Pr*)SN anomalies of the Catoche dolomites are consistent with precipitation in equilibrium with source fluids in slightly oxic to suboxic conditions whereas Eu...

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“…Initially, limestones were considered poor choices of seawater REE proxies, because diagenesis was deemed pervasive and caused increases in REEs in ancient carbonates (e.g., Scherer and Seitz, 1980;Shaw and Wasserburg, 1985). This early concept was replaced by the current paradigm, which suggests that diagenesis, specifically meteoric and mixed water, has no effect on the composition and/or distribution of REEs in carbonates (limestones and dolomites) except in diagenetic systems with extremely large water/rock ratios (e.g., Banner et al, 1988;Barton et al, 2006;Webb and Kamber, 2000;Kamber and Webb, 2001;Nothdurft et al, 2004;Webb et al, 2009).…”

Section: Diagenetic Effectmentioning

confidence: 99%

“…The foremost concern is the loss and/or overprinting of original REE's trends and compositions due to scavenging processes at or near the sediment pore-water interface (e.g., Banner et al, 1988;Webb et al, 2009) or contamination by terrigenous detritus (Webb and Kamber, 2000;Negrel et al, 2006). Of all these concerns, diagenesis was not considered a major problem because the REE content and distribution remained apparently relatively stable and uniform unless carbonates were subjected to alteration in extremely high water/rock ratio systems (e.g., Banner et al, 1988;Webb et al, 2009), although Shaw and Wasserburg (1985) based on increased REE concentrations suggested that limestones may be diagenetically altered.…”

Section: Introductionmentioning

confidence: 99%

“…Some of the oceanographic features identified in REEs are their close affinity to upwelling (productivity), water depth, stratification, circulation, dust deposition (shallow water fertilization) and continental fluvial run-off with consequently increased productivity (e.g., Shaw and Wasserburg, 1985; Shen and Sanford, 1989;Elderfield et al, 1990;Sholkovitz et al, 1994;Sholkovitz and Shen, 1995;Nothdurft et al, 2004). In addition, the ideal proxy of seawater REEs must be resistant to diagenetic effects, incorporate the REE into its mineral structure in proportion with that in the ambient seawater and at sufficient concentration levels, and their shale-normalized patterns should mimic that of the original ambient seawater (cf.…”

Section: Introductionmentioning

confidence: 99%

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Biogenic and abiogenic low-Mg calcite (bLMC and aLMC): Evaluation of seawater-REE composition, water masses and carbonate diagenesis

et al. 2011

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Biogenic low-Mg calcite (brachiopods) Burial calcite cements lREE, REESN seawater compositions Diagenetic lREE and REEsN variations The l;REE and shale-normalized (PAAS) REEsN values of modern brachiopods (biogenic low-Mg calcite: blMC) represented by several species from high-to low latitudes, from shallow-to deep waters and from warm-and cold-water environments, define three distinct average 'seawater' trends. The warm-and cold-water brachiopods define two indistinguishable (p < O.OSO) groups that mimic open -ocean seawater REE chemistry, exhibiting the typical LREE enrichment with a slightly positive to negative Ce anomaly followed by an otherwise invariant series. Other recent brachiopods from an essentially siliciclastic seabed environment are distinct in both l;REE and REEsN trends from the previous two populations, showing a slight enrichment in the MREEs and an increasing trend in the HREEs. Other groups of modern brachiopods are characterized by elevated REEsN trends relative to the 'normal'groups as well as by complexity of the series trends.The most characteristic feature is the decrease in the HREEs in these brachiopods from areas of unusual productivity (i.e., such as upwelling currents, fluvial input and aerosol dust deposition). Preserved brachiopods from the Eocene and Silurian exhibit REEsN trends and Ce anomalies similar to that of the 'open-ocean' modern brachiopods, although, their enriched l;REE concentrations suggest precipitation ofblMC influenced by extrinsic environmental conditions. Preservation of the bLMC was tested by comparing the l;REE and REEsN trends of preserved Eocene brachiopods to those of Oligocene brachiopods that were altered in an open diagenetic system in the presence of phreatic meteoric-water. The altered blMC is enriched by approximately one order of magnitude in both l;REE and REEsN trends relative to that in blMC of their preserved counterparts. Similarly, the l;REE and REEsN of preserved Silurian brachiopod blMC were compared to those of their enclosing altered lime mudstone, which exhibits features of partly closed system, phreatic meteoric-water diagenesis. Despite these differences in the diagenetic alteration systems and processes, the l;REEs and REEsN trends of the blMC of altered brachiopods and of originally mixed mineralogy lime mudstones (now diagenetic low-Mg caldte) are enriched by about one order of magnitude relative to those observed in the coeval and preserved blMC. In contrast to the changes in l;REE and REEsN of carbonates exposed to phreatic meteoric-water diagenesis, are the REE compositions oflate burial calcite cements precipitated in diagenetically open systems from burial fluids. The l;REE and REEsN trends of the burial cements mimic those of their host lime mudstone, with all showing slight LREE enrichment and slight HREE depletion, exhibiting a 'chevron' pattern of the REEsN trends.The overall enrichment or depletion of the cement REEsN trends relative to that of their respective host rock material reflects not only the openness of the diag...

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Sm-Nd in marine carbonates and phosphates: Implications for Nd isotopes in seawater and crustal ages

Cited by 293 publications

References 52 publications

Strontium isotopic variations of Neoproterozoic seawater: Implications for crustal evolution

Strontium isotopic variations of Neoproterozoic seawater: Implications for crustal evolution

Origin of Lower Ordovician dolomites in eastern Laurentia: Controls on porosity and implications from geochemistry

Biogenic and abiogenic low-Mg calcite (bLMC and aLMC): Evaluation of seawater-REE composition, water masses and carbonate diagenesis

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