Old Rb-Sr whole-rock isochron apparent ages from Lower Cambrian psammites and metapsammites, southeastern New York

Spanglet, Mark; Brueckner, Hannes K.; Senechal, Ronald G.

doi:10.1130/0016-7606(1978)89<783:orwiaa>2.0.co;2

Cited by 8 publications

(2 citation statements)

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“…Freshly deposited sediments may be isotopically homogenized by erosion, transportation, and deposition processes, or the isotopic character of source rocks may be partially preserved as a correlation between 87Sr/X6Sr and Rb/Sr. This is observed for marine muds today (Dasch 1969) and for ancient sandstone (Spanglet et al 1978) and shale (Chaudhuri 1976) and must be the explanation for some of our results.…”

Section: Dating Of Sedimentary Rocks By Rb-srmentioning

confidence: 56%

Sr isotopic study of Helikian sediment and diabase dikes in the Athabasca Basin, northern Saskatchewan

Armstrong¹,

Ramaekers²

1985

Can. J. Earth Sci.

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The Athabasca Group overlles 1.8 Ga or older basement of the Churchill Province and predates uranium mineralization at 1.3 Ga. Cross-cutring diabase dikes have been dated by Rb-Sr mineral isochrons at 1.3 1 2 0.07 Ga at Diabase Peninsula, Cree Lake, and 1.16 t 0.04 Ga at Lazy Eklward Bay. Cree Lake. Initial "Sr/''Sr ratios for these dikes are 0.7040 2 0.0005 and 0.7036 k 0.002, respectively. Clastic sedimentary rocks d the Athabasca Group normally show limited variation in Rb/Sr and variable initial "Sr/""Sr. Sedimentary rocks in two areas near the northern margin of the Athabasca Basin scatter about isochrons of 2.6 Ga. reflecting Archean provenance af detrital material and lack of Sr isotopic homogenization since deposition. Sediment of the tuffaccous Wolverine Point Formation, near Rumpel Lake, IS much more variable in Rb/Sr and enriched in Rb relative to Sr and defines a 1.43 2 0.03 Ga isochron with a 0.7057 2 0.0005 initial ratio. This is possibly the age of deposition of the Athabasca Group.LC groupe d'Athabasca recouvre un swle Pgd de 1,8 Ga, ou plus ancien, de la province de Churchill et rtvele que la mininlisation en uranium fut mise en piace anlkrieurement B 1,3 Ga. Les dykes de diabase coupant le groupe ont tte dates B I'aide des isochrones Rb-Sr dc mintraux 21 1.3 1 & 0.07 Ga a la p6ninsule Dlabase, lac Cree, et a 1,16 2 0,04 Ga a la baie Lazy Edward, lac Cree. Les rapports initiaux *'Sr/"Sr F u r ces dykes sont 0,7040 * 0,0005 et 0,7036 * 0,0002, respectivement. Les mches ~Cdirncnfaires clast~qucs du g r o u~ d'Athabasca presentent normalement peu de variation du Rb/Sr et un H7Sr/X'~r initial variable. Lrs rnches ddirnentaires dans deux rtgions pres de la limite nord du bassin d'Athabasca Tournissent des isochrones qavitant autour de 2.6 Ga, tkmoignant de la provenance archkenne des matkriaux detritiques et de I'hCt6rogikit& imtopique du Sr depuis I'accurnulation des ddiments. Le mattriel sedimentaire composant la formation tufacke de Wolverine Point, prks du Iac Rurnpd, fournit un Rb/Sr beaucoup plus variable et est enrichie en Rb relativement au Sr et dCfio11 un isochrone 5 1,43 2 0.03 Cia avec un rapport initial de 0,7057 2 0,0005. Ce qui correspond possiblement a I'bge dc sckfimentntion du gmupe d'Athabasca.[Traduit par le journal]Can.

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Section: Dating Of Sedimentary Rocks By Rb-srmentioning

confidence: 56%

Sr isotopic study of Helikian sediment and diabase dikes in the Athabasca Basin, northern Saskatchewan

Armstrong¹,

Ramaekers²

1985

Can. J. Earth Sci.

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“…This is because Sr isotope homogenization not only results from diagenesis penecontemporaneous with deposition, but also from much later diagenesis, structural deformation and metamorphic recrystallization. Bofinger & Compston 1967;Dasch 1969;Clauer 1973;Perry & Turekian 1974;Gebauer & Grfinenfelder 1974;Chaudhuri 1976;Spanglet et al 1978). In contrast, presence of detrital minerals from an older source region and resistant to isotopic equilibration (e.g.…”

Section: Direct Dating Of Sedimentary Rocksmentioning

confidence: 99%

Precambrian geochronology and the geological record

Moorbath¹,

Taylor²

1985

Memoirs

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SummaryRb-Sr, Sm-Nd and Pb/Pb whole-rock isochron methods and the U-Pb zircon method have been widely applied to dating Precambrian igneous and meta-igneous rocks. Application of these methods in regional geochronological studies provides reliable constraints on the age and temporal evolution of rock units, even when some parent-daughter systems have suffered disturbance in metamorphic and/or metasomatic events which significantly post-date primary rock formation. Initial isotopic compositions of Sr, Nd and Pb aid geological interpretation of isochron age data, constrain crustal residence time of the protoliths and can be used to assess the relative contributions of mantle and crust in magma genesis.Precambrian sediments can be indirectly dated by reference to age data on interbedded volcanics, or by age-bracketing between dated basement rocks and dated cross-cutting intrusives. Significant progress has also been made in the direct dating of sedimentary rocks. Published isotopic age determinations on early Precambrian sediments containing biogenic remains are briefly reviewed. Provided that stratigraphical and geochronological correlations are correct, it appears that stromatohtic limestones were being deposited by c.3400 - 3300 Ma ago, and that true microfossils occur in rocks dated at c.3200 - 3000 Ma. Evidence relating to possible biogenic markers in sediments reliably dated at c.3800 - 3700 Ma is not yet definitive.

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The Dating of the Earliest Sediments on Earth

Moorbath

1983

Cosmochemistry and the Origin of Life

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Old Rb-Sr whole-rock isochron apparent ages from Lower Cambrian psammites and metapsammites, southeastern New York

Cited by 8 publications

References 0 publications

Sr isotopic study of Helikian sediment and diabase dikes in the Athabasca Basin, northern Saskatchewan

Sr isotopic study of Helikian sediment and diabase dikes in the Athabasca Basin, northern Saskatchewan

Precambrian geochronology and the geological record

The Dating of the Earliest Sediments on Earth

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